Pre processing setup of rapid investment casting simulation

UG software is used to save the designed initial gating system file in x-t format and import it into the pre-processing module of Pro cast2016 view mesh. In order to ensure that the calculation results can be as accurate as possible and the simulation calculation time can be reduced as much as possible, different steps are used in the mesh generation, in which the gating system is 5mm and the casting is 3mm. After the common surface is repaired, the surface mesh generation and volume mesh generation are carried out, as shown in Figure 1 (a). After meshing and repairing, the shell is added by using the shelling command. The shell thickness and mesh size are set to 10 mm. After meshing and repairing, the final casting shell is obtained, as shown in Figure 1 (b). The number of meshes after adding the shell to the casting is: face mesh 113862, volume mesh 1220116.

(a) Casting body grid (b) Shell mesh

The processed parts are imported into the cast module to set the boundary conditions, including the following. Gravity vector setting: the diffuser adopts gravity sand casting, so the gravity direction is set down along the gate. As shown in Figure 2.

Related material setting: 304 stainless steel is used for casting, and high strength and high temperature resistant silica sol process is used for shell, that is, chemically bonded shell molding sand mold mode is selected for shell. Among them, the liquidus temperature of 304 stainless steel is 1454 ℃. According to the above parameters and casting experience, in investment casting, the phenomenon of insufficient pouring often occurs when the pouring temperature is too low, but the pouring temperature can not be too high. Too high temperature will make the grain coarsening and reduce the mechanical properties of the casting. For the complex thin-walled parts, the upper limit of pouring temperature is 1600 ℃. At this temperature, pouring shell is not only beneficial to obtain high precision, but also can reduce the tendency of hot cracking of thin-walled parts and complex parts. The selection of preheat temperature of shell before pouring is closely related to the quality of casting. Too high preheat temperature of shell will lead to slow cooling of molten steel, coarse grain, serious decarburization, and decline of mechanical properties of casting. Combined with the actual casting process and considering the shell preparation process, the preheating temperature of shell is 1115 ℃. Finally, the corresponding shell and casting alloy were selected in the software, and the preheating temperature and pouring temperature were set.

Setting of heat exchange interface: coinc is selected as the contact surface between casting and shell. Considering that the heat exchange coefficient between metal and sand is generally 600 ~ 1000W / (M2 · K), H = 750W / (M2 · K) is selected in this paper.

Process conditions setting: select the shell cooling type as air cooling (20 ℃), specifically adding heat condition and boundary condition as air cooling; add the pouring flow inlet condition and set the corresponding pouring parameters, in which the pouring speed is set as 2kg / s and the pouring temperature is 1600 ℃. Finally, the simulation parameters are set, and the casting process is gravity shell casting. The default stop temperature in the program is 1218 ℃, which is consistent with the alloy solid temperature, and other parameters are selected by default.