3 Fundamentals of press design

212 Sheet metal forming and blanking
ate a contoured blank. This is done either by an all round blanking
stroke or by local edge blanking – generally at both ends of the side
member.
The advantage of processing sheet plates is that the blanks do not
assume a camber shape due to the all round blanking cut used in their
manufacture. Thus, the straightening process can be omitted. However,
in this case a lower degree of material utilization is achieved. In the case
of complex side member geometries, involving different flange and
web heights, however, it is possible to save on material input by nesting
the contoured blanks (cf. Fig. 4.5.2 to 4.5.5). The blanking cut leaves
behind scrap webs which are broken down into scrap segments.
Production line concepts
There are two basic line types used to produce side members. These differ
in principle, based on the infeed and outfeed direction of the sheet
metal: Whereas sheet plates below 7m in length can still be fed into the
press through the press uprights transversely to the longitudinal press
axis, longer untreated blanks have to be fed parallel to the longitudinal
press axis.
In lines wheretransport takes place parallel to the longitudinal press axis,
the blanks are fed by means of an infeed conveyor belt inside the press
uprights (Fig. 4.4.13). Cross-feed units simultaneously feed the uncut
blank into the die and the previously contoured blank out of the die
onto the reverse outfeed conveyor. Transport systems making use of
magnets are used to stack the contoured blanks emerging from the outfeed
conveyor. Integrated in the line is also a blank turning station. The
lines are designed in such a way that both, contoured blanks punched
from uncut blanks and side members formed from contoured blanks,
can be manufactured.
Important accessories for use with fully automatic lines include a
blank lubricating or spraying device at the press infeed, a hole pattern
camera to detect punch breakage and a device for edge milling. Fully
automatic lines achieve cycle times of 3 strokes per minute. Taking into
account the need for two passes and without considering the set-up
time of around 15 min required for the change from blanking to bending,
this results in an average line output of some 1.5 side members per
minute. Die changeover also takes place in the longitudinal axis of the
press.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998