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The application and development of CAD in casting process

casting process design is the core technology of casting production. Casting production is a process in which materials are transformed into "solid liquid solid" and formed at one time to complete product production. The particularity of material forming through the change of physical state has brought great difficulties to the casting process design, resulting in many problems in the casting process design, such as long cycle from design to production, many times of modification, lack of scientific design and so on. The rapid development of computer makes it possible to solve these problems that have hindered the development of foundry production for a long time

1 casting process cad

with the rapid development of computer technology, computers are more and more widely used in casting. In the early 1960s, forsund of Denmark used the finite difference approximation method proposed by dusinberre et al. In engineering application for the first time in the heat transfer calculation of casting solidification process, and began the simulation of casting solidification process. Since then, Marrone of Michigan University in the United States and Shigeo Dazhong of Japan have started the simulation of solidification process and made remarkable progress. At the Symposium on "computer simulation of solidification process" held at the 50th International Casting annual conference, the application of numerical simulation of casting solidification process in the study of microstructure and casting properties was discussed in depth, and a series of relations based on solidification process simulation were summarized. It is envisaged that these relations will be used to organically link geometric modulus, solidification parameters, alloy properties and microstructure parameters, The concept of casting process CAD is put forward. The research on Numerical Simulation of casting solidification has been carried out in China since 1978. The research over the past ten years has formed the characteristics of the research on Solidification Simulation Technology in China

the development of casting solidification numerical simulation technology can be divided into three stages: ① basic research stage, focusing on calculation simulation; ② In the prediction research stage, the proposed process scheme is checked to predict the quality, and the scheme is modified through simulated pouring; ③ Optimize process design, including calculation simulation, geometric simulation and database, and combine them organically. Sometimes these three stages are called casting process CAD, sometimes referred to as the third stage. At present, as far as foreign countries are concerned, casting process CAD is in the third stage. Therefore, in the practical research, the casting process CAD should include four parts: numerical simulation of solidification process (thermal field simulation), numerical simulation of mold filling process (flow field simulation), numerical simulation of thermal stress and residual thermal stress (stress field simulation) and microscopic simulation (microstructure simulation)

2 current situation and application of casting process CAD

2.1 current situation of casting process CAD

at present, the research on casting process CAD at home and abroad has reached a considerable level and has gradually entered the practical stage. This is mainly reflected in the following three aspects

(1) preprocessing

establish a solid model (as shown in Figure 1) according to the structure and shape of the actual object, and automatically divide it into polyhedral units (as shown in Figure 2, the enterprise banner: RMB 4000/piece; the exhibition of the negotiation table: RMB 6000 (the enterprise's own x-booth publicity materials). Generally speaking, for the castings with simple shape, the two-dimensional method is usually used to approximate the numerical simulation to obtain more accurate results. For castings with complex structure, 1 Manual clamping is mainly used on single arm and double arm models, and three-dimensional simulation calculation is required to meet the accuracy requirements

Figure 1 solid model

(2) central processing

central processing is the core of numerical simulation. Through numerical simulation calculation method, the thermal balance equation can be analyzed and the shrinkage cavity and porosity can be predicted. At the same time, the filling process can also be simulated by solving Navier Stokes equation

Figure 2 two dimensional lattice

(3) post processing

post processing is to dynamically represent the calculated results through color graphics or images after analysis. For example, the temperature time dynamic curve of a certain section or point of the casting is displayed in two-dimensional mode (as shown in Figure 3), and the temperature change of the casting, the formation of shrinkage cavity and porosity, or the stress field distribution of the casting are displayed in three-dimensional mode

Fig. 3 Simulation of temperature field

because many current software have strong pre and post processing function for applying force to the measured spring, through pre central post processing, the three-dimensional 1 of the casting can be continuously completed, which is an excellent control function for modeling and lattice automatic dissection; Under the given initial and boundary conditions, carry out numerical simulation calculation, and then display the three-dimensional temperature field, stress field and even solid rate field of the casting according to the user's requirements, so that the designer can quickly obtain the quality of the casting produced under this process condition, and modify the process through the simulation results to meet the requirements of the casting quality

2.2 application of casting process CAD since the 1980s, numerical simulation technology has developed rapidly. On the one hand, new mathematical models and various criterions are constantly established in the research process, which makes the simulation results approximate to the measured results. On the other hand, due to the new achievements made in the basic theory of solidification, it is possible to organically combine the macro simulation calculation with the micro crystallization process, and breakthrough achievements have also been made. As for the application of casting process CAD, there are mainly the following aspects

(1) numerical simulation of casting solidification process

the numerical simulation of casting solidification process uses a series of criteria to predict the location, size and time of shrinkage porosity during solidification by calculating the temperature gradient of temperature field and solidification time of solid rate. Through this prediction, the casting process plan can be modified, and then verified by numerical simulation. Figure 4 shows the simulated section temperature distribution. Fig. 5 shows the parts where shrinkage cavity and porosity may occur in the casting predicted by solidification numerical simulation, and the predicted results of this simulation are completely consistent with the measured results. At the same time, the relationship between the inner gate and the casting was determined by the solidification numerical simulation method


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