IMPROVING THE DIRECTIONAL SOLIDIFICATION OF COMPLEX GEOMETRIES THROUGH TAPER ADDITION

摘要

The Niyama criterion identifies centerline shrinkage in simulations of directionally solidifying alloys. Adding taper to the casting surface is an effective strategy to eliminate regions of critical Niyama in and improve the soundness of castings. This taper addition is straightforward to apply to flat plates and will improve the Niyama result. However for complex geometries, there may not be an intuitive taper solution. The Niyama criterion will validate these complex tapers but not guide the design of that taper. When evaluated near the end of solidification, a thermal criterion such as the cooling rate on the surface of the casting can serve as an identification of efficient areas to taper. Once the taper location is found, the overall goal is to reduce design time by using the Niyama criterion to develop a response surface of taper solutions with varying lengths and heights to achieve a minimum addition of material with required soundness. With a moderate number of simulations, the response surface can give us an optimum choice of taper length and height of that region.