JP7663064B2 - drill - Google Patents

Description

The present invention relates to a drill.

A conventional drill is known that has a rake face, a flank face, and a cutting edge (see, for example, Patent Document 1).
The drill of Patent Document 1 has a rake face having a return face and a rake face portion. The return face is located between the outer peripheral surface and the rake face portion. As shown in FIG. 6 of Patent Document 1, the return face is curved 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 face extends toward the rotation direction as it moves radially outward. Such a return face 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).

International Publication No. 2019/021785

This type of drill has the following problems:
When drilling a through hole in a workpiece with a drill, 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. The long chips C are easily bent or spread radially outward by centrifugal force as the drill 100 rotates around the central axis O, and are easily wrapped around the drill 100.

In more detail, as shown in FIG. 14, the chips C generated by the conventional drill 100 are soft and bent as shown by the broken line with two dots in FIG. 14, and have parts P11 that cannot be separated and parts P12 that are tangled. In particular, when the cutting diameter of the drill 100 is large, the thread-like chips C tend to stretch more easily.

One of the objectives of the present invention is to provide a drill that can effectively dispose of chips and prevent extended chips from wrapping around the drill.

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

In the present invention, the "radial rake angle 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 with a "-" added. 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 with a "+" added.

According to the drill of the present invention, the radial rake angle of the second cutting edge located 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 they stretch into a thread-like shape, the centrifugal force of the rotating drill prevents the chips from bending or spreading radially outward. In other words, the chips are easily stretched toward the rear end along the axial direction of the drill, but are difficult to bend, which prevents the stretched chips from wrapping around the drill.

In addition, work hardening of the chips makes it easier for cracks to form in the chips, and makes it easier for elongated chips to break apart. This prevents the chips from growing too long, allowing them to be properly processed.

In addition, the second cutting face extends in the opposite direction to the drill rotation direction as it moves radially outward. 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.

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

In the drill, the cutting face has a thinning rake face arranged radially inward of the first cutting face, the cutting edge has a thinning blade connected to the radially inner end of the first cutting edge and extending along the tip edge of the thinning rake face, the boundary ridge connecting the thinning rake face and the first rake face is a ridge portion that is convex toward the rotation direction of the drill and is connected to the cutting edge , the honing extends over the thinning blade, the first cutting edge and the second cutting edge, and it is preferable that the honing width of the honing increases along the blade length direction in which the cutting edge extends as it approaches the portion where the boundary ridge connecting the thinning rake face and the first cutting face is connected to the cutting edge.

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

In the drill, it is preferable that the radial rake angle of the second cutting edge is greater than or equal to -33° and less than or equal to -27°.

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 are more likely to be discharged toward the rear end along the axial direction of the drill, which further improves chip disposal.

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. This can prevent problems such as unstable cutting by the second cutting edge and chipping of the cutting edge.

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

If 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 ensured to be stable and large. This 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 along the axial direction of the drill, further improving chip disposal.

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 prevents the cutting resistance when the second cutting edge cuts the workpiece from becoming too large, and prevents problems such as unstable cutting by the second cutting edge or chipping of the cutting edge.

In the drill, 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 has a shoulder strength improving surface formed along the shoulder portion, and the shoulder strength improving surface is preferably disposed adjacent to the outer periphery and the relief surface.

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 at the outer periphery of 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 reduces chipping and breakage near the shoulder.

In the drill, the body preferably has a leading edge located at the ridge where the outer peripheral surface and the second rake face are connected, and the leading edge preferably has an outer peripheral honing formed along the leading edge.

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 chips produced by cutting with the second cutting edge are guided radially outward and tend to scrape against the leading edge. This configuration suppresses chipping and breakage near the leading edge.

The drill of the above aspect of the present invention allows for good chip disposal and prevents extended chips from wrapping around the drill.

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

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 has a generally cylindrical shape 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."

In this embodiment, the body 1 is removably attached to the shank 2. In other words, the drill 10 is a replaceable-tip drill. However, this is not limited to the above, and the drill 10 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.

[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. In 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.
A direction perpendicular to the central axis O is called a radial direction. Of the radial directions, a direction approaching the central axis O is called a radially inner direction, and a direction away from the central axis O is called a 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 hole drilling is called the drill rotation direction T. The direction opposite 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.

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

〔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.

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.

The chip discharge groove 4 is a groove that opens to the tip surface 3 and the outer peripheral surface 8 of the body 1 and extends from the tip surface 3 toward the rear end. Specifically, the chip discharge groove 4 extends in the direction opposite to the drill rotation direction as it moves from the tip surface 3 toward the axial rear end. A plurality of chip discharge grooves 4 are provided on the body 1 at intervals in the circumferential direction. In this embodiment, two chip discharge grooves 4 are provided at equal intervals in the circumferential direction.

The rake face 5 is located at least at the tip of the chip discharge 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 .

The thinning rake surface 51 is located at the radially inner end of the tip of the chip discharge groove 4. In this embodiment, the thinning rake surface 51 is a substantially triangular planar surface.

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

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

The radially outer end of the second rake face 53 is connected to the outer peripheral surface 8 via the 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 in the approximate axial direction along the radially outer edge 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.

The second rake face 53 extends in the opposite direction to the drill rotation direction T (i.e., in 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. In other words, the second rake face 53 is a negative radial rake surface over the entire radial area. Therefore, the ridge portion (leading edge 12) where the radial outer end of the second rake face 53 and the end of the outer peripheral surface 8 in the drill rotation direction T connect forms an obtuse angle in cross section.

The radially inner end of the second rake face 53 is connected to the radially outer end of the first rake face 52 via a boundary ridge 54. The boundary ridge 54 is a ridge portion that is convex toward the drill rotation direction T and extends in the approximate axial direction. Specifically, the boundary ridge 54 extends in the opposite direction to the drill rotation direction as it moves toward the rear end side in the axial direction.

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 of the second flank 62 (inclination corresponding to the clearance angle) is larger than the amount of displacement of 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.

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, may be simply referred to as a front view of the drill), the first flank surface 61 has a band shape extending in the radial direction (an approximately polygonal shape that is elongated in the radial direction), and the second flank surface 62 has an approximately fan shape.
In the present 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.

As shown in Figures 1 to 4, the thinning surface 11 is disposed on the tip surface 3. The thinning surface 11 is disposed adjacent to the clearance surface 6 in the direction opposite to the drill rotation. In this embodiment, the thinning surface 11 is disposed adjacent to the second clearance surface 62 in the direction opposite to the drill rotation. The thinning surface 11 extends toward the rear end side in the axial direction as it approaches the direction opposite to the drill rotation. 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 clearance surface 6. The radial inner end of the thinning surface 11 is connected to the thinning rake surface 51.

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

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

The first cutting edge 72 is disposed between both radial ends of the cutting edge 7. The first cutting edge 72 is disposed on the ridge 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. When viewed from the front of the drill, the first cutting edge 72 forms a concave curved shape recessed in the direction opposite to the rotation 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 rotation direction T of the drill.

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

The second cutting edge 73 also extends radially outward and axially toward the rear end. The radially inner end of the second cutting edge 73 connects with the radially outer end of the first cutting edge 72. In this embodiment, the connection between the second cutting edge 73 and the first cutting edge 72 forms a convex curve or convex V-shape that protrudes toward the drill rotation direction T.

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 angle value 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 angle value may be expressed by adding "+".

In the present 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°. That is, the radial rake angle θ of the second cutting edge 73 is equal to or greater than 27° and equal to or less than 33° on the negative angle side.
The radial dimension W of the second cutting edge 73 is 4% to 7% of the diameter D (i.e., blade diameter D) of the rotation locus (virtual circle) when the cutting edge 73 is rotated around the central axis O.

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 rake face 52 and the second rake face 53 in the cross-sectional view of the body 1 (drill 10) (i.e., the opening angle in the cross-sectional view of the boundary ridge 54) (see FIG. 11 of the second embodiment described later).

As shown in Figures 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. In other words, the honing 7a has a convex curved shape in a cross section perpendicular to the blade length direction of the cutting edge 7.

As shown in FIG. 5, the honing width of the honing 7a of the cutting edge 7, i.e., 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 7 a 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 .

As shown in FIGS. 1 to 4 , the outer peripheral surface 8 has a margin 81 and a chamfered surface 82 .
The margin 81 is disposed at the end of the outer peripheral surface 8 in the drill rotation direction T, and extends in the approximate axial direction. Specifically, the margin 81 extends in the counter-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 the 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 counter-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.

The second chamfering surface 82 is disposed adjacent to the margin 81 in the direction opposite to the drill rotation. 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.

As shown in Figures 1, 3, and 6, the shoulder 9 is disposed on the outer periphery of the tip of the body 1. The shoulder 9 extends around the central axis O. Specifically, the shoulder 9 extends slightly toward the rear end as it moves in the direction opposite to the rotation of the drill.

The shoulder 9 has a shoulder strength improving surface 9a formed along the shoulder 9. The shoulder strength improving surface 9a is formed, for example, by honing. In this embodiment, the shoulder strength improving surface 9a is a chamfer honed surface. That is, the shoulder strength improving surface 9a is chamfered. 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.
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.

1 to 4, the leading edge 12 is disposed on a ridge portion where the margin 81 (outer peripheral surface 8) and the second rake face 53 are connected. The leading edge 12 extends in a substantially axial direction, and more specifically, extends in a 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 toward the rear end side in the axial direction.

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. In other words, the peripheral honing 12a has a convex curved shape in a cross section perpendicular to the extension 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.

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

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 into the shank 2. In this way, the body 1 is fixed to the shank 2.

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 contacts a rotation receiving portion (not shown) that faces the drill rotation direction T of the shank 2.

[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, accelerating hardening of the chips.

Figure 7 is a schematic diagram showing the drilling of the workpiece M by the drill 10 of this embodiment. According to this embodiment, the chips C become hard, so that even if the chips C stretch 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. In other words, the chips C are easily stretched toward the rear end along the axial direction of the drill 10, but are not easily bent, so that the stretched chips C are prevented from wrapping around the drill 10.

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. This prevents the chips C from growing too long, and allows the chips C to be processed well.

In more detail, 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.

In addition, in this embodiment, the second rake 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 rake face 53 and are easily guided radially outward. This action also improves chip disposal.

Therefore, according to this embodiment, the chips are effectively processed and the extended chips are prevented from wrapping around the drill 10.

In this embodiment, the cutting edge 7 has a honing 7 a, and the honing 7 a 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.

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. 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.

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.

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 when the second cutting edge 73 cuts the workpiece from becoming too large. This makes it possible to prevent problems such as unstable cutting by the second cutting edge 73 and chipping of the cutting edge.

In this embodiment, the radial dimension W of the second cutting edge 73 is 4% or more and 7% or less of the diameter D (blade diameter D) of the rotational 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 of the second cutting edge 73 is ensured. 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.

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.

In addition, in this embodiment, the angle α formed between the first cutting edge 72 and the second cutting edge 73 in a front view of the drill is equal to or greater than 145° and equal to or less than 155°.
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 from becoming too large when the second cutting edge 73 cuts the workpiece.

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 of the tip of the body 1 where the peripheral speed (i.e., cutting speed) is the fastest and where the processing load is likely to be large during drilling. This suppresses chipping, breakage, and the like in the vicinity of the shoulder 9.

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, the occurrence of large burrs at the opening edge of the drilled hole can be suppressed.

In this embodiment, the leading edge 12 also has a peripheral honing 12a.
As described above, in this embodiment, the second rake 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.

Second Embodiment
Next, a drill 20 according to a second embodiment of the present invention will be described with reference to Figures 9 to 11. In this embodiment, the same components as those in the above-described embodiment are given the same names and reference numerals, and the description thereof will be omitted.

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.

[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.

Figure 12 is a partial side view showing a modified example of the drill 10 described in the first embodiment above. In the modified example shown in Figure 12, as in 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 between the thinning edge 71 and the first cutting edge 72.

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

The honing width of the honing 7a at the connection between the thinning edge 71 and the first cutting edge 72 increases along the cutting edge 7 blade length direction as it approaches the boundary ridge 55 where the thinning rake face 51 and the first rake face 52 are connected, and is maximum on the boundary ridge 55. This boundary ridge 55 is a ridge that is convex in the drill rotation direction T, and extends radially inward as it approaches the rear end side in the axial direction.

The honing width of the honing 7a of the second cutting edge 73 is maximum at the connection between the first cutting edge 72 and the second cutting edge 73, or at the connection between the second cutting edge 73 and the leading edge 12. In the example shown in FIG. 12, the honing width of the honing 7a of the second cutting edge 73 at the connection between the first cutting edge 72 and the second cutting edge 73 is approximately the same as the honing width at the connection between the second cutting edge 73 and the leading edge 12.

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 each ridges that are convex toward the drill rotation direction T and connect 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 connect. 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 connect.

The modified drill 10 shown in FIG. 12 also provides the same effects as the first embodiment described above. And because the honing width of the honing 7a is increased at least at 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.

In the first and second embodiments described above, the drills 10 and 20 are two-blade twist drills, but this is not limiting. The drills 10 and 20 may be one-blade or three or more-blade drills.

The present invention may be implemented by combining the various configurations described in the above-mentioned embodiments and modifications, etc., without departing from the spirit of the present invention, and addition, omission, substitution, and other modifications of configurations are possible. Furthermore, the present invention is not limited to the above-mentioned embodiments, etc., but is limited only by the scope of the claims.

The drill of the present invention allows for good chip disposal and prevents extended chips from wrapping around the drill. Therefore, it has industrial applicability.

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

Claims (6)

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. 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 . 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 . 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 . 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 . 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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