Sand mold casting is a process of pouring high-temperature liquid metal into the mold cavity, cooling and solidification into rough parts. Sand mold casting industry plays an important role in the national manufacturing industry. It is an important industry related to the national economic development. It is widely used in aerospace, transportation, shipbuilding, chemical industry, construction, textile and other fields. In the equipment manufacturing industry, the proportion of sand mold castings in a single mechanical forming system is very high. The proportion of hydraulic parts and pump machinery is 50% – 60%, the proportion of internal combustion engine is about 80%, and the proportion of tractor is 65% – 80%. The important parts of automobile engine are basically formed by sand mold casting. In addition, a large number of heavy castings are also used in key equipment such as metallurgy, mining, power station and national defense. Therefore, the quality of sand mold castings will directly affect the quality and performance of the whole machine.
On the premise of ensuring economy, the requirements for the overall quality and performance of sand mold casting products are increasing day by day. The traditional sand mold casting molding process is mostly designed by trial and error method and experience method. For precision castings and heavy new product sand mold castings with complex structure and shape, it is quite difficult to develop them by using the traditional molding process design, It needs continuous actual production and trial production, which not only leads to long R & D cycle, large economic consumption, but also can not guarantee product quality.
In recent years, the increasingly mature computer technology (casting CAE, computer aided engineering) provides more convenient conditions for the process design of sand mold castings. Casting CAE is a computer simulation technology, which combines heat and mass transfer, numerical simulation and sand mold casting technology, and uses computer dynamic graphics processing technology to conduct qualitative and quantitative analysis by using physical model and mathematical model, so that engineers have the opportunity to see the internal situation of sand mold castings, It provides a favorable basis for optimizing the process parameters of sand mold casting and deepens people’s understanding of the essence of solidification phenomenon of sand mold casting. The purpose of casting CAE is to use the simulation of mold filling and solidification to predict the changes of casting temperature field, stress field, strain, shrinkage cavity and porosity, and then optimize the sand mold casting process. Therefore, in the actual production, the casting CAE technology is fully applied to simulate the mold filling and solidification process of casting, predict the possible defects (cracks, shrinkage porosity and shrinkage cavity) in the casting production process and the mechanical properties of sand mold castings, and then optimize the process parameters on the basis of the results of numerical simulation analysis, so as to ensure the quality of sand mold castings, It also greatly shortens the R & D cycle and saves economic costs. Therefore, expanding the application scope of casting CAE has become the development trend of sand mold casting industry.
In the numerical simulation of sand mold casting molding, it is difficult to calculate the accurate filling and solidification process of sand mold casting and accurately obtain the liquid metal flow field, temperature field and stress field of sand mold casting. We must have accurate initial conditions, boundary conditions and thermophysical parameters of materials. In these conditions, the initial conditions and material thermophysical parameters are relatively easy to obtain, while the interface heat transfer coefficient (IHTC) in the boundary conditions is difficult to obtain, and there are many influencing factors, such as mold type, pouring temperature, pressure, wall thickness, etc. during the solidification of sand mold castings, the metal liquid and sand mold castings in the solidified part will have serious volume shrinkage or linear shrinkage, which will make the mold There is an interface gap between the core and the sand mold casting. The generation of interfacial gap and its continuous expansion during the subsequent cooling of sand mold castings make a significant turning change in the interfacial heat transfer rate. Because the contact conditions between liquid metal and core and the change of gap between sand mold casting and core during subsequent cooling are seriously limited by casting structure, sand mold casting material, core material and other factors, it is almost impossible to obtain the interface heat transfer coefficient by simple calculation or experimental measurement.
Using effective mathematical model and experimental measurement to obtain more accurate interface heat transfer coefficient is an important research direction to improve the accuracy of sand mold casting simulation. Therefore, the key problem that researchers need to deal with is how to obtain the objective and accurate interface heat transfer coefficient.