Remote laser welding of copper x-pins and busbar-to-pin joint for traction system of electric vehicles

Abstract

The rapid transition towards electric vehicles has intensified the demand of high-performance electric motors characterised by high power density and thermal management. Stator winding and busbars are critical of electric motors for efficient electro-mechanical energy conversion. To minimise winding losses and developing torque dense motors; conventional round copper wires are replaced by rectangular pins, which offers high fill factor and improved heat dissipation. While the transition from I-pin (double side welds) configuration to hairpin (single side weld) is well-established, the emerging X-pin winding topology offers further advantages of material saving and reducing the stator stacked height. Additionally, establishing robust connection between busbar plate with copper pins is essential for efficient distribution of current throughout the stator winding.

This thesis investigates the application of novel remote laser welding to study the effect of different angular configuration (30°, 45° and 60°) of X-pin on morphology and mechanical strength of weld joint, with total energy input and number of scans serving as monitored parameters. The study indicates that increasing the X-pin angle necessitates a higher energy input which results in increased fusion area and joint strength, however these attributes involve a trade-off with increased cycle time and a larger radial size of X-pin. Secondly, this thesis work also investigated the effect on busbar-to-pin weld joint at different vertical positions ( -1, 0, +1 and +2 mm) of pin with respect to busbar plate at constant welding parameters. The cross-section analysis and mechanical evaluation demonstrate an upward trend in effective joint area and tensile load by ascending the pin above the surface of busbar plate.