Press forming method and method of manufacturing press-formed part

Abstract

There is provided a method of manufacturing a curved channel part having a curved portion in a vertical wall portion by press forming, the method restricting stretch flange deformation, which occurs in the vertical wall portion and a flange portion. The method includes a shear deformation step as a step of forming the vertical wall portion. In the shear deformation step, a boundary-side portion of a base section of a blank with respect to a deformation section, and an outer portion of the deformation section are individually restrained, a portion to be a vertical wall portion of the deformation section is shear-deformed in a sheet face, and a material is caused to flow from a portion separated from a curved portion toward the curved portion in an outer edge portion of the portion to be the vertical wall portion.

Claims

1. A press forming method for press-forming a flat-sheet-shaped processing material, the processing material including (i) a base section, (ii) a deformation section continuous with the base section, the deformation section including a portion configured to form a vertical wall portion and (iii) a boundary portion between the base section and the portion configured to form the vertical wall portion, the vertical wall portion having a curved portion that is curved in a depressed shape toward the base section, the method comprising: individually restraining a boundary-side portion of the base section with respect to the deformation section and an outer portion of the deformation section, the outer portion forming a flange portion; and shear-deforming the portion configured to form the vertical wall portion to form the vertical wall portion by bending the processing material in at least the boundary portion, wherein the shear-deforming the portion configured to form the vertical wall portion causes a material to flow from a portion separated from the curved portion toward the curved portion of the portion configured to form the vertical wall portion.

2. The press forming method according to claim 1, wherein individually restraining the boundary-side portion of the base section uses a first restraining section of a die that restrains the boundary-side portion, and shear-deforming the portion configured to form the vertical wall portion includes, when viewed in a thickness direction of the processing material, from a state in which a second restraining section of the die that restrains the outer portion of the deformation section is separated from the first restraining section, relatively moving the second restraining section in a direction in which a separation distance between the first restraining section and the second restraining section decreases as the boundary portion is bent.

3. The press forming method according to claim 2, wherein shear-deforming the portion configured to form the vertical wall portion further includes moving the restrained outer portion so that the portion configured to form the vertical wall portion is rotated around a bending point of the curved portion on a boundary line of the boundary portion between the base section and the deformation section.

4. The press forming method according to claim 2, wherein shear-deforming the portion configured to form the vertical wall portion further includes linearly moving the restrained outer portion in a direction in which an angle with respect to a sheet face of the processing material is in the range of 30 to 60.

5. The press forming method according to claim 1, further comprising deep drawing the processing material after shear-deforming the portion configured to form the vertical wall portion.

6. The press forming method according to claim 1, further comprising deep drawing the processing material before shear-deforming the portion configured to form the vertical wall portion.

7. The press forming method according to claim 1, further comprising stamping the processing material after shear-deforming the portion configured to form the vertical wall portion.

8. The press forming method according to claim 1, wherein shear-deforming the portion configured to form the vertical wall portion includes generating a wrinkle in the vertical wall portion, and the method further comprises stretching the wrinkle by pinching the vertical wall portion with a die after shear-deforming the portion configured to form the vertical wall portion.

9. The press forming method according to claim 8, wherein the die includes a press surface configured to contact a surface of the vertical wall portion, the press surface including a depression and a protrusion configured to increase a line length of the vertical wall portion.

10. The press forming method according to claim 1, wherein the processing material is a blank, and shear-deforming the portion configured to form the vertical wall portion includes heating the blank at a temperature in a range of 300 C. to 1000 C.

11. A method of manufacturing a press-formed part formed by press-forming a flat-sheet-shaped processing material into the press-formed part, the processing material including (i) a base section, (ii) a deformation section continuous with the base section, the deformation section including a portion configured to form a vertical wall portion in the press-formed part and (iii) a boundary portion between the base section and the portion configured to form the vertical wall portion, the vertical wall portion having a curved portion that is curved in a depressed shape toward the base section, the method comprising: individually restraining a boundary-side portion of the base section with respect to the deformation section and an outer portion of the deformation section; and shear-deforming the portion configured to form the vertical wall portion to form the vertical wall portion by bending the processing material in at least the boundary portion, wherein the outer portion forms a flange portion in the press-formed part, and the shear-deforming the portion configured to form the vertical wall portion causes a material to flow from a portion separated from the curved portion toward the curved portion of the portion configured to form the vertical wall portion.

12. The press forming method according to claim 11, wherein individually restraining the boundary-side portion of the base section uses a first restraining section of a die that restrains the boundary-side portion, and shear-deforming the portion configured to form the vertical wall portion includes, when viewed in a thickness direction of the processing material, from a state in which a second restraining section of the die that restrains the outer portion of the deformation section is separated from the first restraining section, relatively moving the second restraining section in a direction in which a separation distance between the first restraining section and the second restraining section decreases as the boundary portion is bent.

13. The press forming method according to claim 12, wherein shear-deforming the portion configured to form the vertical wall portion further includes moving the restrained outer portion so that the portion configured to form the vertical wall portion is rotated around a bending point of the curved portion on a boundary line of the boundary portion between the base section and the deformation section.

14. The press forming method according to claim 12, wherein shear-deforming the portion configured to form the vertical wall portion further includes linearly moving the restrained outer portion in a direction in which an angle with respect to a sheet face of the processing material is in the range of 30 to 60.

15. The press forming method according to claim 11, further comprising deep drawing the processing material after shear-deforming the portion configured to form the vertical wall portion.

16. The press forming method according to claim 11, further comprising deep drawing the processing material before shear-deforming the portion configured to form the vertical wall portion.

17. The press forming method according to claim 11, further comprising removing the flange portion from the press-formed part; and stamping the processing material after shear-deforming the portion configured to form the vertical wall portion.

18. The press forming method according to claim 11, wherein shear-deforming the portion configured to form the vertical wall portion includes generating a wrinkle in the vertical wall portion, and the method further comprises stretching the wrinkle by pinching the vertical wall portion with a die after shear-deforming the portion configured to form the vertical wall portion.

19. The press forming method according to claim 18, wherein the die includes a press surface configured to contact a surface of the vertical wall portion, the press surface including a depression and a protrusion configured to increase a line length of the vertical wall portion.

20. The press forming method according to claim 11, wherein the processing material is a blank, and shear-deforming the portion configured to form the vertical wall portion includes heating the blank at a temperature in a range of 300 C. to 1000 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A and FIG. 1B provide illustrations explaining a press forming method of a curved channel part according to an embodiment.

(2) FIG. 2 is a schematic illustration explaining shear deformation.

(3) FIG. 3 is a perspective view showing a curved channel part manufactured in first to fifth embodiments.

(4) FIG. 4 is a cross-sectional view explaining a die and a blank used in an embodiment.

(5) FIG. 5 is a cross-sectional view (corresponding to an A-A cross-sectional view of FIG. 1A) explaining a method of the first embodiment.

(6) FIG. 6 is a cross-sectional view (corresponding to the A-A cross-sectional view of FIG. 1A) explaining a method of the second embodiment.

(7) FIG. 7 is a cross-sectional view (corresponding to the A-A cross-sectional view of FIG. 1A) explaining a method of the third embodiment.

(8) FIG. 8A and FIG. 8B provide cross-sectional views (corresponding to the A-A cross-sectional view of FIG. 1A) explaining a method of the fourth embodiment.

(9) FIG. 9A and FIG. 9B provide cross-sectional views (corresponding to the A-A cross-sectional view of FIG. 1A) explaining a method of the fifth embodiment.

(10) FIG. 10 is a perspective view showing a curved channel part manufactured in a sixth embodiment.

(11) FIG. 11A and FIG. 11B provide cross-sectional views (corresponding to the A-A cross-sectional view of FIG. 1A) explaining a method of the sixth embodiment.

(12) FIG. 12A and FIG. 12B provide illustrations showing another example of a curved channel part being a subject of disclosed embodiments, (FIG. 12A) being a perspective view, (FIG. 12B) being a side view.

(13) FIG. 13A and FIG. 13B provide a plan view (FIG. 13A) explaining a method of the disclosed embodiments executed in an example, and an A-A cross-sectional view (FIG. 13B) thereof.

(14) FIG. 14A and FIG. 14B provide a plan view (FIG. 14A) explaining a method of the disclosed embodiments executed in an example, and an A-A cross-sectional view (FIG. 14B) thereof.

(15) FIG. 15A and FIG. 15B provide a plan view (FIG. 15A) explaining a deep drawing step executed in an example, and an A-A cross-sectional view (FIG. 15B) thereof.

(16) FIG. 16A and FIG. 16B provide a plan view (FIG. 16A) explaining a deep drawing step executed in an example, and an A-A cross-sectional view (FIG. 16B) thereof.

DETAILED DESCRIPTION

(17) Disclosed embodiments are described below; however, this disclosure is not limited to these embodiments. In the embodiments described below, a curved channel part is described as an example of a press-formed part being a subject to be manufactured. However, disclosed embodiments are not limited to the curved channel part. Any part may be a subject of embodiments as long as the part is a press-formed part having a vertical wall portion having a curved portion that is curved in a depressed shape toward a top portion during forming. FIG. 3 provides an example of a shape, in which a boundary portion between a top portion and a vertical wall portion is bent at a curved bending line to form a curved portion so that a vertical wall portion 22 is depressed toward a top portion 21, that is the vertical wall portion 22 is deformed by off-plane deformation (curved) in a direction in which the vertical wall portion 22 is drawn toward the top portion 21.

(18) [First Embodiment]

(19) In this embodiment, the curved channel part shown in FIG. 3 is manufactured. Such a curved channel part is used as, for example, a center pillar part of a vehicle.

(20) As shown in FIG. 3, a curved channel part 2 includes a top portion 21 corresponding to a base section, a vertical wall portion 22 with a curved portion 22a, a vertical wall portion 23 without a curved portion, a flange portion 24 continuous to the vertical wall portion 22 with the curved portion 22a, and a flange portion 25 continuous to the vertical wall portion 23 without a curved portion. The flange portion 24 has a curved portion 24a in a portion continuous to the curved portion 22a of the vertical wall portion 22.

(21) The vertical wall portion 22 with the curved portion 22a and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 are formed by the following method. In this case, a portion other than the curved portion 22a may be formed in a typical deep drawing step. It is to be noted that the vertical wall portion 23 without a curved portion and the flange portion 25 continuous to the vertical wall portion 23 are formed in the typical deep drawing step.

(22) As shown in FIG. 4, a die used for press forming includes a punch 31 arranged below a blank 1 configuring a flat-sheet-shaped processing material, a first pad 32 arranged above the punch 31 with the blank 1 interposed therebetween, a blank holder 33 arranged at a lateral side of the punch 31 with a distance S0 interposed therebetween, and a second pad 34 arranged above the blank holder 33 with the blank 1 interposed therebetween. The installation distance S0 between the punch 31 and the second pad 34 is the same as the height of the vertical wall portion 22 of the curved channel part 2 to be manufactured.

(23) The blank 1 is a uniform single sheet. As shown in FIG. 4, for convenience of description, if it is considered that the blank 1 is separated into a base section 11 which is not deformed and a deformation section 12 which is deformed by press forming, the deformation section 12 includes a portion 12a to be the vertical wall portion 22. Also, in this embodiment, since the curved channel part 2 having the flange portion 24 is manufactured, the deformation section 12 includes a portion to be the flange portion 24.

(24) First, as shown in FIG. 4, a boundary-side portion (a portion of the base section 11 at the boundary side with respect to the deformation section 12) 11a of the base section 11 of the blank 1 is pinched and restrained by the punch 31 and the first pad 32, and an outer portion (the portion to be the flange portion) 12b of the deformation section 12 is pinched and restrained by the blank holder 33 and the second pad 34. A center portion 11b of the base section 11 may be restrained or may not be restrained. In this state, the punch 31 and the first pad 32, and the blank holder 33 and the second pad 34 are separated by the separation distance S0 when viewed in a thickness direction of the blank 1.

(25) In this case, the punch 31 and the first pad 32 configure a first restraining section, and the blank holder 33 and the second pad 34 configure a second restraining section.

(26) Then, as shown in FIG. 5, the blank holder 33 and the second pad 34 that restrain the outer portion 12b are moved along arrow A to approach the punch 31 and the first pad 32 while being turned relatively downward so that the portion 12a to be the vertical wall portion is rotated around a point (a bending point of the curved portion 22a of the vertical wall portion 22) B on the boundary line with respect to the boundary-side portion 11a as indicated by arrow A. This corresponds to a shear deformation step. With the shear deformation step, the portion 12a to be the vertical wall portion of the blank 1 is bent at the boundary between the boundary-side portion 11a and the outer portion 12b, and becomes the vertical wall portion 22 of the curved channel part 2.

(27) In the sharing deformation step, as shown in FIG. 1B, in the blank 1, shear deformation occurs in the sheet face of the portion 12a to be the vertical wall portion of the deformation section 12 by the movement of the outer portion 12b indicated by arrow Y, and the material flows in a direction indicated by arrow X in an outer edge portion of the portion 12a to be the vertical wall portion. Hence, in the curved channel part 2 manufactured in this embodiment, stretch flange deformation hardly occurs in the outer edge portion of the curved portion 22a of the vertical wall portion 22.

(28) Also, with the method of this embodiment, in the shear deformation step, the cross-sectional shape or the dimension of the portion 12a to be the vertical wall portion of the blank 1 is not changed in a portion other than the bent portion. Accordingly, a wrinkle is hardly generated in the vertical wall portion 22 of the curved channel part 2.

(29) Further, since the outer portion 12b is moved while being restrained and hence becomes the flange portion 24, stretch flange deformation hardly occurs in the outer edge portion of the curved portion 24a of the flange portion 24, and a wrinkle is hardly generated in the flange portion 24.

(30) [Second Embodiment]

(31) Also in this embodiment, similarly to the first embodiment, the curved channel part 2 having the shape shown in FIG. 3 is manufactured. The vertical wall portion 22 with the curved portion 22a and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 are formed by the following method shown in FIG. 6.

(32) The method in this embodiment differs from the method in the first embodiment in the moving method of the blank holder 33 and the second pad 34 that restrain the outer portion 12b, and is similar to the method in the first embodiment for the other points.

(33) First, as indicated by a solid line in FIG. 6, the boundary-side portion 11a of the base section 11 of the blank 1 is pinched and restrained by the punch 31 and the first pad 32, and the outer portion (the portion to be the flange portion) 12b of the deformation section 12 is pinched and restrained by the blank holder 33 and the second pad 34.

(34) Then, the blank holder 33 and the second pad 34 that restrain the outer portion 12b are linearly moved obliquely downward to approach the punch 31 and the first pad 32 when viewed in the thickness direction of the blank as indicated by arrow C in FIG. 6. To be specific, the blank holder 33 and the second pad 34 are linearly moved in an oblique direction in which an angle () with respect to the sheet face of the blank 1 is in a range from 30 to 60. Accordingly, the restrained outer portion 12b is linearly moved in the direction of =30 to 60. This corresponds to the shear deformation step.

(35) With this sharing deformation step, as indicated by a two-dot chain line in FIG. 6, not only the portion 12a to be the vertical wall portion of the blank 1 is bent at the boundary between the boundary-side portion 11a and the outer portion 12b, but also an intermediate portion is deformed in a contraction direction and then stretched, and the portion 12a finally becomes the vertical wall portion 22 of the curved channel part 2. Meanwhile, a portion, which is near the boundary with respect to the outer portion 12b, of the portion 12a to be the vertical wall portion is moved along arrow A in FIG. 6 while being bent.

(36) In the sharing deformation step, as shown in FIG. 1B, in the blank 1, shear deformation occurs in the sheet face of the portion 12a to be the vertical wall portion of the deformation section 12 by the movement of the outer portion 12b indicated by arrow Y, and the material flows in the direction indicated by arrow X in the outer edge portion of the portion 12a to be the vertical wall portion. In FIG. 6, it is to be noted that the shear deformation direction is a direction perpendicular to the paper face.

(37) Hence, in the curved channel part 2 manufactured in this embodiment, stretch flange deformation hardly occurs in the outer edge portion of the curved portion 22a of the vertical wall portion 22.

(38) With the method in this embodiment, in the shear deformation step, the cross-sectional shape of the portion 12a to be the vertical wall portion of the blank 1 is changed. If the outer portion 12b is moved by =45, even when press forming is executed at a room temperature, a wrinkle that may cause a problem in quality is hardly present in the vertical wall portion 22 of the curved channel part 2.

(39) If the moving angle () of the outer portion 12b with respect to the sheet face of the blank 1 is not 45, as compared with the case of =45, a possibility of that a wrinkle and a crack are generated in the vertical wall portion 22 increases. If is in the range from 30 to 60, a crack caused by a stretch generated in the vertical wall portion 22 can be avoided, and a wrinkle generated in the vertical wall portion 22 can be removed by post-processing etc.

(40) Further, since the outer portion 12b is moved while being restrained and hence becomes the flange portion 24, stretch flange deformation hardly occurs in the outer edge portion of the curved portion 24a of the flange portion 24, and a wrinkle is hardly generated in the flange portion 24.

(41) Also, if the portion 12a to be the vertical wall portion is further moved from the state in FIG. 6 and is pinched by a side surface of the punch 31 and a side surface of the second pad 34, a wrinkle generated in the portion 12a to be the vertical wall portion in the state in FIG. 6 can be stretched by pinching the wrinkle by the side surface of the punch 31 and the side surface of the second pad 34.

(42) [Third Embodiment]

(43) Also in this embodiment, similarly to the first embodiment, the curved channel part 2 having the shape shown in FIG. 3 is manufactured. The vertical wall portion 22 with the curved portion 22a and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 are formed by the following method shown in FIG. 7.

(44) As shown in FIG. 7, a die to be used for press forming is similar to that in FIG. 4; however, as shown in FIG. 7, a punch 35 having a protruding portion 35a at a side surface (a pressing surface that contacts the vertical wall portion) is arranged below the blank 1. A second pad 36 having a depressed portion 36a at a side surface is arranged above the blank holder 33. The other points are similar to the second embodiment.

(45) Similarly to the method of the second embodiment, the blank holder 33 and the second pad 36 that restrain the outer portion 12b are linearly moved obliquely downward in which the angle () with respect to the sheet face of the blank 1 is in the range from 30 to 60 as indicated by arrow C. By the linear movement, shear deformation occurs in the sheet face of the portion 12a to be the vertical wall portion of the blank 1, and as indicated by a two-dot chain line in FIG. 7, the cross-sectional shape of the portion 12a to be the vertical wall portion of the blank 1 is changed. Meanwhile, a portion, which is near the boundary with respect to the outer portion 12b, of the portion 12a to be the vertical wall portion is moved along arrow A in FIG. 7 while being bent.

(46) Then, by moving the blank holder 33 and the second pad 36, finally, a portion 12f of the portion 12a to be the vertical wall portion is pinched by the protruding portion 35a of the punch 35 and the depressed portion 36a of the second pad 36, and becomes a surface substantially perpendicular to a surface of the flange portion 24. This step is a wrinkle stretching step.

(47) At this time, if a wrinkle is generated in the vertical wall portion when the vertical wall portion is pinched by the die, the wrinkle is likely stretched. In particular, the line length of the portion 12a to be the vertical wall portion is elongated by the amount corresponding to the depressed portion 36a, that is, the line length can be increased. As the result, even if a wrinkle is generated in the vertical wall portion, the wrinkle can be stretched.

(48) The wrinkle stretching step may be executed at last after the shear deformation step described in the first embodiment etc. Since the wrinkle stretching step is executed continuously to the shear deformation step, the number of steps can be prevented from being increased for the wrinkle stretching step.

(49) [Fourth Embodiment]

(50) Also in this embodiment, similarly to the first embodiment, the curved channel part 2 having the shape shown in FIG. 3 is manufactured. The vertical wall portion 22 with the curved portion 22a and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 are formed by the following method shown in FIG. 8.

(51) In this embodiment, the vertical wall portion 22 is formed by two steps including the shear deformation step and then a deep drawing step. Hence, the outer portion 12b that is restrained in the shear deformation step includes a portion of the portion to be the vertical wall portion 22. Also, an inner portion (a portion near the base section 11) 12c being a portion to be the vertical wall portion 22 is shear-deformed in the sheet face.

(52) A die used in the shear deformation step is basically the same as that of the second embodiment. As shown in FIG. 8A, the installation distance S0 between the punch 31 and the second pad 34 is a value corresponding to a half of a height T2 (see FIG. 8B) of the vertical wall portion 22 of the curved channel part 2 to be manufactured or a value obtained by adding or subtracting a previously set margin amount to and from the half of the height T2.

(53) First, the boundary-side portion 11a of the base section 11 of the blank 1 is pinched and restrained by the punch 31 and the first pad 32, and the outer portion (the portion of the portion to be the vertical wall portion 22 and the portion to be the flange portion 24) 12b of the deformation section 12 is pinched and restrained by the blank holder 33 and the second pad 34.

(54) Then, similarly to the method of the second embodiment, the blank holder 33 and the second pad 34 that restrain the outer portion 12b are linearly moved in a direction in which the angle () with respect to the sheet face of the blank 1 is in the range from 30 to 60 as indicated by arrow C in FIG. 8A. Accordingly, the restrained outer portion 12b is linearly moved in the direction at =30 to 60, and shear deformation occurs in the sheet face of the inner portion 12c of the blank 1. This corresponds to the shear deformation step.

(55) This shear deformation step is executed until a timing before the angle between the boundary-side portion 11a of the base section 11 and the inner portion 12c of the deformation section 12 reaches an angle of a final product.

(56) Then, as shown in FIG. 8B, a die 37 is arranged instead of the second pad 34 that restrains the outer portion 12b, the die 37 and the blank holder 33 are moved along arrow B, and thus the deep drawing step is executed. Accordingly, the outer portion 12b is stretched while being drawn toward the punch 31, and the inner portion 12c is also drawn and stretched. Thus, the vertical wall portion 22 is formed.

(57) [Fifth Embodiment]

(58) Also in this embodiment, similarly to the first embodiment, the curved channel part 2 having the shape shown in FIG. 3 is manufactured. The vertical wall portion 22 with the curved portion 22a and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 are formed by the following method shown in FIG. 9.

(59) In this embodiment, the vertical wall portion 22 is formed by two steps including the deep drawing step and then the shear deformation step.

(60) First, as shown in FIG. 9A, the boundary-side portion 11a of the base section 11 of the blank 1 is pinched and restrained by the punch 31 and the first pad 32, and an outer portion 12d of the deformation section 12 (the portion of the portion 12a to be the vertical wall portion 22 and the portion to be the flange portion 24) is pinched by the die 37 and the blank holder 33. In this state, the inner portion 12c of the deformation section 12 of the blank 1 is present while not being restrained. Then, the deep drawing step is executed by moving the die 37 and the blank holder 33 along arrow B while a predetermined tensile force is applied to the outer portion 12d.

(61) Accordingly, the outer portion 12d is bent while being drawn and stretched toward the punch 31, and the blank 1 obtains a shape having a bent portion between the portion 12a to be the vertical wall portion and the outer portion 12b. The deep drawing step is executed until an angle between the portion 12a to be the vertical wall portion and a side surface of the die 37 becomes, for example, in a range from 45 to 60.

(62) Then, as shown in FIG. 9B, the outer portion 12b is restrained by the blank holder 33 and the second pad 34, and the blank holder 33 and the second pad 34 are linearly moved in a direction in which the angle () with respect to the sheet face of the blank 1 becomes in the range from 30 to 60. Accordingly, the restrained outer portion 12b is linearly moved in the direction of =30 to 60. By the linear movement, shear deformation occurs in the sheet face of the portion 12a to be the vertical wall portion of the blank 1, and the vertical wall portion 22 and the flange portion 24 are formed. This corresponds to the shear deformation step.

(63) [Sixth Embodiment]

(64) In this embodiment, a curved channel part shown in FIG. 10 is manufactured. Such a curved channel part is used as, for example, a lower arm part of a vehicle.

(65) As shown in FIG. 10, a curved channel part 4 includes a top portion 41, and a vertical wall portion 42 with a curved portion 42a. In this embodiment, the vertical wall portion 42 is formed by two steps including a shear deformation step and a stamping step. The basic configuration of a die used in the shear deformation step is the same as the second embodiment.

(66) As shown in FIG. 11A, first, the boundary-side portion 11a of the base section 11 of the blank 1 is pinched and restrained by the punch 31 and the first pad 32, and the outer portion (the portion to be transiently the flange portion) 12b of the deformation section 12 is pinched and restrained by the blank holder 33 and the second pad 34. In this state, similarly to the other embodiments, the punch 31 and the first pad 32, and the blank holder 33 and the second pad 34 are separated by the separation distance S0 when viewed in the thickness direction of the blank 1.

(67) Then, the blank holder 33 and the second pad 34 restraining the outer portion 12b are moved so that the portion 12a to be the vertical wall portion is rotated around the boundary point B with respect to the boundary-side portion 11a as indicated by arrow A. This corresponds to the shear deformation step. This movement is stopped at a position at which the portion 12a to be the vertical wall portion is bent by a predetermined angle (, being preferably in a range from 20 to 70, in FIG. 11A, =40). In this state, the portion 12a to be the vertical wall portion becomes an inclined wall portion, and the outer portion 12b becomes a flange portion. It is to be noted that, if is smaller than 20, shear deformation is decreased, and the effect of restricting occurrence of stretch flange deformation is decreased. Also, if exceeds 70, shear deformation occurs sufficiently in the shear deformation step for forming the vertical wall, forming does not have to be executed in the two steps of the shear deformation step and the stamping step.

(68) Then, as shown in FIG. 11B, the second pad 34 and the blank holder 33 restraining the outer portion 12b are released, and the die 37 is arranged on the portion 12a to be the vertical wall portion and the outer portion 12b. Then, by moving the die 37 along arrow B, the bent portion is stretched and hence the vertical wall portion 42 is formed. This corresponds to the stamping step.

(69) It is to be noted that the shear deformation step that is executed before the stamping step may be executed by linearly moving the restrained outer portion 12b in the direction in which the angle () with respect to the sheet face of the blank 1 is in the range from 30 to 60 as indicated by arrow C in FIG. 11A.

(70) Also, the curved channel part shown in FIG. 10 may be manufactured by a method of cutting the flange portion 24 after a flanged formed part is once obtained by the method of the first embodiment or the second embodiment.

(71) [Other Embodiment]

(72) FIG. 12 shows another embodiment of a curved channel part.

(73) As shown in FIG. 12, this curved channel part 60 is an example in which a curved portion is formed so that a vertical wall portion 62 is depressed toward a top portion 61, that is, by deforming the vertical wall portion 62 by in-plane deformation (curving the vertical wall portion 62) in a height direction so that the vertical wall portion 62 is depressed toward the top portion 61, when the boundary portion between the top portion 61 and the vertical wall portion 62 is bent at a curved bending line. By the curve of the vertical wall portion, the top portion 61 also obtains a curved shape to be depressed toward the vertical wall portion.

(74) Even in this curved channel part 60, stretch flange deformation likely occurs. By employing press forming according to embodiments (for example, press forming described in the first to sixth embodiments), a crack due to stretch flange can be restricted.

(75) Since the top portion 61 is also curved, facing surfaces of the punch 31 and the first pad 32 for holding the blank have surface shapes along the curved top portion.

(76) Also, even if the curve of the vertical wall portion is a curved portion deformed in both directions of an off-plane direction and a vertical direction, the curved portion may be a subject of disclosed embodiments.

EXAMPLES

(77) By the method described in any of the first to sixth embodiments and a press forming method of related art (deep drawing), the vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were formed. Also, by the method described in the sixth embodiment and a press forming method of related art (stamping), the curved channel part 4 shown in FIG. 10 was formed.

(78) In deep drawing, a material located at the flange portion is drawn into the vertical wall portion, and hence the shape of the flange portion after forming is different from the method of any of the first to fifth embodiments. The shapes of the blanks were changed between the methods according to the first to fifth embodiments and the deep drawing, so that the flange width near the curved portion of the vertical wall portion was 50 mm after press forming. The shape of the blank for deep drawing was obtained by inverse analysis based on the total strain theory.

(79) Also, for the blank, blanks of five types of materials shown in Table 1 each having a thickness of 1.2 mm were prepared.

(80) TABLE-US-00001 TABLE 1 Thickness Ts (Tensile strength) Sign Material (mm) (MPa) 270 270 MPa grade steel sheet 1.2 301 590 590 MPa grade steel sheet 1.2 602 980 980 MPa grade steel sheet 1.2 985 1180 1180 MPa grade steel sheet 1.2 1183 Al Aluminum alloy sheet 1.2 297

(81) It is to be noted that a blank was heated by using a heating furnace, and the temperature of the blank before forming was measured by using an infrared radiation thermometer.

(82) <Sample No. 1-1>

(83) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were formed only in the shear deformation step by the method of the first embodiment shown in FIG. 5.

(84) FIG. 13A is a plan view of the used die and blank. FIG. 13B is an A-A cross-sectional view thereof.

(85) Portions of inner peripheral surfaces of the punch 31 and the first pad 32, the portions which correspond to the curved portion 22a, each have a curvature radius R1 of 100 mm. Portions of outer peripheral surfaces of the blank holder 33 and the second pad 34, the portions which correspond to the curved portion 22a, each have a curvature radius R2 of 90 mm. The arrangement distance S0 between the punch 31 and the second pad 34 shown in FIG. 13B was set at 100 mm. A chamfering radius R3 of an upper-end corner portion of the punch 31 was set at 10 mm, and a chamfering radius R4 of a lower-end corner portion of the second pad 34 was set at 10 mm.

(86) As shown in FIGS. 5 and 13A, first, the boundary-side portion 11a of the base section 11 of the blank 1 was pinched and restrained by the punch 31 and the first pad 32, and the outer portion (the portion to be the flange portion) 12b of the deformation section 12 was pinched and restrained by the blank holder 33 and the second pad 34.

(87) Then, by moving the blank holder 33 and the second pad 34 along arrow C in FIG. 5, the portion 12a to be the vertical wall portion was rotated along arrow A in FIG. 5. As shown in FIG. 14B, the rotation was executed until a distance S between the punch 31 and the second pad 34 became 10 mm. Accordingly, the portion 12a to be the vertical wall portion of the blank 1 was shear-deformed and the vertical wall portion 22 was formed. FIG. 14

(88) A, is a plan view of the die and blank in this state. FIG. 14B, is an A-A cross-sectional view thereof. A height T of the vertical wall portion 22 in FIG. 14B, was 100 mm.

(89) In this example, the shear deformation step was executed at a room temperature by using a non-heated blank.

(90) For the obtained curved channel part, a generated crack was evaluated as shown in Table 2, and a generated wrinkle was evaluated as shown in Table 3.

(91) TABLE-US-00002 TABLE 2 Sign Crack evaluation No crack Necking X (F) Crack in flange portion X (K) Crack in vertical wall portion

(92) TABLE-US-00003 TABLE 3 Sign Wrinkle evaluation No wrinkle at all by visual inspection Very small wrinkle negligible in quality X Noticeable wrinkle

(93) As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was O (very small wrinkle negligible in quality).

(94) <Sample No. 1-2>

(95) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 1-1 except the following point.

(96) In this example, from the state in FIG. 14B, a wrinkle stretching step was executed by further pinching the vertical wall portion 22 by the punch 31 and the second pad 34.

(97) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(98) <Sample No. 1-3>

(99) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 1-1 except the following point.

(100) In this example, the shear deformation step was executed by using a blank heated at 300 C.

(101) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(102) <Sample No. 1-4>

(103) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 1-1 except the following point.

(104) In this example, the shear deformation step was executed by using a blank heated at 300 C. Also, from the state in FIG. 14B, the wrinkle stretching step was executed by further pinching the vertical wall portion 22 by the punch 31 and the second pad 34.

(105) For each obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(106) <Sample No. 2-1>

(107) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were formed only in the shear deformation step by the method of the second embodiment shown in FIG. 6.

(108) A die the same as that of the sample No. 1-1 was used except that a moving mechanism of the blank holder 33 and the second pad 34 was different. The arrangement distance S0 between the punch 31 and the second pad 34 shown in FIG. 13B was set at 100 mm.

(109) First, the boundary-side portion 11a of the base section 11 of the blank 1 was pinched and restrained by the punch 31 and the first pad 32, and the outer portion (the portion to be the flange portion) 12b of the deformation section 12 was pinched and restrained by the blank holder 33 and the second pad 34.

(110) Then, as shown in FIG. 6, the blank holder 33 and the second pad 34 were linearly moved along arrow C. At this time, the moving angle () with respect to the sheet face of the blank 1 was set at 30. As shown in FIG. 14B, the movement was executed until a distance S between the punch 31 and the second pad 34 became 10 mm. Accordingly, the portion 12a to be the vertical wall portion was shear-deformed and the vertical wall portion 22 was formed. FIG. 14A is the plan view of the die and blank in this state. FIG. 14B is the A-A cross-sectional view thereof. The height T of the vertical wall portion 22 in FIG. 14B was 100 mm.

(111) In this example, the shear deformation step was executed at a room temperature by using a non-heated blank.

(112) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was O (very small wrinkle negligible in quality).

(113) <Sample No. 2-2>

(114) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-1 except the following point.

(115) In this example, from the state in FIG. 14B, the wrinkle stretching step was executed by further pinching the vertical wall portion 22 by the punch 31 and the second pad 34.

(116) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(117) <Sample No. 2-3>

(118) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-1 except the following point.

(119) In this example, the shear deformation step was executed by using a blank heated at 300 C.

(120) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(121) <Sample No. 2-4>

(122) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-1 except the following point.

(123) In this example, the shear deformation step was executed by using a blank heated at 300 C. Also, from the state in FIG. 14B, the wrinkle stretching step was executed by further pinching the vertical wall portion 22 by the punch 31 and the second pad 34.

(124) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(125) <Sample No. 3-1>

(126) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-1 except the following point.

(127) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 45.

(128) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. In the case of the sample No. 3-1, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was O (very small wrinkle negligible in quality).

(129) <Sample No. 3-2>

(130) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-2 except the following point.

(131) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 45.

(132) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(133) <Sample No. 3-3>

(134) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-3 except the following point.

(135) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 45.

(136) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(137) <Sample No. 3-4>

(138) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-4 except the following point.

(139) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 45.

(140) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(141) <Sample No. 4-1>

(142) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-1 except the following point.

(143) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 60.

(144) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. In the case of the sample No. 4-1, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was O (very small wrinkle negligible in quality).

(145) <Sample No. 4-2>

(146) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-2 except the following point.

(147) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 60.

(148) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(149) <Sample No. 4-3>

(150) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-3 except the following point.

(151) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 60.

(152) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(153) <Sample No. 4-4>

(154) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-4 except the following point.

(155) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 60.

(156) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(157) <Sample No. 5-1>

(158) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-1 except the following point.

(159) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 20.

(160) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was x (noticeable wrinkle).

(161) <Sample No. 5-2>

(162) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-2 except the following point.

(163) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 20.

(164) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was x (noticeable wrinkle).

(165) <Sample No. 5-3>

(166) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-3 except the following point.

(167) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 20.

(168) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was x (noticeable wrinkle).

(169) <Sample No. 5-4>

(170) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-4 except the following point.

(171) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 20.

(172) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was x (noticeable wrinkle).

(173) <Sample No. 6-1>

(174) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-1 except the following point.

(175) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 70.

(176) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was x (crack in vertical wall portion), and the wrinkle was x (noticeable wrinkle).

(177) <Sample No. 6-2>

(178) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-2 except the following point.

(179) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 70.

(180) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was x (crack in vertical wall portion), and the wrinkle was x (noticeable wrinkle).

(181) <Sample No. 6-3>

(182) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-3 except the following point.

(183) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 70.

(184) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was x (crack in vertical wall portion), and the wrinkle was x (noticeable wrinkle).

(185) <Sample No. 6-4>

(186) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-4 except the following point.

(187) As shown in FIG. 6, the angle () at which the blank holder 33 and the second pad 34 were linearly moved along arrow C was set at 70.

(188) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was x (crack in vertical wall portion), and the wrinkle was x (noticeable wrinkle).

(189) <Sample No. 7-1>

(190) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were formed in two steps of the deep drawing step and then the shear deformation step by the method of the fifth embodiment shown in FIG. 9.

(191) The die used in the deep drawing step is provided by replacing the second pad 34 with the die 37 in the die shown in FIG. 13. The chamfering radius at a lower-end corner portion of the die 37 is 10 mm being the same as the chamfering radius R4 of a lower-end corner portion of the second pad 34 of the die shown in FIG. 13. A distance L (see FIG. 9A) between the punch 31 and the die 37 was set at 87 mm.

(192) First, as shown in FIG. 9A, the boundary-side portion 11a of the base section 11 of the blank 1 was pinched and restrained by the punch 31 and the first pad 32, and the outer portion 12d of the deformation section 12 of the blank 1 was arranged between the blank holder 33 and the die 37. Then, the deep drawing step was executed, in which the blank holder 33 and the die 37 were moved in the B direction by 50 mm while a tensile force was applied to the outer portion 12d. The deep drawing step was executed until the angle between the portion 12a to be the vertical wall portion and the side surface of the die 37 became 60. Accordingly, the height T1 of the portion 12a to be the vertical wall portion was set at 50 mm.

(193) Then, the die 37 was replaced with the second pad 34, the blank holder 33 and the second pad 34 were connected to the same moving mechanism as that used for the sample No. 2-1, and as shown in FIG. 9B, the outer portion 12d of the deformation section 12 of the blank 1 was restrained between the blank holder 33 and the second pad 34. The arrangement distance S0 between the punch 31 and the second pad 34 was set at 87 mm.

(194) Then, the angle with respective to the sheet face of the portion 12a to be the vertical wall portion of the blank 1 was set at 60, and the blank holder 33 and the second pad 34 were linearly moved along arrow C. The movement was executed until a distance S between the punch 31 and the second pad 34 became 10 mm. Accordingly, the portion 12a to be the vertical wall portion was shear-deformed and the vertical wall portion 22 was formed. A height T2 of the vertical wall portion 22 in FIG. 9B, was 100 mm.

(195) In this example, the shear deformation step was executed at a room temperature by using a non-heated blank.

(196) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was O (very small wrinkle negligible in quality).

(197) <Sample No. 7-2>

(198) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 7-1 except the following point.

(199) In this example, from the state in FIG. 9B, the wrinkle stretching step was executed by further pinching the vertical wall portion 22 by the punch 31 and the second pad 34.

(200) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(201) <Sample No. 7-3>

(202) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 7-1 except the following point.

(203) In this example, the shear deformation step was executed by using a blank heated at 300 C.

(204) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(205) <Sample No. 7-4>

(206) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 7-1 except the following point.

(207) In this example, the shear deformation step was executed by using a blank heated at 300 C. Also, from the state in FIG. 9B, the wrinkle stretching step was executed by further pinching the vertical wall portion 22 by the punch 31 and the second pad 34.

(208) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(209) <Sample No. 8-1>

(210) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were formed in two steps of the shear deformation step and then the deep drawing step by the method of the fourth embodiment shown in FIG. 8.

(211) In the shear deformation step, the same die as that used for the sample No. 2-1 was used, and the arrangement distance S0 (see FIG. 8A) between the punch 31 and the second pad 34 was set at 50 mm.

(212) As shown in FIG. 8A, first, the boundary-side portion 11a of the base section 11 of the blank 1 was pinched and restrained by the punch 31 and the first pad 32, and the outer portion (the portion to be the flange portion) 12b of the deformation section 12 was pinched and restrained by the blank holder 33 and the second pad 34. Then, the shear deformation step was executed by linearly moving the blank holder 33 and the second pad 34 along arrow C while =45. The shear deformation step was executed at a room temperature by using a non-heated blank until a height T1 of the inner portion 12c of the blank 1 became 50 mm.

(213) Then, as shown in FIG. 8B, the second pad 34 was replaced with the die 37, the die 37 and the blank holder 33 were connected to the moving mechanism for deep drawing, and the outer portion 12b of the blank 1 was arranged between the die 37 and the blank holder 33. Then, the deep drawing step was executed, in which the die 37 and the blank holder 33 were moved in the B direction by 50 mm while a tensile force was applied to the outer portion 12b. The deep drawing step was executed until the height T2 of the vertical wall portion 22 became 100 mm.

(214) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was O (very small wrinkle negligible in quality).

(215) <Sample No. 8-2>

(216) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 8-1 except the following point.

(217) In this example, from the state in FIG. 8B, the wrinkle stretching step was executed by further pinching the vertical wall portion 22 by the punch 31 and the die 37.

(218) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(219) <Sample No. 8-3>

(220) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 8-1 except the following point.

(221) In this example, the shear deformation step was executed by using a blank heated at 300 C.

(222) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(223) <Sample No. 8-4>

(224) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 8-1 except the following point.

(225) In this example, the shear deformation step was executed by using a blank heated at 300 C. Also, from the state in FIG. 8B, the wrinkle stretching step was executed by further pinching the vertical wall portion 22 by the punch 31 and the die 37.

(226) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(227) <Sample No. 9-1>

(228) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were formed only in the deep drawing step.

(229) FIG. 15A is a plan view of the used die and blank. FIG. 15B is an A-A cross-sectional view thereof.

(230) The die used for press forming is the same as the die for deep drawing of related art, and includes a die 51, a punch 52, and a pair of blank holders 53. A portion of an inner peripheral surface 51a of a depressed portion of the die 51, which corresponds to the curved portion 22a, has a curvature radius R1 of 100 mm. A depth F of the depressed portion of the die 51 is 100 mm. A portion of an outer peripheral surface 52a of the punch 52, which corresponds to the curved portion 22a, has a curvature radius R2 of 90 mm.

(231) A distance K between the inner peripheral surface 51a of the die 51 and the outer peripheral surface 52a of the punch 52 was set at 10 mm. A chamfering radius R3 of an upper-end corner portion of the punch 52 was set at 10 mm, and a chamfering radius R4 of a lower-end corner portion of the inner peripheral surface 51a of the die 51 was set at 10 mm.

(232) As shown in FIG. 15, first, the blank holders 53 were arranged at both sides of the punch 52, and the blank 1 was arranged on the punch 52 and the blank holders 53. The base section 11 of the blank 1 was arranged on the punch 52, and the deformation section 12 was arranged on the blank holders 53. Then, the die 51 was arranged above the blank 1, and the die 51 was lowered. At this time, a proper tensile force was applied to the deformation section 12 of the blank 1 held by a protruding portion 51b of the die 51 and the blank holders 53. The deep drawing step was executed at a room temperature.

(233) Accordingly, as shown in FIG. 16, the deformation section 12 of the blank 1 is moved toward the punch 52 between the protruding portion 51b of the die 51 and the blank holders 53 as indicated by arrow B while the deformation section 12 is bent by a depressed portion of the die 51 and the punch 52, and the material largely drawn into the area between the punch 52 and the die 51 forms the vertical wall portion 22. By executing the deep drawing step, the curved channel part 2 including the vertical wall portion 22 with a height T of 100 mm was obtained.

(234) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, if the material of the used blank was 270, the crack was , and otherwise, the crack was x (F). If the material of the used blank was any of 270 and aluminum alloy, the wrinkle was O (very small wrinkle negligible in quality), and otherwise, the wrinkle was x (noticeable wrinkle).

(235) That is, in this example, if a 270 MPa grade steel sheet was used as the blank, the wrinkle evaluation had no problem; however, necking occurred at an end portion of the vertical wall portion. If any of 590, 980, 1180 MPa grade steel sheets with high strengths was used as the blank, a noticeable wrinkle was generated in the vertical wall portion, and a crack was generated in the flange portion. If an aluminum alloy sheet was used as the blank, the wrinkle evaluation had no problem; however, a crack was generated in the flange portion.

(236) <Sample No. 9-2>

(237) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 9-1 except the following point.

(238) In this example, the deep drawing step was executed by using a blank heated at 300 C.

(239) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was x (crack in vertical wall portion). If the material of the used blank was any of 980 and 1180, the wrinkle was x (noticeable wrinkle), and otherwise, the wrinkle was O (very small wrinkle negligible in quality).

(240) <Sample No. 10-1>

(241) The curved channel part 4 shown in FIG. 10 was formed by the two steps of the shear deformation step and then the stamping step by the method of the sixth embodiment shown in FIG. 11.

(242) In the shear deformation step, the same die as that used for the sample No. 2-1 was used, and the arrangement distance S0 between the punch 31 and the second pad 34 was set at 50 mm.

(243) As shown in FIG. 11A, first, the boundary-side portion 11a of the base section 11 of the blank 1 was pinched and restrained by the punch 31 and the first pad 32, and the outer portion (the portion to be the flange portion) 12b of the deformation section 12 was pinched and restrained by the blank holder 33 and the second pad 34. Then, the shear deformation step was executed by linearly moving the blank holder 33 and the second pad 34 restraining the outer portion 12b along arrow C while =45.

(244) In this state, the portion 12a to be the vertical wall portion becomes an inclined wall portion, and the outer portion 12b becomes a flange portion. The shear deformation step was executed at a room temperature by using a non-heated blank until a height T1 of the inclined wall portion became 25 mm.

(245) Then, as shown in FIG. 11B, the blank holder 33 and the second pad 34 restraining the outer portion 12b were released, and the die 37 was arranged on the portion (the inclined wall portion) 12a to be the vertical wall portion of the blank 1 and the outer portion (the flange portion) 12b. Then, the stamping step was executed by moving the die 37 along arrow B. Accordingly, the bent portion between the portion 12b transiently being the flange portion and the inclined wall portion 12a were stretched and the vertical wall portion 42 was formed. A height T2 of the vertical wall portion 42 in FIG. 11B was 100 mm.

(246) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was O (very small wrinkle negligible in quality).

(247) <Sample No. 10-2>

(248) The curved channel part 4 shown in FIG. 10 was manufactured by the same method as the sample No. 10-1 except the following point.

(249) In this example, from the state in FIG. 11B, the wrinkle stretching step was executed by further pinching the vertical wall portion 42 by the punch 31 and the die 37.

(250) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(251) <Sample No. 10-3>

(252) The curved channel part 4 shown in FIG. 10 was manufactured by the same method as the sample No. 10-1 except the following point.

(253) In this example, the shear deformation step was executed by using a blank heated at 300 C.

(254) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(255) <Sample No. 10-4>

(256) The curved channel part 4 shown in FIG. 10 was manufactured by the same method as the sample No. 10-1 except the following point.

(257) In this example, the shear deformation step was executed by using a blank heated at 300 C. Also, from the state in FIG. 11B, the wrinkle stretching step was executed by further pinching the vertical wall portion 42 by the punch 31 and the die 37.

(258) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(259) <Sample No. 11-1>

(260) The curved channel part 4 shown in FIG. 10 was manufactured only by stamping.

(261) A die obtained by removing the blank holders 53 from the die shown in FIG. 15 used for the sample No. 9-1 was used, the base section 11 of the blank 1 was arranged on the punch 52, then the die 51 was arranged above the blank 1, the die 51 was lowered, and hence the deformation section 12 of the blank 1 was bent. Thus, the vertical wall portion 42 was formed.

(262) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, if the material of the used blank was 270, the crack was , and otherwise, the crack was x (K). If the material of the used blank was any of 270 and aluminum alloy, the wrinkle was O (very small wrinkle negligible in quality), and otherwise, the wrinkle was x (noticeable wrinkle).

(263) That is, in this example, if a 270 MPa grade steel sheet was used as the blank, the wrinkle evaluation had no problem; however, necking occurred at an end portion of the vertical wall portion. If any of 590, 980, and 1180 MPa grade steel sheets with high strengths was used as the blank, a crack was generated in an end portion of the vertical wall portion, and hence a wrinkle was generated in the vertical wall portion. If an aluminum alloy sheet was used as the blank, the wrinkle evaluation had no problem; however, a crack was generated in an end portion of the vertical wall portion.

(264) <Sample No. 11-2>

(265) The curved channel part 4 shown in FIG. 10 was manufactured by the same method as the sample No. 11-1 except the following point.

(266) In this example, the stamping step was executed by using a blank heated at 300 C.

(267) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was x (crack in vertical wall portion). If the material of the used blank was 1180, the wrinkle was x (noticeable wrinkle), and otherwise, the wrinkle was O (very small wrinkle negligible in quality).

(268) <Sample No. 12-1>

(269) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-1 except the following point. As shown in FIG. 7, the angle () at which the blank holder 33 and the second pad 36 were linearly moved along arrow C was set at 45.

(270) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, in the case of the sample No. 10-1, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(271) <Sample No. 12-2>

(272) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-2 except the following point. As shown in FIG. 7, the angle () at which the blank holder 33 and the second pad 36 were linearly moved along arrow C was set at 45.

(273) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(274) <Sample No. 12-3>

(275) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-3 except the following point. As shown in FIG. 7, the angle () at which the blank holder 33 and the second pad 36 were linearly moved along arrow C was set at 45.

(276) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(277) <Sample No. 12-4>

(278) The vertical wall portion 22 and the flange portion 24 continuous to the vertical wall portion 22 of the curved channel part 2 shown in FIG. 3 were manufactured by the same method as the sample No. 2-4 except the following point. As shown in FIG. 7, the angle () at which the blank holder 33 and the second pad 36 were linearly moved along arrow C was set at 45.

(279) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(280) <Sample No. 13-1>

(281) The vertical wall portion 42 of the curved channel part shown in FIG. 10 was formed by two steps of the shear deformation step and then the stamping step by the method of the sixth embodiment shown in FIG. 11.

(282) In the shear deformation step, the same die as that used for the sample No. 2-1 was used, and the arrangement distance S0 (see FIG. 11A) between the punch 31 and the second pad 34 was set at 50 mm. As shown in FIG. 11A, first, the boundary-side portion 11a of the base section 11 of the blank 1 was pinched and restrained by the punch 31 and the first pad 32, and the outer portion (the portion to be the flange portion) 12b of the deformation section 12 was pinched and restrained by the blank holder 33 and the second pad 34. Then, the shear deformation step was executed by linearly moving the blank holder 33 and the second pad 34 along arrow C while =45. The shear deformation step was executed at a room temperature by using a non-heated blank until the height T1 of the inner portion 12c of the blank 1 became 50 mm.

(283) Then, as shown in FIG. 11B, the second pad 34 and the blank holder 33 restraining the outer portion 12b were released, and the die 37 was arranged on the portion 12a to be the vertical wall portion and the outer portion 12b. Then, the stamping step for forming the vertical wall portion 42 was executed by moving the die 37 along arrow B and hence stretching the bent portion. The stamping step was executed until the height T2 of the vertical wall portion 22 became 100 mm.

(284) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was O (very small wrinkle negligible in quality).

(285) <Sample No. 13-2>

(286) The vertical wall portion 42 of the curved channel part shown in FIG. 10 was manufactured by the same method as the sample No. 11-1 except the following point. In this example, from the state in FIG. 11B, the wrinkle stretching step was executed by further pinching the vertical wall portion 42 by the punch 31 and the die 37.

(287) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(288) <Sample No. 13-3>

(289) The vertical wall portion 42 of the curved channel part shown in FIG. 10 was manufactured by the same method as the sample No. 11-1 except the following point. In this example, the shear deformation step was executed by using a blank heated at 300 C.

(290) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(291) <Sample No. 13-4>

(292) The vertical wall portion 42 of the curved channel part shown in FIG. 10 was manufactured by the same method as the sample No. 11-1 except the following point. In this example, the shear deformation step was executed by using a blank heated at 300 C. Also, from the state in FIG. 11B, the wrinkle stretching step was executed by further pinching the vertical wall portion 42 by the punch 31 and the die 37.

(293) For the obtained curved channel part, a generated crack and a generated wrinkle were evaluated on the basis of Tables 2 and 3. As the result, with any of the materials of the used blank, the crack was O (no crack), and the wrinkle was (no wrinkle at all by visual inspection).

(294) These results are shown in Tables 4 to 6 as follows. Table 4 collectively shows the results of No. 1-1 to No. 9-2 in which the curved channel parts with the flange portions were manufactured. Table 5 collectively shows the results of No. 10-1 to No. 11-2 in which the curved channel parts without a flange portion were manufactured. Table 6 collectively shows the results of No. 12-1 to No. 13-4.

(295) TABLE-US-00004 TABLE 4 Forming method Wrinkle Evaluation Forming step of vertical Blank stretching Crack Wrinkle No. wall portion heating step 270 590 980 1180 Al 270 590 980 1180 Al 1-1 Only shear deformation Absent Absent 1-2 step (rotation) Absent Present 1-3 Present Absent 1-4 Present Present 2-1 Only shear deformation Absent Absent 2-2 step (linear movement Absent Present 2-3 = 30) Present Absent 2-4 Present Present 3-1 Only shear deformation Absent Absent 3-2 step (linear movement Absent Present 3-3 = 45) Present Absent 3-4 Present Present 4-1 Only shear deformation Absent Absent 4-2 step (linear movement Absent Present 4-3 = 60) Present Absent 4-4 Present Present 5-1 Only shear deformation Absent Absent X X X X X 5-2 step (linear movement Absent Present X X X X X 5-3 = 20) Present Absent X X X X X 5-4 Present Present X X X X X 6-1 Only shear deformation Absent Absent X (K) X (K) X (K) X (K) X (K) X X X X X 6-2 step (linear movement Absent Present X (K) X (K) X (K) X (K) X (K) X X X X X 6-3 = 70) Present Absent X (K) X (K) X (K) X (K) X (K) X X X X X 6-4 Present Present X (K) X (K) X (K) X (K) X (K) X X X X X 7-1 Deep drawing step and Absent Absent 7-2 then shear deformation Absent Present 7-3 step (linear movement Present Absent 7-4 = 60) Present Present 8-1 Shear deformation step Absent Absent 8-2 (linear movement = Absent Present 8-3 45) and then deep Present Absent 8-4 drawing step Present Present 9-1 Only deep drawing step Absent Absent X (F) X (F) X (F) X (F) X X X 9-2 Present Absent X (K) X (K) X (K) X (K) X (K) X X

(296) TABLE-US-00005 TABLE 5 Forming method Wrinkle Evaluation Forming step of Blank stretching Crack Wrinkle No. vertical wall portion heating step 270 590 980 1180 Al 270 590 980 1180 Al 10-1 Shear deformation Absent Absent 10-2 step (linear Absent Present 10-3 movement = 45) Present Absent 10-4 and then Present Present stamping step 11-1 Only stamping step Absent Absent X (K) X (K) X (K) X (K) X X X 11-2 Present Absent X (K) X (K) X (K) X (K) X (K) X

(297) TABLE-US-00006 TABLE 6 Forming method Wrinkle Evaluation Forming step of vertical Blank stretching Crack Wrinkle No. wall portion heating step 270 590 980 1180 Al 270 590 980 1180 Al 12-1 Only shear deformation Absent Absent Entirely Entirely 12-2 step (linear movement = Absent Present 12-3 45) Present Absent 12-4 Present Present 13-1 Shear deformation step Absent Absent Same as EXAMPLES 8-1 Same as EXAMPLES 8-1 13-2 (linear movement = Absent Present to 8-4 to 8-4 13-3 45) and then Present Absent 13-4 stamping step Present Present

(298) Referring to these results, the following findings are obtained.

(299) The samples No. 1-1 to No. 4-4 each employ the method of the above-described configuration (3) or (4) as the step of forming the vertical wall portion. Accordingly, if the vertical wall portion is formed only in the shear deformation step, by employing the method of the above-described configuration (3) or (4), the curved channel part with good evaluation results for crack and wrinkle can be obtained with any of all the materials.

(300) The samples No. 5-1 to No. 6-4 each employ, as the step of forming the vertical wall portion, the method of linearly moving the restrained outer portion in the direction at the angle () being 20 or 70 (outside the range from 30 to 60) with respect to the sheet face of the blank.

(301) Accordingly, the wrinkle generated in the vertical wall portion in the shear deformation step could not be removed although the blank heating and/or the wrinkle stretching step was executed (No. 5-2 to 5-4, No. 6-2 to 6-4). Also, in the samples No. 6-1 to No. 6-4 with =70, a crack was generated in the vertical wall portion in the shear deformation step.

(302) However, even in these cases, instead of forming the vertical wall portion only by a shear deformation force, if the vertical wall portion is formed by causing the material to flow while a proper tensile force is applied to the portion to be the vertical wall, the curved channel part in which stretch flange deformation is restricted, hence a crack is not generated, and a wrinkle is improved can be obtained.

(303) In each of the above-described examples, the blank was heated at 300 C. For each of <Samples No. 1-3, 1-4, 2-3, 2-4, 3-3, 3-4, 4-3, 4-4, 7-3, 7-4, 8-3, 8-4, 10-3, 10-4, 13-3, 13-4>, heating was executed with heating temperatures of 600 C., 700 C., 900 C., and 1000 C. The results similar to the above description were obtained.

(304) The curved channel part obtained by heating the blank at 1100 C. and then executing the shear deformation step had better crack and wrinkle evaluation results than the method of related art; however, a thick oxide layer of iron called scale was formed on the surface of the formed part. The thick scale disturbs welding and electro-deposition coating, and hence a removing step of pickling, polishing, or shot blast is required. Therefore the thick scale is not desirable in view of manufacturing cost.

REFERENCE SIGNS LIST

(305) 1 blank

(306) 11 base section of blank

(307) 11b center portion of base section

(308) 11a boundary-side portion of base section

(309) 12 deformation section of blank

(310) 12a portion to be vertical wall portion of deformation section

(311) 12b outer portion of deformation section

(312) 2 curved channel part

(313) 21 top portion

(314) 22 vertical wall portion

(315) 22a curved portion of vertical wall portion

(316) 24 flange portion

(317) 24a curved portion of flange portion

(318) 4 curved channel part

(319) 41 top portion

(320) 42 vertical wall portion

(321) 42a curved portion of vertical wall portion