Energy absorption by metal-vapor-dominated plasma during carbon dioxide laser welding of steels

Abstract

During laser welding, the plasma plume affects the amount of energy reaching the weld surface and the composition and properties of the welds. Light emissions during welding were recorded by emission spectroscopy to understand the energy absorption and the nature of the plasma formed during welding of various grades of steels. The flow of gases and the concentrations of the various metal vapors were computed by solving the Navier Stokes equation and the equations of conservation of various species. The variables studied were shielding gas composition and flow rate and the base metal composition. Until now, self-absorption of emissions arising from species present at high concentrations within the plasma has kept researchers limited to either analyzing ideal situations that are unrelated to the welding process or not accounting for the attenuation of the emissions. It is demonstrated that during welding, the peaks in the emission spectra that are affected by the self-absorption process can be eliminated on the basis of the initial and the terminal energy levels for electronic transitions. By selectively eliminating the affected transitions and by using the numerically computed local concentrations of metal vapors, the absorption of the laser beam energy by the plasma can be accurately determined.