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Title:
METHOD AND TOOL FOR BENDING TITANIUM MEMBER
Document Type and Number:
WIPO Patent Application WO/2012/096392
Kind Code:
A1
Abstract:
A bending tool includes a fine uneven portion with fine asperities having a maximum surface roughness of 3 m or more and 25 m or less on at least part of a portion that is in contact with a titanium member, and a fluorine resin film formed on the fine uneven portion so that only a part of plural top portions included in the fine uneven portion is exposed. The fluorine resin film is tightly attached to a surface of the fine uneven portion.

Inventors:
KOGANEI, Seiji (3-13-10 Nishigaoka, Kita-k, Tokyo 86, 11585, JP)
JIN, Masahiko (4-1 Gakuendai, Miyashiro-machi, Minamisaitama-gu, Saitama 01, 34585, JP)
MOTOI, Akio (4-26-20, Kouhoku Adachi-k, Tokyo 72, 12308, JP)
TAKAHASHI, Masaaki (LTD 7-18-2, Arakawa, Arakawa-k, Tokyo 02, 11600, JP)
ISO, Yukio (Ltd 1256, Ujiie, Sakura-sh, Tochigi 11, 32913, JP)
KOBAYASHI, Yuji (Toyokawa-Seisakusho, 1, Honohara 3-chome, Toyokawa-sh, Aichi 05, 44285, JP)
Application Number:
JP2012/050654
Publication Date:
July 19, 2012
Filing Date:
January 06, 2012
Export Citation:
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Assignee:
SINTOKOGIO, LTD. (28-12, Meieki 3-chome Nakamura-ku, Nagoya-sh, Aichi 02, 45000, JP)
KOGANEI, Seiji (3-13-10 Nishigaoka, Kita-k, Tokyo 86, 11585, JP)
JIN, Masahiko (4-1 Gakuendai, Miyashiro-machi, Minamisaitama-gu, Saitama 01, 34585, JP)
MOTOI, Akio (4-26-20, Kouhoku Adachi-k, Tokyo 72, 12308, JP)
TAKAHASHI, Masaaki (LTD 7-18-2, Arakawa, Arakawa-k, Tokyo 02, 11600, JP)
ISO, Yukio (Ltd 1256, Ujiie, Sakura-sh, Tochigi 11, 32913, JP)
KOBAYASHI, Yuji (Toyokawa-Seisakusho, 1, Honohara 3-chome, Toyokawa-sh, Aichi 05, 44285, JP)
International Classes:
B21D9/04; B05D5/08; B21D35/00; B21D37/18
Foreign References:
US4094749A
GB1228853A
JPS6199525A
US3473361A
JPH04200928A
EP0131429A2
JP2602320B2
JP2010051669A
JPH0220880A
JP2677973B2
JP2004074646A
JPH09193164A
JPH05245848A
Attorney, Agent or Firm:
HASEGAWA, Yoshiki et al. (SOEI PATENT AND LAW FIRM, Marunouchi MY PLAZA 9th fl. 1-1, Marunouchi 2-chome, Chiyoda-k, Tokyo 05, 10000, JP)
Download PDF:
Claims:
CLAIMS

[Claim 1] A method for bending a titanium member made of titanium or titanium alloy in the form of a tubular shape, comprising a bending step of:

storing a bending tool in a hollow portion of the titanium member, wherein the bending tool comprises a fine uneven portion with fine asperities having a maximum surface roughness of 3 urn or more and 25 um or less on at least part of a contact portion that is in contact with the titanium member, and a fluorine resin film formed on the fine uneven portion, wherein the fluorine resin film is tightly attached to a surface of the fine uneven portion; and

bending the titanium member while applying ultrasonic vibrations to the bending tool.

[Claim 2] The method for bending the titanium member according to claim 1 , wherein

the bar-shaped member includes a reduced diameter portion of which a diameter is gradually reduced toward a distal end portion, and a uniform diameter portion which is connected to the reduced diameter portion and of which a diameter is uniform, and

the contact portion is a boundary portion between the reduced diameter portion and the uniform diameter portion and the distal end portion of the bar-shaped member.

[Claim 3] The method for bending the titanium member according to claim 1 or 2, wherein

the bar-shaped member is made of steel except for cemented carbide steel, and the fine uneven portion is formed to have the maximum surface roughness of 10 urn or more and 25 um or less.

[Claim 4] The method for bending the titanium member according to any one of claims 1 to 3, wherein fluorine resin is re-applied on the fine uneven portion when the bending is performed repeatedly.

[Claim 5] The method for bending the titanium member according to any one of claims 1 to 4, wherein, in the bending, the titanium member is bent in a temperature range from an ambient temperature to a warm working temperature range, that is, a range defined from 10 °C to a highest temperature for continued use of fluorine resin.

[Claim 6] A bending tool for bending a titanium member made of titanium or titanium alloy in the form of a tubular shape, comprising: a fine uneven portion with fine asperities having a maximum surface roughness of 3 um or more and 25 μπι or less on at least part of a contact portion that is in contact with the titanium member, and

a fluorine resin film formed on the fine uneven portion, wherein the fluorine resin film is tightly attached to a surface of the fine uneven portion.

[Claim 7] The bending tool for bending the titanium member according to claim 6, wherein

the bending tool is formed from a bar-shaped member having a diameter corresponding to a hollow portion of the titanium member, the bar-shaped member includes a uniform diameter portion having a uniform diameter corresponding to the hollow portion and a reduced diameter portion which is connected to the uniform diameter portion and of which a diameter is gradually reduced toward a distal end portion,

at least a boundary portion between the reduced diameter portion and the uniform diameter portion and the distal end portion of the bar-shaped member are set as the contact portion, and

the fine uneven portion and the fluorine resin film are formed on an entire contact portion.

[Claim 8] The bending tool for bending the titanium member according to claim 6 or 7, wherein

the bar-shaped member is made of steel except for cemented carbide steel, and

the fine uneven portion is formed to have the maximum surface roughness of 10 μιη or more and 25 urn or less.

Description:
DESCRIPTION

Title of Invention

METHOD AND TOOL FOR BENDING TITANIUM MEMBER

Technical Field

[0001] Various aspects and embodiments of the present invention relate to a method and a tool for bending a titanium member that is made of titanium or titanium alloy in the form of a tubular shape.

Background Art

[0002] Various techniques relating to shape forming of a member made of titanium or titanium alloy have been conventionally known. For example, Patent Literature 1 discloses a method of filling an inner side of a titanium pipe material with a filler of a metal round bar having approximately the same diameter as an inner diameter thereof for hot-bending, and removing the filler by chemical milling. Patent Literature 2 also discloses a method of manufacturing an ultrasonic probe for an ultrasonic processing device by area reduction molding of one end side of a rod-like titanium member by using an area reduction molding die. Patent Literature 3 further discloses a method of assembling a titanium tube plate and a titanium lining duplex tube formed by compressing a thin titanium tube against an inner surface of an outer tube made of metal different from titanium.

Citation List

Patent Literature

[0003] Patent Literature 1 Japanese Patent No. 2602320

Patent Literature 2 Japanese Patent Laid-Open No.

2010-51669 Patent Literature 3 Japanese Patent Publication No. 2-20880 Patent Literature 4 Japanese Patent No. 2677973

Patent Literature 5 Japanese Patent Laid-Open No. 2004-74646

Patent Literature 6 Japanese Patent Laid-Open No. 9- 193164

Patent Literature 7 Japanese Patent Laid-Open No. 5-245848 Summary of Invention

Technical Problem

[0004] Titanium or titanium alloy is lightweight and strong and is not subject to corrosion. Thus, titanium or titanium alloy has been used in various fields such as airplanes, automobiles, ships, chemical machineries, and medical machineries.

[0005] However, titanium metal has a great affinity for other metals. Accordingly, the seizure of the titanium metal and a tool or a die is easily caused during shape forming. When a member made of titanium or titanium alloy is molded by press working, lubricant oil is necessary. A cleaning process for cleaning the member after molding is also necessary. In particular, bending a member made of titanium or titanium alloy in the form of a tubular or pipe-like shape (hereinafter referred to as "titanium member") to a predetermined shape causes the problems as described below.

[0006] Lubricant oil used for bending the titanium member is left in a hollow portion of the titanium member. Accordingly, it is required to ensure that the lubricant oil is removed from the hollow portion after a cleaning process. However, such confirmation is extremely difficult.

Since the hollow portion is small or the hollow portion is bent as the titanium member is bent, it is difficult to inspect the hollow portion by an endoscope or the like. Such inspection needs time and effect to manufacture the titanium member, and thus it becomes difficult to simplify a manufacturing process.

[0007] Thus, conventionally, a problem is that there is no other alternative but to consider that the lubricant oil inside the hollow portion should have been removed through the cleaning process in bending the titanium member.

[0008] On the other hand, a fluorine resin film can be formed on a surface of a die as disclosed in Patent Literature 4 to allow a molded product to be easily separated from the die without using lubricant oil. The fluorine resin film, however, is flexible and easily peeled or damaged when the die or the tool is used repeatedly. Thus, a technique for improving durability of the fluorine resin film has been conventionally known (for example, Patent Literatures 5 to 7).

[0009] However, this conventional technique is directed to a die used for molding resin products, rubber products or the like, and is difficult to be applied to a bending tool or a die used for bending a titanium member. The die used for molding the resin products, the rubber products or the like is used as a kind of a frame for forming a desired shape by pouring resin or the like into a space (gap) defined in the die.

[0010] For example, consider dies 100 and 101 as shown in Figure 26. In the dies 100 and 101, a fluorine resin film 102 is formed on surfaces on their inner portions that are in contact with resin or the like. The fluorine resin film 102 receives a pressure fl from the resin 103 in the direction perpendicular to the inner surfaces of the dies 100 and 101. [0011] Consider dies 200, 201, and 202 as shown in Figure 27 that are used for bending a titanium member. When the dies 200, 201 , and 202 are used for bending a titanium member 203, the die 202 moves in the direction shown by an arrow P. At this time, the dies 200, 201, and 202 are strongly pressed or rubbed against the surface of the titanium member 203. Accordingly, the dies 200, 201, and 202 receive from the titanium member 203 a pressure £2 in the direction perpendicular to the surface of the die and a pressure f3 in the direction along the surface.

[0012] The pressure £2 in the direction perpendicular to the surface acts on a fluorine resin film to press against the surface of the die, but the pressure f3 in the direction along the surface acts on the fluorine resin film to scrape it away along the surface of the die. Accordingly, even when the strong fluorine resin film is formed on the surfaces of the dies 200, 201, and 202 according to the conventional technique, the fluorine resin film is easily scraped away along the surfaces of the dies and is easily peeled from the surfaces of the dies by the strong pressure such as the pressure f3 in the direction along the surfaces. Thus, a problem is that, in a die using a fluorine resin film as a film (lubrication film) for improving lubricating property and mold-releasing property of the die and the titanium member, a bending cannot be conducted repeatedly.

[0013] In a method and a tool for bending a titanium member in the technical field, it is desired that the titanium member can be bent without using lubricant oil in a dry environment and durability of the bending tool is enhanced to conduct the bending repeatedly even when a fluorine resin film is used as a lubrication film.

Solution to Problem [0014] According to an aspect of the present invention, a method for bending a titanium member made of titanium or titanium alloy in the form of a tubular shape includes a bending step for bending the titanium member using a bending tool. A fine uneven portion with fine asperities having the maximum surface roughness of 3 um or more and

25 um or less is formed on at least part of a contact portion that is in contact with the titanium member on a surface of a bar-shaped member having a diameter corresponding to a hollow portion of the titanium member, and a fluorine resin film having a thickness exceeding the maximum surface roughness is formed on me fine uneven portion. In the bending step, the bending tool is stored in the hollow portion of the titanium member to allow the fluorine resin film to be directly brought into contact with the hollow portion to bend the titanium member while applying ultrasonic vibrations to the bending tool.

[0015] Since the fine uneven portion is formed on the surface of the bending tool according to the bending method, the surface area of the bending tool is increased. Since the fluorine resin film is formed on the surface of the fine uneven portion, the fluorine resin film is stuck with the asperities of the fine uneven portion. Accordingly, the fine uneven portion prevents the fluorine resin film from moving along the surface. Also, a friction coefficient is reduced since the fluorine resin film is directly contacted to the bending tool across a wide area. The fluorine resin film is present in recessed portions of the fine uneven portion to serve as a lubricant agent during the bending. By bending the titanium member while applying the ultrasonic vibrations, bending deformation resistance and the friction coefficient are reduced as compared when the ultrasonic vibrations are not applied.

[0016] According to an embodiment of the present invention, the bar-shaped member may include a reduced diameter portion and a uniform diameter portion. The reduced diameter portion is gradually reduced in diameter toward a distal end portion. The uniform diameter portion is connected to the reduced diameter portion and has a uniform diameter. A contact portion may be a boundary portion between the reduced diameter portion and the uniform diameter portion and a distal end portion of the bar-shaped member. The fine uneven portion and the fluorine resin film are arranged on a portion of the bending tool where the hollow portion of the titanium member is directly pressed strongly against the surface during the bending.

[0017] According to an embodiment of the present invention, the bar-shaped member may be made of steel except for cemented carbide steel, and the fine uneven portion may be formed to have the maximum surface roughness of 10 μιη or more and 25 μιη or less. By setting the maximum surface roughness in such a range, the friction coefficient can be reduced and the movement of the fluorine resin film can be prevented by the fine uneven portion.

[0018] According to an embodiment of the present invention, fluorine resin may be re-applied on the fine uneven portion when the bending step is performed repeatedly. Thus, the fluorine resin film, which is disappeared by the bending, can be restored by the applied fluorine resin.

[0019] According to an embodiment of the present invention, in the bending step, the titanium member may be bent in a temperature range from an ambient temperature to a warm working temperature range, that is, a range defined from 10°C to a highest temperature for continued use of fluorine resin. In particular, ductility of the titanium member is improved in such a temperature range, so that the titanium member can be easily molded.

[0020] According to another aspect of the present invention, a bending tool for bending a titanium member made of titanium or titanium alloy in the form of a tubular shape includes a fine uneven portion and a fluorine resin film. The fine uneven portion has fine asperities having the maximum surface roughness of 3 um or more and 25 um or less on at least part of a contact portion that is in contact with the titanium member. The fluorine resin film is formed on the fine uneven portion and is tightly attached to the surface of the fine uneven portion.

[0021] According to an embodiment of the present invention, the bending tool may be formed from a bar-shaped member having a diameter corresponding to a hollow portion of the titanium member, the bar-shaped member may include a uniform diameter portion having a uniform diameter corresponding to the hollow portion and a reduced diameter portion which is connected to the uniform diameter portion and of which a diameter is gradually reduced toward a distal end portion, at least a boundary portion between the reduced diameter portion and the uniform diameter portion and the distal end portion of the bar-shaped member may be set as a contact portion, and the fine uneven portion and the fluorine resin film may be formed on an entire contact portion.

[0022] According to an embodiment of the present invention, the bar-shaped member may be made of steel except for cemented carbide steel, and the fine uneven portion may be formed to have the maximum surface roughness of 10 um or more and 25 urn or less.

Advantageous Effects of Invention

[0023] As described above, according to various aspects and embodiments of the present invention, the titanium member can be bent in a dry environment without using lubricant oil and durability of the bending tool can be improved to perform the bending repeatedly even when the fluorine resin film is used as a lubricant film.

Brief Description of Drawings

[0024] [Figure 1] Figure 1 is a schematic view showing a configuration of a bending device according to an embodiment of the present invention.

[Figure 2] Figure 2 shows a bending plug. Figure 2(A) is an elevation view showing an entire bending plug, and Figure 2(B) is an elevation view showing a main part of the bending plug in an enlarged manner.

[Figure 3] Figure 3 is a cross-sectional view schematically showing a fine uneven portion and a surface containing a fluorine resin film in the bending plug, and is a cross-sectional view taken along the line 3-3 of Figure 4.

[Figure 4] Figure 4 is a plan view schematically showing a surface of the bending plug.

[Figure 5] Figure 5 is a cross-sectional view schematically showing a portion where the fine uneven portion, the fluorine resin film, and a titanium tube of the bending plug are in contact with each other.

[Figure 6] Figure 6 is a cross-sectional view schematically showing the fluorine resin film deformed during a bending.

[Figure 7] Figure 7 is a cross-sectional view schematically showing the fine uneven portion and the fluorine resin film after the bending.

[Figure 8] Figure 8 is a cross-sectional view schematically showing another fluorine resin film and fine uneven portion.

[Figure 9] Figure 9 is a side view schematically showing a bending tool manufacturing process. Figure 9(A) shows a bending tool before being manufactured, Figure 9(B) shows the bending tool after the fine uneven portion is formed on the surface, and Figure 9(C) shows the bending tool after the fluorine resin film is formed on the surface of the fine uneven portion.

[Figure 10] Figure 10 is a cross-sectional view schematically showing a state before the bending is executed.

[Figure 11] Figure 11 is a cross-sectional view schematically showing a state after the bending is executed.

[Figure 12] Figure 12 is a cross-sectional view showing the titanium tube and the bending tool in a bending step. Figure 12(A) shows the titanium tube and the bending tool just after the bending is started, and Figure 12(B) shows the titanium tube and the bending tool just after the bending is terminated.

[Figure 13] Figure 13 is an elevation view showing an entire bending plug according to a modification.

[Figure 14] Figure 14 is a photograph of an entire manufactured bending plug.

[Figure 15] Figure 15 is a photograph of a main part of the bending plug. [Figure 16] Figure 16 is a photograph of an external appearance of the titanium tube formed by the bending and an inner portion of a bent portion.

[Figure 17] Figure 17 is a photograph of the inner portion of the bent portion in an enlarged manner.

[Figure 18] Figure 18 is a photograph of the titanium tube f actured by the bending.

[Figure 19] Figure 19 shows a bending shape and a dimension measurement portion of the titanium tube according to an example.

[Figure 20] Figure 20 is a graph showing strength of a tensile load when ultrasonic vibrations are applied.

[Figure 21] Figure 21 is a graph showing strength of a tensile load when ultrasonic vibrations are not applied.

[Figure 22] Figure 22 is a graph showing variations from set values of dimensions LI and L2 when the ultrasonic vibrations are applied.

[Figure 23] Figure 23 is a graph showing the variations when the ultrasonic vibrations are not applied.

[Figure 24] Figure 24 is a chart showing specific numeral values of the results shown in Figures 23 and 24.

[Figure 25] Figure 25 shows change of a friction coefficient when fluorine resin is re-applied. Figure 25(A) shows the change of the friction coefficient before the fluorine resin is re-applied, and Figure 25(B) shows the change of the friction coefficient after the fluorine resin is re-applied.

[Figure 26] Figure 26 is a cross-sectional view showing one example of a conventional die for forming resin and resin. [Figure 27] Figure 27 is a cross-sectional view showing an example of a conventional die for press work and a metal member.

Description of Embodiments

[0025] An embodiment of the present invention will be explained below. Incidentally, similar elements are designated by the same reference numerals, and an explanation thereof is omitted.

[0026] [Structure of Bending Device] A bending device 20 will be explained below with reference to Figure 1. Figure 1 is a schematic view showing the bending device according to an embodiment of the present invention. The bending device 20 is a device for carrying out a bending method according to the embodiment and drying a titanium member. Incidentally, in this embodiment, drying the titanium member means that bending the titanium member in a dry environment without using lubricant agent and a sheet-like member such as a Teflon (registered trademark) sheet.

[0027] As shown in Figure 1, the bending device 20 is provided on a support 1. A guide 2 is fixed on an upper surface of the support 1, and the bending device 20 is provided on the guide 2. The bending device 20 is a NC pipe bender, which includes a hydraulic cylinder 3, an ultrasonic vibration part 6, a horn 7, a chuck 8, a die 9, a die 10, a bending plug 11, and a mandrel 12. All of them are integrally supported by support members 4a and 4b. The bending device 20 further includes an ultrasonic oscillator 13 and a hydraulic mist pump 14.

[0028] The hydraulic cylinder 3 supports the mandrel 12 and drives the mandrel 12. The ultrasonic vibration part 6 and the horn 7 are provided between the hydraulic cylinder 3 and the mandrel 12. The ultrasonic vibration part 6 is a source of ultrasonic vibrations and includes an ultrasonic vibrator 5. The ultrasonic vibrator 5 generates ultrasonic vibrations by high-frequency signals inputted from the ultrasonic oscillator 13. The horn 7 is connected to the ultrasonic vibrator 5. The horn 7 amplifies the ultrasonic vibrations generated by the ultrasonic vibrator 5. Since the mandrel 12 is connected to the horn 7, the ultrasonic vibrations amplified by the horn 7 are transmitted to the mandrel 12.

[0029] One end of the mandrel 12 is connected to the horn 7 and the other end of the mandrel 12 is connected to the bending plug 11. Also, the hydraulic mist pump 14 is connected to the mandrel 12. The chuck 8 supports a portion where the mandrel 12 and the bending plug 11 are connected to each other and maintains the connection state while releasing the supported state to separate them from each other.

[0030] One end of the bending plug 11 is connected to the mandrel 12 and a later-described hollow portion 15a of a titanium tube 15 is inserted to the other end of the bending plug 11. The titanium tube 15 is a member to be bent. The titanium tube 15 is made of pure titanium in the form of an elongated cylindrical shape, and includes the hollow portion 15a along a central axis. The titanium tube 15 is held by the dies 9 and 10.

[0031] The bending plug 11 is a bending tool according to an embodiment, which is like an elongated bar having a circular shape in cross section as shown in Figure 2(A). The bending plug 11 includes a body portion 11a that has a shape like an elongated bar. A screw hole 1 lb is formed on one end of the body portion 11a, into which a distal end of the mandrel 12 can be screwed. When the distal end of the mandrel 12 is screwed into the screw hole 1 lb, the bending plug 11 can be integrated with the mandrel 12. The body portion 11a includes a uniform diameter portion l id having a uniform diameter corresponding to the hollow portion 15a of the titanium tube 15, and a reduced diameter portion lie of which a diameter is gradually reduced toward a distal end portion llf.

[0032] A part (approximately 40%) of the bending plug 11 is a coated portion 11c. In Figures 2(A) and 2(B), the coated portion 11c is dotted. The coated portion 1 lc is at least part of a connection portion that is in contact with the hollow portion 15a of the titanium tube 15. According to this embodiment, as shown in Figure 2(B) in detail, the connection portion includes the distal end portion l lf, the reduced diameter portion l ie, and a part of the uniform diameter portion l id including a boundary portion 1 lg between the reduced diameter portion l ie and the uniform diameter portion l id. When the bending device 20 bends the titanium tube 15, the bending plug 11 is brought into contact with the titanium tube 15. A part of the bending plug 11 that is in contact with the titanium tube 15 receives a particularly strong pressure from the titanium tube 15 during the bending. The coated portion 11c includes such a part of the bending plug 11.

[0033] The coated portion 11c includes a fine uneven portion 50a and a fluorine resin film 55. In the coated portion 11c, the fine uneven portion 50a is formed on a surface of the body portion 11a and the fluorine resin film 55 is formed on a surface of the fine uneven portion 50a. The bending device 20 dries the titanium tube 15 without using lubricant agent and a sheet-like member such as a Teflon sheet, and accordingly, the bending plug 11 is directly brought into contact with the titanium tube 15 during the bending.

[0034] The fine uneven portion 50a includes extremely fine, irregular, and complicatedly-arranged asperities whose shapes and sizes are not clearly perceptible to the naked eye. As shown in Figure 3, the asperities of the fine uneven portion 50a indicate irregularities on a surface, which has different sizes and intervals and includes many top portions, bottom portions, and recessed portions described later.

Figure 3 is a cross-sectional view schematically showing a surface containing the fine uneven portion 50a of the body portion 11a and the fluorine resin film 55, and is a cross-sectional view taken along the line 3-3 of Figure 4. Figure 4 is a plan view schematically showing a surface of the body portion 11a (the coated portion 11 c).

[0035] The fine uneven portion 50a includes a plurality of top portions PI, P3, P5, P7, P9, and PI 1 and a plurality of bottom portions P2, P4, P6, P8, and P10. The fine uneven portion 50a is formed by performing a surface treatment such as blast treatment on the surface of the body portion 11a to have the maximum surface roughness (in this embodiment, hereinafter referred to as the maximum height roughness Rz, which is described below in detail) of 3 um or more and 25 μπι or less. In the fine uneven portion 50a, the top portions are ends and their surroundings of portions projecting to the outside from a reference line L that is a height standard of the fine uneven portion 50a, and the bottom portions are ends and their surroundings of portions recessed to the inside from the reference line L. The recessed portions indicate portions except for the top portions.

[0036] In the fine uneven portion 50a as shown in Figure 3, the maximum surface roughness is evaluated by a difference hi between the height of the top portion (the top portion P5 in Figure 3) projecting to the outermost side of the plurality of top portions and the height of the bottom portion (the bottom portion P4 in Figure 3) recessed to the innermost side of the plurality of bottom portions. In other words, hi is 3.0 um when the maximum surface roughness (the maximum height roughness Rz) is 3.0 μιη. The surface roughness may be evaluated by averaging the differences of the heights of the plurality of bottom portions or top portions PI to PI 1, but the maximum height roughness Rz is used in this embodiment.

[0037] The bending plug 11 is made of metal such as steel. The maximum surface roughness is required to have a certain roughness so that the recessed portion has a certain size. As shown in Figure 3, many recessed portions having irregular sizes and shapes are provided on the surface of the body portion 11a by forming the fine uneven portion 50a on the surface of the body portion 1 la of the bending plug 11. A part of the fluorine resin film 55 is present in the recessed portions to close all recessed portions.

[0038] The maximum surface roughness may be at least 3 μτη or more so that the fluorine resin film 55 present in the recessed portions has a certain volume and the asperities of the fine uneven portion 50a are complicatedly arranged. When the maximum surface roughness is increased, the volume of the fluorine resin film 55 present in the recessed portions is increased, but the fine uneven portion 50a can receive a strong pressure from the titanium tube 15 during the bending. When the maximum surface roughness exceeds 25 μπι, the portions projecting from the reference line L may be easily bent or crashed during the bending. Also, the friction coefficient of the bending plug

11 may become too high.

[0039] Thus, the maximum surface roughness of the fine uneven portion 50a may be 3 um or more and 25 μπι or less. For example, when the bending plug 11 is made of steel except cemented carbide steel, the maximum surface roughness may be 10 um or more and 25 μηι or less. In particular, the maximum surface roughness may be approximately 14.8 μπι to 15 μηι. When the bending plug 11 is made of cemented carbide steel, which is harder than steel other than the cemented carbide steel, the maximum surface roughness may be slightly smaller, i.e. 3 um or more and 10 μηι or less.

[0040] Next, the fluorine resin film 55 will be explained below. The fluorine resin film 55 is formed on the surface of the fine uneven portion 50a. The fluorine resin film 55 has such a thickness that only part of the top portions included in the fine uneven portion 50a is not covered by the fluorine resin film 55 and is exposed. As shown in Figure 4, the fluorine resin film 55 has such a thickness that only the top portion P5 projecting to the outermost side of the top portions PI, P3, P5, P7, P9, and PI 1 is exposed and the other top portions are covered by the fluorine resin film 55 in the fine uneven portion 50a. Thus, the thickness of the fluorine resin film 55 is slightly smaller than that of the maximum surface roughness of the fine uneven portion 50a. [0041] The fluorine resin film 55 is tightly attached to the surface of the fine uneven portion 50a and is present in the recessed portions to cover all recessed portions.

[0042] The fluorine resin film 55 can be formed by coating fluorine resin such as polytetrafluoroethylene (PTFE), perfluoroethylenepropene copolymer (FEP), and perfluoroalkoxyalkane (PFA). In this embodiment, the fluorine resin film 55 is formed by coating fluororesin mixture containing primer on the surface of the fine uneven portion 55a because the directly coated fluorine resin is easily peeled (which is explained later in detail).

[0043] [Operation of Bending Device] The operation of the bending device 20 having the above-described structure will be explained below with reference to Figures 1, 5 to 8, 10, and 11. Figure 5 is a cross-sectional view schematically showing a portion where the fine uneven portion 50a and the fluorine resin film 55 of the coated portion

11c, and the titanium tube 15 are in contact with each other, and Figure 6 is a cross-sectional view schematically showing the fluorine resin film 55 deformed during the bending. Figure 7 is a cross-sectional view schematically showing the fine uneven portion 50a and the fluorine resin film 55 after the bending, and Figure 8 is a cross-sectional view schematically showing another fluorine resin film and the fine uneven portion 50a. Figure 10 is a cross-sectional view schematically showing the state before the bending using the bending device 20 is executed, and Figure 11 is a cross-sectional view schematically showing the state after the bending is executed.

[0044] For executing the bending using the bending device 20, the above-described bending plug 11 is manufactured by a later-described bending tool manufacturing process. Then, a bending step is executed as follows. As shown in Figure 10, in the bending step, the bending plug 11 is stored in the hollow portion 15a of the titanium tube 15 from the side close to the coated portion 1 lc so that the fluorine resin film 55 is directly brought into contact with the hollow portion 15a. Then, the titanium tube 15 is held by the bending plug 11, the mandrel 12, and the chuck 8.

[0045] As shown in Figure 1, the high-frequency signals are inputted from the ultrasonic oscillator 13 to the ultrasonic vibrator 5. Then, the ultrasonic vibrations are generated by the ultrasonic vibrator 5 and are amplified by the horn 7 to be transmitted to the mandrel 12. Since the bending plug 11 is connected to the mandrel 12, the amplified ultrasonic vibrations are applied to the bending plug 11.

[0046] The ultrasonic vibrations are denoted by an arrow f in Figure 10, which are vibrations of longitudinal waves along a central axis CL of the bending plug 11. The dies 9 and 10 are operated while the ultrasonic vibrations f are applied on the bending plug 11 to bend the titanium tube 15.

[0047] When bending the titanium tube 15, the dies 9 and 10 are rotated by approximately 90 degrees as shown in Figure 11. Then, the titanium tube 15 is gradually deformed with the rotation of the dies 9 and 10. At this time, the titanium tube 15 is deformed while being strongly pressed against the bending plug 11. Since the die 10 has a curved portion 10a, the titanium tube 15 is curved along the outer shape of the curved portion 10a. [0048] The bending plug 11 includes the coated portion 11c. The fluorine resin film 55 formed thereon has such a thickness that only the top portion P5 projecting to the outermost side is exposed, and the other top portions are covered by the fluorine resin film 55. Thus, the fluorine resin film 55 is directly brought into contact with the hollow portion 15a of the titanium tube 15 across a wide area. The coefficient of friction between the bending plug 11 and the titanium tube 15 is reduced, so that the fluorine resin film 55 serves as a lubricant agent for better sliding.

[0049] The fluorine resin film 55 is tightly attached to the surface of the fine uneven portion 50a. The surface area of the bending plug 11 is increased because the fine uneven portion 50a is formed on the surface. Since the asperities having irregular shapes and sizes are complicatedly arranged and the fluorine resin film 55 is present in many recessed portions having irregular shapes and sizes, the fluorine resin film 55 is tightly hung up on the asperities of the fine uneven portion 50a. Thus, the fine uneven portion 50a acts to reliably prevent the fluorine resin film 55 from moving along the surface.

[0050] Since only the top portion P5 of the plural top portions is not covered by the fluorine resin film 55 and is exposed, the top portions including the top portion P5 receives the entire fluorine resin film 55 in its thickness direction.

[0051] During the bending, the pressure along the surface of the bending plug 11 (the pressure F2 in Figure 5) is applied on the fluorine resin film 55 from the titanium tube 15. The pressure F2 is applied on the fluorine resin film 55 to scrap away the fluorine resin film 55 along the surface of the bending plug 11. Since the recessed portions and the top portions are formed in the direction perpendicular to the direction of the pressure F2, the recessed portions and the top portions encumbers the movement of the fluorine resin film 55 caused by the pressure F2 to prevent the peeling of the fluorine resin film 55.

[0052] The asperities of the fine uneven portion 50a with irregular sizes and shapes are complicatedly arranged, and fine asperities are formed on each recessed portion as shown in Figure 3. Thus, the fluorine resin film 55 is tightly attached to the fine uneven portion 50a as compared when the asperities of the fine uneven portion 50a are regularly formed.

[0053] Accordingly, the fluorine resin film 55 tends to remain on the surface of the bending plug 11 during the bending. Consequently, the fluorine resin film 55 effectively serves as a lubricant agent that suppresses the friction coefficient generated between the fluorine resin film 55 and the titanium tube 15. Thus, the bending plug 11 has high durability enough to perform the bending repeatedly even when the fluorine resin film 55 is a soft lubricant film.

[0054] In Figure 8, consider the case where a fluorine resin film 105 having the thickness enough to cover all top portions including the top portion P5 (i.e., the thickness larger than the maximum surface roughness) is formed on the bending plug. In the case of using this bending plug, a part of the fluorine resin film 105 is a surface layer portion 106 that is not present in the recessed portions and formed on the outer side (the dotted portion in Figure 8). Since there are no top portions along the surface of the surface layer portion 106, the movement of the surface layer portion 106 is not prevented by the top portions. Thus, the surface layer portion 106 is easily peeled when receiving the pressure in the direction along the surface during the bending.

[0055] The movement of the fluorine resin film 55 can be expected to be prevented by forming the fine uneven portion 50a on the surface of the bending plug 11. However, a fluorine resin film should have such a thickness that only a part of top portions is exposed; otherwise the fluorine resin film would be less likely to serve as a lubricant agent and waste would easily be generated.

[0056] As shown in Figure 5, the fine uneven portion 50a and the fluorine resin film 55 receive the pressure Fl in the direction perpendicular to the surface of the fine uneven portion 50a and the pressure F2 along the surface from the titanium tube 15 during the bending. Since the fluorine resin film 55 is flexible, the fluorine resin film 55 is deformed by the pressures Fl and F2 as shown in Figure 6.

An upper portion of the portion present in the recessed portions is not easily received by the recessed portions relatively as compared to a lower portion.

[0057] For example, as shown in Figure 3, as for the portions of the fluorine resin film 55 present in the recessed portion 50b, the gaps between the top portions PI and P3 and the bottom portion P2 are increased on the upper portion. Accordingly, the degree of adherence of the fluorine resin film 55 to the surface of the fine uneven portion 50a is reduced on the upper portion, and the fluorine resin film 55 easily receives the pressures Fl and F2 from the titanium tube 15. Thus, a part of the fluorine resin film 55 may be peeled along the surface of the fine uneven portion 50a by the bending.

[0058] Consequently, the fluorine resin film 55 may become a little thin, and the top portion P5 and the top portions P3 and P7 which project the second outermost side after the top portion P5 may be exposed as shown in Figure 7. Still, the fluorine resin film 55 is tightly attached to the surface of the fine uneven portion 50a between the two adjacent top portions to remain in the recessed portion. The fluorine resin film 55 remaining in the recessed portion is deformed by the pressure Fl during the bending and is present between the surface of the fine uneven portion 50a and the titanium tube 15 to reduce the friction coefficients thereof and serve as a lubricant agent for better sliding. Thus, by using the bending plug 11, the titanium tube 15 can be bent repeatedly while high lubricant property is maintained.

[0059] As shown in Figure 12(A), a strong contact portion PI is formed on a portion where the bending plug 11 and the titanium tube 15 are in contact with each other at the outer side in the rotation direction of the dies 9 and 10 immediately after the dies 9 and 10 start to rotate for performing the bending using the bending plug 11. The strong contact portion PI represents a portion where the titanium tube 15 is strongly and directly pressed against the surface of the bending plug 11 during the bending. The bending plug 11 includes the reduced-diameter portion l ie. Accordingly, when the dies 9 and 10 start to rotate, for example as shown in Figure 12(A), the titanium tube 15 is pressed against the surface of the reduced-diameter portion 1 le to be bent in the direction shown by the arrow. The direction of the titanium tube 15 is largely changed at the boundary l lg, which is a border line, and accordingly, the strong contact PI is formed on the boundary 1 lg.

[0060] When the titanium tube 15 is bent to substantially a right angle, a strong contact portion P2 is formed as shown in Figure 12(B). The diameter of the reduce-diameter portion 1 le is gradually reduced toward the distal end portion 1 If in the bending plug 11. When the titanium tube 15 is bent to substantially the right angle, the direction of the titanium tube 15 is changed from the distal end portion l lf serving as a working point. The force where the titanium tube 15 is pressed against the bending plug 11 is concentrated on the distal end portion l lf, and therefore, the strong contact portion P2 is formed on the distal end portion l lf and its surrounding.

[0061] When the titanium tube 15 is bent using the bending plug 11, the lubricant property at the strong contact portions PI and P2 may be improved on the surface of the bending plug 11. The fine uneven portion 50a and the fluorine resin film 55 may be formed at least on the strong contact portions PI and P2. Since the bending plug 11 is in the form of a circular shape in cross section, a band-like portion along the boundary 1 lg in the circumferential direction can be the strong contact portion PI. Instead of forming the fine uneven portion 50a and the fluorine resin film 55 only on the band-like portion along the boundary

1 lg, the distal end portion l lf, and its surrounding, they can easily be formed on a certain wider area including the band-like portion along the boundary 1 lg, the distal end portion l lf, and its surrounding. The coated portion 11c described above is formed in view of this point.

[0062] The bending device 20 performs the bending work while applying ultrasonic vibrations to the mandrel 12. By applying the ultrasonic vibrations, the mandrel 12 vibrates with very fine amplitude and thus the bending plug 11 also vibrates with very fine amplitude. Since the titanium tube 15 is in contact with the bending plug 11, the bending deformation resistance (the force against the bending deformation) is applied on the titanium tube 15 with an extremely short period of vibration f equency ff of ultrasonic vibrations by applying the ultrasonic vibrations. The natural frequency fl5 in the bending direction of the titanium tube 15 is far smaller than the vibration frequency ff of ultrasonic vibrations. As compared to the case where the ultrasonic vibrations are not applied, the bending deformation resistance is reduced as being time-averaged and the f iction coefficient between the bending plug 11 and the titanium tube 15 is reduced. By adding ultrasonic vibrations, the lubricant property of the bending plug 11 is further improved.

[0063] The bending device 20 can bend the titanium tube 15 in a dry environment without using lubricant oil by fully using the fluorine resin film 55 and the favorable lubricant property due to the ultrasonic vibrations. The bending device 20 can extremely favorable for bending a titanium member that is easily welded to a bending tool.

[0064] When the bending device 20 bends the titanium tube 15 repeatedly, the fluorine resin film 55 present in the recessed portions is gradually disappeared. Then, the lubricant agent is gradually reduced. Accordingly, the coefficient of friction between the bending plug 11 and the titanium tube 15 may be increased, which is not favorable especially for bending a titanium member that is easily welded to a bending tool.

[0065] When the bending work is repeatedly performed, preferably when the friction coefficient exceeds a predetermined value, fluorine resin may be applied to the surface of at least the fine uneven portion 50a of the bending plug 11 by spraying liquid fluorine resin. Accordingly, the fluorine resin film 55, which is disappeared by repeatedly performed bending, is formed again on the fine uneven portion 50a by sprayed fluorine resin. The lubricant property of the fluorine resin film 55 can be restored. Thus, the bending device 20 can bend the titanium tube 15 further repeatedly. Incidentally, the predetermined value of the friction coefficient may be appropriately 0.2.

[0066] In particular, the bending device 20 may bend a titanium member in a temperature range from an ambient temperature to a warm working temperature range, that is, a range defined from 10°C to the highest temperature (288°C) for continued use of fluorine resin. The ductility of the titanium member is improved in such a temperature range, so that the titanium member can be easily molded.

[0067] [Bending Tool Manufacturing Process] The bending tool manufacturing process will be explained with reference to Figure 9. Figure 9 is a side view schematically showing the bending tool manufacturing process. Figure 9(A) shows a bending tool before being manufactured, Figure 9(B) shows the bending tool after a fine uneven portion is formed on the surface, and Figure 9(C) shows the bending tool after a fluorine resin film is formed on the surface of the fine uneven portion.

[0068] As shown in Figure 9(A), a bending plug 111 is made of metal such as steel using a bar-like member having a diameter corresponding to the hollow portion 15a of the titanium tube 15 for manufacturing the bending plug 11. The bending plug 111 has the same outer shape as the bending plug 11, but is different from the bending plug 11 in that the bending plug 111 does not include the fine uneven portion 50a and the fluorine resin film 55. Next, as shown in Figure 9(B), the fine uneven portion 50a is formed by blasting to rough up at least a part of a portion of the surface of the bending plug 111 that is in contact with the titanium tube 15 (corresponding to the coated portion 1 lc). When the bending plug 111 is made of steel except for cemented carbide steel, the maximum surface roughness is required to be 10 um or more and 25 μπι or less. When the bending plug 111 is made of cemented carbide steel, the maximum surface roughness may be 3 um or more and 10 μπι or less.

[0069] Then, the bending plug 111 is primer coated to be dried and baked. Subsequently, a process of applying fluorine resin coating such as dispersion coating, electrostatic powder coating, fluidized bed coating, and spray coating to the bending plug 111 and baking and cooling the bending plug 111 is repeatedly performed, so that the bending plug 111 is recoated with fluorine resin. Accordingly, a fluorine resin film 25, which is thicker than the maximum surface roughness, is formed on the surface of the fine uneven portion 50a as shown in Figure 9(C). At this time, a mixed coating material of primer and fluorine resin can be applied. Alternatively, the fluorine resin may be applied after the primer is applied.

[0070] The fluorine resin film 25 is removed along the surface by performing the bending with the bending device 20 in advance by using the bending plug 111 with the fluorine resin film 25 as the bending plug 11, or other alternative means so as to form the fluorine resin film 55 described above. At this time, the fluorine resin film 55 is formed so that a part of top portions including the highest top portion of the plural top portions included in the fine uneven portion 50a is not covered by the fluorine resin film 55 and is exposed. With the processes as described above, the bending plug 11 having the fluorine resin film 55 can be manufactured.

[0071] Substantially all of the top portions are covered by the fluorine resin film 55 on the surface of the bending plug 11 with progression of the bending, but a part of the top portions is not covered by the fluorine resin film 55 and is exposed. Since a part of the fluorine resin film 55 is peeled along the surface when the bending is further continued, more top portions are exposed.

Example 1

[0072] An example of the bending using the bending device 20 will be explained below. In the example 1, the bending plug 11 was manufactured as follows. A hot mold alloy tool steel (JIS (Japanese Industrial Standards) SKD61) was thermally treated (HRC60) and then shot blasting was applied to the surface to have roughness of 15 μηιΙΙζ. Further, the hot mold alloy tool steel was coated with fluorine resin film to manufacture the bending plug 11. The external appearance of such a bending plug 11 is shown in Figures 14 and 15. Figure 14 is a photograph of the entire bending plug 11 according to the example 1, and Figure 15 is a photograph around the coated portion 11c of the bending plug 11.

[0073] In this experiment, a commercially-available pure titanium tube class 2 (JIS TTP340C, inner diameter of 12.7 mm, tl.O mm) was used as the titanium tube 15. The bending was performed by the bending device 20 under the following conditions.

Conditions: frequency of ultrasonic vibration: 20.0 kHz, amplitude: 5 μιη

The bending device 20 was connected to the hydraulic mist pump 14. However, the hydraulic mist pump 14 was not operated, and the bending was performed in a dry environment without using lubricant oil.

[0074] As a result of applying rotating and pull-bending to a plurality of titanium tubes 15 (150 titanium tubes), the titanium tubes 15 could be molded without fracture by bending the bending plug 11 (the mandrel 12) while applying ultrasonic vibrations. Such a titanium tube 15 is shown in Figures 16 and 17. Figure 16 is a photograph of the external appearance of the titanium tube 15 formed by the above-described bending and an inner portion of a bent portion thereof, and Figure 17 is a photograph of the inner portion of the bent portion in an enlarged manner.

[0075] For comparison, a bending plug that did not include the coated portion 11c was used instead of the bending plug 11, and the titanium tube 15 was bent without applying ultrasonic vibrations. Consequently, a bent portion was broken as shown in Figure 18. Thus, it was ensured that the titanium tube 15 was molded without lubricant by using the bending plug 11 to bend the titanium tube 15 while applying ultrasonic vibrations.

Example 2 [0076] To evaluate the bending by the bending device 20 using the bending plug 11, the following experiment was carried out. In this experiment, the bending was performed twice to one titanium tube 15 to mold the titanium tube having a generally L-like shape as shown in Figure 19. In Figure 19, Rl indicates a first bending and R2 indicates a second bending. At this time, an axial tensile load applied on the bending plug 11 was measured. Also, to evaluate bending accuracy, variations of dimensions LI and L2 from set values were examined. The amplitude of ultrasonic vibrations was 5 μπι and the frequency of vibration was 20 kHz. For comparison, the same experiment was carried out when the ultrasonic vibrations were not applied (the amplitude was 0 um).

[0077] Figure 20 is a graph showing the strength of the tensile load when the ultrasonic vibrations are applied, and Figure 21 is a graph showing the strength of the tensile load when the ultrasonic vibrations are not applied. In Figures 20 and 21, the vertical axis indicates kN, and the horizontal axis indicates the number of the titanium tubes 15. The "plug tensile load (first bending)" means the tensile load when the titanium tube 15 is firstly bent, and the "plug tensile load (second bending)" means the tensile load when the titanium tube 15 is secondly bent.

[0078] The tensile load when the ultrasonic vibrations were applied was approximately 0.58 kN to 0.75 kN as shown in Figure 20, while the tensile load when the ultrasonic vibrations were not applied was approximately 1 kN to 1.9 kN as shown in Figure 21. It was confirmed that an axial tensile load applied on the bending plug 11 was reduced to substantially half (1/2) or less by applying the ultrasonic vibrations.

[0079] Figure 22 is a graph showing variations of the dimensions LI and L2 from the set vales when the ultrasonic vibrations are applied, and Figure 23 is a graph showing the variations when the ultrasonic vibrations are not applied. In Figures 22 and 23, the vertical axis indicates mm, and the horizontal axis indicates the number of the titanium tubes 15. The "dimension 1 (wide)" means the variation from the set value of the dimension LI shown in Figure 19, and the "dimension 2 (long)" means the variation from the set value of the dimension L2. Figure 24 is a chart showing specific numeral values of these results.

[0080] As shown in Figure 22, the dimensions LI and L2 were approximately -0.3 to 0.3 mm and -0.6 to 0.45 mm, respectively, when the ultrasonic vibrations were applied, while the dimensions LI and L2 were approximately 0.3 to 1 mm and -0.4 to 1.5 mm, respectively, when the ultrasonic vibrations were not applied. As shown in Figure 24, the deviations (the variations) of the dimensions LI and L2 when the ultrasonic vibrations were applied were 0.165 and 0.231, respectively. The deviations of the dimensions LI and L2 when the ultrasonic vibrations were not applied were 0.232 and 0.555, respectively. Thus, it was confirmed that the variations of the dimensions LI and L2 from the set values were reduced by applying the ultrasonic vibrations, so that the dimension accuracy was improved.

Example 3

[0081] An experiment was carried out for confirming that durability of the fine uneven portion was restored by applying liquid fluorine resin. In this experiment, a comparison was made between a friction coefficient of the the bending plug 11 in which the fluorine resin film 55 was peeled during bending and the surface was exposed and a friction coefficient measured after liquid fluorine resin was sprayed to the same bending plug 11 while attached to the bending device 20 (which process is also referred to as spray coating). The former friction coefficient is shown in Figure 25(A), and the latter friction coefficient is shown in Figure 25(B).

[0082] When the bending plug 11 of which the fluorine resin film 55 was peeled was used, the friction coefficient was gradually increased from approximately 0.1 and was reached to 0.2 as shown in Figure 25(A). However, when the fluorine resin was sprayed again, the friction coefficient was substantially consistent and within approximately 0.1. Thus, it was confirmed that the durability of the fine uneven portion was restored by applying the fluorine resin again.

[0083] [Modification] In the above description, the bending plug 11 for performing bending work in a dry environment was used. However, an embodiment of the present invention can be applied to a bending plug 31 as shown in Figure 13. The bending plug 31 differs from the bending plug 11 in that the bending plug 31 includes an oil inlet tube 31a and an oil draining hole 31b. The oil inlet tube 31 a is connected to the screw hole l ib and the oil draining hole 31b, and is formed to penetrate axially in most part of the central portion of the body portion 11a. The oil draining hole 31b is connected to the oil inlet tube 31a and the surface of the body portion 11a. The oil draining hole 31b is formed on the coated portion 11c.

[0084] By using the bending plug 31 instead of the bending plug 11, the titanium tube 15 can be bent in a dry environment as well. Also, the bending using lubricant oil can be performed when the lubricant oil is delivered into the oil inlet tube 31a. At this time, the lubricant oil may be subsidiarily used to be easily postcleaned.

[0085] Although the titanium tube 15 including the hole penetrating the central portion is used as a titanium member as described above, the embodiment of the present invention finds an application for a bottomed cylindrical titanium member having a generally tubular shape in which an end of a hole penetrating a central portion is closed.

[0086] The device and method according to the present invention are not limited to the embodiment described above, but can be variously modified and changed. The device and method according to the present invention may be provided by appropriately combining components, functions, features, or methods described in the embodiment.

Industrial Applicability

[0087] According to various aspects and embodiments of the present invention, the durability of the bending tool can be improved using the fluorine resin film as a lubricant film and the titanium member can be bent repeatedly in a dry environment.

Reference Signs List

[0088] 5... ultrasonic vibrator, 6... ultrasonic vibration part, 9,

10...die, 11, 13... bending plug, 11 a... body portion, l ib...screw hole, l ie..coated portion, l id... uniform diameter portion, l ie... reduced diameter portion, 11 f...distal end portion,

15... titanium tube, 20... bending device, 50a...fine uneven portion, 55...fluorine resin film, PI, P3, P5, P7, P9, PI 1... top portion, P2, P4, P6, P8, P10...bottom portion