Sequential forming method and machining tool used for said sequential forming method

Abstract

In a sequential forming method according to the present invention, the leading end of a machining tool is moved relative to and pressed against a metal plate of which the periphery is held, and the metal plate is gradually deformed in the thickness direction thereof and thereby formed into a three-dimensional shape.　The shape of the leading end of the machining tool is a wedge shape, and the metal plate is formed by moving the machining tool relative to the direction in which the machining tool has a large width of contact with the metal plate such that bending work resulting in a small radius of curvature is possible.

Description

Incremental forming method and processing tool used in the incremental forming method

[0001] The present invention relates to an incremental forming method and a processing tool used in the incremental forming method, and more particularly to an incremental forming method capable of bending with a small radius of curvature and a processing tool used in the incremental forming method.

[0002] Character lines that add definition to the shape of exterior panels such as the hood and fenders of a car are formed. These character lines have a major impact on the impression the car gives, and are therefore extremely important in car design.

[0003] Generally, character lines are formed by a bending process in which a metal plate is sandwiched between a punch and a die of a metal mold, and the punch is lowered to press the metal plate and deform it into the shape of the die.

[0004] However, when a metal plate is bent by press bending using the above-mentioned mold, tensile stress occurs on the outside of the bend and compressive stress occurs on the inside, so if the bending radius is made small, bending cracks will occur, making it impossible to form sharp character lines with a small bending radius. In this type of press bending, although it depends on the thickness of the metal plate, it is generally difficult to bend the plate with a bending radius of less than 5 mm.

[0005] Patent document 1 also describes forming character lines using an incremental forming method in which a metal plate is clamped, a pair of processing tools is brought into contact with the metal plate, and pressure is applied to the metal plate from both sides to gradually deform and process it.

[0006] Japanese Patent Application Publication No. 2000-288640

[0007] However, the machining tool described in Patent Document 1 has a hemispherical tip, and therefore cannot perform bending with a small radius of curvature.

[0008] That is, in the incremental forming method, as in the press bending process described above, the bending radius cannot be made smaller than the radius of curvature of the tip of the processing tool, so when forming a character line with a small bending radius, it is necessary to make the radius of curvature of the tip of the processing tool smaller.

[0009] When a machining tool with a small radius of curvature at its tip is brought into contact with a metal plate and moved while pressing with enough force to plastically deform the metal plate, the contact area between the machining tool and the metal plate becomes small and the surface pressure becomes large, so the metal plate is cut by the machining tool and bending cannot be performed.

[0010] The present invention has been made in view of the problems associated with the prior art, and an object of the present invention is to provide an incremental forming method capable of performing bending with a small radius of curvature.

[0011] As a result of extensive research into achieving the above-mentioned object, the inventors discovered that by making the tip shape of the machining tool wedge-shaped, the contact area between the machining tool and the metal plate is increased and the surface pressure is reduced, thereby achieving the above-mentioned object, and thus completed the present invention.

[0012] That is, the incremental forming method of the present invention is a method in which the tip of a processing tool is pressed against a metal plate whose periphery is held and moved relative to the metal plate, gradually deforming the metal plate in its thickness direction to form a three-dimensional shape. The tip of the processing tool has a wedge shape, and the processing tool is moved relative to the metal plate in a direction in which the contact width with the metal plate is wide.

[0013] The processing tool of the present invention is a processing tool used in the incremental forming method, and is characterized in that the tip shape is wedge-shaped.

[0014] According to the present invention, a machining tool having a wedge-shaped tip is used and moved in a direction in which the contact width with the metal plate is wide, thereby providing an incremental forming method capable of bending with a small radius of curvature, and a machining tool to be used in the incremental forming method.

[0015] It is a figure explaining an incremental forming method. It is a figure explaining the relationship between the tip shape of a processing tool and the movement direction. It is a figure explaining the tip shape of a processing tool. It is a figure explaining an incremental forming method using a mold jig.

[0016] The incremental forming method and processing tool of the present invention will be described in detail. As shown in Figure 1, the incremental forming method is a method in which a processing tool is pressed against one side (upper side in the figure) of a metal plate that is clamped and fixed at its periphery by a support frame and held horizontally, and the metal plate is moved horizontally while plastically deforming, thereby gradually compressing the one side and forming a three-dimensional shape that protrudes from the other side (lower side in the figure) of the metal plate.

[0017] Such an incremental forming method can be carried out, for example, by attaching the processing tool to the hand unit of a multi-axis controlled work robot whose hand unit is movable in the horizontal direction (X-axis-Y-axis directions) and the vertical direction (Z-axis direction).

[0018] As shown in FIG. 2, the incremental forming method of the present invention uses a rod-shaped processing tool with a wedge-shaped tip, which is held vertically and pressed against a metal plate, and then moved in the direction (Y-axis direction) that widens the contact width between the processing tool and the metal plate to form the metal plate.

[0019] That is, when the wedge-shaped machining tool is viewed from the direction of movement (Y-axis direction), its tip has a V-shape as shown on the left side of Figure 3, and when viewed from a direction perpendicular to the direction of movement (X-axis direction), it has a rectangular shape as shown on the right side of Figure 3.

[0020] As a result, the bending radius of the bent metal plate is calculated by the radius of curvature (R Ｘ ), that is, it is possible to make it approximately the same as the radius of curvature of the tip of the V-shape when viewed from the moving direction of the machining tool.

[0021] At this time, the contact area between the processing tool and the metal plate is wider than that of a conventional processing tool having a hemispherical tip.

[0022] In other words, when the bending radius is the same, the contact width between a conventional machining tool with a hemispherical tip shape and a metal plate is the same in the X-axis direction and the Y-axis direction, but the contact width between a machining tool with a wedge-shaped tip shape in the present invention and a metal plate is wider in the Y-axis direction than in the X-axis direction.

[0023] In this way, the incremental forming method of the present invention is a method for determining the radius of curvature (RＸ ) is small, the contact width in the Y-axis direction can be widened to reduce the surface pressure when the processing tool presses against the metal plate.

[0024] Therefore, the radius of curvature of the wedge-shaped cutting tool in the direction perpendicular to the moving direction (X-axis direction) is Ｘ Even if the bending radius is small, the metal plate does not need to be cut, and V-bending with a small bending radius is possible.

[0025] The tip shape of the processing tool preferably has a relief at least on the front side in the direction of movement. In the present invention, the "relief" refers to a shape that curves upward like the front end of a ski.

[0026] By making the amount of pressure the machining tool places into the metal plate smaller than the amount of relief provided by the relief, when the machining tool is pressed against the metal plate and moved while being embedded in the metal plate, the front side of the machining tool in the direction of movement will be above the surface of the metal plate. When the machining tool is moved in this state, the tip of the machining tool will not get caught on the metal plate, allowing the machining tool to move stably.

[0027] If the recess is formed on one side of the movement direction (Y-axis direction) of the machining tool, the machining tool can be moved stably, but by forming it on both ends of the movement direction (Y-axis direction), the machining tool can be moved back and forth without rotating, thereby shortening the molding time.

[0028] In addition, the radius of curvature of the relief (R Ｙ ) is the radius of curvature (R Ｘ ), and specifically, the radius of curvature of the relief (R Ｙ ) is the radius of curvature (R Ｙ ) is preferably 20 to 40 times the

[0029] The recess is formed with a constant radius of curvature from the front to the rear in the direction of movement of the machining tool, and may form an arc when viewed from a direction perpendicular to the direction of movement (X-axis direction), but it is preferable that the central part in the direction of movement (Y-axis direction) is flat.

[0030] The surface pressure pressing the metal plate is constant in the flat portion, and there are no areas where the surface pressure is locally high, so the processing tool can be prevented from cutting the metal plate.

[0031] As described above, in the incremental forming method, it is not possible to perform bending processing in which the bending radius is smaller than the radius of curvature of the tip of the processing tool. Therefore, the radius of curvature (R Ｘ ) must be selected.

[0032] The radius of curvature of the tip shape when the machining tool is viewed from the moving direction (R Ｘ ) and the radius of curvature of the pressing surface of the metal plate to be formed (R Ｐ ) and the bending tool that satisfies the following relationship, it is possible to perform bending with a desired bending radius. Ｘ (mm) 　 < R Ｐ (mm) x thickness of metal plate (mm) x 0.8

[0033] In the incremental forming method of the present invention, as shown in FIG. 1, a processing tool is pressed against one side of a metal plate to plastically deform the metal plate, thereby forming the metal plate. However, as shown in FIG. 4, it is preferable to place a mold jig on the side of the metal plate opposite the processing tool side and press the metal plate against the mold jig to form the metal plate.

[0034] In bending with a small bending radius, springback can make it difficult to achieve the desired bending radius.

[0035] By pressing a metal plate with a processing tool and forcing the metal plate against a jig of the desired shape to form it, the metal plate is supported by the jig and deflection is reduced, so the pressing force on the metal plate is concentrated at the contact point between the metal plate and the processing tool, increasing the amount of plastic deformation, making it easy to process at the desired bending radius.

[0036] Furthermore, the incremental forming method of the present invention makes it possible to form the desired character line by scanning line processing, in which a processing tool is pressed against the bottom of the character line to be formed and moved along the character line, thereby performing V-bending.

[0037] However, in scanning line processing, the processing tool is pressed only on the character line to be formed to perform the V-bending process, so if the bending radius becomes small, stress may concentrate at the bottom of the V-bending process, causing the metal plate to crack, so it is preferable to perform contour line processing.

[0038] Contour machining is a processing method in which a processing tool is moved according to the contour machining data of the formed product, gradually stretching and depressing the metal plate, causing it to protrude on the other side. By using contour machining to gradually form the metal plate, cracks in the metal plate can be prevented.

[0039] The tip of the machining tool is preferably coated with a hard film containing crystalline carbon, which has a small coefficient of friction and therefore can prevent cutting of the metal plate when the machining tool is pressed against the metal plate and moved, and also improves the life of the machining tool.

[0040] The hard film containing crystalline carbon may be a diamond film, which is formed from synthetic diamond produced by chemical vapor deposition (CVD) using a hydrocarbon gas mixture, and may be produced by hot filament CVD or microwave plasma CVD.

[0041] Furthermore, the hard film preferably has a surface Rpk (average height of protruding peaks) of 0.15 μm or less and an Ra (arithmetic mean roughness) of 0.2 μm or less.

[0042] The Rpk (average height of protruding peaks) represents the average height of protruding peaks above the core of the load curve of the roughness curve, and Ra (arithmetic mean roughness) represents the average value of the unevenness of a section of the roughness curve extracted over a reference length.

[0043] When the hard film satisfies the above Rpk and Ra simultaneously, smooth bending without scratches on the surface is possible and the life of the processing tool is improved.

[0044] A hard film that simultaneously satisfies the above Rpk and Ra can be produced by polishing the surface of the hard film with a fixed abrasive polishing sheet in which abrasive grains of uniform size are regularly arranged and the abrasive grains are of uniform height.

[0045] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0046] [Example] Using a wedge-shaped processing tool with the tip shape shown below, a V-bending process was performed on a 2 mm thick metal plate by contour processing with a push-in depth of 0.3 mm to form a character line with a bending radius of 1.1 mm and a 95° included angle. The formed surface of the metal plate was smooth, and no cutting of the metal plate was caused by the processing tool. (Processing tool dimensions) Diameter: 10 mm Wedge included angle: 90° R Ｘ : 1mm R Ｙ : 23 mm Relief amount: 0.35 mm Length of central flat part: 2 mm

[0047] Comparative Example: Character lines were formed in the same manner as in the Example, except that hemispherical processing tools with tip curvature radii of 5 mm, 3 mm, and 1 mm were used. With the processing tools with tip curvature radii of 5 mm and 3 mm, character lines could be formed without cutting the metal plate, but with the hemispherical processing tool with tip curvature radius of 1 mm, the metal plate was cut, and a character line could not be formed.

[0048] 1 Machining tool 2 Metal plate 3 Support frame 4 Mold jig

Claims

1. A sequential forming method of pressing and moving the tip of a processing tool against a metal plate held around, and gradually deforming the metal plate in its thickness direction to form a three-dimensional shape, wherein the tip shape of the processing tool is wedge-shaped, and the processing tool is moved and formed in a direction in which the contact width with the metal plate is wide.

2. The tip shape of the processing tool has a relief at least on the front side in the moving direction, and the radius of curvature (R ｙ ), when viewed from the direction orthogonal to the moving direction, is larger than the radius of curvature (R ｘ ) when viewed from the moving direction. The sequential forming method according to claim 1, characterized in that.

3. The sequential forming method according to claim 2, wherein at least the central portion of the tip shape in the moving direction of the processing tool is flat.

4. The sequential forming method according to claim 2 or 3, wherein the amount of pressing of the processing tool into the metal plate is less than the amount of relief of the relief.

5. The radius of curvature (R ｘ ) of the tip of the machining tool when viewed from the moving direction, and the radius of curvature (R ｐ ) of the pressing surface of the metal plate to be formed satisfy the following relationship. The sequential forming method according to claim 1, characterized in that: R ｘ (mm) < R ｐ (mm) × thickness of the metal plate (mm) × 0.8 6. The sequential forming method according to claim 1, wherein a mold jig is disposed on the side of the metal plate opposite to the processing tool side, and the metal plate is pressed against the mold jig by the processing tool to be formed.

7. The sequential forming method according to claim 1, characterized in that it is formed by contour machining.

8. A processing tool used in the sequential forming method according to any one of claims 1 to 7, characterized in that the tip shape is wedge-shaped.

9. The processing tool according to claim 8, characterized in that the tip is coated with a hard film containing crystalline carbon.

10. The processing tool according to claim 9, characterized in that the surface of the hard film has an Rpk of 0.15 μm or less and an Ra of 0.2 μm or less.

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