128
Blanking and Punching
Dies
Fig. 9.22
Methods
of
positioning the individual blank
or
workpiece:
with
dowels, b
with
ring, c
with
rail.
9.5.4
Pilots
Pilots are used in progressive and compound dies to position the work strip so that the relationships
between stations or previously punched holes and the outside blanked contours of work pieces may be maintained. In Fig. 9.23 are shown various methods for mounting pilots in punches.
The hole that receives the pilot should be extended through the punch so that the pilot may be
removed if it breaks. The pilot should fit the work hole with a tolerance of from 0.02 to 0.15 mm. Pilots are generally made
from tool steel, hardened and polished. They may have a radiused end that terminates in the diameter of the pilot, or the end of the pilot may be blunt.
3
1 1 -punch
5-backing plate 9-spring
2-punch holder 6-die
1
0-screw 3-punch plate
7
-stripper
1
l-die shoe 4-pilot
8-bushing 12-work strip
Fig. 9.23
Various methods mounting
of
pilots
in
punches.
Blanking and Punching Dies
129
1-die 2-blanking punch
3-pilot 4-punch
5-French notch punch
6-guide plate I-punch plate
8-backing plate 9-punch holder
1 0-die shoe 11-guide rail
12-stock guide 13-shank
Fig. 9.24
Compound multi-row die.
Pilots are generally made from tool steel, hardened and polished. They may have a radiused end that terminates in the diameter of the pilot, or the end of the pilot may be blunt. In Fig.
9.24 is shown a multi- row compound die in which the pilot is press-fitted into a hole in the center of the blanking punch.
9.6 CENTER OF DIE PRESSURE
The die pressure should be centered on a vertical line passing through the specific point that defines the resultant force of the punching and blanking forces. There are two ways to determine the center of the die
pressure: mathematically and graphically.
a
Mathematical solution.
As
is known from statics, the coordinates of the point of resultant force are given by the formulas:
i = l
i=l
9.18
where:
=
partial punch and blank forces,
=
coordinate center of gravity of partial punching and blanking parts.
130
Blanking and Punching Dies Assuming that the punch and blank forces are directly proportional to the length of the cut edges Li,
the center of the die pressure may be determined by the following formulas:
+ +
...
+
9.19
i=l
where: Y
=
coordinates of the center of the die pressure,
=
coordinates of the center of gravity of a partial length of cut edge
=
partial length of cut edges.
b
Graphical solution: subdivide the total length of the cut edges in Fig. 9.25 into partial lengths
. . .
of which the center of gravity is known. The size of each partial length is represented as a force applied to the center of each partial length. Use the force polygon and link polygon closed to determine
the main forces and
operating in any two directions preferably at right angles. The point of inter- section of the lines of application will indicate the position of the center of die pressure.
edge length
of
punch edge length of punch
edge length
of
punch -blanking punch
strip s-center of die gravity
Fig. 9.25
of
center
of
die gravity.
Blanking and Punching
Dies 131
9.7 EXAMPLES OF CUTTING DIE DESIGNS
In this section are shown some examples of designs for punching, blanking, compound, and combination dies. Fig. 9.26 shows a design for a single blanking die. The die can produce either a right- or left-hand
part.
A flat blank, sheared by a blank-through type of blanking die, drops through the die block lower
shoe and piles up on top of the bolster plate, or falls through a cored hole in the plate.
.
The die consists of a punch holder
and a die shoe with a guide post
and a guide post bushing 9. The guide posts are press-fitted into the die shoe and secured. The blanking punch
is directly without a
punch plate fixed to a punch holder with screws and dowel 13. On the die shoe 2 is fixed the die
block the stripper
the guide rails and the strip stop 7.
-punch shoe
A
Section A-A
3-die 4-punch
5-stripper 6-guide rail
7-strip stop 8-guide post
9-guide
post
bushing 0-security ring
1 1 -spring
of
guide rail 12-screw
13-dowel
14-work strip
Fig. 9.26
Single blanking die.
In Fig. 9.27 is shown a punching die with a series of punches, which are staggered to reduce the force required to shear through metal, and to prevent punch breakage. The offset of the outside punches over the
center punch is one thickness of the material.
The die consists of a punch holder 1 and die shoe with guide post
and guide post bushing 10. The guide posts are press-fitted into the die shoe and secured. The punches
4 and the stripper with the punch plate 3 and screws and dowels are fixed to the punch holder.
The die shoe holds the die block which also has the function of guiding the workpiece
the workpiece stop
which is attached to the die shoe with a screw and dowels 13.
132
Blanking and Punching Dies
Fig. 9.27
Single punching die with a series of punches staggered.
6
Fig. 9.28
Compound die with parallel positions for punching and
blanking operations.
I
1 -punch holder
2-die shoe 3-punch plate
4-punching punch 5-stripper
6-bellevile spring 7-die
8-workpiece stop 9-guide post
10-guide bushing
1 1 -security ring
13-dowel 14-workpiece
1-punch holder 2-die shoe
3-die 4-punch
5-workpiece stripper 6-scrap stripper
7-blanking punch 8-strip guide
bolt
9-stop pin 1 0-guide post
1 I-guide post bushing 12-workpiece
