Non-contact ultrasonic-assisted laser welding of copper hairpins

The hairpin joints welding poses a significant challenge in flat wire motor manufacturing. Laser spot welding test under argon protection and laser galvanometer scanning welding test under air environment were carried out in the absence of ultrasound. The results show that the joints obtained when the welding time is about 5s are better shaped and have good repeatability during the laser spot welding under argon protection. The shape of the closed welding path gives better joint formation when laser galvanometer scanning welding is used. Compared with the argon protection environment, the repeatability of the joint appearance obtained in the air environment was reduced, and the porosity defects in the weld seam increased significantly. A novel non-contact ultrasonic-assisted laser welding method for copper hairpins was introduced to improve the weld formation quality. The influence laws and mechanisms of ultrasonic process parameters on weld formation were studied. After using ultrasonic-assisted laser welding, the repeatability of weld bead formation is significantly improved, the tendency of weld bead collapse is reduced, but the joint resistance increases. The main reason for the improvement of weld appearance in ultrasonic-assisted laser welding is the compressive effect of the ultrasonic field on the molten pool, which was confirmed by high-speed photographic images. The compression effect of standing-wave points closer to the emitting end on the molten pool is more pronounced. With the increase of ultrasonic power, the weld width and the tensile-shear load resistance of the joint decreased, while the joint resistance increased.