Grinding wheel for surface grinding of hard-to-machine materials on brake discs

Abstract

The present invention relates to grinding wheels (5, 6) for planar or conical grinding of rotationally symmetric workpieces (3) for mass production. [Solution] In this regard, the abrasive coating (20) in the width direction and / or radial direction has a variation in specification adapted to correspond to at least the change in each peripheral speed of the workpiece (3) during grinding. A second aspect of the present invention provides a grinding wheel (5, 6) for planar or conical grinding of a rotationally symmetric workpiece (32) for mass production, wherein the abrasive coating (20) has a variation in molded recess (31) at least in the width direction, so that the concentration of the abrasive is adapted to each peripheral speed, in such a way that the molded recess (31) changes across the width BSS of the abrasive coating (20), so that there is a change in the average specification of the abrasive corresponding to each peripheral speed.

Description

Technical Field

[0001] The present invention relates to a grinding wheel for surface grinding of difficult-to-machine materials on a brake disk or a brake disk-like workpiece.

Background Art

[0002] In addition to achieving high precision in grinding a workpiece, particularly a brake disk, the unit cost plays an important role especially in mass production. There is often a correlation that the lower or medium the precision to be achieved for the workpiece, the more suitable it is for mass production. The more stringent the requirements for grinding the workpiece, the inevitably higher the unit cost accordingly. Such a discrepancy between the quality and the manufacturing cost mainly related to mass production becomes larger as the difficulty of grinding the workpiece increases. This is particularly applicable to workpieces with a high cutting resistance and accompanied by a coating or material containing at least a small amount of, for example, tungsten carbide, silicon carbide, or titanium carbide. Due to these carbide components, the hardness of the surface to be ground of the workpiece becomes extremely high, making grinding more difficult compared to standard materials, such as steel with increased hardness by conventional methods. This is particularly applicable to brake disks.

[0003] Currently, it has been shown that, especially in the case of brake discs requiring high-precision grinding, the unit cost is primarily determined by the tool cost. In this example, this means that the grinding wheel for grinding the aforementioned hard coating or material of the workpiece accounts for a significant portion of the total cost of the workpiece being ground. The aforementioned material or coating of the workpiece, which is extremely hard and highly resistant to grinding, is related to, for example, a brake disc with a wear-resistant coating, and therefore requires the use of a special grinding wheel specifically designed for such applications. It is understood that such a special grinding wheel is more expensive than, for example, a grinding wheel that can be used for hardened materials. In addition to the cost of the grinding wheel, further elements of the manufacturing cost are the cost of the dressing tool and the cost of the actual dressing process between grinding operations. The faster the grinding wheel wears out, the more frequent the dressing will be. Optimization of the total cost is always necessary in relation to the material, or specifications, of the polishing coating for grinding wheels, the dressing, and the precision of the ground workpiece to be achieved. It is understood that reducing the manufacturing cost of the workpiece will correspondingly increase the profit margin on the manufactured or ground workpiece.

[0004] The planar and conically rotationally symmetric regions of the workpiece to be ground are ground at their circumferential end faces, similar to the brake disc described above. The drawback in this case is that the polishing coating, which extends across the entire thickness of the grinding wheel and basically has a constant specification, needs to undergo different material removal amounts, especially as the peripheral speed of the workpiece changes radially. Therefore, the grinding wheel achieves or obtains changes in the amount of material removed by changing the grinding engagement conditions in the radial direction of the section of the workpiece to be ground.

[0005] Within the scope of the present invention, the grinding regions referred to herein as difficult-to-machine materials for rotationally symmetric workpieces relate to workpieces such as brake discs having a difficult-to-machine material as a base material, and workpieces having a special difficult-to-machine coating on the grinding region. In this specification, all embodiments are understood to be difficult-to-machine materials for rotationally symmetric workpieces.

[0006] A grinding wheel engages with a workpiece, such as a brake disc, through circumferential grinding, creating a so-called "peripheral cut" on the workpiece being ground; that is, the grinding marks extend radially around the planar surface. While this shape of grinding marks on a finished grinding workpiece is often desirable, it is not essential.

[0007] As a general rule, grinding wheels for grinding difficult-to-machine materials are more expensive than grinding wheels for ordinary hard materials, and therefore, the manufacturing cost of workpieces with such difficult-to-machine coatings or made from such materials leads to higher manufacturing costs.

[0008] Therefore, Non-Patent Document 1, concerning flat grinding, i.e., planar parallel machining of surfaces using the periphery of a disc, which can be applied to brake discs, mentions CBN and diamond grinding specifications for good material removal performance with respect to so-called ultra-high hardness steel alloys or brittle hard materials. In particular, it is described that abrasive grains as abrasive material can be used in the form of grinding specifications, such as block-shaped, pointed-shaped, or synthetic diamond particles with irregular edges. For example, when grinding a workpiece having a planar side surface and a diameter region, this prior art describes that tools for two-zone grinding can have different specifications, but does not mention, i.e., explain, the difference in material removal amount related to peripheral speed.

[0009] Non-patent document 2 describes that difficult-to-machine workpieces, in particular, contain mixed materials, at least on their surface, for example, brake linings. Furthermore, it describes that the bonding of abrasive grains is specifically designed and adapted for the particular purpose for which it is intended. When grinding brake linings, it is stated that extremely high abrasive retention and a high level of abrasive-free areas must be ensured. Differences in material removal due to differences in peripheral speed, particularly with respect to the planar areas of the workpiece being ground, are not mentioned in the specifications of the grinding tool, even when the grinding tool is intended for a specialized application.

[0010] Patent Document 1 describes the structural design of an abrasive tool. In particular, it provides a coarse abrasive structure and a fine abrasive structure, in which the abrasive tool layer forms a structure on the surface that gradually changes from coarse to fine. Elastic materials, especially rubber, are ground using an abrasive tool with a structural pattern. The abrasive itself is performed on a cylindrical workpiece, and flat surfaces are not polished. This structure formation of the grinding surface is provided to perform coarse and finish grinding in a single pass. Information on adapting the specifications of the grinding wheel to changing peripheral speeds is not described.

[0011] Patent Document 2 describes a profile grinding wheel having a triangular cross-section and a polishing coating that tapers towards the tip, wherein the concentration of abrasive material in the polishing coating changes depending on the load. For this profile grinding wheel, the maximum load occurs at the tip of the polishing coating, and the concentration of abrasive material is much lower on the sides of the polishing coating which has a triangular cross-sectional shape. This profile grinding wheel is not suitable for grinding flat surfaces, and the grinding ratio defined by the peripheral speed is not achieved in terms of the amount of material removed that is appropriate for it.

[0012] Patent Document 3 describes a grinding tool provided specifically for grinding laminated safety glass. For this specialized application, molded recesses are provided in a region of the polishing coating along the circumference of the grinding wheel, consisting of multiple segments. These molded recesses have a basically known design, such as V-shaped or U-shaped recesses. During the grinding of laminated safety glass, meandering pieces of grinding material are generally generated, which unfavorably hinders the further grinding process. Therefore, the objective is to provide molded recesses in the peripheral region of the polishing coating so as not to hinder the actual grinding process. These molded recesses can accommodate the grinding pieces, thereby allowing the polishing coating to have regions with abrasive material and regions without abrasive material. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0246727 [Patent Document 2] U.S. Patent No. 5,853,319 [Patent Document 3] European Patent Application Publication No. 3663043 [Non-patent literature]

[0014] [Non-Patent Document 1] Krebs & Riedel product catalog (KCD-101 / 2010) [Non-Patent Document 2] Winter's first catalog: "Automobiles, Turbines, Roller Bearings" [Overview of the project] [Problems that the invention aims to solve]

[0015] The object of the present invention is to provide a cost-effective solution for mass production, particularly for grinding disc-shaped or rotationally symmetrical workpieces in the form of brake discs or brake disc-like workpieces, where the grinding area is composed of a difficult-to-machine material or coating. Part of this object is to optimize or reduce the tool cost per brake disc to be ground, i.e., the manufacturing cost of the tool per workpiece. Such optimization is understood to be primarily related to brake discs, for example. The optimized grinding tool will be adapted to a wide area of ​​grinding engagement on the planar side surface and, consequently, the abrasive coating, thereby enabling grinding conditions or material removal amounts for specific difficult-to-machine materials to be ground, regardless of the peripheral speed of the workpiece being ground. An important part of the object of the present invention is to provide a grinding wheel that has high grinding quality, a high level of durability, and a favorable purchase price suitable for mass production. In terms of precision, within the grinding engagement area, i.e., the effective area of ​​the grinding wheel, the grinding wheel must be able to reliably meet the tolerances for its thickness, runout, surface flatness quality, and required dimensional tolerances in an operationally reliable manner. The thickness tolerance should be less than 8-10 μm, for example, when grinding the flat and parallel outer surface of a workpiece. Such precision is particularly important when grinding brake discs or brake disc-like workpieces, because if the thickness tolerance range is exceeded when looking at the entire circumference of the brake disc, an intermittent braking effect may occur, which must be avoided or is unacceptable under safety requirements regarding braking and the generation of braking force. Difficult-to-machine materials for the friction surface of brake discs contain carbide components that are harder than hardened steel. [Means for solving the problem]

[0016] This objective is achieved by a grinding wheel having the features described in claim 1, a grinding wheel having the features described in claim 2, and a method having the features described in claim 13. Advantageous improvements are defined in each dependent claim.

[0017] According to a first aspect of the present invention, a surface grinding wheel is described that is suitable for surface grinding of rotationally symmetric workpieces in the form of brake discs or brake disc-like workpieces for mass production. On its outer circumference, i.e., on its circumferential surface, the grinding wheel has an abrasive coating which, according to the present invention, has a variable specification, at least in the width direction. The specification changes to adapt to a specific peripheral speed at least present in the workpiece during grinding. Within the scope of the present invention, “specification” is understood to mean the specification of the abrasive coating relating to the hardness of the abrasive grains, the size of the abrasive grains, the shape of the abrasive grains, the abrasive concentration, the abrasive bonding, and the type of abrasive. During surface grinding, when the grinding surface of the grinding wheel engages with the flat surface of the workpiece to be ground, various peripheral speeds exist across the grinding width, i.e., across the width or thickness of the grinding wheel, and therefore across the width of the abrasive coating. If the specification of the abrasive coating is constant, the grinding conditions will differ for each of the various peripheral speeds, and therefore the amount of material removed will differ. Therefore, grinding wheels can wear out very quickly in the areas under the highest load, and thus in the areas where the largest amount of material is removed, resulting in unnecessarily high costs. This is because abrasive coatings are designed for maximum material removal and therefore maximum load on the grinding wheel across all grinding areas, while the load on the grinding wheel or abrasive coating is low, at least in areas where the peripheral speed of the workpiece is relatively low.

[0018] When grinding difficult-to-machine materials for workpieces in the form of brake discs or for their coatings, high grinding forces are generated in the two effective surface areas of the brake disc, i.e., the friction surfaces, when these areas are engaged with the grinding wheel; these grinding forces can be compensated in the longitudinal axial direction of the brake disc, for example, by grinding both surfaces simultaneously with their respective grinding wheels, thereby substantially compensating for these grinding forces in the axial direction of the workpiece. In particular, with respect to the coated, highly wear-resistant effective surface areas on the brake disc, this coating, or the design of the brake disc with such a highly wear-resistant layer, results in a highly hard, difficult-to-machine surface. This means that each grinding wheel must apply a relatively high grinding force in the axial direction of the workpiece. However, if each grinding wheel engages with each effective surface area on each side of the brake disc during grinding, the high axial grinding force of the workpiece can be absorbed and compensated for. By using one grinding wheel for each plane of the brake disc, the resulting grinding force and grinding time can be minimized, thus achieving a more favorable cost structure, especially for mass production. It is preferable to use a water-soluble grinding emulsion as a cooling lubricant for grinding, but grinding oil may also be used as a cooling lubricant.

[0019] A second aspect of the present invention provides a grinding wheel which is similarly used for surface grinding of rotationally symmetric workpieces in the form of brake discs for mass production, and which is particularly suitable for or designed for grinding hard-to-machine materials or coatings on the surface of the workpiece to be ground.

[0020] According to the present invention, a polishing coating having a forming recess that varies in the width direction according to the present invention is provided on the planar side surface of the grinding wheel, that is, on the circumference. Since these forming recesses are arranged in the circumferential direction of the polishing coating, during grinding, the engagement length of the grinding wheel contributes to reducing the amount of material removed according to the width of the polishing coating. Thus, the average specification of the entire width of the polishing coating is adapted, at least in the workpiece, to the circumferential speeds present therein, by the forming recesses in the polishing coating that extend radially in the width of the polishing coating and on the surface of the workpiece to be coated. "Average specification" is understood to mean that the forming recess is an empty recess in the polishing coating, or with respect to the abrasive, a recess in which no abrasive is present, and that the forming recess is filled in any case with a substance that does not contain abrasive, such as a binding compound. Thereby, various average specifications of the polishing coating are brought about according to the size of the forming recess. Thus, according to the circumferential speed in at least the workpiece at a specific machining site, the amount of material removed is adapted, and if the forming recess in each width section is larger than those in other sections of the width of the polishing coating, the amount of material removed is reduced.

[0021] The specification of the polishing coating is preferably adapted, with respect to the abrasive, at least at each circumferential speed in the workpiece, in terms of the hardness of the abrasive grains, and / or the size of the abrasive grains, and / or the shape of the abrasive grains, and / or the abrasive concentration, and / or the binding of the abrasive. Thus, an abrasive specification that is optimal for specific grinding conditions and a specific material is directly adapted to the tool (grinding wheel), particularly with respect to the circumferential speed in at least the workpiece present at each radial position.

[0022] Also preferably, the specifications of the polishing coating and / or the formed recess are adapted to a specific circumferential speed at a specific material removal rate that varies across the width of the polishing coating. Thus, by changing the specifications or adapting the specifications of the polishing coating to the corresponding circumferential speed in the workpiece, i.e., the brake disk, the same or at least similar grinding conditions prevail across the entire width of the polishing coating, and in each case the material removal rate is guaranteed to be the same or similar, whereby the polishing coating of the grinding wheel is optimally used and, with regard to the dressing required after a certain grinding time, the polishing coating can be dressed substantially uniformly across the entire width. This reduces the dressing effort, i.e., the wear of the diamond dressing tool, and thus also contributes to reducing the manufacturing costs.

[0023] Also preferably, the specifications of the grinding wheel or its formed recess, or the changes in the specifications and formed recess across the entire width of the polishing coating, are designed such that a linear or substantially linear change in the material removal rate is obtained in the workpiece, i.e., the brake disk. In the workpiece, in order to achieve an optimal and material removal rate adapted to a specific circumferential speed, the formed recesses in the polishing coating are preferably rectangular, trapezoidal, triangular, polygonal, rounded, or elliptical with straight or curved side walls. The shape of the formed recess has a direct influence on the average specifications regarding the circumferential speed that extends into a specific radial section, particularly due to the fact that it is filled with a substance such as a binder that does not contain abrasive.

[0024] In some cases, it may be preferable to use some other filler that does not contain abrasive in the formed recess instead of the binder. In this case, the density indicated by the filler or binder and the section of the polishing coating containing abrasive needs to be similar, whereby it can have a direct influence on low-vibration grinding.

[0025] Preferably, since the polishing coating is formed from multiple segments bonded to the grinding wheelbase body, the production of these segments according to peripheral speeds corresponding to various material removal amounts, or specific material removal amounts, is easier than a closing ring that is fastened to it after being installed on the outside of the grinding wheelbase body.

[0026] It is understood that the specifications and / or molded recesses are to be adapted to the effective surface area of ​​the workpiece, particularly the brake disc, and its material.

[0027] The scope of the present invention also includes the design of crown-shaped or concave polishing coatings, the crown-shaped or concave shape being formed based on a rotationally symmetric shape within different micrometer ranges in relation to its size.

[0028] The polishing coating is preferably an abrasive material CBN and / or diamond having a suitable bond.

[0029] Further advantages, design variations, and details of the present invention will now be described with reference to the drawings listed below. [Brief explanation of the drawing]

[0030] [Figure 1] Figure 1 shows a schematic arrangement of the brake disc and the grinding wheels that engage with both sides of the effective surface area of ​​the brake disc. [Figure 2] Figure 2 shows a cross-sectional view of the brake disc. [Figure 3] Figure 3 shows a cross-sectional view of the grinding wheel. [Figure 4] Figure 4 shows a partial view of the arrangement in Figure 1. [Figure 5] Figure 5 shows the grinding area on the brake disc in the observation direction Y of Figure 4. [Figure 6] Figure 6 shows the same diagram as in Figure 1, but with the tool spindle omitted. [Figure 7]Figure 7 shows a diagram illustrating the linear increase in peripheral speed of the workpiece and grinding wheel. [Figure 8A] Figure 8A shows a schematic diagram of the circumference of a grinding wheel, which has molded recesses that increase in size from right to left. [Figure 8B] Figure 8B shows a partial cross-sectional view AA of a grinding wheel passing through an abrasive coating with a molded recess. [Figure 9A] Figure 9A shows a planar side view of the abrasive coating in the form of bonded segments, and a top view of the molded recess that varies over the width. [Figure 9B] Figure 9B shows a cross-sectional view BB of Figure 9A, which shows a molded recess extending across the width of the polishing coating or grinding wheel. [Figure 10] Figure 10 shows a schematic diagram of the arrangement in Figure 1, which includes a grinding area that covers the end face side of the brake disc for grinding the chamfered portion. [Figure 11] Figure 11 shows a top view of a brake disc that has been ground and has a specified grinding groove direction. [Figure 12] Figure 12 shows a conventional arrangement in which a rotationally symmetrical portion having a conical section is ground by a grinding wheel. [Modes for carrying out the invention]

[0031] Figure 1 shows a schematic top view of the arrangement of a clamped workpiece in the form of a brake disc 3, the first effective surface area 3.1 and the second effective surface area 3.2 being ground on their planar sides by opposing grinding wheels 5 and 6. The workpiece spindle 1 rotates the brake disc 3, which is clamped in the clamping device 4, for grinding purposes, by a spindle rotation drive 2. To the right of the workpiece spindle 1 in the illustrated top view, Figure 1 shows a dual arrangement of a first grinding spindle 7 and a second grinding spindle 8, which each support a surface grinding wheel 5 or a surface grinding wheel 6 with a corresponding polishing coating 20. The first grinding wheel 5 and the second grinding wheel 6 have a conical design with respect to their circumferential surfaces and, consequently, to the polishing coating 20. Therefore, when the polishing coating 20 engages parallel to the plane in the opposing effective surface areas 3.1 and 3.2, each grinding spindle 7 and 8 is inclined by an angle α1 or α2 with respect to the centerline 11 extending through the rotational plane of the brake disc 3. The inclination angles α1 and α2 correspond to the apex angles of the polishing coating 20 engaged with each grinding wheel 5 and 6. In the illustrated position, the two grinding wheels 5 and 6 are engaged 15 with the opposing effective surface areas 3.1 and 3.2 of the brake disc 3, respectively. Since the grinding wheels 5 and 6 are located on the opposing planar sides of the brake disc 3, the grinding force is compensated by the grinding wheels 5 and 6 in the state of opposing grinding engagement 15. The grinding spindle 7 represents the rotary drive unit 9 for the first grinding wheel 5, and the rotary drive unit 10 rotates the grinding spindle 9 and, together with it, the second grinding wheel 6. The inclination angle α1 of the first grinding spindle 7 and the inclination angle α2 of the second grinding spindle 8 with respect to the center plane 11 are mechanically defined fixed angles. The angles α1 and α2 of the two grinding spindles 7 and 8 are typically equal. However, in principle, α1 and α2 may be different if it is necessary for technical reasons to correspond to different grinding operations.

[0032] In the arrangement shown in Figure 1, the rotation axes of the first grinding spindle 7 and the second grinding spindle 8 are inclined at an angle of, for example, 12° with respect to the central axis 11, which is a preferred arrangement in grinding machines. This is because it results in a significant simplification of the interfering contour of the machine, allowing each grinding headstock to have a more rigid design. In principle, in special cases, the angles α1=α2=0° can also be achieved. This means that the grinding wheels are designed as cylindrical grinding wheels with planar sides, and are positioned perpendicular to the planes of the effective surface areas 3.1 and 3.2 of the brake disc 3 with respect to their arrangement, including their respective polishing coatings 20.

[0033] Arrangements of grinding spindles 7 and 8 having negative swivel angles α1 and α2 are also possible if necessary for design reasons. Such arrangements with negative swivel angles α1 and α2 are, of course, only possible if the grinding wheel does not come into contact with the tool spindle 1. For example, a desirable arrangement could be such that the first grinding spindle 7 is positioned parallel to the central axis 11 with respect to the rotation axis of its rotary drive unit 9 and has a cylindrical grinding wheel 5 with planar sides, while the second grinding wheel 6, via its second spindle 8, rotates as a conical disc with a negative swivel angle α2, so to speak, toward the rotation axis below the brake disc 3 to be ground.

[0034] Conventionally, the movement of axes along CNC axes Z1, Z2, and X is controlled by at least partially interpolated motion.

[0035] Figure 2 shows the basic shape of the brake disc 3 as a workpiece to be ground using the grinding wheel according to the present invention, in half-section form. The brake disc 3 has a central hole 3.4 through which it is centered and fastened to the vehicle. The brake disc 3 is screwed to the vehicle in a planar manner by its flat contact surface 3.5. For this screw fastening, holes 3.3 are provided in the vehicle for screw connection to the mounting flange of the brake disc 3. A first effective surface area 3.1 and a second effective surface area 3.2 are shown on the brake disc 3, and during braking, the brake pads engage with these to generate a braking effect at the wheel. The effective surface areas 3.1 and 3.2 of the brake disc 3 are provided with extremely hard wear-resistant coatings 3.6 and 3.7, so that wear is minimized and the brake disc 3 has a correspondingly long service life. It is understood that instead of wear-resistant coatings, the brake disc can also be made of wear-resistant material in the area that engages with the brake pads. The thicknesses of the wear-resistant coatings 3.6 and 3.7 are indicated by the dashed lines shown in reference numbers 3.6 and 3.7, respectively. The two effective surface areas 3.1 and 3.2 are also the two grinding areas on the brake disc 3 with the extremely hard wear-resistant coating, and since the brake disc 3 is ground in these two areas, maintaining dimensional accuracy is important for the operation of the brake disc in order to avoid, or at least minimize, vibration, premature wear, and premature damage to these brake components during operation. References A and B of the central hole 3.4 or the flat contact surface 3.5 are important geometric manufacturing dimensions of the brake disc 3. These include runout B on the one hand and centricity A of the central hole 3.4 on the other hand. This runout with respect to reference variable B with position tolerance is shown in reference number 3.8. The accuracy of this runout in the effective surface areas 3.1 and 3.2 is given with respect to the movement path of the brake pad from the non-braking position to the braking position where it engages with the coatings 3.6 and 3.7 of the brake disc 3. The thickness to be maintained is indicated by reference symbol d.In addition to the tolerances of the planar surfaces, the parallelism of the two planar surfaces to be ground, i.e., the effective surface areas 3.1 and 3.2, in the aforementioned region of the brake disc 3 is indicated by reference symbol 3.9. For the brake disc to function reliably in a vehicle, the parallelism 3.9 of the two effective surface areas 3.1 and 3.2 relative to each other is typically, for example, up to 8-10 μm. Runout B and parallelism 3.9 represent important parameters of the nominal dimensions of the brake disc 3, with tolerances in the range of 20-25 μm. The above values ​​relate, for example, to the 350 mm outer diameter of the illustrated brake disc 3. It should be understood that these tolerances do not represent the range in which a certain level of precision can be achieved by grinding for standard steel. However, it should be noted that the brake disc 3 has an extremely hard wear-resistant coating in its effective surface area 3.1 or 3.2, or is entirely made of such a hard wear-resistant material, and therefore these tolerances present a relatively large challenge in grinding. For this reason, and for cost reasons, the brake disc is adjusted to these tolerances as a compromise for mass production grinding operations, taking into account the ultra-hard, difficult-to-machine coating 3.6, 3.7 of the brake disc 3, while still being able to provide reliable function. For cost reasons, it is important that the power output during grinding of the workpiece is as high as possible per unit time, i.e., the cycle time is as short as possible.

[0036] Figure 3 shows a cross-sectional view of a planar grinding wheel, which can be used, for example, as the first grinding wheel 5 or the second grinding wheel 6 in Figure 1. The grinding wheels 5 and 6 are a type of ceramic-bonded diamond grinding wheel suitable for grinding two effective surface areas 3.1 and 3.2 of the brake disc 3. The grinding wheels 5 and 6 have a centering hole 5.1 in their center, which is used to center and house the grinding wheels 5 and 6 on the nose (not shown) of the grinding spindle. The grinding wheels 5 and 6 are mounted on the nose of the grinding spindle with their planar sides and are firmly clamped axially by the grinding wheel flange through the two planar sides 5.2 of the grinding wheels 5 and 6. The planar sides 5.2 on the circumferential sides of the grinding wheels 5 and 6 are located and shown at angles α1 and α2, respectively, in terms of the inclination angles of the first grinding spindle 7 and the second grinding spindle 8. The base body 5.3 of the grinding wheel, having a centering hole 5.1 inside, is generally made of an aluminum alloy, or steel, or carbon, and the diamond polishing coating 5.4 described above, the latter generally ceramic-bonded around its circumference, and the thickness HSS of the polishing coating 5.4 typically has a wearable height of 5 to 8 mm. The width BSS of the polishing coating 5.4 represents the outer circumferential side surface of the grinding wheels 5 and 6. Parameters to be maintained with respect to the dimensions of the grinding wheels 5 and 6, which are equally important for accuracy, are the large radius RSS extending from the axis of rotation of the grinding wheels 5 and 6 to the outermost tip of the polishing coating, and the small radius rSS extending from the axis of rotation of the grinding wheels 5 and 6 to the inner circumferential edge of the polishing coating 5.4. The above measurements or dimensions of the grinding wheels 5 and 6 are important for the grinding wheels according to the present invention, which are described below.

[0037] Figure 4 shows a further diagram in half-section of the arrangement for grinding the brake disc 3, which basically corresponds to the arrangement in Figure 1. The brake disc 3 is rotationally driven by a clamping device 4 on a workpiece spindle 1 equipped with a rotary drive unit 2. The radii rW and RW are shown for the brake disc 3, similar to the radii rSS and RSS of the polishing coatings 20 of the grinding wheels 5 and 6 described with respect to Figure 3. The smaller radial radius rW of the brake disc 3 refers to the inner end of the coating, i.e., the effective surface areas 3.1 and 3.2, by the hard polishing coating 5.4, while the radius RW extends radially from the axis of rotation of the brake disc 3 to its outer circumference. The feeding motion is performed via CNC axes Z1 and Z2, respectively, by the rotation or rotation drive device 2 of the brake disc 3, which is clamped in the clamping device 4, and by the grinding wheels 5, 6 or their grinding spindles 7, 8 that are engaged with the brake disc 3 on the upper and lower sides of this figure, in the grinding direction relative to the planar side of the brake disc 3. Furthermore, movement of the tool spindle 1 in the X direction is shown, which also represents a CNC axis and is used to feed the brake disc 3 into the grinding gap between the two grinding wheels 5, 6 for the planar side of the brake disc 3.

[0038] Figure 5 is a partial view, specifically the field of view "Y" in Figure 4 in the longitudinal axis direction of the tool spindle 1. Here, the brake disc 3 with the clamping device 4 and the two different radii rW and RW represent the planar side surfaces to be ground. These are the effective surface areas 3.1 and 3.2 on the brake disc 3, and are ground by the grinding wheel 6 in the area indicated by the grinding engagement 15. The basic design corresponds to that shown in Figure 1, so in Figure 5, only the elements necessary for direct explanation are shown with corresponding reference symbols.

[0039] Figure 6 also shows a partial cross-sectional view of the first and second grinding wheels 5 and 6, provided for engagement 15 with the effective surface areas 3.1 and 3.2 of the brake disc 3. All other parts or dimensions, such as radius, swivel angles α1 and α2, and overall arrangement, basically correspond to those in Figures 1, 3, and 4. Figure 6 shows that in the effective surface areas 3.1 and 3.2, which are normally assumed to have a flat design, a different convex shape can also be achieved by the corresponding dressing of the grinding wheels 5 and 6. However, this is also possible in the case of a slightly concave design of the effective surface areas 3.1 and 3.2 of the brake disc 3. This convex or concave shape can be considered in the micrometer range and may be possible in specific applications. The shape of such a polishing coating to form the corresponding convex or concave shape on the brake disc 3 can be achieved by the dressing of both grinding wheels 5 and 6.

[0040] Figure 7 schematically shows the characteristics of the peripheral speed vU of the grinding wheels SS5 and SS6, and the peripheral speed vU of the brake disc 3 during the grinding process. Different peripheral speeds result in different grinding conditions on the planar side surface of the workpiece, i.e., the effective surface areas 3.1 and 3.2 of the brake disc 3 or workpiece WS. These multiple different grinding conditions are unavoidable because the task involves surface grinding, where the peripheral speed during rotation increases from the inside to the outside along with the radius.

[0041] In this exemplary embodiment, the outer diameter (effective surface area) of the brake disc is assumed to be approximately DW = 350 mm, and the inner diameter (effective surface area) of the brake disc is assumed to be approximately dW = 230 mm. During grinding, the rotational speed of the clamped brake disc 3 is generally constant over the entire workpiece. The 100% value is assumed to be for the maximum value of the brake disc 3, i.e., the large radius RW = approximately 175 mm. For a smaller radius rW = approximately 115 mm, the peripheral speed during grinding is only about 65% of the value for the large radius RW or outer diameter, given that the rotational speed of the workpiece is constant. Since the allowable grinding area is basically constant over the effective surface areas 3.1 and 3.2 of the brake disc 3, 100% can be assumed at the end face side of the grinding wheel for the amount of material removed per brake disc 3 that must be ground at the large radius RW = approximately 175 mm. For a smaller radius rW = approximately 115 mm, this value is approximately 65% ​​of the larger radius RW = approximately 175 mm. The allowable grinding area on the planar side surface is assumed to be, for example, approximately 0.15 mm. However, the allowable grinding area may vary depending on the coating process. This is also true for the grinding wheel, which is typically, or preferably, a ceramic-bonded diamond or CBN grinding wheel with a coating width of B = 65 mm for the aforementioned diameter ratio of the brake disc 3 (see position 5.4 / Figure 3). When the outer diameter RSS = 250 mm of the grinding wheel, 100% cutting speed is obtained across the majority of the diameter RSS of the grinding wheel. When the mounting angle during cutting of the effective surface areas 3.1, 3.2 of the brake disc 3 is approximately 12°, a small grinding wheel radius rSS of approximately 237 mm is obtained. This diameter corresponds to a diameter ratio of rSS to RSS of approximately 95%. This ratio can be reflected on the same scale as differences in cutting speed. Since the rotational speed of the grinding wheel is constant across the entire grinding wheel, this ratio sets the cutting speed of 95% at the small radius of the brake disc 3 as the ratio to the cutting speed of 100% at the majority of the diameter of the brake disc 3.When the concentration of abrasive grains in the polishing coating 5.4 of grinding wheels 5 and 6 is constant, the difference in radius of the grinding wheels results in a different number of individual abrasive particles being present in the grinding engagement per unit time. In other words, the grinding conditions change depending on the peripheral speed. Note that at the small radius rW of the brake disc 3, the amount of material removed by the tool is only about 65%, which means that the above difference in this case is about 35%.

[0042] As described above, since the grinding wheels 5 and 6 generally operate with angled feed, 5% of the diameter of the grinding wheel is missing from the workpiece, i.e., the majority of the diameter RW of the brake disc 3, and therefore, assuming the same concentration of abrasive grains in the polishing coating, it can be inferred that the amount of abrasive grains in the grinding engagement will be 5% less for the rotation of the reference grinding wheel. Therefore, this 5% difference in the amount of material removed from the brake disc 3 due to the difference in diameter must be subtracted from the aforementioned approximately 35%, and thus, strictly speaking, the overall difference in the change in abrasive concentration is approximately 30%. As a result of the radius ratio RW / rW of the brake disc 3 and the radius ratio RSS / rSS of the grinding wheels 5 and 6, work for the grinding process can be performed using the adapted grinding wheel specifications across the entire width of the polishing coating 20 of the grinding wheels 5 and 6, at the smaller radius rW of the brake disc, because at such locations, the amount of material that must be removed per unit time is much less than at the majority of the diameter RW of the brake disc. Based on the values ​​mentioned here, the inclination values ​​of the grinding wheels 5 and 6 with respect to angles α1 or α2 become less important, and it is shown that for small inclinations at angles significantly smaller than 10°, these angles can even be ignored. In principle, during grinding, the requirements regarding the dimensional tolerances, shape tolerances, and surface requirements of the workpiece being ground can be assumed to be the same across each effective surface area 3.1 and 3.2 of the brake disc 3. Therefore, the grinding wheels 5 and 6 can be adapted or optimized with respect to their specifications so that the specifications for each radius, and consequently each peripheral speed, can be adapted to the effective surface areas 3.1 and 3.2 of the brake disc 3. Such a relationship or pattern is shown in Figure 7, where the peripheral speed of the brake disc 3 extends linearly between the two radii RSS and rSS, i.e., decreasing from RSS to rSS. Since the peripheral speed is proportional to the amount of material removed per unit time across the effective sides 3.1 and 3.2 of the brake disc 3, this also corresponds to the load on the grinding wheels 5 and 6 due to specific machining.In the grinding process, the load on a particular grinding area varies relatively large due to the parameters described above. Therefore, optimizing the specifications of the grinding wheel allows for compensation of the corresponding load, thereby further adapting the grinding wheel to a specific grinding area through its geometry. Thus, the manufacturing cost of the grinding wheel can be adjusted to suit specific conditions / technical requirements regarding the amount of material removed in a particular area of ​​the grinding zone, and to the required dimensions, shape, and surface requirements or precision in the grinding zone. This can be achieved by targeted changes in the shape of the abrasive particles across the grinding zone of the grinding wheel, by targeted changes in the concentration of the abrasive across the grinding zone of the grinding wheel, and especially, regarding the overall difference of approximately 30% mentioned above, by targeted changes in the bonding of the abrasive used across the grinding zone of the grinding wheel and by introducing targeted structures to the polishing coating of the grinding wheel across the grinding zone. These changes can be considered or modified individually within the grinding wheel for specific characteristics, but by appropriately combining them, the grinding characteristics of the grinding wheel can also be changed with respect to the amount of material removed or the changing peripheral speed.

[0043] By using targeted variations on technically required parameters, it is possible to manufacture and use grinding wheels that are optimized in terms of technology and cost.

[0044] Next, we will explain the options for each of the above-mentioned variations regarding abrasives.

[0045] a) Regarding targeted changes in the shape of abrasive particles across the grinding zones of grinding wheels 5 and 6, it is noted that, for manufacturing reasons, the engagement width of the grinding wheel can change the morphology of the abrasive particles in the grinding area. "Form of the abrasive grit particles" is understood to mean the size, sharp edges, and shape of the abrasive particles, such as whether they are elongated, angular, or rounded. Regarding changes in abrasive particles to suit specific peripheral speeds and material removal amounts at the grinding engagement area, it should be noted that this has a significant impact on the service life of the grinding wheel in terms of the surface quality that can be achieved, for example, between dressing intervals or during grinding. An extended service life of the grinding wheel is advantageous because it reduces the tool cost per workpiece being ground.

[0046] b) Targeted variations in the abrasive concentration across the grinding zone of the grinding wheel are also possible to suit a specific amount of material removed per unit time in a particular grinding zone. This means distributing the concentration such that the areas of grinding wheels 5, 6 with the highest amount of material removed per unit time also have the highest concentration of abrasive, and the areas with the lowest amount of material removed per unit time have the lowest concentration of abrasive. This means generating different polishing coatings 20 across the grinding width depending on the peripheral speed vU and the desired amount of material removed. The adaptation with respect to the abrasive concentration can be changed linearly or substantially linearly across the width of the polishing coating 20, which is advantageous due to the fact that the peripheral speed of the workpiece also changes linearly, at least. By providing different concentrations of abrasive in this way, each grinding wheel is obtained that is optimized for the grinding process with respect to a specific amount of material removed per unit time in each grinding area. Since commonly used CBN or diamond grinding wheels are relatively expensive, it has been pointed out that the manufacturing cost of grinding wheels can be reduced by adjusting the concentration of the abrasive, and therefore the tool cost per workpiece produced can also be reduced. Furthermore, regarding the design of grinding wheels with varying abrasive concentrations, a further advantage is provided in that lower concentrations of abrasive in the grinding wheel reduce the wear of the dressing tool, and such optimization of the grinding wheel also reduces the wear of the diamond dressing wheel, resulting in further cost advantages in terms of tool costs. This is particularly important for mass production aimed at the aforementioned objectives of the present invention.

[0047] c) Further variations in the abrasive material are possible indirectly by changing the bonding of the abrasive material across the grinding zone of the grinding wheel. The bonding in the polishing coating needs to be as open as possible so that abrasive grains can be incorporated so that they are properly retained within the polishing coating 20. These requirements represent one type of variation in the bonding of the abrasive material. However, the type of bonding can also be adapted. That is, this adaptation relates to the optimal design of the grinding process and the amount of material removed per unit time, and the bonding or binder is adapted accordingly. It should be noted that the openness of the bonding may be affected by the appropriate compression of the coating of the grinding wheel during its manufacture. The higher the pressure, the narrower the pores and the lower the open porosity.

[0048] d) However, in the sense of changing the abrasive based on peripheral speed and thus the amount of material removed, this change can also be achieved indirectly by introducing open or closed structures into the polishing coating along the grinding zone of the grinding wheel, in addition to the concentration and binding of the abrasive. This is because the structure relates to molded recesses within the polishing coating, and therefore the engagement of the abrasive is less in the grinding direction compared to the circumferential direction. However, this can also be achieved by filling these recesses with a binder, for example, without using abrasive, thereby preventing grinding action in the areas where the filled molded recesses exist, even though the grinding wheel retains a closed design for the polishing coating. Thus, depending on the size of the molded recesses, whether they are open or closed, different average abrasive concentrations can be achieved in the grinding direction along the circumferential direction of the grinding wheel.

[0049] Such examples of molded recesses 21 are shown in Figures 8A and 8B. In this exemplary embodiment, the average concentration of abrasive material in the grinding direction, i.e., in the circumferential direction, across the width BSS of the polishing coating 20 is provided such that the molded recesses 21 do not disrupt the continuity of abrasive material in the polishing coating 20. The shape of these molded recesses 21 can be freely selected, i.e., different from the shape shown in Figure 8A, they may be rounded, elliptical, trapezoidal, or have other shapes. In Figure 8A, the molded recesses 21 or openings are shown as rectangular, and their size changes so as to increase from right to left in the figure, so that the average concentration of abrasive material across the width BSS of the polishing coating 20 of the grinding wheels 5, 6 decreases from right to left. These molded recesses 21 may be open, as shown in the cross-sectional view AA of Figure 8B, or they may be formed by a filler containing an abrasive-free material, the material may be an abrasive-free binder only.

[0050] As shown in Figure 8B, in a particular exemplary embodiment, the molded recess 21 can be provided across the entire thickness HSS of the polishing coating 20, that is, it can extend to the base bodies of the grinding wheels 5 and 6. Further advantages of these molded recesses 21 are that the grinding pressure can be kept essentially constant, and the cooling lubricant can be carried within the molded recesses 21 that form pockets and guided evenly to specific grinding areas.

[0051] Figures 9A and 9B show further exemplary embodiments utilizing commonly used versions of abrasives in the form of CBN and diamond abrasives. The abrasive coating 20 is formed from a plurality of individual segments 30, and when these segments are bonded to the circumferential surfaces of the grinding wheels 5, 6, molded recesses 31 are formed between them, and these molded recesses 31 extend in varying widths over substantially the entire width BSS of the abrasive coating and, consequently, the width BSS of the grinding wheels 5, 6. As can be seen from the design shown in Figure 9A, which shows the cross-section BB in Figure 9B, the shape of the molded recesses 31 can be freely selected and can vary in extension over the width BSS of the grinding wheels 5, 6, and can also extend over the thickness HSS of the abrasive coating. The above variations allow a specific amount of material to be removed, and thus over the width of the grinding wheel and, consequently, over the peripheral speed, to be adapted to specific grinding conditions. In principle, with respect to the shape of the molded recesses 31, unlike that shown in Figure 9A, the interface of the molded recesses 31 may extend in a curved manner rather than linearly.

[0052] As already described in relation to Figures 8A and 8B, the molded recesses 31 may be filled with a filler that does not contain abrasive material, or they may be designed to be open in the sense of pockets, so that, for example, a cooling lubricant can be used to supply these pockets and directed to the remaining area where the grinding operation is being performed during grinding.

[0053] Overall, it should be noted that the individual optimization means for the variation of abrasive material within the polishing coating 20 in the circumferential and / or transverse directions of the grinding wheel can be adapted individually, as well as adapted in specific combinations to achieve the variation of abrasive material in each grinding area of ​​the grinding wheel or the workpiece being ground.

[0054] Figure 10 shows a further embodiment of the grinding wheel, which otherwise has essentially the same design as, for example, Figure 1. The only difference is that the shape of the polishing coating 20 of the grinding wheels 5 and 6 is set such that, while grinding the planar side surfaces of the brake disc 3, i.e., the effective surface areas 3.1 and 3.2, the chamfered portion on the outer circumference of the brake disc 3 is also ground, so that the grinding of the planar side surfaces 3.1 and 3.2 and the chamfered portion are performed in a plunge grinding manner in a single grinding operation.

[0055] Figure 11 shows that a workpiece designed as a brake disc 3, for example as shown in Figures 1 and 4, having an X-axis in the form of a CNC drive axis, reciprocates in the direction of the X-axis. This allows the direction of the grinding marks, as a surface structure during grinding on the finished ground workpiece, to be created with a targeted influence and almost arbitrarily, and can be adapted by the grinding program. An example image of the corresponding grinding marks that can be easily created by such an arrangement is shown in Figure 11.

[0056] Finally, for simplification, Figure 12 shows the grinding of a conical section of a rotationally symmetric workpiece 32 having length L, which can be ground using tapered grinding wheels 5, 6, the grinding wheels 5, 6 being movable across CNC axes X and Z. For such a conical section to be ground, the grinding condition of each grinding area will differ depending on the peripheral speed vU, similar to the grinding of the planar sides 3.1, 3.2 of the brake disc 3. The grinding wheels 5, 6 according to the present invention, having an abrasive coating 20, can be applied here in the same way as the grinding specifications of the abrasive or abrasive coating to suit the desired amount of material removed. The workpiece has a section with a smaller diameter D1 and a section with a larger diameter D2. The workpiece is given reference number 32, and all other reference numbers / symbols have already been mentioned in the preceding drawings and their associated descriptions, so further explanation is omitted. [Explanation of Symbols]

[0057] 1 Workpiece Spindle 2. Rotary drive mechanism for the workpiece 3 Brake discs / workpieces 3.1 First effective surface area 3.2 Second effective surface area 3.3 Perforation 3.4 Central drilling 3.5 Flat contact surface 3.6 Coating of the first effective surface area 3.7 Coating of the second effective surface area 3.8 Runout in the effective surface area 3.9 Parallelism of the effective surface area 4. Clamping device 5. First grinding wheel 5.1 Central drilling of the grinding wheel 5.2 Planar side surface of the grinding wheel 5.3 Grinding Wheelbase Body 5.4 Polishing Coatings 6. Second grinding wheel 7. First grinding spindle 8. Second grinding spindle 9. First rotational drive device for the grinding spindle 10. Second rotational drive device for the grinding spindle 11 Center axis 15 Grinding engagement 20 Polishing coatings 21 Localized molding recess 30 segments of polishing coatings 31 Molded recess, overall width 32 workpieces HSS polishing coating thickness Width of BSS polishing coating vU peripheral speed RW Large Radius Workpiece rW Small Radius Workpiece RSS Large Radius Grinding Wheel rSS Small Radius Grinding Wheel A, B standards Z1, Z2, X CNC axis α1 Swivel angle of the first grinding spindle α2 Swivel angle of the second grinding spindle SS grinding wheel WS Workpiece D1 Small Radius Workpiece D2 Large Radius Workpiece Length of the conical part L

Claims

1. A grinding wheel (5, 6) for planar or conical grinding in the mass production of rotationally symmetric workpieces (2, 32), wherein the grinding wheel (5, 6) has an abrasive coating (20) on its outer circumference, Grinding wheels (5, 6), characterized in that the abrasive coating (20) in the width direction and / or radial direction has variations in specifications, and these variations are adapted to correspond to changes in each peripheral speed of at least the workpiece (2, 32) present during grinding.

2. A grinding wheel (5, 6) for planar or conical grinding in the mass production of rotationally symmetric workpieces (2, 32), wherein the grinding wheel (5, 6) has an abrasive coating (20) on its outer circumference, Grinding wheels (5, 6) characterized in that the polishing coating (20) has variable molding recesses (21, 31) at least in the width direction, and the molding recesses (21, 31) reduce their engagement length during grinding in the circumferential direction of the polishing coating (20) in accordance with the width of the polishing coating, thereby reducing the amount of material removed so that the average specification of the width of the polishing coating changes at least with respect to the polishing coating (20) and the molding recesses (21, 31) along with the respective circumferential speeds of the workpieces (2, 32).

3. The specifications of the polishing coating (20) are characterized in that they are adapted to the peripheral speed of at least the workpiece (2, 32) which varies over the width of the polishing coating (20), with respect to the hardness of the abrasive grains and / or the size and / or shape of the abrasive grains and / or the concentration and / or bonding of the abrasive material, according to claim 1 or 2, the grinding wheel (5, 6).

4. The grinding wheel (5, 6) according to claim 2, characterized in that the molded recesses (21, 31) increase in the width direction of the polishing coating (20) with respect to their cross-sectional size, at least when the peripheral speed of the workpiece (2, 32) is low.

5. The grinding wheel (5, 6) according to any one of claims 1 to 4, characterized in that the specifications of the polishing coating (20) and / or the molded recesses (21, 31) at a specific peripheral speed are adapted to a material removal amount that varies over the width of the polishing coating (20) corresponding to one specific peripheral speed.

6. The grinding wheel (5, 6) according to claim 5, characterized in that the specifications and / or the variation of the molded recesses (21, 31) over the width of the abrasive coating (20) are adapted to a linear change in the amount of material removed from the workpiece (2, 32).

7. The grinding wheel (5, 6) according to any one of claims 2 to 6, characterized in that the molded recesses (21, 31) within the polishing coating (20) are designed to be rectangular, trapezoidal, triangular, polygonal, rounded, or elliptical in shape, having straight or curved side walls.

8. The grinding wheel (5, 6) according to any one of claims 2 to 7, characterized in that the molded recesses (21, 31) are filled with a filler or binder and do not contain abrasive particles.

9. The grinding wheel (5, 6) according to any one of claims 1 to 8, characterized in that the polishing coating (20) is formed from a plurality of segments (30) bonded to the grinding wheelbase body (5, 3).

10. The grinding wheel (5, 6) according to any one of claims 1 to 9, characterized in that the above specifications and / or the molded recesses (21, 31) are adapted to the effective surface area (3.1, 3.2) of the workpiece (2, 32), which is a brake disc (3).

11. The grinding wheel (5, 6) according to any one of claims 1 to 10, characterized in that the polishing coating (20) has a crown shape or concave shape within the micrometer range with respect to rotational symmetry.

12. The grinding wheel (5, 6) according to any one of claims 1 to 11, characterized in that the polishing coating (20) has CBN or diamond as an abrasive.

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