Design modification in a multi-stage deep drawing process

Abstract EN

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, without 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.