3 Fundamentals of press design

278 Sheet metal forming and blanking
due to off-center loading is eliminated. When dies are provided with a
locating pin for clamping in the press, this should be positioned in the
location of the resultant force.
To determine the location of the resulting blanking force, the shape,
scope and position of sheared contours are of importance. The position
of the center of force is generally determined by calculating the center of
gravity of the blanking edges / cut contours or where simple geometries are
involved (circle, rectangle), by ascertaining the center of gravity of the
punch perimeters / cut contour perimeters. Where asymmetrical punch
configurations are involved, this calculation must be made for the x
and the y direction:
For the location of the resultant force in the x direction (distance
from the y axis), the following applies:
x
S
U1⋅ a1 + U2⋅ a2 +…+ U ⋅ a
=
U + U +…+ U
1 2
n n
[ mm]
,
where U [mm] represents the relevant perimeters of the individual
punches and a [mm] is the distance of their centers of gravity from the
selected y axis. If the line centers of gravity are taken as a basis, then
x
S
l1⋅ a1 + 12⋅ a2 +…+ 1n
⋅ an =
[ mm]
,
1 + 1 +…+ 1
1 2
where 1 [mm] is taken to represent the lengths of the blanking edges.
The location of the resulting force in the y direction (distance from the
x axis) is calculated from the corresponding equation for y, by substituting
the distances of the perimeter / blanking edge lengths from the
x axis for b [mm]:
y
y
S
S
U1⋅ b1 + U2⋅ b2 +…+ U ⋅ b
=
U + U +…+ U
1 2
l1⋅ b1 + 12⋅ b2 +…+ 1n
⋅ bn =
mm
1 + 1 +…+ 1
1 2
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
n
n
n
n
n n
[ mm]
[ ]