Guide gib for gib-guided cutting tools

Abstract

A guide gib for gib-guided cutting tools that serves for precision machining of rotationally symmetrical bores is ground on its working surface so as to match the nominal diameter of the tool surface, by grinding with diamond abrasive, the guide gib being a PCD guide with a hardness corresponding to the cobalt proportion of the PCD material used for production. The cobalt proportion is greater than 10%.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] The invention relates to a guide gib for gib-guided cutting tools that are used for precision machining of rotationally symmetrical bores, and to a method for producing such guide gibs, and also to a method for the electrical discharge machining of guide-gib blanks.

[0004] In their use as cutting materials, carbides have been known for a very long time in the field of precision tools, the cutting material used is a PCD material, as described in detail, for example, in the doctoral thesis by Siebert. The title of the doctoral thesis is “Polykristalliner Diamant as Schneidstoff” [Polycrystalline diamond as cutting material] and has the ISBN code 3-446-16435-9. According to the publisher's preface, PCD, in March 1991, as a cutting material in production by machining, had already provided proof of its technological capability when substituted for conventional cutting materials. From the list of references of the dissertation, it can be seen from reference 137, for example, that it was already known in 1961 to use PCD in the machining of aluminum engine parts. For the cutting edges of tools that serve for precision machining, PCD material with an addition of 6% of cobalt has been used for a long time, as the dissertation correctly reports on page 27, paragraph 1.

[0005] During the high-precision grinding of the cutting edges, the PCD material is ground with diamond material, that is to say that the precision tool is ground with diamond. This means a very large amount of abrasion on the grinding wheels. This also means a considerable loss of time due to the long machining duration. The infeed of the grinding wheels to the PCD material to be ground is around 10 micrometres, for example. In order to initiate the grinding operation, there must be a certain contact pressure between the grinding wheel and the material to be ground. If the contact pressure is too low, too little material or scarcely any material is ground off. If the infeed distance of the diamond grinding wheel is too great, it may well be the case that the contact pressure of the grinding wheel is absorbed by the machine frame of the grinding machine, i.e, the machine bed gives way by 10 micrometres and nothing or—virtually nothing—is ground away. If, for example, 10 micrometres is fed in a third time, a breakaway effect may occur and substantially more than the desired 10 micrometres is ground-off. It is, therefore, not the case that virtually every infeed distance is reflected in a corresponding ground-off volume. To the contrary, the grinding may also be effected in a very non-linear manner. In precision tools, this often leads to scrap and it may be the case that this scrap is not noticed.

[0006] In the production of guide gibs, grinding has always been carried out in the same way as when grinding cutting edges: that is to say, with a great deal of time, with a considerable amount of grinding material and with the further abovementioned disadvantages.

[0007] In the literature, DE A 4329553 shows a typical application for guide gibs. Work is carried out there with a coating according to the CBN technology, and, according to this publication, the PCD technology already known at the time is dispensed with, but the problems that occur when producing the guide gibs described there are already mentioned.

[0008] EP 0 713 747 A1 describes the CVD technology. However, this technology must not be confused with the PCD technology, although diamond is involved in both instances.

[0009] Finally, DE 42 02 751 A1 describes the prior art, even if with a later date of, publication than the above-mentioned dissertation.

[0010] It may be pointed out that the PCD guide gibs are in no way coated with diamond. To the contrary, it is, and has always been the case that the guide gibs of PCD material have been produced with a 6% cobalt addition. This 6% cobalt addition leads to a comparatively large amount of polycrystalline diamonds. Accordingly, the PCD material is hard and its machining in the above-mentioned manner is difficult.

[0011] In this case, it should be taken into account that the working surface of the guide gibs must be ground so accurately that it is not much smaller than the pitch circle of the cutting edge. A bevel must also be correctly ground on the leading side of the guide gib that, in the desired case, a suitable lubricant film edge can form in the narrow gap between pitch circle and working surface of the guide gib.

SUMMARY OF THE INVENTION

[0012] The object of the invention is to specify ways of saving time, of saving grinding material and producing guide gibs in a simpler and more accurate manner and to facilitate cuttingout the guide gib blanks from round PCD blanks. According to the invention, this object is achieved by the guide gib being ground on its working surface so as to match the nominal diameter of the cutting tool by grinding with diamond abrasive, the guide gib being a PCD guide gib with a hardness corresponding to the cobalt proportion of the PCD material used for the production, and the cobalt proportion being greater than 10%.

DETAILED DESCRIPTION OF THE INVENTION

[0013] By virtue of the fact that, according to the invention, a higher volume of cobalt is selected for the starting material, the guide gib blank is easier to erode by electrical-discharge machining. This is normally done by electrical-discharge wire cutting. The electrical conductivity of the carbide is increased, and as a result, the electrical-discharge machining rate can accordingly be increased, the fine electrical-discharge cutting wire does not break so frequently, time is saved and the guide-gib blank cut out of the round blank can be fed to its finish machining earlier.

[0014] After the infeed of the grinding wheel, the guide gib to be ground gives way to a smaller extent or not at all, since it is no longer so hard. The thickness of the ground-off guide gib layer corresponds (linearly, at least to some extent) to the size of the infeed. For example, with a jump from 6% to 20% cobalt, the grinding time for the guide gibs can be reduced by about half.

[0015] When the wear curve, which in a fairly pronounced hyperbolic function, is considered, the wear of the grinding material decreases substantially out of proportion, but rather by about fourfold.

[0016] The advantages are in no way gained by the adhesion behavior of the carbide with higher cobalt addition leading to more adhesion or intolerable adhesion of that material at the guide gib that is regularly used for producing passenger car engines, gear casings and chassis parts. The adhesion behavior has hitherto played too important a role. The adhesion behavior of PCD guide gibs with a cobalt addition normally used was, as it were, much too good for benefits to be gained therefrom. The PCD guide gibs according to the invention, in no event wear out quicker than PCD guide gibs with a 6% cobalt addition.

Claims

1. Guide gib for gib-guided cutting tools that serves for precision machining of rotationally symmetrical bores, which guide gib is ground on its working surface so as to match a nominal diameter of a cutting tool, the guide gib being a PCD guide gib with a hardness corresponding to a cobalt proportion of the PCD material :used for a production wherein a cobalt proportion is greater than 10%.

2. The guide gib according to claim 1, in which the cobalt proportion is greater than 11%.

3. The guide gib according to claim 1, in which the cobalt proportion is greater than 12%.

4. The guide gib according to claim 1, in which the cobalt proportion is greater than 13%.

5. The guide gib according to claim 1, in which the cobalt proportion is greater than: 14%.

6. The guide gib according to claim 1, in which the cobalt proportion is greater than 15%.

7. The guide gib according to claim 1, in which the cobalt proportion is greater than 16%.

8. The guide gib according to claim 1, in which the cobalt proportion is greater than 17%.

9. The guide gib according to claim 1, in which the cobalt proportion is greater than: 18%.

10. The guide gib according to claim 1, in which the cobalt proportion is greater than 19%.

11. The guide gib according to claim 1, in which the cobalt proportion is greater than 20%.

12. The guide gib according to claim 1, in which the cobalt proportion is greater than 21 %.

13. The guide gib according to claim 1, in which the cobalt proportion is less than 35%.

14. Method of producing guide gibs from PCD guide-gib blanks, comprising: selecting a percentage by volume of cobalt of the guide gib blank that is greater than 10%, or greater than 11%, or greater than 12%, or greater than 13%, or greater than 14%, or greater than 15%, or greater than 16%, or greater than 17%, or greater than 18%, or greater than 19%, or greater than 20%, or greater than 21%, but is less than 35%, and grinding a functional surface of the guide gib.

15. Method for electrical-discharge machining of guide-gib blanks from round PCD blanks, comprising selecting a material of a round blank PCD having a cobalt proportion of greater than 10%.

16. Method for an electrical-discharge machining of guide-gib blanks from round PCD blanks for cutting tools, comprising: providing a PCD guide gib with a hardness corresponding to a cobalt proportion of a PCD material used for the production, the cobalt proportion being greater than 10%, and grinding the guide gib on its working surface so as to match a nominal diameter of the tool by grinding with diamond abrasive.