THERMOFLUID ANALYSIS AND DESIGN OF A LOW-TEMPERATURE PREFORMING PROCESS

A simplified, one-dimensional analysis is presented for the phenomena related to flow and heat transfer involved in a commercial low-tempera ture molding process for manufacturing porous ceramic preforms. The pr ocess consists of injecting an aqueous slurry of ceramic particles and additives into a mold and freezing the slurry into the shape of the m old cavity. The purpose of this study is to demonstrate the use of red uced-order models in the analysis and design of a complex process. The flow analysis is based on an approximate model using the Bernoulli eq uation accounting for frictional and geometric losses, while the heat- transfer problem of freezing of the slurry inside the mold cavity is s olved using an order-of-magnitude analysis of the interface energy bal ance equation. The thermofluid analysis yields the mold-fill times and freeze times, which are subsequently used in conjunction with practic al considerations of ice crystal formation, complete mold fill, and op erating limits of the processing equipment, to derive design guideline s for the mold temperatures and injection pressures. Experimental inve stigations were carried out on the manufacture of silicon carbide pref orms used in metal-matrix composites for electronic packaging componen ts. Good agreement is demonstrated between the theoretical predictions and the experimental observations. The simplified analysis is shown t o provide valuable information on the class of molding processes at lo w temperatures, for simple part geometries, without resorting to tedio us numerical computations. For complex geometries, the physical groups and the design approach presented in this article may be used to corr elate data from rigorous numerical simulations and experiments.