BACKGROUND
[0002]
PTL 1 discloses a technique for bending and cross-sectioning (processing that transforms
the shape of the cross-section which intersects the longitudinal direction of the tube) a straight
tube using a press die. In the technique disclosed in PTL 1, high shape accuracy is ensured for a
15 hollow shell part after processing by simultaneously performing cross-sectioning and bending on
a straight tube. According to the technique disclosed in PTL 1, a hollow shell part can be
obtained only by pressing from the outside of a tube without requiring complex processes such
as hydroforming, thereby improving the productivity of the hollow shell part.
20 [CITATION LIST]
[PATENT LITERATURE]
[0003]
[PTL 1] Japanese Patent Publication No. 6519984
25
[TECHNICAL PROBLEM]
[0004]
SUMMARY
According to a new finding of the present inventor, when attempting to obtain a hollow
shell part having a curved portion by simultaneously performing cross-sectioning and bending on
30 a straight tube as disclosed in PTL 1, unsatisfactory forming such as wrinkles and buckling is
easily generated on the surface of the curved portion especially when the bend radius of the
curved portion is small.
[SOLUTION TO PROBLEM]
35 [0005]
As means for solving the above problem, the present application discloses
a manufacturing method for a hollow shell part, the method comprising
applying pressure to a bent tube having a curved portion from outside of the tube toward
inside of the tube using a press die, thereby simultaneously performing cross-sectioning of the
curved portion and bending of the curved portion to reduce the bend radius of the curved portion.
5 [0006]
In the manufacturing method of the present disclosure,
the press die may have an upper die and a lower die,
the upper die and the lower die may respectively have press surfaces, and
the cross-sectioning and the bending may be simultaneously performed by pressing the bent
10 tube with the upper die and the lower die from above and below and pressing the press surfaces
against the curved portion of the bent tube.
[0007]
The manufacturing method of the present disclosure may comprise obtaining the bent tube
having the curved portion by at least bending an original tube.
15 [0008]
The manufacturing method of the present disclosure may comprise obtaining the bent tube
having the curved portion by at least bending and cross-sectioning an original tube.
[0009]
In the manufacturing method of the present disclosure, the bending performed on the
20 original tube may comprise applying pressure from the outside of the tube toward the inside of
the tube using a press die to obtain the bent tube.
[0010]
In the manufacturing method of the present disclosure, the bending and the cross-sectioning
performed on the original tube may comprise applying pressure from the outside of the tube
25 toward the inside of the tube using a press die to obtain the bent tube.
[0011]
In the manufacturing method of the present disclosure, the original tube may be a straight
tube.
[0012]
30 In the manufacturing method of the present disclosure, upon completion of the cross-
35
sectioning and bending, in a cross-section orthogonal to the longitudinal direction of the hollow
shell part, an inner surface of the press die may be inclined relative to an outer surface of the
hollow shell part, whereby a gap may be created between the outer surface of the hollow shell
part and the inner surface of the press die.
[ADVANTAGEOUS EFFECTS]
2
[0013]
In the manufacturing method of the present disclosure, a hollow shell part is obtained by
pressing a bent tube having a curved portion so as to reduce the bend radius of the curved portion
while performing cross-sectioning on the curved portion. This makes it possible to suppress
S unsatisfactory forming in the curved portion than when obtaining a hollow shell part having a
curved portion by pressing a straight tube in one step.
BRIEF DESCRIPTION OF DRAWINGS
[0014]
10 FIG. I is a schematic diagram to describe an example of the longitudinal shape of a bent
tube 10.
FIG. 2 is a schematic diagram to describe an example of the longitudinal shape of a hollow
shell part I 00.
FIGS. 3A to 3F are schematic diagrams to describe examples of the cross-sectional shape of
IS the bent tube 10 and the cross-sectional shape of the hollow shell part 100. FIG. 3A
schematically illustrates the cross-sectional shape taken along arrow IliA-IliA of FIG. I; FIG.
3B schematically illustrates the cross-sectional shape taken along arrow IIIB-IIIB of FIG. 1; FIG.
3C schematically illustrates the cross-sectional shape taken along arrow IIIC-IIIC of FIG. 1; FIG.
3D schematically illustrates the cross-sectional shape taken along arrow IIID-IIID of FIG. 2;
20 FIG. 3E schematically illustrates the cross-sectional shape taken along arrow IIIE-IIIE of FIG. 2;
and FIG. 3F schematically illustrates the cross-sectional shape taken along arrow IIIF-IIIF of
FIG.2.
FIGS. 4A to 4C are schematic diagrams to describe an example of a process for pressing the
bent tube I 0 to obtain the hollow shell part I 00. The cross-sectional shape along the longitudinal
2S direction of the tube is illustrated. FIG. 4A is a state before the bent tube 10 abuts dies 20, 30;
FIG. 4B is a state immediately after the bent tube 10 abuts the dies 20, 30; and FIG. 4C is a state
after pressing is completed.
FIGS. SA to SF are schematic diagrams to describe an example of a process for pressing the
bent tube 10 to obtain the hollow shell part 100. FIG. SA illustrates the cross-sectional shape
30 taken along arrow VA-VA of FIG. 4B; FIG. SB illustrates the cross-sectional shape taken along
arrow VB-VB of FIG. 4B; FIG. SC illustrates the cross-sectional shape taken along arrow VCVC
of FIG. 4B; FIG. SD illustrates the cross-sectional shape taken along arrow VD-VD of FIG.
4 C, FIG. SE illustrates the cross-sectional shape taken along arrow VE-VE ofFIG. 4C; and FIG.
SF illustrates the cross-sectional shape taken along arrow VF-VF of FIG. 4C.
3S FIGS. 6A to 6F are schematic diagrams to describe an example of a flow form in the
circumferential direction of a tube relative to press dies during pressing.
3
FIG. 7 is a schematic diagram to describe an example of the shapes of the press dies with an
inclination.
FIGS. SA and SB are schematic diagrams to describe an example of the shape of the
original tube I. FIG. SA illustrates the longitudinal shape, and FIG. SB illustrates the cross-
5 sectional shape taken along arrow VIIIB-VIIIB of FIG. SA.
FIG. 9 is a diagram illustrating an example of a flow of a manufacturing method for a
hollow shell part.
FIG. 10 is a diagram illustrating the result ofFEA to describe pressing conditions according
to Comparative Example.
10 FIG. 11 is a diagram illustrating the result ofFEA to illustrate an example of a hollow shell
15
part according to Comparative Example.
FIG. 12 is a diagram illustrating the result ofFEA to describe pressing conditions according
to Example.
DESCRIPTION OF EMBODIMENTS
[0015]
As illustrated in FIGS. 1 to 7, the manufacturing method for a hollow shell part 100
includes applying pressure to a bent tube 10 having a curved portion 1 Oa from the outside of the
tube toward the inside of the tube using a press die 20, 30, thereby simultaneously performing
20 cross-sectioning of the curved portion lOa and bending of the curved portion lOa to reduce the
bend radius of the curved portion 1 Oa.
[0016]
1. Bent tube
1. 1 Longitudinal shape of the bent tube
25 As illustrated in FIG. 1, the bent tube 10 has a curved portion lOa at least partially. The
"curved portion" refers to a bent portion in the longitudinal shape of the tube. In the present
application, the "bent tube" may have a shape that satisfies, for example, the relationship of R ~
250D wherein R is the bend radius and D is the tube diameter at the curved portion. The bent
tube 10 may be curved in two dimensions or in three dimensions at the curved portion 1 Oa.
30 Although FIG. 1 illustrates a mode in which the bent tube 10 is curved in the up-down direction
of the paper at the curved portion 1 Oa, the bent tube 10 may further be curved in the direction out
of the paper (depth direction) at the curved portion 1 Oa. The bent shape at the curved portion 1 Oa
is not particularly limited. For example, the bent tube 10 may be arched at the curved portion
1 Oa. Note that it is preferable that the bent tube 10 has substantially no discontinuous surface
3 5 such as wrinkles or buckling at the curved portion 1 Oa.
[0017]
4
The bend radius R! o (inner bend radius) at the curved portion 1 Oa is not particularly limited
as long as the bend radius R 10 is greater than the bend radius R 100 that is described below. The
bend radius RIO may be appropriately determined by taking into account the material, the
thickness, and the aperture diameter (equivalent circle diameter) of the bent tube 10, as well as,
5 the bend radius R10o described later. Note that the bent shape (ridge) in the longitudinal direction
at the curved portion 1 Oa may be configured by only one arc or may be configured by a plurality
of arcs combined. The curvature may also vary continuously or discontinuously at the curved
portion 1 Oa from one end in the longitudinal direction toward the other end.
[0018]
10 Although FIG. 1 illustrates a mode in which the bent tube 10 has only one curved portion
1 Oa, the bent tube 10 may have a plurality of curved portions 1 Oa with the same or different bend
radii RJO. When pressing that is described later is performed at each of the plurality of curved
portions 1 Oa, the pressing may be carried out simultaneously with a single die, or the pressing
may be carried out separately with a plurality of dies.
15 [0019]
The bent tube 10 may have a straight tube portion other than the curved portion 1 Oa. The
"straight tube portion" refers to a straight section that is substantially free of bends in the
longitudinal shape of the tube. Alternatively, the bent tube 10 may be configured by only one or
more curved portions 1 Oa.
20 [0020]
The bent tube 10 need not be completely tubular in its entirety. For example, the bent tube
10 may have a notch, a slit, a through-hole, intentional irregularities, and/or the like in a portion
according to its application. These notch, slit, through-hole, irregularities, and/or the like
provided in the bent tube 10 may remain in the hollow shell part 100. On the other hand, the
25 cross-sectional shape of the curved portion 1 Oa may be uninterruptedly annular from the
viewpoint of further increasing the shape accuracy during pressing at the curved portion 1 Oa.
[0021]
The length of the bent tube 10 is not particularly limited and may be appropriately
determined according to its application. However, when the length of the bent tube 10 is
30 extremely short, it may be difficult to carry out a further bending process that is described later.
In the bent tube 10, the length L 10 from one end in the longitudinal direction of the tube to the
other end (the length of the line continuously connecting the centers of the aperture (the centers
of the figures)) may be longer than the aperture diameter (the circle equivalent diameter) DJo.
[0022]
3 5 1.2 Cross-sectional shape of bent tube
The cross-sectional shape (aperture shape) of the bent tube 10 is not particularly limited.
5
FIGS. 3A, 3B, and 3C illustrate the cross-sectional shape of the bent tube 10 to be circular, but
the cross-sectional shape may take various shapes, such as a circular shape, an elliptical shape, a
flattened circular shape, a polygonal shape, a rounded polygonal shape, and a combination of
these shapes. The cross-sectional shape of the bent tube 10 may be appropriately determined in
5 view of insertion into the press die 20, 30, or the like.
[0023]
The cross-sectional shape of the bent tube 10 may be the same shape without changing from
one end in the longitudinal direction of the tube toward the other end, or may continuously or
discontinuously change from one end in the longitudinal direction of the tube toward the other
I 0 end. Note that, when the bent tube 10 has a straight tube portion, as well as, the curved portion
1 Oa, the curved portion 1 Oa and the straight tube portion may have the same cross-sectional
shapes as each other or may have different cross-sectional shapes. Further, when the bent tube 10
has a plurality of curved portions 1 Oa, the curved portions 1 Oa may have the same cross-sectional
shapes as each other or may have different cross-sectional shapes.
15 [0024]
The thickness (wall thickness) of the bent tube 10 is not particularly limited and may be
appropriately determined according to its application. The thickness of the bent tube 10 may be
different from portion to portion.
[0025]
20 1. 3 Material of bent tube
The material of the bent tube 10 may be appropriately determined according to its
application as long as the material is capable of being pressed. For example, the bent tube 10
may be made of metal, such as steel, iron, aluminum, titanium, and magnesium. The
manufacturing method of the present disclosure can also be applied to a high-strength steel tube
25 made of high-strength steel having a tensile strength of 440 MPa or more, 590 MPa or more, or
780 MPa or more measured at room temperature in accordance with JIS Z 2241: 2011 and a
high-strength steel tube made of ultra-high-strength steel having a tensile strength of 980 MPa or
more.
[0026]
30 1.4. Method of obtaining bent tube
The method of obtaining a bent tube 10 is not particularly limited. For example, a bent tube
10 having a curved portion lOa may be obtained by at least bending an original tube (a starting
material tube) 1 as illustrated in FIGS. SA and 8B. In addition, a bent tube 10 having a curved
portion 1 Oa may be obtained by at least bending and cross-sectioning an original tube 1.
35 [0027]
When obtaining a bent tube 10 from an original tube 1, the shape of the original tube 1 is
6
not particularly limited. For example, as illustrated in FIG. 8A, the original tube I may be a
straight tube. Alternatively, the original tube I may have a curved portion with a larger bend
radius than the curved portion lOa of the bent tube 10. Alternatively, the original tube I may
have both a curved portion and a straight tube portion. The cross-sectional shape of the original
5 tube 1 is not particularly limited, and in addition to the circular shape illustrated in FIG. 8B, the
cross-sectional shape may take various shapes, such as an elliptical shape, a flattened circular
shape, a polygonal shape, a rounded polygonal shape, and a combination of these shapes. The
cross-sectional shape of the original tube I may be the same shape without changing from one
end in the longitudinal direction of the tube toward the other end or may continuously or
I 0 discontinuously change from one end in the longitudinal direction of the tube toward the other
end.
[0028]
The method of bending the original tube 1 is not particularly limited. For example, the bent
tube 10 may be obtained by pressing the original tube 1 from the outside of the tube. In other
15 words, the bending performed on the original tube 1 may include applying pressure from the
outside of the tube toward the inside of the tube using a press die to obtain the bent tube 10. In
addition, cross-sectioning may be performed using a press die on the original tube 1. In other
words, the bending and cross-sectioning performed on the original tube 1 may include applying
pressure from the outside of the tube toward the inside of the tube using a press die to obtain the
20 bent tube 10. In either case, a press die (first die) for obtaining the bent tube 10 from the original
tube 1 and press die 20, 30 (second die) for obtaining the hollow shell part 100 from the bent
tube 10 that is described later may be used separately. Specifically, the first die may have a press
surface of a larger bend radius for forming a curved portion than the second die. In this manner,
simply replacing the die, the pressing to transform from the original tube 1 to the bent tube 10
25 and the pressing to transform from the bent tube 10 to the hollow shell part 100 can also be
carried out using the same press machine. In other words, the manufacturing equipment for the
bent tube 10 and the manufacturing equipment for the hollow shell part 100 can be commonized
to improve productivity.
[0029]
30 Further, the bending and cross-sectioning may be simultaneously performed on the original
tube 1 by applying pressure from the outside of the tube toward the inside of the tube using a
press die to obtain the bent tube 10. This further improves the shape accuracy of the bent tube
10.
[0030]
35 In the case of obtaining the bent tube 10 by at least bending the original tube 1, the
minimum bend radius (RlOmin) at which no buckling or wrinkles occurs may be confirmed in
7
advance by experiment or FEM analysis before actually bending the original tube 1. In other
words, when bending the original tube 1, the occurrence of buckling and wrinkles in the bent
tube 10 can be further suppressed by bending the original tube 1 so that the bend radius R 1 o
becomes the minimum bend radius RIO min or more that has been confirmed in advance.
s [0031]
Note that the method of obtaining a bent tube 10 is not limited to the pressing method from
the outside of the tube using the press die described above. For example, a bent tube 10 may be
obtained by performing conventionally known bending, such as rotary draw bending (pipe
bender), tube stretch bending, tube compression bending, intrusion bending, and tube roll
I 0 bending. However, as described above, from the viewpoint of commonizing the manufacturing
equipment and improving productivity, it is preferable to obtain the bent tube 10 from the
original tube I by the pressing method from the outside of the tube using a press die.
[0032]
2. Press die
IS The press die may be any die as long as the press die is capable of simultaneously
performing cross-sectioning of the curved portion 1 Oa and bending of the curved portion 1 Oa to
reduce the bend radius. The material of the press die is not particularly limited, and a general
material for a die can be used. The press die may be configured by a plurality of dies, in which
case, by moving the plurality of dies relative to each other, pressure can be applied from the
20 outside of the bent tube 10 towards the inside of the tube. For example, as illustrated in FIG. 4A,
the press die may have an upper die 20 and a lower die 30. In this case, the upper die 20 and the
lower die 30 may respectively have press surfaces 20a, 30a. As illustrated in FIGS. 4B and 4C,
cross-sectioning and bending can be performed simultaneously by pressing the bent tube 10 from
above and below using the upper die 20 and the lower die 30 and pressing the press surfaces 20a,
2S 30a against the curved portion 1 Oa of the bent tube 10.
[0033]
The shape of the press die corresponds to the shape of the hollow shell part 100. As
illustrated in FIGS. 4A to 4C and SA to SF, for example, when the press die includes an upper
die 20 and a lower die 30, the upper die 20 may have a bottom 21 opposing the upper end 11 a of
30 the bent tube 10 and a side wall 22 opposing the side 12 of the bent tube 1 0; the lower die 30
may have a bottom 31 opposing the lower end 11 b of the bent tube 10 and a side wall 32
opposing the side 12 of the bent tube 10; and as illustrated in FIGS. SD to SF and 6F, with the
upper die 20 and the lower die 30 closed, the entire circumference (perimeter) of the hollow shell
part 100 maybe enclosed by the bottoms 21, 31 and the side walls 22, 32.
3S [0034]
In the manufacturing method of the present disclosure, upon completion of the cross-
8
sectioning and bending on the bent tube 10, in a cross-section orthogonal to the longitudinal
direction of the hollow shell part 100, an inner surface of the press die may be inclined relative to
an outer surface of the hollow shell part I 00, whereby a gap may be created between the outer
surface of the hollow shell part 100 and the inner surface of the press die. For example, in a
5 cross-section orthogonal to the longitudinal direction of the hollow shell part I 00, a portion of
the inner wall of the press die may have a portion that is convex outward relative to the outer
wall of the hollow shell part 100. Let us consider a case where the entire circumference of the
hollow shell part I 00 is enclosed by the inner wall of the press die 40 upon completion of crosssectioning
and bending by the press die 40 as illustrated in FIG. 7. In this case, as illustrated in
10 FIG. 7, in a cross-section orthogonal to the longitudinal direction of the hollow shell part 100,
the hollow shell part 100 may have: a comer portion 1 OOx of a small curvature radius; and a side
1 OOy and a bottom 1 OOz of large curvature radii, and the inner wall of the press die 40 may have:
a portion 40a that is convex outward relative to the outer wall of the side lOOy of the hollow
shell part 1 00; a portion 40b that is convex outward relative to the outer wall of the bottom 1 OOz
15 of the hollow shell part 1 00; and a portion 40c that is convex outward relative to the outer wall of
the comer portion 1 OOx of the hollow shell part 100. At the portions 40a to 40c illustrated in
FIG. 7, in a cross-section orthogonal to the longitudinal direction of the hollow shell part 100,
the inner surface of the press die is inclined relative to the outer surface of the hollow shell part
100, whereby a gap is created between the outer surface of the hollow shell part 100 and the
20 inner surface of the press die. In this manner, the surface of the hollow shell part 100 can be
suppressed from recessing inward by inclining the inner surface of the press die relative to the
outer surface of the hollow shell part 100 to create a gap between the outer surface of the hollow
shell part 100 and the inner surface of the press die, in a cross-section orthogonal to the
longitudinal direction of the hollow shell part 100.
25 [0035]
In the manufacturing method of the present disclosure, as is described later, a hollow shell
part 100 having a curved portion 1 OOa is obtained by pressing with a press die so as to perform
bending that reduces the bend radius R10 of a curved portion 1 Oa of a bent tube 10. The bend
radius RM of the press surface of the press die (see FIG. 4A) may be less than the bend radius
30 R10o of the curved portion lOOa of the hollow shell part 100.
[0036]
When the bent tube 10 has a curved portion 1 Oa that is convex downward as illustrated in
FIGS. 4B and SA to 5C, at least two locations of one and the other longitudinal ends of the
curved portion 1 Oa of the bent tube 10 may be abutted against the lower die 30 and at least one
3 5 location other than the one and other longitudinal ends of the curved portion 1 Oa of the bent tube
10 may be abutted against the upper die 20, immediately after the curved portion 1 Oa is abutted
9
against the upper die 20 and the lower die 30. In this manner, at least three locations of the bent
tube 10 are abutted against the press die immediately after the press die is abutted against the
bent tube 10, thereby suppressing the misalignment of the bent tube 10 relative to the press die
during pressing.
s [0037]
Note that FIGS. 4A to 4C illustrate a pressing mode in which the curved portion lOa of the
bent tube 10 and the curved portion lOOa of the hollow shell part 100 are convex downward, but
pressing may be performed so that the curved portion 1 Oa of the bent tube 10 and the curved
portion lOOa of the hollow shell part 100 are convex upward. However, workability of pressing
10 is considered to be superior when the tube is convex downward because the bent tube 10 can be
easily placed and positioned on the lower die 30. Furthermore, the pressing direction of the press
die is not limited to the up-down direction as illustrated in FIGS. 4A to 4C and may be, for
example, a horizontal direction. However, when considering workability, productivity, and the
like, the pressing direction by the press die may be set as the up-down direction. A known press
IS machine may be used as a press machine in which the press die is installed.
[0038]
3. Cross-sectioning
In the manufacturing method of the present disclosure, cross-sectioning is performed that
changes the cross-sectional shape of the curved portion 1 Oa of the bent tube 10 by applying
20 pressure from the outside of the tube toward the inside of the tube using the press die 20, 30. In
other words, pressing the press surface 20a, 30a of the press die 20, 30 against the curved portion
1 Oa from the outside the curved portion 1 Oa creates a material flow in the circumferential
direction (peripheral direction) of the tube at the curved portion 1 Oa and changes the crosssectional
shape of the curved portion lOa. For example, as illustrated in FIGS. SA to SF, the
2S cross-sectional shape of the curved portion lOa may be transformed from a first shape (for
example, a circular shape) to a second shape (for example, an elliptical shape, a polygonal shape,
a rounded polygonal shape, or a combination of these shapes) by cross-sectioning.
[0039]
Pressure is applied from the outside of the tube toward the inside of the tube during cross-
30 sectioning. In other words, in the manufacturing method of the present disclosure, pressure from
the inside of the tube toward the outside of the tube such as by hydroforming is not applied, and
the cross-sectional shape of the curved portion 1 Oa of the bent tube 10 is transformed only by
pressing from the outside of the tube. Note that a core die or the like may be installed inside of
the tube, for example, at the tube ends or the like for cross-sectioning. This can further suppress
3S dents, crushing, and/or the like at the tube ends and/or the like.
[0040]
10
In the manufacturing method of the present disclosure, upon completion of cross-sectioning,
a gap may or may not be created between the outer wall of the hollow shell part 100 and the
press die in a cross-section orthogonal to the longitudinal direction of the hollow shell part 100.
[0041]
5 Note that, in the manufacturing method of the present disclosure, cross-sectioning on a
portion other than the portion that undergoes bending to be the curved portion 1 OOa is optional.
When obtaining a hollow shell part 100 having a straight tube portion, as well as, the curved
portion 1 OOa, cross-sectioning may or may not be performed on the straight tube portion. When
cross-sectioning is performed on the straight tube portion, different cross-sectioning may be
10 performed between the curved portion lOa and the straight tube portion. Furthermore, when the
bent tube 10 has a plurality of curved portions 1 Oa, the same cross-sectioning or different crosssectioning
may be performed between one curved portion I Oa and the other curved portion 1 Oa.
[0042]
4. Bending
15 In the manufacturing method of the present disclosure, pressing involves bending that
reduces the bend radius R10 of the curved portion lOa of the bent tube 10. In other words,
pressing the press surfaces 20a, 30a of the press dies 20, 30 against the curved portion 1 Oa from
the outside of the tube creates a material flow in the longitudinal direction of the tube at the
curved portion lOa and reduces the bend radius R10 of the curved portion lOa. For example, as
20 illustrated in FIGS. 1 and 2, bending transforms the curved portion lOa of a bend radius RIO to
the curved portion 1 OOa of a bend radius R1oo.
[0043]
Pressure is applied from the outside of the tube toward the inside of the tube during
bending. In other words, in the manufacturing method of the present disclosure, pressure from
25 the inside of the tube toward the outside of the tube such as by hydro forming is not applied, and
the bend radius of the curved portion 1 Oa of the bent tube 10 is reduced only by pressing from
the outside of the tube.
[0044]
In the manufacturing method of the present disclosure, upon completion of bending, a gap
30 may or may not be created between the outer wall of the hollow shell part 100 and the press die
in a longitudinal direction of the hollow shell part 100.
[0045]
Note that, in the manufacturing method of the present disclosure, bending on a portion other
than the curved portion 1 Oa is optional. For example, when the bent tube 10 has a straight tube
3 5 portion, gentle bending may be applied to the straight tube portion to the extent that no wrinkles
or buckling occurs.
11
[0046]
In the manufacturing method of the present disclosure, the above-described bending is
performed simultaneously with the above-described cross-sectioning. In other words, during
pressing, the material flow in the circumferential direction (peripheral direction) of the tube and
5 the material flow in the longitudinal direction of the tube simultaneously proceed at the curved
portion I Oa of the bent tube I 0, thereby ensuring high shape accuracy of the hollow shell part
100. The cross-sectioning and bending of the tube using the press die are performed, for
example, according to a flow as illustrated in FIGS. 6A to 6F. The mode illustrated in FIGS. 6A
to 6F corresponds to the mode illustrated in FIGS. SA and 5D and illustrates a case of
I 0 transforming a circular tube cross-section to a rounded rectangular cross-section. As illustrated in
FIGS. 6A to 6F, the tube can be brought into contact with at least one of the upper die 20 and the
lower die 30 (FIG. 6A), the upper die 20 and the lower die 30 can be brought closer to each other
and a portion of the tube is inserted inside the upper die 20 and the lower die 30 while flowing,
the forming proceeds without biting the tube in the gap between the upper die 20 and the lower
15 die 30 (FIGS. 6B to 6E), and the cross-sectioning and bending of the tube can be completed by
closing the upper die 20 and the lower die 30 (FIG. 6F). Note that in the manufacturing method
of the present disclosure, as long as the cross-sectioning and bending may proceed
simultaneously at a certain point in time, the timing of the start and completion of the crosssectioning
and the timing of the start and completion of the bending need not be strictly
20 simultaneous.
[0047]
When obtaining the hollow shell part I 00 by pressing the bent tube I 0, the minimum bend
radius R100min where buckling and wrinkles do not occur may be confirmed by experiment,
FEM analysis, or the like before actually pressing the bent tube I 0. In other words, when
25 pressing the bent tube I 0, the occurrence of buckling and wrinkles in the hollow shell part 100
can be further suppressed by bending the bent tube I 0 so that the bend radius R100 becomes the
minimum bend radius RlOOmin or more that has been confirmed in advance.
[0048]
5. Hollow shell part
30 5. 1 Longitudinal shape of the hollow shell part
As illustrated in FIG. 2, the hollow shell part 100 has a curved portion lOOa at least
partially. As described above, the hollow shell part 100 may be referred to as a ''press-formed
tube" because the tube has been formed through pressing. The longitudinal direction of the
hollow shell part 100 may correspond to the longitudinal direction of the tube prior to pressing.
35 The hollow shell part 100 may be curved in two dimensions or in three dimensions at the curved
portion lOOa. For example, in FIG. 2, the hollow shell part 100 is illustrated to be curved in the
12
up-down direction of the paper at the curved portion 1 OOa but may be further curved directed out
of the paper at the curved portion lOOa. The bent shape at the curved portion lOOa is not
particularly limited. For example, the hollow shell part 100 may be arched at the curved portion
lOOa. The bent shape of the hollow shell part 100 can be easily changed by changing the shapes
5 of the press surfaces of the press die 20, 30 described above.
[0049]
The bend radius R10o (inner bend radius) at the curved portion lOOa is not particularly
limited as long as the bend radius R10o is smaller than the above-described bend radius R1o.
Note that the bent shape (ridge) in the longitudinal direction of the curved portion lOOa maybe
10 configured by only one arc or may be configured by a plurality of arcs combined. The curvature
may also vary continuously or discontinuously at the curved portion lOOa from one end in the
longitudinal direction toward the other end.
[0050]
Although FIG. 2 illustrates a mode in which the hollow shell part 100 has only one curved
15 portion 1 OOa, the hollow shell part 100 may have a plurality of curved portions 1 OOa with the
same or different bend radii R10o.
[0051]
The hollow shell part 100 may have a straight tube portion other than the curved portion
1 OOa. Alternatively, the hollow shell part 100 may be configured by only one or more curved
20 portions 1 OOa.
[0052]
The hollow shell part 100 need not be fully tubular in its entirety. For example, the hollow
shell part 100 may have a notch or a slit in a portion. The hollow shell part 100 may also have a
through-hole or intentional irregnlarities in a portion.
25 [0053]
The length of the hollow shell part 100 is not particularly limited and may be appropriately
determined according to its application. The length of the hollow shell part 100 may be the same
as or different from the length of the bent tube 10. For example, the length of the hollow shell
part 100 may be shorter than the length of the bent tube 10 by undergoing a process of enlarging
30 the aperture diameter (circle equivalent diameter) relative to the aperture diameter of the bent
tube 10 or other processes, in addition to the bending and cross-sectioning of the present
disclosure. Alternatively, the length of the hollow shell part 100 may be longer than the length of
the bent tube 1 0 by undergoing a process of thinning the tube thickness relative to the bent tube
10 or reducing the diameter of the tube or other processes.
35 [0054]
5.2. Cross-sectional shape of the hollow shell part
13
The cross-sectional shape (aperture shape) of the hollow shell part 100 is not particularly
limited. FIGS. 3D, 3E, and 3F illustrate the cross-sectional shape of the hollow shell part 100 to
be a polygonal shape or an elliptical shape, but the cross-sectional shape may take various
shapes, such as a polygonal shape, an elliptical shape, a circular shape, a flattened circular shape,
5 a rounded polygonal shape, and a combination of these shapes. The cross-sectional shape of the
hollow shell part I 00 may be appropriately determined according to its application. The crosssectional
shape of the hollow shell part 100 can be easily changed by changing the shape of the
press surfaces of the press die 20, 30 described above.
[0055]
I 0 The cross-sectional shape of the hollow shell part 100 may be the same shape without
changing from one end in the longitudinal direction of the tube toward the other end or may
continuously or discontinuously change from one end in the longitudinal direction of the tube
toward the other end as illustrated in FIGS. 3D to 3F. When the hollow shell part 100 has a
straight tube portion, as well as, the curved portion 1 OOa, the curved portion 1 OOa and the straight
15 tube portion may have the same cross-sectional shapes as each other or may have different crosssectional
shapes. Further, when the hollow shell part 100 has a plurality of curved portions 1 OOa,
the curved portions 1 OOa may have the same cross-sectional shapes as each other or may have
different cross-sectional shapes.
[0056]
20 The thickness (wall thickness) of the hollow shell part 100 is not particularly limited and
may be appropriately determined according to its application. The thickness of the hollow shell
part 100 may vary from portion to portion.
[0057]
As described above, in the manufacturing method of the hollow shell part 100 of the present
25 disclosure, a bent tube 10 having a curved portion 1 Oa is pressed so as to reduce the bend radius
of the curved portion 1 Oa while performing cross-sectioning on the curved portion 1 Oa. This
makes it possible to suppress unsatisfactory forming at the curved portion 1 OOa than when
obtaining a hollow shell part 100 having a curved portion 1 OOa by pressing a straight tube in one
step.
30 [0058]
Note that the manufacturing method of the present disclosure can also be applied, for
example, to a case of manufacturing a tapered tube. In other words, a tapered tube may be
obtained as the hollow shell part 100 by cross-sectioning according to the manufacturing method
of the present disclosure, or a tapered tube may be used as the bent tube 10 for obtaining the
35 hollow shell part 100.
[0059]
14
5.3 Examples of the application of the hollow shell part
The application of the hollow shell part 100 obtained by the manufacturing method of the
present disclosure is diverse. For example, the application may be in automobile parts, such as a
bumper beam, a suspension member, a side rail, a trailing arm, an upper arm, a pillar, a torsion
5 beam, a door impact beam, and an instrument panel beam.
[0060]
6. Summary
As described above, the method of the present disclosure is for manufacturing a hollow
shell part 1 00 having a curved portion 1 OOa with a small bend radius by using a press die and
10 simultaneously performing bending and cross-sectioning on a bent tube 10 that has been bent in
advance so as to change the cross-sectional shape of the curved portion lOa of the bent tube 10
while reducing the bend radius of the curved portion 1 Oa. As described above, the method of the
present disclosure may also include a process of preparing the bent tube 10 in advance as a
process separate from bending and cross-sectioning using the above press die. For example, as
15 illustrated in FIG. 9, a bent tube 10 having a curved portion lOa may be obtained by at least
bending (pre-bending) an original tube 1 (as described above, the original tube 1 may be a
straight tube). Thereafter, the obtained bent tube 10 may be arranged inside the press die from
outside the press die, and subsequently, the above-described bending and cross-sectioning may
be performed simultaneously to reduce the bend radius of the curved portion 1 Oa while changing
20 the cross-sectional shape of the curved portion lOa of the bent tube 10 (main forming), thereby
obtaining a hollow shell part 100 having a predetermined curved portion lOOa. As in the method
of the present disclosure, by simultaneously performing bending and cross-sectioning using a
press die on a bent tube 10 that has been bent in advance, a hollow shell part 100 having a curved
portion 1 OOa of a small bend radius can be manufactured while suppressing wrinkles and
25 buckling.
EXAMPLES
[0061]
Hereinafter, the effects of the manufacturing method of the hollow shell part of the present
30 disclosure are described in more detail with Examples.
[0062]
1. Comparative Example
As illustrated in FIG. 10, a hollow shell part was obtained only by main-forming in one
process by simultaneously performing cross-sectioning and bending using a press die on a
35 straight tube (980-MPa class steel tube,