SPH Modeling And Numerical Simulation In Foundry Filling Process

As the first stage of foundry process, filling process has a large influence on casting's quality. Many defects such as gas porosity, flow mark, oxide inclusion, cold shut and misrun are formed during filling process. As the filling process is invisible, using numerical simulation method to calculate and predict the filling process is very useful to not only ensure casting quality but also reduce the trial period and reduce production costs. At present, most simulation methods for the fluid filling process based on Eulerian grid, which are difficult to establish mesh for the casting. The methods also have many difficulties in free surface and interface capture because of artificial diffusion. Smooth particle hydrodynamics (SPH) method which possesses pure Lagrangian properties and non-grid characteristics has great advantages to treat these issues, so that it has good development prospects in filling process simulation. However, there is little study on the application of SPH in the casting process. Such specific issues of fluid filling process simulation require in-depth study. This dissertation aims at study the implementations and applications of SPH method in casting process. Therefore, the following aspects are carried out in this dissertation.The theory and calculation processes of SPH method are studied systematically. Conservation equations of fluid filling process are derived with SPH discrete form. The dealing of boundary conditions in fluid filling process is studied. Repulsive force type model is introduced into wall boundary condition. An inlet region method is proposed to establish inlet boundary condition. Consider the characteristics of fluid filling process, a particle classification search method is proposed based on link list to improve the solution efficiency. The SPH fluid filling simulation program is developed independently, and its effectiveness is proved by two-dimensional and three-dimensional verification model filling process calculation.Ability of the SPH calculation in the discontinuous point issue and particles'irregular distribution issue during filling process is studied. Some one-dimensional examples are calculated to investigate the decrease of the accuracy caused by discontinues vibration and inconsistency. The artificial viscosity method is introduced to the filling process calculation in order to reduce the unphysical vibration at discontinues points. Parameters in artificial viscosity model are investigated and suitable parameters for SPH filling calculation are given. The MLS correction method is introduced in the filling process calculation to strengthen the accuracy in inconsistency problems. Water filling experiment is established to examine the modified SPH filling program's ability in different filling properties. Moreover, the results are compared with the commercial casting simulation software—procast. All the experiments and results from Procast shows good agreement with the modified SPH filing program, which can proves the stability and reliability of the program applying in different filling properties.In order to apply the SPH program in the concrete cases, influence of gas in mould cavity on filling process is investigated as well. A FDM simplified back pressure condition method and SPH two phase coupled model are established respectively. Both of them are verified by water filling experiment. On the other hand, ghost fluid method is introduced into SPH to derive two phase flow conservation equations. The result shows that this method could avoid interface vibration in large density ratio and has good agreement with experimental result.Heat transfer equation is derived in the SPH discrete scheme, the latent heat is considered by the temperature recovery method to calculate thermal conduction of casting. A cooling process of a crankthrow shape part is calculated by FEM method and SPH method respectively, the results show that the heat transfer model established in this dissertation is correct.