Dunming Liao

Heat Transfer Model of Directional Solidification by LMC Process for Superalloy Casting Based on Finite Element Method

With the rapid development of the aviation industry, the turbine blade, a critical component of the aeronautical engine, has come to be widely produced by liquid-metal cooling (LMC) process. A temperature- and time-dependent heat transfer coefficient was used to represent the heat convection between the shell and the cooling liquid, and an improved Monte Carlo ray-tracing approach was adopted to handle the boundary of radiation heat transfer. Unstructured mesh was used to fit the irregular shell boundary, and the heat transfer model of directional solidification by LMC process based on finite element method (FEM) was established. The concept of local matrix was here proposed to guarantee computational efficiency. The pouring experiments of directional solidification by LMC process were carried out, then simulation and experimental results were compared here. The accuracy of the heat transfer model was validated by the cooling curves and grain morphology, and the maximum relative error between simulation and experimental cooling curve was 2 pct. The withdrawal rate showed an important influence on the shape of solidification interface, and stray grain is liable to be generated on the bottom of platform at an excessive withdrawal rate.

Casting CAD/CAE automatic optimal riser design technology

Abstract During the casting process, computer aided design (CAD) and computer aided engineering (CAE) play important roles, but they have been separated from each other. To promote the efficient connection between numerical simulation and casting design, an approach of casting CAD/CAE automatic optimal riser design technology is presented. First, simulate heat transfer and get isolated liquid regions of steel casting without risers. Then, display the isolated liquid regions on Unigraphics and build risers automatically. Finally, use a simple casting to test this CAD/CAE system. The experiment results showed that the designed risers are reasonable. Based on Unigraphics platform and InteCAST software, the casting design (CAD) is combined with the numerical simulation (CAE), and an automatic optimal riser design system for steel casting was developed. It can build three-dimensional risers automatically and provide a proximal optimum design for CAE valuation and even practical producing. This method can shorten the design period and ensure the casting quality.

Numerical Simulation of Casting Thermal Stress and Deformation Based on Finite Difference Method

Thermal stress simulation is an important part in the numerical simulation of casting process. It provides engineers with insights into the evolution of displacement, strain and stress of castings in the solidification process. With thermal stress simulation, some defects of casting, i.e. hot tearing, cold cracking and large deformation can be predicted and the engineers are instructed to optimize and improve the casting process. Based on the finite difference method (FDM), this paper presents an integrated numerical method to simulate the thermal stress and deformation of casting in the solidification process. Practical examples show that the method is capable to predict stress distribution and deformation as well as the defects in the experiment.

Numerical Simulation of the Influence of Temperature and Pressure in CVI of C/C Composite

A reduced model was used to simulate the CVI process from methane. The scale of the preform was 120mm in diameter and 90mm in height. A random pore model was used to describe the evolution of pores in preform. Parameters such as temperatures and pressures were studied to research the deposition process. Effects of these two parameters are similar but have different impact mechanisms according to the analysis of results. Temperature impacts the reaction rate to improve the efficiency of deposition, while pressure impacts the concentrations of all hydrocarbon and then improves the total amount of carbon which also results in an increase of density.

Optimal Riser Design by STL Arbitrarily Slitting Method and Genetic Algorithm

It is essential to consider the proper position and volume of riser during the design of feeding system. In this paper, we are presenting a new method of designing optimal riser in the steel casting processes. A technique of slitting arbitrarily 3D entity model by STL (Stereolithography) was used to obtain accurate values of the partial modulus of casting, and then a mathematical model of the process of the riser design was optimized by a genetic algorithm (GA); with the help of the CAE system, which has an ability to calculate automatically and verify the validity of the optimized results, we will pursue the goal of obtaining the desired riser with optimal size and distribution but without causing any defect in casting. Thus, by combining the numerical optimization with the traditional riser design, our method proposed here will be more practical and reliable. In the end, we give an example to demonstrate the feasibility of our optimized approach in the riser design. Keywords：Riser design, Genetic Algorithm, casting optimization, STL

Research on Air Quantitative Prediction Based on Mold Filling Simulation of High Pressure Die-Casting

Air-entrapped is a common defect for high pressure die-casting, so it is critical to discharge the air out of mold cavity as much as possible. This study takes the research on air quantitative prediction technology based mold-filling process. Firstly, the quantitative prediction technology is introduced and the mathematical model based on a simple die casting is established. Secondly, based on HZCAE technology the paper offers calculation module and post-processing module about air quantitative prediction. And then, water simulation is carried out to validate this air-entrapped prediction technology. Finally, combined with a die-casting case, we use the program to calculate its air quantitative prediction based on the simulation result of HZCAE/InteCAST. Keywords: Air quantitative prediction, HZCAE, High pressure die-casting, Numerical simulation, Mold-filling process

Numerical Simulation of Thermal Stress Fields of Steel Casting

Many defects relative to stress occur during the complicate casting process, such as hot tearing, residual stress concentration and distortion. Modeling of casting thermal stress during casting solidification process is of great significance to predict and analyze casting stress defects. Involving too many complex influencing factors, the stress simulation is very difficult and retains a hot spot of macro simulation in foundry engineering. Currently most researchers adopt integrated FDM/FEM method, i.e. using finite difference method (FDM) to calculate solidification and heat transferring, while finite element method (FEM) to simulate stress. Some universal commercial FEA packages are usually adopted. This study has tried two kinds of approaches to simulate casting thermal stress. One is based on ANSYS, a well-known powerful FEA analysis software. Another is to develop an independent own copyrighted casting stress simulation system based on FDM. The routes of these two methods were given respectively. To calibrate the simulation system, a stress frame sample and a real practical casting were simulated and pouring experiment was also carried on. The results of simulation were in agreement with the experiment results and practical cases. It indicates that these two approaches can all meet demands. When adopting FDM method, thermal analysis and stress analysis can use the same FD model, which can avoid the nodes matching between different models and reduce the errors of thermal load transferring. It makes the simulation of fluid-flow field, temperature field and stress field unify into one model. This system takes full advantages of mature FDM technology and can be used to simulate the forming of residual stress and predict the occurrence of hot tearing.

Numerical Simulation of Filling Process in Vertical Centrifugal Casting Based on Projection-Level Set Method

A three-dimensional incompressible two phase flow model of vertical centrifugal casting is proposed to simulate the fluid flow of mould filling process accurately and effectively. The Projection method is adopted to solve the govern equation of the flow field, and the Level Set method is used to capture the free surface. The mold filling of a complex part with thin-wall is simulated. The numerical result shows that the Projection-Level Set method could simulate centrifugal casting effectively. The present study has a guiding significance to the production of vertical centrifugal casting.

The Through Process Simulation of Mold filling, Solidification, and Heat Treatment of the Al Alloy Bending Beam Low-pressure Casting

The research on the simulation for the through process of low-pressure casting and heat treatment is conducive to combine information technology and advanced casting technology, which will help to predict the defects and mechanical properties of the castings in the through process. In this paper, we focus on the simulation for through process of low-pressure casting and heat treatment of ZL114A Bending beam. Firstly, we analyzethe distribution of the shrinkage and porosities in filling and solidification process, and simulate the distribution of stress and strain in the late solidification of casting. Then, the numerical simulation of heat treatment process for ZL114A Bending beam is realized according to the heat treatment parameters and the corresponding simulation results of temperature field, stress, strain, and aging performance are given. Finally, we verify that simulation platform for the through process of low-pressure casting and heat treatment can serve the production practice perfectly and provide technical guidance and process optimization for the through process of low-pressure casting and heat treatment.

Research and Development of Steel Casting CAD/CAE Integration Technology Based on the Neutral STEP File

The casting process CAD system developed based on the existing three-dimensional CAD software has many inadequacies. This paper innovatively puts forward the steel castings three-dimensional casting process CAD system based on neutral STEP file. In this study, by taking advantage of universal CAD data-exchange standard STEP format for data exchange, a practical three-dimensional CAD system was developed based on Open CASCADE Geometry Kernel. The system has the function of practical casting process modeling, including design and modeling of gating system and riser design and so forth. The system exceeded the deficiencies of the existing casting process CAD system. It resolves the foundry Enterprises dependence and limitations on the type and version of commercial 3D CAD software, enabling to realizethe integration of CAD and CAE on casting process.