Analysis of Mold Filling in Lost Foam Casting of Aluminum: Method

Abstract

This paper is the first in a two-part series on mold filling analysis for lost foam casting of aluminum. Part I describes the analysis method, assumptions, and governing equations, and Part II applies the analysis to a variety of pattern shapes that exhibit different aspects of mold filling behavior, many of which are unique to lost foam. Building on previously developed foam decomposition models, this paper (Part I) proposes companion representations for liquid metal flow and heat transfer that are suited to the special characteristics of the lost foam problem. The mold cavity is idealized as a shell-like region defined by a mid-surface together with a variable thickness. The viscosity of the liquid metal is neglected while the pressure in the metal is assumed to result from gravity alone. The transient mold temperatures, induced by contact with the molten metal, are assumed to penetrate only a short distance into the sand. Their spatial variation normal to the cavity surface is represented by a finite polynomial expansion with coefficients determined by a Galerkin method. A simple criterion is proposed for determining when foam decomposition switches between modes. The result is an analysis method that is not only compatible with the level of detail in the foam decomposition model, but also consistent with the typical part-to-part repeatability of mold filling in the lost foam process. Even for large, complex castings such as an automotive engine block, the analysis can be completed in less than an hour on a standard engineering workstation.