A Microprocessor-Based Control System for Resistance Spot Welding Process

Due to the large number of interrelated variables associated with the process, weld quality of the resistance spot welding is extremely operation-dependent and thus requires on-line monitoring and control of appropriate process variables that can reflect weld quality. One of such variables is instantaneous resistance variation curve during the weld formation. In this paper the dynamic resistance variation is monitored and utilized for a microprocessor-based welding process control. The control objective is to track a desired resistance variation curve (reference dynamic resistance) during the welding process to assure uniform quality of the weld joint regardless of variation of welding conditions. For this purpose a current controller is designed to generate the welding control current, and two types of control algorithms are implemented and tested through a microcomputer: (1) proportional control (P) (2) proportional plus integral control (PI). Tracking performance of these controllers is evaluated through a series of experiments conducted under various welding conditions.