Residual stress in the cylindrical drawing cup of SUS304 stainless steel evaluated by split-ring test

The residual stresses in the wall of a SUS304 stainless steel cylindrical drawing cup were evaluated by split-ring tests, and the influences of stamping die parameters on the residual stress were investigated. A new theoretical model of a split-ring test was developed to evaluate the residual stress in a ring, which was verified to be reasonable and reliable by numerical simulations with ABAQUS code and by nanoindentation tests. Seven groups of split-ring tests were completed, and the residual stresses were calculated according to the theoretical model. The split-ring test results showed that the circumferential residual stress in the wall of the SUS304 stainless steel cylindrical drawing cup was very large and did not change with the different die corner radius. The circumferential residual stress first increased with the increase of drawing punch–die clearance, then was almost unchanged when the clearance increased greater than blank thickness 1 mm. Thus, a smaller clearance was suggested to be chosen to reduce the residual stress in the wall of the SUS304 stainless steel drawing cup.

Seven groups, three samples in each group, and a total of 21 qualified cylindrical drawing cups in Fig. 2 were made from a circular SUS304 stainless steel sheet about 72 mm in diameter and 0.94 mm in thickness by deep drawing with different processing parameters. After the rings were cut from the cup walls, each ring was split along the radial direction. Two ends of each split ring opened a distance to release the circumferential residual stress in the closed ring. After measuring the opening distance, the residual stresses in the drawing cup walls were calculated by Eq. (18) in the newly developed split-ring test theoretical model of this paper. Then reasonable technology measures were found to reduce the residual stress by analyzing the influence of the mold parameters on residual stresses.