Patent Application
20250041994
The present invention relates to a grinding tool and a method for producing such a grinding tool.
Furthermore, the invention relates to an arrangement with such a grinding tool, a method for machining a workpiece in an arrangement and a use of the grinding tool to grind a hard-coated brake disc.
Grinding tools of the type named at the beginning are used above all to machine brake discs with wear-resistant coating, in particular car brake discs, wherein machining by grinding is necessary in order to satisfy the requirements for the standardized surface finishes of brake discs.
To reduce particulate emissions, in particular in connection with e-mobility, wear-resistant, carbide-containing layers, approx. 0.5 mm thick are deposited on both sides of the base body of the brake disc. Above all, hard materials, such as e.g. tungsten carbide (WC), molten tungsten carbides, titanium carbide (TiC), chromium carbide (Cr3C2), niobium carbide (NbC), and metal binders (e.g. stainless steel, titanium aluminide) are used as coating components.
After the coating, the brake discs are ground with grinding tools, in order to satisfy the geometric requirements (e.g. defined brake disc width, remaining layer thickness, axial runout, plane parallelism) and requirements for the surface (e.g. no porosity, roughness, waviness, grinding pattern). The layers applied to both sides are usually machined simultaneously with two grinding tools using the double disc surface grinding process. The measurement for each side is usually between 0.1 and 0.3 mm.
A first difficulty when using such grinding tools is that the different brake disc manufacturers apply different hard materials and binders to different base bodies in different mixing ratios. If brake discs with different coatings or friction linings are to be ground or a particular quality of a coating or friction lining is to be achieved, it is usually necessary to replace the grinding tool on the grinding machine or at least, as shown e.g. in DE 102021132468 B3, a sequential grinding by means of different grinding tools is necessary. For one thing, this can lead to a lot of effort, which is associated with long machining times and high costs. A further disadvantage is that several different grinding tools are needed for the machining of different coatings.
A second difficulty when using grinding tools is their excessive wear when machining wear-resistant brake discs. Thus, although the grinding tool from U.S. Pat. No. 10,875,152 B2 has a grinding layer made of diamond and CBN grains, which appears to promise the advantageous combination of the high hardness of the diamond grains and the inertness and low tendency of the CBN grains to be coated with chips, the grinding tool from U.S. Pat. No. 10,875,152 B2 is equipped with a grinding layer which only consists of a single layer or grain layer, which disadvantageously limits the durability of the grinding tool. This is because as soon as the single grain layer is worn, the grinding tool is unusable and has to be replaced. Because of the single-layered formation as a so-called “single layer”, the grinding tool from U.S. Pat. No. 10,875,152 B2 can in any case be regarded as a non-generic tool.
In contrast to the grinding tool from U.S. Ser. No. 10/875,152 B2, although the grinding tool from JP 2008200780 A is formed multi-layered, it has a very large proportion of CBN grains or a very small proportion of diamond grains. This unfavorable grain mixing ratio again disadvantageously limits the durability of the grinding tool because of the increased wear of the CBN grains.
The object of the present invention is therefore to provide a grinding tool which is improved relative to the state of the art, with which all the usual hard-coated brake discs can be reliably, durably and economically machined and with which, as the only grinding tool, a required geometry and surface quality of a workpiece to be machined is achieved.
This object is achieved by a grinding tool with a base body and a grinding layer, wherein the grinding layer comprises diamond grains and CBN grains. A grain mixing ratio between the diamond grains and the CBN grains is substantially, i.e. in particular taking any manufacturing tolerances into consideration, 1:1 and wherein the, in particular mean, grain sizes of the diamond grains and/or the CBN grains are more than 50 μm.
A first big advantage of the grinding tool according to the invention, which is preferably formed as a grinding wheel, is that all the usual hard-coated brake discs can be machined with the same grinding tool. It is not necessary to replace the grinding tool in the case of a change of coating or brake disc. Compared with solutions of the state of the art, the process times and costs can thus be greatly reduced.
Through the grinding tool according to the invention, therefore, the standardized requirements, in particular standardized by EU regulations, for the geometry and surface finish of brake discs can be satisfied even for different coatings or friction linings.
The grinding layer is a three-dimensional body which grinds or abrades a coated brake disc by means of at least one of its outer faces or a grinding surface. The grinding layer wears down along its grinding surface over time.
Compared with conventional grinding tools with exclusively diamond grains or exclusively CBN grains in a metal bond, the grinding wheel according to the invention has the big advantage that it has a wear reduced by 40-50% (of 0.007-0.008 mm per friction lining for each brake disc), and thereby has a much longer life.
Compared with a grinding tool with a single-layered grinding layer consisting of diamond and CBN grains, the life or service life of the grinding tool according to the invention is many times longer. Diamond breaks in grinding use and CBN splinters, wherein the CBN protects and supports the diamond. In this connection, a self-sharpening grinding layer is also referred to in the case of the present grinding layer, since further grain layers succeed the respectively uppermost worn grain layer. Thus, the full operability of the grinding tool is preserved with a constant grinding power over the whole life.
A further improvement compared with conventional diamond grinding tools is that the drive power of the grinding machine bearing the grinding tool according to the invention can be reduced by approx. 30%.
A further improvement compared with conventional diamond grinding tools is that a much lower grinding pressure is needed to effectively machine hard-coated brake discs in particular. As a result, the elastic deformations of the brake discs are also reduced, with the result that the brake discs can be ground with an evenness of a previously unachieved 0.005 mm axial runout (usually >0.010 mm).
The grain mixing ratio between the diamond and CBN grains is preferably to be understood as a mass ratio between the diamond and CBN grains, wherein the grain mixing ratio can be regarded as an average value and wherein manufacturing tolerances are also incorporated, with the result that the ratio is not exactly 1:1 in every section.
The grain sizes of the diamond and/or CBN grains are preferably to be understood as mean values or average values, in particular as average grain diameters, in particular within the meaning of mean grain sizes, e.g. according to the definition in ISO standard 6106.
The grain sizes, i.e. the mean grain sizes, represent in particular 80-95% of the diamond and/or CBN grains present.
As an alternative to a pure metal bond or a pure resinoid bond, it is possible for the diamond and CBN grains to be bonded in a hybrid bond comprising metal and synthetic resin.
It is particularly preferable that the, in particular mean, grain sizes of the diamond grains and/or the CBN grains, preferably of the diamond grains and the CBN grains, are 51 μm to 300 μm, preferably 91 μm to 252 μm.
It is also preferable that the, in particular mean, grain sizes of the diamond grains and/or the CBN grains, preferably of the diamond grains and the CBN grains, are larger than 74 μm, particularly preferably larger than 88 μm.
The, in particular mean, grain sizes of the diamond grains and/or the CBN grains, preferably of the diamond grains and the CBN grains, are preferably smaller than 180 μm.
Preferably, the grain size ratio between the CBN grains and the diamond grains is from 0.3 to 2.8, particularly preferably from 0.5 to 1.0.
This means that the CBN grains are particularly preferably at least half as large and at most the same size as the diamond grains.
It is particularly preferable that the grinding layer comprises the abrasive materials diamond and CBN and preferably fillers, which are incorporated in a metal bond or metal-containing bond. The abrasive materials of the grinding layer are (apart from minimal deviations due to manufacturing) 50% diamond and 50% CBN according to the invention.
In a preferred variant, the grinding layer consists of 10-35 vol.-% diamond and CBN, and 50-90 vol.-% metal bond, and with the remainder being fillers.
It is particularly preferable that the grinding layer is formed annular, preferably as an annular cylinder or cone body. The grinding layer can in this connection also be called a grinding cylinder.
The grinding layer is applied to at least one bonding surface of the base body or a carrier body fastened to the base body, preferably wherein the bonding surface is formed with an annular surface and/or flat and/or is arranged orthogonal to an axis of rotation of the grinding tool.
The bonding surface can also be formed sloped, conical and/or cylindrical and/or be arranged inclined relative to the axis of rotation of the grinding tool.
However, the bonding surface can also be formed variable, with the result that the grinding layer also has a correspondingly variable shape, in particular wherein the layer height varies within a range of values.
It may also be the case that the grinding layer and/or the base body and/or the carrier body, in particular along the bonding surface, is or are formed ledge- or step-shaped.
The grinding layer has a grinding surface, wherein the grinding surface is the outside of the grinding layer which touches a workpiece to be ground, in particular the friction lining or the coating of a brake disc.
The grinding surface is preferably arranged orthogonal to an axis of rotation of the grinding tool and/or formed substantially flat, wherein it can naturally have roughnesses because of the diamond and CBN grains.
Through the grinding, the layer height on the grinding surface of the grinding layer reduces over time.
In a preferred embodiment, the, in particular annular, grinding layer has:
The layer width is preferably to be understood as the difference between the outside diameter and an inside diameter of the grinding layer, wherein the outside diameter of the grinding layer preferably corresponds at least to the side wall outside diameter of the base body.
The layer width is particularly preferably less than 20 mm, in particular less than 16 mm, particularly preferably less than 12 mm.
In particularly preferred embodiments the layer width is 6 to 8 mm.
The inside diameter of the grinding layer is preferably larger than the side wall inside diameter of the base body. However, the inside diameter can also be the same size as or smaller than the side wall inside diameter.
The outside diameter of the grinding layer is preferably the same size as or larger than the side wall outside diameter or outside diameter of the base body.
These and all further values are preferably to be regarded as constant values taking manufacturing tolerances into consideration.
However, it is also conceivable that the outside diameter, the layer width and/or the layer height are variable, for example polygonal, along the grinding layer.
The at least one layer is preferably formed substantially homogeneous, wherein the homogeneity is an averaged homogeneity because of the grains of the abrasive materials, in particular the diamond and CBN grains present.
In particularly preferred embodiments the grinding layer is formed of segments, which are preferably spaced apart from each other by slits, in particular with the result that abrasive material can be discharged, a passive cooling takes place during the grinding process and/or a precise grinding is guaranteed.
The slits preferably run between the segments substantially radially with respect to an axis of rotation of the grinding tool.
In preferred embodiments the grinding layer has between 85 and 135 segments, preferably between 90 and 125 segments, particularly preferably between 96 and 120 segments.
In particular, the segments are arranged regularly tangentially about the axis of rotation, preferably wherein they extend through an angle of rotation with respect to the axis of rotation of between 2.6° and 4.2°, preferably of between 2.8° and 4.0°, particularly preferably of between 3.0° and 3.8°.
In other words, a breakdown into segments is approx. 2.6° to 4.2°, preferably 2.8° to 4.0°, particularly preferably 3.0° to 3.8°.
A minimum distance between the segments is preferably at least 0.7 mm, particularly preferably at least 1.0 mm.
In a first variant, the slits completely divide the grinding layer, with the result that the grinding layer is formed of separate segments, in particular spaced apart from each other by the slits.
In this first variant, the segments are preferably applied to the base body individually.
In a second variant, the slits only partially cut through the grinding layer, with the result that the grinding layer is formed in one piece and/or is applied to the base body in its entirety.
However, it is also conceivable that segments formed separated touch, i.e. no slit is present.
It is particularly preferable that the grinding layer is applied and/or fastened to the base body by sintering and/or by means of a binder, preferably adhesive, synthetic resin or the like.
It is also conceivable that the connection between base body and grinding layer is produced by welding, soldering, and/or electroplating.
The grinding layer can also have been applied to a carrier body fastened to the base body, preferably by screwing. A carrier body makes it possible to replace the grinding layer, e.g. at the end of its life, without having to exchange the whole grinding tool.
It is particularly preferable that the base body is formed cup-shaped with a base and a side wall adjoining the base, preferably wherein the base has a centrally arranged drilled hole. The grinding tool can in this connection also be called a cup wheel.
In preferred embodiments, the base body has openings for receiving fasteners, in particular bolts and/or screws, preferably wherein the openings:
The openings serve in particular to precisely fasten the grinding tool to, in particular a spindle of, a grinding machine, in particular to a vertical double wheel grinding machine.
The openings particularly preferably have a thread, with the result that the grinding tool can be screwed onto the spindle of a grinding machine.
It is preferable that the base body has at least one extractor opening for, in particular temporarily, receiving an extractor. An extractor guided through the extractor opening helps to release the grinding tool from the grinding machine and/or to separate it from the grinding machine.
The extractor openings particularly preferably have a thread, with the result that screws are fed through and lift and/or pull the grinding tool off the spindle.
In a preferred embodiment, the base body has three extractor openings.
It is particularly preferable that the base body consists of metal, in particular steel and/or aluminum.
However, the base body can also be formed of ceramic, synthetic resin and/or fiber-reinforced plastic, e.g. comprising glass fibers and/or carbon fibers.
The base body preferably has at least one recess for receiving a measuring tool for measuring the layer height of the grinding layer.
The recess can be formed annular and/or as a single indentation and/or be arranged along a side wall and/or an outside of the base body.
Protection is also sought for an arrangement with at least one grinding tool and at least one workpiece to be machined by means of the at least one grinding tool, in particular a hard-coated brake disc. Preferably, at least two grinding tools are provided and the workpiece to be machined is arranged between the at least two grinding tools. Particularly preferably, the at least two grinding tools are aligned symmetrically with respect to the workpiece and the grinding layers of the at least two grinding tools are facing the workpiece.
Furthermore, protection is sought for a method for machining a, preferably rotating, workpiece, preferably a hard-coated brake disc, in an arrangement. The workpiece fixed on a spindle is ground, preferably on both sides, by the at least one grinding tool, preferably the at least two grinding tools, by rotation of the grinding tool or the grinding tools about their respective axes of rotation.
This means that the, preferably rotating, workpiece is preferably machined on both sides by at least two grinding tools, in particular with the result that during the machining or grinding a symmetrical application of pressure to the workpiece takes place and no undesired deformations of the workpiece occur.
It is also conceivable that the workpiece is machined in several locations on both sides by means of in each case two grinding tools or at least one grinding tool pair.
It may be the case that the workpiece is machined by several grinding tool pairs simultaneously and/or one after another.
Protection is also sought for a method for producing a grinding tool according to the invention:
The provision of the grinding layer is particularly preferably effected by the following method steps:
Furthermore, protection is sought for the use of a grinding tool for grinding at least one hard-coated brake disc.
Further advantages and details of advantageous variants of the invention are revealed by the figures and the associated description of the figures, in which:
In this preferred embodiment the grinding tool 1 has:
In this embodiment, the grinding layer 3 is applied to at least one bonding surface 17 of the base body 2, preferably wherein the bonding surface 17 is formed with an annular surface and/or flat and/or is arranged orthogonal to the axis of rotation 10 of the grinding tool 1.
In this preferred embodiment, the grinding layer 3 is formed annular as a grinding cylinder, for which the outside diameter 6, the layer width 7 and the layer height 8 of the grinding layer 3 are marked in
In a particularly preferred variant, the outside diameter 6 is 400 mm, the layer width 7 is 6 mm and the layer height 8 is 8 mm.
Moreover, the grinding surface 9 of the grinding layer 3 is preferably formed substantially flat and/or arranged orthogonal to the axis of rotation 10 of the grinding tool 1.
In this first embodiment, there is a step or ledge in the base body 2 along the bonding surface 17, wherein the bonding surface 17 is preferably defined and/or delimited by the side wall outside diameter 22 of the base body 2 and the inside diameter 21 of the grinding layer 3.
The side wall outside diameter 22 of the base body 2 is preferably the same size as or smaller than or equal to the outside diameter 6 of the grinding layer 3.
This embodiment is a particularly preferred formation of the grinding tool 1 as a cup wheel, wherein the base body 2 is formed cup-shaped with a base 13 and a side wall 15 adjoining the base 13.
In a particularly preferred variant of the base body 2, the side wall outside diameter 22 is 400 mm, the side wall inside diameter 23 is 380 mm and the base height 20 of the base body 2 is 20 mm.
In this embodiment the base 13 of the base body 2 has a centrally arranged drilled hole 16.
It is schematically represented here that the grain size ratio between the CBN grains 5 and the diamond grains 4 is preferably from 0.3 to 2.8, particularly preferably from 0.5 to 1.0. By way of example, the grain sizes 19 of the CBN grains 5 and of the diamond grains 4 are marked in some grains 4, 5 for this.
The grinding layer 3 particularly preferably consists of diamond grains 4, CBN grains 5, a metal bond 18 and preferably fillers.
However, it is also conceivable that it contains further substances or materials.
During the machining of the workpiece 25 it is preferable that the workpiece 25 is rotated about its axis of rotation 26 and/or ground on both sides by two grinding tools 1 by means of rotation of the grinding tools 1 about their respective axes of rotation 10.
The workpiece 25 is preferably fastened to a rotatable workpiece spindle 27 of a grinding machine. The grinding tools 1 are in each case fastened to a rotatable tool spindle 28 of a grinding machine.
The arrows of rotation marked in
However, the workpiece 25 could also be machined by so-called up grinding, wherein the workpiece spindle 27 has the same rotational direction as the at least one tool spindle 28. This means that all spindles 27, 28 have the same rotational direction.
In principle, other and/or mutually different rotational directions of the spindles 27, 28 are also possible.
In the present machining variant, the workpiece 25 is ground in a cross-grinding, which means that there is no tilting of the axis of rotation 10 of the at least one grinding tool 1 relative to the axis of rotation 26 of the workpiece 25. This means that the axes of rotation 10, 26 are aligned parallel to each other.
It is also conceivable that during the machining of the workpiece 25 there is a tilting of the axes of rotation 20, 26 relative to each other or the axes of rotation 10, 26 are not parallel, with the result that there is no cross-grinding.
In this embodiment of the respective grinding tool 1 of the arrangement, the grinding layer 3 is formed of segments 11, preferably wherein the segments 11 are separated and/or spaced apart from each other by slits 12.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 50623/2023 | Aug 2023 | AT | national |
