The application of casting forming technology in foundry of China

Casting is a process of pouring high temperature liquid metal into mold cavity and cooling and solidification to form blank. Foundry industry plays an important role in the national manufacturing industry. It is an important industry related to the economic development of the country. It is widely used in aerospace, transportation, shipping, chemical industry, construction, textile and other fields. In the equipment manufacturing industry, the proportion of castings in a single mechanical forming system is very high. The proportion of hydraulic parts and pumps is 50% – 60%, the proportion of internal combustion engine is about 80%, and the proportion of tractors is 65% – 80%. The important parts of automobile engine are basically formed by casting. In addition, a large number of heavy castings are also used in metallurgy, minerals, power plants, national defense and other key equipment. Therefore, the quality of castings will directly affect the quality and performance of the whole machine. Under the premise of ensuring economy, the requirements for the overall quality and performance of casting products are increasing day by day. Most of the traditional casting forming processes are designed by trial and error method and experience method. For the precision castings with complex structure and shape and heavy new product castings, it is quite difficult to develop by traditional forming process design, which needs continuous actual production and trial production It not only leads to long R & D cycle, high 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 casting process design. Casting CAE It is a computer simulation technology, which combines heat and mass transfer, numerical simulation and casting technology, and uses computer dynamic graphics processing technology, physical model and mathematical model for qualitative and quantitative analysis, so that engineers have a chance to see the internal situation of castings, which provides a favorable basis for optimizing casting process parameters, and deepens people’s influence on casting solidification The understanding of the essence of fixation phenomenon. The purpose of casting CAE is to predict the change rule of temperature field, stress field, strain, shrinkage cavity and porosity of castings by using the simulation of filling and solidification, and then optimize the casting process. Therefore, casting CAE is widely used in practical production The technology simulates the filling and solidification process of the casting, predicts the possible defects (cracks, shrinkage porosity, shrinkage cavity) and the mechanical properties of the casting in the production process of the casting, and then optimizes the process parameters on the basis of the numerical simulation analysis results, which not only guarantees the quality of the casting, but also greatly shortens the R & D cycle and saves the economic cost. Therefore, it has become the development trend of foundry industry to expand the application of CAE.

In the numerical simulation of casting forming, it is very difficult to calculate the accurate filling and solidification process of the casting, and accurately obtain the liquid metal flow field, casting temperature field and stress field we need. We must have accurate initial conditions, boundary conditions and thermal physical parameters of the material. In these conditions, the initial condition and material thermal physical parameters are relatively easy to obtain, while the interface heat transfer coefficient (IHTC) in the boundary condition is very difficult to obtain, and there are many influencing factors, such as mold type, pouring temperature, pressure, wall thickness, etc. during casting solidification, the casting of liquid metal and solidification part will have serious body shrinkage or linear shrinkage, which makes the mold, core and casting There is interface gap between parts. The generation of the interface gap and its continuous expansion during the subsequent cooling of the casting make the interface heat transfer rate change significantly. Because the contact condition between the metal liquid and the core and the change of the gap between the casting and the core during the subsequent cooling are seriously limited by the casting structure, casting material, core material and other factors, it is almost impossible to obtain the interface heat transfer coefficient by simple calculation or test measurement. It is an important research direction to improve the accuracy of casting simulation by using effective mathematical model and experimental measurement to obtain more accurate interfacial heat transfer coefficient. Therefore, the key problem that researchers need to deal with is how to get an objective and accurate interface heat transfer coefficient.

The essence of casting CAE technology is to simulate the solidification process of castings with the help of computer technology, predict the possible casting defects in the casting process, and analyze the corresponding process parameters. The casting CAE technology can simulate both the macro temperature field and the micro structure, among which the macro physical field simulation is the calculation of the macro transmission phenomenon, including the simulation of the flow field when the liquid metal is filled and the temperature field during the solidification process. By using the mature commercial casting CAE software to simulate and analyze the macro physical field, it can effectively guide the formulation of the corresponding process. Compared with the macro simulation, the micro simulation is mainly to predict the changes of defects, microstructure and mechanical properties during the solidification process of castings. From the research content, the CAE technology can be divided into temperature field, flow field, stress field, microstructure and various coupling simulation.