Analysis of the Behaviour of the Winding Head of a Hairpin Stator

Abstract

Electric mobility offers significant potential in the reduction of harmful emissions and is increasingly establishing itself on the market. Despite the long-established existence of electric motors, their use in automotive applications poses major challenges for manufacturers. The so-called hairpin technology, a winding technique with rectangular solid conductors, is increasingly replacing established round wire winding techniques in automotive stator production. The process step of welding can be identified as a quality gate of the entire process chain. The commonly used laser welding in combination with the material properties of the copper hairpins results in a sensitive process step that requires precise welding preparation. To improve the quality of existing clamping procedures or facilitate the development and design of new innovative clamping techniques, a detailed analysis of the forces occurring in a winding head is created. The forces required for aligning the contacting surfaces during welding preparation are calculated based on the geometric deviations of the hairpin ends. This could enable the accurate dimensioning of clamping operations or even an adaptive process in the welding preparation. Hereby, the process reliability in stator production could be sustainably improved. Within the scope of this work, the problem is first examined and geometric deviations after twisting are defined. Then the forces in the winding head are calculated by simulation and analytically and validated by practical tests. The conducted examinations are presented and analysed individually. The results obtained are compared with each other and possible limitations are investigated. Subsequently, the performance of existing clamping methods is analysed and compared with the previously calculated, occurring forces in the winding head. In summary, this work is intended to provide an overview of the forces occurring in a winding head. By means of the procedures determined in the context of this work, an approximated calculation of the forces to be expected in the welding preparation and welding fixture are made possible.