Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
TITLE OF INVENTION
FORMED METAL ITEM INCLUDING TUBULAR PART WITH SLIT, METHOD
FOR PRODUCING THE SAME, AND PRODUCING DEVICE AND DIE
ASSEMBLY USED IN METHOD FOR PRODUCING THE SAME
TECHNICAL FIELD
[0001]
The present invention relates to a formed metal item that includes a tubular
part with a slit, a method for producing the formed metal item, and a
producing
device and a die assembly used in the method for producing the formed metal
item.
BACKGROUND ART
[0002]
Tubular components are widely used in automobile parts and household
appliances. Therefore, the development of techniques to produce tubular
components is promoted. As a typical method for producing a tubular component
using a metal plate as a material, UO forming is known (e.g., Patent
Literature 1 and
2).
[0003]
In recent years, in the automotive field, there is a demand for a tubular
component with a slit in its lengthwise direction. A conventional method for
producing such a tubular component has been to perform bending a plurality of
times.
However, the method has a problem in that it is difficult to form a component
having
a complex shape, and in that the step thereof is cumbersome. Therefore, the
application of the UO forming is expected. However, a typical UO forming is
for
producing a tubular component without a slit, and a butted part of a formed
tubular
component is welded. For this reason, it is still difficult to produce a
tubular
component including a gap in its butted part with precision only by applying a
conventional UO forming.
[00041
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Patent Literature 3 discloses a method for forming a hollow profile with a
slot
in its longitudinal direction. FIG. 3 and FIG. 4 of Patent Literature 3
disclose a
method in which a core (core II) that includes a blade for forming the slot is
used.
In the producing method of Patent Literature 3, closing and welding the slot
after
forming are prerequisite. Therefore, precision of the breadth of the slot and
the
precision of a shape before the welding are not taken in consideration. In
addition,
in the case where the material or the thickness of a metal plate varies, the
amount of
spring back also varies, and thus variations in breadth of the slot occur.
Therefore,
in order to change the material or the thickness of the metal plate, a die
assembly
needs to be modified to adjust the breadth of the slot.
[0005]
Patent Literature 1 discloses a method for forming a tubular member having a
square cross section by bending a plate material. A die assembly used in this
method includes an upper die, a lower die, and side dices. The side dices are
dices
for pressing side parts of a plate material in such a manner that two end
edges facing
each other are brought close to each other. The tubular member formed by this
method has a butted part that is welded after the forming. Therefore, there is
no
sufficient consideration is given to control of a gap between the two end
edges.
[0006]
Furthermore, as the method for producing a tubular component, roll forming
is also known (e.g., Patent Literature 4). However, by the roll forming, it is
difficult
to produce a tubular component having a complex shape, such as a varying-cross-
section pipe the cross-sectional shape of which varies in its lengthwise
direction.
[0007]
As bending of a metal plate, press brake working is known (e.g., Patent
Literature 5). It is conceivable that a tubular component including a gap in
its
butted part is formed by bending with a press brake. However, by the press
brake
working, it is difficult to decrease the breadth of the gap of the butted
part.
[0008]
Also in the conventional U0 forming, an unintended gap may occur in some
cases in a butted part of a tubular component due to spring back after the
forming.
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However, in the conventional U0 forming, it is very difficult to control the
breadth
of the gap of the butted part.
[0009]
In addition, for example, as described in Patent Literature 2 and 3, a core is
used during 0 forming in some cases. In this case, it is conceivable that a
tubular
component including a gap in its butted part is formed by making the width of
a
metal plate shorter than the cross-section peripheral length of a die
assembly.
However, this method has a problem of a large spring back due to forming by
simple
bending. Therefore, also in this case, it is difficult to control the breadth
of the gap
of the butted part.
[0010]
In addition, it is conceivable to design a die assembly by trial and error,
and to
use the die assembly to form a tubular component including a gap in its butted
part
by means of spring back. However, when volume production is taken into
consideration, the material or the thickness of a metal plate slightly varies
between
lots. In this case, the amount of spring back also varies, and thus variations
occur in
the breadth of the gap of the butted part or the shape of the tubular
component.
Therefore, it is difficult to continuously produce tubular components that
have a
constant breadth of the gaps of their butted parts and are in good shape
precision, in
volume. Furthermore, in the case of changing the material or the thickness of
a
metal plate, the die assembly needs to be modified to adjust the breadth of
the gap of
the butted part, which requires a tremendous time and labor, accordingly
leading to
high costs.
[0011]
Patent Literature 6 discloses a method for producing a hollow profile from a
cut blank using a UO forming technique. In the producing method of Patent
Literature 6, a closed hollow profile is formed by butting two opposite edges
of a cut
blank against each another. At this point, the length of the cut blank in a
circumferential direction is made longer than a required forming length by a
given
redundant length. The redundant length is at least I% to 10%. Patent
Literature 6
discloses that areas of the hollow profile abutting on an edge joint are
compressed at
least partly in the circumferential direction. In addition, Patent Literature
6
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describes that the producing method is executed using the UO forming
technique.
However, Patent Literature 6 makes no specific description about how to
execute the
producing method. That is, Patent Literature 6 makes no disclosure about how
to
compress the hollow profile in the circumferential direction using the U0
forming
technique. Moreover, the method of Patent Literature 6 has no envisagement of
freely controlling the width of the slit.
CITATION LIST
PATENT LITERATURE
[0012]
Patent Literature 1: Japanese Patent Application Publication No. 2001-191112
Patent Literature 2: Japanese Patent Application Publication No. 2004-25224
Patent Literature 3: International Application Publication No.
W02005/002753
Patent Literature 4: Japanese Patent Application Publication No. 2000-616
Patent Literature 5: Japanese Patent Application Publication No. 2000-61551
Patent Literature 6: National Publication of International Patent Application
No. 2014-516801
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0013]
In the aforementioned circumstances, an objective of the present invention is
to provide a producing method capable of forming a formed metal item that
includes
a tubular part with a slit with precision, and capable of controlling the
breadth of the
slit.
SOLUTION TO PROBLEM
[0014]
A method in an embodiment of the present invention is a producing method
for producing a formed metal item that includes a tubular part with a slit.
This
producing method includes: (i) a step of forming a U-shaped part having a U-
shaped
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cross section by deforming a metal plate; and (ii) a step of forming the
tubular part
with the slit by deforming the U-shaped part using a die assembly provided
with a
protruding part in such a manner that two end parts of the U-shaped part clamp
the
protruding part. In the step (ii), the cross-section peripheral length LH of
the
tubular part is made shorter than the cross-section length LU of the U-shaped
part.
[0015]
A formed metal item in an embodiment of the present invention is a formed
metal item that includes a tubular part with a slit. When a variation S in
Vickers
hardness in the thickness direction of the cross section of the tubular part
is
expressed by the following expression, an average value of variations S in a
circumferential direction is less than 0.4.
S = (Bmax - Brnin) / Bmax
Here, Bmin is a minimum value of the Vickers hardnesses in the thickness
direction of the cross section. Bmax is a maximum value of the Vickers
hardnesses
in the thickness direction of the cross section.
[0016]
A producing device in an embodiment of the present invention is a producing
device for producing a formed metal item that includes a tubular part with a
slit.
This producing device includes a die assembly and a movement mechanism for
moving the die assembly. The die assembly includes a first die including a
protruding part for forming the slit, and includes a second die. The first and
second
dies include first and second pressing surfaces, respectively, the first and
second
pressing surfaces being configured to deform a U-shaped part having a U-shaped
cross section to form a cylindrical-shape portion with a gap, the gap being to
be the
slit. The die assembly has a configuration to press the outer peripheral
surface of
the cylindrical-shape portion so that the cross-section peripheral length of
the
cylindrical-shape portion is shortened.
[0017]
A die assembly in an embodiment of the present invention is a die assembly
for producing a formed metal item that includes a tubular part with a slit.
This die
assembly includes a first die that includes a protruding part for forming the
slit, and a
second die. The first and second dies include first and second pressing
surfaces,
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respectively, which are configured to deform a U-shaped part having a U-shaped
cross section to form a cylindrical-shape portion with a gap, the gap being to
be the
slit. The die assembly has a configuration to press the outer peripheral
surface of
the cylindrical-shape portion so that the cross-section peripheral length of
the
cylindrical-shape portion is made short.
ADVANTAGEOUS EFFECTS OF INVENTION
[00 I 8]
According to the present invention, it is possible to form a formed metal item
that includes a tubular part with a slit with precision, and to control the
breadth of the
slit. According to the present invention, a formed metal item that includes a
tubular
part with a slit formed with precision is obtained. Furthermore, according to
the
present invention, a producing device and a die assembly suitably used in a
producing method according to the present invention are obtained.
BRIEF DESCRIPTION OF DRAWINGS
[0019]
[FIG. II FIG. 1 schematically illustrates the cross section of an example of a
formed
metal item according to the present invention.
[FIG. 2A] FIG. 2A is a cross-sectional view schematically illustrating an
example of
a step of a producing method according to the present invention.
[FIG. 2131 FIG. 2B is a cross-sectional view schematically illustrating an
example of
a step subsequent to FIG. 2A.
[FIG. 2C1 FIG. 2C is a cross-sectional view schematically illustrating a U-
shaped
part that is formed through steps illustrated in FIG. 2A and FIG. 2B.
[FIG. 3A] FIG. 3A is a cross-sectional view schematically illustrating an
example of
a die assembly that is used in the producing method according to the present
invention.
[FIG. 3B] FIG. 3B is a cross-sectional view schematically illustrating an
example of
a producing step using the die assembly illustrated in FIG. 3A.
[FIG. 3C] FIG. 3C is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 3B.
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[FIG. 3D] FIG. 3D is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 3C.
[FIG. 3E] FIG. 3E is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 3D.
[FIG. 3F] FIG. 3F is a cross-sectional view schematically illustrating an
example of a
formed metal item that is produced through the steps illustrated in FIG. 3B to
FIG.
3E.
[FIG. 4A] FIG. 4A is a cross-sectional view schematically illustrating an
example of
a die assembly that is used in the producing method according to the present
invention.
[FIG. 4B1 FIG. 4B is a cross-sectional view schematically illustrating an
example of
a producing step using the die assembly illustrated in FIG. 4A.
[FIG. 4C] FIG. 4C is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 48.
[FIG. 4D] FIG. 4D is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 4C.
[FIG. 4E] FIG. 4E is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 4D.
[FIG. 4F] FIG. 4F is a cross-sectional view schematically illustrating an
example of a
formed metal item that is produced through the steps illustrated in FIG. 4B to
FIG.
4E.
[FIG. 5A] FIG. 5A is a cross-sectional view schematically illustrating an
example of
a die assembly that is used in the producing method according to the present
invention.
[FIG. 5B1 FIG. 5B is a cross-sectional view schematically illustrating an
example of
a producing step using the die assembly illustrated in FIG. 5A.
[FIG. 5C] FIG. 5C is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 5B.
[FIG. 5D] FIG. 5D is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 5C.
[FIG. 5E] FIG. 5E is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 5D.
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[FIG. 5F] FIG. 5F is a cross-sectional view schematically illustrating an
example of a
formed metal item that is produced through the steps illustrated in FIG. 5B to
FIG.
5E.
[FIG. 6A] FIG. 6A is a cross-sectional view schematically illustrating an
example of
a die assembly that is used in the producing method according to the present
invention.
[FIG. 6B] FIG. 6B is a cross-sectional view schematically illustrating an
example of
a producing step using the die assembly illustrated in FIG. 6A.
[FIG. 6C] FIG. 6C is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 6B.
[FIG. 6D] FIG. 6D is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 6C.
[FIG. 6E] FIG. 6E is a cross-sectional view illustrating an example of a step
subsequent to the step illustrated in FIG. 6D.
[FIG. 6F1 FIG. 6F is a cross-sectional view schematically illustrating an
example of a
formed metal item that is produced through the steps illustrated in FIG. 6B to
FIG.
6E.
[FIG. 7] FIG. 7 is a cross-sectional view schematically illustrating a cross
section of
another example of a die assembly according to the present invention.
[FIG. 8] FIG. 8 is a cross-sectional view illustrating a still another example
of a die
assembly according to the present invention and an example of a tubular part
that is
formed using the example of the die assembly.
[FIG. 9A1 FIG. 9A is a diagram schematically illustrating an example of the
formed
metal item according to the present invention.
[FIG. 9B] FIG. 9B is a diagram schematically illustrating another example of
the
formed metal item according to the present invention.
[FIG. 9C] FIG. 9C is a diagram schematically illustrating a still another
example of
the formed metal item according to the present invention.
[FIG. 9D] FIG. 9D is a diagram schematically illustrating a still another
example of
the formed metal item according to the present invention.
[FIG. 9E] FIG. 9E is a diagram schematically illustrating a still another
example of
the formed metal item according to the present invention.
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[FIG. 10A] FIG. 10A schematically illustrates a step of a method for producing
a
tubular member in Comparative Example 1.
[FIG. 10B] FIG. 10B schematically illustrates a step subsequent to FIG. 10A.
[FIG. l 1A] FIG. 11A schematically illustrates a step of a method for
producing a
tubular member in Comparative Example 2.
[FIG. 11B] FIG. 11B schematically illustrates a step subsequent to FIG. 11A.
[FIG. 12AI FIG. 12A is a graph illustrating strain distributions of tubular
members in
Example 1, Comparative Example 1, and Comparative Example 2, in a thickness
direction.
[FIG. I 2B] FIG. 12B is a graph illustrating strain distributions of tubular
members in
Examples 2 to 4 and Comparative Example 2, in a circumferential direction.
[FIG. 13] FIG. 13 is a graph illustrating relation between the average value
of
variations S in the circumferential direction and the rate of reduction of
uniaxial
compressive strength.
[FIG. 14A] FIG. 14A is a diagram illustrating an example of an operation of an
example of a producing device of the present invention.
[FIG. 14B] FIG. 14B is a diagram illustrating an example of an operation
subsequent
to FIG. 14A.
[FIG. 14C] FIG. 14C is a diagram illustrating an example of an operation
subsequent
to FIG. 14B.
[FIG. I 4D1 FIG. 14D is a diagram illustrating an example of an operation
subsequent
to FIG. 14C.
[FIG. 15A] FIG. 15A is a diagram illustrating an example of an operation of
another
example of the producing device of the present invention.
[FIG. 15B] FIG. 15B is a diagram illustrating an example of an operation
subsequent
to FIG. 15A.
[FIG. 15C1 FIG. I 5C is a diagram illustrating an example of an operation
subsequent
to FIG. 15B.
[FIG. I 5D] FIG. 15D is a diagram illustrating an example of an operation
subsequent
to FIG. 15C.
DESCRIPTION OF EMBODIMENTS
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[0020]
Hereinafter, embodiments of the present invention will be described. The
following description will be made about embodiments of the present invention
by
way of example, but the present invention is not limited to the examples
described
below. Although specific numeric values and materials are exemplified in the
following description in some cases, other numeric values and materials may
apply
as long as they allow the advantageous effects of the present invention to be
obtained.
[0021]
(Method for Producing Formed Metal Item)
A producing method according to the present invention is a method for
producing a formed metal item that includes a tubular part with a slit.
Matters
described about the producing method according to the present invention are
applicable to a formed metal item, a producing device, and a die assembly
according
to the present invention.
[0022]
The formed metal item may include a part other than the tubular part with a
slit. Alternatively, the formed metal item may be constituted by only the
tubular
part with a slit. The formed metal item in this case is a tubular formed item
with a
slit. Examples of the formed metal item to be produced will be described
later.
The producing method according to the present invention includes step (i) and
step
(ii), which will be described below.
[0023]
(Step (i))
In step (i), a metal plate is deformed, whereby a U-shaped part, which has a
U-shaped cross section, is formed. Step (i) has no special limitation, and U
forming
used in conventional U0 forming may be applied thereto. The method for U
forming has no special limitation as long as the method allows the metal plate
to be
formed to have a U-shaped cross section. Examples of the U-forming method
include press forming, roll forming, and other kinds of forming. The U forming
may be performed in a plurality of steps. In addition, before the U forming,
working to bend the ends of the metal plate (working such as what is called C
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forming) may be performed. In addition, after the U forming, trimming
(cutting) of
the U-shaped part may be performed.
[0024]
In the present specification, the cross section of a tubular part means a
cross
section in the circumferential direction of the tubular part, unless otherwise
noted.
In other words, the cross section of the tubular part means a cross section in
a
direction perpendicular to the axis direction (normally the lengthwise
direction) of
the tubular part. The same is true for the cross section of the U-shaped part,
the
cross section of a cylindrical-shape portion, and the cross section of a
pressing
surface of a die assembly. The pressing surface of a die assembly means a
surface
of the die assembly that is to come into contact with the outer peripheral
surface of
the cylindrical-shape portion (or the tubular part), unless otherwise noted.
In the
case where the die assembly is configured by a plurality of members, the cross-
section peripheral length of the pressing surface of the die assembly means
the total
cross-section length of the pressing surfaces of the plurality of members.
[0025]
The metal plate to be subjected to the forming by the producing method
according to the present invention may be hereinafter referred to as a blank.
The
metal plate (blank) has no special limitation as long as the metal plate
allows the
forming. Examples of the metal plate include a steel plate, for example, a hot-
rolled
steel plate, a cold-rolled steel plate, a plated steel plate, and other kinds
of plates.
Furthermore, examples of the metal plate include a metal plate made by joining
a
plurality of metal plates together (what is called a tailored blank). The
tailored
blank may be made by joining a plurality of metal plates together in the axis
direction of the resultant tubular part, or may be made by joining a plurality
of metal
plates together in the circumferential direction of the resultant tubular
part.
Furthermore, as the blank, use may be made of a twin gauge plate, the
thickness of
which differs from area to area. Further, as the blank, use may be made of
what is
called a stacked plate. Examples of the stacked plate include a plate made by
stacking a plurality of metal plates and a plate made by overlaying a
nonmetallic row
material on a metal plate. That is, the formed metal item may contain a
material
other than a metal plate.
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[0026]
The metal plate (blank) may be a thin-wall metal plate or a high-tensile steel
plate (what is called a high-tensile material). These plates tend to have
large spring
backs and are suitable in particular for the present invention. Examples of
the thin-
wall metal plate include a metal plate in which the ratio of the thickness to
the
equivalent diameter, of the metal plate, is 10% or less. The equivalent
diameter is a
value obtained by dividing the cross-section peripheral length of the tubular
part by
3.14. The tensile strength of the high-tensile material is preferably 300 MPa
or
more and may be 440 MPa or more (e.g. 490 MPa or more or 780 MPa or more).
The upper limit of the tensile strength has no special limitation and may be
2000
MPa or less.
[0027]
The material of the metal plate has no special limitation as long as the metal
plate allows the forming. Examples of the material of the metal plate include
Fe-
based, Al-based, Cu-based, and Ti-based metal, and other kinds of metals.
[0028]
The thickness of the metal plate has no special limitation as long as the
thickness allows the forming. The thickness of the metal plate is selected in
consideration of the material of the metal plate, the shape of the formed
metal item,
the usage of the formed metal item, and other factors. As an example, the
thickness
of the metal plate may fall within a range from 0.4 to 5 mm (e.g., a range
from 0.5 to
3 mm or a range from 1 to 3 mm, etc.).
[0029]
The shape of the metal plate is selected in conformity with an intended shape
of the formed metal item. As will be described later, in the producing method
according to the present invention, a cross-section peripheral length LH of
the
tubular part is made shorter than a cross-section length LU of the U-shaped
part. Of
the metal plate, a width W of a portion to be made into the tubular part (a
length in a
direction to be a circumferential direction in the tubular part) is determined
in
consideration of a compressibility C, which will be described later.
[0030]
(Step (ii))
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In step (ii), the tubular part with a slit is formed by deforming the U-shaped
part using a die assembly provided with a protruding part in such a manner
that two
end parts of the U-shaped part clamp the protruding part. In step (ii), the
cross-
section peripheral length LH of the tubular part is made shorter than the
cross-section
length LU of the U-shaped part. The metal plate constituting the tubular part
is
thereby compressed in the circumferential direction. Consequently, the spring
back
of the tubular part is suppressed, which allows the breadth of the slit to be
controlled
with precision. The gap between the two end parts that are butted against each
another across the protruding part (the two end parts of the U-shaped part)
serves as a
slit. That is, a formed metal item including a tubular part with a slit is
produced by
step (ii). Of course, the formed metal item obtained by step (ii) may be
further
worked.
[0031]
The difference between the cross-section peripheral length LH of the tubular
part and the cross-section length LU of the U-shaped part is preferably 0.2%
or more
of the cross-section length LU of the U-shaped part. Specifically, it is
preferable
that the cross-section length LU of the U-shaped part and the cross-section
peripheral
length LH of the tubular part satisfy an expression of 0.2 100 x (LU - LH) /
LU.
If the difference is excessively small, the effect of suppressing the spring
back and
the effect of forming the tubular part with precision may not be obtained.
Hereinafter, the value of 100 x (LU - LU)! LU may be referred to as a
compressibility C(%) of the tubular part. The compressibility C of the tubular
part
may be 0.5% or more.
[0032]
From the viewpoint of inhibiting buckling, the compressibility C may be set at
2% or smaller or may be set at less than 1%. By setting the compressibility C
at
less than 1%, it is possible to inhibit buckling better. In particular, a
small thickness
of the metal plate is likely to give rise to buckling, and thus the
compressibility C is
preferably set at less than 1%. In a preferable example, an expression of 0.2
100
x (LU - LH) / LU < I is satisfied.
[0033]
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If the difference (LU - LH) between the cross-section peripheral length LH of
the tubular part and the cross-section length LU of the U-shaped part is
excessively
large, there is the risk that buckling (folding of the metal plate) occurs or
that the
metal plate is caught in a contact portion between an upper die and a lower
die.
Meanwhile, the larger the thickness of the metal plate, buckling is more
difficult to
bring about even when the compressibility C is increased. In addition, the
smaller
the thickness of the metal plate, the greater the effect obtained by the
compression.
From the viewpoint of this respect, it is preferable that the difference
between the
cross-section peripheral length LH and the cross-section length LU of the U-
shaped
part is determined in consideration of the thickness of the metal plate. For
example,
assuming that the thickness of the metal plate constituting the tubular part
is denoted
by t, the difference between the cross-section peripheral length LH of the
tubular part
and the cross-section length LU of the U-shaped part may be set at 8t or
smaller. In
this case, the difference between the cross-section peripheral length LH of
the tubular
part and the cross-section length LU of the U-shaped part may be set at 0.1t
or larger.
[0034]
In a preferable example, the above compressibility C is 0.2% or more, and the
difference between the cross-section peripheral length LH and the cross-
section
length LU is 8t or smaller. In another preferable example, the above
compressibility C is 0.2% or more and 2% or less. Consider the case of using,
as
the blank, a thin-wall metal plate in which the ratio of the thickness to the
equivalent
diameter, of the metal plate, (the equivalent diameter described above) is 5%
or less.
In this case, the compressibility C is preferably 0.2% or more and less than
I% (e.g..
0.2% or more and less than 0.5%).
[0035]
From the viewpoint of preventing buckling, the compressibility C may be
determined in consideration of a yield stress a (MPa) and the thickness t (mm)
of the
metal plate (blank) constituting the tubular part. For example, the
aforementioned
compressibility C(%) may satisfy the following expression. In this case, any
of the
aforementioned lower limits may be adopted as the lower limit of the
compressibility
C. The metal plate satisfying the following expression may have any thickness
and
- 15 -
may have a thickness that falls within the aforementioned range (e.g., range
from 0.4
to 5 mm).
C (1500 / a) x t
[0036]
Step (ii) may include the following steps (ii-1) and (ii-2). In step (ii-1), a
cylindrical-shape portion is formed by deforming the U-shaped part using a die
assembly in such a manner that the two end parts of the U-shaped part clamp
the
protruding part, the cylindrical-shape portion being to be the tubular part.
The
cylindrical-shape portion is a precursor of the tubular part obtained by the
step (ii),
which can be rephrased into a first tubular part or a tubular part precursor.
In step
(ii-2), the outer peripheral surface of the cylindrical-shape portion is
pressed with the
two end part clamping the protruding part of the die assembly, and the cross-
section
peripheral length of the cylindrical-shape portion is thereby shortened. By
step (ii-
2), the cross-section peripheral length LH of the tubular part is made shorter
than the
cross-section length LU of the U-shaped part. That is, by step (ii-2), the
metal plate
constituting the tubular part is compressed in the circumferential direction.
By
forming the cylindrical-shape portion in step (ii-1) before compressing the
cylindrical-shape portion in the circumferential direction in step (ii-2), it
is possible
to perform the compression stably. Specifically, it is possible to inhibit the
occurrence of buckling and the like at the time of forming the cylindrical-
shape
portion.
[0037]
Description will be made below about three examples of step (ii) (an example
(A), an example (B), and an example (C)). Example (A) and example (B) are
examples including steps (ii-1) and (ii-2).
[0038]
(Example (A) of Step (ii))
A die assembly (a) used in the example (A) has the following configurations
(a-1), (a-2), and (a-3).
(a-1) The die assembly (a) includes a first die provided with a protruding
part, and a
second die.
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(a-2) The first and second dies include first and second pressing surfaces,
respectively, which are configured to deform the U-shaped part to form the
cylindrical-shape portion.
(a-3) At least one die selected from the first die and the second die is
separable into a
plurality of die members.
[0039]
As to the configuration (a-3), both of the first and second dies may be
separable. Alternatively, only the first die may be separable, or only the
second die
may be separable. In the case where both of the first and second dies are
separable,
the cross-section peripheral length LH of the tubular part can be finely
adjusted. As
a result, it is possible to reduce variations more in compressive stress
acting on the
tubular part. Consequently, the slit can be formed with more precision. In an
example in which the first die is separable, the first die is separable into a
first die
member and a second die member. In this case, the protruding part may be
configured by a first protruding part included in the first die member and a
second
protruding part included in the second die member.
[0040]
In step (ii-1) of the example (A), the cylindrical-shape portion is formed by
deforming the U-shaped part using the die assembly (a) while a plurality of
die
members are separated. In the subsequent step (ii-2), the outer peripheral
surface of
the cylindrical-shape portion is pressed by bringing the plurality of die
members
close to each other, which shortens the cross-section peripheral length of the
cylindrical-shape portion. With this configuration, the metal plate
constituting the
tubular part is compressed in the circumferential direction.
[0041]
In a preferable example of the example (A), the die assembly (a) moves only
in a vertical direction in step (ii-1), and the die assembly (a) moves only in
a
horizontal direction in step (ii-2). For example, in the case where only an
upper die
of the die assembly (a) moves in the vertical direction (a pressing
direction), the
upper die is caused to move to a bottom dead point in step (ii-1). Thereafter,
in step
(ii-2), the separated plurality of die members are caused to move in the
horizontal
direction.
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[0042]
(Example (B) of Step (ii))
A die assembly (b) used in the example (B) has the following configurations
(b-1), (b-2), and (b-3).
(b-1) The die assembly (b) includes a first die provided with a protruding
part and a
second die.
(b-2) The first and second dies include first and second pressing surfaces,
respectively, which are configured to deform the U-shaped part to form the
cylindrical-shape portion.
(b-3) At least one die selected from the first die and the second die includes
a body
part and a movable part that is movable relative to the body part.
[0043]
As to the configuration (b-3), the first and second dies may each include the
movable part. Alternatively, only the first die may include the movable part,
or
only the second die may include the movable part. In an example, the first and
second dies include first and second movable parts, respectively, the first
and second
movable parts being movable in the pressing direction (the vertical
direction). In
this case, the first movable part included in the first die may include a
protruding part
for forming the slit. In another example, at least one of the first and second
dies
includes first and second movable parts that are movable in a direction
orthogonal to
the pressing direction. The first and second movable parts are disposed in
such a
manner as to face each other across the cylindrical-shape portion. The two
movable
parts (the first and second movable parts) press the outer peripheral surface
of the
cylindrical-shape portion, which can compress the cylindrical-shape portion in
question in the circumferential direction. Here, the pressing direction means
a
direction in which the body part of the die assembly moves during the forming.
[0044]
In step (ii-1) of the example (B), the U-shaped part is deformed using the die
assembly while the pressing surface of the movable part does not project from
the
pressing surface of the body part. In the subsequent step (ii-2), the outer
peripheral
surface of the cylindrical-shape portion is pressed by causing the pressing
surface of
the movable part to project from the pressing surface of the body part, which
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shortens the cross-section peripheral length of the cylindrical-shape portion.
With
this configuration, the metal plate constituting the tubular part is
compressed in the
circumferential direction. In a typical step (ii-2), the body part is not
caused to
move, and only the movable part is caused to move.
[0045]
(Example (C) of Step (ii))
A die assembly (c) used in the example (C) has the following configurations.
(c-1) The die assembly (c) includes a first die provided with a protruding
part and a
second die.
(c-2) The first and second dies include first and second pressing surfaces,
respectively, which are configured to deform the U-shaped part to form the
cylindrical-shape portion.
(c-3) The cross-section peripheral length of the pressing surfaces of the die
assembly
(the pressing surfaces of the first and second dies) is shorter than the cross-
section
length LU of the U-shaped part.
[0046]
Unlike the die assembly (a) and the die assembly (b), the first die and the
second die constituting the die assembly (c) are each basically a single
piece. The
protruding part of the first die may be however made replaceable. In the
example
(C), the U-shaped part is deformed only by bringing the first die and the
second die
close to each other in step (ii), whereby the tubular part with a slit is
formed. The
example (C) has a simple configuration of the die assembly and has an
advantage
that the production of the formed metal item is easy.
[0047]
In the producing method according to the present invention, the die assembly
may include a pressing surface corresponding to the outer peripheral surface
of the
tubular part, and the cross-section peripheral length of the pressing surface
may be
shorter than the cross-section length LU of the U-shaped part. With this
configuration, the pressing surface of the die assembly presses the outer
peripheral
surface of the U-shaped part to form the tubular part, whereby the cross-
section
peripheral length LH of the tubular part can be made shorter than the cross-
section
length LU of the U-shaped part. As mentioned above, the above die assembly (c)
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has this configuration, and the above die assembly (a) also has this
configuration
basically. The above die assembly (b) may or may not have this configuration.
The cross-section peripheral length of the pressing surface of the die
assembly means
the total cross-section length of the pressing surfaces of a plurality of
members that
constitute the die assembly.
[0048]
In the case of using the above die assemblies (a) and (c), it is normally
considered that the cross-section peripheral length of the pressing surface of
the die
assembly is not considerably different from the cross-section peripheral
length LH of
the tubular part when the tubular part with a slit is formed by closing the
die
assembly completely. In this case, in the present specification, the cross-
section
peripheral length LH of the tubular part can be substituted by the cross-
section
peripheral length of the pressing surface of the die assembly. For example, in
the
aforementioned expression of the compressibility C and the other expression,
the
cross-section peripheral length LH of the tubular part can be substituted by
the cross-
section peripheral length of the pressing surface of the die assembly.
[0049]
Step (ii) of the producing method according to the present invention is
executed typically without using a core, and may be executed, for example,
without
using a core that is to come into contact with most of an inner peripheral
surface (e.g.,
50% or more of the area of the inner peripheral surface) of the tubular part
(or the
cylindrical-shape portion). By executing step (ii) without using the core, the
tubular
part becomes easy to compress uniformly in the circumferential direction. In
the
case of using the core, a metal plate between the die assembly and the core
becomes
difficult to compress in the circumferential direction. However, the core may
be
used in step (ii) as necessary. By using the core, it is possible to stably
form a
formed metal item having a complex cross-sectional shape in the
circumferential
direction. For example, in the case where an angle 0 illustrated in FIG. 1
described
later becomes larger than 180 , the core may be used for a stable forming. In
the
case of using the core, the core may be disposed over the entire part to be
made into
the tubular part or over only a part to be made into the tubular part.
[0050]
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In the producing method according to the present invention, the formed metal
item may be further worked after step (ii). For example, a protrusion or a
flat part
may be added to the formed metal item, or a hole may be opened in the formed
metal
item.
[0051]
The producing method according to the present invention is aimed at
producing a formed metal item that includes a tubular part with a gap in a
butted part.
For this reason, the slit (the butted part with a gap) is basically not welded
after step
(ii). However, part of the butted part may be welded. For example, in the case
where part of the butted part has a gap (slit), and the other part has no gap,
part or the
whole of the butted part having no gap may be welded. Also in this case, it is
preferable not to weld the butted part having the gap. At the time of
assembling a
product including a formed metal item, part of the butted part may be
subjected to
tack welding.
[0052]
(Formed Metal Item)
The formed metal item according to the present invention includes a tubular
part with a slit. From a viewpoint, this tubular part is a tubular part having
a gap in
a butted part. The formed metal item according to the present invention is
produced
by the producing method according to the present invention. As to matters
about
this formed metal item that have already described in another part of the
description,
the redundant description thereof may be omitted. The matters described about
the
formed metal item according to the present invention are applicable to the
producing
method, the producing device, and the die assembly according to the present
invention.
[0053]
The formed metal item according to the present invention may include a part
other than the tubular part with a slit. Alternatively, the formed metal item
may be
constituted by only the tubular part with a slit. The formed metal item in
this case
is a tubular formed item with a slit. The slit is normally formed along the
axis
direction (normally the lengthwise direction) of the tubular part. The slit
may be
formed in the entire tubular part or may be formed only in part of the tubular
part.
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In other words, the formed metal item may have a slit across the overall
length of the
butted part, or may have a slit only in part of the butted part.
[0054]
The shape of the tubular part with a slit has no special limitation as long as
the
shape is formable by the method according to the present invention. The
tubular
part has no special limitation in its cross-sectional shape and may have
various
shapes such as a round, an ellipse, a quadrilateral, a vertically asymmetrical
shape,
and a horizontally asymmetric shape. The tubular part may be round-tube-shaped
or square-tube-shaped.
[0055]
Examples of the shape of the tubular part include a straight pipe, a curved
pipe, a varying-diameter pipe the outer diameter of which varies in its
lengthwise
direction, a varying-cross-section pipe the cross-sectional shape of which
varies in its
lengthwise direction, and the other kinds of pipes. Specifically, examples of
the
tubular part include pipes illustrated in FIG. 9A, FIG. 9B, FIG. 9C, FIG. 9D,
and FIG.
9E (tubular part le). In each of these pipes, a slit 3 is formed in a butted
part 2.
[0056]
The pipe illustrated in FIG. 9A is a straight pipe the cross-sectional shape
in
the circumferential direction of which is round-shaped. The pipe illustrated
in FIG.
9B is a curved pipe the cross-sectional shape in the circumferential direction
of
which is round-shaped. The pipe illustrated in FIG. 9C is a trumpet-shaped
varying-diameter pipe the cross-sectional shape in the circumferential
direction of
which is round-shaped. The pipe illustrated in FIG. 9D is a varying-cross-
section
pipe the cross-sectional shape in the circumferential direction of which
varies from a
round shape to a quadrilateral shape. The pipe illustrated in FIG. 9E is a
pipe
having the cross-sectional shape in the circumferential direction of which is
vertically asymmetrical and horizontally asymmetric. The pipe illustrated in
FIG.
9E is a pipe formed of a tailored blank made by joining different metal plates
in the
circumferential direction.
[0057]
A pipe the cross-sectional shape in the circumferential direction of which is
a
horizontally asymmetric shape and a pipe using a tailored blank as illustrated
in FIG.
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9E are difficult to form into by conventional UO forming. In contrast, by
appropriately selecting the die assembly according to the present invention,
it is
possible to form pipes of various shapes or various types of blanks.
[0058]
The formed metal item according to the present invention is obtained by
subjecting a metal plate (blank) to forming. For this reason, the material of
the
formed metal item is the same as the material of the blank. Furthermore, the
thickness of the formed metal item is substantially the same as the thickness
of the
blank. Therefore, the thickness of the formed metal item (the thickness of the
tubular part) may fall within the range exemplified as the thickness of the
blank.
Some of the physical properties of the formed metal item change from the
physical
properties of the blank in a working step. In the formed metal item according
to the
present invention, in particular, since the tubular part is compressed in the
circumferential direction, the physical properties thereby change.
[0059]
By the producing method according to the present invention, it is possible to
produce the formed metal item according to the present invention. Assuming
that a
variation S in Vickers hardness, of the formed metal item according to the
present
invention, in a thickness direction of the cross section of the tubular part
is expressed
by the following expression, the average value of variations S in the
circumferential
direction is less than 0.4 (0 or more and less than 0.4).
S = (Bmax - Bmin) Bmax
Here, Bmin is a minimum value of the Vickers hardnesses in the thickness
direction of the cross section of the tubular part. Bmax is a maximum value of
the
Vickers hardnesses in the thickness direction of the cross section.
[0060]
The average value of the variations S in the circumferential direction is the
average value of variations S that are measured at three points of one cross
section of
the tubular part (a cross section in the circumferential direction). The three
positions for the measurement are a first position that is in the vicinity of
the slit of
the tubular part, a second position that is the furthest from the first
position in the
circumferential direction, and a third position that is midway between the
first
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position and the second position. Consider that the tubular part is circular-
tube-
shaped and the slit is positioned in an uppermost part of the tubular part. At
this
point, assuming that a bottom part of the tubular part is at 0 around the
center of the
tubular part, the first, second, and third positions lie at about 180 , 0 ,
and 900,
respectively. The first position is set at a distance within a range of 5 mm
or shorter
from an end part facing the slit.
[0061]
In the producing method according to the present invention, a cross-section
peripheral length LH of the tubular part is made shorter than a cross-section
length
LU of the U-shaped part. Therefore, compressive stress acts on the entire
tubular
part in the thickness direction, and a variation in compressive stress acting
on the
tubular part in the circumferential direction is small. For this reason, by
forming
the tubular part by the producing method according to the present invention,
it is
possible to increase a Vickers hardness over the entire cross section of the
tubular
part. As a result, it is possible to reduce the variation in Vickers hardness
over the
entire cross section of the tubular part. Decreasing the variation in Vickers
hardness is useful for the enhancement of the durability and reliability
formed metal
item with the tubular part.
[0062]
In a preferable example, all of the variations S measured at the
aforementioned three positions are less than 0.4 (e.g., less than 0.2). With
this
configuration, the enhancement of the durability and reliability can be
expected.
[0063]
(Method for Measuring Vickers Hardness)
Hereinafter, description will be made about a method for measuring the
Vickers hardness of the tubular part. First, the tubular part is cut in the
circumferential direction, and the cut surface is subject to mechanical
polishing until
the cut surface becomes a mirror plane. Next, to eliminate the influence of
work
hardening by the mechanical polishing, the cut surface is dissolved up to a
depth of
30 to 80 pm from the surface of the cut surface, by chemical polishing or
electropolishing. On the cut surface obtained in such a manner, a Vickers
hardness
is measured.
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[0064]
The Vickers hardness is measured in compliance with the test method of the
Vickers hardness test according to JIS Z 2244 in Japanese Industrial Standards
(ES).
In the Vickers hardness test, an indenter is pressed into a test specimen to
form an
indentation, and a diagonal length of the indentation is measured. To evaluate
the
variation S for the cut surface of the tubular part, a plurality of
indentations are
formed on the cut surface for the measurement. In the case where the tubular
part is
made of a steel, a copper, or a copper alloy, a distance between the centers
of
adjacent two indentations is set at 3d or longer (d is the value of a longer
one of the
diagonal lengths of the indentations), distances from the centers of the
indentations to
the edges of the test specimen (the cut surface of the tubular part) are set
at 2.5d or
longer. In the case where the tubular part is made of a light metal (including
aluminum, an aluminum alloy, titanium, a titanium alloy, magnesium, and a
magnesium alloy), the distance between the centers of adjacent two
indentations is
set at 6d or longer, and the distances from the centers of the indentations to
the edges
of the test specimen are set at 3d or longer. These distances can be adjusted
by
intervals for the measurement of the Vickers hardness and a force to pressing
the
indenter.
[0065]
In the aforementioned first position, Vickers hardnesses are measured at five
points lying in a straight line at regular intervals in the thickness
direction. Then,
from the measured values at the five points, the minimum value Bmin and the
maximum value Bmax of the Vickers hardnesses are determined, and the
aforementioned variation S is calculated. Also in each of the aforementioned
second and third positions, Vickers hardnesses are measured in the same
manner, and
the aforementioned variations S is calculated. Then, by averaging the obtained
three variations S, the average value of the variations S in the
circumferential
direction is obtained.
[0066]
The formed metal item according to the present invention is available for
various applications. Examples of applications of the formed metal item
include
components (suspension components, bodies, structural materials, etc.) of
various
- 25 -
kinds of vehicles (automobiles, railway vehicles, and the other kinds of
vehicles),
components of various kinds of machines, electronic devices, electrical
appliances,
components of various kinds of transport aircraft (vessels, aircraft), and the
other
components.
[0067]
(Producing Device)
A producing device according to the present invention is a producing device
to produce a formed metal item that includes a tubular part with a slit. This
producing device is available for the producing method according to the
present
invention. With this producing device, it is possible to produce the formed
metal
item according to the present invention. This producing device is a pressing
device
from another viewpoint, and to a configuration about which description is not
made
below, the configuration of a well-known pressing device may be applicable. As
to
matters about this producing device that have already described in another
part of the
description, the redundant description thereof may be omitted. The matters
described about the producing device according to the present invention are
applicable to the producing method, the formed metal item, and the die
assembly
according to the present invention.
[0068]
The producing device according to the present invention includes a die
assembly and a movement mechanism for moving the die assembly. The die
assembly includes a first die and a second die. The first die includes a
protruding
part for forming a slit. The first and second dies include first and second
pressing
surfaces, respectively, which are configured to deform a U-shaped part having
a U-
shaped cross section to form a cylindrical-shape portion with a gap serving as
a slit.
The die assembly has a configuration to press the outer peripheral surface of
the
cylindrical-shape portion so that the cross-section peripheral length of the
cylindrical-shape portion is made short.
[0069]
Hereinafter, description will be made about two examples of the producing
device according to the present invention (a producing device (a) and a
producing
device (b)).
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[0070]
(Producing Device (a))
The producing device (a) includes the aforementioned die assembly (a). As
mentioned above, the die assembly (a) has the following configurations (a-1),
(a-2),
and (a-3).
(a-1) The die assembly (a) includes a first die provided with a protruding
part, and a
second die.
(a-2) The first and second dies include first and second pressing surfaces,
respectively, which are configured to deform the U-shaped part to form the
cylindrical-shape portion.
(a-3) At least one die selected from the first die and the second die is
separable into a
plurality of die members.
[0071]
A movement mechanism of the producing device (a) includes a first
movement mechanism and a second movement mechanism. The first movement
mechanism is a movement mechanism to bring the first die and the second die
close
to each other while a plurality of die members are separated. Normally, the
first
movement mechanism brings the first die and the second die close to each other
until
the first die and the second die come into contact with each other, with the
plurality
of die members separated. The second movement mechanism is a movement
mechanism to bring the separated plurality of die members close to each other.
The
first movement mechanism corresponds to the aforementioned step (ii-1) of the
example (A). The second movement mechanism corresponds to the step (ii-2) of
the example (A). With the producing device (a), the aforementioned step (ii)
of the
example (A) can be executed.
[0072]
The first die of the die assembly (a) may be separable into a first die member
and a second die member. In this case, the protruding part for forming the
slit may
be constituted by a first protruding part included in the first die member and
a second
protruding part included in the second die member.
[0073]
(Producing Device (b))
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The producing device (b) includes the aforementioned die assembly (b). As
mentioned above, the die assembly (b) has the following configurations (b-1),
(b-2),
and (b-3).
(b-1) The die assembly (b) includes a first die provided with a protruding
part and a
second die.
(b-2) The first and second dies include first and second pressing surfaces,
respectively, which are configured to deform the U-shaped part to form the
cylindrical-shape portion.
(b-3) At least one die selected from the first die and the second die includes
a body
part and a movable part that is movable relative to the body part.
[0074]
A movement mechanism of the producing device (b) includes a first
movement mechanism and a second movement mechanism. The first movement
mechanism is a movement mechanism to bring the first die and the second die
close
to each other. Normally, the first movement mechanism brings the first die and
the
second die close to each other until the first die and the second die come
into contact
with each other, while the pressing surface of the movable part is not
projecting from
the pressing surface of the body part. The second movement mechanism is a
movement mechanism to move the movable part so that the pressing surface of
the
movable part projects from the pressing surface of the body part. The first
movement mechanism corresponds to the aforementioned step (ii-1) of the
example
(B). The second movement mechanism corresponds to the step (ii-2) of the
example (B). With the producing device (b), the aforementioned step (ii) of
the
example (B) can be executed.
[0075]
As long as the aforementioned operation can be performed, the configurations
of the movement mechanisms of the producing devices (a) and (b) have no
special
limitation, and use may be made of a well-known movement mechanism used in a
pressing device of a double acting type. For example, the movement mechanisms
of the producing devices (a) and (b) may be each configured by combining an
expansion/contraction mechanism and a cam. Examples of the
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expansion/contraction mechanism include a gas cylinder, a hydraulic cylinder,
a
spring, and other mechanisms.
[0076]
A producing device for executing the aforementioned step (ii) of the example
(C) has no special limitation except for using the die assembly (c). The step
(ii) of
the example (C) can be executed with a typical pressing device.
[0077]
(Die Assembly)
A die assembly according to the present invention is a die assembly for
producing a formed metal item that includes a tubular part with a slit. This
die
assembly is available in the producing device according to the present
invention.
Furthermore, this die assembly is available in the producing method according
to the
present invention, specifically in the step (ii) of the producing method
according to
the present invention. By using this die assembly, the formed metal item
according
to the present invention can be produced. As to matters about this die
assembly that
have already described in another part of the description, the redundant
description
thereof may be omitted. The matters described about the die assembly according
to
the present invention are applicable to the producing method, the formed metal
item,
and the producing device according to the present invention.
[0078]
The die assembly according to the present invention includes a first die that
includes a protruding part for forming a slit, and a second die. The first and
second
dies include first and second pressing surfaces, respectively, which are
configured to
deform a U-shaped part having a U-shaped cross section to form a cylindrical-
shape
portion with a gap serving as a slit. In the case of forming a cylindrical-
shape
portion (or a tubular part) the outer circumference of the cross section of
which is a
round shape, the second pressing surface has a semi-cylinder shape, and the
first
pressing surface has a semi-cylinder shape except for the protruding part.
[0079]
The die assembly according to the present invention has a configuration to
press the outer peripheral surface of the cylindrical-shape portion so that
the cross-
section peripheral length of the cylindrical-shape portion is made short. From
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another viewpoint, the die assembly according to the present invention has a
configuration to compress the cylindrical-shape portion in the circumferential
direction. Examples of the die assembly of the present invention include the
aforementioned die assembly (a) and die assembly (b).
[0080]
Use may be made of the first die including the protruding part as an upper
die,
and use may be made of the second die as a lower die. Therefore, in the
present
specification, the first die may be alternatively referred to as the upper
die, and the
second die may be alternatively referred to as the lower die. In addition, the
first
die may be alternatively referred to as the lower die, and the second die may
be
alternatively referred to as the upper die.
[0081]
The protruding part has a shape that allows a slit to be formed. By the use of
the first die in which a plate-shaped protruding part is disposed along the
axis
direction of the tubular part, it is possible to form the slit along the axis
direction of
the tubular part. In a typical example, the protruding part is a plate-shaped
salient
part and provided at a position in an uppermost part of the semicircular
pressing
surface of the upper die. In other words, in a typical example, the protruding
part is
provided in a central portion of the cross section of the pressing surface of
the upper
die (the cross section in the circumferential direction). However, the
protruding
part need not be in the central portion and may be at a position shifted from
the
center. For example, in the case of forming a horizontally-asymmetrical
tubular
part, the protruding part may be at a position shifted from the central
portion. The
position of the protruding part in the circumferential direction may be
changed along
the axis direction. The width of the protruding part may be changed along the
axis
direction. By the use of the protruding part that changes in the axis
direction, it is
possible to form a slit that changes in the axis direction.
[0082]
Assuming that the inner diameter of the tubular part is denoted by Din, and
the thickness of the tubular part is denoted by t, the width of the slit may
be set at t or
larger and (Din - 2t) or smaller. A width of the slit smaller than t may
result in a
CA 02975861 2017-08-03
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sufficient strength of the protruding part of the die assembly. A width of the
slit
larger than (Din-2t) may decrease the advantageous effects of the invention.
[0083]
The width of the protruding part is selected in accordance with the width of
the slit (the gap of the butted part). The width of the protruding part is
preferably
set within 10% of the width of the slit.
[0084]
As mentioned above, in the die assembly (a), at least one die selected from
the
first die and the second die is separable into a plurality of die members.
When the
number of the die members is large, there is the risk that the U-shaped part
is likely
to be clamped between adjacent die members in the forming. In addition, when
the
number of the die members is large, the structures of the die assembly and a
device
using the die assembly become complex. Therefore, in a preferable example of
the
case where the first die is divided into a plurality of die members, the first
die is
divided into two die members. Similarly, in a preferable example of the case
where
the second die is divided into a plurality of die members, the second die is
divided
into two die members.
[0085]
In the case where the first die and/or the second die is separable into a
plurality of die members, the position of the separation has no special
limitation. In
the case where the first die is separable into the first die member and the
second die
member, the protruding part may be constituted by a first protruding part
included in
the first die member and a second protruding part included in the second die
member.
That is, the first die may be divided at the protruding part. With this
configuration,
two end parts of the U-shaped part can be guided by the first and second
protruding
parts, which can prevent the end parts of the U-shaped part from coming into a
space
between the two die members.
[0086]
With the die assembly (a), by moving the plurality of die members
individually, it is possible to perform a fine adjustment of the cross-section
peripheral length LH of the tubular part easily and to reduce variations in
compressive stress acting on the tubular part. Consequently, with the die
assembly
CA 02975861 2017-08-03
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(a), it is possible to suppress the spring back effectively, with the result
that the slit
can be formed with precision.
[0087]
As mentioned above, in the die assembly (b), at least one die selected from
the first die and the second die includes the body part and the movable part
that is
movable relative to the body part.
[0088]
In the die assembly (b), only the first die may include the body part and the
movable part, or only the second die may include the body part and the movable
part.
Alternatively, both of the first and second dies may each include the body
part and
the movable part. In the case where the both dies each include the body part
and
the movable part, the area of the pressing surface of the movable part can be
increased, and as a result, at the time when the cylindrical-shape portion is
pressed
and compressed in the circumferential direction, the press can be performed
stably.
[0089]
The positions at which the movable parts are disposed have no special
limitation as long as the positions allow the adjustment of the cross-section
peripheral length of the tubular part by the movement of the movable part. For
example, the movable parts may be disposed at positions corresponding to a top
part
and a bottom part of the tubular part or may be disposed at positions
corresponding
to two side parts of the tubular part. The movable parts are preferably
disposed at
two positions that are opposed to each other across the center of the tubular
part.
[0090]
The movable parts are disposed at least in a zone where step (ii) of the
example (B) is executed. For example, the movable parts may be disposed over
the
overall length of the die assembly or may be disposed over only in part of the
die
assembly.
[0091]
In the case where the first die includes a body part and a movable part, the
number of movable parts may be one or more. In the case where the number of
movable parts is more than one, the cross-section peripheral length of the
tubular part
is easy to adjust finely in comparison with the case where the number of
movable
CA 02975861 2017-08-03
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parts is one. Similarly, in the case where the second die includes a body part
and a
movable part, the number of movable parts may be one or more. In the case
where
the number of movable parts is more than one, the movable parts may be
disposed at
both of a position corresponding to the top part (or the bottom part) of the
cylindrical-shape portion and positions corresponding to the side parts of the
cylindrical-shape portion.
[0092]
The movable part(s) can be moved by a cylinder, a cam mechanism, or the
like so as to move relative to the body part.
[0093]
In the die assembly according to the present invention, the protruding part
for
forming a slit may be replaceable. For example, in the aforementioned die
assemblies (a), (b) and (c), the protruding part may be replaceable. The
protruding
part easily wears. Thus, by making the protruding part replaceable, the
lifetime of
the die assembly can be extended. In addition, by replacing the protruding
part, the
width of the slit becomes easy to adjust. When the physical properties
(tensile
strength, etc.) or the thickness of a metal plate (blank) varies, the amount
of spring
back varies. Therefore, in a conventional method, the entire die assembly
needs to
be changed whenever the physical properties or the thickness of the metal
plate
varies. However, by replacing the protruding part, the width of the slit
becomes
easy to adjust without changing the entire die assembly.
[0094]
The shape of the die assembly is designed as appropriate in conformity with
the shape and the like of an intended tubular part. For example, as
illustrated in
FIG. 8, the cross-sectional shape in a circumferential direction of the
pressing surface
of a die assembly may be a vertically asymmetric shape or may be a
horizontally
asymmetric shape. The cross-sectional shape in the circumferential direction
of the
pressing surface of the die assembly may be constant in an axis direction or
may
change in the axis direction. In addition, the pressing surface of the die
assembly
may be straight in the axis direction or may be bent relative to the axis
direction.
[0095]
CA 02975861 2017-08-03
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The first die and the second die each may be of a single acting type. The
first die and the second die each may be of a double acting type as necessary.
In the
die assemblies (a) and (b), at least one selected from the first and second
dies is of
the double acting type. The use of a die assembly of the double acting type
allows
the cross-section peripheral length of the cylindrical-shape portion to be
adjusted
finely and allows variations in compressive stress acting on the cylindrical-
shape
portion to be reduced. Therefore, it is possible to suppress in particular
spring back
effectively and to increase in particular the precision of the shape of the
formed
metal item. In the case where the die assembly is of the double acting type, a
producing device including the die assembly includes a mechanism used in a
pressing device of the double acting type or a mechanism including a cylinder,
a cam,
or the like.
[0096]
In the case where the material or the thickness of a metal plate varies, the
amount of spring back also varies accordingly. Therefore, in a forming method
using a conventional die assembly, when the material or the thickness of a
metal
plate varies, the die assembly needs to be changed accordingly. In contrast,
with
the die assembly according to the present invention, it is possible to change
the
compressibility of a tubular part without changing the die assembly. For
example,
with the die assembly (a), the compressibility of the tubular part can be
changed by
changing distances between a plurality of die members. In addition, with the
die
assembly (b), the compressibility of the tubular part can be changed by
changing the
amounts of movement of the movable parts. Therefore, with the die assembly
according to the present invention, even in the case where the material or the
thickness of a metal plate varies, it is possible to control the breadth of
the slit
without changing the die assembly. Consequently, the die assembly according to
the present invention is suitable for volume production of the formed metal
item
according to the present invention.
[0097]
As will be described later, by the use of the die assembly according to the
present invention, it is possible to reduce variations in hardness
distribution in the
thickness direction and variations in hardness distribution in the
circumferential
CA 02975861 2017-08-03
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direction, of the tubular part. Therefore, by the use of the die assembly
according to
the present invention, it is possible to produce a formed metal item having a
high
fatigue strength.
[0098]
Hereinafter, exemplary embodiments of the present invention will be
described with reference to the drawings. In the following description,
similar parts
will be denoted by the same reference characters, and the redundant
description
thereof may be omitted.
[0099]
(First Embodiment)
In a first embodiment, description will be made about an example of the
formed metal item according to the present invention. The formed metal item
according to the present invention includes a tubular part with a slit. FIG. 1
schematically illustrates a cross section in a direction orthogonal to the
axis direction
of the tubular part (a cross section in a circumferential direction). A formed
metal
item 1 includes a tubular part le that is formed with a slit 3 and is
typically
constituted by only the tubular part le. In the slit 3, two end parts El and
E2 are
butted against each another. From another viewpoint, the formed metal item 1
is a
substantially-closed-cross-sectional component (a tubular component having a
substantially-closed cross section). Here, the substantially-closed cross
section
refers to a cross section in which a gap is present between two butted end
parts of a
metal plate that is formed to be tubular. The substantially-closed-cross-
sectional
component may have the gap across the overall length of a butted part or may
have
the gap only in part of the butted part.
[0100]
Here, assume points PI and P2 that are separated from the two end parts El
and E2 by 3 mm along the tubular part le in the circumferential direction,
respectively. Assume that the intersection of a tangential line at the point
PI and a
tangential line at the point P2 is denoted by 0. An angle 0 formed by the line
0P1
and the line 0P2 is preferably 30 or larger. An excessively small angle 0
leads to
little difference in cross section between the tubular part le and the U-
shaped part,
which may decrease the strength (flexural strength) of the tubular part after
forming.
CA 02975861 2017-08-03
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The angle 0 in a typical example is 1500 or larger (e.g., 170 or larger). The
angle 0
is preferably 180 or smaller. An excessively large angle 0 leads to the risk
of an
unstable forming.
[0101]
(Second Embodiment)
In a second embodiment, description will be made about an example of the
producing method according to the present invention and the die assembly used
in
the producing method. In the following embodiments, description will be made
about an example of the case of producing a formed metal item that is
constituted by
only a tubular part. The producing method in the second embodiment includes
step
(i) and step (ii).
[0102]
Step (i) is schematically illustrated in FIG. 2A and 2B. First, as illustrated
in
FIG. 2A, a metal plate (blank) la is disposed between a die 11 and a punch 12.
The
die assembly for U forming is configured by the die 11 and the punch 12. Next,
as
illustrated in FIG. 2B, the metal plate la is subjected to press forming to be
formed
into a U-shaped part lb having a U-shaped cross section. As illustrated in
FIG. 2C,
the U-shaped part lb includes two end parts El and E2.
[0103]
In step (i), the size relation between a width W of a part to be made into a
tubular part (the tubular part le) and the cross-section length LU of the U-
shaped
part lb, of the metal plate, changes under various conditions (the shape of
the tubular
part, the conditions of step (i), etc.). These conditions can result in the
case where
the cross-section length LU is longer than the width W, the case where the
cross-
section length LU is shorter than the width W, and the case where both are
equal to
each other. In the producing method according to the present invention, in
step (ii),
it is important to form the tubular part in such a manner that the cross-
section
peripheral length LH of the tubular part is shorter than the cross-section
length LU of
the U-shaped part. Therefore, the relation between the width W and the cross-
section length LU in step (i) has no special limitation.
[0104]
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FIG. 3A schematically illustrates a die assembly used in step (ii) of in the
second embodiment. A die assembly 20 in the second embodiment is an example
of the aforementioned die assembly (a). The die assembly 20 includes an upper
die
(first die) 21 and a lower die (second die) 22.
[0105]
The upper die 21 includes a plate-shaped protruding part 23 for forming a
slit.
The upper die 21 includes a first upper die (first die member) 21a and a
second upper
die (second die member) 2 lb that are separable in a horizontal direction. The
protruding part 23 is configured by a first protruding part 23a included in
the first
upper die 21a and a second protruding part 23b included in the second upper
die 21b.
The lower die 22 includes a first lower die (first die member) 22a and a
second lower
die (second die member) 22b that are separable in the horizontal direction.
[0106]
The upper die 21 includes a first pressing surface 21p that is configured to
press the outer peripheral surface of the U-shaped part lb to form the
cylindrical-
shape portion Id. The lower die 22 includes a first pressing surface 22p that
is
configured to press the outer peripheral surface of the U-shaped part lb to
form the
cylindrical-shape portion Id (FIG. 3D). The protruding part 23 is a plate-
shaped
salient part, the length of which is equal to or longer than the slit 3 to be
formed.
The cross-section peripheral length of the entire pressing surface of the die
assembly
20 (the first pressing surface 21p and the second pressing surface 22p) is
shorter than
the cross-section length LU of the U-shaped part lb.
[0107]
The next step (ii) will be described with reference to FIG. 3B to FIG. 3E.
Step (ii) in the second embodiment is the aforementioned step of the example
(A)
and includes step (ii-1) and step (ii-2). By step (ii), the tubular part le
with a slit
can be formed from the U-shaped part lb.
[0108]
In step (ii) of the second embodiment, first, the U-shaped part lb is disposed
in the die assembly 20 as illustrated in FIG. 3B. Next, as illustrated in FIG.
3C and
FIG. 3D, the U-shaped part lb is deformed using the die assembly 20, with the
end
part El and the end part E2 of the U-shaped part lb (see FIG. 2C) clamping the
- 37 -
protruding part 23 (Step (ii-1)). Specifically, the upper die 21 and the lower
die 22
are brought close to each other until both come into contact with each other,
so that
the outer peripheral surface of the U-shaped part lb is pressed by the
pressing
surface of the die assembly 20. Step (ii-1) is executed in the state where the
first
upper die 21a and the second upper die 21b are separated in the horizontal
direction,
and the first lower die 22a and the second lower die 22b are separated in the
horizontal direction. In this state, the upper die 21 and/or the lower die 22
is moved
in the vertical direction, so that both are brought close to each other. By
step (ii-1),
the cylindrical-shape portion Id is formed. In the step illustrated in FIG.
3C, the U-
shaped part lb is deformed into a U-shaped part le. At this point, two end
parts of
the U-shaped part lc are butted against the protruding part 23 to stop, so
that a gap is
generated between the end parts. The gap serves as the slit 3 of the tubular
part le.
In the state illustrated in FIG. 3D, the end part El and the end part E2 face
each other
across the protruding part 23 (the protruding parts 23a and 23b).
[0109]
By the producing method in the second embodiment, in the state illustrated in
FIG. 3D, the cross-section length of the U-shaped part lb and the cross-
section
peripheral length of the cylindrical-shape portion id may be made
substantially equal
to each other. This configuration can be implemented by adjusting the interval
between the first upper die 21a and the second upper die 21b, and the interval
between the first lower die 22a and the second lower die 22b. With this
configuration, at the time of deforming the U-shaped part lb by a large amount
to
form the cylindrical-shape portion Id, it is possible to inhibit compressive
force from
acting in the circumferential direction. Therefore, it is possible to inhibit
buckling
or the like from occurring at the time of forming the cylindrical-shape
portion id.
Here, being substantially equal to each other means that the difference
between both
is less than 0.1% (e.g., less than 0.05%) of the length of the larger one.
[0110]
Next, as illustrated in FIG. 3E, by pressing the outer peripheral surface of
the
cylindrical-shape portion Id while the end parts El and E2 of the U-shaped
part lb
are clamping the protruding part 23, the cross-section peripheral length of
the
cylindrical-shape portion id is shortened (Step (ii-2)). Specifically, by
closing the
CA 2975861 2019-06-18
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divided die assembly 20, the cross-section peripheral length is shortened.
More
specifically, the first upper die 21a and the second upper die 21b are moved
in the
horizontal direction to come close to each other, and the first lower die 22a
and the
second lower die 22b are moved in the horizontal direction to come close to
each
other. In the example illustrated in FIG. 3E, the first upper die 21a and the
second
upper die 21b come into contact with each other, and the first lower die 22a
and the
second lower die 22b are brought close to each other until they come into
contact
with each other. That is, in the example illustrated in FIG. 3E, the pressing
surface
of the die assembly 20 in a completely closed state corresponds to the outer
peripheral surface of the tubular part le. By shortening the cross-section
peripheral
length of the cylindrical-shape portion Id in step (ii-2), it is possible to
make the
cross-section peripheral length LH of the tubular part le shorter than the
cross-
section length LU of the U-shaped part lb. In this manner, a tubular part le
(formed metal item) illustrated in FIG. 3F is obtained. The butted part 2 of
the
tubular part le is formed with the slit 3.
[0111]
FIG. 3E illustrates the case where the die assembly is completely closed in a
final phase of the forming. However, in the producing method according to the
present invention, as long as the cross-section peripheral length LH of the
tubular
part le is made shorter than the cross-section length LU of the U-shaped part
1 b, the
die assembly need not be completely closed in the final phase of the forming.
By
determining to what degree the die assembly is closed, the aforementioned
compressibility C can be changed. By determining to what degree the die
assembly
30 is opened in FIG. 3D, and by determining to what degree the die assembly 20
is
closed in FIG. 3E, it is in some cases possible to deal with the case where
the
thickness or the physical properties of the metal plate la vary. Therefore,
even in
the case where the thickness or the physical properties of the metal plate la
vary, it is
in some cases possible to produce a desired tubular part le without changing
the die
assembly. Furthermore, in FIG. 3E, by determining to what degree the die
assembly 20 is closed, it is also possible to change the width of the slit 3.
[0112]
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In the case of producing a tubular component by conventional UO forming,
compressive stress acts on an inner circumferential side of the resultant
tubular
component, and tensile stress acts on an outer circumference side of the
resultant
tubular component. Therefore, spring back increases, which makes it difficult
to
control the spring back. In contrast, in the producing method according to the
present invention, the cross-section peripheral length LH of the tubular part
le is
made shorter than the cross-section length LU of the U-shaped part lb. That
is, in
the producing method according to the present invention, the cylindrical-shape
portion Id is compressed in the circumferential direction, and the tubular
part le is
thereby obtained. As a result, in the tubular part le, compressive stress acts
on both
of the inner circumferential side and the outer circumference side.
Consequently,
the spring back is inhibited, and the slit 3 can be formed with precision.
[0113]
In the producing method according to the present invention, by compressing
the cylindrical-shape portion id in the circumferential direction, the tubular
part le is
formed. Therefore, in the tubular part le, compressive stress acts on both of
the
inner circumferential side and the outer circumference side. Furthermore, in
the
tubular part le, it is possible to reduce variations in the compressive stress
in the
circumferential direction. As a result, it is possible to reduce variations in
hardness
distribution in the thickness direction and to reduce variations in hardness
distribution in the circumferential direction, of the tubular part le.
Consequently,
according to the present invention, it is possible to obtain a tubular part
having a high
fatigue strength.
[0114]
In the producing method according to the second embodiment, the cylindrical-
shape portion Id is compressed by moving all of the die members surrounding
the
cylindrical-shape portion Id relatively. Therefore, by the producing method
and the
die assembly in the second embodiment, it is possible to compress the
cylindrical-
shape portion Id uniformly in the circumferential direction. Consequently, the
spring back can be inhibited effectively, and it is possible to increase the
shape
precision of the tubular part even more.
[0115]
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(Third Embodiment)
In a third embodiment, description will be made about another example of the
producing method according to the present invention and the die assembly used
in
the producing method. The producing method in the third embodiment includes
step (i) and step (ii). Step (i) is the same as step (i) described in the
second
embodiment, and thus the redundant description thereof will be omitted.
[0116]
FIG. 4A schematically illustrates a die assembly used in step (ii) in the
third
embodiment. A die assembly 30 in the third embodiment is an example of the
aforementioned die assembly (b). The die assembly 30 includes an upper die
(first
die) 31 and a lower die (second die) 32.
[0117]
The upper die 31 includes a plate-shaped protruding part 33 for forming the
slit 3. The upper die 31 includes a body part 31a and a movable part 31b that
is
movable relatively to the body part 31a. The movable part 31b is disposed in a
top
part of a pressing surface 3 lap of the body part 31a and includes the
protruding part
33. The lower die 32 includes a body part 32a and a movable part 32b that
is
movable relatively to body part 32a. The movable part 32b is disposed in a
bottom
part of a pressing surface 32ap of the body part 32a. In the die assembly 30
in the
third embodiment, both of the movable parts 31b and 32b are movable in a
pressing
direction (the vertical direction). The movable part 31b can be moved in the
pressing direction together with the body part 31a. The movable part 32b can
be
moved in the pressing direction together with the body part 32a.
[0118]
In the die assembly (b) according to the present invention, the body part and
the movable part can be moved basically together in the pressing direction. In
addition, in the die assembly (b) according to the present invention, end
faces of the
movable parts (the end faces facing a forming space) basically constitute
parts of the
pressing surface, and rolls or the like are not disposed therein. Furthermore,
in the
die assembly (b) according to the present invention, the movable parts are
basically
movable, with first and second body parts lying at a final position in the
forming (a
dead point).
CA 02975861 2017-08-03
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[0119]
The body part 31a and the body part 32a include the pressing surfaces 31ap
and 32ap, respectively, the pressing surfaces 31ap and 32ap being configured
to
press the outer peripheral surface of the U-shaped part lb to form the
cylindrical-
shape portion Id. The movable parts 31b and 32b include pressing surfaces 3Ibp
and 32bp, respectively, the pressing surfaces 31bp and 32bp being configured
to
press the outer peripheral surface of the U-shaped part lb. The pressing
surface
3 lap and the pressing surface 31bp constitute the pressing surface 31p of the
upper
die 31. The pressing surface 32ap and the pressing surface 32bp constitute the
pressing surface 32p of the lower die 32. In the example described in the
third
embodiment, the cross-section peripheral length of the entire pressing surface
is
longer than the cross-section peripheral length LH of the tubular part le. The
cross-
section peripheral length of the entire pressing surface may be substantially
equal to
the cross-section length LU of the U-shaped part lb.
[0120]
The next step (ii) will be described with reference to FIG. 4B to FIG. 4E.
Step (ii) in the third embodiment is the aforementioned step of the example
(B) and
includes step (ii-1) and step (ii-2). By step (ii), the tubular part le with a
slit can be
formed from the U-shaped part lb.
[01211
In step (ii) of the third embodiment, tirst, the U-shaped part lb is disposed
in
the die assembly 20 as illustrated in FIG. 4B. Next, as illustrated in FIG. 4C
and
FIG. 4D, the U-shaped part lb is deformed using the die assembly 30, while the
end
part El and the end part E2 of the U-shaped part lb (see FIG. 2C) are clamping
the
protruding part 33 (Step (ii-1)). Specifically, the upper die 31 and the lower
die 32
are brought close to each other until both come into contact with each other,
so that
the outer peripheral surface of the U-shaped part lb is pressed by the
pressing
surface of the die assembly 30. Step (ii-1) is executed with the pressing
surfaces
31bp and 32bp of the movable parts 31 b and 32b not projecting from the
pressing
surfaces 3 I p and 32p of the body part. By step (ii-1), the cylindrical-shape
portion
1 d is formed. That is, in the example illustrated in FIG. 4D, the pressing
surfaces
31p and 32p correspond to the outer peripheral surface of the cylindrical-
shape
- 42 -
portion Id. In the step illustrated in FIG. 4C, the U-shaped part lb is
deformed into
a U-shaped part lc. At this point, two end parts of the U-shaped part lc are
butted
against the protruding part 33 to stop, so that a gap is generated between the
end
parts. The gap serves as the slit 3 of the tubular part le. In the state
illustrated in
FIG. 4D, the end part El and the end part E2 face each other across the
protruding
part 33.
[0122]
In the producing method in the third embodiment, the cross-section peripheral
length of the entire pressing surface of the die assembly 30 may be made
substantially equal to the cross-section length LU of the U-shaped part lb. In
this
case, at the time of deforming the U-shaped part lb by a large amount to form
the
cylindrical-shape portion id, it is possible to inhibit compressive force from
acting in
the circumferential direction. Therefore, it is possible to inhibit buckling
or the like
from occurring at the time of forming the cylindrical-shape portion id.
[0123]
Next, as illustrated in FIG. 4E, by pressing the outer peripheral surface of
the
cylindrical-shape portion Id while the end parts El and E2 of the U-shaped
part lb
are clamping the protruding part 33, the cross-section peripheral length of
the
cylindrical-shape portion id is shortened (Step (ii-2)). Specifically, by
causing the
pressing surfaces of the movable parts 31b and 32b to project from the
pressing
surfaces of the body parts 31a and 32a, the outer peripheral surface of the
cylindrical-
shape portion Id is pressed. In the third embodiment, the slit 3 and the
positions
facing the slit 3, of the cylindrical-shape portion id, are pressed
vertically. By
shortening the cross-section peripheral length of the cylindrical-shape
portion id in
step (ii-2), the cross-section peripheral length LH of the tubular part le is
made
shorter than the cross-section length LU of the U-shaped part lb. In this
manner, a
tubular part le (formed metal item) illustrated in FIG. 4F is obtained. The
butted
part 2 of the tubular part le is formed with the slit 3.
[0124]
Also in the producing method in the third embodiment, by compressing the
cylindrical-shape portion ld in the circumferential direction, the tubular
part le is
formed. Therefore, as described in the second embodiment, the slit 3 can be
formed
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with precision. In addition, in the producing method in the third embodiment,
it is
possible to change the aforementioned compressibility easily by changing the
amount of movement of the movable parts. Therefore, even in the case where the
thickness or the physical properties of the metal plate I a vary, it is in
some cases
possible to produce a desired tubular part le without changing the die
assembly.
Furthermore, in the die assembly in the third embodiment, the protruding part
33 can
be replaced by replacing the movable part 31b, which makes it easy to replace
the
protruding part 33.
[0125]
In the producing method in the third embodiment, since the compression is
performed by pressing the cylindrical-shape portion Id with the movable parts,
the
cylindrical-shape portion Id is compressed in the state where a contact area
between
the cylindrical-shape portion Id and the die assembly 30 is small. In this
case,
compressive force exerted in the circumferential direction by the movable
parts is
likely to be exerted on the entire cylindrical-shape portion Id. Therefore, by
the
producing method and the die assembly in the third embodiment, it is possible
to
compress the cylindrical-shape portion Id more uniformly in the
circumferential
direction.
[0126]
With reference to FIG. 14A to FIG. 14E, description will be made about an
example of a producing device that can be used in step (ii) in the third
embodiment.
This producing device includes a first support table 141, a second support
table 142,
expansion/contraction mechanisms 141a, and expansion/contraction mechanisms
142a. On the first support table 141, the expansion/contraction mechanisms
14Ia
and the movable part 31b are disposed. The expansion/contraction mechanisms
141a are expandable in the pressing direction and are configured to press the
body
part 31a. On the second support table 142, the expansion/contraction
mechanisms
I42a and the movable part 32b are disposed. The expansion/contraction
mechanisms 142a are expandable in the pressing direction and are configured to
support the body part 32a. The expansion/contraction mechanisms 141a and 142a
have no special limitation, and each may be a gas cylinder, a hydraulic
cylinder, a
spring, or other mechanisms.
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[0127]
In step (ii) of the third embodiment, first, the U-shaped part lb is disposed
in
the die assembly 30 as illustrated in FIG. 14A. Next, as illustrated in FIG.
14B and
14C, the first support table 141 and the second support table 142 are brought
close to
each other. The aforementioned step (ii-1) is thereby performed, and the
cylindrical-shape portion Id is obtained. Next, as illustrated in FIG. 14D, by
causing the expansion/contraction mechanisms to contract, the first support
table 141
and the second support table 142 are brought closer to each other. The
pressing
surfaces of the movable parts 31b and 32b are thereby caused to project from
the
pressing surfaces of the body parts 31a and 32a and press the outer peripheral
surface
of the cylindrical-shape portion Id, as illustrated in FIG. 14D. In this
manner, step
(11-2) is performed.
[0128]
In the device illustrated in FIG. 14A, a mechanism to bring the first support
table 141 and the second support table 142 close to each other (not
illustrated), and
the expansion/contraction mechanism 141a and the expansion/contraction
mechanism 142a not in an expanding/contracting state correspond to the
aforementioned the first movement mechanism of the producing device (b). In
addition, a mechanism to bring the first support table 141 and the second
support
table 142 close to each other, and the expansion/contraction mechanism 141a
and the
expansion/contraction mechanism 142a in the expanding/contracting state
correspond to the second movement mechanism. In this manner, in the die
assemblies (a) and (b), the single constituting member may serve as the first
movement mechanism and the second movement mechanism. These movement
mechanisms may be implemented by using movement mechanisms of a well-known
pressing device with the movement mechanisms adapted to the producing device
according to the present invention.
[0129]
(Fourth Embodiment)
In a fourth embodiment, description will be made about another example of
the producing method according to the present invention and the die assembly
used
in the producing method. The producing method in the fourth embodiment
includes
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step (i) and step (ii). Step (i) is the same as step (i) described in the
second
embodiment, and thus the redundant description thereof will be omitted.
[0130]
FIG. 5A schematically illustrates a die assembly used in step (ii) in the
fourth
embodiment. A die assembly 30 in the fourth embodiment is an example of the
aforementioned die assembly (b). The die assembly 30 includes an upper die
(first
die) 31 and a lower die (second die) 32.
[0131[
The upper die 31 includes a plate-shaped protruding part 33 for forming the
slit 3. The upper die 31 includes a body part 31a and two movable parts 31b
that
are movable relative to the body part 31a. The movable parts 31b are disposed
in
the lowermost part of the pressing surface of the body part 31a. The lower die
32
includes a body part 32a and two movable parts 32b that are movable relative
to
body part 32a. The movable parts 32b are disposed in the uppermost part of the
pressing surface of the body part 32a. In the die assembly 30 in the fourth
embodiment, both of the movable parts 32a and 32b are movable in the
horizontal
direction. The movable part 31b can be moved in the vertical direction
(pressing
direction) together with the body part 31a. Similarly, the movable part 32b
can be
moved in the vertical direction together with the body part 32a.
[0132]
The body part 3 I a and the body part 32a include the pressing surfaces 31ap
and 32ap, respectively, the pressing surfaces 31ap and 32ap being configured
to
press the outer peripheral surface of the U-shaped part lb to form the
cylindrical-
shape portion Id. The movable parts 31b and 32b include pressing surfaces 31bp
and 32bp, respectively, the pressing surfaces 3 I bp and 32bp being configured
to
press the outer peripheral surface of the U-shaped part lb. In the example
described
in the fourth embodiment, the cross-section peripheral length of the entire
pressing
surface is longer than the cross-section peripheral length LH of the tubular
part le.
The cross-section peripheral length of the entire pressing surface may be
substantially equal to the cross-section length LU of the U-shaped part lb.
[0133]
- 46 -
The next step (ii) will be described with reference to FIG. 5B to FIG. 5E.
Step (ii) in the fourth embodiment is the aforementioned step of the example
(B) and
includes step (ii-1) and step (ii-2). By step (ii), the tubular part le with a
slit can be
formed from the U-shaped part lb.
[0134]
In step (ii) of the fourth embodiment, first, the U-shaped part lb is disposed
in
the die assembly 30 as illustrated in FIG. 5B. Next, as illustrated in FIG. 5C
and
FIG. 5D, the U-shaped part lb is deformed using the die assembly 30, while the
end
part El and the end part E2 of the U-shaped part lb (see FIG. 2C) are clamping
the
protruding part 33 (Step (ii-1)). Specifically, the upper die 31 and the lower
die 32
are brought close to each other until both come into contact with each other,
so that
the outer peripheral surface of the U-shaped part lb is pressed by the
pressing surface
of the die assembly 30. Step (ii-1) is executed with the pressing surfaces
31bp and
32bp of the movable parts not projecting from the pressing surfaces 31ap and
32ap of
the body part. By step (ii-1), the cylindrical-shape portion ld is formed. In
the
step illustrated in FIG. 5C, the U-shaped part lb is deformed into a U-shaped
part lc.
At this point, two end parts of the U-shaped part lc are butted against the
protruding
part 33 to stop, so that a gap is generated between the end parts. The gap
serves as
the slit 3 of the tubular part le. In the state illustrated in FIG. 5D, the
end part El
and the end part E2 face each other across the protruding part 33.
[0135]
In the producing method in the fourth embodiment, the cross-section
peripheral length of the entire pressing surface of the die assembly 30 may be
made
substantially equal to the cross-section length LU of the U-shaped part lb. In
this
case, at the time of deforming the U-shaped part lb by a large amount to form
the
cylindrical-shape portion ld, it is possible to inhibit compressive force from
acting in
the circumferential direction. Therefore, it is possible to inhibit buckling
or the like
from occurring at the time of forming the cylindrical-shape portion Id.
[0136]
Next, as illustrated in FIG. 5E, by pressing the outer peripheral surface of
the
cylindrical-shape portion ld while the end parts El and E2 of the U-shaped
part lb
are clamping the protruding part 33, the cross-section peripheral length of
the
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cylindrical-shape portion Id is shortened (Step (ii-2)). Specifically, by
causing the
pressing surfaces 31bp and 32bp of the movable parts 31b and 32b to project
from
the pressing surfaces 31ap and 32ap of the body parts 31a and 32b, the outer
peripheral surface of the cylindrical-shape portion id is pressed. In the
fourth
embodiment, the side faces of the cylindrical-shape portion id are pressed
from right
and left. By shortening the cross-section peripheral length of the cylindrical-
shape
portion Id in step (ii-2), the cross-section peripheral length LH of the
tubular part le
is made shorter than the cross-section length LU of the U-shaped part lb. In
this
manner, a tubular part le (formed metal item) illustrated in FIG. 5F is
obtained.
The butted part 2 of the tubular part le is formed with the slit 3.
[0137]
Also in the producing method in the fourth embodiment, by compressing the
cylindrical-shape portion id in the circumferential direction, the tubular
part le is
formed. Therefore, as described in the second and third embodiments, the slit
3 can
be formed with precision. In addition, in the producing method in the third
and
fourth embodiments, it is possible to change the aforementioned
compressibility
easily by changing the amount of movement of the movable parts. Therefore,
even
in the case where the thickness or the physical properties of the metal plate
la
slightly vary, it is in some cases possible to produce a desired tubular part
le without
changing the die assembly.
[0138]
With reference to FIG. 15A to FIG. 15E, description will be made about an
example of a producing device that can be used in step (ii) in the fourth
embodiment.
This producing device includes a first support table 151, two
expansion/contraction
mechanisms 141a, two shafts 153, and two cam units 154. The
expansion/contraction mechanisms 141a and the shafts 153 are disposed on the
first
support table 151. The expansion/contraction mechanisms 141a are expandable in
the pressing direction and are configured to press the body part 31a.
[0139]
In step (ii) of the fourth embodiment, first, the U-shaped part lb is disposed
in
the die assembly 30 as illustrated in FIG. 15A. Next, as illustrated in FIGS.
15B
and 15C, the first support table 151 is pressed down. The aforementioned step
(ii-
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1) is thereby performed, and the cylindrical-shape portion Id is obtained.
Next, as
illustrated in FIG. 15D, by causing the expansion/contraction mechanisms to
contract,
the first support table 151 is further pressed down. At this point, the two
cam units
154 are moved by the two shafts 153, and the movable parts 3 lb and 32b are
moved
by the cam units 154. The pressing surfaces of the movable parts 31b and 32b
are
thereby caused to project from the pressing surfaces of the body parts 31a and
32a
and press the outer peripheral surface of the cylindrical-shape portion Id, as
illustrated in FIG. 15D. In this manner, step (ii-2) is performed.
[0140]
In the device illustrated in FIG. 15A, a mechanism to move the first support
table 151 downward (not illustrated) and the expansion/contraction mechanisms
141a
not in an expanding/contracting state correspond to the aforementioned the
first
movement mechanism of the producing device (b). In addition, a mechanism to
move the first support table 151 downward, the shafts 153, and the cam units
154
constitute the second movement mechanism. These movement mechanisms may be
implemented by using movement mechanisms of a well-known pressing device with
the movement mechanisms adapted to the producing device according to the
present
invention.
[0141]
(Fifth Embodiment)
In a fifth embodiment, description will be made about another example of the
producing method according to the present invention and the die assembly used
in
the producing method. The producing method in the fifth embodiment includes
step (i) and step (ii). Step (i) is the same as step (i) described in the
second
embodiment, and thus the redundant description thereof will be omitted.
[0142]
FIG. 6A schematically illustrates a die assembly used in step (ii) in the
fifth
embodiment, A die assembly 20 in the fifth embodiment includes an upper die
(first die) 21 and a lower die (second die) 22.
[0143]
The upper die 21 includes a plate-shaped protruding part 23 for forming a slit
3. The first upper die 21 and the second lower die 22 include pressing
surfaces 21p
- 49 -
and 22p, respectively, the pressing surfaces 21p and 22p being configured to
press
the outer peripheral surface of the U-shaped part lb to form the cylindrical-
shape
portion ld. In the die assembly 20 in the fifth embodiment, the cross-section
peripheral length of the entire pressing surface is shorter than the cross-
section length
LU of the U-shaped part lb. By deforming the U-shaped part lb using this die
assembly 20, it is possible to make the cross-section peripheral length LH of
the
tubular part le shorter than the cross-section length LU of the U-shaped part
lb.
[0144]
The next step (ii) will be described with reference to FIG. 6B to FIG. 6E.
Step (ii) in the fifth embodiment is the aforementioned step of the example
(C). In
step (ii) of the fifth embodiment, first, the U-shaped part lb is disposed in
the die
assembly 20 as illustrated in FIG. 6B. Next, as illustrated in FIG. 6C and
FIG. 6D,
the cylindrical-shape portion ld is formed by deforming the U-shaped part lb
using
the die assembly 20 in such a manner that the end part El and the end part E2
of the
U-shaped part lb clamp the protruding part 23. Specifically, the upper die 21
and
the lower die 22 are brought close to each other, so that the outer peripheral
surface
of the U-shaped part lb is pressed by the pressing surface of the die assembly
20.
In the step illustrated in FIG. 6C, the U-shaped part lb is deformed into a U-
shaped
part lc. At this point, two end parts of the U-shaped part 1 e are butted
against the
protruding part 23 to stop, so that a gap is generated between the end parts.
The gap
serves as the slit 3 of the tubular part le.
[0145]
FIG. 6D illustrates an example of the state where the cross-section peripheral
length of the cylindrical-shape portion ld is substantially equal to cross-
section
length LU of the U-shaped part lb. Since the cross-section peripheral length
of the
pressing surface of the die assembly 20 is shorter than the cross-section
length LU of
the U-shaped part lb, the upper die 21 and the lower die 22 are not in contact
with
each other in the stage illustrated in FIG. 6D. That is, in the stage
illustrated in FIG.
6D, the die assembly 20 is not closed.
[0146]
The upper die 21 and the lower die 22 are brought closer to each other from
the stage FIG. 6D, so that die assembly 20 is closed as illustrated in FIG.
6E. For
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example, by moving the upper die 21 to a bottom dead center, the upper die 21
and
the lower die 22 are brought into contact with each other. In this process,
the outer
peripheral surface of the cylindrical-shape portion ld is pressed by the
pressing
surface of the die assembly 20 while the two end part El and end part E2 are
clamping the protruding part 23. A tubular part le that includes a slit 3 in
its butted
part 2 illustrated in FIG. 6F is thereby formed. The cross-section peripheral
length
of the pressing surface of the die assembly 20 is shorter than the cross-
section length
LU of the U-shaped part lb. Therefore, the cross-section peripheral length LH
of
the tubular part I e is made shorter than the cross-section length LU of the U-
shaped
part lb. That is, in the step illustrated in FIG. 6E, the cylindrical-shape
portion Id
is compressed in the circumferential direction to be made into the tubular
part le.
[0147]
In the case where the cross-section peripheral length LH of the tubular part
le
is made shorter than the cross-section length LU of the U-shaped part lb
before the
die assembly 20 is completely closed, the forming can be terminated before the
die
assembly 20 is completely closed. In this case, by adjusting to what degree
the
upper die 21 and the second lower die 22 are brought close to each other, it
is
possible to adjust the compressibility of the tubular part le.
[0148]
Also in the producing method in the fifth embodiment, by compressing the
cylindrical-shape portion Id in the circumferential direction, the tubular
part le is
formed. Therefore, as described in the second embodiment, the slit 3 can be
formed
with precision.
[0149]
In the die assembly according to the present invention, the protruding part
may be replaceable. FIG. 7 illustrates an example of a die assembly that
includes a
replaceable protruding part. A die assembly 20 illustrated in FIG. 7 includes
an
upper die (first die) 21 and a lower die (second die) 22. The upper die 21
includes a
part 24 that includes a protruding part 23. The part 24 is inserted into a
hole 25 of
the upper die 21 and is made replaceable. The protruding part 23 is a part
with
which the two end parts (end parts El and E2) of the U-shaped part are to come
into
contact and is likely to be abraded or deformed. Therefore, the protruding
part 23 is
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preferably made replaceable. Furthermore, by replacing the protruding part 23,
the
aforementioned effect is obtained.
[0150]
From another viewpoint, the present invention provides a method for
producing a substantially-closed-cross-sectional component that includes a gap
in its
butted part. Hereinafter, the producing method in accordance with this
viewpoint is
referred to as a producing method (S). The producing method (S) includes a
first
step and a second step. In the first step, a metal plate is formed to have a U
shape,
whereby a U-formed item is obtained. This U-formed item corresponds to a
formed
item that includes a U-shaped part formed by the aforementioned step (i). In
the
second step, the U-formed item is formed to have a substantially-closed cross
section,
using a die assembly, and the cross-section peripheral length of the
substantially-
closed-cross-sectional component is made shorter than the cross-section
peripheral
length of the U-formed item. The die assembly in use includes a protruding
part
corresponding to the butted part of the substantially-closed-cross-sectional
component and includes a mechanism that is capable of adjusting the cross-
section
peripheral length of the substantially-closed-cross-sectional component.
Examples
of this die assembly include the aforementioned die assemblies (a), (b), and
(c).
The first step and the second step correspond to the aforementioned steps (i)
and (ii),
respectively. The substantially-closed-cross-sectional component including the
gap
corresponds to the aforementioned formed metal item that includes a tubular
part
with a slit. The substantially-closed-cross-sectional component refers to a
component having a substantially-closed cross section. The substantially-
closed
cross section refers to a cross section in which a gap is present between two
butted
end parts of a metal plate that is formed to be tubular. The substantially-
closed-
cross-sectional component may have the gap across the overall length of a
butted part
or may have the gap only in part of the butted part.
[0151]
In the producing method (S), the cross-section peripheral length of the die
assembly may be shorter than the cross-section peripheral length of the U-
formed
item. Here, the cross-section peripheral length of a die assembly refers to
the cross-
section peripheral length of the die assembly when the die assembly is
completely
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closed. By making the cross-section peripheral length of the die assembly when
the
die assembly is completely closed shorter than the cross-section peripheral
length of
the U-formed item, it is possible to make the cross-section peripheral length
of the
substantially-closed-cross-sectional component shorter than the cross-section
peripheral length of the U-formed item. The die assembly having this
configuration
corresponds to the aforementioned die assemblies (a) and (c).
[0152]
In the producing method (S), the die assembly may include an upper die that
includes the protruding part, and a lower die, and at least one of the upper
die and the
lower die may include a body part and a movable part. The die assembly having
this configuration corresponds to the aforementioned die assembly (b).
[0153]
From another viewpoint, the present invention provides a die assembly for
forming a U-formed item to have a substantially-closed cross section so as to
produce a substantially-closed-cross-sectional component that includes a gap
in its
butted part. Hereinafter, this die assembly is referred to as a die assembly
(Ti).
The die assembly (Ti) includes an upper die and a lower die that include a
protruding part corresponding to the butted part of the substantially-closed-
cross-
sectional component. The die assembly (T1) includes a mechanism that is
capable
of adjusting the cross-section peripheral length of the substantially-closed-
cross-
sectional component. In addition, at least one of the upper die and the lower
die is
divided into a plurality of pieces. The die assembly (TI) corresponds to the
aforementioned die assembly (a). In the die assembly (T1), the protruding part
of
the upper die may be divided. An example of the die assembly having this
configuration is the die assembly 20 illustrated in FIG. 3A.
[0154]
From another viewpoint, the present invention provides another die assembly
for forming a U-formed item to have a substantially-closed cross section so as
to
produce a substantially-closed-cross-sectional component that includes a gap
in its
butted part. Hereinafter, this die assembly is referred to as a die assembly
(12).
The die assembly (T2) includes an upper die and a lower die that include a
protruding part corresponding to the butted part of the substantially-closed-
cross-
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sectional component. The die assembly (T2) includes a mechanism that is
capable
of adjusting the cross-section peripheral length of the substantially-closed-
cross-
sectional component. In addition, at least one of the upper die and the lower
die
includes a body part and a movable part. The die assembly (T2) corresponds to
the
aforementioned die assembly (b).
[0155]
In the above die assemblies (Ti) and (T2), the protruding part may be made
replaceable.
EXAMPLES
[0156]
Hereinafter, the present invention will be specifically described by way of
Examples.
[0157]
[Example 1]
In Example 1, a U-formed item (U-shaped part) was formed by the producing
method illustrated in FIGS. 2A to 2B, and further, a tubular member (formed
metal
item) with a slit was fabricated by the producing method illustrated in FIGS.
3B to
3E. As a metal plate (blank), a hot-rolled steel plate having a tensile
strength (TS)
of 590 MPa and a thickness of 2.3 mm was used. The tubular member was made to
have an outer diameter of 50 mm and a length of 200 mm. The width of the
protruding part of the upper die was set at 5 mm.
[0158]
[Example 2]
In Example 2. a tubular member with a slit was fabricated using the metal
plate as in Example 1 by the producing method illustrated in FIGS. 2A to 2B
and
FIGS. 4B to 4E. The dimensions of the tubular member and of the width of the
protruding part of the upper die were set as in Example I.
[0159]
[Example 3]
In Example 3, a U-formed item (U-shaped part) was formed using the metal
plate as in Example I by the producing method illustrated in FIGS. 2A to 2B,
and
further, a tubular member with a slit was fabricated by the producing method
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illustrated in FIGS. 58 to 5E. The dimensions of the tubular member and of the
width of the protruding part of the upper die were set as in Example 1.
[0160]
[Example 4]
In Example 4, a U-formed item (U-shaped part) was formed using the metal
plate as in Example 1 by the producing method illustrated in FIGS. 2A to 2B,
and
further, a tubular member with a slit was fabricated by the producing method
illustrated in FIGS. 6B to 6E. The dimensions of the tubular member and of the
width of the protruding part of the upper die were set as in Example 1.
[0161]
[Comparative Example 1]
In Comparative Example 1, U forming was performed using the metal plate as
in Example 1 by the method illustrated in FIGS. 2A to 2B. Thereafter, as
illustrated
in FIGS. 10A to 10B, a tubular member 50a was fabricated by performing 0
forming
using a die assembly (an upper die Si and a lower die 52) that includes no
protruding
part. The cross-section peripheral length the pressing surface of the die
assembly
when the die assembly is completely closed was made equal to the cross-section
length of the U-formed item (U-shaped part).
[0162]
[Comparative Example 2]
U forming was performed using the metal plate as in Example 1 by the
method illustrated in FIGS. 2A to 2B. Thereafter, as illustrated in FIGS. 11A
to
11 B, 0 forming was performed using a die assembly (an upper die 51 and a
lower
die 52) that includes no protruding part and includes a core 53. In such a
manner, a
tubular member 50b with a slit was fabricated. The cross-section peripheral
length
of the pressing surface of the die assembly when the die assembly is
completely
closed was made longer than the cross-section length of the U-formed item (U-
shaped part).
[0163]
In Examples Ito 4, the compressibility C was set at 0.99%. In Comparative
Examples 1 and 2, the compressibility C was set at about 0%.
[0164]
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[Evaluation]
For the tubular members in Example 1, Comparative Example 1 and
Comparative Example 2, strain distributions in the thickness direction in
their cross
sections were measured. The results of the measurement are illustrated in FIG.
12A.
The ordinate of FIG. 12A represents absolute value of strain. As illustrated
in FIG.
I 2A, the tubular member in Example 1 had a large absolute value of strain in
comparison with the tubular members in Comparative Examples I and 2 and had a
narrow strain distribution in the thickness direction. These results suggest
that, in
the tubular member in Example 1, compressive stress acted over the entire
tubular
member substantially equally in the thickness direction.
[0165]
Furthermore, for the tubular members in Examples 2 to 4 and Comparative
Example 2, strain distributions in the circumferential direction in their
cross sections
were measured. The results of the measurement are illustrated in FIG. 12B. The
ordinate of FIG. 12B represents absolute value of strain. In FIG. I2B, it is
assumed
that the bottom part of the cross section of a tubular member is at 00, and
the butted
part thereof is at 180 . As illustrated in FIG. 12B, the tubular members in
Examples 2 to 4 had large absolute values of strain in comparison with the
tubular
member in Comparative Example 2. These results suggest that, in the tubular
members in Examples 2 to 4, large compressive stresses were generated over the
entire tubular members in the circumferential direction.
[0166]
As illustrated in FIG. 12A and FIG. 12B, by the producing methods in
Examples I to 4, it is possible to equalize compressive stress acting on the
tubular
member in the thickness direction and the circumferential direction even more.
Therefore, by the producing methods in Examples I to 4, it is possible to
suppress
spring back and to produce a formed metal item having a high shape precision.
[0167]
For the tubular members in Example I, Comparative Example 1 and
Comparative Example 2, distributions of Vickers hardness were calculated by
means
of the results of simulations by the finite element method (FEM). From the
distributions, the variation S in Vickers hardness at the aforementioned first
position
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in the thickness direction was calculated. Similarly, the variations S of
Vickers
hardness in the thickness direction were calculated also at the second and
third
positions. The results thereof were that, in tubular member in Example 1, the
variation S was about 0.1 at all of the first, second, and third positions.
That is, in
the tubular member in Example 1, the average value of the variations S in the
circumferential direction was about 0.1. This result suggests that, in the
tubular
member in Example I, the variations in Vickers hardness were small in both of
the
thickness direction and the circumferential direction. Meanwhile, in
Comparative
Examples 1 and 2, the variations S were about 0.7 at all of the first, second,
and third
positions. That is, in the tubular members in Comparative Examples 1 and 2,
the
average values of the variations S in the circumferential direction were about
0.7.
[0168]
FIG. 13 is a graph illustrating relation between the average value of
variations
S in the circumferential direction and the rate of reduction of uniaxial
compressive
strength. The graph illustrated in FIG. 13 is a graph obtained by assuming a
plurality of round tubes in each of which the average value of variations S in
the
circumferential direction is a given value, and simulating the results of a
uniaxial
compression test conducted on the plurality of round tubes. The ordinate of
the
graph illustrated in FIG. 13 represents the rate of reduction of uniaxial
compressive
strength with respect to the average value of variations S of a round tube in
the
circumferential direction being zero. Specifically, a simulation of the
uniaxial
compression test was conducted on the round tubes in question, and the results
of
calculating the rate of reductions (%) of the uniaxial compressive strengths
of other
round tubes with reference to the uniaxial compressive strength at that point
are
illustrated in the ordinate of the graph of FIG. 13.
[0169]
For reference purposed, FIG. 13 illustrates two dotted lines that represent
the
tendencies of changes in rate of reduction of uniaxial compressive strength.
As
illustrated in FIG. 13, when the average value of the variations S in the
circumferential direction is 0.4 or larger, the rate of reduction of uniaxial
compressive strength significantly increased. On the other hand, when the
average
value of the variations S in the circumferential direction is smaller than
0.4, the rate
CA 02975861 2017-08-03
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of reduction of uniaxial compressive strength was low. The results illustrated
in
FIG. 13 suggest that it is important to set the average value of the
variations S in the
circumferential direction at less than 0.4.
[0170]
Conventional 0 forming (the 0 forming in Comparative Examples 1 and 2)
that does not involve compressing a metal plate in the circumferential
direction
results in a large spring back, which makes it difficult to form a slit with
precision.
In contrast, by the producing method according to the present invention, it is
possible
to form the breadth of a slit with precision. in addition, the conventional 0
forming
is simple bending, which thus leads to a small work hardening in a thickness
center,
resulting in a low fatigue strength of the resultant formed item. In contrast,
by the
producing method according to the present invention, a formed metal item
having a
high fatigue strength is obtained. In addition, by a conventional method for
producing a tubular member with a slit, it is in some cases necessary to make
a metal
plate tubular after bending the metal plate gradually or to make a metal plate
tubular
after drawing the metal plate. In comparison with such a conventional
producing
method, according to the present invention, it is possible to reduce the
number of
steps, which consequently enables cost reduction.
INDUSTRIAL APPLICABILITY
[0171]
The present invention is available to a formed metal item that includes a
tubular part with a slit, and a method for producing the formed metal item.
Furthermore, the present invention is available to a producing device for
producing
the formed item, and a die assembly used in the producing device.
REFERENCE SIGNS LIST
[0172]
1 formed metal item
la metal plate
lb. I c U-shaped part
Id cylindrical-shape portion
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le tubular part
2 butted part
3 slit (gap)
11 die
12 punch
20. 30 die assembly
21,31 upper die
21a first upper die
21b second upper die
22, 32 lower die
22a first lower die
22b second lower die
23, 33 protruding part
23a first protruding part
23b second protruding part
31a, 32a body part
31b, 32b movable part
El, E2 end part
