DEFORMATION STATES OF DIES FOR POWDER COMPACTION: COMPARISON BETWEEN ANALYTICAL AND FEM CALCULATIONS

摘要

The reliable design of compaction dies requires a careful calculation of interferences and corresponding stress states. The increasing demand for higher and higher precision of PM parts forces design engineers to predict the inner dimensions of the die with high accuracy, to minimize the incidence of tool cost on the total cost of the part. The maximum die life can be achieved only if the die design is properly carried out, considering die wear, wear resistance of different die materials, part spring-back on ejection, stability of dimensional changes upon sintering. In this study, focused on roto-symmetrical shapes and carried out by FEM, the deformation states of shrink-fitted dies have been analyzed. A radial pressure non-linearly proportional to the axial one has been assumed. For simple geometries, the resuits have been compared with those obtained by analytical calculations, using the available (Lame) formulae. A wide range of geometries has been covered: long or short dies and varying radial thickness, from thin-walled to thick-walled inserts. Conventional HS steel, PM steel and cemented carbide have been considered for the hserts, while for shrink-fitting rings only a high-hardenability quenched and tempered steel has been considered. The analysis of the results and the comparison between data obtained either by analytical method or by FEM show even marked differences. Then, once more, numerical calculations are confirmed to be the most reliable method of tool design. The FEM can be supported by empirical references, based on shop and company experience, to replace analytical solutions, which could be too coarse, or even impossible, especially in case of complicated part profiles.