3 Fundamentals of press design

228 Sheet metal forming and blanking
without the need for an ejector. The output of a press line making use
of a CNC feeder is between 8 and 10 large-sized parts per minute.
When using both, swing arm and CNC feeders, intermediate stations
are required. These intermediate stations are equipped with three to
five programmable axes for part transport in the longitudinal direction,
for transverse and height adjustment and also additional tilting movements.
Automation using robots offers the advantage that it eliminates the
need to deposit parts between the presses (Fig. 4.4.20). The robot’s gripper
arm positions the part directly from the die of one press into the die
of the next. This means that only one robot is required to service each
press without the need for intermediate stations. The main drawback of
robot-linked press lines is that heavy parts can only be transported
slowly or not at all due to the centrifugal forces and the long transport
paths. For this reason, output is largely dependent on part size and currently
lies between 6 and 8 parts per minute. The freely programmable
axes of the robot arm, in contrast, ensure that widely differing part
shapes can be transported into many different part positions.
Die change
In addition to the interlinkage of presses in a line, automatic die changing
systems also play a major role. Among die changing systems for
press lines, moving bolsters with left/right-hand rails or T-tracks have
proved to be the most popular (cf. Fig. 3.4.4). The former require more
space, but offer the shortest possible die changing times. The upper and
lower die of the die set which is no longer required are moved out of the
press on moving bolsters. Subsequently, the opposing bolsters move
the new die sets into the press. Preparation of the dies for the next production
run is performed outside the press during production. As a
result of die changing automation it is possible to achieve changeover
times of between 10 and 30min depending on the workpiece transport
system.
Nowadays, press lines are often enclosed in order to enhance safety
and noise protection. Noise emissions can be reduced by around
15dB(A) if the space between the individual presses and the peripheral
equipment is also enclosed (Fig. 4.4.19).
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998