Melting Characteristics of Various Metals with Combined Lasers of Different Wavelengths
Jonghyun MOON, Masami MIZUTANI, Seiji KATAYAMA, Akira MATSUNAWA
Infrared CO2 and YAG lasers have great difficulty in melting metals such as pure aluminum and copper possessing high reflectivity and high thermal conductivity. On the other hand, the laser absorption of such metals generally increases with a decrease in the wavelength, and thus the development of a laser of higher power and shorter wavelength is promising. Recently, Q-switched SHG (Second Harmonic Generation) YAG laser of the maximum power of 50 W, the wavelength of 532 nm and the maximum repetition rate of 50 kHz has been developed; however, this laser has never been employed as a welding heat source. In this study, therefore, coaxially focusing optical system, in which a pulsed YAG laser beam was combined with a Q-switched SHG laser beam, was designed and constructed to evaluate melting characteristics of various metals with respective laser beams and especially the effect of the combined SHG laser. A deep penetration type of a needle-like weld bead could be produced with the SHG laser alone. It was also found that the penetration of the weld fusion zones produced with the combined laser beams of different wavelengths was 2 to 4 times deeper than that with pulsed YAG laser only. The absorption efficiency of pulsed YAG laser in a metal was confirmed to greatly increase by the combination of the Q-switched SHG YAG laser. The increases in penetration and beam absorption were attributed to the effect of keyholes produced by the high peak power density of Q-switched SHG laser.