JP2004237375A - Small diameter drill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress breakage in a tip part by securing high rigidity of a drill body even if working a small-diameter bore in a high rigidity material. <P>SOLUTION: The tip part 12 comprises: a first tip part 13; and a second tip part 14 which has an outside diameter D2 smaller than the outside diameter D1 of the first tip part 13 by one step and continues to the rear end side of the first tip part 13. The second tip part 14 is made gradually larger in its tip from the outside diameter D2 to the outside diameter D3 toward the rear end side in the axis O direction. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a small-diameter drill used for machining a small-diameter hole in a work material, and particularly to a small-diameter drill used for machining a small-diameter hole in a hard material such as hardened steel.
[0002]
[Prior art]
Conventionally, in order to form a small-diameter hole in a printed circuit board, drilling using a small-diameter drill is often performed (for example, see Patent Documents 1 and 2). Not only the so-called straight type, which has a constant outer diameter from the front end to the rear end of the part, but also provides relief so as to reduce the area of the outer peripheral surface of the cutting edge that contacts the inner wall surface of the processing hole In many cases, a small-diameter drill as shown in FIGS. 3 and 4 is used to improve the accuracy of the inner wall surface of the machined hole.
[0003]
In the small-diameter drill as shown in the schematic side view of FIG. 3, the outer diameter of the cutting edge portion 2 of the drill body 1 rotated around the axis O gradually decreases as it goes toward the rear end side in the axis O direction. Such a so-called back taper type, in which the outer diameter D1 at the tip of the cutting edge 2 is the maximum outer diameter of the cutting edge 2 and the outer diameter D2 at the rear end of the cutting edge 2 is Is the minimum outside diameter.
Further, in the small-diameter drill as shown in the schematic side view of FIG. 4, the cutting edge 2 of the drill body 1 rotated around the axis O has a first cutting edge 2A and an outer diameter D1 of the first cutting edge 2A. Is a so-called undercut type, which is constituted by a second cutting edge portion 2B connected to the rear end side of the first cutting edge portion 2A via a step with a small outer diameter D2, and is substantially the entire length of the first cutting edge portion 2A. Is the maximum outer diameter of the cutting edge portion 2, and the outer diameter D2 that is constant over substantially the entire length of the second cutting edge portion 2B is the minimum outer diameter of the cutting edge portion 2. It is something that has become.
[0004]
[Patent Document 1]
JP-A-55-150905 [Patent Document 2]
JP-A-6-344212
[Problems to be solved by the invention]
By the way, recently, in addition to processing a small-diameter hole in a printed circuit board that is relatively soft and does not apply much cutting resistance to the drill body 1, a standard is also applied to a high-hardness material such as hardened steel that has been subjected to heat treatment. There is an increasing demand for forming a small-diameter hole serving as a start hole for passing a hole or a wire saw by using a small-diameter drill.
Therefore, if a back taper type small-diameter drill as shown in FIG. 3 is used to drill a hardened material such as quenched steel, the supply of the cutting oil is difficult due to the small diameter. In addition to the difficulty, the clearance between the outer peripheral surface of the tip side portion of the cutting edge portion 2 and the inner wall surface of the processing hole is difficult to secure, so that the frictional resistance increases and the number of drilling holes is extremely small. The blade tip 2 was broken.
[0006]
On the other hand, if an undercut type small-diameter drill as shown in FIG. 4 is used to drill a hardened material such as hardened steel, the tip side portion of the cutting edge 2 and the inside of the drilled hole Although the supply of the cutting fluid can be improved by securing a sufficient clearance between the wall and the wall, the lack of rigidity of the drill body still leads to breakage of the cutting edge portion 2 with a small number of drilling holes.
The tendency of the cutting edge 2 to break in such a small-diameter drill is that the work material to be drilled is a high-hardness material, the formed drill hole shrinks, and the drill body 1 It is made of an alloy and is promoted by its low toughness and brittleness. It continues stable drilling of hard materials such as hardened steel without causing breakage of the cutting edge 2. An undercut type small-diameter drill that can be carried out has been eagerly desired.
[0007]
In the undercut type small diameter drill described above, the connecting surface 3 connecting the outer peripheral surface of the first cutting edge 2A and the outer peripheral surface of the second cutting edge 2B extends in a direction perpendicular to the axis O. When the cutting edge portion 2A of the cutting edge portion 2 is drilled from the work material in the process of performing the boring process so that the first cutting edge portion 2A of the cutting edge portion 2 penetrates the work material because the cutting edge portion 2 faces the rear end side in the direction of the axis O. In addition, there is also a problem that the connecting surface 3 extending in the direction orthogonal to the axis O interferes with the inner wall surface of the machined hole and is caught, and in particular, the cutting edge 2 is easily broken.
[0008]
The present invention has been made in view of the above-described problems, and even when a small-diameter hole is machined in a high-hardness material, breakage of a cutting edge occurs by securing a large rigidity of a drill body. It is a first object of the present invention to provide a small diameter drill of an undercut type capable of suppressing the occurrence of an undercut, and when an edge portion is pulled out from a work material, an outer peripheral surface of a first edge portion and a second edge portion are removed. A second object of the present invention is to provide a small diameter drill of an undercut type, which can make it difficult for a connecting surface connecting an outer peripheral surface to be caught on an inner wall surface of a processing hole.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve such an object, the present invention provides a cutting edge portion which is a tip side portion of a drill body rotated around an axis, the first cutting edge portion and the first cutting edge portion. And a second cutting edge connected to the rear end of the first cutting edge with an outer diameter one step smaller than the outer diameter of the cutting edge, and a chip discharge groove extending from the front end toward the rear end side of the outer periphery of the cutting edge. A small-diameter drill, wherein a cutting edge is formed at an intersection ridge portion between a wall surface of the chip discharge groove facing forward in the drill rotation direction and a tip flank of the cutting edge portion. The diameter increases as it goes toward the rear end side in the axial direction.
In the present invention having such a configuration, the outer diameter of the second cutting edge portion is not constant over substantially the entire length as in a conventional undercut type small diameter drill, but rather is the rear end in the axial direction. Since the diameter is increased toward the side, the rigidity of the drill body is increased while ensuring sufficient and sufficient clearance between the outer peripheral surface of the tip side portion of the cutting edge and the inner wall surface of the drilled hole. It is possible.
Therefore, even when drilling is performed on a high-hardness material such as hardened steel, breakage of the cutting edge is less likely to occur, and stable drilling can be continued. .
[0010]
Further, in the present invention, the connecting surface connecting the outer peripheral surface of the first cutting edge portion and the outer peripheral surface of the second cutting edge portion is inclined so as to approach the axis line toward the rear end side in the axial direction. It may be.
In the present invention having such a configuration, in the undercut type small-diameter drill, the connecting surface connecting the outer peripheral surface of the first cutting edge portion and the outer peripheral surface of the second cutting edge portion in the cutting edge portion is formed by a conventional undercut. Unlike small diameter drills of the type, they do not extend in a direction perpendicular to the axis of the drill body, but are inclined so as to approach the axis toward the rear end side in the axial direction.
In this way, in drilling, even when the cutting edge is pulled out from the work material, it is difficult for the connecting surface to be caught on the inner wall surface of the processing hole. Can be suppressed.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
First, a first embodiment of the present invention will be described.
As shown in the schematic side view of FIG. 1, the drill body of the small-diameter drill according to the first embodiment has a substantially multi-stage cylindrical shape centered on an axis O rotated around the axis O, and a rear end portion thereof is machined. The shank 11 has a relatively large diameter to be gripped by the rotating shaft of the machine, and the tip side has a small-diameter cutting edge 12.
In the shank portion 11, the connection portion with the cutting edge portion 12 is formed as a tapered surface 11A whose outer diameter gradually increases toward the rear end side in the axis O direction. A relatively large-diameter shank portion 11 and a small-diameter cutting edge portion 12 are connected.
[0012]
The cutting edge portion 12 has a first cutting edge portion 13 forming a tip portion thereof, and a second cutting edge connected to the rear end side of the first cutting edge portion 13 with an outer diameter D2 smaller than the outer diameter D1 of the first cutting edge portion 13 by a step. The small-diameter drill according to the first embodiment is a so-called undercut type.
The first cutting edge portion 13 of the cutting edge portion 12 has a constant outer diameter D1 over substantially the entire length in the direction of the axis O, and the outer diameter D1 forms the maximum outer diameter of the cutting edge portion 12.
[0013]
On the other hand, the second cutting edge portion 14 of the cutting edge portion 12 has an outer diameter that gradually increases with a constant change tendency toward the rear end side in the axis O direction. The outer diameter at the tip of the portion 14 in the direction of the axis O (the portion connected to the first cutting edge portion 13) is D2, which forms the minimum outer diameter of the cutting edge portion 12, and the axis O of the second cutting edge portion 14 The outer diameter at the rear end in the direction (portion of the shank 11 connected to the tapered surface 11A) is D3. The outer diameter D3 is set to be equal to or less than the outer diameter D1 of the first cutting edge portion 13.
That is, the relationship of D1> D2, D2 <D3, and D1 ≧ D3 (D2 <D3 ≦ D1) holds for the outer diameters D1, D2, and D3 of the cutting edge portion 12.
[0014]
Here, the outer diameter D1 of the first cutting edge portion 13 (the maximum outer diameter of the cutting edge portion 12) is set in a range of D1 ≦ 3 mm, and the outer diameter D2 (the cutting edge) at the tip of the second cutting edge portion 14 in the direction of the axis O. The minimum outer diameter of the portion 12) is set in the range of 0.8D1 ≦ D2 ≦ 0.95D1 in relation to the outer diameter D1 of the first cutting edge portion 13, and further, in the direction of the axis O in the second cutting edge portion 14. The outer diameter D3 at the rear end is set in a range of 0.85D1 ≦ D3 ≦ D1 in relation to the outer diameter D1 of the first cutting edge portion 13.
In addition, the outer diameter D1 of the first cutting edge portion 13 (the maximum outer diameter of the cutting edge portion 12) is set in a range of 0.1 mm ≦ D1 in consideration of a technical limit at the present time.
[0015]
Although not shown, for example, a plurality of chip discharge grooves extending from the front end to the rear end side of the outer periphery of the cutting edge portion 12 are spiraled around the axis O over substantially the entire length of the cutting edge portion 12. The cutting edge is formed at the intersection ridge line between the wall surface of the chip discharge groove facing forward in the drill rotation direction and the flank of the leading edge of the cutting edge portion 12.
[0016]
At this time, the length in the direction of the axis O of the portion where the chip discharge groove is formed in the blade edge portion 12 (substantially the entire length of the blade edge portion 12 in the first embodiment), that is, the blade edge portion 12 that can be used for drilling. Is set in a range of 4D1 ≦ L ≦ 20D1 in relation to the outer diameter D1 of the first cutting edge portion 13, and the length L1 of the first cutting edge portion 13 in the direction of the axis O is set. Is set in the range of 0.5D1 ≦ L1 ≦ 3D1 in relation to the outer diameter D1 of the first cutting edge portion 13.
[0017]
The small-diameter drill as described above is provided with a step feed in the direction of the axis O while the drill body 10 is rotated around the axis O, so that, for example, heat treatment is performed by the cutting blade formed at the tip of the blade edge portion 12. Drilling is performed on a hardened material such as hardened steel, which has a diameter corresponding to the maximum outer diameter (D1) of the cutting edge portion 12. A small hole is formed.
[0018]
In the small-diameter drill according to the first embodiment, the outer diameter of the second cutting edge portion 14 connected to the rear end side of the first cutting edge portion 13 is determined from the outer diameter D2 of the tip, which is a portion connected to the first cutting edge portion 13, Since the shank 11 is formed so as to gradually increase in diameter toward the rear end side in the direction of the axis O up to the outer diameter D3 at the rear end, which is a portion connected to the tapered surface 11A, the conventional undercut type An undercut type that can maintain the rigidity of the drill body 10 in a high state as compared with a small-diameter drill such that the outer diameter of the second cutting edge is constant along the axis O direction. I have.
[0019]
Therefore, even when drilling a high-hardness material such as hardened steel, the clearance between the outer peripheral surface of the tip side portion of the blade edge portion 12 and the inner wall surface of the drilled hole is necessary and sufficient. As a result, the supply of the cutting oil can be improved and the rigidity of the drill body 10 can be maintained high, so that the cutting edge 12 can be hardly broken, and stable drilling can be performed for a long time. Can be continued.
[0020]
The effect of maintaining the rigidity of the drill body 10 in a high state and preventing breakage of the cutting edge portion 12 is different from the first embodiment in that the outer diameter D1 of the first cutting edge portion 13 is 3 mm. (Especially, the outer diameter D1 is 2 mm or less). In a conventional undercut-type small-diameter drill, when the rigidity of the drill body 10 is extremely difficult to be secured, it becomes remarkable. The outer diameters D2 and D3 at the front and rear ends of the second cutting edge portion 14 in the portion 12 are within the ranges described above based on the outer diameter D1 of the first cutting edge portion 13 and the type of work material. It is set appropriately, but more preferably, it is set in the range of 0.85D1 ≦ D2 ≦ 0.95D1, 0.9D1 ≦ D3 ≦ D1.
[0021]
In the first embodiment, the outer diameter of the second cutting edge portion 14 is gradually increased with a constant change tendency toward the rear end side in the axis O, but is not limited thereto. The change tendency may not be constant as long as the outer diameter of the second cutting edge portion 14 is increased toward the rear end side in the axis O direction.
[0022]
Next, a second embodiment of the present invention will be described, and the same parts as those in the above-described first embodiment will be denoted by the same reference numerals and description thereof will be omitted.
The small-diameter drill according to the second embodiment has the same configuration as that of the above-described first embodiment, as shown in the schematic side view of FIG. The connecting surface 15 connecting the surface and the outer peripheral surface of the second cutting edge portion 14 is formed in a tapered surface shape that is inclined so as to approach the axis O toward the rear end side in the direction of the axis O. is there. In other words, the outer diameter of the connecting surface 15 gradually decreases with a constant changing tendency toward the rear end side in the direction of the axis O.
[0023]
When viewed in a cross section including the axis O, a narrow angle θ between the tangent P and the axis O at a portion of the connecting surface 15 intersecting with the outer peripheral surface of the first cutting edge 13 is 10 ° to 60 °. (FIG. 2 is not a view when viewed in a cross section including the axis O, but there is no problem in showing the above-mentioned narrow angle θ. In addition, a straight line parallel to the axis O is defined as 2 It is indicated by the dotted chain line.)
In particular, in the second embodiment, when viewed in a cross section including the axis O, the connecting surface 15 is formed in a substantially linear shape inclined so as to approach the axis O toward the rear end side in the direction of the axis O. Therefore, the narrow angle θ is equal to the narrow angle formed by the connecting surface 15 and the axis O, which are substantially linear in cross section.
[0024]
According to the small-diameter drill according to the second embodiment, in addition to obtaining the same effects as in the above-described first embodiment, in addition to the outer peripheral surface of the first cutting edge portion 13 and the outer peripheral surface of the second cutting edge portion 14, Is formed as a tapered surface inclined so as to approach the axis O toward the rear end side in the direction of the axis O, so that in the process of drilling, the work material is cut from the cutting edge. Even when the 12 is pulled out, the connecting surface 15 can be prevented from being caught on the inner wall surface of the processing hole.
Therefore, it is possible to suppress breakage of the cutting edge portion 12 caused by the hooking, and it is possible to maintain the rigidity of the drill body 10 as described in the first embodiment high. Together with this, more stable drilling can be continued.
[0025]
When viewed in a cross section including the axis O, a narrow angle θ between the tangent P and the axis O at a portion of the connection surface 15 intersecting the outer peripheral surface of the first cutting edge portion 13 (the angle between the connection surface 15 and the axis O). If the narrow angle θ is too small, the effect of changing the cutting edge portion 12 to the undercut type including the first cutting edge portion 13 and the second cutting edge portion 14 may be weakened, while the narrow angle θ is too large. However, there is a possibility that the catch of the connecting surface 15 cannot be prevented.
For this reason, in the second embodiment, by setting the narrow angle θ in the range of 10 ° to 60 ° (preferably in the range of 20 ° to 50 °), more stable continuation of drilling is performed. This is possible for a long time.
[0026]
In the second embodiment, the connecting surface 15 is a tapered surface so as to be substantially linear when viewed in a cross section orthogonal to the axis O. However, the present invention is not limited to this. If the connecting surface 15 is inclined so as to approach the axis O toward the rear end side in the direction, the connecting surface 15 may be a concave curved surface having a substantially concave curved section or a convex curved surface having a substantially convex curved cross section.
[0027]
【Example】
A small diameter drill according to an example of the present invention is referred to as a first example (small diameter drill based on FIG. 1) and a second example (small diameter drill based on FIG. 2). As Conventional Example 2 (small-diameter drill based on FIG. 4), a drilling test was performed, and the number of holes that could be machined before the cutting edge was broken was measured. The result is shown in FIG.
The cutting conditions are as follows.
・ Maximum outer diameter (D1) of the blade tip: 0.7 mm
・ Cutting speed: 35m / min
-Feed: 0.008 mm / rev.
・ Hole depth: 3mm
・ Step feed: 0.07mm
・ Work material: SKD11 (HRC60)
・ Cutting oil: Emulsion [0028]
As shown in FIG. 5, in Conventional Example 1 which is a back taper type, the cutting edge is broken at a very small stage of 84 or 212 holes due to an increase in frictional resistance. Also in the conventional example 2 of the type, the cutting edge portion was broken at a stage where the number of drilled holes was as small as 1,316 and 1,162.
On the other hand, in Example 1, which is an example of the present invention, the number of drilled holes is 2099 and 2161, and stable drilling can be continued without causing breakage of the blade edge portion. In particular, in Example 2, the number of drilled holes was 2320 and 2512, indicating that extremely stable drilling could be continued.
[0029]
【The invention's effect】
According to the present invention, in the undercut type small diameter drill, since the outer diameter of the second cutting edge portion at the cutting edge portion is formed so as to increase toward the rear end side in the axial direction, the leading end side at the cutting edge portion is formed. It is possible to increase the rigidity of the drill body while ensuring the necessary and sufficient clearance between the outer peripheral surface of the part and the inner wall surface of the machined hole. Even in the case where drilling is performed, breakage of the blade edge portion is hardly generated, and stable drilling can be continued.
[0030]
Further, according to the present invention, in the undercut type small diameter drill, the connecting surface connecting the outer peripheral surface of the first cutting edge portion and the outer peripheral surface of the second cutting edge portion in the cutting edge portion is located on the rear end side in the axial direction. Since it is inclined so as to approach the axis as it goes, when the blade tip is pulled out from the work material, the above-mentioned joint surface suppresses the engagement of the processing hole with the inner wall surface, and the blade tip caused by this is suppressed. Breakage can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic side view showing a small diameter drill according to a first embodiment of the present invention.
FIG. 2 is a schematic side view showing a small diameter drill according to a second embodiment of the present invention.
FIG. 3 is a schematic side view showing an example of a conventional small diameter drill.
FIG. 4 is a schematic side view showing another example of a conventional small diameter drill.
FIG. 5 is a graph showing the results of a drilling test.
[Explanation of symbols]
Reference Signs List 10 Drill body 11 Shank portion 11A Tapered surface 12 Cutting edge 13 First cutting edge 14 Second cutting edge 15 Connecting surface D1 Outer diameter of first cutting edge (maximum outer diameter of cutting edge)
D2 Outer diameter of the tip of the second cutting edge (minimum outer diameter of the cutting edge)
D3 Outer diameter L of the rear end of the second cutting edge portion Effective blade length L1 Length of the first cutting edge portion in the axial direction O Axis P Tangent line θ Narrow angle

Claims (2)

A cutting edge, which is a tip side portion of the drill body rotated about the axis, is connected to the rear end of the first cutting edge with an outer diameter one step smaller than the outer diameter of the first cutting edge and the first cutting edge. A chip discharge groove formed on the outer periphery of the cutting edge portion and extending from the front end thereof to the rear end side, and a wall surface of the chip discharging groove facing forward in the drill rotation direction and the cutting edge portion. In a small diameter drill with a cutting edge formed at the intersection ridge line with the tip flank,
A small-diameter drill, wherein the outer diameter of the second cutting edge portion increases as it goes toward the rear end side in the axial direction. The small-diameter drill according to claim 1,
A connecting surface connecting the outer peripheral surface of the first cutting edge portion and the outer peripheral surface of the second cutting edge portion is inclined so as to approach the axis line toward the rear end side in the axial direction. Small diameter drill.

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