Drill bit

Abstract

The utility model belongs to the technical field of cutters, and discloses a drill bit, which is characterized in that a supporting cutting edge is arranged, and alpha-gamma is larger than or equal to 0 degree and smaller than or equal to 1 degree, so that the supporting cutting edge can be in contact with a hole wall when an outer blade is used for drilling, the outer blade can be supported along the radial direction of a cutter bar, vibration during machining is reduced, and the quality of the hole wall is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of drill bits, in particular to a drill bit. Background Art

[0002] The drill bit has an inner blade and an outer blade, wherein the inner blade is closer to the central axis of the drill body than the outer blade, i.e., the inner blade and the outer blade are arranged asymmetrically. When the drill bit is working, the radial forces generated by the inner blade and the outer blade cannot be offset and balanced, resulting in a large radial resultant force in the radial direction, which makes the drill body easily vibrate under the action of the radial resultant force. Utility Model Content

[0003] The utility model aims to provide a drill bit, which can reduce the vibration of the drill bit when it is working and improve the processing quality of the hole wall.

[0004] To achieve this purpose, the utility model adopts the following technical solutions:

[0005] A drill bit, comprising a shank, one end of the shank being a cutting end, two blades being mounted on the cutting end of the shank, the two blades being an inner blade and an outer blade respectively, the inner blade being closer to the central axis of the shank than the outer blade, the blade comprising a blade body provided with a central hole penetrating along the Z direction, the blade body comprising a top surface and a bottom surface arranged oppositely along the Z direction, and four side surfaces connecting the top surface and the bottom surface, the four side surfaces being connected end to end along the circumference of the central hole and arranged oppositely in pairs, and each of the side surfaces being connected to the top surface to form a cutting edge;

[0006] The invention is characterized in that the cutting edge of the outer blade comprises a supporting cutting edge, an arc cutting edge and a main cutting edge, and the supporting cutting edge is smoothly connected with the main cutting edge through the arc cutting edge;

[0007] For the cutting edge of the outer blade that performs cutting, the projections of the supporting cutting edge and the main cutting edge on the first preset plane are the supporting projection and the main projection respectively, the first preset plane is parallel to the bottom surface of the outer blade and the central axis of the tool rod is located in the first preset plane; the supporting projection and the main projection are both straight lines and the included angle is α; the included angle between the supporting projection and the central axis of the tool rod is γ1, 0°≤α-γ1≤1°.

[0008] As an implementation scheme of the above drill bit, the length of the support projection along the axial direction of the arbor is L2, and L2 is less than 2 mm.

[0009] As an implementation scheme of the drill bit, the bottom surface of the outer blade and the bottom surface of the inner blade are located on opposite sides of the first preset plane, one end of the inner blade and the outer blade are located on the same side of a second preset plane, and the other end of the inner blade is located on the other side of the second preset plane; the second preset plane is perpendicular to the bottom surface of the outer blade and the central axis of the shank is located on the second preset plane;

[0010] Two adjacent cutting edges are smoothly connected by a rounded corner structure. For the outer blade, the projection of the rounded corner structure connected to the supporting cutting edge for cutting in the first preset plane is an outer rounded corner projection, and the length of the outer rounded corner projection along the axial direction of the tool bar is L1. The projection of the arc cutting edge in the first preset plane is a transition projection, and the length of the transition projection along the axial direction of the tool bar is L3.

[0011] The outer blade is rotated around the central axis of the blade rod so that the bottom surface of the outer blade is parallel to the bottom surface of the inner blade and the bottom surface of the outer blade and the bottom surface of the inner blade face the same direction to form a virtual blade, the projection of the cutting edge of the virtual blade in the third preset plane is the outer projection, and the projection of the cutting edge of the inner blade in the third preset plane is the inner projection; the third preset plane is parallel to the bottom surface of the inner blade;

[0012] The intersection point of the inner projection and the outer projection is point P. For the inner blade, the projection of the rounded corner structure of the cutting edge close to one end of the outer projection is the inner rounded corner projection. The endpoint of the inner rounded corner projection away from one end of the inner projection is point Q. The length between point P and point Q along the extension direction of the inner projection is L4, and L1+L2+L3≤L4.

[0013] As an implementation scheme of the above drill bit, for the inner blade, the angle between the line connecting the centers of the two rounded structures connected to the cutting edge and the center axis of the tool rod is γ2; 0°<γ2<γ1.

[0014] As a possible implementation scheme of the above drill bit, γ1<10°.

[0015] As an implementation scheme of the above drill bit, the angle between the bottom surface of the inner blade and the bottom surface of the outer blade is β, 4°≤β≤10°.

[0016] As an implementation scheme for the above-mentioned drill bit, the side surface includes a first back tool surface and a second back tool surface, the cutting edge is connected to one side of the first back tool surface, the other side of the first back tool surface is smoothly connected to the second back tool surface, the second back tool surface is connected to the bottom surface, and the second back tool surface is closer to the central axis of the center hole than the first back tool surface.

[0017] As an implementation scheme of the above drill, the length of the first flank along the axial direction of the center hole is H1, the length of the second flank along the axial direction of the center hole is H2, and 0.5 mm

[0018] As an implementation scheme of the above drill bit, the maximum length of the blade body along the axial direction of the center hole is H, and H2≥50%H.

[0019] As a possible implementation scheme for the above drill bit, H2≥2 / 3H.

[0020] Beneficial effects of the utility model: The drill bit provided by the utility model, by setting a supporting cutting edge and limiting 0°≤α3-α2≤1°, enables the supporting cutting edge to contact the hole wall when the outer blade is performing drilling processing, and can play a role in supporting the outer blade along the radial direction of the tool rod, reduce vibration during processing, and improve the quality of the hole wall. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of a drill bit provided by an embodiment of the utility model;

[0022] Figure 2 It is a schematic diagram of the structure of the outer blade provided by an embodiment of the utility model;

[0023] Figure 3 is a side view of a drill bit provided by an embodiment of the utility model;

[0024] Figure 4 It is a schematic projection diagram of the cutting edge of the outer blade provided by an embodiment of the utility model within a first preset plane;

[0025] Figure 5 It is an axial schematic diagram of a drill bit provided by an embodiment of the utility model;

[0026] Figure 6 It is a schematic diagram of the inner blade and the outer blade provided by the embodiment of the utility model in a third preset plane;

[0027] Figure 7 It is a side view of the outer blade provided by the embodiment of the utility model.

[0028] In the figure:

[0029] 100, tool bar; 200, inner blade; 300, outer blade; 400, virtual blade;

[0030] ​1. Blade body; 11. Center hole; 12. Bottom surface; 13. Side surface; 131. First flank surface; 132. Second flank surface; 14. Cutting edge; 141. Support projection; 142. Main projection; 143. Outer fillet projection; 144. Transition projection; 145. Inner fillet projection; 15. Inner projection;

[0031] 10. First preset plane; 20. Second preset plane; 30. Third preset plane. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only the parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0033] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] In the present utility model, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0035] In the description of this embodiment, the terms "upper", "lower", "right", etc., are based on the directions or positions shown in the drawings, and are only for the convenience of description and simplified operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0036] like Figure 1 and Figure 2As shown, an embodiment of the utility model provides a drill bit, including a tool rod 100, and two blades installed on the same end of the tool rod 100, the two blades are an inner blade 200 and an outer blade 300, and along the radial direction of the tool rod 100, the inner blade 200 is closer to the central axis of the tool rod 100 than the outer blade 300.

[0037] The blade includes a blade body 1 having a central hole 11 extending through the blade body 1 in the Z direction, and the blade body 1 includes a top surface and a bottom surface 12 arranged opposite to each other in the Z direction, and four side surfaces 13 arranged opposite to each other in pairs and connected end to end. Specifically, two side surfaces 13 are arranged opposite to each other in pairs in the X direction, and the other two side surfaces 13 are arranged opposite to each other in pairs in the Y direction, and the X direction, the Y direction and the Z direction are perpendicular to each other.

[0038] Please refer to Figure 6 , the blade is roughly square when viewed from the top surface to the bottom surface 12 of the blade, but it is not a square in the strict sense. When installing the blade, a screw is threadedly connected through the center hole 11 and the mounting hole on the arbor 100 to fix the blade on the arbor 100.

[0039] Please refer to Figure 2 The top surface and each side surface 13 are connected to form a cutting edge 14, that is, the blade has four cutting edges 14, and any two adjacent cutting edges 14 are connected smoothly with rounded corners. The four cutting edges 14 are evenly distributed around the central axis of the center hole 11, so that the four cutting edges 14 are equivalent to each other. After one cutting edge 14 is worn, the blade can be rotated 90° and then installed on the tool rod 100, and an adjacent cutting edge 14 can be used to replace the worn cutting edge 14 to improve economy.

[0040] When the drill bit is working, the radial forces generated by the inner blade 200 and the outer blade 300 cannot be offset and balanced, resulting in a large radial force in the radial direction, which makes the drill body easily vibrate under the action of the radial force. Therefore, the structure of the outer blade 300 is improved in this embodiment to reduce the vibration of the drill bit when working and improve the hole wall processing quality.

[0041] like Figure 3 and Figure 4 As shown, the cutting edge 14 of the outer blade 300 includes a supporting cutting edge, an arc cutting edge and a main cutting edge, and the supporting cutting edge is smoothly connected to the main cutting edge through the arc cutting edge; for the cutting edge that plays a cutting role, the projections of the supporting cutting edge and the main cutting edge on the first preset plane 10 are respectively a supporting projection 141 and a main projection 142, and the first preset plane 10 is parallel to the bottom surface 12 of the outer blade 300 and the central axis of the tool rod 100 is located in the first preset plane 10; the supporting projection 141 and the main projection 142 are both straight lines and the angle between them is α, and the angle between the main cutting edge and the central axis of the tool rod 100 is γ1, 0°≤α-γ1≤1°.

[0042] By setting a supporting cutting edge and limiting 0°≤α-γ1≤1°, the supporting cutting edge can contact the hole wall when the outer blade 300 is drilling, and can play a role in supporting the outer blade 300 along the radial direction of the tool rod 100, reduce vibration during processing, and improve the quality of the hole wall.

[0043] In some embodiments, Figure 4 As shown, due to the contact of the support projection 141 with the hole wall, the contact length of the cutting edge 14 with the hole wall will increase, thereby increasing the cutting force exerted on the outer blade 300 during the cutting process. For this reason, the length of the support projection 141 along the axial direction of the tool rod 100 is L2, L2<2mm, which can avoid the length of the support projection 141 being too long and increasing the vibration during processing.

[0044] In some embodiments, Figure 5 As shown, the bottom surface 12 of the outer blade 300 and the bottom surface 12 of the inner blade 200 are located on opposite sides of the first preset plane 10, one end of the inner blade 200 and the outer blade 300 are located on the same side of the second preset plane 20, and the other end of the inner blade 200 is located on the other side of the second preset plane 20; the second preset plane 20 is perpendicular to the bottom surface 12 of the outer blade 300 and the central axis of the tool rod 100 is located in the second preset plane 20.

[0045] In some embodiments, Figure 4 and Figure 6 As shown, two adjacent cutting edges 14 are smoothly connected through a rounded structure. For the outer blade 300, the projection of the rounded structure connected to the supporting cutting edge for cutting in the first preset plane 10 is an outer rounded projection 143, and the length of the outer rounded projection 143 along the axial direction of the tool rod 100 is L1. The projection of the arc cutting edge in the first preset plane 10 is a transition projection 144, and the length of the transition projection 144 along the axial direction of the tool rod 100 is L3.

[0046] The outer blade 300 is rotated around the central axis of the tool rod 100 so that the bottom surface 12 of the outer blade 300 and the bottom surface 12 of the inner blade 200 are parallel and the bottom surface 12 of the outer blade 300 and the bottom surface 12 of the inner blade 200 are oriented in the same direction to form a virtual blade 400, and the projection of the cutting edge 14 of the virtual blade 400 that plays a cutting role in the third preset plane 30 is the outer projection, and the projection of the cutting edge 14 of the inner blade 200 that plays a cutting role in the third preset plane 30 is the inner projection 15; the third preset plane 30 is parallel to the bottom surface 12 of the inner blade 200.

[0047] The intersection point of the inner projection 15 and the outer projection is point P. For the inner blade 200, the projection of the rounded corner structure of the cutting edge 14 close to one end of the outer projection is the inner rounded corner projection 145. The endpoint of the inner rounded corner projection 145 away from one end of the inner projection 15 is point Q. The length between points P and Q along the extension direction of the inner projection 15 is L4, and L1+L2+L3≤L4.

[0048] In this arrangement, the outer blade 300 is rotated around the central axis of the tool rod 100 so that the bottom surface 12 of the outer blade 300 and the bottom surface 12 of the inner blade 200 are parallel and the bottom surface 12 of the outer blade 300 and the bottom surface 12 of the inner blade 200 are oriented in the same direction, and the inner blade 200 completely covers the supporting cutting edge of the outer blade 300, thereby ensuring that when the outer blade 300 is cutting, only a single cutting edge 14 plays a cutting role, so that the four cutting edges 14 of the outer blade 300 are used once each, that is, the outer blade 300 can be used four times.

[0049] In some embodiments, Figure 3 As shown, for the inner blade 200, the angle between the line connecting the centers of the two rounded structures connected to the cutting edge 14 and the central axis of the tool rod 100 is γ2; 0°<γ2<γ1.

[0050] When the cutting edges 14 of the inner blade 200 and the outer blade 300 are the same length, the inner blade 200 will generate greater cutting resistance due to the lower cutting speed of the inner blade 200, and the direction of the main cutting force of the inner blade 200 is perpendicular to the cutting edge 14 of the inner blade 200. After the cutting forces of the inner blade 200 and the outer blade 300 are balanced, the direction of the radial resultant force is closer to the direction of the cutting force of the inner blade 200. Due to the existence of the installation angle γ1 of the inner blade 200 and the installation angle γ2 of the outer blade 300, a radial component force F3 of the inner blade 200 and a radial component force F4 of the outer blade 300 will be generated during cutting, and because the inner blade 200 contacts the workpiece first and then the outer blade 300 contacts the workpiece for the stability of the drilling process, in order to ensure the stability of the force during the drilling process and the radial force during the drilling process is not too large, the outer blade 300 must first be completely in contact with the workpiece, and then the inner blade 200 must be completely in contact with the workpiece, so it is necessary to ensure that γ1>γ2.

[0051] In order to ensure the strength of the drilling point of the inner blade 200 and to ensure that the radial force is not too large, in some embodiments, γ1<10°.

[0052] In some embodiments, Figure 5 As shown, the included angle between the bottom surface 12 of the inner blade 200 and the bottom surface 12 of the outer blade 300 is β, and 4°≤β≤10°.

[0053] When β is 0°, under the influence of γ1 and γ2, the direction of the combined force of F3 and F4 is along the drill center toward the inner blade 200 ( Figure 5 ), which is the negative direction of the X-axis. At the same time, the direction of the main cutting force on the blade is perpendicular to the blade edge and outward. Since the inner blade 200 has a low cutting speed, the inner blade 200 is subjected to the main cutting force F1, and the outer blade 300 is subjected to the main cutting force F2. The direction of the resultant force of F1 and F2 is the direction of F1. Therefore, the direction of the combined force of radial forces F1, F2, F3, and F4 is directed to the second quadrant ( Figure 5 ).

[0054] Since the outer blade 300 is in contact with the hole wall during drill processing, and the inner blade 200 and the drill body are not in contact with the hole wall, the direction of the radial resultant force should be directed to the first quadrant, i.e., the quadrant where the outer blade 300 is located, as much as possible. Therefore, the β angle cannot be set to 0 or negative. The larger the β angle, the more the direction of the radial resultant force is toward the first quadrant. However, the larger the β angle, the larger the magnitude of the radial resultant force, which is not conducive to the stability of processing. After comprehensive consideration, 4°≤β≤10° can meet the requirement that the direction of the radial resultant force is in the first quadrant while ensuring that the magnitude of the radial resultant force is not too large. It should be noted that the specific value of β needs to be adjusted according to the difference in actual cutting force caused by the shape of the inner blade 200 and the outer blade 300 and the length of the cutting force.

[0055] When 4°≤β≤10° and 0°<γ2<γ1<10° are satisfied, it can be ensured that the tool rod 100 bends toward one side of the outer blade 300 under the action of radial force during processing, so that the outer blade 300 is supported by the hole wall through the contact between the outer blade 300 and the hole wall, thereby reducing the vibration of the outer blade 300 and improving the processing quality of the hole wall.

[0056] In some embodiments, Figure 2 and Figure 7 As shown, the side surface 13 includes a first back cutting surface 131 and a second back cutting surface 132, the cutting edge 14 is connected to one side of the first back cutting surface 131, the other side of the first back cutting surface 131 is smoothly connected to the second back cutting surface 132, the second back cutting surface 132 is connected to the bottom surface 12, and the second back cutting surface 132 is closer to the central axis of the center hole 11 than the first back cutting surface 131.

[0057] When processing different materials and working conditions, different blade grooves are often required. The cutting back angle is also an important parameter in the groove. When the blade is installed, the back tool surface is an important positioning surface. In order to ensure that blades with different grooves can be installed on the same tool bar 100, the back tool surface as a positioning surface cannot be changed. In order to take into account the targeted development of the groove and the installation of blades with different grooves on the same tool bar 100, a double back tool surface design is performed. The first back tool surface 131 is used as the cutting back angle and can be changed at will. The second back tool surface 132 is used as the installation positioning surface. The second back tool surface 132 of blades with different grooves of the same specification remains consistent. At the same time, due to the consistency of the second back tool surface 132, blades with different grooves of the same specification can share the lower punch and core rod during production. The production of blades with different grooves only requires the separate production of upper punches and mold sleeves, which can save the development and production costs of the blades.

[0058] The first flank surface 131 is the actual cutting part, and the thickness L1 of the first flank surface 131 cannot be too small, otherwise it will affect the cutting strength. Figure 7 As shown, the length of the first relief surface 131 along the axial direction of the central hole 11 is H1, and H1 is not less than 0.5 mm, that is, H1 ≥ 0.5 mm.

[0059] In some embodiments, Figure 7 As shown, the maximum length of the blade body 1 along the axial direction of the center hole 11 is H, and the length of the second flank 132 along the axial direction of the center hole 11 is H2, H1<H2. H2 cannot be less than 50%H, that is, H2≥50%H, otherwise the supporting torque of the second flank 132 as a positioning surface is insufficient. Exemplarily, H2≥2 / 3H.

[0060] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the scope of protection of the present invention. It is not necessary and impossible to list all implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A drill bit, comprising a shank (100), one end of the shank (100) being a cutting end, the cutting end of the shank (100) being provided with two blades, the two blades being respectively an inner blade (200) and an outer blade (300), the inner blade (200) being closer to the central axis of the shank (100) than the outer blade (300), the blade comprising a blade body (1) provided with a central hole (11) penetrating along the Z direction, the blade body (1) comprising a top surface and a bottom surface (12) arranged opposite to each other along the Z direction, and four side surfaces (13) connecting the top surface and the bottom surface (12), the four side surfaces (13) being connected end to end along the circumference of the central hole (11) and arranged opposite to each other in pairs, each of the side surfaces (13) being connected to the top surface to form a cutting edge (14); It is characterized in that The cutting edge (14) of the outer blade (300) comprises a supporting cutting edge, a circular arc cutting edge and a main cutting edge, wherein the supporting cutting edge is smoothly connected to the main cutting edge via the circular arc cutting edge; For the cutting edge (14) of the outer blade (300) that performs cutting, the projections of the supporting cutting edge and the main cutting edge on the first preset plane (10) are respectively a supporting projection (141) and a main projection (142), the first preset plane (10) is parallel to the bottom surface (12) of the outer blade (300) and the central axis of the tool rod (100) is located in the first preset plane (10); the supporting projection (141) and the main projection (142) are both straight lines and the included angle is α; the included angle between the supporting projection (141) and the central axis of the tool rod (100) is γ1, 0°≤α-γ1≤1°.

2. The drill bit according to claim 1, characterized in that The length of the support projection (141) along the axial direction of the knife rod (100) is L2, and L2 is less than 2 mm.

3. The drill bit according to claim 1, characterized in that The bottom surface (12) of the outer blade (300) and the bottom surface (12) of the inner blade (200) are located on opposite sides of the first preset plane (10); one end of the inner blade (200) and the outer blade (300) are located on the same side of a second preset plane (20); the other end of the inner blade (200) is located on the other side of the second preset plane (20); the second preset plane (20) is perpendicular to the bottom surface (12) of the outer blade (300) and the central axis of the knife rod (100) is located on the second preset plane (20); Two adjacent cutting edges (14) are smoothly connected via a rounded corner structure. For the outer blade (300), the projection of the rounded corner structure connected to the supporting cutting edge for cutting in the first preset plane (10) is an outer rounded corner projection (143), and the length of the outer rounded corner projection (143) along the axial direction of the tool rod (100) is L1. The projection of the arc cutting edge in the first preset plane (10) is a transition projection (144), and the length of the transition projection (144) along the axial direction of the tool rod (100) is L3. The outer blade (300) is rotated around the central axis of the blade rod (100) so that the bottom surface (12) of the outer blade (300) and the bottom surface (12) of the inner blade (200) are parallel and the bottom surface (12) of the outer blade (300) and the bottom surface (12) of the inner blade (200) are oriented in the same direction to form a virtual blade (400), wherein the projection of the cutting edge (14) of the virtual blade (400) in a third preset plane (30) is an external projection, and the projection of the cutting edge (14) of the inner blade (200) in a third preset plane (30) is an internal projection (15), and the third preset plane (30) is parallel to the bottom surface (12) of the inner blade (200); The intersection point of the inner projection (15) and the outer projection is point P. For the inner blade (200), the projection of the rounded structure of the cutting edge (14) that performs cutting function close to one end of the outer projection is the inner rounded projection (145). The end point of the inner rounded projection (145) that is away from one end of the inner projection (15) is point Q. The length between point P and point Q along the extension direction of the inner projection (15) is L4, and L1+L2+L3≤L4.

4. The drill bit according to claim 3, characterized in that For the inner blade (200), the angle between the line connecting the centers of the two rounded structures connected to the cutting edge (14) having a cutting function and the central axis of the tool rod (100) is γ2; 0°<γ2<γ1.

5. The drill bit according to claim 3, characterized in that γ1<10°.

6. The drill bit according to claim 3, characterized in that The angle between the bottom surface (12) of the inner blade (200) and the bottom surface (12) of the outer blade (300) is β, and 4°≤β≤10°.

7. The drill bit according to claim 1, characterized in that The side surface (13) comprises a first flank surface (131) and a second flank surface (132); the cutting edge (14) is connected to one side of the first flank surface (131); the other side of the first flank surface (131) is smoothly connected to the second flank surface (132); the second flank surface (132) is connected to the bottom surface (12); and the second flank surface (132) is closer to the central axis of the central hole (11) than the first flank surface (131).

8. The drill bit according to claim 7, characterized in that The length of the first flank surface (131) along the axial direction of the center hole (11) is H1, and the length of the second flank surface (132) along the axial direction of the center hole (11) is H2, and 0.5 mm < H1 < H2.

9. The drill bit according to claim 8, characterized in that The maximum length of the blade body (1) along the axial direction of the central hole (11) is H, and H2≥50%H.

10. The drill bit according to claim 9, characterized in that H2≥2 / 3H.

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