DRILL INSERT AND INDEXABLE DRILL

Abstract

Provided is a drill insert to ensure sufficient chipping resistance with respect to a large cutting load, which is detachably attached to a distal portion of a drill body which is rotated around an axis, in which a polygon face of a polygonal plate-shaped insert body is a rake face, a side face disposed around the rake face is a flank face, a cutting blade is formed on a ridge portion in which the rake face and the flank face intersect each other, the cutting blade includes a honing face, the honing face includes a first convex curved face continuous with the rake face and a second convex curved face continuous with the flank face, and in a cross section orthogonal to the cutting blade, a curvature radius of the first convex curved face is larger than a curvature radius of the second convex curved face.

Claims

1. A drill insert which is detachably attached to a distal portion of a drill body which is rotated around an axis, wherein a polygon face of a polygonal plate-shaped insert body is a rake face, a side face of the insert body disposed around the rake face is a flank face, and a cutting blade is formed on a ridge portion in which the rake face and the flank face intersect each other, wherein the cutting blade includes a honing face which is formed on a first cutting blade portion continuous with at least one end portion of both end portions of the cutting blade and which gradually rises from the flank face toward the rake face, wherein the honing face includes a first convex curved face continuous with the rake face and a second convex curved face continuous with the flank face, and wherein in a cross section orthogonal to the cutting blade, a curvature radius of the first convex curved face is larger than a curvature radius of the second convex curved face.

2. The drill insert according to claim 1, wherein the first cutting blade portion has a length which is or more of a length of the cutting blade.

3. The drill insert according to claim 1, wherein a breaker groove which has a bottom surface continuous with the honing face is formed on the rake face, and the bottom surface of the breaker groove is inclined to gradually retreat as the bottom surface is separated from the honing surface.

4. The drill insert according to claim 1, wherein a land which gradually retreats from the flank face side toward the rake face is formed on a second cutting blade portion continuous with the other end portion of both end portions of the cutting blade.

5. The drill insert according to claim 4, wherein a third convex curved face is formed between the flank face and the land in the second cutting blade portion, and in the cross section orthogonal to the cutting blade, a curvature radius of the third convex curved face is smaller than the curvature radius of the first convex curved face on the honing face.

6. A cutting edge replacement type drill, wherein the drill insert according to claim 1 is detachably attached to a distal portion of a drill body which is rotated around an axis such that the cutting blade protrudes from the distal end of the drill body, the one end portion of the cutting blade is positioned in the vicinity of the axis and the other end portion of both end portions of the cutting blade is positioned on the outer circumferential side of the drill body when viewed from a rotation direction of the drill body, and the first cutting blade portion and the axis intersect each other.

7. The drill insert according to claim 2, wherein a breaker groove which has a bottom surface continuous with the honing face is formed on the rake face, and the bottom surface of the breaker groove is inclined to gradually retreat as the bottom surface is separated from the honing surface.

8. The drill insert according to claim 2, wherein a land which gradually retreats from the flank face side toward the rake face is formed on a second cutting blade portion continuous with the other end portion of both end portions of the cutting blade.

9. The drill insert according to claim 3, wherein a land which gradually retreats from the flank face side toward the rake face is formed on a second cutting blade portion continuous with the other end portion of both end portions of the cutting blade.

10. The drill insert according to claim 7, wherein a land which gradually retreats from the flank face side toward the rake face is formed on a second cutting blade portion continuous with the other end portion of both end portions of the cutting blade.

11. The drill insert according to claim 8, wherein a third convex curved face is formed between the flank face and the land in the second cutting blade portion, and in the cross section orthogonal to the cutting blade, a curvature radius of the third convex curved face is smaller than the curvature radius of the first convex curved face on the honing face.

12. The drill insert according to claim 9, wherein a third convex curved face is formed between the flank face and the land in the second cutting blade portion, and in the cross section orthogonal to the cutting blade, a curvature radius of the third convex curved face is smaller than the curvature radius of the first convex curved face on the honing face.

13. The drill insert according to claim 10, wherein a third convex curved face is formed between the flank face and the land in the second cutting blade portion, and in the cross section orthogonal to the cutting blade, a curvature radius of the third convex curved face is smaller than the curvature radius of the first convex curved face on the honing face.

14. A cutting edge replacement type drill, wherein the drill insert according to claim 2 is detachably attached to a distal portion of a drill body which is rotated around an axis such that the cutting blade protrudes from the distal end of the drill body, the one end portion of the cutting blade is positioned in the vicinity of the axis and the other end portion of both end portions of the cutting blade is positioned on the outer circumferential side of the drill body when viewed from a rotation direction of the drill body, and the first cutting blade portion and the axis intersect each other.

15. A cutting edge replacement type drill, wherein the drill insert according to claim 3 is detachably attached to a distal portion of a drill body which is rotated around an axis such that the cutting blade protrudes from the distal end of the drill body, the one end portion of the cutting blade is positioned in the vicinity of the axis and the other end portion of both end portions of the cutting blade is positioned on the outer circumferential side of the drill body when viewed from a rotation direction of the drill body, and the first cutting blade portion and the axis intersect each other.

16. A cutting edge replacement type drill, wherein the drill insert according to claim 4 is detachably attached to a distal portion of a drill body which is rotated around an axis such that the cutting blade protrudes from the distal end of the drill body, the one end portion of the cutting blade is positioned in the vicinity of the axis and the other end portion of both end portions of the cutting blade is positioned on the outer circumferential side of the drill body when viewed from a rotation direction of the drill body, and the first cutting blade portion and the axis intersect each other.

17. A cutting edge replacement type drill, wherein the drill insert according to claim 5 is detachably attached to a distal portion of a drill body which is rotated around an axis such that the cutting blade protrudes from the distal end of the drill body, the one end portion of the cutting blade is positioned in the vicinity of the axis and the other end portion of both end portions of the cutting blade is positioned on the outer circumferential side of the drill body when viewed from a rotation direction of the drill body, and the first cutting blade portion and the axis intersect each other.

18. A cutting edge replacement type drill, wherein the drill insert according to claim 7 is detachably attached to a distal portion of a drill body which is rotated around an axis such that the cutting blade protrudes from the distal end of the drill body, the one end portion of the cutting blade is positioned in the vicinity of the axis and the other end portion of both end portions of the cutting blade is positioned on the outer circumferential side of the drill body when viewed from a rotation direction of the drill body, and the first cutting blade portion and the axis intersect each other.

19. A cutting edge replacement type drill, wherein the drill insert according to claim 8 is detachably attached to a distal portion of a drill body which is rotated around an axis such that the cutting blade protrudes from the distal end of the drill body, the one end portion of the cutting blade is positioned in the vicinity of the axis and the other end portion of both end portions of the cutting blade is positioned on the outer circumferential side of the drill body when viewed from a rotation direction of the drill body, and the first cutting blade portion and the axis intersect each other.

20. A cutting edge replacement type drill, wherein the drill insert according to claim 11 is detachably attached to a distal portion of a drill body which is rotated around an axis such that the cutting blade protrudes from the distal end of the drill body, the one end portion of the cutting blade is positioned in the vicinity of the axis and the other end portion of both end portions of the cutting blade is positioned on the outer circumferential side of the drill body when viewed from a rotation direction of the drill body, and the first cutting blade portion and the axis intersect each other.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a perspective view showing a first embodiment of a drill insert of the present invention.

[0022] FIG. 2 is a plan view of the embodiment shown in FIG. 1.

[0023] FIG. 3 is a side view of the embodiment shown in FIG. 1.

[0024] FIG. 4 is a sectional view taken along line X-X in FIG. 2.

[0025] FIG. 5 is a sectional view taken along line Y-Y in FIG. 2.

[0026] FIG. 6 is a sectional view taken along line Z-Z in FIG. 2.

[0027] FIG. 7 is an enlarged sectional view of a lower cutting blade (first cutting blade portion) in FIG. 4.

[0028] FIG. 8 is an enlarged sectional view of a lower cutting blade (second cutting blade portion) in FIG. 6.

[0029] FIG. 9 is a plan view of a distal portion of a drill body showing an embodiment of a cutting edge replacement type drill of the present invention to which the drill insert of the embodiment shown in FIGS. 1 to 8 is attached.

[0030] FIG. 10 is a front view of the cutting edge replacement type drill shown in FIG. 9.

[0031] FIG. 11 is a side view of the cutting edge replacement type drill shown in FIG. 9.

[0032] FIG. 12 is a bottom view of the cutting edge replacement type drill shown in FIG. 9.

[0033] FIG. 13 is a perspective view showing a second embodiment of a drill insert of the present invention.

[0034] FIG. 14 is a plan view showing the embodiment shown in FIG. 13.

[0035] FIG. 15 is a side view of the embodiment shown in FIG. 13.

[0036] FIG. 16 is a sectional view taken along line X-X in FIG. 14.

[0037] FIG. 17 is a sectional view taken along line Y-Y in FIG. 14.

[0038] FIG. 18 is a sectional view taken along line Z-Z in FIG. 14.

DESCRIPTION OF EMBODIMENTS

[0039] FIGS. 1 to 8 show a first embodiment of a drill insert of the present invention, FIGS. 9 to 12 show an embodiment of a cutting edge replacement type drill of the present invention to which the drill insert of the first embodiment is attached. In the drill insert of the present embodiment, an insert body 1 is formed in a polygonal plate shape using a hard material such as sintered hard alloy, and specifically, in the present embodiment, the drill insert is formed in an approximately square plate shape.

[0040] One square surface of the insert body 1 is a rake face 2, four side faces which are disposed around the rake face 2 are flank faces 3, and a cutting blade 4 is formed on each of intersection ridge portions between the rake face 2 and the four flank faces 3. In addition, the other square surface of the insert body 1 is a seating face 5, and an attachment hole 6 penetrating the insert body 1 is formed from the center of the rake face 2 to the center of the seating face 5. The insert body 1 is formed so as to be rotationally symmetrical for each 90 around an insert center line C passing through the center of the attachment hole 6, and the seating face 5 is a flat face perpendicular to the insert center line C.

[0041] In addition, each of the flank faces 3 is inclined so as to gradually retreat toward the inside of the insert body 1 from the cutting blade 4 toward the seating face 5 in the direction of the insert center line C, a clearance angle is formed on the cutting blade 4, and the drill insert of the present embodiment is a positive type insert. In addition, the flank face 3 is inclined to retreat toward the inside of the insert body 1 so as to have a plurality of steps from the cutting blade 4 toward the seating face 5.

[0042] A planar boss face 7 perpendicular to the insert center line C is formed around the attachment hole 6 in the center of the rake face 2, and the boss face 7 is positioned so as to most protrude from the rake face 2 in the direction of the insert center line C. In addition, breaker grooves 8 are formed over the entire circumference of the rake face 2 around the boss face 7, and each of the breaker groove 8 has a bottom surface 8A which is recessed to be inclined so as to gradually retreat in the direction of the insert center line C toward the inside of the rake face 2, and thereafter, is cut upward so as to rise via the concave curved face.

[0043] Meanwhile, when the insert body 1 is attached to a distal portion of a drill body 11 described below, the cutting blades 4 are disposed such that one of the four cutting blades 4 protrudes from the distal end of the drill body 11 and extends from the vicinity of an axis O on the inner circumferential side of the drill body 11 to the outer circumferential side, the end portion of the cutting blade 4 positioned in the vicinity of the axis O is one end portion A, and the end portion positioned on the outer circumferential of the drill body 11 is the other end portion B. Moreover, in the cutting blade 4, a portion continuous with the one end portion A is a first cutting blade portion 4A, a portion continuous with the other end portion B is a second cutting blade portion 4B, and the second cutting blade portion 4B is formed in a convex curve shape having a large curvature radius, a linear shape, or a combination thereof while the first cutting blade portion 4A linearly extends when viewed in a direction facing the rake face 2 in the direction of the insert center line C.

[0044] In addition, in the first cutting blade portion 4A, round honing is performed on the cutting blade 4 so as to form a honing face 9, and the honing face 9 is formed so as to gradually rise in the direction of the insert center line C from the flank face 3 toward the rake face 2. Moreover, the honing face 9 has a first convex curved face 9A continuous with the rake face 2 and a second convex curved face 9B continuous with the flank face 3, and as shown in FIG. 7, in a cross section perpendicular to the cutting blade 4, the honing face 9 is formed such that a curvature radius R1 of the first convex curved face 9A is larger than a curvature radius R2 of the second convex curved face 9B.

[0045] Here, in the present embodiment, each of the first and second convex curved faces 9A and 9B is formed in an arc-shaped cross section having each of the constant curvature radii R1 and R2, and the honing face 9 is formed by the first and second convex curved faces 9A and 9B. That is, as shown in FIG. 7, the first convex curved face 9A comes into contact with the bottom surface 8A of the breaker groove 8 which is inclined to gradually retreat in the direction of the insert center line C as being separated from the honing face 9 toward the inside of the rake face 2, the second convex curved face 9B comes into contact with the flank face 3, and the first and second convex curved faces 9A and 9B are formed so as to come into contact with each other. In addition, in the cross section orthogonal to the cutting blade 4, lengths along the arcs of the first and second convex curved faces 9A and 9B are formed such that the length of the first convex curved face 9A is longer than the length of the second convex curved face 9B.

[0046] In addition, as shown in FIG. 8, in the second cutting blade portion 4B, a land (positive land) 10 which gradually retreats in the direction of the insert center line C from the flank face 3 side toward the rake face 2 is formed, and the land 10 intersects the bottom surface 8A of the breaker groove 8 at an obtuse angle near to a straight angle therebetween. In addition, a third convex curved face 9C is formed between the land 10 and the flank face 3, and the third convex curved face 9C is also formed in an arc shape having a constant curvature radius R3 in the cross section orthogonal to the cutting blade 4. However, the curvature radius R3 of the third convex curved face 9C is set so as to be smaller than the curvature radius R1 of the first convex curved face 9A.

[0047] In addition, when viewed from the direction facing the rake face 2 in the direction of the insert center line C, the first cutting blade portion 4A and the second cutting blade portion 4B intersect each other so as to be bent at a slightly obtuse angle in a case where the first and second cutting blade portions 4A and 4B have linear shapes, and the second cutting blade portions 4B intersect the first cutting blade portion 4A so as to be similarly bent at an obtuse angle or is formed so as to come into contact with the first cutting blade portion 4A in a case where the second cutting blade portion 4B has a convex curve shape. A length from the one end portion A to the intersection or the contact between the first and second cutting blade portions 4A and 4B is longer than the length from the intersection or the contact to the other end portion B, that is, the first cutting blade portion 4A has a length which is or more of a length of the cutting blade 4. In addition, in the portion in which the first and second convex curved face 9A and 9B intersect each other, a transition region may be formed in which the sectional shape of the cutting blade 4 is continuously changed from the honing face 9 of the first cutting blade portion 4A toward the land 10 of the second cutting blade portion 4B and the third convex curved face 9C.

[0048] In addition, in each of corner portions having a square face (polygon face) configured of the rake face 2, a corner blade 4C having a convex curve such as arc or the like when viewed from the direction facing the rake face 2 is formed so as to come into contact with the first and second cutting blade portions 4A and 4B on both end portions A and B of two adjacent cutting blades 4. Moreover, a width of the honing face 9 of the first cutting blade portion 4A is wider than a width of land 10 of the second cutting blade portion 4B, and the breaker groove 8 is formed such that the width of the breaker groove 8 gradually increases from the one end portion A of the cutting blade 4 toward the other end portion B.

[0049] In the cutting edge replacement type drill of an embodiment of the present invention to which the drill insert of the first embodiment is detachably attached, the drill body 11 is formed of a metal material such as a steel material, and the distal portion of the drill body 11 has a columnar shaped outline about an axis O. In the cutting edge replacement type drill, a rear end portion (not shown) is a shank portion and is held by a main spindle of a machine tool, the rear end portion moves to the distal side (lower side in the FIGS. 9, 11, and 12) in the direction of the axis O while rotating in a drill rotation direction T around the axis O, and a workpiece such as stainless steel is drilled by the drill insert which is attached to the distal portion of the drill body 11.

[0050] A pair of scrape discharge grooves 12A and 12B is formed on the outer circumference of the distal portion of the drill body 11, and in the present embodiment, the scrape discharge grooves 12A and 12B are formed so as to be slightly twisted to the rear side in the drill rotation direction T around the axis O toward the rear end side on the sides opposite to each other with an interval therebetween in the circumferential direction. In the pair of scrape discharge grooves 12A and 12B, an inner circumferential insert attachment seat 13A which opens to the distal face of the drill body 11 is formed on the distal inner circumferential portion of a wall face of one scrape discharge groove (right upper scrape discharge groove in FIG. 10) 12A in the drill rotation direction T, and an outer circumferential insert attachment seat 13B which opens to the distal face and the outer circumferential surface of the drill body 11 is formed on the distal outer circumferential portion of a wall face of the other scrape discharge groove (left lower scrape discharge groove in FIG. 10) 12B in the drill rotation direction T.

[0051] Screw holes 13C is formed on bottom surfaces of the inner and outer circumferential insert attachment seats 13A and 13B in the drill rotation direction T. In addition, the rake face 2 is directed to the drill rotation direction T, as described above, one among the four cutting blades 4 protrudes from the distal end of the drill body 11 and is seated on the inner circumferential insert attachment seat 13A, a clamp screw 14 inserted into the attachment hole 6 is screwed to the screw hole 13C, and the drill insert of the first embodiment is detachably attached to the drill body 11.

[0052] In addition, in the attached drill insert of the first embodiment, when viewed from the drill rotation direction T facing the rake face 2, as shown in FIG. 9, in the cutting blade 4 which protrudes from the distal end of the drill body 11, the one end portion A is positioned in the vicinity of the axis O, the outer end portion B is positioned on the outer circumferential side of the drill body 11, and the first cutting blade portion 4A intersects the axis O and is disposed in the vicinity of the axis O. Moreover, in the cutting blade 4 which protrudes from the distal end of the drill body 11, the other end portion B is positioned on the most distal end in the direction of the axis O, and the cutting blade 4 is disposed so as to be gently inclined to the rear end side in the direction of the axis toward the one end portion A. Moreover, the first cutting blade portion 4A extends over the axis O from the intersection between the first and second cutting blade portions 4A and 4B toward the inner circumferential side of the drill body 11, that is, the one end portion A is positioned on the side opposite to the axis with respect to the intersection.

[0053] Meanwhile, an outer circumferential drill insert is also detachably attached to the outer circumferential insert attachment seat 13B by the clamp screw 14. Similarly to the drill insert of the first embodiment, an insert body 15 of the outer circumferential drill insert is formed in a square plate shape using a hard material such as sintered hard alloy. However, differently from the first embodiment, in the outer circumferential drill insert, the present embodiment does not have the first cutting blade portion 4A having the honing face 9 of the first embodiment, and as shown in FIG. 12, chip breakers are formed on the rake face in the drill rotation direction T along cutting blades 16.

[0054] In the outer circumferential drill insert, one cutting blade 16 protrudes from the distal end of the drill body 11, the one cutting blade 16 is positioned on the slightly further rear end side with respect to the protruding cutting blade 4 of the drill insert of the first embodiment shown in FIG. 9, and the outer circumferential drill insert is attached to the drill body such that rotation trajectories around the axis O overlap each other. In addition, the outer circumferential end of the one cutting blade 16 of the attached outer circumferential drill insert slightly further protrudes from the outer circumferential side relative to the outer circumference of the distal portion of the drill body 11.

[0055] Accordingly, in the cutting edge replacement type drill of the embodiment of the present invention configured as described above, as shown in FIG. 9, the inner circumferential portion of a hole drilled in the workpiece is cut by the drill insert of the first embodiment, and the outer circumferential portion of the hole is cut by the outer circumferential drill insert. Accordingly, in the cutting blade 4 which protrudes from the distal end of the drill body 11 of the inner circumferential drill insert of the first embodiment, particularly, a circumferential speed and a cutting speed approach zero in the first cutting blade portion 4A on the axis O side intersecting the axis O, and a cutting load or cutting resistance increases. However, in the first cutting blade portion 4A, the first convex curved face 9A continuous with the rake face 2 and the second convex curved face 9B continuous with the flank face 3 are provided, and the honing face 9 which gradually rises from the flank face 3 toward the rake face 2 is formed. Accordingly, it is possible to ensure sufficient chipping resistance with respect to the cutting load or the cutting resistance.

[0056] That is, since the honing face 9 gradually rises in the direction of the insert center line C from the flank face 3 toward the rake face 2, first, it is possible to increase a lip angle between the honing face 9 which substantially functions as a cutting blade edge in the first cutting blade portion 4A and the flank face 3. In addition, since the second convex curved face 9B continuous with the flank face 3 is formed on the intersection ridge portion between the honing face 9 of the first cutting blade portion 4A and the flank face 3, strength of the cutting blade is ensured, and it is possible to obtain sufficient chipping resistance with respect to the cutting load or the cutting resistance.

[0057] In addition, the first convex curved face 9A continuous with the rake face 2 is formed on the rake face 2 side of the honing face 9, and the curvature radius R1 of the first convex curved face 9A is larger than the curvature radius R2 of the second convex curved face 9B. Accordingly, since the first convex curved face 9A has the arc which is more gentle than that of the second convex curved face 9B in the cross section orthogonal to the cutting blade 4, friction resistance decreases when scraps or chips scratch the honing face 9, and it is possible to prevent cutting heat due to the friction from increasing. Accordingly, it is possible to prevent occurrence of welding even if the workpiece is stainless steel, and it is possible to prevent damage of the cutting blade 4 due to the welding.

[0058] Moreover, in the drill insert of the first embodiment, since the first cutting blade portion 4A has the length which is or more of the length of the cutting blade 4 protruding from the distal end of the drill body 11, when the drill insert is attached to the inner circumferential side of the distal portion of the drill body 11, the first cutting blade portion 4A having a sufficient length can be disposed in the vicinity of the axis O, and it is possible to further reliably ensure the chipping resistance. That is, if the length of the first cutting blade portion 4A is less than of the entire length of one cutting blade 4, when an excessive cutting load or cutting resistance is applied, there is a concern that it is not possible to reliably ensure the chipping resistance on the other end portion B side of the cutting blade 4 rather than the first cutting blade portion 4A.

[0059] Moreover, since the breaker groove 8 which has the bottom surface 8A continuous with the honing face 9 is formed on the rake face 2, and the bottom surface 8A of the breaker groove 8 is inclined to gradually retreat in the direction of the insert center line C as the bottom surface is separated from the honing face 9, even when the honing face 9 which gradually rises in the direction of the insert center line C is formed on the first cutting blade portion 4A to ensure the chipping resistance, it is possible to prevent the cutting resistance from increasing more than is needed. In addition, the bottom surface 8A has the convex curved face of the curvature radius R1 on the honing face 9 side and may come into contact with the first convex curve 9A as described above, or may intersect the first convex curved face 9A at an obtuse angle.

[0060] Meanwhile, in the present embodiment, with respect to the first cutting blade portion 4A of the one end portion A side of the cutting blade 4 in which the chipping resistance is ensured, in the second cutting blade portion 4B on the other end portion B side of the cutting blade 4 which is disposed on the outer circumferential side of the distal end of the drill body 11, the land 10 is formed, which is inclined so as to gradually retreat in the direction of the insert center line C from the flank face 3 side toward the rake face 2. Accordingly, it is possible to increase sharpness of the cutting blade 4 on the outer circumferential side of the cutting blade 4 in which is a certain degree of circumferential speed is generated to ensure the cutting speed, and even when much more scraps are generated on the outer circumferential side than the vicinity of the axis O, it is possible to further decrease the cutting resistance.

[0061] In addition, even in the case where the land 10 is formed on the second cutting blade portion 4B, in the present embodiment, since the third convex curved face 9C is formed on the intersection ridge portion between the land 10 and the flank face 3, it is possible to prevent damage of the cutting blade 4 on the second cutting blade portion 4B. In addition, since the curvature radius R3 of the third convex curved face 9C is smaller than the curvature radius R3 of the first convex curved face 9A in the first cutting blade portion 4A, it is possible to prevent the cutting resistance from increasing more than is needed while preventing damage of the cutting blade 4 on the second cutting blade portion 4B.

[0062] In addition, in the cutting edge replacement type drill of the present embodiment, the outer circumferential drill insert is provided, which is positioned on the outer circumferential side of the drill body 11 from the second cutting blade portion 4B of the drill insert of the first embodiment and cuts the outer circumferential portion of the drilled hole. Since the outer circumferential drill insert does not have the first cutting blade portion 4A having the honing face 9 of the first embodiment and the chip breakers 17 are formed on the rake face along the cutting blade 16, even when the outer circumferential drill insert is separated from the axis O and much more scraps are generated in the outer circumferential drill insert than in the drill insert of the first embodiment, it is possible to reliably remove the scraps. However, according to machining conditions or the like, the drill insert of the first embodiment may be attached to the outer circumferential insert attachment seat 13B.

[0063] Moreover, in the drill insert of the first embodiment, the second cutting blade portion 4B in which the land 10 is formed on the other end portion B side of the cutting blade 4 is provided. However, in a case where there is a concern that a large cutting load or large cutting resistance is applied to the entire length of the cutting blade 4 of the drill insert attached to the inner circumferential side of the drill body 11 according to machining conditions, the size of the insert body 1, the length of the cutting blade 4, or the like, as a drill insert of a second embodiment of the present invention shown in FIGS. 13 to 18, the entire length of the cutting blade 4 may be the first cutting blade portion 4A on which the honing face 9 is formed, which includes the first convex curved face 9A continuous with the rake face 2 and the second convex curved face 9B continuous with the flank face 3 and gradually rises from the flank face 3 toward the rake face 2. In addition, in the second embodiment, the same reference numerals are assigned to the portions common to the first embodiment.

[0064] Accordingly, in the drill insert of the second embodiment, the shape of the cross section over the entire length of the cutting blade 4 is the shape shown in FIG. 7, and it is possible to ensure chipping resistance with respect to a cutting load or cutting resistance and chipping resistance with respect to welding. Accordingly, it is possible to provide a drill insert having a longer service life. In addition, in the second embodiment, the curvature radii R1 and R2 of the first and second convex curved faces 9A and 9B or the width of the honing face 9 are approximately constant over the entire length of the cutting blade 4.

[0065] Moreover, in a case where there is a concern that a large cutting load or large cutting resistance is applied to a portion exceeding the entire length of the cutting blade 4 of the drill insert attached to the inner circumferential side of the drill body 11, the drill insert of the second embodiment is attached to the inner circumferential side of the drill body 11, the drill insert of the first embodiment instead of the outer circumferential drill insert of the cutting edge replacement type drill of the embodiment may be attached to the outer circumferential side. In this case, it is possible to ensure high chipping resistance within a range from the vicinity of the axis O of the drill body 11 to the first cutting blade portion 4A of the outer circumferential drill insert of the first embodiment. Of course, the drill insert of the second embodiment may be attached to both the inner and outer circumferential insert attachment seats 13A and 13B of the drill body 11.

[0066] In addition, in a case where the inner diameter of the drilled hole is small, the outer diameter of the distal portion of the drill body 11 is small, and a large cutting load or large cutting resistance is applied to only the vicinity of the axis O, the drill insert of the first embodiment may be attached to the drill body 11 of the cutting edge replacement type drill having one blade in which only the inner circumferential insert attachment seat 13A is formed. In addition, in a case where a large cutting load or large cutting resistance is applied to the entire length of the cutting blade 4 even through the inner diameter of the drilled hole is small, the drill insert of the second embodiment may be attached to the cutting edge replacement type drill having one blade.

REFERENCE SIGNS LIST

[0067] 1: insert body [0068] 2: rake face [0069] 3: flank face [0070] 4: cutting blade [0071] 4A: first cutting blade portion [0072] 4B: second cutting blade portion [0073] 4C: corner blade [0074] 8: breaker groove [0075] 8A: bottom surface of breaker groove 8 [0076] 9: honing face [0077] 9A: first convex curved face [0078] 9B: second convex curved face [0079] 9C: third convex curved face [0080] 10: land [0081] 11: drill body [0082] 13A, 13B: inner and outer circumferential insert attachment seat [0083] A: one end portion of cutting blade 4 [0084] B: other end portion of cutting blade 4 [0085] C: insert center line [0086] R1 to R3: curvature radii of first to third convex curved faces 9A to 9C [0087] O: axis of drill body 11 [0088] T: drill rotation direction