Drill

Abstract

To provide a drill which can enhance abrasion resistance, thereby can extend the life of a tool.SOLUTION: A cutting edge 7 has a thinning edge 70 arranged on the radial inner end of the cutting edge 7, and a main cutting edge 71 which is arranged on the radial outer side of the thinning edge 70, and is connected to a leading edge 12 through an outer peripheral corner 15, wherein the main cutting edge 71 and the leading edge 12 have a honing having a projecting curve-shaped cross section vertical to each ridge line part, and a honing curvature radius at a position within 1.5 mm toward the rear end side from the outer periphery corner 15 in the leading edge 12 is 25 μm or more and 80 μm or less, and is smaller than a honing curvature radius on the radial outer end connected to the outer periphery corner 15 in the main cutting edge 71.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a drill.

Background Art

[0002] Conventionally, a drill has a chip discharge groove, a rake face disposed in the chip discharge groove and facing the drill rotation direction, a relief face disposed on the drill tip face, a cutting edge disposed at a ridge line portion where the rake face and the relief face are connected, a margin disposed on the outer peripheral surface of the drill and extending along the chip discharge groove, a leading edge disposed at a ridge line portion where the margin and the rake face are connected, an outer peripheral corner disposed at a corner where the cutting edge and the leading edge are connected, and a shoulder disposed at a ridge line portion where the margin and the relief face are connected and extending in a direction opposite to the drill rotation direction (counter-drill rotation direction) from the outer peripheral corner.

[0003] For example, in the drills described in Patent Documents 1 and 2, in order to suppress the problem that chipping is likely to occur at the shoulder particularly during drilling of thin plates while the cutting conditions tend to be severe in order to improve the machining efficiency, the honing widths of the shoulder cutting edge portion (shoulder), the margin cutting edge portion (leading edge), and the boundary (outer peripheral corner) between them are made larger than the honing width of the second cutting edge portion (main cutting edge).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although the drills described in Patent Documents 1 and 2 are advantageous in high-efficiency machining and machining in an unstable state due to thinning and miniaturization of the workpiece (workpiece to be machined), they still have the following problems in low to medium-efficiency machining conditions, which are the mainstream (main machining area) of drilling, and machining of large workpieces. In this specification, the "low to medium-efficiency machining conditions" refer to, for example, machining conditions up to a circumferential speed of vc = about 130 m / min and a feed of fr = about 0.35 mm / rev at a drill diameter of φ6.0 mm, although it depends on the drill diameter.

[0006] That is, when the honing width in the vicinity of the outer peripheral portion of the drill is set large as in Patent Documents 1 and 2, the cutting resistance increases, and wear progresses easily at an early stage. That is, while the defect resistance is enhanced, the wear resistance tends to decrease. In low to medium-efficiency machining conditions and drilling of large workpieces as described above, sudden defects are less likely to occur, and rather, it is important to suppress defects caused by thinning of the cutting edge due to wear progression and wear of the margin.

[0007] An object of the present invention is to provide a drill capable of enhancing wear resistance and thereby achieving a long tool life.

Means for Solving the Problems

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

[0009] 〔Aspect 1 of the Present Invention〕 A drill comprising a body extending axially about a central axis, the body having a chip discharge groove opening to a tip surface and an outer circumferential surface of the body and extending from the tip surface toward the rear end side, a rake face disposed in the chip discharge groove and facing the drill rotation direction about the central axis, a flank face disposed on the tip surface, a cutting edge disposed at a ridge line portion where the rake face and the flank face are connected, a margin disposed on the outer circumferential surface and extending along the chip discharge groove, a leading edge disposed at a ridge line portion where the margin and the rake face are connected, and an outer corner disposed at a corner portion where the cutting edge and the leading edge are connected, the cutting edge having a thinning blade disposed at a radially inner end portion of the cutting edge and a main cutting blade disposed radially outside the thinning blade and connected to the leading edge via the outer corner, the main cutting blade and the leading edge having a honing in which a cross section perpendicular to each of the ridge line portions is a convex curve, a honing curvature radius at a position within 1.5 mm from the outer corner toward the rear end side of the leading edge being 25 μm or more and 80 μm or less and being smaller than a honing curvature radius of a radially outer end portion of the main cutting blade connected to the outer corner.

[0010] In the drill of the present invention, each honing of the main cutting blade and the leading edge has a convex curve shape (convex R shape) in a cross section perpendicular to each ridge line portion, and is so-called round honing. For this reason, in low to medium efficiency machining conditions and in drilling of large workpieces, wear and welding within the honing surface can be suppressed. Specifically, for example, unlike the present invention, if the honing of each component of the cutting edge (especially the main cutting blade, etc.) is chamfer honing having a flat surface, in low to medium efficiency machining conditions and in drilling of large workpieces, crushing wear within the honing surface is promoted, and there is a risk of causing welding and chipping at an early stage.

[0011] Also, a position within 1.5 mm from the outer corner toward the rear end side of the leading edge is located at the tip portion among the leading edges, and is a portion that is likely to receive cutting resistance from the inner circumferential surface of the machined hole of the workpiece to be machined. In the drill of the present invention, the honing radius of curvature at the position of the leading edge is set to be 25 μm or more and 80 μm or less. Thereby, the progress of wear can be stably suppressed.

[0012] Specifically, different from the present invention, if the honing radius of curvature of the leading edge is larger than 80 μm, the area where the radial rake becomes a strong negative angle within the honing increases (resulting in a strong negative honing), the cutting resistance increases significantly, and there is a risk of wear progressing early. On the other hand, even if the honing radius of curvature of the leading edge is less than 25 μm, wear still tends to progress. Also, when the cross-sectional shape of the ridge line part becomes a sharp shape (a shape close to so-called pincado), the functions obtained by honing are reduced, and chipping etc. are likely to occur.

[0013] In the present invention, the honing radius of curvature of the leading edge is made smaller than the honing radius of curvature of the radially outer end portion arranged adjacent to the outer peripheral corner among the main cutting edges. In other words, the honing radius of curvature of the radially outer end portion of the main cutting edge is made larger than the honing radius of curvature of the leading edge. With this configuration, while suppressing chipping etc. at the radially outer end portion where the peripheral speed is the fastest among the main cutting edges, the progress of wear in the vicinity of the leading edge can be stably suppressed.

[0014] From the above, according to the drill of the present invention, the wear resistance can be enhanced, and thereby the long life of the tool can be achieved. In particular, when applied to low to medium efficiency machining conditions or hole drilling of large workpieces, the present invention exhibits particularly remarkable effects.

[0015] In the present invention, the "honing radius of curvature" is closely related to the honing width. The honing width refers to the dimension corresponding to the straight-line distance between both ends of the honing (the straight-line distance between the first end and the second end) in a cross-section perpendicular to the direction in which the honing extends (the ridge line part).

[0016] That is, when the honing radius of curvature is large, the honing width tends to increase accordingly, and when the honing radius of curvature is small, the honing width tends to decrease accordingly. In other words, when the honing width is small, the honing radius of curvature is also small, and when the honing width is large, the honing radius of curvature is also large. Therefore, it is possible to equivalently rephrase the magnitude relationship of each honing radius of curvature of the present invention in terms of the magnitude relationship of each honing width. That is, the magnitude relationship of each honing radius of curvature corresponds to the magnitude relationship of each honing width.

[0017] 〔Aspect 2 of the present invention〕 The main cutting edge is disposed on the radially outer side of the thinning edge, and includes a first cutting edge that forms a concave curved shape that is recessed in a direction opposite to the drill rotation direction around the central axis, and a second cutting edge that is disposed on the radially outer side of the first cutting edge and is connected to the radially outer end of the first cutting edge. The drill according to Aspect 1, wherein the second cutting edge constitutes a radially outer end portion of the main cutting edge that is connected to the outer peripheral corner of the main cutting edge.

[0018] According to the above configuration, when the main cutting edge has a so-called curved cutting edge shape with a concave cutting edge (first cutting edge), the above-described effects of the present invention are achieved.

[0019] 〔Aspect 3 of the present invention〕 The main cutting edge is linear, and with the diameter dimension of the rotational locus of the cutting edge around the central axis being the drill blade diameter, a region within 7% of the drill blade diameter directed radially inward from the outer peripheral corner of the main cutting edge is the radially outer end portion of the main cutting edge that is connected to the outer peripheral corner of the main cutting edge. The drill according to Aspect 1.

[0020] According to the above configuration, when the main cutting edge has a so-called straight cutting edge shape that is linear, the above-described effects of the present invention are achieved.

[0021] 〔Aspect 4 of the present invention〕 Let the honing curvature radius of the portion of the main cutting edge located radially inward of the radially outer end portion be R1, and the honing curvature radius of the radially outer end portion of the main cutting edge be R2. The drill according to any one of Aspects 1 to 3, which satisfies the relationship [0.9 ≦ R1 / R2 ≦ 1.5].

[0022] Among the main cutting edges, the portion located radially inward of this radially outer end portion is more likely to cause crater wear due to the rubbing of the chip, compared to the radially outer end portion connected to the outer peripheral corner. Since crater wear is likely to occur near the boundary between the honing surface and the rake surface, crater wear can be effectively suppressed by increasing the honing size (honing curvature radius).

[0023] From the above viewpoints, it is preferable to set the value of the ratio of the honing curvature radii [R1 / R2] to 1.0 or more, so that the honing curvature radius R1 of the portion of the main cutting edge located radially inward of the radially outer end portion can be stably and sufficiently ensured. However, since the value of the ratio [R1 / R2] may be less than 1.0 due to manufacturing errors or the like when the value of the ratio is close to 1.0, in the above configuration of the present invention, [0.9 ≦ R1 / R2].

[0024] However, in the present invention, since the honing curvature radius R2 is made larger than the honing curvature radius of the leading edge, if the value of the ratio [R1 / R2] is 0.9 or more, the size of the honing curvature radius R1 is also sufficiently ensured. Therefore, the effect of suppressing crater wear can be stably obtained.

[0025] In addition, when the value of the ratio [R1 / R2] is less than 0.9 or exceeds 1.5, due to the increase in the difference between the honing curvature radii R1 and R2, there is a tendency that wear is likely to be promoted in the one with the smaller honing size. Therefore, it is preferable that the above range of [0.9 ≦ R1 / R2 ≦ 1.5] is satisfied.

[0026] 〔Aspect 5 of the present invention〕 The body is disposed at a ridge line portion where the margin and the relief surface are connected, has a shoulder portion extending from the outer peripheral corner in a direction opposite to the drill rotation direction around the central axis, the shoulder portion has a honing with a convex curve shape in a cross section perpendicular to the ridge line portion, and a honing curvature radius of the shoulder portion is smaller than a honing curvature radius of a radially outer end portion connected to the outer peripheral corner among the main cutting edges, the drill according to any one of Aspects 1 to 4.

[0027] In the above configuration, the honing curvature radius of the shoulder portion is made smaller than the honing curvature radius of the radially outer end portion disposed adjacent to the outer peripheral corner among the main cutting edges. In other words, the honing curvature radius of the radially outer end portion of the main cutting edge is made larger than the honing curvature radius of the shoulder portion. With this configuration, particularly in low to medium efficiency machining conditions or in drilling of large workpieces, chipping and the like at the radially outer end portion where the peripheral speed is the fastest among the main cutting edges can be suppressed, and the progress of wear in the vicinity of the shoulder portion can be stably suppressed.

[0028] 〔Aspect 6 of the present invention〕 The thinning blade has a honing with a convex curve shape in a cross section perpendicular to the ridge line portion where the cutting edge is disposed, and taking the diameter dimension of the rotational locus of the thinning blade around the central axis as the drill blade diameter, a honing curvature radius of a region within 7% of the drill blade diameter from the central axis toward the radially outer side among the thinning blades is smaller than a honing curvature radius of a portion of the main cutting edge located radially inward of the radially outer end portion, the drill according to any one of Aspects 1 to 5.

[0029] In this case, during drilling, the cutting edge, particularly in the vicinity of the central axis, of the thinning blade that first bites into the workpiece to be machined is stably sharpened. Therefore, more accurate drilling becomes possible.

[0030] 〔Aspect 7 of the present invention〕 The honing curvature radius of the first cutting edge is the largest at the lowest point located most in the direction opposite to the drill rotation direction among the first cutting edges, the drill according to Aspect 2.

[0031] In a conventional drill, at the lowest point of the concave cutting edge shape (the first cutting edge in the present invention) that forms a concave curve and is located in the most counter-drilling rotation direction, the stress due to chip rubbing is strongly applied, and crater wear damage tends to become significant. Since crater wear is likely to occur near the boundary between the honing surface and the rake surface, by maximizing the honing size (honing curvature radius) at the lowest point of the first cutting edge as in the above configuration of the present invention, crater wear can be effectively suppressed.

[0032] 〔Aspect 8 of the present invention〕 The rake surface has a thinning rake surface connected to the thinning edge, a main rake surface connected to the main cutting edge, and a first boundary ridge line that extends along the boundary where the thinning rake surface and the main rake surface are connected and is convex toward the drill rotation direction. The first boundary ridge line has honing, and the drill according to any one of Aspects 1 to 7.

[0033] In this case, it is suppressed that the first boundary ridge line protruding toward the drill rotation direction chips due to chip rubbing or the like.

[0034] 〔Aspect 9 of the present invention〕 The rake surface has a first rake surface connected to the first cutting edge, a second rake surface connected to the second cutting edge, and a second boundary ridge line that extends along the boundary where the first rake surface and the second rake surface are connected and is convex toward the drill rotation direction. The second boundary ridge line has honing, and the drill according to Aspect 2.

[0035] In this case, it is suppressed that the second boundary ridge line protruding toward the drill rotation direction chips due to chip rubbing or the like.

[0036] 〔Aspect 10 of the present invention〕 The honing of the leading edge extends further toward the rear end side beyond the position 1.5 mm from the outer peripheral corner toward the rear end side of the leading edge, and the drill according to any one of Aspects 1 to 9.

[0037] In this case, the progress of wear on the leading edge and chipping can be stably suppressed over a wider range along the ridge line portion.

Advantages of the Invention

[0038] According to the drill of the above aspect of the present invention, the wear resistance can be enhanced, thereby achieving a longer tool life.

Brief Description of the Drawings

[0039]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0040] The drill 10 of an 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 has a substantially columnar shape centered on the central axis O. In the present 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. Note that the body 1 may also be referred to as a cutting edge portion.

[0041] In the present embodiment, the body 1 is detachably attached to the shank. That is, the drill 10 is a replaceable-tip drill. However, the present invention is not limited to this, and the drill 10 may include only the body 1 and not include the shank. In this case, the drill 10 is a drill head. Note that the shank may also be referred to as a holder. In FIGS. 1 to 4, illustration of a fastening mechanism of the body 1 to the shank and the like is omitted, and the body 1 is simply represented.

[0042] 〔Definition of Directions〕 In the present embodiment, the direction in which the central axis O of the drill 10 extends is referred to as the axial direction. Among the axial directions, the direction from the shank toward the body 1 is referred to as the tip side of the axial direction or simply the tip side, and the direction from the body 1 toward the shank is referred to as the rear end side of the axial direction or simply the rear end side.

[0043] The direction orthogonal to the central axis O is referred to as the radial direction. Among the radial directions, the direction approaching the central axis O is referred to as the inner side in the radial direction, and the direction away from the central axis O is referred to as the outer side in the radial direction. The direction of rotation around the central axis O is referred to as the circumferential direction. Among the circumferential directions, the direction in which the drill 10 is rotated during drilling is referred to as the drill rotation direction T. Further, among the circumferential directions, the direction opposite to the drill rotation direction T may be referred to as the reverse drill rotation direction.

[0044] In the present embodiment, the direction in which each component of the cutting edge 7 (described later) of the body 1 extends is referred to as the cutting edge length direction.

[0045] 〔Shank〕 Although not particularly shown, the shank is columnar and extends in the axial direction about the central axis O. The shank is detachably held, for example, by a spindle of a machine tool (not shown), a chuck of a lathe, etc. (hereinafter abbreviated as the spindle, etc.). While the shank of the drill 10 is rotated in the drill rotation direction T by the spindle, etc., and is fed toward the tip side in the axial direction, the body 1 cuts into the workpiece to perform drilling.

[0046] 〔Body〕 As shown in FIGS. 1 to 4, the body 1 extends in the axial direction about the central axis O. In the present embodiment, the diameter dimension (outer diameter dimension) of the body 1 is, for example, 6 mm or more and 40 mm or less. Since the diameter dimension of the body 1 corresponds to the diameter dimension of the rotation locus around the central axis O of the cutting edge 7 described later, it may be referred to as the drill blade diameter.

[0047] The body 1 has a front end face 3 facing the tip side of the body 1, an outer peripheral face 8 facing the outer side in the radial direction of the body 1, a chip discharge groove 4, a rake face 5, a flank face 6, a thinning face 11, a cutting edge 7, a margin 13, a leading edge 12, a second chamfered face 14, an outer peripheral corner 15, a shoulder 9, a fastening mechanism (not shown) with the shank, and a rotation support portion (not shown).

[0048] The chip discharge groove 4 opens to the front end face 3 and the outer peripheral face 8 of the body 1 and has a groove shape extending from the front end face 3 to the rear end side. Specifically, the chip discharge groove 4 extends while being twisted in the counter-drill rotation direction as it goes from the front end face 3 toward the rear end side in the axial direction. A plurality of chip discharge grooves 4 are provided in the body 1 at intervals in the circumferential direction. In the present embodiment, two chip discharge grooves 4 are provided at equal pitches in the circumferential direction.

[0049] The rake face 5 is disposed in the chip discharge groove 4 and faces the drill rotation direction T. That is, the rake face 5 is disposed on the wall face of the chip discharge groove 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 line 54, and a second boundary ridge line 55.

[0050] The thinning rake face 50 is disposed at the radially inner end of the tip of the chip discharge groove 4. In the present embodiment, the thinning rake face 50 has a substantially triangular shape.

[0051] The main rake face 51 is disposed radially outside 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 a first rake face 52 and a second rake face 53.

[0052] 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 outside the thinning rake face 50 and adjacent to the thinning rake face 50. In the present embodiment, the first rake face 52 has a concave curved surface shape. Although not particularly shown, in a cross-sectional view perpendicular to the central axis O (hereinafter sometimes simply referred to as a cross-sectional view), the first rake face 52 has a concave curved shape that is recessed in the reverse drill rotation direction. The radial dimension of the first rake face 52 is larger than the radial dimension of the thinning rake face 50.

[0053] 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 outside the first rake face 52 and adjacent to the first rake face 52. In the present embodiment, the second rake face 53 has a twisted surface shape. Although not particularly shown, in a cross-sectional view, the second rake face 53 has a linear shape. However, the present invention is not limited to this, and the second rake face 53 may have a concave curved surface shape. In this case, in a cross-sectional view, the second rake face 53 has a concave curved shape that is recessed in the reverse drill rotation direction. Alternatively, the second rake face 53 may have a convex curved surface shape. In this case, in a cross-sectional view, the second rake face 53 has a convex curved shape that bulges in the drill rotation direction T. The radial dimension of the second rake face 53 is smaller than the radial dimension of the thinning rake face 50 and also smaller than the radial dimension of the first rake face 52.

[0054] The second rake face 53 extends substantially in the axial direction along the radially outer edge among the wall surfaces facing the drill rotation direction T of the chip discharge groove 4. Specifically, the second rake face 53 extends while being twisted in the reverse drill rotation direction as it goes toward the rear end side in the axial direction. The radially outer end portion of the second rake face 53 is connected to the outer peripheral surface 8 via a ridge line portion (leading edge 12).

[0055] Further, the second rake face 53 extends in a direction opposite to the drill rotation direction T (that is, the reverse drill rotation direction) as it goes toward the radially outer side. Specifically, the second rake face 53 extends in the reverse drill rotation direction as it goes toward the radially outer side over the entire radial region of the second rake face 53. That is, the second rake face 53 has a negative angle (negative rake angle) over the entire radial region. For this reason, the ridge line portion (leading edge 12) located at the radially outer end of the second rake face 53 forms an obtuse angle in a cross-sectional view.

[0056] The first boundary ridge line 54 extends along the boundary portion where the thinning rake face 50 and the main rake face 51 are connected, and forms a ridge line shape that is convex in the drill rotation direction T. The first boundary ridge line 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 line 54 extends toward the radially inner side as it goes toward the rear end side in the axial direction.

[0057] The second boundary ridge line 55 extends along the boundary portion where the first rake face 52 and the second rake face 53 are connected, and forms a ridge line shape that is convex in the drill rotation direction T. The second boundary ridge line 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 line 55 extends in the reverse drill rotation direction as it goes toward the rear end side in the axial direction.

[0058] The relief face 6 is disposed on the tip face 3. The relief face 6 has a first relief face 61 and a second relief face 62 that is disposed adjacent to the first relief face 61 in the reverse drill rotation direction of the first relief face 61.

[0059] The first relief surface 61 is disposed at the end of the relief surface 6 in the drill rotation direction T. The first relief surface 61 has an elongated planar shape (substantially polygonal planar shape that is long in the radial direction) extending along the substantially radial direction. The first relief surface 61 extends toward the rear end side in the axial direction as it goes toward the reverse drill rotation direction.

[0060] The second relief surface 62 is disposed at a portion of the relief surface 6 other than the end in the drill rotation direction T. The second relief surface 62 has a substantially fan shape, and the circumferential dimension increases as it goes toward the outer side in the radial direction. The second relief surface 62 extends toward the rear end side in the axial direction as it goes toward the reverse drill rotation direction. The amount of displacement in the axial direction per unit length along the circumferential direction (the inclination corresponding to the relief angle) on the second relief surface 62 is larger than the amount of displacement on the first relief surface 61.

[0061] In this embodiment, the relief surface 6 has two inclined surfaces (the first relief surface 61 and the second relief surface 62) with different relief angles, but it is not limited to this. The relief surface 6 may be formed by, for example, a single inclined surface, or may have three or more inclined surfaces arranged side by side in the circumferential direction and having different relief angles from each other.

[0062] The thinning surface 11 is disposed on the tip surface 3. The thinning surface 11 is disposed adjacent to the relief surface 6 in the reverse drill rotation direction of the relief surface 6. In this embodiment, the thinning surface 11 is connected to the end of the second relief surface 62 in the reverse drill rotation direction. The thinning surface 11 extends toward the rear end side in the axial direction as it goes toward the reverse drill rotation direction. The amount of displacement in the axial direction per unit length along the circumferential direction (the inclination corresponding to the relief angle) on the thinning surface 11 is larger than the amount of displacement on the relief surface 6. Further, the radially inner end of the thinning surface 11 is connected to the bottom portion of the thinning scoop surface 50 having a triangular shape.

[0063] The cutting edge 7 is disposed at the ridge line portion where the rake face 5 and the flank face 6 are connected. A plurality of cutting edges 7 are provided on the body 1 at intervals in the circumferential direction. In the present embodiment, two cutting edges 7 are provided at equal pitches in the circumferential direction. That is, the drill 10 of the present embodiment is a two-flute twist drill.

[0064] The cutting edge 7 has a thinning edge 70 and a main cutting edge 71. The thinning edge 70 is disposed at the radially inner end portion of the cutting edge 7. The thinning edge 70 is disposed at the ridge line portion where the thinning rake face 50 and the first flank face 61 are connected. That is, 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 substantially in the radial direction from near the central axis O toward the outside in the radial direction. Further, the thinning edge 70 extends toward the rear end side in the axial direction as it goes toward the outside in the radial direction. In the present embodiment, the thinning edge 70 is substantially linear.

[0065] The main cutting edge 71 is disposed outside the thinning edge 70 in the radial direction. 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 at the ridge line 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. Further, the main cutting edge 71 extends toward the rear end side in the axial direction as it goes toward the outside in the radial direction. An outer peripheral corner 15 is disposed at the outermost end in the radial direction of the main cutting edge 71. The main cutting edge 71 is connected to the leading edge 12 via the outer peripheral corner 15.

[0066] The main cutting edge 71 has a first cutting edge 72, a second cutting edge 73, and a tip 74. In this embodiment, the first cutting edge 72 constitutes a portion of the main cutting edge 71 other than the radially outer end portion. The first cutting edge 72 is disposed at a ridge line 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 on the radially outer side of the thinning blade 70 and has a concave curve shape that is recessed in a 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 blade 70. The connection portion between the first cutting edge 72 and the thinning blade 70 has a convex shape that protrudes in the drill rotation direction T.

[0067] In this embodiment, the second cutting edge 73 constitutes the radially outer end portion of the main cutting edge 71 that is connected to the outer peripheral corner 15. The second cutting edge 73 is disposed at a ridge line portion 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 on the radially outer side of the first cutting edge 72 and is connected to the radially outer end of the first cutting edge 72 via a top portion 74 that is convex in the drill rotation direction T.

[0068] In this embodiment, the second cutting edge 73 is linear. However, it is not limited to this, and the second cutting edge 73 may be concave curve shaped. When the second cutting edge 73 is concave curve shaped, the second cutting edge 73 preferably has a concave curve shape with a large radius of curvature (that is, large R) that is recessed in the reverse drill rotation direction, for example. Alternatively, the second cutting edge 73 may have a convex curve shape that bulges in the drill rotation direction T.

[0069] As shown in Fig. 2, the radial rake angle θ of the second cutting edge 73 is a negative angle (negative rake 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 a virtual straight line VL passing through the second cutting edge 73 (a part thereof) and the central axis O, and the second cutting edge 73, as viewed from the tip side along the axial direction of the drill 10, as shown in Fig. 2. Further, "the radial rake angle θ of the second cutting edge 73 is a negative angle" means the case where the second cutting edge 73 extends in a direction opposite to the drill rotation direction T as it goes radially outward.

[0070] The top 74 connects the radially outer end of the first cutting edge 72 and the radially inner end of the second cutting edge 73. The top 74 has a convex shape protruding in the drill rotation direction T. Therefore, the cutting edge 7 of the present embodiment has a so-called curved blade shape in which the main cutting edge 71 has a concave blade shape (first cutting edge 72) and a convex portion (top 74).

[0071] As shown in Figs. 1 to 4, the margin 13 is disposed on the outer peripheral surface 8 and extends along the chip discharge groove 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 reverse drill rotation direction as it goes toward the rear end side in the axial direction. The margin 13 has a curved surface shape that protrudes radially outward. The margin 13 has an arc shape centered on the central axis O in a cross-sectional view perpendicular to the central axis O.

[0072] The leading edge 12 is disposed at the ridge line portion 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 reverse drill rotation direction as it goes toward the rear end side 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.

[0073] The leading edge 12 may be provided with a back taper. In this case, the leading edge 12 is located slightly radially inward as it extends toward the rear end side in the axial direction.

[0074] The second chamfered surface 14 is disposed on the outer peripheral surface 8. The second chamfered surface 14 is disposed adjacent to the margin 13 in the direction opposite to the drill rotation direction of the margin 13. The second chamfered surface 14 is located radially inward of the margin 13. The second chamfered surface 14 faces the inner peripheral surface of the machined hole of the workpiece with a radial gap during drilling.

[0075] The outer peripheral corner 15 is disposed at the corner where the cutting edge 7 and the leading edge 12 are connected. Specifically, the outer peripheral 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.

[0076] The shoulder 9 is disposed at the ridge line portion where the margin 13 and the first relief surface 61 (relief surface 6) are connected. The shoulder 9 is disposed at the outer peripheral portion of the tip of the body 1 and extends in the circumferential direction around the central axis O. The shoulder 9 extends from the outer peripheral corner 15 in the direction opposite to the drill rotation direction T. Specifically, the shoulder 9 extends slightly toward the rear end side as it extends in the direction opposite to the drill rotation direction.

[0077] Although not particularly shown, the body 1 has a fastening mechanism for the shank. The fastening mechanism has, for example, a substantially cylindrical mounting portion protruding rearward from the rear end surface of the body 1 and a through hole penetrating the body 1 in the axial direction.

[0078] The mounting portion is inserted into a mounting hole (not shown) of the shank. A plurality (for example, a pair) of through holes 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 screw hole of the shank. Thereby, the body 1 is detachably fixed to the shank.

[0079] Although not particularly shown, the rotation support portion is constituted by a surface facing the anti-drill rotation direction provided on a part of the body 1 or the like. The rotation support portion contacts a rotation receiving portion facing the drill rotation direction T of the shank. A plurality (for example, a pair) of sets of the rotation support portion and the rotation receiving portion are provided at intervals in the circumferential direction. Thereby, the body 1 can stably receive the rotational force in the drill rotation direction T transmitted from the spindle or the like via the shank.

[0080] 〔Honing〕 The thinning blade 70, the main cutting edge 71, the leading edge 12, the shoulder 9, the first boundary ridge line 54, and the second boundary ridge line 55 disposed on each ridge line portion of the body 1 each have a honing H in which a cross section perpendicular to each ridge line portion is a convex curve, as schematically shown in FIGS. 5(a) to 5(c). The honing H is a so-called round honing. The honing H extends along each ridge line portion.

[0081] In the following description, in a cross section perpendicular to the ridge line portion (a cross section perpendicular to the direction in which the honing H extends) as shown in FIGS. 5(a) to 5(c), among the both ends h1 and h2 of the honing H, the surface connected to the first end h1 is defined as the first surface 101, and the surface connected to the second end h2 is defined as the second surface 102. The first surface 101 is, for example, the rake face 5 or the like, and the second surface 102 is, for example, the flank face 6 or the like. Details of the first surface 101 and the second surface 102 connected to the honing H of each ridge line portion will be described separately later.

[0082] In each cross section shown in FIGS. 5(a) to 5(c), the first surface 101 may be connected so as to coincide with the tangent line of the honing H passing over the first end h1, that is, so as to contact the first end h1, or may extend in a direction different from the tangent line on the first end h1 and be smoothly connected to the first end h1. Also, in each of the above cross sections, the second surface 102 may be connected so as to coincide with the tangent line of the honing H passing over the second end h2, that is, so as to contact the second end h2, or may extend in a direction different from the tangent line on the second end h2 and be smoothly connected to the second end h2.

[0083] What is indicated by the symbol R in Fig. 5(a) is the radius of curvature of the honing H. The drill 10 of the present embodiment has, first, special technical features regarding the honing radius of curvature R. In the present embodiment, the "honing radius of curvature R" is closely related to the honing width. The honing width refers to the dimension corresponding to the distance between both ends h1 and h2 of the honing H (the straight-line 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).

[0084] 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, it is possible to equivalently rephrase the magnitude relationship of each honing radius of curvature R described later in the present embodiment in terms of the magnitude relationship of each honing width. That is, the magnitude relationship of each honing radius of curvature R corresponds to the magnitude relationship of each honing width.

[0085] The honing radius of curvature R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 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.

[0086] Also, the honing radius of curvature R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is smaller than the honing radius of curvature R of the radially outer end portion (the second cutting edge 73 in the present embodiment) of the main cutting edge 71 that is connected to the outer peripheral corner 15.

[0087] Here, the honing H of the leading edge 12 extends further toward the rear end side beyond the position 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12. Specifically, the honing curvature radius R (honing width) of the leading edge 12 is set to a constant size within a predetermined range including the position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12, and on the rear end side beyond this predetermined range, it is constant or gradually decreases as it goes toward the rear end side.

[0088] More specifically, the honing curvature radius R (honing width) of the leading edge 12 at a position exceeding 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 and within 3 mm is substantially the same as the honing curvature radius R at the position within 1.5 mm or slightly smaller. The honing curvature radius R of the leading edge 12 at a position exceeding 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 and within 3 mm is, for example, 30 μm or more and 70 μm or less.

[0089] Also, in the present embodiment, the honing curvature radius of the portion of the main cutting edge 71 located radially inside the radially outer end portion (the first cutting edge 72 in the present embodiment) is defined as R1, and the honing curvature radius of the radially outer end portion of the main cutting edge 71 (the second cutting edge 73 in the present embodiment) is defined as R2, and the relationship of [0.9 ≦ R1 / R2 ≦ 1.5] is satisfied. Preferably, [R1 / R2] is 1.0 or more. It is more desirable that the honing curvature radius R1 of the first cutting edge 72 is larger than the honing curvature radius R2 of the second cutting edge 73.

[0090] Further, the honing curvature radius R1 of the first cutting edge 72 varies along the blade length direction of the first cutting edge 72. The honing curvature radius R1 of the first cutting edge 72 gradually increases, for example, as it goes from both ends in the blade length direction of the first cutting edge 72 toward the center. The honing curvature radius R1 of the first cutting edge 72 is maximum at the lowest point located in the direction opposite to the drill rotation direction T (anti-drill rotation direction) of the first cutting edge 72.

[0091] The honing curvature radius R1 of the portion of the main cutting edge 71 that is located radially inward of the radially outer end portion (the first cutting edge 72 in the present embodiment) is, for example, 60 μm or more and 100 μm or less. Further, the honing curvature radius R2 of the radially outer end portion (the second cutting edge 73 in the present embodiment) of the main cutting edge 71 that is connected to the outer peripheral corner 15 is, for example, 50 μm or more and 80 μm or less.

[0092] Further, with the diameter dimension of the rotation locus around the central axis O of the cutting edge 7 being defined as the drill blade diameter, in the present embodiment, the honing curvature radius R of the region within 7% of the drill blade diameter directed radially outward from the central axis O of the thinning blade 70 is smaller than the honing curvature radius R1 of the portion of the main cutting edge 71 that is located radially inward of the radially outer end portion (the first cutting edge 72 in the present embodiment). Specifically, the honing curvature radius R of the region within 7% of the drill blade diameter directed radially outward from the central axis O of the thinning blade 70 is, for example, 40 μm or more and 80 μm or less.

[0093] Further, the honing curvature radius R of the shoulder 9 is smaller than the honing curvature radius R2 of the radially outer end portion (the second cutting edge 73 in the present embodiment) of the main cutting edge 71 that is connected to the outer peripheral corner 15. Specifically, the honing curvature radius R of the shoulder 9 is, for example, 40 μm or more and 70 μm or less.

[0094] Further, the drill 10 of the present embodiment secondly has special technical features regarding the width ratio of the honing H. In each of the cross-sections shown in FIGS. 5(a) to 5(c), the distance from the intersection point P of the extension line of the first surface 101 and the extension line of the second surface 102 to the first end portion h1 is defined as the first width dimension L1, the distance from the intersection point P to the second end portion h2 is defined as the second width dimension L2, and [L1 / L2] is defined as the width ratio. In the present embodiment, the width ratio [L1 / L2] may sometimes be simply referred to as the width ratio.

[0095] Fig. 5(a) shows the case where the width ratio [L1 / L2] of the honing H is 1.0. Fig. 5(b) shows the case where the width ratio [L1 / L2] of the honing H is greater than 1.0. Fig. 5(c) shows the case where the width ratio [L1 / L2] of the honing H is less than 1.0.

[0096] The thinning blade 70 and the main cutting edge 71 are such that the first surface 101 is the rake face 5 and the second surface 102 is the flank face 6. Specifically, for the thinning blade 70, the first surface 101 is the thinning rake face 50 and the second surface 102 is the first flank face 61. Also, for the main cutting edge 71, the first surface 101 is the main rake face 51 and the second surface 102 is the first flank face 61. More specifically, for the first cutting edge 72 of the main cutting edge 71, the first surface 101 is the first rake face 52 and the second surface 102 is the first flank face 61. For the second cutting edge 73 of the main cutting edge 71, the first surface 101 is the second rake face 53 and the second surface 102 is the first flank face 61.

[0097] The width ratio [L1 / L2] of the thinning blade 70 is greater than the width ratio [L1 / L2] of the radially outer end portion (the second cutting edge 73 in this embodiment) connected to the outer peripheral corner 15 of the main cutting edge 71. Also, the width ratio of the thinning blade 70 increases as it approaches the central axis O along the blade length direction in which the thinning blade 70 extends. The width ratio [L1 / L2] of the thinning blade 70 is preferably 1.0 or more.

[0098] The width ratio [L1 / L2] of the portion of the main cutting edge 71 located radially inside of the radially outer end portion is greater than the width ratio [L1 / L2] of the radially outer end portion of the main cutting edge 71. 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.

[0099] In addition, the width ratio of the first cutting edge 72 varies along the blade length direction of the first cutting edge 72. For example, the width ratio of the first cutting edge 72 gradually increases as it goes from both ends in the blade length direction of the first cutting edge 72 toward the central portion. The width ratio of the first cutting edge 72 is maximized at the lowest point of the first cutting edge 72 that is located in the direction opposite to the drill rotation direction T (anti-drill rotation direction). The width ratio [L1 / L2] of the first cutting edge 72 is preferably 1.0 or more.

[0100] The width ratio of the second cutting edge 73 is the smallest among the components of the cutting edge 7. More specifically, the width ratio of the outermost end located at the outer peripheral corner 15 of the main cutting edge 71 (the outermost end in the radial direction of the second cutting edge 73) is the smallest among the width ratios of the cutting edge 7. The width ratio [L1 / L2] of the second cutting edge 73 is preferably 1.0 or less.

[0101] The leading edge 12 has the first surface 101 as the rake face 5 and the second surface 102 as the margin 13. Specifically, the leading edge 12 has the first surface 101 as the second rake face 53 and the second surface 102 as the margin 13. The width ratio [L1 / L2] at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is, for example, 0.7 or more and 1.3 or less.

[0102] The shoulder 9 has the first surface 101 as the flank face 6 and the second surface 102 as the margin 13. Specifically, the shoulder 9 has the first surface 101 as the first flank face 61 and the second surface 102 as the margin 13. The width ratio [L1 / L2] of the shoulder 9 is, for example, 0.7 or more and 1.3 or less.

[0103] 〔Advantages and effects of this embodiment〕 In the drill 10 of the present embodiment described above, each honing H of the thinning blade 70, the main cutting edge 71, and the leading edge 12 has a convex curve shape (convex R shape) in a cross section perpendicular to each ridge line portion, and is so-called round honing. Therefore, in low to medium efficiency machining conditions and in hole drilling of large workpieces, wear and welding within the honing surface can be suppressed. Specifically, for example, unlike the present embodiment, if the honing H of each component of the cutting edge 7 (especially the main cutting edge 71, etc.) is chamfer honing or the like where a flat surface exists, in low to medium efficiency machining conditions and in hole drilling of large workpieces, crushing wear within the honing surface is promoted, and there is a risk of causing welding and chipping at an early stage.

[0104] Also, the position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is located at the tip portion among the leading edges 12, and is a portion that is likely to receive cutting resistance from the inner peripheral surface of the machined hole of the workpiece to be cut. In the drill 10 of the present embodiment, the honing curvature radius R at the above position of the leading edge 12 is set to be 25 μm or more and 80 μm or less. Thereby, the progress of wear can be stably suppressed.

[0105] Specifically, unlike the present embodiment, as the honing curvature radius R of the leading edge 12 becomes larger beyond 80 μm, the area with a negative angle having a strong radial rake within the honing H increases (resulting in a honing H with a strong negative), the cutting resistance significantly increases, and there is a risk of wear progressing at an early stage. On the other hand, even if the honing curvature radius R of the leading edge 12 is smaller than 25 μm, wear still tends to progress. Also, since the cross-sectional shape of the ridge line portion becomes a sharp shape (a shape close to so-called pin card), the function obtained by the honing H is reduced, and chipping and the like are likely to occur.

[0106] Also, in the present embodiment, the honing radius of curvature R of the leading edge 12 is made smaller than the honing radius of curvature R (R2) of the radially outer end portion (second cutting edge 73) disposed adjacent to the outer peripheral corner 15 among the main cutting edges 71. In other words, the honing radius of curvature R (R2) of the radially outer end portion (second cutting edge 73) of the main cutting edge 71 is made larger than the honing radius of curvature R of the leading edge 12. With this configuration, while suppressing chipping and the like at the radially outer end portion where the peripheral speed is the highest among the main cutting edges 71, it is possible to stably suppress the progress of wear in the vicinity of the leading edge 12.

[0107] As described above, according to the drill 10 of the present embodiment, the wear resistance can be enhanced, and thereby the tool life can be extended. In particular, when applied to low to medium efficiency machining conditions or hole drilling of large workpieces, the present embodiment exhibits particularly remarkable effects.

[0108] Also, in the present embodiment, the main cutting edge 71 is disposed on the radially outer side of the thinning blade 70, and includes a first cutting edge 72 that is recessed in a concave curve shape facing in the direction opposite to the drill rotation direction T around the central axis O, and a second cutting edge 73 that is disposed on the radially outer side of the first cutting edge 72 and is connected to the radially outer end of the first cutting edge 72. The second cutting edge 73 constitutes the radially outer end portion connected to the outer peripheral corner 15 among the main cutting edges 71. According to the above configuration, when the main cutting edge 71 has a concave blade shape (first cutting edge 72), that is, a so-called curved blade shape, the excellent operational effects of the present embodiment can be obtained.

[0109] Also, in the present embodiment, when the honing radius of curvature of the portion (first cutting edge 72) located radially inward of the radially outer end portion of the main cutting edge 71 is R1, and the honing radius of curvature of the radially outer end portion (second cutting edge 73) of the main cutting edge 71 is R2, the relationship of [0.9 ≦ R1 / R2 ≦ 1.5] is satisfied.

[0110] Among the main cutting edges 71, the portion (first cutting edge 72) located radially inward of the radially outer end portion (second cutting edge 73) connected to the outer peripheral corner 15 is more likely to suffer crater wear due to chip rubbing. 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 increasing the honing size (honing curvature radius R).

[0111] From the above viewpoints, by setting the value of the ratio of honing curvature radii [R1 / R2] to 1.0 or more, it is possible to stably ensure a large honing curvature radius R1 of the portion of the main cutting edge 71 located radially inward of the radially outer end portion, which is preferable. However, since the value of the ratio [R1 / R2] may be less than 1.0 due to manufacturing errors or the like when the value of the ratio is close to 1.0, in the present embodiment, [0.9≦R1 / R2] is set.

[0112] However, in the present embodiment, since the honing curvature radius R2 is larger than the honing curvature radius R of the leading edge 12, if the value of the ratio [R1 / R2] is 0.9 or more, the size of the honing curvature radius R1 is also sufficiently ensured. Therefore, the effect of suppressing crater wear can be stably obtained.

[0113] In addition, when the value of the ratio [R1 / R2] is less than 0.9 or exceeds 1.5, due to the increase in the difference between the honing curvature radii R1 and R2, wear tends to be promoted in the part with the smaller honing size. Therefore, it is preferably in the range of [0.9≦R1 / R2≦1.5].

[0114] Further, in the present embodiment, the shoulder 9 has a honing H whose cross section perpendicular to its ridge line is a convex curve, and the honing curvature radius R of the shoulder 9 is smaller than the honing curvature radius R2 of the radially outer end portion (second cutting edge 73) connected to the outer peripheral corner 15 of the main cutting edge 71.

[0115] In the above configuration, the honing curvature radius R of the shoulder 9 is made smaller than the honing curvature radius R2 of the radially outer end portion (second cutting edge 73) disposed adjacent to the outer peripheral corner 15 of the main cutting edge 71. In other words, the honing curvature radius R2 of the radially outer end portion of the main cutting edge 71 is made larger than the honing curvature radius R of the shoulder 9. With this configuration, particularly in low to medium efficiency machining conditions and drilling of large workpieces, chipping and the like at the radially outer end portion where the circumferential speed is the highest among the main cutting edges 71 can be suppressed, and the progress of wear in the vicinity of the shoulder 9 can be stably suppressed.

[0116] Further, in the present embodiment, the thinning blade 70 has a honing H whose cross section perpendicular to its ridge line portion is a convex curve, and the honing curvature radius R in a region within 7% of the drill blade diameter directed radially outward from the central axis O of the thinning blade 70 is smaller than the honing curvature radius R1 of a portion (first cutting edge 72) of the main cutting edge 71 located radially inward of the radially outer end portion. In this case, during drilling, the cutting edge, particularly in the vicinity of the central axis O, of the thinning blade 70 that first bites into the workpiece to be cut is stably sharpened. Therefore, more accurate drilling becomes possible.

[0117] Further, in the present embodiment, the honing curvature radius R1 of the first cutting edge 72 is maximum at the lowest point located in the direction opposite to the drill rotation direction T among the first cutting edges 72. In a conventional drill, at the lowest point located in the direction opposite to the drill rotation direction among the concave blade shapes (the first cutting edge 72 in the present embodiment) having a concave curve shape, stress due to chip rubbing is strongly applied, and crater wear damage tends to be significant. Since crater wear is likely to occur near the boundary between the honing surface and the rake face 5, by making the honing size (honing curvature radius R) maximum at the lowest point of the first cutting edge 72 as in the present embodiment, crater wear can be effectively suppressed.

[0118] Further, in the present embodiment, a first boundary ridge line 54 that extends along the boundary portion where the thinning rake face 50 and the main rake face 51 are connected and is convex in the drill rotation direction T has the honing H. In this case, it is possible to suppress the first boundary ridge line 54 protruding toward the drill rotation direction T from being chipped due to the rubbing of the chip or the like.

[0119] Further, in the present embodiment, a second boundary ridge line 55 that extends along the boundary portion where the first rake face 52 and the second rake face 53 are connected and is convex toward the drill rotation direction T has honing H. In this case, it is possible to suppress the second boundary ridge line 55 protruding toward the drill rotation direction T from being chipped due to the rubbing of the chip or the like.

[0120] Further, in the present embodiment, the honing H of the leading edge 12 extends further toward the rear end side beyond the position 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12. In this case, it is possible to stably suppress the progress of wear and chipping of the leading edge 12 in a wider range along the ridge line portion.

[0121] Further, 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 blade 70 is larger than the width ratio of the honing H of the radially outer end portion (second cutting edge 73) connected to the outer peripheral corner 15 of the main cutting edge 71 in the drill 10 of the present embodiment. In other words, the width ratio of the honing H of the radially outer end portion of the main cutting edge 71 is smaller than the width ratio of the honing H of the thinning blade 70.

[0122] Specifically, when comparing the width ratios of the respective honings H, in the thinning blade 70, the ratio of the first width dimension L1 on the rake face 5 side is increased, and in the radially outer end portion (second cutting edge 73) of the main cutting edge 71, the ratio of the second width dimension L2 on the flank face 6 side is increased.

[0123] During drilling, in the case of a thinning blade, due to the compressed chips rubbing against it, damage caused by crater wear tends to become prominent. Since crater wear is likely to occur near the boundary between the honing surface and the rake face 5, as in this embodiment, by increasing the width ratio of the thinning blade 70 (increasing the ratio of the first width dimension L1 on the rake face 5 side), crater wear can be stably suppressed.

[0124] Also, at the radially outer end of the main cutting edge, wear on the flank face 6 side tends to occur prominently. Therefore, as in this embodiment, by reducing the width ratio of the radially outer end of the main cutting edge 71 (increasing the ratio of the second width dimension L2 on the flank face 6 side), flank face wear can be stably suppressed.

[0125] Thus, according to the drill 10 of this embodiment, the wear resistance can be enhanced, and thereby the tool life can be prolonged. In particular, when applied to low to medium efficiency machining conditions or drilling of large workpieces, this embodiment exhibits particularly remarkable effects.

[0126] Also, in this embodiment, the width ratio [L1 / L2] at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is 0.7 or more and 1.3 or less.

[0127] Damage due to wear on the margin side tends to increase on the leading edge. In particular, the position within 1.5 mm from the outer peripheral corner toward the rear end side of the leading edge is located at the tip among the leading edges and is a portion that is likely to receive cutting resistance from the inner peripheral surface of the machined hole of the workpiece.

[0128] As a result of intensive research by the present inventor, it was confirmed that when the ratio of the second width dimension L2 on the margin 13 side is increased too much for the width ratio of the honing H of the leading edge 12, the cutting resistance increases significantly and wear progresses early. Also, when the ratio of the first width dimension L1 on the rake face 5 side is small, wear on the rake face 5 side progresses. For the above reasons, the width ratio of the leading edge 12 is preferably 0.7 or more and 1.3 or less, and more preferably closer to 1.0.

[0129] Also, in the present embodiment, the width ratio [L1 / L2] of the portion (first cutting edge 72) of the main cutting edge 71 located radially inward of the radially outer end portion is larger than the width ratio [L1 / L2] of the radially outer end portion (second cutting edge 73) of the main cutting edge 71.

[0130] Among the main cutting edge 71, the portion (first cutting edge 72) located radially inward of the radially outer end portion (second cutting edge 73) connected to the outer peripheral corner 15 is more likely to cause crater wear due to the rubbing of the chip. Since crater wear is likely to occur near the boundary between the honing surface and the rake face 5, by increasing the width ratio of the honing H of the portion of the main cutting edge 71 located radially inward of the radially outer end portion (increasing the ratio of the first width dimension L1 on the rake face 5 side), crater wear can be effectively suppressed.

[0131] Also, at the radially outer end portion (second cutting edge 73) of the main cutting edge 71, wear on the flank face 6 side tends to progress. Therefore, by reducing the width ratio of the honing H of the radially outer end portion of the main cutting edge 71 (increasing the ratio of the second width dimension L2 on the flank face 6 side) as in the above configuration, flank wear can be effectively suppressed.

[0132] Also, in the present embodiment, the width ratio [L1 / L2] of the thinning blade 70 increases as it approaches the central axis O along the blade length direction in which the thinning blade 70 extends.

[0133] In the thinning blade, damage due to crater wear is likely to occur due to the rubbing of the compressed chip. In particular, this crater wear tends to become more prominent as it approaches the central axis along the blade length direction of the thinning blade.

[0134] Therefore, as in the present embodiment, by increasing the width ratio of the honing H of the thinning blade 70 as it approaches the central axis O, it becomes possible to effectively suppress crater wear over the entire blade length including the vicinity of the central axis O of the thinning blade 70.

[0135] Further, in the present embodiment, the width ratio [L1 / L2] of the outermost end located at the outer peripheral corner 15 of the main cutting edge 71 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 the present 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 blade 70), flank wear can be effectively suppressed.

[0136] Further, in the present embodiment, the width ratio [L1 / L2] of the first cutting edge 72 is the largest at the lowest point located in the direction most opposite to the drill rotation direction T among the first cutting edges 72. In a conventional drill, at the lowest point located in the direction most opposite to the drill rotation direction among the concave blade shapes (the first cutting edge 72 in the present embodiment) having a concave curve shape, stress due to chip rubbing is strongly applied, and crater wear damage tends to become significant. Since crater wear is likely to occur near the boundary between the honing surface and the rake face 5, as in the present embodiment, by making the width ratio of the honing H at the lowest point of the first cutting edge 72 the largest (maximizing the ratio of the first width dimension L1 on the rake face 5 side), crater wear can be effectively suppressed.

[0137] Further, in the present embodiment, the width ratio [L1 / L2] of the shoulder 9 is 0.7 or more and 1.3 or less. With the width ratio of the honing H of the shoulder 9 being 0.7 or more and 1.3 or less as in the above configuration, defects such that wear of either one of the flank 6 and the margin 13 arranged on both sides of the shoulder 9 progresses early and affects the tool life are stably suppressed. Note that the width ratio of the shoulder 9 is more preferably closer to 1.0.

[0138] In addition, in the present embodiment, the width ratio [L1 / L2] of the thinning blade 70 is 1.0 or more. In this case, the width ratio of the honing H of the thinning blade 70 can be stably increased (the ratio of the first width dimension L1 on the rake face 5 side is increased), and the effect of suppressing crater wear can be obtained more remarkably.

[0139] In addition, in the present embodiment, the width ratio [L1 / L2] of the first cutting edge 72 is 1.0 or more. In this case, the width ratio of the honing H of the first cutting edge 72 can be stably increased (the ratio of the first width dimension L1 on the rake face 5 side is increased), and the effect of suppressing crater wear can be obtained more remarkably.

[0140] In addition, in the present 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 decreased (the ratio of the second width dimension L2 on the flank face 6 side is increased), and the effect of suppressing flank wear can be obtained more remarkably.

[0141] 〔Other configurations included in the present invention〕 Note that the present invention is not limited to the above-described embodiments, and for example, as described below, changes in configuration and the like are possible without departing from the gist of the present invention.

[0142] In the above-described embodiment, the case where the main cutting edge 71 of the cutting edge 7 has a so-called curved blade shape having a concave blade shape (first cutting edge 72) and a convex portion (top portion 74) has been described, but the present invention is not limited thereto. Although not particularly shown, the main cutting edge 71 may be linear. In this case, the region within 7% of the drill blade diameter directed radially inward from the outer peripheral corner 15 of the main cutting edge 71 is defined as the "radial outer end portion connected to the outer peripheral corner 15 of the main cutting edge 71" (corresponding to the second cutting edge 73 in the above-described embodiment). According to the above configuration, in the case where the main cutting edge 71 has a so-called linear blade shape, excellent operational effects similar to those of the above-described embodiment can be obtained.

[0143] In the above-described embodiment, an example was given in which the first cutting edge 72 and the second cutting edge 73 are connected to each other via a top portion 74 that tapers in the drill rotation direction T. However, the present invention is not limited to this. The first cutting edge 72 and the second cutting edge 73 may be connected to each other so as to smoothly contact (continuously curve) without passing through the pointed top portion 74.

[0144] In the above-described embodiment, an example was given in which the drill 10 is an insert drill or a drill head. However, the present invention is not limited to this. As the drill of the present invention, a solid drill in which the body 1 and the shank are integrally formed by a single member may be employed. Alternatively, for example, a drill in which the body 1 and the shank are separately manufactured and these are integrated by brazing or the like may also be used.

[0145] In the above-described embodiment, an example was given in which the drill 10 is a two-flute twist drill. However, the present invention is not limited to this. The present invention may be applied to a drill having one flute or three or more flutes.

[0146] The present invention may combine each configuration described in the above-described embodiment and modification examples and the like within a range not departing from the gist of the present invention. Also, addition, omission, substitution, and other changes of the configuration are possible. Further, the present invention is not limited by the above-described embodiment and the like, but is limited only by the claims.

Example

[0147] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.

[0148] <Wear Confirmation Test 1> As Wear Confirmation Test 1, a confirmation test by drilling was conducted on the relationship between the honing radius of curvature R of each ridge line portion of the body 1 and the wear resistance.

[0149] As Example 1 of the present invention, the drill 10 of the foregoing embodiment was prepared. Specifically, for the drill 10 of Example 1, the honing radius of curvature R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is 54 μm. Also, the honing radius of curvature R2 of the second cutting edge 73 is 63 μm, and the honing radius of curvature R1 of the first cutting edge 72 is 75 μm.

[0150] Also, as Conventional Comparative Examples 1 and 2, drills having a technical concept partially different from that of the drill 10 described in the foregoing embodiment were prepared respectively. Specifically, for the drill of Comparative Example 1, the honing radius of curvature R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is 64 μm. Also, 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, for the drill of Comparative Example 1, the honing radius of curvature R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is larger than the honing radius of curvature R2 of the second cutting edge 73.

[0151] Also, for the drill of Comparative Example 2, the honing radius of curvature R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is 17 μm. Also, 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, for the drill of Comparative Example 2, the honing radius of curvature R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is outside the numerical range of 25 μm to 80 μm.

[0152] For each of the drills of Example 1 and Comparative Examples 1 and 2, a plurality of hole drilling operations were performed under the following cutting conditions, and observations were made by imaging in the vicinity of each honing H. Note that the number of hole drilling operations was set until wear was recognized in at least one of the drills. The results are shown in FIG. 6 as enlarged images near each cutting edge. Also, in FIG. 6, cross-sectional schematic diagrams near each cutting edge are shown together. <Cutting Conditions> · Drill diameter: φ24.0 mm · Workpiece material: S50C · Peripheral speed: vc = 100 m / min · Feed: fr = 0.35 mm / rev

[0153] As shown in Fig. 6, in Comparative Examples 1 and 2, the progress of wear was confirmed in the vicinity of the leading edge 12 and in the vicinity of the first cutting edge 72. On the other hand, in Example 1 in which the same number of drilling operations as in Comparative Examples 1 and 2 were performed, no progress of wear was observed in all of the vicinity of the leading edge 12, the vicinity of the second cutting edge 73, and the vicinity of the first cutting edge 72.

[0154] Although not particularly shown, as a result of further intensive research by the inventor of the present invention on the relationship between the honing curvature radius R of each ridge line portion of the body 1 and the wear resistance, the following findings were obtained. In many conventional drills mainly composed of solid drills, the honing curvature radius R at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is about 10 to 20 μm. As a result of research by the inventor of the present invention on improving the damage of the margin 13 of the drill 10, it was found that when the honing curvature radius R at the position within 1.5 mm is increased to about 25 to 30 μm, an advantage can be obtained as compared with conventional products. From such findings, the lower limit value of the numerical range of the honing curvature radius R at the position within 1.5 mm is 25 μm or more.

[0155] Also, it was found that if the honing curvature radius R at the position within 1.5 mm is too large, the coating peels off early and wear is promoted. This is considered to be due to an increase in cutting resistance. Since the cutting resistance depends on various conditions such as the tool diameter and cutting conditions, although the appropriate honing size (honing curvature radius R) at the position within 1.5 mm varies according to various conditions, assuming various combinations in the actual drill 10, the upper limit value of the numerical range of the honing curvature radius R at the position within 1.5 mm is 80 μm or less.

[0156] Specifically, regarding the honing curvature radius R at the position within 1.5 mm, a drill with a diameter of 90 μm was prepared as a comparative example. Under the cutting conditions of drill blade diameter: φ18 mm, workpiece material: S50C, peripheral speed: vc = 100 m / min, and feed: fr = 0.3 mm / rev, when drilling was performed, the tool life of the drill in this comparative example was about 60 m in machining length. On the other hand, a drill 10 with a honing curvature radius R of 60 μm at the position within 1.5 mm was prepared as an example of the present invention. When drilling was performed under the same cutting conditions as above, the tool life of the drill 10 in this example reached about 170 m in machining length. Regarding the coating on the body 1, equivalent coatings were formed on each of the drills in the above comparative example and the above example.

[0157] Furthermore, two drills with different coatings formed on the body 1 were prepared. The honing curvature radius R at the position within 1.5 mm of one drill was set to 90 μm, and the honing curvature radius R at the position within 1.5 mm of the other drill was set to 150 μm. That is, both of these two drills are comparative examples. Then, when drilling was performed using the two drills respectively, the tool life of one drill (honing curvature radius R: 90 μm) was about 80 m in machining length. Also, the tool life of the other drill (honing curvature radius R: 150 μm) was about 50 m in machining length. Thus, as the honing curvature radius R at the position within 1.5 mm becomes larger than 80 μm, the cutting resistance increases and the tool life tends to become shorter.

[0158] <Wear Confirmation Test 2> As Wear Confirmation Test 2, a confirmation test by drilling was conducted on the relationship between the width ratio [L1 / L2] of the honing H at each ridge line portion of the body 1 and the wear resistance.

[0159] As Example 2 of the present invention, the drill 10 of the foregoing embodiment was prepared. Specifically, for the drill 10 of Example 2, the width ratio [L1 / L2] at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is 0.91.

[0160] Also, as Comparative Example 3 of the prior art, a drill having a technical concept partially different from that of the drill 10 described in the foregoing embodiment was prepared. Specifically, for the drill of Comparative Example 3, the width ratio [L1 / L2] at a position within 1.5 mm from the outer peripheral corner 15 toward the rear end side of the leading edge 12 is 0.64.

[0161] For each of the drills of Example 2 and Comparative Example 3, a plurality of drilling operations were performed under the same cutting conditions as in the above-described wear confirmation test 1, and observation was carried out by imaging in the vicinity of the honing H. Note that the number of drilling operations was set until wear was observed in at least one of the drills. The results are shown in FIG. 7 as enlarged images in the vicinity of each cutting edge. Also in FIG. 7, schematic cross-sectional views in the vicinity of each cutting edge are shown together.

[0162] As shown in FIG. 7, in Comparative Example 3, the progress of wear was confirmed in the vicinity of the leading edge 12. On the other hand, in Example 2 in which the same number of drilling operations as in Comparative Example 3 were performed, no progress of wear was observed in the vicinity of the leading edge 12.

[0163] Although not particularly shown, as a result of further intensive studies by the inventor of the present invention on the relationship between the width ratio [L1 / L2] of the honing H at each ridge line portion of the body 1 and the wear resistance, the following findings were obtained. In the above 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 side of the leading edge 12 was outside the numerical range of 0.7 or more and 1.3 or less (the smaller side). However, it was found that wear also tends to progress in other examples where the width ratio [L1 / L2] is outside the above numerical range (the larger side).

[0164] When the honing shape is biased towards either the width dimension L1 or L2 to such an extent that the width ratio [L1 / L2] is outside the above numerical range, it is considered that damage is promoted due to a decrease in strength or an increase in cutting resistance caused by a shortage of the width dimension L1 or L2. From this consideration, the width ratio [L1 / L2] at the position within 1.5 mm is set within the above numerical range, and the ideal value is 1.0.

Industrial Applicability

[0165] According to the drill of the present invention, the wear resistance can be enhanced, and thereby the long life of the tool can be achieved. Therefore, it has industrial applicability.

Explanation of Reference Numerals

[0166] 1... Body 3... Tip surface 4... Chip discharge groove 5... Rake face 6... Relief face 7... Cutting edge 8... Outer peripheral surface 9... Shoulder 10... Drill 12... Leading edge 13... Margin 15... Outer peripheral corner 50... Thinning rake face 51... Main rake face 52... First rake face 53... Second rake face 54... First boundary ridge line 55... Second boundary ridge line 70... Thinning cutting edge 71... Main cutting edge 72... First cutting edge 73... Second cutting edge 74... Top H... Honing O... Central axis R, R1, R2... Honing curvature radius T... Drill rotation direction

Claims

1. A drill comprising a body extending axially about a central axis, wherein the body has, a chip discharge groove opening on the tip surface and the outer peripheral surface of the body and extending from the tip surface toward the rear end side, a rake face disposed in the chip discharge groove and facing the drill rotation direction about the central axis, a relief face disposed on the tip surface, a cutting edge disposed at a ridge line portion where the rake face and the relief face are connected, a margin disposed on the outer peripheral surface and extending along the chip discharge groove, a leading edge disposed at a ridge line portion where the margin and the rake face are connected, and an outer peripheral corner disposed at a corner portion where the cutting edge and the leading edge are connected, wherein the cutting edge has, a thinning blade disposed at the radially inner end portion of the cutting edge, and a main cutting blade disposed radially outside the thinning blade and connected to the leading edge via the outer peripheral corner, wherein the main cutting blade and the leading edge have a honing in which a cross section perpendicular to each of the ridge line portions is a convex curve, wherein a honing radius of curvature at a position within 1.5 mm from the outer peripheral corner toward the rear end side of the leading edge is 25 μm or more and 80 μm or less, and is smaller than a honing radius of curvature of a radially outer end portion of the main cutting blade connected to the outer peripheral corner, a drill.

2. The main cutting blade has, a first cutting blade disposed radially outside the thinning blade and having a concave curve shape that is recessed in a direction opposite to the drill rotation direction about the central axis, and a second cutting blade disposed radially outside the first cutting blade and connected to the radially outer end of the first cutting blade, wherein the second cutting blade constitutes a radially outer end portion of the main cutting blade connected to the outer peripheral corner, The drill according to claim 1.

3. The main cutting blade is linear, taking the diameter dimension of the rotational locus of the cutting edge about the central axis as the drill blade diameter, a region within 7% of the drill blade diameter from the outer peripheral corner toward the radially inner side of the main cutting blade is the radially outer end portion of the main cutting blade connected to the outer peripheral corner, The drill according to claim 1.

4. Taking the honing radius of curvature of a portion of the main cutting blade located radially inside the radially outer end portion as R1 and the honing radius of curvature of the radially outer end portion of the main cutting blade as R2, satisfying the relationship of [0.9 ≦ R1 / R2 ≦ 1.5], The drill according to any one of claims 1 to 3.

5. The body is disposed at a ridge line portion where the margin and the relief surface are connected, and has a shoulder portion extending from the outer peripheral corner in a direction opposite to the drill rotation direction around the central axis. The shoulder portion has a honing in which a cross section perpendicular to the ridge line portion is a convex curve. The honing curvature radius of the shoulder portion is smaller than the honing curvature radius of the radially outer end portion connected to the outer peripheral corner among the main cutting edges. The drill according to any one of claims 1 to 3.

6. The thinning blade has a honing in which a cross section perpendicular to the ridge line portion where the cutting edge is disposed is a convex curve. Taking the diameter dimension of the rotation locus of the cutting edge around the central axis as the drill blade diameter, the honing curvature radius of a region within 7% of the drill blade diameter from the central axis toward the radially outer side of the thinning blade is smaller than the honing curvature radius of a portion of the main cutting edge located radially inward of the radially outer end portion. The drill according to any one of claims 1 to 3.

7. The honing curvature radius of the first cutting edge is maximum at the lowest point located in the direction most opposite to the drill rotation direction among the first cutting edges. The drill according to claim 2.

8. The rake face is a thinning rake face connected to the thinning blade, a main rake face connected to the main cutting edge, and has a first boundary ridge line extending along a boundary portion where the thinning rake face and the main rake face are connected and convex toward the drill rotation direction. The first boundary ridge line has a honing. The drill according to any one of claims 1 to 3.

9. The rake face is a first rake face connected to the first cutting edge, a second rake face connected to the second cutting edge, and has a second boundary ridge line extending along a boundary portion where the first rake face and the second rake face are connected and convex toward the drill rotation direction. The second boundary ridge line has a honing. The drill according to claim 2.

10. The honing of the leading edge extends further toward the rear end side beyond a position 1.5 mm from the outer peripheral corner toward the rear end side of the leading edge. The drill according to any one of claims 1 to 3.

Images