An effective method for separating casting components from the runner system using vibration-induced fatigue damage

Abstract

In the final step of the investment casting process, the casting components have to be cutoff at the ingate from the main sprue or the runner system. Cutting the ingates is normally performed using a grinding wheel cutting machine, which is dangerous and consumes a great deal of labor and time. This work thus introduces a vibration method for separating casting parts from the casting tree. First, a V-shaped notch near the ingate of the runner is designed in order to generate the stress concentration effect during the induced vibration process by a pneumatic hammer. Then, the structural modal properties of the casting tree are analyzed to derive the natural frequencies and mode shapes. The flexible modal vibration of the casting parts due to resonance effect during excited vibration will cause fatigue damage at the notch, allowing the castings to be removed from the tree. Mold flow analyses are conducted to design the gating system for optimizing the casting quality. Harmonic response analysis is performed to derive the vibration response incurred by the pneumatic hammer and to predict the maximum principal stress on the notch. The fatigue damage at the notch is evaluated using the modified Goodman theory. The suitability of the proposed scheme is demonstrated via processing experiments and numerical simulations. The proposed method is quicker, safer, and cleaner than traditional grinding cutoff processes and is thus a promising cost-effective method for application in the investment casting industry.