Lightweight manufacturing via rotary swaging process: Validation for hollow railway motor shafts

In response to the demand for low-carbon solutions in railway electric motors, adopting a hollow design for motor rotor shafts proves to be an effective strategy. The use of rotary swaging enables the production of hollow motor shafts with complex internal structures. This study combines both simulations and experimental investigations on hot rotary swaging, and conducts trial production of a hollow shaft with actual dimensions intended for railway motors. A detailed FEM analysis of four-pass rotary swaging process was performed, examining the evolution of stress, strain, forming force, and damage. The maximum damage was 0.8, demonstrating the feasibility of the process. Validation experiments showed that the outer diameter of the formed shaft remained stable with good consistency, while the inner diameter showed a tendency to increase toward the end face along the axial direction. Microstructural observations revealed that the recrystallization fraction in the rotary-swaged region reached 72.29%. The study also analyzed the combined effects of recrystallization and work hardening on the mechanical properties. Quenching and tempering treatment increased the yield strength in the rotary-swaged region by 27.5% compared to the undeformed region, also improving plasticity. Finally, a trial production experiment successfully fabricated a hollow motor shaft with a length of 635 mm and a maximum outer diameter of Φ105mm, achieving a weight reduction of over 30%. This research demonstrates the feasibility of rotary swaging process in manufacturing hollow motor shafts and provides valuable insights for industrial applications.