Formability Investigation for Perforated Steel Sheets

One of the unique characteristics of sheet metals is their formability, which is determined by the forming limit diagrams (FLDs). These diagrams specify the maximum deformation limit before part failure. For several applications of metal sheets, they have to be in the perforated format. The existence of holes in the perforated sheets may adversely deteriorate the forming limit of metal sheets. In this study, the effect of perforated sheets' hole size and hole layout on their formability are investigated. Several specimens of St12 steel with 0.6 mm thickness, different widths, two various hole sizes of 2 mm and 4 mm, and two layouts of triangular and square arrangements were prepared. The specimens were tested using the Nakajima test (stretch with a hemispherical punch) to generate the FLDs. It was observed that both the diameter and layout of the punched holes have a significant effect on the formability of the perforated sheets. The perforated sheets with a triangular hole layout showed higher forming limits due to their larger ligament ratios.