Joint Quality Affected by Electrode Contact Condition During Resistance Spot Welding

The effects of electrical resistance at the workpiece-electrode contact surface or the electrode face on the joint quality, characterized by nugget shape, temperature, cooling rate, and solute concentration responsible for microstructure of the fusion zone during resistance spot welding (RSW), are systematically investigated. The model accounts for electromagnetic force, heat generation due to contact resistance at the faying surface and electrode face, and bulk resistance in the workpieces. Contact resistances composed of different features of constriction and film resistances are functions of hardness, temperature, electrode force, and surface condition. The computed results show that nugget growth and transport processes are independent of the film resistance at the electrode face. An increase in constriction resistance at the electrode face, however, decreases the onset time for nugget formation, cooling rates, and axial and radial heat transfer, and increases the electrode temperature. The workpiece is susceptible to surface melting if the parameter governing constriction resistance at the electrode face is high. Solute concentration and flow patterns affected by constriction resistance at the electrode face are also presented.