U.S. patent application number 11/123196 was filed with the patent office on 2005-11-24 for profile element pipe for hydraulic bulging, hydraulic bulging device using the element pipe, hydraulic bulging method using the element pipe, and hydraulically bulged product.
Invention is credited to Kojima, Masayasu, Tomizawa, Atsushi.
Application Number | 20050257587 11/123196 |
Document ID | / |
Family ID | 32310483 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050257587 |
Kind Code |
A1 |
Tomizawa, Atsushi ; et
al. |
November 24, 2005 |
Profile element pipe for hydraulic bulging, hydraulic bulging
device using the element pipe, hydraulic bulging method using the
element pipe, and hydraulically bulged product
Abstract
A profile element pipe for hydraulic bulging of the present
invention has a peripheral length with an outer diameter gradually
increasing or decreasing from one axial side toward the other
thereof and has a parallel part formed on at least one end thereof.
According to a bulging device and a bulging method using this
profile element pipe, for example, even when a profile steel pipe
having a cross sectional shape varying in the axial direction as in
a tapered pipe is hydraulically bulged, a bulging in which an
internal pressure loading and an shaft pressing are combined with
each other can be performed to provide a larger expansion ratio
than a conventional case and a joining and socket connection
thereof to the other part can also be easily performed.
Inventors: |
Tomizawa, Atsushi;
(Minoo-shi, JP) ; Kojima, Masayasu;
(Takarazuka-shi, JP) |
Correspondence
Address: |
Christopher W. Brody
CLARK & BRODY
Suite 250
1090 Vermont Avenue, NW
Washington
DC
20005
US
|
Family ID: |
32310483 |
Appl. No.: |
11/123196 |
Filed: |
May 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11123196 |
May 6, 2005 |
|
|
|
PCT/JP03/14284 |
Nov 10, 2003 |
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Current U.S.
Class: |
72/61 |
Current CPC
Class: |
B21D 26/033 20130101;
B21D 26/045 20130101 |
Class at
Publication: |
072/061 |
International
Class: |
B21D 026/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2002 |
JP |
2002-325801 |
Claims
What is claimed is:
1. A profile element pipe for hydraulic bulging, wherein said
profile element pipe has a peripheral length with an outer diameter
gradually increasing or decreasing from one axial side to the other
thereof and a parallel part formed on at least one end thereof.
2. The profile element pipe for hydraulic bulging according to
claim 1, wherein a length of said parallel part is equal to, or
more than, a total length of an amount of shaft pressing subjected
in hydraulic bulging and a length necessary for sealing during
hydraulic bulging.
3. The profile element pipe for hydraulic bulging provided for
producing a hydraulically bulged product having a rectangular cross
section or a polygonal cross section according to claim 2, wherein
a radius R of curvature of a corner part in said parallel part is
varied in accordance with a change in a peripheral length in which
an outer diameter of the profile element pipe is gradually
increased or decreased.
4. A hydraulic bulging device characterized by comprising: a pair
of dies, and shaft pressing tools also serving as sealing tools, in
which front end portions of the tools are inserted into both ends
of said dies, for holding said profile element pipe according to
claim 1, while sandwiching the profile element pipe with said dies,
wherein a filling hole for working liquid is provided at any one of
said shaft pressing tools and parallel parts are provided on at
least one end-portion inner surface of said dies and an outer
surface of said shaft pressing tool corresponding to this
end-portion inner surface, respectively.
5. A hydraulic bulging device characterized by comprising: a pair
of dies, and shaft pressing tools also serving as sealing tools, in
which front end portions of the tools are inserted into both ends
of said dies, for holding said profile element pipe according to
claim 2 while sandwiching the profile element pipe with said dies,
wherein a filling hole for working liquid is provided at any one of
said shaft pressing tools and parallel parts are provided on at
least one end-portion inner surface of said dies and an outer
surface of said shaft pressing tool corresponding to this
end-portion inner surface, respectively.
6. A hydraulic bulging device characterized by comprising: a pair
of dies, and shaft pressing tools also serving as sealing tools, in
which front end portions of the tools are inserted into both ends
of said dies, for holding said profile element pipe according to
claim 3, while sandwiching the profile element pipe with said dies,
wherein a filling hole for working liquid is provided at any one of
said shaft pressing tools and parallel parts are provided on at
least one end-portion inner surface of said dies and an outer
surface of said shaft pressing tool corresponding to this
end-portion inner surface, respectively.
7. The hydraulic bulging device according to claim 4, wherein when
an amount of shaft pressing on the small diameter side is defined
as .delta.L, an amount of shaft pressing on the large diameter side
of is defined as .delta.L', a length necessary for sealing on the
small diameter side is defined as L0, and a length necessary for
sealing on the large diameter side is defined as L0', a length of a
parallel part provided on the small diameter side of said die is
.delta.L+L0 or more, a length of a parallel part provided on the
large diameter side of said die is .delta.L'+L0' or more, and a
length of a parallel part provided on the small diameter side of
the shaft pressing tool is .delta.L+L0 or more, and a length of a
parallel part provided on the large diameter side of the shaft
pressing tool is L0' or more.
8. The hydraulic bulging device according to claim 5, wherein when
an amount of shaft pressing on the small diameter side is defined
as .delta.L, an amount of shaft pressing on the large diameter side
of is defined as .delta.L', a length necessary for sealing on the
small diameter side is defined as L0, and a length necessary for
sealing on the large diameter side is defined as L0', a length of a
parallel part provided on the small diameter side of said die is
.delta.L+L0 or more, a length of a parallel part provided on the
large diameter side of said die is .delta.L'+L0' or more, and a
length of a parallel part provided on the small diameter side of
the shaft pressing tool is .delta.L+L0 or more, and a length of a
parallel part provided on the large diameter side of the shaft
pressing tool is L0' or more.
9. The hydraulic bulging device according to claim 6, wherein when
an amount of shaft pressing on the small diameter side is defined
as .delta.L, an amount of shaft pressing on the large diameter side
of is defined as .delta.L', a length necessary for sealing on the
small diameter side is defined as L0, and a length necessary for
sealing on the large diameter side is defined as L0', a length of a
parallel part provided on the small diameter side of said die is
.delta.L+L0 or more, a length of a parallel part provided on the
large diameter side of said die is .delta.L'+L0' or more, and a
length of a parallel part provided on the small diameter side of
the shaft pressing tool is .delta.L+L0 or more, and a length of a
parallel part provided on the large diameter side of the shaft
pressing tool is L0' or more.
10. A hydraulic bulging method, wherein after producing a profile
element pipe having a peripheral length with an outer diameter
gradually increasing or decreasing from one axial side toward the
other thereof and having a parallel part formed on at least one end
thereof by using a hydraulic bulging device according to claim 4,
said profile element pipe is subjected to hydraulic bulging
combined with an internal pressure loading and a shaft
pressing.
11. A hydraulic bulging method, wherein after producing a profile
element pipe having a peripheral length with an outer diameter
gradually increasing or decreasing from one axial side toward the
other thereof and having a parallel part formed on at least one end
thereof by using a hydraulic bulging device according to claim 5,
said profile element pipe is subjected to hydraulic bulging
combined with an internal pressure loading and a shaft
pressing.
12. A hydraulic bulging method, wherein after producing a profile
element pipe having a peripheral length with an outer diameter
gradually increasing or decreasing from one axial side toward the
other thereof and having a parallel part formed on at least one end
thereof by using a hydraulic bulging device according to claim 6,
said profile element pipe is subjected to hydraulic bulging
combined with an internal pressure loading and a shaft
pressing.
13. A bulged product wherein a profile element pipe having a
peripheral length with an outer diameter gradually increasing or
decreasing from one axial side toward the other thereof and having
a parallel part formed on at least one end thereof is set in a die
of a hydraulic bulging device according to claim 4, and said
profile element pipe is subjected to hydraulic bulging combined
with an internal pressure loading and a shaft pressing.
14. A bulged product wherein a profile element pipe having a
peripheral length with an outer diameter gradually increasing or
decreasing from one axial side toward the other thereof and having
a parallel part formed on at least one end thereof is set in a die
of a hydraulic bulging device according to claim 5, and said
profile element pipe is subjected to hydraulic bulging combined
with an internal pressure loading and a shaft pressing.
15. A bulged product wherein a profile element pipe having a
peripheral length with an outer diameter gradually increasing or
decreasing from one axial side toward the other thereof and having
a parallel part formed on at least one end thereof is set in a die
of a hydraulic bulging device according to claim 6, and said
profile element pipe is subjected to hydraulic bulging combined
with an internal pressure loading and a shaft pressing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a profile element pipe for
hydraulic bulging, a hydraulic bulging device using the profile
element pipe, a hydraulic bulging method using the profile element
pipe, and a hydraulically bulged product subjected to the hydraulic
bulging.
[0003] 2. Description of the Related Art
[0004] A hydraulic bulging has more merits as compared with other
forming or forming methods. For example, since a profile element
pipe can be hydraulically bulged to such an intricate configuration
part having different cross-sections in the longitudinal direction
of the product, machine parts, which require welding and joining in
a conventional method, can be formed in one-piece. Further, since
the hydraulic bulging generates work hardening over the entire
hydraulically bulged portions, even if a soft element pipe is used,
a product having high strength can be obtained.
[0005] Further, in the hydraulic bulging, the bulged product has
small springback and a dimensional accuracy of the product is
excellent (shape freeze properties are excellent). Thus a process
for refining product dimension is not required and the omission of
the process is effected.
[0006] In the hydraulic bulging, the above-mentioned excellent
merits are appreciated and the hydraulic bulging has been
particularly adopted as a production method of automotive parts in
recent years.
[0007] Generally, in case that a pipe is formed by hydraulic
bulging, a straight pipe having a uniform circular cross-section in
the longitudinal direction of the pipe (hereinafter referred to as
"straight element pipe") is used as a material, and after this
material was subjected to bending and crushing as a "pre-forming"
hydraulic bulging is performed as a final working process. By
taking such a series of working processes, a hydraulically bulged
product can be manufactured by processing a straight element pipe
to a product of a predetermined configuration.
[0008] FIGS. 1A and 1B are views showing a final working process of
hydraulic bulging by which a product is obtained by using a
conventional straight element pipe. As shown in FIGS. 1A and 1B, in
the hydraulic bulging of the final process, a working liquid is
injected into a straight element pipe P1 set in an upper die 1 and
a lower die 2 through a filling hole 3 to load internal pressure.
Further, in addition to the loading of internal pressure, the
element pipe P1 is axially pressed (hereinafter referred to as
"shaft pressing") from both ends of the pipe by shaft pushing tools
4 and 5 also serving as sealing tools.
[0009] In the hydraulic bulging, the loading of internal pressure
and the shaft pressing are combined with each other so that a
product P2 having various cross-sectional shapes is produced. It is
noted that the shaft pushing tools 4 and 5 serving also as sealing
tools are connected to a hydraulic cylinder (not shown) and during
hydraulic bulging its axial position or shaft pressing force are
controlled.
[0010] The shaft pressing from a pipe end in the axial direction in
the hydraulic bulging has such effects that a metal flow during
bulging of an element pipe is promoted and an expansion limit of
the element pipe is improved. Thus, in the hydraulic bulging, the
shaft pressing from the pipe end is an extremely important working
process.
[0011] Specifically, when the hydraulic bulging is performed only
by the loading of internal pressure without performing shaft
pressing, the wall thickness of the straight element pipe P1 is
remarkably decreased with bulging of the straight element pipe P1.
Therefore, the straight element pipe P1 ends up in rupture halfway
through hydraulic bulging. Namely, it amounts to narrow a formable
range (pipe expansion limit) of the straight element pipe P1.
[0012] Further, the hydraulic bulging has a problem attributable to
a shape of the element pipe. As described above, even if an
intricate configuration having different axial cross-sectional
shapes can be obtained as one of the merits of the hydraulic
bulging, the configuration of a worked product which can be
obtained is limited.
[0013] For example, when the relationship of the increase ratio in
a peripheral length (pipe expansion ratio)=[(outer peripheral
length of a worked product at the portion/circumferential length of
element pipe)-1].times.100% is defined, the limit of increase ratio
in a peripheral length (pipe expansion ratio) is at most 25% or so
except for a region of the pipe end portion where shaft pressing is
effective, although the ratio depends on shape properties required
for a bulged product or conditions (material, sheet thickness) of
an element pipe to be used.
[0014] The hydraulic bulging cannot be performed beyond the limit
of the increase ratio in the peripheral length (pipe expansion
ratio). To increase a degree of freedom in a configuration design
of a worked product and to obtain a worked product having a more
intricate cross-sectional shape, it is necessary to contrive ways
regarding the shape of an element pipe under a restricted condition
of such an increase ratio in a peripheral length (pipe expansion
ratio).
[0015] To deal with this problem, there has been proposed to use a
substantially conical element pipe (hereinafter referred to as
"tapered element pipe") instead of a straight element pipe. Namely,
by using the tapered element pipe, the increase ratio in a
peripheral length due to working can be suppressed to a low level
for parts which are difficult to be formed by using a straight
element pipe, for example, for parts whose peripheral length varies
in the axial direction, thereby enabling predetermined working
shapes to be formed (see for example, Japanese Patent Application
Publication No. 2001-321842, page 1, FIG. 2).
[0016] However, when hydraulic bulging is performed by using a
tapered element pipe whose cross-sectional shape varies in the
axial direction, in case of using a shaft pressing tool for the
straight element pipe shown in FIG. 1, it is found difficult to
apply the shaft pressing on the tapered element pipe.
[0017] FIG. 2 is a view explaining a problem, which arises when
shaft pressing with a conventional shaft-pressing tool for a
straight element pipe was applied on a tapered element pipe. As
shown in FIG. 2, the shaft pressing itself on a tapered element
pipe TP1 cannot be applied on the large diameter side, although the
shaft pressing itself on the tapered element pipe TP1 can be
applied on the small diameter side. However, as a shaft pressing
tool 4 advances into forms 1 and 2 with the shaft pressing,
insufficient restriction of inner and outer surfaces of the tapered
element pipe TP1 by the shaft pressing tool 4 side take places,
thus likely leading up to seal leakage occurs.
[0018] FIGS. 3A to 3C are views explaining hydraulic bulging
process using a conventional tapered element pipe, where FIG. 3A
shows a state before processing, FIG. 3B shows a state before
loading internal pressure, and FIG. 3C shows a state at the finish
of processing.
[0019] In the conventional hydraulic bulging using the tapered
element pipe TP1, as shown in FIGS. 3A to 3C, shaft pressing tools
6 and 7, each having a tapered front end, are to be used. However,
since shaft pressing cannot be performed, hydraulic bulging is
generally completed only by loading internal pressure without shaft
pressing. It is noted that TP2 in FIGS. 3A to 3C denotes a tapered
element pipe subsequent to pipe-end pre-forming and TP3 denotes a
hydraulically bulged product.
[0020] In the working process shown in FIGS. 3A to 3C, since the
shaft pressing of the tapered element pipe TP2 cannot be performed,
the hydraulic bulging can be performed only in a limited range of
forming to such a degree that rupture does not occur in a stage of
hydraulic bulging, as described above. Therefore, in the hydraulic
bulging, a merit of using the tapered element pipe is not in fact
fully utilized.
[0021] Thus, in case where hydraulic bulging is performed using a
tapered element pipe, a technological development, which enables
shaft pressing from the pipe end in the axial direction in addition
to loading internal pressure on the element pipe, has been
desired.
[0022] When hydraulic bulging is performed in a conventional
tapered element pipe, there is a problem which arises when a
hydraulically bulged product is joined with another member, other
than the problem that shaft pressing is difficult.
[0023] FIGS. 4A to 4C are views explaining a problem when a
hydraulically bulged product having a rectangular cross-section is
joined, wherein FIG. 4A shows a shape of a conventional
hydraulically bulged product, and FIG. 4B shows a shape of a
hydraulically bulged product according to the present invention,
along with denoting inclinations of pipe end portions with respect
to the axial direction of each worked product, and wherein FIG. 4C
shows a configuration of a typical cross-section of the
hydraulically bulged products in FIG. 4A or 4B.
[0024] The hydraulically bulged product PT3 using a conventional
tapered element pipe as a material is inclined in the pipe end
portions by .theta. as shown in FIG. 4A. Thus, since accuracy
cannot be ensured in welding and joining with another member, the
joining with another member or the like is not easy.
[0025] Further, when an end of the pipe is socketed into another
part and connected thereto, that is a socket connection, the
accuracy cannot be ensured as well. Thus positioning of the tapered
element pipe becomes difficult. Consequently, finishing process
such as cutting off of very ends of hydraulically bulged product is
required.
SUMMARY OF THE INVENTION
[0026] The present invention has been made taking the
above-mentioned conventional problems into consideration, and the
object of the present invention is to provide a profile element
pipe for hydraulic bulging, a hydraulic bulging device using the
element pipe, a hydraulic bulging method using the element pipe,
and hydraulically bulged product, wherein in hydraulic bulging
using the profile element pipe having various cross sectional
shapes in the axial direction, shaft pressing is enabled from the
pipe ends in the axial direction in addition to loading internal
pressure on the element pipe, thereby enabling a larger pipe
expansion ratio to be achieved.
[0027] To attain the above-mentioned object, a profile element pipe
for hydraulic bulging according to the present invention is
characterized in that the profile element pipe has a varied
peripheral length over the axial length with an outer diameter
gradually increasing or decreasing from one axial side toward the
other thereof and has a parallel part formed on at least one pipe
end thereof.
[0028] In the profile element pipe for hydraulic bulging of the
present invention, a length of the parallel part is preferably not
less than the total of an amount of shaft pressing performed in the
hydraulic bulging and a length necessary for sealing during
bulging.
[0029] Further, in the profile element pipe to be used for
manufacturing a hydraulically bulged product having a rectangular
cross section or a polygonal cross section, it is desirable that a
radius R of curvature of a corner part in the parallel part is
varied in accordance with a change of a peripheral length in which
an outer diameter of the profile element pipe is gradually
increased or decreased.
[0030] And if the profile element pipe of the present invention
comprising such a configuration is set into a form of a hydraulic
bulging device according to the present invention by respectively
providing parallel parts on at least one of end portion inner
surfaces of both an upper die and a lower die and on an outer
surface of a shaft pressing tool which matches with pipe-end inner
surfaces, an internal pressure loading and a shaft pressing in
combined manner can be applied.
[0031] As described above, in the hydraulic bulging, a larger pipe
expansion ratio can be obtained than before, and the joining with
other parts can be easily performed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIGS. 1A and 1B are views explaining a final process in
hydraulic bulging process by which a product is obtained by using a
conventional straight element pipe.
[0033] FIG. 2 is a view explaining a problem, which arises when
shaft pressing of a tapered element pipe is performed with a
conventional shaft-pressing tool for a straight element pipe.
[0034] FIGS. 3A to 3C are views explaining hydraulic bulging
processes using a conventional tapered element pipe, where FIG. 3A
shows a state before bulging, FIG. 3B shows a state before loading
internal pressure, and FIG. 3C shows a state at the end of
bulging.
[0035] FIGS. 4A to 4C are views explaining a problem which is
generated when a hydraulically bulged product having a rectangular
cross-section is joined, where FIG. 4A shows a shape of a
hydraulically bulged product using a conventional tapered element
pipe, FIG. 4B shows a shape of a hydraulically bulged product
according to the present invention, and FIG. 4C shows a shape of a
cross-section of these products.
[0036] FIGS. 5A and 5B are cross-sectional views showing an example
of the shape of a tapered pipe constituting a profile element pipe
for hydraulic bulging according to the present invention.
[0037] FIGS. 6A and 6B are views illustrating the entire
configuration of the profile element pipes according to the present
invention, and particularly FIG. 6A shows an example in which
parallel parts each having a circular cross section are formed on
both ends of the tapered part having circular cross sections and
FIG. 6B shows an example in which parallel parts each having a
rectangular cross section are formed on both ends of the tapered
part having rectangular cross sections.
[0038] FIGS. 7A and 7B are views illustrating the entire
configuration of other profile element pipes according to the
present invention, and show examples having a transitional part
between a parallel part on the large diameter side and a central
tapered part.
[0039] FIGS. 8A to 8C are views explaining a method of producing
the profile element pipe according to the present invention, having
a parallel part on the end portion of a large diameter side
desired, where FIG. 8A is an entire perspective view, FIG. 8B is a
developed view and FIG. 8C is a view showing a trapezoidal shape
similar to the developed view shown in FIG. 8B.
[0040] FIGS. 9A to 9C are views showing another example of the
profile element pipe according to the present invention along with
a shaft pressing tool used in the example, where FIG. 9A is an
entire perspective view, FIG. 9B is an enlarged view of the shaft
pressing tool on the small diameter side and FIG. 9C is an enlarged
view of the shaft pressing tool, which also serves as a small
diameter side sealing tool used in the profile element pipe.
[0041] FIGS. 10A to 10C are views showing shapes of end surfaces of
the profile element pipe of the present invention used in case
where a small diameter side of a hydraulically bulged product has a
rectangular cross section, where FIG. 10A is a cross-sectional view
of the pipe at a position away from the pipe end on the small
diameter side by .delta.L+L0, FIG. 10C is a cross-sectional view of
the end portion, and FIG. 10B is a cross-sectional view at an
arbitrary intermediate position of the pipe.
[0042] FIGS. 11A to 11C are views showing shapes of end surfaces of
the profile element pipe of the present invention used in case
where a large diameter side of a hydraulically bulged product has a
rectangular cross section, and particularly FIG. 11A is a
cross-sectional view at a position away from the pipe end on the
large diameter side by .delta.L'+L0', FIG. 11C is a cross-sectional
view of the end portion of the pipe, and FIG. 11B is a
cross-sectional view at the arbitrary intermediate position of the
pipe.
[0043] FIGS. 12A to 12C are views illustrating cross-sectional
shapes in case that hydraulically bulged products have trapezoidal
cross-sections.
[0044] FIGS. 13A to 13C are views illustrating cross-sectional
shapes in case that hydraulically bulged products have L-shaped
cross-sections.
[0045] FIGS. 14A to 14C are views explaining a first example of a
method of the present invention, and shows the case that a parallel
part of an end portion of profile element pipe is formed prior to
hydraulic bulging, where FIG. 14A is a cross-sectional view showing
of a state of setting a tapered pipe on dies, FIG. 14B is a
cross-sectional view showing a state where the parallel part was
formed before hydraulic bulging, and FIG. 14C is a cross-sectional
view showing a state where hydraulic bulging has been
completed.
[0046] FIGS. 15A to 15C are views showing relationships among an
upper die on the small diameter side, a shaft pressing tool also
serving as a sealing tool and the end portion of profile element
pipe, where FIGS. 15A to 15C are views elaborating on FIGS. 14A to
14C in terms of the dimensional parameter.
[0047] FIGS. 16A to 16C are views showing relationships among an
upper die on the large diameter side, the shaft pressing tool also
serving as a sealing tool and the end portion of profile element
pipe, where FIGS. 16A to 16C are views elaborating on FIGS. 14A to
14C in terms of the dimensional parameter.
[0048] FIGS. 17A to 17C are views explaining a second example of
the method of the present invention, and show a case where the
parallel part of the end portion of profile element pipe is formed
before setting the pipe on a die. Particularly, FIG. 17A is a
cross-sectional view showing a state of setting the profile element
pipe on the die, FIG. 17B is a cross-sectional view showing a state
before hydraulic bulging, and FIG. 17C is a cross-sectional view
showing a state after hydraulic bulging.
[0049] FIGS. 18A to 18C are views explaining a third example of the
method of the present invention, and show another example of the
case where the parallel part of the end portion of profile element
pipe is formed before setting the pipe on the die. FIGS. 18A to 18C
are the same as in the case of FIGS. 17A to 17C.
[0050] FIGS. 19A to 19C are explanatory views showing a fourth
example of the method of the present invention, and show a
configuration example in which an inner cavity of the parallel part
at the large diameter side is axially monotonously increased with
reference to the pipe-end of the large diameter side. FIGS. 19A to
19C are the same as in the case of FIG. 17A to 17C.
[0051] FIGS. 20A to 20D are views showing configuration examples of
the shaft pressing tool, which is a component constituting the
hydraulic bulging device of the present invention, also serving as
a sealing tool.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] FIGS. 5A to 5B are cross-sectional views showing an example
of the shape of tapered pipe constituting a profile element pipe of
the present invention. A profile element pipe 11 for hydraulic
bulging of the present invention is a profile element pipe to be
provided for hydraulic bulging, has a peripheral length with an
outer diameter gradually increasing or decreasing over axial length
from one axial side toward the other thereof and forms parallel
parts 11a, 11b on at least one pipe-end (both pipe ends of a small
diameter side and a large diameter side have parallel parts in the
examples shown in FIGS. 5A and 5B).
[0053] In the profile element pipe for hydraulic bulging according
to the present invention, it is desirable that lengths of the
parallel parts 11a, 11b are equal to or more than a total length of
an amount of shaft pressing in the hydraulic bulging and a length
necessary for sealing.
[0054] FIGS. 6A and 6B are views illustrating the entire
configuration of profile element pipe according to the present
invention, where FIG. 6A shows an example in which parallel parts
each having a circular cross section are formed on both ends of
tapered part having circular cross sections and FIG. 6B shows an
example in which parallel parts having a rectangular cross section
are formed on both ends of the tapered part having rectangular
cross sections.
[0055] Here, the example shown in FIG. 5A is elaborated by using
FIGS. 6A and 6B. FIG. 6A shows the rudimental basic form, in which
parallel parts 11a and 11b each having a circular cross-section are
formed on both ends of tapered part having circular
cross-sections.
[0056] FIG. 6B is an example in which parallel parts 11a and 11b
each having a rectangular cross-section are formed on both ends of
tapered part having rectangular cross-sections. In the example
shown in FIG. 6B, the parallel parts 11a and 11b have a
cross-section shown in FIG. 10A to be described later on a small
diameter side 11a and have a cross-section shown in FIG. 11C to be
described later on a large diameter side 11b over the entire
length.
[0057] FIGS. 7A and 7B are views illustrating the entire
configurations of other profile element pipes according to the
present invention, and show examples having a transitional portion
between a parallel part on the large diameter side and a central
tapered part.
[0058] Next, the details of the example shown in FIG. 5B will be
described by using FIGS. 7A and 7B. FIG. 7A shows a view in which
parallel parts 11a and 11b each having a circular cross section are
formed on both ends of a tapered part having a circular cross
section and a transition portion 11c is provided between the large
diameter side parallel part 11b and the central tapered part.
[0059] FIG. 7B shows a view in which parallel parts 11a and 11b
each having a rectangular cross section are provided on both ends
of a tapered part having a rectangular cross section and a
transition portion 11c is also provided between the large diameter
side parallel part 11b and the central tapered part.
[0060] In FIGS. 6B and 7B, although the parallel parts 11a and 11b
formed on the both ends, each of whose shapes is merely a
rectangular cross section, are shown, the shapes of the parallel
parts 11a and 11b can be a trapezoidal cross section as shown in
FIGS. 12A to 12C to be described later, an L-shaped cross-section
as shown in FIGS. 13A to 13C to be described later, a polygonal
cross section not shown or the like.
[0061] In this case, if the final shape of a hydraulically bulged
end surface is designed so that it agrees with a shape of an end
surface of a product, the yield loss of material may be reduced,
which is appreciated very much.
[0062] Further, in FIGS. 6B and 7B, although the central tapered
part also having rectangular cross sections is shown, the central
part is not particularly required to have rectangular cross
sections and they may be a circular cross section as shown in FIGS.
6A and 7A. Alternatively, the central part may be subjected to
bending or to pressing from upper and lower sides as well as from
right and left sides so that a profile element pipe can be
facilitated to be inserted into a hydraulic bulging die.
[0063] FIGS. 8A to 8C are views explaining a method of producing
the profile element pipe according to the present invention having
a parallel part on end portion of a large diameter side, and
particularly FIG. 8A is an entire perspective view, FIG. 8B is a
developed view and FIG. 8C is a view showing a trapezoidal shape
similar to the developed view shown in FIG. 8B.
[0064] A method of producing a profile element pipe 11 according to
the present invention having a parallel part 11b on a large
diameter side end portion of a tapered part having a circular
cross-section as shown in FIG. 8A will be described as follows.
[0065] If a sheet having a shape shown in FIG. 8B is subjected to a
simple bending and edges of a-b and a'-b', edges of c-d and c'-d',
edges of b-e and c-e, and edges of b'-e and c'-e, are joined
respectively, a profile element pipe 11 having a parallel part 11b
on the large diameter side end portion can be obtained as shown in
FIG. 8A.
[0066] Meanwhile, in FIG. 8C, FIG. 8B is shown in addition by
broken lines and a trapezoidal shape which is close to this is
shown by solid lines.
[0067] As apparent from the comparison between the solid lines and
broken lines, when the trapezoid shown by solid lines in FIG. 8C is
simply bent, a region b-c-e and a region b'-c'-e' constitute a
surplus. Namely, in a sheet bending process using a material of a
trapezoidal shape, it is difficult to produce a profile element
pipe having a parallel part lib at an end portion such as the
profile element pipe 11 according to the present invention.
[0068] Although the most simple method for producing the profile
element pipe is a method comprising the process of simply bending a
plate having a developed shape of a profile element pipe 11
according to the present invention to join with ends, other methods
of producing profile element pipes 11 according to the present
invention having shapes shown in FIGS. 6A and 6B and FIGS. 7A and
7B besides the above-mentioned method will be described.
[0069] In case of the shape shown in FIG. 6A, the profile element
pipe 11 according to the present invention can be obtained by
expanding an inner diameter on the small diameter side and by
reducing an outer diameter on the large diameter side using "a
merely tapered pipe" as a material, for example. Further, in case
of the shape shown in FIG. 6B, it can be obtained by crushing the
central body part in addition to the above-mentioned
pre-forming.
[0070] In the description of the present invention, the term "a
merely tapered pipe" means a material of a profile element pipe of
the present invention and a tapered pipe in which a parallel part
has not yet been formed on one pipe end or both pipe ends.
[0071] In case of the shape shown in FIG. 7A, the profile element
pipe 11 according to the present invention can be obtained by
expanding inner diameters on the small diameter side and the large
diameter side using "a merely tapered pipe" as a material, for
example. Further, in case of the shape shown in FIG. 7B, it can be
obtained by crushing the central body part in addition to the
above-mentioned working process.
[0072] FIGS. 9A to 9C are views showing another example of the
profile element pipe according to the present invention and a shaft
pressing tool used in the example, where FIG. 9A is an entire
perspective view, FIG. 9B is an enlarged view of the profile
element pipe on the small diameter side and FIG. 9C is an enlarged
view of the shaft pressing tool, which also serves as a small
diameter side sealing tool used in the shaft pressing tool. In the
example shown in FIGS. 9A to 9C, an embodiment shown in FIG. 9A
forms parallel parts 11a and 11b each having rectangular cross
section at both ends of a tapered part having rectangular cross
sections.
[0073] Further, in the example shown in FIGS. 9A to 9C, rectangular
cross sections having dimensions of substantially the same width
and height as those of the product are formed on a portion
corresponding to .DELTA.l+L0 in the small diameter side parallel
part 11a and on a portion corresponding to .DELTA.l'+L0' in the
large diameter side parallel part 11b in the merely tapered
pipe.
[0074] Further, by determining a radius R of curvature of a corner
part as described later, extremely smooth pressing of a material
can be performed with dies 12 and 13 and shaft pressing tools 14
and 15 also serving as sealing tools in the hydraulic bulging,
without generating bucking or the like due to shaft pressing during
hydraulic bulging.
[0075] FIGS. 10A to 10C are views showing shapes of end surfaces of
the profile element pipe of the present invention used in case that
a small diameter side of a hydraulically bulged product has a
rectangular cross section, where FIG. 10A shows a cross-sectional
view at a position away from the pipe end on the small diameter
side by .DELTA.l+L0, FIG. 10C shows a cross-sectional view of the
end portion of the pipe, and FIG. 10B is a cross-sectional view at
an arbitrary intermediate position of the pipe.
[0076] Namely, FIGS. 10A to 10C are views explaining a shape in
each of cross sections of the small diameter side parallel part 11a
of a profile element pipe of the present invention, and widths W0
and heights H0 in cross sections of FIGS. 10A to 10C are
substantially constant. Further, the radius R of curvatures of
corner part is gradually changed by previous forming.
[0077] As shown in FIGS. 10A to 10C, if a radius of curvature of
corner part in the small diameter side end portion is R0, a radius
of curvature of corner part at a position away from the small
diameter side pipe end by .DELTA.l+L0 in the axial direction is R1,
and a radius of curvature of corner part at a position away from
the small diameter side pipe end by X in the axial direction is
R(x), these radiuses have relationships of the following expression
(1).
R0.gtoreq.R(x).gtoreq.R1 (1)
[0078] In the examples shown in FIGS. 10A to 10C, the radiuses of
curvatures of four corner parts in each cross section were set as
the same. However, it is not necessary that they are set to be the
same, and different radiuses of curvatures at every corner part may
be used.
[0079] More specifically, a peripheral length difference
.DELTA.d(x) at the position X away from a pipe end while setting a
distance between both pipe-ends of a merely tapered pipe as a
reference length, is obtained from the following expression (2). In
this case, D0 denotes an outer diameter on the small diameter side,
D0' denotes an outer diameter on the large diameter side and LT
denotes a length of the tapered pipe.
.DELTA.d(x)=.pi..multidot.(D0'-D0).multidot.X/LT (2)
[0080] When a cross section of the end portion is pre-formed to a
rectangular cross section having a width of W0 and a height of H0,
the dimension of a radius R(x) of curvature of the corner part is
varied at axial positions in accordance with the peripheral length
difference .delta.d(x) as shown in FIGS. 10A to 10C, so that a
suitable shape of the pipe in pre-forming can be determined.
[0081] FIGS. 11A to 11C are views showing shapes of end surfaces of
the profile element pipe of the present invention used in case that
a large diameter side of a hydraulically bulged product has a
rectangular cross section, where FIG. 11A is a cross-sectional view
of a pipe at the position away from the pipe end on the large
diameter side by .DELTA.l'+L0', FIG. 11C is a cross-sectional view
of the end portion of the pipe, and FIG. 11B is a cross-sectional
view at the intermediate position of the pipe.
[0082] Namely, FIGS. 11A to 11C are views explaining a shape in
each cross section of the large diameter side parallel part 11b of
the profile element pipe of the present invention, and widths W0'
and heights H0' in cross sections in FIGS. 11A to 11C are
substantially constant. Further, the radius R' of curvatures of
corner part is gradually changed by pre-forming.
[0083] As shown in FIGS. 11A to 11C, if the radius of curvature of
corner part in the large diameter side end portion is R0', the
radius of curvature of corner part at a position away from the
large diameter side end portion by .DELTA.l'+L0' in the axial
direction is set to R1', and the radius of curvature of corner part
at a position away from the large diameter side end portion by X in
the axial direction is R'(x), these radiuses have relationships of
the following expression (1').
R0'.ltoreq.R'(x).ltoreq.R1' (1')
[0084] Specifically, the peripheral length difference .delta.d(x)
at a position X away from the edge of pipe end while setting a
distance between both pipe ends of a merely tapered pipe as a
reference length, is obtained from the following expression (2').
In this case, D0 denotes an outer diameter on the small diameter
side, D0' denotes an outer diameter on the large diameter side and
LT denotes a length of the tapered pipe.
.DELTA.d(x)=.pi..multidot.(D0'-D0).multidot.X/LT (2')
[0085] When the cross section of the end portion is previously
formed to the rectangular cross section having a width of W0' and a
height of H0', the dimension of the radius R'(x) of curvature of
corner part is varied at axial positions in accordance with the
peripheral length difference .DELTA.d(x) as shown in FIGS. 11A to
11C, so that the suitable shape of the pipe can be determined.
[0086] Although the case that a hydraulically bulged product has a
rectangular cross section has been described as above, the profile
element pipe of the present invention are not limited thereto.
Alternatively, a combined rectangular shape or a polygonal shape
can be adopted and extremely stable shaft pressing can be performed
during hydraulic bulging.
[0087] FIGS. 12A to 12C are views illustrating cross-sectional
shapes in case that hydraulically bulged products have trapezoidal
cross-sections. FIGS. 13A to 13C are views illustrating
cross-sectional shapes in case that hydraulically bulged products
have L-shaped cross-sections. FIGS. 12 and 13 show examples of
cross-sectional shapes of pre-formed pipes on the large diameter
side, wherein (a) is a cross sectional view at a position away from
the large diameter side pipe end by .DELTA.l'+L0' in the axial
direction, (c) is a cross sectional view of the pipe end portion,
and (b) is a cross sectional view at an intermediate position
therebetween.
[0088] Next, a hydraulic bulging device according to the present
invention and a hydraulic bulging method using the hydraulic
bulging device will be described with reference to drawings.
[0089] FIGS. 14A to 14C are views explaining a first example of a
method of the present invention, and shows the case that a parallel
part of an end portion of profile element pipe is formed prior to
hydraulic bulging, where FIG. 14A is a cross-sectional view showing
of a state of setting a tapered pipe on a die, FIG. 14B is a
cross-sectional view showing a state where the parallel part was
formed before hydraulic bulging, and FIG. 14C is a cross-sectional
view showing a state where hydraulic bulging has been
completed.
[0090] FIGS. 15A to 15C are views showing relationships among an
upper die on the small diameter side, a shaft pressing tool also
serving as a sealing tool and the end portion of the profile
element pipe, where FIGS. 15A to 15C are views elaborating on FIGS.
14A to 14C.
[0091] FIGS. 16A to 16C are views showing relationships among an
upper die on the large diameter side, the shaft pressing tool also
serving as a sealing tool and the end portion of the profile
element pipe, where FIGS. 16A to 16C are views elaborating on FIGS.
14A to 14C.
[0092] FIGS. 17A to 17C are views explaining a second example of
the method of the present invention, and show the case that the
parallel part of the end portion of the profile element pipe is
formed before setting the pipe on a die. Particularly, FIG. 17A is
a cross-sectional view showing a state of setting the profile
element pipe on the die, FIG. 17B is a cross-sectional view showing
a state before hydraulic bulging, and FIG. 17C is a cross-sectional
view showing a state after hydraulic bulging.
[0093] FIGS. 18A to 18C are views explaining a third example of the
method of the present invention, and shows another example of the
case that the parallel part of the end portion of profile element
pipe is formed before setting the pipe on the die. Particularly,
FIG. 18A is a cross-sectional view showing a state of setting the
profile element pipe on the die, FIG. 18B is a cross-sectional view
showing a state before hydraulic bulging, and FIG. 18C is a
cross-sectional view showing a state after hydraulic bulging.
[0094] The hydraulic bulging device of the present invention
includes an upper die 12 and a lower die 13 forming a cavity as
shown in FIGS. 14, 17 and 18, for example, and shaft pressing tools
14 and 15 which also serving as sealing tools, front end portions
of which are inserted into the respective end portions of both dies
12 and 13. And the both dies 12 and 13 as well as the shaft
pressing tools 14 and 15 are constituted so that both ends of the
profile element pipe 11 of the present invention are sandwiched and
held by them.
[0095] Further, any one of the shaft pressing tools is provided
with a filling hole for working liquid, and an inner surface of at
least one end side (both of the small diameter side and a large
diameter side of the die have parallel parts in examples shown in
FIGS. 14, 17 and 18) and an outer surface of the shaft pressing
tool corresponding to the inner surface of this end surface are
provided with parallel parts 12a, 12b, 13a, 13b, 14a and 15a,
respectively.
[0096] The parallel parts 14a and 15a of the outer surfaces of the
shaft pressing tools 14, 15 restrain the element pipe from the
inner surfaces thereof during shaft pressing so that smooth
deformation can be made.
[0097] In this hydraulic bulging device, if the amount of shaft
pressing on the small diameter part side is defined as .DELTA.l,
the amount of shaft pressing on the large diameter part side is
defined as .DELTA.l', the length required for sealing the small
diameter part side is defined as L0, the length required for
sealing the large diameter part side is defined as L0', lengths of
the parallel parts 12a, 12b, 13a and 13b provided on an inner
surface of at least one end side (both of the small diameter side
and the large diameter side of the die have parallel parts in
examples shown in FIGS. 14, 17 and 18) are desirably .DELTA.l+L0 or
more in case of the small diameter side parallel parts, and
.DELTA.l'+L0' or more in case of the large diameter side parallel
parts.
[0098] Also, lengths of the parallel parts 14a and 15a of the shaft
pressing tools 14 and 15 corresponding to the parallel parts 12a,
12b, 13a and 13b provided on dies 12, 13 are desirably .DELTA.l+L0
or more in case of the small diameter side parallel parts, and L0'
or more in case of the large diameter side parallel parts.
[0099] In the hydraulic bulging device of the present invention, a
front end portion of the shaft pressing tool 14 (15) also serving
as a sealing tool on the small diameter side (large diameter side)
must be designed to be inserted into a small diameter side end
portion (large diameter side end portion) of a merely tapered pipe
PT as a material for the profile element pipe 11 or a profile
element pipe 11. At the same time, it is necessary that the
parallel part 14a (15a) does not form a gap between a leading edge
of the parallel part 14a (15a) and the inner surface of the profile
element pipe 11 at the completion of shaft pressing.
[0100] Therefore, for example, as shown in FIGS. 14A to 14C, after
a merely tapered pipe PT as a material for the profile element pipe
11 is set on the upper die 12 and the lower die 13, if parallel
parts 11a and 11b to be formed on the pipe end portions are formed
in the upper die 12 and lower die 13 prior to hydraulic bulging, a
shaft pressing tool also serving as a sealing tool must satisfy the
following conditions A and B.
[0101] A. Shaft pressing tool 14 also serving as a sealing tool on
the small diameter side (see FIG. 15)
[0102] A peripheral length SD0 of an envelope on the front end in
which a locally concave portion was neglected satisfies the
following expression (3).
SD0.ltoreq.(DO-2t/cos .theta.).times..pi. (3)
[0103] wherein
[0104] D0: Outer diameter of the small diameter end portion
[0105] t: Wall thickness of profile element pipe 11
[0106] .theta.=tan.sup.-1 {(D0'-D0)/(2.multidot.LT)}
[0107] LT: Length of tapered pipe PT
[0108] D0': Outer diameter of the large diameter end portion
[0109] B. Shaft pressing tool 15 also serving as a sealing tool on
the large diameter side (see FIGS. 16A to 16C)
[0110] A peripheral length SD0' of an envelope on the front end in
which a locally concave portion was neglected satisfies the
following expression (4).
SD0'.ltoreq.(DO'-2t/cos .theta.).times..pi. (4)
[0111] On the other hand, as shown in FIGS. 17A to 17C, when the
parallel parts 11a and 11b, which are formed on the end portions of
the profile element pipe 11, are previously formed before setting
on the upper die 12 and lower die 13, a shaft pressing tool which
also serving a sealing tool satisfies the following conditions C
and D.
[0112] C. Shaft pressing tool 14 also serving as a sealing tool on
the small diameter side (see FIGS. 17A to 17C)
[0113] A peripheral length SD0 of a front end portion satisfies the
following expression (5)
SD0.ltoreq.Peripheral length SD of the parallel part 14a (5)
[0114] D. Shaft pressing tool 15 which also serving as a sealing
tool on the large diameter side (see FIGS. 17A to 17C)
[0115] A peripheral length SD0' of a front end portion satisfies
the following expression (6)
SD0'.ltoreq.Peripheral length SD' of the parallel part 15a (6)
[0116] When a hydraulically bulged product 17 is formed by using
the hydraulic bulging device according to the present invention, a
merely tapered pipe PT, which is a source material for the profile
element pipe 11 of the present invention, is set in a pair of dies
12 and 13 for a hydraulic bulging device as shown in FIG. 14A, for
example.
[0117] Next, prior to hydraulic bulging, shaft pressing tools 14
and 15 also serving as sealing tools are moved in the axial
direction to form parallel parts 11a and 11b on an end or both ends
of the tapered pipe PT sandwiched by the dies 12, 13 and the shaft
pressing tools 14, 15 as shown in FIG. 14B so that a profile
element pipe 11 according to the present invention is formed.
[0118] At this time it is not necessary to synchronize the timing
of shaft pressing of the profile element pipe 11 by the shaft
pressing tools 14 and 15. For example, when the shaft pressing tool
15 pushes the profile element pipe 11 to some extent pushing by the
shaft pressing tool 14 may be started. Thus, the shaft pressing
timing whereby the profile element pipe 11 is held stably in the
dies 12 and 13 may be selected.
[0119] In this case, if the dimensional design of the shaft
pressing tools 14 and 15 also serving as sealing tools and the dies
12, 13 is made with reference to the above-mentioned dimensions,
the shaft pressing tools 14 and 15 can be smoothly inserted into
the tapered pipe TP.
[0120] In a state of FIG. 14B, as shown in FIGS. 15B and 16B,
parallel parts 11a and 11b having a length of L0 or more,
preferably .DELTA.l+L0 or more on the small diameter side, and
having a length of L0' or more on the large diameter side are
formed on both ends of the tapered pipe PT so that the profile
element pipe 11 of the present invention can be obtained. After
that, an internal pressure is loaded on the profile element pipe 11
in a state where the sealing of working liquid is completely
held.
[0121] Then, while the internal pressure of working liquid is
increased, the shaft pressing tools 14 and 15 are moved in the
axial direction to be subjected to hydraulic bulging. As a result
as shown in FIG. 14C, a hydraulically bulged product 17 is formed
by the method of the present invention.
[0122] Namely, in hydraulic bulging in which the profile element
pipe 11 of the present invention is set on the hydraulic bulging
device of the present invention, the shaft pressing becomes
possible. As a result in the hydraulically bulged product 17
according to the method of the present invention, a larger pipe
expansion ratio can be obtained than a conventional case.
[0123] Further, since an end surface of the hydraulically bulged
product 17 is vertical with respect to the longitudinal axis as
shown in FIG. 4B, the joining or welding with the other part or
member can be easily performed and the positioning of socket
connection becomes possible.
[0124] FIGS. 19A to 19C are explanatory views showing a fourth
example of the method of the present invention, and shows a
configuration example in which an inner cavity of the large
diameter side parallel part is axially monotonously increased with
reference to an end of the large diameter of the pipe.
Particularly, FIG. 19A is a cross-sectional view showing a state of
setting a tapered pipe on the die, FIG. 19B is a cross-sectional
view showing a state where a parallel part is formed before
hydraulic bulging, and FIG. 19C is a cross-sectional view of a
state after hydraulic bulging.
[0125] An example shown in FIGS. 19A to 19C has a different form
from examples shown in FIGS. 14, 17 and 18. That is the example
shown in FIGS. 19A to 19C also has parallel parts 12a, 12b, 13a and
13b on both end portions of both dies 12 and 13. However, a cavity
inside the large diameter side parallel parts 12b and 13b of dies
12 and 13 is monotonously decreased in the axial direction with
reference to the large diameter end without locally narrowing a
portion of the cavity as in the examples shown in FIG. 14 and the
like.
[0126] Since the configuration example shown in FIG. 19A to 19C has
small shaft pressing resistance and advantage over a metal flow, a
formable range (pipe expansion limit) can be increased. Therefore,
in the hydraulic bulging device of the present invention, a shape
of the cavity formed in the dies 12 and 13 is preferably designed
to a shape shown in FIG. 19.
[0127] On the other hand, in parts of an automobile,
cross-sectional shapes of end portions of a product are similar to
a rectangle, a combined rectangle, and a shape of a polygon and the
like which are intricate shapes in many cases.
[0128] As described above, FIGS. 18A to 18C are views showing an
example of a case that the profile element pipe 11 of the present
invention shown in FIG. 9A. In working process by using it, the
profile element pipe 11 shown in FIG. 9A is set in dies 12 and 13.
FIG. 9B shows an enlarged view of the small diameter side profile
element pipe 11 of the present invention. On the other hand, cross
sectional shapes of the small diameter side parallel parts 11a are
as shown in FIGS. 10A to 10C.
[0129] With such profile element pipes 11 having cross sectional
shapes, forming is performed using the shaft pressing tools 14 and
15 also serving as sealing tools, which is one example of the
present invention. FIG. 9C shows the shaft pressing tool 14 also
serving as a small diameter side sealing tool. The parallel part
14a shown in FIG. 9C has a width of W0-2t, a height of H0-2t, and a
radius of curvature in a corner part of R1.
[0130] The shaft pressing tools 14 and 15 are pressed into end
portions from a state shown in FIG. 18A, the forming of end
portions of the profile element pipe 11 is completed at the stage
of FIG. 18B, so that the profile element pipe 11 shown in FIG. 9B
can be obtained while sealing of the working liquid has been fully
held with the internal pressure loaded.
[0131] After that, while increasing the internal pressure of
working liquid, the shaft pressing tools 14 and 15 are moved in the
axial direction so that a hydraulically bulged product 17 according
to the method of the present invention can be obtained.
[0132] It is noted that the forming of the parallel parts 11a and
11b of pipe ends, which is performed prior to hydraulic bulging may
be carried out at pre-forming or at a stage prior to the
pre-forming. The forming can be implemented by existing working
methods such as reducing, hole expanding, swaging, spinning or a
combination thereof.
[0133] FIGS. 20A to 20D are views showing configuration examples of
the shaft pressing tool, which is a component constituting the
hydraulic bulging device, also serving as a sealing tool. FIG. 20A
is a configuration example of sealing the device with an end
surface 14b or 15b, which comes into contact with end surfaces of
the profile element pipe 11, FIG. 20B is also a configuration
example in which a protrusion 14c or 15c is provided on the end
surface 14b or 15b respectively, FIG. 20C is a configuration
example in which steps 14d and 15d are provided on boundary parts
between the parallel part 14a or 15a and the end surface 14b or
15b, and FIG. 20D shows a configuration example in which an O ring
18 is provided on the parallel part 14a or 15a.
[0134] Any of the configuration examples shown in FIGS. 20A to 20D
satisfies the relationships between the parallel parts 14a, 15a and
a peripheral length of a front end shown by the expressions (3) to
(6).
[0135] The above-mentioned examples show one concrete example of
the present invention, and comparatively simple shapes of cavities
for the dies 12 and 13 are shown. However, a three-dimensional
intricate shape of the cavity, which is represented by ordinary
parts of an automobile, may be used.
[0136] Further, in the above-mentioned examples, shaft pressing
applied from both a small diameter side and a large diameter side
is shown. According to the present invention, the shaft pressing
tool has only to be adapted to any one side, and the other side may
be adapted to, for example, a non shaft pressing type as shown in
FIG. 1, which is conventionally applied. Since effects of shaft
pressing are varied by the shapes of products, the scope of
application of the present invention may be determined case by
case.
[0137] Further, in the above-mentioned examples, although, as a
material for the profile element pipe 11, the case using a merely
tapered pipe was described, a welded pipe by combining merely
tapered pipes and a pipe in combination of a tapered pipe with a
general straight pipe can also be applied as source materials of
the profile element pipes 11 of the present invention because each
end portion of the pipe can be closely approximated to the relevant
part of a merely tapered pipe.
INDUSTRIAL APPLICABILITY
[0138] A profile element pipe for hydraulic bulging according to
the present invention has a peripheral length with an outer
diameter gradually increasing or decreasing from one axial side
toward the other thereof and has a parallel part formed on at least
one end thereof. In a hydraulic bulging device and a hydraulic
bulging method using the profile element pipe, parallel parts are
respectively provided on at least one end portion inner surface of
both an upper die and lower die and an outer surface of a shaft
pressing tool corresponding to said end portion inner surface. Then
when the profile element pipe is set in a die, a bulging in which
an internal pressure loading and a shaft pressing in the axial
direction in combined manner can be performed. Thus, in the
hydraulically bulged product, a larger pipe expansion ratio than a
conventional case can be obtained and a joining and socket
connection thereof to the other part can also be easily performed.
Consequently, the hydraulically bulged product can be applied for
use of automobiles and further other industrial machinery
widely.
* * * * *