InvestIgatIon of WeldIng forces and torque MeasureMent usIng octagonal rIng dynaMoMeter In refIll frIctIon stIr spot WeldIng of pure copper

The welding forces and torque in refill friction stir spot welding (RFSSW) play a crucial role in optimizing welding process parameters, understanding material deformation and flow mechanisms, improving welding equipment, and analyzing tool wear. To measure the welding forces and torque during pure copper RFSSW, an octagonal ring dynamometer (ORD) was designed and manufactured based on ring deformation theory. A measurement system for welding forces and torque was established, and the ORD was calibrated and validated. Welding experiments were conducted under different process parameters to measure the welding forces and torque during pure copper RFSSW. The variation patterns of welding forces and torque throughout the welding process were analyzed, and the relationships between welding parameters and the peak welding forces and torque were established. The results show that the calibration errors for axial force, torque, and lateral force were 0.97%, 3.78%, and 1.56%, respectively, with cross-sensitivity errors below 5%. The primary welding force during the RFSSW was the axial force, with a peak value more than 10 times that of the lateral force. The clamping, plunging, and refilling stages were the key phases where both welding forces and torque increased significantly. The maximum welding forces occurred near the second dwell stage before the end of welding, while the maximum torque was observed during the plunging stage. Axial force was most influenced by plunge depth, torque was mainly affected by rotational speed, and lateral force was strongly impacted by the combined effects of plunge depth and rotational speed. The average prediction errors for the axial force, torque, and lateral force models were 0.61%, 2.25%, and 1.20%, respectively, with a maximum error of 4.67%. These findings are instrumental in optimizing process parameters to achieve higher weld quality. The study has practical implications for industrial applications, particularly in manufacturing electrical connectors and thin-sheet heat exchangers, where high-quality copper welds are essential. This work also provides a foundation for future research into enhancing the efficiency and reducing the energy consumption of the RFSSW process. © 2025. The Author(s).