JP7434791B2 - Drill - Google Patents

Description

The present invention particularly relates to a drill used for counterboring holes in inclined or curved surfaces of workpieces.

As such a drill, for example, Patent Document 1 discloses a drill with a tip angle of 180° to 181°, and this drill has a curved cutting edge, and from this cutting edge toward the outer peripheral corner. It is described that the angle between the extending straight line and the straight line extending from the chisel edge to the outer peripheral corner is 18° to 22°, and the land is provided with two margins. Note that the drill described in Patent Document 1 is a two-blade drill.

Patent Document 1 also describes that the groove length is 2 times or more and 5 times or less the diameter of the drill, and the shank length is 5 times or more and 20 times or less the diameter of the drill. Patent Document 1 describes that such a drill can suppress run-out of the drill even when counterboring a workpiece having an inclined or curved surface while maintaining the strength of the cutting edge.

JP2014-034080A

By the way, in a so-called double margin drill in which two margins are provided on the land like the drill described in Patent Document 1, the contact area of the margin with the inner peripheral surface of the machined hole is large, so the friction due to contact is large. If fine chips generated during cutting enter between the two margins, welding is likely to occur due to frictional heat.

However, with a drill whose cutting edge has a flat tip angle of 180° to 181°, if two margins are not formed in the land, the cutting edge will bite into the inclined or curved surface of the workpiece. In this case, the drill runout as described above is likely to occur.

Here, in the drill described in Patent Document 1, as shown in FIGS. 1 and 2 of Patent Document 1, the outer peripheral flank of the cutting edge between the two margins is similar to that of a general drill. In a cross section perpendicular to the axis, it is formed to have a convex curved shape that is more concave than the outer peripheral surfaces of the two margins.

For this reason, even if coolant such as cutting fluid is supplied during counterbore hole drilling, the cutting fluid that has flowed between the two margins will be absorbed by the margin located on the opposite side of the drill rotation direction as the drill body rotates. Therefore, it is difficult to efficiently cool and lubricate the margin (first margin part) located on the side in the rotational direction of the drill with the cutting fluid to prevent welding of chips.

The present invention was made against this background, and is a drill for counterboring holes in which the tip angle of the cutting edge is close to 180°. It is an object of the present invention to provide a drill that can efficiently cool and lubricate these two margin parts with a cutting fluid to prevent welding even if the double margin drill is formed.

In order to solve the above problems and achieve such objects, the present invention provides a tip relief on the outer periphery of the cutting edge on the tip side of the drill body, which is rotated around the axis in the drill rotation direction. Two chip discharge grooves that are open to the surface and extend toward the rear end side are formed at intervals in the circumferential direction, and at the intersection ridge line of the wall surface facing the rotational direction of the drill and the tip flank of these chip discharge grooves. , a drill in which a cutting edge is formed with a tip angle within a range of 178° to 182°, and the outer peripheral surface of the cutting edge portion between the two chip evacuation grooves has an outer peripheral edge of the cutting blade. a first margin portion that continuously projects toward the outer circumferential side of the drill body; and a second margin portion that protrudes toward the outer circumferential side of the drill body at a distance from the first margin portion on the opposite side to the rotational direction of the drill. A concave curve is formed on the outer peripheral surface of the cutting edge between the first margin part and the second margin part, and the concave curve is recessed toward the inner peripheral side of the drill body in a cross section perpendicular to the axis. A plurality of recesses each having a shape are arranged adjacent to each other in the circumferential direction .

In the drill configured in this way, two margin parts, a first margin part and a second margin part, are formed on the outer peripheral surface of the cutting edge part (the outer peripheral surface of the land part) between the two chip discharge grooves. Even with drills for counterboring holes where the tip angle of the cutting edge is close to 180°, it is possible to suppress the whirling of the cutting edge when it bites into the inclined or curved surface of the workpiece. can.

By supplying a coolant such as cutting oil during this counterboring process, the cutting oil that has entered between the two margin parts is removed from the direction of rotation of the drill as the drill body rotates on the outer circumferential side of the cutting edge. It flows to the opposite side to cool and lubricate the second margin part, and at the same time, on the inner peripheral side of the cutting edge part, it is pushed out by the cutting fluid that flows on the outer peripheral side in the opposite direction to the drill rotation direction, so that it is perpendicular to the axis. Convection is formed so as to flow in the direction of rotation of the drill along the bottom surface of the concave portion, which has a concave curve shape recessed toward the inner circumference of the drill body in cross section, and faces toward the outer circumference of the drill body.

Therefore, according to the drill configured as described above, the first margin section can also be cooled and lubricated by the cutting fluid flowing in the direction of rotation of the drill, so both the first and second margin sections can be efficiently cooled and lubricated. Can be lubricated. Therefore, even if fine chips generated during drilling enter between the two margin parts, it is possible to prevent welding due to frictional heat.

Here, a plurality of the recesses may be formed in the outer circumferential surface of the cutting edge so as to be lined up in the circumferential direction. This allows the convection of the cutting fluid as described above to occur between the individual recesses and the inner peripheral surface of the machined hole, and especially in the recesses on the side of the drill rotation direction, the convection of the cutting fluid on the side opposite to the drill rotation direction can be generated. Since the cutting oil before cooling and lubricating the second margin part can be convected to cool and lubricate the first margin part, more efficient cooling and lubrication of the first and second margin parts can be achieved. .

In addition, when a plurality of recesses are formed side by side in the circumferential direction on the outer peripheral surface of the cutting edge in this way, a convex part is formed between adjacent recesses where the concave curves formed by the cross sections of the recesses intersect. In a cross section perpendicular to the axis, the depth in the radial direction from the tip of the convex portion formed between the plurality of concave portions to the bottom of the concave portion adjacent to the convex portion in the circumferential direction is 10 μm. It is desirable that the above is met. If the depth from the tip of the convex part to the bottom of the concave part is less than 10 μm, the concave part will be too shallow relative to the convex part, and there is a possibility that it will be difficult to reliably cause the cutting fluid to convect.

Furthermore, in a cross section orthogonal to the axis, a first margin width is a width along a chord of an arc of a first margin outer circumferential surface that faces the outer circumferential side of the first margin portion and forms an arc centered on the axis. If the second margin width W2, which is the width along the chord of the arc of the first margin outer peripheral surface facing the outer peripheral side of the second margin part and forming an arc centered on the axis, is too large with respect to W1. , the resistance due to the sliding contact of the first and second margin outer circumferential surfaces with the inner circumferential surface of the machined hole increases, making it easier for the cutting edge to whirl around and reducing the driving force for rotating the drill body. There is a risk that frictional heat may increase or high frictional heat may be generated.

On the other hand, if the second margin width W2 is too small compared to the first margin width W1, the cutting edge cannot be reliably supported due to sliding contact between the second margin and the inner peripheral surface of the machined hole, resulting in run-out. There is a risk that it will not be possible to suppress the rotation. Therefore, the second margin width W2 may be within the range of 0.2×W1 to 0.6×W1 with respect to the first margin width W1 when viewed from the tip side in the axial direction. desirable.

Furthermore, the whirling of the cutting edge as described above occurs when the length L in the axial direction of the chip discharge groove is longer than the diameter D of the cutting edge, that is, when the length of the cutting edge is long. Although this is likely to occur, if the length of this cutting edge is too short, it becomes impossible to countersink a hole with a depth greater than the length of this cutting edge, which impairs versatility. Therefore, it is desirable that the length L of the chip discharge groove in the axial direction be within the range of 1×D to 3×D with respect to the diameter D of the cutting edge.

As explained above, according to the present invention, the tip angle of the cutting edge is within the range of 178° to 182°, and even when counterboring an inclined or curved surface of the workpiece, the cutting edge The whirling of the cutting edge when biting can be suppressed by the first and second margin parts, and the concave part formed on the outer peripheral surface between the first and second margin parts allows convection of the cutting fluid. By doing so, these two margin parts can be efficiently cooled and lubricated, and even if fine chips generated during drilling get into the space between the two margin parts, it is possible to prevent welding. becomes.

FIG. 1 is a perspective view showing an embodiment of the present invention. FIG. 2 is an enlarged front view of the embodiment shown in FIG. 1; FIG. 2 is a side view of the tip of the embodiment shown in FIG. 1; FIG. 2 is an enlarged cross-sectional view orthogonal to the axis showing a first margin portion of the embodiment shown in FIG. 1; FIG. 2 is an enlarged cross-sectional view orthogonal to the axis showing a second margin portion of the embodiment shown in FIG. 1; FIG. 2 is an enlarged cross-sectional view orthogonal to the axis showing the outer circumferential surface of the land portion in the cutting edge portion of the embodiment shown in FIG. 1 .

1 to 6 show one embodiment of the drill of the present invention. In this embodiment, the drill body 1 is formed of a hard material such as cemented carbide into a roughly cylindrical shape centered on the axis O, and has a rear end portion (the upper right portion in FIG. 1; the upper portion in FIG. 3). ) is used as the shank portion 2 which remains cylindrical, and the tip portion (the lower left portion in FIG. 1; the lower portion in FIG. 3) is used as the cutting edge portion 3.

In such a drill, the shank portion 2 is gripped by the main shaft of a machine tool, and the drill body 1 is rotated in the drill rotation direction T around the axis O and fed out toward the tip side in the direction of the axis O, so that the cutting edge portion 3 The formed cutting edge 4 performs counterboring on an inclined surface or curved surface that is inclined with respect to the axis O of the workpiece.

Two chip evacuation grooves 6 are provided on the outer periphery of the cutting edge portion 3, opening in the tip flank 5 of the drill body 1 and twisting spirally so as to extend toward the rear end side in the opposite direction to the drill rotation direction T. are formed at intervals (equally spaced) in the circumferential direction, and the cutting edges 4 are formed at the intersection ridgeline portions of the wall surfaces of these chip discharge grooves 6 facing the drill rotation direction T and the tip flank surfaces 5. has been done. That is, the drill of this embodiment is a two-blade twist drill. Note that the drill body 1 is formed in a 180° rotationally symmetrical shape with respect to the axis O.

The tip angle α of these cutting edges 4 is within the range of 178° to 182°, particularly 180° in this embodiment, and the bottom surface of the countersunk hole formed in the workpiece is aligned with the axis. It is assumed to be a plane perpendicular to O. In addition, as shown in FIG. 2 when viewed from the tip side in the direction of the axis O, these cutting edges 4 are formed such that the central part around the axis O and a short part of the outer circumferential part are formed in a substantially straight line, and these central parts and The long portion between the outer circumference and the drill rotation direction T is formed into a concave curve slightly recessed on the opposite side to the drill rotation direction T. Further, the inner periphery of the tip of the chip discharge groove 6 is thinned, and the inner periphery of the cutting blade 4 is formed with a thinning blade 4a.

Further, on the outer circumferential surface of the cutting edge 3, a first margin portion 8 is provided on the land portion 7 between the two chip discharge grooves 6, and extends to the outer circumferential end of the cutting edge 4 and protrudes toward the outer circumferential side of the drill body 1. A second margin part 9 is formed which projects from the first margin part 8 toward the outer circumferential side of the drill body 1 at a distance from the first margin part 8 on the side opposite to the drill rotation direction T.

These first and second margin parts 8 and 9 are formed into a substantially trapezoidal shape when viewed from the front end side in the direction of the axis O. Among these, in the first margin portion 8, the first margin front wall surface 8a facing the drill rotation direction T is linear along the straight line formed by the outer peripheral portion of the cutting edge 4, and is opposite to the drill rotation direction T. The first margin rear wall surface 8b facing the side is inclined so as to extend toward the inner circumferential side of the drill body 1 and toward the opposite side to the drill rotation direction T.

Further, the second margin portion 9 is formed in a substantially isosceles trapezoid shape when viewed from the tip side in the direction of the axis O, and as the second margin front wall surface 9a facing the drill rotation direction T goes toward the inner peripheral side of the drill body 1. The second margin rear wall surface 9b, which is inclined so as to extend in the drill rotation direction T and faces the opposite side to the drill rotation direction T, becomes opposite to the drill rotation direction T as it goes toward the inner peripheral side of the drill body 1. It is slanted so that it extends towards the

However, in this embodiment, the intersecting ridgeline portion between the first margin front wall surface 8a and the first margin outer circumferential surface 8c of the first margin portion 8 facing the outer circumferential side of the drill body 1 is The first margin front face chamfer 8d is chamfered into a convex curve having a smaller radius of curvature than the first margin outer circumferential surface 8c, which is in contact with the first margin front wall surface 8a and the first margin outer circumferential surface 8c.

Similarly, the intersection ridgeline between the second margin front wall surface 9a and the second margin outer peripheral surface 9c of the second margin part 9 facing the outer peripheral side of the drill body 1 is located at the second margin front wall surface 9a in the cross section perpendicular to the axis O. The second margin front bevel 9d is chamfered into a convex curve having a smaller radius of curvature than the second margin outer circumferential surface 9c, which is in contact with the second margin outer circumferential surface 9c.

Note that these first and second margin outer circumferential surfaces 8c and 9c have a diameter D of the cutting blade 4, that is, a radius 1 centered around the axis O, which has a diameter equal to the diameter of a circle formed around the axis O by the outer peripheral end of the cutting blade 4. They are formed so as to be located on two cylindrical surfaces, and are formed in the shape of circular arcs having mutually equal radii centered on the axis O when viewed from the tip side in the direction of the axis O.

Here, in a cross section perpendicular to the axis O direction, the first margin width W1, which is the width along the chord of the arc formed by the first margin outer circumferential surface 8c, is equal to the chord of the arc formed by the second margin outer circumferential surface 9c. The second margin width W2, which is the width along the line, is within the range of 0.2×W1 to 0.6×W1. Further, the chip discharge groove 6 is cut upward toward the outer periphery at the rear end side of the cutting blade 3, and the length L in the direction of the axis O from the cutting blade 4 to the raised part of the chip discharge groove 6 is as follows. The diameter D of the cutting edge is within the range of 1×D to 3×D.

Furthermore, in this embodiment, in the cross section orthogonal to the axis O, the first and second margin front face portions 8d and 9d are formed in a convex circular arc shape, but the radius of curvature thereof is the same as that of the first margin. The radius of curvature R8d of the front bevel 8d is larger than the radius of curvature R9d of the second margin front bevel 9d. In the cross section perpendicular to the axis O, the radius of curvature R8d of the first margin front bevel 8d and the radius of curvature R9d of the second margin front bevel 9d are within the range of 10 μm to 50 μm.

In the present embodiment, in a cross section perpendicular to the axis O, the first margin rear wall surface 8b faces the opposite side to the drill rotation direction T of the first margin portion 8, and the first margin outer peripheral surface 8c faces the outer peripheral side. The intersecting ridgeline portion is also a first margin rear chamfered portion 8e that is chamfered into a convex curve that contacts the first margin rear wall surface 8b and the first margin outer circumferential surface 8c.

Similarly, in a cross section perpendicular to the axis O, the intersection ridgeline portion of the second margin rear wall surface 9b facing opposite to the drill rotation direction T of the second margin portion 9 and the second margin outer peripheral surface 9c facing the outer peripheral side. Also, a second margin rear chamfered portion 9e is chamfered in a convex curve shape and is in contact with the second margin rear wall surface 9b and the second margin outer circumferential surface 9c.

Furthermore, in the cross section perpendicular to the axis O, these first and second margin rear chamfered parts 8e and 9e are also formed in a convex circular arc shape, but the radius of curvature (radius) R8e of the first margin rear chamfered part 8e is larger than that of the first margin rear chamfered part 8e. The radius of curvature R8d of the first margin front chamfer 8d is made larger, and the radius of curvature R9d of the second margin front chamfer 9d is made larger than the radius of curvature (radius) R9e of the second margin rear chamfer 9e.

Furthermore, in the cross section perpendicular to the axis O, the radius of curvature R9e of the second margin rear chamfer 9e is smaller than the radius of curvature R8e of the first margin rear chamfer 8e. The radii of curvature (radii) R8e and R9e of the convex curves (arcs) formed by the first margin rear chamfered portion 8e and the second margin rear chamfered portion 9e in a cross section perpendicular to the axis O are within the range of 10 μm to 50 μm. has been done.

Also, chips are discharged from a portion of the outer peripheral surface of the land portion 7 of the cutting edge portion 3 between the first and second margin portions 8 and 9 and from the second margin portion 9 to the side opposite to the drill rotation direction T. The portion up to the heel 10, which is the intersection ridgeline portion of the groove 6 with the wall surface facing opposite to the drill rotation direction T, is a portion recessed from the first and second margin outer peripheral surfaces 8c and 9c toward the inner peripheral side of the drill body 1. The outer periphery flank face (second cut face) 11 is formed. Note that the corner portion where these outer circumferential relief surfaces 11 and the first margin rear wall surface 8b intersect, and the corner portion where the second margin front wall surface 9a and the second margin rear wall surface 9b intersect are aligned with the axis O. It is formed into a concave curved shape in the orthogonal cross section.

Of the outer circumferential surface of the land portion 7 of the cutting edge portion 3, an outer circumferential relief surface 11 between the first margin portion 8 and the second margin portion 9 is provided with an inner surface of the drill body 1 in a cross section perpendicular to the axis O. A concave portion 12 having a concave curve shape concave toward the circumference is formed. In this embodiment, a plurality (two) of such recesses 12 are formed in the outer circumferential flank surface 11 between the first margin part 8 and the second margin part 9 in a line in the circumferential direction.

Therefore, in a cross section perpendicular to the axis O, a chevron-shaped convex portion 13 that is convex toward the outer circumference of the cutting edge 3 relative to the concave portion 12 is formed between the plurality of concave portions 12. Become. Here, in the present embodiment, the depth d in the radial direction with respect to the axis O from the tip 13a of the convex part 13 to the bottom 12a of the concave part 12 adjacent to the convex part 13 in the circumferential direction is 10 μm or more. There is. Note that the plurality of (two) recesses 12 are formed to have the same shape and the same size, so the depths d in the radial direction with respect to the axis O from the tip 13a of the protrusion 13 to the bottom 12a of these recesses 12 are different from each other. equal.

The concave portion 12 and the first and second margin portions 8 and 9 are arranged in a spiral shape according to the twist of the chip discharge groove 6, as shown in FIGS. 1 and 3, and are perpendicular to the axis O. While maintaining the same cross-sectional shape, the chip discharge groove 6 is continuously formed up to the cut-out portion on the outer peripheral side of the drill body 1.

Furthermore, in this embodiment, as shown in FIG. 2 when viewed from the tip side in the direction of the axis O, the drill rotation of the extension surface of the first margin front wall surface 8a toward the outer circumferential side of the drill body 1 and the first margin outer circumferential surface 8c. The first margin straight line E1 passing through the intersection point P1 with the extension surface in the direction T and the axis O, the extension surface of the second margin front wall surface 9a toward the outer peripheral side of the drill body 1, and the second margin outer peripheral surface 9c of the drill. The intersection angle θ between the intersection point P2 with the surface extending in the rotational direction T and the second margin straight line E2 passing through the axis O is within the range of 30° to 60°.

In the drill configured in this manner, two margin portions, first and second margin portions 8 and 9, are formed on the outer peripheral surface of the land portion 7 between the two chip discharge grooves 6 of the cutting edge portion 3. Therefore, the cutting edge portion 3 can be supported by a total of four margin portions. For this reason, even if the drill is for counterboring holes where the tip angle α of the cutting edge 4 is close to 180° and the counterboring hole is to be formed on an inclined or curved surface of the workpiece, the cutting edge 4 will bite. It is possible to suppress whirling of the cutting edge portion 3 during cutting.

Further, in the drill having the above configuration, the outer peripheral flank 11 of the land portion 7 between the first and second margin portions 8 and 9 is recessed toward the inner peripheral side of the drill body 1 in a cross section perpendicular to the axis O. Since the concave portion 12 having a concave curved shape is formed, when a coolant such as a cutting oil is supplied during counterboring, the cutting fluid that has entered between the first and second margin portions 8 and 9 is On the outer peripheral side of the cutting edge part 3, as the drill body 1 rotates, it flows in the opposite direction to the drill rotation direction T between the drill body 1 and the inner peripheral surface of the drill hole, cooling and lubricating the second margin part 9, On the inner circumferential side of the cutting edge 3, the drill rotates along the bottom surface of the recess 12 facing the outer circumferential side of the drill body 1 by being pushed out by the cutting fluid that has flowed in the opposite direction to the drill rotation direction T on the outer circumferential side. Convection is formed so that it flows in the direction T side.

Therefore, according to the drill configured as described above, the first margin portion 8 can also be cooled and lubricated by the cutting fluid flowing in the drill rotation direction T side. Therefore, both the first and second margin parts 8 and 9 can be efficiently cooled and lubricated, so that fine chips generated during drilling are removed between the first and second margin parts 8 and 9. This makes it possible to prevent welding even if it gets into the surface.

The cutting fluid described above can be supplied to the cutting edge 3 from outside the drill body 1 by external oil supply, but for example, it can be supplied from the rear end surface of the shank 2 of the drill body to the tip of the cutting edge 3. A coolant hole may be formed toward the flank 5 or the like, and cutting fluid may be internally supplied through the coolant hole.

Furthermore, in the present embodiment, a plurality of (two) recesses 12 are lined up in the circumferential direction on the outer peripheral flank 11 between the first and second margin parts 8 and 9 in the land part 7 of the cutting edge part 3. It is formed. Therefore, this allows the above-described convection of cutting fluid to occur between each recess 12 and the inner circumferential surface of the machined hole.

In particular, in the concave portion 12 on the side of the drill rotation direction T, the cutting oil that has not cooled and lubricated the second margin portion 9 on the side opposite to the drill rotation direction T is caused to convect to cool and lubricate the first margin portion 8. becomes possible. Therefore, the first and second margin parts 8 and 9 can be cooled and lubricated more efficiently.

Note that when a plurality of recesses 12 are formed side by side in the circumferential direction on the outer circumferential surface of the cutting edge 3, as described above, between adjacent recesses 12 there are convexities where the concave curves formed by the cross sections of the recesses 12 intersect. A portion 13 is formed, and in a cross section perpendicular to the axis o, from the tip 13a of the convex portion 13 formed between the plurality of concave portions 12, to the concave portion 12 adjacent to the convex portion 13 in the circumferential direction. If the depth d in the radial direction with respect to the axis O to the bottom 12a is small, the recess 12 will be too shallow relative to the protrusion 13, and there is a risk that it will be difficult to reliably convect the cutting fluid.

Therefore, the depth d in the radial direction with respect to the axis O from the tip 13a of the convex portion 13 to the bottom 12a of the concave portion 12 is desirably 10 μm or more as in the present embodiment. By ensuring a sufficient depth d from the tip 13a to the bottom 12a of the recess 12, the cutting fluid can be reliably convected, and even more efficient first and second margin parts 8 and 9 and the machining hole can be formed. It becomes possible to cool and lubricate the inner peripheral surface.

However, if the depth d becomes too large, the rigidity and strength of the cutting edge 3 may be impaired, so the depth d is preferably 100 μm or less. The depth d of the recess 12 can be determined by, for example, applying a dial gauge to the outer peripheral flank 11 between the first and second margin parts in the radial direction with respect to the axis O, and rotating the drill body 1 around the axis O. This can be confirmed by rotating and measuring the height in the radial direction from the bottom 12a of the recess 12 to the tip 13a of the protrusion 13.

In addition, in the present embodiment, in a cross section perpendicular to the axis O, the first margin outer circumferential surface 8c has a width W1 along the chord of an arc centered on the axis O, while the second margin outer circumference The second margin width W2, which is the width along the chord of the arc formed by the surface 9c with the axis O as the center, is within the range of 0.2 x W1 to 0.6 x W1. The whirling of the cutting edge 3 can be reliably suppressed without increasing the driving force for rotation or generating high frictional heat between it and the inner peripheral surface of the machined hole.

That is, if the second margin width W2 is larger than the first margin width W1 by more than 0.6×W1, the first and second margin outer peripheral surfaces 8c and 9c will come into sliding contact with the inner peripheral surface of the machined hole. As the resistance increases, the cutting edge portion 3 is more likely to whirl, and there is a risk that the rotational driving force of the drill body 1 will increase and high frictional heat will be generated. On the other hand, if the second margin width W2 is so small as to be less than 0.2×W1 with respect to the first margin width W1, the cutting edge 3 can be securely held by the sliding contact of the second margin outer circumferential surface 9c with the inner circumferential surface of the machined hole. There is a possibility that the cutting edge portion 3 will not be able to be supported and the whirling of the cutting edge portion 3 will increase.

In this embodiment, the first and second margin front wall surfaces 8a and 9a and the first and second margin rear wall surfaces 8b and 9b intersect with the first and second margin outer circumferential surfaces 8c and 9c. , second margin front chamfered portions 8d, 9d and first and second margin rear chamfered portions 8e, 9e are formed, and the first and second margin widths W1, W2 are defined by the first and second margin front chamfered portions. The width is defined as the width of the portions excluding the portions 8d and 9d and the rear chamfered portions 8e and 9e of the first and second margins, but the width of the entire first and second margin outer circumferential surfaces 8c and 9c is in a cross section perpendicular to the axis O. If it is formed in an arc shape centered on the axis O and intersects the first and second margin front wall surfaces 8a and 9a and the first and second margin rear wall surfaces 8b and 9b at an angle, 1. The second margin widths W1 and W2 are widths along the chord of the arc formed by the entire first and second margin outer peripheral surfaces 8c and 9c.

Further, in this embodiment, the length L of the chip discharge groove 6 in the direction of the axis O is within the range of 1×D to 3×D with respect to the diameter D of the cutting edge 4. As described above, in a drill in which the length L of the chip discharge groove 6 is long, that is, in which the protruding length of the cutting edge 3 is long, whirling of the cutting edge 3 is particularly likely to occur, so in such a drill, According to this embodiment, by forming two margin parts, the first and second margin parts 8 and 9, on the outer circumferential surface of the land part 7 between the two chip discharge grooves 6 of the cutting edge part 3, It is possible to further improve hole accuracy, hole position accuracy, and surface roughness of the inner circumferential surface of the machined hole. Note that if the length L of the chip discharge groove 6 in the direction of the axis O is smaller than 1×D with respect to the diameter D of the cutting edge 4, it will not be possible to countersink a deep hole. Versatility may be impaired.

On the other hand, in this embodiment, the intersection angle θ between the first margin straight line E1 and the second margin straight line E2 is within the range of 30° to 60° when viewed from the tip side in the direction of the axis O. On the other hand, in the drill described in Patent Document 1, as shown in FIGS. 1 and 2 of Patent Document 1, this intersection angle θ is approximately 64°. In this case, the intersection angle θ is small, that is, the interval between the first and second margin portions 8 and 9 in the circumferential direction is small. Therefore, the time from when the first margin outer peripheral surface 8c of the first margin part 8 comes into sliding contact with the inner peripheral surface of the machined hole due to the rotation of the drill body 1 until the second margin outer peripheral surface 9c of the second margin part 9 comes into sliding contact. can be shortened.

Therefore, when the tip angle α of the cutting edge 4 is within the range of 178° to 182° and is close to a straight line perpendicular to the axis O, the axis O obliquely intersects with the inclined surface or curved surface formed on the workpiece. Even when counterboring holes in this manner, the time during which the cutting edge 3 is in an unstable state when the cutting edge 4 bites can be shortened, and whirling of the cutting edge 3 can be prevented. It can be suppressed. Therefore, it is possible to prevent the accuracy of the machined hole and the accuracy of the hole position from deteriorating, and to perform counterboring with even higher precision and quality.

Here, if the intersection angle θ of the first and second margin straight lines E1 and E2 exceeds 60°, the first margin outer circumferential surface 8c slides against the inner circumferential surface of the machined hole, and then the second margin outer circumferential surface 9c slides. It becomes impossible to shorten the time until contact occurs, and there is a possibility that whirling of the cutting edge 3 cannot be sufficiently suppressed. On the other hand, if the intersection angle θ of the first and second margin straight lines E1 and E2 is less than 30°, the first and second margin parts 8 and 9 will be too close to each other, and the cutting edge part 3 will be cut at two points in the circumferential direction. Since it is in a state where it is supported by sliding contact, there is a possibility that whirling of the cutting edge portion 3 is likely to occur when the cutting edge 4 bites.

In addition, in this embodiment, as described above, the first and second margin front facing portions 8d are provided at the intersection ridgeline portions of the first and second margin front wall surfaces 8a and 9a and the first and second margin outer peripheral surfaces 8c and 9c. , 9d are formed, and the first and second margin straight lines E1 and E2 are the extension surfaces of the first and second margin front wall surfaces 8a and 9a toward the outer circumferential side of the drill body 1 and the first and second margin outer circumferences. Although the lines are defined as straight lines passing through the axis O and the intersections P1 and P2 of the surfaces 8c and 9c with the extension surfaces in the drill rotation direction T, such first and second margin front chamfered portions 8d and 9d are formed. First, when the first and second margin front wall surfaces 8a and 9a intersect with the first and second margin outer peripheral surfaces 8c and 9c at an angle, the intersection points P1 and P2 are the first and second margin front wall surfaces. The intersections between 8a and 9a and the first and second margin outer circumferential surfaces 8c and 9c may be used.

Furthermore, in this embodiment, in the cross section perpendicular to the axis O, the intersection ridgeline portion between the first margin front wall surface 8a and the first margin outer circumferential surface 8c of the first margin portion 8 is chamfered in a convex curve shape as described above. The intersection ridgeline portion of the second margin front wall surface 9a and the second margin outer circumferential surface 9c of the second margin portion 9 is chamfered in a convex curve shape. Section 9d.

Here, these first and second margin front facing portions 8d and 9d are formed by the cutting edge 4 as the first and second margin portions 8 and 9 rotate in the drill rotation direction T of the drill body 1. Since this is the part that comes into sliding contact first with the inner circumferential surface of the counterbore hole, by forming the first and second margin front chamfers 8d and 9d with a convex curved cross section in such a part, even if the cutting edge Even if whirling occurs in 3, as in the case where the first and second margin front wall surfaces 8a and 9a and the first and second margin outer peripheral surfaces 8c and 9c intersect at an angle at the intersecting ridge line, this It is possible to prevent the intersecting ridgeline portions from digging into the inner circumferential surface of the machined hole and deteriorating the surface roughness, and from causing chips or the like in the angular intersecting ridgeline portions.

Furthermore, in this embodiment in particular, of the first and second margin front chamfers 8d and 9d, the radius of curvature R8d of the first margin front chamfer 8d is larger than the radius of curvature R9d of the second margin front chamfer 9d. has been done. Therefore, the first margin front bevel 8d, which is located on the drill rotation direction T side than the second margin front bevel 9d and slides into contact with the inner circumferential surface of the machined hole first, is bitten or chipped by the whirling of the cutting edge 3. This makes it possible to more reliably prevent this from occurring.

Furthermore, in this embodiment, in the cross section orthogonal to the axis O, the curvature radii (radii) R8d and R9d of the first and second margin front face portions 8d and 9d are within the range of 10 μm to 50 μm, and the 1. The cutting edge 3 can be supported by the inner circumferential surface of the machined hole and whirling can be suppressed while further reliably preventing the second margin front facing portions 8d and 9d from biting or chipping.

That is, if the curvature radii R8d and R9d of the first and second margin front facets 8d and 9d are smaller than 10 μm, the first and second margin front facets 8d and 9d become sharp to prevent digging and chipping. There is a risk that you will not be able to do so. On the other hand, if the radii of curvature R8d and R9d are larger than 50 μm, the circumferential direction of the first and second margin outer peripheral surfaces 8c and 9c of the first and second margin parts 8 and 9 that are in sliding contact with the inner peripheral surface of the machined hole. There is a possibility that the first and second margin widths W1 and W2, which are the widths, become small, making it impossible to reliably support the cutting edge 3 and suppress whirling.

In addition, in the present embodiment, in the cross section perpendicular to the axis O, the intersection ridgeline portion between the first margin rear wall surface 8b and the first margin outer circumferential surface 8c facing opposite to the drill rotation direction T of the first margin portion 8 is also The first margin rear chamfered portion 8e is chamfered in a convex curved shape, and the second margin rear wall surface 9b and the second margin outer circumferential surface 9c face opposite to the drill rotation direction T of the second margin portion 9. The intersecting ridgeline portion is also chamfered in a convex curve shape to form a second margin rear chamfered portion 9e. Therefore, in contrast to the case where the intersecting ridgeline portions of the first and second margin rear wall surfaces 8b and 9b and the first and second margin outer circumferential surfaces 8c and 9c intersect at an angle, these intersecting ridgeline portions form the cutting edge. It is possible to prevent the portion 3 from digging into the inner circumferential surface of the machined hole or causing chips or the like due to the whirling of the portion 3.

However, the first and second margin front chamfers 8d and 9d, which are located on the T side in the drill rotation direction, bite into the inner peripheral surface of the machined hole more than the first and second margin rear chamfers 8e and 9e. There is a high possibility that cracking or chipping may occur. Therefore, in the present embodiment, in the cross section perpendicular to the axis O, the radius of curvature R8d of the first margin front chamfered portion 8d is made larger than the radius of curvature R8e of the first margin rear chamfered portion 8e, and the second margin front The radius of curvature R9d of the chamfered portion 9d is made larger than the radius of curvature R9e of the second margin rear chamfered portion 9e.

Furthermore, in this embodiment, in the cross section perpendicular to the axis O, the radius of curvature R9e of the second margin rear chamfer 9e is smaller than the radius of curvature R8e of the first margin rear chamfer 8e. Therefore, especially when the second margin width W2 is smaller than the first margin width W1 as in the present embodiment, the second margin width W2 of the second margin outer peripheral surface 9c of the second margin portion 9 is small. The second margin portion 9 can also reliably support the cutting edge portion 3 and suppress whirling.

Furthermore, in this embodiment, in the cross section orthogonal to the axis O, the radii of curvature R8e and R9e of the first and second margin rear chamfered portions 8e and 9e are within the range of 10 μm to 50 μm, so that the first The cutting edge 3 can be supported by the inner peripheral surface of the machined hole and whirling can be suppressed while further reliably preventing biting or chipping at the second margin rear chamfered portions 8e and 9e.

That is, if the radius of curvature R8e, R9e of the first and second margin rear chamfered parts 8e, 9e is smaller than 10 μm, the first and second margin rear chamfered parts 8e, 9e become sharp to prevent digging or chipping. There is a risk that you will not be able to do so. On the other hand, if it is larger than 50 μm, the first and second margin widths W1 and W2 become small, and there is a possibility that the cutting edge 3 cannot be reliably supported and whirl can be suppressed.

1 Drill body 2 Shank part 3 Cutting blade part 4 Cutting blade 4a Thinning blade 5 Tip flank 6 Chip discharge groove 7 Land part 8 First margin part 8a First margin front wall surface 8b First margin rear wall surface 8c First margin outer peripheral surface 8d First margin front chamfered part 8e First margin rear chamfered part 9 Second margin part 9a Second margin front wall surface 9b Second margin rear wall surface 9c Second margin outer peripheral surface 9d Second margin front chamfered part 9e Second margin rear chamfered part Part 10 Heel 11 Peripheral flank 12 Recess 12a Bottom of recess 12 13 Projection 13a Tip of projection 13 O Axis of drill body 1 T Drill rotation direction T
α Point angle of cutting blade 4 R8d Radius of curvature of first margin front chamfer 8d R8e Radius of curvature of first margin rear chamfer 8e R9d Radius of curvature of second margin front chamfer 9d R9e Curvature of second margin front chamfer 9e Radius W1 First margin width W2 Second margin width D Diameter of cutting edge 4 L Length of chip discharge groove 6 in axis O direction P1 Extended surface of first margin front wall surface 8a to the outer peripheral side and first margin outer peripheral surface 8c P2 Intersection point between the extension surface of the second margin front wall surface 9a toward the outer circumferential side and the extension surface of the second margin outer peripheral surface 9c in the drill rotation direction T E1 First margin straight line E2 Second margin straight line θ Intersection angle between the first margin straight line E1 and the second margin straight line E2 d Depth in the radial direction from the tip 13a of the convex part 13 to the bottom 12a of the concave part 12 with respect to the axis O

Claims (4)

On the outer periphery of the cutting edge on the tip side of the drill body, which is rotated around the axis in the drill rotation direction, two chip evacuation grooves are spaced apart in the circumferential direction and open in the tip flank of the drill body and extend toward the rear end. formed with an opening,
A drill in which a cutting edge with a tip angle within a range of 178° to 182° is formed at the intersection ridge line between the wall surface of the chip discharge groove facing the drill rotation direction and the tip flank surface,
On the outer circumferential surface of the cutting edge between the two chip evacuation grooves, there is a first margin section that is connected to the outer circumferential end of the cutting edge and protrudes toward the outer circumferential side of the drill body; a second margin portion protruding toward the outer periphery of the drill body at an interval on the opposite side to the drill rotation direction;
The outer circumferential surface of the cutting edge has a plurality of concave concave portions recessed toward the inner circumferential side of the drill body in a cross section perpendicular to the axis between the first margin portion and the second margin portion. are arranged adjacent to each other in the circumferential direction . In a cross section perpendicular to the axis, the depth in the radial direction with respect to the axis from the tip of the convex formed between the plurality of concave parts to the bottom of the concave adjacent to the convex in the circumferential direction is 10 μm or more The drill according to claim 1, characterized in that: In a cross section perpendicular to the axis, the first margin width W1 is the width along the chord of the arc of the first margin outer circumferential surface, which faces the outer circumferential side of the first margin part and forms an arc with the axis as the center. On the other hand, the second margin width W2, which is the width along the chord of the arc of the first margin outer circumferential surface facing the outer circumferential side of the second margin part and forming an arc centered on the axis, is 0.2× The drill according to claim 1 or 2, wherein the drill is within a range of W1 to 0.6×W1. Claims 1 to 3, wherein the length L of the chip discharge groove in the axial direction is within a range of 1×D to 3×D with respect to the diameter D of the cutting edge. A drill described in any one of these items.

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