| Bulk metal forming technology is a process in which the metallic materials, with the help of forging equipments and corresponding molds mounted upon them, are formed into parts with the desired shapes and properties. Bulk metal forming includes mainly forging, extrusion, rolling, roll forging, cross wedge rolling and so on. In industrial production, bulk metal forming is one of key technologies supporting the development of the national economy and the construction of the national defense. It is widely used in branches such as automobile, aerospace and aviation, equipments manufacturing, weapons, energy, ship building etc. Bulk metal forming process has many advantages, such as high productivity, raw material saving and better mechanical properties of the formed products. It has also certain disadvantages, such as high cost of mold, long production cycle, waste of energy, environmental pollution etc. Under the global tendency of "low carbon economy" and "energy saving & emission reducing", new tasks and requirements in the bulk metal forming technology study are how to make full use of the advantages and avoid disadvantages to acclimatize itself to the new situation of development.Bulk metal forming is a complex physical process, which is influenced by many factors, such as the properties of material, the form of mold, the shape of blank, the process parameters and the temperature etc, so the planning of the process and the designing of the corresponding mold for the bulk metal forming process is quiet difficult, which with the traditional method often has certain malpractices like waste of equipments, material and time. An accurate simulation of the bulk metal forming process can not only reduce the high costs in the experiments, but also has significant theoretical guidance and realistic application value meaning for determining the reasonable forming process and ensuring successful mold design at the first time as well. With the development in calculation method and computer technology, numerical simulation and analysis method has become a powerful tool for the solution of engineering problems. Among them the finite element method (FEM) is the most matured and has played an important role in the numerical simulation of bulk metal forming processes. With the rapid development in the bulk metal forming technology in recent years, the existing finite element software for the bulk metal forming simulation has been unable to meet the requirements in finite element analysis for the bulk metal forming process any more, because of problems such as frequently remeshing, difficulty loading for complex motion and low efficiency in the analysis of large problems. In this paper finite element simulation theory and algorithms and the detailed implementation for bulk metal forming are studied and a finite element simulation software platform based on rigid viscoplastic theory is developed for bulk forming.The three-dimensional (3D) finite element meshing method has been studied. In order to solve the contradiction between precision and unit numbers of the finite element mesh model, a self-adaptive meshing method is proposed and the commonly used self-adaptive meshing method for hexahedral mesh model and tetrahedral mesh model is studied. In order to take the advantages of the two mesh models, a concept, hybrid mesh model of hexahedron and tetrahedron, is proposed and the adaptive generating method for hybrid meshing model is studied. Principles for choosing of the meshing methods are proposed and a matured algorithm for 3D finite element initial meshing is established. Method for 3D finite element mesh regenerating is studied. The method for geometrical form extraction and restoration in the distortion of mesh is researched and a method for transfer of physical field variables between new and old mesh is studied. In order to improve the interpolation precision of physical field variables, a double self-adaptive remeshing algorithm is proposed based on both geometrical characteristic and physical field variables. In order to improve the efficiency in remeshing, a technology for the local remeshing of the 3D finite element mesh is proposed. In view of the interference mesh a method for refinement of the local mesh is proposed. In view of the distortion mesh a method for optimization of the position of local nodes and a method for regeneration of the local mesh are proposed. Also the methods and principles for choosing remeshing method are recommended, and a systematic method for remeshing of three-dimensional mesh is established.The existing theories and methods in finite element simulation have been analyzed and compared and in this study the rigid viscoplastic theory is chosen as the basic theory for analyzing the bulk metal forming with finite element. Based on the rigid viscoplastic theory, the establishing methods and solutions of the whole stiffness equation for different mesh models are researched. The key technology for the finite element simulation in isothermal forming of the 3D bulk metal forming is researched. The description of 3D geometry of the reconstructed mold is presented based on data of STL files. A method to establish of a local coordinate system is proposed to ensure the correct exerting of the boundary conditions and the symmetrical constrained on the contacted mold. The handling methods for complex mold motion, including description method of mold movement, solving methods for mold velocity and location update method of mold, are studied. Handling methods for three-dimensional dynamic boundary conditions are proposed, which include judging of contact of the nodes with mold with the help of relative position method and adjusting of position of the nodes contacted with mold by using the shortest distance method. In order to improve the efficiency of analysis and calculation, reduce storage space consumption, storage compression algorithms and corresponding efficient solutions for the whole stiffness equation are proposed. Based on the research in key technologies, an isothermal simulation system for bulk metal forming with FEM is developed.Based on the isothermal simulation system with FEM, a thermal mechanical coupling simulation system for bulk metal forming with FEM is developed. The basic theory of FEM for 3D temperature field is studied and a system of FEM for 3D temperature field is developed. The basic theory and key technologies of a thermal mechanical coupling simulation with FEM are studied, such as treatment of temperature shock, thermal coupling boundary conditions, and treatment of thermodynamic parameters. In theory and key technologies research, based on the system of 3D temperature field simulation with FEM and the system of 3D isothermal simulation with FEM, the system of 3D thermal mechanical coupling simulation with FEM is developed by indirect coupling method.Based on key technologies and implementation method, supporting subsystems of 3D bulk metal forming simulation system with FEM is developed, including:the pre-treatment system of building finite element model, post-processing system of analysis finite element results, database system of supporting system. The combination of these auxiliary subsystems with the three-dimensional rigid viscoplastic finite element analysis system builds a software platform CASFORM-3D system of the 3D FEM for bulk metal forming. Through simulating with typical parts in practice, and comparing of the simulation results with those results with commercial software DEFORM-3D simulation, it shows a high identity between these two methods, therefore verifies the reliability of the key technologies and feasibility of the associated processing algorithms proposed in this paper. |
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