Comparative study of small scale and ‘large scale’ resistance spot welding

An incrementally coupled electrical–thermal–mechanical model is developed to simulate small scale resistance spot welding (SSRSW) using the finite element method. This numerical model is then employed to study the differences between SSRSW and ‘large scale’ resistance spot welding (LSRSW). The variations in contact area, current distribution, and temperature profile at the workpiece/workpiece interfaces are compared. The computation shows that the difference in electrode force could be the essential reason for other differences between SSRSW and LSRSW. Compared with LSRSW, a much lower electrode force (pressure) applied in SSRSW results in a relatively small contact area and hence a much higher current density, which in turn leads to a greater heating rate and higher temperature at the workpiece/workpiece interface. This small contact area also results in a relatively small nugget diameter in SSRSW, which is only about 30% of the electrode tip diameter. In contrast, the nugget diameter in LSRSW is comparable to the electrode tip diameter. The predicted nugget diameters in both SSRSW and LSRSW of mild steel sheets compare well with experimental results.