| Summary: | 博士 === 國立臺灣科技大學 === 機械工程研究所 === 86 === The drawing process of sheet metal forming is a common and crucial production process. There is a strong request from the industry for a powerful finite element code for simulating sheet metal forming processes and predicting forming defects. This thesis aims at the request from the industry and applies an elasto-plastic incremental finite element method to simulate drawing and redrawing forming processes under axisymmetric condition. In addition, the updated Lagrangian formulation (ULF) is used to construct the material constitutive equation. In the analyzing process, the punch displacement represents the simulation increment, and the displacement increment of the counting step is determined by the yielding situation of the element, contact or separation of the workpiece and tools, and the
incremental confinement of the maximum strain and rotation angle. The friction simulation between workpieces and tools is obtained by the modified Coulomb friction law. The fractured thickness of a specimen in the tension experiment is adopted as the fractured criterion of forming limit of the workpiece. Therefore, when the sheet thickness of the drawing process is less than this criterion, the conclusion of fractured blank is came. The data of deformation histories from drawing and redrawing processes can be obtained by using the finite element simulation. The simulation results include deformation diagrams in different forming stages, relationship between the punch load and the punch displacement, and the variation of sheet thickness and so on. Then, comparisons between the simulation and experiment results can be used to verify the reliability and accuracy of the finite element program developed in this thesis.
A constant strain triangular element and a four-node quadrilateral finite element are used to simulate sheet drawing and redrawing process by using of the cylindrical punch under the axisymmetric condition. Which finite element stiffness integration scheme is appropriated can thus be decided from the simulation results. A set of drawing die, cylindrical punch, blank holder, and a set of redrawing dies and cylindrical punch are designed for experiments. The accuracy of methodologies and programs are verified by experiments performed in a sheet forming machine. Simulation results with the stabilization matrices (SM) scheme show good agreement with experiments in the relationship of the punch load versus the punch travel. The
stiffness integration scheme of the stabilization matrices is suitable for the material adopted in this study.
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