Computer Diagnostics of the Process of Double-Action Pressing of Powder Materials Under Dry-Friction Conditions

Consideration is given to the process of double-action pressing of powder materials possessing plasticity and compressibility. Account is taken of the influence of dry external friction between the material and the lateral walls of the mold, which determines the strong linearity, of the problem in question. Based on computer animation with specialized graphics software packages, the authors have gained clear ideas of the kineti of compaction of a material and have identified the qualitative features of stage development of the propagation of a compaction wave in the material's volume due to the three-dimensional nonstationary character of the process of pressing. To calculate the stressed-strained state of a powder material, use was made of a linear combination of the Fleck–Kuhn–McMeeking and Gurson–Tvergaard–Needleman models, which makes it possible to take account of the wide range of variation in the porosity of materials. Numerical solution of the problem was implemented by a finite-element analysis with isoparametric elements. The increment in plastic strains at each step was determined from nonlinear plastic-flow equations. The distributions of the equivalent stresses and of the value of volume plastic strains in the material have been investigated, and the nonuniformity of the relative density over the height and along the radius of a billet at the end of the period of pressing has also been shown. The obtained results are relevant for predicting optimum regimes of the process of double-action pressing under dry-friction conditions.