drill bit

Abstract

In the drill bit of the present invention, the cutting edge (7) has: a chisel edge grinding edge (70) disposed in the radial inner end of the cutting edge (7); and a main cutting edge (71) disposed in the radial outer side of the chisel edge grinding edge (70) and connected to the edge (12) via the outer peripheral corner (15). The main cutting edge (71) and the edge (12) have a cutting edge grinding with a convex curve cross section perpendicular to each edge portion. The cutting edge grinding curvature radius in the edge (12) at a position within 1.5 mm from the outer peripheral corner (15) toward the rear end side is 25 μm or more and 80 μm or less, and is smaller than the cutting edge grinding curvature radius of the radial outer end of the main cutting edge (71) connected to the outer peripheral corner (15).

Description

Technical Field

[0001] This invention relates to a drill bit.

[0002] This application claims priority based on Japanese Patent Application No. 2023-194492, filed on November 15, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] Previously, a known drill bit included: a chip flute; a rake face disposed in the chip flute and facing the drill rotation direction; a flank face disposed on the front end face of the drill bit; a cutting edge disposed on the ridge portion connecting the rake face and the flank face; a cutting edge disposed on the outer peripheral surface of the drill bit and extending along the chip flute; an edge disposed on the ridge portion connecting the cutting edge and the rake face; an outer peripheral corner disposed on the corner portion connecting the cutting edge and the edge; and a shoulder disposed on the ridge portion connecting the cutting edge and the flank face, extending from the outer peripheral corner in the direction opposite to the drill rotation direction (reverse drill rotation direction).

[0004] For example, in the drill bits described in Patent Documents 1 and 2, in order to improve processing efficiency, cutting conditions have become more stringent, especially in order to suppress the problem of defects easily occurring on the shoulder when drilling thin plates, the grinding width of each cutting edge of the shoulder cutting edge (shoulder), the cutting edge of the cutting edge (edge), and their boundaries (outer peripheral corners) is set to be greater than the grinding width of the cutting edge of the second cutting edge (main cutting edge).

[0005] Patent Document 1: Japanese Patent No. 6722410

[0006] Patent Document 2: Japanese Patent No. 7268691

[0007] While the drill bits described in Patent Documents 1 and 2 are advantageous in machining under unstable conditions caused by increased machining efficiency or the thinning and miniaturization of workpieces (materials being cut), they still have the following problems in low- to medium-efficiency machining conditions or in the machining of large workpieces, which is the mainstream (main machining field) of drilling. Furthermore, the "low- to medium-efficiency machining conditions" mentioned in this specification refer to, for example, the following machining conditions: circumferential speed: approximately vc = 130 m / min; feed rate: although dependent on the drill bit diameter, for example, approximately fr = 0.35 mm / rev at φ6.0 mm.

[0008] That is, as shown in Patent Documents 1 and 2, if the grinding width of the cutting edge near the outer periphery of the drill bit is set to be large, the cutting resistance increases, which easily leads to the early development of wear. In other words, there is a tendency to increase resistance to defects while decreasing wear resistance. In the low- to medium-efficiency machining conditions or drilling of large workpieces as described above, it is less likely to produce sudden defects, and more importantly, it is necessary to suppress defects or wear of the cutting edge caused by the thinning of the cutting edge due to the development of wear. Summary of the Invention

[0009] The purpose of this invention is to provide a drill bit that improves wear resistance, thereby enabling a longer tool life.

[0010] To address the aforementioned issues, the present invention provides the following solutions.

[0011] [Embodiment 1 of the present invention]

[0012] A drill bit comprising a body extending axially about a central axis, wherein the body has: a chip removal groove opening on a front end face and an outer peripheral face of the body and extending from the front end face to a rear end face; a rake face disposed in the chip removal groove and oriented toward the drill bit rotation direction in the direction about the central axis; a flank face disposed on the front end face; a cutting edge disposed on a ridge portion connecting the rake face and the flank face; a cutting edge disposed on the outer peripheral face and extending along the chip removal groove; an edge disposed on a ridge portion connecting the cutting edge and the rake face; and an outer peripheral corner portion disposed on a portion connecting the cutting edge. At the corner of the edge, the cutting edge has: a chisel edge grinding edge disposed at the radially inner end of the cutting edge; and a main cutting edge disposed at the radially outer side of the chisel edge grinding edge and connected to the edge via the outer peripheral corner. The main cutting edge and the edge have a convex curve-shaped cutting edge grinding with a cross section perpendicular to each of the edge portions. The cutting edge grinding curvature radius at a position within 1.5 mm from the outer peripheral corner toward the rear end of the edge is 25 μm or more and 80 μm or less, and is smaller than the cutting edge grinding curvature radius at the radially outer end of the main cutting edge connected to the outer peripheral corner.

[0013] In the drill bit of the present invention, the main cutting edge and each edge are ground in a convex curve shape (convex R shape) on a cross section perpendicular to each edge, which is called rounded edge grinding. Therefore, in low- to medium-efficiency machining conditions or drilling of large workpieces, wear or melting within the ground edge surface can be suppressed. In detail, if, for example, unlike the present invention, the edge grinding of each component of the cutting edge (especially the main cutting edge, etc.) is a chamfered edge grinding with a flat surface, then in low- to medium-efficiency machining conditions or drilling of large workpieces, fragmentation wear may be promoted within the ground edge surface, resulting in premature melting or chipping.

[0014] Furthermore, the position within 1.5mm from the outer corner toward the rear end of the edge is located at the front end of the edge and is a part that is easily subjected to cutting resistance from the inner circumferential surface of the machining hole of the material being cut.

[0015] In the drill bit of the present invention, the radius of curvature of the cutting edge at the stated position is set to be 25 μm or more and 80 μm or less. This allows for the stable suppression of wear development.

[0016] In detail, if, unlike the present invention, the radius of curvature of the edge grinding is larger than 80 μm, then the area where the radial rake angle becomes a strong negative angle in the edge grinding increases (becoming a strong negative edge grinding), the cutting resistance increases significantly, which may lead to the early development of wear.

[0017] On the other hand, even if the radius of curvature of the edge grinding is as small as less than 25μm, wear is easily developed. Furthermore, because the cross-sectional shape of the edge becomes sharp (a shape close to a sharp angle), the function gained by edge grinding is reduced, and chipping and other defects are more likely to occur.

[0018] Furthermore, in this invention, the grinding radius of curvature of the edge is smaller than the grinding radius of curvature of the radially outer end portion of the main cutting edge, which is adjacent to the outer peripheral corner. In other words, the grinding radius of curvature of the radially outer end portion of the main cutting edge is larger than the grinding radius of curvature of the edge. With this structure, chipping and other defects at the radially outer end portion of the main cutting edge, which has the fastest circumferential speed, can be suppressed, and the development of wear near the edge can be stably suppressed.

[0019] In summary, the drill bit according to the present invention improves wear resistance, thereby extending tool life. In particular, the present invention exhibits especially significant effects when applied to drilling operations under low- to medium-efficiency conditions or on large workpieces.

[0020] Furthermore, in this invention, the "edge grinding curvature radius" is closely related to the edge grinding width. The edge grinding width refers to the dimension of the distance between the two ends of the edge grinding (the straight-line distance between the first end and the second end) in a cross section perpendicular to the direction of edge grinding extension (edge ​​portion).

[0021] That is, when the radius of curvature of the cutting edge is large, there is a tendency for the cutting edge width to also increase accordingly; conversely, when the radius of curvature of the cutting edge is small, there is a tendency for the cutting edge width to also decrease accordingly. In other words, when the cutting edge width is small, the radius of curvature of the cutting edge also decreases; when the cutting edge width is large, the radius of curvature of the cutting edge also increases. Therefore, it is acceptable to refer to the relationship between the radii of curvature of the cutting edges in this invention as the relationship between the widths of the cutting edges. That is, the relationship between the radii of curvature of the cutting edges is equivalent to the relationship between the widths of the cutting edges.

[0022] [Embodiment 2 of the present invention]

[0023] According to the drill bit of method 1, the main cutting edge has: a first cutting edge disposed radially outside the chisel edge grinding edge and having a concave curve shape recessed in a direction opposite to the rotation direction of the drill bit in the direction surrounding the central axis; and a second cutting edge disposed radially outside the first cutting edge and connected to the radially outer end of the first cutting edge, the second cutting edge constituting the radially outer end portion of the main cutting edge connected to the outer peripheral corner portion.

[0024] According to the above structure, when the main cutting edge has a so-called curved cutting edge shape with a concave edge shape (first cutting edge), the above-mentioned effects of the present invention are achieved.

[0025] [Embodiment 3 of the present invention]

[0026] According to the drill bit of method 1, wherein the main cutting edge is straight, and when the diameter of the rotation trajectory of the cutting edge around the central axis is taken as the drill bit diameter, the area within 7% of the drill bit diameter from the outer peripheral corner toward the radially inward side of the main cutting edge is set as the radially outer end of the main cutting edge connected to the outer peripheral corner.

[0027] According to the above structure, the above-mentioned effects of the present invention are achieved when the main cutting edge is a so-called straight cutting edge shape.

[0028] [Method 4 of the present invention]

[0029] According to any one of methods 1 to 3, when the grinding radius of the cutting edge of the portion of the main cutting edge located radially inward from the radially outer end is set to R1, and the grinding radius of the cutting edge of the radially outer end of the main cutting edge is set to R2, the relationship [0.9≤R1 / R2≤1.5] is satisfied.

[0030] In the main cutting edge, compared to the radially outer end connected to the outer peripheral corner, the portion located radially inward is more prone to crater wear due to chip rubbing. Crater wear tends to occur near the boundary between the edge dressing surface and the rake face; therefore, increasing the edge dressing dimension (edge ​​dressing radius of curvature) can effectively suppress crater wear.

[0031] Based on the above viewpoint, by setting the ratio of the grinding radius of curvature [R1 / R2] of the cutting edge to 1.0 or more, it is possible to reliably ensure that the grinding radius of curvature R1 of the portion of the main cutting edge located radially inward from the radially outer end is relatively large, which is therefore preferred. However, if the ratio [R1 / R2] is close to 1.0, the ratio [R1 / R2] may be less than 1.0 due to manufacturing errors, etc. Therefore, in the above structure of the present invention, it is set to [0.9≤R1 / R2].

[0032] However, in this invention, since the radius of curvature R2 of the edge grinding is greater than the radius of curvature of the edge grinding, if the ratio [R1 / R2] is 0.9 or higher, the size of the radius of curvature R1 of the edge grinding can also be sufficiently ensured. Therefore, the effect of suppressing crater wear can be stably obtained.

[0033] Furthermore, if the ratio [R1 / R2] is less than 0.9 or greater than 1.5, the difference between the grinding curvature radii R1 and R2 increases, thus the side with the smaller grinding dimension tends to experience faster wear. Therefore, it is preferable to keep the ratio within the range of [0.9 ≤ R1 / R2 ≤ 1.5].

[0034] [Embodiment 5 of the present invention]

[0035] According to any one of methods 1 to 4, the drill bit body has a shoulder, the shoulder is disposed on the ridge portion connecting the cutting edge and the flank face, and extends from the outer peripheral corner portion in a direction opposite to the rotation direction of the drill bit in the direction around the central axis, the shoulder portion has a convex curve-shaped cutting edge grinding with a cross section perpendicular to the ridge portion, and the cutting edge grinding radius of the shoulder portion is smaller than the cutting edge grinding radius of the radially outer end portion of the main cutting edge connected to the outer peripheral corner portion.

[0036] In the above structure, the grinding radius of curvature of the shoulder is smaller than that of the radially outer end of the main cutting edge, which is adjacent to the outer circumferential corner. In other words, the grinding radius of curvature of the radially outer end of the main cutting edge is larger than that of the shoulder. With this structure, especially in low- to medium-efficiency machining conditions or drilling of large workpieces, it is possible to suppress chipping and other defects at the radially outer end of the main cutting edge, which has the fastest circumferential speed, and to stably suppress the development of wear near the shoulder.

[0037] [Solution 6 of the present invention]

[0038] According to any one of methods 1 to 5, the chisel edge grinding edge has a convex curve-shaped cutting edge grinding with a cross section perpendicular to the edge portion on which the cutting edge is disposed, and when the diameter of the rotation trajectory of the cutting edge around the central axis is taken as the drill bit diameter, the cutting edge grinding curvature radius of the region of the chisel edge grinding edge within 7% of the drill bit diameter from the central axis toward the radially outward is smaller than the cutting edge grinding curvature radius of the portion of the main cutting edge located radially inward than the radially outer end.

[0039] In this case, during drilling, the sharpness of the chisel edge, especially near the central axis, can be consistently improved during the initial engagement of the workpiece. Therefore, drilling with higher precision is possible.

[0040] [Solution 7 of the present invention]

[0041] According to the drill bit of method 2, the cutting edge grinding radius of the first cutting edge is maximized at the lowest point of the first cutting edge located in the direction most opposite to the rotation direction of the drill bit.

[0042] Conventional drill bits tend to exhibit the following tendency: at the lowest point of the concave cutting edge (the first cutting edge in this invention), located in the direction opposite to the drill bit's rotation, the stress exerted by the chip rubbing against it is relatively strong, resulting in significant crater wear damage. Since crater wear easily occurs near the boundary between the edge dressing surface and the rake face, as described in the structure of this invention, by maximizing the edge dressing dimension (edge ​​dressing radius of curvature) of the first cutting edge at the lowest point, crater wear can be effectively suppressed.

[0043] [Embodiment 8 of the present invention]

[0044] According to any one of methods 1 to 7, the rake face has: a chisel edge grinding rake face connected to the chisel edge grinding edge; a main rake face connected to the main cutting edge; and a first boundary edge extending along the boundary portion connecting the chisel edge grinding rake face and the main rake face, and protruding toward the rotation direction of the drill bit, wherein the first boundary edge has a grinding edge.

[0045] In this case, the situation where the first boundary edge protruding in the direction of drill bit rotation is lost due to being scraped by chips is suppressed.

[0046] [Method 9 of the present invention]

[0047] According to the drill bit of method 2, the rake face has: a first rake face connected to the first cutting edge; a second rake face connected to the second cutting edge; and a second boundary edge extending along the boundary portion connecting the first rake face and the second rake face, and protruding toward the rotation direction of the drill bit, wherein the second boundary edge has a sharpened cutting edge.

[0048] In this case, the loss of the second boundary edge protruding in the direction of drill bit rotation due to being scraped by chips is suppressed.

[0049] [Embodiment 10 of the present invention]

[0050] According to any one of methods 1 to 9, the cutting edge of the edge is ground beyond a position 1.5 mm from the outer peripheral corner toward the rear end side, and further extends to the rear end side.

[0051] In this case, it is possible to stably suppress the development of edge wear or chipping over a wider range along its edge.

[0052] The drill bit according to the present invention can improve wear resistance, thereby enabling a longer tool life. Attached Figure Description

[0053] Figure 1 This is a perspective view showing a simplified portion (body) of the drill bit according to this embodiment.

[0054] Figure 2 This is a simplified front view of a portion of the drill bit in this embodiment.

[0055] Figure 3 This is a simplified side view of a portion of the drill bit according to this embodiment.

[0056] Figure 4 This is a simplified side view of a portion of the drill bit according to this embodiment.

[0057] Figure 5A It is a schematic cross-sectional view of the drill bit body, perpendicular to each edge (each cutting edge grinding), specifically showing the case where the width ratio of the cutting edge grinding is 1.0.

[0058] Figure 5B It is a schematic cross-sectional view of the drill bit body, perpendicular to each edge (each cutting edge grinding), specifically showing the case where the width ratio of the grinding edge is greater than 1.0.

[0059] Figure 5C It is a schematic cross-sectional view of the drill bit body, perpendicular to each edge (each cutting edge grinding), specifically showing the case where the width ratio of the grinding edge is less than 1.0.

[0060] Figure 6 The figure (table) shows a summary of the results of the “wear confirmation test 1” of the embodiment (enlarged images near each blade tip), and also lists cross-sectional schematic diagrams near each blade tip.

[0061] Figure 7 The figure (table) shows a summary of the results of the “wear confirmation test 2” of the embodiment (enlarged images near each blade tip), and also lists cross-sectional schematic diagrams near each blade tip. Detailed Implementation

[0062] A drill bit 10 according to one embodiment of the present invention will be described with reference to the accompanying drawings.

[0063] like Figures 1-4 As shown, the drill bit 10 includes at least a body 1. The body 1 is generally cylindrical about a central axis O. In this embodiment, the drill bit 10 includes the body 1 and a shank (not shown). The body 1 and the shank are arranged side by side in the direction extending from the central axis O. Alternatively, the body 1 may also be referred to as a cutting edge.

[0064] In this embodiment, the main body 1 is detachably mounted on the shank. That is, the drill bit 10 is an indexable insert drill bit. However, it is not limited to this; the drill bit 10 may also have only the main body 1 and no shank. In this case, the drill bit 10 is a drill head. Alternatively, the shank may also be called a tool holder.

[0065] Furthermore, in Figures 1-4 The diagram of the fastening mechanism of the main body 1 relative to the handle is omitted, and the main body 1 is simplified.

[0066] [Definition of direction]

[0067] In this embodiment, the direction in which the central axis O of the drill bit 10 extends is called the axial direction. In the axial direction, the direction from the shank toward the body 1 is called the axial front end side or simply the front end side, and the direction from the body 1 toward the shank is called the axial rear end side or simply the rear end side.

[0068] Furthermore, the direction orthogonal to the central axis O is called the radial direction. In the radial direction, the direction closer to the central axis O is called the radial inner direction, and the direction farther away from the central axis O is called the radial outer direction.

[0069] The direction of rotation around the central axis O is called the circumferential direction. Within the circumferential direction, the direction in which the drill bit 10 rotates during drilling is called the drill rotation direction T. Furthermore, sometimes the direction in the circumferential direction opposite to the drill rotation direction T is called the reverse drill rotation direction.

[0070] Furthermore, in this embodiment, the direction in which each component of the cutting edge 7 described later in the main body 1 extends is referred to as the cutting edge length direction.

[0071] [Handle]

[0072] Although not shown, the shank is cylindrical and extends axially from the central axis O. The shank can be detachably held, for example, in the spindle of a machine tool (not shown) or the chuck of a drilling machine (hereinafter referred to as the spindle, etc.). The drill bit 10 is fed axially towards its front end while the shank rotates in the drill bit rotation direction T via the spindle, etc., thereby cutting into the workpiece through the body 1 to perform drilling.

[0073] 〔main body〕

[0074] like Figures 1-4 As shown, the main body 1 extends axially around the central axis O. In this embodiment, the diameter (outer diameter) of the main body 1 is, for example, 6 mm or more and 40 mm or less. In addition, the diameter of the main body 1 is equivalent to the diameter of the rotation trajectory of the cutting edge 7 around the central axis O, as described later, and therefore can also be referred to as the drill bit diameter.

[0075] The main body 1 has: a front end face 3 facing the front end of the main body 1; an outer peripheral face 8 facing the radially outer side of the main body 1; a chip removal groove 4; a rake face 5; a flank face 6; a chisel edge grinding surface 11; a cutting edge 7; a cutting edge band 13; an edge 12; a secondary flank face 14; an outer peripheral corner 15; a shoulder 9; a fastening mechanism to the shank (not shown); and a rotating support (not shown).

[0076] The chip removal groove 4 has openings on the front end face 3 and the outer peripheral face 8 of the main body 1, and is groove-shaped extending from the front end face 3 towards the rear end. Specifically, the chip removal groove 4 extends in a twisting manner from the front end face 3 towards the axial rear end towards the direction of reverse drill bit rotation. Multiple chip removal grooves 4 are spaced apart from each other on the main body 1 along the circumferential direction. In this embodiment, two chip removal grooves 4 are provided at equal intervals in the circumferential direction.

[0077] The rake face 5 is disposed in the chip removal groove 4 and faces the drill rotation direction T. That is, the rake face 5 is disposed in the wall surface of the chip removal groove 4 facing the drill rotation direction T.

[0078] The rake face 5 has a cross-cutting rake face 50, a main rake face 51, a first boundary edge 54, and a second boundary edge 55.

[0079] The chisel edge sharpening rake face 50 is located at the radially inner end of the front end of the chip removal groove 4. In this embodiment, the chisel edge sharpening rake face 50 is approximately triangular.

[0080] The main rake face 51 is located on the radial outer side of the rake face 50 used for chisel edge grinding.

[0081] The main rake face 51 has a first rake face 52 and a second rake face 53. That is, the rake face 5 has a first rake face 52 and a second rake face 53.

[0082] The first rake face 52 is disposed in the portion of the main rake face 51 excluding the radially outer end. The first rake face 52 is disposed adjacent to the chisel edge grinding rake face 50 on its radially outer side. In this embodiment, the first rake face 52 is concave. Although not specifically illustrated, in a cross-sectional view perpendicular to the central axis O (hereinafter sometimes simply referred to as the cross-sectional view), the first rake face 52 presents a concave curve recessed towards the direction of reverse drill rotation. The radial dimension of the first rake face 52 is larger than the radial dimension of the chisel edge grinding rake face 50.

[0083] The second rake face 53 is disposed at the radially outer end of the main rake face 51. The second rake face 53 is disposed adjacent to the first rake face 52 on its radially outer side. In this embodiment, the second rake face 53 is twisted. Although not specifically illustrated, in a cross-sectional view, the second rake face 53 appears as a straight line. However, it is not limited to this; the second rake face 53 may also be concave. In this case, in a cross-sectional view, the second rake face 53 is a concave curve that is recessed towards the reverse drill rotation direction. Alternatively, the second rake face 53 may also be convex. In this case, in a cross-sectional view, the second rake face 53 is a convex curve that bulges towards the drill rotation direction T. The radial dimension of the second rake face 53 is smaller than the radial dimension of the chisel edge grinding rake face 50 and smaller than the radial dimension of the first rake face 52.

[0084] The second rake face 53 extends approximately axially along its radially outer end edge in the wall surface facing the drill bit rotation direction T toward the chip removal groove 4. Specifically, the second rake face 53 extends in a twisted manner toward the reverse drill bit rotation direction as it moves toward the rear end side toward the axial direction. The radially outer end of the second rake face 53 is connected to the outer peripheral surface 8 via a ridge portion (edge ​​12).

[0085] Furthermore, the second rake face 53 extends radially outward in the direction opposite to the drill bit rotation direction T (i.e., the reverse drill bit rotation direction). Specifically, the second rake face 53 extends radially outward in the reverse drill bit rotation direction throughout its entire radial region. That is, the radial rake angle of the second rake face 53 is set to a negative angle throughout its entire radial region. Therefore, in the cross-sectional view, the edge portion (edge ​​12) located at the radially outer end of the second rake face 53 has an obtuse angle.

[0086] The first boundary ridge 54 extends along the boundary between the chisel edge grinding rake face 50 and the main rake face 51, and is shaped as a ridge protruding in the drill rotation direction T. The first boundary ridge 54 extends approximately axially along the boundary between the chisel edge grinding rake face 50 and the first rake face 52. Specifically, the first boundary ridge 54 extends radially inward towards the rear end side in the axial direction.

[0087] The second boundary ridge 55 extends along the boundary connecting the first rake face 52 and the second rake face 53, and is a ridge convex in the drill bit rotation direction T. The second boundary ridge 55 extends approximately axially along the boundary connecting the first rake face 52 and the second rake face 53. Specifically, the second boundary ridge 55 extends in the reverse drill bit rotation direction as it moves toward the rear end side in the axial direction.

[0088] The back face 6 is positioned on the front face 3.

[0089] The flank face 6 has a first flank face 61 and a second flank face 62 that is adjacent to the first flank face 61 in the reverse drill rotation direction.

[0090] The first flank face 61 is located at the end of the flank face 6 in the drill rotation direction T. The first flank face 61 is an elongated surface extending in a generally radial direction (a generally polygonal surface that is longer in the radial direction). The first flank face 61 extends toward the axial rear end side as it moves toward the reverse drill rotation direction.

[0091] The second flank face 62 is located in the portion of the flank face 6 other than the end in the drill rotation direction T. The second flank face 62 is generally fan-shaped, and its circumferential dimension increases as it moves radially outward. The second flank face 62 extends axially toward the rear end side as it moves toward the reverse drill rotation direction. The axial displacement per unit length of the second flank face 62 in the circumferential direction (corresponding to the inclination of the clearance angle) is greater than the displacement of the first flank face 61.

[0092] Furthermore, in this embodiment, the flank face 6 has two inclined surfaces (first flank face 61 and second flank face 62) with different clearance angles, but it is not limited to this. The flank face 6 may be formed by a single inclined surface, or it may have three or more inclined surfaces arranged in the circumferential direction with different clearance angles.

[0093] A chisel edge grinding surface 11 is disposed on the front end face 3. The chisel edge grinding surface 11 is disposed adjacent to the rear face 6 in the reverse drill rotation direction. In this embodiment, the chisel edge grinding surface 11 is connected to the end of the second rear face 62 in the reverse drill rotation direction. The chisel edge grinding surface 11 extends axially toward the rear end side in the reverse drill rotation direction. The axial displacement per unit length of the chisel edge grinding surface 11 in the circumferential direction (corresponding to the inclination of the clearance angle) is greater than the displacement of the rear face 6. Furthermore, the radially inner end of the chisel edge grinding surface 11 is connected to the bottom edge of the triangular-shaped chisel edge grinding rake face 50.

[0094] The cutting edge 7 is disposed on the ridge portion connecting the rake face 5 and the flank face 6. Multiple cutting edges 7 are spaced apart from each other along the circumferential direction on the main body 1. In this embodiment, two cutting edges 7 are equally spaced along the circumferential direction. That is, the drill bit 10 in this embodiment is a double-edged twist drill.

[0095] The cutting edge 7 has a chisel edge grinding edge 70 and a main cutting edge 71.

[0096] The chisel edge 70 is disposed at the radially inner end of the cutting edge 7. The chisel edge 70 is disposed at the ridge portion connecting the chisel edge rake face 50 and the first flank face 61. That is, the chisel edge rake face 50 and the chisel edge 70 are connected. The chisel edge 70 extends along the leading edge edge of the chisel edge rake face 50. The chisel edge 70 extends radially outward from near the central axis O. Furthermore, the chisel edge 70 extends axially towards the rear end side as it extends radially outward. In this embodiment, the chisel edge 70 is substantially straight.

[0097] The main cutting edge 71 is disposed radially outside the chisel edge 70. The main cutting edge 71 is connected to the chisel edge 70. The main cutting edge 71 constitutes the portion of the cutting edge 7 other than the chisel edge 70 (the portion of the cutting edge 7 other than the radially inner end). The main cutting edge 71 is disposed at the edge portion connecting the main rake face 51 and the first flank face 61. That is, the main rake face 51 is connected to the main cutting edge 71. The main cutting edge 71 extends along the leading edge edge of the main rake face 51. Furthermore, the main cutting edge 71 extends radially outward and axially toward the rear end side. An outer peripheral corner portion 15 is disposed at the outermost radial end of the main cutting edge 71. The main cutting edge 71 is connected to the edge 12 via the outer peripheral corner portion 15.

[0098] The main cutting edge 71 has a first cutting edge 72, a second cutting edge 73 and a top edge 74.

[0099] In this embodiment, the first cutting edge 72 constitutes the portion of the main cutting edge 71 excluding its radially outer end. The first cutting edge 72 is disposed at the ridge portion connecting the first rake face 52 and the first flank face 61. That is, the first rake face 52 is connected to the first cutting edge 72. The first cutting edge 72 extends along the leading edge of the first rake face 52. The first cutting edge 72 is disposed radially outer of the chisel edge 70 and has a concave curve shape that is recessed in the direction opposite to the drill rotation direction T. The radially inner end of the first cutting edge 72 is connected to the radially outer end of the chisel edge 70. The connection portion between the first cutting edge 72 and the chisel edge 70 has a convex shape that protrudes in the drill rotation direction T.

[0100] In this embodiment, the second cutting edge 73 constitutes the radially outer end portion of the main cutting edge 71 connected to the outer peripheral corner portion 15. The second cutting edge 73 is disposed at the edge portion connecting the second rake face 53 and the first flank face 61. That is, the second rake face 53 is connected to the second cutting edge 73. The second cutting edge 73 extends along the leading edge edge of the second rake face 53. The second cutting edge 73 is disposed radially outside the first cutting edge 72 and is connected to the radially outer end of the first cutting edge 72 via a top 74 protruding toward the drill rotation direction T.

[0101] In this embodiment, the second cutting edge 73 is straight. However, it is not limited to this; the second cutting edge 73 may also be concave. When the second cutting edge 73 is concave, it is preferably a concave curve with a large radius of curvature (i.e., a large R) that is recessed in the reverse drill rotation direction. Alternatively, the second cutting edge 73 may also be a convex curve that bulges out in the drill rotation direction T.

[0102] like Figure 2 As shown, the radial rake angle θ of the second cutting edge 73 is set to a negative angle over the entire length of the second cutting edge 73. Here, "radial rake angle θ of the second cutting edge 73" refers to, as... Figure 2 As shown, when viewing the drill bit 10 along the axial direction from the front end, the angle θ formed between the virtual straight line VL passing through the second cutting edge 73 (a portion) and the central axis O and the second cutting edge 73. Furthermore, "the radial rake angle θ of the second cutting edge 73 is a negative angle" means that the second cutting edge 73 extends in the opposite direction to the drill bit rotation direction T as it moves radially outward.

[0103] The top 74 connects the radially outer end of the first cutting edge 72 to the radially inner end of the second cutting edge 73. The top 74 is convex in the direction of drill rotation T.

[0104] Therefore, in this embodiment, the cutting edge 7 is configured as a so-called curved cutting edge shape with a concave edge (first cutting edge 72) and a convex part (top 74) as the main cutting edge 71.

[0105] like Figures 1-4 As shown, the cutting edge 13 is disposed on the outer peripheral surface 8 and extends along the chip removal groove 4. Specifically, the cutting edge 13 is disposed at the end of the outer peripheral surface 8 in the drill bit rotation direction T, and extends in the direction opposite to the drill bit rotation direction as it moves toward the rear end side in the axial direction. The cutting edge 13 has a curved surface that convexes radially outward. In a cross-sectional view perpendicular to the central axis O, the cutting edge 13 appears as an arc centered on the central axis O.

[0106] Edge 12 is disposed at the ridge portion connecting the cutting edge 13 and the second rake face 53 (rake face 5). The cutting edge 13 and the second rake face 53 are connected to each other via edge 12. Edge 12 extends along the cutting edge 13 and the second rake face 53. Specifically, edge 12 extends toward the reverse drill rotation direction toward the rear end side in the axial direction. The cutting edge 13 lies on a cylindrical rotation trajectory (not shown) obtained by rotating edge 12 about the central axis O.

[0107] Alternatively, an inverted taper can be applied to edge 12. In this case, edge 12 is positioned slightly radially inward as it faces the rear end side in the axial direction.

[0108] The secondary relief face 14 is disposed on the outer peripheral surface 8. The secondary relief face 14 is disposed adjacent to the cutting edge 13 in the reverse drill rotation direction of the cutting edge 13. The secondary relief face 14 is located radially inward of the cutting edge 13. During drilling, the secondary relief face 14 is radially opposed to the inner peripheral surface of the hole to be machined in the workpiece with a clearance.

[0109] The outer peripheral corner 15 is disposed at the corner connecting the cutting edge 7 and the edge 12. Specifically, the outer peripheral corner 15 connects the radially outer end of the second cutting edge 73 of the main cutting edge 71 with the front end of the edge 12.

[0110] A shoulder 9 is disposed at the ridge portion connecting the cutting edge 13 and the first flank face 61 (flank face 6). The shoulder 9 is disposed at the outer periphery of the front end of the main body 1 and extends in a circumferential direction around the central axis O. The shoulder 9 extends from the outer periphery 15 in a direction opposite to the drill rotation direction T. Specifically, the shoulder 9 extends slightly toward the rear end side as it moves toward the reverse drill rotation direction.

[0111] Although not specifically illustrated, the main body 1 has a fastening mechanism for the handle. The fastening mechanism, for example, has a generally cylindrical mounting portion protruding from the rear end of the main body 1 toward the rear end side and a through hole extending axially through the main body 1.

[0112] The mounting part is inserted into a mounting hole (not shown) on the handle. Multiple (e.g., a pair) through holes are spaced apart circumferentially on the main body 1. Screws are inserted into each through hole and screwed into the internal threaded holes of the handle. Thus, the main body 1 is detachably fixed to the handle.

[0113] Although not specifically illustrated, the swivel support is composed of a surface, etc., provided on a part of the main body 1 facing the reverse drill bit rotation direction. The swivel support contacts the swivel receiving part of the shank facing the drill bit rotation direction T. A plurality of groups of swivel support parts and swivel receiving parts are provided at intervals (e.g., a pair) in the circumferential direction. As a result, the main body 1 can stably receive the rotational force in the drill bit rotation direction T transmitted from the spindle, etc., via the shank.

[0114] [Sharpening the blade edge]

[0115] like Figure 5A , Figure 5B , Figure 5C As schematically shown, the cross-cutting edge 70, main cutting edge 71, edge 12, shoulder 9, first boundary edge 54, and second boundary edge 55, all located on the edge portions of the main body 1, each have a cutting edge H with a convex curve cross-section perpendicular to each edge portion. The cutting edge H is a so-called rounded cutting edge. The cutting edge H extends along each edge portion.

[0116] In the following description, such as Figure 5A , Figure 5B , Figure 5C As shown, in a cross-section perpendicular to the edge portion (a cross-section perpendicular to the direction of the edge grinding H), the surface connecting to the first end h1 of the two ends h1 and h2 of the edge grinding H is designated as the first surface (rake face) 101, and the surface connecting to the second end h2 is designated as the second surface (flank face) 102. The first surface 101 is, for example, the rake face 5, and the second surface 102 is, for example, the flank face 6. Details regarding the first surface 101 and the second surface 102 connecting to the edge grinding H of each edge portion will be explained separately.

[0117] exist Figure 5A , Figure 5B , Figure 5C In each of the cross sections shown, the first surface 101 can be connected in a manner consistent with the tangent of the cutting edge H on the first end h1, i.e., tangential to the first end h1, or it can extend in a direction different from the tangent on the first end h1 and be smoothly connected to the first end h1.

[0118] Furthermore, in each of the cross sections, the second surface 102 can be connected in a manner consistent with the tangent of the cutting edge H on the second end h2, i.e., tangential to the second end h2, or it can extend in a direction different from the tangent on the second end h2 and be smoothly connected to the second end h2.

[0119] Figure 5AThe symbol R represents the radius of curvature of the edge grinding H. The drill bit 10 of this embodiment has a unique technical feature regarding the edge grinding radius of curvature R. Furthermore, in this embodiment, the "edge grinding radius of curvature R" is closely related to the edge grinding width. The edge grinding width refers to the dimension in a cross-section perpendicular to the direction (edge ​​portion) of the edge grinding H, corresponding to the distance between the two ends h1 and h2 of the edge grinding H (the straight-line distance between the first end h1 and the second end h2).

[0120] That is, when the radius of curvature R of the edge grinding is large, there is a tendency for the edge grinding width to also increase accordingly; conversely, when the radius of curvature R of the edge grinding is small, there is a tendency for the edge grinding width to also decrease accordingly. In other words, when the edge grinding width is small, the radius of curvature R of the edge grinding also decreases, and when the edge grinding width is large, the radius of curvature R of the edge grinding also increases. Therefore, it is acceptable to refer to the relationship between the magnitudes of the edges grinding radii R described later in this embodiment as the relationship between the magnitudes of the edges grinding widths. That is, the relationship between the magnitudes of the edges grinding radii R is equivalent to the relationship between the magnitudes of the edges grinding widths.

[0121] The radius of curvature R of the cutting edge grinding at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the edge 12 is 25 μm or more and 80 μm or less. More preferably, the radius of curvature R of the cutting edge grinding of the edge 12 is, for example, 40 μm or more and 70 μm or less.

[0122] Furthermore, the edge grinding curvature radius R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side in the edge 12 is preferably smaller than the edge grinding curvature radius R of the radially outer end (the second cutting edge 73 in this embodiment) connected to the outer peripheral corner 15 in the main cutting edge 71, and is more than 50% and less than 90% of the edge grinding curvature radius R of the radially outer end.

[0123] Here, the edge grinding H of the edge 12 extends further to the rear end side beyond a position 1.5 mm from the outer corner 15 towards the rear end side in the edge 12. Specifically, the edge grinding radius of curvature R (edge ​​grinding width) of the edge 12 is set to a constant size within a specified range including the position within 1.5 mm from the outer corner 15 towards the rear end side in the edge 12. Beyond this specified range on the rear end side, the edge grinding radius of curvature R of the edge 12 is constant or gradually decreases towards the rear end side.

[0124] More specifically, the edge grinding curvature radius R (edge ​​grinding width) of the edge 12 within 3 mm of the position extending 1.5 mm from the outer corner 15 towards the rear end is approximately the same as or slightly smaller than the edge grinding curvature radius R at the position within 1.5 mm. For example, the edge grinding curvature radius R of the edge 12 within 3 mm of the position extending 1.5 mm from the outer corner 15 towards the rear end is 30 μm or more and 70 μm or less.

[0125] Furthermore, in this embodiment, when the radius of curvature of the edge grinding of the portion of the main cutting edge 71 located radially inward from the radially outer end (the first cutting edge 72 in this embodiment) is set to R1, and the radius of curvature of the edge grinding of the radially outer end of the main cutting edge 71 (the second cutting edge 73 in this embodiment) is set to R2, the relationship [0.9 ≤ R1 / R2 ≤ 1.5] is satisfied. Additionally, it is preferable that [R1 / R2] is 1.0 or higher. More preferably, the radius of curvature R1 of the edge grinding of the first cutting edge 72 is greater than the radius of curvature R2 of the edge grinding of the second cutting edge 73.

[0126] Furthermore, the grinding radius of curvature R1 of the first cutting edge 72 varies along the length of the cutting edge 72. For example, the grinding radius of curvature R1 of the first cutting edge 72 gradually increases from both ends of the first cutting edge 72 towards the center along the length of the cutting edge. The grinding radius of curvature R1 of the first cutting edge 72 is largest at the lowest point of the first cutting edge 72, which is located in the direction most opposite to the drill bit rotation direction T (reverse drill bit rotation direction).

[0127] The grinding radius of curvature R1 of the portion of the main cutting edge 71 located radially inward from the radially outer end (the first cutting edge 72 in this embodiment) is, for example, 60 μm or more and 100 μm or less. Furthermore, the grinding radius of curvature R2 of the radially outer end of the main cutting edge 71 connected to the outer peripheral corner 15 (the second cutting edge 73 in this embodiment) is, for example, 50 μm or more and 80 μm or less.

[0128] Furthermore, in this embodiment, when the diameter of the rotation trajectory of the cutting edge 7 around the central axis O is used as the drill bit diameter, the edge grinding curvature radius R of the region within 7% of the drill bit diameter radially outward from the central axis O in the chisel edge grinding edge 70 is smaller than the edge grinding curvature radius R1 of the portion of the main cutting edge 71 located radially inward from the radially outer end (the first cutting edge 72 in this embodiment). Specifically, the edge grinding curvature radius R of the region within 7% of the drill bit diameter radially outward from the central axis O in the chisel edge grinding edge 70 is, for example, 40 μm or more and 80 μm or less.

[0129] Furthermore, the grinding radius of curvature R of the shoulder 9 is smaller than the grinding radius of curvature R2 of the radially outer end (the second cutting edge 73 in this embodiment) connected to the outer peripheral corner 15 in the main cutting edge 71. Specifically, the grinding radius of curvature R of the shoulder 9 is, for example, 40 μm or more and 70 μm or less.

[0130] Furthermore, the drill bit 10 of this embodiment has a special technical feature regarding the width ratio of the cutting edge grinding H.

[0131] exist Figure 5A , Figure 5B , Figure 5C In each of the cross sections shown, the distance from the intersection point P of the extension line of the first surface 101 and the extension line of the second surface 102 to the first end h1 is defined as the first width dimension L1, and the distance from the intersection point P to the second end h2 is defined as the second width dimension L2. [L1 / L2] is defined as the width ratio. In addition, in this embodiment, the width ratio [L1 / L2] is sometimes simply referred to as the width ratio.

[0132] Figure 5A This indicates the case where the width ratio [L1 / L2] of the edge grinding H is 1.0. Figure 5B This indicates the case where the width ratio [L1 / L2] of the edge grinding H is greater than 1.0. Figure 5C This indicates the case where the width ratio [L1 / L2] of the edge grinding H is less than 1.0.

[0133] Regarding the chisel edge grinding edge 70 and the main cutting edge 71, the first face 101 is the rake face 5, and the second face 102 is the flank face 6. Specifically, regarding the chisel edge grinding edge 70, the first face 101 is the chisel edge grinding rake face 50, and the second face 102 is the first flank face 61. Furthermore, regarding the main cutting edge 71, the first face 101 is the main rake face 51, and the second face 102 is the first flank face 61. More specifically, regarding the main cutting edge 71, the first face 101 of the first cutting edge 72 is the first rake face 52, and the second face 102 is the first flank face 61. Regarding the main cutting edge 71, the first face 101 of the second cutting edge 73 is the second rake face 53, and the second face 102 is the first flank face 61.

[0134] The width ratio [L1 / L2] of the chisel edge sharpening edge 70 is greater than the width ratio [L1 / L2] of the radially outer end (the second cutting edge 73 in this embodiment) connected to the outer peripheral corner portion 15 in the main cutting edge 71. Furthermore, the width ratio of the chisel edge sharpening edge 70 increases as it approaches the central axis O along the cutting edge length direction of the chisel edge sharpening edge 70 (the direction in which the chisel edge sharpening edge 70 extends). The width ratio [L1 / L2] of the chisel edge sharpening edge 70 is preferably 1.0 or higher.

[0135] The width ratio [L1 / L2] of the portion of the main cutting edge 71 located radially inward from the radially outer end is greater than the width ratio [L1 / L2] of the radially outer end of the main cutting edge 71. That is, in this embodiment, the width ratio [L1 / L2] of the first cutting edge 72 is greater than the width ratio [L1 / L2] of the second cutting edge 73.

[0136] Furthermore, the width ratio of the first cutting edge 72 varies along the cutting edge length direction of the first cutting edge 72. For example, the width ratio of the first cutting edge 72 gradually increases from both ends of the first cutting edge 72 towards the center along the cutting edge length direction. The width ratio of the first cutting edge 72 is largest at its lowest point, located in the direction most opposite to the drill bit rotation direction T (reverse drill bit rotation direction). The width ratio [L1 / L2] of the first cutting edge 72 is preferably 1.0 or higher.

[0137] The width ratio of the second cutting edge 73 is the smallest among the constituent elements of the cutting edge 7. More specifically, the width ratio of the outermost end of the main cutting edge 71 located at the outer peripheral corner 15 (the outermost radial end of the second cutting edge 73) is the smallest among the width ratios of the cutting edges 7. The width ratio [L1 / L2] of the second cutting edge 73 is preferably 1.0 or less.

[0138] Regarding edge 12, the first face 101 is the rake face 5, and the second face 102 is the cutting edge 13. Specifically, regarding edge 12, the first face 101 is the second rake face 53, and the second face 102 is the cutting edge 13. The width ratio [L1 / L2] of edge 12 within 1.5 mm from the outer corner 15 toward the rear end is, for example, 0.7 or more and 1.3 or less.

[0139] Regarding the shoulder 9, the first face 101 is the flank face 6, and the second face 102 is the cutting edge 13. Specifically, regarding the shoulder 9, the first face 101 is the first flank face 61, and the second face 102 is the cutting edge 13. The width ratio [L1 / L2] of the shoulder 9 is, for example, 0.7 or more and 1.3 or less.

[0140] [Effects of this implementation method]

[0141] In the drill bit 10 of this embodiment described above, the edge grinding H of the chisel edge 70, the main cutting edge 71, and the edge 12 is convex curved (convex R shape) in a cross section perpendicular to each edge, and is configured as a so-called rounded edge grinding. Therefore, in low- to medium-efficiency machining conditions or drilling of large workpieces, wear or melting within the edge grinding surface can be suppressed. In detail, if, for example, unlike this embodiment, the edge grinding H of each component of the cutting edge 7 (especially the main cutting edge 71, etc.) is a chamfered edge grinding with a flat surface, then in low- to medium-efficiency machining conditions or drilling of large workpieces, fragmentation wear may be promoted within the edge grinding surface, resulting in premature melting or chipping.

[0142] Furthermore, the position within 1.5 mm from the outer peripheral corner 15 toward the rear end of the edge 12 is located at the front end of the edge 12 and is a part that is easily subjected to cutting resistance from the inner peripheral surface of the machining hole of the material being cut.

[0143] In the drill bit 10 of this embodiment, the radius of curvature R of the cutting edge at the aforementioned position of the edge 12 is set to be 25 μm or more and 80 μm or less. This allows for the stable suppression of wear development.

[0144] In detail, if, unlike this embodiment, the radius of curvature R of the edge 12 is larger than 80 μm, then the area where the radial rake angle becomes a strong negative angle in the edge grinding H increases (becoming a strong negative edge grinding H), and the cutting resistance increases significantly, which may lead to the early development of wear.

[0145] On the other hand, even if the radius of curvature R of the edge 12 is less than 25 μm, wear is still likely to develop. Furthermore, since the cross-sectional shape of the edge portion becomes sharp (a shape that is close to a sharp angle), the function obtained by edge grinding H is reduced, and chipping and other defects are more likely to occur.

[0146] Furthermore, in this embodiment, the grinding radius of curvature R of the edge 12 is smaller than the grinding radius of curvature R (R2) of the radially outer end (second cutting edge 73) of the main cutting edge 71, which is adjacent to the outer peripheral corner 15. In other words, the grinding radius of curvature R (R2) of the radially outer end (second cutting edge 73) of the main cutting edge 71 is larger than the grinding radius of curvature R of the edge 12. With this structure, chipping and other defects at the radially outer end of the main cutting edge 71, which has the fastest circumferential speed, can be suppressed, and the development of wear near the edge 12 can be stably suppressed.

[0147] In summary, the drill bit 10 according to this embodiment improves wear resistance, thereby extending the tool's lifespan. In particular, this embodiment exhibits especially significant effects when applied to drilling operations under low- to medium-efficiency conditions or on large workpieces.

[0148] Furthermore, in this embodiment, the main cutting edge 71 has: a first cutting edge 72, which is disposed radially outside the chisel edge grinding edge 70 and has a concave curve shape that is recessed in the direction opposite to the drill rotation direction T in the direction surrounding the central axis O; and a second cutting edge 73, which is disposed radially outside the first cutting edge 72 and is connected to the radially outer end of the first cutting edge 72, and the second cutting edge 73 constitutes the radially outer end of the main cutting edge 71 that is connected to the outer peripheral corner portion 15.

[0149] According to the above structure, when the main cutting edge 71 has a so-called curved cutting edge shape with a concave cutting edge (first cutting edge 72), the excellent working effect of this embodiment can be obtained.

[0150] Furthermore, in this embodiment, when the radius of curvature of the edge grinding of the portion of the main cutting edge 71 located radially inward from the radial outer end (the first cutting edge 72) is set to R1, and the radius of curvature of the edge grinding of the radial outer end (the second cutting edge 73) of the main cutting edge 71 is set to R2, the relationship [0.9≤R1 / R2≤1.5] is satisfied.

[0151] In the main cutting edge 71, compared to the radially outer end (second cutting edge 73) connected to the outer peripheral corner 15, the portion located radially inner than the radially outer end (first cutting edge 72) is prone to crater wear due to chip rubbing. Crater wear tends to occur near the boundary between the edge grinding surface and the rake face 5, therefore, by increasing the edge grinding size (edge ​​grinding radius of curvature R), crater wear can be effectively suppressed.

[0152] Based on the above viewpoint, by setting the ratio of the grinding radius of curvature [R1 / R2] of the cutting edge to 1.0 or more, it is possible to reliably ensure that the grinding radius of curvature R1 of the portion of the main cutting edge 71 located radially inward from the radially outer end is large, which is therefore preferred. However, if the ratio [R1 / R2] is close to 1.0, the ratio [R1 / R2] may be less than 1.0 due to manufacturing errors, etc. Therefore, in this embodiment, it is set to [0.9≤R1 / R2].

[0153] However, in this embodiment, since the cutting edge grinding radius of curvature R2 is greater than the cutting edge grinding radius of curvature R of edge 12, if the ratio [R1 / R2] is 0.9 or higher, the size of the cutting edge grinding radius of curvature R1 can also be sufficiently ensured. Therefore, the effect of suppressing crater wear can be stably obtained.

[0154] Furthermore, if the ratio [R1 / R2] is less than 0.9 or greater than 1.5, the difference between the grinding curvature radii R1 and R2 increases, thus the side with the smaller grinding dimension tends to experience faster wear. Therefore, it is preferable to keep the ratio within the range of [0.9 ≤ R1 / R2 ≤ 1.5].

[0155] Furthermore, in this embodiment, the shoulder 9 has a convex curve-shaped cutting edge H with a cross section perpendicular to its edge portion, and the cutting edge curvature radius R of the shoulder 9 is smaller than the cutting edge curvature radius R2 of the radially outer end (second cutting edge 73) of the main cutting edge 71 that is connected to the outer peripheral corner portion 15.

[0156] In the above structure, the grinding radius of curvature R of the shoulder 9 is smaller than the grinding radius of curvature R2 of the radially outer end (second cutting edge 73) of the main cutting edge 71, which is adjacent to the outer peripheral corner 15. In other words, the grinding radius of curvature R2 of the radially outer end of the main cutting edge 71 is greater than the grinding radius of curvature R of the shoulder 9. With this structure, especially in low to medium efficiency machining conditions or drilling of large workpieces, it is possible to suppress chipping and other defects at the radially outer end of the main cutting edge 71, which has the fastest circumferential speed, and to stably suppress the development of wear near the shoulder 9.

[0157] Furthermore, in this embodiment, the chisel edge grinding blade 70 has a convex curve-shaped cutting edge grinding H with a cross section perpendicular to its edge portion. The cutting edge grinding curvature radius R of the area within 7% of the drill bit diameter from the central axis O toward the radially outward direction of the chisel edge grinding blade 70 is smaller than the cutting edge grinding curvature radius R1 of the portion of the main cutting edge 71 located radially inward from the radially outer end (the first cutting edge 72).

[0158] In this case, during drilling, the sharpness of the chisel edge 70, which first engages the workpiece, can be consistently improved, especially near the central axis O. Therefore, drilling with higher precision is possible.

[0159] Furthermore, in this embodiment, the grinding radius of curvature R1 of the first cutting edge 72 is maximized at the lowest point of the first cutting edge 72, which is located in the direction most opposite to the rotation direction T of the drill bit.

[0160] Conventional drill bits tend to exhibit the following tendency: at the lowest point of the concave cutting edge (the first cutting edge 72 in this embodiment), which is located closest to the direction of reverse drill rotation, the stress caused by chip rubbing is relatively strong, resulting in significant crater wear damage. Since crater wear tends to occur near the boundary between the edge grinding surface and the rake face 5, as in this embodiment, by maximizing the edge grinding dimension (edge ​​grinding radius of curvature R) of the first cutting edge 72 at the lowest point, crater wear can be effectively suppressed.

[0161] Furthermore, in this embodiment, the first boundary ridge line 54, which extends along the boundary between the cross-edge grinding rake face 50 and the main rake face 51 and protrudes toward the drill rotation direction T, has a cutting edge grinding H.

[0162] In this case, the situation where the first boundary edge 54 protruding in the direction of drill bit rotation T is lost due to being scraped by chips is suppressed.

[0163] Furthermore, in this embodiment, the second boundary ridge 55, which extends along the boundary between the first rake face 52 and the second rake face 53 and protrudes toward the drill rotation direction T, has a cutting edge grinding H.

[0164] In this case, the possibility of the second boundary edge 55 protruding in the direction of drill bit rotation T being missing due to being scraped by chips is suppressed.

[0165] Furthermore, in this embodiment, the edge grinding H of the edge 12 extends beyond the position of the outer peripheral corner 15 towards the rear end side by 1.5 mm, and further extends to the rear end side.

[0166] In this case, the development of wear or chipping of the edge 12 can be stably suppressed over a wider range along its edge portion.

[0167] Furthermore, in the drill bit 10 of this embodiment, when a width ratio [L1 / L2] is defined in a cross section perpendicular to the direction in which each edge grinding H extends, the width ratio of the edge grinding H of the chisel edge grinding edge 70 is greater than the width ratio of the edge grinding H of the radially outer end (second cutting edge 73) of the main cutting edge 71 connected to the outer peripheral corner 15. In other words, the width ratio of the edge grinding H of the radially outer end of the main cutting edge 71 is less than the width ratio of the edge grinding H of the chisel edge grinding edge 70.

[0168] Specifically, when comparing the width ratios of the grinding H of each cutting edge, in the chisel edge grinding edge 70, the proportion of the first width dimension L1 on the rake face 5 side is larger, and in the radial outer end of the main cutting edge 71 (the second cutting edge 73), the proportion of the second width dimension L2 on the flank face 6 side is larger.

[0169] During drilling, the chisel edge regrinding edge tends to exhibit the following tendency: damage caused by crater wear easily becomes significant due to the friction of compressed chips. Crater wear tends to occur near the boundary between the regrinding edge and the rake face 5. Therefore, as in this embodiment, by increasing the width ratio of the chisel edge regrinding edge 70 (increasing the proportion of the first width dimension L1 on the rake face 5 side), crater wear can be stably suppressed.

[0170] Furthermore, the radially outer end of the main cutting edge tends to experience significant wear on the flank face 6 side. Therefore, as in this embodiment, by reducing the width ratio of the radially outer end of the main cutting edge 71 (increasing the proportion of the second width dimension L2 on the flank face 6 side), flank face wear can be stably suppressed.

[0171] Thus, the drill bit 10 according to this embodiment can improve wear resistance, thereby achieving a longer tool life. In particular, this embodiment has a particularly significant effect when applied to drilling operations under low to medium efficiency conditions or for large workpieces.

[0172] Furthermore, in this embodiment, the width ratio [L1 / L2] at a position within 1.5 mm from the outer corner 15 toward the rear end side in the edge 12 is 0.7 or more and 1.3 or less.

[0173] The edge is prone to increased damage due to wear on the cutting edge side. In particular, the area within 1.5 mm from the outer corner toward the rear end of the edge is located at the front end of the edge and is a part that is easily subjected to cutting resistance from the inner circumferential surface of the machined hole of the workpiece.

[0174] Through in-depth research, the inventors have confirmed the following: Regarding the width ratio of the edge 12 during grinding, if the proportion of the second width dimension L2 on the cutting edge 13 side is excessively increased, the cutting resistance increases significantly, leading to early wear development. Furthermore, when the proportion of the first width dimension L1 on the rake face 5 side is small, wear development on the rake face 5 side is also affected.

[0175] For the reasons mentioned above, the width ratio of edge 12 is preferably 0.7 or higher and 1.3 or lower, and the closer it is to 1.0, the better.

[0176] Furthermore, in this embodiment, the width ratio [L1 / L2] of the portion of the main cutting edge 71 located radially inward from the radial outer end (the first cutting edge 72) is greater than the width ratio [L1 / L2] of the radial outer end of the main cutting edge 71 (the second cutting edge 73).

[0177] In the main cutting edge 71, compared to the radially outer end (second cutting edge 73) connected to the outer peripheral corner 15, the portion located radially inward (first cutting edge 72) is prone to crater wear due to chip rubbing. Since crater wear tends to occur near the boundary between the edge grinding surface and the rake face 5, crater wear can be effectively suppressed by increasing the width ratio of the edge grinding H of the portion of the main cutting edge 71 located radially inward (increasing the proportion of the first width dimension L1 on the rake face 5 side).

[0178] Furthermore, the radially outer end of the main cutting edge 71 (the second cutting edge 73) tends to develop wear on the flank face 6 side. Therefore, as described above, by reducing the width ratio of the edge grinding H at the radially outer end of the main cutting edge 71 (increasing the proportion of the second width dimension L2 on the flank face 6 side), flank face wear can be effectively suppressed.

[0179] Furthermore, in this embodiment, the width ratio [L1 / L2] of the chisel edge sharpening edge 70 increases as it approaches the central axis O along the blade length direction of the chisel edge sharpening edge 70 (which is the direction in which the chisel edge sharpening edge 70 extends).

[0180] The chisel edge, when sharpened, is prone to damage caused by crater wear due to the friction of compressed chips. In particular, this crater wear tends to become more pronounced as it moves closer to the central axis along the length of the chisel edge.

[0181] Therefore, as in this embodiment, by increasing the width ratio of the edge grinding H of the chisel edge grinding edge 70 as it approaches the central axis O, it is possible to effectively suppress crater wear throughout the entire area of ​​the cutting edge, including the area near the central axis O of the chisel edge grinding edge 70.

[0182] Furthermore, in this embodiment, the width ratio [L1 / L2] of the outermost end of the main cutting edge 71 located at the outer peripheral corner 15 is the smallest among the width ratios [L1 / L2] of the cutting edge 7.

[0183] Wear on the flank face tends to develop significantly at the outermost end (outer peripheral corner) of the main cutting edge 71. Therefore, as in this embodiment, by setting the width ratio of the edge grinding H at the outermost end (outer peripheral corner 15) of the main cutting edge 71 to be the smallest in the entire cutting edge 7 (main cutting edge 71 and chisel edge grinding edge 70), flank face wear can be effectively suppressed.

[0184] Furthermore, in this embodiment, the width ratio [L1 / L2] of the first cutting edge 72 is maximized at the lowest point of the first cutting edge 72, which is located in the direction most opposite to the rotation direction T of the drill bit.

[0185] Conventional drill bits tend to exhibit the following tendency: at the lowest point of the concave cutting edge (the first cutting edge 72 in this embodiment), located closest to the direction of reverse drill rotation, the stress exerted by the chip rubbing against it is relatively strong, resulting in significant crater wear damage. Since crater wear tends to occur near the boundary between the edge grinding surface and the rake face 5, as in this embodiment, by maximizing the width ratio of the edge grinding H of the first cutting edge 72 at the lowest point (maximizing the ratio of the first width dimension L1 on the rake face 5 side), crater wear can be effectively suppressed.

[0186] Furthermore, in this embodiment, the width ratio [L1 / L2] of the shoulder 9 is 0.7 or more and 1.3 or less. If, as described above, the width ratio of the edge grinding H of the shoulder 9 is 0.7 or more and 1.3 or less, then the premature wear development of either the flank face 6 or the cutting edge 13 located on both sides of the shoulder 9, thus preventing adverse effects on tool life, is stably suppressed. Additionally, a width ratio of the shoulder 9 closer to 1.0 is more preferable.

[0187] Furthermore, in this embodiment, the width ratio [L1 / L2] of the chisel edge grinding edge 70 is 1.0 or higher. In this case, the width ratio of the edge grinding H of the chisel edge grinding edge 70 (the proportion of increasing the first width dimension L1 on the rake face 5 side) can be stably increased, and the effect of suppressing crater wear can be obtained more significantly.

[0188] Furthermore, in this embodiment, the width ratio [L1 / L2] of the first cutting edge 72 is 1.0 or higher.

[0189] In this case, by steadily increasing the width ratio of the edge grinding H of the first cutting edge 72 (increasing the proportion of the first width dimension L1 on the rake face 5), the effect of suppressing crater wear can be obtained more significantly.

[0190] Furthermore, in this embodiment, the width ratio [L1 / L2] of the second cutting edge 73 is 1.0 or less.

[0191] In this case, by steadily reducing the width ratio of the edge grinding H of the second cutting edge 73 (increasing the proportion of the second width dimension L2 on the side of the flank face 6), the effect of suppressing flank face wear can be obtained more significantly.

[0192] [Other structures included in this invention]

[0193] Furthermore, the present invention is not limited to the above-described embodiments. For example, as described below, structural changes may be made without departing from the spirit of the present invention.

[0194] In the aforementioned embodiment, the case where the main cutting edge 71 of the cutting edge 7 is a so-called curved cutting edge shape having a concave edge (first cutting edge 72) and a convex portion (top 74) has been described, but it is not limited to this. Although not specifically illustrated, the main cutting edge 71 can be straight. In this case, the area within 7% of the drill bit diameter in the main cutting edge 71 from the outer peripheral corner 15 toward the radially inward side is defined as the "radially outer end of the main cutting edge 71 connected to the outer peripheral corner 15" (corresponding to the second cutting edge 73 in the aforementioned embodiment).

[0195] According to the above structure, when the main cutting edge 71 is in a straight line shape, the same excellent working effect as the aforementioned embodiment can be obtained.

[0196] Furthermore, in the aforementioned embodiments, an example was given of the first cutting edge 72 and the second cutting edge 73 being connected to each other via a sharp tip 74 facing the drill bit rotation direction T, but this is not a limitation. The first cutting edge 72 and the second cutting edge 73 may be connected in a smooth tangential manner (in a continuously curved manner) without via a sharp tip 74.

[0197] In the foregoing embodiments, examples of drill bit 10 being an indexable cutting tool type drill bit or a drill bit head were given, but the invention is not limited to this. As the drill bit of the present invention, a solid drill bit in which the body 1 and the shank are formed as a single component can be used. Alternatively, for example, a drill bit in which the body 1 and the shank are made as separate components and then integrated by brazing or the like can also be used.

[0198] In the foregoing embodiments, an example of a double-flute twist drill 10 was given, but the invention is not limited to this. The invention can also be applied to drill bits with a single or three or more flutes.

[0199] Without departing from the spirit of the invention, the various structures described in the above embodiments and variations can be combined, and structural additions, omissions, substitutions, and other modifications can be made. Furthermore, the invention is not limited to the above embodiments, but only to the claims.

[0200] Example

[0201] The present invention will now be specifically described through embodiments. However, the present invention is not limited to these embodiments.

[0202] <Wear Confirmation Test 1>

[0203] As wear confirmation test 1, a confirmation test based on drilling was conducted to investigate the relationship between the grinding curvature radius R of each edge of the main body 1 and its wear resistance.

[0204] As Embodiment 1 of the present invention, a drill bit 10 of the aforementioned embodiment is prepared. Specifically, in the drill bit 10 of Embodiment 1, the cutting edge curvature radius R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the edge 12 is 54 μm. Furthermore, the cutting edge curvature radius R2 of the second cutting edge 73 is 63 μm, and the cutting edge curvature radius R1 of the first cutting edge 72 is 75 μm.

[0205] Furthermore, as comparative examples 1 and 2, drill bits with some technical concepts different from the drill bit 10 described in the aforementioned embodiments were prepared.

[0206] Specifically, in the drill bit of Comparative Example 1, the grinding radius of curvature R of the cutting edge 12 within 1.5 mm from the outer corner 15 toward the rear end is 64 μm. Furthermore, the grinding radius of curvature R2 of the second cutting edge 73 is 50 μm, and the grinding radius of curvature R1 of the first cutting edge 72 is 63 μm. Therefore, in the drill bit of Comparative Example 1, the grinding radius of curvature R of the cutting edge 12 within 1.5 mm from the outer corner 15 toward the rear end is greater than the grinding radius of curvature R2 of the second cutting edge 73.

[0207] Furthermore, in the drill bit of Comparative Example 2, the grinding radius of curvature R of the cutting edge 12 within 1.5 mm from the outer corner 15 toward the rear end is 17 μm. Also, the grinding radius of curvature R2 of the second cutting edge 73 is 41 μm, and the grinding radius of curvature R1 of the first cutting edge 72 is 58 μm. Therefore, in the drill bit of Comparative Example 2, the grinding radius of curvature R of the cutting edge 12 within 1.5 mm from the outer corner 15 toward the rear end is outside the range of 25 μm to 80 μm.

[0208] For each drill bit of Example 1 and Comparative Examples 1 and 2, the same number of drilling operations were performed under the following cutting conditions, and observations were made by photographing the area near the tip of each cutting edge after grinding. The number of drilling operations was set until at least one drill bit showed wear. The results are shown as magnified images of the area near each cutting edge. Figure 6 In the middle. And, in Figure 6 The diagram also shows cross-sectional schematics near each blade tip.

[0209] <Cutting Conditions>

[0210] • Drill bit diameter: φ24.0mm

[0211] • Material being cut: S50C

[0212] Circular speed: vc = 100 m / min

[0213] • Feed rate: fr = 0.35 mm / rev

[0214] like Figure 6As shown, in Comparative Examples 1 and 2, when drilling with a cutting length (machining length) of approximately 29 m, wear development was observed near edge 12 or near the first cutting edge 72. On the other hand, in Example 1, where the same number of drilling operations were performed as in Comparative Examples 1 and 2, no wear development was observed near edge 12, near the second cutting edge 73, or near the first cutting edge 72. The wear development in Comparative Examples 1 and 2 could be confirmed by comparing the magnitude of the damage at the same time points as in Example 1. Furthermore, in Example 1, no wear development was observed even when the cutting length was approximately 55 m. Moreover, even when the cutting length exceeded approximately 150 m, it was still machinable.

[0215] Furthermore, although not specifically illustrated, the inventors of this invention have obtained the following insights as a result of further in-depth research on the relationship between the radius of curvature R of the edge grinding of each edge portion of the main body 1 and its wear resistance.

[0216] In many existing drill bits, primarily solid drill bits, the cutting edge grinding radius of curvature R within 1.5 mm from the outer peripheral corner 15 toward the rear end of the edge 12 is set to approximately 10–20 μm. The inventors of this invention, through research on improving damage to the cutting edge 13 of the drill bit 10, discovered that increasing the cutting edge grinding radius of curvature R within this 1.5 mm position to approximately 25–30 μm yields advantages compared to existing products. Based on this insight, the lower limit of the numerical range of the cutting edge grinding radius of curvature R within this 1.5 mm position is 25 μm or more.

[0217] Furthermore, the following insight was gained: even if the cutting edge grinding radius of curvature R is too large at the position within 1.5 mm, the coating will peel off prematurely, thereby promoting wear. This is believed to be caused by the increase in cutting resistance. Cutting resistance depends on various conditions such as tool diameter or cutting conditions, therefore the appropriate cutting edge grinding size (cutting edge grinding radius of curvature R) at the position within 1.5 mm varies depending on various conditions, but in the actual drill bit 10, assuming various combinations, the upper limit of the numerical range of the cutting edge grinding radius of curvature R at the position within 1.5 mm is below 80 μm.

[0218] Specifically, a drill bit with a ground radius of curvature R of 90 μm at a position within 1.5 mm was prepared as a comparative example. Drilling was performed under the cutting conditions of drill bit diameter: φ18 mm, material to be cut: S50C, circumferential speed: vc=100 m / min, and feed: fr=0.3 mm / rev. As a result, the tool life of the drill bit of the comparative example was approximately 60 m for the machining length.

[0219] On the other hand, as an embodiment of the present invention, a drill bit 10 with a cutting edge curvature radius R of 60 μm at a position within 1.5 mm was prepared, and drilling was performed under the same cutting conditions as described above. As a result, the tool life of the drill bit 10 in this embodiment reached a machining length of approximately 170 m. In addition, regarding the coating on the main body 1, the same coating as that of the drill bits in the comparative example and the above embodiment was formed.

[0220] Furthermore, two drill bits with a different coating on the main body 1 were prepared. One drill bit had its cutting edge curvature radius R within 1.5 mm set to 90 μm, and the other drill bit had its cutting edge curvature radius R within 1.5 mm set to 150 μm. These two drill bits were comparative examples. Drilling was performed using both drill bits. The tool life of one drill bit (cutting edge curvature radius R: 90 μm) was approximately 80 m for the machining length. The tool life of the other drill bit (cutting edge curvature radius R: 150 μm) was approximately 50 m for the machining length.

[0221] Thus, as the radius of curvature R of the cutting edge at the position within 1.5mm exceeds 80μm, the cutting resistance increases, and there is a tendency for the tool life to become shorter.

[0222] <Wear Confirmation Test 2>

[0223] As wear confirmation test 2, a confirmation test based on drilling was conducted to investigate the relationship between the width ratio [L1 / L2] of the edge grinding H of each edge of the main body 1 and the wear resistance.

[0224] As an embodiment 2 of the present invention, a drill bit 10 of the aforementioned embodiment is prepared. Specifically, in the drill bit 10 of embodiment 2, the width ratio [L1 / L2] of the edge 12 within 1.5 mm from the outer peripheral corner 15 toward the rear end side is 0.91.

[0225] Furthermore, as a prior comparative example 3, a drill bit with some technical concepts different from the drill bit 10 described in the aforementioned embodiments was prepared. Specifically, in the drill bit of comparative example 3, the width ratio [L1 / L2] of the edge 12 within 1.5 mm from the outer peripheral corner 15 toward the rear end side is 0.64.

[0226] For each drill bit of Example 2 and Comparative Example 3, multiple drilling operations were performed under the same cutting conditions as in the wear confirmation test 1 described above, and observations were made by photographing the area near the tip of the cutting edge after grinding. The number of drilling operations was set until at least one drill bit showed wear. The results are shown as magnified images of the area near each cutting edge. Figure 7 In the middle. And, inFigure 7 The diagram shows a cross-sectional view near each blade tip.

[0227] like Figure 7 As shown, in Comparative Example 3, when drilling with a cutting length (machining length) of approximately 29 m was performed, wear development was observed near edge 12. On the other hand, in Example 2, where the same number of drilling operations were performed as in Comparative Example 3, no wear development was observed near edge 12. The wear development in Comparative Examples 1 and 2 can be confirmed by comparing the magnitude of the damage at the same time points as in Example 1. Furthermore, in Example 2, even when the cutting length was approximately 55 m, no wear development was observed. Moreover, even when the cutting length exceeded approximately 150 m, it remained machinable.

[0228] Furthermore, although not specifically illustrated, the inventors of this invention have obtained the following insights as a result of further in-depth research on the relationship between the width ratio [L1 / L2] of the edge grinding H of each edge portion of the main body 1 and the wear resistance.

[0229] In Comparative Example 3 above, an example was given in which the width ratio [L1 / L2] at a position within 1.5 mm from the outer corner 15 toward the rear end deviated by more than 0.7 and less than 1.3 on the lower side (smaller side). However, it can be seen that in other examples where the width ratio [L1 / L2] deviates from the above range on the upper side (larger side), wear development is also likely to occur.

[0230] This is because, when the cutting edge is ground to a shape that favors either width dimension L1 or L2, and the width ratio [L1 / L2] falls outside the aforementioned range, the insufficient width dimension L1 or L2 leads to reduced strength or increased cutting resistance, thereby promoting damage. Based on this investigation, the width ratio [L1 / L2] at the position within 1.5 mm is set within the aforementioned range, with an ideal value of 1.0.

[0231] Industrial availability

[0232] The drill bit according to the present invention improves wear resistance, thereby enabling a longer tool life. Therefore, it has industrial applicability.

[0233] Explanation of reference numerals in the attached figures

[0234] 1-Main Body

[0235] 3-Front end face

[0236] 4-Chip Removal Groove

[0237] 5-Front face

[0238] 6-Rear face

[0239] 7-Cutting edge

[0240] 8-Outer Peripheral Surface

[0241] 9-Shoulder

[0242] 10-Drill Bit

[0243] 12-Edge

[0244] 13-Blade Band

[0245] 15-Outer peripheral corner

[0246] 50-Chisel edge grinding rake surface

[0247] 51-Main rake face

[0248] 52-First rake face

[0249] 53-Second rake face

[0250] 54-First Boundary Edge

[0251] 55-Second Boundary Edge

[0252] 70-Sharpening the cross-edge

[0253] 71-Main cutting edge

[0254] 72-First cutting edge

[0255] 73-Second Cutting Edge

[0256] 74-Top

[0257] H-Sharpening of the cutting edge

[0258] O-Central Axis

[0259] R, R1, R2 - Radius of curvature for edge grinding

[0260] T - Drill bit rotation direction

Claims

1. A drill bit comprising a body extending axially about a central axis, wherein, The subject has: The chip removal groove opens on the front end face and outer peripheral face of the main body and extends from the front end face to the rear end side; The rake face is positioned in the chip removal groove and faces the drill rotation direction in the direction surrounding the central axis; The flank face is disposed on the front face; A cutting edge is disposed on the ridge portion connecting the rake face and the flank face; A cutting edge is disposed on the outer peripheral surface and extends along the chip removal groove; Edge, configured at the ridge portion connecting the cutting edge and the rake face; and The outer peripheral corner portion is located at the corner connecting the cutting edge and the edge. The cutting edge has: A transverse grinding edge, disposed at the radially inner end of the cutting edge; and The main cutting edge is located radially outside the chisel edge grinding edge and is connected to the edge via the outer peripheral corner. The main cutting edge and the edge have a convex curve-shaped cutting edge that is perpendicular to each of the ridge portions. The radius of curvature of the cutting edge at a position within 1.5 mm from the outer corner toward the rear end of the edge is more than 25 μm and less than 80 μm, and is smaller than the radius of curvature of the cutting edge at the radially outer end of the main cutting edge connected to the outer corner.

2. The drill bit according to claim 1, wherein, The main cutting edge has: The first cutting edge is located radially outside the chisel edge grinding edge and has a concave curve shape that is recessed in the direction opposite to the rotation direction of the drill bit in the direction surrounding the central axis; and The second cutting edge is disposed radially outside the first cutting edge and connected to the radially outer end of the first cutting edge. The second cutting edge constitutes the radially outer end of the main cutting edge that is connected to the outer peripheral corner.

3. The drill bit according to claim 1, wherein, The main cutting edge is straight. When the diameter of the rotation trajectory of the cutting edge around the central axis is taken as the drill bit diameter, The area within 7% of the drill bit diameter from the outer peripheral corner toward the radially inward side of the main cutting edge is defined as the radially outer end of the main cutting edge connected to the outer peripheral corner.

4. The drill bit according to any one of claims 1 to 3, wherein, When the radius of curvature of the edge of the main cutting edge located radially inward from the radially outer end is set to R1, and the radius of curvature of the edge of the radially outer end of the main cutting edge is set to R2, The relationship satisfies [0.9≤R1 / R2≤1.5].

5. The drill bit according to any one of claims 1 to 3, wherein, The main body has a shoulder portion disposed on the ridge portion connecting the cutting edge and the flank face, and extends from the outer peripheral corner portion in a direction opposite to the rotation direction of the drill bit around the central axis. The shoulder portion has a convex curve-shaped cutting edge with a cross-section perpendicular to the ridge portion. The radius of curvature of the blade edge grinding of the shoulder is smaller than the radius of curvature of the blade edge grinding of the radially outer end of the main cutting edge that connects to the outer peripheral corner.

6. The drill bit according to any one of claims 1 to 3, wherein, The cross-section of the grinding blade is convex and curved, perpendicular to the ridge portion on which the cutting edge is disposed. When the diameter of the rotation trajectory of the cutting edge around the central axis is taken as the drill bit diameter, The grinding radius of curvature of the area within 7% of the drill bit diameter from the central axis in the chisel edge grinding edge is smaller than the grinding radius of curvature of the portion of the main cutting edge located radially inward from the radially outer end.

7. The drill bit according to claim 2, wherein, The radius of curvature of the first cutting edge is greatest at the lowest point of the first cutting edge, located in the direction most opposite to the rotation direction of the drill bit.

8. The drill bit according to any one of claims 1 to 3, wherein, The rake face has: The front face of the cross-blade is ground and connected to the grinding edge of the cross-blade; The main rake face is connected to the main cutting edge; and The first boundary edge extends along the boundary between the chisel edge and the main rake face, and protrudes in the direction of drill rotation. The first boundary edge has a sharpened cutting edge.

9. The drill bit according to claim 2, wherein, The rake face has: The first rake face is connected to the first cutting edge; The second rake face is connected to the second cutting edge; and The second boundary edge extends along the boundary connecting the first rake face and the second rake face, and protrudes in the direction of drill rotation. The second boundary edge has a sharpened cutting edge.

10. The drill bit according to any one of claims 1 to 3, wherein, The edge is ground beyond a position 1.5 mm from the outer corner toward the rear end of the edge, and extends further to the rear end.

Images