This paper presents a comparative study of the AC and MFDC resistance spot welding process. Both experiments and finite element simulation were conducted to compare the weld size and energy consumption. The experiments were performed on two identical spot welding machines, one with a single phase ac and the other with a mid-frequency DC weld control. The machines were instrumented such that both the primary and secondary voltage and current signals could be collected for energy calculation. The finite element simulation model was developed to understand the underlying mechanisms of the difference between the ac and MFDC processes. The effect of the current waveform was investigated by using the actual process measurements as an input to the simulation model. It is shown that the MFDC process generally produces larger welds than the AC process with the same root-mean-square welding current. However, this difference is more prominent when the welding current is relatively low. Overall, the AC welding process consumes more energy to make a same sized weld than the MFDC process. The larger the welding current is used, the less efficient the AC welding process will become. The differences between the two welding processes are caused by the contact resistance behavior and the electrical inductance in the AC welding process.
Resistance spot welding is widely used for joining sheet metal materials in the automotive industry. Most of the existing resistance spot welding systems are single-phase AC-based, and with constant current control. The medium frequency DC (MFDC) system with constant heat control (CHC) is new technology in the resistance spot welding industry. This system promises dramatic improvement on the spot weld quality. However, many of the CHC features are still not known and need to be explored. This paper presents an experimental study on a new MFDC/CHC spot welding system. The goal is to characterize the MFDC/CHC welding process in terms of the process parameters, including the target energy level, force, and welding time. Real time process signals such as force, current, and tip voltage were also collected and analyzed to compare with the traditional spot welding process.
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