Cutting tool

Abstract

The cutting tool rotates about a rotation axis and has a tip portion. The tip portion has a surface in the shape of a partial spherical surface that contacts the workpiece. A plurality of recesses are formed on the surface and are arranged separately from each other. The opening edge of each of the plurality of recesses forms a cutting edge.

Description

Technical Field

[0001] The present disclosure relates to a cutting tool.

[0002] This application claims priority based on PCT / JP2020 / 024454, PCT / JP2020 / 024455, and PCT / JP2020 / 024456 of an international application filed on June 22, 2020. All the descriptions recorded in this application are incorporated herein by reference. Background Art

[0003] A cutting tool is described in International Publication No. 2018 / 116524 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2013-212572 (Patent Document 2).

[0004] The cutting tool described in Patent Document 1 has a planar negative land and a flank, and a cutting edge connected to the negative land and the flank. A plurality of recesses are formed in at least one of the negative land and the flank.

[0005] The cutting tool described in Patent Document 2 has a cutting edge and a rake face connected to the cutting edge, and a plurality of recesses are formed in the rake face.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: International Publication No. 2018 / 116524

[0009] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2013-212572 Summary of the Invention

[0010] The cutting tool of the present disclosure rotates about a rotation axis and has a tip portion. The tip portion has a partially spherical surface that contacts a workpiece. A plurality of recesses are formed on the surface and are arranged separately from each other. The opening edge of each of the plurality of recesses forms a cutting edge. Brief Description of the Drawings

[0011] Figure 1 is a perspective view of the cutting tool 100.

[0012] Figure 2 is a schematic enlarged view of the surface 11.

[0013] Figure 3 is Figure 2 a schematic cross-sectional view taken along line III-III of

[0014] Figure 4 is a schematic diagram showing a method for measuring the angle θ.

[0015] Figure 5 It is a schematic view of the front end portion 10 showing the arrangement of the recess 12.

[0016] Figure 6 It is a perspective view of the cutting tool 100 according to the modified example.

[0017] Figure 7 It is a schematic cross-sectional view of the cutting tool 200. Detailed implementation mode

[0018] [Problems to be solved by the present disclosure]

[0019] In the cutting tool described in Patent Document 1, the workpiece is cut by the cutting edge, and a negative land and a recess on the flank are formed to reduce the contact resistance with the workpiece. In the cutting tool described in Patent Document 2, the workpiece is also cut by the cutting edge, and a recess on the rake face is formed to reduce the contact resistance with the workpiece.

[0020] The present disclosure provides a cutting tool that cuts using the opening edge of a recess formed on a partially spherical surface.

[0021] [Effects of the present disclosure]

[0022] According to the cutting tool of the present disclosure, cutting can be performed using the opening edge of a recess formed on a partially spherical surface.

[0023] [Outline of the embodiment]

[0024] First, embodiments of the present invention will be listed and described.

[0025] (1) The cutting tool according to the embodiment rotates around a rotation axis and includes a front end portion. The front end portion has a partially spherical surface that contacts the workpiece. A plurality of recesses are formed on the surface and are arranged separately from each other. The opening edge of each of the plurality of recesses forms a cutting edge.

[0026] According to the cutting tool of (1) above, cutting can be performed using the opening edge of a recess formed on a partially spherical surface.

[0027] (2) Based on the cutting tool of (1) above, the front end portion may be formed of binderless cubic boron nitride or nanocrystalline diamond.

[0028] (3) Based on the cutting tool of (2) above, atoms belonging to Group 13 or Group 15 of the long-period type periodic table may be added to the nanocrystalline diamond.

[0029] (4)Based on the cutting tools in (1) to (3) above, it is also possible that each of the plurality of recesses has a side surface connected to the opening edge. It is also possible that, in more than 80% of the plurality of recesses, the side surface and the portion of the surface connected to the opening edge form an angle of 80° or more and 160° or less.

[0030] (5)Based on the cutting tools in (1) to (4) above, it is also possible that the plurality of recesses are arranged such that the trajectories of the plurality of recesses when the cutting tool rotates around the rotation axis cover the entire surface.

[0031] (6)Based on the cutting tools in (1) to (5) above, it is also possible that a plurality of grooves radially extending from the central portion of the surface are formed on the surface. It is also possible that the plurality of recesses are arranged in the portion of the surface located between the plurality of grooves.

[0032] (7)The cutting tools in (1) to (6) above can also be used with a cutting depth of 10 μm or less.

[0033] [Details of the Embodiment]

[0034] Next, the details of the embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will not be repeated. The cutting tool related to the embodiment is taken as the cutting tool 100.

[0035] (Structure of the Cutting Tool 100)

[0036] Hereinafter, the structure of the cutting tool 100 will be described.

[0037] Figure 1 is a perspective view of the cutting tool 100. As Figure 1 shown, the cutting tool 100 is, for example, a ball nose end mill. The cutting tool 100 rotates around the rotation axis A, thereby performing cutting on the workpiece. The cutting tool 100 is, for example, used for cutting the workpiece with a cutting depth of 10 μm or less. The cutting tool 100 includes a tip portion 10, a main body portion 20, and a connection layer 30.

[0038] The tip portion 10 is located at the tip of the cutting tool 100 in the direction along the rotation axis A. The tip portion 10 has a surface 11. The surface 11 is partially spherical. The surface 11 is, for example, hemispherical. The surface 11 contacts the workpiece. The tip portion 10 is formed of, for example, binderless cubic boron nitride (cBN).

[0039] Binderless cubic boron nitride contains a plurality of cubic boron nitride particles. As a remainder of the binderless cubic boron nitride, boron nitrides having a crystal structure other than cubic crystals such as hexagonal boron nitride (hBN) and wurtzite boron nitride (wBN), and inevitable impurities may be included, but no binder is included. That is, in the binderless cubic boron nitride, the cubic boron nitride grains are directly bonded to each other without passing through a binder. The amount of inevitable impurities is preferably as small as possible, but sometimes several percent of inevitable impurities are contained relative to the total mass.

[0040] In the binderless cubic boron nitride, the median particle size of the cubic boron nitride grains is, for example, less than 1 μm. In the binderless cubic boron nitride, the median particle size of the cubic boron nitride grains is preferably 0.05 μm or less. It should be noted that in the binderless cubic boron nitride, the median particle size of the cubic boron nitride grains is, for example, 0.01 μm or more.

[0041] The median particle size of the cubic boron nitride grains is measured, for example, by the following method. First, an SEM (Scanning Electron Microscope) image in the cross section of the tip 10 is taken. The size of the measurement field of view is 12 μm × 15 μm, and the observation magnification is 10,000 times. Five SEM images are taken at different positions.

[0042] Second, for each of the five SEM images, image analysis is performed using image processing software (Win Roof Ver.7.4.5), whereby the distribution of the equivalent circle diameters of the cubic boron nitride grains is calculated. Based on the distribution of the equivalent circle diameters, the median particle size of the cubic boron nitride grains is calculated. The average value of the median particle sizes obtained from each of the five SEM images is the median particle size of the cubic boron nitride grains.

[0043] The tip 10 may also be formed of nanocrystalline diamond. The nanocrystalline diamond contains a plurality of diamond grains. As a remainder of the nanocrystalline diamond, inevitable impurities may be included, but no binder is included. That is, in the nanocrystalline diamond, the plurality of diamond grains are directly bonded to each other. The inevitable impurities are, for example, hydrogen and oxygen.

[0044] In the nanocrystalline diamond, the median particle size of the diamond grains is, for example, less than 1 μm. Preferably, in the nanocrystalline diamond, the median particle size of the diamond grains is, for example, 0.5 μm or less. In the nanocrystalline diamond, the median particle size of the diamond grains is, for example, 0.01 μm or more. The median particle size of the diamond grains is measured by the same method as the median particle size of the cubic boron nitride grains.

[0045] Atoms belonging to Group 13 or Group 15 of the long-period type periodic table can also be added to the nanocrystalline diamond. Examples of atoms belonging to Group 13 of the long-period type periodic table are boron (B), aluminum (Al), and gallium (Ga). Examples of atoms belonging to Group 15 of the long-period type periodic table are nitrogen (N), phosphorus (P), and arsenic (As).

[0046] In the nanocrystalline diamond to which the above atoms are added, a part of the carbon atoms in the diamond crystal structure can be replaced by the above atoms, or the above atoms can be inserted between carbon-carbon bonds. The addition concentration of the above atoms is, for example, 1 ppm or more and 10,000 ppm or less. The addition concentration of the above atoms in the nanocrystalline diamond can be measured, for example, by SIMS (Secondary Ion Mass Spectrometry) analysis.

[0047] The main body 20 is, for example, a shank. The main body 20 is formed of, for example, cemented carbide. The main body 20 extends along the rotation axis A. The main body 20 is, for example, circular when viewed in a cross-section orthogonal to the rotation axis A. The front end portion 10 is attached to the front end of the main body 20 in the direction along the rotation axis A. The front end portion 10 is attached to the main body 20 via the connection layer 30. The attachment of the front end portion 10 to the main body 20 is performed, for example, by brazing. That is, the connection layer 30 is, for example, a brazing filler metal.

[0048] (Detailed structure of the surface 11)

[0049] Figure 2 is a schematic enlarged view of the surface 11. As Figure 2 shown, a plurality of recesses 12 are formed on the surface 11. The plurality of recesses 12 are arranged separately from each other. When viewed from above, the recesses 12 are, for example, circular. The recesses 12 may not be circular when viewed from above.

[0050] The equivalent circle diameter of the recess 12 is, for example, 100 μm or less. The equivalent circle diameter of the recess 12 is, for example, 1 μm or more. The equivalent circle diameter of the recess 12 is preferably 1 μm or more and 71 μm or less. The equivalent circle diameter of the recess 12 is the square root of the value obtained by dividing the area of the recess 12 when viewed from above by π / 4.

[0051] The proportion of the total area of the plurality of recesses 12 in the area of the surface 11 (hereinafter referred to as "the area ratio of the recesses 12") is, for example, 1% or more. The area ratio of the recesses 12 is preferably 1% or more and 80% or less. The area ratio of the recesses 12 is, for example, 85% or less.

[0052] The ratio of the total area of the plurality of recesses 12 to the area of the surface 11 is measured by the following method. First, an SEM image of the surface 11 is taken. At this time, the size of the measurement field of view is 200 μm × 200 μm, and the magnification is 500 times. Five SEM images are taken at different positions. Second, in each of the five SEM images, the ratio of the total area of the plurality of recesses 12 to the area of the surface 11 is calculated. The average value of the ratios of the total area of the plurality of recesses 12 to the area of the surface 11 obtained from each of the five SEM images is taken as the area ratio of the recesses 12.

[0053] Figure 3 is Figure 2 A schematic cross-sectional view taken along line III-III. The recess 12 has an opening edge 12a and a side surface 12b connected to the opening edge 12a. The opening edge 12a forms the cutting edge of the cutting tool 100. That is, the opening edge 12a is formed as a sharp edge. Let the depth of the recess 12 be the depth D. The depth D is the distance between the opening edge 12a and the bottom of the recess 12 in a cross-sectional view that passes through the center of the recess 12 when viewed from above and is orthogonal to the surface 11. The recess 12 is measured by an optical measuring device or a non-contact three-dimensional measuring machine. The depth D is, for example, 25 μm or less. The depth D is preferably 1 μm or more and 25 μm or less. The depth D is, for example, 0.1 μm or more.

[0054] The portion of the surface 11 connected to the opening edge 12a and the side surface 12b form an angle θ. Figure 4 is a schematic diagram showing a method for measuring the angle θ. The angle θ is measured by Figure 4 the method shown. First, in a cross-sectional view passing through the center of the recess 12 when viewed from above, the coordinates of a plurality of measurement points P on the side surface 12b are measured. The coordinates of the measurement points P are measured by an optical measuring device or a non-contact three-dimensional measuring machine. The plurality of measurement points P are arranged at equal intervals (0.2 μm intervals) from the opening edge 12a to a position 1 μm away from the opening edge 12a in sequence. Second, a curve representing the side surface 12b is determined based on the coordinates of each of the plurality of measurement points P.

[0055] Third, the angle formed by the tangent line L1 and the tangent line L2 is calculated. The tangent line L1 is the tangent line at the opening edge 12a of the curve representing the side surface 12b. The tangent line L2 is the tangent line at the opening edge 12a of the curve representing the portion of the surface 11 connected to the opening edge 12a. The angle formed by the tangent line L1 and the tangent line L2 is the angle θ.

[0056] The angle θ is, for example, 170° or less. Preferably, in more than 80% of the plurality of recesses 12, the angle θ is 80° or more and 160° or less. It should be noted that for any ten of the plurality of recesses 12, if in eight or more of them, the angle θ is in the range of 80° or more and 160° or less, it is regarded as "in more than 80% of the plurality of recesses 12, the angle θ is 80° or more and 160° or less".

[0057] Figure 5 is a schematic view showing the front end portion 10 of the arrangement of the recesses 12. As Figure 5 shown, the plurality of recesses 12 are arranged, for example, in a plurality of columns extending from the central portion of the surface 11. It should be noted that in Figure 5 only two adjacent columns among the plurality of columns are shown. Each of the above-mentioned plurality of columns contains a plurality of recesses 12. One of the above-mentioned plurality of columns is set as the first column. The other of the above-mentioned plurality of columns adjacent to the first column is set as the second column. The recess 12 belonging to the first column is set as the recess 12A. The recess 12 belonging to the second column is set as the recess 12B.

[0058] The recess 12B is arranged, for example, between two adjacent recesses 12A in the direction along the rotation axis A. The equivalent circle diameter of the recess 12B (recess 12A) is, for example, larger than the interval between two adjacent recesses 12A (the interval between two adjacent recesses 12B). Therefore, the trajectories of the plurality of recesses 12A and the recess 12B when the cutting tool 100 rotates around the rotation axis A cover the entire surface of the surface 11.

[0059] The recess 12 is formed, for example, by irradiating the surface 11 with a laser. The laser is, for example, a YAG laser. The shape (equivalent circle diameter, angle θ, and depth D) of the recess 12 varies according to the laser irradiation conditions. The laser irradiation conditions include, for example, the average output (unit: W), the repetition frequency (unit: Hz), and the laser scanning speed (unit: mm / minute). In Table 1, the shape of the recess 12 in the case of changing the laser irradiation conditions is shown as an example.

[0060] Table 1

[0061]

[0062] (Modification example)

[0063] Figure 6 is a perspective view of the cutting tool 100 according to the modification example. As Figure 6 shown, a plurality of grooves 13 may also be formed on the surface 11. The grooves 13 extend radially from the central portion of the surface 11. Although not shown, the plurality of recesses 12 are located between adjacent grooves 13. The edges of the grooves 13 together with the opening edges 12a function as the cutting edges of the cutting tool 100.

[0064] (Effect of the cutting tool according to the embodiment)

[0065] Hereinafter, while comparing with the cutting tool (hereinafter referred to as "cutting tool 200") according to the comparative example, the effect of the cutting tool 100 will be described.

[0066] Figure 7 is a schematic cross-sectional view of the cutting tool 200. In Figure 7 a cross-section of the cutting tool 200 that shows the center of the recess 12 when viewed from above and is orthogonal to the surface 11 is shown. In the cutting tool 200, the recess 12 is formed to reduce the contact resistance with the workpiece. As Figure 7 shown, in the cutting tool 200, in order to prevent the opening edge 12a from being damaged, when viewed in a cross-section that shows the center of the recess 12 when viewed from above and is orthogonal to the surface 11, the opening edge 12a is formed in an arc shape. As a result, in the cutting tool 200, the opening edge 12a does not function as a cutting edge.

[0067] On the other hand, in the cutting tool 100, the opening edge 12a is formed as a sharp edge, so that the opening edge 12a can function as a cutting edge. In this way, by rotating the cutting tool 100 around the rotation axis A in a state where the surface 11 is in contact with the workpiece, the cutting tool 100 can perform cutting processing on the workpiece.

[0068] When a plurality of recesses 12 are arranged in such a way that the trajectories of the plurality of recesses 12 when the cutting tool 100 rotates around the rotation axis A cover the entire surface of the surface 11, the entire surface of the surface 11 can be used for cutting processing of the workpiece, thereby improving the cutting efficiency of the cutting tool 100. In addition, in this case, the machining quality (the glossiness and surface roughness of the workpiece after cutting) of the workpiece after cutting can be improved.

[0069] When a plurality of grooves 13 are formed in the surface 11, not only the opening edge 12a but also the edges of the grooves 13 function as cutting edges, improving the cutting efficiency of the cutting tool 100.

[0070] (Cutting test)

[0071] In order to confirm the effect of the cutting tool 100, a cutting test was conducted. In the cutting test, the first cutting condition, the second cutting condition, the third cutting condition, the fourth cutting condition, the fifth cutting condition, the sixth cutting condition, the seventh cutting condition, and the eighth cutting condition were applied. The first cutting condition to the eighth cutting condition are shown in Table 2.

[0072]

[0073] Under the first to seventh cutting conditions, the rotational speed, feed rate, cutting width, and cutting method of the cutting tool 100 are 40,000 revolutions per minute, 300 mm per minute, 0.002 mm, and plunge cutting, respectively. Under the eighth cutting condition, the rotational speed, feed rate, cutting width, and cutting method of the cutting tool 100 are 40,000 revolutions per minute, 800 mm per minute, 0.005 mm, and plunge cutting, respectively. Under the first cutting condition and the third to seventh cutting conditions, the workpiece is cemented carbide. Under the second cutting condition, the workpiece is quartz glass. Under the eighth cutting condition, the workpiece is hardened steel. Under the first to eighth cutting conditions, a 5 mm × 5 mm plane is machined by cutting.

[0074] Under the first cutting condition and the eighth cutting condition, the depth of cut is 0.005 mm. Under the second to fourth cutting conditions and the seventh cutting condition, the depth of cut is 0.003 mm. Under the fifth cutting condition and the sixth cutting condition, the depth of cut is 0.004 mm. Under the first cutting condition and the third to eighth cutting conditions, cutting is performed while supplying oil in a mist form as a coolant. Under the second cutting condition, cutting is performed by dry machining (i.e., without supplying a coolant).

[0075] In the cutting test, the dimensional error of the workpiece after cutting of each sample with respect to the target shape (hereinafter referred to as "dimensional error"), the glossiness of the workpiece after cutting (hereinafter referred to as "glossiness"), and the arithmetic mean roughness of the workpiece after cutting (hereinafter referred to as "surface roughness") were evaluated. When the absolute value of the dimensional error was less than 4 μm, each sample was evaluated as having functioned as a cutting tool. When the absolute value of the dimensional error was 4 μm or more, each sample was evaluated as not having functioned as a cutting tool.

[0076] The glossiness was measured using a gloss meter. The specular reflectance when the incident angle of a black mirror glass plate with a refractive index of 1.567 was 60° was defined as the case where the glossiness was 100 (specular glossiness).

[0077] In the cutting test, samples 1 to 30 were provided as samples of the cutting tool 100. In each of samples 1 to 30, the presence or absence of the recess 12, the depth D, the equivalent circle diameter of the recess 12, the area ratio of the recess 12, the angle θ, and the constituent material of the tip 10 were changed. It should be noted that in Table 3, "NPD" refers to nanocrystalline diamond, "B-NPD" refers to nanocrystalline diamond doped with boron, and "BL-CBN" refers to binderless cubic boron nitride.

[0078] In sample 27, the plurality of recesses 12 are not configured such that the locus of the plurality of recesses 12 when rotating about the rotation axis A covers the entire surface of the surface 11. In sample 28, the plurality of recesses 12 are configured such that the locus of the plurality of recesses 12 when rotating about the rotation axis A covers the entire surface of the surface 11. In sample 29, a plurality of grooves 13 are formed in the surface 11.

[0079] The condition A is that the depth D is 1 μm or more. The condition B is that the equivalent circle diameter of the recess 12 is 1 μm or more. The condition C is that the area ratio of the recess 12 is 1% or more.

[0080]

[0081] As shown in Table 3, no recess 12 is formed in sample 1. Recess 12 is formed in sample 2. However, in sample 2, although condition C is satisfied, conditions A and B are not satisfied. On the other hand, in samples 3 to 30, two or more of conditions A to C are satisfied.

[0082] The dimensional errors of sample 1 and sample 2 are 4 μm or more, so they cannot be evaluated as functioning as a cutting tool. On the other hand, the dimensional errors of samples 3 to 30 are less than 4 μm, so they function as a cutting tool. From this comparison, it was clarified from an experimental point of view that by making the recess 12 satisfy two or more of conditions A to C, the opening edge 12a functions as a cutting edge.

[0083] In samples 4 and 5, the depth D, the equivalent circle diameter of the recess 12, and the area ratio of the recess 12 are of the same degree. In sample 4, the tip 10 is formed of nanocrystalline diamond, while in sample 5, the tip is formed of nanocrystalline diamond added with boron. In sample 5, a lower surface roughness was obtained compared to sample 4. From this comparison, it was clarified from an experimental point of view that by forming the tip 10 of nanocrystalline diamond added with boron, the machining quality when machining glass can be improved.

[0084] In samples 6 to 10, the equivalent circle diameter of the recess 12 is in the range of 50 μm ± 2 μm. In samples 6 to 10, the area ratio of the recess 12 is in the range of 20% ± 4%, and the angle θ is in the range of 90° ± 1°. In samples 6 to 10, the depth D gradually increases.

[0085] In samples 8 to 10, the depth D is in the range of 1 μm or more and 25 μm or less, and a higher glossiness and a lower surface roughness are obtained. From this, it was clarified from an experimental point of view that by making the depth D 1 μm or more and 25 μm or less, the machining quality when machining with the cutting tool 100 can be improved.

[0086] In Samples 11 to 15, the depth D is in the range of 5 μm ± 0.2 μm. Additionally, in Samples 11 to 15, the area ratio of the recess 12 is in the range of 20% ± 2%, and the angle θ is in the range of 90° ± 1°. In Samples 11 to 15, the equivalent circle diameter of the recess 12 gradually increases.

[0087] In Samples 12 to 14, the equivalent circle diameter of the recess 12 is in the range of 1 μm or more and 71 μm or less, and a high glossiness and a low surface roughness are obtained. From an experimental perspective, it is thus clarified that by setting the equivalent circle diameter of the recess 12 to be 1 μm or more and 71 μm or less, the machining quality during machining with the cutting tool 100 can be improved.

[0088] In Samples 16 to 22, the depth D is in the range of 5 μm ± 0.4 μm. In Samples 16 to 22, the equivalent circle diameter of the recess 12 is in the range of 48 μm ± 2 μm, and the angle θ is in the range of 90° ± 2°. In Samples 16 to 22, the area ratio of the recess 12 gradually increases.

[0089] In Samples 16 to 21, the area ratio of the recess 12 is in the range of 1% or more and 80% or less, and a high glossiness and a low surface roughness are obtained. From an experimental perspective, it is thus clarified that by setting the area ratio of the recess 12 to be 1% or more and 80% or less, the machining quality during machining with the cutting tool 100 can be improved.

[0090] In Samples 23 to 26, the depth D is in the range of 5 μm ± 0.5 μm. In Samples 23 to 26, the equivalent circle diameter of the recess 12 is in the range of 50 μm ± 1 μm, and the area ratio of the recess 12 is in the range of 18% ± 2%. In Samples 23 to 26, the angle θ gradually increases. In Samples 23 to 25, the angle θ is in the range of 80° or more and 160° or less, and a high glossiness and a low surface roughness are obtained. From an experimental perspective, it is thus clarified that by setting the angle θ to be 80° or more and 160° or less, the machining quality during machining with the cutting tool 100 can be improved.

[0091] In Sample 28, compared with Sample 27, a high glossiness and a low surface roughness are obtained. From an experimental perspective, it is thus clarified that by arranging the plurality of recesses 12 such that the locus of the plurality of recesses 12 when rotating around the rotation axis A covers the entire surface of the surface 11, the machining quality during machining with the cutting tool 100 can be improved.

[0092] In Sample 30, a high glossiness and surface roughness were obtained. Thus, it was experimentally clarified that by forming the tip portion 10 with binderless cubic boron nitride, the machining quality during machining of hardened steel using the cutting tool 100 can be improved.

[0093] It should be considered that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the present invention is represented not by the above-described embodiments but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

[0094] Explanation of Reference Numerals

[0095] 10: Tip portion; 11: Surface; 12: Concave portion; 12a: Opening edge; 12b: Side surface; 13: Groove; 20: Main body portion; 30: Connection layer; 100: Cutting tool; 200: Cutting tool; θ: Angle; A: Rotation axis; D: Depth; L1, L2: Tangent lines; P: Measurement point.

Claims

1. A cutting tool that rotates about a rotation axis, wherein, the cutting tool has a tip portion, the tip portion has a surface in the shape of a partial sphere that contacts a workpiece, a plurality of recesses are formed on the surface and are arranged separately from each other, the opening edges of the respective plurality of recesses form cutting edges, the equivalent circle diameter of each of the plurality of recesses is 1 μm or more and 100 μm or less, the tip portion is formed of binderless cubic boron nitride or nanocrystalline diamond, the equivalent circle diameter of the recess is the square root of the value obtained by dividing the area of the recess as viewed from above by π / 4, the plurality of recesses are arranged in a plurality of columns extending from the central portion of the surface.

2. The cutting tool according to claim 1, wherein, Atoms belonging to Group 13 or Group 15 of the long-period periodic table are added to the nanocrystalline diamond.

3. The cutting tool according to claim 2, wherein, The addition concentration of the atoms is 1 ppm or more and 10,000 ppm or less.

4. The cutting tool according to any one of claims 1 to 3, wherein, each of the plurality of recesses has a side surface connected to the opening edge, in 80% or more of the plurality of recesses, the angle between the side surface and the portion of the surface connected to the opening edge is 80° or more and 160° or less.

5. The cutting tool according to any one of claims 1 to 3, wherein, The plurality of recesses are arranged such that the trajectories of the plurality of recesses when the cutting tool rotates about the rotation axis cover the entire surface.

6. The cutting tool according to any one of claims 1 to 3, wherein, The proportion of the total area of the plurality of recesses in the area of the surface is 1% or more and 80% or less.

7. The cutting tool according to any one of claims 1 to 3, wherein, a plurality of grooves extending radially from the central portion of the surface are formed on the surface, the plurality of recesses are arranged in the portion of the surface located between the plurality of grooves.

8. The cutting tool according to any one of claims 1 to 3, wherein, The cutting tool is used with a cutting depth of 10 μm or less.

9. The cutting tool according to any one of claims 1 to 3, wherein, In the binderless cubic boron nitride, the median particle size of the cubic boron nitride grains is less than 1 μm.

10. The cutting tool according to any one of claims 1 to 3, wherein, In the nanocrystalline diamond, the median particle size of the diamond grains is less than 1 μm.

11. The cutting tool according to any one of claims 1 to 3, wherein, In a top view, the recess is circular.

12. The cutting tool according to any one of claims 1 to 3, wherein, The depth of the recess is 1 μm or more and 25 μm or less.

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