JPH11333612A - Small diameter drill for machining printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small diameter drill for machining a printed wiring board most suitable for a high speed spindle brought into practical use and be excellent in cutting quality and chip discharge ability. SOLUTION: A small diameter drill for machining a printed wiring board is formed in the shape of a round rod in appearance and comprises a shank; and a cutting edge part 2. A cutting edge 3 is disposed at the tip of the cutting edge part 2 to form a tip angle. At the rear end of the cutting edge 3, two chip discharge grooves 4 symmetrically stretching along an axis with a twist occurring are disposed at a rear end from the cutting edge 3. The diameter D of a shank is set to 1.5-2.5 mm at which the influence is not exercised by a centrifugal force and a drill grasping force is ensured. A core thickness (t) is 20-40% of a drill diameter, chip discharge ability is improved and a twist angle θ is set to 35-45 deg. with a purpose of improvement of cutting quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-diameter drill for processing a printed wiring board, and more particularly to a small-diameter drill having a drill diameter of 0.3 mm or less suitable for high-speed rotation.

[0002]

2. Description of the Related Art A printed wiring board is mainly made of a laminate of glass fiber, resin, and copper, and is formed with a small-diameter hole to form an electric wiring circuit. Currently, the most widely practiced drilling method is drilling with a small-diameter drill made of a super-hard tool material such as a cemented carbide. In recent years, as wiring circuits have become smaller and denser, small-diameter drills for processing printed wiring boards have also shifted to small-diameter drills. Is basically the same as a drill having a diameter of 0.3 mm or more.

[0003] Conventional small-diameter drills for processing printed wiring boards have no particular rules, but the shank diameter is unified to 1/8 inch (3.175 mm) and is commonly used. As for the shape of the cutting edge, various proposals have been made so far (for example, Japanese Utility Model Laid-Open No. 2-12).
No. 2712, JP-A-2-232111), commercially available small-diameter drills generally have a cutting edge with a core thickness of 40 mm, regardless of the drill diameter.
５０50%, the helix angle of the chip discharge groove is 35 ° or less, and the groove width ratio is 1.4 to 1.8.

[0004] The cutting conditions when using a small diameter drill are limited by the main spindle to be mounted.
The maximum rotation speed of the spindle usually obtained is about 125,000
With a small diameter drill having a diameter of, for example, 0.3 mm, the peripheral speed is 118 m / min.

[0005]

However, in the case of a small-diameter drill having a diameter of 0.3 mm, the peripheral speed suitable for drilling a printed wiring board is 120 to 200 m / min.
The peripheral speed is at the full lower limit. For smaller drill diameters, the preferred peripheral speed range varies slightly depending on the drill diameter, but the peripheral speed becomes smaller in proportion to the drill diameter, so the problem of insufficient peripheral speed becomes noticeable.

However, recently, a hole drilling device for a printed wiring board has been developed, and the maximum rotation speed of a spindle is about to be increased to about 200,000 rotations / minute. this is,
The peripheral speed of a drill having a diameter of 0.3 mm is 189 m / min. High-speed rotation is possible in terms of a processing device, and a small-diameter drill attached to the drill is required to have a shape suitable for high-speed rotation.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has two twisted chip discharge grooves along the axis at one end of a tool body having a round bar shape. The cutting edge is formed symmetrically, and a cutting edge forming a tip angle is disposed at the tip thereof.
mm, the shank of the tool body has a diameter of 1.5 to 2.5 mm.
The core thickness of the cutting edge is 20-40% of the drill diameter
Wherein the twist angle of the chip discharge groove is 35 ° to 45 °.

The present inventor does not know any example in which the cutting edge shape of the drill is determined in relation to the diameter of the shank. However, at high speeds, the conventional small diameter drill increases the centrifugal force due to the shank diameter and reduces the gripping force of the drill holder. Vibration is amplified even if the vibration accuracy is high. Vibrations are directly linked to breakage, especially in very small diameter drills of 0.3 mm or less in diameter. As a shape that can avoid the adverse effects caused by the centrifugal force, the present invention ideally has a shank diameter of 2 mm at which the drill weight is 40% of the conventional one based on various trial results. The upper limit of the shank diameter of 2.5 mm is adopted as an allowable range that is not affected.

On the other hand, the lower limit of the shank diameter is 1.5 m.
For a small diameter drill smaller than m, the effect of the centrifugal force can of course be neglected, but also the gripping force of the drill holder decreases. The larger the shank diameter is, the larger the torque at the gripping portion is, but many conventional general-purpose drills have the same straight shape as the drill diameter and can withstand use. Rather, in the case of a small-diameter drill, the gripping force is reduced not as a problem of torque but as a structural problem of the holder due to its extremely small diameter.

When the peripheral speed of the drill cannot reach an appropriate value as in the prior art, a large torque is applied to the drill. However, under the condition that high-speed cutting can be stably obtained as described above, the cutting resistance is reduced, so that the original performance of the drill such as sharpness and chip discharge can be pursued rather than breakage measures. Become. That is, the core thickness is reduced to 20 to 40% of the diameter of the drill compared with the conventional drill to increase the volume of the chip discharge groove, thereby improving the chip discharge performance. However, when the core thickness is less than 20%, the core thickness is too small, which may cause breakage. Further, by increasing the rake angle by increasing the helix angle of the chip discharge groove to 35 ° to 45 ° as compared with the conventional one, the sharpness and the chip discharge property are improved. However, when the twist angle exceeds 45 °, the cutting edge becomes too sharp, and the cutting edge strength decreases.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings. The small-diameter drill for processing a printed wiring board according to the present invention shown in FIGS. 1 to 3 has a round bar shape in appearance and is constituted by a shank 1 and a cutting blade 2. A cutting edge 3 is disposed at the tip of the cutting edge portion 2 to form a tip angle, and at the rear end of the cutting edge 3, two chips extending symmetrically along the axis with twisting. A discharge groove 4 is provided.

The shank 1 has a shank diameter D of 1.5 to 2.... As a range in which adverse effects due to an increase in centrifugal force during high-speed rotation are reduced and a sufficient gripping force of the drill holder is secured. 5 mm is adopted.

At least the cutting edge 2 is made of a super hard tool material such as a hard metal or a coated hard metal. These materials are high in wear resistance but poor in toughness and are easily broken. Particularly, a very small diameter drill having a drill diameter d of 0.3 mm or less is easily broken. However, since cutting resistance is reduced by adapting to high-speed cutting, it is no longer necessary to increase the core thickness t to provide more strength than necessary. Therefore, the core thickness t is set to 20 to 40% of the drill diameter d. Since the volume of the chip discharge groove 4 is increased, the chip discharge property is improved, and breakage due to chip clogging is also prevented. Accompanying this, the maximum value of the groove width ratio (w1 / w2) can be made larger than before. That is, the groove width ratio is set to 1.4 to 2.0, which contributes to further improvement in chip dischargeability.

Since the cutting resistance is reduced by the high-speed cutting, the torsion angle θ of the chip discharge groove 4 is set to 35 ° to 45 °, which is larger than in the past. Thereby, the cutting blade 3
Is sharpened, so that the sharpness is improved, and as a result, the cutting force is reduced. However, glass fiber,
A large twist angle θ of more than 45 ° with respect to drilling of a printed wiring board, which is a laminate of resin and copper, is not adopted because the blade edge strength cannot be maintained.

[0015]

According to the present invention, a small-diameter drill for processing a printed wiring board has a shank diameter suitable for avoiding adverse effects of vibration amplification and a decrease in gripping force due to centrifugal force during high-speed rotation, and a drill diameter of 0.3 mm or less. Since it has a cutting edge shape suitable for high-speed rotation, it is possible to provide a small-diameter drill that is optimal for a high-speed spindle that is currently in practical use and has excellent sharpness and chip dischargeability.

[Brief description of the drawings]

FIG. 1 is a front view showing an embodiment of the present invention.

FIG. 2 is an enlarged view of a tip of a cutting blade portion of FIG. 1;

FIG. 3 is a side view of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shank 2 Cutting edge part 3 Cutting edge 4 Chip discharge groove D Shank diameter d Drill diameter t Core thickness θ Helix angle

Claims (1)

[Claims] 1. A tool body having a round bar shape has two twisted chip discharge grooves extending symmetrically along an axis at one end of the tool body, and a cutting edge forming a tip angle at the tip. In a small-diameter drill for processing a printed wiring board having a drill diameter of 0.3 mm or less provided and constituting a cutting edge portion, a shank of the tool body has a diameter of 1.5 to 2.5 mm. A small diameter drill for processing a printed wiring board, wherein a core thickness of the portion is 20 to 40% of a drill diameter, and a twist angle of the chip discharge groove is 35 ° to 45 °.