内花键反挤压凸模断裂分析及改进措施

Analysis and improvement on punch fracture of inner spline in backward extrusion process

针对内花键反挤压成形时出现的凸模断裂问题,通过对凸模进行断裂分析,得出断裂的原因为:内花键成形时挤压力较大,阶梯凸模圆角过渡处应力集中,该部位等效应力值为3800 MPa,超过凸模材料ASSAB88的抗弯强度3500 MPa,从而导致凸模在该处产生脆性折断。为避免凸模的早期失效,提出采用组合凸模来避免阶梯凸模圆角过渡处的应力集中问题,数值模拟结果显示,组合凸模工作时无应力集中,成形部分等效应力值约为3150 MPa。生产实践表明,组合凸模可避免凸模的早期失效。

For the problem of the punch fracture in backward extrusion process of inner spline, the failure analysis of the punch was conducted. The analysis result shows that the extrusion force produced in the forming of inner spline is big and the stress concentration ap- pears in the transitional section of ladder-shape punch, where the equivalent stress of 3800 MPa exceeds the materials ASSAB88 bending strength of 3500 MPa, so the brittle fracture is generated in the transitional section. In order to avoid the early failure of punch, the combination punch was adopted. Simulation result shows that the combination punch works without stress concentration and the equivalent stress of its work area is 3150 MPa. The production practice shows that the combination punch can effectively avoid the early failure of punch.