Simulation of nonuniform heating induced by alternating-current rail flash butt welding at the end face

Nonuniform temperature field upsetting is prone to oxide inclusions, and the temperature field of rail flash butt welding (FBW) is primarily formed because of the Joule heat generated by the end-face current. The current distribution at the end face largely determines the heat distribution; thus, the current distribution and heat production at the end face of an alternating-current (AC) FBW must be investigated. This study combined finite element simulation and experimental validation to establish an AC rail FBW electric–magnetic–thermal coupling model to explore the influence of current parameters, end-face temperature, and feed mode on the distribution of the end-face current. The results show that a reduction in the welding current, current frequency, and time in low- and medium-temperature stages can improve the uniformity of the temperature field. The electrode clamping method determines the shape of the temperature field, whereas the proposed hybrid clamping method is the most conducive to uniform heat generation at the end face. Moreover, electrode clamping at 210 mm near the end face yielded uniform temperature fields. The experimental validation results were consistent with the calculated results, indicating that the proposed model is reasonable and reliable. In practical welding operations, it is advisable to optimize current and frequency to achieve an end face temperature > 1000 °C swiftly. This study provides a direction for enhancing the uniformity of the temperature field and improving the expulsion capability of impurities during the upsetting process, thereby optimizing the flash butt welding process for rails.