Abrasive tool

Abstract

Grinding tool (1) for grinding at least one hard-coated brake disc (25), wherein the grinding tool (1) comprises a base body (2) and a grinding layer (3), wherein the grinding layer (3) comprises diamond grains (4) and CBN grains (5), wherein the diamond grains (4) and CBN grains (5) are bonded in multiple layers in a sintered metal bond and / or resin bond (18) in the grinding layer (3), wherein a grain mixture ratio between the diamond grains (4) and the CBN grains (5) is essentially 1:1 and wherein the grain sizes (19) of the diamond grains (4) and / or the CBN grains (5) are greater than 50 µm.

Description

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

[0002] 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 for grinding a hard material-coated brake disc.

[0003] Grinding tools of the type mentioned above are used primarily for machining brake discs with wear-resistant coating, in particular car brake discs, whereby machining by grinding is necessary in order to meet the requirements for the standardized surface properties of brake discs.

[0004] To reduce particulate matter emissions, particularly in connection with e-mobility, wear-resistant, approximately 0.5 mm thick coatings containing carbides are applied to both sides of the brake disc base. The coating components primarily used are hard materials such as tungsten carbide (WC), fused tungsten carbides, titanium carbide (TiC), chromium carbide (Cr3C2), niobium carbide (NbC), and metal binders (e.g., stainless steel, titanium aluminide).

[0005] After coating, the brake discs are ground with grinding tools to meet geometric requirements (e.g., defined brake disc width, remaining coating thickness, axial runout, plane parallelism) and surface requirements (e.g., no porosity, roughness, waviness, surface finish). Typically, the coatings applied to both sides are machined simultaneously with two grinding tools using the double-side grinding process. The allowance per side is typically between 0.1 and 0.3 mm.

[0006] A primary difficulty with using such grinding tools is that different brake disc manufacturers apply different hard materials and binders in different mixing ratios to different base bodies. If brake discs with different coatings or friction linings are to be ground, or if a specific 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, for example, in DE 102021132468 B3, sequential grinding using different grinding tools is required. On the one hand, this can lead to a great deal of effort, which is associated with long processing times and high costs. A further disadvantage is that several different grinding tools are required to machine different coatings.

[0007] A second difficulty with the use of grinding tools is their excessive wear when machining wear-resistant brake discs. For example, the grinding tool in US 10875152 B2 features a grinding coating 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 chipping resistance of the CBN grains. However, the grinding tool in US 10875152 B2 is equipped with a grinding coating consisting of only a single coating or grain layer, which adversely limits the durability of the grinding tool. As soon as the single grain layer is worn, the grinding tool is unusable and must be replaced. Due to its single-layer design, the grinding tool in US 10875152 B2 can be considered a tool of a different type.

[0008] In contrast to the grinding tool in US 10875152 B2, the grinding tool in JP 2008200780 A is multi-layered, but has a very high proportion of CBN grains and a very low proportion of diamond grains. This unfavorable grain mix ratio, in turn, adversely limits the durability of the grinding tool due to the increased wear of the CBN grains.

[0009] The object of the present invention is therefore to provide a grinding tool which is improved compared to the prior art and with which all conventional hard-coated brake discs can be machined reliably, durably and economically and with which, as the only grinding tool, a required geometry and surface quality of a workpiece to be machined is achieved.

[0010] This object is achieved by the features of claim 1, namely by a grinding tool with a base body and an abrasive coating, wherein the abrasive coating comprises diamond grains and CBN grains, wherein a grain mixing ratio between the diamond grains and the CBN grains is substantially 1:1, ie in particular taking into account any manufacturing tolerances, and wherein the, in particular average, grain sizes of the diamond grains and / or the CBN grains are more than 50 µm.

[0011] A first major advantage of the grinding tool according to the invention, which is preferably designed as a grinding disc, is that all conventional hard-coated brake discs can be machined with the same grinding tool. Replacing the grinding tool when changing the coating or brake disc is unnecessary. Compared to prior art solutions, this significantly reduces processing times and costs.

[0012] The grinding tool according to the invention can therefore meet the requirements for the geometry and surface quality of brake discs, which are standardized in particular by EU regulations, even for different coatings or friction linings.

[0013] The abrasive coating is a three-dimensional body that grinds or abrades a coated brake disc using at least one of its outer surfaces or a grinding surface. The abrasive coating wears down over time along its grinding surface.

[0014] Compared to conventional grinding tools with exclusively diamond grains or exclusively CBN grains 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 has a significantly longer service life.

[0015] Compared to a grinding tool with a single-layer abrasive coating made of diamond and CBN grains, the service life of the grinding tool according to the invention is many times longer. The diamond breaks in the grinding insert and the CBN splinters, while the CBN protects and supports the diamond. In this context, the present grinding coating is also referred to as a self-sharpening grinding coating, since further grain layers follow the topmost worn grain layer. This ensures that the grinding tool maintains its full functionality with consistent grinding performance throughout its entire service life.

[0016] A further improvement compared to conventional diamond grinding tools is that the drive power of the grinding machine carrying 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 pressure is required to effectively machine hard-coated brake discs. Consequently, the elastic deformation of the brake discs is also reduced, allowing the brake discs to be ground with a previously unattainable flatness of 0.005 mm axial runout (typically > 0.010 mm).

[0018] 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, whereby the grain mixing ratio can be regarded as an average value and whereby manufacturing tolerances are also taken into account, so that the ratio is not exactly 1:1 in every section.

[0019] 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 in the sense of mean grain sizes, e.g. as defined in the ISO 6106 standard.

[0020] The grain sizes, ie the mean grain sizes, represent in particular 80-95% of the diamond and / or CBN grains present.

[0021] As an alternative to a pure metal bond or a pure resin bond, it is possible for the diamond and CBN grains to be bonded in a hybrid bond comprising metal and resin.

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

[0023] It is particularly preferred that the, in particular average, 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.

[0024] It can also be provided that the, in particular average, grain sizes of the diamond grains and / or the CBN grains, preferably of the diamond grains and the CBN grains, are greater than 74 µm, particularly preferably greater than 88 µm.

[0025] It can also be provided that the, in particular average, grain sizes of the diamond grains and / or the CBN grains, preferably of the diamond grains and the CBN grains, are smaller than 180 µm.

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

[0027] This means that the CBN grains are preferably at least half the size and at most the same size as the diamond grains.

[0028] It is particularly preferred that the abrasive coating comprises the abrasives diamond and CBN, and preferably fillers bound in a metal bond or metal-containing bond. According to the invention, the abrasives of the abrasive coating are 50% diamond and 50% CBN (apart from minimal manufacturing deviations).

[0029] In a preferred variant, the grinding coating consists of 10 - 35 vol.% diamond and CBN, 50 - 90 vol.% metal bond and a remainder of fillers.

[0030] It is particularly preferred that the grinding coating be annular, preferably as an annular cylindrical or conical body. In this context, the grinding coating can also be referred to as a grinding ring.

[0031] The abrasive coating is applied to at least one connecting surface of the base body or a carrier body fastened to the base body, preferably wherein the connecting surface is annular and / or flat and / or is arranged orthogonally to a rotation axis of the grinding tool.

[0032] The bonding surface may also be bevelled, conical and / or cylindrical and / or arranged inclined to the axis of rotation of the grinding tool.

[0033] However, the bonding surface can also be designed to be variable, so that the grinding coating also has a correspondingly variable shape, in particular with the coating height varying within a range of values.

[0034] It may also be the case that the abrasive coating and / or the base body and / or the carrier body is or are edge-shaped or step-shaped, in particular along the bonding surface.

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

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

[0037] As a result of grinding, the thickness of the coating on the grinding surface of the grinding coating is reduced over time.

[0038] In a preferred embodiment, the grinding coating, in particular annular, an outer diameter of 200 to 900 mm, preferably 260 to 800 mm, and / or a covering width of 5 to 40 mm, preferably 15 to 25 mm, and / or a covering height of 5 to 20 mm, preferably 6 to 10 mm, on.

[0039] The coating width is preferably to be understood as the difference between the outer diameter and an inner diameter of the grinding coating, wherein the outer diameter of the grinding coating preferably corresponds at least to the side wall outer diameter of the base body.

[0040] Particularly preferably, the covering width is less than 20 mm, in particular less than 16 mm, particularly preferably less than 12 mm.

[0041] In particularly preferred embodiments, the covering width is 6 to 8 mm.

[0042] The inner diameter of the grinding pad is preferably larger than the inner diameter of the sidewall of the base body. However, the inner diameter can also be the same as or smaller than the inner diameter of the sidewall.

[0043] The outer diameter of the grinding pad is preferably the same size as or larger than the side wall outer diameter or outer diameter of the base body.

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

[0045] However, it is also conceivable that the outer diameter, the pad width and / or the pad height are variable, for example polygonal, along the grinding pad.

[0046] The at least one layer is preferably formed substantially homogeneously, wherein the homogeneity is an average homogeneity due to the grains of the abrasives, in particular the diamond and CBN grains present.

[0047] In particularly preferred embodiments, the grinding coating is formed from segments which are preferably spaced apart from one another by slots, in particular so that grinding material can be removed, passive cooling takes place during the grinding process and / or precise grinding is ensured.

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

[0049] In preferred embodiments, the abrasive coating has between 85 and 135 segments, preferably between 90 and 125 segments, particularly preferably between 96 and 120 segments.

[0050] In particular, the segments are regularly arranged tangentially around the axis of rotation, preferably extending over an angle of rotation with respect to the axis of rotation of between 2.6° and 4.2°, preferably between 2.8° and 4.0°, particularly preferably between 3.0° and 3.8°.

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

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

[0053] In a first variant, the slots separate the grinding coating completely, so that the grinding coating is formed from separate segments, in particular spaced from each other by the slots.

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

[0055] In a second variant, the slots only partially cut through the grinding coating, so that the grinding coating is formed in one piece and / or is applied in its entirety to the base body.

[0056] However, it is also conceivable that separately formed segments touch each other, ie there is no slot.

[0057] It is particularly preferred that the abrasive coating is applied and / or fixed to the base body by sintering and / or by means of a binding agent, preferably adhesive, synthetic resin or the like.

[0058] It is also conceivable that the connection between the base body and the grinding surface is made by welding, soldering and / or galvanic coating.

[0059] The abrasive coating can also be attached to a carrier body attached to the base body, preferably by means of screws. This carrier body allows the abrasive coating to be replaced, for example, after its service life has expired, without having to replace the entire grinding tool.

[0060] It is particularly preferred that the base body be cup-shaped with a base and a side wall adjacent to the base, preferably with the base having a centrally arranged bore. In this context, the grinding tool can also be referred to as a cup grinding wheel.

[0061] In preferred embodiments, the base body has openings for receiving connecting means, in particular bolts and / or screws, preferably wherein the openings are substantially cylindrical and / or have longitudinal axes which are arranged parallel to a rotation axis of the grinding tool and / or are arranged along at least one circle concentric with the rotation axis, preferably regularly spaced from one another.

[0062] The openings serve in particular for the precise fastening of the grinding tool to, in particular a spindle, a grinding machine, in particular to a vertical double-disk grinding machine.

[0063] Particularly preferably, the openings have threads so that the grinding tool can be screwed onto the spindle of a grinding machine.

[0064] It is preferably provided that the base body has at least one puller opening for, in particular temporarily, receiving a puller, wherein a puller guided through the puller opening helps to release the grinding tool from the grinding machine and / or to separate it from the grinding machine.

[0065] Particularly preferably, the puller openings have threads so that screws can be passed through and push and / or pull the grinding tool off the spindle.

[0066] In a preferred embodiment, the base body has three puller openings.

[0067] It is particularly preferred that the base body be made of metal, in particular steel and / or aluminum. However, the base body can also be made of ceramic, synthetic resin, and / or fiber-reinforced plastic, e.g., comprising glass fibers and / or carbon fibers.

[0068] Preferably, the base body has at least one recess for receiving a measuring tool for measuring the coating height of the grinding coating.

[0069] The recess may be annular and / or formed as a single notch and / or arranged along a side wall and / or outer side of the base body.

[0070] 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 material-coated brake disc, preferably wherein at least two grinding tools are provided and the workpiece to be machined is arranged between the at least two grinding tools, particularly preferably wherein the at least two grinding tools are aligned symmetrically with respect to the workpiece and the grinding coatings of the at least two grinding tools face the workpiece.

[0071] Furthermore, protection is sought for a method for machining a preferably rotating workpiece, preferably a hard material-coated brake disc, in an arrangement, wherein the workpiece clamped on a spindle is ground, preferably on both sides, by the at least one grinding tool, preferably the at least two grinding tools, by rotating the grinding tool or the grinding tools about their respective axes of rotation.

[0072] This means that the preferably rotating workpiece is preferably machined on both sides by at least two grinding tools, in particular so that during machining or grinding, a symmetrical application of pressure to the workpiece takes place and no unwanted deformation of the workpiece occurs.

[0073] It is also conceivable that the workpiece is machined at several points on both sides using two grinding tools or at least one pair of grinding tools.

[0074] It may be that the workpiece is machined by several pairs of grinding tools simultaneously and / or one after the other.

[0075] Protection is also sought for a method for producing a grinding tool according to the invention: Providing a base body; providing a preferably segmented abrasive coating comprising diamond grains and CBN grains, o wherein a grain mixing ratio between the diamond grains and the CBN grains is substantially 1:1 and o wherein the, in particular average, grain sizes of the diamond grains and / or the CBN grains are more than 50 µm; applying, preferably sintering and / or gluing, the abrasive coating to the base body or to a carrier body fastened to the base body.

[0076] Particularly preferably, the abrasive coating is provided by the following process steps: Providing a mixture of the diamond grains, CBN grains, the metal bond and / or resin bond, and preferably the fillers; pressing the mixture, in particular under controlled pressure and / or temperature conditions.

[0077] Furthermore, protection is sought for the use of a grinding tool for grinding at least one hard-coated brake disc.

[0078] Further advantages and details of advantageous variants of the invention are apparent from the figures and the associated description. These show: Fig. 1 shows a section through a preferred embodiment of a grinding tool according to the invention, Fig. 2 shows a section of the grinding coating of a grinding tool according to the invention and Fig. 3 shows a section through an arrangement with a grinding tool according to the invention.

[0079] The Fig. 1 shows a section through a preferred embodiment of a grinding tool 1 according to the invention with a base body 2 and a grinding coating 3, preferably wherein the grinding coating 3 is applied to the base body 2 by sintering and / or by means of a binding agent, preferably adhesive.

[0080] In this preferred embodiment, the grinding tool 1 a tool height 24 of 35 to 65 mm, preferably 45 to 55 mm, and / or a base body height 14 of 35 to 50 mm, preferably 40 to 45 mm, and / or an outer diameter 6 of the grinding coating 3 and / or side wall outer diameter 22 of the base body 2 of 350 to 800 mm, preferably 380 to 420 mm, on.

[0081] In this embodiment, the abrasive coating 3 is applied to at least one connecting surface 17 of the base body 2, preferably wherein the connecting surface 17 is annular and / or flat and / or is arranged orthogonal to the rotation axis 10 of the grinding tool 1.

[0082] In this preferred embodiment, the grinding coating 3 is designed as a ring-shaped slip ring, for which purpose Fig. 1 the outer diameter 6, the pad width 7 and the pad height 8 of the grinding pad 3 are shown.

[0083] In a particularly preferred variant, the outer diameter is 6 400 mm, the pad width is 7 6 mm and the pad height is 8 8 mm.

[0084] Furthermore, the grinding surface 9 of the grinding coating 3 is preferably substantially flat and / or arranged orthogonally to the rotation axis 10 of the grinding tool 1.

[0085] In this first embodiment, a step or edge is present in the base body 2 along the connecting surface 17, wherein the connecting surface 17 is preferably defined and / or limited by the side wall outer diameter 22 of the base body 2 and the inner diameter 21 of the abrasive coating 3.

[0086] The side wall outer diameter 22 of the base body 2 is preferably equal to or smaller than the outer diameter 6 of the grinding coating 3.

[0087] This embodiment is a particularly preferred embodiment of the grinding tool 1 as a cup grinding wheel, wherein the base body 2 is cup-shaped with a bottom 13 and a side wall 15 adjacent to the bottom 13.

[0088] In a particularly preferred variant of the base body 2, the side wall outer diameter is 22,400 mm, the side wall inner diameter is 23,380 mm and the base height 20 of the base body 2 is 20 mm.

[0089] In this embodiment, the bottom 13 of the base body 2 has a centrally arranged bore 16.

[0090] The Fig. 2 shows a section of a schematic representation of the abrasive coating 3 on a grinding surface 9 of a grinding tool 1 according to the invention, wherein the abrasive coating 3 comprises diamond grains 4 and CBN grains 5, wherein the diamond grains 4 and CBN grains 5 are bonded in multiple layers in a sintered metal bond and / or synthetic resin bond 18 in the abrasive coating 3 and wherein a grain mixing ratio between the diamond grains 4 and the CBN grains 5 is substantially 1:1 and wherein the, in particular average, grain sizes 19 of the diamond grains 4 and / or the CBN grains 5 are more than 50 µm, preferably 51 µm to 300 µm, particularly preferably 91 µm to 252 µm.

[0091] Here, it is schematically shown that the grain size ratio between the CBN grains 5 and the diamond grains 4 is preferably 0.3 to 2.8, particularly preferably 0.5 to 1.0. For example, the grain sizes 19 of the CBN grains 5 and the diamond grains 4 are shown in some grains 4.5.

[0092] The abrasive coating 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 comprises other substances or materials.

[0093] The Fig. 3 shows a section through an arrangement with two grinding tools 1 and a workpiece 25 to be machined by means of the grinding tools 1, in particular a brake disc 25 with a hard material coating 29, wherein the workpiece 25 is arranged between the two grinding tools 1 and wherein the two grinding tools 1 are aligned symmetrically with respect to the rotation axis 26 of the workpiece 25 and the grinding pads 3 of the two grinding tools 1 face the workpiece 25.

[0094] When machining the workpiece 25, it is preferably provided that the workpiece 25 rotates about its rotation axis 26 and / or is ground on both sides by two grinding tools 1 by rotating the grinding tools 1 about their respective rotation axes 10.

[0095] The workpiece 25 is preferably mounted on a rotatable workpiece spindle 27 of a grinding machine. The grinding tools 1 are each mounted on a rotatable tool spindle 28 of a grinding machine.

[0096] The Fig. 3 The rotation arrows assigned to the spindles 27, 28 are intended to indicate the direction of rotation of the spindles 27, 28. This variant involves so-called synchronous grinding, since the tool spindles 28 carrying the grinding tools 1 have a direction of rotation (here counterclockwise) that is opposite to the direction of rotation of the workpiece spindle 27 carrying the workpiece 25 (here clockwise). As a result, the velocity vectors of the contacting surfaces of the grinding tool and the workpiece point in the same direction.

[0097] However, the workpiece 25 could also be machined by so-called counter-rotation grinding, wherein the workpiece spindle 27 has the same direction of rotation as at least one tool spindle 28. This means that all spindles 27, 28 have the same direction of rotation.

[0098] In principle, other and / or different directions of rotation of the spindles 27,28 are also possible.

[0099] In the present machining variant, the tool 25 is ground in a cross-grinding manner, which means that there is no tilt of the rotational axis 10 of the at least one grinding tool 1 relative to the rotational axis 26 of the workpiece 25. This means that the rotational axes 10, 26 are aligned parallel to one another.

[0100] It is also conceivable that during machining of the workpiece 25, the rotation axes 20, 26 are tilted relative to each other or the rotation axes 10, 26 are not parallel, so that no cross grinding occurs.

[0101] In this embodiment of the respective grinding tool 1 of the arrangement, the grinding coating 3 is formed from segments 11, preferably wherein the segments 11 are separated and / or spaced from one another by slots 12.

Claims

1. Grinding tool (1) for grinding at least one hard material-coated brake disc (25), wherein the grinding tool (1) comprises a base body (2) and a grinding coating (3), wherein the grinding coating (3) comprises diamond grains (4) and CBN grains (5), wherein the diamond grains (4) and CBN grains (5) are bonded in multiple layers in a sintered metal bond and / or synthetic resin bond (18) in the grinding coating (3), characterized in that a grain mixing ratio between the diamond grains (4) and the CBN grains (5) is substantially 1:1 and wherein the grain sizes (19) of the diamond grains (4) and / or the CBN grains (5) are more than 50 µm.

2. Grinding tool (1) according to claim 1, wherein the grain sizes (27) of the diamond grains (4) and / or the CBN grains (5) are 51 µm to 300 µm, preferably 91 µm to 252 µm.

3. Grinding tool (1) according to one of the preceding claims, wherein the grain size ratio between the CBN grains (5) and the diamond grains (4) is 0.3 to 2.8, preferably 0.5 to 1.

0.

4. Grinding tool (1) according to one of the preceding claims, wherein the grinding coating (3) is annular, in particular wherein - an outer diameter (6) is 200 to 900 mm, preferably 260 to 800 mm, and / or - a coating width (7) is 5 to 40 mm, preferably 15 to 25 mm, and / or - a coating height (8) is 5 to 20 mm, preferably 6 to 10 mm, and / or wherein the grinding coating (3) has a grinding surface (9) which is substantially flat and / or is arranged orthogonal to a rotation axis (10) of the grinding tool (1).

5. Grinding tool (1) according to one of the preceding claims, wherein the grinding coating (3) is formed from segments (11), preferably which are spaced apart from one another by slots (12), in particular wherein the slots (12) extend substantially radially with respect to a rotation axis (10) of the grinding tool (1).

6. Grinding tool (1) according to one of the preceding claims, wherein the grinding coating (3) is applied to the base body (2) by sintering, soldering, welding and / or by means of a binding agent, preferably an adhesive.

7. Grinding tool (1) according to one of the preceding claims, wherein the base body (2) is pot-shaped with a base (13) and a side wall (15) adjacent to the base (13), preferably wherein the base (13) has a centrally arranged bore (16).

8. Grinding tool (1) according to one of the preceding claims, wherein the base body (2) consists of metal, in particular steel and / or aluminum.

9. Arrangement with at least one grinding tool (1) according to one of claims 1 to 8 and at least one workpiece (25) to be machined by means of the at least one grinding tool (1), in particular a hard material-coated brake disc (25), preferably wherein at least two grinding tools (1) according to one of claims 1 to 8 are provided and the workpiece (25) to be machined is arranged between the at least two grinding tools (1), particularly preferably wherein the at least two grinding tools (1) are aligned symmetrically with respect to the workpiece (25) and the grinding pads (3) of the at least two grinding tools (1) face the workpiece (25).

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

11. A method for producing a grinding tool (1) according to one of claims 1 to 8: - providing a base body (2); - providing an abrasive coating (3), preferably formed from segments (11), comprising diamond grains (4) and CBN grains (5), o wherein a grain mixing ratio between the diamond grains (4) and the CBN grains (5) is substantially 1:1 and o wherein the grain sizes (19) of the diamond grains (4) and / or the CBN grains (5) are more than 50 µm; - applying, preferably sintering and / or gluing, the abrasive coating (3) to the base body (2) or to a carrier body fastened to the base body (2).

12. Method according to the preceding claim, wherein the provision of the abrasive coating (3) is carried out by the following method steps: - Providing a mixture of the diamond grains (4), CBN grains (5), the metal bond and / or synthetic resin bond (18) and preferably the fillers; - Compressing the mixture, in particular under controlled pressure and / or temperature conditions.

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

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