The shrinkage porosity produced in the solidification process of sand castings is mainly predicted by using the shrinkage porosity criterion. There are many factors affecting the shrinkage porosity, such as the speed of solidification process, alloy composition or section size. At present, foundry workers mainly use niyama criterion to predict shrinkage porosity. The expression of the criterion is:
Where R is the cooling rate and G is the local temperature gradient of the identified area; Cniyama is the critical value. Cniyama is a quantitative stiffness. Because the critical value of niyama criterion is relatively fixed, this criterion is simple, easy to use and widely used. The post-processing program of the software is used to display the position of shrinkage cavity and porosity. The simulation results are shown in the figure.
The simulation diagram based on shrinkage is selected, in which the size and position of shrinkage are represented by different colors. On the reference color bar on the left in the figure, the dark purple at the bottom indicates that there is basically no shrinkage, while the dark red at the top indicates that there are a large number of shrinkage cavities and shrinkage. It can be seen from the figure that the shrinkage of blade sand casting is mainly concentrated at the riser, while there is little shrinkage of blade sand casting body, which shows that the shrinkage cavity and shrinkage casting defects of blade sand casting are mainly concentrated at the riser, indicating the rationality of sand casting process.