Real Time Monitoring Weld Quality of Resistance Spot Welding for Stainless Steel

Resistance spot welding (RSW) is one of the most widely used processes in sheet metal fabrication. Although used in mass production for several decades, RSW has a major problem of inconsistent quality from weld to weld, which results from both the complexity of basic process as well as from various process conditions, noise and errors. There have been a number of investigations on monitoring and controlling the resistance spot welding of low carbon steel by using dynamic resistance, but those for stainless steel are limited because the dynamic resistance has descent property. Dynamic resistance curve in spot welding for low carbon steel has a typical shape: the resistance drops sharply at the beginning, and then rises; before the current is terminated, the resistance starts to drop, which results in a peak. Unlike low carbon steel, dynamic resistance for stainless steel decreases rapidly at the beginning and then decreases at a reducing rate. The objective of this research is to explore the effects of various process conditions in spot welded stainless steel on quality by using dynamic resistance. The process conditions studied in this research are chosen to be the most often observed in production, such as variations of welding parameters, edge weld, small weld spacing, poor fitup and axial misalignment. A series of experiments will be conducted to research how process conditions affect the dynamic resistance. The results show that dynamic resistance responds well to the variations of process conditions and can serve as an important indicator of weld quality.