EFFECT OF STATIC LASER BEAM SHAPING ON LATERAL AND VERTICAL GAP BRIDGING FOR WELDING OF RECTANGULAR COPPER HAIRPIN WINDINGS

In the race towards net-zero transportation, research in electric motor manufacturing is of significant value. Although rectangular hairpin winding provides higher power density for the stator compared to round wire, critical joining challenges need to be addressed. Motivated by the inevitable hairpin-to-hairpin gaps caused by misalignments and part tolerances, this paper investigates the impact of laser beam shaping on gap bridging for Cu-ETP hairpins during laser welding process. Two welding setups were investigated, core-only laser beam (100% core power, 0% ring power) and ring-dominant laser beam (40% core power, 60% ring power). The solidification behaviour of the molten pool was studied via high-speed camera to elucidate the impact of laser beam shaping on gap bridging and the stability of the keyhole and molten pool. Findings indicated that welding with a ring-dominant laser beam results in a more stable process, reduces fluctuations of the keyhole opening, widens the molten pool, and, ultimately, helps to bridge lateral gaps up to 1 mm (50% of the hairpin thickness) and vertical gaps up to 4 mm (200% of the hairpin thickness). The significance of the results is underpinned by the robustness of the selected ring-dominant laser beam which allows to bridge lateral and vertical gaps without changing welding parameters (i.e., number of laser passes). This eliminates the need for expensive adaptive control systems. The same level of robustness could not be achieved with a core-only laser beam.