Grinding tool

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 to a method for manufacturing such a grinding tool.

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

[0003] The grinding tool of the type mentioned at the beginning is used in particular for machining brake discs, in particular brake discs for motor vehicles, which are provided with a wear-resistant coating, the machining being necessary by grinding in order to meet the requirements imposed on the standardized surface properties of the brake discs.

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

[0005] After coating, the brake disc is ground by a grinding tool to meet the geometrical requirements (e.g. defined brake disc width, remaining layer thickness, flatness, surface parallelism) and surface requirements (e.g. absence of porosity, roughness, waviness, grinding marks). Usually, the layer applied on both sides is processed simultaneously by the double-sided grinding method with two grinding tools. In this case, the removal amount per side is usually 0.1-0.3 mm.

[0006] A first problem with the use of such grinding tools is that different brake disc manufacturers apply different hard materials and binders in different mixture ratios to different substrates. If brake discs with different coatings or friction linings are to be ground or if a specific quality of the coating or friction lining is to be achieved, then it is usually necessary to change the grinding tool on the grinding machine or at least to grind successively with different grinding tools, as shown, for example, in DE 102021132468 C1. This, on the one hand, results in high expenditures, which are associated with long processing times and high costs. A further disadvantage is that several different grinding tools are required to process different coatings.

[0007] A second problem in the use of the grinding tool is the excessive wear of the grinding tool when machining wear-resistant brake discs. Indeed, the grinding tool of US Pat. No. 10,875,152 has a grinding layer consisting of diamond and CBN grains, which seems to allow for an advantageous combination of high hardness of the diamond grains, low reactivity of the CBN grains and low possibility of covering the CBN grains with shavings. However, the grinding tool of US Pat. No. 10,875,152 has a grinding layer consisting of only one abrasive layer or layer of abrasives, which disadvantageously limits the durability of the grinding tool, since if only one layer of abrasives is worn out, the grinding tool becomes unusable and has to be replaced. Due to the configuration of the single layer as a so-called "single layer", the grinding tool of US Pat. No. 10,875,152 can in any case be regarded as a tool different from the one described at the beginning.

[0008] Unlike the grinding tool of US Pat. No. 10,875,152, the grinding tool of JP 2008200780 A is indeed multi-layered, but has a very high proportion of CBN grains or a very low proportion of diamond grains. This unfavorable grain mixture ratio also disadvantageously limits the durability of the grinding tool due to increased wear of the CBN grains.

[0009] The object of the present invention is therefore to provide an improved grinding tool compared to the prior art, which can reliably, sustainably and economically machine all conventional brake discs coated with a hard material and achieve the required geometry and surface quality of the workpieces to be machined with a single grinding tool.

[0010] This problem is solved by the features of claim 1, i.e. a grinding tool which comprises a base body and a grinding layer, which comprises diamond grains and CBN grains, the mixing ratio of the diamond grains to the CBN grains being substantially 1:1, i.e. taking into account possible manufacturing errors, and the grain size, in particular the average grain size, of the diamond grains and / or the CBN grains being greater than 50 μm.

[0011] A first major advantage of the grinding tool according to the invention, preferably configured as a grinding wheel, is that all conventional brake discs with a hard material coating can be processed with the same grinding tool. No need to change the grinding tool when changing the coating or brake disc. This allows a significant reduction in process times and process costs compared to prior art solutions.

[0012] The grinding tool according to the invention therefore makes it possible to meet the demands imposed on the geometry and surface properties of brake discs, in particular those standardised by EU regulations, also for different coatings or friction linings.

[0013] The abrasive layer is a three-dimensional object that grinds or polishes the coated brake disc with at least one of its outer surfaces or abrasive surfaces, where the abrasive layer is worn away over time along its abrasive surface.

[0014] Compared to conventional grinding tools which only contain diamond or CBN grits in a metal bond, the grinding wheel according to the invention has the great advantage that it has a 40-50% reduced wear (of 0.007-0.008 mm per friction lining per brake disc) and therefore a significantly longer life.

[0015] In comparison with a grinding tool with a single 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. During the grinding operation, the diamond is broken and the CBN is broken, which protects and assists the diamond. In this connection, the grinding layer according to the invention also refers to a self-sharpening grinding layer, since each worn-out uppermost layer of abrasive grains is followed by a further layer of abrasive grains. In this way, the full functionality of the grinding tool and at the same time a constant grinding performance are maintained throughout the entire service life.

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

[0017] A further improvement compared to conventional diamond grinding tools is that significantly lower grinding pressures are required to effectively process brake discs, especially those coated with hard materials, and therefore the elastic deformation of the brake disc is also reduced, which allows brake discs to be ground to flatnesses of 0.005 mm (usually greater than 0.010 mm), which were not previously achieved.

[0018] The grain mixing ratio of diamond grains to CBN grains is preferably understood as the mass ratio of diamond grains to CBN grains, where the grain mixing ratio may be regarded as an average value and the ratio is not exactly 1:1 in each subsection, since manufacturing errors are also taken into account.

[0019] The grain size of diamond and / or CBN grits is preferably understood as the average or mean value, in particular in the sense of the average grain size as defined, for example, in the ISO 6106 standard, in particular the average grain diameter.

[0020] The grain size, ie the average grain size, in particular represents 80-95% of the diamond and / or CBN grains present.

[0021] As an alternative to pure metal bonds or pure resinoid bonds, diamond and CBN grits can be bonded in a hybrid bond comprising metal and synthetic resin.

[0022] Further advantageous embodiments of the invention are defined in the dependent claims.

[0023] Particularly preferably, the grain size, particularly the average grain size, of the diamond abrasive grains and / or CBN abrasive grains is specified to be 51 μm to 300 μm, preferably 91 μm to 252 μm.

[0024] It may also be specified that the grain size, in particular the average grain size, of the diamond grains and / or CBN grains, preferably the diamond grains and CBN grains, is greater than 74 μm, particularly preferably greater than 88 μm.

[0025] It may also be specified that the grain size, especially the average grain size, of the diamond abrasive grains and / or CBN abrasive grains, preferably the diamond abrasive grains and CBN abrasive grains, is smaller than 180 μm.

[0026] It is specified that the particle size ratio between the CBN abrasive grains and the diamond abrasive grains is preferably 0.3 to 2.8, and particularly preferably 0.5 to 1.0.

[0027] That is, 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 is specified that the grinding layer contains as grinding media diamond and CBN bonded in a metal bond or metal-containing bond and preferably a filler, in which case the grinding media of the grinding layer is, according to the invention, 50% diamond and 50% CBN (apart from minimal manufacturing deviations).

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

[0030] It is particularly preferred that the grinding layer is formed annularly, preferably as an annular cylinder or cone, in which connection the grinding layer is sometimes called a grinding ring.

[0031] The abrasive layer is applied to at least one binding surface of a substrate or a support attached to the substrate, which is preferably annular and / or flat and / or oriented perpendicular to the axis of rotation of the grinding tool.

[0032] The bonding surface may be chamfered, conically and / or cylindrically shaped and / or may be arranged at an angle relative to the rotation axis of the grinding tool.

[0033] However, the connecting surface can also be variably configured, so that the grinding layer also has a correspondingly variable shape, in particular in this case the layer height varies within a given value range.

[0034] It is also possible that the abrasive layer and / or the substrate and / or the support are edge- or step-shaped, particularly along the bonding surface.

[0035] The abrasive layer has a grinding surface, which is the outer surface of the abrasive layer that contacts the workpiece to be ground, in particular the friction lining or coating of a brake disc.

[0036] Preferably, the grinding surface is arranged perpendicular to the rotation axis of the grinding tool and / or is substantially flat. The grinding surface may of course have a roughness due to the diamond and CBN grains.

[0037] Grinding reduces the layer height at the grinding surface of the grinding layer over time.

[0038] In a preferred embodiment, the grinding layer, which is particularly annular, - an outside diameter of 200 to 900 mm, preferably 260 to 800 mm; and / or - a bed width of 5 to 40 mm, preferably 15 to 25 mm, and / or - Abrasive layer height of 5-20 mm, preferably 6-10 mm has.

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

[0040] Particularly preferably, the abrasive layer width is less than 20 mm, in particular less than 16 mm, particularly 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 grinding layer is preferably greater than the inner diameter of the sidewall of the substrate, however, the inner diameter may be less than or equal to the inner diameter of the sidewall.

[0043] The outer diameter of the grinding layer may preferably be equal to or greater than the outer diameter of the sidewall of the substrate.

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

[0045] However, it is also possible that the outer diameter, layer width and / or layer height vary along the grinding layer, for example being polygonal.

[0046] At least one layer is preferably formed substantially homogeneously, where homogeneity is an average homogeneity based on the abrasive grains of the grinding media, in particular the diamond and CBN grains present.

[0047] In a particularly preferred embodiment, the grinding layer is formed from a number of segments, preferably spaced apart from one another by slits, in particular to allow the grinding material to be removed, to provide passive cooling during the grinding process and / or to ensure precise grinding.

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

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

[0050] In particular, the segments are regularly arranged in the tangential direction around the axis of rotation, preferably in this case extending over a rotation angle of 2.6° to 4.2°, preferably 2.8° to 4.0°, particularly preferably 3.0° to 3.8° relative to the axis of rotation.

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

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

[0053] In a first variant, the slits completely separate the grinding layer, so that the grinding layer is formed from individual segments which are in particular spaced apart from one another by the slits.

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

[0055] In a second variant, the slits only partially divide the abrasive layer, so that the abrasive layer is formed in one piece and / or is applied as a whole to the base body.

[0056] However, it is also possible that the separately formed segments are in contact with one another, i.e. no slits are present.

[0057] It is particularly preferred that the abrasive layer is applied and / or attached to the substrate by means of a sintering and / or bonding agent, preferably an adhesive, a synthetic resin or the like.

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

[0059] The abrasive layer may be attached to a support, preferably attached to the base by a screw, which allows replacement of the abrasive layer, for example after end of life, without having to replace the entire grinding tool.

[0060] It is particularly preferred that the base body is pot-shaped with a bottom and a side wall adjacent to the bottom, and preferably the bottom has a centrally located hole, in this connection the grinding tool may also be called a pot-shaped grinding wheel.

[0061] In a preferred embodiment, the base body has a number of openings for receiving the connecting means, in particular pins and / or screws, preferably comprising: - is substantially cylindrically shaped; and / or - has a longitudinal axis arranged parallel to the axis of rotation of the grinding tool; and / or - they are arranged along at least one circle concentric with the axis of rotation, preferably regularly spaced apart from one another.

[0062] The openings are used in particular for precise mounting of grinding tools, in particular on spindles, on grinding machines, in particular on vertical double-head grinding machines.

[0063] Particularly preferably, the opening has a screw thread, by means of which the grinding tool can be screwed onto the spindle of a grinding machine.

[0064] It is preferably specified that the base body has at least one detacher opening for accommodating a detacher, in particular temporarily, through which the detacher guided serves to detach and / or separate the grinding tool from the grinding machine.

[0065] Particularly preferably, the remover opening has a thread, by means of which a screw can be guided through and the grinding tool can be pushed and / or pulled away from the spindle.

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

[0067] It is particularly preferred that the substrate consists of a metal, in particular steel and / or aluminium.

[0068] However, the substrate may also be made of ceramics, synthetic resins and / or fibre-reinforced plastics, including for example glass fibres and / or carbon fibres.

[0069] Preferably, the base body has at least one notch for accommodating a measuring tool for measuring the layer height of the grinding layer.

[0070] The notches may be formed annularly and / or as individual cuts and / or may be located along the sidewall and / or outer surface of the substrate.

[0071] Protection is also sought for an assembly comprising at least one grinding tool and at least one workpiece, in particular a brake disc coated with a hard material, to be machined by the at least one grinding tool, in which preferably at least two grinding tools are provided, the workpiece to be machined is arranged between the at least two grinding tools, and particularly preferably, the at least two grinding tools are positioned symmetrically in relation to the workpiece and the grinding layers of the at least two grinding tools are directed towards the workpiece.

[0072] Furthermore, protection is sought for a method for machining a preferably rotating workpiece, preferably a hard-material coated brake disc, in an assembly, in which the workpiece clamped on a spindle is preferably ground on both sides by at least one grinding tool, preferably at least two grinding tools, by rotation of the grinding tool about the rotation axis or about each rotation axis.

[0073] That is, the preferably rotating workpiece is machined, preferably on both sides, by at least two grinding tools, in particular so that symmetrical pressure is applied to the workpiece during machining or grinding and undesirable deformation of the workpiece does not occur.

[0074] It is also possible for the workpiece to be machined on both sides at several locations, each with two grinding tools or at least one grinding tool pair.

[0075] A workpiece may be machined simultaneously and / or successively by multiple grinding tool pairs.

[0076] There is also provided a method for manufacturing a grinding tool according to the present invention, comprising the steps of: providing a substrate; - providing a grinding layer, preferably segmented, comprising diamond and CBN abrasive grains, the mixing ratio of the diamond and CBN grains being substantially 1:1 and the grain size, in particular the average grain size, of the diamond and / or CBN abrasive grains being greater than 50 μm; - applying, preferably sintering and / or gluing, the abrasive layer to the substrate or to a support attached to the substrate; Protection is also sought for methods, including

[0077] Particularly preferably, providing the grinding layer comprises: - preparing a mixture of diamond grains, CBN grains, a metal bond and / or a resinoid bond and preferably a filler, - pressurizing the mixture under particularly controlled pressure and / or temperature conditions; This is done by.

[0078] Furthermore, protection is sought against the use of a grinding tool for grinding at least one brake disc which has a hard material coating.

[0079] Further advantages and details of advantageous variants of the invention are evident from the drawings and the corresponding illustrations. [Brief description of the drawings]

[0080] [Figure 1] 1 is a cross-sectional view of a preferred embodiment of a grinding tool according to the present invention. [Diagram 2] FIG. 2 is a partial view of the grinding layer of the grinding tool according to the present invention. [Diagram 3] 1 is a cross-sectional view of an assembly including a grinding tool according to the present invention;

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

[0082] In this preferred embodiment, the grinding tool 1 comprises: - Tool height 24 of 35-65 mm, preferably 45-55 mm and / or a base height 14 of 35 to 50 mm, preferably 40 to 45 mm, and / or the outer diameter 6 of the grinding layer 3 and / or the outer diameter 22 of the side wall of the substrate 2 of 350 to 800 mm, preferably 380 to 420 mm; It has.

[0083] In this embodiment, the grinding layer 3 is applied to at least one bonding surface 17 of the substrate 2. Preferably, this bonding surface 17 is annular and / or flat and / or is arranged perpendicular to the rotation axis 10 of the grinding tool 1.

[0084] In this preferred embodiment, the grinding layer 3 is annularly configured as a grinding ring, for which purpose the outer diameter 6, the layer width 7 and the layer height 8 of the grinding layer 3 are indicated in FIG.

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

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

[0087] In this first embodiment, there is a step or edge in the substrate 2 along the bonding surface 17. The bonding surface 17 is preferably defined and / or defined by the outer sidewall diameter 22 of the substrate 2 and the inner diameter 21 of the grinding layer 3.

[0088] The sidewall outer diameter 22 of the substrate 2 is preferably equal to or smaller than the outer diameter 6 of the grinding layer 3 .

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

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

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

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

[0093] 2 shows that the grain size ratio of the CBN grains 5 to the diamond grains 4 is preferably 0.3 to 2.8, and particularly preferably 0.5 to 1.0. For this purpose, the grain sizes 19 of the CBN grains 5 and the diamond grains 4 are shown in some of the grains 4, 5 as an example.

[0094] Particularly preferably, the grinding layer 3 consists of diamond grains 4, CBN grains 5, a metal bond 18 and preferably a filler. However, it is also possible for the grinding layer 3 to comprise other substances or materials.

[0095] 3 shows a cross-sectional view of an assembly with two grinding tools 1 and a workpiece 25 to be machined by the grinding tools 1, in particular a brake disc 25 with a hard material coating 29. The workpiece 25 is arranged between the two grinding tools 1, which are positioned symmetrically with respect to the rotation axis 26 of the workpiece 25, with the grinding layers 3 of the two grinding tools 1 facing towards the workpiece 25.

[0096] It is specified that when machining the workpiece 25, the workpiece 25 is preferably rotated about its rotation axis 26 and / or ground on both sides by two grinding tools 1 by rotating the grinding tools 1 about their respective rotation axes 10.

[0097] In this case, the workpiece 25 is preferably mounted on a rotatable work spindle 27 of a grinding machine. The grinding tools 1 are respectively mounted on a rotatable tool spindle 28 of the grinding machine.

[0098] The rotation arrows assigned to the spindles 27, 28 in Fig. 3 indicate the directions of rotation of the spindles 27, 28. In the variant shown, so-called co-directional rotary grinding is performed, since the tool spindle 28 carrying the grinding tool 18 has a direction of rotation (corresponding to counterclockwise in the figure) that is opposite to the direction of rotation of the workpiece spindle 27 carrying the workpiece 25 (corresponding to clockwise in the figure). This ensures that the velocity vectors of the mutual contact surfaces of the grinding tool and the workpiece are oriented in the same direction.

[0099] However, the workpiece 25 may also be machined by so-called counter-rotary grinding, in which case the work spindle 27 has the same direction of rotation as at least one tool spindle 28, i.e. all spindles 27, 28 have the same direction of rotation.

[0100] In principle, other and / or mutually different directions of rotation of the main shafts 27, 28 are also possible.

[0101] In the illustrated machining variant, the tool 25 is ground by cross grinding, which means that there is no inclination of the rotation axis 10 of the at least one grinding tool 1 relative to the rotation axis 26 of the workpiece 25, i.e. the rotation axes 10, 26 are oriented parallel to one another.

[0102] It is also possible that during machining of the workpiece 25, there is an inclination of the rotation axes 20, 26 relative to one another or the rotation axes 10, 26 are not parallel to one another, so that no cross grinding takes place.

[0103] In this embodiment of each grinding tool 1 of the assembly, the grinding layer 3 is formed from a plurality of segments 11. Preferably, these segments 11 are separated and / or spaced apart from one another 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) comprising a substrate (2) and a grinding layer (3) containing diamond abrasive grains (4) and CBN abrasive grains (5), the diamond abrasive grains (4) and CBN abrasive grains (5) being bonded in multiple layers in a sintered metal bond and / or resinoid bond (18) in the grinding layer (3), A grinding tool (1), characterized in that the abrasive grain mixing ratio of the diamond abrasive grains (4) and the CBN abrasive grains (5) is substantially 1:1, and the grain size (19) of the diamond abrasive grains (4) and / or the CBN abrasive grains (5) is greater than 50 μm.

2. The grinding tool (1) according to claim 1, wherein the grain size (19) of the diamond grains (4) and / or the CBN grains (5) is between 51 μm and 300 μm, preferably between 91 μm and 252 μm.

3. The grinding tool (1) according to claim 1 or 2, wherein the grain size ratio between the CBN grains (5) and the diamond grains (4) is between 0.3 and 2.8, preferably between 0.5 and 1.

0.

4. The grinding layer (3) is formed in an annular shape, and in particular, an outer diameter (6) between 200 and 900 mm, preferably between 260 and 800 mm, and / or the width (7) of the grinding layer is between 5 and 40 mm, preferably between 15 and 25 mm, and / or the height (8) of the grinding layer is between 5 and 20 mm, preferably between 6 and 10 mm; and / or the grinding layer (3) has a grinding surface (9) that is substantially flat and / or that is arranged perpendicular to the rotation axis (10) of the grinding tool (1), Grinding tool (1) according to any one of claims 1 to 3.

5. 5. A grinding tool (1) according to claim 1, wherein the grinding layer (3) is preferably formed from a plurality of segments (11) spaced apart from one another by slits (12), in particular the slits (12) extending substantially radially relative to the rotation axis (10) of the grinding tool (1).

6. 6. Grinding tool (1) according to any one of the preceding claims, wherein the abrasive layer (3) is applied to the substrate (2) by sintering, brazing, welding and / or by means of a bonding agent, preferably an adhesive.

7. 7. The grinding tool (1) according to claim 1, wherein the base body (2) is pot-shaped with a bottom (13) and a side wall (15) adjacent to the bottom (13), and preferably the bottom (13) has a centrally located hole (16).

8. 8. Grinding tool (1) according to any one of the preceding claims, characterized in that the substrate (2) consists of metal, in particular steel and / or aluminum.

9. Assembly comprising at least one grinding tool (1) according to any one of claims 1 to 8 and at least one workpiece (25), in particular a brake disc (25) coated with a hard material, to be machined by the at least one grinding tool (1), preferably at least two grinding tools (1) according to any one of claims 1 to 8 are provided, the workpiece (25) to be machined is arranged between the at least two grinding tools (1), particularly preferably the at least two grinding tools (1) are positioned symmetrically with respect to the workpiece (25) and the grinding layers (3) of the at least two grinding tools (1) are directed towards the workpiece (25).

10. 10. A method for machining a workpiece (25), preferably a hard material coated brake disc (25), in an assembly according to claim 9, wherein the preferably rotating workpiece (25) is preferably ground on both sides by the at least one grinding tool (1), preferably by the at least two grinding tools (1), by rotation of the grinding tool (1) about a rotation axis (10) or by rotation of each of the grinding tools (1) about their respective rotation axes (10).

11. A method for manufacturing a grinding tool (1) according to any one of claims 1 to 8, comprising the steps of: providing a substrate (2), - providing a grinding layer (3), preferably formed from a plurality of segments (11), comprising diamond grains (4) and CBN grains (5), the grain mix ratio of the diamond grains (4) to the CBN grains (5) being substantially 1:1, the grain size (19) of the diamond grains (4) and / or the CBN grains (5) being greater than 50 μm; - applying, preferably sintering and / or gluing, said grinding layer (3) to said substrate (2) or to a support attached to said substrate (2); A method comprising:

12. Preparing the grinding layer (3), - preparing a mixture of said diamond grains (4), said CBN grains (5), said metal and / or resinoid bond (18) and preferably a filler; - compressing said mixture, in particular under controlled pressure and / or temperature conditions; The method according to claim 11, wherein the method is carried out by

13. 9. Use of a grinding tool (1) according to any one of claims 1 to 8 for grinding at least one brake disc (25) which is coated with a hard material.

Images