Three-dimensional transient thermo-elasto-plastic modeling of gas metal arc welding using the finite element method

As an initial step to three-dimensional thermo-elasto-plastic modeling of Gas Metal Arc Welding (GMAW), a three-dimensional finite element transient heat transfer model has been developed for the autogenous Gas Tungsten Arc Welding (GTAW) process which does not require the complicated metal transfer modeling. A mathematical model to calculate arc heat input when the welding torch is inclined at an angle with the vertical is presented and verified by comparing the numerically predicted size of fusion zone and heat-affected zone with experimental measurements. Effect of varying the shielding gas flow rate was also assessed and found to be negligible.The model is extended to simulate metal transfer in GMAW and a finite element thermo-mechanical model is developed for single-pass GMAW to predict residual stresses. The problem consists of one in which the finite element mesh is growing continuously in time to accommodate the filler metal transfer. The procedure of how to incorporate the dynamic mesh growth in the analysis is described. The thermomechanical model incorporates all the thermophysical and mechanical properties of the material as functions of temperature. Convective and radiative boundary conditions including forced convection due to the shielding gas flow are incorporated. Latent heat effect is considered.Because the heat generated due to elasto-visco-plastic straining in welding is negligible in comparison to the arc heat input, the thermomechanical analysis is uncoupled into two parts. The first part performs a three-dimensional transient heat transfer analysis and computes entire thermal history of the weldment. The second part then uses results of the first part and performs a three-dimensional transient thermo-elasto-plastic analysis to compute transient and residual distortions, strains and stresses in the weld.The model is also extended to analyze heat flow in a two-pass GMAW process. Temperature history predicted by numerical model is shown to be in close agreement with direct thermocouple temperature measurements. The material chosen to illustrate the model is mild steel. Numerically predicted dimensions of the fusion zone and heat-affected zone are also in agreement with metallographically measured values. Good qualitative agreement is achieved between calculated and measured transient strains in the single-pass GMAW process.U of I OnlyETDs are only available to UIUC Users without author permissio