Tool and method for machining fiber-reinforced materials

Abstract

A tool for machining fiber-reinforced materials, said tool having a tool body having a particular cutting edge that has at least a main function surface and has a diamond coating applied at least to said main function surface. In order to provide a tool and a method which are especially suitable for machining fiber-reinforced materials, the surface of the diamond coating has a reduced peak height Spk of less than 0.25 m.

Claims

1. A tool for machining fiber-reinforced materials, with a tool body with a particular cutting edge with at least a main function surface, and a diamond coating applied at least to the main function surface, wherein the surface of the diamond coating has a reduced peak height Spk of less than 0.25 m.

2. The tool according to claim 1, wherein the surface of the diamond coating has a reduced peak height Spk of less than 0.2 m.

3. The tool according to claim 1, wherein the surface of the diamond coating has a roughness depth R.sub.z of 0.4 m or more.

4. The tool according to claim 1, wherein the diamond coating has at least one layer made out of nanocrystalline diamond.

5. The tool according to claim 1, wherein the diamond coating is formed out of at least two different layers.

6. The tool according to claim 5, wherein the diamond coating comprises a first layer which adjoins the surface of the tool body and consists of crystalline diamond, and, located further outside, a second layer made out of diamond with a grain size that is less than the grain size of the first layer.

7. The tool according to claim 6, wherein the layer thickness of the second layer is greater than the layer thickness of the first layer.

8. The tool according to claim 1, wherein the diamond coating has an overall layer thickness which is at least 6 m.

9. The tool according to claim 1, wherein the diamond coating has an overall layer thickness which is at most 12 m.

10. The tool according to claim 1, wherein the tool body consists of a hard metal at least at the cutting edge.

11. The tool according to claim 1, wherein the tool is a drilling tool and the main function surface is a surface adjacent to a main cutting edge or secondary cutting edge.

12. A use of a tool according to claim 1 for machining fiber-reinforced materials.

13. A method for machining fiber-reinforced materials, wherein a tool according to claim 1 is used for machining.

14. The method according to claim 13, wherein a sandwich material is machined with the tool wherein the sandwich material has at least one layer made out of a fiber composite and at least one layer made out of a metal alloy.

15. The method according to claim 14, wherein the metal alloy is a titanium alloy or aluminum alloy.

16. The tool according to claim 1, wherein the surface of the diamond coating has a reduced peak height Spk of less than 0.15 m.

17. The tool according to claim 1, wherein the surface of the diamond coating has a roughness depth R.sub.z of 0.7 m or more.

18. The tool according to claim 1, wherein the surface of the diamond coating has a roughness depth R.sub.z of 1.2 m or more.

19. The tool according to claim 6, wherein the second layer consists of nanocrystalline diamond.

20. The tool according to claim 7, wherein the layer thickness of the second layer is 25-fold or more the layer thickness of the first layer.

21. The tool according to claim 7, wherein the diamond coating has an overall layer thickness which is at least 7 m.

22. The tool according to claim 21, wherein the diamond coating has an overall layer thickness which is at least 8 m.

23. The tool according to claim 9, wherein the diamond coating has an overall layer thickness which is at most 11 m.

24. The tool according to claim 23, wherein the diamond coating has an overall layer thickness which is at most 10 m.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) In the following an embodiment of the invention is described in greater detail with reference to drawings. In the figures:

(2) FIG. 1 shows a side view of a drill;

(3) FIG. 2 shows an enlarged illustration of a cross-section through a cutting edge and a main function surface of the drill from FIG. 1;

(4) FIG. 3 shows a schematic illustration of the structure of a coating of the main function surface from FIG. 2;

(5) FIGS. 4a, 4b show exemplary roughness profiles to explain roughness parameters;

(6) FIGS. 5a, 5b show images of drilled holes, which were created with a tool according to an embodiment of the invention and with a comparable tool; and

(7) FIG. 6 shows a partly cutaway side view of a step drill in a workpiece.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a side view of a drill 10 as an example of a tool according to an embodiment of the invention. The drill 10 has a processing area 12 with various cutting edges 20, main cutting edges 2 arranged at the tip and, adjoining this, a spiral area with secondary cutting edges 4. The outer ends of the main cutting edges 2 form cutting corners 8.

(9) Rake faces 3 are adjacent to the main cutting edges 2. Chamfers 6 are formed on the secondary cutting edges 4.

(10) The drill 10 consists of a hard metal material, in particular a WC/Co hard metal, and is coated with a diamond coating 16 in its processing area 12.

(11) Surfaces which are adjacent to the cutting edges 20 are described as main function surfaces of the drill 10. Hence the chamfers 6 of the secondary cutting edges 4 constitute main function surfaces of the drill 10, which are directly adjacent to the cutting edge 20. Likewise, the rake faces 3 on the main cutting edges 2 constitute main function surfaces of the drill 10.

(12) FIG. 2 shows a schematic illustration of a cut through a cutting edge 20 with a diamond coating 16. The cutting edge 20 can be, for example, a main cutting edge or secondary cutting edge 2, 4. For example, in the case of the secondary cutting edge 4, the chamfer 6 of the secondary cutting edge directly adjacent to the cutting edge 20 forms a main function surface of the drill 10.

(13) FIG. 3 shows a schematic illustration of the structure of the diamond coating 16 on the main function surface 6 shown in FIG. 2. In the example shown, this has two layers. First, a first diamond layer 22 made out of microcrystalline diamond is applied to the WC/Co hard metal substrate. A second diamond layer 24 made out of microcrystalline diamond is applied directly onto the first diamond layer 22. The second diamond layer 24 is considerably thicker than the first diamond layer 22.

(14) The outer surface 26 of the diamond coating 16 is formed by the nanocrystalline second diamond layer 24. The surface 26 has a very smooth structure, whereby there are no upwardly protruding peaks, outgrowths or relatively large individual crystals on the surface in particular.

(15) The topology of the surface 26 can be characterized by standardized roughness parameters, here the areal roughness value of the reduced peak height, in short Spk, in particular. The areal roughness value of the reduced peak height Spk is standardized according to EN ISO 25178. The reduced peak height is a surface value which, in particular, takes into account upwardly protruding roughness peaks on an otherwise plateau-like surface, not, however, deeper-lying grooves or respectively roughness valleys.

(16) When assessed, the parameter of the reduced peak height differs considerably from roughness parameters which merely describe the roughness or respectively smoothness of a surface in general, without evaluating protruding peaks in particular. The illustrations in FIGS. 4a, 4b show a symbolic example of two roughness profiles which are inverse to each other, with a peak protruding in the center in FIG. 4a and, inverse to this, a central valley in FIG. 4b. The value of the roughness depth R.sub.z is identical for both profiles in FIGS. 4a, 4b. In contrast, the topology of the profile in FIG. 4b appears considerably more favorable for processing fiber-reinforced materials, since a protruding peak as shown in FIG. 4a is more likely to cause fibers to be torn out during the processing of fiber-reinforced materials, for example CFRP materials.

(17) The parameter of the reduced peak height according to EN ISO 25178 takes this into account. The value can be easily determined with today's optical 3D roughness-measuring devices. The value of the two-dimensional reduced peak height Rpk is defined according to ISO 13565-2. In a preferred calculation method for the Spk value this is calculated identically, albeit on the basis of the surface material curve instead of the material curve which is developed from an individual profile section. For this, the ISO 25178 standard is used.

(18) When assessing exemplary embodiments of the invention, the surfaces were determined with an optical 3D measuring device surf explorer from the company Nano Focus AG. The Spk value is calculated as described above via the related soft analysis software. The form of the tool was taken into account for measuring with a second-order polynomial. The analysis is preferably done on the chamfer 6 of the secondary cutting edge 4, directly below the cutting corner 8. This point is marked by the reference number 14 in FIG. 1.

(19) Due to the smooth surface 26 on the main function surface 6, which is largely free of protruding peaks and outgrowths, the drill 10 is very suitable for processing carbon fiber-reinforced matrix materials like CFRP and CFC in particular.

(20) FIG. 6 shows a step drill (conical drill, countersink) 30 with a first drilling area 32 of smaller diameter and a second drilling area 34 of larger diameter. As shown in schematic form in FIG. 6, the conical drill 30 can be used for producing depressions in a workpiece.

(21) FIG. 5b shows an example of drilled rivet holes produced with a countersink, wherein the main function surface has the surface topology described above, with an Spk value of 0.12 m. For the purposes of comparison, a drilled rivet hole produced under the same conditions with a conventional CVD diamond-coated tool is shown in FIG. 5a. Measured on the surface of the coating on the main function surface, the Spk value of the conventional, comparable tool is 0.3 m.

(22) Even during drilling it becomes apparent that the tool with the smooth surface with a low Spk value runs smoothly, whereas the conventional, comparable tool undergoes considerable vibrations. When the drilled holes are assessed, a clean drilled hole is evident in the case of the smooth surface of the coating, whereas the conventional tool shows unclean, non-round depression surfaces in the CFRP sandwich material, due to an interaction between the carbon fibers contained therein and protruding peaks on the coating.

(23) The application of the coating 16, which in the example shown consists of the diamond layers 22, 24, is carried out in an exemplary embodiment as a CVD diamond coating in the hot-filament process, following pre-treatment of the hard metal substrate.

(24) In this case the hard metal substrate is first chemically and/or electrochemically etched during the pre-treatment. The pre-treatment serves to remove the cobalt harmful to the diamond growth and the layer adhesion. Additionally, it can serve to remove the grinding skin and/or to roughen the surface for improved adhesion by means of a mechanical grouting between layer and substrate. Suitable pre-treatment methods are described in particular in WO 2004/031 437 A1 and in WO 2007/140 931 A1 of the applicant. A treatment by means of sand-blasting to condition the surfaces can take place beforehand.

(25) During the subsequent CVD diamond coating by means of the hot-filament process, the tools are preferably positioned between two parallel rows of vertical filaments, as described in WO 98/35071 of the applicant. The two diamond layers 22, 24 can be produced by predefining various parameters of the coating plant during the coating process, as described in WO 00/60137 A1 of the applicant for example. A nanocrystalline structure of the outer layer 24 can be produced by means of a coating process, which, using its process parameters, commutes between conditions of variously intense carbon supersaturation according to WO 2004/083 484 A1 of the applicant.

(26) The particular topology of the surface becomes thereby possible due to the particularly smooth diamond layers produced with the method given in WO 2004/083 484 A1, which even cause a levelling of the somewhat rougher microcrystalline diamond layer 22 lying beneath it. The chemical etching described above is only carried out gently with little etching depth beforehand, in order to obtain a relatively smooth substrate. The smooth surface 26 is further aided by the structure of the diamond coating 16 made out of a first diamond layer 22 of relatively slight thickness and a considerably thicker nanocrystalline diamond layer 24 lying over it. The overall layer thickness is thereby limited to 12 m at the most for example, most preferably to a minimum of 8 and a maximum of 10 m. With a correspondingly slight layer thickness a smooth surface 26 with the required low Spk value can even be achieved during the production in the CVD process.

(27) Additionally or alternatively, the surface 26 can be subsequently processed, in order to provide the desired roughness parameters. The subsequent processing can be carried out with diamond tools or respectively diamond grinding discs or by means of a plasma smoothing or respectively laser smoothing.

EXAMPLES

(28) An 8 mm drill made out of EMT 100 hard metal having 6 wt % Co is first electrochemically etched and 6 m uniformly removed. Then a particularly gentle chemical pre-treatment is carried out, as described in WO 2004/031 437 A1, which reduces the cobalt near the surface and causes a slight roughness. This pre-treatment reduces the diameter of the drill by a further 2 m. Next, a 0.3 m-thick crystalline layer is applied by means of the hot-filament process in a coating plant type CC800/9 Dia. Finally, the coating parameters are modified in the same process, without vacuum interruption, so that a nanocrystalline layer is applied up to an overall layer thickness of 8 m by means of a process which commutes between various operating conditions according to WO 2004/083 484 A1.

(29) Produced in this way, the tool shows an increased number of holes compared to conventional, CVD diamond-coated tools, when drilling rivet holes in a CFRP material, the drilling quality being considerably enhanced compared to conventional processing, during which frayed fiber ends are visible in the bore hole, as is apparent in the comparison of the illustrations FIGS. 5a, 5b.

(30) In a further example an 8 mm drill is produced, which proceeds from the same tool substrate as in the first example. In order to be able to machine sandwich materials with at least one metal layer made out of an aluminum alloy with said tool, a somewhat deeper etching is carried out during a production process otherwise the same as the one described above. The result is therefore better layer adhesion, even though the roughness is perhaps increased. In this case 3 m is removed during the chemical pre-treatment. The overall layer thickness of the diamond coating is 10 m, somewhat more than in the case of the above tool which is provided above all for purely CFRP processing.

(31) In a further example of a drill for processing sandwich materials with a metal layer made out of a titanium alloy, the production is carried out as described above for the aluminum-sandwich tool, although the substrate is additionally treated by means of sand-blasting beforehand. In this case the overall layer thickness is even a little more, 12 m, so that better characteristics for machining the titanium material are achieved.