Hard coating drill bit

Abstract

In a hard film coated drill bit in which a hard film is coated on the surface of a drill body made of superhard alloy, a smooth area (4) is provided at the boundary between the back cutting edge (2) and the front cutting edge (3) of the body. The surface hardness of the coated hard film is set within the range of Vickers hardness of 2000 to 2500 HV. In addition, the cross-sections of the first ridge line (L1) where the area (4) intersects with the back cutting edge (2) and the second ridge line (L2) where the back cutting edge (2) intersects with the cutting edge (6) are processed into an R shape, and the radius of curvature (r1) (μm) of the first ridge line (L1) in the R shape is set within the range represented by the formula r1=0.45×D+a1 (10≤a1≤25) relative to the diameter (D) (mm) of the body. In addition, the radius of curvature (r2) (μm) of the second ridge line L2 in the R shape is set within the range represented by the formula r2 = 0.65 × D + a2 (39 ≤ a2 ≤ 67). And the thickness (t1) (μm) of the hard film is set within the range represented by the relationship t1 = 0.8 × ln (D) + a3 (0.7 ≤ a3 ≤ 3.0).

Description

Technical Field

[0001] The present invention relates to a cutting tool (drill) coated with a hard film such as TiN (titanium nitride). Background Art

[0002] Generally, a cutting tool such as a drill is used in a state where the surface of a base material (raw material) made of cemented carbide is coated with a hard film such as TiN.

[0003] By coating with a hard film, the wear of the base material during cutting is suppressed and the cutting tool is prevented from being damaged.

[0004] Furthermore, by making the hard film contain various elements such as Cr and Si in arbitrary proportions in addition to TiN (titanium nitride) and the like, various properties can be imparted to the hard film.

[0005] Patent Documents 1 and 2 disclose that the wear resistance and chipping resistance of the entire hard film can be improved by alternately laminating two types of hard films having different component ratios at the middle position of a normal hard film.

[0006] In addition to the hard coating, the wear of the cutting tool during cutting can also be suppressed by setting the flank face and the rake face to specific shapes regarding the shape of the cutting tool.

[0007] Furthermore, by providing a chamfered surface (chamfered edge) on the blade edge, chipping during cutting can be prevented.

[0008] Furthermore, regardless of the presence or absence of a chamfered surface, by performing a minute R chamfering process on the edge of the blade tip, chipping of the edge and film peeling can be prevented.

[0009] Patent Documents 3 and 4 disclose that, in addition to providing a honed surface (chamfered surface) on the cutting edge of a cutting tool, R-chamfering is performed within a predetermined range on the boundary portion with the flank and the outer peripheral corner, thereby suppressing the wear of the cutting tool.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent No. 6222675

[0013] Patent Document 2: Japanese Patent No. 4967505

[0014] Patent Document 3: Japanese Patent Application Publication No. 2014-18883

[0015] Patent Document 4: International Publication No. 2016 / 043098 Summary of the invention

[0016] Technical problem to be solved by the invention

[0017] However, when a hard coating is applied to the surface of a cutting tool, there is a problem in making the radius of curvature of the rounded chamfer of the cutting edge portion uniform regardless of the size (diameter) of the cutting tool.

[0018] When drilling is performed under general cutting conditions, the cutting edge is more likely to be chipped because the cutting resistance generated by the drill during cutting increases as the diameter of the cutting tool (drill) increases, and the force acting on the cutting edge increases.

[0019] Therefore, the chamfer amount (width) needs to be increased in accordance with the size of the tool diameter.

[0020] For the same reason, in order to prevent film destruction (self-destruction of the hard film) at the edge of the blade tip due to external force during cutting, it is necessary to increase the curvature radius of the edge.

[0021] For example, where the radius of curvature is small relative to the diameter of the cutting tool, e.g. Fig.19 As shown, a chamfered surface 104 is provided near the cutting edge of a conventional cutting tool 100 (the boundary between the back cutting surface 102 and the front cutting surface 103), and a hard film is coated on this basis. When a hole opening process is performed, the hard film is destroyed starting from the ridgeline between the back cutting surface 102 and the chamfered surface 104 and a portion of the front edge 107.

[0022] Sometimes, damage such as chipping of cutting tools and wear of the back face of the cutting tool start from these parts and develop until they become defects c1 to c3 (refer to Fig. 20 ).

[0023] On the contrary, when the curvature radius of the round chamfer at the edge of the blade tip is large relative to the diameter of the cutting tool, the curvature radius of the round chamfer is too large for the cutting conditions, and the cutting resistance generated during the drilling process increases.

[0024] As a result, the drill becomes blunt and the processing quality is reduced. In addition, the cutting tool cannot withstand the resistance generated during processing and is prone to breakage.

[0025] Therefore, the object of the present invention is to provide a hard film coated drill bit, which suppresses film damage at the edge of the cutting edge by optimizing the R chamfer relative to the ridgeline forming the cutting edge of the drill bit and the hardness of the hard film according to the characteristics of the coated hard film, thereby improving the closeness between the base material (drill body) and the hard film.

[0026] Solutions for solving technical problems

[0027] In order to solve the above-mentioned technical problems, the present inventors conducted intensive studies on the relationship between the characteristics of the hard coating and the drill body, and as a result, obtained the following findings.

[0028] That is, the self-destruction of the hard film at the edge of the blade tip is caused by the residual stress of the hard film, and the residual stress is greatly related to the thickness and hardness of the film.

[0029] Therefore, when applying a high-hardness hard film (eg, Vickers hardness exceeding 2500 HV) to the drill body, it is necessary to optimize the thickness of the hard film with respect to changes in the diameter of the drill body to prevent self-destruction of the hard film.

[0030] Here, a typical method of self-destruction of the hard film in a conventional drill is given and Fig.21 and Fig. 22 Shown.

[0031] like Fig.21 As shown, the first mode of self-destruction of the hard film is as follows: the hard film is peeled off (peeling part MH1) with the intersection of the first edge line L151, the second edge line L152 and the third edge line L153 as the center, the first edge line L151 serves as the boundary between the back cutting surface 152 and the chamfered surface 154 of the drill bit 150, the second edge line L152 serves as the boundary of the cutting edge 156, and the third edge line L153 serves as the boundary between the chamfered surface 154 and the cutting edge 156.

[0032] like Fig. 22 As shown, as a second method, there is a method in which the hard film is peeled off along the first edge line L161 from the intersection of the first edge line L161, the second edge line L162 and the third edge line L163 (peeling part MH2), the first edge line L161 serves as the boundary between the back cutting surface 162 and the chamfered surface 164 of the drill bit 160, the second edge line L162 serves as the boundary of the cutting edge 166, and the third edge line L163 serves as the boundary between the chamfered surface 164 and the cutting edge 166.

[0033] As described above, residual stress of the hard film is likely to concentrate on the ridgeline which is the corner where the surfaces intersect, and the stress increases as the hard film becomes thicker, so self-destruction is more likely to occur preferentially compared with other parts.

[0034] Not limited to the first and second aspects, the film may self-destruct continuously or discontinuously on any ridge line or at a site where ridge lines intersect.

[0035] That is, if the drill body is covered with a hard film having a higher hardness than necessary, the hard film will self-destruct due to the difference in residual stress between the base material and the hard film, exposing the base material and causing wear to progress.

[0036] Therefore, when coating with a hard film, it is necessary to select a film thickness corresponding to the diameter of the cutting tool.

[0037] In general, the higher the hardness of the hard film, the more the wear resistance of the cutting tool is improved. However, conversely, a hard film with high hardness may also cause self-destruction. Furthermore, as the film thickness increases, the possibility of self-destruction increases accordingly.

[0038] Therefore, if a hard film having a certain thickness is to be coated on the base material (drill body), the hardness of the hard film needs to be adjusted to a relatively low hardness (below 2500 HV) and the drill body needs to be set to the optimal shape for the purpose of suppressing self-destruction of the hard film.

[0039] Therefore, in the present invention, in a hard coating coated drill in which the surface of a drill body made of cemented carbide is coated with a hard coating, a smooth region (smooth surface) is provided in the body at a location where the flank face and the rake face intersect.

[0040] Then, each of two ridge lines, a first ridge line where the smooth surface and the flank face intersect and a second ridge line where the flank face and the land intersect, is processed into an R shape in cross-sectional view (R chamfering).

[0041] In this case, the hardness of the hard film covering the main body of the drill bit is within the range of 2000 to 2500 HV in Vickers hardness.

[0042] Regarding the size of the R chamfering processing, when the diameter of the drill body is set to D (unit: mm), the curvature radius r1 (unit: μm) of the first ridge line is set within the range represented by the relationship r1=0.45×D+a1 (10≤a1≤25).

[0043] Furthermore, the curvature radius r2 (unit: μm) of the second ridgeline is set within the range represented by the relationship formula r2=0.65×D+a2 (39≤a2≤67).

[0044] In addition, when the diameter of the drill body is set to D (unit: mm), the thickness t1 (unit: μm) of the hard film covering the surface of the drill body made of superhard alloy is set within the range represented by the relationship t1=0.8×ln(D)+a3 (0.7≤a3≤3.0).

[0045] It should be noted that "ln" here refers to the natural logarithm with base e.

[0046] The hard film is composed of the first layer, the second layer, and the third layer in order from the main body side of the drill. Regarding the film composition, the first layer is a hard film mainly composed of nitride (AlTiN) containing Al and Ti.

[0047] The second layer is a mixed layer in which two types of hard films having different compositions are alternately laminated.

[0048] The third layer is a hard film mainly composed of nitride (TiSiN) containing Ti and Si.

[0049] The two hard films forming the second layer are a first intermediate hard film mainly composed of nitride (AlTiSiN) containing Ti, Al and Si, and a second intermediate hard film mainly composed of nitride (AlTiSiCN) containing Ti, Al, Cr and Si.

[0050] Effects of the Invention

[0051] The hard film coated drill bit of the present invention optimizes the R chamfer of the specific ridgeline forming the shape of the cutting edge and the hardness and thickness of the coated hard film according to the diameter of the drill body, thereby improving the closeness between the base material and the hard film of the hard film coated drill bit.

[0052] Thus, regardless of the diameter of the hard-coated drill, self-destruction of the hard film at the cutting edge can be prevented, and the tool life can be extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a front view of the main body 1 of the hard film coated drill bit of the present invention.

[0054] Figure 2 It is a top view of the main body 1 of the hard film coated drill bit of the present invention.

[0055] Figure 3 for Figure 1 An enlarged view of part A of the drill body 1 is shown.

[0056] Figure 4 for Figure 2 A sectional view of the drill body 1 taken along line XX is shown.

[0057] Figure 5 It is a schematic diagram of the vicinity of the second ridgeline L2 of the drill body 1.

[0058] Figure 6 It is a schematic diagram of the vicinity of the third ridgeline L3 of the drill body 1.

[0059] Figure 7 Schematic cross-sectional view of the hard film 10 in the drill bit 50 .

[0060] Figure 8 for Figure 7 An enlarged view of part B of the hard film 10 is shown.

[0061] Fig. 9 This is a schematic enlarged view of comparative product 1 (drill 110 ) of Example 1 (rake face side).

[0062] Fig.10 This is a schematic enlarged view of comparative product 2 (drill 120 ) of Example 1 (rake face side).

[0063] Fig.11 This is a schematic enlarged view of the comparative product 3 (drill 130 ) in Example 1 (rake face side).

[0064] Fig.12 This is a schematic enlarged view (rake face side) of the inventive product 1 (drill 200 ) in Example 1.

[0065] Fig.13 This is a schematic enlarged view of comparative product 4 (drill 140 ) of Example 1 (rake face side).

[0066] Fig.14 This is a schematic enlarged view of the comparative product 1 (drill 110 ) of Example 1 (flank side).

[0067] Fig.15 This is a schematic enlarged view of comparative product 2 (drill 120 ) of Example 1 (flank side).

[0068] Fig.16 This is a schematic enlarged view of comparative product 3 (drill 130 ) of Example 1 (flank side).

[0069] Fig.17 This is a schematic enlarged view (flank side) of the inventive product 1 (drill 200) of Example 1.

[0070] Fig.18 This is a schematic enlarged view of comparative product 4 (drill 140 ) of Example 1 (flank side).

[0071] Fig.19 It is an enlarged schematic diagram of the vicinity of the cutting edge of a conventional drill 100 .

[0072] Fig. 20 It is an enlarged schematic diagram showing a defective state of a conventional drill bit 100 .

[0073] Fig.21 It is an enlarged schematic diagram showing a state (first form) of self-destruction MH1 of a hard film of a conventional drill bit 150 .

[0074] Fig. 22 It is an enlarged schematic diagram showing a state (second form) of self-destruction MH2 of the hard film of the conventional drill bit 160.

[0075] Description of Reference Numerals

[0076] 1 drill body; 2 back cutting edge; 3 front cutting edge; 4 smooth area (smooth surface); 5 cutting edge; 6 edge band; 10 hard film; 10A first layer (lowermost layer) of hard film; 10B second layer (middle layer) of hard film; 10C third layer (uppermost layer) of hard film; 10B1 first intermediate hard film; 10B2 second intermediate hard film; 50 hard film coated drill; D diameter of drill body; L1 first ridge; L2 second ridge; L3 third ridge; r1 radius of curvature of first ridge; r2 radius of curvature of second ridge; r3 radius of curvature of third ridge; t1 thickness of hard film. DETAILED DESCRIPTION

[0077] Embodiments of the hard-coated drill bit of the present invention will be described below with reference to the drawings.

[0078] by Figure 1 A front view of a main body 1 of a hard film coated drill bit according to an embodiment of the present invention is shown. Figure 2 A top view thereof is shown.

[0079] In addition, Figure 3 Show Figure 1 The enlarged view of part A in Figure 4 Show Figure 2 XX line section view.

[0080] like Figure 1 and Figure 3 As shown, between the flank 2 and rake 3 of the main body 1 (diameter ΦD) of the cemented carbide drill of the present invention, there is a region (smooth surface) 4 having a smooth surface extending from the center side toward the outer periphery side of the main body 1 of the drill.

[0081] This region 4 is formed by machining the tip portion of the cutting edge 5 and is called a honed surface or a chamfered surface, and is continuously connected (joined) across both the flank face 2 and the rake face 3 .

[0082] Here, the “drill body (drill body)” refers to the state of the material of the drill itself before being coated with the hard film, relative to the final form of the drill coated with the hard film such as TiN.

[0083] Therefore, in the present application, a distinction is made between a "drill body" and a "hard film coated drill" in a final form in which a hard film is coated on the surface of the drill body.

[0084] In addition, a specific ridgeline in the main body 1 of the drill is R-processed (R-chamfered) with a predetermined curvature radius in cross-sectional view.

[0085] The "specific edge" refers to Figure 3 As shown, there is a first ridgeline L1 where the region 4 intersects the flank surface 2 , a second ridgeline L2 where the flank surface 2 intersects the land 6 , and a third ridgeline L3 where the land 6 intersects the region 4 .

[0086] exist Figure 4 The vicinity of the first ridgeline L1 of the drill body is shown in FIG. 2 (sectional view along line XX).

[0087] In addition, Figure 5 FIG. 2 shows a schematic diagram of the vicinity of the second ridge line L2 of the drill body 1. Figure 6 A schematic diagram showing the vicinity of the third ridgeline L3 of the drill body 1 is shown.

[0088] like Figures 4 to 6 As shown, the first to third ridge lines L1 to L3 are processed into R shapes (R chamfering).

[0089] Regarding the size of the R processing, Figure 1 as well as Figure 2 As shown in the figure, when the diameter of the drill body 1 is set to D (mm), the range represented by the mathematical formula r1=0.45×D+a1 (10≤a1≤25) (hereinafter referred to as "Formula 1") is set as the curvature radius r1 (μm) of the first ridgeline L1.

[0090] Furthermore, the curvature radius r2 (μm) of the second ridgeline L2 is set to be within the range represented by a mathematical formula (hereinafter referred to as “Formula 2”) of r2=0.65×D+a2 (39≤a2≤67).

[0091] It should be noted that the curvature radius r3 of the third ridgeline L3 formed by the region 4 and the land 6 is preferably in the range of 25 μm or more and 50 μm or less.

[0092] Next, the hard film coated on the surface of the above-mentioned drill body will be described using the drawings.

[0093] exist Figure 7 A schematic cross-sectional view of the entire hard film 10 of the hard film coated drill bit 50 is shown in FIG. Figure 8 Shown in Figure 7 An enlarged view of part B of the hard film 10 is shown.

[0094] like Figure 7As shown, the hard film 10 coated on the surface of the hard film coated drill 50 includes a first layer 10A corresponding to the bottom layer, a second layer 10B corresponding to the middle layer, and a third layer 10C corresponding to the top layer, stacked in order from the drill body 1 side.

[0095] In addition, the surface hardness of the hard film 10 is in the range of Vickers hardness of 2000 to 2500 HV. When the diameter of the main body 1 of the drill bit is set to D (mm), the thickness t1 (μm) of the hard film 10 is in the range represented by the mathematical formula t1 = 0.8 × ln (D) + a3 (0.7≤a3≤3.0) (hereinafter referred to as "Formula 3").

[0096] The first layer 10A, which is the lowermost layer in the hard film 10, is a hard film covering the position closest to the drill body 1, and its composition is mainly formed of nitride (AlTiN) containing Al and Ti.

[0097] The third layer 10C as the uppermost layer in the hard film 10 is stacked on the first layer 10A and the second layer 10B and covers the position farthest from the drill body 1 , and its chemical composition is nitride (TiSiN) containing Ti and Si.

[0098] The second layer 10B corresponding to the intermediate layer in the hard film 10 is a hard film laminated between the first layer 10A and the third layer 10C, and is a mixed layer in which two hard films having different compositions are alternately laminated.

[0099] The two hard films forming the second layer 10B are a first intermediate hard film 10B1 having a nitride (TiAlSiN) containing Ti, Al and Si as chemical components, and a second intermediate hard film 10B2 having a nitride (TiAlCrSiN) containing Ti, Al, Cr and Si as chemical components.

[0100] If the state in which the first intermediate hard film 10B1 and the second intermediate hard film 10B2 are stacked one layer each is set as a group (one cycle), the mixed layer forming the second layer 10B is set as a layer in which the two hard films 10B1 and 10B2 are stacked in the range of more than 15 groups and less than 60 groups, and its thickness is in the range of more than 0.5μm and less than 5.0μm.

[0101] Example 1

[0102] Since cutting processing tests were conducted using the drill involved in the present invention (hereinafter referred to as the "invention product") and a conventional drill (hereinafter referred to as the "comparison product"), and the relationship between the curvature radius of the first to third ridges of the drill body and the tool life was confirmed, the test results are described.

[0103] The drill bodies made of cemented carbide of the invention product and the comparative product were subjected to R chamfering in various sizes and then coated with a hard film.

[0104] The invention product and the comparative product had the following common specifications: the diameter of the drill body: 6 mm, the flute length of the drill: 42 mm, and the drill length: 82 mm.

[0105] Table 1 shows the curvature radii r1 to r3 (size of R chamfer) of the first to third ridgelines of the invention products 1 to 3 and the comparative products 1 to 4, and the thickness and hardness of the hard coating.

[0106] Inventions 1 to 3 are representative examples of Fig.12 FIG. 2 shows the appearance of the invention product 1 (drill 200) after R chamfering (before hard film coating) observed from the rake face side. Fig.17 The figure shows the state viewed from the flank side.

[0107] In addition, Figures 9-11 and Fig.13 The morphology of the comparative products 1 to 4 (drills 110 to 140) after R chamfering (before hard film coating) as viewed from the rake face side is shown in FIG. Figures 14 to 16 and Fig.18 The shapes observed from the back face side are shown in FIG.

[0108] It should be noted that the comparative product 1 is set to only the leading edge ( Fig. 9 The ridgeline 117 shown in the figure is R-processed and coated with an existing hard film (hardness exceeding 2500 HV). In addition, the curvature radii r1 to r3 of the first to third ridgelines of the invention products 1 to 3 and the comparative products 1 to 4 were measured using a three-dimensional measuring instrument.

[0109] Furthermore, the hardness of the hard film was measured using a micro Vickers hardness tester, and calibration was performed based on JIS Z2244 "Hardness test on curved surface" as required.

[0110] [Table 1]

[0111]

[0112] like Figures 9 to 18 As shown, the flank 202, rake face 203, region 204, margin 206, and leading edge 207 of the drill 200 of the invention product 1 used in the cutting processing test correspond to the flank 112 to 142, rake face 113 to 143, region 114 to 144, margin 116 to 146, and leading edge 117 to 147 of the drills 110 to 140 as comparison products 1 to 4, respectively.

[0113] The first ridgeline L201, the second ridgeline L202, and the third ridgeline L203 of the drill 200 of the invention product 1 correspond to the first ridgelines L111 to 141, the second ridgelines L112 to 142, and the third ridgelines L113 to 143 of the drills 110 to 140 of the comparative products 1 to 4, respectively.

[0114] In both the invention product and the comparative product, the coated hard film is stacked in sequence from the drill body as follows: the bottom layer (first layer) is set to be a hard film of AlTiN (atomic ratio of Al:Ti=60:40), the middle layer (second layer) is set to be a mixed layer composed of a first middle hard film set to be TiAlSiN (atomic ratio of Ti:Al:Si=62.5:30:7.5) and a second middle layer set to be TiAlCrSiN (atomic ratio of Ti:Al:Cr:Si=42.5:35:15:7.5), and the top layer (third layer) is set to be a hard film of TiSiN (atomic ratio of Ti:Si=85:15).

[0115] It should be noted that the cutting test was conducted under the following conditions. The cutting test was terminated when defects in the cutting edge, peripheral corner, etc. were confirmed in both the invention product and the comparative product, and the total cutting length (unit: m) until the end of the test was compared.

[0116] Drill speed: 5300rev / min

[0117] Drill feed speed: 795mm / min

[0118] Drill cutting speed: 100m / min

[0119] Drill feed rate: 0.150mm / rev

[0120] ·Material to be cut: Carbon steel S50C (0.5% C)

[0121] Processing method: blind hole with a depth of 30 mm

[0122] Cooling conditions: External supply of water-soluble cutting oil

[0123] The results of the cutting test will be described.

[0124] First, the outer corner of comparison product 1 was damaged when the total cutting length from the start of hole processing was 43m. Similarly, the outer corner was damaged when the total cutting length of comparison product 2 was 60m, the total cutting length of comparison product 3 was 94m, and the total cutting length of comparison product 4 was 103m, and the cutting processing was completed at this time.

[0125] In contrast, since the outer corner of invention 1 was damaged when the total cutting length from the start of hole processing was 140m, similarly, the outer corner was damaged when the total cutting length of invention 2 was 156m and the total cutting length of invention 3 was 134m, the cutting processing was terminated at this moment.

[0126] When the diameter of the drill body used in this embodiment is 6 mm, the curvature radii r1 and r2 of the first and second ridges and the thickness t1 of the hard film obtained by substituting the above formulas 1 to 3 are r1 = 12.7 ~ 27.7 μm, r2 = 42.7 ~ 70.9 μm, and t1 = 2.13 ~ 4.43 μm.

[0127] The curvature radius of any one of the first ridgeline or the second ridgeline of Comparative Products 1 to 3 is smaller than the aforementioned range, and the curvature radius of the first and second ridgelines of Comparative Product 4 are both outside the aforementioned range.

[0128] In addition, the thickness of the hard film of Comparative Product 4 also exceeds the aforementioned range.

[0129] According to the above test results, the total cutting length of the inventive products 1 to 3 was increased by more than 1.3 times compared with the comparative products 1 to 4, and the tool life was extended.

[0130] This is considered to be because the curvature radii r1 and r2 of the first and second ridgelines and the thickness t1 of the hard coating of the inventive products 1 to 3 are all within the ranges of the above-mentioned Formulas 1 to 3.

[0131] Example 2

[0132] Next, a cutting test was conducted using both the inventive product and the comparative product drills to confirm the relationship between the thickness and hardness of the hard film and the tool life. The test results are described below.

[0133] As in Example 1, the drill bodies made of cemented carbide of the invention product and the comparative product were subjected to R chamfering in various sizes and then coated with a hard film.

[0134] The invention product and the comparative product had the following common specifications: the diameter of the drill body: 2 mm, the groove length of the drill: 15 mm, and the drill length: 49 mm.

[0135] The curvature radii r1 to r3 (R chamfer size) of the first to third ridgelines of the invention products 11, 12 and the comparative products 11 to 13, the thickness and hardness of the hard film are shown in Table 2. As in the case of Example 1, the curvature radii r1 to r3 of the first to third ridgelines of the invention products 11, 12 and the comparative products 11 to 13 were measured using a three-dimensional measuring instrument.

[0136] The hardness of the hard film is measured using a micro Vickers hardness tester, and calibration is performed according to JIS Z2244 "Hardness test on curved surface" as necessary.

[0137] In addition, the chemical composition of the hard film covering the drill body was set to the same chemical composition as that of Example 1.

[0138] [Table 2]

[0139]

[0140] The cutting test was performed under the following conditions. The cutting test was terminated when defects such as cutting edges and peripheral corners were observed in both the invention product and the comparative product. The total cutting length (unit: m) until the end of the test was compared.

[0141] It should be noted that, regarding Comparative Products 11 and 12, when the drill body was coated with a hard film, a portion of the hard film was confirmed to have Fig. 22 The film self-destructs in the manner shown, but the two drill bits of comparative products 11 and 12 were subjected to cutting tests in this state.

[0142] Drill speed: 12739rev / min

[0143] Drill feed speed: 637mm / min

[0144] ·Drill cutting speed: 80m / min

[0145] Drill feed rate: 0.05mm / rev

[0146] ·Material to be cut: Carbon steel S50C (0.5% C)

[0147] Processing method: blind hole with a depth of 10 mm

[0148] Cooling conditions: External supply of water-soluble cutting oil

[0149] The results of the cutting test will be described.

[0150] First, the outer corner of comparison product 11 was defective when the total cutting length from the start of hole processing was 35m, the outer corner of comparison product 12 was defective when the total cutting length was 47m, and the outer corner of comparison product 13 was defective when the total cutting length was 59m, and the cutting processing was completed at this time.

[0151] In contrast, the outer corner of the invention product 11 was broken when the total cutting length from the start of hole processing was 94 m, and similarly, the outer corner of the invention product 12 was broken when the total cutting length was 82 m, and the cutting processing was completed at that time.

[0152] When the diameter of the drill body used in this embodiment is 2 mm, the curvature radii r1 and r2 of the first and second ridges and the thickness t1 of the hard film obtained by substituting the above-mentioned formulas 1 to 3 are r1 = 10.9 ~ 25.9 μm, r2 = 40.3 ~ 68.3 μm, and t1 = 1.25 ~ 3.55 μm.

[0153] The thickness of the hard film of Comparative Product 11 exceeded the aforementioned range, and the hardness of the hard film of Comparative Product 12 exceeded 2500 HV, which is the same as the conventional hardness.

[0154] Therefore, as described above, it was found that the hard coating of Comparative Products 11 and 12 was partially self-destructed before the test, so the total cutting length in this test was inferior to that of the invention product.

[0155] In addition, since the curvature radius of the first ridgeline of Comparative Product 13 exceeded the above range, the close contact of the hard film with the drill base material decreased. Therefore, the total cutting length in this test was also inferior to that of the invention product.

[0156] From the above test results, it can be seen that the invention products 11 and 12 can increase the cutting length to 1.3 times or more compared with the comparative products 11 to 13, thereby extending the tool life.

[0157] This is believed to be because, in addition to the curvature radii of the first and second ridgelines of the invention products 11 and 12 being within the range of the aforementioned equations 1 and 2, the hardness of the hard film is within the range of 2000 to 2500 HV, and the thickness of the hard film is also within the range of the aforementioned equation 3.

[0158] Industrial Applicability

[0159] The hard-coated drill according to the present invention has excellent adhesion between the drill base material and the hard coating, and therefore can contribute to improved cutting quality and longer tool life in the field of cutting tools.

Claims

1. A hard film coated drill bit, characterized in that: The hard film coated drill has a hard film coated on the surface of a drill body made of a super-hard alloy having two or more cutting edges, a flank face, a rake face and a margin, and a smooth area adjacent to the flank face and the rake face is provided on the drill body, and the surface hardness of the hard film is within the range of Vickers hardness of 2000 to 2500 HV. Each of the first ridgeline where the smooth area intersects the flank surface and the second ridgeline where the flank surface intersects the margin is formed into an R shape in cross-sectional view, and when the diameter of the drill body is set to D, the curvature radius r1 of the R shape of the first ridgeline is The relationship between r1=0.45×D+a1 is expressed as follows: 10≤a1≤25, The curvature radius r2 of the R-shaped second ridgeline is given by The relationship between r2=0.65×D+a2 is expressed as follows: 39≤a2≤67, The unit of D is mm, the unit of r1 is μm, the unit of r2 is μm, The hard film is stacked with a first layer, a second layer and a third layer in order from near to far from the drill body side, the first layer is composed of a hard film of AlTiN, the second layer is composed of two hard films with different compositions stacked alternately, and the third layer is composed of a hard film of TiSiN. The second layer is composed of a first intermediate hard film of TiAlSiN and a second intermediate hard film of TiAlCrSiN.

2. The hard film coated drill bit according to claim 1, characterized in that: The thickness t1 of the hard film is determined by The relationship is expressed as t1 = 0.8 × ln (D) + a3, where 0.7 ≤ a3 ≤ 3.0, The unit of t1 is μm.

3. The hard film coated drill bit according to claim 1 or 2, characterized in that: The curvature radius r1 of the R-shaped first ridgeline is in the range of 15 to 35 μm.

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