Numerical simulation and result analysis of solidification process of lost foam castings

The ultimate purpose of numerical simulation of lost foam casting is to analyze the casting solidification process and optimize the lost foam casting process, so as to predict and control the quality of lost foam casting. Figure 1 shows the solidification state and solidification percentage of turbine rear exhaust nozzle at different times.

The formation mechanism and location of shrinkage cavity and porosity of exhaust pipe after turbine can be reflected in the temperature field distribution during solidification, which can accurately predict the quality of lost foam castings. Figure 1 (a ~ d) shows the solidification state and solidification percentage when step = 4800, step = 4820, step = 4870 and step = 5780.

By analyzing the solidification process of lost foam casting of turbine rear exhaust pipe, it can be seen that:

(1) It can be seen from the solidification percentage in Figure 2 that the solidification speed is relatively fast at the beginning, and then the solidification speed becomes slower and slower.

(2) The solidification process of lost foam casting is longer than that of sand casting.

(3) On the whole, as shown in Fig. 2, the longitudinal temperature distribution of the lost foam casting during the whole solidification process is basically that the lower temperature is low and the upper temperature is high, but the solidification is slow at the corner connecting the lower elbow and the longitudinal end face, so shrinkage defects may appear at this part. In the horizontal direction, the temperature of the central part is high and the edge temperature is low. The temperature of the central part is mainly the temperature of the gating system, which can be ignored.

(4) As can be seen from Fig. 2, since the exhaust connecting pipe behind the turbine is a thin-walled curved lost foam casting, and the lost foam casting gating system is stepped pouring, the bottom and top of the lost foam casting solidify first relative to other parts, so it is easy to be unable to feed at the top and bottom of the lost foam casting, and it is easy to form an isolated liquid phase area in the middle, The probability of shrinkage cavity and porosity of lost foam castings will also be very large.

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