Presswork-based thickness addition forming method and expandable member

Abstract

A thickness addition forming method increases at least part of a workpiece by presswork. The method includes pressing part of the workpiece, producing a flow in material of the workpiece, thereby displacing outward at least one of two surfaces opposed to each other in a second direction of the workpiece, increasing at least part of the workpiece in wall thickness, and thereby forming a thickened portion. The thickened portion is formed by displacing an area-to-be-displaced outward while applying a reaction force to the area-to-be-displaced using an elastic member.

Description

TECHNICAL FIELD

[0001] The present invention relates to a presswork-based thickness addition forming method and an expandable member used for the thickness addition forming method.BACKGROUND ART

[0002] It is said that the number of automotive parts is as large as tens of thousands. For example, press-formed products are often used for suspension-related parts. Regarding press-formed products, by applying various types of presswork to plate material such as blank, the plate material is formed into a desired shape, and in the case of suspension-related parts, it is sometimes desired to improve strength and rigidity of specific sites.

[0003] In relation to this, a relevant conventional technique has been disclosed that forms reinforced sites by forming uneven portions on skeleton material and then compressing the uneven portions.CITATION LISTPatent LiteraturesPatent Literature 1: JP 2011-161941 ASUMMARY OF INVENTION

[0005] As a technique related to Patent Literature 1, the inventors have been studying a method for increasing wall thickness of a workpiece using presswork. The inventors have studied methods for increasing the wall thickness of a workpiece by pressing part of plate material such as an end face of the workpiece without going through the process of forming uneven portions by presswork. Among others, by paying attention to the fact that the workpiece can buckle when at least part of the workpiece is increased in wall thickness by compressing part of the workpiece, the inventors have been conducting active studies on method that will not cause buckling.

[0006] The present invention has an object to prevent buckling of a workpiece when at least part of the workpiece is increased in wall thickness by using compression during presswork.

[0007] One aspect of the present invention is a thickness addition forming method that increases at least part of a workpiece in wall thickness by presswork. The method involves pressing part of the workpiece, producing a flow in material of the workpiece, thereby displacing outward at least one of two surfaces opposed to each other in a thickness direction of the workpiece, increasing at least part of the workpiece in wall thickness, and thereby forming a thickened portion. The thickened portion is formed by displacing an area-to-be-displaced outward while applying a reaction force to the area-to-be-displaced using an expandable member.

[0008] Another aspect of the present invention is an expandable member that is used for the thickness addition forming method and able to generate the reaction force when at least one of the two surfaces opposed to each other in the thickness direction is displaced outward.BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a perspective view illustrating a press-formed product according to a first embodiment.

[0010] FIG. 2 is a side view of FIG. 1.

[0011] FIG. 3 is a sectional view taken along line 3-3 in FIG. 2.

[0012] FIG. 4 is a flowchart illustrating a presswork-based thickness addition forming method according to the first embodiment.

[0013] FIG. 5 is a side view illustrating a workpiece before presswork.

[0014] FIG. 6 is an exploded perspective view illustrating a configuration of a thickness addition forming apparatus adapted to form a thickened portion of the press-formed product illustrated in FIG. 1.

[0015] FIG. 7 is a sectional view illustrating how a workpiece is set on the thickness addition forming apparatus illustrated in FIG. 6.

[0016] FIG. 8 is a diagram illustrating how a pressing area on a workpiece is pressed.

[0017] FIG. 9 is a sectional view illustrating a thickened portion formed on a workpiece by the thickness addition forming apparatus illustrated in FIG. 6.

[0018] FIG. 10 is an enlarged view of part EV in FIG. 9.

[0019] FIG. 11 is an enlarged view illustrating corners of a stationary die placed around a site to become a thickened portion as a result of presswork carried out by a thickness addition forming apparatus according to a second embodiment, where the stationary die is a modification of FIG. 10.

[0020] FIG. 12 is an enlarged view corresponding to FIG. 10, illustrating Modification 1 of the second embodiment.

[0021] FIG. 13 is an enlarged view corresponding to FIG. 10, illustrating Modification 2 of the second embodiment.

[0022] FIG. 14 is a sectional view corresponding to FIG. 9, illustrating how a thickened portion is formed by a thickness addition forming apparatus according to a third embodiment.

[0023] FIG. 15 is a perspective view illustrating a surface of a movable die of a thickness addition forming apparatus according to a fourth embodiment.

[0024] FIG. 16 is a sectional view illustrating a surface of a movable die of a thickness addition forming apparatus according to Modification 1 of the fourth embodiment.

[0025] FIG. 17 is a plan view illustrating a surface of a movable die of a thickness addition forming apparatus according to Modification 2 of the fourth embodiment.

[0026] FIG. 18 is a plan view illustrating a surface of a movable die of a thickness addition forming apparatus according to Modification 3 of the fourth embodiment.

[0027] FIG. 19 is a sectional view corresponding to FIG. 7, illustrating a thickness addition forming apparatus according to a fifth embodiment.

[0028] FIG. 20 is a perspective view illustrating a press-formed product according to a modification of the first embodiment.

[0029] FIG. 21 is a perspective view illustrating a press-formed product according to a modification of the first embodiment.

[0030] FIG. 22 is a schematic diagram illustrating a thickness addition forming apparatus according to a comparative example in comparison with an example.DESCRIPTION OF EMBODIMENTS

[0031] Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the following description does not limit the technical scope or the meanings of terms recited in the accompanying claims. Besides, size ratios in the drawings are exaggerated for convenience of explanation and may be different from actual size ratios. Here, an orthogonal coordinate system is illustrated in the drawings, where X corresponds to a longitudinal direction and the like of a press-formed product P1 in FIG. 1 as an example, and is referred to as a first direction X. Y corresponds to a thickness direction of a workpiece b, and is referred to as a second direction Y. Z corresponds to a height direction and the like of the workpiece as an example, and is referred to as a third direction Z.First Embodiment

[0032] FIGS. 1 to 3 are diagrams intended for use in describing the press-formed product P1 according to a first embodiment. The press-formed product P1 formed by a thickness addition forming method according to the first embodiment can be configured as a long member extending in a long form in one direction in an open section as an example. As shown in FIGS. 1 and 2, the press-formed product P1 includes two side walls w1 extending from edges, and a connecting wall w2 that connects the two side walls w1. The press-formed product P1 can be formed of blank (the workpiece b) made of rolled material and the like (see FIGS. 5 and 8). As shown in FIG. 3, the press-formed product P1 can be configured such that a cross-section intersecting the longitudinal direction running along one side is formed into a so-called U-shape having a few bending parts bp (see FIG. 3). However, this shape is exemplary, and the shape of the press-formed product is not limited to FIG. 3 and the like.

[0033] The press-formed product P1 includes a thickened portion t1 placed at a local site and the like that needs rigidity or strength. The thickened portion t1 is formed protruding outward, i.e., in a direction intersecting the longitudinal direction (first direction X) of the press-formed product P1. Consequently, the corresponding site is configured to be larger in wall thickness than other sites devoid of the thickened portion t1 in the longitudinal direction. As described later, the thickened portion t1 is formed, by pressing a pressing area r1 (see FIG. 8), which is part of the workpiece b, and thereby producing a flow in the material of the workpiece b. The thickened portion t1 is formed by displacing outward at least one of the two surfaces opposed to each other in the second direction Y, which corresponds to the thickness direction of the workpiece b, and thereby increasing at least part of the workpiece b in wall thickness. As shown in FIGS. 1 and 2, in the present embodiment, the thickened portion t1 is formed partially on a side wall w1. In the present embodiment, as shown in FIG. 1, the thickened portion t1 is formed as a polygon such as a quadrangle. A hollow substantially rectangular cross-section formed by pairing the press-formed products P1 according to the present embodiment such that openings face each other can be used as at least some of suspension skeleton-related parts such as suspension side members or press-formed skeleton-related parts. Parts such as brackets may be fixed to predetermined sites in the longitudinal direction on structural parts such as side members, and the thickened portion t1 of the press-formed product P1, if provided at a site to which a bracket or the like has been fixed, can be used to meet required standards for strength, rigidity and the like.About Thickness Addition Forming Apparatus

[0034] Next, of manufacturing equipment for the press-formed product P1, a thickness addition forming apparatus that forms the thickened portion t1 will be described. FIGS. 5 to 10 are diagrams intended for use in describing the thickness addition forming apparatus and thickness addition forming method according to the present embodiment. Note that in forming a press-formed product into a substantially U-shaped open section such as the press-formed product P1 shown in FIG. 1, a stationary die and a movable die are often used, where the movable die approaches, and separates from, the stationary die (at least part of a boundary surface between the stationary die and the movable die has been formed into a substantially U-shaped surface). However, a method for forming such an open section shape is publicly known, and thus detailed description thereof will be omitted.

[0035] The thickness addition forming apparatus used to form the thickened portion t1 of the press-formed product P1 includes stationary dies 10, and 20 (which correspond to a first stationary die), stationary dies 30 and 40 (which correspond to a second stationary die), an elastic member 50, and movable dies 60 and 70 as shown in FIGS. 6, 7, and 8. Note that, of the U-shaped section, formation of the thickened portion t1 will be described below.

[0036] In FIGS. 7 and 9, the stationary die 10 is placed so as to abut the workpiece b on the side opposite to the site of the workpiece b to be thickened. As a die adjacent to the area of the workpiece b in which material flow occurs when the thickened portion t1 is formed, the stationary die 10 can slide with respect to the workpiece b.

[0037] On the side opposite to the site placed in contact with the stationary die 10, the stationary die 20 is placed so as to abut the workpiece b in a neighboring site in which the thickened portion t1 is scheduled to be formed. In displacing an area-to-be-displaced of the workpiece b outward, surroundings of the workpiece b other than the area-to-be-displaced are held down by the stationary die 20 placed on the surroundings of the area-to-be-displaced so as not to get displaced outward during the presswork. As shown in FIG. 6, the stationary dies 20 are configured to be placed adjacent to the surroundings of the site to become the thickened portion t1 not only in the first direction X, but also in the third direction Z. A corner 21 of the stationary die 20 which is located on a boundary with the site to become the thickened portion t1 is shaped into a relatively sharp corner in the present embodiment as shown in FIGS. 9 and 10.

[0038] The stationary dies 30 and 40 are placed to hold the elastic member 50 and the movable die 60 movably in the second direction Y. The stationary dies 30 and 40 are configured to support the elastic member 50 by being placed adjacent to the elastic member 50 in the second direction Y in which a reaction force is applied by the elastic member 50. The stationary die 30 is placed adjacent to the elastic member 50 in a travel direction (the second direction Y) of the movable die 60 while the stationary die 40 is placed farther away from the elastic member 50 than the stationary die 30. In the present embodiment, the stationary die 30 and the stationary die 40 are prepared as separate dies and used as an integrated unit. However, as long as the elastic member 50 and the movable die 60 can be held movably, the stationary die 30 and the stationary die 40 may be configured to be an integrated die rather than separate dies.

[0039] The elastic member 50 is constructed integrally with the movable die 60 that can move relative to the stationary dies 20, 30, and 40 and configured to be able to apply a reaction force to one of areas-to-be-displaced via the movable die 60 in a state in which the movable die 60 can come into contact with the workpiece b. The elastic member 50 is configured to be able to expand in a thickening direction (the second direction Y in FIG. 7 and the like) used in forming the thickened portion t1 on the workpiece b and is placed adjacent to the stationary die 30. The formation of the thickened portion t1 described above is performed by displacing the area-to-be-displaced outward while applying a reaction force to the area-to-be-displaced using the elastic member 50. The elastic member 50 is configured to be deformable so as to be pressed in the second direction Y when deforming the workpiece b in such a way as to thicken the workpiece b. The elastic member 50 can be configured to contain material such as resin as a member capable of elastic deformation.

[0040] The movable die 60 is placed on the opposite side of the workpiece b from the stationary die 10 in such a way as to be able to apply a reaction force to the site that comes into contact with the workpiece b and becomes the thickened portion t1 when the pressing area r1 applies a press force to the workpiece b. The movable die 60 is configured to be able to move integrally with the elastic member 50. As shown in FIG. 7, the movable die 60 includes a forward end 61 slidable with respect to the workpiece b such that the thickened portion t1 can be formed on the workpiece b, and a base end 62 formed protruding from the forward end 61 in the second direction Y, which is the travel direction of the die. As with the stationary die 10, the forward end 61 is slidable with respect to the workpiece b as a die adjacent to the area of the workpiece b in which material flow occurs in forming the thickened portion t1.

[0041] As shown in FIG. 8, to form the thickened portion t1, the movable die 70 is placed movably in the third direction Z in order to be able to press the pressing area r1 protruding from around the workpiece b, as an example. The travel direction (the third direction Z in FIG. 8) of the movable die 70 is configured to be substantially orthogonal to a direction (the second direction Y in FIG. 9) in which a site to become the thickened portion t1 protrudes from the workpiece b. The movable die 70 can be placed above or below the workpiece b in FIG. 8 and the like.Thickness Addition Forming Method

[0042] Next, the thickness addition forming method according to the present embodiment will be described, where the method increases at least part of a workpiece in wall thickness by presswork. FIG. 4 is a flowchart illustrating the thickness addition forming method according to the present embodiment.

[0043] First, the stationary dies 10, 20, 30, and 40, the elastic member 50, and the movable dies 60 and 70 are set (S1). Next, the stationary dies 10, 20, 30, and 40 are set so as to immobilize the workpiece b (S2). Whereas it has been explained that the movable die 70 is placed above or below the workpiece b in FIG. 8, in addition to the stationary dies 10, 20, 30, and 40, the stationary dies of the thickness addition forming apparatus can include a stationary die (not shown) placed on the opposite side of the movable die 70 with the workpiece b sandwiched therebetween.

[0044] Next, as shown in FIG. 8, by pressing the movable die 70 against the pressing area r1 of the workpiece b, a press force is applied to the workpiece b (S3). As described above, on the opposite side of the movable die 70, the workpiece b is held by stationary dies such that the overall position of the workpiece b will not change. Therefore, in this state, when a press force is applied to the pressing area r1, material flow occurs in the workpiece b and the material flows in the second direction Y (to the right side of the workpiece b in FIG. 9) in which the material can flow in FIG. 9. It is impossible or difficult for material to move to the site of the workpiece b on which the stationary die 20 is placed, and thus the material flows to the movable die 60, which is movable.

[0045] In doing so, since the elastic member 50 is placed on the opposite side of the movable die 60 from the workpiece b, the material comes into contact with the movable die 60 and flows with a reaction force being applied by the elastic member 50 to the site which is to become the thickened portion t1. In doing so, the workpiece b forms the thickened portion t1 while sliding with respect to the movable die 60 along a surface of contact with the movable die 60 (see FIG. 9). In forming the thickened portion t1, the workpiece b can slide with respect to the stationary die 10 on the opposite side from the movable die 60. Consequently, the thickened portion t1 of the workpiece b deforms so as to thicken while being held down by the movable die 60. Thus, by being formed with a reaction force being applied by the elastic member 50, the thickened portion t1 can prevent itself from being buckled. Furthermore, creasing of the thickened portion can be prevented or curbed.

[0046] After the thickening, the press-formed product P1 is removed from the thickness addition forming apparatus described above by dismantling the stationary dies 10, 20, 30, 40, the elastic member 50, and the movable dies 60 and 70 (S4). Note that the thickness addition forming method described above may be performed either before or after forming the workpiece b from a flat shape into a substantial U-shape in the method for manufacturing the press-formed product P1 shown in FIG. 1.

[0047] As described above, the thickness addition forming method for the workpiece b according to the present embodiment produces a flow in the material of the workpiece b by pressing part of the workpiece b. Then the thickened portion t1 is formed by displacing outward at least one of the two surfaces opposed to each other in the thickness direction of the workpiece b, and thereby increasing at least part of the workpiece b in wall thickness. The formation of the thickened portion t1 is performed by displacing the area-to-be-displaced outward while applying a reaction force to the area-to-be-displaced using the elastic member 50. In this way, in forming the thickened portion t1 on the workpiece b using compression, by keeping the area-to-be-displaced to be thickened from being deformed sharply, the thickened portion can be prevented from being buckled. Furthermore, by causing the area-to-be-displaced to follow the movable die 60 while applying a reaction force, creasing of the thickened portion can be prevented or curbed.

[0048] In displacing the area-to-be-displaced of the workpiece b outward, surroundings of the area-to-be-displaced, i.e., areas other than the area-to-be-displaced, are configured to be held down by the stationary die 20 so as not to get displaced. This configuration makes it possible to control the shape of thickening appropriately.

[0049] The elastic member 50 is supported by the stationary dies 30 and 40 placed adjacent to the elastic member 50 in the second direction Y in which a reaction force is applied. The elastic member 50 is constructed integrally with the movable die 60 that can move relative to the stationary dies 20, 30, and 40. The elastic member 50 is configured to be able to apply a reaction force to the area-to-be-displaced via the movable die 60 in a state in which the movable die 60 can come into contact with the workpiece b. This configuration makes it possible to prevent buckling of the area-to-be-displaced, which is to become the thickened portion t1.

[0050] The area of the workpiece b in which material flow occurs is configured to be able to slide with respect to the stationary die 10, the forward end 61 of the movable die 60, and the like, which are placed adjacent to the area during formation of the thickened portion t1. This configuration makes it possible to form the thickened portion t1 by applying a press force (compressive force) to the pressing area r1 and thereby displacing the area-to-be-displaced of the workpiece b placed adjacent to the stationary die 10 and the movable die 60 in the second direction Y corresponding to the thickness direction when material flow occurs.Second EmbodimentFIGS. 11, 12, and 13 are enlarged views illustrating corners of stationary dies placed around sites to become thickened portions, where the stationary dies are modifications of the first embodiment in FIG. 10. Whereas it has been explained in the first embodiment that the corner 21 of the stationary die 20 which is located on a boundary with the thickened portion t1 of the workpiece b is shaped into a relatively sharp corner, the corner can also be configured as follows. Note that components other than corners of stationary dies are similar to those of the first embodiment, and thus description of components in common with the first embodiment will be omitted.

[0052] Of a stationary die 20a located in surroundings of the workpiece b, at a corner 21 a located on a boundary with the thickened portion t1, as shown in FIG. 11, a rounded shape may be provided as a flow shape for use to facilitate material flow in the workpiece b. As a shape for use to facilitate material flow in the workpiece b, a corner 21b of a stationary die 20b may also be chamfered as shown in FIG. 12. Besides, as shown in FIG. 13, a corner 21c of a stationary die 20c may be tapered in the second direction Y.

[0053] The flow shape described above may be provided for each side of a polygonal shape when the thickened portion t1 is polygonal in shape as shown in FIG. 1.

[0054] As described above, in the present embodiment, on the stationary dies 20a, 20b, and 20c, flow shapes are provided at the corners 21a, 21b, and 21c in order not to obstruct material flow in the workpiece b in the surroundings of the area-to-be-displaced. Consequently, the thickened portion t1 can be formed smoothly by the application of a press force (compressive force) to the pressing area r1.

[0055] When the area-to-be-displaced that is to become the thickened portion t1 is polygonal in shape, the flow shape at the corners 21a, 21b, and 21c of the stationary dies 20a, 20b, and 20c may be provided for each side of a polygonal shape. This makes it possible to form the thickened portion t1 by gathering material to the area-to-be-displaced from various sites through material flow upon application of the press force.Third Embodiment

[0056] FIG. 14 is a sectional view corresponding to FIG. 9, illustrating a thickness addition forming apparatus adapted to form the workpiece b. Whereas it has been explained in the first embodiment that the elastic member 50 is supported by the stationary dies 30 and 40, the stationary die 30 can be configured as follows. Note that in the present embodiment, of the stationary dies that support the elastic member 50, the stationary die 30 adjacent to the base end 62 of the movable die 60 is different in configuration from the first embodiment and other components are similar to those of the first embodiment. Therefore, description of components in common with the first embodiment will be omitted.

[0057] As shown in FIG. 14, in the present embodiment, a stationary die 30d adapted to support the elastic member 50 is configured to be able to come into contact with (abut) the base end 62 of the movable die 60 when the movable die 60 moves by the application of a press force from the movable die 70. That is, the stationary die 30d includes a support 31d adapted to support the elastic member 50 in a manner similar to the first embodiment, and an abutting portion 32d capable of abutting the base end 62 of the movable die 60 by being placed adjacent to the support 31d. A contact surface of the abutting portion 32d is formed into a flat surface substantially orthogonal to the second direction Y, which is the travel direction. However, as long as the contact surface can contact the base end 62 of the movable die 60 at an intended position, it is not necessary that the contact surface of the abutting portion 32d is shaped to be orthogonal to the travel direction or to be flat.

[0058] Note that with the thickness addition forming method using the thickness addition forming apparatus according to the present embodiment, when a press force is applied by the movable die 70, the base end 62 of the movable die 60 bumps against the abutting portion 32d of the stationary die 30d and the movable die 60 stops moving. The other matters are similar to the first embodiment, and thus detailed description of the method will be omitted.

[0059] As described above, in the present embodiment, in displacing the area-to-be-displaced of the workpiece b outward, the base end 62 of the movable die 60 is configured to stop by bumping against the abutting portion 32d of the stationary die 30d. This configuration makes it easier to form the thickened portion t1 with an intended thickness.Fourth Embodiment

[0060] FIG. 15 is a perspective view illustrating a movable die 60e according to a fourth embodiment, FIG. 16 is a sectional view illustrating a movable die 60f, FIGS. 17 and 18 are plan views illustrating surfaces of movable dies 60g and 60h according to modifications of the fourth embodiment.

[0061] It has been explained in the first embodiment that when the area-to-be-displaced is displaced outward by pressing the movable die 70, the area-to-be-displaced of the workpiece b is slidable with respect to the movable die 60. In relation to this, a sliding area of the movable die 60 with respect to a stationary die including the workpiece b can be configured as follows. Note that the present embodiment differs from the first embodiment in the properties of a sliding area between the workpiece on the movable die and the stationary dies 20 and 30, and the rest is similar to the first embodiment, and thus description of components in common with the first embodiment will be omitted.

[0062] In the present embodiment, in forming the thickened portion t1, as an example of treatment to reduce frictional resistance with a mating part, a plurality of grooves 63 that can hold lubricating oil or the like can be provided on a surface of the sliding site as shown in FIG. 15. Whereas, in the present embodiment, grooves 63 are formed along the first direction X and the second direction Y, as long as the frictional resistance with the mating part in the sliding area can be reduced, specific shapes and arrangement of the grooves are not limited to FIG. 15.

[0063] As a method for reducing the frictional resistance with the mating part such as the workpiece b at the sliding site, a layer L1 of solid lubricant may be provided on an outer side of a metal or other part L2, which is a main body of a movable die 60f as shown in FIG. 16.

[0064] As a method for reducing the frictional resistance of a surface, a surface placed in contact with a mating part of the movable die may be formed into a staggered pattern by laser machining as in the case of a movable die 60g in FIG. 17 or a surface placed in contact with a mating part may be formed into a striped pattern by laser machining or the like as in the case of a movable die 60h in FIG. 18. Such treatment to reduce the frictional resistance of a surface may be applied not only to contact surfaces of the movable die 60 with the opposing workpiece b and stationary dies 20, but also to a contact surface of the stationary die 10 with the workpiece b.

[0065] As described above, according to the present embodiment, to facilitate sliding, the treatment to reduce the frictional resistance of the surface is applied to the sliding area used in forming the thickened portion t1. This makes it possible to prevent buckling of the workpiece b in forming the thickened portion t1 on the workpiece b using compression, and prevent or curb creasing of the workpiece b by reducing resistance of the sliding site.

[0066] The above-mentioned treatment to reduce the frictional resistance of the surface is applied to the contact surface of the movable die 60 with the workpiece b, the stationary dies 20 and 30, and the like and / or to the contact surface of the stationary die 10 with the workpiece b. This configuration makes it possible to reduce friction of the movable die 60 and / or the stationary die 10 with surrounding contact elements and thereby form the thickened portion t1 smoothly.Fifth Embodiment

[0067] FIG. 19 is a sectional view corresponding to FIG. 7, illustrating a thickness addition forming apparatus for the workpiece b according to a fifth embodiment. Whereas it has been explained in the first embodiment that the movable die 60 can move relative to the stationary dies 20, 30, and 40, the movable die 60 may have the following configuration. Note that the present embodiment differs only in the configurations of movable dies and the rest is similar to the first embodiment, and thus description of components in common with the first embodiment will be omitted.

[0068] In the present embodiment, on boundaries of a movable die 60k with the stationary die 20 and the stationary die 30, machine elements 80 are placed to facilitate contact between the movable die 60k and the stationary dies 20 and 30. In the present embodiment, the machine elements 80, which are constructed integrally with the movable die 60k, and have a plurality of rotating members such as rollers provided rotatably. When the movable die 60k moves in the second direction Y corresponding to the thickness direction by the application of a press force from the movable die 70, the movable die 60k can reduce contact resistance with the stationary dies 20 and 30 by the machine elements 80. Note that in FIG. 19, the machine elements 80 are provided on both a contact site between the movable die 60k and the stationary die 20 and a contact site between the movable die 60k and the stationary die 30, but may be provided only on one of the contact sites.

[0069] Note that with the thickness addition forming method using the thickness addition forming apparatus according to the present embodiment is similar to the first embodiment except that in forming the thickened portion t1 using the movable die 60k, the movable die 60k moves relative to the stationary dies 20 and 30 by being placed in contact with the machine elements 80, and thus detailed description will be omitted.

[0070] As described above, according to the present embodiment, the machine elements 80 adapted to smoothly move the movable die 60k relative to the stationary dies 20 and 30 through rotation are configured to be installable on the boundary between the movable die 60k and the stationary die 20 as well as on the boundary between the movable die 60k and the stationary die 30. Consequently, when a press force (compressive force) is applied by the movable die 70, the movable die 60k can be moved smoothly relative to the stationary dies 20 and 30, preventing buckling of the area-to-be-displaced and preventing or curbing creasing.

[0071] Note that the present invention is not limited to the embodiment described above and various changes can be made within the scope of the appended claims. It has been explained in the first embodiment that the thickness addition forming apparatus includes the movable die 60. However, as long as the area-to-be-displaced of the workpiece b can be thickened by the application of a press force from the movable die 70, the thickness addition forming apparatus may be configured to place the elastic member 50 directly in contact with the area-to-be-displaced without being equipped with the movable die 60.

[0072] FIGS. 20 and 21 are perspective views illustrating press-formed products P2 and P3 according to modifications of the first embodiment. It has been explained in the first embodiment that the thickened portion t1 of the press-formed product P1 (see FIG. 1) is partially provided on a side wall w1, which is a part in a circumferential direction in a plane intersecting the longitudinal direction. However, when the pressing area is pressed, if geometry and arrangement of the present thickness addition forming apparatus is set up according to a site needing thickening and a thickened portion is formed using a resulting material flow, the shape of the thickened portion is not limited to FIG. 1, FIG. 2, and the like. For example, as with the press-formed product P2 in FIG. 20, a thickened portion t2 may be provided on an entire periphery in a plane intersecting the longitudinal direction and / or may be formed by being spread in the longitudinal direction more widely than the thickened portion t1.

[0073] As shown in FIG. 21, a thickened portion t3 may be provided in such a way as to thicken at least part of the area of the workpiece which is running from a bending part bp to an edge e1 in a cross-section intersecting the longitudinal direction.Comparison

[0074] Both a pressing load applied when a thickened portion was formed on a workpiece and a force acting on a die adjacent to the thickened portion were compared between when an elastic member was provided and when no elastic member was provided, and this will be described below. FIG. 22 is a schematic sectional view illustrating a thickness addition forming apparatus according to a comparative example.

[0075] In the present comparison, the pressure required to deform a plate thickness to a desired plate thickness was compared between when the thickened portion t1 was formed on the workpiece b using the above-mentioned thickness addition forming apparatus such as shown in FIG. 7 and when a thickened portion was formed without using any of the elastic member 50, the movable die 60, and the stationary dies 30 and 40 as shown in FIG. 22. Here, the thickness addition forming apparatus equipped with the elastic member 50 as shown in FIG. 7 is referred to as an example and the thickness addition forming apparatus not equipped with the elastic member 50 as shown in FIG. 22 is referred to as a comparative example.

[0076] In the present comparison, in addition to the pressing load described above, forces acting on the dies adjacent to the workpiece b, such as the stationary dies 30 and 40 in the example, were compared between the example and the comparative example. Here, the thickness addition forming apparatus according to the comparative example were configured similarly to the thickness addition forming apparatus in FIG. 7 except that a stationary die 90 was used instead of the stationary dies 20, 30, and 40, the elastic member 50, and the movable die 60, as shown in FIG. 22. That is, with the stationary die 10 abutted against the workpiece b and with the stationary die 90 spaced away from the workpiece b by a distance equal to the thickness to be increased by the deformation, the thickness addition forming apparatus according to the comparative example pressed the movable die 70 against the pressing area r1 and applied the pressing load.

[0077] By comparing the pressing load applied by the movable die 70 between the example and the comparative example, it was confirmed that the example was able to thicken a specific site such as the thickened portion t1 to a desired thickness with a smaller pressing load than the thickness addition forming apparatus according to the comparative example. From this confirmation result, it is considered that a component that applies a pressing load, such as the movable die 70, can be downsized compared to thickness addition forming apparatus that does not use the elastic member 50.

[0078] Regarding the forces received by the stationary dies 30 and 40 or the stationary die 90, it was confirmed that the example was able to reduce the forces received through the workpiece b compared to the thickness addition forming apparatus according to the comparative example. From this confirmation result, it is considered that components such as the stationary dies 30 and 40 can be downsized compared to components that do not use the elastic member 50, such as the stationary die 90 of the thickness addition forming apparatus. Regarding this point, it is considered that the thickness addition forming apparatus according to the example can reduce an input load from the pressing load thanks to the presence of the elastic member 50 between the workpiece b and the stationary dies 30 and 40 and the like compared to the comparative example.

[0079] The present invention includes the following aspects and forms.

[0080] 1. A presswork-based thickness addition forming method that increases at least part of a workpiece in wall thickness by presswork, the method comprising pressing part of the workpiece, producing a flow in material of the workpiece, thereby displacing outward at least one of two surfaces opposed to each other in a thickness direction of the workpiece, increasing at least part of the workpiece in wall thickness, and thereby forming a thickened portion, wherein the thickened portion is formed by displacing an area-to-be-displaced of the workpiece outward while applying a reaction force to the area-to-be-displaced using an expandable member.

[0081] 2. The presswork-based thickness addition forming method according to 1 above, wherein a long member extending at least in one direction is used for the workpiece in which the thickened portion is formed.

[0082] 3. The thickness addition forming method according to 1 or 2 above, wherein the workpiece is configured such that a cross-section intersecting a direction running along one side is formed into a shape having a bending part

[0083] 4. The thickness addition forming method according to 3 above, wherein the thickened portion is formed in at least part of an area of the workpiece which is running from the bending part to an edge.

[0084] 5. The presswork-based thickness addition forming method according to any one of 1 to 4 above, wherein in displacing the area-to-be-displaced outward, surroundings of the area-to-be-displaced of the workpiece are held down by a first stationary die placed on the surroundings of the area-to-be-displaced, so as not to get displaced during presswork.

[0085] 6. The presswork-based thickness addition forming method according to claim 5, wherein the first stationary die has a flow shape on a boundary with the area-to-be-displaced in the surroundings so as not to obstruct material flow.

[0086] 7. The presswork-based thickness addition forming method according to 6 above, wherein the area-to-be-displaced is formed into a polygon as viewed in the thickness direction and the flow shape on the first stationary die is formed on each side of the polygon.

[0087] 8. The presswork-based thickness addition forming method according to any one of 5 to 7 above, wherein the expandable member is supported by a second stationary die placed adjacent to the expandable member in a direction in which the reaction force is applied, the expandable member is constructed integrally with a movable die that is movable relative to the first stationary die and the second stationary die, and the expandable member is able to apply the reaction force to the area-to-be-displaced via the movable die which is in a state of being able to come into contact with the workpiece.

[0088] 9. The presswork-based thickness addition forming method according to 8 above, wherein in displacing one of the areas-to-be-displaced outward, the movable die stops moving by bumping against any of stationary dies.

[0089] 10. The presswork-based thickness addition forming method according to 8 or 9 above, wherein an area of the workpiece in which material flow occurs slides with respect to an adjacent die during formation of the thickened portion.

[0090] 11. The presswork-based thickness addition forming method according to 10 above, wherein treatment to reduce frictional resistance of a surface is applied to a sliding site for use during formation of the thickened portion.

[0091] 12. The thickness addition forming method according to 11 above, wherein the treatment is applied at least to contact surfaces of the movable die with the workpiece and any of stationary dies.

[0092] 13. The presswork-based thickness addition forming method according to 8 or 9 above, wherein in displacing the areas-to-be-displaced outward using the movable die, the first stationary die, and the second stationary die, a machine element adapted to smoothly move the movable die relative to the first stationary die through rotation is installable on at least one of a boundary between the movable die and the first stationary die and a boundary between the movable die and the second stationary die.

[0093] 14. An expandable member that is used for the thickness addition forming method according to any one of claims 1 to 13 and is able to generate the reaction force when at least one of two surfaces opposed to each other in the thickness direction is displaced outward.REFERENCE SIGNS LIST20 Stationary die (first stationary die)

[0095] 21 Corner (flow shape)

[0096] 30,40 Stationary die (second stationary die)

[0097] 50 Elastic member (expandable member)

[0098] 60 Movable die

[0099] 62 Base end (part bumping against stationary die)

[0100] 70 Movable die

[0101] 80 Machine element

[0102] b Workpiece (long member)

[0103] bp Bending part

[0104] e1 Edge

[0105] t1 Thickened portion

[0106] X First direction (e.g., longitudinal direction of workpiece)

[0107] Y Second direction (thickness direction of workpiece)

Examples

first embodiment

[0032]FIGS. 1 to 3 are diagrams intended for use in describing the press-formed product P1 according to a first embodiment. The press-formed product P1 formed by a thickness addition forming method according to the first embodiment can be configured as a long member extending in a long form in one direction in an open section as an example. As shown in FIGS. 1 and 2, the press-formed product P1 includes two side walls w1 extending from edges, and a connecting wall w2 that connects the two side walls w1. The press-formed product P1 can be formed of blank (the workpiece b) made of rolled material and the like (see FIGS. 5 and 8). As shown in FIG. 3, the press-formed product P1 can be configured such that a cross-section intersecting the longitudinal direction running along one side is formed into a so-called U-shape having a few bending parts bp (see FIG. 3). However, this shape is exemplary, and the shape of the press-formed product is not limited to FIG. 3 and the like.

[0033]The pre...

second embodiment

FIGS. 11, 12, and 13 are enlarged views illustrating corners of stationary dies placed around sites to become thickened portions, where the stationary dies are modifications of the first embodiment in FIG. 10. Whereas it has been explained in the first embodiment that the corner 21 of the stationary die 20 which is located on a boundary with the thickened portion t1 of the workpiece b is shaped into a relatively sharp corner, the corner can also be configured as follows. Note that components other than corners of stationary dies are similar to those of the first embodiment, and thus description of components in common with the first embodiment will be omitted.

[0052]Of a stationary die 20a located in surroundings of the workpiece b, at a corner 21 a located on a boundary with the thickened portion t1, as shown in FIG. 11, a rounded shape may be provided as a flow shape for use to facilitate material flow in the workpiece b. As a shape for use to facilitate material flow in the workpi...

third embodiment

[0056]FIG. 14 is a sectional view corresponding to FIG. 9, illustrating a thickness addition forming apparatus adapted to form the workpiece b. Whereas it has been explained in the first embodiment that the elastic member 50 is supported by the stationary dies 30 and 40, the stationary die 30 can be configured as follows. Note that in the present embodiment, of the stationary dies that support the elastic member 50, the stationary die 30 adjacent to the base end 62 of the movable die 60 is different in configuration from the first embodiment and other components are similar to those of the first embodiment. Therefore, description of components in common with the first embodiment will be omitted.

[0057]As shown in FIG. 14, in the present embodiment, a stationary die 30d adapted to support the elastic member 50 is configured to be able to come into contact with (abut) the base end 62 of the movable die 60 when the movable die 60 moves by the application of a press force from the movabl...

TECHNICAL FIELD

[0001] The present invention relates to a presswork-based thickness addition forming method and an expandable member used for the thickness addition forming method.BACKGROUND ART

[0002] It is said that the number of automotive parts is as large as tens of thousands. For example, press-formed products are often used for suspension-related parts. Regarding press-formed products, by applying various types of presswork to plate material such as blank, the plate material is formed into a desired shape, and in the case of suspension-related parts, it is sometimes desired to improve strength and rigidity of specific sites.

[0003] In relation to this, a relevant conventional technique has been disclosed that forms reinforced sites by forming uneven portions on skeleton material and then compressing the uneven portions.CITATION LISTPatent LiteraturesPatent Literature 1: JP 2011-161941 ASUMMARY OF INVENTION

[0005] As a technique related to Patent Literature 1, the inventors have been studying a method for increasing wall thickness of a workpiece using presswork. The inventors have studied methods for increasing the wall thickness of a workpiece by pressing part of plate material such as an end face of the workpiece without going through the process of forming uneven portions by presswork. Among others, by paying attention to the fact that the workpiece can buckle when at least part of the workpiece is increased in wall thickness by compressing part of the workpiece, the inventors have been conducting active studies on method that will not cause buckling.

[0006] The present invention has an object to prevent buckling of a workpiece when at least part of the workpiece is increased in wall thickness by using compression during presswork.

[0007] One aspect of the present invention is a thickness addition forming method that increases at least part of a workpiece in wall thickness by presswork. The method involves pressing part of the workpiece, producing a flow in material of the workpiece, thereby displacing outward at least one of two surfaces opposed to each other in a thickness direction of the workpiece, increasing at least part of the workpiece in wall thickness, and thereby forming a thickened portion. The thickened portion is formed by displacing an area-to-be-displaced outward while applying a reaction force to the area-to-be-displaced using an expandable member.

[0008] Another aspect of the present invention is an expandable member that is used for the thickness addition forming method and able to generate the reaction force when at least one of the two surfaces opposed to each other in the thickness direction is displaced outward.BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a perspective view illustrating a press-formed product according to a first embodiment.

[0010] FIG. 2 is a side view of FIG. 1.

[0011] FIG. 3 is a sectional view taken along line 3-3 in FIG. 2.

[0012] FIG. 4 is a flowchart illustrating a presswork-based thickness addition forming method according to the first embodiment.

[0013] FIG. 5 is a side view illustrating a workpiece before presswork.

[0014] FIG. 6 is an exploded perspective view illustrating a configuration of a thickness addition forming apparatus adapted to form a thickened portion of the press-formed product illustrated in FIG. 1.

[0015] FIG. 7 is a sectional view illustrating how a workpiece is set on the thickness addition forming apparatus illustrated in FIG. 6.

[0016] FIG. 8 is a diagram illustrating how a pressing area on a workpiece is pressed.

[0017] FIG. 9 is a sectional view illustrating a thickened portion formed on a workpiece by the thickness addition forming apparatus illustrated in FIG. 6.

[0018] FIG. 10 is an enlarged view of part EV in FIG. 9.

[0019] FIG. 11 is an enlarged view illustrating corners of a stationary die placed around a site to become a thickened portion as a result of presswork carried out by a thickness addition forming apparatus according to a second embodiment, where the stationary die is a modification of FIG. 10.

[0020] FIG. 12 is an enlarged view corresponding to FIG. 10, illustrating Modification 1 of the second embodiment.

[0021] FIG. 13 is an enlarged view corresponding to FIG. 10, illustrating Modification 2 of the second embodiment.

[0022] FIG. 14 is a sectional view corresponding to FIG. 9, illustrating how a thickened portion is formed by a thickness addition forming apparatus according to a third embodiment.

[0023] FIG. 15 is a perspective view illustrating a surface of a movable die of a thickness addition forming apparatus according to a fourth embodiment.

[0024] FIG. 16 is a sectional view illustrating a surface of a movable die of a thickness addition forming apparatus according to Modification 1 of the fourth embodiment.

[0025] FIG. 17 is a plan view illustrating a surface of a movable die of a thickness addition forming apparatus according to Modification 2 of the fourth embodiment.

[0026] FIG. 18 is a plan view illustrating a surface of a movable die of a thickness addition forming apparatus according to Modification 3 of the fourth embodiment.

[0027] FIG. 19 is a sectional view corresponding to FIG. 7, illustrating a thickness addition forming apparatus according to a fifth embodiment.

[0028] FIG. 20 is a perspective view illustrating a press-formed product according to a modification of the first embodiment.

[0029] FIG. 21 is a perspective view illustrating a press-formed product according to a modification of the first embodiment.

[0030] FIG. 22 is a schematic diagram illustrating a thickness addition forming apparatus according to a comparative example in comparison with an example.DESCRIPTION OF EMBODIMENTS

[0031] Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the following description does not limit the technical scope or the meanings of terms recited in the accompanying claims. Besides, size ratios in the drawings are exaggerated for convenience of explanation and may be different from actual size ratios. Here, an orthogonal coordinate system is illustrated in the drawings, where X corresponds to a longitudinal direction and the like of a press-formed product P1 in FIG. 1 as an example, and is referred to as a first direction X. Y corresponds to a thickness direction of a workpiece b, and is referred to as a second direction Y. Z corresponds to a height direction and the like of the workpiece as an example, and is referred to as a third direction Z.First Embodiment

[0032] FIGS. 1 to 3 are diagrams intended for use in describing the press-formed product P1 according to a first embodiment. The press-formed product P1 formed by a thickness addition forming method according to the first embodiment can be configured as a long member extending in a long form in one direction in an open section as an example. As shown in FIGS. 1 and 2, the press-formed product P1 includes two side walls w1 extending from edges, and a connecting wall w2 that connects the two side walls w1. The press-formed product P1 can be formed of blank (the workpiece b) made of rolled material and the like (see FIGS. 5 and 8). As shown in FIG. 3, the press-formed product P1 can be configured such that a cross-section intersecting the longitudinal direction running along one side is formed into a so-called U-shape having a few bending parts bp (see FIG. 3). However, this shape is exemplary, and the shape of the press-formed product is not limited to FIG. 3 and the like.

[0033] The press-formed product P1 includes a thickened portion t1 placed at a local site and the like that needs rigidity or strength. The thickened portion t1 is formed protruding outward, i.e., in a direction intersecting the longitudinal direction (first direction X) of the press-formed product P1. Consequently, the corresponding site is configured to be larger in wall thickness than other sites devoid of the thickened portion t1 in the longitudinal direction. As described later, the thickened portion t1 is formed, by pressing a pressing area r1 (see FIG. 8), which is part of the workpiece b, and thereby producing a flow in the material of the workpiece b. The thickened portion t1 is formed by displacing outward at least one of the two surfaces opposed to each other in the second direction Y, which corresponds to the thickness direction of the workpiece b, and thereby increasing at least part of the workpiece b in wall thickness. As shown in FIGS. 1 and 2, in the present embodiment, the thickened portion t1 is formed partially on a side wall w1. In the present embodiment, as shown in FIG. 1, the thickened portion t1 is formed as a polygon such as a quadrangle. A hollow substantially rectangular cross-section formed by pairing the press-formed products P1 according to the present embodiment such that openings face each other can be used as at least some of suspension skeleton-related parts such as suspension side members or press-formed skeleton-related parts. Parts such as brackets may be fixed to predetermined sites in the longitudinal direction on structural parts such as side members, and the thickened portion t1 of the press-formed product P1, if provided at a site to which a bracket or the like has been fixed, can be used to meet required standards for strength, rigidity and the like.About Thickness Addition Forming Apparatus

[0034] Next, of manufacturing equipment for the press-formed product P1, a thickness addition forming apparatus that forms the thickened portion t1 will be described. FIGS. 5 to 10 are diagrams intended for use in describing the thickness addition forming apparatus and thickness addition forming method according to the present embodiment. Note that in forming a press-formed product into a substantially U-shaped open section such as the press-formed product P1 shown in FIG. 1, a stationary die and a movable die are often used, where the movable die approaches, and separates from, the stationary die (at least part of a boundary surface between the stationary die and the movable die has been formed into a substantially U-shaped surface). However, a method for forming such an open section shape is publicly known, and thus detailed description thereof will be omitted.

[0035] The thickness addition forming apparatus used to form the thickened portion t1 of the press-formed product P1 includes stationary dies 10, and 20 (which correspond to a first stationary die), stationary dies 30 and 40 (which correspond to a second stationary die), an elastic member 50, and movable dies 60 and 70 as shown in FIGS. 6, 7, and 8. Note that, of the U-shaped section, formation of the thickened portion t1 will be described below.

[0036] In FIGS. 7 and 9, the stationary die 10 is placed so as to abut the workpiece b on the side opposite to the site of the workpiece b to be thickened. As a die adjacent to the area of the workpiece b in which material flow occurs when the thickened portion t1 is formed, the stationary die 10 can slide with respect to the workpiece b.

[0037] On the side opposite to the site placed in contact with the stationary die 10, the stationary die 20 is placed so as to abut the workpiece b in a neighboring site in which the thickened portion t1 is scheduled to be formed. In displacing an area-to-be-displaced of the workpiece b outward, surroundings of the workpiece b other than the area-to-be-displaced are held down by the stationary die 20 placed on the surroundings of the area-to-be-displaced so as not to get displaced outward during the presswork. As shown in FIG. 6, the stationary dies 20 are configured to be placed adjacent to the surroundings of the site to become the thickened portion t1 not only in the first direction X, but also in the third direction Z. A corner 21 of the stationary die 20 which is located on a boundary with the site to become the thickened portion t1 is shaped into a relatively sharp corner in the present embodiment as shown in FIGS. 9 and 10.

[0038] The stationary dies 30 and 40 are placed to hold the elastic member 50 and the movable die 60 movably in the second direction Y. The stationary dies 30 and 40 are configured to support the elastic member 50 by being placed adjacent to the elastic member 50 in the second direction Y in which a reaction force is applied by the elastic member 50. The stationary die 30 is placed adjacent to the elastic member 50 in a travel direction (the second direction Y) of the movable die 60 while the stationary die 40 is placed farther away from the elastic member 50 than the stationary die 30. In the present embodiment, the stationary die 30 and the stationary die 40 are prepared as separate dies and used as an integrated unit. However, as long as the elastic member 50 and the movable die 60 can be held movably, the stationary die 30 and the stationary die 40 may be configured to be an integrated die rather than separate dies.

[0039] The elastic member 50 is constructed integrally with the movable die 60 that can move relative to the stationary dies 20, 30, and 40 and configured to be able to apply a reaction force to one of areas-to-be-displaced via the movable die 60 in a state in which the movable die 60 can come into contact with the workpiece b. The elastic member 50 is configured to be able to expand in a thickening direction (the second direction Y in FIG. 7 and the like) used in forming the thickened portion t1 on the workpiece b and is placed adjacent to the stationary die 30. The formation of the thickened portion t1 described above is performed by displacing the area-to-be-displaced outward while applying a reaction force to the area-to-be-displaced using the elastic member 50. The elastic member 50 is configured to be deformable so as to be pressed in the second direction Y when deforming the workpiece b in such a way as to thicken the workpiece b. The elastic member 50 can be configured to contain material such as resin as a member capable of elastic deformation.

[0040] The movable die 60 is placed on the opposite side of the workpiece b from the stationary die 10 in such a way as to be able to apply a reaction force to the site that comes into contact with the workpiece b and becomes the thickened portion t1 when the pressing area r1 applies a press force to the workpiece b. The movable die 60 is configured to be able to move integrally with the elastic member 50. As shown in FIG. 7, the movable die 60 includes a forward end 61 slidable with respect to the workpiece b such that the thickened portion t1 can be formed on the workpiece b, and a base end 62 formed protruding from the forward end 61 in the second direction Y, which is the travel direction of the die. As with the stationary die 10, the forward end 61 is slidable with respect to the workpiece b as a die adjacent to the area of the workpiece b in which material flow occurs in forming the thickened portion t1.

[0041] As shown in FIG. 8, to form the thickened portion t1, the movable die 70 is placed movably in the third direction Z in order to be able to press the pressing area r1 protruding from around the workpiece b, as an example. The travel direction (the third direction Z in FIG. 8) of the movable die 70 is configured to be substantially orthogonal to a direction (the second direction Y in FIG. 9) in which a site to become the thickened portion t1 protrudes from the workpiece b. The movable die 70 can be placed above or below the workpiece b in FIG. 8 and the like.Thickness Addition Forming Method

[0042] Next, the thickness addition forming method according to the present embodiment will be described, where the method increases at least part of a workpiece in wall thickness by presswork. FIG. 4 is a flowchart illustrating the thickness addition forming method according to the present embodiment.

[0043] First, the stationary dies 10, 20, 30, and 40, the elastic member 50, and the movable dies 60 and 70 are set (S1). Next, the stationary dies 10, 20, 30, and 40 are set so as to immobilize the workpiece b (S2). Whereas it has been explained that the movable die 70 is placed above or below the workpiece b in FIG. 8, in addition to the stationary dies 10, 20, 30, and 40, the stationary dies of the thickness addition forming apparatus can include a stationary die (not shown) placed on the opposite side of the movable die 70 with the workpiece b sandwiched therebetween.

[0044] Next, as shown in FIG. 8, by pressing the movable die 70 against the pressing area r1 of the workpiece b, a press force is applied to the workpiece b (S3). As described above, on the opposite side of the movable die 70, the workpiece b is held by stationary dies such that the overall position of the workpiece b will not change. Therefore, in this state, when a press force is applied to the pressing area r1, material flow occurs in the workpiece b and the material flows in the second direction Y (to the right side of the workpiece b in FIG. 9) in which the material can flow in FIG. 9. It is impossible or difficult for material to move to the site of the workpiece b on which the stationary die 20 is placed, and thus the material flows to the movable die 60, which is movable.

[0045] In doing so, since the elastic member 50 is placed on the opposite side of the movable die 60 from the workpiece b, the material comes into contact with the movable die 60 and flows with a reaction force being applied by the elastic member 50 to the site which is to become the thickened portion t1. In doing so, the workpiece b forms the thickened portion t1 while sliding with respect to the movable die 60 along a surface of contact with the movable die 60 (see FIG. 9). In forming the thickened portion t1, the workpiece b can slide with respect to the stationary die 10 on the opposite side from the movable die 60. Consequently, the thickened portion t1 of the workpiece b deforms so as to thicken while being held down by the movable die 60. Thus, by being formed with a reaction force being applied by the elastic member 50, the thickened portion t1 can prevent itself from being buckled. Furthermore, creasing of the thickened portion can be prevented or curbed.

[0046] After the thickening, the press-formed product P1 is removed from the thickness addition forming apparatus described above by dismantling the stationary dies 10, 20, 30, 40, the elastic member 50, and the movable dies 60 and 70 (S4). Note that the thickness addition forming method described above may be performed either before or after forming the workpiece b from a flat shape into a substantial U-shape in the method for manufacturing the press-formed product P1 shown in FIG. 1.

[0047] As described above, the thickness addition forming method for the workpiece b according to the present embodiment produces a flow in the material of the workpiece b by pressing part of the workpiece b. Then the thickened portion t1 is formed by displacing outward at least one of the two surfaces opposed to each other in the thickness direction of the workpiece b, and thereby increasing at least part of the workpiece b in wall thickness. The formation of the thickened portion t1 is performed by displacing the area-to-be-displaced outward while applying a reaction force to the area-to-be-displaced using the elastic member 50. In this way, in forming the thickened portion t1 on the workpiece b using compression, by keeping the area-to-be-displaced to be thickened from being deformed sharply, the thickened portion can be prevented from being buckled. Furthermore, by causing the area-to-be-displaced to follow the movable die 60 while applying a reaction force, creasing of the thickened portion can be prevented or curbed.

[0048] In displacing the area-to-be-displaced of the workpiece b outward, surroundings of the area-to-be-displaced, i.e., areas other than the area-to-be-displaced, are configured to be held down by the stationary die 20 so as not to get displaced. This configuration makes it possible to control the shape of thickening appropriately.

[0049] The elastic member 50 is supported by the stationary dies 30 and 40 placed adjacent to the elastic member 50 in the second direction Y in which a reaction force is applied. The elastic member 50 is constructed integrally with the movable die 60 that can move relative to the stationary dies 20, 30, and 40. The elastic member 50 is configured to be able to apply a reaction force to the area-to-be-displaced via the movable die 60 in a state in which the movable die 60 can come into contact with the workpiece b. This configuration makes it possible to prevent buckling of the area-to-be-displaced, which is to become the thickened portion t1.

[0050] The area of the workpiece b in which material flow occurs is configured to be able to slide with respect to the stationary die 10, the forward end 61 of the movable die 60, and the like, which are placed adjacent to the area during formation of the thickened portion t1. This configuration makes it possible to form the thickened portion t1 by applying a press force (compressive force) to the pressing area r1 and thereby displacing the area-to-be-displaced of the workpiece b placed adjacent to the stationary die 10 and the movable die 60 in the second direction Y corresponding to the thickness direction when material flow occurs.Second EmbodimentFIGS. 11, 12, and 13 are enlarged views illustrating corners of stationary dies placed around sites to become thickened portions, where the stationary dies are modifications of the first embodiment in FIG. 10. Whereas it has been explained in the first embodiment that the corner 21 of the stationary die 20 which is located on a boundary with the thickened portion t1 of the workpiece b is shaped into a relatively sharp corner, the corner can also be configured as follows. Note that components other than corners of stationary dies are similar to those of the first embodiment, and thus description of components in common with the first embodiment will be omitted.

[0052] Of a stationary die 20a located in surroundings of the workpiece b, at a corner 21 a located on a boundary with the thickened portion t1, as shown in FIG. 11, a rounded shape may be provided as a flow shape for use to facilitate material flow in the workpiece b. As a shape for use to facilitate material flow in the workpiece b, a corner 21b of a stationary die 20b may also be chamfered as shown in FIG. 12. Besides, as shown in FIG. 13, a corner 21c of a stationary die 20c may be tapered in the second direction Y.

[0053] The flow shape described above may be provided for each side of a polygonal shape when the thickened portion t1 is polygonal in shape as shown in FIG. 1.

[0054] As described above, in the present embodiment, on the stationary dies 20a, 20b, and 20c, flow shapes are provided at the corners 21a, 21b, and 21c in order not to obstruct material flow in the workpiece b in the surroundings of the area-to-be-displaced. Consequently, the thickened portion t1 can be formed smoothly by the application of a press force (compressive force) to the pressing area r1.

[0055] When the area-to-be-displaced that is to become the thickened portion t1 is polygonal in shape, the flow shape at the corners 21a, 21b, and 21c of the stationary dies 20a, 20b, and 20c may be provided for each side of a polygonal shape. This makes it possible to form the thickened portion t1 by gathering material to the area-to-be-displaced from various sites through material flow upon application of the press force.Third Embodiment

[0056] FIG. 14 is a sectional view corresponding to FIG. 9, illustrating a thickness addition forming apparatus adapted to form the workpiece b. Whereas it has been explained in the first embodiment that the elastic member 50 is supported by the stationary dies 30 and 40, the stationary die 30 can be configured as follows. Note that in the present embodiment, of the stationary dies that support the elastic member 50, the stationary die 30 adjacent to the base end 62 of the movable die 60 is different in configuration from the first embodiment and other components are similar to those of the first embodiment. Therefore, description of components in common with the first embodiment will be omitted.

[0057] As shown in FIG. 14, in the present embodiment, a stationary die 30d adapted to support the elastic member 50 is configured to be able to come into contact with (abut) the base end 62 of the movable die 60 when the movable die 60 moves by the application of a press force from the movable die 70. That is, the stationary die 30d includes a support 31d adapted to support the elastic member 50 in a manner similar to the first embodiment, and an abutting portion 32d capable of abutting the base end 62 of the movable die 60 by being placed adjacent to the support 31d. A contact surface of the abutting portion 32d is formed into a flat surface substantially orthogonal to the second direction Y, which is the travel direction. However, as long as the contact surface can contact the base end 62 of the movable die 60 at an intended position, it is not necessary that the contact surface of the abutting portion 32d is shaped to be orthogonal to the travel direction or to be flat.

[0058] Note that with the thickness addition forming method using the thickness addition forming apparatus according to the present embodiment, when a press force is applied by the movable die 70, the base end 62 of the movable die 60 bumps against the abutting portion 32d of the stationary die 30d and the movable die 60 stops moving. The other matters are similar to the first embodiment, and thus detailed description of the method will be omitted.

[0059] As described above, in the present embodiment, in displacing the area-to-be-displaced of the workpiece b outward, the base end 62 of the movable die 60 is configured to stop by bumping against the abutting portion 32d of the stationary die 30d. This configuration makes it easier to form the thickened portion t1 with an intended thickness.Fourth Embodiment

[0060] FIG. 15 is a perspective view illustrating a movable die 60e according to a fourth embodiment, FIG. 16 is a sectional view illustrating a movable die 60f, FIGS. 17 and 18 are plan views illustrating surfaces of movable dies 60g and 60h according to modifications of the fourth embodiment.

[0061] It has been explained in the first embodiment that when the area-to-be-displaced is displaced outward by pressing the movable die 70, the area-to-be-displaced of the workpiece b is slidable with respect to the movable die 60. In relation to this, a sliding area of the movable die 60 with respect to a stationary die including the workpiece b can be configured as follows. Note that the present embodiment differs from the first embodiment in the properties of a sliding area between the workpiece on the movable die and the stationary dies 20 and 30, and the rest is similar to the first embodiment, and thus description of components in common with the first embodiment will be omitted.

[0062] In the present embodiment, in forming the thickened portion t1, as an example of treatment to reduce frictional resistance with a mating part, a plurality of grooves 63 that can hold lubricating oil or the like can be provided on a surface of the sliding site as shown in FIG. 15. Whereas, in the present embodiment, grooves 63 are formed along the first direction X and the second direction Y, as long as the frictional resistance with the mating part in the sliding area can be reduced, specific shapes and arrangement of the grooves are not limited to FIG. 15.

[0063] As a method for reducing the frictional resistance with the mating part such as the workpiece b at the sliding site, a layer L1 of solid lubricant may be provided on an outer side of a metal or other part L2, which is a main body of a movable die 60f as shown in FIG. 16.

[0064] As a method for reducing the frictional resistance of a surface, a surface placed in contact with a mating part of the movable die may be formed into a staggered pattern by laser machining as in the case of a movable die 60g in FIG. 17 or a surface placed in contact with a mating part may be formed into a striped pattern by laser machining or the like as in the case of a movable die 60h in FIG. 18. Such treatment to reduce the frictional resistance of a surface may be applied not only to contact surfaces of the movable die 60 with the opposing workpiece b and stationary dies 20, but also to a contact surface of the stationary die 10 with the workpiece b.

[0065] As described above, according to the present embodiment, to facilitate sliding, the treatment to reduce the frictional resistance of the surface is applied to the sliding area used in forming the thickened portion t1. This makes it possible to prevent buckling of the workpiece b in forming the thickened portion t1 on the workpiece b using compression, and prevent or curb creasing of the workpiece b by reducing resistance of the sliding site.

[0066] The above-mentioned treatment to reduce the frictional resistance of the surface is applied to the contact surface of the movable die 60 with the workpiece b, the stationary dies 20 and 30, and the like and / or to the contact surface of the stationary die 10 with the workpiece b. This configuration makes it possible to reduce friction of the movable die 60 and / or the stationary die 10 with surrounding contact elements and thereby form the thickened portion t1 smoothly.Fifth Embodiment

[0067] FIG. 19 is a sectional view corresponding to FIG. 7, illustrating a thickness addition forming apparatus for the workpiece b according to a fifth embodiment. Whereas it has been explained in the first embodiment that the movable die 60 can move relative to the stationary dies 20, 30, and 40, the movable die 60 may have the following configuration. Note that the present embodiment differs only in the configurations of movable dies and the rest is similar to the first embodiment, and thus description of components in common with the first embodiment will be omitted.

[0068] In the present embodiment, on boundaries of a movable die 60k with the stationary die 20 and the stationary die 30, machine elements 80 are placed to facilitate contact between the movable die 60k and the stationary dies 20 and 30. In the present embodiment, the machine elements 80, which are constructed integrally with the movable die 60k, and have a plurality of rotating members such as rollers provided rotatably. When the movable die 60k moves in the second direction Y corresponding to the thickness direction by the application of a press force from the movable die 70, the movable die 60k can reduce contact resistance with the stationary dies 20 and 30 by the machine elements 80. Note that in FIG. 19, the machine elements 80 are provided on both a contact site between the movable die 60k and the stationary die 20 and a contact site between the movable die 60k and the stationary die 30, but may be provided only on one of the contact sites.

[0069] Note that with the thickness addition forming method using the thickness addition forming apparatus according to the present embodiment is similar to the first embodiment except that in forming the thickened portion t1 using the movable die 60k, the movable die 60k moves relative to the stationary dies 20 and 30 by being placed in contact with the machine elements 80, and thus detailed description will be omitted.

[0070] As described above, according to the present embodiment, the machine elements 80 adapted to smoothly move the movable die 60k relative to the stationary dies 20 and 30 through rotation are configured to be installable on the boundary between the movable die 60k and the stationary die 20 as well as on the boundary between the movable die 60k and the stationary die 30. Consequently, when a press force (compressive force) is applied by the movable die 70, the movable die 60k can be moved smoothly relative to the stationary dies 20 and 30, preventing buckling of the area-to-be-displaced and preventing or curbing creasing.

[0071] Note that the present invention is not limited to the embodiment described above and various changes can be made within the scope of the appended claims. It has been explained in the first embodiment that the thickness addition forming apparatus includes the movable die 60. However, as long as the area-to-be-displaced of the workpiece b can be thickened by the application of a press force from the movable die 70, the thickness addition forming apparatus may be configured to place the elastic member 50 directly in contact with the area-to-be-displaced without being equipped with the movable die 60.

[0072] FIGS. 20 and 21 are perspective views illustrating press-formed products P2 and P3 according to modifications of the first embodiment. It has been explained in the first embodiment that the thickened portion t1 of the press-formed product P1 (see FIG. 1) is partially provided on a side wall w1, which is a part in a circumferential direction in a plane intersecting the longitudinal direction. However, when the pressing area is pressed, if geometry and arrangement of the present thickness addition forming apparatus is set up according to a site needing thickening and a thickened portion is formed using a resulting material flow, the shape of the thickened portion is not limited to FIG. 1, FIG. 2, and the like. For example, as with the press-formed product P2 in FIG. 20, a thickened portion t2 may be provided on an entire periphery in a plane intersecting the longitudinal direction and / or may be formed by being spread in the longitudinal direction more widely than the thickened portion t1.

[0073] As shown in FIG. 21, a thickened portion t3 may be provided in such a way as to thicken at least part of the area of the workpiece which is running from a bending part bp to an edge e1 in a cross-section intersecting the longitudinal direction.Comparison

[0074] Both a pressing load applied when a thickened portion was formed on a workpiece and a force acting on a die adjacent to the thickened portion were compared between when an elastic member was provided and when no elastic member was provided, and this will be described below. FIG. 22 is a schematic sectional view illustrating a thickness addition forming apparatus according to a comparative example.

[0075] In the present comparison, the pressure required to deform a plate thickness to a desired plate thickness was compared between when the thickened portion t1 was formed on the workpiece b using the above-mentioned thickness addition forming apparatus such as shown in FIG. 7 and when a thickened portion was formed without using any of the elastic member 50, the movable die 60, and the stationary dies 30 and 40 as shown in FIG. 22. Here, the thickness addition forming apparatus equipped with the elastic member 50 as shown in FIG. 7 is referred to as an example and the thickness addition forming apparatus not equipped with the elastic member 50 as shown in FIG. 22 is referred to as a comparative example.

[0076] In the present comparison, in addition to the pressing load described above, forces acting on the dies adjacent to the workpiece b, such as the stationary dies 30 and 40 in the example, were compared between the example and the comparative example. Here, the thickness addition forming apparatus according to the comparative example were configured similarly to the thickness addition forming apparatus in FIG. 7 except that a stationary die 90 was used instead of the stationary dies 20, 30, and 40, the elastic member 50, and the movable die 60, as shown in FIG. 22. That is, with the stationary die 10 abutted against the workpiece b and with the stationary die 90 spaced away from the workpiece b by a distance equal to the thickness to be increased by the deformation, the thickness addition forming apparatus according to the comparative example pressed the movable die 70 against the pressing area r1 and applied the pressing load.

[0077] By comparing the pressing load applied by the movable die 70 between the example and the comparative example, it was confirmed that the example was able to thicken a specific site such as the thickened portion t1 to a desired thickness with a smaller pressing load than the thickness addition forming apparatus according to the comparative example. From this confirmation result, it is considered that a component that applies a pressing load, such as the movable die 70, can be downsized compared to thickness addition forming apparatus that does not use the elastic member 50.

[0078] Regarding the forces received by the stationary dies 30 and 40 or the stationary die 90, it was confirmed that the example was able to reduce the forces received through the workpiece b compared to the thickness addition forming apparatus according to the comparative example. From this confirmation result, it is considered that components such as the stationary dies 30 and 40 can be downsized compared to components that do not use the elastic member 50, such as the stationary die 90 of the thickness addition forming apparatus. Regarding this point, it is considered that the thickness addition forming apparatus according to the example can reduce an input load from the pressing load thanks to the presence of the elastic member 50 between the workpiece b and the stationary dies 30 and 40 and the like compared to the comparative example.

[0079] The present invention includes the following aspects and forms.

[0080] 1. A presswork-based thickness addition forming method that increases at least part of a workpiece in wall thickness by presswork, the method comprising pressing part of the workpiece, producing a flow in material of the workpiece, thereby displacing outward at least one of two surfaces opposed to each other in a thickness direction of the workpiece, increasing at least part of the workpiece in wall thickness, and thereby forming a thickened portion, wherein the thickened portion is formed by displacing an area-to-be-displaced of the workpiece outward while applying a reaction force to the area-to-be-displaced using an expandable member.

[0081] 2. The presswork-based thickness addition forming method according to 1 above, wherein a long member extending at least in one direction is used for the workpiece in which the thickened portion is formed.

[0082] 3. The thickness addition forming method according to 1 or 2 above, wherein the workpiece is configured such that a cross-section intersecting a direction running along one side is formed into a shape having a bending part

[0083] 4. The thickness addition forming method according to 3 above, wherein the thickened portion is formed in at least part of an area of the workpiece which is running from the bending part to an edge.

[0084] 5. The presswork-based thickness addition forming method according to any one of 1 to 4 above, wherein in displacing the area-to-be-displaced outward, surroundings of the area-to-be-displaced of the workpiece are held down by a first stationary die placed on the surroundings of the area-to-be-displaced, so as not to get displaced during presswork.

[0085] 6. The presswork-based thickness addition forming method according to claim 5, wherein the first stationary die has a flow shape on a boundary with the area-to-be-displaced in the surroundings so as not to obstruct material flow.

[0086] 7. The presswork-based thickness addition forming method according to 6 above, wherein the area-to-be-displaced is formed into a polygon as viewed in the thickness direction and the flow shape on the first stationary die is formed on each side of the polygon.

[0087] 8. The presswork-based thickness addition forming method according to any one of 5 to 7 above, wherein the expandable member is supported by a second stationary die placed adjacent to the expandable member in a direction in which the reaction force is applied, the expandable member is constructed integrally with a movable die that is movable relative to the first stationary die and the second stationary die, and the expandable member is able to apply the reaction force to the area-to-be-displaced via the movable die which is in a state of being able to come into contact with the workpiece.

[0088] 9. The presswork-based thickness addition forming method according to 8 above, wherein in displacing one of the areas-to-be-displaced outward, the movable die stops moving by bumping against any of stationary dies.

[0089] 10. The presswork-based thickness addition forming method according to 8 or 9 above, wherein an area of the workpiece in which material flow occurs slides with respect to an adjacent die during formation of the thickened portion.

[0090] 11. The presswork-based thickness addition forming method according to 10 above, wherein treatment to reduce frictional resistance of a surface is applied to a sliding site for use during formation of the thickened portion.

[0091] 12. The thickness addition forming method according to 11 above, wherein the treatment is applied at least to contact surfaces of the movable die with the workpiece and any of stationary dies.

[0092] 13. The presswork-based thickness addition forming method according to 8 or 9 above, wherein in displacing the areas-to-be-displaced outward using the movable die, the first stationary die, and the second stationary die, a machine element adapted to smoothly move the movable die relative to the first stationary die through rotation is installable on at least one of a boundary between the movable die and the first stationary die and a boundary between the movable die and the second stationary die.

[0093] 14. An expandable member that is used for the thickness addition forming method according to any one of claims 1 to 13 and is able to generate the reaction force when at least one of two surfaces opposed to each other in the thickness direction is displaced outward.REFERENCE SIGNS LIST20 Stationary die (first stationary die)

[0095] 21 Corner (flow shape)

[0096] 30,40 Stationary die (second stationary die)

[0097] 50 Elastic member (expandable member)

[0098] 60 Movable die

[0099] 62 Base end (part bumping against stationary die)

[0100] 70 Movable die

[0101] 80 Machine element

[0102] b Workpiece (long member)

[0103] bp Bending part

[0104] e1 Edge

[0105] t1 Thickened portion

[0106] X First direction (e.g., longitudinal direction of workpiece)

[0107] Y Second direction (thickness direction of workpiece)

Examples

first embodiment

[0032]FIGS. 1 to 3 are diagrams intended for use in describing the press-formed product P1 according to a first embodiment. The press-formed product P1 formed by a thickness addition forming method according to the first embodiment can be configured as a long member extending in a long form in one direction in an open section as an example. As shown in FIGS. 1 and 2, the press-formed product P1 includes two side walls w1 extending from edges, and a connecting wall w2 that connects the two side walls w1. The press-formed product P1 can be formed of blank (the workpiece b) made of rolled material and the like (see FIGS. 5 and 8). As shown in FIG. 3, the press-formed product P1 can be configured such that a cross-section intersecting the longitudinal direction running along one side is formed into a so-called U-shape having a few bending parts bp (see FIG. 3). However, this shape is exemplary, and the shape of the press-formed product is not limited to FIG. 3 and the like.

[0033]The pre...

second embodiment

FIGS. 11, 12, and 13 are enlarged views illustrating corners of stationary dies placed around sites to become thickened portions, where the stationary dies are modifications of the first embodiment in FIG. 10. Whereas it has been explained in the first embodiment that the corner 21 of the stationary die 20 which is located on a boundary with the thickened portion t1 of the workpiece b is shaped into a relatively sharp corner, the corner can also be configured as follows. Note that components other than corners of stationary dies are similar to those of the first embodiment, and thus description of components in common with the first embodiment will be omitted.

[0052]Of a stationary die 20a located in surroundings of the workpiece b, at a corner 21 a located on a boundary with the thickened portion t1, as shown in FIG. 11, a rounded shape may be provided as a flow shape for use to facilitate material flow in the workpiece b. As a shape for use to facilitate material flow in the workpi...

third embodiment

[0056]FIG. 14 is a sectional view corresponding to FIG. 9, illustrating a thickness addition forming apparatus adapted to form the workpiece b. Whereas it has been explained in the first embodiment that the elastic member 50 is supported by the stationary dies 30 and 40, the stationary die 30 can be configured as follows. Note that in the present embodiment, of the stationary dies that support the elastic member 50, the stationary die 30 adjacent to the base end 62 of the movable die 60 is different in configuration from the first embodiment and other components are similar to those of the first embodiment. Therefore, description of components in common with the first embodiment will be omitted.

[0057]As shown in FIG. 14, in the present embodiment, a stationary die 30d adapted to support the elastic member 50 is configured to be able to come into contact with (abut) the base end 62 of the movable die 60 when the movable die 60 moves by the application of a press force from the movabl...

Claims

1. A presswork-based thickness addition forming method that increases at least part of a workpiece in wall thickness by presswork, the method comprisingpressing part of the workpiece, producing a flow in material of the workpiece, thereby displacing outward at least one of two surfaces opposed to each other in a thickness direction of the workpiece, increasing at least part of the workpiece in wall thickness, and thereby forming a thickened portion, whereinthe thickened portion is formed by displacing an area-to-be-displaced of the workpiece outward while applying a reaction force to the area-to-be-displaced using an expandable member.

2. The presswork-based thickness addition forming method according to claim 1, wherein a long member extending at least in one direction is used for the workpiece in which the thickened portion is formed.

3. The thickness addition forming method according to claim 1, wherein the workpiece is configured such that a cross-section intersecting a direction running along one side is formed into a shape having a bending part.

4. The thickness addition forming method according to claim 3, wherein the thickened portion is formed in at least part of an area of the workpiece which is running from the bending part to an edge.

5. The presswork-based thickness addition forming method according to claim 1, wherein in displacing the area-to-be-displaced outward, surroundings of the area-to-be-displaced of the workpiece are held down by a first stationary die placed on the surroundings of the area-to-be-displaced, so as not to get displaced during presswork.

6. The presswork-based thickness addition forming method according to claim 5, wherein the first stationary die has a flow shape on a boundary with the area-to-be-displaced in the surroundings so as not to obstruct material flow.

7. The presswork-based thickness addition forming method according to claim 6, wherein the area-to-be-displaced is formed into a polygon as viewed in the thickness direction and the flow shape on the first stationary die is formed on each side of the polygon.

8. The presswork-based thickness addition forming method according to claim 5, wherein the expandable member is supported by a second stationary die placed adjacent to the expandable member in a direction in which the reaction force is applied, the expandable member is constructed integrally with a movable die that is movable relative to the first stationary die and the second stationary die, and the expandable member is able to apply the reaction force to the area-to-be-displaced via the movable die which is in a state of being able to come into contact with the workpiece.

9. The presswork-based thickness addition forming method according to claim 8, wherein in displacing one of the areas-to-be-displaced outward, the movable die stops moving by bumping against any of stationary dies.

10. The presswork-based thickness addition forming method according to claim 9, wherein an area of the workpiece in which material flow occurs slides with respect to an adjacent die during formation of the thickened portion.

11. The presswork-based thickness addition forming method according to claim 10, wherein treatment to reduce frictional resistance of a surface is applied to a sliding site for use during formation of the thickened portion.

12. The thickness addition forming method according to claim 11, wherein the treatment is applied at least to contact surfaces of the movable die with the workpiece and any of stationary dies.

13. The presswork-based thickness addition forming method according to claim 8, wherein in displacing the areas-to-be-displaced outward using the movable die, the first stationary die, and the second stationary die, a machine element adapted to smoothly move the movable die relative to the first stationary die through rotation is installable on at least one of a boundary between the movable die and the first stationary die and a boundary between the movable die and the second stationary die.

14. An expandable member that is used for the thickness addition forming method according to claim 1 and is able to generate the reaction force when at least one of two surfaces opposed to each other in the thickness direction is displaced outward.

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