Simulation of EPS foam decomposition in the lost foam casting process

Abstract

The importance of smooth mold filling in the lost foam casting (LFC) process has been recognized for a long time. The more uniform the filling process, the better the quality of the casting products that are produced. Successful computer simulations can help to reduce the number of trials and cut down the lead time in the design of new casting products by better understanding the complex mechanisms and interplay of different process parameters in the mold filling process. In this study, a computational fluid dynamics (CFD) model has been developed to simulate the fluid flow of molten aluminum and the heat transfer involved at the interfacial gap between the metal and the expanded polystyrene (EPS) foam pattern. The commercial code FLOW-3D was used because it can track the front of the molten metal by a Volume of Fluid (VOF) method and allow complicated parts to be modeled by the Fractional Area/Volume Ratios (FAVOR) method. The code was modified to include the effects of varying interfacial heat transfer coefficient (VHTC) based on gaseous gap pressure that is related to foam degradation and coating permeability. The modification was validated against experimental studies and the comparison showed better agreement than the basic constant heat transfer (CHTC) model in FLOW-3D. Metal front temperature was predicted within experimental uncertainty by the VHTC model. Mold filling patterns and filling time difference of 1–4 s, were more precisely captured by the VHTC model than the CHTC model for several geometries. This study has provided additional insight into the effect of important process and design variables in what has traditionally been a very empirical field.