An analysis of the laser material interaction in the welding of steel using a cw CO laser

Abstract

A continuous CO laser has been used to study welding in 0.8 and 6.0 mm thick C/Mn steel for laser powers in the range 0.7 to 1.8 kW. Experimental data including penetration depths, weld widths, and in some cases weld pool profiles, has been obtained using both argon and helium shielding gas. The interaction of the laser light with the weld specimen is analysed here by means of an integrated keyhole and weld pool model. The laser generated plume is represented as a point heat source whose strength involves effectively the only adjustable parameter in the model. This parameter was chosen by matching the calculated weld width at the top of the specimen to its corresponding experimental value. The remaining aspects of the model involve the absorption of laser light on the keyhole wall and in the keyhole plasma. The method has been developed previously for cw CO2 laser material processing. The very restricted nature of the keyhole traps the radiation and causes the walls of the keyhole to behave like a black body. Very satisfactory agreement was obtained between the mathematical model and experiment for both penetration depths as well as weld bead shapes. In general terms cw CO and CO2 lasers appear to perform similarly in their interaction with metals except that CO lasers tend to produce smaller plumes which are easier to disrupt using the shielding gas. It was found that this could lead to interesting effects. In particular it was found that in the case of CO welding that deeper penetration was achievable using argon as the shielding gas than is possible using helium. This is because argon is a heavier gas than helium and therefore better at displacing the plume. The controllability of CO laser generated plumes could constitute a significant advantage of CO lasers over their CO2 counterparts under conditions where plume effects tend to be problem such as in the welding very thick section materials using very low weld translation speeds.A continuous CO laser has been used to study welding in 0.8 and 6.0 mm thick C/Mn steel for laser powers in the range 0.7 to 1.8 kW. Experimental data including penetration depths, weld widths, and in some cases weld pool profiles, has been obtained using both argon and helium shielding gas. The interaction of the laser light with the weld specimen is analysed here by means of an integrated keyhole and weld pool model. The laser generated plume is represented as a point heat source whose strength involves effectively the only adjustable parameter in the model. This parameter was chosen by matching the calculated weld width at the top of the specimen to its corresponding experimental value. The remaining aspects of the model involve the absorption of laser light on the keyhole wall and in the keyhole plasma. The method has been developed previously for cw CO2 laser material processing. The very restricted nature of the keyhole traps the radiation and causes the walls of the keyhole to behave like a black b...