Numerical Simulation of Molten Droplet Shape and Electromagnetic Pinch Effect in Short-Circuit CO₂ Welding

Abstract

In short-circuit CO₂ arc welding, the transfer behavior, process stability and weld quality are strongly affected by the molten droplet shape just before short-circuit and the electromagnetic pinch action on the liquid bridge during short-circuit phase. By using Static Force Balance Model, the effects of electromagnetic force, surface tension and gravity on the molten droplet shape during arc phase are simulated, the electromagnetic force being the dominant factor. To obtain a appropriate molten droplet shape in favor of arc stability and metal transfer, it is preferable to adopt a certain large pulse current in arc prophase and a small arc-keeping current in arc anaphase The numerical analysis to the effects of electromagnetic pinch action on the liquid bridge during short-circuit phase shows that a large current at initial stage will block the molten droplet from well spreading into the weld pool, but a large pulse current at metaphase will facilitate the formation of a neck in the liquid bridge. The simulation results are validated experimentally in waveform-controlled short-circuit CO₂ arc welding, the welding process being improved to be much stable and gentle