Cemented carbide, cutting tool blank, cutting tool, and manufacturing method of machined product

Abstract

The superhard alloy system of the present invention comprises: a plurality of hard particles containing W and C and a bonding phase incorporating the plurality of hard particles; in the degree distribution related to the equivalent circular diameter of the plurality of hard particles in the cross section, when the width of the class of the equivalent circular diameter is 0.05 μm, the mode of the degree distribution is 0.15 μm or more and 0.4 μm or less; the mode of the degree distribution is less than the class value of the class containing the value of the center of the range of the equivalent circular diameter at half-width of the degree distribution; when the degree in the class containing the upper limit value of the equivalent circular diameter at half-width of the degree distribution is defined as F1, and the degree in the class containing the class value of the class containing the upper limit value and the value obtained by adding the half-width of the degree distribution is defined as F2, F1 and F2 satisfy the relationship F2 < F1 / 2.

Description

[Technical Field]

[0001] The embodiments of the present invention relate to a method for manufacturing superhard alloys, cutting tool blanks, cutting tools, and machined workpieces. [Previous Technology]

[0002] Rotary tools for processing printed circuit boards with cutting tips made of superhard alloys are well known. The superhard alloy may comprise a first phase consisting of a plurality of tungsten carbide particles and a cobalt-containing second phase.

[0003] For example, a superhard alloy is known, as shown in WO2023 / 062818, in which the average value of the equivalent circular diameter of the tungsten carbide particles is 0.5 μm to 1.2 μm, and in the basis of the number of tungsten carbide particles, the first tungsten carbide particles with an equivalent circular diameter of 0.3 μm or less account for 13% or less, the second tungsten carbide particles with an equivalent circular diameter of more than 1.3 μm account for 12% or less, and in the histogram showing the distribution of the equivalent circular diameter of the tungsten carbide particles, the ratio of the maximum degree relative to the minimum degree in the range of the equivalent circular diameter of the tungsten carbide particles being more than 0.3 μm and less than 1.3 μm is 7.0 or less, and the cobalt content of the superhard alloy is more than 0% by mass and less than 10% by mass. [Summary of the Invention]

[0004] [Problem to be Solved by the Invention] For example, in order to improve the efficiency of cutting operations using cutting tools, there is a need to improve the wear resistance of cutting tools. Thus, there is still room for further improvement in the wear resistance of cutting tools in the prior art.

[0005] The purpose of this embodiment is to provide a superhard alloy that can improve the wear resistance of cutting tools. [Technical means to solve the problem]

[0006] An embodiment of the superhard alloy system comprises a plurality of hard particles containing W and C and a bonding phase incorporating the plurality of the aforementioned hard particles; in the degree distribution related to the equivalent circular diameter of the plurality of the aforementioned hard particles in the cross-section, when the width of the step of the aforementioned equivalent circular diameter is 0.05 μm, the mode of the aforementioned degree distribution is 0.15 μm or more and 0.4 μm or less; the mode of the aforementioned degree distribution is less than the step value of the step containing the value of the center of the range of the aforementioned equivalent circular diameter that gives the aforementioned degree distribution a full width at half maximum; when the degree in the step containing the upper limit value of the aforementioned equivalent circular diameter that gives the aforementioned degree distribution a full width at half maximum is defined as F1, and the degree in the step containing the step value of the step containing the upper limit value and the value obtained by adding the half width at half maximum of the aforementioned degree distribution is defined as F2, F1 and F2 satisfy the relationship F2 < F1 / 2. [Effects of the Invention]

[0007] Depending on the embodiment, the provided superhard alloy can improve the wear resistance of cutting tools.

Implementation Method

[0009] Hereinafter, the forms of the superhard alloy, cutting tool blank, cutting tool, and method for manufacturing the workpiece of the present invention will be described in detail with reference to the drawings (there are also cases where only "forms of the present invention" are referred to). The superhard alloy, cutting tool blank, cutting tool, and method for manufacturing the workpiece of the present invention are not limited to the forms described below. In the following forms, the same symbol is used for the same part and repeated descriptions are omitted.

[0010] <Cutting Tool> First, let's describe a rotary tool for printed circuit board (PCB) processing as an example of a cutting tool in this embodiment. The workpiece material processed by the rotary tool for PCB processing can be, for example, a printed circuit board (PCB) or a printed wiring board (PWB). As for such a rotary tool for PCB processing, an example is a very small diameter drill bit for drilling holes in printed wiring boards. Hereinafter, the very small diameter drill bit for drilling holes in printed wiring boards may also be referred to as a printed wiring board drill bit (PWB drill bit).

[0011] Hereinafter, an example of an embodiment of the PWB drill bit will be described with reference to Figures 1A and 1B. Figure 1A is a schematic diagram illustrating the structure of the embodiment of the PWB drill bit. Figure 1B is a schematic diagram illustrating the front end of the embodiment of the PWB drill bit.

[0012] As shown in Figure 1A, the PWB drill bit 1 has a cutting edge 2, a shank 3 and a connecting part 4.

[0013] The cutting edge 2 is a cylindrical component with an elongated shape. As shown in Figure 1B, the front end of the cutting edge 2 is provided with a cutting edge 2b. As shown in Figures 1A and 1B, the side of the cutting edge 2 forms an odd or multiple spiral chip-removing grooves 2a extending from the front end to the base end.

[0014] The cutting edge 2 is made of a superhard alloy. This superhard alloy system comprises a hard phase and a bonding phase. The hard phase system contains W (tungsten) and C (carbon). The bonding phase system contains at least one of iron group elements (Co (cobalt), Ni (nickel), and Fe (iron)). The hard phase system comprises a plurality of hard particles containing W and C. The bonding phase system comprises a plurality of bonding particles containing iron group elements. The plurality of hard particles are bonded together by the bonding phase.

[0015] The shank 3 is a cylindrical component, the outer diameter of which is larger than the outer diameter of the cutting edge 2. The shank 3 is made of, for example, stainless steel. In this way, compared to the case where the PWB drill bit 1 is formed entirely of superhard alloy, the manufacturing cost of the PWB drill bit 1 can be reduced.

[0016] The connecting part 4 connects the cutting edge 2 and the handle 3, which have different outer diameters. The connecting part 4 includes a first conical part 4a, a second conical part 4b, and a cylindrical part 4c.

[0017] The first tapered portion 4a has an outer diameter that gradually decreases towards the front end. The first tapered portion 4a is integrally formed with the handle portion 3. That is, the first tapered portion 4a is formed of the same material as the handle portion 3, such as stainless steel.

[0018] The second conical portion 4b has an outer diameter that gradually increases toward the base end. The second conical portion 4b is integrally formed with the cutting edge 2. That is, the second conical portion 4b is formed of the same material as the forming material of the cutting edge 2, such as a superhard alloy.

[0019] The cylindrical portion 4c includes a portion integrally formed with the first conical portion 4a near the base end and a portion integrally formed with the second conical portion 4b near the front end. The portion integrally formed with the first conical portion 4a is formed of the same material as the first conical portion 4a, such as stainless steel. The portion integrally formed with the second conical portion 4b is formed of the same material as the material forming the second conical portion 4b, such as a superhard alloy.

[0020] The portions integrally formed with the first conical portion 4a and the portions integrally formed with the second conical portion 4b are joined at the mating surface 4d located within the cylindrical portion 4c. That is, the portion formed integrally with the first conical portion 4a and made of stainless steel or the like, and the portion formed integrally with the second conical portion 4b and made of superhard alloy, are joined at the mating surface 4d. Thus, the cutting edge 2 and the handle 3 are connected by the cylindrical portion 4c.

[0021] The cutting tool of the embodiment is not limited to a rotary tool for printing board processing, such as the PWB drill bit 1 shown in FIG. 1. There is no particular limitation as long as the cutting edge of the cutting tool of the embodiment contains at least a superhard alloy. The cutting tool of the embodiment may also include, for example, a pull-in insert whose cutting edge contains a superhard alloy and a support portion for fixing such a pull-in insert.

[0022] <Cutting Tool Blank> Next, an example of a cutting tool blank used for manufacturing a rotary tool for printed circuit board processing will be described. As a blank used for manufacturing a rotary tool for printed circuit board processing, an example is the blank used for manufacturing a PWB drill bit as shown in FIG1A and FIG1B.

[0023] Here, an example of a PWB drill bit blank according to an embodiment will be described with reference to FIG2. FIG2 is a diagram that schematically illustrates the structure of the PWB drill bit blank according to an embodiment.

[0024] As shown in Figure 2, the PWB drill bit blank 5 is a cylindrical component with a long strip shape. The length of the long side of the PWB drill bit blank 5 is the sum of the length of the cutting edge 2 of the PWB drill bit 1 in the long side direction shown in Figures 1A and 1B, the length of the second conical part 4b, and the length of the part of the cylindrical part 4c that is integrally formed with the second conical part 4b.

[0025] The end face of the PWB drill bit blank 5 at one end corresponds to the mating surface 4d in the cylindrical portion 4c of the PWB drill bit 1. The PWB drill bit blank 5 is joined to the shank 3, the first conical portion 4a, and the portion of the cylindrical portion 4c integrally formed with the first conical portion 4a in the mating surface 4d by means of laser or the like. Afterwards, the PWB drill bit blank 5 is subjected to edge-sharpening, grinding, or the like, thereby forming the cutting edge 2, the second conical portion 4b, and the portion of the cylindrical portion 4c integrally formed with the second conical portion 4b of the PWB drill bit 1.

[0026] The blank 5 for PWB drill bit is made of the same material as the part of the cutting edge 2, the second conical part 4b and the cylindrical part 4c that is integrally formed with the second conical part 4b in forming the PWB drill bit 1, such as a superhard alloy.

[0027] The PWB drill bit blank 5 can also form a coating on the surface of a substrate formed of superhard alloy. Examples of such coatings include coatings formed of titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), titanium aluminum composite nitride (TiAlN), and aluminum oxide (Al2O3).

[0028] The cutting tool blank of the embodiment is not limited to blanks used for manufacturing rotary tools for printed circuit board processing, such as the PWB drill bit blank 5 shown in FIG. 2. There are no particular limitations if the cutting tool blank of the embodiment contains at least a superhard alloy. The cutting tool blank of the embodiment may also be, for example, a blank used for manufacturing a pull-out insert whose cutting edge contains a superhard alloy.

[0029] <Superhard Alloy> Next, an example of an embodiment of the superhard alloy will be described with reference to Figures 3 and 4. Figure 3 is a schematic cross-sectional view of the embodiment of the superhard alloy. Figure 4 is a histogram schematically illustrating the equivalent circle diameter of the plurality of hard particles contained in the embodiment of the superhard alloy.

[0030] As shown in Figure 3, a cross-sectional photograph of the superhard alloy 10 in the embodiment is obtained. For example, the surface of the superhard alloy 10 is observed using a scanning electron microscope or the like, thereby obtaining a cross-sectional photograph of the superhard alloy 10. The dimensions of the cross-section of the superhard alloy 10 should be such that a degree distribution related to the equivalent circle diameter of the plurality of hard particles 20 is obtained. For example, the cross-section of the superhard alloy 10 is a cross-section with dimensions of 10 μm × 10 μm.

[0031] As shown in Figure 3, the superhard alloy 10 of the embodiment includes a plurality of hard particles 20 and a bonding phase 30. The plurality of hard particles 20 contain tungsten (W) and carbon (C). The plurality of hard particles 20 may also be tungsten carbide (WC) particles. As shown in Figure 3, the plurality of hard particles 20 have various cross-sectional areas in the cross-section of the superhard alloy 10. The bonding phase 30 binds the plurality of hard particles 20. The bonding phase 30 contains a plurality of bonding particles. The plurality of bonding particles contain at least one of iron group elements such as cobalt (Co), nickel (Ni), and iron (Fe). As shown in Figure 3, the plurality of bonding particles also have various cross-sectional areas in the cross-section of the superhard alloy 10.

[0032] For the superhard alloy 10 of the embodiment, a degree distribution related to the equivalent circular diameter of a plurality of hard particles 20 in the cross-section of the superhard alloy 10 is obtained. The equivalent circular diameter of each hard particle 20 refers to the diameter (μm) of a circle whose area is the same as the cross-sectional area of ​​the hard particles 20 in the cross-section of the superhard alloy 10. The equivalent circular diameter of each hard particle 20 is calculated by analyzing the image of the hard particles 20 in the cross-sectional photograph of the superhard alloy 10 using image processing software such as "ImageJ" (developed by Wayne Rasband of the National Institutes of Health). Based on the calculated equivalent circular diameter of each hard particle 20, a degree distribution related to the equivalent circular diameter of a plurality of hard particles 20 in the cross-section of the superhard alloy 10 is obtained.

[0033] The degree distribution related to the equivalent circular diameter of the plurality of hard particles 20 can be a degree distribution table or a degree distribution graph (histogram). For example, a histogram related to the equivalent circular diameter of the plurality of hard particles 20, as shown in Figure 4, can be obtained. As shown in Figure 4, in the histogram related to the equivalent circular diameter of the plurality of hard particles 20, the horizontal axis represents the class of the equivalent circular diameter (μm), and the vertical axis represents the degree of the equivalent circular diameter in each class of the equivalent circular diameter. The degree of the equivalent circular diameter represents the number of hard particles 20 contained in each class of the equivalent circular diameter.

[0034] As shown in Figure 4, the range of the equivalent circle diameter in the degree distribution can be, for example, expressed as the range of the step values ​​of the degree distribution, from 0.15 μm to 1 μm. As shown in Figure 4, the step of the equivalent circle diameter in the degree distribution has a width Bw, which is set to negligible noise of the degree distribution. The width Bw of the step of the equivalent circle diameter in the degree distribution is, for example, 0.05 μm or 0.1 μm.

[0035] As shown in Figure 4, in the superhard alloy 10 of the embodiment, the mode of the degree distribution, Mo, is between 0.15 μm and 0.4 μm. The degree distribution has a maximum degree value, Fmax. The mode of Mo is the degree value of the tier with the maximum degree value, Fmax, in the degree distribution. Here, the terms "tier value" and "mode" are defined as follows: The tier value refers to the median value of the equivalent circle diameter in each tier. The mode refers to the median value of the equivalent circle diameter in the tier with the maximum degree value, Fmax. For example, the "tier value" in the tier with an equivalent circle diameter of 0.125 to 0.175 μm is 0.15 μm. When the tier with an equivalent circle diameter of 0.225 to 0.275 μm has a maximum degree value, Fmax, the "mode" is the median value in this tier, which is 0.25 μm.

[0036] When the mode Mo of the degree distribution is 0.15 μm or more, the proportion of excessively small hard particles 20 can be reduced, thus increasing the hardness of the cutting tool containing the superhard alloy 10 in the cutting edge 2b. When the mode Mo of the degree distribution is 0.4 μm or less, the proportion of large hard particles 20 can be reduced, thus reducing the occurrence of abnormal wear caused by the loss of large hard particles 20. As a result, the wear state of the cutting tool can be stabilized, thus stabilizing the cutting performance of the cutting tool.

[0037] As shown in Figure 4, in the superhard alloy 10 of the embodiment, the mode Mo of the degree distribution is less than the class value of the class of the central value C in the range B (FWHM) of the equivalent circle diameter at half maximum (FWHM) that gives the degree distribution. The range B (FWHM) of the equivalent circle diameter at half maximum (FWHM) that gives the degree distribution refers to the range of class values ​​of the class of degrees that have more than half (Fmax / 2) of the maximum value Fmax. When obtaining the range B (FWHM) of the equivalent circle diameter at half maximum (FWHM) that gives the degree distribution, a curve of degree distribution obtained by curve fitting can be used. In this case, the range B (FWHM) of the equivalent circle diameter at half maximum (FWHM) that gives the degree distribution refers to the range of class values ​​of the class of degrees that have more than half of the peak value of the degree distribution curve.

[0038] When the mode Mo of the degree distribution is less than the class value of the class of the central value C in the range B (FWHM) containing the equivalent circle diameter at half maximum width of the degree distribution, the proportion of small-sized hard particles 20 can be increased, thus reducing the occurrence of abnormal wear caused by the loss of large-sized hard particles 20. As a result, the wear state of the cutting tool can be stabilized, thus stabilizing the cutting performance of the cutting tool.

[0039] As shown in Figure 4, for the superhard alloy 10 of embodiment type, degree F1 and degree F2 are calculated. Degree F1 refers to the degree in the class of the upper limit value Sup of the equivalent circle diameter within the range B (FWHM) of the half-height full width at half maximum given the degree distribution. For degree F2, the class value of the class containing the upper limit value Sup is added to the degree distribution B (HWHM) (half-height half-width; Half Width at Half Maximum) to obtain the value V, and degree F2 refers to the degree in the class containing the value V. Here, the half-height half-width B (HWHM) of the degree distribution is half of the range B (FWHM) of the equivalent circle diameter within the half-height full width at half maximum given the degree distribution. In the superhard alloy 10 of embodiment type, degree F1 and degree F2 satisfy the following relationship: F2 < F1 / 2.

[0040] When the degree F1 and degree F2 satisfy the relationship F2 < F1 / 2, the proportion of large-sized hard particles 20 can be reduced, thus reducing the occurrence of abnormal wear caused by defects in large-sized hard particles 20. As a result, the wear state of the cutting tool can be stabilized, thus stabilizing the cutting performance of the cutting tool.

[0041] As described above, in the superhard alloy 10 of the embodiment, the proportion of excessively small hard particles 20 and the proportion of large hard particles 20 among the plurality of hard particles 20 can be reduced. Therefore, the size of the plurality of hard particles 20 and the dispersion of the size of the plurality of hard particles 20 can be reduced. As a result, the wear resistance of the cutting tool can be improved, and thus the cutting performance of the cutting tool can be improved. For example, when the cutting tool is a rotary tool for printing board processing such as a PWB drill bit 1, the hole position accuracy during hole drilling of the printing board can be improved.

[0042] In the superhard alloy 10 of the embodiment type, the skewness of the degree distribution can be greater than 1. For example, the skewness can be 1.25 or higher. The skewness of the degree distribution is the skewness defined in statistics. In this case, the proportion of small-sized hard particles 20 can be increased, thus reducing the occurrence of abnormal wear caused by defects in large-sized hard particles 20. As a result, the wear state of the cutting tool can be stabilized, thus stabilizing the cutting performance of the cutting tool.

[0043] As shown in Figure 4, the degree distribution system has a central value Me. The central value Me is the class value of the class with the central equivalent circle diameter in the degree distribution. In the superhard alloy 10 of the embodiment type, the difference between the mode Mo and the central value Me of the degree distribution can be less than 0.05 μm. At this time, the size dispersion of the plurality of hard particles 20 can be reduced. As a result, the wear resistance of the cutting tool can be improved, and thus the cutting performance of the cutting tool can be improved.

[0044] In the superhard alloy 10 of embodiment type, the sum of degrees in the steps encompassed by the range B (FWHM) of the equivalent circle diameter with full width at half maximum (FWHM) of the degree distribution can be 70% or more relative to the sum of degrees in the steps encompassed by the range of equivalent circle diameters of 0.15 μm to 1 μm. In this case, the size dispersion of the plurality of hard particles 20 can be reduced. As a result, the wear resistance of the cutting tool can be improved, thus improving the cutting performance of the cutting tool.

[0045] In the superhard alloy 10 of the embodiment, the mode of Mo can be 0.2 μm or more and 0.3 μm or less. When the mode of Mo in the degree distribution is 0.2 μm or more, the proportion of excessively small hard particles 20 can be reduced, thus increasing the hardness of the cutting tool containing the superhard alloy 10 in the cutting edge 2b. When the mode of Mo in the degree distribution is 0.3 μm or less, the proportion of large hard particles 20 can be reduced, thus reducing the occurrence of abnormal wear caused by the loss of large hard particles 20. As a result, the wear state of the cutting tool can be stabilized, thus stabilizing the cutting performance of the cutting tool.

[0046] As shown in Figure 4, in the superhard alloy 10 of the embodiment, the degree F3 in the class containing a value that is twice (2×Mo) or more of the mode Mo is determined. The degree F1 and degree F3 can satisfy the following relationship: F3 < F1 / 10. At this time, the proportion of large-sized hard particles 20 can be reduced, thus reducing the occurrence of abnormal wear caused by the loss of large-sized hard particles 20. As a result, the wear state of the cutting tool can be stabilized, thus stabilizing the cutting performance of the cutting tool.

[0047] <Manufacturing method of superhard alloy> Next, an example of the manufacturing method of the superhard alloy 10 of the embodiment will be described, but the manufacturing method of the superhard alloy 10 of the embodiment is not limited to the manufacturing method described below.

[0048] First, the powders are blended to a total mass of 100%, containing 75-98.9% by mass of tungsten carbide (WC) powder with an average particle size of 0.1-1 μm, 1-20% by mass of cobalt powder, 0.1-5% by mass of carbide powder of at least one element selected from Groups 4, 5, and 6 of the periodic table, and other unavoidable impurities. Furthermore, metallic tungsten (W) powder or carbon black (C) powder may be blended as needed.

[0049] Next, water or an organic solvent and an organic binder are added to the mixed powder and mixed. The mixture is then pulverized and mixed by conventional methods such as ball mills and vibratory mills. After that, it is dried into granules by a spray dryer.

[0050] Next, the granular mixed powder is formed into the shape of a predetermined cutting tool as shown in Figures 1A and 1B by conventional forming methods such as stamping, casting, extrusion, and cold isostatic pressing.

[0051] Next, the molded body is forged in a forging furnace in a vacuum or oxygen-free environment such as Ar or N2 at a forging temperature of 1350-1450°C for 0.5-5 hours. After that, it is sintered at a temperature 5-50°C lower than this forging temperature and a pressure of 5-20 MPa for 0.5-3 hours to produce a superhard alloy for cutting tools.

[0052] Here, the maximum temperature of the forging temperature is uniformly set to the same temperature. On the other hand, the heating rate before the forging temperature reaches the maximum temperature is varied in various ways to control the crystallization state within the superhard alloy.

[0053] Depending on the needs, the manufactured superhard alloy can be used as the substrate of the cutting tool, and a coating can be formed on the surface of the substrate. Examples of coatings include titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), titanium aluminum composite nitride (TiAlN), and aluminum oxide (Al2O3).

[0054] Furthermore, regarding the film formation method for coating, conventional film formation methods such as chemical vapor deposition (thermal CVD, plasma CVD, organic CVD, catalytic CVD, etc.) and physical vapor deposition (ion plating, sputtering, etc.) can be used.

[0055] <Method for Manufacturing a Cut-Workpiece> Next, a method for manufacturing a cut-workpiece using a rotary tool for printed circuit board processing as a cutting tool will be described, as an example of an embodiment of the method for manufacturing a cut-workpiece. As for the rotary tool for printed circuit board processing, the PWB drill bit 1 shown in Figures 1A and 1B can be cited as an example.

[0056] Hereinafter, an example of a method for manufacturing a machined object according to an embodiment will be described with reference to Figures 5A, 5B and 5C. Figures 5A, 5B and 5C are schematic illustrations of a method for manufacturing a machined object according to an embodiment.

[0057] The workpiece is manufactured by cutting the workpiece 100. In Figures 5A, 5B and 5C, for one example of cutting, a hole-making process is illustrated using a hole-making machine. The method for manufacturing the workpiece in the embodiment includes the following steps: (1) rotating the PWB drill 1; (2) bringing the PWB drill 1 into contact with the workpiece 100; and (3) moving the PWB drill 1 relatively away from the workpiece 100.

[0058] More specifically, first, as shown in FIG5A, the PWB drill bit 1 is rotated about the axis CR and brought into contact with the workpiece 100. Next, as shown in FIG5B, the cutting edge 2b of the PWB drill bit 1 is brought into contact with the workpiece 100 to create a hole. And, as shown in FIG5C, the PWB drill bit 1 is moved away from the workpiece 100.

[0059] In Figure 5A, with the workpiece 100 fixed and the PWB drill bit 1 rotating, the PWB drill bit 1 is moved downwards to approach the workpiece 100. Next, in Figure 5B, the cutting edge 2b of the PWB drill bit 1 contacts the fixed workpiece 100 to create a hole in the workpiece 100. Next, in Figure 5C, with the workpiece 100 fixed, the PWB drill bit 1 is moved upwards to move away from the workpiece 100.

[0060] In the cutting process of the manufacturing method of this embodiment, the PWB drill 1 is moved to contact the workpiece 100 or to move away from the workpiece 100. However, the present invention is not limited to this embodiment.

[0061] For example, in step (1), the workpiece 100 can be brought closer to the PWB drill bit 1. Similarly, in step (3), the workpiece 100 can be moved away from the PWB drill bit 1. To continue the cutting process, for example, while maintaining the rotation of the PWB drill bit 1, the steps of bringing the cutting edge 2b of the PWB drill bit 1 into contact with different positions of the workpiece 100 can be repeated.

[0062] Here, taking the cutting material 100 as a representative example, examples include printed circuit boards (PCBs) and printed wiring boards (PWBs). [Example]

[0063] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to the embodiments shown below.

[0064] (Example) First, 92% by mass of tungsten carbide (WC) powder with an average particle size of 0.4 μm and 8% by mass of cobalt powder were mixed to obtain a mixed powder. Next, isopropanol (IPA) was mixed into the obtained mixed powder and pulverized by a vibratory mill. Then, the mixed powder was dried by a spray dryer to obtain granular mixed powder. Next, the obtained granular mixed powder was formed into the shape of PWB drill bit 1 as shown in FIG. 1A by stamping. Next, this formed body was forged in a forging furnace under vacuum at a forging temperature of 1400°C for 1 hour. Afterward, it was sintered by HIP at a temperature 15°C lower than this forging temperature and a pressure of 10 MPa for 1 hour to produce the superhard alloy of the example. Here, the crystallization state within the superhard alloy was controlled by adjusting the heating rate just before the forging temperature reached its maximum temperature.

[0065] Next, the predetermined surface of the obtained superhard alloy was ground, and the ground surface was photographed using a field emission scanning electron microscope (FE-SEM) manufactured by JEOL Ltd. under the following conditions: magnification: 2000x, acceleration voltage: 10 (kV), brightness: 581 and contrast: 4630.

[0066] Next, the captured photograph is analyzed using the image processing software "ImageJ". Here, the equivalent circle diameter of a plurality of hard particles contained in a region of size 10μm × 10μm in the image is calculated. Based on the calculated equivalent circle diameter of the plurality of hard particles, a histogram related to the equivalent circle diameter of the plurality of hard particles is obtained. The width of the steps of the equivalent circle diameter is 0.05μm.

[0067] Figure 6 shows a histogram relating to the equivalent circle diameter of the plurality of hard particles contained in the superhard alloy of the embodiment. The horizontal axis represents the class value of the class of the equivalent circle diameter (μm), and the vertical axis represents the degree in the class of the equivalent circle diameter (μm).

[0068] As shown in Figure 6, the mode of the obtained histogram is 0.25 μm. The mode of the obtained histogram, 0.25 μm, is the class value of the class consisting of the value of the equivalent circle diameter, which is smaller than the middle value of the range of 0.20 μm to 0.35 μm that determines the full width at half maximum (FWHM) of the histogram, i.e., the equivalent circle diameter of 0.275. The degree F1 of the class containing the upper limit value of the equivalent circle diameter within the range of the equivalent circle diameter within the range of the equivalent circle diameter within the FWHM of the obtained histogram is 156. The degree F2 of the class containing the value obtained by adding the class value of 0.35 μm, which is the upper limit value of the equivalent circle diameter within the range of the equivalent circle diameter within the range of the equivalent circle diameter within the FWHM of the obtained histogram, to the half width at half maximum (FWHM) of the histogram, is 63.

[0069] The skewness of the obtained histogram is 1.14. The difference between the mode and the median of the obtained histogram is less than 0.025 μm. The total number of degrees in the steps encompassed by the range of equivalent circle diameters at half maximum and full width at half maximum of the obtained histogram is 747. The total number of degrees in the steps encompassed by the range of equivalent circle diameters between 0.15 μm and 1 μm of the obtained histogram is 1130. The degree F3 in the steps containing twice the value of the mode of the obtained histogram is 54.

[0070] Using a PWB drill bit made of the obtained superhard alloy, a hole was drilled in a printed wiring board under the following drilling conditions: Drilling conditions: Rotation speed: 200 rpm; Feed rate: 2.6 m / min; Drill bit size: φ0.2 × 3 mm; Substrate: E-705G

[0071] When 4000 holes are drilled on the printed circuit board, the wear amount of the PWB drill tip is 13 μm. When 8000 holes are drilled on the printed circuit board, the wear amount of the PWB drill tip is 16 μm. When 12000 holes are drilled on the printed circuit board, the wear amount of the PWB drill tip is 20 μm. When 16000 holes are drilled on the printed circuit board, the wear amount of the PWB drill tip is 25 μm.

[0072] The process capability index Cpk is used to evaluate the degree of hole position deviation when drilling holes in printed wiring boards using a PWB drill bit made of the obtained superhard alloy. The distance between the hole and the target position of the center is measured as hole position accuracy data. Furthermore, the average value and standard deviation of the measured hole position accuracy data are calculated. Finally, using the calculated average value and standard deviation, the process capability index Cpk is calculated according to the following formula: Cpk = (Specification value - Average value) / (3 × Standard deviation) Here, the specification value is ±50μm. The process capability index Cpk is 1.55.

[0073] (Comparative Example 1) The predetermined surface of the superhard alloy of a conventional PWB drill bit was ground, and the ground surface was photographed using a field emission scanning electron microscope (FE-SEM) manufactured by JEOL Ltd. under the same conditions as in Example 1.

[0074] Next, image analysis was performed on the captured photograph in the same manner as in Example 1. Here, the equivalent circle diameter of a plurality of hard particles contained in a region of size 10 μm × 10 μm in the image was calculated. Based on the calculated equivalent circle diameter of the plurality of hard particles, a histogram related to the equivalent circle diameter of the plurality of hard particles was obtained. The width of the steps of the equivalent circle diameter was 0.05 μm.

[0075] Figure 7 is a histogram showing the equivalent circle diameter of the plurality of hard particles contained in the superhard alloy of Comparative Example 1. The horizontal axis represents the class value of the equivalent circle diameter (μm). The vertical axis represents the degree in the class of the equivalent circle diameter (μm).

[0076] As shown in Figure 7, the mode of the obtained histogram is 0.3 μm. The mode of the obtained histogram, 0.3 μm, is less than the class value of 0.3 μm, which is the value of the class that includes the center value of the class within the range of 0.2 μm to 0.4 μm that determines the full width at half maximum (FWHM) of the histogram. The degree F1 of the class that includes the upper limit value of the equivalent circle diameter within the range that determines the full width at half maximum (FWHM) of the obtained histogram is 94. The degree F2 of the class that includes the value of 0.4 μm, which is the class value of the class that includes the upper limit value of the equivalent circle diameter within the range that determines the full width at half maximum (FWHM) of the obtained histogram, plus the value of 0.5 μm of the half width at half maximum (FWHM) of the histogram, is 42.

[0077] The skewness of the obtained histogram is 0.927. The difference between the mode and the median of the obtained histogram is 0. The total number of degrees in the steps encompassed by the range of the equivalent circle diameter that determines the full width at half maximum (FWHM) of the obtained histogram is 664. The total number of degrees in the steps encompassed by the range of the equivalent circle diameter between 0.15 μm and 1 μm of the obtained histogram is 932. The number of degrees F3 in the steps that includes twice the value of the mode of the obtained histogram is 16.

[0078] Using a conventional PWB drill bit, a hole was drilled in the printed wiring board under the same conditions as in Example 1.

[0079] When 4000 holes are drilled on the printed circuit board, the wear amount of the PWB drill tip is 15 μm. When 8000 holes are drilled on the printed circuit board, the wear amount of the PWB drill tip is 20 μm. When 12000 holes are drilled on the printed circuit board, the wear amount of the PWB drill tip is 24 μm. When 16000 holes are drilled on the printed circuit board, the wear amount of the PWB drill tip is 30 μm.

[0080] The process capability index Cpk is 1.2 when drilling holes in a printed wiring board using a conventional PWB drill bit.

[0081] Here, the present technology can achieve the following configuration. (1) A superhard alloy comprising: a plurality of hard particles containing W and C; and a bonding phase bonded to the plurality of the aforementioned hard particles; in a degree distribution related to the equivalent circular diameter of the plurality of the aforementioned hard particles in a cross section, when the width of the class of the aforementioned equivalent circular diameter is 0.05 μm, the mode of the aforementioned degree distribution is 0.15 μm or more and 0.4 μm or less; the mode of the aforementioned degree distribution is less than the class value of the class containing the value of the center of the range of the aforementioned equivalent circular diameter that gives the aforementioned degree distribution a full width at half maximum; when the degree in the class containing the upper limit value of the aforementioned equivalent circular diameter that gives the aforementioned degree distribution a full width at half maximum is defined as F1, and the degree in the class containing the class value of the class containing the upper limit value and the value obtained by adding the half width at half maximum of the aforementioned degree distribution is defined as F2, F1 and F2 satisfy the following relationship: F2 < F1 / 2. (2) The superhard alloy as described in (1), wherein the skewness of the aforementioned degree distribution is greater than 1. (3) The superhard alloy as described in (1) or (2), wherein the difference between the aforementioned mode and the median value of the aforementioned degree distribution is less than 0.05 μm. (4) The superhard alloy as described in any one of (1) to (3), wherein the sum of degrees in the range of the aforementioned equivalent circle diameters that give the aforementioned degree distribution a full width at half maximum (FWHM) is 70% or more relative to the sum of degrees in the range of the aforementioned equivalent circle diameters that are 0.15 μm or more and less than 1 μm. (5) The superhard alloy as described in any one of (1) to (4), wherein the aforementioned mode is 0.2 μm or more and less than 0.3 μm. (6) A superhard alloy as described in any one of (1) to (5), wherein when the degree in the class containing more than twice the aforementioned mode is defined as F3, F1 and F3 satisfy the following relationship: F3 < F1 / 10. (7) A cutting tool blank comprising: a superhard alloy as described in any one of (1) to (6). (8) A cutting tool comprising: a cutting edge comprising a superhard alloy as described in any one of (1) to (6). (9) A cutting tool as described in (8), which is a rotary tool for processing printed circuit boards. (10) A method for manufacturing a workpiece comprising the steps of: rotating a workpiece or a cutting tool as described in (8); bringing the cutting tool into contact with the workpiece; and moving the cutting tool relatively away from the workpiece. (11) A method for manufacturing a workpiece as described in (10), wherein the workpiece is a printed circuit board.

[0082] Those skilled in the art will readily appreciate other benefits and variations of the present invention. Therefore, the broad scope of the present invention is not limited to the specific details and representative embodiments described and illustrated above. Thus, various modifications can be made without departing from the general spirit or scope of the inventive concept defined by the claims and their equivalents. [Simplified Explanation of the Diagram]

[0008] Figure 1A is a schematic diagram illustrating the structure of the PWB drill bit of the embodiment. Figure 1B is a schematic diagram illustrating the front end of the PWB drill bit of the embodiment. Figure 2 is a schematic diagram illustrating the structure of the blank for the PWB drill bit of the embodiment. Figure 3 is a schematic diagram illustrating a cross-sectional view of the superhard alloy of the embodiment. Figure 4 is a schematic diagram illustrating a histogram related to the equivalent circle diameter of the plurality of hard particles contained in the superhard alloy of the embodiment. Figure 5A is a schematic diagram illustrating a method for manufacturing a workpiece of the embodiment. Figure 5B is a schematic diagram illustrating a method for manufacturing a workpiece of the embodiment. Figure 5C is a schematic diagram illustrating a method for manufacturing a workpiece of the embodiment. Figure 6 is a histogram showing the equivalent circle diameter of the plurality of hard particles contained in the superhard alloy of the embodiment. Figure 7 shows a histogram relating the equivalent circle diameters of the multiple hard particles contained in the superhard alloy of Comparative Example 1.

Claims

1. A superhard alloy comprising: a plurality of hard particles containing W and C; and a binding phase binding the plurality of the aforementioned hard particles; in a degree distribution related to the equivalent circular diameter of the plurality of the aforementioned hard particles in a cross-section, when the width of the class of the aforementioned equivalent circular diameter is 0.05 μm, the mode of the aforementioned degree distribution is 0.15 μm or more and 0.4 μm or less; the mode of the aforementioned degree distribution is less than the class value of the class containing the value of the center of the range of the aforementioned equivalent circular diameter that gives the aforementioned degree distribution a full width at half maximum (FWHM); when the degree in the class containing the upper limit value of the aforementioned equivalent circular diameter that gives the aforementioned degree distribution a full width at half maximum (FWHM) is defined as F1, and the degree in the class containing the class value of the class containing the upper limit value and the value obtained by adding the half width at half maximum (FWHM) of the aforementioned degree distribution is defined as F2, the aforementioned F1 and the aforementioned F2 satisfy the following relationship: F2 < F1 / 2.

2. The superhard alloy as described in claim 1, wherein, The aforementioned degree distribution has a skewness greater than 1.

3. The superhard alloy as described in claim 1, wherein, The difference between the aforementioned mode and the median of the aforementioned degree distribution is less than 0.05 μm.

4. The superhard alloy as described in claim 1, wherein, The aforementioned mode is between 0.2μm and 0.3μm.

5. A cutting tool blank comprising: a superhard alloy as described in any one of claims 1 to 4.

6. A cutting tool comprising: a cutting edge comprising a superhard alloy as described in any one of claims 1 to 4.

7. The cutting tool described in claim 6 is a rotary tool for processing printed circuit boards.

8. A method for manufacturing a workpiece by cutting, comprising the steps of: rotating a workpiece or a cutting tool as described in claim 6; bringing the cutting tool into contact with the workpiece; and moving the cutting tool relatively away from the workpiece.

9. A method for manufacturing a machined workpiece as described in claim 8, wherein, The material being cut is a printed circuit board.

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