Drill

Abstract

In a drill according to the present invention, a thinning blade, a main cutting blade, and a leading edge each have honing (H) where a cross section perpendicular to each ridge line part is formed in a convex curved shape. In this cross section, among both end parts (h1) and (h2) of the honing H, a surface connected to the first end part (h1) is defined as a first surface (101), a surface connected to the second end part (h2) is defined as a second surface (102), the distance to the first end part h1 from an intersection point P of an extension line of the first surface (101) and an extension line of the second surface (102) is defined as a first width dimension (L1), the distance to the second end part h2 from the intersection point P is defined as a second width dimension (L2), and [L1 / L2] is defined as a width ratio. The thinning blade and the main cutting blade each have the first surface (101) as a rake face, and the second surface (102) as a flank face, and the width ratio of the thinning blade is larger than the width ratio of a radial outer end part connected to an outer peripheral corner of the main cutting blade.

Description

drill

[0001] This application claims priority to Japanese Patent Application No. 2023-194618, filed November 15, 2023, the contents of which are incorporated herein by reference.

[0002] Conventionally, a drill has been known that includes a chip discharge flute, a rake face that is disposed in the chip discharge flute and faces the direction of drill rotation, a flank that is disposed on the tip face of the drill, a cutting edge that is disposed on a ridge line where the rake face and the flank face are connected, a margin that is disposed on the outer peripheral surface of the drill and extends along the chip discharge flute, a leading edge that is disposed on the ridge line where the margin and the rake face are connected, an outer peripheral corner that is disposed on the corner where the cutting edge and the leading edge are connected, and a shoulder that is disposed on the ridge line where the margin and the flank face are connected and that extends from the outer peripheral corner in the direction opposite to the direction of drill rotation (counter to the direction of drill rotation).

[0003] For example, in the drills described in Patent Documents 1 and 2, while cutting conditions tend to become stricter in order to increase processing efficiency, in order to suppress the problem of chipping occurring easily in the shoulder portion, particularly when drilling thin plates, the honing widths of the shoulder cutting edge portion (shoulder portion), margin cutting edge portion (leading edge) and the boundary between them (peripheral corner) are made larger than the honing width of the second cutting edge portion (main cutting edge).

[0004] Patent No. 6722410 Patent No. 7268691

[0005] Although the drills described in Patent Documents 1 and 2 are advantageous for achieving high-efficiency machining and for machining in unstable conditions due to thin and small workpieces (materials to be cut), they have the following problems when used under low- to medium-efficiency machining conditions, which are still the mainstream (main machining area) of drilling, or when machining large workpieces. Note that "low- to medium-efficiency machining conditions" in this specification refers to machining conditions such as a peripheral speed of up to about vc = 130 m / min, a feed rate of up to about φ6.0 mm and fr = 0.35 mm / rev (depending on the drill bit diameter, as an example).

[0006] That is, when the honing width near the outer periphery of the drill is set large, as in Patent Documents 1 and 2, the cutting resistance increases, which makes wear more likely to progress early. In other words, while fracture resistance is improved, wear resistance tends to decrease. In the low- to medium-efficiency machining conditions and drilling of large workpieces as described above, sudden fractures are unlikely to occur. Rather, it is important to suppress fractures and other issues caused by thinning of the cutting edge due to wear.

[0007] An object of the present invention is to provide a drill that can improve wear resistance and thereby extend the tool life.

[0008] In order to solve the above problems, the present invention provides the following means.

[0009] [Aspect 1 of the present invention] A drill including a body extending in an axial direction about a central axis, the body having a chip flute opening at a tip end surface and an outer peripheral surface of the body and extending from the tip end surface toward a rear end thereof, a rake face disposed in the chip flute and facing the direction of rotation of the drill around the central axis, a flank face disposed on the tip end surface, a cutting edge disposed on a ridge line portion connecting the rake face and the flank face, a margin disposed on the outer peripheral surface and extending along the chip flute, a leading edge disposed on a ridge line portion connecting the margin and the rake face, and an outer peripheral corner disposed on a corner portion connecting the cutting edge and the leading edge, the cutting edge having a thinning edge disposed at a radially inner end of the cutting edge, and a leading edge disposed radially outward of the thinning edge and connecting the leading edge via the outer peripheral corner. a main cutting edge connected to a rake face and a leading edge, the thinning edge, the main cutting edge, and the leading edge each have a honing whose cross section perpendicular to each ridge line is a convex curve, and in the cross section, of both end portions of the honing, a surface connected to a first end portion is defined as a first surface, and a surface connected to a second end portion is defined as a second surface, the distance from an intersection of an extension line of the first surface and an extension line of the second surface to the first end portion is defined as a first width dimension L1, and the distance from the intersection point to the second end portion is defined as a second width dimension L2, with [L1 / L2] being a width ratio, and the first surface of the thinning edge and the main cutting edge is the rake face and the second surface is the relief face, and the width ratio of the thinning edge is greater than the width ratio of a radially outer end portion of the main cutting edge that is connected to the outer peripheral corner.

[0010] In the drill of the present invention, the honings of the thinning edge, main cutting edge, and leading edge each have a convex curve (convex R-shape) in a cross section perpendicular to each ridge, which is known as round honing. This allows for reduced wear and welding within the honing surface when drilling large workpieces or under low- to medium-efficiency machining conditions. Specifically, unlike the present invention, if the honing of each component of the cutting edge (particularly the main cutting edge) is chamfer honing, which has a flat surface, this can promote destructive wear within the honing surface, potentially leading to early welding and chipping when drilling large workpieces or under low- to medium-efficiency machining conditions.

[0011] In the drill of the present invention, when the width ratio [L1 / L2] is defined in a cross section perpendicular to the direction in which each honing extends, the width ratio of the honing of the thinning edge is larger than the width ratio of the honing of the radially outer end of the main cutting edge that is connected to the outer peripheral corner. In other words, the width ratio of the honing of the radially outer end of the main cutting edge is smaller than the width ratio of the honing of the thinning edge.

[0012] Specifically, when comparing the width ratios of each honing, the thinning edge has a larger ratio of the first width dimension L1 on the rake face side, and the radial outer end of the main cutting edge has a larger ratio of the second width dimension L2 on the relief face side.

[0013] During drilling, the thinning edge tends to be subject to significant damage due to crater wear caused by compressed chips scraping against it. Crater wear tends to occur near the boundary between the honing surface and the rake face, so by increasing the width ratio of the thinning edge (increasing the proportion of the first width dimension L1 on the rake face side), as in the present invention, crater wear can be stably suppressed.

[0014] In addition, the radially outer end of the main cutting edge tends to be subject to significant wear on the flank side. Therefore, by reducing the width ratio of the radially outer end of the main cutting edge (increasing the ratio of the second width dimension L2 on the flank side) as in the present invention, flank wear can be stably suppressed.

[0015] As described above, the drill of the present invention can improve wear resistance and thereby extend the tool life. The present invention is particularly effective when applied to low- to medium-efficiency drilling conditions or drilling large workpieces.

[0016] [Aspect 2 of the present invention] The drill according to Aspect 1, wherein the main cutting edge has a first cutting edge that is disposed radially outward of the thinning edge and that forms a concave curve that is recessed around the central axis in a direction opposite to the rotation direction of the drill, and a second cutting edge that is disposed radially outward of the first cutting edge and that is connected to the radial outer end of the first cutting edge, and the second cutting edge constitutes the radial outer end of the main cutting edge that is connected to the outer peripheral corner.

[0017] According to the above configuration, when the main cutting edge has a so-called curved cutting edge shape having a concave cutting edge shape (first cutting edge), the above-described operational effects of the present invention are effectively achieved.

[0018] [Aspect 3 of the present invention] The drill according to Aspect 1, wherein the main cutting edge is linear, and a region of the main cutting edge extending radially inward from the outer peripheral corner within 7% of the drill edge diameter is defined as a radially outer end portion of the main cutting edge connected to the outer peripheral corner, where the diameter of the drill edge is defined as a diameter of the drill edge of the rotational locus of the cutting edge around the central axis.

[0019] According to the above configuration, the above-described operational effects of the present invention are effectively achieved in the case where the main cutting edge is a so-called straight cutting edge having a straight line shape.

[0020] Aspect 4 of the present invention is the drill according to any one of Aspects 1 to 3, wherein the first surface of the leading edge is the rake face and the second surface is the margin, and the width ratio of the leading edge at a position within 1.5 mm from the outer peripheral corner toward the rear end is 0.7 to 1.3.

[0021] The leading edge tends to be more susceptible to wear damage due to wear on the margin side. In particular, the position of the leading edge within 1.5 mm from the outer corner toward the rear end is located at the tip of the leading edge, and is considered to be a location that is more susceptible to cutting resistance from the inner surface of the machined hole in the workpiece.

[0022] As a result of intensive research by the inventors, it was confirmed that, with regard to the width ratio of the leading edge honing, if the ratio of the second width dimension L2 on the margin side is too large, cutting resistance increases significantly and wear progresses early. Also, if the ratio of the first width dimension L1 on the rake face side is small, wear on the rake face side progresses. For the above reasons, it is preferable that the width ratio of the leading edge be 0.7 or more and 1.3 or less, and the closer to 1.0 the better.

[0023] [Aspect 5 of the present invention] The drill according to any one of Aspects 1 to 4, wherein the width ratio of a portion of the main cutting edge that is located radially inward of the radial outer end portion is greater than the width ratio of the radial outer end portion of the main cutting edge.

[0024] The portion of the main cutting edge that is located radially inward of the radial outer end connected to the outer peripheral corner is more likely to suffer from crater wear due to scraping by chips. Because crater wear is likely to occur near the boundary between the honing surface and the rake face, crater wear can be effectively suppressed by increasing the honing width ratio of the portion of the main cutting edge that is located radially inward of the radial outer end (increasing the proportion of the first width dimension L1 on the rake face side).

[0025] Furthermore, wear on the flank side tends to progress easily at the radially outer end of the main cutting edge. Therefore, by reducing the width ratio of the honing at the radially outer end of the main cutting edge (increasing the proportion of the second width dimension L2 on the flank side) as in the above configuration, flank wear can be effectively suppressed.

[0026] [Aspect 6 of the present invention] The drill according to any one of Aspects 1 to 5, wherein the width ratio of the thinning edge increases toward the center axis along the cutting edge length direction in which the thinning edge extends.

[0027] Thinning edges are susceptible to damage caused by crater wear due to the abrasion of compressed chips. Crater wear tends to become more pronounced as the edge approaches the center axis along the cutting length of the thinning edge.

[0028] Therefore, by increasing the width ratio of the honing of the thinning blade as it approaches the central axis, as in the above-mentioned configuration of the present invention, it is possible to effectively suppress crater wear over the entire blade length, including the vicinity of the central axis of the thinning blade.

[0029] [Aspect 7 of the Present Invention] The drill according to any one of Aspects 1 to 6, wherein the width ratio of the outermost end of the main cutting edge located at the outer peripheral corner is the smallest among the width ratios of the cutting edges.

[0030] Wear on the flank side tends to progress significantly at the outermost end (outer peripheral corner) of the main cutting edge. Therefore, by minimizing the honing width ratio at the outermost end (outer peripheral corner) of the main cutting edge as in the above-described configuration of the present invention, flank wear can be effectively suppressed.

[0031] [Aspect 8 of the Present Invention] The drill according to Aspect 2, wherein the width ratio of the first cutting edge is greatest at a lowest point of the first cutting edge that is located furthest in the opposite direction to the rotation direction of the drill.

[0032] In conventional drills, the stress caused by chip abrasion is strong at the lowest point of the concave curved concave cutting edge (the first cutting edge in this invention), which is located furthest in the direction opposite to the drill rotation, and damage caused by crater wear tends to be significant. Because crater wear is likely to occur near the boundary between the honing surface and the rake face, crater wear can be effectively suppressed by maximizing the honing width ratio at the lowest point of the first cutting edge (maximizing the proportion of the first width dimension L1 on the rake face side), as in the above-mentioned configuration of the present invention.

[0033] Aspect 9 of the present invention is the drill according to any one of Aspects 1 to 8, wherein the body has a shoulder portion disposed on a ridge line where the margin and the flank face are connected, the shoulder portion extending from the outer circumferential corner around the central axis in a direction opposite to the rotation direction of the drill, the shoulder portion having a honing whose cross section perpendicular to the ridge line is a convex curve, the first surface of the shoulder portion being the flank face and the second surface being the margin, and the width ratio of the shoulder portion being 0.7 to 1.3.

[0034] When the width ratio of the honing of the shoulder portion is 0.7 or more and 1.3 or less as in the above configuration, problems such as early progress of wear on either the flank face or the margin arranged on both sides of the shoulder portion, which affects the tool life, are stably suppressed. Note that the width ratio of the shoulder portion is more preferably closer to 1.0.

[0035] [Aspect 10 of the Present Invention] The drill according to any one of Aspects 1 to 9, wherein the width ratio of the thinning edge is 1.0 or more.

[0036] In this case, the width ratio of the honing of the thinning edge can be stably increased (the proportion of the first width dimension L1 on the rake face side can be increased), and the effect of suppressing crater wear can be more significantly achieved.

[0037] According to the drill of the above aspect of the present invention, it is possible to improve the wear resistance, thereby achieving a longer tool life.

[0038] FIG. 1 is a simplified perspective view of a portion (body) of the drill of this embodiment. FIG. 2 is a simplified front view of a portion of the drill of this embodiment. FIG. 3 is a simplified side view of a portion of the drill of this embodiment. FIG. 4 is a simplified side view of a portion of the drill of this embodiment. FIG. 5A is a cross-sectional view schematically showing a cross section perpendicular to each ridge line portion (each honing) of the body of the drill, specifically showing a case where the honing width ratio is 1.0. FIG. 5B is a cross-sectional view schematically showing a cross section perpendicular to each ridge line portion (each honing) of the body of the drill, specifically showing a case where the honing width ratio is greater than 1.0. FIG. 5C is a cross-sectional view schematically showing a cross section perpendicular to each ridge line portion (each honing) of the body of the drill, specifically showing a case where the honing width ratio is less than 1.0. Fig. 6 is a diagram (table) showing the results of "Wear Confirmation Test 1" of the example (enlarged images of the vicinity of each cutting edge), along with a schematic cross-sectional view of the vicinity of each cutting edge. Fig. 7 is a diagram (table) showing the results of "Wear Confirmation Test 2" of the example (enlarged images of the vicinity of each cutting edge), along with a schematic cross-sectional view of the vicinity of each cutting edge.

[0039] A drill 10 according to one embodiment of the present invention will be described with reference to the drawings. As shown in FIGS. 1 to 4, the drill 10 includes at least a body 1. The body 1 is generally cylindrical and centered on a central axis O. In this embodiment, the drill 10 includes the body 1 and a shank (not shown). The body 1 and the shank are arranged side by side in the direction in which the central axis O extends. The body 1 may also be referred to as a cutting portion.

[0040] In this embodiment, the body 1 is detachably attached to the shank. That is, the drill 10 is an indexable drill. However, the drill 10 is not limited to this, and may include only the body 1 and not the shank. In this case, the drill 10 is a drill head. The shank may also be referred to as a holder. Also, in Figures 1 to 4, the fastening mechanism of the body 1 to the shank is omitted, and the body 1 is shown in a simplified form.

[0041] [Definition of Directions] In this embodiment, the direction in which the central axis O of the drill 10 extends is referred to as the axial direction. Within the axial direction, the direction from the shank to the body 1 is referred to as the axial tip side or simply the tip side, and the direction from the body 1 to the shank is referred to as the axial rear end side or simply the rear end side.

[0042] Additionally, the direction perpendicular to the central axis O is referred to as the radial direction. Of the radial directions, the direction approaching the central axis O is referred to as the radially inner direction, and the direction away from the central axis O is referred to as the radially outer direction. The direction rotating around the central axis O is referred to as the circumferential direction. Of the circumferential directions, the direction in which the drill 10 is rotated during drilling is referred to as the drill rotation direction T. Of the circumferential directions, the direction opposite to the drill rotation direction T may be referred to as the counter-drill rotation direction.

[0043] In this embodiment, the direction in which each component of a cutting edge 7 (described later) of the body 1 extends is referred to as the cutting edge length direction.

[0044] [Shank] Although not shown, the shank is columnar and extends in the axial direction around a central axis O. The shank is detachably held, for example, by a spindle of a machine tool or a chuck of a drilling press (hereinafter referred to as the spindle, etc.), both of which are not shown. The drill 10 cuts into the workpiece with the body 1 to perform drilling by rotating the shank in the drill rotation direction T by the spindle, etc., and feeding it toward the tip in the axial direction.

[0045] 1 to 4, the body 1 extends in the axial direction around a central axis O. In this embodiment, the diameter (outer diameter) of the body 1 is, for example, 6 mm or more and 40 mm or less. Note that the diameter of the body 1 corresponds to the diameter of the rotational trajectory of the cutting edge 7 (described later) around the central axis O, and may therefore be referred to as the drill bit diameter.

[0046] The body 1 has a tip surface 3 facing the tip side of the body 1, an outer peripheral surface 8 facing radially outward from the body 1, a chip discharge groove 4, a rake face 5, a relief face 6, a thinning surface 11, a cutting edge 7, a margin 13, a leading edge 12, a chamfer surface 14, an outer peripheral corner 15, a shoulder 9, a fastening mechanism with the shank (not shown), and a rotation support portion (not shown).

[0047] The chip discharge flutes 4 are groove-shaped and open to the tip surface 3 and the outer peripheral surface 8 of the body 1, extending from the tip surface 3 toward the rear end. Specifically, the chip discharge flutes 4 extend in a twisted manner in the direction opposite to the rotational direction of the drill as they extend from the tip surface 3 toward the rear end in the axial direction. A plurality of chip discharge flutes 4 are provided in the body 1, spaced apart from one another in the circumferential direction. In this embodiment, two chip discharge flutes 4 are provided at equal intervals in the circumferential direction.

[0048] The rake face 5 is disposed in the chip discharge flute 4 and faces the drill rotation direction T. That is, the rake face 5 is disposed on the wall surface of the chip discharge flute 4 that faces the drill rotation direction T. The rake face 5 has a thinning rake face 50, a main rake face 51, a first boundary ridge 54, and a second boundary ridge 55.

[0049] The thinning rake face 50 is disposed at the radially inner end of the tip of the chip discharge flute 4. In this embodiment, the thinning rake face 50 has a substantially triangular shape.

[0050] The main rake face 51 is disposed radially outward of the thinning rake face 50. The main rake face 51 has a first rake face 52 and a second rake face 53. That is, the rake face 5 has the first rake face 52 and the second rake face 53.

[0051] The first rake face 52 is disposed at a portion of the main rake face 51 other than the radially outer end. The first rake face 52 is disposed radially outward of the thinning rake face 50 and adjacent to the thinning rake face 50. In this embodiment, the first rake face 52 has a concave curved shape. Although not particularly shown, in a cross-sectional view perpendicular to the central axis O (hereinafter sometimes simply referred to as a transverse cross-sectional view), the first rake face 52 has a concave curved shape recessed in the direction opposite to the drill rotation direction. The radial dimension of the first rake face 52 is larger than the radial dimension of the thinning rake face 50.

[0052] The second rake face 53 is disposed at the radially outer end of the main rake face 51. The second rake face 53 is disposed radially outward of the first rake face 52 and adjacent to the first rake face 52. In this embodiment, the second rake face 53 has a twisted surface shape. Although not particularly shown, the second rake face 53 has a straight shape in a cross section. However, this is not limited thereto, and the second rake face 53 may have a concave curved shape. In this case, the second rake face 53 has a concave curved shape that is recessed in the direction opposite to the drill rotation direction in a cross section. Alternatively, the second rake face 53 may have a convex curved shape. In this case, the second rake face 53 has a convex curved shape that bulges in the drill rotation direction T in a cross section. The radial dimension of the second rake face 53 is smaller than the radial dimension of the thinning rake face 50 and is also smaller than the radial dimension of the first rake face 52 .

[0053] The second rake face 53 extends substantially in the axial direction along the radially outer edge of the wall surface of the chip flute 4 that faces the drill rotation direction T. Specifically, the second rake face 53 extends in a twisted manner in the direction opposite to the drill rotation direction as it extends toward the rear end in the axial direction. The radially outer end of the second rake face 53 is connected to the outer peripheral surface 8 via a ridge portion (leading edge 12).

[0054] Furthermore, the second rake face 53 extends radially outward in the opposite direction to the drill rotation direction T (i.e., in the opposite direction to the drill rotation direction). More specifically, the second rake face 53 extends radially outward in the opposite direction to the drill rotation direction over the entire radial area of ​​the second rake face 53. In other words, the radial rake angle of the second rake face 53 is a negative angle over the entire radial area. Therefore, the ridge portion (leading edge 12) located at the radial outer end of the second rake face 53 forms an obtuse angle in cross section.

[0055] The first boundary ridge 54 extends along the boundary portion where the thinning rake face 50 and the main rake face 51 are connected, and forms a ridge shape that is convex in the drill rotation direction T. The first boundary ridge 54 extends substantially in the axial direction along the boundary portion where the thinning rake face 50 and the first rake face 52 are connected. Specifically, the first boundary ridge 54 extends radially inward as it approaches the rear end side in the axial direction.

[0056] The second boundary ridge 55 extends along the boundary portion where the first rake face 52 and the second rake face 53 are connected, and has a ridge shape that is convex toward the drill rotation direction T. The second boundary ridge 55 extends substantially in the axial direction along the boundary portion where the first rake face 52 and the second rake face 53 are connected. Specifically, the second boundary ridge 55 extends in the direction opposite to the drill rotation direction as it moves toward the rear end in the axial direction.

[0057] The flank 6 is arranged on the tip face 3. The flank 6 has a first flank 61 and a second flank 62 arranged adjacent to the first flank 61 in the direction opposite to the rotation direction of the drill.

[0058] The first flank 61 is disposed at the end of the flank 6 in the drill rotation direction T. The first flank 61 has an elongated surface shape (a substantially polygonal surface shape elongated in the radial direction) extending substantially along the radial direction. The first flank 61 extends toward the rear end in the axial direction as it moves in the direction opposite to the drill rotation direction.

[0059] The second flank 62 is located at a portion of the flank 6 other than the end portion in the drill rotation direction T. The second flank 62 is generally fan-shaped, and its circumferential dimension increases radially outward. The second flank 62 extends axially toward the rear end as it approaches the counter-drill rotation direction. The amount of axial displacement of the second flank 62 per unit length along the circumferential direction (inclination corresponding to the clearance angle) is greater than the amount of axial displacement of the first flank 61.

[0060] In the present embodiment, the flank 6 has two inclined surfaces (the first flank 61 and the second flank 62) with different clearance angles, but this is not limiting. For example, the flank 6 may be formed by a single inclined surface, or may have three or more inclined surfaces arranged side by side in the circumferential direction and with different clearance angles.

[0061] The thinning surface 11 is disposed on the tip face 3. The thinning surface 11 is disposed adjacent to the flank 6 in the direction opposite to the drill rotation direction of the flank 6. In this embodiment, the thinning surface 11 is connected to the end of the second flank 62 in the direction opposite to the drill rotation direction. The thinning surface 11 extends toward the rear end in the axial direction as it moves in the direction opposite to the drill rotation direction. The amount of axial displacement per unit length along the circumferential direction of the thinning surface 11 (inclination corresponding to the relief angle) is greater than the amount of displacement of the flank 6. Furthermore, the radially inner end of the thinning surface 11 is connected to the base of the triangular thinning rake face 50.

[0062] The cutting edge 7 is disposed on a ridge line where the rake face 5 and the flank 6 are connected. A plurality of cutting edges 7 are provided on the body 1 at intervals in the circumferential direction. In this embodiment, two cutting edges 7 are provided at equal intervals in the circumferential direction. That is, the drill 10 of this embodiment is a two-flute twist drill.

[0063] The cutting edge 7 has a thinning edge 70 and a main cutting edge 71. The thinning edge 70 is located at the radially inner end of the cutting edge 7. The thinning edge 70 is located at the ridge where the thinning rake face 50 and the first flank 61 are connected. In other words, the thinning rake face 50 is connected to the thinning edge 70. The thinning edge 70 extends along the leading edge of the thinning rake face 50. The thinning edge 70 extends radially outward from near the central axis O, approximately along the radial direction. Furthermore, as the thinning edge 70 extends radially outward, it extends toward the rear end in the axial direction. In this embodiment, the thinning edge 70 is approximately linear.

[0064] The main cutting edge 71 is disposed radially outward from the thinning edge 70. The main cutting edge 71 is connected to the thinning edge 70. The main cutting edge 71 constitutes the portion of the cutting edge 7 other than the thinning edge 70 (the portion of the cutting edge 7 other than the radially inner end portion). The main cutting edge 71 is disposed on the ridge portion where the main rake face 51 and the first flank face 61 are connected. That is, the main rake face 51 is connected to the main cutting edge 71. The main cutting edge 71 extends along the leading edge of the main rake face 51. Furthermore, as the main cutting edge 71 extends radially outward, it extends toward the rear end side in the axial direction. An outer peripheral corner 15 is disposed at the radially outermost end of the main cutting edge 71. The main cutting edge 71 is connected to the leading edge 12 via the outer peripheral corner 15.

[0065] The main cutting edge 71 has a first cutting edge 72, a second cutting edge 73, and an apex 74. In this embodiment, the first cutting edge 72 constitutes the main cutting edge 71 except for the radially outer end portion. The first cutting edge 72 is disposed on a ridge portion where the first rake face 52 and the first flank face 61 are connected. That is, the first rake face 52 is connected to the first cutting edge 72. The first cutting edge 72 extends along the leading edge of the first rake face 52. The first cutting edge 72 is disposed radially outward of the thinning edge 70 and has a concave curved shape recessed in the direction opposite to the drill rotation direction T. The radially inner end portion of the first cutting edge 72 is connected to the radially outer end portion of the thinning edge 70. The connecting portion between the first cutting edge 72 and the thinning edge 70 has a convex shape protruding toward the drill rotation direction T.

[0066] In this embodiment, the second cutting edge 73 constitutes the radially outer end of the main cutting edge 71 that is connected to the outer peripheral corner 15. The second cutting edge 73 is disposed on a ridge where the second rake face 53 and the first flank face 61 are connected. That is, the second rake face 53 is connected to the second cutting edge 73. The second cutting edge 73 extends along the leading edge of the second rake face 53. The second cutting edge 73 is disposed radially outward of the first cutting edge 72 and is connected to the radially outer end of the first cutting edge 72 via an apex 74 that is convex toward the drill rotation direction T.

[0067] In this embodiment, the second cutting edge 73 is linear. However, the present invention is not limited to this, and the second cutting edge 73 may be concavely curved. When the second cutting edge 73 is concavely curved, it is preferable that the second cutting edge 73 has a concave curve with a large radius of curvature (i.e., a large R) that is recessed in the direction opposite to the rotation of the drill. Alternatively, the second cutting edge 73 may have a convex curve that bulges in the rotation direction T of the drill.

[0068] As shown in Fig. 2 , the radial rake angle (radial rake) θ of the second cutting edge 73 is a negative angle over the entire length of the second cutting edge 73. Here, the "radial rake angle θ of the second cutting edge 73" refers to the angle θ formed between the second cutting edge 73 and an imaginary line VL passing through (a part of) the second cutting edge 73 and the central axis O, when the drill 10 is viewed from the tip side along the axial direction, as shown in Fig. 2 . Furthermore, the "radial rake angle θ of the second cutting edge 73 is a negative angle" refers to a case in which the second cutting edge 73 extends in the opposite direction to the drill rotation direction T as it extends radially outward.

[0069] The apex 74 connects the radially outer end of the first cutting edge 72 and the radially inner end of the second cutting edge 73. The apex 74 has a convex shape that protrudes in the drill rotation direction T. Therefore, the cutting edge 7 of this embodiment has a so-called curved cutting edge shape in which the main cutting edge 71 has a concave cutting edge shape (first cutting edge 72) and a convex portion (apex 74).

[0070] As shown in Figures 1 to 4, the margin 13 is disposed on the outer peripheral surface 8 and extends along the chip discharge flute 4. Specifically, the margin 13 is disposed at the end of the outer peripheral surface 8 in the drill rotation direction T, and extends in the direction opposite to the drill rotation direction as it moves toward the rear end in the axial direction. The margin 13 has a curved surface shape that is convex outward in the radial direction. When viewed in a cross section perpendicular to the central axis O, the margin 13 has an arc shape centered on the central axis O.

[0071] The leading edge 12 is located on the ridge where the margin 13 and the second rake face 53 (rake face 5) are connected. The margin 13 and the second rake face 53 are connected to each other via the leading edge 12. The leading edge 12 extends along the margin 13 and the second rake face 53. Specifically, the leading edge 12 extends in the direction opposite to the drill rotation direction as it moves toward the rear end in the axial direction. The margin 13 is located on a cylindrical rotation locus (not shown) obtained by rotating the leading edge 12 around the central axis O.

[0072] The leading edge 12 may be back tapered. In this case, the leading edge 12 is positioned slightly radially inward as it moves axially toward the rear end.

[0073] The relief surface 14 is disposed on the outer peripheral surface 8. The relief surface 14 is disposed adjacent to the margin 13 in the direction opposite to the drill rotation direction of the margin 13. The relief surface 14 is located radially inward of the margin 13. During drilling, the relief surface 14 faces the inner peripheral surface of the machined hole in the workpiece with a radial gap therebetween.

[0074] The outer corner 15 is disposed at a corner where the cutting edge 7 and the leading edge 12 are connected. Specifically, the outer corner 15 connects the radially outer end of the second cutting edge 73 of the main cutting edge 71 and the tip of the leading edge 12.

[0075] The shoulder 9 is located on a ridge where the margin 13 and the first flank 61 (flank 6) are connected. The shoulder 9 is located on the outer periphery of the tip of the body 1 and extends in the circumferential direction about the central axis O. The shoulder 9 extends from the outer periphery corner 15 in the direction opposite to the drill rotation direction T. Specifically, the shoulder 9 extends slightly toward the rear end as it moves in the direction opposite to the drill rotation direction.

[0076] Although not specifically shown, the body 1 has a fastening mechanism for fastening to the shank. The fastening mechanism has, for example, a substantially cylindrical attachment portion that protrudes rearward from the rear end surface of the body 1, and a through-hole that passes through the body 1 in the axial direction.

[0077] The mounting portion is inserted into a mounting hole (not shown) in the shank. A plurality of through holes (for example, a pair) are provided in the body 1 at intervals in the circumferential direction. A screw member is inserted into each through hole and screwed into the female threaded hole in the shank. In this way, the body 1 is detachably fixed to the shank.

[0078] Although not specifically shown, the rotation support portion is formed by a surface provided on a part of the body 1 and facing in the direction opposite to the drill rotation direction. The rotation support portion comes into contact with a rotation receiving portion of the shank facing the drill rotation direction T. Multiple pairs of rotation support portions and rotation receiving portions are provided at intervals in the circumferential direction. This allows the body 1 to stably receive the rotational force in the drill rotation direction T transmitted from the spindle or the like via the shank.

[0079] [Honing] The thinning edge 70, main cutting edge 71, leading edge 12, shoulder 9, first boundary ridge 54, and second boundary ridge 55 arranged on each ridge of the body 1 each have a honing H in which the cross section perpendicular to each ridge is a convex curve, as shown schematically in Figures 5A, 5B, and 5C. The honing H is a so-called round honing. The honing H extends along each ridge.

[0080] 5A, 5B, and 5C , in a cross section perpendicular to the ridgeline portion (a cross section perpendicular to the direction in which the honing H extends), of both end portions h1 and h2 of the honing H, the face connected to the first end portion h1 is referred to as the first surface 101, and the face connected to the second end portion h2 is referred to as the second surface 102. The first end portion h1 is the portion where the honing H and the first surface 101 are connected. The second end portion h2 is the portion where the honing H and the second surface 102 are connected. The first surface 101 is, for example, the rake face 5, and the second surface 102 is, for example, the flank face 6. Details of the first surface 101 and the second surface 102 connected to the honing H of each ridgeline portion will be described separately below.

[0081] 5A, 5B, and 5C, the first surface 101 may be connected so as to coincide with a tangent to the honing H passing over the first end h1, i.e., so as to be tangent to the first end h1, or may extend in a direction different from the tangent to the first end h1 and be smoothly connected to the first end h1. Also, in each of the cross sections, the second surface 102 may be connected so as to coincide with a tangent to the honing H passing over the second end h2, i.e., so as to be tangent to the second end h2, or may extend in a direction different from the tangent to the second end h2 and be smoothly connected to the second end h2.

[0082] The symbol R in Figure 5A indicates the radius of curvature of the honing H. First, the drill 10 of this embodiment has a special technical feature with respect to the honing radius of curvature R. In this embodiment, the "honing radius of curvature R" is closely related to the honing width. The honing width refers to the dimension equivalent to the distance between both ends h1 and h2 of the honing H (the linear distance between the first end h1 and the second end h2) in a cross section perpendicular to the direction in which the honing H extends (the ridge line portion).

[0083] That is, when the honing radius of curvature R is large, the honing width tends to increase accordingly, and when the honing radius of curvature R is small, the honing width tends to decrease accordingly. In other words, when the honing width is small, the honing radius of curvature R also becomes small, and when the honing width is large, the honing radius of curvature R also becomes large. For this reason, the magnitude relationship between the honing radii of curvature R described below in this embodiment can also be expressed as the magnitude relationship between the honing widths. In other words, the magnitude relationship between the honing radii of curvature R corresponds to the magnitude relationship between the honing widths.

[0084] The honing radius of curvature R of the leading edge 12 at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end is 25 μm or more and 80 μm or less. The honing radius of curvature R of the leading edge 12 is more preferably, for example, 40 μm or more and 70 μm or less.

[0085] In addition, the honing radius of curvature R of the leading edge 12 at a position within 1.5 mm from the outer corner 15 toward the rear end is smaller than the honing radius of curvature R of the radial outer end portion of the main cutting edge 71 connected to the outer corner 15 (in this embodiment, the second cutting edge 73).

[0086] Here, the honing H of the leading edge 12 extends beyond a position 1.5 mm from the outer peripheral corner 15 toward the rear end of the leading edge 12. Specifically, the honing radius of curvature R (honing width) of the leading edge 12 is constant within a predetermined range that includes a position within 1.5 mm from the outer peripheral corner 15 toward the rear end of the leading edge 12, and beyond this predetermined range toward the rear end, the radius remains constant or gradually decreases toward the rear end.

[0087] More specifically, the honing radius of curvature R (honing width) of the leading edge 12 at a position within 3 mm of but exceeding 1.5 mm from the outer peripheral corner 15 toward the rear end is approximately the same as or slightly smaller than the honing radius of curvature R at the position within 1.5 mm. The honing radius of curvature R of the leading edge 12 at a position within 3 mm of but exceeding 1.5 mm from the outer peripheral corner 15 toward the rear end is, for example, 30 μm or more and 70 μm or less.

[0088] In this embodiment, the honing radius of curvature of the portion of the main cutting edge 71 located radially inward from the radially outer end (first cutting edge 72 in this embodiment) is defined as R1, and the honing radius of curvature of the radially outer end of the main cutting edge 71 (second cutting edge 73 in this embodiment) is defined as R2, satisfying the relationship [0.9≦R1 / R2≦1.5]. Preferably, [R1 / R2] is 1.0 or greater. It is more desirable that the honing radius of curvature R1 of the first cutting edge 72 be greater than the honing radius of curvature R2 of the second cutting edge 73.

[0089] The honing radius of curvature R1 of the first cutting edge 72 changes along the cutting edge length direction of the first cutting edge 72. For example, the honing radius of curvature R1 of the first cutting edge 72 gradually increases from both ends toward the center in the cutting edge length direction of the first cutting edge 72. The honing radius of curvature R1 of the first cutting edge 72 is greatest at the lowest point of the first cutting edge 72, which is located in the direction opposite the drill rotation direction T (counter to the drill rotation direction).

[0090] The honing radius of curvature R1 of the portion of the main cutting edge 71 located radially inward from the radially outer end (first cutting edge 72 in this embodiment) is, for example, 60 μm to 100 μm. The honing radius of curvature R2 of the radially outer end of the main cutting edge 71 connected to the outer peripheral corner 15 (second cutting edge 73 in this embodiment) is, for example, 50 μm to 80 μm.

[0091] Furthermore, with the diameter dimension of the rotational trajectory of the cutting edge 7 about the central axis O being defined as the drill edge diameter, in this embodiment, the honing radius of curvature R of the thinning edge 70 in a region within 7% of the drill edge diameter radially outward from the central axis O is smaller than the honing radius of curvature R1 of the portion of the main cutting edge 71 (first cutting edge 72 in this embodiment) that is positioned radially inward relative to the radially outer end. Specifically, the honing radius of curvature R of the thinning edge 70 in a region within 7% of the drill edge diameter radially outward from the central axis O is, for example, 40 μm or more and 80 μm or less.

[0092] The honing radius of curvature R of the shoulder 9 is smaller than the honing radius of curvature R2 of the radially outer end (second cutting edge 73 in this embodiment) of the main cutting edge 71 that is connected to the outer peripheral corner 15. Specifically, the honing radius of curvature R of the shoulder 9 is, for example, 40 μm or more and 70 μm or less.

[0093] Secondly, the drill 10 of this embodiment has a special technical feature regarding the width ratio of the honing H. In each cross section shown in Figures 5A, 5B, and 5C, the distance from an intersection P of an extension line of the first surface 101 and an extension line of the second surface 102 to a first end h1 is defined as a first width dimension L1, the distance from the intersection P to a second end h2 is defined as a second width dimension L2, and [L1 / L2] is defined as the width ratio. Note that in this embodiment, the width ratio [L1 / L2] may also be simply referred to as the width ratio.

[0094] Fig. 5A shows a case where the width ratio [L1 / L2] of the honing H is 1.0. Fig. 5B shows a case where the width ratio [L1 / L2] of the honing H is greater than 1.0. Fig. 5C shows a case where the width ratio [L1 / L2] of the honing H is smaller than 1.0.

[0095] The thinning edge 70 and the main cutting edge 71 have a first surface 101 that is the rake face 5 and a second surface 102 that is the flank 6. Specifically, the thinning edge 70 has a first surface 101 that is the thinning rake face 50 and a second surface 102 that is the first flank 61. The main cutting edge 71 has a first surface 101 that is the main rake face 51 and a second surface 102 that is the first flank 61. More specifically, the first surface 101 of the first cutting edge 72 of the main cutting edge 71 is the first rake face 52 and the second surface 102 is the first flank 61. The first surface 101 of the second cutting edge 73 of the main cutting edge 71 is the second rake face 53 and the second surface 102 is the first flank 61.

[0096] The width ratio [L1 / L2] of the thinning edge 70 is greater than the width ratio [L1 / L2] of the radially outer end (the second cutting edge 73 in this embodiment) of the main cutting edge 71 that is connected to the outer peripheral corner 15, and is preferably 1.1 times or more the width ratio [L1 / L2] of the radially outer end, and may be, for example, 1.4 times. Furthermore, the width ratio of the thinning edge 70 increases as it approaches the central axis O along the cutting length direction in which the thinning edge 70 extends. The width ratio [L1 / L2] of the thinning edge 70 is preferably 1.0 or more. The width ratio [L1 / L2] of the thinning edge 70 may be, for example, 1.0 or more and 1.4 or less.

[0097] The width ratio [L1 / L2] of the portion of the main cutting edge 71 that is located radially inward of the radial outer end is greater than the width ratio [L1 / L2] of the radial outer end of the main cutting edge 71, and is preferably 1.1 times or more the width ratio [L1 / L2] of the radial outer end, and may be, for example, 1.3 times. That is, in this embodiment, the width ratio [L1 / L2] of the first cutting edge 72 is greater than the width ratio [L1 / L2] of the second cutting edge 73.

[0098] Furthermore, the width ratio of the first cutting edge 72 varies along the cutting edge length direction of the first cutting edge 72. For example, the width ratio of the first cutting edge 72 gradually increases from both ends of the first cutting edge 72 toward the center in the cutting edge length direction. The width ratio of the first cutting edge 72 is greatest at the lowest point of the first cutting edge 72, which is located in the direction opposite to the drill rotation direction T (counter to the drill rotation direction). The width ratio [L1 / L2] of the first cutting edge 72 is preferably 1.0 or greater. The width ratio [L1 / L2] of the first cutting edge 72 may be, for example, 1.0 or greater and 11.3 or less.

[0099] The width ratio of the second cutting edge 73 is set to be the smallest among the components of the cutting edge 7. More specifically, the width ratio of the outermost end of the main cutting edge 71 located at the outer peripheral corner 15 (the radially outermost end of the second cutting edge 73) is the smallest among the width ratios of the cutting edges 7. The width ratio [L1 / L2] of the second cutting edge 73 is preferably 1.0 or less. The width ratio [L1 / L2] of the second cutting edge 73 may be, for example, 0.8 or more and 1 or less.

[0100] The leading edge 12 has a first surface 101 that is the rake face 5 and a second surface 102 that is the margin 13. Specifically, the leading edge 12 has a first surface 101 that is the second rake face 53 and a second surface 102 that is the margin 13. The width ratio [L1 / L2] of the leading edge 12 at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end is, for example, 0.7 or more and 1.3 or less.

[0101] The shoulder 9 has a first surface 101 which is the flank 6 and a second surface 102 which is the margin 13. Specifically, the shoulder 9 has a first surface 101 which is the first flank 61 and a second surface 102 which is the margin 13. The width ratio [L1 / L2] of the shoulder 9 is, for example, not less than 0.7 and not more than 1.3.

[0102] [Effects of the Present Embodiment] In the drill 10 of the present embodiment described above, the honings H of the thinning edge 70, the main cutting edge 71, and the leading edge 12 each have a convex curve (convex R-shape) in a cross section perpendicular to each ridge, which is a so-called round honing. This reduces wear and welding within the honing surface when drilling large workpieces or under low- to medium-efficiency machining conditions. Specifically, unlike the present embodiment, if the honings H of the components of the cutting edge 7 (particularly the main cutting edge 71, etc.) were chamfer honings with flat surfaces, destructive wear would be accelerated within the honing surface, potentially leading to early welding and chipping when drilling large workpieces or under low- to medium-efficiency machining conditions.

[0103] Furthermore, a portion of the leading edge 12 within 1.5 mm from the outer corner 15 toward the rear end is located at the tip of the leading edge 12, and is a portion susceptible to cutting resistance from the inner peripheral surface of the drilled hole in the workpiece. In the drill 10 of this embodiment, the honing radius of curvature R at this position of the leading edge 12 is set to be 25 μm or more and 80 μm or less. This allows for stable suppression of wear progression.

[0104] Specifically, unlike this embodiment, if the honing radius of curvature R of the leading edge 12 is so large as to exceed 80 μm, the area in the honing H where the radial rake forms a strong negative angle will increase (resulting in a strongly negative honing H), which may significantly increase cutting resistance and lead to early wear. On the other hand, even if the honing radius of curvature R of the leading edge 12 is so small as to be less than 25 μm, wear will still be likely to progress. Furthermore, if the ridgeline portion has a sharp cross-sectional shape (a shape similar to a so-called pin-edge), the function obtained by the honing H will be reduced, and chipping and the like will be more likely to occur.

[0105] Furthermore, in this embodiment, the honing radius of curvature R of the leading edge 12 is smaller than the honing radius of curvature R (R2) of the radially outer end (second cutting edge 73) of the main cutting edge 71 that is located adjacent to the outer peripheral corner 15. In other words, the honing radius of curvature R (R2) of the radially outer end (second cutting edge 73) of the main cutting edge 71 is larger than the honing radius of curvature R of the leading edge 12. This configuration makes it possible to stably suppress the progression of wear near the leading edge 12 while suppressing chipping and the like at the radially outer end, where the peripheral speed of the main cutting edge 71 is the fastest.

[0106] As described above, the drill 10 of this embodiment can improve wear resistance and thereby extend the tool life. This embodiment is particularly effective when applied to low- to medium-efficiency drilling conditions or drilling large workpieces.

[0107] In this embodiment, the main cutting edge 71 has a first cutting edge 72 that is disposed radially outward of the thinning edge 70 and has a concave curved shape that is recessed in the opposite direction to the drill rotation direction T around the central axis O, and a second cutting edge 73 that is disposed radially outward of the first cutting edge 72 and connected to the radial outer end of the first cutting edge 72, and the second cutting edge 73 forms the radial outer end of the main cutting edge 71 that is connected to the outer corner 15. According to the above configuration, the excellent effects of this embodiment can be obtained when the main cutting edge 71 has a so-called curved cutting edge shape with a concave cutting edge shape (first cutting edge 72).

[0108] Furthermore, in this embodiment, when the honing radius of curvature of the portion of the main cutting edge 71 located radially inward from the radial outer end (first cutting edge 72) is defined as R1 and the honing radius of curvature of the radial outer end (second cutting edge 73) of the main cutting edge 71 is defined as R2, the relationship [0.9≦R1 / R2≦1.5] is satisfied.

[0109] Of the main cutting edges 71, the portion (first cutting edge 72) located radially inward of the radial outer end (second cutting edge 73) connected to the outer peripheral corner 15 tends to be more susceptible to crater wear due to scraping by chips, compared to this radial outer end. Because crater wear is likely to occur near the boundary between the honing surface and the rake face 5, crater wear can be effectively suppressed by increasing the honing size (honing radius of curvature R).

[0110] From the above viewpoint, it is preferable to set the ratio value [R1 / R2] of the honing curvature radii to 1.0 or more, as this ensures a stable and large honing curvature radius R1 for the portion of the main cutting edge 71 that is located radially inward of the radially outer end portion. However, if the ratio value [R1 / R2] is close to 1.0, the ratio value [R1 / R2] may be less than 1.0 due to manufacturing errors, etc., so in this embodiment, the ratio value [R1 / R2] is set to [0.9≦R1 / R2].

[0111] However, in this embodiment, the honing radius of curvature R2 is set larger than the honing radius of curvature R of the leading edge 12, so if the ratio [R1 / R2] is 0.9 or greater, the honing radius of curvature R1 is also sufficiently large. As a result, the effect of suppressing crater wear can be stably obtained.

[0112] If the ratio [R1 / R2] is less than 0.9 or exceeds 1.5, the difference between the honing curvature radii R1 and R2 becomes larger, which tends to accelerate wear on the smaller honing size. Therefore, it is preferable that the ratio is in the above range of [0.9≦R1 / R2≦1.5].

[0113] In addition, in this embodiment, the shoulder portion 9 has a honing H whose cross section perpendicular to the ridge line is a convex curve, and the honing radius of curvature R of the shoulder portion 9 is smaller than the honing radius of curvature R2 of the radial outer end portion (second cutting edge 73) of the main cutting edge 71 that is connected to the outer peripheral corner 15.

[0114] In the above configuration, the honing radius of curvature R of the shoulder 9 is smaller than the honing radius of curvature R2 of the radially outer end (second cutting edge 73) of the main cutting edge 71 that is located adjacent to the outer peripheral corner 15. In other words, the honing radius of curvature R2 of the radially outer end of the main cutting edge 71 is larger than the honing radius of curvature R of the shoulder 9. With this configuration, particularly under low- to medium-efficiency machining conditions or when drilling large workpieces, it is possible to stably suppress the progression of wear near the shoulder 9 while suppressing chipping and the like at the radially outer end, where the peripheral speed of the main cutting edge 71 is the fastest.

[0115] Furthermore, in this embodiment, the thinning edge 70 has a honing H in which the cross section perpendicular to the ridgeline is convexly curved, and the honing radius of curvature R of the thinning edge 70 within 7% of the drill edge diameter extending radially outward from the central axis O is smaller than the honing radius of curvature R1 of the portion of the main cutting edge 71 (first cutting edge 72) located radially inward from the radially outer end. In this case, the sharpness of the thinning edge 70, which is the first to bite into the workpiece during drilling, is stably improved, particularly in the vicinity of the central axis O. This enables more accurate drilling.

[0116] Furthermore, in this embodiment, the honing radius of curvature R1 of the first cutting edge 72 is greatest at the lowest point of the first cutting edge 72 that is located furthest in the opposite direction to the drill rotation direction T. In conventional drills, the lowest point of the concave curved concave cutting edge shape (the first cutting edge 72 in this embodiment) that is located furthest in the opposite direction to the drill rotation direction tends to be subject to strong stress due to chip abrasion, resulting in significant crater wear damage. Because crater wear is likely to occur near the boundary between the honing surface and the rake face 5, crater wear can be effectively suppressed by maximizing the honing size (honing radius of curvature R) at the lowest point of the first cutting edge 72, as in this embodiment.

[0117] In this embodiment, the first boundary ridge 54 extends along the boundary between the thinning rake face 50 and the main rake face 51 and is convex in the drill rotation direction T. This prevents the first boundary ridge 54 protruding in the drill rotation direction T from being chipped due to scraping by chips or the like.

[0118] In this embodiment, the second boundary ridge 55 extends along the boundary between the first rake face 52 and the second rake face 53 and is convex in the drill rotation direction T. This configuration prevents the second boundary ridge 55, which protrudes in the drill rotation direction T, from being chipped due to scraping by chips or the like.

[0119] In this embodiment, the honing H of the leading edge 12 extends beyond the position 1.5 mm from the outer peripheral corner 15 toward the rear end of the leading edge 12, and extends further toward the rear end. In this case, the progression of wear and chipping of the leading edge 12 can be stably suppressed over a wider area along the ridge line.

[0120] Furthermore, in the drill 10 of this embodiment, when the width ratio [L1 / L2] is defined in a cross section perpendicular to the direction in which each honing H extends, the width ratio of the honing H of the thinning edge 70 is larger than the width ratio of the honing H of the radially outer end (second cutting edge 73) of the main cutting edge 71 that is connected to the outer peripheral corner 15. In other words, the width ratio of the honing H of the radially outer end of the main cutting edge 71 is smaller than the width ratio of the honing H of the thinning edge 70.

[0121] Specifically, when comparing the width ratios of each honing H, the thinning edge 70 has a larger ratio of the first width dimension L1 on the rake face 5 side, and the radial outer end (second cutting edge 73) of the main cutting edge 71 has a larger ratio of the second width dimension L2 on the relief face 6 side.

[0122] During drilling, the thinning edge tends to be subject to significant damage due to crater wear caused by compressed chips scraping against it. Crater wear is likely to occur near the boundary between the honing surface and the rake face 5. Therefore, by increasing the width ratio of the thinning edge 70 (increasing the proportion of the first width dimension L1 on the rake face 5 side), as in this embodiment, crater wear can be stably suppressed.

[0123] Furthermore, the radial outer end of the main cutting edge tends to be significantly more susceptible to wear on the flank 6 side. Therefore, as in this embodiment, by reducing the width ratio of the radial outer end of the main cutting edge 71 (increasing the ratio of the second width dimension L2 on the flank 6 side), flank wear can be stably suppressed.

[0124] As described above, the drill 10 of this embodiment can improve wear resistance and thereby extend the tool life. This embodiment is particularly effective when applied to low- to medium-efficiency drilling conditions or drilling large workpieces.

[0125] In this embodiment, the width ratio [L1 / L2] of the leading edge 12 at a position within 1.5 mm from the outer circumferential corner 15 toward the rear end is 0.7 or more and 1.3 or less.

[0126] The leading edge tends to be more susceptible to wear damage due to wear on the margin side. In particular, the position of the leading edge within 1.5 mm from the outer corner toward the rear end is located at the tip of the leading edge, and is considered to be a location that is more susceptible to cutting resistance from the inner surface of the machined hole in the workpiece.

[0127] As a result of intensive research by the inventors, it was confirmed that, with respect to the width ratio of the honing H of the leading edge 12, if the ratio of the second width dimension L2 on the margin 13 side is too large, cutting resistance increases significantly and wear progresses early. Furthermore, if the ratio of the first width dimension L1 on the rake face 5 side is small, wear progresses on the rake face 5 side. For the above reasons, the width ratio of the leading edge 12 is preferably 0.7 or more and 1.3 or less, and the closer to 1.0 the better.

[0128] In addition, in this embodiment, the width ratio [L1 / L2] of the portion of the main cutting edge 71 that is located radially inward from the radial outer end (first cutting edge 72) is larger than the width ratio [L1 / L2] of the radial outer end (second cutting edge 73) of the main cutting edge 71.

[0129] Of the main cutting edge 71, compared to the radially outer end (second cutting edge 73) connected to the outer peripheral corner 15, the portion (first cutting edge 72) located radially inward of this radially outer end tends to be more susceptible to crater wear due to abrasion by chips. Because crater wear is likely to occur near the boundary between the honing surface and the rake face 5, crater wear can be effectively suppressed by increasing the width ratio of the honing H in the portion of the main cutting edge 71 located radially inward of the radially outer end (increasing the proportion of the first width dimension L1 on the rake face 5 side).

[0130] Furthermore, wear tends to progress easily on the flank 6 side of the radial outer end (second cutting edge 73) of the main cutting edge 71. Therefore, by reducing the width ratio of the honing H at the radial outer end of the main cutting edge 71 (increasing the proportion of the second width dimension L2 on the flank 6 side) as in the above configuration, flank wear can be effectively suppressed.

[0131] In this embodiment, the width ratio [L1 / L2] of the thinning edge 70 increases as the thinning edge 70 approaches the center axis O along the cutting length direction in which the thinning edge 70 extends.

[0132] Thinning edges are susceptible to damage caused by crater wear due to the abrasion of compressed chips. Crater wear tends to become more pronounced as the edge approaches the center axis along the cutting length of the thinning edge.

[0133] Therefore, as in this embodiment, by increasing the width ratio of the honing H of the thinning blade 70 as it approaches the central axis O, it is possible to effectively suppress crater wear over the entire blade length, including the vicinity of the central axis O of the thinning blade 70.

[0134] Furthermore, in this embodiment, the width ratio [L1 / L2] of the outermost end of the main cutting edge 71, which is located at the outer peripheral corner 15, is the smallest among the width ratios [L1 / L2] of the cutting edge 7. At the outermost end (outer peripheral corner) of the main cutting edge, wear on the flank side tends to progress significantly. Therefore, as in this embodiment, by making the width ratio of the honing H at the outermost end (outer peripheral corner 15) of the main cutting edge 71 the smallest among the entire cutting edge 7 (main cutting edge 71 and thinning edge 70), flank wear can be effectively suppressed.

[0135] Furthermore, in this embodiment, the width ratio [L1 / L2] of the first cutting edge 72 is greatest at the lowest point of the first cutting edge 72 located furthest in the opposite direction to the drill rotation direction T. In conventional drills, the lowest point of the concave curved concave cutting edge shape (the first cutting edge 72 in this embodiment) located furthest in the opposite direction to the drill rotation direction is subject to strong stress due to chip abrasion, which tends to cause significant crater wear damage. Since crater wear is likely to occur near the boundary between the honing surface and the rake face 5, crater wear can be effectively suppressed by maximizing the width ratio of the honing H at the lowest point of the first cutting edge 72 (maximizing the proportion of the first width dimension L1 on the rake face 5 side), as in this embodiment.

[0136] In this embodiment, the width ratio [L1 / L2] of the shoulder portion 9 is 0.7 or more and 1.3 or less. When the width ratio of the honing H of the shoulder portion 9 is 0.7 or more and 1.3 or less as in the above configuration, problems such as early progress of wear on either the flank 6 or the margin 13 arranged on both sides of the shoulder portion 9, affecting the tool life, are stably suppressed. The width ratio of the shoulder portion 9 is more preferably closer to 1.0.

[0137] In this embodiment, the width ratio [L1 / L2] of the thinning edge 70 is 1.0 or greater. In this case, the width ratio of the honing H of the thinning edge 70 can be stably increased (the proportion of the first width dimension L1 on the rake face 5 side can be increased), and the effect of suppressing crater wear can be more significantly achieved.

[0138] In this embodiment, the width ratio [L1 / L2] of the first cutting edge 72 is 1.0 or greater. In this case, the width ratio of the honing H of the first cutting edge 72 can be stably increased (the proportion of the first width dimension L1 on the rake face 5 side can be increased), and the effect of suppressing crater wear can be more significantly achieved.

[0139] In this embodiment, the width ratio [L1 / L2] of the second cutting edge 73 is 1.0 or less. In this case, the width ratio of the honing H of the second cutting edge 73 can be stably reduced (the proportion of the second width dimension L2 on the flank 6 side can be increased), and the effect of suppressing flank wear can be more significantly obtained.

[0140] [Other Configurations Included in the Present Invention] The present invention is not limited to the above-described embodiment, and the configuration can be changed within the scope of the present invention, as described below, for example.

[0141] In the above-described embodiment, the main cutting edge 71 of the cutting edge 7 has a so-called curved cutting edge shape having a concave cutting edge shape (first cutting edge 72) and a convex portion (apex 74). However, this is not limited to this. Although not specifically illustrated, the main cutting edge 71 may have a straight cutting edge. In this case, a region of the main cutting edge 71 extending radially inward from the outer peripheral corner 15 and within 7% of the drill bit diameter is defined as the "radially outer end portion of the main cutting edge 71 connected to the outer peripheral corner 15" (corresponding to the second cutting edge 73 in the above-described embodiment). According to the above-described configuration, when the main cutting edge 71 has a so-called straight cutting edge shape, excellent effects similar to those of the above-described embodiment can be obtained.

[0142] In the above-described embodiment, the first cutting edge 72 and the second cutting edge 73 are connected to each other via the apex 74 that is pointed toward the drill rotation direction T, but this is not limiting. The first cutting edge 72 and the second cutting edge 73 may be connected to each other so as to be in smooth contact with each other (so as to be continuously curved) without the apex 74 being pointed.

[0143] In the above-described embodiment, the drill 10 is an indexable drill or a drill head, but the present invention is not limited to this. The drill of the present invention may be a solid drill in which the body 1 and the shank are integrally formed from a single member. Alternatively, for example, the body 1 and the shank may be manufactured separately and integrated by brazing or the like.

[0144] In the above embodiment, the drill 10 is a two-flute twist drill, but the present invention is not limited to this. The present invention may be applied to a drill with one flute or three or more flutes.

[0145] The present invention may be combined with the various configurations described in the above-described embodiments and modifications, and may also include additions, omissions, substitutions, and other modifications of the configurations, without departing from the spirit of the present invention. Furthermore, the present invention is not limited to the above-described embodiments, but is limited only by the claims.

[0146] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0147] <Wear Confirmation Test 1> In wear confirmation test 1, a confirmation test was carried out by drilling to check the relationship between the honing curvature radius R of each ridge line portion of the body 1 and the wear resistance.

[0148] The drill 10 of the above-described embodiment was prepared as Example 1 of the present invention. Specifically, the drill 10 of Example 1 had a honing radius of curvature R of 54 μm at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end of the leading edge 12. The honing radius of curvature R2 of the second cutting edge 73 was 63 μm, and the honing radius of curvature R1 of the first cutting edge 72 was 75 μm.

[0149] Additionally, conventional comparative examples 1 and 2 were prepared, each of which has a technical concept partially different from that of the drill 10 described in the above embodiment. Specifically, the drill of comparative example 1 has a honing radius of curvature R of 64 μm at a position on the leading edge 12 within 1.5 mm from the outer peripheral corner 15 toward the rear end. The honing radius of curvature R2 of the second cutting edge 73 is 50 μm, and the honing radius of curvature R1 of the first cutting edge 72 is 63 μm. Therefore, the honing radius of curvature R of the drill of comparative example 1 at a position on the leading edge 12 within 1.5 mm from the outer peripheral corner 15 toward the rear end is larger than the honing radius of curvature R2 of the second cutting edge 73.

[0150] Furthermore, the drill of Comparative Example 2 has a honing radius of curvature R of 17 μm at a position on the leading edge 12 within 1.5 mm from the outer peripheral corner 15 toward the rear end. The honing radius of curvature R2 of the second cutting edge 73 is 41 μm, and the honing radius of curvature R1 of the first cutting edge 72 is 58 μm. Therefore, the honing radius of curvature R of the drill of Comparative Example 2 at a position on the leading edge 12 within 1.5 mm from the outer peripheral corner 15 toward the rear end is outside the range of 25 μm to 80 μm.

[0151] For each of the drills of Example 1 and Comparative Examples 1 and 2, the same number of drilling operations were carried out under the following cutting conditions, and observations were carried out by taking images of the vicinity of each honing H. The drilling operations were carried out until wear was observed in at least one drill. The results are shown in Figure 6 as enlarged images of the vicinity of each cutting edge. Figure 6 also shows a schematic cross-sectional view of the vicinity of each cutting edge. <Cutting conditions> Drill cutting diameter: φ24.0 mm Workpiece material: S50C Peripheral speed: vc = 100 m / min Feed: fr = 0.35 mm / rev

[0152] As shown in FIG. 6 , in Comparative Examples 1 and 2, when drilling was performed with a cutting length (machining length) of approximately 29 m, progress of wear was confirmed near the leading edge 12 and the first cutting edge 72. On the other hand, in Example 1, in which the same number of holes as Comparative Examples 1 and 2 were drilled, progress of wear was not confirmed in any of the areas near the leading edge 12, the second cutting edge 73, and the first cutting edge 72. The progress of wear in Comparative Examples 1 and 2 can be confirmed by comparing the magnitude of damage after drilling the same number of holes as Example 1. Note that in Example 1, progress of wear was not confirmed even when the cutting length reached approximately 55 m. Furthermore, machining was possible even when the cutting length exceeded approximately 150 m.

[0153] Although not specifically shown, the inventors of the present invention conducted further intensive research into the relationship between the honing radius of curvature R of each ridgeline of the body 1 and wear resistance, resulting in the following findings: In many conventional drills, primarily solid drills, the honing radius of curvature R at a position within 1.5 mm of the outer peripheral corner 15 of the leading edge 12 toward the rear end is approximately 10 to 20 μm. As a result of research into improving damage to the margin 13 of the drill 10, the inventors of the present invention found that superiority over conventional drills can be achieved by increasing the honing radius of curvature R at this position within 1.5 mm to approximately 25 to 30 μm. Based on this finding, the lower limit of the numerical range of the honing radius of curvature R at this position within 1.5 mm is 25 μm or greater.

[0154] Furthermore, it was found that if the honing radius of curvature R within the 1.5 mm range is too large, the coating peels off early and wear is accelerated. This is thought to be due to increased cutting resistance. Because cutting resistance depends on various conditions such as the tool diameter and cutting conditions, the appropriate honing size (honing radius of curvature R) within the 1.5 mm range varies depending on the various conditions. However, assuming various combinations for a practical drill 10, the upper limit of the numerical range for the honing radius of curvature R within the 1.5 mm range is 80 μm or less.

[0155] Specifically, a drill with a honing radius of curvature R of 90 μm within the 1.5 mm range was prepared as a comparative example. Drilling was performed under the following cutting conditions: drill bit diameter: φ18 mm, workpiece material: S50C, peripheral speed: vc = 100 m / min, feed: fr = 0.3 mm / rev. The tool life of the comparative drill was approximately 60 m. Meanwhile, a drill 10 with a honing radius of curvature R of 60 μm within the 1.5 mm range was prepared as an example of the present invention. When drilling was performed under the same cutting conditions, the tool life of the drill 10 of this example reached approximately 170 m. The body 1 of each drill in the comparative example and the example was coated with the same coating.

[0156] Furthermore, two drills were prepared, each having a different coating formed on the body 1. One drill had a honing radius of curvature R of 90 μm within the 1.5 mm range, and the other drill had a honing radius of curvature R of 150 μm within the 1.5 mm range. In other words, these two drills are comparative examples. When drilling was performed using the two drills, the tool life of one drill (honing radius of curvature R: 90 μm) was approximately 80 m in machining length. The tool life of the other drill (honing radius of curvature R: 150 μm) was approximately 50 m in machining length. Thus, as the honing radius of curvature R within the 1.5 mm range increases beyond 80 μm, cutting resistance tends to increase and tool life tends to shorten.

[0157] <Wear Confirmation Test 2> In wear confirmation test 2, a confirmation test was conducted by drilling to examine the relationship between the width ratio [L1 / L2] of the honing H of each ridge line portion of the body 1 and the wear resistance.

[0158] The drill 10 of the above-described embodiment was prepared as Example 2 of the present invention. Specifically, the drill 10 of Example 2 had a width ratio [L1 / L2] of 0.91 at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end of the leading edge 12.

[0159] Furthermore, a drill having a technical concept partially different from that of the drill 10 described in the above embodiment was prepared as a conventional comparative example 3. Specifically, the drill of comparative example 3 has a width ratio [L1 / L2] of 0.64 at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end of the leading edge 12.

[0160] For each drill of Example 2 and Comparative Example 3, the same number of drilling operations were performed under the same cutting conditions as in the above-mentioned Wear Confirmation Test 1, and observations were made by taking images of the vicinity of the honing H. The drilling operations were repeated until wear was observed in at least one drill. The results are shown in Figure 7 as enlarged images of the vicinity of each cutting edge. Figure 7 also shows a schematic cross-sectional view of the vicinity of each cutting edge.

[0161] As shown in FIG. 7, in Comparative Example 3, when drilling was performed with a cutting length (processing length) of 29 m, progress of wear was confirmed near the leading edge 12. On the other hand, in Example 2, in which the same number of holes as in Comparative Example 3 were drilled, progress of wear was not confirmed near the leading edge 12. The progress of wear in Comparative Examples 1 to 3 can be confirmed by comparing the magnitude of damage when the same number of holes as in Example 2 were drilled. Note that in Example 2, progress of wear was not confirmed even when the cutting length reached approximately 55 m. Furthermore, even when the cutting length exceeded approximately 150 m, processing was still possible.

[0162] Furthermore, although not specifically shown, the inventors of the present invention conducted further intensive research into the relationship between the width ratio [L1 / L2] of the honing H of each ridge line portion of the body 1 and wear resistance, and as a result, the following findings were obtained: In the above-mentioned comparative example 3, an example was given in which the width ratio [L1 / L2] at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end of the leading edge 12 was below (smaller than) the range of 0.7 to 1.3, but it was also found that wear was more likely to progress in other examples in which the width ratio [L1 / L2] was above (larger than) the above range.

[0163] This is thought to be because if the honing shape is biased toward either the width dimension L1 or L2 to the extent that the width ratio [L1 / L2] falls outside the above numerical range, damage will be accelerated due to a decrease in strength or an increase in cutting resistance caused by an insufficient width dimension L1 or L2. Based on this consideration, the width ratio [L1 / L2] at a position within 1.5 mm mentioned above is set to be within the above numerical range, with the ideal value being 1.0.

[0164] The drill of the present invention can improve wear resistance, thereby extending the tool life, and therefore has industrial applicability.

[0165] DESCRIPTION OF SYMBOLS 1...Body 3...Tip surface 4...Chip discharge groove 5...Rake face 6...Flank face 7...Cutting edge 8...Peripheral surface 9...Shoulder 10...Drill 12...Leading edge 13...Margin 15...Peripheral corner 70...Thinning edge 71...Main cutting edge 72...First cutting edge 73...Second cutting edge 74...Top 101...First surface 102...Second surface H...Honing h1...First end h2...Second end L1...First width dimension L2...Second width dimension L1 / L2...Width ratio O...Central axis P...Intersection T...Drill rotation direction

Claims

1. A drill having a body extending in the axial direction about a central axis, the body having: a chip discharge groove opening on a leading surface and an outer peripheral surface of the body and extending from the leading surface to a rear end thereof; a rake face disposed in the chip discharge groove and facing in the direction of drill rotation about the central axis; a relief surface disposed on the leading surface; a cutting edge disposed on a ridge line connecting the rake face and the relief surface; a margin disposed on the outer peripheral surface and extending along the chip discharge groove; a leading edge disposed on a ridge line connecting the margin and the rake face; and an outer peripheral corner disposed at a corner where the cutting edge and the leading edge are connected; the cutting edge having: a thinning blade disposed at a radially inner end of the cutting edge; and a main cutting edge disposed radially outward of the thinning blade and connected to the leading edge via the outer peripheral corner; a drill in which the thinning edge, the main cutting edge and the leading edge have a honing whose cross section perpendicular to each of the ridge lines is a convex curve, and in the cross section, of both ends of the honing, a face connected to a first end is defined as a first face, and a face connected to a second end is defined as a second face, a distance from an intersection point between an extension line of the first face and an extension line of the second face to the first end is defined as a first width dimension L1, and a distance from the intersection point to the second end is defined as a second width dimension L2, and [L1 / L2] is defined as a width ratio, and the first face of the thinning edge and the main cutting edge are the rake face and the second face are the relief face, and the width ratio of the thinning edge is greater than the width ratio of a radially outer end of the main cutting edge connected to the outer peripheral corner.

2. The drill as described in claim 1, wherein the main cutting edge has a first cutting edge arranged radially outward of the thinning edge and forming a concave curve recessed in the opposite direction to the rotation direction of the drill around the central axis, and a second cutting edge arranged radially outward of the first cutting edge and connected to the radial outer end of the first cutting edge, and the second cutting edge constitutes the radial outer end of the main cutting edge that is connected to the outer peripheral corner.

3. The drill as described in claim 1, wherein the main cutting edge is straight, the diameter of the rotational trajectory of the cutting edge around the central axis is defined as the drill edge diameter, and a region of the main cutting edge within 7% of the drill edge diameter extending radially inward from the outer peripheral corner is defined as the radially outer end of the main cutting edge connected to the outer peripheral corner.

4. A drill according to any one of claims 1 to 3, wherein the first surface of the leading edge is the cutting face and the second surface is the margin, and the width ratio of the leading edge at a position within 1.5 mm from the outer peripheral corner toward the rear end is 0.7 or more and 1.3 or less.

5. A drill as claimed in any one of claims 1 to 3, wherein the width ratio of a portion of the main cutting edge located radially inward from the radial outer end is greater than the width ratio of the radial outer end of the main cutting edge.

6. A drill according to any one of claims 1 to 3, wherein the width ratio of the thinning edge increases as the thinning edge approaches the central axis along the cutting edge length direction in which the thinning edge extends.

7. The drill according to any one of claims 1 to 3, wherein the width ratio of the outermost end of the main cutting edges located at the outer peripheral corner is the smallest among the width ratios of the cutting edges.

8. The drill according to claim 2, wherein the width ratio of the first cutting edge is maximum at a lowest point of the first cutting edge that is located in a direction farthest from the rotation direction of the drill.

9. The drill according to any one of claims 1 to 3, wherein the body has a shoulder portion arranged on a ridge line where the margin and the flank face are connected, and extending from the outer peripheral corner around the central axis in a direction opposite to the rotation direction of the drill, the shoulder portion has a honing whose cross section perpendicular to the ridge line is a convex curve, the first surface of the shoulder portion is the flank face and the second surface of the shoulder portion is the margin, and the width ratio of the shoulder portion is 0.7 or more and 1.3 or less.

10. The drill according to any one of claims 1 to 3, wherein the width ratio of the thinning edge is 1.0 or greater.

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