In the casting process, regions of shrinkage porosity can be reduced or eliminated through the implementation of taper, or small angled additions of mass on the boundaries of the part design, before risers are placed on the casting. Taper supplements the effect of risers so that a smaller riser volume is necessary to make a casting sound. Typically, taper is determined for a casting by using industry guidelines that were developed for simple two-dimensional simplifications of a complex casting. There is no accepted method of defining taper directly on part geometry aside from using expert opinions to make final decisions on taper locations and size.
An optimization of taper geometries is performed on two-dimensional casting models to determine if a Niyama based optimization of taper directly on a part design is possible. The Niyama criterion identifies small regions of solidification shrinkage that correspond to shrinkage porosity in casting simulations. The taper optimization was performed on a plate with riser model and a spindle cross section model to determine the effectiveness of the optimization method for multiple geometries. This work concludes that taper optimization based on Niyama constraints is possible and effective, but care must be taken when determining the design space of the taper. It was found that the surface cooling rates of a casting can identify effective locations to taper so optimizations can be performed specifically on the size of the taper to eliminate porosity in a casting.