Numerical Thermal Model of Resistance Spot Welding in Aluminum

Abstract

A three-dimensional thermal model for resistance spot welding in aluminum is presented. The numerical model, validated with experimental findings, considered phase change and the associated weld pool convection. A parametric study was performed to determine the influence of welding features such as welding current, faying surface (workpiece contact surface) electrical contact resistance, and electrode-workpiece (E/W) thermal contact conductance. These parameters have significant effects on the nugget and heat-affected-zone geometry. The phase change morphology, including melting and solidification rates and weld pool dynamics, was also significantly influenced by the parameters studied. The strongest convection was observed at the center of the molten pool in a vertical plane, aligned with gravity. Although two prominent convection cells developed, the phase change morphology was not significantly affected by convection due to the short welding time (less than 0.1 s) and low fluid velocity (smaller than 0.01 mm/s). The nugget grew nonlinearly with increasing current and faying surface electrical contact resistance, whereas it diminished with increasing E/W thermal contact conductance. The influence of electrical contact resistance at the faying surface on nugget size was less pronounced than that of the other parameters. The length of time that the weld pool existed was directly proportional to current and indirectly proportional to E/W thermal contact conductance.