Blue laser-assisted kW-class CW NIR fiber laser system for high-quality copper welding

There has been a growing demand of laser welding for copper materials to manufacture industrial products with high electrical and thermal conductivities. The high thermal conductivity characteristic generates rapid thermal diffusion at a welding spot and hence reduces the power efficiency of laser welding. To overcome this issue, we propose to combine a blue laser beam performing a high absorptivity for copper materials, with a 1070-nm high power laser beam, launched from a single mode fiber laser. The blue laser beam can be focused at the welding spot with a sufficiently narrow beam waist, and the absorption of the blue light for copper materials is much higher than that of infrared light. Therefore, the focused blue laser beam causes rapid and highly efficient heat generation at the welding spot, and this localized heat is expected to improve the quality of laser welding. To generate the high-power blue laser beam efficiently, we fabricated a high power blue LD-integrated SLP which achieves an optical output power of 11.7 W at 10.5 A. We also fabricated a blue-DDL module using multiple SLPs and a stepped structure package adopted with a water-cooling system. The blue-DDL module can output a high fiber-coupled optical power exceeding 150 W. Next, we built a blue-NIR hybrid laser equipment which exhibits the excellent quality of laser welding by accurately controlled optical output power and beam spot diameters of both blue and NIR laser beams. In this paper, we describe the design and performance of blue LD-integrated SLP and blue-DDL module. We also report how the blue-NIR hybrid laser equipment contributes to improve the quality of the laser welding.