A Statistical Analysis of Expulsion Limits in Resistance Spot Welding

Abstract

Expulsion is an important phenomenon in resistance spot welding. It involves loss of metal from the liquid nugget, which often results in the reduction of weld strength. Various models have been proposed to understand expulsion mechanisms. In these models the occurrence of expulsion is often treated as a deterministic event, and depicted by a line (boundary) in conventional lobe diagrams. In this study, statistical analysis is employed to explore expulsion with consideration of the influence of random factors. Models are built based on experimental data, and one steel and two aluminum alloys are used as examples. Expulsion probabilities are presented as a function of electrode force, welding current, and time. Analytical models and their graphical form of expression (contours and surfaces) are created to present expulsion limits under various combinations of welding parameters. This study 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]