drill bit

Abstract

A drill bit main body of a drill bit (1) is rotated about an axis. A plurality of discharge grooves (4) are provided on an outer peripheral surface (31) of the drill bit main body in a spiral shape from a front end portion toward a base end portion. A cutting edge (5) is formed on a ridge line portion between an inner surface of the discharge groove (4) on a rotation direction side of the drill bit main body and a relief surface of the drill bit main body at the front end portion. A dressing edge (7) is provided on the front end portion of the drill bit main body and extends from an inner end of the cutting edge (5) toward a chisel edge (9) which is a front end portion of the drill bit main body. A dressing surface (71) is a rake surface of the dressing edge (7) and connects the dressing edge (7) and the discharge groove (4). A recessed portion (8) is connected to the dressing surface (71), a ridge line between the recessed portion (8) and the relief surface extends in an arc shape from the inner end of the dressing edge (7) and is connected to the discharge groove (4). The recessed portion (8) is connected to the discharge groove (4) while being twisted in a spiral angle along the discharge groove (4).

Description

Technical Field

[0001] This invention relates to a drill bit. Background Technology

[0002] Conventionally, drill bits with a regrinding edge and an R-notch formed at the front end of the drill bit body are known (see, for example, Patent Document 1). The regrinding edge is formed on the inner end side of the cutting edge by regrinding the front end of the drill bit. The ridge line between the R-notch and the flank face extends in an arc shape from the inner end side of the regrinding edge toward the outer peripheral surface of the drill bit. A discharge groove is provided on the outer peripheral surface of the drill bit body. The discharge groove is spirally arranged from the front end of the drill bit body toward the base end.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-59999 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In the aforementioned drill bit, a corner is formed at the portion where the R-notch connects to the discharge groove. For example, when machining aluminum alloys, which are relatively light and soft, small and short chips are easily generated when cutting with the drill bit. In this case, the chips may get stuck in the corner of the drill bit, potentially reducing chip discharge performance.

[0008] The purpose of this invention is to provide a drill bit that can improve chip removal performance.

[0009] Solution for solving the problem

[0010] A drill bit according to one embodiment of the present invention is characterized in that it comprises: a drill bit body that rotates about an axis; a plurality of discharge grooves that are spirally arranged on the outer peripheral surface from the front end of the drill bit body toward the base end; a cutting edge formed on the inner surface of the discharge groove on the rotational direction side toward the drill bit body and the flank face of the drill bit body at the front end; a shaving edge provided at the front end of the drill bit body and extending from the inner end of the cutting edge toward the transverse cutting edge that is the front end portion of the drill bit body; a shaving surface that is the rake face of the shaving edge and connects the shaving edge to the discharge groove; and a notch connected to the shaving surface, wherein the ridge between the notch and the flank face extends in an arc shape from the inner end of the shaving edge and connects to the discharge groove, and the notch is connected to the discharge groove while being twisted along the helical angle of the discharge groove.

[0011] In this drill bit, the notch is twisted along the helix angle of the discharge groove while connecting to it, thus ensuring a smooth connection between the notch and the discharge groove. This improves the chip removal performance of the drill bit.

[0012] In the drill bit of this technical solution, the recessed portion may connect to the discharge groove while twisting in the opposite direction to the rotation direction as it moves from the front end side to the base end side. This allows the drill bit to smoothly connect the recessed portion to the discharge groove, enabling the smooth discharge of chips without clogging the chips.

[0013] In the drill bit of this technical solution, the helix angle of the notch may be within the range of 0° to -6°, based on the helix angle of the discharge groove. The drill bit ensures smooth connection between the notch and the discharge groove, allowing for smooth chip discharge without clogging.

[0014] In the drill bit of this technical solution, when the drill bit diameter is set to D, the length of the recessed portion in the axial direction of the drill bit is within the range of 0.5D to 1.4D. This allows the drill bit to maintain rigidity and improve chip removal performance.

[0015] In the drill bit of this technical solution, the notch may extend in an arc shape from the inner end of the shaving edge toward the radially outer side of the drill bit body and connect with the outer peripheral surface of the drill bit body. By connecting the notch to the outer peripheral surface of the drill bit body, the notch can be enlarged.

[0016] In the drill bit of this technical solution, a back removal portion may be provided on the outer peripheral surface. The recessed portion extends in an arc shape from the inner end of the shaving edge toward the radially outer side of the drill bit body and connects with the back removal portion. The drill bit uses the back removal portion to reduce the frictional resistance between itself and the material being cut, and by connecting the recessed portion to the back removal portion of the drill bit body, the recessed portion can be enlarged.

[0017] In the drill bit of this technical solution, the drill bit may also have three cutting edges. A drill bit with three cutting edges can achieve the same effect as the drill bit of the above-described technical solution.

[0018] In the drill bit of this technical solution, at least the surface of the front end of the drill bit body may be covered with DLC. This improves the weld resistance of the front end of the drill bit body.

[0019] In this technical solution, the drill bit can also be a drill bit used for cutting aluminum alloys. Because aluminum alloys are light and soft, small and short chips are easily generated when cutting with a drill bit. The drill bit can prevent chips from clogging at the connection between the recess and the discharge groove, thus enabling efficient cutting of aluminum alloys. Attached Figure Description

[0020] Figure 1 This is a side view of drill bit 1.

[0021] Figure 2 This is a 3D view of drill bit 1.

[0022] Figure 3 This is the front view of drill bit 1.

[0023] Figure 4 This is a table showing the results of Experiment 1.

[0024] Figure 5 This is a table showing the results of experiment 2.

[0025] Figure 6 This is a graph representing the results of Experiment 3.

[0026] Figure 7 This is a graph representing the results of Experiment 4. Detailed Implementation

[0027] Embodiments of the present invention will be described. The present invention is not limited to the embodiments described below, and design changes can be made as appropriate. For clarity, portions are appropriately shown in the drawings at scales different from actual dimensions. The present invention is not limited to its shape.

[0028] Reference Figures 1-3 Explain the structure of drill bit 1. For example... Figure 1 , Figure 2 As shown, drill bit 1 has three cutting edges, for example, used for cutting aluminum alloys. Drill bit 1 is formed of hard materials such as cemented carbide or high-speed tool steel (high-speed steel). Drill bit 1 has a shank 2 and a body 3. Shank 2 and body 3 are an example of the "drill bit body" of the present invention. Shank 2 is the part mounted on the spindle of a machine tool and is the rear end side of drill bit 1. Body 3 extends from the front end of shank 2 along the axis AX.

[0029] Three discharge grooves 4 with predetermined helix angles θ are spirally formed on the outer peripheral surface 31 of the main body 3. The helix angle θ can be appropriately changed. The discharge grooves 4 discharge chips. The discharge grooves 4 open at the front end of the main body 3, and a cutting edge 5 is formed in the opening portion. The drill bit 1 rotates around the axis AX, thereby cutting the workpiece material (not shown) using the cutting edge 5, and forming a machined hole while discharging chips using the discharge grooves 4. The rotation direction T of the drill bit 1 during machining is counterclockwise in the main view (see reference). Figure 3 The machine tool (illustration omitted) cuts the material by rotating the spindle on which the drill bit 1 is mounted to the right.

[0030] An inner surface 41 is provided in the discharge groove 4. The cutting edge 5 is formed at the ridge portion where the flank face 6 intersects with the inner surface 41 facing the rotation direction T. The cutting edge 5 is approximately S-shaped in the front view. The inner surface 41 on the side of the inner surface 41 closest to the cutting edge 5 is the rake face, which picks up the chips cut by the cutting edge 5 and directs them to the discharge groove 4.

[0031] The portion of the inner surface 41 on the side facing the cutting edge 5 that intersects with the outer peripheral surface 31 of the main body 3 is the leading edge 33. In the outer peripheral surface 31, adjacent leading edges 33 in the circumferential direction are provided with back removal portions 32. The back removal portions 32 are formed radially inward from the outer peripheral surface 31, and their diameter is smaller than the drill diameter D. The drill diameter D can be appropriately varied. Using the back removal portions 32, the drill 1 reduces the frictional resistance generated when forming the machined hole due to the contact between the inner surface of the machined hole and the outer peripheral surface 31 of the main body 3, thus suppressing heat generation and machining torque. The portion of the inner surface 41 on the side opposite to the cutting edge 5 that intersects with the back removal portion 32 is the heel portion 34.

[0032] A chisel edge 9 is provided at the center of the front end of the drill bit 1. The front end of the drill bit 1 is then regrinded. Regrinding is a process used to thin the core thickness near the chisel edge 9. For example, the regrinding process involves rotating a grinding wheel while cutting from the inner end 51 of the cutting edge 5 towards the chisel edge 9 into the opening of the discharge groove 4, forming a regrinding edge 7. The inner end 51 of the cutting edge 5 is the inner end on the axial side. The regrinding edge 7 extends in an arc shape from the inner end 51 towards the chisel edge 9 in the main view. By forming the regrinding edge 7, a regrinding surface 71 is formed at the front end of the drill bit 1. The regrinding surface 71 is the rake face of the regrinding edge 7 facing the rotation direction T.

[0033] During the regrinding process, after forming the regrinding edge 7, the grinding wheel is moved relative to the drill bit 1 towards the heel 34 side to further cut in, forming a recess 8. The recess 8 has a recessed surface 81. The recessed surface 81 is a curved surface that is concave inwards. The length of the recess 8 in the axial direction AX of the drill bit 1 is L (refer to...). Figure 1 As an example, the length L of the notch 8 is machined within the range of 0.5D to 1.4D based on its relationship with the drill diameter D. The ridge line intersecting the notch surface 81 and the flank face 6 extends in an arc shape from the inner end 72 of the sharpening edge 7 toward the outer peripheral surface 31 and connects to the back removal part 32. The inner end 72 of the sharpening edge 7 is the inner end on the axial side. Since the notch 8 is connected to the back removal part 32 of the main body 3, a larger chip groove capacity can be ensured. The chip groove is a space for collecting chips cut using the sharpening edge 7. As a result, the drill 1 can smoothly deliver chips without clogging the discharge groove 4.

[0034] An arcuate groove 10 is formed at the junction of the recessed surface 81 and the grinding surface 71. The arcuate groove 10 extends straight from near the chisel edge 9 toward the discharge groove 4, and its cross-section in the direction of extension is arcuate. The arcuate groove 10 can smoothly push the chips cut by the grinding edge 7 and picked up by the grinding surface 71 toward the recessed portion 8. As a result, the drill bit 1 can reduce cutting resistance and obtain a stable chip shape.

[0035] The recess 8 connects to the discharge groove 4 while twisting in the opposite direction to the rotation direction T, moving from the front end side to the base end side. As an example, the recess 8 is machined to twist within a range of 0° to -6° relative to the helix angle θ of the discharge groove 4. Thus, the recess 8 connects smoothly to the discharge groove 4.

[0036] When machining the workpiece, the grinding edge 7 near the chisel edge 9 cuts into the workpiece, generating chips. The chips are picked up by the grinding surface 71 and pushed out towards the recess 8 via the arc groove 10. The chips are bent and curled by the recess surface 81 and cut by the leading edge 33, then discharged into the discharge groove 4. The recess 8 of this application smoothly connects to the discharge groove 4. Thus, the recess 8 can smoothly discharge chips into the discharge groove 4.

[0037] Three coolant passages 11 extend spirally from the rear end of the shank 2 to the front end of the body 3 within the drill bit 1 along the discharge groove 4 (see reference). Figure 3 Each coolant passage 11 opens at the recess 8, forming an oil hole 12. During machining, cutting oil is supplied into the coolant passage 11 and sprayed from the oil hole 12 toward the machining position of the material being cut. As a result, the drill bit 1 reduces cutting resistance and suppresses heat generation and machining torque. The chips and cutting oil flow together in the discharge groove 4 and are smoothly discharged.

[0038] The flank face 6 is a surface that avoids contact with the machined surface of the workpiece. Facing the direction opposite to rotation T, the flank face 6 sequentially comprises a second flank face 42, a third flank face 43, and a fourth flank face 44. The second flank face 42 is located at the foremost point in the direction of rotation T, extending from the chisel edge 9 to the outer peripheral surface 31. The third flank face 43 bends towards the rear end from approximately the radial center of the edge line on the side of the second flank face 42 opposite to the cutting edge 5. The third flank face 43 extends in the direction opposite to rotation T, tapering towards the foremost point. The fourth flank face 44 bends towards the rear end from the edge line on the side of the third flank face 43 opposite to the side of the second flank face 42. The fourth flank face 44 extends in the direction opposite to rotation T, tapering towards the foremost point. The leading edge of the fourth flank face 44 is a heel portion 34.

[0039] In the drill bit 1 having the above-described structure, it is preferable that at least the front end surface of the body 3 is covered with DLC (Diamond-Like Carbon). DLC is a general term for thin films made of carbon, which has carbon-carbon bonds of both diamond and graphite (black lead), as the main component. As a result, the drill bit 1 can improve the weld resistance of the front end of the body 3.

[0040] Reference Figure 4 Test 1, used to evaluate chip removal performance, describes the chip removal performance of drill bit 1 when the helix angle of the notch 8 was changed. The helix angle of the notch 8 was adjusted within a range of 3° to -8°, based on the helix angle θ of the discharge groove 4, and nine helix angles were verified. The helix angle of drill bit 1 was 3° for No. 1, 2° for No. 2, 1° for No. 3, 0° for No. 4, -2° for No. 5, -4° for No. 6, -5° for No. 7, -6° for No. 8, and -8° for No. 9. The drill diameter D of drill bit 1 was set to φ12.0. Furthermore, in drill bits 1 of No.1 to No.3, when the recess 8 is formed, the recess 8 and the bottom of the groove of the drill bit 1 interfere with each other, making it impossible to achieve the desired shape of the drill bit 1.

[0041] In the machining conditions of Experiment 1, the cutting speed was set to 377 m / min, and the spindle speed was set to 10000 rpm. -1The feed rate is set to 10000 mm / min. The feed rate per revolution of drill bit 1 is set to 1 mm / rev. The machining method is set to non-step machining. The machining depth of the workpiece is set to 90 mm. The workpiece material used is AC4C aluminum alloy casting.

[0042] Drill bits No. 1 through No. 3 failed to achieve the desired cutting performance; therefore, chip removal performance was not verified. Therefore, drill bits No. 4 through No. 9 were used to cut the workpiece, and chip removal performance was verified. The verification results were judged on three levels: 0, △, and ×. 0 indicates no chip clogging. △ indicates that cutting is possible despite chip clogging. × indicates that cutting is impossible due to significant chip clogging.

[0043] Drill bits No. 1 through No. 3 were not verified and therefore cannot be judged. Drill bits No. 4 through No. 7 can cut without causing chip clogging. Therefore, the judgment result is 0. Drill bit No. 8 caused slight chip clogging but can cut without problems. Therefore, the judgment result is △. Drill bit No. 9 caused chip clogging and cannot cut. Therefore, the judgment result is ×.

[0044] Based on the above test results, the following has been confirmed: Preferably, the helix angle of the recess 8 is within the range of 0° to -6°, with the helix angle θ of the discharge groove 4 as the reference.

[0045] Reference Figure 5 Test 2 describes the chip removal performance used to evaluate the chip removal performance. In Test 2, the chip removal performance was verified by varying the length L of the notch 8. For Test 2, eight drill bits 1, No. 1 to No. 8, with different lengths L of the notch 8, were prepared. The length L of the notch 8 was varied between 0.4D and 1.5D based on its relationship with the drill bit diameter D. The length L of the notch 8 was 0.4D for No. 1, 0.5D for No. 2, 0.6D for No. 3, 0.8D for No. 4, 1D for No. 5, 1.2D for No. 6, 1.4D for No. 7, and 1.5D for No. 8. The eight drill bits 1 are identical in that the helix angle of the recess 8 is set to -2°, for example, based on the helix angle θ of the discharge groove 4. Furthermore, other processing conditions are set to the same conditions as in Experiment 1.

[0046] Using drill bits No. 1 through No. 8, the workpiece was cut, and the chip removal performance was verified. The verification results of the chip removal performance were judged according to three levels: 0, △, and ×. 0 indicates no chip clogging. △ indicates minimal chip clogging but still allowing cutting. × indicates significant chip clogging preventing cutting.

[0047] Drill bit 1 (No. 1) produces a large amount of chip clogging and cannot cut. Therefore, the judgment result is ×. Drill bits 1 (No. 2 and No. 3) produce some chip clogging, but can cut without problems. Therefore, the judgment result is △. Drill bits 1 (No. 4 to No. 6) can cut without producing chip clogging. Therefore, the judgment result is 0. Drill bit 1 (No. 7) produces chatter, but the material being cut is not clogged, and it can cut. Therefore, the judgment result is △. Drill bit 1 (No. 8) is damaged. Therefore, the judgment result is ×.

[0048] Based on the above test results, the following has been confirmed: Preferably, when the drill bit diameter is set to D, the length L of the recess 8 in the AX direction of the drill bit 1 is in the range of 0.5D to 1.4D.

[0049] Reference Figure 6 , Figure 7 Tests 3 and 4, used to evaluate the durability of drill bit 1, are described below. In Test 3, the maximum thrust resistance (N) when machining the workpiece using the drill bit 1 of the present invention is measured and compared with that of a conventional drill bit. Thrust resistance is the cutting resistance applied in the direction opposite to the travel direction of drill bit 1. The cutting resistance generated in the vertical direction relative to the cutting edge 5 of drill bit 1, and the thrust resistance is the cutting resistance borne in the axial direction. In Test 4, the maximum cutting torque (N) when machining the workpiece using the drill bit 1 of the present invention is measured and compared with that of a conventional drill bit. Furthermore, conventional drill bits have a corner between the concave surface and the chute.

[0050] In experiments 3 and 4, the drill diameter D of drill bit 1 was set to φ9.8. The helix angle of the notch 8 of drill bit 1 was set to -2° based on the helix angle θ of the discharge groove 4. The length L of the notch 8 was set to 1D. The machining depth of the workpiece was set to 50mm. The cutting speed was set to 298m / min. The spindle speed was set to 9700 rpm. -1 The feed rate is set to 8730 mm / min. The feed rate per revolution of drill bit 1 is set to 0.9 mm / rev. The workpiece material used is an ADC12 die-cast aluminum part.

[0051] like Figure 6As shown, the maximum thrust resistance of conventional drill bits is 1079 (N), while the maximum thrust resistance of drill bit 1 of the present invention is 985 (N). Therefore, it is demonstrated that drill bit 1 of the present invention can reduce the maximum thrust resistance applied during machining compared to conventional drill bits.

[0052] like Figure 7 As shown, the maximum torque of a conventional drill bit is 695 (N·m), while the maximum torque of the drill bit 1 of the present invention is 664 (N·m). Therefore, it is demonstrated that the drill bit 1 of the present invention can reduce the maximum torque applied during machining compared to conventional drill bits.

[0053] As described above, the drill bit 1 of this embodiment includes a main body 3, multiple discharge grooves 4, a cutting edge 5, a regrinding edge 7, and a recess 8. The main body 3 rotates about an axis AX. The multiple discharge grooves 4 are spirally arranged on the outer peripheral surface 31 from the front end of the main body 3 toward the base end. The cutting edge 5 is formed on the ridge portion between the inner surface of the discharge groove 4 on the rotation direction T side toward the main body 3 and the flank face 6 of the main body 3 at the front end. The regrinding edge 7 is provided at the front end of the main body 3 and extends from the inner end of the cutting edge 5 toward the chisel edge 9, which is the front end portion of the main body 3. The regrinding surface 71 is the rake face of the regrinding edge 7, connecting the regrinding edge 7 to the discharge grooves 4. The recess 8 is connected to the regrinding surface 71, and the ridge between the recess 8 and the flank face 6 extends in an arc shape from the inner end of the regrinding edge 7 and connects to the discharge grooves 4. The recess 8 is connected to the discharge grooves 4 while being twisted along the helix angle θ of the discharge grooves 4.

[0054] In drill bit 1, the notch 8 is connected to the discharge groove 4 while being twisted along the helix angle θ of the discharge groove 4, thereby enabling a smooth connection between the notch 8 and the discharge groove 4. As a result, drill bit 1 can improve chip removal performance.

[0055] The recess 8 connects to the discharge groove 4 while being twisted in the opposite direction to the rotation direction T as it moves from the front end side to the base end side. The drill bit 1 enables the portion where the recess 8 connects to the discharge groove 4 to flow smoothly, allowing the chips to be discharged smoothly without clogging the chips.

[0056] The helix angle of the recess 8 is within the range of 0° to -6°, based on the helix angle θ of the discharge groove 4. The drill bit 1 ensures smooth connection between the recess 8 and the discharge groove 4, allowing for smooth chip discharge without clogging.

[0057] When the drill bit diameter is set to D, the length L of the notch 8 in the axial direction of the drill bit 1 is in the range of 0.5D to 1.4D. The drill bit 1 can maintain rigidity and improve chip removal performance.

[0058] The inner end of the recess 8 and the self-refining edge 7 extends in an arc shape and is connected to the back removal portion 32 of the outer peripheral surface 31 of the main body 3, which is radially inward. By connecting the recess 8 to the back removal portion 32 of the main body 3, the drill bit 1 can reduce the frictional resistance between itself and the workpiece and increase the size of the recess 8 by utilizing the back removal portion 32.

[0059] Drill bit 1 has three cutting edges 5. Among three-edge drill bits, drill bit 1 can improve chip removal performance.

[0060] The surface of at least the front end of the body 3 is covered with DLC. The drill bit 1 can improve the weld resistance of the front end of the body 3.

[0061] Drill bit 1 is used for cutting aluminum alloys. Because aluminum alloys are light and soft, small and short chips are easily produced when cutting with drill bit 1. Since drill bit 1 can prevent chips from clogging at the connection between the recess 8 and the discharge groove 4, it can effectively cut aluminum alloys.

[0062] Furthermore, the present invention is not limited to the above-described embodiments, and various modifications are possible. The drill bit 1 is used for machining soft materials such as aluminum alloys, but it can also be used for machining hard materials.

[0063] The material of drill bit 1 is not limited. At least the front surface of the main body 3 is covered with DLC, but DLC may also be covered on the outer peripheral surface 31. Alternatively, DLC may not be covered on the main body 3.

[0064] Drill bit 1 has three flutes, but it can also have two flutes, or even four or more flutes. Drill bit 1 can also be used as a so-called long drill bit.

[0065] The recessed portion 8 can also be formed using methods other than grinding. The recessed portion 8 can be arc-shaped, but it can also be straight. A grinding edge 7 may not be formed.

[0066] The coolant passage 11 extends spirally from the rear end of the handle 2 toward the front end of the body 3, but it may not be spiral; for example, it may be straight. Three arc grooves 10 are provided at the front end of the body 3, but the arc grooves 10 may be omitted.

[0067] The flank face 6 is composed of a second flank face 42, a third flank face 43, and a fourth flank face 44, but it is not limited to this, and the third flank face 43 and the fourth flank face 44 may not exist.

[0068] The back removal portion 32 located on the outer peripheral surface 31 of the drill bit 1 can also be omitted. In this case, the recessed portion 8 can be connected to the outer peripheral surface 31 of the main body 3.

Claims

1. A drill bit, characterized in that, This drill bit has the following features: The drill bit body rotates around its axis. Multiple discharge slots are spirally arranged on the outer peripheral surface from the front end of the drill bit body toward the base end; The cutting edge is formed on the inner surface of the discharge groove on the rotational side of the drill body and the flank face of the drill body at the front end. A sharpening edge is provided at the front end of the drill bit body and extends from the inner end of the cutting edge toward the transverse cutting edge, which is the front end portion of the drill bit body. The grinding surface is the rake face of the grinding blade, which connects the grinding blade to the discharge groove; as well as The notch connects to the grinding surface, and the ridge between the notch and the back face extends in an arc shape from the inner end of the grinding edge and connects to the discharge groove. A back removal portion is provided on the outer peripheral surface. The recessed portion is connected to the discharge groove while being twisted along the helical angle of the discharge groove. When the drill bit body is viewed from the side, the boundary line between the back removal portion and the recessed portion extends from the front end side toward the base end side, and is arc-shaped bulging on the front end side toward the back removal portion side and arc-shaped bulging on the base end side toward the recessed portion side.

2. The drill bit according to claim 1, characterized in that, The recessed portion connects to the discharge groove while twisting in the opposite direction to the rotation direction as it moves from the front end side to the base end side.

3. The drill bit according to claim 1, characterized in that, The helix angle of the recessed portion is within the range of 0° to -6°, based on the helix angle of the discharge groove.

4. The drill bit according to claim 1, characterized in that, When the drill bit diameter is set to D, the length of the notch in the axial direction of the drill bit is in the range of 0.5D to 1.4D.

5. The drill bit according to claim 1, characterized in that, The recessed portion extends in an arc shape from the inner end of the sharpening edge toward the radially outer side of the drill bit body and connects with the back removal portion.

6. The drill bit according to claim 1, characterized in that, The drill bit has three cutting edges.

7. The drill bit according to claim 1, characterized in that, The surface of at least the front end of the drill bit body is covered with diamond-like carbon.

8. The drill bit according to claim 1, characterized in that, The drill bit is used for cutting aluminum alloys.

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