Electrode thermal evolution in resistance spot welding: Comprehensive fluid-structure interaction modeling

Resistance spot welding (RSW), a joining technology widely used in the automotive industry, forms a weld nugget by passing a high current (~10 kA) through a pair of electrodes that are actively water cooled. As successive welds are rapidly performed, the electrodes are exposed to intense heat flux, which can result in overheating and shorten their lifespan. Physics-based modeling of heat flow during RSW is critical to improving electrode life. However, many existing models rely on simplified treatments of electrode water cooling that limit their predictive accuracy. This study presents a comprehensive modeling framework to simulate the thermal evolution of an electrode during RSW of thin steel sheets. The methodology couples a thermo-electro-mechanical finite element (FE) model of the welding process with a fluid-structure interaction (FSI) model of the internal water cooling. Experimentally, high-speed infrared (IR) thermography is used to map the electrode's surface temperature evolution during RSW. The IR temperature profiles, together with experimental weld nugget cross-section, are used to validate the numerical model. The comprehensive model is used to evaluate how commonly used cooling simplifications such as constant film coefficient and fixed surface temperature affect the accuracy of predicted electrode temperature profiles. The framework established can be useful for the rapid assessment of next-generation electrodes with superior cooling capability.