JP7423965B2 - 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 drill where the cutting edge has a substantially flat tip angle of 180° to 181°, when the cutting edge bites into the inclined or curved surface of the workpiece, the drill runs out as described above. easy. On the other hand, in the drill described in Patent Document 1, as shown in FIGS. 1 and 2 of Patent Document 1, the first margin located in the drill rotation direction among the two margins provided on the land is The wall surface facing the drill rotation direction of the section and the outer circumferential surface facing the outer circumferential side intersect at an angle, and the drill rotation direction of the second margin section is located on the opposite side of the drill rotation direction from the first margin section. The wall surface facing toward the wall and the outer peripheral surface facing toward the outer periphery also intersect at an angle.

However, in the drill described in Patent Document 1, if the above-mentioned run-out of the drill occurs when the cutting edge bites, the wall surface facing the drill rotation direction of the angular first margin portion and the outer circumferential surface may The intersecting ridgeline section or the intersecting ridgeline section between the wall surface facing the direction of rotation of the drill and the outer circumferential surface of the second margin section digs into the inner circumferential surface of the machined hole as the drill rotates, causing damage to the inner circumferential surface of the machined hole. There is a risk that the surface roughness may deteriorate or damage such as chipping may occur in the angular intersecting ridgeline portions.

The present invention was made against this background, and uses a drill for counterboring holes where the tip angle of the cutting edge is close to 180°. Even if whirling occurs, the surface roughness of the inner circumferential surface of the machined hole may deteriorate, or chips may occur at the intersection ridge line between the wall surface facing the direction of rotation of the drill and the outer circumferential surface facing the outer circumference at the margin. The aim is to provide a drill that can prevent this.

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. is formed, and in a cross section perpendicular to the axis, a first margin front wall surface of the first margin part facing the drill rotation direction and a circle centered on the axis facing the outer peripheral side of the first margin part. The ridge line intersecting with the arcuate outer circumferential surface of the first margin is a first margin front chamfered in a convex curve, and the second margin front wall face of the second margin faces the drill rotation direction. The intersection ridgeline with the second margin outer circumferential surface, which faces the outer circumferential side of the second margin section and forms an arc centered on the axis having the same radius as the first margin outer circumferential surface, has a convexly chamfered edge. 2-margin front chamfered part , in a cross section perpendicular to the axis, an intersecting ridge line between the first margin rear wall surface facing opposite to the drill rotation direction of the first margin part and the first margin outer circumferential surface; The portion is a first margin rear chamfered portion chamfered in a convex curved shape, and the second margin rear wall surface facing opposite to the drill rotation direction of the second margin portion and the second margin outer circumferential surface are connected. The intersecting ridgeline portion is a second margin rear chamfered portion chamfered in a convex curve shape, and in a cross section perpendicular to the axis, the radius of curvature of the second margin front chamfered portion is equal to the curvature of the second margin rear chamfered portion. It is characterized by being larger than the radius .

In the drill configured in this way, in a cross section perpendicular to the axis, the intersection ridgeline portion of the first margin front wall surface and the first margin outer peripheral surface is a first margin front chamfered portion chamfered in a convex curve shape. In addition, the intersecting ridgeline portion between the second margin front wall surface and the second margin outer circumferential surface is a second margin front beveled portion chamfered in a convex curve shape, and in these intersecting ridgeline portions, The first and second margin front wall surfaces facing the drill rotation direction of the first and second margin portions and the first and second margin outer peripheral surfaces are formed so as not to intersect at an angle.

For this reason, even if the cutting edge whirls around when the cutting edge, which has a point angle within the range of 178° to 182°, bites into the inclined or curved surface of the workpiece, the angular first margin The intersecting ridgeline between the wall surface and the first margin outer circumferential surface and the intersecting ridgeline between the second margin front wall surface and the second margin outer circumferential surface do not dig into the inner circumferential surface of the machined hole. Therefore, the inner circumferential surface of the machined hole may be damaged and the surface roughness may deteriorate, or the intersection ridge line between the front wall surface of the first margin and the outer circumferential surface of the first margin, or the intersection between the front wall surface of the second margin and the outer circumferential surface of the second margin may be damaged. Damage such as chipping can be prevented from occurring at the intersecting ridgeline portions, and it is possible to perform high-precision and high-quality counterboring, and it is also possible to extend the life of the drill.

Here, among these first and second margin front chamfers, the one that comes into sliding contact with the machined hole of the workpiece first as the drill body rotates is the first margin front chamfer located on the drill rotation direction side. Therefore, in the cross section perpendicular to the axis, by making the radius of curvature of the first margin front chamfer larger than the radius of curvature of the second margin front chamfer, it is possible to slide into the machined hole of the workpiece. It is possible to reliably prevent the contacting first margin front chamfer from digging into the inner circumferential surface of the machined hole.

In a cross section perpendicular to the axis, the radius of curvature of the first margin front bevel and the radius of curvature of the second margin front bevel are preferably within the range of 10 μm to 50 μm. If the radius of curvature of these first and second margin front facets is smaller than this range, the intersection ridgeline between the first and second margin front wall surfaces and the first and second margin outer circumferential surfaces will become sharp and cause digging. There is a risk that it will not be possible to prevent chipping, and conversely, if the radius of curvature of the front face of the first and second margins is larger than this range, the outer periphery of the first and second margins that slide into contact with the inner peripheral surface of the machined hole. There is a possibility that the first and second margin widths W1 and W2 of the surface become small, making it impossible to reliably support the cutting edge.

On the other hand, in a cross section perpendicular to the axis, an intersection ridgeline between the first margin rear wall surface facing opposite to the drill rotation direction of the first margin portion and the first margin outer circumferential surface is chamfered into a convex curve. The first margin is a rear chamfered portion, and the intersection ridgeline portion of the second margin rear wall surface facing opposite to the drill rotation direction of the second margin portion and the second margin outer circumferential surface has a convex curved shape. The chamfered second margin may be a rear chamfered portion. As a result, the intersecting ridgeline portions between the rear wall surfaces of the first and second margins and the outer circumferential surfaces of the first and second margins may dig into the inner circumferential surface of the machined hole, or chips may occur in these intersecting ridgeline portions. can be prevented.

In this case, the first and second margin front chamfers are more likely to dig into the inner peripheral surface of the machined hole than the first and second margin rear chamfers, or chipping may occur. Therefore, in a cross section perpendicular to the axis, the radius of curvature of the first margin front chamfer is preferably larger than the radius of curvature of the first margin rear chamfer, and the radius of curvature of the second margin front chamfer is It is desirable that the radius of curvature of the second margin is larger than the radius of curvature of the rear chamfered portion.

In addition, especially when the second margin width W2 is made smaller than the first margin width W1 as described below, in order to secure the circumferential width of the second margin outer circumferential surface that slides into contact with the inner circumferential surface of the machined hole. Similarly, in a cross section perpendicular to the axis, it is desirable that the radius of curvature of the second margin rear chamfer is smaller than the radius of curvature of the first margin rear chamfer. For the same reason as above, in a cross section perpendicular to the axis, the radius of curvature of the first margin rear chamfer and the radius of curvature of the second margin rear chamfer are within the range of 10 μm to 50 μm. This is desirable.

Furthermore, in the cross section perpendicular to the axis, the first margin width W1 is the width along the chord of the arc formed by the first margin outer circumferential surface, and the width along the chord of the arc formed by the second margin outer circumferential surface is If the certain second margin width W2 is too large, the resistance due to sliding contact between the first and second margin outer circumferential surfaces with the inner circumferential surface of the machined hole will increase, making it easier for the cutting edge to whirl around, and There is a risk that the driving force for rotating the drill body will increase or that high frictional heat will 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 when counterboring an inclined or curved surface of a workpiece, the cutting edge Even if whirling occurs in the cutting edge during biting, the intersecting ridgeline between the front wall surface of the first and second margins and the outer peripheral surface of the first and second margins is prevented from digging into the inner peripheral surface of the machined hole. This makes it possible to prevent deterioration of the surface roughness of the inner circumferential surface of the machined hole and prevent damage such as chips from occurring at these intersecting ridge lines, resulting in high precision and high quality. Not only can counterboring holes be performed, but also the life of the drill can be extended.

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

The intersection ridgeline between the first margin front wall surface 8a of the first margin portion 8 facing the drill rotation direction T and the first margin outer peripheral surface 8c of the first margin portion 8 facing the drill body 1 outer peripheral side is shown in FIG. As shown in , in the cross section orthogonal to the axis O, the first margin is chamfered into a convex curved shape having a smaller radius of curvature than the first margin outer circumferential surface 8c that is in contact with the first margin front wall surface 8a and the first margin outer circumferential surface 8c. This is a margin front chamfered portion 8d.

Further, the intersection ridgeline portion of the second margin front wall surface 9a of the second margin portion 9 facing the drill rotation direction T and the second margin outer peripheral surface 9c of the second margin portion 9 facing the drill body 1 outer peripheral side is also defined in FIG. As shown in , in the cross section perpendicular to the axis O, the second margin front surface is chamfered into a convex curved shape having a smaller radius of curvature than the second margin outer circumferential surface 9c that is in contact with the second margin front wall surface 9a and the second margin outer circumferential surface 9c. It is set as a recessed portion 9d.

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. When viewed from the tip side in the direction of the axis O or in a cross section perpendicular to the axis O, they are formed in the shape of circular arcs with equal radii centered on the axis O. .

In addition, in the cross section perpendicular to the axis O, the first margin width W1 is the width along the chord of the arc formed by the first margin outer peripheral surface 8c, and the width along the chord of the arc formed by the second margin outer peripheral surface 9c is The second margin width W2 is within the range of 0.2×W1 to 0.6×W1. Further, the chip discharge groove 6 is cut upward toward the outer circumference at the rear end side of the cutting edge 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 perpendicular 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 (radius) is The radius of curvature R8d of the margin 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.

Further, in this embodiment, in a cross section orthogonal to the axis O as shown in FIG. The intersecting ridgeline portion with the first margin outer circumferential surface 8c is also a first margin rear chamfered portion 8e that is chamfered in a convex curved shape that is in contact with the first margin rear wall surface 8b and the first margin outer circumferential surface 8c.

Similarly, as shown in FIG. 5, in a cross section perpendicular to the axis O, the second margin rear wall surface 9b of the second margin part 9 faces the opposite side to the drill rotation direction T, and the second margin outer peripheral surface faces the outer peripheral side. The intersecting ridgeline portion with 9c is also a second margin rear chamfered portion 9e that is chamfered in a convex curved shape that 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.

On the other hand, 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.

Furthermore, in the present embodiment, in the outer peripheral surface of the land portion 7 of the cutting edge portion 3, the outer peripheral relief surface 11 between the first margin portion 8 and the second margin portion 9 has a cross section perpendicular to the axis O. A concave curved concave portion 12 is formed on the inner peripheral side of the drill body 1. 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 FIGS. 4 and 5, an extension surface of the first margin front wall surface 8a toward the outer peripheral side of the drill body 1 and an extension of the first margin outer peripheral surface 8c in the drill rotation direction T. The first margin straight line E1 passing through the intersection point P1 with the plane and the axis O, the extension surface of the second margin front wall surface 9a toward the outer circumferential side of the drill body 1, and the second margin outer circumferential surface 9c in the drill rotation direction T. The intersection angle θ between the intersection point P2 with the extension surface and the second margin straight line E2 passing through the axis O as seen from the front end side in the direction of the axis O shown in FIG. 2 is within the range of 30° to 60°.

In the drill configured as described above, in a 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 curved shape. The intersection ridgeline between the second margin front wall surface 9a and the second margin outer circumferential surface 9c of the second margin section 9 is chamfered in a convex curve shape as the first margin front bevel 8d. It is said to be 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 chamfering such a part to have a convex curved cross section, even if the cutting edge 3 whirls around, the first and second As in the case where the two margin front wall surfaces 8a, 9a and the first and second margin outer circumferential surfaces 8c, 9c intersect at an angle at the intersecting ridgeline, the intersecting ridgeline may bite into the inner circumferential surface of the machined hole. It is possible to prevent deterioration of the surface roughness and the occurrence of chips or the like in the angular intersecting ridgeline portions. Therefore, it is possible to perform counterboring with high precision and high quality, and to extend the life of the drill.

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. For this reason, 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, may dig in due to the whirling of the cutting edge 3. This makes it possible to more reliably prevent chipping.

Furthermore, in this embodiment, in the cross section orthogonal to the axis O, the radii of curvature 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 The cutting edge portion 3 can be stably supported by the inner circumferential surface of the machined hole and whirling can be suppressed while further reliably preventing the two-margin front chamfered portions 8d and 9d from biting or chipping.

That is, if the radius of curvature R8d, R9d of these first and second margin front facets 8d, 9d is smaller than 10 μm, the first and second margin front facets 8d, 9d become sharp and prevent digging or 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 of the first and second margin front facing portions 8d and 9d are larger than 50 μm, the first and second margin portions 8d and 9 that are in sliding contact with the inner peripheral surface of the machined hole 1. Second margin The first and second margin widths W1 and W2, which are the widths in the circumferential direction of the outer circumferential surfaces 8c and 9c, become smaller, and there is a risk that the cutting edge portion 3 will be supported reliably and the whirling will become larger.

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, due to the whirling of the cutting edge 3, the intersection ridgeline between the first and second margin rear wall surfaces 8b and 9b and the first and second margin outer peripheral surfaces 8c and 9c may dig into the inner peripheral surface of the machined hole. , chipping, etc. can be prevented, and it is also possible to perform counterboring with high precision and high quality, and to extend the life of the drill.

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. For this reason, especially when the second margin width W2 is made smaller than the first margin width W1 as in the present embodiment, the second margin width W2 of the second margin outer circumferential surface 9c of the second margin part 9 is small. The second margin portion 9 also reliably supports the cutting edge portion 3 and suppresses the whirling from increasing.

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 will become small, and there is a risk that the cutting edge 3 will not be able to be supported reliably and the whirling will become large. .

Further, in the present embodiment, in a cross section perpendicular to the axis O, the second margin outer circumference is larger than the first margin width W1, which is the width of the first margin outer circumferential surface 8c along the chord of the arc formed with the axis O as the center. 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 the drill having the above configuration, as described above, the intersections of the first and second margin front wall surfaces 8a, 9a and the first and second margin rear wall surfaces 8b, 9b with the first and second margin outer circumferential surfaces 8c, 9c. Since the first and second margin front chamfers 8d and 9d and the first and second margin rear chamfers 8e and 9e are formed on the ridgeline, the first and second margin widths W1 and W2 are equal to the width of these first margins. , the width of the portion excluding the second margin front chamfered portions 8d, 9d and the first and second margin rear chamfered portions 8e, 9e.

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. By adopting this configuration, according to the present embodiment, it is possible to further improve the machined 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, the axis O will obliquely intersect with the inclined or curved surface formed on the workpiece. Even when counterboring a hole with the cutting edge 4 set in the same position, it is possible to shorten the time during which the cutting edge 3 is in an unstable state when the cutting edge 4 bites, and to suppress whirling of the cutting edge 3. be able to. 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 the present embodiment, the drill body 1 is located between the first and second margin portions 8 and 9 on the outer peripheral surface (outer peripheral flank surface 11) of the land portion 7 of the cutting edge portion 3 in a cross section perpendicular to the axis O. A concave curved concave portion 12 is formed that is concave toward the inner peripheral side of the concave portion. For this reason, as shown in FIGS. 1 and 2 of Patent Document 1, for example, the outer circumferential flank of the cutting edge between the two margins is recessed than the outer circumferential surfaces of the two margins in a cross section perpendicular to the axis. Although the drill body is formed in a convex curved shape, in the case of wet cutting in which counterboring is performed while supplying cutting fluid, the drill body is Since convection of the cutting fluid can be generated as the cutting fluid rotates, it is possible to efficiently cool and lubricate the first and second margin parts 8 and 9 and the inner peripheral surface of the machined hole. It is possible to avoid welding or the like from occurring in the margin parts 8 and 9.

Furthermore, in this embodiment, a plurality of (two) recesses 12 are formed in the outer circumferential flank surface 11 between the first and second margin parts 8 and 9 of the cutting edge part 3 in a line in the circumferential direction. Therefore, convection of the cutting fluid can be generated between the individual recesses 12 and the inner circumferential surface of the machined hole, so that more efficient first and second margin parts 8 and 9 and the inner circumferential surface of the machined hole It is possible to achieve cooling and lubrication of the parts, and it is also possible to prevent welding etc. more reliably.

Furthermore, in this embodiment, when a plurality of recesses 12 are formed in line in the circumferential direction on the outer circumferential flank surface 11 between the first and second margin parts 8 and 9 of the cutting edge part 3, the axis In a cross section perpendicular to O, the depth in the radial direction with respect to the axis O from the tip 13a of the convex part 13 formed between adjacent concave parts 12 to the bottom 12a of the concave part 12 adjacent in the circumferential direction of this convex part 13 d is set to be 10 μm or more.

Therefore, the depth d from the tip 13a of the convex part 13 to the bottom 12a of the concave part 12 can be ensured sufficiently, and the cutting fluid can be reliably convected. It becomes possible to cool and lubricate the inner peripheral surfaces of the holes 8 and 9 and the machined holes. That is, if the depth d is less than 10 μm, the recess 12 becomes too shallow relative to the protrusion 13, and there is a possibility that it will be difficult to reliably cause the cutting fluid to convect. 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 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.

1 Drill body 2 Shank part 3 Cutting blade part 4 Cutting blade 4a Thinning blade 5 Tip flank face 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 circumferential side and first margin outer circumferential 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 (8)

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;
In a cross section perpendicular to the axis, a first margin front wall surface of the first margin portion facing the drill rotation direction and a first margin forming an arc shape with the axis as the center, facing the outer peripheral side of the first margin portion. The intersecting ridgeline with the outer circumferential surface is a first margin front chamfered part that is chamfered in a convex curve shape, and the second margin front wall face facing the drill rotation direction of the second margin part and the second margin part are The intersecting ridgeline portion with the second margin outer circumferential surface, which faces the outer circumferential side and forms an arc centered on the axis having the same radius as the first margin outer circumferential surface, is a second margin front chamfered portion chamfered in a convex curve shape. has been
In a cross section perpendicular to the axis, the intersection ridgeline between the first margin rear wall surface facing opposite to the drill rotation direction of the first margin portion and the first margin outer circumferential surface has a convexly chamfered edge. 1 margin is a rear chamfered portion, and an intersecting ridgeline portion of the second margin rear wall surface facing opposite to the drill rotation direction of the second margin portion and the second margin outer circumferential surface is chamfered in a convex curve shape. The second margin is the rear chamfered part,
In a cross section perpendicular to the axis, the radius of curvature of the second margin front chamfer is larger than the radius of curvature of the second margin rear chamfer . The drill according to claim 1, wherein the radius of curvature of the first margin front bevel is larger than the radius of curvature of the second margin front bevel in a cross section perpendicular to the axis. Claim 1 or claim 1, wherein in a cross section perpendicular to the axis, a radius of curvature of the first margin front bevel and a radius of curvature of the second margin front bevel are within a range of 10 μm to 50 μm. The drill according to claim 2. The radius of curvature of the first margin front chamfer is larger than the radius of curvature of the first margin rear chamfer in a cross section perpendicular to the axis, according to any one of claims 1 to 3. drill. Any one of claims 1 to 4, wherein in a cross section perpendicular to the axis, the radius of curvature of the second margin rear chamfer is smaller than the radius of curvature of the first margin rear chamfer. Drill as described in. In a cross section perpendicular to the axis, the radius of curvature of the first margin rear chamfer and the radius of curvature of the second margin rear chamfer are within a range of 10 μm to 50 μm. A drill according to any one of claims 5 to 6. In a cross section perpendicular to the axis, the first margin width W1 is the width along the chord of the arc formed by the first margin outer peripheral surface, while the width is the width along the chord of the arc formed by the second margin outer peripheral surface. The drill according to any one of claims 1 to 6 , wherein a certain second margin width W2 is within a range of 0.2 x W1 to 0.6 x W1. Claims 1 to 7 , 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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