Abstract
Indirect resistance spot welding process with single-side electrode access was developed for the automotive applications. The variable controls of electrode force and welding current during welding were studied in order to achieve the promotion of weld nugget formation and the suppression of expulsion without sacrificing the productivity and design flexibility of automobiles. The welding experiments were performed on lapped test coupons of 0.7mm thick cold-rolled sheet with tensile strength of 270N/mm2 and 1.6mm thick cold-rolled sheet with tensile strength of 980N/mm2 using a resistance spot welding system consisting of a servo-motor controlled welding gun and an inverter DC power supply. Welding experiments verified that the occurrence of expulsion and formation of molten nugget were significantly influenced by the heat generation and melting process at an initial period during welding and manageable by applying the variable patterns of electrode force and welding current. When the welding was performed under the large shunting condition simply with the constant force and current pattern of 400N in electrode force, the appropriate current range was less than 1kA. On the other hand, it extended to 2.6kA when performed with the variable force and current pattern of 800N in force and 4kA in current at the first stage and 400N in force at the second stage, confirming the fact that the variable pattern successfully suppressed the expulsion and promoted the nugget formation. Numerical simulations were conducted to compare the difference in welding phenomena between the constant force and current pattern and the variable force and current pattern and clarified that the effect of variable force and current pattern on the promotion of nugget formation and the suppression of expulsion.
