- Geometric modeling
The heat transfer between the liquid metal and the pattern occurs during the filling process
Where, ρ P is the density of foam pattern. ρ L is the density of liquid metal; λ L is the thermal conductivity of liquid metal; CL is the specific heat capacity of liquid metal; L is the latent heat of crystallization; Δ FS is the solid phase rate of foam pattern.
Figure 1 is a three-dimensional view of the crawler shoes produced by a company. The outline dimension of the part is 1500mm × １５０ｍｍ × Its minimum wall thickness is 13mm, the maximum wall thickness is 35mm, the volume is about 0.04m3, and the mass is about 310kg. The wall thickness of the parts is uneven, the volume of the internal cavity is large and the structure is complex (see Figure 2). It is required that the structure of the parts is complete, the surface has no defects that affect the strength, and the internal structure is compact without shrinkage cavity, shrinkage porosity, cracks and other defects.
The three-dimensional solid modeling of the casting was carried out by using SolidWorks software. According to the structural characteristics of the track shoe parts, the lost foam casting process scheme was designed. Four open risers were used for feeding and middle pouring. Two open risers with a diameter of 160mm were placed in the area with the maximum wall thickness of 35mm in the middle, The diameter of the sprue is 50 mm, the height is 340 mm, the diameter of the large end face of the sprue is 120 mm, and the cross-section size of the runner is 50 mm × 40mm, 740mm long, and the section size of the ingate is 40mm × The three-dimensional model and mesh division are shown in Figure 3.
- Finite element mesh generation
The 3D solid file generated by SolidWorks is saved as x-t format. The x-t format file is imported into visual mesh program by running ProCAST software. The 3D finite element mesh file is generated after checking and repairing by meshcast module. The length of mesh element of casting and gating system is 10 mm, the length of mesh element of shell and sand mold is 40 mm, the total number of mesh is 1498610, and the total number of nodes is 96830. The three-dimensional finite element mesh division of casting and sand mold is shown in Fig. 3B.
- Boundary condition and parameter setting
The casting grade is zg30simnmov steel, and the refractory coating is made of stainless steel
Zircon sand II, olivine sand; The type of indirect contact between casting and refractory coating is conic, and the heat transfer coefficient of interface is 750W / (M2 ·℃). The type of indirect contact between refractory coating and sand mold is conic, and the heat transfer coefficient of interface is 300W / (M2 ·℃); The stress type of sand mold is rigid body. The ProCAST material library provides complete thermophysical parameters of zg30simnmov, as shown in Figure 4. The solidus temperature of zg30simnmov steel is 1393 ℃, and the liquidus temperature is 1493 ℃.
In the process of solidification, the thermophysical parameters of materials will change with the change of temperature, which is reflected in the numerical simulation equation. Each time step may contain multiple physical property values. Therefore, in the process of numerical simulation, it is difficult to ensure the accuracy of simulation results without an accurate thermophysical parameter.