Method and apparatus for producing pressed component

Abstract

A method or apparatus to produce an L-shaped pressed component includes, where a portion of a blank, having tensile strength of 1180 MPa or more, is held in a state of being clamped by a blank holder and a die, and a portion of the blank, to be formed into a top plate is held in a state of being clamped by a pad and a punch; the second step where a vertical wall, a concave ridge and a flange on the inner side of a curved portion are formed by, bend forming with a bending die, forming one, two or more material inflow promoting portion; and the third step where the die is moved in a direction toward a side where the blank holder is disposed to form a vertical wall, a concave ridge, and a flange on the outer side of the curved portion by draw forming.

Claims

1. A method for producing a pressed component by performing press working on a blank disposed between a punch and a blank holder on one side and a pad, a die and a bending die on another side, the pressed component having a top plate extending in the longitudinal direction, two vertical walls connected to a respective side of the top plate, two concave ridges respectively, connected to the two vertical walls, and two flanges respectively connected to the two concave ridges, and also having a curved portion at which the top plate, the two vertical walls and the two concave ridges are curved as viewed in a plan view from a direction orthogonal to the top plate, wherein the method comprises: a first step of holding a portion of the blank to be formed into the top plate in a state of being clamped by the pad and the punch, and holding a portion of the blank to be formed into a portion disposed further outward of the curved portion than the portion of the blank to be formed into the top plate in a state of being clamped by the blank holder and the die; a second step of relatively moving, after the first step, the bending die in a direction toward a side where the punch is disposed so as to perform the press working on the blank by bend forming, thus forming one of the two vertical walls, one of the two concave ridges connected to the one of the two vertical walls, and one of the two flanges connected to the one of the two concave ridges, which are to be disposed on an inner side of the curved portion; and a third step of relatively moving, after the second step, the die and the blank holder in a direction toward a side where the punch is disposed with the blank held in a state of being clamped by the blank holder and the die so as to perform the press working on the blank by draw forming, thus forming another one of the two vertical walls, another one of the two concave ridges connected to the another one of the two vertical walls, and another one of the two flanges connected to the another one of the two concave ridges, which are disposed on an outer side of the curved portion, wherein in the second step, one or more material inflow promoting portion is formed in a portion of the blank to be formed into a region disposed on the inner side of the curved portion; and the material inflow promoting portion is formed so as to protrude toward a same side as the top plate or protrude toward an opposite side to the top plate.

2. The method for producing a pressed component according to claim 1, wherein: at least one of the following is satisfied: that the blank is formed of an ultrahigh tensile strength steel sheet having tensile strength of 1180 MPa or more; that a projection distance of the vertical walls in a height direction of a product, which is a height of the pressed component, is 70 mm or more; that a radius of curvature of the concave ridge of the pressed component is 10 mm or less as viewed in a side view; or that a radius of curvature of the curved portion of the pressed component on the inner side is 100 mm or less as viewed in the plan view; or at least two or more of the following are satisfied: that the blank is formed of an ultrahigh tensile strength steel sheet having tensile strength of 1180 MPa or more; that a projection distance of the vertical walls in a height direction of a product, which is a height of the pressed component, is 55 mm or more; that a radius of curvature of the concave ridge of the pressed component is 15 mm or less as viewed in a side view; or that a radius of curvature of the curved portion of the pressed component on the inner side is 140 mm or less as viewed in the plan view.

3. The method for producing a pressed component according to claim 1, wherein the material inflow promoting portion is formed on the blank in a region outside a region to be formed into the pressed component.

4. The method for producing a pressed component according to claim wherein: the one of the two concave ridges has a curved region that is included in the curved portion, and a radius of curvature on an inner circumference of the curved region is 140 mm or less in the plan view, and further wherein when a straight line which is in contact with a center position of the inner circumference of the curved region in the plan view is defined as a reference line, and a length of a centerline in a sheet thickness direction of the material inflow promoting portion in a cross-section that is parallel to the reference line in the plan view is defined as a cross-sectional line length, the material inflow promoting portion has a region in which the cross-sectional line length increases as a distance from the center position increases in the plan view.

5. The method for producing a pressed component according to claim 1, wherein the material inflow promoting portion is a projecting bead or a concave bead, the projecting bead projecting in a direction from the flange toward the top plate in a direction along which the flange and the top plate are arranged, the concave bead projecting in a direction from the top plate toward the flange in the direction along which the flange and the top plate are arranged.

6. The method for producing a pressed component according to claim 1, wherein cross-sectional peripheral lengths of the material inflow promoting portion increase in a stepwise manner.

7. The method for producing a pressed component according to claim 4, wherein the material inflow promoting portion has a region in which the cross-sectional line length is constant at positions having different distances from the center position in the plan view.

8. The method for producing a pressed component according to claim 1 comprising a following fourth step after the third step, the fourth step where an unnecessary portion is removed which remains at a part of a periphery of a formed product acquired in the third step, and which includes an entire or a part of the material inflow promoting portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1(a) to FIG. 1(e) are cross-sectional views schematically showing the configuration of a producing apparatus and forming steps according to an embodiment of the present invention.

(2) FIG. 2(a) to FIG. 2(e) are cross-sectional views showing an example of the configuration of another press tooling and forming steps according to the embodiment of the present invention.

(3) FIG. 2A is an explanatory view partially showing an example of the configuration of the producing apparatus according to the embodiment of the present invention.

(4) FIG. 2B is an explanatory view partially showing one example of a second step of forming a vertical wall on the inner side of a curved portion of an intermediate formed product formed by performing press forming with the producing apparatus according to the embodiment of the present invention.

(5) FIG. 2C is an explanatory view showing the positional relationship between a material-inflow-promoting-portion forming mechanism and a concave ridge forming portion of the producing apparatus according to the embodiment of the present invention and a blank.

(6) FIG. 2D is an explanatory view showing a cross section of a conventional punch, provided with no material-inflow-promoting-portion forming mechanism, which corresponds to a cross section A-A in FIG. 2A.

(7) FIG. 2E is an explanatory view showing the positional relationship between the material-inflow-promoting-portion forming mechanism and the concave ridge forming portion of the producing apparatus according to the embodiment of the present invention and the blank, and showing positions of cross sections B, C, D.

(8) FIG. 2F is a graph showing a difference in cross-sectional peripheral length on the cross sections B, C, D of a flange forming portion of a punch with respect to a conventional punch.

(9) FIG. 2G is an explanatory view showing the cross section A-A of the punch provided with the material-inflow-promoting-portion forming mechanism.

(10) FIG. 2H is an explanatory view showing the positional relationship between the material-inflow-promoting-portion forming mechanism and the concave ridge forming portion of the producing apparatus according to the embodiment of the present invention and the blank, and showing positions of the cross sections B, C, D.

(11) FIG. 2I is an explanatory view showing a reason why occurrence of cracks at a portion “a” of the blank can be prevented by providing, to a bending die and the punch, the material-inflow-promoting-portion forming mechanism formed of a recessed portion and a projecting portion.

(12) FIG. 2J(a) to FIG. 2J(f) are explanatory views showing examples of the shape of a constitutional element of various kinds of material-inflow-promoting-portion forming mechanism formed on the punch.

(13) FIG. 3(a) is a plan view showing the shape of a blank before forming is performed, and FIG. 3(b) is a plan view showing the shape of the blank during a forming process.

(14) FIG. 4 is a plan view showing a flow of material in the embodiment of the present invention.

(15) FIG. 5(a) to FIG. 5(d) are explanatory views showing one example of a press tooling used in the present invention.

(16) FIG. 6(a) to FIG. 6(d) are explanatory views showing another example of the press tooling used in the present invention.

(17) FIG. 7(a) to FIG. 7(d) are explanatory views showing another example of the press tooling used in the present invention.

(18) FIG. 8 is an exploded perspective view of the press tooling shown in FIG. 7.

(19) FIG. 9(a) to FIG. 9(c) are a front view, a plan view, and a right side view each showing a pressed component formed in Comparative Examples 1 to 7 and Inventive Examples 1 to 7 of the present invention.

(20) FIG. 10 is a plan view showing the shape of a blank used in the Comparative Examples 1 to 7 and the Inventive Examples 1 to 7 of the present invention.

(21) FIG. 11 is a perspective view showing the configuration of a press tooling used in the Comparative Examples 1 to 7.

(22) FIG. 12 is a plan view showing the shape of a blank used in Inventive Examples 8, 9 of the present invention.

(23) FIG. 13(a) to FIG. 13(c) are a front view, a right side view, and a plan view each showing the shape of an intermediate formed product formed in the Inventive Examples 8, 9 of the present invention.

(24) FIG. 14(a) to FIG. 14(c) are a front view, a right side view, and a plan view each showing the shape of a pressed component formed in the Inventive Examples 8, 9 of the present invention.

(25) FIG. 15 is a perspective view showing the configuration of a press tooling for performing forming by the present invention in the Inventive Examples 8, 9 of the present invention.

(26) FIG. 16 is a perspective view of one example of a frame member which has a hat-shaped cross section and has a straight line shape extending in a longitudinal direction as viewed in a plan view and in a side view.

(27) FIG. 17 is an explanatory view of a front pillar which is a frame member having a hat-shaped cross section, wherein FIG. 17(a) is a perspective view, and FIG. 17(b) is a plan view.

(28) FIG. 18 is a perspective view showing an L-shaped pressed component.

(29) FIG. 19 is a perspective view showing the L-shaped pressed component produced by performing bend forming.

(30) FIG. 20 is an explanatory view showing the L-shaped pressed component, wherein FIG. 20(a) is a perspective view, and FIG. 20(b) is a plan view.

(31) FIG. 21 is a plan view showing the shape of a blank and a blank holder holding region of the blank for performing draw forming.

(32) FIG. 22(a) to FIG. 22(d) are cross-sectional views showing the structure of a press tooling for performing draw forming and a process of the draw forming.

(33) FIG. 23 is a perspective view of a drawn panel formed by performing draw forming.

(34) FIG. 24 is a plan view for describing an inflow of material in performing draw forming.

DESCRIPTION OF EMBODIMENTS

(35) One example of an L-shaped pressed component produced by the present invention, and one example of a method and an apparatus for producing an L-shaped pressed component according to the present invention are sequentially described.

(36) 1. L-Shaped Pressed Component 1

(37) FIG. 18 exemplifies the shape of an L-shaped pressed component 1. The L-shaped pressed component 1 includes a hat-shaped cross section and a curved portion 1a which is curved into an L shape in a longitudinal direction as viewed in a plan view.

(38) The hat-shaped cross section is defined by a top plate 11, vertical walls 12, 14, the concave ridges 16, 17, and flanges 13, 15. The vertical walls 12, 14 are connected to both sides of the top plate 11. The concave ridges 16, 17 are respectively connected to the vertical walls 12, 14. The flanges 13, 15 are respectively connected to the concave ridges 16, 17. The L-shaped pressed component 1 includes the curved portion 1a, thus having an L shape as viewed in a plan view.

(39) The L-shaped pressed component 1 uses, as a starting material thereof, a blank formed of a high tensile strength steel sheet having a sheet thickness of 0.8 mm or more and 3.2 mm or less, and tensile strength of 590 MPa or more, and particularly, 1180 MPa or more and 1800 MPa or less. The high tensile strength steel sheet is generally used for an automobile frame member.

(40) To ensure performance, such as strength, of the automobile frame member, tensile strength of a blank is 200 MPa or more, and is preferably 1800 MPa or less. Particularly, a blank having tensile strength of 500 MPa or more, preferably 590 MPa or more, and more preferably 1180 MPa or more allows a reduction in sheet thickness of the blank, thus reducing weight of the L-shaped pressed component 1.

(41) In the case where any of these high tensile strength steel sheets is used for a blank, when the top plate 11 has an excessively large width as viewed in a plan view, in forming a vertical wall 14 and a flange 15 on the inner side of the curved portion 1a, inflow resistance of a blank 8 increases, thus causing insufficient inflow of the blank 8 to the inner side of the curved portion 1a. Accordingly, it is desirable that the width of the top plate 11 be 400 mm or less as viewed in a plan view. On the other hand, when the width of the top plate 11 is excessively small as viewed in a plan view, a pressurizing device for a pad 74, such as a gas cushion is required to reduce in size, thus preventing a pressurizing force from the pad 74 from being ensured. Accordingly, it is desirable that the width of the top plate 11 be 30 mm or more.

(42) The extremely large projection distance of the vertical wall 12, 14 in a height direction of a product, which is the height of the vertical wall 12, 14 as viewed in a side view, increases inflow resistance of the blank 8 in forming the vertical wall 14, a concave ridge 17 and the flange portion 15 on the inner side of the curved portion 1a, thus causing insufficient inflow of the blank 8 to the inner side of the curved portion 1a. Accordingly, it is desirable that the height of the vertical wall 12, 14 be 300 mm or less.

(43) It is desirable that the height of each of the vertical walls 12, 14 be 70 mm or more. This is because when the height of the vertical walls 12, 14 is less than 70 mm, the L-shaped pressed component 1 can be formed, without use of the present invention, by a forming method disclosed in Patent Document 3 without causing occurrence of cracks in a flange 15.

(44) The extremely small radius of curvature of the concave ridge 16, 17 of the L-shaped pressed component 1 causes insufficient inflow of the blank 8 to the inner side of the curved portion 1a in forming the flange portion 15 on the inner side of the curved portion 1a. Accordingly, it is desirable that the radius of curvature of the concave ridge 16, 17 be 5 mm or more as viewed in a side view.

(45) It is desirable that a radius of curvature of the vertical wall 14 on the inner side of the curved portion 1a be 100 mm or less as viewed in a plan view. This is because when the radius of curvature exceeds 100 mm, the L-shaped pressed component 1 can be formed, without use of the present invention, by the forming method disclosed in Patent Document 3 without causing occurrence of cracks in the flange 15.

(46) It is desirable that the radius of curvature of the concave ridge 16, 17 be 10 mm or less. This is because when the radius of curvature of the concave ridge 17 exceeds 10 mm, the L-shaped pressed component 1 can be formed, without use of the present invention, by the forming method disclosed in Patent Document 3 without causing occurrence of cracks in the flange 15.

(47) It is desirable that at least two or more of the followings be satisfied: that the blank 8 is formed of an ultrahigh tensile strength steel sheet having tensile strength of 1180 MPa or more; that a projection distance of the vertical wall 12, 14 in the height direction of a product, which is the height of the L-shaped pressed component 1, is 55 mm or more; that the radius of curvature of the concave ridge 16, 17 of the L-shaped pressed component 1 is 15 mm or less as viewed in a side view; or that the radius of curvature of the inner side of the curved portion 1a of the L-shaped pressed component 1 is 140 mm or less as viewed in a plan view. This is because when any one of or none of these conditions is satisfied, the L-shaped pressed component 1 can be formed, without use of the present invention, by the forming method disclosed in Patent Document 3 without causing occurrence of cracks in the flange 15.

(48) Further, a sheet thickness reduction rate of the L-shaped pressed component 1: {(maximum value of sheet thickness−minimum value of sheet thickness)/maximum value of sheet thickness}×100 is 15% or less. There has been no L-shaped pressed component 1 having such a low sheet thickness reduction rate. The L-shaped pressed component 1 which is a structural member of a vehicle body of an automobile has a low sheet thickness reduction rate as described above. Accordingly, using, as a blank, a steel sheet having tensile strength of 200 MPa or more, preferably a high tensile strength steel sheet having tensile strength of 590 MPa or more, and more preferably an ultrahigh tensile strength steel sheet having tensile strength of 1180 MPa or more can reduce the sheet thickness of the blank, thus realizing reduction in weight of the L-shaped pressed component 1 having excellent collision safety performance. In practice, the tensile strength of the L-shaped pressed component 1 is 1800 MPa or less.

(49) 2. Method and Apparatus for Producing L-Shaped Pressed Component 1

(50) FIG. 1(a) to FIG. 1(e) are cross-sectional views schematically showing the configuration of the producing apparatus and forming steps according to the embodiment of the present invention.

(51) In the embodiment of the present invention, a press tooling shown in FIG. 1(a) to FIG. 1(e) is used for forming the L-shaped pressed component 1 by performing press forming on the blank 8.

(52) The press tooling includes a punch 72 and a blank holder 73, and a pad 74, a die 71 and a bending die 75 which are disposed so as to oppose the punch 72 and the blank holder 73.

(53) The punch 72 has a shape including respective shapes on the back surface side in the sheet thickness direction of the top plate 11 of the L-shaped pressed component 1, the vertical wall 14, the concave ridge 17 and the flange 15 on the inner side of the curved portion 1a.

(54) The blank holder 73 has a shape including shapes on the back surface side in the sheet thickness direction of a vertical wall 12, a concave ridge 16 and a flange 13 on the outer side of the curved portion 1a.

(55) The pad 74 has a shape including a shape on the front surface side in the sheet thickness direction of the top plate 11 so as to oppose the blank holder 73.

(56) The die 71 has a shape including respective shapes on the front surface side in the sheet thickness direction of the vertical wall 12 and the flange 13 on the outer side of the curved portion 1a.

(57) Further, the bending die 75 has a shape including respective shapes on the front surface side in the sheet thickness direction of the vertical wall 14, the concave ridge 17, and the flange 15 on the inner side of the curved portion 1a.

(58) FIG. 2(a) to FIG. 2(e) are cross-sectional views showing the configuration of another press tooling and forming steps according to the embodiment of the present invention.

(59) A point which makes the press tooling shown in FIG. 2(a) to FIG. 2(e) different from the press tooling shown in FIG. 1 lies in that a locking mechanism 76 described later is mounted on the punch 72.

(60) The locking mechanism 76 is formed of a pin disposed so as to freely enter and withdraw from the punch 72. The locking mechanism 76 is completely accommodated in the punch 72 from the start of forming to the forming bottom dead center (FIG. 2(a) to FIG. 2(c)). The locking mechanism 76 moves and projects to the blank holder 73 side at the forming bottom dead center shown in FIG. 2(d) so as to fix the blank holder 73 to the punch 72.

(61) In releasing a press tooling, the locking mechanism 76 allows the die 71, the pad 74 and the bending die 75 to elevate in a state where the locking mechanism 76 fixes the blank holder 73 to the punch 72 so as to release the press tooling. In this manner, the locking mechanism 76 prevents the formed L-shaped pressed component 1 from being damaged by a pressurizing force from the pad 74.

(62) As the locking mechanism 76, a mechanism may be used which allows a press tooling to release in a state where the locking mechanism 76 fixes (holds) the positional relationship between the pad 74, the bending die 75 and the die 71 (drawing die) at the forming bottom dead center after the forming is completed. For example, the following configurations are exemplified.

(63) (a) A press tooling is released in a state where the mechanism fixes the pad 74 to the bending die 75 and the mechanism fixes the die 71 (drawing die) to the pad 74 or to the bending die 75.

(64) (b) A press tooling is released in a state where a spacer is inserted so as to fix a distance between the blank holder 73 and the pad 74 at the forming bottom dead center.

(65) (c) A press tooling is released in a state where the mechanism fixes (holds) the positional relationship between the pad 74 and the die 71 (drawing die) at the forming bottom dead center.

(66) A blank is formed into the L-shaped pressed component 1 using the press tooling.

(67) In the case where a body of a press machine can perform control of stopping the elevation of a cushion pin of the press machine, which is to be connected to the blank holder 73, for example, the elevation of the blank holder 73 can be stopped. Accordingly, in such a case, the locking mechanism 76 may not be provided to the press tooling, such as the punch 72.

(68) FIG. 2A is an explanatory view partially showing an example of the configuration of a producing apparatus 20 according to the embodiment of the present invention. In FIG. 2A to FIG. 2J, for the sake of convenience in description, constitutional elements of the press tooling and a blank are given symbols which are different from symbols given in FIGS. 1, 2. However, the constitutional elements of the press tooling and the blank in FIG. 2A to FIG. 2J are identical to the constitutional elements of the press tooling and the blank in FIGS. 1, 2.

(69) As shown in FIG. 2A, the producing apparatus 20 includes a bending die 21, a die 22, a blank holder 27, and a punch 23 which is disposed so as to oppose the bending die 21 and the die 22.

(70) The producing apparatus 20 performs cold or hot press working on a blank 24 or a preformed blank (the illustration being omitted) disposed between the die 22, the bending die 21, and a die pad 26 on one side and the punch 23 and the blank holder 27 on the other side, thus producing the L-shaped pressed component 1 having an external shape shown in FIG. 18, or an intermediate formed product 1-1 of the L-shaped pressed component 1. In this specification, “intermediate formed product” means a press formed product before a material inflow promoting portion described later is removed. Removing unnecessary portions, such as the material inflow promoting portion, from the intermediate formed product allows an L-shaped press formed product to be acquired.

(71) The producing apparatus 20 is preferably used when the condition 1 or 2 is satisfied. The reason is as follows. Performing second working disclosed in Patent Document 3 with the condition 1 or 2 satisfied causes occurrence of cracks in the flange 15 on the inner side of the curved portion 1a of the L-shaped pressed component 1 to be acquired. Accordingly, high efficacy of using the producing apparatus 20 can be acquired in such a case.

(72) FIG. 2B is an explanatory view partially showing one example of the intermediate formed product 1-1 formed by performing press forming with the producing apparatus 20. FIG. 2C is an explanatory view showing the positional relationship between a material-inflow-promoting-portion forming mechanism 25 and a concave ridge forming portion 23b of the producing apparatus 20 and the blank 24.

(73) The producing apparatus 20 performs press working by bend forming according to the second step disclosed in Patent Document 3. In addition to the above, as shown in FIGS. 2A, 2C, a recessed portion 21a and a projecting portion 23a are respectively formed on the bending die 21 and the punch 23 as the material-inflow-promoting-portion forming mechanism 25 for forming a material inflow promoting portion 19 on the blank 24. As described above, the material-inflow-promoting-portion forming mechanism 25 is formed of the recessed portion 21a formed on the bending die 21 and the projecting portion 23a formed on the punch 23.

(74) As shown in FIG. 2B, in performing press working by bend forming according to the second step disclosed in Patent Document 3, the producing apparatus 20 forms, in a side by side manner, the material inflow promoting portion 19 in the vicinity of a portion of the blank 24 to be formed into the flange 15 on the inner side of the curved portion 1a of the L-shaped pressed component 1.

(75) As shown in FIGS. 2B, 2C, it is desirable that the material-inflow-promoting-portion forming mechanism 25 forms the material inflow promoting portion 19 on the blank 24 in a region outside a region (a hatched region in FIG. 2C) to be formed into the L-shaped pressed component 1. Forming the material inflow promoting portion 19 in such a region prevents the trace of the material inflow promoting portion 19 from remaining on the L-shaped pressed component 1.

(76) However, in the case where the trace of the material inflow promoting portion 19 is allowed to remain on the L-shaped pressed component 1, the material inflow promoting portion 19 may be formed on a portion of the blank 24 inside a region (a hatched region in FIG. 2C) to be formed into the L-shaped pressed component 1.

(77) Next, the material-inflow-promoting-portion forming mechanism 25 is described in detail.

(78) FIG. 2D is an explanatory view showing a cross section of the conventional punch 23-1, provided with no material-inflow-promoting-portion forming mechanism 25, which corresponds to a cross section A-A in FIG. 2A.

(79) FIG. 2E is an explanatory view showing the positional relationship between the material-inflow-promoting-portion forming mechanism 25 and the concave ridge forming portion 23b of the producing apparatus 20 and the blank 24, and showing positions of the cross sections B, C, D.

(80) FIG. 2F is a graph showing a difference in cross-sectional peripheral length on the cross sections B, C, D of a flange forming portion of the punch 23 with respect to a conventional punch. In the graph of FIG. 2F, cross sections B, C, D in a conventional method are shown on the left side, and cross sections B, C, D in the embodiment of the present invention are shown on the right side. Cross sections below the graph in FIG. 2F show shapes of the blank 24 on the cross sections B, C, D.

(81) Further, FIG. 2G shows the cross section A-A of the punch 23 provided with the material-inflow-promoting-portion forming mechanism 25.

(82) In the case where the condition 1 or 2 is satisfied, when press working is performed on the blank 24 by second working of forming the vertical wall 14 on an inner circumference side of the curved portion 1a using a conventional punch 23-1, cracks occur at a portion “a” shown in FIG. 2D.

(83) As shown in FIGS. 2E, 2F, in the embodiment of the present invention, with the provision of the material-inflow-promoting-portion forming mechanism 25, which is formed of the recessed portion 21a formed on the bending die 21 and the projecting portion 23a formed on the punch 23, the material inflow promoting portion 19 is formed on the intermediate formed product 1-1 formed by performing press forming.

(84) The material inflow promoting portion 19 is formed such that the cross-sectional peripheral lengths on the cross sections B, C, D gradually increase as a distance from an inner surface of the curved portion 1a increases. In this embodiment, the cross sections B, C, D are cross sections arranged in this order in a direction separating from the flange 15 on the inner side of the curved portion 1a of the L-shaped pressed component 1. Each of the cross sections B, C, D extends parallel to a straight line which is in contact with a center position (portion “a”) in a curved circumferential direction on the inner side of the curved portion 1a as viewed in a plan view from a direction orthogonal to the top plate 11, and extends along a direction orthogonal to the top plate (cross section in a direction of material inflow: cross section in the direction of maximum principal strain of the deformation of the flange 15 on the inner side of the curved portion 1a of the L-shaped pressed component 1). This center position is not limited to an exact center position, and it is sufficient that the center position falls within a predetermined region including the exact center position in the curved circumferential direction.

(85) The cross sectional shapes of the material inflow promoting portion 19 are not limited to shapes where cross-sectional peripheral lengths monotonically increase as a distance from the flange 15 on the inner side of the curved portion 1a of the L-shaped pressed component 1 increases. The cross sectional shapes may partially have a constant cross-sectional peripheral length.

(86) As shown in FIG. 2F, compared to a conventional method, where the material-inflow-promoting-portion forming mechanism 25 is not provided, in the embodiment of the present invention, a difference in cross-sectional peripheral length of the flange forming portion of the punch 23 with respect to the conventional punch increases on all of the cross sections B, C, D.

(87) Further, in the embodiment of the present invention, the material-inflow-promoting-portion forming mechanism 25 is provided such that a difference in cross-sectional peripheral length on the cross section C is larger than a difference in cross-sectional peripheral length on the cross section B, and a difference in cross-sectional peripheral length on the cross section D is larger than a difference in cross-sectional peripheral length on the cross section C.

(88) In other words, in the embodiment of the present invention, the material-inflow-promoting-portion forming mechanism 25 has a shape which causes differences in cross sectional line length (inflow amounts) on the cross sections B, C, D to increase, and the material-inflow-promoting-portion forming mechanism 25 is provided on the bending die 21 and the punch 23 in the form of the recessed portion 21a and the projecting portion 23a.

(89) The material inflow promoting portion 19 is exemplified as follows. As shown in FIG. 2G, for example, on a vertical cross section including a straight line orthogonal to, in a horizontal plane, a straight line which is in contact with the center position on the inner side of the curved portion 1a in a state where the second step is finished, the material inflow promoting portion 19 is formed to have an external shape obtained by connecting a part of the blank 24 to be formed into a meeting point between the concave ridge 17 and the flange 15 on the inner side of the curved portion 1a and an edge portion 24a of the blank 24.

(90) FIG. 2H is an explanatory view showing the positional relationship between the material-inflow-promoting-portion forming mechanism 25 and the concave ridge forming portion 23b of the producing apparatus 20 and the blank 24, and showing positions of the cross sections B, C, D.

(91) As has been described above, a variation difference in inflow amount of material made to flow in by the material-inflow-promoting-portion forming mechanism 25 (which means an increased amount of inflow in FIG. 2F (an amount of increase in inflow amount when the method of the present invention is used with respect to an inflow amount when the conventional method, where a material-inflow-promoting-portion forming mechanism is not provided, is used)) increases as a distance from the portion “a” of the blank 24 increases as indicated by a bold arrow in FIG. 2H (cross section B cross section C=cross section D). A variation difference at the portion “a” of the blank 24 facilitates occurrence of cracks and hence, it is almost unnecessary to provide a variation difference at the portion “a” of the blank 24. A region where a variation difference in inflow amount of material is provided may be set up to the position of the end edge of the blank 24 before forming is performed as viewed in a plan view.

(92) Next, the function of the material-inflow-promoting-portion forming mechanism 25 is described.

(93) FIG. 2I is an explanatory view showing a reason why occurrence of cracks at the portion “a” of the blank 24 can be prevented by providing, to the bending die 21 and the punch 23, the material-inflow-promoting-portion forming mechanism 25 formed of the recessed portion 21a and the projecting portion 23a.

(94) Cracks at the portion “a” of the blank 24 are caused by a high tension F in the blank 24 in the circumferential direction of the concave ridge 17 disposed at a position on the portion “a”. In the embodiment of the present invention, press working is performed in a state where the material-inflow-promoting-portion forming mechanism 25 is provided and hence, an inflow amount of material flowing into a portion outward the portion “a” is increased. For this reason, an inflow amount of material from the periphery of the portion “a” increases, thus increasing an inflow amount of material flowing into the portion “a”.

(95) That is, the material-inflow-promoting-portion forming mechanism 25 increases an inflow amount of material flowing into a portion of the blank 24 to be formed into the curved portion 1a. Accordingly, although a direction of main stress of deformation at this portion does not significantly change, an amount of deformation at this portion is reduced.

(96) In this manner, compared to the case where the material-inflow-promoting-portion forming mechanism 25 is not provided, an inflow amount of material flowing into the portion of the blank 24 to be formed into the flange 15 on the inner side of the curved portion 1a of L-shaped pressed component 1 is increased.

(97) Accordingly, tension F in the blank 24 in the circumferential direction of the concave ridge 17 disposed at a position on the portion “a” is reduced. Therefore, a deformation load applied to a portion of the blank 24 to be formed into the curved portion 1a is reduced, thus preventing cracks at the portion “a” of the blank 24.

(98) FIG. 2J(a) to FIG. 2J(f) are explanatory views showing examples of the shape of a constitutional element of various kinds of material-inflow-promoting-portion forming mechanism 25 formed on the punch 23.

(99) As the projecting portion 23a which is a constitutional element of the material-inflow-promoting-portion forming mechanism 25 to be provided to the punch 23, as shown in FIG. 2J(a), a projecting portion may be used which is described with reference to FIG. 2G, and which projects toward the direction of the top plate 11 of the L-shaped pressed component 1.

(100) As shown in FIG. 2J(b), in place of the projecting portion 23a shown in FIG. 2J(a), a recessed portion 23c may be used which projects toward the direction opposite to the top plate 11 of the L-shaped pressed component 1. In this case, it is needless to say that a projecting portion which corresponds to the recessed portion 23c is formed on the bending die 21.

(101) When the blank 24 is small in size, as shown in FIG. 2J(c), it is sufficient to form the projecting portion 23a in a range which allows the blank 24 to come into contact with the projecting portion 23a.

(102) Further, as shown in FIG. 2J(d) and as described above, in the case where a the trace of the material inflow promoting portion 19 is allowed to remain on the L-shaped pressed component 1, the projecting portion 23a may be formed such that the material inflow promoting portion 19 is provided so as to extend to the inside of a region (hatched region in FIG. 2C) of the blank 24 to be formed into the L-shaped pressed component 1.

(103) As shown in FIG. 2J(e), two or more projecting portions 23a may be provided.

(104) Further, as shown in FIG. 2J(f), the projecting portion 23a may be formed in a stepped manner in a direction parallel to the sheet thickness direction of a blank 24.

(105) As described above, the material-inflow-promoting-portion forming mechanism 25 forms one, two or more material inflow promoting portions 19. The material inflow promoting portion 19 increases an inflow amount of material flowing into a portion of the blank 24 to be formed into the flange 15 on the inner side of the curved portion 1a of the L-shaped pressed component 11 at a portion of the blank 24 to be formed into an end portion 1b of the L-shaped pressed component 1 in the longitudinal direction.

(106) In FIG. 2J(a) to FIG. 2J(f), to clearly show the constitutional elements, the projecting portion 23a and the recessed portion 23c having edges are shown. However, it is needless to say that, in an actual apparatus, the edges of the projecting portion 23a and the recessed portion 23c may have a smooth round (curved) shape so as not to prevent the inflow of material.

(107) The L-shaped pressed component 1 which is to be produced by the embodiment of the present invention satisfies the above-mentioned condition 1 or 2. When the conventional method described in Patent Document 3 is used, cracks occur at the portion “a”.

(108) FIG. 3(a) is a plan view showing the shape of the blank 8 before forming is performed, and FIG. 3(b) is a plan view showing the shape of the blank 8 during a forming process. Further, FIG. 4 is a plan view showing a flow of material in the embodiment of the present invention. In FIGS. 3, 4, the material inflow promoting portion 19 and the material-inflow-promoting-portion forming mechanism 25 are omitted.

(109) As shown in FIG. 1(a), the blank 8 having a shape shown in FIG. 3(a) is disposed between the punch 72 and the blank holder 73 on one side and the pad 74, the die 71 and the bending die 75 on the other side.

(110) Next, as shown in FIG. 1(b), a portion of the blank 8 to be formed into the top plate 11 is pressurized and held in a state of being clamped by the pad 74 and the punch 72. At the same time, a portion of the blank 8 to be formed into a portion disposed further outward of the curved portion 1a than the portion of the blank 8 to be formed into the top plate 11 is pressurized and held in a state of being clamped by the blank holder 73 and the die 71.

(111) Next, as shown in FIG. 1(c), the bending die 75 is relatively moved in a direction toward a side where the punch 72 is disposed so as to perform working on the blank 8, thus forming the vertical wall 14, the concave ridge 17 and the flange 15 on the inner side of the curved portion 1a. With such an operation, the blank 8 is formed into a shape shown in FIG. 3(b).

(112) At this point of operation, the blank 8 is pulled only from the inner side of the curved portion 1a so that a portion of the blank 8, which is clamped between the punch 72 and the blank holder 73 on one side and the pad 74 and the die 71 on the other side, also flows into the inner circumference side of the curved portion 1a, and forming is performed.

(113) Accordingly, unlike the draw forming where the curved portion 1a is pulled from both of the outer side and the inner side of the curved portion 1a (see FIG. 24), as shown in FIG. 4, at a flange (portion “D”) on the inner side of the curved portion 1a, the blank 8 does not significantly move from the inner side to the outer side of the curved portion 1a during the forming process. Further, a distal end of the blank 8 in the longitudinal direction flows into the inner side of the curved portion 1a so as to bend the entire blank 8. The flange 15 on the inner side of the curved portion 1a (portion “D”) which is disposed on the inner side of the bending is compressed. Accordingly, an amount of stretch of the flange 15 on the inner side of the curved portion 1a (portion “D”) at the time of performing forming is remarkably reduced compared to draw forming.

(114) Further, as shown in FIG. 1(d), after the vertical wall 14, the concave ridge 17 and the flange 15 on the inner side of the curved portion 1a are formed, with the blank 8 pressurized and held in a state of being clamped by the blank holder 73 and the die 71, the die 71 and the blank holder 73 are moved relative to the blank 8 in a direction toward a side where the blank holder 73 is disposed so as to perform working on the blank 8, thus forming the vertical wall 12, the concave ridge 16 and the flange 13 on the outer side of the curved portion 1a. The L-shaped pressed component 1 shown in FIG. 18 is formed in this manner.

(115) At this point of operation, during a forming process for the vertical wall 14 and the flange 15 on the inner side of the curved portion 1a, a portion to be formed into the top plate 11 and a portion to be formed into the flange 13 also flow into the inner side of the curved portion 1a, thus bringing about a state where the blank 8 contracts in the longitudinal direction, and a compressive stress remains. Accordingly, a corner portion (portion “C” in FIG. 4) forming a meeting portion between the vertical wall 12 on the outer side of the curved portion 1a and the top plate 11, which is significantly stretched during a forming process, is also formed into a shape bulging outward from a state where a compressive stress remains.

(116) Accordingly, compared to draw forming where forming is performed from a state having no compressive stress, required ductility of a material is reduced. As a result, even when a high strength material (for example, high tensile strength steel sheet having tensile strength of 590 MPa or more) having low ductility is used for the blank 8, forming can be preferably performed on the blank 8 while occurrence of cracks is suppressed.

(117) In forming the vertical wall 14 and the flange 15 on the inner side of the curved portion 1a, the vertical wall 14 and the flange 15 are formed by bending with the bending die 75 and hence, it is unnecessary to provide a blank holder holding region to an inner peripheral portion of the curved portion 1a and to a distal end portion in the longitudinal direction. Accordingly, the blank 8 can be reduced in size, thus realizing formation at high material yield rate.

(118) Further, as shown in FIG. 2A to 2C, performing press working with the material-inflow-promoting-portion forming mechanism 25, formed on the bending die 21 and the punch 23, allows the intermediate formed product 1-1 to have at least one material inflow promoting portion 19, which increases an inflow amount of material flowing into a portion to be formed into the flange 15 on the inner side of the curved portion 1a.

(119) Therefore, as described with reference to FIG. 21, the embodiment of the present invention can increase an inflow amount of material flowing into the portion of the blank 24 to be formed into the flange 15 on the inner side of the curved portion 1a of the L-shaped pressed component 1. Accordingly, tension F in the blank 24 in the circumferential direction of the concave ridge 17 disposed at a position on the portion “a” can be reduced and hence, cracks at the portion “a” of the blank 24 can be prevented.

(120) Finally, as shown in FIG. 1(e), in taking out the formed L-shaped pressed component 1 from the inside of the press tooling after forming of the L-shaped pressed component 1 is completed, the blank holder 73 is fixed to the punch 72 by the locking mechanism 76, for example, so as to prevent the relative movement.

(121) Then, in a state where the blank holder 73 is prevented from pressurizing by pressing the formed L-shaped pressed component 1 against the die 71, the pad 74, the die 71 and the bending die 75 are separated from the blank holder 73 and the punch 72 so as to take out the L-shaped pressed component 1. With such an operation, the formed intermediate formed product 1-1 can be taken out without being deformed and damaged by the pressurized pad 74 and the blank holder 73.

(122) Thereafter, an unnecessary portion, which remains at a part of the periphery of the intermediate formed product 1-1 take out, and which includes an entire or a part of the material inflow promoting portion 19, is removed using a proper removing device (for example, a device which is commonly used as a removing device of this kind, such as a cutting device), thus producing the L-shaped pressed component 1 having a desired shape and high strength.

(123) The schematic configuration of the apparatus for producing the L-shaped pressed component 1 has been described heretofore. The structure of the press tooling is described in more detail.

(124) FIG. 5(a) to FIG. 5(d) are explanatory views showing one example of the press tooling used in the present invention. The locking mechanism 76 is omitted in FIGS. 5 to 7.

(125) With respect to the press tooling, each of the bending die 75, the die (drawing die) 71, and the pad 74 is directly supported by a die base 77 and is individually driven with respect to the die base 77. The press tooling does not use a frame or the like which supports the bending die 75 and a drawing die 71 and hence, the press tooling can be reduced in size as a whole.

(126) FIG. 6(a) to FIG. 6(d) are explanatory views showing another example of the press tooling used in the present invention.

(127) The press tooling has a structure where a sub-base 78 holds a pad 74 and a die 71 (drawing die). Eccentric loads of the pad 74 and the die 71 (drawing die) are received by sub-base 78, which is an integral body with a bending die and hence, deformation of the press tooling can be suppressed compared to the press tooling shown in FIG. 5(a) to FIG. 5(d).

(128) FIG. 7(a) to FIG. 7(d) are explanatory views showing another example of the press tooling used in the present invention, and FIG. 8 is an exploded perspective view of the press tooling.

(129) With respect to the press tooling, a pad 74 is incorporated not in a sub-base 78 but instead in a die base 77, thus avoiding a load of the pad 74 being applied to the sub-base 78. The sub-base receives a load in the vertical direction only from a bending die, which is an integral body with the sub-base and hence, deformation of the sub-base of the press tooling can be suppressed compared to the press tooling shown in FIG. 6(a) to FIG. 6(d).

(130) Any of the press tooling exemplified in FIG. 5(a) to FIG. 5(d), FIG. 6(a) to FIG. 6(d), and FIG. 7(a) to FIG. 7(d) is a press tooling having a structure particularly effective in carrying out the producing method according to the present invention. However, the structure for suppressing deformation of the press tooling is affected by the cost or size of the press tooling. Accordingly, which structure of a press tooling to be used may be suitably decided by taking into account size or shape of a component to be produced and, further, strength of a blank to be used or the like so as to take rigidity required for the press tooling into consideration.

EXAMPLE

(131) FIG. 9(a) to FIG. 9(c) are a front view, a plan view, and a right side view each showing a pressed component 1 to be formed in Comparative Examples 1 to 7 and Inventive Examples 1 to 7 of the present invention. FIG. 10 is a plan view showing the shape of a blank 8 used in the Comparative Examples 1 to 7 and the Inventive Examples 1 to 7 of the present invention. Further, FIG. 11 is a perspective view showing the configuration of a press tooling used in the Comparative Examples 1 to 7.

(132) Results of the Comparative Examples 1 to 7 and the Inventive Examples 1 to 9 of the present invention are collectively shown in Table 1.

(133) TABLE-US-00001 TABLE 1 Radius of Radius of curvature R.sub.2 Presence or Difference in cross- curvature R.sub.1 of curved absence of sectional peripheral Blank tensile Blank sheet Product of concave portion on the material inflow length on inner strength (TS) thickness height H ridge inner side promoting periphery of curve in Formed MPa (mm) (mm) (mm) (mm) portion FIG. 2E state Comparative 1180 1.2 70 20 145 absent — X Example 1 Comparative 1180 1.2 50 10 145 absent — X Example 2 Comparative 1180 1.2 50 20 100 absent — X Example 3 Comparative 1180 1.2 55 15 140 absent — X Example 4 Comparative 1180 1.2 60 15 145 absent — X Example 5 Comparative 1180 1.2 50 15 135 absent — X Example 6 Comparative 1180 1.2 65 20 135 absent — X Example 7 Inventive 1180 1.2 70 20 145 present B < C < D ◯ Example 1 Inventive 1180 1.2 50 10 145 present B < C < D ◯ Example 2 Inventive 1180 1.2 50 20 100 present B < C = D ◯ Example 3 Inventive 1180 1.2 55 15 140 present B < C < D ◯ Example 4 Inventive 1180 1.2 60 15 145 present B < C < D ◯ Example 5 Inventive 1180 1.2 50 15 135 present B < C < D ◯ Example 6 Inventive 1180 1.2 65 20 135 present B < C < D ◯ Example 7 Inventive 1470 1.2 60 15 100 present B < C < D ◯ Example 8 Inventive 1180 1.2 80 15 120 present B < C < D ◯ Example 9

(134) In each of the Comparative Examples 1 to 7 and the Inventive Examples 1 to 7 of the present invention, the L-shaped pressed component 1 having the shape shown in FIG. 9(a) to FIG. 9(c) was produced using, as a blank, a high tensile strength steel sheet having tensile strength of 1180 MPa, and a sheet thickness of 1.2 mm by a draw forming method, which is prior art, or the method of the present invention as a producing method.

(135) In the formed state in Table 1, “O” indicates no occurrence of cracks, and “x” indicates occurrence of cracks or occurrence of necking.

(136) In the Comparative Examples 1 to 7, a draw forming method was used which uses a blank having tensile strength of 1180 MPa. Cracks occurred in each of the Comparative Examples 1 to 7 so that the L-shaped pressed component 1 having the shape shown in FIG. 9(a) to FIG. 9(c) was not formed. On the other hand, in the Inventive Examples 1 to 7 of the present invention, the L-shaped pressed component 1 was able to be preferably formed without causing occurrence of cracks also in the case where a blank having tensile strength of 1180 MPa was used.

(137) FIG. 12 is a plan view showing the shape of a blank used in the Inventive Examples 8, 9 of the present invention. FIG. 13(a) to FIG. 13(c) are a front view, a right side view, and a plan view each showing the shape of an intermediate formed product formed in Inventive Examples 8, 9 of the present invention. FIG. 14(a) to FIG. 14(c) are a front view, a right side view, and a plan view each showing the shape of the pressed component 1 formed in the Inventive Examples 8, 9 of the present invention. FIG. 15 is a perspective view showing one example of the configuration of a press tooling for performing forming by the present invention in the Inventive Examples 8, 9 of the present invention.

(138) The Inventive Examples 8, 9 of the present invention are examples where a complicated shape shown in FIG. 14(a) to FIG. 14(c) was formed using, as a blank, a high strength steel sheet having low ductility, tensile strength of 1180 or 1470 MPa, and a sheet thickness of 1.2 mm.

(139) The blank having the shape shown in FIG. 12 was formed into an intermediate formed product having the shape shown in FIG. 13(a) to FIG. 13(c) using a press tooling having the configuration shown in FIG. 15 and, further, post processing was applied to the intermediate formed product. As a result, the pressed component 1 having the shape shown in FIG. 14(a) to FIG. 14(c) was able to be preferably formed without causing occurrence of cracks and wrinkles.