The effect of process parameters on the morphology, mechanical strength and electrical resistance of CW laser-welded pure copper hairpins

Manufacturing of high-performance electric motors has become a key industrial goal over recent years due to increasing demand for electrification, in particular in the automotive field. The use of windings comprising pure copper conductors with a rectangular cross section allows the overall performance of electric motors to be increased. In the present work, the influence of processing parameters on weld quality for joining of copper hairpins with near-infrared laser irradiation performed with a specific welding path. After determining a feasible operating window, the effect of process parameters on fusion zone morphology, presence of pores and mechanical and electrical properties was investigated. The results showed that high power and high welding speed lead to joints characterized by less than 1 % pores. A maximum tensile load of 490 N was achieved during tensile tests performed on specimens obtained with optimized welding parameters, with fracture taking place in the heat affected zone (HAZ). Micro-hardness profiles confirmed slight softening near the HAZ, corresponding to a reduction in mechanical strength in this region. Electrical tests highlighted a correlation between mechanical properties and the electrical resistance of the connection.