| Summary: | 博士 === 國立臺灣科技大學 === 機械工程系 === 92 === This study aims to clarify the process conditions of the V-die bending of a steel sheet metal. It provides a model that predicts not only the correct punch load for bending, but also the precise final shape of products after unloading, based on the tensile properties of the material and the geometry of the tools used. A methodology for formulating an elasto-plastic three-dimensional finite element model, which is based on Prandl-Reuss flow rule and Hill’s yield criterion respectively, associated with an updated Lagrangian formulation, is developed to simulate sheet metal forming process. The shape function derived from a four-node quadrilateral degenerated shell element is associated into the stiffness matrix to constitute the finite element model. An extended rmin algorithm is proposed to formulate the boundary condition, such as nodal penetration and separation, strain increment and rotation increment, and altered elasto-plastic state of material.
A series of experiments were performed to validate the formulation in the theory, leading to the development of the computer codes. The predicted value of the punch load by the finite-element model agrees closely with the results of the experiments. The whole deformation history and the distribution of stress and strain during the forming process were obtained by carefully considering the moving boundary condition in the finite-element method. A special feature of this V-die bending process is the camber profile after unloading. The computer program successfully simulates this camber profile.
According to the developed finite element code, the computer codes are first executed to evaluate the effects of the size of the blank (blank width (W), blank length (L) & blank thickness (t0)) on the V-die bending process. The simulation was primarily to analyze in detail the effects of the size of the blank on the height of the camber, the bend angle after unloading, the distribution of thickness along the bend axis and the punch load. Several simulations and experiments were performed with varying process variables.
The sheet metal V-die bending process is simulated to evaluate the effects of tooling geometry on the V-die bending process. The effects of process variables, such as punch radius (Rp), die radius (Rd), tool width (Wd) and tool angle (At), on the final shape after springback or springforward, the height of the camber, the distribution of thickness along the bend axis and punch load are discussed in detail.
Using the finite-element code, simulations were run to evaluate the effects of strain hardening exponent (n), friction coefficient ( ) and normal anisotropy (R) on the camber height, springback angle after unloading and the distribution of thickness along the bend axis.
The simulation clearly demonstrates the efficiency of the code to simulate various bending processes that proceed under complicated deformation and contact history. This work has provided an improved understanding of the sheet bending process for improving the manufacturing processes and the design of tools.
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