COMPUTER-SIMULATION OF RESISTANCE SPOT-WELDING IN ALUMINUM .2.

A computer-based model has been used to investigate nugget formation in the resistance spot welding of aluminum. As shown in a previous paper, contact resistance at the faying surface is a critical factor in spot welding aluminum. The effect of contact resistance in the presence of a shunt resistance is investigated in the present paper. With contact resistance distributed homogeneously over the area of physical contact at the faying surface, there is an optimum value of contact resistance for efficient nugget formation, depending on the value of the shunt resistance. On the other hand, if contact resistance is not homogeneously distributed over the physical contact area, localized conduction can lead to nugget formation even with high overall contact resistance. In the latter case, a minimum contact resistance is required for efficient nugget formation. Because it incorporates mechanical, as well as thermal/electrical analysis, the computer model is also capable of predicting conditions for the expulsion of weld metal at the faying surface. An example is given of the effect of applied force, acting through domed electrodes, on the conditions for expulsion. A comparison between experimental measurements of nugget growth and an equivalent computer simulation is given.