JP2002028810A - Small-sized drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized drill having high rigidity, good chip discharge performance and high hole position accuracy. SOLUTION: The side of a blade part is provided with one chip discharge groove 15. The outer periphery side rake angle θ made between the outer periphery side of a rake face 15a of a cutting blade 16 and the direction of a tangent A of the outer periphery is set within the range of 90 deg.<=θ<=145 deg.. The ratio α/β of a margin 17 to the outer peripheral surface except the chip discharge groove 15 of the blade part is set 10 to 100%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting tool such as a small drill used mainly for forming a small-diameter deep hole in a printed circuit board.

[0002]

2. Description of the Related Art Generally, a small drill has an extremely small hole to be drilled.
A small-diameter rod-shaped cutting edge portion of about 1-3.175 mm is provided, and a relatively large-diameter shank portion for gripping the drill body on the rotating shaft of the machine tool is provided on the rear end side integrally or with brazing. They are connected by an interference fit or the like.
The material of the cutting edge portion is usually a cemented carbide, and the shank portion is a cemented carbide or a steel material such as steel.
In a conventional small drill, two chips discharge grooves twisted around the axis from the tip of the cutting edge toward the base end are formed facing each other on the side surface of the cutting edge of the small drill rotated around the axis. . In a conventional small-sized drill provided with such two strips of chip discharge grooves, a small-diameter deep hole having a hole diameter D of 1 mm or less and a ratio L / D of the hole depth L to the hole diameter D of 5 or more is provided. In the case of machining, chips are generated, which reduces the accuracy of the inner wall surface of the hole. Further, since the core thickness is reduced by the pair of chip discharge grooves and the rigidity of the small drill is reduced, hole position accuracy is reduced due to hole bending, and breakage of the cutting edge occurs. One of the methods to solve them is step feed, but the drilling speed is extremely reduced and productivity is greatly reduced.

In order to solve the above problems, US Pat.
There is a small drill as disclosed in P55884617. As shown in FIG. 7, the small drill 10 includes a cutting edge 1 and a shank 2, and discharges a single piece of chips twisted around the rotation axis O from the tip of the cutting edge 1 toward the base end. The groove 3 is provided, and the torsion angle γ of the chip discharge groove 3 is continuously increased from the front end to the base end of the cutting edge portion 1 to improve the chip discharge processing. . In this small drill 10, since there is only one chip discharge groove 3, the rigidity can be kept high without reducing the core thickness of the cutting edge portion 1, and the above-mentioned problem is solved to some extent.

[0004]

However, the shape of the cutting edge and the margin on which the chips are generated has not been examined at all, and the shape control of the generated chips becomes insufficient. Is not more than 0.5 mm and the ratio L / D of the hole depth L to the hole diameter D is 10 or more.
It cannot meet the recent demand for smaller diameter and deeper holes.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a small-sized drill for machining small-diameter deep holes, which can maintain high rigidity of the drill, obtain good chip discharge, and has high hole position accuracy. The purpose is to do.

[0006]

A small drill according to the present invention has a hole diameter D of 1 mm or less and a hole depth L.
Is used for small-diameter deep hole drilling where the ratio L / D of the hole diameter D is 5 or more, and has a cutting edge portion and a shank portion, and rotates on the side surface of the cutting edge portion from the tip of the cutting edge portion toward the base end side In a small drill in which a chip discharge groove twisted around the axis is formed, and a wall facing the rotation direction of the chip discharge groove is a rake face, and a cutting edge is formed at an intersection ridge portion of the rake face and the tip flank face, There is only one chip discharge groove formed on the side surface of the cutting edge, and the rake face on the outer peripheral side of the cutting edge is set so that the outer peripheral rake angle θ formed with the tangential direction of the outer peripheral is 90 ° ≦ θ ≦ 145 °. The ratio of the margin provided to the outer peripheral surface excluding the chip discharge groove of the cutting edge is set in a range of 10 to 100%.

[0007] Since there is only one chip discharge groove provided in the cutting edge of the small drill, the core thickness is larger than that of a conventional small drill in which two cutting chips are provided in the cutting edge.
High drill stiffness is obtained. On the contrary, since the chip discharge groove for discharging the chips can be made deep, a good chip discharge property can be obtained. The outer rake angle θ affects the shape and discharge direction of the generated chips, and if the outer rake angle θ is smaller than 90 °, the chips are difficult to be divided and the length increases, and the chips easily become entangled. Emissions are reduced. On the other hand, if the outer peripheral side rake angle θ is larger than 145 °, the cutting resistance applied to the cutting edge becomes too large,
The bending of the drill becomes large and the hole position accuracy is greatly reduced. Here, from the balance between the length and shape of the chips and the cutting resistance, the outer peripheral rake angle θ is preferably set in the range of 100 ° ≦ θ ≦ 130 °. The margin has a deburring effect by being in contact with the inner wall of the machined hole during cutting, and the cutting edge portion offsets the force of being pulled radially outward and guides the cutting edge to improve the straightness of the small drill. There is a function to improve. Therefore, when the margin width is smaller than 10%, the straightness of the drill is impaired, and sufficient hole position accuracy cannot be obtained. The larger the margin ratio is, the more preferable it is. When the margin ratio is 30% or more, the hole position accuracy is particularly improved.

The small drill may be provided with a plurality of margins provided on the outer peripheral surface of the cutting edge of the small drill excluding the chip discharge grooves. In this case, there are a plurality of margins that come into contact with the inner wall of the machined hole, so that stable drill straightness can be obtained. Further, at least one pair or more of the margins provided separately in a plurality may be provided at substantially symmetrical positions about the rotation axis of the small drill. Since the margin receives stress from the inner wall of the drilled hole toward the rotation axis of the small drill, a pair of or more margins provided at positions substantially symmetrical about the rotation axis cancel each other by receiving forces having different directions. And more stable drill straightness can be obtained.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a side view of the small drill according to the first embodiment of the present invention, and FIG. 2 is a front end view of the small drill shown in FIG.

As shown in FIG. 1, a small drill 20 according to a first embodiment of the present invention has a small diameter of, for example, 0.1 to 1 mm and has a substantially columnar shape. A portion 11 and a shank portion 12 made of, for example, SUS or steel having a relatively large diameter (for example, an outer diameter of 2 to 6 mm) and having a substantially cylindrical shape are provided.

The shank portion 12 has a substantially cylindrical hole 13 coaxially with the shank portion 12 at its tip end surface 12a.
A hole is drilled from 2a into the shank portion 12. The opening of the hole portion 13 of the shank portion 12 is not chamfered, and the outer peripheral edge of the tip end surface 12a is located between the shoulder portion 12 and the hole portion 13.
chamfered except for b. Further, the rear end portion is chamfered in a tapered shape to form a chamfered portion 12c.

The cutting edge portion 11 is slightly larger than the inner diameter of the hole portion 13 of the shank portion 12 at room temperature (for example, 1 mm).
0 μm) A substantially cylindrical shaft portion 11b having an outer diameter and fitted into the hole portion 13 by, for example, shrink fitting. A single chip discharge groove 15 is formed in a spiral shape around the rotation axis O from the distal end to the proximal end side of the blade portion 11a located on the distal end side of the shaft portion 11b in the blade tip portion 11. The tip side region of the wall surface of the chip discharge groove 15 facing the small drill rotation direction T is a rake face 15a, and the rake face 1
A cutting edge 16 is formed at the intersection ridgeline between the 5a and the tip flank 14 of the blade 11a.

The outer peripheral surface of the blade portion 11a excluding the chip discharge groove 15, that is, the outer peripheral surface of the land 19 is constituted by a margin 17 and a second cutting surface 18, and like the chip discharge groove 15, from the tip of the blade portion 11a. The small drill 20 is spirally formed by being twisted rearward in the rotation direction T of the small drill 20 toward the base end side. The margin 17 is formed immediately behind the cutting blade 16 in the rotation direction T, and further, a second cutting surface 18 is formed following the rear of the margin 17.

Here, as shown in FIG. 2, the outer peripheral side of the rake face 15a of the cutting blade 16 has a margin 17 and a chip discharging groove 15a.
The outer peripheral side rake angle θ with respect to the tangent A direction at the point on the outer circumference where the intersections (ends 17a to be described later) intersects is 90 ° ≦ θ ≦ 145.
Is set in the range of ゜ (for example, θ = 110 °).
An angle between lines BOC connecting both ends 17a and 17b of the margin 17 and the axis O is defined as α, an end 18a intersecting the chip discharge groove 15 of the second cutting surface 18, and a chip discharge groove 15 of the margin 17. If the angle between the lines BOD connecting the end portions 17a intersecting with the axis and the axis O is β, the blade portion 1
The ratio α / β at which the margin 17 is provided to the outer peripheral surface (the outer peripheral surface of the land 19) excluding the chip discharge groove 15 of 1a.
(Margin ratio) is set to 10 to 100% (for example, assuming α = 90 ° and β = 240 °, the margin ratio α / β = 37.5%).

In the small drill 20 according to the first embodiment, drilling of a workpiece 21 such as a printed board is performed as follows. As shown in FIG.
Is rotated in the rotation direction T, so that the cutting blade 16 cuts the workpiece 21. The chips 22 generated at this time are guided along the chip discharge groove 15 toward the base end of the blade portion 11a, and are discharged to the outside of the machining hole. Then, the small drill 20 guides the inner wall of the processing hole while the margin 17 provided on the outer peripheral surface of the cutting portion 11a guides the inner wall of the processing hole while performing surface finishing such as deburring of the inner wall of the processing hole. While cutting in the direction of the axis O of FIG.

Here, since only one chip discharge groove 15 is formed in the blade portion 11a, the core thickness of the blade portion 11a is not reduced, and the drill portion 11a has high drill rigidity. It is possible to prevent a decrease in position accuracy and breakage of the drill itself. Conversely, the fact that the core thickness is not reduced means that the chip discharge groove 15 can be made deeper, so that the chip discharge property can be improved.

Further, the outer peripheral rake angle θ affects the shape of the chips 22 generated by cutting the work material 21 and the direction in which the chips 22 are discharged, and if the outer peripheral rake angle θ is smaller than 90 °, the chips 22 22 is difficult to be divided, so that the length is increased and the length is easily entangled, and the chip discharging property is deteriorated. On the other hand, if the outer peripheral side rake angle θ is larger than 145 °, the cutting resistance applied to the cutting blade becomes too large, the bending of the drill becomes large, and the hole position accuracy is greatly reduced.
In view of the balance between the length and shape of the chips and the cutting resistance, the outer peripheral rake angle θ is more preferably set in the range of 100 ° ≦ θ ≦ 130 °.

Further, the margin 17 comes into contact with the inner wall of the machined hole during cutting, has a deburring effect, and has a function of guiding the blade portion 11a to improve the straightness of the small drill. If it is less than 10%, the guideability by the margin 17 is impaired, and the rotation balance of the drill about the rotation axis O is lost. As a result, the straightness of the drill is lost, and sufficient hole position accuracy cannot be obtained. The larger the margin ratio, the better.
%, The hole position accuracy becomes particularly stable. In addition, during cutting, as shown in FIG. 3, the cutting blade 16 receives a force P that is pulled radially outward from the rotation axis O by cutting the work material 21, and the margin 17 is formed from the inner wall of the machined hole. It receives a stress Q that is pushed in a direction toward the rotation axis O. When the margin 17 having a certain width is provided, the stress Q applied to the margin 17 increases, which acts to offset the pulling force P of the cutting edge 16 portion, thereby preventing the bending of the drill and making the drill more stable. With the straightness of a small drill,
Hole position accuracy is stable.

Next, FIG. 4 shows a side view of a small drill 30 according to a second embodiment of the present invention. Here, the same or similar parts as those in the above-described first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the small drill according to the second embodiment, a single chip discharge groove 15 is formed in a spiral shape around the rotation axis O from the distal end of the blade portion 11a of the blade edge portion 11 toward the base end side. The tip side region of the wall surface facing the small drill rotation direction T is a rake face 15a, and the rake face 15a
A cutting blade 16 is formed at the intersection ridge line between the tip flank 14 of the blade 11a.

As shown in FIG. 5, the rake face 1 of the cutting blade 16
A tangent line A at a point on the outer periphery where the outer periphery of 5a intersects the first margin 23 and the chip discharge groove 15 (an end 23a to be described later).
Is set in the range of 90 ° to 145 ° (for example, θ = 110 °). The outer peripheral surface of the blade portion 11a excluding the chip discharge groove 15, that is, the outer peripheral surface of the land 19 has a first margin 23, a second margin 2
4 and the second cutting surface 18, and the chip discharge groove 15
Similarly to the above, the small drill 30 is twisted rearward in the rotation direction T from the distal end to the proximal end side of the blade portion 11a to form a spiral shape. The first margin 23 is formed immediately behind the cutting edge 16 in the rotation direction T, and further, the first margin 23
, A second margin surface 18 is formed, and a second margin 24 is formed following the second clearance surface 18. Further, the first margin 23 and the second margin 24 are arranged at positions substantially symmetric with respect to the rotation axis O.

Here, both ends 23 of the first margin 23
a1, the angle between the lines BOC connecting the axes O and 23b, respectively, and α1, and both ends 24a and 24b of the second margin 24.
The angle between the lines DOE connecting the axis and the axis O is α2, and an end 23a intersecting the chip discharge groove 15 of the first margin 23 and an end 24a intersecting the chip discharge groove 15 of the second margin 24 and the axis Assuming that the angle between the lines BOD connecting O and O is β, the margin (the first margin 23 and the second margin in the second embodiment) with respect to the outer peripheral surface (the outer peripheral surface of the land 19) excluding the chip discharge groove 15 of the blade portion 11a. 24)
Ratio α / β (α = α in the second embodiment)
1 + α2) is set to 10 to 100% (for example, α1 = 45 °, α2 = 45 °, β = 240 °, and the margin ratio α / β = 37.5%).

The small drill according to the second embodiment having such a configuration has the same effect as the small drill according to the first embodiment, and the differences are as follows.

The first margin 23 and the second margin 24 come into contact with the inner wall of the machined hole during cutting, have a deburring effect, and have a function of guiding the blade 11a to improve the straightness of the small drill. If the margin ratio is smaller than 10%, the guideability of the first margin 23 and the second margin 24 is impaired, and the rotation balance of the drill about the rotation axis O is lost. As a result, the straightness of the drill is lost, and sufficient hole position accuracy cannot be obtained. In the second embodiment, since two margins are provided, stable straightness of the drill is obtained, and the hole position accuracy is stabilized.
The larger the margin ratio is, the more preferable it is. If it exceeds 30%, the hole position accuracy becomes particularly stable. When cutting,
As shown in FIG. 6, the cutting edge 16 receives a force P that is pulled radially outward from the rotation axis O by cutting the work material 21, and the first margin 23 and the second margin 24 are formed on the inner wall of the processing hole. Receives the stresses Q and Q 'pushed in the direction toward the rotation axis O from. Here, the stress Q that pushes the margin (first margin 23) located immediately behind the cutting edge 16 in the rotation direction T acts so as to cancel the force P that pulls the cutting edge 16 portion, and furthermore, The first margin 23 and the second margin 24, which are located substantially symmetrically with respect to the rotation axis O, also act to offset the forces Q and Q 'received from the inner wall. Stable straightness of the small drill is obtained, and the hole position accuracy is stabilized.

In the present embodiment, the torsion angle of the chip discharge groove 15 twisted around the rotation axis O is determined by the blade portion 11.
Although a is constant from the distal end to the proximal end of a, the torsion angle may be continuously increased from the distal end toward the proximal end side.

In this embodiment, the small drill having the second cutting surface 18 is described. However, the margin ratio α / β is 100%, that is, the outer peripheral portion of the blade portion 11a excluding the chip discharge groove 15. May have no second cut surface and only a margin may be provided. Further, in the present embodiment, the small drill is described in which the number of margins is divided into one or two.However, the present invention is not limited to this, and may have a margin divided into three or more. May be.

The material of the cutting edge 11 is not limited to a cemented carbide, but any other material having a higher hardness than the shank 12, such as cermet, can be used. The material of the shank 12 is also SUS.
The material is not limited to steel or steel, and an appropriate material such as an aluminum alloy can be adopted. In this embodiment, the blade tip 1
Although it is a composite type in which the shaft 1 and the shank portion 12 are fitted, the cutting edge portion 11 and the shank portion 12 may be provided integrally.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A small drill according to an embodiment of the present invention is shown in FIGS.
7 (the margin is only 2 in the third embodiment among the first to seventh embodiments)
And a small drill having a smaller margin ratio α / β than the range of the present invention described above in Comparative Example 1, a small drill having a large outer rake angle θ is shown in Comparative Example 2, and an outer peripheral side. A small drill having a large rake angle θ and a small margin ratio α / β is referred to as a comparative example 3. Further, as a conventional example, a hole of a work material is formed by using a small drill in which two chip discharge grooves 15 are provided in the blade portion 11a. An open test was performed. Table 1 shows the test conditions and results.

[0028]

[Table 1]

In this embodiment, the comparative example and the conventional example, the blade 11
Using a small drill having a diameter of 0.1 mm, an effective blade length of 1.2 mm, and a helix angle of the chip discharge groove 15 of 40 °, cut the work material (0.2 mm thick double-sided BT resin
Plate (LE40 with a thickness of 0.2 mm)
0) and a bottom plate (a bakelite resin plate having a thickness of 1.6 mm) were attached, and a drilling test was performed. Drill speed is 160
000min ^-1 (rpm) feed rate is 0.010mm /
As rev., the workpiece was drilled without step feed, and the number of holes that could be drilled was measured while maintaining the average hole position accuracy for each 100 holes at a value smaller than ± 50 μm. Here, the number of machined holes in Table 1 means that the average hole position accuracy is ± 5.
The number of holes drilled immediately before exceeding 0 μm is shown. As shown in Table 1, the outer peripheral rake angle θ is set in the range of 90 ° ≦ θ ≦ 145 °, and the margin ratio α / β is 10
In Examples 1 to 7 in which the number of drilled holes is set to 4200 or more, stable hole position accuracy can be maintained up to 4200 or more.
In the second to fifth embodiments in which {≦ θ ≦ 130} is set and the margin ratio α / β is set in the range of 30 to 100%, the number of holes drilled is stable to 4900 or more. Accuracy could be maintained and a remarkable effect was observed. In Comparative Example 1 in which the margin ratio α / β was smaller than the range of the present invention, the straightness of the drill was not obtained because the margin width was small, and the number of holes drilled due to hole bending was limited to 3100. Accuracy was not stable. Also,
Comparative Example 2 in which outer peripheral rake angle θ is larger than the range of the present invention
The cutting resistance applied to the cutting blade was increased, and the hole was bent, and the hole position accuracy was stable only up to 2800 holes. Furthermore, in Comparative Example 3 in which the outer peripheral rake angle θ is larger than the range of the present invention and the margin ratio α / β is small, in addition to the large cutting resistance applied to the cutting edge and the small margin width, the straightness of the drill is reduced. The hole position accuracy was not stable until the number of holes drilled due to the occurrence of hole bending was 2300. Further, in the conventional example in which the two chip discharge grooves 15 are formed in the blade portion 11a, the cutting edge is broken when the number of drilled holes is 1400 because the core thickness is small and the drill rigidity is low. As described above, the outer peripheral side rake angle θ is 90
In Examples 1 to 7 in which {≦ θ ≦ 145} is set and the margin ratio α / β is set in the range of 10 to 100%, the margin ratio α / β is more than the range of the present invention.
Comparative Example 1 in which the value of 小 さ い is small, Example 2 in which the outer peripheral side rake angle θ is large, Example 3 in which the outer peripheral side rake angle θ is large and the margin ratio α / β is small, and the two chip discharge grooves 15 in the blade portion 11a.
As compared with the conventional example in which the holes were provided, a large number of holes could be formed while the hole position accuracy was stable.

[0030]

As described above, according to the small drill of the present invention, since only one chip discharge groove is formed on the side surface of the cutting edge of the small drill, two conventional chip discharge grooves are provided. Higher drill stiffness can be obtained and better hole position accuracy can be obtained as compared with the conventional small drills. Further, since the outer peripheral side rake angle θ is set in the range of 90 ° ≦ θ ≦ 145 °, the shape of the generated chips can be sufficiently controlled, and good chip discharge performance can be obtained. Furthermore, if the margin ratio is 1
Since it is set in the range of 0% to 100%, the width of the margin for guiding the cutting edge is increased, so that the straightness of the small drill can be improved, and the hole position accuracy is stabilized. Further, when the margins are separately provided in a plurality, the blade edge is guided by the plurality of margins, so that stable drill straightness is obtained, and the hole position accuracy is stabilized. Furthermore, when at least one pair or more of the margins provided separately in a plurality are arranged substantially symmetrically with respect to the rotation axis, the at least one pair of margins arranged substantially symmetrically respectively rotate the rotation axis from the inner wall of the machining hole. Since it is subjected to a stress in the direction, the bending of the drill is prevented, and more stable drill straightness is obtained, and in particular, the hole position accuracy is stabilized.

[Brief description of the drawings]

FIG. 1 is a side view showing a small drill according to a first embodiment of the present invention.

FIG. 2 is a front end view of the small drill shown in FIG. 1;

FIG. 3 is a front end view showing a state in which the small drill according to the first embodiment of the present invention is cutting a work material.

FIG. 4 is a side view showing a small drill according to a second embodiment of the present invention.

FIG. 5 is a front end view of the small drill shown in FIG. 4;

FIG. 6 is a front end view showing a state in which a small drill according to a second embodiment of the present invention is cutting a work material.

FIG. 7 is a side view showing a conventional small drill.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 blade tip 11a blade 12 shank 14 tip flank 15 chip discharge groove 15a rake face 16 cutting blade 17 margin 18 second cut surface 19 land 20, 30 small drill 21 work material 22 chip 23 first margin 24 first Two margins

Continued on the front page (72) Inventor Kazuhiro Kaneko 1511 Furamaki, Ishishita-cho, Yuki-gun, Ibaraki Prefecture Mitsubishi Materials Corporation Tsukuba Works (72) Inventor Jiro Otani 1511 Furimagi, Ishishita-cho, Yuki-gun, Ibaraki Mitsubishi Materials Corporation 3C037 AA09 BB08 DD01 DD03

Claims (3)

[Claims] 1. A small-diameter deep hole drilling method in which a hole diameter D of a hole to be drilled is 1 mm or less and a ratio L / D of the hole depth L to the hole diameter D is 5 or more, and a cutting edge portion and a shank portion are formed. A chip discharge groove twisted around the rotation axis from the tip of the blade portion toward the base end side is formed on a side surface of the blade edge portion, and a tip side region of a wall surface facing the rotation direction of the chip discharge groove is a rake face. A small-sized drill in which a cutting edge is formed at an intersection ridge line between the rake face and a tip flank, wherein only one chip discharge groove is formed on a side surface of the cutting edge, and a rake on an outer peripheral side of the cutting edge; The rake angle θ of the outer peripheral side of the surface with the tangential direction of the outer periphery is set in the range of 90 ° ≦ θ ≦ 145 °, and the ratio of the margin provided to the outer peripheral surface excluding the chip discharge groove of the cutting edge is 10 to 10. A small-sized drill for drilling small-diameter deep holes, characterized in that it is set in the range of 100%. Le. 2. The small drill according to claim 1, wherein a margin provided on an outer peripheral surface of the cutting edge except for a chip discharge groove is provided in a plurality of parts. 3. The apparatus according to claim 2, wherein at least one or more of the plurality of margins provided separately are provided at substantially symmetric positions about the rotation axis of the small drill. Small drill.