Conference Agenda

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

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

Mikhail Sokolov, Pasquale Franciosa, Dariusz Ceglarek

WMG, University of Warwick, United Kingdom

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

10:15am - 10:30am

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

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

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

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

10:30am - 10:45am

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

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

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

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

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

Investigation of Kovar in PBF-LB/M

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

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

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

10:15am - 10:30am

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

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

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

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

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

10:30am - 10:45am

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

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

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

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

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

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

Yasuhiro Okamoto, Tubasa Okubo, Atsuya Kajitani, Akira Okada

Okayama University, Japan

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

10:15am - 10:30am

Laser structuring of PVD multi-layer coatings for wear reduction

Andreas Stephen1, Bastian Lenz2, Andreas Mehner2, Tim Radel1

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

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

10:30am - 10:45am

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

Rene Liebers, Mandy Gebhardt

3D-Micromac AG, Germany

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

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

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

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

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

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

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

10:15am - 10:30am

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

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

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

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

10:30am - 10:45am

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

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

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

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

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

10:45am - 11:00am

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

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

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

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

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

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

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

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

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

10:15am - 10:30am

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

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

Laser Zenrum Hannover e.V., Germany

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

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

10:30am - 10:45am

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

Nicole Emminghaus, Christian Hoff, Jörg Hermsdorf, Stefan Kaierle

Laser Zentrum Hannover e.V., Germany

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

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

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

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

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

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

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

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

11:30am - 11:45am

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

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

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

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

11:45am - 12:00pm

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

Benjamin Karwoth, Thorsten Mattulat, Peer Woizeschke

Bremer Institut für angewandte Strahltechnik GmbH, Germany

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

12:00pm - 12:15pm

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

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

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

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

12:15pm - 12:30pm

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

Nicolas Meunier

MKS Instruments - Ophir Brand, Germany

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

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

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

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

Elena Bassoli

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


11:45am - 12:00pm

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

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

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

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

12:00pm - 12:15pm

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

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

Laser Zentrum Hannover e.V., Germany

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

12:15pm - 12:30pm

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

Andreas Kempf1, Leonardo Agudo Jácome2, Kai Hilgenberg3

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

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

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

Polymer film processing with a high-power industrial femtosecond laser

Chandra Sekher Reddy Nathala, Victor Matylitsky, Herman Chui

MKS Spectra-Physics

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

11:30am - 11:45am

Roll-to-roll laser processing of flexible devices

Maurice Clair, Christian Scholz, Mandy Gebhardt

3D-Micromac AG, Germany

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

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

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

11:45am - 12:00pm

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

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

Institut für Strahlwerkzeuge IFSW, Germany

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

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

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

12:00pm - 12:15pm

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

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

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

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

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

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

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

Laser Zentrum Hannover e.V., Germany

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

11:30am - 11:45am

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

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

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

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

11:45am - 12:00pm

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

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

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

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

12:00pm - 12:15pm

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

Aurélien Sikora, Girolamo Mincuzzi, Rainer Kling

ALPhANOV, France

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

12:15pm - 12:30pm

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

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

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


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

Study of pointing stabilization unit for femtosecond fiber beam delivery system

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

1GLOphotonics; 2Cailabs

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

11:30am - 11:45am

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

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

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

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

11:45am - 12:00pm

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

Lea Sauerwein, René Geiger, Christian Ebenhöh

Evosys Laser GmbH, Germany

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

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

12:00pm - 12:15pm

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

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

1Cailabs, France; 2Institut Maupertuis, France

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

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

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

12:15pm - 12:30pm

Laser-based manufacturing of ceramic matrix composites

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

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

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

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

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

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

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

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

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

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

1:45pm - 2:00pm

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

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

Laser Zentrum Hannover e.V., Germany

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

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

2:00pm - 2:15pm

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

Sven Müller, Peer Woizeschke

BIAS - Bremer Institut für angewandte Strahltechnik GmbH, Germany

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

2:15pm - 2:30pm

Prediction of Cu-Al weld status using convolutional neural network

Karthik Mathivanan, Peter Plapper

University of Luxembourg, Luxembourg

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

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

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

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

Iker Garmendia, Jon Flores, Carlos Soriano, Mikel Madarieta

Tekniker, Spain

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

1:45pm - 2:00pm

Structure-borne acoustic process monitoring of laser metal deposition

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

Laser Zentrum Hannover e.V., Germany

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

2:00pm - 2:15pm

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

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

Technical University of Munich, Germany

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

2:15pm - 2:30pm

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

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

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

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

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

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

Sebastian Michel, Pascal Volke, Dirk Biermann

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

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

1:45pm - 2:00pm

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

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

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

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

2:00pm - 2:15pm

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

Anne Feuer, Rudolf Weber, Thomas Graf

IFSW, University of Stuttgart, Germany

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

2:15pm - 2:30pm

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

Roberto Ocaña, Joseba Esmoris, Carlos Soriano

TeknikerTekniker-Basque Research & Technology Alliance, Spain

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

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

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

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

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

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

1:45pm - 2:00pm

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

Dhiraj Kumar, Gerhard Liedl

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

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

2:00pm - 2:15pm

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

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

AIMEN - Laser Centre, Spain

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

2:15pm - 2:30pm

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

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

Aalen University, Germany

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

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

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

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

Insa Henze, Thorsten Mattulat, Peer Woizeschke

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

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

3:00pm - 3:15pm

Laser process manipulation by axial beam shaping

Joerg Volpp1, Adrien Da Silva1, Alexander Laskin2

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

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

3:15pm - 3:30pm

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

Peter Hellwig, Klaus Schricker, Jean Pierre Bergmann

Technische Universität Ilmenau, Production Technology Group, Germany

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

3:30pm - 3:45pm

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

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

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

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

3:45pm - 4:15pm

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

Craig B. Arnold, Wenxuan Zhang, Wenyuan Hou

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

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

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

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

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

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

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

3:00pm - 3:15pm

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

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

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

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

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

3:15pm - 3:30pm

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

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

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

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

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

3:30pm - 3:45pm

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

Fabian Fröhlich, Jörg Hildebrand, Jean Pierre Bergmann

Technische Universität Ilmenau, Production Technology Group, Germany

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

3:45pm - 4:00pm

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

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

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

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

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

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

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

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

Berner Fachhochschule Technik und Informatik, Switzerland

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

3:00pm - 3:15pm

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

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

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

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

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

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

3:15pm - 3:30pm

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

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

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

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

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

3:30pm - 3:45pm

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

Falk Braunmüller, Jérémie Diboine, Amédée Zryd, Bernold Richerzhagen

Synova S.A., Switzerland

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

3:45pm - 4:00pm

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

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

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

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

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

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

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

University of Applied Sciences Mittweida, Germany

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

3:00pm - 3:15pm

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

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

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

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

3:15pm - 3:30pm

Laser texturing of heat exchanger tubes for nucleate boiling regime promotion

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

1AIMEN, Spain; 2INTEGASA, Spain

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

3:30pm - 3:45pm

Ultrashort laser coloration on titanium coatings

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

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

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

3:45pm - 4:00pm

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

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

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

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