3 Fundamentals of press design

Press types and press construction
slide
cylinder
slide
slide
ejector
counter
drawing die
draw punch
active draw
cushion
draw cushion
cylinder
Fig. 3.1.10 Single-action hydraulic press with active draw cushion for counter drawing
pression columns into the corner areas of the blank holder on the die
(Fig. 3.1.11 and cf. Fig. 4.4.39). When the slide reaches the bottom dead
center, the draw cushion is moved back to the upper position either in an
uncontrolled, i.e. together with the return motion of the slide, or a controlled
movement, i.e. after a prescribed standstill period, by the lift
cylinder acting in the center of the lifting bridge. Impact damping is
achieved by means of optimized proportional valve technology, ensuring
that the draw cushion reaches its upper end position without vibrations.
The benefit here is that the draw cushion force can be controlled on a
path-dependent and a time-dependent basis during the drawing process.
It is possible, for instance, not only to reduce and increase the overall
blank holder force, but the pressure levels of the four cylinders can also
be modified independently of each other due to the short pressure
response time within a range of 25 to 100% of the rated pressure. As a
result, the blank holder pressure can be individually controlled over the
entire deep drawing process at each of the four corner points of the die.
The precision control of the blank holder follows a prescribed force versus
time profile (Fig. 3.1.12).
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
45