drill tip

Abstract

The invention relates to a drill tip for machining light alloys, such as aluminium alloys, comprising a body having a leading end with an apex region (13), a centre of rotation axis (8) extending rearwardly from the centre of the apex region (13), and at least one cutting structure (10). Each cutting structure (10) comprises a primary rake face (17), a primary clearance surface (18), a cutting edge (11) at the intersection between the primary rake face (17) and the primary clearance surface (18), and a peripheral cutting corner (14). The cutting edge (11) extends radially outwardly from the apex region (13) to the cutting corner (14). When viewed in a leading end view, the primary clearance surface (18) has a width (b) which is the distance normal to the cutting edge (11) and extending from the cutting edge (11) to a primary clearance surface edge (19) which trails the cutting edge (11) in the direction of rotation. The body further has a nominal cutting radius (22) which is the radial distance outwardly from the centre of rotation axis (8) to the cutting corner (14) and is at least 1 mm. The cutting edge (11) has a central portion (32) which extends radially outwardly from the apex region (13) to a radially outer end (23). The radial distance of the radially outer end (23) of the central portion (32) of the cutting edge to the centre of rotation axis (8) is at least 10% of the nominal cutting radius (22). The primary clearance surface width (b) along the central portion (32) of the cutting edge is at least 0.05 mm and is at most 5% of the nominal cutting radius (22).

Description

TECHNICAL FIELD

[0001] The present invention relates to a drill tip for machining light alloys, such as aluminium alloys. BACKGROUND

[0002] Drills for machining light alloys, such as aluminium alloys, are known. The known drills comprise a drill tip, a shank at a rear end of the drill for mounting the drill to a machine spindle, and a straight or tapered section between the drill tip and the shank, the drill tip being a generally conical shaped front end of the drill. The drill tip typically comprises two cutting edges formed by the intersection of a rake face and a clearance face, and extending radially outwards from a central location adjacent a centre axis of rotation. A land connects the two cutting edges across the centre axis of rotation. A flutes is provided in the straight or tapered section for conducting chips away from the cutting edges.

[0003] A problem with such known drills when drilling in light alloys, such as aluminium alloys, is that their centring performance tends to deteriorate, which reduces the ability to machine according to tight tolerances. SUMMARY

[0004] It is an object of the present invention to alleviate the drawbacks of the prior art and to provide a drill tip with improved centring performance.

[0005] This object is achieved according to the invention with the following features.

[0006] The drill tip for machining light alloys, such as aluminium alloys, of the present invention comprises a body having a front end with an apex region, a centre axis of rotation extending rearward from a centre of the apex region, and at least one cutting structure. Each cutting structure comprises a primary rake face, a primary clearance face, a cutting edge at an intersection between the primary rake face and the primary clearance face, and a peripheral cutting corner. The cutting edge extends radially outwards from the apex region to the cutting corner. When viewed in a front end view, the primary clearance face has a width which is a distance normal to the cutting edge and extending from the cutting edge to a primary clearance face edge trailing the cutting edge in the direction of rotation. The body further has a nominal cutting radius which is a radial distance outwards from the centre axis of rotation to the cutting corner, and which is at least 1 mm. The cutting edge has a central portion extending radially outwards from the apex region to a radially outer end. The radially outer end of the central portion of the cutting edge is at least 10% of the nominal cutting radius in radial distance from the centre axis of rotation. The primary clearance face width along the central portion of the cutting edge is at least 0.05 mm, and at most 5% of the nominal cutting radius.

[0007] During operation, the drill tip rotates around the central axis of rotation, where the cutting speed in the direction of rotation will vary from zero at the center to a high speed at the outer peripheral end of the cutting edge. As a result, chips are cut off the machined material along the peripheral part of the cutting edge, while the machined material is mainly plastically deformed in the central part. As a result, no neat chip is formed at the center of the drill.

[0008] In prior art drills, when machining light alloys, such as aluminum alloys, material from the machined workpiece tends to stick to the center of the drill, where no proper chip is formed. This accumulation of material occurs especially at the relief surface behind the cutting edge, close to the center of the drill. It has been found that this is an important reason for the deterioration of the centering performance of the drill.

[0009] Since the drill tip of the present invention has a very narrow relief surface close to the center, the risk of material sticking to the relief surface there is reduced. However, if any material is stuck, it is easily shed from such a narrow surface. As a result, material is less likely to accumulate on the relief surface, thereby improving the centering performance of the drill tip and enabling machining of workpieces according to tight tolerances.

[0010] The drill tip according to the present invention is suitable for machining (e.g. drilling holes) of workpieces belonging to the group of workpiece materials ISO-N according to the ISO classification standard for workpiece materials. This group includes non-ferrous metals, such as light alloys, like aluminum-based alloys.

[0011] For example, the drill tip is made of one or more of cemented carbide, ceramic, cubic boron nitride, polycrystalline diamond and / or cermet. Optionally, the drill tip is coated with a surface coating, including for example titanium nitride, titanium carbonitride, diamond-like carbon (DLC) and / or aluminum oxide.

[0012] The drill tip is configured to rotate in the direction of cutting around the central axis of rotation during machining of a workpiece. Seen from the direction of rotation, the structural features of the drill tip are leading or trailing relative to each other.

[0013] The cutting edge of each cutting structure of the drill head body is formed at the intersection between the main rake face and the main relief surface. Optionally, the cutting edge extends from the central axis of rotation, or from a position close to the central axis of rotation.

[0014] Preferably, the cutting edge has an edge radius of at most 6 pm, and more preferably at most 4 pm. Such a sharp edge radius is advantageous for cutting workpieces of the intended light alloy material. Optionally, the cutting edge radius is constant in the cross-section of the cutting edge, i.e. formed by a circular segment, or the cutting edge radius varies to form an asymmetric edge. Optionally, the cutting edge radius is constant or varies along the cutting edge. For example, the edge radius can be measured using an optical 3D measuring device.

[0015] The cutting edge has an outer end at the cutting corner, which is located at the periphery of the body. The nominal cutting radius of the drill tip is to be understood as the radius from the centre axis of rotation to the cutting corner. The nominal cutting radius of the drill tip is at least 1 mm. Drill tips with a smaller nominal cutting radius inherently have a smaller primary clearance surface width, making them less prone to sticking to the material being processed.

[0016] Preferably, the nominal cutting radius of the drill tip is at most 20 mm. Generally, larger drill tips are less suitable for use in processing light alloys (e.g. aluminium alloys) using existing processes and machines.

[0017] The apex region of the body of the drill tip is to be understood as a small region around the centre axis of rotation at the very tip of the drill tip. For example, in embodiments where the cutting edge has a central end close to the centre axis of rotation, it is a small region in the centre of the central end of the cutting edge; or, in embodiments with a chisel edge, it is the region defined by a circle with the total length of the chisel edge as diameter.

[0018] In each cutting structure, the primary rake surface is the surface portion closest to the cutting edge against which the material removed from the workpiece initially slides. Depending on the embodiment, each cutting section comprises a flute, wherein the primary rake surface is a portion of the flute surface closest to the cutting edge. Thus, an additional rake surface can follow in axial direction behind the primary rake surface.

[0019] In each cutting structure, the primary clearance surface is the forward facing surface directly trailing the cutting edge in the direction of rotation. When seen in a frontal view, or in other words, in a view in the direction towards the centre axis of rotation of the front end, the primary clearance surface has a width from the cutting edge to the primary clearance surface edge trailing in the direction of rotation. Optionally, the primary clearance surface is curved or planar, wherein the primary clearance surface can be angled with respect to a plane normal to the centre axis of rotation. For example, the true width following the curvature of a curved primary clearance surface can deviate from the width seen in the frontal view.

[0020] The primary clearance surface width along the central portion of the cutting edge is at least 0.05 mm and at most 5% of the nominal cutting radius. With smaller widths, the drill tip becomes weaker and can break when subjected to cutting forces during operation. With larger widths, material from the intended workpiece of a light alloy (e.g. aluminium) increasingly starts to stick to the clearance surface.

[0021] Optionally, the width of the primary clearance surface along the central portion of the cutting edge is constant or varies within defined limits. For example, the width is mostly constant, is narrower closest to the rotational centre axis, and continuously widens along the outer portion to align with the wider primary clearance surface located at the outer portion of the cutting edge.

[0022] Preferably, the primary clearance surface width along the central portion of the cutting edge is at most 3% of the nominal cutting radius when the nominal cutting radius is larger than 2 mm. Thus, a drill tip with such a larger nominal cutting radius has a primary clearance surface with a width at the central portion of the cutting edge that is a smaller fraction of the nominal cutting radius. Due to the larger nominal cutting radius, the smaller fraction, which is advantageous in terms of adhesion, will also be strong enough during operation.

[0023] Preferably, the primary clearance surface width along the central portion of the cutting edge is at least 1% of the nominal cutting radius when the nominal cutting radius is larger than 5 mm. Thus, a drill tip with such a larger radius is advantageously stronger, while the width of the primary clearance surface at the central portion of the cutting edge is still small enough to sufficiently prevent adhesion of material from the workpiece of the intended material during operation.

[0024] Preferably, the primary clearance surface width is 10-30% of the nominal cutting radius along the outer portion of the cutting edge extending from the cutting corner and radially inwards to at most the outer end of the central portion of the cutting edge. Since the cutting speed at the cutting edge of the drill tip is higher in the radially outer portion, suitable chips are cut from the machined material in this area, so that the problem of material adhesion to the primary clearance surface is less likely to arise. Thus, advantageously, the width of the primary clearance surface at the radially outer portion of the cutting edge is optimized in terms of cutting performance and strength. A width of at least 10% of the nominal cutting radius achieves an increased strength that can be desirable for certain operations. A width of at most 30% of the nominal cutting radius ensures smooth operation.

[0025] The central portion of the cutting edge extends radially outwards from the apex region, or in other words, from a radially inner end at or near the rotational centre axis. The radially outer end of the central portion of the cutting edge is located at a radial distance from the rotational centre axis of at least 10% of the nominal cutting radius. This is the area where the cutting speed is lowest during operation and the tendency of the machined material to adhere to the primary clearance surface is greatest. Preferably, the radial distance of the radially outer end of the central portion of the cutting edge from the rotational centre axis is at least 35% of the nominal cutting radius.

[0026] According to embodiments, the cutting edge comprises a primary cutting edge extending radially inwards from the cutting corner, and a secondary cutting edge extending radially outwards from the apex region to an inner end of the primary cutting edge. When seen in a frontal view, the primary cutting edge extends at an angle to the secondary cutting edge, and a central portion of the cutting edge forms said secondary cutting edge. For example, in order to provide a more positive cutting geometry, the primary cutting edge is designed to have an extension inwards from the cutting corner towards a location beside the rotational centre axis, and the secondary cutting edge is designed to connect the primary cutting edge with the apex region. For example, the secondary cutting edge extends mainly over the web of the drill tip body. These embodiments are advantageous in that the primary cutting edge and its primary relief surface can be optimized for chip removal machining, while the central portion of the cutting edge, i.e. the secondary cutting edge, is endowed with the properties of the central portion of the cutting edge of the present invention to minimize adhesion.

[0027] According to embodiments of the central portion of the cutting edge in the form of a cutting edge having such a primary cutting edge and a secondary cutting edge, which are at an angle to each other, the primary cutting edge comprises a primary transition edge closest to the secondary cutting edge. Thus, advantageously, sharp corners in the cutting edge can be avoided.

[0028] Preferably, each cutting structure further comprises a frontal end surface facing forwards. The frontal end surface extends radially outwards from the apex region to the periphery of the body, and connects to and trails the primary relief surface edge in the rotational direction. Optionally, the frontal end surface comprises a secondary relief surface or more relief surfaces, which follow sequentially in the rotational direction behind the primary relief surface. According to embodiments, at least a radially outer portion of the primary relief surface edge is straight when seen in a frontal view.

[0029] According to embodiments, the frontal end surface comprises a recess bounded by a recess surface, wherein the recess surface bounds the primary relief surface edge at least along the central portion of the cutting edge. Thus, along the central portion of the cutting edge, the recess surface extends from and axially behind the primary relief surface edge. The recess trails in the rotational direction behind the primary relief surface edge. Providing a recess in the frontal end surface is an effective way of obtaining the required narrow width of the primary relief surface at the central portion of the cutting edge. The recess can be provided, for example, by grinding.

[0030] According to embodiments, each cutting structure further comprises a coolant channel having a coolant opening which is at least partially located in the recess surface. Thus, advantageously, coolant and / or lubricant provided through the coolant channel can reach the central portion of the cutting edge by flowing through the recess. In addition to providing coolant and / or lubricant to the central portion of the cutting edge, the fluid flow helps to achieve less material adhesion from the workpiece to the main relief surface. Preferably, at least most of a radially inner and axially forward quarter of the periphery of the coolant opening borders the recess surface, or in other words, interrupts the recess surface.

[0031] Preferably, the recess is a concave surface. For example, a concave surface can be effectively produced by using a grinding wheel. According to embodiments, the recess surface comprises an axially rearwardly extending curved bottom surface, a radially inner curved portion surface extending from the bottom surface to the apex region, and a radially outer curved portion surface extending from the bottom surface to the coolant opening. Preferably, as seen in the front view, the longitudinal extension of the bottom surface is parallel to the central portion of the cutting edge. Preferably, as seen in the side view, the bottom surface longitudinally extends in the direction of the rotational center axis to at least the axial position of the center of the opening of the coolant channel.

[0032] Optionally, the main body comprises two, three or more cutting structures which are rotationally symmetrically arranged around the rotational center axis. However, embodiments with only one cutting structure are also conceivable.

[0033] According to preferred embodiments, the main body comprises two cutting structures which are rotationally symmetrically arranged around the rotational center axis by 180°. Optionally, the main body comprises a web connecting the cutting edges of the two cutting structures across the apex region. According to embodiments, each cutting edge is connected to the web by a secondary transition edge. Thus, advantageously, sharp corners in the cutting edges can be avoided.

[0034] Preferably, the drill point of the present invention is incorporated in a head of a drill which is optionally an integral part of a solid round tool or a replaceable head which can be connected to a drill body. The drill point then constitutes a front end section of the solid tool, e.g. a drill, or a larger entity such as e.g. a replaceable head.

[0035] According to embodiments, the solid tool in the form of a drill comprising the drill point of the present invention further comprises a shank at the rear end for mounting the drill to a machine spindle, and a straight or tapered section between the drill point and the shank. A chip pocket is provided in said straight or tapered section connected to the drill point such that during operation, the chips can be guided away from the cutting edge. Optionally, the chip pocket is helical or straight. BRIEF DESCRIPTION OF DRAWINGS

[0036] In the following, example embodiments will be described in more detail with reference to the accompanying drawings, in which:

[0037] Figure 1 is a perspective front view of an embodiment of a drill tip according to the present invention, wherein the drill tip is comprised in a front portion of a solid drill;

[0038] Figure 2 is a side view of the entire solid drill of Figure 1 ;

[0039] Figure 3 is a front end view of a drill with a drill tip;

[0040] Figure 4 is a perspective side view of a front portion of a solid drill, wherein the drill tip is in a first angular position;

[0041] Figure 5 and Figure 6 is a side view of a front portion of a solid drill, wherein the drill tip is in two different angular positions.

[0042] All drawings are schematic, not necessarily to scale, and generally only show the parts that are necessary for the elucidation of the respective embodiments, while other parts can be omitted or suggested only. Identical reference signs in different drawings refer to identical parts unless stated otherwise. DETAILED DESCRIPTION

[0043] Figure 1 and Figure 2 shows a solid drill in the form of a twist drill comprising an embodiment of a drill tip 1 according to the present invention. The drill tip 1 according to this embodiment constitutes a generally conical shaped front section 2 of the twist drill. The twist drill further comprises a shank 6 in a rear section 4 for mounting the twist drill in a machine spindle. A straight section 3 extends between the front section 2 and the rear section 4. Helical flutes 5 are arranged in the straight section 3, which flutes 5 continue axially into the drill tip 1. The twist drill is configured to rotate around a centre axis of rotation 8 in a cutting direction 9 during machining of a workpiece, such as for example drilling in an aluminium alloy. As seen in the cutting direction 9, the drill tip 1 and the structural features of the twist drill are leading or trailing relative to each other.

[0044] With reference to Figures 3-6 , an embodiment of a drill tip 1 comprised in a twist drill will be described.

[0045] The drill tip 1 comprises a body having a foremost tip in the form of a chisel edge 7. A centre axis of rotation 8 extends rearwardly in the body from the centre of the chisel edge 7.

[0046] The body further comprises two cutting structures 10 arranged in 180° rotational symmetry with respect to the central axis of rotation 8. Each cutting structure 10 comprises a cutting edge 11, wherein each cutting edge 11 is connected to a respective end of the cross web 7 by a secondary transition edge 12. A central region around the central axis of rotation 8 forms an apex region 13, which comprises the cross web 7 and the secondary transition edge 12.

[0047] Each cutting edge 11 extends from a radially outer end of the secondary transition edge 12 at the apex region 13 to a peripheral cutting corner 14. The radius from the central axis of rotation 8 to the cutting corner 14 forms the nominal cutting radius 22 of the drill point 1 and also of the example twist drill. The drill point of this embodiment has a nominal cutting radius of 5 mm. As seen in the side view, each cutting edge 11 and the secondary transition edge 12 are substantially straight and form an acute angle β of 140°. Other embodiments can have different cutting edge geometries, for example cutting edges extending substantially in an axial plane.

[0048] Each cutting edge 11 is sharp, having a blade radius of at most 4 μιη.

[0049] Each cutting edge 11 comprises a primary cutting edge 15 extending radially inwards from the cutting corner 14, and a central cutting edge portion 32 in the form of a secondary cutting edge 16. The secondary cutting edge 16 extends radially outwards from the secondary transition edge 12 in the apex region, and has a radially outer end 23 at the radially inner end of the primary cutting edge 15. The primary cutting edge 15 comprises a primary transition edge 24 closest to the radially outer end 23 of the secondary cutting edge 16. The radial distance from the central axis of rotation 8 to the radially outer end 23 of the secondary cutting edge 16 is 2.07 mm, i.e. at least 35% of the nominal cutting radius 22, i.e. 1.75 mm.

[0050] As seen in the front view of Figure 3 , the primary cutting edge 15 extends at an angle to the secondary cutting edge 16. The angle a between a line through the central axis of rotation 8 and the radially outer end of the secondary cutting edge 16, and a line along the nominal cutting radius 22 through the central axis of rotation 8 and the cutting corner 14, is 20-40°, and in the illustrated embodiment the angle a is 24°.

[0051] As seen in the front view of Figure 3 , the secondary cutting edge 16 is substantially straight, and the primary cutting edge 15 is concave in the main, with the primary transition edge 24 being straight. The secondary transition edge 12 is concave. Other embodiments can have different cutting edge geometries.

[0052] Each cutting edge 11 is formed at the intersection of the primary rake surface 17 and the primary clearance surface 18. One of the flutes 5 extends rearwardly from each cutting edge 11. The primary rake surface 17 is the portion of the flute surface closest to the cutting edge 11.

[0053] As best seen in Figure 4 and Figure 6 Each secondary cutting edge 16 has a primary rake surface 17 in the form of a thinning surface 26. Close to the rotational center axis 8 at the land 7 and the minor transition edge 12, the thinning surface 26 comprises a concave portion. Axially below most of the radially outer length of the secondary cutting edge 16, the thinning surface 26 comprises a planar portion.

[0054] In each cutting structure 10, the primary clearance surface 18 is the forward facing surface that directly trails the cutting edge 11 in the direction of rotation.

[0055] Each cutting structure 10 also comprises a forward facing nose surface 20. The nose surface 20 extends radially outwardly from the apex region 13 to the periphery of the main body and is connected to and trails the primary clearance surface 18 in the direction of rotation. The primary clearance surface 18 has a trailing edge 19 at the transition to the nose surface 20. The nose surface 20 comprises a secondary clearance surface 21 that trails the primary clearance surface 18 in the direction of rotation. The trailing edge of the secondary clearance surface 21 is connected to an axially forward and rotationally leading surface 31 of the flute 5. The axially forward and rotationally leading surface 31 and the primary rake surface 17 are part surfaces of the same flute 5 but are associated with a respective one of the cutting structures 10. The nose surface 20 follows a portion of the periphery of the main body.

[0056] As seen in the nose view of Figure 3 The primary clearance surface 18 has a width (b) measured perpendicular to the cutting edge 11. The width (b) is the distance from the cutting edge 11 to the primary clearance surface edge 19.

[0057] The width (b) of the primary clearance surface along the secondary cutting edge 16 is 0.06 mm, i.e. greater than 0.05 mm and 1% of the nominal cutting radius 22 and less than 3% of the nominal cutting radius, i.e. 0.15 mm.

[0058] The width (b) of the primary clearance surface along the outer portion of the cutting edge 11 is 0.53 mm, i.e. greater than 10% of the nominal cutting radius 22 and less than 30% of the nominal cutting radius 22, i.e. 1.5 mm. In particular, this larger width (b) is present along most of the primary cutting edge 15 radially inward from the cutting corner 14.

[0059] The width (b) of the main clearance surface 18 is essentially constant along the auxiliary cutting edge 16, continuously widens along the transition portion 24 of the main cutting edge 15, and slightly varies along the outer portion of the main cutting edge 15 due to its concave curvature.

[0060] Each forward facing nose surface 20 comprises a recess 25, which is bounded by a recess surface, which borders the main clearance surface 18 along the minor transition edge 12, along the auxiliary cutting edge 16 and along a radially central portion of the main cutting edge 15 comprising the main transition edge 24. Radially outwardly, the recess surface borders the auxiliary clearance surface 21 and the axially forwardly preceding surface 31 of the rotation direction of the flute 5.

[0061] Due to the recess 25, the said portion of the main clearance surface 18 with the narrow width (b) of the invention is located on a ridge. The ridge has a rotation direction preceding flank in the form of a thinning surface 26 as a rake surface 17, and a rotation direction trailing flank in the form of the recess surface.

[0062] The recess surface is a concave surface, comprising an axially rearwardly extending curved bottom surface 27, a radially inner curved portion surface 28 extending from the bottom surface 27 to the apex region 13 and a radially outer curved portion surface 29, see Figure 4 and Figure 6 .

[0063] As seen in the nose view of Figure 3 , the radially inner curved portion surface 28 extends along the auxiliary cutting edge 16 of both cutting structures 10, and across the apex region 13. In particular, the radially inner curved portion surface 28 of the first cutting structure borders the thinning surface 26 of the second cutting structure, and the radially inner curved portion surface 28 of the second cutting structure borders the thinning surface 26 of the first cutting structure. Due to the difference in the concave curvature of the radially inner curved portion surface 28 and the thinning surface 26, a common edge is formed at the intersection of the radially inner curved portion surface 28 and the thinning surface 26.

[0064] Each cutting structure 10 further comprises a coolant channel having a coolant opening 30. The coolant opening 30 is partly located in the recess surface, and partly located in the rotation direction preceding surface 31 of the flute 5. Thus, the coolant opening 30 is located in the radially outer curved portion surface 29 of the recess 25, wherein almost radially inner and axially forwardly half of the perimeter of the coolant opening 30 is located in the recess surface.

[0065] As can be seen in the Figures 4-6As best seen, due to the recess 25 of the present invention, coolant exiting through the coolant openings 30 is directed towards the auxiliary cutting edge 16. In combination with the narrow width of the present invention along the primary relief surface 18 of the auxiliary cutting edge 16, the risk of material sticking to the relief surface 18 is greatly reduced.

Claims

1. A drill tip for machining light alloys, the drill tip comprising a body having: - Front end with vertex region (13), - A rotation center axis (8), which extends rearward from the center of the vertex region (13), and - At least one cutting structure, Each cutting structure includes: - Main rake face (17). - Main clearance surface (18). - The cutting edge (11) at the intersection between the main rake face (17) and the main clearance surface (18), and - Peripheral cutting corners (14). in: - The cutting edge (11) extends radially outward from the vertex region (13) to the cutting corner (14), and - When viewed in the front view, the main clearance surface (18) has a width (b) that is perpendicular to the cutting edge (11) and extends from the cutting edge (11) to the edge (19) of the main clearance surface, which follows the cutting edge (11) in the rotational direction. The main body also has a nominal cutting radius (22), which is the radial distance from the rotation center axis (8) outward to the cutting corner (14), and the nominal cutting radius (22) is at least 1 mm. Characterized by the fact that the cutting edge (11) has a central cutting edge portion (32) extending radially outward from the vertex region (13) to the radially outer end (23), wherein - The radial distance from the radially outer end (23) of the central cutting edge portion (32) to the rotation center axis (8) is at least 10% of the nominal cutting radius (22), and wherein - The width (b) of the primary clearance surface along the central cutting edge portion (32) is at least 0.05 mm and at most 5% of the nominal cutting radius (22). Wherein, along the outer portion of the cutting edge (11), the width (b) of the main clearance surface is 10-30% of the nominal cutting radius (22), and the outer portion of the cutting edge (11) extends from the cutting corner (14) and radially inward to at most the radially outer end (23) of the central cutting edge portion (32).

2. The drill bit according to claim 1, wherein, When the nominal cutting radius (22) is greater than 2 mm, the width (b) of the main clearance surface along the central cutting edge portion (32) is at most 3% of the nominal cutting radius (22).

3. The drill bit according to claim 1 or 2, wherein, When the nominal cutting radius (22) is greater than 5 mm, the width (b) of the main clearance surface along the central cutting edge portion (32) is at least 1% of the nominal cutting radius (22).

4. The drill bit according to any one of claims 1-2, wherein, The radial distance from the radial outer end (23) of the central cutting edge portion (32) to the rotation center axis (8) is at least 35% of the nominal cutting radius (22).

5. The drill bit according to any one of claims 1-2, wherein, The cutting edge (11) includes: - The main cutting edge (15) extends radially inward from the cutting corner (14), and - An auxiliary cutting edge (16) extends radially outward from the vertex region (13) to the inner end of the main cutting edge. in, - When viewed in the front view, the main cutting edge (15) extends at an angle to the auxiliary cutting edge, and - The central cutting edge portion (32) forms the auxiliary cutting edge (16).

6. The drill bit according to claim 5, wherein, The main cutting edge (15) extends at an angle relative to the auxiliary cutting edge (16) such that, when viewed in the front view, the angle (α) between the line passing through the radially outer end (23) of the rotation center axis (8) and the auxiliary cutting edge (16) and the line passing through the rotation center axis (8) and the cutting corner (14) is 20-40°.

7. The drill bit according to any one of claims 1-2, wherein, The cutting edge (11) has a cutting radius of up to 4 μm.

8. The drill bit according to any one of claims 1-2, wherein, Each cutting structure also includes a forward-facing front end surface (20): - Extending radially outward from the vertex region (13) to the periphery of the body, and - Connected to the edge of the main clearance surface (19) and following the edge of the main clearance surface (19) in the rotational direction. in, - The forward-facing front surface (20) includes a recess (25) defined by a recessed surface, and - The concave surface is at least along the central cutting edge portion (32) and the edge (19) of the main clearance surface.

9. The drill bit according to claim 8, wherein, Each cutting structure also includes a coolant channel having a coolant opening (30) that is at least partially located in the recessed surface.

10. The drill bit according to claim 9, wherein, At least a majority of the radially inner and axially upper quarter of the perimeter of the coolant opening (30) is in contact with the surface of the recess.

11. The drill bit according to claim 9 or 10, wherein, The concave surface is a concave surface, including: - A curved bottom surface extending axially backward (27). - The radially inwardly curved portion of the surface (28) extending from the bottom surface (27) to the apex region (13), and - The radially outer curved portion of the surface (29) extending from the bottom surface (27) to the coolant opening (30).

12. The drill bit according to claim 11, wherein, The main body includes two cutting structures arranged 180° rotationally symmetrically around the rotation center axis (8), and wherein the main body includes a transverse blade (7) that crosses the vertex region (13) and connects the cutting edges (11) of the two cutting structures.

13. The drill bit according to claim 12, wherein: - The first thinning surface extends axially rearward from the chisel edge (7) below the main rake face (17) of the central cutting edge portion (32) of the first cutting structure in the two cutting structures. - The second thinning surface extends axially rearward from the chisel edge (7) below the main rake face (17) of the central cutting edge portion (32) of the second cutting structure in the two cutting structures. in - The radially inwardly curved portion surface (28) of the concave surface of the first cutting structure borders the second thinned surface via a common edge, and - The radially inwardly curved portion surface (28) of the concave surface of the second cutting structure is connected to the first thinned surface via a common edge.

14. The drill bit according to claim 1, wherein, The light alloy is an aluminum alloy.

15. A solid drill bit comprising a drill tip (1) according to any one of claims 1-14.

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