System Technology and Process Control (LiM 2021)

System design for reliable and robust laser-welding of copper in automotive series production
Stefan Mücke, Pravin Sievi

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

Keywords: E-Mobility, laser welding of copper, pattern recognition, robust system design, process know-how;


Laser technologies for battery pack production - acomprehensive overview with a focus on the structuralcomponents
Mauritz Möller, Max Rettenmeier

The global mobility revolution is in full swing. The demand for components for electric cars and alternative drives is rising
continuously. Many production approaches are making use of the benefits of laser technologies. It connects battery cells
to form modules or packs. It ensures tightness and crash safety when joining battery packs and trays.
This paper offers an insight into the requirements of battery packs as well as the innovative joining technology solutions
for the material specifics, which are made possible by the use of novel laser and system developments in industrial
practice. Furthermore, the trends regarding the structural components of future battery packs will be presented. Finally,
a spotlight will present the next generation of laser and joining technologies for use in battery system manufacturing and
place them in the context of existing material-specific challenges, such as helium-tight welding of aluminum alloys.

Keywords: Battery pack; Structural components; Laser technologies; Laser manufacuturing; Battery electric vehicle; Laser welding


Water jet guided laser as a versatile turning method for industrial applications
Jehan Moingeon, Jeremie Diboine, Amédée Zryd, Bernold Richerzhagen

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

Keywords: Laser; water jet; turning.


Laser-induced forward transfer (LIFT) of micro-LED devices
Alberto Piqué, Ray Auyeung, Kristin Charipar, Heungsoo Kim, Michael Malito, Nicholas Charipar

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

Keywords: Laser-induced forward transfer; Additive manufacturing; Micro-LED


Automated synthesis of colloidal nanoparticles powered by microchip lasers
Tobias Bessel, Sarah Dittrich, Bilal Gökce, Stephan Barcikowski, Friedrich Waag

Energy and health, two topics with continuing high relevance for our society, which require intensive R&D. Nanoparticles, with their unique properties, already make an important contribution to both fields and will play an even more essential role in the future. Access to high-quality nanoparticles for R&D is still difficult, especially when high purity and material diversity are required. Moreover, limited shelf-life, batch-to-batch-variability, and time-consuming ordering or shipping procedures hinder development progress. Pure colloidal nanoparticles of numerous combinations of particle material and dispersion medium become available by pulsed laser ablation, but automation has not been achieved affordably, yet. Compact microchip lasers now enable the transfer of the synthesis method from the laser lab to any R&D lab as a benchtop, easy-to-use machine. The low-power q-switched, cavity-limited lasers impress with unprecedented power-specific ablation efficiency in the laser synthesis of colloids. In addition, innovative solutions in measurement and control technology make full automation of nanoparticle production possible.

Keywords: Benchtop; Infrared; Nanoseconds; Nanomaterials; Productivity


Monitoring of Laser Welding and Cladding Processes with Edge Artificial Intelligence Combining Thermal and Visual Cameras
Beñat Arejita, Juan Fernando Isaza, Aitzol Zuloaga

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

Keywords: Welding; EdgeAI; Process Monitoring; Temperature Control


Superimposed beam deflection using acousto-optical deflectors in combination with a galvanometer scanner
Daniel Franz, Gian-Luca Roth, Stefan Rung, Cemal Esen, Ralf Hellmann

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. To fundamentally characterize the scanning movement of the hybrid system, the roundness of the focal spots within an AOD scan field and its dimensions are analyzed by ablated geometries in thin indium tin oxide films for different galvanometer deflections and focus levels. The investigations show that focal spots roundness of more than 90 % in a z-range of 200 μm, i.e. 36 % of the Rayleigh length, can be realized in a galvanometer scanning field of 30 x 30 mm2. Maximum deflection speeds of 843 m/s within an AOD scan field highlight the great potential for highly dynamic laser micromachining.

Keywords: laser beam deflection; ultra-short pulse laser; acousto-optical deflector (AOD); hybridsystem;


Optical system for multi Bessel beam high power ultrashort pulsed laser processing using a spatial light modulator
Christian Lutz, Simon Schwarz, Stefan Rung, Jan Marx, Cemal Esen, Ralf Hellmann

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

Keywords: Bessel beam; axicon; optical system; ultrashort pulsed laser; material ablation


Real-time adaptation of the dross attachment level in the laser cutting process based on process emission images
Matteo Pacher, Mara Tanelli, Silvia Strada, Davide Gandolfi, Sergio M. Savaresi and Barbara Previtali

In the field of melt and blow metal laser cutting, dross attachment is the most important quality indicator. Accordingly, process parameters are generally optimized to ensure high productivity while minimizing the level of dross attachment. The resulting set of parameters often penalizes the productivity to increase reliability. As a result, there exists a productivity margin that could be exploited by controlling the quality level in closed-loop, thus optimizing the process parameters in real-time. To closed-loop control the process, two steps must be performed: a real-time, reliable estimate of cutting quality must be available and, a closed-loop controller should adapt the process parameters according to the desired quality level. This work presents the design and experimental validation of a real-time estimation and control algorithm based on process emission images that adapts the cutting speed to fulfill a desired dross attachment level.
Project Name: LT4.0. Funding from LP6/99 Autonomous Province of Trento

Keywords: laser cutting; dross attachment; monitoring and control; camera monitoring; process emission


Arrangement for the benchmarking of in-situ process monitoring of topographical process signatures within the Laser Powder Bed Fusion process
Karen Schwarzkopf, Eric Eschner, Michael Schmidt

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

Keywords: additive manufacturing; laser powder bed fusion; in-situ process monitoring; topographical process signatures; low coherence imaging


Adaptive real-time anomaly detection in laser welding using multiple convolutional neural networks on embedded devices
Christian Knaak, Jakob von Eßen, Peter Abels, Arnold Gillner

The application of machine learning approaches for process monitoring in complex manufacturing processes such as laser materials processing enables the detection of defects based on complex sensor signals but remains challenging in industrial practice. Therefore, a novel and adaptive approach is proposed to detect weld anomalies in real-time without the need for labor-intensive and continuous data labeling. The monitoring setup consists of a coaxially integrated camera that observes the thermal radiation emitted by the laser interaction zone at a specific wavelength. The image data are subsequently used together with semi-automatically generated annotations to build four convolutional neural networks (CNNs) running in parallel to detect process anomalies during the welding process. Experimental results indicate that the proposed approach can be used for real-time anomaly detection at high frame rates (>840fps) and low latency using a GPU-based embedded system.

Keywords: Machine learning; laser materials processing; neural networks


Spatially resolved melt pool monitoring for process characterization in laser powder bed fusion (LPBF)
Dieter Tyralla, Peer Woizeschke, Thomas Seefeld

Laser powder bed fusion (LPBF) is a frequently used manufacturing process for complex shaped geometries, e.g. bionic structures. The part quality often depends not only on process parameters but also on geometrically induced changes in thermal conditions. Thus, already identified parameters may need to be adjusted to the geometry. Here, a temperature measurement provides information about the current process state due to its recognition of heat input, accumulation and conduction during build-up and thus assists the parameter development.
The present work applies a spatially resolved temperature measurement for process monitoring in LPBF using 2-channel-pyrometry. A lateral resolution of 10 μm is achieved within the complete build-up volume of 250x250x250 mm³ by the coaxial integration of the pyrometric camera system into the beam path of a LPBF machine. The melt pool area was identified as a suitable indicator which enables the prediction of part density during build-up process.

Keywords: Additive manufactruing; Laser powder bed fusion; process monitoring; temperature field measurement; melt pool geometry


Active mirrors for plane field correction in laser material processing
Paul Böttner, Claudia Reinlein, Aoife Brady, Ramona Eberhardt, Stefan Nolte

This paper reports on an approach to increase the scan field and the dynamic range of post objective scanners. An active mirror in combination with a fixed focusing lens is used to adjust the optimal focus length depending on the beam position in the scan field. The active mirror has an adjustment range of 0.52 dpt with a step response time of 2 ms. The scan field is determined by the focal length of the focusing lens. A permissible spot eccentricity of 0.4 and a focal length of 250 mm enable a work field of (186x140) mm². Doubling the focal length increases the scan field to (420x372) mm². Simulations with a raw beam diameter of 10 mm and a wavelength of 633 nm provide a spot diameter of 29.5 μm with a focal length of 250 mm and 57.4 μm with a focal length of 500 mm.

Keywords: active mirror; material processing, plane field correction, post -objective scanning


Study of pointing stabilization unit for femtosecond fiber beam delivery system
Benoit Beaudou, Pierre Guay, Fetah Benabid, Ivan Gusachenko, Clément Jacquard, Gwenn Pallier, Guillaume Labroille

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.

Keywords: Fiber coupling; beam pointing


Laser technologies for the production of microLEDs
Mandy Gebhardt, Uwe Wagner, Markus Müller

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

Keywords: microLED; Laser Lift-Off (LLO); Laser Induced Forward Transfer (LIFT); display; laser processing


High speed temperature measurement in ultrashort pulse laser micromachining
Jiri Martana,*, Lucie Prokesovàa, Denys Moskala, Bernardo Campos Ferreira de Fariaa, Milan Honnera, Vladislav Lang

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

Keywords: Ultrashort pulse lasers; laser micromachining; process monitoring


Open-loop control complex pulse shapes for laser beam welding
Marc Seibold, Klaus Schricker, Jean Piere Bergmann

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

Keywords: open loop control; pulsed laser beam welding


Remote laser welding system with automatic 3D teaching, in-line 3D seam tracking, and adaptive power control
Matija Jezeršek, Matjaž Kos, Erih Arko, Hubert Kosler

An adaptive remote laser welding system based on triangulation feed-back control is presented. It enables off-line measuring of a workpiece 3D shape, in-line 3D seam tracking, and in-line laser power control, which are extremely important features for producing sound welds on complex geometries. The 3D measuring is done by a triangulation camera and the laser’s pilot beam. The same camera is utilized to determine the 3D seam position and to monitor the key process features, including the weld depth. Results show high 3D measuring precision in the lateral (0.05 mm) and vertical (0.3 mm) direction. Additionally, laser power control significantly reduces penetration depth and plasma oscillations. Thus, the adaptive laser welding can be used for small series and customized production of parts where a highly flexible, precise, and cost-effective joining technology is required.

Keywords: Remote laser welding; triangulation; 3D object measurement; 3D seam tracking; laser power control


Additive manufacturing: The need to get the laser beam right
Nicolas Meunier

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

Keywords: additive manufacturing; selective laser manufacturing; laser beam parameters; non-contact measurement;, Rayleigh scattering; reproducibility; quality; troubleshooting


Fixture free laser beam welding for the automotive body shop
Georgij Safronov, Alexander Grimm, Florian Schlather, Markus Puschmann, Philipp Engelhardt, Markus Lachenmaier

The current automotive body shop is dominated by resistance spot welding due to its low costs and robustness, especially regarding quality variations of the single parts. In contrast, laser beam welding is struggling to create a solid business case in big numbers despite its technological advancements like the welding speed. To economically resolve this issue, an approach is needed that creates a balanced synergy between both joining processes. BMW, together with the Fraunhofer Institute for Machine Tools and Forming Technology (IWU) and the Institute for Machine Tools and Industrial Management (iwb) from the Technical University Munich, approached this challenge by developing a method to combine both welding processes through a lap-joint-flange integrated geometry, which can be installed off-tool in the press-shop. These functional geometries allow the advantages of resistance spot welding to be used to fix the geometry and create a laser-suitable gap situation without clamping tools for the following laser beam welding. Within this paper the technological and the financial viability of this method is proved, which is why this could be a major breakthrough for laser beam welding in the automotive industry.

Keywords: fixture free, resistance spot welding, laser beam welding, functional geometry, automotive production


RECILS: High resolution and high-speed SLA 3D printerusing a plane building platform and a cylindrical window
Kentaro Soeda, Hirosuke Suzuki, Shuichi Yokobori, Kuniaki Konishi,Hiroharu Tamaru, Norikatsu Mio, Makoto Kuwata-Gonokami and Junji Yumoto

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

Keywords: 3D printer, SLA, cylindrical window, raster scanning, UV-curable resin;


The final steps towards guaranteed quality and first-time-right - 3D printing with powder and wire enabled by OCT sensor technology
Markus Kogel-Hollacher, Frédéric Adam, Christian Staudenmaier, Rüdiger Moser, Steffen Boley

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

Keywords: DED-LB; LMD; 3D Printing; OCT; Low coherence interferometry; Industry 4.0