Thermofluid analysis and design of a low-temperature preforming process

Abstract

A simplified, one-dimensional analysis is presented for the phenomena related to flow and heat transfer involved in a commercial low-temperature molding process for manufacturing porous ceramic preforms. The process consists of injecting an aqueous slurry of ceramic particles and additives into a mold and freezing the slurry into the shape of the mold cavity. The purpose of this study is to demonstrate the use of reduced-order models in the analysis and design of a complex process. The flow analysis is based on an approximate model using the Bernoulli equation accounting for frictional and geometric losses, while the heat-transfer problem of freez-ing of the slurry inside the mold cavity is solved using an order-of-magnitude analysis of the interface energy balance equation. The thermofluid analysis yields the mold-fill times and freeze times, which are subsequently used in conjunction with practical considerations of ice crystal formation, complete mold fill, and operating limits of the processing equipment, to derive design guidelines for the mold temperatures and injection pressures. Experimental investigations were carried out on the manufacture of silicon carbide preforms used in metal-matrix composites for electronic packaging components. Good agreement is demonstrated between the theoretical pre-dictions and the experimental observations. The simplified analysis is shown to provide valuable information on the class of molding processes at low temperatures, for simple part geometries, without resorting to tedious numerical computations. For complex geometries, the physical groups and the design approach presented in this article may be used to correlate data from rigorous numerical simulations and experiments.