The Benefits of Closed-Loop Control for the Resistance Welding Process

Closed-loop resistance welding power supplies use current and voltage feedback sensors to control the energy delivered to the parts. Closed-loop technologies provide many benefits for the resistance welding process. Taking full advantage of these benefits requires a good understanding of resistance welding principles.

At the beginning of a resistance weld there is high electrical resistance at the electrode-to-part and part-to-part contact areas (Figure 1). If too much energy is applied before the electrodes have a chance to seat properly, these contact areas can overheat, resulting in expulsion, electrode sticking, and weak welds. Closed-loop power supplies allow a very precise upslope to be programmed at the beginning of the weld pulse. This upslope of current, voltage, or power helps to reduce the initial contact resistance and focus weld heat into the parts. The length of the upslope period can be programmed to suit the application. A long upslope is recommended for very hard or resistive parts.