BURR

Abstract

A burr includes a shaft portion and a milling portion. Cutters are separated by main flutes having a main flute depth. The cutters extend helically at a first twist angle. Each cutter has a cutting edge between a rake face and a relief face. The rake face forms a rake angle, and the relief face forms a relief angle. Chip breakers in each relief face have a chip breaker depth. At the largest diameter of the milling portion, the chip breaker depth is between 5 and 25 percent of the main flute depth, the rake angle is between −3 degrees and +14 degrees, the relief angle is between 10 degrees and 20 degrees, the first twist angle is greater than 25 degrees, and the number of main flutes is less than 15.

Claims

1-16. (canceled)

17. A burr for an electrically or pneumatically operated, hand-held, or automatically operated tool for milling a metal surface, comprising: a shaft portion having an axis of rotation; a milling portion adjoining the shaft portion and ending in a milling tip, wherein the milling portion defines a largest diameter and a milling length; a plurality of cutters separated by a plurality of main flutes in the milling portion, wherein the plurality of main flutes have a main flute depth, and the plurality of cutters extend helically along the milling length in a first twist direction at a first twist angle α from the axis of rotation; each cutter of the plurality of cutters has a cutting edge between a rake face and a relief face, wherein the rake face forms a rake angle γ from a line perpendicular to the axis of rotation, and the relief face forms a relief angle δ from a line tangent to the cutting edge; a plurality of chip breakers in each relief face, wherein each chip breaker has a chip breaker depth, and chip breakers on adjacent cutters extend helically in a second twist direction with a second twist angle β from the axis of rotation; and at the largest diameter of the milling portion, the chip breaker depth is between 5 and 25 percent of the main flute depth, the rake angle γ is between −3 degrees and +14 degrees, the relief angle δ is between 10 degrees and 20 degrees, the first twist angle α is greater than 25 degrees, and the number of main flutes is less than 15.

18. The burr as in claim 17, wherein at the largest diameter of the milling portion, the chip breaker depth is between 10 percent and 20 percent of the main flute depth.

19. The burr as in claim 17, wherein at the largest diameter of the milling portion, the chip breaker depth is between 0.1 mm and 0.25 mm with the main flute depth between 0.5 mm and 2.5 mm.

20. The burr as in claim 17, wherein each chip breaker has a width measured along the cutting edge, and the chip breaker depth is less than or equal to the chip breaker width.

21. The burr as in claim 17, wherein the plurality of chip breakers are separated from the shaft portion by at least 1 mm.

22. The burr as in claim 17, wherein the plurality of chip breakers are separated from the milling tip by at least 1 mm.

23. The burr as in claim 17, wherein at the largest diameter of the milling portion, the relief angle δ is between 12 degrees and 18 degrees.

24. The burr as in claim 17, wherein at the largest diameter of the milling portion, the relief angle δ is between 13 degrees and 15 degrees.

25. The burr as in claim 17, wherein at the largest diameter of the milling portion, the rake angle γ is between 0 degrees and +12 degrees.

26. The burr as in claim 17, wherein at the largest diameter of the milling portion, the rake angle γ is between +5 degrees and +10 degrees.

27. The burr as in claim 17, wherein at the largest diameter of the milling portion, the relief face has a width of 0.2 mm to 1 mm.

28. The burr as in claim 17, wherein at the largest diameter of the milling portion, the relief face has a width of 0.4 mm to 0.8 mm.

29. The burr as in claim 17, wherein the first twist angle α is greater than 27.5 degrees.

30. The burr as in claim 17, wherein the first twist angle α is between 29 degrees and 32 degrees.

31. The burr as in claim 17, wherein the second twist angle β is between −75 degrees and −88 degrees.

32. The burr as in claim 17, wherein the second twist angle β is between −78 degrees and −85 degrees.

33. The burr as in claim 17, wherein the milling tip has a radius, and the cutting edges on opposite sides of the milling portion merge into one another at the milling tip.

34. The burr as in claim 17, wherein the cutting edges on opposite sides of the milling portion form an S-shape in a plan view of the milling tip.

35. The burr as in claim 17, wherein the number of main flutes is less than or equal to the largest diameter of the milling portion measured in mm.

36. The burr as in claim 17, wherein the number of main flutes is between 5 and 7 when the largest diameter of the milling portion is less than or equal to 6 mm, the number of main flutes is between 7 and 9 when the largest diameter of the milling portion is greater than 6 mm and less than or equal to 8 mm, the number of main flutes is between 9 and 11 when the largest diameter of the milling portion is greater than 8 mm and less than or equal to 13 mm, and the number of main flutes is between 11 and 13 when the largest diameter of the milling portion is greater than 13 mm and less than or equal to 16 mm.

37. The burr as in claim 17, wherein the plurality of chip breakers do not extend beyond the relief face.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In the following, the invention is explained in more detail using figures:

[0044] FIG. 1 is a side view of a burr according to the invention;

[0045] FIG. 2 is a cross-sectional view along A-A in FIG. 1;

[0046] FIG. 3 is a detailed enlargement of FIG. 2;

[0047] FIG. 4 is a cross-sectional view similar to FIG. 3, but here through a chip breaker;

[0048] FIG. 5 is a perspective sectional view of the milling portion; and

[0049] FIG. 6 is a top view of the burr.

DETAILED DESCRIPTION OF THE INVENTION

[0050] FIGS. 1-6 show a first design example of a burr 1 according to the invention. According to the side view of FIG. 1, a burr 1 has a cylindrical shaft portion 2 and an essentially conical, slightly outwardly curved milling portion 4, the latter having a milling length f and ending in a milling tip 6. The shaft portion 2 serves for fastening in a manually operated or automatic machine-operated tool which sets the shaft portion 2 and thus the entire burr 1 in rotation about a direction of rotation 9 in order to grind a metal workpiece. For this purpose the shaft portion 2 and the milling portion 4 are rotationally symmetrical to an axis of rotation 8.

[0051] At least the milling portion 4 consists of hard metal. The shaft portion 2 can also be made of hard metal (which is preferred) and is then preferably formed in one piece with the milling portion 4; alternatively, the shaft portion 2 is made of steel and is brazed to the milling portion 4, for example. The milling portion 4 can have different geometries. Instead of an essentially conical or tapered cross-section, the milling portion 4 can be designed with a constant or spherical cross-section. Many other shapes are possible, as well as mixed shapes, all of which are known to the skilled person.

[0052] In the milling portion 4, cutters 10 and main flutes 14 alternate in the direction of rotation 9 of the burr 1, whereby these cutters 10 and main flutes 14 run along the milling portion 4, seen in the direction of the milling tip 6, in a first twist direction 16 with a first, here constant, twist angle α of 30° (see FIG. 1). The first twist angle α is measured—in the region of the milling portion 4 with the largest diameter, in this case near the transition from the milling portion 4 to the shaft portion 2—between a tangent applied to the cutting edge 12 (see below) of a cutter 10 and a line parallel to the axis of rotation 8. The first twist direction 16 runs in the direction of rotation 9. The number of main flutes 14 is chosen low and is smaller than 15. In the design example shown, there are ten main flutes 14 and thus also ten cutters 10 (see FIG. 2).

[0053] According to the invention, the first twist angle α is greater than 25°, preferably greater than 27.5°, and is preferably in the range between 29° and 32°. The present figures show a particularly preferred design with a constant first twist angle α of 30°. Also possible are designs in which the at least two successive cutters 10 have a different first twist angle α, for example a first twist angle α of 0.5°, 1°, or 2° different from each other.

[0054] As can be seen in particular in FIG. 2, each of the cutters 10 has a cutting edge 12. On the side of each cutting edge 12 facing the direction of rotation 9, there is a known rake face 20 which forms a rake angle γ with a straight line perpendicular to and running through the axis of rotation 8 of burr 1 (see FIG. 3). On the side of each cutting edge 12 facing away from the direction of rotation 9, there is a relief face 24 (also called “primary relief”) which forms a relief angle δ with a tangent to the cutting edge 12, this tangent being applied to an imaginary circle touching the cutting edges 12 (see FIG. 3). A further relief face (also called “secondary relief”), which would follow the first relief 24 against the direction of rotation 9, is not provided and is generally not preferred.

[0055] In the embodiment shown in the figures, the rake angle γ is around 7° and is preferentially in the range between −3° and +14°, preferably in the range between 0° and +12° and especially preferably in the range between +5° and +10°.

[0056] Variable rake angles are also possible. Such variable rake angles can be realized for one or more individual cutters and/or between different cutters.

[0057] In the embodiment shown in the figures, the relief angle δ is around 15° and is, according to the invention, generally in the range between 10° and 20°, preferably between 12° and 18°, and particularly preferably between 13° and 15°. The relief face 24 preferably has a width l, measured in the direction of rotation 9 of the burr 1, of 0.2 mm to 1 mm, preferably of 0.4 to 0.8 mm.

[0058] For burrs having a defined front radius, which is true for the burr 1 shown in the FIGS. 1-6, the rake angle γ at the milling tip of each cutter 10 preferably lies between −3° and 0°. Burrs without a defined end radius have, e.g., a cylindrical- or cone-shaped milling portion.

[0059] In each relief face 24 of the cutters 10 along their course, several chip breakers 30 are provided in the first twist direction 16. The chip breakers 30 each have a chip breaker depth s, which according to the invention is small compared to the main flute depth h (see FIG. 4). The chip breakers 30 of adjacent cutters 10 follow one another in the form of a helix, which runs in a second twist direction 32, which is opposite to the first twist direction 16 and thus also to the direction of rotation 9. The second twist angle is measured between a tangent to a connecting line of adjacent but obliquely offset chip breakers 30 provided in successive relief faces 24 and a line parallel to the axis of rotation 8. The second twist angle β is preferably constant, as in the shown embodiment.

[0060] The mentioned chip breaker depth s is, according to invention, in the range between 5 and 25% of the main flute depth h, preferably in the range between 10% and 20% of the main flute depth h. It has been found that such a chip breaker depth s, which is small in relation to the main flute depth h, has great advantages in terms of the effective cutting length of the cutters 10, increases the longevity and reduces the wear of the cutters 10, and yet effectively performs the main task of the chip breakers 30, namely, to improve chip control and at the same time reduce cutting resistance.

[0061] In the design example shown in the figures, the chip breaker depth s is approx. 17% of the main flute depth h.

[0062] Given in exemplary absolute numbers, the chip breaker depth s is preferably in the range between 0.1 and 0.25 mm. In one example, the chip breaker depth s is 0.1 mm with a main flute depth h of 1 mm. In another example, the chip breaker depth s is 0.2 mm for a main flute depth h of 2 mm. In these two examples the chip breaker depth is 10% of the main flute depth h. According to the percentage ranges given above, it is also possible if the chip breaker depth s is 0.2 mm with a main flute depth h of 1 mm, i.e., the ratio of the two depths is 20%.

[0063] The chip breaker width b (see FIG. 5), which is related to the chip breaker height h due to the manufacture of chip breakers 30 by means of cutting wheels known per se, is preferably greater than the chip breaker depth s and for example twice as great. For example, for a milling portion 4 with a 12 mm diameter, the chip breaker depth s can be 0.2 mm and the chip breaker width 0.4 mm.

[0064] The number of chip breakers 30 along a cutting edge 12 depends on the milling length f, the diameter of the milling portion 4, and/or the number of cutters 10. For example, the number of chip breakers 30 along a cutter 10 is between four and eight, for example five or six. In the design example shown, five chip breakers 30 are provided for each cutter 10.

[0065] It is particularly advantageous if the chip breakers 30 run completely in the relief face 24 or are embedded in it, as can be seen in the perspective sectional view of FIG. 5.

[0066] It is preferred if chip breakers 30 have a distance a to the boundary region between the milling portion 4 and the shaft portion 2 (see FIG. 1), whereby this distance a is preferably at least 1 mm. It is also preferred if there is a corresponding distance between chip breakers 30 and the milling tip 6 (not drawn in, but recognizable in FIG. 6). Both measures serve to ensure that the effective length of a cutting edge 12 between a chip breaker 30 and the free end of the cutting edge 12 does not become too small, so that the risk of breaking this cutting edge section does not significantly increase when grinding or milling a workpiece.

[0067] The said second twist angle β formed by the chip breakers 30, which are provided in cutters 10 in succession in the opposite direction to the direction of rotation 9 and which run helically on the milling portion 4, is 81° in the embodiment shown in the figures, and generally is preferentially in the range between −75° and −88°, preferably between −78° and −85° and particularly preferably between −80° and −82°.

[0068] In the design example shown in the figures, the second twist angle β is negative; however, it can also be positive and advantageously lies between +75° and +88°, preferably between +78° and +85°, and particularly preferably between +80° and +82°. In this case, the first twist direction 16 and the second twist direction 32 both run in rotation direction 9.

[0069] As can be seen in particular from the plan view in FIG. 6, the cutters 10 of at least one pair of cutters 10, which run on opposite sides of the milling portion 4, merge into one another at the milling tip 6 and form an S-shape 18 in the plan view. Other cutters 10, which preferably run opposite each other on milling portion 4, can also merge into each other, so that, for example, four such cutters 10 form a cross shape (with curved arms) in plan view.

[0070] It has already been mentioned above that, according to invention, the number of main flutes 14 is chosen relatively small. In the design example shown in the figures, there are ten main flutes 14 and ten cutters 10, as explained above. It has proved to be advantageous if the number of main flutes 14 is less than or equal to the largest diameter of the milling portion 4, measured in mm.

[0071] The values given for the design example shown in the figures (in particular for the chip breaker depth s, the main flute depth h, the rake angle γ, the relief angle δ, the relief face 24) refer to the region of the milling portion 4 with the largest diameter, i.e., here to the region of transition between the milling portion 4 and the shaft portion 2. In this way a uniform reference point is given, which also applies to milling portions 4 with different geometry (for example spherical). A somewhat less precise, but also understandable for the skilled person, the designation “basic body of the milling portion 4” could be chosen, especially to distinguish it from the region of the milling tip 6.

LIST OF REFERENCE NUMBERS

[0072] 1 burr [0073] 2 shaft portion [0074] 3 transition [0075] 4 milling portion [0076] 6 milling tip [0077] 8 axis of rotation [0078] 9 direction of rotation [0079] 10 cutters [0080] 12 cutting edge [0081] 14 main flutes [0082] 16 first twist direction [0083] 18 S-shape [0084] 20 rake face [0085] 24 relief face [0086] 30 chip breaker [0087] 32 second twist direction [0088] f milling length [0089] h main flute depth [0090] s chip breaker depth [0091] b chip breaker width [0092] l relief face width [0093] a distance [0094] α first twist angle [0095] β second twist angle [0096] γ rake angle [0097] δ relief angle