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: 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

AMPLITUDE, France

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

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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.