The role of transient convection in the melting and solidification in arc weldpools

Abstract

A mathematical formulation has been developed to describe the transient growth and collapse of axisymmetric weldpools in spot welding operations. In the statement of the problem allowance is made for both conductive and convective heat transfer. In describing convection, the driving forces included buoyancy, electromagnetic forces, and surface tension forces. In most cases it was found that convection played a major role in affecting the weldpool shape, and that this convection was often dominated by surface tension forces. The model also allowed us to represent the transient collapse of weldpools upon the cessation of the heat and current supply. It was found that the melt velocity was reduced as the weldpool shrank. Most of the solidification took place from a circulating weldpool. By calculating both the growth rate and the relevant temperature gradients, it was possible to estimate the dendrite arm spacing which was found to be of the order of tens of microns.