JP2004195561A - Drill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate careless reduction in rigidity of an edge part even if a sufficient recess is imparted to an outer peripheral surface by forming a back taper in the edge part. <P>SOLUTION: The edge part 12 is composed of a back taper part 12A having an outer diameter for gradually diametrally contracting toward the axis O directional rear end side and a straight part 12B continuing with the rear end of this back taper part 12A and having an outer diameter set substantially constant in the axis O direction. In the back taper part 12A, an outer diameter of first and second margin parts 52 and 54 is gradually diametrally contracted while substantially invariably maintaining an outer diameter of a relieving surface 53 except for the first and second margin parts 52 and 54 in a land part 50 toward the axis O directional rear end side. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drill used for drilling for forming a machined hole in a work material with a high level of hole position accuracy, and for example, to a drill for forming a machined hole having a deep hole.
[0002]
[Prior art]
As an example of such a drill, a pair of chip discharge grooves extending toward the rear end side is formed on the outer periphery of a cutting edge portion rotated around an axis, and the chip discharge grooves are directed forward in the drill rotation direction T. A cutting edge is formed at the intersection ridgeline between the wall surface and the tip flank of the cutting edge, and first and second margins adjacent to the chip rotation groove in the drill rotation direction rear and front sides of the land of the cutting edge. The first and second margin portions have a role of guiding the blade edge portion 1 by contacting the inner wall surface of the formed hole to be formed (for example, see Patent Document 1). 1).
[0003]
[Patent Document 1]
JP-A-7-40117
[Problems to be solved by the invention]
By the way, in the conventional drill, the contact area with the inner wall surface of the margin portion (first and second margin portions) that comes into contact with the inner wall surface of the formed hole is reduced to reduce the cutting resistance. In order to achieve this, a back taper may be applied to the cutting edge so that the outer diameter of the cutting edge gradually decreases at a constant rate toward the rear end side in the axial direction.
However, since such a back taper is provided over the entire length of the cutting edge portion, when a large back taper is provided in order to provide sufficient clearance to the outer peripheral surface of the cutting edge portion, the back taper toward the axial direction is provided. The cutting edge portion whose outer diameter gradually decreases toward the rear end side in the axial direction has a smaller outer diameter than necessary, and there is a problem that the rigidity of the cutting edge portion is reduced. Such a tendency becomes remarkable especially in a drill used for forming a deep hole, that is, a drill in which the entire length of the cutting edge is set to be long.
[0005]
The present invention has been made in view of the above-mentioned problem, and eliminates the possibility of inadvertently lowering the rigidity of the cutting edge portion even if the cutting edge portion is provided with a back taper so that sufficient clearance is provided on the outer peripheral surface thereof. The aim is to provide a drill that can.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve such an object, the present invention provides a chip discharge extending toward the rear end side to the outer periphery of a cutting edge portion which is a front end portion of a drill body rotated around an axis. In a drill in which a groove is formed and a cutting edge is formed at an intersection ridge portion between an inner wall surface of the chip discharge groove facing forward in the drill rotation direction and a tip flank of the cutting edge portion, the cutting edge portion has an outer diameter. A back taper portion whose diameter is gradually reduced toward the rear end side in the axial direction, and a straight portion connected to the rear end of the back taper portion and having an outer diameter substantially constant along the axial direction. .
According to the present invention as described above, the back taper portion forming the tip side portion of the cutting edge portion can be provided with a back taper capable of sufficiently securing the escape to the outer peripheral surface, but the back taper portion is formed after the back taper portion. The outer diameter of the straight portion, which continues to the end side and forms the rear end portion of the cutting edge, is maintained substantially constant, and does not become smaller than the outer diameter at the rear end of the back taper portion. The rigidity of the portion is not inadvertently reduced.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the drill body 10 of the drill according to the present embodiment is formed of a hard material such as a cemented carbide in a substantially columnar shape around an axis O, and the rear end portion thereof is rotated by a machine tool. The shank 11 is gripped by a shaft, and the tip side portion is a cutting edge 12.
The cutting edge portion 12 has a back taper portion 12A whose outer diameter gradually decreases at a constant rate toward the rear end side in the direction of the axis O, and smoothly connects to the rear end of the back taper portion 12A. And a straight portion 12B whose diameter is substantially constant along the axis O direction. At this time, the ratio L1: L2 of the length L1 of the back taper portion 12A along the axis O direction to the length L2 of the straight portion 12B along the axis O direction is, for example, 1: 1 to 1: 6. Is set.
[0008]
On the outer periphery of the cutting edge portion 12, a pair of chip discharge grooves 20, 20 that are twisted rearward in the drill rotation direction T at a constant twist angle from the front flank 13 toward the rear end side in the axis O direction are formed on the axis O. The cutting edges 30 are formed symmetrically with respect to the chip discharge grooves 20, and are formed at the intersection ridges between the inner wall surfaces 21, 21 facing forward in the drill rotation direction T and the tip flank 13 of the chip discharge grooves 20, 20, respectively. ing.
[0009]
As shown in FIG. 2, the tip flank 13 of the cutting edge portion 12 has a first flank in which the chip discharge grooves 20, 20 cross each other, so that the cutting blades 30, 30 are formed on the ridge line portion on the front side in the drill rotation direction T. Each of the cutting edges 30 and 30 has a multi-stage surface configuration including surfaces 13A and 13A and second flank surfaces 13B and 13B connected to the first flank surfaces 13A and 13A on the rear side in the drill rotation direction T. A relief is provided so as to increase in a multi-stage manner toward the rear side in the drill rotation direction T, including the thinning portions 40, 40 described later.
Further, the tip flank 13 is inclined toward the rear end side of the cutting edge portion 12 from the inner peripheral side toward the outer peripheral side so that the cutting blades 30 have a predetermined tip angle. It has become.
[0010]
The second flank 13B of the tip flank 13 is provided around the axis O in the same manner as the chip discharge groove 20 from the shank 11 toward the tip in the direction of the axis O inside the drill body 10. A pair of coolant holes 10A, 10A extending while being twisted are opened, and during cutting, coolant is supplied from the coolant holes 10A, 10A to a cutting portion.
[0011]
The inner wall surface 21 of the chip discharge groove 20 which faces the front side in the drill rotation direction T intersects with the land portion 50 of the cutting edge portion 12 at the outer peripheral side thereof and is shown in FIG. 5 in a cross section orthogonal to the axis O. As described above, the first convex curved surface portion 22 that has a convex curve shape that is convex forward in the drill rotation direction T, and a cross section that is located on the inner peripheral side of the first convex curved surface portion 22 and that is also orthogonal to the axis O. , And a first concave curved surface portion 23 having a concave curve shape that is concave rearward in the drill rotation direction T.
[0012]
Further, the inner wall surface 24 of the chip discharge groove 20 facing the rear side in the drill rotation direction T reaches the heel portion 51 on the outer peripheral side thereof (intersects the land portion 50 of the cutting edge portion 12) and is orthogonal to the axis O. In the cross section, a second convex curved surface portion 25 having a convex curve shape protruding rearward in the drill rotation direction T, and a cross section located on the inner peripheral side of the second convex curved surface portion 25 and also orthogonal to the axis O And a second concave curved surface portion 26 having a concave curve shape that is concave forward in the drill rotation direction T.
[0013]
The chip discharge groove 20 is connected so that the convex and concave curves formed by the cross sections of the first concave and convex curved surface portions 22 and 23 of the inner wall surface 21 facing the front side in the drill rotational direction T smoothly contact with each other, and the drill rotational direction. The concave and convex curves formed by the cross sections of the second concave and convex curved surface portions 25 and 26 of the inner wall surface 24 facing the rear side of T are connected so as to smoothly contact with each other, and the first and second concave curved surface portions 23 of both the inner wall surfaces 21 and 24 are connected. , 26 are connected so that the concave curves formed by the cross sections of the chip and the chip discharge groove 20 smoothly contact each other.
[0014]
In the cutting edge 30 formed at the intersection ridge line between the inner wall surface 21 facing the front side in the drill rotation direction T and the tip flank 13 of the chip discharge groove 20, the inner wall surface 21 is formed by the first uneven curved surface portion 22. , 23, as shown in FIG. 2, a convex curved cutting edge portion 31 is formed on the outer peripheral side so as to be convex toward the front side in the drill rotation direction T, and is formed on the rear end side. The first convex curved surface portion 22 is continuous with the convex curved cutting edge portion 31, and the convex curved cutting edge portion 31 has a curved shape concave on the rear side in the drill rotation direction T on the inner peripheral side to smoothly form the convex curved cutting edge portion 31. A concave curved cutting blade portion 32 is formed so as to be in contact with and continuous with the first concave curved surface portion 23 at the rear end side.
As a result, the cutting edge 30 has an S-shape that is gently curved when viewed from the tip side in the direction of the axis O between the concave and convex curved cutting edge portions 31 and 32. In addition, since the outer peripheral side part of the cutting blade 30 is the convex curved cutting blade part 31, the radial rake angle formed by the cutting blade 30 at the outer peripheral end 30A is set to the negative angle side.
[0015]
Further, on the tip side of the inner wall surfaces 21 and 24 facing the front and rear sides in the drill rotation direction T of the chip discharge groove 20, the second concave curved surface portion 26 and the second convex surface from the inner peripheral side of the first concave curved surface portion 23. The intersection ridge line with the front flank 13 (the first flank 13A and the second flank 13B) up to the curved surface 25 is cut toward the inside of the chip discharge groove 20 along the rear end side of the cutting edge 12. The thinning portion 40 is formed so as to reach the land portion 50 including the heel portion 51 so as to be chipped.
[0016]
Therefore, the inner peripheral end side of the cutting edge 30 is formed at the intersection ridge line between the thinning portion 40 and the first flank 13A, and the center of the tip flank 13 from the inner peripheral end of the concave curved cutting edge 32. Is formed as a thinning cutting edge 33 extending toward the axis O.
In the cutting blade 30, a portion where the thinning cutting blade 33 intersects with the concave curved cutting blade 32 is a curve or a straight line that is convex forward in the drill rotation direction T when viewed from the tip side in the axis O direction. Connected smoothly.
[0017]
In the thinning portion 40 extending to the front end side while intersecting the inner wall surfaces 21 and 24 of the chip discharge groove 20, the land portion 50 (heel portion) intersects with the inner wall surface 24 of the chip discharge groove 20 which faces rearward in the drill rotation direction T. 51 and a flat portion 43 that is formed in a flat shape that is inclined toward the rear end side in the direction of the axis O along the drill rotation direction T rearward. Have been.
[0018]
On the other hand, in the thinning portion 40, a portion of the chip discharge groove 20 where the inner wall surfaces 21 and 24 facing forward and rearward in the drill rotation direction T intersects, that is, a groove bottom of the chip discharge groove 20 (first and second). The portion extending from the concave curved surface portions 23 and 26 to the axis O located at the center of the tip flank 13 is formed so as to form a concave-valley-shaped valley. The valley bottom 41 is inclined toward the inner peripheral side of the cutting edge portion 12 with respect to the inner wall surfaces 21 and 24 so as to retreat toward the inner peripheral end of the cutting blade 30, that is, toward the inner peripheral end of the thinning cutting blade 33. And is formed to extend toward the distal end.
[0019]
Here, the outer peripheral surface of the cutting edge portion 12 excluding the pair of chip discharge grooves 20 and 20 in the back taper portion 12A, that is, the land portion 50 in the back taper portion 12A is viewed in a cross section orthogonal to the axis O in FIG. As shown in the figure, a first arc-shaped first centered on the axis O intersects the outer peripheral ridge of the first convex curved surface portion 22 on the inner wall surface 21 of the chip discharge groove 20 facing the front side in the drill rotation direction T. The second margin portion 52 has a substantially circular arc shape centered on an axis O having an outer diameter one step smaller than the circular arc formed by the first margin portion 52 and connected to the rear side of the first margin portion 52 in the drill rotation direction T. The outer peripheral side ridge line portion of the second convex curved surface portion 25 on the inner wall surface 24 continuous with the cutting surface 53 and the rear side in the drill rotation direction T of the second cutting surface 53 and facing the rear side of the chip discharge groove 20 in the drill rotation direction T. Heel part 5 ) Intersects the, and a second margin portion 54 having a substantially arcuate shape centered on the axis O having the same outer diameter and an arc on which the first margin portion 52 formed.
[0020]
The first and second margin portions 52 and 54 and the second cutting surface 53 are, like the chip discharge groove 20, drilled from a portion intersecting the front clearance surface 13 toward the rear end side in the axis O direction. The back taper portion 12A is formed so as to be twisted rearward in the rotation direction T over substantially the entire length in the direction of the axis O of the back taper portion 12A.
Further, of the first and second margin portions 52, 54 and the second cutting surface 53, the first margin portion 52 adjacent to the chip discharge groove 20 on the rear side in the drill rotation direction T is connected to the rear side of the drill rotation direction T. The second cutting surface 53 is configured to maintain the width in the circumferential direction around the axis O substantially constant over substantially the entire length of the back taper portion 12A, while being located forward of the chip discharge groove 20 in the drill rotation direction. The second margin portion 54 adjacent to the side has a stepwise increased width in the circumferential direction at a portion on the way from the rear end of the back taper portion 12A toward the front end side in the direction of the axis O.
[0021]
The second margin portion 54 extending in the circumferential direction toward the distal end side in the axis O direction by one step increases the land portion including the heel portion 51 of the thinning portion 40 at the distal end portion in the axial line O direction. It will intersect with the planar portion 43 reaching 50.
At this time, when the back taper portion 12A is viewed from the front end side in the direction of the axis O, as shown in FIG. 2, the width of the first margin portion 52 in the circumferential direction is maintained substantially constant in the direction of the axis O. Therefore, it is formed in a small part from the outer peripheral end 30A of the cutting blade 30 to the outer peripheral end 13D of the intersection ridge 13C of the first flank 13A and the second flank 13B toward the rear side in the drill rotation direction T. On the other hand, the second margin portion 54 has a second clearance from the heel portion 51 where the thinning portion 40 intersects (the tip 51A of the heel portion 51 in the direction of the axis O) toward the front side in the drill rotation direction T. It is formed in a large portion up to the vicinity of the outer peripheral end 42A of the intersection ridge line portion 42 between the surface 13B and the thinning portion 40.
[0022]
More specifically, when viewed from the tip side in the direction of the axis O, the second margin portion 54 is defined by a point 54A located on the front side in the drill rotation direction T in the second margin portion 54 and the axis O. The intersection angle θ formed by the straight line X connecting the second flank 13B (the tip flank 13) and the outer peripheral end 42A of the intersection ridge 42 of the thinning portion 40 and the straight line Y connecting the axis O to the straight line X is Is set in the range of −5 ° to 10 °, when the position is located forward of the straight line Y in the drill rotation direction T as a positive value.
In the present embodiment, when viewed from the front end side in the direction of the axis O, the point 54A located on the front side in the drill rotation direction T in the second margin portion 54 is the second flank 13B and the thinning portion 40. The intersection angle θ between the straight lines X and Y is set to 0 °.
[0023]
Here, the flat portion 43 of the thinning portion 40 where the second margin portion 54 intersects at the front end portion in the direction of the axis O is inclined toward the rear end side in the direction of the axis O along the drill rotation direction T rearward. Therefore, the distal end portion of the second margin portion 54 is notched in the oblique direction crossing the width direction by the flat portion 43 of the thinning portion 40 at the rear side in the drill rotation direction T.
Therefore, the second margin portion 54 extending in the circumferential direction toward the tip end side in the direction of the axis O with one step increase in width extends to a region crossing the portion intersecting the flat portion 43 of the thinning portion 40, that is, the heel portion. In the region of the portion 51 on the distal end side in the axis O direction from the distal end 51A in the axis O direction, the width in the circumferential direction is gradually reduced toward the distal end side in the axis O direction, and the second margin portion 54 In the direction of the axis O in FIG.
[0024]
The point located at the most distal end in the direction of the axis O in the second margin portion 54 is the point located most forward in the drill rotation direction T of the second margin portion 54 as viewed from the distal end in the direction of the axis O. Therefore, the width of the second margin portion 54 in the circumferential direction becomes approximately 0 near this point 54A.
In the present embodiment, when viewed from the front end side in the direction of the axis O, the point 54A located on the front side in the drill rotation direction T in the second margin portion 54 is the intersection ridge line between the second flank 13B and the thinning portion 40. The width of the second margin portion 54 in the circumferential direction is 0 at this point 54A because it is substantially coincident with the outer peripheral end 42A of the portion 42.
[0025]
Further, the outer diameter of the back taper portion 12A is gradually reduced at a constant rate as it goes toward the rear end side in the direction of the axis O (for example, 0.35 / 100 to 0.40 / 100). In other words, the outer diameter of a virtual circle having a cross section perpendicular to the axis O of the first and second margins 52 and 54 constituting the land 50 as a circular arc has a constant outer diameter toward the rear end side in the direction of the axis O. The diameter is gradually reduced at a certain rate.
Accordingly, the outer diameter of a virtual circle having a cross section orthogonal to the axis O of the second cutting surface 53 located between the first and second margin portions 52 and 54 in the back taper portion 12A is also The diameter of the back taper portion 12A is gradually reduced at a constant rate toward the rear end side in the direction of the axis O. Therefore, the second cutting depth a of the second cutting surface 53 is set to a constant value (for example, 0.05 mm to 0.10 mm) over substantially the entire length of the back tapered portion 12A.
[0026]
The straight portion 12B connected to the rear end side of the back taper portion 12A has a land portion 50, which is not shown, but which is in front of the chip discharge groove 20 in the drill rotation direction T when viewed in a cross section orthogonal to the axis O. In the inner wall surface 24 facing the drill rotation direction T rear side of the chip discharge groove 20 from the portion of the inner wall surface 21 facing the outer peripheral side ridge line of the first convex curved surface portion 22 toward the drill rotation direction T rear side. A marginal portion 55 having a substantially arc shape centered on the axis O extends to a portion of the second convex curved surface portion 25 that intersects the outer peripheral side ridge portion (heel portion 51).
Further, similarly to the chip discharge groove 20, the margin portion 55 is located on the rear side in the drill rotation direction T from the front end of the straight portion 12B connected to the rear end of the back taper portion 12A toward the rear end in the axis O direction. The straight portion 12B is formed over substantially the entire length of the straight portion 12B in the direction of the axis O.
[0027]
Here, the outer diameter of the straight portion 12B, that is, the outer diameter of the arc formed by the cross section of the margin portion 55 forming the land portion 50 is determined by the cross section of the second cutting surface 53 forming the land portion 50 of the back taper portion 12A. It is set slightly smaller than the outer diameter of the arc to be formed, and the leading end of the straight portion 12B is connected to the rear end of the back taper portion 12A via a slight step.
[0028]
That is, in the blade edge portion 12, when the margin portion 55 constituting the land portion 50 of the straight portion 12B extends from the rear end of the straight portion 12B toward the front end side in the direction of the axis O, the straight portion 12B When approaching the front end (the rear end of the back taper portion 12A), the first and second margin portions 52, 54 and the second cutting surface 53 of the land portion 50 of the back taper portion 12A are connected via a slight step.
[0029]
Further, in the present embodiment, the surface of the cutting edge portion 12 of the drill body 10, that is, the land portion 50 which is the outer peripheral surface of the cutting edge portion 12, the tip flank 13, the inner wall surfaces 21 and 24 of the chip discharge groove 20, and the thinning portion A hard coating such as TiN, TiCN, or TiAlN is coated on the surface such as 40.
Polishing is performed by applying a paste containing hard particles such as diamond particles to a brush and polishing the entire surface of the cutting edge portion 12 covered with the hard film, As a result, the surface roughness Ra (arithmetic average roughness specified in JIS B 0601-1994) is set in a range of Ra = 0.1 μm to 0.3 μm (in a state before polishing is performed). , Ra = 0.5 μm-1.0 μm).
When expressed by surface roughness Rz (ten-point average roughness specified in JIS B 0601-2001) instead of surface roughness Ra, the surface roughness Rz after polished is Rz is set in the range of 0.4 μm to 1.2 μm (Rz = 2.0 μm to 4.0 μm before polishing).
[0030]
In the drill according to the present embodiment having the above-described configuration, when the second margin portion 54 formed on the land portion 50 of the back taper portion 12A of the cutting edge portion 12 is viewed from the tip side in the axis O direction. The point located on the most front side in the drill rotation direction T is positioned near the outer peripheral end 42A of the intersection ridgeline portion 42 between the second flank 13B and the thinning portion 40. It is formed over a large area toward the front side.
For this reason, the tip (point 54A) in the direction of the axis O in the second margin portion 54 is also located near the outer peripheral end 42A of the intersection ridge 42 between the second flank 13B and the thinning portion 40. In other words, the distance h along the axis O direction between the tip of the first margin portion 52 in the direction of the axis O and the tip of the second margin portion 54 in the direction of the axis O is the same as that of the conventional double margin type drill (the thinning portion 40 is connected to the land portion). (For example, the above-described distance h is equal to the maximum outer diameter D of the cutting edge portion 12 (the outer diameter at the tip of the cutting edge portion 12)). On the other hand, it is set in the range of 0.07D to 0.20D).
[0031]
Therefore, for example, as shown in FIGS. 6A to 6C, the position of the processing hole K to be formed is shifted from the center C1 of the cross hole C with respect to the cross hole C formed in the work material in advance. Even when the drilling process is performed such that the cutting edge portion 12 passes through the inner wall surface of the cross hole C, both the first and second margin portions 52 and 54 immediately K comes into contact with the inner wall surface of the outlet portion forming the opening to the inner wall surface of the cross hole C at K, and the first and second margin portions 52 and 54 can stably guide the blade edge portion 12. It becomes possible.
[0032]
Therefore, even when a force is applied to the tip portion of the cutting edge portion 12 in the lateral direction (X direction in the drawing) intersecting the direction of the axis O when the cutting edge portion 12 comes out to the inner wall surface of the cross hole C, The guide action by the first and second margin portions 52 and 54 makes it possible to reduce the run-out of the cutting edge portion 12, thereby keeping the inner wall surface roughness of the formed processing hole K favorable, and cutting the cutting edge. It is possible to reduce the risk of the chip 30 being in contact with another wall surface and causing breakage or breakage of the cutting edge portion 12.
[0033]
Here, regarding the point 54A located on the forward side in the drill rotation direction T in the second margin portion 54 when viewed from the tip side in the direction of the axis O, the position is set such that the above-mentioned intersection angle θ is smaller than −5 °. If so, the distance h in the direction of the axis O between the tip of the first margin portion 54 and the tip of the second margin portion 54 (point 54A) may not be able to be set sufficiently small.
On the other hand, if the point 54A is positioned so that the intersection angle θ is greater than 10 °, the area of the margin portion 54 that contacts the inner wall surface of the processing hole K increases, and May cause an increase in cutting resistance.
[0034]
Further, in the drill according to the present embodiment, since the cutting edge portion 12 is composed of the back tapered portion 12A constituting the front end portion and the straight portion 12B constituting the rear end portion, the back tapered portion thereof is formed. With respect to the portion 12A, the first and second margin portions 52 and 54 formed in the land portion 50 are provided with a relief so as to increase toward the rear end side in the direction of the axis O, thereby providing the first and second margin portions 52 and 54. By contacting only the front end portions of the second margin portions 52 and 54 in the direction of the axis O with the inner wall surface of the processing hole K, it is possible to suppress an increase in cutting resistance during drilling.
[0035]
The cutting edge portion 12 located on the rear end side in the direction of the axis O with respect to the rear end of the back taper portion 12A where the outer diameter of the back taper portion 12A is the smallest and sufficient clearance is provided, that is, the back The straight portion 12B smoothly connected to the rear end of the tapered portion 12A maintains an outer diameter substantially the same as the outer diameter at the rear end of the back tapered portion 12A in the direction of the axis O. The rigidity of the portion 12 is not unnecessarily reduced.
As described above, when the blade edge portion 12 is configured by the back taper portion 12A and the straight portion 12B, when the back taper is formed over substantially the entire length of the blade edge portion 12, the rigidity tends to be reduced, particularly for deep hole machining. In a drill, that is, a drill in which the length L along the axis O direction of the cutting edge portion 12 is set to be long, a remarkable effect can be exhibited.
Note that, for example, as shown in FIG. 1, the drill for deep hole drilling has a length L (= L1 + L2) along the direction of the axis O of the blade edge portion 12 and a maximum outer diameter D (a blade edge portion) of the blade edge portion 12. 12 (outer diameter at the tip of 12) is set in the range of 5 to 30.
[0036]
Further, in the drill according to the present embodiment, after the surface of the cutting edge portion 12 is coated with the hard film, at least the surfaces of the first and second margin portions 52 and 54 (in the present embodiment, the surface of the cutting edge portion 12). The entire surface is polished and the surface roughness is set small (Ra = 0.1 μm to 0.3 μm). The first and second margin portions 52 and 54 can prevent the inner wall surface of the processing hole K from being roughened.
In other words, while the hard coating is coated on the surface of the cutting edge portion 12 to improve the wear resistance, the first and second margin portions 52 and 54 where the surface roughness tends to be relatively large due to the hard coating are formed. By performing polishing, the inner wall surface of the processing hole K is not roughened, and the surface roughness of the first and second margin portions 52 and 54 is reduced by friction with the inner wall surface of the processing hole K. Even in the initial stage of cutting when the phenomenon of reduction in size does not occur, the inner wall surface roughness of the machined hole K can be kept good.
[0037]
Furthermore, in this embodiment, since the entire surface of the cutting edge portion 12 coated with the hard coating is polished, the inner wall surfaces 21 and 24 of the chip discharge groove 20 are also polished. The surface roughness Ra is set as small as 0.1 μm to 0.3 μm.
For this reason, when the chips generated by the cutting blade 30 are guided to the rear end side of the cutting edge portion 12 by the chip discharging groove 20, when the chips are slid on the inner wall surfaces 21 and 24 of the chip discharging groove 20. The frictional resistance can be reduced, the smooth discharge of the chips can be promoted, the occurrence of chip clogging can be suppressed, and the breakage of the cutting edge portion 12 can be prevented.
[0038]
Here, if the surface roughness Ra of the first and second margin portions 52 and 54 after the polishing is set to be smaller than 0.1 μm, a great amount of labor is required for performing the polishing. On the contrary, if it is set to be larger than 0.3 μm, the inner wall surface roughness of the formed hole K may not be able to be maintained satisfactorily.
[0039]
In the embodiment described above, the opening of the tip flank 13 to the second flank 13B of the coolant hole 10A formed through the inside of the drill body 10 is simply a round hole. However, for example, as shown in FIG. 7, the inner wall surface 24 facing the chip rotation direction T rear side of the chip discharge groove 20 from the round hole-shaped opening of the coolant hole 10A toward the drill rotation direction T rear side. The notch 10B having a groove-shaped cross section may be formed by cutting out a portion (the second flank 13B and the flat portion 43 of the thinning portion 40) until the second crossed curved portion 26 intersects. The coolant supplied from the hole 10A can be efficiently introduced into the chip discharge groove 20.
[0040]
【The invention's effect】
As described above, according to the present invention, the back taper portion forming the tip side portion of the cutting edge portion can be provided with a back taper that can sufficiently secure the escape to the outer peripheral surface, The outer diameter of the straight portion, which is continuous with the rear end side of the portion and forms the rear end portion of the cutting edge portion, is maintained substantially constant, and does not become smaller than the outer diameter at the rear end of the back taper portion. Therefore, even in the case of a drill for deep hole drilling, the rigidity of the cutting edge is not inadvertently reduced.
[Brief description of the drawings]
FIG. 1 is a side view showing a drill according to an embodiment of the present invention.
FIG. 2 is a front end view of a cutting edge of a drill according to an embodiment of the present invention.
FIG. 3 is a view in the direction of arrow A in FIG. 2;
FIG. 4 is a view in the direction of arrow B in FIG. 2;
FIG. 5 is a sectional view taken along line CC in FIG. 1;
FIG. 6 is an explanatory view showing a state of drilling using a drill according to the embodiment of the present invention.
FIG. 7 is a front end view showing a modification of the cutting edge of the drill according to the embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 10 Drill body 12 Blade tip 12A Back taper 12B Straight part 13 Tip flank 20 Chip discharge groove 30 Cutting edge 40 Thinning part 42 Cross ridge 42A Outer end 50 Land 51 Heel 52 First margin 54 Second margin

Claims (1)

A chip discharge groove extending toward the rear end side is formed on an outer periphery of a cutting edge portion which is a tip side portion of the drill body rotated about an axis, and an inner wall surface facing the front side in the drill rotation direction of the chip discharging groove and the cutting edge In the drill where the cutting edge was formed at the intersection ridge line with the flank of the tip of the part,
The cutting edge portion has a back taper portion whose outer diameter gradually decreases as going toward the rear end side in the axial direction, and a continuous rear end of the back taper portion, and the outer diameter extends along the axial direction. A drill comprising a substantially constant straight portion.

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