ROTARY TOOL FOR PRECISION MACHINING OF A DRILLED HOLE IN A WORKPIECE, AND METHOD FOR PRECISION MACHINING OF A DRILLED HOLE

Abstract

In order to achieve as highly accurate an alignment of the frictional tool as possible and therefore as high a drilled hole quality as possible during the precision machining of a drilled hole, the cutting edges of the frictional tool are divided into two cutting groups, the cutting edges of which are spaced apart with respect to one another in each case by an axial spacing from one another. Here, the axial spacing is selected in such a way that, at a predefined first, slower feed speed, merely the cutting edges of the first cutting edge group are in engagement with the workpiece and, at a higher, predefined second feed speed, all cutting edges are in engagement with the workpiece.

Claims

1-13. (canceled)

14. A rotary tool for precision machining of a drilled hole in a workpiece, the rotary tool comprising: a tool head which extends in an axial direction, the tool head having a plurality of cutting edges on its circumference, wherein the cutting edges are arranged on an identical cutting circle, the cutting edges being divided into a first cutting edge group and a second cutting edge group, the two cutting edge groups being spaced apart from one another in the axial direction by an axial spacing which is selected such that: at a predefined first feed speed, only the cutting edges of the first cutting edge group are in engagement with the workpiece, and at a predefined second feed speed which is faster than the first feed speed, the cutting edges of both the first and the second cutting edge group are in engagement with the workpiece, wherein, with respect to a circumferential direction of the tool head: the cutting edges of each of the first and second cutting edge groups, respectively, are arranged to be substantially identically distributed around the circumference, and each cutting edge of the second cutting edge group is arranged asymmetrically at different angular spacings with respect to a first neighboring cutting edge and a second neighboring cutting edge of the first cutting edge group.

15. The rotary tool as claimed in claim 14, wherein each cutting edge of the first cutting edge group is arranged asymmetrically at different angular spacings with respect to a first neighboring cutting edge and a second neighboring cutting edge of the second cutting edge group.

16. The rotary tool as claimed in claim 14, wherein, with respect to the circumferential direction of the tool head, the cutting edges of the first and the second cutting edge group are arranged alternately with respect to one another.

17. The rotary tool as claimed in claim 14, wherein the two cutting edge groups each have the same number of cutting edges.

18. The rotary tool as claimed in claim 14, wherein the first feed speed is in a range between 0.01 to 0.05 mm axial feed per cutting edge and the second feed speed is between 5 times and 10 times the first feed speed.

19. The rotary tool as claimed in claim 14, wherein the axial spacing is between 0.03 mm and 0.1 mm.

20. The rotary tool as claimed in claim 14, wherein the angular spacing of each cutting edge of the second cutting edge group from a first neighboring cutting edge of the first cutting edge group is selected in such a way that, at a predefined second feed speed, the cutting capacity of the cutting edges of the first cutting edge group is identical with respect to the cutting edges of the second cutting edge group.

21. The rotary tool as claimed in claim 14, wherein: the angular spacing of each cutting edge of the second cutting edge group from the first neighboring cutting edge of the first cutting edge group is greater than the angular spacing from the second neighboring cutting edge of the first cutting edge group; the first neighboring cutting edge of the first cutting edge group being a leading cutting edge, and the second neighboring cutting edge of the first cutting edge group being a trailing cutting edge.

22. The rotary tool as claimed in claim 14, wherein more than two cutting edge groups are provided and the cutting edges of each cutting edge group are spaced apart axially from the cutting edges of the other cutting edge groups.

23. The rotary tool as claimed in claim 14, wherein the rotary tool comprises a frictional tool.

24. A method for precision machining of a workpiece with the aid of a rotary tool as claimed in claim 14, wherein, at the beginning of the machining, a first slower feed speed is set, and the feed speed is increased after a predefined axial feed.

25. The method as claimed in claim 24, comprising a switchover to a second, higher feed speed.

26. The method as claimed in claim 25, wherein the switchover is made to the higher feed speed at an axial feed between 0.2 mm and 0.5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the following text, an exemplary embodiment of the invention will be explained in greater detail using the figures, in which, in each case in diagrammatic illustrations:

[0022] FIG. 1 shows a simplified illustration from the side of a frictional tool, shown in details, in engagement with a pilot-drilled workpiece, shown in section, in accordance with the prior art,

[0023] FIG. 2 shows a flattened illustration of the cutting edges of the frictional tool according to FIG. 1 with the trajectories of the cutting corners at a predefined feed speed,

[0024] FIG. 3 shows an enlarged illustration of a cutting edge of that region of FIG. 2 which is identified by a circle, with supplementary explanations,

[0025] FIG. 4 shows a flattened illustration, similar to FIG. 2, of a frictional tool according to the invention with two cutting edge groups which are spaced apart from another by an axial spacing at a predefined slow feed speed,

[0026] FIG. 5 shows an illustration according to FIG. 4, the trajectories of the cutting edges at a second, higher feed speed additionally being shown,

[0027] FIG. 6 shows a diagrammatic illustration of the angular distribution of the cutting edges of the first and the second cutting edge group,

[0028] FIG. 7 shows the flattened illustration according to FIGS. 4 and 5 with the angular distribution of the cutting edges according to FIG. 6, and

[0029] FIG. 8 shows a flattened illustration of the trajectories of a rotary tool with three cutting groups with cutting edge groups which are offset in each case with respect to one another by an axial spacing.

DETAILED DESCRIPTION OF THE INVENTION

[0030] In the figures, identically acting parts are provided with the same designations.

[0031] The rotary tool which is configured as a frictional tool 2 has a tool head 4 with a plurality of cutting edges 6 which are arranged distributed around the circumference and are configured as cutting bars. The frictional tool 2 extends along a rotational axis which at the same time forms a center axis in the axial direction 8 from the tool head 4 to a rear shank 10 (shown only in details here) which is adjoined at the rear end by a clamping shank, by way of which the frictional tool 2 is clamped into a machine tool. In the exemplary embodiment, the cutting edges 6 extend parallel to the axial direction 8, beginning on the end side. As an alternative, they can also be of helical configuration. No further cutting edges are arranged in addition to the (reaming) cutting edges 6. Each cutting edge 6 is assigned a respective flute 12. During the precision machining of a drilled hole 14 of a workpiece 16, the frictional tool 2 rotates about the rotational axis in the rotational direction 18. Here, the frictional tool 2 is advanced in the feed direction 20 counter to the axial direction 8 which is shown. As a result of the superimposed movement directions, the individual cutting edges 6, more precisely the frontmost cutting edges, run along spiral trajectories 22 in relation to the workpiece 6.

[0032] FIG. 2 shows the situation from FIG. 1 in a linearly flattened state. Here, the trajectories 22 are shown by obliquely running lines. Here, the inclination of the trajectories 22 is defined by the feed speed which is set. At a defined feed speed v, the cutting capacity of a respective cutting edge 6 is defined by the engagement length, l, of a respective cutting edge 6 in the axial direction 8, which engagement length, l, is defined at the same time by the spacing between two trajectories 22.

[0033] Here, the region which is shown using dashed lines in FIG. 2 specifies the material-removing volume and therefore the material-removing capacity of the fourth cutting edge 6.

[0034] The situation at the cutting corner at different feed speeds v1, v2 is shown using the enlarged illustration according to FIG. 3.

[0035] The cutting edge 6 first of all has a clearance angle y. At a low feed speed v1, the corresponding trajectory 22A has merely a small angle and, at a faster feed speed, the corresponding trajectory 22B (shown using a dashed line) has a greater angle of inclination. Here, the clearance angle y in each case has to be greater than the angle of inclination which is defined by the feed speed v.

[0036] Embodiments according to the invention of the frictional tool 2 will now be explained in greater detail using FIGS. 4 to 8. In the case of said frictional tool 2, the cutting edges 6 are divided into two cutting groups A, B, the cutting edges of cutting group A being provided with the designation 6A and those of the cutting group B being provided with the designation 6B. It is then of essential significance that the cutting edges 6A, 6B of the two cutting groups A, B are spaced apart from one another by an axial spacing x, that is to say the cutting edges 6B are arranged set back in the axial direction 8 by the axial spacing x. Here, the cutting edges 6A, 6B of a respective cutting group A, B are arranged in each case at the same axial height. As is also apparent, in particular, from FIG. 6, the cutting corners of all cutting edges 6A, 6B are arranged on a common cutting circle 24.

[0037] FIG. 4 shows the machining situation at a low first feed speed v1. As can be seen using the trajectories 22A, the cutting edges 6B lie in each case in the shadow of the respectively leading cutting edge 6A on account of the set-back arrangement. The cutting edges 6B are therefore not in engagement with the workpiece 16 at the selected low feed speed v1. As a result, only a few cutting edges 6A are in engagement at the beginning of the machining operation, that is to say when the frictional tool 2 is moved up to the drilled hole 14 and is introduced into the latter. Highly accurate alignment of the frictional tool 2, in particular of its center axis with respect to the drilled-hole axis, is achieved as a result. In the ideal case, said two axes should be oriented in an axially parallel manner and should coincide.

[0038] The illustration according to FIG. 5 then shows a situation when the frictional tool is advanced at a higher, second feed speed v2. Correspondingly, the associated trajectories 22B are also inclined at a greater angle, with the result that the cutting edges 6B of the second cutting edge group B then also come into engagement and contribute to the removal of material. The material-removing capacity is therefore then distributed to all six cutting edges 6A, 6B at the second feed speed v2.

[0039] As can be gathered from FIG. 5, however, the cutting capacity is distributed differently to the cutting edges 6A and 6B. The cutting edges 6A of the first cutting group A contribute a greater proportion of the material-removing capacity, which leads to premature wear.

[0040] In order to avoid this, an angular distribution of the cutting edges 6A, 6B is then performed, as can be gathered from FIGS. 6 and 7. In general, depending on the selected second, higher feed speed v2, the angular spacing of a respective cutting edge 6B of the second cutting edge group B from the leading and trailing cutting edge 6A of the first cutting edge group is selected differently, with the result that the cutting edge 6B is arranged asymmetrically with regard to said two cutting edges 6A. As can be gathered, in particular, from FIG. 6, the angular spacing 0 from the leading cutting edge is greater than the angular spacing from the trailing cutting edge 6A. Here, the angular spacing , is selected in such a way that the cutting capacity is distributed homogeneously to the cutting edges 6A, 6B, as is shown in FIG. 7. Here, the cutting capacity of the individual cutting edge groups A, B is shown in each case in the illustrations of FIGS. 5 and 7 by the lower case letters a, b. As can be seen in FIG. 7, the cutting capacities a, b are identical.

[0041] In the exemplary embodiment, six cutting edges are provided for the frictional tool 2. Here, the cutting edges of the respective cutting edge group A, B are arranged in each case distributed at least substantially identically, that is to say in each case have an angular spacing of 120 from one another. Slight deviations from said angular spacing are partially desired, in order to counteract an inclination to rattle.

[0042] In addition, fewer or more cutting edges 6 can also be provided. Typical parameter values for the different relevant variables result from the following table, in particular also depending on the diameter of the frictional tool.

TABLE-US-00001 Diameter, tool [mm] B 8-25 25 Number of cutting edges 4 6 8 Number of cutting edges, 2 3 4 group A Number of cutting edges, 2 3 4 group B v1 feed speed [mm/ 0.02 0.04 0.02 0.04 0.02 0.04 0.06 cutting edge] Limiting feed [mm/ 0.048 0.052 0.048 0.052 0.048 0.052 0.15 cutting edge] v2 feed speed [mm/ 0.12 0.2 0.12 0.2 0.12 0.2 0.03 cutting edge] Limiting axial spacing 0.01 0.02 0.01 0.02 0.01 0.02 0.03 [mm] x, axial spacing [mm] 0.03 0.03 0.03 0.03 0.1 , angular spacing from 112.5 103.5 75 69 56.25 51.75 60 the leading cutting edge 6A , angular spacing from 67.5 76.5 45 51 33.75 36.25 30 the trailing cutting edge 6A

[0043] As can be gathered from this, the values for the first, slow feed speed typically lie in the range from 0.01 to 0.08 and, in particular, at 0.02 mm per cutting edge. The limiting feed specified in the table in millimeters per cutting edge and revolution results from the selected total number of cutting edges in the case of an assumed homogeneous distribution of the cutting edges in two cutting edge groups. Here, the limiting feed defines the minimum feed speed of the second higher feed speed, from which the cutting edges 6B of the second cutting edge group B also pass into engagement.

[0044] Furthermore, it can be gathered from the table that the second, higher feed speed typically lies in the range between 0.1 and approximately 0.8, preferably in the region of 0.2.

[0045] Taking the number of cutting edges into consideration (in the case of a uniform distribution to the two groups), the first feed speed v1 then results in a limiting axial spacing which has to at least be maintained, in order to ensure that merely the cutting edges 6A of the first cutting edge group are in engagement. In order to set a sufficient tolerance spacing here, the axial spacing x is preferably selected to be in the range from approximately 0.03 to 0.08 mm.

[0046] Finally, the last two lines of the table indicate typical values for the angular spacing from the leading and from the trailing cutting edge. Here, the angular spacing from the leading cutting edge is defined by the angular spacing between two first cutting edges 6A plus the quotient from the axial spacing in millimeters divided by the second, higher feed speed in millimeters per degree.

[0047] In the case of a total of four cutting edges, the angular spacing therefore lies approximately in the range between 100 and 115, depending on the selected axial spacing and the second feed speed. In the case of six cutting edges, the angular spacing 5 lies in the range from approximately 65 to 80 and, in the case of eight cutting edges, it lies in the range from approximately 50 to 65 (in each case in the case of an at least approximately identical distribution of the first cutting edges 6A).

[0048] Finally, FIG. 8 shows a situation with a third cutting edge group C with third cutting edges 6C. In this exemplary embodiment, the frictional tool 2 then has a total of nine cutting edges, that is to say three cutting edges 6A, 6B, 6C for each group. A switch over to a third feed speed v3 which is defined by a third trajectory 22C is additionally also provided.

[0049] The consideration as described in conjunction with FIGS. 4 to 7 with regard to the selection of the angular spacing between the individual cutting edges 6A, 6B, 6C can also be transferred to this variant in a corresponding manner.

[0050] In the machining method with a frictional tool 2 of this type, the procedure is then such that the frictional tool 2 is first of all advanced at the low feed speed v1 at the beginning of the machining operation and is switched over to the higher feed speed v2 after reaching a predefined axial position within the workpiece 16. As a result, first of all only the cutting edges of the first cutting group A are in engagement at the beginning of the machining method, and subsequently all cutting edges are in engagement with the same material-removing capacity. Here, the switch over takes place after an axial feed x in the range from 0.2 mm to 0.5 mm (cf. FIG. 1 with respect to the axial feed x).

[0051] For the angular distribution of the individual cutting edges 6A, 6B, the additional cutting capacity at the machining start of the cutting edges 6A can also be taken into consideration in addition, with the result that this is also compensated for by corresponding angular positioning of the cutting edges 6A, 6B for a respective application.