Abstract
Resistance spot welding is one of the most commonly used processes for joining-metal the automotive, and electronics industry. When joining a car body, the method of welding dissimilar three sheets, including high strength steel is frequently used. Studies on the dissimilar welding of high strength steel and low carbon steel are being conducted in an attempt to improve the weldability. However, the dissimilar welding of TWIP steel with other steel grades is extremely challenging due to the high resistivity of the base metal. Therefore, further studies are required to improve the weldability of three sheets including the low carbon steel. In general, the resistance spot welding process is conducted in the field by the constant current control method. In this study, the constant power control method was applied in order to reduce the occurrence of expulsion and to improve the weldability of three dissimilar steel sheets consisting of SGACEN, DP steel, and TWIP steel. The constant current control was compared with constant power control, through the evaluation of weldability by using the suitable welding range lobe curve, which takes into account the tensile shear strength, and nugget diameter. Additionally, the current, voltage, resistance, and power signal were also analyzed. The constant power control prevented the occurrence of expulsion as a result of high heat not being generated at the early stage, compared to the constant current control method. Regarding the welding time being long, an increase in heat was applied so that there was a considerable improvement of weldability, compared to the constant current control.
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