Conference Agenda

Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).

Program for LiM 2021
Date: Monday, 21/June/2021
1:00pm - 1:40pmWelcome and WLT Award Ceremony
Location: Room 1
Session Chair: Prof. Michael Rethmeier, Bundesanstalt für Materialforschung und -prüfung (BAM), Germany
Session Chair: Prof. Ludger Overmeyer, Laser Zentrum Hannover e.V., Germany
Room 1 

Welcome to LiM

Ludger Overmeyer, Michael Rethmeier

German Scientific Laser Society (WLT e.V.)

LiM Opening

WLT Award Ceremony

Ludger Overmeyer

German Scientific Laser Society (WLT e.V.)

WLT Award Ceremony

Presentation of the WLT Award Laureate

WLT Award Laureate

German Scientific Laser Society (WLT e.V.)

Presentation of the WLT Award Laureate

2:00pm - 3:00pmLiM Keynote Session
Location: Room 1
Session Chair: Prof. Michael Rethmeier, Bundesanstalt für Materialforschung und -prüfung (BAM), Germany
Room 1 

Keynote Talk: Trends and prospective of additive manufacturing of large metal parts

Gleb Andreevich Turichin

SMTU, Peter the Great St.Petersburg Polytechnic University, Russia


Keynote Talk: Emission of X-rays during ultrashort pulse laser processing

Herbert Legall, Jörn Bonse, Jörg Krüger

Bundesanstalt für Materialforschung und -prüfung (BAM), Germany

Ultrashort laser pulses have found their way into industrial material processing. They take advantage of the fact that moderate laser fluences can produce high quality material removal without significant thermal influence. The growing availability of powerful, highly repeating laser sources and an advanced laser beam control have favored these developments. However, the laser-matter interaction can be accompanied by the production of X-rays. Small doses per laser pulse can accumulate to significant dose rates at high laser pulse repetition rates which may exceed the permitted X-ray limits for human exposure. Consequently, a proper radiation shielding must be considered in laser material processing. The paper summarizes the current state of the art in the field of undesired generation of X-ray radiation during ultrashort pulse laser material processing in air.

3:30pm - 4:45pmJoint Session with CLEO/Europe: Micro Machining
Location: Room 1
Session Chair: Prof. Emmanuel I. Stratakis, Institute of Electronic Structure and Lasers, Greece
Room 1 
3:30pm - 3:45pm

High speed temperature measurement in ultrashort pulse laser micromachining

Jiri Martan, Lucie Prokešová, Denys Moskal, Bernardo Campos Ferreira de Faria, Milan Honner, Vladislav Lang

University of West Bohemia, Czech Republic

Ultrashort pulse laser micromachining is affected by the heat accumulation resulting from the previous laser pulses. Up to now, most of the works analysed the accumulation by numerical modelling. The present work focussed on development of a temperature measurement system and its application directly during the process in nanosecond and microsecond time ranges. The measurement system was based on the infrared radiometry and a specific calibration was done in order to obtain temperatures from the measured signal. Micromachining of grooves was done using a picosecond laser with different pulse energies, repetition frequencies and scanning speeds. Obtained heat accumulation temperature ranged from 300°C to 2600°C. Surface roughness and ablation rate were determined by 3D confocal microscope. Good correlation was found between the roughness and the heat accumulation temperature, thus confirming the validity of calibration. Measured heat accumulation temperature was surprisingly the highest for the most efficient ablation parameters producing low roughness.

3:45pm - 4:00pm

Ultrafast laser micromachining of x-ray gratings and sub-micron hole patterns with differ ents beam shapes

Romain Carreto1, Beat Lüscher1, Ronald Holtz1, Bojan Resan1,2

1Institute of Product and Production Engineering (IPPE), University of Applied Sciences and Arts Northwestern Switzerland (FHNW), Switzerland; 2Faculty of Medicine, Josip Juraj Strossmayer University, Croatia


4:00pm - 4:15pm

Laser shock micro-forming of stainless steel: thermal effects at high repetition ps-pulses

David Munoz-Martin1,2, José Manuel López1,3, Miguel Morales1,3, Laura Rivera1,4, Juan José Moreno-Labella1,3, Arturo Chávez-Chávez4, Gilberto Gomez-Rosas4, Carlos Molpeceres1,3

1Centro Láser, Universidad Politécnica de Madrid, Spain; 2Escuela Técnica Superior de Ingeniería y Diseño Industrial, Universidad Politécnica de Madrid, Spain; 3Escuela Técnica Superior de Ingeniería Industrial, Universidad Politécnica de Madrid, Spain; 4Departamento de Física, Centro Universitario de Ciencias Exactas e Ingeniería, Universidad de Guadalajara, Guadalajara, Jalisco, Mexico.

A solid-state ps-pulsed laser, emitting at 1064 nm and repetition rate from 0.4 to 10 kHz, was used to laser peen form thin stainless steel metal sheets (50 μm thick). The laser repetition rate and the scanning speed were adjusted to keep the pitch distance between consecutive laser pulses constant.

The effect of the treatment was measured by the bending angle induced. When using the lowest repetition rate, up to 90º bending angles are achieved. As the laser repetition rate increases, the bending angle is dramatically reduced although every sample was processed with the same total number of pulses and with the same pulse energy.

Despite the small temperature increase in the whole sample, the local accumulative thermal effect at high pulse repetition has a strong influence on the bending angle. High temperature relaxes the stress induced by laser peen treatment and thus prevents bending the sample.

4:15pm - 4:30pm

Femtosecond laser micromachining and rocket propulsion of microparticles optically trapped in hollow-core photonic crystal fibre

Mariia Romodina, Shangran Xie, Abhinav Sharma, Francesco Tani, Philip Russel

Max Planck Institute for the Science of Light, Germany


4:30pm - 4:45pm

Cut edge quality in laser ablation of micrometer-scale grating structures

Meike Zilm, Tim Radel

Bremer Institut für angewandte Strahltechnik GmbH, Germany

During the production of grid structures heat accumulation occurs due to the limited surface area for heat dissipation via the ridge structures. This impairs the edge quality, affecting the ridge width and rectangularity. Due to thermal stresses and expansions, in combination with the low stiffness of the ridges, distortion or failure of these can occur. The aim of this study is to quantify the influence of the strategy for cutting out a single cutout with regard to the cut edge quality. For this purpose, 100 µm thick aluminium foils are processed by means of picosecond laser with different scanning strategies and subsequently examined for their ridge width. It is shown that a laser starting point at half the length of the ridges reduces the ridge width deviation. Furthermore, the ridge width deviation can be reduced by an adapted scanning strategy of the entire grid.

3:30pm - 4:45pmJoint Session with CLEO/Europe: Welding and Cutting
Location: Room 2
Session Chair: Prof. Uwe Reisgen, RWTH Aachen University, Germany
Room 2 
3:30pm - 3:45pm

3-dimensional beam shaping for dynamic adjustment of focus position and intensity distribution for laser welding and cutting

Axel Jahn1, Dirk Dittrich1, Stephan Boerner1, Jens Standfuss1, Patrick Herwig1, Claudia Reinlein2

1Fraunhofer Institute for Material and Beam Technology IWS, Germany; 2Robust AO GmbH, Germany

Beam shaping, using highly dynamic beam oscillation, offers a high potential for the process control and thus the adaptation to specific process requirements. The realization of beam oscillation in 3 spatial directions opens up new possibilities for specific adjustment of the energy distribution in the melting zone and also creates prerequisites for high dynamic 3D welding and cutting.

A novel 3D optical system will be presented containing galvo-x/y-scanners combined with a new piezo-driven focus modulation (z-modul). This concept enables a synchronous high-frequency axis-control of the 3 spatial directions in a compact optics design.

In the lecture, construction concept and mode of operation of the 3D-system as well as achievable complex 3D energy distributions will be presented. Further, results of process investigations for welding Al alloys and 3D contours are shown and advantages in process stability and joint quality are derived.

3:45pm - 4:00pm

On-the-fly laser beam shaping with acousto-optofluidics

Martí Duocastella1,2, Alessandro Zunino2,3, Salvatore Surdo2

1Department of Applied Physics, Universitat de Barcelona, Spain; 2CHT, Istituto Italiano di Tecnologia, Italy; 3Department of Physics, University of Genoa, Italy


4:00pm - 4:15pm

Ultra-high quality through-transmission micro-welding and cutting of glass with ultrashort pulse lasers

Terence Hollister, Jim Bovatsek

MKS Spectra-Physics, United States of America

In recent years, glass has seen a renaissance of sorts, expanding into a wide variety of thicknesses, shapes, compositions and uses. Novel forms of glass are now widely used in microelectronics packaging, mobile device, automotive and bio-medical applications. Technologies to process glass have evolved as well, with ultrashort pulse (USP) laser technology becoming an important capability. Ultrashort pulse widths offer precision processing with controlled heat input that can minimize or even eliminate chipping and cracking. Combined with Bessel beam optics, high quality cutting of ultrathin glass (UTG) down to 100 µm thick can be realized. Operating at high pulse repetition frequencies, controlled thermal phenomena allows micro-welding of glass-to-glass and other materials. In this work, we demonstrate UTG cutting with roughness in the 10s of nm and ~1 m/s throughput as well as glass-glass and glass-aluminum micro-welding, with throughput approaching 500 mm/s and line widths of 10s of µm.


Date: Tuesday, 22/June/2021
10:00am - 11:00amMacro: Welding, Steel
Location: Room 1
Session Chair: Prof. Michael Rethmeier, Bundesanstalt für Materialforschung und -prüfung (BAM), Germany
Room 1 
10:00am - 10:15am

High-power joining of duplex steels using laser beam-submerged arc hybrid welding

Rabi Lahdo1, Sarah Nothdurft1, Jörg Hermsdorf1, Patrick Urbanek2, Markus Puschmann2, Frank Riedel2, Stefan Kaierle1, Ludger Overmeyer1

1Laser Zentrum Hannover e.V., Germany; 2Fraunhofer-Institut für Werkzeugmaschinen und Umformtechnik IWU, Germany

Duplex steels are used in many application fields due to their outstanding performance in respect to strength, toughness and corrosion resistance. These properties result from a microstructure of delta ferrite and at least 30 % of austenite. Hitherto, duplex steels are welded using multi-pass arc welding characterized by a low efficiency. Beam welding has not been successful due to the low ratio of austenite formed. Aim of this study is the development of a reliable and efficient laser beam-submerged arc hybrid welding process for duplex steel 1.4462 (t= 15 mm) with a high proportion of austenite using a disc laser beam source (PL= 16 kW). The influence of the process parameters on the stability of the process are investigated by cross-section and visual inspection. As a result, a stable and efficient one-layer hybrid process was archived. Furthermore, a higher ratio of austenite compared to laser beam welded seams forms.

10:15am - 10:30am

Joining ultra-high strength steels by edge welds

Christoph Wendt1, Martin Dahmen2, Viktoria Olfert3, Alexander Sagel1

1Scansonic MI, Schwarze-Pumpe-Weg 16, 12681 Berlin, Germany; 2Fraunhofer Institute for Laser Technology, Steinbachstrasse 15, 52074 Aachen, Germany; 3Laboratory for Material and Joining Technology, Paderborn University.Pohlweg 47-49, 33098 Paderborn, Germany

An advantage of edge welding is the possible reduction in the required flange length compared to conventionally welded lap joints. As part of a pilot study, this method has been applied to welding of a press hardened martensitic chromium steel in similar and dissimilar joints to current high and ultra-high strength steels. A dedicated optical set-up was used to implement these welds. High-frequency beam oscillation was used to ensure mixing of the different materials and to prevent crack formation which appeared mainly in the combination with the ferritic-pearlitic grade. The welding results are evaluated using micrographs, hardness tests and tensile tests. For the tensile testing, an adapted LWF-KS2-sample geometry was designed to generate for the first time reliable comparative results compared to conventionally overlap-welded laser welds.

10:30am - 10:45am

Joining technology and mechanical properties of laser-beam welded joints with martensitic chromium steels

Martin Dahmen1, Jörg Baumgartner4, Benjamin Möller2, Viktoria Olfert3, Rainer Wagener2

1Fraunhofer Institute for Laser Technology, Germany; 2Fraunhofer Institute for Structural Durability and System Reliability, Bartningstrasse 47, 64289 Darmstadt, Germany; 3Laboratory for Material and Joining Technology, Paderborn University.Pohlweg 47-49, 33098 Paderborn, Germany; 4Technical University of Darmstadt, Mechanical Engineering Department, Research Group SAM, Otto-Berndt-Strasse 2, 64287 Darmstadt, Germany

Investigations were undertaken on welding of press-hardened martensitic stainless steels in similar joints as well as in combination with state-of-the-art and modern steel grades. Parameter development was conducted for square-butt and lap joint configuration aiming at the production of defect-free welds. In order to homogenise the mechanical properties of the weld area, a heat treatment has been developed and applied successfully. Tests on load capacity of lap joints have been carried out under quasi-static and dynamic loading using the LWF-KS2 concept. Emphasis is laid on the investigation of contour welds. Especially for the chromium steel a strong dependence on the load angle was detected. Heat treatment led to a significant improvement of strength and ductility. Independent of heat treatment and seam weld shape, uni-directional fatigue testing of lap joints shows similar endurable load amplitudes. The critical location of failure is the intersection of the fused zone with the joint plane.

10:45am - 11:00am

Impact of sulphur content on spattering and weld seam shape in steel specimens using modified side-gas application technique

Goran Jovic1,4, Axel Bormann1, Johannes Proell2, Thomas Niendorf3, Stefan Boehm4

1Robert Bosch GmbH, Manufacturing Center of Competence Laser Welding, Am Börstig 2, 96052 Bamberg, Germany; 2Robert Bosch GmbH, BaP/TEF1.2 – Laser Material Processing and Joining Technology, Am Börstig 2, 96052 Bamberg, Germany; 3Institute of Materials Engineering – Metallic Alloys, University of Kassel, Mönchebergstr. 3, 34125 Kassel, Germany; 4Department for Cutting and Joining Manufacturing Processes, University of Kassel, Kurt-Wolters-Str. 3, 34125 Kassel, Germany

Laser welding experiments have been carried out using stainless steel specimens (1.4003/1.4005) with different sulphur contents (S1:10ppm, S2:210ppm, S3:2770ppm). A parameter for spatter control, the capillary widening ratio mainly affected by the side-gas jet is considered. This value can be controlled by welding speed, laser power and side-gas pressure. Decreasing the sulphur content resulted in (1) a shift of the humping threshold to higher side-gas pressure and (2) an increase in weld seam bulge while decreasing spatter quantity at the same time. For S1 and S2, aspect ratios of R≥3 were achieved while spattering could not be detected by high speed imaging at 2000 fps. By increasing the welding speed from 1.5m/min to 3.0m/min and a simultaneous adaption of laser power, differences in spattering and weld seam shape between S1 and S2 were minor, indicating that higher melt pool velocities acting in welding direction dominate the surface tension driven effects.

10:00am - 11:00amAdditive Manufacturing: Directed Energy Deposition 1
Location: Room 2
Session Chair: Prof. Jean Pierre Bergmann, Technische Universität Ilmenau, Germany
Room 2 
10:00am - 10:15am

Development of laser-arc hybrid process for additive manufacturing of aluminum alloy and copper alloy

Dehua Liu, Shengnan Wu, Guangyi Ma, Fangyong Niu, Dongjiang Wu

Dalian University of Technology, Dalian, People's Republic of China

Laser-arc hybrid process was recently suggested as a feasible method for 3D printing the metal structural with high properties and low defects. To promote an understanding of the effect of laser on manufacturing process, this paper are performed to preparing aluminum alloy and cooper alloy using the integrating laser beam and tungsten inert gas (TIG) arc system. The microstructure evolution of aluminum alloy and copper alloy under different laser power are analyzed. Moreover, the elongation of the deposited aluminum alloy is improved on the higher tensile strength. The elongation of copper alloy sample is more than 40%. Relationship between the employed laser-arc manufacturing strateries and microstructure characteristics and mechanical properties are established. Laser-arc hybrid provides a new idea for additive manufacturing materials which are difficult to manufacture (high reflectivity, high thermal conductivity, et al.), and expand the application of laser additive manufacturing.

10:15am - 10:30am

Acoustic emissions of laser metal deposited NiTi structures

Julian Ulrich Weber1, Alexander Bauch1, Johannes Jahnke1, Claus Emmelmann2

1Fraunhofer IAPT, Hamburg, Germany; 2Institute of Laser and System Technologies (iLAS), Hamburg, Germany

Laser Metal Deposition (LMD) is an additive manufacturing process that enables the metal part production of complex near net-shape parts. Precise material deposition increases material efficiency and prevents the excessive use of costly materials. In a fully automated manufacturing process with minimized scrap production, these benefits are enabled by material specific process monitoring and parameter development.

Acoustic emissions were monitored for the LMD process of the costly shape memory alloy. Acoustic emission monitoring values were defined and evaluated regarding of NiTi structural defect formation. For the evaluation of defect formation, the degree of delamination for each specimen has been identified. Concurrent measurement of the oxygen content in the process chamber was carried out to correlate defects to the process atmosphere.

Distinct defect frequencies were detected for NiTi structures indicating delamination and cracks. The acquired data was used to design an LMD process control concept based on acoustic emission monitoring.

10:30am - 10:45am

Effect of atmosphere conditions on additive manufacturing of Ti4Al6V by coaxial W-DED-LB process

Eva Vaamonde, Rosa Arias, Pilar Rey, Iago Troncoso

AIMEN Technology Center, Spain

Additive Manufacturing is being a strategic tool for industrial applications even for large size structural parts where high deposition rates, as achieved by Directed Energy Deposition (DED) techniques based on wire deposition, are required. However, manufacturing of large components on reactive materials as titanium alloys requires specific atmosphere conditions to reach the specified properties on the deposited material. In this paper coaxial laser wire deposition (W-DED-LB) of titanium grade 5 alloy has been studied to achieve the highest deposition rate and process stability and the effect of protective conditions has been assessed. Three different configurations (local, inert chamber, local + inert chamber) were tested in order to bring a deep understanding of the influence of protective conditions on process stability, surface quality, metallurgy, hardness and oxygen content of deposited material.

10:45am - 11:00am

Processing of a low-alloyed case-hardening steel by means of DED-LB/M

Dominic Bartels1,2, Wolfgang Burgmayr1, Jonas Dauer1, Oliver Hentschel1,2, Michael Schmidt1,2

1Institute of Photonic Technologies (LPT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Konrad-Zuse-Straße 3/5, 91052 Erlangen, Germany; 2Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Paul-Gordan-Straße 6, 91052 Erlangen, Germany

Low-alloyed steels are typically exposed to additional case-hardening post-processing to improve the mechanical properties in the case area of the material for increased hardness and wear resistance. Another possibility for improving these material properties is provided by in-situ alloying using laser-based directed energy deposition of metals (DED-LB/M). However, this requires basic understanding of the mechanisms when processing the base material. Within this work, different processing strategies for defect-free fabrication of a low-alloyed case-hardening steel are presented. This includes the correlation of geometrical properties and internal defects like pores or cracks with the applied process parameters. It is found that track geometry and diffusion zone are highly dependent on laser power and scanning speed. Additionally, hardness measurements are performed for analyzing the influence of different processing strategies on material properties. It is found that the corresponding material hardness varies inside a layer and that a hardness gradient is formed.

10:00am - 11:00amMicro: Ablation 1
Location: Room 3
Session Chair: Johannes Heberle, Bayerisches Laserzentrum GmbH (blz), Germany
Room 3 
10:00am - 10:15am

Plasma dynamics induced by single-pulse femtosecond laser ablation of dielectrics and metals

Bruno Gonzalez-Izquierdo, Haruyuki Sakurai, Ryohei Yamada, Kuniaki Konishi, Makoto Kuwata-Gonokami, Junji Yumoto

The University of Tokyo, Japan

The generation of plasma is inherent to subtractive laser processing phenomena and often determines energy absorption and damage characteristics. However, few experimental studies have directly focused on quantitatively analyzing such laser-induced plasma dynamics. Here, shadowgraph and interferogram techniques were combined in a pump-probe configuration to investigate experimentally the temporal (from sub-ps to ns) and spatial dynamics of ablation plasma generated under single-pulse, ultrashort (90-400fs) laser ablation of sapphire and copper. From the measurements, we derived the electron-plasma density and plasma distribution for each time delay. The results clearly reveal time evolution differences between the materials. In sapphire, the plasma expands predominantly perpendicularly to the surface and attains higher electron-plasma densities. In copper, more shocked air-plasma is produced which, instead, expands uniformly. These results provide new insights into the underlying physics of laser-induced plasma dynamics which could facilitate, for instance, the optimization of recent high repetition rate configurations in laser processing.

10:15am - 10:30am

Ultrafast pump-probe microscopy reveals the influence of a water layer on the early stage ablation dynamics of gold

Maximilian Spellauge1,2, Carlos Doñate-Buendia2, Stephan Barcikowski2, Bilal Gökce2, Heinz P. Huber1

1Munich University of Applied Sciences, Department of Applied Sciences and Mechatronics, Lothstrasse 34, 80335 München, Germany; 2Universität Duisburg-Essen, Lehrstuhl für Technische Chemie I, Universitätsstrasse 7, 45141 Essen, Germany

Despite the tremendous amount of research carried out in the field of pulsed laser ablation in liquids, there are only a few works available regarding the early stage ablation dynamics. A description how the liquid influences ablation on time scales ranging from pico- to microseconds would give valuable information regarding the physical processes involved. In this work we report on ultrafast pump-probe microscopy measurements of a high purity bulk gold sample immersed in air and water. Our setup enables the observation of transient dynamics ranging from pulse impact on the picosecond timescale to shock wave and cavitation bubble propagation on the nanosecond to microsecond timescale. We find that the water layer significantly influences the ablation dynamics on the whole investigated temporal range.

10:30am - 10:45am

Advanced metal ablation based on highly flexible ultra-short pulsed laser platforms

Marc Sailer1, Axel Fehrenbacher1, Aleksander Budnicki1, Steffen Rübling2, Ulf Quentin2

1TRUMPF Laser GmbH, Germany; 2TRUMPF Laser und Systemtechnik GmbH, Germany

Considering the energy efficiency and the ablation quality, micromachining of several metals is examined for different processing regimes depending on timescales from fs to µs. Choosing an optimized temporal energy deposition can address a variety of machining aspects like ablation efficiency and surface morphologies. Using the unique features of the TRUMPF TruMicro series, the temporal energy deposition can be influenced during operation on a femto- up to a microsecond timescale by tuning parameters such as the ultrashort pulse duration or employing bursts in the MHz- and GHz-regime. This enhanced flexibility paired with patent-pending process strategies leads to cutting-edge processing speeds and surface qualities.

10:00am - 11:00amMacro: Cutting 1
Location: Room 4
Session Chair: Jannik Lind, University of Stuttgart, Germany
Room 4 
10:00am - 10:30am

Invited Talk: Laser cutting - past and present

John Powell

Laser Expertise, United Kingdom

Laser Cutting is over 50 years old! It has passed though its childhood, difficult teenage years, and early adulthood, to become the mature technology we know today.

Dr John Powell has worked in the subject since the early 1980’s and will present a talk which describes some of the early difficulties of the process and how they were overcome.

The talk will combine a general history of laser cutting with personal anecdotes - including a few comments on laser cutting in the days before laser safety was invented (Luckily, the plastic pipes exploded before the flames reached the hydrogen bottle).

10:30am - 10:45am

Fundamental characteristics of fiber laser beam sawing of 10 mm thick stainless steel

Madlen Borkmann, Achim Mahrle, Patrick Herwig, Andreas Wetzig

Fraunhofer-Institut für Werkstoff- und Strahltechnik IWS Dresden, Germany

AISI 304 stainless steel plates of 10 mm thickness were separated by fibre laser beam sawing trials. The applied sawing technique as a new variant of laser cutting with an oscillating beam relies on periodical changes of the focusing length of the optical setup by integrated mirrors with adjustable curvature radius. As a result, the focal plane position can be forced to oscillate with a frequency of up to 4800 Hz and amplitudes up to 6 mm. The resulting temporally averaged beam profile is characterized by a nearly constant beam diameter over the whole spatial oscillation range. Variations of oscillation frequency, amplitude and nominal focal layer position were performed to get first insights into the effect mechanisms of fibre laser beam sawing. It is found that the cut kerf geometry can be adjusted to improve cutting gas flow characteristics and melt removal.

10:45am - 11:00am

Monitoring of the melt pool for fiber laser cutting using a high-speed camera

Max Schleier1, Benedikt Adelmann1, Uwe Glatzel2, Ralf Hellmann1

1University of Applied Sciences Aschaffenburg; 2University Bayreuth

We demonstrate an in-situ and coaxial monitoring system based on a high-speed camera with a spectral response in the visible range, which is designed to be integrated into a cutting head between the collimator and processing lens. The thermal radiation from the melt pool is measured in the visible spectral range, without external illumination, spatially and temporally resolved from the top view. The dependencies of the laser power and feed rate on the spectral and geometric information captured from the images of the melt pool in the cut kerf are evaluated. In addition, we developed and show an algorithm to detect incomplete cuts caused by laser power and feed rate from the captured images.

10:00am - 11:00amMachine Learning for Laser Processing
Location: Room 5
Session Chair: Anne Feuer, University of Stuttgart, Germany
Room 5 
10:00am - 10:30am

Invited Talk: Applications of artificial intelligence and machine learning in laser materials processing

Kilian Wasmer

Laboratory for Advanced Materials Processing, EMPA, Switzerland

Laser materials processing (welding / additive manufacturing) are known to be highly dynamic. The reason is the non-linear nature of light-matter interactions. This not only complicates the reproducibility of the process quality in mass production but it is also a challenge for in situ and real-time quality monitoring and control.

Under such circumstances, our approach has been to record signals from different sensors such as acoustic emission and optical sensors. However, due to the complex character of the signals, traditional signal processing methods are limited to extract the useful information about the process quality. To overcome this difficulty, we use state-of-the-art artificial intelligence and machine learning methods as they allow building complex empirical models from complex structured datasets.

The presentation makes an overview of our approach and results for laser processes.

10:30am - 10:45am

Determination of the beam position in laser deep penetration welding using coaxially acquired images of the keyhole front and machine learning

Pablo Dilger1,2, Carola Forster1, Elias Klein1, Silvana Burger1,2, Eric Eschner1,2, Michael Schmidt1,2

1Institute of Photonic Technologies (LPT), Friedrich-Alexander-Universität Erlangen-Nürnberg, Konrad-Zuse-Straße 3/5, 91052 Erlangen, Germany; 2Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg, Paul-Gordan-Straße 6, 91052 Erlangen, Germany

The joining technology of laser beam welding offers high flexibility and productivity. However, the small laser beam focus demands dependable quality assurance to ensure a sufficient connection of the parts. In keyhole welding of metal sheets in butt joint configuration, a gap is visible at the keyhole front, which correlates with the leading joint position. This process feature can be used for quality control by arranging a high-speed camera coaxially to the laser beam to monitor the keyhole. Here, we present a machine learning approach for a robust determination of the beam position relative to the joint based on the keyhole front morphology. For this purpose, we conducted a series of experiments to produce a set of labeled images, which are used to train a convolutional neural network. After training on the data the network can predict the keyhole front gap position, setting the foundation for a quality control system.

10:45am - 11:00am

Use of hyperspectral imaging (HSI) in combination with machine learning methods for the critical powder parameters and corresponding part properties. prediction of

Martin Schäfer1, Christoph Wilsnack2, Florian Gruber2, Axel Marquardt3, Sebastian Witte2

1Siemens AG, Germany; 2Fraunhofer IWS; 3TU Dresden

Additive manufacturing processes are generally operated in an industrial environment with defined parameters for specific materials and specific applications. The machines used can only be individually controlled to a limited extent. This means that the material properties are directly related to the component qualities. The evaluation of materials before and during the construction process is thus an essential component in the quality management of the AM production chain and the basis for optimized use and reuse of production value materials.

The analysis of metal powders by HSI represents a potential novel method for the qualification of powders.

To this end, the use of hyperspectral imaging, in combination with machine learning methods, for the prediction of critical powder parameters such as the rheology, the morphology and the chemical properties of the powders will be demonstrated. Furthermore, it is discussed if a prediction of the component properties by HSI sensing.

11:15am - 12:30pmMacro: Welding Simulation
Location: Room 1
Session Chair: Eveline Reinheimer, Universität Stuttgart, Institut für Strahlwerkzeuge, Germany
Room 1 
11:15am - 11:45am

Invited Talk: Numerical Simulations as Versatile Tool for Understanding and Optimizing Laser Material Processing

Andreas Otto, M. Buttazzoni, C. Zenz

Vienna University of Technology, Austria

Multiphysical simulations of laser material processing enable for a deep insight into the process dynamics. Thus they support gaining thorough process knowledge prerequisite for optimizing the process parameters with respect to the process result.

Within the presentation an introduction into a simulation model developed within the past 15 years and capable for simulating virtually every laser process from the micro to the macro scale, from ultrafast to laser based additive processes, is given. Results from basic research work and industrial applications with a focus on deep penetration welding demonstrate the capabilities of the model. Furthermore an outlook on current developments including the implementation of grain growth models and thermo-mechanics is given.​

11:45am - 12:00pm

Experimental and numerical analysis of local gas supplies for spatter reduced high speed laser beam welding

Leander Schmidt, Klaus Schricker, Jean Pierre Bergmann

Technische Universität Ilmenau, Production Technology Group, Germany

Spatter formation is a major issue in deep penetration welding with solid-state lasers at high welding speeds above 8 m/min. To avoid spatter formation, the use of local gas supply proved to be very effective. This publication examines the flow conditions and mechanical effects of a local supply of Argon/Helium by welding stainless steel (X5CrNi18-10/AISI304) at welding speeds beyond 8 m/min to get a deeper understanding of the acting mechanisms. By varying the flow rate, the flow field characteristics were visualized by Schlieren imaging and quantified by Schlieren imaging velocimetry (flow pattern, flow velocity). In order to specify the resulting pressure field, a computational fluid dynamics analysis have been performed based on a k-ω-SST multi component turbulence model. By combining the experimental und numerical findings, it was possible to derive a comprehensive model representation of the fundamental effect mechanisms.

12:00pm - 12:15pm

Numerical study of the bulging effect in deep penetration laser beam welding

Antoni Artinov1, Xiangmeng Meng1, Marcel Bachmann1, Michael Rethmeier3,1,2

1BAM Federal Institute for Materials Research and Testing, Germany; 2Fraunhofer Institute for Production Systems and Design Technology, Pascalstraße 8-9, 10587 Berlin, Germany; 3Institute of Machine Tools and Factory Management, Technische Universität Berlin, Pascalstraße 8-9, 10587 Berlin, Germany

This article is devoted to the study of the bulging effect in deep penetration laser beam welding. Experimental and numerical investigations are combined to study the relationship between the bulging effect and the hot cracking formation, as well as the mixing of alloying elements in the weld pool. The widening of the molten pool is visualized by utilizing a butt joint configuration of transparent quartz glass and 12 mm thick structural steel. The weld pool shape is monitored in real time with a high-speed camera and two thermal imaging cameras. A simplified numerical model with a fixed keyhole shape based on experimental observations is applied to examine the bulge influence on hot cracking during complete penetration. Additionally, a numerical model considering a dynamic keyhole is developed to analyze the mixing of alloying elements during partial penetration. The link between the bulge and the studied phenomena is found to be significant.

12:15pm - 12:30pm

Numerical simulation of power control in laser-assisted metal-polymer joining

Klaus Schricker, Jean Pierre Bergmann

Technische Universität Ilmenau, Production Technology Group, Germany

Laser-assisted joining enables a direct connection between polymers and metals without using additional elements (e.g. screws, rivets) or adhesives. The process is well known in terms of surface pretreatment, achievable mechanical properties and materials. However, the quality of the joint is affected by varying manufacturing conditions, e.g. heat accumulation at edges, heating of the clamping device or different material batches. The article is dedicated to power control in laser-based joining of polymers with metals for this reason. A PID controller was integrated to control the beam power of a diode laser as a function of temperature based on a transient thermal model. The investigations were carried out on polypropylene in combination with aluminum and high-alloy steel. A comparison of surface/interface temperatures, controlled/uncontrolled processes and the introduction of disturbances allow conclusions on process control and on implementation in real production processes.

11:15am - 12:30pmAdditive Manufacturing: Systems Engineering
Location: Room 2
Session Chair: Prof. Peter Loosen, Fraunhofer Institute for Laser Technology ILT, Germany
Room 2 
11:15am - 11:30am

RECILS: high resolution and high-speed SLA 3D printer using a plane building platform and a cylindrical glass window

Kentaro Soeda, Hirosuke Suzuki, Shuichi Yokobori, Kuniaki Konishi, Hiroharu Tamaru, Norikatsu Mio, Makoto Kuwata-Gonokami, Junji Yumoto

The University of Tokyo, Japan

We propose a novel stereolithography 3D printer configuration, called RECILS, achieved by combining a plane building platform (BP) and a cylindrical glass window (CW). The BP is deployed above the sidewall of the CW placed horizontally with a gap of 10 micrometer to 40 micrometer. UV curable resin is supplied into the gap and cured by the UV laser light passing through the CW. The UV laser light with a spot size of 10 micrometer is scanned lineally along the gap by a polygon mirror. The UV light is modulated by the STL data, and the BP is translated in a direction perpendicular to the laser-scan direction, synchronized exactly with the laser scan. This operation is equivalent to a raster scan. The subsequent layers are formed below the previous layer and accurate 3D-modeling is enabled. Additionally, the use of a CW eliminates peeling process and greatly reduces the manufacturing time.

11:30am - 11:45am

Additive manufacturing & the need to get the laser beam right

Nicolas Meunier

MKS Instruments - Ophir Brand, Germany

Is additive manufacturing ready for mass-production? The answer really boils down to reproducibility. When it comes to selective laser melting, the constancy of the laser parameters is of great importance. Both, the manufacturers of the laser systems and the users thereof should be aware of the quality of the focused beam. As measuring a (high power) laser beam in the limited space of a production chamber is a challenge, new measurement technology had to be developed. Today, different technologies are available to measure the focused beam quickly and cost-effectively within the process.

Nicolas Meunier, Business Development Manager High Power und Automotive Products Ophir, introduces key measurement techniques, outlines their impact on the way to mass production and explains how to achieve reproducibility in laser-based additive manufacturing.

11:45am - 12:00pm

Arrangement for the benchmarking of in situ process monitoring of topographical process signatures within the laser powder bed fusion process

Karen Schwarzkopf1,2, Eric Eschner1,2, Michael Schmidt1,2

1Institute of Photonic Technologies, Friedrich-Alexander-Universität Erlangen-Nürnberg, Konrad-Zuse-Str. 3/5, 91052 Erlangen, Germany; 2Graduate School in Advanced Optical Technologies, Friedrich-Alexander-Universität Erlangen-Nürnberg, Paul-Gordan-Str. 6, 91052 Erlangen, Germany

Additive manufacturing technologies such as powder bed fusion of metals by a laser beam (PBF-LB/M) offer great potential for production of geometrically complex components. Yet, physical defect mechanisms lack fundamental understanding. Crucial for broadening process knowledge is in-situ monitoring of observable process signatures related to the powder heating, melting, and solidification processes. Whereas the geometry and temperature profile of the melt pool have been intensively examined, little is known about topographical process signatures occurring in PBF-LB/M. In this paper we (i) identify topographical process signatures within PBF-LB/M, (ii) relate them to physical defect mechanisms and (iii) evaluate monitoring approaches proposed in literature to access them. Based on that, we present an experimental set-up with high spatial and temporal resolution consisting of a high-speed imaging (HSI) camera and a low coherence imaging (LCI) system. The coaxial arrangement enables simultaneous observation of the melt pool behavior and topographical process features within PBF‑LB/M.

12:00pm - 12:15pm

Spatially resolved melt pool monitoring for process characterization in laser powder bed fusion (LPBF)

Dieter Tyralla, Peer Woizeschke, Thomas Seefeld

BIAS - Bremer Institut für angewandte Strahltechnik GmbH, Germany

Laser powder bed fusion (LPBF) is a frequently used manufacturing process for complex shaped geometries, e.g. bionic structures. The part quality often depends not only on process parameters but also on geometrically induced changes in thermal conditions. Thus, already identified parameters may need to be adjusted to the geometry. Here, a temperature measurement provides information about the current process state due to its recognition of heat input, accumulation and flux during build-up and thus assists the parameter development.

The present work applies a spatially resolved temperature measurement for process monitoring in LPBF using 2-channel-pyrometry. A lateral resolution of 10 µm is achieved within the complete build-up volume of 250x250x250 mm³ by the coaxial integration of the pyrometric camera system into the beam path of a LPBF machine. The melt pool area was identified as a suitable indicator which enables the prediction of part density during build-up process.

12:15pm - 12:30pm

The final steps towards guaranteed quality and first-time-right - 3D printing with powder and wire enabled by OCT sensor technology

Markus Kogel-Hollacher1, Frédéric Adam1, Christian Staudenmaier1, Rüdiger Moser1, Steffen Boley2

1Precitec GmbH & Co. KG, Germany; 2Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Germany

Today’s manufacturing processes, especially 3D printing with powder or wire, presuppose Industry 4.0 solutions, which require supervision of every single production step. Transforming machine elements into intelligent cyber physical systems involves the integration of smart sensors for condition and process monitoring. As photonic solutions are by nature contact free processes it would be advantageous if the sensor is based on light as well, if the light could be coupled into the beam path of the processing laser and if the sensor can really measure surface topography in micrometer resolution. In this case the production process can be directly connected to the CAD data set, the process could be controlled to eliminate geometrical deviations to the desired geometry and first-time-right is not a pious hope anymore. We talk about controlled individualized lot size 1 production based on OCT sensor technology.

11:15am - 12:30pmMicro: Ablation 2
Location: Room 3
Session Chair: Stefanie Kohl, Institute of Photonic Technologies (LPT), Germany
Room 3 
11:15am - 11:30am

Laser ablation of thermoplastic composite for aerospace application

Hagen Dittmar, Simon Hirt, Verena Wippo, Peter Jaeschke, Stefan Kaierle, Ludger Overmeyer

Laser Zentrum Hannover e.V., Germany

Carbon fibre reinforced plastic (CFRP) is a well-established material in modern aerospace products. While primary structural components contain a thermoset matrix material, secondary components are increasingly made of thermoplastic matrix systems. Due to their superb performance and advantageous production properties, thermoplastics matrices are now also pushing into primary structural applications like fuselage, cowlings, and wings.

These structures are subject to an increased risk of damage during operation. Thus, repair strategies that address thermoplastic CFRP come to the fore. The repair by conventional tooling faces challenges that result from the thermoplastics’ abilities to melt, which cause the tools to clog and decrease process efficiency. Laser ablation poses an alternative approach allowing precise material removal without material related wear and thus a constant process quality.

This study demonstrates process efficiency of a laser ablation process on a CFRP with polyphenylene sulphide (PPS) matrix and the used processing parameters on the repair quality.

11:30am - 11:45am

Magnetic field assisted laser ablation of silicon by using short and ultrashort laser pulses

Yiyun Kang1, Garik Torosyan1, Falicienne G. Keabou1, Hicham Derouach1, Mareike Schäfer1, Pavel N. Terekhin2, Bärbel Rethfeld2, Johannes A. L'huillier1

1Photonik-Zentrum Kaiserslautern e.V. and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany; 2Department of Physics and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany

A controlled machining process with optimum energy-matter coupling in micro-scale by short and ultrashort laser pulses brings great benefits in industrial applications. The influence of external magnetic field on the ablation process of silicon irradiated by laser pulses in the infrared range was investigated. The external field is applied parallel to the laser beam to prevent escaping of the charge carriers in the laser-induced plasma plume from the ablation area. We performed single- and multi-pulse ablation in three different duration ranges: femtosecond, picosecond and nanosecond. We observed that the effect of external magnetic field depends strongly on pulse duration. An essential improvement in the quality and efficiency of material removal was achieved for pulses with longer durations. Additionally, by femtosecond excitation in multi-pulse mode a change of the surface texture around the ablation point was observed, which could be suppressed by means of the magnetic field.

11:45am - 12:00pm

Modeling of selective laser ablation of lithium-ion battery electrodes

Max-Jonathan Kleefoot1, Simon Ruck1, Jiří Martan2, Jens Sandherr1, Marius Bolsinger1, Volker Knoblauch1, Harald Riegel1

1Aalen University, Germany; 2University of West Bohemia, Czech Republic

Lithium-ion batteries are an important component of the current energy and mobility transition. Various approaches are being pursued in current research regarding the production of fast chargable electrodes. These electrode layers consist of various components that can be divided into two groups. One is the active material phase and the other is the binder material phase. In addition to laser perforation, selective laser ablation to remove inactive electrode components is also being investigated in research. Within this study, a model was developed that predicts the temperatures during the laser process inside the electrode at different depths. Experimental investigations were also able to show that the active material is permanently damaged by an excessively high energy input. A comparison with the model shows good agreement here. Thus, with the help of the model, a parameter optimisation can be carried out in which the active material particles are exposed but not damaged.

12:00pm - 12:15pm

Theoretical analysis of the incubation effect on the ablation behavior using spatial shaped ultra-short pulse laser

Marco Smarra1, Evgeny Gurevich2, Cemal Esen1, Andreas Ostendorf1

1Ruhr-Universität Bochum, Germany; 2Fachhochschule Münster, Germany

Ultra-short laser pulses are well known for their low thermal effect on the ablation process and therefore are used in numerous applications like surface texturing and functionalization. However, high peak fluence leads to a reduction in ablation efficiency. Beam shaping can be used to solve this issue. Beam errors, like defocus or astigmatism, lead to larger beam diameter and to decreasing peak fluence on the surface of the workpiece. This paper is focused on the theoretical study of the incubation effect and its influences on the ablated volume per pulse by analyzing the effects of the waist position of the laser beam and the ablation threshold of the sample material. This work is fundamental for handling the ablation process using high pulse energies.

12:15pm - 12:30pm

Expanding perspectives for processing with agile high power femtosecond lasers

Eric Audouard, Guillaume Bonamis, Martin Delaigue, Benoît Tropheme, Julien Pouysegur, Florent Basin, Jorge Sanabria, Eric Mottay, Clemens Honniger


300 W industrial laser is already available, and the mean power will reach soon the kW level. We are at a turning point in femtosecond technologies, which will enable new fields of use and new methods of production: The "agility" of the lasers and associated beam engineering make them relevant tools for flexible, reconfigurable production. We report on a versatile industrial high power femtosecond laser platform responding to the most demanding application requirements and opening the way to “macro” applications to femtosecond lasers. The platform generates femtosecond pulses at more than 300 W average power, the capability for efficient frequency conversion to 343 nm, free triggering of the laser output pulses, and burst generation and shaping over a wide range of parameters including GHz bursts.

11:15am - 12:30pmMacro: Cutting 2
Location: Room 4
Session Chair: Jannik Lind, University of Stuttgart, Germany
Room 4 
11:15am - 11:30am

3D simulation of spatial and temporal modulation in laser beam fusion cutting

Ulrich Halm1, Wolfgang Schulz1,2

1RWTH Aachen University, Germany; 2Fraunhofer Institute for Laser Technology ILT

Mean profile height and perpendicularity are, along with adherence of dross, the main quality features in laser fusion cutting of sheet metals. Research indicates that the dynamics of the thin melt film and the beam shape have a strong effect on these quality features. Recent measures to reduce the mean profile height include spatial and temporal modulation of the laser beam. A 3D simulation of the melt film dynamics is used to analyze the effect of these measures on the mean profile height and the perpendicularity of the cut surface. Insight into the temperature distribution inside the solid material allows a deeper understanding of how spatial and temporal modulation of the laser beam act on the cut surface. Furthermore, the effect of artificial additional beam sources can be analyzed. The most positive effect on the cut surface was created by a homogenous illumination of the side of the cutting front.

11:30am - 11:45am

Potential health risks due to emission of hazardous substances during outdoor laser cutting

Jürgen Walter, Christian Hennigs, Michael Hustedt, Jörg Hermsdorf, Stefan Kaierle

Laser Zentrum Hannover e.V., Germany

In contrast to well-defined industrial laser processes, there is limited knowledge regarding secondary hazards due to emission of gaseous and particulate hazardous substances during outdoor-laser applications, such as facades cleaning, pipelines repair and rescue from crashed vehicles, including hazardous-substances capturing and handling.

According to the German Clean-Air Act (TA-Luft), results of emission measurements in the exhaust air of a 2.5 kW laser-cutting process of typical automotive-multilayer structures were correlated with assessment criteria for the main hazardous components found, leading to requirements for exhaust-air cleaning. Complementary, air measurements at the operation site according to TRGS 402 were performed to evaluate whether the inhalation-exposure limits for hazardous substances released from the laser-process zone and not captured by the exhaust equipment were complied with, considering assessment criteria according to TRGS 900 and TRGS 910. The investigations showed that additional measures to reduce hazardous-substance concentrations are dispensable, if the exhaust unit is dimensioned correctly.

11:45am - 12:00pm

Striation formation at the cut edge of oxygen assisted fibre laser cutting

Handika Sandra Dewi

Luleå University of Technology, Sweden

Laser cut edges show parallel grooves features or striations. A high-quality cut edge is identified by fine striations at the cut edge. In order to gain a better understanding in striation formation at the cut edge and improve the cutting quality, striations at the cut edge and melt flow during laser cutting processes were investigated. Oxygen assisted fibre laser cutting processes were carried out on 1-mm-thick and 20-mm-thick steels at varied processing parameters and recorded using high speed imaging with borosilicate glass as replacement edge. The size of striations at the cut edge and frequency of the molten ripples were measured. The striation widths show a linear correlation with the gas pressure and cutting speed, but inverse correlation was found between striation widths and the nozzle diameter. Gas pressure is most likely the main influencing factor affecting the striation widths.

12:00pm - 12:15pm

Advanced beam shaping for high power cutting & welding

Natalia Trela-McDonald, Alex Griffiths, Gilles Diederich, Eoin Murphy

PowerPhotonic Ltd, United Kingdom

Beam shaping of light from high power fiber lasers to improve cutting or welding performance can be challenging, due to (i) high power density; (ii) short length optical train; (iii) uniformity of the shaped beam over the tolerance range of the application. We present novel approaches to the design and manufacture of high efficiency beam shaping elements for multi-mode and single-mode fiber lasers. Beam structures that are emerging as important for industrial processing – such as rings – are considered. Importantly, these designs can be manufactured with sufficient low loss and low scatter by a laser-writing freeform optical manufacturing technique.

11:15am - 12:30pmMacro: Laser Processing for Electrical Components
Location: Room 5
Session Chair: Jakob R. Ermer, Bayerisches Laserzentrum GmbH (blz), Germany
Room 5 
11:15am - 11:30am

Laser in vacuum spot welding of electrical steel sheets with 3.7% Si-content

Thomas Krichel, Simon Olschok, Uwe Reisgen

Welding and Joining Institute, RWTH - Aachen University, Germany

The energy efficiency of electric motors is largely determined by the magnetic and electrical properties of the soft magnetic core material. For high-frequency applications in the automotive sector, the cores usually consist of iron-silicon alloys with several lamellae electrically insulated from each other to minimize eddy current loss. To join these lamellae, a novel method with individual, statistically distributed weld spots instead of continuous linear welds is used. The influence of beam power and beam intensity on the weld geometry, grain structure and torsional strength of the material is investigated.

11:30am - 11:45am

Solutions of laser material processing for electric mobility – evaluation of the Technology Readiness Level

Christoph Wunderling, Christian Bernauer, Christian Geiger, Korbinian Goetz, Sophie Grabmann, Lucas Hille, Andreas Hofer, Michael K. Kick, Johannes Kriegler, Lukas Mayr, Maximilian Schmoeller, Christian Stadter, Lazar Tomcic, Tony Weiss, Avelino Zapata, Michael F. Zaeh

Technical University of Munich, Institute for Machine Tools and Industrial Management, Germany

Battery technology and lightweight design are central fields of research and development when it comes to making electric mobility technically and economically attractive for producers and customers. In this context, laser material processing will be a driver to enable innovations in future product generations. For this reason, the publication addresses the most relevant laser-based production technologies that are currently being researched or about to be transferred to applications in electric mobility. In order to give a structured and uniform overview, the advantages of individual processes are mentioned and the technology-specific state of the art is quantitatively presented based on a methodical procedure for the evaluation of the Technology Readiness Levels. Upon this, the challenges for the deployment in industrial production are specified, which is the basis to describe the need for adaption and further development in laser material processing

11:45am - 12:00pm

System and process development for functionalization of electrical components by laser-based gold micro deposition

Tobias Schmid1, Henning Janssen1, Christian Brecher1,2

1Fraunhofer Institute for Production Technology IPT, Germany; 2Laboratory for Machine Tools and Production Engineering (WZL) of RWTH Aachen University

During the manufacture of electrical contact components, the contacts are coated with precious metals. Currently, energy- and resource-intensive electroplated coatings are used. A sustainable alternative is the local functionalization of sheet parts using small gold spots with the appropriate system technology for laser-based micro wire deposition. However, the necessary process reliability and required short cycle times represent a challenge for the technology. Within this paper, the system development of a stand-alone coating system is described. The approach presented is based on a laser beam deflection unit, fully automatic laser system control, a 5-axis wire head and a quality assurance system. An analysis of the deposition results was carried out, taking into account crucial process parameters. The resource efficiency study shows significantly reduced gold usage through local sustainable coating. Almost 100% material utilization is achieved, while gold spots geometry and position can be adjusted and replace the full surface electroplating coating.

12:00pm - 12:15pm

Laser technologies for battery pack production

Mauritz Möller

TRUMPF, Germany

The global mobility revolution is in full swing. The demand for components for electric cars and alternative drives is rising continuously. Many production approaches are making use of the benefits of laser technologies. It connects battery cells to form modules or packs. It ensures tightness and crash safety when joining battery packs and trays.

This paper offers an insight into the requirements of battery packs as well as the innovative joining technology solutions for the material specifics, which are made possible by the use of novel laser and system developments in industrial practice. Furthermore, the trends of future battery packs will be presented. Finally, a spotlight will present the next generation of laser and joining technologies for use in battery system manufacturing and place them in the context of existing material-specific challenges, such as helium-tight welding of aluminum alloys.

12:15pm - 12:30pm

Contacting of cylindrical lithium-ion batteries using short pulse laser

Lukas Mayr, Lazar Tomcic, Michael K. Kick, Christoph Wunderling, Michael F. Zaeh

Technical University of Munich, Institute for Machine Tools and Industrial Management, Garching, Germany

The increasing demand for electric vehicles requires innovative manufacturing processes to improve the electrical performance and decrease the production costs of energy storages. Laser beam welding (LBW) is a highly flexible and fast process for connecting multiple battery cells automatically. Highly electrical conductive materials such as copper and aluminum are challenging in terms of LBW. A possibility to overcome these challenges, such as the high reflectivity and thermal conductivity, is the use of nanosecond laser pulses with peak powers up to several kilowatts. In experiments, this process was found to achieve narrow welds with high aspect ratio and low heat input. Beam oscillation was investigated in order to widen the weld seams and enhance the electrical conductivity and mechanical strength. This study shows the proof of concept and parameter investigation for the use of short pulse LBW for difficult to weld lap joints containing copper and aluminum or hilumin.

1:30pm - 2:30pmMacro: Welding, Cu and Al
Location: Room 1
Session Chair: Sarah Nothdurft, Laser Zentrum Hannover e.V., Germany
Room 1 
1:30pm - 1:45pm

Influence of beam parameters on the capillary formation and the depth progress in laser spot welding of copper

Frauke Faure, Rudolf Weber, Thomas Graf

Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany

Laser spot welding of copper with a welding depth in the range of several millimeters has gained increasing attention due to the growing field of electromobility. Deep spot welds require the formation of a capillary and this again defines the process time for each weld which is of particular interest for achieving high productivity. The capillary formation and the depth progress are influenced by the laser beam parameters. Spot welding with a laser power of up to 16 kW, a wavelength of 1030 nm and beam diameters of 200 µm and 600 µm were investigated. High-speed X-Ray imaging with a temporal resolution of 0.5 ms during the welding process was used to analyze the depth progress. With the maximum power of 16 kW, a welding depth of 4 mm was achieved in copper within 5 ms. In this talk, the critical beam parameters influencing the depth progress will be discussed.

1:45pm - 2:00pm

Influence of defocusing in deep penetration welding of copper by using visible wavelengths

Florian Kaufmann1, Jakob Ermer1,2, Andreas Maier1, Markus Müller1, Stephan Roth1,2, Michael Schmidt1,2,3

1Bayerisches Laserzentrum GmbH (blz), Germany; 2Erlangen Graduate School in Advances Optical Technologies (SAOT); 3Institute of Photonic Technologies (LPT)

High-quality joining of copper materials has become a key factor in any electric application like electric engines, batteries or power electronics. By now high-power laser beam sources emitting visible laser radiation are available to promote the already well-suited joining method of laser beam welding. Consequently, this process can now face the challenges of welding highly reflective materials, such as copper, which originate mainly in the low absorption of conventionally used infrared wavelengths at room temperature and the rapid jump of the absorption at the transition from solid to liquid state. However, up to now mostly the heat conduction welding process has been examined and the effects of shorter wavelengths on deep welding have been neglected. Thus, for this work the scope lies on the wavelength dependent intensity needed to overcome the deep penetration welding threshold and the alteration of energy incoupling into the vapour capillary.

2:00pm - 2:15pm

Process control of aluminum-copper mixed joints during laser beam welding in vacuum

Uwe Reisgen, Simon Olschok, Niklas Holtum, Christian Frey

RWTH Aachen University - Welding and Joining Institute ISF, Aachen, 52062, GERMANY

The creation of aluminum-copper mixed joints are difficult to produce in all welding processes. This is due to the unavoidable formation of intermetallic phases (IMP), which reduce the mechanical technological properties of the weld and to the different melting points of pure aluminum and copper.

Laser beam welding in vacuum with a single-mode fiber laser ensures precise temporal and local energy input, allowing a controlled degree of melting copper and homogeneous mixing of both materials. The aim is to record the radiation characteristics of the mixed joint in vacuum to determine the degree of copper and consequently the IMP.

It is shown that the currently used 4-wire method does not allow inference of IMP. A more promising method, which was successfully tested on laser beam in vacuum welds, is detection of the characteristic copper wavelength 521.8 nm, which allows conclusions to be drawn about the copper content in the weld.

2:15pm - 2:30pm

Remote laser beam welding of copper to aluminum using a frequency-doubled disk laser

Lazar Tomcic, Christoph Neumeier, Michael F. Zaeh

Technical University of Munich, Institute for Machine Tools and Industrial Management, Germany

When joining copper and aluminum, intermetallic compounds with complex properties can form and negatively affect the mechanical and electrical properties of the weld seam. Laser beam sources with emission in the visible wavelength range enable welding of copper with high process efficiency since its absorptivity is significantly higher there than for the near-infrared wavelength range. In this study, copper was welded to aluminum in an overlap configuration, using a continuous wave laser beam source emitting at 515 nm. Preliminary experiments were carried out to identify a suitable process window for further experiments. Subsequently, the electrical resistance and the tensile joint strength in dependence of the feed rate were determined. Through metallographic cross-sections, the weld seam and the formation of intermetallic compounds were investigated. The results show that dissimilar joints with good physical properties can be obtained using green laser radiation, enabling new possibilities for joining copper and aluminum.

1:30pm - 2:30pmAdditive Manufacturing: Innovations for Powderbed Fusion
Location: Room 2
Session Chair: Dr. Dirk Herzog, Hamburg University of Technology, Germany
Room 2 
1:30pm - 2:00pm

Invited Talk: Advances on the Laser Powder Bed Fusion of Structural Materials: microstructure, processing and material strength

Sergio Amancio

Institute of Materials Science, Joining and Forming, Graz University of Technology, Austria


2:00pm - 2:15pm

Laser-based powder bed fusion with 16 kW

Artur Leis1,2, Stefan Bechler1, Rudolf Weber1, Thomas Graf1

1Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Germany; 2Graduate School of Excellence advanced Manufacturing Engineering (GSaME), University of Stuttgart, Germany

Laser-based Powder Bed Fusion (LPBF) is typically performed at laser powers between 500-1000W, and laser beam diameters between 50-500µm. The generation of parts therefore requires a significant amount of time because the average power basically defines the productivity. To reduce the processing time, the laser power was set to 16kW and the laser beam diameter was adjusted to produce continuous melt beads. Additively manufactured samples of AlSi10Mg were used for the high-power experiments. The melting process was recorded with a high-speed camera. The generated beads were analysed metallographically to determine the extent and shape of the molten region, the crystallographic structure and the porosity. It was found that it was possible to generate continuous melt beads with laser beam diameters between 2.5-3.8mm at feed rates between 0.5-1.5m/s with a laser power of 16kW, at the expense of hydrogen-induced porosity. In the talk, the results will be presented and discussed.

2:15pm - 2:30pm

Manufacturing knowledge: model instead of experience, a big step towards reproducibility and first-time-right in the production of complex component geometries using PBF-LB/M

Hannes Korn1, Stefan Holtzhausen2, Claudia Ortmann3, Felix Gebhardt1, Ralph Stelzer2, Welf-Guntram Drossel1

1Fraunhofer Institute for Machine Tools and Forming Technology IWU, Germany; 2Technical University of Dresden, Institute of Machine Elements and Machine Design, Germany; 3Mathys Orthopädie GmbH, Germany

The cost structure and geometry freedom of laser powder bed fusion (PBF-LB/M) holds great potential for lightweight-capabilities, customization and on-demand manufacturing of metal parts. Obstacles currently exist in first-time-right manufacturing and reliable reproducibility under changing process conditions. Reasons are the many setting variables (laser-parameters, process-parameters, scan-strategy) and disturbance variables (powder-batch, operator, ambient conditions), which have a difficult to quantify influence on the quality characteristics of the component (warpage, surface-roughness, porosity).

Compared to the so far widespread experience-based parameterization of the process, statistical modeling has great potential for describing and understanding the effects of the setting- and disturbance variables on the quality characteristics quantitatively. The influence of scan-strategy and laser-parameters on the warpage and surfaces of PBF-LB/M-components is evaluated on cantilever-like bridge specimens according to an optimized experimental plan. The relation between setting variables and quality characteristics is quanified in a linear model approach afterwards and its predictive power is evaluated.

1:30pm - 2:30pmMicro: System Technology and Process Control
Location: Room 3
Session Chair: Clemens Roider, Institute of Photonic Technologies (LPT), Germany
Room 3 
1:30pm - 1:45pm

Optical system for multi Bessel beam high power ultrashort pulsed laser processing using a spatial light modulator

Christian Lutz1, Simon Schwarz1, Stefan Rung1, Jan Marx2, Cemal Esen2, Ralf Hellmann1

1University of Applied Science Aschaffenburg, Germany; 2Ruhr University Bochum, Germany

We report on an optical setup for multi Bessel beam processing combining refractive axicon and spatial light modulator technology. Based on their particular beam profile, Bessel beams exhibit various advantages over conventional Gaussian beams for ultrashort pulsed laser processing. Especially for micromachining of transparent materials, applications like drilling micro-holes or the generation of voids benefit from the increased focal length of a Bessel beam. In addition, on account of the significantly increased average output power of industrial ultrashort pulsed lasers over the last years, there is a high demand on multi spot applications for using the available laser power in efficient production processes. Our optical concept combines the dynamic possibilities of beam splitting using spatial light modulator with the benefits of Bessel beams facilitating multi Bessel beam processing.

1:45pm - 2:00pm

Water jet guided laser as a versatile tool for industrial turning applications

Jehan Moingeon, Jeremie Diboine, Amedee Zryd, Bernold Richerzhagen

Synova SA, Switzerland

The Laser Microjet® technology couples a nanosecond pulsed Nd:YAG laser into a thin cylindrical water jet. It comes with numerous advantages such as a reduced heat affected zone and a parallel energy beam over several centimeters. Laser turning is in high demand to process hard or fragile materials allowing the production of complex solids of revolution. However, conventional laser must still contend with heat management, as well as the energy needed to ablate the whole volume. The LMJ technology can both cut-out large section in facets as well as fully turn the surface by ablation. Effective and efficient strategies of roughing and finishing become therefore possible and can yield high throughput. A surface roughness with Ra as low as 0.2µm can be reached. This paper presents several water jet guided laser turning strategies and their implementation in challenging industrial turning applications.

2:00pm - 2:15pm

Automated synthesis of colloidal nanoparticles powered by microchip lasers

Tobias Bessel, Sarah Dittrich, Bilal Gökce, Stephan Barcikowski, Friedrich Waag

Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Germany

Energy and health, two topics with continuing high relevance for our society, which require intensive R&D. Nanoparticles, with their unique properties, already make an important contribution to both fields and will play an even more essential role in the future. Access to high-quality nanoparticles for R&D is still difficult, especially when high purity and material diversity are required. Pure colloidal nanoparticles of numerous combinations of particle material and dispersion medium become available by pulsed laser ablation. Novel microchip lasers now enable the transfer of the synthesis method from the laser lab to any R&D lab as a compact, easy-to-use machine. The low-power lasers impress with unprecedented power efficiency in the laser synthesis of colloids. In addition, innovative solutions in measurement and control technology make full automation of the nanoparticle production possible.

2:15pm - 2:30pm

Mastering micro-filamentation for semiconductor-metal ultrafast laser welding

Maxime Chambonneau1, Qingfeng Li1, Vladimir Yu. Fedorov2, Markus Blothe1, Stelios Tzortzakis2, Stefan Nolte1,3

1Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Germany; 2Science Program, Texas A&M University at Qatar, Qatar; 3Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Germany

While ultrafast laser welding is a proven technique for bonding a wide variety of materials together, it has no equivalent for semiconductor-metal, which would be particularly interesting for applications in microelectronics. We explain this nonexistence by the strong nonlinear propagation effects in the semiconductor. Nonlinear propagation imaging shows significant nonlinear focal shift values, in excellent agreement with self-focusing theory. We demonstrate that this nonlinear focal shift leads to a drastic depletion of the light intensity at the exit surface of silicon, at levels insufficient for laser welding applications. By determining and precompensating the nonlinear focal shift, the energy delivered at the interface is optimized, leading to the very first demonstration of semiconductor-metal laser welding. A maximum shear joining strength of 2.2 MPa is measured between the samples, which is compatible with applications. Ultimately, material analyses of the welds shed light on the underlying physical mechanisms.

1:30pm - 2:30pmMacro: System Technology and Process Control 1
Location: Room 4
Session Chair: Manuel Henn, Institut für Strahlwerkzeuge IFSW, Germany
Room 4 
1:30pm - 1:45pm

Open-loop control of complex pulse shapes for laser beam welding

Marc Seibold, Klaus Schricker, Jean Pierre Bergmann

Technische Universität Ilmenau, Germany

Pulsed laser beam welding is of high importance in micro-welding applications and used for materials susceptible to hot cracking, e.g. 6xxx aluminum alloys. Pulse shapes are adjusted to prevent hot cracks by reducing solidification rates which is accompanied by decreased welding speeds. Numerical simulations are now used for optimizing the tradeoff between crack-free welds and highest possible welding speeds. This procedure requires small deviations between the nominal value of the laser beam power calculated by numerical simulations and the actual value in the experiment. A methodology is developed and validated for fiber laser and Nd:YAG laser beam sources (IPG YLM-450/4500-QCW, LASAG SLS 200CL60HP) using different pulse shapes. The differences between nominal and actual values were identified by high-speed power measurements and reduced from 13% down to 2% for complex pulse shapes over time. This paper will show how to set up power compensation to emit an accurate complex pulse shape.

1:45pm - 2:00pm

Monitoring of laser welding and cladding processes with edge artificial intelligence combining thermal and visual cameras

Beñat Arejita1,2, Juan Fernando Isaza1, Aitzol Zuloaga2

1EXOM Engineering, Spain; 2UPV/EHU, Spain

Laser welding and cladding are well known for their complexity and high dynamics, therefore being challenging for in situ and real-time quality control and monitoring. To tackle this challenge, this work presents a dedicated hardware implementation performing real time image processing of a multi camera configuration with a visual and a NIR camera coaxially set up with the laser beam and an off-axis stereoscopic camera. The coaxial images are analysed by edge artificial intelligence technics allowing real-time closed loop temperature control and an adaptive scanner head positioning to perform a precise melt pool monitoring and process traceability. In parallel, the volumetric positioning of the scanner head and laser job interpretation are done using the stereoscopic information, linking it with the job definition of the part being processed. The presented system can be used during Nickel-strip welding of big battery packs or during identification of milled recesses in cladding applications.

2:00pm - 2:15pm

Real-time adaptation of the dross attachment level in the laser cutting process based on process emission images

Matteo Pacher1, Mara Tanelli2,4, Silvia C. Strada2, Davide Gandolfi1, Sergio M. Savaresi2, Barbara Previtali3

1Adige S.P.A., BLMGROUP, Via per Barco 11, 38056, Levico Terme (TN), Italy; 2Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, via G. Ponzio 34/5, 20133 Milano, Italy; 3Dipartimento di Meccanica, Politecnico di Milano, Via La Masa 1, 20156 Milano, Italy; 4Istituto di Elettronica e Ingegneria dell’Informazione e delle Telecomunicazioni - IEIIT CNR Corso Duca degli Abruzzi 24, 10129 Torino, Italy

In the field of melt and blow metal laser cutting, dross attachment is the most important quality indicator. Accordingly, process parameters are generally optimized to ensure high productivity while minimizing the level of dross attachment. The resulting set of parameters often penalizes the productivity to increase reliability. As a result, there exists a productivity margin that could be exploited by controlling the quality level in closed-loop, thus optimizing the process parameters in real-time. To closed-loop control the process, two steps must be performed: a real-time, reliable estimate of cutting quality must be available and, a closed-loop controller should adapt the process parameters according to the desired quality level. This work presents the design and experimental validation of a real-time estimation and control algorithm based on process emission images that adapts the cutting speed to fulfill a desired dross attachment level.

Project Name: LT4.0. Funding from LP6/99 Autonomous Province of Trento

2:45pm - 4:00pmBeam Shaping
Location: Room 1
Session Chair: Dr. Klaus Schricker, Technische Universität Ilmenau, Germany
Room 1 
2:45pm - 3:00pm

Beam shaping with free-form optics for optimal material processing

Ulrike Fuchs1, Henrike Wilms1, Stephan Gräf2

1asphericon GmbH, Germany; 2Otto Schott Institute of Materials Research (OSIM), FSU Jena, Germany

The number of applications in material processing, where the focal intensity distributions should deviate from the Gaussian shape, is rapidly increasing. Of particular interest are not only top-hat or donut distributions, but also non-rotationally symmetric distributions such as squares or ellipses. We present refractive freeform beam shaping elements to generate such focal distributions. Moreover, these elements can generate patterns in the focal region with 3x3 or 4x4 spots. Here, the absolute size of all focal distributions is scalable with the NA of the used focusing lens.

Simulation results will be compared with measured intensity profiles to show good agreement. Furthermore, first experiments on stainless steel will show the different effect of the different intensity distributions on the material interaction. Since the refractive beam shaping elements used are also low dispersion, this opens new possibilities for material processing with ultrashort laser pulses.

3:00pm - 3:15pm

Cleaving tailored edges and curved surfaces of transparent materials by ultrafast lasers through advanced beam shaping concepts

Daniel Flamm, Jonas Kleiner, Myriam Kaiser, Felix Zimmermann, Daniel Grossmann, Max Kahmann

TRUMPF Laser- und Systemtechnik GmbH, Germany

Concepts for laser cleaving transparent materials trough volume modifications and mechanical, thermal or chemical separation gained increasing recognition for a broad bandwidth of industrial use by ultrafast lasers and application specific adapted optics. The deterministic energy deposition into the working volume is achieved by advanced spatio-temporal beam shaping. With these concepts single-pass, full-thickness modifications with m/s-feed rates were demonstrated for plane substrates with complex inner and outer contours and thicknesses of up to >10 mm at the same time with low edge roughness, low chipping and high edge stability.

These developed processing strategies lead to an increased demand for customized glass edges, including chamfer as well as bevel structures. This enables a reduction of potential edge fractures, an increased edge stability as well as the capability of e. g. curved surfaces. The efficacy of our concepts is presented by evaluating surface and edge qualities of different separated glass structures.

3:15pm - 3:30pm

Simulations on beam shaping in LPBF processes

Pareekshith Allu1, Frieder Semler2

1Flow Science Inc., United States of America; 2Flow Science Deutschland GmbH, Germany

To enable wider adoption, LPBF processes require manufacturing features with varying levels of detail at high production speeds. This becomes challenging when working with single mode lasers that operate exclusively in either the Gaussian or top hat modes. By varying spot sizes and beam shapes, new laser technologies can switch real time between different heat flux distributions that enable faster builds with higher detail.

In this presentation we discuss how CFD models built in FLOW-3D AM are used to analyze different heat flux distributions for single mode and ring beam modes that affect the melt pool dynamics. Gaussian distributions have higher localized temperatures resulting in high rates of vaporization compared to ring beam modes that distribute heat fluxes evenly over a larger area. Such CFD models also help generate process windows that utilize higher scan speeds for the various ring beam modes, ensuring higher productivity rates while maintaining process stability.

2:45pm - 4:00pmAdditive Manufacturing: Innovations
Location: Room 2
Session Chair: Prof. Michael F. Zaeh, Technical University of Munich, Germany
Room 2 
2:45pm - 3:00pm

Fabrication strategies with fixed diffractive optical elements for high speed two-photon polymerization

Francisco Gontad, Sara M. Vidal, Nerea Otero-Ramudo, Pablo Romero-Romero

AIMEN Technology Centre, O Porriño, ES36418, Pontevedra, Spain

The benefits of Two-Photon Polymerization (TPP) are well known for the fabrication of 3D structures with micron and even submicron sizes. However, the fabrication time of these structures is still far from being competitive with other techniques. In this work, the use of fixed Diffractive Optical Elements (DOEs) is presented as a valid approach to boost the fabrication speed of TPP. In this way, the fabrication strategy for different 2.5D and 3D microstructures, taking advantage of the use of DOEs with different optical configurations, is presented and discussed. The results of this study suggest that the fabrication speed can be increased up to 20 times through the correct combination of DOE and path planning, without the need of an excessive average power.

3:00pm - 3:15pm

Process strategies on laser-based melting of glass powder

Thomas Schmidt1, Susanne Kasch1, Fabian Eichler2, Laura Katharina Thurn2

1ifw Jena GmbH, Germany; 2Fachhochschule Aachen, Germany

This paper presents the laser-based powder bed fusion (L-PBF) using various glass powders (borosilicate, quartz glass). Compared to metals, these require adapted process strategies. First, the glass powders were characterized by means of various methods with regard to their material properties and their processability in the powder bed. This was followed by investigations of the melting behavior of the glass powders with different laser wavelengths (10.6µm, 1070nm). In particular, the experimental setup of a CO2 laser was adapted for the processing of glass powder. An experimental setup with integrated coaxial temperature measurement/control and an inductively heatable build platform was created. This allowed the L-PBF process to be carried out at the transformation temperature of the glasses. Furthermore, the component’s material quality was analyzed on three-dimensional test specimen with regard to porosity, roughness, density and component accuracy in order to evaluate the developed L-PBF parameters and to open up possible applications.

3:15pm - 3:30pm

Comparison of different density measurement techniques for laser assisted powder bed fusion

Lisa Schade1, Gabor Matthäus1, Hagen Kohl1, Burak Yürekli1, Tobias Ullsperger1, Brian Seyfarth1, Stefan Nolte1,2

1Friedrich-Schiller-Universität Jena, Germany; 2Fraunhofer Institute for Applied Optics and Precision Engineering, IOF Jena, Germany

One of the major quality control criteria for additively manufactured parts is the density achieved. Besides fundamental properties like microstructure, residual strain or impurities, the density fundamentally defines how the final product matches the intended material properties. In general, mostly surface inspections of randomly prepared cross sections are undertaken. On the one hand side, this approach delivers important information regarding the morphology and distribution of pores, however, on the other hand side, this characterization only considers a small fraction of the entire sample volume and therefore cannot reflect the true density without a significant level of uncertainty. In this work, we investigate three different measurement techniques, light microscopy, x-ray tomography and pycnometry with a focus on their advantages and disadvantages. The results show significant differences of the obtained density values with deviations in the range of several percent depending on the underlying material.

3:30pm - 3:45pm

Developing process parameters through CFD simulations

Pareekshith Allu1, Frieder Semler2

1Flow Science Inc., United States of America; 2Flow Science Deutschland GmbH, Germany

Laser-material interaction is complex, and to accurately simulate it requires implementing the physics models that are relevant at these temporal and spatial scales. Process parameters such as laser power, scanning velocity, geometric scanning path, pre-heating temperature and powder size distribution influence the melt pool dynamics, which controls the stability of the additive manufacturing process. In this presentation, we will look at underlying mechanisms behind the formation of defects such as balling, porosity and spatter using computational thermal-fluid dynamics models built in FLOW-3D AM. While low energy densities can lead to lack of fusion defects, high energy densities result in strong recoil pressure and unstable keyholes that can lead to the formation of porosity and spatter. In addition to helping with process parameter development for both LPBF and DED processes, such models also output thermal gradient and cooling rate data that can be used to predict microstructure evolution.

3:45pm - 4:00pm

Laser-induced forward transfer (LIFT) of micro-LED devices

Alberto Piqué, Ray Auyeung, Kristin Charipar, Heungsoo Kim, Michael Malito, Nicholas Charipar

U.S. Naval Research Laboratory, United States of America

We explore the application of laser-induced forward transfer (LIFT) techniques for laser printing of micro-LED devices. LIFT enables printing of functional materials ranging from silver nano-inks to working devices such as bare-die semiconductor components over a wide range of surfaces in an additive fashion achieving high transfer throughputs. LIFT is a non-mechanical, non-contact device transfer process operating beyond the size limits of pick-and-place methods. That is, LIFT offers a ‘lase-and-place’ approach for transferring the building blocks required for the fabrication of a wide range of functional circuits. LIFT techniques are being investigated by the U.S. Naval Research Laboratory to print micro-LED devices for applications in hybrid electronics. Examples of structures and circuits made by LIFT and their role in the development of next generation laser micro processing techniques will be presented.

This work was funded by the Office of Naval Research (ONR) through the Naval Research Laboratory Basic Research Program.

2:45pm - 4:00pmMicro: Ablation 3
Location: Room 3
Session Chair: Moritz Späth, Institute of Photonic Technologies (LPT), Germany
Room 3 
2:45pm - 3:00pm

Comparison of ultrafast laser ablation of CrMnFeCoNi high entropy alloy to the conventional stainless steel AISI 304

David Redka1,4, Christian Gadelmeier2, Jan Winter1,3, Maximilian Spellauge1, Ján Minár4, Heinz P. Huber1

1Department of Applied Sciences and Mechatronics, Hochschule München University of Applied Sciences, Germany; 2Metals and Alloys, University of Bayreuth, Germany; 3Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universit¨at Erlangen-Nürnberg, Germany; 4New Technologies-Research Center, University of West Bohemia, Czech Republic

Ultrafast lasers as tools are nowadays mainly used in the field of high-precision laser micromachining. However, for technical applications, besides process optimization, the development of new functional materials is of crucial importance. In this work, we present a novel study on single-pulse laser ablation (530 fs, 1056 nm) of CrMnFeCoNi high entropy alloy (HEA), and compare results to the conventional stainless steel AISI 304. While HEAs are known to have a high damage resistance against high-energy particle radiation we find that this is not true for electromagnetic radiation, as the damage threshold of CrMnFeCoNi HEA is 0.24 J/cm2, which is lower than that of AISI 304 (0.27 J/cm2). A detailed analysis of the crater morphology, ablation depths as well as ablation volumes shows that the ablation mechanisms for both alloys are comparable, but contrary to expectations, CrMnFeCoNi HEA laser ablation is energetically more efficient in comparison to AISI 304.

3:00pm - 3:15pm

Electric field-assisted laser ablation of silicon in air by using ultrashort laser pulses

Yiyun Kang1, Garik Torosyan1, Hicham Derouach1, Mareike Schäfer1, Pavel N. Terekhin2, Bärbel Rethfeld2, Johannes A. L'huillier1

1Photonik-Zentrum Kaiserslautern e.V. and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany; 2Department of Physics and Research Center OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany

Precisely processing on silicon, as widely used material in electronic devices, has shown a rising interest in laser micromachining. To optimize this process, we apply an external electric field parallel to the laser beam axis during irradiation of samples with ultrashort laser pulses. When the electric field is turned on, the free electrons and holes are redistributed within silicon due to electron drift. The electrons can be localized near the surface area which is supposed to influence the laser excitation process. Thus, the external electric field influences the absorption process due to the reorganized spatial distribution of electrons. We investigated the effect of an applied static strong electric field during single- and multi-pulse treatment of silicon. We observe an enhancement of ablation depth by applying the electric field in the direction of laser radiation.

3:15pm - 3:30pm

Influence of the build angle dependent surface quality on the ultra-short pulsed laser ablation of additive manufactured AlSi10Mg samples

Simon Ruck1,2, David K. Harrison2, Anjali De Silva2, Max-Jonathan Kleefoot1, Harald Riegel1

1Aalen University, Germany; 2Glasgow Caledonian University, United Kindom

Additive Manufacturing (AM) been proved as a method to offer new possibilities for the production of highly complex parts. One new interesting but yet small field of application is the 3D printing of complex optical elements, e.g. complex reflective mirror optics with integrated lightweight structures. However, to achieve surfaces with an optical quality on additive manufactured metal parts, mostly mechanical machining processes such as diamond turning or pad polishing are used. The studying of laser material processing, e.g. ultra-short pulsed laser ablation as a post-processing method for additive manufactured optical components is of great importance. In this study, we investigate the influence of the initial surface quality on the ultra-short pulsed laser ablation process. Therefore, we varied the build angles of our samples and used different laser parameter setups to determine e.g. the ablation rate, achievable surface quality and process efficiency.

2:45pm - 4:00pmMacro: System Technology and Process Control 2
Location: Room 4
Session Chair: Jonas Wagner, Universität Stuttgart, Germany
Room 4 
2:45pm - 3:00pm

Active mirrors for plan field correction in laser material processing

Paul Böttner1, Aoife Brady1, Claudia Reinlein3,2, Ramona Eberhardt1, Stefan Nolte1,2

1Fraunhofer IOF, Germany; 2FSU Jena, Germany; 3Robust AO GmbH, Germany

This paper reports on an approach to increase the scan field and the dynamic range of post objective scanners. An active mirror in combination with a fixed focusing lens is used to adjust the optimal focus length depending on the beam position in the scan field.

The active mirror has an adjustment range from infinity to 0.5 dpt with a step response time of 2 ms. The scan field is determined by the focal length of the focusing lens. When using a focal length of 250 mm, a scan field of (100 x 100) mm² is achieved. Doubling the focal length increases the scan field to (500 x 500) mm². Measurements with a raw beam diameter of 20 mm and a wavelength of 1064 nm provide a spot diameter of 34 µm with a focal length of 250 mm and 75 µm with a focal length of 500 mm.

3:00pm - 3:15pm

Fixture-free laser-beam-welding

Georgij Safronov1, Alexander Grimm1, Florian Schlather1, Markus Puschmann2, Philipp Ronald Engelhardt1, Markus Lachenmaier1

1BMW AG, Germany; 2Fraunhofer Institute for Machine Tools and Forming Technology, Germany

Today’s automotive Bodyshop is dominated by resistance-point-welding due to low cost and robustness, especially regarding part-quality-variations. In contrast laser-beam-welding is struggling to create a solid business case in big numbers even so it has technological advancements like the welding-speed. To economically resolve this competition, we need an approach to create a balanced synergy between both joining methods. BMW together with the Fraunhofer Society (IWU) and the Technical University Munich (iwb) approached this challenge by developing a method to combine both welding procedures through a lap-joint-flange integrated geometry, which can be brought in off-tool in the press-shop.

These functional geometries allow us to use the advantages of resistance-point-welding to fix the geometry and create a laser-suitable gap-situation without clamping-tools for the following laser-welding. We also proved the technological and the financial viability of this method and we believe this could be a game-changer for laser-welding in the automotive industry.

3:15pm - 3:30pm

Remote laser welding system with automatic 3D teaching, in-line 3D seam tracking, and adaptive power control

Matija Jezersek1, Matjaž Kos1, Erih Arko2, Hubert Kosler2

1University of Ljubljana, Faculty of Mechanical Engineering, Laboratory for Laser Techniques, Aškerčeva cesta 6, 1000 Ljubljana, Slovenia; 2Yaskawa Slovenija d.o.o., Lepovče 23, 1310, Ribnica, Slovenia

An adaptive remote laser welding system, based on triangulation feedback control is presented. It enables off-line measuring of a workpiece 3D shape, in-line 3D seam tracking, and in-line laser power control, which are extremely important features for producing sound welds on complex geometries. The 3D measuring is done by a triangulation camera and the laser’s pilot beam. The same camera is utilized to determine the 3D seam position and to monitor the key process features, including the weld penetration depth.

Results show high 3D measuring precision in the lateral (0.05 mm) and vertical (0.3 mm) direction. Additionally, laser power control significantly reduces penetration depth and plasma oscillations. Thus, adaptive laser welding can be used for small series and customized production of parts where a highly flexible, precise, and cost-effective joining technology is required.

3:30pm - 3:45pm

Image-based Real-Time Defect Detection during Laser Welding using Ensemble Deep Learning on Low Power Embedded Computing Boards

Christian Knaak, Jakob von Eßen, Peter Abels, Arnold Gillner

Fraunhofer ILT, Germany

Advanced and intelligent process monitoring strategies are required to enable an unambiguous diagnosis of the process situation and thus of the final component quality. Additionally, the ability to recognize the current process situation in terms of quality is also a key requirement for autonomous manufacturing systems. To address these needs, this study investigates a novel ensemble deep learning architecture based on convolutional neural networks (CNN), gated re-current units (GRU) combined with high performance classification algorithms such as k-nearest neighbors (kNN) and support vector machines (SVM). The architecture uses spatio-temporal features extracted from infrared image sequences to locate critical welding defects including lack of fusion (false friends), sagging and lack of penetration, and geometric deviations of the weld seam. In order to evaluate the proposed architecture, this study investigates a comprehensive scheme based on classical machine learning methods using manual feature extraction and state of the art deep learning algorithms. Optimal hyperparameters for each algorithm are determined by an extensive grid search.

3:45pm - 4:00pm

System design for reliable and robust laser-welding of copper in automotive series production

Stefan Mücke, Pravin Sievi, Steffen Walter, Florian Albert

Scansonic MI GmbH, Germany

The evolution of mobility away from ICEs towards electric or electrified drives also created some new challenges for the series production of drive train components. With copper, a new material moves into focus in the drive train which needs to be welded. No matter if e-motors, e-boxes or batteries, copper needs to be welded and the laser fits best for the requests in most cases. The presentation will focus on what has to be considered for welding copper and to face these issues with an intelligent system-design to fit series production needs. Beside the design of the welding system with high-speed scanners and arrangement of the necessary components, the presentation also will focus on the matter of detecting the welding areas correctly to create a robust process that reduces costs and can cope with series production conditions.


Date: Wednesday, 23/June/2021
10:00am - 11:00amMacro: Welding, Aluminum
Location: Room 1
Session Chair: Prof. Thomas Graf, University of Stuttgart, Germany
Room 1 
10:00am - 10:15am

Remote laser welding of die casting aluminum parts for automotive applications with beam oscillation and adjustable ring mode laser

Mikhail Sokolov, Pasquale Franciosa, Dariusz Ceglarek

WMG, University of Warwick, United Kingdom

Aluminum die casting alloys are frequently used in the automotive industry for front and rear rails, corner nodes and interface blocks to weld together varying cross sections of aluminum extrusions in lightweight chassis structures. However, these materials have limited weldability due to entrapped gases which generate pores or cavities. Therefore, the thermal cycle during welding as well as the overall heat balance need to be carefully controlled in order to reduce the porosity level and hence achieve the desired joint integrity. This paper focuses on the selection of process parameters for the material combination of Al die casting C611 to Al extrusion AA6063. Results showed that the porosity level can be significantly reduced from 5-6% to below 2% of the weld area through the combination of beam oscillation and dual beam welding with Adjustable Ring Mode laser. Additionally, the selected parameters resulted in an average ultimate tensile strength of 120 MPa.

10:15am - 10:30am

Analytical approach for the transition to an equiaxed dendritic solidification during laser beam welding of aluminium alloys

Constantin Böhm1, Yassin Nasr1, Jonas Wagner2, Christian Hagenlocher2, Stefan Weihe1

1University of Stuttgart, Materials Testing Institute (MPA), Pfaffenwaldring 32, 70569 Stuttgart, Germany; 2University of Stuttgart, Institut für Strahlwerkzeuge (IFSW), Pfaffenwaldring 43, 70569 Stuttgart, Germany

An equiaxed solidification in a laser beam welded seam is beneficial. It leads to grain refinement, which increases mechanical strength and hot cracking resistance. The effects of filler wire addition and welding parameters on the resulting grain structure are experimentally well studied. Up until now, there has been no description of the process window for equiaxed solidification in terms of the process parameters. This work presents an analytical approach to access the description of the columnar-to-equiaxed transition based on fundamental solidification theory for a wide-range of aluminium alloys and laser welding parameters. To validate the approach, the theoretically calculated powers are compared to experimental results of full penetrated weld seams. This study provides an overview of the key process parameters and the material characteristics, which determine the solidification mode – in this case columnar or equiaxed dendritic. Furthermore, a process window for grain refinement of aluminium alloys is derived.

10:30am - 10:45am

High-speed synchrotron X-ray investigation of full penetration welding of aluminum sheets

Jonas Wagner1, Christian Hagenlocher1, Marc Hummel2, Alexander Olowinsky3, Rudolf Weber1, Thomas Graf1

1Institut für Strahlwerkezuge (IFSW), Universität Stuttgart, Germany; 2Chair for Laser Technology LLT, RWTH Aachen University, Germany; 3Fraunhofer Institute for Laser Technology ILT, Aachen, Germany

Full penetration laser beam welding of aluminum alloys is widely applied in industrial welding processes of sheet metal components. It is characterized by a capillary, which fully penetrates two or more sheets in overlap configuration and is open at its top and bottom. Compared to partial penetration laser beam welding, full penetration welding is associated with a stable capillary and therefore a more reliable process because the additional opening at the bottom side results in the avoidance of a collapsing capillary tip. The behavior of the capillary was analyzed by means of high-speed X-ray imaging at the DESY-synchrotron for welding of aluminum sheets with thicknesses of 1 mm and 2 mm. The results prove the stabilization of the capillary if it opens at the bottom side of the sheet. Despite the reliable avoidance of capillary collapses, the formation of pores is still observed.

10:00am - 11:00amAdditive Manufacturing: Powderbed, Metal 1
Location: Room 2
Session Chair: Dr. Peer Woizeschke, BIAS – Bremer Institut für angewandte Strahltechnik GmbH, Germany
Room 2 
10:00am - 10:15am

Investigation of Kovar in PBF-LB/M

Arvid Abel1, Jakob Pufal1, Vitaly Rymanov2, Christian Hoff1, Jörg Hermsdorf1, Stefan Kaierle1, Andreas Stöhr2,3, Sumer Maklouf3, Jörg Lackmann3

1Laser Zentrum Hannover e.V., Germany; 2Microwave Photonics GmbH, Germany; 3Universität Duisburg-Essen, Zentrum für Halbleitertechnik und Optoelektronik, Germany

The iron-nickel-cobalt alloy Kovar is highly desirable in glass-to-metal hybrid components, e.g., hermetic seals, or as packaging material in high-frequency microsystems due to its thermal expansion coefficient similar to borosilicate glass. Hitherto, the processability of Kovar in additive manufacturing has only been insufficiently investigated, leaving the potential of this material for functional integrated components unused. This paper describes the processing in PBF-LB/M and the understanding of the process parameters to achieve a relative density over 99.9 % in test specimens, large volumes, and complex structures. The investigated factors were laser power, scanning speed, and hatch distance. The initial experiments were done as full factorial designs. Subsequent investigations were done within the design of experiments to develop an empirical process model for the fabrication of Kovar in the PBF-LB/M. The best results were fabricated with volumetric energy densities between 200 to 350 to achieve a maximum density of 99.94 %.

10:15am - 10:30am

Machine-comprehensive study of comparability and reproducibility for laser powder bed fusion of corrosion resistant steel 316L/1.4404

Florian Bittner1, Bernhard Müller1, Maximilian Zinke2, Aitor Echaniz3, Sebastian Matthes4, Burghardt Klöden5, Christian Kolbe6

1Fraunhofer IWU - Institute for Machine Tools and Forming Technology; 2AM metals GmbH; 3Robert Bosch GmbH; 4ifw Jena - Günter Köhler-Institut für Fügetechnik und Werkstoffprüfung; 5Fraunhofer IFAM - Institute for Manufacturing Technology and Advanced Materials, Location Dresden; 6FKT GmbH

Additive Manufacturing of metallic components by laser powder bed fusion (LPBF) earns increasingly importance for industrial applications. However, for further industrial penetration different challenges have to be overcome. The most urging challenge is the warranty and control of a constant high quality, which includes machine-comprehensive comparability of components goodness. Important factors are the respective machine concept, used powder as well as respective processing parameters.

The results of a standard VDI 3405-2 based round robin test for steel 316L (1.4404) are discussed, at which five partners with different machines participated. The implementation is not based on ideal conditions, but addresses the respective individual best practise. Thereby, the differences between included machine concepts and scattering within a manufacturing order are discussed. With this, the existing gap of standardisation of properties for LPBF of the well-established material 316L/1.4404 shall be closed analogue to a series of other materials within the VDI-standard family 3405.

10:30am - 10:45am

Oxide dispersion strengthened steel manufactured by laser powder bed fusion and directed energy deposition

Carlos Doñate-Buendia1,2, Philipp Kürnsteiner3,4, Markus Benjamin Wilms5, Baptiste Gault3,6, Bilal Gökce1,2

1Department of Materials Science and Additive Manufacturing, University of Wuppertal, 42119 Wuppertal, Germany; 2Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, 45141 Essen, Germany; 3Department Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, 40237 Düsseldorf, Germany; 4Christian Doppler Laboratory for Nanoscale Phase Transformations, Center for Surface and Nanoanalytics (ZONA), Johannes Kepler UniversityLinz, Altenberger Straße 69, 4040 Linz, Austria; 5Fraunhofer Institute for Laser Technology, 52074 Aachen, Germany; 6Department of Materials, Royal School of Mines, Imperial College, Exhibition Road, London, SW7 2AZ, UK

Additive manufacturing technologies appear ideal for the generation of custom geometries and parts. In the context of specific applications such as high-temperature industrial processes like gas turbines or furnaces, the development of parts with enhanced high-temperature strength and oxidation resistance is highly desired. Oxide dispersion strengthened (ODS) steels are considered as suitable materials for such high temperature application. To assess the effect of the processing technique on the manufacturing of ODS steels and its properties, an Fe-Cr based steel powder decorated with a 0.08 wt% of laser generated Y2O3 nanoparticles is processed by laser powder bed fusion (LPBF) and directed energy deposition (DED). We show that the produced specimens show superior mechanical properties at 600ºC compared to the reference part built without nanoparticle-addition. The enhanced mechanical properties are explained by the microstructure and nanoparticle dispersion in the generated ODS steels and confirmed by melt pool simulations.

10:00am - 11:00amMicro: Ablation, Drilling and Cutting 1
Location: Room 3
Session Chair: Dr. Hans-Joachim Krauß, Bayerisches Laserzentrum GmbH, Germany
Room 3 
10:00am - 10:15am

Formation of smooth and flat area for monocrystalline diamond by ns pulsed laser

Yasuhiro Okamoto, Tubasa Okubo, Atsuya Kajitani, Akira Okada

Okayama University, Japan

The combination of ns pulsed laser and acid cleaning can achieve a smooth and flat surface below Ra=0.2 µm for monocrystalline diamond, when laser fluence is controlled around the threshold of removal. Although Gaussian mode is used, shiny and flat surface can be obtained in parallel direction to top surface of workpiece. Therefore, formation method of smooth and flat surface was experimentally investigated by repeating linear grooving, when ns pulsed laser of top-hat mode (1060 nm) was employed. However, subsequent linear grooving to previous one made it difficult to create flat surface with a constant depth, and two-step irradiation method was proposed. Non-removal areas were kept between processed lines in the first step, and the remained area between processed lines of the first step was removed in the second step. The two-step irradiation method was effective to achieve a wide flat-area, and it could improve the controllability of groove depth.

10:15am - 10:30am

Laser structuring of PVD multi-layer coatings for wear reduction

Andreas Stephen1, Bastian Lenz2, Andreas Mehner2, Tim Radel1

1BIAS GmbH, Germany; 2Leibniz-IWT, Germany

Surface texturing is an effective way of improving tribological properties. Its main effect mechanisms are to trap wear particles and store lubricants. One of these technologies is texturing the surface with micro dimples by laser ablation. In this paper, the selective texturing of multi-layer systems, i.e., removing only the top layer by ultra-short pulse laser processing is presented. The removal of the top layer with 1 µm in thickness of the systems (TiN/MoS2:Ti and TiN/a-C:H:Ti/MoS2:Ti:C) is proven by laser confocal microscopy and EDX analysis. The selective laser structuring of the multi-layer systems generated by PVD synthesis developed for tribological applications, among others for the aerospace industry, results in precise structures with depth deviations of less than 0.2 µm without burrs or melt residues. These textures will further on result in reduced wear depending on the structured layer systems and the geometry of the textures regarding dimple diameter and density.

10:30am - 10:45am

Optimized laser cutting processes and system solutions for separation of ultra-thin glass for OLED lighting and display applications

Rene Liebers, Mandy Gebhardt

3D-Micromac AG, Germany

For some years now, laser cutting processes based on filament technology with ultrashort pulse (USP) lasers have been increasingly adopted in industrial applications. The main reasons for this are the good edge quality that can be achieved with simultaneous easy automation and free-form capability. This ability to be automated is of critical importance, especially for applications that target the mass market with their end products. However, the real advantage of the technology comes from its almost unlimited free-form capability. In addition to established manufacturing processes for glasses of medium thickness from 0.2-2 mm, an increasing number of applications with ultra-thin glasses of 30-100 µm are entering the market. These applications also require further development of the process and fab technology.

This presentation covers the possibilities of laser technology based on applications for OLED-based lighting and glass components in the display area.

10:00am - 11:00amMicro: Surface Functionalization 1
Location: Room 4
Session Chair: Dr. Thomas Stichel, Bayerisches Laserzentrum GmbH (blz), Germany
Room 4 
10:00am - 10:15am

Fabrication of complex periodic patterns on a metallic drum for high throughput roll-to-roll processing

Bogdan Voisiat1, Max Menzel1, Wei Wang1, Yangxi Fu1, Marcos Soldera1, Andrés Fabian Lasagni1,2

1Dresden University of Technology, Germany; 2Fraunhofer Institute for Material and Beam Technology, Germany

In this study, the development of complex periodic structures on massive metal drums by means of direct laser interference patterning (DLIP) is demonstrated. The DLIP technology allows the formation of high-resolution periodical structures (even with sub-micrometer resolution) at high fabrication speeds on large surface areas. These advantages drastically reduce the patterning costs of the drums that are broadly used in roll-to-roll processing. We demonstrate the ability to control individually each laser spot (e.g. period) to form complex periodical patterns to be used as decorative elements exhibiting structural colors. These patterns are then replicated on a polymer foil by an industrial hot-embossing roll-to-roll process at speeds up to 50 m/min. This process brings the industrial fabrication of such patterns to the next level in terms of throughput and is thus suitable for mass production.

10:15am - 10:30am

Improving the bond strength of metal-FRP-hybrids with thermal sprayed copper using pulsed laser-based processing approaches

Jana Gebauer1, Volker Franke1, Kevin Gustke2, Udo Klotzbach1, Thomas Lampke2, Andrés Fabian Lasagni1,3

1Fraunhofer IWS, Germany; 2Chemnitz University of Technology, Germany; 3Technische Universität Dresden, Germany

Ablation processes during laser treatment of carbon fiber-reinforced plastics with pulsed lasers of various wavelengths and pulse durations are investigated. Three general surface pretreatment strategies are used, including laser-roughening, selective matrix removal and laser micro-structuring. Various ablation mechanisms, including evaporation and matrix delamination are observed, depending on the employed laser source. Selected laser structured substrates were coated with copper by a wire arc spraying process. Bonding strengths up to 18.1 ± 2.6 MPa and 18.7 ± 2.0 MPa were achieved in pull-off tests and shear tensile tests, respectively, by the combination of the roughening process and the micro-structuring approach. Consequently, the bonding strength could be increased up to ~ 200 % compared to the common pre-treatment by grit-blasting.

10:30am - 10:45am

Low temperature and high concentration laser doping system for fabrication of 4H-SiC power devices

Toshifumi Kikuchi1, Takuma Yasunami1, Akira Mizutani2, Daisuke Nakamura1, Hiroshi Ikenoue1

1Grad. Sch. ISEE. Kyushu Univ.,; 2Dept. of Gigaphoton Next GLP, Kyushu Univ.

We propose a high-concentration and low crystal damage doping method by irradiating KrF excimer laser to the deposited films contains of dopant atoms on the 4H-SiC surfaces. This laser doping method is a low-temperature process that reduces the thermal stress to the substrate, and can achieve doping concentration of ~1020 cm-3 or more, which exceeds the limit of the ion implantation method.

In this study, we investigated the peak energy dependence of the crystal damage and surface roughness by controlling the pulse width of the laser for doping. As a result, it is found that the crystal damage and surface roughness were reduced by suppressing the peak energy. In addition to this, we report on the construction of a laser doping system to improve compatibility with the manufacturing process of 4H-SiC power devices.

10:45am - 11:00am

Excimer laser annealing method with the controlled grain size of poly-Si films for large display panels

Akira Mizutani1, Fuminobu Hamano2, Daisuke Nakamura2, Tetsuya Goto3, Aid SitiRahmah4, Hiroshi Ikenoue1,2

1Department of Gigaphoton Next GLP, Kyushu University; 2Graduate School of Information Science and Electrical Engineering, Kyushu University; 3New Industry Creation Hatchery Center, Tohoku University; 4Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia

Low-temperature polycrystalline Si thin film transistors (TFTs) crystallized using the Excimer Laser Annealing (ELA) method have been used as backplanes for active matrix organic displays due to their high electron mobility. However, the current ELA method requires a long axis of the line beam which is equivalent to the short axis of the substrate's size, and there is a limitation in application to a large glass substrate. One of the methods to overcome this problem is to anneal the entire surface by folding back the beam. However, in the overlapping region of the laser, the crystal grain size becomes large, and the device characteristics become ununiform. In this study, we report on the results of evaluating the TFT characteristics by controlling the crystal grain position and size by laser annealing with a periodic intensity distribution induced by a dot array mask to form the same crystal grain size in the overlap regions.

10:00am - 11:00amAdditive Manufacturing: Powderbed, Ti-6Al-4V
Location: Room 5
Session Chair: Richard Rothfelder, Institute of Photonic Technologies (LPT), Germany
Room 5 
10:00am - 10:15am

Effect of microstructure for additively manufactured Ti64 plate on modulated pulses by vacuum SLM.

Yuta Mizuguchi1, Tsuneyoshi Arimura2, Masahiro Ihama1, Yuji Sato3, Norio Yoshida3, Minoru Yoshida2, Masahiro Tsukamoto3

1Graduate School of Engineering, Osaka University, 1-1 Yamadaoka, Suita, Osaka, 565-0871, Japan; 2Graduate School of Science and Engineering, Kindai University, 3-4-1 Kowakae, Higasiosaka, Osaka, 577-8502, Japan; 3Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka, 567-0047, Japan

Selective laser melting (SLM), which is an additive manufacturing technology, is a method that metal powder was melted and solidified by laser. There was a problem that distribution of crystal grain size was caused inhomogeneous by excessive input because of laser irradiation layer by layer. It was thought that anisotropy could be eliminated by controlling grain growth through precise control of heat input. In order to control a heat input, modulated pulses for laser were used. Purpose in this study, Ti64, which is clinical applied as an implant material due to its biocompatibility as well as its high corrosion and mechanical resistance, was fabricated with modulation pulses of laser. As the results, it was found that the pulse energy increase with increase the grain size of Ti64 plate fabrication.

10:15am - 10:30am

Development of a machine concept for the processing of Ti6Al4V in the LPBF process under silandized argon atmosphere

Marijan Tegtmeier, Nicole Emminghaus, Jannes August, Marius Lammers, Christian Hoff, Jörg Hermsdorf, Ludger Overmeyer, Stefan Kaierle

Laser Zenrum Hannover e.V., Germany

The presence of oxygen in the LPBF process leads to embrittlement in the workpiece in materials with high affinity to oxygen. Especially the metal powder Ti6Al4V requires a special protective atmosphere during processing. By doping the argon 1.5% with monosilane, the residual oxygen of a usual argon atmosphere is bound and reduced to a value typical for XHV (Extreme High Vacuum).

Basically, the development of an LPBF system according to VDI 2221 is presented. The admixture of silane requires an innovative machine concept in order to ensure the compatibility of the materials used and to prevent the process gases from becoming hazardous. The phases of development are accompanied by comprehensive reaction studies and flow simulations. The resulting concept relies on a compact machining area (Ø100x100mm) and breaks new ground in the processing of special materials, not only through the process gases used, but also in powder and workpiece management.

10:30am - 10:45am

Influence of laser focus shift on porosity and surface quality of additively manufactured Ti-6Al-4V

Nicole Emminghaus, Christian Hoff, Jörg Hermsdorf, Stefan Kaierle

Laser Zentrum Hannover e.V., Germany

In laser-based powder bed fusion of metals (PBF-LB/M) an increase of the laser spot size by shifting the focus position offers the opportunity of reducing the overall scanning time as well as achieving a more stable melt pool behavior. However, the influence on porosity and surface roughness of bulk samples has received little attention so far. In this work, the influence of laser focus shift (Yb-fiberlaser, minimum beam diameter of 35 µm) on part porosity as well as top and side surface roughness is investigated for additively manufactured Ti-6Al-4V. The focusing lens position relative to its standard setting is varied between 1.2 mm and -8.7 mm and the resulting track width is evaluated. Further, the main processing parameters are varied. The influences and interaction effects of all varied parameters are statistically evaluated according to the design of experiments approach. Optimum settings for low porosity and surface roughness are presented.

11:15am - 12:30pmMacro: Joining 1
Location: Room 1
Session Chair: Dr. Andrey Gumenyuk, Bundesanstalt für Material Forschung und -prüfung (BAM), Germany
Room 1 
11:15am - 11:30am

Investigations on the weld seam geometry of ultrasonic assisted laser beam welded round bars in and beside antinode position

Jan Grajczak1, Christian Nowroth2, Sarah Nothdurft1, Jörg Hermsdorf1, Jens Twiefel2, Jörg Wallaschek2, Stefan Kaierle1

1Laser Zentrum Hannover e.V., Germany; 2Gottfried Wilhelm Leibniz Universität Hannover

Laser beam welds are usually symmetric. They can be forced to form asymmetric weld seams by introducing ultrasound.

Ultrasound can be used for grain refinement and reducing segregation. The investigations describe ultrasonic assisted laser beam welding around antinode position of a stationary ultrasonic wave.

The experiments are carried out with 2.4856 round bars, a laser beam power of 6 kW, a welding speed of 0.95 m/min and ultrasonic amplitudes of 0 µm and 4 µm. The welding positions are placed 0/7.5/15.0 mm on the right and left side of antinode position. Afterwards sample macrographs and micrographs of metallgraphic cross sections are made. It turns out that the asymmetry is direction dependent. In result, the understanding of interactions between welding area and passing ultrasound is improved.

11:30am - 11:45am

Observation of the weld pool shape in partial penetration welding and its influence on solidification crack formation for high-power laser beam welding

Nasim Bakir1, Ömer Üstündag1, Andrey Gumenyuk1,2, Michael Rethmeier3,1,2

1Bundesanstalt für Materialforschung und -prüfung (BAM), Germany; 2Fraunhofer Institute for Production Systems and Design Technology; 3Institute of Machine Tools and Factory Management, Technische Universität Berlin

Solidification cracking is still a particular problem in laser beam welding, especially in the welding of thick-walled plates. In this study, the influence of weld pool geometry on solidification cracking in partial penetration welding of thick plates is a subject of discussion. For this purpose, a special experimental setup of steel and quartz glass in butt configuration and lateral with high speed camera was used to capture the weld pool shape. Additionally, laser beam welding experiments were carried out to compare the crack positions and the cross section with the high-speed camera observations. The results showed a bulge in the weld pool root separated from the upper region by a nick area. This leads to the fact that three different longitudinal lengths with different solidification areas are taking place. This temporal sequence of solidification strongly promotes the solidification cracks in the weld root.

11:45am - 12:00pm

Occurrence of coating-related accumulations within the seam in laser beam deep penetration welding of aluminum-silicon coated press-hardened steels

Benjamin Karwoth, Thorsten Mattulat, Peer Woizeschke

Bremer Institut für angewandte Strahltechnik GmbH, Germany

In case of laser beam deep penetration welding of press-hardened and Al-Si-coated Mn-B-steels being coated to protect the base metal from scaling during press hardening, a reduced joint strength is observed in relation to the basemetal. One influencing factor is the insertion of coating constituents into the weld seam during the welding process. The objective of this study was to investigate the influence of partially decoated sheets on the amount of accumulation occurring in the seam of the overlap weld of two sheets. For this purpose, the samples were partially decoated in different ways before the joining process. The welds were analyzed by means of cross-sections. The results indicate that especially the coating on the contact surfaces of the sheets in the lap joint affects the accumulation of coating constituents. Partial decoating of one or both contact surfaces was able to significantly reduce the amount and size of the accumulations.

12:00pm - 12:15pm

Thermal cycles and cahrpy impact toughness of single-pass hybrid laser-arc welded thick-walled steels

Ömer Üstündag1, Nasim Bakir1, Andrey Gumenyuk1,2, Michael Rethmeier3,1,2

1Bundesanstalt für Materialforschung und -prüfung, Germany; 2Fraunhofer Institute for Production Systems and Design Technology; 3Institute of Machine Tools and Factory Management, TU Berlin

The study deals with the influence of the heat input on the grain sizes, thermal cycles and Charpy impact toughness for hybrid laser-arc welding of 25 mm thick structural steel S355J2 using a 20-kW high-power laser in combination with an electromagnetic weld pool support. The main focus is on the change of the mechanical properties over the entire seam thickness. The cooling times were measured using a pyrometer in combination with an optical fibre in three different locations near to fusion lines corresponding to different heights of the seam. Also, Charpy impact specimens were taken from different parts of the weld joint corresponding to the different heights. The heat input was variated between 1.8 kJ/mm and 3.2 kJ/mm. Despite the observed decreased values of both t8/5 cooling time and the Charpy impact toughness in the root part of the seam, the required values could be reached in dependance on applied heat input.

12:15pm - 12:30pm

Non-contact focus spot and focus shift measurement of high power lasers in the manufacturing of differential gears

Nicolas Meunier

MKS Instruments - Ophir Brand, Germany

The higher the power and energy density in the focus of the laser beam, the more efficient is the process in terms of traverse speed, hardness increase, deformation and other effects. Even a minimal focus shift or an imprecisely adjusted tool center point (TCP) shows extremely negative impact on the quality of the weld. Traditional measurement methods are too complex to capture the focus shift or to quickly check the focus position. The non-contact beam profiling technology developed by MKS Ophir eliminates limits in terms of power, and the measurement takes only seconds. Especially for 24/7 industrial use, MKS Ophir developed a fully automated, robust device with an easy to use operating interface.

Nicolas Meunier, Business Development Manager High Power und Automotive Products Ophir, explains the measurement principle and presents real world use cases.

11:15am - 12:30pmAdditive Manufacturing: Powderbed, Metal 2
Location: Room 2
Session Chair: Dr. Peer Woizeschke, BIAS – Bremer Institut für angewandte Strahltechnik GmbH, Germany
Room 2 
11:15am - 11:45am

Invited Talk: Insight into fatigue behaviour of additively manufactured alloys: results of the DREAM project

Elena Bassoli

Department of Engineering „Enzo Ferrari“, Univ. Modena e Reggio Emilia, Italy


11:45am - 12:00pm

3D printing of Al-Li with increased Li content using laser assisted powder bed fusion

Burak Yürekli1, Dongmei Liu2, Tobias Ullsperger1, Hagen Kohl1, Lisa Schade1, Gabor Matthäus1, Markus Rettenmayr2, Stefan Nolte1,3

1Institute of Applied Physics, Friedrich Schiller University Jena, Germany; 2Otto Schott Institute of Materials Research, Friedrich Schiller University Jena, Germany; 3Fraunhofer Institute for Applied Optics and Precision Engineering, IOF Jena, Germany

Based on the extremely low atomic mass of Li, the binary alloy Al-Li holds high potential for future light-weight alloys. In particular, the elastic modulus significantly increases with rising Li content, offering the potential of extremely high stiffness as compared to conventional Al alloys. However, due to the limited solubility of Li accompanied by the formation of brittle δ-AlLi phase during solidification, the maximum Li content is generally limited to about 2 wt. %. Here we present laser assisted 3D printing using Al-Li with an increased Li content of 4 wt. %. The process is based on custom-made Al-Li powder, which is characterized in terms of powder particle size, density, absorption, and thermal conductivity. In contrast to common approaches, here, ultrashort laser pulses are used for the melting process, delivering 3D printed parts with a drastically reduced fraction δ-AlLi phase due to the increased solidification rates of the melt pool.

12:00pm - 12:15pm

Adjusting the surface roughness of WE43 components manufactured by laser-based powder bed fusion

Tjorben Griemsmann, Niclas Söhnholz, Christian Hoff, Jörg Hermsdorf, Stefan Kaierle

Laser Zentrum Hannover e.V., Germany

The outstanding characteristics of magnesium alloys make them promising materials for biomedical or lightweight construction applications, especially in combination with the advantages of laser-based powder bed fusion. While most research in this field focusses porosity and microstructural properties, the surface quality is left out. Because the surface is an important factor for corrosion and notch effects, this work addresses the adjustment of the surface roughness from parts made out of a WE43 alloy. Using design of experiments contour scan trials are carried out for vertical and down skin surfaces. As a result, the roughness of vertical surfaces is reduced from approximately 27.1 µm (Ra) and 172.2 µm (Rz) without contour scans to 10.9 µm and 87.4 µm with contour scans. The applicability of the contour parameters is approved by cross sections to investigate the porosity of the contour volume interface and a topology optimized gear housing is manufactured for validation.

12:15pm - 12:30pm

Influence of process-relevant parameters and heat treatments on the microstructure and resulting mechanical behavior of additively manufactured AlSi10Mg via laser powder bed fusion

Andreas Kempf1, Leonardo Agudo Jácome2, Kai Hilgenberg3

1Volkswagen AG, Werkstofftechnik, 38436 Wolfsburg, Deutschland; 2Bundesanstalt für Materialforschung und -prüfung (BAM), Division 5.1 – Materialographie, Fraktographie und Alterung technischer Werkstoffe, 12205 Berlin, Deutschland; 3Bundesanstalt für Materialforschung und -prüfung (BAM), Division 9.6 – Additive manufacturing of metallic components, 12205 Berlin, Deutschland

Within the group of additive manufacturing (AM) technologies for metals, laser powder bed fusion (L-PBF) has a leading position. Nevertheless, reproducibility of part properties has not reached sufficient maturity hindering the use for industrial applications especially for safety-relevant components. This article presents the results of various experimental tests performed with the aluminium alloy AlSi10Mg identifying reasons for the high deviations in mechanical properties. Herein, it is discussed how microstructure is influenced by different process parameters (laser power, scanning speed, energy density, building time) and how it can be adjusted by suitable post process heat treatments. The impact of resulting changes in microstructure on the mechanical behavior is shown by quasistatic and cyclic tests considering samples manufactured with different L-PBF machines.

11:15am - 12:30pmMicro: Ablation, Drilling and Cutting 2
Location: Room 3
Session Chair: Lisa Ackermann, Institute of Photonic Technologies (LPT), Germany
Room 3 
11:15am - 11:30am

Polymer film processing with a high-power industrial femtosecond laser

Chandra Sekher Reddy Nathala, Victor Matylitsky, Herman Chui

MKS Spectra-Physics

Polymer materials are increasingly important for medical device, flat panel display and microelectronics applications. Due to the high thermal sensitivity of polymers, femtosecond laser processing can minimize heat deposition, and high powers are needed to achieve fast processing. In our work, we present ablation thresholds and cutting speeds for two common polymer materials, polyethylene terephthalate (PET) and polyimide, processed with a 100 W femtosecond laser with single and burst pulses and at infrared and green wavelengths. Cutting speeds were determined for both single-pass and multi-pass strategies. In addition to determining the ablation thresholds and the maximum cutting speed, the processed samples were analyzed for kerf width and heat affected zone (HAZ). The effect of burst mode operation and spot size on cutting speed, kerf width and HAZ were determined. With optimized parameters, high speed, high quality cutting of PET and polyimide films was demonstrated with a high-power femtosecond laser.

11:30am - 11:45am

Roll-to-roll laser processing of flexible devices

Maurice Clair, Christian Scholz, Mandy Gebhardt

3D-Micromac AG, Germany

In the manufacturing of flexible thin-film devices precision, throughput, and machining quality on ever-smaller structures are playing an important role.

The presentation will give a brief overview of different case studies where roll-to-roll (R2R) laser processing achieve new dimensions in terms of precision, quality and process efficiency.

An example application is the ablation of thin-film layers for medical sensors. In this case, the on-the-fly laser ablation takes place by using an excimer laser and mask projection. The layout of the products is adaptable by various projection masks. The high-repetition rate of the excimer laser allows the production of up to 150 sensors per second. Furthermore, thin-film annealing and cutting of metal substrates with ns lasers as well as thin-film patterning and cutting of polymer substrates with ultrashort pulse laser in a R2R process will be discussed.

11:45am - 12:00pm

Combining LPBF and ultrafast laser processing to produce parts with deep microstructures

Manuel Henn, Matthias Buser, Volkher Onuseit, Rudolf Weber, Thomas Graf

Institut für Strahlwerkzeuge IFSW, Germany

Laser Powder Bed Fusion (LPBF) is limited in the achievable accuracy, surface quality and structure size due to its inherent melting process. The achievable structure sizes are mainly dependent on the focal diameter and the grain size of the powder. Smaller structures, especially deep and narrow slits with a width below 100 µm, are still a major challenge.

Combining continuous wave and ultrashort pulsed lasers in the same optical system enables consecutive additive and subtractive processes. This results in a quasi-simultaneous manufacturing process, where the emerging part can be precisely machined with ultrafast laser ablation after each additively added layer.

In the talk the system technology used for the superposition of the lasers as well as the results of the combined additive and subtractive processes for the fabrication of deep and narrow slits in stainless steel parts will be shown.

12:00pm - 12:15pm

Towards in situ monitoring and feedback control of femtosecond laser-induced nanogratings formation in dielectrics

Olivier Bernard1, Andrea Kraxner2, Assim Boukhayma2,3, Ata Golparvar2, Yves Bellouard1, Christian Enz2

1Galatea Lab, École polytechnique fédérale de Lausanne, Rue de la Maladière 71b, CH-2002 Neuchâtel, Switzerland; 2Integrated Circuits Laboratory, École polytechnique fédérale de Lausanne, Rue de la Maladière 71b, CH-2002 Neuchâtel, Switzerland; 3Senbiosys SA, Rue de la Maladière 71c, CH-2000 Neuchâtel, Switzerland

Tightly focused non-ablative femtosecond laser pulses induce a variety of structural modifications in the bulk of dielectrics. Among those, sub-wavelength nanogratings are particularly interesting as a means not only to locally enhance the material etching selectively (and thus, enabling bulk 3D-micro-fabrication), but also for encoding rich information in high-density permanent data storage media. Femtosecond laser-based processes are subject to perturbations, affecting the repeatability and accuracy of the results. To increase the performance of these processes, we explore a feedback method based on direct monitoring of the laser-affected zone (LAZ) using a probe beam. Specifically, we report on the use of weak signals resulting from the interaction of a femtosecond laser probe-beam with the nanogratings index-modulation as objective functions in feedback loop algorithms.

11:15am - 12:30pmMicro: Surface Functionalization 2
Location: Room 4
Session Chair: Martin Hohmann, Institute of Photonic Technologies (LPT), Germany
Room 4 
11:15am - 11:30am

Molded parts with functional surfaces – how laser microstructuring can be used for low-cost mass products

Maik Steinbach, Jürgen Koch, Peter Jäschke, Stefan Kaierle, Ludger Overmeyer

Laser Zentrum Hannover e.V., Germany

Microstructuring via ultrashort pulse laser enables the targeted generation of functional surface structures. With this technology, progress in material behavior has been shown in tribological, optical and haptical properties, liquid wettability and cell adhesion. In cases where the effect is mainly based on the laser-generated microstructures instead of laser-induced chemical changes of the surface material, injection molding offers a possibility to make the usually high-priced laser surface functionalization accessible to low-cost mass products. This technique leaves the chemistry of the molded parts unaffected, which makes it especially attractive for biomedical applications. Molding inverts the surface topography and can be associated with resolution, durability and demoldability restrictions. We present our current results and findings on basic as well as on application-oriented issues. Selected applications including a technique for piracy protection are discussed.

11:30am - 11:45am

Towards optimization of femtosecond laser pulse nano-structuring for high-intensity laser interactions

Ulrich Teubner1,3, Imgrunt Jürgen1, Andreev Alexander1,2

1Institut für Laser und Optik, Hochschule Emden/Leer – University of Applied Sciences, Constantiaplatz 4, 26723 Emden, Germany; 2Sankt Petersburg State University, Sankt Petersburg, Russia; 3Institut für Physik, Carl von Ossietzky Universität Oldenburg, Ammerländer Heerstr. 114-118, 26111 Oldenburg, Germany

The interaction of intense femtosecond laser pulses with solid targets is a topic that has attracted large interest in science and applications. For many of the related experiments a large energy deposition or absorption and an efficient coupling to XUV- and/or X-ray photons and/or high energy particles is important. Here, beside improvements in laser pulse properties also those of the target are relevant. The present work investigates the formation of laser-induced periodic surface structures on massive metal targets by femtosecond laser pulses in vacuum. The experimental results and the ripple formation mechanisms have been analysed and interpreted with newly developed theoretical models. The present results contribute to a simple optimization of targets by nano-structuring their surface in-situ which leads to a significantly enhanced absorption and conversion efficiency into XUV emission, X-rays and/or high energy electrons and protons after irradiation with a subsequent intense laser pulse.

11:45am - 12:00pm

Targeting mass production of nano/micro textured surfaces by USP laser: the New Skin project

Girolamo Mincuzzi, Alexandra Bourtereau, Marc Faucon, Laura Gemini, Simon Nourry, Aurélien Sikora, Rainer Kling

Alphanov, Aquitaine Institute of Optic - Rue F. Mitterand 33400 Talence (France)

Ultra-Short Pulse laser texturing (USP-LT) is a key technology for functionalisation of materials surface. Although the texturing of ≈1m2 surfaces have been successfully shown, extend USP-LT over several m2 surfaces represents an issue due to the need of high P, and a difficult process control. The “New Skin” project could represent a turning point pushing the readiness of USP-LT with a significant up-scale of the production volume.
Here we show the preliminary results obtained with the implementation of a demonstrative pilot line based on a 350 W, fs laser and a polygon scanner. We report the optimisation of the structures morphology on steel when P exceeds few hundreds of watts as well as the impact of the repetition rate (up to 10 MHz) and the hatch. A roll-to-roll approach is proposed jointly with an in-line monitoring system based on scatterometry. Finally, possible applications and values propositions are introduced and discussed.

12:00pm - 12:15pm

In-line monitoring of submicron laser texturing: a test bench for scatterometry

Aurélien Sikora, Girolamo Mincuzzi, Rainer Kling

ALPhANOV, France

Laser Induced Periodic Surface Structures (LIPSSs) with a submicronic periodicity induce a variety of surface properties (iridescence, hydrophobicity, antibacterial, etc.). In-line monitoring of LIPSS dimensions is challenging since the resolution of optical based microscopy techniques is insufficient or unable to withstand with harsh, industrial environment. These issues can be overcome using indirect measurement techniques such as scatterometry. It makes possible an indirect measurement of LIPSS morphology by analysing the reflection and/or diffraction pattern of an incoming light having a known spectrum and polarisation. We show that by using a proper configuration, scatterometry is barely sensitive to vibrations and fast enough for in-line monitoring fitting industrial requirements. In the frame of the NewSkin H2020 project, a scatterometer has been integrated and tested in a roll-to-roll machine including a fast polygon scanner (up to 200 m/s) and a 350 W femtosecond laser targeting mass production of LIPSS for antibacterial stainless steel.

12:15pm - 12:30pm

Effects of various misalignments and beam impurities on creation of optical needle using Pancharatnam-Berry phase elements

Pavel Gotovski1,2, Paulius Slevas1,3, Sergej Orlov1, Orestas Ulsinas1,3, Antanas Urbas1,3

1Center for Physical Sciences and Technology, Vilnius University, Lithuania; 2Vilnius Gediminas Technical University, Faculty of Electronics, Lithuania; 3Workshop of Photonics


11:15am - 12:30pmProcess Innovations
Location: Room 5
Session Chair: Prof. Jean Pierre Bergmann, Technische Universität Ilmenau, Germany
Room 5 
11:15am - 11:30am

Study of pointing stabilization unit for femtosecond fiber beam delivery system

Benoit Beaudou1, Pierre guay1, Fetah Benabid1, Ivan Gusachenko2, Clément Jacquard2, Gwenn Pallier2, Guillaume Labroille2

1GLOphotonics; 2Cailabs

Recent development of hollow-core inhibited coupling fibres paves the way to fibre beam delivery for femtosecond laser manufacturing applications. Nevertheless, reaching sufficient quality and reliability for such a functionality in industrial environment requires a Laser-fiber coupling system immunes to thermal and vibration fluctuations. As the Microstructure hollow-core fiber damage threshold is dependent of beam pointing stability of the laser system, beam stabilization sub-system has to be implemented to insure stable operation. This study attempts to qualify two beam stabilisation systems. The first one is two piezo motors coupled with Four quadrant detectors. The second one is Cailabs’ all-optical mode-cleaner system based Multi-Plane Light Conversion (MPLC) technology. MPLC enables a high control of modes propagation: a misaligned beam is projected on an adapted mode basis and the unwanted energy is then dumped. To do such output fibre transmission efficiency and beam quality are investigated under controlled fluctuation of beam pointing.

11:30am - 11:45am

Superimposed beam deflection using acousto-optical deflectors in combination with a galvanometer scanner

Daniel Franz1, Gian-Luca Roth1, Stefan Rung1, Cemal Esen2, Ralf Hellmann1

1Applied Laser and Photonics Group, University of Applied Sciences Aschaffenburg, 63739 Aschaffenburg,Germany; 2Applied Laser Technologies, Ruhr-University Bochum, 44801 Bochum, Germany

We report on the deflection behavior of a combined scanning system consisting of two acousto-optical deflectors (AOD) and a galvanometer scanner for ultra-short laser pulses. Firstly, the dynamic behavior and the precision of the individual AOD subsystem are characterized within it’s deflection range at different positioning frequencies. For the combined scanning system the roundness of the focus spot within an AOD scan field and the scan field dimensions at different galvanometer deflections are analyzed. In addition, the roundness of the spot and the scan field dimensions are determined as a function of galvanometer deflection and focus level. The investigations show that focus spot roundness’s > 90 % in a z-range of 200 µm can be realized in a galvanometer scanning field of 30 x 30 mm with positioning frequencies of up to 1 MHz using the superimposed laser beam deflection, highlighting it´s great potential for highly dynamic laser micromachining.

11:45am - 12:00pm

Advanced quasi-simultaneous welding – a new approach to laser welding of polymers

Lea Sauerwein, René Geiger, Christian Ebenhöh

Evosys Laser GmbH, Germany

Evosys Laser GmbH is developing a new variant of laser plastic welding, the so called Advanced Quasi-Simultaneous Welding (AQW). It combines two monochromatic laser beam sources and wavelengths in a sequential time pattern. By using two different wavelengths in a quasi-simultaneous welding process, the specific deposition of radiation energy and heat into each joining partner can be better controlled. This results into a more reliable welding operation with an enlarged process window.

Trials employing the new AQW process show that a significant improvement in weld seam quality is possible compared to the standard process with only one laser source. Due to the wavelength of the secondary laser source, more energy is deposited in the transmissive joining partner. The increased volume of plasticized material in this part is leading to an increased weld strength. Furthermore, it facilitates processing high-performance thermoplastics which often impose challenges to the laser welding process.

12:00pm - 12:15pm

Fully reflective annular laser beam shaping for laser beam welding at 16kW

Matthieu Meunier1, Romain Cornee2, Aymeric Lucas1, David Lemaitre2, Pierre Vernaz-Gris1, Gwenn Pallier1, Eric Laurensot2, Olivier Pinel1

1Cailabs, France; 2Institut Maupertuis, France

Laser Beam Welding (LBW) is commonly used in many fields of the industry, ranging from automotive and naval to aerospace. In order to improve LBW performance (process speed and quality as well as thickness of the parts to be weld) handling higher power, shaping the laser beam and reducing the focus shift are key.

We describe here a beam shaper compatible with industry standard equipment. The fully reflective design ease the heat evacuation leading to a reduced focus shift thanks to the absence of thermal gradient inside the optics, leading to better beam stability and process.

We demonstrate here the system capability to shape the input beam into an annular shape of high quality. The process tests are performed at multi-kW level up to 16kW with a high stability over the whole process. The process test results and the weld quality improvements are described for different materials.

12:15pm - 12:30pm

Laser-based manufacturing of ceramic matrix composites

Willy Kunz1, Clemens Steinborn1, Stefan Polenz2, Benjamin Braun3, Alexander Michaelis1

1Fraunhofer IKTS, Germany; 2Fraunhofer IWS, Germany; 3Space Structures GmbH, Germany

Ceramic matrix composites (CMCs) are quasi-ductile ceramics with excellent high-temperature properties. The main area of application is in aircraft engines as a replacement for nickel-based superalloys. Besides the high cost of the fiber material, the production of CMCs is quite expensive as advanced furnace technology is required. Furthermore, the joining of CMC components is still insufficiently developed.

This paper presents a novel manufacturing process that uses a laser as a heat source to locally solidify the ceramic material by generating a transient liquid matrix phase. Material properties as well as microstructural investigations are shown. The process is classified with regard to potential areas of application.

1:30pm - 2:30pmMacro: Joining 2
Location: Room 1
Session Chair: Artur Leis, University of Stuttgart, Germany
Room 1 
1:30pm - 1:45pm

Correlation between the spatial weld seam morphology and the spatial-temporal temperature profile in laser transmission welding of polypropylene

Thomas Stichel1, Edgar Mayer1, Stephan Roth1,3, Michael Schmidt1,2,3

1Bayerisches Laserzentrum GmbH (blz), Germany; 2University of Erlangen-Nürnberg, Institute of Photonic Technologies, Germany; 3Erlangen Graduate School in Advanced Optical Technologies (SAOT), Germany

Laser welding of thermoplastic polymers is a well-known joining technology that is particularly efficient for joining thermoplastic polymers. Although the process is already in industrial use, the basic process-structure-property relationships are not fully understood. The key to understand the correlations between process parameters and final weld properties are the mechanisms of origin of crystallinity and spherulitic structures. Understanding is made difficult by the fact that the laser welding process is a highly dynamic thermomechanical process and therefore very sensitive to experimental circumstances and parameters.

In this study, the spatial distribution of microstructural features inside the weld seam is investigated. For this purpose, the occurrence and size of spherulitic structures of polypropylene in the weld seam is examined by microscopy as well as differential scanning calorimetry is performed in order to measure the crystallinity. The results are correlated with the spatial-temporal temperature profile inside the weld seam which is derived by a thermal simulation model applied with COMSOL.

1:45pm - 2:00pm

Investigations on the transmissivity and scattering behavior of additively manufactured components for laser transmission welding applications

Julian Kuklik, Verena Wippo, Peter Jaeschke, Stefan Kaierle, Ludger Overmeyer

Laser Zentrum Hannover e.V., Germany

Additive manufacturing (AM) of thermoplastic parts is a common technique for prototypes, small batches and mass customization products. A widely used AM process is the fused deposition modeling (FDM), where a part has an inhomogeneous volume structure, because it is build up line by line, layer by layer.

An industrial established joining technology is the laser transmission welding (LTW), e.g. for joining injection molded parts in the automotive sector. For this technique, the transmissivity of one joining partner has a high influence on the resulting weld seam quality and the welding process itself. In order to use LTW for joining AM parts, the transmissivity and scattering behavior of AM parts were investigated. The optical properties were analyzed with spectroscopy and shear tensile tests were performed with welded samples to enhance the knowledge about the relationship between the FDM process, the optical behavior and the weld seam strength.

2:00pm - 2:15pm

Methodology for analyzing the influence of contact temperatures in laser beam brazing

Sven Müller, Peer Woizeschke

BIAS - Bremer Institut für angewandte Strahltechnik GmbH, Germany

In laser beam brazing, the contact temperature between the brazing material and the substrate as well as the wetting behavior play decisive roles. In order to analyze the process by model experiments, droplet tests or tests with pre-placed small amounts of brazing material on the base material have been carried out up to now. While in the first case a certain comparatively high overheating of the molten brazing material is required to allow droplet formation, in the second case it is not possible to determine the emerging contact brazing temperature in the interface with sufficient accuracy. This contribution presents a novel setup and its ability to characterize the influence of the contact temperature on the laser beam brazing process. The setup enables the investigation of process temperatures slightly above the liquidus temperature of the brazing material and the surface temperature measurement of the brazing material shortly before contact generation.

2:15pm - 2:30pm

Prediction of Cu-Al weld status using convolutional neural network

Karthik Mathivanan, Peter Plapper

University of Luxembourg, Luxembourg

Welding copper (Cu) and aluminum (Al) result in brittle intermetallic (IMC) phases, which reduces the performance. The key for a strong joint is to maintain an optimum amount of Al and Cu composition in the joint. To implement this without the destruction of the sample is a challenge. For this purpose, high-resolution images of the weld zone are utilized after welding. With the image processing technique, the presence of (Al/Cu) material melted is distinguished. Therefore the different weld type/status like insufficient melt, optimum melt, and excessive melt is detected from the images.

This paper analyses the weld images and applies the neural network technique to predict the weld type. The microstructural analysis of the fusion zone and mechanical strength of each weld types are correlated to the weld images.

1:30pm - 2:30pmAdditive Manufacturing: Directed Energy Deposition 2
Location: Room 2
Session Chair: Prof. Stephan Barcikowski, University of Duisburg-Essen, Chemical Technology, Germany
Room 2 
1:30pm - 1:45pm

In-situ clad geometry measurement in wire laser metal deposition process

Iker Garmendia, Jon Flores, Carlos Soriano, Mikel Madarieta

Tekniker, Spain

Wire Laser Metal Deposition (w-LMD) is a promising technique that could generate significant cost reductions. However, process control still needs to be developed to ensure product quality. Due to the high temperature of the melt pool and the resulting light radiation, current commercial equipment can only measure the geometry of the clad after the process or between the deposition of different layers, which affects the heating and cooling cycles of the part and the manufacturing time. In this work, a measurement system based on a side mounted vision camera and laser light projection is developed, which allows an in-situ measurement of the clad geometry data. This enables to know the nozzle-to-part distance, the surface where the successive layers are deposited, or bead parameters related to the quality of the deposition.

1:45pm - 2:00pm

Structure-borne acoustic process monitoring of laser metal deposition

Irene Buchbender, Christian Hoff, Jörg Hermsdorf, Volker Wesling, Stefan Kaierle

Laser Zentrum Hannover e.V., Germany

Acoustic emissions have been used as a means for process monitoring and non-destructive testing in welding to determine process characteristics, detect anomalies and infer the quality of the welded part. While air-borne noise has been studied extensively, research on the application of body-borne sound in the process monitoring of laser metal deposition remains limited. This paper examines the use of structure-borne sound for in-process monitoring of the deposition of the Nickel-based Superalloy CMSX-4. Due to the low weldability of the material and its susceptibility to hot-cracking, there arises a need for an in-process, non-destructive method for monitoring cracking. A high-frequency-impulse-measuring device (QASS GmbH) up to 50 MHz was attached to the substrate mount. The frequency data of the signal over time was evaluated by analysing the Short-Time Fourier transform (STFT) of the raw acoustic data, the acoustic characteristics of the process were determined, acceptable thresholds set and cracking detected.

2:00pm - 2:15pm

Studies on the direction-independent temperature measurement of a coaxial laser metal deposition process with wire

Avelino Zapata, Christian J. Bernauer, Melanie Hell, Michael F. Zaeh

Technical University of Munich, Germany

Among the Directed Energy Deposition (DED) processes, the Laser Metal Deposition with wire (LMD-w) combines the advantages of a high precision and a high deposition rate. Recently, optical systems have been developed that form an annular laser spot, facilitating a direction-independent process. However, when a pyrometer is coupled to the optical system, also the measurement spot assumes the form of a ring. This work studies the inline temperature signal of a pyrometer with a ring-shaped measurement spot for the LMD-w process. High-speed videos are used to interpret the signals based on process observations. The two modalities of a single and a two-color measurement are compared regarding their reliability. The measurement setup is varied to study the influence of different process conditions on the signal. At last, a configuration is identified that allows a valid measurement. The reliable inline temperature measurement opens the opportunity to monitor and control the process.

2:15pm - 2:30pm

Process development for laser hot-wire deposition welding with high-carbon cladding material AISI 52100

Laura Budde, Marius Lammers, Jörg Hermsdorf, Stefan Kaierle, Ludger Overmeyer

Laser Zentrum Hannover e.V., Hollerithallee 8, D-30419 Hannover, Germany

An increase in wear resistance and thus an increase in service life is of great importance for many components. The production of hybrid components with high-carbon steel as cladding material offers the possibility of achieving these goals. However, materials with a carbon equivalent of more than 0.65 are considered difficult to weld due to their tendency to crack. In this study, a laser hot-wire deposition welding process with bearing steel AISI 52100 as cladding material is used to investigate the influence of laser power, wire feed speed, scanning speed, overlap ratio and wire preheating as well as interactions of these parameters on process stability, the formation of cracks and pores, the cladding waviness and the dilution. Layers of eight adjacent weld seams are welded onto an austenitic stainless steel. A stable process is observed for most parameter combinations except for samples with low wire feed speed and major wire preheating.

1:30pm - 2:30pmMicro: Drilling
Location: Room 3
Session Chair: Dr. Florian Klämpfl, Institute of Photonic Technologies (LPT), Germany
Room 3 
1:30pm - 1:45pm

Experimental investigations of a helical laser drilling process for pilot holes on complex surfaces

Sebastian Michel, Pascal Volke, Dirk Biermann

Institute of Machining Technology (ISF), Technical University Dortmund, Germany

Increasing requirements and a high degree of freedom in design increasingly demand the manufacturing of bore holes with small diameters and high length-to-diameter ratios on complex shaped surfaces. Injection nozzles, medical tools and implants, cooling holes or oil channels are just a few examples. Unlike mechanical drilling tools, the laser beam is not deflected on inclined or curved surfaces and can therefore be used to create pilot holes for a subsequent mechanical drilling process. In this paper, the generation of pilot holes on flat and inclined surfaces using a Nd:YAG laser is investigated. A helical laser drilling process is used to drill holes with a diameter of 1.5 mm in X2CrNiMo17-12-2 stainless steel. Hole depth, diameter, roundness, conicity and material influences are evaluated. Application tests with single-lip drilling tools prove the potential of the laser holes to serve as a drilling guide for the mechanical deep hole drilling process.

1:45pm - 2:00pm

Laser microdrilling of thin aluminium sheets for metal-composite adhesion promotion

Félix Ares1, Ivette Coto1, Tamara Delgado1, Francisco Gontad1, Laura Mera1, Pablo Romero1, Sara Vidal1, Pascal Massé2, Nerea Otero1

1AIMEN, Spain; 2Rescoll, Société de Recherche, France

Thin (200 µm) aluminum sheets were drilled using a 1070 nm, CW fiber laser to improve hybrid metal-composite adhesion. The laser beam was guided by a BEO D35 laser cutting head. Micro holes of several diameters (40 – 220 µm) were generated with different spacing among them. The aluminum sheets were later coated with an adhesion promotion spray and thermoformed with a thin (200 µm) Carbon Fiber Reinforced Polymer (PA66) tape. InterLaminar Shear Strength (ILSS) and Single Lap Joint (SLJ) tests were performed on the following thermoformed samples: 1) Drilled, uncoated samples, 2) Non-drilled, coated samples, 3) Drilled, coated samples. The results show that a significant adhesion improvement for the drilled, coated aluminum samples is accomplished, reaching up to 100% higher apparent interlaminar shear strength than plain, coated samples. Finally, the pattern that provided the best ILSS values was replicated with a ns pulsed fiber laser, resulting in an equally strong bonding, while increasing productivity tenfold.

2:00pm - 2:15pm

Fluence dependence of the edge quality of microhole exits for percussion drilling with ultrashort laser pulses

Anne Feuer, Rudolf Weber, Thomas Graf

IFSW, University of Stuttgart, Germany

For many applications, edge quality and shape accuracy of microholes are crucial. One assumption is that the fluence at the tip of the microhole during drilling is a key parameter for the quality of the microhole’s exit. It was therefore investigated experimentally how the fluence affects the edge quality. The experiments were performed in 0.5 mm thick steel using a Ti:Sapphire laser system operating at a wavelength of 800 nm, a pulse duration of 1 ps, and a repetition rate of 1 kHz. For the quantitative analysis of the edge quality, microscope images were evaluated using a machine learning approach. Two key figures, groove size and perimeter ratio, were defined that proved to be significant in characterizing the edge quality of exits. In the current talk it will be shown that the quality of exits of percussion-drilled microholes could be significantly improved if the fluence dependence is considered.

2:15pm - 2:30pm

High-speed offline and real-time monitoring and control for laser micro-drilling of large Ti sheets

Roberto Ocaña, Joseba Esmoris, Carlos Soriano

TeknikerTekniker-Basque Research & Technology Alliance, Spain

High-throughput laser micro-drilling is a highly demanded technology for several applications, including making filters, creating surfaces with better aerodynamic performance, etc. However, it is usually found that the sensitivity of the laser process to small deviations is quite high. That is why, while parameterizing, it is convenient to have techniques that allow us to monitor and control the process to ensure reproducible results. For this, we have developed several methods that combine monitoring and control in real-time and offline. For real-time control and monitoring, we have used optical coherence tomography and captured the scattered laser radiation during the process by means of photodiodes. Regarding offline monitoring, a procedure using a high-speed camera and an algorithm for measuring the dimensions of the microholes provides us the quality characteristics and statistical information of complete micro-perforated Ti sheets. Both methods work as fast as the laser process, i.e., 300 holes per second.

1:30pm - 2:30pmMicro: Surface Functionalization 3
Location: Room 4
Session Chair: Dr. Stephan Roth, Bayerisches Laserzentrum GmbH (blz), Germany
Room 4 
1:30pm - 1:45pm

Enhanced forming behavior of conditioning lines by inserted microstructures for the production of 3D waveguides

Alexander Wienke1, Mohd Khairulamzari Hamjah2, Gerd-Albert Hoffmann1, Jürgen Koch1, Peter Jäschke1, Jörg Franke2, Ludger Overmeyer1, Stefan Kaierle1

1Laser Zentrum Hannover e.V., Germany; 2Institute for Factory Automation and Production Systems, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany

In today's increasingly connected world, more and more data is being produced and processed. To meet these challenges, the OPTAVER research group is conducting research on an innovative manufacturing process for 3D waveguides. In this process, so-called conditioning lines are first applied to a PMMA substrate by means of flexographic printing. Between those the waveguide is applied by aerosol-jet in a subsequent process. If the degree of forming is too high, the conditioning lines crack and become unusable, since material accumulation of the waveguide material leads to strong scattering and high attenuation of the waveguides. By inserting microstructures in the flexographic printing form at points where a high degree of forming is to be expected, material voids occur in the printing. These act as a predetermined breaking point, leaving the critical areas of the conditioning line untouched. This can significantly increase the 3D capability, as demonstrated in forming tests.

1:45pm - 2:00pm

Femtosecond laser structuring of nodular cast iron for anti-corrosion and thermally stable superhydrophobic surface

Dhiraj Kumar, Gerhard Liedl

Institute of Production Engineering and Photonics Technologies, TU Wien, Austria

The superhydrophobic surface has many applications, such as anti-corrosion, anti-icing, and self-cleaning. In this paper, we describe superhydrophobic surfaces on nodular cast iron produced by femtosecond laser pulses. A rapid transformation of surface characteristics from hydrophilic to superhydrophobic has been achieved after placing the samples in a high vacuum chamber for 10 hours, indicating a significant reduction in the storage time required to develop hydrophobic properties. Thermal stability has been assessed after heating the samples at different temperatures for an hour in a furnace. Consequently, the static contact angle has been measured after cooling at room temperature. Samples irradiated at 0.63 J/cm2 and 3.18 J/cm2 with hatch distance of 20 µm show stable superhydrophobic characteristics up to 180°C. Corrosion tests have also been carried out on untreated and lasertreated samples at room condition in a 3.5% NaCl solution. Results indicate that a superhydrophobic surface has better resistance toward corrosion.

2:00pm - 2:15pm

Structural coloration and wettability control of stainless steel by a DLIP process

Tamara Delgado, Clovis Alleaume, Sara M. Vidal, Francisco J. Gontad, Félix Ares, Pablo Romero, Nerea Otero

AIMEN - Laser Centre, Spain

We present the use of a Direct Laser Interference Patterning (DLIP) process to modify both optical and wettability properties of stainless steel. A picosecond (30 ps) pulsed Ytterbium fiber laser operating at its fundamental wavelength (1030 nm) was combined with a DLIP setup based on the use of a Michelson interferometer. A line-like pattern with a 6 µm spatial period and a good intensity contrast was produced by the interference of two beams. Thus, line-like periodic microstructures were engraved on the surface of stainless steel samples by a laser surface texturing process. Through the modification of the surface topography, both structural coloration and wettability control were achieved.

2:15pm - 2:30pm

Superhydrophobic surfaces using ultra-short pulse structuring of thin metal layers

Fabian Schäfer, Simon Ruck, Max-Jonathan Kleefoot, Wadim Schulz, Florian Köhn, Joachim Albrecht, Harald Riegel

Aalen University, Germany

Fabrication of superhydrophobic surfaces induced by ultra short pulse lasers is a hotspot of surface studies. We report a way of generating superhydrophobic surfaces on stainles steel (304S15). The method for fabricating this water-repellant surfaces is to microstructure by irridating with ultra short pulses. Contact angle measurements were used to investigate the wettability of the surface in relation to the laser parameters (laser fluence and scan line separation). The steady conctact angle was investigated in the range of 140°.

Investigations with optical measuring methods (white light interferometer, light microscope) could be confirmed by scanning electron images. The generated surface shows hierarchical structures with nano and micro roughness similar to a lotus leaf. In further experiments, different materials shall be sputtered to obtain a thin stainless steel surface. Subsequent laser structuring should produce a functional surface with water repellent properties

2:45pm - 4:00pmMacro: Joining 3
Location: Room 1
Session Chair: Frauke Faure, University of Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany, Germany
Room 1 
2:45pm - 3:00pm

Effects of separately laser-induced metal vapor amounts on the stability of a TIG arc

Insa Henze, Thorsten Mattulat, Peer Woizeschke

BIAS-Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany

Arc stability during welding can be improved by using a laser process and the associated implementation of a hybrid welding process. Various effects are assumed to be the causes of process stabilization by the additional laser beam. To investigate the metal vapor influence in a more decoupled manner, the metal vapor in this study is generated by a laser beam guided on an external substrate. The laser beam axis is oriented horizontally and thus perpendicular to the simultaneously ignited arc between a TIG welding torch and a counter electrode. The amount of metal vapor is adjusted by varying the laser power. The laser process causes the arc voltage to increase with the amount of metal vapor. This means an increasing electrical resistance and thus effects on the arc stability.

3:00pm - 3:15pm

Laser process manipulation by axial beam shaping

Joerg Volpp1, Adrien Da Silva1, Alexander Laskin2

1Luleå University of Technology, Sweden; 2AdlOptica GmbH, Germany

The laser beam is a highly flexible tool, which is used for many material processing applications. However, new beam shaping technologies open even further possibilities and processing options in order to control the heat input into the material. Beam shaping is usually done by manipulating the spatial intensity distribution in one layer to create. A new beam shaping device offers the possibility to create up to four focal spots in axial direction, which enables an extended depth of focus and tailoring the distribution of the energy along the beam axis. In this work, the impact of different axial beam shaping settings on process behaviours during laser material processing is shown. At low processing velocities, the amounts of measured spatters at the bottom side of the processed sheets show a reduced number compared to higher speeds. It is assumed that a stable keyhole opening is achieved that prevents the spattering.

3:15pm - 3:30pm

Spatter formation in high-speed laser processing of high-alloyed steel

Peter Hellwig, Klaus Schricker, Jean Pierre Bergmann

Technische Universität Ilmenau, Production Technology Group, Germany

Balancing processes require highly precise mass corrections especially in case of high-speed turning rotors. In order to hold profitable cycle times, these mass corrections have to be carried out in a short time. The application of cw-mode laser radiation represents a novel approach for these balancing processes. Thereby, spatter formation was identified as the primary removal mechanism. It is necessary to characterize the processing zone sufficiently to provide a deeper understanding of spatter formation at processing speeds beyond 60 meter per minute. In this study, a glass plate was used for flanking the processing zone to realize high-speed videography in a half section setup. This approach allows to perform measurements directly in the processing zone regarding melt pool dimensions, keyhole front and their interaction. In combination with image processing, precise weighings and metallographic examinations, a classification of certain process regimes referring to the processing speed is given.

3:30pm - 3:45pm

High-speed synchrotron X-ray imaging of the formation of wedge-shaped capillaries during laser beam welding at high feed rates

Eveline Reinheimer1, Marc Hummel2, Alexander Olowinsky3, Rudolf Weber1, Thomas Graf1

1Universität Stuttgart, Institut für Strahlwerkzeuge, Pfaffenwaldring 43, 70569 Stuttgart; 2Chair for Laser Technology LLT, RWTH Aachen University, Steinachstraße 15, 52074 Aachen; 3Fraunhofer Institute for Laser Technology ILT, Steinbachstraße 15, 52074 Aachen

Especially in case of high feed rates, the geometry of the capillary elongates in feed direction. At certain feed rates it might suddenly change to a wedge-shaped geometry. For the determination of the capillary-geometry during welding high-speed-X-ray imaging was performed at the IFSW X-ray-facility and at the synchrotron at DESY. The investigations addressed the transition of the capillary-geometry from a high aspect ratio to a wedge-shape geometry. In order to access the melt flow during welding, the movement of tungsten carbide particles was analyzed in the image sequences. The comparison of different laser spot diameter from 100 µm to 1360 µm and feed rates of up to 2 m/s resulted in the identification of the critical feed rate for the transition to the wedge-shaped capillary for each spot diameter. In the talk, the phenomena occurring during the transition will be presented and possible reasons for the transition will be discussed.

3:45pm - 4:15pm

Invited Talk: Melt-track merging and instabilities in multi-laser additive manufacturing

Craig B. Arnold, Wenxuan Zhang, Wenyuan Hou

Princeton Institute for the Science and Technology of Materials, Princeton University, United States of America

Control over laser beam shape can enable precision control over the resulting materials properties in any laser processing application. One simply way to control the intensity profile of the material illumination is through the use of multiple laser sources or beamlets. However the use of multiple beams can introduce unexpected phenomena and instabilities that can create undesired effects in the material. In this work, we use synchronized laser beams to create two molten pools running parallel to each other in a powder bed fusion system where the beams are separated by a controlled spatial and temporal offset. Through varying the offset, results reveal that besides the completely merged and completely separated regimes, there exists a third regime in which periodic coalescence occurs between the two molten pools. We examine the instability that leads to this periodic structure as well as how to control its formation.

2:45pm - 4:00pmAdditive Manufacturing: Non-metal
Location: Room 2
Session Chair: Leander Schmidt, Technische Universität Ilmenau, Germany
Room 2 
2:45pm - 3:00pm

Additive manufacturing of magnetic parts by laser powder bed fusion of iron oxide nanoadditivated polyamide powders

Carlos Doñate-Buendia1,2, Alexander Sommereyns3,4, Jochen Schmidt5, Michael Schmidt3,4, Stephan Barcikowski2, Bilal Gökce1,2

1Department of Materials Science and Additive Manufacturing, University of Wuppertal, 42119 Wuppertal, Germany; 2Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitaetsstrasse 7, 45141 Essen, Germany; 3Institute of Photonic Technologies (LPT), Friedrich-Alexander Universität Erlangen-Nürnberg, Konrad-Zuse-Str. 3-5, 91052 Erlangen, Germany; 4Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander Universität Erlangen-Nürnberg, Germany; 5Institute of Particle Technology (LFG), Friedrich-Alexander Universität Erlangen-Nürnberg, Cauerstr. 4, 91058 Erlangen, Germany

Laser powder bed fusion allows the processing of polymer powders with design freedom, achieving highly complex geometry required for medical and aerospace applications. The characteristics of the generated parts and processability depends on the initial polymer powder properties. A route to achieve a controlled modification of the polymer powders and adapt the properties of the final parts to the desired application is the nanoadditivation of the powders. The generation of superparamagnetic iron oxide nanoparticles by laser fragmentation and supporting on polyamide (PA12) is shown to transfer the magnetic response to the resulting nanoadditivated powder even when the nanoparticle loading is only 0.1 wt%. The characterization of the as built parts confirms that the saturation magnetization and structure of the iron oxide nanoparticles are not influenced by laser powder bed fusion processing, proving the successful transfer of the initial nanoparticle properties to the 3D-printed part.

3:00pm - 3:15pm

Polymer powders with enhanced absorption in the NIR for laser powder bed fusion with diode lasers

Michael Willeke, Carlos Donate-Buendia, Tim Hupfeld, Stephan Barcikowski, Bilal Gökce

Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitaetsstrasse 7, 45141 Essen, Germany

Additive manufacturing techniques represent an ideal manufacturing process for series components, for example in the automotive industry when good mechanical properties and precision are needed. In that sense, Laser Powder Bed Fusion (LPBF) is a manufacturing technique already employed in several applications where polymer parts with complex geometries are required. However, since the employed polymer powders exhibit a low absorption in the visible and NIR wavelength range, the laser sources employed in polymer LPBF are limited.

To address this difficulty, the addition of near-infrared absorbing LaB6 nanoparticles is proposed and tested on the most employed polymer powder for LPBF, i.e. polyamide 12 (PA12). The nanoparticles are generated by laser ablation in liquid and homogeneously dispersed on the polymer surface by dielectrophoretic deposition. The resulting nanoadditivated polymer powder exhibits an absorption maximum at 800 nm, suitable for its processability by LPBF with NIR laser sources.

3:15pm - 3:30pm

Powder bed fusion of ultra-high molecular weight polyethylene using ultra-short laser pulses

Tobias Ullsperger1, Yannick Wencke2, Burak Yürekli1, Gabor Matthäus1, Gerrit Luinstra2, Stefan Nolte1,3

1Institute of Applied Physics, Friedrich-Schiller University Jena; 2Institute for Technical and Macromolecular Chemistry, University of Hamburg; 3Fraunhofer Institute for Applied Optics and Precision Engineering, IOF Jena

Laser powder bed fusion (L-PBF) of ultra-high molecular weight polyethylene (UHMWPE) is a new approach to fabricate complex components for medical implants. CO2 laser radiation is the method of choice to selectively heat up the powder particles above the melting point. Although previous studies have shown the feasibility to fuse UHMWPE, the produced sprecimen lack of warping and material degradation. Moreover the achievable geometrical resolution is limited by the large spot size of several 100 µm.

In this paper, we demonstrate an alternative approach for L-PBF of UHMWPE by using 500 fs laser pulses at a wavelength of 1030 nm. The peak intensity of several 100 MW/cm2 allows for an efficient multi-photon absorption in the transparent polymer. Thus, it was possible to completely melt the powder with less degradation. Furthermore, the achieved tensile strength of 4 MPa is 60 % higher in comparison to produced samples using conventional CO2 L-PBF.

3:30pm - 3:45pm

Experimental investigations on lateral path overlay and the degree of mixing of additively manufactured soda-lime and borosilicate glass structures

Fabian Fröhlich, Jörg Hildebrand, Jean Pierre Bergmann

Technische Universität Ilmenau, Production Technology Group, Germany

In this scientific paper, the influence of the lateral distance between the welding lines on the geometric dimensions and the degree of mixing of the additively manufactured glass structure is investigated. Initial experimental investigations have shown that the additive manufacturing of quartz, soda-lime and borosilicate glass is possible when material- and process-specific process parameters are taken into account. Using a CO2-laser, the silicate glasses and the rod-based additive material are melted. For this experimental investigation, the ratio between welding and feeding speed of the filler material, as well as the laser power, is kept constant. The fabricated structures are subjected to post heat treatment to relieve thermally induced stresses and are examined with photoelasticity. Geometrical dimensions, such as layer height, width and bond angle, as well as the degree of mixing are quantified after materialogprahy sample preparation. The knowledge is used to optimise near-net-shape additive manufacturing of glass components.

3:45pm - 4:00pm

Manufacturing of fused silica volume parts by means of laser glass deposition

Katharina Rettschlag1,2, Simon Stieß1, Peter Jäschke1, Stefan Kaierle1, Roland Lachmayer1,2

1Laser Zentrum Hannover e.V., Germany; 2Institute for product development, Leibniz University Hannover, Germany

Additive manufacturing (AM) of polymers and metals is already established in the industry. Materials such as glass create significant challenges based on their material properties. Especially mechanical and thermal properties as well as the viscosity behavior are difficult to handle. So far, only few specialized glass AM processes exist and are established in research and development.

The Laser Glass Deposition (LGD) process offers the possibility to deposit glass fibers without using binder materials. For the application area of optical components, manufactured parts must fulfill high requirements for transparency, surface quality, material purity and homogeneity of the material. Investigations on the printing of individual single-layer quartz glass structures have already been carried out with the LGD process. Within this article the influence of laser power, axis speed and fiber feeding speed on the deposition characteristics is investigated shortly. Subsequently, a multilayer deposition is investigated to manufacture solids with an optical transparency.

2:45pm - 4:00pmMicro: Micro Machining
Location: Room 3
Session Chair: Oliver Hentschel, Institute of Photonic Technologies (LPT), Germany
Room 3 
2:45pm - 3:00pm

Laser machining of different steel grades with 10ps laser pulses: the influence of carbides onto the surface roughness and structures for different laser parameters

Stefan M. Remund, Severin N. Herren, Josef Zürcher, Beat Neuenschwander

Berner Fachhochschule Technik und Informatik, Switzerland

When steel is machined with ultra-short pulses the specific removal rate strongly depends on the pulse fluence, the wavelength and, in case of bursts, on the number of pulses whereas the steel grade has a minor influence. This situation changes for the surface roughness. Beside the laser parameters, the initial surface and the number of machined layers the obtainable surface roughness also depends on the carbides located in the steel as well as their size and distribution and therefore it is strongly influenced by the steel grade. E.g. for a given set of parameters a surface roughness (sq) value of 350nm, 410nm and 500nm was achieved for CK75 (no carbides), M390 (small carbides) and K100 (large carbides). We will present the results of a systematic study for different steel grades in the application of surface structuring and smoothening of surfaces machined by alternative technologies as e.g. electrical discharge machining (EDM).

3:00pm - 3:15pm

Scaling the throughput of high-quality silicon laser micromachining using a 1-kW sub-picosecond laser

Daniel Holder1, Rudolf Weber1, Christoph Röcker1, Gerhard Kunz2, David Bruneel3, Martin Delaigue4, Thomas Graf1, Marwan Abdou Ahmed1

1IFSW, University of Stuttgart, Germany; 2Robert Bosch GmbH, Germany; 3Lasea, Belgium; 4Amplitude Systemes, France

Recently, laser processing of silicon with ultrafast lasers has gained widespread attention for manufacturing of optics for THz radiation, an emerging topic with applications in medical imaging, security and communication. Such THz-optics require high-quality surfaces with low roughness in order to provide high transmission and low scattering. In the past, the low average power of ultrafast lasers limited the achievable throughput in silicon laser micromachining.

In this work a processing strategy for high-quality high-throughput micromachining of silicon with a 1-kW sub-picosecond laser is presented, which takes benefit of pulse bursts, low fluences and high feed rates.

As a result, laser micromachining could be demonstrated as a suitable technology for manufacturing of smooth structures on silicon while maintaining a high throughput. Surfaces with an appropriate roughness of Sa ≤ 0.6 µm were produced with a high material removal rate of 230 mm³/min and a machining depth of up to 313 µm.

3:15pm - 3:30pm

Ultra-short laser micro-machining by spatially shaped ps- and fs-pulses for depth-selective µ-TLM resistivity test structures in TCO contact layers

Stephan Krause1,2, Stefan Lange2, Gao Yiding2, Volker Naumann2, Christian Hagendorf2, Paul-Tiberiu Miclea1,2

1Fraunhofer CSP, Germany; 2Martin-Luther-University Halle/Wittenberg

We applied spatially shaped ultra-short pulse laser micro-machining for a new processing approach of µ-TLM test structures. These structures are used for resistivity measurements of multilayer systems with highly resistive interface layers, e.g. in TCO top contacts for solar cells. For precise measurements of the electrical sheet and contact resistivity of the individual layers, isolating trenches and homogenous ablation areas are required that can be fabricated by matching of pulse overlapping based on rectangular spots in µm-dimensions.

Ultrashort pulses by 10 ps and 200 fs (515/532/1030 nm) as well as optical beam shaping elements for redistribution to top-hat intensity profiles enables a selective removal of the top TCO. Thus, thermal damage is minimized in the underlying material and multilayer adjacent region of the laser trenches by ultrafast ablation mechanism. Morphology and microstructure of heat-affected zones were characterized by high-resolution transmission electron microscopy to optimize laser recipes for enhancing ablation selectivity.

3:30pm - 3:45pm

Automated cutting by water jet-guided laser machining using a break-through sensor

Falk Braunmüller, Jérémie Diboine, Amédée Zryd, Bernold Richerzhagen

Synova S.A., Switzerland

The Laser Micro-Jet® is now a well-established technology among others for micro-machining and high-quality machining of hard and composite materials, with the advantages of narrow parallel cut walls without focus adaptation, minimizing the heat-affected zone and the avoidance of burrs.
This contribution describes the development of a break-through sensor measuring light from the laser plasma through the water jet. By detecting a completed cut, additional safety cutting passes can be reduced and the cutting is stopped just in time.
The sensor enables an optimized, automatized cutting, which represents a significant step towards industry 4.0. The technology is now employed on an industrial scale by several customers, showing the high potential of the technology: The processing time is reduced by 5-20%.
Finally, first results of a cutting sensor with spectrally resolved plasma detection will be presented, which shall enable a targeted ablation by detecting various layers in a multi-layer material.

3:45pm - 4:00pm

Laser turning using ultra-short laser pulses and intensity distribution techniques

Julian Zettl1, Christian Bischoff2,3, Stefan Rung1, Cemal Esen3, Andrés Fabián Lasagni4, Ralf Hellmann1

1University of Applied Sciences Aschaffenburg, Germany; 2Topag Lasertechnik GmbH, Germany; 3Ruhr University Bochum, Germany; 4Technical University Dresden, Germany

We report on the fabrication of rotationally symmetric parts by using focused ultra-short laser pulses while impinging the rotating work piece tangentially. The use of ultra-short laser pulses enables this process to fabricate parts in a non-contact manner, even from materials that are hard to machine such as stellite or fused silica. The target geometry is realized by moving the constantly rotating specimen according to the specified geometry under the focused laser spot. In order to further enhance this manufacturing approach, a spatial distribution of the laser power on the work piece is investigated. Beam shaping techniques are applied to alter the shape of the focal spot and to study the effects on the resulting ablation rate, process efficiency and surface quality.

2:45pm - 4:00pmMicro: Surface Functionalization 4
Location: Room 4
Session Chair: Clemens Roider, Institute of Photonic Technologies (LPT), Germany
Room 4 
2:45pm - 3:00pm

High-rate laser machining for large-area and high-throughput surface profiling and functionalization

Joerg Schille, Stefan Mauersberger, Andreas Gruner, Lutz Schneider, Kristian Kujawa, Udo Loeschner

University of Applied Sciences Mittweida, Germany

High-rate laser machining will be introduced as key technology for large-area surface texturing and bio-inspired functionalization. In fact, the polygon-mirror based scan technique allowing high-precision laser beam raster-scanning at hundreds meters per second is the core feature to bring high optical powers from kilowatt class lasers to industrial production. This is favourable for power scaling in micro machining as processing rate and throughput scale-up with higher pulse repetition frequency and laser powers. The great advantage of ultrafast beam movements is that unfavourable effects can easily be avoided, such as high thermal loads to the substrates and subsequent material melting as well as laser beam shielding by interactions with the previously induced plasma/particle plume. Inspired by sharks´ skin, this will be demonstrated by the example of riblet-like surface profiles and their replications in plastic materials thus providing a high potential for drag reduction in turbulent flows in technical applications.

3:00pm - 3:15pm

Laser polishing of laser micro weld seams on Cu-ETP and CuSn6 with green laser radiation

Moritz Küpper1, Marc Hummel1, Rakesh Kumar Pandey2, Constantin Häfner1

1RWTH Aachen University, Germany; 2Politecnico di Milano, Italy

Copper and copper alloys used for example in electrical applications can be contacted by laser micro welding. The achievable roughness of these micro weld seams can be too large for some applications (like sealing surfaces or to minimize surface oxidation). Up to now laser polishing, which smoothens the surface due to surface tension in the molten state, of copper could not be demonstrated successfully with industry common infrared high power laser systems typically used for laser polishing. This study investigates the use of green 515 nm wavelength high power laser sources for laser polishing of pure copper (Cu-ETP) and a widely used copper alloy (CuSn6). A suitable process window is identified by variation of process parameters (laser beam diameter, scanning speed, laser power) for single and overlapping remelting tracks. The best parameters are tested on laser micro weld seams created with the same setup to smoothen their rough surface.

3:15pm - 3:30pm

Laser texturing of heat exchanger tubes for nucleate boiling regime promotion

Félix Ares1, Ivette Coto1, Tamara Delgado1, Francisco Gontad1, Roberto Eiró2, Sara Vidal1, Nerea Otero1, Pablo Romero1

1AIMEN, Spain; 2INTEGASA, Spain

Titanium tubes of 16 mm diameter and 0.8 mm thickness, were textured using a CW, single mode, 1070 nm fibre laser. The laser beam was guided by a galvanometer scanner. Textures of homogeneous, parallel grooves of 60-80 µm width and 70-110 µm depth were generated on the exterior tubular surface. A wide range of parameters: laser power, laser speed, tube rotating speed or focal distance was studied to improve the homogeneity of the generated textures. These tubes were later tested in both controlled and industrial environments, along with non textured tubes, and their heat transfer behaviour was analysed under an ammonia nucleate boiling regime. Results indicate that laser textured tubes show a consistent increase of 60% of their heat transfer coefficient, when compared to original smooth tubes. These results prove that laser texturing is a suitable technique to significantly increase performance of heat exchangers that work under nucleate boiling regime

3:30pm - 3:45pm

Ultrashort laser coloration on titanium coatings

Eva Rodríguez Vidal1, Goretti Alberdi1, Borja Coto1, Oihane Hernandez1, Beatriz Diaz1, Aleix Ribera2

1TEKNIKER, Polo Tecnológico de Eibar, Calle Iñaki Goenaga 5, 20600, Gipuzcoa, Spain; 2INVESTPLASMA, Polígono Industrial Riu Sec, 105, 1, 12190 Borriol, Castellón, Spain

This study reports on the fabrication of structural and intrinsic colors from the oxide layers via ultrashort laser pulses on titanium coatings deposited on glass substrate. Surface modifications are tuned by adjusting laser parameters of wavelength, pulse length, scanning speed and energy per pulse. Two thickness (up to 1µm) of titanium coatings were deposited on glass substrates by physical vapor deposition. A comprehensive study of the physical and chemical measurements leading to the different appearances is presented. Different physical modifications, at micro and nanoscale levels, were identified depending on laser processing conditions. Quantitative analysis regarding chromaticity coordinates of the generated colors as well as phase composition of oxide layers were characterized by spectrophotometer and x-ray diffraction, respectively. Uniform and repetitive color palette on titanium coatings was developed by ultrashort laser processing.

3:45pm - 4:00pm

Direct laser-writing of metal nanostructures from the gas phase by two-photon absorption process

Nicolai Schwarz1,2, Michael Bassler1, Thomas Walther2, Thomas Klotzbuecher1

1Fraunhofer-Institut für Mikrotechnik und Mikrosysteme IMM, Mainz, Germany; 2Institut für Angewandte Physik, Technische Universität Darmstadt, Darmstadt, Germany

The fabrication of metallic 3D-nanostructures has received a lot of attention through new applications in plasmonics, e.g. metamaterials with a negative refractive index for optical cloaking and non-diffraction-limited optics. A new approach for the generation of three-dimensional metal nanostructures is introduced, based on two-photon-absorption of fs-laser radiation on silver-precursor molecules in the gas phase. A process chamber has been set up, allowing for evaporating a liquid organometallic silver-precursor under controlled temperature and pressure conditions. An inverse microscope objective of NA=0.65 and a working distance of 0.57 mm is used to focus the beam. The focus is moved in space by means of piezo-driven stage with nm-resolution. First two-dimensional structures with dimensions in the sub-micrometer range, are successfully deposited from the gas phase on glass substrates. The deposition parameters with respect to pressure, temperature and laser power, are going to be optimized to reach nm-resolution in structure size and building up 3D structures.


Date: Thursday, 24/June/2021
10:00am - 11:00amMacro: Surface Treatment
Location: Room 1
Session Chair: Daniel Holder, University of Stuttgart, Germany
Room 1 
10:00am - 10:15am

Effect of femtosecond laser shock peening on surface morphology and hardness of nickel titanium alloy

Hao Wang1, Evgeny L. Gurevich2, Andreas Ostendorf1

1Ruhr-Universität Bochum; 2Münster University of Applied Sciences

Nickel-titanium alloy (NiTi) has been widely used for the fabrication of microelectromechanical and body implants, so it is very important to enhance its surface mechanical property. Laser shock peening as a new and important surface treatment technique has been used to enhance the mechanical properties of different metal materials. Normally, the nanosecond laser with pulse-width between 5 ns and 20 ns is used to induce a high-pressure shock wave that can generate plastic deformation in the top layer of metals. In this paper, the surface morphology and hardness of NiTi alloy after femtosecond laser shock peening in the air are studied, which shows that the surface roughness and hardness increased after femtosecond laser treatment.

10:15am - 10:30am

Influence of multi-pass laser hardening on surface residual stress and distortion

Yang Lu1, Heiner Meyer2, Tim Radel1

1Bremer Institut für angewandte Strahltechnik GmbH; 2Leibniz-Institut für Werkstofforientierte Technologien

Laser hardening is used to harden the surface layer with minimal distortion and to induce residual compressive stress. Within the literature, the approach of increasing the hardness and hardening depth by multi-pass laser hardening based on accumulation effects is shown. Within this study, the effect of multi-pass laser hardening of normalized AISI 4140 on the surface residual stress and distortion is examined. The multi-pass laser hardening is carried out using a continuous wave laser with a rectangular beam shape using different process velocities and number of cycles without heat accumulation after each cycle. The results show that for a comparable hardening depth, there is less distortion at single pass hardening with low scanning speed compared to the multi-pass hardening with high scanning speed. These findings indicate that multi-pass laser hardening is therefore only preferable if technical limitations like the available laser power prevents the required hardening depth.

10:30am - 10:45am

Interaction between laser radiation and antifouling coating underwater

Stanislav Zimbelmann1, Benjamin Emde1, Jörg Hermsdorf1, Stefan Kaierle1, Tim Heusinger von Waldegge2, Dorothea Stübing2, Markus Baumann3

1Laser Zentrum Hannover e.V., Germany; 2Fraunhofer IFAM, Germany; 3Laserline GmbH, Germany

The biofouling on a ship´s hull has an enormous economic impact on its operation. Increasing biofouling leads to the introduction and spread of invasive species, a raised frictional drag in the water, an increased fuel consumption and thus an additional emission of greenhouse gases. In this context, the prevention or removal of biofouling becomes essential. Conventional, mechanical in-water-cleaning methods have several ecological and regulatory disadvantages. In the context of a laser-based underwater ship cleaning, that is currently under development, we investigated the interaction between laser radiation and a self-polishing copolymer (SPC) antifouling coating. Important process parameters were investigated to determine the laser power damage threshold of the SPC coating. These include the measurement of the reflection properties and the surface properties of the SPC coating.

10:45am - 11:00am

Laser cleaning as a productive surface post-treatment method for LPBF parts

Markus Hofele1,2, Johannes Neuer1, Malena Lindenberger-Ullrich1, Jochen Schanz1,2, David K. Harrison2, Anjali K. M. De Silva2, Harald Riegel2

1Aalen University, Germany; 2Glasgow Caledonian University, United Kingdom

Laser Powder Bed Fusion (LPBF) is the most common additive manufacturing technique for rapid prototyping and industrial manufacturing of complex individual metal parts. The LPBF process offers the opportunity to directly build solid metal parts with less geometric restrictions, low porosity and good mechanical properties. However, the surface of the parts exhibits a rough surface with massive powder contamination combined with a thick oxide layer on it. Laser cleaning provides the possibility of a contact-free and full-automatable surface treatment with high area rates.

This work deals with the investigation on laser cleaning of LPBF surfaces made of Aluminum AlSi10Mg. Laser cleaning with an nanosecond pulsed fiber laser by variation of the beam intensity, fluency and number of cleaning repetitions are investigated. Threshold beam intensities for the powder and oxide removal and base material ablation are determined. The ablation efficiency is analyzed by means of SEM, WLI and microscopic images.

10:00am - 11:00amAdditive Manufacturing: Directed Energy Deposition 3
Location: Room 2
Session Chair: Nicole Emminghaus, Laser Zentrum Hannover e.V., Germany
Room 2 
10:00am - 10:15am

Analysis and recycling of bronze grinding waste to produce maritime components using directed energy deposition

Vinzenz Müller1, Angelina Marko1, Tobias Kruse2, Max Biegler1, Michael Rethmeier1,3

1Fraunhofer Institute for Production Systems and Design Technology IPK, Germany; 2Mecklenburger Metallguss GmbH, Germany; 3Bundesanstalt für Materialforschung und -prüfung (BAM), Germany

Additive manufacturing promises a high potential for the maritime sector. Directed Energy Deposition (DED) in particular offers the opportunity to produce large-volume maritime components like propeller hubs or blades without the need of a costly casting process. The post processing of such components usually generates a large amount of aluminum bronze grinding waste. The aim of the presented project is to develop a sustainable circular AM process chain for maritime components by recycling aluminum bronze grinding waste to be used as raw material to manufacture ship propellers with a laser-powder DED process. In the present paper, the main challenges and promising measures and methods to recycle metallic grinding waste are shown. Two types of grinding waste are investigated using a CamSizer particle analysis system and compared to commercial DED powder. To be able to compare the material quality and to verify DED process parameters, semi-academic sample geometries are manufactured.

10:15am - 10:30am

Evaluation of steady state via thermography during laser and wire based directed energy deposition

Anton Emil Odermatt, Nikolai Kashaev

Helmholtz-Zentrum Geesthacht, Institute of Materials Mechanics, Department of Laser Processing and Structural Assessment

Additive manufacturing of structures in one continuous deposition process is appealing because defects at the start and end-points of a track are avoided. For the evaluation of process stability, a steady state process needs to be reached. A methodology for the determination of the interpass temperature for processes using a positioner for movement of the work piece has been developed. This methodology was applied to a laser and wire based directed energy deposition process. The approach of the steady state process can be described by an exponential growth law. From the interpass temperature a cooling rate can be calculated. The evolution of the interpass temperature can be used for process control and the cooling rate can be related to material properties. A comparison with results from the literature shows that the convergence rate is mainly dependent on the power level of the energy source and the size of the structure.

10:30am - 10:45am

Influence analysis of the layer orientation on mechanical and metallurgic characteristics of DED manufactured parts

Florian M. Dambietz1, Tobias S. Hartwich1, Julian Scholl-Corrêa2, Dieter Krause1, Peter Hoffmann2

1Hamburg University of Technology, PKT; 2ERLAS Erlanger Lasertechnik GmbH

With an increasing trend in product individualization, manufacturing custom-designed solutions and focusing on the explicit industry’s needs are crucial to the manufacturer’s success. Especially within high-tech industries such as aerospace industry, high-strength, large-sized but still lightweight metal parts are required. Although the Direct-Energy-Deposition (DED)-technology offers a proven outset point for targeting this issue, there are few material-, metallurgic-, process-, and geometry specific data available to support the initial design process of such parts. This contribution presents a profound study of different steel- and aluminium materials with respect to their metallurgic and mechanical characteristics. Using a state-of-the art DED-Laser system, tensile test specimens have been manufactured with alternative layer orientations. These specimens are analysed with regard to the required milling oversize, heat-induced stress deformation, metallurgic characteristics and their tensile characteristics. As a result of this investigation, a suitable baseline for the future generation of a DED design-by-feature catalogue is given.

10:45am - 11:00am

Investigation on laser cladding of rail steel without preheating

Christian Brunner-Schwer1, Max Biegler1, Michael Rethmeier3,1,2

1Fraunhofer Institute for Production Systems and Design Techology, Pascalstraße 8-9, 10587, Berlin, Germany; 2Bundesanstalt für Materialforschung und –prüfung, Unter den Eichen, 87 12205, Berlin, Germany; 3Institute of Machine Tools and Factory Management, Technische Universität Berlin, Pascalstraße 8-9, 10587, Berlin, Germany

The contact between train wheels and rail tracks is known to induce material degradation in the form of wear, and rolling contact fatigue in the railhead. Rails with a pearlitic microstructure have proven to provide the best wear resistance under severe wheel-rail interaction in heavyhaul application. High speed laser cladding, a state-of-the-art surface engineering technique, is a promising solution to repair damaged railheads. However, without appropriate preheating or processing strategies, these steel grades lead to martensite formation and cracking during deposition welding.

In this study, laser cladding of low-alloy steel at very high speeds were investigated, without preheating the railheads. Process speeds of up to 27 m/min and Laser power of 2 kW are used. The clad, heat affected zone and base material are examined for cracks and martensite formation by hardness tests and metallographic inspections. A methodology for process optimization is presented and the specimens are characterized for suitability.

10:00am - 11:00amAdditive Manufacturing: Medical Applications
Location: Room 3
Session Chair: Dr. Florian Klämpfl, Institute of Photonic Technologies (LPT), Germany
Room 3 
10:00am - 10:30am

Invited Talk: Selective laser sintering 3D printing of bespoke medications

Atheer Awad

University College London, United Kingdom

3D printing is a rapid manufacturing technology that has found promising applications in many fields, including pharmacy. In particular, laser-based technologies enable the creation of precise and intricate structures, potentially causing a paradigm shift in medicine design, manufacture and use. As an example, early-phase drug development (such as preclinical studies and first-in-human trials) could be expedited by using these technologies to rapidly produce formulations with excellent dose flexibility at low cost, on demand. Similarly, they could support formulation development because they have the capability to produce rapid product iterations for testing, such as excipient compatibility and drug release. Within hospitals and pharmacies, such technologies could accelerate the field of personalised medicine by moving treatment away from a ‘one size fits all approach’ towards personalisation. This presentation will give an overview on the use of a laser-based 3D printing technology and its promising applications, highlighting its potential in personalising medications.

10:30am - 10:45am

Laser directed energy deposition produces improved cp Ti for dental prosthetic applications

Óscar Barro1,2, Felipe Arias-González3, Fernando Lusquiños1,5, Rafael Comesaña4, Jesús del Val1, Antonio Riveiro4, Aida Badaoui4, Félix Gómez-Baño2, Juan Pou1,5

1CINTECX, University of Vigo, LaserON Research Group, Vigo, SPAIN; 2Corus-Fegoba, A Coruña, SPAIN; 3School of Dentistry, Universitat Internacional de Catalunya, Barcelona, SPAIN; 4Materials Engineering, Applied Mechanics and Construction Department, University of Vigo, Vigo, SPAIN; 5Galicia Sur Health Research Institute (IIS Galicia Sur), SERGAS-UVIGO, Vigo, SPAINin

Titanium and titanium alloys are widely employed in biomedical applications by virtue of their remarkable corrosion resistance, biocompatibility, exceptional specific strength and relatively low elastic modulus. Commercially pure titanium (cp-Ti) is a designation for titanium with reduced content of alloying elements, having a great resistance to corrosion and reduced cytotoxicity.

Laser directed energy deposition (LDED) is an additive manufacturing method able to produce metallic materials of great quality. By controlling the cooling rates, the material microstructure can be tuned in order to improve its mechanical/chemical properties. In the present work, LDED using a high power diode laser as energy source, was used to produce cp-Ti parts of grade 4. The cp-Ti obtained by LDED showed a higher mechanical performance than the commercial counterpart: 7% increment of ultimate tensile strength and 30% increment of toughness. These results can be attributed to a specific microstructure modification inherent to the LDED process.

10:45am - 11:00am

Additive manufacturing for minimally invasive endomicroscopy

Robert Kuschmierz, Elias Scharf, Jürgen Czarske

TU Dresden, Germany

Miniaturized flexible endoscopes employ coherent fiber bundles (CFB) to transfer intensity information by using lenses. This increases the footprint of the endoscope to several millimeters. Furthermore, the phase information of the light is distorted during transfer due to manufacturing errors of the CFB, which limits the endoscope to 2D imaging. Calibrating and compensating the phase distortion allows for lens less imaging. We present, the use of additive manufacturing to apply diffractive optical elements (DOE) onto the fiber facet for phase compensation. Using 2P-polymerization axial resolutions better than 20 nm can be achieved. This enables robust and cost efficient, endoscopes for 3D imaging. The influence of the DOE quality especially the axial resolution towards the image quality is discussed. With a total diameter below 400 µm, novel applications for instance for in-vivo cancer diagnostics in the brain can be envisioned.

10:00am - 11:00amFundamentals and Process Simulation
Location: Room 4
Session Chair: Dr. Klaus Schricker, Technische Universität Ilmenau, Germany
Room 4 
10:00am - 10:15am

Corrosion resistant blackmarking via numerical modeling and simulation

Urs Eppelt, Daniel Seitz, Jörg Ziegler

Coherent Munich, Germany

Classical Laser Blackmarking with USP laser sources is a well-established process that is commercially available nowadays since a few years. This is especially true for its wide use on stainless steel supplies of the medical industry. Surprisingly, other industries (like household and consumer products industries) have even higher requirements on wear behavior (like corrosion resistance) than the medical industry with its strict approval procedures.

With the help of mathematical modeling and numerical simulation we wanted to understand the in-depth reasons for the limitations of classical blackmarking and develop a new laser marking process that could also fulfill the demands for acid resistance on products like white goods, sanitary fittings or automotive accessories which have not yet been opened up for this kind of laser process. We describe our success in modeling and simulation as well as process development in that field which is then evaluated by corrosion testing procedures.

10:15am - 10:30am

Estimating heat accumulation upon ultrafast laser irradiation

Liliana Cangueiro1, Thomas Kiedrowski2, Nikolaï Schroeder3, David Bruneel1, Andrés Lasagni3, J.A. Ramos-de-Campos1

1LASEA, Belgium; 2Robert Bosch GmbH; 3Institut für Fertigungstechnik Technische, Universität Dresden

Ultrafast lasers micromachining results depend both on the processing parameters and the material properties. The obtained thermal effects are negligible if a good combination of processing parameters is chosen. However, optimizing the processing parameters leading to the required surface quality on a given material can be quite complex and time consuming. Within the framework of the European project LAMpAS, we developed a model to estimate the heat accumulation on a surface as a function of the laser fluence, scanning speed and line pitch. The simulation results were correlated with experimental ones on different materials. The predictions of the model allow evaluating the heat distribution on the surface, as well as optimizing the ultrafast laser micromachining strategy yielding negligible thermal damage.

10:30am - 10:45am

Experimental setup for determination of absorption coefficient of laser radiation in molten metals as a function of temperature and angle

Tjorben Bokelmann1, Marius Lammers1, Jörg Hermsdorf1, Sobhan Emadmostoufi2, Oleg Mokrov2, Rahul Sharma2, Uwe Reisgen2, Stefan Kaierle1

1Laser Zentrum Hannover e.V., Germany; 2Welding and Joining Institute, RWTH Aachen University, Germany

For the process development of laser assisted double wire welding with nontransferred arc (LDNA), the simulation of the molten pool and its interaction with the laser radiation is of great importance. Therefore, an experimental setup for the determination of the temperature and angle dependent absorption coefficient of laser radiation in molten metals such as stainless steel and aluminum will be presented. A Yb:YAG disc laser with 1030 nm and a 940-1020 nm diode laser are used as laser beam sources. The stationary molten metal is inductively warmed and superheated by the laser beam with approximately 300-1000 W, whose radiation profile is shaped by homogenizing optics and ensures equal intensity when the angle is adjusted.

11:15am - 12:30pmMicro: Joining (Welding and Brazing)
Location: Room 1
Session Chair: Florian Kaufmann, Bayerisches Laserzentrum GmbH (blz), Germany
Room 1 
11:15am - 11:30am

OCT keyhole depth measurement in copper micro welding

Tobias Beck

Robert Bosch GmbH, Germany

The transition of the powertrain from combustion to electric systems increases the demand for reliable copper connections. For such applications, laser welding has become a key technology. Due to the complexity of laser welding, especially at micro welding with small weld seam dimensions and short process times, reliable in-line process monitoring has proven to be difficult. By using a green laser (515 nm), the welding process of copper benefits of the increased absorption, resulting in a shallow and stable deep penetration welding process. In this contribution, the monitoring of the capillary depth in micro copper welding, with welding depth of up to 1 mm, was performed coaxially, using an optical coherence system with a measurement wavelength of 840 nm. By comparing the measured capillary depth and the actual welding depth, independently of the investigated process parameters and the stability, a good correlation between two measured values could be shown.

11:30am - 11:45am

Determination of thermophysical process limitations for the laser-based droplet brazing process using different droplet and substrate materials

Jakob Ermer1,3, Florian Kohlmann1, Markus Müller1, Florian Kaufmann1, Stephan Roth1,3, Michael Schmidt1,2,3

1Bayerisches Laserzentrum GmbH (blz), Konrad-Zuse-Straße 2-6, 91052 Erlangen, Germany; 2Institute of Photonic Technologies (LPT), Friedrich-Alexander-Universität Erlangen-Nürnberg, Konrad-Zuse-Straße 3-5, 91052 Erlangen, Germany; 3Erlangen Graduate School in Advanced Optical Technologies (SAOT), Paul-Gordan-Straße 6, 91052 Erlangen, Germany

The demand for microelectronic components is rising constantly over the last few decades due to the progress in digitalization. Along with this, the requirements for joining technologies are growing since they are highly responsible for progress in microelectronics. Laser-based droplet brazing shows unique features like a quasi-force-free joining process and high-temperature stable connections and is therefore on the way to its industrial implementation. While the first developments have been limited to the contacting of silver metallizations on piezo actuators, today the transferability of the process with regard to different solder and substrate materials is a major goal. In this work the relation between the solidification time of the droplet and diffusion processes depending on the substrate layout and material properties is investigated via highspeed imaging and EDX analysis. Based on the thermophysical behaviour of the process, the scalability for future applications can be derived for different material combinations.

11:45am - 12:00pm

Temporally and spatially highly resolved reconstruction of vapor capillary geometry during laser beam welding using synchrotron radiation

Marc Hummel1, André Häusler2, Sören Hollatz2, Christian Hagenlocher3, Jannik Lind3, Ulrich Halm4, Christoph Schöler4, Alexander Olowinsky2, Arnold Gillner1,2

1RWTH Aachen University, Chair for Laser Technology LLT, Germany; 2Fraunhofer Institute for Laser Technology LLT, Germany; 3University of Stuttgart, Institut für Strahlwerkzeuge IFSW, Germany; 4RWTH Aachen University, Nonlinear Dynamics of Laser Manufacturing Processes NLD, Germany

Welds of electrical components made of aluminum and copper need high electrical and mechanical quality. Process instabilities do not allow a continous reproducibility. To generate a deeper understanding of the process and to evaluate process dynamics, it is possible to use modern in situ analysis methods.

In this work, in situ phase-contrast high-speed videography using synchrotron radiation is presented. The phase contrast method reveals the phase boundaries between solid, liquid and gaseous phases. A spatial resolution down to <20 µm is possible due to the high coherence of the synchrotron beam, which allows to observe small vapor capillaries of fiber lasers with <100 µm diameter. 3D capillary geometries are reconstructed from 2D image data of welds on aluminum using a fiber laser and disc laser. Ray tracing is performed using this reconstruction, which allows the time resolved tracking of the laser beam inside the vapor capillary for quantitative estimations.

12:00pm - 12:15pm

Direct welding of glass and copper with a large gap by femtosecond laser pulse bursts

Qingfeng LI1, Gabor Matthäus1, Stefan Nolte1,2

1Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Albert-Einstein-Straße 15, 07745 Jena, Germany; 2Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Center of Excellence in Photonics, Albert-Einstein-Straße 7, 07745 Jena, Germany

We report on the welding of borosilicate glass to copper using bursts of femtosecond laser pulses with a pulse duration of 265-fs and a wavelength of 1030-nm. The systematical analysis demonstrated in this paper represents a fundamental step towards the robust laser micro-welding of glass-to-metal.

The highest bonding strength is achieved with a laser fluence 2.5 times higher than the laser-induced damage threshold of the glass sample. Moreover, the glass-metal interface must be located within the Rayleigh range of the focused laser beam representing a focal diameter of 3.7-µm, and the gap size between both components must be less than 2-µm. The highest value, in the region of 14-MPa, compares well with proof-of-principle demonstrations published before. However, in contrast to previous achievements, no clamping is required. Consequently, the presented work demonstrates an easy glass-to-metal welding approach as an alternative to traditional bonding techniques based on adhesives or sample-pretreatments.

12:15pm - 12:30pm

Investigations on the influence of the material selection of the clamping device during laser transmission welding of multi-layer polymer films with wavelength-adapted laser beam sources

Maximilian Brosda, Phong Nguyen, Alexander Olowinsky, Arnold Gillner

Fraunhofer-Institut für Lasertechnik ILT, Germany

In lasertransmissionwelding process of polymers with wavelength adapted laser beam sources, the joining partners are fixed in an overlap arrangement. A sufficient energy absorption is ensured by addressing the material-dependent intrinsic absorption bands. The fixing is realized by a clamping device to achieve a technical zero gap between the joining partners in order to ensure heat exchange and melt permeation. The materials are in direct contact with the polymers and influence the heat dissipation as well as the propagation of the laser beam. While the upper material must be transparent for the laser radiation, a variety of materials are available for the lower part. Hence, it is investigated how the individual material combinations affect the process.To investigate the influence of material combinations as well as the influence of roll-to-roll processing or possible process limits welding tests are performed. The weld seam is analyzed by cross sections and tensile tests.

11:15am - 12:30pmAdditive Manufacturing: Powderbed, Copper
Location: Room 2
Session Chair: Dr. Stefan Kaierle, Laser Zentrum Hannover e.V., Germany
Room 2 
11:15am - 11:30am

Development of SLM 3D printing system using galvano scanner for pure copper additive manufacturing by 200W blue diode laser

Keisuke Takenaka1, Yuji Sato1, Koji Tojo2, Masahiro Tsukamoto1

1Joining and Welding Research Institute, Osaka University, Japan; 2Shimadzu Corporation, Japan

Selective laser melting (SLM) is one of laser additive manufacturing technologies. Because absorptance of blue light on pure copper materials is higher than that of conventional near-infrared light, a blue diode laser is expected to effective in shaping pure copper parts. In our previous study, we developed a high power and high intensity blue diode laser with the wavelength of 450 nm. Output power and fiber core diameter was 200 W and 100 µm, respectively. In this study, we have developed a SLM machine using galvano laser scanner with the 200 W blue diode laser. The laser power and the scanning speed were changed to form a pure copper parts in the SLM method, and the influence of them on the cross-sectional area of the parts was investigated.

11:30am - 11:45am

3D printing of high-density copper parts using common NIR CW laser systems at moderate powers

Hagen Kohl1, Lisa Schade1, Gabor Matthäus1, Tobias Ullsperger1, Burak Yürekli1, Brian Seyfarth1,2, Bernd Braun3, Stefan Nolte1,2

1Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Germany; 2Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Center of Excellence in Photonics, Germany; 3Nuremberg Institute of Technology Georg Simon Ohm, Germany

Additive manufacturing (AM) of pure copper using laser assisted powder bed fusion (LPBF) at a wavelength of 1070 nm is demonstrated. In comparison to established LPBF materials, pure copper exhibits an extremely high reflectivity for wavelengths around 1 µm and the highest thermal conductivity among other AM materials. Although, pure copper is one of the most interesting materials for AM, the interplay of these characteristics still prevents copper to be applied using common laser-based AM machines. In this work, we demonstrate a wide processing window for 3D-printing of high-density copper parts based on a fiber laser as widely used in common AM machines. These achievements were obtained with the help of a self-developed numerical model that guided our experimental studies during the LPBF process. After process optimization, relative densities over 99 % can be demonstrated without the help of intense preheating or post processing like hot isostatic pressing.

11:45am - 12:00pm

Energy coupling in laser powder bed fusion of copper using different laser wavelengths

Klaus Behler2, Daniel Heussen1, Marvin Kupper1, Nobert Pirch1, Tim Lantzsch1, Johannes Henrich Schleifenbaum3

1Fraunhofer-Institut für Lasertechnik ILT, Aachen, Germany; 2Technische Hochschule Mittelhessen, Friedberg, Germany; 3RWTH Aachen University Lehrstuhl für Digital Additive Production DAP

Highly conductive pure copper is crucial for high current applications in electrical and mechanical engineering. The additive manufacturing of components from pure copper using laser powder bed fusion (LPBF) with conventional machine technology and "infrared" laser radiation (λ ≈ 1070 nm) is challenging due to the high reflectivity of copper for infrared laser light. Fraunhofer ILT has been investigating possibilities to use lasers within the visible spectral range (green @ λ=515 nm and blue @ λ=450 nm) in the LPBF process. It has been shown that there is a potential to improve energy coupling and process stability applying such lasers in the LPBF process. In this paper calorimetric absorptivity measurements are presented, showing the influence of wavelength and process parameters as well as material conditions on the effective energy input for the melting of copper substrate material as well as of powder material.

12:00pm - 12:15pm

Laser powder bed fusion (L-PBF) of pure copper using a 1000 W green laser TruDisk

Guillaume Nordet1,2, Cyril Gorny1, Pierre Lapouge1, Albin Effernelli2, Etienne Blanchet2, Frederic Coste1, Patrice Peyre1

1PIMM Laboratory - ENSAM Paris; 2AddUp

Additive manufacturing of pure copper with lasers is complex using usual near IR laser wavelength, due to a high reflectance (~95 % at 1.07µm) combined with a high conductivity. This results in limited parts density, never exceeding 99%, whereas other metals can easily reach 99.9 % density. A possible way of improvement is to reduce the laser wavelength (from near IR to green) to enhance laser absorption and reduce the power needed to provide deep and stable tracks. In the current work, a detailed study was carried out with the use of a 1 kW cw green laser implemented on a L-PBF prototype. Two objectives were considered: (1) investigating the laser absorbance during single L-PBF tracks at various energy densities and welding regimes (conduction, keyhole) and (2) building various 3D parts and optimizing their density. Finally, parametric study allowed obtaining up to 99.9 % dense parts from pure copper powder.

12:15pm - 12:30pm

Additive manufacturing of conductive copper traces on 3D geometries by laser-sintering

Ejvind Olsen, Ludger Overmeyer

Leibniz Universität Hannover, Germany

These days, additive manufacturing processes cover an extensive range of materials. A new trend is a growing interest in the implementation of additional functions like electrical circuits. Combining full-surface primer and copper ink coating from printed electronics with laser processing enables integrating conductive traces directly on the surface of 3D-printed components. Priming reduces the roughness of the 3D printed (multi-jet modeling) circuit carrier below 100 nm. Afterward, the metal-containing ink is dip-coated, dried, and sintered locally by laser processing. The used laser system includes a focused and pulsed 1064 nm laser beam controlled by a scanner with three optical axes (x, y and z-direction). This research presents a detailed investigation on the influence of 3D geometrical factors like radii and sidewall angle on the resulting conductive trace resistance. Electron beam imaging technology with energy dispersive x-ray spectroscopy characterizes the conductive tracks regarding geometric and material properties.

11:15am - 12:30pmMicro: Innovations
Location: Room 3
Session Chair: Prof. Michael Schmidt, Institute of Photonic Technologies (LPT), Germany
Room 3 
11:15am - 11:45am

Invited Talk: Ultrashort pulsed laser micro processing: Multi-pulse and beam forming strategies for high throughput at high average powers

Beat Neuenschwander, Stefan M. Remund, Markus Gafner, Michalina W. Chaja

Bern University of Applied Sciences, Switzerland

The development of ultrashort pulsed laser systems actually goes far beyond the kW level. But e.g. for metals and single pulses todays standard methods like galvo scanners are not suited for higher average powers and alternative approaches have to be developed. We will get an insight into actual developments using multi-pulse strategies in temporal representation as pulse bursts and in spatial representation as multi-beams or with direct beam forming. A combination of these methods with synchronized scanning or real pulse on demand option could pave the way for using high average powers.

11:45am - 12:00pm

Excimer laser sintering of ceramic thin films for solid state batteries

Matthias Trenn1, Ralph Delmdahl2, Karsten Lange1

1Fraunhofer Institut für Lasertechnik ILT, Germany; 2Coherent LaserSystems GmbH & Co. KG, Göttingen

The geopolitical dependence on limited fossil resources and the increasing number of environmental disasters are enormous challenges for today’s society. An important element to overcome these essential problems is to increase the performance of energy storage systems and the efficiency of energy conversion devices. Promising solutions are solid state batteries and solid oxide fuel cells. Both cell systems demanding high standards on new production technologies. Temperature-sensitive thin film systems make conventional sintering processes impossible.
In the underlying investigation, a new highly scalable excimer laser-based sintering process of ceramic thin films is presented. The nanosecond pulses selectively melt surface the powder grains. Due to the 248 nm wavelength of the excimer laser, sintering depths of 3 - 8 µm can be achieved. In the process, the crystalline phase and thus also the electrochemical properties of the material are retained.

12:00pm - 12:15pm

Laser-based 3D-magnetic field sensor formation

Markus Müller, Mandy Gebhardt

3D-Micromac AG, Germany

A world with intelligent electronic devices in every machine and every pocket needs a wide range of sensor technologies. One rapidly growing technology is the sensing of magnetic fields, which can be used in numerous industrial applications. Very sensitive magnetic sensor chips can be realized by using GMR or TMR (Giant or Tunneling magnetoresistance) sensors in a Wheatstone bridge circuit built in a monolithic design.

This presentation gives an overview to selective laser annealing for 3D-magnetic field sensor formation, which provides several advantages over thermal annealing for magnetic sensor manufacturing. Its higher precision enables processing of smaller magnetic device structures, which in turn leads to more devices per wafer. In addition, its ability to set different reference magnetization directions on sensors across a single wafer reduces process steps and simplifies the manufacturing flow, enabling more cost-effective production of integrated monolithic sensor packages.

12:15pm - 12:30pm

Top-hat profile beam to weld polymeric microfluidics chips with ultra-short pulsed laser

Marc Décultot1, Jérôme Patars1, Anne Henrottin1, José Antonio Ramos-de-Campos1, Ivan Gusachenko2, Clément Jacquard2, Guillaume Labroille2, Gwenn Pallier2

1Lasea, Belgium; 2Cailabs, France

The microfluidics field, due to its various possibilities in the study of chemical and biological reactions with only few consumables, is expanding significantly. To follow this growing, we have developed a flexible solution, based on ultra-short pulsed laser technology, to engrave different microfluidic channels on a chip, and to seal them with a complete, hermetical, and resistant welding.

In order to improve the competitiveness of our solution for industrial production purpose, we have focused in particular our work on the improvement of the welding’s speed. Using the Canunda-Pulse solutions from Cailabs for manipulating high-power femtosecond lasers, we have made a complete study on laser welding parameters with a top-hat profile beam. Canunda-Pulse is a fully reflective passive optical module based on the Multi-Plane Light Conversion (MPLC) technology. Thanks to this beam shaper, we have deduced advantages of a top-hat profile beam, compared to a gaussian profile beam.

11:15am - 12:30pmMicro: Surface Functionalization 5
Location: Room 4
Session Chair: Dr. Stephan Roth, Bayerisches Laserzentrum GmbH (blz), Germany
Room 4 
11:15am - 11:30am

Improved thermal joining of aluminum and aluminum-polymer composites for battery applications through laser surface structuring

Christian Geiger, Lucas Hille, Célestine Singer, Michael F. Zaeh

Institute for Machine Tools and Industrial Management (iwb), Technical University of Munich, Boltzmannstr. 15, 85748 Garching, Germany

Lithium-ion batteries are the main electrochemical energy storage solution for electromobility applications because of their advantageous characteristics compared to other battery technologies. Currently, three cell designs (prismatic hardcase, prismatic pouch and cylindrical cells) with specific advantages and disadvantages are present in the market. Novel cell concepts aim to combine the strengths. For example, the good mechanical stability of hardcase cells should be merged with the high gravimetric energy density of pouch cells. Therefore, a laser structuring process is presented, which significantly improves the adhesion between aluminum-polymer composite foils and solid aluminum during thermal joining. Microscopic structures were formed on the aluminum surface by nano-second laser pulses. The results of a laser parameter study were analyzed by optical means (laser scanning microscopy and scanning electron microscopy) and in terms of adhesion strengths between the components. In conclusion, strategies and recommendations for the laser structuring process are derived.

11:30am - 11:45am

Laser-assisted selective fabrication of copper traces on polymers by electroplating

Vitalij Fiodorov1, Gediminas Račiukaitis1, Karolis Ratautas1, Zenius Mockus2

1Center for Physical Sciences and Technology, Department of Laser Technologies, Vilnius, Lithuania; 2Center for Physical Sciences and Technology, Department of Chemical Engineering and Technology, Vilnius, Lithuania

The paper reports a facile and low-cost laser-assisted method for selective deposition of copper traces on polymer surfaces. The technique uses a laser for selective polymer surface modification. The electrical conductivity of some polymers could be increased due to laser irradiation. Kapton PI film was used in our experiment. Samples were patterned using a picosecond laser at 1064 nm wavelength. The experiments were performed using average powers ranging from 4 to 8.5 W in 0.5 W increments, pulse repetition rates from 10 to 100 kHz and a constant scan rate of 100 mm/s. The sheet resistance was measured using the four-probe method, and it was reduced to < 50 Ω per square after laser patterning. Afterwards, the modified surface was metal deposited by electroplating.

Selective deposition of copper on polymers could be used in flexible electronic devices. This technology shows a huge potential in many fields: consumable electronics, automotive, etc.

11:45am - 12:00pm

Manufacturing of functional surfaces by replicating glass moulds structured by multiphoton polymerization

Sara María Vidal Álvarez, Nerea Otero Ramudo, Felix Ares Blanco, Maria Ivette Coto Moretti, Francisco José Gontad Fariña, Tamara Delgado García, Pablo Romero Romero

AIMEN Technology Centre, Spain

The present work deals with the fabrication of very low aspect ratio microstructures generated by Multi-Photon Polymerization (MPP) on glass substrates for their further use as good quality and high resolution replication moulds for optoelectronic devices. A commercial UV-curable resin from the ORMOCER® family was employed for the fabrication of the polymeric microstructures on two different substrates: glass and sapphire. These microstructures were replicated by injection moulding on polymeric components with an area of several cm2. The results of this work indicate that high resolution moulds can be fabricated through MPP, favouring the fabrication of high-quality replications. Additionally, the microstructures are proven to be resistant to their use through multiple replications. In fact, the topographical characterizations of the first and last replicas show similar characteristics, proving the reliability MPP for the fabrication of high quality moulds.

12:00pm - 12:15pm

Improved catalytic activity and surface functionalization of nanoparticles by pulsed laser-post processing of colloids.

Sven Reichenberger, Swen Zerebecki, Stephan Barcikowski

University of Duisburg-Essen, Germany

The presented talk intends to cover advances in laser-based post-processing of colloidal nanoparticles by laser fragmentation and -defect engineering for catalyst development. First, a new setup which provides a 100 µm thick flat liquid jet for laser post-processing of nanoparticles and favors a 10 times lower laser intensity deviation compared to the conventional cylindrical liquid jet will be presented. Due to the uniform laser intensity in the flat liquid jet, colloidal 3 nm gold nanoparticles with narrow size distribution (PDI < 0.1) were gained. In the second part of the talk, recent advances on laser-based defect engineering and related surface functionalization will be presented at the example of cobalt-spinel-based catalysts. It will be shown, that the catalytic activity is significantly improved especially when less than 3 laser pulses are employed per nanoparticle. In this context, laser-based surface doping and favorable process scalability will be discussed.

12:15pm - 12:30pm

Metallic surface functionalization by femtosecond laser beam shaping and LIPSS for industrial applications

Jérôme Patars, Liliana Cangueiro, David Bruneel, J. A. Ramos-de-Campos

Lasea, Belgium

Literature demonstrated the advantages of surface nanoscale texturation in many industrial applications, including batteries, medical implants and linear encoders. The next step is to find a cost-effective and non-invasive solution to replace actual material deposition and tooling techniques at industrial scale.

In the scope of the LASER4SURF project, we developed a new automated workstation enabling fast texturing of large surface samples (i.e. A4 format), using state of the art beam shaping techniques involving DOE and SLM combined with LIPSS generation to increase functionalization performances of the textured materials.

A key part of the workstation is its ability to automatically determine optimal laser processing parameters based on preliminary study done on any other laser processing device.

We also demonstrate that LIPSS texturation increases battery collectors charging capabilities, as well as their lifetime. We also demonstrate better bio-integration of medical implant for the human body, as well as increased accuracy linear encoders.

1:30pm - 2:30pmMacro: Beam Oscillation
Location: Room 1
Session Chair: Prof. Thomas Graf, University of Stuttgart, Germany
Room 1 
1:30pm - 1:45pm

High speed videography of gap bridging with beam oscillation and wire feeding during the laser welding of stainless steel and aluminum alloys

Davide Maria Boldrin, Matteo Colopi, Simone D'Arcangelo, Leonardo Caprio, Ali Gökhan Demir, Barbara Previtali

Politecnico di Milano, Italy

Laser beam welding is known for its quality and speed. Given its susceptibility to gaps, the technology is applied in the industrial field with hard automation and dedicated fixtures rather than small-batch production. The latter cannot always guarantee the strict conditions on the fit-up of joints, especially with complex geometries. Gap-bridging techniques may be exploited to overcome these inaccuracies. The present work investigates the simultaneous use of low frequency circular beam oscillation and wire feeding as means to produce a continuous weld seam in the presence of constant air gaps. Lap joint welding of 2 mm-thick AISI301LN and butt joint welding of 3 mm-thick AW6005A-T6 alloy were conducted with gaps up to 1mm. High-speed imaging at 10kHz provided an insight in the dynamics of the oscillating weld pool and spatter formation. Optical inspection and metallographic analyses were used to verify the gap-bridging capability as well as the resulting seam quality.

1:45pm - 2:00pm

Influence of laser beam welding with overlaid high-frequency beam oscillation on weld seam quality and fatigue strength of aluminium wrought and die-cast joints

Benjamin Keßler, Dirk Dittrich, Robert Kühne, Markus Wagner, Axel Jahn

Fraunhofer Institute for Material and Beam Technology IWS, Dresden

Legal regulations with the aim of avoiding carbon dioxide emissions are drivers of innovation for lightweight automotive design.The economic production of such components is mainly achieved by using aluminium die-casts. A limiting factor for the use of aluminium die-castings is their weldability. The laser beam welding with overlaid high-frequency beam oscillation (LBW-HF) is a suitable solution to overcome this limitation.

In the proposed paper, weld specimens in form of aluminium mixed joints (wrought and die-cast alloys) were produced with the LBW-HF and with the static laser beam welding process (LBW). The weld seam quality is correlated with the tensile and fatigue strength properties. Furthermore, the results from the fatigue test are classified in the existing IIW regulations and their applicability with regard to laser-welded aluminium joints will be discussed. The results show an increased fatigue strength, especially for the LBW-HF process, compared to current used standards for design.

2:00pm - 2:15pm

Investigation of the influence of beam oscillation on the laser beam cutting process using high-speed X-ray imaging

Jannik Lind1,2, Jonas Wagner1, Niklas Weckenmann2, Weber Rudolf1, Thomas Graf1

1Institut für Strahlwerkzeuge (IFSW), University of Stuttgart, Germany; 2Precitec GmbH & Co. KG, Germany

Recently, it was shown that oscillating the laser beam during laser beam cutting can increase the maximum cutting feed rate compared to cutting with a static beam. In order to investigate this phenomenon, the geometry of the laser cutting front was observed by means of online high-speed X-ray imaging. Fusion cutting of 10 mm thick samples of stainless steel was recorded with a framerate of 1000 Hz. When the beam was oscillated in longitudinal direction, the maximum cutting feed rate could be increased by 25% compared to cutting with a static laser beam. In the talk, the influence of the oscillation parameters on the cutting speed, the cutting front geometry and the resulting cut quality will be discussed.

2:15pm - 2:30pm

CFD simulations for laser oscillation welding

Pareekshith Allu1, Frieder Semler2

1Flow Science Inc., United States of America; 2Flow Science Deutschland GmbH, Germany

Computational fluid dynamics (CFD) models have shown that laser keyhole welding at high speeds and powers can result in weld joints with reduced porosity. However, the process is limited by available laser powers (~6kW) and by insufficient penetration due to high welding velocities. To enable high speed welds with reduced porosity and optimal gap bridging, researchers have investigated laser oscillation welding. In this presentation, we look at some case studies where CFD models that simulate the laser-material interaction, melt pool dynamics and keyhole formation are developed to investigate laser oscillation welding in Zinc-coated steels. Additionally, these models helped identify zones of high Zinc vapor pressure that led to spatter and the data is compared to melt pool videos taken of the welding process. Such CFD models help develop welding schedules that limit the build of Zinc Vapor pressure in the melt pool and reduce spatter in laser oscillation welding.

1:30pm - 2:30pmAdditive Manufacturing: LIFT
Location: Room 2
Session Chair: Antoni Artinov, BAM Federal Institute for Materials Research and Testing, Germany
Room 2 
1:30pm - 1:45pm

Cavitation phenomena in BA-LIFT

Juan José Moreno Labella1,2, Miguel Morales Furió1,2, David Muñoz Martín1,3, Carlos Molpeceres Álvarez1,2

1Centro Láser, Universidad Politécnica de Madrid, Spain; 2Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica de Madrid, Spain; 3Escuela Técnica Superior de Ingeniería y Diseño Industrial, Universidad Politécnica de Madrid, Spain

Blister-Actuated Laser-Induced Forward Transfer (BA-LIFT) allows transferring high-resolution voxels or droplets of fluids with a wide range of viscosities. When compared to similar techniques, BA-LIFT stands out in its flexibility in design and the absence of a nozzle that may get clogged. The physics involved in the process is not easy to understand, so image acquisition systems and simulation are the main methods to gain insight into the dynamics of the process. The simulation of the transference process using a Phase-Field Finite-Element Model aids the task of understanding how the transferred material behaves. BA-LIFT long-time secondary effects, such as bulgy shapes and secondary jets, have been simulated including the effects that a mechanically-induced cavitation bubble would induce. An evaluation of its appearance causes has been carried out. Finally, the bubble has been photographed by modifying the setup to avoid optical distortion.

1:45pm - 2:00pm

Laser technologies for the production of microLEDs

Markus Müller, Uwe Wagner, Mandy Gebhardt

3D-Micromac AG, Germany

MicroLEDs have a tremendous potential for future displays. However, there are several technical challenges to overcome prior to widespread deployment of MicroLEDs. One key hurdle is developing a process to release the dies from the sapphire growth wafer. Another is a process to transfer these to the display substrate with micron level precision and reliability.
Laser processing offers several opportunities for MicroLED display production, such as Laser Lift-Off (LLO) to separate the finished MicroLEDs from the sapphire growth wafer and Laser Induced Forward Transfer (LIFT) to move the devices from a donor to the substrate.
In this presentation, laser-based system solutions for the different manufacturing steps for MicroLEDs, will be presented. Integrated process control and monitoring is used to assure stable and reliable operation to ensure high throughput and low yield losses.

2:00pm - 2:30pm

Invited Talk: Additive Manufacturing of Electronics by LIFT

Alberto Piqué

U.S. Naval Research Laboratory, United States of America

Laser-induced forward transfer (LIFT) techniques have generated significant interest for applications in Additive Manufacturing of Electronics (AME). LIFT enables printing of functional materials ranging from silver nano-inks to working devices such as bare-die semiconductor components over a wide range of surfaces in an additive fashion achieving high transfer throughputs. This technique is a non-mechanical, non-contact direct-write process capable of operating in additive and subtractive modes ideally suited for applications in 3D microscale fabrication and in printed electronics. LIFT techniques are well suited for IoT applications as exemplified by their use in prototyping of hybrid electronics and embedded components. This presentation will provide an overview of the current state-of-the-art through examples of structures and circuits made by LIFT and discuss their role in the development of next generation laser-based techniques for AME.

This work was funded by the Office of Naval Research (ONR) through the Naval Research Laboratory Basic Research Program.

1:30pm - 2:30pmMicro: Processing of Transparent Materials 1
Location: Room 3
Session Chair: Dr. Thomas Stichel, Bayerisches Laserzentrum GmbH (blz), Germany
Room 3 
1:30pm - 1:45pm

Micromachining of transparent biocompatible polymers used as vision implants with bursts of femtosecond laser pulses

Simas Butkus, Evaldas Kažukauskas, Vytautas Jukna, Domas Paipulas, Valdas Sirutkaitis

Laser Research Center, Vilnius University, Lithuania

Biocompatible plastics are used for many different purposes (catheters, artificial heart components, dentistry products, etc.). An important field biocompatible polymers is the production of vision implants known as intraocular lenses (IOLs) or custom-shape contact lenses, which are typically produced by means of milling, turning or lathe cutting and subsequent polishing. The multiple-step process is expensive and may take up days to produce the final part which is individually customized to meet the patient's needs.

In this work we propose a novel, all-laser-based method for the production of custom-shape lenses which may work as eye-implants. The shape of the lens from the plastic material (Contamac CONTAFLEX 26% UV-IOL) is produced by means of femtosecond ablation in a few minutes and afterwards it is polished by utilizing burst of femtosecond pulses in the GHz regime. In this way, transparent optical-quality lenses are produced in under 5 minutes of laser fabrication.

1:45pm - 2:00pm

Solvent evaporation and annealing of solution-processed organic materials by laser irradiation on flexible substrates

Frederik Kiel1, Cemal Esen1, Andreas Ostendorf1, Volker Wirth2

1Ruhr-Universität Bochum, Germany; 2Focuslight LIMO GmbH, Bookenburgweg 4-8, 44319 Dortmund, Germany

The market for flexible, printed and organic electronics is rapidly growing. The production is often based on wet-chemical processes and the residual solvent needs to be removed. Conventional methods for solvent evaporation or annealing of functional layers in roll-to-roll (R2R-) processing are circulating-air- or infrared-dryers. These methods require a relatively large drying section and entail a long exposure time at elevated temperatures for the flexible substrates. By utilizing a diode-laser as heating source the installation space and especially the exposure time at elevated temperatures could be minimized.

A LIMO line laser system (450 W, 980 nm) was used to investigate the substitution of conventional drying/ annealing methods on a lab scale (laser line FWHM: 12,22x0,06 mm²) for organic photovoltaic cells resulting in comparable power conversion efficiencies to conventional methods at processing speeds of 1m/min.

These results are expected to be transferred from the lab scale to a R2R-system.

2:00pm - 2:15pm

Processing and wetting behavior of microstructured polymer foils

Felix Bouchard1, Marcos Soldera2, Robert Baumann1, Andrés-Fabián Lasagni1,3

1Technische Universität Dresden, Institut für Fertigungstechnik, George-Baehr-Str. 3c, 01069 Dresden, Germany; 2PROBIEN-CONICET, Dto. de Electrotecnia, Universidad Nacional del Comahue, Buenos Aires 1400, Neuquén 8300, Argentina; 3Fraunhofer-Institut für Werkstoff- und Strahltechnik (IWS), Winterbergstraße 28, 01277 Dresden, Germany

The demand for surface functionalized plastics is constantly rising. Therefore, industrial-scalable methods capable to provide surfaces with new functions are necessary. In this study, we demonstrate a strategy to apply hierarchical microstructures to transparent polyethlyene therepthalate (PET) foils by plate to plate hot embossing. To that end, a stainless steel stamp was patterned using two laser based processes, namely Direct Laser Writing (DLW) and Direct Laser Interference Patterning (DLIP). Several single scale and multi scale structures with feature sizes in the range 3 µm up to 50 µm and depths between 0.1 µm and 10 µm were processed on the metal master and transfered to the PET surface. The topography characterization by confocal microscopy and scanning electron microscopy revealed a satisfactory replication of the micostructures from the stamp to the polymer, even for the smallest features with lateral sizes of ~100 nm. The patterned surfaces showed an increased hydrophobic behavior characterized by static water contact angles up to 105°.

2:15pm - 2:30pm

Femtosecond laser-assisted mould fabrication for metal casting at the micro-scale

Enrico Casamenti1, Luciano Borasi2, Adeline Durand2, Samuel Rey1, Raphaël Charvet2, Cyril Dénéreaz2, Andreas Mortensen2, Yves Bellouard1

1Galatea Laboratory, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland; 2Laboratory of Mechanical Metallurgy (LMM), École Polytechnique Fédérale de Lausanne (EPFL), Switzerland

Existing technologies for the production of metallic 3D micro-components are, in their current state, either too slow to be economically viable or produce porous and imperfect metal structures. Here we overcome those barriers by bringing metal casting to the realm of microfabrication. We present a process that enables the production of freeform, dense, 3D metal architectures at speeds well above alternative approaches for metal 3D printing at the same resolution. Using femtosecond laser micro-machining combined with chemical etching, arbitrarily shaped 3D-cavities are carved out of fused quartz substrates and subsequently pressure-infiltrated with high melting point metals, such as pure silver, copper and gold and their alloys. The resulting glass/metal combinations contain interconnected dense metal 3D structures that are shaped freely with micrometric resolution to enable new types of micro-devices and composite structures.

1:30pm - 2:30pmMicro: Surface Functionalization 6
Location: Room 4
Session Chair: Florian Huber, Institute of Photonic Technologies (LPT), Germany
Room 4 
1:30pm - 1:45pm

Friction reduction of stainless steel surfaces by laser microstructuring

Niklas Berger1, Benjamin Keim2, Munehiro Chijiiwa1, Hicham Derouach1, Senta Schauer2, Mareike Schäfer Schäfer1, Johannes A. L'huilier1

1Photonik-Zentrum Kaiserslautern e. V. (PZKL), Germany; 2EPflex Feinwerktechnik GmbH, Germany

Recently, friction reduction has become important in a wide range of technical applications. One limiting factor is the abrasion of two surfaces when they are moved against each other, causing friction losses. To overcome this, a functional optimization is necessary and thus the effectiveness of components will be increased by structuring the surfaces. Our approach is to introduce a dimple structure by laser microstructuring into the surface and thus significantly reduce the friction. In order to avoid burr around these dimples it is necessary to operate good heat management. For this reason, we carried out experiments using a USP laser with a pulse duration of 10 ps. Dimples with a diameter of 10 - 30 micrometers were made and systematic investigations were carried out by changing the depth and the arrangement of the dimples. By optimizing these parameters, friction could be reduced by 30 % compared to an unstructured surface.

1:45pm - 2:00pm

Impact of confined laser plasma plumes on the formation of LIPSS structures on stainless steel 316L

Anupam Ghosal1, Olivier Allegre1, Zhu Liu1, Gordon Jones2

1The University of Manchester, United Kingdom; 2Waters Plc, United Kingdom

Laser-induced periodic surface structures (LIPSS) has been used for functionalisation of the surface. Hence, the control of the formation of the LIPSS structures is considered an important feature. In this work, picosecond pulsed laser irradiation (wavelength 355nm, pulse duration 10ps, frequency 404.7 kHz) were performed on stainless steel 316L under the conditions of confined laser plasma plumes in an air environment. The plasma plumes generated due to laser-metal interaction were confined by covering the metal surface with a transparent glass plate at varying distances (Δz = 0, 150, 300, 450, 900 μm). The impact of the gap between metal and glass surface, towards the formation of uniform high-spatial-frequency-LIPSS (HSFL) was studied experimentally. Additionally, low-spatial-frequency-LIPSS (LSFL) was observed at higher fluence along with scattered metal deposits on the surface. This work demonstrated the possibility of creating uniform HSFL using confined laser plasma plumes as the impacting medium.

2:00pm - 2:15pm

Surface carbon enrichment of stainless steel using nanosecond pulsed laser surface alloying of graphite based coating

Hasib Mustafa, Matthias Feinaeugle, G.R.B.E. Römer

Chair of Laser Processing, Department of Mechanics of Solids, Surfaces & Systems (MS3), Faculty of Engineering Technology, University of Twente, P.O. Box 217, 7500 AE, Enschede, the Netherlands

Laser surface alloying is a promising technique for modifying and/or improving surface properties of forming tools used in the fabrication thermoplastic composite parts. In this article, the results of a study on laser surface alloying of graphite based coatings on ferritic stainless steel using a nanosecond laser source is presented. The effect of different laser processing parameters and coating types on the laser-induced carbon diffusion are analyzed. The morphology of the processed areas was characterized using confocal microscopy and scanning electron microscopy. The atomic concentration of diffused carbon was determined using energy-dispersive X-ray spectroscopy. It was found that the surface carbon content of stainless steel can be increased substantially up to 70%. Cross-sectional analysis revealed the dependence of diffusion thickness on accumulated laser fluence, having a maximum at 6 µm. In comparison with low and high carbon steel, and unprocessed stainless steel, laser processed samples demonstrated improved wear properties.

2:15pm - 2:30pm

The effect of chemical components on wettability at ps laser micromachined surface on stainless steel 304

Munehiro Chijiiwa1, Niklas Berger1, Mareike Schäfer1, Rolf Merz2, Michael Kopnarski2, Peter Mitschang3, Johannes A. L'huillier1

1Photonik-Zentrum Kaiserslautern e.V., 67633 Kaiserslautern, Germany and Research Center OPTIMAS, TU Kaiserslautern, 67663 Kaiserslautern, Germany; 2Institute of Surface and Thin Film Analytics, IFOS, Research Center OPTIMAS, TU Kaiserslautern, 67663 Kaiserslautern, Germany; 3IVW—Institute for Composite Materials GmbH, Manufacturing Science, 67663 Kaiserslautern, Germany

Recently, controlling the wettability of metallic surfaces by laser micromachining has become important for many technical applications. However, there is still a challenge in understanding chemical effects on contact angle (CA) since there is even a big gap in knowledge of the laser micromachining’s influence on the surface chemistry. In this study, the relationship between the local surface chemistry at ps laser micromachined surfaces on stainless steel 304 and CA was discussed by using a new model description, based on a multiple regression analysis. The proposed model was verified by using experimental wetting behavior of different kinds of liquid and surface chemistry, characterized by XPS spectroscopy. To have a variety of different wettability of the samples, different structures, storage conditions, and post processes were tested. As a result, our proposed model showed a nice correlation between predicted CA from chemical components and measured CA.

2:45pm - 4:00pmMacro: Welding, Dissimilar Materials
Location: Room 1
Session Chair: Oliver Seffer, Laser Zentrum Hannover e.V., Germany
Room 1 
2:45pm - 3:00pm

Vapor plume behavior during a standalone laser pulse on the dissimilar aluminum/titanium interface: high-speed imaging with 810 nm band-pass filter

Manoj Raja Kumar, Iryna Tomashchuk, Jean-Marie Jouvard, Melanie Duband

Université de Bourgogne Franche-Comté, France

The understanding of plume behavior in dissimilar laser welding is little studied and can bring an insight to the concurrent vaporization process and keyhole dynamics. The present study is dedicated to the high-speed imaging and post-mortem characterization of a standalone Yb:YAG laser pulse on aluminum A5754/titanium interface with different offsets to the joint line. Plume morphology, dimensions, orientation and propagation velocities were characterized basing on the videos performed with a 810 nm band-pass filter. The main observed feature of the plume was its pronounced initial inclination towards aluminum side, accentuated by the beam offset on aluminum and reduced by the offset on titanium, followed by a progressive redressing resulting in a close-to-vertical jet. This behavior was attributed to the domination of the vapor jet from titanium side over that of aluminum side during the evolution of keyhole curvature. SEM observations of the melt were found in agreement with this statement.

3:00pm - 3:15pm

New strategies for joining of aluminum alloys to steel by means of laser

Daniel Wallerstein1, Antti Salminen2, Fernando Lusquiños1, Rafael Comesaña3, Jesús del Val1, Antonio Riveiro3, Aida Badaoui3, Juan Pou1

1CINTECX, University of Vigo, LaserON Research Group, Vigo, SPAIN; 2Department of Mechanical and Materials Engineering, University of Turku, Turku, FINLAND; 3Materials Engineering, Applied Mechanics and Construction Dpt., University of Vigo, EEI, Vigo, SPAIN

Joining steel and aluminum, is still a challenging task. This is due to significant differences in their fusion, expansion coefficients, thermal conductivity, and the practically zero solubility of Fe in Al. This low solubility leads to formation of intermetallic compounds (IMCs) on the interface between aluminum and steel.

IMCs are necessary to effectively join aluminum and steel, but the intermetallic layer can seriously deteriorate the mechanical properties of the joint.The growth of the IMC layer is the consequence of a diffusion process and, therefore, it is dependent on the welding thermal cycle. In this context, laser welding stands out relative to other welding processes by providing high energy densities and processing, with a moderate heat input.

This paper presents recent developments on the laser joining of aluminum alloys to steel. Succesfull examples of this type of dissimilar welding will be shown, comparing the mechanical performance of the final joint parts.

3:15pm - 3:30pm

Joining dissimliar materials: a new approach based on laser beam welding and melt displacement by electromagnetic forces

Jennifer Heßmann, Marcel Bachmann, Kai Hilgenberg

BAM, Germany

In order to reduce weight of vehicles, the interest in multi-material-design has been growing within the last few years. For vehicles the combination of steel and aluminium alloys offers the most promising compromise between weight, strength and formability. Thermal joining of these dissimilar materials is still a challenge to overcome. A possible approach is a new joining technology, whereby a combination of laser beam welding and contactless induced electromagnetic forces are used to displace the generated melt of one joining partner into a notch of the other. This paper presents the working principle and shows numerical analyses to improve the understanding of this joining process. The simulations help to calculate the thermal development of the joining partners, which is important for the formation of intermetallic phases. Furthermore, the calculation of the time required for a complete displacement is possible. The numerical results are validated by experimental results.

3:30pm - 3:45pm

Temperature measurement for heat conduction laser joining of metals to polymers

Mahdi Amne Elahi, Max Hennico, Peter Plapper

University of Luxembourg, Luxembourg

Laser joining of metals to polymers offers several advantages to produce hybrid assemblies of metals and polymers. One of the most important ones is the exceptional control over the heat input which defines the temperature at the interface of the materials. For the current study, the materials are joined in an overlap configuration with the heat conduction laser joining technique. To enlarge the joining area, beam trajectory was implemented with a continuous-wave fiber laser. The temperature was recorded simultaneously at different areas between the materials with K type thermocouples to identify the behavior of polymer at different temperatures. The results show that due to excessive heat input, polyamide degrades and leaves porosities near the interface of metal/polymer. The optimum condition considering mechanical properties of the welded samples and the absence of the porosities is achievable in a narrow process window between the melting range and the degradation of the polyamide.

3:45pm - 4:00pm

Metallurgy of dissimilar laser beam welded lap joints of supra-ductile and ultra-high strength steels

Martin Dahmen, Berkan Deniz, Dirk Petring

Fraunhofer Institute for Laser Technology, Steinbachstrasse 15, 52014 Aachen, Germany

Results of research on laser beam welding of a high manganese X30MnCrN16-14 (1.4678) to a press hardened X46Cr13 (1.4304), a dual phase steel (1.0944), and a press-hardened manganese boron steel (1.5528) in lap joint configuration will be reported. A pre-assessment of the local mechanical properties by micro hardness measurements revealed their uneven distribution over the weld zone. Based on metallographic inspection the underlying microstructures were revealed. By EDS analyses the local alloy constitutions were determined and assed by of COHMS diagrams. It was confirmed that in the combination with the high manganese steel the formation of ferritic phases, ferrite is largely suppressed to the favour of austenite and α’ and ε martensite. These findings were in part confirmed by nano indentation. The results allow an insight into the properties linked to melt transport, but indicate some further research.

2:45pm - 4:00pmAdditive Manufacturing: Directed Energy Deposition 4
Location: Room 2
Session Chair: Dr. Elena Lopez, AGENT-3D e.V., Germany
Room 2 
2:45pm - 3:00pm

Optical monitoring sensor system for laser-based directed energy deposition

Bohdan Vykhtar, Alexander Marek Richter

Fraunhofer Research Institution for Additive Manufacturing Technologies IAPT

To achieve homogeneous material properties and thus high-quality components, a constant melt pool geometry and temperature are essential during the laser-based directed energy deposition processes. Especially at high deposition rates, process instabilities can appear, which lead to deviations in melt pool properties consequently resulting in the discrepancy in the target/actual comparison and, in the worst case, in the disposal of the component. To monitor the continuity of the melt pool properties, this paper presents an optical monitoring sensor system, which is capable of monitoring the process by guiding, filtering, and analyzing the optical signals of the melt pool. The presented sensor system is mounted on-axis to accomplish image acquisition and monitor the melt pool emissions but is also off-axis integrable in hybrid and wire-arc-based (AM)-processes. The system is demonstrated for melt pool monitoring while processing stainless steel and an outlook is given on using that information to control the whole process.

3:00pm - 3:15pm

A measuring system based on chromatic confocal displacement sensor integrated with laser head for monitoring of laser metal deposition process

Piotr Koruba, Adrian Zakrzewski, Piotr Jurewicz, Michał Ćwikła, Jacek Reiner

Wroclaw University of Science and Technology, Poland

The measurement of geometrical properties of a sample during laser material processing is still an open research issue. Thus, the knowledge about the laser focus in relation to sample before, during and after the process is considered as one of the most crucial parameters. In this study, we indicate that the chromatic confocal displacement sensor integrated with laser head can serve as an alternative for current solutions used in monitoring of laser metal deposition process. Therefore, the design procedures of measuring system is described, consisting in numerical modelling, selection of system components. Moreover, in order to determine the functionality parameters of the system it was experimentally characterized in two regimes i.e. off-line and on-line (with and without presence of laser beam, respectively). Additionally, the various methods for spectral data processing were presented. Finally, the preliminary measurement results obtained with the measuring system during laser metal deposition were presented and discussed.

3:15pm - 3:30pm

Rotary straightening of fine wire for LMD-W applications

Sirko Pamin, Maximilian Grafe, Marius Lammers, Jörg Hermsdorf, Stefan Kaierle, Ludger Overmeyer

Laser Zentrum Hannover e.V., Germany

In wire-based high-precision laser applications as micro welding or micro laser metal deposition the straightness of the wire used plays an essential role. Small process windows require constant input conditions and thus straight wire without deformations. Uncoiled commercial wire exhibits a spatial, often helix-like curvature as a result of previous recoil processes on comparatively small reels. With the rotary straightener developed in this work, stainless steel wires with diameters of 75 µm and 100 µm, respectively, were straightened from average curvature levels of 22.56 1/m down to 0.61 1/m by alternating bending. This cold forming process causes crystallographic irregularities (dislocations) and residual stresses, which additionally lead to a rise in hardness and yield strength of the wire. For subsequent laser processes the changed material properties are advantageous, as they increase process robustness and enable a longer wire stick-out.

3:30pm - 3:45pm

Height variation in scanned hot-wire laser surfacing processes

Alexander Barroi, Kai Biester, Laura Budde, Marius Lammers, Jörg Hermsdorf, Ludger Overmeyer

Laser Zentrum Hannover e.V., Germany

The use of hot wire in laser cladding can raise the energy efficiency and the deposition rate of the process drastically. This study shows that when using hot wire, the process faces stronger restrictions to one of the process parameters, the wire nozzle height. A change of three millimeters in wire nozzle height can double the dilution. This is because of the impact of stick out length on the wire heating. But not only the heating has an effect when changing the height, it also changes the wire positioning, a parameter which is sensible for the process stability.

3:45pm - 4:00pm

Automatic changing of weld deposit for additive manufacturing of hybrid metal-glass components using direct laser deposition

Marius Lammers1,2, Kai Biester1, Nick Schwarz1,2, Jörg Hermsdorf1, Stefan Kaierle1, Henning Ahlers2

1Laser Zentrum Hannover e.V., Germany; 2Hochschule Hannover – University of Applied Sciences and Arts, Germany

Direct Laser Deposition is a manufacturing process, which enables Additive Manufacturing of nearly any fusible material. For example metal or glass materials can be processed.

For generating hybrid components out of metal and fused silica, systems technology with coaxial beam guidance using different laser beam sources can be used enabling direct manufacturing of optical, structural and thermal elements. To suit both processes, a wide velocity range regarding the weld material feed from 0.1 to 5 m/min is required.

In this paper a prototype machine for material feeding and changing is presented. The system is designed for metal wire and glass fibre feeding. In order to determine process-critical parameters, preliminary tests are carried out to determine the requirements for the system. The paper also shows how the prototype system performs in terms of changing and conveying the wires as well as fibers with a focus on wear and changing cycles.

2:45pm - 4:00pmMicro: Processing of Transparent Materials 2
Location: Room 3
Session Chair: Dr. Kristian Cvecek, Institute of Photonic Technologies (LPT), Germany
Room 3 
2:45pm - 3:00pm

Deep engraving of fused silica glass using bursts of femtosecond pulses with intra-burst frequencies in the range of 25 - 100 GHz

Simas Butkus1,2, Martynas Barkauskas1,2, Aurimas Augus1, Martynas Kojelis1, Jonas Pocius1, Linas Giniūnas1

1Light Conversion, Lithuania; 2Laser Research Center, Vilnius University, Lithuania

Due to the high precision offered by ultrashort pulse micromachining, femtosecond laser systems are applied in both industrial and scientific fields. To accompany the needs of the industry, a trend towards high average power (>100 W) femtosecond laser systems for micromachining has become apparent. However, upscaling the micromachining throughput is not straightforward and typically results in a decrease in the micromachining quality. To this end, new ideas are sought to increase the efficiency of an ablation-based process.

In this work we present data on deep engraving of fused silica glass using burst of femtosecond pulses with a custom-built laser capable of tuning the intra-burst temporal gap producing a variable effective repetition rate of 25 – 100 GHz. By adjusting the average power, number of sub-pulses within the burst and the intra-burst gap it was found that the ablation efficiency can be increased by several-fold as compared to the convention single-pulse regime.

3:00pm - 3:15pm

Fully reflective Bessel beam generation with constant energy distribution over the propagation axis for complex glass cutting

Siddharth Sivankutty, Antonin Billaud, Gwenn Pallier, Pu Jian, Olivier Pinel, Guillaume Labroille

Cailabs, France

Glass cutting with femtosecond lasers is spreading led by the touch panel displays development. Bessel beams are very efficient and precise way to process glass thanks to their extended depth of focus 100 times longer than a standard Gaussian beam and their central beam which can be smaller than the diffraction limit.

High quality glass cutting with a reflective axicon has already been demonstrated with no oscillations leading to cleaner cuts and faster processes. The beam is able to propagate through a galvo-scanner and a F-theta lens. The reflective design is compatible with extreme high peak and average power.

Here we describe the generation of a complex Bessel beam profile flatter over the propagation axis based on a reflective design. The tail of this profile is five times sharper compared to standard Bessel beams paving the way to complex glass cutting such as multi-layer glasses.

3:15pm - 3:30pm

Optical coherence tomography for 3D weld seam localization in absorber-free laser transmission welding

Frederik Maiwald1, Clemens Roider2, Michael Schmidt2,3, Stefan Hierl1

1Ostbayerische Technische Hochschule Regensburg, Labor Lasermaterialbearbeitung, Technologie Campus Parsberg-Lupburg, Am Campus 1, 92331 Parsberg, Germany; 2Institute of Photonic Technologies, Friedrich-Alexander-Universität Erlangen-Nürnberg, Konrad-Zuse-Straße 3/5, 91052 Erlangen, Germany; 3Erlangen Graduate School in Advanced Optical Technologies (SAOT), Paul-Gordan-Str. 6, 91052 Erlangen, Germany

Thulium fibre lasers emit in the intrinsic absorption spectrum of polymers and enable welding of transparent parts without absorbent additives. Focusing with high NA provides large intensity gradients inside the workpiece, enabling selective fusing of the joining zone without affecting the surface. Therefore, absorber-free laser transmission welding is well suited to fulfil the high demands on quality and reliability in manufacturing of optical and medical devices. However, monitoring the welding process is required, since seam size and position are crucial for quality.

The aim of this work is the volumetric acquisition of the weld seam’s location and size using optical coherence tomography. Due to the change of the optical properties during melting, the seam can be distinguished from the base material. The results coincide with microscopic images of microtome sections and demonstrate that weld seam localization in polyamide 6 is possible with an accuracy better than a tenth of a millimetre.

3:30pm - 3:45pm

Laser-manufactured glass microfluidic devices with embedded sensors

Krystian L. Wlodarczyk1,2, William N. MacPherson2, Duncan P. Hand2, M. Mercedes Maroto-Valer1

1Research Centre for Carbon Solutions, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, UK; 2Applied Optics and Photonics group, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, UK

Recently, we have developed a laser process that enables the rapid fabrication of microfluidic devices using widely-available borosilicate glass slides. In contrast to conventional manufacturing techniques, there is no requirement for projection masks and hazardous glass etchants, such as hydrofluoric acid. Instead, a single item of equipment, i.e. an ultrashort pulsed picosecond laser (Trumpf TruMicro 5x50), is used to: (a) write microfluidic patterns directly onto the glass surface by ablating the material and (b) permanently enclose the microfluidic structure from the top by welding this glass substrate to another glass slide that typically contains inlet/outlet ports. In this work, we demonstrate that this process also allows us to manufacture customised glass microfluidic devices with embedded sensors, which enable local, real-time monitoring of various parameters, such as pressure and pH, inside the microfluidic patterns.

3:45pm - 4:00pm

Ultrashort pulse laser cutting of colorless polyimide and hard coat film stacks for flexible OLED displays

Jim Bovatsek, Terence Hollister

MKS Spectra-Physics, United States of America

New mobile devices include flexible and foldable OLED displays which require new protective cover materials. Options for this include ultrathin glass (UTG) as well as a new type of colorless polyimide (CPI), which is transparent at visible wavelengths. The CPI is combined with a scratch resistant hard coat (HC) layer and a final PET (polyethylene terephthalate) protective film. Here we present results for cutting thick CPI/HC/PET layered stacks using high power UV ultrashort pulse lasers. Ablation thresholds were found to vary by almost a factor of ten, and a layer-optimized cutting approach was used. The optimized cutting process is of high quality and throughput, with heat-affect zone (HAZ) of <10 µm and cutting speed of >400 mm/s. These results are comparable to that for individual sheets of polymers used in OLED display manufacturing.

2:45pm - 4:00pmMicro: Surface Functionalization 7
Location: Room 4
Session Chair: Dr. Stephan Roth, Bayerisches Laserzentrum GmbH (blz), Germany
Room 4 
2:45pm - 3:00pm

Improvement of hardness and wear-resistance of direct laser interference patterned bearing steel surface using laser surface heating approach

Mikhael El-Khoury1, Marko Seifert2, Sven Bretschneider2, Martin Zawischa2, Tim Kunze2, Andrés Fabián Lasagni1,2

1Institut für Fertigungstechnik, Technische Universität Dresden, George-Bähr-Str. 3c, 01069 Dresden, Germany; 2Fraunhofer-Institut für Werkstoff- und Strahltechnik IWS, Winterbergstr. 28, 01277 Dresden, Germany

Direct Laser Interference Patterning (DLIP) has emerged as a practical technology to enhance surface functionality, for instance, to improve tribological properties of steel parts. In fact, the life of tribo-pairs with enhanced tribological properties is related to the durability of those microstructured patterns that can be significantly improved by increasing their hardness. In this study, we report on the laser heat treatment of periodic topographies produced on bearing steel plates using DLIP technology. The hardening treatment allowed to tune the surface hardness from 210 HV to 827 HV. The combination of the patterning and laser hardening approaches permitted to improve the wear-resistance of the structured surface by ~ 50 % at contact point pressure of ~17.87 GPa. The outcomes indicated that by applying the proposed joined methodology it is conceivable to hold the higher hardness of the bearing steel plates and simultaneously to keep intact surface microstructures.

3:00pm - 3:15pm

Laser melt injection for homogenous particle distribution in copper materials

Anika Langebeck, Annika Bohlen, Thomas Seefeld

BIAS - Bremer Institut fuer angewandte Strahltechnik GmbH, Germany

MMC (metal matrix composite) layers have great potential to improve abrasive wear resistance of tool surfaces such as injection molds. For this, laser melt injection is used to disperse hard particles into the molten tool surfaces.

Injection molding tools are often made of copper materials which are characterized by a high thermal conductivity and have low absorptivity for the wavelength of a disk laser (1030 nm). This makes coupling into the material and thus a stable process more difficult. In this work coupling is improved by increasing the laser power density. In combination with beam modulation a large melt pool can be generated. It can be demonstrated that low process velocities are mandatory for a homogenous particle distribution. For the analyzed MMC system of aluminum bronze reinforced with tungsten carbide, a welding speed of 300 mm/min leads to a homogenous distribution whereas faster process velocities result in a graded particle distribution.

3:15pm - 3:30pm

Laser-based coating process of PA12 on stainless steel substrates

Alexander Wittmann1,3, Oliver Hentschel1,3, Jakob Ermer2,3, Alexander Sommereyns1,3, Florian Huber1,3, Michael Schmidt1,2,3

1Institute of Photonic Technologies (LPT), Friedrich-Alexander-Universität Erlangen-Nürnberg, Konrad-Zuse-Straße 3/5, 91052 Erlangen, Germany; 2Bayerisches Laserzentrum GmbH (blz), Konrad-Zuse-Straße 2/6, 91052 Erlangen, Germany; 3Erlangen Graduate School in Advanced Optical Technologies (SAOT), Paul-Gordan-Straße 6, 91052 Erlangen, Germany

Thermoplastic coatings are of great interest for multiple applications in industry e.g. to protect the surface from corrosion and to prevent excessive wear. In the present study a laser-based coating process for PA12 powder on stainless steel substrates is investigated. To evaluate the influence of the wavelength on the resulting coating characteristics, ytterbium (λ=1.07 µm) and thulium fiber laser (λ=1.94 µm) are used to consolidate the manually deposited PA12 powder. In addition, the effects of substrate preheating on substrate adhesion are examined. The specimens are analyzed by optical and confocal laser scanning microscopy. Furthermore, powder material and coatings are characterized by differential scanning calorimetry. Results show that dense and adherent coatings can be applied on stainless steel substrates. Coatings melted by ytterbium fiber laser exhibit a lower degree of particle melting. In case of thulium fiber laser, the adhesion is further increased by additional substrate preheating.

3:30pm - 3:45pm

Processing of an organosilazane-based glass/ZrO2 composite coating system by laser pyrolysis

Alexander Horcher1, Katja Tangermann-Gerk2, Walter Krenkel1, Günter Motz1

1Universität Bayreuth, Germany; 2Bayerisches Laserzentrum Erlangen, Germany

Protective ceramic-based coatings are frequently the most suitable and cost-effective solutions for problems like corrosion, oxidation and wear. It has been shown, that the polymer-derived ceramics technology is suitable for the preparation of ceramic coatings by pyrolysis in a furnace. However, the required high temperatures for the preparation of the ceramic coatings only allow the use of temperature-resistant substrates. A very innovative approach to overcome this restriction is the use of laser radiation as an energy source for the pyrolysis of the preceramic polymer. For this reason, a composite coating system composed of an organosilazane with ZrO2 and glass particles as fillers was developed suitable for pyrolysis with a Nd:YAG laser. The composite coating slurry was applied onto stainless steel substrates by spraying and afterwards irradiated with a Nd:YAG laser. Finally, the microstructure, chemical composition, abrasions resistance as well as the mechanical properties and the corrosion behavior was investigated.

3:45pm - 4:00pm

Laser sintering of ceramic-based solid-state battery materials

Linda Hoff

Fraunhofer Institute for Laser Technology (ILT), Germany

Ceramic solid-state batteries can increase gravimetric energy density and safety compared to conventional lithium-ion batteries. The ceramic materials are applied to a metallic carrier foil by screen printing and then thermally post treated (dried and sintered) to produce adhesive layers with the highest possible density.

Disadvantages of conventional oven processes are the possible diffusion between adjacent layers due to long process times (in the range of minutes) at high temperatures. Furthermore, multilayer systems, containing different materials with varying decomposition temperatures, cannot be treated successfully.

Laser processing shows potential for reducing diffusion processes and preservation the materials crystal structure (meaning preserving their electrochemical properties) due to short interaction times within the range of seconds. In this work, the laser sintering of ceramic micro particle battery layers is presented, addressing the challenges of reaching a rather homogeneous temperature profile across the coating thickness within short processing times while preserving the materials integrity.

4:00pm - 4:10pmClosing Session
Location: Room 1
Session Chair: Prof. Michael Rethmeier, Bundesanstalt für Materialforschung und -prüfung (BAM), Germany
Room 1