PUNCH FORCE 4g handbook vukotaboljanovicsheetmetalformingprocesses
Blanking and Punching
0.4 to 0.5 0.6
to
2.0 2.1
to
3.0
41
0.10 0.15
0.20 0.25
0.27 0.30
0.05 1961
1765 1560
1375 1175
1080 980
2100 1900
1670 1130
1225 1125
1030 2250
2010 1765
1520 1275
1080
Table 4.5 Value for specific pressure p
RINGED SCRAP CROSS-SECTION
Material
thickness
Punching and shaving operations can be done with the same punch at one stroke of the press. For such combinations, different shapes of punches may be used depending on the workpiece material. The gradual
punch shown in Fig. 4.14 is used for shaving brass, bronze, and aluminum alloys.
Workpiece Punch
Fig
4.14
Gradual punch for punching and shaving.
The first step of the punch is a smaller dimension, punching the work material, and the second level of punch is a larger dimension, shaving the hole. At the punching stage, the material is sheared by plane
AB, between the cutting edges of the die and the first punch level. If the punch is given the shape of a conic section, as shown in Fig
4.15, the process is completed in two phases. In the first, the punch penetrates into the material to a depth of
0.5 to but the materi-
al does not divide. In the second phase, the first crack appears and the scrap begins to slip. This method improves the surface finish of the punched hole. Another advantage of this type of punch is its ability to
be sharpened many times.
Punch
Fig.
4.15
Frustum cone punch for punching and shaving
42
Blanking and Punching In an analogous process of deformation, the material is punched with the conic punch shown in
Fig 4.16 but, in this design the punch penetrates the material to a depth of 0.7 to 0.9 T before the
material begins to shear. Two or even three shaves may be required to improve the edge straightness
and surface finish. The progressive punch shown in Fig. 4.17 makes it practical to produce a smooth edge on a
piece during a single press stroke. The first step of the punch punches a hole, whose diameter is: mm.
4.15 The second step
of the punch uses a sharp edge, and accomplishes the rough shaving of the hole, whose diameter is:
mm. 4.16
=
90 Punch
Die
Fig. 4.16
Cone punch
for
punching and shaving hole.
The third step of the punch has rounded edges which perform the final shaving and improvement of the surface finish. The diameter of this step
of the punch is: 4.17
=
m m .
A progressive punch is used for shaving holes of diameter d
=
3 to
12 mm, and material thickness 3
mm. Progressive punch
Fig. 4.17
Progressive punch for shaving.
Blanking and Punching
43
Material thickness