3 Fundamentals of press design

288 Sheet metal forming and blanking
decoiler with
coil
cropping shear
straightener
threading unit scrap container
coil loop
roller feed and
cut-to-length shear
infeed area with lateral
coil guidance
Fig. 4.6.4 Cut-to-length lines: coil line, cut-to-length shear and stacking line
blank stacking cart
straightening (cf. Sect. 4.8.3). As the sheared blank also moves at the
same speed as the coil, there is no need to accelerate the blank as it is
the case when using stationary shearing methods. Compared to the
stop and go method used with roller feed and stationary shears, the
return movement involved in the flying shear method results in a
slightly lower output when working with short cut lengths.
Rotating shears achieve the highest number of cutting operations.
Their output lies at over 150 parts per minute, making them twice as
productive as a blanking press. In the case of rotating shears, the coil
material runs at a constant speed between two cutting tools moving in
opposite directions. The cutting tools are arranged over the complete
coil material width at right angles to the feed direction, so that the sheet
metal is separated transversely to the feed direction when it makes contact
with the cutting tools. When using this process, the surface edge
speed of the cutting tools and the speed of the coil stock must match at
the moment of shearing. While the cutting tools are not engaged, their
rotation speed is accelerated or reduced by the drive system in order to
produce the required blank lengths.
As is the case with flying shears, the feed rate and consequently also
the output of rotating shears depend heavily on the blank lengths. For
both shear types, it is necessary to have the supply loop for coil material
and the pit required to accommodate it, as shown in Fig. 4.6.4. Lines
with continuous feed are consequently shorter in comparison to coil
lines equipped with stationary shears.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998