Comparative analysis between multi-pulse and constant welding current for resistance spot welding process

In this work, a new welding current mode, which was three-pulse and step increment welding current, was introduced to improve the mechanical performance of DP590 welded joints during resistance spot welding (RSW) process, which is a commonly employed and predominant metal joining process in vehicle manufacturing. To compare the welds obtained from RSW operations using conventional constant welding current and three-pulse and step increment welding current, actual experiments were conducted. Through lap-shear strength tests and metallurgical observation, it can be proved that the welds obtained from the new welding mode had a relatively larger strength, and the strength improvement percentages were from 0.95 to 35.68% for 6 arrays of experiments. In addition, a thermal-electrical–mechanical coupled numerical model with the same conditions as actual experiments was established to analyze the RSW process, and the accuracy and reliability of the model were verified by two key process signals. Through the comparison of temperature fields under two modes of welding current, the three-pulse and step increment welding current could generate higher temperature and obtain larger nugget size than that using constant welding current, and the improvement percentages were respectively 13.55, 11.01, 4.05 and 6.44% for 4 arrays of experiments which can obtain measurable nuggets, and the improvements coincided with previous lap-shear strength experimental and analysis results. In addition, the effect of cooling time between pulse welding currents on the RSW process was numerically and experimentally explored. The work is supposed to serve the welding schedule optimization and benefit to RSW-related areas in future.