Numerical simulation technology of sand casting

Numerical simulation of sand casting process is an interdisciplinary subject involving various disciplines such as information, materials, mechanics and computer. It is the frontier field of manufacturing science. With the development of computer simulation technology, the combination of computer simulation technology and sand casting process has become a trend.

The numerical simulation of sand casting process can predict the defects of sand casting, such as shrinkage cavity, porosity, crack, pore and insufficient pouring, and visually display its position and size through images, so as to provide reference for technicians. Making a reasonable process plan before production can reduce the waste caused by repeated trial production. By observing the temperature field, technicians can analyze defects such as pores and insufficient pouring; By observing the flow field distribution during liquid metal filling, we can analyze whether the design of gating system is reasonable or not; Through the analysis of solidification process, defects such as shrinkage cavity, shrinkage porosity, stress concentration and crack can be predicted. Through the analysis of mold filling and solidification process, we can find the optimal sand casting process parameters and the specific content and process of sand casting numerical simulation process.

At present, experts and scholars mainly study the filling and solidification process in the process of sand casting, and have made great progress in aging, engineering practicability and the establishment of mathematical model. Numerical simulation of sand casting process is one of the frontier fields of the combination of materials science and manufacturing industry, which involves many aspects, such as metalology, numerical calculation theory, hydrodynamics and solidification theory. The liquid metal flow in the mold filling process belongs to unsteady flow, and the flow field and temperature field are always changing. In this process, with various heat transfer phenomena, it is difficult to accurately determine the condition of the free surface at any time, and the heat transfer coefficient between the sand casting mold and the liquid metal is constantly changing; In addition, the latent heat of crystallization, the pressure of gas in the cavity and the jet conditions all have an impact on the filling process. Therefore, the corresponding simplification should be made when calculating the simulation of the filling process.

The numerical simulation of solidification process involves the simulation of macro temperature, flow field, stress and microstructure. By simulating the solidification process, the change of solid rate of sand casting with time is observed, so as to predict the location, size and shape of shrinkage cavity and shrinkage porosity defects; It can also predict the occurrence of cracks in the mold and make targeted improvements in the design of the mold, so as to improve the service life of the mold.

The main research directions and contents of sand casting simulation include the following aspects: (1) temperature field simulation, which uses the principle of heat transfer to predict defects through the change of temperature field; (2) Flow field simulation, based on hydrodynamics simulation of mold filling process, predict the defects such as air entrainment and insufficient pouring, and then optimize the pouring system; (3) Stress field simulation, using mechanical principles, such as elastic-plastic model, analyzes the stress distribution of sand castings and predicts cold crack, hot crack and other defects: (4) microstructure simulation, including macro and micro microstructure simulation. Based on the mathematical model, calculate the number of nucleation and the growth rate of dendrites.

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