WO2006046789A1

WO2006046789A1 - Precision machining tool using composite material

Info

Publication number: WO2006046789A1
Application number: PCT/KR2004/003117
Authority: WO
Inventors: Sang-Gon Kim
Original assignee: Vision Inno-Tech Corp.
Priority date: 2004-10-29
Filing date: 2004-11-30
Publication date: 2006-05-04
Also published as: KR100683943B1; KR20060038072A

Abstract

The present invention relates to a circular inner surface precision machining tool provided with a separable cutting head, it is an object that a precision machining tool is provided to allow high speed machining to be performed using a composite material and the circular inner surface to be easily fabricated into desired shape, and has a relatively cheap manufacturing cost. The tool includes a body provided with an approximately circular cross-section and being in a thin and long shape; and a cutting head separably connected to one end of the body and exchangeably installed thereon at least one cutter to fabricate the circular inner surface of the work piece. The body includes a composite material unit made of a composite material and provided with a hollow tube part being in a form of an approximately cylinder shape and passing through the body in a longitudinal direction; and cover unit being in a form of a pipe, made of a metal material and encompassing an outer surface of the composite material unit.

Description

[DESCRIPTION] [Invention Title]

PRECISION MACHINING TOOL USING COMPOSITE MATERIAL [Technical Field]

<i> The present invention relates to a precision machining tool employing a composite material; and more particularly, to a precision machining tool, e.g., a reamer, provided with a body made of a composite material and a cutting head being separable from the body and including at least one cutter formed on an outer surface of the cutting head. [Background Art]

<2> Generally, a reaming bar having a large length-to-diameter (L/D) ratio has been used for fabricating a hole such as a cylinder head cam hole of a vehicle engine. One of types of reaming bar has a long and thin shape and is provided with a head unit, wherein at least one cutter is placed at an end portion of the head unit.

<3> If a tool steel is used as a material of such reaming bar, the L/D ratio does not become larger than 5 since there occurs a chattering due to a low static stiffness and damping ratio when the L/D ratio increases, and in case when an additional element is attached to an outer surface of the tool to increase the L/D ratio, there is a limitation in shapes which can be fabricated since the diameter of the tool increases. And also, since a resonance frequency of the reaming bar is relatively small due to a low specific stiffness of the tool steel, it operates at low rotation speed; and, therefore, the operational speed becomes slower.

<4> Therefore, a metal material such as a tungsten carbide alloy or a heavy metal having a large static stiffness and damping ratio has been employed as a material of the reaming bar in a conventional method. For example, since the tungsten carbide alloy has larger static stiffness and damping ratio than the tool steel, a reaming bar made of the tungsten carbide alloy can machine without generating the chattering until the L/D ratio thereof becomes 8. However, since these materials have limitations in a high speed machining due to a small increment of the specific stiffness in comparison with the tool steel and, due to a large hardness of the materials, it is difficult to manufacturing the tool into a desired shape. Further, since a specific weight of the materials is large, the tool becomes to be heavy and a fabrication device becomes to be large to support the tool. Cost is also increased in manufacturing and using the tool because of the expensive material. On the other hand, in case when a device such as a cutter of the reaming bar is exchanged during the use of the reaming bar, states such as an alignment state of a blade of the cutter should be reset, since the conventional reaming bar is provided with a mounting bar and a head as one body, there is a problem that a setting device becomes large and a setting operation becomes complex in comparison with a case of a tool having a head which can be separated from the body. [Disclosure] [Technical Problem]

<5> It is, therefore, an object of the present invention to provide a cutting tool of a light weight and a relatively cheap manufacturing cost which is capable of being easily fabricated into a desired shape and having high operational speed using a composite material with a large damping ratio, a large specific stiffness and a small specific weight.

<6> And also, it is another object of the present invention to provide a precision machining tool capable of performing a setting of the tool using only a cutting head by constructing the cutting head of the precision machining tool to be separated from a body while maintaining a precision of the tool. [Technical Solution]

<7> In accordance with one aspect of the present invention, there is provided a tool for precision machining a circular inner surface of a work piece, the tool comprising: a body provided with an approximately circular cross-section and being in a thin and long shape; and a cutting head separably connected to one end of the body and exchangeably installed thereon at least one cutter to fabricate the circular inner surface of the work piece; wherein the body includes: a composite material unit made of a composite material and provided with a hollow tube part being in a form of an approximately cylinder shape and passing through the body in a longitudinal direction; and a cover unit made of a metal material and being in a form of a pipe encompassing an outer surface of the composite material unit.

[Advantageous Effects]

<8> In accordance with a preferred embodiment of the present invention, it can provide a cutting tool of a light weight and a relatively cheap manufacturing cost which is capable of being easily fabricated into a desired shape at high speed using a composite material with a large damping ratio, a large specific stiffness and a small specific weight.

<9> And also, the present invention can perform a setting work of a device such as a cutter using only a cutting head in a work such as a resetting work by constructing the precision machining tool so as to separate the cutting head from a body with maintaining a precision of the tool. [Description of Drawings]

<io> These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:

<ii> Fig. 1 shows a perspective view of a precision machining tool in accordance with an embodiment of the present invention;

<i2> Fig. 2 is an exploded perspective view of the precision machining tool in accordance with the embodiment of the present invention;

<13> Fig. 3 represents a diagram showing a composite material unit of the precision machining tool in accordance with the embodiment of the present invention;

<14> Fig. 4 depicts a cross-sectional diagram taken along a line A-A shown in Fig.3; and

<15> Fig. 5 illustrates a diagram showing a cutting head and a head adapter of the precision machining tool in accordance with the embodiment of the present invention. [Best Mode]

<i6> Fig. 1 shows a perspective view of a precision machining tool in accordance with an embodiment of the present invention; and Fig. 2 is an exploded perspective view of the precision machining tool shown in Fig 1.

<17> A tool 1 in accordance with one embodiment of the present invention includes a body 10 of a thin and long shape and a cutting head 20 separably connected to one end of the body 10. The body 10 has an approximately circular cross-section and is provided with a composite material unit 12 made of a composite material and a cover unit 14 made of a metal material and encompassing an outer surface of the composite material unit 12. In the composite material unit 12, a hollow part 13 passing through the composite material unit 12 in a longitudinal direction is prepared (see Fig. 3). In the cutting head 20, at least one cutter 22 is placed to fabricate a circular inner surface of a work piece. Preferably, the cutter 22 is exchangeable.

<18> The composite material unit 12 is made of a fiber reinforced composite material, particularly; it is preferable that it is made of a pitch based high modulus carbon/epoxy composite. Although the high modulus carbon/epoxy composite, for example, has a 70% static stiffness in comparison with a tungsten carbide alloy, a damping ratio and a specific stiffness of the high modulus carbon/epoxy composite are 10 times of those of the tungsten carbide alloy. The cover unit 14 is made of a metal material, e.g., steel, and has a shape of a pipe encompassing an outer surface of the composite material unit 12. The cover unit 14 protects a surface of the composite material unit 12 having a relatively small stiffness and increases the stiffness of the tool.

<19> In the embodiment of the present invention, a pitch based high modulus carbon/epoxy composite material, e.g., an URN ,300 commercially sold by SK Chemicals located at Seoul in Korea, is used as a composite material. The following Table 1 represents physical properties of the composite material used in the embodiment of the present invention. <20> [Table 1]

<21>

A speci f ic st i f fness of the above-descr ibed mater ial is a value of approximately 21.8x10 m. A Young ' s Modulus of a tungsten carbide al loy is ,

-3 for example, approximately 460 GPa, a damping ratio approximately 2.2x10 and

a specific stiffness approximately 3.3.xl0m. Accordingly, although a static stiffness of the composite material becomes to reduce to 70% in comparison with that of the tungsten carbide, a damping ratio of the composite material is approximately 10 times that of the tungsten carbide and a specific stiffness of the composite material is approximately 7 times that of the tungsten carbide. Therefore, since a resonance frequency of the tool becomes to increase in comparison with that of a conventional tool, a work piece can be fabricated at high speed without generating a chatter effect. Whereas, a

3 density of the tungsten carbide alloy is approximately 14,000 kg/m , but a

density of the composite material is no more than 1,755 kg/m as about 1/90 value of that of the tungsten carbide alloy as shown in the above-mentioned table 1. Therefore, a load to the fabricating device mounting the tool is reduced and a size of the fabricating device can be reduced since a weight of the tool 1 is reduced. Further, since a stiffness of the composite material is smaller than that of the tungsten carbide alloy, there is an advantage that the tool 1 is easily fabricated into a desired shape.

<22> The cover unit 14 is in the form of a pipe having an approximately predetermined thickness and covers an outer surface of the composite material unit. The cover unit 14 can be made of one element or can be made of at least two elements. In the embodiment of the present invention, the cover unit 14 is made of two elements. This configuration is adapted for the purpose that the composite material unit 12 and the cover unit 14 can be easily combined to each other during the manufacturing of the tool 1. In the embodiment of the present invention, steel is employed as a material of the cover unit 14. Since the steel has a small specific stiffness and a low damping ratio in comparison with those of the composite material, a resonance frequency of the tool 1 is reduced according to an increment of a thickness of the cover unit 14, thereby making a maximum machining speed slower. Therefore, it is preferable that the thickness of the cover unit 14 is as thin as possible. According to experiments, the thickness of the cover unit 14 is more affective to the specific stiffness of the tool 1 rather than the damping ratio of the tool 1.

<23> On the outer surface of the cover unit 14, at least one guide pad can be installed. The guide pad plays a role of supporting the tool 1 by contacting with a machining surface of the work piece while the tool 1 performs the machining work. For example, a surface of the guide pad is coated with a material such as a diamond to reduce a friction between the surface of the work piece and the surface of the guide pad.

<24> As shown in Fig. 2, it is preferable that a core 16 is arranged at a hollow part 13 of the composite material unit 12. In this embodiment, the core 16 is in a shape of a cylinder type sealing material made of steel. Since the steel as the material of the core 16 has a relatively low specific stiffness in comparison with that of the composite material, the resonance frequency of the tool 1 becomes to reduce as a diameter of the core 16 increases. Since the reduction trend of the resonance frequency is related to a square of the diameter of the core 16, if the diameter of the core 16 is small, the resonance frequency of the tool 1 is not nearly changed, but if the diameter of the tool 1 becomes to increase, the resonance frequency of the tool 1 is drastically decreased. On the other hand, the diameter of the core 16 has to be large in order to reduce the use amount of the relatively high price composite material in comparison with the steel and to easily stack the composite material during the manufacture of the composite material unit 12. Accordingly, it is preferable that the diameter of the core 16 is determined as a largest value within a range which does not affect the resonance frequency of the tool 1 greatly.

<25> Preferably, an adhesive layer(not shown) is placed between the composite material unit 12 and the cover unit 14. The adhesive layer is made of an adhesive material and plays a role of combining the composite material unit 12 with the cover unit 14. It is preferable that the adhesive is a material having a viscoelastic property. If the material having the viscoelastic property exists between the elastic materials, there occurs a great structural damping in comparison with a material damping of the structure by generating a constraint damping effect. That is, as in the present invention, in case when the composite material unit 12 as an elastic material and the cover unit 14 are combined through the medium of the adhesive having the viscoelastic property, the damping ratio of the tool 1 rather increases in comparison with when only the composite material is used. In this embodiment, an epoxy adhesive is used as the adhesive. The adhesive layer is formed by coating the epoxy adhesive on the outer surface of the composite material unit 12, after the composite material unit 12 coated by the adhesive is inserted into inside of the cover unit 14, and by solidifying the composite material unit 12 at a high temperature. According to the experiment, in case when the thickness of the adhesive layer is below a predetermined thickness, e.g., 0.1 mm, both the resonance frequency and the damping ratio of the tool 1 increase. And also, when the adhesive is solidified at the high temperature, an adhesive intensity has the most excellent value in case that the adhesion thickness is below a predetermined thickness. Therefore, the thickness of the adhesive layer is determined based on these properties of the adhesive layer.

<26> In this embodiment, the composite material unit 12 is provided with a plurality of protrusion parts 19 which is approximately of ring-shaped and O

diameters are larger than in other portions of the composite material unit 12. These protrusion parts 19 are placed at a predetermined interval along a longitudinal direction of the composite material unit 12. In Fig. 4, a transverse direction cross-section of one of the protrusion parts 19 is depicted. After the adhesive is coated on the outer surface of the composite material unit 12, in case when the coated composite material unit 12 is inserted into inside of the cover unit 14, the protrusion parts 19 prevent the non-solidified adhesive from being pushed and flowing out to the outside of the cover unit 14. It is preferable that maximum diameters of the protrusion parts 19 are smaller than an inner diameter of the cover unit 14. By this configuration, the adhesive can move through a space between the protrusion parts 19 and the cover unit 14.

<27> Fig. 5 describes the cutting head 20 and the head adapter 30 in accordance with the present invention. The head adapter 30 is depicted as a partial cut view for the purpose of showing an inside structure of the head adapter 30. In this embodiment, the cutting head 20 is connected to the body 10 of the tool via the head adapter 30. It is preferable that the head adapter 30 is made of a metal material; and the head adapter 30 is inserted into one end of the body 10 and engaged with the cutting head 20, thereby connecting the cutting head 20 to the body 10.

<28> It is preferable that the cutting head 20 is made of a metal material and at least one cutter 22 is arranged on an outer surface of the cutting head 20. The cutter 22 is provided with an edge to fabricate the surface of the work piece and it is supported to the cutting head 20 by means of a device such as a clamp. On one side end surface of the cutting head 20, the outer surface is tapered and the protruded part 24 is prepared in such a way that a central axis of the protruded part 24 is aligned with a central axis of the cutting head 20. In this embodiment of the present invention, the protruded part 24 is approximately in a shape of a truncated cone. And also, on the same end surface of the cutting head 20, the position determining pine 26 is placed at a position offset from the central axis of the cutting head 20. Corresponding to this, the head adapter 30 is at one side thereof provided with an insertion hole 32 which has an inner surface corresponding to the tapered outer surface of the protruded part 24 of the cutting head 20 and a central axis substantially aligned with the central axis of the body 10, and a hole 34 into which the position determining pin 26 is inserted. By this configuration, in case when the protruded part 24 of the cutting head 20 and a position determining pin 26 are respectively inserted into the insertion hole 32 and the hole 34 of a head adapter 30, a central axis of the cutting head 20 is substantially aligned with that of the body 10. In this result, a directionality of the tool 1 is assured. The position determining pin 26 determines positions of each direction of the cutting head 20 with regard to the body 10.

<29> For example, the cutting head 20 and the head adapter 30 are connected to each other by an LS screw 40. The LS screw 40 is in a form of a cylinder and is provided with a left screw fabricated on an approximately half of an outer surface and a right screw fabricated on the remaining part of the outer surface. One side of the LS screw 40 is inserted into the protruded part 24 of the cutting head 20 and the other side of the LS screw 40 is inserted into the hole prepared at the head adapter 30.

<3o> The tool 1 including the body 10 and the cutting head 20 is connected to the machining device via a shank 50. In Fig. 1, the tool 1 combined with the shank 50 is shown. A large amount of heat is generated when the tool 1 fabricates the surface of the work piece at high speed. The material properties of the composite material and the adhesive can be deteriorated by the heat. Therefore, in this embodiment, a path is prepared to move a coolant inside of the tool 1. The path receives the coolant from the fabricating device by connecting it to the path prepared at the shank 50 and the coolant is transmitted to the cutting head 20 through the path prepared at the head adapter 30. In the cutting head 20, a coolant path connected to the path of the head adapter 30 is prepared and a plurality of branch paths directing from the coolant path to the outer surface of the cutting head 20 is prepared. In the present embodiment, in the LS screw connecting the cutting head 20 to the head adapter 30, a hollow path is prepared to move the coolant along the central axis of the LS screw. The coolant can be supplied between an edge of the cutter 22 and the surface of the work piece during the machining of the work piece by extending the branch paths to the outer surface adjacent to the cutter 22. If the core 18 is placed at the hollow part of the body 10, a moving path of the coolant can be formed along the central axis of the core 18. If a fluid exists in the core 18, the damping ratio of the tool 1 becomes to increase since an amount of the metal material is relatively reduced.

<31>

Claims

[CLAIMS] [Claim 1] <33> A tool for precision machining a circular inner surface of a work piece, the tool comprising: <34> a body provided with an approximately circular cross-section and being in a thin and long shape; and <35> a cutting head separably connected to one end of the body and exchangeably installed thereon at least one cutter to fabricate the circular inner surface of the work piece! <36> wherein the body includes:

<37> a composite material unit made of a composite material and provided with a hollow part of an approximately cylinder shape and passing through the body in a longitudinal direction; and <38> a cover unit being in a form of a pipe, made of a metal material and encompassing an outer surface of the composite material unit.

<39>

[Claim 2]

<40> The tool of claim 1, further comprising a head adapter installed on one end of the composite material unit of the body to receive the cutting head and made of a metal material.

<41>

[Claim 3]

<42> The tool of claim 2, wherein a protruded part in a shape of a circular truncated cone is prepared at one end of cutting head, wherein an outer surface of the protruded part is tapered and a central axis of the protruded part is substantially aligned with that of the cutting head and the head adapter is provided with an insertion hole of which has an inner surface corresponding to the tapered outer surface of the protruded part and a central axis substantially aligned with that of the body.

<43>

[Claim 4] <44> The tool of claim 2 or 3, wherein a position determining pin is prepared at one end of the cutting head, a hole to insert the position determining pin thereinto is prepared at the head adapter and the position determining pin is arranged at one end of the cutting head with being offset from the central axis of the cutting head.

<45>

[Claim 5]

<46> The tool of claim 1, further comprising an adhesion layer placed between the composite material unit and the cover unit to combine the composite material unit and the cover unit.

<47>

[Claim 6]

<48> The tool of claim 5, wherein an outer diameter of the composite material unit is smaller than an inner diameter of the cover unit over an overall longitudinal direction.

<49>

[Claim 7]

<50> The tool of claim 5 or 6, wherein the composite material unit is provided with at least two protrusion parts which are approximately of ring- shaped and diameters are larger than in other portions of the composite material unit.

<51>

[Claim 8]

<52> The tool of claim 1, further comprising a core made of a metal material placed at the hollow part of the composite material unit to be combined with the composite material unit and provided with a hollow path extending along a longitudinal direction of the core.

<53>

[Claim 9]

<54> The tool of claim 8, wherein the cutting head includes: <55> an inner path connected to the hollow path of the core; and at least one branch path extending to a neighboring of the external surface at which each cutter of the cutting head is placed.

<56>