Effect of Gap on AHSS RSW Weldability

When a gap exists in a resistance spot welded (RSW) joint, the lack of intimate contact between the members at the faying interface can have a significant influence on sheet steel spot weldability, especially for advanced high strength steels. Several test joints simulating gap conditions observed in typical auto body structures have been designed for study of the effect of gap magnitude on the resistance spot weldability of such AHSS as DP980, DP780 and DP600. Tests show that an existing gap reduces the confinement of the molten zone during the welding process, increasing the probability of expulsion and therefore decreasing the current range. Increasing the electrode force helps reduce the gap influence and broadens the current range. Employing a longer weld time also has a beneficial effect when used in combination with an appropriate electrode force. Based on the results of this study, no significant influence of gap on tension shear and cross tension strengths (TSS and CTS) was observed for the joint configurations and materials evaluated.