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<p>During the cold extrusion of 20Cr motor gears, cracks were observed on the top surface of the inner teeth. To investigate the crack formation mechanism, finite element analysis and experiment methods were employed. The results revealed that the regions approximately 1&#xa0;mm from the lower end of the top surface experienced high-stress concentrations, with damage values exceeding the critical threshold, making them prone to crack formation. Stress–strain analysis and scanning electron microscopy observations indicated that the tensile-shear stress, primarily tensile stress, was the key factor, in crack development. To address this issue, an enhanced die structure was proposed. The response surface method was then employed to optimize four critical parameters: datum height, die entry angle, entry fillet radius, and forming friction coefficient. The implementation of these optimized parameters significantly reduced the damage value and improved stress concentration. When applied to mass production, the rate of cracks decreased from 50 to 1%, demonstrating that the enhanced die structure effectively mitigates crack defects in gear cold extrusion.</p>

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Crack Formation Mechanism and Control Method of a Motor Gear Part Formed by Cold Extrusion Process

  • 期刊论文

  • 发表日期：

    2025年8月26日

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  • Wenzheng Dong,
  • Aoyu Zhao,
  • Dan Wang,
  • Qiquan Lin,
  • Yong Zhou

摘要

During the cold extrusion of 20Cr motor gears, cracks were observed on the top surface of the inner teeth. To investigate the crack formation mechanism, finite element analysis and experiment methods were employed. The results revealed that the regions approximately 1 mm from the lower end of the top surface experienced high-stress concentrations, with damage values exceeding the critical threshold, making them prone to crack formation. Stress–strain analysis and scanning electron microscopy observations indicated that the tensile-shear stress, primarily tensile stress, was the key factor, in crack development. To address this issue, an enhanced die structure was proposed. The response surface method was then employed to optimize four critical parameters: datum height, die entry angle, entry fillet radius, and forming friction coefficient. The implementation of these optimized parameters significantly reduced the damage value and improved stress concentration. When applied to mass production, the rate of cracks decreased from 50 to 1%, demonstrating that the enhanced die structure effectively mitigates crack defects in gear cold extrusion.