The effect of the cathode tip angle on the gas tungsten arc welding arc and weld pool: II. The mathematical model for the weld pool

In part I, the effect of the electrode tip angle on the arc properties was investigated. In part II, a mathematical model for the weld pool is developed in order to study the effect of the electrode tip angle on the weld pool properties. The information required to simulate the flow in the weld pool including the heat flux to the workpiece, the input current density and the gas shear stress, was derived from the arc model. By individually examining the various driving forces in the weld pool, it is found that the buoyancy and electromagnetic forces do not play major roles in determining the flow pattern in the weld pool for a 200 A arc. Instead, the relative magnitude of the gas shear stress and the surface tension and also the sign of the surface tension determine the flow pattern in the weld pool. The electrode tip angle which alters the gas shear stress and especially the heat flux to the workpiece can produce a significant change in the overall shape and size of the weld pool. With a very sharp tungsten electrode, the heat-flux distribution over the weld pool tends to be flatter. In addition, there is a very strong shear stress due to gas flow at the top of the workpiece. The overall result of these two effects is a wider and shallower weld pool.