粉末冷压成形弹性后效及非同步双向压制模拟研究

Numerical simulation of spring back and non-synchronous bidirectional pressing in powder cold pressing

本文采用有限单元法,基于更新的Lagrange格式和弹塑性大变形理论,模拟分析了金属粉末冷压成形后的弹性后效现象,以及非同步双向压制下的压坯密度分布规律。结果表明:脱模后的节点密度下降量与高径比呈线性递增关系,据此可有效辅助模具设计,提高压坯尺寸精度。距离运动模冲越近,由于积聚的应变能较大,脱模后节点密度下降得越多,弹性后效大。应力的重新分布使距离运动模冲较远处的密度反而略微增加。降低摩擦能整体减小弹性后效程度和密度下降量。非同步双向压制对台阶件等复杂零件生产的适应性要优于同步双向压制。非同步双向压制获得的压坯密度均匀性取决于两模冲的压下量。采取先动作模冲的压下量接近所需的总压下量,之后另一模冲轻微反向压制到最终尺寸的方法,可使密度均匀性大为提高,达到甚至超过同步双向压制的均匀度。

Based on the updated Lagrangian method and large deformation elastic-plastic theory,the finite element method was used to simulate and investigate the spring back of compacting metal powder at room temperature and the density distribution of compacts under the non-synchronous bidirectional pressing.The results show a linear relationship between the aspect ratio and the decrease of node density after ejection,which can effectively guide the mold design and ensure the dimensional accuracy of compacts.Being close to the moving punch,the accumulation of internal deformation energy is relatively high,thus the decreases of node density after ejection and spring back are relatively significant.However,the redistribution of stress leads to a slight increase of density away from the pressing punch.Reducing friction can decrease both the overall spring back and the decline of node density.To produce the complex powder metallurgy components with stages,the non-synchronous bidirectional pressing method is superior to the synchronous bidirectional pressing method.The density uniformity of compacts achieved by the non-synchronous bidirectional pressing method depends on the reductions of two punches.In the non-synchronous bidirectional pressing,if the reduction of the first moving punch is close to the necessary total reduction,and a slight reverse pressing is performed by the other punch until the final size of compact is achieved,then the uniformity of density by the non-synchronous bidirectional pressing can be greatly improved,and even may exceed that of the synchronous bidirectional pressing.