Abstract: This article describes the CA precision casting process. The application of computer-aided engineering including three-dimensional CAD and numerical simulation of solidification process in the development of precision castings was highlighted. IDEAS can be easily 3D-designed or reverse-engineered to obtain a 3D model. Rapid prototyping can then be used to quickly obtain casting prototypes. ProCast's casting process can be simulated to optimize casting parameters and eliminate casting defects.
Keywords: CA precision casting computer aided engineering
1 Introduction:
Precision casting is a method of molding a casting using a soluble (melt) primary model. The biggest advantage of precision casting is the smooth surface and precise dimensions. The disadvantages are complex process, long production cycle, and many factors that affect the quality of castings. The material and process requirements are very strict in production [1]. In the production process, mold design and manufacturing take a long period of time. It may take a year or more to design and manufacture a complex thin-walled part. With the progress of the world's industry and the improvement of people's living standards, the product development cycle is getting shorter and shorter, and the design requires a short response time. In particular, when the structural design needs to be modified, the previous mold manufacturing costs and the manufacturing period are wasted. As a result, mold design and manufacturing have become the bottleneck of new product development. The development of computer-aided engineering has made the integration of traditional industries and new technologies possible. Three-dimensional CAD can free the design from the drawing board, greatly simplifying the designer's design process and reducing the chance of error. And with the rapid prototyping (RP) technology, especially the development of laser selective sintering process (SLS) [2, 3, 4], the three-dimensional model can be quickly transformed into a prototype required for precision casting through RP equipment, breaking the mold design. The bottleneck. In addition, in the traditional casting, the development of a new casting, the process of stereotypes through multiple tests, repeated exploration, and finally based on a variety of test results of the casting results, select the casting process that can meet the design requirements. Repeated trials cost a lot of manpower, material resources and financial resources. The numerical simulation of solidification process can guide the optimization of casting process parameters, predict the number and location of defects, and effectively improve the casting yield. CA precision casting technology is the application of computer-aided engineering to the precision casting process, combined with other advanced casting technologies, to complete the research and development of complex products and trial production with high quality, low cost and short cycle. At present, with the CA precision casting technology, a variety of key components such as aerospace, aviation, and weapons have been tested and achieved satisfactory results.
2 Materials and Experimental Methods
CA casting can be applied to stainless steel, heat-resistant steel, high-temperature alloys, aluminum alloys and other alloys, CA casting process shown in Figure 1. The three-dimensional model can be designed using three-dimensional design software such as IDEAS, UGII, and PROE. The process structure and model conversion are processed and repaired with MagicRp, prototyped on the AFSMZ320 automatic forming system, and prototyped with melt infiltration. The solidification process is numerical The simulation was performed using PROCAST and finite difference software. 
Key issues and related technology discussion of 3CA precision casting process
In recent years, great progress has been made in the three-dimensional CAD design, reverse engineering, rapid prototyping, casting system CAD, casting process numerical simulation (CPS), and special casting technologies related to CA Casting Technology. These achievements have been achieved. The foundation of the integrated CA precision casting technology lays the foundation and promotes the rapid development and application of CA precision casting technology. In order for each monomer technology to be successfully used for CA casting, the interfaces between each other must be eliminated and these technologies must be combined organically. In order to achieve true development of advanced design + advanced materials + advanced manufacturing in product development.
3.1 Three-Dimensional Model Generation and Electronic Document Exchange How to get accurate electronic data models of components is a crucial first step for CA Casting. With the development of 3D CAD software, reverse engineering and other technologies, this work has become simple and quick. This section mainly introduces the process of entity modeling and data conversion using IDEAS. IDEAS9 integrates 3D modeling and reverse engineering modeling. The complex model can be obtained through the MasterModeler module (see Figure 2), which can not only perform parametric design with full geometric constraints, but also allow free and innovative design of arbitrary geometry and engineering constraints; the surface design includes variable sweeps, boundary surfaces, etc. Freeform surface modeling function. Reverse Engineering Freeform can process the point cloud information collected by the digitizer to create curves and surfaces. After the surface is generated, the RPM file can be directly generated, and can also be returned to the main modeling module for processing (see Figure 4). After the entity file is generated, it needs to be converted into an STL file (see Figure 3) as input to the RP device. The conversion process should pay attention to choose the name of the molding equipment, usually choose SLA500, the output accuracy of the triangular slice is between 0.005~0.01. The use of MagicRp processing should be multiplied by 25.4 to get the actual design size. 
3.2 Numerical simulation of solidification process
3.2.1 Principles of Numerical Simulation of Solidification Process Casting is a process in which a liquid metal fills a cavity, where it solidifies and cools, and contains many complex phenomena that affect the quality of the casting. In actual production, it is often judged by experience whether a process is feasible. For a casting, the process setting needs to pass multiple tests and trial and error, and finally according to the casting results of various test schemes, the casting process scheme that can meet the design requirements is selected. Repeated trials cost a lot of manpower, material resources, and financial resources.
Although the casting process is very complex and has many accidental factors, it still follows basic scientific theories such as fluid mechanics, heat transfer, metal solidification, and solid mechanics. In this way, the casting process can be abstracted to solve the problem of liquid metal flow, solidification, and temperature changes. It is to solve the Fourier heat conduction equations and elasto-plastic equations under given initial conditions and boundary conditions. The development of computer technology makes it possible to solve numerical solutions of physical processes. Using computer numerical simulations, quantitative descriptions can be made of extremely complex casting processes.
Abstracted by mathematical and physical methods, the casting process can be characterized as the coupling of several types of equations:
1 Thermal conservation equation: 2 Continuity equation: 3 Momentum equation: The commonly used numerical simulation methods are finite difference method and finite element method. The finite element difference method has a simple mathematical model, simple and easy to understand, and uses less memory. However, the calculation accuracy is general. When the casting has a complex boundary shape, the error is large. When the stress is analyzed, the difference mesh needs to be converted into a finite element mesh for calculation. The finite element method technology calculates the unit according to the variational principle, and then performs the overall synthesis of the unit, which has high simulation accuracy and can solve the problems of castings with complex shapes. No matter what numerical method is used, the numerical simulation software of the casting process should include three parts: pre-processing, intermediate calculation and post-processing. The pre-processing mainly provides the geometry information of castings and shells for intermediate calculation; various physical parameters and casting process information of castings and shells. The intermediate calculation mainly provides a calculation model for numerical calculation based on the physical field designed by the casting process, and predicts the quality of the casting based on the relationship between the quality of the casting or the relationship between the defect and the physical field. Post-processing refers to visually expressing the results of the calculations graphically. Figure 5 shows the composition of the numerical simulation system for the casting process.
The main purpose of the calculation of the flow field and temperature field during the casting process is to predict the shrinkage shrinkage that may occur in the casting, optimize the process design, and control the internal quality of the casting.
Through the simulation of the casting process on the computer, the temperature field, flow field and stress field distribution of the castings at various stages can be obtained, and the occurrence and location of defects can be predicted. Comparing various process schemes and selecting the best process can greatly improve the product quality and increase the product yield.
3.2.2 numerical simulation software for the casting process [5]
After years of research and development, there are a large number of commercially available casting process numerical simulation software, indicating that this technology has matured. Most of these softwares can simulate temperature field, stress field, and flow field in sand casting, metal casting, precision casting, and pressure casting, and can predict defects such as shrinkage, porosity, cracks, and deformation of castings and various parts of castings. The fibrous tissue, and data conversion interface with the CAD solid model, can be used for finite element analysis.
ProCAST is currently a relatively successful casting process simulation software. This is particularly useful in the development and production of complex, thin-walled castings and near-net castings. It is the only system that can perform heat transfer-flow-stress coupling analysis of the casting process. The software is mainly composed of eight modules: finite element meshing, heat transfer analysis and pre-processing, flow analysis, stress analysis, thermal radiation analysis, microstructure analysis, electromagnetic induction analysis, and reverse solution.
It can simulate most problems and physical phenomena in the casting process. In the analysis of the technology filling process, it can provide the influence of gas, filtration, high pressure, rotation, etc. on the filling of the casting, and can simulate the filling process of almost all casting processes such as lost foam casting, low pressure casting and centrifugal casting. , and simulate the filling process of injection molding, wax molding and pressed powder materials. ProCAST can solve heat transfer, convection and thermal radiation three kinds of heat transfer problems, especially through the "grey net body radiation method" model, making it more adept at solving the problem of precision casting, especially single crystal casting. Elasto-plastic and viscoplastic models are used in stress to make it possible to analyze the stress and deformation of castings.
When analyzing castings, a simple model grid can be generated directly at ProCAST. The complex model can be generated by software such as IDEAS. After dividing the mesh, the *.unv common exchange file is output. This file should have node and unit information. The Meshcast module reads the grid file and outputs the tetrahedral element for preprocessing. PreCast defines the parameters such as material, interface heat transfer, boundary conditions, and pouring speed of the model, and is finally calculated by the ProCAST module.
Using IDEAS and ProCAST, we simulated the solidification process of an engine component. Due to the thin dimension in one direction, the component is prone to cracks and deformations in the pouring process. Through simulation, the structure of the gating system is optimized, stress concentration is reduced, deformation and cracking are prevented, and obvious results are obtained.
in conclusion:
1. The CA precision casting technology, which is a combination of computer-aided engineering and precision casting, has strong versatility and can shorten the development cycle and save development costs.
2. With the cooperation of IDEAS and RPOCAST, it is possible to simulate complex parts in the casting process.
3. The computer solidification simulation technology can be used to design and optimize the gating system of complex parts, and can accurately predict the defects and their location, deformation cracking tendency, and is used to guide the optimization of the gating system.