Drill and machining method

Abstract

A drill according to the present invention rotates about an axis. The drill has a body. The body has a first body part, a second body part, and a connecting part. The first body part is positioned at the front end of the drill. A cutting edge is provided in the first body part. The second body part is positioned in the axial direction from the front end toward the rear end of the drill along the axis relative to the first body part. The connecting part is provided between the first body part and the second body part. The connecting part is contiguous with each of the first body part and the second body part. Twisted flutes are provided in a spiral shape around the axis in the first body part, the connecting part, and the second body part. When the diameter of the cutting edge is defined as a cutting edge diameter, the length of each of the twisted flutes in the axial direction is six times or more the cutting edge diameter. The first body part has a back taper. The maximum diameter of the second body part is greater than the cutting edge diameter.

Description

Drills and machining methods

[0001] The present disclosure relates to drills and machining methods.

[0002] Japanese Patent Laid-Open Publication No. 2010-064186 (Patent Document 1) describes an axial drill that rotates around its axis. The cutting edge portion at the tip of the drill body has an outer diameter at the rear end in the axial direction that is smaller than the outer diameter of the cutting edge. A guide portion is formed at the rear end of the cutting edge portion. The guide portion has a maximum outer diameter portion. The outer diameter of the maximum outer diameter portion is equal to or smaller than the outer diameter of the cutting edge.

[0003] JP 2010-064186 A

[0004] The drill according to the present disclosure rotates around an axis. The drill includes a body. The body includes a first body portion, a second body portion, and a connecting portion. The first body portion is located at the front end of the drill. A cutting edge is provided in the first body portion. The second body portion is located axially relative to the first body portion along the axis from the front end to the rear end of the drill. The connecting portion is provided between the first body portion and the second body portion. The connecting portion is connected to each of the first body portion and the second body portion. A spiral helical flute is provided around the axis in the first body portion, the connecting portion, and the second body portion. When the diameter of the cutting edge is defined as the cutting edge diameter, the length of the spiral flute in the axial direction is six times or more the cutting edge diameter. The first body portion is provided with a back taper. The maximum diameter of the second body portion is larger than the cutting edge diameter.

[0005] FIG. 1 is a schematic side view showing the configuration of a drill according to a first embodiment. FIG. 2 is an enlarged schematic view showing region II in FIG. 1 . FIG. 3 is an enlarged schematic view showing region III in FIG. 2 . FIG. 4 is a first enlarged schematic cross-sectional view showing the configuration of a drill according to the first embodiment. FIG. 5 is a second enlarged schematic cross-sectional view showing the configuration of a drill according to the first embodiment. FIG. 6 is a schematic view showing the rotation trajectory of a drill according to the first embodiment. FIG. 7 is a schematic front view showing the configuration of a drill according to the first embodiment. FIG. 8 is an enlarged schematic perspective view showing the configuration of a drill according to the first embodiment. FIG. 9 is a schematic cross-sectional view showing the configuration of a drill according to a second embodiment. FIG. 10 is a schematic view showing the rotation trajectory of a drill according to a third embodiment. FIG. 11 is a flow chart outlining a machining method according to this embodiment. FIG. 12 is a schematic cross-sectional view showing a step of forming a pilot hole in a workpiece. FIG. 13 is a schematic view showing the relationship between time and the rotation speed and feed rate of the drill. FIG. 14 is a partial cross-sectional view showing the state of the drill when the first body portion enters the pilot hole. Fig. 15 is a partial cross-sectional view showing the state of the drill when the second body portion enters the pilot hole. Fig. 16 is a cross-sectional view showing the state after a hole has been drilled in a workpiece. Fig. 17 shows the amount of hole deflection for holes drilled using the drills of Samples 1 to 3.

[0006] [Problem to be Solved by the Present Disclosure] In the drill described in Patent Document 1, the outer diameter of the maximum outer diameter portion of the guide portion is equal to or smaller than the outer diameter of the cutting edge. Therefore, during the process of drilling a hole, a gap may occur between the inner wall surface of the hole formed by the cutting edge and the guide portion. This may prevent sufficient reduction in vibration of the drill. As a result, it may not be possible to reduce bending of the hole.

[0007] An object of the present disclosure is to provide a drill that can reduce bending of a hole. [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a drill that can reduce bending of a hole.

[0008] [Outline of the embodiment] First, an outline of the embodiment of the present disclosure will be described.

[0009] (1) A drill according to the present disclosure rotates around an axis. The drill has a body. The body has a first body portion, a second body portion, and a connecting portion. The first body portion is located at the front end of the drill. A cutting edge is provided in the first body portion. The second body portion is located axially relative to the first body portion along the axis from the front end to the rear end of the drill. The connecting portion is provided between the first body portion and the second body portion. The connecting portion is connected to each of the first body portion and the second body portion. A helical flute is provided in the first body portion, the connecting portion, and the second body portion, spirally around the axis. When the diameter of the cutting edge is the cutting edge diameter, the length of the helical flute in the axial direction is six times or more the cutting edge diameter. The first body portion has a back taper. The maximum diameter of the second body portion is larger than the cutting edge diameter. This allows the second body portion to guide the entire drill along the extension direction of the hole formed by the drill. As a result, the bending of the hole can be reduced.

[0010] (2) In the drill according to (1) above, the axial distance between the front end and the portion of the second body with the largest outer diameter may be between 1 and 3 times the diameter of the cutting edge. By making the axial distance between the front end and the portion of the second body with the largest outer diameter at least 1 time the diameter of the cutting edge, it is possible to sufficiently increase the grinding allowance when re-grinding the cutting edge.

[0011] (3) In the drill according to (1) or (2), the value obtained by subtracting the cutting edge diameter from the maximum diameter of the second body portion may be 0.005 mm or more and 0.08 mm or less. The length of the second body portion in the axial direction may be 1.5 times or more and 5 times or less the cutting edge diameter. This reduces the frictional force generated between the second body portion and the workpiece.

[0012] (4) In the drill according to any one of (1) to (3), the second body portion may have a first end and a second end. The second end may be located between the first end and the rear end. The outer diameter of the second body portion at the first end may be the same as the outer diameter of the second body portion at the second end.

[0013] (5) In the drill according to any one of (1) to (3) above, the second body portion may be provided with a back taper. The slope of the back taper of the second body portion is equal to or smaller than the slope of the back taper of the first body portion. This reduces the frictional force generated between the second body portion and the workpiece.

[0014] (6) In the drill according to any one of (1) to (5) above, the body may have an outer peripheral margin surface. The outer peripheral margin surface may be located on the outermost periphery of the body. The outer peripheral margin surface may have a first outer peripheral margin surface portion and a second outer peripheral margin surface portion. The first outer peripheral margin surface portion may be formed by a connecting portion. The second outer peripheral margin surface portion may be formed by a second main body portion. The second outer peripheral margin surface portion may be continuous with the first outer peripheral margin surface portion. In a cross section including the axis and intersecting each of the first outer peripheral margin surface portion and the second outer peripheral margin surface portion, an angle formed by a tangent to the first outer peripheral margin surface portion at the boundary between the first outer peripheral margin surface portion and the second outer peripheral margin surface portion and the axis may be 30° or less. This reduces the surface roughness of the inner wall surface of a hole formed by the drill.

[0015] (7) In the drill according to (6) above, the first outer peripheral margin surface portion may be concave and arc-shaped in a cross section that includes the axis and intersects with each of the first outer peripheral margin surface portion and the second outer peripheral margin surface portion, thereby reducing the time required to manufacture the drill.

[0016] (8) According to the drill of (7) above, in a cross section that includes the axis and intersects with each of the first outer peripheral margin surface portion and the second outer peripheral margin surface portion, the radius of curvature of the first outer peripheral margin surface portion may be 0.2 mm or more.

[0017] (9) In the drill according to any one of (1) to (8), the first body portion may have a front end surface. A coolant hole for discharging coolant may be provided in the body. The coolant hole may be open in the front end surface. This can reduce the frictional force generated between the second body portion and the workpiece.

[0018] (10) A processing method according to the present disclosure is a processing method using a drill according to any one of (1) to (9) above. The processing method according to the present disclosure includes the following steps: A pilot hole is formed in a workpiece; The drill is inserted into the pilot hole while being rotated; After the step of inserting the drill into the pilot hole, a hole is formed in the workpiece using the drill; The value obtained by subtracting the diameter of the pilot hole from the maximum diameter of the second body portion is equal to or greater than 0 mm and equal to or less than 0.05 mm. Therefore, the second body portion can guide the entire drill along the extension direction of the pilot hole. This can reduce bending of the hole.

[0019] (11) According to the machining method of (10), the rotation speed of the drill at a first time point when the first body portion enters the pilot hole may be defined as a first rotation speed, the feed rate of the drill at the first time point may be defined as a first feed rate, and the rotation speed of the drill at a second time point when the second body portion enters the pilot hole may be defined as a second rotation speed, and the feed rate of the drill at the second time point may be defined as a second feed rate. The second rotation speed may be greater than the first rotation speed. The second feed rate may be smaller than the first feed rate. This can reduce the surface roughness of the inner wall surface of the hole formed.

[0020] [Details of the embodiment] Hereinafter, details of the embodiment of the present disclosure (hereinafter also referred to as the present embodiment) will be described with reference to the drawings. Note that the same or corresponding parts in the following drawings are designated by the same reference numerals, and the description thereof will not be repeated.

[0021] First Embodiment <Drill> First, the configuration of a drill 100 according to the first embodiment will be described. Fig. 1 is a schematic side view showing the configuration of the drill 100 according to the first embodiment. As shown in Fig. 1, the drill 100 according to the first embodiment mainly has a front end 1, a rear end 2, a body 3, and a shank 7.

[0022] The front end 1 is a portion that faces a workpiece (not shown). The rear end 2 is a portion that faces a spindle (not shown) of a machine tool that rotates the drill 100. The drill 100 rotates around an axis X. The axis X passes through the front end 1 and the rear end 2. The drill 100 is used, for example, to machine metal materials.

[0023] The direction from the front end 1 to the rear end 2 along the axis X is referred to as the axial direction 101. The direction from the front end 1 to the rear end 2 along the axis X is also referred to as the rearward axial direction. The direction from the rear end 2 to the front end 1 along the axis X is also referred to as the forward axial direction. The direction perpendicular to the axial direction 101 and from the axis X toward the outer circumferential surface 4 is referred to as the radial direction 102. The direction from the outer circumferential surface 4 toward the axis X along the radial direction 102 is also referred to as the inner radial direction. The direction from the axis X toward the outer circumferential surface 4 along the radial direction 102 is also referred to as the outer radial direction.

[0024] As shown in FIG. 1 , a helical groove 9 is provided in a body 3. The helical groove 9 is provided in a spiral shape around an axis X. The body 3 has an outer peripheral surface 4 and a helical groove surface 5. The outer peripheral surface 4 is provided in a spiral shape around the axis X. The helical groove surface 5 is continuous with the outer peripheral surface 4. The helical groove surface 5 is provided in a spiral shape around the axis X. The helical groove surface 5 forms the helical groove 9.

[0025] The shank 7 is located axially rearward of the body 3. The shank 7 is continuous with the body 3. The shank 7 is a part that is attached to the spindle of the machine tool. The shape of the shank 7 may be, for example, cylindrical.

[0026] 2 is an enlarged schematic diagram showing region II in FIG. 1. As shown in FIGS. 1 and 2, a cutting edge 8 is provided in the body 3. The cutting edge 8 is provided at a position close to the front end 1. The diameter of the cutting edge 8 is defined as a cutting edge diameter W1. The cutting edge diameter W1 is twice the distance in the radial direction 102 between the outermost end of the cutting edge 8 and the axis X. The cutting edge diameter W1 is not particularly limited, but is, for example, about 8 mm.

[0027] As shown in FIG. 1 , the length of the spiral flute 9 in the axial direction 101 (first length L1) is six times or more the cutting edge diameter W1. The first length L1 may be, for example, 30 times the cutting edge diameter W1. The drill 100 is, for example, a long drill. The first length L1 may be, for example, eight times or more the cutting edge diameter W1, or ten times or more the cutting edge diameter W1. The first length L1 may be, for example, 40 times or less the cutting edge diameter W1, or 35 times or less the cutting edge diameter W1. The length of the body 3 in the axial direction 101 is longer than the first length L1.

[0028] As shown in FIG. 2 , the drill 100 has a flank 40. The flank 40 is the front end surface of the first main body portion 31. Hereinafter, the flank 40 will also be referred to as the front end surface 40. A coolant hole 30 is provided in the body 3. The coolant hole 30 opens at the front end surface 40 of the first main body portion 31. The coolant hole 30 discharges coolant forward in the axial direction. The coolant is, for example, cutting oil.

[0029] 2 , the outer peripheral surface 4 has a first outer peripheral margin surface 10, a second outer peripheral margin surface 20, and an outer peripheral intermediate surface 19. The first outer peripheral margin surface 10 is provided spirally around the axis X. The first outer peripheral margin surface 10 is located at the outermost periphery of the body 3.

[0030] The second outer peripheral margin surface 20 is provided spirally around the axis X. The second outer peripheral margin surface 20 is spaced apart from the first outer peripheral margin surface 10. In the radial direction 102, the second outer peripheral margin surface 20 is located at substantially the same position as the first outer peripheral margin surface 10. From another perspective, the second outer peripheral margin surface 20 is located at the outermost periphery of the body 3.

[0031] Fig. 3 is an enlarged schematic view showing region III in Fig. 2. As shown in Fig. 3, the body 3 has a first main body portion 31, a connecting portion 34, and a second main body portion 32. As shown in Fig. 2, the first main body portion 31 is located at the front end 1. A cutting edge 8 is provided in the first main body portion 31.

[0032] 3 , the connecting portion 34 is provided axially rearward of the first body portion 31. The connecting portion 34 is continuous with the first body portion 31. The second body portion 32 is provided axially rearward of the first body portion 31. Specifically, the second body portion 32 is provided axially rearward of the connecting portion 34. From another perspective, the connecting portion 34 is provided between the first body portion 31 and the second body portion 32. The second body portion 32 is continuous with the connecting portion 34.

[0033] As shown in Fig. 2, the second body portion 32 has a first end 36 and a second end 37. As shown in Fig. 3, the second body portion 32 is continuous with the connecting portion 34 at the first end 36. In the second body portion 32, the first end 36 is the end located forward in the axial direction. As shown in Fig. 2, the second end 37 is located rearward in the axial direction relative to the first end 36. In other words, in the second body portion 32, the second end 37 is the end located rearward in the axial direction.

[0034] As shown in FIG. 2 , the body 3 has a third body portion 33. The third body portion 33 is provided between the second body portion 32 and the shank 7 (see FIG. 1 ). The third body portion 33 is continuous with both the second body portion 32 and the shank 7. Specifically, the second body portion 32 is continuous with the third body portion 33 at a second end portion 37. The body 3 has a helical groove 9 extending from the front end 1 to the third body portion 33. From another perspective, the helical groove 9 is provided in the first body portion 31, the connecting portion 34, and the second body portion 32. The helical groove 9 is provided in a portion of the third body portion 33.

[0035] 3, the first outer peripheral margin surface 10 has a third outer peripheral margin surface portion 13, a first outer peripheral margin surface portion 11, and a second outer peripheral margin surface portion 12. The third outer peripheral margin surface portion 13 is formed by a first main body portion 31. The third outer peripheral margin surface portion 13 is continuous with a relief surface 40 (see FIG. 2).

[0036] The first outer periphery margin surface portion 11 is formed by the connection portion 34. The first outer periphery margin surface portion 11 is located axially rearward of the third outer periphery margin surface portion 13. The first outer periphery margin surface portion 11 is continuous with the third outer periphery margin surface portion 13.

[0037] The boundary between the third outer peripheral margin surface portion 13 and the first outer peripheral margin surface portion 11 is a first boundary 61. The first main body portion 31 is a portion of the body 3 located between the front end 1 (see FIG. 2 ) and the first boundary 61 in the axial direction 101.

[0038] The second outer periphery margin surface portion 12 is formed by the second main body portion 32. The second outer periphery margin surface portion 12 is located axially rearward of the first outer periphery margin surface portion 11. The second outer periphery margin surface portion 12 is continuous with the first outer periphery margin surface portion 11.

[0039] The boundary between the first outer peripheral margin surface portion 11 and the second outer peripheral margin surface portion 12 is a second boundary 62. The connection portion 34 is a portion of the body 3 located between the first boundary 61 and the second boundary 62 in the axial direction 101.

[0040] As shown in Fig. 3, the second outer peripheral margin surface 20 has a sixth outer peripheral margin surface portion 23, a fourth outer peripheral margin surface portion 21, and a fifth outer peripheral margin surface portion 22. The sixth outer peripheral margin surface portion 23 is formed by the first main body portion 31. The sixth outer peripheral margin surface portion 23 is continuous with the relief surface 40 (see Fig. 2). In the axial direction 101, the sixth outer peripheral margin surface portion 23 is located at substantially the same position as the third outer peripheral margin surface portion 13.

[0041] The fourth outer circumferential margin surface portion 21 is formed by the connection portion 34. The fourth outer circumferential margin surface portion 21 is located axially rearward of the sixth outer circumferential margin surface portion 23. The fourth outer circumferential margin surface portion 21 is continuous with the sixth outer circumferential margin surface portion 23. In the axial direction 101, the fourth outer circumferential margin surface portion 21 is located at substantially the same position as the first outer circumferential margin surface portion 11.

[0042] The fifth outer circumferential margin surface portion 22 is formed by the second main body portion 32. The fifth outer circumferential margin surface portion 22 is located axially rearward of the fourth outer circumferential margin surface portion 21. The fifth outer circumferential margin surface portion 22 is continuous with the fourth outer circumferential margin surface portion 21. In the axial direction 101, the fifth outer circumferential margin surface portion 22 is located at substantially the same position as the second outer circumferential margin surface portion 12.

[0043] As shown in Figure 2, the outer peripheral surface 4 has a first connecting surface 14. The first connecting surface 14 is located between the first outer peripheral margin surface 10 and the outer peripheral intermediate surface 19. The first connecting surface 14 is continuous with both the first outer peripheral margin surface 10 and the outer peripheral intermediate surface 19. Specifically, the first connecting surface 14 is continuous with the second outer peripheral margin surface portion 12 (see Figure 3). The first connecting surface 14 is located rearward in the axial direction relative to the second outer peripheral margin surface portion 12. The first connecting surface 14 is defined by the third main body portion 33.

[0044] The boundary between the first outer peripheral margin surface 10 and the first connecting surface 14 is a third boundary 63. The second main body portion 32 is a portion of the body 3 located between the second boundary 62 (see FIG. 3 ) and the third boundary 63 in the axial direction 101. From another perspective, the second boundary 62 is located at substantially the same position as the first end 36 of the second main body portion 32 in the axial direction 101. The third boundary 63 is located at substantially the same position as the second end 37 of the second main body portion 32 in the axial direction 101.

[0045] 2 and 3 , the length of the second body portion 32 in the axial direction 101 is defined as a second length L2. The second length L2 is the distance in the axial direction 101 between the second boundary 62 and the third boundary 63. The second length L2 is, for example, 1.5 to 5 times the cutting edge diameter W1. The second length L2 may be, for example, two times or more the cutting edge diameter W1, or 2.5 times or more the cutting edge diameter W1. The second length L2 may be, for example, 4.5 times or less the cutting edge diameter W1, or 4 times or less the cutting edge diameter W1.

[0046] As shown in FIG. 2 , the outer peripheral surface 4 has a second connecting surface 24. The second connecting surface 24 is located between the second outer peripheral margin surface 20 and the outer peripheral intermediate surface 19. The second connecting surface 24 is continuous with both the second outer peripheral margin surface 20 and the outer peripheral intermediate surface 19. Specifically, the second connecting surface 24 is continuous with the fifth outer peripheral margin surface portion 22 (see FIG. 3 ). The second connecting surface 24 is located rearward in the axial direction relative to the fifth outer peripheral margin surface portion 22. The second connecting surface 24 is defined by the third main body portion 33. In the axial direction 101, the second connecting surface 24 may be located at substantially the same position as the first connecting surface 14.

[0047] FIG. 4 is a first enlarged cross-sectional schematic view showing the configuration of the drill 100 according to the first embodiment. The cross-section shown in FIG. 4 includes the axis X and intersects with each of the first boundary 61 and the second boundary 62. From another perspective, the cross-section shown in FIG. 4 intersects with each of the first outer peripheral margin surface portion 11 and the second outer peripheral margin surface portion 12. Hereinafter, the cross-section shown in FIG. 4 will also be referred to as a first cross-section CS1. As shown in FIG. 4, the third outer peripheral margin surface portion 13 and the first outer peripheral margin surface portion 11 are smoothly connected at the first boundary 61, for example.

[0048] In the first cross section CS1, the first outer peripheral margin surface portion 11 is, for example, concave. Specifically, in the first cross section CS1, the first outer peripheral margin surface portion 11 is concave radially inward with respect to a line passing through the first boundary 61 and the second boundary 62.

[0049] In the first cross section CS1, the first outer peripheral margin surface portion 11 is, for example, arc-shaped. In the first cross section CS1, the radius of curvature of the first outer peripheral margin surface portion 11 (first radius of curvature R1) is, for example, 0.2 mm or more. The first radius of curvature R1 may be, for example, 0.3 mm or more, or 0.5 mm or more. The first radius of curvature R1 may be, for example, 5 mm or less, or 3 mm or less.

[0050] In FIG. 4 , the first virtual line 93 is a straight line parallel to the axis X. As shown in FIG. 4 , in the first cross section CS1, the angle formed by the tangent (first tangent 91) to the first outer peripheral margin surface portion 11 at the boundary (second boundary 62) between the first outer peripheral margin surface portion 11 and the second outer peripheral margin surface portion 12 and the axis X (see FIGS. 1 to 3 ) is defined as a first angle θ1. The first angle θ1 is the same as the angle formed by the first tangent 91 and the first virtual line 93. The first angle θ1 is, for example, 30° or less. The first angle θ1 may be, for example, greater than 0°, 3° or greater, or 5° or greater. The first angle θ1 may be, for example, 25° or less, 20° or less, or 15° or less.

[0051] Fig. 5 is a second enlarged cross-sectional schematic view showing the configuration of the drill 100 according to the first embodiment. The cross section shown in Fig. 5 is a cross section that includes the axis X and intersects with each of the fourth outer peripheral margin surface portion 21 and the fifth outer peripheral margin surface portion 22. Hereinafter, the cross section shown in Fig. 5 will also be referred to as a second cross section CS2.

[0052] 5, the configuration of the fourth outer peripheral margin surface portion 21 is substantially the same as the configuration of, for example, the first outer peripheral margin surface portion 11. Specifically, in the second cross section CS2, the fourth outer peripheral margin surface portion 21 is, for example, concave. In the second cross section CS2, the fourth outer peripheral margin surface portion 21 is, for example, arc-shaped. In the second cross section CS2, the radius of curvature of the fourth outer peripheral margin surface portion 21 (second radius of curvature R2) is, for example, 0.2 mm or more.

[0053] 5, the second imaginary line 94 is a straight line parallel to the axis X. The angle (second angle θ2) formed by the tangent (second tangent 92) to the fourth outer peripheral margin surface portion 21 at the boundary between the fourth outer peripheral margin surface portion 21 and the fifth outer peripheral margin surface portion 22 and the axis X (see FIGS. 1 to 3) is 30° or less. The second angle θ2 is the same as the angle formed by the second tangent 92 and the second imaginary line 94.

[0054] FIG. 6 is a schematic diagram showing a rotation trajectory 110 of the drill 100 according to the first embodiment. FIG. 6 schematically shows a trajectory of the outermost surface of the drill 100 passing through a plane including the axis X when the drill 100 is rotated about the axis X. Hereinafter, a trajectory of a component of the drill 100 passing through a plane including the axis X when the drill 100 is rotated about the axis X will also be referred to as a rotation trajectory of the component. As shown in FIG. 6 , the rotation trajectory 110 of the drill 100 includes a first trajectory 51, a second trajectory 52, a third trajectory 53, a fourth trajectory 54, a fifth trajectory 55, and a sixth trajectory 56.

[0055] The first locus 51 and the second locus 52 indicate the rotation loci of the outermost peripheral surface of the first main body portion 31. Specifically, the first locus 51 is the rotation locus of the cutting edge 8. The second locus 52 is the rotation locus of the third outer peripheral margin surface portion 13. The second locus 52 is substantially the same as the rotation locus of the sixth outer peripheral margin surface portion 23. The second locus 52 is continuous with the first locus 51. The width of the first locus 51 in the radial direction 102 corresponds to the diameter of the cutting edge 8 (cutting edge diameter W1).

[0056] As shown in FIG. 6 , the width of the second locus 52 in the radial direction 102 decreases with increasing distance from the first locus 51. From another perspective, the first body portion 31 has a back taper. The gradient of the back taper in the first body portion 31 is, for example, 0.3 / 100 or more and 0.35 / 100 or less. A back taper gradient of Y / 100 means that the diameter is reduced by Y mm per 100 mm of length in the axial direction 101. The cutting edge diameter W1 is the maximum diameter of the first body portion 31. The outer diameter of the first body portion 31 at the end opposite the front end 1 is defined as a first outer diameter D1. From another perspective, the first outer diameter D1 is the outer diameter of the first body portion 31 at the first boundary 61 (see FIG. 3 ). The first outer diameter D1 is smaller than the cutting edge diameter W1.

[0057] The third locus 53 indicates the rotation locus of the outermost surface of the connection portion 34. Specifically, the third locus 53 is the rotation locus of the first outer peripheral margin surface portion 11. The third locus 53 is substantially the same as the rotation locus of the fourth outer peripheral margin surface portion 21. The third locus 53 is continuous with the second locus 52. The third locus 53 is, for example, concave. The third locus 53 is, for example, arc-shaped. The radius of curvature of the third locus 53 is substantially the same as the first radius of curvature R1 (see FIG. 4 ).

[0058] The fourth locus 54 indicates the rotation locus of the outermost peripheral surface of the second main body portion 32. Specifically, the fourth locus 54 is the rotation locus of the second outer peripheral margin surface portion 12. The fourth locus 54 is substantially the same as the rotation locus of the fifth outer peripheral margin surface portion 22. The fourth locus 54 is connected to the third locus 53.

[0059] The width of the fourth locus 54 in the radial direction 102, for example, decreases with increasing distance from the third locus 53. From another perspective, the second main body portion 32 is provided with, for example, a back taper. The gradient of the back taper in the second main body portion 32 is equal to or smaller than the gradient of the back taper in the first main body portion 31. The gradient of the back taper in the second main body portion 32 is, for example, equal to or greater than 0.3 / 100 and equal to or smaller than 0.35 / 100.

[0060] The outer diameter (second outer diameter D2) of the second main body portion 32 at the first end 36 is larger than the outer diameter (third outer diameter D3) of the second main body portion 32 at the second end 37. The second outer diameter D2 is the maximum diameter of the second main body portion 32. From another perspective, the first end 36 is the portion of the second main body portion 32 with the largest outer diameter.

[0061] As shown in FIG. 6 , the second outer diameter D2 is larger than the cutting edge diameter W1. In other words, the maximum diameter of the second body portion 32 is larger than the cutting edge diameter W1. The value obtained by subtracting the cutting edge diameter W1 from the second outer diameter D2 is, for example, 0.005 mm or more and 0.08 mm or less. The value obtained by subtracting the cutting edge diameter W1 from the second outer diameter D2 may be, for example, 0.01 mm or more, or 0.015 mm or more. The value obtained by subtracting the cutting edge diameter W1 from the second outer diameter D2 may be, for example, 0.06 mm or less, or 0.04 mm or less. The third outer diameter D3 is, for example, smaller than the cutting edge diameter W1.

[0062] 2 and 6 , the distance E in the axial direction 101 between the front end 1 and the portion of the second body portion 32 with the largest outer diameter (first end 36) is, for example, 1 to 3 times the cutting edge diameter W1. The distance E may be, for example, 1.2 times or more, or 1.5 times or more, of the cutting edge diameter W1. The distance E may be, for example, 2.8 times or less, or 2.5 times or less, of the cutting edge diameter W1.

[0063] 6 , a fifth locus 55 and a sixth locus 56 indicate rotation loci of the outermost peripheral surface of the third main body portion 33. Specifically, the fifth locus 55 is the rotation locus of the first connecting surface 14. The fifth locus 55 is substantially the same as the rotation locus of the second connecting surface 24. The fifth locus 55 is continuous with the fourth locus 54. The width of the fifth locus 55 in the radial direction 102 decreases with increasing distance from the fourth locus 54.

[0064] The sixth locus 56 is a rotation locus of the outer circumferential intermediate surface 19. The sixth locus 56 is continuous with the fifth locus 55. The sixth locus 56 is located radially inward with respect to each of the second locus 52 and the fourth locus 54.

[0065] Fig. 7 is a schematic front view showing the configuration of the drill 100 according to the first embodiment. Fig. 7 shows the configuration of the first body portion 31 when viewed in the axial direction 101. Fig. 8 is an enlarged perspective schematic view showing the configuration of the drill 100 according to the first embodiment. As shown in Figs. 7 and 8 , the flank 40 is continuous with the spiral flute surface 5. The ridge between the flank 40 and the spiral flute surface 5 forms the cutting edge 8. The spiral flute surface 5 close to the cutting edge 8 functions as a rake face. The flank 40 has a first flank portion 43 and a second flank portion 44.

[0066] The first flank portion 43 is continuous with the cutting edge 8. The second flank portion 44 is located rearward in the rotation direction relative to the first flank portion 43. The second flank portion 44 is continuous with the first flank portion 43. The second flank portion 44 is inclined relative to the first flank portion 43. The coolant hole 30 opens in the second flank portion 44.

[0067] 8 , the drill 100 has a thinning surface 6. The thinning surface 6 is continuous with each of the first flank portion 43 and the spiral flute surface 5. The ridgeline between the thinning surface 6 and the first flank portion 43 forms a cutting edge 8.

[0068] 7 and 8 , the first outer peripheral margin surface 10 is continuous with the first flank portion 43. The second outer peripheral margin surface 20 is continuous with the second flank portion 44. The second outer peripheral margin surface 20 is located rearward of the first outer peripheral margin surface 10 in the rotational direction.

[0069] The outer peripheral intermediate surface 19 is continuous with each of the first flank surface portion 43 and the second flank surface portion 44. In the rotational direction, the outer peripheral intermediate surface 19 is located between the first outer peripheral margin surface 10 and the second outer peripheral margin surface 20. The outer peripheral intermediate surface 19 is located radially inward from the first outer peripheral margin surface 10.

[0070] The outer peripheral surface 4 has a first side surface 15 and a second side surface 16. The first side surface 15 is continuous with each of the first outer peripheral margin surface 10 and the outer peripheral intermediate surface 19. In the radial direction 102, the first side surface 15 is located between the first outer peripheral margin surface 10 and the outer peripheral intermediate surface 19. The first side surface 15 is located rearward in the rotational direction relative to the first outer peripheral margin surface 10. The first side surface 15 is inclined, for example, radially inward relative to the first outer peripheral margin surface 10.

[0071] The second side surface 16 is continuous with each of the second outer peripheral margin surface 20 and the outer peripheral intermediate surface 19. In the radial direction 102, the second side surface 16 is located between the second outer peripheral margin surface 20 and the outer peripheral intermediate surface 19. The second side surface 16 is located forward in the rotational direction relative to the second outer peripheral margin surface 20. The second side surface 16 is inclined, for example, radially inward relative to the second outer peripheral margin surface 20.

[0072] 7 and 8 , the cutting edge 8 has a thinning cutting edge portion 81 and a major cutting edge portion 82. The major cutting edge portion 82 is continuous with the thinning cutting edge portion 81. The major cutting edge portion 82 is located radially outward from the thinning cutting edge portion 81. The major cutting edge portion 82 is continuous with each of the first flank portion 43 and the spiral groove surface 5. The thinning cutting edge portion 81 is continuous with each of the first flank portion 43 and the thinning surface 6.

[0073] In the drill 100 according to the first embodiment, a margin portion forming the first outer peripheral margin surface 10 and a margin portion forming the second outer peripheral margin surface 20 are provided for each cutting edge 8. The drill 100 according to the first embodiment has two cutting edges 8, four margin portions, two helical flute surfaces 5, and two flank surfaces 40. When viewed in the axial direction 101, the shape of the drill 100 is substantially rotationally symmetric with respect to the axis X. When the number of cutting edges 8 of the drill 100 is N, the shape of the drill 100 is substantially N-fold symmetric with respect to the axis X. When the number of cutting edges 8 of the drill 100 is two, the shape of the drill 100 is substantially 2-fold symmetric with respect to the axis X.

[0074] Second Embodiment Next, the configuration of a drill 100 according to a second embodiment will be described. The drill 100 according to the second embodiment differs from the drill 100 according to the first embodiment mainly in that the first outer periphery margin surface portion 11 is linear in the first cross section CS1, but is substantially identical to the drill 100 according to the first embodiment in other respects. Below, the differences from the drill 100 according to the first embodiment will be mainly described.

[0075] FIG. 9 is a cross-sectional schematic diagram showing the configuration of the drill 100 according to the second embodiment. The cross section shown in FIG. 9 corresponds to the cross section shown in FIG. 4. As shown in FIG. 9, in the first cross section CS1, the first outer peripheral margin surface portion 11 may be linear. In the first cross section CS1, the first outer peripheral margin surface portion 11 extends along a straight line connecting the first boundary 61 and the second boundary 62. In the first cross section CS1, the angle formed by the first outer peripheral margin surface portion 11 and the axis X is substantially the same as the first angle θ1.

[0076] Third Embodiment Next, the configuration of a drill 100 according to a third embodiment will be described. The drill 100 according to the third embodiment differs from the drill 100 according to the first embodiment mainly in that a back taper is not provided in the second body portion 32, but is substantially identical to the drill 100 according to the first embodiment in other respects. Below, the differences from the drill 100 according to the first embodiment will be mainly described.

[0077] FIG. 10 is a schematic diagram showing a rotation trajectory 110 of a drill 100 according to the third embodiment. The rotation trajectory 110 shown in FIG. 10 corresponds to the rotation trajectory 110 shown in FIG. 6 . As shown in FIG. 10 , the width of the fourth trajectory 54 in the radial direction 102 may be constant from the boundary between the third trajectory 53 and the fourth trajectory 54 to the boundary between the fourth trajectory 54 and the fifth trajectory 55. From another perspective, the outer diameter of the second body portion 32 may be constant from the first end 36 to the second end 37. A back taper may not be provided in the second body portion 32. From another perspective, the gradient of the back taper in the second body portion 32 may be 0 / 100. The second outer diameter D2 and the third outer diameter D3 may be substantially the same. The third outer diameter D3 may be greater than the cutting edge diameter W1.

[0078] <Processing Method> Next, a processing method according to this embodiment will be described. Fig. 11 is a flow chart that schematically shows the processing method according to this embodiment. As shown in Fig. 11, the processing method according to the first embodiment mainly includes a step (S10) of drilling a pilot hole in a workpiece, a step (S20) of inserting a drill into the pilot hole, and a step (S30) of drilling a hole in the workpiece using the drill.

[0079] First, a step (S10) of forming a pilot hole in a workpiece is performed. Fig. 12 is a schematic cross-sectional view showing the step (S10) of forming a pilot hole in a workpiece. As shown in Fig. 12, a pilot hole 98 is formed in a workpiece 99 using, for example, a pilot drill (not shown).

[0080] The diameter W2 of the pilot hole is equal to or smaller than the maximum diameter of the second body portion 32 (second outer diameter D2, see FIG. 6 ). The value obtained by subtracting the diameter W2 from the second outer diameter D2 is equal to or larger than 0 mm and equal to or smaller than 0.05 mm. The value obtained by subtracting the diameter W2 from the second outer diameter D2 may be, for example, equal to or larger than 0.01 mm or equal to or larger than 0.015 mm. The value obtained by subtracting the diameter W2 from the second outer diameter D2 may be, for example, equal to or smaller than 0.04 mm or equal to or smaller than 0.03 mm. The depth F of the pilot hole 98 is, for example, equal to or larger than 1 time and equal to or smaller than 3 times the cutting edge diameter W1. The depth F of the pilot hole 98 is, for example, greater than the distance E in the axial direction 101 between the front end 1 of the drill 100 and the first end 36 of the second body portion 32.

[0081] Next, a step (S20) of inserting a drill into the pilot hole is performed. The drill 100 according to this embodiment is prepared. The drill 100 is positioned facing the pilot hole 98 but spaced apart from the pilot hole 98. The drill 100 is positioned so that the axis X and the axis C of the pilot hole 98 overlap. The drill 100 is rotated about the axis X. The drill 100 is moved along the axis X in a direction from the drill 100 toward the pilot hole 98.

[0082] Fig. 13 is a schematic diagram showing the relationship between time and the number of rotations per unit time of the drill 100 (hereinafter simply referred to as "number of rotations") and the feed amount per rotation of the drill 100 (hereinafter simply referred to as "feed amount"). In Fig. 13, the upper vertical axis indicates the number of rotations of the drill 100, and the lower vertical axis indicates the feed amount of the drill 100. In Fig. 13, the horizontal axis indicates time. In Fig. 13, the time when the movement of the drill 100 starts is defined as start time T0.

[0083] 13 , at the start time T0, the rotation speed of the drill 100 is a first rotation speed A1. The first rotation speed A1 is, for example, 1000 rpm or less. At the start time T0, the feed rate of the drill 100 is a first feed rate B1. The first feed rate B1 is, for example, 0.5 mm / revolution or more and 1 mm / revolution or less.

[0084] Figure 14 is a partial cross-sectional schematic view showing the state of the drill 100 at the time when the first body portion 31 enters the pilot hole 98. As shown in Figure 14, the time when the front end 1 enters the pilot hole 98 is the time when the first body portion 31 enters the pilot hole 98. The time when the first body portion 31 enters the pilot hole 98 is the first time point T1. As shown in Figure 13, the rotation speed of the drill 100 at the first time point T1 is a first rotation speed A1. The feed rate of the drill 100 at the first time point T1 is a first feed rate B1.

[0085] The rotation speed of the drill 100 is maintained at the first rotation speed A1, and the feed rate of the drill 100 is maintained at the first feed rate B1. As a result, a part of the first body portion 31 is inserted into the pilot hole 98.

[0086] Next, a step (S30) of drilling a hole in a workpiece using a drill is performed. As shown in FIG. 13 , the rotation speed of drill 100 is increased from a first rotation speed A1 to a second rotation speed A2. Second rotation speed A2 is, for example, approximately 4000 rpm. Second rotation speed A2 may be, for example, 3000 rpm or more. The feed rate of drill 100 is decreased from a first feed rate B1 to a second feed rate B2. Second feed rate B2 is, for example, 0.25 mm / revolution. Second feed rate B2 may be, for example, 0.15 mm / revolution or more and 0.35 mm / revolution or less.

[0087] Figure 15 is a partial cross-sectional schematic view showing the state of the drill 100 at the time when the second body portion 32 enters the pilot hole 98. As shown in Figure 15, the time when the first end 36 enters the pilot hole 98 is defined as the time when the second body portion 32 enters the pilot hole 98. The time when the second body portion 32 enters the pilot hole 98 is defined as a second time point T2.

[0088] 13, the rotation speed of the drill 100 at the second time point T2 is a second rotation speed A2. The rotation speed of the drill 100 at the second time point T2 (second rotation speed A2) is greater than the rotation speed of the drill 100 at the first time point T1 (first rotation speed A1).

[0089] The feed rate of the drill 100 at the second point in time T2 is a second feed rate B2. The feed rate of the drill 100 at the second point in time T2 (second feed rate B2) is smaller than the feed rate of the drill 100 at the first point in time T1 (first feed rate B1).

[0090] The rotation speed of the drill 100 is maintained at the second rotation speed A2, and the feed rate of the drill 100 is maintained at the second feed rate B2. As a result, the second body portion 32 is inserted into the pilot hole 98. As the drill 100 continues to move, the cutting edge 8 cuts the bottom of the pilot hole 98. While the cutting edge 8 cuts the pilot hole 98, coolant is ejected, for example, from the coolant hole 30. Specifically, cutting oil, for example, is ejected as the coolant. As a result of the above, a hole 97 is formed in the workpiece 99.

[0091] Fig. 16 is a schematic cross-sectional view showing a state in which a hole 97 has been formed in a workpiece 99. As shown in Fig. 16, the hole 97 is formed in the workpiece 99. The hole 97 may, for example, penetrate the workpiece 99. The hole 97 is formed by a pilot hole portion 95 and a machined hole portion 96. The pilot hole portion 95 is the inner wall surface of the portion where the pilot hole 98 was formed. The machined hole portion 96 is the inner wall surface formed by cutting the workpiece 99 with the drill 100.

[0092] Next, the effects of the drill 100 and processing method according to this embodiment will be described. In order to reduce the frictional force generated between the drill and the workpiece when the drill is used to form a hole in the workpiece, the drill may be provided with a back taper. In this case, a gap is generated between the outer peripheral surface of the drill and the inner wall surface of the hole in the workpiece. Therefore, vibration of the drill and vibration of the front end of the drill may occur during the hole formation process. Furthermore, a skipping rope motion may occur. The skipping rope motion refers to the movement of the drill rotating while bending around the contact point between the drill and the workpiece as a fulcrum. For example, a skipping rope motion may occur around the front end of the drill as a fulcrum. As a result, the hole may bend.

[0093] The drill 100 according to this embodiment includes a first body portion 31 and a second body portion 32. The first body portion 31 is provided with a cutting edge 8. The second body portion 32 is located axially rearward of the first body portion 31. The maximum diameter of the second body portion 32 is greater than the cutting edge diameter W1. Therefore, when drilling a hole in a workpiece using the drill 100, a gap between the inner wall surface of the hole formed by the cutting edge 8 cutting the workpiece and the second body portion 32 is substantially eliminated. Therefore, the outer peripheral surface of the second body portion 32 is more likely to come into contact with the inner wall surface of the hole. By continuing to cut the workpiece while the second body portion 32 is in contact with the inner wall surface of the hole, the second body portion 32 can guide the entire drill 100 along the direction of the hole. This reduces vibration of the drill 100. As a result, hole bending can be reduced.

[0094] The second body portion 32 guides the entire drill 100 along the direction of the hole, thereby reducing runout of the front end 1 of the drill 100. When the drill 100 starts to perform a skipping motion, the contact point between the second body portion 32 and the workpiece serves as a fulcrum, causing a skipping motion between the fulcrum and the rear end 2. This reduces the impact of the vibration of the drill 100 caused by the skipping motion on the cutting edge 8. As a result, hole bending can be further reduced.

[0095] Because the maximum diameter of the second body portion 32 is larger than the cutting edge diameter W1, the outer peripheral surface of the second body portion 32 can expand the inner wall surface of the hole when forming the hole, thereby reducing the surface roughness of the inner wall surface of the hole.

[0096] The outer peripheral surface of the second body portion 32 expands the inner wall surface of the hole, causing work hardening in the portion of the workpiece material close to the inner wall surface of the hole. This increases the hardness of the portion of the workpiece material close to the inner wall surface of the hole. This reduces scratches on the inner wall surface of the hole that are caused by contact between the inner wall surface of the hole and chips generated when the drill 100 cuts the workpiece material.

[0097] According to the drill 100 of this embodiment, the length of the helical flute 9 in the axial direction 101 is six times or more the cutting edge diameter W1. As such, the drill 100 of this embodiment can form a hole that is relatively deep. The drill 100 of this embodiment can reduce hole bending as described above, even when forming a deep hole.

[0098] In the drill 100 according to this embodiment, the distance E in the axial direction 101 between the front end 1 and the portion of the second body portion 32 with the largest outer diameter is equal to or greater than the cutting edge diameter W1. By making the distance E equal to or greater than the cutting edge diameter W1, it is possible to sufficiently increase the grinding allowance when regrinding the worn cutting edge 8.

[0099] When drilling a hole in a workpiece using the drill 100, a pilot hole may be formed in advance in the workpiece. In this case, the largest outer diameter portion of the second body portion 32 is inserted into the pilot hole before the cutting edge 8 begins cutting the bottom of the pilot hole, allowing the second body portion 32 to more effectively guide the entire drill 100. From another perspective, when the depth of the pilot hole is equal to or greater than the distance E, the second body portion 32 can more effectively guide the entire drill 100. However, if the pilot hole is excessively deep, the accuracy of the pilot hole decreases. As a result, the accuracy of the hole formed in the workpiece decreases.

[0100] According to the drill 100 of this embodiment, the distance E is three times the cutting edge diameter W1 or less. This allows the pilot hole to be shallower. This improves the accuracy of the pilot hole. As a result, the accuracy of the hole formed in the workpiece can be improved.

[0101] If the value obtained by subtracting the cutting edge diameter W1 from the maximum diameter (second outer diameter D2) of the second body portion 32 is excessively large, the frictional force generated between the second body portion 32 and the workpiece becomes excessively large. In this case, the drill 100 will wear excessively. Furthermore, the frictional force may cause the drill 100 to break. In the drill 100 according to this embodiment, the value obtained by subtracting the cutting edge diameter W1 from the maximum diameter (second outer diameter D2) of the second body portion 32 is 0.08 mm or less. Therefore, the frictional force generated between the second body portion 32 and the workpiece can be reduced. This reduces wear on the drill 100. Furthermore, the frequency of breakage of the drill 100 can be reduced.

[0102] If the length of the second body portion 32 is excessively long, the contact area between the second body portion 32 and the workpiece may become excessively large. In this case, the frictional force generated between the second body portion 32 and the workpiece becomes excessively large. According to the drill 100 of this embodiment, the length of the second body portion 32 in the axial direction 101 is not more than five times the cutting edge diameter W1. This reduces the contact area between the second body portion 32 and the workpiece. As a result, the frictional force generated between the second body portion 32 and the workpiece can be reduced.

[0103] According to the drill 100 according to the first embodiment, a back taper is provided in the second body portion 32. Therefore, the distance in the radial direction 102 between the second body portion 32 and the workpiece can be increased toward the rear end 2 of the drill 100. This reduces the contact area between the second body portion 32 and the workpiece. As a result, the frictional force generated between the second body portion 32 and the workpiece can be reduced.

[0104] When the second body portion 32 has a back taper, the maximum diameter of the second body portion 32 can be reduced by regrinding the second body portion 32. Therefore, if the cutting edge diameter W1 is reduced by regrinding the cutting edge 8, the amount of change in the difference between the cutting edge diameter W1 and the maximum diameter of the second body portion 32 can be reduced by regrinding the second body portion 32. This allows the second body portion 32 to effectively guide the entire drill 100 even after regrinding the cutting edge 8. As a result, hole bending can be reduced even after regrinding the cutting edge 8.

[0105] According to the drill 100 of this embodiment, the angle (first angle θ1) formed by the tangent to the first outer peripheral margin surface portion 11 at the boundary (second boundary 62) between the first outer peripheral margin surface portion 11 and the second outer peripheral margin surface portion 12 and the axis X on the first cross section CS1 is 30° or less. If the first angle θ1 is excessively large, the first outer peripheral margin surface portion 11 and the second outer peripheral margin surface portion 12 may scrape the inner wall surface of the hole when the drill 100 contacts the workpiece at the second boundary 62. According to the drill 100 of this embodiment, since the first angle θ1 is 30° or less, the first outer peripheral margin surface portion 11 can expand the inner wall surface of the hole as the drill 100 advances axially forward. This prevents the inner wall surface of the hole from being scraped. This more effectively reduces the surface roughness of the inner wall surface of the hole.

[0106] According to the drill 100 of this embodiment, the first outer peripheral margin surface portion 11 is concave and arc-shaped on the first cross section CS1. Therefore, when manufacturing the drill 100, the first outer peripheral margin surface portion 11 can be easily formed using a grindstone. This reduces the time required to manufacture the drill 100.

[0107] According to the drill 100 of this embodiment, the coolant hole 30 is provided in the front end surface 40 of the first body portion 31. This allows coolant to be supplied between the second body portion 32 and the workpiece, thereby reducing the frictional force generated between the second body portion 32 and the workpiece.

[0108] The machining method according to this embodiment includes a step (S10) of forming a pilot hole in a workpiece. The value obtained by subtracting the diameter W2 of the pilot hole 98 from the maximum diameter of the second body portion 32 is 0 mm or greater. Therefore, the drill 100 can form the hole 97 while the second body portion 32 is in contact with the inner wall surface of the pilot hole 98. As a result, by continuing to cut the workpiece while the second body portion 32 and the inner wall surface of the pilot hole 98 are in contact, the second body portion 32 can guide the entire drill 100 along the extension direction of the pilot hole 98. This reduces vibration of the drill 100. As a result, bending of the hole 97 can be reduced.

[0109] The second body portion 32 guides the entire drill 100 along the extension direction of the pilot hole 98, thereby reducing runout of the front end 1 of the drill 100. Furthermore, when the drill 100 starts to perform a skipping motion, the contact point between the second body portion 32 and the workpiece serves as a fulcrum, thereby reducing the impact of the vibration of the drill 100 caused by the skipping motion on the cutting edge 8. As a result, bending of the hole 97 can be further reduced.

[0110] According to the machining method of this embodiment, the value obtained by subtracting the diameter W2 of the pilot hole 98 from the maximum diameter of the second body portion 32 is 0.05 mm or less. This reduces the frictional force generated between the second body portion 32 and the inner wall surface of the pilot hole 98. This reduces wear on the drill 100. It also reduces the frequency of breakage of the drill 100.

[0111] If the rotation speed of the drill 100 is excessively low when the second body portion 32 enters the pilot hole 98 (second time point T2), the second body portion 32 may not be able to plastically deform the workpiece 99 so as to expand the inner wall surface of the pilot hole 98 when it contacts the inner wall surface of the pilot hole 98. In this case, the inner wall surface of the pilot hole 98 may be damaged. As a result, the surface roughness of the inner wall surface of the formed hole 97 increases. According to the machining method of this embodiment, the rotation speed of the drill 100 at the second time point T2 is higher than the rotation speed of the drill 100 at the time when the first body portion 31 enters the pilot hole 98 (first time point T1). Therefore, the rotation speed of the drill 100 at the second time point T2 is sufficiently increased. This allows the second body portion 32 to expand the inner wall surface of the pilot hole 98 by utilizing the energy of the rotational motion when inserted into the pilot hole 98. As a result, the surface roughness of the inner wall surface of the formed hole 97 can be reduced.

[0112] If the rotation speed of the drill 100 is excessively high before the first body portion 31 enters the pilot hole 98, the drill 100 will vibrate excessively. According to the machining method of this embodiment, the rotation speed of the drill 100 at the first time point T1 is reduced. Therefore, the vibration of the drill 100 can be reduced before the first body portion 31 enters the pilot hole 98.

[0113] According to the machining method of this embodiment, the feed rate of the drill 100 at the second time point T2 is smaller than the feed rate of the drill 100 at the first time point T1. Therefore, when the first body portion 31 is inserted into the pilot hole 98, the drill 100 can be inserted into the pilot hole 98 relatively quickly. This reduces the time required to form a hole in the workpiece 99.

[0114] (Sample Preparation) First, the drills 100 according to Samples 1 to 3 were prepared. The drills 100 according to Samples 1 and 2 were used as comparative examples. The drill 100 according to Sample 3 was used as an example. The drill 100 according to Sample 3 was the drill 100 according to the first embodiment. The drill 100 according to Sample 1 did not have the second main body portion 32. From another perspective, the first outer peripheral margin surface 10 was constituted by the third outer peripheral margin surface portion 13. The second outer peripheral margin surface 20 was constituted by the sixth outer peripheral margin surface portion 23. The drills 100 according to Samples 2 and 3 had the second main body portion 32.

[0115]

[0116] Table 1 shows the configurations of the drills 100 according to Samples 1 to 3. As shown in Table 1, the cutting edge diameter W1 of the drill 100 according to Sample 1 was 7.866 mm. The cutting edge diameter W1 of the drill 100 according to Sample 2 was 7.877 mm. The cutting edge diameter W1 of the drill 100 according to Sample 3 was 7.890 mm.

[0117] In the drill 100 according to Sample 2, the maximum diameter (second outer diameter D2) of the second body portion 32 was smaller than the cutting edge diameter W1. The second outer diameter D2 of the drill 100 according to Sample 2 was 7.860 mm.

[0118] In the drill 100 according to Sample 3, the second outer diameter D2 was larger than the cutting edge diameter W1. The second outer diameter D2 of the drill 100 according to Sample 3 was 7.918 mm. In Samples 2 and 3, the portion of the second body portion 32 with the largest outer diameter was the first end portion 36.

[0119] The second body portion 32 of the drill 100 according to Sample 2 was not provided with a back taper. The second body portion 32 of the drill 100 according to Sample 3 was provided with a back taper. The gradient of the back taper was 0.3 / 100 or more and 0.35 / 100 or less.

[0120] (Evaluation Method 1) The amount of hole bending was evaluated using the drills 100 according to Samples 1 to 3. Specifically, five holes 97 were formed in a workpiece 99 using each of the drills 100 according to Samples 1 to 3. The material of the workpiece 99 was S50C. S50C is a carbon steel defined in JIS (Japanese Industrial Standards) G 4051:2016. The workpiece 99 had a plate-like shape. The thickness of the workpiece 99 was 155 mm.

[0121] In Samples 1 to 3, a pilot hole 98 was formed in the workpiece 99 before forming the five holes 97. The diameter W2 of the pilot hole 98 was set to be equal to or greater than 7.883 mm and equal to or less than 7.903 mm. The depth F of the pilot hole 98 was set to be 15 mm.

[0122] In Samples 1 to 3, the cutting speed Vc when forming the five holes 97 was set to 100 m / min. The rotation speed was set to approximately 4000 rpm. Cutting oil was supplied from the coolant holes 30 toward the front end 1 of the drill 100. Each of the five holes 97 penetrated the workpiece 99. The depth of each of the five holes 97 was 155 mm.

[0123] The amount of hole deflection was evaluated for each of the five holes 97. Specifically, the hole 97, which penetrates the workpiece 99, has two openings, one at the entrance of the drill 100 and one at the exit of the drill 100. The center positions of each of the two openings were measured. When viewed from a direction perpendicular to the surface of the workpiece 99, the absolute value of the difference between the center positions of the two openings was taken as the amount of hole deflection. A contact sensor attached to a machining center was used to measure the amount of hole deflection.

[0124] (Evaluation result 1)

[0125]

[0126] Table 2 shows the amount of hole curvature of the holes 97 formed using the drills 100 according to Samples 1 to 3. FIG. 17 shows the amount of hole curvature of the holes 97 formed using the drills 100 according to Samples 1 to 3. In FIG. 17, the dots represent the average value of the amount of hole curvature of each sample. In FIG. 17, the lower and upper limits of the error bars represent the minimum and maximum values ​​of the amount of hole curvature of each sample, respectively. The value obtained by subtracting the minimum value from the maximum value of the amount of hole curvature of each sample is taken as the variation in the amount of hole curvature of each sample.

[0127] As shown in Table 2 and FIG. 17, in sample 1, the amount of hole bending was 0.097 mm or more and 0.279 mm or less. The average amount of hole bending was 0.161 mm. In sample 2, the amount of hole bending was 0.081 mm or more and 0.198 mm or less. The average amount of hole bending was 0.126 mm. In sample 3, the amount of hole bending was 0.044 mm or more and 0.097 mm or less. The average amount of hole bending was 0.070 mm.

[0128] From the above, it was confirmed that the drill 100 according to the example can reduce the amount of hole bending compared to the drill 100 according to the comparative example. It was also confirmed that the drill 100 according to the example can reduce the variation in the amount of hole bending compared to the drill 100 according to the comparative example.

[0129] (Evaluation Method 2) Next, the hole diameters of the holes 97 formed using the drills 100 according to Samples 1 to 3 were evaluated. Specifically, for each of the five holes 97 formed by the above-described Evaluation Method 1, the hole diameter of the pilot hole portion 95 and the hole diameter of the machined hole portion 96 were measured.

[0130] (Evaluation result 2)

[0131]

[0132] Table 3 shows the hole diameters of the holes 97 formed using the drill 100 according to Samples 1 to 3. As shown in Table 3, in Sample 1, the hole diameter of the pilot hole portion 95 was 7.894 mm or greater and 7.901 mm or less. The average hole diameter of the pilot hole portion 95 was 7.898 mm. The hole diameter of the machined hole portion 96 was 7.863 mm or greater and 7.868 mm or less. The average hole diameter of the machined hole portion 96 was 7.867 mm.

[0133] In sample 2, the hole diameter of the pilot hole portion 95 was 7.896 mm or more and 7.899 mm or less. The average hole diameter of the pilot hole portion 95 was 7.897 mm. The hole diameter of the machined hole portion 96 was 7.870 mm or more and 7.876 mm or less. The average hole diameter of the machined hole portion 96 was 7.873 mm.

[0134] In sample 3, the hole diameter of the pilot hole portion 95 was 7.918 mm or more and 7.921 mm or less. The average hole diameter of the pilot hole portion 95 was 7.919 mm. The hole diameter of the machined hole portion 96 was 7.917 mm or more and 7.920 mm or less. The average hole diameter of the machined hole portion 96 was 7.919 mm.

[0135] From the above, it was confirmed that the drill 100 according to the embodiment can reduce the absolute value of the difference between the hole diameter in the pilot hole portion 95 and the hole diameter in the machined hole portion 96, compared to the drill 100 according to the comparative example.

[0136] As shown in Table 3, in Sample 3, the hole diameter of pilot hole 98 before hole 97 was formed was 7.896 mm or more and 7.898 mm or less. The hole diameters of pilot hole portion 95 and machined hole portion 96 were each approximately the same as the maximum diameter of second body portion 32. Therefore, in Sample 3, it is believed that second body portion 32 pushed out the inner wall surface of hole 97, causing plastic deformation of workpiece material 99. Note that in Samples 1 and 2, the hole diameter of pilot hole 98 before hole 97 was approximately the same as the hole diameter of pilot hole portion 95.

[0137] (Evaluation Method 3) Next, the surface roughness of the inner wall surfaces of the holes 97 formed using the drills 100 according to Samples 1 to 3 was evaluated. Specifically, the surface roughness of the inner wall surface of the third hole (hole 3) formed among the five holes 97 formed by the above-described Evaluation Method 1 was measured. The arithmetic mean roughness Ra was used as an index of surface roughness. The arithmetic mean roughness Ra is a surface property parameter defined in JIS B0601:2013. The arithmetic mean roughness Ra was measured for the machined hole portion 96.

[0138] (Evaluation result 3)

[0139]

[0140] Table 4 shows the surface roughness of the inner wall surface of the hole 97 formed using the drill 100 according to Samples 1 to 3. As shown in Table 4, the arithmetic mean roughness Ra of the inner wall surface of the hole 97 was 0.721 μm or more in Samples 1 and 2. The arithmetic mean roughness Ra of the inner wall surface of the hole 97 in Sample 3 was 0.243 μm.

[0141] From the above, it was confirmed that the drill 100 according to the example can reduce the surface roughness of the inner wall surface of the hole 97 formed, compared to the drill 100 according to the comparative example. In the drill 100 according to the example, it is thought that the second body portion 32 expands the inner wall surface of the hole 97, thereby reducing the surface roughness of the inner wall surface of the hole 97.

[0142] (Evaluation Method 4) Next, the drills 100 according to Samples 1 to 3 were evaluated for cutting resistance applied to the drills 100 when forming the holes 97. Specifically, the average values ​​of the cutting torque and thrust resistance were measured when forming the third hole (third hole) of the five holes 97 formed by the above-described Evaluation Method 1.

[0143] (Evaluation result 4)

[0144]

[0145] Table 5 shows the measurement results of cutting torque and thrust resistance for Samples 1 to 3. As shown in Table 5, for Sample 1, the cutting torque was 4.737 N m and the thrust resistance was 1631 N. For Sample 2, the cutting torque was 4.679 N m and the thrust resistance was 1493 N. For Sample 3, the cutting torque was 6.237 N m and the thrust resistance was 1486 N.

[0146] From the above, it was confirmed that the drill 100 according to the example had an increased cutting torque and the same thrust resistance as the drill 100 according to the comparative example. It is believed that the increased cutting torque was caused by the second body portion 32 forming the hole 97 while expanding the inner wall surface of the hole 97 in the drill 100 according to the example.

[0147] 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 by the above description, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0148] 1 Front end, 2 Rear end, 3 Body, 4 Outer peripheral surface, 5 Spiral groove surface, 6 Thinning surface, 7 Shank, 8 Cutting edge, 9 Spiral groove, 10 First outer peripheral margin surface, 11 First outer peripheral margin surface portion, 12 Second outer peripheral margin surface portion, 13 Third outer peripheral margin surface portion, 14 First connecting surface, 15 First side surface, 16 Second side surface, 19 Outer peripheral intermediate surface, 20 Second outer peripheral margin surface, 21 Fourth outer peripheral margin surface portion, 22 Fifth outer peripheral margin surface portion, 23 Sixth outer peripheral margin surface portion, 24 Second connecting surface, 30 Coolant hole, 31 First main body portion, 32 Second main body portion, 33 Third main body portion, 34 Connecting portion, 36 First end portion, 37 Second end portion, 40 Front end surface (flank), 43 First flank portion, 44 Second flank portion, 51 First locus, 52 Second locus, 53 Third trajectory, 54 Fourth trajectory, 55 Fifth trajectory, 56 Sixth trajectory, 61 First boundary, 62 Second boundary, 63 Third boundary, 81 Thinning cutting edge portion, 82 Main cutting edge portion, 91 First tangent, 92 Second tangent, 93 First virtual line, 94 Second virtual line, 95 Pilot hole portion, 96 Machined hole portion, 97 Hole, 98 Pilot hole, 99 Workpiece, 100 Drill, 101 Axial direction, 102 Radial direction, 110 Rotation trajectory, A1 First rotation speed, A2 Second rotation speed, B1 First feed rate, B2 Second feed rate, C Axis, CS1 First cross section, CS2 Second cross section, D1 First outer diameter, D2 Second outer diameter, D3 Third outer diameter, E Distance, F Depth, L1 First length, L2 Second length, R1 First curvature radius, R2 second curvature radius, T0 start time, T1 first time, T2 second time, W1 cutting edge diameter, W2 diameter, X axis, θ1 first angle, θ2 second angle.

Claims

1. A drill that rotates around an axis, comprising a body, the body including: a first body portion located at the front end of the drill and having a cutting edge; a second body portion located axially relative to the first body portion along the axis from the front end to the rear end of the drill; and a connecting portion located between the first body portion and the second body portion and continuing to each of the first body portion and the second body portion, wherein a helical flute is formed around the axis in the first body portion, the connecting portion, and the second body portion, and when the diameter of the cutting edge is defined as the cutting edge diameter, the length of the helical flute in the axial direction is six times or more the cutting edge diameter, and the first body portion is provided with a back taper, and the maximum diameter of the second body portion is larger than the cutting edge diameter.

2. A drill as described in claim 1, wherein the distance in the axial direction between the front end and the part of the second body portion with the largest outer diameter is between 1 and 3 times the cutting edge diameter.

3. A drill as described in claim 1 or claim 2, wherein the value obtained by subtracting the cutting edge diameter from the maximum diameter of the second body portion is 0.005 mm or more and 0.08 mm or less, and the length of the second body portion in the axial direction is 1.5 times or more and 5 times or less the cutting edge diameter.

4. A drill as claimed in any one of claims 1 to 3, wherein the second body portion has a first end and a second end located between the first end and the rear end, and the outer diameter of the second body portion at the first end is the same as the outer diameter of the second body portion at the second end.

5. A drill as described in any one of claims 1 to 3, wherein a back taper is provided in the second body portion, and the gradient of the back taper in the second body portion is equal to or less than the gradient of the back taper in the first body portion.

6. A drill as claimed in any one of claims 1 to 5, wherein the body includes an outer peripheral margin surface located on the outermost periphery of the body, the outer peripheral margin surface having a first outer peripheral margin surface portion constituted by the connecting portion and a second outer peripheral margin surface portion constituted by the second main body portion and connected to the first outer peripheral margin surface portion, and in a cross section including the axis and intersecting each of the first outer peripheral margin surface portion and the second outer peripheral margin surface portion, the angle formed by the axis and a tangent to the first outer peripheral margin surface portion at the boundary between the first outer peripheral margin surface portion and the second outer peripheral margin surface portion is 30° or less.

7. The drill according to claim 6, wherein in a cross section that includes the axis and intersects with each of the first outer peripheral margin surface portion and the second outer peripheral margin surface portion, the first outer peripheral margin surface portion is concave and arc-shaped.

8. A drill as described in claim 7, wherein in a cross section that includes the axis and intersects with each of the first outer peripheral margin surface portion and the second outer peripheral margin surface portion, the radius of curvature of the first outer peripheral margin surface portion is 0.2 mm or more.

9. A drill as claimed in any one of claims 1 to 8, wherein the first main body portion has a front end surface, the body is provided with a coolant hole for discharging coolant, and the coolant hole is open at the front end surface.

10. A machining method using the drill according to any one of claims 1 to 9, comprising the steps of: forming a pilot hole in a workpiece; inserting the drill into the pilot hole while rotating the drill; and, after the step of inserting the drill into the pilot hole, forming a hole in the workpiece using the drill, wherein the value obtained by subtracting the diameter of the pilot hole from the maximum diameter of the second body portion is 0 mm or more and 0.05 mm or less.

11. The processing method described in claim 10, wherein the rotation speed of the drill at a first time point when the first body portion enters the pilot hole is defined as a first rotation speed, the feed rate of the drill at the first time point is defined as a first feed rate, the rotation speed of the drill at a second time point when the second body portion enters the pilot hole is defined as a second rotation speed, and the feed rate of the drill at the second time point is defined as a second feed rate, the second rotation speed is greater than the first rotation speed, and the second feed rate is smaller than the first feed rate.

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