Drill

Abstract

To provide a drill improved in performance of discharging chips, while securing abrasion resistance of a hard film in the vicinity of a cutting blade.SOLUTION: A drill comprises a shaft-shape tool main body that is rotated around a center shaft, which also comprises a chip discharge groove formed at an outer periphery of the tool main body and a cutting blade formed at a crossing ridge line part between a flank face at a tip of the tool main body and the chip discharge groove. The tool main body has a substrate and a hard film formed on a region away by a predetermined length from a tip of the substrate. The chip discharge groove has a first section having first surface roughness and a second section having second surface roughness smaller than the first surface roughness positioned closer to a rear end than the first section, in this order from the tip of the tool main body. The first section has a length equal to at least a half of a diameter D of the tool. The hard film is formed in the first section, while the hard film is not formed in the second section.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a drill. [Background technology]

[0002] Conventionally, there has been known a drill in which the surface of a hard coating provided in a chip discharge groove is smoothed to improve chip discharge performance (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6828824 Summary of the Invention [Problem to be solved by the invention]

[0004] Smoothing the inner surface of the chip discharge groove can suppress chip clogging. However, polishing the surface of the hard coating on the rake face connected to the cutting edge reduces the wear resistance of the hard coating. In addition, since the surface of the hard coating is originally rough, there was a problem that it was difficult to obtain good chip discharge performance when the chip discharge groove was long, even if the surface of the hard coating was smoothed.

[0005] An object of the present invention is to provide a drill that has improved chip removal performance while ensuring the wear resistance of the hard coating near the cutting edge. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a drill including a shaft-shaped tool body that rotates around a central axis, a chip discharge groove formed on the outer periphery of the tool body, and a cutting edge formed on a ridge line where the chip discharge groove intersects with the tip flank of the tool body. The tool body has a substrate and a hard coating formed in a region of a predetermined length from the tip of the substrate. The chip discharge groove has, in the central axis direction, a first section having a first surface roughness, and a second section located on the rear end side of the first section and having a second surface roughness smaller than the first surface roughness, in that order from the tip of the tool body. The first section has a length of at least 0.5 times the tool diameter D. The hard coating is formed in the first section, while the hard coating is not formed in the second section.

[0007] According to the above configuration, the hard coating is formed only on the tip of the drill, and the substrate surface with a small surface roughness is exposed in the chip discharge groove in the second section behind the hard coating. This allows the chips moving in the chip discharge groove in the second section to move smoothly to the rear end side. Compared to a configuration in which the hard coating is formed on the entire chip discharge groove or a configuration in which the substrate surface of the normal grinding is exposed in the chip discharge groove on the rear side, the chip discharge performance can be improved. In addition, a hard coating is formed in the first section of the tip, resulting in a large surface roughness. The smoothed hard coating is partially removed or thinned, making it more susceptible to wear on the rake face and other areas that are subject to a large load. In this configuration, the surface of the hard coating in the first section has a large surface roughness, so wear is less likely to occur around the cutting edge.

[0008] The surface roughness of the substrate in the second section may be smaller than the surface roughness of the substrate in the first section. The surface roughness of the sections may be made different depending on the surface roughness of the substrate. Since the surface roughness in the second section can be further reduced, chip removal performance is improved.

[0009] The first section may have a surface of the hard coating having directional streaks, and the second section may have a smooth surface of the mirror-ground substrate. Since the hard coating near the cutting edge has a streaked surface, it becomes easier for the lubricant to penetrate to the cutting edge, and damage to the cutting edge can be suppressed.

[0010] The hard coating may be formed in a third section between the first section and the second section, the third section having a third surface roughness smaller than the first surface roughness and larger than the second surface roughness, and the hard coating may be formed in the third section.

[0011] The present invention may be configured such that a third section is provided between the first section and the second section, the third section has a third surface roughness smaller than the first surface roughness and larger than the second surface roughness, and the hard coating is not formed in the third section.

[0012] The surface roughness of the base material in the second section and the third section may be smaller than the surface roughness of the base material in the first section. A surface of the hard coating having directional striations may be exposed in the first section, and a smooth surface of the mirror-ground substrate may be exposed in the second section. Effect of the Invention

[0013] According to one aspect of the present invention, there is provided a drill that improves chip removal performance while ensuring the wear resistance of a hard coating near the cutting edge. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a side view of a drill according to an embodiment. [Diagram 2] FIG. 2 is an enlarged partial side view showing a tip portion of the drill according to the embodiment. [Diagram 3] FIG. 3 is a front view of the drill according to the embodiment. [Figure 4] FIG. 4 shows a first embodiment of the drill. [Diagram 5] FIG. 5 shows a second embodiment of the drill. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Fig. 1 is a side view of the drill of this embodiment, Fig. 2 is a partial side view showing an enlarged tip portion of the drill of this embodiment, and Fig. 3 is a front view of the drill of this embodiment.

[0016] The drill 1 of this embodiment is a drill for deep hole drilling. The drill 1 is generally cylindrical and centered on a central axis (axis line) O. The drill 1 has an axis-shaped body (tool main body) 10 and a shank 11, each of which extends along the central axis O. The drill 1 rotates around the central axis O with the tip face of the body 10 facing the workpiece to machine the workpiece. The drill 1 of this embodiment is a solid drill having a substrate made of cemented carbide etc. The drill 1 has a hard coating made of metal nitride etc. that coats the surface of the substrate.

[0017] The direction along the central axis O of the drill 1 (the direction in which the central axis O extends) is called the axial direction. In the axial direction, the direction from the shank 11 to the body 10 is called the front end side, and the direction from the body 10 to the shank 11 is called the rear end side. The direction perpendicular to the central axis O is called the radial direction. Of the radial directions, the direction approaching the central axis O is called the radially inner direction, and the direction away from the central axis O is called the radially outer direction. The direction rotating around the central axis O is called the circumferential direction. In addition, within the circumferential direction, the direction in which the body 10 rotates during drilling is called the front side of the rotation direction, and the opposite side is called the rear side of the rotation direction.

[0018] The body 10 has a pair of cutting edges 15, 15 located at the tip of the body 10, and a pair of chip discharge grooves 14, 14 extending spirally around the outer periphery of the body 10 from the cutting edges 15, 15 toward the rear end side.

[0019] In the drill 1, two coolant holes 9 are formed symmetrically from the rear end face of the shank 11 toward the tip end, twisted with the same lead as the chip discharge groove 14 with respect to the central axis O. These coolant holes 9 pass between the chip discharge grooves 14 in the body 10 and open to the tip flank 13. When drilling a hole using the drill 1, coolant such as cutting oil or compressed air is ejected from the two coolant holes 9. In addition, the tip flank 13 is formed by a two-stage flank. Of the two-stage tip flank 13, the flank located on the opposite side to the tool rotation direction T has a larger flank angle. The coolant hole 9 opens to the flank located on the opposite side to the tool rotation direction T of the two-stage flank.

[0020] The chip discharge groove 14 is twisted rearward in the tool rotation direction T at a constant twist angle on the outer periphery of the body 10 from the cutting edge 15 toward the rear end in the direction of the central axis O. The pair of chip discharge grooves 14, 14 are disposed symmetrically with respect to the central axis O. The drill 1 of this embodiment is for deep hole drilling, and the length of the chip discharge groove 14 along the direction of the central axis O is, for example, in the range of 8.0D to 30.0D relative to the outer diameter of the cutting edge 15 of the drill 1. The outer diameter of the cutting edge 15 is the outer diameter of a circle formed by a rotation locus around the central axis O at the outer periphery end of the cutting edge 15, i.e., the tool diameter D.

[0021] The cutting edges 15, 15 are formed at the tip of the body 10 at the intersection ridge between the inner wall surfaces of the pair of chip discharge grooves 14, 14 facing forward in the tool rotation direction T and the tip flank 13. The pair of cutting edges 15, 15 are disposed symmetrically with respect to the central axis O. The cutting edge 15 extends toward the rear end as it approaches the outer periphery (radially outward) of the body 10, and is given a tip angle.

[0022] The body 10 has lands 16, 16 between the two chip discharge grooves 14, 14. A first margin 16A is provided at the end of the land 16 on the front side in the tool rotation direction T. A second margin 16B is provided at the end of the land 16 on the rear side in the tool rotation direction T. The first margin 16A and the second margin 16B extend spirally along the edge of the chip discharge groove 14. The body 10 has a chamfered surface 16C recessed radially inward between the first margin 16A and the second margin 16B.

[0023] In the drill 1 of this embodiment, the hard coating is formed only on the tip portion of the body 10, and the chip discharge groove 14, except for the tip portion, is smoothed by mirror grinding. That is, the hard coating is formed in a region of a predetermined length from the tip of the base material. With this configuration, the chip discharge groove 14 of the drill 1 is divided into a plurality of sections with different surface roughness along the axial direction. The drill 1 of this embodiment will be described in more detail below with reference to two examples.

[0024] (First Example) FIG. 4 is a diagram showing a first example of the drill 1 according to the present embodiment. 4, the hard coating 17 is formed only on the tip end portion of the base material of the drill 1, and is not formed on the rear end portion of the base material. In the first embodiment, the hard coating 17 is formed on about 1 / 3 of the area from the tip of the body 10.

[0025] As shown in the lower part of Fig. 4, the wall surface of the chip discharge groove 14 of the base material of the drill 1 is partially mirror-finished. More specifically, the tip side portion of the chip discharge groove 14 is ground using a normal grindstone, and the base material surface has a surface shape with directional streaks. On the other hand, the rear end side portion of the chip discharge groove 14 is formed with a normal grindstone, and then the surface is smoothed by mirror grinding using an elastic grindstone or the like. The mirror-ground base material surface has a smooth surface with reduced streaks.

[0026] The rearmost portion of the chip discharge groove 14 is not mirror ground. This is because the rearmost portion of the chip discharge groove 14 becomes shallower toward the rear end and contributes little to chip discharge, while grinding this region imposes a high grinding load and affects productivity. Note that the chip discharge groove 14 may be mirror ground up to the rear end.

[0027] In the first embodiment, the rear end edge 17a of the hard coating 17 is located rearward of the leading edge 14a of the mirror-ground region of the substrate. That is, the rear end portion of the hard coating 17 and the leading end portion of the mirror-ground region of the substrate overlap. As a result, the wall surface of the chip discharge groove 14 of the drill 1 is divided into four sections, a first section S1, a second section S2, a third section S3, and a fourth section S4, by a combination of two sections divided by the difference between normal grinding and mirror-ground grinding of the substrate and two sections divided by the presence or absence of the hard coating 17.

[0028] The first section S1 is located at the tip of the drill 1, and the wall surface of the chip discharge groove 14 is configured such that a hard film 17 is formed on the surface of a normally ground base material. The second section S2 is located in an area from the center of the drill 1 toward the rear end, where the hard coating 17 is not formed, and the mirror-ground surface of the base material is exposed on the wall surface of the chip discharge groove 14. The third section S3 is located between the first section S1 and the second section S2, and the wall surface of the chip discharge groove 14 is configured such that a hard coating 17 is formed on the surface of the mirror-ground base material. The third section S3 is the region between the rear end edge of the hard coating 17 and the leading edge 14a of the mirror-ground region of the base material. The fourth section S4 is located on the rear end side of the second section S2, where the hard coating 17 is not formed, and the surface of the base material for normal grinding is exposed on the wall surface of the chip discharge groove 14.

[0029] In the first section S1, the uneven shape caused by streaks on the surface of the substrate that has been normally ground is superimposed on isotropic undulations caused by microparticles of the hard coating 17, so that the surface roughness of the first section S1 (first surface roughness) is the greatest among the first section S1 to the fourth section S4. In the second section S2, the mirror-ground substrate surface is exposed, and therefore the surface roughness in the second section (second surface roughness) is the smallest among the first section S1 to the fourth section S4. In the third section S3, a hard coating 17 is formed on the mirror-ground substrate surface, resulting in a surface roughness (third surface roughness) that is smaller than the first surface roughness in the first section S1 and larger than the second surface roughness in the second section S2. In the fourth section S4, the normally ground substrate surface is exposed, and therefore the surface roughness is smaller than the first surface roughness in the first section S1 and smaller than the second surface roughness in the second section S2.

[0030] The arithmetic mean roughness Sa of the substrate surface in the second section S2 is preferably 0.8 or 0.5 times the arithmetic mean roughness Sa of the hard coating 17 surface in the first section S1. The arithmetic mean roughness Ra of the substrate surface in the second section S2 is preferably 0.8 or 0.5 times the arithmetic mean roughness Ra of the hard coating 17 surface in the first section S1.

[0031] In the first section S1, the arithmetic mean roughness Sa or Ra of the surface of the hard coating 17 is preferably 1.6 μm or less, or 0.4 μm or less. If the surface roughness in the first section S1 is too large, chips are less likely to be discharged near the cutting edge 15, which may increase the cutting resistance.

[0032] The mirror-ground substrate surface in the second section S2 preferably has a small value of the interface developed area ratio Sdr defined in ISO 25178. The smaller the interface developed area ratio Sdr value, the closer the measurement target area is to a flat surface. The interface developed area ratio Sdr of the mirror-ground substrate surface in the second section S2 is preferably 0.2 or less, and more preferably close to 0.

[0033] The surface roughness of the hard coating 17 in the first section S1 is a value measured on the rake face continuing to the cutting edge 15. The surface roughness in the second section S2, the third section S3, and the fourth section S4 is a value measured at the deepest position of the chip discharge groove 14 near the center in the axial direction of each section. Since the boundary between sections is easily affected by the surface roughness of the adjacent section, it is preferable to measure the surface roughness in the center of each section. The arithmetic mean roughness Sa, Ra, and the developed area ratio Sdr of the interface are determined, for example, by using a laser microscope (VK-X3000) equipped with a white light interferometer manufactured by Keyence Corporation, observing with a cutoff value of 0.25 mm and a magnification of 100 times, measuring three areas of 50 μm × 50 μm, and averaging the obtained measurements.

[0034] In the drill 1 of this embodiment, the first section S1 has a length in the axial direction of at least 0.5×D. This is because if the portion with low surface roughness is too close to the cutting edge 15, the hard coating 17 is more likely to wear in the portion with low surface roughness. The axial length of the region where the hard coating 17 is formed is preferably equal to or less than 10 × D. Since the region where the hard coating 17 is formed has a large surface roughness, the longer the hard coating 17 extends toward the rear end side, the more resistance is applied to the chips in the chip discharge groove 14, and the more likely the cutting resistance is to increase.

[0035] According to the drill 1 of the first embodiment having the above-mentioned configuration, the hard coating 17 is formed only on the tip of the drill 1, and the mirror-ground base material surface is exposed in the chip discharge groove 14 in the second section S2 behind it. This allows chips moving in the chip discharge groove 14 in the second section S2 to move smoothly toward the rear end. Compared to a configuration in which a hard coating is formed over the entire chip discharge groove or a configuration in which the normally ground base material surface is exposed in the chip discharge groove on the rear side, the chip discharge performance can be improved.

[0036] In the drill 1 of the first embodiment, a hard coating 17 is formed on the surface of the normally ground substrate in the first section S1 of the tip. If the surface of the hard coating is smoothed, the hard coating is partially removed or thinned, making the hard coating more likely to wear on the rake face and other areas that are subject to a large load. In contrast, in the drill 1 of the first embodiment, the hard coating 17 is provided around the cutting edge 15 where chips are generated, and therefore wear is less likely to occur.

[0037] Furthermore, since the surface of a substrate that has been ground normally has directional grains, the surface of the hard coating in the first section S1 also has a surface shape with directional grains, which makes it easier for the lubricant to penetrate to the cutting edge 15, thereby suppressing damage to the cutting edge 15. Furthermore, in this embodiment, only a portion of the chip discharge groove 14 needs to be mirror-finished. This shortens the process time compared to when the entire chip discharge groove 14 is mirror-finished, thereby ensuring productivity in tool manufacturing.

[0038] Moreover, the drill 1 of the first embodiment has a third section S3 in which the hard coating 17 is formed on the mirror-ground surface of the substrate, and therefore the region in which the hard coating 17 is formed is relatively long. As the tool diameter becomes smaller, it is preferable to shorten the region in which the hard coating 17 is formed, but if the region in which the hard coating 17 is formed is too short, the thickness of the hard coating cannot be ensured. In this case, by coating a part of the mirror-ground substrate surface with the hard coating 17 as in this embodiment, the hard coating 17 can be formed to a predetermined thickness even in a small-diameter drill, and the life performance of the drill can be ensured.

[0039] In the first embodiment, the axial position of the rear end edge 17a of the hard coating 17 and the axial position of the leading edge 14a of the mirror-ground region of the substrate may be configured to coincide with each other. In this case, the drill 1 of the first embodiment is configured such that the first section S1 and the second section S2 are adjacent to each other and the third section S3 is not provided. Even in this case, the effect of providing the first section S1 and the second section S2 can be obtained.

[0040] (Second Example) 5 is a diagram showing a second example of the drill 1 according to the present embodiment. Description of parts common to the first example shown in FIG. 5, the hard coating 17 is formed only on the tip end portion of the base material of the drill 1, and is not formed on the rear end portion of the base material. In the first embodiment, the hard coating 17 is formed in an area of ​​about 1 / 5 from the tip of the body 10.

[0041] As shown in the lower part of Fig. 5, the tip end portion of the chip discharge groove 14 is ground with a normal grindstone, and the substrate surface has a surface shape with directional streaks. Meanwhile, the central portion of the chip discharge groove 14 has its surface smoothed by mirror grinding with an elastic grindstone or the like. The rearmost portion of the chip discharge groove 14 is not mirror ground.

[0042] In the second embodiment, the rear end edge 17a of the hard coating 17 is located further forward than the leading edge 14a of the mirror-ground region of the substrate. That is, the region where the hard coating 17 is formed and the mirror-ground region of the substrate do not overlap each other. As a result, in the drill 1 of the second embodiment, the wall surface of the chip discharge groove 14 of the drill 1 is also divided into four sections: a first section S1, a second section S2, a third section S3, and a fourth section S4.

[0043] The first section S1 is located at the tip of the drill 1, and the wall surface of the chip discharge groove 14 is configured such that a hard film 17 is formed on the surface of a normally ground base material. The second section S2 is located in an area from the center of the drill 1 toward the rear end, where the hard coating 17 is not formed, and the mirror-ground surface of the base material is exposed on the wall surface of the chip discharge groove 14. The third section S3 is located between the first section S1 and the second section S2, and the surface of the base material for normal grinding is exposed to the wall surface of the chip discharge groove 14. The fourth section S4 is located on the rear end side of the second section S2, where the hard coating 17 is not formed, and the surface of the base material for normal grinding is exposed on the wall surface of the chip discharge groove 14.

[0044] In the first section S1, the uneven shape caused by streaks on the surface of the substrate that has been normally ground is superimposed on isotropic undulations caused by microparticles of the hard coating 17, so that the surface roughness of the first section S1 (first surface roughness) is the greatest among the first section S1 to the fourth section S4. In the second section S2, the mirror-ground substrate surface is exposed, and therefore the surface roughness in the second section (second surface roughness) is the smallest among the first section S1 to the fourth section S4. In the third section S3, the substrate surface that has been normally ground is exposed, resulting in a surface roughness (third surface roughness) that is smaller than the first surface roughness in the first section S1 and larger than the second surface roughness in the second section S2. In the fourth section S4, the normally ground substrate surface is exposed, and therefore the surface roughness is smaller than the first surface roughness in the first section S1 and larger than the second surface roughness in the second section S2.

[0045] In the drill 1 of the second embodiment having the above configuration, the hard coating 17 is formed only on the tip of the drill 1, and the mirror-ground substrate surface is exposed in the chip discharge groove 14 in the second section S2 behind the tip of the drill 1. This provides the drill 1 with excellent chip discharge properties, similar to the first embodiment. Also in the drill 1 of the second embodiment, the hard coating 17 is formed on the surface of the normally ground substrate in the first section S1 of the tip portion. This makes it difficult for the hard coating 17 to wear around the cutting edge 15 where chips are generated.

[0046] In the drill 1 of the second embodiment, the surface of the substrate that is normally ground extends to the rear end side beyond the region where the hard coating 17 is formed. When the tool diameter of the drill is large, the thickness of the hard coating 17 is easily ensured even if the range of the hard coating 17 is relatively short, so that the configuration of the second embodiment is easily applicable. The drill 1 of the second embodiment can be designed with regrinding in mind. When regrinding is repeated, the mirror-ground region of the substrate gradually approaches the tip. Therefore, if the normal ground surface of the substrate is short, there is a concern that a mirror-ground surface will be generated at the tip of the drill 1 when regrinding is repeated, and wear of the hard coating on the rake face and the like will be accelerated. In contrast, in the drill 1 of the second embodiment, the normal ground region of the substrate can be made long, so that the mirror-ground surface is unlikely to be located near the cutting edge 15 even when regrinding is repeated.

[0047] However, the third section S3, where the surface of the normally ground substrate is exposed, has a relatively large surface roughness and is likely to hinder the movement of chips. Therefore, the axial length of the third section S3 in the second embodiment is preferably 2×D or less. [Explanation of symbols]

[0048] 1. Drill 10...Body (tool body) 11...Shank 13...Tip relief surface 14...Chip discharge groove 14a…Edge of mirror-finished area 15…Cutting edge 16…Rand 16A…First margin 16B…Second margin 16C...Second cut surface 17...Hard coating 17a…Rear edge of hard coating D…Tool diameter O…Central axis (axis line) Ra, Sa: Arithmetic mean roughness S1: First section S2: Second section S3: Third section S4: Section 4 Sdr: Ratio of developed surface area of ​​interface T…Tool rotation direction

Claims

1. A drill includes a shaft-shaped tool body that is rotated around a central axis, the tool body having a chip discharge groove formed on an outer periphery thereof, and a cutting edge formed on an intersection ridge between a tip flank of the tool body and the chip discharge groove, The tool body has a substrate and a hard coating formed in a region of a predetermined length from a tip of the substrate, the chip discharge groove has, in a central axial direction, a first section having a first surface roughness, and a second section located on a rear end side of the first section and having a second surface roughness smaller than the first surface roughness, in this order from a tip end of the tool body; The first section has a length of at least 0.5 times the tool diameter D, the hard coating is formed in the first section, whereas the hard coating is not formed in the second section; drill.

2. The surface roughness of the substrate in the second section is smaller than the surface roughness of the substrate in the first section. The drill of claim 1.

3. In the first section, a surface of the hard coating having directional striations is exposed, In the second section, a smooth surface of the mirror-ground substrate is exposed. The drill of claim 1.

4. A third section is provided between the first section and the second section, the third section has a third surface roughness smaller than the first surface roughness and larger than the second surface roughness; The hard coating is formed on the third section. The drill of claim 1.

5. A third section is provided between the first section and the second section, the third section has a third surface roughness smaller than the first surface roughness and larger than the second surface roughness; The hard coating is not formed in the third section. The drill of claim 1.

6. The surface roughness of the base material in the second section and the third section is smaller than the surface roughness of the base material in the first section. A drill according to claim 4 or 5.

7. In the first section, a surface of the hard coating having directional striations is exposed, In the second section, a smooth surface of the mirror-ground substrate is exposed. A drill according to claim 4 or 5.

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