Strength Design And Stress Analysis Of Cold Extrusion Die

Due to the energy transforming and the high velocity of the material flow in the extrusion process, the cold extrusion die prone to failure when subjected to the high temperature and the super-high frequency cyclical loading. Hence, enhancing the stiffness of the die is a prerequisite to ensure its long-term stability. In order to reduce the peak stress in the wall of die and the uniform stress level along wall thickness direction, autofrettage technology and pre-stressed structure were introduced in this essay. The forward gain function of work stress field produced by residual stress field was analyzed. The investigations provided theoretical support for the strength design of the die.Based on the elastic-plastic theory and the finite element method and the optimization method, the strengthening mechanism of the integral autofrettage die, multilayer com-bined die and two-layer combined die with autofrettage-shrink treatment were discussed. The main researches are given as follows:Based on the bidirectional power hardening constitutive condition and the maximum strain energy theory, the mechanical model of the integral die with autofrettage treat-ment was established.The influence factors of the maximum load capacity of autofrettage die under working condition as well as the optimum elastic-plastic radius of autofrettage were analyzed. Autofrettage process of die was simulated by the finite element models. The numerical solution results and analytical solution results are in good agreement.The comparison of the change trend of equivalent stress before and after the auto-frettage process was conducted to validate the effectiveness that the autofrettage treatment can improve load capacity of die.Based on the theories of thick-well cylinders, the load characteristics of the integral die under working condition were analyzed, and the limitations that the die strength can be improved by increasing wall thickness were discussed. In order to improve the load capacity, multi-layer pre-stressed composite die was discussed.The maximum strain energy theory was proposed as strength conditions. Under the premise of the knowledge that the total diameter ratio and material parameters of each layer for combination die, the diameter ratio of each layer was regarded as design vari-ables, and the maximum load capacity of combined die was regarded as the op-timization goal. The parameters on combination die were optimized by using Lagrange multiplier method. The analytical solution on the best ratio of each layer, ultimate load capacity of die, optimal shrinkage stress and optimal interference were acquired.Combined autofrettage technique and multi-layer shrinkage method, the elastic ul-timate load pressure of die can be further studied. On the premise of guarantee die str-ength, the die structure can be compacted to reduce manufacturing cost.Analysis methods and conclusions of this paper on the improvement of the strength design of cold extrusion die, increasing the life of die have a certain reference value and theoretical significance.