Grinding tools

Abstract

To provide an improved grinding tool capable of reliably, durably and economically machining brake discs, and achieving, as the only grinding tool feasible, a required geometry and surface quality of a workpiece to be machined.SOLUTION: There is provided a grinding tool (1) for grinding at least one hard-coated brake disc. The grinding tool (1) comprises a base body (2) and a grinding layer (3), and the grinding layer (3) includes diamond grains and CBN grains. The diamond grains and CBN grains are bonded multi-layered in a sintered metal bond and / or resinoid bond in the grinding layer (3). In the grinding tool (1); a grain mixing ratio between the diamond grains and the CBN grains is substantially 1:1; and grain sizes of the diamond grains and / or the CBN grains are more than 50 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a grinding tool according to the features of the preamble of claim 1 and a method for manufacturing such a grinding tool.

[0002] Furthermore, the present invention relates to an assembly comprising such a grinding tool, a method for machining a workpiece in the assembly, and the use of a grinding tool for grinding a hard material-coated brake disc.

[0003] The grinding tool in the form described at the beginning is used, in particular, for machining brake discs provided with wear-resistant coatings, especially automotive brake discs. In order to meet the requirements imposed on the standardized surface properties of the brake disc, machining by grinding is necessary.

[0004] Particularly in combination with e-mobility to reduce fine dust emissions, a layer with a thickness of about 0.5 mm containing wear-resistant carbides is applied to both sides of the brake disc substrate. As coating components, in particular hard materials such as tungsten carbide (WC), tungsten molten carbide, titanium carbide (TiC), chromium carbide (Cr3C2), niobium carbide (NbC) and metal binders (such as special steel, titanium aluminide) are used.

[0005] After coating, the brake disc is ground by a grinding tool in order to meet the geometric requirements (such as the specified brake disc width, remaining layer thickness, flatness, parallelism of the surfaces) and the requirements imposed on the surface (such as porosity-free, roughness, waviness, grinding streaks). Usually, the layers applied to both sides are machined simultaneously in a double-sided face method by two grinding tools. In this case, the removal per side is usually 0.1 to 0.3 mm.

[0006] The first problem with using such grinding tools is that various brake disc manufacturers adhere a variety of hard materials and binders to various substrates in various mixing ratios. When grinding brake discs with various coatings or friction linings, or when it is necessary to achieve a specified quality for a coating or friction lining, it is usually necessary to change the grinding tool on the grinding machine, or at least to perform continuous grinding with various grinding tools, as shown, for example, in German Patent Invention No. 102021132468. This results in significant labor, which in turn leads to long processing times and high costs. A further drawback is that multiple types of grinding tools are required to process different coatings.

[0007] The second problem with using grinding tools is the excessive wear of the grinding tool when machining wear-resistant brake discs. Indeed, the grinding tool described in U.S. Patent No. 10875152 has a grinding layer consisting of diamond abrasive grains and CBN abrasive grains, which seems to take advantage of the favorable combination of the high hardness of the diamond abrasive grains, the low reaction of the CBN abrasive grains, and the low possibility of the CBN abrasive grains being covered by chips. However, the grinding tool described in U.S. Patent No. 10875152 has a grinding layer consisting of only one abrasive layer or abrasive grain layer, which unfavorably limits the durability of the grinding tool. This is because when even one abrasive grain layer is worn, the grinding tool becomes unusable and must be replaced. Based on its single-layer configuration as a so-called "single layer," the grinding tool described in U.S. Patent No. 10875152 can be considered a different tool from the one described at the beginning.

[0008] Unlike the grinding tool described in U.S. Patent No. 10875152, the grinding tool described in Japanese Patent Application Publication No. 2008200780, while indeed multilayered, contains either an extremely high proportion of CBN abrasive grains or an extremely low proportion of diamond abrasive grains. This unfavorable abrasive grain mixing ratio unfavorably limits the durability of the grinding tool due to increased wear of the CBN abrasive grains.

[0009] Therefore, the object of the present invention is to provide an improved grinding tool compared to the prior art that can reliably, sustainably, and economically process any ordinary brake disc coated with a hard material, and achieve the required geometric shape and surface quality of the workpiece to be processed with just one grinding tool.

[0010] This problem is solved by the features of claim 1, namely a grinding tool comprising a substrate and a grinding layer, wherein the grinding layer contains diamond abrasive grains and CBN abrasive grains, the mixing ratio of the diamond abrasive grains and the CBN abrasive grains is substantially, i.e., taking into account any possible manufacturing tolerances, 1:1, and the particle size of the diamond abrasive grains and / or CBN abrasive grains, in particular the average particle size, is greater than 50 μm.

[0011] A first major advantage of the grinding tool according to the present invention, preferably formed as a single grinding wheel, is that it can process any ordinary brake disc coated with a hard material using the same grinding tool. This eliminates the need to change the grinding tool when changing the coating or the brake disc. Thus, process time and process cost can be significantly reduced compared to the solutions of the prior art.

[0012] Therefore, the grinding tool according to the present invention can satisfy the requirements imposed on the geometric shape and surface properties of brake discs, particularly those standardized by EU regulations, even for various different coatings or friction linings.

[0013] The abrasive layer is a three-dimensional object. This three-dimensional object grinds or polishes the coated brake disc by at least one of its multiple outer surfaces, or the grinding surface. In this case, the abrasive layer is worn down over time along the grinding surface.

[0014] Compared to conventional grinding tools that contain only diamond or CBN abrasive particles in the metal bond, the grinding wheel according to the present invention has the significant advantage of having a much longer lifespan, as it exhibits 40-50% less wear (0.007-0.008 mm per friction lining per brake disc).

[0015] Compared to grinding tools equipped with a single-layer abrasive layer consisting of diamond abrasive grains and CBN abrasive grains, the lifespan or service life of the grinding tool according to the present invention is many times longer. During grinding, the diamond is crushed and the CBN breaks. At this time, the CBN protects and assists the diamond. In this regard, the abrasive layer in the present invention also refers to an abrasive layer that has a self-sharpening effect. This is because, in each case, a further layer of abrasive grains follows the uppermost worn abrasive layer. In this way, sufficient functionality of the grinding tool and a certain level of grinding performance are maintained throughout its entire lifespan.

[0016] A further improvement over conventional diamond grinding tools is that the drive output of the grinding machine supporting the grinding tool according to the present invention can be reduced by approximately 30%.

[0017] A further improvement over conventional diamond grinding tools is the significantly lower grinding pressure required, particularly for effectively machining brake discs coated with hard materials. Consequently, elastic deformation of the brake disc is also reduced, allowing the brake disc to be ground to a flatness of 0.005 mm (compared to typically over 0.010 mm), which was previously unattainable.

[0018] The abrasive mixing ratio of diamond abrasive grains to CBN abrasive grains is preferably understood as the mass ratio of diamond abrasive grains to CBN abrasive grains. In this case, the abrasive mixing ratio may be considered an average value, and since manufacturing tolerances are also taken into account, the ratio is not exactly 1:1 in each sub-compartment.

[0019] The particle size of the diamond abrasive grains and / or CBN abrasive grains is preferably understood to be an average value or average value in the sense of average particle size as defined in, for example, ISO 6106, and more specifically, the average abrasive grain diameter.

[0020] The particle size, i.e., the average particle size, specifically represents 80-95% of the diamond and / or CBN abrasive grains present.

[0021] As an alternative to pure metal bonds or pure resinoid bonds, diamond abrasive grains and CBN abrasive grains can be bonded within a hybrid bond containing metal and synthetic resin.

[0022] Another advantageous embodiment of the present invention is provided in the dependent claims.

[0023] Particularly preferred are the particle sizes of the diamond abrasive grains and / or CBN abrasive grains, especially the average particle size, which are specified to be 51 μm to 300 μm, preferably 91 μm to 252 μm.

[0024] Furthermore, the particle size of the diamond abrasive grains and / or CBN abrasive grains, preferably the diamond abrasive grains and CBN abrasive grains, in particular the average particle size, may be specified to be greater than 74 μm, and particularly preferably greater than 88 μm.

[0025] Furthermore, the particle size of the diamond abrasive grains and / or CBN abrasive grains, preferably the diamond abrasive grains and CBN abrasive grains, in particular the average particle size, may be specified to be smaller than 180 μm.

[0026] Preferably, the particle size ratio of CBN abrasive grains to diamond abrasive grains is specified to be 0.3 to 2.8, and particularly preferably 0.5 to 1.0.

[0027] In other words, the CBN abrasive grains are particularly preferably at least half the size of the diamond abrasive grains, and at most the same size as the diamond abrasive grains.

[0028] Particularly preferably, it has been specified that the grinding abrasive layer, as a grinding medium, contains diamond and CBN bonded in a metal bond or a metal-containing bond and preferably also a filler. In this case, the grinding medium of the grinding abrasive layer is, according to the invention, 50% diamond and 50% CBN (except for the minimum possible manufacturing-related deviations).

[0029] In a preferred variant, the grinding abrasive layer consists of 10 - 35% by volume of diamond and CBN, 50 - 90% by volume of a metal bond, and the remaining filler.

[0030] Particularly preferably, it has been specified that the grinding abrasive layer is formed annularly, preferably as an annular cylinder or cone. In this context, the grinding abrasive layer may also be referred to as a grinding ring.

[0031] The grinding abrasive layer is applied to at least one bonding surface of a base body or a support attached to the base body. Preferably, this bonding surface is formed annularly and / or flatly and is arranged perpendicular to the axis of rotation of the grinding tool.

[0032] The bonding surface may be chamfered and formed conically and / or cylindrically and may also be arranged inclined with respect to the axis of rotation of the grinding tool.

[0033] However, the bonding surface may be variably formed, whereby the grinding abrasive layer also has a correspondingly variable shape. In particular, in this case, the height of the abrasive layer varies within a predetermined value range.

[0034] Furthermore, the grinding abrasive layer and / or the base body and / or the support may be formed, in particular, along the bonding surface in an edge-like or stepped manner.

[0035] The grinding abrasive layer has a grinding surface. This grinding surface is the outer surface of the grinding abrasive layer that comes into contact with the workpiece to be ground, in particular the friction lining or coating of a brake disk.

[0036] Preferably, the grinding surface is positioned perpendicular to the rotation axis of the grinding tool and / or is formed substantially flat. The grinding surface may, of course, have roughness, based on diamond abrasive grains and CBN abrasive grains.

[0037] During grinding, the height of the abrasive layer on the grinding surface of the abrasive layer decreases over time.

[0038] In preferred embodiments, in particular, an annular abrasive layer, - Outer diameter of 200-900 mm, preferably 260-800 mm and / or - Abrasive layer width of 5-40 mm, preferably 15-25 mm and / or - Abrasive layer height of 5-20 mm, preferably 6-10 mm It holds.

[0039] The width of the abrasive layer is preferably understood as the difference between the outer diameter and the inner diameter of the abrasive layer. In this case, the outer diameter of the abrasive layer preferably corresponds to at least the outer diameter of the side wall of the substrate.

[0040] Particularly preferable is a polishing layer width of less than 20 mm, more preferably less than 16 mm, and most preferably less than 12 mm.

[0041] In a particularly preferred embodiment, the abrasive layer width is 6 to 8 mm.

[0042] The inner diameter of the abrasive layer is preferably larger than the inner diameter of the side wall of the substrate. However, the inner diameter may be less than or equal to the inner diameter of the side wall.

[0043] The outer diameter of the abrasive layer may preferably be equal to or greater than the outer diameter of the side wall of the substrate.

[0044] Preferably, these values ​​and all further values ​​can be considered constant values, taking into account manufacturing tolerances.

[0045] However, the outer diameter, abrasive layer width, and / or abrasive layer height can be variable along the grinding layer, and can even be polygonal, for example.

[0046] At least one layer is preferably formed substantially homogeneously. In this case, the homogeneity is an averaged homogeneity based on the abrasive grains of the grinding media, particularly the diamond and CBN abrasive grains present.

[0047] In a particularly preferred embodiment, the abrasive layer is preferably formed from a plurality of segments spaced apart from each other by slits, in particular, which allows the abrasive material to be guided out, passive cooling to occur during the grinding process and / or ensures precise grinding.

[0048] Preferably, the slits between the segments extend substantially radially with respect to the rotation axis of the grinding tool.

[0049] In a preferred embodiment, the abrasive layer has 85 to 135 segments, preferably 90 to 125 segments, and particularly preferably 96 to 120 segments.

[0050] In particular, the segments are regularly arranged tangentially with respect to the axis of rotation. Preferably, in this case, the segments extend over a rotation angle of 2.6° to 4.2°, preferably 2.8° to 4.0°, and especially preferably 3.0° to 3.8° with respect to the axis of rotation.

[0051] In other words, the segment division is approximately 2.6° to 4.2°, preferably 2.8° to 4.0°, and particularly preferably 3.0° to 3.8°.

[0052] The minimum spacing between segments is preferably at least 0.7 mm, and particularly preferably at least 1.0 mm.

[0053] In the first variant, the slit completely separates the abrasive layer, and this abrasive layer is formed from individual segments that are separated from each other, particularly by the slit.

[0054] In this first variant, the segments are preferably individually attached to the substrate.

[0055] In the second variant, the slits only partially divide the abrasive layer, so the abrasive layer is formed as a single unit and / or is attached to the substrate as a whole.

[0056] However, it is also possible that the separated and formed segments are in contact with each other, meaning that no slits exist.

[0057] Particularly preferred is that the abrasive layer is adhered to and / or attached to the substrate by a sintering and / or binder, preferably an adhesive, synthetic resin, or similar.

[0058] The bond between the substrate and the abrasive layer may also be achieved by welding, brazing, and / or electroplating coating.

[0059] The abrasive layer may preferably be attached to a support that is mounted to a substrate by screws. The support allows for the replacement of the abrasive layer, for example, after its lifespan has expired, without the need to replace the entire grinding tool.

[0060] Particularly preferred is that the base is formed in a pot shape, comprising a bottom and side walls adjacent to the bottom, and preferably the bottom has a hole located in the center. In this regard, the grinding tool is sometimes called a pot-shaped grinding wheel.

[0061] In a preferred embodiment, the substrate has a plurality of openings for accommodating coupling means, particularly pins and / or screws, and preferably these openings are - Formed substantially in a cylindrical shape, and / or - Having a longitudinal axis positioned parallel to the rotation axis of the grinding tool, and / or - They are arranged along at least one circle that is concentric with respect to the axis of rotation, preferably regularly spaced apart from one another.

[0062] The opening is used, in particular, to precisely mount grinding tools to spindles, grinding machines, and especially vertical double-ended grinding machines.

[0063] Particularly preferable is that the opening has a screw thread, thereby allowing the grinding tool to be screwed onto the spindle of the grinding machine.

[0064] Preferably, the substrate has at least one removal tool opening for housing a removal tool, particularly temporarily, and the removal tool guided through this removal tool opening is specified to serve to detach and / or separate a grinding tool from the grinding machine.

[0065] Particularly preferable is that the removal opening has a screw thread, thereby guiding the screw through and pushing and / or pulling the grinding tool away from the spindle.

[0066] In a preferred embodiment, the base has three openings for a remover.

[0067] Particularly preferred is that the substrate is made of a metal, especially steel and / or aluminum.

[0068] However, the substrate may be formed from ceramics, synthetic resins, and / or fiber-reinforced plastics, such as glass fibers and / or carbon fibers.

[0069] Preferably, the substrate has at least one notch for housing a measuring tool for measuring the abrasive layer height of the grinding abrasive layer.

[0070] The notches may be formed in an annular shape and / or as individual cuts and / or arranged along the side walls and / or outer surfaces of the substrate.

[0071] Furthermore, protection is also required for assemblies comprising at least one grinding tool and at least one workpiece to be machined by this at least one grinding tool, particularly a brake disc coated with a hard material, wherein at least two grinding tools are provided, the workpiece to be machined is positioned between at least two grinding tools, and particularly preferably these at least two grinding tools are positioned symmetrically with respect to the workpiece, and the abrasive layers of at least two grinding tools are directed toward the workpiece.

[0072] Furthermore, protection is required for a method for machining a workpiece, preferably a hard material coated brake disc, which is preferably rotating within an assembly, and which grinds the workpiece, which is clamped to a spindle, preferably on both sides by at least one grinding tool, preferably at least two grinding tools, by the rotation of the grinding tools around a rotation axis or by the rotation of each grinding tool around a rotation axis.

[0073] In other words, preferably a rotating workpiece is machined on both sides by at least two grinding tools, and in particular, this ensures that symmetrical pressure is applied to the workpiece during machining or grinding, preventing undesirable deformation of the workpiece.

[0074] Furthermore, the workpiece can be machined on both sides at multiple locations using two grinding tools or at least one pair of grinding tools.

[0075] A workpiece may be machined simultaneously and / or sequentially by multiple pairs of grinding tools.

[0076] Furthermore, the present invention relates to a method for manufacturing a grinding tool, - Preparing the substrate, - Preferably, a segmented abrasive layer is prepared containing diamond abrasive grains and CBN abrasive grains, wherein the abrasive grain mixing ratio of diamond abrasive grains to CBN abrasive grains is substantially 1:1, and the particle size of the diamond abrasive grains and / or CBN abrasive grains, particularly the average particle size, is greater than 50 μm. - The abrasive layer is attached to a substrate or a support attached to the substrate, preferably by sintering and / or bonding. Protection is also required for methods that include this.

[0077] Particularly preferable is preparing an abrasive layer. - A method for preparing a mixture comprising diamond abrasive grains, CBN abrasive grains, a metal bond and / or a resinoid bond and preferably a filler, - A method for pressurizing a mixture under particularly controlled pressure and / or temperature conditions. It is done by [method].

[0078] Furthermore, protection is required against the use of grinding tools to grind at least one brake disc coated with a hard material.

[0079] Further advantages and details of favorable variations of the present invention are evident from the drawings and corresponding illustrations. [Brief explanation of the drawing]

[0080] [Figure 1] This is a cross-sectional view of a preferred embodiment of the grinding tool according to the present invention. [Figure 2] This is a partial view of the abrasive layer of the grinding tool according to the present invention. [Figure 3] This is a cross-sectional view of an assembly equipped with a grinding tool according to the present invention.

[0081] Figure 1 shows a cross-sectional view of a preferred embodiment of the grinding tool 1 according to the present invention. This grinding tool 1 comprises a base body 2 and a grinding abrasive layer 3. Preferably, the grinding abrasive layer 3 is attached to the base body 2 by sintering and / or a binder, preferably an adhesive.

[0082] In this preferred embodiment, the grinding tool 1 is - Tool height 24 and / or 35~65mm, preferably 45~55mm - Base height 14 and / or 35-50 mm, preferably 40-45 mm - Outer diameter 6 of the abrasive layer 3, preferably 380-420 mm, and / or outer diameter 22 of the side wall of the base 2 It has.

[0083] In this embodiment, the abrasive layer 3 is attached to at least one bonding surface 17 of the substrate 2. Preferably, this bonding surface 17 is formed in an annular and / or flat shape and / or is positioned perpendicular to the rotation axis 10 of the grinding tool 1.

[0084] In this preferred embodiment, the abrasive layer 3 is formed in an annular shape as a grinding ring. For this reason, Figure 1 shows the outer diameter 6, the width 7, and the height 8 of the abrasive layer 3.

[0085] In a particularly preferred variant, the outer diameter 6 is 400 mm, the abrasive layer width 7 is 6 mm, and the abrasive layer height 8 is 8 mm.

[0086] Furthermore, the grinding surface 9 of the abrasive layer 3 is preferably formed substantially flat and / or positioned perpendicular to the rotation axis 10 of the grinding tool 1.

[0087] In this first embodiment, a stepped portion or edge portion exists on the base 2 along the bonding surface 17. Preferably, the bonding surface 17 is defined and / or specified by the outer diameter 22 of the side wall of the base 2 and the inner diameter 21 of the abrasive layer 3.

[0088] The outer diameter 22 of the side wall of the base body 2 is preferably less than or equal to the outer diameter 6 of the abrasive layer 3.

[0089] This embodiment represents a particularly preferred configuration of a grinding tool 1 as a pot-shaped grinding wheel. In this case, the base 2 is formed in a pot shape, comprising a bottom portion 13 and a side wall 15 adjacent to the bottom portion 13.

[0090] In a particularly preferred variant of the base 2, the outer diameter 22 of the side wall of the base 2 is 400 mm, the inner diameter 23 of the side wall is 380 mm, and the bottom height 20 is 20 mm.

[0091] In this embodiment, the bottom 13 of the base 2 has a hole 16 located in the center.

[0092] Figure 2 shows a schematic diagram of the abrasive layer 3 on the grinding surface 9 of the grinding tool 1 according to the present invention. This abrasive layer 3 contains diamond abrasive grains 4 and CBN abrasive grains 5. The diamond abrasive grains 4 and CBN abrasive grains 5 are bonded in multiple layers within the abrasive layer 3 in a sintered metal bond and / or resinoid bond 18, and the abrasive grain mixing ratio of diamond abrasive grains 4 and CBN abrasive grains 5 is substantially 1:1, and the particle size 19 of the diamond abrasive grains 4 and / or CBN abrasive grains 5, in particular the average particle size 19, is greater than 50 μm, preferably 51 μm to 300 μm, and particularly preferably 91 μm to 252 μm.

[0093] Figure 2 schematically shows that the particle size ratio of CBN abrasive grains 5 to diamond abrasive grains 4 is preferably 0.3 to 2.8, and particularly preferably 0.5 to 1.0. For this reason, the particle sizes 19 of CBN abrasive grains 5 and diamond abrasive grains 4 are exemplified and inscribed within some of the abrasive grains 4 and 5.

[0094] Particularly preferred, the abrasive layer 3 consists of diamond abrasive grains 4, CBN abrasive grains 5, a metal bond 18, and preferably a filler. However, the abrasive layer 3 may also contain other substances or materials.

[0095] Figure 3 shows a cross-sectional view of an assembly comprising two grinding tools 1 and a workpiece 25 to be machined by these grinding tools 1, specifically a brake disc 25 having a hard material coating 29. The workpiece 25 is positioned between the two grinding tools 1, which are positioned symmetrically with respect to the rotation axis 26 of the workpiece 25, and the abrasive layers 3 of the two grinding tools 1 are directed toward the workpiece 25.

[0096] When machining the workpiece 25, it is preferably specified that the workpiece 25 is rotated about its rotation axis 26 and / or ground on both sides by two grinding tools 1, each rotating about its own rotation axis 10.

[0097] In this case, the workpiece 25 is preferably mounted on the rotatable workpiece spindle 27 of the grinding machine. Each grinding tool 1 is mounted on the rotatable tool spindle 28 of the grinding machine.

[0098] The rotational arrows assigned to the spindles 27 and 28 in Figure 3 represent the rotational directions of the spindles 27 and 28. In the illustrated modification, so-called co-directional rotational grinding is performed. This is because the tool spindle 28, which supports the grinding tool 18, has a rotational direction opposite to that of the workpiece spindle 27, which supports the workpiece 25 (which corresponds to clockwise in the figure) (which corresponds to counterclockwise in the figure). As a result, the velocity vectors of the contact surfaces between the grinding tool and the workpiece are directed in the same direction.

[0099] However, the workpiece 25 may be machined by so-called reverse rotation grinding. In this case, the workpiece spindle 27 has the same rotation direction as at least one tool spindle 28. That is, all spindles 27, 28 have the same rotation direction.

[0100] Basically, different rotational directions for the main spindles 27 and 28, and / or rotational directions different from each other, are also possible.

[0101] In the illustrated machining transformation, the tool 25 is ground using cross grinding. This means that there is no inclination of the rotation axis 10 of at least one grinding tool 1 with respect to the rotation axis 26 of the workpiece 25. In other words, the rotation axes 10 and 26 are oriented parallel to each other.

[0102] Furthermore, when machining the workpiece 25, there may be an inclination between the rotation axes 20 and 26, or the rotation axes 10 and 26 may not be parallel to each other, which may result in cross grinding not being performed.

[0103] In this embodiment, each grinding tool 1 of the assembly, the abrasive layer 3 is formed from a plurality of segments 11. Preferably, these segments 11 are separated from each other and / or spaced apart by slits 12.

Claims

1. A grinding tool (1) for grinding at least one brake disc (25) coated with a hard material, the grinding tool (1) comprises a base (2) and a grinding layer (3) which are rotationally driven about a rotation axis (10), the grinding layer (3) comprises diamond abrasive grains (4) and CBN abrasive grains (5), the diamond abrasive grains (4) and CBN abrasive grains (5) are bonded in multiple layers within the grinding layer (3) in a sintered metal bond and / or resinoid bond (18), in the grinding tool (1), A grinding tool (1) characterized in that the abrasive mixing ratio of the diamond abrasive grains (4) and the CBN abrasive grains (5) is substantially 1:1, and the particle size (19) of the diamond abrasive grains (4) and / or the CBN abrasive grains (5) is 91 μm to 252 μm.

2. The grinding tool (1) according to claim 1, wherein the particle size ratio of the CBN abrasive grains (5) to the diamond abrasive grains (4) is 0.3 to 2.8, preferably 0.5 to 1.

0.

3. The abrasive layer (3) is formed in an annular shape, and in particular, - The outer diameter (6) is 200 to 900 mm, preferably 260 to 800 mm, and / or - The abrasive layer width (7) is 5 to 40 mm, preferably 15 to 25 mm, and / or - The abrasive layer height (8) is 5 to 20 mm, preferably 6 to 10 mm. And / or the abrasive layer (3) has a substantially flat abrasive surface (9) that is positioned perpendicular to the rotation axis (10) of the grinding tool (1), A grinding tool (1) according to claim 1 or 2.

4. The grinding abrasive layer (3) is preferably formed from a plurality of segments (11) separated from each other by slits (12), and in particular, the slits (12) extend substantially radially with respect to the rotation axis (10) of the grinding tool (1), according to claim 1 or 2.

5. The grinding tool (1) according to claim 1 or 2, wherein the abrasive layer (3) is attached to the substrate (2) by sintering, brazing, welding and / or by a binder, preferably an adhesive.

6. The base (2) is formed in a pot shape, comprising a bottom (13) and a side wall (15) adjacent to the bottom (13), and preferably the bottom (13) has a hole (16) located in the center, according to claim 1 or 2, the grinding tool (1).

7. The grinding tool (1) according to claim 1 or 2, wherein the substrate (2) is made of a metal, particularly steel and / or aluminum.

8. An assembly comprising at least one grinding tool (1) according to claim 1 or 2, and at least one hard material coated brake disc (25) to be machined by the at least one grinding tool (1), preferably comprising at least two grinding tools (1) according to claim 1 or 2, wherein the brake disc (25) to be machined is positioned between the at least two grinding tools (1), particularly preferably the at least two grinding tools (1) are positioned symmetrically with respect to the brake disc (25), and the abrasive layers (3) of the at least two grinding tools (1) are directed toward the brake disc (25).

9. A method for machining a hard material coated brake disc (25) in an assembly according to claim 8, wherein the brake disc (25), preferably rotating, is preferably ground on both sides by the rotation of the grinding tools (1) around a rotation axis (10) or by the rotation of the grinding tools (1) around each rotation axis (10).

10. A method for manufacturing the grinding tool (1) according to claim 1 or 2, - Prepare substrate (2), - Preferably, a grinding layer (3) is formed from a plurality of segments (11) and contains diamond abrasive grains (4) and CBN abrasive grains (5), wherein the mixing ratio of the diamond abrasive grains (4) and the CBN abrasive grains (5) is substantially 1:1, and the particle size (19) of the diamond abrasive grains (4) and / or the CBN abrasive grains (5) is 91 μm to 252 μm. - The abrasive layer (3) is attached to the substrate (2) or to a support attached to the substrate (2), preferably by sintering and / or bonding. Methods that include...

11. To prepare the abrasive layer (3) - A method for preparing a mixture comprising the diamond abrasive grains (4), CBN abrasive grains (5), the metal bond and / or resinoid bond (18), and preferably a filler, - A method for compressing the mixture under particularly controlled pressure and / or temperature conditions. The method according to claim 10, performed by the means described above.

12. Use of the grinding tool (1) according to claim 1 or 2 for grinding at least one brake disc (25) coated with a hard material.

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