Predictions of metal droplet formation in gas metal arc welding. II.

Predictions of metal droplet formation in gas metal arc welding (GMAW) are made for mild steel wires with argon as a shielding gas, using a generalized theory for predictions of arc and electrode properties in arc welding. The theory is a unified treatment of the arc and the electrodes and includes a detailed analysis of the anode sheath region, together with a free surface treatment for the molten metal at the tip of the welding wire. Results of calculations made for a mild steel wire of 0.12 and 0.16 cm diameters are in good agreement with experimental measurements of droplet diameter and droplet detachment frequency at currents between 150 and 330 A. The results indicate that the anode sheath region and the effects due to variation of surface tension with temperature have an important influence on the dynamics of droplet growth at the tip of the wire in GMAW. Predictions are made for the transition from the globular to the spray mode of metal transfer, in agreement with experimental observations in arc welding. (C) 1998 American Institute of Physics. [S0021-8979(98)04919-6].