| Summary: | 博士 === 國立臺灣科技大學 === 機械工程系 === 89 === A hole-flanging process on a circular plate with a pre-determined smaller hole in its center has been analyzed using the incremental updated Lagrangian of the elasto-plastic finite element code. Based on the flow theory of isotropy strain-hardening, while adopting the theory of finite deformation of Euler stress in Jaumann rate, and the concept of ULF (updated Lagrangian formulation), the general constitutive equation for an elasto-plastic work-hardening material was derived. To assure a reasonable loading increment for punch, each loading increment is determined by the yield of element, the contact or the separation between the blank and the tool, the maximum strain and rotation of the element, and the translation of sliding or sticking states at the contact interface. The fractured thickness of a specimen in the simple tension test is adopted as the fracture criterion of forming limit in simulation. Numerical results, such as deformation history, punch load, thickness distribution, as well as the final shape of the product after unloading, and the limit forming ratio etc. in the process, have been obtained and compared with the corresponding experimental ones to verify the reliability and accuracy of the computer code.
Several simulations and experiments were performed on various blanks with a pre-cut initial hole in its center using various cylindrical punches with different profile radius and various truncated conical punches with different cone semi-angles in this study. The experimental and simulated results obtained are summarized as follows.
(1) The limiting forming ratio (LFR) is independent of both the profile radius of cylindrical punches, and the cone semi-angle of truncated conical punches. The LFR for low-carbon ( ) sheet with a thickness of 1.18 mm amounts to about 3.16.
(2) The maximum punch force increases remarkably with the increase in cone semi-angle of the truncated conical punch in the process. On the other hand, the maximum punch force decreases, as the profile radius of cylindrical punch and initial hole of blank increase.
(3) The cone semi-angle of truncated conical punch and the profile radius of cylindrical punch have great influence on the finished shapes in the hole-flanging process.
(4) The linear relation of LFR between the diameter of expanded and initial hole can be used to predict a perfect finished neck. It is very useful for engineers in designing hole-flanging processes.
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