A Comparative Study of Single-Phase AC and Medium Frequency DC Resistance Spot Welding Using Finite Element Modeling

This work deeply explored differences between single-phase AC resistance spot welding (RSW) and three phase medium frequency DC RSW systems. The main difference between the two types of RSW systems was that they used different electrical structures, which led to different energy delivery modes. The RSW operation with former type had a simple but low cost structure, while the latter type had opposite features in these two aspects. In this work, a two-dimensional (2D) finite element (FE) model, which combined characteristics of thermal, electrical, and mechanical fields, was established, and then three modes of input welding currents, which were DC input mode, standard sinusoidal input mode and standard single-phase AC RSW input mode, were delivered into the welding system in the FE model. The three modes of welding currents had strictly the same effective values, and effected the same welding time. By means of iterative calculations between thermal-electrical and mechanical fields, the information of temperature increasing trend, dynamic resistance and electrode displacement under the three input modes were obtained. Some important characteristics about the energy delivery and absorptions, and mechanical properties variations under different welding current input modes which cannot be accurately obtained by actual welding operations had been obtained in this work. Also, other analyses about actual data processing and applications, and mechanical variations of the facilities during the welding process were provided. The work can supple valuable references for actual welding applications.