Drill

Abstract

Provided is a drill (10) having a body (1) extending in the axial direction around a central axis (O). The body (1) includes: chip discharge grooves (4) that open in a leading end face (3) and an outer peripheral surface (8) of the body (1) and that extend from the leading end face (3) to the trailing end side; recessed thinnings (5) that are disposed at the distal end of the body (1) and that are continuous with the chip discharge grooves (4) and the leading end face (3); and cutting edges (7) that are disposed at the distal end of the body (1). The cutting edges (7) have thinning edges (70) that are disposed at the radially inner ends of the cutting edges (7). The thinning edges (70) have curved concave-curved edges (71) that are continuous with ridge lines (6) at which the thinnings (5) and the leading end face (3) meet and that are recessed toward the side opposite to the drill rotation direction (T) about the central axis (O).

Description

drill

[0001] This application claims priority from Japanese Patent Application No. 2024-033127, filed on March 5, 2024, the contents of which are incorporated herein by reference.

[0002] A drill described in Patent Document 1, for example, is known. The drill in Patent Document 1 includes a main cutting edge and a thinning cutting edge that is connected to the main cutting edge and is closer to the axis than the main cutting edge when viewed in the axial direction along the axis. The thinning cutting edge includes a curved thinning cutting edge portion that is convex forward in the rotational direction, and a straight thinning cutting edge portion that is connected to the curved thinning cutting edge portion and is closer to the axis than the curved thinning cutting edge portion when viewed in the axial direction. The straight thinning cutting edge portion is connected to the ridgeline between the thinning surface and the flank (the heel middle portion) via a concavely curved inner heel portion (hereinafter sometimes referred to as a corner R) with a small radius of curvature.

[0003] Japanese Patent No. 7206572 (B)

[0004] In the drill of Patent Document 1, chips generated by the thinning cutting edge tend to concentrate stress near the corner R (near the chisel portion). In particular, the vicinity of the chisel portion accounts for a high proportion of the cutting resistance distribution, making it difficult to reduce cutting resistance or ensure strength.

[0005] An object of the present invention is to provide a drill that can reduce stress concentration due to chips generated by the thinning edge, reduce cutting resistance near the rotation center (chisel part) of the drill, and ensure strength.

[0006] In order to solve the above problems, the present invention provides the following means.

[0007] [Aspect 1 of the present invention] A drill including a body extending in the axial direction around a central axis, wherein the body has a chip discharge flute that opens into a tip surface and an outer peripheral surface of the body and extends from the tip surface toward a rear end, a concave thinning that is disposed at the tip portion of the body and connected to the chip discharge flute and the tip surface, and a cutting edge that is disposed at the tip portion of the body, wherein the cutting edge has a thinning edge that is disposed at an inner end in the radial direction of the cutting edge, and the thinning edge is continuous with a ridge line that connects the thinning and the tip surface, and has a curved concave curved edge that is concave around the central axis in the opposite direction to the direction of drill rotation.

[0008] In the drill of the present invention, even if the radius of curvature of the ridge connecting the tip face of the body to the thinning edge and the connection portion (concave curved corner R) with the thinning edge is small, as in the above-mentioned Patent Document 1 (Japanese Patent No. 7206572), the cutting load can be distributed from this connection portion to the concave curved edge of the thinning edge. This reduces stress concentration near the rotation center (chisel portion) of the drill, ensuring strength. In particular, since the vicinity of the chisel portion accounts for a high proportion of cutting resistance distribution, the present invention effectively improves the strength of the vicinity of the chisel portion. Furthermore, by distributing the cutting load, cutting resistance is kept low.

[0009] According to the present invention, it is possible to reduce stress concentration due to chips generated by the thinning edge, reduce cutting resistance near the rotation center (chisel portion) of the drill, and ensure strength.

[0010] [Aspect 2 of the Present Invention] The drill according to aspect 1, wherein the concave curved cutting edge has a radius of curvature that increases radially outward.

[0011] In this case, the radius of curvature of the concave curved blade increases as it moves radially outward from the connection portion (the corner R with the smaller radius of curvature), making it easier to distribute the cutting load more stably and reduce stress concentration.

[0012] [Aspect 3 of the present invention] The drill according to aspect 2, wherein the concave curved cutting edge is formed by combining a plurality of arc cutting edges each having a different radius of curvature.

[0013] In this case, the radius of curvature of the concave curved blade can be gradually increased radially outward using a simple structure, thereby more stably achieving the effects of the present invention described above.

[0014] Aspect 4 of the present invention is the drill according to any one of Aspects 1 to 3, wherein at least the thinning edge of the cutting edges has a honing, and the honing has a curved honing ridgeline that extends parallel to the concave curved edge and is concave in the opposite direction to the rotation direction of the drill.

[0015] [Aspect 5 of the Present Invention] The drill according to Aspect 4, wherein the curved honing ridge has a radius of curvature that increases radially outward.

[0016] In this case, the same effect as the concave curved blade can be obtained by using a curved honing ridge that is concave on the opposite side to the direction of rotation of the drill.

[0017] Aspect 6 of the present invention is the drill according to Aspect 4 or 5, wherein the honing of the thinning edge has a honing width changing portion located at a radially inner end of the thinning edge, and the honing width changing portion increases in size and then decreases in size as the honing width changes away from the ridge line connecting the thinning edge and the tip face in the direction in which the concave curved edge extends.

[0018] In this case, it is easy to make the maximum honing width of the honing width change portion located at the radially inner end of the thinning blade wider than the honing width of the portion other than the honing width change portion (portion other than the radially inner end).This makes it possible to more stably increase the cutting edge strength near the chisel portion of the concave curved blade, where cutting resistance tends to be particularly large.

[0019] According to the above aspect of the present invention, it is possible to provide a drill that can reduce stress concentration due to chips generated by the thinning edge, reduce cutting resistance near the rotation center (chisel portion) of the drill, and ensure strength.

[0020] Fig. 1 is a side view showing a drill of this embodiment. Fig. 2 is a side view showing an enlarged view of part II in Fig. 1. Fig. 3 is a front view showing the drill. Fig. 4 is a front view showing an enlarged view of a part of the drill. Fig. 5 is a front view showing a drill of a modified example of this embodiment.

[0021] A drill 10 according to one embodiment of the present invention will be described with reference to Figures 1 to 4. As shown in Figure 1, the drill 10 is cylindrical and has a central axis O as its center. In this embodiment, the drill 10 includes a body 1, a shank 2, and a coolant hole 15. The body 1 and the shank 2 are disposed at different positions in the direction in which the central axis O of the drill 10 extends. The body 1 may also be referred to as a cutting portion or the like.

[0022] [Definition of Directions] In this embodiment, the direction in which the central axis O of the drill 10 extends is referred to as the axial direction. Within the axial direction, the direction from the shank 2 to the body 1 is referred to as the axial tip side or simply the tip side, and the direction from the body 1 to the shank 2 is referred to as the axial rear end side or simply the rear end side.

[0023] Additionally, the direction perpendicular to the central axis O is referred to as the radial direction. Of the radial directions, the direction approaching the central axis O is referred to as the radially inner direction, and the direction away from the central axis O is referred to as the radially outer direction. The direction rotating around the central axis O is referred to as the circumferential direction. Of the circumferential directions, the direction in which the drill 10 is rotated during drilling (cutting) is referred to as the drill rotation direction T. Of the circumferential directions, the rotation direction opposite to the drill rotation direction T is referred to as the opposite side to the drill rotation direction T or the counter-drill rotation direction.

[0024] Furthermore, if there are any directions to be defined other than the above-mentioned directions, they will be defined separately when explaining each component.

[0025] [Shank] The shank 2 is columnar and extends axially about a central axis O, and in this embodiment, is cylindrical. The shank 2 is disposed at least at the rear end of the drill 10. The shank 2 is detachably held, for example, by a spindle of a machine tool or a chuck of a drilling press (not shown) (hereinafter abbreviated as the spindle, etc.). The drill 10 cuts into the workpiece with the body 1 to perform drilling by rotating the shank 2 in the drill rotation direction T by the spindle, etc., and feeding the shank 2 toward the tip end in the axial direction.

[0026] [Body] The body 1 is generally columnar and extends axially around a central axis O. The body 1 is disposed at least at the tip end of the drill 10, and in this embodiment, is disposed at a portion other than the rear end. As shown in FIG. 2 , the diameter (outer diameter) D of the body 1 corresponds to the diameter of the rotation locus of the cutting edge 7, which will be described later, around the central axis O. Therefore, the diameter D of the body 1 may also be referred to as the cutting edge diameter D.

[0027] As shown in Figures 2 and 3, the body 1 has a tip surface 3 facing the tip side of the body 1, an outer peripheral surface 8 facing radially outward of the body 1, a chip discharge groove 4, a thinning 5, a chisel portion 9, a cutting edge 7, a first margin 13A, a second margin 13B, a leading edge 12, and a chamfer surface 14.

[0028] The chip flutes 4, thinnings 5, cutting edges 7, first margins 13A, second margins 13B, leading edges 12, and relief surfaces 14 are each provided in plurality at intervals in the circumferential direction on the body 1. In this embodiment, two chip flutes 4, thinnings 5, cutting edges 7, first margins 13A, second margins 13B, leading edges 12, and relief surfaces 14 are each provided at equal intervals in the circumferential direction. In other words, the drill 10 of this embodiment is a two-flute twist drill provided with two sets of cutting edges 7.

[0029] The chip discharge flute 4 is a groove that opens to the tip surface 3 and the outer peripheral surface 8 of the body 1 and extends from the tip surface 3 toward the rear end. Specifically, the chip discharge flute 4 extends in a twisted manner in the direction opposite to the rotational direction of the drill as it extends from the tip surface 3 toward the rear end in the axial direction.

[0030] The thinning 5 is disposed at the tip of the body 1 and is connected to the chip discharge groove 4 and the tip surface 3. The thinning 5 is concave and is formed so as to cut out a portion of each of the chip discharge groove 4 and the tip surface 3. The thinning 5 has a thinning rake face 51 and a bottom surface 52.

[0031] The thinning rake face 51 is disposed on one of the inner surfaces of the thinning 5 (the multiple wall surfaces constituting the thinning 5) that faces the drill rotation direction T. As shown in Figure 2, the thinning rake face 51 has a substantially triangular surface shape. The axial dimension of the thinning rake face 51 increases radially outward.

[0032] The bottom surface 52 is disposed on a wall surface of the inner surface of the thinning 5 that faces in the direction opposite to the rotational direction of the drill. The bottom surface 52 is disposed in the direction of rotation T of the thinning rake face 51 of the drill and is connected to the thinning rake face 51. The bottom surface 52 extends toward the rear end as it moves in the direction opposite to the rotational direction of the drill. When viewed from the tip of the drill shown in FIG. 3 , the bottom surface 52 is substantially fan-shaped.

[0033] The bottom surface 52 has a concave curved shape. Therefore, a ridgeline 6 of the bottom surface 52 that forms an edge in the drill rotation direction T (the ridgeline 6 connecting the bottom surface 52 and the tip surface 3) has a concave curved shape that is recessed toward the drill rotation direction T. In this embodiment, this ridgeline 6 may be referred to as the "ridgeline 6 connecting the thinning 5 and the tip surface 3." The radially outer end of the ridgeline 6 is connected to a wall surface of the chip discharge flute 4 that faces in the direction opposite to the drill rotation direction. The radially outer end of the ridgeline 6, i.e., the intersection A between the ridgeline 6 and the chip discharge flute 4, is located radially inward from the outer circumferential surface 8.

[0034] 2 and 3 , the tip end surface 3 has a first flank 31 and a second flank 32. A plurality of pairs of the first flank 31 and the second flank 32 are provided at intervals in the circumferential direction on the body 1. In the present embodiment, two pairs of the first flank 31 and the second flank 32 are provided at equal intervals in the circumferential direction.

[0035] The first flank 31 has a generally polygonal shape extending in the radial direction. The first flank 31 extends axially toward the rear end as it extends in the direction opposite to the rotation direction of the drill.

[0036] The second flank 32 is disposed adjacent to the first flank 31 in the direction opposite to the drill rotation direction of the first flank 31. The second flank 32 is generally fan-shaped, and the circumferential dimension increases radially outward. The second flank 32 also extends axially toward the rear end as it extends radially opposite to the drill rotation direction. The amount of axial displacement of the second flank 32 per unit length along the circumferential direction (the inclination corresponding to the clearance angle) is greater than the amount of axial displacement of the first flank 31.

[0037] In this embodiment, the tip end face 3 has two types of inclined surfaces (first flank 31 and second flank 32) with different clearance angles, but this is not limited to this. Although not particularly shown, the tip end face 3 may have one type of inclined surface (flank) with a constant clearance angle, or may have three or more types of inclined surfaces (flank) with different clearance angles.

[0038] The chisel portion 9 is disposed in the center (rotation center) of the tip end face 3. Specifically, the chisel portion 9 is disposed on the ridge line where a pair of flanks (a pair of the first flank 31 and the second flank 32) are connected, and is located on the central axis O. The chisel portion 9 is disposed so as to be sandwiched between the pair of thinnings 5. The chisel portion 9 extends so as to connect the pair of thinnings 5.

[0039] The cutting edge 7 is disposed at the tip of the body 1. The cutting edge 7 is disposed at a ridge line connecting the wall surfaces of the chip discharge flutes 4 and the thinning 5, which face in the drill rotation direction T, to the tip face 3. The cutting edge 7 has a thinning edge 70, a main cutting edge 75, and a connecting convex edge 76.

[0040] The thinning edge 70 is disposed at the radially inner end of the cutting edge 7. The thinning edge 70 is disposed at the ridge where the thinning rake face 51 and the first flank face 31 are connected. The thinning edge 70 extends radially outward from near the central axis O, generally along the radial direction. Specifically, in this embodiment, the thinning edge 70 is center-down. In other words, the radial rake (radial rake angle) of the thinning edge 70 is a positive angle (positive angle). Furthermore, the thinning edge 70 extends radially outward toward the rear end in the axial direction.

[0041] As shown in Figure 3, the thinning blade 70 has a concave curved blade 71 that is connected to the ridge line 6 connecting the thinning 5 and the tip face 3 and is curved in a direction opposite to the drill rotation direction T, and a straight blade 72 that is connected to the concave curved blade 71.

[0042] The radius of curvature of the concave curved blade 71 increases radially outward. Specifically, the concave curved blade 71 is formed by combining a plurality of arc-shaped blades each having a different radius of curvature. In this embodiment, the concave curved blade 71 is formed by combining two arc-shaped blades 71 a and 71 b.

[0043] The two arc-shaped blades 71 a, 71 b include a first arc-shaped blade 71 a that is continuous with the ridge line 6 that connects the bottom surface 52 and the second flank surface 32, and a second arc-shaped blade 71 b that is continuous with the first arc-shaped blade 71 a. The first arc-shaped blade 71 a and the second arc-shaped blade 71 b each have an arc shape that is concave in the direction opposite to the rotational direction of the drill.

[0044] The radius of curvature of the second arc-shaped blade 71b is larger than the radius of curvature of the first arc-shaped blade 71a. In this embodiment, the diameter dimension (blade diameter dimension) of the rotation trajectory of the cutting blade 7 about the central axis O is D, and for example, the radius of curvature of the first arc-shaped blade 71a is about 0.02D, and the radius of curvature of the second arc-shaped blade 71b is about 0.10D. In addition, the blade length of the second arc-shaped blade 71b is longer than the blade length of the first arc-shaped blade 71a.

[0045] The ridge line 6 and the first arc-shaped blade 71 a are smoothly and continuously connected to each other so as to have a common tangent at their connecting portion (connection point).Furthermore, the first arc-shaped blade 71 a and the second arc-shaped blade 71 b are smoothly and continuously connected to each other so as to have a common tangent at their connecting portion.

[0046] The straight blade 72 is disposed radially outward of the concave curved blade 71. The straight blade 72 extends linearly. The straight blade 72 is smoothly and continuously connected to the radially outer end of the concave curved blade 71 (the radially outer end of the second arc-shaped blade 71b in this embodiment). In this embodiment, the blade length of the straight blade 72 is shorter than the blade length of the concave curved blade 71 (the sum of the blade lengths of the first arc-shaped blade 71a and the second arc-shaped blade 71b).

[0047] The main cutting edge 75 is disposed radially outward of the thinning edge 70. The main cutting edge 75 is disposed on a ridge line connecting the wall surface of the chip discharge flute 4 facing the drill rotation direction T and the first flank 31. The main cutting edge 75 is center-up. In other words, the radial rake of the main cutting edge 75 is a negative angle.

[0048] 2, the main cutting edge 75 extends radially outward and then axially toward the rear end. The leading edge 12 is connected to the radial outer end B of the main cutting edge 75. The radial outer end B of the main cutting edge 75, i.e., the connection point between the main cutting edge 75 and the leading edge 12, can also be referred to as the outer circumferential corner B. The outer circumferential corner B is a corner that is sharpened toward the outer circumferential tip.

[0049] As shown in Fig. 3, the connecting convex edge 76 is disposed between the thinning edge 70 and the main cutting edge 75. The connecting convex edge 76 has a curved shape that is convex toward the drill rotation direction T. The connecting convex edge 76 is connected to the radially outer end of the thinning edge 70 (the radially outer end of the straight edge 72 in this embodiment) and the radially inner end of the main cutting edge 75. The connecting convex edge 76 is smoothly and continuously connected to the thinning edge 70 and the main cutting edge 75. As shown in Fig. 2, the connecting convex edge 76 extends radially outward and toward the rear end in the axial direction.

[0050] As shown in Fig. 4, at least the thinning edge 70 of the cutting edge 7 has a honing. In this embodiment, the cutting edge 7 has a honing over its entire cutting length, and specifically, the honing is formed over the thinning edge 70, the connecting convex edge 76, and the main cutting edge 75. The honing extends along the cutting edge 7. The honing in this embodiment is, for example, a chamfer honing.

[0051] The honing of the thinning edge 70 has a curved honing ridge 81 and a straight honing ridge 82 .

[0052] The curved honing ridge 81 extends parallel to the concave curved blade 71 and forms a curve that is concave in the opposite direction to the drill rotation direction T. The radius of curvature of the curved honing ridge 81 increases as it extends radially outward. Specifically, the radius of curvature of the ridge portion of the curved honing ridge 81 that extends parallel to the second arc-shaped blade 71b is larger than the radius of curvature of the ridge portion that extends parallel to the first arc-shaped blade 71a.

[0053] The straight honing ridge 82 is disposed radially outward of the curved honing ridge 81. The straight honing ridge 82 extends in a straight line. The straight honing ridge 82 is smoothly and continuously connected to the radially outer end of the curved honing ridge 81.

[0054] The honing of the thinning blade 70 also has a honing width changing portion 83 located at the radially inner end of the thinning blade 70. The honing width of the honing width changing portion 83 increases and then decreases as the honing width increases along the direction in which the concave curved blade 71 extends from the ridge 6 connecting the thinning 5 and the tip surface 3. The honing width of the thinning blade 70 is greatest at the honing width changing portion 83. Note that the "direction in which the concave curved blade 71 extends" may also be rephrased as the blade length direction of the concave curved blade 71. In this embodiment, the chisel portion 9 is connected to the honing width changing portion 83.

[0055] As shown in Figures 2 and 3, the first margin 13A is disposed on the outer peripheral surface 8 and extends along the chip flute 4. Specifically, the first margin 13A is disposed on a portion of the outer peripheral surface 8 adjacent to the chip flute 4 in the counter-drill rotation direction. The first margin 13A extends in the counter-drill rotation direction as it extends axially toward the rear end. The first margin 13A has a curved surface shape that is convex radially outward. When viewed in a cross section perpendicular to the central axis O, the first margin 13A has an arc shape centered on the central axis O.

[0056] The second margin 13B is disposed on the outer peripheral surface 8 and extends along the chip discharge flute 4. The second margin 13B is disposed away from the first margin 13A in the counter-drill rotation direction. Specifically, the second margin 13B is disposed in a portion of the outer peripheral surface 8 adjacent to the chip discharge flute 4 in the drill rotation direction T. The second margin 13B extends in the counter-drill rotation direction as it moves toward the rear end in the axial direction. The second margin 13B has a curved surface shape that is convex radially outward. When viewed in a cross section perpendicular to the central axis O, the second margin 13B has an arc shape centered on the central axis O.

[0057] The leading edge 12 is disposed on a ridge line connecting the wall surface of the chip flute 4 facing the drill rotation direction T and the first margin 13A. The leading edge 12 extends along the wall surface of the chip flute 4 facing the drill rotation direction T and the first margin 13A. Specifically, the leading edge 12 extends in the direction opposite to the drill rotation direction as it moves toward the rear end in the axial direction.

[0058] The leading edge 12 may be back tapered. In this case, the leading edge 12 extends slightly radially inward as it approaches the rear end in the axial direction.

[0059] The relief surface 14 is disposed on the outer peripheral surface 8. The relief surface 14 is disposed between the first margin 13A and the second margin 13B in the circumferential direction. The relief surface 14 is formed recessed radially inward from the first margin 13A and the second margin 13B. During drilling, the relief surface 14 faces the inner peripheral surface of the machined hole in the workpiece with a radial gap therebetween.

[0060] [Coolant Hole] As shown in FIG. 1 , the coolant hole 15 extends through the shank 2 and the body 1 inside the drill 10. Note that part of the coolant hole 15 is not shown in FIG. 1 . The coolant hole 15 penetrates the drill 10 in the axial direction. A plurality of coolant holes 15 are provided at intervals in the circumferential direction; in this embodiment, two coolant holes 15 are provided at equal intervals in the circumferential direction. The coolant hole 15 extends spirally in the drill rotation direction T as it extends toward the tip side in the axial direction. As shown in FIG. 3 , in this embodiment, the tip of the coolant hole 15 opens into the second flank 32 of the tip face 3.

[0061] Effects of the Present Embodiment The drill 10 of the present embodiment described above can distribute the cutting load from the connection (concave curved corner R) between the ridge 6 connecting the tip surface 3 of the body 1 and the thinning 5 and the thinning edge 70, as in the above-mentioned Patent Document 1 (Japanese Patent No. 7206572), to the concave curved edge 71 of the thinning edge 70. This reduces stress concentration near the rotation center (chisel portion 9) of the drill 10, ensuring strength. In particular, because the cutting resistance distribution accounts for a high proportion near the chisel portion 9, this embodiment effectively improves the strength near the chisel portion 9. Furthermore, by distributing the cutting load, cutting resistance is kept low.

[0062] According to this embodiment, it is possible to reduce stress concentration due to chips generated by the thinning edge 70, thereby reducing cutting resistance near the center of rotation of the drill 10 (chisel portion 9) and ensuring strength.

[0063] In this embodiment, the radius of curvature of the concave curved edge 71 of the thinning edge 70 increases as it moves radially outward. In this case, the radius of curvature of the concave curved edge 71 increases as it moves radially outward from the connecting portion (the angle R with the small radius of curvature), which makes it easier to distribute the cutting load more stably and reduce stress concentration.

[0064] In this embodiment, the concave curved blade 71 is configured by combining a plurality of arcuate blades 71a, 71b having different radii of curvature. In this case, the radius of curvature of the concave curved blade 71 can be gradually increased radially outward using a simple structure. This allows the effects of this embodiment to be more stably achieved.

[0065] In this embodiment, the honing of the thinning edge 70 extends parallel to the concave curved edge 71 and has a curved honing ridge 81 that is concave in the opposite direction to the drill rotation direction T. The radius of curvature of the curved honing ridge 81 increases as it extends radially outward. In this case, the curved honing ridge 81 that is concave in the opposite direction to the drill rotation direction T can also achieve the same effects as the concave curved edge 71 described above.

[0066] Furthermore, in this embodiment, the honing of the thinning blade 70 has a honing width changing portion 83 located at the radially inner end of the thinning blade 70, and the honing width of the honing width changing portion 83 increases and then decreases as it moves away from the ridge line 6 connecting the thinning 5 and the tip face 3 along the direction in which the concave curved blade 71 extends.

[0067] In this case, it is easy to make the honing width (maximum value) of the honing width changing portion 83 located at the radially inner end of the thinning blade 70 wider than the honing width of the portion other than the honing width changing portion 83 (portions other than the radially inner end). This makes it possible to more stably increase the cutting edge strength of the concave curved blade 71, particularly in the vicinity of the chisel portion 9 where cutting resistance tends to be large.

[0068] Furthermore, in this embodiment, the radially outer end of the ridge line 6 connecting the thinning 5 and the tip face 3, i.e., the intersection A between the ridge line 6 and the chip discharge groove 4, is located away from the outer peripheral surface 8 and radially inward. In this case, chips generated by the thinning cutting edge 70 are prevented from flowing from the thinning 5 onto the outer peripheral surface 8. In other words, since chips are less likely to reach the gap between the outer peripheral surface 8 of the drill 10 and the inner peripheral surface of the machined hole, chip jamming can be suppressed, improving the accuracy of the machined surface. Furthermore, chips are stably discharged to the outside of the machined hole through the chip discharge groove 4, improving chip disposal efficiency.

[0069] In the case of a two-blade drill 10 as in this embodiment, the angle ∠AOB between the intersection point A centered on the central axis O and the outer peripheral corner B, as viewed from the tip of the drill as shown in FIG. 3, is preferably in the range of 70 to 100°.

[0070] [Other Configurations Included in the Present Invention] The present invention is not limited to the above-described embodiment, and configurations can be modified within the scope of the present invention, as described below, for example. In the illustrations of the modified examples, the same components as those in the above-described embodiment are denoted by the same reference numerals, and the following mainly describes the differences.

[0071] 5 is a front view of a drill 10A according to a modification of the embodiment described above. While the main cutting edge 75 of the drill 10 according to the embodiment described above has a straight cutting edge, the main cutting edge 75 of the drill 10A according to this modification has a curved cutting edge, including a concave cutting edge 75a and a convex cutting edge 75b.

[0072] The concave cutting edge 75a is smoothly connected to the radial outer end of the connecting convex cutting edge 76 and has a curved shape that is concave in the opposite direction to the drill rotation direction T. The convex cutting edge 75b is disposed radially outward of the concave cutting edge 75a. The convex cutting edge 75b is smoothly connected to the radial outer end of the concave cutting edge 75a and has a curved shape that is convex in the drill rotation direction T. The radial outer end (outer peripheral corner) B of the convex cutting edge 75b is connected to the leading edge 12. The drill 10A of this modified example also provides excellent effects similar to those of the drill 10 of the above-described embodiment.

[0073] In the above-described embodiment and modified examples, the drill 10, 10A is a double-margin drill having two types of margins (first margin 13A and second margin 13B) spaced apart in the circumferential direction, but the drill is not limited to this. The drill may be a single-margin drill having one type of margin, a triple-margin drill having three types of margins spaced apart in the circumferential direction, or the like.

[0074] In the above-described embodiment and modified examples, the drill 10, 10A is a two-flute twist drill having two cutting edges 7, but the present invention is not limited to this. The drill may be a three-flute or more drill having three or more cutting edges.

[0075] Although not specifically shown, when the drill is a three-blade drill, it is preferable that the angle ∠AOB between the radial outer end (intersection point) A of the ridge line 6 centered on the central axis O and the radial outer end (outer peripheral corner) B of the main cutting edge 75 is in the range of 40 to 70° when viewed from the tip of the drill (see Figure 3).

[0076] In the above-described embodiment and modified example, the thinning edge 70 is formed to be center-down, but this is not limiting. That is, the thinning edge 70 may be formed to be center-up. In other words, the radial rake of the thinning edge 70 may be formed to be a negative angle.

[0077] Furthermore, the thinning blade 70 does not have to have the straight blade 72. In this case, the concave curved blade 71 of the thinning blade 70 may be directly connected to the connecting convex blade 76.

[0078] Furthermore, the cutting edge 7 does not necessarily have to have the connecting convex edge 76. In this case, the thinning edge 70 and the main cutting edge 75 may be directly connected to each other.

[0079] Furthermore, the drills 10 and 10A described in the above-described embodiment and modified examples are solid drills in which the body 1 and the shank 2 are integrally formed from a single member, but this is not limiting. For example, the body 1 and the shank 2 may be manufactured separately and integrated by brazing or the like.

[0080] Alternatively, although not specifically shown, the drill may be an indexable drill in which a body is detachably attached to a shank. In this case, the shank may be referred to as a holder. Also, the drill may have only a body and not a shank. In this case, the drill may be referred to as a drill head or the like.

[0081] The present invention may be combined with the various configurations described in the above-described embodiments and modifications, and may also include additions, omissions, substitutions, and other modifications of configurations, without departing from the spirit of the present invention. Furthermore, the present invention is not limited to the above-described embodiments, but is limited only by the scope of the claims.

[0082] The drill of the present invention can reduce stress concentration due to chips generated by the thinning edge, reduce cutting resistance near the rotation center (chisel part) of the drill, and ensure strength, and therefore has industrial applicability.

[0083] REFERENCE SIGNS LIST 1 Body 3 Tip surface 4 Chip discharge groove 5 Thinning 6 Ridge line 7 Cutting edge 8 Outer circumferential surface 10, 10A Drill 70 Thinning edge 71 Concave curved edge 71a First arcuate edge (arcuate edge) 71b Second arcuate edge (arcuate edge) 81 Curved honing edge 83 Honing width change portion O Central axis T Drill rotation direction

Claims

1. A drill having a body extending in the axial direction around a central axis, wherein the body has: a chip discharge flute that opens onto a tip face and an outer peripheral face of the body and extends from the tip face toward the rear end; a concave thinning that is arranged at the tip of the body and connected to the chip discharge flute and the tip face; and a cutting edge that is arranged at the tip of the body, wherein the cutting edge has a thinning edge that is arranged at the radially inner end of the cutting edge, and the thinning edge is continuous with a ridge line that connects the thinning and the tip face, and has a curved concave curved edge that is concave around the central axis in the opposite direction to the direction of drill rotation.

2. The drill according to claim 1, wherein the radius of curvature of the concave curved cutting edge increases radially outward.

3. The drill according to claim 2, wherein the concave curved cutting edge is formed by combining a plurality of arc cutting edges each having a different radius of curvature.

4. The drill according to claim 1, wherein at least the thinning edge of the cutting edges has a honing, and the honing has a curved honing ridge that extends parallel to the concave curved edge and is concave in the opposite direction to the rotation direction of the drill.

5. The drill according to claim 4, wherein the curved honing ridge has a radius of curvature that increases radially outward.

6. A drill as set forth in claim 4, wherein the honing of the thinning edge has a honing width changing portion located at the radially inner end of the thinning edge, and the honing width changing portion increases in size and then decreases in size as it moves away from the ridge line connecting the thinning edge and the tip face in the direction in which the concave curved edge extends.

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