PRESS FORMING METHOD

Abstract

In a press forming method including pressing a plate material to form an intermediate formed body including an intermediate ridge line portion with an edge radius larger than an edge radius of a ridge line portion of a target formed body, and pressing the intermediate formed body to form the target formed body including the ridge line portion, in a cross section of the intermediate formed body along a direction orthogonal to an extending direction of the ridge line portion, the intermediate formed body includes first and second slack portions on both sides of an included-angle center line, the first and second slack portions bulging more outward in a direction of the edge radius than the target formed body, the included-angle center line bisecting an angle between first and second sides that are located on both sides of the ridge line portion of the target formed body.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Chinese Patent Application No. 202211209997.2 filed on Sep. 30, 2022, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a press forming method for forming a plate material into a predetermined shape.

Description of the Related Art

An outer panel of an automobile is generally produced by press-forming a plate material made of metal. When a ridge line portion having a small radius of curvature is formed in a metal plate by press-forming, wrinkles and cracks can occur. Thus, an advanced technique is required. For example, WO 2019/102972 A1 discloses a press forming method in which a ridge line portion having a small radius of curvature is formed by a first step of forming an intermediate formed body having a radius larger than an edge radius of the ridge line portion and a second step of forming a target formed body from the intermediate formed body.

SUMMARY OF THE INVENTION

In the above-described press forming method, the intermediate formed body is provided so as to bulge outward from the target formed body in advance, thereby securing in advance an elongation allowance for formation of the ridge line portion. However, when the angle (dihedral angle θ) between the planes at the ridge line portion decreases, the elongation in the vicinity of the ridge line portion further increases accordingly. Thus, it is necessary to further increase the bulge of the intermediate formed body accordingly. However, it has been found that if the bulge of the intermediate formed body is too large, when the intermediate formed body is held between the upper die and the blank holder, the intermediate formed body comes into contact with the upper die, which makes it difficult to hold the intermediate formed body between the upper die and the blank holder and also causes damage to the formed product.

It is an object of the present invention to solve the above problems.

According to one aspect of the present disclosure, there is provided a press forming method including: pressing a plate material to form an intermediate formed body including an intermediate ridge line portion with an edge radius larger than an edge radius of a ridge line portion of a target formed body; and pressing the intermediate formed body to form the target formed body including the ridge line portion, wherein, in a cross section of the intermediate formed body along a direction orthogonal to an extending direction of the ridge line portion, the intermediate formed body includes a first slack portion and a second slack portion on both sides of an included-angle center line, the first slack portion and the second slack portion bulging more outward in a direction of the edge radius than the target formed body, the included-angle center line bisecting an angle between a first side and a second side that are located on both sides of the ridge line portion of the target formed body.

In the press forming method of the above aspect, the intermediate formed body includes the slack portions on both sides of the included-angle center line. Thus, the maximum deviation in the stroke direction between the target formed body and the slack portions of the intermediate formed body can be suppressed, and the interference between the intermediate formed body and the upper die can be suppressed.

The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a target formed body formed by a press forming method according to an embodiment;

FIG. 2 is a cross-sectional view of an intermediate formed body according to the embodiment;

FIG. 3A is an explanatory diagram (part 1) illustrating a method for determining a shape of an intermediate formed body of FIG. 2 according to an embodiment;

FIG. 3B is an explanatory diagram (part 2) illustrating the method for determining the shape of the intermediate formed body of FIG. 2 according to the embodiment;

FIG. 4 is an explanatory diagram (part 3) illustrating the method for determining the shape of the intermediate formed body according to the embodiment;

FIG. 5A is an explanatory view of a step of disposing the intermediate formed body of FIG. 3A in a forming die of a second step;

FIG. 5B is an explanatory view of a step of holding the intermediate formed body of FIG. 5A between a blank holder and an upper die;

FIG. 6A is an explanatory view showing a state in which the upper die is being lowered toward a lower die;

FIG. 6B is an explanatory view of a state in which a matching region of the intermediate formed body of FIG. 6A is in contact with the lower die;

FIG. 7A is a cross-sectional view of an intermediate formed body according to a comparative example; and

FIG. 7B is an explanatory view showing interference between the intermediate formed body of FIG. 7A and a forming die (comparative example).

DETAILED DESCRIPTION OF THE INVENTION

A press forming method described below is applied to the manufacture of a roof panel of an automobile or an outer panel 10 of a trunk of an automobile, as shown in FIG. 1, for example. This press forming method is suitable for forming an outer panel 10 having a ridge line portion 16 between flat portions 14 that intersect each other at the internal angle of 90° or less, such as a spoiler 12. In this embodiment, an example of forming a rectangular plate material 18 shown in FIG. 1 will be described. The illustrated plate material 18 has the shape of a target formed body 20 obtained after press forming, and is the outer panel 10 of the trunk. In FIG. 1, the target formed body 20 is shown in a state of being cut in half at a line II-II indicating the center in the vehicle width direction.

The target formed body 20 has a product portion 22 and a discarded portion (waste margin) 24. The product portion 22 is a portion to be used as a product, and the discarded portion 24 is a portion to be cut and removed after press forming. The discarded portion 24 is a band-shaped portion located at the peripheral edge portion of the plate material 18 and surrounding the product portion 22. The product portion 22 has the ridge line portion 16. The ridge line portion 16 has a small radius of curvature (edge radius) of, for example, 2.5 mm to 9 mm, and has a sharp blade-shaped appearance. The ridge line portion 16 is, for example, the spoiler 12 formed integrally with the outer panel 10. The target formed body 20 has a first slope face 26 on one side of the ridge line portion 16 and a second slope face 28 on the other side. The ridge line portion 16 is sandwiched between the first slope face 26 and the second slope face 28. A dihedral angle θ at the ridge line portion 16 between the first slope face 26 and the second slope face 28 is, for example, 30° to 90°.

The plate material 18 used in the press forming method of the present embodiment is, for example, a metal plate such as a steel plate or an aluminum-alloy plate having thicknesses of 0.3 mm to 3 mm. In the press forming method of the present embodiment, a plate material 18 such as a steel plate or an aluminum alloy plate is pressed to form a target formed body 20 having a ridge line portion 16 with a small radius of curvature. In order to form such a target formed body 20, the press forming method according to the present embodiment includes two press forming steps, i.e., a first step and a second step.

In the first step, for example, press forming (drawing) is performed. In the first step, a flat plate material 18 is subjected to press-forming to form an intermediate formed body 32 as shown in FIG. 2.

The intermediate formed body 32 shown in FIG. 2 has an intermediate ridge line portion 30, a matching region 34, and a discarded portion 24. The intermediate ridge line portion 30 has an inner region 36 and slack portions 38. The inner region 36 deviates downward from the target formed body 20 by a maximum deviation (maximum distance, first maximum deviation) Ha in the press stroke direction. The value of the maximum deviation Ha is a value set in accordance with the elongation rate L of the discarded portion 24 at a time of forming the intermediate formed body 32 into the target formed body 20. The value of the maximum deviation Ha is equal to a separation distance H_2nd between the matching region 34 and an upper die 42 in a holding step described later.

The slack portions 38 are respectively disposed on a side portion of the inner region 36 in a first direction and a side portion thereof in a second direction. Each slack portion 38 is connected to the inner region 36 by a smooth curved surface. The matching region 34 is located in a portion surrounding the intermediate ridge line portion 30. That is, the slack portion 38 includes a first slack portion 46 located on a side portion of the inner region 36 in the first direction and a second slack portion 48 located on a side portion of the inner region 36 in the second direction.

The first slack portion 46 and the second slack portion 48 are curved so as to bulge outward in the direction of the edge radius from the target formed body 20. Of them, the first slack portion 46 deviates outward with respect to the first slope face 26 of the target formed body 20. The first slack portion 46 is connected to the inner region 36 by a smooth arc line. A farthest distance between the first slack portion 46 and the first slope face 26 in the press stroke direction is referred to as a maximum deviation (maximum distance, second maximum deviation) Hb1. The maximum deviation Hb1 of the first slack portion 46 is set to a value smaller than the value of the maximum deviation Ha between the inner region 36 and the target formed body 20.

The deviation (distance) between the first slack portion 46 and the target formed body 20 gradually decreases, from the position indicating the maximum deviation Hb1 toward the matching region 34. The first slack portion 46 is connected to the matching region 34 that matches the shape of the target formed body 20, in the vicinity of the outer periphery of the product portion 22. The first slack portion 46 is connected to the discarded portion 24 via the matching region 34.

The second slack portion 48 deviates outward from the second slope face 28 of the target formed body 20. The second slack portion 48 is connected to the inner region 36 by a smooth arc line. A farthest distance between the second slack portion 48 and the second slope face 28 of the target formed body 20 in the press stroke direction is referred to as a maximum deviation (maximum distance, second maximum deviation) Hb2 of the second slack portion 48. The maximum deviation Hb2 of the second slack portion 48 is set to the same value as the maximum deviation Hb1 of the first slack portion 46.

The deviation (distance) between the second slack portion 48 and the target formed body 20 gradually decreases, from the position indicating the maximum deviation Hb2 toward the matching region 34. The second slack portion 48 is connected to the matching region 34 that matches the shape of the target formed body 20, in the vicinity of the outer periphery of the product portion 22.

The maximum inclination angle θ1 of the first slack portion 46 is smaller than the maximum inclination angle θr1 of the first slope face 26 of the target formed body 20. Further, the maximum inclination angle θ2 of the second slack portion 48 is smaller than the maximum inclination angle θr2 of the second slope face 28 of the target formed body 20. Therefore, in the first step (press forming), the intermediate formed body 32 can suppress the elongation of the first slack portion 46 and the second slack portion 48. It is possible to form the intermediate formed body 32 in a state in which the decrease in tension and thickness is suppressed.

The matching region 34 is located in a portion surrounding the outer periphery of the intermediate ridge line portion 30. The matching region 34 is a region, in the product portion 22, that has the same shape as that of the target formed body 20. The intermediate ridge line portion 30 is connected to the discarded portion 24 via the matching region 34.

The discarded portion 24 is positioned on the outer peripheral side of the product portion 22. As shown in FIG. 5B, the discarded portion 24 is a portion to be held between a blank holder 40 and the upper die 42 in the second step. As shown in FIG. 2, the discarded portion 24 is located outside the matching region 34 and surrounds the matching region 34.

The discarded portion 24 includes a step portion 52 and a fixing structure 54. The step portion 52 is adjacent to the outer side of the product portion 22. The step portion 52 is inclined downward at a steeper angle than the first slope face 26 and the second slope face 28. The upper end of the step portion 52 constitutes the upper end of the discarded portion 24. The upper end of the step portion 52 is connected to the matching region 34 of the product portion 22.

The fixing structure 54 is a portion to be held between the blank holder 40 and the upper die 42 in the holding step. The fixing structure 54 is adjacent to an outer side of the step portion 52. The fixing structure 54 extends outwardly at a smaller angle than the inclination angle of the step portion 52. The fixing structure 54 surrounds the outer periphery of product portion 22. The fixing structure 54 is formed with a groove-shaped lock bead 56. Although not particularly limited, the lock bead 56 to be used in the first step may be a round bead having a semicircular cross-sectional shape with an upward concave shape. The lock bead 56 is engaged with a lock concave portion 58 of the blank holder 40 and a lock convex portion 60 of the upper die 42 to prevent the plate material 18 from moving in the direction of the forming surface.

Hereinafter, a method for determining the specific shape of the intermediate formed body 32 of FIG. 2 will be described.

The shape of the intermediate ridge line portion 30 is determined based on the cross-sectional shape of the target formed body 20 shown in FIG. 3A. First, as shown in the drawing, a cross section 62 of the target formed body 20 along a direction orthogonal to the extending direction of the ridge line portion 16 is acquired. Next, in the cross section 62, a tangent line of a portion of the first slope face 26 that is closest to the ridge line portion 16 is obtained as a first side 64. In addition, a tangent line of a portion of the second slope face 28 that is closest to the ridge line portion 16 is obtained as a second side 66. The first side 64 and the second side 66 intersect with each other above the ridge line portion 16. An angle formed by the first side 64 and the second side 66 is an included angle θ.

Next, a straight line passing through an intersection point 68 between the first side 64 and the second side 66 and bisecting the included angle θ is obtained as an included-angle center line 50.

Next, as shown in FIG. 3B, a separation distance H_2nd between the matching region 34 and the upper die 42 in the holding step is determined. As the value of the separation distance H_2nd increases, the maximum deviations Hb1 and Hb2 of the first slack portion 46 and the second slack portion 48 increase. However, if the separation distance H_2nd is excessively large, elongation of the step portion 52 of the discarded portion 24 increases when the target formed body 20 is formed, so that the quality of the outer panel 10 is deteriorated. Therefore, the separation distance H_2nd is set in a range in which the thickness change due to the elongation of the discarded portion 24 is, for example, 20% or less.

Next, as shown in FIG. 3B, a profile line obtained by shifting the cross-sectional shape of the target formed body 20 from the intersection point 68 upward in the press stroke direction by a separation distance H_2nd is set as an imaginary upper-die profile line 70. Further, an imaginary line 76 is obtained. The imaginary line 76 is a straight line that perpendicularly intersects the included-angle center line 50 at a position spaced a separation distance H_2nd downward in the press stroke direction from the intersection point 68.

Next, as shown in FIG. 4, a first tangent line 72 and a second tangent line 74 that pass through the intersection point 68 and are tangent to or intersect the imaginary upper-die profile line 70 are set. The first tangent line 72 is a straight line (tangent line) that touches or intersects, at one point, a portion of the imaginary upper-die profile line 70 that lies on the first direction side, and the second tangent line 74 is a straight line (tangent line) that touches or intersects, at one point, a portion of the imaginary upper-die profile line 70 that lies on the second direction side.

Next, a first circular arc 78 tangent to the imaginary line 76 and the first tangent line 72, and a second circular arc 80 tangent to the imaginary line 76 and the second tangent line 74 are determined. The first circular arc 78 has a tangent point with the imaginary line 76 as one end and a tangent point with the first tangent line 72 as the other end. The radius of curvature R1 of the first circular arc 78 is set such that product quality is guaranteed (i.e., line deviations are prevented) when the first step is performed by using press forming. The radius of curvature R1 has a value larger than the edge radius of the ridge line portion 16 of the target formed body 20. More preferably, the radius of curvature R1 is set such that the point of tangent between the first circular arc 78 and the imaginary line 76 is located in the vicinity of the included-angle center line 50, and the point of tangent between the first circular arc 78 and the first tangent line 72 is located in the vicinity of the point of tangent between the first tangent line 72 and the imaginary upper-die profile line 70.

The second circular arc 80 has a tangent point with the imaginary line 76 as one end and a tangent point with the second tangent line 74 as the other end. The radius of curvature R2 of the second circular arc 80 is set such that product quality is guaranteed (i.e., line deviations are prevented) when the first step is performed by using press forming. The radius of curvature R2 has a value larger than the edge radius of the ridge line portion 16 of the target formed body 20. More preferably, the radius of curvature R2 is set such that the point of tangent between the second circular arc 80 and the imaginary line 76 is located in the vicinity of the included-angle center line 50, and the point of tangent between the second circular arc 80 and the second tangent line 74 is located in the vicinity of the point of tangent between the second tangent line 74 and the imaginary upper-die profile line 70.

By connecting the first circular arc 78 and the second circular arc 80, the shape of the inner region 36, a portion of the first slack portion 46, and a portion of the second slack portion 48 is determined.

Next, a second intersection point 82 at which the first tangent line 72 and a line obtained by shifting the target formed body 20 upward (i.e., the imaginary upper-die profile line 70) intersect each other is obtained. Then, a third circular arc 84 smoothly connecting the second intersection point 82 and the first circular arc 78 is obtained. The center of curvature of the third circular arc 84 is located outside the target formed body 20. The third circular arc 84 is a curved line that is convex toward the inside of the target formed body 20. The radius of curvature R3 of the third circular arc 84 is set such that the third circular arc 84 smoothly connects the first circular arc 78 and the matching region 34 of the first slope face 26.

In addition, a third intersection point 86 at which an extension line of the second tangent line 74 and a line obtained by shifting the target formed body 20 upward (i.e., the imaginary upper-die profile line 70) intersect each other is obtained. Then, a fourth circular arc 88 smoothly connecting the third intersection point 86 and the second circular arc 80 is obtained. The center of curvature of the fourth circular arc 88 is located outside the target formed body 20. The fourth circular arc 88 is a curved line that is convex toward the inside of the target formed body 20. The radius of curvature R4 of the fourth circular arc 88 is preferably set such that the fourth circular arc 88 smoothly connects the second circular arc 80 and the matching region 34 of the second slope face 28.

The shape of the intermediate ridge line portion 30 is determined by connecting the first circular arc 78, the second circular arc 80, the third circular arc 84, and the fourth circular arc 88. Thereafter, the shape of the matching region 34 matching the shape of the product portion 22 of the target formed body 20 is set on the outside of the intermediate ridge line portion 30, and the matching region 34 and the intermediate ridge line portion 30 are connected. Further, the shape of the discarded portion 24 is set outside the matching region 34. The shape of the discarded portion 24 is matched with the discarded portion 24 of the imaginary upper-die profile line 70.

By the above step (shape determination step), the cross-sectional shape of the intermediate ridge line portion 30 is obtained. The cross-sectional shapes of the intermediate ridge line portion 30 as described above are sequentially obtained along the ridge line portion 16, and the entire shape of the intermediate formed body 32 is determined by connecting these cross-sectional shapes.

Next, the second step of the press forming method according to the present embodiment will be described.

The second step is a step of press-forming the intermediate formed body 32 to form the target formed body 20 as shown in FIGS. 5A to 6B. In the second step, the intermediate ridge line portion 30 having a relatively large edge radius is shaped into the ridge line portion 16 having a smaller edge radius.

First, as shown in FIG. 5A, the intermediate formed body 32 is placed into the forming die 90 for the second step. The forming die 90 includes a lower die 44, an upper die 42, and a blank holder 40. In the intermediate formed body 32, the product portion 22 is disposed above the lower die 44, and the discarded portion 24 is disposed above the blank holder 40.

Next, as shown in FIG. 5B, a holding step is performed in which the intermediate formed body 32 is held between the upper die 42 and the blank holder 40. The holding step is performed by using the blank holder 40 and the upper die 42. The upper die 42 is lowered toward the blank holder 40. By lowering the upper die 42, the discarded portion 24 of the intermediate formed body 32 is pressed against the blank holder 40. As a result, the intermediate formed body 32 is held and sandwiched between the blank holder 40 and the upper die 42.

Meanwhile, an intermediate formed body 32A according to a comparative example illustrated in FIG. 7A has a slack portion 38A only on one side of an inner region 36A. When the included angle (dihedral angle) 0 becomes smaller, the slack portion 38A of the intermediate formed body 32A needs to be expanded more largely.

In such an intermediate formed body 32A, the maximum inclination angle θ0 (FIG. 4) of the slack portion 38A is larger than the maximum inclination angle θr2 of the second slope face 28 of the target formed body 20. Therefore, in the intermediate formed body 32A of the comparative example, the elongation rate L and the tension of the intermediate formed body 32A increase (changes in thicknesses) in the first step.

Further, as shown in FIG. 7B, the intermediate formed body 32A having such a large slack portion 38A interferes with the upper die 42 in the holding step. Then, in the second step, the intermediate formed body 32A slides in a state of being in contact with the upper die 42, so that the slack portion 38A is scratched or damaged.

On the other hand, as shown in FIG. 5B, the maximum deviations Hb1 and Hb2 of the first slack portion 46 and the second slack portion 48 of the intermediate formed body 32 of the present embodiment are set to be smaller than the separation distance H_2nd between the matching region 34 and the upper die 42. Therefore, according to the press forming method of the present embodiment, it is possible to prevent interference between the intermediate formed body 32 and the upper die 42 in the holding step, and it is possible to prevent occurrence of scratches or dents in the intermediate formed body 32.

Thereafter, as shown in FIG. 6A, a press forming step is performed in which the intermediate formed body 32 is pressed by the upper die 42 and the lower die 44. The upper die 42 is displaced toward the lower die 44 in the press stroke direction (downward). The intermediate formed body 32 is pressed by the upper die 42 and the lower die 44 and is gradually deformed. The plate material 18 moves from the first slack portion 46 and the second slack portion 48 toward the inner region 36 in accordance with the elongation accompanying the deformation of the intermediate ridge line portion 30. A sufficient amount of the plate material 18 is supplied from the first slack portion 46 and the second slack portion 48 positioned on both sides of the ridge line portion 16. As a result, as shown in FIG. 6B, the target formed body 20 is formed, and the ridge line portion 16 having the acute included angle (dihedral angle) 0 is formed. The press forming method of the present embodiment can prevent occurrence of cracks in the ridge line portion 16 and a decrease in plate thickness of the ridge line portion 16.

The above disclosure is summarized as follows.

An aspect of the present invention is characterized by the press forming method including: the first step of pressing the plate material 18 to form the intermediate formed body 32, 32A including the intermediate ridge line portion 30, 30A with the edge radius larger than the edge radius of the ridge line portion 16 of the target formed body 20; and the second step of pressing the intermediate formed body 32 to form the target formed body 20 including the ridge line portion 16, wherein, in a cross section 62 of the intermediate formed body 32 along a direction orthogonal to the extending direction of the ridge line portion 16, the intermediate formed body 32 includes the first slack portion 46 and the second slack portion 48 on both sides of the included-angle center line 50, the first slack portion and the second slack portion bulging more outward in the direction of the edge radius than the target formed body 20, the included-angle center line bisecting the angle between the first side 64 and the second side 66 that are located on both sides of the ridge line portion 16 of the target formed body 20.

With the above-described press forming method, a large elongation allowance can be secured while suppressing the deviation in the stroke direction, by providing the slack portions bulging outward in the edge radius direction from the target formed body 20 on both sides of the included-angle center line 50. Therefore, it is possible to form the target formed body 20 having a sharp ridge line without causing a crack in the ridge line portion 16 and without causing surface distortion, while avoiding interference between the upper die 42 and the intermediate formed body 32.

In the above-described press forming method, the intermediate formed body 32 may include the inner region 36 at a portion around the included-angle center line 50, the inner region deviating more inward in the direction of the edge radius than the target formed body 20, and the maximum deviation (first maximum deviation) Ha in the press stroke direction between the intermediate formed body 32 and the target formed body 20 in the inner region 36 may be larger than the maximum deviation (second maximum deviation) Hb1, Hb2 in the press stroke direction between the intermediate formed body 32 and the target formed body 20 in each of the first slack portion 46 and the second slack portion 48. In this press forming method, interference between the upper die 42 and the intermediate ridge line portion 30 can be prevented by suppressing bulging of the slack portion. Therefore, in this press forming method, it is possible to prevent the occurrence of scratches caused by the intermediate ridge line portion 30 sliding in a state of being in contact with the upper die 42, and it is possible to form the target formed body 20 without scratches.

The above press forming method may further include the shape determination step of determining the shape of the intermediate formed body 32, and the shape determination step may include: drawing the included-angle center line 50 at a position bisecting the angle between the first side 64 and the second side 66 that are located on the both sides of the ridge line portion 16 of the target formed body 20; drawing the imaginary upper-die profile line 70 obtained by shifting the target formed body 20 upward in the press stroke direction by the maximum deviation Ha; drawing the first tangent line 72 tangent to a portion of the imaginary upper-die profile line 70 that lies on the first direction side, and the second tangent line 74 tangent to a portion of the imaginary upper-die profile line 70 that lies on the second direction side, from the intersection point 68 of the included-angle center line 50, the first side 64, and the second side 66; drawing the imaginary line 76 orthogonal to the included-angle center line 50 at a position located, by the maximum deviation Ha, downward in the press stroke direction from the intersection point 68; determining the first circular arc 78 inscribed in the first tangent line 72 and the imaginary line 76, and the second circular arc 80 inscribed in the imaginary line 76 and the second tangent line 74; determining the third circular arc 84 connecting an end portion of the first circular arc 78 on the first direction side and the matching region 34 on the first direction side that matches the shape of the target formed body 20; and determining the fourth circular arc 88 connecting the end portion of the second circular arc 80 on the second direction side and the matching region 34 on the second direction side that matches the shape of the target formed body 20. This press forming method can achieve both suppression of the elongation rate L of the ridge line portion 16 and prevention of interference between the intermediate ridge line portion 30 and the upper die 42.

In the above press forming method, the intermediate formed body 32 may include the discarded portion 24 held between the blank holder 40 and the upper die 42, and when the intermediate formed body 32 is held between the blank holder 40 and the upper die 42, the separation distance H_2nd in the press stroke direction between the matching region 34 and the upper die 42 may be equal to the maximum deviation Ha. This press forming method can suppress displacement (line deviation) of the intermediate formed body 32 in the forming surface direction, in the second step.

In the above press forming method, the maximum inclination angle θ0 of the intermediate ridge line portion 30 of the intermediate formed body 32 may be smaller than the maximum inclination angle θr1 of the target formed body 20. In this press forming method, tension occurring in the intermediate formed body 32 in the first step can be suppressed.

Note that the present invention is not limited to the embodiment described above, and various configurations can be adopted therein without departing from the essence and gist of the present invention.

Claims

1. A press forming method comprising:

pressing a plate material to form an intermediate formed body including an intermediate ridge line portion with an edge radius larger than an edge radius of a ridge line portion of a target formed body; and

pressing the intermediate formed body to form the target formed body including the ridge line portion,

wherein, in a cross section of the intermediate formed body along a direction orthogonal to an extending direction of the ridge line portion, the intermediate formed body includes a first slack portion and a second slack portion on both sides of an included-angle center line, the first slack portion and the second slack portion bulging more outward in a direction of the edge radius than the target formed body, the included-angle center line bisecting an angle between a first side and a second side that are located on both sides of the ridge line portion of the target formed body.

2. The press forming method according to claim 1, wherein the intermediate formed body includes an inner region at a portion around the included-angle center line, the inner region deviating more inward in the direction of the edge radius than the target formed body, and a first maximum deviation in a press stroke direction between the intermediate formed body and the target formed body in the inner region is larger than a second maximum deviation in the press stroke direction between the intermediate formed body and the target formed body in each of the first slack portion and the second slack portion.

3. The press forming method according to claim 2, further comprising determining a shape of the intermediate formed body, wherein the determining of the shape includes:

drawing the included-angle center line at a position bisecting the angle between the first side and the second side that are located on the both sides of the ridge line portion of the target formed body;

drawing an imaginary upper-die profile line obtained by shifting the target formed body upward in the press stroke direction by the first maximum deviation;

drawing a first tangent line tangent to a portion of the imaginary upper-die profile line that lies on a first direction side, and a second tangent line tangent to a portion of the imaginary upper-die profile line that lies on a second direction side, from an intersection point of the included-angle center line, the first side, and the second side;

drawing an imaginary line orthogonal to the included-angle center line at a position located, by the first maximum deviation, downward in the press stroke direction from the intersection point;

determining a first circular arc inscribed in the first tangent line and the imaginary line, and a second circular arc inscribed in the imaginary line and the second tangent line;

determining a third circular arc connecting an end portion of the first circular arc on the first direction side and a matching region on the first direction side that matches a shape of the target formed body; and

determining a fourth circular arc connecting an end portion of the second circular arc on the second direction side and a matching region on the second direction side that matches the shape of the target formed body.

4. The press forming method according to claim 3, wherein the intermediate formed body includes a discarded portion held between a blank holder and an upper die, and when the intermediate formed body is held between the blank holder and the upper die, a separation distance in the press stroke direction between the matching region and the upper die is equal to the first maximum deviation.

5. The press forming method according to claim 1, wherein a maximum inclination angle of the intermediate ridge line portion of the intermediate formed body is smaller than a maximum inclination angle of the target formed body.