Computational modeling of rubber multiaxial pressing applied to ceramic materials

Abstract

Uniaxial and isostatic powder pressing are well known processes. However, disadvantages such as the production of heterogeneous parts or low productivity, respectively, are intrinsic drawbacks. Rubber Multiaxial Pressing (RMP) is an alternative process to overcome these disadvantages. In RMP, the pressing tool consists of a flexible rubber mold, confined in a rigid die, where pressing takes place by the action of a piston. This loading is transferred to the powder in the inner cavity of the rubber mold, whose distribution depends on the geometry of the tool parts and the tribological conditions between them. One drawback of RMP lies in the tool design stage due to the challenge of accurately predicting the shape of the flexible mold in its deformed configuration. The complexity of the deformed geometry is due to inhomogeneous strains induced by the nonlinear mechanical behavior of rubber and powder, as well as by the tribological conditions. In this context, this study aims to investigate the process characteristics and use the finite element (FE) simulation to assist in tool design for RMP, thus enabling the manufacture of compacted parts with a geometry that meets the dimensional requirements and a mechanical strength that allows the part to retain its integrity during the next stages of processing. To perform reliable numerical analysis, a characterization of the mechanical behavior of the involved materials is required. Mechanical tests were performed to characterize the rubber used in the mold and the alumina powder. Once the constitutive models were identified, FE analyses of the RMP were performed. The case study explored by this research project was the pressing of an alumina ceramic femoral head for hip implant. Finally, experimental and computational results were compared in order to highlight the accuracy of the numerical analyses implemented.