Heat generation and transfer in micro resistance spot welding of enameled wire to pad

The single-sided micro resistance spot welding (MRSW) of enameled copper wire to pad is widely applied in electronics manufacturing. The welding quality is significantly influenced by the process of heat generation and transfer which are gradually changing and quite uncertain in production. This work is to investigate the thermal process variation under the common influence factors of electrode wear and thermal contact conductance (TCC). Multi signals such as dynamic resistance and electrode temperature were detected to analyze the welding process. A finite element model of electrical-thermal-mechanical coupling was established to simulate the heat generation and transfer in MRSW. The coupled model was validated by comparing the simulated results of temperature and voltage with the experimental measurement. The results show that the electrode wear in single-sided MRSW of enameled wire to pad causes an increase in the resistance and temperature of electrode tip rather than decrease, and it requires reducing the welding parameters instead of increasing. In case of electrode wear, maintaining a consistent temperature rise of electrode tip helps to ensure welding quality. Due to the insulation coating of enameled wire, the normal TCC between electrode tip and workpieces significantly changes in the MRSW process and rapidly rises after the decomposition of insulation coating. TCC needs to be controlled within a reasonable range to prevent insufficient or excessive heat transfer in production.