3 Fundamentals of press design

304 Sheet metal forming and blanking
Notching machines can be equipped with supplementary attachments
for special applications. These include devices for the production of
– interrupted hole patterns,
– tapered lamination stacks and
– skewed lamination stacks.
Blanking lines with complete blanking dies
Medium-sized batches of electric motors, finished segments, raw segments
and pole blanks are generally produced using complete blanking
dies (Fig. 4.6.13). Here, the external contours, holes and notches are
blanked in a single work process, generally using straight-sided presses
(cf. Fig. 3.1.1). The press concept used here is similar to that of universal
mechanical presses (cf. Sect. 4.4.1). It is also possible to manufacture
circular blanks, which are frequently used for further processing in
notching machines. The width of the individual blanks, strips or coil
material can be anywhere between 300 and 1,250 mm. These presses
are constructed for blanking forces ranging from 1,250 to 5,000 kN. The
stroking rate can be adjusted continuously between 15 and 150 strokes
per minute depending on the size of the machine and the process engineering
concept used.
The dies are often constructed in such a way that the punch with the
outside contours is located in the bottom die holder and the female die
is located in the upper die holder. Several parts can be produced simultaneously.
In some cases, the scrap is punched by the bottom die.
The separate stripper plate in the bottom die strips the scrap web
while the ejector in the upper die ejects the finished part. This requires
a plate or crossbar ejector in the press slide which is active near the top
dead center.
The gib columns generally extend out of the gib bushes when the die
opens. Therefore, they are usually manufactured of steel, while the gib
bushes are made of bronze. The coil guiding elements are combined
with the stripper plate.
As a single-unit welded construction, the press body is configured for
a high degree of rigidity. Considering that high-quality blanking dies
are used, the precision of the slide gib is of particular importance. The
eight-track roller gib system has proven to be an ideal system here
(cf. Fig. 3.1.6). The slide is equipped with a total of 16 roller elements,
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998