JP4725369B2 - Drill - Google Patents

Description

  The present invention relates to a drill used for drilling for forming a processed hole in a workpiece.

Conventionally, as such a drill, a cutting edge portion is formed on the front end side of a drill body rotated about an axis, and a pair of chip discharge grooves extending toward the rear end side are formed on the outer periphery of the cutting blade portion. A drill is known in which cutting edges are formed at the intersection ridgeline between the wall surface of the chip discharge groove facing the front side of the drill rotation direction and the tip flank of the cutting edge.
In such a drill, the drill body is rotated around the axis and fed in the axial direction, and is pressed against the workpiece, thereby cutting the workpiece with a cutting blade and machining holes with a predetermined inner diameter. Is formed.

  In cutting with such a drill, if chips generated during cutting accumulate inside the hole, the cutting resistance increases due to the chips, and the drill breaks, or the chips enter the cutting edge. It is known that various troubles may occur such as the inability to cut by welding, or the inner wall surface of a processing hole being damaged by chips.

Thus, for example, in the drill disclosed in Patent Document 1, the cutting edge is composed of two straight blades, a primary straight blade and a second straight blade, and the first is located at the outer peripheral end of the cutting blade. The radial rake angle of the next straight blade is set to the negative side from -25 ° to -15 °. By setting it as such a cutting-blade shape, the length of a chip can be shortened and the chip | tip discharge property can be aimed at.
JP 63-52908 A

By the way, when forming a processed hole with a drill, the inner wall surface of the processed hole is cut at the outer peripheral end portion of the cutting blade. Here, in the cutting edge shape as disclosed in Patent Document 1, the radial rake angle of the outer peripheral end portion of the cutting edge is set to a large negative side from -25 ° to -15 °. Becomes worse, the inner wall surface of the machining hole and the outer peripheral edge of the cutting edge slide, and the inner wall surface of the machining hole is work-hardened.
When the inner wall surface of a processed hole is hardened, when the threaded hole is processed into the processed hole or when a pin is press-fitted, the deformation resistance of the processed hole increases and these operations cannot be performed efficiently. There was a problem.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the drill which can suppress the work hardening of the inner wall surface of a working hole by improving the sharpness of a cutting blade.

  In order to solve this problem, according to the present invention, a chip discharge groove extending toward the rear end side is formed on the outer periphery of a cutting edge portion provided on the tip side of a drill body rotated about an axis, and the chip In a drill in which a cutting edge is formed at a crossing ridge line portion between a wall surface facing the front side in the drill rotation direction of the discharge groove and the tip flank surface of the cutting edge portion, the cutting blade is located on the rear side in the drill rotation direction when viewed from the front end. It consists of a concave curved blade and a convex curved blade that continues to the outer peripheral side of the concave curved blade and protrudes forward in the direction of drill rotation. The radius of curvature R1 of the concave curved blade is 1 × with respect to the drill outer diameter D. The radius of curvature R2 of the convex curve blade is set within a range of 0.04 × D ≦ R2 ≦ 0.07 × D, and is set within a range of D ≦ R1 ≦ 3 × D. The radial rake angle γ1 at the outer peripheral edge of the blade is set within a range of −12 ° ≦ γ1 ≦ −8 °. It is characterized by being defined.

In the drill of this configuration, the cutting edge is constituted by a concave curved blade that is recessed toward the rear side in the drill rotation direction and a convex curved blade that is connected to the outer peripheral side of the concave curved blade and projects forward in the drill rotation direction. As a result, the entire cutting edge is not cut into the workpiece at once, and the cutting resistance can be reduced.
Further, since the radial rake angle γ at the outer peripheral edge of the cutting edge is set within the range of −12 ° ≦ γ ≦ −8 °, the cutting edge outer peripheral edge can be improved and the cutting edge outer periphery can be improved. It is possible to secure the strength at the end and prevent the cutting edge from being damaged by the cutting resistance.

  Moreover, since the radius of curvature R1 of the concave curve blade is set within the range of 1 × D ≦ R1 ≦ 3 × D with respect to the drill outer diameter D, the sharpness of the entire cutting blade is improved by the concave curve blade. This can improve the strength of the concave curved blade and prevent the strength of the concave curved blade from greatly decreasing. In addition, since the radius of curvature R2 of the convex curve blade is set in the range of 0.04 × D ≦ R2 ≦ 0.07 × D, the strength of the outer peripheral edge of the cutting blade is ensured and the cutting resistance is ensured. It is possible to reliably prevent the cutting edge from being damaged.

  Here, the ratio L1 / L2 between the length L1 of the concave curve blade and the length L2 of the convex curve blade viewed from the side facing the tip flank is within a range of 25 ≦ L1 / L2 ≦ 35. By setting, the length of the concave curve blade mainly used for cutting can be ensured and cutting can be performed satisfactorily, and the strength of the outer peripheral edge of the cutting blade can be reliably ensured. Moreover, a uniform sharpness can be ensured over the entire cutting edge.

  In addition, the wall surface facing the front side in the drill rotation direction of the chip discharge groove is connected to the concave curve portion recessed on the rear side in the drill rotation direction and the outer periphery side of the concave curve portion in the cross section orthogonal to the axis. It is comprised with the convex curve part which protruded ahead, and the curvature radius R3 of the said concave curve part is set in the range of 0.7 * D <= R3 <= 0.9 * D with respect to the said drill outer diameter D. In addition, the radius of curvature R4 of the convex curve portion is set within a range of 0.1 × D ≦ R4 ≦ 0.2 × D, and the radial rake angle γ2 at the outer peripheral end of the chip discharge groove is set to −2 ≦ γ2. By setting it within the range of ≦ + 3 °, the resistance when the rear end portion of the cutting edge slides against the inner wall surface of the machining hole can be kept small, and the strength of the outer peripheral edge of the chip discharge groove can be secured. This can prevent the drill body from being damaged.

Furthermore, by setting the core height H of the cutting edge to be within the range of 0.06 × D ≦ H ≦ 0.1 × D with respect to the drill outer diameter D, the flank face connected to the cutting edge is reduced. The true rake angle of the cutting edge can be increased and the cutting edge of the entire cutting edge can be further improved, and the cutting edge can be prevented from being damaged due to cutting resistance by securing the strength of the cutting edge.
In addition, in order to achieve such an effect reliably, it is preferable to set the core height H within a range of 0.07 ≦ H ≦ 0.09.

  Further, the groove width ratio W1 / W2 in the cross section orthogonal to the axial direction is set within a range of 0.3 ≦ W1 / W2 ≦ 0.6, and the curvature radius R of the groove bottom portion of the chip discharge groove is set as follows: By setting within the range of 0.1 × D ≦ R ≦ 0.25 × D, the chips generated by the cutting blade and guided into the chip discharge groove are forced along the radius of curvature R of the groove bottom. Since the chips can be cut into short pieces by curling, it is possible to improve the chip discharge performance of this drill.

  ADVANTAGE OF THE INVENTION According to this invention, the drill which can suppress the work hardening of the inner wall surface of a process hole can be provided by improving the sharpness of a cutting blade.

A drill according to an embodiment of the present invention will be described with reference to the accompanying drawings. 1 to 3 show a drill according to an embodiment of the present invention.
As shown in FIG. 1, this drill has a drill body 10 having a substantially cylindrical shape with an axis O as the center, and the rear end side (upper side in FIG. 1) of the drill body 10 is a rotating shaft of the machine tool. The tip end side (lower side in FIG. 1) of the drill body 10 is a cutting edge portion 12.

  On the outer periphery of the cutting edge portion 12, a pair of chip discharge grooves 20, 20 that twist to the rear side in the drill rotation direction T from the front flank 13 toward the rear end side in the axis O direction rotate 180 ° with respect to the axis O. It is formed symmetrically. The chip discharge groove 20 has a wall surface 21 that faces the front side of the drill rotation direction T, a groove bottom portion 22 that faces the outer side of the drill body 10 in the radial direction, and a wall surface 23 that faces the rear side of the drill rotation direction T.

Further, cutting edges 15 and 15 are formed at the intersecting ridge line portions of the wall surfaces 21 and 21 facing the front side of the drill rotation direction T of the chip discharge grooves 20 and 20 and the tip flank 13 respectively.
Here, the tip end side of the wall surface 21 facing the front side of the drill rotation direction T of the chip discharge groove 20 is connected to the concave curved surface that is recessed toward the rear side of the drill rotation direction T and the outer peripheral end of the concave curved surface. Accordingly, the cutting edge 15 formed at the intersecting ridge line portion of the wall surface 21 facing the front side of the drill rotation direction T and the tip flank 13 is formed in the drill rotation direction T. The concave curved blade 15A is recessed to the rear side, and the convex curved blade 15B is connected to the outer peripheral side of the concave curved blade 15A and protrudes forward in the drill rotation direction T.

The radius of curvature R1 of the concave curved blade 15A is set within a range of 1 × D ≦ R1 ≦ 3 × D with respect to the drill outer diameter D. In this embodiment, R1 = 1.34 × D. ing. Further, the curvature radius R2 of the convex curve blade 15B is set within a range of 0.04 × D ≦ R2 ≦ 0.07 × D with respect to the drill outer diameter D. In this embodiment, R2 = 0. 04 × D is set.
And the radial rake angle γ1 at the outer peripheral end of the cutting edge 15 is set to be within a range of −12 ° ≦ γ1 ≦ −8 °, and in this embodiment, γ1 = −8 °. .

  Furthermore, when the concave curve blade 15A and the convex curve blade 15B are viewed from the side facing the tip flank 13, the ratio L1 / L2 between the length L1 of the concave curve blade 15A and the length L2 of the convex curve blade 15B is 25. ≦ L1 / L2 ≦ 35 is set, and in this embodiment, L1 / L2 = 30 is set. That is, most of the cutting blade 15 is constituted by the concave curve blade 15A, and the convex curve blade 15B is slightly disposed at the outer peripheral end portion of the concave curve blade 15A.

In addition, the rear end side of the wall surface 21 facing the front side of the drill rotation direction T of the chip discharge groove 20 has a concave curve portion 21A that is recessed toward the rear side of the drill rotation direction T in the cross section orthogonal to the axis O and the concave curve. It has a convex curve portion 21B that continues to the outer peripheral end of the portion 21A and protrudes forward in the drill rotation direction T. The radius of curvature R3 of the concave curve portion 21A is set in a range of 0.7 × D ≦ R3 ≦ 0.9 × D, and in this embodiment, R3 = 0.76 × D. . Further, the radius of curvature R4 of the convex curve portion 21B is set within a range of 0.1 × D ≦ R4 ≦ 0.2 × D, and in this embodiment, R4 = 0.12 × D. Yes.
And the radial rake angle γ2 of the outer peripheral end portion of the chip discharge groove 20 is set in the range of −2 ° ≦ γ2 ≦ + 3 °, and in this embodiment, γ2 = 0 °.

  The core height H of the cutting edge 15 (the protruding height of the cutting edge 15 from the reference line at the center of the spindle) is within the range of 0.06 × D ≦ H ≦ 0.1 × D with respect to the drill outer diameter D. Preferably, it is set within the range of 0.07 × D ≦ H ≦ 0.08 × D. In this embodiment, H is set to 0.076 × D.

As shown in FIG. 2, the tip flank 13 of the cutting edge 12 has a first cutting edge 15, 15 formed on the ridge line portion on the front side in the drill rotation direction T when the chip discharge grooves 20, 20 intersect. The flank faces 13A, 13A and the second flank faces 13B, 13B connected to the first flank face 13A, 13A on the rear side in the drill rotation direction T have a multi-step surface shape. Is provided with a relief that increases in a multi-step manner as it goes backward in the drill rotation direction T. In the present embodiment, the clearance angle formed by the first flank 13A is 7 °, and the clearance angle formed by the second flank 13B is 25 °.
Here, in this embodiment, since the core height H is set to H = 0.076 × D, the first flank 13A is made small as shown in FIG. .

Further, the tip flank 13 is inclined so as to gradually go to the rear end side of the cutting edge portion 12 as it goes outward in the radial direction of the drill body 10, and a predetermined tip angle α is given to the cutting edges 15, 15. It has come to be. In the present embodiment, the tip angle α is set to α = 135 °.
Further, the cutting edge portion 12 is provided with a back taper so that the outer diameter gradually becomes smaller toward the rear end side of the cutting edge portion 12, and in this embodiment, the back taper amount is 0.3 / 100 to 0.35 / 100.

Further, at the tip of the cutting edge portion 12, the groove bottom portion 22 of the chip discharge groove 20, the wall surface 23 facing the rear side in the drill rotation direction T, and the tip flank 13 (first flank 13A and second flank 13B) intersect. The thinning portion 16 is formed so as to cut out the ridge line portion toward the inner side of the chip discharge groove 20 as it crosses the axis O and moves toward the rear end side of the cutting edge portion 12.
Therefore, on the inner peripheral end side of the cutting edge 15, it is connected to a thinning cutting edge 17 that is formed at the intersecting ridge line portion of the thinning portion 16 and the first flank 13 A and extends linearly toward the axis O. .

Here, as shown in FIG. 2, the outer peripheral surface of the cutting edge portion 12 excluding the pair of chip discharge grooves 20, 20, that is, the land portion 30 in this drill, is a cross section orthogonal to the axis O, as shown in FIG. A margin part 31 having a substantially arc shape centering on the axis O intersecting with the outer peripheral side ridge line part of the wall surface 21 facing the front side of the drill rotation direction T of the margin part 31 is connected to the rear side of the drill part T in the drill rotation direction T. And a second picking surface 32 having a substantially arc shape centering on an axis O having an outer diameter one step smaller than the circular arc formed by the margin portion 31, and the drilling direction T rear side of the second picking surface 32 The end, that is, the outer peripheral end portion of the wall surface facing the drill rotation direction T rear side of the chip discharge groove 20 is a heel portion 33.
Further, like the chip discharge groove 20, the margin portion 31 and the second picking surface 32 are arranged on the rear side in the drill rotation direction T from the portion intersecting the tip flank 13 toward the rear end side in the axis O direction. It is formed to be twisted.

  In the cutting edge portion 12, as shown in FIG. 3, the groove width W <b> 1 of the chip discharge groove 20 is smaller than the land width W <b> 2 of the land portion 30, specifically, orthogonal to the axis O. The groove width ratio W1 / W2, which is the ratio of the groove width W1 of the chip discharge groove 20 and the land width W2 of the land portion 30 in the cross section, is set within a range of 0.3 ≦ W1 / W2 ≦ 0.6, and more Preferably, it is set within the range of 0.4 ≦ W1 / W2 ≦ 0.5. In the present embodiment, the groove width ratio W1 / W2 = 0.48.

  Further, as described above, the chip discharge groove 20 has a wall surface 21 facing the front side in the drill rotation direction T, a groove bottom portion 22 facing the outer side in the radial direction of the drill body, and a wall surface 23 facing the rear side in the drill rotation direction T. In the cross section perpendicular to the axis O, the radius of curvature R of the concave curve formed by the groove bottom 22 is set within the range of 0.1 × D ≦ R ≦ 0.25 × D with respect to the drill outer diameter D. More preferably, 0.15 × D ≦ R ≦ 0.2 × D is set. In the present embodiment, the radius of curvature R is 0.15 × D.

Further, the twist angle of the chip discharge groove 20, that is, the angle θ formed by the axis O and the center line of the chip discharge groove 20 is set within a range of 15 ° ≦ θ ≦ 35 °, and more preferably 20 ° ≦ θ. It is set within a range of ≦ 30 °. In the present embodiment, the twist angle θ is 25 °.
Further, in the present embodiment, the surface of the cutting edge portion 12 in the drill body 10, that is, the surface of the land portion 30 that is the outer peripheral surface of the cutting blade portion 12, the tip flank 13, the chip discharge groove 20 and the thinning portion 16. On the other hand, a hard film such as TiN, TiCN, or TiAlN is coated.

  In the drill configured as described above, the shank portion 11 formed at the rear end of the drill body 10 is gripped by the rotating shaft of the machine tool and rotated around the axis O, and at the front end side in the axis O direction. It is sent toward and pressed against the material to be cut to form a processed hole having a predetermined inner diameter in the material to be cut. Moreover, the drill of this embodiment is used when forming a through hole in a flange portion in which, for example, the plate thickness t is t = 1 × D with respect to the drill outer diameter D, as the processing hole, The hole depth L of the processed hole is L = 1 × D.

  In the drill according to the present embodiment configured as described above, the cutting blade 15 is connected to the concave curved blade 15A recessed toward the rear side in the drill rotational direction T and the outer peripheral side of the concave curved blade 15A, and the drill rotational direction. Since it is comprised by the convex curve blade 15B which protruded to T front side, the cutting force 15 can be reduced, without cutting the cutting blade 15 whole at a time into a to-be-cut material.

  Further, the radius of curvature R1 of the concave curved blade 15A is set within a range of 1 × D ≦ R1 ≦ 3 × D with respect to the drill outer diameter D, and in this embodiment, R1 = 1.34 × D. Therefore, the sharpness of the entire cutting blade can be improved by the concave curved blade, and the strength of the concave curved blade can be prevented from greatly decreasing. Further, the radius of curvature R2 of the convex curve blade 15B is set within the range of 0.04 × D ≦ R2 ≦ 0.07 × D, and in this embodiment, R2 = 0.04 × D. In addition to improving the sharpness of the outer periphery of the cutting blade 15, it is possible to ensure the strength of the cutting blade 15 and reliably prevent the cutting blade 15 from being damaged.

  Further, the radial rake angle γ1 at the outer peripheral end of the cutting edge 15 is set within a range of −12 ° ≦ γ1 ≦ −8 °, and in this embodiment, γ1 = −8 °. It is possible to improve the sharpness at the outer peripheral edge of 15 and prevent work hardening of the inner wall surface of the processing hole, to ensure the strength of the cutting edge at the outer peripheral edge of the cutting edge 15, and to reliably prevent the cutting edge 15 from being damaged by cutting resistance. .

  Further, when the concave curved blade 15A and the convex curved blade 15B are viewed from the side facing the tip flank 13, the ratio L1 / L2 between the length L1 of the concave curved blade 15A and the length L2 of the convex curved blade 15B is 25. ≦ L1 / L2 ≦ 35 is set, and in this embodiment, L1 / L2 = 30 is set. Therefore, the length of the concave curved blade 15A mainly used for cutting is secured. Thus, the cutting resistance can be reduced, and the strength of the cutting edge 15 at the outer peripheral end portion can be further ensured by making the outer peripheral end of the cutting edge 15 the convex curve edge 15B. Further, a uniform sharpness can be ensured over the entire cutting edge 15.

  Further, the wall surface 21 facing the front side of the drill rotation direction T of the chip discharge groove 20 is connected to the concave curve portion 21A recessed toward the rear side of the drill rotation direction T and the outer peripheral side of the concave curve portion in a cross section orthogonal to the axis O. This is composed of a convex curve portion 21B protruding forward in the drill rotation direction T, and the radius of curvature R3 of the concave curve portion 21A is set within a range of 0.7 × D ≦ R3 ≦ 0.9 × D. In the embodiment, R3 = 0.76 × D is set, and the radius of curvature R4 of the convex curve portion 21B is set in a range of 0.1 × D ≦ R4 ≦ 0.2 × D. In this embodiment, R4 = 0.12 × D, the radial rake angle γ2 at the outer peripheral end of the chip discharge groove 20 is set within the range of −2 ≦ γ2 ≦ + 3 °, and in this embodiment, γ2 = 0 °. Therefore, when the rear end side portion of the cutting edge portion 12 slides on the inner wall surface of the machining hole, While resistance can be suppressed small, the intensity | strength of the outer peripheral end of the chip | tip discharge groove | channel 20 can be ensured, and it can prevent that the drill main body 10 is damaged by cutting resistance.

  Further, the center height H of the cutting edge 15 is preferably 0.07 ≦ H ≦ 0.0.0 so that the drill outer diameter D is within the range of 0.06 × D ≦ H ≦ 0.1 × D. Is set within the range of 09, and in the present embodiment, H = 0.076 × D, and therefore the first flank 13A connected to the rear side of the drill rotation direction T of the cutting blade 15 is reduced, The true rake angle of the cutting blade 15 can be increased, and the sharpness of the entire cutting blade 15 can be improved. Furthermore, the strength of the cutting blade 15 can be ensured, and the chipping of the cutting blade 15 due to cutting resistance can be reliably prevented.

  Further, the groove width ratio W1 / W2 in the cross section perpendicular to the direction of the axis O is set within a range of 0.3 ≦ W1 / W2 ≦ 0.6, and more preferably 0.4 ≦ W1 / W2 ≦ 0.5. In this embodiment, since the groove width ratio is W1 / W2 = 0.48, the portion of the drill body 10 that is notched is reduced, and the rigidity of the drill body 10 is improved. be able to. Therefore, there is little vibration when the drill is rotated at high speed, and the processed hole can be formed with high dimensional accuracy.

Further, the radius of curvature R of the groove bottom portion 22 of the chip discharge groove 20 is set within a range of 0.1 × D ≦ R ≦ 0.25 × D, and more preferably 0.15 × D ≦ R ≦ 0.2. In this embodiment, the radius of curvature is R = 0.15 × D. Therefore, the chip generated by the cutting blade 15 and guided into the chip discharge groove 20 is the bottom 22 of the groove. The chips can be cut short by forcibly curling along the radius of curvature R. Therefore, the chip discharging property of this drill can be improved.
In the present embodiment, since the hole depth L of the processed hole is L = 1 × D with respect to the drill outer diameter D, the distance that the chip passes through the chip discharge groove 20 is short, and chip clogging occurs. Less likely to occur.

Furthermore, since the twist angle θ of the chip discharge groove 20 is set to θ = 25 °, the chips generated at the bottom of the processed hole can be reliably discharged to the rear end side of the drill and the drilling process can be performed satisfactorily. In addition, the portion of the drill body 10 notched in the cross section perpendicular to the axis O is reduced, the rigidity of the drill body 10 can be improved, and the occurrence of vibration when the drill is rotated at high speed is reliably prevented. The processed hole can be formed with higher dimensional accuracy.
Further, since the surface of the cutting edge portion 12 in the drill body 10 is coated with a hard film such as TiN, TiCN, or TiAlN, the wear resistance can be improved and the life of the drill can be extended.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
For example, the tip angle, the groove width ratio, and the like are not limited to this embodiment, and can be any shape. However, the shape of the cutting edge and the radial rake angle of the outer peripheral edge of the cutting edge need to be set within the scope of the present invention.

Moreover, although this embodiment demonstrated as what coated the ceramic coating, such as TiN, TiCN, TiAlN, on the surface of the cutting-blade part, it is not limited to this, Even if these hard films are not coat | covered Good.
Furthermore, although it demonstrated as a drill which forms the processing hole by which the hole depth L was set to L = 1xD with respect to the drill outer diameter D, it is not limited to this, The deep hole of L> 1xD It may be. In addition, when processing a deep hole, in order to improve chip discharge | emission property, it is preferable to make groove width ratio larger than this embodiment.

Below, the result of the comparative experiment conducted in order to confirm the effect of this invention is demonstrated. In this comparative experiment, using a drill (drill outer diameter 14 mm) with a modified blade shape and core height H, a carbon steel plate as a material to be cut was drilled to a depth of 7 mm and Vickers hardness around the hole entrance Measurement and observation of the metal structure were performed. The cutting conditions were a cutting speed of 73 m / min and a feed speed of 0.23 mm / rev.
The experimental results are shown in Table 1.

As shown in Table 1, in Comparative Example 1 in which the core height H was 0.13 × D with a straight cutting edge, a work hardened layer was observed around the work hole. In Comparative Example 2 in which the core height H is 0.1 × D with a straight cutting edge and in Comparative Example 3 in which the core height H is 0.15 × D with a curved cutting edge, a clear work hardened layer is not confirmed. Deformation of the metal structure was observed. Further, the Vickers hardness was 367 Hv in Comparative Example 2 and 322 Hv in Comparative Example 3, and it was confirmed that each was work-hardened.
On the other hand, in the examples of the present invention, no clear deformation of the metal structure was observed, the Vickers hardness was as small as 277 Hv, and it was confirmed that the work hardening of the inner wall surface of the processed hole was suppressed.

It is a side view of the drill which is embodiment of this invention. It is a X direction arrow line view in FIG. It is YY sectional drawing in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Drill main body 12 Cutting edge part 13 Tip flank 15 Cutting edge 15A Concave curve blade 15B Convex curve blade 20 Chip discharge groove 21 Wall surface 21A which faces a drill rotation direction front side Concave curve part 21B Convex curve part 22 Groove bottom part 23 Drill rotation direction Wall facing backward

Claims (5)

A chip discharge groove extending toward the rear end side is formed on the outer periphery of the cutting edge portion provided on the tip side of the drill body rotated about the axis, and a wall surface facing the front side in the drill rotation direction of the chip discharge groove and In the drill in which the cutting edge is formed in the crossing ridge line part with the tip flank of the cutting edge part,
The cutting edge is composed of a concave curved blade that is recessed rearward in the drill rotation direction when viewed from the tip, and a convex curved blade that is continuous with the outer peripheral side of the concave curved blade and protrudes forward in the drill rotational direction. The curvature radius R1 is set within the range of 1 × D ≦ R1 ≦ 3 × D with respect to the drill outer diameter D, and the curvature radius R2 of the convex curve blade is 0.04 × D ≦ R2 ≦ 0. .07 x D,
A radial rake angle γ1 at an outer peripheral end of the cutting blade is set within a range of −12 ° ≦ γ1 ≦ −8 °.   A ratio L1 / L2 between the length L1 of the concave curved blade and the length L2 of the convex curved blade as viewed from the side facing the tip flank is set within a range of 25 ≦ L1 / L2 ≦ 35. The drill according to claim 1, wherein the drill is provided. The wall surface facing the front side in the drill rotation direction of the chip discharge groove is connected to the concave curve portion recessed toward the rear side in the drill rotation direction and the outer peripheral side of the concave curve portion in the cross section perpendicular to the axis. A radius of curvature R3 of the concave curve portion is set within a range of 0.7 × D ≦ R3 ≦ 0.9 × D with respect to the drill outer diameter D. , The radius of curvature R4 of the convex curve portion is set within a range of 0.1 × D ≦ R4 ≦ 0.2 × D,
3. The drill according to claim 1, wherein a radial rake angle γ <b> 2 at an outer peripheral end of the chip discharge groove is set in a range of −2 ≦ γ2 ≦ + 3 °.   The core height H of the cutting edge is set within a range of 0.06 × D ≦ H ≦ 0.1 × D with respect to the drill outer diameter D. The drill according to any one of 3 above. The groove width ratio W1 / W2 in the cross section orthogonal to the axial direction is set within a range of 0.3 ≦ W1 / W2 ≦ 0.6,
The radius of curvature R of the groove bottom portion of the chip discharge groove is set within a range of 0.1 × D ≦ R ≦ 0.25 × D with respect to the drill outer diameter D. The drill according to claim 4.

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