J. Haidar

CSIRO Telecommunications and Industrial Physics
P O Box 218, Lindfield NSW 2070, Australia
jawad.haidar@tip.csiro.au

A two-dimensional dynamic theory for predictions of arc and electrode properties in arc welding has been used to investigate heat transfer phenomena in the droplets formed at the tip of the welding wire in Gas Metal Arc Welding (GMAW). The theory is a unified treatment of the welding wire, the plasma and the workpiece and includes a free surface treatment for the welding drops, accounting for the effects of inertia, gravity, surface tension, arc pressure, magnetic forces and viscous drag by the gas flow around the drop. Also, the theory accounts for the variation of the surface tension coefficient with temperature and includes thermal and dynamic phenomena within the solid and liquid phases of the wire, together with a detailed treatment for the electrode sheath regions. Calculations are made for arcs in argon with wires of mild steel at currents between 150 A and 325 A. Results of calculations for heat fluxes within the wire suggest that evaporation from the surface of the droplet has an important influence on the heat balance of the wire. The calculated evaporation rates are found to be much higher than measured rates of fume formation in GMAW, suggesting an important recondensation process at the surface of the workpiece. It is also found that the rate of evaporation from the droplet surface decreases slightly with increases in arc current from the globular mode to the spray mode of metal transfer.