Numerical simulation and result analysis of rapid investment casting

ProCAST simulation software was used to simulate the gating system, and the temperature field changes and casting defects during filling and solidification were analyzed. The simulation results of diffuser investment casting are shown in Figure 1. Figure 1 shows the distribution of flow field and temperature field in the pouring process at different times. It can be seen from the figure that the liquid metal is filled along the sprue and runner respectively, and then the blade is filled along the diffuser from bottom to top. It is not difficult to find that the filling of the upper part of the diffuser blades is completed in t = 4.8s, and the liquid metal rises smoothly in the process, without turbulence and splash. Then start to fill the diffuser side blades. When t = 9.1, the filling of the side blades is completed. However, according to Fig. 1 (b), when t = 6.9s, the alloy temperature at the outer edge of the upper 8 blades is below the liquid phase. Therefore, it can be considered to increase the pouring speed properly in the actual pouring process. When t = 14.1s, the casting basically completed pouring, and the casting was in the liquid shrinkage stage. At this time, the shrinkage occurred in the liquid condition, which mainly showed that the liquid metal in the gate cup decreased. When t = 14.15s, the casting begins to solidify. At this time, the alloy temperature first drops below the liquid temperature at most of the upper blade and the upper sharp corner of the side blade.

Figure 2 shows the change of solidification rate of casting and gating system after mold filling. The solidification sequence is that the impeller is gradually solidified from the outside to the inside, the gating system is solidified from the bottom to the top, and finally the sprue is solidified. Because the diffuser blade is thin, the solidification is completed first. It can be seen from Fig. 2 (a) that the outer blade of diffuser impeller begins to solidify first, and the blade basically completes solidification when t = 266.7s. T = 816.7s, the matrix connected with the blade began to solidify. When t = 2086.7s in Fig. 2 (d), the diffuser basically solidified. Finally, the sprue and the gate cup are solidified to realize the sequential solidification, which plays a role in feeding the casting.

The solidification time of the diffuser is shown in Fig. 3. The blade part of the casting solidifies first, and then the casting solidifies gradually from the outside to the inside. From most of the initial thickness of the part to the sprue of the gating system, the solidification process realizes the sequential solidification, and the casting can be fully fed, so as to avoid defects such as insufficient pouring and shrinkage porosity.

Figure 4 shows the distribution of shrinkage porosity, in which figure 4 (1) and Figure 4 (2) are the cross sections of the upper and lower blades respectively. It is not difficult to find that the shrinkage is mainly concentrated in the gating system, and there is no shrinkage defect in different parts of the blade. Because the gating system is removed after casting, the defects in gating system will not affect the quality of casting. The rationality of the gating system is proved.

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