Manufacturing method and manufacturing apparatus of press-formed body

Abstract

A press-formed body (15) made of a high-tensile strength steel sheet of 390 MPa or more including a groove bottom part (15a), ridge line parts (15b, 15b) continuous to the groove bottom part (15a), and side wall parts (15c, 15c) continuous to the ridge line parts (15b, 15b), and in which an outward flange (16) is formed at an end part in a longitudinal direction is manufactured by a press-forming apparatus including a punch (11), a die (12), and a pad (14) which presses and binds a press-forming material (13) to the punch (11), thereby forming the press-formed body (15) without providing cutouts at a ridge line part flange portion of the outward flange, or generating lowering of material yield.

Claims

1. A manufacturing method of a press-formed body comprising a high-tensile strength steel sheet of 390 MPa or more having a groove-shaped cross section, the groove-shaped cross section comprising a groove bottom part; at least two ridge line parts, each one of the at least two ridge line parts being adjacent to an end portion of the groove bottom part; and at least two side wall parts, each one of the at least two side wall parts being adjacent to one of the at least two ridge line parts; the manufacturing method comprising: a first step of performing the press-forming while the pad presses (a) and (b) to the punch: (a) a portion of areas of the press-forming material, which are to be formed into each of the at least two ridge line parts, (b) a different area of the press-forming material, which is to be formed into the grove bottom part, wherein (a) is in the vicinity of an outward flange, and has a predetermined length of a cross-sectional peripheral length starting at connecting parts which connect each of the at least two ridge line parts to the groove bottom part, wherein the outward flange is formed across the at least two ridge line parts, and is further formed in at least one end part in a longitudinal direction of the pressed-formed body, and wherein the press-forming is performed by a press-forming apparatus which includes a punch, a die, and a pad which presses the press-forming material to the punch; and a second step of performing press-forming of other areas of the press-forming material so as to form parts of the press-formed body which are not formed by the first step, wherein cutouts are not formed or provided at any portion of the at least two ridge line parts that are in the vicinity of the outward flange, or at any portion of the outward flange.

2. The manufacturing method of the press-formed body according to claim 1, wherein said predetermined length of a cross-sectional peripheral length is one-third or more of the cross-sectional peripheral length, and wherein the pad presses said one-third or more of the cross-sectional peripheral length.

3. The manufacturing method of the press-formed body according to claim 1, wherein the pad presses the portion of the press-forming material to be formed into the at least two ridge line parts within a predetermined range from a root part of the outward flange in a longitudinal direction.

4. The manufacturing method of the press-formed body according to claim 1, wherein the groove-shaped cross section further comprises curved parts continuous to the at least two side wall parts, and additional flanges continuous to the curved parts.

5. The manufacturing method of the press-formed body according to claim 1, wherein the press-forming is bend-forming.

6. The manufacturing method of the press-formed body according to claim 1, wherein the press-forming is drawing.

7. The manufacturing method of the press-formed body according to claim 1, wherein, in the first step, the groove bottom part, a portion of the at least two ridge line parts, a portion of the at least two side wall parts, and the outward flange are formed, and, in the second step, a remaining portion of the at least two ridge line parts and a remaining part of the at least two side wall parts, not formed in the first step, are formed.

8. The manufacturing method of the press-formed body according to claim 1, wherein: the punch and the pad move relative to the die; and the punch and the pad move in the same direction, and towards the die.

9. A manufacturing apparatus for manufacturing a press-formed body, the press-formed body comprising a high-tensile strength steel sheet of 390 MPa or more having a groove-shaped cross section, the groove-shaped cross section comprising a groove bottom part; at least two ridge line parts, each one of the at least two ridge line parts being adjacent to an end portion of the groove bottom part; and at least two side wall parts, each one of the at least two side wall parts being adjacent to one of the at least two ridge line parts; the manufacturing apparatus comprising: a punch; a die; and a pad which presses a press-forming material to the punch, wherein the pad presses (a) and (b) to the punch, wherein (a) is a portion of areas of the press-forming material, which are to be formed into each of the at least two ridge line parts, and (b) is a different area of the press-forming material, which is to be formed into the groove bottom part; wherein (a) is in the vicinity of an outward flange, and has a predetermined length of a cross-sectional peripheral length starting at connecting parts which connect each of the at least two ridge line parts to the groove bottom part, wherein the outward flange is formed across the at least two ridge line parts, and is further formed in at least one end part in a longitudinal direction of the pressed-formed body; wherein the punch and the pad move relative to the die, wherein the punch and the pad move in the same parallel direction, and towards the die; and wherein cutouts are not formed or provided at any portion of the at least two ridge line parts that are in the vicinity of the outward flange, or at any portion of the outward flange.

10. The manufacturing apparatus of the press-formed body according to claim 9, wherein said predetermined length of a cross-sectional peripheral length is one-third or more of the cross-sectional peripheral length, and wherein the pad has a shape pressing said one-third or more of the cross-sectional peripheral length.

11. The manufacturing apparatus of the press-formed body according to claim 9, wherein the pad presses the portion of the press-forming material to be formed into the at least two ridge line parts within a predetermined range from a root part of the outward flange in a longitudinal direction.

12. The manufacturing apparatus of the press-formed body according to claim 9, wherein the groove-shaped cross section further comprises curved parts continuous to the at least two side wall parts, and additional flanges continuous to the curved parts.

13. The manufacturing apparatus of the press-formed body according to claim 9, wherein the press-forming is bend-forming.

14. The manufacturing apparatus of the press-formed body according to claim 9, wherein the press-forming is drawing.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A is a view schematically illustrating a schematic configuration of a manufacturing apparatus of a press-formed body according to an embodiment and a first step;

(2) FIG. 1B is a sectional view illustrating a transverse cross-sectional shape of a press-formed body manufactured in the present embodiment;

(3) FIG. 1C is a perspective view illustrating a configuration at around a ridge line pad in the first step;

(4) FIG. 1D is a view when the press-formed body manufactured in the present embodiment is seen from a lateral side in a longitudinal direction;

(5) FIG. 2A is a perspective view of a press-formed body of an analysis example 1;

(6) FIG. 2B is a II arrow view in FIG. 2A;

(7) FIG. 2C is a transverse sectional view of the press-formed body of the analysis example 1;

(8) FIG. 3A is a perspective view illustrating a punch, a die, and a press-forming material at a forming time according to the invented method;

(9) FIG. 3B is a perspective view illustrating the punch, a ridge line pad, and the press-forming material at the forming time according to the invented method;

(10) FIG. 3C is a perspective view enlargedly illustrating a square surrounded part in FIG. 3B;

(11) FIG. 3D is a sectional view in FIG. 3C;

(12) FIG. 4A is a perspective view illustrating a punch, a die, a pad, and a press-forming material at a forming time according to a conventional method;

(13) FIG. 4B is a perspective view illustrating the punch, the pad, and the press-forming material at the forming time according to the conventional method;

(14) FIG. 4C is a perspective view enlargedly illustrating a square surrounded part in FIG. 4B;

(15) FIG. 5A is a characteristic diagram illustrating a numerical analysis result of a relationship between a pressing angle of the press-forming material by the pad and a maximum value of a sheet thickness decrease at an end part of a ridge line part flange portion of an outward flange in the analysis example 1;

(16) FIG. 5B is a view illustrating evaluation positions (a crack threat part) of the sheet thickness decrease being evaluation objects in the analysis example 1;

(17) FIG. 6A is a perspective view of a press-formed body of an analysis example 2;

(18) FIG. 6B is a VI arrow view in FIG. 6A;

(19) FIG. 6C is a transverse sectional view of the press-formed body of the analysis example 2;

(20) FIG. 7A is a perspective view illustrating a punch, a die, a ridge line pad, and a press-forming material at a forming time according to the invented method;

(21) FIG. 7B is a perspective view illustrating the punch, the ridge line pad, and the press-forming material at the forming time according to the invented method;

(22) FIG. 7C is a perspective view enlargedly illustrating a square surrounded part in FIG. 7B;

(23) FIG. 7D is a VII-VII sectional view in FIG. 7C;

(24) FIG. 8A is a perspective view illustrating a punch and a die at a forming time according to the conventional method;

(25) FIG. 8B is a perspective view illustrating the punch, a pad, and a press-forming material at the forming time according to the conventional method;

(26) FIG. 8C is a perspective view enlargedly illustrating a square surrounded part in FIG. 8B;

(27) FIG. 9A is a characteristic diagram illustrating a numerical analysis result of a relationship between a pressing angle of the press-forming material by the pad and a minimum value of sheet thickness decrease in a vicinity of a root part of a ridge line part flange portion of an outward flange in the analysis example 2;

(28) FIG. 9B is a view illustrating evaluation positions (a wrinkling threat part) of the sheet thickness decrease being evaluation objects in the analysis example 2;

(29) FIG. 10A is a perspective view of a press-formed body of an analysis example 3;

(30) FIG. 10B is an X arrow view in FIG. 10A;

(31) FIG. 10C is a transverse sectional view of the press-formed body of the analysis example 3;

(32) FIG. 11A is a view to explain a maximum value of a sheet thickness decrease at evaluation positions (a crack threat part) of a sheet thickness decrease according to the invented method;

(33) FIG. 11B is a view to explain a maximum value of a sheet thickness decrease at evaluation positions (a crack threat part) of a sheet thickness decrease according to the conventional method;

(34) FIG. 12A is a perspective view of a floor cross member;

(35) FIG. 12B is an XII arrow view in FIG. 12A;

(36) FIG. 13A is an explanatory view schematically illustrating drawing; and

(37) FIG. 13B is an explanatory view schematically illustrating bend-forming.

DESCRIPTION OF EMBODIMENTS

(38) Hereinafter, embodiments of the present invention are described with reference to the attached drawings.

(39) FIG. 1A to FIG. 1D are explanatory views conceptually illustrating characteristics of a manufacturing method and a manufacturing apparatus of a press-formed body according to an embodiment where the present invention is applied. FIG. 1A is a view schematically illustrating a schematic configuration of the manufacturing apparatus of the press-formed body according to the embodiment and a first step. FIG. 1B is a sectional view illustrating a transverse sectional shape of the press-formed body manufactured in the present embodiment. FIG. 1C is a perspective view illustrating a configuration at around a ridge line pad in the first step. FIG. 1D is a view when the press-formed body manufactured in the present embodiment is seen from a lateral side in a longitudinal direction. Note that in each of FIG. 1B and FIG. 1D, a sheet thickness is represented by a heavy line.

(40) 1. Press-Formed Body

(41) As illustrated in FIG. 1B, the press-formed body manufactured in the present embodiment is a press-formed body 15 which is long and made of a high-tensile strength steel sheet of 390 MPa or more, having approximately a groove-shaped cross section including a groove bottom part 15a, ridge line parts 15b, 15b continuous to the groove bottom part 15a, side wall parts 15c, 15c continuous to the ridge line parts 15b, 15b, curved parts 15d, 15d continuous to the side wall parts 15c, 15c, and flanges 15e, 15e continuous to the curved parts 15d, 15d. An outward flange 16 is formed at a whole periphery of an end part in a longitudinal direction, namely, along the groove bottom part 15a, the ridge line parts 15b, 15b, the side wall parts 15c, 15c, the curved parts 15d, 15d, and the flanges 15e, 15e.

(42) The press-formed body 15 manufactured in the present embodiment is a press-formed body which does not have cutouts at a ridge line part flange portion 16a of the outward flange 16 different from the one illustrated in FIG. 12A, FIG. 12B.

(43) Besides, the press-formed body 15 manufactured in the present embodiment has a cross-sectional height of 20 mm or more. Further, from a point of view of securing a continuous region for welding such as spot welding, laser welding, or plasma welding, a flange width of the outward flange 16 is approximately 5 mm or more at a flange flat part at a part of at least the groove bottom part 15a, the ridge line part 15b, and the side wall part 15c. Besides, at the ridge line part 15b, the flange width is approximately 2 mm or more from a point of view of securing performances such as impact characteristics, torsional rigidity even if joining is not performed.

(44) Note that in the present embodiment, a hat-shaped press-formed body having approximately a groove-shaped cross section illustrated in FIG. 1B is described, but the present invention is applicable as long as it is a press-formed body having approximately a groove-shaped cross section including at least the groove bottom part 15a, the ridge line parts 15b, 15b, and the side wall parts 15c, 15c.

(45) Besides, an example in which the outward flange 16 is formed at the whole periphery at the end part in the longitudinal direction is described, but the present invention is applicable as long as it is a press-formed body in which the outward flange 16 including the ridge line part flange portion 16a is formed, in other words, the outward flange 16 is formed at a range across the ridge line part 15b, at least a portion of each of the groove bottom part 15a and the side wall part 15c at both sides thereof.

(46) 2. Manufacturing Apparatus of Press-Formed Body (Press-Forming Apparatus)

(47) As illustrated in FIG. 1A, a press-forming apparatus 10 includes a punch 11, a die 12, and a pad 14 which presses and binds a press-forming material 13 to the punch 11. In the present embodiment, the pad 14 is to bind not only a part to be formed into the groove bottom part 15a but also parts to be formed into the ridge line parts 15b, 15b at the press-forming material 13, and it is called as a ridge line pad.

(48) The ridge line pad 14 has a shape binding the part to be formed into the groove bottom part 15a and the parts to be formed into the ridge line parts 15b, 15b in a vicinity of the outward flange 16 at the press-forming material 13.

(49) A publicly-known pad binds the part to be formed into the groove bottom part 15a, but does not bind the parts to be formed into the ridge line parts 15b, 15b. On the other hand, the ridge line pad 14 binds not only the part to be formed into the groove bottom part 15a but also the parts to be formed into the ridge line parts 15b, 15b in the vicinity of the outward flange 16. According to the ridge line pad 14, a shape of the ridge line pad 14 is approximately formed by stretching out only a material at that part. Moving of the material at around a part where the ridge line pad 14 is in contact is thereby suppressed, expansion and shrinkage deformations of a peripheral material to be a factor of cracks and wrinkling are suppressed, and therefore, it is possible to reduce occurrences of stretch flange cracks at the ridge line part flange portion 16a of the flange 16 and wrinkling at a proximity part of the flange 16 (refer to a proximity part 1b in FIG. 12A) at the ridge line part 15b.

(50) The ridge line pad 14 is aimed for an effect suppressing the moving of the peripheral material by stretching out and forming the shape of the ridge line part 15b in the vicinity of the outward flange 16. Accordingly, it is desirable to bind a part having a length of one-third or more of a cross-sectional peripheral length of the ridge line parts 15b, 15b starting from a connecting part 15a-b from among the part to be formed into the ridge line part 15b, more preferably to bind a whole of the cross-sectional peripheral length of the part to be formed into the ridge line part 15b. In this case, if it has a shape of a degree in which only a single part of the side wall part 15c, for example, a part of the side wall part 15c having a length of 20 mm or less in addition to the ridge line part 15b are pressed, a problem in which a pad load is insufficient and cannot afford to press is difficult to occur, and therefore, it is acceptable as a pad in the present invention.

(51) Besides, it is preferable that a range bound by the ridge line pad 14 in a longitudinal direction of the part to be formed into the ridge line part 15b (“1” illustrated in FIG. 19) is set to be in the vicinity of the outward flange 16, namely, at least a portion of a predetermined range from a root part of the outward flange 16 in a direction where the ridge line part 15b extends. The predetermined range is set to be the same degree as a flange width of the ridge line part flange portion 16a of the outward flange 16. For example, when the flange width of the ridge line part flange portion 16a of the outward flange 16 is 20 mm, the predetermined range is set to be approximately 20 mm, and when the flange width of the ridge line part flange portion 16a is 30 mm, the predetermined range is set to be approximately 30 mm. In this case, it is not necessary to bind the part to be formed into the ridge line part 15b at a whole area of this predetermined range, and it is no problem if a part of the predetermined range is bound.

(52) Other elements such as a size and a material of the ridge line pad 14 other than the above-stated matters may be the same as a publicly-known pad.

(53) 3. Manufacturing Method of Press-Formed Body

(54) In the press-forming apparatus 10, the press-forming is performed while binding the part to be formed into the groove bottom part 15a and the parts to be formed into the ridge line parts 15b, 15b in the vicinity of the outward flange 16 at the press-forming material 13 by using the ridge line pad 14.

(55) To form parts which cannot be formed by this press-forming (a first press-forming step), a second press-forming step being a post-step is performed. The part which cannot be formed by the first press-forming step is concretely a part positioning directly below the ridge line part 15b which is bound by the ridge line pad 14 as represented by oblique lines in FIG. 1D. The second press-forming step being the post-step is performed to form the part represented by the oblique lines in FIG. 1D, namely, parts to be formed into a part of the side wall parts 15c, 15c, parts to be formed into a part of the curved parts 15d, 15d, and parts to be formed into a part of the flanges 15e, 15e.

(56) In the second press-forming step, the press-forming may be one using only a die and a punch without using the pad (stamp press-forming), or may be the normal press-bending using the pad.

(57) Note that there is a case when a remaining part of the part to be formed into the ridge line part 15b which cannot be formed by the first press-forming step exists depending on the region bound by the ridge line pad 14. In this case, the remaining part of the part which is formed into the ridge line part 15b is also press-formed by the second press-forming step. For example, when one-third of the part to be formed into the ridge line part 15b is formed by the first press-forming step, the remaining two-thirds of the part to be formed into the ridge line part 15b is formed by the second press-forming step.

(58) As stated above, the press-forming material 13 is press-formed (the first press-forming step, the second press-forming step) by the press-forming apparatus including the punch 11, the die 12, and the ridge line pad 14 pressing and binding the press-forming material 13 to the punch 11, and thereby, it is possible to manufacture the press-formed body 15 which is long and made of the high-tensile strength steel sheet of 390 MPa or more having approximately a groove-shaped cross section including the groove bottom part 15a, the ridge line parts 15b, 15b continuous to the groove bottom part 15a, the side wall parts 15c, 15c continuous to the ridge line parts 15b, 15b, the curved parts 15d, 15d continuous to the side wall parts 15c, 15c, and the flanges 15e, 15e continuous to the curved parts 15d, 15d in which the outward flange 16 is formed at the whole periphery of the end part in the longitudinal direction illustrated in FIG. 1B.

(59) Note that a concave and convex shape part of 0.1 mm or more is formed at a boundary part between the ridge line part 15b and the side wall part 15c corresponding to the end part of the ridge line pad 14 at the press-forming time because two times press-formings are performed.

(60) Hereinbelow, a reason why the press-forming is performed by binding not only the part to be formed into the groove bottom part 15a but also the parts to be formed into the ridge line parts 15b, 15b in the vicinity of the outward flange 16 by using the ridge line pad 14 is described with reference to a numerical analysis result by a finite element method.

Analysis Example 1

(61) FIG. 2A to FIG. 2C are explanatory views illustrating a shape of a press-formed body 20 of an analysis example 1. FIG. 2A is a perspective view of the press-formed body 20, FIG. 2B is a II arrow view in FIG. 2A, and FIG. 2C is a transverse sectional view of the press-formed body 20 (an outward flange 20f is not illustrated).

(62) The press-formed body 20 of the analysis example 1 is made of a high-strength steel sheet (590 MPa class DP (Dual phase) steel), and a sheet thickness thereof is 1.4 mm.

(63) The press-formed body 20 includes a groove bottom part 20a, ridge line parts 20b, 20b continuous to the groove bottom part 20a, side wall parts 20c, 20c continuous to the ridge line parts 20b, 20b, curved parts 20d, 20d continuous to the side wall parts 20c, 20c, and flanges 20e, 20e continuous to the curved parts 20d, 20d. A curvature radius at a sheet inner side of the ridge line parts 20b, 20b is 12 mm.

(64) The outward flanges 20f are formed at a whole periphery of both end parts in a longitudinal direction of the press-formed body 20, and a ridge line part flange portion 20g becomes a curved portion. A flange width of the outward flange 20f is 25 mm at a part formed along the groove bottom part 20a, and 30 mm at a part formed along the side wall parts 20c, 20c.

(65) A cross sectional wall angle of the press-formed body 20 is 70 degrees, and a cross sectional height is 100 mm. In the analysis example 1, the press-formed body 20 is manufactured by the press-forming by bend-forming using a developed blank.

(66) FIG. 3A is a perspective view illustrating a punch (lower forming-tool) 21, a die (upper forming-tool) 22, and a press-forming material 24 at a forming time according to the invented method. FIG. 3B is a perspective view illustrating the punch (lower forming-tool) 21, a ridge line pad 25, and the press-forming material 24 at the forming time according to the invented method. FIG. 3C is a perspective view enlargedly illustrating a square surrounded part in FIG. 3B. FIG. 3D is a sectional view in FIG. 3C.

(67) On the other hand, FIG. 4A is a perspective view illustrating a punch (lower forming-tool) 21, a die (upper forming-tool) 22, a pad 23, and a press-forming material 24 at a forming time according to a conventional method. FIG. 4B is a perspective view illustrating the punch (lower forming-tool) 21, the pad 23, and the press-forming material 24 at the forming time according to the conventional method. FIG. 4C is a perspective view enlargedly illustrating a square surrounded part in FIG. 4B.

(68) FIG. 5A is a characteristic diagram illustrating a numerical analysis result of a relationship between a pressing angle of the press-forming material 24 by the pads 23, 25 and a maximum value of a sheet thickness decrease at an end part of the ridge line part flange portion 20g of the outward flange 20f formed at the press-formed body 20. In FIG. 5B, evaluation positions of a sheet thickness decrease (ranges each surrounded by a dotted line, a crack threat part) being evaluation objects in the analysis example 1 are illustrated. The pressing angle means a center angle of a range of the ridge line part 20b bound by the pads 23, 25 while setting a position of a connecting part with the groove bottom part 20a as “0” (zero) degree from among a part to be formed into the ridge line part 20b at the press-forming material 24. Besides, as a maximum value of the sheet thickness decrease becomes large, stretch flange cracks occur.

(69) In the conventional method, namely, in the bend-forming using the normal pad 23, the pad 23 binds a whole or only a part of the part to be formed into the groove bottom part 20a at the press-forming material 24 as illustrated in FIG. 4A to FIG. 4C. Namely, it is a shape in which a part to be formed into the ridge line part 20b is not bound, and the pressing angle is “0” (zero) degree.

(70) In this case, as illustrated in FIG. 5A, a maximum value if the sheet thickness decrease at the end part of the ridge line part flange portion 20g is a value of approximately 36% which far exceeds 30%, and it can be seen that a possibility in which the stretch flange cracks occur is high.

(71) On the other hand, in the invented method, namely, in the bend-forming using the ridge line pad 25, as illustrated in FIG. 3A to FIG. 3D, the ridge line pad 25 binds the part to be formed into the ridge line part 20b in addition to the part to be formed into the groove bottom part 20a in a vicinity of the outward flange 20f (a range within 10 mm from a root part of the outward flange 20f in a direction where the ridge line part 20b extends).

(72) Then, analyses are performed under conditions in which a region where the ridge line pad 25 binds the press-forming material 24 is changed into one-third, two-thirds, and a whole of a cross-sectional peripheral length of the ridge line part 20b starting from a connecting part from among the part to be formed into the ridge line part 20b.

(73) In this case, as illustrated in FIG. 5A, it can be seen that a maximum value of the sheet thickness decrease at the ridge line part flange portion 20g is suppressed as the region where the ridge line pad 25 binds the press-forming material 24 (pressing angle) becomes large. In particular, a suppression effect is remarkable when the binding region is one-third or more, and it is possible to avoid the stretch flange cracks.

Analysis Example 2

(74) FIG. 6A to FIG. 6C are explanatory views illustrating a shape of a press-formed body 30 of an analysis example 2. FIG. 6A is a perspective view of the press-formed body 30, FIG. 6B is a VI arrow view in FIG. 6A, and FIG. 6C is a transverse sectional view of the press-formed body 30 (an outward flange 30f is not illustrated).

(75) The press-formed body 30 of the analysis example 2 is made of the high-strength steel sheet (590 MPa class DP steel), and a sheet thickness thereof is 1.4 mm.

(76) The press-formed body 30 includes a groove bottom part 30a, ridge line parts 30b, 30b continuous to the groove bottom part 30a, side wall parts 30c, 30c continuous to the ridge line parts 30b, 30b, curved parts 30d, 30d continuous to the side wall parts 30c, 30c, and flanges 30e, 30e continuous to the curved parts 30d, 30d. A curvature radius at a sheet inner side of the ridge line parts 30b, 30b is 12 mm.

(77) The outward flange 30f is formed at a whole periphery of both end parts in a longitudinal direction of the press-formed body 30, and a ridge line part flange portion 30g becomes a curved portion. A flange width of the outward flange 30f is 20 mm at a part formed along the groove bottom part 30a, and 25 mm at a part formed along the side wall parts 30c, 30c.

(78) A cross sectional wall angle of the press-formed body 30 is 82 degrees, and a cross sectional height is 60 mm. In the analysis example 2, the press-formed body 30 is manufactured by the press-forming by bend-forming using a developed blank.

(79) FIG. 7A is a perspective view illustrating a punch (lower forming-tool) 31, a die (upper forming-tool) 32, a ridge line pad 35, and a press-forming material 34 at a forming time according to the invented method. FIG. 7B is a perspective view illustrating the punch (lower forming-tool) 31, the ridge line pad 35, and the press-forming material 34 at the formed time according to the invented method. FIG. 7C is a perspective view enlargedly illustrating a square surrounded part in FIG. 7B. FIG. 7D is a VII-VII sectional view in FIG. 7C.

(80) On the other hand, FIG. 8A is a perspective view illustrating a punch (lower forming-tool) 31, a die (upper forming-tool) 32 at a forming time according to the conventional method. FIG. 8B is a perspective view illustrating the punch (lower forming-tool) 31, a pad 33, and a press-forming material 34 at the forming time according to the conventional method. FIG. 8C is a perspective view enlargedly illustrating a square surrounded part in FIG. 8B.

(81) FIG. 9A is a characteristic diagram illustrating a numerical analysis result of a relationship between a pressing angle of the press-forming material 34 by the pads 33, 35 and a minimum value of a sheet thickness decrease in a vicinity of a root part of the ridge line part flange portion 30g of the outward flange 30f formed at the press-formed body 30. In FIG. 9B, evaluation positions of a sheet thickness decrease (ranges each surrounded by a dotted line, a wrinkling threat part) being evaluation objects in the analysis example 2 are illustrated. The pressing angle means a center angle of a range of the ridge line part 30b bound by the pads 33, 35 while setting a connecting part with the groove bottom part 30a as “0” (zero) degree from among a part to be formed into the ridge line part 30b at the press-forming material 34. Besides, as a minimum value of the sheet thickness decrease becomes small, a possibility in which wrinkling occurs becomes high.

(82) In the conventional method, namely, in the bend-forming using the normal pad 33, the pad 33 binds only a part to be formed into the groove bottom part 30a at the press-forming material 34 as illustrated in FIG. 8A to FIG. 8C. Namely, it is a shape in which a part to be formed into the ridge line part 30b is not bound, and the pressing angle is “0” (zero) degree.

(83) In this case, as illustrated in FIG. 9A, a minimum value of the sheet thickness decrease at the root part of the ridge line part flange portion 30g is a value of approximately −65%, and it is obvious that the winkling occurs at a proximity part 30b-1 of the flange 30f at the ridge line part 30b.

(84) On the other hand, in the invented method, namely, in the bend-forming using the ridge line pad 35, as illustrated in FIG. 7A to FIG. 7D, the ridge line pad 35 binds the part to be formed into the ridge line part 30b in addition to the part to be formed into the groove bottom part 30a in a vicinity of the outward flange 30f (a range within 10 mm from a root part of the outward flange 30f in a direction where the ridge line part 30b extends).

(85) Then, analyses are performed under conditions in which a region where the ridge line pad 35 binds the press-forming material 34 is changed into one-third, two-thirds, a whole of a cross-sectional peripheral length of the ridge line part 30b starting from a connecting part from among the part to be formed into the ridge line part 30b.

(86) In this case, as illustrated in FIG. 9A, it can be seen that thickening at the proximity part 30b-1 of the flange 30f at the ridge line part 30b is suppressed as the region where the ridge line pad 35 binds the press-forming material 34 (pressing angle) becomes large. In the analysis result, a thickening amount is large because it is originally a shape difficult to suppress the wrinkling. Therefore it is desired to suppress a thickening rate to be less than 20% by setting the region binding the ridge line part 30b to be two-thirds or more, but even when the region binding the ridge line part 30b is approximately one-third or more, the thickening of a part where the wrinkling occurrence is concerned is suppressed to be a half or less compared to the normal pad, and it can be seen that a thickening suppression effect by the ridge line pad 35 is very large.

Analysis Example 3

(87) In each of the analysis examples 1, 2, a cold-rolled steel sheet is described, but the present invention is able to be applied for a hot-rolled steel sheet.

(88) FIG. 10A to FIG. 10C are explanatory views illustrating a shape of a press-formed body 40 of an analysis example 3. FIG. 10A is a perspective view of the press-formed body 40, FIG. 10B is a X arrow view in FIG. 10A, and FIG. 10C is a transverse sectional view of the press-formed body 40 (an outward flange 40f is not illustrated).

(89) The press-formed body 40 of the analysis example 3 is made of the high-strength steel sheet (590 MPa class DP steel), and a sheet thickness thereof is 2.9 mm.

(90) The press-formed body 40 includes a groove bottom part 40a, ridge line parts 40b, 40b continuous to the groove bottom part 40a, and side wall parts 40c, 40c continuous to the ridge line parts 40b, 40b.

(91) The outward flange 40f is formed at a whole periphery of both end parts in a longitudinal direction of the press-formed body 40, and a ridge line part flange portion 40g becomes a curved portion.

(92) A cross sectional wall angle of the press-formed body 40 is 82 degrees, and a cross sectional height is 50 mm. In the analysis example 3, the press-formed body 40 is manufactured by the press-forming by bend-forming using a developed blank.

(93) Also in the analysis example 3, the conventional method using the pad in which a part to be formed into the groove bottom part 40a is bound, but parts to be formed into the ridge line parts 40b, 40b are not bound and the invented method using a ridge line pad in which not only the part to be formed into the groove bottom part 40a but also the parts to be formed into the ridge line parts 40b, 40b in the vicinity of the outward flange 40f are bound are compared.

(94) As illustrated in FIG. 11B, in the conventional method, a maximum value of the sheet thickness decrease at the evaluation positions of the sheet thickness decrease (ranges each surrounded by a dotted line, a crack threat part) is a value of approximately 20%. On the other hand, in the invented method, a maximum value of the sheet thickness decrease at the evaluation positions of the sheet thickness decrease (ranges each surrounded by a dotted line, a crack threat part) is suppressed to a value of approximately 14%.

(95) As stated above, the present invention is described with various embodiments, but the present invention is not limited only to these embodiments, and modifications and so on within a range of the invention are possible.

(96) For example, in each of the analysis examples, a case when the press-forming is the bend-forming is exemplified, but the present invention is not limited thereto, and the press-forming may be drawing.

(97) Besides, a mode in which the lower forming-tool is made up by the punch and the upper forming-tool is made up by the die and the pad is exemplified, but the present invention is not limited to the mode. It goes without saying that a structure in which the upper and lower metal forming-tools are reversed, namely, the upper forming-tool is made up by the punch and the lower forming-tool is made up by the die and the pad is acceptable.

INDUSTRIAL APPLICABILITY

(98) The present invention can be used for manufacturing a press-formed body made of a high-tensile strength steel sheet of 390 MPa or more having approximately a groove-shaped cross section including a groove bottom part, ridge line parts continuous to the groove bottom part, and side wall parts continuous to the ridge line parts, and in which an outward flange is formed at a range across the ridge part, at least a portion of each of the groove bottom part and the side wall part at both sides thereof, from among an end part in a longitudinal direction, without being limited to a floor cross member.