Patent Application
20140206269
The invention relates to a tool for grinding toothed workpieces using dressable grinding tools which were optimized with regard to the maximum tool diameter by collision surfaces, like interference contours or limitations from the preprocessing, such as tool run-out.
Known tools for generating grinding of tooth systems always have a tool holding mandrel or flange by means of which the tool is held in the grinding machine. This mandrel/flange requires a certain minimum diameter in order to have the necessary stability. The tool(s) is(are) fitted on this mandrel/flange and generally fastened to the mandrel/flange by laterally arranged fastening elements. So that a collision between the tool and holding mandrel/flange does not occur during grinding, the usable tool diameter only begins after this region. A certain minimum tool diameter results due to this design principle and due to the coating thickness necessary in the abrasive coating for an economical grinding process.
Modern transmissions contain, in addition to the classic gears with bore (“bored workpieces”), input-, intermediate-, and drive shafts as well, which have one or more toothings which are directly connected to the shaft and/or come from a raw material. A characteristic of these components is a workpiece geometry that has so-called collision teeth, i.e. a further toothing, a shaft collar, another interference contour is next to the toothing to be processed, or the toothing does not end in an end surface but instead runs out with a radius. This must be considered with regard to the design of the toothing tool already during machining before heat treatment (roughing with hob or form cutter). During the hard-fine machining necessary after hardening, the tool diameter may often only have maximally the same diameter as during the machining before heat treatment.
In general, these workpieces are processed after the heat treatment using the following hard-fine machining processes:
1. Generating grinding using electrically coupled CBN worm grinding wheels
2. Profile grinding using electrically coupled CBN profile grinding wheels
3. Gear honing and
4. Generating grinding using dressable cutting material (aluminum oxide, CBN or similar)
5. Profile grinding using dressable cutting material (aluminum oxide, CBN or similar)
If dressable tools are used (methods 4 & 5), then, due to the collision situation at grinding wheels and worm grinding wheels and a conventional tool design, the installation space is lacking for the necessary coating thickness which is required in order to always generate new, fresh, easy to cut grinding tool surfaces, even during multiple dressing of small cutting material coatings. Due to this circumstance, dressable profile- and generating worm grinding wheels are not economical in this application, even though these cutting materials are used extremely successfully in “collision-free” tooth systems.
For this reason, these tooth systems have often been hard-fine processed using methods 1-3 up until now. This is due to economic reasons and because tools made from dressable cutting materials can be more easily re-profiled; however, a process with dressable tools would be desirable. It is, however, necessary for this purpose that a certain minimum coating thickness is realized in order to obtain an economically usable tool. At the same time, the tool mandrel requires a minimum diameter so that the necessary stability and stiffness is realized. These two limiting conditions define or delimit the possible radial installation space for the tool.
DE 101 04 410 A1 discloses a tool for generating grinding of tooth systems during which the grinding tool consists of a bearing ring and an abrasive body which is fitted on a conical mounting flange. By this means, the grinding tool is fixed without play. The deformation resistance of the bearing ring is thereby greater than that of the abrasive body. Due to this embodiment, displacements and deformations of the worm grinding wheel caused by centrifugal forces are minimized. Disadvantageous in this embodiment are the spatial requirements required in order to accommodate all function elements in the tool and at the same time guarantee the necessary stability of the holder.
WO 94/19135 discloses a single-part galvanically-coated tool having two different portions. These two portions are coated with hard materials in order to undertake different grinding tasks during the hard-fine machining process. The grinding tool comprises a conical mounting sleeve with which it is fitted on the round tool mandrel and tightened. This embodiment also requires a certain minimum height for the tool. In connection with a stable round mandrel for the tool, this results in a certain minimum tool diameter. In this embodiment of the tool, the tool diameter and/or the coating thickness are no longer changed thereby, since no dressing of the abrasive coating takes place. If this tool is worn out, it must first be decoated in order to be subsequently newly recoated. Disadvantageous in this embodiment is that changes to the profile shape of the grinding tool can only be generated during the manufacture thereof. During the hard-fine machining, such changes or re-profilings are no longer possible due to the low coating thickness of the abrasive material. This is only possible using dressable grinding tools.
DE 10 2004 020 364 A1 likewise describes a tool for generating grinding of tooth systems having a multi-part grinding tool with dressable abrasive bodies. In this case, a multi-part tool is described in which different abrasive bodies are clamped on a common base mandrel.
It would be desirable to make a new type of tool available to a person skilled in the art for economical hard-fine machining of workpieces having an interference contour which is next to the toothing to be processed.
A use of grinding tools with dimensions according to the prior art is no longer possible for tooth systems of this type due to reasons of collisions. If a tool with a reduced outer diameter is used, which has, however, a conventional design, then the remaining residual wall thickness of the dressable abrasive coating is reduced to such an extent that an economical use is no longer possible.
It is thus the object of the present invention to configure the structure of the grinding tool such that the necessary stiffness of the holding mandrel is guaranteed in order to generate the required grinding quality and at the same time the necessary coating thickness is provided for an economical number of dressing cycles.
This problem is solved by a tool having the features of claim 1.
The essential aspect of the invention is a tool for generating grinding having a dressable worm grinding wheel with a small outer diameter and a coating thickness necessary for a repeated dressing cycle. This is achieved, in contrast to conventional tool design, in that the abrasive coating is no longer fitted on and tightened onto the tool holder, which consists in particular of a tool mandrel or a mounting sleeve, but instead the abrasive coating is glued directly to the tool holder, in particular the tool mandrel or mounting sleeve.
Due to this design, the stops arranged laterally adjacent to the tool and the previously necessary fastening and fixing units are not needed. In addition, the worm grinding wheel sleeve, on which the worm grinding wheel is usually glued in conventional tool design, is also not needed, in particular if the grinding tool is composed of grinding wheel segments.
Due to this development, significantly smaller tool diameters can be realized for dressable tools and thus enable an economical and flexible machining of workpieces having collision contours, even while using dressable grinding tools. Due to the segmented design of the grinding tool, tool widths, which cannot be realized using a single-part tool design, can be realized. The maximum width of the worm blank is known to be limited by the production method thereof. Beginning at a certain ratio of worm width to material thickness, the worm blank can no longer press with the necessary homogeneity. This tool would then have a disadvantage, e.g. due to different grinding behavior across the width thereof or different absorption capacity for coolants, which would again lead to problems during balancing of the tool.
Further advantageous embodiments of the method are the subject matter of the claims subsequently dependent on the main claim.
The glued tool can again be combined with further tools, in case multiple tooth systems should be processed serially on a workpiece, in the case that a toothing should be processed with different grinding processes, e.g. generating grinding and profile grinding. Further, it is also possible to machine different grinding processes, like toothing grinding and grinding outer diameters, surfaces, grooves, or slots with a tool according to the invention. A combination of dressable and non-dressable tools is also possible in order to machine one or more tooth systems of surfaces.
A combination is also conceivable, made of a dressable grinding tool to machine a collision contour together with a non-dressable tool. By this means, a still smaller collision contour can be machined, at which machining using a dressable tool is no longer economically presentable. This enables according to the invention e.g. the machining of tooth systems that up until now could not be economically processed using generating grinding.
A further application of these tools is for workpieces in which the tooth system does not end in an end face, but rather in a tool run-out. In this case, the diameter of the grinding tool may not be larger than the diameter from the preprocessing.
Further features, details, and advantages of the invention will be described by means of embodiments depicted schematically in the drawings. As seen in:
The design of the worm grinding wheel can likewise be seen, which design consists of a plurality of individual segments 65 which are glued radially to the outer circumference of the tool mandrel.
a to 3e exemplarily show different embodiments of the tool arrangement with one or more grinding tools which are engaged with a workpiece having a collision contour, in the example of the double toothing 50 from
a shows a dressable worm grinding wheel 60 which consists of circular segments 65 glued radially to the outer diameter on the tool mandrel 40. The slanted position of the tool is determined, among other reasons, by the helix angle and the tool design.
A dressable worm grinding wheel is likewise shown in
The combination tool shown in
The tool arrangement with two worm grinding wheels, as is shown in
e shows a tool arrangement with a single-sided mounting cone for the tool in the tool holder.
Exemplary workpieces, as they can be machined according to the invention using a grinding tool, are depicted in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 001 197.3 | Jan 2013 | DE | national |
