In this research an analysis of multi-stage deep drawing process is carried out
for 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 the
experimental 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 the
drawing ratio between the neighboring stages was reduced so as to achieve more
uniform deformation in the cross-section. The study confirms the real deformation
mechanism and inspects the contact conditions at the tool-blank interface. In the
second and third stage of drawing, three direct re-drawing methods were used to
re-draw the cup produced from the first stage (By using internal blank holder, with
out blank holder, and by using centering block method).
The analysis reveals that the difference in the drawing ratio, and the irregular
contact condition between the blank and die (which occur when using second and
third method of re-drawing), induces non-uniform metal flow, which cause
wrinkling, tearing, and severe extension of metal during the re-drawing process. for
There the first method (By using internal blank holder) was chosen for detailed
analysis 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 has
been found that the drawing force decrease for each successive stage of drawing
process, increasing the value of effective strain distribution over the cup wall with
die nose radius, the radial and hoop strain increases remarkably for each successive
stage of drawing, while the thickness strain increases slightly, which lead to
produce a uniform wall thickness of the re-draw cup. It was found that, the use of
internal blank holder in re-drawing process, increases cup formability, extends tool
life by eliminating wrinkling and tearing, reduces the possibility of failures,
improves part quality and increase production speed.