Predictions of metal droplet formation in arc welding

A two-dimensional time-dependent model has been developed for the prediction of droplet formation in gas metal arc welding. The model is a unified treatment of the arc, the welding wire, taken as the anode, and the workpiece, taken as a plane cathode. Predictions are made of the formation and shape of the welding droplets as a function of time, accounting for effects of surface tension, gravity, inertia and magnetic pinch forces. The wire feed rate and gas flow rates are also incorporated into the model. Calculations are made of current densities, electric potentials, temperatures, pressures and velocities in two dimensions both in the arc and also within the molten drop and solid electrodes. For an arc in argon with a mild steel wire of 1.6 mm diameter and a current of 325 A or more, we predict the formation of small drops of diameter 1.2 mm or less and large drop frequencies consistent with the spray transfer mode observed in welding. At currents of less than 275 A, we predict large drop sizes of about 3.8 mm in diameter or more, consistent with the globular transfer mode in welding. At a current of 300 A, in a transition zone between the two modes, we predict the presence of both small and large drops.