JP2001212703A - Polycrystalline hard sintered cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tool using a polycrystalline hard sintered body providing a fine surface roughness on finished surface and high accuracy in machining dimensions. SOLUTION: A cutting blade is formed of a polycrystalline hard sintered body 11 containing a cubic nitrogen boron of 20 vol.% or higher, and the sectional radius of curvature of ridge line part 15 of the cutting blade is 5 μm or more and 30 μm or less. A tool flank 12 is connected to a tool face 13 or a nega land face 14 smoothly at the sectionally radius of curvature, and the surface roughness of the cutting blade ridge line part 15 is 0.1 μm or higher and 1.0 μm or less in 10-point average roughness (Rz).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycrystalline hard sintered cutting tool containing cubic boron nitride and having a cutting edge.

[0002]

2. Description of the Related Art A material obtained by sintering fine cubic boron nitride powder with various binders exhibits excellent performance for cutting a high-hardness iron group metal or cast iron. Particularly in the processing of a hardened steel material having a high hardness, when the processing is performed using a cubic boron nitride sintered body tool, the finished surface roughness equivalent to the grinding processing and the processing dimensional accuracy can be obtained. For this reason, a part of the cutting of the hardened steel has been replaced by the cutting using a cubic boron nitride sintered body tool from the grinding using a conventional grindstone.

[0003] In recent years, this movement has progressed further, and there has been a particularly strong desire to replace the machining field requiring high precision, which was conventionally only possible with grinding, with cutting. The cutting object of the tool containing cubic boron nitride is
It is a hard material such as hardened steel or cast iron. Conventionally, it has hardly been conceived to cut this material into a mirror-finished surface. The processing accuracy referred to here is the surface roughness of the cut surface and dimensional accuracy such as roundness.

On the other hand, the most advanced precision cutting is cutting of non-ferrous metal using single crystal diamond. The main field of application is the processing of aluminum alloys such as memory disk substrates and polygon mirrors. Recently, there is a trend to replace this single crystal with polycrystalline diamond that is cheaper and easier to process.
In the case of a polycrystalline diamond tool, if large irregularities are formed on the cutting edge due to a step at the crystal interface or the like, the irregularities cannot be removed even if the flank or rake face is polished. This unevenness remains on the polished surface and is transferred to the work material, so that there is a problem that high-precision processing cannot be performed.

In the case of a polycrystalline diamond cutting tool described in Japanese Patent Application Laid-Open No. Hei 6-190610, this problem has been solved by chamfering the cutting edge. That is,
A technology is disclosed in which a flank of a cutting edge of a chip using polycrystalline diamond is formed on a polished surface without polishing marks, and the cutting edge is chamfered to a small width by polishing to smooth the cutting edge. ing. However, a polycrystalline diamond tool cannot be used for cutting hardened steel or cast iron because carbon constituting diamond reacts with steel.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, the present invention provides a method for cutting a hardened steel or the like to have a surface roughness Rz of 1.6 μm or less, for example, The purpose is to increase the circularity to a dimensional accuracy of 3 μm or less. For such applications, a work material having a diameter of about 30 mm or less is often used. In other words, by improving the shape and surface roughness of the cutting edge of a polycrystalline hard sintered body cutting tool containing cubic boron nitride, it is intended to realize excellent finished surface roughness and high processing dimensional accuracy. is there. Rz is a 10-point average roughness defined in JIS B0601 “Surface Roughness—Definition and Display”.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided a polycrystalline hard sintered compact cutting tool having a cutting edge with a cutting edge, wherein the cutting edge contains at least 20% by volume of cubic boron nitride. The cutting edge ridge portion has a cross-sectional radius of curvature of 5 μm or more and 30 μm or less, and the tool flank and the tool rake surface or the negative land surface are smoothly connected with the above-mentioned cross-sectional curvature radius, and the surface roughness of the cutting edge ridge Is 10-point average roughness (Rz)
Is 0.1 μm or more and 1.0 μm or less. With this configuration, the work material can be processed with high accuracy.

[0008] Another feature of the present invention is that the tool rake face,
Or the surface roughness of the negative land surface is the ten-point average roughness (Rz)
Is 0.1 μm or more and 0.5 μm or less. With such a configuration, the surface roughness of the cutting edge ridge portion can be kept small even if the cutting edge ridge portion wears out and retreats during use.
A long-life cutting tool can be provided.

Another feature is that a wedge angle between the tool flank and the tool rake face or a tool flank and the negative land face is 65 ° or more and 125 ° or less. With such an angle, the cutting edge of the cutting tool can be economically processed.

Another feature is that the polycrystalline hard sintered body contains cubic boron nitride in an amount of 20% by volume or more and has an average particle diameter of 0.01 μm or more and 5 μm or less. With such a configuration, the cutting edge of the cutting tool can be economically processed.

Still another feature is that the polycrystalline hard sintered body is joined to a tool base material made of a hard metal. This is because a polycrystalline hard sintered body must be joined to a highly rigid tool base material in order to perform high-precision processing.

[0012] Still another feature is that a pair of straight cutting edges connected to the nose radius r from the respective ends of the nose radius r of the polycrystalline hard sintered body toward the side of the throw-away tip are each 0.2 mm. Having a length in the range of .about.0.6 mm, and the angle formed between a straight line bisecting the nose radius portion and each of the straight cutting edges is 42 ° ≦ θ ₁₀ , θ ₁₁ ≦ 4.
By providing the straight edge of 5 °, the straight cutting edge portion exposes the work surface, and the surface roughness of the finished surface of the work material is further improved. Here, θ
₁₀ and θ ₁₁ are equal.

Still another feature is that the coating layer is formed on the surface by chemical vapor deposition or physical vapor deposition. As a result, the wear of the cutting edge ridge portion is reduced, the surface roughness of the finished surface of the work material is improved, and the life of the tool can be extended.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a polycrystalline hard sintered compact cutting tool used in the present invention. Polycrystalline hard sintered body 1
1 has a two-layer structure integrated with the cemented carbide substrate 3,
This is brazed to the corner of the cemented carbide tool base material 1 to form a cutting tool. The present application can naturally be used for a cutting tool that does not use the cemented carbide substrate 1. The cutting tool is, for example, a holder (not shown) using the mounting hole 2.
Attached to. For the cutting tool, a throw-away tip shown in FIG.
There are tools that are directly brazed to the holders used in. The present invention relates to the structure of the cutting edge ridgeline which is the most important part relating to the cutting performance of these cutting tools.

The present inventor has intensively studied a cutting tool for a polycrystalline hard sintered body containing cubic boron nitride, which can perform cutting with high precision. The result will be described with reference to FIGS. 2 and 3 show a cutting tool according to the present invention in FIG.
FIG. 5 is an enlarged view of a cross section when cut along a plane perpendicular to a line 16 constituting the cutting blade of FIG. FIG. 2 is an enlarged sectional view of the cutting tool having the negative land surface 14. 11 denotes a polycrystalline hard sintered body, 12 denotes a tool flank, 13 denotes a tool rake face, 1
Reference numeral 5 denotes a cutting edge ridge portion.

The cutting edge ridge 15 has a negative land surface 14 or a tool rake surface 13 and a tool flank 12 with a radius of curvature R in cross section.
And each is connected smoothly. Here, “smoothly connected” means continuous connection, in other words, no corners. Angle theta ₁ between the horizontal line and the negative land surface or tool rake face serving as a reference at the time of cutting tool rake angle, the angle theta ₂ between the vertical line and the tool clearance angle showing the tool clearance angle. In the case of FIG. 2, the rake angle θ ₁ is minus, and in the case of FIG. 3, the rake angle is in the plus direction, and there is no negative land surface. theta ₃ shows the tool edge wedge angle angle such as the tool flank and the tool rake face.

The cutting edge ridge portion 15 is formed between the tool flank 12 and the tool rake surface 13 or the tool flank 12 and the negative land surface 1.
4 are formed at the intersections. The inventor has found that the cross-sectional radius of curvature R of the cutting edge ridge 15 and the surface roughness of the ridge are important. That is, the cutting edge ridge is 5
Formed by a curve having a cross-sectional radius of curvature in the range of .about.30 .mu.m, the curve being the tool flank 12, the tool rake 1
3. It is important that it is smoothly connected to the negative land surface 14 and the like. By setting the surface roughness of the ridge of the cutting edge to a ten-point average roughness (Rz) within the range of 0.1 to 1 μm, excellent finished surface roughness can be realized and high-precision machining can be performed. Was found.

Conventionally, a polycrystalline hard sintered compact cutting tool containing cubic boron nitride has a diamond grain size of # 6.
A rake face and a flank face have been ground by using a diamond grindstone of about 00 and have been bladed. It was found that the cutting edge ridge of the sintered compact cutting tool produced in this way had severe irregularities such as a partially large cutting edge ridge.

When cutting a high hardness material such as hardened steel with a cubic boron nitride sintered body cutting tool, the shape of the cutting edge ridge is easily transferred to the surface to be processed. For this reason, when machining a high-hardness material to an excellent finished surface roughness, a cutting tool that has a smooth and small surface roughness with little chipping of the cubic boron nitride sintered body at the cutting edge ridge is required. there were. If the cutting resistance is high, so-called chatter or the like is likely to occur on the surface of the work material. Therefore, in order to solve the problem of the present invention, the first
The present inventors considered that the surface roughness of the above-mentioned cutting edge ridge portion should be made small and smooth, and secondly, it was an important task to reduce the cutting resistance.

A cutting tool having a cutting edge having a small surface roughness simply has a diamond grain size of # 3,000 to # 14,
With a diamond grindstone having particles as small as about 000, it was possible to form the cutting edge with time and effort.
However, it has been difficult to smoothly connect the rake face of the tool, the flank of the tool, and the ridge of the cutting edge.

The polycrystalline hard sintered compact cutting tool of the present invention uses a diamond grindstone having a diamond grain size of about # 600 to # 3,000 to grind the tool flank and the tool rake face for cutting. Next, diamond free abrasive grains having a particle size of about # 1,500 to # 3,000 were applied to a rotating brush, and the area near the blade was ground and polished. That is, it was possible to obtain a cutting tool in which the surface roughness of the cutting edge ridge was small and smooth, and the cutting edge ridge was smoothly connected to the tool rake face and the tool flank. By connecting smoothly, chips can be discharged smoothly.

Next, in order to reduce the cutting resistance, a study was made to reduce the sectional radius of curvature R. In this process, if the radius of curvature of the cross section is too small, it has become clear that the target surface roughness cannot be obtained industrially. This is because the recess of the missing portion cannot be smoothly formed with a small radius of curvature of the section. Therefore, samples having various cross-sectional radii of curvature were prepared by the above-mentioned polishing method and examined. As a result, the sectional radius of curvature R
Was in the range of 5 to 30 μm, a cutting tool having a small cutting resistance could be obtained. In the development, it was thought that the radius of curvature of the section had to be considerably smaller than 5 μm, but surprisingly, it was found that the surface roughness was better at 5 μm or more.

As described above, in order to obtain the surface roughness of the present invention by performing the polishing process for eliminating the detached portion by the free abrasive grains after the polishing with the blade, the cross-sectional radius of curvature of the ridge portion of the cutting edge is 5.
It is preferably at least μm. When the radius of curvature of the cutting edge ridgeline section exceeds 30 μm, the actual rake angle increases in the negative direction, so that the cutting resistance increases and the sharpness during machining decreases. In particular, when processing a high-hardness material with high precision, it is difficult to obtain high processing dimensional accuracy because the back force is large and the amount of variation is large. For this reason, the cross-sectional radius of curvature of the cutting edge ridge portion is 5 to 3
It is preferably in the range of 0 μm.

On the other hand, in the conventional processing of a hard material by grinding, the surface roughness of the processed surface to be finished is about 1.6 μm or less in ten-point average roughness (Rz), which is the present invention. I am aiming. In order to achieve this, it is preferable that the surface roughness of the cutting edge ridge portion of the cutting tool is 1.0 μm or less in ten-point average roughness (R). Also,
In order to finish the surface roughness of the cutting edge ridge portion to less than 0.1 μm, a great deal of labor is required and it is not preferable from the viewpoint of economy, so the surface roughness of the cutting edge ridge portion has a ten-point average roughness. It is preferable that the thickness (Rz) is in the range of 0.1 μm or more and 1.0 μm or less.

Further, the cutting edge is retreated due to wear of the tool cutting edge with the continuation of machining, but the newly formed cutting edge is formed from the worn tool flank and the tool rake face or the negative land face. Will be done. For this reason, in order to maintain excellent surface roughness even during continuous machining, it is necessary that the tool rake surface or the negative land surface have a small surface roughness. The surface roughness required for the cutting edge ridge is 1.0 μm or less, and considering that the surface roughness deteriorates due to use, the surface roughness of the tool rake face or the negative land surface is the ten-point average roughness. (Rz) is preferably in the range of 0.1 to 0.5 μm.

On the other hand, in order to process a high hardness material, a high hardness is also required for the tool material. Therefore, the content of cubic boron nitride in the polycrystalline hard sintered body needs to be 20% by volume or more and 95% by volume or less. In consideration of hardness, single-crystal cubic boron nitride is also considered as a tool material in such a processing application. However, in the case of a single crystal, since there is a problem that chipping due to cleavage is likely to occur, a polycrystalline cubic boron nitride sintered body that is difficult to be cleaved is used in processing such a hard material. Is more preferred.

The wedge angle θ _{3 of the} tool cutting edge formed by the tool flank and the tool rake face, or the tool flank and the negative land face.
If the angle is less than 65 °, the chip edge of the cutting edge of the tool is small, so that the high-hardness material tends to be chipped at the beginning of cutting. On the other hand, when the cross-section crossing angle exceeds 125 °, the cutting resistance increases significantly, so that the desired finished surface roughness can be obtained, but the required dimensional accuracy cannot be obtained. For this reason, the tool flank and the tool rake surface, or the tool flank and the negative land surface make the wedge angle of the tool edge,
It is preferably in the range of 65 ° to 125 °.

Further, the roughness of the ridge of the cutting edge is 0.1-1.
In order to fall within the range of 0 μm, the average particle diameter of the polycrystalline cubic boron nitride sintered body to be contained is preferably 5 μm or less, more preferably 1 μm or less. Further, when the average particle size of the cubic boron nitride contained is less than 0.01 μm, such fine particles are likely to aggregate in the sintered body, and the chipping of the cutting edge is likely to occur due to this. Become.
Therefore, the average particle diameter of the polycrystalline cubic boron nitride sintered body is preferably in the range of 0.01 to 5 μm. Also,
The tool base material joining the hard sintered body can be a cemented carbide, a steel material, or the like. However, in order to process a high-hardness material with high precision, a high rigidity is also required for the tool base material. For this reason,
As a tool base material, a cemented carbide is most suitable.

In addition to these, as shown in FIG. 5, a pair of straight cutting edges L connected to the side of the throw-away tip and connected to the nose radius r from the respective ends of the nose radius r of the polycrystalline hard sintered body. And L ′ each have a length in the range of 0.2 to 0.6 mm, and the angle formed by a straight line bisecting the nose radius portion and the straight cutting edges L and L ′ is 42 ° ≦ θ. _{In the case of 10} , θ ₁₁ ≦ 45 °, since the straight cutting edge portion finishes so as to expose the work surface in turning, the finished surface roughness is remarkably improved. Needless to say, θ ₁₀ and θ ₁₁ are equal.

Here, if the length of the straight cutting edge is less than 0.2 mm, the effect of exposing the work surface is small.
If it exceeds m, the contact portion with the work surface increases, so that the cutting resistance increases and it becomes difficult to secure the processing accuracy. Considering the above, the length of the straight cutting edge should be 0.2 ~
It is preferable to be within the range of 0.6 (mm). Also,
In consideration of the balance between the processing accuracy and the finished surface roughness, it is more preferable to be within the range of 0.3 to 0.5 (mm).

Similarly, when the angle formed between the straight line that bisects the nose radius and the straight cutting edges L and L ′ is less than 42 °, the effect of exposing the work surface is reduced. On the other hand, if the angle exceeds 45 °, the contact portion with the work surface increases, so that the cutting resistance increases, and it becomes difficult to secure the processing accuracy. In consideration of the above, it is preferable that the angle between the straight line that bisects the nose radius portion and the straight cutting edges L and L ′ is 42 ° ≦ θ ₁₀ and θ ₁₁ ≦ 45 °.
In consideration of the balance between the processing accuracy and the finished surface roughness, it is more preferable that 43.5 ° ≦ θ ₁₀ and θ ₁₁ ≦ 45 °.

Further, in order to further improve the finished surface roughness and extend the life of the tool, a coating layer is formed on the surface of the polycrystalline hard sintered body by chemical vapor deposition and physical vapor deposition. This is preferable because it is possible to reduce and maintain excellent finished surface roughness for a long time.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a cutting tool according to the present invention will be described below. (Example 1) The cross-sectional radius of curvature of the cutting edge ridge and the roughness of the cutting edge of the polycrystalline hard sintered tool containing cubic boron nitride affect the finished surface roughness and machining accuracy of the work material. The effects were investigated. Table 1 shows examples of prepared polycrystalline sintered body throw-away chips containing various cubic boron nitrides. The wedge angle of the tool edge was 83 ° in all cases.

The throwaway chips in Table 1 are as follows:
As shown in FIG. 1, a polycrystalline hard sintered body 11 containing 50% by volume of cubic boron nitride having an average particle diameter of 0.5 to 1 μm is brazed to a corner portion. # 1,00
The blade was polished with a 0 diamond grindstone. Thereafter, diamond free abrasive grains having a particle diameter of 5 to 8 μm (corresponding to # 2,000) are applied to the surface of the brush that performs a rotating motion, and the diamond free abrasive grains are pressed from the rake face of the throw-away tip to obtain a tool cutting edge ridge. Honing was performed on the part. When viewed from the cross section of the cutting edge ridge, the tool flank and the negative land surface were smoothly connected. Then, by changing the processing time, the sample was produced by changing the cross-sectional radius of curvature of the cutting edge ridge line portion variously.

The cross-sectional radius of curvature of the ridge of the cutting edge was measured using a contracer. The measurement principle of the contracer is the same as that of a surface roughness meter, and the curvature of a curve obtained by measuring at the same vertical and horizontal magnifications is measured. Also, as shown in FIG. 4, the cutting tool 1 is tilted in a 45 ° direction on the V block 23,
The roughness of the cutting edge ridge of each sample was measured. The knife edge-shaped terminal 22 is moved along the direction of the cutting edge ridge 15 of the cutting tool,
The roughness of the cutting edge line 15 was measured under the following conditions. Measuring element shape: Knife edge terminal Measuring length: 1 mm Measuring element feed rate: 0.03 mm / sec Cut-off length: 0.08 mm Measurement vertical magnification: 20,000 times Measurement horizontal magnification: 100 times

[0036]

[Table 1]

As a result, in the sample 1A having a small cross-sectional radius of curvature of the cutting edge ridge portion, the chipping generated on the cutting edge ridge portion at the time of machining the tool rake face or the tool flank face cannot be removed by honing. It became clear that the surface roughness was large. A cutting test was performed on these five samples under the following conditions.

The work material and cutting conditions are shown below. Workpiece: cylindrical carburized Irizai (SCM415) inner diameter 10mm ones of inner diameter cutting work material hardness: the peripheral surface speed of the H _RC 62 Workpiece: 100 (m / min) Tool depth of cut: 0. 05 (mm) Tool feed speed: 0.03 (mm / rev) Cutting time: 5 (min) Machining method: bore boring Work material required finished surface roughness: Rz = 1.6 (μm) or less Roundness: 3 μm or less

Table 2 shows the results of the surface roughness and the roundness after the cutting test. Sample 1A with a small radius of curvature of the cutting edge ridge
Although the cutting resistance was small and the roundness was excellent, the finished surface roughness to be transferred was large due to the large roughness of the cutting edge ridge portion, and the desired finished surface roughness could not be obtained. On the other hand, in the sample 1E having a large radius of curvature of the cutting edge ridge portion, although the surface roughness of the cutting edge ridge portion is small and the finished surface roughness to be transferred is excellent, since the cutting resistance is large, the fluctuation is large, so Could not achieve roundness.

On the other hand, it is clear that the samples 1B to 1D falling within the scope of the present invention can obtain excellent finished surface roughness because the surface roughness of the cutting edge ridge is small. Was. In addition, it has been clarified that since the cross-sectional radius of curvature of the cutting edge ridge portion is small, an increase in cutting resistance is suppressed, and processing can be performed within the required precision for roundness, and high-precision processing can be performed.

[0041]

[Table 2]

(Example 2) The rake face roughness and the roughness of the edge of the cutting edge of the polycrystalline sintered tool containing cubic boron nitride were
The effect of the work material on the finished surface roughness was investigated. Table 3 shows examples of the prepared polycrystalline hard sintered compact throw-away tips containing various cubic boron nitrides having a wedge angle of 115 ° at the tool tip.

The throw-away chips in Table 3 are 1
A polycrystalline hard sintered body containing 65% by volume of cubic boron nitride having an average particle diameter of ３3 μm is joined to a corner of a cemented carbide tool base material by brazing. # 1,
Polishing with a 200 diamond grindstone was performed.

Thereafter, the sample 2A was subjected to honing at the ridge of the cutting edge by pressing a wire brush, in which diamond abrasive grains equivalent to # 800 were embedded, against the cutting edge while rotating. On the other hand, the sample 2B has a particle diameter of 8 to 16 μm (# 1, 50
(Equivalent to 0) of diamond free abrasive grains, and pressed against the rake face side of the throw-away insert to perform honing on the cutting edge ridge. Sample 2C
Is 5 to 8 μm on the brush surface by the same method as in 2B.
Honing was performed by applying diamond free abrasive grains having a particle size (corresponding to # 2,000). Also,
When viewed from the cross section of the cutting edge ridge, the tool flank and the negative land surface were smoothly connected.

Thereafter, the roughness of the cutting edge line of each sample was measured in the same manner as in Example 1. Further, the surface roughness of the rake face was different from that of FIG. 4 and a needle-shaped terminal was used. The measurement conditions are shown below. The tool rake face was measured by measuring the roughness by scanning the stylus in a direction perpendicular to the direction in which the rake face was polished. Measuring element shape: Knife edge terminal, needle terminal Measuring length: 1 mm Measuring element feed rate: 0.03 mm / sec Cutoff length: 0.08 mm Measurement vertical magnification: 20,000 times Measurement horizontal magnification: 100 times

[0046]

[Table 3]

As a result, the sample 2A, whose edge is honed by a diamond wire brush having a relatively coarse grain size, has a low effect of improving the roughness of the tool rake face and the tool flank, and is formed by these two faces. It became clear that the surface roughness of the cutting edge ridge was a large value. Cutting tests were performed on these three samples under the following conditions.

The work material and cutting conditions are shown below. Work material: Round bar with outer diameter 100 mm made of bearing steel (SUJ2) Work material hardness: _HRC 63 Peripheral surface speed of work material: 120 (m / min) Depth of cut of tool: 0.04 (mm) Tool feed speed: 0.02 (mm / rev) Cutting time: 15 (min) Machining method: outer diameter turning Work material required finished surface roughness: Rz = 1.0 (μm) or less Table 4 shows the results of the surface roughness after processing for 15 minutes.

[0049]

[Table 4]

As a result, in Sample 2A, the required surface roughness could not be obtained from the initial stage of cutting because the roughness of the cutting edge ridge was large and was transferred to the surface of the work material.
On the other hand, the samples 2B and 2C having a small roughness
In Example 1, excellent finished surface was obtained from the beginning of cutting, and required surface roughness was able to be secured.

Particularly, sample 2C having a small tool rake surface roughness
Is that even when the cutting edge of the tool wears as the cutting process progresses and the ridge of the cutting edge recedes, the roughness of the tool rake face is small,
Since the roughness of the newly created cutting edge ridge line becomes small, it has been clarified that excellent finished surface roughness can be obtained stably.

(Example 3) The average particle size of cubic boron nitride of a polycrystalline hard sintered tool containing cubic boron nitride was
The effects on the roughness of the cutting edge ridge and the finished surface roughness of the work material were investigated. The prepared tool edge wedge angle is 108 °, and Table 5 shows examples of various cubic boron nitride sintered tools.

[0053]

[Table 5]

The cutting tool shown in Table 5 is a cutting tool, which is a polycrystalline hard material containing a cubic boron nitride having an average particle diameter shown in Table 5 at a tip of a steel shank of φ6 mm having a circular cross section. The sintered body is joined. The content of cubic boron nitride is 55% by volume in each case. This was subjected to cutting with a grindstone having a diamond particle size of # 1,000. Then, the results of honing the tool edge in the same procedure as in Example 1 are shown in Table 5. In addition,
At this time, the cross-sectional radius of curvature of the cutting edge ridge was 20 μm. In addition, when viewed from the cross section of the cutting edge ridge portion, the tool flank and the negative land surface were smoothly connected.

Among them, the sample 3A having a very fine grain size of the sintered body has a low cutting edge strength due to the presence of a non-uniform structure due to the aggregation of the fine particles in the sintered body, and chipping during the formation of the cutting edge. Was easy to occur. A cutting test was performed on the samples 3B to 3F in which chipping did not occur on the tool edge under the following conditions.

The work material and cutting conditions are shown below. Work material: cylindrical die steel (SKD11), inner diameter 20m
Internal diameter cutting of m Work material hardness: _HRC 65 Internal surface speed of work material: 70 (m / min) Cutting depth of tool: 0.05 (mm) Feeding speed of tool: 0.03 mm / rev) Cutting distance: 2 (km) Processing method: inner diameter boring Required surface roughness: Rz = 1.6 (μm) or less Table 6 shows the surface roughness of the inner diameter of the obtained work material.

[0057]

[Table 6]

As a result, in Sample 3F having a large average particle diameter of CBN, the required roughness of the finished surface of the work material could not be ensured because the roughness of the cutting edge line was large.
On the other hand, it is clear that the samples 3B to 3E of the present invention can stably secure the required finished surface roughness and can perform high-precision processing because the roughness of the cutting edge ridge is small. It became.

(Example 4) Influence of the wedge angle of the tool edge, which is the angle between the tool flank and the negative land surface, on the cubic boron nitride sintered tool on the machining accuracy and the finished surface roughness of the work material. Was examined. Table 7 shows examples of various prepared cubic boron nitride sintered body throw-away tips.

[0060]

[Table 7]

At the corners of the indexable inserts in Table 7, a polycrystalline hard sintered body containing 70% by volume of cubic boron nitride having an average particle size of 1.2 μm was formed by brazing with a cemented carbide. It is joined to the tool base material.
The wedge angle of the tool tip between the tool flank and the negative land is variously changed. The diamond particle size is # 1,
After performing the blade treatment using 500 diamond grindstones, samples 4A to 4I having a sectional radius of curvature of the cutting edge ridge portion of 28 μm were obtained in the same procedure as in Example 1. When viewed from the cross section of the cutting edge ridge, the tool flank and the rake face or the negative land face were smoothly connected. At this time, the surface roughness of the ridge of the cutting edge was in the range of Rz = 0.3 to 0.8 μm. Using these cutting tools, cutting tests were performed under the following conditions.

Work Material: Cylindrical carburized and quenched material (SCM420) inner diameter 1
Internal diameter cutting of 5 mm workpiece hardness: _HRC 59 Peripheral surface speed of workpiece: 100 (m / min) Cutting depth of tool: 0.07 (mm) Feeding speed of tool: 0.06 (mm) / Rev) Cutting time: 5 (min) Processing method: inner diameter boring processing Required surface roughness: Rz = 2 μm or less Required roundness: 3 μm or less

[0063]

[Table 8]

As is clear from Table 8, 4A having a small wedge angle formed by the tool flank and the negative land surface has a small wedge angle at the cutting edge, so that chipping occurs at an early stage of cutting, and continuous evaluation is not possible. It was impossible. On the other hand, 4I with a large wedge angle of the tool edge between the tool flank and the negative land surface
However, since the cutting force was high and the fluctuation was large, chatter occurred and continuous evaluation was impossible. On the other hand, 4B to 4H, which are the products of the present invention, have a small cutting resistance and a small variation in the cutting resistance. It became clear that we could do it.

(Embodiment 5) In the following embodiment, in order to clarify the difference due to the cutting test, the cutting length is set to be at least twice the length of the first to fourth embodiments. The influence of the length of a pair of straight cutting edges formed on the side surface from the end of the nose radius r of the polycrystalline hard sintered body on the work surface was examined. The polycrystalline hard sintered body indexable insert containing cubic boron nitride was honed with free abrasive grains to prepare the same sample as sample No. 2C of Example 2, and a cutting test was performed under the following conditions. . The work material and cutting conditions are shown below. Work material: case hardened steel (SCM415) diameter 50 (m)
m) the outer diameter cutting work material hardness of round bars in the longitudinal length 100 (mm): the peripheral surface speed of the H _RC 60 Workpiece:. 120 (m / min) Tool depth of cut: 0.05 (mm ) Tool feed speed: 0.08 (mm / rev) Cutting length: 5 km Holder model number: PCLNR2525-33 Test chip shape: Approximately 80 with a straight Sarae blade with an inscribed circle size of 12.7 mm゜ Rhombus throwaway tip Angle formed by the bisector of the nose radius and the straight Sarae blade: 4
4.5 degrees

[0066]

[Table 9]

From this result, as the width of the straight cutting edge increases, the surface roughness is improved because the effect of exposing the work surface is large. However, when the width of the straight cutting edge is increased, the cutting resistance is increased, so that the roundness is also increased. For this reason, it became clear that the preferable width of the straight cutting edge capable of forming appropriate roundness and surface roughness is in the range of 0.2 to 0.6 (mm).

(Example 6) A pair of straight lines bisecting the nose radius of the polycrystalline hard sintered body and the ends of the nose radius r, each facing the side surface of the throw-away tip and connected to the nose radius r. The effect of the angle formed with the straight cutting edge on the work surface was investigated. Sample No. 2C of Example 2 was produced by honing a polycrystalline hard sintered body throwaway tip containing cubic boron nitride.
A cutting test was performed on these samples under the following conditions.

The work material and cutting conditions are shown below. Work material: carburized and hardened steel (SCr420), diameter 60 (m)
m) the longitudinal length 120 (mm) outer diameter cutting work material hardness of round bar: the peripheral surface speed of the H _RC 60 Workpiece:. 100 (m / min) Tool depth of cut: 0.06 (mm ) Tool feed speed: 0.07 (mm / rev) Cutting length: 4 km Holder model number: PWCLNR2525-33 Test chip shape: Substantially hexagonal shape with a straight inscribed circle with an inscribed circle of 12.7 mm Tip angle 80 ° Indexable insert Length of straight Sarae blade: 0.4 (mm)

[0070]

[Table 10]

From this result, as the intersection angle between the bisector of the nose radius portion and the straight cutting edge increases, the effect of exposing the work surface is increased, and the surface roughness is improved. However, as the intersection angle increases, the cutting resistance increases, and the roundness also increases. For this reason, a preferable range of the crossing angle at which an appropriate roundness and surface roughness can be formed is 42.0.
It was found to be within the range of ４５45.0 (degrees).

Example 7 The effect of forming a coating layer on the surface of a polycrystalline hard sintered body by chemical vapor deposition and physical vapor deposition was examined. The following samples were prepared using Sample No. 2C of Example 2 using a polycrystalline hard sintered body throw-away tip containing cubic boron nitride. 10A is a chip without a coating layer, and 10B is a chip having a thickness of 2 (μ
m) Chip with coating layer of TiN formed, 10C is PV
This is a chip on which a coating layer of 2 μm thick TiAlN is formed by the method D.

[0073]

[Table 11] Cutting tests were performed on these samples under the following conditions. The work material and cutting conditions are shown below. Workpiece: carburized hardened steel (SCM415) Workpiece Hardness: the peripheral surface speed of the H _RC 58 Workpiece: (. M / min) 70 tool depth of cut: 0.05 (mm) Feed speed of the tool : 0.03 (m / min.) Cutting length: 5km

Table 12 shows the results of the cutting test.

[Table 12] From the results, it has been clarified that the tip coated by the PVD method has less abrasion development at the cutting edge ridge than the conventional non-coated tip, so that more excellent surface roughness can be maintained for a long time.

[0075]

According to the present invention, a cutting tool having a cutting edge ridge having a cross-sectional radius of curvature of 5 μm to 30 μm and a surface roughness of the cutting edge ridge of 0.1 μm to 1.0 μm is a hardened steel. Materials such as steel and cast iron could be machined with high precision by cutting. That is, by using the cutting tool of the present invention, the surface roughness of the work material was 1.6 μm or less and the roundness was 3 μm or less. Therefore, the machining efficiency was dramatically improved by replacing the process which had conventionally depended on the grinding process with poor efficiency with the cutting process.

[Brief description of the drawings]

FIG. 1 is a perspective view of a cutting tool according to the present invention.

FIG. 2 is an enlarged sectional view of a cutting tool according to the present invention.

FIG. 3 is an enlarged sectional view of a cutting tool according to the present invention.

FIG. 4 is a view showing a method of measuring the roughness of a cutting edge ridge portion according to the present invention.

FIG. 5 is an explanatory view of straight cutting blades L and L 'according to the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 tool base material 2 mounting hole 3 cemented carbide substrate 11 polycrystalline hard sintered body 12 tool flank 13 tool rake face 14 negative land face 15 cutting edge ridge line 16 line 21 stylus 22 knife edge terminal 23 V block R section curvature Radius θ ₁ Tool rake angle θ ₂ Tool clearance angle θ ₃ Tool wedge angle θ ₁₀ , θ ₁₁ Angle between bisector of nose radius and straight cutting edge

Claims (7)

[Claims] The cutting edge is made of a polycrystalline hard sintered body containing 20% by volume or more of cubic boron nitride, and the cutting edge has a cross-sectional radius of curvature of 5 μm or more and 30 μm or less; The tool rake surface or the negative land surface is smoothly connected with the above-mentioned radius of curvature of the cross section, and the surface roughness of the ridge portion of the cutting edge is 0.1 μm or more and 1.0 μm or less in ten-point average roughness (Rz). , Polycrystalline hard sintered cutting tool. 2. The tool rake surface or the negative land surface has a ten-point average roughness (Rz) of 0.1 μm or more,
The polycrystalline hard sintered compact cutting tool according to claim 1, wherein the cutting tool has a diameter of 0.5 µm or less. 3. A wedge angle between a tool flank and a tool rake face or a tool flank between a tool flank and a negative land face is 65 ° or more and 125 ° or less. 2. A cutting tool for a polycrystalline hard sintered body according to item 1. 4. The polycrystalline hard sintered body contains at least 20% by volume of cubic boron nitride and has an average particle diameter of 0.01%.
The polycrystalline hard sintered compact cutting tool according to any one of claims 1 to 3, wherein the cutting tool has a thickness of not less than 5 µm and not more than 5 µm. 5. The cutting of a polycrystalline hard sintered body according to claim 1, wherein the polycrystalline hard sintered body is joined to a tool base material made of a cemented carbide. tool. 6. A pair of straight cutting edges connected to the nose radius r from the respective ends of the nose radius r of the polycrystalline hard sintered body toward the side of the throw-away tip, respectively. A straight blade having a length within the range of 6 mm and an angle formed by a straight line bisecting the nose radius portion and each of the straight cutting edges is 42 ° ≦ θ ₁₀ and θ ₁₁ ≦ 45 ° is formed. The indexable insert according to any one of claims 1 to 5, characterized in that: 7. The surface of the cutting tool of the polycrystalline hard sintered body includes elements of groups 4a, 5a and 6a of the periodic table and Al, Si,
At least one element selected from the group consisting of element B or at least one compound selected from nitrides, carbides, oxides and solid solutions of at least one metal selected from the group The indexable chip of any one of claims 1 to 6, wherein a coating layer comprising: