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The 1.5kW fiber coupled blue diode laser with a fiber core diameter of 400μm was newly developed and pure copper plates were performed bead on plate welding tests. Laser welding has been usually employed near infrared ray [IR] laser with approximately 1000nm wavelength, such as a fiber laser, a disk laser, and a diode laser. However, it is difficult to weld pure copper with the IR laser due to the low light absorption rate of copper. In the blue region, on the other hand, copper has the high light absorption rate and the fluctuation of this rate with rising temperature is small. Thus, a blue diode laser is suitable for welding copper. Pure copper plates are used in this study. The high speed and high quality copper welding is required for several industries since copper is essential for various products such as fuel cells, automotive motors, and busbars for realization of a carbon-neutral society. Although blue diode lasers have been created worldwide, the keyhole welding was difficult because of the insufficiency of laser power density. Therefore, we developed the 1.5kW high-power blue diode laser and irradiated 10mmw×30mml×2mmt pure copper plates with sweep speed of 25mm/s and spot diameter of 300μm. The melting and solidification dynamics were observed with high-speed video camera and spectrometer for elucidation of welding mechanism with the blue diode laser. As the results, one of fluctuation factors was found to be presence of neutral Cu and CuO in the laser plume, which may cause instabilities due to interference them with the laser.

Highly efficient welding of pure copper was achieved using a hybrid laser system, which combined a blue diode laser and a single-mode fiber laser. Pure copper is used as a motor coil for electric vehicles (EVs). However, the processing efficiency of laser welding for pure copper is low since it has a low light absorption rate for the wavelength of the fiber laser. In this study, a hybrid laser system, which combined coaxially with a blue diode laser and a high-power single-mode fiber laser, was developed to realize highly efficient laser welding for pure copper. The beam profile of hybrid laser was alimented to set a stair-shape beam at the processing point. To investigate the effect of the beam profile, the hybrid laser was irradiated onto a 3 × 3 × 20 mm3 copper wire for welding, and the molten volume of copper wire was evaluated. As a result, it was found that the molten volume with a blue diode laser became 1.8 times larger than that without it. Moreover, the welding efficiency of the hybrid laser was 1.45 times higher than that of the fiber laser only.

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A welding of a pure copper wire was conducted with a hybrid laser system, which combines a blue laser and an infrared (IR) laser to achieve a highly efficient and spatterless laser welding of pure copper. In the experiment, a blue-IR hybrid laser was irradiated onto a 3 × 3 × 20 mm3 pure copper wire, and the intensity of the blue laser was varied to clarify the effect of the combining of the blue diode laser. While irradiating the laser, the sample was observed by using a high-speed video camera, and the temperature of the processing point was measured by using a thermal camera. After laser irradiation, a molten volume and welding efficiency was evaluated. It was clarified that the welding efficiency of the pure copper wire increased as the intensity of the blue laser increased. At the maximum, the welding efficiency with a 6.31 × 107 W/cm2 IR laser became 1.88 times higher by combining a 9.98 × 105 W/cm2 blue laser. This finding can contribute to a further increase in the welding efficiency of pure copper wires, leading to high production efficiency in the pure copper welding process.