JP2022182994A - Metal plate bending method, metal mold for metal plate bending and bent article comprised of metal plate - Google Patents

Abstract

To provide bending method for manufacturing a bent article which has high dimensional accuracy and is suppressed in spring back, and in which there is no possibility of poor strength at a bent portion.SOLUTION: A metal plate bending method is provided for bending a metal plate as a raw material 3 using a punch 1, the punch 1 comprises a pair of punch die surfaces 1b, and a projecting portion 1c provided at a punch tip. An apical surface of the projecting portion 1c is a convex surface having a curvature radius equivalent to a length of 30% or more and 50% or less of a plate thickness of the raw material 3, and a length of the projecting portion 1c is equivalent to a length of 30% or more and 60% or less of the plate thickness of the raw material 3. A die 2 is equipped with V-shaped groove-like die recess portion for the pair of punch die surfaces 1b, and a bottom of the die recess portion is equipped with a concave surface 2b having a curvature radius equivalent to a length of 60% or less of the plate thickness of the raw material 3. The punch 1 and the die 2 are caused to approach each other, and the punch 1 and the die 2 are each caused to be closer to the raw material 3, and at least a part of the projection 1c of the punch 1 is press-fitted into the raw material 3.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method for bending a metal plate, a mold for bending the metal plate, and a bent product made of the metal plate.

Exterior building materials and interior building materials include members used in easily visible locations such as window frames and curtain walls. Such a member is required to have design and beauty such as precise dimensions without distortion, a small diameter of the bent portion, and a sharp bent ridge line. In recent years, there is a tendency to use metal materials having a high yield strength of 300 MPa or more for such members from the viewpoint of ensuring strength as structural members.

When a metal plate material with high yield strength is subjected to bending, the dimensional accuracy after bending may be lowered. If the processing conditions are made stricter in order to improve the dimensional accuracy, cracks may occur at the bent portion. In addition, if the processing conditions are made stricter, there are cases where the design is impaired due to the occurrence of scratches and galling defects. In particular, it becomes a problem when applied to building materials in which aesthetic appearance is emphasized.

Patent Literature 1 describes a grooved austenitic stainless steel sheet that enables the provision of a grooved steel sheet material capable of forming sharp ridgelines with excellent design properties by bending. However, in Patent Document 1, it is necessary to provide a V-groove on the surface of the steel plate, which is disadvantageous in terms of cost. In addition, since the thickness of the steel sheet is reduced by providing the V-groove on the surface of the steel sheet, the thickness of the bent portion of the bent product after bending is reduced, which may result in insufficient strength.

In Patent Document 2, in bending a metal plate using a bending device composed of a punch and a die, at least a part of the convex side of the metal plate that has undergone the bending process is used in the final step of the forming stroke. describes a press working method for providing recesses with a depth of 20% or less of the metal plate thickness. However, the processed product manufactured by the press working method described in Patent Document 2 has a concave portion formed on the convex surface side, which may spoil the appearance, and it is difficult to use it as a material for exterior building materials or interior building materials. be. Moreover, since Patent Document 2 assumes a soft aluminum alloy plate as a raw material, there is a possibility that it cannot be applied to bending of a metal plate material having a high yield strength.

Patent Document 3 discloses a die and a punch for bending a work material having a thickness of t at a desired angle. It describes a method of bending and forming a workpiece using a bending die in which the die surface is raised by at most 10% higher than the other die surfaces and the top corner of the die is rounded with a radius of about t. However, in the bending method described in Patent Document 3, it is difficult to suppress springback after bending.

JP 2008-169423 A Japanese Patent No. 3633012 Japanese Patent Publication No. 47-25266

The present invention has been made in view of the above circumstances, and it is possible to stably obtain a bent product with high dimensional accuracy, it is possible to suppress springback, and there is no risk of insufficient strength at the bent portion. An object of the present invention is to provide a method for bending a metal plate, a die for bending the metal plate, and a bent product made of the metal plate.

In order to solve the above problems, the present invention employs the following configuration.
[1] An arranging step of arranging a material made of a metal plate material between a punch and a die;
A bending method for a metal plate material, comprising: a forming step in which the punch and the die are brought relatively close to each other to perform the bending process on the material,
The material is a metal plate material that satisfies a 0.2% yield strength of 300 MPa or more, a yield ratio of 0.9 or less, and a plate thickness t of 6 mm or less,
The punch includes a pair of punch die faces that approach each other toward the tip of the punch, and a protrusion provided at the tip of the punch, and the tip face of the protrusion is 30% of the plate thickness of the material. a convex curved surface with a radius of curvature corresponding to a length of 50% or less, and a length of the protrusion corresponding to 30% or more and 60% or less of the plate thickness of the material,
The die is provided with a V-shaped groove-shaped die recess for the pair of punch die surfaces, and the bottom of the die recess has a curvature corresponding to a length of 20% or more and 60% or less of the plate thickness of the material. A concave surface of radius is provided,
The forming step is a step of bringing the punch and the die closer to each other to bring the punch and the die into close contact with the material, and press-fitting at least a part of the protrusion of the punch into the material. A bending method for plate materials.
[2] The method for bending a metal plate material according to [1], wherein the projecting portion has the convex curved surface and a side wall surface connected to the convex curved surface and having a width of the projecting portion.
[3] An arranging step of arranging a material made of a metal plate material between the punch and the die;
A bending method for a metal plate material, comprising: a forming step in which the punch and the die are brought relatively close to each other to perform the bending process on the material,
The material is a metal plate material that satisfies a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.9.0 or less, and a plate thickness t of 6.0 mm or less,
The punch includes a pair of punch die faces that approach each other toward the tip of the punch, and a protrusion provided at the tip of the punch, and the tip face of the protrusion is 30% of the plate thickness of the material. It is a convex curved surface with a radius of curvature corresponding to a length of 50% or more, the length of the projection is 30% or more and 60% or less of the plate thickness of the material, and the length of the projection is The width is set to a length corresponding to 50% or more and 150% or less of the plate thickness of the material, and a concave curved surface is provided at the boundary between the pair of punch die surfaces and the protrusion, and the concave curved surface has a radius of curvature. is a radius of curvature corresponding to a length of 150% or less of the plate thickness of the material,
The die is provided with a V-shaped groove-shaped die recess for the pair of punch die surfaces, and the bottom of the die recess has a curvature corresponding to a length of 20% or more and 60% or less of the plate thickness of the material. A concave surface of radius is provided,
The forming step is a step of bringing the punch and the die closer to each other to bring the punch and the die into close contact with the material, and press-fitting at least a part of the protrusion of the punch into the material. A bending method for plate materials.
[4] In [3], the projecting portion is provided with the convex curved surface, a side wall surface forming the width of the projecting portion, and an inclined surface between the convex curved surface and the side wall surface. A method for bending the metal plate described above.
[5] A mold for bending a material made of a metal sheet satisfying a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.9 or less, and a thickness t of 6 mm or less,
a punch comprising a pair of punch die faces approaching each other toward the tip of the punch; and a protrusion provided at the tip of the punch;
a die consisting of a die block provided with a V-shaped die recess for the pair of punch die faces,
The tip surface of the protrusion is a convex curved surface with a radius of curvature corresponding to a length of 30% or more and 50% or less of the thickness of the material, and the length of the protrusion is 30% or more of the thickness of the material. A length corresponding to 60% or less,
A mold for bending a metal plate material, wherein the bottom of the V-groove recess is provided with a concave curved surface having a curvature radius corresponding to a length of 20% or more and 60% or less of the plate thickness of the material. .
[6] The mold for bending a metal plate material according to [5], wherein the protrusion has the convex curved surface and a side wall surface connected to the convex curved surface and having the width of the protrusion.
[7] A mold for bending a material made of a metal sheet material satisfying a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.90 or less, and a thickness t of 6.0 mm or less, ,
a punch comprising a pair of punch die faces approaching each other toward the tip of the punch; and a protrusion provided at the tip of the punch;
a die consisting of a die block provided with a V-shaped die recess for the pair of punch die faces,
The tip surface of the protrusion is a convex curved surface with a radius of curvature corresponding to a length of 30% or more and 50% or less of the thickness of the material, and the length of the protrusion is 30% or more of the thickness of the material. The length is equivalent to 60% or less, the width of the protrusion is a length equivalent to 50% or more and 150% or less of the plate thickness of the material, and the pair of punch die faces and the protrusion A concave curved surface is provided at the boundary with the part, and the radius of curvature of the concave curved surface is a radius of curvature corresponding to a length of 150% or less of the plate thickness of the material,
A mold for bending a metal plate material, wherein the bottom of the V-groove recess is provided with a concave curved surface having a curvature radius corresponding to a length of 20% or more and 60% or less of the plate thickness of the material. .
[8] The metal plate material according to [7], wherein the projecting portion has the convex curved surface, a side wall surface forming the width of the projecting portion, and an inclined surface between the convex curved surface and the side wall surface. A mold for bending.
[9] A plate member made of a metal plate material satisfying a 0.2% yield strength of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness of 6.0 mm or less, and a bent portion provided in the plate member,
The radius of curvature of the convex curved surface on the outer side of the bending portion is a radius corresponding to the thickness of the plate member or less,
A bent product made of a metal plate, wherein the minimum thickness of the bent portion is 0.75 times or more the plate thickness t of the plate portion.
[10] The metal plate member according to [9], wherein a concave portion is provided along the longitudinal direction of the bent portion on the inner side of the bent portion, and a concave curved surface is provided on the inner surface of the concave portion. Bending products.
[11] The ratio of the Vickers hardness HV _r at the bent portion to the Vickers hardness _HV m at the plate portion (HV _r /HV _m ) is in the range of 1.50 or more and 1.90 or less, [9] or [ 10].

According to the metal plate bending method of the present invention, when bending a material using a punch and a die, a punch having a projection provided at the tip of the punch and a V-groove-shaped die recess are used. By using a die with a concave curved bottom, at least a part of the protrusion of the punch is press-fitted into the material, so that the material is press-fitted to the bottom of the die recess and the material flows to the bottom of the die recess. become. In addition, since the radius of curvature of the concave surface at the bottom of the die recess is set to a length corresponding to 60% or less of the plate thickness of the material, the radius of curvature of the convex surface on the bending outer side of the bent portion becomes small. Furthermore, by pressing the protrusion into the material, the distribution of residual stress in the bent portion is different from the distribution of residual stress in the bent portion when die bending is performed using a punch without protrusions. state. In conventional die bending, it is thought that springback occurs due to tensile residual stress on the outside of the bend and compressive residual stress on the inside of the bend. As a result, the springback after die bending is reduced. Therefore, according to the present invention, a metal plate material satisfying a 0.2% yield strength of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness of 6.0 mm or less is used as a material, and a bent product with high dimensional accuracy is stably produced. can be produced effectively. In other words, according to the processing method of the present invention, the radius of curvature of the convex curved surface on the outside of the bent portion is small and the shape is sharp, so that a bent product with small springback after die bending can be manufactured.

Further, according to the method for bending a metal plate material of the present invention, the width of the protrusion is set to 50 to 150% of the plate thickness of the material, and a concave curved surface having a predetermined radius of curvature is provided at the boundary between the punch die surface and the protrusion. As a result, the frequency of breakage of the protrusions can be reduced in the case of repeated processing.

According to the die for bending a metal plate material of the present invention, it is provided with a punch having a projection provided at the tip of the punch, and a die having a concave curved bottom at the bottom of the V-shaped groove-shaped die recess. , This mold is used as a mold for bending a material made of a metal plate material that satisfies a 0.2% yield strength of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness of 6.0 mm or less. Therefore, a bent product with high dimensional accuracy can be stably manufactured.

Further, according to the metal plate bending die of the present invention, the width of the protrusion is set to 50 to 150% of the plate thickness of the material, and the boundary between the punch die surface and the protrusion is a recess having a predetermined radius of curvature. By providing the curved surface, it is possible to reduce the frequency of breakage of the protrusions in the case of repeated machining.

According to the bent product made of the metal plate material of the present invention, the radius of curvature of the convex curved surface on the outer side of the bent portion is equal to or less than the plate thickness of the plate portion. A sharp shape with a small radius of curvature can be obtained. Further, since the minimum thickness of the bent portion is 0.75 times or more the plate thickness of the plate member, the strength of the bent portion can be made sufficient.

Further, the bent product made of the metal plate material of the present invention is provided with a concave portion along the longitudinal direction of the bent portion, and a concave curved surface is provided inside the concave portion. This recess is an indentation formed by the protrusion of the punch during die bending. By providing such an indentation, the bent portion of the bent product is in a state in which a compressive residual stress is applied in the thickness direction of the bent portion. Therefore, according to the present invention, the springback caused by the conventional relationship between the compressive residual stress and the tensile residual stress is reduced, and the springback can be reduced. In addition, since the inner surface of the recess is a concave curved surface, it is possible to prevent cracks originating from the recess.

Further, according to the bent product made of the metal plate material of the present invention, the ratio (HV _r /HV _m ) of the Vickers hardness _{HV r at} the bent portion to the Vickers hardness HV m at the plate portion is 1.50 to 1.90. , and the Vickers hardness of the bent portion is high. Sufficient strength can be imparted.

FIG. 1 is a schematic diagram showing a mold for bending a metal plate according to the first embodiment of the present invention. FIG. 2 is a schematic diagram for explaining the method for bending a metal plate according to the first embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a method for bending a metal plate according to the first embodiment of the present invention. FIG. 4 is a schematic diagram for explaining the method for bending a metal plate according to the first embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of a bent product made of a metal plate according to the first embodiment of the present invention. FIG. 6 is a schematic diagram illustrating a conventional method for bending a metal plate. FIG. 7 is a schematic diagram explaining the length of the protrusion in the mold of the first embodiment of the present invention. FIG. 8 is a schematic diagram showing a mold for bending a metal plate according to a second embodiment of the present invention. FIG. 9 is a partially enlarged schematic diagram showing the main part of the punch of the mold in FIG. FIG. 10 is a partially enlarged view of FIG. 9, and is a schematic diagram for explaining the relationship between the range of the tip surface (angle θr) and the angle θq of the inclined surface. FIG. 11 is a schematic diagram illustrating the length of the protrusion in the mold of the second embodiment of the present invention.

(First embodiment)
Hereinafter, a method for bending a metal plate material (hereinafter, may be referred to as a bending method), a mold for bending a metal plate material (hereinafter, may be referred to as a mold), which is a first embodiment of the present invention. ) and a bent product made of a metal plate (hereinafter sometimes referred to as a bent product).

The outline of this embodiment is as follows. The bending method of this embodiment includes, as shown in FIG. and a forming step for bending the material 3 by bringing the die 2 relatively close to each other. The material 3 is a metal plate having a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.90 or less, and a thickness t of 6.0 mm or less. As shown in FIG. 1, the punch 1 has a pair of punch die faces 1b and a protrusion 1c provided at the tip end 1a of the punch. The tip surface 1e of the projection 1c is a convex curved surface, and the length H of the projection 1c is set to a predetermined length. The die 2 is provided with a V-shaped groove-shaped die recess 2a for the pair of punch die faces 1b. The bottom 2d of the die recess 2a is provided with a concave curved surface 2b having a predetermined radius of curvature. Then, in the forming step, the punch 1 and the die 2 are brought close to each other so that the punch 1 and the die 2 are brought into close contact with the material 3 , and at least a part of the protrusion 1 c of the punch 1 is press-fitted into the material 3 . As a result, as shown in FIG. 5, the radius of curvature Rout of the convex curved surface 4c on the outer side of the bent portion becomes small, and the bent product 4 having the sharply shaped bent portion 4b is obtained.
Hereinafter, this embodiment will be described in sequence.

(material)
The material 3 according to the present embodiment is a metal plate material satisfying a 0.2% yield strength of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness t of 6.0 mm or less.
Reasons for limiting the metal plate suitable for the material 3 will be described below.

<0.2% yield strength>
The 0.2% yield strength of the metal plate material according to this embodiment is set to 300 MPa or more. As a result, sufficient strength can be ensured when the metal plate material of the present embodiment is used as a material for an exterior building material or an interior building material. If the 0.2% proof stress is less than 300 MPa, the strength will be insufficient.

<Yield ratio>
The yield ratio of the metal plate material according to this embodiment is set to 0.90 or less. This makes it possible to suppress cracking of the bent portion, especially the outer surface of the bent portion, during bending. If the yield ratio exceeds 0.90, cracking occurs on the outer surface of the bent portion during bending, making it impossible to provide a bent product with an excellent appearance. The ratio of yield strength (YS) to tensile strength (TS) is called yield ratio (YS/TS), and 0.2% proof stress is defined as yield strength (YS) here.

<Thickness>
The plate thickness t of the metal plate material according to this embodiment is 6.0 mm or less, preferably 4.0 mm or less. The lower limit of the plate thickness t may be 0.5 mm or more, or 1 mm or more. By setting the plate thickness t to 6.0 mm or less, the springback of the bent product after bending can be reduced.

(Mold)
Next, referring to FIG. 1, a mold for bending a metal plate material, which is used when manufacturing the bent product of the present embodiment, will be described.
The mold K according to this embodiment is a so-called mold for bending. That is, the die K according to this embodiment is used as a die for a working method in which the die K (the punch 1 and the die 2) is pressed from above and below the material 3 with both ends 3a of the material 3 as free ends. The mold K of this embodiment will be described below.

A mold K according to this embodiment is composed of a punch 1 and a die 2 .

As shown in FIG. 1, the punch 1 is provided with a pair of punch die faces 1b which are inclined so as to approach each other toward the punch tip 1a, and a protrusion 1c provided at the punch tip 1a. . The pair of punch die faces 1b have a relative angle θp in the range of, for example, 80 to 100°, preferably 85 to 95°, more preferably 88 to 92°, and even more preferably. is 90°. A pair of punch die faces 1b form the outer shape of the punch 1 and are inclined toward the tip end 1a of the punch so as to approach each other. The punch tip 1a has a protrusion 1c.

The protrusion 1c protrudes from the punch tip 1a toward the die 2 side. As shown in FIG. 1, the projecting portion 1c has a side wall surface 1d in contact with the punch die surface 1b and a tip end surface 1e in contact with the side wall surface 1d. 1d of side wall surfaces are made into a plane, and the front end surface 1e is made into the convex curved surface.

A tip surface 1e of the protrusion 1c is a convex curved surface having a radius of curvature Rp. The radius of curvature Rp of the tip surface 1e is set to a length of 30% or more and 50% or less of the plate thickness t of the material 3, that is, a radius corresponding to a length of 0.30t to 0.50t. By setting the curvature radius Rp to a radius corresponding to a length of 30% or more (0.30t) of the plate thickness t of the material 3, as will be described later, a sufficient compressive stress is applied to the bent portion 4b. can reduce the springback of the bent product 4 . Further, by setting the curvature radius Rp to a radius corresponding to a length of 50% or less (0.50 t) of the plate thickness t of the material 3, the curvature radius Rout can be made small. Further, by forming the tip surface 1e into a convex curved surface, cracking of the bent portion 4b of the bent product 4 can be prevented.

The length H of the protrusion 1c is set to a length corresponding to 30% or more and 60% or less of the plate thickness t of the material 3, that is, a length corresponding to 0.30t to 0.60t. The length H of the protrusion 1c, as shown in FIG. 1, is the length in the direction in which the protrusion 1c protrudes, and is the length from the boundary between the side wall surface 1d and the punch die surface 1b to the tip end surface 1e. Satoru. By setting the length H of the protrusion 1c to a length corresponding to 30% or more (0.30t) of the plate thickness t of the material 3, the material flow to the bottom of the die recess 2a is promoted, and the The radius of curvature Rout of the convex curved surface 4c on the outer side of the bent portion 4b can be reduced. In addition, sufficient compressive stress can be applied to the bent portion 4b, and springback of the bent product can be suppressed. Further, by setting the length H of the protrusion 1c to a length corresponding to 60% or less (0.60t) of the plate thickness t of the material 3, when the punch 1 reaches the bottom dead center, the punch of the punch 1 The material 3 can be restrained between the punch 1 and the die 2 by bringing the material into close contact with the mold surface 1b and the die concave portion 2a, so that bending can be performed reliably. In addition, the projecting portion 1c does not excessively intrude into the material 3, and the thickness of the bent portion 4b of the bent product can be sufficiently secured, and spring go can be suppressed.

The length H of the protrusion 1c is the length from the position of the boundary between the side wall surface 1d and the punch die surface 1b to the tip surface 1e, but when the position of the boundary between the side wall surface 1d and the punch die surface 1b is unclear. may determine the length H of the protrusion 1c as follows. That is, as shown in FIG. 7, the position of the intersection X between the extension of the outline of the punch die surface 1b and the extension of the outline of the side wall surface 1d is specified, and from the intersection X, the width W direction of the protrusion 1c is measured. Draw an imaginary horizontal line M at . The length H of the protrusion 1c is defined as the distance between the horizontal line M and the tip of the protrusion 1c (apex of the convex curved surface).

The interval between the side wall surfaces 1d of the protrusions 1c, that is, the width W of the protrusions 1c can be set to a length corresponding to 50% or more and 150% or less (0.50t to 1.50t) of the plate thickness t of the material 3. preferable.

The curvature radius Rj of the concave curved surface 1g provided at the boundary between the pair of punch die surfaces 1b and the protrusion 1c is set to a curvature radius corresponding to a length of 150% or less (1.50t) of the plate thickness t of the material 3. is preferred.

Next, the die 2 will be explained. The die 2 consists of a die block 2A provided with a die recess 2a, as shown in FIG. The die recess 2a is provided on the upper surface 2m of the die block 2A. The cross-sectional shape of the die recess 2a is V-shaped with respect to the punch die surface 1b of the punch 1. As shown in FIG. That is, the die recess 2a is defined by a pair of die surfaces 2c corresponding to the pair of punch die surfaces 1b and a concave surface 2b provided on the bottom 2d of the die recess 2a. The pair of die surfaces 2c are inclined so as to approach each other toward the bottom 2d of the die recess 2a. The concave surface 2b is located between the pair of die surfaces 2c. A pair of die surface 2c and concave curved surface 2b are in contact with each other.

The curvature radius Rd of the concave curved surface 2b of the die recess 2a is set to a length of 20% or more and 60% or less of the plate thickness t of the material 3, that is, a radius corresponding to a length of 0.20t to 0.60t. . When the punch 1 having projections is used for bending, stress is concentrated on the concave surface 2b of the die recess 2a. This stress concentration increases as the radius of curvature Rd of the concave curved surface 2b decreases. or cracking may occur. Therefore, the curvature radius Rd of the concave surface 2b of the die recess 2a is set to 20% or more of the plate thickness t of the material 3 (0.20t). Further, by setting the curvature radius Rd to a radius of 60% (0.60t) or less of the plate thickness t of the material 3, a space in which the material can flow is secured in the bottom 2d of the die recess 2a, and the bent portion after bending It is possible to reduce the radius of curvature Rout of the convex curved surface 4c on the outside of the bend 4b, and to apply a moderate amount of compressive stress that does not cause spring go to the bent portion 4b, thereby preventing springback. can be suppressed.

Next, the bending method of this embodiment will be described with reference to FIGS. 2 to 4. FIG. In the bending method of the present embodiment, the bent portion 4b is formed in the material 3 by subjecting the material 3 to die bending using the punch 1 and the die 2. As shown in FIG. A punch 1 and a die 2 used for bending are as shown in FIG. The bending method of this embodiment includes an arrangement step and a forming step.

(Placement process)
In the placement step, as shown in FIG. 2, the material 3 is placed on the upper surface 2m of the die block 2A of the die 2, and the punch 1 is placed thereabove. The material 3 is placed on the die 2 so that the upper surface 3b faces the punch 1 side and the lower surface 3c is in contact with the upper surface 2m of the die block 2A. Thus, the material 3 is placed between the punch 1 and the die 2. Both ends 3a of the material 3 are free ends without restraint. The punch 1 and the die 2 are attached to a press molding machine (not shown).

(Molding process)
Next, in the forming process, the press forming machine is operated to bring the punch 1 and the die 2 closer to each other, and the material 3 is subjected to a shape bending process.

In the forming process, as shown in FIG. 3, the punch 1 and the die 2 are brought relatively close to each other, and the protrusion 1c of the punch 1 is pressed against the upper surface 3b of the material 3. As shown in FIG. The material 3 against which the protrusion 1c is pressed is further pushed into the die recess 2a by the punch 1. As shown in FIG. As a result, the material 3 starts bending deformation (plastic deformation) at the location where the protrusion 1c is in contact.

When the punch 1 and the die 2 are moved relatively closer together, the material 3 undergoes bending deformation (plastic deformation), and the bottom surface 3c of the material comes into close contact with the die surface 2c of the die 2. As shown in FIG. On the other hand, the lower surface 3c of the blank 3 is spaced from the upper surface 2m of the die 2. At this stage, the lower surface 3c of the material does not contact the concave curved surface 2b of the bottom 2d of the die 2, leaving a gap S1. On the other hand, the upper surface 3b of the material 3 is in contact only with the protrusion 1c, and the upper surface 3b of the material 3 and the punch die surface 1b are not in contact. As a result, a space S2 is created between the upper surface 3b of the material 3 and the punch die surface 1b. There remains room for further pushing down the punch 1 until this space S2 is eliminated.

When the punch 1 and the die 2 are moved relatively close to each other until the punch die surface 1b of the punch 1 is in close contact with the upper surface of the material 3, the punch die surface 1b and the die surface 1b are formed on the upper surface 3b and the lower surface 3c of the material 3 as shown in FIG. The die surfaces 2c are in close contact with each other, and the protruding portion 1c is press-fitted inside the bent portion 4b. The bent portion 4b is subjected to a process similar to forging as a result of applying a compressive stress in the thickness direction by the protrusion 1c. As a result, material flow occurs in the bent portion 4b, and part or all of the gap S1 existing between the lower surface 3c of the material 3 and the concave curved surface 2b of the die 2 is filled by the material flow. As a result, the radius of curvature Rout of the convex curved surface 4c on the outer side of the bent portion 4b is reduced. As a result, the bent product 4 having the bent portion 4b as shown in FIG. 5 is manufactured.

For comparison, FIG. 6 shows a schematic cross-sectional view of a punch 111 that does not have protrusions. When the material 3 is subjected to form bending by a punch 111 having no protrusions, as shown in FIG. and the die 2 are moved relatively close to each other, but since the punch 111 has no protrusion, material flow does not occur at the bent portion 14b, leaving a gap S1 between the lower surface 3c of the material 3 and the concave curved surface 2b of the die 2. In this state, the die bending process is completed. Therefore, in a bent product manufactured using a punch 111 having no protrusions, it is not possible to reduce the radius of curvature Rout of the bent outer convex curved surface 4c of the bent portion 14b. Moreover, since compressive residual stress is not applied in the thickness direction of the bent portion 14b, it is difficult to suppress springback.

Next, the bent product 4 according to this embodiment will be described. FIG. 5 shows a schematic cross-sectional view of the bent product of this embodiment.

The bent product 4 according to the present embodiment includes a plate member 4a made of a metal plate material having a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness t of 6.0 mm or less, and the plate member 4a A bent portion 4b is provided. A convex curved surface 4c is provided on the outer side of the bent portion 4b, and a concave portion 4d is provided on the inner side of the bent portion.

The bending angle θ of the bent portion 4b is in the range of 85° to 95°, preferably in the range of 88° to 92°, and more preferably 90°. This means that when the target bending angle θ is 90°, the bending angle θ at the bent portion 4b is within the range of ±5° or ±2°. By setting the bending angle .theta.

Also, the radius of curvature Rout of the convex curved surface 4c on the outer side of the bend is set to a radius corresponding to the thickness of the plate member 4a or less. By setting the radius of curvature Rout of the convex curved surface 4d on the outside of the bend to be equal to or less than the plate thickness of the plate member 4a, the appearance of the outside of the bend of the bend 4b becomes angular and sharp, making it suitable as a material for exterior building materials and interior building materials. can be used.

A concave portion 4d is provided inside the bent portion 4b. This concave portion 4d is an indentation formed by press-fitting the protrusion 1c of the punch 1 in the final stage of the forming process. The recess 4d is provided with a concave curved surface 4e formed by the tip surface 1e of the projection 1c.
Since the inside of the concave portion 4d is the concave curved surface 4e, cracks originating from the concave portion 4d are prevented from occurring.

Further, since the concave portion 4d is provided on the inner side of the bent portion 4b, the thickness of the bent portion 4b is smaller than the plate thickness t of the plate portion 4a. It must be 0.75 times the thickness t (0.75t) or more. Thereby, the strength of the bent portion 4b can be made sufficient.

Also, the ratio ( _HVr / _HVm ) of _the Vickers hardness _HVr at the bent portion 4b to the Vickers hardness HVm at the plate portion 4a is preferably in the range of 1.50 or more and 1.90 or less. In addition to work hardening caused by plastic deformation of the material 3, the bent portion 4b according to the present embodiment also has work hardening due to residual stress in the thickness direction given by the protrusion 1c during the molding process. Join. Therefore, the hardness of the bent portion 4b of the bent part 4 according to the present embodiment is higher than the hardness of the plate member 4a, and the strength of the bent portion 4b is increased. On the other hand, if the hardness of the bent portion 4b is too high, cracks are likely to occur in the bent portion 4b. Therefore, the ratio (HV _r /HV _m ) of the Vickers hardness _{HV r of} the bent portion 4b to the Vickers hardness HV m of the plate portion 4a is preferably in the range of 1.50 to 1.90.

The bent product 4 of the present embodiment as described above can be suitably used as a material for exterior building materials and interior building materials.

As described above, according to the metal plate bending method of the present embodiment, when the blank 3 is bent using the punch 1 and the die 2, the projection 1c is provided at the punch tip 1a. and a die 2 having a concave curved surface 2b at the bottom 2d of the V-shaped die recess 2a, and at least a part of the protrusion 1c of the punch 1 is press-fitted into the material 4, thereby forming a material. 3 is press-fitted to the bottom 2d of the die recess 2a, and the material flows to the bottom 2d of the die recess 2a.

Further, since the radius of curvature of the concave curved surface 2b of the bottom portion 2d of the die concave portion 2a is set to a length corresponding to 20% or more and 60% or less of the plate thickness of the material 3, the curvature of the convex curved surface 4c on the bending outer side of the bent portion 4b is The radius Rout becomes smaller.

Furthermore, by press-fitting the projection 1c into the material 3, the distribution of residual stress in the bent portion 4b is compared with the distribution of residual stress in the bent portion when die bending is performed using a punch without the projection 1c. can have different distributions. That is, in conventional die bending, it is thought that springback occurs due to the tensile residual stress on the outside of the bend and the compressive residual stress on the inside of the bend. , the springback after die bending is reduced.

Therefore, according to the present embodiment, a metal plate material satisfying a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness t of 6.0 mm or less is used as the material 3, and bending is performed with high dimensional accuracy. The product 4 can be stably manufactured. That is, according to the processing method of the present embodiment, it is possible to manufacture a bent product 4 with a small curvature radius Rout of the convex curved surface 4c on the outer side of the bent portion, a sharp shape, and a small springback after die bending.

According to the mold K for bending a metal plate material of the present embodiment, the punch 1 having the projection 1c provided at the punch tip 1a and the bottom 2d of the V-shaped die recess 2a are formed into the concave surface 2b. A material 3 made of a metal plate material satisfying a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness t of 6.0 mm or less. is used as the mold K for the bending process, the bent product 4 with high dimensional accuracy can be stably manufactured.

According to the bent product 4 of the present embodiment, the radius of curvature Rout of the convex curved surface 4c on the outer side of the bent portion 4b is a radius corresponding to the plate thickness t or less of the plate member 4a. The curvature radius Rout of the convex curved surface 4c can be made small and sharp. Further, since the minimum thickness of the bent portion 4b is 0.75 times or more the plate thickness t of the plate member 4a, the strength of the bent portion 4b can be made sufficient.

Further, the bent product 4 of the present embodiment is provided with a concave portion 4d along the longitudinal direction of the bent portion 4b, and a concave curved surface 4e is provided inside the concave portion 4d. The recess 4d is an indentation formed by the projecting portion 1c of the punch 1 during die bending. By providing such an indentation, the bent portion 4b of the bent product 4 is in a state in which compressive residual stress is applied in the thickness direction of the bent portion 4b. Therefore, according to the present embodiment, the springback caused by the conventional relationship between the compressive residual stress and the tensile residual stress is reduced, and the springback can be reduced. Moreover, since the inner surface of the concave portion 4d is the concave curved surface 4e, it is possible to prevent cracks originating from the concave portion 4d.

Further, according to the bent product 4 of the present embodiment, the ratio (HV _r /HV _m ) of the Vickers hardness _{HV r at} the bent portion 4b to the Vickers hardness HV m at the plate portion 4a is 1.50 to 1.90. Since the Vickers hardness of the bent portion 4b is high, even if the thickness of the bent portion 4b becomes smaller than the plate thickness t of the plate portion 4a by providing the concave portion 4d in the bent portion 4b, Regardless, sufficient strength can be imparted to the bent portion 4b.

(Second embodiment)
Next, a second embodiment of the invention will be described.
A change of the second embodiment from the first embodiment is to change the shape of the tip portion of the punch. Specifically, by widening the width of the protrusion, damage to the tip of the punch that may occur when the die bending process is repeated can be prevented. A mold, a bending method using the mold, and a bent product according to the present embodiment will be described below.

(Mold)
As shown in FIG. 8, a mold L according to this embodiment is a mold for bending, as in FIG. A mold L is composed of a punch 11 and a die 2 . The shape of the die 2 is the same as in the first embodiment.

The punch 11 is provided with a pair of punch die faces 11b which incline so as to approach each other toward the punch tip 11a, and a protrusion 11c provided at the punch tip 11a. The relative angle θp between the pair of punch die faces 11b is set to, for example, 80 to 100°, preferably 85 to 95°, more preferably 88 to 92°, still more preferably 90°, as in the first embodiment.

As shown in FIG. 9, the protrusion 11c includes a pair of side wall surfaces 11d having a width W of the protrusion 11c, a tip surface 11e (convex curved surface) of the protrusion 11c, and a gap between the sidewall surface 11d and the tip surface 11e. and an inclined surface 11f at . The side wall surface 11d is connected to the punch die surface 11b. A concave curved surface 11g having a radius of curvature Rj is present between the side wall surface 11d and the punch die surface 11b. The side wall surfaces 11d are parallel to each other. An inclined surface 11f is connected to the side wall surface 11d, and a tip surface 11e is connected to the inclined surface 11f. The inclined surface 11f is inclined at an inclination angle θq with respect to the side wall surface 11d. Thus, the projection 11c is composed of the side wall surface 11d, the tip surface 11e (convex curved surface) and the inclined surface 11f, and the concave curved surface 11g having the curvature radius Rj is present between the projection 11c and the punch die surface 11b. .

A tip surface 11e of the protrusion 11c is a convex curved surface having a radius of curvature Rp. The curvature radius Rp of the tip surface 11e is set to a radius corresponding to a length of 30% or more and 50% or less (0.30t to 0.50t) of the plate thickness t of the material 3, as in the first embodiment. . By setting the curvature radius Rp to 30% (0.30t) or more of the plate thickness t of the material 3, a sufficient compressive stress is applied to the bent portion 4b of the bent product 4, and the bent product 4 becomes a spring. Back can be reduced. Further, by setting the radius of curvature Rp to 50% (0.50t) or less of the plate thickness t of the material 3, the radius of curvature Rout of the bent outer convex curved surface 4c of the bent portion 4b after bending can be reduced. Further, by forming the tip surface 11e into a convex curved surface, cracking of the bent portion 4b of the bent product 4 can be prevented.

Further, the distal end surface 11e of the present embodiment has an arc-shaped contour when viewed in cross section as shown in FIG. When the range of the tip surface 11e formed by the arc-shaped outline is defined by the central angle at the center O of the arc, the range of the tip surface 11e is relative to the normal direction L passing through the center of the width W direction of the protrusion 11c. Therefore, it is preferable that the angle θr is 25° or more and 65° or less. By setting the tip end surface 11e within such a range, the durability of the punch 11 can be enhanced in the case of repeated die bending.

The inclined surface 11f is an extension of both ends of the tip surface 11e. Moreover, the side wall surface 11d in contact with the inclined surface 11f extends parallel to the normal direction L. As shown in FIG. Accordingly, the angle θq of the inclined surface 11f with respect to the side wall surface 11d is determined within the range of 25° or more and 65° or less in accordance with the specification of the preferred range of the tip surface 11e. As shown in FIG. 10, since the relationship θr+θq=90° is established, θq is uniquely determined when the value of θr is determined. By setting the angle θq of the inclined surface 11f within this range, it is possible to increase the durability of the punch 11 when repeated die bending is performed.

The distance between the side wall surfaces 11d of the protrusions 11c, that is, the width W of the protrusions 11c is set to a length corresponding to 50% or more and 150% or less (0.50t to 1.50t) of the plate thickness t of the material 3. By setting the width W of the projecting portion 11c to 50% (0.50 t) or more of the plate thickness t of the material 3, stress concentration on the projecting portion 11c during die bending is alleviated, and repeated die bending is performed. It is possible to prevent the protrusion 11c from being damaged during processing. For the above reasons, the lower limit of the width W of the protrusion 11c is preferably 60% (0.60t), more preferably 80% (0.80t), and even more preferably 100% (1. 00t). In addition, by setting the width W of the protrusion 11c to 150% (1.50t) or less of the plate thickness t of the material 3, the radius of curvature Rout of the bent outer convex curved surface 4c in the bent portion 4b after processing is small and sharp. shape. Further, it becomes easier to press-fit the projecting portion 11c into the material 3 during the molding process, and a sufficient compressive stress can be applied to the bent portion 4b, so that the bent product 4 can be prevented from springback.

The length H of the protrusion 11c is set to a length (0.30t to 0.60t) corresponding to 30% or more and 60% or less of the plate thickness t of the material 3, as in the first embodiment. By setting the length H of the protruding portion 11c to 30% (0.30t) or more of the plate thickness t of the material 3, the material flow to the bottom portion of the die concave portion 2a is promoted, and the bent portion 4b after bending is bent. The radius of curvature on the outer side of the bend can be reduced. Moreover, sufficient compressive stress can be applied to the bent portion 4b, and springback of the bent product 4 can be suppressed. Further, by setting the length H of the protrusion 11c to 60% (0.60t) or less of the plate thickness t of the material 3, when the punch 11 reaches the bottom dead center, the punch die surface 11b of the punch 11 and the The material 3 can be restrained between the punch 11 and the die 2 by bringing the material into close contact with the die recess 2a, and the bending can be reliably performed. In addition, the projecting portion 11c does not excessively intrude into the material 3, and a sufficient thickness can be secured at the bent portion 4b of the bent product, and spring go can be suppressed.

As shown in FIG. 11, the length H of the protrusion 11c is the length in the direction in which the protrusion 11c protrudes, and is determined as follows. That is, as shown in FIG. 11, the position of the intersection X between the extension of the outline of the punch die surface 11b and the extension of the outline of the side wall surface 11d is specified, and from the intersection X, the width W direction of the protrusion 11c is measured. Draw an imaginary horizontal line M at . The length H of the projection 11c is defined as the distance between the horizontal line L and the tip of the projection 11c (apex of the convex curved surface).

The curvature radius Rj of the concave curved surface 11g provided at the boundary between the pair of punch die surfaces 11b and the protrusion 11c is set to a curvature radius corresponding to a length of 150% or less (1.50t) of the plate thickness t of the material 3. be. By setting the radius of curvature Rj of the concave curved surface 11g to 150% or less (1.50t), sufficient compressive stress can be applied to the bent portion 4b during the forming process, and springback of the bent product 4 can be suppressed. Further, when the punch 11 of the present embodiment is used for die bending, stress is most concentrated on the concave curved surface 11g between the protrusion 11c and the punch die surface 11b, which tends to cause damage. In order to alleviate the stress concentration, it is preferable that the radius of curvature Rj of the concave curved surface 11g is 40% or more of the plate thickness t of the material 3 (0.40t). By setting the curvature radius Rj to 40% (0.40t) or more of the plate thickness t of the blank 3, stress concentration on the concave curved surface 11g during die bending can be prevented, and damage to the punch 11 can be suppressed. For the above reasons, the lower limit of the curvature radius Rj of the concave surface 11g is preferably 50% (0.50t), more preferably 60% (0.60t), and even more preferably 70% (0 .70t).

In the bending method of this embodiment, in the same manner as in the case of the first embodiment except that the die L is changed, by performing die bending on the material 3 using the punch 11 and the die 2, A bent portion is formed in the material 3 . The punch 11 and die 2 used for bending are as shown in FIGS. In the bending method of the present embodiment, similarly to the first embodiment, the arranging process and the forming process are sequentially performed.

2, the material 3 is placed on the upper surface 2m of the die 2, and the punches 11 shown in FIGS. 8 and 9 are placed thereabove. Both ends of the material 3 are free ends without restraint.

Next, in the forming step, the punch 11 and the die 2 are moved relatively close to each other to form the material 3 in the same manner as in FIG. The material 3 against which the projecting portion 11 c is pressed is pushed into the die recess 2 a by the punch 11 . As a result, the material 3 starts bending deformation (plastic deformation) at the location where the protruding portion 11c is in contact. 4, the punch 11 and the die 2 are moved relatively close to each other until the punch die surface 11b of the punch 11 is in close contact with the upper surface 3b of the material 3. As shown in FIG. As a result, the projecting portion 11c is press-fitted into the bent inner side of the bent portion of the material 3, and as a result of the compressive stress applied to the bent portion in the thickness direction by the projecting portion 11c, processing similar to forging is performed, and the bent portion is Material flow occurs, and the radius of curvature of the convex curved surface on the outside of the bent portion becomes smaller. As described above, a bent product is manufactured.

According to this embodiment, a bent product equivalent to the bent product 4 obtained in the first embodiment can be obtained. Further, by using the die L of the present embodiment, even if the die bending process is repeated, damage to the punch 11 can be prevented.

According to the metal mold L and the metal plate bending method of the present embodiment, the width W of the protruding portion 11c of the tip 11a of the punch 11 is set to a length corresponding to 50% or more and 150% or less of the plate thickness t of the material 3. Therefore, the concentration of stress on the protrusion 11c during die bending can be alleviated, and the protrusion 11c can be prevented from being damaged when the die bending is repeatedly performed.

Further, according to the metal mold L and the metal plate bending method of the present embodiment, the concave curved surface 11g is provided at the boundary between the pair of punch die surfaces 11b and the protrusion 11c, and the concave curved surface 11g has a radius of curvature Rj However, since the radius of curvature corresponds to a length of 150% or less of the plate thickness t of the material 3, stress concentration on the concave curved surface 11g during die bending is prevented, and when repeated die bending is performed damage of the punch 11 can be suppressed.

Furthermore, according to the metal mold L and the metal plate bending method of the present embodiment, the protruding portion 11c has the tip surface (convex surface) 11e, the side wall surface 11d, and the inclined surface 11f. Since there is an inclined surface 11f between the tip surface 11e of the protrusion 11c and the side wall surface 11d, the width W of the protrusion 11c can be secured even if the radius of curvature Rp of the tip surface 11e is reduced. As a result, it is possible to increase the durability of the punch when repeated die bending is performed, and to form a sharp shape with a small radius of curvature Rout of the convex curved surface 4c on the outside of the bent portion 4b after bending. can be done.

The technical scope of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.
As the metal material for the bending method and bending product of the above embodiment, for example, a two-phase ferrite-austenite having a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness t of 6.0 mm or less A stainless steel plate is preferably used. A duplex stainless steel plate has sufficient strength, is less expensive than an austenitic stainless steel plate, and has better corrosion resistance than a ferritic stainless steel plate. However, since it has a higher yield strength than austenitic stainless steel and ferritic stainless steel, bending may reduce the dimensional accuracy after bending. If the processing conditions are made stricter in order to improve the dimensional accuracy, cracks may occur at the bent portion. In addition, if the processing conditions are made stricter, there are cases in which scratches or galling defects occur, impairing the design and appearance. Therefore, it has been difficult to apply duplex stainless steel sheets as exterior building materials and interior building materials that require bending to be used in easily visible locations. By applying the present invention, bending can be performed without causing such problems, and a bent product with excellent design and aesthetics can be provided.

As such a stainless steel plate, for example, the chemical composition is mass%, C: 0.050% or less, Si: 2.00% or less, Mn: 1.00 to 8.00%, P: 0.050% Below, S: 0.0500% or less, Ni: 0.10 to 6.00%, Cr: 17.00 to 25.00%, Mo: 0.10 to 2.50%, Cu: 0.10 to 3 00%, N: 0.080 to 0.300%, and the balance being Fe and impurities.
In addition, in the above stainless steel plate, instead of part of Fe, the mass% is further Sn: 0.01 to 1.00%, W: 0.01 to 1.00%, V: 0.01 to 1.00%, may contain one or more.
Furthermore, in the above stainless steel plate, instead of a part of Fe, the mass % of Ca: 0.0050% or less, Mg: 0.0050% or less, Al: 0.50% or less, and rare earth elements: 0.005%. 50% or less, may contain one or more.
Furthermore, the above stainless steel plate may further contain, in mass %, Nb: 0.100% or less in place of part of Fe.

In order to ensure the corrosion resistance of the steel sheet, the amount of C may be 0.050% or less, preferably 0.040% or less. On the other hand, C is an element that forms austenite that constitutes a two-phase structure, so the content is preferably 0.005% or more, more preferably 0.010% or more.

For deoxidation, Si is preferably contained in an amount of 0.01% or more, more preferably 0.10% or more, and still more preferably 0.30% or more. If the Si content exceeds 2.00%, precipitation of the σ phase is promoted, so the Si content is preferably 2.00% or less, more preferably 0.60% or less.

Mn is 1.00% or more, preferably 1.50% or more, and more preferably 2.00% or more, as a deoxidizing material and an austenite stabilizing element for forming a two-phase structure. On the other hand, if the Mn content exceeds 8.00%, the corrosion resistance deteriorates, so the Mn content is preferably 8.00% or less, preferably 5.00% or less, and more preferably 4.00% or less. good.

P deteriorates hot workability and toughness, so the P content is limited to 0.050% or less, preferably 0.035% or less. On the other hand, if the amount of P is excessively reduced, the refining cost will increase, so it may be 0.005% or more.

Since S degrades hot workability, toughness and corrosion resistance, the S content is limited to 0.0500% or less, preferably 0.0100% or less, more preferably 0.0010% or less. On the other hand, if the amount of S is excessively reduced, the raw material cost and the refining cost increase, so the amount may be 0.0003% or more.

When Ni is contained in the steel sheet coating, it has the effect of suppressing the occurrence of pitting corrosion when the Fe concentration of the coating is high and the effect of suppressing the progress of corrosion when corrosion occurs. On the other hand, if the amount of Ni is excessive, the Cr concentration in the film is too low, and sufficient corrosion resistance cannot be obtained. Therefore, it is preferable to set the Ni amount in the range of 0.10 to 6.00%. The lower limit of the Ni amount is preferably 0.30% or more, 0.50% or more, or 1.00% or more. The upper limit of the Ni amount is preferably 5.00% or less, 4.00% or less, or 3.00% or less.

In order to impart sufficient corrosion resistance to steel, the Cr content is preferably in the range of 17.00 to 25.00%. The lower limit of the Cr content is preferably 18.00% or more, more preferably 20.00% or more, still more preferably 21.00% or more. The upper limit of the Cr content is preferably 24.00% or less, more preferably 22.00% or less.

Mo is an element that improves corrosion resistance, and its effect is exhibited at a content of 0.10% or more. Mo may be contained as long as it is 2.50% or less, but if the Mo content exceeds 2.50%, the σ phase tends to precipitate during hot working. Therefore, the lower limit of the Mo content is 0.10% or more, preferably 0.20% or more, and more preferably 0.50% or more. The upper limit of Mo content is 2.50% or less, preferably 2.00% or less, and more preferably 1.50% or less.

When 0.10% or more of Cu is contained, the effect of suppressing the progress of corrosion when corrosion occurs can be obtained. Cu may be contained in an amount of 3.00% or less. Moreover, when the amount of Cu exceeds 3.00%, cracks may easily occur during casting. Therefore, the lower limit of the Cu content is 0.10% or more, preferably 0.30% or more, and more preferably 0.50% or more. The upper limit of the amount of Cu is 3.00% or less, preferably 2.50% or less, and more preferably 2.00% or less.

N is an element that remarkably increases corrosion resistance and increases the amount of austenite phase, and is preferably contained in an amount of 0.080% or more as an austenite stabilizing element. The lower limit of the N content is preferably 0.150% or more. On the other hand, if the amount of N is excessive, nitrides are formed in the steel to lower the corrosion resistance and toughness, so the upper limit of the amount of N is preferably 0.300% or less. The upper limit of the amount of N is preferably 0.250% or less.

In addition, when a trace amount of Sn is contained, the corrosion resistance is improved. Therefore, Sn is an element useful for improving corrosion resistance, and may be contained within a range that does not impair the cost. If the amount of Sn is less than 0.001%, the effect of improving the corrosion resistance is not exhibited, and if the amount of Sn exceeds 1.00%, the cost increases and workability decreases, so the appropriate range of the amount of Sn is 0.001 to 1.00%. The lower limit of Sn content is preferably 0.01% or more, and the upper limit of Sn content is preferably 0.50% or less. Note that Sn is an optional element and does not have to be contained. That is, the Sn content may be 0%.

V and W may be contained as necessary in order to improve corrosion resistance, particularly crevice corrosion resistance. However, excessive amounts of V and W degrade workability and saturate the effect of improving corrosion resistance. The upper limit of each amount is 1.00% or less. The lower limit of each of V and W is preferably 0.04% or more, and the upper limit of each of V and W is preferably 0.50% or less. Note that V and W are optional elements and may not be contained. That is, the amount of V and the amount of W may each be 0%.

Ca, Mg, and REM are elements that improve hot workability, and for that purpose, one or more of Ca, Mg, and REM may be contained. Since the effects of Ca and Mg are exhibited at amounts of 0.0002% or more, the lower limits of the amounts of Ca and Mg are set to 0.0002% or more. In the case of REM, the lower limit shall be 0.001% or more. Note that Ca, Mg, and REM are optional elements and may not be contained. That is, each of the Ca amount, Mg amount, and REM amount may be 0%.

However, since an excessive content of any of these elements conversely reduces the hot workability, it is preferable to set the upper and lower limits of the content as follows. That is, the respective amounts of Ca and Mg are 0.0002 to 0.0050%, and the amount of REM is 0.001 to 0.50%.

The lower limit of each amount of Ca and Mg is preferably 0.0005% or more. The upper limit of each of Ca and Mg is preferably 0.0015% or less. The lower limit of the REM content is preferably 0.005% or more, and the upper limit of the REM content is preferably 0.30% or less.

Here, the rare earth element (REM) is a generic term for two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu), according to a general definition. . It may be contained singly or as a mixture. The REM amount is the total amount of these elements.

Al is useful as a deoxidizing element, but should not be contained in a large amount because it deteriorates workability. It is preferable to limit the upper limit of the amount of Al to 0.50% or less. A preferable range of Al content is 0.30% or less. The lower limit of Al content is 0.01% or more. Note that Al is an optional element and may not be contained. That is, the Al content may be 0%.

Nb has a strong affinity with N and preferentially forms nitrides over chromium, thereby suppressing a decrease in the amount of chromium in the material and improving corrosion resistance. Therefore, it may be contained as necessary. However, if Nb is contained excessively, toughness is lowered, so the Nb content is set to 0.100% or less, and may be 0.060% or less. On the other hand, in order to obtain the above effects, the Nb content is preferably 0.005% or more, more preferably 0.010% or more, and even more preferably 0.020% or more. Note that Nb is an optional element and may not be contained. That is, the Nb amount may be 0%.

The balance other than the elements described above is Fe and impurities, but in addition to the elements described above, it is possible to contain the elements within a range that does not impair the effects of the present embodiment.

By using the stainless steel having the above chemical composition as the material of the bent product 4, the bent product 4 of the present embodiment has excellent strength and corrosion resistance, and can be suitably used as an exterior building material and an interior building material. can.

Further, for example, a metal plate material having a tensile strength of 750 MPa or more and/or a total elongation of 20% or more may be used as the metal material.

(Example 1)
A ferrite/austenite duplex stainless steel sheet having the chemical composition shown in Table 1 and the plate thickness t shown in Table 2 was prepared. Table 1 shows the mechanical properties of the ferrite-austenite duplex stainless steel sheet. A metal plate material made of a ferrite/austenite duplex stainless steel plate was cut into a size of 100 mm in length and 30 mm in width to obtain a material.
In Table 2, YS is yield strength, TS is tensile strength, and T. El means total elongation, and 0.2 yield strength was indicated as yield strength (YS).

Also, a mold having a punch and a die as shown in FIG. 1 was prepared. The punch was provided with projections having convex curved surfaces and side wall surfaces connected to the convex curved surfaces. The relative angle θp of the punch die faces of the punch was set to 90°. The width of the punch was 80 mm, and the length (length in the depth direction in FIG. 1) was 60 mm. The width of the die recess was 80 mm, and the length of the die recess (length in the depth direction in FIG. 1) was 60 mm.

The punch and die were then attached to the press molding machine, and the material was placed between the punch and die as shown in FIG. At that time, the material was arranged so that the length direction of the material coincided with the depth direction in FIG. Also, the center of the material in the width direction was aligned with the center of the mold. Then, the press molding machine was operated to bring the punch and the die closer to each other until the punch and the die were in close contact with the material, thereby performing V-bending on the material to form a bent portion. Thus, a bent product having a bent portion was manufactured.

The bending angle θ at the bent portion of the obtained bent product was measured. For the bending angle θ, four measuring points were set at intervals of 1 cm along the longitudinal direction of the bent portion, and the bending angle θ on the inner side of the bent portion was measured at each measuring point. Then, the average value of the bending angles θ at the four measurement points was obtained. Δθ (=θ−θp) was obtained from the obtained average value of the bending angles θ and the relative angle θp (=90°) of the punch die surface. .DELTA..theta. is the amount of change in angle of the bent product with respect to the bending punch. When .DELTA..theta.>0, spring back occurs, and when .DELTA..theta.<0, spring go occurs. From the viewpoint of shape fixability, it is desirable that the absolute value of Δθ is small. More specifically, when Δθ is 0 or more and 1.5/t or less, the spring back is evaluated as good, and when Δθ is less than 0 -1.5/t or more, the spring go is good. and evaluated.
It should be noted that, depending on the plate thickness t, the likelihood of springback or spring go, and the magnitude of the absolute value of the angle change amount Δθ of the bent product with respect to the bending punch differ. /t or more and 1.5/t or less was defined as an acceptable range.
Table 2 shows the results.

As shown in Table 2, all of Inventive Examples A1 to A11 were die-bent under conditions satisfying the scope of the present invention. As a result, in the obtained bent product, the radius of curvature of the convex curved surface on the outside of the bent portion (outer diameter Rout in Table 2) is equal to or less than the plate thickness t of the plate portion, and the minimum thickness of the bent portion ( tm is 0.75 times or more the plate thickness t of the plate material portion, and the angle change amount (Δθ in Table 2) of the bent product with respect to the bending punch satisfies −1.5/t or more and 1.5/t or less. Therefore, in the bent products of Examples A1 to A11 of the present invention, spring back and spring go were suppressed, there was no risk of insufficient strength at the bent portion, and the shape of the outer side of the bent portion was sharp.

In all of the invention examples A1 to A11, the ratio (HV _r /HV _m ) of the Vickers hardness HV _r at the bent portion to the Vickers hardness HV _m at the plate portion was in the range of 1.50 to 1.90. rice field.

On the other hand, as shown in Table 2, in Comparative Example B1, the curvature radius of the tip surface of the protrusion of the punch was less than 30% of the plate thickness of the material, so the compressive force of the bent portion was small, and the springback was reduced. got bigger.

In Comparative Example B2, the curvature radius of the tip surface of the protrusion of the punch was more than 50% of the plate thickness of the material, so the curvature radius of the outer side of the bent portion exceeded the plate thickness, resulting in a sharp shape. I didn't.

In Comparative Example B3, the length of the protrusion of the punch was less than 30% of the plate thickness of the material, so the radius of curvature of the outside of the bent portion exceeded the plate thickness, and a sharp shape could not be obtained. In addition, the springback has also increased.

In Comparative Example B4, the length of the protrusion of the punch exceeds 60% of the plate thickness of the material, creating a space between the punch die surface and the material, and the punch cannot sufficiently restrain the material. I couldn't do it anymore, and my spring go got bigger. In addition, the minimum wall thickness decreased, and the strength and rigidity of the bent portion decreased.

In Comparative Example B5, the curvature radius of the bottom surface of the die concave portion of the die exceeded 60% of the plate thickness of the material, and a space for material flow was not secured, so the curvature radius outside the bent portion was less than the plate thickness. was exceeded, and a sharp shape could not be obtained. Also, the compressive force on the bent portion was too strong, resulting in a large spring go.

In Comparative Example B6, the radius of curvature of the bottom surface of the die concave portion of the die was less than 20% of the plate thickness of the material, and cracks occurred in the bottom surface of the die concave portion during bending, making it impossible to continue bending.

In each test example, the width W of the projection is a length corresponding to 50% or more and 150% or less of the plate thickness of the material, and the curvature radius Rj of the concave surface provided at the boundary between the punch die surface and the projection is a radius of curvature corresponding to a length of 150% or less of the plate thickness of the material.

(Example 2)
In the same manner as in Example 1, a ferrite/austenite duplex stainless steel plate having the chemical composition shown in Table 1 and the plate thickness t shown in Table 3A was prepared. Table 1 shows the mechanical properties of the ferrite-austenite duplex stainless steel sheet. A metal plate material made of a ferrite/austenite duplex stainless steel plate was cut into a size of 100 mm in length and 30 mm in width to obtain a material.

Also, a mold having a punch and a die as shown in FIGS. 8 and 9 was prepared. The punch was provided with projections 11c having a tip surface 11e (convex curved surface), a side wall surface 11d, and an inclined surface 11f. The relative angle θp of the punch die faces of the punch was set to 90°. The width of the punch was 80 mm, and the length (length in the depth direction in FIGS. 8 and 9) was 60 mm. The width of the die recess was 80 mm, and the length of the die recess (length in the depth direction in FIG. 8) was 60 mm.

The punch and die were then attached to the press molding machine, and the material was placed between the punch and die. At that time, the material was arranged so that the length direction of the material coincided with the depth direction in FIGS. Also, the center of the material in the width direction was aligned with the center of the mold. Then, the press molding machine was operated to bring the punch and the die closer to each other until the punch and the die were in close contact with the material, thereby performing V-bending on the material to form a bent portion. Thus, a bent product having a bent portion was manufactured.

As in Example 1, the bending angle θ at the bent portion of the obtained bent product was measured, and springback and springgo were evaluated. Also, the ratio (HV _r /HV _m ) of the Vickers hardness HV _r at the bent portion to the Vickers hardness HV _m at the plate portion was measured. Results are shown in Table 3B.

Also, 1,000 metal materials were prepared, and the presence or absence of punch deformation was evaluated when these metal materials were subjected to V-bending using one mold. Evaluation was performed according to the following evaluation criteria. Results are shown in Table 3B.

A: No deformation of the punch even after 1000 times.
B: Deformation occurred in the punch at 800 times or more and less than 1000 times.
C: Deformation occurred in the punch at 600 times or more and less than 800 times.
D: Deformation occurred in the punch at 100 times or more and less than 600 times.

Moreover, comprehensive evaluation was performed according to the following criteria. In the bent product, the curvature radius of the convex curved surface on the outside of the bent portion (outer diameter Rout in Table 3B), the minimum thickness of the bent portion (tm in Table 3B), and the angle change amount of the bent product with respect to the bending punch (Table If any of 3B Δθ) failed, no evaluation of mold deformation was performed.

Passed (○): The evaluation of mold deformation was A.
Passed (Δ): The evaluation of mold deformation was B to D.
Rejected (x): Mold deformation was not evaluated (in the bent product, the radius of curvature of the convex curved surface on the outside of the bent part is large, the minimum thickness of the bent part is small, or the bending against the bending punch The angle change amount of the processed product was large).

As shown in Tables 3A and 3B, all of Inventive Examples A21 to A37 were die-bent under conditions satisfying the scope of the present invention. As a result, in the obtained bent product, the radius of curvature of the convex curved surface on the outside of the bent portion (outside diameter Rout in Table 3B) is equal to or less than the plate thickness t of the plate portion, and the minimum thickness of the bent portion (Table 3B tm is 0.75 times or more the plate thickness t of the plate material portion, and the angle change amount of the bent product with respect to the bending punch (Δθ in Table 3B) satisfies −1.5/t or more and 1.5/t or less. Therefore, the bent products of Examples A21 to A37 of the present invention were suppressed in spring back and spring go, and there was no risk of insufficient strength at the bent portion, and the shape of the outer side of the bent portion was sharp.

Further, in all of the invention examples A21 to A37, the ratio (HV _r /HV _m ) of the Vickers hardness _{HV r} at the bent portion to the Vickers hardness HV m at the plate portion was in the range of 1.50 to 1.90. rice field.

Further, it was confirmed that the dies in Examples A21 to A37 of the present invention did not deform the punches and dies even after 1000 times of processing, or had permissible durability even if they were deformed.

On the other hand, as shown in Tables 3A and 3B, in Comparative Example B21, the curvature radius Rp of the tip surface of the protrusion of the punch was less than 30% of the plate thickness of the material, so the compressive force of the bent portion was small. , springback increased.

In Comparative Example B22, the curvature radius Rp of the tip surface of the protrusion of the punch was more than 50% of the plate thickness of the material, so the curvature radius of the outside of the bent portion exceeded the plate thickness, and a sharp shape was obtained. I couldn't.

In Comparative Example B23, the length H of the protrusion of the punch was less than 30% of the plate thickness of the material, so the radius of curvature of the outside of the bent portion exceeded the plate thickness, and a sharp shape could not be obtained. . In addition, the springback has also increased.

In Comparative Example B24, the length H of the protrusion of the punch exceeds 60% of the plate thickness of the material, creating a space between the punch die surface and the material, and the punch does not sufficiently constrain the material. can no longer be used, and Spring Go has become larger. In addition, the minimum wall thickness decreased, and the strength and rigidity of the bent portion decreased.

In Comparative Examples B25 and B27, the width W of the protrusion of the punch was more than 150% of the plate thickness of the material, so the radius of curvature of the bending outer side of the bent portion exceeded the plate thickness, resulting in a sharp shape. I didn't. In addition, the protruding portion of the punch was not press-fitted into the material, and the compression force applied to the bent portion became insufficient, resulting in increased springback.

In Comparative Examples B26 and 28, the radius of curvature Rj of the concave curved surface of the punch was more than 150% of the plate thickness of the material, resulting in large springback.

In Comparative Example B29, the curvature radius of the bottom surface of the die concave portion of the die exceeded 60% of the plate thickness of the material, and a space for material flow was not secured. was exceeded, and a sharp shape could not be obtained. Also, the compressive force on the bent portion was too strong, resulting in a large spring go.

In Comparative Example B30, the radius of curvature of the bottom surface of the die concave portion of the die was less than 20% of the plate thickness of the material, and cracks occurred in the bottom surface of the die concave portion during bending, making it impossible to continue bending.

DESCRIPTION OF SYMBOLS 1... Punch 1a... Punch tip 1b... Punch die surface 1c... Protrusion 1e... Tip surface of protrusion 2... Die 2A... Die block 2a... Die recess 2c... Concave surface of die 2d ... Bottom 3 ... Material 4 ... Bent product (bent product made of metal plate material) 4a ... Plate material part 4b ... Bending part 4c ... Convex curved surface on the bending outer side of the bending part 4d ... Concave part of the bending part 4e . . . Concave curved surface of the concave portion.

Claims (11)

an arrangement step of arranging a material made of a metal plate material between the punch and the die;
A bending method for a metal plate material, comprising: a forming step in which the punch and the die are brought relatively close to each other to perform the bending process on the material,
The material is a metal plate material that satisfies a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.9 or less, and a plate thickness of 6 mm or less,
The punch includes a pair of punch die faces that approach each other toward the tip of the punch, and a protrusion provided at the tip of the punch, and the tip face of the protrusion is 30% of the plate thickness of the material. a convex curved surface with a radius of curvature corresponding to a length of 50% or less, and a length of the protrusion corresponding to 30% or more and 60% or less of the plate thickness of the material,
The die is provided with a V-shaped groove-shaped die recess for the pair of punch die surfaces, and the bottom of the die recess has a curvature corresponding to a length of 20% or more and 60% or less of the plate thickness of the material. A concave surface of radius is provided,
The forming step is a step of bringing the punch and the die closer to each other to bring the punch and the die into close contact with the material, and press-fitting at least a part of the protrusion of the punch into the material. A bending method for plate material. 2. The method for bending a metal plate material according to claim 1, wherein said projecting portion has said convexly curved surface and a side wall surface connected to said projectingly curved surface and forming a width of said projecting portion. an arrangement step of arranging a material made of a metal plate material between the punch and the die;
A bending method for a metal plate material, comprising: a forming step in which the punch and the die are brought relatively close to each other to perform the bending process on the material,
The material is a metal plate material that satisfies a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness t of 6.0 mm or less,
The punch includes a pair of punch die faces that approach each other toward the tip of the punch, and a protrusion provided at the tip of the punch, and the tip face of the protrusion is 30% of the plate thickness of the material. It is a convex curved surface with a radius of curvature corresponding to a length of 50% or more, the length of the projection is 30% or more and 60% or less of the plate thickness of the material, and the length of the projection is The width is set to a length corresponding to 50% or more and 150% or less of the plate thickness of the material, and a concave curved surface is provided at the boundary between the pair of punch die surfaces and the protrusion, and the concave curved surface has a radius of curvature. is a radius of curvature corresponding to a length of 150% or less of the plate thickness of the material,
The die is provided with a V-shaped groove-shaped die recess for the pair of punch die surfaces, and the bottom of the die recess has a curvature corresponding to a length of 20% or more and 60% or less of the plate thickness of the material. A concave surface of radius is provided,
The forming step is a step of bringing the punch and the die closer to each other to bring the punch and the die into close contact with the material, and press-fitting at least a part of the protrusion of the punch into the material. A bending method for plate materials. 4. The metal according to claim 3, wherein the projecting portion is provided with the convex curved surface, a side wall surface forming the width of the projecting portion, and an inclined surface between the convex curved surface and the side wall surface. A bending method for plate materials. A mold for bending a material made of a metal plate material satisfying a 0.2% yield strength of 300 MPa or more, a yield ratio of 0.9 or less, and a plate thickness of 6 mm or less,
a punch comprising a pair of punch die faces approaching each other toward the tip of the punch; and a protrusion provided at the tip of the punch;
a die consisting of a die block provided with a V-shaped die recess for the pair of punch die faces,
The tip surface of the protrusion is a convex curved surface with a radius of curvature corresponding to a length of 30% or more and 50% or less of the thickness of the material, and the length of the protrusion is 30% or more of the thickness of the material. A length corresponding to 60% or less,
A mold for bending a metal plate material, wherein the bottom of the V-groove recess is provided with a concave curved surface having a curvature radius corresponding to a length of 20% or more and 60% or less of the plate thickness of the material. . 6. The die for bending a metal sheet material according to claim 5, wherein said projecting portion has said convexly curved surface and a side wall surface connected to said projectingly curved surface and forming a width of said projecting portion. A mold for bending a material made of a metal sheet satisfying a 0.2% proof stress of 300 MPa or more, a yield ratio of 0.90 or less, and a thickness of 6.0 mm or less,
a punch comprising a pair of punch die faces approaching each other toward the tip of the punch; and a protrusion provided at the tip of the punch;
a die consisting of a die block provided with a V-shaped die recess for the pair of punch die faces,
The tip surface of the protrusion is a convex curved surface with a radius of curvature corresponding to a length of 30% or more and 50% or less of the thickness of the material, and the length of the protrusion is 30% or more of the thickness of the material. The length is equivalent to 60% or less, the width of the protrusion is a length equivalent to 50% or more and 150% or less of the plate thickness of the material, and the pair of punch die faces and the protrusion A concave curved surface is provided at the boundary with the part, and the radius of curvature of the concave curved surface is a radius of curvature corresponding to a length of 150% or less of the plate thickness of the material,
A mold for bending a metal plate material, wherein the bottom of the V-groove recess is provided with a concave curved surface having a curvature radius corresponding to a length of 20% or more and 60% or less of the plate thickness of the material. . 8. The bending of a metal plate material according to claim 7, wherein the protrusion has the convex curved surface, a side wall surface forming the width of the protrusion, and an inclined surface between the convex curved surface and the side wall surface. mold for A plate member made of a metal plate material satisfying a 0.2% yield strength of 300 MPa or more, a yield ratio of 0.90 or less, and a plate thickness of 6.0 mm or less, and a bent portion provided in the plate member,
The radius of curvature of the convex curved surface on the outer side of the bending portion is a radius corresponding to the thickness of the plate member or less,
A bent product made of a metal plate, wherein the minimum thickness of the bent portion is 0.75 times or more the plate thickness t of the plate portion. 10. The bent product made of the metal plate material according to claim 9, wherein a concave portion is provided along the longitudinal direction of the bent portion on the inner side of the bent portion, and a concave curved surface is provided on the inner surface of the concave portion. . According to claim 9 or 10, the ratio (HV _r /HV _m ) of the Vickers hardness HV _r at the bent portion to the Vickers hardness HV _m at the plate portion is in the range of 1.50 or more and 1.90 or less. A bent product made of the metal plate material described.

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