drill bit

Abstract

The drill bit has a helical fluted surface, a rear clearance surface, and a land. The land and the rear clearance surface constitute a land cutting edge. The land cutting edge has a curved land cutting edge portion and a straight land cutting edge portion. The curved land cutting edge portion projects forward in the direction of rotation. The straight land cutting edge portion is connected to the curved land cutting edge portion. The curved land cutting edge portion has a first end portion and a second end portion. The first end portion is a boundary between the curved land cutting edge portion and the straight land cutting edge portion. As the curved land cutting edge portion separates from the first end portion, an axial rake angle of the curved land cutting edge portion at a cross section perpendicular to a tangent line of the curved land cutting edge portion when viewed from the axial direction becomes larger. A radius of curvature of the curved land cutting edge portion when viewed from the axial direction is 15% or more and 35% or less of a diameter of the drill bit.

Description

Technical Field

[0001] This invention relates to drill bits. Background Technology

[0002] Japanese Patent Application Publication No. 2008-093805 (Patent Document 1) describes a drill bit with a sharpened cutting edge.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2008-093805 Summary of the Invention

[0004] The drill bit involved in this invention rotates about an axis and has a helical groove surface, a clearance surface, and a dressing surface. The helical groove surface is helical about the axis. The clearance surface is connected to the helical groove surface. The dressing surface is connected to both the helical groove surface and the clearance surface. The edges of the helical groove surface and the clearance surface constitute the main cutting edge. The edges of the dressing surface and the clearance surface constitute the dressing cutting edge. The dressing cutting edge is connected to the main cutting edge. When viewed from the axial direction along the axis, the dressing cutting edge is closer to the axis than the main cutting edge. The dressing cutting edge includes a curved dressing cutting edge portion and a straight dressing cutting edge portion. The curved dressing cutting edge portion protrudes forward in the direction of rotation. The straight dressing cutting edge portion is connected to the curved dressing cutting edge portion. The straight dressing cutting edge portion is closer to the axis than the curved dressing cutting edge portion. A straight line passing through the axis and separated from the outermost peripheral end of the main cutting edge by a predetermined peripheral core height in the direction of rotation is defined as the first straight line. When viewed from the axial direction, the angle between the first straight line and the straight-grinding cutting edge is 135° or more and 160° or less. When viewed from the axial direction, the length of the straight-grinding cutting edge is 10% or less of the drill bit diameter. When viewed from the axial direction, in a cross-section perpendicular to and intersecting the straight-grinding cutting edge, the axial tilt angle of the straight-grinding cutting edge is -10° or more and 0° or less. The curved-grinding cutting edge has a first end and a second end. The first end is the boundary between the curved-grinding cutting edge and the straight-grinding cutting edge. The second end is located on the opposite side of the first end. As it separates from the first end, the axial tilt angle of the curved-grinding cutting edge increases in a cross-section perpendicular to the tangent of the curved-grinding cutting edge when viewed from the axial direction. When viewed from the axial direction, in a cross-section perpendicular to the tangent of the curved-grinding cutting edge at the second end and including the second end, the axial tilt angle of the curved-grinding cutting edge is 5° or more and 20° or less. When viewed from the axial direction, the radius of curvature of the curved cutting edge is at least 15% and no more than 35% of the drill bit diameter.

[0005] the following. Attached Figure Description

[0006] Figure 1 This is a top view schematic diagram showing the structure of the drill bit according to the first embodiment.

[0007] Figure 2This is a slanted view of the front end of the drill bit according to the first embodiment.

[0008] Figure 3 This is a front view showing the structure of the drill bit according to the first embodiment.

[0009] Figure 4 yes Figure 3 A magnified diagram of region IV.

[0010] Figure 5 It is along Figure 3 A cross-sectional view of the V-V line.

[0011] Figure 6 It is along Figure 3 A cross-sectional view of line VI-VI.

[0012] Figure 7 It is a schematic diagram showing the relationship between the distance from the axis of the cutting edge and the axial forward tilt angle of the cutting edge.

[0013] Figure 8 yes Figure 1 A magnified top view of region VIII.

[0014] Figure 9 It is along Figure 8 A cross-sectional view of the IX-IX line.

[0015] Figure 10 It is along Figure 1 A cross-sectional view of the X-ray.

[0016] Figure 11 This is a slanted view of the front end of the drill bit according to the second embodiment.

[0017] Figure 12 This is a front view showing the structure of the drill bit according to the second embodiment.

[0018] Figure 13 yes Figure 12 An enlarged schematic diagram of region XIII.

[0019] Figure 14 The image shows a photograph of the chips produced using the drill bit involved in Sample 1.

[0020] Figure 15 The image shows a photograph of the chips produced using the drill bit involved in Sample 2.

[0021] Figure 16 The image shows a photograph of the chips produced using the drill bit involved in Sample 3.

[0022] Figure 17The image shows a photograph of the chips formed when the drill bit in Sample 1 was used under low feed conditions.

[0023] Figure 18 This is a photograph of the chips formed when using the drill bit involved in Sample 2 under low feed conditions.

[0024] Figure 19 This is a photograph of the chips formed when using the drill bit involved in Sample 3 under low feed conditions. Detailed Implementation

[0025] [The problem to be solved by this invention]

[0026] The object of this invention is to provide a drill bit capable of suppressing chip deposition.

[0027] [Effects of the Invention]

[0028] According to the present invention, a drill bit capable of suppressing chip deposition can be provided.

[0029] [Summary of Implementation Methods]

[0030] First, a summary of the embodiments of the present invention will be described.

[0031] (1) The drill bit 100 of the present invention rotates about axis O. The drill bit has a helical groove surface 5, a first clearance surface 10, and a grinding surface 6. The helical groove surface 5 is helical about axis O. The first clearance surface 10 is connected to the helical groove surface 5. The grinding surface 6 is connected to both the helical groove surface 5 and the first clearance surface 10. The edges of the helical groove surface 5 and the first clearance surface 10 form the main cutting edge 3. The edges of the grinding surface 6 and the first clearance surface 10 form the grinding cutting edge 4. The grinding cutting edge 4 is connected to the main cutting edge 3. When viewed from the axial direction along axis O, the grinding cutting edge 4 is closer to axis O than the main cutting edge 3. The grinding cutting edge 4 includes a curved grinding cutting edge portion 43 and a second straight grinding cutting edge portion 42. The curved grinding cutting edge portion 43 protrudes forward in the direction of rotation. The second straight grinding cutting edge portion 42 is connected to the curved grinding cutting edge portion 43. The second straight-line grinding cutting edge 42 is closer to the axis O than the curved grinding cutting edge 43. The first straight line 121 is defined as the straight line passing through the axis O and separating the outer peripheral position 55 from the outermost peripheral end 59 of the main cutting edge 3 in the direction of rotation at a predetermined outer peripheral core height F. When viewed from the axial direction, the angle between the first straight line 121 and the second straight-line grinding cutting edge 42 is 135°.

[0032] The angle is greater than or equal to 160° and less than 160°. When viewed from the axial direction, the length of the second straight-line grinding cutting edge 42 is less than 10% of the diameter of the drill bit 100. When viewed from the axial direction, in a cross-section perpendicular to and intersecting the second straight-line grinding cutting edge 42, the axial forward tilt angle of the second straight-line grinding cutting edge 42 is greater than -10° and less than 0°. The curved grinding cutting edge 43 has a first end 51 and a second end 52. The first end 51 is the boundary between the curved grinding cutting edge 43 and the second straight-line grinding cutting edge 42. The second end 52 is located on the opposite side of the first end 51. As it separates from the first end 51, the axial forward tilt angle of the curved grinding cutting edge 43 at a cross-section perpendicular to the tangent of the curved grinding cutting edge 43 when viewed from the axial direction increases. When viewed from the axial direction, the cross-section perpendicular to and including the tangent of the curved grinding cutting edge 43 of the second end 52 has an axial forward tilt angle of 5° or more and 20° or less. When viewed from the axial direction, the radius of curvature of the curved grinding cutting edge 43 is 15% or more and 35% or less of the diameter of the drill bit 100.

[0033] (2) According to the drill bit 100 mentioned in (1) above, the grinding surface 6 may include a grinding forward slope surface 61, a grinding pit wall portion 63, and an intermediate surface 62. The grinding forward slope surface 61 may be connected to the spiral groove surface 5 and the first back clearance surface 10 respectively. The grinding pit wall portion 63 may be located in front of the grinding cutting edge 4 in the direction of rotation. The intermediate surface 62 may be connected to the grinding forward slope surface 61 and the grinding pit wall portion 63 respectively. The first back clearance surface 10 may include a first back clearance surface 11 and a second back clearance surface 12. The first back clearance surface 11 may be connected to the spiral groove surface 5 and the grinding surface 6 respectively. The second back clearance surface 12 may be connected to the first back clearance surface 11. The second back clearance surface 12 may be located behind the first back clearance surface 11 in the direction of rotation. The straight line along the boundary line of the grinding pit wall portion 63 and the intermediate surface 62 is designated as the second straight line 122. When viewed from the axial direction, the direction perpendicular to the ridge line of the first rear clearance surface 11 and the second rear clearance surface 12 and pointing radially inward is designated as the top view direction 101. When viewed from the top view direction 101, the section perpendicular to the second straight line 122 and intersecting the boundary line of the grinding pit wall portion 63 and the intermediate surface 62 is designated as the third section CS3. In the third section CS3, the grinding pit wall portion 63 can be curved. In the third section CS3, the radius of curvature of the grinding pit wall portion 63 can be more than 10% and less than 30% of the diameter of the drill bit 100. In the third section CS3, the angle formed by the tangent of the grinding forward slope surface 61 at the boundary of the grinding forward slope surface 61 and the intermediate surface 62 and the tangent of the grinding pit wall portion 63 at the boundary of the grinding pit wall portion 63 and the intermediate surface 62 can be more than 105° and less than 125°.

[0034] (3) According to the drill bit 100 described in (1) or (2) above, the main cutting edge 3 may include a curved cutting edge portion 31. The curved cutting edge portion 31 may be recessed rearward in the direction of rotation. When viewed from the axial direction, the radius of curvature of the curved cutting edge portion 31 may be more than 40% and less than 100% of the diameter of the drill bit 100. When viewed from the axial direction, the maximum distance H between the third straight line 123, which passes through the outer peripheral end of the curved cutting edge portion 31 and is parallel to the first straight line 121, and the curved cutting edge portion 31 may be more than 0.5% and less than 4% of the diameter of the drill bit 100. The grinding surface 6 may constitute a first top cutting edge 91. The first top cutting edge 91 may be connected to the grinding cutting edge 4. The first top cutting edge 91 may be positioned in front of the grinding cutting edge 4 in the direction of rotation. The spiral groove surface 5 may constitute a second top cutting edge 92. The second top cutting edge 92 may be connected to the first top cutting edge 91. The second cutting edge 92 may be positioned in front of the main cutting edge 3 in the direction of rotation. The second cutting edge 92 may include a curved portion 95. The curved portion 95 may be recessed in front of the main cutting edge 3 in the direction of rotation. When viewed from the axial direction, the radius of curvature of the curved portion 95 may be more than 15% and less than 25% of the diameter of the drill bit 100. In a cross-section perpendicular to the axis O, the central angle of the helical groove surface 5 may be more than 0.55 times and less than 1.0 times the central angle of the portion other than the helical groove surface.

[0035] (4) According to the drill bit 100 mentioned in (3) above, the main cutting edge 3 may include a reinforcing cutting edge 32. The reinforcing cutting edge 32 may be connected to the curved cutting edge 31. The reinforcing cutting edge 32 may form the outermost peripheral end 59. When viewed from the axial direction, the straight line including the axis O and the boundary between the curved cutting edge 31 and the reinforcing cutting edge 32 is designated as the fourth straight line 124. When viewed from the axial direction, the reinforcing cutting edge 32 may be inclined rearward in the direction of rotation relative to the fourth straight line 124. When viewed from the axial direction, the angle between the reinforcing cutting edge 32 and the fourth straight line 124 may be 15° or more and 30° or less. When viewed from the axial direction, the length of the reinforcing cutting edge 32 may be 1% or more and 2% or less of the diameter of the drill bit 100.

[0036] [Detailed Description of Embodiments of the Invention]

[0037] Hereinafter, embodiments of the present invention (hereinafter also referred to as "this embodiment") will be described in detail based on the accompanying drawings. Furthermore, in the following drawings, the same or equivalent parts are labeled with the same reference numerals, and their descriptions will not be repeated.

[0038] (First Embodiment)

[0039] First, the structure of the drill bit 100 according to the first embodiment will be described. Figure 1 This is a top view schematic diagram showing the structure of the drill bit 100 according to the first embodiment. (See attached diagram.) Figure 1As shown, the drill bit 100 according to the first embodiment mainly has a front end 1, a rear end 2, a main cutting edge 3, a grinding surface 6, a first clearance surface 10, an outer peripheral surface 9, a helical groove surface 5, and a shank 17. The drill bit 100 according to the first embodiment is a drill bit for metalworking. Figure 1 As shown, the outer peripheral surface 9 is spirally oriented around the axis O. The spiral groove surface 5 forms a chip removal groove. The spiral groove surface 5 is spirally oriented around the axis O. The outer peripheral surface 9 is connected to the spiral groove surface 5. The main cutting edge 3 is positioned close to the front end 1 of the drill bit 100.

[0040] The grinding surface 6 is connected to the spiral groove surface 5. The first clearance surface 10 is connected to the outer peripheral surface 9. The front end 1 of the drill bit 100 is the part opposite to the material being cut. The rear end 2 of the drill bit 100 is the part opposite to the tool spindle that rotates the drill bit 100. The shank 17 is the part mounted on the tool spindle.

[0041] Axis O passes through front end 1 and rear end 2. The direction along axis O is the axial direction. The direction perpendicular to the axial direction is radial. In this specification, the direction from front end 1 towards rear end 2 is called the rearward direction of the axial direction. Conversely, the direction from rear end 2 towards front end 1 is called the forward direction of the axial direction. In this specification, the direction perpendicular to the axial direction and approaching axis O is called the radially inward direction. Conversely, the direction perpendicular to the axial direction and away from axis O is called the radially outward direction. Drill bit 100 rotates about axis O.

[0042] Figure 2 This is a perspective view of the front end of the drill bit 100 according to the first embodiment. Figure 2 As shown, the drill bit 100 also has a second clearance surface 20. The second clearance surface 20 is connected to the first clearance surface 10, the grinding surface 6, the spiral groove surface 5, and the outer peripheral surface 9. The edges of the first clearance surface 10 and the second clearance surface 20 form the chisel edge 8.

[0043] The edges of the spiral groove surface 5 and the first clearance surface 10 form the main cutting edge 3. The spiral groove surface 5, close to the main cutting edge 3, functions as a forward-inclined surface. The grinding surface 6 is connected to the first clearance surface 10. The edges of the grinding surface 6 and the first clearance surface 10 form the grinding cutting edge 4. The grinding cutting edge 4 is connected to the main cutting edge 3. The grinding cutting edge 4 is radially inward relative to the main cutting edge 3. The grinding cutting edge 4 and the main cutting edge 3 constitute the cutting edge of the drill bit 100.

[0044] The first rear clearance surface 10 has a first rear clearance face 11 and a second rear clearance face 12. The first rear clearance face 11 is connected to the spiral groove surface 5 and the grinding surface 6, respectively. The second rear clearance face 12 is connected to the first rear clearance face 11. The second rear clearance face 12 is inclined relative to the first rear clearance face 11. The edge lines of the first rear clearance face 11 and the second rear clearance face 12 are the first boundary lines 15.

[0045] The second back clearance surface 20 has a third back clearance surface 23 and a fourth back clearance surface 24. The third back clearance surface 23 is connected to the first back clearance surface 10. The fourth back clearance surface 24 is connected to the third back clearance surface 23, the spiral groove surface 5, and the grinding surface 6, respectively. The fourth back clearance surface 24 is inclined relative to the third back clearance surface 23. The edge lines of the third back clearance surface 23 and the fourth back clearance surface 24 are the second boundary lines 25.

[0046] The outer peripheral surface 9 has a first outer peripheral surface 19 and a second outer peripheral surface 29. The first outer peripheral surface 19 is connected to the first rear clearance surface 11 and the spiral groove surface 5, respectively. The edges of the first outer peripheral surface 19 and the spiral groove surface 5 form the leading edge 7. The second outer peripheral surface 29 is connected to the first rear clearance surface 11 and the second rear clearance surface 12, respectively. The first outer peripheral surface 19 is radially outward relative to the second outer peripheral surface 29. The first outer peripheral surface 19 forms the outer peripheral cutting edge.

[0047] The grinding surface 6 has a grinding forward tilting surface 61, a middle surface 62, and a grinding recess wall portion 63. The grinding forward tilting surface 61 is connected to the spiral groove surface 5 and the first rear clearance surface 10, respectively. Specifically, the grinding forward tilting surface 61 is connected to the first rear clearance surface 11 of the first rear clearance surface 10. The middle surface 62 is connected to the grinding forward tilting surface 61, the second rear clearance surface 20, and the spiral groove surface 5, respectively. The grinding forward tilting surface 61 is located between the middle surface 62 and the first rear clearance surface 10. The grinding recess wall portion 63 is connected to the middle surface 62, the spiral groove surface 5, and the second rear clearance surface 20, respectively. Specifically, the grinding recess wall portion 63 is connected to the fourth rear clearance surface 24 of the second rear clearance surface 20. The middle surface 62 is located between the grinding recess wall portion 63 and the grinding forward tilting surface 61.

[0048] The pre-sloping surface 61 has a first portion 81, a second portion 82, and a third portion 83. The first portion 81 is connected to the spiral groove surface 5, the first rear clearance surface 10, and the intermediate surface 62. The second portion 82 is connected to the first portion 81, the first rear clearance surface 10, and the intermediate surface 62. The third portion 83 is connected to the second portion 82, the first rear clearance surface 10, and the intermediate surface 62. The third portion 83 is radially inward relative to the first portion 81. The second portion 82 is located between the first portion 81 and the third portion 83.

[0049] The grinding cutting edge 4 has a first straight grinding cutting edge portion 41, a curved grinding cutting edge portion 43, and a second straight grinding cutting edge portion 42. The first straight grinding cutting edge portion 41 is connected to the main cutting edge 3. The first straight grinding cutting edge portion 41 is located radially inward relative to the main cutting edge 3. The first straight grinding cutting edge portion 41 is formed by the ridge line of the first rear clearance surface portion 11 of the first rear clearance surface 10 and the first portion 81 of the grinding forward tilt surface portion 61.

[0050] The curved grinding cutting edge 43 is connected to the first straight grinding cutting edge 41. The curved grinding cutting edge 43 is located radially inward relative to the first straight grinding cutting edge 41. The curved grinding cutting edge 43 is located on the opposite side of the main cutting edge 3 relative to the first straight grinding cutting edge 41. From another viewpoint, the first straight grinding cutting edge 41 is located between the main cutting edge 3 and the curved grinding cutting edge 43. The curved grinding cutting edge 43 is formed by the ridge line of the first rear clearance surface 11 of the first rear clearance surface 10 and the second part 82 of the grinding forward tilt surface 61.

[0051] The second straight-line grinding cutting edge 42 is connected to the curved grinding cutting edge 43. The second straight-line grinding cutting edge 42 is located radially inward relative to the curved grinding cutting edge 43. The second straight-line grinding cutting edge 42 is located on the opposite side of the first straight-line grinding cutting edge 41 relative to the curved grinding cutting edge 43. From another viewpoint, the curved grinding cutting edge 43 is located between the first straight-line grinding cutting edge 41 and the second straight-line grinding cutting edge 42. The second straight-line grinding cutting edge 42 is formed by the ridge line of the first rear clearance surface 10's first rear clearance surface 11 and the third portion 83 of the grinding forward tilt surface 61.

[0052] The grinding surface 6 forms the first top edge 91. Specifically, the edges of the grinding surface 6 and the second back clearance surface 20 form the first top edge 91. The first top edge 91 is connected to the grinding cutting edge 4. The first top edge 91 has an inner circumferential portion 93 and a middle portion 94.

[0053] The spiral groove surface 5 forms the second cutting edge 92. Specifically, the edge line of the spiral groove surface 5 and the fourth rear clearance surface 24 of the second rear clearance surface 20 forms the second cutting edge 92. The second cutting edge 92 is connected to the first cutting edge 91. The second cutting edge 92 is located radially outward relative to the first cutting edge 91. The second cutting edge 92 has a curved portion 95 and a cutting edge outer peripheral portion 96.

[0054] The inner periphery 93 of the top edge is connected to the second straight grinding cutting edge 42 of the grinding cutting edge 4. The inner periphery 93 of the top edge is formed by the edge lines of the second back clearance surface 20 and the middle surface 62.

[0055] The middle portion 94 of the top edge is connected to the inner peripheral portion 93 of the top edge. The middle portion 94 of the top edge is located radially outward relative to the inner peripheral portion 93 of the top edge. The middle portion 94 of the top edge is formed by the fourth rear clearance portion 24 of the second rear clearance surface 20 and the ridge line of the grinding recess wall portion 63.

[0056] The curved portion 95 is connected to the center portion 94 of the top edge. The curved portion 95 is located radially outward relative to the center portion 94 of the top edge. The curved portion 95 is located on the opposite side of the inner circumference portion 93 of the top edge relative to the center portion 94 of the top edge. From another viewpoint, the center portion 94 of the top edge is located between the inner circumference portion 93 of the top edge and the curved portion 95.

[0057] The outer periphery 96 of the top edge is connected to the curved portion 95. The outer periphery 96 of the top edge is radially outward relative to the curved portion 95. The outer periphery 96 of the top edge is on the opposite side of the middle portion 94 of the top edge relative to the curved portion 95. From another viewpoint, the curved portion 95 is located between the middle portion 94 of the top edge and the outer periphery 96 of the top edge.

[0058] Figure 3 This is a front view showing the structure of the drill bit 100 according to the first embodiment. (As shown) Figure 3 As shown, when viewed from the axial direction, the main cutting edge 3 can be recessed rearward in the direction of rotation. The diameter of the drill bit 100 is designated as the first diameter D1. The first diameter D1 is the diameter of the main cutting edge 3. In other words, when viewed from the axial direction, the first diameter D1 is twice the distance between the outermost circumferential end 59 of the main cutting edge 3 and the axis O.

[0059] like Figure 3 As shown, the curved grinding cutting edge 43 protrudes forward in the direction of rotation. The curved grinding cutting edge 43 has a first end portion 51 and a second end portion 52. The first end portion 51 is the boundary between the curved grinding cutting edge 43 and the second straight grinding cutting edge 42. In other words, at the first end portion 51, the curved grinding cutting edge 43 is connected to the second straight grinding cutting edge 42.

[0060] The second end 52 is located on the opposite side of the first end 51. From another viewpoint, when viewed along the axial direction, the distance between the second end 52 and the axis O is longer than the distance between the first end 51 and the axis O. The second end 52 is the boundary between the curved grinding cutting edge 43 and the first straight grinding cutting edge 41. In other words, at the second end 52, the curved grinding cutting edge 43 connects to the first straight grinding cutting edge 41.

[0061] like Figure 3 As shown, when viewed from the axial direction, the second straight-grinding cutting edge 42 is closer to the axis O than the curved-grinding cutting edge 43. When viewed from the axial direction, the second straight-grinding cutting edge 42 is straight. When viewed from the axial direction, the first straight-grinding cutting edge 41 is farther from the axis O than the curved-grinding cutting edge 43. When viewed from the axial direction, the first straight-grinding cutting edge 41 is straight.

[0062] The second rear gap surface 12 of the first rear gap surface 10 is located behind the first rear gap surface 11 in the rotational direction. When viewed from the axial direction, the first boundary line 15 is straight. When viewed from the axial direction, the direction perpendicular to the first boundary line 15 and radially inward is defined as the top view direction 101.

[0063] The fourth rear gap surface 24 of the second rear gap surface 20 is located behind the third rear gap surface 23 in the rotational direction. When viewed from the axial direction, the second boundary line 25 is straight. When viewed from the axial direction, the second boundary line 25 can be substantially parallel to the first boundary line 15.

[0064] The first rear gap surface 11 of the first rear gap surface 10 is connected to the third rear gap surface 23 of the second rear gap surface 20. The transverse blade 8 intersects the axis O. In other words, the boundaries of the first rear gap surface 11 and the third rear gap surface 23 intersect the axis O.

[0065] like Figure 3 As shown, when viewed from the axial direction, the inner periphery 93 of the tip edge is curved. The middle portion 94 of the tip edge is concave forward in the direction of rotation. The curved portion 95 is concave forward in the direction of rotation. At the boundary between the middle portion 94 and the curved portion 95, the first tip edge 91 and the second tip edge 92 bulge rearward in the direction of rotation. From another viewpoint, when viewed from the axial direction, the boundary between the middle portion 94 and the curved portion 95 is an inflection point. The outer periphery 96 of the tip edge may bulge rearward in the direction of rotation.

[0066] The grinding recess wall 63 is positioned in front of the grinding cutting edge 4 in the direction of rotation. The first top cutting edge 91 is positioned in front of the grinding cutting edge 4 in the direction of rotation. The second top cutting edge 92 is positioned in front of the main cutting edge 3 in the direction of rotation.

[0067] When viewed from the axial direction, the shape of drill bit 100 is substantially rotationally symmetric with respect to axis O. With N cutting edges, the shape of drill bit 100 is substantially N-fold symmetric with respect to axis O. With 2 cutting edges, the shape of drill bit 100 is 2-fold symmetric with respect to axis O when viewed from the axial direction. Rotating the first clearance surface 10 by 180° with axis O as the center of rotation, the shape of the first clearance surface 10 is substantially identical to the shape of the second clearance surface 20. The first clearance surface portion 11 of the first clearance surface 10 corresponds to the third clearance surface portion 23 of the second clearance surface 20. The second clearance surface portion 12 of the first clearance surface 10 corresponds to the fourth clearance surface portion 24 of the second clearance surface 20.

[0068] Figure 4 yes Figure 3 An enlarged diagram of region IV. (See attached diagram.) Figure 4As shown, the boundary between the main cutting edge 3 and the regrinding cutting edge 4 is designated as the first boundary point 58. In other words, at the first boundary point 58, the main cutting edge 3 and the regrinding cutting edge 4 are connected. The first straight line 121 is defined as the straight line passing through the outer peripheral position 55, separated from the axis O by a specified outer peripheral core height F, from the outermost peripheral end 59 of the main cutting edge 3 in the direction of rotation. When viewed from the axial direction, the outer peripheral position 55 is located on the outer periphery of the drill bit 100. From another viewpoint, when viewed from the axial direction, the distance between the outer peripheral position 55 and the axis O is 50% of the first diameter D1.

[0069] The first straight line 121 may be substantially parallel to the first boundary line 15. The first straight line 121 may also be substantially parallel to the second boundary line 25. The outer core height F is the distance between the outermost peripheral end 59 and the outer peripheral position 55 in the direction of rotation, viewed from the axial direction. The outer core height F is, for example, 8% of the first diameter D1. The outer core height F may also be, for example, 10% or 12% of the first diameter D1.

[0070] When viewed from the axial direction, the angle formed by the first straight line 121 and the second straight line grinding the cutting edge 42 is defined as the first angle θ1. The first angle θ1 is 135° or more and 160° or less. The lower limit of the first angle θ1 is not particularly limited, for example, it can be 140° or more or 143° or more. The upper limit of the first angle θ1 is not particularly limited, for example, it can be 155° or less or 152° or less.

[0071] like Figure 4 As shown, when viewed from the axial direction, the length of the second straight-line grinding cutting edge 42 is defined as the first length L1. The first length L1 is 10% or less of the first diameter D1. The upper limit of the first length L1 is not particularly limited, for example, it can be 8% or less of the first diameter D1, or it can be 5% or less of the first diameter D1. The lower limit of the first length L1 is not particularly limited, for example, it can be more than 1% of the first diameter D1, or it can be more than 3% of the first diameter D1.

[0072] like Figure 4 As shown, when viewed from the axial direction, the curved grinding cutting edge 43 can be arc-shaped. When viewed from the axial direction, the radius of curvature of the curved grinding cutting edge 43 is set as a first radius of curvature R1. The first radius of curvature R1 is 15% to 35% of the first diameter D1. The lower limit of the first radius of curvature R1 is not particularly limited; for example, it can be 20% or more of the first diameter D1, or 23% or more of the first diameter D1. The upper limit of the first radius of curvature R1 is not particularly limited; for example, it can be 30% or less of the first diameter D1, or 27% or less of the first diameter D1.

[0073] like Figure 4 As shown, when viewed from the axial direction, the main cutting edge 3 can be arc-shaped. When viewed from the axial direction, the radius of curvature of the main cutting edge 3 is set as a second radius of curvature R2. The second radius of curvature R2 can be greater than the first radius of curvature R1. The second radius of curvature R2 is, for example, more than 40% and less than 100% of the first diameter D1. The lower limit of the second radius of curvature R2 is not particularly limited; for example, it can be more than 50% of the first diameter D1, or more than 60% of the first diameter D1. The upper limit of the second radius of curvature R2 is not particularly limited; for example, it can be less than 90% of the first diameter D1, or less than 80% of the first diameter D1.

[0074] like Figure 4 As shown, when viewed from the axial direction, the curved portion 95 can be arc-shaped. When viewed from the axial direction, the radius of curvature of the curved portion 95 is set as a third radius of curvature R3. The third radius of curvature R3 can be smaller than the second radius of curvature R2. The third radius of curvature R3 is, for example, 15% or more and 25% or less of the first diameter D1. The lower limit of the third radius of curvature R3 is not particularly limited; for example, it can be 17% or more of the first diameter D1, or 19% or more of the first diameter D1. The upper limit of the third radius of curvature R3 is not particularly limited; for example, it can be less than 23% of the first diameter D1, or less than 21% of the first diameter D1.

[0075] When viewed from the axial direction, the line parallel to the first line 121 and passing through the outermost peripheral end 59 of the main cutting edge 3 is designated as the fifth line 125. The maximum distance between the fifth line 125 and the main cutting edge 3 is designated as the maximum distance H. The maximum distance H is, for example, more than 0.5% and less than 4% of the first diameter D1. The lower limit of the maximum distance H is not particularly limited, for example, it can be more than 1% of the first diameter D1 or more than 1.5% of the first diameter D1. The upper limit of the maximum distance H is not particularly limited, for example, it can be less than 3.5% of the first diameter D1 or less than 3% of the first diameter D1.

[0076] Figure 5 It is along Figure 3 A cross-sectional view of the V-V line. Figure 5 The cross-section shown is perpendicular to and intersects with the second straight grinding cutting edge 42 when viewed from the axial direction. Hereinafter, this cross-section, which is perpendicular to and intersects with the second straight grinding cutting edge 42 when viewed from the axial direction, will also be referred to as the first cross-section CS1. Figure 5 As shown, in the first cross-section CS1, the grinding-forward inclined surface 61 of the grinding surface 6 can be straight. In the first cross-section CS1, the angle formed by the first rear clearance surface 11 of the first rear clearance surface 10 and the grinding-forward inclined surface 61 of the grinding surface 6 is, for example, an acute angle.

[0077] In the first section CS1, the straight line parallel to the axis O and including the second straight grinding cutting edge 42 is designated as the sixth straight line 126. The angle formed by the sixth straight line 126 and the grinding forward tilting part 61 of the grinding surface 6 is designated as the first axial forward tilting angle θ11. The first axial forward tilting angle θ11 is the axial forward tilting angle of the second straight grinding cutting edge 42 in the first section CS1.

[0078] In section CS1, the first axial tilt angle θ11 is greater than -10° and less than 0°. The lower limit of the first axial tilt angle θ11 is not particularly limited; for example, it can be greater than -8° or greater than -6°. The upper limit of the first axial tilt angle θ11 is not particularly limited; for example, it can be less than -2° or less than -4°.

[0079] Furthermore, in this specification, a "negative" axial tilt angle of the cutting edge means, when viewed radially, that the tip of the cutting edge is tilted forward in the direction of rotation relative to a straight line parallel to axis O. Conversely, in this specification, a "positive" axial tilt angle of the cutting edge means, when viewed radially, that the tip of the cutting edge is tilted backward in the direction of rotation relative to a straight line parallel to axis O.

[0080] Figure 6 It is along Figure 3 A cross-sectional view of line VI-VI. Figure 6 The cross-section shown, when viewed from the axial direction, is perpendicular to the tangent of the curved grinding cutting edge 43 at the second end 52 and includes the second end 52. Hereinafter, this cross-section, which is perpendicular to the tangent of the curved grinding cutting edge 43 at the second end 52 and includes the second end 52 when viewed from the axial direction, will also be referred to as the second cross-section CS2. Figure 6 As shown in the second section CS2, the grinding-forward inclined surface 61 of the grinding surface 6 can be straight. In the second section CS2, the angle formed by the first rear clearance surface 11 of the first rear clearance surface 10 and the grinding-forward inclined surface 61 of the grinding surface 6 is an acute angle.

[0081] In the second section CS2, the straight line parallel to the axis O and including the curved grinding cutting edge 43 is designated as the seventh straight line 127. The angle formed by the seventh straight line 127 and the grinding forward tilting part 61 of the grinding surface 6 is designated as the second axial forward tilting angle θ12. The second axial forward tilting angle θ12 is the axial forward tilting angle of the curved grinding cutting edge 43 in the second section CS2. The second axial forward tilting angle θ12 is greater than the first axial forward tilting angle θ11.

[0082] In section CS2, the second axial tilt angle θ12 is greater than 5° and less than 20°. The lower limit of the second axial tilt angle θ12 is not particularly limited; for example, it can be greater than 8° or greater than 10°. The upper limit of the second axial tilt angle θ12 is not particularly limited; for example, it can be less than 17° or less than 15°.

[0083] Figure 7 This is a schematic diagram showing the relationship between the distance from the axis O of the cutting edge and the axial forward tilt angle of the cutting edge. Figure 7 In the diagram, the vertical axis shows the axial tilt angle of the cutting edge, and the horizontal axis shows the distance from the axis O of the cutting edge. The distance from the axis O to the end of the second straight-grinding cutting edge 42, located opposite the first end 51, is designated as the reference distance E0. The distance from the axis O to the first end 51 is designated as the first distance E1. The distance from the axis O to the second end 52 is designated as the second distance E2. The distance from the axis O to the first boundary point 58 is designated as the third distance E3. The distance from the axis O to the outermost peripheral end 59 is designated as the fourth distance E4.

[0084] The axial forward tilt angle of the first straight-line grinding cutting edge 41 at the first boundary point 58 is set as the third axial forward tilt angle θ13. The first straight-line grinding cutting edge 41 extends along the tangent of the curved grinding cutting edge 43 at the second end 52; therefore, the third axial forward tilt angle θ13 is substantially the same as the second axial forward tilt angle θ12. The axial forward tilt angle of the main cutting edge 3 at the outermost peripheral end 59 is set as the fourth axial forward tilt angle θ14. The fourth axial forward tilt angle θ14 is greater than the third axial forward tilt angle θ13. The fourth axial forward tilt angle θ14 is, for example, 30°.

[0085] like Figure 7 As shown, in the second straight-grinding cutting edge 42, the axial tilt angle can be substantially constant. In the curved-grinding cutting edge 43, the axial tilt angle monotonically increases. As it separates from the first end 51, the axial tilt angle of the curved-grinding cutting edge 43 at the section perpendicular to the tangent of the curved-grinding cutting edge 43 when viewed from the axial direction increases. From the first end 51 to the second end 52, the axial tilt angle of the curved-grinding cutting edge 43 changes from the first axial tilt angle θ11 to the second axial tilt angle θ12. Furthermore, the curved-grinding cutting edge 43 can have a portion with a constant axial tilt angle. In the first straight-grinding cutting edge 41, the axial tilt angle can be substantially constant.

[0086] In the main cutting edge 3, the axial tilt angle increases monotonically. As it approaches the outermost circumferential end 59, the axial tilt angle of the main cutting edge 3 at the section perpendicular to the tangent of the main cutting edge 3 when viewed from the axial direction increases. From the first boundary point 58 to the outermost circumferential end 59, the axial tilt angle of the main cutting edge 3 changes from the third axial tilt angle θ13 to the fourth axial tilt angle θ14. Furthermore, the main cutting edge 3 may have a portion with a constant axial tilt angle.

[0087] The change in axial tilt angle per unit length of the curved grinding cutting edge 43 is defined as the first rate of change. Specifically, the first rate of change is obtained by dividing the absolute value of the difference between the second axial tilt angle θ12 and the first axial tilt angle θ11 by the absolute value of the difference between the second distance E2 and the first distance E1. The change in axial tilt angle per unit length of the main cutting edge 3 is defined as the second rate of change. Specifically, the second rate of change is obtained by dividing the absolute value of the difference between the fourth axial tilt angle θ14 and the third axial tilt angle θ13 by the absolute value of the difference between the fourth distance E4 and the third distance E3. The first rate of change can be greater than the second rate of change.

[0088] Figure 8 yes Figure 1 A magnified top view of region VIII. Figure 8 The enlarged top-view diagram shown illustrates the structure of the front end of the drill bit 100 as viewed from top direction 101. (As shown...) Figure 8 As shown, the boundary line between the grinding recess wall 63 and the intermediate surface 62 can be a straight line. The straight line along the boundary line between the grinding recess wall 63 and the intermediate surface 62 is designated as the second straight line 122. Furthermore, if the boundary line between the grinding recess wall 63 and the intermediate surface 62 is curved, the second straight line 122 is defined as a straight line encompassing both ends of the boundary line between the grinding recess wall 63 and the intermediate surface 62. When viewed from the top view 101, the boundary line between the grinding recess wall 63 and the intermediate surface 62 intersects the axis O. When viewed from the top view 101, the second straight line 122 intersects the axis O. When viewed from the top view 101, the inner periphery 93 of the first top cutting edge 91 intersects the axis O.

[0089] Figure 9 It is along Figure 8 A cross-sectional view of the IX-IX line. Figure 9 The cross-section shown is a cross-section that is perpendicular to the second straight line 122 and intersects the boundary line of the grinding pit wall 63 and the intermediate surface 62 when viewed from the top direction 101. Figure 9 The cross section shown intersects the boundary of the second part 82 of the grinding-forward inclined surface 61 and the intermediate surface 62, as well as the curved grinding cutting edge 43. Hereinafter, the cross section that is perpendicular to the second straight line 122 and intersects the boundary line of the grinding pit wall 63 and the intermediate surface 62 when viewed from the top direction 101 will also be referred to as the third cross section CS3.

[0090] In section CS3, the grinding recess wall 63 is curved. In section CS3, the grinding recess wall 63 can also be arc-shaped. In section CS3, the radius of curvature of the grinding recess wall 63 is set as a fourth radius of curvature R4. The fourth radius of curvature R4 is 10% to 30% of the first diameter D1. The lower limit of the fourth radius of curvature R4 is not particularly limited; for example, it can be 15% or more of the first diameter D1, or 18% or more of the first diameter D1. The upper limit of the fourth radius of curvature R4 is not particularly limited; for example, it can be less than 25% of the first diameter D1, or less than 22% of the first diameter D1.

[0091] In the third section CS3, the intermediate surface 62 can be arc-shaped. The radius of curvature of the intermediate surface 62 is smaller than the fourth radius of curvature R4. In the third section CS3, the tangent of the grinding-forward-tilting surface 61 at the boundary between the grinding-forward-tilting surface 61 and the intermediate surface 62 is designated as the first tangent 131. In the third section CS3, the tangent of the grinding-recess wall 63 at the boundary between the grinding-recess wall 63 and the intermediate surface 62 is designated as the second tangent 132. The angle formed by the first tangent 131 and the second tangent 132 is designated as the second angle θ2.

[0092] The second angle θ2 is greater than 105° and less than 125°. The lower limit of the second angle θ2 is not particularly limited; for example, it can be greater than 110° or greater than 113°. The upper limit of the second angle θ2 is not particularly limited; for example, it can be less than 120° or less than 117°.

[0093] Figure 10 It is along Figure 1 A cross-sectional view of the X-ray. Figure 10 The cross-section shown is perpendicular to axis O. In the axial direction, Figure 10 The distance between the cross section shown and the front end 1 of the drill bit 100 is the same as the first diameter D1.

[0094] like Figure 10 As shown, the core thickness of drill bit 100 is set to the second diameter D2. The second diameter D2 is, for example, more than 20% and less than 40% of the first diameter D1. Furthermore, the core thickness of drill bit 100, in a cross-section perpendicular to axis O, is twice the shortest distance between axis O and the helical groove surface 5.

[0095] like Figure 10As shown, in a cross-section perpendicular to axis O, the central angle of the helical groove surface 5 is set as the first central angle θ21, and the central angle of the portion outside the helical groove surface 5 is set as the second central angle θ22. The first central angle θ21 is the angle formed by the line segment connecting the end of the helical groove surface 5 in the direction of rotation forward to axis O and the line segment connecting the end of the helical groove surface 5 in the direction of rotation backward to axis O. The end of the helical groove surface 5 in the direction of rotation forward is the boundary between the second outer peripheral surface 29 and the helical groove surface 5. The end of the helical groove surface 5 in the direction of rotation backward is the boundary between the first outer peripheral surface 19 and the helical groove surface 5. When the number of cutting edges of the drill bit 100 is N, the second central angle θ22 is the value obtained by subtracting the first central angle θ21 from the value obtained by dividing 360° by N. When the number of cutting edges of the drill bit 100 is 2, the second central angle θ22 is the value obtained by subtracting the first central angle θ21 from 180°.

[0096] In a section perpendicular to axis O, the first central angle θ21 is, for example, more than 0.55 times and less than 1.0 times the second central angle θ22. In a section perpendicular to axis O, the lower limit of the first central angle θ21 is not particularly limited; for example, it can be more than 0.6 times or more than 0.65 times the second central angle θ22. In a section perpendicular to axis O, the upper limit of the first central angle θ21 is not particularly limited; for example, it can be less than 0.9 times or less than 0.85 times the second central angle θ22.

[0097] (Second Implementation)

[0098] Next, the structure of the drill bit 100 according to the second embodiment will be described. The drill bit 100 according to the second embodiment differs from the drill bit 100 according to the first embodiment in that it has a reinforced cutting edge; otherwise, it is substantially the same as the drill bit 100 according to the first embodiment. Hereinafter, the description will focus on the differences from the drill bit 100 according to the first embodiment.

[0099] Figure 11 This is a perspective view of the front end of the drill bit 100 according to the second embodiment. Figure 11 The diagram of the oblique view shown is similar to Figure 2 The diagram shown corresponds to the oblique view. For example... Figure 11 As shown, the drill bit 100 may also have a reinforced forward inclination surface 39. The reinforced forward inclination surface 39 is connected to the first rear clearance surface 10, the spiral groove surface 5, and the first outer peripheral surface 19. The edges of the reinforced forward inclination surface 39 and the first outer peripheral surface 19 form the leading edge 7.

[0100] The main cutting edge 3 may have a curved cutting edge portion 31 and a reinforced cutting edge portion 32. The curved cutting edge portion 31 is connected to the first straight grinding cutting edge portion 41. The reinforced cutting edge portion 32 is connected to the curved cutting edge portion 31. The reinforced cutting edge portion 32 is located radially outward relative to the curved cutting edge portion 31. The reinforced cutting edge portion 32 is formed by the edges of the first rear clearance surface 10 and the reinforced forward inclined surface 39.

[0101] Figure 12 This is a front view showing the structure of the drill bit 100 according to the second embodiment. Figure 12 The front view diagram shown is consistent with Figure 3 The front view shown corresponds to the diagram shown. Figure 13 yes Figure 12 An enlarged schematic diagram of region XIII. (See attached diagram.) Figure 12 and Figure 13 As shown, the curved cutting edge 31 is recessed rearward in the direction of rotation. When viewed from the axial direction, the reinforcing cutting edge 32 appears as a straight line, for example. The reinforcing cutting edge 32 forms the outermost peripheral end 59.

[0102] like Figure 12 and Figure 13 As shown, the boundary between the curved cutting edge 31 and the reinforced cutting edge 32 is designated as the second boundary point 57. The second boundary point 57 is the outer peripheral end of the curved cutting edge 31. When viewed from the axial direction, the straight line including the second boundary point 57 and the axis O is designated as the fourth straight line 124. When viewed from the axial direction, the reinforced cutting edge 32 is inclined rearward in the rotational direction relative to the fourth straight line 124. When viewed from the axial direction, the angle formed by the reinforced cutting edge 32 and the fourth straight line 124 is designated as the third angle θ3. The third angle θ3 is, for example, 15° or more and 30° or less. The lower limit of the third angle θ3 is not particularly limited, for example, it can be 18° or more or 21° or more. The upper limit of the third angle θ3 is not particularly limited, for example, it can be 27° or less or 24° or less.

[0103] like Figure 13 As shown, when viewed from the axial direction, the length of the reinforcing cutting edge 32 is defined as a second length L2. Furthermore, when the reinforcing cutting edge 32 is curved when viewed from the axial direction, the second length L2 is defined as the length of the line segment connecting the two ends of the reinforcing cutting edge 32. The second length L2 is, for example, 1% to 2% of the first diameter D1. The lower limit of the second length L2 is not particularly limited; for example, it can be 1.2% or more of the first diameter D1, or 1.4% or more of the first diameter D1. The upper limit of the second length L2 is not particularly limited; for example, it can be 1.8% or less of the first diameter D1, or 1.6% or less of the first diameter D1.

[0104] like Figure 13As shown, the line passing through the second boundary point 57 and parallel to the first line 121 is designated as the third line 123. In other words, the line passing through the outer periphery of the curved cutting edge 31 and parallel to the first line 121 is designated as the third line 123. When the main cutting edge 3 has a curved cutting edge 31, the maximum distance H is defined as the maximum distance between the third line 123 and the curved cutting edge 31 when viewed from the axial direction. When viewed from the axial direction, the curved cutting edge 31 can be arc-shaped. When the main cutting edge 3 has a curved cutting edge 31, the second radius of curvature R2 is defined as the radius of curvature of the curved cutting edge 31.

[0105] Furthermore, while the above description describes the case where the drill bit 100 has two main cutting edges 3, the number of main cutting edges 3 is not limited to two. The number of main cutting edges 3 can also be three or more. The material being cut can be, for example, stainless steel (SUS) or other metals. The material being cut can also be carbon steel, alloy steel, or a difficult-to-cut material.

[0106] Next, the effects of the drill bit 100 involved in this embodiment will be explained.

[0107] In cases where there is a large variation in the axial rake angle at the cutting edge of drill bit 100, the variation in cutting resistance experienced by the cutting edge increases around this portion. Consequently, the pressure exerted by drill bit 100 on the workpiece concentrates around this portion. As a result, chip deposition sometimes occurs around this portion.

[0108] According to the drill bit 100 of this embodiment, as it separates from the first end 51, the axial tilt angle of the curved-grind cutting edge 43 at a section perpendicular to the tangent of the curved-grind cutting edge 43 when viewed from the axial direction increases. When viewed from the axial direction, the radius of curvature (first radius of curvature R1) of the curved-grind cutting edge 43 is more than 15% of the diameter (first diameter D1) of the drill bit 100. Therefore, compared with the case where the radius of curvature of the curved-grind cutting edge 43 is too small, the length of the curved-grind cutting edge 43 can be increased. As a result, the change in the axial tilt angle per unit length of the curved-grind cutting edge 43 can be reduced. Therefore, the abrupt change in cutting resistance experienced by the cutting edge of the drill bit 100 can be suppressed. As a result, the melting of chips onto the cutting edge can be suppressed.

[0109] Furthermore, when the length of the curved-grind cutting edge 43 is sufficiently long, the distance between the second end 52 and the outermost peripheral end 59 of the curved-grind cutting edge 43 becomes shorter. Therefore, the axial forward tilt angle of the curved-grind cutting edge 43 at the second end 52 is close to the fourth axial forward tilt angle θ14. In other words, the axial forward tilt angle of the curved-grind cutting edge 43 at the second end 52 becomes larger. This reduces the cutting resistance of the curved-grind cutting edge 43.

[0110] When viewed from the axial direction, if the angle (first angle θ1) between the first straight line 121 and the grinding cutting edge 4 is too large, the distance between the first end 51 of the curved grinding cutting edge 43 and the axis O increases. Therefore, the length of the curved grinding cutting edge 43 becomes shorter. Consequently, the change in the rake angle per unit length of the curved grinding cutting edge 43 increases. As a result, chips may melt onto the cutting edge. According to the drill bit 100 of this embodiment, when viewed from the axial direction, the angle between the first straight line 121 and the grinding cutting edge 4 is 160° or less. Therefore, it is possible to suppress the shortening of the length of the curved grinding cutting edge 43. As a result, it is possible to suppress the melting of chips onto the cutting edge.

[0111] When the axial tilt angle of the second straight-grinding cutting edge 42 is greater than 0°, the cutting edge of the drill bit 100 is retoughened, thereby causing the second straight-grinding cutting edge 42 to retract in the rotational direction. As a result, the length of the chisel edge 8 becomes shorter. Consequently, the strength of the center portion of the drill bit 100 may decrease. Consequently, the drill bit 100 may become damaged. According to the drill bit 100 of this embodiment, in a cross-section (first cross-section CS1) perpendicular to and intersecting the second straight-grinding cutting edge 42 when viewed from the axial direction, the axial tilt angle (first axial tilt angle θ11) of the second straight-grinding cutting edge 42 is 0° or less. Therefore, damage to the drill bit 100 can be suppressed. Furthermore, according to the drill bit 100 of this embodiment, in the first cross-section CS1, the first axial tilt angle θ11 is -10° or more. Therefore, it is possible to prevent the cutting resistance of the second straight grinding cutting edge 42 from becoming excessively large.

[0112] According to the drill bit 100 of this embodiment, the shaving recess wall portion 63 can be positioned in front of the shaving cutting edge 4 in the rotational direction. In a cross-section (third cross-section CS3) perpendicular to the second straight line 122 and intersecting the boundary line of the shaving recess wall portion 63 and the intermediate surface 62 when viewed from the top direction 101, the radius of curvature (fourth radius of curvature R4) of the shaving recess wall portion 63 can be more than 10% and less than 30% of the diameter (first diameter D1) of the drill bit 100. Therefore, a portion of the chips approaching the axis O of the drill bit 100 is collected in the shaving recess wall portion 63 and flows there. Consequently, the chips are easily broken, improving the chip removal performance of the drill bit 100.

[0113] According to the drill bit 100 of this embodiment, in a cross section (third cross section CS3) perpendicular to the second straight line 122 and intersecting the boundary line of the grinding pit wall portion 63 and the intermediate surface 62 when viewed from the top direction 101, the angle (second angle θ2) formed by the tangent line (first tangent 131) of the grinding forward slope portion 61 at the boundary of the grinding forward slope portion 61 and the intermediate surface 62 and the tangent line (second tangent 132) of the grinding pit wall portion 63 at the boundary of the grinding pit wall portion 63 and the intermediate surface 62 can be 105° or more. Therefore, the volume of the groove formed by the grinding pit wall portion 63 can be increased. As a result, chip removal performance can be improved.

[0114] According to the drill bit 100 of this embodiment, the main cutting edge 3 may have a curved cutting edge portion 31. When viewed from the axial direction, the radius of curvature (second radius of curvature R2) of the curved cutting edge portion 31 can be 40% or more and 100% or less of the diameter (first diameter D1) of the drill bit 100. Therefore, compared with the case where the main cutting edge 3 is straight, when viewed from the axial direction, the tangent of the curved cutting edge portion 31 at the outer peripheral end of the curved cutting edge portion 31 is significantly inclined forward in the rotational direction relative to the straight line including the axis O and the outer peripheral end of the curved cutting edge portion 31. Therefore, the sharpness of the main cutting edge 3 at the periphery of the outer peripheral end of the curved cutting edge portion 31 can be improved. When viewed from the axial direction, setting the second radius of curvature R2 to 40% or more of the first diameter D1 can suppress the reduction in strength of the main cutting edge 3 at the periphery of the outer peripheral end of the curved cutting edge portion 31. When viewed from the axial direction, setting the second radius of curvature R2 to less than 100% of the first diameter D1 can suppress the reduction in the sharpness of the main cutting edge 3.

[0115] When the main cutting edge 3 is straight, the newly formed chip is also straight. In this case, the straight chip is curled by the curved portion 95 of the second cutting edge 92. Therefore, the chip deformation is greater, and the cutting resistance is greater. On the other hand, when the main cutting edge 3 is curved, the newly formed chip is also curved. In this case, the curved chip is curled by the curved portion 95 of the second cutting edge 92. Therefore, compared with the case where the main cutting edge 3 is straight, the chip deformation is smaller, and the cutting resistance is smaller. According to the drill bit 100 of this embodiment, the main cutting edge 3 may have a curved cutting edge portion 31. Therefore, the chip formed by the main cutting edge 3 is curved. As a result, the cutting resistance can be reduced.

[0116] According to the drill bit 100 of this embodiment, when viewed from the axial direction, the radius of curvature (third radius of curvature R3) of the curved portion 95 of the second cutting edge 92 can be smaller than the radius of curvature (second radius of curvature R2) of the curved cutting edge portion 31 of the main cutting edge 3. Therefore, as the chips flow from the helical groove surface 5 near the main cutting edge 3 toward the helical groove surface 5 near the second cutting edge 92, the curling radius of the chips gradually decreases.

[0117] The drill bit 100 according to this embodiment may have a reinforced cutting edge 32. The reinforced cutting edge 32 may be formed at the outermost peripheral end 59. The reinforced cutting edge 32 is inclined rearward in the rotational direction relative to the fourth straight line 124. Therefore, compared with the case without the reinforced cutting edge 32, the strength of the cutting edge can be improved around the outermost peripheral end 59. As a result, even when cutting materials with a hardness of HB300 or higher, cutting edge damage can be suppressed.

[0118] When the length of the reinforcing cutting edge 32 is excessively long when viewed from the axial direction, the cutting resistance increases, resulting in a thicker chip. Consequently, the chip strength increases, and the chip strongly rubs against the helical groove surface of the drill bit. As a result, wear occurs on the drill bit 100 along the traces left by the chip flow. According to the drill bit 100 of this embodiment, when viewed from the axial direction, the length of the reinforcing cutting edge 32 (the second length L2) can be less than 2% of the diameter of the drill bit 100 (the first diameter D1). Therefore, it is possible to suppress the excessive lengthening of the reinforcing cutting edge 32. As a result, wear on the drill bit 100 can be suppressed.

[0119] When the length of the reinforced cutting edge 32 is excessively long, the cutting resistance of the reinforced cutting edge 32 becomes excessively large. Therefore, the change in cutting resistance at the boundary between the curved cutting edge 31 and the reinforced cutting edge 32 increases. Consequently, chip melting easily occurs at the cutting edge. According to the drill bit 100 of this embodiment, when viewed from the axial direction, the length of the reinforced cutting edge 32 (second length L2) can be less than 2% of the diameter of the drill bit 100 (first diameter D1). This suppresses chip melting at the cutting edge.

[0120] Example 1

[0121] (Sample preparation)

[0122] First, drill bits 100 for samples 1 to 3 were prepared. Drill bits 100 for samples 1 and 2 are comparative examples. Drill bit 100 for sample 3 is an example.

[0123] In the drill bit 100 of Sample 1, the first radius of curvature R1 of the curved grinding cutting edge 43 is set to 10% of the diameter of the drill bit 100. In the drill bit 100 of Sample 1, the second axial tilt angle θ12 of the curved grinding cutting edge 43 is set to 0°. The diameter (first diameter D1) of the drill bits 100 involved in Samples 1 to 3 is set to 19.25 mm.

[0124] In the drill bit 100 of sample 2, the first radius of curvature R1 of the curved grinding cutting edge 43 is set to 10% of the diameter of the drill bit 100. In the drill bit 100 of sample 2, the second axial tilt angle θ12 of the curved grinding cutting edge 43 is set to 10°.

[0125] The drill bit 100 of sample 3 has a troweled recess wall portion 63. In the drill bit 100 of sample 3, the fourth radius of curvature R4 of the troweled recess wall portion 63 is set to 15% of the diameter of the drill bit 100. In the drill bit 100 of sample 3, the first radius of curvature R1 of the curved troweled cutting edge portion 43 is set to 25% of the diameter of the drill bit 100. In the drill bit 100 of sample 3, the second axial tilt angle θ12 of the curved troweled cutting edge portion 43 is set to 13°.

[0126] (Evaluation Method)

[0127] Next, the thrust component of the cutting resistance was evaluated using the drill bits 100 described in Samples 1 to 3. Holes were formed in the workpiece material using the drill bits 100 described in Samples 1 to 3. The workpiece material was set to SS400. The hole depth was set to 40 mm. The number of holes was set to 3. While forming holes in the workpiece material using the drill bits 100 described in Samples 1 to 3, the thrust component of the cutting resistance was measured. The average value of the thrust component of the cutting resistance experienced by the drill bit 100 when forming 3 holes was calculated. The chips generated by forming the holes were confirmed. The cutting speed Vc was set to 120 m / min. The feed rate f was set to 0.3 mm / revolution. Coolant was supplied via internal oil supply.

[0128] (Evaluation Results)

[0129] Table 1 shows the average thrust component of the cutting resistance experienced by the drill bit 100 during hole formation using the drill bits 100 involved in Samples 1 to 3. As shown in Table 1, the thrust component of the cutting resistance experienced by the drill bit 100 when forming a hole using the drill bit 100 involved in Sample 3 is less than the thrust component of the cutting resistance experienced by the drill bit 100 when forming a hole using the drill bits 100 involved in Samples 1 and 2. These results confirm that the drill bit 100 of the embodiments can reduce cutting resistance compared to the drill bit 100 of the comparative examples.

[0130] [Table 1]

[0131]

[0132] Figure 14 The image shows a photograph of the chips produced using the drill bit 100 involved in Sample 1. Figure 15 The image shows a photograph of the chips produced using the drill bit 100 involved in Sample 2. Figure 16 These are photographs of the chips produced using drill bit 100, which is involved in sample 3. (Example:) Figure 14 , Figure 15 and Figure 16 As shown, scratches 99 are generated on the surface of the chips 98 formed by the drill bits 100 involved in samples 1 and 2, in the direction of chip flow 98. It is conceivable that scratches 99 are generated due to the contact between chips that have fused to the cutting edge and newly formed chips. Therefore, it is conceivable that chip fusion to the cutting edge occurs in the drill bits 100 involved in samples 1 and 2. On the other hand, almost no scratches 99 are generated on the surface of the chips 98 formed by the drill bit 100 involved in sample 3, in the direction of chip flow 98. Thus, it is confirmed that the drill bit 100 of the embodiment can suppress chip fusion to the cutting edge compared with the drill bit 100 of the comparative example.

[0133] like Figure 14 , Figure 15 and Figure 16 As shown, the length of the chip 98 formed by the drill bit 100 involved in sample 3 is shorter than the length of the chip 98 formed by the drill bits 100 involved in samples 1 and 2 respectively. This confirms that the chip removal performance of the drill bit 100 of the embodiment is improved compared with that of the comparative drill bit 100.

[0134] Example 2

[0135] (Evaluation Method)

[0136] Next, the chip removal performance under low feed conditions was evaluated using drill bit 100, which was involved in samples 1 to 3. The workpiece material was set to SS400. The hole depth was set to 40 mm. Chips generated during hole formation were confirmed. The cutting speed Vc was set to 120 m / min. The feed rate f was set to 0.2 mm / rpm. Coolant was supplied via internal oil supply.

[0137] (Evaluation Results)

[0138] Figure 17 This is a photograph of the chips formed when using the drill bit 100 involved in Sample 1 under low feed conditions. Figure 18 This is a photograph of the chips formed when using the drill bit 100 involved in Sample 2 under low feed conditions. Figure 19 These are photographs of the chips produced when using drill bit 100, as described in Sample 3, under low feed conditions. Figure 17 and Figure 18 As shown, the chips 98 formed by the drill bit 100 involved in Samples 1 and 2 include chips 98 with a length of 50 mm or more. On the other hand, as Figure 19 As shown, the length of the chip 98 formed by the drill bit 100 involved in sample 3 is less than 50 mm. This confirms that the chip removal performance of the drill bit 100 of the embodiment is improved compared with that of the comparative drill bit 100.

[0139] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the invention is defined not by the above embodiments, but by the claims, and includes all modifications within the scope and equivalents of the claims.

[0140] Explanation of the label

[0141] 1. Front end, 2. Rear end, 3. Main cutting edge, 4. Grinding cutting edge, 5. Spiral groove surface, 6. Grinding surface, 7. Leading edge, 8. Chisel edge, 9. Outer peripheral surface, 10. First clearance surface, 11. First clearance surface, 12. Second clearance surface, 15. First boundary line, 17. Shank, 19. First outer peripheral surface, 20. Second clearance surface, 23. Third clearance surface, 24. Fourth clearance surface, 25. Second boundary line, 29. Second outer peripheral surface, 31. Curved cutting edge, 32. Reinforced cutting edge, 39. Reinforced forward tilt surface, 41. First straight edge Sharpening the cutting edge: 42. Sharpening the second straight cutting edge; 43. Sharpening the curved cutting edge; 51. First end; 52. Second end; 55. Outer periphery; 57. Second boundary point; 58. First boundary point; 59. Outermost periphery; 61. Sharpening the forward-leaning surface; 62. Middle surface; 63. Sharpening the recessed wall; 81. First part; 82. Second part; 83. Third part; 91. First top edge; 92. Second top edge; 93. Inner periphery of top edge; 94. Middle part of top edge; 95. Curved part; 96. Outer periphery of top edge; 98. Chips. 99 damage, 100 drill bit, 101 top view, 121 first straight line, 122 second straight line, 123 third straight line, 124 fourth straight line, 125 fifth straight line, 126 sixth straight line, 127 seventh straight line, 131 first tangent, 132 second tangent, CS1 first profile, CS2 second profile, CS3 third profile, D1 first diameter, D2 second diameter, E0 reference distance, E1 first distance, E2 second distance, E3 third distance, E4 fourth distance. F represents the outer core height, H represents the maximum distance, IV, VIII, and XIII regions, L1 represents the first length, L2 represents the second length, O represents the axis, R1 represents the first radius of curvature, R2 represents the second radius of curvature, R3 represents the third radius of curvature, R4 represents the fourth radius of curvature, θ1 represents the first angle, θ2 represents the second angle, θ3 represents the third angle, θ11 represents the first axial tilt angle, θ12 represents the second axial tilt angle, θ13 represents the third axial tilt angle, θ14 represents the fourth axial tilt angle, θ21 represents the first central angle, and θ22 represents the second central angle.

Claims

1. A drill bit that rotates about an axis, This drill bit has the following features: A spiral groove surface, which is spirally shaped around the axis; The rear clearance surface, which is connected to the spiral groove surface; and The grinding surface is connected to both the spiral groove surface and the rear clearance surface. The edges of the spiral groove surface and the rear clearance surface constitute the main cutting edge. The edges of the grinding surface and the back clearance surface form a grinding cutting edge connected to the main cutting edge. When viewed from the axial direction along the axis, the sharpening cutting edge is closer to the axis than the main cutting edge. The sharpening of the cutting edge includes: The cutting edge is curved and protrudes forward in the direction of rotation; and A straight-line grinding cutting edge is connected to the curved grinding cutting edge and, when viewed from the axial direction, is closer to the axis than the curved grinding cutting edge. When the first straight line is defined as the straight line passing through the axis and the outer peripheral position separated from the outermost peripheral end of the main cutting edge by a predetermined outer peripheral core height in the direction of rotation, When viewed from the axial direction, the angle formed by the first straight line and the grinding cutting edge of the straight line is 135° or more and 160° or less. When viewed from the axial direction, the length of the straight-line grinding cutting edge is less than 10% of the drill bit's diameter. A cross-section perpendicular to and intersecting the straight-line grinding cutting edge when viewed from the axial direction, wherein the axial forward tilt angle of the straight-line grinding cutting edge is greater than -10° and less than 0°. The curved grinding cutting edge has a first end portion, which is the boundary between the curved grinding cutting edge portion and the straight grinding cutting edge portion, and a second end portion located on the opposite side of the first end portion. As the blade separates from the first end, the axial forward tilt angle of the curved grinding cutting edge at a section perpendicular to the tangent of the curved grinding cutting edge when viewed from the axial direction increases. A cross-section that is perpendicular to the tangent of the curved grinding cutting edge at the second end when viewed from the axial direction and includes the second end, wherein the axial forward tilt angle of the curved grinding cutting edge is 5° or more and 20° or less. When viewed from the axial direction, the radius of curvature of the curved grinding cutting edge is more than 15% and less than 35% of the diameter of the drill bit.

2. The drill bit according to claim 1, wherein, The polished surface includes: The forward-tilting surface is ground and connected to both the spiral groove surface and the rear clearance surface. The recessed wall is ground down, positioned in front of the grinding cutting edge in the direction of rotation. as well as The middle surface is connected to both the pre-grinding surface and the wall of the grinding pit. The rear clearance surface includes: The first rear clearance surface is connected to both the spiral groove surface and the grinding surface; and The second rear gap facet, which is connected to the first rear gap facet and is located behind the first rear gap facet in the rotational direction, The straight line along the boundary line between the wall of the grinding pit and the intermediate surface is designated as the second straight line. When viewed from the axial direction, with the direction perpendicular to the ridge lines of the first and second rear gap surfaces and pointing radially inward as the top-viewing direction, A cross-section that is perpendicular to the second straight line and intersects the boundary line of the grinding pit wall and the intermediate surface when viewed from the top direction. The wall of the grinding pit is curved. Furthermore, the radius of curvature of the groove wall being ground is more than 10% and less than 30% of the diameter of the drill bit. Furthermore, the angle between the tangent of the grinding-forward tilted surface at the boundary between the grinding-forward tilted surface and the intermediate surface and the tangent of the grinding-recess wall at the boundary between the grinding-recess wall and the intermediate surface is 105° or more and 125° or less.

3. The drill bit according to claim 1 or 2, wherein, The main cutting edge includes a curved cutting edge portion that is recessed rearward in the direction of rotation. When viewed from the axial direction, the radius of curvature of the curved cutting edge is more than 40% and less than 100% of the diameter of the drill bit. When viewed from the axial direction, the maximum distance between the third straight line, which passes through the outer periphery of the curved cutting edge and is parallel to the first straight line, and the curved cutting edge is more than 0.5% and less than 4% of the diameter of the drill bit. The grinding surface forms the first top edge connected to the grinding cutting edge. The first top cutting edge is positioned in front of the grinding cutting edge in the direction of rotation. The spiral groove surface forms a second top edge that is connected to the first top edge. The second top cutting edge is positioned in front of the main cutting edge in the direction of rotation. The second top cutting edge includes a curved portion that is recessed forward in the direction of rotation. When viewed from the axial direction, the radius of curvature of the curved portion is more than 15% and less than 25% of the diameter of the drill bit. In a cross-section perpendicular to the axis, the central angle of the spiral groove is more than 0.55 times and less than 1.0 times the central angle of the portion outside the spiral groove.

4. The drill bit according to claim 3, wherein, The main cutting edge includes a reinforcing cutting edge that is connected to the curved cutting edge and forms the outermost peripheral end. When viewed from the axial direction, if the straight line containing the axial line and the boundary between the curved cutting edge and the reinforced cutting edge is defined as the fourth straight line... When viewed from the axial direction, the reinforced cutting edge is inclined rearward relative to the fourth straight line in the direction of rotation. When viewed from the axial direction, the angle between the reinforced cutting edge and the fourth straight line is 15° or more and 30° or less. When viewed from the axial direction, the length of the reinforced cutting edge is more than 1% and less than 2% of the diameter of the drill bit.

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