Effect of reverse dome stretching on dome height and forming limits of sheet materials

Reverse bending and stretching of sheet materials is often employed in press forming of complex automotive components. In this work, hemispherical dome stretching tests were followed by reverse dome tests on automotive aluminum sheet specimens to assess the influence of the strain and shape on dome height at neck formation and limit strains. The above test scheme offers a means of subjecting the sheet material to reverse bending and stretching and thereby changing its strain path during the process. The results indicate significant improvements in dome height as a function of pre-strain (or initial dome height) compared to the simple dome stretching process. The forming limit strains, on the other hand, are lowered. The reason is attributed to the redistribution of strain (more uniform deformation) through the punch/specimen contact during the reverse bending and stretching process.