Melting characteristics of metals by combined laser beams with different wavelengths

Abstract

Infrared CO2 and yttritium–aluminum–garnet (YAG) lasers have great difficulty in melting metals such as pure aluminum and copper possessing high reflectivity and high thermal and electrical conductivity. On the other hand, the laser absorptance of such metals generally increases with the decrease in the wavelength, and thus the application of laser with higher power and shorter wavelength is required for welding highly conductive materials. Recently, a Q-switched second harmonic generation (SHG) YAG laser of the maximum power of 50 W, and the maximum repetition rate of 50 kHz has become commercially available. However, this laser has not as yet been employed as a welding heat source. Therefore, in this study, melting tendencies of various metallic materials were compared using a pulsed YAG laser only, a SHG YAG laser alone, and combined lasers of different wavelengths. Coaxial optical focusing system combining pulsed YAG laser and SHG YAG laser was constructed. A deep penetration of needle-like weld bead could be produced with the SHG laser itself. But it was found that the penetration depths of the weld fusion zones made with the combined beams of different wavelengths were 2–4 times deeper than those with a pulsed YAG laser only and with a SHG laser alone. The beam absorption efficiency of metals with the normal pulsed YAG laser was increased greatly by combining the output of the Q-switched SHG YAG laser.Infrared CO2 and yttritium–aluminum–garnet (YAG) lasers have great difficulty in melting metals such as pure aluminum and copper possessing high reflectivity and high thermal and electrical conductivity. On the other hand, the laser absorptance of such metals generally increases with the decrease in the wavelength, and thus the application of laser with higher power and shorter wavelength is required for welding highly conductive materials. Recently, a Q-switched second harmonic generation (SHG) YAG laser of the maximum power of 50 W, and the maximum repetition rate of 50 kHz has become commercially available. However, this laser has not as yet been employed as a welding heat source. Therefore, in this study, melting tendencies of various metallic materials were compared using a pulsed YAG laser only, a SHG YAG laser alone, and combined lasers of different wavelengths. Coaxial optical focusing system combining pulsed YAG laser and SHG YAG laser was constructed. A deep penetration of needle-like weld bead ...