Designing CAD-models for calculating thermal stresses
The paper describes the technique of designing computer (CAD) casting models with an internal adjustable cellular structure of the Wigner-Seitz type and the sequence of their preparation for the numerical calculation of the stress state in the system of the casting model-the ceramic shell mold. The advantage of this type of cell in front of the standard square and triangular cellular structures is the appearance of moments in the nodes of the cell design, which significantly reduces the expansion of the design of the molding model during heating. To build a CAD-model, the AutoDesk Inventor Professional software is used. During the design, to create a unit cell Wigner-Seitz, as the cell design used beam cylindrical and semi cylindrical elements. The result of the construction is a sample of a molding model system - a ceramic shell mold. To carry out numerical calculation of stresses in the molding model - ceramic shell mold system, the software complex Ansys Workbench 16.0 is used for heating. The task of the calculation is to determine the maximum stresses in the ceramic shell mold as the temperature rises at a certain rate. To solve the problem, a finite element grid with the required size is created in the design sample. After construction of the grid and its optimization, boundary conditions are set. In this case, the boundary conditions are the thermal load, the standard earth gravity, the restriction of displacement. To increase the calculation speed, the geometry is simplified as much as possible and represents the segment of the calculated sample of the molding model system - ceramic shell mold. The analysis of the calculated data obtained can be represented as the dependence of the stresses in the ceramic shell mold on the heating rate. This method of calculation allows predicting the destruction of the ceramic shell when burning the material of the molding model and adjusting the geometric parameters of the internal controlled cellular structure to reduce the shape rejection and increase the yield of suitable metal castings.