Papers by Author: Xia Chen

Abstract: Melt flow and casting solidification are essential parts of the permanent mold casting process and affect significantly the quality of castings．For this reason, accurate prediction of mold filling pattern and temperature field in permanent mold castings plays on an important role in producing sound castings. In this paper, the model filling and solidification of a box casting produced from an aluminum alloy is studied. Different casting processes are employed, simulated and optimized to obtain sound castings. Simulation results reveal that with appropriate gating system, pouring rate, cooling line, a smooth mold filling, reduced shrinkages and other defects are available and desired sound castings can be produced.

Abstract: A 3-D modeling based on the numerical resolution of fluid flow and heat transfer are utilized to investigate the thermal phenomena during laser laser-cladding processes of BT20 alloy. From this model, it has been found that the shape and size of the molten pool in the work piece are affected by laser cladding parameters such as scanning speed and the incident laser power. The effects of process parameters on the melt pool are quantitatively discussed by numerical analysis. Furthermore, it has been observed that the surface tension temperature coefficient, Marangoni convection, which is sensitive to the active elements in the titanium alloy composition, also affect the pattern of the fluid flow in the molten pool.

Abstract: In this research paper, the sand casting process of a cover-type part for wind turbine was investigated with ProCAST software . The cover-type casting part is big in two dimensions and it is heavy in some local positions where shrinkage cavity and porosity are very likely to from. A non-uniform mesh is used corresponding to the non-uniform wall thickness. Different casting processes are employed, simulated and optimized to obtain sound castings. Simulation results reveal that with appropriate pouring temperature, correct number, size and location of chills and risers, a smooth mold filling, reduced shrinkage and other defects are available and desired sound castings can be produced

Abstract: In this paper, a stable lattice Boltzmann model (LBM) based on non-ideal gases is presented for simulation of incompressible two-phase flows with large density ratio. To reduce the parasitic currents across the interface and correspondingly increase the numerical stability, the stress and potential forms of the surface tension force is employed. The applications to a stationary bubble and capillary-gravity wave with density ratio 1000 are given to verify this model. The numerical solutions is agree well with analytic solutions of the Laplace's law and capillary-gravity wave.

Abstract: A three-dimensional thermo-mechanically coupled FEM-simulation of the production of a connecting rod has been performed between dies (pre- and final-forging). According to the part’s characters and its dimensions, a hammer die forging process was determined. According to the hammer die process, three-dimensional connecting nod model was built in UG software and two different cases for pre-forging was designed. Different forming case was simulated by Deform-3D FEM program, the effective stress field and effective strain field were analyzed by comparison; it proved that optimized performing process was reasonable and can be used as reference in production.

Abstract: In this research work, ProCAST software is employed to study the sand casting process of a box-type part for wind turbine. The casting part is big in size, non-uniform in wall thickness, and heavy in some local positions. Shrinkage cavity and porosity are very likely to from at these locations. By numerical simulation, the influence of the parameters such as pouring temperature, chills, riser on mold filling and solidification is analyzed. Simulation researches reveal that with appropriate pouring temperature, correct number, size and location of chills and risers, a smooth mold filling, reduced shrinkage and other defects are available and desired sound castings can be produced.

Abstract: A 3-D modeling based on the numerical resolution of fluid flow and heat transfer for laser-cladding processes of In718 Superalloy is proposed. The implementation of developed procedures allowed us to treat the problem with specific and complex boundary conditions. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam diameter and scanning speed. The effects of process parameters on the melt pool are quantitatively discussed by numerical analysis. The computational results present good coincidences with the corresponding experiments of laser cladding process.

Abstract: In this paper, the CSP (compact strip production) technology was studied with the aid of elastic-plastic and thermal-mechanical coupled FEM using commercial software ABAQUS. The distribution and change of temperature, stress and strain field in rolling process were analyzed. In the view of boundary conditional influence on temperature, some factors such as thermal exchange between the work-roll and the thin slab, plastic deforming quantity of heat, cooling flux, convection and radiation heat exchange were considered during simulation. The results show contact heat conduction and deformation heat are the main factors that influence the temperature change of the thin slab. A good agreement was found between the predicted and the experimental data.

Abstract: According to the process feature of the coke dry quenching (CDQ), the factors of the destructive mechanism that influence the sequence function properties of the brick were analyzed. The countermeasures have been adopted for the defects of the bricks for CDQ, such as inferior thermal shock stability and short lifetime, etc. In order to search the effect of thermal expansion stress and mechanical load stress on the CDQ, the temperature field and stress field of the flue in the CDQ were analyzed according to the thermal elastic and plastic theory. The Drucker-Prager plasticity model combined with a tension cut-off criterion was described material behavior. All material properties were taken as temperature dependent. The result indicates that the support bracket under high gradient temperature will bring on the highest thermal stress, which is the main reason of fracture of the support bracket. The cycling temperature has the ability to cause repeated crack propagation throughout the whole service period. To solve this problem, the design of the structure, the method of the heat exchange and the properties of the materials will be improved. The obtained results give a good insight into the reasons of material failure and help to find counter-measures for prolonging the lifetime of CDQ.

Abstract: In order to study the influence of the geometry and material properties on the service life of converters, different geometry and material properties of the converters were analyzed by using finite element method in this paper. A mechanical and thermal coupling diagram was introduced to optimize the geometric figure and material properties of the converter by software ABAQUS. The damage of converters was investigated, especially in the lower brick layers of the wall (the bottom wall transition zone). The result indicates both the ladder of the converter with small steps and a proper inclination at the joint between the bottom and wall of converters can reduce the stresses, which make the refractory material damage decrease. The working lining with high conductivity and low thermal expansion will make the thermal stress of the converter lower, which reduces the crack of the converter. The relations between the obtained results and the corresponding lining design and the material properties give a good insight into the reasons of refractory material failure and help to find counter-measures.