Modelisation du comportement des poudres metalliques lors du pressage (French text).

摘要

Numerical simulations of die powder compaction were done and also the evolution of friction's coefficient was investigated during this doctoral project. Four types of powder were analyzed, each of them having different particle's shape and hardness and two-step pieces were fabricated to validate the simulation work. The opportunity of using the Gurson model and the critical state model Cam-Clay in powder compaction was evaluated for different levels of density. The local density variation was evaluated through superficial hardness measure method Rockwell 15-T, calibrated initially on thin samples to minimize the friction effect. A correlation between hardness and local density was established for each type of powder and isodensity maps were traced using bidimensional interpolation.; The influence of each parameter of the models on the local density was investigated. The values of the parameter were taken from the literature. It was found that an irregular particle's shape needs more shear stress to achieve the same densification level obtained for a round particle of the same material. The most important density variation was found around the inner corner of the part; the experimental work has confirmed the same position that in some cases is the cracking zone appearing during the ejection phase. An automatic remeshing procedure would be recommendable to avoid the high deformation of the mesh around the inner comer. No significant difference was found between the distributions and values of local density in the case of the 2D and the 3D simulations.; The friction coefficient variation plays a more accentuated influence on the surfaces parallel to the direction of pressing than on the surfaces normal to the same direction. The part dimension is an important factor in local density distribution. The use of a decreasing friction coefficient is more realistic. The graphical user interface build in Matlab using previous experimental data confirm this type of evolution.; Finally, using a combination of the two models (or a modified Cam Clay model) would describe more accurately the local density evolution in different stages of the pressing process.