【正文】 eased by pressure wave induced vibration. Garlick and Wallace [11] conducted an experiment of solidification with nonferrous pure metals and alloys under controlled vibration and obtained refined grain structure to some extent. was allowed to solidify under the influence of lowfrequency vibration energy (50 cycle/s) by Sankaran and Sreenivasa [12]. The results showed that the vibrational energy effected a decrease in solidification time, reduction in grain size, and substantial improvement in feeding efficiency, density, and mechanical properties. Ivanic et al. [13] estimated the influence of themophysical features, vibration parameters and mold shape on the resultant grain size in % Cu alloy.The purpose of this study is to propose a new plaster die casting process to improve prototyping of steel die casting, and to develop a plaster die casting machine implementing the process proposed. The rapid prototyping process laminated object manufacturing (LOM) is employed to make the patterns to prepare silicone molds. Even though silicone molding is generally used for producing wax patterns, in this process, it is applied to produce plaster molds repeatedly. In addition, the process bines pressurizing and vibrating the molten metal simultaneously to fill the mold pletely and to facilitate the creation of nuclei in the molten metal, respectively. Preliminary experiments examined the effects of pressurization and vibration on the quality of castings [14]. Based on the data obtained from the experiments, a plaster die casting machine employing pressurization and vibration has been developed which has a structure similar to that of a die casting machine. The machine utilizes an oil cylinder for pressurization and a magnetic actuator for vibration.Problems in conventional simulated die castingSimulated die castings using RP provide a reliable and accurate substitute for prototyping purposes, but there are some differences between the die casting and plaster casting process. Generally, plaster castings have inferior mechanical properties with a range of 70 to 80% of the die castings. Table 1 shows the parison of mechanical properties between plaster castings and die castings [8].In die casting, molten metal is forced into a steel mold by high pressure and velocity, and is held under the pressure during solidification so that the molten metal fills the mold pletely and rapidly. On the contrary, plaster casting produces castings with low pressure and a longer filling time. Therefore, at pouring, the plaster mold should be kept at a relatively high temperature in order to reduce heat loss and maintain fluidity of the molten metal. Due to their very low heat conductivity of under W/InK, plaster molds prevent outward heat transfer from the castings. This slows down the cooling rate of the castings. A slow cooling rate typically yields a large grain structure during solidification of metals. Obviously, plaster castings have larger grain structures than those of die castings.The cooling rate also affects the surface roughness of the castings. Due to the rapid cooling rate, die castings have a finer surface roughness than plaster castings. In parison of porosity between die castings and plaster castings, die castings usually have less porosity near the surface due to faster cooling of the part during the solidification. Because most diecast parts have fine sections and details, the prototyping of die casting using plaster casting can result in inpletely filled prototypes of castings.3 Piaster die casting bined with pressurization and vibrationPrevious work has shown that the application of vibration to solidifying metals in molds is beneficial to their mechanical properties in many ways. The applied vibration prevents the growth of columnar and dendritic grains and facilitates the formation of fine equiaxed grains during solidification. As a result, the diameter of the critical stable nucleus size of the solidifying castings decreases and consequently the castings have improved mechanical properties.In the preliminary experiments, an end clutch cover, a typical diecast part, has been cast in pure aluminum by using the plaster die casting adopting pressurization and vibration [14]. A test apparatus was made to perform the plaster die casting process. In order to examine the effect of pressurization and vibration on the quality of castings, preliminary experiments were carried out for two end clutch covers: one by conventional plaster casting and the other by the developed plaster die casting. From the preliminary experiments it was found that the applied vibration during the solidification of castings facilitated the creation of nuclei in the castings and resulted in a finer grain structure and that the pressurization increased the filling rate of in the cavities.Based on the results of the preliminary experiments, a new plaster die casting machine was developed. Pressurization and vibration are applied to the molten metal in the machine, which has a structure quite similar to that of a die casting machine. A plaster die casting machine employing pressurization and vibrationFigure 1 shows the configuration of the developed plaster die casting machine that is posed of two parts: a magnetic vibration part and a pressurization part using hydraulic pressure. As shown in Fig. l, the casting machine has a structure similar to that of a typical die casting machine. In a die casting process, the molten metal is injected at high speed and high pressure into