3 Fundamentals of press design

Sheet metal forming lines
4.4.4 Destackers and blank turnover stations
Destackers
Destackers separate the blanks and feed them into the press in synchronization
with the press cycle. Where low stroking rates are
involved, the destacking and feeding operation is performed by feeders.
In the case of higher stroking rates, after destacking the blank is transferred
onto magnetic belts which transport them into the centering station,
for example the pick up position of the press transfer.
Destackers with feeder and suction cup tooling
In the case of press lines (cf. Sect. 4.4.5) with a stroking rate of about 10
to 12 parts per minute and where suitable blank shapes are being
processed, feeder systems are used. In case of a die change, the entire
tooling is replaced together with the attached suction cups. During
destacking, the tooling suction cups pick up the top blank from a stack.
The operation is supported by fanning magnets whose magnetic field
fans the top-most blanks in order to prevent the blanks from sticking to
each other. The magnets can be positioned manually or automatically
near the stack. Both permanent fanning magnets and electrically pulsating
magnets are used.
When processing non-magnetic materials, e.g. blanks from aluminium
or stainless steel, only suction cups can be used. In this case, compressed
air is blown in from the side of the stack to enhance the separation
of the individual blanks.
Destackers with magnetic belts
This design is equipped with one or two cylinder-actuated destacking
units provided with vacuum cups or magnets (Fig.4.4.15). These are
lowered between the magnet belts on the top-most blank of the respective
stack, and then raise and transfer the suspended blank to the magnetic
belt conveyor. Here, too, fanning magnets are used to support the
removal of individual blanks. Using these systems, up to 25 relatively
small and up to 15 larger parts per minute can be fed into the press.
To ensure that the press is able to operate continuously when changing
from one stack to the next, either two destacking stations or systems
with a reserve magazine are used. In the case of dual stacking feeders,
switchover from the finished to the new stack takes place automatically.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
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