Mathematical Modelling of Pattern Sublimation in Rapid Ice Investment Casting

Investment Casting (IC), using the wax pattern, produces metal parts with a high surface finish and complex geometries within acceptable tolerances. However, removing the wax patterns can have processing challenges, such as thermal expansion during wax melting for pattern removal leading to shell cracking defects, the release of hydrocarbons from melting wax, and the burnt residue from this process. To overcome these challenges, it has been proposed to replace wax with ice as a pattern material. Ice has an inherent benefit of reduction of volume during its phase change from solid to liquid. It helps to reduce cracking due to expansion. Rapid Freeze Prototyping (RFP) and Freeze Cast Process (FCP) can produce the ice pattern. In the process of Rapid Ice Investment Casting (RIIC), the ice pattern is invested with a low-temperature ceramic slurry to make ceramic shells for metal casting. Sublimation is used for ice pattern evacuation at sub-zero conditions using a vacuum. Estimating various properties like time for total sublimation, concentration gradient, and energy usage are vital for process characterization and optimization. A diffusion-based mathematical model has been proposed and experimentally verified to sublimate the ice patterns in this research. Experimental results show a close correlation (96.74%) with the theoretical model. The demonstration of ice investment casting has been carried out, and it reported close dimensional accuracy.

Automated summary

Ice investment casting is a novel casting process that uses ice as a pattern material to address the challenges faced by wax patterns in processing, offering high dimensional accuracy.