Beam Shaping and Oscillation (LiM 2021)

Beam shaping with free-form optics for optimal material processing
Henrike Wilms, Ulrike Fuchs, Frank A. Müller, Stephan Gräf

The number of applications in material processing, where the focal intensity distributions should deviate from the Gaussian shape, is rapidly increasing. Of particular interest are not only top-hat or donut distributions, but also non-rotationally symmetric distributions such as squares or ellipses. We present refractive freeform beam shaping elements to generate such focal distributions. Moreover, these elements provide patterns in the focal region with 3x3 or 4x4 spots. Here, the absolute size of all focal distributions is scalable with the NA of the used focusing lens. Simulation results will be compared with measured intensity profiles to show good agreement. Furthermore, first experiments on stainless steel will show the different effect of the various intensity distributions on the material interaction. Since the refractive beam shaping elements used are also low dispersion, this opens new possibilities for material processing with ultrashort laser pulses.

Keywords: beam shaping; laser material processing; surface functionalization; ablation


Simulations on beam shaping in laser powder bed fusion
Pareekshith Allu

To enable wider adoption, LPBF processes require manufacturing features with varying levels of detail at high production speeds. This becomes challenging when working with single mode lasers that operate exclusively in either the Gaussian or top hat modes. By varying spot sizes and beam shapes, new laser technologies can switch real time between different heat flux distributions that enable faster builds with higher detail.
In this presentation we discuss how CFD models built in FLOW-3D AM are used to analyze different heat flux distributions for single mode and ring beam modes that affect the melt pool dynamics. Gaussian distributions have higher localized temperatures resulting in high rates of vaporization compared to ring beam modes that distribute heat fluxes evenly over a larger area. Such CFD models also help generate process windows that utilize higher scan speeds for the various ring beam modes, ensuring higher productivity rates while maintaining process stability.

Keywords: CFD simulations, laser powder bed fusion process, FLOW-3D, melt pool dynamics, direct energy deposition


3-dimensional beam shaping for dynamic adjustment of focus position and intensity distribution for laser welding and cutting
Jahn, Axel; Dittrich, Dirk; Börner, Stephan; Standfuss, Jens; Herwig, Patrick; Reinlein, Claudia

Beam shaping, using highly dynamic beam oscillation, offers a high potential for the process control and thus the adaptation to specific process requirements. The realization of beam oscillation in 3 spatial directions opens up new possibilities for specific adjustment of the energy distribution in the melting zone and also creates prerequisites for high dynamic 3D welding and cutting.
A novel 3D optical system will be presented containing galvo-x/y-scanners combined with a new piezo-driven focus modulation (z-modul). This concept enables a synchronous high-frequency axis-control of the 3 spatial directions in a compact optics design.
In the lecture, construction concept and mode of operation of the 3D-system as well as achievable complex 3D energy distributions will be presented. Further, results of process investigations for welding Al alloys and 3D contours are shown and advantages in process stability and joint quality are derived.

Keywords: 3D beam oscillation; 3D optic; highly dynamic beam shaping; piezo driven moduls; focus adaption; material processing; laser beam welding


Top-hat profile beam to weld polymeric microfluidics chips with ultra-short pulsed laser
M. Décultota,*, J. Patarsa, A. Henrottina, Ivan Gusachenkob, Clément Jacquardb, Gwenn Pallierb, J. A. Ramos-de-Camposa

The microfluidics field, due to its various possibilities in the study of chemical and biological reactions with only few consumables, is expanding significantly. To follow this growing, we have developed a flexible solution, based on ultra-short pulsed laser technology, to engrave different microfluidic channels on a chip, and to seal them with a complete, hermetical, and resistant welding. In order to improve the competitiveness of our solution for industrial production purpose, we have focused in particular our work on the improvement of the welding’s speed. Using the Canunda-Pulse® solutions from Cailabs for manipulating high-power femtosecond lasers, we have made a complete study on laser welding parameters with a top-hat profile beam. Canunda-Pulse® is a fully reflective passive optical module based on the Multi-Plane Light Conversion (MPLC) technology. Thanks to this beam shaper, we have deduced advantages of a top-hat profile beam, compared to a gaussian profile beam.

Keywords: ultra-short pulsed laser; welding; transparent polymer; microfluidics; beam shaping


Influence of laser beam welding with overlaid high-frequency beam oscillation on weld seam quality and fatigue strength of aluminum wrought and die-cast joints
Benjamin Kessler, Dirk Dittrich, Robert Kuehne, Markus Wagner, Axel Jahn

Laser beam welding of aluminum die cast components using high frequency beam oscillation could massively improve the process stability and tightness of cooling components. The application of the newly developed laser beam welding processes to fatigue loaded components makes it necessary for designers to dimension the components and welds using existing guidelines. Up to now, however, no experience has been obtained with the applicability of the existing regulations.
For this purpose within this study, weld specimens in form of aluminium mixed joints (wrought and die-cast alloys) were produced with standard laser beam welding process (LBW) and laser beam welding with overlaid high-frequency beam oscillation (LBW-HF). The weld seam quality is correlated with the fatigue strength properties. Furthermore, the results from the fatigue tests are classified in the existing IIW regulations and their applicability with regard to laser-welded aluminium joints will be discussed. The results show an increased fatigue strength, especially for the LBW-HF process, compared to current used standards for design.

Keywords: laser; laser beam welding; aluminum; beam oscillation; fatigue strength; high-frequent oscillation


Investigation of the influence of beam oscillation on the laser beam cutting process using high-speed X-ray imaging.
Jannik Lind, Jonas Wagner, Niklas Weckenmann, Rudolf Weber, Thomas Graf

Recently, it was shown that oscillating the laser beam during laser beam cutting can increase the maximum cutting feed rate compared to cutting with a static beam. In order to investigate this phenomenon, the geometry of the laser cutting front was observed by means of online high-speed X-ray imaging. Fusion cutting of 10 mm thick samples of stainless steel was recorded with a framerate of 1000 Hz. When the beam was oscillated in longitudinal direction, the maximum cutting feed rate could be increased by 24% compared to cutting with a static laser beam. In addition, the global angle of incidence on the cutting front decreases with an increasing feed rate for both cases. When comparing the global angle of incidence of the two cases at the maximum feed rate for each case, it can be seen that the angle is smaller in case of cutting with an oscillated beam. As a consequence, the absorptivity increases by approximately 20%, which explains an increase of the maximum feed rate due to beam oscillation

Keywords: laser beam cutting, cutting front, beam oscillation, online high-speed X-ray imaging, stainless steel


Fully reflective annular laser beam shaping for laser beam welding at 16kW
Matthieu Meunier, Romain Cornee, Aymeric Lucas, David Lemaitre, Pierre Vernaz-Gris, Gwenn Pallier, Eric Laurensot, Olivier Pinel

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.

Keywords: Multi-Plane Light Conversion ; Beam Shaping ; Laser Beam Welding ; multi-kW ; Focus shift


High speed videography of gap bridging with beam oscillation and wire feeding during the laser welding of stainless steel and aluminum alloys
Davide Maria Boldrin, Matteo Colopi, Simone D’Arcangelo, Leonardo Caprio, Ali Gökhan Demir, Barbara Previtali

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

Keywords: laser welding; high-speed imaging; beam oscillation; wire-feeding; gap-bridging


CFD simulations for laser oscillation welding
Pareekshith Allu

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

Keywords: laser welding, CFD, simulations, oscillation welding


Cleaving tailored edges and curved surfaces of transparent materials by ultrafast lasers through advanced beam shaping concepts
D. Flamm, J. Kleiner, M. Kaiser, F. Zimmermann, D. Grossmann, and M. Kahmann

Concepts for laser cleaving transparent materials through volume modifications and mechanical, thermal or chemical separation gained increasing recognition for a broad bandwidth of industrial use using industrial ready ultrafast lasers and application specific adapted optics. The fully controlled deterministic energy deposition into the working volume is achieved by advanced spatio-temporal beam shaping. With these concepts single-pass, full-thickness modifications with m/s-feed rates were demonstrated for plane substrates with complex inner and outer contours. Thicknesses of up to more than 10 mm at the same time with low edge roughness, low chipping and high edge stability have been achieved.
Substrates with tailored edges as known from chamfered, beveled or c-shaped edges will protect the glass article by reducing cross sections and by improving impact resistance. This enables a reduction of potential edge fractures, an increased edge stability as well as the capability of e. g. curved surfaces. The efficacy of our concepts is presented by evaluating surface and edge qualities of different separated glass structures.

Keywords: ultrafast lasers; ultrafast optics; beam shaping; transparent materials