3 Fundamentals of press design

Fine blanking
blanking
force
F s
I II
F s max
FAbriß
time[s], stroke[mm]
Fig. 4.7.5 Press force-stroke curves for standard and fine blanking
III
IV
The smooth section of the cut surface and the blanking clearance are
closely related: the greater the blanking clearance, the lower the
smooth cut proportion. In addition to its size, the uniformity of the gap
along the part contour is also important. The gap should remain constant
when subjected to load during the blanking operation.
The size of the blanking clearance is primarily determined by the
sheet metal thickness to be cut, but also by the nature and strength of
the workpiece material. In contrast to the blanking clearance occurring
during standard blanking of around 5 to 10% of the sheet metal thickness,
the corresponding value for fine blanking lies at around 0.5%
(Fig. 4.7.6). In certain cases, the blanking clearance can also vary over
the part contour. Parts with toothing, for example, are manufactured
with a blanking clearance which is greater in the area of the tooth root
than it is at the tooth tip.
Vee-ring
The vee-ring is a characteristic feature of fine blanking dies. It runs in
the form of a raised serrated jag at a defined distance from the blanking
line and is pressed into the scrap web. Its function is to hold the
punched material outside the blanking line and so prevent lateral flow
of the material during the blanking process. In addition, it serves to
apply compressive stress to the sheet metal, so improving the flow
process.
To simplify maintenance, where sheet metal thicknesses of up to
4.5mm are being processed, the vee-ring is mounted on the pressure
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
fine blanking
standard
blanking
335