JP7497588B2 - Drill - Google Patents

Description

The present invention relates to a drill in which a chip discharge groove is formed on the outer periphery of the tip of an axial drill body that is rotated around an axis in the direction of drill rotation, and a cutting edge is formed at the intersection ridge between the wall surface of the chip discharge groove that faces the direction of drill rotation and the tip relief surface of the drill body.

When drilling holes using this type of drill, the challenge is to reduce the burrs that form at the opening of the through hole when drilling through metal, carbon fiber reinforced plastic (CFRP), or a laminated material made of metal and CFRP.

One way to reduce these burrs is to increase the twist angle of the chip discharge groove and increase the axial rake angle of the cutting edge toward the positive side, thereby increasing the force opposite to the machining direction and reducing the thrust load, while reducing the cutting edge angle to improve sharpness.

However, if the twist angle of the chip discharge groove is increased, the overall length of the chip discharge groove increases, impairing chip discharge performance and causing chip clogging. In addition, if the cutting edge angle is reduced, the strength of the cutting edge decreases, and there is a risk of the drill reaching the end of its life sooner due to chipping or damage to the cutting edge.

For example, Patent Document 1 describes a drill that includes a rod-shaped drill body, a main cutting edge that is located at the tip of the drill body and has a straight portion when viewed toward the tip, a chip discharge groove that is provided on the outer periphery of the drill body and extends in a spiral shape around the rotation axis of the drill body from the rear of the main cutting edge toward the rear end side of the drill body, and a main rake face that is provided along the main cutting edge and between the main cutting edge and the chip discharge groove, and the main rake face has a flat portion that is provided along the straight portion and a recess that is located between the flat portion and the chip discharge groove and is recessed further than the chip discharge groove.

In such drills, the flat portion on the main rake face is connected to a recess that is recessed deeper than the chip discharge groove, so that the axial rake angle of the straight portion of the main cutting edge at this flat portion is larger on the positive side than the twist angle of the chip discharge groove. Therefore, the straight portion of the main cutting edge can be sharpened without increasing the overall length of the chip discharge groove.

Patent No. 6343005

However, the drill described in Patent Document 1 has a minor cutting edge located adjacent to the main cutting edge toward the rear end of the drill body, and the flat portion provided along the straight portion of the main rake face is away from this minor cutting edge and is not formed to reach the outer periphery of the main cutting edge, so that burrs generated on the outer periphery of the main cutting edge are removed by the minor cutting edge.

However, in drilling through holes as described above, burrs are likely to occur on the peripheral portion of the opening where the through hole exits. If the flat portion described above is not formed on the outer periphery of the main cutting edge that cuts such a portion and the axial rake angle is not increased to the positive side, the sharpness of the main cutting edge that mainly forms the through hole will become dull, making it difficult to completely remove the burrs that occur with the secondary cutting edge.

On the other hand, at the inner circumference of the drill body, where a large thrust load acts due to the slow peripheral speed around the axis, the straight portion of the main cutting edge has a flat portion, so the cutting edge angle is small. For this reason, there is a risk that the straight portion of the main cutting edge on the inner circumference of the drill body may be more susceptible to breakage or chipping.

The present invention was made against this background, and aims to provide a drill that can effectively suppress the generation of burrs at the opening of the through hole without causing damage or chipping of the cutting edge or clogging of the chip discharge groove.

In order to solve the above problems and achieve the above object, the present invention provides a drill in which a chip discharge groove is formed on the outer periphery of the tip of an axial drill body centered on the axis, which is rotated in the drill rotation direction around the axis, and a cutting edge is formed at the intersection ridge between the wall surface of the chip discharge groove facing the drill rotation direction and the tip relief surface of the drill body, and the cutting edge comprises a main cutting edge formed on the inner periphery side of the drill body and a minor cutting edge connected to the main cutting edge on the outer periphery side of the drill body, and the axial rake angle of the minor cutting edge is larger on the positive angle side than the axial rake angle of the main cutting edge.

In a drill configured in this way, the axial rake angle of the minor cutting edge that is connected to the main cutting edge on the outer periphery of the drill body is larger on the positive side than the axial rake angle of the main cutting edge, so that the cutting edge can be sharpened on the outer periphery side, and when drilling through holes in metal, CFRP, or a laminated material made of metal and CFRP, burrs that occur at the opening of the through hole can be removed and suppressed.

On the other hand, the main cutting edge on the inner circumference of the drill body has a larger axial rake angle on the negative side compared to the minor cutting edge, so the cutting edge strength can be maintained by ensuring a large cutting angle. This makes it possible to prevent breakage or chipping even when a large thrust load is applied, and to extend the drill's life. In addition, the twist angle of the chip discharge groove can be set to match the axial rake angle of the main cutting edge, which prevents the overall length of the chip discharge groove from becoming too long and prevents chip clogging.

Here, it is desirable that the radial width of the minor cutting edge relative to the axis is within the range of 0.05 x D to 0.20 x D of the diameter D of the cutting edge. If the radial width of the minor cutting edge relative to the axis is less than 0.05 x D of the diameter D of the cutting edge, it may be difficult to reliably remove burrs that occur at the opening of the through hole, while if it exceeds 0.20 x D of the diameter D of the cutting edge, the minor cutting edge with a large axial rake angle on the positive side and a small cutting angle may take up too much of the total length of the cutting edge, causing chipping or breakage.

It is also desirable that the axial rake angle of the minor cutting edge is within the range of 10° to 50°, and that of the major cutting edge is within the range of 0° to 40°. If the axial rake angles of the minor cutting edge and the major cutting edge are larger on the positive angle side than the above range, the cutting angle of the minor cutting edge in particular becomes too small, making it easier for chipping and breakage to occur, while if they are larger on the negative angle side than the above range, there is a risk of increased cutting resistance. The axial rake angles of the minor cutting edge and the major cutting edge may change in the radial direction relative to the axis of the drill body, in which case it is sufficient that the axial rake angles at the outer circumferential ends of the minor cutting edge and the major cutting edge are within the above range.

Here, the rake face of the minor cutting edge may be formed in a triangular or rectangular shape when viewed from the direction of rotation of the drill. By configuring it in this way, after manufacturing a normal drill in which the axial rake angle of the cutting edge matches the axial rake angle of the main cutting edge, the axial rake angle of the minor cutting edge can be easily made larger on the regular side than that of the main cutting edge by simply sharpening the rake face of the minor cutting edge into a triangular shape when viewed from the direction of rotation of the drill only at the minor cutting edge.

When the rake face of the minor cutting edge is formed in a square shape when viewed from the drill rotation direction, the radial width relative to the axis is greater than the length in the axial direction. This makes it possible to lengthen the portion of the cutting edge where the axial rake angle is large on the positive side, thereby reducing the cutting resistance. Conversely, when the cutting edge is formed in a square shape where the length in the axial direction is greater than the width in the radial direction relative to the axis, it is possible to ensure a large amount of re-grinding by grinding the tip relief face to sharpen a new cutting edge when the cutting edge wears.

The minor cutting edge may extend further in the drill rotation direction than the main cutting edge when viewed from the axial tip side, but it is preferable for the minor cutting edge to extend further in the opposite direction to the drill rotation direction than the main cutting edge when viewed from the axial tip side, as this facilitates manufacturing, particularly when, as described above, a normal drill is manufactured and then the rake face of the minor cutting edge is sharpened to make the axial rake angle of the minor cutting edge larger than that of the main cutting edge.

In this case, the main cutting edge and the minor cutting edge have a step when viewed from the tip side in the axial direction, and the step between the minor cutting edge and the main cutting edge has a curved connection when viewed from the tip side in the axial direction. This is desirable because it prevents the radial rake angle of the minor cutting edge from being significantly different from that of the main cutting edge and prevents the step from becoming too sharp and causing chipping.

However, the minor cutting edge may be connected to the main cutting edge in a broken line shape when viewed from the tip side in the axial direction, or may be formed in a convex curve that is tangent to the main cutting edge when viewed from the tip side in the axial direction. In this case, a step is not generated between the minor cutting edge and the main cutting edge, so chipping can be prevented more reliably, and the chips generated by the main cutting edge and minor cutting edge are not divided by the step, so chip clogging caused by the divided chips becoming entangled can be prevented.

On the other hand, the minor cutting edge may be formed in a concave curve that is concave from the main cutting edge in the opposite direction to the drill rotation direction when viewed from the axial tip side. In this case, the chips are generated by being divided between the main cutting edge and the minor cutting edge, but the chips generated by the minor cutting edge flow out along the concave curve to the inner side of the drill body, so they do not damage the inner surface of the drilled hole.

As explained above, according to the present invention, it is possible to prevent chipping and damage to the cutting edge, thereby extending the life of the drill, and to prevent chip clogging in the chip discharge groove, thereby enabling stable drilling. Furthermore, when drilling through holes in metal, CFRP, or a laminated material made of metal and CFRP, burrs that occur at the opening of the through hole at the exit are removed by the secondary cutting edge, thereby suppressing the burrs, enabling high-quality drilling.

1 is a front view of a drill body as viewed from the axial tip, showing a first embodiment of the present invention. FIG. FIG. 2 is a plan view taken along the arrow X direction in FIG. 1 . FIG. 2 is a side view taken in the direction of the arrow Y in FIG. 1 . FIG. 11 is a front view of a drill body as viewed from the axial tip, showing a second embodiment of the present invention. FIG. 5 is a plan view seen in the direction of the arrow X in FIG. 4 . FIG. 11 is a plan view showing a third embodiment of the present invention. FIG. 13 is a front view of a drill body as viewed from the axial tip, showing a fourth embodiment of the present invention. FIG. 13 is a front view of a drill body as viewed from the axial tip, showing a fifth embodiment of the present invention. FIG. 13 is a front view of a drill body as viewed from the axial tip, showing a sixth embodiment of the present invention.

Figures 1 to 3 show a first embodiment of the present invention. In this embodiment, the drill body 1 is made of a hard material such as cemented carbide and has a generally cylindrical shaft shape centered on axis O, with the rear end (not shown) remaining cylindrical as a shank portion and the tip portion serving as a cutting edge portion 2.

The shank of this type of drill is held by the spindle of a machine tool and rotated around axis O in the drill rotation direction T while being fed toward the tip side in the direction of axis O. The cutting blade 3 at the tip of the cutting blade portion 2 drills holes in metal, CFRP, or a laminated material made of metal and CFRP.

A chip discharge groove 5 is formed on the outer periphery of the cutting edge portion 2, opening on the tip flank 4, which is the tip surface of the drill body 1, and heading toward the rear end (the right side in Figures 2 and 3). In this embodiment, multiple (two) chip discharge grooves 5 are formed at equal intervals in the circumferential direction, twisting in the opposite direction to the drill rotation direction T as they head toward the rear end of the drill body 1.

The tip of the wall surface of the chip discharge groove 5 facing the drill rotation direction T is the rake face 6 of the cutting edge 3, and the cutting edge 3 is formed at the intersection ridge between this rake face 6 and the tip relief face 4. Here, the tip relief face 4 is inclined toward the rear end of the drill body 1 as it moves toward the outer periphery of the drill body 1 and the opposite side to the drill rotation direction T, thereby giving the cutting edge 3 a predetermined tip angle and relief angle.

In this embodiment, the tip flank 4 is formed by first and second tip flanks 4a and 4b, whose flank angles gradually increase in the direction opposite to the drill rotation direction T. Of these, the second tip flank 4b has coolant holes 1a formed in the drill body 1 that open in the circumferential direction and pass between the chip discharge grooves 5.

In addition, a margin portion 7a is formed on the outer peripheral surface of the cutting edge portion 2 adjacent to the wall surface of the chip discharge groove 5 facing the drill rotation direction T on the opposite side of the drill rotation direction T, and the opposite side of this margin portion 7a to the drill rotation direction T is an outer peripheral relief surface 7b whose outer diameter is slightly smaller than that of the margin portion 7a.

Furthermore, a thinning portion 8 is formed on the inner peripheral portion of the tip of the chip discharge groove 5 by cutting the inner peripheral portion toward the axis O of the drill body 1. In this embodiment, the thinning portion 8 extends from the inner peripheral portion of the rake face of the cutting edge 3 to the heel portion where the wall surface of the chip discharge groove 5 facing away from the drill rotation direction T intersects with the outer peripheral relief surface 7b.

Furthermore, the cutting edge 3 includes a thinning edge 3a formed at the intersection ridge between the thinning rake surface 6a formed in the thinning portion 8 of the rake surface 6 and the tip flank 4, a main cutting edge 3b connected to the outer periphery of the drill body 1 of the thinning edge 3a and formed at the intersection ridge between the main rake surface 6b on the inner periphery of the wall surface facing the drill rotation direction T of the chip discharge groove 5 and the tip flank 4, and a secondary cutting edge 3c connected to the outer periphery of the main cutting edge 3b and formed at the intersection ridge between the secondary rake surface 6c on the outer periphery of the wall surface facing the drill rotation direction T of the chip discharge groove 5 and the tip flank 4.

As described above, the chip discharge groove 5 twists in the opposite direction to the drill rotation direction T as it approaches the rear end of the drill body 1, so that the main cutting edge 3b and the minor cutting edge 3c, whose rake faces 6 are the wall surfaces of the chip discharge groove 5 facing the drill rotation direction T, are given positive axial rake angles θ1 and θ2. As shown in FIG. 3, the axial rake angle θ2 of the minor cutting edge 3c is set to be greater on the positive side than the axial rake angle θ1 of the main cutting edge 3b.

In this embodiment, the axial rake angle θ2 of the minor cutting edge 3c is in the range of 10° to 50°, and the axial rake angle θ1 of the main cutting edge 3b is in the range of 40° or less, with θ2 > θ1 within these ranges. Note that the axial rake angle θ1 of the main cutting edge 3b and the axial rake angle θ2 of the minor cutting edge 3c may change in the radial direction relative to the axis O of the drill body 1, as long as the axial rake angles θ1 and θ2 at the outer circumferential ends of the main cutting edge 3b and the minor cutting edge 3c are within the above ranges as shown in FIG. 3.

In addition, in this embodiment, when viewed from the tip side in the direction of the axis O, the thinning edge 3a extends from the vicinity of the axis O on the inner peripheral side of the tip flank 4 toward the outer periphery of the drill body 1 in a convex curve that is convex in the drill rotation direction and contacts the inner peripheral end of the main cutting edge 3b, and the main cutting edge 3b extends in a straight line toward the outer periphery from the contact point with the thinning edge 3a. In contrast, the minor cutting edge 3c extends in the opposite direction to the drill rotation direction T than the main cutting edge 3b when viewed from the tip side in the direction of the axis O.

More specifically, in this embodiment, as shown in FIG. 1 when viewed from the tip side in the direction of axis O, the minor cutting edge 3c is formed to extend parallel to the main cutting edge 3b with a step on the opposite side of the drill rotation direction T. In addition, a curved connection portion 3d is formed at the step between the minor cutting edge 3c and the main cutting edge 3b, and in this embodiment, this connection portion 3d is formed in a concave curve such as a concave arc. In other words, the main cutting edge 3b and the minor cutting edge 3c, and the main cutting surface 6b and the minor cutting surface 6c are discontinuous.

Furthermore, as shown in Figure 2 when viewed from the drill rotation direction T side, the auxiliary rake face 6c is formed in a triangular shape. This auxiliary rake face 6c is formed in a concave shape that is recessed in the opposite direction to the drill rotation direction T with respect to the main rake face 6b, and is formed so that as it moves away from the auxiliary cutting edge 3c and toward the rear end side of the drill body 1, it recesses in the opposite direction to the drill rotation direction T at a larger inclination angle than the main rake face 6b, and then cuts up to the main rake face 6b in a concave curved surface.

Furthermore, in this embodiment, the radial width W of the minor cutting edge 3c relative to the axis O is within the range of 0.05 x D to 0.20 x D of the diameter D of the cutting edge 3 (the diameter of the circle that the outer circumferential end of the cutting edge 3 forms around the axis O). Note that the radial width W of the minor cutting edge 3c relative to the axis O is the width from the outer circumferential end of the main cutting edge 3b, including the above-mentioned connecting portion 3d, to the outer circumferential end of the minor cutting edge 3c, and the minor cutting edge 3c does not reach the thinning edge 3a.

In a drill configured in this manner, the axial rake angle θ2 of the minor cutting edge 3c, which is connected to the main cutting edge 3b on the outer periphery of the drill body 1, is greater on the positive side than the axial rake angle θ1 of the main cutting edge 3b, so that the cutting edge 3 can be sharpened on the outer periphery side. Therefore, when drilling through holes in metal, CFRP, or a laminated material in which metal and CFRP are laminated, burrs that occur at the opening of the through hole can be removed and suppressed by the minor cutting edge 3c, and high-quality drilling can be performed.

On the other hand, the main cutting edge 3b, which is closer to the inner circumference of the drill body 1 than the minor cutting edge 3c, has a larger negative axial rake angle θ1 than the minor cutting edge 3c, so a large cutting tool angle can be ensured. This allows the strength of the cutting edge to be maintained, so that even on the inner circumference of the drill body 1 where a large thrust load acts, damage and chipping can be prevented, making it possible to extend the life of the drill. Moreover, the twist angle of the chip discharge groove 5 can be set to match the axial rake angle θ1 of the main cutting edge 3b, so that the overall length of the chip discharge groove 5 can be prevented from becoming too long, and chip clogging can also be prevented.

In addition, in this embodiment, the radial width W of the minor cutting edge 3c relative to the axis O is set within the range of 0.05 x D to 0.20 x D of the diameter D of the cutting edge 3, so that the occurrence of burrs can be reliably suppressed while also preventing breakage and chipping.

In other words, if the width W of the minor cutting edge 3c is less than 0.05 × D of the diameter D of the cutting edge 3, it may be difficult to reliably remove burrs that occur at the opening of the through hole. On the other hand, if the width W of the minor cutting edge 3c exceeds 0.20 × D of the diameter D of the cutting edge 3, the minor cutting edge 3c, which has a large axial rake angle θ2 on the positive side and a small cutting angle, will take up too much of the total length of the cutting edge 3, which may cause chipping or damage.

In addition, in this embodiment, the axial rake angle θ2 of the minor cutting edge 3c is set within the range of 10° to 50°, and the axial rake angle θ1 of the main cutting edge 3b is set within the range of 40° or less, which also prevents damage or chipping of the main cutting edge 3b and minor cutting edge 3c while preventing cutting resistance from increasing more than necessary.

In other words, if the axial rake angles θ1, θ2 of the main cutting edge 3b and the minor cutting edge 3c are larger on the positive side than within the above ranges, the cutting angle of the minor cutting edge 3c in particular will be too small, making chipping and breakage more likely to occur, while if they are larger on the negative side than within the above ranges, there is a risk of increased cutting resistance. Note that the axial rake angle θ1 of the main cutting edge 3b may be 0°, that is, the axial rake angle θ1 of the main cutting edge 3b may be in the range of 0° to 40°.

When manufacturing such a drill, first, a normal drill is manufactured in which the axial rake angle of the cutting edge 3 is adjusted to the axial rake angle θ1 of the main cutting edge 3b, and then the minor cutting edge 3c of this drill is sharpened by grinding the minor rake face 6c when viewed from the drill rotation direction T, thereby forming the minor cutting edge 3c at the intersection ridge between the minor rake face 6c and the tip clearance face 4.

In this embodiment, in such a case, the auxiliary cutting surface 6c is formed in a triangular shape when viewed from the drill rotation direction T, so the area required to sharpen the auxiliary cutting surface 6c is small, and the axial rake angle θ2 of the auxiliary cutting edge 3c can be easily made larger on the positive side than the axial rake angle θ1 of the main cutting edge 3b.

However, in this embodiment, the sub-rake surface 6c is formed in a triangular shape as seen from the drill rotation direction T, but it may be formed in a rectangular shape. In this case, for example, as in the second embodiment of the present invention shown in Figures 4 and 5 and the third embodiment shown in Figure 6, the sub-rake surface 6c may be formed in a rectangular shape (approximately a parallelogram) extending with a substantially constant width W as seen from the drill rotation direction T. The second and third embodiments can also achieve the same effects as the first embodiment. Note that in these second and third embodiments and the fourth to sixth embodiments described later, the same reference numerals are used for parts common to the first embodiment, and explanations are omitted.

Here, in the second embodiment shown in Figures 4 and 5, the auxiliary rake face 6c is formed in a square shape with a radial width W relative to the axis O larger than the length in the direction of the axis O, and this allows the auxiliary cutting edge 3c with a large axial rake angle θ2 on the positive side to be lengthened, thereby reducing the cutting resistance. Conversely, in the third embodiment shown in Figure 6, the auxiliary rake face 6c is formed in a square shape with a length in the direction of the axis O larger than the radial width W relative to the axis O, and when the cutting edge 3 is worn out and a new cutting edge 3 is sharpened by grinding the tip flank 4, a large amount of regrinding can be ensured, thereby extending the life of the drill.

In addition, in these first to third embodiments, the auxiliary cutting surface 6c is formed in a concave shape recessed in the opposite direction of the drill rotation direction T relative to the main cutting surface 6b, and the auxiliary cutting edge 3c extends so as to be positioned on the opposite side of the drill rotation direction T than the main cutting edge 3b when viewed from the tip side in the axis O direction. Therefore, after manufacturing a normal drill as described above, the auxiliary cutting surface 6c can be sharpened by grinding, so that the axial rake angle θ2 of the auxiliary cutting edge 3c can easily be made larger than the axial rake angle θ1 of the main cutting edge 3b.

However, instead of forming the minor cutting edge 3c to extend further in the opposite direction to the drill rotation direction T than the main cutting edge 3b when viewed from the tip side in the direction of the axis O, when manufacturing the drill body 1, a convex portion that protrudes in the drill rotation direction T may be formed at the outer peripheral end of the main rake face 6b, and the minor rake face 6c may be formed on the wall surface of this convex portion facing the drill rotation direction T, so that the minor cutting edge 3c with an axial rake angle θ2 larger on the positive side than the axial rake angle θ1 of the main cutting edge 3b may be formed at the intersection ridge with the tip flank 4.

Also, as in the first to third embodiments, even if a concave sub-cutting surface 6c is formed at the outer peripheral end of the main cutting surface 6b, which is concave in the opposite direction to the drill rotation direction T relative to the main cutting surface 6b, if the sub-cutting surface 6c is discontinuous with the main cutting surface 6b via a step or the like, the sub-cutting edge 3c may be formed to extend in a straight line with the main cutting edge 3b when viewed from the tip side in the direction of the axis O.

Furthermore, in the first to third embodiments, the main cutting edge 3b and the minor cutting edge 3c have a step when viewed from the tip side in the direction of the axis O, and the step between the minor cutting edge 3c and the main cutting edge 3b has a connection portion 3d that is curved when viewed from the tip side in the direction of the axis O. Therefore, as described above, the minor cutting edge 3c can be made parallel to the main cutting edge 3b when viewed from the tip side in the direction of the axis O, and the radial rake angle of the minor cutting edge 3c does not need to be significantly changed relative to the radial rake angle of the main cutting edge 3b. This makes it possible to prevent the chip flow direction from being different between the main cutting edge 3b and the minor cutting edge 3c, and also makes it possible to prevent the step portion (connection portion 3d) from becoming sharp and causing chipping.

In addition, instead of forming the main cutting edge 3b and the minor cutting edge 3c so that they are connected via a step portion when viewed from the tip side in the direction of the axis O as in the first to third embodiments, the minor cutting edge 3c may be connected to the main cutting edge 3b in a broken line shape when viewed from the tip side in the direction of the axis O and extend in the opposite direction to the drill rotation direction T as in the fourth embodiment shown in Figure 7, or the minor cutting edge 3c may be formed in a convex curve tangent to the main cutting edge 3b when viewed from the tip side in the direction of the axis O and extend in the opposite direction to the drill rotation direction T as in the fifth embodiment shown in Figure 8.

According to the fourth and fifth embodiments, a step portion (connection portion 3d) is not formed between the minor cutting edge 3c and the main cutting edge 3b as in the first to third embodiments, so chipping of the cutting edge 3 can be more reliably prevented. In addition, particularly in the fourth embodiment, the chips generated by the main cutting edge 3b and the minor cutting edge 3c are not divided by the step portion, so chip clogging caused by the divided chips becoming entangled can be prevented.

On the other hand, as in the sixth embodiment shown in FIG. 9, the minor cutting edge 3c may be formed in a concave curved shape that is concave from the main cutting edge 3b on the opposite side of the drill rotation direction T when viewed from the tip side in the axial O direction. According to this sixth embodiment, the chips are generated by being divided between the main cutting edge 3b and the minor cutting edge 3c, but the chips generated by the minor cutting edge 3c flow out along the concave curved minor cutting edge 3c to the inner periphery of the drill body 1, so that the inner periphery of the drilled hole can be prevented from being damaged by the chips.

Next, the effects of the present invention will be described with reference to an example of the present invention. In this example, based on the first embodiment described above, a drill was manufactured in which the diameter D of the cutting edge 3 is 1/4 inch (6.35 mm), the axial rake angle θ1 of the main cutting edge 3b is 30°, the axial rake angle θ2 of the minor cutting edge 3c is 40°, and the radial width W of the minor cutting edge 3c relative to the axis O is 0.12 x D with respect to the diameter D of the cutting edge 3.

As a comparative example for this embodiment, a drill was also manufactured that was the same as the embodiment except that the minor cutting edge 3c and the minor rake face 6c were not formed. The surface of the drill body 1 of the drill of this embodiment and the comparative example was diamond coated.

Using the drills of the example and the comparative example, a laminated material made of 10 mm thick CFRP and 5 mm thick aluminum plate was first drilled by non-step machining at a cutting speed of 100 m/min and a feed rate of 0.02 mm/rev to form the same number of through holes, and the height of the burrs was measured. During this drilling process, compressed air was sprayed from the coolant hole 1a.

As a result, in the case of drilling using the comparative example drill, the burr height was 0.01 inch to 0.015 inch, whereas in the case of drilling using the example drill, the burr height was 0.01 inch or less, including holes where no burrs were generated. This result shows that according to the present invention, it is possible to reliably suppress the generation of burrs as described above. Furthermore, no damage or chipping of the cutting edge 3 was observed in the example drills and the comparative example drills.

Next, using the drills of the examples and the comparative example, drilling was performed on the same laminated material as above, with the cutting speed kept at 100 m/min and the feed rate set at 0.10 mm/rev, five times faster than the above conditions, under highly efficient conditions, to form the same number of through holes using the same non-step process, and the height of the burrs was measured.

As a result, in the case of drilling using the comparative example drill, the burr height was 0.015 inches to 0.02 inches, which was larger than the above case, whereas in the case of drilling using the example drill, the burr height was 0.01 inches or less, including cases where no burrs were generated, as in the above case. From these results, it can be seen that according to the present invention, it is possible to reliably suppress the generation of burrs even in drilling under the high efficiency conditions described above.

1 Drill body 1a Coolant hole 2 Cutting edge portion 3 Cutting edge 3a Thinning edge 3b Main cutting edge 3c Minor cutting edge 3d Connection portion 4 Tip flank 4a First tip flank 4b Second tip flank 5 Chip discharge groove 6 Rake face 6a Thinning rake face 6b Main rake face 6c Minor rake face 7a Margin portion 7b Outer flank 8 Thinning portion O Axis of drill body 1 T Drill rotation direction θ1 Axial rake angle of main cutting edge 3b θ2 Axial rake angle of minor cutting edge 3c W Radial width of minor cutting edge 3c relative to axis O D Diameter of cutting edge 3

Claims (12)

A drill in which a chip discharge groove is formed on the outer periphery of a tip portion of an axis-shaped drill body centered on the axis and rotated in a drill rotation direction about an axis, and a cutting edge is formed on an intersection ridge between a wall surface of the chip discharge groove facing the drill rotation direction and a tip flank surface of the drill body,
The cutting edge includes a main cutting edge formed on the inner peripheral side of the drill body and a sub-cutting edge continuing from the main cutting edge on the outer peripheral side of the drill body,
The axial rake angle of the minor cutting edge is larger than the axial rake angle of the main cutting edge on the positive angle side,
The drill has a radial width of the minor cutting edge relative to the axis line within a range of 0.05×D to 0.20×D of the diameter D of the cutting edge . A drill in which a chip discharge groove is formed on the outer periphery of a tip portion of an axis-shaped drill body centered on the axis and rotated in a drill rotation direction about an axis, and a cutting edge is formed on an intersection ridge between a wall surface of the chip discharge groove facing the drill rotation direction and a tip flank surface of the drill body,
The cutting edge includes a main cutting edge formed on the inner peripheral side of the drill body and a sub-cutting edge continuing from the main cutting edge on the outer peripheral side of the drill body,
The axial rake angle of the minor cutting edge is larger than the axial rake angle of the main cutting edge on the positive angle side,
The drill , wherein the rake face of the minor cutting edge is formed in a triangular or rectangular shape when viewed from the side in the rotation direction of the drill . A drill in which a chip discharge groove is formed on the outer periphery of a tip portion of an axis-shaped drill body centered on the axis and rotated in a drill rotation direction about an axis, and a cutting edge is formed on an intersection ridge between a wall surface of the chip discharge groove facing the drill rotation direction and a tip flank surface of the drill body,
The cutting edge includes a main cutting edge formed on the inner peripheral side of the drill body and a sub-cutting edge continuing from the main cutting edge on the outer peripheral side of the drill body,
The axial rake angle of the minor cutting edge is larger than the axial rake angle of the main cutting edge on the positive angle side,
The drill has a rake face of the minor cutting edge formed in a quadrangle shape whose radial width relative to the axis is greater than its length in the direction along the axis when viewed from the side in the rotation direction of the drill. A drill in which a chip discharge groove is formed on the outer periphery of a tip portion of an axis-shaped drill body centered on the axis and rotated in a drill rotation direction about an axis, and a cutting edge is formed on an intersection ridge between a wall surface of the chip discharge groove facing the drill rotation direction and a tip flank surface of the drill body,
The cutting edge includes a main cutting edge formed on the inner peripheral side of the drill body and a sub-cutting edge continuing from the main cutting edge on the outer peripheral side of the drill body,
The axial rake angle of the minor cutting edge is larger than the axial rake angle of the main cutting edge on the positive angle side,
The drill has a rake face of the minor cutting edge formed in a quadrangle shape whose length along the axis is greater than its width in a radial direction relative to the axis when viewed from the drill rotation direction. The drill according to any one of claims 1 to 4, characterized in that , when the tip of the drill body is viewed in a direction along the axis, the minor cutting edge extends in a direction opposite to the rotation direction of the drill relative to the main cutting edge. A drill in which a chip discharge groove is formed on the outer periphery of a tip portion of an axis-shaped drill body centered on the axis and rotated in a drill rotation direction about an axis, and a cutting edge is formed on an intersection ridge between a wall surface of the chip discharge groove facing the drill rotation direction and a tip flank surface of the drill body,
The cutting edge includes a main cutting edge formed on the inner peripheral side of the drill body and a sub-cutting edge continuing from the main cutting edge on the outer peripheral side of the drill body,
The axial rake angle of the minor cutting edge is larger than the axial rake angle of the main cutting edge on the positive angle side,
The minor cutting edge extends in a direction opposite to the rotation direction of the drill relative to the main cutting edge when the tip of the drill body is viewed in a direction along the axis . The drill according to claim 5 or 6, characterized in that the main cutting edge and the minor cutting edge have a step when the tip of the drill body is viewed in a direction along the axis, and a connection portion that is curved when the tip of the drill body is viewed in a direction along the axis is formed at the step portion between the minor cutting edge and the main cutting edge . The drill according to claim 5 or 6 , wherein the minor cutting edge is connected to the main cutting edge in a broken line when the tip of the drill body is viewed in a direction along the axis. The drill according to claim 5 or 6 , characterized in that the minor cutting edge is formed in a convex curved shape tangent to the main cutting edge when the tip of the drill body is viewed in a direction along the axis. The drill according to claim 5 or 6, characterized in that the auxiliary cutting edge is formed in a concave curved shape that is concave from the main cutting edge in the opposite direction to the rotation direction of the drill when the tip of the drill body is viewed in a direction along the axis . The drill according to any one of claims 2 to 10, characterized in that the radial width of the auxiliary cutting edge relative to the axis is within a range of 0.05 x D to 0.20 x D of the diameter D of the cutting edge. The drill according to any one of claims 1 to 11, characterized in that the axial rake angle of the minor cutting edge is within a range of 10° to 50°, and the axial rake angle of the main cutting edge is within a range of 0° to 40°.

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