Experimental study on pure copper welding with the 1.5kW blue diode laser for realization of a carbon-neutral society

Abstract

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 10mm^w×30mm^l×2mm^t 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.