3 Fundamentals of press design

Fine blanking
plate of the die, while for thicker materials a second vee-ring is required
on the blanking plate. Where the inner forms are particularly large, the
ejector also features a vee-ring, which is pressed into the inner form slugs
inside the blanking line. Depending on the thickness and shape of the
part, the vee-ring is being increasingly placed on the die plate. In individual
cases, fine blanking also takes place without the use of a vee-ring.
The dimensions of the vee-ring and the distance from the blanking
edge depend on the thickness of the sheet metal (Fig.4.7.7). In some
cases, vee-rings are mounted only partly in the die area where a smooth
cut is required for functional reasons.
Work result
Generally, normal blanked parts feature a smooth and a fractured cut surface
(Fig. 4.7.8). The proportion of the smooth portion relative to the
fractured surface depends on a wide number of different influencing variables,
with for example as little as 1 / 4 smooth to 3 / 4 fractured surface. The
smooth area features the die-roll, while on the opposite side is the blanking
burr (cf. Sect. 4.5). The flatness and dimensional tolerances of the
standard blanked part are inferior. The fine blanked surface, in contrast,
is tear and fracture-free over the entire thickness of the sheet metal and
u ~ 5 % s
s
fracture zone
blanking punch
burr
vee-ring plate
blanking plate
ejector
smooth cut zone
die-roll
Fig. 4.7.8 Work result for standard blanking (left) and fine blanking (right)
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
u ~ 0,5 % s
s
337