Predication of steady-state thermal characteristics of a resistance spot welding transformer in battery manufacturing application

This article introduces a novel finite-element-method-based model designed to analyze the electromagnetic-thermal dynamics of resistance spot welding (RSW) transformers used in battery manufacturing. The RSW process, inherently multiphysics and sensitive to temperature fluctuations, involves phase changes within the metal materials. This complexity, combined with frequent electrode connections and disconnections during welding (variable structure), renders traditional steady-state analysis methods inadequate for accurately capturing temperature and electromagnetic parameters under thermal steady-state conditions, and the effect of changing power electronics parameters (frequency, number of cycles, and firing angle) on continuous operation is also unpredictable. The article proposes a method capable of determining temperature trends during electrode opening (rest period). It simplifies the temperature characteristics and material properties of the welding spot. These variations are equated and simplified as a constant temperature and an equivalent material, respectively. The proposed model, rooted in finite-element analysis and experimentally validated, enables a bidirectional electromagnetic-thermal simulation through steady-state thermal analysis. This simulation generates results for temperature and electromagnetic values during steady-state operation, demonstrating close agreement with experimental results. Consequently, the developed model showcases its capability in predicting the impacts and sensitivities of various factors, such as voltage cycle number, firing angle, and rest period duration within the RSW process.