An analysis of the formation of metal droplets in arc welding

A dynamic two-dimensional are model has been used to investigate the effects of the various forces acting on the droplet in gas metal are welding (GMAW). The model is based on the equations of conservation of mass, energy, momentum and current, Ohm's law and a Maxwell equation. The model treats the welding wire, the plasma and the workpiece. For molten metal droplets at the tip of the welding wire, we account for effects of inertia, gravity, surface tension, magnetic force, viscous drag force and are pressure. Calculations are presented for a 1.6 mm diameter wire of mild steel for arcs in argon to determine the separate effects of these forces on droplet formation. It is found that, for arcs in pure argon at currents around the transition from the globular transfer mode to the spray transfer mode, viscous drag and are pressure effects are approximately self-cancelling. It is also found that j(z) x B forces have a much larger effect than do j(r) x B forces on the transition from globular to spray modes of metal transfer.