JPH02237711A - Twist drill - Google Patents

Abstract

PURPOSE:To drill a hole without causing burrs or peeling due to reinforcing fibers by forming a twisted groove into a helical shape advancing in the direction of rotation according as it goes from the tip side toward the base end side, and making web thickness of a drill body 8-20% of the diameter of the drill. CONSTITUTION:A twisted groove 2 is formed into a helical shape advancing in the direction of rotation according as it goes from the tip side toward the base end side, and web thickness of a drill body 1 is kept at 8-20% of the diameter of the drill. Aa a result, axial rake angle of a cutting edge 3 becomes minus, and reinforcing fibers can be cut as if they were cut off with scissors. No reinforcing fibers thus remain on the surface machined by the cutting edge 3, and frictional resistance between the drill body 1 and a hole is small since the web thickness of the drill body 1 is thin. Reinforcing fibers can thus be cut with good cutting action, and thereby generation of burrs or peeling on the edge part and the inner periphery of the hole can be efficiently prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application in "Industry" 2] This invention relates to a twist drill suitable for use in drilling holes in fiber-reinforced Togo materials made of carbon fibers, Kevlar fibers, etc.

“Conventional technology and its issues” In recent years, the development of fiber reinforced composite materials has progressed rapidly, and FR
Materials made of P or the like are often machined. For example, CFRP is a synthetic resin reinforced with carbon fibers, and the tensile strength of the synthetic resin is increased by interposing woven carbon fibers within the synthetic resin.

However, machining of CFRP and the like has been extremely difficult due to the presence of reinforcing fibers inside it. In particular, when drilling holes with a twist drill (hereinafter abbreviated as a drill), reinforcing fibers remain as bulges and rips not only on the entry and exit sides of the drill but also on the inner periphery of the hole.
It was almost impossible to drill holes. For this reason, there has been a strong demand for a drill suitable for drilling holes in fiber-reinforced composite materials.

[Object of the Invention] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a drill that can perform hole drilling without causing the reinforcing fibers to peel or peel.

[Means for Solving the Problems] The drill of the present invention has a twisted groove formed in a spiral shape that advances in the rotational direction from the distal end side to the proximal end side, and the core thickness of the drill body is set to 8% to 20% of the drill diameter. %.

[Function] For example, consider cutting a thin thread with scissors.
If there is a gap between the two blades of the scissors, the thread will not cut properly. In other words, the two blades are pressed strongly against each other,
As a result, the thread cannot be cut properly unless it is tightly pinched between two blades, and this is the same when cutting reinforcing fibers such as CFRP with the cutting blade. In the drill configured as described above, since the helix direction of the helical groove is opposite to that of conventional drills, the axial rake angle of the cutting edge is inevitably negative. When drilling, for example, C F R P with such a cutting edge, the reinforcing fibers are strongly pressed against the synthetic resin side by the rake surface because the axial rake angle of the cutting edge is negative. As a result, the reinforcing fibers and the synthetic resin are cut off as if using scissors, with the synthetic resin as the lower blade and the cutting blade as the upper blade. Therefore, no reinforcing fibers remain on the surface processed by the cutting blade, and it is possible to prevent the occurrence of burrs due to the reinforcing fibers.

Furthermore, the core thickness is 8% to 20% of the drill diameter, which is that of a conventional drill. Since it is significantly smaller than the previous one, the thrust load during drilling is small, which makes it possible to cut the reinforcing fibers with good sharpness. This can be effectively prevented, and since the length of the effective cutting edge portion is long, the cutting quality is good, and heat generation at the center of the hole can be prevented.

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 is a side view showing a drill according to an embodiment. In the figure, reference numeral 1 indicates the drill body.

The drill body l is made of, for example, cemented carbide or cermet, and is designed to be rotated clockwise, that is, rightward, when viewed from the base end. Two helical grooves 2 are formed on the outer periphery of the drill body 1, and a cutting edge 3 is formed at the tip ridgeline of the wall surface facing the direction of rotation of the helical grooves 2. The above points are the same as conventional drills.

However, the core thickness T of the drill body 1 is ~8% of the drill diameter D.
It is set to 20%. The lower limit of this numerical limitation is a value necessary to maintain the rigidity of the drill body 1. In addition, the upper limit value reduces the thrust load and
This value is necessary to improve the sharpness of the hole and prevent heat generation in the center of the hole.

Moreover, the twisted groove 2 is formed in a spiral shape that progresses in the rotational direction from the distal end side to the proximal end side. In other words, the twisted groove 2 is twisted counterclockwise to the left when viewed from the tip in the axial direction.

Therefore, the axial rake angle of the cutting edge 3 is negative. Here, the helix angle of the helix groove 2 is 15° ~
It is set to 75°, preferably << is set to 20 to 60°, and more preferably << is set to 30' to 50'. The lower limit of this numerical limitation is a range that can more effectively prevent the occurrence of cracks and peeling, and the upper limit is a range that allows chips to flow out more smoothly and prevents chip clogging.

In addition, the wall surface of the helical groove 2 is formed into a concave curved surface so as to be concave in the cross section perpendicular to the axis or concavely curved toward the rear in the rotational direction. For this reason, the helical groove 2 has a left-handed helix, and the cutting edge 3 has a shape that (j?) is deeply recessed toward the rear in the rotational direction when viewed from the tip in the axial direction. The radial rake angle is large and in the positive direction. In other words, as the axial rake angle of the cutting edge 3 increases toward the negative side, the la/al rake angle increases toward the positive side, thereby preventing the cutting resistance from increasing excessively.

Here, a line segment connecting the intersection of the cutting blade 3 with a circle centered on the axis and having a diameter of 60% of the drill diameter and the outer periphery of the cutting blade 3, and a line extending from the axis to the outer periphery of the cutting blade 3. The angle φ formed with the extended line segment is set to 5° to 60°, preferably 10'
~50°, more preferably 1, < is set to 15° to 40°. The lower limit value of this numerical limitation is a range in which the cutting resistance can be further reduced, and the upper limit value is a range in which the strength at the outer peripheral end of the cutting blade 3 can be further increased.

Second, since the shape of the helical groove 2 is a concave curved surface, the cutting edge 3 (FIG. 1) when viewed from the side also has a concave curved shape concave toward the end side. With such a shape of the cutting edge 3, it is possible to extremely easily drill holes in the fiber-reinforced composite material.

In other words, some drills have a special tip shape called a candlestick type or a finoch tail point type. These are mainly used for drilling holes in thin plates.The former makes the tip angle of the center part of the drill tip larger than the outer circumference, which improves the biting of the steel plate and reduces the vibration of the drill. Defense+L It's L's. On the other hand, the latter has a tip angle of 180' or more, so by cutting along the contour of the hole, it is possible to prevent the hole edge from being swallowed due to cutting thrust. The disadvantage is that the IJ is easily vibrated. In the drill of the example, since the cutting edge 3 has a concave curve shape that extends toward the base side in side view, the candleboin 1 and
The outer periphery of the die and the cutting edge 3 has a fishtail shape, so that it is possible to prevent the vibration of the drill and the occurrence of cracks, cracks, and cracks.

Here, in order to obtain the shape of the cutting edge 3 as shown in ``2'',
It is desirable that the tip angle θ of the cutting blade 3 be 150° or more.
However, in order to prevent chipping and chinobing at the outer peripheral end of the cutting edge 3, the tip angle θ should be 175° or less. Note that the tip angle O in this case refers to the angle formed by the line segment connecting the axis P and the outer periphery Q of the cutting blade 3.

Furthermore, the groove width ratio A:B of the twisted groove 2 is 1.51 or more.
This is set large (compared to about 0.9:1 for conventional drills), and together with the fact that the core thickness T is 8% to 20%, the outflow area of chips becomes extremely large. This is because the drill of the present invention has a left-handed twist that prevents chips from flowing out, so the purpose is to increase the chip flow area and improve discharge performance. Width ratio A2B
is preferably 31 or less.

Next, the operation when drilling, for example, CFR1) with the drill configured as described above will be described with reference to FIG. 5. FIG. 5 shows a cross section of the cross-cut material A that is perpendicular to the cutting edge 3. Inside the cross-cut material A, countless reinforcing fibers F are woven vertically and horizontally in a plan view. From Figure 5 1
Since the axial rake angle of the cutting blade 3 is negative as shown in FIG. In other words, the reinforcing fiber F is combined with the synthetic resin M.
The resin M is used as the lower blade and the cutting knife 3 is used as the upper blade, and the resin is cut as if using scissors. Therefore, the reinforcing fibers F will not remain in the machining process B by the cutting blade 3.

Furthermore, in the above drill, the core thickness 'r of the drill body 1 is set to 8% to 20% of the drill diameter D, which is significantly smaller than that of conventional drills. The thrust load is small, which makes it possible to cut the reinforced oak fibers with good sharpness, and together with this, it is possible to more effectively prevent the occurrence of cracks and scratches, especially on the exit side of the hole, and the cutting edge 3 Because the length of the effective part is long, it cuts well and prevents heat generation in the center of the hole. Therefore, drilling of fiber-reinforced composite materials can be performed smoothly in the same way as drilling of metal materials.

In addition, although the above embodiment is an application of the present invention to a solid drill, the same effect can be achieved even if the present invention is applied to a brazed drill or throw-away drill in which only the cutting edge is made of cemented carbide or the like. be able to. Further, in the above embodiment, the drill body l is rotated clockwise when viewed from the base end side, so the helical groove 2 is left-handed; however, when the drill body l is rotated counterclockwise, Of course, it will be a right-handed twist.

[Effects of the Invention] As explained above, in the drill of the present invention, the helical groove is formed in a spiral shape that advances in the direction of rotation from the distal end to the proximal end, and the core thickness of the drill body is set to 8% to 8% of the drill diameter. 2
Since it is set to 0%, the cutting blade has a negative Ashisharrake angle, and can cut the reinforcing fibers as if they were being cut with scissors. Therefore, there is no chance of reinforcing fibers remaining on the surface processed by the cutting blade, and since there is less frictional resistance between the drill body and the hole, the reinforcing fibers can be cut with good sharpness, and the hole can be cut easily. It is possible to effectively prevent the occurrence of cracks and pimples on the edges and inner periphery.

Furthermore, the thrust load during the drilling process is small, so the reinforcing fibers can be cut with good sharpness, and together with this, it is possible to more effectively prevent the occurrence of peeling, especially on the exit side of the hole, and The length of the effective part of the cutting blade is long, so it cuts well and prevents heat generation in the hole. Therefore, drilling of fiber-reinforced composite materials can be performed smoothly in the same way as drilling of metal materials.

[Brief explanation of drawings]

1 to 5 are views showing embodiments of the present invention, in which FIG. 1 is a side view showing a drill, FIG. FIG. 4 is a view taken in the IV direction of FIG. 3, and FIG. 5 is a sectional view perpendicular to the cutting blade showing a state in which a hole is being drilled in FRP. l...Drill body, 2...Twisted groove, 3...Cutting edge, 4...Margin.

Claims (6)

[Claims] (1) In a twist drill, a twist groove is formed on the outer periphery of a drill body that is rotated around an axis, and a cutting edge is formed on the tip ridgeline of the wall surface facing the rotation direction of the twist groove. A twist drill characterized in that it is formed in a spiral shape that advances in the rotational direction as it goes from the side to the proximal end, and the core thickness of the drill body is 8% to 20% of the drill diameter. (2) The wall surface of the helical groove facing the rotation direction is formed into a concave curved surface so that the shape in a cross section perpendicular to the axis is a concave curve concave toward the rear in the rotation direction. Twist drill as described in section. (3) a line segment connecting the intersection of the cutting blade with a circle centered on the axis and having a diameter of 60% of the drill diameter and the outer peripheral end of the cutting blade;
The angle formed by the line segment connecting the axis and the outer peripheral edge of the cutting blade is 5.
Claim 2 characterized in that the angle is between 60° and 60°.
Twist drill as described in section. (4) The twist drill according to any one of claims 1 to 3, wherein the twist angle of the twist groove is 15° to 75°. (5) The twist drill according to any one of claims 1 to 4, characterized in that the groove width ratio is 1.5 to 3:1. (6) The twist drill according to any one of claims 1 to 5, wherein the cutting edge has a tip angle of 150° or more.