3 Fundamentals of press design

294 Sheet metal forming and blanking
and die output increases. Conveyor belts for transportation of blanked
parts are frequently arranged under the press. The parts drop out of the
female die onto an ejection channel, which is frequently oriented, onto
the conveyor belts. There is a separator integrated in the ejection channel
which segregates defective parts from the start of the coil, the end
of the coil or parts of the coil which lie outside the specified tolerances.
Link-up between this device and the downstream processing stations
for washing, annealing, polishing, inspection, coating or packaging of
parts is increasingly implemented using conveyor belts or handling
devices (cf. Sect. 4.6.4).
Stamping scrap is often collected in boxes and transported away. More
satisfactory than this method is continuous disposal by means of conveyor
belts positioned underneath the press. The scrap can either be fed
away directly through the female die or outside the die by means of
scrap chutes. If a scrap web is created, this is generally chopped by a
shear at the outfeed side of the press.
In order to reduce storage of material and capital tie-up to a minimum,
small batch sizes also have to be produced economically on highspeed
blanking lines. Short die change and resetting times are an essential
requirement here. Resetting for the manufacture of a different part
includes set-up of the feed and removal devices, the preparation of dies,
die change, conversion of the press and a final check of die and press
setting data (cf. Sect. 3.4).
As the blanking process is the major factor in determining the precision
of punched parts and also the service life of dies, steps must be taken
to minimize the vibration occurring between the punch and the female
die in the vertical and horizontal direction at the moment of sheet metal
breakthrough by executing the necessary measures at the machine
(Fig. 4.6.7).
Vertical vibrations are created as a result of the play existing in the
force flow of the press and of the elastic properties of the entire press
system. They cause an increase in the penetration depth of the blanking
punch in the female die, the extent of which depends on the
stroking rate. The result is increased punch wear (Fig. 4.6.9).
Compared to a press with friction bearings, vertical play is considerably
reduced when using an eccentric shaft running in roller bearings
(Fig.4.6.8). In conjunction with the hydraulic slide adjustment clamp,
the total vertical play is reduced to a minimum. A high degree of verti-
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998