Mathematical Simulation of Heat Flow and Microstructure Prediction for GTAW

Abstract

The objective of this work is to establish a thermal simulation for the gas tungsten arc welding process. Two computer programs, based on the 2-D heat flow models, have been developed to analyse the welding thermal data.

The models consider the moving of heat source with a constant welding speed over the workpiece surface.

Two approaches have been adopted for the two models. One was analytical and the other was numerical. The first approach; the analytical; was a simplified model with practical descriptions of welding parameters, whereas more detailed and accurate descriptions of these parameters were incorporated in the second model. The metal was assumed to be a solid with constant properties far from the arc heat source in the analytical model.

The unsteady-state numerical thermal model based on the finite difference technique and the dependence of physical properties on temperature, has been formulated and the resulting heat conduction equation was solved. The model considers a Gaussian distribution of heat flux supplied by the arc. The release rate of latent heat of fusion was treated as an effective specific heat term over th!! temperature range from solidus to liquidus points. Radiative and convective heat losses were allowed to change over the weld plate. The heat transfer coefficient was taken as a function of plate surface temperature.

The models are capable of computing the temperature distribution through the weld plate during the welding process in the form of thermal cycles, time-temperature profiles, and isotemperature contours. The two programs have been used to determine the peak temperatures in the heat-affected zone and the weld pool. In addition, heat-affected width and weld bead half-width were estimated for different conditions.