Pretreatment setting of mold filling and solidification simulation in sand casting

Physical and chemical changes such as oxidation, heat transfer and heat loss will occur in the filling process of molten metal. Ensuring the correct filling process can effectively avoid casting defects such as insufficient pouring, cold shut and slag inclusion. ProCAST is a casting process simulation software based on finite element numerical calculation, which can realize the simulation calculation of casting filling, solidification and cooling process, and provide prediction of distortion, residual stress and casting defects. The software is suitable for sand casting, investment casting, lost foam casting and so on.

Firstly, it is necessary to import the CAD model of casting and mold. In a single casting technology, the mold is not modeled, so it is necessary to set the virtual sand box size, while the composite mold needs to assemble the imported mold module. Secondly, the surface mesh surface grid and volume grid are drawn for the casting and mold model. After the inspection and repair of the surface mesh and volume grid, the setting of casting simulation parameters can be completed in the visual cast module, including metal thermophysical parameters, interface heat transfer coefficient, boundary conditions, initial conditions and operation parameters. Finally, the pouring data operation is started, and the simulation results are viewed and analyzed in the visual viewer module.

Taking the composite mold pouring simulation of the process optimization design scheme as an example, the surface grid and volume grid division of the composite mold are shown in Figure 1. Among them, grids of different colors represent different mold modules. For example, the red part represents mold 2# and the blue part represents mold 1# and mold 4# respectively. The assembly surface of the mold module is also displayed as grid planes of different colors.

Figure 2 shows a summary of casting simulation parameters. Among them, the cooling mode of setting the sand box is air cooling (FilmCo = 10, t = 20 ℃), and the molding materials of the mold module are set according to the above process setting scheme, which are green molding sand and self hardening resin sand respectively. Set the initial temperature of the mold as 25 ℃, the pouring temperature as 1380 ℃, and the metal brand as en-gjl-200.

The end cover of the motor is poured and verified by ProCAST software. The simulation ends when the liquid metal reaches the solidus temperature. Fig. 3 shows the schematic diagram of the process of 5.3% to 98% of the mold filling of the casting. It can be seen from the diagram that the filling of the sprue and feeding riser is incomplete due to the shrinkage of liquid metal during the solidification process of the casting, and some shrinkage defects appear on the transverse sprue, but this part will be removed eventually, which will not affect the quality of the casting body.

Fig. 4 shows the pouring quality verification results when the critical pore solid fraction is set to 0.35. It can be obtained that the process optimization design scheme of motor end cover casting and composite mold is qualified and can be used in actual production.

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