Melting Characteristics of Metals by Combined Laser Beams with Different Wavelength

摘要

Infrared laser beams have large reflectivity on the metal surface and it is not easy to melt metals having high electric conductivity such as pure Aluminum and Copper by CO_2 and YAG lasers. In general the light with shorter wavelength has higher absorptivity on the metal surface. However, the photon cost of shorter wavelength laser is usually high and it is not easy to construct a high power laser that can be applied to welding. The present authors combined the high power YAG laser with basic wavelength (1,064 nm) and low power Q-switched YAG laser with second high harmonic wavelength (532 nm) by using a beam mixing optics and conducted calorimetric measurement of absorbed heat by various metals. It was confirmed that the thermal efficiency of pure copper was less than 10 % when a basic wavelength YAG laser was irradiated and no melting took place. However the heat efficiency was very much increased when the basic and second high harmonic beams were simultaneously irradiated on the copper surface and the pure copper could be melted effectively. In other metals such as aluminum alloys and stainless steel, too, the heat absorption as well as melting efficiency increased considerably when combined beams were irradiated.