Drill

Abstract

The linear core thickness (S) is 0 to 0.100 D. The linear core thickness (S) is the distance dimension in a perpendicular direction between a corner part (55) of a cutting edge (5A) and a corner part (55) of a second cutting edge (5B). When a body (3) is viewed from the tip side, a first groove bottom part (81) and a second groove bottom part (82) are provided on inner surfaces of each of the discharge grooves (4A, 4B). The first groove bottom part (81) having a curved shape is provided on a first inner surface (41). The second groove bottom part (82) having a curved shape is provided on a second inner surface (42). The second inner surface (42) among the inner surfaces of each of the discharge grooves (4A, 4B) faces in the direction opposite the rotation direction (T).

Description

Drill

[0001] The present invention relates to a drill.

[0002] The drill described in Patent Document 1 includes a body. The body rotates around an axis. The body has a chip discharge groove on the outer periphery of the tip portion. The chip discharge groove extends toward the rear end side of the body. The body has an intersecting ridge line portion. The intersecting ridge line portion is a ridge line portion where the inner wall surface of the chip discharge groove and the tip relief surface of the body intersect. The inner wall surface of the chip discharge groove faces the drill rotation direction. The body has a cutting edge on the intersecting ridge line portion. The cutting edge has a concave curved cutting edge portion on the inner peripheral end side. The concave curved cutting edge portion is a curved shape that is concave on the rear side in the drill rotation direction.

[0003] Since the cutting edge has a concave curved cutting edge portion, during workpiece machining, stress from the workpiece tends to concentrate on the corner portion which is the outer peripheral end side of the cutting edge. Therefore, the above cutting edge has a convex curved cutting edge portion at the corner portion. The convex curved cutting edge portion is a curved shape that is convex in the drill rotation direction. In addition, a drill having a chamfered corner portion of the cutting edge is also known.

[0004] Japanese Patent No. 4120185

[0005] In the drill described in Patent Document 1, the rake angle in the radial direction of the corner portion may become negative due to the convex curved cutting edge portion of the cutting edge. Also, the rake angle in the radial direction of the corner portion may become negative by chamfering the corner portion. When the rake angle in the radial direction is negative, there is a problem that the thrust resistance applied to the body increases. When the thrust resistance increases, springback may occur particularly in the machining of soft materials.

[0006] An object of the present invention is to provide a drill capable of reducing the thrust resistance during workpiece cutting.

[0007] The drill of the present invention comprises a round bar-shaped body having a predetermined core thickness and a conical tip, an discharge groove provided on the outer circumferential surface of the body and extending spirally from the tip toward the rear end of the body, a straight cutting edge formed on the ridge between the first inner surface of the discharge groove facing the rotation direction of the body and the relief surface at the tip, wherein the discharge groove is a plurality of discharge grooves including a first discharge groove and a second discharge groove, the relief surface is a plurality of relief surfaces including a first relief surface adjacent to the first discharge groove and a second relief surface adjacent to the second discharge groove, and the cutting edge is formed between the first inner surface of the first discharge groove and the first relief surface The body comprises a plurality of cutting edges, including a first cutting edge formed on the ridge and a second cutting edge formed on the ridge between the first inner surface and the second relief surface of the second discharge groove. When the diameter of the body is D, the straight core thickness, which is the distance between the corner of the first cutting edge and the corner of the second cutting edge in the perpendicular direction, is 0 to 0.100D. When the body is viewed from the tip side, the inner surfaces of the first discharge groove and the second discharge groove are provided with a curved first groove bottom on the first inner surface and a curved second groove bottom on the second inner surface facing the opposite direction to the rotation direction.

[0008] According to the present invention, since the cutting edge is linear, the drill of this embodiment can alleviate stress concentration on the cutting edge compared to a drill with a hook-shaped cutting edge. Furthermore, in the present invention, the linear core thickness of the first and second cutting edges is limited to 0 to 0.100D. This allows the drill to form the radial rake angle of the corner portion of the first cutting edge and the radial rake angle of the corner portion of the second cutting edge in a positive direction. As a result, the drill can improve the cutting performance at the corner portion compared to when the radial rake angle is formed at a large negative angle. Because the cutting performance at the corner portion is improved, the drill can suppress the generation of Poisson burrs. Since the cutting edge is linear and simple, the cutting edge is easy to resharpen.

[0009] In the present invention, a third groove bottom may be provided in the inner surface of the first discharge groove and the second discharge groove, in the portion between the bottom of the first groove and the bottom of the second groove, that contacts the core thickness, and that curves radially outward along the curved outer circumference of the core thickness. This allows the drill to approach zero linear core thickness.

[0010] The present invention may also include thinning blades provided at the tip of the body, extending from the inner ends of the first and second cutting edges toward the center of the tip of the body. This further reduces the thrust resistance acting on the body of the drill.

[0011] The thinning blade of the present invention may also be a straight X-thinning blade. Because the thinning blade is X-thinning, the drill can reduce thrust resistance during workpiece cutting and improve its cutting performance. X-thinning is particularly effective for drills with a large web thickness. Web thickness refers to the diameter from the center of the tool body to the bottom of the discharge groove. X-thinning can be formed more easily than thinning blades of other shapes.

[0012] This is a perspective view of drill 1. This is a side view of drill 1. This is a perspective view of drill 1 from a different angle than in Figure 1. This is a front view of drill 1. This is a front view of round bar 300. This is a bar graph showing the torque results. This is a graph showing the thrust resistance results. This is a bar graph showing the thrust resistance results.

[0013] One embodiment of the present invention is described below. The present invention is not limited to the following embodiment, and design modifications can be made as appropriate. For clarity of explanation, there are parts in the drawings where the dimensional ratio differs from the actual dimensional ratio. The present invention is not interpreted as being limited to the shape of the following embodiment. In this embodiment, the tip of the drill 1 is the front of the drill 1, and the rear end of the drill 1 is the back of the drill 1.

[0014] The structure of the drill 1 will be explained with reference to Figures 1 to 5. The drill 1 shown in Figure 1 is made of a hard material such as cemented carbide or high-speed tool steel. As shown in Figure 4, when viewed at the tip of the drill 1, the centerlines A1 and A2 of the drill 1 are perpendicular to each other. The axis AX of the drill 1 passes through the intersection of the centerlines A1 and A2. The intersection of the centerlines A1 and A2 is the center P. The drill 1 cuts the workpiece and forms a machined hole by rotating around the axis AX. The rotation direction T of the drill 1 is counterclockwise when the drill 1 is viewed from the front.

[0015] As shown in Figures 1 to 3, the drill 1 comprises a shank 2 and a body 3 mounted coaxially. The shank 2 is a round bar and is mounted on the spindle of a machine tool (not shown). The body 3 is a round bar extending from the shank 2 along the axis AX and having the tip angle θ shown in Figure 2. The tip angle θ is the angle obtained when the two cutting edges 5A and 5B, described later, are projected parallel to a plane parallel to the axis AX of the drill 1, and is, for example, 118°. The diameter D of the drill 1 is, for example, 12.5 mm.

[0016] As shown in Figure 4, the body 3 has a core thickness portion 10. The core thickness portion 10 has a circular cross-sectional shape centered on the axis AX. The core thickness portion 10 is the thickness of the web at the tip of the drill 1. The web is the portion formed by the groove bottoms of the discharge grooves 4A and 4B, which will be described later. The diameter of the core thickness portion 10 should be the diameter required for cutting the workpiece and the diameter required for the rigidity and strength of the drill 1.

[0017] The body 3 is provided with two discharge grooves 4A and 4B on its outer circumferential surface 31. The discharge grooves 4A and 4B are formed in a spiral shape clockwise when viewed from the front, from the tip of the body 3 toward the rear end of the shank 2 (see Figures 1 and 2). The discharge grooves 4A and 4B open at the tip of the body 3. The discharge grooves 4A and 4B discharge chips from the machining hole during workpiece machining.

[0018] Referring to Figure 5, the inner surface shapes of the discharge grooves 4A and 4B will be described. Figure 5 is a front view of a round bar 300 with a tip angle of 140°, after a grinding wheel has been run over the outer surface of the round bar 300 to form the discharge grooves 4A and 4B. The round bar 300 is the base material of the body 3. Since the inner surface shapes of the discharge grooves 4A and 4B are identical, in this embodiment, only the inner surface shape of discharge groove 4A will be described.

[0019] The inner surface of the discharge groove 4A includes a first inner surface 41 and a second inner surface 42. The first inner surface 41 is a surface facing the rotation direction T. The second inner surface 42 is a surface facing the opposite direction to the rotation direction T. The ridge portion where the first inner surface 41 and the outer circumferential surface 31 intersect is the leading edge 33. The ridge portion where the second inner surface 42 and the outer circumferential surface 31 intersect is the heel portion 34.

[0020] A first groove bottom 81 is provided on the first inner surface 41, which is closer to the core thickness portion 10 than the leading edge 33. The first groove bottom 81 is a portion that curves in a gentle arc shape in the opposite direction to the rotation direction T and toward the core thickness portion 10.

[0021] A second groove bottom 82 is provided on the second inner surface 42, which is closer to the core thickness portion 10 than the heel portion 34. The second groove bottom 82 is a portion that curves in a gentle arc shape in the rotational direction T and toward the core thickness portion 10.

[0022] A third groove bottom 83 is provided between the first groove bottom 81 and the second groove bottom 82. The third groove bottom 83 is the part where the inner surface of the discharge groove 4 and the outer edge of the core thickness 10 come into contact, and it is a part that curves in an arc shape radially outward along the outer circumference of the core thickness 10. In other words, the inner surface of the discharge groove 4 is recessed at the first groove bottom 81 and the second groove bottom 82, and has a bulging shape at the third groove bottom 83 sandwiched between them. Note that the bulging shape of the third groove bottom 83 is shown by a dashed line in Figures 1 to 3. Although not explained here, the inner surface of the discharge groove 4B also has a first groove bottom 81, a second groove bottom 82, and a third groove bottom 83, similar to the inner surface of the discharge groove 4A.

[0023] As shown in Figure 4, back reliefs 32 are provided between adjacent leading edges 33 in the circumferential direction. The back reliefs 32 have a smaller diameter than the drill diameter D. The back reliefs 32 reduce frictional resistance caused by contact between the inner surface of the machined hole and the outer circumferential surface 31 of the body 3 when forming the machined hole, thereby suppressing heat generation and machining torque.

[0024] As shown in Figure 4, two relief surfaces 6A and 6B are provided at the tip of the body 3. The two relief surfaces 6A and 6B are positioned symmetrically with respect to the center P. The relief surfaces 6A and 6B and the discharge grooves 4A and 4B are arranged alternately in the circumferential direction. Specifically, from upstream to downstream in the rotation direction T, they are arranged in the order of relief surface 6A, discharge groove 4A, relief surface 6B, and discharge groove 4B. Each of the relief surfaces 6A and 6B is provided with a second relief surface 62 and a third relief surface 63. The second relief surface 62 is positioned adjacent to either the discharge groove 4A or 4B. The third relief surface 63 is positioned upstream of the second relief surface 62 in the rotation direction.

[0025] A cutting edge 5A is provided at the ridge where the first inner surface 41 of the discharge groove 4A and the second relief surface 62 of the relief surface 6A intersect. A cutting edge 5B is provided at the ridge where the first inner surface 41 of the discharge groove 4B and the second relief surface 62 of the relief surface 6B intersect. Cutting edges 5A and 5B are straight cutting edges.

[0026] The cutting edge 5A extends linearly from the leading edge 33 toward the center P. A curved portion 51 is provided on the radially inner portion of the cutting edge 5A. The curved portion 51 curves in an arc toward the rotational direction T as it moves from the straight portion of the cutting edge 5A toward the center P. The cutting edge 5A cuts the workpiece. The first inner surface 41 near the cutting edge 5A is the rake face. The rake face scoops up the chips cut by the cutting edge 5A. Note that the cutting edge 5B has the same shape as the cutting edge 5A, so its description is omitted.

[0027] As shown in Figure 4, a chisel 9 is formed at the center P. A thinning blade 7 extends linearly from the inner end 52 of the curved portion 51 of the cutting edge 5A toward the center P. The two thinning blades 7, 7 are formed symmetrically with respect to the center P. The two thinning blades 7, 7 are X-thinning. The thinning blades 7, 7 thin the chisel 9. Since the X-thinning is linear, it is easy to process in grinding and regrinding using an automated machine (not shown). X-thinning reduces thrust resistance during workpiece cutting and improves grip, so improved accuracy of the machined hole can be expected.

[0028] Referring to Figure 4, the linear core thickness S of the drill 1 will be explained. At the tip of the drill 1 having the shape described above, the linear core thickness S is 0 to 0.100D. The linear core thickness S is the perpendicular distance between the corner portion 55 of the cutting edge 5A and the corner portion 55 of the cutting edge 5B.

[0029] In this embodiment, the linear core thickness S of the drill 1 is adjusted to within the above numerical range. As a result, the radial rake angles of the cutting edges 5A and 5B are formed in the positive direction. The radial rake angle in this embodiment is, for example, 0 to -5.7°. In this way, the drill 1 can avoid having an acute radial rake angle, thereby mitigating stress concentration at the corner portions 55 of the cutting edges 5A and 5B. Furthermore, since the radial rake angle is not a large negative angle, the drill 1 can ensure good cutting performance at the corner portions 55 of the cutting edges 5A and 5B. In addition, because the cutting performance of the corner portions 55 is improved, the drill 1 can suppress the occurrence of Poisson burrs. Moreover, since the cutting edges 5A and 5B have a simple linear shape, regrinding is easy.

[0030] Referring to Figure 5, the relationship between the linear core thickness S and the groove bottom shape of the discharge grooves 4A and 4B will be explained. In conventional methods, to reduce the linear core thickness, the groove bottom of the discharge groove is deepened to bring the linear cutting edge closer to the centerline. To deepen the groove bottom of the discharge groove, it is necessary to reduce the diameter of the core thickness portion 10. Deepening the groove bottom of the discharge groove widens the chip pocket of the discharge groove. However, since the diameter of the core thickness portion 10 becomes smaller, the rigidity and strength of the drill 1 are weakened.

[0031] On the other hand, increasing the linear core thickness increases the diameter of the core thickness portion 10, thereby improving the rigidity and strength of the drill 1. However, increasing the linear core thickness results in a negative radial rake angle at the corner of the cutting edge. In this case, thrust resistance increases. Also, the chip pocket of the discharge groove becomes narrower, reducing chip discharge performance. Therefore, in order to solve these problems, in this embodiment, it is important to keep the linear core thickness S small while ensuring a sufficient diameter of the core thickness portion 10.

[0032] As shown in Figure 5, in this embodiment, a first groove bottom 81 and a second groove bottom 82 are arranged on both sides of the core thickness 10 in the rotational direction T on the inner surfaces of the discharge grooves 4A and 4B. Furthermore, the first groove bottom 81 and the second groove bottom 82 are connected by a third groove bottom 83 on the outer circumference of the core thickness 10. This allows the drill 1 to bring the cutting edges 5A and 5B closer to the centerline A2, thereby reducing the linear core thickness S. Furthermore, the drill 1 can secure the diameter of the core thickness 10, thus ensuring the rigidity and strength of the drill 1. In addition, since the drill 1 is equipped with a first groove bottom 81 and a second groove bottom 82 on the inner surfaces of the discharge grooves 4A and 4B, the respective chip pockets can be made wider. Therefore, the drill 1 can improve the chip discharge performance in the discharge grooves 4A and 4B.

[0033] Next, a machining test was conducted to confirm the effect of limiting the linear core thickness. In this test, five types of drills with linear cutting edges, each with a linear core thickness that differed from one another, were prepared. The linear core thicknesses were 0 mm, 0.2 mm, 0.8 mm, 1.25 mm, and 2 mm. As a comparative example, a drill with an S-shaped hook cutting edge was also prepared. In this test, holes were drilled in the workpiece with each linear core thickness drill, and the torque and thrust resistance applied to the drill during machining were measured. The drilling was done to create blind holes. The drilling was performed twice, and the average value was calculated. The machining conditions were as follows: ・Drill diameter = φ12.5 mm ・Workpiece = S53C ・Cutting speed = 70 m / min ・Feed rate = 0.25 mm / rev ・Machining depth: 20 mm blind ・Cutting fluid: Water-soluble cutting fluid

[0034] Referring to Figure 6, the torque results are explained below. The average torque for the first hole of the hook-type drill was 1023 (Ncm), and the average torque for the second hole was 1033 (Ncm). For the drill with a straight core thickness of 0 mm, the average torque for the first hole was 944 (Ncm), and the average torque for the second hole was 947 (Ncm). For the drill with a straight core thickness of 0.2 mm, the average torque for the first hole was 944 (Ncm), and the average torque for the second hole was 947 (Ncm). For the drill with a straight core thickness of 0.8 mm, the average torque for the first hole was 1024 (Ncm), and the average torque for the second hole was 1006 (Ncm).

[0035] For a drill with a straight core thickness of 1.25 mm, the average torque for the first hole was 1037 (Ncm), and the average torque for the second hole was 1011 (Ncm). For a drill with a straight core thickness of 2.0 mm, the average torque for the first hole was 1114 (Ncm), and the average torque for the second hole was 1114 (Ncm).

[0036] Considering these results, the average torque was lower than the average torque of the hook-type drill for four types of drills with linear core thicknesses of 0 mm, 0.2 mm, 0.8 mm, and 1.25 mm. Within the range of linear core thickness from 0 to 1.25 mm, the average torque was reduced compared to the hook-type drill. The average torque for a linear core thickness of 2 mm was higher than the average torque of the hook-type drill. From these results, since the drill diameter D is 12.5 mm, it was found that the torque was reduced compared to the hook-type drill within the range of linear core thickness from 0 to 0.100 D.

[0037] The thrust resistance results will be explained with reference to Figures 7 and 8. As shown in Figure 7, the average thrust resistance of the first hole drilled with a hook bit was 1810 (N), and the average thrust resistance of the second hole was 1832 (N). The average of these two measurements is 1821 (N). The average of the two thrust resistance measurements is shown by a dotted line in Figures 7 and 8. Hereafter, the average thrust resistance will be referred to as the "average thrust value."

[0038] For a drill with a straight core thickness of 0 mm, the average thrust value for the first hole was 1429 (N), and for the second hole, it was 1425 (N). For a drill with a straight core thickness of 0.2 mm, the average thrust value for the first hole was 1429 (N), and for the second hole, it was 1425 (N). For a drill with a straight core thickness of 0.8 mm, the average thrust value for the first hole was 1589 (N), and for the second hole, it was 1545 (N).

[0039] For a drill with a straight core thickness of 1.25 mm, the average thrust value for the first hole was 1690 N, and for the second hole, it was 1626 N. For a drill with a straight core thickness of 2 mm, the average thrust value for the first hole was 2272 N, and for the second hole, it was 2254 N.

[0040] Considering these results, the average thrust value was lower than that of the hook-cut drill for four types of drills with linear core thicknesses of 0 mm, 0.2 mm, 0.8 mm, and 1.25 mm. Within the range of linear core thickness from 0 to 1.25 mm, the average thrust value was reduced compared to the hook-cut drill. The average thrust value for a linear core thickness of 2 mm was higher than that of the hook-cut drill. From these results, since the drill diameter D is 12.5 mm, it was found that the thrust resistance was reduced compared to the hook-cut drill within the range of linear core thickness from 0 to 0.100 D.

[0041] Based on the analysis of the above test results, it has been demonstrated that by setting the linear core thickness within the range of 0 to 0.100D, the torque and thrust resistance generated during workpiece cutting can be reduced compared to a hook blade.

[0042] In the above description, cutting edge 5A is an example of the "first cutting edge" of the present invention. Cutting edge 5B is an example of the "second cutting edge" of the present invention. Discharge groove 4A is an example of the "first discharge groove" of the present invention. Discharge groove 4B is an example of the "second discharge groove" of the present invention. Relief surface 6A is an example of the "first relief surface" of the present invention. Relief surface 6B is an example of the "second relief surface" of the present invention.

[0043] As described above, the drill 1 of this embodiment comprises a body 3, discharge grooves 4A and 4B, and cutting edges 5A and 5B. The body 3 is a round bar shape with a predetermined core thickness 10 and a conical tip having a predetermined tip angle θ. The discharge grooves 4A and 4B are provided on the outer circumferential surface of the body 3 and extend spirally from the tip to the rear end of the body 3. The cutting edge 5A is formed on the ridge between the first inner surface 41 of the discharge groove 4A and the relief surface 6A. The cutting edge 5B is formed on the ridge between the first inner surface 41 of the discharge groove 4B and the relief surface 6B. The first inner surface 41 is the surface of each of the inner surfaces of the discharge grooves 4A and 4B that faces the rotation direction T of the body 3.

[0044] When the diameter of the body 3 is D, the straight web thickness S is 0 to 0.100D. The straight web thickness S is the dimension of the interval in the right-angle direction between the corner portion 55 of the cutting edge 5A and the corner portion 55 of the cutting edge 5B. When the body 3 is viewed from the tip side, a first groove bottom 81 and a second groove bottom 82 are provided on the inner surfaces of the discharge grooves 4A and 4B, respectively. The first groove bottom 81 having a curved shape is provided on the first inner surface 41. The first groove bottom 81 having a curved shape is provided on the second inner surface 42. The second inner surface 42 is the inner surface facing the direction opposite to the rotation direction T among the inner surfaces of the discharge grooves 4A and 4B, respectively.

[0045] Since the cutting edges 5A and 5B are linear, the drill 1 can relieve the stress concentration applied to the corner portions 55 of the cutting edges 5A and 5B as compared with a hook-shaped cutting edge. Further, the straight web thickness S is limited to 0 to 0.100D. Thereby, the drill 1 can form the radial rake angle of the corner portion 55 of the cutting edge 5A and the radial rake angle of the corner portion 55 of the cutting edge 5B in the positive direction. Thereby, the drill 1 can improve the sharpness of the corner portion 55 as compared with when the radial rake angle is formed at a large negative angle. Since the cutting edge is linear and simple, the regrinding of the cutting edge is easy.

[0046] Note that the present invention is not limited to the above-described embodiment, and various modifications are possible. The drill 1 has two cutting edges, but may have three or more cutting edges. The relief 32 provided on the outer peripheral surface 31 of the body 3 may be omitted. A coolant passage may be provided in the flank surfaces 6A and 6B. Further, the flank surfaces 6A and 6B include a second flank surface 62 and a third flank surface 63, but the number of flank surfaces may be more or less than this. The thinning blades 7 and 7 may be omitted. The thinning blades 7 and 7 are X-thinning, but may be thinning of other shapes, for example, R-thinning, S-thinning, N-thinning, XR-thinning, or the like.

Claims

1. A round bar-shaped body having a predetermined core thickness and a conical tip; a discharge groove provided on the outer circumferential surface of the body and extending spirally from the tip toward the rear end of the body; a linear cutting edge formed on the ridge between the first inner surface of the discharge groove facing the rotation direction of the body and the relief surface at the tip; the discharge groove is a plurality of discharge grooves including a first discharge groove and a second discharge groove; the relief surface is a plurality of relief surfaces including a first relief surface adjacent to the first discharge groove and a second relief surface adjacent to the second discharge groove; the cutting edge is a plurality of cutting edges including a first cutting edge formed on the ridge between the first inner surface of the first discharge groove and the first relief surface and a second cutting edge formed on the ridge between the first inner surface of the second discharge groove and the second relief surface; when the diameter of the body is D, the linear core thickness, which is the distance between the corner of the first cutting edge and the corner of the second cutting edge in the perpendicular direction, is 0 to 0.100D. A drill characterized in that, when the body is viewed from the tip side, the inner surfaces of the first discharge groove and the second discharge groove are provided with a curved first groove bottom on the first inner surface and a curved second groove bottom on the second inner surface facing the opposite direction to the rotation direction.

2. The drill according to claim 1, characterized in that a third groove bottom is provided in the inner surface of the first discharge groove and the second discharge groove, between the bottom of the first groove and the bottom of the second groove, in the portion that contacts the core thickness, and which curves radially outward along the curved outer circumference of the core thickness.

3. The drill according to claim 1 or 2, characterized in that it is provided with a thinning blade on the tip of the body, extending from the inner ends of the first cutting edge and the second cutting edge toward the center of the tip of the body.

4. The drill according to claim 3, characterized in that the thinning blade is a straight X-thinning blade.

Images