DESCRIPTION
TITLE OF INVENTION: PRESS-FORMING METHOD
TECHNICAL FIELD
[0001] The present invention relates to a pressforming
method of forming a plate-shaped workpiece
into a cup shape.
BACKGROUND ART
[0002] As a part used for a transmission of a
vehicle, or the like, an axisymmetric part having a
cup sidewall portion and a cup bottom portion has
been known. When general drawing is used in order to
obtain a cup-shaped axisymmetric part, normally, the
limit of a drawing ratio (drawing ratio = blank
diameter/cup outside diameter after forming) becomes
2.1 or so (see Non Patent Literature).
Note that Patent Literature 1 or Patent
Literature 2 discloses a thickening and pressing
method to suppress occurrence of a crack and the like.
CITATION LIST
PATENT LITERATURE
[0003] Patent Literature 1: Japanese Laid-open
Patent Publication No. 2001-047175
Patent Literature 2: Japanese Laid-open Patent
Publication No. 2010-089139
NON PATENT LITERATURE
[000 4] Non Patent Literature 1: Transactions of The
Japan Society of Mechanical Engineers (Series C) Vol.
59 No. 560 (1993-4)
- 1 -
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0005] When a drawing ratio exceeds 2.1 in general
drawing, during forming, deformation concentrates to
cause a risk that a cup shoulder portion or a cup
sidewall portion whose sheet thickness is reduced
largely is fractured.
[000 6] An object of the present invention is to
provide a press-forming method capable of suppressing
fracture in a deformation concentrated portion even
at the time of forming with a large drawing ratio.
SOLUTION TO PROBLEM
[0007] (1) In order to solve the above-described
object, a press-forming method according to the
present invention is a press-forming method for a
plate-shaped workpiece that uses a second-stage
forming punch, a first-stage forming punch disposed
along an outer periphery of the second-stage forming
punch, an axial pressing punch disposed along an
outer periphery of the first-stage forming punch, a
counter punch disposed to face the second-stage
forming punch in a central axis direction, and a d i_ e
including:, from a leading end side where the firststage
and second-stage forming punches are inserted,
a first die shoulder portion that expands outward as
it goes to the leading end; a first die hole portion
parallel to a central axis; a second die shoulder
portion that faces the first-stage forming punch and
the axial pressing punch in the central axis
- 2 -
i
7
direction and expands outward as it goes to the
leading end; and a second die hole portion connected
to the second die shoulder portion, central axes of
all of which are disposed coaxially, the method
including: a step SI of moving the first-stage and
second-stage forming punches relatively to the die
and inserting the first-stage and second-stage
forming punches into the first die hole portion, to
thereby push the workpiece into the first die hole
portion through the first die shoulder portion to
form a first cup-shaped v/orkpiece having a cup bottom
portion and a circumferential cup sidewall portion
rising from a circumferential edge portion of the cup
bottom portion; a step S2 of moving the axial
pressing punch relatively to the die to abut on a cup
opening end of the cup sidewall portion, and while
constraining the cup opening end, moving the secondstage
forming punch relatively to the die to insert
the second-stage forming punch into the second die
hole portion and pushing a part of the first cupshaped
workpiece into the second die hole portion
through the second die shoulder portion, to thereby
reduce the cup sidewall portion in diameter and
thicken the cup sidewall port.Ion; and a step S3 of,
in a state of the constraint of the cup opening end
by the axial pressing punch being released, moving
the second-stage forming punch relatively to the die
and further pushing the first cup-shaped workpiece
deeper in the second die hole portion, to thereby
- 3 -
form a second cup-shaped v/orkpiece smaller in
diameter than the first cup-shaped v/orkpiece.
[0008] (2) In the press-forming method according to
(1), a counter punch disposed to face the secondstage
forming punch in the central axis direction is
further used and along an outer periphery of the
counter punch, the second die hole portion is
disposed, the step S 2 includes a step S21 of, while
constraining the cup opening end by the axial
pressing punch and while constraining deformation of
the cup sidewall portion on the cup bottom portion
side in a sheet thickness direction by the secondstage
forming punch and the second die hole portion,
bringing the counter punch close to the second-stage
forming punch to compress the cup bottom portion in
the second die hole portion by the counter punch and
the second-stage forming punch, to thereby form a cup
shoulder portion connecting the cup bottom portion
and the cup sidewall portion into an orthogonal shape
and cause a material of the cup bottom portion to
flow into the cup shoulder portion to thicken the cup
shoulder portion, and ill the step S3, while
compressing the cup bottom portion, the second-stage
forming punch and the counter punch may also be moved
deeper in the second die hole portion relatively to
the die.
[0009] (3) In order to solve the above-described
ob j ect, a press"-forming method according to the
present invention is a press-forming method for a
- 4 -
plate-shaped workpiece that uses a second-stage
forming punch, a first-stage forming punch disposed
along an outer periphery of the second-stage forming
punch, an axial pressing punch disposed along an
outer periphery of the first-stage forming punch, a
counter punch disposed to face the second-stage
forming punch in a central axis direction, and a die
including:, from a leading end side where the firststage
and second-stage forming punches are inserted,
a first die shoulder portion that expands outward as
it goes to the leading end; a first die hole portion
parallel to a central axis; a second die shoulder
portion that faces the first-stage forming punch and
the axial pressing punch in the central axis
direction and expands outward as it goes to the
leading end; and a second die hole portion disposed
along an outer periphery of the counter punch,
central axes of all of which are disposed coaxially,
the method including: a step SA1 of moving the firststage
and second-stage forming punches relatively to
the die and inserting the first-stage and secondstage
forming punches into the first die hole portion,
to thereby push the v/orkpiece into the first die hole
portion through the first die shoulder portion to
form a first cup-shaped v/orkpiece having a cup bottom
portion and a circumferential cup sidewall portion
rising from a circumferential edge portion of the cup
bottom portion; a step SA2 of bringing the axial
pressing punch to abut on a cup opening end of the
_ 5 _
cup side wall portion, and v/hile constraining the cup
opening end, moving the axial pressing punch
relatively to the die and pushing a part of the first
cup-shaped workpiece into the second die hole portion
through the second die shoulder portion, to thereby
reduce the cup sidewall portion in diameter and
thicken the cup- sidewall portion; a step SA3 of,
v/hile constraining the cup opening end by the axial
pressing punch, bringing the second-stage forming
punch and the counter punch close to each other,
compressing the cup bottom portion in the second die
hole portion by the second-stage forming punch and
the counter punch to form the flat cup bottom portion,
and causing a material of the cup bottom portion to
flow into a cup shoulder portion connecting the cup
bottom portion and the cup sidewall portion to
thicken the cup shoulder portion; and a step SA4 of
moving the second-stage forming punch relatively to
the die and further pushing the first cup-shaped
workpiece deeper in the second die hole portion, to
thereby form a second cup-shaped workpiece smaller in
diameter than the first cup-shaped workpiece,
[0010] ( 4 ) In the press-forming method according to
(3), in the step SA4 , the second cup-shaped workpiece
is pushed into the second die hole portion until the
cup opening end is positioned in the second die hole
portion, and the press-forming method may also
further include a step SA5 of, v/hile compressing the
cup bottom portion by the second-stage forming punch
- 6
and the counter punch and while constraining
deformation of the cup sidewall portion on the cup
bottom portion side in a sheet thickness direction by
the second-stage forming punch and the second die
hole portion, moving the second-stage forming punch
and the counter punch relatively in a direction to
come close to the first-stage forming punch to cause
the cup opening end to butt against the first-stage
forming punch, to thereby form the cup shoulder
portion into an orthogonal shape.
[0011] (5) In- the press-forming method according to
any one of (1) to (4), in the steps S3 and SA4, the
first cup-shaped v/orkpiece may also be pushed into
the second die hole portion until the cup opening end
is positioned on the second die shoulder portion, to
thereby form the second cup-shaped v/orkpiece provided
v/ith an expanded opening portion that expands outv/ard
as it goes to the cup opening end side.
[0012] (6) In order to solve the above-described
object, a press-formed product according to the
present invention is characterized in that it is
formed by the press-forming method according to any
one of (1) to (5) .
ADVANTAGEOUS EFFECTS OF INVENTION
[0013] According to the present invention, it is
possible to provide a press-forming method capable of
suppressing fracture in a deformation concentrated
portion even when a large drav/ing ratio is taken.
BRIEF DESCRIPTION OF DRAWINGS
[0014] [Fig. 1] Fig. 1 is a schematic constitution
view of a press-forming apparatus of a first
embodiment in the present invention.
[Fig. 2 ] Fig. 2 is a view illustrating a
modified example of a first-stage forming punch in
the present invention.
[Fig. 3] Fig. 3 is a flowchart used for
explaining a press-forming method in the present
invention.
[Fig. 4 ] Fig. 4 is a view illustrating a step of
first-stage drawing in the present invention.
[Fig. 5] Fig. 5 is a view illustrating a step of
second-stage drawing to be performed while pressing a
cup opening end in the present invention.
[Fig. 6] Fig. 6 is a view illustrating how a cup
sidewall portion is thickened in the second-stage
drawing in the present invention.
[Fig. 7] Fig. 7 is a view illustrating a second
cup-shaped workpiece that has completed being formed
with an expanded opening portion provided therewith
in the present i nvention.
[Fig. 8] Fig. 8 is a view illustrating the
second cup-shaped workpiece that has completed being
formed without an expanded opening portion provided
therewith in the present invention.
[Fig. 9] Fig. 9 is a flowchart used for
explaining a press-forming method of a second
embodiment in the present invention.
- 8 -
[Fig. 10] Fig. 10 is a view illustrating a step
of compressing a cup bottom portion in the present
invention.
[Fig. 11] Fig. 11 is a view illustrating a step
of drawing to be performed while compressing the cup
bottom portion in the present invention.
[Fig. 12] Fig. 12 is a view illustrating the
second cup-shaped workpiece that has completed being
formed in the present invention.
[Fig. 13] Fig. 13 is a flowchart used for
explaining a press-forming method of a third
embodiment in the present invention.
[Fig. 14] Fig. 14 is a view illustrating a step
of second-stage drawing to be performed while
pressing the cup opening end in the present invention.
[Fig. 15] Fig. 15 is a view illustrating the
step of second-stage drawing to be performed while
pressing the cup opening end in the present invention.
[Fig. 16] Fig. 16 is a view illustrating a step
of compressing the cup bottom portion in the present
invention.
[Fig. 17] Fig. 17 is a view illustrating the
step of compressing the cup bottom portion in the
present invention.
[Fig. 18] Fig. 18 is a view illustrating that a
cup shoulder portion is formed into an orthogonal
shape by the compression of the cup bottom portion in
the present invention.
[Fig. 19] Fig. 19 is a view illustrating that
the cup sidewall portion is brought to butt against
the first-stage forming punch in the present
invention.
[Fig. 20] Fig. 2 0 is a view illustrating that
the cup sidewall portion is brought to butt against
the first-stage forming punch in the present
invention.
[Fig. 21] Fig. 21 is a view illustrating that
the cup shoulder portion is formed into an orthogonal
shape by the butting of the cup sidewall portion in
the present invention.
DESCRIPTION OF EMBODIMENTS
[001/5] Hereinafter, each embodiment of the present
invention will be explained with reference to the
drawings.
(First embodiment)
Fig. 1 is a schematic constitution view of a
press forming apparatus of a first embodiment. In
the drawings of Fig. 1 and after, the cross section
of the press forming apparatus including the central
axis is axisymmetric across the central axis. In
order to simplify the drawings, only the cross
section on one side across the centra.! axis of the
press forming apparatus is illustrated.
[0016] The press forming apparatus performs press
forming in which a disk-shaped (plate-shaped)
workpiece A is formed into a first cup-shaped
workpiece, and then v/hile thickening a cup side wall
portion, the cup-shaped workpiece is reduced in
- 10 -
diameter and a second cup-shaped workpiece smaller in
diameter than the first cup-shaped workpiece is
formed. The press forming apparatus performs press
forming using a press mold including: a second-stage
forming punch 11; a first-stage forming punch 12; an
axial pressing punch 13; a counter punch 14; and a
die 15. These second-stage forming punch 11 to die
15 each being a component of the mold are
axisymmetrically disposed with respect to a central
axis 10 of the press forming apparatus, and can be
raised and lowered independently. Note that press
forming similar to that in the case of raising and
lowering the respective punches of the second-stage
forming punch 11 to the counter punch 14 and the die
15 independently is also possible by fixing the die
15 and moving the second-stage forming punch 11, the
first-stage forming punch 12, the axial pressing
punch 13, and the counter punch 14 relatively to the
die 15, for example.
[0017] The second-stage forming punch 11 has a
column shape, and has a flat leading end surface 111
extending in a direction perpendicular to the central
axis 10 formed on a leading end surface thereof
facing the counter punch 14. At a leading end corner
portion of the second-stage forming punch 11, an Rshaped
second punch shoulder portion 113 is formed.
In other words, the second punch shoulder portion 113
is formed at a position connecting a peripheral edge
portion of the flat leading end surface 111 and a
- 11 -
lower end portion of an outer peripheral surface 112
of the second-stage forming punch 11.
[0018] The first-stage forming punch 12 has a
cylindrical hollow shape and is disposed along the
outer periphery of the second-stage forming punch 11.
At a leading end portion of the first-stage forming
punch 12, an R-shaped first punch shoulder portion
121 is formed. In this embodiment, the first punch
shoulder portion 121 is formed at a position
connecting, of the first-stage forming punch 12, a
lower end portion of an inner peripheral surface 122
parallel to the central axis 10 and a lower end
portion of an outer peripheral surface 12 3 parallel
to the central axis 10. Here, when the explanation
is made with reference to Fig. 20 to be described
later, an abutting surface of the first punch
shoulder portion 121 to abut on a cup opening end C21
is preferably formed to extend in a radial direction
perpendicular to the central axis 10. This makes it
possible to increase an abutting area of the first
punch shoulder portion 121 and the cup opening end
C21 .
[00191 However, when the abutting surface of the
first punch shoulder portion 121 becomes too long as
illustrated in Fig. 2 (namely, a flat leading end
surface 120 is formed), a cup shoulder portion B3
becomes small, and when a cup-shaped workpiece B is
further drawn by a later-described second die
shoulder portion 154, a force to be given to a cup
- 12 -
bottom portion Bl and the cup shoulder portion B3 has
to be increased. In contrast to this, as illustrated
in Fig. 1, when the flat leading end surface 120 does
not exist and the first punch shoulder portion 121 is
formed into a shape extending from the lower end
portion of the inner peripheral surface 122, when the
cup-shaped workpiece B is formed by a later-described
first die shoulder portion 152, the cup shoulder
portion B3 can be formed largely. Therefore, when
the cup-shaped workpiece B is further drawn by the
later-described second die shoulder portion 154, only
a small force, which is given to the cup bottom
portion Bl and the cup shoulder portion B3, is
required and drawing can be well performed.
[0020] With reference to Fig. 1 again, the axial
pressing punch 13 has a cylindrical hollow shape, and
is disposed along the outer periphery of the firststage
forming punch 12.
The counter punch 14 has a column shape, and is
disposed to face the second-stage forming punch 11 in
the direction of the central axis 10. At a facing
surface of the counter punch 14 facing the secondstage
forming punch 11, a flat leading end surface
141 extending in a direction perpendicular to the
central axis 10 is formed.
[0021] The die 15 has a circular ring shape and has
an insertion hole portion 151 extending in the axial
direction. The insertion hole portion 151 includes:
the first die shoulder portion 152; a first die hole
13 -
portion 15 3; the second die shoulder portion 15 4; and
a second die hole portion 155 in the order from the
leading end side where the first-stage and secondstage
forming punches 12 and 11 are inserted (the
upper side in Fig. 1). The first die shoulder
portion 152 expands outward as it goes to the leading
end of the insertion hole portion 151. The first die
hole portion 153 extends parallel to the central axis
10 and has an upper end portion thereof connected to
a lower end portion of the first die shoulder portion
152. A distance Dl in the radial direction between
an inner peripheral surface 1531 of the first die
hole portion 153 and the outer peripheral surface 123
of the first-stage forming punch 12 {namely the
radius difference) results in a size similar to the
thickness of the disk-shaped workpiece A (including
uncertainties).
[0022] The second die shoulder portion 154 is
disposed to face the first-stage forming punch 12 and
the axial pressing punch 11 in the direction of the
central axis 10, expands outward as it goes to the
leading end (upward), and has an upper end portion
thereof connected to a lower end portion of the first
die hole portion 153. The second die shoulder
portion 15 4 has a tapered surface, and includes: a
draw portion 1541 with an upper end portion thereof
connected to the lower end portion of the first die
hole portion 153; and an R-shaped portion 154 2
connecting the draw portion 1541 and the second die
- 14 -
hole portion 155.
[002 3] The second die hole portion 155 extends
parallel to the central axis 10, and has an upper end
portion thereof connected to a lower end portion of
the second die shoulder portion 154. The second die
hole portion 155 is disposed along the outer
periphery of the counter punch 14. A distance D2 in
the radial direction between an inner peripheral
surface 1551 of the second die hole portion 155 and
the outer peripheral surface 112 of the second-stage
forming punch 11 is slightly larger than the
thickness of the disk-shaped workpiece A. An upper
end surface 156 of the die 15 has a circular ring
shape in a planar view, and is a flat surface
parallel to a direction perpendicular to the central
axis 10.
[0024] Fig. 3 is a flowchart used for explaining a
forming operation (press-forming method) of the
press-forming apparatus. Hereinafter, the forming
operation of the press-forming apparatus will be
explained. With reference to Fig. 1, the disk-shaped
workpiece A is first set on the die 15 {step SO}.
Subsequently, as illustrated in Fig. 4, the pressforming
apparatus integrally lowers the first-stage
and second-stage forming punches 12 and 11 and
inserts them into the first die hole portion 15 3 so
that their respective lower ends are brought to the
same position in the direction of the central axis 10,
to thereby push the disk-shaped workpiece A into the
- 15
first die hole portion 153 through the first die
shoulder portion 152,
[0025] Thereby, the press-forming apparatus forms
the disk-shaped workpiece A into the first cup-shaped
workpiece B (step SI). The first cup-shaped
workpiece B includes: the cup bottom portion Bl; a
circumferential cup sidewall portion B2 rising from a
circumferential edge portion of the cup bottom
portion Bl; and the R-shaped cup shoulder portion B3
connecting the cup sidewall portion B2 and the cup
bottom portion Bl.
[0026] Subsequently, as illustrated in Fig. 5, the
press-forming apparatus lowers the axial pressing
punch 13 to abut on the cup opening end B21 of the
cup sidewall portion B2, to thereby constrain rising
of the cup opening end B21. Subsequently, as
illustrated in Fig. 6, the press-forming apparatus
further lowers the second-stage forming punch 11 to
insert it into the second die hole portion 155, to
thereby push the first cup-shaped workpiece B into
the second die hole portion 155 through the second
die shoulder portion 154 (s t ep S 2) . On this occasion,
the press-forming apparatus lowers the second-stage
forming punch 11 and lowers the axial pressing punch
13 simultaneously, to thereby perform the step S2
while suppressing extension of the cup opening end
B21 in a direction parallel to the direction of the
central axis 10.
[0027] On this occasion, the press-forming apparatus
16 -
reduces the cup sidewall portion B2 of the first cupshaped
workpiece B in diameter by the second die
shoulder portion 154 while constraining the cup
opening end B21, so that it is possible to promote
thickening of the cup sidewall portion B2 on the
second die shoulder portion 154. Further, the pressforming
apparatus draws the cup sidewall portion B2
while constraining the cup opening end B21, so that
it is possible to suppress variations in position of
the cup opening end B21 (edge) in the direction of
the central axis 10. Incidentally, when such
variations in position exist, the cup opening end B21
is deformed unevenly, for example, wavily or the like,
but by the constraint of the cup opening end B21 by
the axial pressing punch 13, evenness of the cup
opening end B21 can be ensured.
[0028] Incidentally, during drawing performed by the
lowering of the second-stage forming punch 11, the
press-forming apparatus lowers the first-stage
forming punch 12 down to the position where the first
punch shoulder portion 121 can smoothly guide the cup
sidewall portion B2 to move downward at a portion
extending from the first die hole portion 153 to the
second die shoulder portion 154. That is, as
illustrated in Fig. 7, the press-forming apparatus
lowers the first-stage forming punch 12 down to the
position where a space substantially equal to a sheet
thickness t of the first cup-shaped workpiece B is
formed between the first punch shoulder portion 121
- 17 -
and the portion extending from the first die hole
portion 153 to the second die shoulder portion 154.
Further, the axial pressing punch 13 is lowered down
to the lowermost position in the vicinity of a
boundary line between the first die hole portion 153
and the second die shoulder portion 154, and keeps
constraining the cup opening end B21 at the most when
the second-stage forming punch 11 is lowered (see Fig
7) -
[0029] Subsequently, the press-forming apparatus, as
illustrated in Fig. 7 , lowers the second-stage
forming punch 11 in a state where lowering of the
axial pressing punch 13 is stopped in the vicinity of
the boundary line between the first die hole portion
153 and the second die shoulder portion 154, namely
in a state where the constraint of the cup opening
end B21 by the axial pressing punch 13 is released.
Thereby, the first cup-shaped workpiece B is further
pushed deeper in the second die hole portion 155, and
thereby a second cup-shaped workpiece C smaller in
d i a meter than the first cup-shaped workpiece B is
formed as illustrated in Fig. 8 (step S3).
[0030] Incidentally, the press - forming apparatus, as
illustrated in Fig. 7, can also stop pushing the
first cup-shaped workpiece B into the second die hole
portion 155 at the position where the cup opening end
B21 is positioned on the second die shoulder portion
154. Thereby, the first cup-shaped workpiece B may
also be formed into the second cup-shaped workpiece C
- 18 -
provided with an expanded opening portion C4 that
expands outward as it goes to the cup opening end C21
side .
[0031] In this embodiment as above, two-stage
drawing in which the disk-shaped workpiece A is drawn
into the first cup-shaped workpiece B and then the
first cup-shaped workpiece B is further drawn is
performed. Particularly, at the time of the secondstage
drawing of the first cup-shaped workpiece B,
v/hile constraining deformation of the cup opening end
B21 by the axial pressing punch 13, the drawing is
performed. Therefore, it is possible to promote
thickening of the cup sidewall portion B2 at the time
of the second-stage drawing of the first cup-shaped
workpiece B and to suppress cracking of the cup
sidewall portion B2 at the time of the drawing. Thus,
in this embodiment, even when a drawing ratio {blank
diameter/cup outside diameter after forming) is set
to be large, which is not less than 2.1 nor more than
4.0, the disk-shaped workpiece A can be well drawn
into the second cup-shaped workpiece C.
[003 2] {Second embodiment)
Fig. 9 is a flowchart used for explaining a
press-forming method in this embodiment, and Fig. 10
is a view illustrating a step S21 of compressing the
cup bottom portion Bl to be performed in the middle
of the step S2 of drawing the first cup-shaped
workpiece B.
The press-forming apparatus in this embodiment
- 19 -
also performs the steps SO and Si of forming the
disk-shaped workpiece A into the first cup-shaped
workpiece B, and then performs the step S2 of drav/ing
the first cup-shaped workpiece B while constraining
the cup opening end B21 by the axial pressing punch
13, similarly to the first embodiment.
[0033] The press-forming apparatus first performs a
step S20 of drav/ing the first cup-shaped workpiece B
while constraining the cup opening end B21 by the
axial pressing punch 13 in the step S2. In this step
S20, the cup opening end B21 is brought into a state
of being constrained by the axial pressing punch 13
and deformation of the cup sidewall portion B2 on the
cup bottom portion Bl side in a sheet thickness
direction is brought into a state of being
constrained by the second-stage forming punch 11 and
the second die hole portion 155 as referred in Fig. 6.
In this step S20, as in an example illustrated by a
two-dot chain line in an abbreviated manner in Fig. 6,
the center portion of the cup bottom portion Bl is
sometimes curved downward from the second-stage
forming punch 11, to thereby cause unevenness in the
cup bottom portion Bl.
[0034] Thus, the press-forming apparatus, as
illustrated in Fig. 10, brings the counter punch 14
close to the second-stage forming punch 11 to
compress the cup bottom portion Bl in the second die
hole portion 155 by the counter punch 14 and the
second-stage forming punch 11, to thereby correct the
.- 20 -
cup bottom portion Bl to be flat. Further, the
press-forming apparatus compresses the cup bottom
portion Bl while constraini
sidewall portion B2 on the
in the sheet thickness dire
cup shoulder portion B3 int
Further, the press-forming
bottom portion Bl to be fla
redundant material derived
portion Bl to flow into the
and thereby the cup shoulde
(step S21).
[0035] Subsequently, the p
illustrated in Fig. 11, low
punch 13, and whi1e constra
B21, lowers the second-stag
counter punch 14 while comp
portion Bl, to thereby draw
workpiece B (step S22).
[003 6] Then, the press-forming apparatus lowers the
axial pressing punch 13 down to the vicinity of the
boundary line between the first die hole portion 153
and the second die shoulder portion 154, to then
release the constraint of the cup opening end B21 by
the axial pressing punch 13. In this released state,
the press-forming apparatus, as illustrated in Fig.
12, lowers the second-stage forming punch 11 and the
counter punch 14 while compressing the cup bottom
portion Bl, to thereby form the second cup-shaped
- 21 -
ng deformation of the cup
cup bottom portion Bl side
ction, to thereby form the
o an orthogonal shape.
apparatus corrects the cup
t, to thereby cause a
from the cup bottom
cup shoulder portion B3,
r portion B3 is thickened
ress-forming apparatus, as
ers the axial pressing
ining the cup opening end
e forming punch 11 and the
ressing the cup bottom
the first cup-shaped
workpiece C (step S3).
[0037] Here, in the steps S22 and S3, when the first
cup-shaped workpiece B is pushed into the second die
hole portion 155, as referred in Fig. 11, the cup
sidewall portion B2 is drav/n into a space betv/een the
second-stage forming punch 11 and the second die hole
portion 155, and thereby a tensile load in an up and
down direction is applied. Therefore, the
orthogonal-shaped cup shoulder portion B3 is pulled
upward (see an up-arrow in Fig. 11), to be formed
into an R shape in close contact with the second
punch shoulder portion 113 of the second-stage
forming punch 11 as referred in Fig. 12, but in the
second cup-shaped workpiece C, the effect of
thickening a cup shoulder portion C3 remains.
[003 8] Incidentally, in the step S3, the secondstage
forming punch 11 and the counter punch 14 are
lowered while compressing the cup bottom portion Bl,
to thereby push the first cup-shaped workpiece B
deeper in the second die hole portion 155. T h i s
embodiment is not limited to this, and by pressing
only the second-stage forming punch 11, the first
cup-shaped workpiece B may also be pushed deeper in
the second die hole portion 155.
[0039] In this embodiment, after the compression of
the cup bottom portion Bl, the axial pressing punch
13 is lowered again to draw the first cup-shaped
workpiece B, but it is also possible to, after the
compression of the cup bottom portion Bl, stop
- 22
lowering of the axial pressing punch 13 and draw the
first cup-shaped workpiece B in a state of constraint
of the cup opening end B21 being released (the step
S22 is unnecessary). Even when the above is applied,
at the stage prior to compression, drawing is
performed while constraining the cup opening end B21,
so that it is possible to maintain the effect of
suppressing formed unevenness of the cup opening end
B21 and the effect of promoting thickening of the cup
sidewall portion B2.
[0040] Here, when normal drawing is performed
conventionally, a cup shoulder portion abutting on a
shoulder R portion of a drawing punch is thinned, and
thus as measures against this, .there are known
techniques of Patent Literature 3 (Japanese Laid-open
Patent Publication No. 08-141662) and Patent
Literature 4 (Japanese Laid-open Patent Publication
No. 2007-289989) .
[0041] In Patent Literature 3, drawing is first
performed by an apparatus for drawing, and a
workpiece is formed into a cup shape. Next, in
Pateiit Literature 3, by an apparatus for coining, a
cup bottom portion of the cup-shaped workpiece is
subjected to coining, to thereby cause a material of
the cup bottom portion to flow into a cup shoulder
portion that is thinned by drawing to thicken the cup
shoulder portion.
[0042] In Patent Literature 4, a punch is inserted
into a cup-shaped workpiece to constrain an inner
- 23 -
peripheral surface of a cup sidewall portion, and
then an outer peripheral surface of the cup sidewall
portion is subjected to ironing from a cup opening
portion si-de to a cup bottom portion side by a roller,
to thereby thicken a cup shoulder portion.
[0043] However, in Patent Literature 3, since the
cup bottom portion is subjected to coining, there is
a problem that a part of the cup bottom portion is
thinned and the cup bottom portion loses flatness,
and in Patent Literature 4, since the cup sidewall
portion is subjected to ironing, there is a problem
that the cup sidewall portion is thinned. Further,
since Patent Literatures 3 and 4 are also ones in
which a workpiece is formed into a cup-shaped
workpiece and then a cup shoulder portion is
thickened, there is a problem that fracture in the
cup shoulder portion and/or the cup sidewall portion
caused when the workpiece is drawn at a drawing ratio
of 2.1 or more cannot be suppressed.
[0044] As measures against such problems, in this
embodiment, at the time of drawing of the first cupshaped
workpiece B, deformation of the cup opening
e-nd R 2 1 is constrained by the axial pressing punch 13,
and thus thickening of the cup sidewall portion B2
can be promoted, and even when the drawing ratio is
set to be large, which is not less than 2.1 nor more
than 4.0, forming can be well performed. Further, at
the time of reduction in diameter, thickening of the
cup sidewall portion B2 can be promoted, so that
- 24 -
thinning of the cup sidewall portion B2 can also be
prevented. Further, in this embodiment, the cup
bottom portion Bl is compressed, and thereby the cup
bottom portion Bl can be shape-corrected to be flat,
and by the compression of the cup bottom portion Bl,
the cup shoulder portion B3 can be thickened. In
this embodiment, such respective effects can be
achieved simultaneously.
[004 5] (Third embodiment)
Fig. 13 is a flowchart used for explaining a
press-forming method of this embodiment, and Fig. 14
is a view used for explaining a step SA2 of drawing
the first cup-shaped workpiece B.
The press-forming apparatus in this embodiment
also first lowers the first and second-stage forming
punches 12 and 11 integrally, to thereby form the
disk-shaped workpiece A into the first cup-shaped
workpiece B, similarly to the first and second
embodiments (steps SAO and SA1).
[0046] On this occasion, the press-forming apparatus,
as referred in Fig. 14, in the step SA2 to be
described later, does not have to lower the first and
second-stage forming punches 12 and 11 down to the
position close to the second die shoulder portion 154
enough to be capable of guiding the cup sidewall
portion B2 to move downward by the first-stage
forming punch 12 at the portion extending from the
first die hole portion 153 to the second die shoulder
portion 154, and may also stop the lowering at an
- 25 -
appropriate position.
[0047] After the steps SAO and SAl, the pressforming
apparatus lowers the axial pressing punch 13
to abut on the cup opening end B21 of the cup
sidewall portion B2, and further lowers the axial
pressing punch 13 while constraining the cup opening
end B21. On this occasion, the press-forming
apparatus lowers the first and second-stage forming
punches 12 and 11 down to the portion extending from
the first die hole portion 153 to the second die
shoulder portion 154. Thereby, the press-forming
apparatus, as illustrated in Fig. 15, pushes the
first cup-shaped workpiece B into the second die hole
portion 155 through the second die shoulder portion
154, to thereby reduce the cup sidewall portion B2 in
diameter at the second die shoulder portion 154 to be
thickened (step SA2).
[0048] On this occasion, the press-forming apparatus
can suppress formed unevenness of the cup opening end
B21 because the axial pressing punch 13 presses the
cup opening end B21. incidentally, in this step SA2,
the press-forming apparatus stops lowering of the
axial pressing punch 13 at the position where the cup
opening end B21 side of the cup sidewall portion B2
is positioned between the first-stage forming punch
12 and the first die hole portion 153. This is
better because in the following step SA3 of
compressing the cup bottom potion Bl, the cup opening
end B21 side of the cup sidewall portion B2 can be
- 26
constrained also in the sheet thickness direction and
can be pressed more strongly. In this step SA2, the
cup bottom portion Bl is curved to lose flatness.
[004 9] Subsequently, the press-forming apparatus, as
illustrated in Fig. 16, stops lowering of the axial
pressing punch 13, and further lowers the secondstage
forming punch 11 and raises the counter punch
14 to bring the second-stage forming punch 11 and the
counter punch 14 close to each other. Then, the
press-forming apparatus, as illustrated in Fig. 17,
constrains the cup opening end B21 by the axial
pressing punch 13 and constrains the cup bottom
portion Bl side of the cup sidewall portion B2 by the
second-stage forming punch 11 and the second die hole
portion 155. Then, in such a constrained state, the
press-forming apparatus compresses the cup bottom
portion Bl in the second die hole portion 155 by the
second-stage forming punch 11 and the counter punch
14 .
[0050] Thereby, the press-forming apparatus, as
illustrated in Fig. 18, shape-corrects the cup bottom
portion Bl to be flat and thickens the cup bottom
portion Bl. Further, the press-forming apparatus
causes a redundant material derived from the cup
bottom portion Bl to flow into the cup shoulder
portion B3 to thicken the cup shoulder portion B3,
and forms the cup shoulder portion B3 into an
orthogonal shape so as to bulge outward in the radial
direction of the cup bottom portion Bl {step SA3).
- 27 -
Incidentally, in the second embodiment, the cup
bottom portion Bl in the state illustrated in Fig. 6
is compressed, to thereby thicken the cup shoulder
portion B3 as illustrated in Fig. 10. In. this
embodiment, the cup bottom portion Bl in the state
illustrated in Fig. 16 that is curved more largely
than in the state illustrated in Fig. 6 is compressed,
to thereby thicken the cup shoulder portion B3 as
illustrated in Fig. 18, so that it is possible to
obtain an effect of thickening the cup shoulder
portion B3 rather than the second embodiment.
[0 051] Subsequently, the press-forming apparatus, as
illustrated in Fig. 19, lowers the second-stage
forming punch 11 and the counter punch 14 while
compressing the cup bottom portion Bl, to thereby
complete drawing, and the second cup-shaped workpiece
C is obtained {step SA4 ) . In the step SA4, the
second cup-shaped workpiece C is pushed deeper until
the cup opening end C21 enters the second die hole
portion 155. Further, in the step SA4, without
lowering the axial pressing punch 13, the pressforming
apparatus performs drawing in a state of the
cup opening end B21 being released. In this case,
the press-forming apparatus may also lower the axial
pressing punch 13 down to the halfway position where
the cup sidewall portion B2 is drawn into the second
die hole portion 155, to thereby constrain the cup
opening end B21.
[0052] Further, in this step SA4, when the first
- 28 ~
cup-shaped workplace B is pushed into the second die
hole portion 155, the cup sidewall portion B2 is
drawn into a space between the second-stage forming
punch 11 and the second die hole portion 155, and
thereby a tensile load in an up and down direction is
applied. The orthogonal-shaped cup shoulder portion
B3 is pulled upward (see an up-arrow in Fig. 19), so
that as illustrated in Fig. 19, the cup shoulder
portion B"3 in a state of being thickened is formed
into an R shape while being in close contact with the
second punch shoulder portion 113.
[0 053] The outer surface of the cup shoulder portion
C3 is preferably formed into an orthogonal shape
depending on application. Thus, after the step SA4
where drawing is completed, the press-forming
apparatus, as illustrated in Fig. 20, raises the
second-stage forming punch 11 and the counter punch
14 while compressing a cup bottom portion Cl by the
second-stage forming punch 11 and the counter punch
14 and while constraining deformation of a cup
sidewall portion C2 on the cup bottom portion Cl side
in the sheet thickness direction by the second-stage
forming punch 11 and the second die hole portion 155.
[0054] The press-forming apparatus, as illustrated
in Fig. 21, causes the cup opening end C21 to butt
against the first-stage forming punch 12 and presses
the cup sidewall portion C2 downward, to thereby form
the cup shoulder portion B3 in close contact with the
second punch shoulder portion 113 into an orthogonal
- 29 -
shape (step SA5).
[0055] Note that in this embodiment, forming may
also be completed in the step SA4 of drawing. In the
case, in the step SA4, drawing may be finished at the
position where the cup opening end B21 is on the
second die shoulder portion 154, and the second cupshaped
workpiece C provided v/ith the expanded opening
portion C4 may also be formed (see Fig. 7 ).
[0056] (Modified examples)
In the first to third embodiments, the tools may
also be disposed in the direction opposite to each
other. That is, the counter punch 14 and the die 15
may also be disposed on the upper side and the first
and second-stage forming punches 12 and 11 and the
axial pressing punch 13 may also be disposed on the
lower side.
[0057] In the respective steps of the first to third
embodiments, when the operational advantage obtained
by movements of certain tools of this embodiment (for
example, the first and second-stage forming punches
12 and 11 and the axial pressing punch 13) can also
be obtained by movement of another tool (for example
the die 15} to work on the workpieces A to C in
cooperation with the certain tools, in place of the
movements of the certain tools of this embodiment,
the side of another tool to work in cooperation with
the certain tools (for example, the die 15 side) may
also be moved.
[0058] For example, in the first to third
30
embodiments, it is also possible that the pressforming
apparatus raises the die 15 at the time of
the first-stage drawing {steps SI and SA1) and moves
the first and second-stage forming punches 12 and 11
relatively to the die 15 to insert the first and
second-stage forming punches 12 and 11 into the
insertion hole portion 151, to thereby push the diskshaped
workpiece A into the insertion hole portion
151 and form the disk-shaped workpiece A into the
cup-shaped workpiece B.
[005 9] Further, it is also possible that at the time
of the second-stage drawing in the first and second
embodiments {steps S2 and S20), the press-forming
apparatus raises the first-stage forming punch 12,
raises the die 15 in a state of the first-stage
forming punch 12 being separated from the cup bottom
portion Bl, and moves the second-stage forming punch
11 relatively to the die 15 to insert the secondstage
forming punch 11 into the second hole portion
155, to thereby draw the first cup-shaped v/orkpiece B.
On this occasion, the press-forming apparatus raises
the axial pressing punch 13 in a manner to correspond
to the raise of the die 15, to thereby constrain the
cup opening end B21.
[0060] Further, it is also possible that at the time
of the second-stage drawing in the third embodiment
as well (step SA2), the press-forming apparatus, in a
state of the first and second-stage forming punches
12 and .11 being separated from the cup bottom portion
- 31 -
Bl and in a state of the axial pressing punch 13
being kept at the same position to constrain the cup
opening end B21, raises the die 15 and inserts the
first cup-shaped v/orkpiece B into the second hole
portion 155, to thereby draw the first cup-shaped
workpiece B.
[0061] In the first to third embodiments, it is also
possible that the distance D2 in the radial direction
betv/een the inner peripheral surface 1551 of the
second die hole portion 155 and the outer peripheral
surface 112 of the second-stage forming punch 11 is
made larger than the sheet thickness of the v/orkpiece
A and is made equal to or less than the sheet
thickness on the second die shoulder portion 154 that
is increased by the reduction in diameter at the time
of the second-stage drawing, and thereby the cup
sidewall portion C2 is thickened to have a thickness
of the distance D2.
INDUSTRIAL APPLICABILITY
[00 62] According to the present invention, it is
possible to provide a press-forming method capable of
suppressing fraction in a deformation concentrated
portion even at the time of forming with a large
drawing ratio, and to achieve and secure
superexcellent properties in automobile parts and the
like manufactured by this method,

CLAIMS
[Claim 1] A press-forming method for a plate-shaped
workpiece that uses a second-stage forming punch, a
first-stage forming punch disposed along an outer
periphery of the second-stage forming punch, an axial
pressing punch disposed along an outer periphery of
the first-stage forming punch, and a die including:,
from a leading end side where the first-stage and
second-stage forming punches are inserted, a first
die shoulder portion that expands outward as it goes
to the leading end; a first die hole portion parallel
to a central axis; a second die shoulder portion that
faces the first-stage forming punch and the axial
pressing punch in a central axis direction and
expands outward as it goes to the leading end; and a
second die hole portion connected to the second die
shoulder portion, central axes of all of which are
disposed coaxially, the method comprising:
a step Si of moving the first-stage and secondstage
forming punches relatively to the die and
inserting the first-stage and second-stage forming
punches into the first die hole portion, to thereby
push the workpiece into the first die hole portion
through the first die shoulder portion to form a
first cup-shaped workpiece having a cup bottom
portion and a circumferential cup sidewall portion
rising from a circumferential edge portion of the cup
bottom portion;
a step S2 of moving the axial pressing punch
- 33 -
relatively to the die to abut on a cup opening end of
the cup sidewall portion, and while constraining the
cup opening end, moving the second-stage forming
punch relatively to the die to insert the secondstage
forming punch into the second die hole portion
and pushing a part of the first cup-shaped workpiece
into the second die hole portion through the second
die shoulder portion, to thereby reduce the cup
sidewall portion in diameter and thicken the cup
sidewall portion; and
a step S3 of, in a state of the constraint of the
cup opening end by the axial pressing punch being
released, moving the second-stage forming punch
relatively to the die and further pushing the first
cup-shaped workpiece deeper in the second die hole
portion, to thereby form a second cup-shaped
workpiece smaller in diameter than the first cupshaped
workpiece.
[Claim 2] The press-forming method according to
claim 1, wherein
a counter punch disposed to face the second-stage
forming punch in the central axis direction is
further used and along an outer periphery of the
counter punch, the second die hole portion is
disposed,
the step S2 includes a step S21 of, while
constraining the cup opening end by the axial
pressing punch and while constraining deformation of
the cup sidewall portion on the cup bottom portion
- 34 -
side in a sheet thickness direction by the secondstage
forming punch and the second die hole portion,
bringing the counter punch close to the second-stage
forming punch to compress the cup bottom portion in
the second die hole portion by the counter punch and
the second-stage forming punch, to thereby form a cup
shoulder portion connecting the cup bottom portion
and the cup sidewall portion into an orthogonal shape
and cause a material of the cup bottom portion to
flow into the cup shoulder portion to thicken the cup
shoulder portion, and
in the step S3, while compressing the cup bottom
portion, the second-stage forming punch and the
counter punch are moved deeper in the second die hole
portion relatively to the die.
[Claim 3] A press-forming method for a plate-shaped
workpiece that uses a second-stage forming punch, a
first-stage forming punch disposed along an outer
periphery of the second-stage forming punch, an axial
pressing punch disposed along an outer periphery of
the first-stage forming punch, a counter punch
disposed to face the second-stage forming punch in a
central axis direction, and a die including:, from a
leading end side where the first-stage and secondstage
forming punches are inserted, a first die
shoulder portion that expands outward as it goes to
the leading end; a first die hole portion parallel to
a central axis; a second die shoulder portion that
faces the first-stage forming punch and the axial
- 35
pressing punch in the central axis direction and
expands outward as it goes to the leading end; and a
second die hole portion disposed along an outer
periphery of the counter punch, central axes of all
of which are disposed coaxially, the method
comprising:
a step SAl of moving the first-stage and secondstage
forming punches relatively to the die and
inserting the first-stage and second-stage forming
punches into the first die hole portion, to thereby
push the workpiece into the first die hole portion
through the first die shoulder portion to form a
first cup-shaped workpiece having a cup bottom
portion and a circumferential cup sidewall portion
rising from a circumferential edge portion of the cup
bottom portion;
a step SA2 of bringing the axial pressing punch
to abut on a cup opening end of the cup sidewa 1. .1
portion, and while constraining the cup opening end,
moving the axial pressing punch relatively to the die
and pushing a part of the first cup-shaped workpiece
into the second die hole portion through the second
die shoulder portion, to thereby reduce the cup
sidewall portion in diameter and thicken the cup
sidewall portion;
a step SA3 of, while constraining the cup opening
end by the axial pressing punch, bringing the secondstage
forming punch and the counter punch close to
each other, compressing the cup bottom portion in the
- 36 -
second die hole portion by the second-stage forming
punch and the counter punch to form the flat cup
bottom portion, and causing a material of the cup
bottom portion to flow into a cup shoulder portion
connecting the cup bottom portion and the cup
sidewall portion to thicken the cup shoulder portion;
and
a step SA4 of moving the second-stage forming
punch relatively to the die and further pushing the
first cup-shaped workpiece deeper in the second die
hole portion, to thereby form a second cup-shaped
workpiece smaller in diameter than the first cupshaped
workpiece.
[Claim 4] The press-forming method according to
claim 3, wherein
in the step SA4 , the second cup-shaped workpiece
is pushed into the second die hole portion until the
cup opening end is positioned in the second die hole
portion, the method further comprising:
a step SA5 of, while compressing the cup bottom
portion by the second-stage forming punch and the
counter punch and while constraining deformation of
the cup sidewall portion on the cup bottom portion
si.de in a sheet thickness direction by the secondstage
forming punch and the second die hole portion,
moving the second-stage forming punch and the counter
punch relatively in a direction to come close to the
first-stage forming punch to cause the cup opening
end to butt against the first-stage forming punch, to
- 37 -
thereby form the cup shoulder portion into an
orthogonal shape.
[Claim 5] The press-forming method according to any
one of claims 1 to 4, wherein
in the steps S3, SA4, the first cup-shaped
workpiece is pushed into the second die hole portion"
until the cup opening end is positioned on the second
die shoulder' portion, to thereby form the second cupshaped
workpiece provided with an expanded opening
portion that expands outward as it goes to the cup
opening end side.
[Claim 6] A press-formed product formed by the
press-forming method according to any one of claims 1
to 5.