JP2000190108A - Polycrystalline hard sintered body cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high machining accuracy and excellent machined surface roughness by specifying the radius of curvature of a curve produced in the intersection point part of a flank and a cutting face or a flank and a negative land face by cutting edge attaching operation. SOLUTION: A stepped support seat is provided in a corner part of a cemented carbide-made tool base material 2, a cBN polycrystalline sintered body 3 containing 20 vol.% or more of cBN particles having the particle diameter ranging from 0.01 μm to 5 μm is joined to the support seat by brazing, and then the sintered body 3 is subjected to cutting edge attaching operation to make a cutting tool. Cutting edge operation is performed by grinding using a diamond grinding wheel, and an intended cutting edge 6 is formed in an intersection part of a cutting face 4 and a flank 5. The cutting edge 6 is shaped like a section having a negative land 7 for strengthening the knife edge or like a section without a negative land, and the flank 5 and the cutting face 4 or the flank 5 and the negative land face 7 are connected to each other through a curve 8 with a radius of curvature of 0.1 μm to 5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a polycrystalline sintered tool containing cubic boron nitride, which is capable of forming a cutting edge with excellent sharpness and enabling high-precision and high-surface roughness cutting of a hard material. The present invention relates to a compacted polycrystalline sintered tool.

[0002]

2. Description of the Related Art Fine cBN (cubic boron nitride)
Is sintered by using various kinds of binders, that is, polycrystalline c
The BN sintered body shows excellent performance for cutting a high hardness iron group metal or cast iron. In particular, when used for machining hardened steel with high hardness, high machining accuracy and excellent finished surface roughness can be obtained. For hardened steel, a cBN sintered body tool was used from the previous grinding process. It has been replaced by cutting.

[0003] However, this cBN sintered body, which exhibits excellent performance in the processing of a high-hardness material, is also required when extremely high processing accuracy and extremely excellent finished surface roughness are required in the processing of a high-hardness material. Unable to answer the request,
When the demands on processing accuracy and finished surface roughness are severe, processing has still to rely on costly grinding.

[0004] Therefore, an object of the present invention is to devise a cutting edge portion of a polycrystalline cBN sintered compact cutting tool so as to obtain higher machining accuracy and superior finished surface roughness than ever before. And

[0005]

According to the present invention, there is provided a cutting tool having a cutting edge formed of a polycrystalline hard sintered body containing 20% by volume or more of cBN. And a rake face or a flank face and a negative land (negative brand) face for strengthening the cutting edge are connected by a curve in a sectional view, and the radius of curvature of the curve is 0.1 μm.
That is, it was in the range of 5 μm.

This tool uses cB contained in a polycrystalline sintered body.
It is preferable to limit the particle size of the N particles to a range of 0.01 μm to 5 μm.

The wedge angle of the cutting edge of the tool is preferably in the range of 90 ° to 125 ° when there is a negative land, and 65 ° to 125 ° when there is no negative land.

[0008] Further, it is preferable that the cutting tool constituted by joining the polycrystalline sintered body to a tool base material of a different material uses a tool base material made of cemented carbide.

Note that a curve having a radius of curvature of 5 μm or less is represented by ♯
It can be formed by a method of performing blade processing using a diamond grindstone of about 3,000 to $ 14,000.

[0010]

1 and 2 are schematic views showing the vicinity of the cutting edge of a polycrystalline sintered compact cutting tool containing cBN. A conventional cutting tool of this type has a cutting edge provided with a diamond grindstone of about $ 800. The finished cutting edge is such that the flank 5 and the rake face 4 of the tool, or the flank 5 and the negative land surface 7 for strengthening the cutting edge are connected via a curve 8 (roundness generated in processing). The radius of curvature R of the curve 8 in the section perpendicular to the longitudinal direction of the cutting edge at this time is 10 μm.
m, and a radius of curvature smaller than that cannot be obtained by the conventional processing method.

The inventor of the present invention has found that even with such a small radius of curvature, the curve 8 obstructs the substantial rake angle of the cutting edge to meet the strict requirements for processing accuracy in high-hardness material processing and finished surface roughness. I found out what was causing the failure.

The cutting force, especially the backing force, has a great effect on the processing accuracy and the finished surface roughness. The sharpness of the cutting edge of the conventional cutting edge having a curvature radius R of the curve 8 of about 10 μm is insufficient. It was found that the back force increased due to the decrease in sharpness, and that the cutting edge abrasion occurred early due to the large cutting force. As a result, it was found that there was a limit to the processing accuracy and the finished surface roughness.

In the cutting of a high-hardness material, since the back force is particularly high and the fluctuation amount of the back force is large, the degree of sharpness of the blade greatly affects the processing accuracy and the finished surface roughness. Will be. The inventors have obtained such a conclusion and first studied a method for obtaining a curve 8 having a radius of curvature R of 10 μm or less.
It has been found that the purpose can be achieved by grinding with a diamond grindstone of about 0 to $ 14,000.

Next, when an appropriate value of the radius of curvature R of the curve 8 was examined by performing a cutting experiment with a prototype, the value was found to be 0.1.
It was found to be in the range of 1 μm to 5 μm, more preferably 0.1 μm to 1 μm. In terms of sharpness, the smaller the radius of curvature R is, the better.
It is actually difficult to obtain a radius of curvature of 1 μm or less.
Was set to 0.1 μm.

In this manner, the radius of curvature of the curve generated at the intersection between the flank and the rake face or the intersection between the flank and the negative land is in the range of 0.1 μm to 5 μm, the actual rake angle of the tool is reduced, and the sharpness of the cutting edge is reduced. The cutting force, especially the backing force, is reduced, and the processing accuracy and the finished surface roughness are superior to those in the conventional processing of hardened materials.

In the case of processing a high-hardness material, a high hardness is also required for the tool material. Therefore, the sintered body used in the present invention has a cBN content of 20% by volume or more. In addition, since the polycrystalline sintered body is unlikely to cause chipping due to cleavage observed in single-crystal cBN, the sintered body used was a polycrystalline product.

In addition, cBN contained in the polycrystalline sintered body
When the particle size of the particles is less than 0.01 μm, agglomerated portions of fine particles that cause chipping of the cutting edge in the sintered body are easily generated,
On the other hand, if the cBN particle is larger than 5 μm, it becomes difficult to control the radius of curvature of the edge portion to a target range due to the dropout of the particle. Therefore, the particle size of the contained cBN particles is 0.
It is preferably in the range of from 01 μm to 5 μm.

The intersection angle between the flank and the rake face is 65 °.
If it is less than 1, the wedge angle of the cutting edge is too small, and the chipping of the cutting portion is likely to occur at the beginning of cutting. Further, if the intersection angle between the flank and the rake face or the flank and the negative land face exceeds 125 °, the increase in cutting resistance becomes remarkable, and the required processing accuracy cannot be obtained. Therefore, the intersection angle is preferably limited to a range of 65 ° to 125 °.

Further, a steel base material can be considered as a tool base material for joining the hard sintered body, but a high rigidity is also required for the tool base material in high-precision processing of a high-hardness material. Hard alloys are best.

[0020]

DETAILED DESCRIPTION OF THE INVENTION FIGS. 3 (a), 3 (b) and 3 (c)
1 shows an embodiment of a cutting tool according to the present invention. This is an example of application to a throw away tip. Each of the indexable inserts 1 is provided with a stepped support seat at the corner portion of the cemented carbide tool base material 2, and cBN particles having a particle size in the range of 0.01 μm to 5 μm are provided on the support seat. It is made by brazing and joining a cBN polycrystalline sintered body 3 containing at least 20% by volume (in FIG. 3 (c), with a base metal), and then subjecting the sintered body 3 to a blade process. The blade processing is
The target cutting edge 6 is formed at the intersection of the rake face 4 and the flank face 5 by polishing with a diamond grindstone of $ 3,000 to $ 14,000. The cutting edge 6
It has a cross-sectional shape as shown in FIG. 1 having a negative land 7 for strengthening the cutting edge, or a cross-sectional shape as shown in FIG. 2 having no negative land, and is formed between the flank 5 and the rake surface 4 or between the flank 5 and the negative land 7. The intervals are connected via a curve 8 having a radius of curvature of 0.1 μm to 5 μm.

1 and 2 are the rake angle of the tool, α is the clearance angle, δ in FIG. 1 is the negative land angle (the intersection angle between the negative land surface 7 and the flank 5), and β in FIGS. The wedge angle of the cutting edge is shown. In the case of the indexable insert of FIG. 3, β is 90 ° to 125 ° for the one having the cutting edge structure of FIG. 1, and β is 65 ° to 12 ° for the one having the cutting edge structure of FIG.
It is set to a numerical value in a preferable range of 5 °.

The shape of the indexable insert to which the present invention is applied is not limited to the shape shown in FIG. The application of the present invention is not limited to a throw-away tip.

Hereinafter, detailed embodiments of the present invention will be described.

Example 1 A small piece of a cBN polycrystalline sintered body containing 50 volume% of cBN particles having a particle size of about 0.5 μm is brazed to a corner portion of a cemented carbide tool base material and thrown. I got away chips. The prototype throwaway inserts are the four types shown in Table 1, and all have a cutting edge having a cross-sectional shape shown in FIG. In addition, the comparative product A has been subjected to cutting with a diamond grindstone of $ 800, and the inventive products B, C and D have been subjected to cutting with a diamond grindstone of $ 3,000 or more. The radius of curvature of the curve 8 formed between the negative land surface 7 and the negative land surface 7 is different as shown in Table 1.

[0025]

[Table 1]

The cutting performance of these four samples A to D was evaluated by performing a cutting test under the following cutting conditions. Table 2 shows the results.

[0027] Cutting Conditions working method: outer径旋cutting Workpiece: cylindrical carburized Irizai (SCM415) Workpiece Hardness: rotational speed of H _RC 62 Workpiece outer peripheral surface: 100 m / min cut: 0.2 mm Feed: 0.05 mm / rev Cutting time: 5 minutes Required finished outer diameter: 30 mm ± 10 μm Required roundness: Error 3 μm or less

[0028]

[Table 2]

As can be seen from Table 2, comparative product A does not have the required finished diameter and roundness required. On the other hand, the required accuracy was satisfied for all of the inventions B, C, and D, and the effectiveness of setting the radius of curvature R of the curve 8 in FIGS.

Example 2 In order to investigate the effect of the particle size of the cBN particles contained in the hard sintered body on the radius of curvature of the curve 8 and the processing accuracy, Table 3 was used.
Comparative Examples E and J were prepared by producing a polycrystalline hard sintered body containing 65% by volume of each of the cBN particles shown in (1), and brazing the sintered body to the tip of a 5 mm-diameter cemented carbide columnar shank.
In addition, boring tools for Inventions F to I were prepared.

In all of the samples E to J, the cutting was performed using a diamond grindstone of $ 10,000.

Table 3 shows the radius of curvature of the curve formed at the intersection of the flank of the cutting edge and the negative land surface by the cutting process.

[0033]

[Table 3]

The comparative product E had a non-uniform structure due to agglomeration of cBN particles, so that the blade portion was chipped during the blade processing.

Next, in order to evaluate the cutting performance of the other samples F to J except the comparative product E in which the cutting edge could not be formed well, cutting was performed under the following conditions.

[0036] Cutting Conditions working method: inner diameter boring Workpiece: cylindrical bearing steel (SUJ2) Workpiece Hardness: rotational speed of H _RC 60 Workpiece diameter surface: 80 m / min cut: 0.05 mm Feed: 0 .04 mm / rev Cutting time: 3 minutes Required finished inner diameter: 5.5 mm ± 5 μm Required roundness: Error 2 μm or less Table 4 shows the results of this cutting test.

[0037]

[Table 4]

The comparative product J, in which the cBN particles contained had a large particle size and the radius of curvature of the curve generated between the flank and the negative land surface was about 10 μm, had a large cutting resistance and a large fluctuation in the resistance. In such a case, so-called chattering occurred, and it was impossible to continue processing. On the other hand, invention products F to I
It was found that the required accuracy was satisfied in each case, and that the particle size of the contained cBN particles had a great effect on the effect of the invention.

Example 3 It was investigated how the flank and rake face of the tool, or the intersection angle between the flank face and the negative land face and the wedge angle of the cutting edge affect machining performance and machining accuracy.

For the investigation, a 0.7 μm particle size cB
Indexable chips K to S having a structure in which a cBN polycrystalline sintered body containing 63% by volume of N particles was brazed and joined to a corner portion of a cemented carbide tool base material. In all of these samples, the cutting was performed using a diamond grindstone of $ 8,000, and the radius of curvature of the curve of the cutting edge was 1 μm.
There is almost no difference. Table 5 shows the relief angle (α in FIG. 1), negative land angle (δ in FIG. 1), and wedge angle of the cutting edge (β in FIG. 1) for each sample.

[0041]

[Table 5]

Table 6 shows the evaluation results of the samples shown in Table 5.
The cutting conditions for the evaluation are as follows.

[0043] Cutting Conditions working method: outer径旋cutting Workpiece: cylindrical die steel (SKDII) Workpiece Hardness: rotational speed of H _RC 65 Workpiece peripheral surface: 100 m / min cut: 0.1 mm Feed: 0.1mm / rev Required finish outer diameter: 15mm ± 8μm Required roundness: Error 3μm or less

[0044]

[Table 6]

In this test, the specimen K having a small wedge angle at the cutting edge lacked the cutting edge strength, and the cutting portion was lost at the beginning of cutting.
Continuous processing was not possible.

The sample S having a wedge angle exceeding 125 ° had a large cutting resistance and a large variation in the resistance, and chatter occurred during the cutting, so that the evaluation by continuous cutting could not be performed. On the other hand, the samples L to R all satisfy the required accuracy.

As can be seen from the above experimental results, when the radius of curvature of the curve generated at the intersection between the flank and the rake face or the intersection of the flank and the negative land is set to 5 μm or less, and the wedge angle of the cutting edge is appropriately set. Thus, high-precision processing of a high-hardness material can be performed as compared with the related art.

[0048]

As described above, the polycrystalline hard sintered tool of the present invention has a hard radius of curvature of a curve generated at the intersection between a flank and a rake face or an intersection between a flank and a negative land face by cutting. By adjusting the particle size of the cBN particles contained in the sintered body and using a diamond grindstone with an extremely small grain size of 3,000 or more, the cutting edge is cut to a size of 5 μm or less, which was not obtained conventionally. As the taste has been further enhanced, machining accuracy and finished surface roughness are higher than in the past when cutting hardened materials.Even when extremely high machining accuracy and extremely excellent finished surface roughness are required. The processing cost can be reduced by replacing the grinding with the cutting.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a cross section of a cutting edge of a tool according to the present invention.

FIG. 2 is a schematic view showing another example of the cross section of the cutting edge.

FIG. 3 (a) is a perspective view showing an example of the tool of the present invention (triangular throwaway tip). FIG. 3b is a perspective view showing another example of the tool of the present invention (quadrangular throwaway tip). Perspective view showing another example of a tool (rhombic indexable insert)

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 indexable insert 2 tool base material 3 cBN polycrystalline sintered body 4 rake face 5 flank face 6 cutting edge 7 negative land face 8 curve R Curvature radius of curve 8 α relief angle β wedge angle γ rake angle δ negative land angle

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kunihiro Tomita 1-1-1, Koyokita, Itami-shi In Itami Works, Sumitomo Electric Industries, Ltd. (72) Tetsuo Nakai 1-1-1, Koyokita, Itami-shi Sumitomo Electric Industries, Ltd. Itami Works

Claims (4)

[Claims] 1. A cutting tool in which a cutting edge is formed by a polycrystalline hard sintered body containing cubic boron nitride in an amount of 20% by volume or more, a flank and a rake face of the tool, or a flank and a negative land face for strengthening a cutting edge. Are connected by a curve in a sectional view, and the radius of curvature of the curve is in the range of 0.1 μm to 5 μm. 2. The cutting tool according to claim 1, wherein the particle diameter of the cubic boron nitride particles contained in the polycrystalline sintered body is limited to a range of 0.01 μm to 5 μm. 3. The wedge angle of the cutting edge is set in the range of 90 ° to 125 ° for a tool having a negative land, and 65 ° to 125 ° for a tool without a negative land.
Or a polycrystalline hard sintered compact cutting tool according to 2 above. 4. The polycrystalline sintered compact cutting tool according to claim 1, wherein the polycrystalline sintered compact is joined to a cemented carbide tool base material.