JPH0724616A - Drill - Google Patents

Abstract

PURPOSE:To optimize work, particularly, of a CFRP raw material by obtaining high centripetal performance, and restraining a temperature rise in a cutting part of a material to be cut or the occurrence of a burr. CONSTITUTION:A cutting edge tip 24 is fixed to the tip of a drill body 21, and two chip discharging grooves 25 and 25 are formed along the drill axis O, and the tip flanks 26 and 27 are arranged. The tip cutting edges 30 and 31 composed of the first cutting edge parts 30a and 31a proceeding to the tip side in the drill axis direction as a position proceeds to the outer peripheral side from the drill rotating center C and the second cutting edge parts 30b and 31b which are continued to these first cutting edge parts 30a and 31a at intersections 32 and 33 and proceed to the base end side in the drill axis direction as a position proceeds to the drill outer peripheral side, are formed respectively along the crossing ridgeline part between the tip flanks 26 and 27 and the wall surfaces 25a and 25a turning in the drill rotating direction of the bottom surfaces of these chip discharging grooves 25 and 25. Air holes 35A and 35B are formed in the tip flanks 26 and 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a fiber reinforced plastic (FR) using a reinforcing material such as glass fiber or carbon fiber.
P) relates to a drill most suitable for drilling.

[0002]

2. Description of the Related Art Among such fiber reinforced plastics, for example, carbon fiber reinforced plastic (CFRP) is
It has many advantages over conventional metals such as specific rigidity, specific strength, fatigue resistance, wear resistance, chemical resistance, and vibration damping. The products used are applied in a wide range of fields from daily necessities to aerospace equipment. The applications are also expanding from secondary constituent members to primary constituent members, small simple shape members to large simple shape members, and small complex shape members to large complex shape members. Along with this, high processing performance has been required for tools for processing such CFRP materials.

FIGS. 4 to 8 show a conventional drill used for drilling such CFPR material. Of these drills, Figures 4-6
What is shown in FIG. 1 is a so-called gun drill, and its drill body 1 is a cylindrical driver 2 that is attached to a tool holding part of a machine tool (not shown) and is rotated around the drill axis O, and this driver 2 The shank 3 is coaxially fitted into the center hole of the shank, and the cutting edge tip 4 made of cemented carbide is fixed to the tip of the shank 3 by brazing or the like.

A cutting edge tip 4 is provided on the outer periphery of the drill body 1.
From the shank to the shank 3, a single chip discharge groove 5 is opened at the tip end surface of the cutting blade tip 4 and extends toward the base end side in the axial direction of the drill.
Are formed. The chip discharge groove 5 has a bottom surface composed of a surface 5a facing the drill rotation direction (counterclockwise direction in FIG. 6) and a surface 5b facing the drill rotation direction rear side, and as shown in FIG. It is formed so as to have a substantially V shape in a cross-sectional view orthogonal to the drill axis O. In addition, the chip discharge groove 5 is formed on the tip surface of the cutting blade tip 4.
A tip flank 6 is provided so as to extend from the opening to the rear side in the direction of rotation of the drill. Then, at the tip of the cutting blade tip 4, along the ridge portion of the intersection of the tip flank 6 and the surface 5a of the chip discharge groove 5 facing the drill rotation direction,
A tip cutting edge 7 is formed which extends from the vicinity of the center of rotation C of the tip of the drill body 1 to the outer periphery.

A hollow pipe line 8 having a circular cross section is formed in the drill body 1 so as to penetrate the drill body 1 from the driver 2 through the shank 3 to the cutting edge tip 4 along the drill axis direction. It is set up. The hollow conduit 8 is for supplying compressed air, cutting oil, etc. for cooling and discharging chips to the tip of the drill body 1, and the tip of the hollow conduit 8 is the above-mentioned tip. The clearance surface 6 is opened to form an air hole (not shown).

On the other hand, FIG. 7 shows what is called a flat flute drill, in which a drill axis O is sandwiched at the tip of a shaft-shaped drill body 11 made of cemented carbide or the like, and a drill axial direction base is provided. A pair of inclined surfaces 12, 12 is formed toward the outer peripheral side of the drill body 11 as it goes toward the end side. Further, both side portions of these inclined surfaces 12 and 12 are notched in a direction of retracting toward the base end side in the axial direction of the drill as it goes from the rotation center C of the tip of the drill body 11 toward the outer peripheral side. Notch surfaces 13 and 13 are formed so that the tip of the drill body 11 is shaped like an arrowhead. Then, at the ridge line portion of the tip of the drill body 11 where the side portions of the inclined surfaces 12, 12 facing the direction of drill rotation and the notch surfaces 13, 13 are provided with two tip cuts so as to be symmetrical with respect to the drill axis O. The blades 14 and 14 are formed, and the tip angle θ ₁ thereof is generally set to an acute angle.

Further shown in FIG. 8 is a so-called candle type drill. In this drill, two spiral chip discharge grooves 16, 1 are provided on the outer periphery of the drill body 15.
6 is formed, on the other hand, at the tip of the drill body 15, two tip cutting blades 17, 17 are provided along the ridge line intersecting with the tip surface of the drill body 15 and the bottom surface of the chip discharge grooves 16, 16. It is formed so as to be symmetrical with respect to O, and the tip angle θ ₂ of the tip cutting edges 17, 17 is generally set to be an obtuse angle.

[0008]

However, each of these drills has problems with drilling or with forming during the manufacture of the drill. That is, first, since the gun drill shown in FIGS. 4 to 6 has only one tip cutting edge 7, the force applied to the drill body 1 in the radial direction by the cutting resistance acting on the tip cutting edge 7 during cutting causes the rotation of the drill. The drill body 1 is displaced in the radial direction to cause an increase in the diameter of the hole formed, and the roundness and surface accuracy are reduced. Further, since there is only one tip cutting edge 7, the amount of cutting per one rotation of the drill is limited, so that the processing conditions are limited such that the axial feed cannot be increased.

On the other hand, in the flat flute drill as shown in FIG. 7, since the two tip cutting edges 14 and 14 are formed at the tip of the drill body 11, both tip cutting edges 14 and 1 are formed.
The above-mentioned radial component forces of the cutting resistance acting on No. 4 cancel each other out, and the amount of cutting per one rotation of the drill can be doubled in calculation as compared with the case where one tip cutting edge is used. .

However, in such a flat flute drill, it is difficult to provide an air hole formed on the flank of the tip of the gun drill. This means that by setting the tip angle θ ₁ of the tip cutting blades 14 and 14 at an acute angle, the tilt angles of the inclined surfaces 12 and 12 formed at the tip of the drill body 11 are inevitably small, and therefore, the drill body is inevitable. Even if the hollow pipe line that opens to these inclined surfaces 12 and 12 is provided in 11, the opening becomes an ellipse that recedes toward the base end side in the drill axial direction as shown by the broken line in FIG. 7. is there. For this reason, in such a flat flute drill, compressed air, cutting oil, etc. are not sufficiently supplied to the tip of the tip cutting blades 14, 14 and the cutting site becomes extremely hot, and chip clogging and cutting resistance are reduced. May cause increase. Then, particularly when the work material is the CFRP material as described above, there is a problem that the material of the work material deteriorates when the temperature of the cutting portion becomes high.

Further, as described above, the tip cutting edges 14, 14
If the tip angle θ ₁ is set to an acute angle, each tip cutting edge 14 becomes elongated in the drill axis direction. For this reason, when the feed is the same when forming a through hole in the work material, the tip cutting edge bites into the work material compared to the above-mentioned candle type drills where the tip angle is set to an obtuse angle. It takes a long time for the rear end of the tip cutting edge to completely penetrate the work material, which causes a drawback that an increase in processing time cannot be avoided. Furthermore, since the tip angle θ ₁ is an acute angle, it is difficult to secure the strength of the cutting edge and chipping is likely to occur.

On the other hand, in the case of the candle type drill shown in FIG. 8, since the tip angle θ ₂ of the tip cutting edges 17 and 17 is set to an obtuse angle, an air hole is formed in the vicinity of the center C of the drill rotation. In addition, it is possible to prevent defects such as an increase in processing time and chipping of the cutting edge caused by setting the tip angle to an acute angle. However, when the tip angle θ ₂ is made obtuse in this way, the biting of the tip tip cutting blades 17, 17 to the work material is deteriorated, and the tip tip cutting blade 17 is sharper than when the tip angle is acute. , 17 has a cutting form in which the work material is cut while expanding it, so that the guideability of the drill is generally impaired and the drill shakes during drilling, resulting in the roundness and surface accuracy of the formed hole. As a result, it is possible to further promote the deterioration of Further, since the action of spreading the work piece by the tip cutting blades 17, 17 becomes strong, burrs are likely to be generated, for example, in a crevice when forming a through hole in the work piece. And this is the CFRP
This tendency becomes particularly noticeable when drilling a material or the like. Furthermore, in such a candle type drill, since the chip discharge grooves 16 and 16 are formed in a spiral shape, the total length naturally becomes long, which causes a problem that the chip discharge property deteriorates.

In addition to these problems, in these drills, the tip cutting edge bites the work material at one point at the tip of the drill axial direction, and the cutting progresses. When processing a work material that has both hard and non-hard parts, or when making a hole on a curved surface such as a spherical surface, the point where the tip cutting edge bites into the work material There is a risk that the material may be kicked by the boundary surface or curved surface of the hardness of the material and may be displaced, resulting in a significant loss of centripetality. As a result, the drill axis is swayed, which causes an increase in the diameter of the hole to be formed, and the degree of progress at the time of drilling and the surface accuracy of the formed hole are significantly deteriorated.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has an opening on the outer peripheral surface of a drill body that is rotated around an axis and an opening at the tip surface of the drill body. Two chips discharging grooves are formed toward the base end side in the axial direction, and a tip flank is provided on the tip surface of the drill body so as to be continuous to the rear side of the opening of the chips discharging groove in the drill rotation direction. One end of the hollow conduit formed in the drill body is opened at the tip flank, and the tip of the drill body further faces the drill rotation direction of the chip discharge groove from the center of rotation of the drill body tip. And two tip cutting edges are formed along the ridge line intersecting with the tip flank, and each of these two tip cutting edges is directed toward the tip end side in the axial direction from the rotation center toward the outer peripheral side. One Blade portion and the second to reach the outer periphery of the drill body retracts to the axial direction base end side toward the outer peripheral side from the rotation center side continuous with the cutting edge of the first
And a cutting edge portion of the.

[0015]

According to the drill having such a structure, first, there are two tip cutting edges, and the component forces in the radial direction of the drill of the cutting forces acting on each tip cutting edge cancel each other out. It is possible to suppress the deviation of the drill rotation axis due to the change of the acting direction with the rotation of the drill. Further, since the number of the tip cutting edges is two, the cutting amount per one rotation of the drill can be doubled as compared with the case where the number of the tip cutting edges is one.

Further, since the first cutting edge portion is formed so as to be recessed toward the base end side in the axial direction of the drill, even if the length of the tip cutting edge is the same, as in the flat flute drill described above, The length of the tip cutting edge occupying in the drill axis direction can be shortened as much as the first cutting edge portion is recessed, as compared with a drill that entirely protrudes toward the tip side in the drill axis direction. For this reason,
It is possible to shorten the distance from the air hole provided on the tip flank to the tip of the cutting edge, and it is possible to sufficiently cool the tip of this cutting edge and the cutting part of the work material, while Processing time, such as when forming a through hole in a cutting material, can be shortened.

Further, according to the present invention, the tip angle of the second cutting edge portion is set to be small even if the length of the tip cutting edge occupying in the drill axial direction is the same as that of the candle type drill as described above. It is possible to reduce the pushing and spreading action of the work material by the tip cutting edge, and it is possible to improve the guideability of the drill in the axial direction. Further, since the pushing and spreading action is reduced on the outer peripheral side of the tip cutting edge in this way, it is also possible to suppress the occurrence of burrs at the crease when forming a through hole in the work material.

In addition to this, in the drill of the above construction, the first
While the cutting edge portion of the second cutting edge portion is formed in the direction toward the tip end side in the drill axial direction from the rotation center portion of the drill toward the outer peripheral side, the second cutting edge portion is the drill axis line toward the outer peripheral side, conversely. It is formed in the direction toward the base end side. That is, when viewed from the side of the drill body, each tip cutting edge is formed in a chevron shape in which the intersection point between the first cutting edge portion and the second cutting edge portion protrudes most toward the tip side in the drill axial direction, As a result, the inner side of these two intersections forms an M-shape that is recessed toward the base end side in the axial direction of the drill. Therefore, in the present invention, the cutting progresses while the above-mentioned two intersection points bite into the work material, and compared with the conventional drill described above that cuts into the work material with only one point, the CFPR material or the like is partially cut. Even when drilling a material having a different hardness or drilling a curved surface, it is possible to suppress the shift of the biting portion and improve centripetality.

Further, since the first cutting edge portion is recessed toward the base end side in the axial direction of the drill, the portion cut by the first cutting edge portion, conversely, protrudes in a conical shape. It is scraped off while taking the shape. During drilling, the cutting proceeds while the first cutting edge of both cutting edges engages with the conical protruding work material part, which causes the drill body to move in the radial direction. Is restrained and the swing of the drill axis is suppressed, so that the centripetal property of the drill can be further improved in combination with the above action.
Further, according to the above configuration, even if the tip angle of the second cutting edge portion is set to be small, the tip angle of the first cutting edge portion is appropriately set, so that the crossing angle of both cutting edge portions at the intersection point portion is set. Since it is possible to set a large value, it is possible to prevent the cutting edge from being chipped at the biting portion.

Regarding the tip angles of the first and second cutting blade portions, the tip angle of the first cutting blade portion is 200 ° to 2 °.
It is desirable to set in the range of 40 °, and it is desirable to set the tip angle of the second cutting edge portion in the range of 20 ° to 30 °. This is because, if the tip angle of the first cutting edge portion is larger than the above range and the tip angle of the second cutting edge portion is smaller than the above range, the first cutting edge portion and the This is because the angle of intersection with the second cutting edge portion becomes small and the cutting edge strength at the intersection point of both cutting edge portions may not be maintained. On the other hand, when the tip angle of the first cutting edge portion is smaller than the above range, the two first cutting edge portions of each tip cutting edge are arranged in a state of being close to a straight line, impairing the centripetality of the drill. May be Further, when the tip angle of the second cutting edge portion is larger than the above range, the pushing and spreading action of the second cutting edge portion becomes strong, which may cause burrs.

However, the tip angle of the cutting edge is the angle of the cutting edge when the tip cutting edge is projected in parallel on a virtual plane parallel to the drill axis, and in the present invention, as described above, the first cutting edge. Since the portion is formed in the direction toward the tip end side in the drill axial direction as it goes toward the outer peripheral side of the drill, the tip angle can theoretically be set within the range of 180 ° to 360 °.
Similarly, since the second cutting edge portion is formed in the direction toward the base end side in the drill axial direction as it goes toward the outer peripheral side of the drill, its tip angle is theoretically set in the range of 0 ° to 180 °. It is possible.

Further, when the length of the second cutting edge portion becomes long in the drill having such a structure, both of the above-mentioned two intersection points come close to the drill axis, and as a result, the work material is bitten at one point. There is a possibility that the effect of the present invention may not be obtained because it is no different from the conventional drill. On the contrary, if the length of the second cutting edge portion is shortened, the pushing and spreading action of the first cutting edge portion becomes relatively strong, which is not preferable. Therefore, the length of the second cutting edge portion is preferably set to 5 mm to 7 mm.

[0023]

1 to 3 show one embodiment of the present invention. In this embodiment, as shown in FIG. 1, the drill main body 21 has a cylindrical driver 22 that is attached to a tool holding portion of a machine tool and is rotated around a drill axis O, and is coaxial with a central hole 22a of the driver 22. The shank 23 is fitted into the shank 23, and a cutting blade tip 24 made of cemented carbide is fixed to the tip of the shank 23 by brazing.

On the outer periphery of the drill body 21, the cutting edge tip 2
No. 4, the two chip discharge grooves 25, 2 that open toward the base end side of the drill main body 21 along the drill axis direction.
5 is formed from the cutting edge tip 24 to the shank 23 so as to sandwich the drill axis O. Each of these chip discharge grooves 25, 25 has a wall surface 25a whose bottom surface faces the drill rotation direction (counterclockwise direction in FIG. 3),
A wall surface 25b facing the rear side in the direction of rotation of the drill is formed, and as shown in FIG. 3, the narrow angle is an obtuse angle when viewed from the tip end side in the direction of the drill axis. . Further, the wall surfaces 25a, 25a of the both chip discharge grooves 25, 25 facing the drill rotation direction are formed on the same plane including the drill axis O, while the wall surfaces 25b, 25b facing the rear side of the drill rotation direction. Are shaped to be parallel to each other.

On the other hand, on the tip surface of the cutting edge tip 24,
Tip flanks 26 and 27 are provided so as to be continuous from the respective openings of the chip discharge grooves 25 and 25 to the rear side in the drill rotation direction. These tip flanks 26 and 27 are respectively the tip flanks of the cutting tip 24. The first flanks 26a, 27a on the drill rotation center C side and the second flank 2 on the drill outer peripheral side
6b and 27b. Further, the first flanks 26a and 27a and the second flanks 26b and 2 are provided on the rear side of the tip flanks 26 and 27 in the drill rotation direction.
7b, and each wall surface 25a, 25b of the chip discharge groove 25, 25 is inclined toward the base end side in the drill axis direction.
Is provided with leading end surfaces 28 and 29.

Further, among these flanks, first flanks 26a and 27a are both formed in a direction intersecting the drill axis O at the same angle, and
The intersection line intersects the drill axis O, and the intersection angle is set to be an obtuse angle on the drill body 21 side. On the other hand, the second flanks 26b, 27b also intersect the drill axis O at the same angle,
Further, the intersection line is formed so as to intersect the drill axis O, but the intersection angle is set to be an acute angle on the drill body 21 side.

However, these tip flanks 26, 27 are formed asymmetrically with respect to the drill axis O in this embodiment. That is, one tip flank 26 is formed so that the drill axis O intersects the ridge of the first flank 26a, while the other tip flank 27 is formed.
Is formed at a position slightly separated from the drill rotation center C without the first flank 27a intersecting the drill axis O. Therefore, the one tip flank 26 and the other tip flank 27 are respectively the first flank 2
6a and the first flank 27a do not actually intersect, but both tip flanks 26, 27 are set so as to overlap each other in a rotation locus about the drill axis O.

Then, tip cutting edges 30 and 31 are formed at the intersecting ridges of the tip flanks 26 and 27 and the wall surfaces 25a and 25a of the chip discharge grooves 25 and 25, respectively, which face the drill rotation direction. ing. Here, as described above, the respective tip flanks 26, 27 are respectively two flanks 26.
Since they are composed of a, 26b and flanks 27a, 27b, these two tip cutting edges 30, 31 are also composed of two cutting edge portions, respectively. That is, the one tip cutting edge 30 has the first flank 26 a of the tip flank 26.
From the first cutting edge portion 30a formed at the ridge line portion intersecting with the wall surface 25a and the second cutting edge portion 30b formed at the ridge line portion intersecting the second flank 26b and the wall surface 25a. Composed. The other tip cutting edge 31 has a tip flank 27.
Of the first flank 27a and the wall surface 25a of the first cutting edge portion 31a formed on the ridge line, and the second flank 27
b and a second cutting edge portion 31b formed at the ridge portion intersecting the wall surface 25a.

Since the wall surfaces 25a, 25a connected to the tip cutting edges 30, 31 are formed on the same plane including the drill axis O as described above, the tip cutting edges 30, 31 also have the same shape. It will be included in the same plane. The tip flanks 26 and 27 are respectively the first
The flanks 26a, 27a of the second flank 26b, 27b in a direction intersecting the drill axis O at an obtuse angle.
Since they are formed in a direction intersecting with each other at an acute angle, each of the tip cutting edges 30, 31 also has its first cutting edge portion 30a, 3 respectively.
1a is formed so as to be directed toward the tip end side in the drill axial direction from the drill rotation center C portion toward the drill outer peripheral side, while the second cutting edge portions 30b and 31b are directed toward the drill outer peripheral side and in the drill axial direction base end side. Will be formed toward.

That is, each of the tip cutting edges 30, 31 has a first cutting edge portion 30a, 31a and a second cutting edge portion 30, respectively.
The intersections 32 and 33 with b and 31b are formed in a mountain shape that protrudes most toward the tip end side in the drill axis direction. Therefore, as a whole, the tip cutting edge has a drill rotation center C side in a side view orthogonal to the wall surface 25a. It will have an M-shape that is recessed on the proximal side. In this embodiment, since the two tip flanks 26, 27 are formed asymmetrically as described above, the first flank 26a of the one tip flank 26 is formed on the ridge portion of the first flank 26a. The cutting edge portion 30a extends from the intersection 32 toward the drill axis O side to a portion slightly beyond the drill rotation center C. Further, the first cutting edge portion 31a formed on the ridge side of the first flank 26b of the other tip flank 27 extends from the intersection 33 toward the drill axis O side but reaches the drill rotation center C. There is no such thing. However, since the two tip flanks 26 and 27 are set to overlap each other on the rotation locus about the drill axis O, the tip cutting edges 30 and 31 also overlap each other on the above rotation locus, and thus the above-mentioned 2 The two intersections 32, 33 are also arranged at positions axially symmetrical with respect to the drill axis O.

Here, in this embodiment, as shown in FIG. 2, the first cutting edge portion 30 is formed in the both cutting edges 30, 31.
The tip angle α formed by a and 31a is set in the range of 200 ° to 240 °, while the tip angle β formed by the second cutting edge portions 30b and 31b is set in the range of 20 ° to 30 °. . Further, the length L of each second cutting edge portion 30b, 31b is
It is set in the range of 5 mm to 7 mm.

Further, in this embodiment, the drill body 21 is branched from the hollow hole 22a of the driver 22 by the shank 23 to the cutting edge tip 24.
Two hollow conduits 34A, 34B having a circular cross section are bored so as to pass through along the drill axis direction. Then, one end of each of the hollow conduits 34A, 34B on the tip end side in the drill axis direction has the tip flanks 26, 27, respectively.
To form air holes 35A and 35B. In the present embodiment, the air hole 35A formed on the one tip flank 26 of the air holes 35A, 35B is the first and second flanks 26a, 26a which constitute the tip flank 26, It is opened on the crossing ridge line of 26b. The other tip flank 2
The air holes 35B formed in No. 7 are the first and second
The flanks 27a and 27b are formed at the intersections between the intersecting ridge lines and the tip surface 29 that is continuous with the flanks 27a and 27b.

According to the drill having such a structure, first, the tip cutting edges 30 and 31 are formed in the same plane with the drill axis O interposed therebetween so as to overlap each other in the rotation locus thereof. Since the component forces in the radial direction of the drilling force acting on the cutting forces acting on the components 31 and 31 cancel each other out, the drill body 21 is not shaken by changing the direction in which the component force acts, unlike the conventional gun drill. Further, since the two tip cutting edges 30 and 31 are provided, the amount of cutting per one rotation of the drill can be doubled as compared with the case where one cutting edge is used. Therefore, the feed is increased to improve the drilling efficiency. It is possible.

Further, since the first cutting edge portions 30a, 31a of the tip cutting edges 30, 31 are formed so as to be recessed toward the base end side in the axial direction of the drill, when the lengths of the tip cutting edges are the same. However, for example, the length of the tip cutting edges 30 and 31 occupied in the drill axial direction can be shortened as compared with the conventional flat flute drill. As a result, first, the second on the outer peripheral side of the drill
Even when the crossing angle of the cutting edge portions 30b and 31b of the is set to an acute angle, the air hole 3 opening to the tip flanks 26 and 27
The positions of 5A and 35B can be brought close to the tip cutting edges 30 and 31. For this reason, it becomes possible to sufficiently cool the tip portion of the cutting edge and the cutting portion of the work material, and particularly when the work material is a CFPR material or the like, deterioration of the material due to the high temperature of the cutting portion is effective. Can be prevented. Along with this, in the case of forming a through hole in the work material, the time from the bite of the drill hitting the work material until the rear end of the tip cutting edge 30, 31 comes out is shortened, and the machining time is greatly shortened. Can be planned.

Further, in the drill having the above-mentioned configuration, even if the lengths of the tip cutting edges 30 and 31 occupied in the drill axial direction are the same as those of the conventional candle type drill, the second cutting edge portions 30b and 31b have the same length. It is possible to set the tip angle β to an acute angle as described above. As a result, the tip cutting edge 30b,
It is possible to reduce the pushing and spreading action of the work material by 31b, and it is possible to improve the guideability of the drill in the axial direction. Further, in this way, since the spreading action of the second cutting edge portions 30b and 31b on the outer peripheral side of the drill of the tip cutting edges 30 and 31 is reduced, when the through holes are formed in the work material, It is possible to suppress the occurrence of burrs at the edge of the gap, and it is possible to perform high-quality drilling.

In addition to these, each tip cutting edge 30, 3
1, the intersection points 32 and 33 of the first cutting edge portions 30a and 31a and the second cutting edge portions 30b and 31b project to the most distal end side in the drill axial direction as described above, and the tip cutting edge as a whole has these two. The inside of the intersections 32 and 33 has an M-shape that is recessed toward the base end side in the drill axis direction. Moreover, the tip cutting edges 30 and 31 are formed so that the rotation loci about the drill axis O overlap with each other, and thus the above-mentioned 2
The two intersections 32, 33 are arranged in axial symmetry with respect to the drill axis O. That is, these two intersection points 32 and 33, which are equidistant from the drill axis O, bite into the work material at the same time, and two points are required for a drill bite into the work material with only one point as in various conventional drills. Since the cutting progresses while biting into the work material, for example, the work material is a CFPR material or the like, and there are microscopically different hardness portions as described above, or holes are formed in a curved surface such as a spherical surface. Even in such a case, it is possible to prevent such a situation that the biting parts of the tip cutting edges 30 and 31 are kicked due to the boundary surface or the curved surface of the parts having different hardnesses and are displaced, and the centripetality of the drill is significantly improved. It becomes possible.

Further, the first cutting edge portions 30a, 31a of the tip cutting edges 30, 31 have a shape recessed toward the base end side in the drill axial direction, so that they are cut by these first cutting edge portions 30a, 31a. On the contrary, the central part of the bottom of the hole is carved away while taking a conical protruding shape. Therefore, during drilling, the first cutting edge portions 30a and 31a are engaged with the central portion of the bottom of the hole protruding in a conical shape, and the cutting edge tip 24 at the tip of the drill body 21 moves in the radial direction. Cutting will proceed with the condition of being restrained, and the straight movement of the drill will be promoted. Therefore, according to the drill having the above-mentioned configuration, the above-mentioned tip cutting edge can further enhance the centripetality of the drill in combination with the action of biting at two points, so that the hole formed by suppressing the swing of the drill axis line. It is possible to prevent the diameter from expanding and to perform high-precision drilling, and it is possible to significantly improve the progress in processing and the surface accuracy of holes.

Furthermore, in the drill having the above construction, the total of the tip cutting edges is four cutting edge portions 30a, 30b, 31a, 3 in total.
1b, and therefore the chips produced by the tip cutting edge are divided into four chips from the time of production.
Further, the chips generated by the second cutting blade portions 30b and 31b are the chips discharging grooves 25 and 2 from the direction of the cutting blade portions.
Since the inside of 5 is pushed toward the inside of the drill and the chips generated by the first cutting edge portions 30a and 31a rub the insides of the chip discharge grooves 25 and 25 substantially along the axial direction of the drill, both cuttings are performed. The chips generated by the blade portion are chip discharge grooves 25,
It collides within 25 and is divided into smaller pieces. As described above, according to the drill having the above-described configuration, chips can be finely divided to facilitate smooth chip discharge, and a situation in which undivided chips are entangled with the shank 23 can be prevented. In addition to this,
The chips generated by the first cutting blade portions 30a and 31a and rubbed in the chip discharge grooves 25 and 25 along the drill axis direction also force the chips generated by the second cutting blade portions 30b and 31b. The chips are discharged along the axis of the drill, and a better chip discharging property can be obtained.

On the other hand, in the present embodiment, the tip flank 2
By forming 6 and 27 asymmetrically, also in the two tip cutting edges 30 and 31, the first cutting edge portion 30a of one of them extends from the intersection point 32 to a position exceeding the drill rotation center C, and the other The first cutting edge portion 31a is the center of rotation C of the drill.
Is stopped at a position that does not reach
0 and 31 overlap each other on the rotation locus about the drill axis O. Therefore, according to the present embodiment, a portion that does not work, such as a chisel portion of a normal twist drill, is not formed on the tip cutting edge, and therefore, the pushing force of the drill can be reduced. The advantage is obtained.

In the present embodiment, the second cutting edge portion 30b,
Even if the tip angle β of 31b is set to be smaller on the acute angle side, by setting the tip angle α of the first cutting edge portions 30a and 31a within the above range, the tip cutting edges 30 and 31 depend on the outer peripheral side of the drill. While holding down the spreading action, the two intersection points 32,
Each cutting edge portion 30a, 30b and 31a, 3 in 33
The crossing angle of 1b can be increased to prevent chipping of the cutting edge. Here, in the present invention, as described above, the tip angle α of the first cutting blade portions 30a and 31a is between 180 ° and 360 °, and the tip angle β of the second cutting blade portions 30b and 31b is 0 °.
Each can be set between 180 ° and 180 °. However, if the tip angle α is larger than 240 ° or the tip angle β is smaller than 20 °, the crossing angle becomes small accordingly, and the cutting edge strength at the intersection points 32, 33 is reduced. Is not preferable because it may not be maintained. If the tip angle α is smaller than 200 °, both cutting edge portions 30a and 31a are arranged in a state of being close to a straight line, which may impair the centripetality of the drill, while the tip angle β is 30 °. If it is larger than the above range, the above-described spreading effect may become strong, and thus both are not preferable.

Further, even if the tip angles α and β are set in this way, when the length L of the second cutting edge portions 30b and 31b becomes long, both of the two intersection points 32 and 33 approach the drill axis O. As a result, there is a possibility that the above-mentioned effects will not be obtained as the result of the conventional drill biting into the work material at one point. On the contrary, when the length L is shortened, the effect of suppressing the spreading action by setting the tip angle β of the second cutting edge portions 30b and 31b within the above range is impaired, and the first cutting edge portion is reduced. There is a possibility that the spreading action of 30a and 31a may become stronger. In this embodiment, the length L of the second cutting edge portions 30b and 31b is 5
This is the reason why it is set in the range of mm to 7 mm.

Next, the effectiveness of the present invention will be demonstrated with reference to experimental examples. In this experiment, the tip angles α and β and the length L of the second cutting edge portions 30b and 31b in the above-described embodiment are set.
3 types of drills (drill diameters are all 6.35 mm) were changed as shown in Table 1. These are Experimental Examples 1 to
Set to 3. And with these drills, thickness 11mm
Through holes were formed in the CFPR material of No. 1, and burrs at the outlet, expansion margin, surface roughness, and heat generation were measured. The results are shown in Table 1. Here, the expansion allowance means the difference between the required hole diameter and the diameter of the hole actually formed,
In this experimental example, it is shown as the difference between the drill diameter and the formed hole diameter. Further, in Table 1, the enlargement allowance shows a negative value because the work material is a CFPR material and the formed hole tends to be reduced in diameter after drilling.

On the other hand, as a comparative example to these experimental examples, a flat flute drill as shown in FIG. 7 was manufactured, and the hole diameter was 6.350 m in the CFPR material as in the above experimental example.
Drilling of m was performed and its performance was compared with the drill of the experimental example. However, in this comparative example, the tip angle θ1 is set to 35 °. The results of drilling according to this comparative example are shown in Table 1 together with the above experimental example. However, the cutting conditions for drilling according to this experimental example and comparative example are as follows:
Drill rotation speed is 2100r.pm and feed is 15mm / mi
It was n. The material of the drill is cemented carbide in both the experimental example and the comparative example.

[0044]

[Table 1]

From the results shown in Table 1, the drills of Experimental Examples 1 to 3 produced few burrs, and particularly the drill of Experimental Example 1 gave good results. In addition, in the drills of Experimental Examples 1 to 3, the expansion allowance was suppressed small and the surface roughness was also good, and in regard to these points, particularly good results could be obtained with the drill of Experimental Example 3. . Further, the heat generated at the cutting edge of the tip cutting edge and the work material was small, and no deterioration of the work material due to high temperature was observed. On the other hand, with the drill of the comparative example, the surface roughness was relatively similar to that of the drills of Experimental Examples 1 to 3, and relatively good results were obtained, but the expansion allowance tended to increase. In addition to this, burr was remarkably generated, and the heat generated by the cutting edge and the non-cutting material was also very large, and deterioration of the material due to high temperature was observed.

[0046]

As described above, according to the present invention, the two tip cutting edges formed at the tip of the drill body are respectively
A first cutting edge portion directed toward the tip end side in the drill axis direction from the center of rotation of the drill toward the tip end in the drill axis direction, and a second cutting edge portion connected to the first cutting edge portion toward the base end side in the drill axis direction toward the drill outer circumference. By being configured with the cutting edge portion, the drill bites into the work material at two points of the respective intersecting points of the first cutting edge portion and the second cutting edge portion of each tip cutting edge, and Since the cutting progresses while the first cutting edge portions engage with the central portion of the hole bottom that is cut into a conical shape, the centripetality of the drill can be greatly improved.
This prevents the drill from swinging to prevent the diameter of the hole from expanding, which enables high-precision drilling, and also makes it possible to significantly improve the degree of progress in drilling and the surface accuracy of the hole.

Further, in the present invention, since the position of the air hole can be brought close to the tip cutting edge, it is possible to prevent the cutting edge of the cutting edge and the cutting portion of the work material from being heated and raised in temperature during drilling, and to drill. Since the push-out action by the tip cutting edge portion on the outer peripheral side is reduced, it is possible to obtain advantages such as preventing the occurrence of burrs in the through holes. Therefore, according to the present invention, particularly high centripetality is required,
It is possible to provide a drill most suitable for drilling a fiber reinforced plastic such as a CFPR material in which material deterioration and burrs easily occur due to high heat.

[Brief description of drawings]

FIG. 1 is a partially cutaway side view showing an embodiment of the present invention.

2 is an enlarged side view of the drill tip of the embodiment shown in FIG. 1. FIG.

FIG. 3 is an enlarged view of a front end surface of the embodiment shown in FIG.

FIG. 4 is a side view showing a conventional gun drill.

5 is an enlarged side view of the tip portion of the gun drill shown in FIG.

6 is a cross section perpendicular to the axis O of the tip of the gun drill shown in FIG.

FIG. 7 is a side view showing a conventional flat flute drill.

FIG. 8 is a side view showing a conventional candle type drill.

[Explanation of symbols]

 21 Drill Main Body 22 Driver 23 Shank 24 Cutting Edge Tip 25 Chip Discharge Groove 26, 27 Tip Relief Surface 30, 31 Tip Cutting Edge 30a, 31a First Cutting Edge 30b, 31b Second Cutting Edge 34A, 34B Hollow Pipeline 35A, 35B Air hole O Drill axis C Drill rotation center α Tip angle of the first cutting edge portions 30a, 31a β Tip angle of the second cutting edge portions 30b, 31b L Second cutting edge portion 30b, 31b length

Claims (4)

[Claims] 1. A chip discharge groove formed on the outer periphery of a drill body rotated about an axis line, the chip discharge groove extending toward the tip end surface of the drill body and extending toward the base end side in the axial direction. A tip flank is provided on the tip face so as to be continuous to the rear side in the drill rotation direction of the opening of the chip discharge groove, and the tip flank has one end of the hollow pipe formed in the drill body. It is opened, and further, at the tip of the drill body, two pieces are provided along the intersecting ridge portion between the surface facing the drill rotation direction of the chip discharge groove from the center of rotation of the tip of the drill body and the tip flank. A tip cutting edge is formed, and each of these two tip cutting edges has a first cutting edge portion that extends toward the tip side in the axial direction from the rotation center toward the outer peripheral side, and the first cutting edge. Center of rotation above A drill comprising: a second cutting edge portion that retreats toward the base end side in the axial direction and reaches the outer circumference of the drill main body from the part side toward the outer circumference side. 2. The tip angle formed by the first cutting edge portion among the cutting edge portions forming the two leading edge cutting edges is 200 ° to 24 °.
The drill according to claim 1, wherein the drill is 0 °. 3. The tip angle formed by the second cutting edge portion among the cutting edge portions forming the two leading edge cutting edges is 20 ° to 30 °.
The drill according to claim 1 or 2, wherein 4. The drill according to claim 1, 2 or 3, wherein the length of the second cutting edge portion is 5 mm to 7 mm.