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.

A bead on plate welding test of pure copper plate was conducted with a hybrid laser which combined a high-power infrared (IR) laser and a blue laser to achieve a deep penetration and spatter-less welding of pure copper. A 1.5 kW class IR laser which has the wavelength around 1000 nm and a 1.5 kW class blue diode laser which has the wavelength of 450 nm were used as a heat source. The IR laser and the blue diode laser were irradiated perpendicular to the sample at the angles of 0° and 45°, respectively. Each laser was focused onto 2 mm thick pure copper sample and combined on the surface of it as a hybrid laser. The hybrid laser was scanned on the sample at 100 mm/s varying the output power of the IR laser and the blue diode laser. While scanning the lasers, the dynamics of melt pool formation and the spatters were observed with a high-speed video camera. After laser irradiation, the cross-section of the sample was observed and the penetration depth of the bead was measured. As the results, it was found that the penetration depth of pure copper increased and the number of spatters generated per scanning length decreased with the increase of blue laser intensity. Also, it was clarified that the melt pool dynamics affects the amount of spatter generated during welding.