Methods for manufacturing stamped products and stamping machine sets.

Abstract

The present invention is a press-molding device (30) for producing a press-molded article having a hat-shaped cross section by compressing a preform having a hat-shaped cross section between a punch (31), which is a first mold, and dies (32a, 32b), which are a second mold, and is characterized by being provided with: the punch (31) and the dies (32a, 32b), which constitute a compression mechanism for compressing side walls and a flange of the hat shape of the preform; compression blocks (34a, 34b), which constitute a first pressing mechanism for pressing an outer end portion of the flange of the hat shape of the preform; and a pad (35a), which constitutes a second pressing mechanism for pressing an upper end portion of the side walls of the hat shape of the preform.

Description

Method for manufacturing press-molded product and press-molding device

[0001] The present invention relates to a method for manufacturing a press-formed product and a press-forming apparatus.

[0002] A method for manufacturing a press-formed product has been known in the past, in which a blank with a U-shaped cross section is obtained by bending a raw sheet, and the vertical wall portions are compressed in the up-down direction between an upper die and a lower die while the lower ends of the vertical wall portions, which form the open side of the U-shape, are abutted against the lower die (see, for example, Patent Document 1). This manufacturing method prevents springback, which acts to open the vertical wall portions, thereby improving the dimensional accuracy of the resulting press-formed product.

[0003] Patent No. 6527544

[0004] Meanwhile, many long members typically used in vehicle body frames have a closed cross-section structure in which hat-shaped cross-section halves (half shells) are joined together and flanges corresponding to the hat-shaped flanges are welded together. Therefore, a method for manufacturing such hat-shaped press-formed products is also desirable that can prevent springback. However, in manufacturing methods for hat-shaped press-formed products, it is necessary to prevent not only springback that acts to open the vertical walls, but also springback that acts to open the angle between the vertical walls and the flanges. Therefore, conventional methods for manufacturing press-formed products (see, for example, Patent Document 1) are unable to sufficiently improve the dimensional accuracy of hat-shaped press-formed products.

[0005] An object of the present invention is to provide a method for manufacturing a press-formed product and a press-forming device that can produce a press-formed product having a hat-shaped cross section with excellent dimensional accuracy by a simple process, in which springback is sufficiently suppressed.

[0006] The manufacturing method of the press-molded product of the present invention, which solves the above-mentioned problems, is characterized in that a second hat-shaped cross-section bent plate is obtained by in-plane compressing the first hat-shaped cross-section bent plate between a first mold and a second mold, along the circumferential direction of the hat shape from the side wall forming the hat-shaped peak portion of the first hat-shaped cross-section bent plate to the hat-shaped flange.

[0007] The press forming apparatus of the present invention, which has solved the above-mentioned problems, is a press forming apparatus for compressing a first hat-shaped cross-section bent plate between a first mold and a second mold to obtain a second hat-shaped cross-section bent plate, wherein the hat-shaped cross-section bent plate has side walls formed to correspond to the peaks of the hat shape and extending in the height direction of the peaks, and a flange formed to correspond to the brim of the hat shape and extending so as to protrude in a direction away from the end of the side wall on the opening side of the peaks, and the first mold has a first wall surface formed to correspond to the side wall of the second hat-shaped cross-section bent plate and a second wall surface formed to correspond to the flange of the second hat-shaped cross-section bent plate, which are continuous at a first corner. the second mold comprises a die in which a third wall surface parallel to the first wall surface and a fourth wall surface parallel to the second wall surface are continuous to form a second corner, and the first mold comprises a compression mechanism that brings the first corner and the second corner closer together to compress the side wall and the flange of the first hat-shaped cross-section bent plate body between the first wall surface and the third wall surface and between the second wall surface and the fourth wall surface, a first pressing mechanism that presses an end of the flange of the first hat-shaped cross-section bent plate body opposite to the first corner side toward the first corner side, and a second pressing mechanism that presses an end of the side wall of the first hat-shaped cross-section bent plate body opposite to the first corner side toward the first corner side.

[0008] According to the present invention, it is possible to provide a method for manufacturing a press-formed product and a press-forming device that can obtain a press-formed product with a hat-shaped cross section and excellent dimensional accuracy in a simple process by sufficiently suppressing springback.

[0009] 5A is a partial perspective view showing an example of a press-formed product that can be obtained by a manufacturing method according to an embodiment of the present invention; FIG. 5B is a configuration explanatory diagram of a press forming apparatus according to an embodiment of the present invention; FIG. 5C is a partial enlarged view of part III of FIG. 2; FIG. 5D is a process explanatory diagram of a method for manufacturing a press-formed product according to an embodiment of the present invention, showing a process of placing a preform (first hat-shaped cross-section bent plate) as a compression material in a punch; FIG. 5E is a process explanatory diagram of a method for manufacturing a press-formed product according to an embodiment of the present invention, showing a process of pressing an end of a spring-back flange of a preform (first hat-shaped cross-section bent plate) as a compression material in a surface direction; FIG. 5F is a process explanatory diagram of a method for manufacturing a press-formed product according to an embodiment of the present invention, showing a process of compressing a side wall of the preform (first hat-shaped cross-section bent plate); FIG. 5G is a process explanatory diagram of a method for manufacturing a press-formed product according to an embodiment of the present invention, showing a state in which the side wall of the preform (first hat-shaped cross-section bent plate) is compressed in-plane; FIG. 5H is a process explanatory diagram of a method for manufacturing a press-formed product according to an embodiment of the present invention, showing a state in which a press-formed product (second hat-shaped cross-section bent plate) is obtained in a mold; FIG. 5G is a configuration explanatory diagram of a modified example of the press forming apparatus according to the present invention; and FIG. 5G is an operation explanatory diagram of a press forming apparatus according to a modified example of FIG.

[0010] Next, a method for manufacturing a press-formed product according to an embodiment of the present invention (hereinafter, sometimes simply referred to as a press-forming method) and a press-forming apparatus for carrying out this method will be described in detail with reference to the drawings. The press-forming method according to this embodiment involves in-plane compression of a preform having a hat-shaped cross section made of a plate material such as a steel plate in a mold to obtain a final formed product having a hat-shaped cross section.

[0011] In the following, an example of a press-formed product obtained in this embodiment will be described, followed by a description of a press-forming apparatus and a press-forming method. The up-down direction in the following description is based on the up-down direction of the press-forming apparatus. The up-down direction of the press-formed product is aligned with the up-down direction of the press-formed product obtained in the press-forming apparatus.

[0012] <Press-formed product> Figure 1 is a partially enlarged perspective view showing an example of a press-formed product 10 that can be obtained by the press-forming method according to this embodiment. The press-formed product 10 in this embodiment is intended to be a long structural member made of high-tensile steel plate used in automobile body frames, etc., but is not limited thereto and can be applied to structural members made of various metal materials used in various fields. Note that the press-formed product 10 in Figure 1 is shown partially cut away for the convenience of drawing a cross-section.

[0013] As shown in Fig. 1, the press-formed product 10 is a member (long member) that is long in one direction, and has a hat-shaped cross section intersecting the longitudinal direction. As is well known, the hat shape includes a pair of side walls 13a, 13b that form the side surfaces of a crest 11, a peak 14 of the crest 11 that connects one end (upper end) of the pair of side walls 13a, 13b, and a pair of flanges 15a, 15b that form a brim 12. The crest 11 has a generally U-shape in which one end of the pair of side walls 13a, 13b is closed at the peak 14 and the other end (lower end) of the side walls 13a, 13b is open. The flanges 15a, 15b are formed on the opening side of the approximately U-shaped ridge portion 11 so as to protrude outward (away from the opening) from the respective end edges (lower edges) of the pair of side walls 13a, 13b.

[0014] In this embodiment, the peak 14 of the ridge portion 11 includes a lateral wall 16 that is connected to one end of each of the side walls 13a and 13b via chamfered portions 17a and 17b. In this embodiment, the chamfered portions 17a and 17b that form the peak 14 are formed as inclined surfaces in which the width between the chamfered portions 17a and 17b gradually narrows as the peak 14 extends upward from the end of each of the side walls 13a and 13b. However, these inclined surfaces can also be replaced by curved surfaces (R-shaped surfaces) that bulge upward. Furthermore, the peak 14 can also be configured such that the lateral wall 16 is connected to one end of each of the side walls 13a and 13b at a predetermined angle without the chamfered portions 17a and 17b or curved surfaces (not shown).

[0015] In addition, although the press-formed product 10 in this embodiment is assumed to have a hat-shaped cross section throughout the entire longitudinal direction, it may also have a hat-shaped cross section only partially in the longitudinal direction. Furthermore, each of the side walls 13a, 13b and the lateral wall 16 is not limited to being flat along the longitudinal direction, and may also include a curved surface that curves in the longitudinal direction. Each of the side walls 13a, 13b and the lateral wall 16 may also include slight irregularities such as steps or beads formed in the surface direction. Each of the side walls 13a, 13b and the lateral wall 16 may also have a hole formed through it in the plate thickness direction.

[0016] In the press-formed product 10 of this embodiment, the height (vertical direction) of the crest 11 of one of the side walls 13a, 13b is shorter than that of the other side wall 13b, but the lengths of the pair of side walls 13a, 13b may be the same. In the press-formed product 10 of this embodiment, the widths (lengths in a direction intersecting the longitudinal direction) of the pair of flanges 15a, 15b are the same, but the widths of the pair of flanges 15a, 15b may be different from each other.

[0017] In the press-formed product 10 of this embodiment, flanges 15a, 15b are connected to another prepared member (not shown) by spot welding or the like, thereby forming a closed cross section between the other prepared member and the inside of the crest 11. Incidentally, examples of the other prepared member include, but are not limited to, a panel material forming a floor panel or a dashboard lower of a vehicle body, and a three-dimensional structure such as another hat-shaped member (another half) to which the press-formed product 10 is joined as a half in a shell-like manner.

[0018] The press-formed product 10 as the final product is formed using a press-forming apparatus 30 (see FIG. 2 ) described later, and corresponds to the "second hat-shaped cross-section bent plate" in the claims. The press-formed product 10 is different from the preformed product 20 (see FIG. 4A ) that is supplied as a material to the press-forming apparatus 30 to obtain the press-formed product 10. This preformed product 20 corresponds to the "first hat-shaped cross-section bent plate" in the claims. The preformed product 20 will be described in detail later together with the explanation of the "press-forming method."

[0019] <Press-forming apparatus> FIG. 2 is a diagram illustrating the configuration of a press-forming apparatus 30 according to this embodiment. FIG. 2 schematically illustrates the press-forming apparatus 30 as viewed from the front. As shown in FIG. 2, the press-forming apparatus 30 is mainly configured to include a punch 31, a pair of dies 32a and 32b, a cam mechanism 40 that drives each of the dies 32a and 32b, and a pad 35a that holds a preformed product 20 (see FIG. 4A ) (described below) placed on the punch 31 and presses the side walls 23a and 23b (see FIG. 4A ). The press-forming apparatus 30 according to this embodiment is configured to in-plane compress the side walls 23a and 23b (see FIG. 4A ) and flanges 25a and 25b (see FIG. 4A ) of the preformed product 20 (see FIG. 4A ) using the punch 31, the dies 32a and 32b, and the pad 35a, as will be described in detail later.

[0020] (Punch and Die) The punch 31 in this embodiment is assumed to be a fixed die and corresponds to the "first die" in the claims. The dies 32a and 32b in this embodiment are assumed to be movable dies and correspond to the "second die" in the claims. Note that in the press molding device 30, the dies 32a and 32b can be set on the fixed side, and the punch 31 can be set on the movable side.

[0021] Fig. 3 is a partial enlarged view of part III in Fig. 2. As shown in Fig. 3, the punch 31 in this embodiment has a compression molding surface that imitates the concave surface 19 side of the convex surface 18 and the concave surface 19 of the press-formed product 10 (see Fig. 1) that has a hat-shaped cross section and is elongated in one direction.

[0022] The punch 31 (see FIG. 3) is formed in the shape of a long rail in one direction (a direction perpendicular to the plane of FIG. 3) to match the press-formed product 10 (see FIG. 1). Specifically, as shown in FIG. 3, the punch 31 has a base portion 31a formed of an elongated, approximately rectangular parallelepiped, and a protruding portion 31b also formed of an elongated, approximately rectangular parallelepiped. The protruding portion 31b is formed at the center of the base portion 31a in the width direction (the left-right direction on the plane of FIG. 3) so as to protrude upward with a width narrower than that of the base portion 31a.

[0023] The punch 31 of this embodiment has first wall surfaces 53a, 53b of the protruding portion 31b corresponding to the side walls 13a, 13b (see FIG. 1), respectively, of the convex portion 11 (see FIG. 1) of the press-formed product 10, and second wall surfaces 55a, 55b of the base portion 31a corresponding to the flanges 15a, 15b (see FIG. 1). The first wall surface 53a is continuous with the second wall surface 55a via a first corner portion 58a, and the first wall surface 53b is continuous with the second wall surface 55b via the first corner portion 58b.

[0024] The base portion 31a has an outer end surface 36a that intersects with the second wall surface 55a on the opposite side of the first corner 58a. The base portion 31a also has an outer end surface 36b that intersects with the second wall surface 55b on the opposite side of the first corner 58b. These outer end surfaces 36a, 36b are formed along the vertical direction. Furthermore, fifth wall surfaces 37a, 37b of the compression blocks 34a, 34b (described later) can abut against the outer end surfaces 36a, 36b of the base portion 31a at the bottom dead centers of the dies 32a, 32b.

[0025] The punch 31 has a top 31c formed to correspond to the top 14 (see FIG. 1) of the press-formed product 10 (see FIG. 1). Specifically, the punch 31 has a side wall surface 56 formed to correspond to the side wall 16 (see FIG. 1) of the press-formed product 10 (see FIG. 1). The punch 31 also has inclined wall surfaces 57a, 57b formed to correspond to the chamfered portions 17a, 17b (see FIG. 1) of the press-formed product 10 (see FIG. 1). The inclined wall surfaces 57a, 57b are continuous with the first wall surfaces 53a, 53b at a predetermined angle.

[0026] The length from one side of the second wall surface 55a, first corner portion 58a, first wall surface 53a, and inclined wall surface 57a of such a punch 31, via the lateral wall surface 56, to the other side of the inclined wall surface 57b, first wall surface 53b, first corner portion 58b, and second wall surface 55b, i.e., the circumferential length of the punch 31, is set to be equal to the circumferential length of the corresponding press-molded product 10.

[0027] Next, the dies 32a and 32b will be described. As shown in Fig. 2, in this embodiment, the dies 32a and 32b are each integrated with a cam slider 41a or 41b (described later) of a cam mechanism 40 that can move forward and backward at a predetermined angle relative to the compression molding surface of the punch 31. The dies 32a and 32b are arranged in pairs at positions that sandwich the protruding portion 31b of the punch 31 in the lateral direction (the left and right directions on the paper surface of Fig. 2) with the protruding portion 31b of the punch 31 at the center. In other words, each of the dies 32a and 32b is formed of an elongated member that is long in one direction (the direction perpendicular to the paper surface of Fig. 2) so as to correspond to the rail-shaped punch 31.

[0028] Specifically, in the front view shown in Fig. 3, the dies 32a and 32b are arranged so as to be substantially symmetrical with respect to the central axis Ax of the protrusion 31b extending in the up-down direction. Note that the central axis Ax of the protrusion 31b in this embodiment can be defined by an axis extending vertically (coinciding with the up-down direction in Fig. 3) at the center of the lateral wall surface 56 in the horizontal direction (the left-right direction on the paper surface in Fig. 2).

[0029] The die 32a includes a die body 33a and a compression block 34a integrally attached to the die body 33a. The die 32b includes a die body 33b and a compression block 34b integrally attached to the die body 33b.

[0030] One die body 33a, which is disposed so as to correspond to one first wall surface 53a of the punch 31, has a third wall surface 63a that faces and is parallel to the first wall surface 53a. The other die body 33b, which is disposed so as to correspond to the other first wall surface 53b of the punch 31, has a third wall surface 63b that faces and is parallel to the first wall surface 53b.

[0031] The die body 33a is parallel to the second wall surface 55a of the punch 31 and has a fourth wall surface 65a that is continuous with the third wall surface 63a via a second corner 68a. The die body 33b is parallel to the second wall surface 55b of the punch 31 and has a fourth wall surface 65b that is continuous with the third wall surface 63b via a second corner 68b. The circumferential length of the die body 33a, which extends from the third wall surface 63a via the second corner 68a to the fourth wall surface 65a, is set to be equal to the circumferential length of the punch 31, which extends from the first wall surface 53a of the punch 31 to the second wall surface 55a via the first corner 58a. In addition, the circumferential length of the other die body 33b, which extends from the third wall surface 63b via the second corner portion 68b to the fourth wall surface 65b, is set to be equal to the circumferential length of the punch 31, which extends from the first wall surface 53b of the punch 31 to the second wall surface 55b via the first corner portion 58b.

[0032] Next, the compression blocks 34a and 34b will be described. As shown in Fig. 3, the compression block 34a is the base end of the die body 33a located on the side of a cam slider 41a (described later), and is disposed below the die body 33a so as to be integrated with the die body 33a. The compression block 34b is the base end of the die body 33b located on the side of a cam slider 41b (described later), and is disposed below the die body 33b so as to be integrated with the die body 33b.

[0033] In this embodiment, each of the compression blocks 34a, 34b is assumed to be a block body consisting of a substantially rectangular parallelepiped that is long in one direction (a direction perpendicular to the plane of FIG. 3 ) so as to correspond to the press-formed product 10. Incidentally, in this embodiment, the compression blocks 34a, 34b are assumed to be separate from the die bodies 33a, 33b and attached to the die bodies 33a, 33b. However, each of the compression blocks 34a, 34b may also be molded integrally with the die bodies 33a, 33b.

[0034] The compression block 34a has a fifth wall surface 37a that faces and is parallel to the outer end surface 36a of the base portion 31a. The compression block 34b has a fifth wall surface 37b that faces and is parallel to the outer end surface 36b of the base portion 31a. The fifth wall surfaces 37a, 37b of the compression blocks 34a, 34b are capable of contacting the outer end surfaces 36a, 36b of the punch 31 at the bottom dead centers of the dies 32a, 32b, respectively, as described below.

[0035] (Cam Mechanism) Next, the cam mechanism 40 (see FIG. 2) will be described. As shown in FIG. 2, the cam mechanism 40 is mainly composed of a pair of cam sliders 41a, 41b provided to correspond to the dies 32a, 32b, respectively, a pair of cam bases 42a, 42b provided to correspond to the cam sliders 41a, 41b, and a pair of cam drivers 43a, 43b provided to correspond to the cam sliders 41a, 41b. Incidentally, the cam sliders 41a, 41b, cam bases 42a, 42b, and cam drivers 43a, 43b are formed of elongated members that are long in one direction (the direction perpendicular to the plane of FIG. 2) to correspond to the dies 32a, 32b.

[0036] The cam slider 41a moves the die 32a toward the punch 31 or moves the die 32a away from the punch 31 by raising and lowering the inclined surface 45a of the cam base 42a in the inclined direction. The cam slider 41b moves the die 32b toward the punch 31 or moves the die 32b away from the punch 31 by raising and lowering the inclined surface 45b of the cam base 42b in the inclined direction.

[0037] That is, each of the cam sliders 41a, 41b moves each of the dies 32a, 32b toward the punch 31 at angles θa, θb formed by the horizontal plane Hp and each of the inclined surfaces 45a, 45b on the narrow angle side. Incidentally, the angles θa, θb can be set within a range of more than 0 degrees and less than 90 degrees (0° (deg) < θa, θb < 90° (deg)), but are preferably set to 15 degrees or more and 60 degrees or less, and particularly around 15 degrees. Such angles θa and θb may be the same or different. In this embodiment, each of the angles θa, θb is assumed to be 15 degrees.

[0038] The cam bases 42a and 42b support the cam sliders 41a and 41b, respectively, so that the cam sliders 41a and 41b can slide along the inclined surfaces 45a and 45b. In this embodiment, the cam bases 42a and 42b are integrally formed. The central portion where the cam bases 42a and 42b are connected also serves as a support portion for the punch 31.

[0039] The cam bases 42a, 42b are each provided with biasing means 46a, 46b, such as a coil spring, that bias the cam sliders 41a, 41b in a direction away from the punch 31. There are no particular limitations on the biasing means 46a, 46b, and they may have a well-known structure in which a spring S is disposed between the cam base 42a and the cam slider 41a, and between the cam base 42b and the cam slider 41b. Examples of the spring S include a gas spring and a coil spring. It is assumed that a plurality of such biasing means 46a, 46b are arranged in a line along the longitudinal direction (the direction perpendicular to the plane of FIG. 2 ) of each of the cam bases 42a, 42b.

[0040] In this embodiment, the cam drivers 43a, 43b are integrated with the pad unit 35 including the pad 35a described below, and have a generally downwardly opening E-shape when viewed from the front of the press forming apparatus 30 shown in Fig. 2. That is, each of the cam drivers 43a, 43b is connected to a pad support part 35c that extends horizontally below the lifting mechanism 39 described below and is movable up and down. Specifically, the upper end of each of the cam drivers 43a, 43b is connected to the pad support part 35c so as to sandwich the pad unit 35 in the center. The cam drivers 43a, 43b form cam surfaces 44a, 44b that extend downward from the pad support part 35c side and drive the cam sliders 41a, 41b.

[0041] The cam surfaces 44a, 44b are formed on the lower end surfaces of the cam drivers 43a, 43b that face the cam sliders 41a, 41b. Each of these cam surfaces 44a, 44b is configured as an inclined surface that gradually displaces downward the further away from the pad 35a sandwiched in the center. Slide members 47a, 47b are attached to the upper surfaces of the cam sliders 41a, 41b, respectively, and slide against the cam surfaces 44a, 44b to guide the cam sliders 41a, 41b along the cam surfaces 44a, 44b.

[0042] When the lifting mechanism 39, which includes, for example, a hydraulic cylinder, moves the pad support portion 35c downward, the cam drivers 43a, 43b move the cam sliders 41a, 41b toward the punch 31 via the cam surfaces 44a, 44b. In other words, the cam surfaces 44a, 44b push the cam sliders 41a, 41b toward the punch 31 at the angles θa, θb against the biasing forces of the biasing means 46a, 46b.

[0043] Conversely, when the lifting mechanism 39 moves the pad support portion 35c upward, the pressing force (thrust force) of the cam surfaces 44a and 44b against the cam sliders 41a and 41b is released, and the cam sliders 41a and 41b are restored to their original positions by the biasing forces of the biasing means 46a and 46b.

[0044] (Pad) Next, the pad 35a (see FIG. 2) will be described. The pad 35a in this embodiment is configured as a substantially rectangular parallelepiped block that is long in one direction (a direction perpendicular to the paper surface of FIG. 2) so as to correspond to the press-formed product 10 (see FIG. 1). As shown in FIG. 2, the pad 35a is attached to a pad support portion 35c via a cushion member 35b (described later) so as to be located above the punch 31.

[0045] As shown in Fig. 3, the pad 35a has a groove 35d at its lower end facing the punch 31, into which the top 31c of the punch 31 fits. The groove 35d is formed to extend in one direction (a direction perpendicular to the plane of the paper in Fig. 3) so as to correspond to the press-formed product 10 (see Fig. 1). Specifically, the groove 35d has a bottom surface 35d1 formed to correspond to the lateral wall 16 (see Fig. 1) of the press-formed product 10 (see Fig. 1), and side surfaces 35d2 and 35d3 formed to correspond to the chamfered portions 17a and 17b (see Fig. 1) of the press-formed product 10 (see Fig. 1).

[0046] In this embodiment, the cushion member 35b (see FIG. 2) is assumed to be a coil spring, but other springs such as a gas spring can also be used as the cushion member 35b. As shown in FIG. 2, the cushion member 35b in this embodiment is housed in a cylindrical space 35e formed above the groove 35d and extending in the up-down direction of the pad 35a. The lower end of the cushion member 35b is attached to a spring seat (not shown) provided at the bottom of the cylindrical space 35e, and the upper end is attached to the pad support portion 35c. A plurality of such cushion members 35b are arranged in the longitudinal direction of the pad 35a (the direction perpendicular to the plane of FIG. 3).

[0047] The spring constant of the cushion member 35b is adjusted so that there is a contraction allowance from the state in which the pad 35a is separated from the punch 31 as shown in FIG. 2 until the state in which the pad 35a (see FIG. 4C) starts compression molding the apex 24 (see FIG. 4C) of the preformed product 20 (see FIG. 4C), as described below. The cushion member 35b is unable to contract from the state in which compression molding of the apex 24 (see FIG. 4C) starts (see FIG. 4C) until the pad 35a reaches at least the bottom dead center (see FIG. 4E). The spring constant of the cushion member 35b is adjusted so that the pad 35a can hold the apex 24 (see FIG. 4A) of the preformed product 20 (see FIG. 4A) from the state shown in FIG. 2 to the state shown in FIG. 4C.

[0048] <Press-forming method> Next, the operation of the press-forming apparatus 30 (see FIG. 2) according to this embodiment will be described, along with a description of the press-forming method according to this embodiment performed by this press-forming apparatus 30. FIGS. 4A to 4E are explanatory diagrams of the steps of the press-forming method. FIG. 4A is a diagram showing a step (first step) of placing the preformed piece 20 (first hat-shaped cross-section bent plate) on the punch 31. FIG. 4B is a diagram showing a step (second step) of pressing the ends of the spring-back flanges 25a, 25b of the preformed piece 20 (first hat-shaped cross-section bent plate) in the plane direction. FIG. 4C is an explanatory diagram of a step (third step) of compressing the side walls 23a, 23b of the preformed piece (first hat-shaped cross-section bent plate). FIG. 4D is a diagram showing in-plane compression of the side walls 23a, 23b of the preformed piece 20 (first hat-shaped cross-section bent plate). FIG. 4E is a diagram showing the state in which the press-formed product 10 (second bent plate body having a hat-shaped cross section) is obtained in the mold (punch 31, dies 32a, 32b).

[0049] (First Step) As shown in Figure 4A, in the first step of the press forming method of this embodiment, the preformed piece 20 is placed on the punch 31. As described above, this preformed piece 20 (first hat-shaped cross-section bent plate) corresponds to the "first hat-shaped cross-section bent plate" in the claims. Note that Figure 4A shows a state in which the preformed piece 20 is placed on the punch 31 with the pad 35a and punch 31 separated from each other as shown in Figure 2, and then the lifting mechanism 39 is lowered to hold the top 24 of the preformed piece 20 with the pad 35a.

[0050] A preform 20, which is the material from which the press-formed product 10 (see FIG. 1) is obtained, can be produced by supplying a blank such as a high-tensile steel plate to a press-forming device equipped with a die (not shown) having a compression-forming surface that imitates the convex surface 18 (see FIG. 1) of the press-formed product 10, and a punch (not shown) having a compression-forming surface that imitates the concave surface 19 (see FIG. 1) of the press-formed product 10. Such a preform 20 generates so-called springback due mainly to stress generated in the bent portion of the blank.

[0051] Specifically, as shown in FIG. 4A , when the top portion 24 of the preform 20 is held above the punch 31 by the pad 35a, each of the side walls 23a, 23b of the preform 20 is raised from each of the first wall surfaces 53a, 53b of the punch 31. In the first step of this embodiment, as shown in FIG. 4A , a preform 20 is prepared in which each of the side walls 23a, 23b is longer than the side walls 13a, 13b (see FIG. 1) of the press-formed product 10 (see FIG. 1). Furthermore, the length of each of the flanges 25a, 25b of the preform 20 is approximately the same as the length of each of the flanges 15a, 15b (see FIG. 1) of the press-formed product 10 (see FIG. 1). However, the preform 20 is not limited to this, and the length of the flanges 25a, 25b can also be changed, as will be described later as another embodiment of the present invention.

[0052] (Second Step) Next, the second step of the press-forming method of this embodiment will be described. In this second step, as shown in FIG. 4B , the compression blocks 34a, 34b press the outer ends 28a, 28b of the spring-back flanges 25a, 25b. In this second step, first, the lifting mechanism 39 (see FIG. 2 ) moves the pad support portion 35c (see FIG. 2 ) downward from the position of the pad 35a shown in FIG. 4A , and the pad 35a abuts against the top portion 24 of the preform 20 as shown in FIG. 4B . At this time, as shown in FIG. 4B , the cushion member 35b contracts and presses even more strongly against the top portion 24 of the preform 20 via the pad 35a.

[0053] On the other hand, the cam drivers 43a and 43b shown in Fig. 2 move the cam sliders 41a and 41b toward the punch 31 by causing the lifting mechanism 39 (see Fig. 2) to move the pad support portion 35c (see Fig. 2) downward. As a result, the dies 32a and 32b provided on the cam drivers 43a and 43b approach the punch 31 as shown in Fig. 4B.

[0054] Specifically, the second corners 68a, 68b of the dies 32a, 32b move toward the first corners 58a, 58b of the punch 31. The fifth wall surfaces 37a, 37b of the compression blocks 34a, 34b press the outer end portions 28a, 28b of the flanges 25a, 25b of the preform 20 toward the first corners 58a, 58b of the punch 31. The dies 32a, 32b (compression blocks 34a, 34b), the cam mechanism 40, and the lifting mechanism 39 that press the flanges 25a, 25b constitute a "first pressing mechanism" as defined in the claims.

[0055] (Third Step) Next, the third step of compressing the side walls 23a, 23b of the preform 20 (first hat-shaped cross-section bent plate) will be described. In this third step, as shown in FIG. 4C , a gap G is formed between the punch 31 and the top 24 of the preform 20. This gap G is formed by the compression blocks 34a, 34b further pressing the outer ends 28a, 28b of the flanges 25a, 25b from the positions shown in FIG. 4B , respectively. That is, as shown in FIG. 4C , this gap G is formed by the top 24 of the preform 20 lifting the pad 35a upward to provide clearance for the excess part of the preform 20 pressed between the die 32a (die 32b is not shown) and the punch 31 by the compression block 34a (compression block 34b is not shown).

[0056] When the lifting mechanism 39 (see FIG. 2) moves the pad support portion 35c downward from the position of the pad 35a shown in FIG. 4C, the non-contractible cushion member 35b causes the pad 35a to press the top portion 24 of the preform downward. As a result, the upper ends 29a, 29b of the side walls 23a, 23b are pressed toward the first corner 58 of the punch 31. The pad 35a, which presses the upper ends 29a, 29b of the side walls 23a, 23b in this manner, and the lifting mechanism 39 (see FIG. 2) constitute a "second pressing mechanism" as defined in the claims.

[0057] In this third step, the cam drivers 43a, 43b (see FIG. 2) cause the elevating mechanism 39 (see FIG. 2) to move the pad support portion 35c (see FIG. 2) downward. As a result, as shown in FIG. 4D , the dies 32a, 32b provided on the cam sliders 41a, 41b move so that the second corners 68a, 68b approach the first corners 58a, 58b of the punch 31. As a result, the side walls 23a, 23b and flanges 25a, 25b of the preform 20 (first bent plate body having a hat-shaped cross section) are compressed between the punch 31 and the die 32a, 32b.

[0058] The press forming method of this embodiment is configured to perform a second step of pressing outer end portions 28a, 28b of the flanges 25a, 25b of the preformed product 20 toward a first corner 58 of the punch 31, in parallel with a third step of compressing the side walls 23a, 23b and flanges 25a, 25b of the preformed product 20 between the dies 32a, 32b and the punch 31, as shown in Fig. 4D . That is, as shown in Fig. 4D , the preformed product 20 (first bent plate having a hat-shaped cross section), which has a circumferential length longer than that of the punch 31, is pressed onto the punch 31 so as to match the circumferential length of the punch 31 and eliminate the excess length. As a result, the flanges 25a, 25b and side walls 23a, 23b of the preformed product 20 are compressed in-plane in the circumferential direction of the hat shape of the preformed product 20.

[0059] Then, as shown in Figure 4E, the in-plane compressed flanges 25a, 25b and side walls 23a, 23b form flanges 15a, 15b and side walls 13a, 13b, respectively, and a press-molded product 10 is formed within the mold consisting of punch 31, dies 32a, 32b, and pad 35a.

[0060] <<Functions and Effects>> Next, the functions and effects achieved by the press-forming method and the press-forming apparatus 30 of this embodiment will be described.

[0061] In the press-forming method of this embodiment, the press-formed product 10 (second hat-shaped cross-section bent plate) is obtained by in-plane compression of the side walls 23a, 23b and flanges 25a, 25b of the preformed product 20 (first hat-shaped cross-section bent plate) along the circumferential direction of the hat shape. According to this press-forming method, when the side walls 23a, 23b and flanges 25a, 25b are in-plane compressed along the circumferential direction of the hat shape, stress generated in the bent portion of the hat shape is canceled. Therefore, unlike conventional press-forming methods using deep drawing (see, for example, Patent Document 1), the press-forming method of this embodiment can eliminate springback that occurs in the preformed product 20 through a simple process such as compression molding. Furthermore, the press-formed product 10 obtained by this press-forming method has excellent dimensional accuracy due to the suppression of springback.

[0062] Furthermore, in the press molding method of this embodiment, a second step is performed in which outer end portions 28a, 28b of the flanges 25a, 25b of the preformed product 20 are pressed toward the first corner portion 58 of the punch 31 in parallel with a third step in which the side walls 23a, 23b and the flanges 25a, 25b of the preformed product 20 are compressed between the die 32 and the punch 31. This press molding method makes it possible to impart in-plane compression to the side walls 23a, 23b and the flanges 25a, 25b of the preformed product 20 (first bent plate body having a hat-shaped cross section) in a simpler process.

[0063] The press-forming apparatus 30 of this embodiment includes a compression mechanism consisting of dies 32a, 32b and a punch 31 that compress the side walls 23a, 23b and flanges 25a, 25b of the preform 20, a first pressing mechanism that presses outer end portions 28a, 28b of the flanges 25a, 25b, and a second pressing mechanism that presses upper end portions 29a, 29b of the side walls 23a, 23b. Such a press-forming apparatus 30 can achieve the effects of the above-described press-forming method and can implement the press-forming method with a simple configuration.

[0064] In the press forming apparatus 30 of this embodiment, the first pressing mechanism and the second pressing mechanism are linked via a cam mechanism 40. With this press forming apparatus 30, when performing the compression process of the flanges 25a, 25b and the side walls 23a, 23b, it is possible to easily control the process of pressing the outer end portions 28a, 28b of the flanges 25a, 25b and the process of pressing the upper end portions 29a, 29b of the side walls 23a, 23b, which are performed in conjunction with the compression process. This allows for more accurate in-plane compression of the flanges 25a, 25b and the side walls 23a, 23b.

[0065] In the press forming apparatus 30 of this embodiment, the first pressing mechanism has fifth wall surfaces 37a, 37b that approach the outer end surfaces 36a, 36b of the punch 31 as the second corners 68a, 68b of the dies 32a, 32b approach the first corners 58a, 58b of the punch 31. In other words, the fifth wall surfaces 37a, 37b of the compression blocks 34a, 34b constituting the first pressing mechanism are integrated with the die bodies 33a, 33b to form the dies 32a, 32b. According to this press forming apparatus 30, the compression mechanism consisting of the dies 32a, 32b and the punch 31 can be interlocked with the first pressing mechanism that presses the outer ends 28a, 28b of the flanges 25a, 25b. This simplifies the configuration of the compression mechanism and the first pressing mechanism, allowing the press forming apparatus 30 to be made more compact.

[0066] In the press forming apparatus 30 of this embodiment, the second pressing mechanism is a pad 31c that presses the top portion 31c of the preform 20 when the second corner portions 68a, 68b of the dies 32a, 32b relatively approach the first corner portions 58a, 58b of the punch 31. According to this press forming apparatus 30, the compression mechanism consisting of the dies 32a, 32b and the punch 31 can be operated in conjunction with the first pressing mechanism consisting of the pad 35c. This simplifies the configurations of the compression mechanism and the second pressing mechanism, allowing the press forming apparatus 30 to be made more compact.

[0067] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0068] FIG. 5A is a diagram illustrating the configuration of a first modified example of the press-forming apparatus 30. FIG. 5B is a diagram illustrating the operation of the press-forming apparatus 30 according to the first modified example of FIG. 5A. As shown in FIG. 5A, in the press-forming apparatus 30 according to the first modified example, the punch 31 is divided into an upper punch 311 and a lower punch 312. A lifter 313 is disposed between the upper punch 311 and the lower punch 312. The lifter 313 is formed of a cushion member such as a coil spring. When the first step shown in FIG. 4A is performed, the lifter 313 uses a biasing force to lift the upper punch 311, which holds the top portion 24 of the preform 20, with a predetermined gap between it and the pad 35a.

[0069] 5B , in the press forming apparatus 30 according to the first modification, when the pad 35a presses down the top 24 of the preform 20 against the biasing force of the lifter 313, the gap between the upper punch 311 and the lower punch 312 disappears. As a result, when the pad 35a compresses the side walls 23a, 23b and the flanges 25a, 25b between the punch 31 and the dies 32a, 32b, the pad 35a presses the upper end portions 29a, 29b of the side walls 23a, 23b toward the first corner portions 58a, 58b of the punch 31.

[0070] According to the press forming apparatus 30 of the first modified example, the amount by which the pad 35a presses down the upper end portions 29a, 29b can be determined by the gap between the upper punch 311 and the lower punch 312, so that the amount of pressing down can be quantified. Note that in Fig. 5B, reference numerals 34a, 34b denote compressed blocks.

[0071] In addition, in the press forming apparatus 30 (see FIG. 3 ) of the above embodiment, the first wall surfaces 53a, 53b of the punch 31 are inclined so that the distance therebetween gradually narrows as they extend upward. However, there are no particular limitations on the relative inclination of the first wall surfaces 53a, 53b. In other words, in the press forming apparatus 30, the compression blocks 34a, 34b are disposed on the die 32a, 32b side. Therefore, the first wall surfaces 53a, 53b may be parallel to each other in a front view of the press forming apparatus 30 shown in FIG. 3 , or may be undercut, as opposed to the first wall surfaces 53a, 53b shown in FIG. 3 . Incidentally, the undercut first wall surfaces 53a, 53b can be subjected to prospective forming. Furthermore, although not shown, ensuring the accuracy of press-formed products with straight walls or walls close to straight walls requires the use of undercut-shaped dies. However, this processing is not possible with existing press forming apparatuses. In contrast to this, the press forming device 30 of this embodiment can be configured to use a mold with such an undercut shape by combining the cam mechanism 40 and the compression blocks 34a, 34b.

[0072] In the press-forming method of the above embodiment, the preformed product 20 has side walls 23a, 23b longer than the side walls 13a, 13b of the press-formed product 10. However, the preformed product 20 is not limited to this. In other words, in the press-forming method of the present invention, as described above, when the second step is performed in parallel with the third step, a preformed product 20 having a circumferential length longer than that of the punch 31 is placed on the punch 31. Therefore, as described above, the length of the flanges 25a, 25b of the preformed product 20 is generally set to be approximately the same as that of the flanges 15a, 15b of the press-formed product 10. However, the length of the flanges 25a, 25b of the preformed product 20 may be slightly increased or decreased relative to the length of the flanges 15a, 15b of the press-formed product 10 (see FIG. 1 ), provided that the preformed product 20 has a circumferential length longer than that of the punch 31.

[0073] DESCRIPTION OF SYMBOLS 10 Press-molded product 11 High-ridge portion 12 Flange portion 13a Side wall 13b Side wall 14 Top portion 15a, 15b Flange 16 Lateral wall 18 Convex surface 19 Concave surface 20 Pre-formed product 23a, 23b Side wall 24 Top portion 25a, 25b Flange 28a, 18b Outer end portion 29a, 29b Upper end portion 30 Press-molding device 31 Punch 31a Base portion 31b Protruding portion 31c Top portion 32 Die 32a Die 32b Die 33a Die body 33b Die body 34 Compression block 34a Compression block 34b Compression block 35 Pad unit 35a Pad 35b Cushion member 35c Pad support portion 35d Groove portion 35e Cylindrical space 36a Outer end surface 36b Outer end surface 37 Fifth wall surface 37a Fifth wall surface 37b Fifth wall surface 39 Elevating mechanism 40 Cam mechanism 41a Cam slider 41b Cam slider 42a Cam base 42b Cam base 43a, 43b Cam drivers 44a, 44b Cam surface 45a Inclined surface 45b Inclined surface 46a Urging means 47a Slide member 53a First wall surface 53b First wall surface 55a Second wall surface 55b Second wall surface 56 Side wall surface 57a Inclined wall surface 57b Inclined wall surface 58 First corner portion 58a First corner portion 58b First corner portion 63a Third wall surface 63b Third wall surface 65a Fourth wall surface 65b Fourth wall surface 68a Second corner portion 68b Second corner portion 35d1 Bottom surface 35d2 Side surface Ax Central axis G Gap Hp Horizontal surface S Spring