Dynamic electrical resistance effects in resistance spot welding

The effects of dynamic electrical resistance subject to AC on transport variables, cooling rate and nugget shape during resistance spot welding are realistically investigated. The model accounts for electromagnetic force, heat generations and contact resistances at the faying surface and electrode-workpiece interfaces and bulk resistance in workpieces. Contact resistances are comprised of constriction and film resistances, which are functions of hardness, temperature, electrode force and surface condition. Except for the early stage of film breakdown, it is found that the influences of film resistance on the variations of dynamic resistances, contact and bulk resistances as well as transport processes are insignificant. The computed nugget thickness versus AC agrees well with available experimental data.