An experimental investigation was carried out to determine the deformation leading to failure of the hole periphery in the hole flanging process using a conical punch. Circular plates of various hole sizes and of different materials were tested to different depths of punch penetration and the lip strain paths as well as the variation of thickness around the periphery of the lip were studied. In all cases, failure of the plate was due to lip fracture and the onset of lip instability was determined from the examination of the secondary surface texture of the lip of the plate during various stages of lip deformation. The instability strain in the hole flanging process was then calculated and it was found to be influenced by the process geometry and the plastic properties of the material. Hill’s model of plastic anisotropy for orthotropic materials was applied to a plane stress case to predict the variation of thickness around the periphery of the lip and the results were compared with experimental data. The influence of the anisotropic behavior of the material on the direction of lip fracture was also investigated.

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