Experimental analysis on pure copper weld with high intensity blue diode laser by in-situ high speed x-ray imaging

Recently along with the advancement of EV shift in the automobile industry and the advancement of lithium ion batteries accompanying the advancement of mobile devices, expectations for laser welding of pure copper are increasing. In the laser welding, although a fiber laser, disk laser and direct diode laser with the wavelength of near infrared ray (IR) are generally, employed, it is difficult for pure copper to weld because of its low light absorption rate to copper. Thus, we have developed a high brightness blue diode laser system with absorption rate about 6 times that of IR laser, and demonstrated for it possible to form a weld bead of pure copper. The intensity of 1.3 × 106 W/cm2 on the substrate was easily obtained at the output power of 100 W and the laser spot diameter of 100 μm. In this study, the copper micro bead formation was investigated with respect to the height, penetration depth and contact angle to the substrate by in situ high speed x ray imaging in order to analysis the fusion bonding. As the results, it was found that the bead thickness was depended on the contact angle to the substrate while the laser irradiation. The interfaces between a pure copper and substrate were joined well without cracks or pores.