Role of beam absorption in plasma during laser welding

Abstract

The relationship between beam focus position and penetration depthin CW laser welding was studied numerically and experimentally for differentwelding conditions. Calculations were performed using a transient hydrodynamicmodel that incorporates the effect of evaporation recoil pressure and theassociated melt expulsion. The simulation results are compared withmeasurements made on a series of test welds obtained using a 1650 W CO2laser. The simulations predict, and the experiments confirm, that maximumpenetration occurs with a specific location of the beam focus, with respect tothe original sample surface, and that this relationship depends on theprocessing conditions. In particular, beam absorption in the plasma has asignificant effect on the relationship between penetration and focus position.When the process parameters result in strong beam absorption in the keyholeplasma, the maximum penetration will occur when the laser focus is at or abovethe sample surface. In a case of weak absorption however, the penetrationdepth reaches its maximum value when the beam focus is located below thesample surface. In all cases, the numerical results are in good agreement withthe experimental measurements.