drill

Abstract

To provide a drill capable of reducing thrust force and suppressing cutting resistance even in highly efficient processing.SOLUTION: A drill is provided with a thinning unit 5. The thinning unit 5 has: a thinning wall surface 5a connected to a leading end face and inclining rearward in a rotating direction toward a rear end; a thinning cutting blade 5b extending toward a radially inner side from a radially inner end of a main cutting blade; and a thinning rake face 5c connecting the thinning cutting blade 5b and the thinning wall surface 5a and facing a front side in the rotating direction. As viewed from an axial direction, a direction extending from a central axis toward a radially outer side along an extending direction of the thinning cutting blade 5b is set as a first direction D1, and a direction orthogonal to the first direction D1 and extending from the central axis toward a radially outer side is set as a second direction D2, the thinning unit 5 is formed beyond the center axis in the first direction D1 and the second direction D2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a drill. [Background technology]

[0002] Conventionally, drills with thinning at the tip of the drill body have been known (for example, Patent Document 1). In such drills, the core thickness of the drill is sufficiently secured to maintain the rigidity of the drill, while the thinning is performed to shorten the chisel edge and reduce the cutting resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-42879 A Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the rake angle of the cutting edge is smaller toward the center of the drill, and the chisel edge has a negative rake angle. Therefore, the drill crushes the workpiece near the center to cut it, which causes an increase in thrust force during cutting.

[0005] The present invention has been made under such a background, and has an object to provide a drill that can reduce thrust force. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, a drill according to one embodiment of the present invention includes a drill body that is rotated around a central axis, and the drill body is provided with a tip surface that faces the tip side and faces a workpiece, a chip discharge groove that extends from the tip surface to the rear end side, a main cutting edge that is located at an intersection ridge between a front wall surface of the chip discharge groove that faces forward in the rotation direction and the tip surface, and a thinning portion that is located between a rear wall surface of the chip discharge groove that faces rearward in the rotation direction and the tip surface, and the thinning portion is connected to the tip surface and extends rearward in the rotation direction as it moves toward the rear end side. a thinning wall surface inclined toward the center of the cutting edge, a thinning cutting edge extending radially inward from a radial inner end of the main cutting edge, and a thinning rake face connecting the thinning cutting edge and the thinning wall surface and facing the front side in the rotation direction, wherein, as viewed from the axial direction, a direction extending from the central axis toward the radially outward direction along the extension direction of the thinning cutting edge is defined as a first direction, and a direction perpendicular to the first direction and extending from the central axis toward the radially outward direction is defined as a second direction, and the thinning portion is formed beyond the central axis in the first direction and the second direction. The thinning cutting edge has an inner thinning edge located in the radially inner region and an outer thinning edge located in the radially outer region, the inner thinning edge inclined toward the tip end as it moves radially outward, and the outer thinning edge inclined toward the rear end as it moves radially outward.

[0007] According to the above-mentioned configuration, the thinning portion is formed beyond the central axis in the first direction, which is the direction in which the thinning cutting edge extends. Therefore, a chisel portion is not formed in the center of the tip surface of the drill body. In a typical drill, the workpiece is crushed in the chisel portion to perform cutting, so that thrust force is large. In contrast, according to the above-mentioned configuration, a chisel portion is not provided, and the cutting edge is formed even in the center of the tip surface, so that the drill does not crush the workpiece. This makes it possible to reduce thrust force during cutting. Furthermore, since the thinning cutting edge is formed up to the center of the tip surface, welding of the workpiece to the center of the tip surface can be suppressed.

[0008] The above-mentioned drill may be a two-blade drill having a pair of chip discharge grooves, a pair of main cutting edges, and a pair of thinning portions, and when viewed from the side, the pair of thinning cutting edges may intersect in a V-shape about a central axis to form a V-shaped cutting edge.

[0009] According to the above-mentioned configuration, by using a two-blade drill, it is possible to perform stable cutting while ensuring sufficient rigidity of the drill body. Furthermore, since the rotation trajectories of the pair of thinning cutting edges intersect with each other at the central axis, cutting can be performed reliably at the central axis. Furthermore, according to the above-mentioned configuration, since the thinning portion is formed beyond the central axis in a second direction perpendicular to the thinning cutting edges, the pair of thinning cutting edges are separated from each other in the second direction. This makes it possible to ensure sufficient rigidity of each thinning cutting edge even in the vicinity of the central axis.

[0010] In the above-mentioned drill, the opening diameter of the V-shaped cutting edge may be 30% or less of the diameter of the drill body.

[0011] According to the above-mentioned configuration, the length of the cutting edge continuing radially outward from the V-shaped cutting edge can be set to approximately 70% or more of the diameter of the drill body. This allows the overall length of the main cutting edge to be sufficiently long. The main cutting edge has sufficiently high rigidity compared to the V-shaped cutting edge. According to the above-mentioned configuration, cutting can be performed with the high-rigidity main cutting edge in an area where the peripheral speed is high and sufficiently away from the central axis, and damage to the cutting edge can be suppressed.

[0012] In the above-mentioned drill, the opening diameter of the V-shaped cutting edge may be configured to be 5% to 15% of the diameter of the drill body.

[0013] According to the above-mentioned configuration, it is possible to ensure a sufficient length of the thinning cutting edge near the central axis while ensuring a sufficient length of the main cutting edge, thereby providing a drill that has a good balance between ensuring rigidity and reducing thrust force for the cutting edges as a whole.

[0014] In the above-described drill, the V-shaped cutting edge may be configured such that an angle between the two thinning cutting edges is equal to or greater than 10° and equal to or less than 70°.

[0015] According to the above-mentioned configuration, by making the angle between the pair of thinning cutting edges 10° or more, the tip of the thinning cutting edge does not become too sharp, and the strength of the thinning cutting edge near the tip can be secured. As a result, damage to the thinning cutting edge can be suppressed. In addition, increasing the angle between the pair of thinning cutting edges means that the thinning angle of the thinning part is made flat. Therefore, if the angle between the pair of thinning cutting edges is made too large, a problem occurs in that the thinning rake face cannot be secured to be sufficiently wide. According to the above-mentioned configuration, by making the angle between the pair of thinning cutting edges 70° or less, the thinning rake face can be secured to be sufficiently wide. As a result, the chips generated by the thinning cutting edge can be guided and discharged to the chip discharge groove without causing clogging.

[0016] In the above-described drill, the V-shaped cutting edge may be configured such that an angle between the pair of thinning cutting edges is 45° or more and 65° or less.

[0017] According to the above-mentioned configuration, the above-mentioned effects related to the angle of the thinning cutting edge can be obtained more significantly.

[0018] In the above-described drill, the distance between the pair of thinning cutting edges constituting the V-shaped cutting edge in the second direction may be 2 mm or less.

[0019] According to the above-mentioned configuration, by setting the distance between the thinning cutting edges to 2 mm or less, the workpiece in the area facing the central axis can be machined reliably by the thinning cutting edges. Effect of the Invention

[0020] According to the present invention, it is possible to provide a drill that can reduce thrust force. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a front view of a drill according to one embodiment. [Diagram 2]FIG. 2 is a side view of the drill according to the embodiment as viewed from a direction II in FIG. [Diagram 3] FIG. 3 is a side view of the drill according to the embodiment as viewed from a direction III in FIG. [Figure 4] FIG. 4 is a partially enlarged view of FIG. [Diagram 5] FIG. 5 is a front view of the drills of Comparative Examples 1-1 and 1-2. [Figure 6] FIG. 6 is a front view of the drills of Comparative Example 2-1 and Comparative Example 2-2. [Figure 7] FIG. 7 is a front view of the drills of Comparative Examples 3-1 and 3-2. [Figure 8] FIG. 8 is a graph showing the measurement results of thrust force in verification test 1. [Figure 9] FIG. 9 is a graph showing the torque measurement results in verification test 1. [Figure 10] FIG. 10 is a photograph of the drill of Comparative Example 1-1 after drilling. [Figure 11] FIG. 11 is a photograph of the drill of Comparative Example 2-1 after drilling. [Figure 12] FIG. 12 is a photograph of the drill of Comparative Example 3-1 after drilling. [Figure 13] FIG. 13 is a photograph of the drill of Example 1 after drilling. [Figure 14] FIG. 14 is a graph showing the measurement results of thrust force in verification test 2. [Figure 15] FIG. 15 is a graph showing the torque measurement results in verification test 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, a drill 10 according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a front view of a drill 10 according to the present embodiment. Fig. 2 is a side view of the drill 10 as viewed from a direction II in Fig. 1. Fig. 3 is a side view of the drill 10 as viewed from a direction III in Fig. 1. Fig. 4 is a partially enlarged view of Fig. 1.

[0023] The drill 10 of this embodiment is used, for example, when drilling holes in a work material such as an aluminum alloy, etc. In this embodiment, the drill 10 is a solid drill.

[0024] As shown in Figs. 1 to 3, the drill 10 of this embodiment includes a substantially cylindrical drill body 1. The drill body 1 has a central axis O. A cutting portion is provided on one end of the drill body 1 in the direction along the central axis O, and a shank portion (not shown) is provided on the other end. The shank portion of the drill body 1 is detachably attached to, for example, a spindle of a machine tool or a drilling press.

[0025] The drill body 1 is rotated in a rotation direction T in the circumferential direction around the central axis O relative to the workpiece, and is sent out toward the tip side in the axial direction, where the cutting edge cuts into the workpiece to drill a hole. That is, the drill body 1 rotates around the central axis O with the tip face 1a facing the workpiece to drill a hole.

[0026] The direction along the central axis O of the drill body 1 (the direction in which the central axis O extends) is called the axial direction. Within the axial direction, the direction from the shank portion of the drill body 1 toward the cutting edge is called the front end side, and the direction from the cutting edge toward the shank is called the rear end side. The direction perpendicular to the central axis O is called the radial direction. Of the radial directions, the direction approaching the central axis O is called the radially inner direction, and the direction away from the central axis O is called the radially outer direction. The direction rotating around the central axis O is called the circumferential direction. In addition, within the circumferential direction, the direction in which the drill body 1 rotates during drilling is called the forward rotation direction, and the opposite side is called the rearward rotation direction.

[0027] As shown in FIG. 1, the drill body 1 is provided with a tip face 1a, a chip discharge groove 2, a main cutting edge 4, and a thinning portion 5. The tip face 1a faces the tip side and faces the workpiece. The chip discharge groove 2 extends from the tip face 1a to the rear end side. The main cutting edge 4 is located at the intersection ridge between the tip face 1a and a front wall face 2a that faces forward in the rotation direction of the chip discharge groove 2. The thinning portion 5 is located between the tip face 1a and a rear wall face 2b that faces backward in the rotation direction of the chip discharge groove 2.

[0028] The chip discharge flute 2 extends in a spiral shape from the tip end to the rear end on the outer periphery of the drill body 1. The chip discharge flute 2 opens to the tip face 1a of the drill body 1. The chip discharge flute 2 twists in the opposite direction to the rotation direction T as it extends from the tip face 1a to the rear end in the axial direction.

[0029] In this embodiment, a pair of chip discharge grooves 2 is formed on the outer periphery of the drill body 1. Accordingly, two each of the main cutting edges 4 and the thinning portions 5 are also formed on the drill body 1. That is, the drill 10 of this embodiment is a two-blade drill. However, the drill may have a single blade, three blades, four blades, etc. The pair of chip discharge grooves 2 are arranged at equal pitches in the circumferential direction on the outer periphery of the drill body 1 so as to be rotationally symmetrical with respect to the central axis O. The chip discharge groove 2 has an inner periphery that is a concave curved surface.

[0030] Although not shown in the drawings, the chip discharge grooves 2 are cut upward toward the outside in the radial direction in a region located from near the axial center of the drill body 1 to the rear end side, for example, on the outer circumferential surface of the drill body 1. The range of the drill body 1 where the chip discharge grooves 2 are located in the axial direction is defined as the cutting portion, and the range rearward of this range is defined as the shank portion.

[0031] A land portion 15 is provided on the outer periphery of the drill body 1 between adjacent chip discharge grooves 2 in the circumferential direction. The land portion 15 has a margin portion 11 disposed adjacent to a front wall surface 2a of the chip discharge groove 2. The margin portion 11 is located on an imaginary circle that is approximately equal to the outermost diameter of the main cutting edge 4. The margin portion 11 extends spirally from the axial tip to the rear end side as the chip discharge groove 2 extends spirally. A leading edge (peripheral cutting edge) is formed at least at the axial tip of the intersection ridge portion between the front wall surface 2a of the chip discharge groove 2 and the margin portion 11.

[0032] The tip surface 1a has a first tip flank 6 arranged adjacent to the main cutting edge 4 on the rear side in the rotational direction, and a second tip flank 7 arranged adjacent to the first tip flank 6 on the rear side in the rotational direction.

[0033] The first tip flank 6 gradually inclines toward the rear end in the axial direction as it moves rearward in the rotation direction from the main cutting edge 4. The second tip flank 7 gradually inclines toward the rear end in the axial direction as it moves rearward in the rotation direction from the first tip flank 6, and has a larger clearance angle than the first tip flank 6. In other words, the amount of axial displacement per unit length along the circumferential direction of the drill in the second tip flank 7 (the inclination corresponding to the clearance angle) is larger than the amount of displacement in the first tip flank 6.

[0034] As shown in FIG. 1, in a front view of the drill body 1 from the axial tip to the rear end, the first tip flank 6 has a radially extending band shape (a roughly rectangular shape that is elongated in the radial direction), and the second tip flank 7 has a fan shape. In the example of this embodiment, the tip surface 1a has two different inclined surfaces (the first tip flank 6 and the second tip flank 7), but is not limited thereto. The tip surface 1a may be formed by a single inclined surface, or may have three or more inclined surfaces arranged in the circumferential direction of the drill.

[0035] Although not particularly shown, the drill body 1 may have a coolant hole formed therein. The coolant hole extends inside the drill body 1. The coolant hole extends twistedly inside the drill body 1 along the chip discharge groove 2. The coolant hole opens to the tip surface 1a of the drill body 1 or the chip discharge groove 2. Coolant (air, semi-dry, cutting oil, etc.) is supplied into the coolant hole through, for example, the spindle of a machine tool. The coolant is sprayed through the coolant hole toward the cutting part of the drill body 1 and the machining site of the workpiece.

[0036] The main cutting edge 4 is formed on the intersection ridge between the tip of the front wall surface 2a of the chip discharge groove 2 and the first tip flank surface 6 of the tip surface 1a. The main cutting edge 4 extends radially outward and axially toward the rear end. The main cutting edge 4 is formed in a concave curve that is concave toward the rear side in the rotational direction.

[0037] As shown in FIG. 2, the main cutting edge rake face 21 of the main cutting edge 4 is provided near the tip of the front wall surface 2a. The main cutting edge rake face 21 is connected to the main cutting edge 4. The main cutting edge rake face 21 extends from the main cutting edge 4 toward the rear end in the axial direction. A thinning rake face 5c, which will be described later, is disposed radially inside the main cutting edge rake face 21. Meanwhile, the first tip rake face 6 and the second tip rake face 7, which are the flank faces of the main cutting edge 4, are disposed on the rear side of the main cutting edge 4 in the rotation direction of the tip face 1a. The first tip rake face 6 and the second tip rake face 7 are arranged in this order from the main cutting edge 4 toward the rear side in the rotation direction.

[0038] A thinning cutting edge 5b is continuous with an end portion on the radially inner side of the main cutting edge 4. The main cutting edge 4 and the thinning cutting edge 5b configure a cutting edge 9. That is, the cutting edge 9 has the main cutting edge 4 and the thinning cutting edge 5b located on the radially inner side of the main cutting edge 4.

[0039] 1, the thinning portion 5 has a thinning wall surface 5a, a thinning cutting edge 5b, a thinning rake face 5c, and a thinning front edge 5d. The thinning portion 5 is formed so as to cut out the tip portion of the chip discharge flute 2 in the drill body 1.

[0040] The thinning wall surface 5a and the thinning rake surface 5c are ground surfaces formed by thinning, while the thinning cutting edge 5b and the thinning front end edge 5d are edges located on the boundary ridge between the ground surface formed by thinning and the tip surface 1a.

[0041] The drill body 1 of this embodiment is provided with a pair of thinning portions 5. The pair of thinning portions 5 are formed rotationally symmetrical with respect to each other about the central axis O. In the following description, when the pair of thinning portions 5 are to be distinguished from each other, one will be referred to as a first thinning portion 5A and the other will be referred to as a second thinning portion 5B.

[0042] The thinning wall surface 5a is a plane that is connected to the tip surface 1a and inclines rearward in the rotation direction as it approaches the rear end. The thinning wall surface 5a faces the tip side in the axial direction and the rear side in the rotation direction. The thinning wall surface 5a is formed between the tip surface 1a and the rear wall surface 2b of the chip discharge groove 2 adjacent to the tip surface 1a on the rear side in the rotation direction.

[0043] The thinning wall surface 5a has a larger clearance angle than the tip surface 1a (the first tip clearance surface 6 and the second tip clearance surface 7). Therefore, the amount of axial displacement (inclination equivalent to the clearance angle) per unit length along the circumferential direction of the drill in the thinning wall surface 5a is larger than the amount of displacement in the tip surface 1a.

[0044] The thinning leading edge 5d is disposed forward in the rotational direction relative to the thinning wall surface 5a. The thinning leading edge 5d is located on the boundary ridge between the thinning wall surface 5a and the tip surface 1a. The thinning leading edge 5d has a radially inner region located on the boundary ridge between the thinning wall surface 5a and the first tip flank 6, and a radially outer region located on the boundary ridge between the thinning wall surface 5a and the second tip flank 7. In the following description, when the thinning leading edge 5d is simply referred to, it means the radially inner region of the above-mentioned boundary ridge.

[0045] As shown in Fig. 2, the thinning rake face 5c is a face that connects between the thinning cutting edge 5b and the thinning wall surface 5a and faces forward in the rotation direction. The thinning rake face 5c has a rectangular shape. The main cutting edge rake face 21 is disposed radially outward of the thinning rake face 5c.

[0046] As shown in Fig. 4, the thinning cutting edge 5b extends radially inward from the radially inner end of the main cutting edge 4. The thinning cutting edge 5b extends linearly. The thinning cutting edge 5b has an inner thinning edge 51 located in a radially inner region and an outer thinning edge 52 located in a radially outer region.

[0047] The first thinning portion 5A and the second thinning portion 5B are disposed adjacent to each other across the central axis O. The inner thinning edge 51 of the first thinning portion 5A is located on the intersection ridge between the thinning rake face 5c of the first thinning portion 5A and the thinning wall face 5a of the second thinning portion 5B. Similarly, the inner thinning edge 51 of the second thinning portion 5B is located on the intersection ridge between the thinning rake face 5c of the second thinning portion 5B and the thinning wall face 5a of the first thinning portion 5A.

[0048] On the other hand, the outer thinning edge 52 of the first thinning portion 5A is located at the intersection ridge between the first tip flank 6 of the main cutting edge 4 connected to the outer thinning edge 52 and the thinning rake face 5c of the first thinning portion 5A. Similarly, the outer thinning edge 52 of the second thinning portion 5B is located at the intersection ridge between the first tip flank 6 of the main cutting edge 4 connected to the outer thinning edge 52 and the thinning rake face 5c of the second thinning portion 5B.

[0049] The inner thinning blade 51 is disposed on the rear side in the rotational direction with respect to the central axis O. Therefore, the inner thinning blade 51 of the first thinning portion 5A and the inner thinning blade 51 of the second thinning portion 5B are disposed spaced apart from each other in the second direction D2 via a slight gap of a distance h.

[0050] A thinning cross ridge 5s is provided between the inner thinning edge 51 of the first thinning portion 5A and the inner thinning edge 51 of the second thinning portion 5B. The thinning cross ridge 5s is located at the cross ridge between the thinning wall surface 5a of the first thinning portion 5A and the thinning wall surface 5a of the second thinning portion 5B.

[0051] As shown in Fig. 2, the inner thinning edge 51 inclines toward the tip end as it moves radially outward. On the other hand, the outer thinning edge 52 inclines toward the rear end as it moves radially outward. For this reason, the thinning cutting edge 5b protrudes toward the tip end at the boundary between the inner thinning edge 51 and the outer thinning edge 52. Here, in the thinning cutting edge 5b, the boundary between the inner thinning edge 51 and the outer thinning edge 52 is referred to as the thinning cutting edge tip portion 5p. The thinning cutting edge tip portion 5p is continuous with the thinning front end edge 5d.

[0052] The inner thinning blade 51 of the first thinning portion 5A and the inner thinning blade 51 of the second thinning portion 5B intersect in a V-shape when viewed from the side. The inner thinning blades 51 of the first thinning portion 5A and the second thinning portion 5B both face forward in the rotational direction. Therefore, the inner thinning blades 51 of the first thinning portion 5A and the second thinning portion 5B face in opposite directions relative to each other about the central axis O when viewed in the axial direction.

[0053] The inner thinning edges 51 of the first thinning portion 5A and the second thinning portion 5B form a V-shaped cutting edge 53 that intersects in a V shape about the central axis. The V-shaped cutting edge 53 has the inner thinning edge 51 of the first thinning portion 5A and the inner thinning edge 51 of the second thinning portion 5B. The V-shaped cutting edge 53 is formed in a region connecting the thinning cutting edge tip portion 5p of the first thinning portion 5A and the thinning cutting edge tip portion 5p of the second thinning portion 5B.

[0054] 4, when viewed from the axial direction, a direction extending from the central axis O toward the radially outward direction along the extension direction of the thinning cutting edge 5b is defined as a first direction D1. Also, when viewed from the axial direction, a direction perpendicular to the first direction D1 and extending from the central axis O toward the radially outward direction is defined as a second direction D2. The thinning portion 5 is formed by bringing a grindstone into contact with the drill body 1 and grinding it in a first direction D1 and a second direction D2 as viewed in the axial direction.

[0055] In this embodiment, the thinning portion 5 is formed beyond the central axis O in the first direction D1 and the second direction D2. Therefore, each thinning wall surface 5a of the first thinning portion 5A and the second thinning portion 5B is formed beyond the central axis O in the first direction D1 and the second direction D2, and intersects with each other on the central axis O to form a thinning intersection ridge line 5s.

[0056] The first thinning portion 5A will be described with reference to Fig. 4. In Fig. 4, the positive direction of the first direction D1 is the direction in which the thinning cutting edge 5b of the first thinning portion 5A extends relative to the central axis O. Also, in Fig. 4, the positive direction of the second direction D2 is the direction in which the thinning wall surface 5a of the first thinning portion 5A extends relative to the central axis O.

[0057] The thinning cutting edge 5b of the first thinning portion 5A is disposed in a negative region in the second direction D2. Also, the thinning front end edge 5d of the first thinning portion 5A is disposed in a negative region in the first direction D1.

[0058] According to this embodiment, the thinning portion 5 is formed beyond the central axis O in the first direction D1. Therefore, no chisel portion is formed in the center of the tip surface 1a of the drill body 1. In a typical drill, the workpiece is crushed in the chisel portion to perform cutting, resulting in a large thrust force. In contrast, according to this embodiment, no chisel portion is provided, and a cutting edge (thinning cutting edge 5b) is formed even in the center of the tip surface 1a, so that the drill 10 does not crush the workpiece. This makes it possible to reduce the thrust force during cutting.

[0059] In addition, in a typical drill, the chisel portion crushes the workpiece at the center of the tip face, causing the workpiece to weld to the chisel portion. In contrast, according to this embodiment, the thinning cutting edge 5b is formed up to the center of the tip face 1a, so that the weld of the workpiece at the center of the tip face 1a can be suppressed.

[0060] The drill 10 of this embodiment is a two-blade drill provided with a pair of chip discharge grooves 2, a pair of main cutting edges 4, and a pair of thinning portions 5. This allows stable cutting to be performed while ensuring sufficient rigidity of the drill body 1. In addition, when viewed from the side, the pair of thinning cutting edges 5b intersect with each other in a V-shape about the central axis O to form a V-shaped cutting edge 53. This allows cutting to be performed reliably on the central axis O, since the rotation trajectories of the pair of thinning cutting edges 5b intersect with each other on the central axis O.

[0061] The thinning portion 5 of this embodiment is formed beyond the central axis O in the second direction D2 perpendicular to the thinning cutting edges 5b. Therefore, the pair of thinning cutting edges 5b are slightly spaced apart from each other in the second direction D2. This makes it possible to ensure sufficient rigidity of each thinning cutting edge 5b even in the vicinity of the central axis O, and to suppress damage to the thinning cutting edges 5b.

[0062] The distance h between the pair of thinning cutting edges 5b constituting the V-shaped cutting edge 53 (more specifically, the distance between the pair of inner thinning edges 51) is preferably 2 mm or less. By making the distance between the thinning cutting edges 5b 2 mm or less, the workpiece in the area facing the central axis O can be reliably machined by the thinning cutting edges 5b. It is more preferable that the distance h between the thinning cutting edges 5b is 0.1 mm or more and 0.3 mm or less. By making the distance h 0.1 mm or more, the pair of thinning cutting edges 5b can be reliably separated to ensure the rigidity of each. Furthermore, by making the distance h 0.3 mm or less, even if the feed rate per rotation of the drill 10 during cutting is increased, the workpiece on the central axis O can be reliably cut by the pair of thinning cutting edges 5b.

[0063] 3 illustrates the opening diameter d of the V-shaped cutting edge 53, the diameter D of the drill body 1, and the angle φ between the pair of thinning cutting edges 5b of the V-shaped cutting edge 53. The direction of the arrow in FIG. 3 (direction III shown in FIG. 1) coincides with the second direction D2. In this specification, the angle φ is also referred to as the center bit angle.

[0064] In this embodiment, the opening diameter d of the V-shaped cutting edge 53 is preferably 30% or less of the diameter D of the drill body 1. It means the diameter of the rotation locus of the opening of the V-shaped cutting edge 53. The opening diameter d of the V-shaped cutting edge 53 is also the distance between the thinning cutting edge tips 5p of the first thinning portion 5A and the second thinning portion 5B.

[0065] By setting the length to 30% or less of the diameter D of the drill body 1, the length of the cutting edges (the outer thinning edge 52 and the main cutting edge 4) continuing radially outward from the V-shaped cutting edge 53 can be set to approximately 70% or more of the diameter D of the drill body 1. This allows the overall length of the main cutting edge 4 to be sufficiently long. The main cutting edge 4 has sufficiently high rigidity compared to the V-shaped cutting edge 53. According to the above-mentioned configuration, in an area where the peripheral speed is high and sufficiently distant from the central axis O, cutting can be performed by the main cutting edge 4 with high rigidity, and damage to the cutting edge can be suppressed.

[0066] It is more preferable that the opening diameter d of the V-shaped cutting edge 53 is 5% to 15% of the diameter D of the drill body 1. By setting the opening diameter d of the V-shaped cutting edge 53 to 5% to 15% of the diameter D of the drill body 1, it is possible to ensure that the thinning cutting edge 5b is sufficiently long in the radial direction in the vicinity of the central axis O while ensuring a sufficient length of the main cutting edge 4. This makes it possible to provide a drill that has a good balance between improved rigidity and reduced thrust force for the cutting edges as a whole.

[0067] In the V-shaped cutting edge 53, the angle (central bit angle) φ formed by the pair of thinning cutting edges 5b (more specifically, the pair of inner thinning edges 51) is preferably 10° or more and 70° or less.

[0068] According to this embodiment, the center bit angle φ is set to 10° or more, so that the tip of the thinning cutting edge 5b (thinning cutting edge tip portion 5p) does not become too sharp. Therefore, the strength of the thinning cutting edge 5b in the vicinity of the thinning cutting edge tip portion 5p can be ensured, and damage to the thinning cutting edge 5b can be suppressed. This effect can be obtained more significantly when the angle between the pair of thinning cutting edges 5b is set to 45° or more.

[0069] Increasing the center bit angle φ means that the thinning angle of the thinning portion 5 is made flat. If the center bit angle φ is made too large, a problem occurs in that the thinning rake face 5c cannot be secured to be sufficiently wide. According to this embodiment, the center bit angle φ is set to 70° or less, so that the thinning rake face 5c can be secured to be sufficiently wide. As a result, the chips generated by the thinning cutting edge 5b can be guided and discharged to the chip discharge groove 2 without clogging. Such an effect can be obtained more remarkably when the angle formed by the pair of thinning cutting edges 5b is set to 65° or less. EXAMPLES

[0070] Next, the effects of the drill 10 according to the above-described embodiment will be specifically verified based on examples and comparative examples.

[0071] (Example) As Example 1 of the drill 10 according to the above embodiment, a drill body 1 having a diameter of 9 mm was prepared, and as Example 2, a drill body 1 having a diameter of 12 mm was prepared. The opening diameter d of the V-shaped cutting edge 53 in Example 1 is 0.9 mm (i.e., 10% of the diameter D of the drill body 1), the central bit angle φ is 70°, and the distance h between the pair of thinning cutting edges 5b constituting the V-shaped cutting edge 53 is 0.2 mm. On the other hand, the opening diameter d of the V-shaped cutting edge 53 in Example 2 is 1.2 mm (i.e., 10% of the diameter D of the drill body 1), the central bit angle φ is 70°, and the distance h between the pair of thinning cutting edges 5b constituting the V-shaped cutting edge 53 is 0.2 mm.

[0072] (Comparative Example) Drill 10X was prepared using a thinning process called X-thinning, the front view of which is shown in Figure 5. Comparative Example 1-1 had a drill body 1 with a diameter of 9 mm, and Comparative Example 1-2 had a drill body 1 with a diameter of 12 mm. Drill 10Z was prepared using a thinning process called Z-thinning, the front view of which is shown in FIG. 6. Comparative Example 2-1 had a drill body 1 with a diameter of 9 mm, and Comparative Example 2-2 had a drill body 1 with a diameter of 12 mm. Drill 10Y was prepared using a thinning process called Y cross thinning, the front view of which is shown in Figure 7. Comparative Example 3-1 had a drill body 1 with a diameter of 9 mm, and Comparative Example 3-2 had a drill body 1 with a diameter of 12 mm.

[0073] (Verification test 1) As a verification test 1, a verification test is carried out to compare the samples of the above-mentioned embodiment and comparative example, the samples having the drill body 1 with a diameter of 9 mm.

[0074] As shown in Tables 1 and 2, the samples of Comparative Example 1-1, Comparative Example 2-1, Comparative Example 3-1, and Example 1 were used to drill holes in a workpiece (aluminum die-cast material ADC12) under cutting conditions of Conditions 1 to 5, and the thrust force and torque during machining were measured. The measurement results of the thrust force and torque are summarized in Figures 8 and 9.

[0075] [Table 1]

[0076] [Table 2]

[0077] 9, the torque during cutting was almost the same for each cutting condition for the drills of Comparative Example 1-1, Comparative Example 2-1, Comparative Example 3-1, and Example 1. From this, it was confirmed that the drill of Example 1 did not show an increase in cutting resistance compared to other types of conventionally known drills.

[0078] As shown in Fig. 8, it was confirmed that the thrust force of the drill of Example 1 was smaller than that of the comparative example under each cutting condition. From this, it was confirmed that the drill of Example 1 has a certain effect in reducing the thrust force compared to the conventionally known drill.

[0079] Fig. 10 to Fig. 13 are photographs taken from the front of the drills of the samples after the above-mentioned machining test. Fig. 10 shows Comparative Example 1-1, Fig. 11 shows the drill of Comparative Example 2-1, Fig. 12 shows the drill of Comparative Example 3-1, and Fig. 13 shows the drill of Example 1.

[0080] It was confirmed that the amount of deposition near the center was suppressed in the drill of Example 1 in Fig. 13 compared to other drills of Comparative Examples. This is believed to be because the drill of Example 1 has a thinning cutting edge in the center of the tip face, and therefore can cut the workpiece even in the vicinity of the central axis.

[0081] (Verification test 2) As a verification test 2, a verification test is carried out to compare the samples of the above-mentioned embodiment and comparative example, in which the drill body 1 has a diameter of 12 mm.

[0082] As shown in Tables 3 and 4, the samples of Comparative Example 1-2, Comparative Example 2-2, Comparative Example 3-2, and Example 2 were used to drill holes in a workpiece (aluminum die-cast material ADC12) under cutting conditions of Conditions 6 to 10, and the thrust force and torque during drilling were measured. The measurement results of the thrust force and torque are summarized in Figures 14 and 15.

[0083] [Table 3]

[0084] [Table 4]

[0085] In the verification test 2 using a drill with a diameter of 12 mm, the same results as those in the verification test 1 were obtained. That is, it was confirmed that the use of the drill of Example 2 makes it possible to reduce the thrust force while suppressing an increase in cutting resistance.

[0086] Although the embodiments of the present invention and examples thereof have been described above, the configurations and combinations thereof in the embodiments are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited to the embodiments.

[0087] For example, in the above-described embodiment, the chip discharge flute 2 is a twisted flute, but the present invention is not limited to this. Although not particularly shown, the chip discharge flute 2 may extend parallel to the central axis O. Furthermore, the drill 10 described in the above-described embodiment is a two-blade twist drill, but the present invention is not limited to this. The drill 10 may be a three or more-blade drill.

[0088] The drill 10 described in the above embodiment is a solid drill, and the drill body 1 constitutes the entire solid drill. However, the present invention is not limited to this, and for example, the drill body 1 may be at least the tip of the solid drill. In this case, the drill body 1 is integrally joined to the tip of a shank (not shown) by brazing or the like. The drill body 1 may also be a drill head of an indexable drill. In this case, the drill body 1 is detachably attached to the tip of a holder of the indexable drill. [Explanation of symbols]

[0089] 1…Drill body 1a…Tip surface 2...Chip discharge groove 2a…Front wall 2b…Rear wall 4…Main cutting edge 5…Thinning section 5a…Thinning wall 5b…Thinning cutting edge 5c…Thinning rake face 10, 10X, 10Y, 10Z…Drill 53…V-shaped cutting edge d…Aperture diameter D…Diameter D1…first direction D2…Second direction O…Central axis T…Rotation direction φ…Angle (center engagement angle)

Claims

1. A drill body that can be rotated around a central axis, The drill body includes: A tip surface facing the tip side and facing the workpiece; A chip discharge groove extending from the tip surface to a rear end side; a main cutting edge located at an intersection ridge between a front wall surface of the chip discharge groove facing forward in a rotation direction and the tip end surface; a thinning portion located between a rear wall surface of the chip discharge groove facing rearward in the rotation direction and the tip surface, The thinning portion is a thinning wall surface that is connected to the tip surface and inclined toward the rear side in the rotation direction as it moves toward the rear end side; A thinning cutting edge extending radially inward from a radially inner end of the main cutting edge; A thinning rake surface that connects between the thinning cutting edge and the thinning wall surface and faces forward in the direction of rotation, When viewed from the axial direction, a direction from the central axis toward the radially outward direction along the extension direction of the thinning cutting edge is defined as a first direction, and a direction perpendicular to the first direction and toward the radially outward direction from the central axis is defined as a second direction, the thinning portion is formed beyond the central axis in the first direction and the second direction, The thinning cutting edge is an inner thinning edge located in a radially inner region; and an outer thinning edge located in a radially outer region, The inner thinning edge is inclined toward the tip side as it moves radially outward, The outer thinning edge is inclined toward the rear end side as it moves radially outward. drill.

2. A two-blade drill including a pair of the chip discharge grooves, a pair of the main cutting edges, and a pair of the thinning portions, When viewed from the side, the inner thinning edges of the pair of thinning cutting edges intersect in a V-shape around the central axis to form a V-shaped cutting edge. The drill of claim 1.

3. The drill according to claim 2 , wherein an opening diameter of the V-shaped cutting edge is 30% or less of a diameter of the drill body.

4. The drill according to claim 3 , wherein an opening diameter of the V-shaped cutting edge is 5% to 15% of a diameter of the drill body.

5. In the V-shaped cutting edge, the angle between the inner thinning edges of the pair of thinning cutting edges is 10° or more and 70° or less. A drill according to any one of claims 2 to 4.

6. In the V-shaped cutting edge, the angle between the inner thinning edges of the pair of thinning cutting edges is 45° or more and 65° or less. The drill according to claim 5.

7. The distance between the inner thinning edges of the pair of thinning cutting edges constituting the V-shaped cutting edge in the second direction is 2 mm or less. A drill according to any one of claims 2 to 6.

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