The transient temperature distribution in the gas tungsten arc (GTA) welding process was analysed by employing a three-dimensional finite element model. In the formulation, the solution domain which moves with the welding heat source was introduced to minimize the number of elements, and consequently the computation time of the three-dimensional program. Since the moving solution domain is small compared with the real weld structure, there are two kinds of boundaries, namely, solid metal-atmosphere boundary and solid metalsolid metal boundary. The heat loss through the solid metal-solid metal boundary was considered through a conduction heat flow and the heat flow through the solid metal-atmosphere boundary through a convection heat flow. As the solution domain moves with the progress of welding, new boundary conditions and new elements were generated in front of the heat source, while some elements disappeared in the rear of it. The initial temperature distribution of the new elements was determined by considering the continuous temperature gradient. To verify the numerical analysis, GTA welding experiments were performed on a medium-carbon steel and the isothermal lines examined. The transient isothermal lines of fusion and heat affected zone boundaries obtained numerically and experimentally were in good agreement. Thus, with the small moving solution domain the change of the fusion zone shape in long welds can be easily analysed, so that, for example, the transient melting characteristics at the start of welding in automatic welding can be effectively simulated for the process optimization.
Exact Solution of Heat Transport Equation for a Heterogeneous Geothermal Reservoir
