3 Fundamentals of press design

Deep drawing and stretch drawing
metal remains unchanged since an increase in the surface area does not
occur, as it occurs in a stretch drawing process.
The material flow in the drawing process can be controlled, as
required, by adjusting the pressure of the blank holder in between pure
stretch drawing, in which no sheet metal can flow out of the flange area
into the draw die, and deep drawing, in which there is a wrinkle-free and
unrestricted material flow (cf. Fig. 2.1.32).
In deep drawing, as a first step, a cup is produced from the flat blank.
This cup can then be further processed, for example by an additional
drawing, reverse drawing, ironing or extrusion process. In all deep drawing
processes, the pressing force is applied over the draw punch onto the
bottom surface of the drawn part. It is further transferred from there to
the perimeter in the deformation zone, between the die and the blank
holder.
The workpiece is subjected to radial tension forces F R and tangential
compression forces F T (Fig.4.2.1). The material is compressed in the tangential
direction and stretched in the radial direction. As the draw
F R
F T
F T
F R
F T
Fig. 4.2.1 Pressing forces in deep drawing of a round cup with a blank holder
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
F R
F R
F T
157