Design Modification in a Multi-stage Deep Drawing Process

Abstract

In this research an analysis of multi-stage deep drawing process is carried outfor process design of cylindrical cup drawing with large drawing ratio ( β = 3.416).A three stage deep drawing tooling was designed and constructed to carry out theexperimental work required to produce a cylindrical cup of (25mm outer diameter)formed from a circular flat blank (82 mm diameter) comprised of mild steel of(0.15%) carbon content, without any intermediate annealing. The difference in thedrawing ratio between the neighboring stages was reduced so as to achieve moreuniform deformation in the cross-section. The study confirms the real deformationmechanism and inspects the contact conditions at the tool-blank interface. In thesecond and third stage of drawing, three direct re-drawing methods were used tore-draw the cup produced from the first stage (By using internal blank holder, without blank holder, and by using centering block method).The analysis reveals that the difference in the drawing ratio, and the irregularcontact condition between the blank and die (which occur when using second andthird method of re-drawing), induces non-uniform metal flow, which causewrinkling, tearing, and severe extension of metal during the re-drawing process. forThere the first method (By using internal blank holder) was chosen for detailedanalysis because it ensures reduction in wrinkling and tearing of the cup wall.From the comparison between the results of the three stages of drawing, it hasbeen found that the drawing force decrease for each successive stage of drawingprocess, increasing the value of effective strain distribution over the cup wall withdie nose radius, the radial and hoop strain increases remarkably for each successivestage of drawing, while the thickness strain increases slightly, which lead toproduce a uniform wall thickness of the re-draw cup. It was found that, the use ofinternal blank holder in re-drawing process, increases cup formability, extends toollife by eliminating wrinkling and tearing, reduces the possibility of failures,improves part quality and increase production speed.