Evaluation of heat transfer within numerical models of resistance spot welding using high-speed thermography

The automotive industry is demanding more sophisticated resistance spot welding (RSW) models with an emphasis on integrated computational materials engineering (ICME) to better design welded structures. RSW process models are often validated using experimental weld nugget diameter measurements that verify the maximum temperature prediction but not the entire transient temperature response. The accuracy of temperature data on-cooling is essential to reduce error in integrated process-material models during the simulation of microstructural evolution. In this study, two existing 3D finite element (FE) models of RSW (general-purpose and RSW-dedicated) that were previously optimized for 1.5 mm thick Usibor (R) 1500 steel are conventionally validated using experimental nugget diameter and electrode indentation measurements and then modified to represent half-section RSW. The half-section RSW simulation results are directly compared to experimental temperature data captured using high-speed thermography (HST). Analysis of HST showed that the thermal history and t(8/5) predicted by RSW-dedicated model were more consistent with the HST data, but the generalpurpose model more accurately predicted half-section RSW nugget diameter by 8 % and electrode indentation by 11 % as a function of welding current. The models' material properties, specifically workpiece thermal conductivity and specific heat as a function of temperature, had a significant effect on the RSW model temperature fields on-cooling. Overall, HST of half-section RSW provided a quantitative comparison of experimental and simulated temperature results and was a viable technique to validate the thermal history outputted by RSW FE models.