Computer-aided modeling and experimental verification of optimal gating system design for investment casting of precision rotor

17-4 PH stainless steel rotors used for hemodialysis machines need to meet strict quality requirements because they are subjected to high-speed rotation. The presence of shrinkage, incomplete filling, and gas porosity in a rotor might cause creep failure, which can be dangerous during operation. Therefore, computer-aided modeling and experimental verifications are conducted in this work to optimize the investment casting of rotors. Six casting processes and five gating system schemes are designed to optimize the casting qualities. The probability of defect occurrence during casting is assessed based on the retained melt modulus incorporated with the Niyama criterion model. Numerical simulation and experimental results show good agreement. Thermodynamic analysis results show that a high cooling rate increases the flow resistance of molten metal between the dendrite arm spaces, resulting in insufficient feeding in the mushy zone. With proper designs of the runner and riser systems, the problems of flow turbulence and insufficient feeding are almost obviated. Surface sinks and interior shrinkage are also completely eliminated.