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 are 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 o n the weld pool properties. The information required to simulate the f low in the weld pool including the heat flux to the workpiece, the inp ut current density and the gas shear stress, was derived from the are model. By individually examining the various driving forces in the wel d pool, it is found that the buoyancy and electromagnetic forces do no t play major roles in determining the flow pattern in the weld pool fo r a 200 A are. Instead, the relative magnitude of the gas shear stress and the surface tension and also the sign of the surface tension dete rmine the flow pattern in the weld pool. The electrode tip angle which alters the gas shear stress and especially the heat flux to the workp iece can produce a significant change in the overall shape and size of the weld pool. With a very sharp tungsten electrode, the heat-flux di stribution 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 workpi ece. The overall result of these two effects is a wider and shallower weld pool.