Drill

Abstract

To provide a drill which can enhance abrasion resistance, thereby can extend the life of a tool.SOLUTION: A thinning edge, a main cutting edge and a leading edge have a honing H having a projecting curve-shaped cross section vertical to each ridge line part, in the cross section, among both ends h1 and h2 of the honing H, a surface connected to a first end h1 is defined as a first surface 101, a surface connected to a second end h2 is defined as a second surface 102, a distance between the first end h1 and an intersection P between the extended line of the first surface 101 and the extended line of the second surface 102 is defined as a first width dimension L1, a distance between the second end h2 and the intersection P is defined as a second width dimension L2, [L1 / L2] is defined as a width ratio, as for the thinning edge and the main cutting edge, the first surface 101 is defined as a rake surface, the second surface 102 is defined as a rake surface, and the width ratio of the thinning edge is larger than the width ratio of the radial outer end connected to an outer peripheral corner in the main cutting edge.SELECTED DRAWING: Figure 5

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 (reverse 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 increase 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 peripheral speed of vc = about 130 m / min and a feed of fr = about 0.35 mm / rev for a drill diameter of φ6.0 mm, although it depends on the drill diameter.

[0006] That is, as in Patent Documents 1 and 2, when the honing width in the vicinity of the outer peripheral portion of the drill is set large, 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 and the like caused by thinning of the cutting edge due to the progress of wear.

[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, wherein the body has a chip discharge groove opening to a tip surface and an outer peripheral surface of the body and extending rearward from the tip surface, 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; the cutting edge has 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 peripheral corner; the thinning blade, the main cutting blade, and the leading edge each have a honing in which a cross section perpendicular to each ridge line portion is a convex curve; in the cross section, of both ends of the honing, a surface connected to a first end is defined as a first surface, a surface connected to a second end is defined as a second surface, a distance from an intersection of an extension line of the first surface and an extension line of the second surface to the first end is defined as a first width dimension L1, a distance from the intersection to the second end is defined as a second width dimension L2, [L1 / L2] is defined as a width ratio; the thinning blade and the main cutting blade have the first surface as the rake face and the second surface as the relief face, and the width ratio of the thinning blade is larger than the width ratio of a radially outer end portion of the main cutting blade connected to the outer peripheral corner.

[0010] In the drill of the present invention, the honing of each of the thinning edge, the main cutting edge, and the leading edge forms a convex curve (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 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 edge, etc.) is chamfer honing with 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] And 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 made larger than the width ratio of the honing of the radially outer end portion connected to the outer peripheral corner of the main cutting edge. In other words, the width ratio of the honing of the radially outer end portion of the main cutting edge is made smaller than the width ratio of the honing of the thinning edge.

[0012] Specifically, when comparing the width ratios of each honing, in the thinning edge, the ratio of the first width dimension L1 on the rake face side is made larger, and in the radially outer end portion of the main cutting edge, the ratio of the second width dimension L2 on the flank face side is made larger.

[0013] During drilling, in the thinning edge, due to the compressed chips rubbing, damage due to crater wear tends to become prominent. Since crater wear is likely to occur near the boundary between the honing surface and the rake face, by increasing the width ratio of the thinning edge (increasing the ratio of the first width dimension L1 on the rake face side) as in the present invention, crater wear can be stably suppressed.

[0014] Also, at the radially outer end of the main cutting edge, wear on the relief surface side tends to occur significantly. Therefore, as in the present invention, 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 relief surface side), wear on the relief surface can be stably suppressed.

[0015] As described 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.

[0016] 〔Aspect 2 of the present invention〕 The main cutting edge is disposed outside the radially outer side of the thinning edge, and includes a first cutting edge that is recessed in a concave curve shape facing in the direction opposite to the drill rotation direction around the central axis, and a second cutting edge that is disposed outside 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.

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

[0018] 〔Aspect 3 of the present invention〕 The main cutting edge is linear, and taking the diameter dimension of the rotation locus of the cutting edge around the central axis as the drill blade diameter, a region within 7% of the drill blade diameter from the outer peripheral corner of the main cutting edge toward the radially inner side 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.

[0019] According to the above configuration, when the main cutting edge has a so-called straight blade shape that is linear, the above-described operational effects of the present invention are achieved.

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

[0021] The leading edge tends to be easily damaged due to wear on the margin side. In particular, the position within 1.5 mm from the outer peripheral corner of the leading edge toward the rear end side is located at the tip portion 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.

[0022] As a result of intensive research by the present inventor, it was confirmed that when the width ratio of the honing of the leading edge is such that the ratio of the second width dimension L2 on the margin side is too large, the cutting resistance increases significantly and wear progresses early. Also, when 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, the width ratio of the leading edge is preferably 0.7 or more and 1.3 or less, and more preferably closer to 1.0.

[0023] 〔Aspect 5 of the present invention〕 The width ratio of the portion of the main cutting edge located radially inward of the radially outer end portion of the main cutting edge is larger than the width ratio of the radially outer end portion of the main cutting edge. The drill according to any one of Aspects 1 to 4.

[0024] Among the main cutting edges, the portion located radially inward of the radially outer end portion connected to the outer peripheral corner is more likely to cause crater wear due to chip rubbing. Since 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 width ratio of the honing of the portion of the main cutting edge located radially inward of the radially outer end portion (increasing the ratio of the first width dimension L1 on the rake face side).

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

[0026] 〔Aspect 6 of the present invention〕 The width ratio of the thinning blade is increased as it approaches the central axis along the blade length direction in which the thinning blade extends, for the drill according to any one of Aspects 1 to 5.

[0027] In the thinning blade, damage due to crater wear is likely to occur as the compressed chips rub against it. 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.

[0028] Therefore, as in the above configuration of the present invention, by increasing the width ratio of honing of the thinning blade as it approaches the central axis, it becomes 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 width ratio of the outermost end located at the outer peripheral corner of the main cutting edge is the smallest among the width ratios of the cutting edges, for the drill according to any one of Aspects 1 to 6.

[0030] At the outermost end (outer peripheral corner) of the main cutting edge, wear on the flank face side tends to progress significantly. Therefore, as in the above configuration of the present invention, by making the width ratio of honing at the outermost end (outer peripheral corner) of the main cutting edge the smallest among the entire cutting edges (main cutting edge and thinning blade), flank face wear can be effectively suppressed.

[0031] 〔Aspect 8 of the present invention〕 The width ratio of the first cutting edge is the largest at the lowermost point located in the direction opposite to the drill rotation direction among the first cutting edges, for the drill according to Aspect 2.

[0032] 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, stress due to chip rubbing is strongly applied, and crater wear damage tends to become prominent. Since crater wear is likely to occur near the boundary between the honing surface and the rake surface, as in the above configuration of the present invention, by maximizing the width ratio of honing at the lowest point of the first cutting edge (maximizing the ratio of the first width dimension L1 on the rake surface side), crater wear can be effectively suppressed.

[0033] 〔Aspect 9 of the present invention〕 The body is disposed at a ridge line portion where the margin and the flank 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 whose cross section perpendicular to the ridge line portion forms a convex curve, the shoulder portion has the first surface as the flank and the second surface as the margin, and the width ratio of the shoulder portion is 0.7 or more and 1.3 or less. The drill according to any one of Aspects 1 to 8.

[0034] As in the above configuration, when the width ratio of the honing of the shoulder portion is 0.7 or more and 1.3 or less, problems such that wear of either the flank or the margin disposed on both sides of the shoulder portion progresses early and affects the tool life are stably suppressed. Note that the closer the width ratio of the shoulder portion is to 1.0, the more preferable it is.

[0035] 〔Aspect 10 of the present invention〕 The width ratio of the thinning blade is 1.0 or more. The drill according to any one of Aspects 1 to 9.

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

Effects of the Invention

[0037] 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

[0038]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0039] 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 part.

[0040] In this embodiment, the body 1 is detachably attached to the shank. That is, the drill 10 is a drill with replaceable cutting edges. Note that the drill 10 is not limited to this, and may include only the body 1 and not have a shank. In this case, the drill 10 is a drill head. Note that the shank may also be referred to as a holder. Also, in FIGS. 1 to 4, the illustration of the fastening mechanism of the body 1 to the shank and the like is omitted, and the body 1 is represented in a simplified manner.

[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. 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.

[0042] Also, 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 of the radial direction, and the direction away from the central axis O is referred to as the outer side of the radial direction. The direction of revolving 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. Also, among the circumferential directions, the direction opposite to the drill rotation direction T may be referred to as the reverse drill rotation direction.

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

[0044] 〔Shank〕 Although not particularly illustrated, the shank is columnar and extends axially around the central axis O. The shank is detachably held, for example, by a spindle of a machine tool (not shown), a chuck of a ball screw machine, etc. (hereinafter abbreviated as the spindle, etc.). The drill 10 is rotated in the drill rotation direction T by the spindle, etc., and is sent to the tip side in the axial direction, so that the body 1 cuts into the workpiece to perform drilling.

[0045] 〔Body〕 As shown in FIGS. 1 to 4, the body 1 extends in the axial direction about the central axis O. In this 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.

[0046] The body 1 has a tip surface 3 facing the tip side of the body 1, an outer peripheral surface 8 facing the radially outer side 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 chamfering 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).

[0047] The chip discharge groove 4 opens to the tip surface 3 and the outer peripheral surface 8 of the body 1 and has a groove shape extending from the tip surface 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 tip surface 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 this embodiment, two chip discharge grooves 4 are provided at equal pitches in the circumferential direction.

[0048] 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 surface 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.

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

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

[0051] The first scooping surface 52 is disposed on a portion of the main scooping surface 51 other than the radially outer end portion. The first scooping surface 52 is disposed adjacent to the thinning scooping surface 50 on the radially outer side of the thinning scooping surface 50. In the present embodiment, the first scooping surface 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 scooping surface 52 has a concave curve shape that depresses toward the reverse drill rotation direction. The radial dimension of the first scooping surface 52 is larger than the radial dimension of the thinning scooping surface 50.

[0052] The second scooping surface 53 is disposed at the radially outer end portion of the main scooping surface 51. The second scooping surface 53 is disposed adjacent to the first scooping surface 52 on the radially outer side of the first scooping surface 52. In the present embodiment, the second scooping surface 53 has a twisted surface shape. Although not particularly shown, in a cross-sectional view, the second scooping surface 53 is linear. However, the second scooping surface 53 is not limited to this and may have a concave curved surface shape. In this case, in a cross-sectional view, the second scooping surface 53 has a concave curve shape that depresses toward the reverse drill rotation direction. Alternatively, the second scooping surface 53 may have a convex curved surface shape. In this case, in a cross-sectional view, the second scooping surface 53 has a convex curve shape that bulges toward the drill rotation direction T. The radial dimension of the second scooping surface 53 is smaller than the radial dimension of the thinning scooping surface 50 and also smaller than the radial dimension of the first scooping surface 52.

[0053] The second scooping surface 53 extends substantially in the axial direction along the radially outer edge of the wall surface of the chip discharge groove 4 facing the drill rotation direction T. Specifically, the second scooping surface 53 extends while twisting toward 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 scooping surface 53 is connected to the outer peripheral surface 8 via a ridge line portion (leading edge 12).

[0054] Further, the second rake face 53 extends in a direction opposite to the drill rotation direction T (i.e., the reverse drill rotation direction) as it extends radially outward. Specifically, the second rake face 53 extends in the reverse drill rotation direction as it extends radially outward over the entire radial region of the second rake face 53. That is, the second rake face 53 has a negative (negative angle) radial rake 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.

[0055] 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, forming a ridge line 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 radially inward as it extends toward the rear end side in the axial direction.

[0056] 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, forming a ridge line 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 extends toward the rear end side in the axial direction.

[0057] 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.

[0058] The first relief face 61 is disposed at the end in the drill rotation direction T of the relief face 6. The first relief face 61 forms an elongated planar shape (substantially polygonal planar shape that is long in the radial direction) extending substantially along the radial direction. The first relief face 61 extends toward the rear end side in the axial direction as it extends in the reverse drill rotation direction.

[0059] The second relief surface 62 is disposed on a portion of the relief surface 6 other than the end portion 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 in 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.

[0060] 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.

[0061] 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 portion in the reverse drill rotation direction of the second relief surface 62. The thinning surface 11 extends toward the rear end side in the axial direction as it goes in 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 portion of the thinning surface 11 is connected to the bottom portion of the thinning flute surface 50 having a triangular shape.

[0062] The cutting edge 7 is disposed on the ridge line portion where the flute surface 5 and the relief surface 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 pitches 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 blade 70 is disposed at the radially inner end portion of the cutting edge 7. The thinning blade 70 is disposed at the ridge line portion where the thinning rake face 50 and the first relief face 61 are connected. That is, the thinning rake face 50 is connected to the thinning blade 70. The thinning blade 70 extends along the leading edge of the thinning rake face 50. The thinning blade 70 extends substantially along the radial direction from near the central axis O toward the outside in the radial direction. Further, the thinning blade 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 blade 70 is substantially linear.

[0064] The main cutting edge 71 is disposed outside the thinning blade 70 in the radial direction. The main cutting edge 71 is connected to the thinning blade 70. The main cutting edge 71 constitutes the portion of the cutting edge 7 other than the thinning blade 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 relief 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.

[0065] The main cutting edge 71 has a first cutting edge 72, a second cutting edge 73, and a tip 74. In the present embodiment, the first cutting edge 72 constitutes the portion of the main cutting edge 71 other than the radially outer end portion. The first cutting edge 72 is disposed at the ridge line portion where the first rake face 52 and the first relief 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 outside the thinning blade 70 in the radial direction and has a concave curved shape that is recessed in the direction opposite to the drill rotation direction T. The inner end portion of the first cutting edge 72 in the radial direction is connected to the outer end portion of the thinning blade 70 in the radial direction. 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.

[0066] 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 the 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 radially outside the first cutting edge 72 and is connected to the radially outer end of the first cutting edge 72 via the top portion 74 that protrudes toward the drill rotation direction T.

[0067] In this embodiment, the second cutting edge 73 is linear. However, it is not limited thereto, and the second cutting edge 73 may be concave curved. When the second cutting edge 73 is concave curved, the second cutting edge 73 preferably forms a concave curve having a large radius of curvature (i.e., large R) that is recessed in the reverse drill rotation direction, for example. Alternatively, the second cutting edge 73 may form a convex curve that bulges in the drill rotation direction T.

[0068] As shown in FIG. 2, the radial rake angle 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 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 when the drill 10 is viewed from the tip side along the axial direction as shown in FIG. 2. Further, “the radial rake angle θ of the second cutting edge 73 is a negative angle” means a case where the second cutting edge 73 extends in a direction opposite to the drill rotation direction T as it goes radially outward.

[0069] The top portion 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 portion 74 has a convex shape that protrudes toward the drill rotation direction T. Therefore, the cutting edge 7 of this embodiment has a so-called curved blade shape in which the main cutting edge 71 has a concave blade shape (the first cutting edge 72) and a convex portion (the top portion 74).

[0070] 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 counter-drill rotation direction as it goes toward the rear end side in the axial direction. The margin 13 has a curved surface that bulges outward in the radial direction. The margin 13 has an arc shape centered on the central axis O in a cross-sectional view perpendicular to the central axis O.

[0071] 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 counter-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.

[0072] Note that a back taper may be provided to the leading edge 12. In this case, the leading edge 12 is located slightly radially inward as it goes toward the rear end side in the axial direction.

[0073] 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 counter-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.

[0074] The outer corner 15 is disposed at the 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 disposed at a 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 goes in the counter-drill rotation direction.

[0076] Although not particularly shown, the body 1 has a fastening mechanism with 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.

[0077] The mounting portion is inserted into a mounting hole (not shown) of the shank. The through holes are provided in the body 1 in a plurality (for example, a pair) 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 respectively. Thereby, the body 1 is detachably fixed to the shank.

[0078] Although not particularly shown, the rotation support portion is constituted by a surface facing the counter-drill rotation direction provided on a part of the body 1. 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 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.

[0079] 〔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.

[0080] 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.

[0081] 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 be in contact with 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 be in contact with 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.

[0082] 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 first has special technical features regarding the honing radius of curvature R. Note that in the present embodiment, the "honing radius of curvature R" is closely related to the honing width. The honing width refers to a 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).

[0083] That is, when the honing curvature radius R is large, the honing width tends to increase accordingly, and when the honing curvature radius R is small, the honing width tends to decrease accordingly. In other words, when the honing width is small, the honing curvature radius R also becomes small, and when the honing width is large, the honing curvature radius R also becomes large. Therefore, it is possible to equivalently rephrase the magnitude relationship of each honing curvature radius R described later in this embodiment in terms of the magnitude relationship of each honing width. That is, the magnitude relationship of each honing curvature radius R corresponds to the magnitude relationship of each honing width.

[0084] 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 25 μm or more and 80 μm or less. The honing curvature radius R of the leading edge 12 is more preferably, for example, 40 μm or more and 70 μm or less.

[0085] Also, 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 smaller than the honing curvature radius R of the radially outer end portion (the second cutting edge 73 in this embodiment) of the main cutting edge 71 connected to the outer peripheral corner 15.

[0086] 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 magnitude 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 beyond this predetermined range on the rear end side, it is constant or gradually decreases toward the rear end side.

[0087] 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 and within 3 mm is substantially the same as or slightly smaller than the honing curvature radius R at a position within the 1.5 mm. 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 and within 3 mm is, for example, 30 μm or more and 70 μm or less.

[0088] In this embodiment, the honing curvature radius of the portion of the main cutting edge 71 located radially inward of the radially outer end portion (the first cutting edge 72 in this 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 this embodiment) is defined as R2, satisfying the relationship of [0.9 ≦ R1 / R2 ≦ 1.5]. 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.

[0089] Also, 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, 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 maximized at the lowest point located in the direction opposite to the drill rotation direction T (anti-drill rotation direction) in the first cutting edge 72.

[0090] The honing curvature radius R1 of the portion of the main cutting edge 71 located radially inward of the radially outer end portion (the first cutting edge 72 in this embodiment) is, for example, 60 μm or more and 100 μm or less. Also, the honing curvature radius R2 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 is, for example, 50 μm or more and 80 μm or less.

[0091] Also, with the diameter dimension of the rotation locus around the central axis O of the cutting edge 7 as the drill blade diameter, in this 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 (the first cutting edge 72 in this embodiment) of the main cutting edge 71 located radially inward of the radially outer end portion. 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.

[0092] Also, 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 this embodiment) of the main cutting edge 71 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.

[0093] Second, the drill 10 of this embodiment has special technical features regarding the width ratio of the honing H. In each cross-section shown in FIGS. 5(a) to (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 h1 is defined as the first width dimension L1, and the distance from the intersection point P to the second end h2 is defined as the second width dimension L2, and [L1 / L2] is defined as the width ratio. In this embodiment, the width ratio [L1 / L2] may sometimes be simply referred to as the width ratio.

[0094] 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.

[0095] For the thinning blade 70 and the main cutting edge 71, 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.

[0096] The width ratio [L1 / L2] of the thinning blade 70 is larger 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.

[0097] The width ratio [L1 / L2] of the portion of the main cutting edge 71 located radially inside the radially outer end portion is larger 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 larger than the width ratio [L1 / L2] of the second cutting edge 73.

[0098] Also, the width ratio of the first cutting edge 72 changes along the blade length direction of the first cutting edge 72. The width ratio 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 central portion. The width ratio of the first cutting edge 72 is maximum at the lowest point located in the direction most opposite to the drill rotation direction T (the reverse drill rotation direction) of the first cutting edge 72. The width ratio [L1 / L2] of the first cutting edge 72 is preferably 1.0 or more.

[0099] 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 (the outermost end in the radial direction of the second cutting edge 73) located at the outer peripheral corner 15 of the main cutting edge 71 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.

[0100] 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.

[0101] 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.

[0102] 〔Operational Effects of the Present Embodiment〕 In the drill 10 of the present embodiment described above, the honings H of the thinning blade 70, the main cutting edge 71, and the leading edge 12 are each in a convex curve shape (convex R shape) in a cross section perpendicular to each ridge line portion, and are so-called round honings. 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, different from the present embodiment, if the honing H of each component of the cutting edge 7 (especially the main cutting edge 71, etc.) is a chamfer honing with a flat surface present, 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 early welding and chipping.

[0103] Further, 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 machined. In the drill 10 of the present embodiment, the honing curvature radius R at the above-mentioned 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.

[0104] 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 strong negative angle of the 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 that wear will progress early. On the other hand, even if the honing curvature radius R of the leading edge 12 is smaller than 25 μm, wear is still likely to progress. In addition, due to the cross-sectional shape with a sharp ridge line portion (a shape close to a so-called pin card), the functions obtained by the honing H are reduced, and chipping and the like are likely to occur.

[0105] Also in the present embodiment, the honing curvature radius R of the leading edge 12 is made smaller than the honing curvature radius R (R2) of the radially outer end portion (the second cutting edge 73) disposed adjacent to the outer peripheral corner 15 among the main cutting edges 71. In other words, the honing curvature radius R (R2) of the radially outer end portion (the second cutting edge 73) of the main cutting edge 71 is made larger than the honing curvature radius 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 fastest among the main cutting edges 71, the progress of wear in the vicinity of the leading edge 12 can be stably suppressed.

[0106] From the 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.

[0107] In this embodiment, the main cutting edge 71 is disposed on the radially outer side of the thinning edge 70, and includes a first cutting edge 72 that forms a concave curved shape that is recessed in a 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 a radially outer end portion connected to the outer peripheral corner 15 of the main cutting edge 71. According to the above configuration, when the main cutting edge 71 has a so-called curved blade shape with a concave blade shape (the first cutting edge 72), the excellent operational effects of this embodiment can be obtained.

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

[0109] Among the main cutting edge 71, the portion (the first cutting edge 72) located radially inward of the radially outer end portion is more likely to cause crater wear due to the rubbing of the chips compared to the radially outer end portion (the second cutting edge 73) connected to the outer peripheral corner 15. 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 radius of curvature R).

[0110] From the above perspective, by setting the value of the ratio of the honing radii of curvature [R1 / R2] to be 1.0 or more, it is possible to stably and significantly ensure the honing radius of curvature R1 of the portion of the main cutting edge 71 located radially inward of the radially outer end portion, which is preferable. However, when the value of the ratio [R1 / R2] is close to 1.0, the value of the ratio [R1 / R2] may be less than 1.0 due to manufacturing errors or the like. Therefore, in this embodiment, [0.9 ≦ R1 / R2] is set.

[0111] However, in the present embodiment, since the honing curvature radius R2 of the honing is larger than the honing curvature radius R of the leading edge 12, if the ratio value [R1 / R2] is 0.9 or more, the size of the honing curvature radius R1 is also sufficiently ensured. For this reason, the effect of suppressing crater wear can be stably obtained.

[0112] In addition, when the ratio value [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 more easily in the part with the smaller honing size. Therefore, it is preferably in the range of [0.9 ≦ R1 / R2 ≦ 1.5].

[0113] Also, 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.

[0114] In the above configuration, 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) 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 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 peripheral speed is the fastest 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.

[0115] Also, in the present embodiment, the thinning blade 70 has a honing H whose cross section perpendicular to its ridge line is a convex curve, and the honing curvature radius R in 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 (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 of the thinning blade 70 that first bites into the workpiece is stably sharpened particularly near the central axis O. Therefore, more accurate drilling becomes possible.

[0116] Also, in this embodiment, the honing curvature radius R1 of the first cutting edge 72 is the largest at the lowest point of the first cutting edge 72 that is located in the direction opposite to the drill rotation direction T. In a conventional drill, at the lowest point of the concave cutting edge shape (the first cutting edge 72 in this embodiment) that forms a concave curve, the 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) at the lowest point of the first cutting edge 72 the largest as in this embodiment, crater wear can be effectively suppressed.

[0117] Also, in this 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 toward the drill rotation direction T has honing H. In this case, it is suppressed that the first boundary ridge line 54 protruding toward the drill rotation direction T chips due to chip rubbing or the like.

[0118] Also, in this 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 suppressed that the second boundary ridge line 55 protruding toward the drill rotation direction T chips due to chip rubbing or the like.

[0119] Also, in this 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, the progress of wear and chipping of the leading edge 12 can be stably suppressed in a wider range along the ridge line portion.

[0120] 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 made 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 other words, the width ratio of the honing H of the radially outer end portion of the main cutting edge 71 is made smaller than the width ratio of the honing H of the thinning blade 70.

[0121] Specifically, when comparing the width ratios of the 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.

[0122] During drilling, in the thinning blade, since the compressed chips rub against it, damage due to 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.

[0123] Also, at the radially outer end portion 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 portion of the main cutting edge 71 (increasing the ratio of the second width dimension L2 on the flank face 6 side), flank wear can be stably suppressed.

[0124] Thus, according to the drill 10 of this 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 drilling of large workpieces, this embodiment exhibits particularly remarkable effects.

[0125] In the present 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.

[0126] The leading edge tends to be easily damaged due to wear on the margin side. In particular, the position within 1.5 mm from the outer peripheral corner of the leading edge toward the rear end side is located at the tip portion 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.

[0127] 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 excessively increased with respect to the width ratio of the honing H of the leading edge 12, the cutting resistance increases remarkably 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.

[0128] In the present embodiment, the width ratio [L1 / L2] of the portion (first cutting edge 72) located radially inside the radially outer end of the main cutting edge 71 is larger than the width ratio [L1 / L2] of the radially outer end portion (second cutting edge 73) of the main cutting edge 71.

[0129] Among the main cutting edge 71, the portion (first cutting edge 72) located radially inside this radially outer end portion has a tendency to be more likely to cause crater wear due to chip rubbing compared to the radially outer end portion (second cutting edge 73) connected to the outer peripheral corner 15. 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 located radially inside the radially outer end portion of the main cutting edge 71 (increasing the ratio of the first width dimension L1 on the rake face 5 side), crater wear can be effectively suppressed.

[0130] 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 easily. Therefore, as in the above configuration, by reducing the width ratio of the honing H at 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), flank face wear can be effectively suppressed.

[0131] 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.

[0132] In the thinning blade, damage due to crater wear is likely to occur when the compressed chips rub against it. 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.

[0133] 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.

[0134] Also, 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 face 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 face wear can be effectively suppressed.

[0135] Also, in the present embodiment, the width ratio [L1 / L2] of the first cutting edge 72 is the largest at the lowermost point located in the direction opposite to the drill rotation direction T in the first cutting edge 72. In a conventional drill, at the lowest point of the concave cutting edge shape (the first cutting edge 72 in this embodiment) that forms a concave curve and is located farthest in the direction opposite to the drill rotation direction, the stress due to chip rubbing is strongly applied, and crater wear damage 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 maximizing the width ratio of the honing H at the lowest point of the first cutting edge 72 (maximizing the ratio of the first width dimension L1 on the rake face 5 side), crater wear can be effectively suppressed.

[0136] Also, in this embodiment, the width ratio [L1 / L2] of the shoulder 9 is 0.7 or more and 1.3 or less. With the above configuration, when the width ratio of the honing H of the shoulder 9 is 0.7 or more and 1.3 or less, among the flank faces 6 and the margin 13 arranged on both sides of the shoulder 9, any problem that one of the wear progresses early and affects the tool life is stably suppressed. Note that the closer the width ratio of the shoulder 9 is to 1.0, the more preferable it is.

[0137] Also, in this 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 (increasing the ratio of the first width dimension L1 on the rake face 5 side), and the effect of suppressing crater wear can be obtained more significantly.

[0138] Also, in this 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 (increasing the ratio of the first width dimension L1 on the rake face 5 side), and the effect of suppressing crater wear can be obtained more significantly.

[0139] Also, 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 decreased (increasing the ratio of the second width dimension L2 on the flank face 6 side), and the effect of suppressing flank wear can be obtained more significantly.

[0140] [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, configuration changes and the like are possible without departing from the spirit of the present invention.

[0141] 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 it is not limited to this. Although not particularly shown, the main cutting edge 71 may be linear. In this case, a 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 straight blade shape that is linear, excellent operational effects similar to those of the above-described embodiment can be obtained.

[0142] Also, in the above-described embodiment, an example where the first cutting edge 72 and the second cutting edge 73 are connected to each other via a pointed top portion 74 that tapers in the drill rotation direction T has been given, but it 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.

[0143] In the above-described embodiment, an example where the drill 10 is an exchangeable tip drill or a drill head has been given, but it 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 integrated by brazing or the like may also be used.

[0144] In the above-described embodiment, an example where the drill 10 is a two-flute twist drill has been given, but it 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 combine each configuration described in the foregoing embodiments, modifications, etc. within a range not departing from the gist of the present invention, and addition, omission, substitution, and other changes of the configuration are possible. Further, the present invention is not limited by the foregoing embodiments, etc., and is limited only by the scope of the claims.

Example

[0146] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.

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

[0148] As Example 1 of the present invention, the drill 10 of the foregoing embodiment was prepared. Specifically, in the drill 10 of Example 1, 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 54 μm. Further, the honing curvature radius R2 of the second cutting edge 73 is 63 μm, and the honing curvature radius R1 of the first cutting edge 72 is 75 μm.

[0149] Further, as Conventional Comparative Examples 1 and 2, drills having a technical idea partially different from that of the drill 10 described in the foregoing embodiment were prepared respectively. Specifically, in the drill of Comparative Example 1, 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 64 μm. Further, the honing curvature radius R2 of the second cutting edge 73 is 50 μm, and the honing curvature radius R1 of the first cutting edge 72 is 63 μm. Therefore, in the drill of Comparative Example 1, 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 larger than the honing curvature radius R2 of the second cutting edge 73.

[0150] Further, in the drill of Comparative Example 2, 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 17 μm. Also, the honing curvature radius R2 of the second cutting edge 73 is 41 μm, and the honing curvature radius R1 of the first cutting edge 72 is 58 μm. Therefore, in the drill of Comparative Example 2, 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 outside the numerical range of 25 μm to 80 μm.

[0151] For each of the drills of Example 1 and Comparative Examples 1 and 2, a plurality of 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 drilling operations was up to the point where wear was recognized in at least one of the drills. The results are shown in FIG. 6 as enlarged images in the vicinity of each cutting edge. Also, in FIG. 6, schematic cross-sectional views in the vicinity of each cutting edge are shown together. <Cutting conditions> · Drill blade 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, 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 where 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.

[0153] 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 the inventor of the present invention researching the improvement of 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, advantages can be obtained 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.

[0154] 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.

[0155] Specifically, a drill with a honing curvature radius R of 90 μm at the position within 1.5 mm was prepared as a comparative example, and drilling was performed under the cutting conditions of drill blade diameter: φ18 mm, workpiece material: S50C, peripheral speed: vc = 100 m / min, feed: fr = 0.3 mm / rev. As a result, 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, and drilling was performed under the same cutting conditions as above. As a result, 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.

[0156] Furthermore, two drills with different coatings from the above applied to the body 1 were prepared. The honing curvature radius R at a position within 1.5 mm of one drill was set to 90 μm, and the honing curvature radius R at a 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, 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 a position within 1.5 mm becomes larger than 80 μm, the cutting resistance increases and the tool life tends to become shorter.

[0157] <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 part of the body 1 and the wear resistance.

[0158] As Example 2 of the present invention, the drill 10 of the above-described embodiment was prepared. Specifically, in 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.

[0159] Also, as Comparative Example 3 of the prior art, a drill having a technical idea partially different from that of the drill 10 described in the above embodiment was prepared. Specifically, in 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.

[0160] For each drill of Example 2 and Comparative Example 3, a plurality of hole 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 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. 7 as enlarged images in the vicinity of each cutting edge. In Fig. 7, a schematic cross-sectional view in the vicinity of each cutting edge is also shown.

[0161] As shown in Fig. 7, in Comparative Example 3, progress of wear was confirmed in the vicinity of the leading edge 12. On the other hand, in Example 2 where the same number of hole drilling operations as in Comparative Example 3 were performed, progress of wear was not recognized in the vicinity of the leading edge 12.

[0162] 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 deviated below (smaller side) the numerical range of 0.7 or more and 1.3 or less. However, it was found that wear also tends to progress in other examples where the width ratio [L1 / L2] deviates above (larger side) the above numerical range.

[0163] This is presumably because when the honing shape is biased toward either the width dimension L1 or L2 to such an extent that the width ratio [L1 / L2] is outside the above numerical range, damage is promoted due to a decrease in strength or an increase in cutting resistance due to 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

[0164] According to the drill of the present invention, the wear resistance can be enhanced, and thereby the tool life can be extended. Therefore, it has industrial applicability.

Explanation of Signs

[0165] 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 70…Thinning blade 71…Main cutting edge 72…First cutting edge 73…Second cutting edge 74…Tip 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 point 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 among those around 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, an outer 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, a main cutting blade disposed outside the radially thinning blade and connected to the leading edge via the outer corner, wherein the thinning blade, 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, in the cross section, of both ends of the honing, a surface connected to a first end is defined as a first surface, and a surface connected to a second end is defined as a second surface, a distance from an intersection of an extension line of the first surface and an extension line of the second surface to the first end is defined as a first width dimension L1, and a distance from the intersection to the second end is defined as a second width dimension L2, [L1 / L2] is defined as a width ratio, wherein for the thinning blade and the main cutting blade, the first surface is the rake face and the second surface is the relief face, the width ratio of the thinning blade is larger than the width ratio of the radially outer end portion of the main cutting blade connected to the outer corner, a drill.

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

3. The main cutting blade is linear, With the diameter dimension of the rotation locus of the cutting edge around the central axis being defined as the drill blade diameter, Among the main cutting edges, a region within 7% of the drill diameter directed radially inward from the outer peripheral corner is the radially outer end portion connected to the outer peripheral corner of the main cutting edge. The drill according to claim 1.

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

5. The width ratio of the portion of the main cutting edge located radially inward of the radially outer end portion is larger than the width ratio of the radially outer end portion of the main cutting edge. The drill according to any one of claims 1 to 3.

6. The width ratio of the thinning edge increases as it approaches the central axis along the blade length direction in which the thinning edge extends. The drill according to any one of claims 1 to 3.

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

8. The width ratio of the first cutting edge is maximum at the lowest point located most in the direction opposite to the drill rotation direction among the first cutting edges. The drill according to claim 2.

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

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

Images