Measurement of contact parameters at electrode/sheet interface during resistance spot welding process

The numerical simulation of the resistance spot welding process requires a precise understanding of the thermal conditions at the electrode/sheet interface. This necessitates a knowledge of the thermal contact resistance R-TC which prevails tit the interface, and the partition coefficient of generated heat flux at the intetface alpha. This coefficient draws its significance from the non-conservative character of the generated heat flux in the disturbed zone of the contact. Consequently, on the macroscopic scale, only a fraction alpha (alpha<1) of the heat flux generated at the interface contributes to the temperature change at the electrode/sheet interface. The present work reports an experimental study relating to the simultaneous estimation of R-TC and a at the electrode/sheet interface during the resistance spot welding process. Both parameters, R-TC and alpha, depend on the electrode/sheet interface structure. Consequently, R-TC and alpha are time dependent during the welding process. The results of measurement of temperature as well as the estimations of R-TC(t) and alpha(t) show that the developed experimental methodology is reproducible and reliable. The analysis of the results of the estimations allowed the interpretation of the evolution of R-TC and alpha during the weld cycle as functions of current intensity and electrode force. Although the estimations are based on a one-dimensional heat transfer assumption, the results are in agreement with the physical phenomena that prevail at the electrode/sheet interface.