Laser-induced plasma control in CO2 laser welding

摘要

Abstract: A series of technological parameters in controlling plasma in deep penetration CO$-2$/ laser welding at an arrange of power level from 1 kW to 5 kW were investigated by using a precise declined-blow system by which the gas-assisting pressure and nozzle position can be precisely adjusted for various gas species and laser power levels. The mechanism of plasma-control by assist gas was also clarified on the basis of pressure measurement of assist gas, estimation of metallic vapor pressure in the cavity, and monitoring of plasma brightness by using phototransistors. It was found that the effect of assist gas on penetration depth can be divided three regions with the change of the assist gas pressure. No matter what gas species were used, only is the gas pressure slightly higher than the vapor pressure, plasma can be suppressed by forcing the vapor to flow away from the incidental laser beam along the cavity rear wall, then optimum weld beads can be obtained.!6