A boundary condition coupling strategy for the modeling of metal casting processes

A generalized temperature boundary condition coupling strategy for the modeling of conventional casting processes was implemented via experiments and numerical simulations with cylindrical aluminum, aluminum alloy and tin specimens in copper, graphite and sand molds. This novel strategy related the heat transfer coefficient at the metal-mold interface to the following process variables: the size of the air gap which forms at the metal-mold interface, the roughness of the mold surface, the conductivity of the gas in the gap, and the thermo-physical properties of both the metal and mold. The objective of this study was to obtain, apply and evaluate the effect of incorporating an experimentally derived relationship for specifying transient heat transfer coefficients in a general conventional casting process.; A systematic experimental approach (not limited to a specific industrial process) was implemented to determine the heat transfer coefficient, and characterize the formation of the air gap at the metal-mold interface. The heat transfer mechanisms at the interface were identified, and seen to vary in magnitude during four distinct stages, as the air gap formed and grew. An semi-empirical inverse equation was used to characterize the heat transfer coefficient-air gap relationship, across the various stages, for experimental data from the literature and this study, and a correlation was presented in non-dimensional form for experimental data from this study. The effect of surface roughness was observed to be pronounced at small relative gap sizes, reducing the heat transfer coefficient at least one order of magnitude below that predicted for perfectly flat surfaces. The effect was observed to progressively diminish with increasing gap sizes, and approached an analytical 'perfectly flat' solution for larger gap sizes.; A simplified visco-elastic plastic numerical model was developed for a cylindrical coordinate system to predict the growth of the air gap. The model's predictions of the gap growth compared well with the experimental measurements for each system examined. Application of the correlation via coupling with the energy equation was seen to improve the accuracy of an uncoupled casting model, bettering the predicted air gap formation, and eliminating the previously existing time lag for initial formation of the gap.