Microstructure and properties analysis of hairpin laser welded joints for new energy vehicles flat wire motors

Taking the flat wire drive motor of new energy vehicles as the main body, the laser welding process of hairpin connecting wires in the manufacturing process of flat wire motors was studied. The manufacturing feasibility and welding quality reliability of laser welding for flat wire motor hairpins had been verified through testing methods of metallography, high-speed photography, tensile testing, hardness testing, and scanning electron microscopy. The results showed that the optimal welding process parameters were laser power of 3 000 W, welding speed of 200 mm/s, defocus distance of 0 mm, and welding trajectory ϕ2.5 mm circle with 5 repetitions. Under unprotected gas conditions, laser welding of hairpins might result in porosity inside hairpin welding joints. EDS testing showed that pores were mainly caused by oxygen elements. The metallographic results showed that the internal porosity of the joint was 0.5%, and the maximum porosity diameter was 0.1 mm. The tensile test showed that the tensile force could reach 1 414 N, far exceeding the standard requirements. The micro-hardness test results showed that under different welding heat inputs, both the weld area and heat affected area of hairpin joints softened to a certain extent, but the softening effect on the weld area was more significant.