A synchrotron study of residual stresses in a Al6022 deep drawn cup

Fueled by pressures to reduce scrap and tooling costs, the modeling and prediction of springback has become a major focus of interest in sheet metal forming. Finite element codes and packages are being developed or improved but face the demand for higher predictive accuracy which, in turn, requires accurate property data and a more complete understanding of the stresses that are responsible for the elastic part of the springback. In order to provide experimental data for these calculations, synchrotron X-ray diffraction measurements were carried out in order to determine the through-thickness distribution of axial and tangential residual stresses in an Al6022 deep drawn cup. The technique is able to provide true spatial resolutions of 0.05 mm for a strain measurement on a cup with 0.92 mm wall thickness. It is found that both axial and tangential stresses exhibit non-linear gradients through thickness and both exhibit a pronounced dependency on the axial position. The springback measured on a split ring cut from the cup agrees within 3% accuracy with the value predicted from the average of measured through-thickness stresses.