Cemented carbide, blank for cutting tool, cutting tool, and method for manufacturing cut workpiece

Abstract

This cemented carbide comprises a plurality of hard particles containing W and C, and a binding phase that binds the plurality of hard particles, wherein: if the width of a class of equivalent circle diameters in a frequency distribution relating to the equivalent circle diameters of the plurality of hard particles in a cross-section is 0.05 μm, the mode of the frequency distribution is 0.15 μm or more and 0.4 μm or less, the mode of the frequency distribution is smaller than the class value of the class including the central value of the range of equivalent circle diameters that gives the full width at half maximum of the frequency distribution, and a frequency F1 in a class including the upper limit value of the equivalent circle diameter in the range of equivalent circle diameters that gives the full width at half maximum of the frequency distribution and a frequency F2 in a class including a value obtained by adding the half width at half maximum of the frequency distribution to the class value of the class including the upper limit value satisfy the relationship F2<F1 / 2.

Description

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

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate to methods of manufacturing cemented carbide, cutting tool blanks, cutting tools, and machined workpieces.

[0002] A rotary tool for machining printed circuit boards is known, which has a cutting edge made of cemented carbide. The cemented carbide may have a first phase made of tungsten carbide particles and a second phase containing cobalt.

[0003] For example, a cemented carbide alloy is known in which the average equivalent circle diameter of the tungsten carbide particles is 0.5 μm or more and 1.2 μm or less, the tungsten carbide particles contain 13% or less by number of first tungsten carbide particles having an equivalent circle diameter of 0.3 μm or less, and the tungsten carbide particles contain 12% or less by number of second tungsten carbide particles having an equivalent circle diameter of more than 1.3 μm, and in a histogram showing the distribution of the equivalent circle diameters of the tungsten carbide particles, the ratio of the maximum frequency to the minimum frequency is 7.0 or less in the range of the equivalent circle diameters of the tungsten carbide particles from more than 0.3 μm to 1.3 μm, and the cobalt content of the cemented carbide alloy is more than 0% by mass and 10% by mass or less (see, for example, WO 2023 / 062818).

[0004] A cemented carbide according to one aspect of the embodiment comprises a plurality of hard particles containing W and C, and a binder phase that bonds the plurality of hard particles, and when the width of the circle-equivalent diameter class in a frequency distribution for the circle-equivalent diameters of the plurality of hard particles in a cross section is 0.05 μm, the mode of the frequency distribution is 0.15 μm or more and 0.4 μm or less, the mode of the frequency distribution is smaller than the class value of a class including a median value in the range of circle-equivalent diameters that provides a full width at half maximum of the frequency distribution, and a frequency F1 in a class including an upper limit value of the circle-equivalent diameter in the range of circle-equivalent diameters that provides the full width at half maximum of the frequency distribution and a frequency F2 in a class including a value obtained by adding the class value of the class including the upper limit value to the half width at half maximum of the frequency distribution satisfy the relationship F2<F1 / 2.

[0005] FIG. 1A is a diagram schematically showing an example of the configuration of a PWB drill according to an embodiment. FIG. 1B is a diagram schematically showing an example of a tip portion of a PWB drill according to an embodiment. FIG. 2 is a diagram schematically showing an example of the configuration of a blank for a PWB drill according to an embodiment. FIG. 3 is a diagram schematically showing an example of a cross section of a cemented carbide according to an embodiment. FIG. 4 is a diagram schematically showing an example of a histogram relating to the circle-equivalent diameters of a plurality of hard particles contained in a cemented carbide according to an embodiment. FIG. 5A is a diagram schematically showing an example of a method for manufacturing a machined product according to an embodiment. FIG. 5B is a diagram schematically showing an example of a method for manufacturing a machined product according to an embodiment. FIG. 5C is a diagram schematically showing an example of a method for manufacturing a machined product according to an embodiment. FIG. 6 is a diagram showing a histogram relating to the circle-equivalent diameters of a plurality of hard particles contained in a cemented carbide according to an example. FIG. 7 is a diagram showing a histogram relating to the circle-equivalent diameters of a plurality of hard particles contained in a cemented carbide according to Comparative Example 1.

[0006] Hereinafter, modes for carrying out the methods for manufacturing cemented carbide, cutting tool blanks, cutting tools, and machined products according to the present disclosure (hereinafter referred to as "embodiments") will be described in detail with reference to the drawings. The methods for manufacturing cemented carbide, cutting tool blanks, cutting tools, and machined products according to the present disclosure are not limited to the embodiments described below. In the following embodiments, the same components are designated by the same reference numerals, and redundant explanations will be omitted.

[0007] For example, in order to improve the efficiency of cutting processing using a cutting tool, it is required to improve the wear resistance of the cutting tool. Thus, the conventional techniques have room for further improvement in terms of improving the wear resistance of cutting tools.

[0008] Therefore, there is a need for a technology that can overcome the above-mentioned problems and improve the wear resistance of cutting tools.

[0009] <Cutting Tool> First, a rotary tool for machining printed circuit boards will be described as an example of a cutting tool according to an embodiment. The workpiece to be machined by the rotary tool for machining printed circuit boards is a printed circuit board such as a printed circuit board (PCB) or a printed wiring board (PWB). An example of such a rotary tool for machining printed circuit boards is a very small diameter drill for drilling holes in printed wiring boards. Hereinafter, the very small diameter drill for drilling holes in printed wiring boards will be referred to as a PWB drill.

[0010] 1A and 1B, an example of a PWB drill according to an embodiment will be described. Fig. 1A is a diagram schematically illustrating an example of the configuration of a PWB drill according to an embodiment. Fig. 1B is a diagram schematically illustrating an example of a tip portion of a PWB drill according to an embodiment.

[0011] As shown in FIG. 1A, the PWB drill 1 has a cutting portion 2, a shank portion 3, and a connecting portion 4.

[0012] The blade portion 2 is a long, cylindrical member. As shown in Fig. 1B, a cutting edge 2b is provided at the tip of the blade portion 2. As shown in Figs. 1A and 1B, one or more spiral chip discharge grooves 2a are formed on the side surface of the blade portion 2, extending from the tip to the base end.

[0013] The cutting portion 2 is made of a cemented carbide alloy including a hard phase containing W (tungsten) and C (carbon) and a binder phase containing an iron group element (at least one of Co (cobalt), Ni (nickel), and Fe (iron)). The hard layer is made of a plurality of hard particles containing W and C. The binder phase is made of a plurality of binder particles containing an iron group element. The binder phase bonds the plurality of hard particles.

[0014] The shank portion 3 is a cylindrical member with an outer diameter larger than that of the cutting portion 2. The shank portion 3 is made of, for example, stainless steel, which reduces the manufacturing cost of the PWB drill 1 compared to when the entire PWB drill 1 is made of cemented carbide.

[0015] The connecting portion 4 connects the cutting portion 2 and the shank portion 3, which have different outer diameters, and has a first tapered portion 4a, a second tapered portion 4b, and a cylindrical portion 4c.

[0016] The first tapered portion 4a has an outer diameter that gradually decreases toward the tip end. The first tapered portion 4a is integrally formed with the shank portion 3. That is, the first tapered portion 4a is formed of the same material as the material forming the shank portion 3, such as stainless steel.

[0017] The second tapered portion 4b has an outer shape that gradually increases toward the base end. The second tapered portion 4b is integrally formed with the cutting portion 2. That is, the second tapered portion 4b is formed of the same material as the cutting portion 2, such as cemented carbide.

[0018] The cylindrical portion 4c has a portion formed integrally with the first tapered portion 4a at the base end and a portion formed integrally with the second tapered portion 4b at the tip end. The portion formed integrally with the first tapered portion 4a is made of the same material as the first tapered portion 4a, such as stainless steel. The portion formed integrally with the second tapered portion 4b is made of the same material as the second tapered portion 4b, such as cemented carbide.

[0019] The portion integrally formed with the first tapered portion 4a and the portion integrally formed with the second tapered portion 4b are joined at a joining surface 4d located within the cylindrical portion 4c. That is, the stainless steel or the like forming the portion integrally formed with the first tapered portion 4a and the cemented carbide forming the portion integrally formed with the second tapered portion 4b are joined at the joining surface 4d. In this way, the cutting portion 2 and the shank portion 3 are connected by the cylindrical portion 4c.

[0020] The cutting tool according to the embodiment is not limited to a rotary tool for machining a printed circuit board, such as the PWB drill 1 shown in Fig. 1. The cutting tool according to the embodiment is not particularly limited as long as it includes at least a cutting edge including a cemented carbide. For example, the cutting tool according to the embodiment may include an insert having a cutting edge including a cemented carbide and a holder for fixing the insert.

[0021] <Cutting Tool Blank> Next, a blank for manufacturing a rotary tool for processing a printed circuit board will be described as an example of a cutting tool blank according to the embodiment. An example of a blank for manufacturing a rotary tool for processing a printed circuit board is a PWB drill blank for manufacturing a PWB drill 1 as shown in FIGS. 1A and 1B .

[0022] An example of a blank for a PWB drill according to an embodiment will now be described with reference to Fig. 2. Fig. 2 is a diagram schematically showing an example of the configuration of a blank for a PWB drill according to an embodiment.

[0023] 2, the PWB drill blank 5 is a long, cylindrical member. The length of the PWB drill blank 5 in the longitudinal direction is equal to or greater than the sum of the length of the cutting edge 2 in the longitudinal direction of the PWB drill 1 shown in FIGS. 1A and 1B, the length of the second tapered portion 4b, and the length of the cylindrical portion 4c that is integrally formed with the second tapered portion 4b.

[0024] The cross section of the PWB drill blank 5 at one end thereof corresponds to the joining surface 4d of the cylindrical portion 4c of the PWB drill 1. The PWB drill blank 5 is joined at the joining surface 4d by a laser or the like to the shank portion 3, the first tapered portion 4a, and a portion of the cylindrical portion 4c that is integral with the first tapered portion 4a. The PWB drill blank 5 is then sharpened by mechanical grinding, polishing, or the like to form the cutting portion 2 of the PWB drill 1, the second tapered portion 4b, and a portion of the cylindrical portion 4c that is integral with the second tapered portion 4b.

[0025] The blank 5 for the PWB drill is formed from the same material, such as cemented carbide, as the material forming the cutting portion 2 of the PWB drill 1, the second tapered portion 4b, and the portion of the cylindrical portion 4c that is integrally formed with the second tapered portion 4b.

[0026] In the PWB drill blank 5, a coating film may be formed on the surface of a substrate made of cemented carbide. Examples of such coating films include titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), titanium-aluminum composite nitride (TiAlN), and aluminum oxide (Al ２ O ３ ) and the like.

[0027] The cutting tool blank according to the embodiment is not limited to a blank for manufacturing a rotary tool for processing a printed circuit board, such as the PWB drill blank 5 shown in Fig. 2. The cutting tool blank according to the embodiment is not particularly limited as long as it contains at least a cemented carbide. The cutting tool blank according to the embodiment may be, for example, a blank for manufacturing an insert having a cutting edge containing a cemented carbide.

[0028] <Cemented Carbide> Next, an example of a cemented carbide according to an embodiment will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a diagram schematically showing an example of a cross section of a cemented carbide according to an embodiment. Fig. 4 is a diagram schematically showing an example of a histogram relating to the circle-equivalent diameters of a plurality of hard particles contained in the cemented carbide according to an embodiment.

[0029] As shown in Figure 3, for the cemented carbide 10 according to the embodiment, a photograph of the cross section of the cemented carbide 10 is obtained. For example, a scanning electron microscope or the like is used to observe the surface of the cemented carbide 10, thereby obtaining a photograph of the cross section of the cemented carbide 10. The cross section of the cemented carbide 10 has a size that makes it possible to obtain a frequency distribution of the circle-equivalent diameters of the plurality of hard particles 20. For example, the cross section of the cemented carbide 10 has a size of 10 µm x 10 µm.

[0030] As shown in FIG. 3 , the cemented carbide 10 according to the embodiment includes a plurality of hard particles 20 and a binder phase 30. The plurality of hard particles 20 contain tungsten (W) and carbon (C). The plurality of hard particles 20 may be tungsten carbide (WC) particles. As shown in FIG. 3 , the plurality of hard particles 20 have various cross-sectional areas in the cross section of the cemented carbide 10. The binder phase 30 bonds the plurality of hard particles 20. The binder phase 30 includes a plurality of binder particles. The plurality of binder particles contain at least one iron group element, such as cobalt (Co), nickel (Ni), and iron (Fe). As shown in FIG. 3 , the plurality of binder particles have various cross-sectional areas in the cross section of the cemented carbide 10.

[0031] For the cemented carbide 10 according to the embodiment, a frequency distribution of the circular equivalent diameters of the plurality of hard particles 20 in the cross section of the cemented carbide 10 is obtained. The circular equivalent diameter of each hard particle 20 means the diameter (μm) of a circle having the same area as the cross-sectional area of ​​the hard particle 20 in the cross section of the cemented carbide 10. The circular equivalent diameter of each hard particle 20 is calculated by analyzing an image of the hard particle 20 in a photograph of the cross section of the cemented carbide 10 using image processing software such as "ImageJ" (manufactured by Wayne Rasband National Institutes of Health). Based on the calculated circular equivalent diameter of each hard particle 20, a frequency distribution of the circular equivalent diameters of the plurality of hard particles 20 in the cross section of the cemented carbide 10 is obtained.

[0032] The frequency distribution of the equivalent circle diameters of the plurality of hard particles 20 may be a frequency distribution table or a frequency distribution diagram (histogram). For example, a histogram of the equivalent circle diameters of the plurality of hard particles 20 is obtained as shown in FIG. 4. In the histogram of the equivalent circle diameters of the plurality of hard particles 20 as shown in FIG. 4, the horizontal axis and the vertical axis represent the class of equivalent circle diameter (μm) and the frequency of the equivalent circle diameter in the class of equivalent circle diameter. The frequency of the equivalent circle diameter indicates the number of hard particles 20 included in the class of equivalent circle diameter.

[0033] As shown in Fig. 4, the range of equivalent circle diameters in the power distribution may be, for example, 0.15 µm or more and 1 µm or less, expressed as a range of class values ​​of the power distribution classes. As shown in Fig. 4, the classes of equivalent circle diameters in the power distribution have a width Bw that allows noise in the power distribution to be ignored. The width Bw of the classes of equivalent circle diameters in the power distribution is, for example, 0.05 µm or 0.1 µm.

[0034] As shown in FIG. 4 , in the cemented carbide 10 according to the embodiment, the mode Mo of the frequency distribution is 0.15 μm or more and 0.4 μm or less. The frequency distribution has a maximum frequency value Fmax. The mode Mo is the class value of the class having the maximum frequency value Fmax in the frequency distribution. The terms "class value" and "mode" mentioned above have the following meanings. The class value is the median of the numerical values ​​of the equivalent circle diameter in each class. The mode is the median of the numerical values ​​of the equivalent circle diameter in the class having the maximum frequency value Fmax. For example, the "class value" for a class having an equivalent circle diameter of 0.125 to 0.175 μm is 0.15 μm. When the class having an equivalent circle diameter of 0.225 to 0.275 μm has the maximum frequency value Fmax, the "mode" is 0.25 μm, which is the median of the numerical values ​​in this class.

[0035] When the mode Mo of the frequency distribution is 0.15 μm or more, it is possible to reduce the proportion of hard particles 20 that are too small, thereby improving the hardness of the cutting tool including the cutting edge 2b that includes the cemented carbide 10. When the mode Mo of the frequency distribution is 0.4 μm or less, it is possible to reduce the proportion of hard particles 20 that are large, thereby reducing the occurrence of abnormal wear such as chipping caused by large hard particles 20. As a result, it is possible to stabilize the wear state of the cutting tool, thereby stabilizing the cutting performance of the cutting tool.

[0036] As shown in FIG. 4 , in the cemented carbide 10 according to the embodiment, the mode Mo of the frequency distribution is smaller than the class value of the class including the median value C in the range B (FWHM: Full Width at Half Maximum) of equivalent circle diameters that gives the full width at half maximum of the frequency distribution. The range B (FWHM) of equivalent circle diameters that gives the full width at half maximum of the frequency distribution means the range of class values ​​of classes having frequencies equal to or greater than half the maximum frequency value Fmax / 2. When determining the range B (FWHM) of equivalent circle diameters that gives the full width at half maximum of the frequency distribution, a frequency distribution curve obtained by curve fitting may be used. In this case, the range B (FWHM) of equivalent circle diameters that gives the full width at half maximum of the frequency distribution means the range of class values ​​of classes having frequencies equal to or greater than half the peak value of the frequency distribution curve.

[0037] When the mode Mo of the frequency distribution is smaller than the class value of the class including the median value C in the range B of equivalent circle diameters (FWHM) that gives the full width at half maximum of the frequency distribution, it becomes possible to increase the proportion of small-sized hard particles 20, thereby reducing the occurrence of abnormal wear such as chipping caused by large-sized hard particles 20. As a result, it becomes possible to stabilize the wear state of the cutting tool, and therefore the cutting performance of the cutting tool.

[0038] As shown in Figure 4, in the cemented carbide alloy 10 according to the embodiment, the frequency F1 is determined in a class including an upper limit value Sup of the equivalent circle diameter in the range B (FWHM) of the equivalent circle diameter that provides the full width at half maximum of the power distribution. Also, the frequency F2 is determined in a class including a value obtained by adding the half width at half maximum B (HWHM) of the power distribution to the class value of the class including the upper limit value Sup. Here, the half width at half maximum B (HWHM) of the power distribution is half the range B (FWHM) of the equivalent circle diameter that provides the full width at half maximum of the power distribution. In the cemented carbide alloy 10 according to the embodiment, the frequency F1 and the frequency F2 satisfy the relationship F2 < F1 / 2.

[0039] When the power F1 and the power F2 satisfy the relationship F2<F1 / 2, it is possible to reduce the proportion of large-sized hard particles 20, thereby reducing the occurrence of abnormal wear such as chipping caused by the large-sized hard particles 20. As a result, it is possible to stabilize the wear state of the cutting tool, and therefore, it is possible to stabilize the cutting performance of the cutting tool.

[0040] As described above, in the cemented carbide 10 according to the embodiment, it is possible to reduce the proportion of hard particles 20 that are too small and the proportion of hard particles 20 that are too large among the plurality of hard particles 20. Therefore, it is possible to reduce the size of the plurality of hard particles 20 and also reduce the size variance of the plurality of hard particles 20. As a result, it is possible to improve the wear resistance of the cutting tool, and therefore the cutting performance of the cutting tool. For example, when the cutting tool is a rotary tool for processing printed circuit boards, such as the PWB drill 1, it is possible to improve the hole position accuracy in drilling holes in printed circuit boards.

[0041] In the cemented carbide 10 according to the embodiment, the skewness of the frequency distribution may be greater than 1. For example, the skewness may be 1.25 or greater. The skewness of the frequency distribution is a skewness defined in statistics. In this case, it is possible to increase the proportion of small-sized hard particles 20, thereby reducing the occurrence of abnormal wear such as chipping caused by large-sized hard particles 20. As a result, it is possible to stabilize the wear state of the cutting tool, and therefore, it is possible to stabilize the cutting performance of the cutting tool.

[0042] As shown in FIG. 4 , the frequency distribution has a median Me of the frequency distribution. The median Me is the class value of the class having the central equivalent circle diameter in the frequency distribution. In the cemented carbide 10 according to the embodiment, the difference between the mode Mo and the median Me of the frequency distribution may be 0.05 μm or less. In this case, it is possible to reduce the size variance of the multiple hard particles 20. As a result, it is possible to improve the wear resistance of the cutting tool, and therefore the cutting performance of the cutting tool.

[0043] In the cemented carbide 10 according to the embodiment, the sum of the frequencies in the classes included in the range B (FWHM) of the equivalent circle diameters that gives the full width at half maximum of the frequency distribution may be 70% or more of the sum of the frequencies in the classes included in the range of the equivalent circle diameters of 0.15 μm or more and 1 μm or less. In this case, it is possible to reduce the size dispersion of the plurality of hard particles 20. As a result, it is possible to improve the wear resistance of the cutting tool, and therefore the cutting performance of the cutting tool.

[0044] In the cemented carbide 10 according to the embodiment, the mode Mo may be 0.2 μm or more and 0.3 μm or less. When the mode Mo of the frequency distribution is 0.2 μm, it is possible to reduce the proportion of hard particles 20 that are too small, thereby improving the hardness of a cutting tool including a cutting edge 2b that includes the cemented carbide 10. When the mode Mo of the frequency distribution is 0.3 μm or less, it is possible to reduce the proportion of hard particles 20 that are large, thereby reducing the occurrence of abnormal wear such as chipping caused by large hard particles 20. As a result, it is possible to stabilize the wear state of the cutting tool, thereby stabilizing the cutting performance of the cutting tool.

[0045] As shown in Figure 4, for the cemented carbide 10 according to the embodiment, the frequency F3 is calculated in a class including a value that is equal to or greater than twice the mode Mo (2 x Mo). The frequency F1 and the frequency F3 may satisfy the relationship F3 < F1 / 10. In this case, it is possible to reduce the proportion of large-sized hard particles 20, thereby reducing the occurrence of abnormal wear such as chipping caused by large-sized hard particles 20. As a result, it is possible to stabilize the wear state of the cutting tool, and therefore the cutting performance of the cutting tool.

[0046] <Method for manufacturing cemented carbide> Next, an example of a method for manufacturing the cemented carbide 10 according to the embodiment will be described. The method for manufacturing the cemented carbide 10 according to the embodiment is not limited to the following manufacturing method.

[0047] First, various powders are blended together to make a total of 100 mass % containing 75 to 98.9 mass % tungsten carbide (WC) powder having an average particle size of 0.1 to 1 μm, 1 to 20 mass % cobalt powder, 0.1 to 5 mass % 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) may be blended as desired.

[0048] Next, water or an organic solvent and, if desired, an organic binder are added to the prepared mixed powder and mixed, and the mixture is pulverized and mixed using a known method such as a ball mill or a vibration mill, and then dried in a spray dryer to form granules.

[0049] Next, this granular mixed powder is molded into a predetermined cutting tool shape as shown in FIGS. 1A and 1B by a known molding method such as press molding, casting, extrusion molding, or cold isostatic pressing.

[0050] Next, this compact is placed in a baking furnace under vacuum or Ar or N ２The mixture is fired in a non-oxidizing atmosphere such as a sintered body at a firing temperature of 1350 to 1450°C for 0.5 to 5 hours, and then hot isostatic pressing (HIP) sintering is carried out at a temperature 5 to 50°C lower than the firing temperature, at a pressure of 5 to 20 MPa, and for 0.5 to 3 hours to produce a cemented carbide for cutting tools.

[0051] In addition, while the maximum firing temperature itself is kept the same for all materials, the crystalline state within the cemented carbide is controlled by varying the rate of temperature rise just before the firing temperature reaches the maximum temperature.

[0052] If desired, the produced cemented carbide may be used as the substrate of a cutting tool, and a coating film may be formed on the surface of the substrate. Examples of the coating film include titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), titanium aluminum composite nitride (TiAlN), and aluminum oxide (Al ２ O ３ ) etc.

[0053] The coating film can be formed by known methods such as chemical vapor deposition (thermal CVD, plasma CVD, organic CVD, catalytic CVD, etc.) and physical vapor deposition (ion plating, sputtering, etc.).

[0054] Next, as an example of a method for manufacturing a machined product according to an embodiment, a method for manufacturing a machined product using a rotary tool for machining a printed circuit board as a cutting tool will be described. An example of the rotary tool for machining a printed circuit board is a PWB drill 1 as shown in FIGS. 1A and 1B .

[0055] Here, an example of a method for manufacturing a machined product according to an embodiment will be described with reference to Figures 5A, 5B, and 5C, which are diagrams that schematically show an example of a method for manufacturing a machined product according to an embodiment.

[0056] The machined product is produced by cutting the workpiece 100. 5A, 5B, and 5C illustrate drilling performed using a drilling machine as an example of cutting. The manufacturing method of the machined product in the embodiment includes: (1) a step of rotating the PWB drill 1; (2) a step of bringing the workpiece 100 and the PWB drill 1 into contact with each other; and (3) a step of moving the PWB drill 1 relatively away from the workpiece 100.

[0057] More specifically, first, as shown in Fig. 5A, the PWB drill 1 is rotated around the axis CR and brought relatively close to the workpiece 100. Next, as shown in Fig. 5B, the cutting edge 2b of the PWB drill 1 is brought into contact with the workpiece 100 to drill a hole in the workpiece 100. Then, as shown in Fig. 5C, the PWB drill 1 is moved relatively away from the workpiece 100.

[0058] In Fig. 5A, the workpiece 100 is fixed and the PWB drill 1 is moved downward while being rotated, thereby bringing the PWB drill 1 closer to the workpiece 100. In Fig. 5B, the cutting edge 2b of the PWB drill 1 is brought into contact with the fixed workpiece 100 to drill a hole in the workpiece 100. In Fig. 5C, the PWB drill 1 is moved upward while the workpiece 100 is fixed, thereby moving the PWB drill 1 away from the workpiece 100.

[0059] In the cutting process in the manufacturing method of the embodiment, the PWB drill 1 is moved in each step to bring the PWB drill 1 into contact with the workpiece 100 or to move the PWB drill 1 away from the workpiece 100, but of course this is not limited to this form.

[0060] For example, in step (1), the workpiece 100 may be brought closer to the PWB drill 1. Similarly, in step (3), the workpiece 100 may be moved away from the PWB drill 1. To continue the cutting process, for example, the PWB drill 1 may be kept rotating, and the step of bringing the cutting edge 2b of the PWB drill 1 into contact with different locations on the workpiece 100 may be repeated.

[0061] Representative examples of the workpiece 100 include printed circuit boards such as printed circuit boards (PCB) and printed wiring boards (PWB).

[0062] Examples of the present disclosure will be specifically described below, but the present disclosure is not limited to the examples shown below.

[0063] (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, isopropyl alcohol (IPA) was added to the resulting mixed powder and pulverized using a vibration mill. The mixed powder was then dried using a spray dryer to obtain a granular mixed powder. The resulting granular mixed powder was then press-molded into the shape of the PWB drill 1 shown in FIG. 1A. Next, this compact was sintered in a sintering furnace under vacuum at a sintering temperature of 1400°C for 1 hour. Subsequently, HIP sintering was performed at a temperature 15°C lower than the sintering temperature and a pressure of 10 MPa for 1 hour to produce a cemented carbide according to the example. The crystalline state of the cemented carbide was controlled by adjusting the heating rate just before the sintering temperature reached its maximum temperature.

[0064] Next, a predetermined surface of the obtained cemented carbide was polished, and the polished surface was photographed using a field emission scanning electron microscope (FE-SEM) manufactured by JEOL under the following conditions: magnification: 2000 times, acceleration voltage: 10 (kV), brightness: 581, and contrast: 4630.

[0065] Next, the captured photographic image was analyzed using image processing software "ImageJ" (manufactured by Wayne Rasband National Institutes of Health). Here, the circular equivalent diameters of multiple hard particles contained in an area having a size of 10 μm × 10 μm in the image were calculated. Based on the calculated circular equivalent diameters of the multiple hard particles, a histogram of the circular equivalent diameters of the multiple hard particles was obtained. The width of the circular equivalent diameter class was 0.05 μm.

[0066] 6 is a histogram showing the circle-equivalent diameters of a plurality of hard particles contained in the cemented carbide according to the example. The horizontal axis shows the class value of the circle-equivalent diameter (μm). The vertical axis shows the frequency in the circle-equivalent diameter (μm) class.

[0067] As shown in Figure 6, the mode of the obtained histogram was 0.25 µm. The mode of 0.25 µm of the obtained histogram was a class value of a range of equivalent circle diameters smaller than 0.275, which is the median value in the range of equivalent circle diameters of 0.20 µm to 0.35 µm that gives the full width at half maximum of the histogram. The frequency F1 of the class including the upper limit of the range of equivalent circle diameters that gives the full width at half maximum of the obtained histogram was 156. The frequency F2 of the class including the value obtained by adding the half width at half maximum of 0.45 µm of the histogram to the class value of 0.35 µm that gives the upper limit of the range of equivalent circle diameters that gives the full width at half maximum of the obtained histogram was 63.

[0068] The skewness of the obtained histogram was 1.14. The difference between the mode of the obtained histogram and the median of the obtained histogram was 0.025 μm or less. The sum of the frequencies in the classes included in the range of equivalent circle diameters giving the full width at half maximum of the obtained histogram was 747. The sum of the frequencies in the classes included in the range of equivalent circle diameters of 0.15 μm or more and 1 μm or less of the obtained histogram was 1130. The frequency F3 in the class including a value that is twice the mode of the obtained histogram was 54.

[0069] Using the PWB drill made of the obtained cemented carbide, holes were drilled into printed wiring boards under the following drilling conditions: Drilling conditions: Rotation speed: 200 krpm, Feed: 2.6 m / min, Drill size: φ0.2 × 3 mm, Substrate: E-705G

[0070] The amount of wear on the cutting edge of the PWB drill when 4,000 holes were drilled in the printed wiring board was 13 μm. The amount of wear on the cutting edge of the PWB drill when 8,000 holes were drilled in the printed wiring board was 16 μm. The amount of wear on the cutting edge of the PWB drill when 12,000 holes were drilled in the printed wiring board was 20 μm. The amount of wear on the cutting edge of the PWB drill when 16,000 holes were drilled in the printed wiring board was 25 μm.

[0071] The degree of hole position deviation when drilling holes in a printed wiring board using a PWB drill made of the obtained cemented carbide was evaluated using the process capability index Cpk. The distance between the drilled hole and the target center position was measured and used as hole position accuracy data. The average value and standard deviation of the measured hole position accuracy data were then calculated. Finally, the process capability index Cpk was calculated using the calculated average value and standard deviation according to the formula: Cpk = (standard value - average value) / (3 x standard deviation). Here, the standard value was set to ±50 μm. The process capability index Cpk was 1.55.

[0072] Comparative Example 1 A predetermined surface of the cemented carbide of a conventional PWB drill was polished, and the polished surface was photographed under the same conditions as in Example 1 using a field emission scanning electron microscope (FE-SEM) manufactured by JEOL.

[0073] Next, the photographed image was analyzed in the same manner as in Example 1. Here, the circular equivalent diameters of a plurality of hard particles contained in an area having a size of 10 μm × 10 μm in the image were calculated. Based on the calculated circular equivalent diameters of the plurality of hard particles, a histogram of the circular equivalent diameters of the plurality of hard particles was obtained. The width of the circular equivalent diameter class was 0.05 μm.

[0074] 7 is a histogram showing the circle-equivalent diameters of a plurality of hard particles contained in the cemented carbide according to Comparative Example 1. The horizontal axis shows the class value of the circle-equivalent diameter (μm), and the vertical axis shows the frequency in the circle-equivalent diameter (μm) class.

[0075] As shown in Figure 7, the mode of the obtained histogram was 0.3 µm. The mode of the obtained histogram, 0.3 µm, was smaller than the class value of 0.3 µm, which included the median value in the range of equivalent circle diameters from 0.2 µm to 0.4 µm, which gave the full width at half maximum of the histogram. The frequency F1 in the class including the upper limit of the range of equivalent circle diameters giving the full width at half maximum of the histogram was 94. The frequency F2 in the class including the value obtained by adding the half width at half maximum of the histogram, 0.5 µm, to the class value of 0.4 µm, which included the upper limit of the range of equivalent circle diameters giving the full width at half maximum of the histogram, was 42.

[0076] The skewness of the obtained histogram was 0.927. The difference between the mode of the obtained histogram and the median of the obtained histogram was 0. The sum of the frequencies in the classes included in the range of equivalent circle diameters giving the full width at half maximum of the obtained histogram was 664. The sum of the frequencies in the classes included in the range of equivalent circle diameters of 0.15 μm or more and 1 μm or less of the obtained histogram was 932. The frequency F3 in the class including a value that is twice the mode of the obtained histogram was 16.

[0077] Using a conventional PWB drill, drilling was performed on a printed wiring board under the same conditions as in Example 1.

[0078] The amount of wear on the cutting edge of the PWB drill when 4,000 holes were drilled in the printed wiring board was 15 μm. The amount of wear on the cutting edge of the PWB drill when 8,000 holes were drilled in the printed wiring board was 20 μm. The amount of wear on the cutting edge of the PWB drill when 12,000 holes were drilled in the printed wiring board was 24 μm. The amount of wear on the cutting edge of the PWB drill when 16,000 holes were drilled in the printed wiring board was 30 μm.

[0079] When a conventional PWB drill was used to drill holes in a printed wiring board, the process capability index Cpk was 1.2.

[0080] The present technology can be configured as follows: (1) A cemented carbide comprising: a plurality of hard particles containing W and C; and a binder phase bonding the plurality of hard particles together; wherein, when a frequency distribution of the equivalent circle diameters of the plurality of hard particles in a cross section has a class width of 0.05 μm, the mode of the frequency distribution is 0.15 μm or more and 0.4 μm or less, the mode of the frequency distribution is smaller than a class value of a class including a median value in the range of equivalent circle diameters that provides a full width at half maximum of the frequency distribution, and a frequency F1 in a class including an upper limit value of the equivalent circle diameter in the range of equivalent circle diameters that provides the full width at half maximum of the frequency distribution and a frequency F2 in a class including a value obtained by adding the class value of the class including the upper limit value to the half width at half maximum of the frequency distribution satisfy the relationship F2<F1 / 2. (2) The cemented carbide according to (1), wherein the skewness of the frequency distribution is greater than 1. (3) The cemented carbide according to (1) or (2), wherein the difference between the mode and the median of the frequency distribution is 0.05 μm or less. (4) The cemented carbide according to any one of (1) to (3), wherein the sum of frequencies in classes included in the range of equivalent circle diameters giving the full width at half maximum of the frequency distribution is 70% or more of the sum of frequencies in classes included in the range of equivalent circle diameters of 0.15 μm or more and 1 μm or less. (5) The cemented carbide according to any one of (1) to (4), wherein the mode is 0.2 μm or more and 0.3 μm or less. (6) The cemented carbide according to any one of (1) to (5), wherein the frequency F1 and a frequency F3 in a class including a value that is at least twice the mode satisfy the relationship F3<F1 / 10. (7) A cutting tool blank, comprising the cemented carbide according to any one of (1) to (6). (8) A cutting tool having a cutting blade including the cemented carbide according to any one of (1) to (6). (9) The cutting tool according to (8), which is a rotary tool for processing printed circuit boards. (10) A method for manufacturing a machined product, comprising the steps of: rotating a workpiece or the cutting tool according to (8), bringing the workpiece and the cutting tool into contact, and moving the cutting tool relatively away from the workpiece.(11) The method for manufacturing a machined product according to (10), wherein the workpiece is a printed circuit board.

[0081] Further advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

[0082] REFERENCE SIGNS LIST 1 PWB drill 2 Cutting edge 2a Chip discharge groove 2b Cutting edge 3 Shank portion 4 Connecting portion 4a First tapered portion 4b Second tapered portion 4c Cylindrical portion 4d Joint surface 5 PWB drill blank 100 Workpiece

Claims

a plurality of hard particles containing W and C; a binder phase that bonds the plurality of hard particles; Equipped with In a frequency distribution of the circle equivalent diameters of the plurality of hard particles in a cross section, When the width of the circle equivalent diameter class is 0.05 μm, the mode of the frequency distribution is equal to or greater than 0.15 μm and equal to or less than 0.4 μm, the mode of the frequency distribution is smaller than the class value of a class including a median value in the range of the equivalent circle diameter that gives the full width at half maximum of the frequency distribution, A power F1 in a class including the upper limit value of the equivalent circle diameter in the range of the equivalent circle diameter that gives the full width at half maximum of the power distribution, and a power F2 in a class including the value obtained by adding the half width at half maximum of the power distribution to the class value of the class including the upper limit value, are F2<F1 / 2 Satisfy the relationship of Cemented carbide. The skewness of the frequency distribution is greater than 1. The cemented carbide according to claim 1. 　 the difference between the mode and the median of the frequency distribution is 0.05 μm or less; 3. The cemented carbide according to claim 1 or 2. 　 a total of powers in classes included in the range of the equivalent circle diameter that gives the full width at half maximum of the power distribution is 70% or more of a total of powers in classes included in the range of the equivalent circle diameter that is 0.15 μm or more and 1 μm or less; 4. The cemented carbide according to claim 1. 　 The mode is 0.2 μm or more and 0.3 μm or less.

5. The cemented carbide according to claim 1. 　 The frequency F3 in a class including the frequency F1 and a value that is twice or more of the mode is F3<F1 / 10 Satisfy the relationship of 6. The cemented carbide according to any one of claims 1 to 5. 　 The cemented carbide according to any one of claims 1 to 6. Including, Cutting tool blanks. 　 A cutting blade comprising the cemented carbide according to any one of claims 1 to 6. Equipped with cutting tools. 　 It is a rotary tool for processing printed circuit boards. The cutting tool according to claim 8. 　 rotating a workpiece or the cutting tool according to claim 8; bringing the workpiece into contact with the cutting tool; moving the cutting tool relatively away from the workpiece; Equipped with Manufacturing method for machined products. 　 The workpiece is a printed circuit board. The method for manufacturing a machined product according to claim 10.

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