DRILL TIP AND METHOD FOR PRODUCING A DRILL TIP

Abstract

The invention relates to a drill tip (2), comprising a center (4), at which a chisel edge (6) is arranged, and comprising a main cutting edge (8), which adjoins the chisel edge (6) and runs outward from the center (4). A rake angle is formed along the chisel edge (6) and the main cutting edge (8). The main cutting edge (8) has an inner portion (10), which adjoins the chisel edge (6) and is arranged within the center (4). The main cutting edge (8) has an outer portion (12), which outwardly adjoins the inner portion (10) and is arranged outside of the center (4). A point thinning (16) is formed on the drill tip (2), which point thinning is curved in such a way that the inner portion (10) runs arcuately from an outer edge of the center (4) toward the chisel edge (6). The invention further relates to a method for producing a drill tip (2) of this type.

Claims

1. A drill tip, comprising: a center, in which a chisel edge is disposed; and a main cutting edge, which adjoins the chisel edge and extends outward from the center, wherein a rake angle is formed along the chisel edge and the main cutting edge, wherein the main cutting edge comprises an inner portion, which adjoins the chisel edge and which is disposed inside the center, wherein the main cutting edge comprises an outer portion, which adjoins the inner portion to the outside and which is disposed outside the center, wherein a point thinning is formed, which is curved in such a way that the inner portion extends arcuately from an outer edge of the center toward the chisel edge.

2. The drill tip according to claim 1, wherein the inner portion is continuously curved and extends from the outer edge to the chisel edge in a continuously arcuate manner.

3. The drill tip according to claim 1, wherein the inner portion is shaped in an arcuate manner and comprises a plurality of straight subsections, which are disposed at an angle to one another.

4. The drill tip according to claim 3, wherein the inner portion comprises at least three straight subsections.

5. The drill tip according to claim 4, wherein two consecutive straight subsections are connected to one another via a rounded corner.

6. The drill tip according to claim 1, wherein at least two main cutting edges are formed, each comprising an arcuate inner portion, wherein the two inner portions are S-shaped when viewed together.

7. The drill tip according to claim 1, wherein the chisel edge is bordered by a plurality of free surfaces, which are configured such that the chisel edge extends in an S-shaped manner.

8. The drill tip according to claim 1, wherein the point thinning connects a flute and a free surface and is additionally convex such that the point thinning extends from the flute in the direction of the free surface in an outwardly curved manner.

9. The drill tip according to claim 1, wherein the point thinning comprises a base, which is concave when viewed in radial direction.

10. The drill tip according to claim 1, wherein the point thinning adjoins a free surface and together with said free surface forms an edge which, starting at the chisel edge, extends in an S-shaped manner within the center.

11. The drill tip according to claim 1, wherein said drill tip comprises an outer surface, which is located radially on the outside, and wherein the point thinning connects a flute and a free surface and extends to the outer surface, so that the free surface is completely spaced apart from the flute by the point thinning.

12. The drill tip according to claim 1, wherein the rake angle at a transition point (P) from the main cutting edge to the chisel edge changes in a non-continuous manner.

13. The drill tip according to claim 1, wherein the rake angle along the chisel edge is smaller than along the main cutting edge.

14. The drill tip according to claim 1, wherein the rake angle is negative along the chisel edge and greater than 2 and in particular positive along the main cutting edge.

15. The drill tip according to claim 1, wherein the rake angle varies along the chisel edge and increases toward the inner portion.

16. The drill tip according to claim 1, wherein the rake angle along the inner portion is constant.

17. The drill tip according to claim 1, wherein the rake angle along the outer portion varies and decreases toward the inner portion.

18. The drill tip according to claim 1, wherein a clearance angle is formed along the main cutting edge, which varies along the inner portion.

19. The drill tip according to claim 1, wherein a plurality of main cutting edges are formed, each of which is followed by an adjoining free surface, and wherein the chisel edge is laterally bounded only by the free surfaces.

20. A method for producing a drill tip according to claim 1, wherein a point thinning is formed, which is curved in such a way that the inner portion extends arcuately from an outer edge of the center toward the chisel edge.

21. The method according to claim 20, wherein the entire point thinning is ground in a single grinding pass and along a single and continuous grinding path.

Description

DESCRIPTION OF THE FIGURES

[0051] Design examples of the invention are explained in more detail in the following with the aid of a drawing. The figures show schematically:

[0052] FIG. 1 a drill tip of a drill in a front view,

[0053] FIG. 2 the drill of FIG. 1 in a side view,

[0054] FIG. 3 an enlarged section of the drill tip of FIG. 1,

[0055] FIG. 4 a perspective view of the drill trip of FIG. 1,

[0056] FIG. 5 a variant of the drill tip in a front view,

[0057] FIG. 6 a perspective view of the drill trip of FIG. 5,

[0058] FIG. 7 a further perspective view of the drill trip of FIG. 5,

[0059] FIG. 8 the drill trip of FIG. 5 in a side view,

[0060] FIG. 9 the drill trip of FIG. 5 in a further side view,

[0061] FIG. 10 the drill trip of FIG. 5 in a further side view,

[0062] FIG. 11 a further variant of the drill tip in a front view,

[0063] FIG. 12 a perspective view of the drill trip of FIG. 11,

[0064] FIG. 13 the drill trip of FIG. 11 in a side view,

[0065] FIG. 14 a detail of a grinding wheel in a sectional view,

[0066] FIG. 15 the grinding wheel of FIG. 14 during the production of a drill tip,

[0067] FIG. 16 a further variant of the drill tip in a front view,

[0068] FIG. 17 an enlarged detail of FIG. 16,

[0069] FIG. 18 the drill tip of FIG. 16 in a side view,

[0070] FIG. 19 the drill tip of FIG. 16 in a perspective view,

[0071] FIG. 20 the drill tip of FIG. 16 in a different perspective view,

[0072] FIG. 21 a sectional view of the view of FIG. 20.

DESCRIPTION OF THE DESIGN EXAMPLES

[0073] The figures show various design examples of a drill tip 2, which is a part of a drill that is shown only in sections. FIGS. 1 to 4 show a first variant of the drill tip 2, FIGS. 5 to 10 show a second variant and FIGS. 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. Lastly, FIGS. 16 to 21 show a fourth variant of the drill tip 2. The drill tip 2 here is an integral component of a drill and as such is monolithically connected to a shank. In a not depicted variant, on the other hand, the drill tip 2 is a separate part and is then configured as an insert that can be inserted into a 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 around an axis of rotation L, which is also an axis of rotation of the drill as a whole and which also corresponds to a longitudinal axis of the drill tip 2 and the drill as a whole and generally extends in a longitudinal direction.

[0074] The drill tip 2 comprises a center 4, in which a chisel edge 6 is disposed. In FIG. 1, the center is indicated with a dashed circle. When viewing the drill tip 2 from the front along the axis of rotation L, the center 4 is correspondingly located in the center, as can be seen in FIG. 1. In FIG. 2, the drill and the 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 specifically the drill tip 2.

[0075] The drill tip 2 comprises a number of main cutting edges 8, in this case two, each of which adjoins the chisel edge 6 and extends outward from the center 4. In a not depicted variant, the drill tip 2 has a different number of main cutting edges 8. The main cutting edges 8 and the chisel edge 6 are respectively also referred to in short simply as the cutting edge and overall together form a cutting geometry of the drill tip 2.

[0076] A respective main cutting edge 8 here is divided into two sections, namely an inner portion 10 which adjoins the chisel edge 6 and is disposed inside the center 4, and an outer portion 12 which adjoins the inner portion 10 to the outside and is disposed outside the center 4. The transition from the inner portion 10 to the outer portion 12 thus defines the center 4 of the drill tip 2, so that the inner portion 10 is on the inside and the outer portion 12 is on the outside. The outer portion 12 then extends outward to an outer surface 14 of the drill tip 2.

[0077] Each of the cutting edges 6, 8 is adjoined by a surface which points in the direction of rotation U and via which any produced chips are removed. The orientation of this surface relative to a workpiece is characterized by the so-called rake angle, which, depending on the configuration, can in principle also assume different values at different locations along the cutting edges 6, 8.

[0078] The rake angle is now modified in the center 4 by a specific point thinning 16. The point thinning 16 is disposed in the center 4 and is initially used to shorten the chisel edge 6, i.e. is ground in on the front during production to shorten the chisel edge 6. The point thinning 16 is furthermore curved in such a way that the inner portion 10 extends arcuately from an 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 FIGS. 1 to 13. In a second variant, on the other hand, the inner portion 10 is kinked in an arcuate manner, as shown in the design example of FIGS. 16 to 21.

[0079] The outer edge and the center 4 are indicated in FIG. 1 with a dashed circle. The point thinning 16 is generally a curved point thinning 16, i.e. it comprises a first curvature K1, which is configured such that the point thinning 16 curves axially, i.e. quasi in the direction of rotation U. The first curvature K1 is explicitly indicated in FIGS. 4, 7, 16, 18 and 19 with a curved, dashed line. It is also evident that the first curvature K1 and thus the point thinning 16 have a first radius of curvature R1, which in particular indicates the radius with which the point thinning 16 is curved. In FIG. 4, the first radius of curvature R1 also corresponds to the radius of the inner portion 10.

[0080] The described first curvature K1 of the point thinning 16 automatically results in an arcuate course of the main cutting edge 8 in the center 4, so that the inner portion 10 is also formed when the point thinning 16 is formed. The arcuate course of the main cutting edge 8 allows said main cutting edge to be taken particularly far into the center 4 and the chisel edge 6 to be shortened as already mentioned. The main cutting edge 8 is correspondingly lengthened.

[0081] In a leading position, i.e. in the direction of rotation U in front of a respective main cutting edge 8, a respective flute 18 is formed, which adjoins the associated main cutting edge 8. The flute 18 is used to convey a chip that is removed by the main cutting edge 8. On the other side of the main cutting edge 8, i.e. opposite to the flute 18 and in the direction of rotation U behind the main cutting edge 8, a free surface 20 is configured which generally faces toward the front. For each main cutting edge 8 of the drill tip 2, a flute 18 and free surface 20 are now configured, which surround the respective main cutting edge 8 accordingly.

[0082] The two main cutting edges 8 shown in the respective design example each have an arcuate inner portion 10, which are S-shaped when viewed together. This is specifically emphasized in FIG. 1 with a dashed and S-shaped line, which is drawn slightly offset for better visibility. However, the S-shaped can also be seen directly in FIGS. 3 to 6, 11, 12, 16 and 17. The inner portions 10 are thus all curved in the same direction and together extend toward the chisel edge 6. The chisel edge 6 is then disposed in the center of the S-shaped course.

[0083] In the design examples shown, the chisel edge 6 itself is also S-shaped. For this purpose, the chisel edge 6 is correspondingly enclosed by twisted free surfaces 20, so that an S-shaped course results. This is particularly evident in the detail views in FIGS. 3 and 17, whereby a dashed and S-shaped line is additionally included in FIG. 3 to illustrate the S-shaped course. The S-shape of the chisel edge 6 is not mandatory, however; the chisel edge 6 can also have other geometries.

[0084] A respective free surface 20 is bounded toward the front by a main cutting edge 8 and toward the rear by a point thinning 16 or a flute 18 and a point thinning 16. To the outside, a respective free surface 20 is bounded by the outer surface 14 of the drill tip 2. In the center 4, on the other hand, a respective free surface 20 is bounded by the chisel edge 6. The free surfaces 20 are now preferably twisted such that an S-shaped chisel edge 6 results. In the present case, the chisel edge 6 is laterally bounded only by the free surfaces 20. Only the end points of the chisel edge 6, i.e. the transition points P to the main cutting edges 8, abut a respective point thinning 16, so that the chisel edge 6 extends between the two opposite point thinnings 16. The chisel edge 6 is thus completely enclosed by the free surfaces 20 and only at the end is in a quasi point connection with the point thinning 16. In a not depicted variant, on the other hand, the chisel edge 6 is not S-shaped.

[0085] In the variants shown in FIGS. 1 to 4, the point thinning 16 is merely curved as indicated in FIG. 4. In the variants of FIGS. 5 to 13 and 16 to 21, however, the point thinning 16 is additionally convex such that it extends from one of the flutes 18 and in the direction of one of the free surfaces 20 in an outwardly curved manner. In addition to the axial, first curvature K1 of the point thinning 16, said point thinning is also radially curved; i.e. in addition to the first curvature K1 it has a second curvature K2, which is then a radial curvature K2. This additional second curvature K2 is explicitly indicated in the perspective illustrations in FIGS. 6 and 7 with a dashed curve K2 and is also clearly visible in the sectional view of FIG. 13. The second curvature K2 and the point thinning 16 thus have a second radius of curvature R2, which indicates the radius with which the point thinning 16 is curved and the radius with which the point thinning 16 transitions from the flute 18 into the free surface 20.

[0086] The first curvature K1 is not explicitly indicated in FIG. 6, but is nonetheless present and is explicitly shown in the perspective view of FIG. 7 in addition to the second curvature K2. The point thinning 16 is thus curved and connects the flute 18 of one of the main cutting edges 8 to the free surface 20 of the corresponding leading main cutting edge 8. In addition to the first, axial curvature K1 of the point thinning 16, said point thinning is thus also radially curved by the second curvature K2. Overall, therefore, the point thinning 16 is a curved and convex point thinning 16. The convex course results in a bulbous configuration of the point thinning 16 in the region between the free surface 20 and the flute 18. This can be seen particularly clearly in FIG. 7. FIGS. 8 to 10 further show respective side views of the drill with the drill tip 2 of FIG. 5, whereby the specific geometry of the point thinning 16 is evident in these side views as well. The point thinning 16 is curved outward and counter to the direction of rotation U, i.e. backwards when viewed from the leading main cutting edge 8, and in the direction of the not depicted workpiece.

[0087] The convex course advantageously eliminates an edge in the transition region from the point thinning 16 to the flute 18 and, as shown here, instead produces a continuous transition. The first, axial curvature K1, on the other hand, when viewed toward the center 4, results in the rake angle of the main cutting edge 8 being correspondingly increased.

[0088] FIGS. 11 to 13 show a further configuration, in which the point thinning 16 comprises a base 22 that is concave when viewed in radial direction. This can be seen particularly clearly in the perspective view in FIG. 12. The concave base 22 is created during the production of the drill tip 2 using a convex, i.e. outwardly curved, grinding wheel 3. Such a grinding wheel 3 has a grinding surface which faces radially outward with respect to an axis of rotation A of the grinding wheel 3 and is convex in cross-section perpendicular to the axis of rotation A. The point thinning 16 is then curved inward, i.e. in the direction of a rear side of the drill tip 2 and into said drill tip.

[0089] The point thinning 16 with the concave base 22 thus has a third curvature K3, which is specifically shown in FIG. 12 with a dashed line. The third curvature K3 and the point thinning 16 then have a third radius of curvature R3, which indicates the radius with which the base 22 is concave and the radius of the outer surface of the grinding wheel 3. The first curvature K1 is then explicitly indicated in FIG. 11 with a dashed line. The second curvature K2 is indicated in FIG. 13 with a dashed line. FIGS. 11 to 13 each also show the associated radii of curvature R1, R2, R3.

[0090] The design example of FIG. 20 shows a fourth curvature K4 which, like the first curvature K1, results in a convex point thinning 16, not in the direction of rotation U, however, but rather when viewed in radial direction from the inside to the outside, so that the point thinning 16 slopes downward from the center 4 toward the outer surface 14.

[0091] It can clearly be seen in FIGS. 11 to 13 that the convex point thinning 16 with the concave base 22 has a saddle-shaped course and is therefore configured as a saddle surface between the flute 18 and the free surface 20. Due to the first curvature K1, the saddle surface is also curved in the direction of rotation U.

[0092] Overall it is evident that different configurations of the drill tip 2 result from the fact that, in addition to the first curvature K1, the curved point thinning 16 has a second curvature K2, a third curvature K3, a fourth curvature K4 or any combination thereof. A convex course, i.e. a second curvature K2, K4, results in a bulbous configuration of the point thinning 16 in the region between the free surface 18 and the flute 20 as can be seen in FIGS. 6, 13 and 20, for example. A third curvature K3 results in a base 22, which also defines the rake angle and, if necessary, undercuts the inner portion 10 accordingly.

[0093] In the present case, in FIGS. 1 to 4 and 16 to 21, the point thinning 16 extends to the outer edge of the drill tip 2, i.e. to its radially outer outer surface 14, so that, when viewed in clockwise direction, i.e. counter to the direction of rotation U, starting from the main cutting edge, the free surface 20 is completely spaced apart from the flute 18 by the point thinning 16 and the flute 18 and the free surface 20 are then not adjacent to one another. In FIGS. 5 to 13, on the other hand, the point thinning 16 is not continuous to the outer surface 14, but here is continuous only to half the radius, i.e. a quarter of the diameter D of the drill tip 2. The configuration of the point thinning 16 to the outer surface 14 is independent of whether the point thinning has one or more further curvatures K2, K3, K4 in addition to the first curvature K1. The concepts for the curvatures K1-K4 described in connection with the individual variants of the drill tip 2 can be combined with one another as desired and also with a point thinning 16 extending to the outer surface 14.

[0094] As can be seen in particular in FIGS. 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 at which the point thinning 16 accordingly also meets the free surface 20 that laterally adjoins chisel edge 6. At the transition point P, the rake angle changes from the main cutting edge 8 to the chisel edge 6 in a non-continuous, i.e. abrupt manner. At the transition point P there is therefore a corner, which connects the inner portion 10 to the chisel edge 6. Between the free surface 20 and the point thinning 16 there is correspondingly an edge, which causes the rake angle S to change abruptly. As a matter of principle, the edge generally ends where the inner portion 10 transitions into the outer portion 12. The rake angle of the inner portion 10 is thus defined by the point thinning 16, whereas the rake angle of the chisel edge 6 is defined by the free surface 20.

[0095] In the design example of FIGS. 16 to 21, the inner portion 10 is kinked in an arcuate manner and comprises a plurality of straight subsections 24, which are disposed at an angle to one another. In the present case there are exactly three straight subsections 24. The subsections 24 are disposed roughly along an arc, which results in an overall arcuate course. When viewed toward the free surface 20, two consecutive 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 greater than the further outward angle W.

[0096] Two consecutive straight subsections 24 are connected to one another via a rounded corner 26 such that a continuously arcuate transition is formed between two subsections 24. The overall twice-kinked course can be seen particularly well in the detail view of FIG. 17. As can further be seen in FIG. 17, the outermost subsection 24 in the present case transitions into the outer portion 12 of the main cutting edge 8 in a straight manner, so that there is no kink at the transition from the inner portion 10 to the outer portion 12. The straight subsections 24 also each have a length L2 which increases here when viewed from the inside to the outside, so that a further outward subsection 24 is longer than a further inward subsection 24.

[0097] The point thinning 16 generally adjoins a free surface 20 and, specifically in the design examples shown, forms an edge 28 with said free surface. In the design example of FIGS. 16 to 21, the edge 28 characteristically extends in an S-shape starting at the chisel edge 6 and inside the center 4. Starting at the transition point P between the chisel edge 6 and the inner portion 10, a first edge radius R4 is formed, which forms a transition from the base 22 of the point thinning 16 to the free surface 20. This can be seen particularly well in FIG. 17 and in the perspective view in FIG. 20. The first edge radius R4 is outwardly adjoined by a second edge radius R5, whereby said second edge radius has opposite curvature, however, so that an overall S-shape results. Both edge radii R4, R5 are located inside the center 4. To the outside, as can be seen in FIG. 20, for example, the second edge radius R5 transitions into a straight line which, in the shown design example, extends to the outer surface 14. In the present case, when viewed from the front, the first, i.e. the inner, edge radius R4 is greater than the second, i.e. the outer, edge radius R5.

[0098] FIG. 21 shows the same view as FIG. 20, but with a section from the point thinning 16 to the flute 18, so that the free surface 20 is not visible, but the two edge radii R4, R5 which are emphasized by additional circles are. On the other hand, in the sectional view, and thus without considering the free surfaces 20, the inner edge radius R4 is smaller than the outer edge radius R5 as shown in FIG. 21.

[0099] In the design examples shown, the rake angle is negative along the chisel edge 6 and positive along the main cutting edge 8 and is thus smaller along the chisel edge 6 than along the main cutting edge 8. The rake angle varies along the chisel edge 6 and increases toward the inner portion 10. On the other hand, the rake angle along the inner portion 10 here is constant, i.e. keeps the same value. This is accomplished by the specific curved configuration of the point thinning 16. The rake angle varies again along the outer portion 12 and, as with the chisel edge 6, increases to the outside. The free surface 20, which follows a respective main cutting edge 8, forms a clearance angle which here varies along the outer portion 12 and in particular also along the inner portion 10 and thereby increases to the inside.

[0100] The drill tip 2 has a diameter D, which is in the range of 1 mm to 40 mm and is 8.5 mm in the design examples. The center 4 has a center diameter ZD, which is 20% to 75% of the diameter D. In the design examples, the center diameter CD is in the range of 2 mm to 4 mm. The chisel edge 6 has a length of 0.5% to 15% of the diameter D and in the design examples is between 0.17 mm and 1.27 mm, measured along a not depicted straight line which connects the end points of the chisel edge 6, i.e. the transition points P.

[0101] During production of the drill tip 2, a grinding wheel 3 is used, which is guided along a grinding path and removes material from the center 4. As a result, a cutting corner originally formed by the chisel edge 6 and the main cutting edge 8 is ground off and replaced with the curved inner portion 10 and the chisel edge 6 is shortened at the same time. A design example for a grinding wheel 3 is shown in FIG. 14; the use of this grinding wheel 3 for producing a drill tip 2 is shown in FIG. 15. The entire point thinning 16 is ground in a single grinding pass and along a single and continuous grinding path. In the case of the point thinning 16 that is both curved and convex shown in FIGS. 5 to 13, the result is a grinding path which follows a multiple curved course, so that the correspondingly formed curvatures K1, K2, K3 are carried out in a superimposed manner or successively. The grinding path is then a superposition of the curvatures K1, K2, K3, which are traversed successively or in a superimposed manner, i.e. simultaneously or partially simultaneously, and which are curved in different planes. To produce the curved point thinning 16, i.e. the first curvature K1 that forms the inner portion 10, the grinding wheel 3 is tilted or inclined perpendicular to an axis of rotation A of the grinding wheel 3. To produce the convex point thinning 16, i.e. the second curvature K2 via which a flute 18 transitions into a free surface 20 in an arcuate manner, on the other hand, the grinding wheel 3 is rolled over its grinding surface. The third curvature results automatically from the grinding contour of the grinding wheel 3. This grinding contour becomes particularly clear with the example in FIG. 14. The grinding wheel 3 shown there comprises an outer surface, which is generally formed by a first radius SR1, by two straight lines G1, G2, and a further, i.e. second, radius SR2. The first radius SR1 connects the two straight lines G1, G2 that in a sense represent radially outward-facing flanks 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 in particular shows that the grinding wheel 3 is not necessarily symmetrical. It is also evident that the first radius SR1 in this case corresponds to the third radius of curvature R3.