| The application of finite element process simulation in cold forming is studied in this thesis. First, the basic theories and constitutive formulations that may be involved in the simulation and solution methods are reviewed. Then the challenging problems of simulation such as contact simulations, ductile fracture simulations, remeshing and adaptive meshing techniques are discussed. The simulation methods and algorithms provided by the used software are discussed and evaluated. Conditions and limitations of certain algorithms and formulations are pointed out and application advice is given to the process simulation of cold forming. Later, three typical cold forming application examples are studied, they are: backward extrusion of a cup, combined extrusion, and multi-stage closed die forming. In the applications, the whole process systems including work piece, punch set, die set and ejection pins are simulated. In the multi-stage forming case, simulations are done from stage to stage continuously. At each stage, the entire process procedures from preloading to loading, and later to unloading, and work piece ejection are all simulated. In the last piercing stage simulation, fracture initiation and propagation and even the forming of bur are shown clearly. Plenty of information is given for the entire forming process, such as distribution of stresses and strains, punch load-stroke curves, metal flow diagrams, residual stresses and deformation shapes of preforms and of final product, etc., which enables the optimal process design to be performed later. 'Virtual manufacture' is implemented to some extent in this application. |
