阅读说明：本技术 钻尖和用于产生钻尖的方法 (Drill tip and method for producing a drill tip ) 是由 H.R.考珀 J.施韦格里 C.斯特劳赫曼 J.特姆佩尔迈尔 于 2019-07-18 设计创作，主要内容包括：本发明涉及一种钻尖(2),包括中心(4)并且包括切削刃(8),横刃(6)布置在所述中心处,所述切削刃邻接所述横刃(6)并且从所述中心(4)向外延伸。沿着所述横刃(6)和所述切削刃(8)形成前角。所述切削刃(8)具有内部部分(10),所述内部部分邻接所述横刃(6)并且布置在所述中心(4)内。所述切削刃(8)具有外部部分(12),所述外部部分向外邻接所述内部部分(10)并且布置在所述中心(4)外部。刃磨(16)形成于所述钻尖(2)上,所述刃磨以使得所述内部部分(10)从所述中心(4)的外边缘朝向所述横刃(6)弓形延伸的方式弯曲。本发明还涉及一种用于产生此类型的钻尖(2)的方法。(The invention relates to a drill tip (2) comprising a center (4) at which a chisel edge (6) is arranged and comprising a cutting edge (8) adjoining the chisel edge (6) and extending outwardly from the center (4). A rake angle is formed along the chisel edge (6) and the cutting edge (8). The cutting edge (8) has an inner portion (10) adjoining the chisel edge (6) and arranged within the center (4). The cutting edge (8) has an outer portion (12) which adjoins the inner portion (10) outwards and is arranged outside the center (4). A sharpening (16) is formed on the drill tip (2), the sharpening being curved in such a way that the inner portion (10) extends arcuately from the outer edge of the centre (4) towards the chisel edge (6). The invention also relates to a method for producing a drill tip (2) of this type.)

1. A drill tip (2) is provided,

comprises a center (4) in which a chisel edge (6) is arranged,

comprising a main cutting edge (8) adjoining the chisel edge (6) and extending outwardly from the center (4),

wherein a rake angle is formed along the chisel edge (6) and the main cutting edge (8),

wherein the main cutting edge (8) comprises an inner portion (10) adjoining the chisel edge (6) and arranged inside the center (4),

wherein the main cutting edge (8) comprises an outer portion (12) adjoining the inner portion (10) to the outside and being arranged outside the center (4),

wherein a sharpening (16) is formed which is curved in such a way that the inner portion (10) extends arcuately from the outer edge of the centre (4) towards the chisel edge (6).

2. The drill tip (2) according to claim 1,

wherein the inner portion (10) is continuously curved and extends in a continuous arcuate manner from the outer edge to the chisel edge (6).

3. The drill tip (2) according to claim 1,

wherein the inner part (10) is bent in an arcuate manner and for this purpose comprises a plurality of straight subsections (24) arranged at an angle to one another.

4. The drill tip (2) according to claim 3,

wherein the inner portion (10) comprises at least three straight subsections (24).

5. The drill tip (2) according to claim 4,

wherein two consecutive straight subsections (24) are connected to each other by rounded corners (26).

6. The drill tip (2) according to any one of claims 1 to 5,

wherein at least two main cutting edges (8) are formed, each comprising an arcuate inner portion (10), wherein the two inner portions (10) are S-shaped when viewed together.

7. The drill tip (2) according to any one of claims 1 to 6,

wherein the chisel edge (6) is delimited by a plurality of free surfaces (20) which are configured such that the chisel edge (6) extends in an S-shaped manner.

8. The drill tip (2) according to any one of claims 1 to 7,

wherein the sharpening (16) connects a flute (18) and a free surface (20) and is additionally convex such that the sharpening (16) extends from the flute (18) in an outwardly curved manner in the direction of the free surface (20).

9. The drill tip (2) according to any one of claims 1 to 8,

wherein the blade sharpening (16) comprises a base (22) that is concave when viewed in a radial direction.

10. The drill tip (2) according to any one of claims 1 to 9,

wherein the sharpening (16) abuts a free surface (20) and forms with it an edge (28) which starts at the chisel edge (6) and extends in an S-shaped manner in the center (4).

11. The drill tip (2) according to any one of claims 1 to 10,

wherein the drill tip comprises an outer surface (14) located radially outside,

wherein the sharpening (16) connects a flute (18) and a free surface (20) and extends to the outer surface (14) such that the free surface (20) is fully spaced from the flute (18) by the sharpening (16).

12. The drill tip (2) according to any one of claims 1 to 11,

wherein the rake angle at a transition point (P) from the main cutting edge (8) to the chisel edge (6) varies in a discontinuous manner.

13. The drill tip (2) according to any one of claims 1 to 12,

wherein the rake angle along the chisel edge (6) is less than the rake angle along the main cutting edge (8).

14. The drill tip (2) according to any one of claims 1 to 13,

wherein the rake angle along the chisel edge (6) is negative and greater than-2 °, and the rake angle along the main cutting edge (8) is particularly positive.

15. The drill tip (2) according to any one of claims 1 to 14,

wherein the rake angle varies along the chisel edge (6) and increases in particular towards the inner portion (10).

16. The drill tip (2) according to any one of claims 1 to 15,

wherein the rake angle along the inner portion (10) is constant.

17. The drill tip (2) as claimed in one of claims 1 to 16,

wherein the rake angle along the outer portion (12) varies and decreases in particular towards the inner portion (10).

18. The drill tip (2) as claimed in one of claims 1 to 17,

wherein a relief angle is formed along the main cutting edge (8), the relief angle varying along the inner portion (10).

19. The drill tip (2) as claimed in one of claims 1 to 18,

wherein a plurality of main cutting edges (8) are formed, each of which adjoins behind a free surface (20),

wherein the chisel edge (6) is laterally limited only by the free surface (20).

20. A method for producing a drill tip (2) according to one of claims 1 to 19,

wherein a sharpening (16) is formed which is curved in such a way that the inner portion (10) extends arcuately from the outer edge of the centre (4) towards the chisel edge (6).

21. The method of claim 20, wherein the first and second portions are selected from the group consisting of,

wherein the entire sharpening (16) is ground in a single grinding pass and along a single and continuous grinding path.

Technical Field

Background

The invention relates to a drill tip and a method for producing a drill tip.

Drills are rotary tools used for machining workpieces. The drill has a drill tip at the front side, said drill tip comprising several cutting edges for machining material. As the drill rotates in the direction of rotation, the cutting edge removes chips from the workpiece, which are then typically transported away by flutes in the drill. The drill typically has a chisel edge in the center that is adjoined to the outer portion by a plurality of primary cutting edges. The chisel edge itself generally has no chip removing effect, but merely serves to displace material from the center.

Of particular importance for the drill is so-called centering, which indicates the extent to which the drill is affected by lateral forces and deviates from an ideal rotation about the axis of rotation during operation. During operation, improper centering can sometimes lead to uncontrolled lateral deviation of the drill and thus to increased mechanical stresses. Therefore, the service life of the drill is disadvantageously shortened. Centering depends to a large extent on the specific design of the cutting edge and in particular on the size of the chisel edge, which, as described, is detrimental to cutting performance.

The chip forming behavior of the drill is also important. For example, forming many small chips may be different from forming only one long chip on the respective cutting edge. The chip forming behavior is also strongly influenced by the specific design of the cutting edge.

DE 102013201062 a1 describes a drill tip with a special sharpening (point sharpening) which extends in a main direction and which transitions convexly from the free surface into the flute. As a result, particularly effective chisel edge thinning (sharpening) and large relief angles can be achieved in the chisel edge region.

Disclosure of Invention

In this respect, it is an object of the invention to improve the centering of the drill. At the same time, the best possible chip forming behavior should be ensured.

Achieve the object

According to the invention, the object is achieved by a drill tip with features according to claim 1 and a method for producing a corresponding drill tip with features according to claim 20. Advantageous configurations, further developments and variants are the subject matter of the dependent claims. Statements made in connection with the drill tip also apply correspondingly to the method and vice versa.

In particular, the drill tip is part of a drill. In a first design, the drill tip is an integral part of the drill and is thereby integrally connected to the shank. In a second design, the drill tip is a separate part and is then configured as an insert that is insertable into the carrier, such that the carrier and drill tip together form a modular drill. During operation, the drill tip rotates about a rotation axis, which is also the rotation axis of the entire drill, and also corresponds to the longitudinal axis of the drill tip. During operation, the drill tip is rotated in one rotational direction.

The drill point comprises a center, and a chisel edge is arranged at the center. Thus, when the drill tip is viewed from the front along the axis of rotation, the center is located in the middle and also contains the axis of rotation. The drill, in particular the drill tip, comprises in particular several flutes, which define the center as a region of the central position between the flutes. The center is generally circular and has a radius corresponding to the radius of the drill tip or the entire drill minus the flute depth. The center is also referred to as the core.

The drill tip further includes a primary cutting edge adjacent the chisel edge and extending outwardly from the center. In particular, the drill tip comprises a plurality of main cutting edges, i.e. at least two main cutting edges, which extend outwardly from the chisel edge, respectively. In the following, without loss of generality, it is assumed that the drill tip has exactly two main cutting edges. However, designs with a different number of main cutting edges and in principle also with only one main cutting edge are also possible and suitable. The main cutting edge and the chisel edge together form the cutting geometry of the drill tip. The main cutting edge and the chisel edge are also referred to simply as cutting edges, respectively.

Each of the cutting edges abuts a surface that points in the direction of rotation and through which any generated chips are removed. The orientation of this surface relative to the workpiece is characterized by a so-called rake angle. Specifically, the rake angle determines the cutting performance of the corresponding cutting edge. The rake angle is thus configured along the chisel edge and the main cutting edge, which rake angle can in principle also assume different values at different positions along the cutting edge, depending on the design of the cutting edge.

In the case of the invention, the main cutting edge is divided into two parts. In other words: the main cutting edge comprises an inner portion, here adjoining the chisel edge and arranged inside the center, and the main cutting edge further comprises an outer portion, adjoining the inner portion to the outside and arranged outside the center. Thus, the transition from the inner portion to the outer portion also defines or marks the center of the drill tip, such that the inner portion is inside and the outer portion is outside. In particular, this is a result of the inner part being produced during manufacture by sharpening, by means of which the material of the centre is removed, so that the chisel edge is shortened and the main cutting edge is lengthened and guided to the centre. The outer portion extends outwardly, in particular to the outer surface of the drill tip.

The drill tip further comprises sharpening, i.e. sharpening arranged on the drill tip. The sharpening is centrally located. Sharpening is used to shorten the chisel edge, i.e. to grind in ahead during production to shorten the chisel edge. In doing so, the main cutting edge is correspondingly elongated. The sharpening here is further bent in such a way that the inner portion extends arcuately from the central outer edge towards the chisel edge. Thus, sharpening is curved sharpening. Thus, the bent sharpening includes a first bend that is particularly configured to cause the sharpening to bend axially and is therefore also referred to as an axial bend. The sharpening is thus bent in particular about an axis which extends parallel to or corresponds to the axis of rotation. Thus, the sharpening appears to bend in the direction of rotation. This is in contrast to the concave sharpening mentioned at the outset in DE 102013201062 a1, in DE 102013201062 a1 the sharpening is radially curved, i.e. curved about an axis perpendicular to the axis of rotation. The first bend and the sharpening generally have a first radius of curvature which particularly indicates the radius of the bend in the direction of rotation which is preferably sharpened. In one suitable arrangement, the first radius of curvature corresponds to a radius of the inner portion. The first radius of curvature is suitably between 5% and 40% of the diameter of the drill tip. The first radius of curvature is constant or varies along the bend.

The described bend of the sharpening automatically creates an arcuate path (course) of the main cutting edge in the center so that when the sharpening is made, an internal portion is also formed. In particular, the advantage is now evident that the arcuate course of the main cutting edge allows said main cutting edge to enter particularly into the center and to allow the chisel edge to be correspondingly significantly shortened. This results in advantageously particularly short chisel edges, and thus a particularly good centering of the drill tip. The risk of lateral splitting during handling is significantly reduced. Thus, the overall service life of the drill tip is advantageously increased. The correspondingly elongated main cutting edge also brings the cutting effect to the center, so that during operation, a single, particularly long and advantageous helical chip is advantageously produced instead of a large number of short chips. In other words: the particularly long main cutting edge and its arcuate configuration in the center significantly improve the chip forming behavior in the center. This also contributes to a more stable concentricity of the drill tip and thus to improved centering. Overall, therefore, the arcuate main cutting edge and the advantageously shortened chisel edge make the center particularly stable. Sharpening also provides additional chip space to contain chips during operation.

Sharpening is particularly configured as an uninterrupted and continuous surface, i.e. not itself comprising any discontinuous transitions or edges or steps (steps), but is generally smooth. However, edges are in principle possible when transitioning to adjacent other surfaces, such as flutes or free surfaces.

The chip flute is arranged in particular in the leading position, i.e. in the direction of rotation in front of the main cutting edge. The flute thus adjoins the main cutting edge, in particular the outer part, while the sharpening adjoins the inner part, which finally leads the chip into the flute. The flutes are used to convey chips removed by the main cutting edges. The flutes are usually helical and extend from the front to the rear, so that the chips are conveyed to the rear in the axial direction, respectively. The free surface is arranged in particular on the other side of the main cutting edge, i.e. opposite the chip flute, i.e. in the direction of rotation behind the main cutting edge and follows the main cutting edge during operation. The free surface faces generally forward toward the workpiece. The free surface forms a relief angle with the workpiece or imaginary plane perpendicular to the axis of rotation. For each main cutting edge of the drill tip, a respective flute and free surface are preferably provided, which respectively surround the main cutting edge.

The entire inner portion extends in an arcuate manner, i.e. the inner portion follows an arcuate path. In principle, two variants are possible and advantageous. In a first variant, the inner portion is continuously arched, while in a second variant it is not continuous but is bent in an arched manner (kink). The sharpening is then correspondingly continuous or bent in a curved manner. The two variants can in principle be combined with each other in such a way that the first part of the inner part is continuously arcuate and the second part of the inner part is bent in an arcuate manner.

According to a first variant of the inner portion, the inner portion in the preferred configuration is thus continuously arcuate and extends in a continuously arcuate manner from the outer edge to the chisel edge. Thus, the entire inner portion forms a single continuous arc that does not have discontinuities or bends, nor has a straight section. At each position along the inner portion, the portion thus has a certain radius of curvature, which need not be the same at each position. The radius of curvature preferably increases, i.e. becomes larger, from the inside to the outside. When sharpening is configured, so is the grinding path of the grinding wheel, and so is the axial curvature.

In the context of the second variant of the inner portion, a configuration in which the inner portion is bent in an arcuate manner and for this purpose comprises a plurality of straight subsections which are arranged at an angle to one another is preferred. This is also true of the curved grinding path of the grinding wheel when sharpening is configured. Particularly preferred is an arrangement in which the inner part comprises exactly three straight subsections. Thus, the subsections are generally arranged along an arc, which results in a generally arcuate path. In contrast to the continuous arcuate variant, the inner part in the bent arcuate variant comprises at least two straight subsections which are arranged at an angle to one another and thus form an arc. Viewed in the direction of the free surface, two successive subsections then enclose an angle of less than 180 ° and preferably in the range from 100 ° to 175 °. More than two subsections correspondingly form at least two angles, whereby in one suitable configuration the further inward angle is larger than the further outward angle. Thus, similar to the outwardly increasing radius of curvature of the continuous arcuate variant, an inwardly increasing curvature is also achieved. However, conversely, a configuration in which the other inward angle is smaller than the other outward angle is also suitable.

The two continuous straight subsections are preferably connected to each other by rounded corners such that a continuous arcuate transition is formed between the two subsections. The three straight subsections are then correspondingly connected to one another by two rounded corners. Preferably, the respective rounded corners are configured with a radius of curvature in the range of 0.05mm to 3 mm. In particular, the rounded corners are shorter than the straight subsections.

In the case of a straight main cutting edge, the outermost subsection preferably transitions straight to the outer portion of the main cutting edge, so that there is no bend at the transition from the inner portion to the outer portion, and the outer portion continues through the outer portion into the center without interruption, for example until the next subsection optionally adjoins at an angle by means of a fillet.

Each straight subsection has a corresponding length. In a substantially suitable configuration, all of the subsections have the same length. However, a preferred configuration is one in which the length increases from the inside to the outside, such that the further outward subsection is longer than the further inward subsection. In case the subsections have different lengths, the longest subsection is preferably at most ten times the shortest subsection.

At least two main cutting edges are suitably formed, each comprising an arcuate inner portion, wherein the two inner portions are S-shaped when viewed together. All the main cutting edges of the drill tip are therefore further developed in the above-described manner, preferably by using corresponding curved sharpening. The resulting inner portions are then all curved in the same direction and extend together towards the chisel edge. Then, the arcuate inner portions of the two main cutting edges form an S-shaped course, with a chisel edge disposed at the center thereof.

The chisel edge is preferably likewise S-shaped. In one suitable arrangement, the chisel edge is delimited by a plurality of, in particular twisted, free surfaces which are configured such that the chisel edge accordingly extends in an S-shaped manner. This particular shape further improves the centering and chip forming behavior. The free surfaces on both sides of the chisel edge have enlarged surfaces in the S-shaped path compared to a straight path, so that the friction is reduced and the risk of lateral breakage during operation is also reduced. The respective free surface abuts behind the respective main cutting edge in the direction of rotation, and thus follows the respective main cutting edge during operation.

For the forward, free surface is generally limited by the main cutting edge. For the rear, the free surface is limited in particular by a flute, which thus follows the free surface during operation. For the outside, the free surface is limited in particular by the outer surface of the drill tip. In the center, on the other hand, the free surface is bounded by the chisel edge. The free surface is now preferably twisted, resulting in an S-shaped chisel edge. The chisel edge is preferably only laterally limited by the free surface, i.e. the chisel edge is not limited by sharpening. In effect, only the end point of the chisel edge abuts the respective sharpening, so that the chisel edge extends between the two opposed sharpenings. The end point is in particular also the transition point at which the main cutting edge adjoins the chisel edge. Thus, in the case of a drill tip having two main cutting edges, the four surfaces meet each other centrally; i.e. two free surfaces laterally surrounding the chisel edge and two sharpening edges spaced from each other by the chisel edge.

The drill tip is in particular configured such that the main cutting edge is subdivided by sharpening into an inner part and an outer part in the front and in particular only adjoins the free surface in the rear. In other words: the main cutting edge abuts the free surface at the rear, the inner portion abuts the sharpening at the front, and the outer portion abuts the flute at the front.

In one advantageous configuration, the blade sharpening connects the flute and the free surface and is additionally convex such that the blade sharpening extends from the flute in the direction of the free surface in an outwardly curved manner. Thus, the sharpening is curved. The sharpening therefore has a second bend. Sharpening connects the flute of one of the primary cutting edges to the free surface of the corresponding leading primary cutting edge. The male sharpening is preferably configured as described in the aforementioned DE 102013201062 a 1. The resulting complex route of sharpening is correspondingly expensive to produce, but it offers significant advantages in terms of the centering and chip forming behaviour of the drill tip. Sharpening is also radially curved, in addition to axially curved; i.e. it has, in addition to the first bend, a second bend which is followed by a radial bend and is also referred to as radial bend. Specifically, the second curved portion is continuous and unbent. The second bend and corresponding sharpening therefore has a second radius of curvature which is specifically indicative of the radius of the sharpening bend. The second radius of curvature specifically indicates the radius at which the sharpening transitions from the flute to the free surface; i.e. in particular the radius of the bend around the radial direction, wherein the radial direction is perpendicular to the longitudinal axis. In one suitable configuration, the second radius of curvature is between 5% and 60% of the diameter of the drill tip.

Alternatively or additionally, in one suitable arrangement the sharpening comprises a base which is concave and, viewed in the longitudinal direction, in particular undercuts (undercuts) the inner portion. The sharpening therefore has a third bend. Preferably, a convex, i.e. outwardly curved, grinding wheel is used, yielding a concave seat during the creation of the drill tip. Such grinding wheels have a grinding surface which faces radially outwards with respect to the axis of rotation of the grinding wheel and which, in a cross section perpendicular to the axis of rotation, is convex, in particular in the manner of a tire. Then sharpening, such as bending inward; i.e. in the rear direction of and into the drill tip. The sharpening thus forms a recess, viewed in cross-section of the longitudinal axis. The recess also produces, in particular, a cross section perpendicular to the second bend. A convex sharpening with a concave base therefore has a saddle shaped course and is therefore configured as a saddle shaped surface between the flute and the free surface. Due to the first curvature, the saddle-shaped surface is also curved in the direction of rotation. The third sharpened bend with the concave base extends particularly about an axis of curvature that is perpendicular to both the longitudinal axis and the radial direction. The third bend is preferably perpendicular to both the first bend and the second bend. The third bend and corresponding sharpening has a third radius of curvature which specifically indicates the radius of concavity of the sharpening, i.e., the manner in which the base is shaped and sized. The third radius of curvature also specifically indicates the radius forming the outer surface of the abrasive wheel. In one suitable arrangement, the third radius of curvature is between 5% and 60% of the diameter of the drill tip.

In a particularly advantageous design, the outer surface of the grinding wheel is formed by the aforementioned radius, which is the first radius, and two straight lines and a further radius, which is the second radius. The first radius connects two straight lines which in a sense represent the radially outward facing side of the grinding wheel, and the second radius forms a rounded transition of one of the straight lines to a lateral surface of the grinding wheel, wherein the lateral surface extends in particular perpendicularly to the axis of rotation. The grinding wheels are not necessarily symmetrical with respect to a plane perpendicular to the axis of rotation.

In a preferred arrangement the sharpening abuts the free surface and forms with it an edge which starts at the chisel edge and extends centrally in an S-shaped manner. Such characteristic S-shaped edges can be particularly produced when sharpening is produced using a particular grinding path for the grinding wheel. Moving the grinding wheel all the way into the center creates a first edge radius that starts at the transition point between the chisel edge and the inner portion and in particular due to the outwardly curved grinding wheel having a convex grinding surface. This first edge radius also defines, among other things, the aforementioned base of the sharpening and forms a transition from the base to the free surface. The first edge radius is outwardly contiguous with the second edge radius, however wherein the second edge radius has opposing bends, thereby creating an overall S-shape. The two edge radii are located inside the center. For the outer portion, the second edge radius especially transitions into a straight line which preferably extends all the way to the outer surface. The edge radii may in principle have the same size, but it is useful that the two radii differ. In one suitable configuration, the first edge radius, i.e., the inner edge radius, is greater than the second edge radius, i.e., the outer edge radius, when viewed from the front; preferably, 1.1 to 5 times greater. Conversely, configurations in which the first inner edge radius is smaller than the second outer edge radius are also suitable, whereby the outer edge radius is preferably 1.1 to 5 times larger.

In one preferred arrangement, the sharpening has a fourth bend such that the sharpening slopes downwardly and towards the outer surface as viewed in the radial direction. Thus, the sharpening is convex in the radial direction and then inclined towards the back when viewed from the inside to the outside. During production, this is achieved in particular by moving the grinding wheel in an arcuate manner in the direction of the centre from the outer surface into the drill tip, so that the sharpening is convex in the radial direction. At the same time, this also results in the above-mentioned edge of the free surface, among other things.

In general, a number of suitable configurations are because the curved sharpening has a second bend, a third bend, or a fourth bend, or a combination thereof, in addition to the first bend. The convex path, the second bend, produces a bulbous configuration of the sharpening in the region between the free surface and the flute. In other words: the sharpening curves outwardly, opposite to the direction of rotation, i.e. rearwardly when viewed from the direction leading the primary cutting edge and in the direction of the workpiece. The convex path advantageously eliminates the edge in the transition region from sharpening to the flute and instead creates a continuous transition that improves chip removal. On the other hand, the first axial bend, i.e. the curved path, when viewed towards the centre, causes the rake angle of the main cutting edge in this region to be correspondingly increased compared to a configuration without such sharpening. Similar to the first bend, the fourth bend creates a bulbous configuration, but in a direction substantially perpendicular to the first bend; i.e. not in the direction of rotation, but from the inside to the outside in the radial direction. The third bend differs from the first, second and fourth bends finally in that it affects the smaller section of the sharpening, namely the base, which is centrally disposed, close to the chisel edge, and undercuts in particular the inner part and thereby also defines in particular here the rake angle.

In one suitable arrangement, the drill tip includes an outer surface located radially outwardly and the sharpening connects the flute and the free surface and extends to the outer surface such that the free surface is fully spaced from the flute by the sharpening, particularly when viewed in a clockwise direction, i.e. a direction opposite to the direction of rotation and starting from the primary cutting edge. In other words: the sharpening extends to the outer edge of the drill tip, i.e. to the radially outer surface of said drill tip, so that the free surface is completely spaced from the flute by the sharpening, as viewed in the clockwise direction from the main cutting edge, and the flute and the free surface are thus not in immediate proximity to each other. In the counter-clockwise direction, i.e. in the direction of rotation, the free surface abuts the main cutting edge and then transitions to a different flute and a different sharpening.

Sharpening allows for optimum adjustment of the rake angle centrally along the main cutting edge. Due to the curved path of sharpening, material is removed from the flute during the creation of the drill tip, causing an increase in the rake angle in the region of the main cutting edge.

The inner portion of the main cutting edge and the chisel edge meet at a transition point where the sharpening also correspondingly meets the free surface of the laterally adjacent chisel edge. In one suitable arrangement, the rake angle at the transition point varies in a discontinuous manner, i.e., discontinuously or abruptly, from the main cutting edge to the chisel edge. Thus, there is a corner at the transition point connecting the inner portion to the chisel edge. Accordingly, there is a corresponding presence, in particular, between the free surface and the sharpening, of the above-mentioned edge, which causes the rake angle to change abruptly. Generally, the rake angle of the inner portion is defined by sharpening, while the rake angle of the chisel edge is preferably defined by a free surface. Thus, the rake angle may advantageously be adjusted along the chisel edge and the inner portion, respectively, individually and independently.

The rake angle along the chisel edge is preferably less than the rake angle along the main cutting edge. The cutting performance of the main cutting edge is then correspondingly particularly high, and at the same time the smaller rake angle of the chisel edge improves the centering.

The rake angle along the chisel edge is preferably negative and therefore less than the rake angle along the main cutting edge. In a particularly preferred arrangement, the rake angle along the chisel edge is negative and greater than-2 °, and the rake angle along the main cutting edge is preferably positive. In one suitable arrangement, the rake angle along the chisel edge is-20 ° or even more negative, i.e., negative and at least 20 ° in magnitude. The rake angle along the main cutting edge is suitably positive or 0 ° or slightly negative, i.e. greater than-2 ° and for example-1 °. This positive rake angle or substantially positive rake angle of the main cutting edge, in particular of the inner portion, results in a stable center. A particularly short chisel edge further enhances this effect.

The rake angle along the chisel edge preferably varies and in particular increases towards the inner part, i.e. towards the outer part. This significantly improves chip formation behavior and centering. The rake angle along the chisel edge, i.e. in particular in the free surface, is preferably-40 ° to-70 °, i.e. negative and 40 ° to 70 °.

The rake angle along the inner portion is preferably constant. This is achieved in particular by a particularly curved arrangement of the sharpening, which is correspondingly incorporated into the drill tip. A constant rake angle along the inner portion improves chip formation behavior. The rake angle along the inner portion, i.e. in sharpening, is preferably-10 to + 10.

The rake angle preferably varies along the outer portion and in particular decreases towards the inner portion, i.e. increases towards the outside. This further improves the chip forming behavior, as more material is removed, especially towards the outside. The rake angle along the outer portion, i.e. in the flute, is preferably 10 ° to 40 °. The rake angle along the outer portion preferably varies in a similar manner to the rake angle along the chisel edge, i.e. in each case the rake angle increases towards the outer portion, so that similar advantages are achieved in both regions.

Some or all of the aforementioned configurations are preferably combined with each other in terms of their rake angles. In a particularly preferred configuration, viewed from the inside to the outside, the rake angle first increases along the chisel edge, then remains constant along the inner portion, and then increases further along the outer portion. In another advantageous development, the rake angle along the chisel edge is negative and the rake angle along the main cutting edge is positive. A rake angle of 0 ° is in particular considered to be a positive rake angle.

Along the main cutting edge a relief angle is formed, which preferably varies along the inner portion and thereby increases, in particular from the outside towards the inside. The clearance angle also varies in particular along the outer portion and here also increases from the outside towards the inside. However, the variation, i.e. the difference between the minimum and maximum relief angles, is preferably larger on the inner part than on the outer part. In particular in the inner part, the clearance angle increases from the outside to the inside, preferably significantly, i.e. in particular by at least 10 °. On the inner part, the relief angle preferably increases to at least 30 ° towards the chisel edge. For example, the relief angle is 10 ° at the outer edge and 38 ° at the center of the chisel edge. On the inner part, the clearance angle is suitably in the range of 4 ° to 50 °. In a likewise suitable variant, on the other hand, the relief angle is constant along the inner or outer portion or along the entire main cutting edge.

As indicated above, in one preferred configuration, a plurality of main cutting edges are formed, each of which adjoins the free surface behind, wherein the chisel edge is then limited laterally only by the free surface, i.e. exclusively by the free surface. The chisel edge is therefore completely surrounded by the free surface and is connected to the sharpening only at the tip with a quasi point connection (square point connection). Thus, the design of the chisel edge is advantageously decoupled from the sharpening configuration so that the rake angle along the chisel edge can be advantageously set and also set independently of the rake angle of the main cutting edge during the creation of the drill point.

The drill tip is in particular made of metal, preferably hard metal. The drill tip is suitably formed as a single piece, i.e. is formed in one piece or even integrally, i.e. not in a modular manner. In one suitable arrangement, the cutting edge or a portion thereof is provided with an additional coating.

The drill tip in particular has a diameter preferably in the range of 1mm to 40 mm. The central diameter is preferably at least 20% and at most 75% of the diameter. The length of the chisel edge is preferably 2% to 15% of the diameter measured along a line connecting the end points of the chisel edge. If the inner portion is bent in an arcuate manner, the respective flat subsection preferably has a length in the range of 1% to 20% of the diameter of the drill tip.

To create a drill point as described above, a sharpening is made which bends in such a way that the inner portion extends arcuately from the outer edge of the center toward the chisel edge. These advantages arise accordingly.

During production, in particular grinding wheels are used, which are guided along a grinding path and remove material from the center of the drill tip. Thus, in particular, the cutting corner initially formed by the chisel edge and the main cutting edge is ground off and replaced by a curved inner portion. The formation of the sharpening also advantageously shortens the chisel edge.

In a particularly preferred arrangement, the entire sharpening is ground in a single grinding pass and along a single and continuous grinding path. This brings about the following advantages, among others: the grinding wheel does not have to be removed but moved in a single pass. Even if the grinding path is correspondingly complex depending on the configuration of the sharpening, the overall production is particularly simple and fast since the forming sharpening is carried out only one grinding pass.

Sharpening, which is curved and convex, in particular, produces an abrasive path that follows a double curved path. The grinding path then has two curved portions which are traversed in sequence and curved in different planes. In order to produce a curved sharpening, i.e. to form a curved portion of the inner portion, the grinding wheel is suitably inclined or skewed perpendicular to the axis of rotation of the grinding wheel. In order to produce a convex sharpening, i.e. a transition of the flutes in an arcuate manner to the curvature through which the free surface passes, on the other hand, the grinding wheel must roll locally, for example on its grinding surface. The two movements are suitably performed in a superimposed manner or in sequence, i.e. one after the other.

The object is also achieved, inter alia, by a drill having a drill tip as described above, which drill tip is configured as an insert for a carrier and which drill tip, when connected to the carrier, forms a modular drill, as well as a separate drill tip. The object is also achieved, inter alia, by a grinding wheel for producing a drill tip as described. All statements regarding drill tips and methods apply analogously to drill and grinding wheels.

Drawings

In the following, design examples of the invention are explained in more detail with the aid of the figures. The figures show schematically:

the drill tip of the drill in the front view of figure 1,

the drill of figure 1 in the side view of figure 2,

figure 3 is an enlarged cross-section of the drill tip of figure 1,

figure 4 a perspective view of the drill tip of figure 1,

a variation of the drill tip in the front view of figure 5,

figure 6 a perspective view of the drill tip of figure 5,

figure 7 another perspective view of the drill tip of figure 5,

the drill tip of figure 5 in side view of figure 8,

figure 9 the drill tip of figure 5 in another side view,

the drill tip of figure 5 in another side view of figure 10,

another variation of the drill tip in the front view of figure 11,

figure 12 a perspective view of the drill tip of figure 11,

the drill tip of figure 11 in side view of figure 13,

details of the grinding wheel in the cross-sectional view of figure 14,

figure 15 the grinding wheel of figure 14 during the creation of the drill tip,

another variation of the drill tip in the front view of figure 16,

figure 17 is an enlarged detail of figure 16,

the drill tip of figure 16 in the side view of figure 18,

the drill tip of figure 16 in the perspective view of figure 19,

figure 20 the drill tip of figure 16 in a different perspective view,

fig. 21 is a cross-sectional view of the view of fig. 20.

Detailed Description

The figures show various design examples of a drill tip 2, which is a part of a drill shown only in section. Fig. 1 to 4 show a first variant of the drill tip 2, fig. 5 to 10 show a second variant, and fig. 11 to 13 show a third variant. Fig. 14 then shows a particularly advantageous grinding wheel 3 for producing the drill tip 2, and fig. 15 shows such a production. Finally, fig. 16 to 21 show a fourth variant of the drill tip 2. The drill tip 2 here is an integral part of the drill and is thereby integrally connected to the shank. In a variant not depicted, on the other hand, the drill tip 2 is a separate part and is then configured as an insert that can be inserted into the carrier, so that the carrier and the drill tip 2 together form a modular drill. During operation, the drill tip 2 rotates in a direction of rotation U about a rotation axis L, which is also the rotation axis of the entire drill and which also corresponds to the longitudinal axis of the drill tip 2 and the entire drill and extends substantially in the longitudinal direction.

The drill tip 2 comprises a centre 4 in which a chisel edge 6 is arranged. In fig. 1, the center is indicated by a dashed circle. When the drill tip 2 is viewed from the front along the axis of rotation L, the center 4 is correspondingly located at the center, as can be seen in fig. 1. In fig. 2, the drill and drill tip of fig. 1 are shown from the side. Fig. 3 shows an enlarged view of the center 4. Fig. 4 shows a perspective view of the drill and in particular the drill tip 2.

The drill tip 2 comprises several, in this case two, main cutting edges 8, each of which adjoins the chisel edge 6 and extends outwardly from the center 4. In a variant not depicted, the drill tip 2 has a different number of main cutting edges 8. The main cutting edge 8 and the chisel edge 6 are also referred to simply as cutting edges, respectively, and together form the cutting geometry of the drill tip 2 as a whole.

The respective main cutting edge 8 is here divided into two sections, an inner portion 10 adjoining the chisel edge 6 and arranged inside the center 4, and an outer portion 12 adjoining the inner portion 10 to the outside and arranged outside the center 4. The transition from the inner portion 10 to the outer portion 12 thus defines the centre 4 of the drill tip 2, such that the inner portion 10 is inside and the outer portion 12 is outside. The outer portion 12 then extends outwardly to the outer surface 14 of the drill tip 2.

Each of the cutting edges 6, 8 abuts a surface which is directed in the direction of rotation U and through which any generated chips are removed. The orientation of this surface relative to the workpiece is characterized by a so-called rake angle, which, depending on the configuration, can in principle also assume different values at different positions along the cutting edge 6, 8.

Now, in the center 4, the rake angle is modified by a specific sharpening 16. A sharpening 16 is provided at the centre 4 and is initially used to shorten the chisel edge 6, i.e. ground in front during production to shorten the chisel edge 6. The sharpening 16 is further bent in a manner such that the inner portion 10 extends arcuately from the outer edge of the center 4 toward the chisel edge 6. Two variants are possible. In a first variant, the inner portion 10 is continuously arcuate; this is the case in the design examples of fig. 1 to 13. In a second variant, on the other hand, the inner portion 10 is bent in an arcuate manner, as shown in the design examples of fig. 16 to 21.

The outer edge and the centre 4 are indicated in fig. 1 by dashed circles. The sharpening 16 is generally a bent sharpening 16, i.e., it includes a first bend K1 configured to bend the sharpening 16 axially, i.e., approximately in the direction of rotation U. The first bend K1 is explicitly indicated in fig. 4, 7, 16, 18 and 19 by a bend dashed line. It is also apparent that the first bend K1, and thus the sharpening 16, has a first radius of curvature R1 which specifically indicates the radius at which the sharpening 16 is bent. In fig. 4, the first radius of curvature R1 also corresponds to the radius of the inner portion 10.

The described first curved section K1 of the sharpening 16 automatically creates an arcuate path of the primary cutting edge 8 at the center 4 so that when the sharpening 16 is formed, the inner portion 10 is also formed. The arcuate course of the main cutting edge 8 allows said main cutting edge to enter the center 4 in particular and to shorten the chisel edge 6, as already mentioned. The main cutting edge 8 is correspondingly elongated.

In the leading position, i.e. in the direction of rotation U in front of the respective main cutting edge 8, a respective flute 18 is formed, which adjoins the associated main cutting edge 8. The flutes 18 serve to convey chips removed by the main cutting edge 8. On the other side of the main cutting edge 8, i.e. opposite the flute 18 and in the direction of rotation U behind the main cutting edge 8, a free surface 20 is arranged, which faces substantially forwards. For each main cutting edge 8 of the drill tip 2, a flute 18 and a free surface 20 are now provided, which accordingly surround the respective main cutting edge 8.

The two main cutting edges 8 shown in the respective design examples each have an arcuate inner portion 10 which, when viewed together, is S-shaped. This is particularly emphasized in fig. 1 with the dashed and sigmoid lines drawn as slightly offset for more clear visibility. However, the S-shape can also be seen directly in fig. 3 to 6, 11, 12, 16 and 17. Thus, the inner portions 10 all curve in the same direction and extend together towards the chisel edge 6. The chisel edge 6 is then arranged in the center of the S-shaped path.

In the design example shown, the chisel edge 6 itself is also S-shaped. For this purpose, the chisel edge 6 is correspondingly surrounded by a twisted free surface 20, so that an S-shaped course is produced. This is particularly evident in the detailed views of fig. 3 and 17, where dashed and S-shaped lines are additionally included in fig. 3 to illustrate the S-shaped course. However, the S-shape of the chisel edge 6 is not mandatory; the chisel edge 6 may also have other geometries.

The respective free surface 20 is bounded forwardly by the primary cutting edge 8 and rearwardly by the sharpening 16 or flute 18 and the sharpening 16. For the outside, the respective free surface 20 is limited by the outer surface 14 of the drill tip 2. On the other hand, in the centre 4, the respective free surface 20 is bounded by the chisel edge 6. The free surface 20 is now preferably twisted, resulting in an S-shaped chisel edge 6. In the case of the present invention, the chisel edge 6 is only laterally limited by the free surface 20. Only the end point of the chisel edge 6, i.e. the transition point P to the primary cutting edge 8, abuts the respective sharpening 16, so that the chisel edge 6 extends between the two opposing sharpens 16. The chisel edge 6 is therefore completely surrounded by the free surface 20 and is in a point-of-sight connection with the sharpening 16 only at the ends. In a variant not depicted, on the other hand, the chisel edge 6 is not S-shaped.

In the variant shown in fig. 1 to 4, the sharpening 16 is bent only as indicated in fig. 4. In the variants of fig. 5 to 13 and 16 to 21, however, the sharpening 16 is additionally convex, so that it extends in an outwardly curved manner from one of the flutes 18 and in the direction of one of the free surfaces 20. In addition to the axial first bend K1 of the sharpening 16, the sharpening is also radially bent; that is, in addition to the first bend K1, the sharpening has a second bend K2, which is followed by a radial bend K2. The perspective view of this additional second bend K2 in fig. 6 and 7 is explicitly indicated with a dashed bend K2 and is also clearly visible in the sectional view of fig. 13. Thus, the second bend K2 and the sharpening 16 have a second radius of curvature R2, which indicates the radius at which the sharpening 16 bends and the radius at which the sharpening 16 transitions from the flute 18 to the free surface 20.

The first bend K1 is not explicitly indicated in fig. 6, but is still present and is explicitly shown in the perspective view of fig. 7 in addition to the second bend K2. The sharpening 16 is thus curved and connects the flute 18 of one of the primary cutting edges 8 to the free surface 20 of the corresponding leading primary cutting edge 8. In addition to the first axial bend K1 of the sharpening 16, the sharpening is thus also bent radially by the second bend K2. Thus, in general, the sharpening 16 is a curved and convex sharpening 16. The convex path creates a bulbous configuration of the sharpening 16 in the region between the free surface 20 and the flute 18. This can be seen particularly clearly in fig. 7. Fig. 8 to 10 further show respective side views of a drill with the drill tip 2 of fig. 5, whereby the particular geometry of the sharpening 16 is also apparent in these side views. The sharpening 16 is bent outwards and is opposite to the direction of rotation U, i.e. backwards when viewed from the leading main cutting edge 8 and in the direction of the workpiece not depicted. The convex path advantageously eliminates edges in the transition region from the point edge 16 to the flute 18 and, as shown herein, instead creates a continuous transition. On the other hand, the first axial bend K1 causes the rake angle of the main cutting edge 8 to increase correspondingly when viewed towards the center 4.

Figures 11 to 13 show another arrangement in which the sharpening 16 comprises a base 22 which is concave when viewed in a radial direction. This can be seen particularly clearly in the perspective view in fig. 12. During the production of the drill tip 2, a concave seat 22 is produced using a convex, i.e. outwardly curved, grinding wheel 3. Such a grinding wheel 3 has a grinding surface which faces radially outwards with respect to the axis of rotation a of the grinding wheel 3 and which is convex in a cross-section perpendicular to the axis of rotation a. The sharpening 16 then bends inwards, i.e. in the rear direction of and into the drill tip 2.

The sharpening 16 with the concave base 22 therefore has a third bend K3, which is shown in detail in broken lines in fig. 12. The third bend K3 and the sharpening 16 then have a third radius of curvature R3, which indicates the radius of the base 22 that is concave and the radius of the outer surface of the grinding wheel 3. The first bend K1 is then explicitly indicated in fig. 11 with a dashed line. The second curved portion K2 is indicated by a broken line in fig. 13. Fig. 11 to 13 also each show an associated radius of curvature R1, R2, R3.

The design example of fig. 20 shows a fourth bend K4 which produces a convex sharpening 16 as the first bend K1 but not in the direction of rotation U, but rather when viewed in a radial direction from the inside to the outside, such that the sharpening 16 slopes downwardly from the center 4 toward the outer surface 14.

As can be clearly seen in fig. 11 to 13, the convex sharpening 16 with the concave base 22 has a saddle shaped course and is therefore configured as a saddle shaped surface between the flute 18 and the free surface 20. Due to the first curved portion K1, the saddle-shaped surface is also curved in the direction of rotation U.

Overall, it is clear that the different configurations of the drill tip 2 are due to the curved sharpening 16 having, in addition to the first curve K1, a second curve K2, a third curve K3, a fourth curve K4, or any combination thereof. For example, as can be seen in fig. 6, 13 and 20, the convex course, i.e. the second bends K2, K4, produces a bulbous configuration of the sharpening 16 in the region between the free surface 18 and the flute 20. The third bend K3 creates a seat 22 that also defines a front corner and undercuts the inner portion 10 accordingly, if necessary.

In the case of the invention, in fig. 1 to 4 and 16 to 21, the sharpening 16 extends to the outer edge of the drill tip 2, i.e. to the radially outer surface 14 of said drill tip, so that the free surface 20 is completely spaced from the flute 18 by the sharpening 16, when viewed in the clockwise direction starting from the main cutting edge, i.e. opposite to the direction of rotation U, and then the flute 18 and the free surface 20 are not adjacent to each other. In figures 5 to 13, on the other hand, the sharpening 16 is not continuous with the outer surface 14, but is here continuous with only half of the radius, i.e. one quarter of the diameter D of the drill tip 2. The configuration of the sharpening 16 to the outer surface 14 is independent of whether the sharpening has one or more additional bends K2, K3, K4 in addition to the first bend K1. The concepts of the bends K1-K4 described in connection with the various variants of the drill tip 2 can be combined with each other and also with the sharpening 16 extending to the outer surface 14 as desired.

As can be seen in particular in fig. 4 to 7, 11 and 17, the inner portion 10 of the main cutting edge 8 and the chisel edge 6 meet at a transition point P where the sharpening 16 also meets correspondingly the free surface 20 of the laterally adjoining chisel edge 6. At the transition point P, the rake angle changes in a discontinuous, i.e. abrupt, manner from the main cutting edge 8 to the chisel edge 6. Thus, there is a corner at the transition point P connecting the inner portion 10 to the chisel edge 6. There is a corresponding edge between the free surface 20 and the sharpening 16 which causes the rake angle S to change abruptly. In principle, the edge substantially ends where the inner portion 10 transitions to the outer portion 12. The rake angle of the inner portion 10 is thus defined by the sharpening 16, while the rake angle of the chisel edge 6 is defined by the free surface 20.

In the design example of fig. 16 to 21, the inner part 10 is bent in an arcuate manner and comprises a plurality of straight subsections 24 arranged at an angle to one another. In the case of the present invention, there are exactly three straight subsections 24. The subsections 24 are generally arranged along an arc, which results in a generally arcuate path. When viewed towards the free surface 20, two successive subsections 24 enclose an angle W which is smaller than 180 ° and in one case here is approximately 155 ° and 145 °, whereby the further inward angle W is larger than the further outward angle W.

Two consecutive straight subsections 24 are connected to each other by rounded corners 26 such that a continuous arcuate transition is formed between the two subsections 24. The overall double fold path can be seen particularly clearly in the detailed view of fig. 17. As can further be seen in fig. 17, the outermost subsection 24 in the case of the present invention transitions in a straight manner to the outer portion 12 of the main cutting edge 8, so that there is no bend at the transition from the inner portion 10 to the outer portion 12. The straight subsections 24 also each have a length L2, where the length L2 increases when viewed from the inside to the outside, such that the other outward subsection 24 is longer than the other inward subsection 24.

The sharpening 16 substantially abuts the free surface 20 and, in the design example shown, forms an edge 28 therewith. In the design example of fig. 16 to 21, the edge 28 characteristically extends starting from the chisel edge 6 in an S-shape and inside the center 4. Beginning at the transition point P between the chisel edge 6 and the inner portion 10, a first edge radius R4 is formed which forms the transition from the base 22 of the sharpening 16 to the free surface 20. This can be seen particularly clearly in fig. 17 and also in the perspective view in fig. 20. The first edge radius R4 is outwardly contiguous with the second edge radius R5, however with the second edge radius having opposing bends, creating an overall S-shape. The two edge radii R4, R5 are located inside the center 4. For the outer part, as can be seen in fig. 20, for example, the second edge radius R5 transitions into a straight line which, in the design example shown, extends to the outer surface 14. In the case of the present invention, the first edge radius R4, i.e. the inner edge radius R4, is larger than the second edge radius R5, i.e. the outer edge radius R5, when viewed from the front.

Fig. 21 shows the same view as fig. 20, but with the section from the sharpening 16 to the flute 18 such that the free surface 20 is not visible, but the two edge radii R4, R5, emphasized by the additional circles, are visible. On the other hand, in cross-sectional view, and therefore regardless of free surface 20, inner edge radius R4 is less than outer edge radius R5, as shown in fig. 21.

In the design example shown, the rake angle along the chisel edge 6 is negative and the rake angle along the main cutting edge 8 is positive, and thus the rake angle along the chisel edge 6 is smaller than the rake angle along the main cutting edge 8. The rake angle varies along the chisel edge 6 and increases towards the inner portion 10. On the other hand, the rake angle of the inner portion 10 along here is constant, i.e. maintains the same value. This is achieved by the particular curved configuration of the sharpening 16. The rake angle again varies along the outer portion 12 and, like the chisel edge 6, increases towards the outside. The free surface 20 following the respective main cutting edge 8 forms a relief angle which here varies along the outer portion 12 and in particular also along the inner portion 10 and thus increases inwardly.

The diameter D of the drill tip 2 is in the range 1mm to 40mm, and in the design example 8.5 mm. The centre 4 has a centre diameter ZD which is 20% to 75% of the diameter D. In a design example, the center diameter CD is in the range of 2mm to 4 mm. The length of the chisel edge 6 is 0.5% to 15% of the diameter D and in the design example between 0.17mm and 1.27mm, as measured along a straight line not depicted, which connects the end points of the chisel edge 6, i.e. the transition points P.

During the production of the drill tip 2, a grinding wheel 3 is used, which is guided along a grinding path and removes material from the core 4. Thus, the cutting angle initially formed by the chisel edge 6 and the main cutting edge 8 is ground away and replaced by the curved inner portion 10, and the chisel edge 6 is shortened at the same time. Fig. 14 shows a design example of the grinding wheel 3; fig. 15 shows the use of this grinding wheel 3 for producing a drill tip 2. The entire sharpening 16 is ground in a single grinding pass and along a single and continuous grinding path. In the case of the curved and convex sharpening 16 shown in fig. 5 to 13, an abrasive path following a multi-curved path is created such that the correspondingly formed curves K1, K2, K3 proceed in a superimposed or sequential manner. The grinding path is then a superposition of bends K1, K2, K3 which are traversed in succession or in superposition, i.e. simultaneously or partly simultaneously, and which are bent in different planes. To produce the curved sharpening 16, i.e. the first bend K1 forming the inner portion 10, the grinding wheel 3 is tilted or inclined perpendicular to the axis of rotation a of the grinding wheel 3. In order to produce a convex sharpening 16, i.e. a second curve K2 through which the flute 18 transitions in an arcuate manner into the free surface 20, on the other hand, the grinding wheel 3 rolls on its grinding surface. The third bend is automatically created by the grinding profile of the grinding wheel 3. This grinding profile becomes particularly clear in the example of fig. 14. The grinding wheel 3 shown therein comprises an outer surface which is substantially formed by a first radius SR1, two straight lines G1, G2 and a further straight line, i.e. a second radius SR 2. The first radius SR1 connects two straight lines G1, G2 which in a sense represent the radially outward facing side of the grinding wheel 3, and the second radius SR2 forms a rounded transition of the straight line G2 to a lateral surface SF of the grinding wheel 3, wherein the lateral surface SF here extends perpendicular to the axis of rotation. Fig. 15 specifically shows that the grinding wheel 3 is not necessarily symmetrical. It is also apparent that in this case, the first radius SR1 corresponds to the third radius of curvature R3.