The main problem in the manufacture of ductile iron: shrinkage shrinkage

- Nov 08, 2019-

Due to its paste-like solidification characteristics, ductile irons often produce defects such as shrinkage cavities and shrinkage due to poor shrinkage. In order to predict these defects before casting production, the casting process was carried out at home and abroad. Numerical analogy. The numerical analogy of the casting process is based on the numerical analogy technique, which is analogous to the actual casting formation process in the virtual environment of the computer, including the filling process of the metal liquid, the cooling solidification process, the stress formation process, and the degree of influence of the main elements in the molding process. Organization, performance, and possible defects provide a basis for optimizing processes to reduce waste.

In 1962, Forsund of Denmark first adopted the solidification process of analog castings of electronic computers. Since then, the United States, Britain, Germany, Japan, France and so on have carried out research in this area. In the late 1970s, Dalian University of Technology and Shenyang Foundry Research Institute took the lead in conducting research on this technology in China, and published research reports in 1980 (Guo Keren et al., Digital Analogy of Solidification Process of Large Castings, Dalian Institute of Technology Journal, 1980 (2) 1-16; Shenyang Foundry Research Institute, casting solidification thermal field electronic computer analogy, foundry, 1980 (1) 14-22, and since then invested a lot of manpower in China's colleges and universities to carry out this research.

During the "Sixth Five-Year Plan" and "Seventh Five-Year Plan" period, there are research projects in the middle of the national key projects. The "sixth five-year" project is "large-scale steel casting solidification control" and the "seven-five" project is "large-scale casting". "Steel casting technology CAD", the organization of production, learning, research and joint research, greatly promoted the development of this technology in China, Tsinghua University, Huazhong University of Science and Technology have been able to provide FT-Star and Huazhu CAE-Inte 4.0 commodity chemistry The software was applied in units such as Sanming Heavy Machinery Co., Ltd. and achieved good results.

The computer numerical analogy consists of three parts: pre-processing, intermediate calculation and post-processing, including the establishment of geometric model, grid division, determination of solution conditions (initial conditions and boundary conditions), numerical calculation, processing of calculation results and graphical display. The basic methods of numerical analogy used are mainly finite difference method, finite element method and boundary element method.

(1) Numerical analogy of the solidification process, mainly for heat transfer analysis in the casting process. Including the selection of numerical calculation methods, latent heat treatment, shrinkage shrinkage prediction, and heat transfer problems in castings and molds.

(2) The numerical analogy of the flow field involves the transfer of momentum, energy and mass, which is difficult. The numerical solution techniques used are MAC method, SAMC method, SOLA-AOF method and SOLA-MAC method.

(3) Casting stress analogy, this research is carried out later, mainly in the elastoplastic state stress division, including Heyn model, elastoplastic model, Perzyna model, unified internal variable model.

(4) Organizational analogy, still in its infancy. Divided into a giant, meso and microscopic analogy. Can calculate the number of nucleation, analyze the type of primary crystal, dendritic growth rate, analog tissue transformation, and predict mechanical properties. There are deterministic models, such as Monte, Cellular, Automaton and other statistical methods, phase field models.

Computers and their applications are rapidly developing technology fields. Casting is one of the important industrial fields and should be strengthened. Research and development of computer applications in the field of foundry research and production, completely change the past "blinking type, closed eye pouring" state, computer applications will also promote the application and development of ductile iron.