Effect of Gap between Steel Sheet and Electrode on Resistance Spot Welding

Abstract

If resistance spot welding (RSW) is conducted when there is a gap between a steel sheet and an unmovable electrode, the steel sheets are bended by a movable electrode, and the quality of RSW is influenced. Therefore, it is necessary to understand the effect of the gap on RSW. In this study, two high-tensile strength steel sheets were welded with the gap. In addition, cross-section observations and cross tension tests were conducted to verify the effect of the gap on weldability and joint strength. Consequently, two notable results were obtained. First, the observation indicated that deformation around the corona-bond was varied depending on the gap. Second, the cross tension tests showed that the gap decreased the joint strength even though the nugget was large enough. These result indicated that controlling the gap is important to ensure the quality of RSW.

Evaluation of corona bond strength of resistance spot welding

“…(4) Cross tension test (JISZ 3137, ISO/DIS 14272: 1994) was conducted. (5) The corona bond strength (unit: MPa) was derived by dividing the CTS by the corona bond area measured from a fracture surface.…”

“…However, only few studies have evaluated the strength of a corona bond [4]. As an example of evaluating the influence of corona bond on joint strength, Matsui et al [5] carried out a spot welded joint without a corona bond part by creating a gap between the steel sheet and the electrode and conducted a cross tensile test. The result shows that the cross tension strength (CTS) of the joint without corona bond part is inferior to that of the joint with corona bond.…”

Effect of galvannealed coating on corona bond strength of resistance spot welding

“…Additionally, Matsui et al [6] fabricated an RSW joint without a corona bond using DP590 steel by forming a gap between the steel sheet and the electrode during RSW, and they conducted a cross tensile test. The cross tensile strength (CTS) of the RSW joint without the corona bond was lower than that of a joint with the corona bond.…”