Numerical investigation of flash formation and asymmetrical cooling in resistance projection welding

In resistance projection welding, the softened material is squeezed out from the joint area. The two workpieces being joined together often have different geometries, leading to asymmetrical cooling. The flash formation and asymmetrical cooling are not well quantified in the literature. This study developed a coupled electrical-thermal-mechanical model with adaptive remeshing and glued contact activation techniques for projection welding of steel fitting to a steel shell. The model was used to calculate the evolution of temperature distribution in the fitting and shell for welds made under two different hold times. The cooling rates were then inputted into a literature model to predict the joint hardness values, which correlated well with the experimental data. Additionally, the main factors for the accurate prediction of flash shape and size were the use of temperature-activated glued contact and high-temperature flow stress. Specifically, a combination of no glued contact and low flow stress can lead to an overprediction of the flash geometry.