环形薄壁类粉末冶金零件压坯残余应力分析

针对环形薄壁类粉末冶金零件压坯的残余应力进行分析,采用修正的Drucker-Prager Cap弹塑性本构模型对金属粉末压坯压制、卸载和脱模过程进行数值模拟,同时考虑不同零件压坯几何参数(高径比和厚径比)以及压制工艺条件(摩擦条件和脱模角度)对压坯内残余应力的影响.研究结果表明,压坯脱模后的残余应力分布规律是压坯侧表面出现明显的压应力层,内部为拉应力区域,且越靠近压坯中心值越小.随着高径比和厚径比的增加,其残余应力逐渐减小;随着摩擦系数的增加,压坯表面的轴向残余压应力不断增大且压坯内部的拉应力也不断加大;适当增加脱模角度有利于压坯内应力释放而减小残余应力.通过正交模拟试验及方差分析可知,厚径比和脱模角度对金属粉末成形脱模后压坯残余应力影响更为显著.

Analysis of residual stress in green compact of circular thin-wall powder metallurgy parts

Esidual stress of the compacted circular thin - walled powder metallurgy parts was analyzed, and the modified Drucker-Prager Cap model was used to simulate the pressing, unloading, and stripping process of the metal powder compact. Influences of the geometrical parameters ( aspect ratio and ratio of thickness to diameter) of the green compact and pressing conditions (friction conditions and die taper) on the residual stress in the green compact were investigated. The results showed that the residual stress after crust stripping has a significant compressive stress layer on the side of the green compact. The inside of the green compact there is a tensile stress region, and the value is smallest in the center of the compact. With increase of the ratios of height to diameter and thickness to diameter, the residual stress decreases; With increase of the friction coefficient, the axial residual compressive stress of the green compact surface increases and the tensile stress inside the green compact also increased;An appropriate increase in the die taper is beneficial to release the stress in the green compact and reduce the residual stress. Through the orthogonal simulation test and the analysis of variance, it was found that the ratio of thickness to diameter and the die taper have a more significant effect on the residual stress of the green compact after forming and stripping the metal powder.