Development of techniques for predicting ceramic shell properties for investment casting

Abstract Investment casting research is being carried out at The University of Birmingham sponsored by the Engineering and Physical Sciences Research Council (EPSRC) and a consortium of industrial companies. The programme is aimed at developing a fundamental understanding of the process, with a view to routinely producing sound, net shape castings. As part of this programme, work has been carried out to model flow and solidification using commercially available computer simulation packages. To ensure realistic predictions it has been necessary to provide fundamental thermophysical and mechanical data for various ceramic mould materials used by the industry. Measurement of thermophysical, mechanical, and fundamental property data required for process modelling is time consuming and costly. The present paper reports on the work carried out to determine the applicability of the use of the theory of mixtures to predict properties of shell mould systems. Individual tensile strength and stress-strain properties were measured for the unfired ceramic layer by layer, as the shell was built up. Permeability measurements for the fired shell were also determined layer by layer. This gave a unique insight into the factors which control mechanical properties and performance of the shell during the dewax and casting stages of the process. From these results, a determination of the applicability of a 'rule of mixtures' was made. This may allow formulae to be devised and applied to the majority of conventional moulds by consideration of the constituent materials.