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针对阀螺钉冷挤压成形时出现的凸模断裂问题,通过对断口的宏观观察,发现有疲劳特征。运用Deform2D/3D对模具的模拟显示凸模台阶圆角过渡处应力集中,等效应力2 930 MPa,超过凸模材料抗弯强度(2 500 MPa),是模具在此部分发生脆性折断的重要原因。为避免凸模阶梯圆角处应力集中,采用组合凸模的设计方法。数值模拟显示,组合凸模在工作时无应力集中。根据改进后的凸模设计方案进行实验,对实验中出现的孔成形凸模硬度不足问题,确定了成形孔的凸模硬度应达到62 HRC,有效的解决了生产中凸模早期失效的问题。
Aiming at the problem of the rupture of the punch during the cold extrusion of the valve screw, the fatigue characteristics were found through the macroscopic observation of the fracture. The simulation of the mold by Deform2D / 3D shows that the stress concentration at the transition of the punch step radius is 2930 MPa, which exceeds the bending strength of the punch material (2 500 MPa), which is an important reason for the brittle fracture of the die in this part . In order to avoid stress concentration in the convex step of the male mold, the design method of the combined punch is adopted. Numerical simulation shows that the combined punch has no stress concentration at work. According to the improved design scheme of the punch, the hardness of the punch in the forming hole was found to be 62 HRC. The problem of early failure of the punch in the production was solved effectively.