Assessment of the upper and lower levels of permissible strains in the manufacture of sheet and thin-walled parts based on the forming limit diagram

Forming limit diagrams (FLDs) are currently widely used in the analysis of sheet metal forming without destruction and in assessing the technological capabilities of metal forming. This paper is devoted to the FLD-based assessment of the maximum and minimum limiting strains of the forming of thin-walled workpieces. Theoretical analysis of well-known criteria is used, including the criteria for the occurrence of scattered and localized necks, the so-called energy (static) criteria, as well as the criterion of abrupt local thinning of the sheet, the so-called kinematic criterion. This paper considers a two-way analysis of the forming limits of thin-walled workpieces according to FLDs, which allows one to determine the upper and lower estimates of the limiting strains of the forming. The analysis is based on the FLD study results obtained by various authors and published both in Russia and abroad. The presented research results can be used as a first-order analysis tool for evaluating and predicting the technological capabilities of the molded material in the manufacture of thin-walled parts. They are also relevant to metal processing by pressure and plastic forming of thin-walled sheets.