Simple model for sand casting mechanisms

The low thermal conductivity of a sand mold can result in longer casting time and higher temperature gradient, and thus a denser mesh in the mold than in the metal is usually required for numerical heat transfer analysis. Most computing effort is spent on the mold solution that is of less interest. If the solidification problem of a casting process can be solved without explicitly handling the heat transfer in the mold, the computing cost can be reduced substantially. In this paper, a mathematical boundary curvature method is set up to replace the effect of the sand mold by an equivalent coefficient of heat transfer. Two data bases of the coefficient versus time-dependent curvature are built for both considering the contact resistance (between the sand mold and the metal) and not. The finite difference method is used to solve the heat transfer problems. The source term method is employed to deal with the nonlinear term of latent heat. A rectangle casting was used to test the model. As compared to the result of having the mold enmeshed, the proposed model saves the computing time up to 84%. It was also found that the flow field induced by natural convection has little effect on the temperature distribution of liquid metal. To further testify this model, the experimental result of an L-shape casting was used to compare with the computing ones for two sets of the equivalent heat transfer coefficient. The computing results are similar to those of the experiment. It is shown that the one with contact resistance has the better result than the other one without the resistance. Finally, the method is modified to handle the casting of irregular shape and verified by a wrench-shape casting problem.