CA2772925C

CA2772925C - Curved parts and method for manufacturing the same

Info

Publication number: CA2772925C
Application number: CA 2772925
Authority: CA
Inventors: Takayuki Futatsuka; Kazuhiko Higai; Yoshikiyo Tamai; Takaaki Hira; Takeshi Fujita; Yuji Yamasaki
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2009-09-29
Filing date: 2010-09-28
Publication date: 2015-02-03
Anticipated expiration: 2030-09-28
Also published as: JP5515566B2; WO2011040623A1; EP2484461A4; CN102574192B; EP2484461A1; KR101443990B1; CA2772925A1; EP2484461B1; US20120171506A1; JP2011073010A; CN102574192A; KR20120055616A

Abstract

Disclosed is a method for forming a bent member, which comprises a bending step for bending blanks (1, 2) in the bending profile shape corresponding to the bending of a bent member (30) in the length direction into the cross-section shape corresponding to a cross-section shaped split part of the bent member, and a joining step for joining two (or three or more) members (10, 20) obtained by the bending step. In conventional methods for forming bent members, when a single plate of a high-strength steel plate is used as a raw material, the forming into a desired bent member cannot be obtained in integral press forming, or when a single plate of a low-strength steel plate is used as the raw material, the forming into the bent member can be obtained, but an increase in the weight caused by an increase in reinforcement components is created because the shortage of member strength is created, resulting in insufficient component strength.

Description

DESCRIPTION
[Title of Invention] CURVED PARTS AND METHOD FOR
MANUFACTURING THE SAME
[Technical Field]
[0001]
The present invention relates to a method of forming plates into curved parts (more specifically, curved frame parts). More particularly, the present invention 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 Art]

[0002]
Curved parts have hitherto been obtained by press forming single metal plates. In the press forming, various forming modes including drawing, stretch forming, stretch flanging, and bending are combined. (The press forming will hereunder be referred to as "conventional press forming.") Further, a method of bending forming a cylindrical material (PTL 1), a roll forming technology (PTL 2), and bending forming using a hollow part (PTL 3 and PTL 4) are proposed.
As an example of reinforcing curved parts, a method of filling with resin foam (PTL 5) is proposed.
[Citation List]
[Patent Literature]

[0003]

PTL 1: Japanese Unexamined Patent Application Publication No. 9-30345 PTL 2: Japanese Unexamined Patent Application Publication No. 11-129045 PTL 3: Japanese Unexamined Patent Application Publication No. 8-174047 PTL 4: Japanese Unexamined Patent Application Publication No. 2005-1490 PTL 5: Japanese Unexamined Patent Application Publication No. 11-348813 [Summary of Invention]
[Technical Problem]

[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 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 is 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). Here, 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, in order 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 (PTL 1 to PTL 4). From the viewpoints of formability of the materials and process constraints, it is difficult of 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 (PTL 5). 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.
[Solution to Problem]

[0007]
The present invention for solving the aforementioned problems provides the following:
(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.
According to another aspect of the present invention, there is provided a curved-part forming method for obtaining a curved part having a closed sectional shape and a curve in a longitudinal direction, the method comprising:
preparing two or more planar blanks each formed of a single metal plate, each of the two or more planar blanks having a curved outline corresponding to the curve of the curved part;
bending each of the two or more planar blanks into a sectional shape corresponding to a division portion of the sectional shape of the curved part to form a division part;
and joining two or more of the division parts obtained by the bending together to form the curved part having the closed sectional shape.
(2) The curved-part forming method as described above, wherein, prior to the bending process, a folding line is formed in the blank, or a cut is further formed in the blank.
(3) The curved part manufactured using the curved-part forming method as described above.
(4) A curved-part manufacturing method for manufacturing a curved part using the curved-part forming method as described above.
[Advantageous Effects of Invention]

[0008]
According to the present invention, 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 5a addition, as a result of the shape of the curved part, which is a target to be formed, being reflected in the outline of the blank, it is possible to expect easy obtainment of 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 Drawings]

[0009]
[Fig. 1] Fig. 1 is a schematic view of an embodiment of the present invention.
[Fig. 2] Fig. 2 is a schematic view of an embodiment of the present invention (differing from the already mentioned embodiment).
[Fig. 3] Fig. 3 is a schematic view of an embodiment of the present invention (differing from the already mentioned embodiments).
[Fig. 4] Fig. 4 is a schematic view of an embodiment of the present invention (differing from the already mentioned embodiments).
[Fig. 5] Fig. 5 is a schematic view of an embodiment of the present invention (differing from the already mentioned embodiments).
[Fig. 6] Fig. 6 is a schematic view of an embodiment of the present invention (differing from the already mentioned embodiments).
[Fig. 7] Fig. 7 is a schematic view of an embodiment of the present invention (differing from the already mentioned embodiments).
[Fig. 8] Fig. 8 is a schematic view of an embodiment of the present invention (differing from the already mentioned embodiments).
[Fig. 9] Fig. 9 is a sectional view of various exemplary sectional shapes of curved parts.
[Fig. 10] Fig. 10 is a schematic view of examples of how folding lines are formed.
[Fig. 11] Fig. 11 is a schematic view of an exemplary curved part formed by conventional press forming.
[Description of Embodiments]

[0010]
Figs. 1 to 8 are schematic views of different embodiments of the present invention.
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.

[0011]
In these embodiments, 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. It goes without saying that the blanks 1 and 2 may be previously provided with working holes or beads, etc. 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 according to the present invention, 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 the press bending, forming materials primarily undergo deformation of bending forming, and are formed into target shapes.

[0012]
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.
Although the embodiments shown in Figs. 1 to 6 are those in which the blanks are formed into a part sectional shape shown in Fig. 9(a), the present invention is not limited thereto. It is obvious that the present invention is 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 embodiments shown in Figs. 7 and 8 are those in which the blanks are formed into a part sectional shape shown in Fig. 9(d).

[0013]
Although, the embodiments shown in Figs. 1 to 6 and Fig.
8 use two blanks having the same planar shape for one curved part, the present invention is not limited thereto.
It is obvious that the present invention is applicable to a case 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.
Further, in the present invention, in order 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. The present invention is 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.
Here, 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.

[0014]
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.
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.
[First Examples]

[0015]
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 the examples of the present invention, curved parts substantially having target shapes and without having cracks or wrinkles were obtained.

. CA 02772925 2012-03-01 [0016]
[Table 1]
MATERIAL PLATE YS (MPa) TS (MPa) El ( %) SYMBOL THICKNESS
(mm) A 1.6 710 990 17 B 1.6 810 1190 13 C 1.6 1300 1500 9 [0017]
[Table 2]
No. MATERIAL FORMING METHOD RESULT OF FORMING REMARKS
SYMBOL

CONVENTIONAL NO GOOD CRACKS/WRINKLES COMPARATIVE
PRESS FORMING PRODUCED EXAMPLE

EXAMPLE OF
ILLUSTRATED IN CRACKS/WRINKLES PRESENT
FIG. I PRODUCED INVENTION

EXAMPLE OF
ILLUSTRATED IN CRACKS/WRINKLES PRESENT
FIG. 4 PRODUCED INVENTION

EXAMPLE OF
ILLUSTRATED IN CRACKS/WRINKLES PRESENT
FIG. 7 PRODUCED INVENTION , B CONVENTIONAL NO
GOOD CRACKS/WRINKLES COMPARATIVE
PRESS FORMING PRODUCED EXAMPLE ¨

EXAMPLE OF
ILLUSTRATED IN CRACKS/WRINKLES PRESENT
FIG. 3 PRODUCED INVENTION

EXAMPLE OF
ILLUSTRATED IN CRACKS/WRINKLES PRESENT
FIG. 6 PRODUCED INVENTION

EXAMPLE OF
ILLUSTRATED IN CRACKS/WRINKLES PRESENT
FIG. 8 PRODUCED INVENTION

CONVENTIONAL NO GOOD CRACKS/WRINKLES COMPARATIVE
PRESS FORMING PRODUCED EXAMPLE
C METHOD GOOD NO EXAMPLE OF
ILLUSTRATED IN CRACKS/WRINKLES PRESENT
FIG. 5 PRODUCED INVENTION
11 c METHOD GOOD NO
EXAMPLE OF
ILLUSTRATED IN CRACKS/WRINKLES PRESENT
FIG. 2 PRODUCED INVENTION
12 c METHOD GOOD NO
EXAMPLE OF
ILLUSTRATED IN CRACKS/WRINKLES PRESENT
FIG. 7 PRODUCED INVENTION

[0018]
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 the examples of the present invention, 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 of the present invention (that is, curved parts whose dimensional precisions were good) were obtained.

[0019]
[Table 3]
No. MATERIAL V V FORMING RESULT OF FORMING DIMENSIONAL REMARKS
SYMBOL GROOVE GROOVE METHOD PRECISION
DEPTH
(%) EXAMPLE OF
FORM ILLUSTRATED CRACKS/WRINKLES PRESENT
IN FIG. 1 PRODUCED INVENTION

EXAMPLE OF
FORM ILLUSTRATED CRACKS/WRINKLES PRESENT
IN FIG. 2 PRODUCED INVENTION

EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES PRESENT
FORM IN FIG. 3 PRODUCED INVENTION

EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES PRESENT
FORM IN FIG. 4 PRODUCED INVENTION

LINE ILLUSTRATED CRACKS/WRINKLES PRESENT
FORM IN FIG. 5 PRODUCED INVENTION
6 A DOTTED-16 METHOD 'GOOD NO GOOD EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES PRESENT
FORM IN FIG. 6 PRODUCED INVENTION

FORM ILLUSTRATED CRACKS/WRINKLES PRESENT
IN FIG. 7 PRODUCED INVENTION

FORM ILLUSTRATED CRACKS/WRINKLES PRESENT
INVENTION
IN FIG. 8 , PRODUCED
, FORM ILLUSTRATED CRACKS/WRINKLES PRESENT
IN FIG. 5 PRODUCED INVENTION

FORM ILLUSTRATED CRACKS/WRINKLES PRESENT
IN FIG. 6 PRODUCED INVENTION

11 B 'DOTTED-4 METHOD GOOD NO GOOD EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES PRESENT
FORM IN FIG. 1 PRODUCED INVENTION
, LINE ILLUSTRATED CRACKS/WRINKLES PRESENT
FORM IN FIG. 2 PRODUCED INVENTION

LINE ILLUSTRATED CRACKS/WRINKLES PRESENT
FORM IN FIG. 3 PRODUCED INVENTION

LINE ILLUSTRATED CRACKS/WRINKLES PRESENT
FORM IN FIG. 4 PRODUCED INVENTION

LINE ILLUSTRATED CRACKS/WRINKLES PRESENT
FORM IN FIG. 7 PRODUCED INVENTION

= CA 02772925 2012-03-01 -Table 3 continued LINE ILLUSTRATED CRACKS/WRINKLES
PRESENT
FORM IN FIG. 8 PRODUCED
INVENTION

EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES
PRESENT
FORM IN FIG. 3 PRODUCED
INVENTION

EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES
PRESENT
FORM IN FIG. 4 PRODUCED
INVENTION

EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES
PRESENT
FORM IN FIG. 5 PRODUCED
INVENTION

EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES
PRESENT
FORM IN FIG. 6 PRODUCED
INVENTION

EXAMPLE OF
FORM ILLUSTRATED CRACKS/WRINKLES
PRESENT
IN FIG. 1 PRODUCED
INVENTION

EXAMPLE OF
FORM ILLUSTRATED CRACKS/WRINKLES
PRESENT
IN FIG. 2 PRODUCED
INVENTION

EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES
PRESENT
FORM IN FIG. 7 PRODUCED
INVENTION

EXAMPLE OF
LINE ILLUSTRATED CRACKS/WRINKLES
PRESENT
FORM IN FIG. 8 PRODUCED
INVENTION
Reference Signs List [0020]
1, 2 Blanks 1F, 2F Flanges, Portions corresponding to flanges 10, 20 Portions constituting curved parts according to present invention 30 Curved part according to present invention (target to be formed) 50 Curved part formed by conventional press forming (50A and 50B denote portions constituting curved part 50)

Claims

WHAT IS CLAIMED IS:

1. A curved-part forming method for obtaining a curved part having a closed sectional shape and a curve in a longitudinal direction, the method comprising:
preparing two or more planar blanks each formed of a single metal plate, each of the two or more planar blanks having a curved outline corresponding to the curve of the curved part;
bending each of the two or more planar blanks into a sectional shape corresponding to a division portion of the sectional shape of the curved part to form a division part;
and joining two or more of the division parts obtained by the bending together to form the curved part having the closed sectional shape.

2. The curved-part forming method according to claim 1, wherein, the curved outline of each of the two or more planar blanks includes a pair of end sides and a pair of curved sides that connect the end sides, each of the pair of curved sides having a curve corresponding to the curve of the curved part in the longitudinal direction; and the bending bends each of the two or more planar blanks along a curved bending line that extends between the end sides.

3. The curved part forming method according to claim 1 or 2, wherein, prior to the bending, a folding line is formed in each of the two or more planar blanks, or a cut is further formed in each of the two or more planar blanks.

4. The curved part manufactured using the curved-part forming method according to any one of claims 1 to 3.