JPH11291103A - Coated cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated cutting tool capable of maintaining a high- accuracy cutting at a high efficiency. SOLUTION: In this cutting tool made of ceramic, cemented carbide, cermet or high-speed steel as a base material, at least one of a cutting face, flank, cutting edge ridge and chip flowing groove is coated so that a hard carbon film containing nitrogen is the outermost layer wherein the ratio of nitrogen to carbon is not less than 2 atom % and not more than 30 atom %.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called coated cutting tool in which a wear-resistant coating is formed on the surface of a cutting tool among milling, turning, drilling, gear cutting and the like. It is.

[0002]

2. Description of the Related Art New cutting tool materials are being developed one after another in order to satisfy the demand for higher efficiency and higher precision in cutting. In such a flow of material development, ceramic coating technology on various tool materials has become one of the indispensable tool manufacturing technologies. Further, as a recent trend, in order to further improve the processing efficiency, the cutting speed is becoming higher, and the wear of the cutting edge tends to become more and more intense. In order to suppress such abrasion, titanium carbide (T
iC), titanium nitride (TiN), titanium carbonitride (TiC)
Hard wear-resistant films formed of titanium-based ceramics such as N) are currently most widely used.

However, the wear-resistant coating as described above has a so-called "weld defect" in which a material to be cut (hereinafter referred to as a work material) is welded to the vicinity of a cutting edge of a tool to induce chipping of the cutting edge. There was a disadvantage that the suppression effect was insufficient. This is because the adhesion between the deposit and the wear-resistant coating is high,
This is considered to be because the growth of the constituent cutting edge was caused, and as a result, a phenomenon such as a large-scale chipping at the tip of the cutting edge was caused. In drilling, in particular, when drilling deep holes, the flow-out resistance of chips increases, and the effect of eliminating the phenomenon of causing troubles such as breakage of the drill was insufficient.

As one method of preventing such welding of the work material and suppressing the outflow resistance of chips, a lubricating film made of a layered compound such as molybdenum disulfide is laminated on the above-mentioned wear-resistant film. Tools have also been proposed and are commercially available, but layered compounds such as molybdenum disulfide tend to wear due to their low mechanical strength and exhibit good properties immediately after the start of cutting, but with the wear of the lubricating film, There is a disadvantage that the effect of preventing welding is lost.

A tool coated with a hard coating made of diamond or diamond-like carbon has also been proposed and partially put to practical use. However, since the adhesion strength to a tool base material is low or unstable, the tool is not suitable. There was a problem that the film was easily peeled off and the performance was unstable. As described above, conventional tool materials and coating film materials have not been able to sufficiently satisfy these needs.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention prevents the welding of a work material on the surface of a coated cutting tool, while taking advantage of the advantages of a ceramic coating, and at the same time prevents the work material An object of the present invention is to provide a revolutionary coated cutting tool capable of improving the slip with chips.

[0007]

SUMMARY OF THE INVENTION A first feature of the present invention is that a portion of a surface of a cutting tool made of a cemented carbide, a high-speed steel, or the like, which is involved in cutting, that is, a cutting portion. Any one or more of the flank rubbing with the material, the rake face rubbing with the chips, the cutting edge ridge line at the boundary between these two surfaces, and the four parts of the groove through which the chips flow, And a hard carbon film containing nitrogen.

The second feature is that the ratio of nitrogen to carbon in the nitrogen-containing hard carbon film is not less than 2 atomic% and not more than 30 atomic%, and that hydrogen is contained as one of the inevitable impurities.

A nitrogen-containing hard carbon film directly coated on a substrate, or a single-layer structure, or the nitrogen-containing hard carbon film is formed on an underlayer formed adjacent to the substrate,
The components of the underlayer are carbides, nitrides, carbonitrides, and AlN, Si of the elements of groups IVa, Va and VIa of the periodic table.
A third feature is that it is composed of C, Si ₃ N ₄ , B ₄ C, BN and their compounds, mixtures, and multilayer structures.

[0010] Applications of such coated cutting tools include:
It is suitable for cutting soft and easy-to-seize materials such as aluminum alloys and copper alloys, as well as the most common iron-based alloys, which is another characteristic. The types of cutting include all types of cutting such as turning, milling, milling with an end mill, drilling with a drill, and gear cutting with a cutter.

[0011]

As described above, in a cutting tool, the friction and wear characteristics of a portion in contact with a cutting material or a chip are an important factor influencing the performance of the tool. The present inventor has studied coatings that can make use of various characteristics of various ceramics, and found that a portion of the cutting tool involved in cutting, that is, a flank surface that rubs with the work material, rubs with chips. A rake face, a ridge line at the boundary between the two faces, and one or more of the four portions with a groove through which the chips flow are coated with a hard carbon film containing nitrogen. It has been found that if it is done, it is possible to eliminate the welding phenomenon during the cutting process and to suppress the chip outflow resistance. It has also been found that it is possible to eliminate the peeling phenomenon that has been apt to occur in the conventionally used diamond or diamond-like carbon film. The reason for this is that the addition of nitrogen causes the hard carbon film, which has a material and structure close to that of a diamond-like carbon film, to reduce the internal compressive stress, improve the wear resistance of the film itself, and have an affinity with the underlying layer (adhesion This is considered to be due to improvement in the aspect such as improvement of the abrasion resistance.

The present inventor has investigated the effect of the addition of nitrogen to the hard carbon film on the internal stress of the film. As a result, when the residual compressive stress of the diamond-like carbon film containing no nitrogen is set to 1,
The residual compressive stress of a nitrogen-containing hard carbon film in which the ratio of nitrogen to carbon is 3 atomic% is 0.8, and the residual compressive stress of the hard carbon film is remarkably reduced by adding several atomic% of nitrogen. Was. If the compressive stress is too high, not only the film itself is crushed, but also external stress during cutting is applied, and the film tends to be damaged.
Therefore, it is presumed that the addition of nitrogen is effective in suppressing the compression damage of the membrane.

Next, the present inventor investigated the effect of the addition of nitrogen to the hard carbon film on the wear resistance of the film. As a result, when the wear amount of the diamond-like carbon film containing no nitrogen was set to 1,
In the case of a nitrogen-containing hard carbon film in which the ratio of nitrogen to carbon was 3 atomic%, the wear amount was 0.6, and it was found that the wear resistance of the hard carbon film was remarkably improved by adding several atomic% of nitrogen. . In this test, the opposing material was a steel ball of bearing steel (JIS SUJ2), and a ball-on-disk test was performed under the condition that no lubricating oil was used. The reason why the wear resistance is remarkably improved in this way is presumably due to the reduction of the residual compressive stress due to the addition of nitrogen. Another reason is considered to be the formation of a carbon nitride compound. A carbon nitride compound is a new material expected as a hard substance exceeding diamond, but there is no example of a carbon nitride synthesized in perfect form. Although only a small amount of nitrogen is present inside the film of the nitrogen-containing hard carbon film according to the present invention,
It is possible that the carbon nitride has a structure in which fine particles of carbon nitride are dispersed in a matrix of diamond-like carbon, and this carbon nitride component is considered to have had a favorable effect on the improvement of wear resistance.

The present inventors have confirmed that the addition of nitrogen to the diamond-like carbon film has a favorable effect on the adhesion strength of the film. In the present invention, excellent effects can be obtained even if the nitrogen-containing hard carbon film is formed directly on the surface of the tool base material.

Another feature of the present invention is that carbides, nitrides, carbonitrides, and AlN, SiC, Si ₃ N ₄ , B _{4 of} elements IVa, Va, and VIa of the periodic table.
A multi-layer structure in which a nitrogen-containing hard carbon film is formed as an outermost layer via one or more intermediate layers made of C, BN, a compound thereof, and a mixture is used. It is known that elements such as group IVa, Va, and VIa of the periodic table, Al, Si, and B easily react with nitrogen and carbon.

The present inventor, together with co-workers, utilizes the reaction with this carbon to form a diamond or diamond-like carbon film on a substrate, thereby forming a group IVa, Va, or VIa of the periodic table. It has been proposed to use the element itself or elements such as Al, Si, and B, or their carbides, carbonitrides, etc.
No. 58372, JP-A-58-126972,
JP-A-61-104078, JP-A-62-116
767). However, these proposals differ from the present invention in that the outermost layer is a diamond or hard carbon film (diamond-like carbon film). That is, as described above, in order to improve the adhesion between the intermediate layer material and the hard carbon film, it is extremely effective to add even a small amount of nitrogen to the hard carbon film. This is because carbon often changes to a “low-hardness graphitic substance”, and the low-hardness substance is formed in the material, which impairs the mechanical strength of the interface and the material itself. In this case, it is presumed that the presence of nitrogen can suppress the formation of a graphitic substance, and also has the effect of improving the adhesion strength by causing a nitridation reaction with an element in the intermediate layer constituent material.

The amount of nitrogen added to the hard carbon film is preferably such that the ratio of nitrogen to carbon is 2 atomic% or more and 30 atomic% or less. If the ratio of nitrogen is less than 2 atomic%, the effect of adding nitrogen cannot be obtained. The nitrogen ratio is 3
When the amount exceeds 0 atomic%, the hardness of the film tends to be extremely reduced, which is not preferable. The ratio of carbon to nitrogen is important. When the composition ratio (content) of carbon and nitrogen in the nitrogen-containing hard carbon film is A atomic% and B atomic%, respectively, the ratio of nitrogen to carbon is It was assumed that the ratio of nitrogen (atomic%) = B ÷ (A / 10B) × 100. For the measurement of such a composition ratio, any method such as chemical analysis and physical analysis can be applied.
The present inventors performed analysis using X-ray photoelectron analysis (XPS method). In the analysis, "ion beam sputtering" for physically removing adsorbed impurities on the outermost surface of the film was used.

When a hydrocarbon gas is used in forming the nitrogen-containing hard carbon film, hydrogen is contained as the inevitable impurity. The content can be changed depending on the conditions. For example, the composition ratio to carbon is about 30 to 40 atomic%. Hydrogen lowers the hardness of the film and lowers the compressive residual stress, and thus has the effect of increasing the film thickness. Therefore, when a nitrogen-containing hard carbon film is formed from solid carbon as a raw material, hydrogen is not included as an unavoidable impurity, but hydrogen may be added to the film-forming atmosphere to contain hydrogen if necessary.

As a use of the coated cutting tool of the present invention, it is particularly preferable to process a soft cutting material such as an aluminum alloy or a copper alloy, which is likely to be fused to the tool surface.
The details will be described with reference to embodiments. Although only the results for the drill are described in the embodiments, the same effect can be obtained even with tools other than the drill, for example, an end mill, a cutting tool, a tip-changeable insert, a metal saw, a gear cutting tool, and a reamer. Needless to say. In the embodiment, only the tool made of high-speed steel and cemented carbide is described. However, it is considered that similar effects can be obtained with other materials for cutting tools such as ceramics and cermets.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be shown in Examples.

[0021]

EXAMPLE In a known method of forming a diamond-like carbon film by a plasma CVD method in a high-frequency electric field, a nitrogen-containing hard carbon film was formed by adding nitrogen gas to methane gas as a raw material gas. The thickness of the obtained nitrogen-containing hard carbon film was 1 μm. By changing the ratio of nitrogen gas added to the raw material gas, 0 atomic% was obtained.
And a nitrogen-added hard carbon film having a nitrogen ratio of up to 35 at%. This nitrogen-added hard carbon film is formed by high-speed steel SK
It is formed so as to cover the blade part surface of a twist drill using H51 as a base material. The size of the drill was 3.2 mm in diameter and 150 mm in length. Various intermediate layer materials were formed on the surface of the drill by using a sputtering method, an arc ion plating method, a hollow cathode discharge ion plating method, etc., and a drill having a nitrogen-containing hard carbon film formed thereon was also prepared. .

The drills were drilled with an aluminum alloy (JIS A5052) to evaluate the performance of the drills. The cutting conditions are 100 cutting speeds around the periphery of the drill.
m / min, feed rate 0.2mm / rotation, hole depth 50mm, water-soluble cutting oil external lubrication method, change in cutting resistance when drilling, number of drilling holes when drill breaks, drill at the end of test holly Was observed. Table 1 shows the film structures tested and the cutting test results. As can be seen from Table 1, each of Examples 1 to 20 has a smaller cutting resistance, an extremely long drill life, and a hard carbon film in a sound state even after the test is completed, as compared with Comparative Examples 1 to 5. Was confirmed.

[0023]

[Table 1]

In the same manner as described above, a nitrogen-containing hard carbon film was formed by a plasma CVD method using a DC electric field instead of a high-frequency electric field. The base material is cemented carbide (JIS P30)
Using a twist drill having an oil hole of φ8.5, a prototype of the film structure shown in Table 2 was produced. Drilling of aluminum alloy (ADC12) was performed on these drills, and the performance of the drills was evaluated. The cutting conditions were as follows: cutting speed at the outer periphery of the drill: 500 m / min, feed: 0.4 mm / rotation
A hole depth of 26 mm, a water-soluble cutting oil was used as an internal lubrication method, and changes in cutting resistance during drilling and the state of the drill at a cutting length of 30 m were observed. Table 2 shows the film structures that were tested and the cutting test results. As can be seen from Table 2, Examples 21 to 4
0 is smaller than Comparative Examples 6 to 10, the cutting resistance is smaller,
It was confirmed that the drill life was extremely long and that the hard carbon film was in a healthy state even after the test was completed.

[0025]

[Table 2]

[0026]

According to the present invention, it is possible to prevent the welding of a work material at a part involved in cutting, such as a rake face and a flank face of a cutting tool, and to make the flow of chips smooth, thereby reducing the wear of the tool. Not only can proceed gently, but also the wear resistance of the coating film can be maximized. The present invention is useful because it can be used in all of drilling, end milling, milling, and turning.

Claims (8)

[Claims] 1. A cutting tool based on ceramics, cemented carbide, cermet or high-speed steel, wherein the cutting tool has a rake face, a flank face, a cutting edge ridge portion, and a groove through which chips flow. At least one or two or more of them are coated with a wear-resistant coating, and the outermost layer of the wear-resistant coating has carbon as a main component and a nitrogen to carbon ratio of 2 to 30 atomic%. A coated cutting tool comprising: a nitrogen-containing hard carbon film containing unavoidable impurities as components other than carbon and nitrogen. 2. The coated cutting tool according to claim 1, wherein one of the unavoidable impurities is hydrogen. 3. The coated cutting tool according to claim 1, wherein the nitrogen-containing hard carbon film is directly formed on the surface of the cutting tool substrate. 4. The coated cutting according to claim 1, wherein the coated cutting has a multilayer wear-resistant coating structure in which one or more intermediate layers are provided between the nitrogen-containing hard carbon film and the cutting tool base material. tool. 5. The intermediate layer in contact with the nitrogen-containing hard carbon film,
Carbide, nitride, carbonitride, and AlN, SiC, Si ₃ N ₄ , B ₄
The coated cutting tool according to claim 1, 2 or 4, comprising C, BN, a compound thereof, and a mixture thereof. 6. The coated cutting tool according to claim 1, wherein the cutting tool is for non-ferrous metal cutting. 7. The coated cutting tool according to claim 6, wherein the cutting tool is any one of a drill, an end mill, a cutting tool, a tip-changeable insert, a metal saw, a gear cutting tool, and a reamer used for cutting an aluminum alloy. 8. A titanium nitride film is formed directly on the surface of a drill or end mill base made of cemented carbide or high-speed steel, and the outermost layer is formed via a titanium carbide film provided on the titanium nitride film. Item 6. A coated cutting tool comprising the nitrogen-containing hard carbon film according to item 1 or 2.