Finite-element simulation of hole-flanging process of circular sheets of anisotropic materials

A hole-flanging operation on a flat circular sheet with a hole in the center is simulated by an incremental elasto-plastic finite-element method, which incorporates strain-hardening and anisotropy in the direction normal to the sheet, with care taken to describe the boundary conditions of penetration, separation and the alternation of the sliding-sticking state of friction. The simulation clearly demonstrates the processes of generation of deformation shape until;unloading, The calculated sheet geometries and the relationship of punch load to punch stroke are in;good agreement with the experimental data. The stress at the hole periphery in the flange is assumed to a state of circumferential uniaxial tension, in order to simplify the fracture mode as a simple tension test. By making use of the instability of uniaxial tension, an approximate relationship to determine the onset of necking of the hole periphery in the hole-hanging process is derived and it is found to be influenced by the process geometry and the plastic properties of the material, such as the stress-concentration factor K, strain-hardening n and normal anisotropy R, and the estimated value, being obtained by the derived equation, agrees well with the experimental data. It is noted that the derived relationship for estimating the instability of the hole-hanging process can be combined into the developed finite-element model to simulate the critical condition of the limiting deformation of the hole-hanging process. This combined method could possibly be applied towards improving both the manufacturing process and the design of tools for the hole-hanging operation. Copyright (C) 1996 Elsevier Science Ltd.