Drill

Abstract

The present invention is such that, when viewed along the central axis thereof, the start point phase of a first discharge groove is located in a range of +10° to +90° with respect to a center cutting edge, the end point phase of the first discharge groove is located in a range of -40° to 0° with respect to the center cutting edge, the start point phase of a second discharge groove is located in a range of +10° to +90° with respect to an outer peripheral blade, and the end point phase of the second discharge groove is located in a range of -40° to 0° with respect to the outer peripheral blade. The first discharge groove has a first front groove section and a first rear groove section connected to the first front groove section. The second discharge groove has a second front groove section and a second rear groove section connected to the second front groove section. The torsion angle of the first front groove section monotonically decreases when approaching the first rear groove section. The torsion angle of the second front groove section monotonically decreases when approaching the second rear groove section. The torsion angle of each of the first rear groove section and the second rear groove section is 0°.

Description

drill

[0001] The present disclosure relates to a drill. This application claims priority to international application PCT / JP2023 / 025141, filed July 6, 2023, the entire contents of which are incorporated herein by reference.

[0002] International Publication No. 2013 / 018764 (Patent Document 1) describes a cutting tool holder having a spiral groove portion and a linear groove portion, in which the spiral groove portion intersects with a rotation axis at a certain angle when viewed from the side.

[0003] International Publication No. 2013 / 018764

[0004] The drill according to the present disclosure is a drill that rotates around a central axis and includes a first cutting insert, a second cutting insert, and a body portion. The first cutting insert has a central cutting edge. The second cutting insert has a peripheral cutting edge. The first cutting insert and the second cutting insert are attached to the body portion. The body portion is provided with a first discharge groove and a second discharge groove. The first discharge groove discharges chips cut by the central cutting edge. The second discharge groove discharges chips cut by the peripheral cutting edge. When viewed along the central axis, the start phase of the first discharge groove is located in a range of +10° to +90° relative to the central cutting edge, the end phase of the first discharge groove is located in a range of -40° to 0° relative to the central cutting edge, the start phase of the second discharge groove is located in a range of +10° to +90° relative to the peripheral cutting edge, and the end phase of the second discharge groove is located in a range of -40° to 0° relative to the peripheral cutting edge. The first discharge groove has a first front groove portion and a first rear groove portion connected to the first front groove portion. The second discharge groove has a second front groove portion and a second rear groove portion connected to the second front groove portion. The twist angle of the first front groove portion monotonically decreases toward the first rear groove portion. The twist angle of the second front groove portion monotonically decreases toward the second rear groove portion. The twist angles of the first rear groove portion and the second rear groove portion are each 0°. At the boundary between the first front groove portion and the first rear groove portion, a value obtained by dividing a change in the twist angle of the first discharge groove by a change in position in the direction along the central axis is continuous. At the boundary between the second front groove portion and the second rear groove portion, a value obtained by dividing a change in the twist angle of the second discharge groove by a change in position in the direction along the central axis is continuous. The main body portion is provided with a first pocket portion connected to the first discharge groove and located forward of the first cutting insert in the rotational direction. The distance from the front end of the first cutting insert to the rear end of the first pocket portion in the direction along the central axis is 1.5 times or more the tool diameter.

[0005] FIG. 1 is a first schematic perspective view showing the configuration of a drill according to this embodiment. FIG. 2 is a second schematic perspective view showing the configuration of a drill according to this embodiment. FIG. 3 is a left side view showing the configuration of a drill according to this embodiment. FIG. 4A is a first schematic front view showing the configuration of a drill according to this embodiment. FIG. 4B is a second schematic front view showing the configuration of a drill according to this embodiment. FIG. 5 is a cross-sectional view taken along line V-V in FIG. 4A. FIG. 6 is a cross-sectional view taken along line VI-VII in FIG. 4A. FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. 4A. FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 4A. FIG. 9A is a first schematic rear view showing the configuration of a drill according to this embodiment. FIG. 9B is a second schematic rear view showing the configuration of a drill according to this embodiment. FIG. 10 is a cross-sectional view taken along line X-X in FIG. 9A. FIG. 11 is a cross-sectional view taken along line XI-XI in FIG. 9A. Fig. 12 is a virtual plane obtained by rotationally projecting each of the first cutting insert and the second cutting insert. Fig. 13 is a virtual plane obtained by rotationally projecting each of the first cutting insert and the second cutting insert. Fig. 14 is a diagram showing the displacement amounts of the drills of Samples 1 to 9. Fig. 15 is a diagram showing the height profile of the wall surface of a hole formed using the drill of Sample 4. Fig. 16 is a diagram showing the height profile of the wall surface of a hole formed using the drill of Sample 10. Fig. 17 is a cross-sectional schematic diagram showing the shape of a hole formed using each of the drills 100 of Samples 4, 11, and 12.

[0006] [Problem to be Solved by the Present Disclosure] An object of the present disclosure is to provide a drill that can improve chip discharge performance while suppressing a decrease in rigidity.

[0007] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a drill that can improve chip discharge performance while suppressing a decrease in rigidity.

[0008] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0009] (1) The drill 100 according to the present disclosure is a drill 100 that rotates around a central axis A and includes a first cutting insert 10, a second cutting insert 20, and a main body 9. The first cutting insert 10 has a central cutting edge 11. The second cutting insert 20 has a peripheral cutting edge 21. The first cutting insert 10 and the second cutting insert 20 are attached to the main body 9. The main body 9 is provided with a first discharge groove 1 and a second discharge groove 2. The first discharge groove 1 discharges chips cut by the central cutting edge 11. The second discharge groove 2 discharges chips cut by the peripheral cutting edge 21. When viewed along the central axis A, the start phase of the first discharge groove 1 is located in a range of +10° to +90° relative to the central cutting edge 11, and the end phase of the first discharge groove 1 is located in a range of -40° to 0° relative to the central cutting edge 11. The start phase of the second discharge groove 2 is located in a range of +10° to +90° relative to the peripheral cutting edge 21, and the end phase of the second discharge groove 2 is located in a range of -40° to 0° relative to the peripheral cutting edge 21. The first discharge groove 1 has a first front groove portion 51 and a first rear groove portion 52 connected to the first front groove portion 51. The second discharge groove 2 has a second front groove portion 61 and a second rear groove portion 62 connected to the second front groove portion 61. The twist angle of the first front groove portion 51 monotonically decreases toward the first rear groove portion 52. The twist angle of the second front groove portion 61 monotonically decreases toward the second rear groove portion 62. The twist angle of each of the first rear groove portion 52 and the second rear groove portion 62 is 0°. At the boundary between the first front groove portion 51 and the first rear groove portion 52, the value obtained by dividing the amount of change in the twist angle of the first discharge groove 1 by the amount of change in position in the direction along the central axis A is continuous. At the boundary between the second front groove portion 61 and the second rear groove portion 62, the value obtained by dividing the amount of change in the twist angle of the second discharge groove 2 by the amount of change in position in the direction along the central axis A is continuous. The main body portion 9 is provided with a first pocket portion 32 that is continuous with the first discharge groove 1 and is located forward of the first cutting insert 10 in the rotational direction. In the direction along the central axis A, the distance from the front end of the first cutting insert 10 to the rear end of the first pocket portion 32 is 1.5 times the tool diameter or more.

[0010] (2) According to the drill 100 of (1) above, the length of each of the first discharge groove 1 and the second discharge groove 2 in the direction along the central axis A may be greater than or equal to two times and less than or equal to eight times the tool diameter.

[0011] (3) In the drill 100 according to either (1) or (2) above, when the length of the first front groove portion 51 is defined as the first front length, the length of the first rear groove portion 52 is defined as the first rear length, the length of the second front groove portion 61 is defined as the second front length, and the length of the second rear groove portion 62 is defined as the second rear length, in the direction along the central axis A, the value obtained by dividing the first front length by the first rear length may be 0.3 or more and 3.0 or less, and the value obtained by dividing the second front length by the second rear length may be 0.3 or more and 3.0 or less.

[0012] (4) In the drill 100 according to any one of (1) to (3) above, in a cross section perpendicular to the central axis A, when the cross-sectional area of ​​the first front groove portion 51 is defined as the first front area, the cross-sectional area of ​​the first rear groove portion 52 is defined as the first rear area, the cross-sectional area of ​​the second front groove portion 61 is defined as the second front area, and the cross-sectional area of ​​the second rear groove portion 62 is defined as the second rear area, the value obtained by dividing the first front area by the first rear area may be 1.01 or greater and 1.02 or less, and the value obtained by dividing the second front area by the second rear area may be 1.01 or greater and 1.02 or less.

[0013] (5) According to the drill 100 according to any one of (1) to (4) above, in a cross section perpendicular to the central axis A, the cross-sectional area of ​​the first discharge groove 1 may be larger than the cross-sectional area of ​​the second discharge groove 2.

[0014] (6) According to the drill 100 according to any one of (1) to (5) above, in an imaginary plane formed by rotational projection of each of the first cutting insert 10 and the second cutting insert 20, the forwardmost position of the central cutting edge 11 is defined as the first position 71, the intersection of the central axis A and the central cutting edge 11 is defined as the second position 72, and the intersection of an imaginary line segment extending from the second position 72 perpendicular to the central axis A and the peripheral cutting edge 21 is defined as the third position 73. In this case, the distance from the central axis A to the first position 71 in the radial direction extending radially from the central axis A may be 30% to 40% of half the tool diameter, and the distance from the central axis A to the third position 73 in the radial direction may be 80% to 100% of half the tool diameter.

[0015] (7) According to the drill 100 described in (6) above, if the intersection of the central cutting edge 11 and the peripheral cutting edge 21 on an imaginary plane is defined as the fourth position 74, the radial distance from the central axis A to the fourth position 74 may be greater than the radial distance from the fourth position 74 to the outermost end of the peripheral cutting edge 21.

[0016] (8) In the drill 100 according to either (6) or (7) above, the sine of the angle between a line perpendicular to the central axis A and a line tangent to the center cutting edge 11 at the second position 72 on an imaginary plane may be equal to or less than the tool diameter multiplied by 0.0070 / mm. The angle is expressed in degrees, and the tool diameter is expressed in mm.

[0017] (9) According to the drill 100 according to any one of (1) to (8) above, the main body 9 may be provided with a second pocket 42 that is continuous with the second discharge flute 2 and is located forward in the rotational direction relative to the second cutting insert 20. In the direction along the central axis A, the rear end of the first pocket 32 ​​may be located axially rearward of the rear end of the second pocket 42.

[0018] [Details of the embodiment of the present disclosure] Next, details of the embodiment of the present disclosure (hereinafter also referred to as the present embodiment) will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and redundant description will not be repeated.

[0019] First, the configuration of a drill 100 according to this embodiment will be described. FIG. 1 is a first perspective schematic view showing the configuration of the drill 100 according to this embodiment. FIG. 2 is a second perspective schematic view showing the configuration of the drill 100 according to this embodiment. As shown in FIGS. 1 and 2 , the drill 100 according to this embodiment includes a first cutting insert 10, a second cutting insert 20, a body portion 9, a central cutting edge mounting screw 19, and a peripheral cutting edge mounting screw 29. The first cutting insert 10 has a central cutting edge 11. The second cutting insert 20 has a peripheral cutting edge 21. The first cutting insert 10 and the second cutting insert 20 are attached to the body portion 9. The first cutting insert 10 is attached to the body portion 9 using the central cutting edge mounting screw 19. The second cutting insert 20 is attached to the body portion 9 using the peripheral cutting edge mounting screw 29.

[0020] The drill 100 is rotatable around a central axis A. The main body 9 is provided with a first discharge flute 1 and a second discharge flute 2. The first discharge flute 1 discharges chips cut by the central cutting edge 11. The second discharge flute 2 discharges chips cut by the peripheral cutting edge 21.

[0021] As shown in FIG. 1 , the main body 9 has a first body region 3, a second body region 6, and a shank 5. The front end surface 101 of the main body 9 is formed by the first body region 3. The front end surface 101 of the main body 9 is the portion that faces the workpiece. The second body region 6 is continuous with both the first body region 3 and the shank 5. The second body region 6 is located between the first body region 3 and the shank 5. The rear end surface 102 of the main body 9 is located on the opposite side of the front end surface 101. The rear end surface 102 of the main body 9 is formed by the shank 5. The shank 5 is the portion that is attached to a device that rotates the drill 100.

[0022] In this specification, the direction parallel to the central axis A and from the rear end face 102 toward the front end face 101 is referred to as the axially forward direction. Conversely, the direction parallel to the central axis A and from the front end face 101 toward the rear end face 102 is referred to as the axially rearward direction. In a plane perpendicular to the central axis A, directions extending radially from the central axis A are referred to as the radial direction.

[0023] As shown in FIG. 1 , the first body region 3 is provided with a first insert placement surface portion 31 and a first pocket portion 32. A first insert placement groove 33 is formed in the first insert placement surface portion 31. The first cutting insert 10 is placed in the first insert placement groove 33. The first pocket portion 32 is located forward of the first cutting insert 10 in the rotational direction. The first pocket portion 32 is continuous with the first discharge groove 1. At least a portion of the first pocket portion 32 is located forward of the first discharge groove 1 in the axial direction. The first pocket portion 32 is continuous with a front end face 101.

[0024] As shown in Fig. 2, the first body region 3 is provided with a second insert placement surface portion 41 and a second pocket portion 42. A second insert placement groove 43 is formed in the second insert placement surface portion 41. The second cutting insert 20 is placed in the second insert placement groove 43. The second pocket portion 42 is located forward of the second cutting insert 20 in the rotational direction. The second pocket portion 42 is continuous with the second discharge groove 2. At least a portion of the second pocket portion 42 is located axially forward of the second discharge groove 2. The second pocket portion 42 is continuous with the front end face 101.

[0025] 1 and 2 , the first main body region 3 has a first outer peripheral surface 4. The first discharge groove 1 and the second discharge groove 2 are each exposed to the outside at the first outer peripheral surface 4. The first insert placement surface portion 31 and the first pocket portion 32 may each be continuous with the first outer peripheral surface 4. Similarly, the second insert placement surface portion 41 and the second pocket portion 42 may each be continuous with the first outer peripheral surface 4.

[0026] 3 is a left side view schematically illustrating the configuration of the drill 100 according to this embodiment. As shown in FIG. 3 , when viewed in a direction along the central axis A, the first outer peripheral surface 4 is arc-shaped. The outer peripheral surface of the second body region 6 surrounds the first outer peripheral surface 4. When viewed in a direction along the central axis A, the outer peripheral surface of the second body region 6 is substantially circular. Two coolant supply holes 7 may be formed in the body portion 9. The two coolant supply holes 7 are exposed at a front end surface 101 of the body portion 9.

[0027] The first cutting insert 10 is disposed at a position closer to the central axis A than the second cutting insert 20. When viewed in a direction along the central axis A, the first cutting insert 10 may intersect with the central axis A. More particularly, when viewed in a direction along the central axis A, the central cutting edge 11 of the first cutting insert 10 may intersect with the central axis A. The second cutting insert 20 is disposed at a position farther from the central axis A than the first cutting insert 10. When viewed in a direction along the central axis A, the second cutting insert 20 is separated from the central axis A. More particularly, when viewed in a direction along the central axis A, the peripheral cutting edge 21 of the second cutting insert 20 does not intersect with the central axis A.

[0028] As shown in FIG. 3 , when viewed in a direction along the central axis A, a ray connecting the central axis A and the outermost peripheral end of the central cutting edge 11 and extending radially from the central axis A is referred to as a thirteenth ray D13. When viewed in a direction along the central axis A, the angle formed by the thirteenth ray D13 and the ridge line between the first pocket portion 32 and the front end face 101 is, for example, 45° to 120°. Similarly, when viewed in a direction along the central axis A, a ray connecting the central axis A and the outermost peripheral end of the peripheral cutting edge 21 and extending radially from the central axis A is referred to as a 23rd ray D23. When viewed in a direction along the central axis A, the angle formed by the 23rd ray D23 and the ridge line between the second pocket portion 42 and the front end face 101 is, for example, 45° to 120°.

[0029] 4A and 4B are schematic front views showing the configuration of the drill 100 according to this embodiment. As shown in FIGS. 4A and 4B , the first discharge flute 1 includes a first front flute portion 51 and a first rear flute portion 52. The first rear flute portion 52 is continuous with the first front flute portion 51. The first rear flute portion 52 is located axially rearward of the first front flute portion 51. The helix angle θ3 of the first front flute portion 51 monotonically decreases toward the first rear flute portion 52. The helix angle θ3 of the first rear flute portion 52 is 0°. From another perspective, the first rear flute portion 52 extends along the central axis A.

[0030] At the boundary (first boundary 57) between the first front groove portion 51 and the first rear groove portion 52, the value obtained by dividing the amount of change in the twist angle θ3 of the first discharge groove 1 by the amount of change in position in the direction along the central axis A is continuous. At the boundary (first boundary 57) between the first front groove portion 51 and the first rear groove portion 52, the twist angle θ3 changes gradually. Specifically, in the region from the boundary (first boundary 57) between the first front groove portion 51 and the first rear groove portion 52 axially forward to a position that is 1.0 times the tool diameter, the value obtained by dividing the amount of change in the twist angle θ3 of the first discharge groove 1 by the amount of change in position in the direction along the central axis A (i.e., 1.0 times the tool diameter) is (2.0)° / mm or less.

[0031] In the direction along the central axis A, the length of the first front groove portion 51 is defined as a first front length B11, and the length of the first rear groove portion 52 is defined as a first rear length B12. The value obtained by dividing the first front length B11 by the first rear length B12 is, for example, 0.3 to 3.0. The value obtained by dividing the first front length B11 by the first rear length B12 may be, for example, 0.5 to 2.0, or 0.7 to 1.5.

[0032] 5 is a schematic cross-sectional view taken along line V-V in FIG. 4A. The cross-sectional view shown in FIG. 5 is perpendicular to the central axis A. In the cross section perpendicular to the central axis A, the cross-sectional area of ​​the first discharge groove 1 may be larger than the cross-sectional area of ​​the second discharge groove 2. The cross-sectional area of ​​the first discharge groove 1 is the area of ​​the region surrounded by the surface of the main body 9 constituting the first discharge groove 1 and a first imaginary arc F1 along the first outer peripheral surface 4. Similarly, the cross-sectional area of ​​the second discharge groove 2 is the area of ​​the region surrounded by the surface of the main body 9 constituting the second discharge groove 2 and a second imaginary arc F2 along the first outer peripheral surface 4. The radii of curvature of the first imaginary arc F1 and the second imaginary arc F2 are each substantially the same as the radii of curvature of the first outer peripheral surface 4.

[0033] Fig. 6 is a schematic cross-sectional view taken along line VI-VI in Fig. 4A. The cross-sectional view shown in Fig. 6 is perpendicular to the central axis A. As shown in Figs. 1 and 6, the main body portion 9 is provided with a first front end groove 91 and a second front end groove 92. The first front end groove 91 is provided in the first insert placement surface portion 31. The second front end groove 92 is provided in the first pocket portion 32. The second front end groove 92 is spaced apart from the first front end groove 91.

[0034] 1 and 4A , the first front end groove 91 and the second front end groove 92 are each located axially forward of the first front groove 51. The first front end groove 91 and the second front end groove 92 are each continuous with the first front groove 51. The position where the first front end groove 91 and the second front end groove 92 join together is defined as the boundary between the first front groove 51 and the first front groove 51 and the second front end groove 92, respectively. In other words, the boundary between the first front groove 51 and the position where the first front end groove 91 and the second front end groove 92 join together is defined as the start position of the first discharge groove 1.

[0035] FIG. 7 is a schematic cross-sectional view taken along line VII-VII in FIG. 4A. The cross-sectional view shown in FIG. 7 is perpendicular to the central axis A. The position in the axial direction of the cross-sectional view shown in FIG. 7 corresponds to the start position (first start position 55) of the first discharge groove 1. The eleventh half ray D11 is a half ray that passes through the bottom of the first discharge groove 1 and the central axis A at the first start position 55. The bottom of the first discharge groove 1 is the point on the first discharge groove 1 that is closest to the central axis A in a cross section perpendicular to the central axis A. The start phase of the first discharge groove 1 corresponds to the phase of the eleventh half ray D11. The phase of the central cutting edge 11 corresponds to the phase of the thirteenth half ray D13. The phase of the central cutting edge 11 is set to 0°.

[0036] As shown in FIG. 7 , the start phase (first start phase θ11) of the first discharge groove 1 is located in the range of +10° to +90° relative to the central cutting edge 11 when viewed along the central axis A. When viewed along the central axis A, the first start phase θ11 may be located in the range of +20° to +80° relative to the central cutting edge 11, or in the range of +30° to +70° relative to the central cutting edge 11. In this specification, the forward direction of rotation is defined as a positive phase. Conversely, the backward direction of rotation is defined as a negative phase. Furthermore, when the same phase is achieved after N rotations in the rotational direction, the phase is defined as N×360° (where N is an integer). For example, when the same phase is achieved after one rotation in the forward direction, the phase is defined as +360°, and when the same phase is achieved after two rotations in the rotational direction, the phase is defined as +720°.

[0037] Fig. 8 is a schematic cross-sectional view taken along line VIII-VIII in Fig. 4A. The cross-sectional view shown in Fig. 8 is perpendicular to the central axis A. The position in the axial direction of the cross-sectional view shown in Fig. 8 corresponds to the end position (first end position 56) of the first discharge groove 1. The twelfth ray D12 is a ray that passes through the bottom of the first discharge groove 1 and the central axis A at the first end position 56. The end phase of the first discharge groove 1 corresponds to the phase of the twelfth ray D12.

[0038] 7 and 8 , when viewed along the central axis A, the end phase of the first discharge groove 1 (first end phase θ12) is located in the range of −40° to 0° relative to the central cutting edge 11. When viewed along the central axis A, the first end phase θ12 may be located in the range of −30° to 0° relative to the central cutting edge 11, or in the range of −20° to 0° relative to the central cutting edge 11.

[0039] In the axial direction, the first end point position 56 may be the same as the end point position (second end point position 66) of the second discharge groove 2. The 22nd ray D22 is a ray that passes through the bottom of the second discharge groove 2 and the central axis A at the second end point position 66. The bottom of the second discharge groove 2 is the point on the second discharge groove 2 that is closest to the central axis A in a cross section perpendicular to the central axis A. The end point phase of the second discharge groove 2 corresponds to the phase of the 22nd ray D22.

[0040] As shown in Fig. 8 , when viewed along the central axis A, the 22nd half ray D22 and the 12th half ray D12 may be located on the same line. From another perspective, the phase of the 22nd half ray D22 may be rotated +180° relative to the 12th half ray D12. As shown in Fig. 8 , at the end position of the first discharge groove 1, the distance between the bottom of the second discharge groove 2 and the central axis A is greater than the distance between the bottom of the first discharge groove 1 and the central axis A. From another perspective, at the end position of the first discharge groove 1, the cross-sectional area of ​​the second discharge groove 2 is smaller than the cross-sectional area of ​​the first discharge groove 1.

[0041] 9A and 9B are schematic rear views illustrating the configuration of the drill 100 according to this embodiment. As shown in FIGS. 9A and 9B , the second discharge flute 2 includes a second front flute portion 61 and a second rear flute portion 62. The second rear flute portion 62 is continuous with the second front flute portion 61. The second rear flute portion 62 is located axially rearward of the second front flute portion 61. The helix angle θ3 of the second front flute portion 61 monotonically decreases toward the second rear flute portion 62. The helix angle θ3 of the second rear flute portion 62 is 0°. From another perspective, the second rear flute portion 62 extends along the central axis A.

[0042] At the boundary (second boundary 67) between the second front groove portion 61 and the second rear groove portion 62, the value obtained by dividing the amount of change in the twist angle θ3 of the second discharge groove 2 by the amount of change in position in the direction along the central axis A is continuous. At the boundary (second boundary 67) between the second front groove portion 61 and the second rear groove portion 62, the twist angle θ3 changes gradually. Specifically, in the region from the boundary (second boundary 67) between the second front groove portion 61 and the second rear groove portion 62 axially forward to a position that is 1.0 times the tool diameter, the value obtained by dividing the amount of change in the twist angle θ3 of the second discharge groove 2 by the amount of change in position in the direction along the central axis A (i.e., 1.0 times the tool diameter) is 2.0° / mm or less.

[0043] In the direction along the central axis A, the length of the second front groove portion 61 is a second front length B21, and the length of the second rear groove portion 62 is a second rear length B22. The value obtained by dividing the second front length B21 by the second rear length B22 is, for example, 0.3 to 3.0. The value obtained by dividing the second front length B21 by the second rear length B22 may be, for example, 0.5 to 2.0, or 0.7 to 1.5.

[0044] Fig. 10 is a schematic cross-sectional view taken along line X-X in Fig. 9A. The cross-sectional view shown in Fig. 10 is perpendicular to the central axis A. As shown in Figs. 2 and 10, the main body portion 9 is provided with a third front end groove 93 and a fourth front end groove 94. The third front end groove 93 is provided in the second insert placement surface portion 41. The fourth front end groove 94 is provided in the second pocket portion 42. The fourth front end groove 94 is spaced apart from the third front end groove 93.

[0045] As shown in Fig. 2 , the third front end groove 93 and the fourth front end groove 94 are each located axially forward of the second discharge groove 2. The third front end groove 93 and the fourth front end groove 94 are each continuous with the second front groove 61. The position where the third front end groove 93 and the fourth front end groove 94 join together is defined as the boundary between the third front end groove 93 and the fourth front end groove 94 and the second front groove 61. In other words, the boundary between the position where the third front end groove 93 and the fourth front end groove 94 join together and the second front groove 61 is defined as the start position of the second discharge groove 2.

[0046] The axial position in the cross-sectional view shown in Figure 6 corresponds to the start position (second start position 65) of the second discharge groove 2. The 21st half line D21 is a half line that passes through the bottom of the second discharge groove 2 and the central axis A at the second start position 65. The start phase of the second discharge groove 2 corresponds to the phase of the 21st half line D21. The phase of the peripheral cutting edge 21 corresponds to the phase of the 23rd half line D23. The phase of the peripheral cutting edge 21 is set to 0°.

[0047] 6 , when viewed along the central axis A, the start phase of the second discharge groove 2 (second start phase θ21) is located in the range of +10° to +90° relative to the peripheral cutting edge 21. The second start phase θ21 may be located in the range of +20° to +80° relative to the peripheral cutting edge 21, or in the range of +30° to +70° relative to the peripheral cutting edge 21.

[0048] 6 and 8, the end phase of the second discharge groove 2 (second end phase θ22) is located in the range of −40° to 0° relative to the peripheral cutting edge 21. The second end phase θ22 may be located in the range of −30° to 0° relative to the peripheral cutting edge 21, or in the range of −20° to 0° relative to the peripheral cutting edge 21.

[0049] Fig. 11 is a schematic cross-sectional view taken along line XI-XI in Fig. 9A. The cross-sectional view shown in Fig. 11 is perpendicular to the central axis A. The main body portion 9 is provided with a first rear end groove 54 and a second rear end groove 64. As shown in Fig. 9A, more specifically, each of the first rear end groove 54 and the second rear end groove 64 is provided in the second body region 6. The diameter of the second body region 6 is larger than the diameter of the first body region 3. The second body region 6 has a portion whose diameter widens axially rearward.

[0050] The first rear end groove 54 is continuous with the first rear groove 52. The first rear end groove 54 is located axially rearward of the first rear groove 52. As shown in Figures 8 and 11 , in a cross section perpendicular to the central axis A, the cross-sectional area of ​​the first rear end groove 54 is smaller than the cross-sectional area of ​​the first rear groove 52. The cross-sectional area of ​​the first rear end groove 54 in a cross section perpendicular to the central axis A decreases axially rearward.

[0051] The second rear end groove 64 is continuous with the second rear groove 62. The second rear end groove 64 is located axially rearward of the second rear groove 62. As shown in Figures 8 and 11 , in a cross section perpendicular to the central axis A, the cross-sectional area of ​​the second rear end groove 64 is smaller than the cross-sectional area of ​​the second rear groove 62. The cross-sectional area of ​​the second rear end groove 64 in a cross section perpendicular to the central axis A decreases axially rearward.

[0052] In a cross section perpendicular to the central axis A, the cross-sectional area of ​​the first front groove portion 51 is defined as a first front area, and the cross-sectional area of ​​the first rear groove portion 52 is defined as a first rear area. The first front area may be larger than the first rear area. The value obtained by dividing the first front area by the first rear area may be 1.01 or greater and 1.02 or less. The value obtained by dividing the first front area by the first rear area may be 1.012 or greater and 1.018 or less, or 1.014 or greater and 1.016 or less.

[0053] In a cross section perpendicular to the central axis A, the cross-sectional area of ​​the second front groove portion 61 is defined as a second front area, and the cross-sectional area of ​​the second rear groove portion 62 is defined as a second rear area. The second front area may be larger than the second rear area. The value obtained by dividing the second front area by the second rear area may be 1.01 or greater and 1.02 or less. The value obtained by dividing the second front area by the second rear area may be 1.012 or greater and 1.018 or less, or 1.014 or greater and 1.016 or less.

[0054] 12 and 13 are imaginary planes obtained by rotating and projecting each of the first cutting insert 10 and the second cutting insert 20 around the central axis A. As shown in Fig. 12, an imaginary plane 150 includes the central axis A. On the imaginary plane 150, the foremost end position of the central cutting edge 11 is defined as a first position 71. The first position 71 is located most forward in the axial direction. On the imaginary plane 150, the intersection of the central axis A and the central cutting edge 11 is defined as a second position 72.

[0055] 13 , on the imaginary plane 150, the intersection of an imaginary line segment extending from the second position 72 in a direction perpendicular to the central axis A and the peripheral cutting edge 21 is defined as the third position 73. The tool radius is the distance from the central axis A to the outermost edge of the peripheral cutting edge 21 in the radial direction. The outermost edge of the peripheral cutting edge 21 is defined as the fifth position 75. In other words, the tool diameter E is twice the distance from the central axis A to the fifth position 75 in the radial direction. The radial direction is the direction extending radially from the central axis A. The radial direction is perpendicular to the central axis A.

[0056] 12 , the radial distance from the central axis A to the first position 71 is 30% to 40% of the tool radius. The radial distance from the central axis A to the first position 71 may be 23% to 37% of the tool radius, or 26% to 34% of the tool radius.

[0057] 13 , the radial distance from the central axis A to the third position 73 is 80% to 100% of the tool radius. The radial distance from the central axis A to the third position 73 may be 84% to 96% of the tool radius, or 88% to 92% of the tool radius.

[0058] On the imaginary plane 150, the intersection of the central cutting edge 11 and the peripheral cutting edge 21 is defined as a fourth position 74. The radial distance from the central axis A to the fourth position 74 may be greater than the radial distance from the fourth position 74 to the fifth position 75. The radial distance from the central axis A to the fourth position 74 corresponds to the effective radial length of the central cutting edge 11. The radial distance from the fourth position 74 to the fifth position 75 corresponds to the effective radial length of the peripheral cutting edge 21.

[0059] The radial distance from the central axis A to the fourth position 74 may be 1.05 times or more, or 1.1 times or more, the radial distance from the fourth position 74 to the fifth position 75 of the peripheral cutting edge 21. The radial distance from the central axis A to the fourth position 74 may be 2 times or less, or 1.8 times or less, the radial distance from the fourth position 74 to the fifth position 75.

[0060] 4A , the length of the first discharge groove 1 in the direction along the central axis A is defined as a first overall length B13. The first overall length B13 may be two to eight times the tool diameter. The first overall length B13 is the sum of the lengths of the first front groove portion 51 and the first rear groove portion 52. In the direction along the central axis A, the first overall length B13 may be two to seven times the tool diameter.

[0061] 4A , the distance from the front end of the first cutting insert 10 to the rear end of the first pocket portion 32 in the direction along the central axis A is defined as a first pocket length C1. The first pocket length C1 is 1.5 times or more the tool diameter. The front end of the first cutting insert 10 corresponds to the front-most position of the central cutting edge 11. The rear end of the first pocket portion 32 is a boundary between the surface of the first pocket portion 32, the first outer peripheral surface 4 of the first body region 3, and the surface of the first front groove portion 51.

[0062] In the direction along the central axis A, the first pocket length C1 may be 1.8 times or more the tool diameter, or may be 2 times or more the tool diameter. In the direction along the central axis A, the first pocket length C1 may be 3 times or less the tool diameter, or may be 2.5 times or less the tool diameter.

[0063] 9A , the length of the second discharge groove 2 in the direction along the central axis A is a second total length B23. The second total length B23 may be two to eight times the tool diameter. The second total length B23 is the sum of the lengths of the second front groove portion 61 and the second rear groove portion 62. In the direction along the central axis A, the second total length B23 may be two to seven times the tool diameter.

[0064] 9A , the distance from the front end of the second cutting insert 20 to the rear end of the second pocket portion 42 in the direction along the central axis A is defined as a second pocket length C2. The second pocket length C2 may be shorter than the first pocket length C1. The front end of the second cutting insert 20 corresponds to the front-most position of the peripheral cutting edge 21. The rear end of the second pocket portion 42 is a boundary between the surface of the second pocket portion 42, the first outer peripheral surface 4 of the first body region 3, and the surface of the fourth front end groove portion 94. In the direction along the central axis A, the rear end of the first pocket portion 32 may be located axially rearward of the rear end of the second pocket portion 42.

[0065] As shown in FIG. 13 , a line perpendicular to the central axis A is defined as a third line D3. A tangent to the central cutting edge 11 at the second position 72 is defined as a fourth line D4. The third line D3 passes through the second position 72. The angle formed by the third line D3 and the fourth line D4 is defined as a fourth angle θ4. The fourth angle θ4 may be 8° or less, 6° or less, or 4° or less. The fourth angle θ4 may be 1° or greater, or 2° or greater. The sine of the fourth angle θ4 (i.e., sin θ4) may be equal to or less than the value obtained by multiplying the tool diameter by 0.0070 / mm. The sine of the fourth angle θ4 may be equal to or less than the value obtained by multiplying the tool diameter by 0.0060 / mm, or may be equal to or less than the value obtained by multiplying the tool diameter by 0.0050 / mm. The sine of the fourth angle θ4 may be equal to or greater than the value obtained by multiplying the tool diameter by 0.0010 / mm, or may be equal to or greater than the value obtained by multiplying the tool diameter by 0.0020 / mm. The unit of the fourth angle θ4 is degrees. The unit of the tool diameter is mm.

[0066] Next, the effects of the drill 100 according to this embodiment will be described. In deep-hole drilling, chips generated during drilling tend to stagnate inside the hole, easily causing chip clogging. Increasing the helix angle θ3 of the discharge flute is effective for improving chip discharge. However, as the helix angle θ3 increases, the capacity of the discharge flute increases, reducing the rigidity of the main body 9 of the drill 100. As a result, the drill 100 vibrates significantly during drilling, degrading the quality of the hole formed in the workpiece.

[0067] According to the drill 100 of this embodiment, the main body 9 is provided with a first discharge flute 1 and a second discharge flute 2. The first discharge flute 1 discharges chips cut by the central cutting edge 11. The second discharge flute 2 discharges chips cut by the peripheral cutting edge 21. When viewed along the central axis A, the start phase of the first discharge flute 1 is located in a range of +10° to +90° relative to the central cutting edge 11, and the end phase of the first discharge flute 1 is located in a range of -40° to 0° relative to the central cutting edge 11. The start phase of the second discharge flute 2 is located in a range of +10° to +90° relative to the peripheral cutting edge 21, and the end phase of the second discharge flute 2 is located in a range of -40° to 0° relative to the peripheral cutting edge 21. The first discharge flute 1 has a first front groove portion 51 and a first rear groove portion 52 connected to the first front groove portion 51. The second discharge groove 2 has a second front groove portion 61 and a second rear groove portion 62 that is continuous with the second front groove portion 61. The twist angle θ3 of the first front groove portion 51 monotonically decreases toward the first rear groove portion 52. The twist angle θ3 of the second front groove portion 61 monotonically decreases toward the second rear groove portion 62. The twist angle θ3 of each of the first rear groove portion 52 and the second rear groove portion 62 is 0°. This makes it possible to improve chip discharge performance while suppressing a decrease in the rigidity of the main body portion 9. As a result, it is possible to improve the quality of the hole formed in the workpiece.

[0068] Furthermore, with the drill 100 according to this embodiment, at the boundary between the first front flute 51 and the first rear flute 52, the value obtained by dividing the amount of change in the helix angle θ3 of the first flute 1 by the amount of change in position in the direction along the central axis A is continuous. At the boundary between the second front flute 61 and the second rear flute 62, the value obtained by dividing the amount of change in the helix angle θ3 of the second flute 2 by the amount of change in position in the direction along the central axis A is continuous. This allows the first front flute 51 and the first rear flute 52 to smoothly connect, thereby preventing chips from stagnating in the first flute 1. Similarly, the second front flute 61 and the second rear flute 62 to smoothly connect, thereby preventing chips from stagnating in the second flute 2.

[0069] Since the central blade 11 is located radially closer to the central axis A than the peripheral blade 21, the cutting speed of the central blade 11 is lower than the cutting speed of the peripheral blade 21. Therefore, chips cut by the central blade 11 are more difficult to discharge than chips cut by the peripheral blade 21. In other words, the chip discharge ability of the first discharge groove 1 is lower than the chip discharge ability of the second discharge groove 2.

[0070] According to the drill 100 of this embodiment, the body 9 is provided with a first pocket 32 ​​that is continuous with the first discharge flute 1 and is located forward of the first cutting insert 10 in the rotational direction. In the direction along the central axis A, the distance from the front end of the first cutting insert 10 to the rear end of the first pocket 32 ​​is 1.5 times the tool diameter or more. Chips cut by the central cutting edge 11 curl in the first pocket. By ensuring that the distance from the front end of the first cutting insert 10 to the rear end of the first pocket 32 ​​is 1.5 times the tool diameter or more, sufficient space can be secured for chip curling. This improves the discharge of chips cut by the central cutting edge 11.

[0071] According to the drill 100 of this embodiment, the length of each of the first discharge flute 1 and the second discharge flute 2 may be two to eight times the tool diameter in the direction along the central axis A. This makes it possible to form a deep hole in the workpiece.

[0072] In the drill 100 according to the present embodiment, when the length of the first front flute portion 51 is defined as a first front length B11, the length of the first rear flute portion 52 is defined as a first rear length B12, the length of the second front flute portion 61 is defined as a second front length B21, and the length of the second rear flute portion 62 is defined as a second rear length B22, the value obtained by dividing the first front length B11 by the first rear length B12 may be 0.3 or more and 3.0 or less, and the value obtained by dividing the second front length B21 by the second rear length B22 may be 0.3 or more and 3.0 or less. This makes it possible to improve chip discharge performance while suppressing a decrease in rigidity.

[0073] The first front groove 51 has a greater effect on chip dischargeability than the first rear groove 52. Similarly, the second front groove 61 has a greater effect on chip dischargeability than the second rear groove 62.

[0074] According to the drill 100 of this embodiment, in a cross section perpendicular to the central axis A, when the cross-sectional area of ​​the first front flute portion 51 is defined as the first front area, the cross-sectional area of ​​the first rear flute portion 52 is defined as the first rear area, the cross-sectional area of ​​the second front flute portion 61 is defined as the second front area, and the cross-sectional area of ​​the second rear flute portion 62 is defined as the second rear area, the value obtained by dividing the first front area by the first rear area may be 1.01 or greater and 1.02 or less, and the value obtained by dividing the second front area by the second rear area may be 1.01 or greater and 1.02 or less. This makes it possible to further improve chip dischargeability while suppressing a decrease in rigidity.

[0075] According to the drill 100 of this embodiment, the cross-sectional area of ​​the first discharge flute 1 may be larger than the cross-sectional area of ​​the second discharge flute 2 in a cross section perpendicular to the central axis A. This makes it possible to improve the chip discharge performance of the first discharge flute 1 while suppressing a decrease in rigidity.

[0076] According to the drill 100 of this embodiment, on an imaginary plane 150 formed by rotating and projecting each of the first cutting insert 10 and the second cutting insert 20, the foremost position of the central cutting edge 11 is defined as a first position 71, the intersection of the central axis A and the central cutting edge 11 is defined as a second position 72, and the intersection of an imaginary line segment extending from the second position 72 perpendicular to the central axis A and the peripheral cutting edge 21 is defined as a third position 73. The distance from the central axis A to the first position 71 in the radial direction extending radially from the central axis A may be 30% to 40% of half the tool diameter, and the distance from the central axis A to the third position 73 in the radial direction may be 80% to 100% of half the tool diameter. This reduces cutting resistance when the drill 100 bites into a workpiece. This reduces variation in the diameter of the hole formed in the workpiece. Furthermore, the surface quality of the hole is improved.

[0077] According to the drill 100 of this embodiment, when the intersection of the central cutting edge 11 and the peripheral cutting edge 21 on the imaginary plane 150 is defined as a fourth position 74, the radial distance from the central axis A to the fourth position 74 may be greater than the radial distance from the fourth position 74 to the outermost edge of the peripheral cutting edge 21. This balances the cutting force of the peripheral cutting edge 21 and the cutting force of the central cutting edge 11 during cutting. This reduces variation in the diameter of the hole formed in the workpiece.

[0078] When the drill 100 bites into the workpiece, a large force is generated in the drill 100, which tends to cause the drill 100 to vibrate. By reducing the angle between a line perpendicular to the central axis A and a tangent to the center cutting edge 11, the force applied to the cutting insert when the center cutting edge 11 comes into contact with the workpiece can be reduced. This reduces the vibration of the drill 100. As a result, the hole diameter enlargement allowance at the entrance of the hole formed in the workpiece can be reduced.

[0079] Also, if the ratio of the holder projection length to the tool diameter is constant, the amount of displacement of the hole diameter corresponding to the hole diameter enlargement margin is proportional to (sinθ) / (tool diameter). The proportionality constant here is a value determined by the holder material, etc., and is 2 mm 2 ~200mm 2where θ is the angle between a line perpendicular to the central axis A and a tangent to the central cutting edge 11. In other words, the smaller the tool diameter, the greater the hole diameter enlargement allowance at the hole entrance. In a drill with a small tool diameter, the hole diameter enlargement allowance can be reduced by reducing the angle between a line perpendicular to the central axis A and a tangent to the central cutting edge 11.

[0080] The amount of hole diameter displacement (δ) can be calculated using the following formula 1. Here, F sin θ is the cutting resistance, θ is the central cutting edge angle, L is the protrusion length, E is Young's modulus, which depends on the material, and I is the second moment of area. I is (constant) x (tool diameter). 4 I depends on the cross-sectional shape.

[0081]

[0082] The amount of displacement of the hole diameter when the tool diameter is the reference diameter (for example, 20.0 mm) (δ s ) can be calculated using the following formula 2. The tool diameter is D S The protrusion length is L S The ratio of the extension length to the tool diameter is, for example, 5. The central cutting edge angle is θ S The cutting resistance is F sinθ S The Young's modulus is E. The second moment of area is I S It is. S is (constant) x (tool diameter) 4 That is, I S is (constant) × (D S ) 4 is.

[0083]

[0084] The amount of displacement of the hole diameter (δ) when the tool diameter is the development diameter (for example, 25.0 mm, 15.0 mm, etc.) d ) can be calculated using the following formula 3. The tool diameter is D d The protrusion length is L d When the tool diameter is the reference diameter and when the tool diameter is the developed diameter, the ratio of the extension length to the tool diameter is constant. d / D d Is, L S / D S The central cutting edge angle is equal to θ d The cutting resistance is F sinθ d The Young's modulus is E. The second moment of area is I d It is. d is (constant) x (tool diameter) 4 That is, I d is (constant) × (D d ) 4 That is, I d (D d ) 4 / (D s ) 4 ×I s As shown in Equation 3, the displacement of the holder is proportional to (sin θ) / (tool diameter), where C is a proportionality constant. Therefore, by measuring the displacement of the holder, which is the reference diameter, it is possible to calculate the displacement of different tool diameters (developed diameters).

[0085]

[0086] According to the drill 100 of this embodiment, the sine of the angle between a line perpendicular to the central axis A and a tangent to the center cutting edge 11 at the second position 72 on the imaginary plane 150 may be equal to or less than the tool diameter multiplied by 0.0070 / mm. This reduces vibration of the drill 100 when biting into the workpiece. Therefore, even when the tool diameter is small, the hole diameter enlargement allowance can be reduced.

[0087] According to the drill 100 of this embodiment, the body 9 may be provided with a second pocket 42 that is continuous with the second discharge flute 2 and is located forward in the rotational direction of the second cutting insert 20. In the direction along the central axis A, the rear end of the first pocket 32 ​​may be located axially rearward of the rear end of the second pocket 42. Chips cut by the peripheral cutting edge 21 need to curl with a small curvature, while chips cut by the central cutting edge 11 desirably curl with a large curvature. Chip disposal can be stabilized by adjusting the pocket width to suit each chip.

[0088] Example 1 (Sample Preparation) First, the drills 100 of Samples 1 to 9 were prepared. The drills 100 of Samples 3 to 8 are examples. In the examples, each of the first end point phase and the second end point phase was set to be greater than or equal to -40° and less than or equal to 0°. The drills 100 of Samples 1, 2, and 9 are comparative examples. In the comparative examples, each of the first end point phase and the second end point phase was set to be an angle smaller than -40° or greater than 0°. The first end point phase and the second end point phase in each sample are as shown in Table 1.

[0089]

[0090] As shown in Table 1, in the drills 100 of Samples 1-9, the first start phase and the second start phase were each set to 45°. The cross-sectional area of ​​the second front flute 61 was set to be smaller than the cross-sectional area of ​​the first front flute 51. The cross-sectional area of ​​the second rear flute 62 was set to be smaller than the cross-sectional area of ​​the first rear flute 52. The cross-sectional area of ​​the first front flute 51 was set to be larger than the cross-sectional area of ​​the first rear flute 52. The cross-sectional area of ​​the second front flute 61 was set to be larger than the cross-sectional area of ​​the second rear flute 62.

[0091] The length of the first pocket portion 32 was 1.58 times the tool diameter. The cutting edge length of the central cutting edge 11 was 6.7 mm. The length of the first front groove portion 51 was 49 mm. The length of the first rear groove portion 52 was 45 mm. The length of the second pocket portion 42 was 0.91 times the tool diameter. The cutting edge length of the peripheral cutting edge 21 was 6.23 mm. The length of the second front groove portion 61 was 49 mm. The length of the second rear groove portion 62 was 45 mm.

[0092] (Evaluation conditions) Next, external stress was applied to each of the cutting edges of the central cutting edge 11 and the peripheral cutting edge 21. The external stress in the direction perpendicular to the cutting face was set to 600 N. The external stress in the direction along the central axis A was set to 720 N. The external stress in the direction from the outer periphery of the cutting edge toward the central axis A was set to 100 N. For each sample, the amount of displacement at the tip at the center of the holder was measured. The amount of displacement at the tip is the distance from the three-dimensional coordinates of the measurement point before the application of the external stress to the three-dimensional coordinates of the measurement point after the application of the external stress.

[0093] (Evaluation Results) Fig. 14 is a diagram showing the displacement amounts of the drills 100 of Samples 1 to 9. As shown in Fig. 14, when each of the first end point phase and the second end point phase was between -40° and 15°, the displacement amounts were small. On the other hand, when each of the first end point phase and the second end point phase was greater than 0°, chip evacuation was difficult.

[0094] From the above results, it was confirmed that when the first end point phase and the second end point phase are each between -40° and 0°, the amount of holder displacement is small and high chip discharge performance can be achieved.

[0095] Example 2 (Sample Preparation) Next, the drills 100 of Samples 4 and 10 were prepared. The drill 100 of Sample 4 is an example. In the example, the first pocket length C1 (the length of the pocket portion on the center cutting edge side) was set to 1.5 times or more the tool diameter. Specifically, the first pocket length C1 was set to 1.58 times the tool diameter. The drill 100 of Sample 10 is a comparative example. In the comparative example, the first pocket length C1 was set to less than 1.5 times the tool diameter. Specifically, the first pocket length C1 was set to 1.01 times the tool diameter.

[0096] As shown in Table 2, for each of the drills 100 of Samples 4 and 10, the first start phase and the second start phase were each set to 45°. The first end phase and the second end phase were each set to -5°. The second pocket length C2 (the length of the pocket portion on the peripheral cutting edge side) was set to 0.91 times the tool diameter. The cutting edge length of the central cutting edge 11 was set to 6.7 mm. The length of the first front groove portion 51 was set to 49 mm. The length of the first rear groove portion 52 was set to 45 mm. The cutting edge length of the peripheral cutting edge 21 was set to 6.23 mm. The length of the second front groove portion 61 was set to 49 mm. The length of the second rear groove portion 62 was set to 45 mm.

[0097]

[0098] (Evaluation Conditions) Next, drilling was performed on workpieces using the drills 100 of Samples 4 and 10. An NVX5080 manufactured by DGM Mori Seiki Co., Ltd. was used as a vertical machining center. The workpiece was JIS G 4051 S50C. The peripheral speed Vc was 150 m / min. The feed rate f was 0.08 mm / revolution. Coolant was supplied from inside the drill 100. The oil supply pressure was 2 MPa. The wall height profile was measured on the surface of the hole formed in the workpiece.

[0099] (Evaluation Results) Figure 15 is a diagram showing the height profile of the wall surface of a hole formed using the drill 100 of Sample 4. The horizontal axis of Figure 15 represents the position in the depth direction of the hole. The horizontal axis of Figure 15 represents the height of the wall surface of the hole. The arithmetic mean roughness Ra of the hole wall surface was 1.496 µm. The root mean square roughness Rq of the hole wall surface was 1.858 µm. The maximum height roughness Rz of the hole wall surface was 9.477 µm.

[0100] FIG. 16 is a diagram showing the height profile of the wall surface of a hole formed using the drill 100 of sample 10. The horizontal axis of FIG. 16 represents the position in the depth direction of the hole. The horizontal axis of FIG. 16 represents the height of the wall surface of the hole. The arithmetic mean roughness Ra of the hole wall surface was 2.259 μm. The root mean square roughness Rq of the hole wall surface was 2.885 μm. The maximum height roughness Rz of the hole wall surface was 13.18 μm.

[0101] As shown in Figures 15 and 16, it was confirmed that increasing the first pocket length C1 reduced the surface roughness (Ra, Rq, Rz) of the hole wall. Reducing the surface roughness of the hole wall facilitates chip evacuation. Therefore, using the drill 100 of Sample 4 improved chip evacuation performance.

[0102] Example 3 (Sample Preparation) Next, drills 100 of Samples 4, 11, and 12 were prepared. The drills 100 of Samples 4 and 12 are examples. In Sample 4, the tool diameter was 20 mm, and the angle between the center cutting edge 11 and a line perpendicular to the central axis A was 8°. In Sample 12, the tool diameter was 18.5 mm, and the angle θ between the center cutting edge 11 and a line perpendicular to the central axis A was 4°. As shown in Table 3, in each of the drills 100 of Samples 4 and 12, the sine of the angle θ (i.e., sin θ) between the center cutting edge 11 and a line perpendicular to the central axis A was equal to or less than the tool diameter (mm) multiplied by 0.0070 / mm.

[0103] The drill 100 of Sample 11 is a comparative example. In Sample 11, the tool diameter was 18.5 mm, and the angle between the center cutting edge 11 and a line perpendicular to the central axis A was 8°. In the drill 100 of Sample 11, the sine of the angle θ (i.e., sin θ) between the center cutting edge 11 and a line perpendicular to the central axis A was greater than the tool diameter (mm) multiplied by 0.0070 / mm.

[0104] As shown in Table 3, for each of the drills 100 of Samples 4, 11, and 12, the first start phase and the second start phase were each set to 45°. The first end phase and the second end phase were each set to -5°. The second pocket length C2 (the length of the pocket portion on the peripheral cutting edge side) was set to 0.91 times the tool diameter. The length of the first pocket portion 32 was set to 1.58 times the tool diameter.

[0105]

[0106] (Evaluation Conditions) Next, drilling was performed on the workpiece 80 using each of the drills 100 of Samples 4, 11, and 12. An NVX5080 manufactured by DGM Mori Seiki Co., Ltd. was used as a vertical machining center. The workpiece was JIS G 4051 S50C. The peripheral speed Vc was 150 m / min. The feed rate f was 0.06 mm / revolution. Coolant was supplied from inside the drill 100. The oil supply pressure was 2 MPa.

[0107] (Evaluation Results) Figure 17 is a cross-sectional schematic diagram showing the shapes of holes formed using the drills 100 of Samples 4, 11, and 12. As shown in Figure 17, the diameter of the hole is enlarged at the entrance of the hole formed in the workpiece 80. The hole diameter at the back is a first diameter W1. The first diameter W1 is substantially the same as the tool diameter. The hole diameter at the entrance is a third diameter W3. The third diameter W3 is larger than the first diameter W1.

[0108] As shown in Table 1, the first diameter W1 at the depth of the hole formed using the drills 100 of Samples 4, 11, and 12 was 20.1 mm, 18.8 mm, and 18.8 mm, respectively. The third diameter W3 at the entrance of the hole formed using the drills 100 of Samples 4, 11, and 12 was 20.2 mm, 20.0 mm, and 18.8 mm, respectively. The hole diameter enlargement W2, which is the difference between the third diameter W3 and the first diameter W1, was 0.1 mm, 1.2 mm, and 0.0 mm, respectively. The cutting forces at the entrance of the hole formed using the drills 100 of Samples 4, 11, and 12 were 550 N, 750 N, and 500 N, respectively.

[0109] From the above results, it was confirmed that by setting the sine of the angle θ (i.e., sin θ) between the center cutting edge 11 and a line perpendicular to the center axis A to a value equal to or less than the tool diameter multiplied by 0.0070 / mm, it is possible to reduce the cutting resistance at the entrance of the hole and the hole diameter expansion allowance W2.

[0110] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not the above description, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0111] 1 First discharge groove, 2 Second discharge groove, 3 First body region, 4 First outer peripheral surface, 5 Shank, 6 Second body region, 7 Coolant supply hole, 9 Body portion, 10 First cutting insert, 11 Central cutting edge, 19 Central cutting edge mounting screw, 20 Second cutting insert, 21 Peripheral cutting edge, 29 Peripheral cutting edge mounting screw, 31 First insert placement surface portion, 32 First pocket portion, 33 First insert placement groove, 41 Second insert placement surface portion, 42 Second pocket portion, 43 Second insert placement groove, 51 First front groove portion, 52 First rear groove portion, 54 First rear end groove portion, 55 First start point position, 56 First end point position, 57 First boundary, 61 Second front groove portion, 62 Second rear groove portion, 64 Second rear end groove portion, 65 Second start point position, 66 Second end point position, 67 Second boundary, 71 First position, 72 Second position, 73 Third position, 74 Fourth position, 75 Fifth position, 80 Workpiece, 91 First front end groove portion, 92 Second front end groove portion, 93 Third front end groove portion, 94 Fourth front end groove portion, 100 Drill, 101 Front end face, 102 Rear end face, 150 Virtual plane, A Central axis, B11 First front length, B12 First rear length, B13 First overall length, B21 Second front length, B22 Second rear length, B23 Second overall length, C1 First pocket length, C2 Second pocket length, D11 Eleventh half ray, D12 Twelfth half ray, D13 Thirteenth half ray, D21 Twenty-first half ray, D22 Twenty-second half ray, D23 Twenty-third half ray, D3 Third line, D4 ​​Fourth line, E Tool diameter, F1 First virtual arc, F2 Second virtual arc.

Claims

1. A drill that rotates around a central axis, comprising: a first cutting insert having a central blade; a second cutting insert having a peripheral blade; and a main body to which the first cutting insert and the second cutting insert are attached, the main body being provided with a first discharge groove for discharging chips cut by the central blade and a second discharge groove for discharging chips cut by the peripheral blade, wherein, as viewed along the central axis, a start phase of the first discharge groove is located in a range of +10° to +90° relative to the central blade, an end phase of the first discharge groove is located in a range of -40° to 0° relative to the central blade, a start phase of the second discharge groove is located in a range of +10° to +90° relative to the peripheral blade, and an end phase of the second discharge groove is located in a range of -40° to 0° relative to the peripheral blade, the first discharge groove has a first front groove portion and a first rear groove portion connected to the first front groove portion, the second discharge groove has a second front groove portion and a second rear groove portion connected to the second front groove portion, a twist angle of the first front groove portion monotonically decreasing toward the first rear groove portion, the twist angle of the second front groove portion monotonically decreasing toward the second rear groove portion, each of the twist angles of the first rear groove portion and the second rear groove portion is 0°, a value obtained by dividing an amount of change in the twist angle of the first discharge groove by an amount of change in position in the direction along the central axis at a boundary between the first front groove portion and the first rear groove portion is continuous, a value obtained by dividing an amount of change in the twist angle of the second discharge groove by an amount of change in position in the direction along the central axis at a boundary between the second front groove portion and the second rear groove portion is continuous, the main body portion is provided with a first pocket portion connected to the first discharge groove and located forward of the first cutting insert in a rotational direction, A drill, wherein a distance from a front end of the first cutting insert to a rear end of the first pocket portion in a direction along the central axis is 1.5 times or more of a tool diameter.

2. The drill according to claim 1, wherein the length of each of the first discharge groove and the second discharge groove in the direction along the central axis is not less than two times and not more than eight times the tool diameter.

3. A drill as described in claim 1 or claim 2, wherein, in a direction along the central axis, when the length of the first front groove portion is a first front length, the length of the first rear groove portion is a first rear length, the length of the second front groove portion is a second front length, and the length of the second rear groove portion is a second rear length, a value obtained by dividing the first front length by the first rear length is greater than or equal to 0.3 and less than or equal to 3.0, and a value obtained by dividing the second front length by the second rear length is greater than or equal to 0.3 and less than or equal to 3.

0.

4. The drill according to any one of claims 1 to 3, wherein, in a cross section perpendicular to the central axis, when the cross-sectional area of ​​the first front groove portion is a first front area, the cross-sectional area of ​​the first rear groove portion is a first rear area, the cross-sectional area of ​​the second front groove portion is a second front area, and the cross-sectional area of ​​the second rear groove portion is a second rear area, a value obtained by dividing the first front area by the first rear area is equal to or greater than 1.01 and equal to or less than 1.02, and a value obtained by dividing the second front area by the second rear area is equal to or greater than 1.01 and equal to or less than 1.

02.

5. The drill according to any one of claims 1 to 4, wherein in a cross section perpendicular to the central axis, the cross-sectional area of ​​the first discharge groove is larger than the cross-sectional area of ​​the second discharge groove.

6. A drill as claimed in any one of claims 1 to 5, wherein, in an imaginary plane formed by rotational projection of each of the first cutting insert and the second cutting insert, the forward end position of the central blade is defined as a first position, the intersection of the central axis and the central blade is defined as a second position, and the intersection of a virtual line segment extending from the second position in a direction perpendicular to the central axis and the peripheral blade is defined as a third position, wherein the distance from the central axis to the first position in a radial direction extending radially from the central axis is between 30% and 40% of half the tool diameter, and the distance from the central axis to the third position in the radial direction is between 80% and 100% of half the tool diameter.

7. A drill as described in claim 6, wherein, when the intersection of the central cutting edge and the peripheral cutting edge on the imaginary plane is defined as a fourth position, the distance from the central axis to the fourth position in the radial direction is greater than the distance from the fourth position in the radial direction to the outermost end of the peripheral cutting edge.

8. The drill according to claim 6 or 7, wherein the sine of the angle between a straight line perpendicular to the central axis and a tangent to the central cutting edge at the second position on the imaginary plane is equal to or less than the tool diameter multiplied by 0.0070 / mm, the angle is expressed in degrees, and the tool diameter is expressed in mm.

9. A drill as described in any one of claims 1 to 8, wherein the main body portion is provided with a second pocket portion that is connected to the second discharge groove and is located forward in the direction of rotation than the second cutting insert, and in the direction along the central axis, the rear end of the first pocket portion is located axially rearward of the rear end of the second pocket portion.

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