Numerical Simulation Investigation Of High Speed Bulk Forming Process

High speed bulk forming is an important technology in industry, and has been playing a good application in aerospace industry. Dynamic effect is obvious during the deformation because of high forming velocity, which is different from quisi-static bulk forming. When the finite element method is used to analyze this kind of dynamic deformation, dynamic analysis method is proper to be adopted, and the energy transform relation must be considered to accurately reflect the real deformation characteristic. However, existing FE methods can not take the two aspects into account simultaneously. In this paper, some key techniques of finite element analysis for the high speed bulk deformation process are analyzed, and the deformation and flow law of metal are researched, which provides a method for optimizing numerical simulation of high speed bulk forming.The energy transfer mechanism during the deformation is analyzed according to the operating principle of energy-restricted equipment, and the calculated method of hammer velocity is proposed. The finite element formulation for dynamic analysis of high speed bulk deformation process is provided based on the above theory. Meanwhile, the deformation process is treated as an adiabatic process, and a coupled thermal-mechanical finite element equation is derived.The master-slave search algorithm is used to treat the contact problem during high speed bulk deformation process. A coordinate quadrant method is proposed to judge the contact state between workpiece and die for two-dimensional problem. And the penalty method is used to calculate normal contact force. In the developed two-dimensional FE analysis code, an indirect arithmetic of the quadrilateral mesh generation is presented. The background triangular mesh is generated by combining the Delaunay and advancing front method firstly, and then the background triangular mesh is merged to quadrilateral mesh. After quadrilateral mesh is generated, the quality of mesh is improved by using Laplacian smoothing method. Moreover, the remeshing is realized in two-dimensional FE simulation system.The high speed upsetting processes of block and cylinder under drop hammer impact are analyzed with the developed three-dimensional and two-dimensional finite element analysis code. The flow law of metal is studied, and the effects of impact energy and height-to-diameter ratio on the deformation process are researched. The high speed upsetting tests of block and cylinder were carried out on a drop hammer impact test machine. The effect law of impact energy and height-to-diameter ratio of billet on the deformed shape, forming load, deformation energy are studied. The results of finite element analysis agree with experimental ones, which verify the effectiveness of developed three-dimensional finite element analysis code.In order to study the influence of stress wave propagation on the deformation process, the stress wave propagation during the dynamic upsetting process is analyzed with the developed finite element analysis code. The influence of stress wave propagation on the stress and strain distribution is analyzed. Industrial pure lead, OFHC copper and 7039 aluminum alloy are chosen to investigate the effect of material parameters on the stress wave propagation.The hammer forging process of disk-shaped workpiece is analyzed with the developed two-dimensional finite element analysis code. The flow law of metal and inertial filling is studied by the velocity vector and plastic strain distribution in the workpiece, and the effect of impact energy, height-to-diamter ratio of billet, draft angle and interface friction on the deformation process are analyzed. The hammer forging tests of disk-shaped workpiece were carried out on a drop hammer impact test machine. The effect law of impact energy and height-to-diameter ratio of billet on the deformed shape, forming load are studied. The numerical simulation results agree with experimental ones, which verify the effectiveness of developed two-dimensional finite element analysis code.