Sabau A S, Viswanathan S

Abstract: Determining the pattern tooling dimensions is crucial to the dimensional control of the investment casting process. Recent surveys conducted by the Investment Casting Institute on dimensioning practices used in the investment casting industry found that the assignment of tooling dimensions for pattern die dimensioning is not consistent across the industry. To date, there are no industry-wide guidelines for tooling engineers that can be used for die dimensioning, and no comprehensive models are available for predicting dimensional changes in investment castings. In this study, relevant properties of materials and process variables that have an important effect on tooling dimensions are identified. A review of waxes, shell materials, and investment casting alloys was conducted in order to identify constitutive models of those properties of the wax, shell, and alloy that need to be considered for accurate prediction of the final part dimensions. The literature survey indicates that dimensional changes between a pattern die and its casting part occur as a result of complex phenomena such as thermal expansion/contraction and hot deformation (elastic, plastic, and creep) during the processing of the pattern material (wax), mold material (shell), and solidifying alloy. Factors that affect tooling allowances are determined by the material (wax, shell, and alloy), thermophysical properties, material (wax, shell, and alloy) thermomechanical properties, process parameters, and the restraint due to geometrical features of the casting and gating system.

Keywords: Critical dimensions, Investment casting, Material properties, Pattern tooling, Predicting.