This PDF file contains the front matter associated with SPIE Proceedings Volume 11994, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

In the present paper we present advances on BrightLine Weld technology addressing following three topics: A) the novel implementation of beam shaping of CW high power laser in the visible wavelength range. Due to the higher absorption in this wavelength range, applications related to welding of copper, copper alloys and gold profit from this modality. We demonstrate thereby the increase of process window in welding of copper with a 3kW laser power at wavelength of 515nm, B) the combination of BrightLine Weld with multi-spot technology for welding of casted aluminum parts. With the presented strategy gas-tight welding of the aluminum alloys for parts like casted power electronics housings, heat exchangers and extrusion profiles is enabled. C) advantages that arise by dynamically changing the split-ratio of the laser power between core and ring during the welding process while utilizing the full available power of the laser. Thereby dynamic beam shaping reduces the process time and increases the quality at the same time. We demonstrate how a fast process like welding of copper hairpin with an NIR high-power laser benefits from this modality.

We report on a new generation of laser scanners and their utilization with a 24 kW CW laser at BPP 4 mm*mrad equipped with BrightLine Weld beam shaping functionality. Herewith, excellent weld seam quality, large welding depth, high welding speed and a large working distance are achieved. Those advantages are demonstrated with application results involving keyhole welding of copper.

At high feed rates, the laser beam welding process is very efficient and stable, resulting in a high weld seam quality. However, at a certain feed rate, the weld seam begins to suffer from undercuts, and, when further increasing the feed rate in addition humping occurs. It is known that the increase of the feed rate leads to an elongation of the capillary opposite to the feed direction. This has a significant influence on the melt flow and therefore on the formation of undercuts and humps. In the present work, the geometry of the capillary was studied as a function of the feed rate by means of X-Ray imaging during welding. It was found that if a critical feed rate was exceeded, the capillary geometry switched from a U-shape to a wedge-shape. The wedge-shaped capillary was found to be directly related to the occurrence of undercuts. It was also found that the critical feed rate for the formation of a wedge-shaped capillary increases with the reduction of the laser beam diameter. Furthermore, a possibility to shift the critical feed rate to higher feed rates by the means of beam shaping is shown.

In recent years, Laser Powder Bed Fusion (L-PBF) has become an industrially established manufacturing technique due to the possibility to manufacture highly complex parts without additional tools. State-of-the-art L-PBF machines use single-mode fiber lasers in combination galvanometer scanners due to their broad availability, high dynamic capability and excellent focusability. To increase system productivity the manufacturing task is parallelized by the utilization of multiple laser-scanner-systems leading to increased machine costs. Alternative approaches for the scaling of L-PBF productivity such as beam shaping and variable laser beam diameters for the use of higher laser powers (PL < 400 W) are hardly used in L-PBF machines. In consequence the high peak intensities of Gaussian intensity distribution with d_s = 50 – 100 μm of state-of-the-art L-PBF machines limit the usable laser powers due to the risk of part defects resulting from keyhole formation. Hence, non-Gaussian intensity distribution such as ring-mode laser beams as well as laser beam diameter variation exhibit great potential for high-power L-PBF systems. As part of the Digital Photonic Production (DPP) Research Campus funded by the BMBF L-PBF machine setups with a switchable ring-mode fiber laser and a defocused Gaussian laser intensity distribution were developed, validated and compared for the processing nickel-base alloy 625. By implementation of these approaches build-up rates up to 150% higher than those of conventional L-PBF machines were achieved while maintaining relative densities above 99.9%.

It becomes clearer and clearer that there is more than a gradual transition in automotive industry, especially when it comes to the future propulsion systems. Whether we talk about e-mobility or hydrogen drive, laser and photonics industry take the chance to transform manufacturing processes, convince decision makes on the undoubted advantages of photonic tools in the relevant production chains. As most of the applications e.g., in e-mobility start from scratch one can directly use the most profitable manufacturing tools. There is no need to transform an already existing process from the “pre laser age” into modern times. This paper reviews some of the applications in battery production from the perspective of a supplier of sensor technology and processing tools, without claim of completeness. The focus will concentrate on laser welding as here process monitoring and control plays an important role, laser marking, drilling, surface processing will not be part of the deliberations. This contribution to the Photonics West '22 LASE conference describes the intersection between photonics and demands when it comes to efficient production tools for tomorrow’s mobility. Further intersections with respect to Industry 4.0 and artificial intelligence haven’t even been mentioned, but here we easily find more examples which underscore the uniqueness of the laser in the context of e-mobility.

The global demand for air travel and air transport is expected to increase again in the next couple of years and so the environmental protection will also increasingly come into focus again. In the aviation sector, this means not only saving fuel and reducing emissions but also reducing the noise pollution caused by aircrafts. A typical method for noise reduction is the use of acoustic liners for sound insulation. Among different designs, acoustic liners can consist of sandwich panels, with one perforated, micro-drilled skin layer, a honeycomb structure and a closed rear layer. Wherever the operating conditions allow, the skin layers are made of carbon fiber reinforced plastics (CFRP), due to weight reasons. Compared to conventional drilling methods for CFRP, laser drilling offers unique benefits such as significantly smaller achievable bore diameters, wear free cutting and flexibility in bore diameter. However, for a large-scale application of laser micro drilling, the process efficiency must be increased and a process control is necessary to avoid damage due to excessive heat input. In this investigation, a process control method based on thermography is presented and evaluated. The control mechanism uses the temperature course in the drilling area to decide whether the process can be terminated in order to avoid time losses and unnecessary heat input. This method was found to be very reliable, however, the synchronization between temperature recording and laser irradiation and the data interpretation need further improvement.

Thermal lensing is a well-known but undesired effect in high power laser optics for welding, 3D-printing and other technologies. Stability and performance of laser processing depend on the possibility to control and minimize the thermo-optical effects induced by non-uniform (gradient) heating due to absorption of laser energy in optical elements: paraxial focus shift and thermally induced aberration, which lead to a change in size and intensity profile of the focal spot. Analysis of primary physical effects: geometrical deformation of optical surfaces and the material transformation into a gradient refractive medium, allows the quantitative estimation of the wavefront beam distortion leading to focus shift and aberration. It also allows formulating an optimal relationship between the physical properties of optical materials to reduce the change in the wavefront through mutual compensation of thermo-optical effects induced by the thermal expansion and the refractive index change – athermalization condition. Athermal optics exhibit minimized thermal focus shift and aberration even when absorbing laser energy in the bulk material and coatings, by contamination or scratches. Considering physical characteristics the Temperature Coefficient of the Optical Pathlength and ThermoOptical Ratio allows determining the optimal materials for optics: athermal crystalline Quartz and specialty glasses, Sapphire with high thermal conductivity. Weak birefringence of Quartz and Sapphire doesn’t prevent their successive use in laser optics. The comparison of the theoretical analysis and experimental validation results of optics made of Fused Silica, N-BK7, crystalline Quartz and Sapphire confirm the theoretical method for reducing the thermal focus shift and effectiveness of the suggested approach.

The development of laser driven plasma accelerators with high average power in solids requires simple and robust autofocus systems to determine, with accuracy, the focal position with respect to a rapidly refreshing target. Trial-and-error processes used in single shot experiment are not useful in this scenario. In this work we present a passive pre-alignment procedure to calibrate an autofocus setup, for fast refreshing solid target system, based on an astigmatic optical system. The calibration technique uses a hard aperture and a photodetector, located at the target position, to find the focal point with an experimental error, standard deviation, of less than 5 μm, which represents our translation stage resolution, achieved for a Rayleigh length of 35 μm. A geometrical analysis and numerical simulation have been done to demonstrate the effectiveness of the calibration technique and the accuracy of the astigmatic autofocus system. System accuracy can be improved with a better resolution of the translation stage.

The generation of a low surface roughness of the cut edge during laser beam cutting is a challenge, especially when cutting thick metal sheets. The striations, which determine the surface roughness are caused by the local melt flow inside the cutting kerf. The melt flow and the geometry of the cutting kerf was analysed with a high-speed X-ray imaging system that recorded the fusion cutting process. A local bulge of the cutting kerf is present in case of interrupted striations on the surface of the cut edge. The occurrence of a bulge coincides with a melt flow, which has a significant flow direction against the cutting direction. The absorbed irradiance and temperature on the cutting front present a maximum at the cutting depth where the bulge is localized. In case of regular striations on the surface of the cut edge, no bulge is visible. Furthermore, the values of the absorbed irradiance and the temperature are almost constant over the cutting depth and the maximum values are lower compared to a cut edge surface with interrupted striations.

The increasing pixel density in displays demand a high quality in the production of Fine Metal Masks (FMMs). The production process of FMMs boils down to structuring tiny holes in thin metal sheets or foils. The manufacturing requirements of FMMs are high precision in terms of the hole geometry in order to let enough light escape from each diode and high productivity to produce the required amount. To achieve both objectives, high power Ultra Short Pulse (USP) lasers can be utilized. Since USP lasers fall short of the productivity requirements, they are combined with multi-beam scanners. During production, the multi-beam scanners deposit a lot of heat in the metal foil which can ultimately yield temperature-induced distortions. In order to understand and finally avoid such distortions, a process simulation is sought. In a preceding study, the structuring of a single hole (the micro-scale) has been investigated, but due to the large differences in the time and spatial scales involved, it is not feasible to simulate the production of a whole part (the macro-scale). Within this treatise, a multiscale approach is described, taken into account the necessary information from the micro-scale to describe temperature-induced distortions on the macro-scale. First, a Representative Volume Element (RVE) is generated from the results of the micro-scale model. Then, this RVE is utilized in the thermo-elastic structural mechanics simulation on the macro-scale. The multiscale model is validated numerically against a hole-resolved computation which shows good agreement. Naturally, the simulation is highly dependent on the micro-scale model which in turn depends on the material properties. In order to handle material changes well, an experimental calibration has to be performed. This calibration is not part of this treatise, but will be described in a future publication. Besides the calibration process, the validation against experiments is still to be conducted in future research. Additionally, the authors envision the automation of the whole process resulting in a first-time-right approach for the development of FMMs. Last but not least, the procedure might be extended to the requirements of other filtration purposes.

In the aviation industry, carbon fiber reinforced plastics (CFRP) are used as a standard material. Due to the high strength-to-weight ratio, weight can be saved and the fuel consumption, for example of airplanes or cars, can be reduced. More and more thermoplastics are used as matrix materials, because they enable new production and repair processes. In order to reduce repair costs, an automated, reliable and fast process is needed. For the repair of CFRP with polyamide 6 (PA6) matrix material, a laser-based ablation process for the removal of the damaged material and a laser welding process for the refill of the scarf with a patch are being developed. The ablation of the scarf and the cutting of the patch are conducted with a high power nanosecond pulsed laser, which has a maximum power of P_L = 1500 W and emits at a wavelength of λ = 1030 nm. For the joining process, an automatically controlled heat conduction welding process is developed. Therefore, a diode laser with a maximum average power of P_L = 300 W and a wavelength of λ = 940 nm is utilized. For the analysis of the ablation and cutting process, samples were analyzed in order to determine the heat affected zone. For the evaluation of the welding process, overlap samples were welded and tested to determine the weld seam strength. In addition, cross sections were prepared and analyzed for defects. Finally, the results were correlated in order to determine a high process quality.

Process visualization is typically used to explore different phenomena involved in laser material processing. The interaction between the laser beam and the workpiece material creates different emission sources during the laser cutting process, as a result of material heating, beam reflection and scattering, which can be visualized with the appropriate hardware. The recently growing industrial interest in fiber lasers has led to contributions demonstrating the importance of the melt flow dynamics on cut quality and process performance, especially considering the effect of multiple reflections during cutting with a 1 µm wavelength. Within this work, the cutting process with a 4 kW Ytterbium fiber laser is visualized by means of different approaches and the relationship between them is investigated. Moreover, the melt flow dynamics is also observed in the trim-cut configuration to analyze the cutting front geometry with boundary conditions close to industrial processing. Eventually, the requirements for real-time process monitoring and guidelines for laser cutting visualization are formulated.

Laser Shock Peening (LSP) is an industrial mechanical surface treatment process used mainly by the aeronautical and nuclear industry. This process consists in focusing a high-energy pulsed laser (ns-range) on a metal target to create a high-pressure plasma that will lead to a deep plastic deformation of the target through the propagation of a shock wave. Compressive residual stresses (CRS) are generated in depth up to more than 1 mm (making this process much more effective than conventional Shot Peening), which then helps to enhance the fatigue life by slowing down crack propagation. Through theoretical and experimental studies, a new configuration has been developed: the Fast LSP (FLSP). Small laser spot sizes, high overlap ratios and high-frequencies laser for treatments is the core of this new configuration. The purpose of this work is to implement the FLSP from the laboratory to the industry. The THEIA (1 J, 10 ns, 200 Hz) laser system (made by Thales) was developed, and we investigated multiple conditions on Al-2024 samples. They were treated with various spot sizes (0.72 mm, 1.25 mm and 2 mm) and with 3 overlap ratios: 1000 %, 3000 % and 5000 %, and CRS were measured through X-Ray diffraction. A high-speed camera was used to measure both the renewing and the ejection of the water layer used to confine the plasma. Though challenges were faced, and a blowing system was developed to make sure that the ejected water will not interact with the following laser pulses, thus avoiding parasitic plasmas.

Laser shock peening as one kind of surface technique is used to enhance the mechanical property of metals, like aluminum alloy, stainless steel, and titanium alloy. The Ti6Al4V alloy specimens are processed with laser shock peening technology by nanosecond laser with a square laser spot. The hardness near-surface region and residual stress distribution in the top layer of Ti6Al4V alloy specimen are measured by Vickers hardness tester and hole drilling tester. The results show that the shock wave formed by laser shock peening can induce compressive residual stress in the top layer of Ti6Al4V alloy, which is beneficial for the improvement of fatigue life of Ti6Al4V alloy when it is used in aviation. The hardness of the near-surface region increases slightly in this research.

Laser transmission welding (LTW) is a known technique to join conventionally produced high volume thermoplastic parts, e.g. injected molded parts for the automotive sector. For using LTW for additively manufactured parts (usually prototypes, small series, or one-off products), this technique has to be evolved to overcome the difficulties in the part composition resulted in the additive manufacturing process itself. In comparison to the injection molding process, the additive manufacturing process leads to an inhomogeneous structure with trapped air inside the volume. Therefore, a change in the transmissivity results due to the additive manufacturing process. In this paper, a method is presented to enhance the weld seam quality of laser welded additively manufactured parts assisted by a neural network-based expert system. The designed expert system supports the user setting up the additive manufacturing process. With the results of a preliminary work, a neural network is trained to predict the transmissivity values of the transparent samples. To validate the expert system, specimen of transparent polylactide are additively manufactured with various manufacturing parameters in order to change the transmissivity. The transmissivity of the parts are measured with a spectroscope. The parameters of the additive manufacturing process are used to predict the transmissivity with the neural network and are compared to the measurements. The transparent samples are welded to black polylactide samples with different laser power in overlap configuration and shear tensile tests are performed. With these experiments, the prediction of additive manufacturing parameters with the expert system in order to use the parts for a LTW process is demonstrated.

The use of asbestos, a substance widely recognized as toxic, is banned in many countries, and the demolition of asbestos-containing buildings has increased in recent years in Japan. Conventional methods of removing asbestos-containing materials pose a risk of lung cancer and other diseases because they scatter asbestos in the air. Here, we demonstrate that a laser beam can be used to detoxify asbestos and suppress its scattering. The scattering of amorphous materials with the same composition as asbestos was observed in dust of asbestos-containing materials.

Laser drilling is one of the oldest applications in the field of laser material processing and is widely used in industry. The creation of large (~Ø500μm) and deep holes (~5mm) has only been possible by utilizing a melt-based ablation process so far, but material defects as melt layers or (delamination) cracks occur. For micro holes (~Ø100μm), ultrashort pulse (usp) lasers offer the possibility to create precise hole geometries without material defects. Despite of the superior hole quality compared to melt-based processes, no such large and deep holes have been created with usp-lasers so far because of the low average power, small ablation rates and other usp-drilling based phenomena. In this paper the development of a deep hole drilling process with a commercially available ultrafast laser beam source will be presented. The goal is to create large and deep holes by ultrashort pulse laser radiation which could only be created by a melt dominated process so far. In a first step, the principal approach to reach such high depths while maintaining a high material ablation rate is explained. Then, the boundary conditions that come along with this approach are discussed. With a prototype optical system, the feasibility of this concept is shown and some exemplary results are presented. The discussed deep drilling process allows to create precise and cylindrical holes with a diameter <200 μm up to an aspect ratio of 20 in metals without any metallurgical defects in a few minutes.

Today, parts based on fiber reinforced thermoplastics are used in many different applications in the aerospace and automotive industry. Furthermore, the number of parts made of semicrystalline polyphenylene sulfide (PPS) or polymers belonging to the polyaryletherketone (PAEK) family are increasing due to their excellent chemical and mechanical resistance. For some applications, these parts have to be joined to more complex structures. Besides mechanical fastening or adhesive bonding, laser transmission welding can be used when one of the joining members consists of a natural or glass fiber reinforced thermoplastic. The transmissivity of the joining members for the wavelength of the laser has an influence on the welding parameters. Often, diode lasers are used emitting in a wavelength range from 808nm to 980nm. At this wavelength range, PPS and PAEK have a lower transmissivity than for example at 1530nm. Therefore, a change of the used wavelength should affect the welding process. In order to determine this influence, a study was conducted comparing the welding process with diode lasers emitting at 940nm and 1530nm focusing on welding times. In these investigations, the joining members were made of glass fiber reinforced PPS and carbon fiber reinforced PPS.

We demonstrate how high-energy ultrafast laser sources can be used to efficiently drive well-known low-energy micro-machining applications such as surface structuring of opaque and transparent materials. The presented optical concept employs micro-lens arrays, thus standard components, as central beam splitting elements to generate multiple focal spots for parallel processing. Here, a simple and robust opto-mechanical concept enables to control the number of foci ranging from a few ten up to a few hundred spots. Throughput scaling and complete use of the industry-grade ultrafast laser platform is discussed by means of selected micro-machining examples.

High power DDL operating in the 445 nm region are rapidly evolving as one of the preferred laser technologies for welding, cutting, and engraving of highly reflective materials. Until recently, industrial blue laser sources have lacked the beam quality for performing remote processing of materials at the large working distances that are often preferred in many processes. In this paper we will demonstrate laser material processing results obtained with a new generation of industrial blue lasers with BPP of 1.4 mm*mrad. We will present results from remote laser processes including, conduction welding, keyhole welding, and engraving at long working distances.