Modern battery and e-drive production requires the material bonding of copper enabling highest power densities to be transmitted and functional integration to be increased. Laser beam welding has become an established manufacturing technique in this sector in recent years due to its flexibility and reproducibility. Near infrared laser beam sources are often used for the copper welding applications, as these are broadly available and proven equipment from car body manufacturing. However, they reach their limits when processing highly reflective surfaces, as the low absorptivity of copper in this wavelength range can lead to unstable incoupling or back reflection issues. The use of visible laser radiation, which is available with brilliant beam quality and kW output power at 515 nm, is an appropriate strategy to overcome these challenges. Recent studies reported on altered energy coupling and changed defect formation. However, the question of a targeted application of a green or near infrared laser system in copper welding is rarely addressed in comparative analyses in literature. In this work, an experimental comparison was performed using two disk lasers of 515 nm and 1030 nm wavelength with similar spot characteristics in order to investigate this topic from the perspective of both seam properties and efficiency. Experimental investigations are combined with analytical models, to reveal benefits of each wavelength in copper welding for a wide range of processing parameters. The results underscore the effectiveness of green laser radiation for heat conduction welding and small capillary aspect ratios. Additionally, observed wavelength-related differences in the seam properties affect the efficiency metrics.

The rapid development of laser beam sources and adapted welding technologies in recent years lead to an increased use of laser welding techniques in automated production nowadays. Especially its precision and local energy input are key features for joining applications in electric vehicle components, where joints have to meet both mechanical and electrical requirements as current-carrying connections. However, the copper materials used are difficult to weld due to their physical properties, making a stable process with fewest seam imperfections only feasible within a limited process window. Recently available beam sources emitting visible laser radiation have proven to overcome the low absorptivity at process start, but spattering is still a prone defect significantly affecting process efficiency and quality. Literature approaches for modifying the energy input point to laser beam shaping as a method for reducing process imperfections, which, however, has not been extensively researched in copper processing using green laser radiation. Thus, this study investigates the influence of a shaped intensity profile for visible laser radiation created with a reflective diffractive optical element in laser beam welding with laser powers up to 3 kW. A characterization of the process dynamics is performed by use of high-speed imaging, and metallographic analysis is used to elaborate benefits of the applied beam shapes. With beam shaping, an enlarged heat conduction welding regime and an advantageous seam shape are found. Furthermore, a decrease in spatter formation during deep penetration welding is detected for the elliptical beam profile, which correlates with an oscillation movement of the capillary.

One of the fundamental effects of laser material processing is laser beam absorption. The absorptivity in the laser welding process is subjected to temporal and spatial fluctuations due to temperature and phase changes and is furthermore dependent on the wavelength used. Currently, experimental absorptivity data for copper at high temperatures is rarely available, and discussions of investigation are largely based on theoretical assumptions. However, this property is essential for a fundamental understanding of the phenomena involved in laser-matter interaction and for efficient process design, especially for the emerging manufacturing processes for electric vehicles, where copper materials are widely used. In this work, a specially designed, low-cost experimental arrangement was built to measure the laser absorption during the process in different welding modes, which enables the derivation of coupling efficiency values in these regimes. Brilliant laser beam sources with lambda = 515 nm and lambda = 1030 nm radiation and comparable spot characteristics on the workpiece were used for the investigation. Results captured with microsecond resolution show several important features, including the points of melting and vapor capillary formation for both pulsed and continuous process guiding. General tendencies known from literature could be confirmed by our measurements, and the comparison of the absorptivity data with microscopic inspection and a weld seam crosssectional analysis shows a significant correlation of the characteristics.

Laser beam welding of metals has progressed dramatically over the last years mainly arising from joining applications in the field of electromobility. Allowing the flexible, automated manufacturing of mechanically, electrically, and thermally stressed components, the process is more frequently applied for joining highly reflective materials, for example for battery tab and busbar connections. The local, non-contact energy input favors this welding technology; however, joining of copper and aluminum sheets still poses a challenge due to the physical properties of the joining partners and intermetallic phases from dissimilar metal interaction, which reduce seam performance. The use of green laser radiation compared to infrared laser radiation offers the advantage of a significantly increased absorptivity for copper materials. A changed incoupling behavior is observed, and a lower deep penetration threshold has been already proven for 515 nm wavelength. When copper and aluminum are welded with the former as top sheet, this welding mode is essential to overcome limited aspect ratios from heat conduction welding. However, the opportunities of applying these beam sources in combination with spatial power modulation to influence the interconnection area of copper-aluminum joints have not yet been studied. The aim of this work is therefore to investigate the seam properties and process stability of different overlap welding strategies using green laser radiation for dissimilar metal welding. A microstructural analysis of the different fusion zones and mechanical strength of the joints are presented. In addition, the experimental parameter sets were analyzed regarding their application in battery module busbars by examining the electrical resistance and temperature distribution after welding. A parameter window was identified for all investigated welding strategies, with the stitched seam achieving the most stable results.

Laser welding of copper is being used with increasing demand for contacting applications in electric components such as batteries, power electronics, and electric drives. With its local, non-contact energy input and high automation capability enabling reproducible weld quality, this joining technology represents a key enabler of future mobility systems. However, a major challenge in process design is the combination of energy efficiency and precise process guidance in terms of weld seam depth and defect prevention (i.e., spatter and melt ejections) due to the high electrical and thermal conductivity of copper. High-power lasers in the near infrared wavelength range (𝜆 ≈ 1 μm) and excellent beam quality provide an established joining solution for this purpose; nevertheless, the low absorptivity (≤5%) advocates novel beam sources at visible wavelengths due to altered absorptivity (40% at 515 nm) characteristics as an improved tool. In order to understand the influence of laser wavelength and process parameters on the vapor capillary geometry, in situ synchrotron investigations on Cu-ETP with 515 nm and 1030 nm laser sources with the same spot diameter are compared. The material phase contrast analysis was successfully used to distinguish keyhole and melt pool phase boundaries during the welding process. A significantly different sensitivity of the keyhole depth in relation to the feed rate was found, which is increased for the infrared laser. This behavior could be attributed to the increased effect of multiple reflections at 1030 nm.

The increasing demand for contacting applications in electric components such as batteries, power electronics and electric drives is boosting the use of laser-based copper processing. Laser beam welding is a key for an efficient and high-quality electric vehicle production due to its local, non-contact energy input and high automation capability enabling reproducible weld quality. Nevertheless, a major challenge in process design is the combination of energy-efficiency and precise process guidance with regard to weld seam depth and defect prevention (i.e. spatter, melt ejections), partly caused by the high thermal conductivity of copper. High power lasers in the near infrared range and emerging visible laser beam sources with excellent beam quality can provide a suitable joining solution for this purpose. However, the underlying physical phenomena are currently only partly understood and a reflection on the challenges of laser beam welding of copper compared to well researched steel processing has not yet been carried out. In order to improve the understanding of the effect of the different material properties and the influence of process parameters on the vapor capillary and melt pool geometry in laser beam welding, in situ synchrotron investigations on Cu-ETP and S235 using 515 and 1030 nm laser sources were conducted. The material phase contrast analysis was successfully used to distinguish vapor capillary and melt pool phase boundaries during the welding process with high spatial and temporal resolution up to 5 kHz. A significantly different vapor capillary geometry and sensitivity to parameter variation were found between the steel and copper material. In addition, the visualization of characteristic melt flows revealed different melt pool dynamics and a pronounced eddy close to the melt pool surface for copper, which is assumed to be causal for the observation of pronounced spatter formation during copper welding in a certain process window.

Laser beam welding is being more frequently employed to join copper materials. The use of green laser radiation shows the advantage of significantly higher absorptivity for these metals compared to near-infrared radiation. Therefore, a change in process stability and defect formation is expected. In addition, the effect of modifying the intensity distribution on the formation of weld seam defects and the geometric properties of the seam in deep penetration mode is largely unexplored. Thus, the aim of this work is the characterization of process dynamics and defect formation in correlation to the focal position and the intensity distribution by means of high-speed imaging and metallographic analysis. A significant reduction of seam imperfections is observed for a gaussian beam profile compared to a Top Hat intensity distribution. An advantageous seam shape and the earlier onset of the deep penetration welding process are favorable reasons for the application of this intensity distribution, while medium to high processing speeds further improve the processing quality.

Duplex stainless steels (DSS) combine excellent corrosion resistance with outstanding mechanical properties. Typical applications can be found in chemical, gas and offshore industries, where corresponding components usually feature a high degree of customization. This makes additive manufacturing an economically interesting production approach. However, a major challenge in additive manufacturing of DSS is a precise process control to achieve the required material properties. In this work, DED-LB\M was used to process DSS 2205. A multistage experimental procedure was developed to generate nearly fully dense cuboidal specimens (relative density > 99.9 %). In addition, the complex interaction mechanisms between process parameters and resulting material properties such as microstructure and hardness were investigated. For specific process conditions, the desired ferrite-austenite balance of DSS could be obtained. Furthermore, the hardness was found to decrease with increasing build height and correlates with grain size as well as the slightly decreasing ferrite content.

The demand for semiconductors and microelectronic components is greater than ever and will continuously rise in the future due to increasing automation and digitalization. Also, there is a growing need for robust, high-temperature resistant electrical connections which are essential for the circuit function. Previous investigations have shown that laser-based droplet brazing can create high temperature stable joints e.g. on thin silver layers, without applying an external force on the micro-component to be joined. In order to expand the application field of this process, further combinations of different brazing and substrate materials are investigated. In this paper the influence of additionally induced thermal energy at the diffusion zone was analyzed via shear tests. The studies show, that using brazing alloy CuSn11 in combination with a substrate heating provides the most robust joints on the tested substrate material.

With the increasing demand for copper connections in the field of renewable energies, e.g., for electric vehicle applications, various approaches were pursued to reduce the challenging spatter and melt ejection susceptibility in laser beam welding of copper materials. One is the use of adjustable intensity profiles of multi-mode beam sources with a combination of a core and ring beam in order to affect a modification of the flow field in the melt pool surrounding the highly dynamic keyhole in the deep penetration welding process. This should favor a reduction of spattering and melt pool ejections, especially at low weld speeds and high penetration depths in pure copper, therefore enabling a more stable deep penetration welding process. In this work, the influence of different superimposed intensity distribution ratios for green laser radiation with summarized power up to 3 kW on the generation of process imperfections was investigated conducting welding experiments on Cu-ETP using high-speed imaging for enhanced process understanding. In addition, the effects of different power distribution conditions and welding speeds on the seam dimensions were analyzed. It was found that a significant amount of laser power in the ring beam leads to a widening of the melt pool in the area near the sample top-surface, which effectively reduces spatter behavior. The associated change in process zone morphology in laser beam direction was furthermore observed via sandwich analysis, allowing a detailed view into the laser–matter interaction area through a borosilicate glass sheet clamped in front of a processed sample. This setup was found to be a cost-effective method for obtaining further information about the keyhole formation mechanism and melt dynamics under comparative boundary conditions.

With its excellent automation capability and localized energy input enabling precise, reproducible welds, laser beam welding represents a preferred industrial joining technology. Electro-mobility drastically increases the need for defect-free and automatable copper joining technologies. However, copper welds that are produced with state-of-the-art infrared lasers often suffer from spattering and porosity. Recent publications show distinct improvements using novel beam sources at visible wavelengths, attributing them to increased absorptivity. Nevertheless, this cannot fully explain the steadier process behavior. This wavelength-dependent process stability has not yet been investigated sufficiently. Therefore, we have developed a predictive material-dependent criterion indicating process stability based on the example of copper heat-conduction spot welding. For this purpose, we combined energy balances with thermo-physical material properties, taking into account the wavelength and temperature dependence of the optical properties. This paper presents the key mechanism that we identified as decisive for process stability. The criterion revealed that X-points (unique, material-specific wavelengths) represent critical stability indicators. Our calculations agree very well with experimental results on copper, steel and aluminum using two different wavelengths and demonstrate the decisive, material-dependent wavelength impact on process stability. This knowledge will help guide manufacturers and users to choose and develop beam sources that are tailored to the material being processed.

Joining of copper materials has become a key factor in laser material processing of electric components like electric engines, batteries, or power electronics. A paramount challenge is the design of the laser welding process, which has to fulfil the requirements of high energy efficiency and highest seam quality at the same time. By now, high-power laser beam sources emitting visible laser radiation are available to promote the well-suited noncontact joining method, which is furthermore characterized by local energy input and high automation potential. These laser sources can now face the challenges of welding highly conductive and reflective materials, such as copper, which originate mainly in the low absorption of conventionally used infrared wavelengths at room temperature and the rapid jump of absorptivity at transition from solid to liquid state. An increase in absorption of electromagnetic radiation to more than 40% for copper at room temperature for λ = 515 nm leads to increasing energy input in the material and promotes a more efficient process therefore. However, up to now, mostly the heat conduction welding regime has been examined and the effects of shorter wavelengths on deep penetration welding have not been understood in detail. A strong deviation in weld seam depth between infrared and green laser radiation is observed for identical process parameters depending on the use of additional gas supply [F. Kaufmann, A. Meier, J. Ermer, S. Roth, and M. Schmidt, “Influence of defocusing in deep penetration welding of copper by using visible wavelength,” in Proceedings of the Eleventh International WLT-Conference on Lasers in Manufacturing, Munich, 21–24 June 2021 (M. Reth, Munich, 2021)]. Consequently, radiation attenuation by the metal vapor inside and above the keyhole plays a substantial role in the case of 515 nm laser welding [M. Haubold, A. Ganser, T. Eder, and M. F. Zäh, “Laser welding of copper using a high power disc laser at green wavelength,” Procedia CIRP 74, 446–449 (2018)]. In this work, we investigate in situ measurements of plume attenuation during laser beam welding of copper with 515 and 1030 nm laser beam sources. Both laser sources are equipped with comparable optical setups to achieve identical focal diameters on the material surface. We investigate the plume characteristics in the deep penetration welding mode of copper. A range of industry-relevant process parameters are investigated to create a basis for comparison with theoretical models. It is found that a significant difference in the attenuation of both laser wavelengths occurs in the case of deep penetration welding copper specimen and blowing the vapor plume out of the beam path is recommended therefore for an efficient welding process.

Due to the tendency of miniaturization of electronic components, the increased use of thermally sensitive circuit boards e.g. LCDs, a large number of requirements arises for a selective laser beam soldering process. To enhance the possibilities of selective soldering, a system technology for quasi-simultaneous, pyrometric controlled laser soldering was qualified. The systems capability is to enable a controlled laser soldering process at different spot-sizes, varying electronic device layouts and different irradiation strategies. An inline emission measurement via pyrometer gains live-data from the soldering process, evaluates them and transfers them in a closed loop cycle to the laser power control. To enable a process control over a large scanning field, a chromatic corrected f-theta optic, which compensates the chromatic aberration between laser and pyrometer wavelength was used. Different scanning strategies and varying laser power profiles have been evaluated regarding their influence on the process quality.