Front Tracking Model of Simultaneous Melting and Solidification During Multiple Layer Deposition in GMA Welding

The authors present a new meso-scale numerical model of gas metal arc welding of steel. The heat input from the arc, and the deposition of liquid filler metal into the notch of the parent material in butt welding in multiple passes, result in a thermal cycle whereby the thermal effects of the current pass are superimposed onto those of the previous pass. This results in dynamic melting and solidification throughout the weld pool. A simplified method of mass/heat addition is employed in order to focus on the dynamic phase transformation process, which can be modelled using the authors’ Front Tracking algorithm. Melting is characterized with the advancement of the liquidus isotherm, while solidification proceeds due to the advancement of the columnar dendritic front as well as equiaxed nucleation/growth in the undercooled melt. The evolving weld pool solidifies as purely columnar, as the high thermal gradient present in the weld pool results in very low levels of undercooling ahead of the columnar front. Equiaxed growth never approaches a level where it could potentially block the advancing columnar front under the condition employed in the case study of this paper.