JP2003225816A - Drill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure strength particularly in the outer circumferential end side of a cutting edge 5 while suppressing the deterioration of sharpness of the whole of the cutting edge 5, and prevent the shortening of a tool life due to wear and breakage even in a harsh machining condition such as high-speed dry cutting. <P>SOLUTION: In a drill, a chip discharge groove 3 extending toward a rear end side is formed in the tip part outer circumference of a drill body 1 rotated around an axis O, and the cutting edge 5 is formed in a crossing ridgeline part between an inner wall face 4 facing the drill rotating direction of the chip discharge groove 3 and a tip flank relief 2 of the drill body 1. The cutting edge 5 is formed so that a rake angle γ in a cross section perpendicular to the cutting edge 5 is gradually increased from the inner circumference of the drill body 1 toward an outer circumference side until it reaches a transition point X on the cutting edge 5, and it is gradually decreased toward the outer circumference side from the transition point X. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drill capable of smooth and stable drilling even under severe working conditions such as high speed dry cutting.

[0002]

2. Description of the Related Art A chip discharge groove extending toward the rear end is formed on the outer periphery of the tip of a drill body rotated around an axis.
As a drill in which a cutting edge is formed at the ridge line intersecting the inner wall surface of the chip discharge groove facing the direction of rotation of the drill and the flank of the tip of the drill main body, for example, Japanese Patent No. 267412 has hitherto been known.
The one described in Japanese Patent Publication No. 4 is known. Further, as a drill intended to cope with the severe machining conditions using the dry type or a very small amount of cutting oil as described above, for example, a drill disclosed in Japanese Patent Laid-Open No. 2000-198011 has been proposed. In other words, in the drill described in this publication, on the outer peripheral side of the cutting edge formed at the tip of the drill body, an outer corner cutting edge is formed that recedes in the drill rotation direction at an angle from the middle part of the cutting edge. The outer corner cutting edge and the margin of the outer periphery of the drill body can have an obtuse angle, which prevents the outer edge of the cutting edge from being chipped even under the above processing conditions. Is possible.

[0003]

By the way, in such a drill, the rake angle of the cutting edge in a cross section orthogonal to the cutting edge, that is, the right angle rake angle of the cutting edge is usually
It is designed to gradually increase from the axis side of the drill body, that is, from the inner peripheral side to the outer peripheral side.
The drills proposed in the above two publications are no exception (see, for example, drills E and F described later and FIG. 11). Therefore, in the drill described in the former publication in which the cutting edge is formed in a straight line except for the thinning portion on the inner peripheral side of the drill body, the rake angle is the maximum at the outer peripheral end of the cutting edge, and conversely of the cutting edge. Since the cutting edge angle is the smallest, the cutting speed becomes the most distant from the axis line that is the center of rotation of the drill body, and the cutting speed becomes the highest, so even in the drilling process that is the dry high-speed cutting At the outer peripheral edge, it becomes difficult to secure the strength of the cutting edge, which makes it highly likely that chipping or chipping will occur in the cutting edge, and that flank wear progresses rapidly.

On the other hand, in the drill described in the latter publication in which an outer corner cutting edge that retracts in the drill rotation direction is provided on the outer peripheral side of the cutting edge, in the outer corner cutting edge, the radial rake angle of the cutting edge is on the negative angle side. Although the right angle rake angle of the cutting edge becomes smaller as it increases, this rake angle is gradually increased toward the outer peripheral side, so it is sufficient even for the severe conditions described above. In order to secure a high cutting edge strength, the rake angle must be reduced over the entire length of the cutting edge.
For this reason, the cutting edge becomes less sharp, which leads to an increase in cutting resistance.In severe cutting conditions such as high-speed dry cutting, wear progresses markedly and the service life may be shortened in some cases. There is a possibility that excessive torque may be applied due to the increase in resistance and the drill body may be broken.

The present invention has been made under such a background, and while suppressing the deterioration of the sharpness of the entire cutting edge, especially at the outer peripheral end side of the cutting edge, the strength is secured, and high speed dry cutting or the like is performed. It is an object of the present invention to provide a drill capable of preventing shortening of tool life due to wear and breakage even under severe machining conditions.

[0006]

In order to solve the above-mentioned problems and to achieve such an object, the present invention extends toward the rear end side on the outer periphery of the front end portion of a drill body rotated around an axis. In a drill in which a chip discharge groove is formed, and a cutting edge is formed at the ridge line intersecting the inner wall surface of the chip discharge groove that faces the drill rotation direction and the tip flank of the drill body, The rake angle in the cross section orthogonal to the blade is gradually increased from the inner circumference of the drill body toward the outer circumference to reach the transition point on the cutting edge, and on the outer circumference side from this transition point, the outer circumference is approached. It is characterized in that the rake angle is gradually reduced. Therefore, in the drill configured in this way, the right angle rake angle of the cutting edge on the inner peripheral side from the transition point increases as it goes to the outer peripheral side, so that it is possible to maintain good cutting performance and keep the cutting resistance low. On the other hand, the rake angle is reduced on the outer peripheral side of this inflection point, so the cutting edge angle is increased, which ensures cutting edge strength and chipping or chipping.
It is possible to suppress the early progress of flank wear and the like.

Here, the transition point at which the rake angle of the cutting edge changes from the inner circumference toward the outer circumference from a gradually increasing tendency to a gradually decreasing tendency is the rotation of the cutting edge from the axis toward the radially outer circumference. It is preferably located within 70-90% of the radius. This is because if this transition point is located on the inner circumference side of the axis from 70% of the radius of gyration of the cutting edge, the rake angle gradually decreases toward the outer circumference, and the cutting edge portion becomes longer and the cutting resistance of the entire cutting edge increases. If the transition point is on the outer peripheral side from the axis of 90% of the turning radius of the cutting edge, the rake angle gradually decreases and the cutting edge is too short. This is because the cutting edge strength on the outer peripheral side may not be reliably ensured.

Further, a convex curved cutting edge portion having a curved shape which is convex in the drill rotation direction is formed on the outer peripheral end side of the cutting edge, and on the inner peripheral side of the convex curved cutting edge portion. Is the outer periphery of the convex curved cutting edge portion when a concave curved cutting edge portion is formed that is concave toward the rear side in the drill rotation direction and smoothly connects to the convex curved cutting edge portion. On the side, that is, at the intersection with the margin of the outer periphery of the drill body, the intersection angle can be increased to further improve the cutting edge strength and prevent chipping and chipping, while the convex curved cutting edge On the inner peripheral side, since the curved edge from the concave curved cutting edge portion to the outer peripheral edge of the cutting edge from the convex curved cutting edge portion is formed into a smooth curved shape, the cutting edge is angled at its intermediate portion. The drill described in the latter publication is retracted rearward in the direction of rotation of the drill. Without such chips in the inner periphery of the cutting edge is divided as sufficiently curled so as to involve the chip on the inner circumferential side by the concave-curved cutting edge,
It becomes possible to process smoothly. Further, in this case, the rake angle is changed from the gradually increasing tendency to the gradually decreasing tendency by arranging the transition point at the inflection portion between the concave curved cutting edge portion and the convex curved cutting edge portion. By this, the stress generated in the cutting edge at this transition point can be dispersed,
It is also possible to prevent a situation where stress is concentrated at this transition point and damage is caused by severe cutting conditions in high-speed dry cutting.

Incidentally, the rake angle γ of the cutting edge which changes gradually from the inner circumference to the outer circumference in the gradual increase / decrease tendency before and after the transition point is measured from the axis toward the outer circumference in the radial direction. At a position in the range of 37.5% or more and less than 82.6% of the turning radius r of the cutting edge, an angle y approximated by the following formula 1 with respect to a ratio x of the radius from the axis of this position to the turning radius r is obtained. Within a range of ± 7 ° of the cutting edge, a range of 82.6% to 100% of the turning radius r of the cutting edge is within a range of ± 7 ° of an angle y approximated by the following equation 2 for the ratio x: It is desirable to be able to change each. That is, when the rake angle γ of this cutting edge exceeds the range of Expressions 1 and 2, there is a possibility that the cutting edge has a portion where the cutting edge angle becomes too small, and the cutting blade is likely to be damaged at that portion particularly in high-speed dry cutting. On the other hand, on the contrary, when the value is below the range of Expressions 1 and 2, there is a possibility that cutting resistance increases at that portion, wear of the cutting edge is promoted, or excessive torque is generated. In addition, TiN, at least on the surface of the tip of the drill body,
By coating a hard coating such as TiCN or TiAlN, the wear resistance of the tip of the drill body can be improved and the life of the drill body can be further extended.

[0010]

[Equation 3]

[0011]

[Equation 4]

[0012]

1 to 9 show one embodiment of the present invention. In the present embodiment, the drill body 1 is formed of a hard material such as cemented carbide into a substantially cylindrical shape centered on the axis O, and its tip portion is constant from the tip flank 2 toward the rear end side. A pair of chip discharge grooves 3 and 3 which are twisted rearward in the drill rotation direction T at a twist angle of are formed symmetrically with respect to the axis O. The cutting edges 5 and 5 are respectively formed on the ridges where the inner wall surfaces 4 and 4 facing each other and the above flank 2 intersect.
Are formed. In addition, at the tip of the drill body 1, the outer peripheral surface, the tip flank 2, the chip discharge groove 3, Ti
A hard coating such as N, TiCN, TiAlN is coated.

Here, the inner wall surface 4 has a convex curve which is located on the outer peripheral side thereof, intersects with the margin portion 6, and is convex in the drill rotation direction T as shown in FIG. 2 in a cross section orthogonal to the axis O. The first convex curved surface portion 7 to be formed and the inner peripheral side of the first convex curved surface portion 7, and in the cross section, the drill rotation direction T
And a first concave curved surface portion 8 having a concave curved shape which is concave toward the rear side of the concave convex curved surface portion 7, and the convex and concave curved surfaces formed by the cross sections of the first convex and concave curved surface portions 7 and 8 are connected so as to be smoothly in contact with each other at a contact point P1. Has been. Further, in the present embodiment, the inner wall surface 9 of the chip discharge groove 3 facing the rear side in the drill rotation direction T is also positioned on the outer peripheral side thereof and reaches the heel portion 10, and the above-mentioned cross section is convex in the rear side in the drill rotation direction T. From the second convex curved surface portion 11 forming a convex curve and the second concave curved surface portion 12 located on the inner peripheral side of the second convex curved surface portion 11 and having a concave curved shape whose cross section is concave in the drill rotation direction T side. The second uneven curved surface portion 1 is configured.
The above-mentioned concave and convex curves formed by 1 and 12 are also connected so as to be in contact with each other smoothly at the contact point P2, and the concave curves formed by the cross sections of the first and second concave curved surface portions 8 and 12 of both inner wall surfaces 4 and 9 are contact points. At P3, they are smoothly contacted and continuous. The outer peripheral surface of the land portion, which extends from the margin portion 6 to the rear side in the drill rotation direction T to the heel portion 10, is formed in a cylindrical surface shape receding from the margin portion 6 toward the inner peripheral side by one step.

Further, in the present embodiment, in the above-mentioned cross section, the convex-concave curves formed by the first and second convex-concave curved surface portions 7, 8, 11, 12 respectively have radii R1 centered on points C1 to C4.
The center C1 of the convex arc formed by the first convex curved surface portion 7 is the intersection of the first convex curved surface portion 7 and the margin portion 6, that is, the outer circumference of the inner wall surface 4. It is located on the inner circumference side of the straight line Q1 in contact with the margin portion 6 at the end 13, and the center C3 of the arc formed by the second convex curved surface portion 11 is the circle formed by the outer circumference end 13 around the axis O and the second. At the intersection 14 with the extension line of the arc formed by the convex curved surface portion 11, it is also positioned on the inner peripheral side of the straight line Q2 tangent to the circle. Therefore, the first convex curved surface portion 7
Is convex to the drill rotation direction T side with respect to the first virtual straight line S1 connecting the axis O and the outer peripheral end 13 of the inner wall surface 4, and the tangent line of the first convex curved surface portion 7 at the outer peripheral end 13 is the outer peripheral side. So that it extends toward the rear side of the drill rotation direction T toward
While being inclined with respect to the virtual straight line S1, the straight line Q1 orthogonal to the first virtual straight line S1 intersects the straight line Q1 at an obtuse angle. The second convex curved surface portion 11 is also convex toward the rear side in the drill rotation direction T with respect to the straight line connecting the intersection with the heel portion 10 and the axis O. On the other hand, the centers C2 and C4 of the arc formed by the first and second concave curved surface portions 8 and 12
Since these arcs are in contact with each other at the contact point P3, both of them are located on an extension line of a straight line passing through the contact point P3 from the axis O. Further, since the contact point P3 serves as the groove bottom of the chip discharge groove 3, in the present embodiment, the circle passing through the contact point P3 with the axis O as the center is the core thickness circle of the drill body 1, and the diameter of the core thickness circle, The core thickness d of the drill body 1 is 0.15 × D to the diameter of the circle formed by the outer peripheral end 15 of the cutting edge 5 around the axis O, that is, the outer diameter D of the cutting edge 5.
It is set in the range of 0.3 × D.

The contact point P1 of the convex-concave curve formed by the first convex-concave curved surface portions 7 and 8 is located on the outer peripheral side of the circle having the diameter of 2/3 of the outer diameter D of the cutting edge 5 about the axis O. More preferably, it is located on the outer peripheral side of a circle having a diameter of 5/6 of the outer diameter D about the axis O. Further, the size of the recess of the first recessed curved surface portion 8 toward the rear side in the drill rotation direction T is such that the recess amount L1 from the first virtual straight line S1 is −0.06 × with respect to the outer diameter D of the cutting edge 5. It is set in the range of D to 0, and the size of the recess of the second recessed curved surface portion 12 toward the drill rotation direction T is the first in the above cross section.
The dent amount L2 from the second virtual straight line S2 orthogonal to the virtual straight line S1 with the axis O is set to fall within the range of −0.06 × D to 0.06 × D. However, the amount of these recesses L
1 and L2 are straight lines parallel to the first and second virtual straight lines S1 and S2, respectively, and a straight line which is in contact with the concave curve formed by the first and second concave curved surface portions 8 and 12 and the first and second virtual straight lines S1 and S1, respectively. S
2 and the distance between the two, as shown in FIG.
Regarding the recess amount L1 of the first concave curved surface portion 8, the first virtual straight line S
1, the drill rotation direction T side is positive, the rear side is negative, and conversely, with respect to the recess amount L2 of the second concave curved surface portion 12, the drill rotation direction T side is negative and the rear side is positive from the second virtual straight line S2. . Therefore, in the present embodiment, the entire first concave curved surface portion 8 is not located on the drill rotation direction T side with respect to the first virtual straight line S1.

Further, in the above section, the radii R1 to R4 of the arc formed by the first and second curved surface portions 7, 8, 11, 12 are formed.
Is the radius R1 of the first convex curved surface portion 7 with respect to the outer diameter D of the cutting edge 5.
Is in the range of 0.1 to 0.8 × D, the radius R2 of the first concave curved surface portion 8 is in the range of 0.18 to 0.35 × D, and the radius R3 of the second convex curved surface portion 11 is 0.1. To 0.8 × D, the radius R4 of the second concave curved surface portion 12 is 0.2 to 0.5 × D,
Each is set. In this embodiment, the radius R4 of the second concave curved surface portion 12 is the first concave curved surface portion 8 among them.
Is larger than the radius R2. The groove width ratio of the chip discharge groove 3 thus formed is 0.
The range is 8 to 1.2: 1.

In the cutting edge 5 formed at the intersection ridge of the inner wall surface 4 of the chip discharge groove 3 and the tip flank 2 as described above, the inner wall surface 4 is formed by the first curved surface portions 7 and 8. By being formed, on the outer peripheral end 15 side thereof, a convex curved cutting edge portion 1 having a curved shape that is convex in the drill rotation direction T is formed.
6 is formed and the first convex curved surface portion 7 is connected to the rear end side thereof, and the inner peripheral side of the convex curved cutting edge portion 16 has a curved shape that is concave toward the rear side in the drill rotation direction T. The concave curved cutting edge portion 17 is formed so as to be in smooth contact with the convex curved cutting edge portion 16 and is continuous, and the first concave curved surface portion 8 is continuous at the rear end side thereof. 16, 17
In the meantime, the cutting edge 5 has an S-shape that gently curves when viewed from the front end in the direction of the axis O. However, the cutting edge 5 has a tip angle because the tip flank 2 is inclined toward the rear end side of the drill body 1 from the inner peripheral side toward the outer peripheral side. Since the groove 3 is spirally twisted, the concave and convex curved cutting edge portions 16 and 1 of the cutting edge 5 are formed.
The S-shaped concave-convex curve formed by 7 in the tip view in the direction of the axis O is a concave-convex curve formed by the first convex-concave curved surface portions 7 and 8 of the inner wall surface 4 in a cross section orthogonal to the axis O. The shape gradually shifts toward the rotation direction T side. Therefore, in the tip view in the direction of the axis O, the tangent line at the outer peripheral end 15 of the convex curved cutting edge portion 16 is larger than the tangent line at the outer peripheral end 13 of the convex curve formed by the first convex curved surface portion 7 in the cross section. And the crossing angle with the margin portion 6 is made larger than the obtuse angle formed by the first convex curved surface portion 7 as it goes toward the outer peripheral side toward the rear in the drill rotation direction T. The radial rake angle α formed at 15 is set to the negative angle side.

On the other hand, on the tip side of the inner wall surfaces 4 and 9 of the chip discharge groove 3, the tip escape from the inner peripheral side of the first concave curved surface portion 8 to the second concave curved surface portion 12 and the second convex curved surface portion 11. A thinning portion 18 reaching the heel portion 10 is formed by notching the ridge line portion intersecting with the surface 2 toward the rear end side of the drill body 1 toward the inside of the chip discharge groove 3, and thus the cutting portion 18 is formed. The inner peripheral end side of the blade 5 is formed at an intersecting ridge line portion between the thinning portion 18 and the tip flank 2, and the axis line of the center of the tip flank 2 from the inner peripheral end of the concave curved cutting edge portion 17 is formed. O
It is a thinning cutting edge portion 19 extending toward. In the cutting edge 5, the portion where the thinning cutting edge portion 19 and the concave curved cutting edge portion 17 intersect is smoothly connected by a curved line or a straight line which is convex in the drill rotation direction T when viewed from the tip of the axis O direction. ing.

Here, a portion of the thinning portion 18 that intersects the inner wall surfaces 4 and 9 of the chip discharge groove 3 and extends toward the tip side is referred to as a first thinning portion 20, and the first thinning portion 20 is formed. The portion extending to the heel portion 10 side intersecting the inner wall surface 9 of the chip discharge groove 3 facing the drill rotation direction T rear side is formed in a flat shape, while facing the inner wall surface 9 and the drill rotation direction T side. The part where the inner wall surface 4 intersects,
That is, the portion extending from the contact point P3 portion of the first and second concave curved surface portions 8 and 12 toward the center of the tip flank 2 is seen from the direction toward the center of the tip flank 2 as shown in FIG. In this case, it is formed to have a concave curved valley shape, and the concave valley bottom portion 21 is inclined so as to recede toward the inner peripheral side of the drill body 1 with respect to the inner wall surfaces 4 and 9. Meanwhile, it is formed so as to extend toward the tip side toward the inner peripheral end of the cutting blade 5, that is, the inner peripheral end of the thinning cutting blade portion 19. The radius of curvature of the concave curve formed by the concavely curved valley bottom portion 21 of the first thinning portion 20 is 0.1 to 0.1.
It is set within the range of 0.5 mm. In addition, this valley bottom 2
The radius of curvature of the concave curve formed by the cross section of 1 may be increased toward the rear end side.

Further, in the portion where the above-mentioned valley bottom portion 21 at the extreme end of the first thinning portion 20 is about to reach the inner peripheral edge of the cutting edge 5, the drill main body 1 is further added to the valley bottom portion 21.
A second valley-shaped thinning portion 22 that extends toward the inner peripheral end side of the cutting edge 5 while being inclined one step so as to recede toward the inner peripheral side is formed, and in the vicinity of the axis O at the center of the tip flank 2 The second thinning portion 22 intersects the tip flank 2 and the inner peripheral edge of the cutting edge 5 is formed on the intersecting ridge line portion. Here, the radius of curvature of the valley bottom of the second thinning portion 22 is
The radius of curvature is smaller than the radius of curvature of the valley bottom portion 21 of the first thinning portion 20 and less than 0.1 mm. In some cases, the radius of curvature is 0, that is, the valley bottom portion is formed in a V-shaped valley shape without concave curvature. Also, the first thinning section 20
Like the valley bottom portion 21 of the above, it may be formed so as to become larger toward the rear end side of the drill body 1. In addition, the inner peripheral edge of the cutting blade 5 is formed at the ridge line portion where the second thinning portion 22 and the tip flank 2 that are inclined further than the first thinning portion 20 in this way are formed, and thus the tip of the drill main body 1 is formed. The distance between the pair of cutting blades 5 and 5, that is, the width of the chisel defined at the center of the tip flank 2 is the first thinning portion 20.
Is narrower than that in which the inner peripheral end of the cutting edge 5 is formed by intersecting the tip flank 2 as it is, and this chisel width is in the range of 0 to 0.2 mm in the present embodiment. The inner peripheral ends of the blades 5 and 5 may be aligned on the axis O.

Further, the cutting edge 5 has a rake angle γ in a cross section orthogonal to the cutting edge 5, that is, a right angle rake angle, which is gradually increased from the inner circumference of the drill body 1 toward the outer circumference thereof. The transition point X on the blade 5 is reached, and the outer peripheral side of the transition point X is gradually reduced toward the outer peripheral side. That is, in this embodiment, as shown in FIGS. 4 to 9, the rake angle γ is
When a cross section orthogonal to the cutting edge 5 is taken at one point on the cutting edge 5, the first convex-concave curved surface portions 7 and 8 of the inner wall surface 4 which are continuous with the cutting edge 5 and serve as a rake surface are formed in the cross section. The curve is an angle formed at the one point with respect to the reference plane passing through the one point including the axis O, and this rake angle γ is shown in FIG.
As indicated by the line Y, when the one point moves from the inner peripheral side to the outer peripheral side of the drill body 1 along the cutting edge 5, the transition point set at a predetermined position on the cutting edge 5 It tends to gradually increase until reaching X, and becomes maximum at the transition point X,
When moving further to the outer peripheral side beyond the transition point X, there is a tendency for the rake angle γ to gradually decrease.

Further, in this embodiment, this transition point X is
A contact point P1 of an irregular curve formed by the first curved surface portions 7 and 8 of the inner wall surface 4 of the chip discharge groove 3 in a cross section orthogonal to the axis O.
Is extended toward the tip side along the spiral chip discharge groove 4, that is, around the inflection point between the concave curved cutting edge portion 16 and the convex curved cutting edge portion 17 of the cutting edge 5 as shown in FIG. It is located in the inflection part of. Incidentally, in the present embodiment, the transition point X is 82.6% of the turning radius r (= D / 2) of the cutting edge 5 from the axis O of the drill body 1 toward the radially outer side.
7 (the ratio x to r is 0.826), and the rake angle γ of the cutting edge 5 reaches a maximum of 33 ° at this transition point X, as shown in FIG.

If the cutting edge 5 has a curved shape, such as the case where the cutting edge 5 is formed in the S shape by the uneven curved cutting edge portions 16 and 17 as in the present embodiment, the cutting edge 5 has a curved shape. The cross section orthogonal to each other may be a cross section orthogonal to the tangent to this curve at the above-mentioned one point. In addition, as described above, the tip flank 2
When the cutting blade 5 has a tip angle by being inclined toward the rear end side of the drill body 1 from the inner peripheral side toward the outer peripheral side, the cross section orthogonal to the cutting blade 5 has the above-mentioned 1
As it goes from the point toward the rear end side, the surface is inclined toward the inner peripheral side and obliquely intersects the axis O. Further, when the thinning cutting edge portion 19 is formed on the inner peripheral end side of the cutting edge 5, the rake angle γ in the thinning cutting edge portion 19 tends to gradually increase toward the outer peripheral side as described above. It doesn't have to be. That is, the rake angle γ may have the above-described gradual increase / decrease tendency from the inner circumference to the outer circumference of the drill body 1 excluding the thinning cutting edge portion 19. More specifically, Although depending on the size of the core thickness d and the like, as shown in FIG. 10, a circle formed by the outer peripheral end 15 of the cutting edge 5 around the axis O from the axis O toward the outer peripheral side in the radial direction of the drill body 1. Radius, that is, the turning radius r of the cutting edge 5 (= D /
2) 37.5% position, ie 0.37 from axis O
It suffices if such a tendency occurs on the outer peripheral side of the position of 5 × r (the position where the ratio x is 0.375).

Therefore, in the thus constructed drill, the rake angle (right angle rake angle) γ of the cutting edge 5 in the cross section orthogonal to the cutting edge 5 is the thinning cutting edge portion 19.
Since the drill body 1 is gradually increased from the inner circumference to the outer circumference to reach the transition point X on the cutting edge 5, the outer circumference is closer to the inner periphery than the transition point X. As the turning radius from the axis O increases toward the side, the cutting speed gradually increases and the cutting resistance also increases, while the rake angle γ also gradually increases, so the cutting edge 5 increases.
The sharpness of the drill body can be increased, the increasing resistance can be suppressed, an excessive torque is prevented from acting on the drill body 1, and breakage and progress of wear of the drill body 1 can be prevented. On the other hand, on the outer peripheral side of the transition point X, the rake angle γ is designed to be gradually reduced toward the outer peripheral side, so that the cutting edge angle of the cutting edge 5 is gradually increased conversely. Therefore, on the outer peripheral end 15 side of the cutting edge 5 located on the outermost peripheral side of the drill body 1 where the maximum cutting resistance acts, high cutting edge strength can be secured, and chipping or chipping at this portion, or It is possible to prevent early progress of flank wear. Therefore, according to the drill having the above configuration, it is possible to prevent the drill life from being shortened due to these abrasions and damages even under severe processing conditions such as high-speed dry cutting, and for a long period of time. It is possible to perform stable and smooth drilling. Moreover, in the drill of the present embodiment, the tip of the drill body 1 including the cutting edge 5 has Ti
Since the hard coating of N, TiCN, TiAlN or the like is coated, it is possible to improve the wear resistance of the drill body 1, and it is possible to further prolong the life of the drill.

Incidentally, the transition point X at which the rake angle γ of the cutting edge 5 changes from the inner circumference of the drill body 1 toward the outer circumference side to gradually decrease from the gradual increase tendency to the gradual decrease tendency in this way is the rake angle γ on the cutting body 5. If the rake angle γ on the inner peripheral side of the transition point X is too large, the portion where the rake angle γ on the inner peripheral side gradually increases toward the outer peripheral side becomes too short, and conversely the rake angle γ becomes the outer peripheral side. Since the part that tends to gradually decrease toward
There is a possibility that the effect of reducing the cutting resistance by adopting the above configuration may not be sufficiently achieved. However, if the transition point X is located too close to the outer peripheral side of the drill body 1 on the cutting edge 5, contrary to the above, the rake angle γ
Is gradually reduced toward the outer peripheral side, and in the case of high speed dry cutting, it is difficult to secure sufficient cutting edge strength on the outer peripheral end 15 side of the cutting edge 5 where the greatest resistance acts. May occur. Therefore, the position of the transition point X is 70 to 70 with respect to 1/2 of the rotation radius r of the cutting edge 5, that is, the outer diameter D of the cutting edge 5 from the axis O of the drill body 1 toward the outer peripheral side in the radial direction. It is desirable to be located within 90%.

By the way, in the present embodiment, as described above,
On the outer peripheral end 15 side of the cutting blade 5, a convex curved cutting edge portion 16 having a curved shape that is convex in the drill rotation direction T is formed, and
On the inner peripheral side of the convex curved cutting edge portion 16, on the contrary, a concave curved curved cutting edge portion is formed which is concave toward the rear side in the drill rotation direction T and smoothly connects to the convex curved cutting edge portion 16. 17 are formed. Therefore, on the outer peripheral side of the convex curved cutting edge portion 16, that is, on the outer peripheral side of the cutting edge 5 on which the largest cutting resistance acts, the radial rake angle of the cutting edge 5 is gradually reduced toward the outer peripheral side. Since the cutting edge strength can be ensured more reliably because it is increased to the negative angle side, in particular, the angle of the intersection of the margin portion 6 and the cutting edge 5 on the outer periphery of the drill body 1 can be increased, It is possible to improve the strength of the drill body 1 at the intersection and prevent chipping or chipping. On the other hand, since the convex curved cutting edge portion 16 and the concave curved cutting edge portion 17 formed on the inner peripheral side thereof are formed smoothly and continuously,
For example, as in the drill described in JP 2000-198011 A, in which the cutting edge has an outer corner cutting edge that is angled at its intermediate portion and is retracted rearward in the direction of rotation of the drill, chips are formed on the inner and outer circumferences of the intermediate portion. Is not divided, and the concave curved cutting edge portion 17 allows the chips to be rolled up toward the inner peripheral side to be sufficiently curled and smoothly processed.

Further, in the present embodiment, the inflection in which the concave curved cutting edge portion 17 and the convex curved cutting edge portion 16 of the cutting edge 5 thus constructed are in smooth contact with each other to bend the curve. The transition point X is located at an inflection portion near the point, and the rake angle γ of the cutting edge 5 transitions from the gradually increasing tendency toward the outer peripheral side to the gradually decreasing tendency at the inflection portion. Has been done. However, at the portion where the rake angle γ of the cutting edge 5 changes in this way, the cutting resistance acting on the cutting edge 5 is also changed from the gradually decreasing tendency to the gradually increasing tendency toward the outer peripheral side. While stress on the blade 5 tends to concentrate, in the present embodiment, an inflection in which the concave-convex curved cutting edge portions 16 and 17 of the cutting edge 5 which has this transition point unevenly curved as described above makes a smooth contact. By arranging it at the portion, for example, this transition point X is located at the most convex portion in the rotational direction T of the convex curved cutting edge portion 16, or conversely, the concave curved cutting edge portion 17 is located.
In comparison with the case where the cutting edge 5 is located in the most recessed portion on the rear side in the rotation direction T, the stress can be dispersed, and the stress concentration causes damage to the cutting edge 5 in the vicinity of the transition point X. Can be prevented.

When the transition point X is located at the inflection portion of the cutting edge 5 in this way, in this embodiment, the inflection portion (inflection point) is the first uneven curved surface portion 7 of the inner wall surface 4. Contact P1 of 8
Is located on the extension side of a circle having a diameter of 2/3 of the outer diameter D of the cutting edge 5 about the axis O and more preferably 5 / of the outer diameter D. Since it is supposed to be positioned on the outer peripheral side of the circle having the diameter of 6, when considering this and the range of the transition point X with respect to the rotation radius r of the cutting edge 5, it is 7 with respect to this rotation radius r.
It is even more desirable to be located within the range of 0-83%. However, this transition point X does not necessarily have to be exactly coincident with the inflection point of the cutting edge 5, and as described above, the most convex portion in the rotational direction T of the convex curved cutting edge portion 16 or As long as it is not located at the most recessed portion on the rear side of the concave curved cutting edge portion 17 in the rotation direction T, it may be disposed in the vicinity of the inflection point between these portions.

Further, the change of the rake angle γ of the cutting edge 5 in the present embodiment is as shown by the line Y in FIG. 10, but in the drill according to the present invention, the line A shown in FIG. It is desirable that the rake angle γ be changed within a range surrounded by the line B. When this is expressed by an approximate expression, the turning radius r of the cutting edge 5 toward the outer peripheral side in the radial direction from the axis O is shown. At a position in the range of 37.5% or more and less than 82.6%, the ratio y of the radius from the axis O at this position to the radius of gyration r is approximated by ± 1 of the angle y approximated by the following equation 1.
In the range of 7 °, the turning radius r of the cutting edge 5 is 8
In the position within the range of 2.6% to 100%, the above ratio x
It is desirable that the displacement be performed in the range of ± 7 ° of the angle y approximated by the following Expression 2.

[0030]

[Equation 5]

[0031]

[Equation 6]

This means that the rake angle γ of the cutting edge 5 which is displaced as described above exceeds the range of + 7 ° of the angle y obtained by the above equations 1 and 2, and the rake angle γ is larger than the line Y. If it becomes too large, the cutting edge angle of the cutting edge 5 becomes too small at the portion where the rake angle γ becomes large, and in particular in high speed dry cutting, the cutting edge strength cannot be sufficiently secured and the cutting edge 5 is damaged. This is because it may occur. On the other hand, conversely, the deviation of the rake angle γ is − of the angle y of the equations 1 and 2.
If the rake angle γ becomes too small with respect to the line Y below the range of 7 °, the cutting resistance cannot be reliably reduced, the wear of the cutting edge 5 is promoted, and excessive torque is generated to cause the drill body. 1 may be broken. For this reason,
It is desirable that the rake angle γ of the cutting edge 5 be within the range of ± 7 ° of the angle y of the expressions 1 and 2 as described above.

Here, the following Table 1 shows the drill Y of the present embodiment which makes the transition of the rake angle γ shown by the line Y in FIG. 10, and the transition of the rake angle γ exceeds the angle y + 7 ° of the expressions 1 and 2. And the drill B whose displacement of the rake angle γ is smaller than the angle y-7 ° of the formulas 1 and 2, and the patent No. 2674124 described above as a comparative example for these.
And the drill E described in Japanese Patent Laid-Open No. 2000-1980
11 is a comparison of the drill life when drilling is performed at a cutting speed vc = 80 and 150 m / min with the drill F described in Japanese Patent Publication No. Also, FIG.
As in FIG. 10, reference numeral 1 denotes a line Y showing a change in the rake angle γ with respect to the position of the cutting edge 5 in the drill Y of the present embodiment, and rake angle (right angle with respect to the position of the cutting edge in the drills E and F of the comparative example). The lines E and F showing the change in the rake angle are collectively shown.

Here, the drills Y, A, B, at this time,
Both E and F have an outer diameter D of the cutting edge of 8 mm, and S
Feed rate fr = 0.2 mm / rev for 50 C workpiece
With a hole depth of ld = 25mm
The drill life was compared by the cutting length up to that life. Note that these processes were initially performed by a dry method, but especially with the drills E and F, the cutting speed vc = 80 m / mi
Even in the case of n, damage occurred soon before comparison and machining became impossible, so that wet drilling using a water-soluble cutting fluid was performed for all drills. In addition, as a result of Table 1, what is indicated by ○ is that the cutting edge shows normal wear, and even if the number of holes is 4000 (the cutting length is about 100 m), it can be used continuously. The symbol Δ indicates normal wear, but the service life was earlier than that of the symbol ○. It shows the cutting length that could be drilled for. On the other hand, the mark "X" indicates that abnormal wear occurred during drilling and the life was consumed at that time, and the cause is also described.

[0035]

[Table 1]

From the results shown in Table 1, the cutting speed vc = 80
Even when it is as small as m / min, the comparative drills E and F have a life of about 70% that of the drills Y and A of the embodiment, and when the cutting speed vc = 150 m / min is large, the shoulder portion, i.e. Due to the lack of the drill body at the intersection of the outer peripheral edge of the blade and the margin and the initial breakage of the drill body, the service life was consumed early. On the other hand, in the drill Y according to the embodiment, the cutting speed vc = 8
Not only in the case of 0 m / min, but also in the case of high-speed cutting of vc = 150 m / min, the above-mentioned number of holes does not reach the end of life, and the deviation of the rake angle γ exceeds the line A or the line B.
Even with drills A and B whose diameters are below the range, since the rake angle γ changes from the gradual increase tendency to the gradual decrease tendency toward the outer peripheral side, although the life is shorter than that of the drill Y, it is possible to machine a certain number of holes. The life of the drill can be extended. Incidentally, in the drill Y of the embodiment, even if the dry drilling was performed under the same favorable conditions as described above, abnormal wear such as chipping or breakage did not occur up to the number of holes.

In addition to these, in the above embodiment,
A thinning portion 18 is formed on the tip end side of the chip discharge groove 3, whereby the inner peripheral end side of the cutting edge 5 is a thinning cutting edge portion 19 that extends toward the center of the tip flank surface 2. A portion where the portion 19 and the concave curved cutting edge portion 17 intersect with each other is formed into a convex curved shape or a linear shape that smoothly connects to both cutting edge portions 17 and 19, and the thinning cutting edge portion 1
Since the first thinning portion 20 connected to 9 has a valley shape in which the valley bottom portion 21 is concavely curved, the above-mentioned bending point is not formed over the entire length of the cutting blade 5, and The inner peripheral side portion of the chips generated by the thinning cutting edge portion 19 is also moved to the inner peripheral side along a concave curve formed by the cross section of the valley bottom portion 21 of the first thinning portion 20 as shown by a black arrow in FIG. It can be curled so that it can be rolled up. Therefore, in combination with the fact that the concave curved cutting edge portion 17 causes the chips to be caught on the inner peripheral side, the chip disposability can be further improved, which is particularly effective in processing difficult-to-cut materials. is there. In the present embodiment, the radius of curvature of the concave curve formed by the valley bottom portion 21 of the first thinning portion 20 is set to 0.1 to 0.5 mm. This is because if the radius of curvature is larger than this, This is because it is possible that the inner peripheral side portion cannot be sufficiently rolled up and curled, while conversely, if it is smaller than this, the inner peripheral side portion of the chips may be clogged in the thinning portion 18.

At the tip of the thinning portion 18,
A second thinning portion 22 is formed to reach the tip flank 2 by further inclining one step from the valley bottom portion 21 of the first thinning portion 20, and on the ridge line portion where the second thinning portion 22 and the tip flank 2 intersect. Since the inner peripheral edge of the cutting edge 5 is formed on the cutting edge 5 and the radius of curvature of the groove bottom of the second thinning portion 22 is less than 0.1 mm, which is smaller than that of the valley bottom portion 21, the cutting edge 5 The inner circumference end of the chisel is located closer to the inner circumference side, so that the width of the chisel is 0 to 0.2.
The width is very short, mm. Therefore, when the drill bites into the workpiece, the biting property and straight running stability can be improved to perform more stable and highly accurate machining, and the thrust acting on the drill body 1 in the axial direction thereof can be achieved. The force can be suppressed, and it becomes possible to promote further reduction of the drill driving force. Moreover, since the thinning portion 18 is formed by the first and second plurality of thinning portions 20 and 22 having a large inclination toward the inner peripheral edge of the cutting edge 5 in this manner, the second thinning portion 22 at the tip is formed. The tip angle of the drill body 1 in the cross section along the groove bottom of
Since the groove bottom of a single thinning portion becomes larger than that in the case where the groove bottom is inclined so as to have the same chisel width, according to the present embodiment, sufficient strength is secured around the rotation center of the tip of the drill body 1. It is possible to provide a drill that is not damaged by an impact load when biting. However, the second thinning portion 22 may be omitted as long as the biting property of the drill body 1 and the straight running stability and strength can be secured only by the first thinning portion 20.

On the other hand, such an uneven curved cutting edge portion 16,
In order to form the cutting edge 5 provided with 17, in the present embodiment,
On the inner wall surface 4 of the chip discharge groove 3 which faces the drill rotation direction T, first concave and convex curved surface portions 7 and 8 which are respectively continuous with the concave and convex curved cutting edge portions 16 and 17 are formed, and are thus divided by the cutting edge 5. The chips that are continuously generated in the width direction without being rolled up are curled further by being rolled up on the inner peripheral side and pressed against the first concave curved surface portion 8 while slidingly contacted, and the rotation of the drill body 1 is increased. Along with that, it is pushed out to the rear end side and discharged. Further, on the inner peripheral side of the first concave curved surface portion 7, the second concave curved surface portion 12 of the inner wall surface 9 of the chip discharge groove 3 facing the rear side in the drill rotation direction T is smooth with the first concave curved surface portion 7. Since the second concave curved surface portion 12 is formed so as to be recessed in the drill rotation direction T contrary to the first concave curved surface portion 8, the second concave curved surface portion 12 is further reduced by the first concave curved surface portion 8. The curled chips are smoothly discharged as described above without obstructing the flow of the chips. Moreover, in the present embodiment, the second convex curved surface portion 11 is formed on the outer peripheral side of the second concave curved surface portion 12 so as to be smoothly continuous,
Therefore, the flow of chips is not blocked on the heel portion 10 side, and the strength of the drill body 1 at the heel portion 10 can be secured.

Further, in the present embodiment, these first and second
With respect to the concave amounts L1 and L2 of the concave curved surface portions 8 and 12, from the first virtual straight line S1 connecting the axis O and the outer peripheral end 13 of the inner wall surface 4 to the outer diameter D of the cutting edge 5 in the first concave curved surface portion 8. -0.06
In order to be in the range of xD to 0 (however, the rear side of the drill rotation direction T is negative), and for the second concave curved surface portion 12 from the second virtual straight line S2 orthogonal to the first virtual straight line S1 at the axis O- It is set so as to fall within the range of 0.06 × D to 0.06 × D (however, the drill rotation direction T side is negative), so that the first and second concaves are not too weak and not too weak. It can be brought into sliding contact with the curved surface portions 8 and 12 to give an appropriate braking action. For this reason, the chips can be reliably curled and processed without causing the chips to be crushed by an excessive braking action to impair the smooth discharging property and to increase the drill rotation driving force. In order to more reliably bring out such an effect, the curvature radius R2 of the concave curve (concave arc) formed by the first concave curved surface portion 8 is cut in the cross section orthogonal to the axis O as in the present embodiment. 0.18 for outer diameter D of blade 5
It is desirable that the radius of curvature R4 of the second concave curved surface portion 12 be set to a range of 0.2 to 0.5 × D, respectively.

Further, in the present embodiment, these first and second
Even between the concave curved surface portions 8 and 12, the radius of curvature of the concave curve formed by the second concave curved surface portion 12, that is, the radius R4 in the cross section orthogonal to the axis O, is the radius of curvature of the concave curve formed by the first concave curved surface portion 8, that is, It is designed to be larger than the radius R2, so that the chips generated by the cutting blade 5 are first slidably contacted with the first concave curved surface portion 8 having the relatively small radius R2, so that the chips are sufficiently wound. By curling with a habit and allowing the curled chips to flow out toward the second concave curved surface portion 12 side having a relatively large radius R4, the chips may be pressed too strongly in the second concave curved surface portion 12. It is possible to promote smoother discharge and further reduce the driving force for rotating the drill. Moreover, in the present embodiment, the concave curve formed by the first and second concave curved surface portions 8 and 12 is designed to draw a continuous concave curve in contact with the contact point P3 of 1. It becomes possible to make the flow of the chips from the second concave curved surface portion 12 smoother to promote smoother chip discharge.

However, instead of forming the first and second concave curved surface portions 8 and 12 in such a manner that the concave curves formed by the cross-sections thereof are in contact with each other at the contact point P3 and are smoothly continuous, for example, shown in FIG. As described above, the first and second concave curved surface portions 8 and 12
Between the first concave curved surface portion 8 in the cross section orthogonal to the axis O.
Is formed on both the concave curve formed by the second concave curved surface portion 12 and the concave curve formed by the second concave curved surface portion 12, and a tangential connecting surface 23 that is in contact with the contact points P4 and P5 is formed. 12 may be smoothly connected. Also in this case, the first
The second concave curved surface portion 12 does not impair the flow of the chips having a curl due to the concave curved surface portion 8 and further strongly press against the connecting surface 23 to increase the drill rotation driving force. It becomes possible to discharge it smoothly to the side. On the other hand, when such a connecting surface 23 is interposed between the first and second concave curved surface portions 8 and 12, the radius of curvature R of the first and second concave curved surface portions 8 and 12 is
Since the groove width of the chip discharge groove 3 can be set without being limited to 2 and R4, for example, conversely to the above, the second concave curved surface portion 12 can be sufficiently chipped depending on the material of the workpiece. Even if the radius of curvature R4 is made small when it must be slidably contacted and curled, it is possible to secure a sufficiently large chip width and maintain a smooth chip discharging property.

Further, in this embodiment, the first and second
The radii of curvature R1 and R3 of the convex curve (convex arc) formed by the convex curved surface portions 7 and 11 in the above cross section are set in the range of 0.1 to 0.8 × D with respect to the outer diameter D of the cutting edge 5, respectively. And
As a result, the strength around the margin portion 6 and the strength around the heel portion 10 at the inner wall surface 4 of the drill body 1 and the outer peripheral ends 13 and 15 of the cutting edge 5 and the strength around the heel portion 10 are sufficiently secured, and
It is possible to prevent the radial widths of the concave curved surface portions 8 and 12 from becoming too small, and to reliably improve the chip disposability.
Even under conditions such as high-speed dry cutting, in order to more reliably ensure the strength of the drill body 1 and the improvement of the chip disposability in this way, the first uneven curved surface in the cross section as in the present embodiment is used. The contact point P1 of the uneven curve formed by the parts 7 and 8 is
The cutting edge 5 is positioned on the outer peripheral side of a circle having a diameter of ⅔ of the outer diameter D, more preferably on the outer peripheral side of a circle having a diameter of 5/6 of the outer diameter D, and the chip discharge groove 3 The groove width ratio of 0.8
It is desirable to set the range to 1.2: 1.

Further, in the present embodiment, as the chip disposability is improved and the drill rotation driving force is reduced, the load applied to the drill body 1 itself during processing is also reduced, which reduces the load. The core thickness d can also be set to a relatively small range of 0.15 × D to 0.3 × D with respect to the outer diameter D of the cutting edge 5. Therefore, particularly the thrust force of the load received by the drill main body 1 is reduced, and the cross-sectional area of the chip discharge groove 3 is increased to promote smoother chip discharge, thereby further increasing the power for drilling. Can be reduced. On the other hand, the cross-sectional area of the drill main body 1 is large on the outer peripheral side by the curvature radii R1 to R4 being set in an appropriate range as described above, and particularly by the first and second convex curved surface portions 7 and 11. By doing so, it is possible to ensure the necessary and sufficient level, and therefore the rigidity of the drill body 1 can be maintained, and in addition to the fact that the machining power can be further reduced as described above,
It is possible to more reliably prevent a situation in which the drill life is consumed due to breakage during machining.

[0045]

As described above, according to the present invention,
The rake angle of the cutting edge is gradually increased from the inner circumference of the drill body to the outer circumference side up to the transition point on this cutting edge, and gradually decreased on the outer circumference side from this transition point.
It becomes possible to give a high cutting edge strength to the outer peripheral end side where a particularly large resistance of this cutting edge acts, while maintaining good sharpness of the entire cutting edge and suppressing an increase in cutting resistance. For this reason,
Even under the severe machining conditions such as high-speed dry cutting, it is possible to prevent the situation where the drill life is consumed early, and it is possible to perform efficient and smooth drilling efficiently and stably.

[Brief description of drawings]

FIG. 1 is a front view of an embodiment of the present invention as viewed from the front end in the direction of an axis O. FIG.

2 is a cross-sectional view orthogonal to the axis O of the embodiment shown in FIG.

3 is a perspective view of a tip portion of the drill body 1 showing a thinning portion 18 of the embodiment shown in FIG. 1. FIG.

4 is a perspective view showing a cross section orthogonal to the cutting edge 5 at a position of 0.500 × r (position of x = 0.500) with respect to a rotation radius r of the cutting edge 5 on the outer peripheral side from the axis O. FIG. .

5 is a perspective view showing a cross section orthogonal to the cutting edge 5 at a position of 0.625 × r (position of x = 0.625) with respect to the rotation radius r of the cutting edge 5 from the axis O to the outer peripheral side. .

FIG. 6 is a perspective view showing a cross section orthogonal to the cutting edge 5 at a position of 0.750 × r (position of x = 0.750) with respect to the rotation radius r of the cutting edge 5 from the axis O to the outer peripheral side. .

FIG. 7 is a perspective view showing a cross section orthogonal to the cutting edge 5 at a position of 0.826 × r (position of x = 0.826) with respect to the rotation radius r of the cutting edge 5 from the axis O to the outer peripheral side. .

8 is a perspective view showing a cross section orthogonal to the cutting edge 5 at a position of 0.925 × r (position of x = 0.925) with respect to a rotation radius r of the cutting edge 5 from the axis O to the outer peripheral side. .

9 is a perspective view showing a cross section orthogonal to the cutting edge 5 at a position of an outer peripheral end 15 of the cutting edge 5 (position of 1.000 × r, x = 1.000 with respect to radius of gyration r).

FIG. 10 is a line Y showing a change in the rake angle γ of the cutting edge 5 of the embodiment, and lines A and B that are ± 7 ° with respect to the line Y.
FIG.

FIG. 11 is a rake angle γ of the cutting edge 5 of the drill Y according to the embodiment.
It is the figure which showed together the line Y which shows the change of, and the lines E and F which show the change of the rake angle of the drills E and F used as a comparative example.

FIG. 12 is a connection surface 2 between the first and second concave curved surface portions 8 and 12.
It is sectional drawing which shows the case where 3 is formed.

[Explanation of symbols]

1 drill body 2 Tip flank 3 Chip discharge groove 4,9 Inner wall surface of chip discharge groove 3 5 cutting edges 15 Outer peripheral edge of cutting edge 5 16 Convex curved cutting edge 17 Concave curved cutting edge 19 Thinning cutting edge O Drill body 1 axis T drill rotation direction γ Rake angle of cutting edge 5 (Right angle rake angle) X transition point

Continued front page    (72) Inventor Takeshi Inoue             1528, Nakashinden, Yokoi, Kobe-cho, Anpachi-gun, Gifu Prefecture             Address Mitsubishi Materials Corporation Gifu Factory             Within F term (reference) 3C037 AA02 BB00 DD01

Claims (5)

[Claims] 1. A chip discharge groove extending toward the rear end is formed on the outer periphery of the front end of a drill body rotated about an axis.
A drill having a cutting edge formed at an intersecting ridge of an inner wall surface of the chip discharge groove facing the drill rotation direction and a tip flank of the drill body, wherein the cutting edge has a cross section orthogonal to the cutting edge. The rake angle at is gradually increased from the inner circumference of the drill body toward the outer circumference to reach the transition point on the cutting edge, and the rake angle gradually increases toward the outer circumference on the outer circumference side from this transition point. A drill characterized by being reduced. 2. The transition point is located within the range of 70 to 90% of the radius of gyration of the cutting edge from the axis toward the outer peripheral side in the radial direction. Drill. 3. A convex curved cutting edge portion having a curved shape which is convex in the drill rotation direction is formed on the outer peripheral end side of the cutting edge, and the inner peripheral side of the convex curved cutting edge portion is formed. On the rear side of the drill rotation direction, a concave curved cutting edge is formed which is concave toward the rear side in the direction of rotation of the drill and smoothly connects to the convex curved cutting edge, and the transition point is the concave curved cutting edge. The drill according to claim 1 or 2, wherein the drill is located at an inflection portion between the blade portion and the convex curved cutting edge portion. 4. The rake angle γ of the cutting edge is 3 of the radius of rotation r of the cutting edge toward the radially outer side from the axis.
At a position in the range of 7.5% or more and less than 82.6%, in the range of ± 7 ° of the angle y approximated by the following equation 1 with respect to the ratio x of the radius from the axis at this position to the radius r of rotation, 82.6% or more of the turning radius r of the cutting edge 1
For the position in the range of up to 00%, the ratio x is
4. The drill according to claim 1, wherein the drill is displaced within a range of ± 7 ° of the angle y approximated by. [Equation 1] [Equation 2] 5. The drill according to claim 1, wherein at least the surface of the tip of the drill body is coated with a hard coating.