Drill

Abstract

To provide a drill that can maintain excellent chip discharge performance while reducing loads in cutting of cutting blades to suppress the cutting blades from being abraded, in drilling a material to be cut made of hard brittle materials, which can stably extend a tool life thereof.SOLUTION: A drill comprises a body 3 provided with a coating film including diamond. Chip discharging grooves 4 have tip grooves 41, formed in a groove shape denting from a tip surface 3a of the body 3 toward a rear end thereof, whose groove widths become larger as going toward outsides in a radial direction thereof, and outer peripheral grooves 42, connected to outer end parts in the radial direction of the tip grooves 41, which extend toward the opposite side of a rotating direction T of the drill as going toward the rear end. Cutting blades 7 extend toward the rear end as going to outside in the radial direction thereof. Four pairs of the tip grooves 41 and the cutting blades 7 are provided side by side around a central shaft C. The four cutting blades 7 have a pair of long blades 7A and a pair of short blades 7B arranged alternately around the central shaft C. The pair of tip grooves 41 arranged on respective sides of the short blade 7B communicate with each other, inside in the radial direction of the short blades 7B.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a drill.

Background Art

[0002] Conventionally, drills for machining hard and brittle materials for drilling holes in workpieces made of hard and brittle materials such as cemented carbide, ceramics, and single-crystal silicon are known. For example, Patent Document 1 discloses a two-flute drill for hard and brittle materials in which at least the cutting edge portion at the tip of the drill body is coated with a hard carbon film or a diamond electrodeposited abrasive grain layer (coating film containing diamond).

[0003] For this type of drill, there is a desire to extend the tool life. For example, if peeling of the coating film or the like can be suppressed by reducing the cutting load per cutting edge of the drill to suppress wear, the tool life can be extended. Therefore, as a drill for hard and brittle materials, it is conceivable to employ a four-flute drill as disclosed in Patent Document 2, for example.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when drilling a workpiece made of a hard and brittle material, simply making the number of cutting edges of the drill four flutes may reduce the chip evacuation performance and cause chip jamming. If chip jamming occurs, wear at the tip of the drill progresses, so that the tool life cannot be sufficiently extended.

[0006] The object of the present invention is to provide a drill that can reduce the cutting load of each cutting edge, suppress wear, maintain good chip discharge performance, and thereby stably extend the tool life when drilling a workpiece made of a brittle material.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention provides the following means.

[0008] 〔Aspect 1 of the Present Invention〕 A drill comprising a body that extends axially about a central axis and is provided with a coating film containing diamond at least at its tip portion, the body having a cutting edge disposed at the tip portion of the body, and a chip discharge groove that opens to the tip surface and the outer peripheral surface of the body and extends from the tip surface toward the rear end side, the chip discharge groove being in the form of a groove that is recessed from the tip surface of the body toward the rear end side and has a groove width that widens as it goes radially outward, a tip groove, and a groove that is recessed radially inward from the outer peripheral surface of the body and is connected to the radially outer end portion of the tip groove and extends toward the rear end side in a direction opposite to the drill rotation direction around the central axis, the cutting edge being disposed at a ridge line portion where the wall surface of the tip groove facing the drill rotation direction and the tip surface of the body are connected and extending toward the rear end side as it goes radially outward, the combination of the tip groove and the cutting edge being provided in four rows side by side around the central axis, the four cutting edges having a pair of long cutting edges and a pair of short cutting edges having a shorter cutting edge length than the long cutting edges, the long cutting edges and the short cutting edges being alternately arranged side by side around the central axis, and the pair of tip grooves disposed on both sides of the short cutting edge around the central axis communicating with each other inside the short cutting edge in the radial direction.

[0009] The drill of the present invention is suitable for drilling a workpiece made of a brittle material such as cemented carbide, ceramics, or single crystal silicon. Since this brittle material drill has four cutting edges, the cutting load per cutting edge can be reduced and wear can be suppressed as compared with a conventional two-cutting-edge drill. As a result, peeling of the coating film containing diamond and the like can be suppressed, and the tool life can be extended.

[0010] More specifically, in the machining mode of the drill, the cutting distance of the outer peripheral portion (radial outer end portion) of the cutting edge becomes long, and wear at the outer peripheral portion tends to progress. By making the number of cutting edges four as in the present invention, the cutting distance at the outer peripheral portion of each cutting edge can be suppressed to be short, the progress of wear can be suppressed, and the service life can be extended.

[0011] Furthermore, the drill of the present invention is a four-flute drill in which a pair of long flutes and a pair of short flutes are alternately arranged around the central axis. Therefore, it is possible to configure a communication between a pair of tip grooves arranged on both sides around the central axis of the short flute (that is, in the drill rotation direction and the reverse drill rotation direction of the short flute) via the inner side in the radial direction of the short flute. Thereby, a sufficient chip discharge space can be secured near the center of the drill tip portion. In particular, even in the drilling of hard and brittle materials where fine chips are likely to be generated, the chip discharge property at the center of the drill tip is maintained well, and the occurrence of chip jamming can be suppressed.

[0012] Also, since the center of the drill tip is a two-flute structure with only a pair of long flutes, the biting into the workpiece during drilling is improved, and the machining stability is enhanced. Specifically, for example, unlike the present invention, in the case of a so-called "core connection" configuration in which four cutting edges are radially connected at the center of the drill tip as in Patent Document 2 (Japanese Patent Application Laid-Open No. 2022-159631), in the drilling of hard and brittle materials, the biting into the workpiece may deteriorate and the machining stability may be impaired.

[0013] Note that, unlike the present invention, for example, when the drill has five or more flutes, the cutting resistance during drilling becomes too large, and the workpiece made of hard and brittle material may crack. Also, it becomes difficult to sufficiently secure the groove width dimension and the groove depth dimension of each chip discharge groove, the chip discharge property deteriorates, and chip jamming may occur. Also, unlike the present invention, for example, if the drill has an odd number of flutes such as three flutes, the balance around the central axis of the long flute and the short flute deteriorates, and the machining stability may be impaired.

[0014] As described above, according to the four-edge drill of the present invention, when drilling a workpiece made of a hard and brittle material, the cutting load on each cutting edge can be reduced to suppress wear, while maintaining good chip evacuation performance. As a result, the tool life can be stably extended.

[0015] 〔Aspect 2 of the present invention〕 The drill according to Aspect 1, wherein the blade length dimension of each of the short blades is 25% or more and 49% or less with respect to the diameter dimension of the rotation locus of the cutting edge around the central axis.

[0016] With the above configuration, with the diameter dimension of the rotation locus of the cutting edge around the central axis (i.e., the blade diameter dimension) as a reference (100%), if the blade length dimension of each short blade is 25% or more, each short blade can perform stable cutting.

[0017] Further, with the diameter dimension of the rotation locus of the cutting edge around the central axis as a reference, since the blade length dimension of each short blade is 49% or less, the tip grooves can be stably communicated with each other inside the radial direction of each short blade.

[0018] 〔Aspect 3 of the present invention〕 The drill according to Aspect 1 or 2, wherein the tip groove has a first edge which is an edge of both end edges of the tip groove around the central axis and is the edge in the drill rotation direction, and a second edge which is an edge of both end edges of the tip groove around the central axis and is the edge on the side opposite to the drill rotation direction, and when viewing the body from the tip side in the axial direction, the tip groove opening angle formed between the first edge and the second edge is 30° or more and 80° or less.

[0019] In the above configuration, among the both end edges (both end edges of the groove width) of the tip groove around the central axis, the second edge corresponds to the cutting edge. With the above configuration, if the tip groove opening angle is 30° or more, the groove width of the tip groove is sufficiently widened toward the outside in the radial direction. Therefore, the chips generated from the cutting edge flow stably toward the outside in the radial direction without clogging in the tip groove. For this reason, the chip evacuation performance can be further improved.

[0020] In addition, when the tip groove opening angle is 80° or less, providing a tip groove with a wide groove width suppresses excessive reduction in the thickness of the drill tip portion. Therefore, the rigidity of the drill tip portion can be stably ensured.

[0021] 〔Aspect 4 of the present invention〕 The drill according to any one of Aspects 1 to 3, wherein a tip groove notch angle formed between a virtual straight line orthogonal to the central axis and the groove bottom of the tip groove is 10° or more and 50° or less when the body is viewed in the radial direction.

[0022] If the tip groove notch angle is 10° or more as in the above configuration, the depth of the groove bottom of the tip groove (groove depth) can be sufficiently ensured, and the chips can stably flow outward in the radial direction without clogging in the tip groove. Therefore, chip dischargeability can be further improved.

[0023] In addition, when the tip groove notch angle is 50° or less, providing a tip groove with a deep groove depth suppresses excessive reduction in the thickness of the drill tip portion. Therefore, the rigidity of the drill tip portion can be stably ensured.

Advantages of the Invention

[0024] According to the drill of the above aspect of the present invention, when drilling a workpiece made of a hard and brittle material, the cutting load on each cutting edge can be reduced to suppress wear, while maintaining good chip dischargeability, thereby stably extending the tool life.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0026] A drill 1 according to an embodiment of the present invention will be described with reference to the drawings. The drill 1 of the present embodiment is suitable for drilling a workpiece made of a brittle material. Specifically, the brittle material is, for example, a high-hardness brittle material such as cemented carbide, ceramics, or single-crystal silicon. The drill 1 of the present embodiment may also be referred to as a drill for brittle materials or the like.

[0027] As shown in FIG. 1, the drill 1 has a columnar shape centered on the central axis C. The drill 1 includes a shank 2 and a body 3. The shank 2 and the body 3 are arranged at different positions in the direction in which the central axis C extends. Note that the body 3 may also be referred to as a cutting edge portion, a blade portion, or the like.

[0028] 〔Definition of directions〕 In the present embodiment, the direction in which the central axis C of the drill 1 extends is referred to as the axial direction. Among the axial directions, the direction from the shank 2 toward the body 3 is referred to as the tip side of the axial direction or simply the tip side, and the direction from the body 3 toward the shank 2 is referred to as the rear end side of the axial direction or simply the rear end side. The direction orthogonal to the central axis C is referred to as the radial direction. Among the radial directions, the direction approaching the central axis C is referred to as the inner side of the radial direction, and the direction away from the central axis C is referred to as the outer side of the radial direction. The direction of orbiting around the central axis C is referred to as the circumferential direction. Among the circumferential directions, the direction in which the drill 1 is rotated during drilling is referred to as the drill rotation direction T, and the side opposite to the drill rotation direction T is referred to as the reverse drill rotation direction. Also, in the present embodiment, the direction in which a cutting edge 7 (described later) of the body 3 extends may be referred to as the blade length direction.

[0029] 〔Shank〕 The shank 2 has a cylindrical shape extending in the axial direction around the central axis C. In the present embodiment, the diameter dimension (outer diameter dimension) of the shank 2 is larger than the diameter dimension of the body 3. The shank 2 is detachably attached to a spindle of a machine tool (not shown), a chuck of a ball screw, or the like (hereinafter, may be abbreviated as a spindle or the like). The drill 1 is fed toward the tip side in the axial direction while the shank 2 is rotated in the drill rotation direction T by the spindle or the like, and the body 3 cuts into the workpiece to perform drilling.

[0030] 〔Body〕 As shown in FIGS. 1 to 3, the body 3 is substantially columnar and extends in the axial direction about the central axis C. The diameter dimension (cutting edge diameter dimension) of the body 3 is, for example, 1 mm or more and 3 mm or less, and in this embodiment, it is about 1.1 mm. Therefore, the drill 1 may be alternatively referred to as a small-diameter drill or the like.

[0031] The base material of the body 3 is, for example, made of cemented carbide. A coating film containing diamond (hereinafter, may be abbreviated as the coating film) is provided on at least the surface of the tip portion of the base material of the body 3. That is, the body 3 is provided with a coating film containing diamond at least at its tip portion. Note that the coating film may be provided on the entire body 3.

[0032] Specifically, examples of the coating film include hard carbon films such as diamond coating and DLC coating, or diamond electrodeposited abrasive grain layers formed by electrodepositing diamond abrasive grains with a metal plating phase. When performing drilling on a workpiece made of a hard and brittle material with the drill 1 of this embodiment, the processed surface of the workpiece is shaved like grinding with a grinding stone by fine irregularities such as hard carbon particles such as diamond particles contained in the coating film and diamond abrasive grains, and fine powdery chips (swarf) are generated.

[0033] The body 3 has a chip discharge groove 4, a cutting edge 7, a margin 8, a leading edge 9, and a second chamfered surface 10.

[0034] The chip discharge groove 4 opens to the tip surface 3a facing the tip side in the axial direction of the body 3 and the outer peripheral surface facing the radially outer side. The chip discharge groove 4 extends from the tip surface 3a to the rear end side in the axial direction. A plurality of chip discharge grooves 4 are provided in the body 3 at intervals in the circumferential direction. Specifically, four chip discharge grooves 4 are provided at equal pitches in the circumferential direction. Note that four chip discharge grooves 4 may be provided at unequal pitches in the circumferential direction.

[0035] The chip discharge groove 4 has a tip groove 41 disposed at the tip of the body 3 and an outer peripheral groove 42 disposed on the outer peripheral portion of the body 3.

[0036] The tip groove 41 forms a groove shape that is recessed from the tip surface 3a of the body 3 toward the rear end side. As shown in FIG. 3, the tip groove 41 extends from near the central axis C of the body 3 toward the radially outer side. Specifically, the tip groove 41 extends in the counter-drill rotation direction as it goes toward the radially outer side. The tip groove 41 has a wider groove width as it goes toward the radially outer side. Also, the tip groove 41 has a greater groove depth as it goes toward the radially outer side. Note that the tip groove 41 may be alternatively referred to as a thinning or a thinning groove.

[0037] The tip groove 41 has a pair of wall surfaces 41a, 41b and a groove bottom 41c located between the pair of wall surfaces 41a, 41b. The pair of wall surfaces 41a, 41b are each planar. Of the pair of wall surfaces 41a, 41b of the tip groove 41, one wall surface 41a located in the drill rotation direction T extends toward the tip side as it goes toward the drill rotation direction T. One wall surface 41a is a groove wall facing the counter-drill rotation direction. Of the pair of wall surfaces 41a, 41b of the tip groove 41, the other wall surface 41b located in the counter-drill rotation direction extends toward the drill rotation direction T as it goes toward the rear end side in the axial direction. The other wall surface 41b is a groove wall facing the drill rotation direction T.

[0038] The groove bottom 41c is disposed between the one wall surface 41a and the other wall surface 41b in the circumferential direction around the central axis C. The groove bottom 41c is the portion where the groove depth is deepest in the tip groove 41. As shown in FIG. 2, when the body 3 is viewed from the radial direction, the tip groove notch angle α formed between the virtual straight line VL orthogonal to the central axis C and the groove bottom 41c of the tip groove 41 is, for example, 10° or more and 50° or less. In this embodiment, the tip groove notch angle α is, for example, about 30°.

[0039] The groove bottom 41c extends linearly toward the rear end side as it goes radially outward. Also, as shown in FIG. 3, the groove bottom 41c extends linearly toward the counter-drill rotation direction as it goes radially outward.

[0040] Further, the tip groove 41 has a first edge 41d that is an edge on the drill rotation direction T side among both edges in the circumferential direction (corresponding to the groove width direction of the tip groove 41) around the central axis C of the tip groove 41, and a second edge 41e that is an edge on the side opposite to the drill rotation direction T. The first edge 41d is disposed at a ridge line portion (boundary portion) where the tip groove 41 and the tip surface 3a of the body 3 adjacent to the drill rotation direction T of this tip groove 41 are connected. Also, the second edge 41e is disposed at a ridge line portion (boundary portion) where the tip groove 41 and the tip surface 3a of the body 3 adjacent to the counter-drill rotation direction of this tip groove 41 are connected. The second edge 41e corresponds to the cutting edge 7 of the body 3.

[0041] As shown in FIG. 3, when the body 3 is viewed from the axial tip side, the tip groove opening angle β formed between the first edge 41d and the second edge 41e (cutting edge 7) is, for example, 30° or more and 80° or less. In the present embodiment, the tip groove opening angle β is, for example, about 70°.

[0042] As shown in FIGS. 2 and 3, the outer peripheral groove 42 forms a groove shape that is recessed radially inward from the outer peripheral surface of the body 3. The outer peripheral groove 42 is connected to the radially outer end portion of the tip groove 41, and extends toward the side opposite to the drill rotation direction T as it goes from this connection portion toward the rear end side.

[0043] The cutting edge 7 is disposed at the tip portion of the body 3. The cutting edge 7 is disposed at a ridge line portion where the wall surface (the other wall surface) 41b facing the drill rotation direction T of the tip groove 41 and the tip surface 3a of the body 3 are connected. The other wall surface 41b serves as the rake face of the cutting edge 7, and the tip surface 3a of the body 3 serves as the flank face of the cutting edge 7. The axial rake angle of the cutting edge 7 is negative (negative angle). Also, the radial rake angle of the cutting edge 7 is negative. The flank angle of the cutting edge 7 (which may also be referred to as the bottom edge secondary angle) is, for example, about 20°.

[0044] The cutting edge 7 extends linearly in the reverse drill rotation direction as it goes radially outward. Also, the cutting edge 7 extends linearly toward the rear end side as it goes radially outward. The combination of the tip groove 41 and the cutting edge 7 is provided in four in the circumferential direction around the central axis C. That is, the drill 1 of the present embodiment is a four-flute drill. The four cutting edges 7 are arranged at equal pitches in the circumferential direction. Note that the four cutting edges 7 may be arranged at unequal pitches in the circumferential direction.

[0045] The diameter dimension of the rotation locus obtained by rotating the cutting edge 7 around the central axis C corresponds to the cutting edge diameter dimension of the body 3. Also, the tip angle γ of the cutting edge 7 obtained from the above rotation locus is less than 180°, and in the present embodiment, it is, for example, about 168° (see FIG. 2).

[0046] As shown in FIG. 3, the four cutting edges 7 have a pair of long cutting edges 7A and a pair of short cutting edges 7B whose dimension (cutting edge length dimension) along the cutting edge length direction is shorter than that of the long cutting edges 7A. The long cutting edges 7A and the short cutting edges 7B are arranged alternately in the circumferential direction around the central axis C. The radial position of the radially outer end of the long cutting edge 7A and the radial position of the radially outer end of the short cutting edge 7B are the same as each other. Also, the radial position of the radially inner end of the short cutting edge 7B is radially outside the radial position of the radially inner end of the long cutting edge 7A.

[0047] In the circumferential direction around the central axis C, a pair of tip grooves 41 arranged on both sides of the short cutting edge 7B (that is, in the drill rotation direction T and the reverse drill rotation direction) communicate with each other inside the short cutting edge 7B in the radial direction. In other words, for a pair of tip grooves 41 arranged side by side with the short cutting edge 7B sandwiched therebetween in the circumferential direction, the radially inner end portions of each are connected to each other. Also, with respect to the diameter dimension (cutting edge diameter dimension) of the rotation locus of the cutting edge 7 around the central axis C, the cutting edge length dimension L of each short cutting edge 7B is, for example, 25% or more and 49% or less.

[0048] As shown in FIGS. 1 to 3, the margin 8 is disposed on the outer peripheral surface of the body 3. The margin 8 is disposed adjacent to the chip discharge groove 4 in the reverse drill rotation direction of the chip discharge groove 4. The margin 8 extends along the outer peripheral groove 42 of the chip discharge groove 4. Specifically, the margin 8 extends in the reverse drill rotation direction as it goes toward the rear end side in the axial direction. Four margins 8 are provided, which is the same number as the chip discharge grooves 4.

[0049] As shown in FIG. 2, the tip of the margin 8 is formed to taper so as to be notched by the tip groove 41. The margin width (circumferential dimension) of the margin 8 is constant at portions other than the tip of the margin 8, and gradually decreases toward the tip side at the tip of the margin 8.

[0050] The leading edge 9 is disposed on the outer peripheral portion of the body 3. The leading edge 9 may also be referred to as an outer peripheral cutting edge or the like. However, the leading edge 9 does not necessarily function as a cutting edge that cuts into the work material.

[0051] The leading edge 9 is disposed at the ridge line portion where the chip discharge groove 4 and the margin 8 are connected. The tip portion of the leading edge 9, which is disposed at the ridge line portion where the wall surface (the other wall surface) 41b facing the drill rotation direction T of the tip groove 41 and the margin 8 are connected, extends in the reverse drill rotation direction as it goes toward the tip side. The rake angle of the tip portion of the leading edge 9 is negative (negative angle).

[0052] The chamfered surface 10 is disposed on the outer peripheral portion of the body 3. The chamfered surface 10 is disposed in the circumferential direction between the margin 8 and the chip discharge groove 4 adjacent to the margin 8 in the reverse drill rotation direction. The chamfered surface 10 is located radially inside the margin 8. The axial tip portion of the chamfered surface 10 is connected to the tip surface 3a of the body 3 and one wall surface 41a of the tip groove 41.

[0053] 〔Advantages of the Present Embodiment〕 The drill 1 of the present embodiment described above is suitable for drilling a workpiece made of a brittle material such as cemented carbide, ceramics, or single-crystal silicon. Since this brittle material drill has four cutting edges, the cutting load per cutting edge can be reduced compared to a conventional two-edge drill, and wear can be suppressed. As a result, peeling of the coating film containing diamond and the like can be suppressed, and the tool life can be extended.

[0054] More specifically, in the machining mode of the drill, the cutting distance of the outer peripheral portion (radial outer end portion) of the cutting edges becomes long, and wear tends to progress at the outer peripheral portion. By setting the number of cutting edges to four as in the present embodiment, the cutting distance at the outer peripheral portion of each cutting edge 7 can be kept short, the progress of wear can be suppressed, and the tool life can be extended.

[0055] Furthermore, the drill 1 of the present embodiment is a four-edge drill in which a pair of long edges 7A and a pair of short edges 7B are alternately arranged around the central axis C. Therefore, it is possible to configure a communication between a pair of tip grooves 41 arranged on both sides around the central axis C of the short edge 7B (that is, in the drill rotation direction T and the reverse drill rotation direction of the short edge 7B) via the radially inner side of the short edge 7B. As a result, a sufficient chip discharge space can be secured near the center of the drill tip portion. In particular, even in the drilling of brittle materials where fine chips are likely to be generated, the chip discharge property at the center of the tip of the drill 1 is maintained well, and the occurrence of chip jamming can be suppressed.

[0056] In addition, since the central portion of the tip of the drill 1 is formed as a two-edge structure with only a pair of long edges 7A, the biting into the workpiece during drilling is improved, and the machining stability is enhanced. Specifically, for example, different from the present embodiment, in the case of a so-called "core connection" configuration in which four cutting edges are radially connected at the central portion of the tip of the drill as in Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2022-159631), in the drilling of brittle materials, the biting into the workpiece may deteriorate and the machining stability may be impaired.

[0057] Note that, unlike this embodiment, when a drill with five or more cutting edges is used, for example, the cutting resistance during drilling becomes too large, and there is a risk that the workpiece made of a hard and brittle material may crack. Also, it becomes difficult to sufficiently ensure the groove width dimension and the groove depth dimension of each chip discharge groove, resulting in a decrease in chip discharge performance and a risk of chip jamming. Also, unlike this embodiment, when a drill with an odd number of cutting edges, such as three cutting edges, is used, the balance around the central axis of the long and short cutting edges may deteriorate, and there is a risk that the machining stability may be impaired.

[0058] From the above, according to the four-edge drill 1 of this embodiment, when drilling a workpiece made of a hard and brittle material, the cutting load on each cutting edge 7 can be reduced to suppress wear, while maintaining good chip discharge performance, thereby stably extending the tool life.

[0059] Also, in this embodiment, with respect to the diameter dimension of the rotation locus around the central axis C of the cutting edge 7, the blade length dimension L of each short cutting edge 7B is set to be 25% or more and 49% or less.

[0060] With the above configuration, with the diameter dimension of the rotation locus around the central axis C of the cutting edge 7 (i.e., the blade diameter dimension) as a reference (100%), if the blade length dimension L of each short cutting edge 7B is 25% or more, each short cutting edge 7B can stably perform cutting.

[0061] Also, with the diameter dimension of the rotation locus around the central axis C of the cutting edge 7 as a reference, since the blade length dimension L of each short cutting edge 7B is 49% or less, the tip grooves 41 can be stably communicated with each other inside the radial direction of each short cutting edge 7B.

[0062] Also, in this embodiment, the tip groove 41 has a first edge 41d which is an edge of both end edges around the central axis C of the tip groove 41 and is the edge in the drill rotation direction T, and a second edge 41e which is an edge of both end edges around the central axis C of the tip groove 41 and is the edge on the side opposite to the drill rotation direction T. When viewing the body 3 from the tip side in the axial direction, the tip groove opening angle β formed between the first edge 41d and the second edge 41e is set to be 30° or more and 80° or less.

[0063] In the above configuration, of both edge portions (both edge portions of the groove width) around the central axis C of the tip groove 41, the second edge portion 41e corresponds to the cutting edge 7. If the tip groove opening angle β is 30° or more as in the above configuration, since the groove width of the tip groove 41 is sufficiently widened as it goes radially outward, the chips generated from the cutting edge 7 flow stably outward in the radial direction without clogging in the tip groove 41. Therefore, the chip dischargeability can be further improved.

[0064] Also, when the tip groove opening angle β is 80° or less, it is possible to suppress the excessive reduction of the thickness of the drill tip portion by providing the tip groove 41 with a wide groove width. Therefore, the rigidity of the drill tip portion can be stably ensured.

[0065] Also, in the present embodiment, when the body 3 is viewed in the radial direction, the tip groove notch angle α formed between the virtual straight line VL orthogonal to the central axis C and the groove bottom 41c of the tip groove 41 is set to be 10° or more and 50° or less.

[0066] If the tip groove notch angle α is 10° or more as in the above configuration, the depth (groove depth) of the groove bottom 41c of the tip groove 41 can be sufficiently ensured, and the chips flow stably outward in the radial direction without clogging in the tip groove 41. Therefore, the chip dischargeability can be further improved.

[0067] Also, when the tip groove notch angle α is 50° or less, it is possible to suppress the excessive reduction of the thickness of the drill tip portion by providing the tip groove 41 with a deep groove depth. Therefore, the rigidity of the drill tip portion can be stably ensured.

[0068] 〔Other configurations included in the present invention〕 The present invention is not limited to the above-described embodiment. For example, as described below, modifications and the like of the configuration are possible without departing from the spirit of the present invention.

[0069] In the above-described embodiment, an example in which the diameter dimension (cutting edge diameter dimension) of the body 3 is 3 mm or less is given, but the present invention is not limited to this. The cutting edge diameter dimension of the body 3 may exceed 3 mm.

[0070] Further, the drill 1 may be configured such that the body 3 and the shank 2 are integrally formed by a single member, or the body 3 and the shank 2 may be separately manufactured and joined and integrated by brazing or the like. Alternatively, the body 3 and the shank 2 may be provided separately and assembled by fitting, fastening, or the like.

[0071] The present invention may combine the respective configurations described in the above-described embodiments and modifications within a range not departing from the gist of the present invention, and addition, omission, substitution, and other changes of the configuration are possible. Further, the present invention is not limited by the above-described embodiments or the like, and is limited only by the scope of the claims.

Example

[0072] Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

[0073] 〔Tool life confirmation test by drilling hard and brittle materials〕 Using each drill of the example of the present invention and a conventional comparative example, a hole was drilled in a workpiece made of a hard and brittle material, and a confirmation test was conducted on the number of processed holes until the tool life was reached.

[0074] As an example of the present invention, the drill 1 described in the above-described embodiment was prepared. Further, as a conventional comparative example 1, a two-flute diamond-coated drill was prepared. Further, as a conventional comparative example 2, a four-flute diamond-coated drill was prepared. Specifically, the drill of Comparative Example 2 has a so-called "heart knot" configuration in which the cutting edge lengths of the four cutting edges are the same as each other and the inner ends in the radial direction of the four cutting edges are connected near the central axis C.

[0075] For both the example and Comparative Examples 1 and 2, the cutting conditions were as follows. <Cutting conditions> · Workpiece: SiC · Rotational speed: 13000 min-1 · Cutting speed: 4.5 m / min · Feed rate: 2 mm / min · Feed per revolution: 0.00015 mm / rev · Machined hole depth: 1.75 mm · Step: 0.020 mm · Protrusion length: 11 mm · Cutting oil: Emulsion · Machine used: Small-diameter machining machine

[0076] As a result of the above confirmation test, for Comparative Example 1, peeling of the coating film was observed when 50 holes were drilled, and this was the tool life. Also, for Comparative Example 2, progress of wear was observed at the center of the drill tip (near the central axis) when 70 holes were drilled, and this was the tool life. On the other hand, for the examples of the present invention, even when 70 holes were drilled, no progress of peeling or wear that would be judged as the tool life was observed, and drilling could continue to be performed well.

Industrial Applicability

[0077] According to the drill of the present invention, when drilling a work material made of a hard and brittle material, the cutting load on each cutting edge can be reduced to suppress wear, while chip evacuation can be maintained well, and thus the tool life can be stably extended. Therefore, it has industrial applicability.

Explanation of Signs

[0078] 1... Drill 3... Body 3a... Tip surface 4... Chip evacuation groove 7... Cutting edge 7A... Long cutting edge 7B... Short cutting edge 41... Tip groove 41b... The other wall surface (the wall surface facing the drill rotation direction of the tip groove) 41c... Groove bottom 41d... First edge 41e... Second edge 42…Outer peripheral groove C…Central axis L…Cutting edge length dimension T…Drill rotation direction VL…Virtual straight line α…Tip groove notch angle β…Tip groove opening angle

Claims

1. A body that extends axially about a central axis and is provided with a coating film containing diamond at least at its tip portion, wherein the body, has a cutting edge disposed at the tip of the body, and has a chip discharge groove that opens to the tip surface and the outer peripheral surface of the body and extends from the tip surface toward the rear end side, wherein the chip discharge groove, forms a groove shape that is recessed from the tip surface of the body toward the rear end side, and has a tip groove whose groove width widens as it goes radially outward, forms a groove shape that is recessed radially inward from the outer peripheral surface of the body, is connected to the radially outer end portion of the tip groove, and has an outer peripheral groove that extends toward the rear end side and toward the side opposite to the drill rotation direction around the central axis, the cutting edge is disposed at a ridge line portion where a wall surface facing the drill rotation direction of the tip groove and the tip surface of the body are connected, and extends toward the rear end side as it goes radially outward, a set of the tip groove and the cutting edge is provided in four arranged around the central axis, the four cutting edges, include a pair of long cutting edges, and a pair of short cutting edges whose cutting edge length dimension is shorter than that of the long cutting edges, the long cutting edges and the short cutting edges are alternately arranged around the central axis, a pair of the tip grooves disposed on both sides of the short cutting edge around the central axis communicate with each other inside the short cutting edge in the radial direction, a drill.

2. The cutting edge length dimension of each short cutting edge is 25% or more and 49% or less with respect to the diameter dimension of the rotation locus of the cutting edge around the central axis, The drill according to claim 1.

3. The tip groove, has a first edge which is an edge in the drill rotation direction among both edges of the tip groove around the central axis, and a second edge which is an edge on the side opposite to the drill rotation direction among both edges of the tip groove around the central axis, when the body is viewed from the tip side in the axial direction, the tip groove opening angle formed between the first edge and the second edge is 30° or more and 80° or less, The drill according to claim 1 or 2.

4. When the body is viewed radially, the tip groove notch angle formed between a virtual straight line perpendicular to the central axis and the groove bottom of the tip groove is 10° or more and 50° or less, The drill according to claim 1 or 2.

Images