| With the fast development of national economy and people's living level, aluminum profile products are getting wider employment in production and living fields. Extrusion die is the key equipment of aluminum profile extrusion production. At present, design of profile extrusion die is mainly based on engineering analogy and experience accumulation in our nation, the designed die has to be tested and repaired frequently in order to adjust process parameters. The traditional production mode which depend on experimental design, die testing and repairing has been not satisfied the rapid development of aluminum profile industry. The scientific design and analysis tools are urgently needed to develop the design of aluminum profile extrusion die from experienced design up to scientific design. Computational numerical simulation has been a powerful tool for the die and process design of material deformation process. Aluminum profile extrusion process is the large deformation process. It usually can not be effectively analyzed by conventional analysis method. Therefore, developing the theoretical model and numerical calculation method to suit severe plastic deformation process, and researching the flowing law of metals and the effect of relative parameters on quality of profile in aluminum profile extrusion process has a great significance on reasonable design of extrusion process and die structure, reducing testing time of die, and improving quality of profile.Finite element method (FEM) is widely used in numerical simulation of metal plastic forming process, but it has a big problem in simulating extrusion process with severe deformation: the mesh is easily distorted and need to be remeshed frequently, which sometimes cause the simulation even impossible to go on. Finite volume method (FVM) is the most popular method used in computational fluid dynamics at present. Its discrete equations have good conservation and clear physical meaning, and its computational cost is relatively small. The prominent advantage of FVM is that the Euler grids employed by this method is the background grids which don't move with the materials and don't be distorted. So FVM is more suitable for the large deformation problems such as aluminum extrusion process because the grids can avoid to be remeshed. At present, FVM software used by researchers is mainly the general-purpose software, which doesn't consider the process characteristics of aluminum extrusion process. At the same time, the theories and key technologies of FVM numerical simulation of plastic deformation process have not been perfect yet. There are some problems such as longer time cost, lower surface quality and so on. These problems cause these FVM software can not guide the process and die design of aluminum profile extrusion process effectively.This paper is aimed to introduce FVM which is widely used in computational fluid dynamics into plastic deformation process based on characteristics of aluminum alloy and deformation mechanism, die structure, process conditions and so on of aluminum extrusion process, establish a efficient, flexible and stable numerical simulation method and its key technologies of aluminum profile extrusion process, then develop the numerical analysis system, primarily realize the non-orthogonal grids based FVM simulation of extrusion process, including the thin walled profile extrusion process with the large reduction, the pocket die extrusion process with effect on redistribution of flow, the hollow profile porthole die extrusion process with complex die structures and flow patterns, and so on. Then optimize the die structure and process parameters based on obtained velocity fields, stress fields, strain fields and so on, and provide the theoretical guidance of profile extrusion process.Aiming at the research status and mainly existing problems of numerical simulation of aluminum extrusion process, FVM method which is suitable for large deformation problems is introduced into the plastic deformation field. The base theories of FVM are researched, the governing equations and grid character of FVM are given. The discrete methods of governing equations are researched, and the common used interpolation schemes of FVM are discussed. The variable storage arrangement of FVM is introduced, and the implementation process of SIMPLE algorithm which is a coupling solution of solving pressure and velocity is researched.Die structure, process conditions, deformation mechanism and flow character of materials, mechanical properties and constitutive relation of aluminum alloy are researched. By applying the rigid-viscoplastic model and neglecting the elastic deformation of materials, the aluminum alloy under high temperature can be regard as a kind of rigid-visoplastic, isotropic, incompressible non-newtonian fluid. The relationship of viscosity, stress, strain rate and temperature of aluminum alloy deformation process is researched, and the dynamic viscosity equation is established in order to lay the foundation of introducing FVM into aluminum alloy profile extrusion process.By combining process character of aluminum profile extrusion process and FVM base theories, the mathematical model of FVM simulation of aluminum profile extrusion process based on non-orthogonal grids has been researched and established. Aiming at the poor adaptation of irregular calculation domain and the difficult treatment of friction boundary conditions bring by using traditional orthogonal grids which is commonly used in FVM, non-orthogonal grids are used to adapt to irregular calculate domain, realize the exactly fitting of curved face boundary, and make the reasonable implementation of boundary conditions become more easily. The governing equations are discretized on non-orthogonal grids by Cartesian coordinate directly, so the complicated coordinate transformation which used by body-fitted method is avoided. The problems casused by girds' nonorthogonality are researched, such as the connecting line of adjacent center points don't vertical to the interface, and don't pass through the center point of interface. The discrete schemes of governing equations based on non-orthogonal grids are researched, the discretization equations of 3D unstable problems based on non-orthogonal grids are deduced and established, and effect caused by grids' nonorthogonality has been eliminated. Aiming at the difficulty of implementing SIMPLE algorithm using staggered variable arrangement based on non-orthogonal grids, SIMPLE algorithm using collocated variable arrangement based on non-orthogonal grids is deduced and built. The deferred correction approach is used to interpolate values on interface. This approach can bring in pressure difference of neighbor nodes, so the pressure oscillation can be filtered out. The pressure correction equation can't be written into unified form of general discrete equation because of the grids' nonorthogonality, so twice pressure correction method is used to solve this problem. Aiming at the process character and flow law of aluminum extrusion process, the initial and boundary conditions of FVM simulation of aluminum extrusion process based on non-orthogonal grids are built. The simulation system is developed base on above mathematical model, and simulation steps and flow chart of the system are given.The key technologies of 3D unsteady FVM simulation of aluminum extrusion process base on non-orthogonal grids are researched and built. Nodes numbering and data storage on non-orthogonal collocated grids are researched, and the friction boundary is implemented on non-orthogonal grids. VOF method which is used to tracking flow's free surface is built on non-orthogonal grids, the calculate formulas of VOF method are developed by aiming at the grids' nonorthogonality. A simple method is used to determining the orientation of free surface conveniently. Some key technologies, such as the character and solution method of algebraic equations obtained by FVM based on non-orthogonal grids, the convergence criterion of inner and outer iteration, time step auto control, and so on, are researched. Then the simulation system of FVM simulation of aluminum extrusion process based on non-orthogonal grids has been further developed by above key technologies.Aiming at the hollow profile extrusion process, key simulation technologies of FVM based on non-orthogonal block structured grids are established. Data structure of block interface is researched and built. Solution method of FVM based on is researched and the strong implicit procedure is built to solve algebraic equations on the global calculation domain unitively. The treatment of VOF method on block interface is researched and VOF method is built on non-orthogonal block structured grids. FVM simulation system of aluminum extrusion process based on non-orthogonal block structured grids is developed based on above key technologies, and the numerical simulation of hollow profile extrusion process using porthole die is realized.Some numerical cases are simulated to verify the feasibility and exactness of the mathematical model, key technologies and relative numerical system, and the simulation results are compared with the results obtained by FEM software Deform, FVM software SuperForge and experiment under the same conditions. These results comparisons indicate that the mathematical model of FVM simulation of aluminum extrusion process is correct and efficient, and it has a good applicability for extrusion process with large deformation. The developed system can realize extrusion process including thin walled profile pocket die extrusion with large deformation, hollow profile porthole die extrusion. The die structure's effect to flow law of metals has been researched, and the extrusion die structure has been optimized by the simulation, which can provide theoretical guidance of practice of extrusion process.
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