Forming Limit Diagram Prediction of Thick Anisotropic Sheet Metals at Warm Conditions Using Finite Element Modelling of Hemispherical-Punch Stretch Forming

Forming limit diagrams (FLD) are powerful and efficient tools to determine limit strains, plastic instability, and prediction of necking as well as tearing during various sheet metal forming processes. These diagrams illustrate the range of strains at which the sheet material can be drawn without fracture. One of the popular methods to determine forming limit diagrams is the hemispherical-punch stretch forming process. In this research study, the forming limit diagram of thick anisotropic sheet metals in warm conditions has been determined using finite element modeling of the hemispherical-punch stretch forming process. To take the anisotropy of the sheet metals into account, the anisotropic Hill-48 yield criterion has been used. To determine the necking point of the sheet metals the second derivative of equivalent plastic strain has also been used. Keeler’s theory has been selected to validate the finite element modeling results. The results indicate that finite element modeling can predict forming limit diagrams well.