Marciniak–Kuczynski type modelling of the effect of Through-Thickness Shear on the forming limits of sheet metal

Forming of high strength titanium sheet at room temperature

Formability Issues in the Application of Tailor Welded Blank Sheets

Adhesion of coatings to sheet metal under plastic deformation

As a lightweight material, magnesium is being increasingly used for automotive parts. However, due to a hexagonal-closed-packed (hcp) crystal structure, in which only the basal plane can move, magnesium alloy sheets exhibit a low ductility and formability at room temperature. Press forming of magnesium alloy sheets is conventionally performed at elevated temperatures of 200 °C to 250 °C and thus is known as energy consumed forming. Therefore, in view of an energy saving forming technology, we study magnesium alloy sheet forming by a rotational incremental sheet forming (RISF) at room temperature, where the rotational tool generates local heat of specimen enough to accelerate plastic deformation. The flow curves of the magnesium alloy sheet are obtained and calculated at elevated temperatures, while the yield loci of the magnesium alloy sheet are measured at room temperature. Using RISF, a square cup of 80-mm width, 80-mm length, and 25-mm height is then formed from a magnesium alloy sheet at room temperature. In addition, the strain distribution is obtained and compared with the forming limit curve (FLC) by considering the effect of the tool radius and is found to effectively predict the forming limit of a magnesium alloy sheet in RISF.

Study of Forming Limit for Rotational Incremental Sheet Forming of Magnesium Alloy Sheet

Recent work on sheet metal formability had shown that the position of forming limit diagrams (FLDs) in punch stretching is higher than that in in-plane stretching because of a strain gradient effect resulting from bending a flat sheet into a curved sheet by punch stretching. To our knowledge, none of the developed theoretical models in the study of localized necking can be used to predict this phenomenon accurately so far. In this study, a new model, using Barlat and Lian’s new nonquadratic anisotropic yield criterion, is proposed by introducing a strain gradient term in the constitutive equation to consider the effect of the first order strain gradient (curvature), in the thickness direction resulting from bending, on the localized necking in anisotropic sheets. The developed model is used to study the effects of curvature on FLDs and to predict FLDs in punch stretching and inplane stretching for various materials. It is found that the theoretical predicted results are in good agreement with experimental data.

Effect of strain gradient and curvature on forming limit diagrams for anisotropic sheets

Ironing is a very useful process when employed in combination with deep drawing to produce a uniform wall thickness and to increase the wall height. The analysis of the ironing process is conducted based on the general two-dimensional axisymmetrical shell theory incorporated with the Tresca maximum shear stress yield criterion for isotropic thin and thick sheets and the Hosford nonquadratic anisotropic yield criterion for anisotropic thin sheets. A complete plastic solution is obtained and the plastic stress field is found in closed form. A governing equation for a limit ironing ratio (LIR) is found and the total ironing force is also given in the closed form. The predicted maximum ironing reduction under some optimal conditions can reach up to 60%–70%, which is in good agreement with experimental observations. The results of the limit ironing ratio, stress field, and the total ironing force are given and compared with some results based on the finite element technique. The normal and tangential forces are compared with experimental results and it is shown that this prediction gives reasonable results.

J. C. Gerdeen

Papers

Effect of strain gradient and curvature on forming limit diagrams for anisotropic sheets

A Theoretical study of the ironing process in sheet metal forming