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).

Please note that all times are shown in the time zone of the conference. The current conference time is: 29th Jan 2022, 05:40:21am CET

Only Sessions at Location/Venue 
Program for LiM 2021
Location: Room 1
ICM Ground Floor 125
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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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