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

A computer-based model has been used to investigate nugget formation i n the resistance spot welding of aluminum. As shown in a previous pape r, contact resistance at the faying surface is a critical factor in sp ot welding aluminum. The effect of contact resistance in the presence of a shunt resistance is investigated in the present paper. With conta ct resistance distributed homogeneously over the area of physical cont act at the faying surface, there is an optimum value of contact resist ance for efficient nugget formation, depending on the value of the shu nt resistance. On the other hand, if contact resistance is not homogen eously distributed over the physical contact area, localized conductio n can lead to nugget formation even with high overall contact resistan ce. In the latter case, a minimum contact resistance is required for e fficient 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 s urface. An example is given of the effect of applied force, acting thr ough domed electrodes, on the conditions for expulsion. A comparison b etween experimental measurements of nugget growth and an equivalent co mputer simulation is given.