ANALYSIS: E-MOBILITY


“This process combines high quality with increased productivity – and at


significantly lower costs”


Cross-section of a copper hairpin welded in a vacuum hairpin


copper welding with infrared lasers requires high laser powers for deep welding, LaVa welding can even achieve welding depths >1mm per 1,000W due to the increase in process efficiency. For example, copper sheets with a thickness of 6mm can be welded with a power of approximately 6kW with free


root formation and without pores. At the same time, the weld scaling is very fine and also free of ejections and adherent spatter. According to current studies, the maximum welding depth that can be achieved with 12kW beam power on ETP copper is up to 11mm. The following application


examples show the advantages of laser beam welding in a vacuum when joining components for electromobility: Copper busbars for battery


packs: To manufacture lithium- ion battery packs, the individual cells are welded with so-called cell connectors, also known as busbars. When joining individual lithium-ion batteries, care must be taken to ensure the integrity of the battery cells is not compromised and the battery bodies are not heated to more than 80°C. When laser welding in a vacuum (with pressure of 20mbar) with a 2kW single-mode fibre laser, Cu-ETP busbars can already be welded almost pore-free, with a power of only 1kW at a welding speed of 50mm/s. Bipolar plates for fuel


Cross-section of an aluminium weld performed in a vacuum on a 5mm thick busbar with 1,800W laser power


cells: In addition to lithium- ion batteries, fuel cells are considered a key technology


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in the energy transition, with tens of millions expected to be produced annually. Therefore, high demands are placed on the cost-effectiveness of the welding process. When using conventional, single-mode fibre lasers, however, humping occurs from a welding speed of approximately 700mm/s. The quality of the weld seam becomes insufficient due to this effect. LaVa welding has the advantage over conventional laser beam welding – the energy required for welding can be reduced by up to 60 per cent. This enables practically distortion-free welding, which is a major advantage, especially with the 80μm thick stainless steel foils usually used for bipolar plates. The defined atmosphere also enables oxide-free welding, as well as targeted influence on the melt by varying the composition of the shielding gas composition. With LaVa welding, a welding speed of 900mm/s can be achieved with a beam power of only 150W. A rough vacuum of approximately 100mbar enables rapid evacuation within approximately 10s. The use of a pressure stage system also allows a continuous flow


of components, so that the bipolar plates can be welded ‘on the fly’. Evacuation as a non- productive time is therefore completely eliminated. Copper hairpins for electric motors: In stators in electric motors, the ends of the individual conductors are welded as so-called hairpins. However, conventional laser beam welding of Cu-ETP hairpins with an insulating coating produces many pores and spatters. For Cu-ETP hairpins, LaVa welding has the significant advantage that the energy required for the laser beam can be reduced by up to 50 per cent. By reducing the evaporation temperature, the temperature of the melt pool decreases, which leads to a stabilisation and thus to a significant reduction of spatter. Furthermore, the formation of pores is reduced, since outgassing from the melt is facilitated in a vacuum. For example, LaVa welding can be performed with a 2kW single- mode fibre laser at a pressure of 20mbar – with an evacuation time of just three seconds. In addition to all the qualitative features, the reduction in energy consumption in particular also plays an important role in the LaVa welding process. In addition to the cost reduction and the increased quality, this is another important plus point for laser welding in a vacuum – and can secure a competitive advantage in the long term. l


Dr Christian Otten is CEO at LaVa-X


SUMMER 2022 LASER SYSTEMS EUROPE 21


LaVa-X


LaVa-X


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