Development of Condition Monitoring System for Electric Resistance Spot Welding Used to Manufacture Railway Car Bodies

Abstract

Stainless steel railway car bodies are assembled by joining the outer plates and the pillar materials using resistance spot welding. In recent years, more and more car bodies are being assembled using laser welding in addition to the resistance spot welding. For this laser welding system, we developed a condition monitoring system considering the processes before and after laser welding as a single system, and obtained and put into practical use an appropriate condition that suppresses spatter generation during laser welding. On the other hand, in resistance spot welding, the current, weld time, electrode load, and electrode tip shape are the main factors that determine the welding quality. Therefore, the configuration of the equipment is less complicated than that of laser welding system, and the condition monitoring is easier than that of the laser welding. In this study, by transferring the concept of the condition monitoring system developed for laser welding to resistance spot welding, we achieved a reduction of more than 60% in terms of electricity consumption and improved the appearance of the car body by optimizing the indentation shape. In addition to this technical achievement, we also present in this paper a case study showing the opportunity for innovation by restructuring the technological paradigm of the resistance spot welding in the production of stainless steel car body shells.