TITLE OF THE INVENTION
HYDROFORMING METHOD AND HYDROFORMING DEVICE
5
FIELD OF THE INVENTION
[0001] This invention relates to a hydroforming method
for forming a metal tube into a predetermined shape by
inserting the metal tube into a hydroforming die
10 assembly, clamping the hydroforming die assembly, and
thereafter compressing the metal tube in its axial
direction while applying hydraulic pressure to Lhe
interior of the metal tube, and to a hydroforming device
used to implement the method.
15
BACKGROUND ART
[0002] The ordinary conventional hydroforming method
will be explained with reference to FIG. 12. When
ordinary hydroforming is performed, a metal tube 103 is,
20 as shown in FIG. 12(a), first inserted in a cavity 115
formed by a pair of hydroforming dies 111, 113. Next, as.
shown in FIG. 12(b), the pair of hydroforming dies 111,
113 is closed. Then, as shown in FIG. 12(c), axial
compression cylinders 131 installed at opposite ends of
25 the metal tube 103 are driven to press seal punches 133
attached to the axial compression cylinders 131 onto the
tube end faces 103b of the metal tube 103 and thereby
seal the opposite ends 103a of the metal tube 103. Next,
as shown in FIG. 12(c) and FIG. 12(d), water or other
30 pressure medium W is supplied into the interior of the
metal tube 103 to apply internal pressure by which the
metal tube 103 is expanded to form a hydroformed product
of an outer shape conforming to the shape of the cavity
115 between the hydroforming dies 111 and 113.
35 [0003 ] If the applied internal pressure is apt to
expand the metal tube 103 greatly, a countermeasure that
is sometimes taken to prevent bursting or buckling of the
-2-
metal tube 103 at this time is to minimize expansioninduced
thinning of the metal tube 103 by using the axial
compression cylinders 131 to compress the metal tube 103
in its axial direction and thus inject the material in
5 the axially inward direction of the metal tube 103.
[0004] When the opposite ends 103a of the metal tube
103 are to be sealed and the metal tube 103 compressed in
the axial direction during hydroforming, the practice
generally adopted is, as shown in FIG. 12, to carry out
10 the sealing and compression by driving axial compression
cylinders 131 located at the opposite ends of the metal
tube 103. However, Patent Document 1 teaches an example
in which an axial compression cylinder 131 is installed
at only one end 103a of the metal tube 103, this one end
15 103a is sealed using the axial compression cylinder 131
located at the one end, and the metal tube 103 is axially
compressed only from one end thereof.
CITATION LIST
20 Patent Documents
[0005 ] PLT 1e Japanese Patent Publication (A) No. 11-
33640
PLT 20 Japanese Patent Publication (A) No. 2002-
66663
25
SUMMARY OF THE INVENTION
Technical Problem
[0006 ] In this connection, recent years have seen
advances in the application of hydroforming technology to
30 the production of automotive and other parts with
complicated shapes. A need is therefore felt for
hydroforming technologies that enable production not only
of simply-shaped products with straight axes like the
hydroformed product 105 shown in FIG. 12(d) but also of
35 hydroformed products 105 formed to complicated shapes
whose axes 105a include two-dimensional or threedimensional
bending, like those in FIGS. 13 and 14. When
- 3 -
5
hydroforming is used to produce hydroformed products 105
with complicated shapes like those in FIGs. 13 and 14,
the pair of axial compression cylinders 131 located at
the opposite ends of the metal tube 103 cannot be
arranged on the same axis and the axes must be arranged
at an angle.
[0007] The pair of hydroforming dies 111, 113 is
usually installed in a space like that of a press but in
Patent Document 2 is installed in a C-shaped frame. In
10 either case, the small space available for the pair of
hydroforming dies 111, 113 has made it very difficult to
arrange the axes of the pair of axial compression
cylinders 131 at an angle. This tendency is particularly
pronounced in the case where, as shown, in FIG. 14, the
15 axis 105a of the hydroformed product 105 to be produced
is formed to include three-dimensional bending.
[0008 ] This has led to the use of excessively large
hydroforming devices or, depending on the shape of the
hydroformed product 105, to resorting to some other
20 strategy such as of abandoning the idea of fabricating it
from a single member and instead producing a part
configured to the desired shape of the hydroformed
product from a plurality of straight divisional members.
[0009 ] As a way to overcome this problem, it is
25 conceivable, as in the aforesaid Patent Document 1, to
install the axial compression cylinder 131 only at one
end of the metal tube 103 without installing, i.e., doing
away with, the axial compression cylinder 131 at the
other end. However, adopting this approach makes it
30 impossible to compress the metal tube 103 from the side
with no axial compression cylinder 131. Still, when
conducting hydroforming to produce a hydroformed product
105 with a straight axis, such as shown in FIG. 12, no
major problem is encountered because the compression from
35 only the side where the axial compression cylinder 131 is
installed enables good injection of the material to the
opposite side. However, when conducting hydroforming to
-4-
produce a hydroformed product 105 of complicated shape
whose axis 105a includes bending, such as shown in FIGS.
13 and 14, the compression from only the side where the
axial compression cylinder 131 is installed cannot ensure
5 adequate injection of the material to the opposite side,
so that bursting and buckling of the metal tube 103 tends
to occur. Hydroforming becomes difficult to conduct as a
result. Another solution has therefore been desired.
[0010 ] The present invention was accomplished with
10 consideration to the aforesaid problem. Its object is to
enable ready production of a complicatedly-shaped
hydroformed product whose axis includes bending, while
also avoiding excessive enlargement of the hydroforming
device. More specifically, the, object is to provide a
15 hydroforming method that performs compression by an axial
compression cylinder only from one end of the tube and
also enables sealing and compression from the other end
having no axial compression cylinder, and a hydroforming
device that enables the method.
20
Solution to Problem
[0011] The inventors invented the hydroforming method
and hydroforming device set out below in order to
overcome the aforesaid problem.
25 [0012] (1) A hydroforming method wherein no axial
compression cylinder is installed at one end of a metal
tube inserted in a hydroforming die assembly, an axial
compression cylinder is installed only at another end of
the metal tube, the metal tube is compressed axially by
30 the axial compression cylinder, and a pressure medium is
supplied into the interior of the metal tube sealed at
both ends to apply internal pressure, which hydroforming
method is characterized by comprising a step prior to
closing the hydroforming die assembly of inserting the
35 metal tube into the hydroforming die assembly and a
standalone punch at one end of the metal tube, and a step
at the time of closing the hydroforming die assembly of
-5-
using the closing force of the hydroforming die assembly
to advance the standalone punch in the tube axial
direction to seal the one end of the metal tube with the
standalone punch and simultaneously compress the metal
5 tube in the axial direction.
[0013 ] (2) A hydroforming method as set out in (1),
characterized in that when the standalone punch is
advanced in the tube axial direction the one end of the
metal tube is sealed by inserting an insert member at a
10 forward end of the standalone punch into the interior of
the one end of the metal tube.
[0014 ] (3) A hydroforming method as set out in (2),
characterized in that when the standalone punch is
advanced in the tube axial direction the insert member of
15 the standalone punch, which has an attached 0-ring, is
inserted into the interior of the one end of the metal
tube to reinforce the seal of the one end of the metal
tube by the 0-ring.
[0015] (4) A hydroforming device wherein no axial
20 compression cylinder is installed at one end of a metal
tube inserted in a hydroforming die assembly, an axial
compression cylinder is installed only at another end of
the metal tube, the axial compression cylinder compresses
the metal tube in the axial direction, and a pressure
25 medium is supplied into the interior of the metal tube
sealed at both ends to apply pressure, which hydroforming
device is characterized by comprising a standalone punch
inserted in the hydroforming die assembly together with
the metal tube at one end of the metal tube, the closing
30 force of the hydroforming die assembly at the time of
closing the hydroforming die assembly being used to
advance the standalone punch in the tube axial direction
to seal the one end of the metal tube with the standalone
punch and simultaneously compress the metal tube in the
35 axial direction.
[0016] (5) A hydroforming device as set out in (4),
characterized by a structure which, when the standalone
punch is advanced in the tube axial direction, enables
sealing of the one end of the metal tube by inserting an
insert member at a forward end of the standalone punch
into the interior of the one end of the metal tube.
5 [0017 ] (6) A hydroforming device as set out in (5),
characterized in that an 0-ring is attached to the insert
member of the standalone punch.
Effect of the Invention
10 [0018] In the production of a hydroformed product of a
complicated shape including axial bending, the present
invention enables the metal tube to be compressed from
both ends to inject the material in the tube axial
direction from both ends of the tube. As a result, even a
15 hydrbformed product of complicated shape including axial
bending can be readily produced, and in the production of
a hydroformed product of complicated shape including
axial bending, installation of an axial compression
cylinder is made unnecessary at one end of the metal
20 tube. Therefore, the conventionally required installation
of a pair of axial compression cylinders with mutually
angled axes becomes unnecessary, sb that the size of the
hydroforming device can be proportionally reduced. In
addition, the elimination of one of a pair of axial
25 compression cylinders makes it possible to realize the
hydroforming device at lower cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a top sectional view showing the
30 structure of a hydroforming device according to a first
embodiment.
FIG. 2(a) is a sectional view taken along line A-A
in FIG. 1. FIG. 2(b) is a sectional view taken along line
B-B in FIG. 1.
35 FIG. 3(a) is a sectional view taken along line C-C
in FIG. 1. FIG. 3(b) is view for explaining the operating
state of the hydroforming device according to the first
-7-
embodiment at the sectional location along line C-C in
FIG, 1.
FIG. 4(a) is a sectional view taken along line D-D
in FIG. 1, and FIG. 4(b) is a sectional view taken along
5 line F-F in FIG. 1. FIG. 4(c) is a sectional view taken
along line F-F in FIG. 1, and FIG. 4(d) is a sectional
view taken along line G-G in FIG. 1.
FIG. 5 is a set of diagrams showing the state= after
a metal tube was inserted in a hydroforming die assembly
10 in the course of the hydroforming method according to the
present invention, in which FIG. 5(a) is a partial side
sectional view and FIG. 5(b) is a top sectional view.
FIG. 6 is a set of diagrams showing the opposite
ends of a metal tube in a sealed state, in which FIG.
15 6(a) is a partial side sectional view and FIG. 6(b) is a
top sectional view.
FIG. 7 is a set of diagrams showing the state after
closing of a hydroforming die assembly was completed in
the course of the hydroforming method according to the
20 present invention, in which FIG. 7(a) is a partial side
sectional view and FIG. 7(b) is atop sectional view.
FIG. 8 is a set of diagrams showing the state after
completion of the hydroforming method according to the
present invention, in which FIG. 8(a) is a partial side
25 sectional view and FIG. 8(b) is a top sectional view.
FIG. 9(a) is a partial side sectional view showing
the structure of a hydroforming device according to a
second embodiment, and FIG. 9(b) is a partial side
sectional view showing the structure of a hydroforming
30 device according to a third embodiment.
FIG. 10 is a set of diagrams showing the structure
of a hydroforming device used in an example, in which
FIG. 10(a)is a top sectional view, FIG. 10(b) is a
sectional view taken along line J-J in FIG. 10(a), FIG.
35 10(c) is a sectional view taken along line K-K in FIG.
10(a), FIG. 10(d) is a sectional view taken along line LL
in FIG. 10(a), and FIG. 10(e) is a sectional view taken
along line M-M in FIG. 10(a)
FIG. 11 is a diagram for explaining a hydroforming
method performed in an example.
FIG. 12 is a diagram for explaining an ordinary
5 conventional hydroforming method.
FIG. 13 is a perspective view showing an example of
a hydroformed product formed to include two-dimensional
axial bending.
FIG. 14 is a perspective view showing an example of
10 a hydroformed product formed to include three-dimensional
axial bending.
DESCRIPTION OF EMBODIMENTS
[0020] Modes for implementing the hydroforming method
15
and hydroforming device embodying the present invention
are explained below in detail with reference to the
drawings.
[0021] The hydroforming method according to the
present invention is ideal for use in producing a
20 hydroformed product 5 that, as shown in FIGs. 13 and 14,
is formed to include an axis 5a including two-dimensional
or three-dimensional bending. Moreover, the hydroforming
method according to the present invention can of course
also be used for producing a hydroformed product 5 formed
25 to have a straight axis 5a.
[0022] A first embodiment of the hydroforming device
according to the present invention is explained next.
[0023 ] FIG. 1 is a top sectional view showing the
structure of a hydroforming device 1 according to a first
30 embodiment. Further, FIG. 2(a) is a sectional view taken
along line A-A in FIG. 1. FIG. 2(b) is a sectional view
taken along line B-B in FIG. 1, and FIG. 3(a) is n
sectional view taken along line C-C in FIG. 1. FIG. 3(b)
is a view for explaining the operating state of the
35 hydroforming device 1 according to the first embodiment
at the sectional location along line C-C in FIG. 1. FIG.
4(a) is a sectional view taken along line D-D in FIG. 1.
9
FIG. 4(b) is a sectional view token along line E-E in
FIG. 1. FIG. 4(c) is a sectional view taken along line FF
in FIG. 1. FIG. 4(d) is a sectional view taken along
line G-G in FIG. 1. In addition, the alternate long and
5 short dash line L1 in FIG. 1 indicates where the axis of
the hydroformed product 5 produced by the hydroforming
device 1 according to the first embodiment passes.
[0024 ] The hydroforming device 1 according to the
present invention is equipped with a pair of hydroforming
10 dies 11, 13, a standalone punch 21 installed at one end
of a metal tube 3 inserted between the hydroforming dies
11, 13, and an axial compression cylinder 31 installed at
the other end of the metal tube 3. In the following
explanation, the one side of the metal tube 3 where no
15 axial compression cylinder 31is installed will be called
the cylinderless end and the other side of the metal tube
3 where the axial compression cylinder 31 is installed
will be called the cylinder end.
[0025 ] One of the pair of hydroforming dies 11, 13 is
20 fixed and the other is configured to be driven in one
direction by a drive unit not shown in the drawings. The
driving of the latter in the one direction closes the
dies. In the first embodiment, the hydroforming dies 11,
13 of the pair are spaced vertically. The lower hydroform
25 die 11 is fixed and the upper hydroform die 13 is
configured to be driven.
[0026 ] The hydroforming dies 11, 13 are internally
grooved to from a cavity 15. A metal tube 3 is inserted
in the middle section 15a of the cavity 15 as the
30 material for a hydroformed product 5. In the first
embodiment, the metal tube 3 installed is one of circular
cross-section whose axis is formed to include a bond at
one location.
[0027] When the opposing surfaces 14 of the pair of
35 hydroforming dies 11, 13 are brought into contact, the
middle section 15a of the cavity 15 forms a shape
substantially the same as the outer configuration of the
10 -
hydroformed product 5. The middle section 15a of the
cavity 15 in the first embodiment is formed in order from
the cylinder end to the cylinderless end with a region of
circular cross-sectional shape as shown in FIG. 4(a), a
5 region of rectangular cross-sectional shape as shown in
FIG. 4(b), a region of rectangular cross-sectional shape
as shown in FIG. 4(c), a region of rectangular crosssectional
shape as shown in FIG. 4(d), and a region of
circular cross-sectional shape as shown in FIG. 3(a). The
10 hydroformed product 5 produced by the hydroforming method
according to the first embodiment is formed to have an
outer configuration corresponding to the middle section
15a of such a cavity 15.
[0028 ] The cylinder end 15b of the cavity 15
15,
communicates with the exterior in the axial direction of
the metal tube 3 inserted in the cavity 15. A seal punch
33 attached to the forward end of the axial compression
cylinder 31 is mounted to be slidable in the axial
direction of the metal tube 3 inserted the cavity 15.
20 [0029 ] In the first embodiment, the cylinderless end
15c of the cavity 15 does not communicate with the
exterior in the axial direction of the metal tube 3
inserted in the cavity 15 and has a bottom face 15d
axially outward of the tube. The standalone punch 21 is
25 mounted at the cylinderless end 15c of the cavity 15 to
be slidable in the axial direction of the metal tube 3
inserted in the cavity 15.
[0030 ] When the pair of hydroforming dies 11, 13 is
closed, the standalone punch 21 operates to seal the tube
30 end 3a on the cylinderless end of the metal tube 3 and
compress the metal tube 3 from the cylinderless end. In
the first embodiment, the standalone punch 21 is
detachably mounted without engagement with the pair of
hydroforming dies 11, 13 or other members.
35 [0031] The standalone punch 21 is configured so that
its forward end 21a located on the side of the metal tube
3 inserted in the cavity 15 has the same outer shape as
- 11 -
the tube end 3a on the cylinderless end of the metal tube
3, and in the first embodiment, is configured to have a
solid circular cross-sectional shape. Moreover, the
standalone punch 21 is formed on its forward end face
5 with a sealing surface 21c capable of making surface
contact with the tube end face 3b on the cylinderless end
of the metal tube 3, and in the first embodiment, the
sealing surface 21c is formed orthogonal to the axial
direction of the metal tube 3 inserted in the cavity 15.
10 Furthermore, the standalone punch 21 is formed on its
rearward end face with an inclined surface 21d capable of
making surface contact with an inclined surface 41a of a
wedge member 41 or the like (explained later) when the
pair of hydroforming dies 11, 13 is closed. The inclined
15 surface 21d is formed at an angle to the axial direction
of the metal tube 3 inserted in the cavity 15.
[0032 ] The standalone punch 21 is preferably
structured to slide in the axial direction of the metal
tube 3 in the cavity 15 but to be restricted from
20 rotation around the tube axial direction. For example,
when the forward end 21a of the standalone punch 21 is
configured in a circular cross-sectional shape, as in the
first embodiment, it is possible to form its rearward end
21b in a rectangular, polygonal, elliptical or other
25 noncircular shape and give the cylinderless end 15c of
the cavity 15 a shape corresponding to the rearward end
21b of the standalone punch 21, so that rotation is
restricted when they are mated at the time of installing
the standalone punch 21 in the cavity 15. Moreover, when
30 the forward end 21a of the standalone punch 21 is formed
in a rectangular, polygonal, elliptical or other
noncircular shape, rotation is restricted irrespective of
the shape of the rearward end 21b of the standalone punch
21, and the shape of the rearward end 21b of the
35 standalone punch 21 need not be particularly defined in
this case.
[0033] In the first embodiment, the wedge member 41 is
- 12 -
attached to the upper hydroform die 13, i.e., the driven
one of the pair of hydroforming dies 11, 13, at the
cylinderless end 15c of the cavity 15. The wedge member
41 operates. to advance the standalone punch 21 when the
5 pair of hydroforming dies 11, 13 is closed. The wedge
member 41 is formed on its forward end face with the
inclined surface 41a that makes surface contact with the
inclined surface 21d of the standalone punch 21 when the
pair of hydroforming dies 11, 13 is closed.
10 [0034 ] In the first embodiment, a tube end arrester 51
is provided in the cavity 15 to be attached to the upper
hydroform die 13, i.e., the driven one of the pair of
hydroforming dies 11, 13. The tube end arrester 51 is
attached to the upper hydroform die 13, through a coil
15 spring or other biasing member 53, and a housing 15e is
formed in the cavity 15 to accommodate the tube end
arrester 51 when the'tube end arrester 51 moves out of
its initial position.
[0035] As shown in FIG. 3(b), the tube end arrester 51
20 is configured to contact the opposing surface 14 of one
hydroform die 11 when the pair of hydroforming dies 11,
13 is closed and thereafter be biased by the biasing
member 53. At this time, the tube end arrester 51 is
biased by the biasing member 53 so as to press down the
25 metal tube 3 in the cavity 15 of the hydroform die 11 on
the fixed side. As a result, the sealing of the tube end
3a of the metal tube 3 can be maintained during die
closing, as explained later. In the first embodiment, a
contact surface 51a provided on the tube end arrester 51
30 for contacting the metal tube 3 is formed to have a shape
corresponding to the outer shape of the tube end 3a of
the metal tube 3 so as to make surface contact with the
tube end 3a of the n3 over an extensive range.
[0036 ] In the first embodiment, the tube end arrester
35 51 is configured also to contact the standalone punch 21
when the pair of hydroforming dies 11, 13 is closed.
[0037 ] The hydroforming device 1 according to the
- 13 -
present invention is equipped with a pressure medium
supply unit, not shown in the drawings, for supplying
water, a rust-inhibitor-in-water emulsion or other
pressure medium W to the interior of the metal tube 3.
5 The first embodiment is configured to supply the pressure
medium W to the cylinder end through a pressure medium
supply hole 35 formed in the seal punch 33 of the axial
compression cylinder 31. Although the hydroforming=device
1 can be structured to supply the pressure medium W to
10 the interior of`the metal tube 3 from either the cylinder
end or the cylinderless end, supply from the cylinder end
can be realized with a simpler structure.
[0038 ] The details of the hydroforming method
according to the present invention are explained next
15 together with the operation of the aforesaid hydroforming
device. FIGs. 5 to 8 are diagrams for explaining the
hydroforming method.
[0039] First as shown in FIG. 5, the metal tube 3
serving as the starting material is inserted in the
20 hydroform die 11. The metal tube 3 inserted as the
material at this time is one that has been bent in
advance to a shape corresponding to the desired
hydroformed product 5. For example, in order to produce a
hydroformed product 5 that, as in the first embodiment,
25 is formed to have an axis Ll including two-dimensional
bending, the inserted metal tube 3 is formed to include
axial bending similar to the bending of the hydroformed
product 5. And when the metal tube 3 is inserted into the
hydroform die 11, the standalone punch 21 is inserted
30 together with it.
[0040 ] The pair of hydroforming dies 11, 13 is then
closed. The closing step is divided into a first half of
closing up to the point that the tube end 3a of the metal
tube 3 is sealed by the axial compression cylinder 31 and
35 a second half from after the sealing by the axial
compression cylinder 31 up to completion of the closing.
[0041] In the first half of the closing step, the
- 1.4 -
hydroform die 13 on the driven side is driven toward the
other hydroform die 11, and after the inclined surface
41a of the wedge member 41 comes into surface contact
with the inclined surface 21d of the standalone punch 21,
5 the inclined surface 41a of the wedge member 41 makes
sliding surface contact with the inclined surface 21d of
the standalone punch 21 in accordance with the amount of
driving of the hydroform die 13, thereby advancing=the
standalone punch 21 toward the metal tube 3. Therefore,
10 as shown in FIG. 6, the sealing surface 21c of the
standalone punch 21 is pressed onto the tube end face 3b
of the metal tube 3, whereafter the tube end 3a of the
cylinderless end of the metal tube 3 is kept sealed.
[ 0042] At this time, the pressure medium W is
15 preferably supplied gradually before and during the
closing step to complete the sealing of the tube end 3c
on the cylinder end of the metal tube 3 and the charging
of the pressure medium W substantially simultaneously
with the sealing of the tube end 3a on the cylinderless
20 end of the metal tube 3. This makes it possible for the
standalone punch 21 and seal punch 33 to promptly
compress the metal tube 3 internally charged with the
pressure medium W. The sealing of the tube end 3c on the
cylinder end of the metal tube 3 is performed by, inter
25 alia, using the axial compression cylinder 31 to advance
the seal punch 33 toward the metal tube 3 to press the
sealing surface 33a that is the end face on the forward
end of the seal punch 33 onto the tube end face 3d on the
cylinder end of the metal tube 3, as shown in FIG. 6(b).
30 [0043 ] In the second half of the closing step, the
inclined surface 41a of the wedge member 41 further
advances the standalone punch 21 in accordance with the
amount of driving of the hydroform die 13, whereby the
metal tube 3 is compressed in the axially inward
35 direction from the cylinderless end by the standalone
punch 21. At this time, the compression by the standalone
punch 21 is preferably started after completion of the
- 1.5 -
sealing of the two tube ends 3a and 3b of the metal tube
3 and the charging of the pressure medium. However,
depending on the shape and roughness of the tube end 3a
of the metal tube 3, the metal tube 3 may sometimes
5 already be somewhat compressed at the time the charging
of the pressure medium W and the sealing are completed.
Therefore, in order to resolve this issue, a
configuration like that of the second embodiment or third
embodiment set out below is preferably adopted to
10 compress the metal tube 3 after completion of the sealing
and charging of the pressure medium W.
[0044] Moreover, once the sealing of the two tube ends
3a and 3c of the metal tube 3 has been completed,
internal pressure can be applied to the metal tube 3 by
15 the pressure medium W during closing, as illustrated in
FIG. 7. Here, in the application of internal pressure to
the metal tube 3 during die closing, the tube ends 3a and
3c of the metal tube 3 tend to be swollen by the internal
pressure because closing of the pair of hydroforming dies
20 11, 13 has not been completed. At this time, it is
preferable at the stage preceding the application of
internal pressure to the metal tube 3 to bring the tube
end arrester 51 into contact with the opposing surface 14
of the hydroform die 11 and bias the metal tube 3 by
25 pressing it with the biasing member 53. This constrains
the swelling of the tube ends 3a and 3c of the metal tube
3 by the application of the pressure medium W internal
pressure and maintains the sealing of the tube ends 3a
and 3c of the metal tube 3. Worth noting is that when
30 the space between the pair of hydroforming dies 11, 13 is
smaller than the thickness of the metal tube 3, the
constraint by the pair of hydroforming dies 11, 13
ensures that even if the internal pressure deforms the
tube ends 3a and 3c of the metal tube 3, the metal tube 3
35 is not deformed to a degree that causes loss of the
sealing. In such case, therefore, the tube end arrester
51 is not necessary.
- 16
[0045] In the second half of the closing, the amount
of compression of the metal tube 3 by the standalone
punch 21 can be controlled by regulating the inclination
angles of the inclined surface 21d of the standalone
5 punch 21 and the inclined surface 41a of the wedge member
41, and their contact timing. Therefore, when it is, for
example, desired to promote injection of the material,
the amount of compression by the standalone punch 21 can
be increased by, for example, enlarging the inclination
10 angles and advancing the contact timing.
[0046] Moreover, in the first half and second half of
the closing, whether or not the metal tube 3 is to be
compressed from the cylinder end by the seal punch 33 of
the axial compression cylinder,31 can be decided as
15 desired.
[0047 ] As shown in FIG. 7, after the opposing surfaces
14 of the pair of hydroforming dies 11, 13 have come into
contact to complete the closing, the metal tube 3 can, if
necessary, be sharply formed as shown in FIG. 8 by
20 further increasing the internal pressure of the metal
tube 3 produced by the pressure medium W. If necessary in
such a case, the axial compression cylinder 31 can be
driven to compress the metal tube 3 from the cylinder
end.
25 [0048 ] Then, inter alia, the internal pressure
produced by pressure medium W is lowered, whereafter the
hydroformed product 5 is removed from the cavity 15 to
complete the series of operations.
[0049 ] In the production of a hydroformed product 5 of
30 a complicated shape including bending of the axis L1, the
present invention enables the metal tube 3 to be
compressed from both ends to inject the material In the
tube axial direction from both ends of the tube. As a
result, even a hydroformed product 5 of such complicated
35 shape can be readily produced. And in the production of a
hydroformed product 5 of such complicated shape,
installation of an axial compression cylinder is made
17
unnecessary at one end of the metal tube 3, so that the
conventionally required installation of a pair of axial
compression cylinders with mutually angled axes becomes
unnecessary to enable a proportional reduction of the
5 size of the hydroforming device. The elimination of one
of a pair of axial compression cylinders further enables
a commensurate reduction of the cost of realizing the
hydroforming device.
[0050] The present invention can also be configured as
10 in the second embodiment and third embodiment set out
below. In the following explanation of these embodiments,
constituents identical to constituents set out above are
assigned the same symbols so as not to require
explanation.
15 [0051 ] FIG. 9 is a set of partial side sectional views
showing the structures of hydroforming devices 1
according to a second embodiment and a third embodiment.
In the second embodiment and third embodiment, the
structure of the standalone punch 21 differs from than in
20 the first embodiment.
[0052 ] In the second embodiment, an insert member 2le
is shaped to be insertable into the tube end 3a of the
metal tube 3 when the standalone punch 21 is advanced in
the axial direction relative to the forward end of the
25 standalone punch 21. The insert member 21e of the
standalone punch 21 is formed to have an outer shape
substantially the same as the inner shape of the tube end
3a of the metal tube 3. In the second embodiment, the
insert member 21e of the standalone punch 21 is conformed
30 to the cross-sectionally circular tube end 3a of the
metal tube 3 by giving it a columnar shape with an
outside diameter substantially equal to the inside
diameter of the tube end 3a. Insertion of this insert
member 21e of the standalone punch 21 into the tube end
35 3a of the metal tube 3 causes the tube end 3a of the
metal tube 3 to be sealed by the insert member 21e of the
standalone punch 21.
- 18 -
[0053] When the tube end 3a of the metal tube 3 is
sealed by the standalone punch 21 in this manner, the
sealability of the tube end 3a of the metal tube 3 can be
further enhanced. Moreover, in this case, the tube end 3a
5 of the metal tube 3 can be pressed inward by the sealing
surface 21c of standalone punch 21 after completion of
the sealing by the insert member 21e of the standalone
punch 21 and the charging of the pressure medium W-,
thereby making it possible prevent the tube end 3a of the
10 metal tube 3 from being pressed inward by the standalone
punch 21 before the charging of the pressure medium W is
finished.
[0054 ] In the third embodiment, an 0-ring 61 made of
rubber or the like is attached, to the insert member 21e
15 of the standalone punch 21. The O-ring 61 is attached by
fitting it into a groove formed around the circumference
of the insert member 21e of the standalone punch 21. When
the insert member 21e of the standalone punch 21 is
inserted into the tube end 3a of the metal tube 3, the 0-
20 ring 61 is forced into contact with the inner peripheral
surface of the tube end 3a of the metal tube 3 to
reinforce the sealing of the tube end 3a of the metal
tube 3.
[0055] Use of the O-ring 61 thus further improves the
25 sealability of the tube end 3a of the metal tube 3.
[0056] While embodiments of the present invention are
set out in detail in the foregoing, the aforesaid
embodiments are nothing more than concretely defined
examples for illustrating implementation the present
30 invention and are not to be construed as limiting the
technical scope of the present invention.
[0057] For example, although hydroforming device 1 was
described as having the wedge member 41 in the aforesaid
embodiments, the wedge member 41 can be eliminated by
35 forming the cavity 15 of the hydroform die 13 to have an
inclined surface whose shape and location are the same as
that of the inclined surface 41a of the wedge member 41.
19 -
EXAMPLE
[0058 ] The effects of the present invention are
explained further with an example in the following. In
5 this example, the possibility of actually performing the
hydroforming according to the present invention on a
metal tube 3 was checked using a hydroforming device 1
like that shown in FIG. 10. FIG. 10(a) is a top sectional
view. FIG. 10(b) is a sectional view taken along line J-J
10 in FIG. 10(a). FIG. 10(c) is a sectional view taken along
line K-K in FIG. 10(a), where the tube expansion ratio at
the section is 70%. FIG. 10(d) is a sectional view taken
along line L-L in FIG. 10(a), where the tube expansion
ratio at the section is 17%. FIG. 10(e) is a sectional
15 view taken along line M-M in FIG.. 10(a), where the tube
expansion ratio at the section is 23%.
[0059] The metal tube 3 in this example was a steel
tube of 60.5 mm outside diameter, 2.5 mm wall thickness,
and 500 mm total length. The tube used was a STKM11A
20 carbon steel tube for machine structural use conforming
to JIS G3445. The metal tube 3 was rotary-draw bent
beforehand to impart a bending radius of 181.5 mm and a
bending angle of 55°.
[0060] The hydroforming device 1 used in this example
25 was the same as that described in the first embodiment.
The inclined surface 21d of the standalone punch 21 used
was inclined 30° relative to a plane orthogonal to the
axial direction.
[0061] The metal tube 3 was inserted in the hydroform
30 die 11 with the opposite tube end faces 3b and 3d
respectively spaced 5 mm away from the sealing surface
21c of the standalone punch 21 and the sealing surface
33a of the seal punch 33. The standalone punch 21 and
wedge member 41 were set so that the inclined surface 21d
35 of the standalone punch 21 and the inclined surface 41a
of the wedge member 41 made mutual surface contact 26 mm
before the bottom dead center of the upper hydroform die
- 20
13. And they were set so that following the mutual
surface contact between the inclined surfaces 21d and
41a, the standalone punch 21 would advance about 15 mm in
the tube axial direction by completion of the die
5 closing. The tube end arrester 51 was set so as to
contact the opposing surface 14 of the lower hydroform
die 11 30 mm before the bottom dead center of the upper
hydroform die 13.
[0062 ] In the actual hydroforming, first, as shown in
10 FIG. 10, the metal tube 3 and standalone punch 21 were
inserted in the hydroform die 11, then, as shown in FIG.
11(a) and (b), die closing was performed by lowering the
upper hydroform die 13 while supplying pressure medium W
from the seal punch 33 on the side of the axial
15 compression cylinder 31. As explained earlier, the
setting was such that during the die closing the inclined
surface 41a of the wedge member 41 advanced the
standalone punch 21 by 15 mm in the tube axial direction,
and the tube end 3a on the cylinderless end of the metal
20 tube 3 came to be pressed in by 10 mm from its initial
position when the bottom dead center was reached. The
setting was such that, simultaneously during the die
closing, the seal punch 33 of the axial compression
cylinder 31 also advanced by 15 mm in the tube axial
25 direction. As a result, the tube end 3c on the cylinder
end of the metal tube 3 was similarly pressed in by
10 mm. The internal pressure produced in the metal tube 3
by the pressure medium W was set to reach 34 MPa while
the two tube ends 3a and 3c of the metal tube 3 were
30 being pressed in by the standalone punch 21 and the seal
punch 33.
[0063 ] After completion of the die closing, thu upper
hydroform die 13 was pressed down with a clamping force
of 10,000 M. In this state, as shown in FIG. 11(c) and
35 FIG. 11(d), the internal pressure by the pressure medium
W was increased from 34 MPa to 38 MPa, whereafter the
tube end 3c on the cylinder end of the metal tube 3 was
- 21 -
pressed in an additional 20 run by the seal punch 33. The
tube end 3c on the cylinder end of the metal tube 3
therefore came to be pressed in a total of 30 mm,
including the 10 mm that it was pressed in during die
5 closing. Next, with the axial compression cylinder 3]_
kept in a fixed position, only the internal pressure by
the pressure medium W was increased to 150 MPa to sharply
shape the metal tube 3.
[0064 ] After the metal tube 3 had been shaped into the
10 desired hydroformed product 5, the internal pressure by
the pressure medium W was lowered, the axial compression
cylinder 31 was retracted in the axial direction, and the
hydroform die 13 was lifted, whereafter the hydroformed
product 5 was removed from the, hydroform die 13.
15 [0065 ] The aforesaid series of operations made it
possible to produce the hydroformed product 5 shaped to
include axial bending using the invention hydroforming
device 1 equipped with only one axial compression
cylinder 31.
20 [0066] Moreover, in this example the sealing of the
metal tube 3 by the standalone punch 21 was performed
using the standalone punch 21 sealing surface 21c formed
orthogonal to the axial direction of the metal tube 3.
However, a decrease in initial water leakage was realized
25 by utilizing the standalone punch 21 which, as in the
second embodiment shown in FIG. 9(a), was formed with the
columnar insert member 21e having an outer diameter
substantially equal to the 55.5 mm inner diameter of the
metal tube 3. In addition, initial water leakage was
30 almost totally absent when utilizing the standalone punch
21 with the O-ring 61 attached to its insert member 21e,
as in the third embodiment shown in FIG. 9(b).
INDUSTRIAL APPLICABILITY
35 [0067 ] As set out above, the present invention enables
easy production of even a hydroformed product of
complicated shape including axial bending. The present
- 22 -
invention therefore expands the range of hydroformed
product application and enables unification of components
and weight reduction. Particularly worth noting is that
application to automobile parts helps to reduce vehicle
5 weight, which in turn improves fuel economy and thus
contributes to the alleviation of global warming.
Moreover, application can be expected to expand into
industrial sectors that have so far seen little
utilization, such as home appliances, furniture,
10 construction machinery parts, two-wheeled vehicle parts,
and construction materials. The present invention has
high usefulness in industry.
15
20
25
30
35
Explanation of Reference Symbols
[0068 ] 1 Hydroforming device
3 Metal tube
3a (Cylinderless end) tube end
3b (Cylinderless end) tube end
3c (Cylinder end) tube end
3d (Cylinder end) tube end
5 Hydroformed product
5a Axis
11 Hydroform die
13 Hydroform die
14 Opposing surface
15 Cavity
15a Middle section
15b Cylinder end
15c Cylinderless end
15d Bottom face
15e Housing
21 Standalone punch
21a Forward end
21b Rearward end
21c Sealing surface
21d Inclined surface
21e Insert member
- 23 -
10
31 Axial compression cylinder
33 Seal punch
33a Sealing surface
35 Pressure medium supply hole
41 Wedge member
41a Inclined surface
51 Tube end arrester
51a Contact surface
53 Biasing member
61 O-ring
W Pressure medium

CLAIMS
1. A hydroforming method wherein no axial
compression cylinder is installed at one end of a metal
tube inserted in a hydroforming die assembly, an axial
5 compression cylinder is installed only at another end of
the metal tube, the metal tube is compressed axially by
the axial compression cylinder, and a pressure medium is
supplied into the interior of the metal tube sealed at
both ends to apply internal pressure, which hydroforming
10 method is characterized by comprising:
a step prior to closing the hydroforming
die assembly of inserting the metal tube into the
hydroforming die assembly and a standalone punch at one
end of the metal tube; and
15 a step at the time of closing the
hydroforming die assembly of using the closing force of
the hydroforming die assembly to advance the standalone
punch in the tube axial direction to seal the one end of
the metal tube with the standalone punch and
20 simultaneously compress the metal tube in the axial
direction.
2. A hydroforming method as set out in claim 1,
characterized in that when the standalone punch is
advanced in the tube axial direction the one end of the
25 metal tube is sealed by inserting an insert member at a
forward end of the standalone punch into the interior of
the one end of the metal tube.
3. A hydroforming method as set out in claim 2,
characterized in that when the standalone punch is
30 advanced in the tube axial direction the insert member of
the standalone punch, which has an attached 0-ring, is
inserted into the interior of the one end of the metal
tube to reinforce the seal of the one end of the metal
tube by the O-ring.
35 4. A hydroforming device wherein no axial
compression cylinder is installed at one end of a metal
tube inserted in a hydroforming die assembly, an axial
- 25 -
compression cylinder is installed only at another end of
the metal tube, the axial compression cylinder compresses
the metal tube in the axial direction, and a pressure
medium is supplied into the interior of the metal tube
5 sealed at both ends to apply pressure, which hydroforming
device is characterized by comprising: -
. a standalone punch inserted in the
hydroforming die assembly together with the metal tube at
one end of the metal tube,
10 the closing force of the hydroforming die
assembly at the time of closing the hydroforming die
assembly being used to advance the standalone punch in
the tube axial direction to seal the one end of the metal
tube with the standalone punch and simultaneously
15 compress the metal tube in the'axial direction.
5. A hydroforming device as set out in claim 4,
characterized by a structure which, when the standalone
punch is advanced in the tube axial direction, enables
sealing of the one end of the metal tube by inserting an
20 insert member at a forward end of the standalone punch
into the interior of the one end of the metal tube.
6. A hydroforming device as set out in claim 5,
characterized in that an 0-ring is attached to the insert
member of the standalone punch.