The practical and reliable criterion of shrinkage porosity and shrinkage cavity defect is the most key content for the accurate prediction of shrinkage porosity and shrinkage cavity defect. Through the above analysis, the main defect prediction criteria at present. Recent studies have shown that there are many factors affecting the formation of shrinkage defects, and the temperature field is no longer the only factor to be considered. At present, most studies are looking for a new and effective criterion model to accurately predict the occurrence of defects. Carison of Iowa University in the United States introduced a multiphase model to predict the pressure, flow, formation and growth of shrinkage defects of metal melt in the solidification process of steel castings. They used Darcy’s law to deal with the flow in the solid / liquid paste region, while the whole liquid phase was treated as Stokes flow, and then combined the momentum equation with the continuity equation considering solid phase, liquid phase and gas phase. The control equation of mass transfer considered the macro segregation of gas caused by flow. They have developed the multiphase model into a general casting simulation program.
For the die casting process, Dazhong Yixiong and others in Japan put forward a new numerical simulation method for metal mold filling process and predicting shrinkage defects. This method considers the back pressure of the cavity, coupling the cavity gas pressure and metal melt pressure to calculate the flow field of liquid metal. The simulation results show that the filling process and the last filling part are affected by the back pressure. In the commercial software ProCAST, American software company has developed a model based on finite element to simulate the fraction and distribution of micro shrinkage defects in multicomponent alloy castings. The model numerically calculates the change of pressure and the transmission of gaseous solutes such as hydrogen and nitrogen during solidification, and considers that the solubility of these elements is a function of temperature and alloy composition, so as to accurately predict the location and distribution of micro shrinkage defects Volume fraction and hole size. They believe that the transport calculation of gas forming elements is very important for the accuracy of shrinkage defect prediction. Emadi et al. Of Canada proposed a mathematical model to analyze the mechanism of increasing solidification shrinkage defects in the alloy after modification. The analysis shows that the decrease of a12si hydrogen solid solubility, eutectic temperature and surface tension after the addition of SR is the main reason for the increase of shrinkage defects in the modified alloy.
The introduction of the above aspects undoubtedly points out the new development direction of defect prediction, that is, comprehensively considering various factors of defect formation, seeking a new faster and more accurate calculation model and implementing accurate prediction.