Setting of initial and boundary conditions of frame sand casting process

The solidification simulation analysis of temperature field adopts “instantaneous filling”, that is, the influence of the pouring and filling process of sand castings on the temperature field of sand castings is ignored in the simulation process, so the initial temperature of sand castings is set to 1580 ℃; Sand mold and cold iron need to be preheated by hot air before pouring, and their initial temperature is set to 150 ℃.

In sand casting, the interface heat transfer coefficient between casting and mold has a great influence on the accuracy of simulation results. When dealing with the value of interface heat transfer coefficient, rrocast software regards the consistent nodes as a set of nodes on the contact surface in meshing, while in calculating and determining the heat transfer coefficient of the contact surface, it is regarded as two sets of nodes corresponding to each other on the contact surface. Each pair of nodes represent different temperatures at the same position, and then the value of interface heat transfer coefficient can be determined. According to the above theoretical methods, select the typical value of interface heat transfer coefficient, set the interface heat transfer coefficient between cold iron and sand mold as 800W / (M2 · K), and set the interface heat transfer coefficient between casting and sand mold as 500W / (M2 · K).

The application of boundary conditions in stress analysis mainly includes two aspects: 1) constraints imposed to prevent rigid body displacement of castings, which are generally imposed on the bottom and symmetry plane; 2) Consider the constraints imposed by the interaction between the casting and the mold during solidification. In the simulation, X-direction, y-direction and Z-direction displacement constraints are mainly applied on the bottom and symmetry plane of the sand mold casting frame.

When calculating the thermal stress coupling of sand mold casting frame, it is necessary to set relevant settings in the operating parameters. Firstly, the maximum number of calculation steps, the final cooling temperature and the maximum time step are selected. Due to the long solidification cooling time of the sand casting frame, it usually takes 10-15 days to cool to the temperature when beating the box. A lot of calculation is required in the simulation analysis. The final cooling temperature is 600 ℃ and the maximum time step is 50s. In the setting, the temperature field calculation and stress field calculation are selected at the same time, and the calculation frequency and result saving frequency of temperature and stress data are set. So far, all pre-processing settings are completed, and the simulation operation is started after saving.

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