Study on piercing mechanism of small holes

FEM analysis and experiments were conducted on small hole piercing to clarify the piercing mechanism. In this paper, small hole piercing is defined as a piercing performed using a punch with a diameter smaller than the material thickness. To discuss the mechanism, new concepts on the incremental ratio are introduced in addition to an aspect ratio already known. The results of this study clarified the following: the piercing mechanism distinctly changes with increasing aspect ratio. When the ratio is larger than one, the initial stage resembles simple indenting and the latter stage resembles traditional blanking. High aspect piercing up to 12.5 was successfully achieved with the aid of good lubricants.