A frozen sand mold is produced by freezing a mixture of sand and water, thus casting processes using the frozen sand mold have less environmental load. Therefore, this process is getting an attention. In this study, the effects of grain size of sand, water content of mold, and pouring temperature on the cooling behavior of bronze cast (CAC902) made by using a frozen sand mold were investigated. The cooling speed of the bronze cast increased with increasing grain size of the sand and water content of the mold. In particular, the water content of the mold was found to be effective for improving the cooling rate of the bronze just after pouring, and thus a finer microstructure was obtained by increasing water content. The microstructure of the cast poured at 1413K showed a columnar structure. In contrast, the microstructure poured at 1373K exhibited an equiaxed structure, because the temperature of the molten bronze rapidly decreased below liquidus temperature. From these results, it is clear that the cooling behavior of the cast can be controlled by changing the grain size of sand, water content, and pouring temperature. As a result, the microstructure of the cast can also be controlled.

View full abstract

  In the expandable pattern casting (EPC) process, molten metal is poured into the cavity by the thermal decomposition of the expandable polystyrene pattern (EPS). Decomposition gas escapes into the dry sand through the coat layer, making the mold filling mechanism in the EPC process very complicated. In the present study, a simple simulation of the mold filling of molten aluminum alloy in the EPC process was carried out, considering the thermal decomposition of EPS pattern and discharge of decomposition gas through the coat. When there was no reduced pressure in the flask, the thickness of thermal decomposition gas layer decreased with increasing the coat permeability, but the effect on the melt velocity was not so significant. Under reduced pressure, the thickness of the gas layer was smaller and the melt velocity was lager than the case without reduced pressure, and the effect of coat permeability on the melt velocity was remarkable. The analytical values of the filling time of molten aluminum alloy were compared with the experimental values using the plate EPS pattern and were in relatively good agreement with the experimental values.

View full abstract

  In CAE analysis of casting phenomena such as mold filling and solidification, the finite difference method is often adopted when building the difference equations. However, this generally results in poor shape approximation accuracy since meshes created for highly curved and complex casting surfaces have to include step formations at end sections. Consequently, this causes predictions for mold filling and other phenomena to diverge from actual results, and is one reason why analysis accuracy is not sufficient to provide general solutions. To resolve this issue, an analysis technique was developed using the porous media method. This method enables highly accurate analysis within a practical calculation timeframe by improving shape approximation accuracy without reducing mesh pitch.

View full abstract