In order to predict and confirm the location, size and range of shrinkage defects in the pouring and feeding system in advance, based on the understanding of the metal contour wall thickness and casting cavity temperature, the critical pressure and critical solid rate of the defect occurrence were set, and the influence of linear shrinkage, volume shrinkage, liquid metal fluidity and gas precipitation amount were comprehensively considered, On the basis of heat energy conservation, mass conservation and kinetic energy conservation, the mathematical model equation of solidification process is as follows:
Where:
T — temperature (℃);
T — time (s);
C — specific heat capacity (J / kg. K);
P — Density (kg / DM;
λ – heat transfer coefficient;
x. Y, Z — heat energy propagates in three directions;
W — potential heat energy released by casting solidification (J / kg).
The numerical calculation method can be used to predict the location of casting defects, so it is widely used in practical production. Through the theoretical model, the whole casting model and casting blank are divided into several small elements, so that the seemingly complex change process in the overall structure is decomposed into simple variables of each small element, and the change process of the small element is controlled by the node of the element, and then the node temperature of each element is calculated by using the mathematical formula. In the process of numerical simulation, it is also necessary to change the conditions of potential heat release phenomenon and change the whole calculation process to simulate the heat transfer process. The computer is used to deal with the phenomenon of metal solidification, so as to achieve the effect of numerical simulation.