3 Fundamentals of press design

Shearing lines
The blanking process used (Fig. 4.6.3) depends on the production
volume and the degree of material utilization. Rectangular blanks can
be produced using simple cut-to-length lines. Trapezoidal and parallelogram
shaped blanks require a swivel mounted shear or a swivelling die
in the blanking press, which move the shear or the die to the other
swivel position respectively during each feed movement. The feed unit
is driven either hydraulically or using program-controlled servomotors.
Closed contours can only be produced on presses with blanking dies (cf.
Fig. 2.1.29).
Lines for cut-to-length shearing
In cut-to-length lines, the coil stock is cut by means of stationary, flying
or rotating shears.
In lines with stationary shears, the roller feed indexes the coil stock
forward one step at a time. Cutting takes place when the material is stationary
(Fig. 4.6.4). This represents the lowest cost solution and uses a
fixed or swivel-mounted shear.
Flying shears are accelerated briefly to match the speed of the coil for
shearing. After completing the cut, the shear returns to its starting position.
The benefits of this design are continuous feed with a constant
straightening machine speed and elimination of the pit to accommodate
the coil loop, so ensuring that the material is not bent again after
straight
shear
swivel-mounted
fixed shear
swivel-mounted shear,
moving during feed stop
Fig. 4.6.3 Blank geometries, arranged according to the type of blanking line
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
contoured
blanking die
287