Effect of Forge-Time on Electrode Indentation, Thermal and Residual Stress Fields in Resistance Spot Weld Joints of AISI 1008 Steel Sheets

Resistance spot welding is extensively used in automotive, aerospace, electronics and nuclear industries owing to its ease of automation and economy. However, the stability of a welded structure depends on the joint strength, which in turn depends on the nugget size and residual stresses across the nugget. In the present simulations-based study, the effect of forge (hold) time on electrode displacement, sheet metal deformation and residual stresses is being explored and discussed. 2D axisymmetric fully coupled phenomena model is developed in COMSOL software by considering the elastoplasticity of sheet metals and temperature dependent properties of sheet and electrode materials. Contact conductance model for resistances to the transport phenomena across the interfaces and apparent heat capacity model for phase change (melting and solidification) effects are used. For the selected process parameters (load, current and time), a close agreement is found between the predicted and measured nugget diameter. Also, it is found that increasing the forge time has lowered the residual stresses below the yield stress and a transition from tensile to compressive stresses in the heat-affected zone. Further, the coupled model predicted the minimum forge (hold) time required for an electrode indentation on the sheets, which signifies the nugget zone.