PRESS FORMING APPARATUS AND METHOD FOR PRODUCING PRESS-FORMED ARTICLE

Description

TECHNICAL FIELD

The present invention relates to a press forming apparatus and a method for producing a press-formed article.

BACKGROUND ART

As press-formed articles obtained by performing press forming on a steel sheet, automobile suspension arms can be exemplified (e.g., see Patent Documents 1 and 2). The automobile suspension arms have been required to have both improved performances required of components (strength and rigidity) and reduced weights, from the viewpoints of improving merchantability of automobiles, increasing service lives, recent requests for reducing CO₂ emissions, and increasing cruising distances as conversion toward electrification of motors progresses. As an effective approach to weight reduction of automobile components, integration (omission of component) by integrating functions of peripheral accessories of a press-formed article can be exemplified in addition to reduction in sheet thickness by increasing in strength (increasing in tensile strength) of a material.

For the suspension arms, development of a suspension arm of a collar-integrated structure type in which collar components taking a role of fastening the suspension arm and a vehicle body are omitted by disposing burring portions opposed to each other on a pair of flanges of an arm end portion has been underway.

However, under constraints of a current press forming step for mass production, mass production of such a structure involves difficulty.

The reason for the involvement of difficulty is in formability of the burring portions disposed opposed to each other. Patent Document 1 describes a configuration in which a pair of flanges, that is, vertical wall portions at two locations are disposed opposed to each other for burring. Patent Document 1 discloses press tooling for processing burred holes opposed to each other in two flange parts of a workpiece having a U-shaped section. The press tooling includes a pair of burring punches (32, 33) disposed in such a manner as to sandwich two flange parts (Fb, Fb) and a pair of semicircular slide dies (5, 6), the pair of slide die (5, 6) being disposed between the two flange parts (Fb, Fb) and forming a die hole (27) when combined together. By the burring punches (32, 33) penetrating the two flange parts (Fb, Fb) to reach the die hole (27), two burred holes (B, B) are simultaneously formed in the two flange parts (Fb, Fb). After the burred holes (B, B) are formed, the burring punches (32, 33) are moved in a direction of separating from each other, and the slide dies (5, 6) are moved in a direction of separating from each other. A workpiece (W) is then taken out upward from the burring press tooling. However, such a configuration requires moving the burring press tooling in the various directions. As a result, a design of the press tooling becomes complicated, and as many as at least two to four steps are needed. Therefore, it is difficult to provide such a number of steps under existing constraints.

LIST OF PRIOR ART DOCUMENTS

Patent Document

Patent Document 1: Japanese Patent No. 3674287

Patent Document 2: JP2012-188076

SUMMARY OF INVENTION

Technical Problem

As a method for forming burring portions on a pair of flanges in fewer steps, there is a method that includes performing burring on a flat, sheet-shaped starting material before a stage of performing erecting formation on the pair of flanges, rather than performing the burring process as described in Patent Document 1 (e.g., see Patent Document 2). In such a burring method, the flanges are formed by erecting portions of the flat, sheet-shaped starting material after the burring. Accordingly, a configuration for operating a punch and a die of burring press tooling in many directions is not needed. Thus, the burring step can be performed in one step, thus enabling a burring process in an existing facility under constraints, without leading to a significant increase in cost.

However, the method for forming the pair of flanges by erecting the portions of the starting material after the burring requires the erecting formation to be performed on the locations including the burring portions after the burring to form the pair of flanges. In order to prevent interference between the burring portions (flanges) and press tooling in the erecting step of bending the portions of the starting material to erect the pair of flanges, and to separate a press-formed article from the press tooling after a final step, it is necessary to dispose a hollow location between upper and lower pieces of press tooling. In the hollow location, it is not possible to closely sandwich the press-formed article between the upper and lower pieces of press tooling. As a result, there is a possibility that deviation or distortion in a shape may occur at a location opposed to the hollow location after the erecting formation. Thus, there is a need to solve a problem of keeping a shape accuracy that is required of a suspension arm.

This is not only a problem of a suspension arm. A similar problem lies with press-formed articles to be used as other products. In light of such a background, an objective of the present invention is to provide a press forming apparatus and a method for producing a press-formed article capable of producing a press-formed article having a high dimensional accuracy by a simpler technique.

Solution to the Problem

The present invention has a gist of a press forming apparatus and a method for producing a press-formed article described below.

(1) A press forming apparatus including:

• • a die, a punch, and a die pad, wherein
  • the die pad is disposed inside the die,
  • the die pad is disposed opposed to the punch,
  • at a bottom dead center, surfaces of the die pad and the punch have a hole, the surfaces extending in a pressing direction,
  • at the bottom dead center, the surfaces face the die, and an edge portion of the hole is formed by the die pad and the punch.

(2) A method for producing a press-formed article, the method using the press forming apparatus according to (1), the method including:

• • sandwiching a workpiece between the punch and the die pad; and
  • bringing the punch and the die close to each other in the pressing direction, wherein
  • the workpiece includes a convex portion on a surface of the workpiece on the punch side,
  • at the bottom dead center, the convex portion is located inside the hole,
  • around the convex portion located inside the hole, the workpiece is sandwiched between the die and the surfaces of the die pad and the punch, the surfaces extending in the pressing direction, and
  • the workpiece is absent between the die pad and the convex portion located inside the hole.

Advantageous Effect of Invention

According to the present invention, it is possible to produce a press-formed article having a high dimensional accuracy by a simpler technique.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view of a press-formed article according to an embodiment of the present invention.

FIG. 2(A) is a front view of the press-formed article, FIG. 2(B) is a plan view of the press-formed article, and FIG. 2(C) is a side view of the press-formed article.

FIG. 3(A) is a schematic plan view of a blank. FIG. 3(B) is a schematic plan view of an intermediate formed article.

FIG. 4 is a schematic perspective view illustrating the intermediate formed article and a press forming apparatus for burring.

FIG. 5(A) is a schematic plan view of an intermediate formed article before a trimming process, and FIG. 5(B) is a schematic plan view of an intermediate formed article after the trimming process.

FIG. 6 is a schematic perspective view of main parts of a press forming apparatus for a first erecting step and the intermediate formed article.

FIG. 7(A) and FIG. 7(B) are each a cross-sectional view of a workpiece, and FIG. 7(C) is a diagram illustrating a modification of the workpiece.

FIG. 8 is a schematic perspective view of main parts of a press forming apparatus for a second erecting step and the workpiece.

FIG. 9 is a side view of the main parts of the press forming apparatus for the second erecting step at a bottom dead center.

FIG. 10(A) to FIG. 10(C) are each a longitudinal sectional view of a modification of the main parts of the press forming apparatus for the second erecting step at the bottom dead center, taken along a longitudinal direction and a height direction.

FIG. 11 is a diagram illustrating the main parts of the press forming apparatus for the second erecting step in a form of a cross section of the press forming apparatus, illustrating a state where the press forming apparatus is at a top dead center.

FIG. 12 is a diagram illustrating the main parts of the press forming apparatus for the second erecting step in a form of a cross section of the press forming apparatus, illustrating a state where the press forming apparatus is at the bottom dead center.

FIG. 13 is a diagram illustrating a modification of both end portions of a wide portion in the press forming apparatus for the second erecting step.

FIG. 14 is a diagram illustrating main parts of a press forming apparatus for an erecting step relating to a modification in a form of a cross section of the press forming apparatus, illustrating a state where the press forming apparatus is at a bottom dead center PL.

DESCRIPTION OF EMBODIMENTS

A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. In the present description and drawings, components having substantially the same functions and structures are denoted by the like reference characters, and the redundant description thereof will be omitted.

Embodiment

First, a press-formed article according to an embodiment of the present invention will be described. FIG. 1 is a schematic perspective view of a press-formed article 60 according to the embodiment of the present invention. FIG. 2(A) is a front view of the press-formed article 60, FIG. 2(B) is a plan view of the press-formed article 60, and FIG. 2(C) is a side view of the press-formed article 60.

<Configuration of Press-Formed Article 60>

As illustrated in FIG. 1 to FIG. 2(C), the press-formed article 60 is a structural component of an automobile. Examples of such a structural component include a chassis component. Examples of the chassis component include an arm component or a link component of a suspension component, specifically a lower arm, a front upper arm, a rear upper arm, a trailing arm, and the like.

The description of the present embodiment will be given of a mode in which the press-formed article 60 is a suspension arm, for example. More specifically, the description of the present embodiment will be given of a mode in which the press-formed article 60 is a rear lower arm, for example.

In the present embodiment, the press-formed article 60 is a sheet-based member that is formed by subjecting a steel sheet to press forming a plurality of times and has an open section. As a steel sheet to be formed into the press-formed article 60, a high-strength hot-rolled steel sheet, a hot-dip galvanized hot-rolled steel sheet, and the like can be exemplified. These steel sheets have tensile strengths of, for example, 440 MPa or more, for example, 590 MPa or more, or for example, 780 MPa or more. With an increase in the tensile strength of the steel sheet, formability in forming the press-formed article 60 tends to decrease. The press-formed article 60 has a sheet thickness of, for example, 1.6 mm to 4.0 mm.

In the present embodiment, the press-formed article 60 is formed into a long, narrow, straight shape extending in a longitudinal direction X1, which is a direction corresponding to a right-left direction of a vehicle. Note that a shape of the press-formed article 60 is not limited to a straight shape, and the press-formed article 60 may be formed into another shape such as a groove shape or an A shape.

The press-formed article 60 includes a body 62 that has a groove-shaped cross section and includes a base 61 and a pair of vertical walls 63A and 63B connected to the base 61, a pair of flanges 64A and 64B adjacent to one sides of the pair of vertical walls 63A and 63B in the longitudinal direction X1 and disposed opposed to each other, a pair of convex portions 65A and 65B respectively provided on opposed surfaces 64aA and 64aB of the pair of flanges 64A and 64B, a pair of flanges 66A and 66B adjacent to the other sides of the pair of vertical walls 63A and 63B in the longitudinal direction X1 and disposed opposed to each other, and a pair of convex portions 67A and 67B respectively provided on opposed surfaces 67aA and 67aB of the pair of flanges 66A and 66B. The vertical walls mean walls that stand with respect to the base. The vertical walls are not limited to walls that are upright with respect to the base.

Since the body 62 has a groove-shaped section, the press-formed article 60 is a member having an open section. The open section refers to a cross section perpendicular to the longitudinal direction X1 that has no closed shape and has end portions in a circumferential direction of a shape of the section. The body 62 need only be a groove shape. Examples of the groove shape include a shape with flanges, such as a section in a hat shape, or a shape having a curved groove bottom portion, such as a section in a U shape.

In the present embodiment, the base 61 is formed into a shape that is straight and flat in the longitudinal direction X1. Note that the base 61 need not be a straight shape. A cross section of the base 61 may be, for example, a C shape. The base 61 may include a portion that is inclined toward one side of the base 61 in a sheet thickness direction as the base 61 extends to its end portion in the longitudinal direction X1. One end of the base 61 in the longitudinal direction X1 includes a base edge portion 61a that is adjacent to the pair of flanges 64A and 64B. A cross section passing across the base edge portion 61a is formed into a shape in which a curved portion 61b, a straight-line portion 61c, and a curved portion 61d are connected together. End portions of the base edge portion 61a in a transverse direction Y1, which is perpendicular to the longitudinal direction X1, are boundary portions between the base 61 and the flanges 64A and 64B. A length of the base edge portion 61a between the pair of vertical walls 63A and 63B is a length Lp. The pair of vertical walls 63A and 63B extend from a pair of end portions of the base 61 in the transverse direction Y1.

The pair of vertical walls 63A and 63B and the base 61 form a groove portion. Furthermore, a cross section passing across the groove portion is an open section. In the present embodiment, an angle θ of each of the vertical walls 63A and 63B with respect to the base 61 need only be within the range of 0 degrees<θ≤90 degrees. In the present embodiment, the vertical walls 63A and 63B extend, between a front surface 61e and a back surface 61f of the base 61, on the back surface 61f side (downward in a height direction Z1).

In the present embodiment, the pair of flanges 64A and 64B are disposed parallel to each other. In the present embodiment, angles of the flanges 64A and 64B with respect to the base 61 are the same as the angle θ. The angles formed between the base 61 and the flanges 64A and 64B need not be the same, and the flanges 64A and 64B need not be parallel to each other. In the present embodiment, the flanges 64A and 64B are each formed in an annular shape in side view. However, the flanges 64A and 64B each may be in an elliptic ring shape or in a polygonal ring shape. That is, there is no particular constraint on a contour shape of each of the flanges 64A and 64B.

In the present embodiment, the height direction Z1 is a direction that is perpendicular to the longitudinal direction X1 and the transverse direction Y1. As a gap 68 between the pair of flanges 64A and 64B is visible in plan view, at least a part of between the pair of flanges 64A and 64B is uncovered with the base 61. That is, in the longitudinal direction X1, an edge portion 61a of the base 61 is cut at a position inward of a location where the convex portions 65A and 65B are disposed. In producing the press-formed article 60, when a pair of planned flange portions are formed into a pair of flanges 64A and 64B by bending a pair of planned vertical walls with respect to a planned base portion in a workpiece, which is a steel sheet starting material, this configuration enables pieces of press tooling to be inserted between both sides of each of the pair of flanges 64A and 64B in the height direction Z1. As a result, a distance between the pair of flanges 64A and 64B can be set to a desired value with high accuracy. The planned portions mean regions of the workpiece to be specific regions of the press-formed article 60. A method for producing the press-formed article 60 will be described later in detail. It is preferable that, between upper and lower end portions of the pair of flanges 64A and 64B on the base 61 side in the height direction ZI is uncovered with the base 61, thus being opened in the height direction Z1. More preferably, the entire gap 68 between the pair of flanges 64A and 64B in the longitudinal direction X1 is opened in the height direction Z1 as in the present embodiment.

The pair of convex portions 65A and 65B are provided for attaching bushings, which are not illustrated, to the press-formed article 60. The bushings are connected to a vehicle body with bolts and the like, which are not illustrated. In the present embodiment, the convex portions 65A and 65B are formed integrally with the respective flanges 64A and 64B by burring and extend from edge portions of hole portions formed in the respective flanges 64A and 64B in sheet thickness directions of the respective flanges 64A and 64B. The convex portions 65A and 65B are each formed into a cylindrical shape between the flanges 64A and 64B. In the present embodiment, the pair of convex portions 65A and 65B are separated from each other.

In the present embodiment, the press-formed article 60 is formed in a shape symmetrical in the longitudinal direction X1. Therefore, configurations of the pair of flanges 66A and 66B and the pair of convex portions 67A and 67B are the same as configurations of the pair of flanges 64A and 64B and the pair of convex portions 65A and 65B and thus will not be described in detail.

<Method for Producing Press-Formed Article and Configuration of Press Forming Apparatus for Producing Press-Formed Article>

Next, an example of a method for producing the press-formed article 60 and an example of a configuration of press forming apparatuses 100, 200, and 300 for producing the press-formed article 60 will be described. The method for producing the press-formed article 60 includes a blanking step of cutting out a blank from a steel sheet (step S1), a starting hole forming step of forming starting holes for the burring on the blank (step S2), a burring step of subjecting an intermediate formed article formed with the starting holes to a burring process to form convex portions (step S3), a trimming step of trimming off a circumference of the intermediate formed article, which is a burred material formed with the convex portions (step S4), a first erecting step of shaping the intermediate formed article subjected to the trimming process into a workpiece of the press-formed article 60 (step S5), and a second erecting step of shaping the workpiece into the press-formed article 60 (step S6). Note that, in the present embodiment, the first erecting step (step S5) and the second erecting step (step S6) will be also collectively referred to as an erecting step. The erecting step is a step of forming the workpiece from the intermediate formed article and further forming the workpiece into the press-formed article 60. The steps need not be necessarily performed in a consecutive manner. For example, the erecting step may be performed on a purchased blank.

In the present embodiment, an example including the trimming step (step S4) will be described as the method for producing the press-formed article 60. However, the trimming step (step S4) may be omitted. For example, the trimming step (step S4) can be omitted in a case where the press-formed article 60 has such a simple shape that the press-formed article 60 can be formed without occurrence of underfill (a shortage of the material) or a surplus even when the blank is cut out along a precise line corresponding to the shape of the press-formed article 60 in the blanking step (step S1). Therefore, it suffices that the trimming step (step S4) is applied as necessary.

In the present embodiment, an example including the first erecting step (step S5) will be described as the method for producing the press-formed article 60. However, the first erecting step (step S5) may be omitted. For example, instead of omitting the first erecting step (step S5), the press-formed article 60 may be formed in one step from the intermediate formed article subjected to the trimming process via the workpiece by subjecting the intermediate formed article to a process to be described in description of the second erecting step (step S6). Therefore, it suffices that the first erecting step (step S5) is applied as necessary based on, for example, a difficulty in forming the press-formed article 60.

<blanking Step (Step S1)>

In the blanking step, a steel sheet not illustrated is first prepared. From this steel sheet, a blank 10 is cut out by a pressing process or the like. FIG. 3(A) is a schematic plan view of the blank 10. The blank 10 has a contour shape that is substantially the same as a shape into which the press-formed article 60 is unfolded, and assumes a shape in which locations to form the convex portions 65A, 65B, 67A, and 67B are flat.

<Starting Hole Forming Step (Step S2)>

In the starting hole form process, starting holes 11A, 11B, 12A, and 12B are formed in the blank 10. Specifically, as illustrated in FIG. 3(B), the starting holes 11A, 11B, 12A, and 12B are formed with a punch, a die, and the like, which are not illustrated, at locations at which the convex portions 65A, 65B, 67A, and 67B are to be formed. The blank 10 is thereby formed into an intermediate formed article 20. FIG. 3(B) is a schematic plan view of the intermediate formed article 20. Note that the intermediate formed article is synonymous with a workpiece. However, in the present embodiment, a component to be processed in the second erecting step of forming the press-formed article 60 will be referred to as the workpiece, and a component to be processed into the workpiece will be referred to as the intermediate formed article.

<Burring Step (Step S3)>

In the burring step, the intermediate formed article 20 is subjected to burring with a press forming apparatus 100 for the burring. FIG. 4 is a schematic perspective view illustrating the intermediate formed article 20 and the press forming apparatus 100 for the burring. In the burring step, the pair of convex portions 65A and 65B and the pair of convex portions 67A and 67B are formed on the intermediate formed article 20, which is a starting material of the press-formed article 60, and the intermediate formed article 20 is thereby formed into an intermediate formed article 30, which is a burred material.

As illustrated in FIG. 4, the press forming apparatus 100 includes a plurality of pieces of first press tooling 110 (punches), a piece of second press tooling 120 (a blank holder), and a piece of third press tooling 130 (a die).

In the burring step, the intermediate formed article 20 is placed on the piece of third press tooling 130 of the press forming apparatus 100. Next, the intermediate formed article 20 is held to the piece of third press tooling 130 by the piece of second press tooling 120. In this state, the pieces of first press tooling 110 are displaced toward the piece of third press tooling 130. This causes the plurality of pieces of first press tooling 110 to perform the burring process on the starting holes 11A, 11B, 12A, and 12B of the intermediate formed article 20, thus forming the convex portions 65A, 65B, 67A, and 67B in both end portions of the intermediate formed article 20 in the longitudinal direction. By performing the burring process on the intermediate formed article 20 with the press forming apparatus 100, the intermediate formed article 20 is formed into the intermediate formed article 30 as illustrated in FIG. 5(A). FIG. 5(A) is a schematic plan view of the intermediate formed article 30 before the trimming process.

<Trimming Step (Step S4)>

In the trimming step, the circumference of the intermediate formed article 30 is trimmed off. The trimming may be performed with a press forming apparatus not illustrated or may be performed with a cutter not illustrated. There is no limitation on a specific method for the process. Through the trimming step, the intermediate formed article 30 is formed into an intermediate formed article 40 as illustrated in FIG. 5(B). FIG. 5(B) is a schematic plan view of the intermediate formed article 40 after the trimming process. Portions of the intermediate formed article 30 before the trimming process that are cut in the trimming step are illustrated with two-dot-dash lines in FIG. 5(B). A shape of the intermediate formed article 40 corresponds to a shape of a development into which the press-formed article 60 is unfolded into a planar shape.

<First Erecting Step (Step S5)>

In the first erecting step, press forming (first erecting formation) is performed on the intermediate formed article 40 with a press forming apparatus 200 for the first erecting step. FIG. 6 is a schematic perspective view of main parts of the press forming apparatus 200 for the first erecting step and the intermediate formed article 40. FIG. 7(A) and FIG. 7(B) are each a cross-sectional view of a workpiece 50. As illustrated in FIG. 1, FIG. 6, FIG. 7(A) and FIG. 7(B), and FIG. 8 described later, in the first erecting step, the workpiece 50 is formed from the intermediate formed article 40.

The workpiece 50 includes a planned base portion 51 serving as a planned portion for the base 61, a pair of planned vertical walls 53A and 53B that are formed as planned portions for the pair of vertical walls 63A and 63B and are erected from the planned base portion 51, and a pair of planned flange portions 54A and 54B serving as planned portions for the pair of flanges 64A and 64B. In the cross section of the workpiece 50, the planned base portion 51 is, for example, in a curved shape that is convex toward one side in the height direction Z1. The pair of planned vertical walls 53A and 53B are flat-shape portions that are adjacent to both ends of the planned base portion 51 in the transverse direction Y1 of the workpiece 50. The pair of planned flange portions 54A and 54B are flat-shape portions that are adjacent to the pair of planned vertical walls 53A and 53B in the longitudinal direction X1. In the cross section, both ends of the planned base portion 51 in the transverse direction Y1 are curved, which makes the pair of planned flange portions 54A and 54B, which are flush with the planned vertical walls 53A and 53B, opposed to each other in the transverse direction Y1. In the pair of planned flange portions 54A and 54B, the convex portions 65A and 65B are disposed on opposed surfaces 54aA and 54aB of the pair of planned flange portions 54A and 54B, respectively. The workpiece 50 may further include a pair of planned flange portions 56A and 56B that are formed into shapes symmetrical in the longitudinal direction X1 of the workpiece 50 and serve as planned portions for the pair of flanges 66A and 66B. In the cross section of the workpiece 50, a distance between the planned vertical walls 53A and 53B may increase with distance from the planned base portion 51.

Press tooling of the press forming apparatus 200 has a configuration in which a plurality of pieces of press tooling each having a shape that is long and narrow in a longitudinal direction X2 as a horizontal direction and short in a transverse direction Y2 as a horizontal direction perpendicular to the longitudinal direction X2 are arranged in a height direction Z2, which is perpendicular to the longitudinal direction X2 and the transverse direction Y2. The longitudinal direction X2, the transverse direction Y2, and the height direction Z2 respectively match the longitudinal direction X1, the transverse direction Y1, and the height direction ZI of the workpiece 50 in the press forming apparatus 200 when the intermediate formed article 40 is formed into the workpiece 50 with the press forming apparatus 200. The height direction, an upward direction, and a downward direction are included in a pressing direction. The horizontal direction is a direction perpendicular to the pressing direction. The pressing directions are represented in this manner because the pressing direction is often a vertical direction. However, the horizontal direction in the present disclosure does not necessarily mean a direction perpendicular to the vertical direction.

Note that pieces of the press tooling of the press forming apparatus 200 each may be formed into a shape symmetrical in the longitudinal direction X2. In addition, an operation by the pieces of the press tooling of the press forming apparatus 200 to form the intermediate formed article 40 into the workpiece 50 is also symmetrical in the longitudinal direction X2. Accordingly, description of a pressing operation by the press forming apparatus 200 will be given mainly of a configuration on one side in the longitudinal direction X2, and detailed description of a configuration on the other side in the longitudinal direction X2 will be omitted.

The press forming apparatus 200 includes a piece of first press tooling 210 (a lower piece of press tooling, a punch), a piece of second press tooling 220 (a die pad), and pieces of third press tooling 230 (dies).

The piece of first press tooling 210 includes a punch convex portion 212. The punch convex portion 212 is fixed to a bed not illustrated. The punch convex portion 212 is a convex portion extending along the longitudinal direction X2 and is erected from the bed toward the second press tooling 220.

The punch convex portion 212 includes a planned-base-portion forming portion 215.

The planned-base-portion forming portion 215 is provided for forming the planned base portion 51 of the workpiece 50 from the intermediate formed article 40. The planned-base-portion forming portion 215 is formed into a shape that extends along a shape of a back surface of the planned base portion 51.

At locations of the punch convex portion 212 that face the convex portions 65A and 65B, concave portions 218A and 218B are formed on a pair of side surfaces of the punch convex portion 212 in the transverse direction Y2. In the transverse direction Y2, a distance between the concave portions 218A and 218B is shorter than a width of the planned-base-portion forming portion 215. When the intermediate formed article 40 is subjected to the press forming by the press forming apparatus 200, this configuration causes front ends of the convex portions 65A and 65B to enter the corresponding concave portions 218A and 218B, thus preventing the front ends from coming into contact with the punch convex portion 212.

The piece of second press tooling 220 is provided for holding the intermediate formed article 40 to the first press tooling 210. The piece of second press tooling 220 includes a holding portion 222 for holding the planned base portion 51 to the planned-base-portion forming portion 215.

The pieces of third press tooling 230 perform the burring process on the intermediate formed article 40 by moving toward the first press tooling 210 with the piece of first press tooling 210 and the piece of second press tooling 220 sandwiching the intermediate formed article 40.

The pieces of third press tooling 230 include a pair of divided bodies 231A and 231B that are arranged in the transverse direction Y2. The pair of divided bodies 231A and 231B include a pair of planned-vertical-wall forming portions 232A and 232B and a pair of planned-flange-portion forming portions 233A and 233B. This is not limiting. The third press tooling 230 may be a single piece of press tooling that includes regions corresponding to the divided bodies 231A and 231B. The piece of second press tooling 220 is disposed between the divided bodies 231A and 231B. In a case where the third press tooling 230 is a single piece of press tooling, the piece of second press tooling 220 is disposed inside the third press tooling 230. In both cases, the piece of second press tooling 220 is disposed inside the third press tooling 230.

The pair of planned-vertical-wall forming portions 232A and 232B are provided for forming the pair of planned vertical walls 53A and 53B from the intermediate formed article 40. The pair of planned-vertical-wall forming portions 232A and 232B are formed on inner surfaces of the pair of divided bodies 231A and 231B and include surfaces that are inclined with respect to the height direction Z1. The pair of planned-flange-portion forming portions 233A and 233B are provided for forming the pair of planned flange portions 54A and 54B. The pair of planned-vertical-wall forming portions 232A and 232B are formed on inner surfaces of the pair of divided bodies 231A and 231B and include surfaces that are inclined with respect to the height direction Z1.

In the press forming apparatus 200, the intermediate formed article 40 is placed on the punch convex portion 212 of the piece of first press tooling 210, and then the piece of second press tooling 220 is moved toward the first press tooling 210 by an actuator not illustrated. As a result, the intermediate formed article 40 is sandwiched between the piece of first press tooling 210 and the piece of second press tooling 220. Next, the third press tooling 230 is moved toward the first press tooling 210 to a predetermined bottom dead center by an actuator not illustrated. This causes the pair of divided bodies 231A and 231B of the pieces of third press tooling 230 to pass by both sides of the piece of second press tooling 220 in the transverse direction Y2 and to move toward the first press tooling 210. At this time, the pair of planned-vertical-wall forming portions 232A and 232B press down, toward the first press tooling 210, portions of the intermediate formed article 40 that protrude from the punch convex portion 212 in the transverse directions Y2, thus forming the pair of planned vertical walls 53A and 53B. In addition, the pair of planned-flange-portion forming portions 233A and 233B press down, toward the first press tooling 210, portions of the intermediate formed article 40 that protrude from the punch convex portion 212 in the transverse directions Y2, thus forming the pair of planned flange portions 54A and 54B. Furthermore, the piece of first press tooling 210, the piece of second press tooling 220, and the pieces of third press tooling 230 cooperatively form the planned base portion 51. Note that the press forming apparatus 200 also forms the pair of planned flange portions 56A and 56B that are the same as the pair of planned flange portions 54A and 54B. As a result, the intermediate formed article 40 is formed into the workpiece 50.

In the workpiece 50, an angle θ2 of the planned vertical walls 53A and 53B and the planned flange portions 54A, 54B, 57A, and 57B with respect to the height direction Z1 is set within the range of 90 degrees or less as appropriate in accordance with a tensile strength, a sheet thickness, and the like of the workpiece 50. Note that the workpiece 50 illustrated in FIG. 7(A) and FIG. 7(B), and FIG. 7(C) described later is merely an example of the workpiece. A space between the pair of planned flange portions 54A and 54B is opened on both sides in the height direction ZI (a pressing direction P described later). Likewise, a space between the pair of planned flange portions 56A and 56B is opened on both sides in the pressing direction P. The planned base portion 51 includes a base-planned-portion edge portion 51a that is adjacent to the pair of planned flange portions 54A and 54B. In the present embodiment, the base-planned-portion edge portion 51a is formed in a curved shape having a predetermined curvature radius as viewed in the longitudinal direction X1.

As viewed in the longitudinal direction X1, the planned base portion 51 is formed into, for example, a single arch shape illustrated in FIG. 7(A) and FIG. 7(B). The planned base portion 51 may be formed into a shape that includes arch shapes on both sides of the planned base portion 51 in the transverse direction Y1, as in a modification illustrated in FIG. 7(C). The arch shapes are each formed into, for example, a shape that is convex toward the front surface side of the planned base portion 51 (an upper side). In the shape illustrated in FIG. 7(C), the arch shapes are formed at both ends of the planned base portion 51 in the transverse direction Y1, and one ends of the arch shapes are coupled together by a straight-line shape. In the present embodiment, as viewed in the longitudinal direction X1, a length of the base-planned-portion edge portion 51a between the pair of planned vertical walls 53A and 53B is a length Lq.

As mentioned above, the length of the base edge portion between the pair of vertical walls 63A and 63B is the length Lp (FIG. 2(C)). Taking FIG. 2(C), FIG. 7(A), and FIG. 7(C) as an example, it is preferable that 1.0<Lq/Lp<1.2 be satisfied. If Lq/Lp falls below a lower limit of the range, a heavy tensile load tends to be produced in the base-planned-portion edge portion 51a for planned base portion 51 when the workpiece 50 is formed into the press-formed article 60. This causes wall opening, in which a distance between front ends of the pair of vertical walls 63A and 63B increases, which degrades a dimensional accuracy of the press-formed article 60. On the other hand, if Lq/Lp exceeds an upper limit of the range, the planned base portion 51 deforms in such a manner as to extend significantly in the transverse direction Y1 when the workpiece 50 is formed into the press-formed article 60. As a result, wall closing, in which front ends of the pair of vertical walls 63A and 63B in the height direction Z1 become excessively close to each other, occurs, which tends to degrade the dimensional accuracy of the press-formed article 60. In contrast, by setting Lq/Lp within the range, the planned base portion 51 moderately deforms such that a difference in linear length (Lq-Lp) is dissolved (becomes zero) when the workpiece 50 is formed into the press-formed article 60. As a result, the wall opening (a warp amount S) can be prevented, and a tensile stress that results from the wall opening and is produced on an outer side of a bend can be relieved. The warp amount S is a value indicating how long the front end of the vertical wall 63A or the front end of the vertical wall 63B is shifted in position in the transverse direction Y1 from a position where it should be. Furthermore, in the present embodiment, a compressive stress that is produced on an inner side of a bend of the press-formed article 60 can be made such that the compressive stress is increased compared to a tensile stress produced on the outer side of the bend, and thus the wall opening can be further prevented. According to an example of a computer simulation conducted by the present inventors, under conditions of the press-formed article 60 having a tensile strength of 780 MPa and a sheet thickness=2.3 mm, in a case of Lq/Lp=1.1, the warp amount S (an amount of wall opening) was able to be reduced by about 30% at maximum compared to a case of Lq/Lp=1.0 (no difference in linear length).

<Second Erecting Step (Step S6)>

In the second erecting step, press forming (second erecting formation) is performed on the workpiece 50 with the press forming apparatus 300 for the second erecting step. FIG. 8 is a schematic perspective view of main parts of the press forming apparatus 300 for the second erecting step and the workpiece 50. FIG. 9 is a side view of the main parts of the press forming apparatus 300 at a bottom dead center PL. FIG. 10(A) to FIG. 10(C) are each a longitudinal sectional view of a modification of the main parts of the press forming apparatus 300 at the bottom dead center, taken along the longitudinal direction X2 and the height direction Z2. FIG. 11 is a diagram illustrating the main parts of the press forming apparatus 300 in a form of a cross section of the press forming apparatus 300, illustrating a state where the press forming apparatus 300 is at a top dead center PU. FIG. 12 is a diagram illustrating the main parts of the press forming apparatus 300 in a form of a cross section of the press forming apparatus 300, illustrating a state where the press forming apparatus 300 is at the bottom dead center PL. As illustrated in FIG. 8 to FIG. 12, in the second erecting step, a press-formed article 60 is formed from the workpiece 50.

In the press forming apparatus 300, positions of a punch 310, a die pad 320, and a die 330 when the members 310, 320, and 330 are closest to one another constitute the bottom dead center PL. The positions of the punch 310, the die pad 320, and the die 330 when the members 310, 320, and 330 are separated farthest from one another constitute the top dead center PU. In the present embodiment, in the pressing direction P, a direction from the die pad 320 toward the punch 310 is a first direction P1, and an opposite direction to the first direction P1 is a second direction P2. In the present embodiment, the first direction P1 is the downward direction, and the second direction P2 is the upward direction.

Press tooling of the press forming apparatus 300 has, as with the press forming apparatus 200, a configuration in which a plurality of pieces of press tooling each having a shape that is long and narrow in a longitudinal direction X2 and short in a transverse direction Y2 are arranged in a height direction Z2. The longitudinal direction X2, the transverse direction Y2, and the height direction Z2 respectively match the longitudinal direction X1, the transverse direction Y1, and the height direction Z1 of the workpiece 50 when the workpiece 50 is placed in the press forming apparatus 300. In the present embodiment, the height direction Z2 matches the pressing direction P in the press forming apparatus 300.

Note that pieces of the press tooling of the press forming apparatus 300 each may be formed into a shape symmetrical in the longitudinal direction X2. In addition, an operation by the pieces of the press tooling of the press forming apparatus 300 to form the workpiece 50 into the press-formed article 60 is also symmetrical in the longitudinal direction X2. Accordingly, description of a pressing operation by the press forming apparatus 300 will be given mainly of a configuration on one side in the longitudinal direction X2, and detailed description of a configuration on the other side in the longitudinal direction X2 will be omitted.

The press forming apparatus 300 includes the punch 310, the die pad 320, and the die 330. In the present embodiment, the die pad 320 and the die 330 move in the pressing direction P with respect to the punch 310.

The punch 310 includes a punch body 312. The punch body 312 is fixed to a bed not illustrated. The punch body 312 is a convex portion extending along the longitudinal direction X2.

The punch body 312 includes first flange forming portions 313A and 313B, a stopper 314, a base forming portion 315, and vertical wall forming portions 316A and 316B.

The first flange forming portions 313A and 313B are portions that face, in the transverse direction Y2, the planned flange portions 54A and 54B of the workpiece 50 placed on the punch 310. Receiving a part of the opposed surfaces 54aA and 54aB of the planned flange portions 54A and 54B, the first flange forming portions 313A and 313B form the planned flange portions 54A and 54B into the flanges 64A and 64B. The first flange forming portions 313A and 313B are provided at a pair of end surfaces of the punch body 312 in the transverse direction Y2. In the present embodiment, the first flange forming portions 313A and 313B receives the opposed surfaces 54aA and 54aB (inner surfaces) of the pair of planned flange portions 54A and 54B in the second erecting step. In the present embodiment, the first flange forming portions 313A and 313B are flat surfaces extending along the pressing direction P and are perpendicular to the transverse direction Y2. The first flange forming portions 313A and 313B are disposed on one end side of the punch body 312 in the longitudinal direction X2 (on the right side of FIG. 8). In the present embodiment, the first flange forming portions 313A and 313B are configured in such a manner as to respectively come into contact with the planned flange portions 54A and 54B over an angular range corresponding to most of the planned flange portions 54A and 54B in a circumferential direction (about ⅔ of 360 degrees) in the press forming. In addition, the first flange forming portions 313A and 313B are provided at the punch 310 that is a lower piece of press tooling of the press forming apparatus 300, and thus, in the pressing direction P, the first flange forming portions 313A and 313B are disposed between one ends (lower ends) of the pair of planned flange portions 54A and 54B and receive the planned flange portions 54A and 54B.

The punch body 312 is formed with concave portions 318A and 318B on its pair of end surfaces in the transverse direction Y2 at locations adjacent to the first flange forming portions 313A and 313B. In the transverse direction Y2, a distance (width) between the concave portions 318A and 318B is shorter than a width of the base forming portion 315 and shorter than a distance between the first flange forming portions 313A and 313B. In the punch body 312, at the locations at which the concave portions 318A and 318B are formed, the stopper 314 is formed.

In the press forming by the press forming apparatus 300, the stopper 314 is between the convex portions 65A and 65B of the workpiece 50. The stopper 314 receives the front ends of the convex portions 65A and 65B, thus functioning as a positioning member for the convex portions 65A and 65B in the second erecting step. More specifically, a pair of end surfaces of the stopper 314 in the transverse direction Y2 receive the convex portions 65A and 65B. In the present embodiment, the pair of end surfaces of the stopper 314 are surfaces extending along pressing direction P and are perpendicular to the transverse direction Y2. Lower portions of the pair of end surfaces of the stopper 314 are formed into circular-arc shapes that extend along shapes of the convex portions 65A and 65B. Upper end portions of the pair of end surfaces of the stopper 314 are opened toward the die pad 320.

A front end surface 314a (an upper end portion) of the stopper 314 is disposed downward (on one side in the pressing direction P) of an upper end surface of the punch body 312 on which the base forming portion 315 is formed. That is, in the pressing direction P, the front end surface 314a of the stopper 314 is disposed at a location set back from the base forming portion 315. An offset amount OF, which is a distance from the base forming portion 315 to the upper end surface 314a of the stopper 314, is preferably 0 mm or more to OFmax or less, for example. When the offset amount OF=OFmax, a height position of an upper end of the upper end surface 314a matches height positions of upper ends of the convex portions 65A and 65B of the press-formed article 60 placed on the punch 310 when the second erecting step is completed. If the offset amount OF exceeds an upper limit of the range, there is a risk that the convex portions 65A and 65B may interfere with second flange forming portions 324A and 324B described later when the die 330 moves in the first direction P1 with the die pad 320 holding the workpiece 50, and third flange forming portions 333A and 333B displace the planned flange portions 54A and 54B toward the second flange forming portions 324A and 324B. If the convex portions 65A and 65B interfere with the second flange forming portions 324A and 324B, a state where the planned vertical walls 53A and 53B of the workpiece 50 cannot be brought close to each other sufficiently. In this state, if the workpiece 50 is forcibly pressurized with the third flange forming portions 333A and 333B, the shapes of the convex portions 65A and 65B distort and deform. As a result, the press forming fails to form a formed article shape as desired. In the present embodiment, a shape of the front end surface 314a of the stopper 314 is a circular-arc shape as viewed in the transverse direction Y2. The shape of the front end surface 314a may be a circular-arc shape having a constant curvature radius, may be a circular-arc shape having a plurality of curvature radii, or may be a shape that fits a shape of a front end surface 323a of a wide portion 323 described later.

The base forming portion 315 is provided for forming the base 61 of the press-formed article 60 from the workpiece 50. The base forming portion 315 is formed into a shape that extends along a shape of a back surface of the base 61. The base forming portion 315 is provided on the upper end surface of the punch body 312. In the present embodiment, the base forming portion 315 is formed into a shape that is flat and whose both end portions in the transverse direction Y2 are curved as viewed in the longitudinal direction X2. From both ends of the base forming portion 315 in the transverse direction Y2, the vertical wall forming portions 316A and 316B extend downward.

The vertical wall forming portions 316A and 316B are provided for forming the vertical walls 63A and 63B of the press-formed article 60 from the workpiece 50. The pair of vertical wall forming portions 316A and 316B are formed on the pair of end surfaces of the punch body 312 in the transverse direction Y2. In the present embodiment, the pair of vertical wall forming portions 316A and 316B include surfaces parallel to the pressing direction P.

The die pad 320 sandwiches the planned base portion 51 as a planned portion for the base 61 in cooperation with the punch 310. The die pad 320 is disposed opposed to the punch 310 in the pressing direction P. The die pad 320 is also disposed inside the die 330. In the present embodiment, at the bottom dead center PL, the die pad 320 is disposed in a space demarcated by divided bodies 331A and 331B described later of the die 330. The die pad 320 is a member that extends long and narrow in the longitudinal direction X2. The die pad 320 is moved in the pressing direction P by an actuator not illustrated. The die pad 320 is a part that extends long and narrow in the longitudinal direction X2 and has a shape that allows the divided bodies 331A and 331B of the die 330 to pass.

The die pad 320 includes a shaft-like portion 321 that extends in the longitudinal direction X2, a holding portion 322 that is formed on the shaft-like portion 321 and is configured to hold the planned base portion 51, and the wide portion 323 that is formed on the shaft-like portion 321, is disposed on one side of the holding portion 322 in the longitudinal direction X2, and has a width wider than a width of the shaft-like portion 321.

The holding portion 322 is disposed on the die pad 320 at a location opposed to the base forming portion 315 in the pressing direction P. In the present embodiment, the holding portion 322 is formed on a lower end surface of the holding portion 322 and is a surface that is long and narrow in the longitudinal direction X2.

The wide portion 323 is provided as a core for receiving the pair of planned flange portions 54A and 54B between the opposed surfaces 54aA and 54aB of the pair of planned flange portions 54A and 54B. The wide portion 323 is disposed on the die pad 320 side (an upper side) in the pressing direction P between the pair of planned flange portions 54A and 54B. Although the wide portion 323 is provided as a portion of the die pad 320 in the present embodiment, this is not limiting. For example, the wide portion 323 may be configured as a member separate from the die pad 320 and movable in the pressing direction P independently of the die pad 320. In this case as well, the wide portion 323 is a pad inside the die and is therefore regarded as a portion of the die pad 320.

The wide portion 323 is a portion of the shaft-like portion 321 that is opposed to the stopper 314 of the punch 310 in the pressing direction P and protrudes downward from the shaft-like portion 321. A pair of end surfaces of the wide portion 323 in the transverse direction Y2 include the second flange forming portions 324A and 324B. In the press forming, the second flange forming portions 324A and 324B receive the opposed surfaces 54aA and 54aB (the inner surfaces) of the pair of planned flange portions 54A and 54B. In the present embodiment, the second flange forming portions 324A and 324B are flat surfaces extending parallel to the pressing direction P and are perpendicular to the transverse direction Y2. In the present embodiment, the second flange forming portions 324A and 324B are configured in such a manner as to respectively come into contact with the planned flange portions 54A and 54B over an angular range corresponding to a part of the planned flange portions 54A and 54B in the circumferential direction (about ⅓ of 360 degrees) in the press forming. The second flange forming portions 324A and 324B are formed into shapes that extend along shapes of the opposed surfaces 64aA and 64aB of the flanges 64A and 64B.

In the present embodiment, a width W32 of the wide portion 323 (between the second flange forming portions 324A and 324B) in the transverse direction Y2 matches a distance between the opposed surfaces 64aA and 64aB of the pair of flanges 64A and 64B and matches a width between the first flange forming portions 313A and 313B. In the present embodiment, the width W32 is larger than a width W31 of the shaft-like portion 321. This prevents the die pad 320 and the die 330 from interfering with each other.

At the bottom dead center PL, the wide portion 323 is disposed in a space S3. The space S3 is a space between the front end surface 314a of the stopper 314 and a front end surface 312a of the punch body 312 (the base forming portion 315) in the punch 310 as viewed in the transverse direction Y2. Therefore, the wide portion 323 is disposed between the other ends (upper ends) of the pair of planned flange portions 54A and 54B in the pressing direction P. The first and second flange forming portions 313A, 313B, 324A, and 324B are disposed in such a manner as to receive the opposed surfaces 54aA and 54aB of the respective pair of planned flange portions 54A and 54B when the press forming apparatus 300 brings the pair of planned flange portions 54A and 54B close to each other to form the pair of flanges 64A and 64B.

In more detail, at the bottom dead center PL, the second flange forming portions 324A and 324B are disposed at locations close to the planned base portion 51 in the pressing direction P (on the upper side), and the first flange forming portions 313A and 313B are disposed on the opposite side of the planned base portion 51 (the lower side). At the bottom dead center PL, the wide portion 323 formed with the second flange forming portions 324A and 324B may be either in contact with or separated from the stopper 314. In the longitudinal direction X2, a length of the second flange forming portions 324A and 324B need only be not more than a length of the stopper 314. The first and second flange forming portions 313A and 324A are preferably arranged coplanar with each other because the arrangement can make the flange 64A flatter. Likewise, the first and second flange forming portions 313B and 324B are preferably arranged coplanar with each other because the arrangement can make the flange 64B flatter. The larger an area in which the first and second flange forming portion 313A, 313B, 324A, and 324B face the opposed surfaces 54aA and 54aB of the planned flange portions 54A and 54B is, the higher a dimensional accuracy of the flanges 64A and 64B when the planned flange portions 54A and 54B are subjected to the press forming by the press forming apparatus 300 to be formed into the flanges 64A and 64B.

As illustrated in FIG. 9, as viewed in the transverse direction Y2, that is, in a longitudinal section taken along the longitudinal direction X2 and the height direction Z2, the front end surface 323a of the wide portion 323 is formed into an arc shape. In the present embodiment, the wide portion 323 is formed into a circular-arc shape. At the bottom dead center PL, as viewed in the transverse direction Y2, a center of curvature of the front end surface 323a of the wide portion 323 substantially matches a center of curvature of the front end surface 314a of the stopper 314. Note that the front end surface 323a may be formed into an elliptic-arc shape as viewed in the transverse direction Y2.

The above description is given of an example of a mode in which the shape of the wide portion 323 is an arc shape as viewed in the transverse direction Y2. However, this is not limiting. For example, as in Modifications 1 to 3 of the wide portion 323 illustrated in FIG. 10(A) to FIG. 10(C), a shape of the longitudinal section of the front end surface 323a of the wide portion 323 may be formed into a wedge shape or the like. In Modification 1 illustrated in FIG. 10(A), the shape of the longitudinal section of the front end surface 323a of the wide portion 323 is formed in an inclined shape that extends toward the upper side in the pressing direction P (in the second direction P2 side) with distance from the base forming portion 315 in the longitudinal direction X2. In Modification 2 illustrated in FIG. 10(B), the shape of the longitudinal section of the front end surface 323a of the wide portion 323 is parallel to the longitudinal direction X2. In Modification 3 illustrated in FIG. 10(C), the shape of the longitudinal section of the front end surface 323a of the wide portion 323 is formed in an inclined shape that extends toward the lower side in the pressing direction P (the first direction P1 side) with distance from the base forming portion 315 in the longitudinal direction X2.

By forming the shape of the longitudinal section of the front end surface 323a of the wide portion 323 into an arc shape, a wedge shape, or the like as described above, the wide portion 323 can be smoothly inserted into or taken out from a gap between the pair of flanges 64A and 64B.

As illustrated in FIG. 12, at the bottom dead center PL, surfaces of the die pad 320 and the punch 310 that extend along the pressing direction P are the first and second flange forming portions 313A and 324A and the first and second flange forming portions 313B and 324B. At the bottom dead center PL, the first and second flange forming portions 313A and 324A and the first and second flange forming portions 313B and 324B all face the die 330 in the transverse direction Y2. At the bottom dead center PL, the first and second flange forming portions 313A and 324A have a hole 400A, and the first and second flange forming portions 313B and 324B have a hole 400B. Edge portions 400aA and 400aB of the holes 400A and 400B are formed by the die pad 320 and the punch 310.

The holes 400A and 400B are at locations where the concave portions 318A and 318B are disposed. In the present embodiment, the edge portions 400aA and 400aB of the holes 400A and 400B are present at locations other than gaps 401 between the die pad 320 and the punch 310. That is, the narrower the gaps 401 between the die pad 320 and the punch 310 are, the larger ranges in circumferential directions of the holes 400A and 400B where the edge portions 400aA and 400aB are present are. In the present embodiment, the edge portions 400aA and 400aB are present over the substantially entire region of the holes 400A and 400B in the circumferential directions, respectively. The edge portion 400aA is connected to the first and second flange forming portions 313A and 324A, and the edge portion 400aB is connected to the first and second flange forming portions 313B and 324B.

As illustrated in FIG. 12, both end portions 323b and 323c in the transverse direction Y2 of a front edge portion of the wide portion 323 in the first direction P1 that face the pair of flanges 64A and 64B each have a curved shape. In the present embodiment, when t denotes a length between both end portions 323b and 323c of the wide portion 323 in the transverse direction Y2, a curvature radius r of each of both end portions 323b and 323c is set to r<t/2. Formation of such curved shape portions enables the wide portion 323 and the planned flange portions 54A and 54B (the flanges 64A and 64B) to be smoothly brought into contact with each other.

Note that, as illustrated in FIG. 13, both end portions 323b and 323c each may have a chamfered shape in place of the curved shape. FIG. 13 is a diagram illustrating a modification of both end portions 323b and 323c of the wide portion 323. In this case, a length C of a chamfered portion is C<t √2/2. Formation of such chamfered shape portions enables the wide portion 323 and the planned flange portions 54A and 54B (the flanges 64A and 64B) to be smoothly brought into contact with each other.

As illustrated in FIG. 8 to FIG. 12, the die 330 moves toward the punch 310 (the first direction P1 side in the pressing direction P) with the punch 310 and the die pad 320 sandwiching the workpiece 50, thereby forming the workpiece 50 into the press-formed article 60.

The die 330 includes a pair of divided bodies 331A and 331B that are arranged in the transverse direction Y2. This is not limiting. The die 330 may be a single piece of press tooling that includes regions corresponding to the divided bodies 331A and 331B. The die pad 320 is disposed between the divided bodies 331A and 331B. In a case where the die 330 is a single piece of press tooling, the die pad 320 is disposed inside the die 330. In any case, the die pad 320 is disposed inside the die 330. The pair of divided bodies 331A and 331B are each formed into a shape that is long and narrow in the longitudinal direction X2. The pair of divided bodies 331A and 331B is configured to be movable together in the pressing direction P by an actuator not illustrated. The pair of divided bodies 331A and 331B is movable in the pressing direction P independently of the die pad 320 and disposed in such a manner as to sandwich the die pad 320 in the transverse direction Y2.

The pair of divided bodies 331A and 331B include a pair of vertical wall forming portions 332A and 332B and the pair of third flange forming portions 333A and 333B.

The pair of vertical wall forming portions 332A and 332B are provided for forming the pair of planned vertical walls 53A and 53B into the pair of vertical walls 63A and 63B. The pair of vertical wall forming portions 332A and 332B are formed on inner surfaces of the pair of divided bodies 331A and 331B. In the present embodiment, upper portions of the pair of vertical wall forming portions 332A and 332B extend parallel to the pressing direction P and perpendicular to the transverse direction Y2. The pair of third flange forming portions 333A and 333B are disposed such that the pair of vertical wall forming portions 332A and 332B are arranged in the longitudinal direction X2.

The pair of third flange forming portions 333A and 333B form the pair of flanges 64A and 64B cooperatively with the pair of first flange forming portions 313A and 313B and the pair of second flange forming portions 324A and 324B. The pair of third flange forming portions 333A and 333B are formed on inner surfaces of the pair of divided bodies 331A and 331B. The pair of third flange forming portions 333A and 333B receive outer surfaces 54bA and 54bB that are surfaces on an opposite side of the pair of planned flange portions 54A and 54B to the opposed surfaces 54aA and 54aB, respectively. Upper portions 333bA and 333bB, which are portions of the pair of third flange forming portions 333A and 333B excluding first-direction-side end portions 333aA and 333aB, extend parallel to the pressing direction P. As viewed in the longitudinal direction X2, the first-direction-side end portions 333aA and 333aB are formed into curved shapes. In the present embodiment, the first-direction-side end portions 333aA and 333aB are formed into circular-arc shapes. At the bottom dead center PL, the first-direction-side end portions 333aA and 333aB are in curved shapes that are convex toward the first flange forming portions 313A and 313B of the punch 310. In the present embodiment, the first-direction-side end portions 333aA and 333 aB are formed over an angular range of 90 degrees and are connected to lower end surfaces of the pair of divided bodies 331A and 331B. The lower end surfaces are horizontal surfaces in the present embodiment.

As viewed in the longitudinal direction X2, curvature radii of the first-direction-side end portions 333aA and 333aB are curvature radius R. At the bottom dead center PL, at locations where the flange forming portions 313A, 333A, 313B, and 333B are provided, a length in the pressing direction P of a region where the punch 310 and the die 330 are opposed to each other is a length hl. A height of the pair of flanges 64A and 64B in the pressing direction P is a height h2. A sheet thickness of the workpiece 50 is small compared to an amount of the pressing operation (a stroke) in the pressing direction P in the press forming apparatus 300. Therefore, an upper-end start point of the height h1 and an upper-end start point of the height h2 are at substantially the same position. In the present embodiment, the curvature radius R is set to 10 mm≤R≤(h1−h2) mm (where h1−h2 is 10 mm or more).

In this manner, by setting the curvature radius R of the first-direction-side end portions 333aA and 333aB to not less than the lower limit of the range, the curvature radius R can be set to a sufficiently large value. As a result, when the planned flange portions 54A and 54B are subjected to bending by the press forming apparatus 300 to be formed into the flanges 64A and 64B, moments of power (a cause of a warp) that result from unbending deformation (bending-unbending action) of the flanges 64A and 64B and are produced in the vertical walls 63A and 63B when the die 330 is returned from the bottom dead center PL to the top dead center PU can be made to have small values. This can prevent curvature deformation of the vertical walls 63A and 63B and the flanges 64A and 64B (deformation that develops toward outer surfaces 64bA and 64bB as the flanges 64A and 64B extend in the first direction P1), and a warp amount S (an amount of wall opening) between the front end of the pair of vertical walls 63A and 63B can be made remarkably small. The warp amount S is a value indicating how long the front end of the vertical wall 63A or the front end of the vertical wall 63B is shifted in position in the transverse direction Y1 from a position where it should be. In the present embodiment, as viewed in the longitudinal direction X2, the first-direction-side end portions of the pair of vertical wall forming portions 332A and 332B are formed into the same shapes as the first-direction-side end portions 333aA and 333aB of the third flange forming portions 333A and 333B.

Next, press workings of the press forming apparatus 300 will be described. As illustrated in FIG. 11, in the press forming apparatus 300, after the workpiece 50 is placed on the punch body 312 of the punch 310, the die pad 320 as a pad is moved toward the punch 310 (in the first direction P1) prior to the die 330 by an actuator not illustrated. This causes the punch 310 and the die pad 320 to sandwich the workpiece 50, and the die pad 320 prevents a shift in position of the workpiece 50. At this time, the wide portion 323 of the die pad 320 enters between the pair of planned flange portions 54A and 54B of the workpiece 50 before the second erecting step. That is, the first flange forming portions 313A and 313B and the second flange forming portions 324A and 324B enter between the pair of planned flange portions 54A and 54B of the workpiece 50 before the second erecting step.

Next, as illustrated in FIG. 12, the die 330 is moved toward the punch 310 (in the first direction P1) to the predetermined bottom dead center PL by an actuator not illustrated, which causes the punch 310 and the die 330 to come close to each other in the pressing direction P. At this time, the pair of vertical wall forming portions 332A and 332B press the planned vertical walls 53A and 53B of the workpiece 50 against the vertical wall forming portions 316A and 316B of the punch 310, thereby bringing the pair of planned vertical walls 53A and 53B close to each other. As a result, the pair of planned vertical walls 53A and 53B is formed into the pair of vertical walls 63A and 63B.

The pair of third flange forming portions 333A and 333B of the die 330 press the planned flange portions 54A and 54B of the workpiece 50 against the first flange forming portions 313A and 313B of the punch 310 and against the second flange forming portions 324A and 324B of the die pad 320. As a result, the pair of planned flange portions 54A and 54B are brought close to each other to be formed into the pair of flanges 64A and 64B. At the bottom dead center PL, the convex portions 65A and 65B formed on the opposed surfaces 54aA and 54aB on the punch 310 side of the planned flange portions 54A and 54B of the workpiece 50 are in the holes 400A and 400B, respectively.

At the bottom dead center PL, the workpiece 50 (the planned flange portions 54A and 54B) around the convex portions 65A and 65B in the holes 400A and 400B is sandwiched between surfaces of the die pad 320 and the punch 310 extending along the pressing direction P (the first flange forming portions 313A and 313B and the second flange forming portions 324A and 324B) and the third flange forming portions 333A and 333B of the die 330. The workpiece 50 is absent between the convex portions 65A and 65B and the die pad 320 in the holes 400A and 400B. In other words, the side surfaces of the convex portions 65A and 65B and the die pad 320 in the holes 400A and 400B directly face each other. That is, there is nothing between the die pad 320 and the convex portions 65A and 65B.

In addition, the punch 310, the die pad 320, and the die 330 cooperatively form the planned base portion 51 into the base 61.

As is clear from the above description, in the second erecting step, the first flange forming portions 313A and 313B are disposed between the pair of planned flange portions 54A and 54B from one side in the pressing direction P in the press forming apparatus 300, and the second flange forming portions 324A and 324B are disposed from the other side in the pressing direction P. In this state, the die 330 of the press forming apparatus 300 is relatively moved toward the punch 310 along the pressing direction P. In this manner, the pair of planned vertical walls 53A and 53B are brought close to each other to be formed into the vertical walls 63A and 63B, and the pair of planned flange portions 54A and 54B are brought close to each other to be formed into the pair of flanges 64A and 64B.

Note that pieces of the press tooling of the press forming apparatus 300 are each formed into a shape symmetrical in the longitudinal direction X1. The pair of flanges 66A and 66B is thereby formed in the same manner as the pair of flanges 64A and 64B. As a result, the workpiece 50 is formed into the press-formed article 60.

After the workpiece 50 is formed into the press-formed article 60, the die pad 320 and the die 330 move with respect to the punch 310, for example, simultaneously in the second direction P2, thus returning to the top dead center PU. Thereafter, the press-formed article 60 is taken out from the punch 310 without interference with the punch 310, the die pad 320, or the die 330.

As described above, by forming the workpiece 50 into the press-formed article 60 while filling a space between the punch 310 and the die pad 320 with the wide portion 323 of the die pad 320, it is possible to form the vertical walls including the convex portions 65A and 65B while straightening deviation and distortion in the shape. Moreover, it is possible to implement a step of forming the flanges 64A and 64B after forming the convex portions 65A and 65B. Therefore, in steps under existing constraints for example, it is possible to form a suspension arm component including convex portions 65A and 65B disposed opposed to each other. In addition, with the convex portions 65A and 65B disposed opposed to each other, a suspension arm having an integral structure that integrates and omits collar components taking a role of fastening the press-formed article 60 and a vehicle body together.

To prevent the distortion in shapes of the flanges 64A and 64B, which is one of the problems to be solved in the present invention, the prior art before the structure of the punch 310 and the die pad 320 is conceived requires some contrivance in a press tooling structure to fill a hollow location between the planned flange portions 54A and 54B. Hence, the inventors of the present application first devised a shape of a punch of a press forming apparatus corresponding to the press forming apparatus 300 and studied an alteration of a sectional shape of the punch perpendicular to the longitudinal direction from a convex-type (a shape including the first flange forming portions 313A and 313B and the stopper 314) to an I-type (a shape in which shapes corresponding to the second flange forming portions 324A and 324B are added to upper ends of the first flange forming portions 313A and 313B). However, when a mass production process of the press-formed article is taken into account, it is necessary to lift and take out the press-formed article from the press forming apparatus after the formation has been completed. Therefore, in a case of a section of the I-type, the convex portions and the punch unavoidably interfere with each other, making an operation of taking out the press-formed article from the punch impossible. As a result of further studies, a scheme to provide a protruding portion, namely the wide portion 323, to the die pad 320 as an upper pad successfully avoided interference between the convex portions and the punch at a timing of separating the die pad 320 and the die 330 from the punch 310 after the completion of the formation. Thus, the problem of how to prevent distortion in the shapes of the flanges was successfully solved in the mass production process.

As described above, according to the present embodiment, when the workpiece 50 is subjected to the press forming to be formed into the press-formed article 60 by the press forming apparatus 300, the punch 310 and the die pad 320 can receive the planned flange portions 54A and 54B from both sides of the convex portions 65A and 65B in the pressing direction P while keeping away from the convex portions 65A and 65B. It is thus possible to prevent interference of the convex portions 65A and 65B with the punch 310 and the die pad 320 and to prevent distortion from occurring in the pair of planned flange portions 54A and 54B (the flanges 64A and 64B). That is, by disposing the first flange forming portions 313A and 313B and the second flange forming portions 324A and 324B between the pair of planned flange portions 54A and 54B from both sides in the pressing direction P, it is possible to prevent distortion in the shapes of the flanges 64A and 64B when the pair of planned flange portions 54A and 54B are formed into the pair of flanges 64A and 64B. As a result, unnecessary deformation of the flanges 64A and 64B can be prevented, and it is possible to produce the press-formed article 60 having a high dimensional accuracy.

Moreover, in the present embodiment, the erecting step (the first erecting step and the second erecting step) is performed after the convex portions 65A and 65B are formed in the burring step. In the second erecting step, the punch 310, the die pad 320, and the die 330 of the press forming apparatus 300 perform relative movements only in the pressing direction P, which is a straight-line direction, and thus it is possible to insert the first flange forming portions 313A and 313B and the second flange forming portions 324A and 324B between the planned flange portions 54A and 54B of the workpiece 50 and to take out the first flange forming portions 313A and 313B and the second flange forming portions 324A and 324B from the planned flange portions 54A and 54B. In this manner, the workpiece 50 can be formed into the press-formed article 60 by a simple technique with a simple operation of the punch 310, the die pad 320, and the die 330. As a result, the burring process, which requires many additional steps after the erecting step, can be dispensed with. This eliminates a need to perform the burring on the pair of flanges 64A and 64B with a punch and a die for the burring disposed in a narrow space between the pair of flanges. Accordingly, a configuration for operating a punch and a die of burring press tooling in many directions is not needed. Thus, the burring step can be performed in one step or a minimal number of steps (step S3). As a result, even in a case where an existing facility with constraints is used, the burring process can be performed by a simple technique without adding many steps, that is, without leading to an increase in costs.

The inventors of the present application conducted a computer simulation on an effect of preventing distortion from occurring in the pair of flanges 64A and 64B by providing the first flange forming portions 313A and 313B and the second flange forming portions 324A and 324B in the second erecting step using the press forming apparatus 300. Specifically, a configuration in which the press forming apparatus 300 in the present embodiment was used to perform the second erecting step was taken as an inventive example, and the same configuration as in the inventive example except that the wide portion 323 (the second flange forming portions 324A and 324B) was not provided was taken as a comparative example. Under conditions of the press-formed article 60 having a tensile strength of 780 MPa and a sheet thickness=2.3 mm, the press-formed article 60, which is a product in the inventive example, and a press-formed article, which is a product in the comparative example, were compared as to how distortion occurred in their flanges 64A and 64B. More specifically, how long one end portions 641A and 641B (FIG. 1) on the base 61 side in the height direction Z1 were shifted in position inward in the transverse direction Y1 with respect to corresponding other end portions 642A and 642B in the flanges 64A and 64B was measured. In the comparative example, the one end portion 641A was shifted in position by about 1.26 mm with respect to the other end portion 642A, and the one end portion 641B was shifted in position by about 1.26 mm with respect to the other end portion 642B. In contrast, in the inventive example, such shifts in position did not occur. Thus, distortion in the shapes of the flanges 64A and 64B that occurs when the pair of planned flange portions 54A and 54B are formed into the pair of flanges 64A and 64B was able to be prevented significantly.

In addition, according to the present embodiment, in the pressing direction P, the first flange forming portions 313A and 313B of the press forming apparatus 300 are disposed between one ends (lower ends) of the pair of planned flange portions 54A and 54B, and the second flange forming portions 324A and 324B are disposed between the other ends (upper ends) of the pair of planned flange portions 54A and 54B. In this configuration, by disposing portions of the press tooling for receiving the planned flange portions 54A and 54B at, in the planned flange portions 54A and 54B, both pairs of end portions of the pair of flanges 64A and 64B in the pressing direction P, it is possible to prevent distortion in the flanges 64A and 64B in the second erecting step. In this manner, the first flange forming portions 313A and 313B and the second flange forming portions 324A and 324B are disposed between the flanges 64A and 64B at locations where distortion is most likely to occur in the flanges 64A and 64B and can prevent the distortion. Thus, the dimensional accuracy of the flanges 64A and 64B can be further increased.

In addition, according to the present embodiment, the stopper 314 can receive the pair of convex portions 65A and 65B between the pair of convex portions 65A and 65B in the second erecting step. This avoids making a distance between the pair of convex portions 65A and 65B excessively narrow for required dimensions of a component. Thus, the dimensional accuracy of the press-formed article 60 can be further increased.

In addition, according to the present embodiment, the second flange forming portions 324A and 324B of the press forming apparatus 300 are disposed at locations close to the planned base portion 51 in the pressing direction P (at portions on the second direction P2 side) in the second erecting step. With this configuration, it is possible to simply implement a configuration in which the second flange forming portions 324A and 324B are provided on the die pad 320.

In addition, according to the present embodiment, in the pressing direction P, the front end surface 314a of the stopper 314 of the press forming apparatus 300 is disposed at a location set back from a front end of the punch 310 close to the die pad 320 (the upper end, the base forming portion 315). With this configuration, it is possible to dispose the second flange forming portions 324A and 324B at locations on the first direction P1 side in the pressing direction P away from the base forming portion 315 of the punch 310. This enables the second flange forming portions 324A and 324B to receive the pair of flanges 64A and 64B at locations closer to the stopper 314 disposed between the convex portions 65A and 65B. Therefore, an area in which the second flange forming portions 324A and 324B are opposed to the opposed surfaces 64aA and 64aB of the pair of flanges 64A and 64B can be made larger. As a result, the effect of preventing the distortion in the pair of flanges 64A and 64B by the second flange forming portions 324A and 324B can be further increased.

In addition, according to the present embodiment, the first flange forming portions 313A and 313B are provided on the punch 310, and the second flange forming portions 324A and 324B are provided on the die pad 320. With this configuration, the first flange forming portions 313A and 313B and the second flange forming portions 324A and 324B need not be provided with dedicated press tooling. Furthermore, in the present embodiment, the stopper 314 is provided on the punch 310. The stopper 314 also need not be provided with dedicated press tooling.

The embodiment and the modifications of the present invention are described above. However, the present invention is not limited to the embodiment and the modifications, and various modifications may be made within the scope described in claims.

For example, in the embodiment and modifications, the intermediate formed article 40 is formed into the workpiece 50 by the first erecting step using the press forming apparatus 200, and subsequently the workpiece 50 is formed into the press-formed article 60 by the second erecting step using the press forming apparatus 300. However, this is not limiting. For example, as illustrated in FIG. 14, the intermediate formed article 40 may be formed into the press-formed article 60 by one erecting step using the press forming apparatus 300. In this case, in a middle stage of forming the press-formed article 60 from the intermediate formed article 40, the intermediate formed article 40 is formed into the workpiece 50 for a brief period, and then the workpiece 50 is formed into the press-formed article 60 as the pressing operation progresses.

In addition, the workpiece 50 is not limited to a configuration in which the convex portions 65A and 65B are formed on the respective planned flange portions 54A and 54B. The convex portion 65A or the convex portion 65B may be formed on only one of the planned flange portions 64A and 64B.

A configuration of the convex portions 65A and 65B of the workpiece 50 is not limited to a configuration formed by the burring process. For example, the convex portions 65A and 65B may be formed by attaching components to a workpiece 50 such as a weld nut. The convex portions may be formed by, for example, performing press forming on the workpiece to swell, out the starting material.

INDUSTRIAL APPLICABILITY

The present invention is applicable as a press forming apparatus and a method for producing a press-formed article.

REFERENCE SIGNS LIST

• • 50 workpiece
  • 65A, 65B convex portion
  • 300 press forming apparatus
  • 310 punch
  • 313A, 313B first flange forming portion (surface along the pressing direction)
  • 320 die pad
  • 324A, 324B second flange forming portion (surface along the pressing direction)
  • 330 die
  • 400A, 400B hole
  • 400aA, 400aB edge portion of hole
  • P pressing direction
  • PL bottom dead center