3 Fundamentals of press design

214 Sheet metal forming and blanking
Die concept
The blanking and bending die each comprise a basic die equipped with
trimming and piercing modules in accordance with the various side
member lengths. Side members are structured in such a way that certain
groups of holes, for example those used to fasten the front and rear
suspension mounting, are identical and only change relative to the
wheel base. In the area of the driver’s cab at the front end of the side
member, the contour and hole patterns are identical. The modules are
accordingly adjusted and positioned according to the requirements of
each individual side member type:
– front module for the area of the driver’s cab,
– main module, for example for the rear axle area,
– intermediate module to bridge different side member lengths and
– the end module.
If at all possible, right and left-hand side members should have the same
hole pattern. Only then it is possible to minimize the effort required for
drawing and mounting piercing hole punches when changing set-up
from right-hand to left-hand side members. The shearing edges required
for blanking the side member contour do not have to be reset, as for
example the left-hand contoured blank is produced from the right-hand
contoured blank by simply rotating it in the turning station. However,
for the bending process, bending dies, forming edges and ejector beams
in the asymmetrical areas must be changed for a new set-up.
As the position of the front module does not change, if the length of
the side members decreases, the position of the workpieces in the
blanking and bending dies becomes increasingly off-center. If a singlesided
coping cut is to be carried out at the same time, e. g. for example
when trimming the front, an additional off-center load is applied. The
off-center forces must be accounted for, either by a balancing module or
by providing a suitable press concept. Otherwise an unacceptable
amount of slide tilting action will occur.
To reduce the blanking force, the edges of the blanking die and
punch are configured in a saw-tooth arrangement and the piercing hole
punches are staggered on several blanking levels. The aim is to achieve
uniform loading over the entire length of the workpiece at every blanking
plane.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998