MATHEMATICAL-MODELING OF KEY-HOLE LASER-WELDING

Laser welding is a unique way of joining materials with less thermal distortion and minimum metallurgical damage to the workpiece. The molten pool formed during welding determines the shape of the final welded region. At high laser intensities, the molten material vaporizes and a key hole is formed during the welding process. This vapor and the shape of the molten pool affect the absorption of laser at the liquid surface. The forces generated at the liquid-vapor interface due to surface tension gradient induce thermocapillary convection in the weld pool. This paper presents a mathematical model by considering these surface forces and the energy balance at the liquid-vapor and solid-liquid interfaces. The model is used to predict the surface velocity and temperature distributions, weld pool shape, key-hole depth and diameter. The velocity field is found to be large in the radial and azimuthal directions before the key hole is formed, and it changes to a radially and axially dominant field after the formation of the key hole. The results of this model are also compared with experimental data. (C) 1995 American Institute of Physics.