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采用上限分析法对棒材在圆锥形模具中挤压时的中心开裂缺陷进行预测,提出了一个包括径向速度和角速度分量的运动许可速度场,提出了一个新的预测中心开裂缺陷产生的标准,并提出了一个表示开裂程度的参数b_(obt)。通过最小化挤压过程中总功率耗散,采用入口处的边界形状来计算参数b_(obt)。当b_(obt)≥bcr时发生中心开裂现象。此外,研究了中心开裂缺陷与挤压过程参数(模具半锥角、面积减小率和摩擦因数)的关系。结果表明:棒材的中心开裂缺陷主要受面积减小率和摩擦因数的影响。将本文作者所提出的方法与FEM模拟数据及已有文献数据进行了比较。
The upper limit analysis method was used to predict the center crack of bar during extrusion in conical die. A moving speed field containing radial velocity and angular velocity components was proposed. A new criterion for predicting center cracking was proposed , And proposed a parameter b_ (obt) indicating the degree of cracking. By minimizing the total power dissipation during extrusion, the boundary shape at the entrance is used to calculate the parameter b_ (obt). When b_ (obt) ≥ bcr central cracking occurs. In addition, the relationship between cracking at the center and extrusion process parameters (mold half taper angle, area reduction rate and friction coefficient) was studied. The results show that the central crack of the bar is mainly affected by the area reduction rate and friction coefficient. The method proposed by the author is compared with the FEM simulation data and the existing literature data.