JP2000084719A - Boring tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance rigidity and improve bore position accuracy. SOLUTION: A small size drill 20 for through holes of a printed board is provided with a pair of chip discharge grooves on the outer circumferential surface of an edge 5, which includes a cutting edge on the tip, from the tip toward the base end. The web thickness 22 of the edge 5 is equipped with a first web thickness portion 24 including approximately identical thickness dimension from a d1 on the end to a d2 on the base end side of the web thickness 22 of the edge 5, a second web thickness portion 26 including web thickness of approximately identical thickness from d3 to d4 larger than the first web thickness portion 24, and an intermediate thickness portion 28 smoothly connecting the first and the second web thickness portions 24, 26 together. The intermediate web thickness portion 28 is of approximately a tapered shape having an inclination of a range from 1/20 to 1/1. Thus not only is the shape of the web thickness portions kept unchanged even if the cutting edge is repolished but chip discharging property and breaking-proof property are satisfactory.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Generally, a small drill used for boring a printed circuit board has a very small hole to be drilled.
A cutting blade having a small diameter of about 1-3.175 mm is provided, and a relatively large shank portion for gripping a drill body on a rotating shaft of a machine tool at the rear end side is integrated with the blade portion or by brazing or the like. They are connected and provided. The material of the blade portion is usually a cemented carbide, and the shank portion is a cemented carbide or a steel material such as steel. By the way, when a small drill is used to pierce a printed circuit board, usually, the printed circuit board is formed by attaching aluminum foil, copper foil, glass fiber, or the like to a synthetic resin plate. ,
For example, four printed circuit boards 1 are laminated, and furthermore, a small drill 4 is used to punch holes in the four printed circuit boards at once at a state in which the contact plate 2 and the floor plate 3 are in close contact with each other.

[0003] Such a small drill 4 has, for example, a structure shown in Figs. That is, a drill body is provided with a blade portion 5 and a shank portion 6, and the outer peripheral surface of the blade portion 5 has, for example, a pair of chip discharge grooves around a rotation axis O from a distal end surface 7 to a proximal end side. 8, 8 are spirally formed facing each other. The intersection ridge line between each chip discharge groove 8, 8 and the front end face 7 is a pair of cutting edges 9, 9, and the front end face 7 has, for example, an obtuse end angle, and the flank face of each cutting edge 9, 9 is provided. The tip side area of the chip discharge grooves 8 is a rake face. In the front end face 7 shown in FIG. 6, the outer peripheral surface of the blade portion 5 connected to the outer edge of the cutting blade 9 has a margin 10 connected to the outer edge of the cutting blades 9, 9, and the outer side of the margin 10 from the rotation axis O. Peripheral flank 11 with short diameter
(Second face). And the rotation axis O
The thickness portion between the chip discharge grooves 8, 8 is a core thick portion 13. The core thick portion 13 has a thickness dimension t0 at the tip end surface 7 of the blade portion 5 shown in FIG. 6, and is shown in a virtual cross-sectional view for explaining the shape of the core thick portion 13 along the rotation axis O in FIG. In the meantime, the chip discharge grooves 8, 8
Is formed in a tapered shape that forms a straight line in a sectional view so that the thickness t gradually increases uniformly from t0 to the end portion of.

[0004]

However, printed circuit boards are becoming finer and multilayered year by year, and with this, there is an increasing demand for smaller hole diameters and deeper hole diameters, and higher precision in hole positions. Therefore, it is becoming difficult for the core thick portion 13 formed in the uniform taper shape as described above to sufficiently meet these requirements. That is, when the core thick portion 13 formed in a uniform taper shape as described above is made thicker as a whole, the rigidity of the small drill 4 is increased, but the thrust resistance is increased on the distal end side, and the bite on the printed circuit board is reduced. There is a disadvantage that the position of the hole is easily deteriorated and the displacement of the hole is liable to occur, and the chip thickness groove 13 is also large on the base end side, so that the chip discharge groove 8 becomes shallow and the chip discharge performance is deteriorated during deep hole processing. In the drill, the good biting on the rotation axis O overlapping the vertex of the tip angle of the tip face 7 determines the hole position accuracy. Conversely, if the thickness of the core thick portion 13 is reduced to improve the biting and chip discharging properties, there is a disadvantage in that the drill stiffness is reduced and the drill is easily broken. In addition, if the inclination of the taper of the core thick portion 13 is increased, the depth of the chip discharge groove 8 can be secured while increasing the drill rigidity. However, when the aspect ratio becomes 15 or more, the groove depth at the base end side of the chip discharge groove 8 is increased. There is also a disadvantage that the chip discharge performance is similarly deteriorated because the depth is further reduced.
In addition, satisfactory results were not obtained even when the hole forming test was performed by changing the tip angle, the torsion angle, the groove width ratio, the margin width, and the like of the blade portion 5 in addition to the core thickness portion 13 and changing the combination. .

The present invention has been made in view of the above circumstances, and has as its object to provide a drilling tool capable of improving drilling accuracy and maintaining drill rigidity.

[0006]

A drilling tool according to the present invention has a blade portion and a shank portion, and a chip discharge groove is provided on an outer peripheral surface of the blade portion from a tip side to a base end side. In a drilling tool in which a cutting edge is provided at an intersection ridge line between a chip discharge groove and a distal end surface of a blade portion, a core thickness of the blade portion has substantially the same thickness dimension from the distal side toward the proximal side. One core thick portion, a second core thick portion having a thickness larger than the first core thick portion and having substantially the same thickness, and an intermediate core for smoothly connecting the first core thick portion and the second core thick portion. And a thick portion. By setting the first core thickness part to be relatively small and almost the same thickness, the bite into the work material during drilling is good, it is difficult to cause hole displacement and hole bending, and the cutting blade has worn out Even when re-polishing, the thickness of the core thickness hardly changes, so that the same hole position accuracy as a new product can be obtained. In addition, the second core thick portion is thicker than the first core thick portion, so that the rigidity of the drill is high, and since the thickness is almost the same, the chip discharging property is good. And, since the thickness of the first core thick section increases smoothly from the thickness of the second core thick section in the middle core thick section, the chip flow is smooth and the chip discharge property is good, and there is a step difference in the thickness and the step Since the shape does not suddenly change, stress is not concentrated on the connection portion between the first thick core portion and the second thick core portion, and breakage of the tool does not occur. It should be noted that the substantially same thickness in the first core thick portion and the second core thick portion includes a straight shape and a slightly tapered shape.

[0007] It is more preferable to change the thickness of the intermediate core thick portion smoothly without a step and to make the thickness change more steeply in order to secure rigidity. The thickness of the tip of the first thick part is d1, and the thickness of the connection part between the first thick part and the middle thick part is d1.
2. The thickness of the connecting portion between the intermediate core thick portion and the second core thick portion is d3, the thickness of the rear end of the second core thick portion is d4, and the cutting blade outer diameter of the blade portion is D.
, D1 ≦ d2 <d3 ≦ d4, and d1
Is 0.15D to 0.60D, d2 is 0.15D to 0.7
0D, d3 is 0.30D to 0.90D, d4 is 0.30D
D to 0.90D. Thereby, particularly suitable characteristics can be exhibited particularly in a small-diameter drill with D = 3.175 mm or less.

The diameter of the cutting edge of the blade is 3.175 mm.
It may be as follows. In a small drill having a small diameter such that the cutting edge has a diameter of 3.175 mm or less, since the outer diameter of the blade portion is relatively small, setting the core thickness as in the present invention improves the hole position accuracy and In addition, the chip discharging property, the rigidity, and the breakage resistance can be improved and balanced. Further, the intermediate core thick portion may be formed in a substantially tapered shape having an inclination in a range of 1/20 to 1/1. 1 slope
If the thickness is less than / 20, the change in thickness between the first core thick part and the second core thick part is small. Therefore, if the thickness of the first core thick part is increased, the rigidity is improved, but the bite to the work material is poor. If the hole position shifts or the hole bends, the hole position accuracy decreases and the chip discharge performance decreases.On the contrary, if the thickness is reduced, the bite into the work material and the hole position accuracy and the chip discharge performance improve. , The rigidity is reduced, and it is easy to break in the middle core thick portion and the like. On the other hand, the slope is 1/1
If the thickness exceeds, the thickness changes too rapidly and changes in a substantially stepwise manner, so that the chip flow deteriorates, the chip discharge performance is reduced, and stress is concentrated at the intermediate core thick portion to cause breakage easily.

[0009]

FIG. 1 is a block diagram showing an embodiment of the present invention.
However, the same or similar parts as those of the above-described related art will be described using the same reference numerals. FIG. 1 is a cross-sectional view of a virtual main part for describing the shape of a core thick portion of a small drill according to an embodiment. A small drill 20 for drilling a printed circuit board shown in FIG. 1 includes a blade portion 5 and a shank portion 6 like the small drill 4 of the prior art, and discharges a pair of chips with the rotation axis O interposed on the outer peripheral surface of the blade portion 5. The grooves 8, 8 are formed facing each other. The core thick portion 22 formed between the chip discharge grooves 8 extends from the tip end face 7 of the blade portion 5 to the end of the chip discharge groove 8, and extends in the extending direction of the chip discharge groove 8. The minimum thickness dimension between the pair of chip discharge grooves 8
The thickness di is 2. In particular, in the small drill 20 according to the present embodiment, the core thick portion 22 is located on the distal end side as shown in FIG. 1 and is located on the proximal end side with the first core thick portion 24 having a relatively small thickness. The second core thick portion 26 having a larger thickness dimension than the first core thick portion 24 and the first and second core thick portions 24, 26 are connected, for example, a tapered shape in which the thickness di of the core thickness changes smoothly. And an intermediate core thick portion 28.

Here, the thickness of the tip of the first core thick part 24 is d
1. The thickness of the connecting portion between the first thick core portion 24 and the middle thick portion 28 is d2, the thickness of the connecting portion between the middle thick portion 28 and the second thick portion 26 is d3, after the second thick portion 26 When the thickness of the end is d4 and the cutting edge outer diameter of the blade portion 5 is D, d1 ≦ d2 <d3 ≦ d4, and d1 is 0.15D to 0.60D, and d2 is 0.15D to 0. 70D, d3 is 0.30D to 0.90
D and d4 are set in the range of 0.30D to 0.90D. By satisfying such conditions, particularly preferable characteristics as described later can be exhibited particularly when the small diameter drill 20 has a cutting edge outer diameter D of 3.175 mm or less.

Here, the core thickness dimension d1 of the first core thickness portion 24 is 0.15D to 0.60D, and d2 is 0.15D to 0.70D.
D, and d1, d of the first core thick portion 24.
For the outer peripheral surface shape between the two, the inclination is, for example, 0/1000.
A straight shape or a slight tapered shape (this is called substantially the same thickness) is set as a range of up to 15/1000. As a result, the biting of the cutting blade 9 is good at the time of drilling a printed circuit board, and the hole position deviation can be suppressed, the hole position accuracy can be improved, and the drill rigidity in this region can be secured. FIG.
The first core thick portion 24 has a straight shape of 0/1000. If the length (effective groove length) of the chip discharge groove 8 along the rotation axis is L, the length L1 of the first core thick portion 24 along the rotation axis O is 0.03L to 0.25L, for example, L1 = The range is 0.05 to 5.0 mm. By setting the length of the first core thick part 24 to L1, the cutting blades 9, 9 formed at the intersection ridge line between the tip end face 7 and the chip discharge grooves 8, 8 are worn by drilling. In this case, when the cutting blade 9 is sharpened several times by re-grinding, the shape of the first core thick portion 24 can be prevented from changing.

The core thickness d3 of the second core thickness portion 26 is set to 0.30D to 0.90D, and d4 is set to 0.30D to 0.90D.
D and d3, d of the second core thick portion 26
The shape of the outer peripheral surface between the four has a slope of, for example, 0/1000 to 15
The range of / 1000 is set to a straight shape or a slight tapered shape (this is called substantially the same thickness). As a result, the rigidity of the small drill 20 can be improved, and the generated chips can be smoothly discharged to the outside through the chip discharge grooves 8, 8 even in deep hole processing in which the aspect ratio exceeds 15. Can be favorably maintained.
In FIG. 1, the second core thick portion 26 has a straight shape of 0/1000.

In an intermediate core thick portion 28 connecting the first core thick portion 24 and the second core thick portion 26, the thickness di is d2 on the tip side.
To d3 on the base end side, for example, in a substantially tapered shape, d2 is 0.15D to 0.70D, d
3 is set in the range of 0.30D to 0.90D, and the taper (slope) between d2 and d3 is 1/20 to 1/1.
Is set in the range. The length L along the rotation axis O
2 is 0.03 L to 0.25 L, for example, 0.05 to 5.0.
mm. Here, the intermediate core thickness portion 28
Is smaller than 1/20, the difference between the thickness dimensions d2 and d3 is relatively small. Therefore, if d2 is large, biting is poor at the first core thickness portion 24, and the hole position accuracy is reduced. In the portion 26, the chip discharge groove 8 becomes shallow, and the chip discharge performance is reduced. Conversely, if d2 is small, there is a problem that the rigidity of the second core thick portion 26 is insufficient and the drill rigidity is insufficient. If the inclination is greater than 1/1, the middle core thick portion 28
As a result, a large step is generated in the chip discharge groove 8 and the chip flow becomes poor, causing chip clogging, and there is a problem that stress is concentrated during drilling and the chip is easily broken.

The intermediate core portion 28 does not necessarily need to be formed in a linear tapered shape. For example, in the cross-sectional view, the first core portion 24 and the second core portion 26 are curved to opposite sides. The first and second core thick portions 24 and 26 may be smoothly connected to each other by connecting two substantially arc-shaped curves to each other, or may have one convex or concave shape as a whole in cross section. May be formed in a substantially arc shape. By forming the intermediate core thick portion 28 into a smooth tapered or curved shape in cross section and connecting the first and second core thick portions 24 and 26, the drill rigidity gradually increases toward the base end side. In addition, since no step is formed, the flow of the chips can be made smooth and the chips can be sent out to the chip discharge grooves 8 in the region of the second thick core portion 26.

Since the small drill 20 according to the present embodiment is configured as described above, the first core thick portion 24 has a relatively small thickness d1 to d1 from the distal end to the proximal end.
By setting the diameter d2 in the range, the bite into the work material at the time of drilling is improved, and the hole position accuracy is improved without causing a hole position shift or a hole bending. Since the thickness between the core thicknesses d1 and d2 hardly changes even after polishing, the same hole position accuracy as a new product can be obtained. Moreover, the second core thick portion 26 has a thickness d3 to d4 larger than the first core thick portion 24, so that the drill has high rigidity. Further, since d3 and d4 have almost the same thickness, the chip discharging property is good. is there.
Then, the thickness di in the middle core thick portion 28 is inclined 1/20 to 1 /
Since the flow smoothly increases from d2 to d3 in the range of 1, the chip flow is smooth and the dischargeability is good, and the first core thick portion 24 is not formed because there is no step or the thickness changes stepwise. The stress is not concentrated on the connecting portion between the second core thickness portion 26 and the small drill 20 and the small drill 20 does not break. Therefore, the rigidity of the entire small drill 20 can be increased to suppress the positional deviation and the bending of the hole at the time of biting, thereby improving the hole position accuracy. And breakage resistance can be kept good. Moreover, even if the cutting blade 9 is worn and polished again, the thickness dimension of the first core thick portion 24 hardly changes, so that the same hole position accuracy as that of a new product can be obtained.

Next, a drilling test performed on an embodiment of the present invention will be described. As an example, a small drill 20 having the shape of the core thick portion 22 shown in FIG. 1 was used, and for comparison, a small drill 4 having a uniform tapered core thick portion 13 shown in FIG. 7 was used as a conventional example. Each was subjected to a drilling test. Examples and conventional small drills 20, 4
Are as shown in Table 1. The thicknesses d1 and t0 of the tips of the core thick portions 22 and 13 are both 0.130.
It is.

List of dimensions of small drills for testing (unit: mm)

[Table 1]

As a work material, a three-layer printed circuit board in which three 1.6 mm-thick substrates each formed by stacking four Cu foils were used, and an aluminum-made 0.1-mm thick board was formed thereon.
A 5-mm patch plate was placed, and a bake 1.6 mm-thick laying plate was adhered underneath, and drilling was performed using the small drills 20 and 4 of the embodiment and the conventional example. . The rotation speed N of the small drill is 70 Krpm, the feed speed F is 1.8 m / min, and the cutting depth f per rotation is 25.
5,000 hits (number of times) in single processing with 71 μm
Was drilled. Note that the stroke, which is the distance between the tip of the small drills 20, 4 at the initial position mounted on the machine tool and the printed circuit board, is 9.85 mm. The results of the drilling test were as shown in FIG. 2 and Table 2 in the case of the small drill 20 according to the embodiment, and as shown in FIGS. 3 and 3 in the case of the small drill 4 according to the conventional example. .

Hole Position Accuracy Report of Example

[Table 2]

Hole Position Accuracy Report of Comparative Example

[Table 3]

In Tables 2 and 3, "average value" refers to "average hole position deviation amount" in a direction orthogonal to the depth direction from the target position to the actual hole exit position. The “shoot amount” indicates the amount of bending of the hole, and indicates the maximum amount of deviation due to bending of the hole in a direction perpendicular to the depth direction from the entrance of the hole. The “slip amount” refers to a deviation amount from a target position at the start of drilling to an actual hole entrance position. In general, the hole position accuracy is calculated as “average value + 3”
It is mainly determined by the magnitude of “σ”. According to the test results, in the hole drilling according to the embodiment, as shown in FIG.
(Start) ~ 1000 hits, 1001-2000 hits, 2001-3000 hits, 3001-4000 hits
At each stage of 1000 hits of 400 hits and 400 hits to 5000 hits, the amount of deviation from the intersection of the X axis and the Y axis, which is the target position for drilling, is small. That is, as shown in Table 2, the “average value + 3σ” based on the normal distribution is 52 μm, 63 μm, and 71 μm in the hits at each stage.
m, 71 μm, 68 μm, and similarly the “shoot amount”
Also 40 μm, 51 μm, 58 μm, 59 μm, 55 μm
It became. On the other hand, in the drilling according to the conventional example, the “average value + 3σ” by the normal distribution is 86 μm at each stage hit.
m, 104 μm, 115 μm, 118 μm, 114 μm
Similarly, the “shoot amount” is 71 μm, 93 μm,
It was 104 μm, 106 μm, and 104 μm. Therefore, in the embodiment, the amount of deviation of the hole position from the target position and the amount of bending of the hole are clearly smaller than in the conventional example, and the hole position accuracy is greatly improved.

In the above embodiment, the core thick portion 22
Is composed of a first core thick part 24, an intermediate core thick part 28, and a second core thick part 26 which form a coaxial axis. However, the present invention is not limited to such a configuration, and the second core thick part A straight or micro tapered shape in which the thickness is sequentially increased through a plurality of intermediate core portions by connecting a third core thick portion having a larger thickness di to a second 26 through a second intermediate core portion. May be formed in a substantially multi-stage shape. In short, it may be configured by connecting a plurality of core portions having different taper thicknesses before and behind the intermediate core portion having a tapered or concave or convex curved surface (referred to as a substantially tapered shape). In the embodiment, a pair of the chip discharge grooves 8 is provided as a twist groove. However, the present invention is not limited to this. The chip discharge grooves may be linear grooves, and the number of the chip discharge grooves may be set arbitrarily. Good. In the present invention, the cutting edge diameter is 3.1.
Although the present invention is suitable for a small-diameter drill 20 for a printed board of 75 mm or less, the present invention is not limited to the embodiment, and can be applied to a drill having a larger cutting edge diameter. Further, the present invention is not limited to drills, but can be applied to various drilling tools such as reamers.

[0023]

As described above, in the drilling tool according to the present invention, the core thickness of the blade portion is substantially the same from the distal end to the proximal end, and the first core thick portion has the same thickness. A second core thick part having a thickness dimension larger than the first core thick part and having substantially the same thickness dimension, and an intermediate core thick part for smoothly connecting the first core thick part and the second core thick part. From the first core thickness part, the bite to the work material at the time of drilling is good, the hole position shift and hole bending can be suppressed, and even if the cutting edge is worn out, the thickness of the core thickness even if re-polishing Is almost unchanged, so that the same hole position accuracy as that of a new product can be obtained, and the drill thickness is high due to the second core thick portion, and the chip discharging property is good. And even if it has an intermediate core thickness part, the chip flow is smooth and the dischargeability is good, and furthermore, since there is no step or sudden change in thickness in a step shape, the first core part and the second core part The stress is not concentrated on the thick connection portion, and the drilling tool does not break.

The diameter of the cutting edge of the blade is 3.175 mm.
From the following, in such a small drill, the hole position accuracy can be improved, and the chip dischargeability, rigidity, and breakage resistance can be improved and balanced. In addition, since the intermediate core portion has a substantially tapered shape having a slope in the range of 1/20 to 1/1, the hole position accuracy can be improved, and chip clogging can be suppressed to improve chip dischargeability. It is possible to maintain good rigidity and breakage resistance and balance.

[Brief description of the drawings]

FIG. 1 is a virtual sectional view along a rotation axis for explaining a shape of a core thick portion of a small drill according to an embodiment of the present invention.

FIG. 2 is a diagram showing the accuracy of a hole position in a hole drilling test with a small drill according to an embodiment in units of 1000 hits.

FIG. 3 is a diagram showing the accuracy of a hole position in a hole drilling test with the conventional small drill according to FIG. 7 in units of 1000 hits.

FIG. 4 is a general view showing a state of piercing a printed circuit board by a small drill.

FIG. 5 is a side view of a general small drill.

FIG. 6 is a front end view of the small drill shown in FIG. 5;

FIG. 7 is a virtual sectional view taken along a rotation axis for explaining a shape of a core thick portion of a conventional small drill.

[Explanation of symbols]

 Reference Signs List 5 blade part 6 shank part 8 chip discharge groove 9 cutting blade 20 small drill 22 core thick part 24 first core thick part 26 second core thick part 28 middle core thick part

Claims (3)

[Claims] 1. A cutting part is provided with a blade part and a shank part, and a chip discharge groove is provided on an outer peripheral surface of the blade part from a tip end side to a base end side,
In a drilling tool in which a cutting edge is provided at an intersection ridge line between the chip discharge groove and the tip surface of the blade portion, the core thickness of the blade portion is
A first core thick portion having substantially the same thickness dimension from the distal end side toward the base end side, a second core thick portion having a thickness dimension larger than the first core thick portion and having substantially the same thickness dimension, A drilling tool, comprising: an intermediate core portion that smoothly connects the first core portion and the second core portion. 2. The diameter of the cutting edge of the blade is 3.175 mm.
The drilling tool according to claim 1, wherein: 3. The drilling tool according to claim 1, wherein the intermediate core portion has a substantially tapered shape having an inclination in a range of 1/20 to 1/1.