Defects and Microstructure Research of the Denture Crown in the Centrifugal Casting

Because of the thin wall and the complex shape, there are usually some defects in the denture crown prepared by the centrifugal casting method, such as shrinkage cavity, dispersed shrinkage, porosity, filling incompleteness, and etc. Sometimes the design only can be amended with the traditional trial and error method which costs too much as we know. With the development of numerical simulation technology, it is convenient to forecast the defects in the castings. It can not only ensure the quality of the casting, but also reduce the manufacturing cost.In this study, CAD models of the gating system were constructed. Based on the Procast software, the filling and solidification process of the denture crown during the centrifugal casting were simulated. And therefore the defects and microstructure were predicted. The effects of the process parameters and the gating system on the defects were studied as well. At the same time, moulds were designed and Ni-Cr alloy denture crowns were centrifugally casted. The defects on the surface and profile were observed, and metallographs were taken, then the results were compared with the simulation results.The predicted results of defects agreed with the experimental ones. Settings of the process parameters had an effect on the defects’locations, sizes, and etc. In an appropriate span, the shrinkage reduced with the filling speed, the pouring temperature, the rotative velocity and the mould temperature. In addition, the gating system has a very important influence on the defects. In this paper, a reasonable gating system was designed, the castings were free of shrinkage porosity due to a progressive solidification process during the casting course.Microstructure Simulation results showed that the nucleation model, KGT growth model and CA model were rational to simulate the microstructure of Ni-Cr alloy denture crown. From the outer side of the casting to the centre which were both close to the investment, the grain size firstly decreased, and then increased.