U.S. patent application number 13/395477 was filed with the patent office on 2012-07-05 for curved parts and method for manufacturing the same.
This patent application is currently assigned to JFE STEEL CORPORATION. Invention is credited to Takeshi Fujita, Takayuki Futatsuka, Kazuhiko Higai, Takaaki Hira, Yoshikiyo Tamai, Yuji Yamasaki.
Application Number | 20120171506 13/395477 |
Document ID | / |
Family ID | 43826424 |
Filed Date | 2012-07-05 |
United States Patent
Application |
20120171506 |
Kind Code |
A1 |
Futatsuka; Takayuki ; et
al. |
July 5, 2012 |
CURVED PARTS AND METHOD FOR MANUFACTURING THE SAME
Abstract
A curved-part forming method for obtaining a curved part by
performing forming on a blank formed of a single metal plate, the
method including a bending process in which the blank having a
curved outline corresponding to a curve of the curved part in a
longitudinal direction is bent into a sectional shape corresponding
to a division portion of a sectional shape of the curved part; and
a joining process in which two or more portions obtained by the
bending process are joined together.
Inventors: |
Futatsuka; Takayuki; (Tokyo,
JP) ; Higai; Kazuhiko; (Tokyo, JP) ; Tamai;
Yoshikiyo; (Tokyo, JP) ; Hira; Takaaki;
(Tokyo, JP) ; Fujita; Takeshi; (Tokyo, JP)
; Yamasaki; Yuji; (Tokyo, JP) |
Assignee: |
JFE STEEL CORPORATION
Tokyo
JP
|
Family ID: |
43826424 |
Appl. No.: |
13/395477 |
Filed: |
September 28, 2010 |
PCT Filed: |
September 28, 2010 |
PCT NO: |
PCT/JP2010/067312 |
371 Date: |
March 12, 2012 |
Current U.S.
Class: |
428/577 ;
72/362 |
Current CPC
Class: |
B21D 47/01 20130101;
B21D 5/015 20130101; E04C 2003/0465 20130101; E04C 3/07 20130101;
E04C 2003/0439 20130101; B21C 37/14 20130101; Y10T 428/12229
20150115; E04C 2003/0413 20130101 |
Class at
Publication: |
428/577 ;
72/362 |
International
Class: |
B21C 1/00 20060101
B21C001/00; B21D 31/00 20060101 B21D031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2009 |
JP |
2009-224515 |
Claims
1. A curved-part forming method for obtaining a curved part by
performing forming on a blank formed of a single metal plate, the
method comprising: a bending process in which the blank having a
curved outline corresponding to a curve of the curved part in a
longitudinal direction is bent into a sectional shape corresponding
to a division portion of a sectional shape of the curved part; and
a joining process in which two or more portions obtained by the
bending process are joined together.
2. The method according to claim 1, wherein, prior to the bending
process, a folding line is formed in the blank or a cut is further
formed in the blank.
3. A curved part manufactured according to the method of claim
1.
4. A curved part manufactured according to the method of claim 2.
Description
RELATED APPLICATIONS
[0001] This is a .sctn.371 of International Application No.
PCT/JP2010/067312, with an international filing date of Sep. 28,
2010 (WO 2011/040623 A1, published Apr. 7, 2011), which is based on
Japanese Patent Application No. 2009-224515, filed Sep. 29, 2009,
the subject matter of which is incorporated by reference.
TECHNICAL FIELD
[0002] This disclosure relates to a method of forming plates into
curved parts (more specifically, curved frame parts). More
particularly, the disclosure relates to a forming method that makes
it possible to form high-strength steel sheets having a tensile
strength (TS) that is greater than or equal to 590 MPa into curved
parts, curved parts, and a method for manufacturing the same.
BACKGROUND
[0003] Curved parts have hitherto been obtained by press forming
single metal plates. In such press forming, various forming modes
including drawing, stretch forming, stretch flanging, and bending
are combined. (Press forming will hereunder be referred to as
"conventional press forming.") Further, a method of bending forming
a cylindrical material (Japanese Unexamined Patent Application
Publication No. 9-30345), a roll forming technology (Japanese
Unexamined Patent Application Publication No. 11-129045), and
bending forming using a hollow part (Japanese Unexamined Patent
Application Publication Nos. 8-174047 and 2005-1490) are proposed.
As an example of reinforcing curved parts, a method of filling with
resin foam (Japanese Unexamined Patent Application Publication No.
11-348813) is proposed.
[0004] Increasing the strength of a steel sheet in accordance with
the demand for reducing weight causes at the same time a reduction
in drawing ability, stretch forming ability, and stretch flanging
ability on the steel sheet. Therefore, in conventional pressing
forming, defects such as cracks or wrinkles, occur. In particular,
as the shape becomes complex, there are cases where curved parts
cannot be obtained. For example, if portions 50A and 50B (which are
curved in an X direction and a Y direction in plan view, and in a Z
direction) of a curved part 50 shown in FIG. 11 are formed by
performing conventional press forming on a single high-strength
steel sheet having a tensile strength (TS) that is greater than or
equal to 590 MPa, wrinkles occur in a planar section (such as a
wrinkle section in FIG. 11), and cracks occur in a vertical wall at
a side surface or in flanges (such as a crack section in FIG. 11).
It is possible to suppress the occurrence of cracks/wrinkles up to
a certain extent by changing the shapes of parts or optimizing
forming conditions of, for example, a blank holder. However, in
such a method, to satisfy the need of reducing weight, there is a
limit with regard to achieving a higher tensile strength (TS) that
is greater than 980 MPa.
[0005] A method of obtaining high-strength curved parts by
performing bending forming or roll forming on cylindrical materials
is disclosed in JP '345, JP '045, JP '047 and JP '490. From the
viewpoint of formability of the materials and process constraints,
it is difficult to obtain complex curved shapes, and there are
serious productivity problems such as an increase in the number of
processes. For example, when low-strength materials are used,
complex shapes can be easily obtained, but parts have insufficient
strength. Therefore, there are, for example, technologies for
obtaining reinforcing effects by filling with resin foam (JP '813).
However, from the viewpoints of costs, production, and recycling,
it is actually not easy to say that such technologies are
necessarily useful technologies.
[0006] That is, in conventional forming methods, when single
high-strength steel sheets are used as materials, forming into
desired curved parts cannot be performed by one-piece press
forming, or, when single low-strength steel sheets are used as
materials, forming into curved parts can be performed, but the
parts have insufficient strength, thereby making it necessary to,
for example, increase the number of reinforcing pats, as a result
of which weight is increased.
SUMMARY
[0007] We thus provide the following: [0008] (1) A curved-part
forming method for obtaining a curved part by performing forming on
a blank formed of a single metal plate. The method includes a
bending process in which the blank having a curved outline
corresponding to a curve of the curved part in a longitudinal
direction is bent into a sectional shape corresponding to a
division portion of a sectional shape of the curved part, and a
joining process in which two or more portions obtained by the
bending process are joined together. [0009] (2) The curved-part
forming method according to (1), wherein, prior to the bending
process, a folding line is formed in the blank, or a cut is further
formed in the blank. [0010] (3) The curved part manufactured using
the curved-part forming method according to (1) or (2). [0011] (4)
A curved-part manufacturing method for manufacturing a curved part
using the curved-part forming method according to (1) or (2).
[0012] Since the material is bent and deformed almost without being
variously deformed by drawing, stretch forming, and stretch
flanging, it is possible to perform one-piece pressing forming of a
single high-strength steel sheet into portions of the curved part.
In addition, as a result of the shape of the curved part, which is
a target shape to be formed, being reflected in the outline of the
blank, it is possible to easily obtain parts having high strength
and having a complex curved shape that could not be hitherto
obtained, enlargement of space due to a reduction in the cross
section of the parts, and a large reduction in weight because, for
example, plate thickness is reduced and reinforcing parts are not
used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic view of an example of a curved
part.
[0014] FIG. 2 is a schematic view of another example of a curved
part.
[0015] FIG. 3 is a schematic view of yet another example of a
curved part.
[0016] FIG. 4 is a schematic view of still another example of a
curved part.
[0017] FIG. 5 is a schematic view of a further example of a curved
part.
[0018] FIG. 6 is a schematic view of a still further example of a
curved part.
[0019] FIG. 7 is a schematic view of a selected example of a curved
part.
[0020] FIG. 8 is a schematic view of another selected example of a
curved part.
[0021] FIG. 9 is a sectional view of various exemplary sectional
shapes of curved parts.
[0022] FIG. 10 is a schematic view of examples of how folding lines
are formed.
[0023] FIG. 11 is a schematic view of an exemplary curved part
formed by conventional press forming.
REFERENCE SIGNS
[0024] 1, 2 Blanks [0025] 1F, 2F Flanges, Portions corresponding to
flanges [0026] 10, 20 Portions constituting curved parts [0027] 30
Curved part (target to be formed) [0028] 50 Curved part formed by
conventional press forming (50A and 50B denote portions
constituting curved part 50)
DETAILED DESCRIPTION
[0029] FIGS. 1 to 8 are schematic views of different examples of
curved parts.
[0030] FIGS. 1 and 2 each show an exemplary case in which a curve
of a curved part 30 in a longitudinal direction is along folding
lines in only one of two opposite directions. Further, in FIG. 1,
the sectional size is constant in the longitudinal direction of the
part and, in FIG. 2, the sectional size changes in the longitudinal
direction of the part. FIGS. 3 and 4 each show an exemplary case in
which a curve of a curved part 30 in the longitudinal direction
along folding lines changes from either one of two opposite
directions to the other one of the two opposite directions.
Further, in FIG. 3, the sectional size is constant in the
longitudinal direction of the part and, in FIG. 4, the sectional
size changes in the longitudinal direction of the part. FIGS. 5, 6,
7, and 8 each show an exemplary case in which a curve of a curved
part 30 in the longitudinal direction is such that the curved part
30 is continuously curved in only one of two opposite directions
(FIGS. 7 and 8 each show an exemplary case in which the curved part
has a warped sectional shape in the longitudinal direction).
Further, in FIG. 5, the sectional size is constant in the
longitudinal direction of the part and, in FIGS. 6, 7, and 8, the
sectional size changes in the longitudinal direction of the
part.
[0031] In these examples, two blanks 1 and 2 have the same planar
shape, and the planar shape thereof has a side-bend outline
corresponding to the curve of the curved part 30, which is a target
to be formed, in the longitudinal direction of the curved part 30.
The blanks 1 and 2 may be previously provided with working holes or
beads and the like. In a bending process, the blanks 1 and 2 are
each bent into a sectional shape corresponding to a division
portion of a sectional shape of the curved part 30 so that portions
10 and 20 constituting the curved part 30 are formed. Reference
numerals 1F and 2F denote portions corresponding to flanges of the
blanks 1 and 2 or denote the flanges of the portions 10 and 20. In
FIGS. 1 to 8, broken lines and dotted lines that are formed in
regions of the shapes of the blanks 1 and 2 represent mountain
folding and valley folding, respectively, and indicate places
corresponding to bend portions (protrusion edges and recess edges)
formed by bending in the bending process. In the bending process,
using a die, the blanks are press bended so that forming portions
of the blanks become bend portions that are in correspondence with
target parts. By press bending, forming materials primarily undergo
deformation of bending forming, and are formed into target
shapes.
[0032] Next, in a joining process, the portions 10 and 20 are
joined together to obtain the curved part 30. Joining methods may
be any one of, for example, welding, caulking, riveting, and
adhesion using an adhesive.
[0033] Although the examples shown in FIGS. 1 to 6 are those in
which the blanks are formed into a part sectional shape shown in
FIG. 9(a), methods and curved parts are not limited thereto. Our
methods and curved parts are applicable to cases in which, for
example, as shown in FIG. 9(b), the blanks are formed into a part
sectional shape that is the reverse of that in FIG. 9(a) at the
left and right sides or, as shown in FIG. 9(c), the blanks are
formed into a part sectional shape so that the flanges 2F of only
the structural portion 20 are bent. The examples shown in FIGS. 7
and 8 are those in which the blanks are formed into a part
sectional shape shown in FIG. 9(d).
[0034] Although, the examples shown in FIGS. 1 to 6 and FIG. 8 use
two blanks having the same planar shape for one curved part, our
curved parts are not limited thereto. Our method and curved parts
are applicable to cases in which three or more blanks are used for
one curved part, with at least one of the blanks having a planar
shape that differs from the planar shapes of the remaining
blanks.
[0035] Further, to increase position precision of the bend portions
during the bending, it is desirable to previously provide folding
lines in portions of the blanks where the mountain folding and the
valley folding are performed. We are not only limited to
(continuously) forming the folding lines along an entire bending
processing portion. The folding lines may be (intermittently)
formed in only portions of the bending processing portion according
to the circumstances. As a method of forming the folding lines, it
is desirable to use, for example, coining. Another example thereof
is a method of continuously transferring the unevenness of a roller
surface to surfaces of the materials. Suitable forms of folding
lines may be provided by forming V grooves such as that shown in
FIG. 10(d), in a linear form (10(a)), a broken-line form (10(b)),
or a dotted-line form (10(c)), or in a combination of any of these
forms. It is desirable that the depth of the V grooves be less than
or equal to 20% of the thickness of a metal plate (abbreviated as
"plate thickness"). If the depth of the V grooves exceeds 20% of
the plate thickness, the strength of the parts required for, for
example, the frame of an automobile may be reduced, or cracks may
be formed in the bend portions and, in a high-strength metal
material, it is not easy to form the grooves deeply, thereby
causing serious production and cost problems.
[0036] The shape of the grooves is not limited to a V shape (the
grooves are not limited to the V groove shown in FIG. 10(d)) so
that the grooves may have various recessed shapes such as U shapes.
When the curvature radius of the bend portions is large, a
plurality of long and narrow grooves may be formed parallel to each
other.
[0037] When there are localized portions where wrinkles or cracks
are very likely to be formed due to localized excessive stretching
or compression during bending (for example, when there are a
plurality of localized portions at portions of the blanks
corresponding to the flanges that are likely to be subjected to
excessive stretch flanging or shrink flanging), previously forming
cuts in such localized portions makes it possible to more reliably
prevent the formation of cracks and wrinkles, which is
desirable.
EXAMPLE 1
[0038] Blanks formed of thin steel sheets (material symbols A, B,
and C) having plate thicknesses and tensile properties (yield
strength YS, tensile strength TS, elongation El) shown in Table 1
were formed into curved parts by forming methods based on Table 2,
and the shapes of the obtained curved parts were visually observed,
to evaluate the forming methods. The results are as shown in Table
2. In conventional press forming according to a Comparative
Example, wrinkles are formed in the wrinkle section and cracks are
formed in the crack section shown in FIG. 11, whereas in our
Examples, curved parts substantially having target shapes and
without having cracks or wrinkles were obtained.
TABLE-US-00001 TABLE 1 PLATE MATERIAL THICKNESS YS TS El SYMBOL
(mm) (MPa) (MPa) (%) A 1.6 710 990 17 B 1.6 810 1190 13 C 1.6 1300
1500 9
TABLE-US-00002 TABLE 2 MATERIAL FORMING No. SYMBOL METHOD RESULT OF
FORMING REMARKS 1 A CONVENTIONAL NO CRACKS/WRINKLES COMPARATIVE
PRESS FORMING GOOD PRODUCED EXAMPLE 2 A METHOD ILLUS- GOOD NO
CRACKS/ EXAMPLE TRATED IN FIG. 1 WRINKLES PRODUCED 3 A METHOD
ILLUS- GOOD NO CRACKS/ EXAMPLE TRATED IN FIG. 4 WRINKLES PRODUCED 4
A METHOD ILLUS- GOOD NO CRACKS/ EXAMPLE TRATED IN FIG. 7 WRINKLES
PRODUCED 5 B CONVENTIONAL NO CRACKS/WRINKLES COMPARATIVE PRESS
FORMING GOOD PRODUCED EXAMPLE 6 B METHOD ILLUS- GOOD NO CRACKS/
EXAMPLE TRATED IN FIG. 3 WRINKLES PRODUCED 7 B METHOD ILLUS- GOOD
NO CRACKS/ EXAMPLE TRATED IN FIG. 6 WRINKLES PRODUCED 8 B METHOD
ILLUS- GOOD NO CRACKS/ EXAMPLE TRATED IN FIG. 8 WRINKLES PRODUCED 9
C CONVENTIONAL NO CRACKS/WRINKLES COMPARATIVE PRESS FORMING GOOD
PRODUCED EXAMPLE 10 C METHOD ILLUS- GOOD NO CRACKS/ EXAMPLE TRATED
IN FIG. 5 WRINKLES PRODUCED 11 C METHOD ILLUS- GOOD NO CRACKS/
EXAMPLE TRATED IN FIG. 2 WRINKLES PRODUCED 12 C METHOD ILLUS- GOOD
NO CRACKS/ EXAMPLE TRATED IN FIG. 7 WRINKLES PRODUCED
EXAMPLE 2
[0039] Folding lines provided by V grooves (whose depths are shown
in Table 3) in a linear form, a broken-line form, or a dotted-line
form such as those shown in FIG. 10, were previously formed in
blanks formed of thin steel sheets (material symbols A, B, and C)
having plate thicknesses and tensile properties (yield strength YS,
tensile strength TS, extension El) shown in Table 1. Then, the
blanks were formed into curved parts using forming methods based on
Table 3, and the shapes of the obtained curved parts were visually
observed, to evaluate the forming methods. The results are as shown
in Table 3. In our Examples, cracks or wrinkles were not produced,
and curved parts whose shapes more closely matched the target
shapes compared to the curved parts in the first Examples (that is,
curved parts whose dimensional precisions were good) were
obtained.
TABLE-US-00003 TABLE 3 V MATERIAL V GROOVE FORMING DIMENSIONAL No.
SYMBOL GROOVE DEPTH (%) METHOD RESULT OF FORMING PRECISION REMARKS
1 A LINEAR 7 METHOD GOOD NO CRACKS/ GOOD EXAMPLE FORM ILLUSTRATED
WRINKLES IN FIG. 1 PRODUCED 2 A LINEAR 6 METHOD GOOD NO CRACKS/
GOOD EXAMPLE FORM ILLUSTRATED WRINKLES IN FIG. 2 PRODUCED 3 A
BROKEN- 12 METHOD GOOD NO CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED
WRINKLES FORM IN FIG. 3 PRODUCED 4 A BROKEN- 19 METHOD GOOD NO
CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED WRINKLES FORM IN FIG. 4
PRODUCED 5 A DOTTED- 10 METHOD GOOD NO CRACKS/ GOOD EXAMPLE LINE
ILLUSTRATED WRINKLES FORM IN FIG. 5 PRODUCED 6 A DOTTED- 16 METHOD
GOOD NO CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED WRINKLES FORM IN FIG.
6 PRODUCED 7 A LINEAR 12 METHOD GOOD NO CRACKS/ GOOD EXAMPLE FORM
ILLUSTRATED WRINKLES IN FIG. 7 PRODUCED 8 A LINEAR 5 METHOD GOOD NO
CRACKS/ GOOD EXAMPLE FORM ILLUSTRATED WRINKLES IN FIG. 8 PRODUCED 9
B LINEAR 10 METHOD GOOD NO CRACKS/ GOOD EXAMPLE FORM ILLUSTRATED
WRINKLES IN FIG. 5 PRODUCED 10 B LINEAR 8 METHOD GOOD NO CRACKS/
GOOD EXAMPLE FORM ILLUSTRATED WRINKLES IN FIG. 6 PRODUCED 11 B
DOTTED- 4 METHOD GOOD NO CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED
WRINKLES FORM IN FIG. 1 PRODUCED 12 B DOTTED- 15 METHOD GOOD NO
CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED WRINKLES FORM IN FIG. 2
PRODUCED 13 B BROKEN- 6 METHOD GOOD NO CRACKS/ GOOD EXAMPLE LINE
ILLUSTRATED WRINKLES FORM IN FIG. 3 PRODUCED 14 B BROKEN- 13 METHOD
GOOD NO CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED WRINKLES FORM IN FIG.
4 PRODUCED 15 B DOTTED- 16 METHOD GOOD NO CRACKS/ GOOD EXAMPLE LINE
ILLUSTRATED WRINKLES FORM IN FIG. 7 PRODUCED 16 B DOTTED- 6 METHOD
GOOD NO CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED WRINKLES FORM IN FIG.
8 PRODUCED 17 C BROKEN- 8 METHOD GOOD NO CRACKS/ GOOD EXAMPLE LINE
ILLUSTRATED WRINKLES FORM IN FIG. 3 PRODUCED 18 C BROKEN- 12 METHOD
GOOD NO CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED WRINKLES FORM IN FIG.
4 PRODUCED 19 C DOTTED- 4 METHOD GOOD NO CRACKS/ GOOD EXAMPLE LINE
ILLUSTRATED WRINKLES FORM IN FIG. 5 PRODUCED 20 C DOTTED- 9 METHOD
GOOD NO CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED WRINKLES FORM IN FIG.
6 PRODUCED 21 C LINEAR 3 METHOD GOOD NO CRACKS/ GOOD EXAMPLE FORM
ILLUSTRATED WRINKLES IN FIG. 1 PRODUCED 22 C LINEAR 5 METHOD GOOD
NO CRACKS/ GOOD EXAMPLE FORM ILLUSTRATED WRINKLES IN FIG. 2
PRODUCED 23 C BROKEN- 5 METHOD GOOD NO CRACKS/ GOOD EXAMPLE LINE
ILLUSTRATED WRINKLES FORM IN FIG. 7 PRODUCED 24 C BROKEN- 10 METHOD
GOOD NO CRACKS/ GOOD EXAMPLE LINE ILLUSTRATED WRINKLES FORM IN FIG.
8 PRODUCED
* * * * *