drill

Abstract

To provide a drill capable of having chips processed well and suppressing twining of extended chips around the drill.SOLUTION: A drill 10 comprises a body 1 extending in an axial direction around a central axis O; the body 1 has a chip discharge groove 4, a rake face, a flank 6, and a cutting edge 7 disposed on a ridge line part where the rake face and the flank 6 are connected to each other; the rake face has a first rake face and a second rake face disposed on a radial direction outer side of the first rake face, and connected to an outer peripheral surface 8; the second rake face extends toward a direction opposite to a drill rotating direction T around the central axis O as the second rake face approaches the radial direction outer side; the cutting edge 7 has a first cutting edge 72 extending along a tip edge of the first rake face, and a second cutting edge 73 coupled to an end part on the radial direction outer side of the first cutting edge 72, and extending along a tip edge of the second rake face; the second cutting edge 73 has a linear shape or concave curve shape; and an axial direction rake angle θ of the second cutting edge 73 is supposed to be a negative angle over an entire length of the second cutting edge 73.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a drill. [Background technology]

[0002] 2. Description of the Related Art A conventional drill is known that has a rake face, a flank face, and a cutting edge (for example, see Patent Document 1). The drill of Patent Document 1 has a rake face having a return surface and a rake face portion. The return surface is located between the outer peripheral surface and the rake face portion. As shown in FIG. 6 of Patent Document 1, the return surface curves toward the opposite end to the rotation direction with respect to a straight line perpendicular to the outer peripheral surface. Therefore, the radially outer end of the return surface extends toward the rotation direction as it moves radially outward. Such a return surface enhances the sharpness of the radially outer end of the cutting edge and prevents work hardening of the workpiece surface (i.e., the inner peripheral surface of the machined hole). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 021785 Summary of the Invention [Problem to be solved by the invention]

[0004] This type of drill has the following problems: When a drill is used to drill a through hole in a workpiece, chips generated by the thinning blade located at the radially inner end of the cutting blade tend to be easily broken into small pieces. On the other hand, as shown in Fig. 13 of the present application, after the thinning blade 101 penetrates the workpiece M, chips C generated by the cutting blade portion 102 located radially outward from the thinning blade 101 tend to be long and thread-like. When the drill 100 rotates around the central axis O, the long chips C are bent or spread radially outward due to centrifugal force, and tend to wrap around the drill 100.

[0005] Specifically, as shown in Fig. 14, the chips C generated by the conventional drill 100 are soft and bent as indicated by the two-dot chain line in Fig. 14, and have portions P11 that cannot be separated and tangled portions P12. In particular, when the cutting diameter of the drill 100 is large, the thread-like chips C tend to be more elongated.

[0006] An object of the present invention is to provide a drill that can effectively dispose of chips and prevent elongated chips from wrapping around the drill. [Means for solving the problem]

[0007] One aspect of the present invention is a drill having a body extending in an axial direction about a central axis, the body having a chip discharge groove that opens to a tip surface and an outer peripheral surface of the body and extends from the tip surface to a rear end side, a rake face that is located at least at the tip of the chip discharge groove and faces the drill rotation direction around the central axis, a relief surface that is disposed on the tip surface, and a cutting edge that is disposed on a ridge portion where the rake face and the relief surface are connected, the rake face being a first rake face and a second rake face that is disposed radially outward of the first rake face. and a second rake face connected to the outer peripheral surface, the second rake face extending in a direction opposite to the rotation direction of the drill around the central axis as it moves radially outward, the cutting edge having a first cutting edge extending along a tip edge of the first rake face and a second cutting edge connected to a radially outer end of the first cutting edge and extending along a tip edge of the second rake face, the second cutting edge being linear or concavely curved, and the radial rake angle of the second cutting edge being a negative angle over the entire length of the second cutting edge. a boundary ridgeline connecting the first cutting face and the second cutting face is a ridgeline portion that is convex toward the rotation direction of the drill and is connected to the cutting edge, the cutting edge has a honing formed on the cutting edge, the honing extends across the first cutting edge and the second cutting edge, and a honing width of the honing increases as it approaches a portion where the boundary ridgeline and the cutting edge are connected along a cutting edge length direction in which the cutting edge extends. .

[0008] In the present invention, the "radial rake angle (radial rake) of the second cutting edge" refers to the angle formed between the second cutting edge and a virtual line passing through (a part of) the second cutting edge and the central axis when the drill is viewed from the tip side along the axial direction. In addition, the "radial rake angle of the second cutting edge is a negative angle" refers to the case where the second cutting edge extends in the opposite direction to the drill rotation direction as it moves radially outward. When the radial rake angle is a negative angle, the angle value may be expressed by adding "-". Also, unlike the present invention, the "radial rake angle of the second cutting edge is a positive angle" refers to the case where the second cutting edge extends in the drill rotation direction as it moves radially outward. When the radial rake angle is a positive angle, the angle value may be expressed by adding "+".

[0009] According to the drill of the present invention, the radial rake angle of the second cutting edge arranged at the radial outer end of the cutting edges is a negative angle over the entire cutting length of the second cutting edge. This increases the cutting resistance when the second cutting edge cuts the workpiece, and applies a large load to the chips generated, promoting hardening of the chips. By hardening the chips, even if the chips are elongated into a thread-like shape, the chips are prevented from bending or spreading radially outward due to the centrifugal force of the rotation of the drill. In other words, the chips are easily elongated toward the rear end along the axial direction of the drill, but are difficult to bend, so that problems such as the elongated chips wrapping around the drill are suppressed.

[0010] In addition, the work hardening of the chips makes it easier for cracks to occur in the chips, and the elongated chips are easily broken up. This prevents the chips from growing too long, and allows the chips to be properly processed.

[0011] In addition, the second cutting face extends radially outward in the opposite direction to the drill rotation direction. Therefore, chips generated by cutting with the second cutting edge come into contact with the second cutting face and are easily guided radially outward. This action also improves chip disposal.

[0012] Therefore, according to the present invention, the chips can be effectively disposed of and the long chips can be prevented from wrapping around the drill.

[0015] In the drill, the rake face has a thinning rake face arranged radially inward of the first rake face, the cutting edge has a thinning edge connected to an end portion of the first cutting edge on the radially inner side and extending along a tip edge of the thinning rake face, and a boundary ridge line connecting the thinning rake face and the first rake face. teeth, A ridge portion that is convex toward the rotation direction of the drill and is connected to the cutting edge ,before The honing extends across the thinning edge, the first cutting edge, and the second cutting edge, and a honing width of the honing is, along a blade length direction in which the cutting edges extend, The thinning rake face and the first rake face are connected. It is preferable that the thickness increases as it approaches the portion where the boundary ridge line and the cutting edge are connected.

[0016] The portion where the boundary ridge between each rake face and the cutting edge are connected has a convex shape facing the rotation direction of the drill, so cutting resistance is likely to concentrate. According to the above configuration, the honing width is increased at the portion of the cutting edge that is connected to each boundary ridge, so that the occurrence of chipping of the cutting edge at each connected portion can be suppressed. In other words, the chipping resistance of the cutting edge 7 is further improved.

[0017] In the drill, it is preferable that a radial rake angle of the second cutting edge is not less than −33° and not more than −27°.

[0018] When the radial rake angle of the second cutting edge is -27° or less (i.e., 27° or more on the negative angle side), the cutting resistance when the second cutting edge cuts the workpiece is stably increased, the chips are more likely to harden, and they are more likely to be discharged toward the rear end along the axial direction of the drill, thereby further improving chip disposal.

[0019] When the radial rake angle of the second cutting edge is -33° or more (i.e., 33° or less on the negative angle side), the cutting resistance when the second cutting edge cuts the workpiece can be prevented from becoming too large. Therefore, problems such as unstable cutting by the second cutting edge and chipping of the cutting edge can be prevented.

[0020] In the drill, it is preferable that a radial dimension of the second cutting edge is 4% to 7% of a diameter of a rotation locus when the cutting edge is rotated around the central axis.

[0021] When the radial dimension of the second cutting edge is 4% or more of the diameter of the rotation path of the cutting edge (i.e., the blade diameter), the cutting edge length of the second cutting edge is stably secured to be large, which stably increases the cutting resistance when the second cutting edge cuts the workpiece, making it easier for the chips to harden and to be discharged toward the rear end side along the axial direction of the drill, thereby improving chip disposal.

[0022] When the radial dimension of the second cutting edge is 7% or less of the diameter of the rotation path of the cutting edge (i.e., the blade diameter), the blade length of the second cutting edge is prevented from becoming too long. This makes it possible to prevent the cutting resistance when the second cutting edge cuts the workpiece from becoming too large, and to prevent problems such as unstable cutting by the second cutting edge and chipping of the cutting edge.

[0023] In the drill, it is preferable that the body has a shoulder portion disposed on the outer periphery of the tip of the body and extending around the central axis, the shoulder portion having a shoulder strength enhancing surface formed along the shoulder portion, the shoulder strength enhancing surface being disposed adjacent to the outer periphery and the relief surface.

[0024] The shoulder strength-improving surface is formed, for example, by honing. The shoulder strength-improving surface increases the strength of the shoulder, which is the part of the outer periphery at the tip of the body where the circumferential speed (i.e., cutting speed) is the fastest during drilling and where the processing load is likely to be large. This suppresses chipping and breakage near the shoulder.

[0025] In the drill, it is preferable that the body has a leading edge that is located on a ridge where the outer peripheral surface and the second cutting face are connected, and the leading edge has an outer peripheral honing formed along the leading edge.

[0026] As described above, in the present invention, the second cutting face extends radially outward in the opposite direction to the drill rotation direction, so that the chips generated by cutting with the second cutting edge are guided radially outward and tend to scrape against the leading edge. With the above configuration, chipping and breakage near the leading edge are suppressed. Effect of the Invention

[0027] According to the drill of the above aspect of the present invention, chips are effectively disposed of, and elongated chips can be prevented from wrapping around the drill. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a perspective view showing a drill according to a first embodiment. [Diagram 2] FIG. 2 is a front view showing the drill of the first embodiment. [Diagram 3] FIG. 3 is a side view showing the drill of the first embodiment. [Figure 4] FIG. 4 is a side view showing the drill of the first embodiment. [Diagram 5] FIG. 5 is an enlarged view of a portion V in FIG. [Figure 6] FIG. 6 is an enlarged perspective view showing the VI arrow in FIG. [Figure 7] FIG. 7 is a schematic diagram showing the state of chips when a workpiece is drilled with the drill of the first embodiment. [Figure 8] FIG. 8 is an image showing chips generated when a hole is drilled in a workpiece by the drill of the first embodiment. [Figure 9] FIG. 9 is a front view showing the drill of the second embodiment. [Figure 10]FIG. 10 is a side view showing the drill of the second embodiment. [Figure 11] FIG. 11 is a cross-sectional view (transverse cross-sectional view of the body) showing a drill according to the second embodiment. [Figure 12] FIG. 12 is a partial side view showing a modification of the drill of the first embodiment. [Figure 13] FIG. 13 is a schematic diagram showing the state of chips when a workpiece is drilled with a conventional drill. [Figure 14] FIG. 14 is an image showing chips generated when a hole is drilled into a workpiece using a conventional drill. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] First Embodiment A drill 10 according to a first embodiment of the present invention will be described with reference to FIGS. As shown in Fig. 1, the drill 10 includes at least a body 1. The body 1 is generally cylindrical and centered on a central axis O. In this embodiment, the drill 10 includes the body 1 and a shank 2. The body 1 and the shank 2 are arranged side by side in the direction in which the central axis O extends. The body 1 may also be referred to as a "blade portion."

[0030] In this embodiment, the body 1 is detachably attached to the shank 2. That is, the drill 10 is a replaceable-tip drill. However, the drill 10 is not limited to this, and may include only the body 1 and not the shank 2. In this case, the drill 10 may be referred to as a drill head.

[0031] [Direction definition] In this embodiment, the direction in which the central axis O of the drill 10 extends is referred to as the axial direction. Within the axial direction, the direction from the shank 2 to the body 1 is referred to as the axial tip side or simply the tip side, and the direction from the body 1 to the shank 2 is referred to as the axial rear end side or simply the rear end side. The direction perpendicular to the central axis O is called the radial direction. Of the radial directions, the direction approaching the central axis O is called the radially inner direction, and the direction away from the central axis O is called the radially outer direction. The direction rotating around the central axis O is called the circumferential direction. Among the circumferential directions, the direction in which the drill 10 is rotated during drilling is called the drill rotation direction T. The opposite direction to the drill rotation direction T may be called the counter-drill rotation direction. In this embodiment, the direction in which a cutting edge 7 of the body 1, which will be described later, extends may be referred to as the blade length direction.

[0032] 〔shank〕 The shank 2 is columnar and extends in the axial direction about a central axis O. The shank 2 is removably held, for example, by a spindle of a machine tool or a chuck of a drilling machine (hereinafter, abbreviated to the spindle or the like) (not shown). The drill 10 cuts into the workpiece with the body 1 to perform a hole drilling process by feeding the shank 2 axially toward the tip side while rotating the shank 2 by the spindle or the like in a drill rotation direction T.

[0033] 〔body〕 1 to 4, the body 1 extends in the axial direction about a central axis O. In this embodiment, the diameter of the body 1, that is, the blade diameter D, is, for example, 16 mm to 40 mm.

[0034] The body 1 has a tip surface 3 facing the tip side of the body 1, an outer peripheral surface 8 facing radially outward of the body 1, a chip discharge groove 4, a rake face 5, a clearance face 6, a thinning surface 11, a cutting edge 7, a shoulder portion 9, a leading edge 12, an attachment portion 13, a screw hole 14, and a rotation support portion 15.

[0035] The chip discharge groove 4 is a groove that opens to the front end surface 3 and the outer peripheral surface 8 of the body 1 and extends from the front end surface 3 toward the rear end. Specifically, the chip discharge groove 4 extends in the counter drill rotation direction as it moves from the front end surface 3 toward the rear end 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 pitch in the circumferential direction.

[0036] The rake face 5 is located at least at the tip of the chip flute 4 and faces the rotation direction T of the drill. The rake face 5 has a thinning rake face 51 , a first rake face 52 , and a second rake face 53 .

[0037] The thinning rake face 51 is disposed at a radially inner end of the tip of the chip discharge groove 4. In this embodiment, the thinning rake face 51 has a substantially triangular flat surface.

[0038] The first rake face 52 is disposed radially outward of the thinning rake face 51. In other words, the thinning rake face 51 is disposed radially inward of the first rake face 52. In this embodiment, the first rake face 52 is a concave curved surface. Although not particularly shown, in a cross-sectional view perpendicular to the central axis O (hereinafter, may be simply referred to as a transverse cross-sectional view), the first rake face 52 forms a concave curved shape recessed in the direction opposite to the drill rotation direction. The dimension of the first rake face 52 along the radial direction (i.e., the width dimension) is larger than the dimension of the thinning rake face 51 along the radial direction.

[0039] The second rake face 53 is disposed radially outward of the first rake face 52. In this embodiment, the second rake face 53 is flat. However, the present invention is not limited to this, and the second rake face 53 may be a concave curved surface. In this case, in a cross-sectional view, the second rake face 53 has a concave curved shape recessed in the direction opposite to the drill rotation direction. The dimension of the second rake face 53 along the radial direction is smaller than the dimension of the thinning rake face 51 along the radial direction, and is also smaller than the dimension of the first rake face 52 along the radial direction.

[0040] The radially outer end of the second rake face 53 is connected to the outer peripheral surface 8 via a ridge portion (leading edge 12). That is, the second rake face 53 is connected to the outer peripheral surface 8. The second rake face 53 extends substantially in the axial direction along the radially outer edge portion of the wall surface of the chip discharge groove 4 that faces the drill rotation direction T. Specifically, the second rake face 53 extends in the opposite direction to the drill rotation direction as it moves toward the rear end side in the axial direction.

[0041] The second rake face 53 extends in the opposite direction to the drill rotation direction T (i.e., the opposite drill rotation direction) as it moves radially outward. More specifically, the second rake face 53 extends in the opposite drill rotation direction as it moves radially outward over the entire radial area of ​​the second rake face 53. That is, the second rake face 53 is a negative radial rake surface over the entire radial area. For this reason, a ridge portion (leading edge 12) where the radial outer end of the second rake face 53 and the end of the outer circumferential surface 8 in the drill rotation direction T connect forms an obtuse angle in cross section.

[0042] The radially inner end of the second cutting face 53 is connected to the radially outer end of the first cutting face 52 via a boundary ridgeline 54. The boundary ridgeline 54 is a ridgeline portion that is convex toward the drill rotation direction T and extends substantially in the axial direction. Specifically, the boundary ridgeline 54 extends in the opposite direction to the drill rotation direction as it approaches the rear end side in the axial direction.

[0043] The flank 6 is disposed on the tip face 3. The flank 6 has a first flank 61 and a second flank 62 disposed adjacent to the first flank 61 in the counter drill rotation direction. The first flank 61 extends toward the rear end in the axial direction as it approaches the direction opposite to the drill rotation direction. The second flank 62 extends toward the rear end in the axial direction as it approaches the direction opposite to the drill rotation direction, and has a larger clearance angle than the first flank 61. That is, the amount of axial displacement per unit length along the circumferential direction in the second flank 62 (inclination equivalent to the clearance angle) is larger than the amount of displacement in the first flank 61. Note that in this embodiment, the clearance angle of the first flank 61 is, for example, 6° or more and 8° or less.

[0044] As shown in FIG. 2, in a front view of the body 1 (drill 10) seen from the tip side along the axial direction (hereinafter, sometimes simply referred to as a front view of the drill), the first flank 61 has a radially extending band shape (an approximately polygonal shape that is elongated in the radial direction), and the second flank 62 has an approximately fan shape. In this embodiment, the flank 6 has two inclined surfaces (the first flank 61 and the second flank 62) having different clearance angles, but is not limited thereto. The flank 6 may be formed of, for example, a single inclined surface, or may have three or more inclined surfaces arranged in the circumferential direction.

[0045] As shown in Figs. 1 to 4, the thinning surface 11 is disposed on the tip surface 3. The thinning surface 11 is disposed adjacent to the flank 6 in the counter-drill rotation direction. In this embodiment, the thinning surface 11 is disposed adjacent to the second flank 62 in the counter-drill rotation direction. The thinning surface 11 extends toward the rear end side in the axial direction as it approaches the counter-drill rotation direction. The amount of axial displacement per unit length along the circumferential direction in the thinning surface 11 (inclination equivalent to the clearance angle) is greater than the amount of displacement in the flank 6. The radial inner end of the thinning surface 11 is connected to the thinning rake face 51.

[0046] The cutting edge 7 is disposed on a ridge portion where the rake face 5 and the flank 6 are connected. A plurality of cutting edges 7 are provided on the body 1 at intervals in the circumferential direction. In this embodiment, two cutting edges 7 are provided at equal intervals in the circumferential direction. That is, the drill 10 of this embodiment is a two-blade twist drill.

[0047] The cutting edge 7 has a thinning edge 71 , a first cutting edge 72 , and a second cutting edge 73 . The thinning edge 71 is disposed at the radially inner end of the cutting edge 7. The thinning edge 71 is disposed at the ridge where the thinning rake face 51 and the first flank face 61 are connected. That is, the thinning edge 71 extends along the tip edge of the thinning rake face 51. When viewed from the front of the drill, the thinning edge 71 extends along the radial direction from near the central axis O toward the radially outward side. Furthermore, as the thinning edge 71 extends toward the radially outward side, it extends toward the rear end side in the axial direction. In this embodiment, the thinning edge 71 is straight.

[0048] The first cutting edge 72 is disposed between both ends of the cutting edge 7 in the radial direction. The first cutting edge 72 is disposed on a ridge portion where the first rake face 52 and the first clearance face 61 are connected. That is, the first cutting edge 72 extends along the leading edge of the first rake face 52. The first cutting edge 72 forms a concave curved shape recessed in the direction opposite to the rotational direction of the drill when viewed from the front of the drill. The first cutting edge 72 also extends toward the rear end side in the axial direction as it moves radially outward. The radially inner end of the first cutting edge 72 is connected to the radially outer end of the thinning edge 71. In this embodiment, the connection portion between the first cutting edge 72 and the thinning edge 71 forms a convex curved shape protruding toward the rotational direction T of the drill.

[0049] The second cutting edge 73 is disposed at the radially outer end of the cutting edge 7. The second cutting edge 73 is disposed at a ridge portion where the second rake face 53 and the first clearance face 61 are connected. That is, the second cutting edge 73 extends along the leading edge of the second rake face 53. In this embodiment, the second cutting edge 73 is linear. However, this is not limited thereto, and the second cutting edge 73 may be concavely curved. When the second cutting edge 73 is concavely curved, it is preferable that the second cutting edge 73 has a concave curve with a large radius of curvature (i.e., a large R) recessed in the direction opposite to the drill rotation. When the second cutting edge 73 is concavely curved, the maximum dimension by which the second cutting edge 73 is recessed relative to a virtual straight line passing through the radial inner end of the second cutting edge 73 (the connection portion with the first cutting edge 72) and the radial outer end (the connection portion with the leading edge 12 and the shoulder portion 9) is, for example, 0.001 mm or more and 0.015 mm or less.

[0050] The second cutting edge 73 extends radially outward and then axially rearward. A radially inner end of the second cutting edge 73 is connected to a radially outer end of the first cutting edge 72. In this embodiment, the connection portion between the second cutting edge 73 and the first cutting edge 72 forms a convex curve or a convex V shape that protrudes toward the drill rotation direction T.

[0051] 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. In this embodiment, the "radial rake angle (radial rake) θ of the second cutting edge 73" refers to the angle θ formed between the second cutting edge 73 and a virtual straight line VL passing through (a part of) the second cutting edge 73 and the central axis O when the drill 10 is viewed from the tip side along the axial direction, as shown in FIG. 2. In addition, the "radial rake angle θ of the second cutting edge 73 is a negative angle" refers to a case in which the second cutting edge 73 extends in the opposite direction to the drill rotation direction T as it moves radially outward. When the radial rake angle θ is a negative angle, the numerical value of the angle may be expressed by adding "-". Also, unlike this embodiment, the "radial rake angle θ of the second cutting edge 73 is a positive angle" refers to a case in which the second cutting edge 73 extends in the drill rotation direction T as it moves radially outward. When the radial rake angle θ is a positive angle, the numerical value of the angle may be expressed by adding "+".

[0052] In this embodiment, the radial rake angle θ of the second cutting edge 73 is not less than −33° and not more than −27°. That is, the radial rake angle θ of the second cutting edge 73 is not less than 27° and not more than 33° on the negative angle side. Furthermore, the dimension W of the second cutting edge 73 along the radial direction is 4% to 7% of the diameter D of the rotation locus (imaginary circle) when the cutting edge 7 is rotated around the central axis O (ie, the blade diameter D).

[0053] In the front view of the drill shown in Fig. 2, the angle α formed between the first cutting edge 72 and the second cutting edge 73 is, for example, 145° or more and 155° or less. Note that the angle α corresponds to the angle formed between the first cutting face 52 and the second cutting face 53 in the cross-sectional view of the body 1 (drill 10) (i.e., the opening angle of the boundary ridge 54 in the cross-sectional view) (see Fig. 11 of the second embodiment described later).

[0054] As shown in Figs. 1 to 4, the cutting edge 7 has a honing 7a formed on the cutting edge of the cutting edge 7. The honing 7a extends over at least the entire length of the second cutting edge 73. In this embodiment, the honing 7a extends over the thinning edge 71, the first cutting edge 72, and the second cutting edge 73. In this embodiment, the honing 7a of the cutting edge 7 is a round honing. That is, the honing 7a has a convex curved shape in a cross section perpendicular to the blade length direction of the cutting edge 7.

[0055] As shown in FIG. 5, the honing width of the honing 7a of the cutting edge 7, that is, the width dimension of the honing 7a along the direction perpendicular to the blade length direction of the cutting edge 7, is maximum at the connecting portion between the first cutting edge 72 and the second cutting edge 73. Specifically, in this embodiment, the honing width of the honing 7a of at least the first cutting edge 72 is maximum at the connecting portion between the first cutting edge 72 and the second cutting edge 73. The honing width of the honing 7a of the second cutting edge 73 is also maximum at the connecting portion between the first cutting edge 72 and the second cutting edge 73. However, this is not limited to this, and although not particularly shown, the honing width of the honing 7a of the second cutting edge 73 may be maximum at the connecting portion between the second cutting edge 73 and the leading edge 12. The honing width of the honing 7a at the connecting portion between the first cutting edge 72 and the second cutting edge 73 is larger than the honing width of the honing 7a of the thinning edge 71. In this embodiment, the honing width of the honing 7a at the connection portion between the first cutting edge 72 and the second cutting edge 73 increases as it approaches the boundary ridge 54 along the blade length direction of the cutting edge 7, and is maximum on the boundary ridge 54.

[0056] As shown in FIGS. 1 to 4, the outer circumferential surface 8 has a margin 81 and a chamfered surface . The margin 81 is disposed at an end of the outer peripheral surface 8 in the drill rotation direction T, and extends substantially in the axial direction. Specifically, the margin 81 extends in the direction opposite to the drill rotation direction as it approaches the rear end side in the axial direction. The margin 81 and the second rake face 53 are connected to each other via a ridge portion (leading edge 12). That is, the margin 81 is connected to the second rake face 53. The margin 81 is disposed adjacent to the leading edge 12 in the direction opposite to the drill rotation direction. The margin 81 is located on a cylindrical rotation trajectory (not shown) obtained by rotating the leading edge 12 around the central axis O. The margin 81 forms an arc shape centered on the central axis O in a cross-sectional view perpendicular to the central axis O.

[0057] The second chamfering surface 82 is disposed adjacent to the margin 81 in the counter drill rotation direction. The second chamfering surface 82 is disposed radially inward from the margin 81. During drilling, the second chamfering surface 82 faces the inner peripheral surface of the machined hole in the workpiece with a radial gap therebetween.

[0058] 1, 3 and 6, the shoulder 9 is disposed on the outer periphery of the front end of the body 1. The shoulder 9 extends around the central axis O. Specifically, the shoulder 9 extends slightly toward the rear end in the direction opposite to the rotational direction of the drill.

[0059] The shoulder portion 9 has a shoulder portion strength improving surface 9a formed along the shoulder portion 9. The shoulder portion strength improving surface 9a is formed, for example, by honing. In this embodiment, the shoulder portion strength improving surface 9a is a chamfer honing. That is, the shoulder portion strength improving surface 9a is chamfered. The honing width of the shoulder portion strength improving surface 9a is smaller than the honing width of the honing 7a of the cutting edge 7. The shoulder strength improving surface 9a is disposed adjacent to the outer peripheral surface 8 and the flank 6. More specifically, the shoulder strength improving surface 9a is disposed between the tip end of the margin 81 and the radially outer end of the first flank 61, and is connected to the margin 81 and the first flank 61, respectively.

[0060] As shown in Figures 1 to 4, the leading edge 12 is disposed on a ridge where the margin 81 (outer peripheral surface 8) and the second rake face 53 are connected. The leading edge 12 extends substantially in the axial direction, and more specifically, extends in the direction opposite to the drill rotation direction as it approaches the rear end side in the axial direction. The leading edge 12 has a negative radial rake angle over the entire length in the extension direction. The leading edge 12 may be back tapered. In this case, the leading edge 12 is positioned slightly radially inward as it moves toward the rear end in the axial direction.

[0061] As shown in Figures 5 and 6, the leading edge 12 has a peripheral honing 12a formed along the leading edge 12. In this embodiment, the peripheral honing 12a of the leading edge 12 is a round honing. That is, the peripheral honing 12a has a convex curved shape in a cross section perpendicular to the extending direction of the leading edge 12. The honing width of the peripheral honing 12a of the leading edge 12 is smaller than the honing width of the honing 7a of the cutting edge 7.

[0062] 1 to 4, the mounting portion 13 protrudes toward the rear end from the rear end surface of the body 1. The mounting portion 13 is generally columnar and centered on a central axis O. The mounting portion 13 is inserted into a mounting hole (not shown) of the shank 2.

[0063] The screw hole 14 is a through hole that passes through the body 1 in the axial direction. A plurality of screw holes 14 (a pair in this embodiment) are provided at intervals from each other in the circumferential direction. A screw member (not shown) is inserted into the screw hole 14 and screwed to the shank 2. In this way, the body 1 is fixed to the shank 2.

[0064] The rotation support portion 15 is disposed between the chip discharge groove 4 and the second cutting surface 82 in the circumferential direction. The rotation support portion 15 faces in the direction opposite to the drill rotation direction. A plurality of rotation support portions 15 (a pair in this embodiment) are provided at intervals from each other in the circumferential direction. The rotation support portion 15 comes into contact with a rotation receiving portion (not shown) facing the drill rotation direction T of the shank 2.

[0065] [Effects of this embodiment] According to the drill 10 of the present embodiment described above, the radial rake angle θ of the second cutting edge 73 disposed at the radial outer end of the cutting edge 7 is a negative angle over the entire cutting length of the second cutting edge 73. This increases the cutting resistance when the second cutting edge 73 cuts the workpiece, and applies a large load to the generated chips, facilitating hardening of the chips.

[0066] 7 is a schematic diagram showing the drilling of a workpiece M by the drill 10 of this embodiment. According to this embodiment, the chips C are hardened, so that even if the chips C are elongated into a thread-like shape, the chips C are prevented from bending or spreading radially outward due to the centrifugal force of the rotation of the drill 10. That is, the chips C are easily elongated toward the rear end along the axial direction of the drill 10 and are not easily bent, so that the elongated chips C are prevented from wrapping around the drill 10.

[0067] In addition, by work-hardening the chips C, cracks can be easily generated in the chips C, and the elongated chips C can be easily broken. Therefore, the chips C are prevented from elongating too long, and the chips C can be well processed.

[0068] Specifically, as shown in Fig. 8, the chips C generated by the drill 10 of this embodiment are hard to bend due to work hardening, and tend to elongate in a substantially fixed direction as shown by the straight two-dot chain line in Fig. 8. Moreover, instead of having bent portions, the chips C have divided portions P1. In particular, when the cutting diameter D of the drill 10 is large as in this embodiment, the effect of being able to effectively process the elongated chips C becomes more pronounced compared to conventional drills.

[0069] In this embodiment, the second cutting face 53 extends radially outward in the opposite direction to the drill rotation direction T. Therefore, chips generated by cutting with the second cutting edge 73 come into contact with the second cutting face 53 and are easily guided radially outward. This action also improves chip disposal.

[0070] Therefore, according to this embodiment, the chips are effectively disposed of, and the long chips are prevented from wrapping around the drill 10.

[0071] In this embodiment, the cutting edge 7 has a honing 7a, and the honing 7a is disposed over at least the entire length of the second cutting edge 73 in the blade length direction. As described above, in this embodiment, the cutting resistance of the second cutting edge 73 is actively increased to improve chip disposal. As described above, the honing 7a is applied over the entire cutting length of the second cutting edge 73, thereby suppressing chipping and breakage of the second cutting edge 73 and extending the tool life of the drill 10.

[0072] In this embodiment, the honing 7a extends across the thinning edge 71, the first cutting edge 72, and the second cutting edge 73. The honing width of the honing 7a at least on the first cutting edge 72 is maximum at the connection portion between the first cutting edge 72 and the second cutting edge 73. In this embodiment, the honing width of the honing 7a on the second cutting edge 73 is also maximum at the connection portion between the first cutting edge 72 and the second cutting edge 73. The connecting portion between the first cutting edge 72 and the second cutting edge 73 has a convex shape facing the drill rotation direction T, so cutting resistance is likely to concentrate thereon. According to the above configuration, the honing widths of the first cutting edge 72 and the second cutting edge 73 are maximized at the connecting portion between the first cutting edge 72 and the second cutting edge 73, so that chipping of the cutting edge or the like can be suppressed at this connecting portion.

[0073] In this embodiment, the radial rake angle θ of the second cutting edge 73 is equal to or greater than −33° and equal to or less than −27°. When the radial rake angle θ of the second cutting edge 73 is -27° or less (i.e., 27° or more on the negative angle side), the cutting resistance when the second cutting edge 73 cuts the workpiece is stably increased, the chips are more likely to harden, and are more likely to be discharged toward the rear end along the axial direction of the drill 10, thereby further improving chip disposal.

[0074] When the radial rake angle θ of the second cutting edge 73 is −33° or more (i.e., 33° or less on the negative angle side), it is possible to prevent the cutting resistance from becoming too large when the second cutting edge 73 cuts the workpiece. Therefore, it is possible to prevent problems such as unstable cutting by the second cutting edge 73 and chipping of the cutting edge.

[0075] In this embodiment, the radial dimension W of the second cutting edge 73 is 4% to 7% of the diameter D (blade diameter D) of the rotation path when the cutting edge 73 is rotated around the central axis O. When the radial dimension W of the second cutting edge 73 is 4% or more of the blade diameter D, a stable and large blade length is ensured for the second cutting edge 73. This stably increases the cutting resistance when the second cutting edge 73 cuts the workpiece, making it easier for the chips to harden and to be discharged toward the rear end side along the axial direction of the drill 10, thereby improving chip disposal.

[0076] When the radial dimension W of the second cutting edge 73 is 7% or less of the blade diameter D, the blade length of the second cutting edge 73 is prevented from becoming too long. This prevents the cutting resistance when the second cutting edge 73 cuts the workpiece from becoming too large, and prevents problems such as unstable cutting by the second cutting edge 73 and chipping of the cutting edge.

[0077] In this embodiment, the angle α formed between the first cutting edge 72 and the second cutting edge 73 is equal to or greater than 145° and equal to or less than 155° in a front view of the drill. If the angle α is equal to or greater than 145°, the cutting resistance when the second cutting edge 73 cuts the workpiece can be stably increased. If the angle α is 155° or less, it is possible to prevent the cutting resistance when the second cutting edge 73 cuts the workpiece from becoming too large.

[0078] In this embodiment, the shoulder 9 has a shoulder strength improving surface 9 a adjacent to the outer circumferential surface 8 and the flank surface 6 . The shoulder strength improving surface 9a enhances the strength of the shoulder 9, which is the part of the outer periphery at the tip of the body 1 where the circumferential speed (i.e., cutting speed) is the fastest during drilling and where the processing load is likely to be large. This suppresses chipping, breakage, and the like near the shoulder 9.

[0079] In this embodiment, the honing width of the shoulder strength improving surface 9a is smaller than the honing width of the honing 7a of the cutting edge 7. In particular, the honing width of the shoulder strength improving surface 9a is smaller than the honing width of the honing 7a at the radial outer end of the second cutting edge 73. In this case, when the drill 10 is used to drill a hole in a workpiece, it is possible to prevent large burrs from being generated at the opening edge of the drilled hole.

[0080] Also in this embodiment, the leading edge 12 has a peripheral honing 12a. As described above, in this embodiment, the second cutting face 53 extends radially outward in the opposite direction to the drill rotation direction T, so that chips generated by cutting with the second cutting edge 73 are guided radially outward and tend to scrape against the vicinity of the leading edge 12. With the above configuration, chipping, breakage, and the like near the leading edge 12 are suppressed.

[0081] <Second embodiment> Next, a drill 20 according to a second embodiment of the present invention will be described with reference to Fig. 9 to Fig. 11. In this embodiment, the same configurations as those in the above-mentioned embodiment are given the same names and reference numerals, and the description thereof will be omitted.

[0082] 9 to 11, in the drill 20 of this embodiment, the body 1 and the shank 2 are integrally formed from a single member. That is, the drill 20 of this embodiment is a solid drill. Note that, for example, the drill 20 may have a configuration in which the body 1 and the shank 2 are manufactured separately from each other and integrated by brazing or the like. The drill 20 of this embodiment also provides the same effects as the drill 10 of the above-described first embodiment.

[0083] [Other configurations included in the present invention] The present invention is not limited to the above-described embodiment, and the configuration may be modified within the scope of the present invention, for example as described below.

[0084] Fig. 12 is a partial side view showing a modified example of the drill 10 described in the first embodiment. In the modified example shown in Fig. 12, similarly to the first embodiment, the honing 7a extends across the thinning edge 71, the first cutting edge 72, and the second cutting edge 73. In this modified example, the honing width of the honing 7a on the thinning edge 71 is maximum at the connection portion between the thinning edge 71 and the first cutting edge 72.

[0085] 12, the honing width of honing 7a on first cutting edge 72 is maximum at the connection portion between thinning edge 71 and first cutting edge 72, or at the connection portion between first cutting edge 72 and second cutting edge 73. In the example shown in FIG.

[0086] Furthermore, the honing width of honing 7a at the connection portion between thinning edge 71 and first cutting edge 72 increases along the cutting edge 7's blade length direction as it approaches boundary ridge 55 where thinning rake face 51 and first rake face 52 are connected, and is maximum on boundary ridge 55. This boundary ridge 55 is a ridge portion that is convex in the drill rotation direction T, and extends radially inward toward the rear end side in the axial direction.

[0087] Furthermore, the honing width of honing 7a of second cutting edge 73 is maximum at the connection portion between first cutting edge 72 and second cutting edge 73 or at the connection portion between second cutting edge 73 and leading edge 12. In the example shown in Fig. 12, the honing width of honing 7a of second cutting edge 73 at the connection portion between first cutting edge 72 and second cutting edge 73 is approximately the same as the honing width at the connection portion between second cutting edge 73 and leading edge 12.

[0088] More specifically, the boundary ridge 55 connecting the thinning rake face 51 and the first rake face 52, and the boundary ridge 54 connecting the first rake face 52 and the second rake face 53 are ridges that are convex toward the drill rotation direction T and are connected to the cutting edge 7. The honing width of the honing 7a increases along the cutting edge length direction in which the cutting edge 7 extends, as it approaches the portion where the boundary ridge 55 and the cutting edge 7 are connected. The honing width of the honing 7a increases along the cutting edge length direction in which the cutting edge 7 extends, as it approaches the portion where the boundary ridge 54 and the cutting edge 7 are connected.

[0089] 12, the drill 10 of the modified example shown in FIG. 12 also provides the same effects as those of the first embodiment described above. Since the honing width of the honing 7a is increased at least in the portions where the cutting edge 7 intersects (connects) with the boundary ridges 54, 55, the chipping resistance of the cutting edge 7 is further improved.

[0090] In the above-described first and second embodiments, the drills 10 and 20 are twist drills with two blades, but the present invention is not limited to this. The drills 10 and 20 may be drills with one blade or three or more blades.

[0091] The present invention may be combined with the various configurations described in the above-mentioned embodiments and modifications, and may include additions, omissions, substitutions, and other modifications, without departing from the spirit of the present invention. The present invention is not limited to the above-mentioned embodiments, but is limited only by the claims. [Industrial Applicability]

[0092] INDUSTRIAL APPLICABILITY The drill of the present invention can effectively dispose of chips and prevent elongated chips from wrapping around the drill, and therefore has industrial applicability. [Explanation of symbols]

[0093] 1. Body 3…Tip surface 4...Chip discharge groove 5…Scooping surface 6…Flank 7…Cutting edge 7a…Honing 8...Outer surface 9...Shoulder area 9a…Shoulder strength improvement surface 10,20…Drill 12…Leading edge 12a…Outer honing 51...Thinning rake face 52…First scooping face 53…Second scooping face 54,55…Boundary ridge 71...Thinning blade 72…First cutting edge 73…Second cutting edge D: Diameter of the cutting edge when it is rotated around the central axis (blade diameter) O…Central axis T…Drill rotation direction W…Dimension along the radial direction of the second cutting edge θ…Radial rake angle

Claims

1. A drill having a body extending axially about a central axis, The body includes: a chip discharge groove that opens to a front end surface and an outer circumferential surface of the body and extends from the front end surface to a rear end side; a rake face located at least at a tip end of the chip discharge groove and facing a drill rotation direction around the central axis; A flank surface disposed on the tip surface; A cutting edge is disposed on a ridge portion where the rake face and the flank face are connected, The rake face is A first rake face; A second rake surface is disposed radially outward of the first rake surface and connected to the outer circumferential surface, The second rake face extends in a direction around the central axis opposite to the drill rotation direction as it moves radially outward, The cutting blade is a first cutting edge extending along a leading edge of the first rake face; a second cutting edge connected to a radially outer end of the first cutting edge and extending along a tip edge of the second cutting face; The second cutting edge is linear or concavely curved, A radial rake angle of the second cutting edge is a negative angle over the entire length of the second cutting edge, a boundary ridge line connecting the first rake face and the second rake face is a ridge line portion that is convex toward the rotation direction of the drill and is connected to the cutting edge; The cutting blade has a honing formed on a cutting edge of the cutting blade, the honing extends across the first cutting edge and the second cutting edge; The honing width of the honing increases along the blade length direction in which the cutting edge extends as it approaches a portion where the boundary ridge line and the cutting edge are connected. drill.

2. The rake face has a thinning rake face disposed radially inward of the first rake face, The cutting edge has a thinning edge that is connected to a radially inner end of the first cutting edge and extends along a tip edge of the thinning rake face, A boundary ridge line connecting the thinning rake face and the first rake face is a ridge line portion that is convex toward the rotation direction of the drill and is connected to the cutting edge, The honing extends across the thinning edge, the first cutting edge, and the second cutting edge; The honing width of the honing increases along the cutting edge length direction in which the cutting edge extends as it approaches a portion where the boundary ridge line connecting the thinning rake face and the first rake face is connected to the cutting edge. The drill of claim 1.

3. The radial rake angle of the second cutting edge is -33° or more and -27° or less. A drill according to claim 1 or 2.

4. A dimension along a radial direction of the second cutting edge is 4% to 7% of a diameter of a rotation path when the cutting edge is rotated around the central axis. A drill according to any one of claims 1 to 3.

5. the body has a shoulder disposed on a distal outer periphery of the body and extending about the central axis; the shoulder portion has a shoulder strength improving surface formed along the shoulder portion, The shoulder strength improving surface is disposed adjacent to the outer circumferential surface and the relief surface. A drill according to any one of claims 1 to 4.

6. The body has a leading edge disposed on a ridge portion where the outer circumferential surface and the second rake surface are connected, the leading edge having a peripheral honing formed along the leading edge; A drill according to any one of claims 1 to 5.

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