Computer-assisted engineering determination of the formability limit for thin sheet metals by a modified Marciniak method

Abstract

Development of a new sheet-metal-forming technology in a digital environment demands accurate and reliable mechanical properties and forming limits of the selected material. It is essential to determine the forming limits for thin sheets and foils. Implementation of the Marciniak procedure with strip-shaped specimens defining the left-hand side of the forming limit diagram (FLD) results in tearing outside the observed area of the specimen. Therefore, new shapes of test pieces were designed with a strip-shaped central area and enlarged outer areas, which were in contact with the die during the forming process. The radius of the specimen enlargement enabled a co-axial contact of its edge and direction of the material flow over the die radius during the forming process. The shape of the redesigned geometry of the specimen was analysed using the finite element (FE) program ABAQUS to minimize undesired stress concentrations at the die radius. Finally, strain paths variations due to shape change were analysed. The new specimen concept was verified on TS-275 tinplate steel with a thickness of 0.24 mm. By implementing the necessary redesigned specimen shapes and by analysis of the tearing limit of the TS-275 material, the forming limit curve for the tinplate material under investigation was constructed.