Blue Laser Conduction Spot Welding of Pure Copper Hairpins.

Joining rectangular copper hairpins significantly improves the performance of hairpin motors. Copper welding poses a significant challenge due to its low laser absorptivity when using conventional infrared lasers. Although employing keyhole welding with a high-power and small-spot infrared laser can increase the absorption rate through multi reflections, it introduces instabilities caused by the multi-recoil forces within the keyhole and the absorptivity differences among solid, liquid, and keyhole states of copper. The proposed solution adopts a 450 nm blue laser, which exhibits a superior laser absorptivity toward copper and facilitates stable conduction mode spot welding with an enlarged laser spot. This research achieved successful blue laser conduction spot welding of copper hairpins with a gap and, for the first time, systematically analyzed the force and instability factors of a molten pool. The results demonstrated that with a laser power of 1950 W, laser spot diameter of 0.6 mm, and defocusing amount of -3 mm, only 0.7 s of welding time was required to join copper hairpins with a 0.6 mm gap. Notably, there were no noticeable defects in weld beads during blue laser welding. Meanwhile, the study identified recoil force as a significant uncertain factor inducing defects, particularly in the keyhole mode. Compared to infrared technology, the blue laser, characterized by a higher absorption rate and a larger spot diameter, effectively reduced uncertainty through conduction welding. This research showcased the significant potential for blue lasers in manufacturing copper hairpin motors. [ABSTRACT FROM AUTHOR]