Study of safety operation of AC resistance spot welding system

This study deals with the safety operation of AC resistance spot welding (RSW) system. The input of the RSW system is the firing angle of the silicon-controlled rectifier (SCR) during each control cycle. Wrongly choosing a firing angle may induce disastrous consequence. The range of firing angle depends on the system´s power factor angle; the relation between the firing angle, power factor angle and conduction angle is highly non-linear. After comparing three methods, a simple mathematical model is proposed in this study to facilitate the online calculation of the power factor angle and selection of the proper firing angle, so that the safety operation of RSW system can be guaranteed. In this condition, the RSW machine can work at the machine´s the most capacity, the calculated value of power factor angle should be the lowest limit for actual selected firing angle of SCR. Finally, experimental results confirmed the effectiveness of the proposed mathematical model.