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Process Reliable Laser Welding of Hairpin Windings for Automotive Traction Drives

Driven by current developments in the electrification of the automotive drive chain, new technologies for the production of windings for electric drives are focused in automotive industry and research institutes. Especially for the manufacturing of drives with high power density for battery electric vehicles (BEV), the application of distributed windings produced from conductors with rectangular cross-sections gains in importance. To be able to manufacture these windings, hairpin technology is pushed forward at present. The essential feature of this kind of winding is that it consists of pre-formed elements, the so called hairpins, that are assembled to the stator laminations and contacted afterwards to produce the winding. One key process within the production chain for this kind of winding is the contacting operation, because a high number of contacts needs to be realized. However, this production step poses several challenges for which in particular laser welding processes show potentials. Another complication is the fact that no established methods for the quantification of the quality of these joints are available at present. In addition, the suitability of the laser welding process for this application must be proven and error influencing variables must be identified in order to be able to advance the serial application of this process. For that reason in this paper quality criteria from the requirements contacts in electric traction drives have to face are analysed. Based on these, the achievable process capability is evaluated and the welding strategy is optimized.