3 Fundamentals of press design

126 Sheet metal forming and blanking
ensured (cf. Fig. 4.5.2 to 4.5.5). The workpiece remains fixed to the strip
skeleton up until the last operation. The parts are transferred when the
entire strip is shifted further in the work flow direction after the blanking
operation. The length of the shift is equal to the center line spacing
of the dies and it is also called the step width. Side shears, very precise
feeding devices or pilot pins ensure feed-related part accuracy. In the
final production operation, the finished part, i. e. the last part in the
sequence, is disconnected from the skeleton. A field of application for
progressive blanking tools is, for example, in the production of metal
rotors or stator blanks for electric motors (cf. Fig. 4.6.11 and 4.6.20).
In progressive compound dies smaller formed parts are produced in
several sequential operations. In contrast to progressive dies, not
only blanking but also forming operations are performed. However,
the workpiece also remains in the skeleton up to the last operation
(Fig. 4.1.3 and cf. Fig. 4.7.2). Due to the height of the parts, the metal
strip must be raised up, generally using lifting edges or similar lifting
devices in order to allow the strip metal to be transported mechanically.
Pressed metal parts which cannot be produced within a metal strip
Fig. 4.1.3 Reinforcing part of a car produced in a strip by a compound die set
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998