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<p>To address the problems of high forming torque, severe tap wear, and tap fracture during cold extrusion of large-diameter internal threads in high-strength materials, this study proposes a novel internal thread cold extrusion method using specially shaped preformed holes. An M20 × 2.5 internal thread made of Ti-6Al-4V titanium alloy was selected as a representative case. Considering material plasticity, frictional behavior, and strain hardening, a mathematical model of extrusion torque was established to clarify the torque generation mechanism and its dominant influencing factors. Based on this model, several preformed-hole geometries were designed, and finite element simulations were performed to investigate the effects of preformed-hole geometry on extrusion torque, forming temperature, axial load-bearing capacity, and tap wear. The results show that specially shaped preformed holes can effectively modify material flow behavior and the tap–workpiece contact state, thereby reducing extrusion torque and tap wear. By comprehensively considering forming difficulty, thread mechanical performance, tap wear, and manufacturing feasibility, the keyway-shaped preformed hole was identified as the optimal design. Compared with the conventional circular preformed hole, the keyway-shaped preformed hole reduced the extrusion torque, forming temperature, and tap wear by 14.79%, 4.43%, and 12.93%, respectively, while the axial load-bearing capacity decreased by only 10.22%. Experimental validation showed that the relative errors between the experimental and simulated results for extrusion torque, forming temperature, and thread height were 2.80%, 7.73%, and 8.18%, respectively, indicating that the finite element model has good predictive accuracy. The proposed method provides a theoretical basis and practical process reference for the cold extrusion of large-diameter internal threads in high-strength materials.</p>

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Numerical simulation and experimental investigation of internal thread cold extrusion using specially shaped preformed holes

  • 期刊论文

  • 发表日期：

    2026年7月20日

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  • Hong-Ling Hou,
  • Jia-Le Dong,
  • Zhao-Le Yu,
  • Xi-Xin Wang,
  • Tao Yan,
  • Jing Liu,
  • Yong-Qiang Zhao,
  • Jian-Qiang Jin

摘要

To address the problems of high forming torque, severe tap wear, and tap fracture during cold extrusion of large-diameter internal threads in high-strength materials, this study proposes a novel internal thread cold extrusion method using specially shaped preformed holes. An M20 × 2.5 internal thread made of Ti-6Al-4V titanium alloy was selected as a representative case. Considering material plasticity, frictional behavior, and strain hardening, a mathematical model of extrusion torque was established to clarify the torque generation mechanism and its dominant influencing factors. Based on this model, several preformed-hole geometries were designed, and finite element simulations were performed to investigate the effects of preformed-hole geometry on extrusion torque, forming temperature, axial load-bearing capacity, and tap wear. The results show that specially shaped preformed holes can effectively modify material flow behavior and the tap–workpiece contact state, thereby reducing extrusion torque and tap wear. By comprehensively considering forming difficulty, thread mechanical performance, tap wear, and manufacturing feasibility, the keyway-shaped preformed hole was identified as the optimal design. Compared with the conventional circular preformed hole, the keyway-shaped preformed hole reduced the extrusion torque, forming temperature, and tap wear by 14.79%, 4.43%, and 12.93%, respectively, while the axial load-bearing capacity decreased by only 10.22%. Experimental validation showed that the relative errors between the experimental and simulated results for extrusion torque, forming temperature, and thread height were 2.80%, 7.73%, and 8.18%, respectively, indicating that the finite element model has good predictive accuracy. The proposed method provides a theoretical basis and practical process reference for the cold extrusion of large-diameter internal threads in high-strength materials.