Blanking and Punching Dies
111
Material thickness
mm 3.0
to
5.0
Table 9.1 Value of Dimension Depends on Material Thickness
0.5 5.1
to
10.0 5.1
to
10.0
10.1
to 15.0
9.2.2 Fastening to the Die Shoe
There are many methods for fastening a die block to a shoe. In Fig. is shown one method, in which
socket head screws are inserted from the bottom of the die shoe into threaded holes in the die block. Dowels are used to prevent a shift in the position
of the block. Sometimes the die opening is made from a bushing and inserted into a machine steel retainer. If the
bushing has a shoulder, it is held in the retainer as shown on Fig. If it has no shoulder, it is pressed into
the retainer as shown in Fig. The lower end of the bushing has a reduced diameter to insure alignment
when it is pressed into the retainer. The bushing can be fastened into the retainer with a ball and screw, as shown in
The purpose is to save the cost of large amounts of tool steel. This type of fastening is gen- erally used to allow replacement
of the die ring if it is worn or damaged. Sometimes a bushing is used at the bottom, as is shown in Fig.
The purpose is to save the cost of large amounts of tool steel.
Section A-A
-die
shoe
2-die block 3-dowel
4-socked head screw
Fig.
9.2
a
Fastening
a
die block to a shoe; b, c, d, e Methods
of inserting a bushing into a machined retainer.
112
Blanking and Punching Dies
9.2.3 Sectioned
Die
If a workpiece is large, or if the die opening is complicated, and the contours are difficult to machine, the die may be made in sections. If possible, the die sections should be
of approximately the same dimensions
to ensure economic use of the tool steel. Several types of sectional dies and punches are shown in Fig. 9.3. It is also possible to use a bevel-cut angle
on the face of a sectional die. The bevel shear may be convex or
concave see Fig. 4.6.
1-Segment of
die 2-Segment of punch
Incorrect Incorrect
Section A-A
I I
Section Section
Fig. 9.3 Types of sectioned die and punches.
To save very expensive tool steel, a die and punch with welded edges, as shown in Fig. 9.4, is often
used, primarily for blanking parts of larger dimensions and material thickness up to T
=
1.5 mm. The die is made of carbon alloy steel, and the edges are welded with a special electrode of alloy steel, and then
machined. The welded edge may have a hardness of up to 60 Rc. This type of die is cheap, and repair is
easy. Carbide dies are widely used to produce small electrical parts at lower cost per piece compared with
steel dies. When a carbide insert is subjected to high-impact load,
it
must be supported externally by press-
ing the carbide ring into a hardened steel holder. Suitable steels for die holders include SAE 4140, 4340, and 6145 hardened to
38
to 42 Rc.
A
ratio of between the case and the carbide insert has been satis-
factory for most applications, but the ratio can be less for light work.
Blanking and Punching
Dies
UTS 117
245 392
C 0.6
0.8
1
113
784
1.3
1 -die
2-punch 3-punch holder
4-die shoe 5-stripper
6-spring 7-guide post
8-guide bushing 9-guide pin
10-die stop 1 1 -work strip
12-security screw
Fig. 9.4
A die
and punch
with
welded edges.
9.2.4 Calculation of Die Block Dimensions
A die block for blanking and punching operations is loaded at force About 40 percent of this force is
exerted in a way that would fracture the die block in the radial plane. However, the die block is addition- ally loaded with the friction force produced when the blanked or punched material is pushed through the
opening of the die. The calculations for the die block dimensions are very often simplified, making use of two empirical formulas calculating only the thickness of the die block
and the width of the wall e Fig. 9.5. The height thickness H of the die block is calculated by the formula:
=
+
5T
+
where: T
=
material thickness,
=
constant whose value depends on the mechanical properties of the workpiece material and is
a, b
=
opening die dimensions, given in Table 9.2.
The wall thickness e is given by the formula:
e
=
10
114
Blanking and Punching Dies
Fig. 9.5
Schematics for calculation of die block dimensions.
If the opening die has a contour with angle less than 90 degrees, the value of
e
needs to be increased from 15 to 20 percent.
The dimensions of the rectangular die block in Fig. are:
The maximal bend moment for a rectangular die block is: 8
The resistance moment at section is:
B
-
bH 6
The stress bending of the die block is:
=
0.75 6F1
W B- bH
For a rectangular die block, the following formula must be applied:
where:
=
permitted bending stress. For heat-hardened alloy tool steels, the value of
=
Blanking and Punching Dies
