| Summary: | 碩士 === 國立屏東科技大學 === 機械工程系所 === 104 === Investment casting is a type of near net shape process in which the castings have complex and high-precision structures and high mechanical performance. This study therefore adopted investment casting to develop an enclosed impeller for a centrifugal pump. Impellers operate long term in acidic and alkaline fluids, which easily result in corrosion, cavitation, and torsional creeping. This means that the commonly seen shrinkage porosity, dispersed shrinkage, and gas porosity
defects in investment casting must be remedied. Using computer-aided engineering (CAE), we optimized the pre-casting process of SUS304 stainless steel enclosed impellers. First, we incorporated the initial gating system into mold flow analysis for numerical simulation and observed the processes of filling and solidification. Based on the retained melt modulus and the Niyama criterion, we predicted the probability of porosity defect formation. By assessing the locations and mechanisms of defects in numerical simulations and products, we modified the pouring model and process parameters. We designed three types of modification schemes, namely, bottom gating, side gating, and top gating, and experimented on various runner locations, inlet sizes, and top riser and vent hole designs. By observing their influence on pouring speed, pouring temperature, and molding temperature, we identified the optimal scheme to provide reference for the development of enclosed impellers. The results indicate that the size optimization of the gating system, a pressure reduction design in the vent hole, a feeding design for the top riser, and other process parameter adjustments can effectively reduce the probability of porosity defect formation in casting, thereby enhancing casting quality, yield, and mechanical properties as well as shortening the product development process and reducing costs.
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