Drill bit

Abstract

When viewed along the center axis, the start phase of the first discharge groove is in the range of + 10 DEG to + 90 DEG with respect to the center blade, the end phase of the first discharge groove is in the range of-40 DEG to 0 DEG with respect to the center blade, and the start phase of the second discharge groove is in the range of + 10 DEG to + 90 DEG with respect to the outer peripheral blade. The termination phase of the second discharge groove is within the range of-40 DEG to 0 DEG with respect to the outer 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. 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 torsion angles of the first rear groove portion and the second rear groove portion are respectively 0 degree.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a drill bit. This application claims priority based on International Application No. PCT / JP2023 / 025141 filed on July 6, 2023. The entire disclosure of the application is incorporated herein by reference. BACKGROUND

[0002] In International Publication No. 2013 / 018764 (Patent Literature 1), a holder for a cutting tool having a helical groove portion and a straight groove portion is described. The helical groove portion intersects with a rotation center axis at a certain angle when viewed from the side.

[0003] PRIOR ART DOCUMENTS PATENT LITERATURE Patent Literature 1: International Publication No. 2013 / 018764 SUMMARY

[0004] The drill bit according to the present disclosure rotates around a center axis, and includes a first cutting insert, a second cutting insert, and a main body portion. The first cutting insert has a center edge. The second cutting insert has a peripheral edge. The first cutting insert and the second cutting insert are attached to the main body portion. A first discharge groove and a second discharge groove are provided in the main body portion. The first discharge groove discharges chips cut by the center edge. The second discharge groove discharges chips cut by the peripheral edge. When viewed along the center axis, a start phase of the first discharge groove is located in a range of +10° or more and +90° or less with respect to the center edge, an end phase of the first discharge groove is located in a range of -40° or more and 0° or less with respect to the center edge, a start phase of the second discharge groove is located in a range of +10° or more and +90° or less with respect to the peripheral edge, and an end phase of the second discharge groove is located in a range of -40° or more and 0° or less with respect to the peripheral 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. A twist angle of the first front groove portion monotonously decreases toward the first rear groove portion. A twist angle of the second front groove portion monotonously decreases toward the second rear groove portion. Twist angles of the first rear groove portion and the second rear groove portion are 0°, respectively. At a boundary between the first front groove portion and the first rear groove portion, a value obtained by dividing a change amount of the twist angle of the first discharge groove by a change amount of a position in a direction along the center axis is continuous. At a boundary between the second front groove portion and the second rear groove portion, a value obtained by dividing a change amount of the twist angle of the second discharge groove by a change amount of a position in a direction along the center axis is continuous. A first recessed groove portion connected to the first discharge groove and located forward of the first cutting insert in a rotation direction is provided in the main body portion. A distance from a front end of the first cutting insert to a rear end of the first recessed groove portion in the direction along the center axis is 1.5 times or more of a tool diameter. BRIEF DESCRIPTION OF DRAWINGS

[0005] Figure 1 is a first perspective view showing the configuration of the drill bit according to the present embodiment.

[0006] Figure 2 is a second perspective view showing the configuration of the drill bit according to the present embodiment.

[0007] Figure 3 is a left side view showing the configuration of the drill bit according to the present embodiment.

[0008] Figure 4A is a first front view showing the configuration of the drill bit according to the present embodiment.

[0009] Figure 4B is a second front view showing the configuration of the drill bit according to the present embodiment.

[0010] Figure 5 is a cross-sectional view along the V-V line of Figure 4A .

[0011] Figure 6 is a cross-sectional view along the VI-VI line of Figure 4A .

[0012] Figure 7 is a cross-sectional view along the VII-VII line of Figure 4A .

[0013] Figure 8 is a cross-sectional view along the VIII-VIII line of Figure 4A .

[0014] Figure 9A is a first back view showing the configuration of the drill bit according to the present embodiment.

[0015] Figure 9B is a second back view showing the configuration of the drill bit according to the present embodiment.

[0016] Figure 10 is a cross-sectional view along the X-X line of Figure 9A .

[0017] Figure 11 is a cross-sectional view along the XI-XI line of Figure 9A .

[0018] Figure 12 are imaginary planes obtained by rotating and projecting the first cutting insert and the second cutting insert, respectively.

[0019] Figure 13is a virtual plane after the rotational projection of the first cutting insert and the second cutting insert, respectively.

[0020] Figure 14 is a graph showing the displacement amount of the drill bit of Sample 1 to Sample 9.

[0021] Figure 15 is a graph showing the height profile of the wall surface of the hole formed using the drill bit of Sample 4.

[0022] Figure 16 is a graph showing the height profile of the wall surface of the hole formed using the drill bit of Sample 10.

[0023] Figure 17 is a cross-sectional schematic view showing the shape of the hole formed using the drill bit 100 of Sample 4, Sample 11, and Sample 12, respectively. DETAILED DESCRIPTION

[0024] [Problem to be Solved by the Present Disclosure] An object of the present disclosure is to provide a drill capable of suppressing a decrease in rigidity and improving chip dischargeability.

[0025] [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a drill capable of suppressing a decrease in rigidity and improving chip dischargeability.

[0026] [Explanation of Embodiments of the Present Disclosure] First, an embodiment of the present disclosure will be described.

[0027] (1) The drill bit 100 according to the present disclosure rotates around a center axis A, and has a first cutting insert 10, a second cutting insert 20, and a main body 9. The first cutting insert 10 has a center blade 11. The second cutting insert 20 has an outer peripheral blade 21. The first cutting insert 10 and the second cutting insert 20 are installed in the main body 9. A first discharge groove 1 and a second discharge groove 2 are provided in the main body 9. The first discharge groove 1 discharges chips cut by the center blade 11. The second discharge groove 2 discharges chips cut by the outer peripheral blade 21. When viewed along the center axis A, a start phase of the first discharge groove 1 is located in a range of +10° or more and +90° or less with respect to the center blade 11, an end phase of the first discharge groove 1 is located in a range of -40° or more and 0° or less with respect to the center blade 11, a start phase of the second discharge groove 2 is located in a range of +10° or more and +90° or less with respect to the outer peripheral blade 21, and an end phase of the second discharge groove 2 is located in a range of -40° or more and 0° or less with respect to the outer peripheral blade 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. A twist angle of the first front groove portion 51 monotonously decreases as it goes toward the first rear groove portion 52. A twist angle of the second front groove portion 61 monotonously decreases as it goes toward the second rear groove portion 62. Twist angles of the first rear groove portion 52 and the second rear groove portion 62 are 0° respectively. At a boundary between the first front groove portion 51 and the first rear groove portion 52, a value obtained by dividing a change amount of the twist angle of the first discharge groove 1 by a change amount of a position in a direction along the center axis A is continuous. At a boundary between the second front groove portion 61 and the second rear groove portion 62, a value obtained by dividing a change amount of the twist angle of the second discharge groove 2 by a change amount of a position in a direction along the center axis A is continuous. The main body 9 is provided with a first recess portion 32 connected to the first discharge groove 1 and located forward of the first cutting insert 10 in a rotation direction. A distance from a front end of the first cutting insert 10 to a rear end of the first recess portion 32 in a direction along the center axis A is 1.5 times or more of a tool diameter.

[0028] (2) According to the drill bit 100 according to the above (1), the length of the first discharge groove 1 and the length of the second discharge groove 2 in a direction along the center axis A can each be 2 times or more and 8 times or less of the tool diameter.

[0029] (3) The drill bit 100 according to any one of the above (1) or (2) can also be such that, in a direction along the central axis A, in a case where a length of the first front groove portion 51 is a first front length, a length of the first rear groove portion 52 is a first rear length, a length of the second front groove portion 61 is a second front length, and a length of the second rear groove portion 62 is a second rear length, a value obtained by dividing the first front length by the first rear length is 0.3 or more and 3.0 or less, and a value obtained by dividing the second front length by the second rear length is 0.3 or more and 3.0 or less.

[0030] (4) The drill bit 100 according to any one of the above (1) to (3) can also be such that, in a cross section perpendicular to the central axis A, in a case where a cross-sectional area of the first front groove portion 51 is a first front cross-sectional area, a cross-sectional area of the first rear groove portion 52 is a first rear cross-sectional area, a cross-sectional area of the second front groove portion 61 is a second front cross-sectional area, and a cross-sectional area of the second rear groove portion 62 is a second rear cross-sectional area, a value obtained by dividing the first front cross-sectional area by the first rear cross-sectional area is 1.01 or more and 1.02 or less, and a value obtained by dividing the second front cross-sectional area by the second rear cross-sectional area is 1.01 or more and 1.02 or less.

[0031] (5) The drill bit 100 according to any one of the above (1) to (4) can also be such that, in a cross section perpendicular to the central axis A, the cross-sectional area of the first discharge groove 1 is larger than the cross-sectional area of the second discharge groove 2.

[0032] (6) The drill bit 100 according to any one of the above (1) to (5) can also be such that, in an imaginary plane in which the first cutting insert 10 and the second cutting insert 20 are respectively rotationally projected, in a case where a most front end position of the center blade 11 is a first position 71, an intersection of the central axis A and the center blade 11 is a second position 72, and an intersection of an imaginary line segment extending from the second position 72 in a direction perpendicular to the central axis A and the outer peripheral blade 21 is a third position 73, a distance in a radial direction from the central axis A to the first position 71 is 30% or more and 40% or less of half of a tool diameter, and a distance in the radial direction from the central axis A to the third position 73 is 80% or more and 100% or less of half of the tool diameter.

[0033] (7) The drill bit 100 according to the above (6) can also be such that, in the imaginary plane, in a case where an intersection of the center blade 11 and the outer peripheral blade 21 is a fourth position 74, a distance in the radial direction from the central axis A to the fourth position 74 is larger than a distance in the radial direction from the fourth position 74 to a most outer peripheral end of the outer peripheral blade 21.

[0034] (8) The drill bit 100 according to any one of the above (6) or (7) can also be such that, in the imaginary plane, the sine of the angle formed by the straight line perpendicular to the center axis A and the tangent line to the center blade 11 at the second position 72 is equal to or less than the value obtained by multiplying the tool diameter by 0.0070 / mm. The angle is in °, and the tool diameter is in mm.

[0035] (9) The drill bit 100 according to any one of the above (1) to (8) can also be such that the main body 9 is provided with a second recessed groove portion 42 connected to the second discharge groove 2 and located forward of the second cutting insert 20 in the rotation direction. It can also be such that, in the direction along the center axis A, the rear end of the first recessed groove portion 32 is located rearward of the rear end of the second recessed groove portion 42 in the axial direction.

[0036] [Details of Embodiments of the Present Disclosure] Next, the details of an 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 equivalent parts are denoted by the same reference numerals, and repeated descriptions will not be given.

[0037] First, the configuration of the drill bit 100 according to the present embodiment will be described.

[0038] Figure 1 is a first perspective view showing the configuration of the drill bit 100 according to the present embodiment. Figure 2 is a second perspective view showing the configuration of the drill bit 100 according to the present embodiment. As Figure 1 and Figure 2 shown, the drill bit 100 according to the present embodiment is provided with a first cutting insert 10, a second cutting insert 20, a main body 9, a center blade mounting screw 19, and a peripheral blade mounting screw 29. The first cutting insert 10 has a center blade 11. The second cutting insert 20 has a peripheral blade 21. The first cutting insert 10 and the second cutting insert 20 are mounted to the main body 9. The first cutting insert 10 is mounted to the main body 9 using the center blade mounting screw 19. The second cutting insert 20 is mounted to the main body 9 using the peripheral blade mounting screw 29.

[0039] The drill bit 100 is rotatable around a center axis A. 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 center blade 11. The second discharge groove 2 discharges chips cut by the peripheral blade 21.

[0040] As Figure 1As shown, the main body 9 has a first main body region 3, a second main body region 6, and a shank 5. The front end face 101 of the main body 9 is formed by the first main body region 3. The front end face 101 of the main body 9 is the portion opposite to the workpiece being cut. The second main body region 6 is connected to both the first main body region 3 and the shank 5. The second main body region 6 is located between the first main body region 3 and the shank 5. The rear end face 102 of the main body 9 is located on the opposite side of the front end face 101. The rear end face 102 of the main body 9 is formed by the shank 5. The shank 5 is the portion mounted on the device that rotates the drill bit 100.

[0041] In this specification, the direction parallel to the central axis A and extending from the rear end face 102 toward the front end face 101 is referred to as the axial forward direction. Conversely, the direction parallel to the central axis A and extending from the front end face 101 toward the rear end face 102 is referred to as the axial rearward direction. In a plane perpendicular to the central axis A, the direction extending radially from the central axis A is referred to as the radial direction.

[0042] like Figure 1 As shown, a first insertion configuration surface 31 and a first recessed portion 32 are provided in the first main body region 3. A first insertion configuration groove 33 is formed in the first insertion configuration surface 31. A first cutting blade 10 is disposed in the first insertion configuration groove 33. The first recessed portion 32 is located in front of the first cutting blade 10 in the rotational direction. The first recessed portion 32 is connected to the first discharge groove 1. At least a portion of the first recessed portion 32 is located in front of the first discharge groove 1 in the axial direction. The first recessed portion 32 is connected to the front end surface 101.

[0043] like Figure 2 As shown, a second insertion configuration surface 41 and a second recessed portion 42 are provided in the first main body region 3. A second insertion configuration groove 43 is formed in the second insertion configuration surface 41. A second cutting blade 20 is disposed in the second insertion configuration groove 43. The second recessed portion 42 is located in front of the second cutting blade 20 in the rotational direction. The second recessed portion 42 is connected to the second discharge groove 2. At least a portion of the second recessed portion 42 is located in front of the second discharge groove 2 in the axial direction. The second recessed portion 42 is connected to the front end surface 101.

[0044] like Figure 1 as well as Figure 2 As shown, 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 exposed outward from the first outer peripheral surface 4. The first insertion configuration surface 31 and the first groove portion 32 can also be connected to the first outer peripheral surface 4. Similarly, the second insertion configuration surface 41 and the second groove portion 42 can also be connected to the first outer peripheral surface 4.

[0045] Figure 3 This is a left-side schematic diagram showing the configuration of the drill bit 100 according to this embodiment.Figure 3 As shown, the first outer peripheral surface 4 is circular arc-shaped as viewed in the direction along the center axis A. The outer peripheral surface of the second main body region 6 surrounds the first outer peripheral surface 4. The outer peripheral surface of the second main body region 6 is substantially circular as viewed in the direction along the center axis A. Two coolant supply holes 7 can also be formed in the main body portion 9. The two coolant supply holes 7 are exposed at the front end surface 101 of the main body portion 9.

[0046] The first cutting insert 10 is disposed closer to the center axis A than the second cutting insert 20. The first cutting insert 10 can intersect the center axis A as viewed in the direction along the center axis A. More specifically, the central edge 11 of the first cutting insert 10 can intersect the center axis A as viewed in the direction along the center axis A. The second cutting insert 20 is disposed farther from the center axis A than the first cutting insert 10. The second cutting insert 20 is farther from the center axis A as viewed in the direction along the center axis A. More specifically, the outer peripheral edge 21 of the second cutting insert 20 does not intersect the center axis A as viewed in the direction along the center axis A.

[0047] As shown, the first outer peripheral surface 4 is circular arc-shaped as viewed in the direction along the center axis A. The outer peripheral surface of the second main body region 6 surrounds the first outer peripheral surface 4. The outer peripheral surface of the second main body region 6 is substantially circular as viewed in the direction along the center axis A. Two coolant supply holes 7 can also be formed in the main body portion 9. The two coolant supply holes 7 are exposed at the front end surface 101 of the main body portion 9. Figure 3 As shown, the first outer peripheral surface 4 is circular arc-shaped as viewed in the direction along the center axis A. The outer peripheral surface of the second main body region 6 surrounds the first outer peripheral surface 4. The outer peripheral surface of the second main body region 6 is substantially circular as viewed in the direction along the center axis A. Two coolant supply holes 7 can also be formed in the main body portion 9. The two coolant supply holes 7 are exposed at the front end surface 101 of the main body portion 9.

[0048] Figure 4A As shown, the first outer peripheral surface 4 is circular arc-shaped as viewed in the direction along the center axis A. The outer peripheral surface of the second main body region 6 surrounds the first outer peripheral surface 4. The outer peripheral surface of the second main body region 6 is substantially circular as viewed in the direction along the center axis A. Two coolant supply holes 7 can also be formed in the main body portion 9. The two coolant supply holes 7 are exposed at the front end surface 101 of the main body portion 9. Figure 4B As shown, the first outer peripheral surface 4 is circular arc-shaped as viewed in the direction along the center axis A. The outer peripheral surface of the second main body region 6 surrounds the first outer peripheral surface 4. The outer peripheral surface of the second main body region 6 is substantially circular as viewed in the direction along the center axis A. Two coolant supply holes 7 can also be formed in the main body portion 9. The two coolant supply holes 7 are exposed at the front end surface 101 of the main body portion 9. Figure 4A As shown, the first outer peripheral surface 4 is circular arc-shaped as viewed in the direction along the center axis A. The outer peripheral surface of the second main body region 6 surrounds the first outer peripheral surface 4. The outer peripheral surface of the second main body region 6 is substantially circular as viewed in the direction along the center axis A. Two coolant supply holes 7 can also be formed in the main body portion 9. The two coolant supply holes 7 are exposed at the front end surface 101 of the main body portion 9. Figure 4B As shown, the first outer peripheral surface 4 is circular arc-shaped as viewed in the direction along the center axis A. The outer peripheral surface of the second main body region 6 surrounds the first outer peripheral surface 4. The outer peripheral surface of the second main body region 6 is substantially circular as viewed in the direction along the center axis A. Two coolant supply holes 7 can also be formed in the main body portion 9. The two coolant supply holes 7 are exposed at the front end surface 101 of the main body portion 9.

[0049] 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 the position in the direction of 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 slowly. Specifically, in the region from the boundary (first boundary 57) between the first front groove portion 51 and the first rear groove portion 52 to the position separated by the tool diameter x 1.0 in the axial forward direction, 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 the position in the direction of the central axis A (in other words, the tool diameter x 1.0) is (2.0)° / mm or less.

[0050] In the direction of the central axis A, the length of the first front groove portion 51 is a first front length B11, and the length of the first rear groove portion 52 is 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 or more and 3.0 or less. The value obtained by dividing the first front length B11 by the first rear length B12 can be, for example, 0.5 or more and 2.0 or less, or 0.7 or more and 1.5 or less.

[0051] Figure 5 is a cross-sectional view along the V-V line of Figure 4A . Figure 5 The cross-sectional view shown in FIG. 8 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 can 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 portion 9 constituting the first discharge groove 1 and the first imaginary circular arc F1 along the first outer peripheral surface 4. Likewise, the cross-sectional area of the second discharge groove 2 is the area of the region surrounded by the surface of the main body portion 9 constituting the second discharge groove 2 and the second imaginary circular arc F2 along the first outer peripheral surface 4. The radii of curvature of the first imaginary circular arc F1 and the second imaginary circular arc F2 are substantially the same as the radius of curvature of the first outer peripheral surface 4, respectively.

[0052] Figure 6 is a cross-sectional view along the VI-VI line of Figure 4A . Figure 6 The cross-sectional view shown in FIG. 10 is perpendicular to the central axis A. As shown in FIG. 10, the first front end groove portion 91 and the second front end groove portion 92 are provided in the main body portion 9. Figure 1 Figure 6 As shown in FIG. 11, the first front end groove portion 91 is provided in the first insertion arrangement surface portion 31. The second front end groove portion 92 is provided in the first recess portion 32. The second front end groove portion 92 is separated from the first front end groove portion 91.

[0053] As shown in FIG. 12, the first front end groove portion 91 is provided in the first insertion arrangement surface portion 31. The second front end groove portion 92 is provided in the first recess portion 32. The second front end groove portion 92 is separated from the first front end groove portion 91. Figure 1 Figure 4A ​​As shown, in the axial direction, the first front end groove 91 and the second front end groove 92 are respectively located in front of the first front groove 51. The first front end groove 91 and the second front end groove 92 are respectively connected to the first front groove 51. The position where the first front end groove 91 and the second front end groove 92 meet is the boundary between the first front end groove 91 and the second front end groove 92 and the first front groove 51. In other words, the position where the first front end groove 91 and the second front end groove 92 meet and the boundary of the first front groove 51 is the starting position of the first discharge groove 1.

[0054] Figure 7 It is along Figure 4A A schematic diagram of the cross section of line VII-VII. Figure 7 The cross-sectional view shown is perpendicular to the central axis A. Figure 7 The axial position of the cross-sectional view shown corresponds to the starting position (first starting position 55) of the first discharge groove 1. The eleventh half-line D11 is a half-line passing through the bottom of the first discharge groove 1 and the central axis A at the first starting position 55. The bottom of the first discharge groove 1 is the point on the first discharge groove 1 closest to the central axis A in the cross-section perpendicular to the central axis A. The starting phase of the first discharge groove 1 corresponds to the phase of the eleventh half-line D11. The phase of the central blade 11 corresponds to the phase of the thirteenth half-line D13. The phase of the central blade 11 is 0°.

[0055] like Figure 7 As shown, when viewed along the central axis A, the initial phase (first initial phase θ11) of the first discharge groove 1 is located in the range of +10° to +90° relative to the central blade 11. When viewed along the central axis A, the first initial phase θ11 can be located in the range of +20° to +80° relative to the central blade 11, or it can be located in the range of +30° to +70° relative to the central blade 11. Furthermore, in this specification, the phase forward of the rotation direction is positive. Conversely, the phase backward of the rotation direction is negative. Additionally, the phase is N × 360° (where N is an integer) when rotating N revolutions in the rotation direction to achieve the same phase. For example, the phase is +360° when rotating one revolution forward in the rotation direction to achieve the same phase, and +720° when rotating two revolutions in the rotation direction to achieve the same phase.

[0056] Figure 8 It is along Figure 4A A schematic diagram of the cross section of line VIII-VIII. Figure 8 The cross-sectional view shown is perpendicular to the central axis A. Figure 8The position of the axis of the cross-sectional view corresponds to the termination position (first termination position 56) of the first discharge groove 1. The twelfth half-line D12 is a half-line that passes through the bottom of the first discharge groove 1 and the center axis A at the first termination position 56. The termination phase of the first discharge groove 1 corresponds to the phase of the twelfth half-line D12.

[0057] As shown in Figure 7 and Figure 8 shown, the termination phase (first termination phase θ12) of the first discharge groove 1, as viewed along the center axis A, is located in a range of -40° or more and 0° or less with respect to the center blade 11. The first termination phase θ12, as viewed along the center axis A, can be located in a range of -30° or more and 0° or less with respect to the center blade 11, or in a range of -20° or more and 0° or less with respect to the center blade 11.

[0058] In the axial direction, the first termination position 56 can also be the same as the termination position (second termination position 66) of the second discharge groove 2. The twelfth half-line D22 is a half-line that passes through the bottom of the second discharge groove 2 and the center axis A at the second termination position 66. The bottom of the second discharge groove 2 is a point on the second discharge groove 2 that is closest to the center axis A in a cross section perpendicular to the center axis A. The termination phase of the second discharge groove 2 corresponds to the phase of the twelfth half-line D22.

[0059] As shown in Figure 8 and Figure 8 shown, the twelfth half-line D22 and the twelfth half-line D12 can be located on the same straight line, as viewed along the center axis A. From another viewpoint, the phase of the twelfth half-line D22 can be located at a position that is rotationally moved by +180° with respect to the twelfth half-line D12. As shown in

[0060] Figure 9A and Figure 9B is a back surface schematic view that shows the configuration of the drill bit 100 according to the present embodiment. As shown in Figure 9A and Figure 9B shown, the second discharge groove 2 has a second front groove portion 61 and a second rear groove portion 62. The second rear groove portion 62 is connected to the second front groove portion 61. The second rear groove portion 62 is located axially rearward with respect to the second front groove portion 61. The twist angle θ3 of the second front groove portion 61 monotonically decreases as it goes toward the second rear groove portion 62. The twist angle θ3 of the second rear groove portion 62 is 0°. From another viewpoint, the second rear groove portion 62 extends along the center axis A.

[0061] 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 change amount of the twist angle θ3 of the second discharge groove 2 by the change amount of the position in the direction of 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 slowly. Specifically, in the region from the boundary (second boundary 67) between the second front groove portion 61 and the second rear groove portion 62 to the position separated by the tool diameter x 1.0 in the axial forward direction, the value obtained by dividing the change amount of the twist angle θ3 of the second discharge groove 2 by the change amount of the position in the direction of the central axis A (that is, the tool diameter x 1.0) is 2.0° / mm or less.

[0062] In the direction of 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 or more and 3.0 or less. The value obtained by dividing the second front length B21 by the second rear length B22 can be, for example, 0.5 or more and 2.0 or less, or 0.7 or more and 1.5 or less.

[0063] Figure 10 is a cross-sectional view along the X-X line of Figure 9A . Figure 10 The cross-sectional view shown in FIG. 8 is perpendicular to the central axis A. As shown in FIG. 8, the second front groove portion 61 and the second rear groove portion 62 are connected to each other. Figure 2 As shown in FIG. 8, the second front groove portion 61 and the second rear groove portion 62 are connected to each other. Figure 10 As shown in FIG. 8, the second front groove portion 61 and the second rear groove portion 62 are connected to each other.

[0064] As shown in FIG. 8, in the axial direction, the third front groove portion 93 and the fourth front groove portion 94 are located forward of the second discharge groove 2, respectively. The third front groove portion 93 and the fourth front groove portion 94 are connected to the second front groove portion 61, respectively. The position at which the third front groove portion 93 and the fourth front groove portion 94 converge is the boundary of the second front groove portion 61 for each of the third front groove portion 93 and the fourth front groove portion 94. In other words, the position at which the third front groove portion 93 and the fourth front groove portion 94 converge and the boundary of the second front groove portion 61 are the start position of the second discharge groove 2. Figure 2

[0065] Figure 6 ​The axial position of the cross-sectional view shown corresponds to the starting position (second starting position 65) of the second discharge groove 2. The twenty-first half-line D21 is a half-line passing through the bottom of the second discharge groove 2 and the central axis A at the second starting position 65. The starting phase of the second discharge groove 2 corresponds to the phase of the twenty-first half-line D21. The phase of the outer peripheral blade 21 corresponds to the phase of the twenty-third half-line D23. The phase of the outer peripheral blade 21 is 0°.

[0066] like Figure 6 As shown, when viewed along the central axis A, the initial phase (second initial phase θ21) of the second discharge groove 2 is located in the range of +10° to +90° relative to the outer peripheral blade 21. The second initial phase θ21 can be located in the range of +20° to +80° relative to the outer peripheral blade 21, or it can be located in the range of +30° to +70° relative to the outer peripheral blade 21.

[0067] like Figure 6 as well as Figure 8 As shown, the termination phase (second termination phase θ22) of the second discharge groove 2 is located in the range of -40° or more and 0° or less relative to the outer peripheral blade 21. The second termination phase θ22 can be located in the range of -30° or more and 0° or less relative to the outer peripheral blade 21, or it can be located in the range of -20° or more and 0° or less relative to the outer peripheral blade 21.

[0068] Figure 11 It is along Figure 9A A schematic diagram of the cross section of the XI-XI line. Figure 11 The cross-sectional view shown is perpendicular to the central axis A. A first rear end groove 54 and a second rear end groove 64 are provided in the main body 9. Figure 9A As shown, and more specifically, the first rear end groove 54 and the second rear end groove 64 are respectively disposed in the second main body region 6. The diameter of the second main body region 6 is larger than the diameter of the first main body region 3. The second main body region 6 has a portion whose diameter increases as it moves axially rearward.

[0069] The first rear end groove 54 is connected to the first rear end groove 52. The first rear end groove 54 is located axially rearward than the first rear end groove 52. Figure 8 as well as Figure 11 As shown, in a cross-section perpendicular to the central axis A, the cross-sectional area of ​​the first rear end groove 54 is smaller than that of the first rear end groove 52. The cross-sectional area of ​​the first rear end groove 54 in the cross-section perpendicular to the central axis A decreases as it moves axially rearward.

[0070] The second rear end groove 64 is connected to the second rear end groove 62. The second rear end groove 64 is located axially rearward than the second rear end groove 62. Figure 8 as well as Figure 11As shown, in a section perpendicular to the central axis A, the cross-sectional area of ​​the second rear end groove 64 is smaller than that of the second rear end groove 62. The cross-sectional area of ​​the second rear end groove 64 in the section perpendicular to the central axis A decreases as it moves axially rearward.

[0071] In a cross-section perpendicular to the central axis A, with the cross-sectional area of ​​the first front groove 51 as the first front area and the cross-sectional area of ​​the first rear groove 52 as the first rear area, the first front area can be larger than the first rear area. The value obtained by dividing the first front area by the first rear area can be 1.01 or more and 1.02 or less. The value obtained by dividing the first front area by the first rear area can be 1.012 or more and 1.018 or less, or 1.014 or more and 1.016 or less.

[0072] In a cross-section perpendicular to the central axis A, where the cross-sectional area of ​​the second front groove 61 is taken as the second front area and the cross-sectional area of ​​the second rear groove 62 is taken as the second rear area, the second front area can be larger than the second rear area. The value obtained by dividing the second front area by the second rear area can be 1.01 or more and 1.02 or less. The value obtained by dividing the second front area by the second rear area can be 1.012 or more and 1.018 or less, or 1.014 or more and 1.016 or less.

[0073] Figure 12 as well as Figure 13 This is an imaginary plane projected after rotating the first cutting blade 10 and the second cutting blade 20 around the central axis A. For example... Figure 12 As shown, the imaginary plane 150 includes a central axis A. In the imaginary plane 150, the foremost position of the central blade 11 is the first position 71. The first position 71 is located at the foremost point axially. In the imaginary plane 150, the intersection of the central axis A and the central blade 11 is the second position 72.

[0074] like Figure 13 As shown, in the imaginary plane 150, the intersection of the imaginary line segment extending from the second position 72 in a direction perpendicular to the central axis A and the outer peripheral cutting edge 21 is the third position 73. The tool radius is the radial distance from the central axis A to the outermost peripheral end of the outer peripheral cutting edge 21. The outermost peripheral end of the outer peripheral cutting edge 21 is the fifth position 75. That is, the tool diameter E is twice the radial distance from the central axis A to the fifth position 75. Furthermore, radial refers to the direction extending radially from the central axis A. The radial direction is orthogonal to the central axis A.

[0075] like Figure 12As shown, the radial distance from the central axis A to the first position 71 is more than 30% and less than 40% of the tool radius. The radial distance from the central axis A to the first position 71 can be more than 23% and less than 37% of the tool radius, or it can be more than 26% and less than 34% of the tool radius.

[0076] like Figure 13 As shown, the radial distance from the central axis A to the third position 73 is more than 80% and less than 100% of the tool radius. The radial distance from the central axis A to the third position 73 can be more than 84% and less than 96% of the tool radius, or it can be more than 88% and less than 92% of the tool radius.

[0077] In the imaginary plane 150, the intersection of the central cutting edge 11 and the outer peripheral cutting edge 21 is the fourth position 74. The radial distance from the central axis A to the fourth position 74 can 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 outer peripheral cutting edge 21.

[0078] The radial distance from the central axis A to the fourth position 74 can be more than 1.05 times or more than 1.1 times the radial distance from the fourth position 74 to the fifth position 75 of the outer peripheral blade 21. The radial distance from the central axis A to the fourth position 74 can be less than 2 times or less than 1.8 times the radial distance from the fourth position 74 to the fifth position 75.

[0079] like Figure 4A As shown, the length of the first discharge groove 1 along the central axis A is a first total length B13. The first total length B13 can be more than 2 times and less than 8 times the tool diameter. The first total length B13 is the sum of the length of the first front groove portion 51 and the length of the first rear groove portion 52. Along the central axis A, the first total length B13 can be more than 2 times and less than 7 times the tool diameter.

[0080] like Figure 4A As shown, the distance from the front end of the first cutting blade 10 to the rear end of the first groove portion 32 along the central axis A is the length C1 of the first groove. The length C1 of the first groove is more than 1.5 times the tool diameter. The front end of the first cutting blade 10 corresponds to the foremost position of the central cutting edge 11. The rear end of the first groove portion 32 is the boundary between the surface of the first groove portion 32, the first outer peripheral surface 4 of the first main body region 3, and the surface of the first front groove portion 51.

[0081] Along the central axis A, the length C1 of the first groove can be more than 1.8 times the tool diameter or more than 2 times the tool diameter. Along the central axis A, the length C1 of the first groove can be less than 3 times the tool diameter or less than 2.5 times the tool diameter.

[0082] like Figure 9A As shown, the length of the second discharge groove 2 along the central axis A is the second total length B23. The second total length B23 can be more than 2 times and less than 8 times the tool diameter. The second total length B23 is the sum of the length of the second front groove portion 61 and the length of the second rear groove portion 62. Along the central axis A, the second total length B23 can be more than 2 times and less than 7 times the tool diameter.

[0083] like Figure 9A As shown, the distance from the front end of the second cutting blade 20 to the rear end of the second groove portion 42 along the central axis A is the length C2 of the second groove. The length C2 of the second groove can be smaller than the length C1 of the first groove. The front end of the second cutting blade 20 corresponds to the foremost position of the outer peripheral cutting edge 21. The rear end of the second groove portion 42 is the boundary between the surface of the second groove portion 42, the first outer peripheral surface 4 of the first main body region 3, and the surface of the fourth front end groove portion 94. Along the central axis A, the rear end of the first groove portion 32 can be located axially rearward than the rear end of the second groove portion 42.

[0084] like Figure 13 As shown, the straight line perpendicular to the central axis A is the third straight line D3. The tangent to the central cutting edge 11 at the second position 72 is the fourth straight line D4. The third straight line D3 passes through the second position 72. The angle between the third straight line D3 and the fourth straight line D4 is the fourth angle θ4. The fourth angle θ4 can be less than 8°, less than 6°, or less than 4°. The fourth angle θ4 can be greater than 1° or greater than 2°. The sine of the fourth angle θ4 (that is, sinθ4) can be less than or equal to the value obtained by multiplying the tool diameter by 0.0070 / mm. The sine of the fourth angle θ4 can be less than or equal to the value obtained by multiplying the tool diameter by 0.0060 / mm, or less than or equal to the value obtained by multiplying the tool diameter by 0.0050 / mm. The sine of the fourth angle θ4 can be greater than or equal to the value obtained by multiplying the tool diameter by 0.0010 / mm, or greater than or equal to the value obtained by multiplying the tool diameter by 0.0020 / mm. Furthermore, the unit of the fourth angle θ4 is °. The unit of the tool diameter is mm.

[0085] Next, the effects of the drill bit 100 described in this embodiment will be explained.

[0086] In deep hole machining, chips generated at the time of machining are likely to be retained inside the hole, and thus, clogging of the chips is likely to occur. In order to improve the dischargeability of the chips, it is effective to increase the twist angle θ3 of the discharge groove. However, if the twist angle θ3 is increased, the capacity of the discharge groove is increased, and thus, the rigidity of the main body portion 9 of the drill 100 is decreased. As a result, the drill 100 is greatly vibrated at the time of hole machining, and the quality of the hole formed in the workpiece is deteriorated.

[0087] According to the drill 100 related to the present embodiment, the first discharge groove 1 and the second discharge groove 2 are provided in the main body portion 9. The first discharge groove 1 discharges chips cut by the center blade 11. The second discharge groove 2 discharges chips cut by the peripheral blade 21. When viewed along the center axis A, the start phase of the first discharge groove 1 is located in a range of +10° or more and +90° or less with respect to the center blade 11, the end phase of the first discharge groove 1 is located in a range of -40° or more and 0° or less with respect to the center blade 11, the start phase of the second discharge groove 2 is located in a range of +10° or more and +90° or less with respect to the peripheral blade 21, and the end phase of the second discharge groove 2 is located in a range of -40° or more and 0° or less with respect to the peripheral blade 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 θ3 of the first front groove portion 51 monotonously decreases toward the first rear groove portion 52. The twist angle θ3 of the second front groove portion 61 monotonously decreases toward the second rear groove portion 62. The twist angles θ3 of the first rear groove portion 52 and the second rear groove portion 62 are 0°, respectively. Thus, it is possible to suppress the decrease in the rigidity of the main body portion 9, and to improve the dischargeability of the chips. As a result, it is possible to improve the quality of the hole formed in the workpiece.

[0088] Further, according to the drill 100 related to the present embodiment, 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 θ3 of the first discharge groove 1 by the amount of change in the position in the direction along the center 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 θ3 of the second discharge groove 2 by the amount of change in the position in the direction along the center axis A is continuous. Thus, the first front groove portion 51 and the first rear groove portion 52 are smoothly connected, and thus, it is possible to suppress the retention of the chips in the first discharge groove 1. Similarly, the second front groove portion 61 and the second rear groove portion 62 are smoothly connected, and thus, it is possible to suppress the retention of the chips in the second discharge groove 2.

[0089] In the radial direction, the center blade 11 is located on the side of the central axis A than the outer peripheral blade 21, so the cutting speed of the center blade 11 becomes lower than the cutting speed of the outer peripheral blade 21. Therefore, the chip cut by the center blade 11 is harder to discharge than the chip cut by the outer peripheral blade 21. That is, the discharge property of the chip of the first discharge groove 1 becomes lower than the discharge property of the chip of the second discharge groove 2.

[0090] According to the drill 100 according to the present embodiment, the first recessed groove portion 32 connected to the first discharge groove 1 and located on the front side in the rotation direction than the first cutting blade 10 is provided in the main body portion 9. In the direction along the central axis A, the distance from the front end of the first cutting blade 10 to the rear end of the first recessed groove portion 32 is 1.5 times or more of the tool diameter. The chip cut by the center blade 11 is curled in the first recessed groove. By setting the distance from the front end of the first cutting blade 10 to the rear end of the first recessed groove portion 32 to be 1.5 times or more of the tool diameter, a space for curling the chip can be sufficiently ensured. Thereby, the discharge property of the chip cut by the center blade 11 can be improved.

[0091] According to the drill 100 according to the present embodiment, in the direction along the central axis A, the length of the first discharge groove 1 and the length of the second discharge groove 2 can each be 2 times or less of the tool diameter. Thereby, a deep hole can be formed in the workpiece.

[0092] According to the drill 100 according to the present embodiment, in the direction along the central axis A, in a case where the length of the first front groove portion 51 is a first front length B11, the length of the first rear groove portion 52 is a first rear length B12, 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 first front length B11 by the first rear length B12 can 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 can be 0.3 or more and 3.0 or less. Thereby, a decrease in rigidity can be suppressed, and the discharge property of the chip can be improved.

[0093] The first front groove portion 51 has a greater influence on the discharge property of the chip than the first rear groove portion 52. Similarly, the second front groove portion 61 has a greater influence on the discharge property of the chip than the second rear groove portion 62.

[0094] According to the drill 100 according to the present embodiment, in a cross section perpendicular to the center axis A, in a case where a cross-sectional area of the first front groove portion 51 is a first front area, a cross-sectional area of the first rear groove portion 52 is a first rear area, a cross-sectional area of the second front groove portion 61 is a second front area, and a cross-sectional area of the second rear groove portion 62 is a second rear area, a value obtained by dividing the first front area by the first rear area can be 1.01 or more and 1.02 or less, and a value obtained by dividing the second front area by the second rear area can be 1.01 or more and 1.02 or less. Thereby, a decrease in rigidity can be suppressed, and dischargeability of chips can be further improved.

[0095] According to the drill 100 according to the present embodiment, in a cross section perpendicular to the center axis A, the cross-sectional area of the first discharge groove 1 can be larger than the cross-sectional area of the second discharge groove 2. Thereby, a decrease in rigidity can be suppressed, and dischargeability of chips of the first discharge groove 1 can be improved.

[0096] According to the drill 100 according to the present embodiment, in the imaginary plane 150 after the first cutting insert 10 and the second cutting insert 20 are respectively rotationally projected, in a case where a most front end position of the center blade 11 is a first position 71, an intersection of the center axis A and the center blade 11 is a second position 72, and an intersection of an imaginary line segment extending in a direction perpendicular to the center axis A from the second position 72 and the outer peripheral blade 21 is a third position 73, a distance in a radial direction from the center axis A to the first position 71 can be 30% or more and 40% or less of half of the tool diameter, and a distance in the radial direction from the center axis A to the third position 73 can be 80% or more and 100% or less of half of the tool diameter. Thereby, cutting resistance when the drill 100 bites into a workpiece is reduced. Thus, a deviation in diameter of a hole formed in the workpiece is reduced. In addition, the quality of a surface of the hole is improved.

[0097] According to the drill 100 according to the present embodiment, in the imaginary plane 150, in a case where an intersection of the center blade 11 and the outer peripheral blade 21 is a fourth position 74, a distance in the radial direction from the center axis A to the fourth position 74 can be larger than a distance in the radial direction from the fourth position 74 to an outermost end of the outer peripheral blade 21. Thereby, in cutting processing, cutting force of the outer peripheral blade 21 and cutting force of the center blade 11 are balanced. Thus, a deviation in diameter of a hole formed in a workpiece is reduced.

[0098] When the drill bit 100 bites into the workpiece, a large force is generated at the drill bit 100, and thus the drill bit 100 is likely to vibrate. If the angle formed by the straight line perpendicular to the central axis A and the tangent line of the center blade 11 is reduced, the force applied to the cutting insert when the center blade 11 contacts the workpiece can be reduced. Thus, the vibration of the drill bit 100 can be reduced. As a result, the amount of hole diameter expansion at the hole entrance of the workpiece can be reduced.

[0099] In addition, if the ratio of the protruding length of the holder to the tool diameter is constant, the displacement amount of the hole diameter corresponding to the amount of hole diameter expansion is proportional to (sin θ) / (tool diameter). The proportional constant at this time is a value determined depending on the material of the holder and the like, and is 2 mm 2 ~ 200 mm 2 . θ is the angle formed by the straight line perpendicular to the central axis A and the tangent line of the center blade 11. That is, the smaller the tool diameter, the more likely the hole diameter expansion amount at the hole entrance is to be large. In a drill bit having a small tool diameter, by reducing the angle formed by the straight line perpendicular to the central axis A and the tangent line of the center blade 11, the hole diameter expansion amount can be reduced.

[0100] Further, the displacement amount (δ) of the hole diameter is found by the following mathematical expression 1. Here, F sin θ is the cutting resistance. θ is the center blade angle. L is the protruding length. E is the Young's modulus. E depends on the material. I is the second moment of area. I is found by (constant) x (tool diameter) 4 . I depends on the cross-sectional shape.

[0101] [Num 1]

[0102] The displacement amount (δ s ) of the hole diameter when the tool diameter is the reference diameter (for example, 20.0 mm) is found by the following mathematical expression 2. The tool diameter is D S . The protruding length is L S . The ratio of the protruding length to the tool diameter is, for example, 5. The center blade angle is θ S . The cutting resistance is F sin θ S . The Young's modulus is E. The second moment of area is I S . I S is found by (constant) x (tool diameter) 4 . That is, I S is (constant) x (D S ) 4 .

[0103] [Num 2]

[0104] The displacement amount (δ) of the hole diameter when the tool diameter is the expanded diameter (e.g., 25.0 mm, 15.0 mm, etc.) d is found by the following mathematical expression 3. The tool diameter is D d . The protrusion length is L d . The ratio of the protrusion length to the tool diameter is constant in the case of the reference diameter and in the case of the expanded diameter. That is, L d / D d is equal to L S / D S . The center blade angle is θ d . The cutting resistance is F sin θ d . The Young's modulus is E. The second moment of area is I d . I d is found by (constant) x (tool diameter) 4 . That is, I d is (constant) x (D d ) 4 . That is, I d is (D d ) 4 / (D s ) 4 x I s . As shown in mathematical expression 3, the displacement amount of the holder is proportional to (sin θ) / (tool diameter). Furthermore, C is a proportional constant. Therefore, by measuring the displacement amount of the holder that becomes the reference diameter, the displacement amount of a different tool diameter (expanded diameter) can be calculated.

[0105] [Num 3]

[0106] According to the drill 100 according to the present embodiment, in the imaginary plane 150, the sine of the angle formed by the straight line perpendicular to the center axis A and the tangent line to the center blade 11 at the second position 72 can be 0.0070 / mm or less of the tool diameter. Thereby, it is possible to reduce the vibration of the drill 100 when biting into the workpiece. Therefore, even in the case of a small tool diameter, it is possible to reduce the hole diameter expansion amount.

[0107] According to the drill 100 according to the present embodiment, a second groove portion 42 connected to the second discharge groove 2 and located forward in the rotation direction from the second cutting insert 20 can also be provided in the main body portion 9. In the direction along the center axis A, the rear end of the first groove portion 32 can be located at a position axially rearward from the rear end of the second groove portion 42. The chips cut by the peripheral blade 21 need to be curled with a small curvature, and in contrast, the chips cut by the center blade 11 are preferably curled with a large curvature. By adjusting the width of the groove according to the respective chips, it is possible to stabilize the chip processing.

[0108] Example 1 (Sample Preparation) First, the drill bits 100 of Samples 1 to 9 were prepared. The drill bits 100 of Samples 3 to 8 are examples. In the examples, the first termination phase and the second termination phase are set to an angle of -40° or more and 0° or less, respectively. The drill bits 100 of Samples 1 and 2 and Sample 9 are comparative examples. In the comparative examples, the first termination phase and the second termination phase are set to an angle smaller than -40° or an angle larger than 0°, respectively. The first termination phase and the second termination phase in each sample are as described in Table 1.

[0109] [Table 1]

[0110] As shown in Table 1, in the drill bits 100 of Samples 1 to 9, the first start phase and the second start phase are 45°, respectively. The cross-sectional area of the second front groove portion 61 is smaller than that of the first front groove portion 51. The cross-sectional area of the second rear groove portion 62 is smaller than that of the first rear groove portion 52. The cross-sectional area of the first front groove portion 51 is larger than that of the first rear groove portion 52. The cross-sectional area of the second front groove portion 61 is larger than that of the second rear groove portion 62.

[0111] The length of the first recess portion 32 is 1.58 times the tool diameter. The cutting edge length of the center blade 11 is 6.7 mm. The length of the first front groove portion 51 is 49 mm. The length of the first rear groove portion 52 is 45 mm. The length of the second recess portion 42 is 0.91 times the tool diameter. The cutting edge length of the outer peripheral blade 21 is 6.23 mm. The length of the second front groove portion 61 is 49 mm. The length of the second rear groove portion 62 is 45 mm.

[0112] (Evaluation Conditions) Next, an external stress was applied to the tip of the center blade 11 and the tip of the outer peripheral blade 21, respectively. The external stress in the direction perpendicular to the rake face was 600 N. The external stress in the direction along the center axis A was 720 N. The external stress in the direction from the cutting edge outer peripheral side toward the center axis A was 100 N. In each sample, the displacement amount in the tip end portion of the holder center was measured. The displacement amount of the tip end portion is the distance from the three-dimensional coordinates of the measurement point before the external stress was applied to the three-dimensional coordinates of the measurement point after the external stress was applied.

[0113] (Evaluation Results) Figure 14 is a graph showing the displacement amounts of the drill bits 100 of Samples 1 to 9. As shown in Figure 14As shown, in the case where the first termination phase and the second termination phase are each -40° or more and 15° or less, the displacement amount is small. On the other hand, in the case where the first termination phase and the second termination phase are each larger than 0°, chip discharge is difficult.

[0114] It was confirmed from the above results that, in the case where the first termination phase and the second termination phase are each -40° or more and 0° or less, the displacement amount of the holder is small, and high chip discharge performance can be achieved.

[0115] <Example 2> (Sample Preparation) Next, the drill bits 100 of Sample 4 and Sample 10 were prepared. The drill bit 100 of Sample 4 was an example. In the example, the first flute length Cl (length of the flute portion on the center blade side) was 1.5 times or more the tool diameter. Specifically, the first flute length Cl was 1.58 times the tool diameter. The drill bit 100 of Sample 10 was a comparative example. In the comparative example, the first flute length Cl was less than 1.5 times the tool diameter. Specifically, the first flute length Cl was 1.01 times the tool diameter.

[0116] As shown in Table 2, in each of the drill bits 100 of Sample 4 and Sample 10, the first start phase and the second start phase were each 45°. The first termination phase and the second termination phase were each -5°. The second flute length C2 (length of the flute portion on the outer peripheral blade side) was 0.91 times the tool diameter. The cutting edge length of the center blade 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 cutting edge length of the outer peripheral blade 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.

[0117] [Table 2]

[0118] (Evaluation Conditions) Next, drilling of a workpiece was performed using the drill bits 100 of Sample 4 and Sample 10. As a vertical machining center, an NVX5080 manufactured by DGM Seiki Co., Ltd. was used. The workpiece was JIS G 4051 S50C. The peripheral speed Vc was 150 m / minute. The feed amount f was 0.08 mm / revolution. A coolant was supplied from the inside of the drill bit 100. The supply pressure was 2 MPa. The height profile of the wall surface of the hole formed in the workpiece was measured.

[0119] (Evaluation Results) Figure 15 is a graph showing the height profile of the wall surface of the hole formed using the drill bit 100 of Sample 4.Figure 15 The horizontal axis is the position in the depth direction of the hole. Figure 15 The horizontal axis is the height of the wall surface of the hole. The arithmetic average roughness Ra of the wall surface of the hole was 1.496 μm. The root mean square roughness Rq of the wall surface of the hole was 1.858 μm. The maximum height roughness Rz of the wall surface of the hole was 9.477 μm.

[0120] Figure 16 is a graph showing the height profile of the wall surface of the hole formed using the drill bit 100 of sample 10. Figure 16 The horizontal axis is the position in the depth direction of the hole. Figure 16 The horizontal axis is the height of the wall surface of the hole. The arithmetic average roughness Ra of the wall surface of the hole was 2.259 μm. The root mean square roughness Rq of the wall surface of the hole was 2.885 μm. The maximum height roughness Rz of the wall surface of the hole was 13.18 μm.

[0121] As shown in Figure 15 and Figure 16 , it was confirmed that the surface roughness (Ra, Rq, Rz) of the wall surface of the hole was reduced by increasing the first groove length C1. If the surface roughness of the wall surface of the hole is reduced, the chip is easily discharged. Therefore, the chip discharge performance was improved by using the drill bit 100 of sample 4.

[0122] Example 3 (Sample Preparation) Next, the drill bits 100 of sample 4, sample 11, and sample 12 were prepared. The drill bits 100 of sample 4 and sample 12 are examples. In sample 4, the tool diameter was 20 mm, and the angle θ formed by the straight line perpendicular to the center axis A and the center blade 11 was 8°. In sample 12, the tool diameter was 18.5 mm, and the angle θ formed by the straight line perpendicular to the center axis A and the center blade 11 was 4°. As shown in Table 3, in each of the drill bits 100 of sample 4 and sample 12, the sine of the angle θ formed by the straight line perpendicular to the center axis A and the center blade 11 (that is, sin θ) was a value obtained by multiplying the tool diameter (mm) by 0.0070 / mm or less.

[0123] The drill bit 100 of sample 11 is a comparative example. In sample 11, the tool diameter was 18.5 mm, and the angle formed by the straight line perpendicular to the center axis A and the center blade 11 was 8°. In the drill bit 100 of sample 11, the sine of the angle θ formed by the straight line perpendicular to the center axis A and the center blade 11 (that is, sin θ) was larger than a value obtained by multiplying the tool diameter (mm) by 0.0070 / mm.

[0124] As shown in Table 3, in each of the drill bits 100 of Sample 4, Sample 11, and Sample 12, the first start phase and the second start phase were 45°, respectively. The first end phase and the second end phase were -5°, respectively. The second groove length C2 (length of the groove portion on the outer peripheral edge side) was 0.91 times the tool diameter. The length of the first groove portion 32 was 1.58 times the tool diameter.

[0125] [Table 3]

[0126] (Evaluation Conditions) Next, drilling was performed on the workpiece 80 using the drill bits 100 of Sample 4, Sample 11, and Sample 12, respectively. As the vertical machining center, an NVX5080 manufactured by DGM Seiki Co., Ltd. was used. The workpiece was JIS G4051 S50C. The peripheral speed Vc was 150 m / minute. The feed rate f was 0.06 mm / revolution. The coolant was supplied from the inside of the drill bit 100. The supply pressure was 2 MPa.

[0127] (Evaluation Results) Figure 17 is a cross-sectional view showing the shape of the hole formed using the drill bit 100 of Sample 4, Sample 11, and Sample 12, respectively. As shown in Figure 17 , at the entrance of the hole formed in the workpiece 80, the diameter of the hole is enlarged. The hole diameter on the inside is the first diameter W1. The first diameter W1 is substantially the same as the tool diameter. The hole diameter at the entrance is the third diameter W3. The third diameter W3 is larger than the first diameter W1.

[0128] As shown in Table 1, the first diameter W1 on the inside of the hole formed using the drill bits 100 of Sample 4, Sample 11, and Sample 12, respectively, 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 drill bits 100 of Sample 4, Sample 11, and Sample 12, respectively, was 20.2 mm, 20.0 mm, and 18.8 mm, respectively. The difference between the third diameter W3 and the first diameter W1, that is, the hole diameter enlargement amount W2, was 0.1 mm, 1.2 mm, and 0.0 mm, respectively. The cutting resistance at the entrance of the hole formed using the drill bits 100 of Sample 4, Sample 11, and Sample 12, respectively, was 550 N, 750 N, and 500 N, respectively.

[0129] From the above results, it was confirmed that by setting the sine of the angle θ formed by the straight line perpendicular to the central axis A and the center edge 11, that is, sin θ, to be the value obtained by multiplying the tool diameter by 0.0070 / mm or less, the cutting resistance at the entrance of the hole and the hole diameter enlargement amount W2 can be reduced, respectively.

[0130] It should be considered that the embodiments and examples disclosed herein are illustrative in all respects, rather than restrictive. The scope of the application is not indicated by the above description but by the claims, with the intention to include all alternatives falling within the meaning of the claims, and all modifications necessary for the practical implementation.

[0131] BRIEF DESCRIPTION OF DRAWINGS 1: first discharge groove; 2: second discharge groove; 3: first main body region; 4: first outer peripheral surface; 5: shank; 6: second main body region; 7: coolant supply hole; 9: main body portion; 10: first cutting insert; 11: central blade; 19: central blade mounting screw; 20: second cutting insert; 21: peripheral blade; 29: peripheral blade mounting screw; 31: first insertion arrangement surface portion; 32: first recess portion; 33: first insertion arrangement groove; 41: second insertion arrangement surface portion; 42: second recess portion; 43: second insertion arrangement groove; 51: first front groove portion; 52: first rear groove portion; 54: first rear end groove portion; 55: first start position; 56: first end position; 57: first boundary; 61: second front groove portion; 62: second rear groove portion; 64: second rear end groove portion; 65: second start position; 66: second end 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 bit; 101: front end surface; 102: rear end surface; 150: imaginary 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 recess length; C2: second recess length; D11: eleventh half line; D12: twelfth half line; D13: thirteenth half line; D21: twenty-first half line; D22: twenty-second half line; D23: twenty-third half line; D3: third line; D4: fourth line; E: tool diameter; F1: first imaginary circular arc; F2: second imaginary circular arc.

Claims

1. A drill bit that rotates about a central axis, wherein, The drill bit has the following features: The first cutting insert has a center cutting edge; The second cutting insert has an outer peripheral cutting edge; as well as The main body is for mounting the first cutting blade and the second cutting blade. The main body is provided with: The first discharge groove discharges the chips cut by the central cutting edge; as well as The second discharge groove discharges the chips cut by the outer peripheral blade. Viewed along the central axis, The initial phase of the first discharge groove is located in the range of +10° to +90° relative to the central blade. The termination phase of the first discharge groove is located in the range of -40° to 0° relative to the central blade. The initial phase of the second discharge groove is located in the range of +10° to +90° relative to the outer peripheral edge. The termination phase of the second discharge groove is located in the range of -40° to 0° relative to the outer peripheral edge. The first discharge channel has a first front channel portion and a first rear channel portion connected to the first front channel portion. The second discharge channel has a second front channel portion and a second rear channel portion connected to the second front channel portion. The torsion angle of the first front groove decreases monotonically as it moves toward the first rear groove. The torsion angle of the second front groove decreases monotonically as it moves toward the second rear groove. The torsion angles of the first rear groove and the second rear groove are both 0°. At the boundary between the first front groove and the first rear groove, the value obtained by dividing the change in the torsion angle of the first discharge groove by the change in position along the central axis is continuous. At the boundary between the second front groove and the second rear groove, the change in the torsion angle of the second discharge groove divided by the change in position along the central axis is a continuous value. The main body is provided with a first groove that is connected to the first discharge groove and is located in front of the first cutting blade in the rotational direction. Along the central axis, the distance from the front end of the first cutting blade to the rear end of the first groove is more than 1.5 times the tool diameter.

2. The drill bit according to claim 1, wherein, Along the central axis, the lengths of the first discharge groove and the second discharge groove are more than twice and less than eight times the diameter of the tool, respectively.

3. The drill bit according to claim 1 or 2, wherein, Along the central axis, when the length of the first front groove is the first front length, the length of the first rear groove is the first rear length, the length of the second front groove is the second front length, and the length of the second rear groove is the second rear length, the value obtained by dividing the first front length by the first rear length is 0.3 or more and 3.0 or less, and the value obtained by dividing the second front length by the second rear length is 0.3 or more and 3.0 or less.

4. The drill bit 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 is taken as the first front area, the cross-sectional area of ​​the first rear groove is taken as the first rear area, the cross-sectional area of ​​the second front groove is taken as the second front area, and the cross-sectional area of ​​the second rear groove is taken as the second rear area, the value obtained by dividing the first front area by the first rear area is 1.01 or more and 1.02 or less, and the value obtained by dividing the second front area by the second rear area is 1.01 or more and 1.02 or less.

5. The drill bit 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 channel is larger than that of the second discharge channel.

6. The drill bit according to any one of claims 1 to 5, wherein, In an imaginary plane after rotating and projecting the first cutting blade and the second cutting blade respectively, with the foremost position of the central cutting edge as the first position, the intersection of the central axis and the central cutting edge as the second position, and the intersection of an imaginary line segment extending from the second position in a direction perpendicular to the central axis and the outer peripheral cutting edge as the third position, the radial distance from the central axis extending radially to the first position is more than 30% and less than 40% of half the tool diameter, and the radial distance from the central axis to the third position is more than 80% and less than 100% of half the tool diameter.

7. The drill bit according to claim 6, wherein, In the imaginary plane, when the intersection of the central blade and the outer peripheral blade is taken as the fourth position, the radial distance from the central axis to the fourth position is greater than the radial distance from the fourth position to the outermost peripheral end of the outer peripheral blade.

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

9. The drill bit according to any one of claims 1 to 8, wherein, The main body is provided with a second groove that is connected to the second discharge groove and is located in front of the second cutting blade in the rotational direction. Along the central axis, the rear end of the first groove is located axially rearward than the rear end of the second groove.

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