Initial Strength Joining of Flat Conductor-Based Shaped Coils for Optimised Laser Welding Preparation in Hairpin Technology

The rising electromobility represents a solution to stronger regulations and increasing environmental awareness, but also brings its own set of obstacles [1]. In order to meet increasing demand, innovative electric motor topologies have been developed, with hairpin stator technology in particular [2]. While this technology promises high potential on both the product and process side, there are still challenges that need to be addressed. Currently high scrap rates are largely attributable to laser welding. As a decisive quality-determining process step, laser welding is thus considered as a quality gate in the process chain as it represents a highly sensitive and strongly interacting process. Furthermore, the main cause of scrap in hairpin welding is often ascribed to direct and indirect weld preparation. More specifically, to the geometric alignment and clamping of the joint. Traditionally used clamping devices for this process represent a compromise between positioning accuracy and process integrity. The use of fixtureless processes, the so-called initial strength joining, promises to be a remedy. Here, an active decoupling of laser welding from the upstream processes is established. In the context of this paper, the clamping and alignment methods currently used in hairpin production are analysed. Subsequently, existing fixtureless joining techniques are collected and additionally novel approaches are developed. Here, joining techniques with the functional methods of forming, additional elements and functional integration are considered, described and evaluated with regard to their potential and functionality. Concluding, the integration capability of the developed approaches into the existing process chain is examined.