Incremental forming tool and incremental forming method

Abstract

To prevent or suppress formation of a tool mark in incremental forming.SOLUTION: According to the present invention, in incremental forming in which an incremental forming tool T is pressed against a metal sheet W whose periphery is held and moved to gradually deform the metal sheet in a sheet thickness direction and form the metal sheet into a final shape, a distal end has a continuous R shape on a long axis side of an elliptic curve in a cross section along a central axis, and a short side axis of an elliptic shape has an elliptic shape parallel to the central axis.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sequential forming tool used for sequentially forming a metal plate into a three-dimensional shape by pressing and moving a tool against a metal plate held around, and a sequential forming method using the sequential forming tool.

Background Art

[0002] As a technique known as a sequential forming tool, there is one described in Patent Document 1. The sequential forming tool described in Patent Document 1 has a large-diameter pressing member with a spherical tip and a small-diameter pressing member inserted on the axis of the large-diameter pressing member. The small-diameter pressing member has a spherical tip with a radius of curvature smaller than the radius of curvature of the tip of the large-diameter pressing member. The small-diameter pressing member is configured to be able to advance and retract so as to project and retract with respect to the tip of the large-diameter pressing member.

[0003] The above sequential forming tool gradually deforms the metal plate in the plate thickness direction by pressing and moving it against a metal plate held around. At this time, the above sequential forming tool projects or retracts the small-diameter pressing member according to the part of the formed product, and selectively switches between the tip of the large-diameter pressing member and the tip of the small-diameter pressing member. In Patent Document 1, a mold is arranged on one side of the metal plate, and the metal plate is formed by pressing it against the mold with a sequential forming tool.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The inventors of the present invention have focused on the fact that tool marks may occur on the formed product depending on the shape of the tool tip of the sequential forming tool, and have been earnestly studying.

[0006] An object of the present invention is to prevent tool marks from occurring on a metal plate in sequential forming.

Means for Solving the Problems

[0007] In one aspect of the present invention, in sequential forming in which a tool is pressed against and moved along a metal plate held around it, gradually deforming the metal plate in the plate thickness direction and forming it into a final shape, in a cross section along the central axis, the tip has a continuous R shape on the major axis side of an elliptical curve, and consists of an elliptical shape in which the minor axis of the elliptical shape is parallel to the central axis. Further, in one aspect of the present invention, sequential forming is performed by pressing the tool against the metal plate while maintaining the orientation of the sequential forming tool so that the angle formed by the metal plate and the axis of the sequential forming tool is substantially orthogonal.

Advantages of the Invention

[0008] According to the above sequential forming tool and sequential forming method, it is possible to prevent tool marks from occurring on the metal plate in sequential forming.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. In the drawings, the same members are denoted by the same reference numerals, and redundant descriptions are omitted. In the drawings, the sizes and ratios of the respective members may be exaggerated for easy understanding of the embodiments and may be different from the actual sizes and ratios.

[0011] The sequential forming tool T shown in FIG. 1 is used when pressing and moving the sequential forming tool T while holding the periphery of the flat metal plate W shown in FIG. 3, gradually deforming the metal plate W in the plate thickness direction, and forming it into the final shape. The sequential forming tool T has a main body portion M whose cross section perpendicular to the axis is substantially circular as shown in FIG. 2 and has a constant diameter, and a pointed portion A continuous with the tip of the main body portion M (see FIG. 1). The sequential forming tool T has an outer peripheral surface in a predetermined range in the axial direction from the tip, which is the outer peripheral surface of the pointed portion A, as a machining surface. The machining surface is formed of an elliptical curve whose radius of curvature continuously changes in a cross section along the axial direction. The machining surface is a curved surface, and the radius of curvature of the machining surface is configured to continuously decrease from the tip toward the base end direction.

[0012] As shown in FIG. 1, the sequential forming tool T is configured such that the curve forming the machining surface of the pointed portion A is an elliptical curve having the tip surface as the maximum radius of curvature. The sequential forming tool T smoothly connects the straight line forming the outer surface of the main body portion M and the elliptical curve forming the pointed portion A in a cross section along the axis. The sequential forming tool T is configured such that the tip surface of the pointed portion A has the maximum radius of curvature by making the axis parallel to the minor axis of the ellipse, and the radius of curvature gradually decreases in the base end direction. In other words, the cross section along the central axis of the pointed portion A of the sequential forming tool T is formed in a continuous R shape on the long axis side of the elliptical curve when viewed from the side (corresponding to the horizontal diameter d1 in FIG. 1), and the minor axis of the elliptical shape is formed to be the elliptical radius r1 parallel to the central axis.

[0013] The inventors focused on the fact that tool marks can be formed on the metal plate W when forming the metal plate W using a sequential forming tool, and earnestly studied how to eliminate these tool marks. To this end, they reached the conclusion that by changing the way the metal plate W and the tool contact each other, the radius of curvature of the contact part of the tool can be adjusted without changing the angle of the metal plate W with respect to the plane before forming, with the minor axis of the sequential forming tool T along the axis and the tip part having an elliptical curve shape with the major axis.

[0014] According to the forming angle formed between the metal plate W and the tool, the radius of curvature of the sequential forming tool T according to this embodiment can change. However, the maximum radius of curvature of the sequential forming tool T can be set as follows. 1) The range of the minimum R of the tool that is not recognized as a tool mark (undulation) at each forming angle of the product surface was obtained through experiments. The range was obtained from experiments. Using a product material, for example, a φ190 disk-shaped flat plate material of material: SP781_BQ and plate thickness: 0.7mmt, and using tools with a single R R = 10 to 200mm at the tip and different diameters respectively, with a constant pitch Pz = 0.3mm, sequential forming was performed while holding the periphery using a lathe processing machine, and the relationship between the minimum R of the tool where no tool mark is recognized and the forming angle θ was obtained. The following formula 1 was derived as an approximate curve for the relationship between the forming angle θ and the minimum R of the tool where no tool mark is recognized based on the results of this experiment (refer to the graph in Fig. 5).

[0015]

Formula

[0016] A curve connecting the minute intervals of the plane coordinates (x, y) on this ellipse continuously can derive a surface shape that follows the elliptic function equation.

[0017] Note that when the material, thickness, and feed pitch Pz during sequential forming of the metal plate W are different, the range of the minimum R of the tool that is not recognized as tool marks (undulations) at each forming angle of the product surface is also different. Therefore, for each combination of material, thickness, and feed pitch Pz, it is necessary to obtain an approximate curve equation from experiments for the range of the minimum R of the tool that is not recognized as tool marks (undulations) at each forming angle. By configuring in this way, the tip R with the maximum curvature can be brought into contact with the metal plate W at each forming angle, so that tool marks at the component level can be prevented regardless of the forming angle. Also, the maximum R0 of the tool is configured to have the maximum value at the radius position of the major axis of the ellipse. By configuring in this way, tool marks at the component level can be prevented regardless of the forming angle.

[0018] The sequential forming tool T is moved linearly at least temporarily while in contact with the metal plate W during sequential forming for forming the metal plate W such as the body of an automobile. Θ in Equation 1 corresponds to the angle formed by the tangent line formed by the contact point between the metal plate W and the sequential forming tool T on the moving plane for linearly moving the sequential forming tool T and the horizontal line (see FIG. 4). R in Equation 1 corresponds to the radius of curvature at the contact point on the metal plate W.

[0019] Also, the tip A, which is the tip part of the sequential forming tool T, can be coated with a hard film containing crystalline carbon. By configuring in this way, the friction coefficient at the tool tip part can be reduced to prevent tool marks from occurring.

[0020] Further, the hard film on the tip A of the sequential forming tool T can be configured to include diamond (film). By configuring it in this way, the friction coefficient at the tool tip can be lowered to prevent tool marks from occurring. Further, as the hard metal base material constituting the sequential forming tool T, it suffices if it has high hardness and can form a diamond film. For example, a cemented carbide in which tungsten carbide (WC) is mixed with cobalt (Co) can be mentioned. Further, the metal plate W that can be formed by the sequential forming tool T is not particularly limited as long as it can be plastically deformed. As an example of the metal plate W, metal plates such as galvanized steel, mild steel, high-tensile steel, stainless steel, and aluminum alloy can be used.

[0021] Further, the surface roughness of the hard film at the tool tip is R pk ≦0.15 μm, and R a ≦0.2 μm can be set. By configuring it in this way, the roughness of the surface of the molded product can be made so small that it cannot be recognized by an inspector who inspects it, and tool marks can be prevented from occurring.

[0022] In the sequential forming method using the sequential forming tool T, the periphery of the flat metal plate W is held by a fixing device. In FIGS. 3 and 4, it is configured to include a lower fixture 1A and an upper movable fixture 1B, and the metal plate W is firmly held in a state where the periphery of the metal plate W is sandwiched between the fixture 1A and the movable fixture 1B.

[0023] The sequential forming tool T is held in a state where the tip is directed toward the metal plate W by a driving device (not shown) and is configured to be movable in three orthogonal axial directions. As the driving device, a multi-axis control type robot or an NC machine tool can be used.

[0024] In the sequential forming method, while maintaining the orientation of the sequential forming tool T such that the angle formed by the axis of the sequential forming tool T and the plane of the metal plate W is substantially orthogonal along a predetermined movement path, the sequential forming tool T is pressed against the metal plate W at a predetermined location of the metal plate W held at the periphery to perform forming. As an example, the sequential forming tool T can linearly move from the outside to the inside of the metal plate W when viewed in plan while moving in the plate thickness direction. In the sequential forming method, the pushing amount (forward amount · descending amount) and the movement path of the sequential forming tool T are changed step by step. At this time, the movement path can be displaced step by step toward the center side of the metal plate W. By configuring in this way, tool marks can be prevented from occurring on the metal plate W.

[0025] Thereby, in the sequential forming method, the metal plate W is gradually deformed in the plate thickness direction to push down the bottom, so that the inclined side portion S (see FIG. 4) can be formed, and the metal plate W can be formed into a three-dimensional shape.

[0026] In the present embodiment, forming is performed without changing the orientation of the sequential forming tool T with respect to the clamping direction of the metal plate W. While the orientation of the tool is kept constant, the forming angle between the metal plate W and the tool changes according to the forming stage, and thereby the contact portion with the tool changes. Therefore, the radius of curvature at the time of forming can be changed according to the contact portion.

[0027] The sequential forming tool T is a single tool formed by an elliptical curve in which the entire machining surface of the pointed head portion A is smoothly continuous, and there are no protrusions or gaps on the machining surface. Thereby, by changing the way the tool hits the metal plate W, the radius of curvature of the portion to be machined can be changed, and thereby the replacement of the tool can be made unnecessary. Forming using the sequential forming tool according to the present embodiment can move the tool at a constant pitch, and for example, the pitch is about 0.3 mm.

[0028] (Experiment 1) Next, it will be described that when machining the metal plate W with a tool for sequential forming of an elliptical tip shape when viewed from the side, the tool marks were confirmed for a tool (Example) in which the minor axis of the elliptical shape of the tip portion is parallel to the axis and a tool (Comparative Example) in which the minor axis intersects the axis.

[0029] In this experiment, tool marks were confirmed when machining the metal plate W with a tool according to an example in which the major axis intersects the axis and a tool according to a comparative example in which the minor axis intersects the axis as a tool of φ20 mm. The shape of the tip portion A from the main body portion M was derived from an elliptical equation with the major axis being R = 100 mm. As the material of the tool, a superhard alloy in which tungsten carbide was mixed with cobalt was diamond-coated on the surface and polished was used.

[0030] As the material of the metal plate W, SP781_BQ with a thickness of 0.7 mm, a length of 1480 mm, and a width of 1800 mm was used. The metal plate W was machined while maintaining a state in which the direction orthogonal to the forming surface of the metal plate W before forming was aligned with the axis of the tool using the tool according to the above-described example or comparative example. Then, the angle between the metal plate W and the tool that changes due to machining using the tool was set to 1 to 40°, and the surface roughness Rz of the metal plate W at 1°, 10°, 20°, 30°, and 40° was measured using a stylus-type roughness meter. The evaluation length was 100 mm, and the cut-off value was evaluated with Lc8 mm / Ls0.8 mm. The measurement results are shown in the following table.

[0031]

Table 1

[0032] As is clear from Table 1, according to the tool according to the comparative example, it was confirmed that the surface roughness of each part was 2.5 μm or more, which is the surface roughness at which the inspector can see tool marks during mass production, at any angle. On the other hand, it was confirmed that for the tool according to the example, the surface roughness of each part was less than the surface roughness at which tool marks can be confirmed.

[0033] (Experiment 2) Next, an explanation will be given regarding the content confirmed for the hard film of the sequential forming tool described above, similar to the specifications described in International Publication WO2021229254.

[0034] The surface of a hard metal substrate (cemented carbide) containing 6% cobalt on a rod-shaped tungsten carbide with a diameter of 20 mm was polished, and a free curve portion with a desired shape was formed. Then, at room temperature, the free curve portion was immersed in a 5% nitric acid aqueous solution for 10 minutes to elute cobalt in the hard metal substrate and roughen the surface.

[0035] A hard film (diamond film = diamond film formed by CVD method) containing crystalline carbon with a thickness of 20 μm was formed on the free curve portion of the hard metal substrate with the roughened surface by the hot filament CVD method.

[0036] A polishing sheet of fixed abrasive grains (3M Tri-Zact Diamond Lapping Film) in which abrasive grains of a constant size were regularly arranged and the heights of the abrasive grains were uniform was brought into contact with the surface of the hard film, and a jig having a slightly smaller curvature than the free curved surface of the sequential forming tool was pressed against it to back up the polishing sheet. Then, while rotating the sequential forming tool and oscillating the jig, the polishing sheet was moved in one direction and polished for about 12 hours to obtain a sequential forming tool.

[0037] [Example 2] - [Example 11] A sequential forming tool was obtained in the same manner as in Example 1, except that the hard metal substrate was roughened and the hard film was polished under the conditions shown in Table 2. After roughening the hard metal substrate and polishing the hard film respectively, the surface roughness of each of the hard metal substrate and the hard film was measured, and the immersion time of the hard metal substrate and the polishing time of the hard film were finely adjusted to obtain a desired roughness.

[0038] [Comparative Example 1] A sequential forming tool was obtained in the same manner as in Example 1, except that a polishing sheet (3M Diamond Lapping Film) in which abrasive grains were dispersed and fixed on the sheet and the heights of the abrasive grains were uneven was used for polishing under the conditions shown in Table 2.

[0039] [Comparative Example 2] A sequential forming tool was obtained in the same manner as in Example 1, except that a diamond sintered body (PCD) was formed on the surface of a hard metal substrate and polished under the conditions shown in Table 2.

[0040] <Evaluation of Sequential Forming Tool> The sequential forming tools of Examples 1 to 11 and Comparative Examples 1 and 2 were evaluated by the following method. The evaluation results are shown in Table 2 together with the polishing conditions.

[0041] (Measurement of Surface Roughness) Using a stylus-type surface roughness meter, the R of the hard film pk (Average height of protruding peaks) was measured in accordance with JIS B 0671-2002, and R a (Arithmetic mean roughness) was measured in accordance with the provisions of JIS B 0601-2001. Also, the hard film was peeled off, and the R on the surface of the hard metal substrate was measured in the same manner as for the hard film. pk (Average height of protruding peaks) and R a (Arithmetic mean roughness) were measured.

[0042]

Table 2

[0043] <Evaluation of Formed Product (Metal Plate)> The sequential forming tools according to Examples 1 to 11 and Comparative Examples 1 and 2 above were attached to an industrial articulated robot, and sequential forming was performed under the conditions shown in Table 3 below with the average sliding speed of the sequential forming tool being 0.1 m / sec.

[0044]

Table 3

[0045] The R of the formed product a (Arithmetic mean roughness) and appearance were evaluated as follows. The evaluation results for the zinc-plated steel sheet are shown in Table 4.

[0046] (Surface Roughness) The R of the formed product (metal plate) a(Arithmetic mean roughness) was arbitrarily measured at five locations using a stylus-type surface roughness meter and averaged in accordance with the provisions of JIS B 0601-2001.

[0047] (Appearance evaluation) 〇: No roughness on the processed surface.

[0048] △: There is roughness on a part of the processed surface.

[0049] ×: There is roughness across the entire processed surface.

[0050]

Table 4

[0051] For the appearance of metal plates of mild steel, high-tensile steel (high-tensile steel plate), stainless steel, and aluminum alloy, the same results as those of the metal plate of zinc-plated steel were obtained.

[0052] From the results in Table 4, for the hard film on the hard metal substrate according to the example where R pk (Average height of protruding peaks) is 0.15 μm or less and R a (Arithmetic mean height) is 0.2 μm or less, it was confirmed that the molded product does not cause roughness.

[0053] Note that the present invention is not limited only to the above-described embodiments, and various modifications are possible within the scope of the claims. The following embodiments are also included in the scope of the present invention: The sequential forming tool according to claim 1 having the features of claim 2; The sequential forming tool according to claim 1 or claim 2 having the features of claim 3; The sequential forming tool according to claim 3 having the features of claim 4; The sequential forming tool according to claim 3 or claim 4 having the features of claim 5; The sequential forming method using the sequential forming tool according to any one of claims 1 to 5 having the features of claim 6

Explanation of reference numerals

[0054] T Sequential forming tool, A Tip, W Metal plate.

Claims

1. In a sequential forming process where a tool is pressed against and moved along a metal plate while holding the periphery thereof, gradually deforming the metal plate in the plate thickness direction and forming it into a final shape, a sequential forming tool having an elliptical shape in a cross section along the central axis, with the tip being a continuous R shape on the major axis side of the elliptical curve and the minor axis of the elliptical shape being parallel to the central axis.

2. The sequential forming tool according to Claim 1, wherein the maximum R of the continuous R of the elliptical curve exhibits a maximum value at the 1 / 2 position of the major axis.

3. The sequential forming tool according to Claim 1, wherein the tip of the tool is coated with a hard film containing crystalline carbon.

4. The sequential forming tool according to Claim 3, wherein the hard film containing crystalline carbon is diamond.

5. The sequential forming tool according to Claim 3, wherein the surface roughness of the hard film is Rp k ≤ 0.15 μm and Ra ≤ 0.2 μm.

6. A sequential forming method in which, while maintaining the orientation of the sequential forming tool such that the angle formed by the metal plate and the axis of the sequential forming tool according to any one of Claims 1 to 5 is substantially orthogonal, the tool is pressed against the metal plate to perform sequential forming.

Images