Constant current vs. constant power control in AC resistance spot welding

Constant current control (CCC) and constant power control (CPC) are two of the most popular control strategies employed in resistance spot welding (RSW). They have their individual respective advantages; for example, with CCC, it is easy to control energy delivery, while CPC can deliver more heat in particular situations. CPC can be accomplished by means of CCC. The performance of CPC is not as good as that of CCC, because CPC involves more interfering elements. Dynamic resistance is employed to analyze the welding process. Corresponding analysis shows a more reliable welding process can be obtained and the first melting point can be detected earlier when CCC is employed rather than CPC. Though the overall nugget growth trends may show a very small difference when using one strategy versus the other, CCC can provide a larger nugget size because the initial energy allotment is more reasonable and the energy delivery is much steadier. We conducted experiments to validate all of the theoretical analysis. This work can serve to inform actual welding production to obtain a more reliable welding process, enable welders to choose a proper control strategy and help improve energy efficiency in practice.