Pulsed laser welding of laminated electrical steels

Stator core is one of the parts in the magnetic circuit, which playing an important role in the performance of the electric machine. Commonly the non-oriented electrical steel laminations are assembled into a stator stack by welding to meet the demand of strength at high-speed rotation. However, the effects of residual stress, microstructure change and inter-conduction among laminations introduced during welding process result in a great deterioration in magnetic properties of stator core. The pulsed laser welding of ultra-thin electrical steel laminations is adopted to decrease the iron loss while ensuring sufficient strength simultaneously. As two important indicators of the stator core, peak load after welding determines the maximum load torque and iron loss affects the energy conversion efficiency. There is currently no model that can accurately predict peak load and iron loss of the stator core after pulsed laser welding, and the influence of peak power and duty cycle on peak load and iron loss also needs to be further studied. In this paper, the peak load of stator core is studied based on the tensile test of a novel rectangular specimen which has the same stress state with the ring ones subjected to torsional load. An empirical model of peak load is proposed by the two-step fitting method considering the effect of peak power and duty cycle. Then an analytical model of iron loss of welded laminations is developed considering eddy current circuit in weld seam caused by damage of insulation coating. All peak load and iron loss models with small relative errors can obtain accurate prediction results. Finally, the weld lobe for pulsed laser welding is drawn, whose left and right boundaries are determined by peak load and iron loss, respectively. By selecting the appropriate process parameters, iron loss of the stator core using pulsed laser welding decreases, compared with traditional continuous laser welding.