U.S. patent application number 12/842378 was filed with the patent office on 2011-02-03 for apparatus and method of hot bulge forming, and product formed by hot bulge forming.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to Yoshimitsu Ishihara, Takayuki Kanou, Daisuke Yamamoto.
Application Number | 20110023568 12/842378 |
Document ID | / |
Family ID | 43525715 |
Filed Date | 2011-02-03 |
United States Patent
Application |
20110023568 |
Kind Code |
A1 |
Yamamoto; Daisuke ; et
al. |
February 3, 2011 |
APPARATUS AND METHOD OF HOT BULGE FORMING, AND PRODUCT FORMED BY
HOT BULGE FORMING
Abstract
In a hot bulge forming apparatus 1, a preheated tubular material
10b is disposed in a cavity 33A defined by dies 21A, 31A, air is
supplied into an interior of the tubular material 10b so that the
tubular material 10b is pressed against cavity surfaces 211A, 311A
by the pressure of the air to thereby form the tubular material 10b
into a shape defined by the cavity 33A. Thereafter, the resulting
tubular material 10c is disposed in a cavity 33B defined by dies
21B, 31B, and air is supplied into an interior of the tubular
material 10c so that the tubular material 10c is pressed against
cavity surfaces 211B, 311B by the pressure of the air to thereby
form the tubular material 10c into a shape defined by the cavity
33B while the tubular material 10c is cooled by the cavity surfaces
211B, 311B. Projecting portions 331 each having an arc-shaped
section are formed at portions of the cavity surfaces 211A, 311A
against which lengthwise end sides of the tubular material 10b are
pressed.
Inventors: |
Yamamoto; Daisuke; (Hagagun,
JP) ; Ishihara; Yoshimitsu; (Hagagun, JP) ;
Kanou; Takayuki; (Hagagun, JP) |
Correspondence
Address: |
RANKIN, HILL & CLARK LLP
38210 GLENN AVENUE
WILLOUGHBY
OH
44094-7808
US
|
Assignee: |
HONDA MOTOR CO., LTD.
Tokyo
JP
|
Family ID: |
43525715 |
Appl. No.: |
12/842378 |
Filed: |
July 23, 2010 |
Current U.S.
Class: |
72/61 |
Current CPC
Class: |
B21D 37/16 20130101;
B21D 26/041 20130101; B21D 26/033 20130101 |
Class at
Publication: |
72/61 |
International
Class: |
B21D 26/00 20060101
B21D026/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2009 |
JP |
2009-178953 |
Claims
1. A hot bulge forming apparatus comprising: a first die; and a
second die, wherein a preheated tubular workpiece is formed by
disposing the preheated tubular workpiece in a cavity of the first
die, supplying a fluid into an interior of the workpiece so as to
press the workpiece against a cavity surface of the first die by
virtue of a pressure of the fluid to form the workpiece into a
shape defined by the cavity surface, and thereafter, disposing the
workpiece in a cavity of the second die, and supplying a fluid into
the interior of the workpiece so as to press the workpiece against
cavity surface of the second die by virtue of a pressure of the
fluid so that the workpiece is cooled by the cavity surface while
being formed into a shape defined by the cavity surface, and
wherein the hot bulge forming apparatus further comprises a
projecting portion having an arc-shaped section and formed at a
portion of the cavity surface of the first die against which a
lengthwise end side of the workpiece is pressed.
2. A hot bulge forming method comprising: providing a recess
portion having an arc-shaped section at a lengthwise end side of a
tubular workpiece; and forming the tubular workpiece by disposing
the tubular workpiece which is preheated and provided with the
recessed portion in a cavity of a die and supplying a fluid into an
interior of the workpiece so as to press the workpiece against a
cavity surface of the die by virtue of a pressure of the fluid.
3. A product which is formed through hot bulge forming and
comprises a recess portion having an arc-shaped section at a
lengthwise end side of the product.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a hot bulge forming
apparatus, a hot bulge forming method and a product formed through
hot bulge forming. More particularly, the invention relates to a
hot bulge forming apparatus and method in which a preheated tubular
workpiece is disposed in a cavity defined between dies, a fluid is
supplied into the tubular workpiece in the cavity to press the
workpiece against cavity surfaces of the dies by virtue of the
pressure of the fluid so as to form the tubular workpiece, and
thereafter the formed workpiece is cooled in the dies, and a
product formed by the hot bulge forming apparatus according to the
hot bulge forming method.
[0003] 2. Related Art
[0004] Conventionally, there has been known a hot bulge forming
process in which high-pressure air is supplied into a cavity
defined between dies so as to form a tubular workpiece disposed in
the cavity into a desired configuration.
[0005] Specifically, in this hot bulge forming process, for
example, a tubular workpiece is preheated, and the preheated
tubular workpiece is disposed between a pair of dies. Next, the
dies are clamped together while the workpiece is restrained at both
lengthwise ends thereof, and high-pressure air is supplied into a
cavity defined between the clamped dies so that the workpiece is
pressed against cavity surfaces of the dies. Thereafter, this state
is maintained for a certain length of time to cool the workpiece in
the dies. Then, the dies are opened to release the internal
pressure therein, and the formed workpiece is removed from the dies
(for example, refer to US2005/0029714).
[0006] Incidentally, when the internal pressure is released, the
force is reduced which presses the inner side of the workpiece, and
therefore, the workpiece largely shrinks. As this occurs, a degree
of shrinkage at both lengthwise end sides of the workpiece is
larger than a degree of shrinkage at a lengthwise central side
thereof. Because of this, the lengthwise central side is dragged by
the shrinkage at both the lengthwise end sides and a part of the
lengthwise central side dents, generating a dent. In particular, as
is shown in FIG. 10, in the case of a sectional shape of a
lengthwise central side of a workpiece 110 being rectangular, a
rigidity of longer side portions 111 is lower than a rigidity of
shorter side portions, and therefore, the longer side portions
largely dent.
[0007] This kind of phenomenon is occurred by the following
reason.
[0008] When forming bulges, since high-pressure air is supplied in
such a state that the workpiece is restrained at both the
lengthwise end sides thereof, the lengthwise central side of the
workpiece is pressed against the cavity more strongly by the
pressure of the supplied air than the lengthwise end sides are.
Therefore, the lengthwise central side of the workpiece is cooled
more quickly than the lengthwise end sides thereof, and cooling is
progressed further at the lengthwise central side than at the
lengthwise end sides before the internal pressure is released.
Consequently, when the internal pressure is released, the workpiece
shrinks more largely at the lengthwise end sides than at the
lengthwise central side, and the lengthwise central side of the
workpiece is dragged by the shrinkage at both the lengthwise end
sides to dent, generating a dent thereat.
SUMMARY OF THE INVENTION
[0009] One or more embodiments of the invention provide a hot bulge
forming apparatus which can suppress a generation of a dent at a
lengthwise central side of a workpiece.
[0010] In accordance with one or more embodiments of the invention,
in a hot bulge forming apparatus (for example, a hot bulge forming
apparatus 1, of an exemplary embodiment), a preheated tubular
workpiece (for example, a tubular workpiece 10b) is formed into a
desired shape by disposing the preheated tubular workpiece in a
cavity (for example, a cavity 33A) defined by first dies (for
example, a lower die 21A, an upper die 31A), supplying a fluid (for
example, air) into an interior of the workpiece so as to press the
workpiece against cavity surfaces (for example, cavity surfaces
211A, 311A) of the first dies by virtue of a pressure of the fluid
to form into a shape defined by the cavity surfaces, and
thereafter, disposing the workpiece in a cavity (for example, a
cavity 33B) of second dies (for example, a lower die 21B, an upper
die 31B) and supplying a fluid into the interior of the workpiece
so as to press the workpiece against cavity surfaces (for example,
cavity surfaces 211B, 311B) of the second dies by virtue of a
pressure of the fluid so that the workpiece is cooled by the cavity
surfaces while being formed into a shape defined by the cavity
surfaces. In the hot bulge forming apparatus projecting portions
(for example, projecting portions 331) each having an arc-shaped
section are formed at portions of the cavity surfaces of the first
dies against which lengthwise end sides of the workpiece are
pressed.
[0011] According to this structure, the projecting portions each
having the arc-shaped section are formed at the portions of the
cavity surfaces of the first dies against which the lengthwise end
sides of the workpiece are pressed.
[0012] Consequently, when the workpiece is formed by the first
dies, the projecting portions formed on the cavity surfaces are
transferred on to the workpiece, whereby recess portions each
having an arc-shaped section are formed at the lengthwise end sides
of the workpiece. Thereafter, when the workpiece is formed into the
shape defined by the second dies and is then cooled by the second
dies so as to release an internal pressure in the cavity, the
workpiece attempts to shrink more largely at the lengthwise side
ends than at the lengthwise central side. Namely, a circumferential
length of the workpiece at the lengthwise side ends attempts to
decrease largely.
[0013] However, since the lengthwise end sides and the lengthwise
central side of the workpiece are connected continuously, the
shrinking deformation occurring at the lengthwise end sides of the
workpiece is restrained by the lengthwise central side thereof.
Consequently, the recess portion is tensioned, and the recess
portion is deformed by the tensile force, whereby the curvature of
the arc-like shape of the recess portion is reduced. Because of
this, an attempt to reduce the circumferential length of the
workpiece at the lengthwise end sides is suppressed.
[0014] As a result, the generation of a dent at the lengthwise
central side of the workpiece can be suppressed which would
otherwise occur by the lengthwise central side being dragged by the
shrinkage occurring at the lengthwise end sides of the
workpiece.
[0015] Moreover, in accordance with one or more embodiments of the
invention, a hot bulge forming method includes the steps of:
providing a recess portion having an arc-shaped section at a
lengthwise end side of a tubular workpiece; and forming the tubular
workpiece by disposing the tubular workpiece which is preheated and
provided with the recessed portion in a cavity of a die and
supplying a fluid into an interior of the workpiece so as to press
the workpiece against a cavity surface of the die by virtue of a
pressure of the fluid.
[0016] In addition, in accordance with one or more embodiments of
the invention, a product which is formed through hot bulge forming
is provided with a recess portion having an arc-shaped section at a
lengthwise end side of the product.
[0017] According to the embodiments, when the workpiece is formed
by the first dies, the projecting portions formed on the cavity
surfaces are transferred on to the workpiece, whereby the recess
portions each having the arc-shaped section are formed at the
lengthwise end sides of the workpiece. Thereafter, the workpiece is
formed and cooled by the second dies, and the internal pressure is
released. As this occurs, the workpiece attempts to shrink more
largely at the lengthwise end sides than at the lengthwise central
side. Namely, the circumferential length of the workpiece attempts
to decrease largely at the lengthwise end sides. However, since the
lengthwise end sides of the workpiece are continuously connected to
the lengthwise central side thereof, the shrinking deformation
occurring at the lengthwise end sides is restrained by the
lengthwise central side of the workpiece. Consequently, the recess
portions are tensioned and are deformed by the tensile force,
whereby the curvature of the arc-like shape of the recess portion
is reduced. Therefore, the attempt to reduce the circumferential
length at the lengthwise end sides of the workpiece is suppressed.
As a result, the generation of a dent at the lengthwise central
side of the workpiece can be suppressed which would otherwise occur
by the lengthwise central side being dragged by the shrinkage at
the lengthwise end sides of the workpiece.
[0018] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a flow chart showing operations of a hot bulge
forming apparatus according to an exemplary embodiment of the
invention.
[0020] FIG. 2 ((a) portion to (d) portion) shows perspective views
of a workpiece that is formed by the hot bulge forming
apparatus.
[0021] FIG. 3 is a sectional view of a first bulge forming device
which makes up the hot bulge forming apparatus.
[0022] FIG. 4 is a sectional view showing sections of dies of the
first bulge forming device.
[0023] FIG. 5 is a sectional view of a second bulge forming device
which makes up the hot bulge forming apparatus.
[0024] FIG. 6 is a sectional view showing sections of dies of the
second bulge forming device.
[0025] FIG. 7 is a sectional view of a third bulge forming device
which makes up the hot bulge forming apparatus.
[0026] FIG. 8 is a sectional view showing sections of dies of the
third bulge forming device.
[0027] FIG. 9 ((a) portion and (b) portion) shows diagrams
illustrating a deformation of the workpiece in the third bulge
forming device.
[0028] FIG. 10 is a diagram illustrating a deformation of a
workpiece according to a conventional example.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0029] An exemplary embodiment of the invention will be described
by reference to the drawings.
[0030] FIG. 1 is a flow chart showing operations of a hot bulge
forming apparatus 1 according to the exemplary embodiment of the
invention.
[0031] FIG. 2 ((a) portion to (d) portion) shows perspective views
of tubular materials 10a to 10d which represent workpieces which
are formed at respective steps by the hot bulge forming apparatus
1.
[0032] The hot bulge forming apparatus 1 is designed to execute an
energization heating process 2, a bulge forming process 3 and a
squashing process 4 which constitutes a pre-forming process, and a
section shaping process 5 which constitutes a final forming process
sequentially in that order.
[0033] Specifically, in the energization heating process 2, a
tubular material 10a, which is made of an aluminum alloy and which
extends substantially rectilinearly, is heated.
[0034] In the bulge forming process 3, portions of the tubular
material 10a which lie closer to ends thereof are expanded by a
first bulge forming device 6 (refer to FIG. 3) so as to form the
tubular material 10a into a tubular material 10b.
[0035] In the squashing process 4, a sectional shape of the tubular
material 10b is formed into a substantially oval shape and the
tubular material 10b is curved at an intermediate portion thereof
by a second bulge forming device 7 (refer to FIG. 5) so as to form
the tubular material 10b into a tubular material 10c.
[0036] In the section shaping process 5, a sectional shape of the
tubular material 10c is formed into a substantially rectangular
shape by a third bulge forming device 8 (refer to FIG. 7) so as to
form the tubular material 10c into a tubular material 10d.
[0037] FIG. 3 is a sectional shape showing a schematic
configuration of the first bulge forming device 6. FIG. 4 is a
sectional view of dies of the first bulge forming device 6.
[0038] The first bulge forming device 6 includes a lower die
mechanism 20 which includes a lower die 21 which supports the
tubular material 10a, 10b, an upper die mechanism 30 which includes
an upper die 31 which holds the tubular material 10a, 10b together
with the lower die 21 from above and below the tubular material
10a, 10b, a holding mechanism 40 for holding both end sides of the
tubular material 10a, 10b, a pressing mechanism 50 for pressing
both the end sides of the tubular material 10a, 10b in axial
directions, an air supply mechanism 60 for supplying air into an
interior of the tubular material 10a, 10b and heating units 70 for
heating the lower die 21 and the upper die 31.
[0039] The lower die mechanism 20 includes the lower die 21 as a
fixed die and a base 22 which supports the lower die 21. A cavity
surface 211 is formed on the lower die 21.
[0040] The upper die mechanism 30 includes the upper die 31 as a
movable die which is disposed above the lower die 21 so as to
confront the lower die 21 and a lifting unit 32 for lifting up and
down the upper die 31. A cavity surface 311 is formed on the upper
die 31.
[0041] When the lifting unit 32 is driven to cause the upper die 31
to approach the lower die 21 so that the upper and lower dies are
clamped together, a cavity 33 is defined by the cavity surface 311
of the upper die 31 and the cavity surface 211 of the lower die
21.
[0042] The holding mechanism 40 includes a pair of holders 41 which
are provided at axial end sides of the tubular material 10a, 10b on
the lower die 21 and reciprocating units 42 for causing the pair of
holders 41 to reciprocate along an axial direction of the tubular
material 10a, 10b.
[0043] The holder 41 has a substantially cylindrical shape.
[0044] The reciprocating units 42 cause the corresponding holders
41 to approach the tubular material 10a, 10b so as to fit on both
the end sides of the tubular material 10a, 10b, whereby the tubular
material 10a, 10b is held by the holders 41.
[0045] The pressing mechanism 50 includes a pair of pressing
members 51 which are inserted individually into the pair of holders
41 and pressing units 52 for causing the pressing members 51 to
reciprocate along the axial direction of the tubular material 10a,
10b.
[0046] The pressing units 52 cause the corresponding pressing
members 51 to approach the tubular material 10a, 10b to be inserted
individually into the corresponding holders 41 so as to press both
ends of the tubular material 10a, 10b which is held by the holders
41, so that the tubular member 10a, 10b is compressed towards a
center axis direction.
[0047] The air supply unit 60 includes air supply lines 61 which
pass through the pair of pressing members 51 of the pressing
mechanism to reach both the end sides of the tubular material 10a,
10b and an air pump, not shown, which supplies high-pressure air to
these air supply lines 61.
[0048] The heating units 70 are incorporated in the lower die 21
and the upper die 31. A high-frequency current heating means, a
heater heating unit and the like are raised for use as the heating
units 70.
[0049] FIG. 5 is a sectional view showing a schematic configuration
of the second bulge forming device 7. FIG. 6 is a sectional view of
dies of the second bulge forming device 7.
[0050] The second bulge forming device 7 differs from the first
bulge forming device 6 in that a cavity 33A defined by a cavity
surface 311A of an upper die 31A and a cavity surface 211A of a
lower die 21A has a different shape, in that an air supply unit 60
has a different construction, and in that the holding mechanism 40
and the pressing mechanism 50 are not provided but a restraining
mechanism 80 is provided. The other configurations of the second
bulge forming device 7 are similar to those of the first bulge
forming device 6.
[0051] Namely, projecting portions 331 each having an arc-shaped
section are formed at both lengthwise end sides of the cavity
surface 311A of the upper die 31A and the cavity surface 211A of
the lower die 21A, that is, portions of those cavity surfaces
against which both the lengthwise end sides of the tubular material
10b, 10c are pressed.
[0052] In addition, the restraining mechanism 80 includes a pair of
restraining beads 81 which are provided so as to hold the tubular
material 10b, 10c on the lower die 21A from axial directions and
reciprocating units 82 for causing the pair of restraining beads 81
to reciprocate along an axial direction of the tubular material
10b, 10c.
[0053] A recess portion 811 is formed in the restraining bead
81.
[0054] The reciprocating units 82 cause the corresponding
restraining beads 81 to approach the tubular material 10b, 10c so
as to allow both end sides of the tubular material 10b, 10c to fit
in the corresponding recess portions 811, whereby the tubular
material 10b, 10c is restrained at both the end sides thereof.
[0055] In addition, air supply lines 61A of an air supply unit 60
pass through the pair of restraining beads 81 to reach both the end
sides of the tubular material 10b, 10c.
[0056] FIG. 7 is a sectional view showing a schematic configuration
of the third bulge forming device 8. FIG. 8 is a sectional view of
dies of the third bulge forming device 8.
[0057] The third bulge forming device 8 differs from the second
bulge forming device 7 in that a cavity 33B defined by a cavity
surface 311B of an upper die 31B and a cavity surface 211B of a
lower die 21B has a different shape, and in that heating units 70B
have a different configuration. The other configurations of the
third bulge forming device 8 remain similar to those of the second
bulge forming device 7.
[0058] Namely, no projecting portion 331 is formed on the cavity
surface 311B of the upper die 31B and the cavity surface 211B of
the lower die 21B.
[0059] In addition, a fluid heating means is used as the heating
unit 70B.
[0060] Hereinafter, a bulge forming procedure by the hot bulge
forming apparatus 1 will be described.
[0061] A bulge forming process includes an energization heating
process, a bulge forming process, a squashing process and a section
shaping process.
[0062] Firstly, the tubular material 10a which is made of an
aluminum alloy is heated to about 500.degree. C. in the
energization heating process.
[0063] Next, the bulge forming process is carried out. Specifically
speaking, firstly, the dies 21, 31 are heated to about 500.degree.
C., that is, a recrystallization temperature of the tubular
material 10a or higher by the heating units 70.
[0064] Next, the tubular material 10a heated in the way described
above is disposed on the lower die 21.
[0065] Next, the lifting unit 32 of the upper die mechanism 30 is
driven to lower the upper die 31, and the dies 21, 31 are clamped
together.
[0066] Next, the reciprocating units 42 of the holding mechanism 40
are driven to cause the holders 41 to fit on the end sides of the
tubular material 10a so as to hold the tubular material 10a.
[0067] Next, the pressing members 51 of the pressing mechanism 50
are driven, so that the ends of the tubular material 10a which is
held by the holders 41 are pressed in compressing directions by the
pressing members 51. At the same time, the air pump of the air
supply unit 60 is driven to supply high-pressure air into the
cavity 33.
[0068] Then, hot bulge forming occurs in the tubular material 10a
in which the tubular material 10a is allowed to bulge to follow the
configuration of the cavity 33, whereby the tubular material 10a is
formed into the tubular material 10b.
[0069] Next, the squashing process is carried out. Specifically,
firstly, the dies 21A, 31A are heated to about 500.degree. C. or
the recrystallization temperature of the tubular material 10b or
higher by the heating units 70.
[0070] Next, the tubular material 10b, which has been subjected to
hot bulge forming, is transferred to be disposed on the lower die
21A by a known transfer means, not shown, while the heating state
is maintained.
[0071] Next, the reciprocating units 82 of the restraining
mechanism 80 are driven to cause the restraining beads 81 to fit on
both the end sides of the tubular material 10b.
[0072] In addition, the lifting unit 32 of the upper die mechanism
30 is driven to lower the upper die 31A, and the dies 21A, 31A are
clamped together. At the same time, the air pump of the air supply
unit 60 is driven to supply high-pressure air into the cavity
33A.
[0073] Then, the tubular material 10b, which has been subjected to
hot bulge forming, is hot squashed (at about 500.degree. C.) to
follow the configuration of the cavity 33A, whereby the tubular
material 10b is formed into the tubular material 10c. As this
occurs, the projecting portions 331 formed on the cavity surfaces
211A, 311A are transferred on to the tubular material 10c, and
recess portions 11 each having an arc-shaped section are formed at
both lengthwise end sides of the tubular material 10c (refer to (a)
portion and (b) portion of FIG. 9).
[0074] Next, the section shaping process is carried out.
Specifically speaking, firstly, the lower die 21B and the upper die
31B are heated to about 200.degree. C. or the recrystallization
temperature of the tubular material 10c or lower by the heating
units 70B.
[0075] Next, the tubular material 10c, which has been subjected to
the squashing operation, is rotated substantially 90.degree. about
the a center axis by a rotating means, not shown, and is thereafter
transferred to be disposed on the lower die 21B by a known transfer
means, riot shown.
[0076] Next, the reciprocating units 82 of the restraining
mechanism 80 are driven to cause the restraining beads 81 to fit on
both the end sides of the tubular material 10c, whereby the tubular
material 10c is restrained at both the end sides thereof. In
addition, the lifting unit 32 of the upper die mechanism 30 is
driven to lower the upper die 31B, and the dies 21B, 31B are
clamped together. At the same time, the air pump of the air supply
unit 60 is driven to supply high-pressure air into the cavity
33B.
[0077] Then, the section of the tubular material 10c, which has
been subjected to the squashing operation, is shaped to follow the
configuration of the cavity 33B, whereby the tubular material 10c
is formed into the tubular material 10d.
[0078] In this section shaping process, since the temperatures of
the dies 21B, 31B are about 200.degree. C., the heat of the tubular
material 10c is conducted to the dies 21B, 31B, whereby the
temperature of the tubular material 10c is decreased. However, hot
bulge forming is implemented to some extent.
[0079] Next, the temperatures of the dies 21B, 31B are held to the
recrystallization temperature of the tubular material 10d or lower,
and the clamping state of the dies 21B, 31B is maintained for a
certain length of time for cooling the tubular material 10d. By
doing this, the tubular material 10d is cooled so as to allow a
thermal shrinkage to occur therein, and thereafter, the internal
pressure in the dies is released.
[0080] As this occurs, since the tubular material 10d is restrained
at both end portions thereof by the restraining beads 81, an axial
thermal shrinkage of the tubular material 10d is suppressed.
[0081] Here, as is shown in (a) portion of FIG. 9, one lengthwise
end side of the tubular material 10c on which recess portions 11
each having an arc-shaped section are formed is referred to as an
end portion 12, and a lengthwise central side of the tubular
material 10c is referred to as a central portion 13.
[0082] When the tubular material 10c is cooled by the dies 21B, 31B
to release the internal pressure, the end portion 12 of the tubular
material 10c attempts to shrink more largely than the central
portion 13 of the tubular material 10c. Namely, as is shown in (b)
portion of FIG. 9, a circumferential length of the end portion 12
of the tubular material 10c attempts to decrease largely.
[0083] However, since the end portion 12 of the tubular material
10c is continuously connected to the central portion 13 thereof,
the shrinking deformation occurring at the end portion 12 of the
tubular material 10c is restrained by the central portion 13 of the
tubular material 10c. Consequently, the recess portions 11 are
tensioned in directions indicated by white arrows in (b) portion of
FIG. 9 and are deformed by the tensile force, whereby the curvature
of the arc-like shape of the recess portion 11 is reduced.
Consequently, the attempted reduction in circumferential length of
the end portion 12 of the tubular material 10c is suppressed.
[0084] According to the exemplary embodiment that has been
described heretofore, the following advantage is provided. (1) The
projecting portions 331 each having the arc-shaped section are
formed at portions of the upper die 31A and the lower die 21A
against which the lengthwise end sides of the tubular material 10c
are pressed.
[0085] Consequently, when forming the tubular material 10 by the
dies 21A, 31A, the projecting portions 331 which are formed on the
cavity surfaces 211A, 311A are transferred on to the tubular
material 10c, and the recess portions 11 each having the arc-shaped
section are formed at both the lengthwise end sides of the tubular
material 10c. Thereafter, when the tubular material 10c is formed
by the dies 21B, 31B and is then cooled by the dies 21B, 31B to
release the internal pressure therein, the recess portions 11 are
tensioned and are then deformed by the tensile force, whereby the
curvature of the arc-like shape of the recess portion 11 is
decreased. Consequently, the attempted reduction in circumferential
length of the end sides of the tubular material 10c is suppressed.
As a result, the generation of a dent at the lengthwise central
side of the workpiece can be suppressed which would otherwise occur
by the lengthwise central side being dragged by the shrinkage
occurring at the lengthwise end sides of the workpiece.
[0086] While the invention has been described in connection with
the specific exemplary embodiment, it will be obvious to those
skilled in the art that various changes and modifications may be
made therein without departing from the present invention.
[0087] For example, in the exemplary embodiment, while the
projecting portions 331 are formed on the dies 21A, 31A of the
second bulge forming device 8 and the projecting portions 331 are
then transferred on to the tubular material 10b when the squashing
process is implemented, the invention is not limited thereto.
Namely, projecting portions may be formed on the dies 21, 31 of the
first bulge forming device 6 so that the projecting portions are
transferred on to the tubular material 10a when the bulge forming
process is implemented.
[0088] In addition, in the exemplary embodiment, while the tubular
material which takes the form of tubular materials 10a to 10d is
described as being made of aluminum alloy, the invention is not
limited thereto, and hence, the tubular material may be made of
other metals.
[0089] In addition, in the exemplary embodiment, while air is
supplied into the interior of the tubular material which takes the
forms of tubular materials 10a to 10d by the air supply unit 60,
the invention is not limited thereto, and hence, other fluids may
be supplied thereinto.
[0090] It is aimed, therefore, to cover in the appended claims all
such changes and modifications falling within the scope of the
present invention.
DESCRIPTION OF REFERENCE NUMERALS AND SIGNS
[0091] 1 hot bulge forming apparatus; 10a to 10d tubular material;
11 recess portion; 21A lower die (first die); 33A upper die (first
die); 21B lower die (second die); 31B upper die (second die); 33A,
33B cavity; 211A, 211B, 311A, 311B cavity surface; 331 projecting
portion.
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