JPH0780713A - Miniature drill coated with hard carbon film - Google Patents

Abstract

PURPOSE:To sharply improve chipping resistance by increasing the coating thickness of a hard carbon film in a cutting edge ridge part than the film thickness of the hard carbon film in a flank. CONSTITUTION:The coating thickness t1 of a carbon film C applied to a cutting edge ridge part K is increased than the coating thickness t2 of a carbon film C applied to flanks 2a and 2b (that is, t1/t2>1). Consequently the entrainment of a chip into a groove part is sharply restrained to sharply increase the discharge of the chip to prevent the breakage of a drill to the utmost, and also to sharply restrain lowering cuttingness. Effect for improving chip discharge can efficiently be displayed by making t1/t2 over 1 like this, but on the other hand, since trouble such as lowering working accuracy appears when the carbon film coating thickness t1 in the cutting edge ridge part K is too thickened, it is preferable that the thickness is to be adjusted so that t1/t2 can become 1.5 or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a miniature drill comprising a base material such as cemented carbide and the surface of the base material coated with a hard carbon film, with improved breakage resistance and excellent cutting performance for a long time. The present invention relates to an improved miniature drill that can be effectively used.

[0002]

2. Description of the Related Art Conventionally, as a drill for drilling, a drill having a base material of cemented carbide or various ceramics, or a drill in which a cutting action portion of the drill is coated with high hardness ceramics such as TiN or TiC is practically used. Has been converted. However, in recent years, work materials used for cutting work tend to have higher hardness and harder to cut, and the conventional tools as described above are often difficult to handle.

For example, in the field of processing electronic integrated circuit laminated boards (printed boards) and the like, as the printed boards are multi-layered and the strength of the boards is increased, for example, the difficulty of cutting due to the resin reinforcement by various glass fibers is rapidly increasing. A small-diameter drill (miniature drill) having excellent wear resistance and breakage resistance that can cope with these difficult-to-cut materials has been earnestly desired.

In order to meet these demands, measures have been taken such as devising cutting conditions during drilling and devising the composition of cemented carbide which is a general base material of miniature drills. The drill life is not satisfactory even by the means.

As a measure for solving such a problem, a method of coating various hard films on the surface of a base material forming a drill has been studied. Above all, research on vapor phase synthesis of a hard carbon film typified by diamond and application development thereof for cutting tools and the like are actively underway. This is a diamond T
This is because it has higher hardness and higher thermal conductivity than conventional metal compound-based hard films such as iN, and has excellent wear resistance and heat dissipation during cutting. It has attracted attention as a coating material that enables machining of difficult-to-cut materials, high-speed machining, and precision machining that metal compound-based hard film coated tools cannot handle.

That is, an attempt to improve wear resistance by coating the cutting action portion of a drill with a hard carbon film such as diamond is disclosed in, for example, JP-B-61-50724 and JP-A-2-48106. Kaihei 4-2758
No. 12, Japanese Patent Laid-Open No. 4-210315 and the like. However, even with these disclosed techniques, the cutting performance for the above-mentioned difficult-to-cut materials is insufficient.

The biggest problem is breakage of the drill,
Especially, in the case of an ultra-fine miniature drill having a drill shaft diameter of about 0.5 mm or less, this breakage is pointed out as a serious problem. For example, as described in JP-A-4-13506, when ceramics is used as the base material, the toughness is worse than that using the cemented carbide base material, and thus the breakage resistance is worse. In addition, JP-A-4-275812
As described in Japanese Patent Laid-Open Publication No. JP-A No. 2003-242242, improvement measures such as specifying the hard carbon film-covered portion to the cutting edge portion have been taken, but even with these means, the breakage resistance cannot be sufficiently improved.

That is, in the conventional miniature drill coated with a hard carbon film, the drill breaks before the excellent wear resistance of the hard carbon film is effectively exhibited.
It is a major cause of shortening the life.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its purpose is to provide a drill coated with a carbon film as an abrasion resistant film, particularly a miniature drill. The present invention aims to provide a miniature drill having improved breakage resistance and capable of sustaining excellent cutting performance for a long period of time.

[0010]

Means for Solving the Problems The constitution of the present invention which has been able to solve the above problems is to cover a hard carbon film at a cutting edge in a miniature drill in which at least a cutting action part is covered with a hard carbon film. The gist is that the thickness (t ₁ ) is made larger than the coating thickness (t ₂ ) of the hard carbon film on the flank. In this drill, the ratio of the coating thickness t ₁ to t ₂ (t ₁ /
t ₂ ) is preferably more than 1.0 and 1.5 or less, and such a structural feature is applied to a miniature drill having a shaft diameter of 0.5 mm or less and a twist angle of 20 to 30 degrees. Sometimes more effective.

[0011]

[Function] The general shape and structure of the drill are shown in FIG. 1 (A) (front view), FIG. 1 (B) (side view of essential parts) and FIG.
-I line main section enlarged cross-sectional view), in the figure A is a cutting action portion, 1 is a scooping surface, 2a is a first flank surface, 2b is a second
The flank surface, B is the base material, C is the hard carbon film, D is the shaft diameter, and θ is the twist angle. The film thickness t of the hard carbon film C is substantially constant over the entire cutting surface. It is configured.

The inventors of the present invention have investigated the cause of breakage from various angles for the hard carbon film-covered miniature drill having such a shape and structure. As a result, the main cause of the breakage of the drill is the chip discharge property of the cutting material. In this case, in many cases, the chip discharge performance of metal materials such as aluminum used as an entry board during cutting has a significant adverse effect, rather than the chip discharge performance of resin-reinforced glass fibers, etc. Was confirmed.

That is, the cut chips must be sequentially discharged to the outside along the groove portion as the cutting progresses. However, in the conventional carbon film-covered miniature drill as shown in FIG. 1 (C), Since the carbon film coating reduces the sharpness of the cutting edge, metal chips such as aluminum are continuously connected and wound into the groove. Particularly in a miniature drill having a small shaft diameter, the chips are clogged in the thin groove portion, which causes a great resistance to the rotation of the drill, which causes breakage of the tip portion of the drill and also has a great adverse effect on the cutting performance.

Therefore, it is considered that if the chip discharging property is improved, the breakage of the drill is suppressed and the cutting property is also improved. Therefore, the research was advanced along the line mainly on the shape and structure of the drill. As a result, the coating thickness of the hard carbon film coated on the cutting action portion A is devised, and the coating thickness t ₂ of the carbon film C coated on the cutting edge portion K as shown in FIG.
If the coating thickness t ₁ of the carbon film C coated on a and 2b is made larger (that is, t ₁ / t _{2 is set} to 1 or more), the inclusion of chips in the groove portion is significantly suppressed, and its dischargeability is improved. Is significantly increased, and breakage of the drill is prevented as much as possible.
I have learned that the reduction in machinability can be greatly suppressed.

Although the reason why the chip discharging property is improved by increasing the thickness of the carbon film of the cutting edge portion has not been clarified yet, the cutting edge portion having such a structure has It is speculated that the form of will change and that it will have a positive effect on its emission properties.

The above-mentioned effect of improving the chip discharge property is effectively exhibited by setting t ₁ / t ₂ to 1 or more as described above, but on the other hand, the coating thickness of the carbon film in the cutting edge portion K is t
_{If 1} is too thick, obstacles such as deterioration in processing accuracy will appear. Therefore, it is desirable to adjust the wall thickness so that t ₁ / t ₂ is 1.5 or less. Further, the coating thickness t ₁ of the cutting edge portion and the coating thickness t _{2 of the} flank face may vary slightly depending on their respective positions, but even if the above requirements are locally deviated, they are average. If the coating thickness ratio satisfies the above requirements, the object of the present invention can be sufficiently achieved.

The carbon film, particularly the carbon film coating thickness t ₁ of the ridge of the cutting edge, is preferably thick from the viewpoint of life. This is because the time until the worn surface reaches the film / base material interface is delayed as the film thickness increases. However, this film thickness also affects the processing accuracy, and the sharpness of the cutting edge portion decreases as the carbon film becomes thicker.
In order to obtain excellent wear resistance while maintaining a sufficient cutting effect, the coating thickness of the carbon film C is preferably about 5 to 30 μm.

Further, the present inventors have further studied the size and structure of the drill that can more effectively exhibit the breakage prevention effect by adjusting the carbon film thickness as described above, and as a result, the shaft diameter is 0. It has been found that when the twist angle is 20 to 30 degrees and the diameter is 5 mm or less, it is more effectively exhibited.

The hard carbon film C coated on the outer surface of the cutting action portion A of the drill according to the present invention is a conventional scanning electron microscope,
It can be confirmed as an aggregate of carbonaceous fine particles by an instrumental analysis method such as a transmission electron microscope, X-ray diffraction or electron diffraction, and the crystal structure of the carbonaceous fine particles mainly has a crystalline diamond structure. is there. However, the hard carbon film C in the present invention does not have to be entirely composed of crystalline diamond fine particles, and is a mixture with amorphous diamond or graphite, or a trace amount that is not substantially carbonaceous. It may contain a small amount of an added metal component or the like.

Further, the method of forming the carbon film C is not particularly limited, but a general method is, for example, a microwave plasma CVD method, a hot filament method, or a high frequency plasma CVD method.
Method, ion beam method, and other vapor phase synthesis methods. As a raw material gas used in this synthesis, a hydrocarbon-based gas such as methane or ethane, an alcohol-based gas such as methanol or ethanol, or a carbon oxide-based gas such as carbon monoxide can be used. A mixed gas of a carbon-containing gas and hydrogen is used. Further, as the material forming the base material of the drill, various ceramics other than cemented carbide can be used.

[0021]

EXAMPLES Next, examples of the present invention will be shown, but the present invention is not limited by the following examples, and may be carried out with appropriate modifications within a range compatible with the gist of the preceding and following description. Of course, it is possible, and all of them are included in the technical scope of the present invention.

Example 1 Microwave plasma CVD was applied to the tip surface including the cutting action part in a miniature drill base material having a shaft diameter of 0.85 mm and made of a K-type cemented carbide (binder component: Co, TaC) as a base material. A carbon film was coated by contacting a methane-hydrogen mixed gas excited by the method. At this time, the coating thickness of the ridge of the cutting edge (t
₁ ) and flank face coating thickness (t ₂ ) ratio (t ₁ / t ₂ ) is 0.9
The carbon film having five types of coating forms was formed by changing the arrangement direction of the substrate in the reaction space so that the carbon film had a thickness of ˜1.9. still,
Methane concentration and gas pressure during film formation were 2% and 25%, respectively.
It was set to torr. In each case, ultrasonic treatment was performed in an ethanol suspension containing diamond abrasive grains (average particle size of about 0.5 μm) before coating the carbon film. S after carbon film coating
As a result of EM and Raman spectroscopic analysis, in all drills, the carbon film was mainly composed of crystalline diamond and partially contained amorphous diamond.

Next, a drilling test was performed on the printed circuit board using these five types of drills. As a work material,
A plywood sheet in which three 1.5 mm-thick epoxy resin substrates (four-layer boards) were stacked was used, and an 0.25 mm-thick Al plate was used as an entry board. The processing conditions were a rotation speed of 75,000 rpm and a feed rate of 3 m / min.

The results are shown in Table 1, where t ₁ / t ₂
When the value exceeds 1, no breakage of the drill is observed, and in particular, the value of 1.5 or less is very excellent in machining accuracy. In Comparative Example 1, the state of the broken drill was examined, and it was found that the breakage was due to clogging of chips, particularly aluminum used as the entry board and the copper groove constituting the substrate, and the breakage resistance with the Example. The difference in sex seemed to be due to the goodness of chip production.

[0025]

[Table 1]

Example 2 Class K cemented carbide (binder component: Co, VC, Cr ₃ C
₂ ) As the base material, microwave plasma CVD is performed on the tip surface including the cutting action part in the miniature drill base material with a shaft angle of 0.35 mm and a twist angle changed from 16 to 30 degrees.
A carbon film was coated by contacting a methane-hydrogen mixed gas excited by the method. At this time, as the ratio of the coating thickness of the cutting edge portion covering thickness (t ₁₎ and flank _{(t 2) (t 1 /} t 2) is 1.07, the arrangement of the substrate in the reaction space Adjusted the direction. The methane concentration and gas pressure during film formation were 3
%, 20 torr. In each case, ultrasonic treatment was performed in an ethanol suspension containing diamond abrasive grains (average particle size of about 0.5 μm) before coating the carbon film. As a result of SEM and Raman spectroscopic analysis after coating the carbon film, in all drills, the carbon film was mainly composed of crystalline diamond and partially contained amorphous diamond.

As a comparative material, t
A miniature drill having a twist angle of 29 ° or 30 ° and the same shaft diameter, which was coated with a carbon film so that the ₁ / t ₂ ratio was 1.00, was produced.

Using each of the obtained miniature drills, a punching test was performed on the printed circuit board. As a work material,
A plywood sheet in which two epoxy resin substrates (four-layer boards) having a thickness of 1.5 mm were stacked was used, and an Al plate having a thickness of 0.2 mm was used as an entry board. The processing conditions are the number of revolutions
The feed rate was 70,000 rpm and the feed rate was 2 m / min.

The results are shown in Table 2, and the breakage resistance and the working accuracy are considerably changed depending on the twist angle. That is,
When the twist angle is 30 degrees or less, the breakage resistance is obviously improved, and when it is set to 20 degrees or more, the processing accuracy is improved. When the state of the broken drills was examined for Comparative Examples 2 and 3, the breakage was caused by clogging of chips, that is, aluminum, copper or epoxy resin in the groove portion, as in the case of Example 1, and The difference in breakage resistance from the example was considered to be due to the goodness of chip discharge property.

[0030]

[Table 2]

[0031]

The present invention is configured as described above, and by properly adjusting the hard carbon film coating thickness of the cutting edge ridge and the hard carbon film coating thickness of the flank in the cutting action portion of the miniature drill. Therefore, it has become possible to provide a miniature drill which can remarkably improve breakage resistance and exhibits excellent cutting performance over a long period of time.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the structure of a miniature drill.

FIG. 2 is an enlarged cross-sectional explanatory view of essential parts showing a cutting edge portion of the miniature drill according to the present invention.

[Explanation of symbols]

 A Cutting action part B Base material C Hard carbon film 1 Scooping surface 2a 1st flank surface 2b 2nd flank surface

Claims (4)

[Claims] 1. In a miniature drill in which at least a cutting action portion is covered with a hard carbon film, the coating thickness (t ₁ ) of the hard carbon film at the cutting edge portion is the coating thickness of the hard carbon film at the flank ( A hard carbon film-covered miniature drill characterized by being made larger than t ₂ ). 2. The hard carbon film-coated miniature drill according to claim ₁ , wherein the ratio (t ₁ / t ₂ ) between the film thicknesses t ₁ and t ₂ is more than 1.0 and not more than 1.5. 3. The twist angle is 20 to 30 degrees.
Alternatively, the hard carbon film-coated miniature drill described in 2. 4. A shaft diameter of 0.5 mm or less
The hard carbon film-coated miniature drill according to any one of 3 above.