Studies of High Power CO₂ Gas Laeser as a Heat Source (Report 4)

Interaction between Focused Laser Beam and Metal

Abstract

Interaction between focused CO₂ laser beam and metallic specimen was discussed based on the heat conduction theory and observation using high speed camera. The laser beam absorption characteristics under various surface conditions were analyzed from these results.
Conclusions obtained may be summerized as follows:
(1) A CO₂ laser-weldability under several hundred watts was the best in titanium, zirconium, type 304 stainless steel etc., and it was the worst in silver, copper etc. When the absorptance was enhanced sufficiently, aluminium sheet was the most suitable metal for high speed welding.
(2) When melting point of the thin surface layer coated on the base metal was higher than the metal's one, the layer can remain on the surface of metal in molten state to enhance the absorptance.
(3) The absorptance of sheet metal having higher thermal diffusivity and lower melting point can be effectively enhanced by the surface treatment but depends hardly on the kind of the surface treatment.
(4) An evaporation during laser heating was violent in the case of the specimen coated with non-metallic finepowder. The reaction of the evaporation induced an appreciable convection in the liquid metal, and affected the shape of fusion isotherm in the case of low thermal diffusivity metal such as type 304 stainless steel.
(5) Under sufficient laser power, a deep penetration is obtained as well as the case of electron beam. But when the laser was excited with ac (60Hz) electric power supply, the deep penetration may be considerably suppressed.