Cold compaction of ceramic powder: Computational analysis of the effect of pressing method and die shape

Abstract

This paper deals with a computational analysis of the influence of the pressing method and part geometry on the final density distribution in the cold compaction process of ceramic alumina powders. The analysis is based on the explicit finite-element model proposed and validated in a previous study. The mechanical behavior of the processing material is described using a multisurface elastoplastic model, the modified Drucker-Prager/Cap model Keywords: cold compaction, powder metallurgy, FEM, computational analysis, Drucker-Prager cap model, pressing method, die shape 1. Introduction. Powder metallurgy is a near net-shape manufacturing technology, which is based on the use of metallic, ceramic, or organic powders as raw materials. Nowadays, powder metallurgy is widely used for several structural and pharmaceutical applications. The most relevant steps of powder metallurgy are the production of powders, the powder cold compaction process, and the sintering process. Sometimes, after the above processes, a part is subjected to finishing processes, such as recompaction, resintering, heat treatment, and machining operations, to improve its geometrical and mechanical properties.Cold compaction processes are used to shape powder and to obtain porous parts, called greens, whose mechanical resistance allows manipulating them during the sintering process. The powder compaction process is very important to obtain a final product characterized by the desired mechanical and geometrical features. Indeed, plasticity phenomena, internal friction of a porous medium, and frictional effects between the die wall and the processing material may induce inhomogeneous distributions of density and residual stress. As a consequence, nonuniform shrinkage, local distortions, or cracks may happen during the sintering process. Typical processes of powder compaction are uniaxial (single and double action) pressing, isostatic pressing, high speed forming, extrusion forming, vibration forming, centrifugal forming, rolling forming, continuous forming, gravity forming, and mixture forming. Different pressing methods involve different stress-strain distributions into the processing material, whose sensitivity to the specific deformation process has been outlined in [1].Nowadays, the powder metallurgy industry is based on expensive trial and error procedures for product and die design, as well as for process parameter setup. Analytical modeling and continuum approaches provide very useful information about the mechanical behavior of geotechnical, granular, and granular composite materials [2,4]. A theoretical approach to the modeling of elastic wave effects in the above materials can be found in [5][6][7][8][9][10][11][12][13][14]. Several studies evidenced that finite-element analysis can be employed as a very useful tool for stress-strain analysis of three-dimensional bodies [15], as well as for effective process investigation and development [16][17][18][19][20][21].A relevant limit of the proposed models, however, is that only two-dimensional or a...

The effect of the coefficient of friction between the roller and the powder on the rolling process

“…In simulations of powder deformation, Drucker Prager Cap is one of the most widely used physical models [5][6][7] . Drucker Preger Cap was developed on the basis of Drucker Prager, which controlled the volumetric expansion of the material during shear by adding a Cap-shaped yield surface [8] .…”