TITLE OF INVENTION: PRESS FORMING METHOD
TECHNICAL FIELD
[0001] The present invention relates to a press
forming method- used for a workpiece formed in a cup
shape.
BACKGROUND ART
[0002] As parts used for transmissions and so on of
vehicles, an axisymmetric part having a cup
longitudinal wall portion and a cup bottom wall
portion has been known. Using ordinary drawing in
order to obtain the axisymmetric part in a cup shape
results in thinning of a cup shoulder portion which
abuts on a shoulder R portion of a drawing punch. In
order to avoid and improve this, there have
conventionally been used forging, upsetting which
pushes a cup upper end portion (Patent Literature 1),
rolling (Patent Literature 2), ironing (Patent
Literatures 3, 4), and the like.
CITATION LIST
PATENT LITERATURE
[0003] Patent Literature 1: Japanese Laid-open
Patent Publication No. 2001-47175
Patent Literature 2: Japanese Laid-open Patent
Publication No. 2007-289989
Patent Literature 3: Japanese Laid-open Patent
Publication No. 05-329558
Patent Literature 4: Japanese Laid-open Patent
Publication No. 07-155855
_ I _ •
Patent Literature 5: Japanese Laid-open Patent
Publication No. 07-124657
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0004] However,- in the conventional forging method
and upsetting method which suppress the thinning of
the cup shoulder portion, a forming load is large and
a large forming device has been accordingly essential
In the conventional rolling method which suppresses
the thinning of the cup shoulder portion, the
thinning of the cup longitudinal wall portion has
been basically essential. Methods for suppressing
the thinning of the cup shoulder portion further
include a method of thickening the cup shoulder
portion by applying ironing to a workpiece which has
been formed into a cup shape and whose cup shoulder
portion has been reduced.
[0005] Fig. 16 to Fig. 18 are explanatory views of
.the conventional ironing method which thickens a cup
shoulder portion Al.
In the conventional ironing method which thickens
the cup shoulder-portion Al, in a press forming
device, an inner punch 101 is first moved down
relatively to a cup-shaped workpiece A placed on a
die 103 so that an outer peripheral surface of the
inner punch 101 comes into contact with an inner
peripheral surface A2 2 of the workpiece A, whereby
the workpiece A is sandwiched by the inner punch 101
and the die 10 3.
- 2 -
Here, an outer punch 102 has a smaller inside
diameter than an outside diameter of the workpiece A.
As illustrated in Fig. 17 and Fig. 18, the outer
punch 102 is moved down to thin a cup longitudinal
wall portion A2 of the workpiece A and an amount by
which its thickness is reduced is filled in the cup
shoulder portion Al to thicken the cup shoulder
port ion Al.
However, the conventional ironing method has a
problem that, though the cup shoulder portion Al can
be thickened, the cup longitudinal wall portion A2 is
accordingly thinned.
[000 6] Further, as a forming method for thickening a
base end portion of a boss portion of a workpiece
having a flat plate portion and the hollow boss
portion formed by burring, Patent Literature 5
discloses one in which a punch having a tapered
portion is press-fitted from a tip side of the boss
portion and is pressed toward the base end portion
while the tip side of the boss portion is radially
widened by the tapered portion, but its target is not
a cup-shaped workpiece.
[0007] It is an object of the present invention to
provide a press forming method capable of thickening
a cup shoulder portion while reducing a forming load
without thinning a cup longitudinal wall portion.
SOLUTION TO PROBLEM
[0008] The gist of the present invention for solving
the aforesaid problem is as follows.
3 -
(1) A press forming method which applies press
forming to a cup-shaped workpiece having a cup
longitudinal wall portion, a cup bottom portion, and
a cup shoulder portion connecting the cup
longitudinal wall portion and the cup bottom portion,
by using a press forming device, wherein
the press forming device includes an inner punch,
an annular outer punch, and a die whose center axes
are disposed on the same axis, the outer punch being
disposed so as to be apart from the inner punch in a
radial direction perpendicular to the center axis by
a first space which is larger than a plate thickness
of the cup longitudinal wall portion, and the die
being disposed to face the inner punch in a direction
of the center axis, and an inner peripheral surface
of the outer punch has, on a side thereof, closer to
the die in terms of the center axis direction, a
punch shoulder portion widening as the punch shoulder
portion goes toward the die, the method including:
a first step of sandwiching the cup bottom
portion by the inner punch and the die while an outer
peripheral surface of the inner punch and an inner
peripheral surface of the cup longitudinal wall
portion are apart from each other by a second space;
and
a second step of performing drawing to radially
reduce the cup longitudinal wall portion by pushing
the cup longitudinal wall portion toward the outer
peripheral surface of the inner punch by the outer
punch while moving the outer punch relatively to the
inner punch and the die along the center axis to make
the outer punch abut on the cup longitudinal wall
portion from the punch shoulder portion, thereby
making a surplus mat.erial of the workpiece flow into
the cup shoulder portion to thicken the cup shoulder
port ion.
(2) The press forming method according to (1),
wherein, in the second step, the cup longitudinal
wall portion is radially reduced until reaching a
position where an outside diameter of an outer
peripheral surface of the cup longitudinal wall
portion becomes equal to an outside diameter of the
die .
(3) The press forming method according to (1) or
(2), wherein the cup shoulder portion is formed into
a right-angled shape.
(4) The press forming method according to (1) ,
.wherein, when the thickening is completed in the
second step, a space is formed between the inner
peripheral surface portion, of the outer punch, which
is in contact with the cup shoulder portion and an
outer peripheral surface portion, of the die, which
faces the inner peripheral surface portion in the
radial direction.
(5) The press forming method according to (4),
wherein, in the second step, an outer peripheral
surface of the cup shoulder portion is formed so as
to be flush with an outer peripheral surface of the
- 5
cup longitudinal wall portion, by the inner
peripheral surface of the outer punch, and on a
bottom surface outer edge portion of the cup bottom
portion, a surplus portion projecting from the bottom
surface is formed by the surplus material made to
escape to the space.
(6) The press forming method according to any one
of (1) to (5), wherein the punch shoulder portion has
a rounded shape or a tapered shape widening as the
punch shoulder portion goes toward the die.
(7) The press forming method according to any one
of (1) to (6), wherein:
on the inner peripheral surface of the outer
punch, an end surface pushing portion in a
circumferential shape projecting in the radial
direction from the inner peripheral surface is
formed; and
in the second step, at the time of thickening the
cup shoulder portion by relatively moving the outer
punch, the cup longitudinal wall portion is pushed
toward the die by the end surface pushing portion.
ADVANTAGEOUS" EFFECTS OF INVENTION
[0009] According to the present invention, it is
possible to provide a press forming method capable of
thickening a cup shoulder portion while reducing a
forming load, without thinning a cup longitudinal
wall portion.
BRIEF DESCRIPTION OF DRAWINGS
[0010] [Fig. 1] Fig. 1 is a schematic structural
- 6 -
view of a press forming device of a first embodiment
[Fig. 2] Fig. 2 is a view illustrating an
example of a forming state of press forming by the
press forming device of the first embodiment.
[Fig. 3] Fig. 3 is a view illustrating an
example of a. forming completion state of the press
forming by the press forming device of the first
embodiment.
[Fig. 4] Fig. 4 is a view illustrating another
plan of the press forming device of the first
embodiment.
[Fig. 5] Fig. 5 is a schematic structural view
of a press forming device of a second embodiment.
[Fig. 6] Fig. 6 is a view illustrating an
example of a forming completion state of press
forming by the press forming device of the second
embodiment.
[Fig. 7A] Fig. 7A is a view illustrating an
.example of a cup-shaped workpiece to which the
present invention is applicable.
[Fig. 7B] Fig. 7B is a view illustrating an
example of the cup-shaped workpiece to which the
present invention is applicable.
[Fig. 7 C] Fig. 7C is a view illustrating an
example of the cup-shaped workpiece to which the
present invention is applicable.
[Fig. 8] Fig. 8 is a schematic structural view
of a press forming device of a third embodiment.
[Fig. 9] Fig. 9 is a view illustrating an
- 7 -
example of a forming state of press forming by the
press forming device of the third embodiment.
[Fig. 10] Fig. 10 is a view illustrating an
example of a forming completion state of press
forming by the press, forming device of the third
embodiment.
[Fig. 11] Fig. 11 is a view illustrating another
plan of the press forming device of the third
embodiment.
[Fig. 12] Fig. 12 is a schematic structural view
of a press forming device of a fourth embodiment.
[Fig. 13] Fig. 13 is a schematic structural view
of a press forming device of a fifth embodiment.
[Fig. 14] Fig. 14 is a view illustrating an
example of a forming completion state of press
forming by the press forming device of the fifth
embodiment.
[Fig. 15A] Fig. 15A is a view illustrating an
.example of a cup-shaped workpiece to which the
present invention is applicable.
[Fig. 15B] Fig. 15B is a view illustrating an
example of the cup-shaped workpiece to which the
present invention is applicable.
[Fig. 15C] Fig. 15C is a view illustrating.an
example of the cup-shaped workpiece to which the
present invention is applicable.
[Fig. 16] Fig. 16 is an explanatory view of a
conventional press forming method of thickening a cup
shoulder portion.
- 8 -
[Fig. 17] Fig. 17 is a view illustrating an
example of a forming state of the conventional press
forming method of thickening the cup shoulder portion.
[Fig. 18] Fig. 18 is a view illustrating an
example of a- forming completion state of the
conventional- press forming method of thickening the
cup shoulder portion.
DESCRIPTION OF EMBODIMENTS
[0011] Hereinafter, modes for carrying out the
present invention will be described with reference to
the attached drawings.
(First Embodiment)
Fig. 1 is a schematic structural view of a press
forming device of a first embodiment•
In this embodiment, after a pressing step of
pres s-forming a disk-shaped workpiece into a
workpiece A having a cup shape (hereinafter, referred
to as a cup-shaped workpiece A) is executed, a
thickening step of thickening a cup shoulder portion
Al of the cup-shaped workpiece A is executed. By the
pressing step, the cup-shaped workpiece A is formed
into a bottomed cylindrical shape having a cup
longitudinal wall portion A2 whose one end side forms
a cup opening portion A14, a cup bottom portion A15,
and the cup shoulder portion Al in a rounded shape
connecting the other end side of the cup longitudinal
wall portion A2 and the cup bottom portion A15.
[0012] The press forming device of the first
embodiment has an inner punch 11, an outer punch 12,
and a die 13. The inner punch 11, the outer punch 12,
and the die 13 are disposed on the same center axis
10. The inner punch 11 and the outer punch 12 are
each capable of independently moving up and down.
[0013] The outer punch 12 is formed in an annular
shape whose inside diameter is larger than an outside
diameter of the inner punch 11. The outer punch 12
is disposed so as to be apart from the inner punch 11
in a radial direction perpendicular to the center
axis 10 by a first'space SI. The first space SI is
set larger than a plate thickness T of the cup
longitudinal wall portion A2 .
[0014 ] Further, the outer punch 12 is disposed at a
position where it overlaps with a thick portion of
the cup longitudinal wall portion A2 in the radial
direction. An inner peripheral surface 121 of the
outer punch 12 has, on its lower end side (die 13
side) in terms of a direction of the center axis 10,
a punch shoulder R portion 12A widening as it goes
downward fin a punching direction to the cup
longitudinal wall portion A2). The inside diameter
of the outer punch 12 is practically equal to an
outside diameter of the die 13 (a case where it is
slightly larger than the outside diameter of the die
13 is included). By moving down, the outer punch 12
radially reduces the cup longitudinal wall portion A2
until the cup longitudinal wall portion A2 reaches a
position where an outside diameter of an outer
peripheral surface 21A of the cup longitudinal wall
- 10 -
portion A2 becomes equal to the outside diameter of
the die 13, which will be described in detail later.
[0015] The inner punch 11 is formed in a columnar
shape whose outside diameter is smaller than an
inside diameter of the. cup-shaped workpiece A. The
inner punch 11 is disposed to face the die 13 in an
up and down direction (direction of the center axis
10), with an outer peripheral surface 111 of the
inner punch 11 being apart in the radial direction
from an inner peripheral surface A2 2 of the cup
longitudinal wall portion A2 by a second space S2.
In this embodiment, the first space Si between the
outer punch 12 and the inner punch 11 and the second
space S2 between the inner punch 11 and the cup
longitudinal wall portion A2 are set to sizes
allowing the cup longitudinal wall portion A2 to abut
on the outer peripheral surface 111 of the inner
punch 11 and ensuring the forming of the cup
longitudinal wall portion A2 along the direction of
the center axis 10 at the time of the later-described
radial reduction of the cup longitudinal wall portion
A2. However, the cup longitudinal wall portion A2
does not necessarily have to abut on the outer
peripheral surface 111 of the inner punch 11 at the
time of the radial reduction of the cup longitudinal
wall portion A2. For example, the first space SI and
the second space S2 may be set to such sizes that the
outer peripheral surface 111 of the inner punch 11 is
located at a position very much closer to the center
11 -
axis 10, that is, that the cup longitudinal wall
portion A2 does not abut on the outer peripheral
surface 111 of the inner punch 11 at the time of the
radial reduction of the cup longitudinal wall portion
A2 .
[0016] The die 13 has a columnar shape. An outside
diameter of an abutting surface 131, of the die 13,
which abuts on the cup bottom portion A15 is larger
than the outside diameter of the inner punch 11 and
is practically equal to the inside diameter of the
outer punch 12 (a case where it is slightly smaller
than the inside diameter of the outer punch 12 is
included). Consequently, when the thickening of the
cup shoulder portion Al performed by moving down the
outer punch 12 is completed, an outer edge portion
132 of the abutting surface 131 and an inner
peripheral surface portion 122 (Fig. 3) of the outer
punch 12 located on a radially outer side of the
outer edge portion 132 are located close to each
other to prevent a material forming the cup shoulder
portion Al from flowing into a gap therebetween,
which will be described later.
[0017] Hereinafter, a forming operation (press
forming method) of the press forming device will be
described. Referring to Fig. 1, after the cup-shaped
workpiece A is placed on the die 13, the inner punch
11 is moved down and the inner punch 11 is inserted
into the cup-shaped workpiece A via the cup opening
portion A14. While the outer peripheral surface 111
- 12 -
of the inner punch 11 and the inner peripheral
surface A2 2 of the cup longitudinal wall portion A2
are apart from each other by the second space S2, the
cup bottom portion A15 is sandwiched by the inner
punch 11 and the die 13 (first step). An initial
position of the outer punch 12 is above the cup
longitudinal wall portion A2.
[0018] Next, as illustrated in Fig. 2, the outer
punch 12 is moved down and from its punch shoulder R
portion 12 A, the outer punch 12 is made to abut on
the cup longitudinal wall portion A2. Then, the
punch shoulder R portion 12A and the inner peripheral
surface 121 of the outer punch 12 push the cup
longitudinal wall portion A2 in order of the cup
opening portion A14 side to the cup bottom portion
A15 side, toward the outer peripheral surface 111 of
the inner punch 11 to radially reduce the cup
longitudinal wall portion A2, whereby the cup
longitudinal wall portion A2 is subjected to drawing
( second step) .
[0019] When the cup longitudinal wall portion A2 is
pressed by the outer punch 12, the material of the
cup longitudinal wall portion A2 moves toward the
outer peripheral surface 111 of the inner punch 11.
At this time, a diameter of the cup longitudinal wall
portion A2 becomes smaller, and accordingly a surplus
material occurs in the material. Since the first
space SI between the inner punch 11 and the outer
punch 12 is larger than the plate thickness T before
13
the radial reduction, the surplus material thickens
the cup longitudinal wall portion A2. Of the surplus
material, a portion which becomes surplus even after
the thickening of the cup longitudinal wall portion
A2 is led downward by the outer punch 12. Such a
phenomenon continuously occurs at the time of the
drawing of the cup longitudinal wall portion A2 , and
therefore, when the outer punch 12 is moved down to a
side of the cup bottom portion A15 to apply the
drawing to the cup longitudinal wall portion A2, the
portion which becomes surplus even after the
thickening of the cup longitudinal wall portion A2 ,
of the surplus material of the cup longitudinal wall
portion A2 occurring by the drawing, finally thickens
the cup shoulder portion Al as illustrated in Fig. 3.
Thus, in this embodiment, the surplus material of the
cup longitudinal wall portion A2 occurring by the
drawing contributes to the thickening of the cup
longitudinal wall portion A2 and the cup shoulder
portion Al, which makes it possible to thicken the
cup shoulder portion Al without thinning the cup
longitudinal wall portion A2.
[0020] Further, at this time, by moving down the
outer punch 12, the cup longitudinal wall portion A2
is radially reduced until it reaches the position
where the outside diameter of the outer peripheral
surface A21 of the cup longitudinal wall portion A2
becomes equal to the outside diameter of the die 13
since the inside diameter of the outer punch 12 and
- 14 -
the outside diameter of the die 13 have practically
the same size. Further, the outside diameter of the
abutting surface 131 of the die 13 and a diameter of
the inner peripheral surface 121 of the outer punch
12 have practically the same size, and therefore, at
the completion of the thickening of the cup shoulder
portion A2, the outer edge portion 132 of the
abutting surface 131 and the inner peripheral surface
portion 122, of the outer punch 12, which is located
on the radially outer side of the outer edge portion
132 are located at positions close to each other,
which prevents the material forming the cup shoulder
portion Al from flowing into a gap therebetween
Consequently, when an amount of the thickening
material flowing into the cup shoulder portion Al is
sufficient, the cup shoulder portion Al is formed
into a right-angled shape in a view taken along an
axial direction of the cup-shaped workpiece A.
[0021] As"described above, in this embodiment, since
the thickening of the cup shoulder portion Al is
performed by the drawing of the cup longitudinal wall
portion A2, it is possible to thicken the cup
shoulder portion Al while reducing a forming load.
Further, since the drawing is performed while the
space Si between the outer punch 12 and the inner
punch 11 is set equal to or more than the thickness T
of the cup longitudinal wall portion A2, the cup
longitudinal wall portion A2 is not thinned.
Further, in the conventional forging method and
- 15 -
upsetting method, when an attempt is made to form the
cup shoulder portion Al into the same right-angled
shape as that of a die shape, the forming load
reaches several thousand tons. On the other hand, in
the press forming method of this embodiment, the cup
shoulder portion Al is thickened by the drawing, and
therefore, even when the cup shoulder portion Al is
formed into the right-angled shape, it is possible to
reduce the forming load to about several hundred tons
which is smaller than that of the conventional
forging method and upsetting method by a single digit.
By setting the outside diameter of the inner
punch 11 and the inside diameter of the outer punch
12 still smaller, it is possible to more increase a
radial reduction ratio of the cup longitudinal wall
portion A2 to more thicken the cup shoulder portion
Al.
[0022] Incidentally, when the cup-shaped workpiece A
is installed on the die 13, a center axis of the cupshaped
workpiece A may be aligned with the center
axis 10, but the center axis of the cup-shaped
workpiece A may be deviated from the center axis 10
within a range allowing the inner punch 11 to move
down to a region on a more radially inner side than
the cup longitudinal wall portion A2. In this case,
the outer punch 12 is moved down while the cup-shaped
workpiece A is sandwiched by the inner punch 11 and
the die 13 with a force allowing the cup-shaped
workpiece A to displace in the radial direction. At
- 16 -
this time, since the punch shoulder R portion 12A of
the outer punch 12 abuts on the annular cup
longitudinal wall portion A2 in a biased state, the
cup-shaped workpiece A displaces, so that the center
axis of the cup-shaped workpiece A coincides with the
center axis 10. After the center axis of the cupshaped
workpiece A coincides with the center axis 10,
the cup-shaped workpiece A is sandwiched by the inner
punch 11 and the die 13 and the outer punch 12 is
further moved down.
[0023] Further, preferably, the punch shoulder
portion of the outer punch 12 is the'punch shoulder R
portion 12A which widens as it goes in the punching
direction of the outer punch 12 to the cup
longitudinal wall portion A2, or is a tapered portion
2 2A which widens as it goes in the punching direction
as in an outer punch 22 illustrated in Fig. 4. Thus
structuring the punch shoulder portions of the outer
punch 12, 2 2 makes it possible to radially reduce the
cup longitudinal wall portion A2 gently and
continuously in order of its cup opening portion A121
side to its cup bottom portion A15 side, and also
enables a reduction of a contact angle of the cup
longitudinal wall portion A2 and each of the outer
punches 12, 22, which makes it possible to reduce a
contact reaction force in the vertical direction to
reduce a frictional force of each of the outer
punches 12, 22 with the cup longitudinal wall portion
A2. Accordingly, a forming force in a vertically
17 -
downward direction to a portion near the cup bottom
portion Al5 in the cup longitudinal wall portion A2
and to the cup shoulder portion Al can be made
smaller than that of the conventional ironing, which
can suppress the occurrence of inward folding in the
cup shoulder.portion Al.
[0024] (Second Embodiment)
Fig. 5 is a schematic structural view of a press
forming device of a second embodiment.
The press forming device of this embodiment
differs from that of the first embodiment only in a
shape of an outer punch 32, and what are different
from the first embodiment will be described below.
In this embodiment, on an inner peripheral
surface 321 of the outer punch 32, an end surface
pushing portion 32B in a circumferential shape
projecting in a radial direction from the whole
circumference of the inner peripheral surface 321 is
formed. The end surface pushing portion 3 2B is
disposed at a position where the inner peripheral
surface 321 becomes longer than the whole height of a
cup-shaped workpiece A.
[0025] A press forming method of this embodiment is
different from that of the first embodiment in that,
in a second step of drawing a cup longitudinal wall
portion A2 by moving down the outer punch 32, at the
time of thickening forming of a cup shoulder portion
Al, a cup upper end portion A3 of the cup-shaped
workpiece A is pushed in by using the end surface
- 1:
pushing portion 32B of the outer punch 32 , as
illustrated in Fig. 6. Consequently, in this
embodiment, it is possible to improve accuracy of the
transfer of a die shape to the cup shoulder portion
Al and the c-up longitudinal wall portion A2.
[0026] Incidentally, in a press forming method of
this embodiment, a forming condition is close to that
of closed die forging, so that a forming load
increases. Therefore, it is preferable that a volume
VI of the cup-shaped workpiece A and a volume V2 of a
vacant portion formed by an inner punch 11, the outer
punch 12, and a die 13 satisfy a relation of VI < V2.
[0027] (Modification Examples)
Fig 7A to Fig. 7C are views illustrating examples
of the cup-shaped workpiece to which the press
forming method of the present invention is applicable
As the shape of the cup-shaped workpiece to which
the press forming method of the present invention is
applicable, not only the simple bottomed cylindrical
shape illustrated in the first and second embodiments
but also appropriate ones are usable. For example,
as illustrated in Fig. 7A, a perforated cup-shaped
workpiece All having a hole A151 in a cup bottom
portion A15 may be used. Further, as illustrated in
Fig. 7B, a cup-shaped workpiece A12 with boss on
whose cup bottom portion A15 a boss A152 projecting
outward is formed may be used, or as illustrated in
Fig. 7C, a cup-shaped workpiece A13 with boss on
whose cup bottom portion A15 a boss A15 3 projecting
- I1
inward is formed may be used.
Further, as a material of the cup-shaped
workpiece to which the press forming method of the
present invention is applicable, various well-known
ones which can be plastically worked, such as metals
such as steel, aluminum, and copper or alloys of
these, and so on can be adopted.
[0028] In the second step of the first and second
embodiments, the cup shoulder portion Al is thickened
by moving the outer punch 12 (22, 32) toward the
inner punch 11, the die 13, and the cup-shaped
workpiece A, but the cup shoulder portion Al may be
thickened by moving the inner punch 11, the die 13,
and the cup-shaped workpiece A toward the outer punch
12 (22, 32) .
Further, the first and second embodiments
describe the examples where the inner punch 11 and
the outer punch 12 (22, 32) are above the die 13, but
.the positions of the inner punch 11 and the outer
punch 12 (22, 32) and the position of the die 13 may
be vertically reversed.
[0029] (Third Embodiment)
Fig. 8 is a schematic structural view of a press
forming device of.a third embodiment.
In this embodiment, after a pressing step of
press- forming a disk-shaped workpiece into a
workpiece B having a cup shape (hereinafter, referred
to as a cup-shaped workpiece B) is executed, a
thickening step of thickening a cup shoulder portion
- 20
Bl of the cup-shaped workpiece B is executed. By the
pressing step, the cup-shaped workpiece B is formed
into a bottomed cylindrical shape having a cup
longitudinal wall portion B2 whose one end side forms
a cup opening portion B14, a cup bottom portion B15,
and the cup shoulder portion Bl in a rounded shape
connecting the other end side of the cup longitudinal
wall portion B2 and the cup bottom portion B15.
[0030] The press forming device of the third
embodiment has an inner punch 11, an outer punch 4 2,
and a die 43. The inner punch 11, the outer punch 42,
and the die 43 are disposed on the same center axis
10. The inner punch 11 and the outer punch 42 are
each capable of independently moving up and down.
[0031] The outer punch 42 is formed in an annular
shape whose inside diameter is larger than an outside
diameter of the inner punch 11. The outer punch 42
is disposed so as to be apart from the inner punch 11
in a radial direction perpendicular to the center
axis 10 by a first space SI. The first space Si is
set larger than a plate thickness T of the cup
longitudinal wall portion B2.
[0032] Further, the outer punch 42 is disposed at a
position where it overlaps with a thick portion of
the cup longitudinal wall portion B2 in the radial
direction. An inner peripheral surface 421 of the
outer punch 42 has, on its lower end side (die 43
side) in terms of a direction of the center axis 10,
a punch shoulder R portion 42A widening as it goes
- 21 -
downward (in a punching direction to the cup
longitudinal wall portion B2) .
[0033] The inner punch 11 is formed in a columnar
shape whose outside diameter is smaller than an
inside diameter of .the cup-shaped workpiece B. The
inner punch 11 is disposed to face the die 43 in an
up and down direction (direction of the center axis
10), with an outer peripheral surface 111 of the
inner punch 11 being apart from an inner peripheral
surface B22 of the cup longitudinal wall portion B2
in the radial direction by a second space S2. In
this embodiment, the first space Si between the outer
punch 42 and the inner punch 11 and the second space
S2 between the inner punch 11 and the cup
longitudinal wall portion B2 are set to sizes
allowing the cup longitudinal wall portion B2 to abut
on the outer peripheral surface 111 of the inner
punch 11 and ensuring the forming of the cup
•longitudinal wall portion B2 along the direction of
the center axis 10 at the time of later-described
radial reduction of the cup longitudinal wall portion
B2. However, the cup longitudinal wall portion B2
does not necessarily have to abut on the outer
peripheral surface 111 of the inner punch 11 at the
time of the radial reduction of the cup longitudinal
wall portion B2. For example, the first space SI and
the second space S2 may be set to such sizes that the
outer peripheral surface 111 of the inner punch 11 is
located at a position very much closer to the center
22
axis 10, that is, that the cup longitudinal wall
portion B2 does not abut on the outer peripheral
surface 111 of the inner punch 11 at the time of the
radial reduction of the cup longitudinal wall portion
B2 .
[0034] The die 43 has a columnar shape and its
outside diameter is larger than the outside diameter
of the inner punch 11 and is smaller than the inside
diameter of the outer punch 42. The die 43 may have
an outside diameter practically equal to the outside
diameter of the inner punch 11, but when it is larger
than the outside diameter of the inner punch 11, it
is possible to keep the cup bottom portion B15
flatter through a later-described press forming step
of the cup-shaped workpiece B. Because the outside
diameter of the die 43 is smaller than the inside
diameter of the outer punch 42, when the outer punch
4 2 moves down to thicken the cup shoulder portion Bl
of the cup-shaped workpiece B, an escape space S3,
which will be described later, is formed between an
inner peripheral surface portion 422 (Fig. 10), of
the outer punch 42, which is in contact with the cup
shoulder portion Bl and an outer peripheral surface
portion 431 (Fig. 10), of the die 43, which faces the
inner peripheral surface portion 422 in the radial
direction.
[0035] Hereinafter, a forming operation (press
forming method) of the press forming device will be
described. Referring to Fig. 8, after the cup-shaped
- 23 -
workpiece B is placed on the die 43, the inner punch
11 is moved down and the inner punch 11 is inserted
into the cup-shaped workpiece B via the cup opening
portion B14. While the outer peripheral surface 111
of the inner punch 11 and the inner peripheral
surface B2 2 of the cup longitudinal wall portion B2
are apart from each other by the second space S2, the
cup bottom portion B15 is sandwiched by the inner
punch 11 and the die 43 (first step). An initial
position of the outer punch 4 2 is above the cup
longitudinal wall portion B2.
[0036] Next, as illustrated in Fig. 9 , the outer
punch 4 2 is moved down, and from the punch shoulder R
portion 42A, the outer punch 42 is made to abut on
the cup longitudinal wall portion B2. Then, the
punch shoulder R portion 42A and the inner peripheral
surface 421 of the outer punch 42 push the cup
longitudinal wall portion B2 in order of its cup
opening portion B14 side to its cup bottom B15 side,
toward the outer peripheral surface 111 of the inner
punch 11 to radially reduce the cup longitudinal wall
portion B2, whereby the cup longitudinal wall portion
B2 is subjected to drawing (second step).
[0037] When the cup longitudinal wall portion B2 is
pressed by the outer punch 42, the material of the
cup longitudinal wall portion B2 moves toward the
outer peripheral surface 111 of the inner punch 11.
At this time, a diameter of the cup longitudinal wall
portion B2 becomes smaller, and accordingly a surplus
- 24 -
material occurs in the material. Since the first
space SI between the inner punch 11 and the outer
punch 42 is larger than the plate thickness T before
the radial reduction, the surplus material thickens
the cup longitudinal wall portion B2. Of the surplus
material, a portion which becomes surplus even after
the thickening of the cup longitudinal wall portion
B2 is led downward by the outer punch 42. Such a
phenomenon continuously occurs at the time of the
drawing of the cup longitudinal wall portion B2, and
therefore, -when the outer punch 42 is moved down to a
side of the cup bottom portion B15 to apply the
drawing to the cup longitudinal wall portion B2, the
portion which becomes surplus even after the
thickening of the cup longitudinal wall portion B2,
of the surplus material of the cup longitudinal wall
portion B2 occurring by the drawing, finally thickens
the cup shoulder portion Bl as illustrated in Fig.10.
Thus, in this embodiment, the surplus material of the
cup longitudinal wall portion B2 occurring by the
drawing contributes to the thickening of the cup
longitudinal wall portion B2 and the cup shoulder
portion Bl, which makes it possible to thicken the
cup shoulder portion Bl without thinning the cup
longitudinal wall portion B2.
[0038] In this case, by adjusting the thickness T of
the cup longitudinal wall portion B2 or sizes of the
spaces SI to 3, it is possible to make the thickening
material of the cup longitudinal wall portion B2
25
sufficiently flow into the cup shoulder portion Bl,
and an outer peripheral surface BIO of the cup
shoulder portion Bl can be formed so as to be flush
with an outer peripheral surface B21 of the cup
longitudinal-wall portion B2 by the inner peripheral
surface 421 of the outer punch 42. Consequently, the
cup shoulder portion Bl can be formed in a rightangled
shape. At this time, between the inner
peripheral surface portion 422, of the outer punch 42,
which is in contact with the cup shoulder portion Bl
and the outer peripheral surface portion 431, of the
die 43, which faces the inner peripheral surface
portion 4 22 in the radial direction, the escape space
S3 is formed. Consequently, when the surplus
material occurs in the thickening material of the cup
shoulder portion Bl, it is possible to make the
surplus material escape to the escape space S3. On
an outer edge portion of the bottom surface B150 of
.the cup bottom portion B15, a surplus portion B4
projecting from a bottom surface B15 0 is formed by
the surplus material escaping to the escape space S3.
[0039] As described above, in this embodiment, since
the thickening of the cup shoulder portion Bl is
performed by the drawing of the cup longitudinal wall
portion B2, it is possible to thicken the cup
shoulder portion Bl while reducing a forming load.
Further, since the drawing is performed while the
space SI between the outer punch 42 and the inner
punch 11 is set equal to or more than the thickness T
- 26 -
of the cup longitudinal wall portion B2, the cup
longitudinal wall portion B2 is not thinned.
Further, in the conventional forging method and
upsetting method, when an attempt is made to form the
cup shoulder portion Bl into the same right-angled
shape as that of a die shape, the forming load
reaches several thousand tons. On the other hand, in
the press forming method of this embodiment, the cup
shoulder portion Bl is thickened by the drawing, and
therefore, even when the cup shoulder portion Bl is
formed into the right-angled shape, it is possible to
reduce the forming load to about several hundred tons
which is smaller than that of the conventional
forging method and upsetting method by a single digit
By setting the outside diameter of the inner
punch 11 and the inside diameter of the outer punch
4 2 still smaller, it is possible to more increase a
radial reduction ratio of the cup longitudinal wall
•portion B2 to more thicken the cup shoulder portion
Bl.
[0040] In the press forming method of this
embodiment, when the cup shoulder portion Bl is
formed into the right-angled shape, the surplus
portion B4 is formed on the outer edge portion of the
bottom surface B150 of the cup bottom portion Bl5 by
the surplus material of the cup-shaped workpiece B
which material is made to escape to the escape space
S3 between the die 43 and the outer punch 42. This
necessitates an additional step of removing the
27 -
surplus portion B4 in a later step, but the size of
the surplus portion B4 is generally about several
millimeters. Further, when the cup-shaped workpiece
B is worked, with its material being changed, since a
behavior of the material during the working changes
(in this embodiment, since a state of plastic flow of
the cup longitudinal wall portion B2 and the cup
shoulder portion Bl during the drawing changes), a
different die whose dimension is adjusted differently
is generally used in many cases. In this embodiment,
even when the material of the cup-shaped workpiece B
is changed, an amount of the surplus material of the
cup-shaped workpiece B which is made to escape to the
escape space S3 between the die 4 3 and the outer
punch 42 only changes, which reduces the necessity
for changing the die according to the change of the
material. Further, since the escape space S3 is
provided, a closed die forging state does not
structurally occur, which can suppress a rapid
increase of the forming load during the forming to
reduce tuning for safely operating the press forming
device. Therefore, even if the trouble of removing
the surplus portion B4 by cutting or the like is
taken into consideration, this embodiment can enjoy
the merit.
[004 1] Incidentally, when the cup-shaped workpiece B
is installed on the die 43, a center axis of the cupshaped
workpiece B may be aligned with the center
axis 10, but the center axis of the cup-shaped
- 28 -
workpiece B may be deviated from the center axis 10
within a range allowing the inner punch 11 to move
down to a region on a more radially inner side than
the cup longitudinal wall portion B2. In this case,
the outer punch 12 is moved down while the cup-shaped
workpiece B is sandwiched by the inner punch 11 and
the die 4 3 with a force allowing the cup-shaped
workpiece B to displace in the radial direction. At
this time, since the punch shoulder R portion 42A of
the outer punch 4 2 abuts on the annular cup-shaped
longitudinal wall portion B2 in a biased state, the
cup-shaped workpiece B displaces, so that the center
axis of the cup-shaped workpiece B coincides with the
center axis 10. After the center axis of the cupshaped
workpiece B coincides with the center axis 10,
the cup-shaped workpiece B is sandwiched by the inner
punch 11 and the die 43 and the outer punch 42 is
further moved down.
[0042] Further, preferably, the punch shoulder
portion of the outer punch 4 2 is the punch shoulder
portion 4 2A which widens as it goes in the punching
direction of the outer punch 4 2 to the cup
longitudinal wall portion B2, or is a tapered portion
5 2A which widens as it goes in the punching direction
as in an outer punch 52 illustrated in Fig.11. Thus
structuring the punch shoulder portions of the outer
punches 42, 5 2 makes it possible to radially reduce
the cup longitudinal wall portion B2 gently and
continuously in order of its cup opening portion B14
- 29 -
side to its cup bottom portion A15 side and also
enables a reduction of a contact angle of the cup
longitudinal wall portion B2 and each of the outer
punches 42, 52, which makes it possible to reduce a
contact reaction force in a vertical direction to
reduce a frictional force of each of the outer
punches 42, 52 with the cup longitudinal wall portion
B2. Accordingly, a forming force in a vertically
downward direction to a portion near the cup bottom
portion B15 in the cup longitudinal wall portion B2
and to the cup shoulder portion Bl can be made
smaller than that of the conventional ironing, which
can suppress the occurrence of inward folding in the
cup shoulder portion Bl.
[004 3] (Fourth Embodiment)
Fig. 12 is a schematic structural view of a press
forming device of a fourth embodiment.
In the press forming device of this embodiment, a
die 43 is formed in a stepped shape whose end portion
432 abutting on a cup bottom portion B15 has a
diameter smaller than a diameter of a main body
portion 433 of the die 43. The other structure is
the same as that of the third embodiment, and
hereinafter, what are different from the third
embodiment will be mainly described.
In this embodiment as in the third embodiment, at
the time of drawing of a cup-shaped workpiece B, an
escape space S3 is formed between an inner peripheral
surface portion 422, of an outer punch 42, which is
30 -
in contact with a cup shoulder portion Bl and an
outer peripheral surface portion 431, of the die 4 3,
which faces the inner peripheral surface portion 422
in. a radial direction. Conseguently, when a surplus
material occurs in a thickening material flowing into
the cup shoulder portion Bl, the surplus material can
be made to escape to the escape space S3. Therefore,
it is possible to thicken the cup shoulder portion Bl
while reducing a forming load, without thinning a cup
longitudinal wall portion B2.
[0044] (Fifth Embodiment)
Fig. 13 is a schematic structural view of a press
forming device of a fifth embodiment.
The press forming device of this embodiment is
different from that of the third embodiment only in a
shape of an outer punch 62, and what are different
from the third embodiment will be mainly described
below.
In this embodiment, on an inner peripheral
surface 621 of the outer punch 62, an end surface
pushing portion 62B in a circumferential shape
projecting in a radial direction from the whole
circumference of the inner peripheral surface 621 is
formed. The end surface pushing portion 6 2B is
disposed at a position where the inner peripheral
surface 62 1 becomes longer than the whole height of a
cup-shaped workpiece B.
[0045] A press forming method of this embodiment is
different from that of the third embodiment in that,
31 -
in a second step of drawing a cup longitudinal wall
portion B2 by moving down the outer punch 62, at the
time of thickening forming of a cup shoulder portion
Bl, a cup upper end portion B3 of the cup-shaped
workpiece B is pushed in by using the end surface
pushing portion 62B of the outer punch 62, as
illustrated in Fig. 14. Consequently, in this
embodiment, it is possible to improve accuracy of the
transfer of a die shape to the cup shoulder portion
Bl and the cup longitudinal wall portion B2.
[004 6] (Modification Examples)
Fig 15A to Fig. 15C are views illustrating
examples of the cup-shaped workpiece to which the
press forming method of the present invention is
applicable.
As the shape of the cup-shaped workpiece to which
the press forming method of the present invention is
applicable, not only the simple bottomed cylindrical
shape illustrated in the third to fifth embodiments
but also appropriate ones are usable. For example,
as illustrated in Fig. 15A, a perforated cup-shaped
workpiece Bll having a hole B151 in a cup bottom
portion Bl5 may be used. Further, as illustrated in
Fig. 15B, a cup-shaped workpiece B12 with boss on
whose cup bottom portion B15 a boss B152 projecting
outward is formed may be used, or as illustrated in
Fig. 15C, a cup-shaped workpiece B13 with boss on
whose cup bottom portion B15 a boss B153 projecting
inward is formed may be used.
- 32 -
Further, as a material of the cup-shaped
workpiece to which the press forming method of the
present invention is applicable, various well-known
ones which can be plastically worked, such as metals
such as steel, aluminum, and copper or alloys of
these, and so on can be adopted.
[0047] In the second step of the third to fifth
embodiments, the cup shoulder portion Bl is thickened
by moving the outer punch 42 {52, 62) toward the
inner punch 11, the die 43, and the cup-shaped
workpiece B, but the cup shoulder portion Bl may be
thickened by moving the inner punch 11, the die 43,
and the cup-shaped workpiece B toward the outer punch
42 (52, 62} .
Further, the third to fifth embodiments describe
the examples where the inner punch 11 and the outer
punch 42 (52, 62) are above the die 43, but the
positions of the inner punch 11 and the outer punch
42 (552, 62) and the position of the die 43 may be
vertically reversed.
[0048] In the foregoing, the present invention is
described together with the various embodiments, but
the present invention is not limited to these
embodiments, and modifications and so on can be made
within a range of the present invention.
INDUSTRIAL APPLICABILITY
[0049] The present invention is applicable to a
press forming method of applying press forming to a cup-shaped workpiece used, for example, for
transmissions and so on of vehicles.

CLAIMS
[Claim 1] A press forming method which applies press
forming to a cup-shaped workpiece having a cup
longitudinal wall portion, a cup bottom portion, and
a cup shoulder portion connecting the cup
longitudinal wall portion and the cup bottom portion,
by using a press forming device, wherein
the press forming device includes an inner punch,
an annular outer punch, and a die whose center axes
are disposed on the same axis, the outer punch being
disposed so as to be apart from the inner punch in a
radial direction perpendicular to the center axis by
a first space which is larger than a plate thickness
of the cup longitudinal wall portion, and the die
being disposed to face the inner punch in a direction
of the center axis, and an inner peripheral surface
of the outer punch has, on a side thereof closer to
the die in terms of the center axis direction, a
punch shoulder portion widening as the punch shoulder
portion goes toward the die, the method comprising:
a first step of sandwiching the cup bottom
portion by the inner punch and the die while an outer
peripheral surface of the inner punch and an inner
peripheral surface of the cup longitudinal wall
portion are apart from each other by a second space;
and
a second step of performing drawing to radially
reduce the cup longitudinal wall portion by pushing
the cup longitudinal wall portion toward the outer
35 -
peripheral surface of the inner punch by the outer
punch while moving the outer punch relatively to the
inner punch and the die along the center axis to make
the outer punch abut on the cup longitudinal wall
portion from the punch shoulder portion, thereby
making a surplus material of the workpiece flow into
the cup shoulder portion to thicken the cup shoulder
portion.
[Claim 2] The press forming method according to
claim 1, wherein, in the second step, the cup
longitudinal wall portion is radially reduced until
reaching a position where an outside diameter of an
outer peripheral surface of the cup longitudinal wall
portion becomes equal to an outside diameter of the
die .
[Claim 3] The press forming method according to
claim 1 or 2, wherein the cup shoulder portion is
formed into a right-angled shape.
[Claim 4] The press forming method according to
claim 1, wherein, when the thickening is completed in
the second step, a space is formed between the inner
peripheral surface portion, of the outer punch, which
is in contact with the cup shoulder portion and an
outer peripheral surface portion, of the die, which
faces the inner peripheral surface portion in the
radial direction.
[Claim 5] The press forming method according to
claim 4 , wherein, in the second step, an outer
peripheral surface of the cup shoulder portion is
- 36 -
formed so as to be flush with an outer peripheral •
surface of the cup longitudinal wall portion, by the
inner peripheral surface of the outer punch, and on a
bottom surface outer edge portion of the cup bottom
portion, a surplus portion projecting from the bottom
surface is formed by the surplus material made to
escape to the space.
[Claim 6] The press forming method according to'any
one of claims 1 to 5, wherein the punch shoulder
portion has a rounded shape or a tapered shape
widening as the punch shoulder portion goes toward
the die.
[Claim 7] The press forming method according to any
one of claims 1 to 6 , wherein:
on the inner peripheral surface of the outer
punch, an end surface pushing portion in a
circumferential shape projecting in the radial
direction from the inner peripheral surface is
formed; and
in the second step, at the time of thickening the
cup shoulder portion by relatively moving the outer
punch, the cup longitudinal wall portion is pushed
toward the die by the end surface pushing portion.