The present invention relates to a forming die, and an undercut forming
method.
Priority is claimed on Japanese Patent Application No. 2014-097796 filed on
May 9,2014, the contents of which are incorporated herein by reference.
[Related Art]
[0002]
As methods of fornling a product having an undercut part, a method of forming
an undercut part through cutting in a post-process, and a method using a forming die
having a collapsible core or a sliding core as arc known. The collapsible core is
constituted of a plurality of cores disposed in a circu~nfcrentiadl irection, and a center
pin disposed at the center of the plurality of corcs. In the collapsible core, the diameter
of the respective cores is increased by pushing in the center pin, and tlie diameter of the
respective cores is reduced by pulling out the center pin.
[0003]
Additionally, forming dies having a sliding core are disclosed in Patent
Document 1 and Patent Document 2. In the forming die of Patent Document 1, by
alternately providing sliding surfaces with a small incli~iationa ngle and a large
inclination angle at a center core, alternately disposing split corcs having angles
corresponding to the respective sliding surfaces around the center core, and making the
split cores slide via inverted trapezoidal grooves provided in the respective sliding
surfaces, the diameters of undercut forming parts of the split cores are reduced.
[0004]
In tlie forming die of Patent Document 2, after first split cores and second split
cores are alternately disposed at an outer periphery of a center core, and the diameter of
the first split cores is reduced toward a central axis of the center core, the second split
cores arc moved in a direction that intersects an extraction direction and a
diameter-decreasing direction of the first split cores.
[Citation List]
[Patent Documents]
[0005]
[Patent Document 11 Japanese Unexamined Patent Application, First
Publication No. H5-57760
[Patent Docutnent 21 Japanese Unexanlined Patent Application, First
Publication No. 2013-237212
[Disclosure of the Invention]
[Problems to be Solved by the hlvention]
[0006]
However, in the method of forming an undercut part though cutting, cost is
increased due to an increase in the number of processes. Additionally, in the method
using the collapsible core, a driving inechanisnl of the collapsible core is complicated,
and substantial titne is required for assembly and adjustment. Therefore, cost
reduction is difficult.
[0007]
Additionally, it1 Patent Document 1, machining of the inverted trapezoidal
grooves having negative angles, and engaging projection parts that make a pair \vitlith
these grooves and that are provided in the split cores, is dificult, and die cost becomes
high. Additionally, in Patent Docutnent 2, additional components, such as support
members and holders for driving the split cores, are required, the number of cotnponents
of the die increases, and die cost becomes high.
[OOOS]
The invention has been tnade in view of the above circumstances, and an object
thereof is to provide a forming die and at1 undercut forming method that can form a
formed product having an undercut part at low cost.
[Means for Solving the Problem]
[0009]
In order to solve the above problems, the invention has adopted the following.
(1) A forming die related to a first aspect of the invention includes a lower
forming die having a bottom part and a side wall part; an upper forming die that is
movable toward the bottom part of the lower forming die along an axis parallel to the
side wall part of the lower forming die; and a push-in die that is movable toward the
bottotn part of the lower forming die along the axis between the side wdl part of the
lower forming die and the upper forming die. The npper fornling die includes a die
body that is provided to be movable toward the bottom part of the lower forming die
along the axis, in a state where a central axis coincides with the axis, a first split core
that abuts against a bottom surface of the die body and is provided to be movable in a
direction that extends radially with the axis as a center, a tilovable shaft mernber that is
provided to be lion-detachable down~vard fro111 the bottom surface of the die body and
be insertable into an inside of the die body from the bottotn surface of the die body
along tile axis, in a state wv11ere a ce~ltraal xis coincides with the axis, a second split corc
that is provided to be tllovable in a direction that extends radially fiom a lower end of
the ~novables haft rnetnber with the axis as a centel: The first and second split cores
alter~~atedlyis posed around the axis. The first and second split cores respectively have
forming surfaces that separate from the die body, as the first arid second split cores
move apa1-t from the axis in the extending direction. The first aud second split cores
are present illside an outer edge of the die body and the second split core is disposed
below the first split core, it1 a state where the movable shaft member is exposed 111ost
from the die body. ' The second split core approaches the bottotl~s urface of the die
body wvlde slidiug OII the first split core, in a process in whic11 the movable shaft
member is insetted into the inside of the die body, and thereby, the first and secot~dsp lit
cores respectively move to positions \vllere the forming surfaces of the first and second
split cores protrude outside of the outer edge of the die body.
(2) The aspect described in the above (1) may be configured as followvs.
The first split core fi~l-theirn cludes a pair of first inclined surfaces that are joined
together so as to narrow with an upper surface of the first split core as a center while
sandwiching the upper surface of the first split core therebetweell. The second split
core further includes a second inclined surface that is a surface mating with the first
split core and comes into contact with the first inclined surfaces of the first split core.
Portions of the first inclined sutfaces of the first split core overlap the second inclined
surface of the second split core, in a state where the movable shaft member is exposed
most from the die body. In a process in whichthe movable shaft member is inserted
into the inside of the die body, the first split core and the second split core move while
the first inclined surfaces of the first split core and the second inclined surface of the
second split core slide on each other until the first inclined surfaces of the first split core
and the second inclined surface of the second split corc are mated with each othee
(3) The aspect described in the above (1) or (2) may be configured as followvs.
The die body includes a first guide part that has a columt~ars hape and extends toward a
radial outer side. The movable shaft member includes a second guide past that has a
columnar shape and extends toward the radial outer side. The first split core fi~rther
includes a first housi~lgp ast that slides along tl~ex tending direction of the first guide
past with respect to the first guide past and houses the first guide past. The second split
core further includes a second housing past that slides along the extending direction of
tlle second guide part with respect to the second guide part and houses the second guide
past.
(4) In the aspect described in the above (3), the hardness of the first guide
part may be lower tliatl the liardness of the first split core, and the hardness of the
second guide part may be lower than the hardness of the second split core.
(5) 'Uie aspect described in any one of the above (1) to (4) may be configured
as follows. Thc first split core fi~rtheirn cludes a protrusion that is provided on an
upper surface of the first split core. The second split core fiuther includes a protrusiori
that is provided 011 an upper surface of the second split core. The die body further
includes an abutting surface that abuts against the protrusion of the first split core and
the protrusion of the second split core.
[OO 101
(6) An undercut forming method related to another aspect of the invention is
a method of forming an undercut part in a stock having an opening, using the forming
die according to any one of above (1) to (5). The method includes a first process in
which the stock is placed on the lolver forming die along the bottom part and the side
wall part; a second process in which the second split core is made to approach the
bottom surface of tile die body while being made to slide on the first split core at a
predetermined position within the opening of tlie stock, and the forming surfaces of the
first and second split cores are made to protrude outside of the outer edge of the die
body; a third process in which the push-in die is moved toward the bottom part of the
lower forming die wl~ileb eing made to abut against the stock and a portion of an inside
surface of the stock and is made to abut against the forming surfaces of the first and
second split cores; and a fourth process in which the upper forming die is moved ui a
direction away from the botton~p art of the lower forming die.
(7) In the above aspect (6), in the first process, the outside surface of the
stock may be made to abut against the side wall part of the lower forming die, and in the
third process, the push-in die may be moved toward the bottom part of the lower
forming die \v11ile being made to abut against an upper end surface of the stock.
[Effects of the Itlvention]
[OOll]
According to the above respective aspects of the invention, a formed product
having an undercut part can be formed by the fornling die with a simple structure.
Consequently, a formed product having an undercut part can be formed at low cost.
[Brief Description of the Drawings]
[0012]
FIG. 1A is a view showing a forming die related to a first emboditnerit of the
invention, and is a longitudinal sectional view showing a half on tlie left of an axis of
the forming die in a section including the axis.
FIG. 1 B is a view sliowing tlie fonnitig die, and is a longitudinal sectional view
slio\ving a state \vliere an upper fonning die is lo\vered to a bottom dead center.
FIG. 1C is a view showing the fortning die, and is a longitudinal sectional view
showing a state where a stock is pressed by a push-in die.
FIG. 1D is a view showing the fornling die, and is a longit~tdinasl ectional view
showing a state where the upper forming die is pulled out from a stock.
FIG. 1E is a view showing the forming die, and is a longitudinal sectional view
sliowing a state \vhere the push-in die is raised.
FIG. 2 is a perspective view showing a center core of the fonning die.
FIG. 3 is a perspective view showing a guide core, first split cores, and second
split cores of tlie forniing die.
FIG. 4 is a view sliowing the upper forming die of the forming die, and is a
perspective view showing a diameter-reduced state before forming.
FIG. 5 is a view sliowing the upper fonning die, and is a perspective view
showing a diameter-increased state when the upper forming die is lowered to the bottom
dead center.
FIG. 6 is a view for explaining the operation of each first split core and each
second split core of the upper forming die, and is a plan schematic view showing a
diameter-reduced state before forming.
FIG. 7 is a view for explaining the operation of each first split core and each
second split core of the upper fortning die, and a longitudinal sectional view as seen in a
section including the axis of the upper forming die.
FIG. 8 is a perspective view showing a rnodification example of the first split
cores and the second split cores of the upper fo~mingd ie.
FIG. 9A is a longitudinal sectional view showing a modification example of an
undercot forming method using the forming die related to the above first embodiment.
FIG. 9B is a longitudinal sectional view showing the continuation of the
forming method according to the modification example.
FIG. !OA is a view sho\ving a forming die related to a second enibodi~nenot f
the invention, and is a longitudinal sectional view showing a half on the left of an axis
of the forming die in a section including the axis.
FIG. 10B is a longitudinal sectional view showing the continuation of a
forming method using the forming die.
FIG. 10C is a longihrdinal sectional view showing the continuation of the
forming metliod using tlie fonning die.
FIG. 10D is a longituditial sectiotial view showing the continuation of tlie
forming method using the fomiing die.
FIG. 11A is a view showing a forming die related to a third embodiment of thc
invention, and is a longitudi~~saelc tional view showing a half on the left of an axis of
tlie forming die in a section including the axis.
FIG. 11B is a longitudinal sectional view showing the continuation of a
forming method using the forming die.
FIG. 11C is a longitudinal sectional view showing the continuation of tlie
forming method using the forming die.
FIG. I 1 D is a longitudinal sectional view showing the continuation of the
forming method using the forming die.
FIG. 12 is a longitudinal sectional view showing a modification example of the
forming die related to the above third embodiment.
FIG. 13 is a view showing a forming die related to a fourth embodiment of tlie
invention, and is a longitudinal sectional view showing a half on the left of an axis of
the forming die in a section including the axis.
FIG. 14 is a longitudinal sectional view showing a state where each first split
core and each second split core have moved toward a radial outer side before forming,
in the forming die related to the above third embodiment.
[Embodiments of the Itivention]
[0013]
Hereinafter, respective embodiments of the invention will be described in detail,
referring to tlie drawings. In addition, in the present specification and drawings,
constituent elements having substantially the same functional configurations will be
designated by the same reference signs, and thereby duplicate description thereof will
be omitted.
[00 141
(First etiibodiment)
First, a forming die 1 (undercut formitig die) related to a first embodiment of
the irivention will be described. FIGS. 1A to 1E are longitudinal sectional views
showing the forming die 1 related to the present embodiment, and are views for
explaining a method of forming an undercut part 86 in a stock 80. As shown in FIGS.
lAto lE, the forming die 1 is used when fonning the undercut part 86 in the
cup-shaped (bottomed cylindrical) stock 80 having a bottom wall part 84 and a vertical
wall pat? 82 fol-nied at an outer edge of the bottom wall part 84. Here, the undercut
part 86 Incans a portion of an iruier surlace (inside surface) of the vertical wall part 82
of the stock 80 that swvells toward a radial outer side of the stock 80, or a portion of the
ilulcr surface of the vertical wall part 82 of the stock 80 that protrudes toward tlic radial
outer side of the stock 80.
In addition, the inethod of forllling the undercut part 86 using the fornliag die 1
will be described below.
[OO 151
The material of the stock 80 is, for example, metal, such as iron, stainless steel,
aluminum, titanium, magnesiutn, or alloy steel. In addition, the materials of the stock
80 are not limited to only those enumerated above, but the materials just have to be
plastically deformable materials.
[0016]
The forming die 1 related to the present embodiment, as shown in FIG. IA,
includes an upper forming die 10, a lower forming die 60, and a push-in die 70. In
addition, the upper fanning die 10, tlie lower forming die 60, and the push-in die 70 are
iristalled in a pressing machine (not shown). Although the pressing niachine may be
an ordinary pressing machine, it is preferable that the pressing machine is a selvo type
pressing macl~inein which the bottotn dead center position of the die on a driving side
and the lowering speed of the die to a bottom dead center can be adjusted arbitrarily.
[00 171
The lower forming die 60 has a bottom part 61 that abuts against and suppol-ts
a bottom wall part 84 of the stock 80, and a side wall part 62 that abuts against and
supports tlie vertical wall part 82 of the stock 80 from the periphery thereof. Then,
when forming is performed, the stock 80 is placed within the lower forming die 60.
[OOI 81
As shown in FIGS. 1A and 3, the upper forming die 10 has a colu~nnacr enter
core 1 I (die body), a columnar guide corc 21 (movable shaft member) inserted into the
center core I1 so as to become coaxial with a central axis CL of the center core I I, thee
first split cores 31, and three second split cores 41. Tile center core 11 is attached to a
driving shaft of the pressing machine, and reciprocates linearly along the central axis
CL. The upper forming die 10 is inserted into a recessed part formed by the vertical
wall part 82 and the bottom wall part 84 of the stock 80 through an opening of the stock
kom above the stock 80.
In FIG. 1 A, reference sign CL represents a movelnent axis of the upper forming
die 10 that is tlie central axis and is parallel to the side \ d l part 62 of the lower forming
die 60. In addition, the above movement axis CL coincides with the central axis of the
center corc 11 and a central axis of the guide core 21.
[00 191
A stopper 23 is provided at an upper end of the guide core 21. Thc stopper 23
abuts against a stepped part 14 provided inside tlie center core 11, and prevents falling
of the guide core 21 resulting fiat11 its o~vnw eight. Tliat is, tlie guidc core 21 is
non-detachable dowvn\vard fron~th e center core 11 by the stopper 23.
[0020]
The push-in die 70 is movable along tlie movement axis CL, and an presses an
upper end surface 82a of the vettical wall part 82 of the stock 80 downward in a vertical
direction.
[002 11
FIG. 2 is a view showing the center core 11, and is a perspective view as seen
from a bottoii~s urface 1l b side. As showvn in FIG. 2, the center core 11 has battoin
surface 1 lb (lower end sarface) perpendicular to the central axis CL. The center of the
bottom surface 11 b of the center core 11 is provided with a cylindrical boss part 12
(cylindrical projection) that protrudes downward in the vertical direction of the center
core 11 fro111 the bottom surface 1 lb. A central axis of the boss part 12 coincides with
the central axis CL of the center core 11. The boss part 12 is provided with a circular
hole 13 that passes therethrough from a lower end surface of the boss part 12 along the
central axis ofthe boss part 12 toward the inside of the center core 11. A central axis
of the circular hole 13 also coincides with the central axis of the center core 11. The
circular hole 13 is used as an attachment hole 13 (insertion hole) for attaching the guide
core 21. Moreover, the botton~s urface I l b of the center core 11 is provided with six
groove parts 15 that extend from an outer peripheral surface of the boss patt 12 toward a
radial outer side of the center core 11 with the central axis as a center The groove
parts 15 are provided at intervals of 60" around the central axis. Also, an abutting
surface 16 is provided at one end part (an end part located on a radial outer side of the
center core 11) of each groove part 15.
[0022]
The boss pal? 12 has three guide pins 19 (first guide part) that radially extend
from an outer peripheral surface near a lower end of the boss part 12 toward the radial
outer side of the boss part 12 with the central axis as a center. The guide pins 19 are
provided at intervals of 120" around the central axis. In addition, three attachment
holes 17 are provided at intervals of 120" around the central axis on the outer peripheral
surface of the boss part 12, and the guide pins 19 (tlie first guide part) are each inserted
into the attachment holes 17.
The shape of the guide pins 19 is not limited to a colunu~ars hape, and, for
exanlple, a quadrangular prismatic shape, a triangular prismatic shape, or the like niay
be adopted. 111 addition, although \\till be described below, the first split cores 31 are
attached to the guide pins 19.
[0023]
The boss part 12 has thee ctdout parts 18 (recessed parts) that extend inward
(upward) in a longitudinal direction of the boss part 12 fiom the lower end surface of
the boss part 12. The cutout parts 18 are provided in three places (more specifically,
positio~lsth at deviate by 60" around the central axis from the guide pins 19) at intervals
of 120" around the central axis of the boss part 12.
In addition, when seen to face the bottom surface I lb of the center core 11,
regions where the cutout parts 18 and the groove parts 15 are continuously present in a
radial direction of the center core 11, and regions \vhere the guide pins 19 and the
groove parts 15 are present in an overlapping manner in the radial direction of the center
core 11, are alternately present at intet~also f 60" around the central axis.
[0024]
FIG. 3 is a perspective view showing the guide core 21, the three first split
cores 3 1, and the three second split cores 4 1. As shown in FIG. 3, the three first split
cores 31 and the three second split cores 41 are alternately disposed around the central
axis so as to surround the guide core 21. Additionally, the guide core 21 has three
guide pins 22 (second guide part) that radially extend from an outer peripheral surface
near a lower end of the guide core 21 toward the radial outer side of the guide core 21
with the central axis as a center. The guide pins 22 are provided at intervals of 120"
around the central axis.
[0025]
Each first split core 3 1 is provided so as to face the bottom surface 1 lb of the
center core 11, and has an upper surface 35 that abuts against the bottom surface 1 lb of
the center core 11, a pair of inclined surfaces 37 (first inclined surfaces) that are inclined
with respect to the central axis, a formit~gp ast 32 that abuts against an i~lnesru rface of
the vertical wall part 82 of the stock 80, and a protrusion 33 that is provided on the
upper surface 35. The pair of inclined surfaces 37 is both end surfaces in a
circumferential direction of each first split core 3 1, and is joined together so as to
narrow with the upper surface 35 as a center while sandwiching the upper surface 35
therebetween.
[0026]
The formit~gp art 32 of each first split core 3 1 is constituted of at1 inclined
surface 32a (forming surface) that is connected to the upper surface 35 and is inclined
with respect to the cet~traal xis, and a vertical plane 32b that is con~lectedt o the inclined
surface 32a and is perpendicular to the upper surface 35 (parallel to the central axis).
In addition, the inclined surface 32a is a surface that widens from the upper surface 35
toward a radial outer side, as seen in a plan view. In other words, the inclined surface
32a is an undercut forming surface that is separated from the center core 11 as the
inclined surface is apart fro111 the central axis in the radial direction (a direction that
extends radially with the central axis as a center).
[0027]
Additionally, an attaclunent hole 38 (first housing part) is provided in a surface
of each first split core 3 1 on a radial inner side. Also, each first split core 3 1 is
attached to the center core 11 by inse~tinge ach guide pin 19 (refer to FIG. 2) of the
center core 11 into each attachment hole 38 in a state where each protrusion 33 is
incorporated into each groove part 15 that overlap the guide pin 19 when the bottom
surface 1 lb of the center core 11 is seen in the plan view.
[0028]
Each second split core 41 is provided so as to face the bottom surface 1 lb of
the center core 11, and has an upper surface 45 that abuts against the bottom surface 1 lb
of the center core 11, a pair of inclined surfaces 47 (mating surfaces with each first split
core 3 1: second inclined surfaces) that are inclined with respect to the central axis, a
forming part 42 that abuts against the inner surface of the vertical wall part 82 of the
stock 80, and a protrusion 43 that is provided on the upper surface 45 (second abutting
surface). The pair of inclined surfaces 47 is both end surfaces in a circumferential
direction of each second split core 41, and is joined together so as to widen with the
upper surface 45 as a center while sandwiching the upper surface 45 therebetween.
[0029]
The forming part 42 of each second split core 41 is constituted of an inclined
surface 42a (forming surface) that is connected to the upper surface 45 and is inclined
with respect to the central axis, and a vettical plane 42b that is connected to the inclined
surface 42a and is perpendicular to the upper surface 45 (parallel to the central axis).
In addition, the inclined surface 42a is a surface that widens from the upper surface 45
toward the radial outer side, as seen in a plan view. In other words, the inclined
surface 42a is an undercut forming surlace that is separated from the center core 11 as
the inclined surface is apart from the central axis in the radial direction (the direction
that extends radially with the central axis as a center).
[0030]
Additionally, an attachtnent l~ole4 8 (second housing part) is provided in a
surface of each second split core 41 on the radial inner side. Also, each second split
core 41 is attached to the guide core 21 by insertiug each guide pi11 22 of the guide core
21 into each attachment hole 48 in a state where each protlusion 43 is ir~corporatcdi nto
each groove part 15 that is contiuuous with each cutout part 18 wllcn the bottolll surface
11 b of the center core 11 is seen in plan view.
[003 11
Here, the three first split cores 3 1 and tlie thee second split cores 41 are
obtained, for example, by splitting an annular forming core into six pieces in the
circumferential direction.
[0032]
FIG. 4 is a perspective view showing the upper forming die 10, and is a view
showing a state before the start of fornling. As described above, the first split cores 3 1
are attached to the center core 11, and the second split cores 41 are attached to the guide
core 21. As shown in FIG. 4, the guide core 21 is tnovably attached to the attachment
hole 13 (refer to FIG. 2) of the center core 11 such that each guide pin 22 of the guide
core 21 is located a position that deviates by 60" around the central axis fro111 each
guide pin 19 of the center core 11, and is niovable along tile central axis. In addition,
when the guide core 21 is attached to the center core 11, the stopper 23 just has to be
fixed to an upper end of the guide core 21 afier the guide core 21 in a state wvhere there
is no stopper 23 is inserted from below the center core 11.
[0033]
In a state where the guide core 21 is attached to the center core 11, the stopper
23 abuts against the stepped part 14 formed in the center core 11 (refer to the FIG. 1 A),
so that the guide core 21 can be prevented from falling out from the attachment hole 13
of the center core 11 due to its own weight. In this case, the guide core 21 is brought
into a state where tlie guide core is exposed most from the center core 11. In addition,
the guide core 21 is located at a position apart by a predetermined distance in the
direction of the central axis from the center core 11, and a distance between each first
split core 3 1 and each second split core 41 (a distance between the upper surface 35 of
each first split core 3 1 and the upper surface 45 of each second split core 41) becomes H.
That is, each guide pi11 22 of the guide core 21 is disposed so as to be separated by the
distance H downward in the direction of the central axis from each guide pin 19 of the
center core 11.
[0034]
Additionally, as shown in FIG. 4, in a state before the start of fornling (a state
where the guide core 21 is exposed most from the center core 1 I), as seen from the axis
of the central axis, the first split cores 31 and the second split cores 41 are alternately
disposed around the central axis such that a poi-tion of the bottoni surface 36 of cach
first split core 3 1 overlaps the bottonl surface 46 of each second split core 4 1. In
addition, in the present specification, a state \vhere a portion of the bottoin surface 36 of
each first split core 3 1 overlaps the bottom surface 46 of each second split core 41 is
referred to as a "diameter-reduced state". That is, in the diameter-reduced state,
portions of the inclined surfaces 37 of each first split core 31 overlap the inclined
surfaces 47 of each second split core 41. Additionally, in the dianleter-reduced state,
as seen from tlie axis of the central axis, the tlxee first split cores 3 1 and the tlxee
second split cores 41 are covered with the center core 11 (are present inside an outel
edge of the center core 11).
[0035]
Since each guide pin 19 of the center core 11 is inserted into the attachment
hole 38 of each flst split core 31, each first split core 31 slides along each guide pin 19
(in the radial direction). Also, the distance of the forming part 32 of each first split
core 3 1 from the vertical plane 32b to the central axis of the center core 11 is smaller
than the radius of the bottom surface l l b of the center core 11 ill the diameter-reduced
state.
[0036]
Since each guide piti 22 of the guide core 21 is inserted into the attachment
hole 48 of each second split core 41, each second split core 41 slides alotig the guide pin
22. Also, the distance of the forming part 42 of each second split core 41 from the
vertical plane 42b to the central axis is smaller than the radius of the bottom surface 1 lb
of tlie center core 11 in the diameter-reduced state.
[0037]
Next, the method of forming the undercut part 86 in tlie stock 80 using the
forming die 1 related to the present embodiment will be described. First, as shown in
FIG. 1 A, the stock 80 is placed within the lower forming die 60 such that an outer
surface of the cup-like stock 80 comes into contact with an inner surface of tlie lower
forining die 60. In a state where the stock 80 is placed within the lower forming die 60,
the bottom wall part 84 of the stock 80 abuts against the bottoin part 61 of the lower
forniing die 60, and the vertical wall part 82 of the stock 80 abuts against the side wall
part 62 of the lower forniing die 60.
[0038]
Subsequently, the upper forming die 10 is inserted into the stock 80. In this
case, the guide core 21 is brought into a state where the guide core is exposed most
froni the centcr core 11, and the first split cores 3 1 and the second split cores 41 are in
the diameter-reduced state where these split cores do not protrude ft~rthetro the radial
outer side than the bottom surface 11 b of the center core 11. That is, as see11 from the
axis of the cel~traal xis, the first split cores 3 1 and the second split cores 41 are bro~~ght
into a state where these split cores are covered with the bottom surface 1 lb of the center
core 11.
[0039]
Additionally, as shown in FIG. lA, a predetem~ined gap is provided between
the outer peripheral surface 1 la of the center core 11 and the inner surface of the
vertical wall past 82 of the stock 80. Also, the push-in die 70 is disposed above the
stock 80 between the lower forniing die 60 and the upper forming die 10 so as to touch
the inner surface of the lower forming die 60 and the outer peripheral surface lla of the
center core 11.
[0040]
Next, as showvll in FIG. lB, the center core 11 is lowered along the central axis,
and the bottom surface 46 of each second split core 41 is brought into contact with the
bottom wall part 84 of the stock 80. By bringing the bottonl surface 46 of each second
split core 41 into contact with the bottom wall part 84 of the stock 80, the guide core 21
is pushed up and the stopper 23 in contact with the stepped part 14 of the center core 11
is detached from the center core 11. Therefore, the center core 11 is loxvered relative
to the guide core 21 by further lowering the center core 11.
[0041]
That is, in a state shown in FIG. lA, each first split core 31 is at a positioti high
by the distance H than each second split core 41, and as the center core 11 is lowered,
the distance H becomes gradually small. Then, as the inclined surfaces 37 of each first
split core 3 1 and the inclined surfaces 47 of each second split core 4 1 adjacent to each
other in the circumferetitial direction come in contact with each other, each first split
core 3 1 moves along each guide pin 19 of the center core 11, and each second split core
41 moves along the guide pin 22 of the guide core 21. That is, each first split core 31
is pressed against each second split core 41 due to the lowering of the center core 11,
the second split core 41 moves toward the radial outer side, and the first split core 3 1
tnoves toward the radial outer side due to a reactior~f orce received from the second split
core 41.
[0042]
As a result, as show11 in FIG. 5, each first split core 3 1 and each second split
core 41 tnoves toward the radial outer side, respectively, and the upper surface 35 of the
first split core 3 1 and the upper surface 45 of the second split core 41 coincide with each
other in a case where the botto~isl urface 36 of tlie lirst split core 31 and the bottorn
surface 46 of the second split core 41 are seen alo~igth e central axis. In other words,
tlie inclined surfaces 37 of tlic first split core 3 1 and the inclined surfaces 47 of the
second split core 41 adjacent to each other in the circu~nferentiadl irection are brought
into a state where these inclined surfaces are joined together. In addition, in the
present embodiment, the state as shown in FIG. 5 where the inclined surfaces 37 of the
first split core 31 and the inclined surfaces 47 of the second split core 41 adjacetlt to
each other in the circumferential direction are joined together is referred to as
"dianieter-increased state". In the diameter-increased state, the forming part 32 of each
first split core 3 1 and the forming part 42 of each second split core 41 protrude from the
outer peripheral surface 1 la of the center core 11 in a plan view.
[0043]
In addition, as shown in FIG. 5, cutout parts 34 and 44 are respectively
provided in each first split core 31 and each second split core 41. Therefore, when the
first split cores 31 and the second split cores 41 move in the radial direction, the first
split cores 3 1 and the second split cores 41 can be prevented from interfering with each
other.
[0044]
Additionally, as shown in FIG. 5, in the diameter-increased state, the forming
part 32 of each first split core 3 1 and the forming part 42 of each second split core 41
are smoothly cotitinuous, and the three first split cores 3 1 and the three second split
cores 41 fonns one disk shape. From above, the preparation for forming the undercut
part 86 in the stock 80 is completed.
[0045]
In addition, in the diameter-increased state, each first split core 3 1 is positioned
with respect to the center core I I by the side surface 33a (radial outside surface) of tlie
prot~usion3 3 of the first split core 3 1 abutting against the abutting surface 16 of each
groove part 15 of the center core 11 and the upper surface 35 of the first split core 31
abutting against the bottom surface 1 lb of the center core 11, (refer to FIGS. 2 and 3).
Additionally, each second split core 41 is positioned with respect to the center core 11
by the side surface 43a of tlie protrusion 43 of the second split core 41 abutting against
the abutting surface 16 of the groove part 15 of the center core 11 and the upper surface
45 of the second split core 41 abutting against the bottom surface 11 b of the center core
11.
[0046]
Next, as shown in FIG. 1C, thc push-in die 70 is lowered to press the upper end
surface 82a of tlic vertical wall part 82 of the stock 80. In this case, since tlie vertical
wall part 82 of tlie stock 80 is constrained by the side wall part 62 of the lower ihr~ning
die 60, a portion of tlic vertical wall part 82 of the stock 80 is increased in thickness by
pressing the upper end surface 82a of the vertical wall part 82 of the stock 80. As a
result, the undercut part 86 can be fornied in the stock 80.
[0047]
Subsequently, as sliown in FIG. ID, in order to extract tlie upper for~ningd ie 10
ftom a stock 80, the center core 11 is raised along the central axis. Similarly, since the
inclined surface 32a of the forming part 32 colnes into contact with the undercut part 86
of the stock 80, each first split core 3 1 is pushed to tlie radial inner side. In this case,
since the inclined surface 42a of tlie forming part 42 colnes into contact with the
undercut part 86 of the stock 80, each second split core 41 is pushed to the radial inner
side.
[0048]
When the center core 11 is raised, tlie stopper 23 of the guide core 21 is
separated by the distance H from the stepped part 14 of the center core 11 to the upper
side of tlie central axis (refer to FIG. 1C). Therefore, if the center core I1 is raised
along the central axis, each second split core 41 is separated fiom the center core 11
along the central axis. Consequently, when forces facing the radial inner side have
acted on each first split core 31 and each second split core 41, any interference between
the first split core 3 1 and the second split core 41 can be avoided. Therefore, the first
split core 3 1 and the second split core 441 can each be moved toward the radial i~uiers ide,
and the upper forming die 10 can be extracted froni tlie stock 80.
[0049]
Finally, as showti in FIG. IE, the stock 80 can be taken out fiom the lower
forming die 60 by raising the push-in die 70.
[OOSO]
As described above, the diameter-increasing operation and the
diameter-reducing operation of the first split cores 3 1 are performed by tlie attachment
holes 38 of tlie first split cores 3 1 and the guide pins 19 of the center core 1 I.
Therefore, by tlic diameter-increasing operation and the diameter-reducing operation of
tlie first split cores 3 1, the side surface 33a of the protri~sion3 3 of each first split core
31, the upper surface 35 of the first split core 3 1, the abutting surface 16 of the center
core 11, and the bottoni surface I lb of the center core 11 are not worn out, and a decline
in positioning accuracy can be prevented.
[0051]
Similarly, the diameter-increasitig operation and the diameter-reducing
operation of the second split cores 41 are performed by the guide holes 48 of the second
split cores 41 and thc guide pins 22 of the guide core 21. Therefore, by tlie
diameter-increasing operation and the diameter-reducing operation of the second split
cores 41, the side surface 43a of the protrusion 43 of each second split core 41, the
upper surface 45 of tlie second split core 41, the abutti~igs urface 16 of the center core
11, and the bottom surface 1 lb of the center core 11 are not w70r1i out, and a decline in
positioning accuracy can be prevented.
[0052]
Next, respective parameters of each first split core 31 and each second split
core 41 will be described with reference to FIGS. 6 and 7. FIG. 6 is a plan sche~natic
view showing each first split core 3 1 and each second split core 41 as seen from the
direction of the central axis in the diameter-reduced state. In addition, in FIG. 6, a
region where tlie first split core 3 1 overlaps the second split core 41 is shown by
hatching.
[0053]
The radius of the first split core 3 1 atid the second split core 41 in tlie
diameter-increased state is defined as RL, the radius of the first split core 31 and the
second split core 41 in the diameter-reduced state is defined as Rs, the radial movable
distance of the first split core 3 1 and the seco~idsp lit core 41 is defined as AR, the total
core nuniber (the number of times of core splitting) of the first split core 31 and the
second split core 41 is defined as N, the core angle of the first split core 31 and the
second split core 41 is defined as 26, [rad], and the radius of the center core 11 is
defined as c In this case, the core angle 26, becomes 8, = dN. Jf tlie condition (Rs I
r) for pulling out the forming part 32 of the first split core 31 and the forming part 42 of
the second split core 41 from tlie stock 80 in which the undercut part 86 is formed are
taken into consideration, a radial movable distance AR of the first split core 3 1 and the
second split core 41 is expressed by tlie following Forniula (1) from a geometric shape.
[0054]
[For~nula1 1
AR=RL cos 0,- r sin Carccos f(RL / r ) sinfl.)] (1)
[0055]
Additionally, if an angle formed between tlie bottom surface 36 and each
inclined surface 37 of tlie first split core 3 1 is defined as 01 [rad], and an angle forn~ed
between the bottom surface 46 and each i~iclineds urface 47 of the seeorid split core 41
is defined as 02 [rad] (refer to FIG. 3), there is a relationship of 81 = n - 82. Also, if the
amount of overlap between the first split core 31 and the second split core 41 in the
dialneter-reduced state shown in FIG. 6 is defined as OL, 01, is expressed by the
following Formula (2).
[0056]
[Fol.niula 21
[0057]
If a required minimum distance of the movement distance of the guide core 21
along the central axis is defined as AH, AH is expressed by the following Formula (3).
[0058]
[Fornlula 31
[0059]
AH is expressed by the following Formula (4) by substituting the above
Formulas (1) and (2) in the above Formula (3).
[0060]
[Fonnula 41
AH= 2 X I R c~os 0,- r sin farccos I(Rl. / r ) sin0,jl'l sin O , ( 4 )
[0061]
FIG. 7 is a front schematic view showing each first split core 31 and each
second split core 41. In addition, a right view of FIG. 7 sliows an A-A sectional view
of FIG. 4, and a left view of FIG. 7 shows a B-B sectional view of FIG. 5. If an angle
between the inclined surface 32a of the forming pat-t 32 of the first split core 3 1 and the
bottom surface 36 of the first split core 31 and an angle between the inclined snrface
42a of the forming pal; 42 of the second split core 41 and the bottom surface 46 of the
second split core 41 are defined as O3 [rad], the distance H in the direction of the
central axis between the first split core 3 41 and the second split core 441 is expressed by
the following Formula (5).
[0062]
[Formula 51
[0063]
The required minimum distance AH is expressed by the following Fom~nla( 6)
fsorn the above Formtrla (3) and (5).
[0064]
[Fornn~la6 1
[0065]
93 is expressed by the following For~nula( 7) by substituting the above Forrnula
(3) in the above Formula (6).
[0066]
[Fornnila 71
0 ,Zarctan 1 2 sin (I, . tan ( 0 3) (7)
[0067]
According to the above Formulas (1) to (7), the respective paraineters when
forming the undercut part 86 in the stock 80 can be determined. In the present
embodiment, a case \vhere the number N of times of core splitting is 6. Ho\vever, the
number of N just has to be four or more. In addition, it is preferable that the number N
of times of core splitting is 6 because tlie number of colnponents is small. Additionally,
in order to prevent forces acting on forming components fiom coucentrating in one
direction, it is preferable that the angle 81 of the first split core 3 1 is 2n13 _< 91 55~16,
and it is preferable that the angle 9, of the first split core 3 1 and the second split core 41
is n16 5 03 5 n13.
[0068]
Additionally, in the present enibodiment, the materials of the first split core 31
and the second split core 41 are SKDll, and the materials of eacli guide pin 19 of the
center core I1 and eacli guide pin 22 of the guide core 21 are S45C. In this way, if
material selectioii is performed such that the hardness of the guide pin 19 of t!~e center
core 11 and the guide pin 22 of the guide core 21 become lower than the hardness of tlie
first split core 3 1 and the second split core 41, the guide pins 19 and 22 with lower
hardness is first \vorn out. Therefore, when maintenance against wear factors is
performed, the replace~ne~firte quency of tlie guide pins 19 and 22 can be enhanced, arid
the replacenlent fsequency of tlie relatively expensive first split core 3 1 arid second split
core 41 can be suppressed. Consequently, an increase in die cost resulting from wear
factors call be suppressed.
[0069]
According to the present embodiment described above, each first split core 3 1
and eacli second split core 41 are disposed so as to overlap each other in the
diameter-reduced state, and the center core 11 presses the inclined surfaces 37 of the
first split core 31 against the inclined surfaces 47 of the second split core 41, tlie first
split core 3 1 and the second split core 41 move toward the radial outer side while
sliding on eacli other.
Additionally, since tlie forming part 32 of the first split core 3 1 has the inclined
surface 32a and the forming part 42 of the second split core 41 has the inclined surface
42a, the first split core 3 1 and the second split core 41 move to the radial inner side
when pulling out the upper forming die 10 along the axis of the central axis from the
stock 80.
Consequently, since a sliding mechanism of the die that fornis an undercut can
be made simple, the undercut part 86 can be fornied in the stock 80 at low cost.
[0070]
Here, in the related art, in a case where a thick fornied product having an
undercut part is formed, the thick formed product having the undercut part is formed
from a thick stock by cutting work. In contrast, in the present embodiment, the
undercut part 86 can be formed in the stock 80, and the thickness of the stock 80 can be
increased. Therefore, for example, a thick formed product having an undercut part can
be formed from a thin stock. Consequently, since a thick formed product having an
undercut part can be formed by press working, cost reduction can be achieved.
[0071]

In the present embodiment, a case where the annular forming core is split into
the first split cores and the second split cores is shown. However, a forming core
having a polygonal shape in a plan view may be split into the first split cores and the
second split cores. For example, as shown in FIG. 8, a forming core having a
hexagonal shape in a plan view nlay be split into tlie three first splii cores atid the three
second split cores. In this way, in a case where the forming core liaving a polygonal
shape is split, the nuniber of vertices of the polygon needs to be even. In addition, in a
case where the number of vertices of a polygonal shape is equal to a riulnber obtained
by totaling the number of the first split cores 3 1 and the secotid split cores 41, in order
lo tilake the radial niovable distance AR of eacli first split core 3 1 and the second split
core 41, it is preferable to dispose the axial center of each guide pin 22 on a surface
formed by the celitral axis CL of the center core 11 and the vertices of the polygonal
shape.
[0072]
Additionally, it1 the present embodiment, a case where the undercut part 86 is
formed as the push-in die 70 presses the upper end surface 82a of the stock 80 to
increase the thickness of the stock 80. 14owever, as shown in FIGS. 9A and 9B, the
vertical wall part 82 of the stock 80 may have a shape along the fornling part 32 of each
first split core 3 1 and tlie forming part 42 of each second split core 41 by forming a
stepped part 82b in advance in the vertical wall part 82 of tlie stock 80, and pushing in
the push-in die 70 between the vertical wall part 82, and the side wall part 62 of the
lower forming die 60 having tlie inclined surlace at the tip thereof. Eveti in this case,
the undercut part 86 can be formed in the stock 80.
[0073]
(Second embodiment)
Next, a formir~gd ie 200 related to a second embodiment of the invention will
be described. In addition, the same constituent elements as the above-described
constituent element will be designated by the same reference signs, and thereby, the
duplicate description thereof will be omitted below.
[0074]
FIGS. IOA to 10D are longitudinal sectional views showing the fanning die
200 related to the present embodiment. As shown in FIG. IOA, the fanning die 200 is
different from the forming die 1 related to the above first embodiment in that a
columnar punch part 227 is provided at the lower end of the guide core 21 and a stepped
part 263 is provided at a lower end of the side wall part 62 of the lower forming die 260.
Additionally, in the above first embodiment, a case where the undercut part 86
is formed in the stock 80 in which hole is not provided in the bottom wall pai-t 84. In
contrast, the forming die 200 related to the present embodiment is used when for~iling
the undercut part 86 and a boss part 285 it1 a stock 280 having a bottom wall part 284 in
which the circular hole is provided (refer to FIG. 10D).
[0075]
A method of forming the undercut part 86 and the boss part 285 in the stock
280 will be described with reference to FIGS. 10A to IOD. First, as shown in FIG.
10A, the stock 280 is placed on the lower forriling die 260 such that the bottom wall
part 284 of the stock 280 abuts against the stepped part 263 of the lower fanning die
260. Thereafter, the upper forming die 210 is inserted into the stock 280, and the
punch pai-t 227 is made to abut against the bottom wall part 284 of the stock 280.
[0076]
Subscquentll: as shown in FIG. 10B, the center core 11 is lowered. In this
case, since the bottom surface 46 of each second split core 41 abuts against an upper
surface 227a of the punch part 227, the movement of the second split core 41 in the
direction of the central axis is restricted. Therefore, each first split core 3 1 is pressed
against each second split core 41 by lowering the center core 11. Accordingly, the first
split cores 31 and the second split cores 41 begin to increase in diameter toward the
radial outer side. Then, if tlie first split cores 3 1 and the second split cores 41 reach
diameter-increased state, the pressing force of the center core 11 is transmitted to the
punch part 227 via the first split cores 3 1 and the second split cores 41.
[0077]
Subsequently, if the center core 11 is further pushed in from tlie state sho\vn in
FIG. 10B, as shown in FIG. 10C, the bottom wall part 284 of the stock 280 is formed for
hole expansion by the punch part 227, and the boss part 285 is formed. Thereafter, by
lowering the push-in die 70 to press the upper end surface 82a of the stock 280 similar
to the first embodiment, as shown in FIG. IOD, the undercut part 86 is formed in the
stock 280. In addition, since the processes after this are the same as those of the first
embodiment, a description thereof will be omitted.
[0078]
The undercut part 86 and the boss part 285 can be formed in the stock 280 by
the above-described forming method. 111 addition, a disk having a circr~larh ole can
also be used instead of the stock 280. In this case, the above disk is subjected to
cupping draw in a cup by the punch part 227, the bottom surface 36 of each first split
core 31, the bottom surface 46 of each second split core 41, and the lower forming die
260, and is formed in the state of FIG. 10C.
[0079]
(Third Embodiment)
Next, a forming die 300 related to a third embodiment of the invention will be
described. In addition, the same constituent elements as the above-described
constituent element will be designated by the same reference signs, and therebj: a
duplicate description thereof will be omitted below.
[0080]
FIGS. 11A to 1 ID are longitudinal sectional views showing the forming die
300 related to the present embodiment. As show11 in FIG. 11 A, in the forming die 300,
an upper forming die 310 has first split cores 33 1 each having a curved surface-shaped
(convex surface) forming part 332, second split cores 341 each having curved
surface-shaped (convex surface) forming part 342, and a hemispherical punch part 327
provided at tlie lower end of the guide core 21. Additionally in the forming die 300, a
curved part 364 (concave surface) is ptovided in the lower forming die 360.
[0081]
In the above first embodiment, a case where the undercut part 86 is forlned by
increasing the thickness of the vertical wall part 82 of the cup-like stock 80 is showti.
However, in the present etnbodinient, the undercut part 386 is formed by tlie first split
cores 331 and the second split cores 341 pressing an inlier surface of tlie stock 380, and
a reduction in the thicktiess of the ondercut part 386 is suppressed by pushing in the
upper end surface 82a of the vertical wall part 82 of tlie stock 380 with the push-in die
70.
[0082]
A method of forming tlie nndercut part 386 in the stock 380 will be described
with reference to FIGS. 11A to 1 ID. First, as shown in FIG. 11A, the stock 380 is set
within the lower forming die 360 it1 which the curved part 364 recessed in a direction
orthogo~iatlo the central axis is for~ned. In addition, in the stock 380, in order to
press-form a spherical overhang shape, the bottom wall part 384 of the stock 380 is
preformed in a hemisplierical shape. Then, if the upper forming die 3 10 is lowered,
the punch part 327 abuts against the bottom wall part 384 of the stock 380.
[0083]
FIG. 11B is a view slio\ving a state where the center core 11 is lowered to the
bottom dead center from the state shown in FIG. 11A. As shown in FIG. 1 lB, if the
center core 11 reaches the bottoni dead center, the first split cores 331 and the second
split cores 341 are brought into the diameter-increased state. By bringing the first split
cores 331 atid the second split cores 341 into the diameter-increased state, a portion of
the vertical wall part 82 of the stock 380 is pushed into the curved part 364 of the lower
forming die 360 and curved.
[0084]
Moreover, by lowering the push-in die 70 to push in the upper end surface 82a
of the vertical wall part 82 of the stock 380 in conjunction with the lowering of the
center core 11 and the diameter-increasing operation of the first split cores 33 1 and the
second split cores 341, the undercut past 386 is formed while making the material of the
ve1-tical wall part 82 of the stock 380 flow to the cunled part of the stock 380. Tlien,
by controlling the atnount of push-in of the upper end surface 82a of the vertical wall
part 82 of tlie stock 380, a reduction in the plate thickness of the undercut part 386 can
be suppressed.
[OOSS]
Subscquentl): as shown in FIG. 1 lC, the push-in die 70 is raised along the
central axis, and the center core 11 is raised. In this case, since the diameter of the first
split cores 331 and the second split cores 341 is reduced wit11 the ascent of the center
core 11, the upper forming die 310 can be pulled out from the stock 380 after the
forming. Additionally, as shown in FIG. 11D, the lower forming die 360 is split into
two by a plane passing along the central axis. Thus, the stock 380 can be taken out by
moving the lower forming die 360 toward the radial outer side using a radial moving
mechanism (not sho\nl). According to the present embodiment, a formed product
having a spherical overhang shape at the bottom of the cup and having a uniform
thickness can be obtained.
[0086]
In tlie present embodiment, a case where the lower forming die 360 has a split
structure in order to take out the stock 380 after the forming is shown. Howevel; as
showvn in FIG. 12, the lower forming die 360 may be split by a plane that is
perpendicular to the central axis and passes through the curved part 364. That is, the
lower forming die 360 may be constituted of a first split lower forming die 360a and a
second split lower forming die 360b. In this case, at the time of the take-out of the
stock 380 after the forming, the moving mechanism that moves the lower forming die
360 in the radial direction is unnecessary, and the stock 380 after the forming can be
taken out simply by moving the center core 11, the push-in die 70, and the first split
lower forming die 360a along the central axis.
[0087]
(Fout-th Embodiment)
Next, a forming die 400 related to a fourth embodiment of the invention will be
described. In addition, the same constituent elements as the above-described
constituent element \ d l be designated by the same reference signs, and thereby, the
duplicate description thereof will be omitted below.
[0088]
FIG. 13 is a longitudinal sectioilal view sho\ving the forming die 400 related to
the present embodiment. As shown in FIG. 13, the forming die 400 different from the
forming die 300 related to the third embodiment in that an upper forn~itigd ie 410 has a
split core driving ~nechanisrn4 5 1.
[0089]
In the third embodiment, the diameter of the first split cores 331 and the second
split cores 341 are reduced by the contact of the stock 380 with the undercut part 386
(the same applies to the first and second embodiments). how eve^., in the present
etitbodiment, the diameter-reducing operation of the first split cores 33 1 and the sccond
split cores 341 is performed by using the split core drivi~igm echanism 45 1.
[0090]
At the time of application to mass production, it is necessary to increase the
operating speed of the center core 11. For example, in the forming die 300 related to
the third embodimeut, as sho\vn in FIG. 14, the diameter-increased state may be brought
out due to a counteraction against the lowering of the center core 11 belore the first split
cores 331 and the secoud split cores 341 are inserted into the stock 380. 111 this case,
the first split cores 331 and the second split cores 341 come into contact with the upper
end surface 82a of tlie vertical wall part 82 of the stock 380, xvhich causes an abnormal
stop of a press apparatus. Additionally, in products in wl~ichth e surface precision of
the undercut part 386 of the stock 380 has an influence on performance, the contact
between the first split cores 33 1 and the second split cores 341 at the time of diameter
reduction is not preferable.
[0091]
Thus, the diameter-reduced state can be maintained in an unloaded state by
using the split core driving mechanism 451 shown in FIG. 13. As the split core driving
mechanism 451, for example, a coil spring, a solenoid, or the like can be used.
Additionally, in forming large-sized components, a hydraulic mechanism may be used.
[0092]
Although the respective embodiments of the invention have been described
above, these embodiments are presented as examples, and the scope of tlie invention are
not limited only to these embodiments. These embodiments can be carried out in other
various forms, and various omissions, substitutions, and alteniations can be perfor~ned
without departing fsoni the concept of the invention. These etnbodin~entsa nd their
modifications are embraced in the scope of the invention and its equivalent as defined in
the claims, similar to being embraced in the scope and concept of the invention.
[0093]
For example, in the above first embodiment, the lower forming die 60 is fixed,
and the stock 80 is fornled in a predetermined shape by moving the center core 11 and
the push-in die 70. However, the center core 11 and the push-in die 70 may be fixed,
and the lower forming die 60 may be raised. Additionally, tlie stock 80 may be formed
in a predetermined shape by independently driving all of the center core 11, the push-in
die 70, and the lo\ver forming die 60.
[0094]
Additionall): for example, in the above respective emboditnents, the tnethod of
forlning the undercut part in the cup-like stock is shown. IIowever, an nndercut part
may bc formed in an inner surface of a hollow pipe, using the fom~ingd ie related to the
ia\~eation.
[Industrial Applicability]
[0095]
According to the invention, the forming die and the undercut fornling method
that can fom~a formed product having an undercut part at low cost can be provided.
[Brief Description of the Reference Symbols]
[0096]
1: FORMING DIE (FIRST EMBODIMENT)
10: UPPER FORMING DIE
11 : CENTER CORE (DIE BODY)
1 1 a: CENTER CORE OUTER PERIPHERAL SURFACE
11 b: BOTTOM SURFACE
12: BOSS PART
13: A7TACHMENT HOLE (INSERTION HOLE)
14: STEPPED PART
15: GROOVE PART (SLIDING GROOVE)
16: ABUTTING SURFACE
17: ATTACHMENT HOLE (INSERTION HOLE)
18: CUTOUT PART (RECESSED PART)
19: GUIDE PIN (FIRST GUIDE PART)
21: GUIDE CORE (MOVABLE SHAFT MEMBER)
22: GUIDE PIN (SECOND GUIDE PART)
23: STOPPER
3 1 : FIRST SPLIT CORE
32: FORMING PART
32a: INCLINED SURFACE (FORMING SURFACE) OF FORMING PART
32b: VERTICAL PLANE OF FORA4ING PART
33: PROTRUSION OF FIRST SPLIT CORE
34: CUTOUT PART OF FIRST SPLIT CORE
35: UPPER SURFACE OF FIRST SPLIT CORE
36: BOTTOM SURFACE OF FIRST SPLIT CORE
37: INCLINED SURFACE (FIRST INCLINED SURFACE) OF FIRST
SPLIT CORE
38: ATTACHMENT HOLE (FIRST HOUSING PART)
4 1 : SECOND SPLIT CORE
42: FORMING PART OF SECOND SPLIT CORE
42a: INCLINED SURFACE (FORMING SURFACE) OF FORMING PART
42b: VERTICAL PLANE OF FORMING PART
43: PROTRUSION OF SECOND SPLIT CORE
44: CUTOUT PART OF SECOND SPLIT CORE
45: UPPER SURFACE OF SECOND SPLIT CORE
46: BOTTOM SURFACE OF SECOND SPLIT CORE
47: INCLINED SURFACE OF SECOND SPLIT CORE (MATING
SURFACE WITH FIRST SPLIT CORE 3 1: SECOND INCLINED SURFACE)
48: ATTACHMENT HOLE (SECOND HOUSING PART)
60: LOWER FORMING DIE
61: BOTTOM PART
62: SIDE WALL PART
70: PUSH-IN DIE
80: STOCK
82: VERTICAL WALL PART
82a: UPPER END SURFACE OF VERTICAL WALL PART
84: BOTTOM WALL PART
86: UNDERCUT PART
CL: CENTRAL AXIS (MOVEMENT AXIS)

CLAIMS
1. A forming die comprising:
a lower forming die having a bottoni part and a side wall part;
an upper forming die that is tnovable toward the bottom part of the lower
forniing die along an axis parallel to the side wall part of tlie lower forliiing die; and
a push-it1 die that is movable toward tlie bottom part of the lower forming die
along the axis between the side wall part of the lower forming die and the upper
forniing die,
wherein the upper forming die includes:
a die body that is provided to be tnovable toward the bottoni part of the lower
fornling die along the axis, in a state where a central axis coincides with the axis;
a first split core that abuts against a bottom surface of the die body and is
provided to be movable in a direction that extends radially with tlie axis as a center;
a movable shaft member that is provided to be non-detachable downward from
the bottom surface of the die body and be insertable into an inside of the die body from
the bottom surface of the die body along the axis, in a state where a central axis
coincides with the axis; and
a second split core that is provided to be movable in a direction that extends
radially from a lower end of the movable shaft member with the axis as a center,
wherein the first and second split cores alternately disposed around the axis,
wherein the first and second split cores respectively have forming surfaces that
separate from the die body, as the first and second split cores move apart from the axis
in tlie extending direction,
wherein the first and second split cores are present inside an outer edge of the
die body, and the second split core is disposed below the fitst split core, in a state where
the movable shaft member is exposed most from the die body, and
wherein the second split core approaches tlie bottom surface of the die body
while sliding on the first split core, in a prceess in which the movable shaft member is
inserted into the inside of the die body, and thereby, the first and second split cores
respectively move to positions where tlie forming surfaces of the first and second split
cores protn~deo utside of the outer edge of the die body.
2. The forming die according to Claim 1,
wherein the first split core further includes a pair of first inclined surfaces that
are joined together so as to narrow with an upper surface of the first split core as a
center while sandwicliing the upper surface of the first split core therebetween,
wherein the second split core further includes a second inclined surface that is
a surface mating with the first split core and comes into contact with the first inclined
surfaces of the first split core,
wherein portions of the first inclined surraces of the first split core overlap the
second inclined surface of the second split core, in a state where the movable shaft
member is exposed most from the die body, and
wherein, in a process in \vhich the movable shaft member is inserted into the
inside of the die body, tlie first split core and the second split core move \vliile the first
inclined surfaces of the first split core and tlie second inclined surface of the second
split core slide on each other until the first inclined surfaces of the first split core and the
second inclined surface of the second split core are nmated with each othec
3. The forniing die according to Claim 1 or 2,
wherein the die body includes a first guide part that has a columnar shape and
extends toward a radial outer side,
wherein the tilovable shaft member includes a second guide part that has a
columnar shape and extends toward the radial outer side,
wherein the first split core further includes a first housing part that slides along
the extending direction of the first guide part with respect to the first guide part and
houses the first guide part, and
wherein the second split core further includes a second housing part that slides
along the extending direction of the second guide part with respect to the second guide
part and houses the second guide part.
4. The forniing die according to Claim 3,
wherein the hardness of the first guide part is lower than the hardness of the
first split core, and
wherein the hardness of the second guide pait is lo\ver than the hardness of the
second split core.
5. The forming die according to any one of Claims 1 to 4,
wherein the first split core further includes a protrusion that is provided on an
upper surface of the first split core,
wherein the second split core further incliides a protrusion that is provided on
an upper surface of the second split core, and
wherein the die body further includes an abutting surface that abuts against the
protrusion of the first split core and the protrusion of the second split core.
6. A method of forming at1 undercut part in a stock having an ol~eningu, sing the
fornling die according to any one of Clai~ils1 to 5, the method comprising:
a first process in which the stock is placed on the lower forming die along the
bottotn part and tlie sidc wall part;
a second process in wliicli the second split core is nlade to approach tlie botto~n
surface of the die body while being made to slide on the first split core at a
predetermined position within the openii~go f the stock, and tlie for~ningsu rfaces of the
first and second split cores are made to protrude outside of the outer edge of the die
body;
a third process in \vliicli the push-in die is moved toward the botto~np art of the
lower for~ningd ie wvliile being made to abut against the stock, and a portion of an inside
surface of the stock at~dis tnade to abut against the for~nit~stg~ rfaceso f the first and
second split cores; and
a fourtl~p rocess in which the upper forming die is moved in a direction away
fsom tlie bottoin past of tlle lower forming die.
7. The undercut for~ningm ethod according to Claim 6,
wherein in the first process, an outside surface of the stock is made to abut
against tlie side wall part of tlie lower fornling die, and
wherein it1 the third process, the push-it1 die is moved toward the bottom part
of the lower forming die wllile being tnade to abut against an upper end wuface of the
stock.