Pretreatment of lost foam casting simulation based on ProCAST

Lost foam casting is a special gravity casting. Because of the existence of foam solid shape in the cavity, it is very different from the traditional cavity casting. Therefore, when using ProCAST to simulate lost foam casting, the setting of basic parameters is roughly the same as that of sand casting, but there are some special settings. The workflow of the pre-processing module is shown in Figure 1:

1) Geometric model:

Lost foam casting geometry should contain at least three components: the empty part of the gating system, the foam filled “cavity” and the dry sand mold, as shown in Figure 2.

2) Material settings:

The hollow gating system should be equipped with liquid metal material, gray iron, set to “casting”, empty = yes; “Cavity” material is set to “foam”, empty = no; Breathable sand mold is selected for dry sand (the specific setting is shown in Figure 3). The parameters such as thermal conductivity, density, specific heat and latent heat of combustion should be defined for lost foam casting cast iron and foam materials.

3) Interface definition:

The interface type between “casting” and “foam” is defined as “equiv”, that is, there is a continuous system between them, which can transfer continuous temperature field and flow field. The interface type between “casting” and “mold”, “foam” and “mold” is defined as “coin”. The specific setting method is shown in Figure 4:

4) Boundary conditions:

In addition to the usual thermal boundary conditions (other than cooling the mold) and inlet temperature, two pressure boundaries need to be added. One is added to the entire surface of the top of the sprue, and the other is used for the outside of the mold. The former is slightly higher than the latter, and the difference between the two is the negative pressure value. If the lost foam casting is symmetrical, in order to simplify the calculation, we often use only 1 / 2 or 1 / 4 of the model for calculation. At this time, we need to set the “symmetry” of the symmetry plane. Figure 5 illustrates the method of setting boundary conditions:

5) Operating parameters:

Using ProCAST to simulate the mold filling and solidification process and predict the defects of lost foam casting, it is necessary to set the operating parameters. The setting of thermal and flow parameters has a decisive impact on the simulation results of lost foam casting, especially the filling parameters, including whether there is gas influence and ambient pressure in the analysis process. See Fig. 6 and Fig. 7 for the specific setting; General parameters mainly include time step setting (20000 steps), output frequency (0.01), calculation stop condition: lost foam casting is cooled to 25 โ„ƒ, etc.

6) Other operating parameters:

The expansion coefficient of graphite is 0.5 according to the actual expansion effect of the trial production process; The heat balance calculation parameters, radiation operation parameters, turbulent operation parameters and stress operation parameters all maintain the default settings of the system.