milling pin

Description

[0001] The invention relates to a milling cutter according to the preamble of claim 1, as known for example from DE 299 12 978 U1.

[0002] Such milling cutters are also known as rotary files (in English: bur or burr). According to the definition in DIN 8032 / 8033 and ANSI, they are used in both handheld and automated tools, both powered by an electric motor or pneumatically, and are used for manual and automatic (including robot-guided) grinding of metal surfaces through fine material removal.

[0003] Known burrs for the aforementioned purpose have a shank section and a milling section that adjoins the shank section and terminates in a free milling tip. At least the milling section is made of hard metal, for example, tungsten carbide. The shank section and the milling section are rotationally symmetrical about a rotation axis. The milling section has a milling length and a plurality of cutting edges separated by spaced-apart main grooves. A typical number of main grooves in known burrs with a diameter of 12.7 mm (1 / 2") is, for example, 24. The main grooves have a groove depth, hereinafter referred to as the main groove depth, and extend helically in a first helix direction with a first helix angle along the milling section.Each of the cutting edges has a rake face and a flank face as well as a cutting edge at the transition between the rake face and the flank face, forming a rake angle and a clearance angle. The first helix angle is measured between a tangent to the cutting edge and a line parallel to the axis of rotation. A plurality of chip breakers are provided in each flank face. The chip breakers have a depth, which is referred to below as the chip breaker depth, and extend helically in a second helix direction with a second helix angle along the milling section. The second helix angle is measured between a tangent to the connecting line between adjacent chip breakers provided in successive flank faces, which are offset at an angle to one another, and the said line parallel to the axis of rotation.The first helix direction runs in the direction of rotation of the burr, while the second helix direction can run opposite to the first helix direction and thus also opposite to the direction of rotation of the burr; the second helix angle is then negative. Alternatively, the second helix direction can also run in the direction of rotation of the burr, in which case the second helix angle is positive.

[0004] The function of chip breakers is, on the one hand, to control chip formation and, on the other hand, to reduce cutting resistance. If the chips can be broken to a suitable length, they won't wrap around the workpiece, vibrations are suppressed, and the likelihood of damage to the burr is reduced. Low cutting resistance prevents premature breakage of the cutting edge due to vibration. Low cutting resistance also contributes to reducing load and heat generation and can delay wear.

[0005] Commercially available milling cutters of the aforementioned type have the disadvantage that their cutting performance can hardly be increased without significantly shortening their service life. To date, no milling cutter has been identified that offers an optimal balance between good milling performance and a long service life.

[0006] It is an object of the present invention to provide a milling cutter with a high cutting performance and at the same time a long service life, i.e. low wear.

[0007] This problem is solved by a milling cutter having the features of claim 1.

[0008] A milling cutter according to the invention is generally designed according to DIN 8032 / 8033 and ANSI standards.

[0009] Furthermore, the milling pin according to the invention with its milling section made of hard metal is particularly adapted to the machining of steel surfaces.

[0010] In the characterizing part of claim 1, the term "in the region of the milling section with the largest diameter" is used, thus providing a uniform reference point even for different geometries of the milling cutters according to the invention. Thus, for example, the features according to the invention can be identified for both a cylindrical and a spherical milling section. Somewhat less precise, but still understandable to the person skilled in the art, the term "main body of the milling section" could be chosen, particularly to distinguish it from the area of ​​the milling tip.

[0011] According to the invention, the chipbreaker depth of a milling cutter according to the invention in the region of the milling section with the largest diameter is between 5 and 25% of the main groove depth. Such a chipbreaker depth is significantly lower than known from the prior art. Due to manufacturing reasons, a small chipbreaker depth is also accompanied by a relatively small chipbreaker width (measured along the cutting edge). The technical effect achieved by these features is that a greater linear length of the main grooves is achieved compared to the known deeper and wider chipbreaker depths. In contrast, chipbreaker depths of up to 80% of the main groove depths are known in the prior art.

[0012] Furthermore, the clearance angle in the area of ​​the milling section with the largest diameter is between 10° and 20°. This, in conjunction with the other features of the invention, ensures that the cutting edges are more resilient and therefore subject to less wear.

[0013] Furthermore, the rake angle in the area of ​​the milling section with the largest diameter is between -3° and +14°. It has been shown that this relatively small rake angle, compared to conventional milling cutters, contributes to achieving good cutting performance and low wear.

[0014] Furthermore, according to the invention, the first helix angle is greater than 25°. This, in conjunction with a relatively small number of main flutes, allows for increased strength of the main flutes, thus extending the service life of the burr. A relatively large helix angle also allows more cutting edges to come into contact with the workpiece. This reduces the load on the cutting edges and improves the surface quality of the workpiece.

[0015] A further feature of the invention is that the number of main grooves is less than 15 and preferably no more than 12. This also achieves a high cutting performance, whereby, in the interaction of all features of claim 1, the wear of the milling section is surprisingly very low, which is at least partly achieved by the increased strength of the main grooves.

[0016] When the expression "between value a and value b" is used generally in the context of this disclosure, this is to be understood as also including the two final values ​​a and b.

[0017] The overall technical effect of all the aforementioned features is that the burr according to the invention achieves outstanding performance at the start of the grinding process. Tests have shown that a performance increase of 80% or more can be achieved compared to comparable known burrs. Even after 40 minutes of grinding, the grinding performance of tested burrs according to the invention is approximately 30% higher than that of conventional burrs. Surprisingly, this performance increase does not come at the expense of the service life of the burrs according to the invention. The inventors assume that this unexpected effect is due in particular to the small chip breaker depth compared to the main flute depth (and the associated small width of the chip breakers along the cutting edge) as well as to the small clearance angle.

[0018] Based on the above, an important feature of the burr according to the invention is that its chipbreakers have a very small depth (and thus also width) compared to known burrs, while maintaining the purpose of the chipbreakers, i.e., the reduction of chips during the grinding process. The small depth and the associated, manufacturing-related narrow width of the chipbreakers maximize the linear length of the available cutting edge.

[0019] It has proven particularly advantageous if the chip breaker depth in the area of ​​the milling section with the largest diameter is between 10% and 20% of the main groove depth.

[0020] Alternatively, additionally or supplementarily, the chip breaker depth in the region of the milling section with the largest diameter is preferably between 0.1 and 0.25 mm and is particularly preferably not greater than 0.2 mm. If the previously mentioned preferred feature with regard to the chip breaker depth, i.e. the chip breaker depth is in the range between 10% and 20% of the main groove depth, is taken as a reference, then the main groove depth is between 0.5 mm and 2.5 mm, and preferably not greater than 20 mm. In exemplary embodiments, the chip breaker depth can be 0.1 mm in the case of a main groove depth of 1 mm. In another exemplary embodiment, the chip breaker depth is 0.2 mm in the case of a main groove depth of 2 mm.

[0021] The chipbreaker depth in the area of ​​the milling section with the largest diameter is advantageously not greater than the maximum width of the chipbreaker (chipbreaker width), measured along the cutting edge. For example, the chipbreaker width is preferably twice the chipbreaker depth. Such a ratio of chipbreaker width to chipbreaker depth is achieved, for example, when using a chipbreaker wheel with a 90° angle.

[0022] The chip breakers are particularly preferably completely integrated into the flank surface, i.e. they do not extend into the main groove facing away from the direction of rotation or the subsequent chip space.

[0023] Preferably, all chip breakers have a distance from the transition between the shank section and the milling section and / or the milling tip. This distance is, for example, and preferably, at least 1 mm. This ensures that no weak points develop on the cutting edges, which could break off if the distance between the chip breakers and the shank section or the milling tip is too small.

[0024] It has proven very advantageous if the clearance angle in the area of ​​the milling section with the largest diameter is between 12° and 18°, particularly preferably between 13° and 15°. In conjunction with the other features of the burr according to the invention, this has produced the best results in terms of grinding performance and durability.

[0025] Very good cutting performance with only low wear was achieved with rake angles on the cutting edges in the range between 0° and +12°, with the range between +5° and +10° proving to be particularly favorable.

[0026] According to advantageous embodiments, the flanks in the region of the milling section with the largest diameter have a width, measured in the direction of rotation of the milling pin, of 0.2 mm to 1 mm, preferably of 0.4 to 0.8 mm.

[0027] Particularly preferably, the said relief surface, which begins directly at the respective cutting edge and runs counter to the direction of rotation of the burr, is the only relief created during the production of the main grooves. This relief surface is also called the "primary relief" in English. A further relief surface ("secondary relief") therefore does not adjoin the said relief surface (counter to the direction of rotation of the burr). Rather, the main groove with the corresponding chip space begins immediately adjacent to the (first) relief surface. On the one hand, this design facilitates the production of the cutting edges or main grooves, but on the other hand, providing an additional relief surface has proven to be disadvantageous.

[0028] As mentioned at the beginning, a typical first helix angle for known milling cutters is 25°. According to the invention, the first helix angle is selected to be larger, preferably greater than 27.5°. Particularly preferably, the first helix angle is in the range between 29° and 32°, and most preferably 30°.

[0029] The second helix angle, i.e., the pitch angle formed by the chip breakers, preferably has a smaller pitch than the first helix angle. It has proven advantageous if this is in the range between -75° and -88°, preferably between -78° and -85°, and particularly preferably between -80° and -82°. Alternatively, the second helix angle can be selected to be positive and is then preferably between +75° and +88°, preferably between +78° and +85°, and particularly preferably between +80° and +82°.

[0030] In the milling cutters according to the invention, the first helix angle of all cutting edges and main grooves is preferably the same. However, embodiments within the teachings of the invention are also possible in which the cutting edges and main grooves of at least two consecutive cutting edges (and main grooves) have a slightly different first helix angle. Furthermore, the first helix angle is preferably constant along the milling length. It is also preferred if the second helix angle for the chip breakers is also constant.

[0031] Generally, variable first and / or second helix angles are possible. Variable first helix angles can be implemented, for example, for one or more individual main grooves and / or between different main grooves. With regard to a variable second helix angle, a possible embodiment can, for example, have a pitch increasing from the shank to the cutter tip. Other embodiments with regard to a variable second helix angle are possible without restriction.

[0032] In the case of milling cutters according to the invention with a radius at the milling tip (which, for example, does not include milling cutters with a cylindrical milling section), the two cutting edges of at least one pair of cutting edges, which run on opposite sides of the milling section, advantageously merge into one another at the milling tip. In contrast to known milling cutters, in which the individual cutting edges end freely at the milling tip, in the advantageous embodiment mentioned, at least two cutting edges form a common cutting edge at the milling tip. These two cutting edges of the said at least one pair preferably form an S-shape in the plan view of the milling tip. The stability of the milling tip can thereby be increased. It is also possible - to a limited extent - to carry out cutting or drilling operations with the milling tip. It is also possible that, for example,six cutting edges converge at the front tip in the center of the tool.

[0033] It is particularly preferred that the number of main grooves be less than or equal to the largest diameter, measured in mm, of the milled section. Accordingly, it has been found to be positive with regard to the machining result – with low wear – that with a largest diameter of the milling section of 6 mm the number of main grooves is 5 to 7, preferably 6, with a largest diameter of the milling section of 8 mm the number of main grooves is 7 to 9, preferably 8, with a largest diameter of the milling section of 10 mm the number of main grooves is 8 or 9, preferably 8, with a largest diameter of the milling section of 12 or 12.7 mm the number of main grooves is 9 to 11, preferably 10, and / or with a largest diameter of the milling section of 15 or 16 mm the number of main grooves is 11 to 13, preferably 12.

[0034] All of the aforementioned lower and upper limits for parameter values ​​should not be considered closed or fixed pairs. For example, the preferred lower limit of one specified pair of values ​​can be combined with the upper limit of another specified pair of values ​​to form a further advantageous range. For example, it is possible for a preferred chip breaker depth to be between 5% (claim 1) and 20% (claim 2) of the main groove depth.

[0035] The milling sections of the burrs according to the invention can be provided with various coatings that contribute to reducing wear and increasing service life. Such special coatings can consist of TiN, TiAIN, AlTiN, DLC, CH-NFE, and CH-FEP, for example.

[0036] It is understood that for different geometries of the milling sections, different numerical values ​​with regard to the physical parameters mentioned (helix angle, clearance angle, rake angle, chip breaker depth, number of main grooves) within the stressed areas lead to an optimal result in terms of cutting performance and service life of the milling cutters.

[0037] Advantageous further developments are characterized by the features of the subclaims.

[0038] The invention is explained in more detail below with reference to the figures. They show: Fig. 1 a side view of a milling pin according to the invention; Fig. 2 a cross-sectional view along AA in Fig. 1 ; Fig. 3 a detailed enlargement of the Fig. 2 ; Fig. 4 a cross-sectional view of a detail similar to the Fig. 3 , but here running through a chip breaker; Fig. 5 a perspective sectional view of the milling section; and Fig. 6 a top view of the burr.

[0039] In the Fig. 1-6 A first embodiment of a milling pin 1 according to the invention is shown. According to the side view of the Fig. 1 A milling cutter 1 has a cylindrical shaft section 2 and a milling section 4, which is essentially conical and slightly curved outward on the circumference, the latter having a milling length f and terminating in a milling tip 6. The shaft section 2 serves for fastening in a manually or automatically operated tool that rotates the shaft section 2 and thus the entire milling cutter 1 in a direction of rotation 9 in order to grind a metal workpiece. For this purpose, the shaft section 2 and the milling section 4 are designed to be rotationally symmetrical to a rotation axis 8.

[0040] At least the milling section 4 is made of hard metal. The shaft section 2 can also—which is also preferred—be made of hard metal and is then preferably formed integrally with the milling section 4; alternatively, the shaft section 2 is made of steel, in which case the shaft section 2 is connected to the milling section 4, for example, by soldering. The milling section 4 can have different geometries. Instead of a substantially conical or tapered cross-section, the milling section 4 can be formed with a constant or spherical cross-section. Many other shapes are possible, as are mixed shapes, all of which are known to those skilled in the art.

[0041] At the milling section 4, cutting edges 10 and main grooves 14 alternate in the direction of rotation 9 of the milling cutter 1, whereby these cutting edges 10 and main grooves 14 run helically along the milling section 4, viewed in the direction of the milling tip 6, in a first helix direction 16 with a first, here constant, helix angle α of 30° (see Fig. 1 ). The first helix angle α is measured - in the area of ​​the milling section 4 with the largest diameter, here in the area of ​​the transition from the milling section 4 to the shank section 2 - between a tangent applied to the cutting edge 12 (see below) of a cutting edge 10 and a parallel to the rotation axis 8. The first helix direction 16 runs in the direction of rotation 9. The number of main grooves 14 is selected to be low and is less than 15. In the illustrated embodiment, there are ten main grooves 14 and thus also ten cutting edges 10 (see Fig. 2 ).

[0042] According to the invention, the first helix angle α is greater than 25°, preferably greater than 27.5° and is preferably in the range between 29° and 32°.

[0043] A particularly preferred embodiment is shown in the figures, in which the first helix angle α is a constant 30°. Embodiments are also possible in which the at least two consecutive cutting edges 10 have a different first helix angle α from one another, for example, with a first helix angle α that differs by 0.5°, 1°, or 2°.

[0044] As in particular the Fig. 2 As can be seen, each of the cutting edges 10 has a cutting edge 12. On the side of each cutting edge 12 facing the direction of rotation 9 of the milling cutter 1, there is known to be a rake face 20 which forms a rake angle γ with a straight line running perpendicular to and through the axis of rotation 8 of the milling cutter 1 (see Fig. 3 ). On the side of each cutting edge 12 facing away from the direction of rotation 9, there is a clearance surface 24 (primary relief) which forms a clearance angle δ with a tangent adjacent to the cutting edge 12, said tangent being applied to an imaginary circle touching the cutting edges 12 (see Fig. 3 ). A further relief (in English: secondary relief), which would adjoin the said first relief 24 opposite to the direction of rotation 9, is not provided and is also generally not preferred.

[0045] The rake angle γ in the embodiment shown in the figures is approximately +7° and is preferably generally in the range between -3° and +14°, preferably between 0° and +12° and particularly preferably in the range between +5° and +10°.

[0046] Variable rake angles are also possible. Such variable rake angles can be implemented for one or more individual cutting edges and / or between different cutting edges.

[0047] The clearance angle δ in the embodiment illustrated in the figures is approximately 15° and, according to the invention, generally ranges between 10° and 20°, preferably between 12° and 18°, and particularly preferably between 13° and 15°. The clearance surface 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 0.4 to 0.8 mm.

[0048] For milling cutters with a defined front radius, such as the milling cutter 1 according to the Fig. 1-6 The rake angle γ of the cutting edges 10 at the milling tip 6 is preferably between -3° and 0°. Milling cutters without a defined face radius, for example, have a cylindrical or conical milling section.

[0049] In each flank 24 of the cutting edges 10, a plurality of chip breakers 30 are provided along their extension in the first helix direction 16. The chip breakers 30 each have a chip breaker depth s, which, according to the invention, is small compared to the main groove depth h (see Fig. 4 ). The chip breakers 30 of adjacent cutting edges 10 follow one another in the form of a helix, which extends in a second helix direction 32, which is opposite to the first helix direction 16 and thus also to the direction of rotation 9. The second helix angle β is measured between a tangent to a connecting line between adjacent chip breakers 30 provided in successive flanks 24, but offset at an angle to one another, and a line parallel to the axis of rotation 8. The second helix angle β formed in this way is, as in the illustrated embodiment, preferably constant.

[0050] According to the invention, the mentioned chip breaker depth s lies in the range between 5 and 25% of the main groove depth h, preferably in the range between 10% and 20% of the main groove depth h. It has been found that such a small chip breaker depth in relation to the main groove depth h has great advantages with regard to the effective cutting length of the cutting edges 10, increases the longevity and reduces the wear of the cutting edges 10 and yet effectively performs the main task of the chip breaker 30, namely to improve chip control and at the same time reduce the cutting resistance.

[0051] In the embodiment shown in the figures, the chip breaker depth s is approximately 17% of the main groove depth h.

[0052] Given in exemplary absolute numbers, the chipbreaker depth s is preferably in the range between 0.1 and 0.25 mm. In one example, the chipbreaker depth s is 0.1 mm with a main groove depth h of 1 mm. In another example, the chipbreaker depth s is 0.2 mm with a main groove depth h of 2 mm. In both of these examples, the chipbreaker depth s is 10% of the main groove depth h. However, in accordance with the percentage ranges given above, it is also perfectly possible for the chipbreaker depth s to be 0.2 mm with a main groove depth h of 1 mm, i.e. the ratio of the two depths is 20%.

[0053] The chip breaker width b (see Fig. 5 ), which is related to the chipbreaker depth s due to the manufacture of the chipbreakers 30 using conventional cutting wheels, is preferably greater than the chipbreaker depth s and, for example, twice as large. For a milling section 4 with a 12 mm diameter, the chipbreaker depth s can be, for example, 0.2 mm and the chipbreaker width b can be, for example, 0.4 mm.

[0054] The number of chip breakers 30 along a cutting edge 12 depends on the milling length f, the diameter of the milling section 4, and / or the number of cutting edges 10. The number of chip breakers 30 along a cutting edge 10 is, for example, between four and eight, for example, five or six. In the illustrated embodiment, five chip breakers 30 are provided per cutting edge 10.

[0055] It is particularly advantageous if the chip breakers 30 run completely in the respective flank 24 or are embedded in it, as shown in the perspective sectional view of the Fig. 5 is recognizable.

[0056] It is preferred if chip breakers 30 have a distance a from the boundary area between the milling section 4 and the shaft section 2 (see Fig. 1 ), wherein this distance a is preferably at least 1 mm. It is also preferred if there is a corresponding distance from chip breakers 30 to the milling tip 6 (not shown, but in Fig. 6 visible). Both measures serve to ensure that the effective length of a cutting edge 12 between a chip breaker 30 and the freely extending end of the cutting edge 12 does not become too small, so that the risk of this cutting edge section breaking during grinding or milling of a workpiece does not increase significantly.

[0057] The said second helix angle β, which is formed by the chip breakers 30, which are provided in cutting edges 10 following one another counter to the direction of rotation 9 and which rotate helically on the milling section 4, is approximately -81° in the embodiment shown in the figures, and generally advantageously in the range between -75° and -88°, preferably between -78° and -85° and particularly preferably between -80° and -82°.

[0058] In the embodiment illustrated in the figures, the second twist angle β is negative; however, it can also be positive and advantageously lie 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 extend in the direction of rotation 9.

[0059] As can be seen from the top view of the Fig. 6 As can be seen, the cutting edges 10 of at least one pair of cutting edges 10, which run on opposite sides of the milling section 4, merge into one another at the milling tip 6 and, in the present case, form an S-shape 18 in plan view. Further cutting edges 10, which preferably run opposite one another on the milling section 4, can also merge into one another, so that, for example, four such cutting edges 10 form a cross shape (with curved arms) in plan view.

[0060] As already mentioned above, according to the invention, the number of main grooves 14 is chosen to be relatively small. In the exemplary embodiment illustrated in the figures, as explained above, there are ten main grooves 14 and ten cutting edges 10. It has proven advantageous if the number of main grooves 14 is less than or equal to the maximum diameter of the milling section 4, measured in mm.

[0061] The values ​​specified for the exemplary embodiment illustrated in the figures (in particular for the chipbreaker depth s, the main groove depth h, the rake angle γ, the clearance angle δ, and the flank surface 24) refer to the area of ​​the milling section 4 with the largest diameter, i.e., in this case, the transition area between the milling section 4 and the shank section 2. In this way, a uniform reference point is specified that also applies to milling sections 4 with a different geometry (e.g., spherical head-shaped). Somewhat less precise, but still understandable for the expert, the term "base body of the milling section 4" could be chosen, particularly to distinguish it from the area of ​​the milling tip 6. Bezugszeichenliste

[0062] 1 Burr 2 Shank section 3 Transition 4 Milling section 6 Milling tip 8 Rotation axis 9 Direction of rotation 10 Cutting edges 12 Cutting edge 14 Main grooves 16 First twist direction 18 S-shape 20 Chip face 24 Free face 30 Chip breaker 32 Second twist direction fMilling length hMain groove depth sChipbreaker depth bChipbreaker width lWidth of the flank aDistance αFirst helix angle βSecond helix angle γRake angle δClearance angle

Claims

1. A burr (1) for an electrically or pneumatically operated, hand-held or automatically operated tool for milling metal surfaces, comprising: - a shaft portion (2), and - a milling portion (4) made from hard metal adjoining the shaft portion (2) and ending in a milling tip (6), the milling portion (4) having a milling length (f) and a plurality of cutters (10) separated by spacedapart main flutes (14) having a main flute depth (h) and extending helically in a first twist direction (16) with a first twist angle (α) along the milling length (f), each of the cutters (10) having a rake face (20) and a relief face (24) and a cutting edge (12) at the transition between the rake face (20) and the relief face (24) forming a rake angle (γ) and a relief angle (δ), wherein a plurality of chip breakers (30) is provided in each relief face (24), the chip breakers (30) having a chip breaker depth (s) and extending helically in a second twist direction (32) with a second twist angle (β) along the milling portion (4), wherein in the region of the milling portion (4) having the largest diameter: - the rake angle (γ) is in the range between -3° and +14°, - the relief angle (δ) is in the range between 10° and 20°, characterized in that in the region of the milling portion (4) having the largest diameter: - the chip breaker depth (s) is in the range between 5 and 25% of the main flute depth (h), - the first twist angle (α) is greater than 25°, and - the number of main flutes (14) is less than 15, preferably not greater than 12.

2. A burr (1) according to claim 1, characterized in that in the region of the milling portion (4) having the largest diameter the chip breaker depth (s) is in the range between 10% and 20% of the main flute depth (h).

3. A burr (1) according to any of the preceding claims, characterized in that in the region of the milling portion (4) having the largest diameter the chip breaker depth (s) is in the range between 0.1 and 0.25 mm at a main flute depth (h) between 0.5 mm and 2.5 mm, for example 0.1 mm for a main flute depth of 1 mm and / or 0.2 mm for a main flute depth of 2 mm.

4. A burr (1) according to any of the preceding claims, characterized in that the chip breaker depth (s) is at most as large as the chip breaker width (b) measured along the cutting edge (12), and for example half as large.

5. A burr (1) according to any of the preceding claims, characterized in that the chip breakers (30) run completely in the relief face (24).

6. A burr (1) according to any of the preceding claims, characterized in that all chip breakers (30) have a distance (a) from the transition between the shaft portion (2) and the milling portion (4) and / or from the milling tip (6), this distance preferably being at least 1 mm.

7. A burr (1) according to any of the preceding claims, characterized in that in the region of the milling portion (4) having the largest diameter the relief angle (δ) is in the range between 12° and 18°, preferably between 13° and 15°.

8. A burr (1) according to any of the preceding claims, characterized in that in the region of the milling portion (4) having the largest diameter said rake angle (γ) is in the range between 0° and +12°, and most preferred in the range between +5° and +10°.

9. A burr (1) according to any of the preceding claims, characterized in that in the region of the milling portion (4) having the largest diameter said relief face (24) has a width (l) of 0.2 mm to 1 mm, preferably between 0.4 and 0.8 mm, measured in the direction of rotation (9) of the burr (1).

10. A burr (1) according to any of the preceding claims, characterized in that said relief face (24) is the only relief face created during the production of the main flutes (14), so that there is no other relief face adjacent to said relief face (24) in the direction of rotation (9) of the burr (1).

11. A burr (1) according to any of the preceding claims, characterized in that the first twist angle (α) is greater than 27.5° and preferably in the range between 29° and 32°, particularly preferred at 30°.

12. A burr (1) according to any of the preceding claims, characterized in that the second twist angle (β) is in the range between -75° and -88°, preferably between -78° and -85°, particularly preferred between -80° and -82°; or that said second twist angle (β) is in the range between +75° and +88°, preferably between +78° and +85°, particularly preferred between +80° and +82°.

13. A burr (1) according to any of the preceding claims, characterized in that the milling portion (4) at its milling tip (6) has a radius and that the cutting edges (12) of at least one pair of cutting edges (12) running on opposite sides of the milling portion (4) merge into one another at the milling tip (6), wherein the two cutting edges (12) of said at least one pair preferably form an S-shape (18) in the plan view of the milling tip (6).

14. A burr (1) according to any of the preceding claims, characterized in that the number of main flutes (14) is less than or equal to the largest diameter of the milling portion (4) measured in mm.

15. A burr (1) according to any of the preceding claims, characterized in that - for a largest diameter of the milling portion (4) of 6 mm, the number of main flutes (14) is 5 to 7, preferably 6, - for a largest diameter of the milling portion (4) of 8 mm, the number of main flutes (14) is 7 to 9, preferably 8, - for a largest diameter of the milling portion (4) of 10 mm, the number of main flutes (14) is 8 or 9, preferably 8, - for a largest diameter of the milling portion (4) of 12 or 12,7 mm, the number of main flutes (14) is 9 to 11, preferably 10, and / or - for a largest diameter of the milling portion (4) of 15 or 16 mm, the number of main flutes (14) is 11 to 13, preferably 12.