Drill

Abstract

A drill (10) is provided with a body (1) extending in the axial direction about a central axis (O). The body (1) is provided with a cutting edge (7) disposed at the tip of the body (1). In a drill tip view, in which the drill (10) is viewed from the tip side along the axial direction, the cutting edge (7) includes a chisel edge (74) passing on top of the central axis (O), and a thinning edge (70) connected to the radially outer end of the chisel edge (74). The thinning edge (70) has a concave curved edge (71) forming a curved shape that is concave in the drill counter-rotation direction around the central axis (O). The concave curved edge (71) includes a first arcuate edge (71a) connected to the chisel edge (74), and a second arcuate edge (71b) connected to the radially outer end of the first arcuate edge (71a) and having the smallest radius of curvature in the concave curved edge (71).

Description

Drill

[0001] The present invention relates to a drill. This application claims priority based on Japanese Patent Application No. 2024-192355 filed in Japan on October 31, 2024, and incorporates its content herein by reference.

[0002] Conventionally, for example, a drill described in Patent Document 1 is known. The drill of Patent Document 1 includes a thinning blade that extends from the inner end of the cutting edge (main cutting edge) toward the chisel portion, which is the tip portion of the drill body. Further, as shown in FIG. 3 of Patent Document 1, an arc groove 10 with a small radius of curvature R is formed at the radially inner end portion of the thinning blade. The arc groove 10 is connected to the chisel 9 (chisel blade).

[0003] Japanese Patent No. 6588625 (B)

[0004] In Patent Document 1, when forming the arc groove 10 during drill manufacturing, it is difficult to control the size of the radius of curvature R to be constant. That is, since the radius of curvature R of the arc groove 10 is very small, the size of the radius of curvature R is likely to vary due to manufacturing errors or the like. When the radius of curvature R of the arc groove 10 varies, the length of the chisel 9 connected to the arc groove 10 also changes. For example, when the length of the chisel 9 increases, the centering property during drilling decreases, affecting the accuracy of the drilling. Also, the cutting resistance during drilling increases, and the vicinity of the chisel 9 wears out early, affecting the tool life. That is, the performance of the drill is likely to vary according to the change in the length of the chisel 9.

[0005] An object of the present invention is to provide a drill capable of suppressing variations in the length of the chisel blade during drill manufacturing and stabilizing the performance of the drill.

[0006] To solve the above problems, the present invention provides the following means.

[0007] [Aspect 1 of the present invention] A drill having a body extending axially with respect to a central axis, wherein the body is provided with a cutting edge disposed at the tip of the body, and the cutting edge has, as viewed from the tip side of the drill in the axial direction, a chisel blade passing along the central axis and a thinning blade connected to the radially outer end of the chisel blade, the thinning blade having a concave curved blade that is concave in the direction opposite to the drill rotation around the central axis, the concave curved blade having a first arc blade connected to the chisel blade and a second arc blade connected to the radially outer end of the first arc blade and having the smallest radius of curvature among the concave curved blades.

[0008] In the drill of the present invention, the thinning blade is equipped with a concave curved blade at its radially inner end. Specifically, the concave curved blade has a first circular arc blade connected to the chisel blade and a second circular arc blade connected to the radially outer end of the first circular arc blade, which has the smallest radius of curvature among the concave curved blades. For this reason, the second circular arc blade (the most curved blade) among the concave curved blades is not connected to the chisel blade, and the chisel blade is connected to the first circular arc blade, which has a larger radius of curvature than the second circular arc blade.

[0009] Therefore, even if the radius of curvature of the second arc-shaped cutting edge varies due to manufacturing tolerances during drill manufacturing, it does not affect the chisel cutting edge, and the length of the chisel cutting edge does not change. Furthermore, since the radius of curvature of the first arc-shaped cutting edge connected to the chisel cutting edge is larger than that of the second arc-shaped cutting edge, the radius of curvature of the first arc-shaped cutting edge is less likely to vary due to manufacturing tolerances. Consequently, the length of the chisel cutting edge connected to the first arc-shaped cutting edge also remains constant.

[0010] As a result, according to the present invention, centering during drilling is well maintained, and the accuracy of drilling is stably improved. In addition, cutting resistance during drilling is stably reduced, preventing problems such as premature wear of the chisel blade.

[0011] Based on the above, the present invention can suppress variations in the length of the chisel blade during drill manufacturing, thereby stabilizing the performance of the drill. In other words, the chisel blade can be manufactured stably in a predetermined shape (as designed).

[0012] Furthermore, the present invention makes it possible to keep the length of the chisel blade short due to the aforementioned concave curve blade configuration. This reduces the cutting load during drilling and further improves the cutting performance of the drill. In addition, it becomes easier to ensure clearance for the concave curve blade of the thinning blade during drilling, thus suppressing the occurrence of flank wear caused by so-called secondary contact.

[0013] [Aspect 2 of the present invention] The drill according to aspect 1, wherein the radius of curvature of the first arc blade is 1.5 times or more the radius of curvature of the second arc blade.

[0014] In this case, a large and stable radius of curvature of the first arc-shaped cutting edge is ensured. During drill manufacturing, variations in the size of the radius of curvature of the first arc-shaped cutting edge due to manufacturing errors are more reliably suppressed. As a result, the length of the chisel cutting edge connected to the first arc-shaped cutting edge also becomes more stable and constant, and the effects of the present invention described above become even more pronounced.

[0015] [Aspect 3 of the present invention] The drill according to aspect 1 or 2, wherein the thinning blade is angled downwards.

[0016] By setting the thinning blade downwards, the present invention can be applied to drills more effectively. Specifically, as the center height of the thinning blade increases towards the downward side, it becomes possible to increase the radius of curvature of the second arc blade (make the curve gentler) accordingly. Therefore, variations in the radius of curvature of the second arc blade due to manufacturing errors during drill manufacturing can be suppressed. Alternatively, it becomes possible to position the second arc blade further radially outward from the chisel blade, increasing the freedom of drill design.

[0017] Furthermore, by making the thinning blade angle downwards, it becomes easier to keep the cutting edge length of the chisel blade short. In addition, the radial rake of the thinning blade can be set to a positive angle (concentric angle). This improves the grip performance on the workpiece during drilling, enhances centering, and improves machining accuracy.

[0018] [Aspect 4 of the present invention] The drill according to any one of aspects 1 to 3, wherein the body comprises a chip discharge groove opening to the front surface and outer peripheral surface of the body and extending from the front surface toward the rear end, and a concave thinning positioned at the front of the body and connected to the chip discharge groove and the front surface, the ridge connecting the thinning and the front surface being connected to the thinning blade and having a curved portion that is concave in the direction of drill rotation around the central axis, and the curved portion being smoothly connected to the first arc blade.

[0019] In this case, the curved section connected to the first arc blade can also be made to have a large radius of curvature, similar to the first arc blade. This stably improves the chip evacuation performance generated near the concave curved edge of the thinning blade (the radially inner end of the thinning blade) during drilling. Furthermore, because the first arc blade and the curved section are smoothly connected, local forces acting on this connection point during drilling are suppressed, and chipping near the chisel blade is reduced.

[0020] [Aspect 5 of the present invention] In a longitudinal cross-sectional view of the drill along the direction in which the chisel blade extends, the thinning extends radially outward as it moves from the connection portion with the chisel blade toward the rear end in the axial direction, as described in aspect 4 of the drill.

[0021] In this case, the wall thickness near the connection point between the chisel blade and the thinning material is ensured, increasing rigidity and thus suppressing chipping and other damage near the chisel blade.

[0022] According to the above-mentioned aspect of the present invention, a drill is provided that can suppress variations in the length of the chisel blade during drill manufacturing and stabilize the performance of the drill.

[0023] Figure 1 is a side view showing the drill according to this embodiment. Figure 2 is an enlarged side view showing part II of Figure 1. Figure 3 is a front view of the drill according to this embodiment, viewed from the tip side in the axial direction. Figure 4 is an enlarged front view showing part IV of Figure 3. Figure 5 is a cross-sectional view (longitudinal cross-sectional view) showing section VV of Figure 4. Figure 6 is a front view of a reference example drill, viewed from the tip side in the axial direction. Figure 7 is a cross-sectional view (longitudinal cross-sectional view) showing section VII-VII of Figure 6.

[0024] A drill 10 according to one embodiment of the present invention will be described with reference to Figures 1 to 5. As shown in Figure 1, the drill 10 is columnar in shape with a central axis O. In this embodiment, the drill 10 comprises a body 1, a shank 2, and a coolant hole 15. The body 1 and the shank 2 are positioned at different locations from each other in the direction in which the central axis O of the drill 10 extends. The body 1 may also be referred to as the cutting edge or the like.

[0025] [Definition of Direction] In this embodiment, the direction in which the central axis O of the drill 10 extends is called the axial direction. Of the axial directions, the direction from the shank 2 toward the body 1 is called the axial tip side or simply the tip side, and the direction from the body 1 toward the shank 2 is called the axial rear end side or simply the rear end side.

[0026] Furthermore, the direction perpendicular to the central axis O is called the radial direction. Within the radial direction, the direction approaching the central axis O is called the radially inward direction, and the direction moving away from the central axis O is called the radially outward direction. The direction of rotation around the central axis O is called the circumferential direction. Within the circumferential direction, the direction in which the drill 10 is rotated during drilling (cutting) is called the drill rotation direction T. Also, within the circumferential direction, the rotation direction opposite to the drill rotation direction T is called the opposite side of the drill rotation direction T, or the anti-drill rotation direction.

[0027] Furthermore, if there are any directions other than those mentioned above that need to be defined, they will be defined separately when describing each component.

[0028] [Shank] The shank 2 is columnar in shape, extending axially with respect to the central axis O, and in this embodiment, it is cylindrical. The shank 2 is located at least at the rear end of the drill 10. The shank 2 is detachably held, for example, by the spindle of a machine tool (not shown) or the chuck of a drilling machine (hereinafter sometimes referred to as the spindle, etc.). The drill 10 is fed towards the tip in the axial direction while the shank 2 is rotated in the drill rotation direction T by the spindle, etc., so that the body 1 cuts into the workpiece and performs drilling.

[0029] [Body] The body 1 extends axially around the central axis O and is roughly columnar in shape. The body 1 is located at least at the tip of the drill 10, and in this embodiment, it is located in the part other than the rear end. As shown in Figure 2, the diameter dimension (outer diameter dimension) D of the body 1 corresponds to the diameter dimension of the rotational trajectory of the cutting edge 7 around the central axis O, which will be described later. For this reason, the diameter dimension D of the body 1 may be rephrased as the cutting edge diameter dimension D.

[0030] As shown in Figures 2 and 3, the body 1 has a tip surface 3 facing the front end of the body 1, an outer peripheral surface 8 facing radially outward of the body 1, a chip evacuation groove 4, a thinning 5, a cutting edge 7, a first margin 13A, a second margin 13B, a leading edge 12, and a secondary beveling surface 14.

[0031] Multiple chip evacuation grooves 4, thinning 5, cutting edge 7, first margin 13A, second margin 13B, leading edge 12, and secondary bevel face 14 are provided on the body 1 at intervals from each other in the circumferential direction. In this embodiment, two sets of chip evacuation grooves 4, thinning 5, cutting edge 7, first margin 13A, second margin 13B, leading edge 12, and secondary bevel face 14 are provided at equal pitches in the circumferential direction. In other words, the drill 10 of this embodiment is a two-blade twist drill with two sets of cutting edge 7.

[0032] The chip evacuation groove 4 opens into the front surface 3 and the outer peripheral surface 8 of the body 1 and is groove-shaped, extending from the front surface 3 toward the rear end. Specifically, the chip evacuation groove 4 twists in the direction opposite to the drill rotation direction as it extends from the front surface 3 toward the rear end in the axial direction.

[0033] The thinning 5 is positioned at the tip of the body 1 and is connected to the chip discharge groove 4 and the tip surface 3. The thinning 5 is recessed radially inward from the chip discharge groove 4 and recessed toward the rear end from the tip surface 3. In other words, the thinning 5 is concave and is formed to cut out a portion of both the chip discharge groove 4 and the tip surface 3. The thinning 5 has a thinning rake surface 51 and a bottom surface 52.

[0034] The thinning rake face 51 is located on the inner surface of the thinning 5 (one of the multiple wall surfaces constituting the thinning 5) that faces the drill rotation direction T. As shown in Figure 2, the thinning rake face 51 has a roughly triangular shape. The axial dimension of the thinning rake face 51 increases towards the radially outward direction.

[0035] The bottom surface 52 is positioned on the inner surface of the thinning 5, on the wall surface facing the opposite direction of drill rotation and towards the tip. The bottom surface 52 is positioned adjacent to the thinning rake face 51 in the drill rotation direction T of the thinning rake face 51. The bottom surface 52 extends towards the rear end as it moves in the opposite direction of drill rotation. As shown in Figure 3, in a view of the drill tip as seen from the axial tip side of the drill 10, the bottom surface 52 has a roughly fan shape.

[0036] The bottom surface 52 has a concave curved shape. Therefore, the ridge line 6 that forms the edge of the bottom surface 52 in the drill rotation direction T (the ridge line 6 to which the bottom surface 52 and the tip surface 3 are connected) has a concave curved shape that is recessed toward the drill rotation direction T. In this embodiment, this ridge line 6 is sometimes referred to as "the ridge line 6 to which the thinning 5 and the tip surface 3 are connected". In this embodiment, the radial outer end of the ridge line 6 is connected to the wall surface of the chip evacuation groove 4 facing away from the direction of drill rotation. The radial outer end of the ridge line 6, that is, the intersection point A of the ridge line 6 and the chip evacuation groove 4, is located radially inward from the outer peripheral surface 8.

[0037] The ridge line 6 connecting the thinning 5 and the tip surface 3 is connected to the thinning blade 70 of the cutting edge 7 (described later) and has a curved portion 60 that is recessed in the drill rotation direction T. In the view of the drill tip in Figure 3, the radius of curvature of the curved portion 60 gradually or in steps increases as it moves radially outward. The curved portion 60 is formed, for example, as part of a logarithmic spiral having a predetermined shape.

[0038] In this embodiment, the curved section 60 is composed of a combination of multiple circular arc sections with different radii of curvature, specifically, a combination of three or more circular arc sections. Each circular arc section of the curved section 60 is smoothly and continuously connected such that it has a common tangent at its connection point.

[0039] Figure 4 is an enlarged view of section IV of Figure 3, showing a view of the drill tip of the drill 10 as seen from the axial tip side. The symbol P in Figure 4 represents the vertex P of the curved section 60 that is furthest in the drill rotation direction T. The vertex P is also the point furthest in the drill rotation direction T within the ridge line 6. The vertex P can also be described as the tip of the curved section 60 (ridge line 6) in the drill rotation direction T. The vertex P is located radially outward from the vicinity of the central axis O (near the chisel blade 74, which will be described later).

[0040] As shown in Figures 2 and 3, the tip surface 3 has a first relief surface 31 and a second relief surface 32. Multiple sets of the first relief surface 31 and the second relief surface 32 are provided on the body 1 at intervals from each other in the circumferential direction. In this embodiment, two sets of the first relief surface 31 and the second relief surface 32 are provided at equal pitches in the circumferential direction.

[0041] The first relief surface 31 has a substantially polygonal shape that extends in the radial direction. The first relief surface 31 extends toward the rear end in the axial direction as it is directed away from the direction of drill rotation.

[0042] The second relief surface 32 is positioned adjacent to the first relief surface 31 in the direction opposite to the drill rotation of the first relief surface 31. The second relief surface 32 has a substantially fan shape, and its circumferential dimension increases as it extends radially outward. Furthermore, the second relief surface 32 extends toward the rear end in the axial direction as it moves in the direction opposite to the drill rotation. The amount of axial displacement per unit length along the circumferential direction of the second relief surface 32 (inclination corresponding to the relief angle) is made larger than the amount of displacement of the first relief surface 31.

[0043] In this embodiment, the tip surface 3 has two types of inclined surfaces (first relief surface 31 and second relief surface 32) with different relief angles, but it is not limited to this. Although not shown in particular, the tip surface 3 may have one type of inclined surface (relief surface) with a constant relief angle, or it may have three or more types of inclined surfaces (relief surfaces) with different relief angles.

[0044] The cutting edge 7 is disposed at the tip of the body 1. The cutting edge 7 is disposed at a ridge line portion where the wall surfaces facing the drill rotation directions T of the chip discharge groove 4 and the thinning 5 are connected to the tip surface 3. As shown in FIGS. 3 and 4, the cutting edge 7 has a chisel edge 74, a thinning edge 70, and a main cutting edge 75.

[0045] The chisel edge 74 is disposed at the center portion (rotation center portion) of the tip surface 3. Specifically, the chisel edge 74 is disposed at a ridge line portion where a pair of relief surface sets (the set of the first relief surface 31 and the second relief surface 32) are connected to each other. In the present embodiment, the chisel edge 74 is disposed at a ridge line portion where a pair of the first relief surfaces 31 are connected to each other.

[0046] The chisel edge 74 forms a straight line passing through the center axis O in a front view of the drill tip shown in FIG. 4. That is, the chisel edge 74 extends in the radial direction. The axial position of the chisel edge 74 is substantially constant over the entire length of the chisel edge 74. The chisel edge 74 is disposed so as to be sandwiched between a pair of thinnings 5. Specifically, the chisel edge 74 is disposed between a pair of bottom surfaces 52 (see FIG. 5 described later). The chisel edge 74 extends so as to connect a pair of thinnings 5 to each other.

[0047] The portions of the cutting edge 7 other than the chisel edge 74 (the thinning edge 70 and the main cutting edge 75) and the ridge line 6 are connected to each other via the radially outer end of the chisel edge 74, forming a continuous single ridge line portion. Here, the reference symbol RL shown in FIG. 4 represents a virtual straight line obtained by extending the chisel edge 74 radially outward in the front view of the drill tip. In the present embodiment, this virtual straight line is referred to as a reference line RL.

[0048] The ridge line 6 is disposed in the drill rotation direction T with respect to the reference line RL in the front view of the drill tip and does not contribute to cutting during drilling. The thinning edge 70 and the main cutting edge 75 disposed in the direction opposite to the drill rotation direction with respect to the reference line RL in the front view of the drill tip contribute to cutting during drilling. Also, the chisel edge 74 located on the reference line RL may contribute to cutting. Thus, the cutting contribution portion (cutting edge 7) and the non-cutting contribution portion (ridge line 6) can be distinguished with the reference line RL as a boundary. Note that the cutting contribution portion may be referred to as a cutting portion, and the non-cutting contribution portion may be referred to as a non-cutting portion or the like.

[0049] Figure 5 shows a partial cross-sectional view (longitudinal cross-sectional view) of the drill 10 that includes the reference line RL and the central axis O of Figure 4 in its plane, specifically showing the VV section of Figure 4. As shown in Figure 5, in a longitudinal cross-sectional view of the drill 10 along the direction in which the chisel blade 74 extends (the direction in which the reference line RL extends), the thinning 5 extends radially outward as it moves from the connection point with the chisel blade 74 toward the rear end in the axial direction. Specifically, the bottom surface 52 of the thinning 5 is directly connected to the radially outer end of the chisel blade 74, and extends radially outward as it moves from this connection point toward the rear end in the axial direction. Therefore, the wall thickness between the pair of thinning 5 gradually increases as it moves from the chisel blade 74 toward the rear end in the axial direction.

[0050] As shown in Figure 4, the thinning blade 70 is connected to the radially outer end of the chisel blade 74. The thinning blade 70 is located at the radially inner end of the cutting blade 7. The thinning blade 70 is located on the ridge where a part of the thinning rake face 51 and bottom face 52 (radially inner end) is connected to the first relief face 31. The thinning blade 70 extends approximately radially outward from near the central axis O.

[0051] Specifically, in this embodiment, the thinning blade 70 is angled downwards. In other words, the radial rake angle of the thinning blade 70 is a positive angle (contrary angle). Also, as shown in Figure 2, the thinning blade 70 extends towards the rear end in the axial direction as it moves radially outward.

[0052] As shown in Figure 4, the thinning blade 70 has a concave curved blade 71 that is connected to the ridge line 6 where the thinning 5 and the tip surface 3 are connected and has a curved shape that is recessed in the direction opposite to the drill rotation, a straight blade 72 connected to the concave curved blade 71, and a convex curved blade 73 connected to the straight blade 72.

[0053] The concave curve blade 71 is positioned at the radially inner end of the thinning blade 70. The concave curve blade 71 is connected to the radially inner end of the curved portion 60 of the ridge line 6. The concave curve blade 71 is composed of a combination of multiple arc blades 71a and 71b with different radii of curvature.

[0054] Specifically, the concave curve blade 71 has a first arc blade 71a connected to the chisel blade 74, and a second arc blade 71b connected to the radially outer end of the first arc blade 71a, which has the smallest radius of curvature among the concave curve blades 71. The first arc blade 71a and the second arc blade 71b each have an arc shape that is concave in the direction opposite to the drill rotation.

[0055] The first arc-shaped blade 71a is smoothly connected to the curved portion 60 of the ridge line 6 via the radially outer end of the chisel blade 74. Specifically, the radially inner end of the curved portion 60 and the radially inner end of the first arc-shaped blade 71a are smoothly and continuously connected such that they have a common tangent at their connection point (corresponding to the radially outer end of the chisel blade 74).

[0056] The radius of curvature R1 of the first arc blade 71a is greater than the radius of curvature R2 of the second arc blade 71b. Specifically, the radius of curvature R1 of the first arc blade 71a is set to be 1.5 times or more the radius of curvature R2 of the second arc blade 71b, and more preferably 2 times or more. Although not particularly limited, the radius of curvature R1 of the first arc blade 71a may be 30 times or less the radius of curvature R2 of the second arc blade 71b, or it may be 10 times or less.

[0057] The second arc blade 71b is positioned radially outward of the first arc blade 71a. The radial inner end of the second arc blade 71b and the radial outer end of the first arc blade 71a are smoothly and continuously connected such that they share a common tangent at their connection point.

[0058] In this embodiment, D is defined as the diameter dimension (blade diameter dimension) of the rotational trajectory of the cutting edge 7 around the central axis O. For example, the radius of curvature R1 of the first arc blade 71a is approximately 0.05D to 0.15D, and the radius of curvature R2 of the second arc blade 71b is approximately 0.01D to 0.02D. Furthermore, the blade length of the first arc blade 71a is longer than the blade length of the second arc blade 71b.

[0059] The straight blade 72 is positioned radially outward of the concave curve blade 71. The straight blade 72 extends in a straight line. The radial inner end of the straight blade 72 is smoothly and continuously connected to the radial outer end of the second arc blade 71b. In this embodiment, the blade length of the straight blade 72 is longer than the blade length of the concave curve blade 71 (the sum of the blade lengths of the first arc blade 71a and the second arc blade 71b).

[0060] Here, we will explain the definitions of the direction of the thinning blade 70 in the direction of its blade length (Y-axis direction) and the direction perpendicular to its blade (X-axis direction). In this embodiment, as shown in Figure 4, when viewing the drill tip from the axial tip side of the drill 10, the direction in which the straight blade 72 of the thinning blade 70 extends is called the blade length direction of the thinning blade 70 or simply the blade length direction. The blade length direction of the thinning blade 70 corresponds to the Y-axis direction.

[0061] The drill 10 in this embodiment is a two-blade drill and has a pair of cutting edges 7. The pair of cutting edges 7 are positioned at different locations relative to each other in the direction of the cutting edge length of the thinning edge 70. In this embodiment, of the pair of cutting edges 7 (7A, 7B), the direction from one cutting edge 7A to the other cutting edge 7B along the cutting edge length direction of the thinning edge 70 is called the other side (-Y side) of the cutting edge length direction of the thinning edge 70, and the direction from the other cutting edge 7B to one cutting edge 7A is called the one side (+Y side) of the cutting edge length direction of the thinning edge 70.

[0062] Furthermore, in the view of the drill tip shown in Figure 4, the direction perpendicular to the straight edge 72 of the thinning blade 70 is called the direction perpendicular to the thinning blade 70 or simply the direction perpendicular to the blade. The direction perpendicular to the thinning blade 70 corresponds to the X-axis direction.

[0063] In this embodiment, along the direction perpendicular to the blade of the thinning blade 70, the direction in which one cutting edge 7A faces the drill rotation direction T is referred to as the one side (+X side) perpendicular to the blade of the thinning blade 70, and the direction in which the other cutting edge 7B faces the drill rotation direction T is referred to as the other side (-X side) perpendicular to the blade of the thinning blade 70.

[0064] In this embodiment, as described above, the thinning blade 70 is angled downwards. Therefore, the thinning blade 70 of one cutting blade 7A is positioned at a distance LX from the thinning blade 70 of the other cutting blade 7B on the other side (-X side) perpendicular to the blade. The distance LX is set to a range of, for example, 0 < LX ≤ 0.10D, where D is the diameter dimension (blade diameter dimension) of the rotational trajectory of the cutting blade 7 around the central axis O. Also, the radius of curvature R2 of the second arc blade 71b is smaller than the distance LX. The radius of curvature R1 of the first arc blade 71a is larger than the distance LX.

[0065] Furthermore, in this embodiment, the vertices P of each curved portion 60 of the pair of ridge lines 6 are opposite each other in the direction of the blade length (Y-axis direction). In other words, the pair of thinnings 5 ​​overlap each other when viewed from the direction perpendicular to the blade (X-axis direction) (i.e., they are opposite each other in the direction of the blade length). The pair of vertices P are positioned at a distance LY in the direction of the blade length while being opposite each other.

[0066] However, this is not limited to this example, and although not specifically shown in the diagram, the vertices P of each curved portion 60 of a pair of edges 6 do not necessarily have to be opposite each other in the direction of the blade length (Y-axis direction). In other words, the pair of thinnings 5 ​​do not necessarily have to overlap each other when viewed from the direction perpendicular to the blade (X-axis direction) (i.e., they do not have to be opposite each other in the direction of the blade length).

[0067] Alternatively, although not specifically shown in the diagram, the vertices P of each curved portion 60 of a pair of edges 6 may coincide with each other when viewed from the direction perpendicular to the thinning blade 70 (X-axis direction). That is, the positions of the pair of vertices P in the blade length direction (Y-axis direction) may be the same, and the distance LY may be 0.

[0068] The convex curved blade 73 is positioned radially outward from the straight blade 72. The convex curved blade 73 is positioned at the radially outer end of the thinning blade 70. The convex curved blade 73 has a curved shape that is convex in the direction of drill rotation T. The radially inner end of the convex curved blade 73 is smoothly and continuously connected to the radially outer end of the straight blade 72.

[0069] As shown in Figure 3, the main cutting edge 75 is positioned radially outward of the thinning edge 70. The main cutting edge 75 is positioned on the ridge where the wall surface of the chip evacuation groove 4 facing the drill rotation direction T connects to the first relief surface 31. In the view of the drill tip shown in Figure 3, the main cutting edge 75 extends in a straight line. Furthermore, the main cutting edge 75 is angled upward. In other words, the radial rake of the main cutting edge 75 is set to a negative angle. As shown in Figure 4, the radial inner end of the main cutting edge 75 is smoothly and continuously connected to the radial outer end of the convex curved blade 73. That is, the main cutting edge 75 is connected to the thinning edge 70.

[0070] As shown in Figure 2, the main cutting edge 75 extends radially outward towards the axial rear end. The leading edge 12 is connected to the radial outer end B of the main cutting edge 75. The radial outer end B of the main cutting edge 75, that is, the connection point between the main cutting edge 75 and the leading edge 12, can also be called the outer circumferential corner B. The outer circumferential corner B is a pointed corner that extends toward the outer circumference of the tip.

[0071] Although not specifically shown in the illustrations, at least the thinning edge 70 of the cutting edge 7 may have honing at its cutting edge. Honing can be, for example, chamfer honing or round honing.

[0072] As shown in Figures 2 and 3, the first margin 13A is located on the outer circumferential surface 8 and extends along the chip evacuation groove 4. Specifically, the first margin 13A is located at the end of the outer circumferential surface 8 in the direction of drill rotation T. In other words, the first margin 13A is located on the outer circumferential surface 8 in the portion adjacent to the chip evacuation groove 4 in the direction opposite to drill rotation. The first margin 13A extends in the direction opposite to drill rotation as it approaches the rear end in the axial direction. The first margin 13A has a curved shape that is convex radially outward. In a cross-sectional view perpendicular to the central axis O, the first margin 13A has an arc shape centered on the central axis O.

[0073] The second margin 13B is located on the outer circumferential surface 8 and extends along the chip evacuation groove 4. The second margin 13B is located away from the first margin 13A in the direction opposite to the drill rotation. Specifically, the second margin 13B is located at the end of the outer circumferential surface 8 in the direction opposite to the drill rotation. In other words, the second margin 13B is located on the outer circumferential surface 8 in the portion of the chip evacuation groove 4 adjacent to the drill rotation direction T. The second margin 13B extends in the direction opposite to the drill rotation as it approaches the rear end in the axial direction. The second margin 13B has a curved shape that is convex radially outward. In a cross-sectional view perpendicular to the central axis O, the second margin 13B has an arc shape centered on the central axis O.

[0074] The leading edge 12 is positioned on the ridge where the wall surface of the chip evacuation groove 4 facing the drill rotation direction T connects to the first margin 13A. The leading edge 12 extends along the wall surface of the chip evacuation groove 4 facing the drill rotation direction T and the first margin 13A. Specifically, the leading edge 12 extends in the direction opposite to the drill rotation direction as it approaches the rear end in the axial direction.

[0075] The leading edge 12 may also be provided with a back taper. In this case, the leading edge 12 extends so that it is slightly radially inward as it approaches the rear end in the axial direction.

[0076] The secondary chamfering surface 14 is positioned on the outer peripheral surface 8. In the circumferential direction, the secondary chamfering surface 14 is positioned between the first margin 13A and the second margin 13B. The secondary chamfering surface 14 is formed recessed radially inward from the first margin 13A and the second margin 13B. During drilling, the secondary chamfering surface 14 faces the inner peripheral surface of the machined hole in the workpiece with a radial gap between them.

[0077] [Coolant Holes] As shown in Figure 2, the coolant holes 15 open into the tip surface 3 of the drill 10 and extend through the body 1 and shank 2 inside the drill 10. The coolant holes 15 are provided penetrating the drill 10 in the axial direction. Multiple coolant holes 15 are provided spaced apart from each other in the circumferential direction, and in this embodiment, two are provided at equal pitches in the circumferential direction. The coolant holes 15 extend spirally in the direction opposite to the drill rotation as they move from the tip surface 3 toward the rear end in the axial direction. As shown in Figure 3, in this embodiment, the tip of the coolant hole 15 opens into the second relief surface 32 of the tip surface 3.

[0078] [Effects of this embodiment] In the drill 10 of this embodiment described above, the thinning blade 70 is equipped with a concave curve blade 71 at its radially inner end. Specifically, the concave curve blade 71 has a first circular arc blade 71a connected to the chisel blade 74, and a second circular arc blade 71b connected to the radially outer end of the first circular arc blade 71a, which has the smallest radius of curvature among the concave curve blades 71. For this reason, the second circular arc blade (maximum curvature blade) 71b, which is the most curved of the concave curve blades 71, is not connected to the chisel blade 74, and the first circular arc blade 71a, which has a larger radius of curvature than the second circular arc blade 71b, is connected to the chisel blade 74.

[0079] Therefore, even if the radius of curvature R2 of the second arc blade 71b varies due to manufacturing errors during drill manufacturing, it does not affect the chisel blade 74, and the length of the chisel blade 74 does not change. Furthermore, since the radius of curvature R1 of the first arc blade 71a connected to the chisel blade 74 is larger than the radius of curvature R2 of the second arc blade 71b, the radius of curvature R1 of the first arc blade 71a is less likely to vary due to manufacturing errors. Consequently, the length of the chisel blade 74 connected to the first arc blade 71a also remains constant.

[0080] As a result, according to this embodiment, centering during drilling is well maintained, and the accuracy of drilling is stably improved. In addition, since the cutting resistance during drilling is stably reduced, problems such as premature wear of the chisel blade 74 are prevented.

[0081] Based on the above, this embodiment makes it possible to suppress variations in the length of the chisel blade 74 during drill manufacturing and stabilize the performance of the drill 10. In other words, the chisel blade 74 can be manufactured stably in a predetermined shape (as designed).

[0082] Furthermore, in this embodiment, the configuration of the concave curved blade 71 described above makes it possible to keep the length of the chisel blade 74 short. This reduces the cutting load during drilling and further improves the cutting performance of the drill 10. In addition, it becomes easier to ensure clearance for the concave curved blade 71 of the thinning blade 70 during drilling, thus suppressing the occurrence of flank wear due to so-called secondary contact.

[0083] Furthermore, in this embodiment, the radius of curvature R1 of the first arc blade 71a is set to be 1.5 times or more the radius of curvature R2 of the second arc blade 71b. In this case, a large and stable radius of curvature R1 of the first arc blade 71a is ensured. During drill manufacturing, variations in the size of the radius of curvature R1 of the first arc blade 71a due to manufacturing errors, etc., are more reliably suppressed. As a result, the length of the chisel blade 74 connected to the first arc blade 71a also becomes more stable and constant, and the effects of this embodiment described above become even more remarkable.

[0084] Furthermore, in this embodiment, the thinning blade 70 is set to a downward-center position. By setting the thinning blade 70 to a downward-center position, the present invention can be applied to the drill 10 more effectively. Specifically, as the center height of the thinning blade 70 increases towards the downward-center side (-X side), the distance LX shown in Figure 4 increases by that amount, and accordingly, it becomes possible to increase the radius of curvature R2 of the second arc blade 71b (to make the curve gentler). Therefore, during drill manufacturing, it is possible to suppress variations in the size of the radius of curvature R2 of the second arc blade 71b due to manufacturing errors, etc. Alternatively, it becomes possible to position the second arc blade 71b further radially outward from the chisel blade 74, increasing the degree of freedom in drill design.

[0085] Furthermore, by making the thinning blade 70 angled downwards, it becomes easier to keep the cutting edge length of the chisel blade 74 short. In addition, the radial rake of the thinning blade 70 can be set to a positive angle (concentric angle). This improves the grip performance on the workpiece during drilling, enhances centering, and improves machining accuracy.

[0086] In this embodiment, the curved portion 60 of the ridge line 6 to which the thinning 5 and the tip surface 3 are connected is smoothly connected to the first arc blade 71a of the thinning blade 70. In this case, the curved portion 60 connected to the first arc blade 71a can also be made to have a large radius of curvature, similar to the first arc blade 71a. This makes it easier to stably improve the chip evacuation performance generated near the concave curved blade 71 of the thinning blade 70 (the radially inner end of the thinning blade 70) during drilling. In addition, because the first arc blade 71a and the curved portion 60 are smoothly connected, local forces acting on this connection part during drilling are suppressed, and chipping near the chisel blade 74 is suppressed.

[0087] Furthermore, in this embodiment, as shown in Figure 5, in a longitudinal cross-sectional view of the drill 10 along the direction in which the chisel blade 74 extends, the thinning 5 extends radially outward as it moves from the connection point with the chisel blade 74 toward the rear end in the axial direction. In this case, the wall thickness near the connection point between the chisel blade 74 and the thinning 5 is ensured, and the rigidity is increased, thereby suppressing chipping and other damage near the chisel blade 74.

[0088] Here, the reference example drill 100 will be described with reference to Figures 6 and 7. As shown in Figure 6, the reference example drill 100 has a thinning blade 70 that is centered upward, and the radial rake of the thinning blade 70 is set to a negative angle. For this reason, the thinning blade 70 of one cutting edge 7A is positioned at a distance LX from the thinning blade 70 of the other cutting edge 7B on one side (+X side) perpendicular to the blade of the thinning blade 70.

[0089] In this reference example drill 100, the maximum curvature portion (the portion with the smallest radius of curvature) 65, which is located near the chisel blade 74, is positioned in the non-cutting contribution portion (non-cutting portion) in the drill rotation direction T relative to the reference line RL. That is, the maximum curvature portion 65 is located on the ridge line 6 side of the reference line RL. Even with this configuration, unlike the aforementioned Patent Document 1 (Japanese Patent No. 6588625), it is possible to position the maximum curvature portion 65 without connecting it to the chisel blade 74.

[0090] However, in the above example, as shown in Figure 7, in a longitudinal cross-sectional view of the drill 100 along the direction in which the chisel blade 74 extends, the thinning 5 extends straight toward the rear end along the axial direction from the connection point with the chisel blade 74, and then extends radially outward as it moves toward the rear end along the axial direction. This is because the thinning rake face 51 of the thinning 5 is directly connected to the chisel blade 74. For this reason, in the drill 100 of the example, it is difficult to ensure sufficient wall thickness near the connection point between the chisel blade 74 and the thinning 5.

[0091] Therefore, it is important not only to position the maximum curved portion 65 away from the chisel blade 74, but also, as in this embodiment, to position the maximum curved portion (second arc blade 71b) on the thinning blade 70 (concave curve blade 71) in the cutting contribution portion (cutting portion) area, while also positioning it away from the chisel blade 74.

[0092] [Other configurations included in the present invention] The present invention is not limited to the embodiments described above, and the configuration can be modified, for example, as described below, without departing from the spirit of the present invention.

[0093] In the above-described embodiment, the bottom surface 52 of the thinning 5 is a concave curved surface, and as shown in Figure 3, the radial outer end (intersection A) of the ridge line 6 to which the thinning 5 and the tip surface 3 are connected is positioned radially inward from the outer circumferential surface 8. However, the configuration is not limited to this. Although not specifically shown, for example, the bottom surface 52 of the thinning 5 may be planar, the radial outer end of the bottom surface 52 may reach the outer circumferential surface 8, and the radial outer end of the ridge line 6 may be connected to the outer circumferential surface 8. In this case, the ridge line 6 has a concave curved portion 60 connected to the first arc blade 71a, and a straight portion (not shown) connected to the radial outer end of the curved portion 60. This drill may have a shape called so-called X-thinning when viewed from the drill tip.

[0094] Furthermore, although the above-described embodiment uses a configuration in which the thinning blade 70 has a straight blade 72 as an example, it is not limited to this. Although not specifically shown, the thinning blade 70 may have a curved blade that has a large radius of curvature, such as a concave or convex curve, instead of a straight blade 72. In this case, the direction in which a virtual straight line extends passing through the radial outer end of the second arc blade 71b and the radial inner end of the convex curve blade 73, as viewed from the drill tip, can be defined as the blade length direction (Y-axis direction) of the thinning blade 70.

[0095] Furthermore, although the above-described embodiment uses a configuration in which the main cutting edge 75 extends in a straight line as an example, it is not limited to this. Although not specifically shown in the figures, the main cutting edge 75 may be a so-called curved blade shape. In this case, the main cutting edge 75 may have, for example, a concave blade positioned radially outside the convex curved blade 73 and connected to the convex curved blade 73, which is concave in the direction opposite to the drill rotation direction, and a convex blade positioned radially outside the concave blade and connected to the concave blade, which is convex in the direction of the drill rotation direction T.

[0096] Furthermore, in the above-described embodiment, the drill 10 is a double margin drill and has two types of margins (first margin 13A and second margin 13B) that are spaced apart from each other in the circumferential direction, but the configuration is not limited to this. The drill may also be a single margin drill having one type of margin, or a triple margin drill having three types of margins that are spaced apart from each other in the circumferential direction, etc.

[0097] Furthermore, although the above-described embodiment showed the drill 10 as a two-blade twist drill having two cutting edges 7, it is not limited to this. The drill may also be a three-blade or more drill having three or more cutting edges.

[0098] Furthermore, the drill 10 described in the above-mentioned embodiment is a solid drill in which the body 1 and shank 2 are integrally formed from a single material, but it is not limited to this. For example, the body 1 and shank 2 may be manufactured separately and then integrated into a solid drill by brazing or the like.

[0099] Alternatively, although not specifically illustrated, the drill may be an indexable drill with a body detachably attached to the shank. In this case, the shank may be referred to as a holder. Furthermore, the drill may consist only of a body and not have a shank. In this case, the drill may be referred to as a drill head, etc.

[0100] The present invention may be combined in any way that does not depart from the spirit of the invention, as described in the above embodiments and modifications, and the configurations may be added, omitted, substituted, or otherwise modified. Furthermore, the present invention is not limited by the above embodiments, but is limited only by the claims.

[0101] The drill of the present invention can suppress variations in the length of the chisel blade during drill manufacturing, thereby stabilizing the performance of the drill. Therefore, it has industrial applicability.

[0102] 1 Body 3 Tip surface 4 Chip evacuation groove 5 Thinning 6 Ridge 7, 7A, 7B Cutting edge 8 Outer surface 10 Drill 60 Curved section 70 Thinning blade 71 Concave curved blade 71a First arc blade 71b Second arc blade 74 Chisel blade O Center axis R1, R2 Radius of curvature T Drill rotation direction

Claims

1. A drill having a body extending axially with respect to a central axis, wherein the body is provided with a cutting edge positioned at the tip of the body, the cutting edge having, in a view of the drill tip as seen from the tip side in the axial direction of the drill, a chisel blade passing along the central axis, and a thinning blade connected to the radially outer end of the chisel blade, the thinning blade having a concave curved blade that is concave in the direction opposite to the drill rotation around the central axis, the concave curved blade having a first arc blade connected to the chisel blade, and a second arc blade connected to the radially outer end of the first arc blade and having the smallest radius of curvature among the concave curved blades, the drill.

2. The drill according to claim 1, wherein the radius of curvature of the first arc-shaped cutting edge is 1.5 times or more the radius of curvature of the second arc-shaped cutting edge.

3. The drill according to claim 1 or 2, wherein the thinning blade is angled downwards.

4. The drill according to claim 1 or 2, wherein the body comprises a chip discharge groove opening to the front surface and outer surface of the body and extending from the front surface toward the rear end, and a concave thinning positioned at the front of the body and connected to the chip discharge groove and the front surface, the ridge connecting the thinning and the front surface being connected to the thinning blade and having a curved portion recessed in the direction of drill rotation around the central axis, and the curved portion being smoothly connected to the first arc blade.

5. In a longitudinal cross-sectional view of the drill along the direction in which the chisel blade extends, the thinning extends radially outward as it moves from the connection portion with the chisel blade toward the rear end in the axial direction, as described in claim 4.

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