3 Fundamentals of press design

Fine blanking
punches, as well as the effect of the vee-ring. The die-roll width b E
depends on the die-roll height h E. In most cases, the following applies:
b 5 h mm
≈ ⋅ [ ]
E E
Burr-free fine blanking is not possible. The blanking burr is located
opposite to the die-roll, and occurs as soon as the first part is blanked
due to edge preparation at the blanking plate and the blanking punch.
As a result of wear of the active elements, the height and width of the
burr increase with the increasing number of blanking operations. The
blanking burr is generally removed by belt or flat grinding.
The cut surfaces are not at absolute right angles to the plane of the
sheet metal. The outside contours of a blank on the burr side are greater
than at the die-roll side – inner contours are smaller on the burr side
than on the die-roll side. As a guideline, the difference amounts to
0.0026 mm per 1mm of blank thickness, and depends on a number of
influencing variables, such as dimensioning of the blanking plate, configuration
of the blanking plate with or without shrink ring, preparation
and coating of active elements.
Application examples
The following pictures provide examples of fine blanked parts. In
Fig. 4.7.19, an automatic car transmission is illustrated to indicate the
hE hE
R hG R hG � �
Fig. 4.7.18 Geometry and die-roll on a fine blanked part:
R corner radius; b E die-roll width; β corner angle;
s blank thickness; h G burr height; h E die-roll height
b E
s s
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
bE
349