A statistical analysis of expulsion limits in resistance spot welding

Expulsion is an important phenomenon in resistance spot welding. It involve s loss of metal from the liquid nugget, which often results in the reductio n of weld strength. Various models have been proposed to understand expulsi on mechanisms. In these models the occurrence of expulsion is often treated as a deterministic event, and depicted by a line (boundary) in conventiona l lobe diagrams. In this study, statistical analysis is employed to explore expulsion with consideration of the influence of random factors. Models ar e built based on experimental data, and one steel and two aluminum alloys a re used as examples. Expulsion probabilities are presented as a function of electrode force, welding current, and time. Analytical models and their gr aphical form of expression (contours and surfaces) are created to present e xpulsion limits under various combinations of welding parameters. This stud y provides not only quantitative model predictions on expulsion limits for the materials studied, but also a generic statistical methodology that can be used for analyzing expulsion in various material systems. [S1087-1357(00 )00602-X].