Research on the cold extrusion process of internal threads with arc-notched in special-shaped bottom holes

Abstract To address the issue of excessive torque in thread forming, this study proposes an innovative special-shaped preform hole design for internal thread cold forming, departing from conventional circular hole approaches. Through comparative analysis of thread profile geometry, distribution characteristics, and manufacturability, the four arcs preform hole configuration was developed. Numerical simulations of the forming process were conducted followed by tensile strength evaluation of the formed threads. The orthogonal experiment method combined with entropy-weighted TOPSIS optimization revealed that threads formed with non-special-shaped holes achieve 90.34% of circular hole formed thread strength while exhibiting 7.12% greater strength than cut threads, meeting all connection requirements. This research establishes a novel solution for torque reduction in thread forming processes, demonstrating that the optimized special-shaped preform design reduces forming torque while maintaining adequate mechanical performance.