THE UNSTEADY DEVELOPMENT OF A GTA WELD POOL

The governing equations for momentum, energy and electric transport are solved numerically to obtain the unsteady development of an axially symmetric gas tungsten arc weld pool. The effects of Marangoni, Lorentz and buoyancy forces are included. The finite difference method is used to solve the equations and the grid is made to adapt to the shape of the melt front and to move with the front as melting occurs. In general, convection is found to decrease the energy losses from the weld pool by evaporation. This increases the size of the weld pool. Convection has a large effect on the depth of the weld pool but only a small effect on the width. The Lorentz force causes fluid motions which increase the depth of the weld pool. The effects of the Marangoni force depend on the sign of the surface tension temperature coefficient, gamma(T). A negative value for gamma(T) causes fluid motions which suppress the effects of the Lorentz force and result in a fairly shallow weld pool. A positive value for gamma(T) causes fluid motions which enhance the effects of the Lorentz force and result in a very deep weld pool.