drill bit

Abstract

A drill bit rotating around an axis has a rear flank, a land, an outer peripheral surface, and a chip discharge surface. The land is connected to the rear flank. The outer peripheral surface is connected to the rear flank and the land, respectively. The chip discharge surface is connected to the rear flank and the outer peripheral surface, respectively. An edge line between the rear flank and the chip discharge surface constitutes a cutting edge. A first land band and a second land band are provided on the outer peripheral surface. The first land band is connected to the cutting edge and the rear flank, respectively. The second land band is located rearward of the first land band in a rotation direction and is separated from the rear flank and the land, respectively. The outer peripheral portion of the first land band and the outer peripheral portion of the second land band each have an inverted cone with the same angle. In a direction parallel to the axis, a distance between a front end of the first land band and a front end of the second land band is 3 mm or more and 5 mm or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a drill. BACKGROUND

[0002] A drill having a first land and a second land is described in Japanese Patent Application Publication No. 2020-44616 (Patent Literature 1).

[0003] Patent Literature 1: Japanese Patent Application Publication No. 2020-44616 SUMMARY

[0004] The drill according to the present application rotates around an axis, and has a clearance face, a land, an outer peripheral face, and a chip discharge face. The land is connected to the clearance face. The outer peripheral face is connected to each of the clearance face and the land. The chip discharge face is connected to each of the clearance face and the outer peripheral face. An edge line between the clearance face and the chip discharge face constitutes a cutting edge. A first land and a second land are provided on the outer peripheral face. The first land is connected to each of the cutting edge and the clearance face. The second land is located rearward in a rotation direction with respect to the first land and is separated from each of the clearance face and the land. An outer peripheral portion of the first land and an outer peripheral portion of the second land each have a back taper of the same angle. In a direction parallel to the axis, a distance between a leading end of the first land and a leading end of the second land is 3 mm or more and 5 mm or less. BRIEF DESCRIPTION OF DRAWINGS

[0005] Figure 1 is a plan view schematically showing a structure of the drill according to the first embodiment.

[0006] Figure 2 is a front view schematically showing a structure of the drill according to the first embodiment.

[0007] Figure 3 is a partially enlarged oblique view schematically showing a structure of the drill according to the first embodiment.

[0008] Figure 4 is an enlarged plan view schematically showing a region IV of Figure 1

[0009] Figure 5 is a cross-sectional view along a line V-V of Figure 4

[0010] Figure 6 is a view schematically showing a relationship between a distance from the axis and a position in the axial direction.

[0011] Figure 7 is an enlarged plan view schematically showing a structure of the drill according to the second embodiment.

[0012] Figure 8 is a cross-sectional view along a line V-V of Figure 7 ​​Fig. 8 is a cross-sectional view taken along line VIII-VIII of Fig. 7.

[0013] Figure 9 Fig. 9 is an enlarged plan view showing the structure of a drill bit according to the third embodiment.

[0014] Figure 10 Fig. 10 is a cross-sectional view taken along line IX-IX of Fig. 9. Figure 9

[0015] Figure 11A Fig. 11 is a partial cross-sectional view showing a process of performing inclined through processing on a workpiece using the drill bit.

[0016] Figure 11B Fig. 12 is a partial cross-sectional view showing a method of measuring the roundness of a through hole.

[0017] Figure 12 Fig. 13 is a side view showing the structure of a crank shaft.

[0018] Figure 13 Fig. 14 is a graph showing the relationship between the current value and the time. DETAILED DESCRIPTION

[0019] [PROBLEMS TO BE SOLVED BY THE INVENTION]

[0020] An object of the present application is to provide a drill bit that maintains high rigidity and improves the roundness of a hole.

[0021] [EFFECTS OF THE INVENTION]

[0022] According to the present application, it is possible to provide a drill bit that maintains high rigidity and improves the roundness of a hole.

[0023] [SUMMARY OF EMBODIMENTS OF THE INVENTION]

[0024] First, a summary of the embodiments of the present application will be described.

[0025] (1) A drill bit 100 according to the present application rotates around an axis X, and has a rear clearance face 8, a land 9, an outer peripheral face 6, and a chip discharge face 5. The land 9 is connected to the rear clearance face 8. The outer peripheral face 6 is connected to each of the rear clearance face 8 and the land 9. The chip discharge face 5 is connected to each of the rear clearance face 8 and the outer peripheral face 6. An edge line between the rear clearance face 8 and the chip discharge face 5 constitutes a cutting edge 3. A first land band 10 is connected to each of the cutting edge 3 and the rear clearance face 8, and a second land band 20 is located rearward in the direction of rotation with respect to the first land band 10 and is separated from each of the rear clearance face 8 and the land 9. The outer peripheral portion of the first land band 10 and the outer peripheral portion of the second land band 20 each have an inverted cone with the same angle. In a direction parallel to the axis X, the distance between the leading end of the first land band 10 and the leading end of the second land band 20 is 3 mm or more and 5 mm or less.​

[0026] (2) In the drill 100 according to the above (1), the front end of the second land 20 can extend in a direction perpendicular to the axis X when viewed from a direction perpendicular to the axis X.

[0027] (3) In the drill 100 according to the above (1) or (2), the length of the chip discharge surface 5 in a direction parallel to the axis X can be 10 times or more and 55 times or less of the diameter of the drill 100.

[0028] (4) In the drill 100 according to any one of the above (1) to (3), the second land 20 can be separated from the chip discharge surface 5.

[0029] [Details of Embodiments of the Invention]

[0030] Details of an embodiment of the present invention (hereinafter, also referred to as the present embodiment) will be described below based on the drawings. Furthermore, the same reference numerals are assigned to the same or equivalent portions in the following drawings, and the description thereof will not be repeated.

[0031] (First Embodiment)

[0032] First, the structure of the drill 100 according to the first embodiment will be described. Figure 1 is a schematic plan view showing the structure of the drill 100 according to the first embodiment. As shown in Figure 1 , the drill 100 according to the first embodiment mainly has a front end 1, a rear end 2, a relief surface 8, a grinding surface 9, an outer peripheral surface 6, a chip discharge surface 5, and a shank 7. The drill 100 according to the first embodiment is a drill 100 for metalworking. As shown in Figure 1 , the outer peripheral surface 6 is provided in a spiral shape around the axis X. The outer peripheral surface 6 is continuous with the chip discharge surface 5. The chip discharge surface 5 constitutes a fluted groove. The chip discharge surface 5 is provided in a spiral shape around the axis X. The cutting edge 3 is provided on the front end side of the drill 100.

[0033] The front end 1 of the drill 100 is a portion that opposes a workpiece. The rear end 2 of the drill 100 is a portion that opposes a tool spindle that rotates the drill 100. The shank 7 is a portion that is attached to the tool spindle. The axis X passes through the front end 1 and the rear end 2. The direction along the axis X is the axial direction. The direction perpendicular to the axial direction is the radial direction. In the present specification, the direction from the front end 1 toward the rear end 2 is referred to as the rearward direction in the axial direction. Conversely, the direction from the rear end 2 toward the front end 1 is referred to as the forward direction in the axial direction. The drill 100 rotates around the axis X.

[0034] Figure 2 is a schematic front view showing the structure of the drill 100 according to the first embodiment. As shown in Figure 2As shown, the drill bit 100 also has a clearance surface 8 and a shaving surface 9. The edge between the clearance surface 8 and the chip discharge surface 5 forms the cutting edge 3. The chip discharge surface 5 near the cutting edge 3 functions as a forward-tilting surface. The shaving surface 9 is connected to the clearance surface 8. The shaving surface 9 is located behind the clearance surface 8 in the direction of rotation. The clearance surface 8 has a first region 41 and a second region 42. The first region 41 forms the cutting edge 3. The second region 42 is connected to the first region 41. The second region 42 is located behind the first region 41 in the direction of rotation. The second region 42 is connected to the shaving surface 9. The second region 42 is located between the first region 41 and the shaving surface 9.

[0035] like Figure 2 As shown, cooling holes 30 can be provided on the rear clearance surface 8. For example, the cooling holes 30 can be provided in the second region 42. Figure 2 As shown, when viewed along axis X, the boundary between the second region 42 and the grinding surface 9 is, for example, curved (R-grinding). Alternatively, when viewed along axis X, the boundary between the second region 42 and the grinding surface 9 can be, for example, straight (X-grinding). A first cutting edge 10 and a second cutting edge 20 are provided on the outer peripheral surface 6. The second cutting edge 20 is positioned rearward relative to the first cutting edge 10 in the rotational direction. The second cutting edge 20 is separate from the first cutting edge 10. The outer peripheral surface 6 has an outer peripheral region 31. The outer peripheral region 31 is located between the first cutting edge 10 and the second region 42. Figure 2 As shown, when viewed along axis X, the outer peripheral region 31 is, for example, arc-shaped.

[0036] Figure 3 This is a partially enlarged perspective view showing the structure of the drill bit 100 according to the first embodiment. (See attached image.) Figure 3 As shown, the outer peripheral surface 6 is connected to both the clearance surface 8 and the grinding surface 9. The chip discharge surface 5 is connected to both the clearance surface 8 and the outer peripheral surface 6. The grinding surface 9 is connected to the chip discharge surface 5. The first cutting edge 10 is connected to both the cutting edge 3 and the clearance surface 8. Specifically, the first cutting edge 10 is connected to a portion of the first region 41 of the clearance surface 8. The first cutting edge 10 is connected to the boundary between the chip discharge surface 5 and the outer peripheral surface 6.

[0037] The first land 10 has a first front end 13, a first peripheral portion 11, and a first flank portion 12. The first front end 13 is continuous with the cutting edge 3. The first peripheral portion 11 is continuous with the first front end 13. In the direction along the axis X, the first peripheral portion 11 is located at a position further toward the rear end 2 than the first front end 13. The first flank portion 12 is continuous with the first front end 13. In the direction along the axis X, the first flank portion 12 is located at a position further toward the rear end 2 than the first front end 13. The first flank portion 12 is continuous with each of the first peripheral portion 11 and the peripheral region 31. The first flank portion 12 is located rearward in the direction of rotation with respect to the first peripheral portion 11. From another viewpoint, the first peripheral portion 11 is located, in the direction of rotation, between the chip discharge face 5 and the first flank portion 12.

[0038] The second land 20 is separated from each of the relief face 8 and the grinding face 9. The second land 20 is continuous with the boundary between the chip discharge face 5 and the peripheral face 6. The second land 20 has a second front end 23, a second peripheral portion 21, and a second flank portion 22. The second front end 23 is continuous with the peripheral region 31. The second peripheral portion 21 is continuous with the second front end 23. In the direction along the axis X, the second peripheral portion 21 is located at a position further toward the rear end 2 than the second front end 23. The second flank portion 22 is continuous with the second front end 23. In the direction along the axis X, the second flank portion 22 is located at a position further toward the rear end 2 than the second front end 23. The second flank portion 22 is continuous with each of the second peripheral portion 21 and the peripheral region 31. The second flank portion 22 is located forward in the direction of rotation with respect to the second peripheral portion 21. From another viewpoint, the second peripheral portion 21 is located, in the direction of rotation, between the chip discharge face 5 and the second flank portion 22.

[0039] Figure 4 is an enlarged plan view of the region IV of Figure 1 If the distance between the front end of the first land 10 (the first front end 13) and the front end of the second land 20 (the second front end 23) is set as a first distance Al in the direction parallel to the axis X, the first distance Al is 3 mm or more and 5 mm or less. The lower limit of the first distance Al is not particularly limited, but for example, it can be 3.2 mm or more, or 3.4 mm or more. The upper limit of the first distance Al is not particularly limited, but for example, it can be 4.8 mm or less, or 4.6 mm or less.

[0040] As shown in Figure 4 , the distance between the front end 1 of the drill 100 and the first front end 13 of the first land 10 in the direction parallel to the axis X is a third distance A3. As shown in Figure 4 , the third distance A3 can be shorter than the first distance Al. As shown in Figure 4As shown, when viewed from a direction perpendicular to axis X, the second tip 23 of the second cutting edge 20 can extend in a direction perpendicular to axis X. From another viewpoint, the second tip 23 can be parallel to a plane perpendicular to axis X. The second tip 23 extends in the direction of rotation of the drill bit.

[0041] like Figure 4 As shown, the drill bit 100 according to the first embodiment has two cutting edges 3. When viewed from a direction perpendicular to the axis X and perpendicular to the line segment connecting the outer peripheral ends of the first cutting edge 3 on one side and the second cutting edge 3 on the other side, the distance between the outer peripheral ends of the first cutting edge 3 on one side and the second cutting edge 3 on the other side is the diameter D of the drill bit 100. The diameter D of the drill bit 100 is not particularly limited, for example, it is 5 mm. Figure 1 As shown, in the direction parallel to the axis X, the length L of the chip discharge surface 5 is, for example, more than 10 times and less than 55 times the diameter D of the drill bit 100. The lower limit of the length L of the chip discharge surface 5 is not particularly limited, but may, for example, be more than 15 times or more than 20 times the diameter D of the drill bit 100. The upper limit of the length L of the chip discharge surface 5 is not particularly limited, but may, for example, be less than 50 times or less than 45 times the diameter D of the drill bit 100.

[0042] Figure 5 It is along Figure 4 A schematic diagram of the cross-section of the V-V line. Figure 5 The cross-section shown is perpendicular to the axis X and intersects both the first cutting edge 10 and the second cutting edge 20. For example... Figure 5 As shown, in the direction of rotation, the width of the second cutting edge 20 (second width C2) is greater than the width of the first cutting edge 10 (first width C1). The lower limit of the second width C2 is not particularly limited, but it can be, for example, more than 1.5 times or more than 2 times the first width C1.

[0043] like Figure 5 As shown, the outer peripheral region 31 is connected to both the first side portion 12 and the second side portion 22. The first side portion 12 is located in front of the outer peripheral region 31 in the direction of rotation. The second side portion 22 is located behind the outer peripheral region 31 in the direction of rotation. In the radial direction, the first outer peripheral portion 11 is located further outward than the outer peripheral region 31. Similarly, in the radial direction, the second outer peripheral portion 21 is located further outward than the outer peripheral region 31. In the radial direction, the positions of the first outer peripheral portion 11 and the second outer peripheral portion 21 are the same. From another viewpoint, in a cross-section perpendicular to the axis X, the distance between the axis X and the first outer peripheral portion 11 is the same as the distance between the axis X and the second outer peripheral portion 21.

[0044] Figure 6is a diagram showing the relationship between the position in the axial direction and the distance from the axis X. In Figure 6 , the horizontal axis shows the position in the axial direction. Figure 6 The left side of is the front end side of the drill bit 100. Figure 6 The right side of is the rear end side of the drill bit 100. In Figure 6 , the vertical axis shows the distance from the axis X. The 1st position P1 is the position of the front end 1 of the drill bit 100. The 2nd position P2 is the position of the front end (1st front end 13) of the 1st land 10. In the direction parallel to the axis X, the 2nd position P2 is located between the 1st position P1 and the rear end 2 of the drill bit 100. The 3rd position P3 is the position of the front end (2nd front end 23) of the 2nd land 20. In the direction parallel to the axis X, the 3rd position P3 is located between the 2nd position P2 and the rear end 2 of the drill bit 100. The 4th position P4 is the position of the rear end of the 1st land 10 and the position of the rear end of the 2nd land 20. In the direction parallel to the axis X, the 4th position P4 is located between the 3rd position P3 and the rear end 2 of the drill bit 100.

[0045] As shown in Figure 6 , in the direction parallel to the axis X, the 1st land 10 is provided in the region from the 2nd position P2 to the 4th position P4. In the direction parallel to the axis X, the 2nd land 20 is provided in the region from the 3rd position P3 to the 4th position P4. In the direction parallel to the axis X, the distance from the front end (2nd front end 23) of the 2nd land 20 to the rear end of the 2nd land 20 is the 2nd distance A2. The 2nd distance A2 can be longer than the 1st distance Al. The 2nd distance A2 is the length of the 2nd land 20 in the direction parallel to the axis X. The sum of the 1st distance Al and the 2nd distance A2 is the length of the 1st land 10 in the direction parallel to the axis X. In the direction parallel to the axis X, the length of the 1st land 10 can be longer than the length of the 2nd land 20.

[0046] The 1st outer peripheral portion 11 of the 1st land 10 and the 2nd outer peripheral portion 21 of the 2nd land 20 each have an inverse taper. The angle of the inverse taper of the 1st outer peripheral portion 11 of the 1st land 10 is the same as the angle of the inverse taper of the 2nd outer peripheral portion 21 of the 2nd land 20. In other words, the 1st outer peripheral portion 11 of the 1st land 10 and the 2nd outer peripheral portion 21 of the 2nd land 20 each have an inverse taper of the same angle. From another viewpoint, the 1st outer peripheral portion 11 and the 2nd outer peripheral portion 21 are located on the same conical surface.

[0047] As shown in Figure 6The value obtained by subtracting the distance between the first outer peripheral portion 11 of the first blade band 10 at the third position P3 and the axis X from the distance between the first outer peripheral portion 11 of the first blade band 10 at the second position P2 and the axis X is the first length B1. The tangent of the angle of the reverse taper of the outer peripheral portion of the first blade band 10 is the value obtained by dividing the first length B1 by the first distance Al. Likewise, the value obtained by subtracting the distance between the second outer peripheral portion 21 of the second blade band 20 at the fourth position P4 and the axis X from the distance between the second outer peripheral portion 21 of the second blade band 20 at the third position P3 and the axis X is the second length B2. The tangent of the angle of the reverse taper of the outer peripheral portion of the second blade band 20 is the value obtained by dividing the second length B2 by the second distance A2. The angle of the reverse taper of the outer peripheral portion of the first blade band 10 and the angle of the reverse taper of the outer peripheral portion of the second blade band 20 are, for example, arctan(0.35 mm / 100 mm / 2) (unit: rad). The angle of the reverse taper of the outer peripheral portion of the first blade band 10 and the angle of the reverse taper of the outer peripheral portion of the second blade band 20 are, for example, 0.00175 rad.

[0048] As shown in FIG. 2, the distance between the first outer peripheral portion 11 of the first blade band 10 in the radial direction and the axis X monotonously decreases as it goes toward the rear end 2 side. Likewise, the distance between the second outer peripheral portion 21 of the second blade band 20 in the radial direction and the axis X monotonously decreases as it goes toward the rear end 2 side. The radial distance between the first outer peripheral portion 11 at the second position P2 and the axis X is greater than the radial distance between the second outer peripheral portion 21 at the third position P3 and the axis X. The radial distance between the first outer peripheral portion 11 at the second position P2 and the axis X is greater than the radial distance between the first outer peripheral portion 11 at the third position P3 and the axis X. The radial distance between the first outer peripheral portion 11 at the third position P3 and the axis X is the same as the radial distance between the second outer peripheral portion 21 at the third position P3 and the axis X. Figure 6 Likewise, the radial distance between the first outer peripheral portion 11 at the third position P3 and the axis X is greater than the radial distance between the second outer peripheral portion 21 at the fourth position P4 and the axis X. The radial distance between the first outer peripheral portion 11 at the third position P3 and the axis X is greater than the radial distance between the first outer peripheral portion 11 at the fourth position P4 and the axis X. The radial distance between the first outer peripheral portion 11 at the fourth position P4 and the axis X is the same as the radial distance between the second outer peripheral portion 21 at the fourth position P4 and the axis X.

[0049] (Second Embodiment)

[0050]

[0051] ​Next, the structure of the drill bit 100 according to the second embodiment will be described. The structure of the drill bit 100 according to the second embodiment is different from the structure of the drill bit 100 according to the first embodiment in that the second land 20 is wide, and is the same as the structure of the drill bit 100 according to the first embodiment in other respects. Hereinafter, the structure of the drill bit 100 according to the second embodiment will be described focusing on the difference from the structure of the drill bit 100 according to the first embodiment.

[0052] Figure 7 is an enlarged plan view showing the structure of the drill bit 100 according to the second embodiment. Figure 8 is a cross-sectional view along the line VIII-VIII of Figure 7 . The cross section shown in Figure 8 is a cross section perpendicular to the axis X and intersecting each of the first land 10 and the second land 20. As shown in Figure 7 and Figure 8 , the second land 20 of the drill bit 100 according to the second embodiment is wider (second width C2) than the second land 20 of the drill bit 100 according to the first embodiment (second width C2). As shown in Figure 8 , the lower limit of the second width C2 is not particularly limited, but for example, can be 3 times or more the first width Cl, or can be 4 times or more. The upper limit of the second width C2 is not particularly limited, but for example, can be 8 times or less the first width Cl, or can be 6 times or less.

[0053] (Third Embodiment)

[0054] Next, the structure of the drill bit 100 according to the third embodiment will be described. The structure of the drill bit 100 according to the third embodiment is different from the structure of the drill bit 100 according to the first embodiment in that the second land 20 is separated from the chip discharge surface 5, and is the same as the structure of the drill bit 100 according to the first embodiment in other respects. Hereinafter, the structure of the drill bit 100 according to the third embodiment will be described focusing on the difference from the structure of the drill bit 100 according to the first embodiment.

[0055] Figure 9 is an enlarged plan view showing the structure of the drill bit 100 according to the third embodiment. Figure 10 is a cross-sectional view along the line IX-IX of Figure 9 . The cross section shown in Figure 10 is a cross section perpendicular to the axis X and intersecting each of the first land 10 and the second land 20. As shown in Figure 9 and Figure 10 , the second land 20 of the drill bit 100 according to the third embodiment is separated from the chip discharge surface 5. From another viewpoint, the second land 20 is separated from the boundary line between the chip discharge surface 5 and the outer peripheral surface 6.

[0056] As Figure 10 shown, the second blade band 20 has a second peripheral portion 21, a second side surface portion 22, and a third side surface portion 24. The second peripheral portion 21 is connected to each of the second side surface portion 22 and the third side surface portion 24. The third side surface portion 24 is located rearward in the rotation direction with respect to the second side surface portion 22. The third side surface portion 24 is located on the opposite side of the second side surface portion 22. In the rotation direction, the second peripheral portion 21 is located between the second side surface portion 22 and the third side surface portion 24. The second side surface portion 22 is connected to the peripheral region 31. The third side surface portion 24 is connected to the peripheral region 31 rearward in the rotation direction with respect to the second peripheral portion 21. As Figure 10 shown, the peripheral region 31 is provided on both sides of the second blade band 20 in the rotation direction.

[0057] Figure 11A is a partial cross-sectional schematic view showing a process of performing inclined through-machining using the drill bit 100 with respect to a workpiece. As Figure 11A shown, the drill bit 100 forms a through-hole 60 in a workpiece 50. The workpiece 50 has an exit end surface 53. The drill bit 100 moves along a travel direction F parallel to the plane of the paper while rotating about an axis X. The travel direction F of the drill bit 100 is inclined with respect to the exit end surface 53. Also, the travel direction F of the drill bit 100 is inclined with respect to a plane perpendicular to the plane of the paper and perpendicular to the exit end surface 53. The through-hole 60 has a first exit end portion 51 and a second exit end portion 52. In a case where the drill bit 100 is in a first state S1, the peripheral end of the cutting edge 3 is located at the second exit end portion 52. In a case where the drill bit 100 is in a second state S2, the peripheral end of the cutting edge 3 is located at the first exit end portion 51.

[0058] The roundness is defined by the magnitude of the error of a circular body with respect to a geometrically correct circle as prescribed in JIS (Japanese Industrial Standards) B0621-1984. The roundness is expressed by the difference between the radii of two concentric geometric circles when the circular body is sandwiched by the two concentric geometric circles, in a case where the interval between the two concentric geometric circles is the smallest. The unit of the roundness is pm.

[0059] Figure 11B is a partial cross-sectional schematic view showing a method of measuring the roundness of the through-hole 60. Figure 11B is a cross-sectional schematic view along the XIB-XIB line of Figure 11A . Figure 11BThe illustrated cross section is a view of a cross section intersecting a plane H perpendicular to the axis X and at a 5th distance G from the 2nd outlet end portion 52, as viewed from a direction opposite to the advancing direction F. The 5th distance G is, for example, 5 mm. A direction projecting to the plane H from the axis X in a direction toward the 2nd outlet end portion 52, perpendicular to the axis X, is defined as a 1st direction 101. In the plane H, a direction after rotating the 1st direction 101 by 90° counterclockwise is defined as a 2nd direction 102. In the plane H, the axis X is marked as an origin, coordinates of the 1st direction 101 are marked as I, coordinates of the 2nd direction 102 are marked as J, and a position in the plane H is marked as (I, J). In the plane H, an intersection line between the cut material 50 and the through-hole 60 is defined as an intersection line K. In the plane H, positions of 4 points on the intersection line K arranged at equal angles with respect to the axis X are measured, and thus a roundness is found.

[0060] The roundness is found, specifically, in the following manner. An intersection point of a direction from the axis X toward the 1st direction 101 and the intersection line K is defined as an intersection point Q1. An intersection point of a direction from the axis X toward the 2nd direction 102 and the intersection line K is defined as an intersection point Q2. An intersection point of a direction from the axis X toward a direction opposite to the 1st direction 101 and the intersection line K is defined as an intersection point Q3. An intersection point of a direction from the axis X toward a direction opposite to the 2nd direction 102 and the intersection line K is defined as an intersection point Q4. First, coordinates of the intersection point Q1, the intersection point Q2, the intersection point Q3, and the intersection point Q4 are measured as (I1, 0), (0, J2), (I3, 0), and (0, J4), respectively. Next, distances from the origin, that is, the axis X to the above 4 points are calculated using the coordinates of the intersection point Q1, the intersection point Q2, the intersection point Q3, and the intersection point Q4 as V(I1 2 ), V(J2 2 ), V(I3 2 ), and V(J4 2 ), respectively. In the calculated distances, a difference between a maximum value and a minimum value is a provisional value of the roundness. In measuring the roundness, a center (I0, J0) of the intersection line K does not necessarily coincide with the axis X, that is, the origin (0, 0). The center (I0, J0) of the intersection line K is determined in such a manner that a difference between a maximum value and a minimum value among distances calculated between the temporarily decided center of the intersection line K and the intersection point Q1, the intersection point Q2, the intersection point Q3, and the intersection point Q4 becomes the smallest, as a target function. When the target function becomes the smallest, the minimum value of the target function becomes the roundness.

[0061] The roundness measured in the above-described manner is referred to as a minimum zone roundness. A more detailed measurement method of the minimum zone roundness is described, for example, in a non-patent literature (Mori, Yoshitsugu, "Hajimete no Shinendo Sokutei", Precision Engineering Society, vol. 82, No. 9, 2016, pp. 803-806).

[0062] Reference is made to Figure 11A In a case where the drill bit 100 is in the position of the 2nd state S2, if the distance (4th distance E) from the outer peripheral end of the cutting edge 3 of the drill bit 100 to the 2nd exit end portion 52 is shorter than the 1st distance Al (refer to Figure 4 ), the 2nd land 20 does not reach the 2nd exit end portion 52. Therefore, at the 2nd exit end portion 52, the drill bit 100 is not guided by the 2nd land 20. As a result, the drill bit 100 moves to the right lower side of Figure 11A . Thereby, the through-hole 60 expands to the right lower side, and thus the roundness of the exit of the through-hole 60 deteriorates. On the other hand, if the distance (4th distance E) from the outer peripheral end of the cutting edge 3 of the drill bit 100 to the 2nd exit end portion 52 is longer than the 1st distance Al, the 2nd land 20 contacts the 2nd exit end portion 52. Therefore, at the 2nd exit end portion 52, the drill bit 100 is guided by the 2nd land 20. As a result, it is possible to suppress the movement of the drill bit 100 to the right lower side of Figure 11A . Thereby, it is possible to suppress the deterioration of the roundness of the exit of the hole.

[0063] Further, the machined material 50 is, for example, a metal such as steel. The machined material 50 can be, for example, a low-priced microalloyed steel, i.e., 38MnS6. The machined material 50 can be a carbon steel, can be an alloy steel, can be a difficult-to-cut material, or can be a stainless steel material (SUS). The machining method can be, for example, MQL (Minimum Quantity Lubrication) machining.

[0064] Next, the effect of the drill bit 100 according to the present embodiment will be described.

[0065] In a case where the distance between the front end of the 1st land 10 and the front end of the 2nd land 20 is short, at the start of the hole opening, only the 1st land 10 contacts the inner wall surface of the hole, but immediately thereafter, both the 1st land 10 and the 2nd land 20 contact the inner wall surface of the hole. Therefore, at the time of the hole opening machining, an excessive torque is applied to the inner wall surface of the hole. As a result, the roundness of the hole deteriorates. On the other hand, in a case where the distance between the front end of the 1st land 10 and the front end of the 2nd land 20 is long, for a period from the start of the hole opening, only the 1st land 10 continuously contacts the inner wall surface of the hole. Thereafter, both the 1st land 10 and the 2nd land 20 contact the inner wall surface of the hole. Therefore, at the time of the hole opening machining, it is possible to suppress the application of an excessive torque to the inner wall surface of the hole. As a result, the roundness of the hole improves. In particular, in MQL machining, difficult-to-cut material machining, or SUS machining, there is a tendency that the hole shrinks after the machining, and thus the torque applied to the inner wall surface of the hole easily becomes excessive. The drill bit 100 according to the present embodiment particularly exerts an effect in MQL machining, difficult-to-cut material machining, or SUS machining.

[0066] In addition, in a case where the distance between the front end of the first land 10 and the front end of the second land 20 is too long, the drill 100 cannot be guided by the second land 20 when the drill 100 penetrates the inclined hole. Therefore, the drill 100 interferes with the inner wall surface of the hole. As a result, the roundness of the hole cannot be improved.

[0067] According to the drill 100 related to the above-described embodiment, the distance between the front end of the first land 10 and the front end of the second land 20 is 3 mm or more and 5 mm or less in the direction parallel to the axis X. By setting the distance between the front end of the first land 10 and the front end of the second land 20 to be 3 mm or more, it is possible to suppress the application of excessive torque to the inner wall surface of the hole. By setting the distance between the front end of the first land 10 and the front end of the second land 20 to be 5 mm or less, it is possible to suppress the interference of the drill 100 with the inner wall surface of the hole when the drill 100 penetrates the inclined hole. As a result, it is possible to improve the roundness of the hole formed in the machined material 50.

[0068] In addition, as a method of lengthening the distance between the front end of the first land 10 and the front end of the second land 20, a method of increasing the grinding surface 9 to form the second land 20 such that the front end of the second land 20 is continuous with the grinding surface 9 is considered. However, if the grinding surface 9 is increased, the core thickness of the drill 100 becomes small. As a result, the rigidity of the drill 100 decreases.

[0069] According to the drill 100 related to the above-described embodiment, the second land 20 is separated from each of the clearance surface 8 and the grinding surface 9. Therefore, it is possible to lengthen the distance between the front end of the first land 10 and the front end of the second land 20 without increasing the grinding surface 9. Therefore, it is possible to maintain the rigidity of the drill 100 high and improve the roundness of the hole.

[0070] According to the drill 100 related to the above-described embodiment, the front end of the second land 20 can extend in the direction perpendicular to the axis X when viewed from the direction perpendicular to the axis X. In a case where the front end of the second land 20 extends obliquely with respect to a straight line perpendicular to the axis X, the width of the second land 20 in the direction of rotation is smaller than in a case where the front end of the second land 20 extends along the straight line perpendicular to the axis X. Therefore, in a case where the front end of the second land 20 extends obliquely with respect to the straight line perpendicular to the axis X, the strength of the second land 20 decreases and the second land 20 is likely to be damaged compared to a case where the front end of the second land 20 extends along the straight line perpendicular to the axis X. By extending the front end of the second land 20 in the direction perpendicular to the axis X when viewed from the direction perpendicular to the axis X, it is possible to improve the strength of the front end of the second land 20. As a result, it is possible to suppress the damage to the front end of the second land 20.

[0071] Example

[0072] (Sample Preparation)

[0073] First, the drill bits 100 of sample 1 and sample 2 were prepared. The drill bit 100 of sample 1 is the drill bit 100 involved in the comparative example. The drill bit 100 of sample 2 is the drill bit 100 involved in the embodiment. In the drill bit 100 of sample 1, the second land 20 is connected to the rear clearance face 8. In the direction parallel to the axis X, the distance between the front end of the first land 10 and the front end of the second land 20 was set to 1.5 mm. In the drill bit 100 of sample 2, the second land 20 is separated from the rear clearance face 8 and the relief face 9. In the direction parallel to the axis X, the distance between the front end of the first land 10 and the front end of the second land 20 (first distance Al) was set to 4 mm.

[0074] (Evaluation method)

[0075] Next, the drill bits 100 of sample 1 and sample 2 were used to form oil holes in the crankshaft. Figure 12 is a side view showing the structure of the crankshaft. As shown in Figure 12 , the crankshaft 70 mainly has a crankshaft journal 71, a counterweight 72, and a crankpin 73. As shown in Figure 12 , the drill bits 100 of sample 1 and sample 2 were used to form oil holes 74 in the crankshaft 70 (machined material). The oil holes 74 were formed to pass from the crankpin 73 to the crankshaft journal 71. The machined material was set to 38MnS6. The diameter of the drill bit 100 was set to 4.95 mm. The diameter of the hole was set to 4.8 (+0.3 / -0.1) mm. The depth of the hole was set to 100.2 mm. The cutting speed (peripheral speed) was set to 80 m / min. The feed speed f was set to 0.15 mm / rev. The equipment used was DH524 manufactured by Nisshinbo Industries, Inc. While the drill bits 100 of sample 1 and sample 2 were used to form the oil holes 74 in the crankshaft 70, the load current value of the main shaft of the machining equipment was measured. In addition, the roundness of the oil holes formed in the crankshaft 70 was measured.

[0076] (Evaluation results)

[0077] Figure 13 is a graph showing the relationship between the current value and the time. In Figure 13 , the horizontal axis shows the time (unit: millisecond). In Figure 13 , the vertical axis shows the load current value of the main shaft of the machining equipment (unit: ampere). In Figure 13 , data of five different line types are shown. Different line types show data of different drill bits. In Figure 13 , five drill bits were used for each of the drill bits of sample 1 and sample 2 (N = 5). The first count value is the data of the first drill bit machining. The 40th count value is the data of the 40th drill bit machining. The 80th count value is the data of the 80th drill bit machining.

[0078] like Figure 13 As shown in the fluctuations of the current value during the actual processing time, at the first count value, the current value of the drill bit in sample 2 was more stable than that in sample 1. Furthermore, as the 40th count value, 80th count value, and number of processing operations increased, the current value of the drill bit in sample 1 fluctuated significantly during the actual processing time, becoming unstable. On the other hand, even with increases in the number of processing operations at the 40th and 80th count values, the current value of the drill bit in sample 2 remained small and stable during the actual processing time. Figure 13 As shown, at the 40th count, the current value of the drill bit of Sample 2 remained stable compared to the current value of the drill bit of Sample 1. Similarly, at the 80th count, the current value of the drill bit of Sample 2 remained stable compared to the current value of the drill bit of Sample 1.

[0079] Table 1

[0080] Position of the hole Sample 1 Sample 2 1st site 26.1 μm 9.6 μm 2nd site 31.7 μm 14.5 μm

[0081] Table 1 shows the roundness of the hole (oil hole 74). The roundness of the hole was measured using a roundness measuring instrument (model: Crystal-Apex C9166) manufactured by Mitutoyo. During measurement, a super-hard shaft with an effective length of 27.5 mm and a stylus (Mitutoyo, model: MS2-3R27.5) with a ruby ​​ball at the front end with a diameter of 3 mm was used. Regarding the first and second locations, the roundness of the hole was measured as follows: First, in a cross-section intersecting a plane H 5 mm from the second exit end 52, the line of intersection between the material to be cut 50 and the through hole 60 was designated as the intersection line K. Next, in plane H, the positions of four points on the intersection line K, arranged at equal angles with respect to the axis X, were measured. The roundness of the hole was determined based on the positions of these four points in the manner described above. The first location is... Figure 12 The oil hole 74 shown on the left (the third crankpin 73 from the left passes through the oil hole 74 of the second crank journal 71 from the left). The second part is... Figure 12 The oil hole 74 shown on the right side (the oil hole 74 from the 6th crank pin 73 from the left to the 4th crank journal 71 from the left). As shown in Table 1, the roundness of the oil hole formed at the first location using the drill bit 100 of Sample 1 is 26.1 μm. The roundness of the oil hole formed at the second location using the drill bit 100 of Sample 1 is 31.7 μm. On the other hand, the roundness of the oil hole formed at the first location using the drill bit 100 of Sample 2 is 9.6 μm. The roundness of the oil hole formed at the second location using the drill bit 100 of Sample 2 is 14.5 μm. Based on the above results, it is confirmed that the roundness of the oil hole of the drill bit 100 of the embodiment is significantly improved compared with that of the comparative example drill bit 100.

[0082] It should be considered that the embodiments and examples disclosed herein are illustrative in all aspects and are not restrictive. The scope of the present application is not indicated by the above description, but is indicated by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0083] Explanation of reference numerals

[0084] 1 front end, 2 rear end, 3 cutting edge, 5 chip discharge surface, 6 outer peripheral surface, 7 shank portion, 8 rear clearance surface, 9 dressing surface, 10 first land, 11 first outer peripheral portion, 12 first flank portion, 13 first front end, 20 second land, 21 second outer peripheral portion, 22 second flank portion, 23 second front end, 24 third flank portion, 30 cooling hole, 31 outer peripheral region, 41 first region, 42 second region, 50 work material, 51 first exit end portion, 52 second exit end portion, 53 exit end surface, 60 through hole, 70 crankshaft, 71 crank journal, 72 counterweight, 73 crankpin, 74 oil hole, 100 drill, 101 first direction, 102 second direction, Al first distance, A2 second distance, A3 third distance, Bl first length, B2 second length, Cl first width, C2 second width, D diameter, E fourth distance, G fifth distance, F direction of travel, L length, Pl first position, P2 second position, P3 third position, P4 fourth position, Sl first state, S2 second state, X axis line.

Claims

1. A drill bit which rotates around an axis, the drill bit having: a rear flank surface; a land surface which is continuous with the rear flank surface; a peripheral surface which is continuous with each of the rear flank surface and the land surface; and a chip discharge surface which is continuous with each of the rear flank surface and the peripheral surface, an edge line between the rear flank surface and the chip discharge surface constituting a cutting edge, a first land band which is continuous with each of the cutting edge and the rear flank surface, and a second land band which is located rearward of the first land band in a rotational direction and is separated from each of the rear flank surface and the land surface are provided in the peripheral surface, the peripheral portion of the first land band and the peripheral portion of the second land band each have a same angle inverted cone, a distance between a leading end of the first land band and a leading end of the second land band in a direction parallel to the axis is 3 mm or more and 5 mm or less.

2. The drill bit according to claim 1, wherein the leading end of the second land band extends in a direction perpendicular to the axis when viewed from a direction perpendicular to the axis.

3. The drill bit according to claim 1 or 2, wherein a length of the chip discharge surface in a direction parallel to the axis is 10 times or more and 55 times or less of a diameter of the drill bit.

4. The drill bit according to claim 1 or 2, wherein the second land band is separated from the chip discharge surface.

5. The drill bit according to claim 3, wherein the second land band is separated from the chip discharge surface.

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