3 Fundamentals of press design

290 Sheet metal forming and blanking
eccentric presses, representing a reduction in the noise level of some
12 dB(A) (cf. Fig. 3.2.3). In addition, secondary measures are applied to
reduce the noise emission from blanking shock in presses, for example
by providing a sound enclosure. This can serve to reduce noise by as
much as 25 dB(A).
As a rule, modern presses are mounted on rocker elements in order to
reduce floor vibrations. With a natural line frequency of some 3 Hz, this
type of solution achieves an isolating efficiency of around 80%.
To allow blanking presses to also produce straight and trapezoidal
blanks, swivel dies are used. These are generally configured in the form
of impact dies. Vertical guidance of the upper die is integrated directly
into the die set. The swivel movement is generated by hydraulic cylinders
or electric motors, nowadays generally using servomotors and gear
drive. The PLC control specifies the swivel angle.
Stacking lines
Both in the case of contour blanking lines and cut-to-length lines, the
produced blanks are stacked onto pallets by automatic stacking units
(Fig.4.6.4). Conveyor belts arranged crosswise or lengthwise, relative to
the longitudinal axis of the press, transport the blanks either lying or
hanging out of the blanking line up to the adjustable stops, where they
are located and ejected onto pallets. The pallets are put on stacking
carts equipped with lifting devices which are lowered continuously in
order to permit precise stacking. Using two stacking carts in each stacking
device, continuous operation is possible.
Die change
In blanking presses, die change is performed fully automatically using
two moving bolsters (cf. Fig. 3.4.3). The moving bolsters move out of the
press towards the operating side and are arranged in the form of T-tracks
(cf. Fig. 3.4.4). Positioning takes place automatically in the machine, on
the set-up station and in the exchange position. This configuration
allows to achieve die change times of under 5 min.
Modern coil lines are also automatically reset (cf. Sect. 4.3). The control
system automatically executes the sequences “fetching the coil”,
“depositing the coil”, “coil insertion”, “finish processing of the coil”,
“welding seam disposal” and “scrap metal disposal”.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998