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

Abstract

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 at the interface, and the partition coefficient of generated heat flux at the interface α. 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 α (α< 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 α at the electrode/sheet interface during the resistance spot welding process. Both parameters, R_TC and α, depend on the electrode/sheet interface structure. Consequently, R_TC and α are time dependent during the welding process. The results of measurement of temperature as well as the estimations of R_TC(t) and α (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 α 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.