Robustness of the sheet metal springback cup test

Abstract

The robustness of a proposed test for elastic springback characterization of sheet metal has been examined using a matrix of defined experimental errors. A series of flat bottom deep drawn cups made from AISI 1010 steel sheet were examined. It was found that misalignment of the blank over the forming tool and error in the vertical location where the springback ring was cut from the cup sidewall had the largest effect on the resulting springback opening. Other experimental errors involving cup height and ring width were found to be less important. The effect of in-plane anisotropy of mechanical properties on springback was negligible. The results are examined in terms of measured through thickness residual stresses and elastic bending of beams with circumferential thickness gradients.

Cylindrical Cup Manufacturing Using 12 mm Thick Circular Blanks of AISI 1040 Graded Medium Carbon Steel: an Innovative Approach

“…Herein, lines connected to data points indicate to an increasing propensity in spring back behaviours (split ring gaps) of cups in every draw stage, agreed by Foecke and Herold. 19) Moreover, it is also observed that the degree of spring back tendencies reduces on advancement of draw steps, which perhaps due to decrease in residual hoop stresses on cup walls, caused by increasing predominance of wall ironing 12) in second and third draw steps. Further, the trends of split ring gaps of cup walls (Fig.…”

“…9, the peaks of the thickness strains are observed near base/bottom portion of the cups in three draw stages, which implies deformations farther beyond the yield stress, thus reducing the hoop stress, and also the magnitude of the through-thickness strain in-homogeneities (difference in plastic strain from one location to another) decreases, 19) which, in turn, decreases the split ring gaps (Fig. 11).…”

“…The effects of cup drawing processes, such as dimensions as well as quality of cups, wall thickness distribution profiles, drawability and ironability parameters, empirically calculated punch force history, hardness distribution profiles, strain distribution profiles, and evolution of microstructures during such complex deformation processes, were determined and discussed. Also, spring back tendencies along the cup walls were determined by conducting a simple and repeatable Demeri split ring test, as described by Foecke and Herold; 19) Danckert. 12) For this, ring specimens (7 mm wide) cut from the cups at different heights and then were mechanically slitted longitudinally along their radial planes, schematically shown in Fig.…”

“…were calculated by using volume constancy formula, Eq. (19), and slab method, Eq. (20), respectively.…”

“…Considering the wall thickness distribution profiles of cups, Foecke and Herold 19) have stated that a higher standard deviation of wall thickness along vertical position indicates an increased circumferential material flow and higher strain levels attribute to reducing spring-back as more material is deformed beyond the yield stress. In the present investigation, estimation shows the standard deviations of the cup wall thicknesses, such as 0.150821, 0.091756 and 0.079243 respectively for cups of first, second, and third draw stages.…”