Note: Descriptions are shown in the official language in which they were submitted.
CA 02785962 2012-08-14
DESCRIPTION
DIE FOR PUNCHING SHEET METAL AND SHEET METAL PUNCHING
APPARATUS HAVING THE DIE
The present application has been divided out of Canadian Patent Application
Serial No. 2,686,479 filed internationally on May 22, 2008 as International
Application
No. PCT/JP2008/001280 and published internationally on November 27, 2008 as
WO 2008/142870.
TECHNICAL FIELD
[0001]
The present invention relates to a die for punching sheet metal and a sheet
metal punching apparatus having the die.
BACKGROUND ART
[0002]
[Patent Document 1] JP-A-2005-262263
[Patent Document 2] JP-A-2002-153920
[0003]
A punching apparatus has been proposed in which a punch, which includes a
cylindrical punch body having a smaller outside diameter than the hole
diameter of a die
and a conical projection formed integrally on one end face of this cylindrical
punch
body, is pressed against sheet metal to form in advance a pierced hole in the
sheet metal
by the projection of the punch. As the punch body is further inserted into the
circular
hole of the die through the opening of the circular hole of the die in a state
in which the
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_
_
movement of the sheet metal is restricted by the projection inserted in the
pierced hole,
the sheet metal is fractured in cooperation with the punch body around an
annular edge
of an inner peripheral surface of the die, which defines one end of the
circular hole of
the die, to thereby form a through hole in the sheet metal (refer to Patent
Documents 1
and 2).
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DISCLOSURE OF THE INVENTION
PROBLEMS THAT THE INVENTION IS TO SOLVE
[0004]
According to such a punching apparatus, the sheet metal is positioned by the
projection, and a through hole corresponding to the shape of the outer
peripheral surface
of the punch body is formed by applying mainly a tensile force rather than a
shearing
force to the sheet metal by the punch body and the die to thereby tear off the
sheet metal
between the punch body and the die, so that the through hole can be formed
accurately
in the sheet metal without producing burrs. However, in the case of the sheet
metal
with a plate thickness of 0.8 mm or more, for instance, cutting based on a
shearing force
rather than cutting based on a tensile (tearing-off) force constitutes the
principal force.
As a result, there is a possibility that large burrs due to shearing are
undesirably formed
on one surface of the sheet metal around the through hole.
[0005]
Accordingly, in the case of the sheet metal with a plate thickness not
exceeding
0.8 mm, the punching apparatuses proposed in Patent Documents 1 and 2 are
extremely
effective, but are not yet sufficiently satisfactory for the sheet metal with
a plate
thickness of 0.8 mm or more in terms of the occurrence of large (high) burrs.
[0006]
The present invention has been devised in view of the above-described aspects,
and its object is to provide a die for punching sheet metal and a sheet metal
punching
apparatus having the die, which make it possible to effect punching with
respect to not
only sheet metal not exceeding 0.8 mm but also sheet metal of 0.8 mm or more
while
making it possible to sufficiently avoid the occurrence of burrs.
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MEANS FOR OVERCOMING THE PROBLEMS
[0007]
A die for punching sheet metal in accordance with the invention comprises:
an end face opposing sheet metal to be punched; a through hole which is open
at the end
face and into which a punch is inserted through an opening in the end face;
and an inner
peripheral surface defining the through hole, wherein the end face and the
inner
peripheral surface are contiguously connected to each other with an acute
angle 0 at the
opening of the through hole in the end face.
[0007a]
In a particular embodiment there is provided a sheet metal punching apparatus
comprising: an upper die holder; a pressing pad suspended from the upper die
holder; a
punch secured to the pressing pad; a lower die on which a sheet metal to be
punched is
placed; and a die embedded in the lower die to punch said sheet metal in
cooperation
with said punch, said die including a first end face opposing said sheet metal
to be
punched; a second end face opposing said first end face in an axial direction;
a through
hole having a first opening which is disposed on the first end face and
through which a
punch is inserted into the through hole and a second opening which is disposed
on the
second end face through which a punched scrap is discharged from the through
hole; an
inner peripheral surface defining said through hole; and an outer peripheral
surface, said
first end face extending in such a manner as to be inclined with respect to an
axis of the
punch, and said inner peripheral surface and said outer peripheral surface,
respectively,
extending in parallel to the axis of said punch, said first end face being
contiguously
connected at an inner end thereof to one end of the inner peripheral surface
in the axial
direction, said first end face and said inner peripheral surface being
intersected to each
other with an acute angle 0 at the first opening of said through hole in said
first end
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face, said first end face being contiguously connected at an outer end thereof
to a first
end of the outer peripheral surface in the axial direction, said second end
face being
contiguously connected at an inner end thereof to another end of the inner
peripheral
surface in the axial direction, said second end face being contiguously
connected at an
outer end thereof to a second end of the outer peripheral surface in the axial
direction,
and said outer peripheral surface comprising a straight cylindrical surface
which
straightly contiguously extends in parallel to the axial direction from the
first end of the
outer peripheral surface to the second end of the outer peripheral surface,
said lower die
having an upper surface on which said sheet metal is placed, and said inner
end of the
first end face and said upper surface being made flush with each other,
wherein said
punch includes a columnar punch body and a projection provided integrally on
one end
face of said columnar punch body for forming a pierced hole in the sheet
metal, said
projection including a cylindrical portion and a conical portion, whereby the
sheet metal
is punched in cooperation with said first end face, said inner peripheral
surface of said
die and said columnar punch body in a state where the movement of the sheet
metal is
restricted by the cylindrical portion of the projection which is inserted in
the pierced
hole.
[0008]
According to the above-described die for punching sheet metal, since the
mutually contiguous connection of the end face and the inner peripheral
surface is
effected with the acute angle 0, i.e., since the mutually contiguously
connected portion
between the end face and the inner peripheral surface, which constitutes the
die edge of
the die, has the acute angle 0, when the sheet metal is punched in cooperation
with the
punch, an extremely large concentrated stress can be generated in the sheet
metal at the
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mutually contiguously connected portion between the end face and the inner
peripheral
surface with the acute angle 0. As a result, the elongation of the sheet metal
can be
suppressed as much as possible, and the sheet metal can be cut at the mutually
contiguously connected portion between the end face and the inner peripheral
surface.
Hence, it is possible to effect punching with respect to not only the sheet
metal with a
plate thickness not exceeding 0.8 mm but also the sheet metal with a plate
thickness of
0.8 mm or more while making it possible to sufficiently avoid the occurrence
of burrs.
[0009]
In a preferred example, the end face extends in such a manner as to be
inclined
3b
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with respect to an axis of the punch, and the inner peripheral surface extends
in parallel
to the axis of the punch, and wherein the end face extending in the inclined
manner and
the inner peripheral surface extending in parallel are contiguously connected
to each
other with an acute angle 0 at the opening of the through hole in the end
face. In
another preferred example, the end face extends perpendicularly to the axis of
the punch,
and the inner peripheral surface extends in such a manner as to be inclined
with respect
to the axis of the punch, and wherein the end face extending perpendicularly
and the
inner peripheral surface extending in the inclined manner are contiguously
connected to
each other with an acute angle 0 at the opening of the through hole in the end
face.
[0010]
The acute angle 0 may be as small as possible, but if it is too small, the
mechanical strength declines, possibly causing early deterioration and damage
of the die
edge. From such a viewpoint, the acute angle 0 is preferably 45 to 87 , more
preferably 65 to 85 , or still more preferably 75 to 83 .
[0011]
The opening which constitutes the shape of the hole in the punched sheet metal
is not limited to the shape of a circle, and may be formed in the shape of an
ellipse, an
elongated circle, a triangle, a rectangle including a square and an oblong
rectangle, a
polygon, or other shape. In the case of a shape having corners, such as a
rectangle
including a square and an oblong rectangle, a polygon, or the like, corners
may be
rounded, as required.
[0012]
A sheet metal punching apparatus in accordance with the invention comprises:
the die for punching sheet metal according to any one of the above-described
aspects;
and the punch which is inserted into the through hole of the die, wherein the
punch
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includes a columnar punch body having a tubular surface extending in parallel
to the
axis and a projection provided integrally on one end face of the punch body on
a side of
insertion into the through hole of the die, the one end face of the punch body
provided
with the projection including an annular surface surrounding a bottom plane of
the
projection and extending perpendicularly to the axis and a curved surface
extending
from an annular outer edge of the annular surface to an annular edge of the
tubular
surface, whereby the sheet metal is punched in cooperation with the end face
and the
inner peripheral surface of the die which are contiguously connected to each
other with
the acute angle 0 on the one hand, and the curved surface of the punch body on
the othr
hand.
[0013]
The die in accordance with the invention and the sheet metal punching
apparatus in accordance with the invention using the die are not limited to
those which
are used for punching sheet metal with a plate thickness exceeding 0.8 mm, but
may be
used in the punching of sheet metal with a plate thickness of 0.8 mm or less.
If they
are used for punching such sheet metal, it is possible to manufacture punched
sheet
metal which is free of burrs and can be extremely satisfactory, as compared
with
conventional ones.
[0014]
In the invention, the curved surface of the punch may preferably have a radius
of curvature R of 0.1 mm to 5 mm in order to subject the sheet metal to
tensile fracture
more satisfactorily while reducing the effect of shear constituting a cause of
burring.
[0015]
If the thickness of the sheet metal is assumed to be t, the difference, i.e.,
a
clearance, between the punch body and the inner peripheral surface of the die
defining
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the through hole at the portion of the die edge is sufficient if it is not
less than 0.15t and
not more than 2 mm.
[0016]
As for the sheet metal which is punched by the sheet metal punching apparatus
in accordance with the invention, its thickness is 0.4 mm to 2.0 mm or
thereabouts to
obtain a satisfactory result. To obtain a more satisfactory result, however,
its thickness
is 0.6 mm to 1.6 mm or thereabouts.
ADVANTAGES OF THE INVENTION
[0017]
According to the present invention, it is possible to provide a die for
punching
sheet metal and a sheet metal punching apparatus having the die, which make it
possible
to effect punching with respect to not only sheet metal not exceeding 0.8 mm
but also
sheet metal of 0.8 mm or more while making it possible to sufficiently avoid
the
occurrence of burrs.
[0018]
Hereafter, a more detailed description will be given of the present invention
on
the basis of the preferred embodiment illustrated in the drawings. It should
be noted
that the present invention is not limited to such an embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019]
Fig. 1 is a cross-sectional view of a preferred embodiment of the present
invention;
Fig. 2 is an explanatory view of a portion of a punch used in the embodiment
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shown in Fig. 1;
Fig. 3 is a front elevational view of the punch shown in Fig. 2;
Fig. 4 is an explanatory diagram of the punch and a die used in the embodiment
shown in Fig. 1;
Fig. 5 is a front elevational view of the die used in the embodiment shown in
Fig. 1;
Fig. 6 is a diagram explaining the operation of the embodiment shown in Fig.
1;
Fig. 7 is a diagram explaining the operation of the embodiment shown in Fig.
1;
Fig. 8 is a diagram explaining the operation of the embodiment shown in Fig.
1;
Fig. 9 is a diagram explaining the operation of the embodiment shown in Fig.
1;
Fig. 10 is a cross-sectional view of another preferred embodiment of the die
in
accordance with the present invention;
Fig. 11 is a front elevational view of the other preferred embodiment of the
die
in accordance with the present invention;
Fig. 12 is a front elevational view of still another preferred embodiment of
the
die in accordance with the present invention; and
Fig. 13 is a cross-sectional view of the still other preferred embodiment of
the
die in accordance with the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0020]
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In Figs. 1 to 5, a sheet metal punching apparatus 1 in accordance with this
embodiment includes an upper die holder 2 which is raised and lowered by a
hydraulic
ram and the like; a pressing plate 3 secured to the upper die holder 2; a
pressing pad 5
suspended from the upper die holder 2 through a resilient member 4; a punch
holder 7
constructed as a punch unit secured to the pressing pad 5 by means of a bolt 6
and the
like; a lower die 9 on which thin sheet metal 8 to be subjected to punching is
placed;
and a die 10 embedded in the lower die 9.
[0021]
The punch holder 7 includes a hollow cylindrical case 11 secured to the
pressing pad 5 by means of the bolt 6 and the like; a hollow cylindrical
slider 12 fitted
to the case 11 vertically slidably; a punch 13 fitted in the slider 12
vertically slidably; a
returning means having a coil spring 14 which is disposed in the slider 12 and
is
adapted to return the punch 13 and the slider 12 to their initial positions by
upwardly
resiliently urging the slider 12 by means of the punch 13; and a slide guiding
member
15 provided in the case 11 so as to guide the vertical movement of the punch
13.
[0022]
The slider 12 has a recess 21, and is adapted to engage at the recess 21 a
detent
pin 22 secured to the case 11, so that the slider 12 does not come off the
case 11 by the
resiliency of the coil spring 14. The slider 12 is adapted to be pressed
downward by
the pressing plate 3 when the upper die holder 2 is lowered.
[0023]
The punch 13 for punching the sheet metal 8 includes a punch body 25 formed
in the shape of a circular cylinder; a projection 27 formed integrally on a
circular end
face 26, i.e., one end face, of the punch body 25; and a collar 29 provided
integrally on
a circular end face 28, i.e., other end face, of the punch body 25.
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[0024]
The punch body 25 has a cylindrical surface 32 serving as a tubular surface
extending in parallel to an axis 31, an annular surface 33 extending
perpendicularly to
the axis 31, and a curved surface 34 extending from an outer edge of the
annular surface
33 to an outer edge of the cylindrical surface 32. The diameter D1 (= 2 x r1)
of the
punch body 25 is in the range of 1 mm to 25 mm, 1 mm to 10 mm, or 1 mm to 5
mm,
and the radius of curvature r2 of the curved surface 34 is in the range of 0.1
mm to 5
mm.
[0025]
The projection 27 includes a cylindrical portion 43 with a height h and a
conical portion 45, the cylindrical portion 43 having a circular bottom plane
41 and a
circular top plane 42 with a smaller diameter D3 (= 2 x r3) than the diameter
D1 of the
circular end face 26, the circular bottom plane 41 and the circular top plane
42 being
disposed concentrically with that circular end face 26, the cylindrical
portion 43 being
provided integrally at the circular bottom plane 41 on the one circular end
face 26 of the
punch body 25; and the conical portion 45 having a circular bottom plane 44
with the
same diameter as the diameter D3 of the circular top plane 42, the circular
bottom plane
44 being disposed concentrically with that circular top plane 42, the conical
portion 45
being provided integrally at the circular bottom plane 44 on the circular top
plane 42 of
the cylindrical portion 43. The circular bottom plane 41 of the cylindrical
portion 43 is
surrounded by the annular surface 33 of the punch body 25.
[0026]
In the above-described punch 13, if it is assumed that the radius of the punch
body 25 is rl Dl x 1/2), the radius of curvature of the curved surface 34
is r2, the
radius of the cylindrical portion 43 is r3 (= D3 x 1/2), the height of the
cylindrical
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portion 43 is h, and the thickness of the sheet metal 8 to be punched is t,
then r3 < rl ¨
r2, and h > t + r3.
[0027]
The coil spring 14 abuts against the collar 29 at one end thereof and a flange
portion 51 of the slide guiding member 15 at the other end thereof. The slide
guiding
member 15 has, in addition to the flange portion 51, a cylindrical portion 53
formed
integrally with the flange portion 51 and fitted in the case 11 in a hole 52
of the case 11,
and slidably guides and supports a lower end portion of the punch body 25 of
the punch
13 by the inner peripheral surface of the cylindrical portion 53.
[0028]
The die 10 has an annular end face 60 opposing the sheet metal 8 to be
punched; a circular hole 62 which is open at the end face 60 and serves as a
through
hole into which the punch body 25 of the punch 13 is inserted through an
opening 61 in
the end face 60; an inner peripheral surface 63 defining the circular hole 62;
a circular
hole 65 continuous with the circular hole 62 and having a larger diameter than
the
circular hole 62 to discharge a punched scrap 64 (see Fig. 9); and a
cylindrical outer
peripheral surface 66.
[0029]
The end face 60 constituting an outer surface of a truncated cone extends in
such a manner as to be inclined with respect to the axis 31 of the punch 13,
and the
inner peripheral surface 63 constituting a cylindrical surface extends in
parallel to the
axis 31 of the punch 13. The end face 60 extending in the inclined manner and
the
inner peripheral surface 63 extending in parallel are contiguously connected
to each
other with an acute angle 0 at the opening 61 of the circular hole 62 in the
end face 60.
Thus, the die 10 has a die edge 67 with the acute angle 0 at the opening 61.
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[0030]
The ratio D1/D4 of the diameter D4 of the circular hole 62 to the diameter D1
of the circular end face 26 is not less than 0.80, and if the thickness of the
sheet metal 8
to be punched is assumed to be t, the difference (clearance) f between the
radius rl
D1 x 1/2) of the circular end face 26 and the radius r4 (= D4 x 1/2) of the
circular hole
62 of the die 10 is not less than 0.15t and not more than 2 mm. The die 10 is
embedded in the lower die 9 by being fitted and secured at its outer
peripheral surface
66.
[0031]
In the above-described punching apparatus 1, as the pressing plate 3, the
pressing pad 5, and the punch holder 7 are lowered in conjunction with the
lowering of
the upper die holder 2, the sheet metal 8 placed on the lower die 9 is pressed
by the
pressing pad 5 and is fixed by being clamped between the lower die 9 and the
pressing
pad 5. At the same time, the slider 12 is pressed by the pressing plate 3, and
the punch
13 is lowered in conjunction with the pressing down of the slider 12. As the
punch 13
is lowered, a pierced hole 71 is formed in the sheet metal 8 by the conical
portion 45 of
the projection 27, as shown in Fig. 6, and subsequently by the cylindrical
portion 43.
In a state in which the movement of the sheet metal 8 is restricted by the
cylindrical
portion 43 of the projection 27 inserted in the pierced hole 71, the punch 13
is further
lowered, and the punch body 25 of the punch 13 is inserted into the circular
hole 62 of
the die 10, as shown in Fig. 7, whereby the sheet metal 8 in contact with the
annular
surface 33 of the circular end face 26 is pressed by that annular surface 33
and is
lowered in conjunction with the lowering of the punch body 25. In this
lowering, the
sheet metal 8 at its portion located between the curved surface 34 of the
circular end
face 26 and the die edge 67 of the die 10 is pulled and elongated by the
curved surface
1]
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34 of the circular end face 26 and the die edge 67 of the die 10, and the
sheet metal 8 is
subsequently torn off and fractured on the die edge 67 side of the die 10 in
conjunction
with shearing, as shown in Fig. 8. After the fracturing of the sheet metal 8
on the die
edge 67 side of the die 10, the punch 13 is raised, while the punched scrap 64
is
discharged through the circular hole 65, as shown in Fig. 9; thus, a through
hole 72 is
formed in the sheet metal 8.
[0032]
Incidentally, in the die 10, since the mutually contiguous connection of the
end
face 60 and the inner peripheral surface 63 is effected with the acute angle
0, i.e., since
the die edge 67 of the die 10 has the acute angle 0, when the sheet metal 8 is
punched in
cooperation with the punch body 25 of the punch 13, an extremely large
concentrated
stress is generated in the sheet metal 8 at the mutually contiguously
connected portion
between the end face 60 and the inner peripheral surface 63 with the acute
angle 0. As
a result, the elongation of the sheet metal 8 in the vicinity of the die edge
67 can be
suppressed as much as possible, and the sheet metal 8 can be cut accurately at
the
mutually contiguously connected portion between the end face 60 and the inner
peripheral surface 63. Hence, it is possible to effect punching with respect
to not only
the sheet metal with a plate thickness not exceeding 0.8 mm but also the sheet
metal
with a plate thickness of 0.8 mm or more while sufficiently avoiding the
occurrence of
burrs.
[0033]
Moreover, with the punching apparatus 1 which is adapted to effect punching
in the sheet metal 8 in cooperation with the end face 60 and the inner
peripheral surface
63 which are contiguously connected to each other with the acute angle 0, and
the
curved surface 34, the projection 27 has the cylindrical portion 43 which is
integrally
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provided on the one annular surface 33 of the punch body 25 and has the
circular
bottom plane 41 and the circular top plane 42. Therefore, even if the conical
angle of
the distal end of the conical portion 45 of the projection 27 is made large so
as to make
it possible to obtain sufficient strength and durability, and even if the
overall projection
27 is made high so as to make it possible to prevent the projection 27 from
coming off
the pierced hole 71 after the formation of the pierced hole 71 by the
projection 27, the
annular surface 33 surrounding the circular bottom plane 41 of the cylindrical
portion
43 of the projection 27 and extending perpendicularly to the axis 31 can be
secured on
the circular end face 26 of the punch body 25 with a sufficient breadth.
Hence, the
through hole 72 can be formed in the sheet metal 8 with high precision by
reliably
fracturing the sheet metal 8 around the die edge 67 of the die 10 in
cooperation with the
punch body 25. Moreover, since the curved surface 34 has the radius of
curvature r2
of 0.1 mm to 5 mm, the sheet metal 8 can be subjected to tensile fracture more
satisfactorily while reducing the effect of shear constituting a cause of
burring here. In
addition, since the ratio D1/D4 is not less than 0.80, and the difference f is
not less than
0.15t, tensile fracture can be mainly caused in addition to some shear,
thereby making it
possible to effectively form the through hole 72 in the sheet metal 8.
[0034]
According to the die 10 having the inclined end face 60, it is unnecessary to
further process the end face 60 in correspondence with the shape of the sheet
metal 8,
thereby making it possible to attain cost reduction.
[0035]
With the punching apparatus 1, the through hole 72 is formed by vertically
moving the punch 13, but the through hole 72 may be formed in an inclined
portion of
the sheet metal 8 by obliquely moving the punch 13.
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[0036]
With the above-described die 10, although the die edge 67 having the acute
angle 0 is embodied by the end face 60 which extends in such a manner as to be
inclined with respect to the axis 31 of the punch 13, an arrangement may be
provided in
substitution thereof or in conjunction therewith such that, as shown in Fig.
10, the inner
peripheral surface 63 is formed as an inner surface of a truncated cone by
being
extended in such a manner as to be inclined with respect to the axis 31 of the
punch 13,
and the end face 60 and the inner peripheral surface 63 are contiguously
connected to
each other with the acute angle 0 at the opening 61 of the circular hole 62 in
the end
face 60. In this case, the end face 60 may extend perpendicularly to the axis
31 of the
punch 13.
[0037]
Although the opening 61 in the above-described embodiment is formed in the
shape of a circle, an arrangement may be provided in substitution thereof, the
opening
61 may be formed in the shape of a quadrangle with its corners rounded, as
shown in
Fig. 11, or an elongated circle, as shown in Fig. 12, or another shape such as
an ellipse,
a triangle, a rectangle, or a polygon.
[0038]
In addition, with the die 10 in the above-described embodiment, the circular
hole 65 is formed continuously with the circular hole 62, but an arrangement
may be
provided such that, as shown in Fig. 13, a circular hole 75, which has an only
slightly
smaller diameter than the diameter of the circular hole 62, is concentric with
the circular
hole 62, and has a larger diameter than the diameter of the punch body 25, is
interposed
between the circular hole 62 and the circular hole 65. In this case, in the
lowering of
the punch 13 after the formation of the through hole 72, the punched scrap 64
is pushed
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Out to the circular hole 75, and in the raising of the punch 13 after the
pushing out of the
punched scrap 64 to the circular hole 75, the punched scrap 64 is caught by an
inner
peripheral surface 76 of the die 10, which defines the circular hole 75, so
that the
punched scrap 64 can be reliably discharged to the circular hole 65 without
being raised
by being dragged by the punch 13.
