3 Fundamentals of press design

Sheet metal forming lines
Press layout
The design of a large-panel transfer press depends on the number of stations
and the distribution of forces. The four to seven die sets required
for the production of sheet metal parts are distributed over one, two or
three slides. The transfer step depends on the size of the parts. The
slides are guided in eight tracks (cf.Fig.3.1.5). In two- and three-upright
presses, two, three or six die sets are each distributed to one slide
(Fig. 4.4.28c). Here, tilting of the slide can occur as a result of off-center
loads, and must be partially compensated by appropriate countermeasures
in the die set. In the case of extremely high drawing forces in the
first work station, a four-upright press with a separate slide for the first
station is recommended (Fig. 4.4.28c).
Modern large-panel transfer presses are equipped with link drive systems
in order to reduce the closing speed of the dies (cf. Fig. 3.2.3). The
press crown is split into two parts, the press bed into two or three parts.
The press body is clamped by hydraulically pre-tensioned tie rods (cf.
Fig. 3.1.1).
Automation
Blank feed, workpiece transport, draw cushion control, part removal
and in some cases also the stacking of finished parts as well as electrical
control of the entire transfer press are fully automatic (Fig. 4.4.11).
When changing from one stack to the next and when ejecting double
blanks, continuous operation of the destacker is essential. Supplementary
attachments for washing and lubricating the blank in the destacker are
also frequently integrated. The first blank is separated off the stack by fanning
magnets and lifted by suction units. It is then transferred to the centering
station by means of magnetic belts and roller conveyors (cf. Sect.
4.4.4). The feeder to the first station lifts the blank from the centering station
and transfers it to the first press station. Subsequent workpiece transport
is performed by the tri-axis gripper rails. The gripper rails index the
workpieces from one station to the next (Fig. 4.4.29). Depending on the
blank geometry, the rails are equipped with pneumatically actuated active
grippers or shovels which support the workpiece during transport. In
order to achieve a higher output, the gripper rail mechanism is manufactured
for optimum weight savings as a box-type construction using hollow
profiles. The entire transfer system is electronically monitored to
check for part presence, position and other functions.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
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