Research on the deformation mechanism for current-assisted splitting spinning forming of small-module gear-shaped parts with extreme diameter-to-module ratios

Small-module gear-shaped parts (SMGSPs, module m < 1) with extreme diameter-to-module ratios ( D / m >100) are critical components in miniature precision systems for spatial transmission and lightweight structural applications. However, it exhibits restricted fatigue strength and excessive material wastage when manufactured by conventional machining processes. A novel current-assisted splitting spinning forming (CASSF) method combining the precision of spinning technology with the electroplastic effects of pulsed current synergistically was proposed to realize the high-performance near-net shape forming of SMGSPs. A finite element model coupled with the electroplasticity effect is constructed. Finite element model (FEM) simulations and experimental studies systematically investigated the distribution of the electric field, temperature field, the equivalent stress and strain, and the dynamic material flow of small module gears during CASSF. The results revealed that the current density of the SMGSP is concentrated near the contact area of the roller, so the softening region, due to the electroplasticity effect, highly overlaps with the deformation region of the SMGSP. The gear profile deformation exhibits a non-uniform stress-strain distribution, with peak stress concentrations localized at the exit-side tooth root arc. The application of pulsed current effectively reduced equivalent stress and enhanced material deformability, achieving saturation thresholds at 17.5 A/mm² current density ( J p ) and 40 % duty ratio ( d ). Five distinct material flow orientations develop during CASSF, forming four flow division surfaces between them. The uneven tooth height defect originates from asymmetric material flow between the entry and exit sides, whereas tooth underfilling stems from insufficient axial material flow. A forward-reversed forming strategy with intensified pulsed current eliminated tooth height discrepancies and improved tooth saturation ( γ ) to 97.8 %, demonstrating the potential of CASSF potential for forming extreme ratio SMGSPs.