3 Fundamentals of press design

Part transfer
There is a broad range of possible solutions for part transfer, including
transport devices in the broader sense, such as tilting mechanisms
for billet containers, steep conveyors (pusher or chain conveyors),
vibrating conveyors, separating devices and scales. Therefore, these will
not be dealt with here. This chapter will concentrate instead on the
loading station and the transfer study for a mechanical cold forming
press with 2D transfer (cf. Sect. 4.4.6).
6.6.1 Loading station
The wide diversity of parts that must be fed into a forming press calls
for a number of different loading station concepts. Where cylindrical
billets with a length/diameter (L/D) ratio greater than 0.8 are being
processed, they are loaded from above into the feeding station by
means of a feed channel (Fig. 6.6.1, top). The bottom-most parts are
held in a holder, generally cylindrical in shape, that is provided with
recesses on the side to allow for the closing movement of the gripper.
Following the removal of the first part, the weight of the column causes
it to drop onto the base plate at the level of the transport plane.
Where billets with different dimensions are fed, if necessary the feed
channel and the exchangeable parts or the complete feed unit can be
exchanged with the aid of quick-acting clamps. The grippers are
equipped for cylindrical parts with prismatic active gripper elements
whose height should be approx. 50% of the billet length to ensure a
reliable gripping action.
If the L/D ratio is below around 0.8 to 1, or if formed parts with relatively
flat geometry are being processed (Fig. 6.6.1, bottom), then the
parts are conveyed into the loading station side by side in specially
designed feed channels. The parts are positioned initially below the
transport plane, and are raised by a pusher to transport level in synchronization
with the press cycle. After the pusher returns to its starting position,
the next part slips into the loading station to be raised to the transport
plane. The starting height and feed angle of the feed channels are
configured in such a way that the billets continue to slide under their
own weight. In the case of formed parts, the grippers are designed for
shaped fit if a prismatic gripper exhibits an unfavorable L/D ratio and
there is a danger that billets could rotate while being held by the gripper.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
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