Abrasive wheel for the planar and conical grinding of difficult-to-machine materials on rotationally symmetrical workpieces

Abstract

The invention relates to an abrasive wheel (5, 6) which is intended for the planar or conical grinding of rotationally symmetrical workpieces (3) for large-scale manufacturing and on which the abrasive coating (20) has, in the width direction and / or radial direction, a variation in specification adapted correspondingly to the variation in the respective circumferential speed which at least the workpiece (3) undergoes during the grinding operation. A second aspect of the invention provides for an abrasive wheel (5, 6) which is intended for the planar or conical grinding of rotationally symmetrical workpieces (32) for large-scale manufacturing and on which the abrasive coating (20) has, at least in the width direction, varying shaped recesses (31), so that the concentration of abrasive material is adapted to the respective circumferential speed by the shaped recesses (31) varying over the width BSS of the abrasive coating (20), and so there is a variation in the average specification of the abrasive material corresponding to the respective circumferential speed.

Description

[0001] GRINDING WHEEL FOR PLANE-SIDE AND TAPER-SHAPED GRINDING OF DIFFICULT-TO-MACHINE MATERIALS ON ROTATIONALLY SYMMETRICAL WORKPIECES

[0002] The invention relates to a grinding wheel for flat and conical grinding of difficult-to-machine materials on rotationally symmetrical workpieces.

[0003] In addition to achieving high levels of accuracy when grinding workpieces, unit costs play a major role, particularly for large-scale production. It is often the case that workpieces requiring lower or more moderate levels of accuracy are better suited for large-scale production. The more precisely the workpieces must be ground, the higher the unit costs will logically be. This discrepancy between quality and manufacturing costs, especially for large-scale production, becomes greater the more difficult the workpieces are to grind. This is especially true for workpieces with coatings or materials with high cutting resistance, which contain at least a portion of tungsten carbide, silicon carbide, or titanium carbide, for example.These carbide components mean that the surfaces to be ground on the workpiece are very hard and are therefore more difficult to grind than normal materials such as steels hardened using conventional processes.

[0004] It has now been shown that the unit costs, especially for workpieces that must be ground with high precision, are largely determined by the tool costs. In the present case, this means that the grinding wheel for grinding the above-mentioned hard coatings or materials of the workpieces represents a very significant proportion of the total cost of a workpiece to be ground. The above-mentioned very hard materials or coatings of the workpieces that have a high grinding resistance relate, for example, to brake discs, which have wear-resistant coatings, for which grinding wheels specially designed for these applications must be used. It goes without saying that such special grinding wheels also have higher costs than grinding wheels that can be used for, for example, hardened materials.In addition to the costs for grinding wheels, another component of manufacturing costs is the cost of dressing tools and the actual dressing process between grinding operations. The sooner a grinding wheel wears out, the more frequently it needs to be dressed. Optimization is always required between the grinding wheel material, the so-called specification, and the dressing and the accuracy to be achieved in the ground workpieces with regard to overall costs. It is understood that reducing the manufacturing costs of the workpieces can correspondingly increase the profit margin for produced or ground workpieces.

[0005] Both the flat and the conical, rotationally symmetrical areas of the workpieces to be ground are ground with their circumferential end faces, as is the case with the aforementioned brake discs. The disadvantage here is that the grinding coating, which extends across the thickness of the grinding wheel, essentially with a constant specification, must achieve varying grinding removal rates due to the changing circumferential speed, particularly of the workpiece, in the radial direction. As a result, the grinding wheel has changed grinding engagement conditions in the radial direction of the workpiece section to be ground and thus also realizes or exhibits changed cutting volumes.

[0006] The grinding areas referred to here as difficult-to-machine materials of rotationally symmetrical workpieces in the context of the invention refer to workpieces that have a difficult-to-machine material as their base material, as well as to workpieces that have a special coating in the grinding area that is difficult to machine. Both embodiments are to be understood here as difficult-to-machine materials of rotationally symmetrical workpieces.

[0007] The grinding wheel, which is brought into grinding engagement with the workpiece, such as a brake disc, via its peripheral side, creates a so-called peripheral grinding pattern on the workpiece to be ground. This pattern of grinding marks runs radially around the flat side. This shape of grinding marks is often desired on the finished, ground workpiece, but is not mandatory.

[0008] In principle, grinding wheels for grinding difficult-to-machine materials are more expensive than grinding wheels for normally hard materials, so that the manufacturing costs of workpieces with such difficult-to-machine coatings or made of such material are associated with higher manufacturing costs.

[0009] For example, the Krebs & Riedel product catalog (KCD-101 / 2010) for surface grinding, i.e., the plane-parallel machining of surfaces with a disk circumference such as those used for brake disks, refers to grinding specifications made of CBN and diamond for good stock removal rates due to so-called high-hardness iron and steel alloys or brittle-hard materials. In particular, it is pointed out that the abrasive grain can be used as an abrasive in one form of the grinding specification with irregular edges, in blocky form, in pointed form, or as synthetic diamond grains. If, for example, workpieces with flat sides and diameter ranges are to be ground, this prior art describes that the tool can have different specifications for, for example, two-zone grinding, whereby different cutting volumes due to peripheral speed are not mentioned, i.e., not described.

[0010] Winter's catalog number 1, "Automotive, Turbines, Roller Bearings," points out that workpieces that are difficult to grind are particularly those that have mixed materials, at least on their surfaces, such as brake pads. It also points out that the bonds for the abrasive grains are specially designed and adapted for the respective application. When grinding brake pads, it is pointed out that extremely high grain retention force and a high degree of grain clearance must be ensured. The different cutting volumes caused by different peripheral speeds of the workpieces to be ground, particularly the flat areas, are not mentioned in the specifications of the grinding tools themselves for special applications.

[0011] The object of the present invention is to provide a cost-effective solution for grinding, particularly for large-scale production, disc-shaped or rotationally symmetrical workpieces whose grinding area consists of difficult-to-machine materials or coatings. Part of the objective is to optimize or reduce the tool costs per workpiece, i.e., the manufacturing costs of the tool per workpiece. It is understood that these optimizations should essentially be suitable for many workpieces and not be limited to, for example, brake discs.The optimized grinding tools should be adapted to the various areas of grinding engagement of the flat sides and thus of the grinding surface in such a way that, regardless of the peripheral speed of the workpiece to be ground, optimized grinding conditions or machining volumes can be achieved for the particularly difficult-to-machine material to be ground. A key part of the object of the invention is to provide a grinding wheel that combines high grinding quality, great stability, and a low purchase price suitable for large-scale production. In terms of accuracy, the grinding wheel should always be able to reliably maintain tolerances in its grinding engagement area, i.e., in its effective range, with regard to its thickness, axial runout, the quality of the flatness of the surfaces, and the required dimensional tolerances.The thickness tolerance should be < 8 to 10 pm, for example, if plane-parallel outer surfaces of workpieces are to be ground. This level of accuracy is particularly important when grinding brake discs or brake disc-like workpieces, for example, because deviations from the specified thickness tolerance range can result in pulsating braking effects across the circumference of the brake disc. This must be avoided or is not permitted under safety requirements when braking and generating the braking force.

[0012] This object is achieved with a grinding wheel having the features according to claim 1 and with a grinding wheel having the features according to claim 2. Appropriate further developments are defined in the respective dependent claims.

[0013] According to a first aspect of the invention, a grinding wheel is described which is suitable for the flat-side or conical grinding of rotationally symmetrical workpieces for large-scale production. The grinding wheel has an abrasive coating on its outer circumference, i.e., on its circumferential side, which, according to the invention, has a varying specification in the width direction and / or in the radial direction. The specification changes and is adapted accordingly to the respective peripheral speeds present during grinding, at least of the workpiece. In the context of this invention, specification is understood to mean the specification of the abrasive coating with regard to abrasive grain hardness, abrasive grain size, abrasive grain shape, abrasive concentration, abrasive bond, and abrasive type.When grinding flat surfaces, when the grinding surfaces of the grinding wheel are in contact with the flat surfaces of the workpiece to be ground, different peripheral speeds are present across the grinding width, i.e. across the width or thickness of the grinding wheel and thus the width of the grinding layer, which, with a constant specification of the grinding layer, has different grinding conditions and thus different cutting volumes for each different peripheral speed.This not only means that a grinding wheel can wear out excessively quickly in the areas where the greatest load is present and the largest chip volume is removed, but it also makes the grinding wheel unnecessarily expensive because the grinding surface is designed for the highest chip volume and thus the highest load for the grinding wheel in all grinding areas, whereas in areas with lower peripheral speeds, at least of the workpiece, there is only a lower load on the grinding wheels or the grinding surface.When difficult-to-machine materials have to be ground for the workpiece or for its coating, high grinding forces occur on the two active surfaces of a brake disc, for example, when the grinding wheel engages in these areas. These grinding forces can be compensated for in the direction of the longitudinal axis of the brake disc, for example, by grinding both surfaces simultaneously with respective grinding wheels, so that the grinding forces in the axial direction of the workpiece essentially compensate each other. In particular, in the case of the coated and extremely wear-resistant active surfaces on a brake disc, the coating or the design of the brake disc with such extremely wear-resistant layers results in high-strength surfaces that are difficult to machine. This means that each grinding wheel must apply relatively high grinding forces in the axial direction of the workpiece.However, if a separate grinding wheel engages each effective surface on each side of the brake disc during grinding, the high grinding forces in the axial direction of the workpiece can be absorbed and compensated. By using a grinding wheel on each flat surface of the brake disc, the resulting grinding forces are minimized, as are the grinding times, thus achieving a more favorable cost structure, especially for large-scale production. A water-soluble grinding emulsion is preferably used as a cooling lubricant for grinding, although grinding oil can also be used as a cooling lubricant.

[0014] According to a second aspect of the invention, a grinding wheel is provided which is used for the flat-side or conical grinding of rotationally symmetrical workpieces, also for large-scale production, and is designed with an abrasive coating on its outer circumference, which is particularly suitable or designed for grinding materials that are difficult to machine or coatings on the surface of the workpiece to be ground.

[0015] According to the invention, a grinding coating is provided on the flat sides, i.e., on the circumference of the grinding wheel, which according to the invention has shaped recesses that vary in the width direction. These shaped recesses are arranged in the circumferential direction of the grinding coating such that the engagement length of the grinding wheel during grinding contributes to reducing the metal removal volume in accordance with the grinding coating width. The average specification of the entire grinding coating width is adapted by the shaped recesses in the grinding coating to the circumferential speeds present at the respective peripheral speeds of at least the workpiece, based on the width of the grinding coating and on the surface of the workpiece to be ground, which extends in the radial direction.Average specification means that the mold recesses are either empty recesses in the abrasive coating or recesses in the mold containing abrasives, that there are no abrasives in the mold recesses, and that the mold recesses are filled with abrasives-free materials, such as a binding compound without abrasives. Depending on the size of the mold recesses, this results in a different average specification of the abrasive coating. Depending on the peripheral speed of at least the workpiece at the respective machining point, the machining volume is adjusted. The machining volume decreases if the mold recesses are larger in the respective width sections than in other sections of the abrasive coating width.

[0016] The specification of the abrasive coating preferably varies with regard to the abrasive to the respective peripheral speed of at least the workpiece with regard to the abrasive grain hardness and / or abrasive grain size and / or abrasive grain shape and / or abrasive concentration and / or abrasive bond, so that for the respective grinding conditions and respective materials the optimal abrasive specifications are directly adapted to the tool, the grinding wheel, and specifically to the peripheral speed of at least the workpiece present at the respective radial location.

[0017] Furthermore, the specifications and / or the shaped recesses of the grinding layer are preferably adapted to the respective peripheral speed to a respective cutting volume corresponding to these peripheral speeds, which changes across the width of the grinding layer. Thus, by changing the specification or adapting the specification of the grinding layer to the corresponding peripheral speed on the workpiece, it is ensured that the same or at least similar grinding conditions prevail across the entire width of the grinding layer, with the same or similar cutting volume in each case, so that the grinding layer of the grinding wheel can be optimally utilized, so that when dressing is required after a certain grinding time, the grinding layer can be dressed essentially evenly across the entire width. This reduces the dressing effort, i.e.the wear of the diamond dressing tool, and thus also contributes to reducing manufacturing costs.

[0018] Further preferably, the change in the specification of the grinding wheel or its shaped recesses, or the specification and the shaped recesses, across the width of the grinding coating is designed such that a linear or nearly linear change in the machining volume on the workpiece results. In order to achieve optimal machining volumes on the workpiece, adapted to the respective peripheral speed, the shaped recesses within the grinding coating are preferably rectangular, trapezoidal, triangular, polygonal, round, or oval with smooth or curved side walls. The shape of the shaped recesses has a direct influence on the average specification with regard to the peripheral speed prevailing at the respective radial sections, especially due to the fact that they are filled with abrasive-free materials such as bonding agents.

[0019] Preferably, another abrasive-free filler can be used for the mold recesses instead of a bonding material, wherein similar densities should be present between the filler or bonding material and the sections of the grinding coating provided with abrasive, whereby a direct influence on low-vibration grinding can be exerted.

[0020] Further preferably, the grinding coating is formed from segments which are glued to a grinding wheel base body, so that the production of the segments according to the different cutting volumes or the circumferential speeds corresponding to the respective cutting volumes are easier to produce than a self-contained ring which is applied to the outside of the grinding wheel base body and then fastened there.

[0021] It is understood that the specifications and / or the mold recesses are adapted to an effective surface of the workpiece, in particular a brake disc, as well as to its material.

[0022] Also included within the scope of this invention are designs of the grinding coatings in a spherical or concave shape, wherein this spherical or concave shape is designed in the micrometer range deviating from the rotationally symmetrical shape in terms of its size.

[0023] Preferably, the grinding coating is CBN and / or diamond abrasive with the appropriate bond.

[0024] Further advantages, design variants, and details of the present invention will now be described with reference to the following figures. The drawing shows: Figure 1 shows a basic arrangement of a brake disc and grinding wheels engaging its effective surface on both sides;

[0025] Figure 2 is a sectional view of a brake disc;

[0026] Figure 3 is a sectional view of a grinding wheel;

[0027] Figure 4 is a partial view of an arrangement according to Figure 1;

[0028] Figure 5 shows the grinding area on the brake disc in the direction of view Y according to Figure 4;

[0029] Figure 6 is a representation according to Figure 1 with the tool spindle omitted;

[0030] Figure 7 is a diagram illustrating the linear increase in the peripheral speed of the workpiece and grinding wheel;

[0031] Figure 8A is a schematic view of a grinding wheel on its circumference with shaped recesses of increasing size from right to left;

[0032] Figure 8B is a partial sectional view AA of the grinding wheel through the grinding coating with shaped recesses;

[0033] Figure 9A is a plan view of the flat side of the abrasive coating in the form of glued-on segments and shape recesses varying across the width;

[0034] Figure 9B is a sectional view BB of Figure 9A showing the mold recess extending across the width of the grinding coating or grinding wheel;

[0035] Figure 10 is a schematic view of an arrangement according to Figure 1, but with a

[0036] Grinding area spanning the front side of the brake disc for grinding chamfers;

[0037] Figure 11 shows a brake disc in plan view with ground grinding grooves in a defined direction; and Figure 12 shows an arrangement according to a second aspect of the invention, in which a rotationally symmetrical part with a conical section is ground with a grinding disc according to the invention.

[0038] Figure 1 shows, as a partial representation in plan view, a basic arrangement of a clamped workpiece in the form of a brake disc 3, the first and second active surfaces 3.1, 3.2 of which are ground on the flat sides by opposing grinding wheels 5, 6. A workpiece spindle 1, which, by means of a rotary drive 2 of the spindle, drives the brake disc 3 clamped in a clamping device 4 for the purpose of grinding. In Figure 1, in the plan view shown, to the right of the workpiece spindle 1 is a double arrangement of a first grinding spindle 7 and a second grinding spindle 8, which each carry a grinding wheel 5 or 6 with corresponding grinding pads 20. The first grinding wheel 5 and the second grinding wheel 6 are conical with respect to their circumferential surfaces and thus with respect to the grinding pad 20, so that when the grinding pads 20 engage plane-parallel on the active surfaces 3.1, 3.2 when arranged opposite one another, the respective grinding spindles 7, 8 are inclined at an angle cd or a2 with respect to the center line 11 running through the plane of rotation of the brake disc 3. The angles of inclination cd or a2 correspond to the cone angle of the grinding pads 20 engaging with the respective grinding disc 5, 6. In the position shown, the two grinding discs 5, 6 are in grinding engagement 15 on the respective opposite active surfaces 3.1, 3.2 of the brake disc 3. The grinding discs 5, 6 are arranged on the opposite flat sides of the brake disc 3, so that the grinding forces are compensated by the grinding discs 5, 6 arranged opposite one another in grinding engagement 15. The grinding spindle 7 represents the rotary drive 9 for the first grinding disc 5, whereas the rotary drive 10 drives the grinding spindle 9 and with it the second grinding disc 6 in rotation.The inclination angles cd of the first grinding spindle 7 and a2 of the second grinding spindle 8 relative to the center plane 11 are predetermined by the machine and are fixed angles. Typically, the angles cd and a2 are the same for both grinding spindles 7 and 8. However, in principle, depending on the different grinding tasks, it is also entirely possible for cd and a2 to be different, if this should be necessary for technical reasons.

[0039] In the arrangement shown in Figure 1, the axes of rotation of the first grinding spindle 7 and the second grinding spindle 8 are inclined with respect to the central axis 11 by an angle of, for example, 12°. This angle is a preferred arrangement in the grinding machine because it results in significant simplifications due to the interfering contours in the machine and the respective grinding headstocks can be made more rigid. In principle, it is also possible for the angles a1 = a2 = 0° as a special case. This would mean that the grinding wheels are designed as grinding wheels with cylindrical flat sides and, with regard to their arrangement, including the respective grinding coatings 20, are arranged at right angles to the plane of the active surfaces 3.1, 3.2 of the brake disc 3.

[0040] An arrangement of the grinding spindles 7, 8 with a negative pivoting angle a1, a2 would also be possible, provided there is a design requirement for this. Such an arrangement with negative pivoting angles a1, a2 is of course only possible to the extent that the grinding wheel does not touch the tool spindle 1. For such desired arrangements, it would also be conceivable, for example, for the first grinding spindle 7 to be arranged parallel to the central axis 11 with respect to the axis of rotation of its rotary drive 9 and to have a cylindrical grinding wheel 5 with flat sides, whereas the second grinding wheel 6 is pivoted via its second spindle 8 by means of a negative pivoting angle a2 as a conical disk, so to speak, into the axis of rotation, below the brake disc 3 to be ground.

[0041] Conventionally, the axis movements along CNC axes Z1, Z2 and X are controlled in at least partially interpolating motion.

[0042] Figure 2 shows a half-section of the basic shape of a brake disc 3 as a workpiece to be ground with a grinding disc according to the present invention. The brake disc 3 has a central bore 3.4, via which the brake disc 3 is centered on a vehicle. The brake disc 3 is screwed to the vehicle with its flat contact surface 3.5 on the flat side. For the corresponding screw connection, bores 3.3 for a screw connection are provided on the receiving flange of the brake disc 3 on the vehicle. The brake disc 3 shows the first active surface 3.1 and the second active surface 3.2, on which the brake blocks or brake shoes engage during braking and thereby generate the braking effect on the wheels. The active surfaces 3.1, 3.2 of the brake disc 3 are provided with a very hard and wear-resistant coating 3.6, 3.7 so that wear is minimized and the brake discs 3 have a correspondingly long service life.It is understood that instead of a wear-resistant coating, the brake discs can also be made of wear-resistant material in the area where the brake pads engage. The thicknesses of the wear-resistant coating 3.6, 3.7 are indicated by the respective dash-dotted lines with the reference numbers 3.6 and 3.7. Since the two active surfaces 3.1, 3.2 are also the two grinding areas with very hard and wear-resistant coatings on the brake disc 3, where the brake disc 3 is ground in these two areas, it follows that important dimensional accuracy dimensions must be maintained for the operation of the brake discs in order to avoid or at least significantly minimize vibrations, premature wear, and premature damage to these brake components during operation. The references A, B on the central bore 3.4 and on the flat contact surface 3.5 are important geometric manufacturing dimensions of the brake disc 3.This includes, on the one hand, the axial runout B and, on the other hand, the centricity A of the central bore 3.4. This axial runout is indicated by the reference number 3.8 in relation to the reference value B with the position tolerance. The accuracy of this axial runout of the effective areas 3.1, 3.2 is shown because of the movement path of the brake pads from the non-braking position to the braking position in engagement with the coatings 3.6, 3.7 of the brake disc 3. The thickness to be maintained is designated by d. In addition to the flat side tolerance, the parallelism of the two ground flat sides, i.e. the effective surfaces 3.1, 3.2, in these areas of the brake disc 3 is indicated by the reference number 3.9. For the brake disc to function reliably in the vehicle, the parallelism 3.9 of the two effective surfaces 3.1, 3.2 to one another is usually a maximum of 8 to 10 pm. The axial runout B and the parallelism 3.9 represent important parameters of the nominal dimensions of the brake discs 3, with the tolerance in the range of 20 to 25 pm. The values ​​given refer, as an example, to an outer diameter of the brake disc 3 shown of 350 mm. It is understood that these tolerances for normal steel do not represent the range to which precision can be achieved. However, it should be noted that the brake discs 3 are ground on their effective surfaces 3.1 and 3.2 are provided with very hard and wear-resistant coatings or consist entirely of such hard and wear-resistant materials, so that these tolerances represent a relatively great challenge when grinding, which is why brake discs are cut to these tolerances for cost reasons and their reliable function can still be fulfilled, so to speak as a compromise for carrying out the grinding operations in large-scale production, taking into account the extremely hard and difficult to grind coatings 3.6, 3.7 of the brake disc 3. For cost reasons, it is important to ensure that the output when grinding the workpieces per unit of time is as high as possible, ie the cycle times are as short as possible.

[0043] Figure 3 shows a sectional view of a grinding wheel, such as that used as the first grinding wheel 5 or second grinding wheel 6 according to Figure 1, for example. The grinding wheel 5, 6 is a vitrified bonded diamond grinding wheel 5, 6 which is suitable for grinding the two active surfaces 3.1, 3.2 of the brake disc 3. The grinding wheel 5, 6 has a centering bore 5.1 in its center, which serves to centrally hold the grinding wheel 5, 6 on a grinding spindle nose (not shown). The grinding wheel 5, 6 is attached to a flat side of the grinding spindle nose and is axially clamped by a grinding wheel flange over the two flat sides 5.2 of the grinding wheel 5, 6. The flat sides 5.2 arranged on the circumference of the grinding wheel 5, 6 are provided and drawn at the respective angle a1, a2 in the sense of the angle of inclination of the first grinding spindle 7 and the second grinding spindle 8.The base body 5.3 of the grinding wheel, which has a centering bore 5.1 inside, is generally made of an aluminum alloy, steel, or carbon with the aforementioned generally vitrified-bonded diamond grinding coating 5.4 on the circumference, wherein the thickness Hss of the grinding coating 5.4 has a wearable height of typically 5 to 8 mm. The width Bss of the grinding coating 5.4 represents the outer circumferential side of the grinding wheel 5, 6. Other parameters that are also important for accuracy and that must be observed with regard to the dimensions of the grinding wheel 5, 6 are the large radius Rss, which extends from the rotational axis of the grinding wheel 5, 6 to the outermost grinding coating tip, and the small radius rss, which extends from the rotational axis of the grinding wheel 5, 6 to the inner circumferential edge of the grinding coating 5.4.The specified dimensions of the grinding wheel 5, 6 are important for the grinding wheel according to the invention described below.

[0044] Figure 4 shows a further illustration of the arrangement for grinding a brake disc 3, shown in half section, which basically corresponds to the arrangement shown in Figure 1. The brake disc 3 is driven in rotation by means of a clamping device 4 on the workpiece spindle 1 with its rotary drive 2. Analogous to the radii rss and Rss of the grinding coating 20 of the grinding wheel 5, 6 described in Figure 3, the radii rw and Rw are entered here for the brake disc 3. The small radius rw, which in the radial direction of the brake disc 3 designates the inner end of its coating with the hard grinding coating 5.4, i.e. the active surfaces 3.1, 3.2, whereas the radius Rw extends from the axis of rotation of the brake disc 3 in the radial direction to its outer circumference. The rotation or the rotary drive 2 of the brake disc 3 clamped in the clamping device 4 as well as the perpendicular to the active surfaces 3.1, 3.2 The infeed movement to be performed in the grinding direction toward the flat sides of the brake disc 3 is realized via the CNC axes Z1 and Z2, respectively, on the grinding wheels 5, 6 engaged at the top and bottom of the brake disc 3 in the drawing, respectively, via the CNC axes Z1 and Z2. Additionally, the movement of the tool spindle 1 in the X direction is shown, which also represents a CNC axis and the infeed of the brake disc 3 into the grinding gap between the two grinding wheels 5, 6 for the flat sides of the brake disc 3. Figure 5 shows a partial view, the view “Y” according to Figure 4, in the direction of the longitudinal axis of the tool spindle 1, wherein the brake disc 3 with the clamping device 4 and the radii rw and Rw in their difference from one another show the flat sides to be ground, which are the active surfaces 3.1, 3.2 on the brake disc 3 and which are ground by means of the grinding wheel 6 in the specified area in the grinding engagement 15.Since the basic structure corresponds to that shown in Figure 1, only the elements required for direct explanation are shown in Figure 5 by the corresponding reference numbers.

[0045] Figure 6 again shows a partial sectional view of the first grinding wheel 5 and second grinding wheel 6 intended for engagement 15 on the active surfaces 3.1, 3.2 of the brake disc 3. All other parts and dimensions such as the radii, the pivot angles cd, a2 and the general arrangement basically correspond to those according to Figures 1, 3 and 4. Figure 6 further indicates that it is also possible to achieve different forms of crowning on the normally formed flat active surfaces 3.1, 3.2 by appropriate dressing of the grinding wheels 5, 6. This is also possible, however, in the case of a slightly concave design of the active surfaces 3.1, 3.2 of the brake disc 3. This crowning or concavity is conceivable in the micrometer range and is possible for certain applications.Such a shape of the grinding coating in order to produce the corresponding crowning or concavity on the brake disc 3 can be achieved by dressing both grinding wheels 5, 6.

[0046] Figure ? shows in principle how the peripheral speeds v of the grinding wheels SS 5, 6 and the peripheral speed v of the brake disc 3 behave during the grinding process. The different peripheral speeds lead to different grinding conditions on the flat surfaces to be ground, i.e., the active surfaces 3.1, 3.2 on the brake disc 3 and the workpiece WS, respectively. These different grinding conditions cannot be avoided, since this is a surface grinding task in which the peripheral speeds increase with the radius from the inside to the outside during rotation.

[0047] This embodiment assumes a brake disc outer diameter (effective area) of Dw = approx. 350 mm and an inner diameter (effective area) of dw = approx. 230 mm. As a rule, during grinding, the rotational speed of the brake disc 3 in the clamped state is a constant value for the entire workpiece. For the maximum, i.e., the large radius Rw = approx. 175 mm of the brake disc 3, a value of 100% is assumed. For the smaller radius rw = approx. 115 mm, the peripheral speed during grinding is then only approx. 65% of the value for the large radius Rw or the outer diameter at a constant workpiece rotational speed. The grinding allowance is essentially constant across the effective surfaces 3.1, 3.2 of the brake disc 3, so that for the machining volume per brake disc 3 that must be ground at the large radius Rw = approx. 175 mm, a value of 100% can be assumed on the front side of the grinding wheel. For the smaller radius rw = approx.115 mm, this value is then around 65% compared to the large radius with Rw = around 175 mm. The grinding allowance on the flat sides is assumed to be around 0.15 mm as an example. However, the grinding allowance can vary depending on the coating process. The same applies to the grinding wheel, which is normally or preferably a vitrified bonded diamond or CBN grinding wheel with a coating width of, for example, B = 65 mm (see position 5.4 / figure 3) for the above-mentioned diameter ratios of the brake disc 3. With a grinding wheel outer radius Rss = 250 mm, the cutting speed at the large radius Rss of the grinding wheel is 100%. With an approach angle of around 12° when grinding the active surfaces 3.1, 3.2 of the brake disc 3, the small grinding wheel radius is around rss = 237 mm. This diameter then corresponds to a diameter ratio of rss to Rss of approximately 95%.This ratio can then be applied to the difference in cutting speed to the same extent. Since the speed of the grinding wheel is constant for the entire grinding wheel, this ratio will set the cutting speed at the small radius of the brake disc 3 at 95% compared to the cutting speed at the large radius of the brake disc 3 at 100%. If the concentration of the abrasive grains in the grinding coating 5.4 of the grinding wheels 5, 6 is constant, the differences in the radii of the grinding wheel will result in different numbers of individual abrasive grains being in grinding contact per unit of time, i.e. the grinding conditions will change depending on the peripheral speed. It should be noted that at the small radius rw of the brake disc 3, only approximately 65% ​​of the cutting volume is generated on the tool, which means that the difference in this case is approximately 35%.

[0048] As shown, the grinding wheel 5, 6 generally operates at an angled cut, so that at the large diameter Rw of the workpiece, i.e., the brake disc 3, 5% of the grinding wheel diameter is missing relative to the grinding wheel. It can therefore be assumed that these 5% fewer abrasive grains are in grinding engagement for each grinding wheel revolution, assuming the same concentration of abrasive grains in the grinding coating. For this reason, these 5% must be subtracted from the approximately 35% difference in the metal removal volume on the brake disc 3 relative to the different diameters, resulting in a total difference in the variation in the abrasive concentration of approximately 30%.Due to the ratios of the radii of the brake disc 3 Rw / rw and the grinding wheels 5, 6 Rss / rss, it follows that across the width of the grinding layer 20 of the grinding wheel 5, 6, an adapted grinding wheel specification can be used for the grinding process at the small radius of the brake disc rw, since significantly less material needs to be removed per unit of time there than is the case at the large radius of the brake disc Rw. Based on the numerical values ​​given here, it can be seen that the value from the inclination of the grinding wheels 5, 6 by the angles a1 and a2 is significantly less significant, and for smaller inclinations, for example, at angles well below 10°, these angles can even be neglected.In principle, it can be assumed that the requirements for a workpiece to be ground during grinding with regard to dimensional tolerances, shape tolerances and surface requirements are identical on the entire respective effective surface 3.1, 3.2 of the brake disc 3, which is why it is possible to adapt or optimise the grinding wheel 5, 6 with regard to its specification in such a way that the specification can be adapted to the respective radius and thus to the respective peripheral speed on the effective surface 3.1, 3.2 of the brake disc 3. This dependency or this curve is shown in Figure 7, wherein the peripheral speed of the brake disc 3 runs linearly between the two radii Rss and rss, i.e. decreasing from Rss to rss. Since the peripheral speed relates to the machining volume per unit time across the effective surfaces 3.1, 3.2 of the brake disc 3 behaves proportionally, this is also to be equated with the load on the grinding wheel 5, 6 due to the respective machining operation. During the grinding process, the load in the respective grinding area varies relatively greatly due to the aforementioned parameters, so that optimizing the grinding wheel with regard to its specification enables appropriate load compensation. In addition, the grinding wheel geometry can be used to adapt the grinding wheel to the respective grinding areas. This also makes it possible to adapt the manufacturing costs of the grinding wheel to the respective conditions / technical requirements with regard to the respective machining volume in the respective area of ​​the grinding zone, as well as to the required dimensional, shape and surface requirements and accuracies in the grinding zone.This can be achieved by deliberately varying the shape of the abrasive grains across the grinding zone of the grinding wheel, by deliberately varying the concentration of the abrasive across the grinding zone of the grinding wheel, specifically with regard to the aforementioned overall difference of approximately 30%, by deliberately varying the bond of the abrasive used across the grinding zone of the grinding wheel, and by deliberately introducing structures into the grinding coating of the grinding wheel via the grinding zone. These variations can be individually considered or varied in the grinding wheel according to their respective properties, but they can also be combined appropriately with one another to vary the grinding properties of the grinding wheel accordingly with regard to the metal removal rate or the varying peripheral speed.

[0049] Through targeted variations, a technologically / price-optimized grinding wheel can be manufactured and used with regard to the technically required parameters.

[0050] The following are explanations of the individual variation options for the abrasive as described above. a) With regard to a targeted variation of the shape of the abrasive grains across the grinding zone of the grinding wheel 5, 6, it should be noted that, for manufacturing reasons, it is possible to change the shape of the abrasive grains in the grinding area across the grinding wheel engagement width. The shape of the grinding wheels refers to their size, sharpness of edges, and shape, for example, whether the abrasive grains are more elongated, more angular, or more rounded. With regard to the variation of the abrasive grains, which is adapted to the respective peripheral speeds and the respective metal removal volume at the grinding engagement points, it should be noted that this has a significant influence on the service life of the grinding wheel, for example between dressing intervals or with regard to the surface quality to be achieved during grinding.If the service life of the grinding wheel can be extended, this will have a positive impact on the tool costs per ground workpiece. b) It is also possible to specifically vary the concentration of the abrasive across the grinding zone of the grinding wheel in such a way that it is adapted to the respective metal removal volume per unit of time in the respective grinding zone. This means that the distribution of the concentration is designed in such a way that the area of ​​the grinding wheels 5, 6 with the greatest metal removal volume per unit of time also has the highest concentration of abrasive and that the area with the lowest metal removal volume per unit of time has the lowest concentration of abrasive. This means that the abrasive coating 20 is produced differently across the grinding width depending on the peripheral speed vu and the desired size of the metal removal volume.The adjustment of the abrasive concentration can be changed linearly or almost linearly across the width of the grinding layer 20, which is advantageous in view of the fact that the peripheral speed of at least the workpiece also changes linearly. This different formation of the abrasive concentration therefore leads to a grinding wheel that is optimized for the grinding process in relation to the respective metal removal volume per unit of time in each grinding area. It should be noted that the CBN or diamond grinding wheels generally used are relatively expensive, so that the measure of adjusting the abrasive concentration can reduce the manufacturing costs of the grinding wheels and thus also reduce the tool costs per manufactured workpiece.In addition, a grinding wheel design with a varying concentration of abrasive offers a further advantage in that with a lower concentration of abrasive in the grinding wheel, the dressing tools also wear to a lesser extent, so that the wear of the diamond dressing wheels is also reduced with this optimization of the grinding wheel, which leads to a further cost advantage in terms of tool costs. This is particularly important for large-scale production tailored to the specific task. c) A further variation of the abrasive is possible indirectly by varying the bond of the abrasive across the grinding zone of the grinding wheel. On the one hand, the bond in the grinding layer should be as open as possible so that the abrasive grains can be incorporated in such a way that they are held accordingly in the grinding layer 20.These requirements represent one orientation for the variation of the abrasive bond. However, adjustments can also be made to the type of bond. This means that this adjustment relates to the optimal design of the grinding process and the metal removal rate per unit of time, and the bond or bond material is adapted accordingly. Regarding the openness of the bond, it should be noted that this can be influenced by appropriate compression of the grinding wheel coating during its production. The higher the compression pressure, the narrower the pores become, which leads to a lower porosity.d) In addition to the concentration of abrasive and bond in the sense of a variation of the abrasive in relation to the peripheral speed and thus to the metal removal rate, it is also possible to achieve this variation indirectly by introducing open or closed structures into the abrasive coating via the grinding zone into the grinding wheel. This means that the structures affect shaped recesses in the abrasive coating so that less abrasive is brought into contact in the grinding direction, relative to the circumference. This can also be achieved by filling the shaped recesses without abrasive, by filling these recesses with a bond, for example, so that the grinding wheel still has a closed abrasive coating, but there is no grinding effect in places where the shaped recesses are filled.In the grinding direction along the circumference of the grinding wheels, a different average abrasive concentration is achieved depending on the size of the shaped recesses, whether open or closed. One such example of the shaped recesses 21 is shown in Figures 8A and 8B. In this exemplary embodiment, the average concentration of abrasive formed across the width Bss of the grinding layer 20 in the grinding direction, i.e., in the circumferential direction, ensures that the continuity of abrasive in the grinding layer 20 is interrupted. These shaped recesses 21 can be freely selected in their shape, i.e., they can be round, oval, trapezoidal, or other shapes, deviating from the shapes shown in Figure 8A.In Figure 8A, the mold recesses 21 or cutouts are shown in rectangular form and vary in size in such a way that they increase in size from right to left in the drawing, so that the average concentration of abrasive decreases from right to left across the width Bss of the abrasive coating 20 of the grinding wheel 5, 6. These mold recesses 21 can be open, as shown in the sectional view AA in Figure 8B, but they can also be formed by filling them with a corresponding abrasive-free material, which can also be simply a bonding material without an abrasive.

[0051] According to Figure 8B, it can be seen that, in a special embodiment, the shaped recesses 21 can also be formed over the full thickness Hss of the grinding coating 20, i.e., extend to the base body of the grinding wheel 5, 6. Further advantages of these shaped recesses 21 are that the grinding pressures are kept almost constant during grinding and that cooling lubricant can be carried along in the shaped recesses 21, which also form pockets, and can be evenly directed to the respective grinding points.

[0052] Figures 9A and 9B show a further embodiment in which the commonly used abrasive version in the form of CBN and diamond abrasives is used. The abrasive coating 20 is formed from individual segments 30, between which, when glued to the circumferential side of the grinding wheel 5, 6, shaped recesses 31 are formed, which extend in variable width essentially over the width of the abrasive coating Bss and thus of the grinding wheel 5, 6. Based on the design shown in Figure 9A, which is illustrated in section BB in Figure 9B, it can be seen that the shape of the shaped recesses 31 is freely selectable and can extend and vary over the width Bss of the grinding wheel 5, 6 as well as over the thickness Hss of the abrasive coating.Due to the described variation, the respective cutting volume can be adapted to the respective grinding conditions via the grinding wheel width and thus via the peripheral speed. In principle, it is also possible for the boundary surfaces of the mold recesses 31 to be curved rather than straight, unlike what is shown in Figure 9A.

[0053] As already explained in connection with Figures 8A and 8B, the mold recesses 31 can either be filled with abrasive-free filling material or can be designed open in the sense of pockets, so that when, for example, cooling lubricant is supplied, cooling lubricant is available in these pockets and can be fed to the remaining areas where the grinding process is carried out directly during grinding.

[0054] Overall, it can be stated that the individual optimization measures with regard to the variation of the abrasive within the grinding coating 20 in the circumferential direction of the grinding wheel and / or in the transverse direction thereto must be adapted not only individually, but also in respective combinations with one another in order to realize the variation of the abrasive to the respective grinding areas of the grinding wheels or the workpiece to be ground.

[0055] Figure 10 shows a further embodiment of the grinding wheel, with otherwise basically the same structure as, for example, according to Figure 1. The only difference is that the grinding coating 20 on the grinding wheels 5, 6 is profiled in such a way that during the grinding of the flat sides of the brake disc 3, i.e. the active surfaces 3.1, 3.2, the chamfers present on the outer circumference of the brake disc 3 are also ground, so that the grinding of the flat sides 3.1, 3.2 and the chamfers are ground in a kind of plunge grinding during one grinding process.

[0056] Figure 11 shows that the workpiece, designed as a brake disc 3, as depicted, for example, in Figures 1 and 4, performs a pendulum motion in the direction of the X-axis with the X-axis in the form of a CNC drive axis, so that the groove direction as a surface structure can be specifically influenced during grinding on the finished workpiece / can be achieved almost arbitrarily and can be adjusted via the grinding program. A corresponding groove pattern, which can be easily created using such an arrangement, is shown as an example in Figure 11.

[0057] And finally, for the sake of simplicity, Figure 12 shows the grinding of a conical section of a rotationally symmetrical workpiece 32 with its length L, which can be ground with a conical grinding wheel 5, 6, wherein the grinding wheel 5, 6 is movable via CNC axes X and Z. For such conical sections to be ground, analogous to the grinding of the flat sides 3.1, 3.2 of brake discs 3, the grinding situation for the individual grinding areas varies depending on the respective different peripheral speed vu, so that the grinding wheel 5, 6 according to the invention with the grinding coating 20 can also be used here in analogy to the adaptation of the abrasive or the grinding specifications of the grinding coating to the desired machining volume. The workpiece has a section with a smaller diameter D1 and a section with a larger diameter D2.It bears the reference number 32, all other reference numbers are already mentioned in the previous figures and the associated description, so that a further explanation in this regard is omitted here.

[0058] List of reference symbols

[0059] 1 workpiece spindle Hss thickness grinding pad

[0060] 2 Rotary drive Workpiece Bss Width Grinding pad

[0061] 3 Brake disc / workpiece vu peripheral speed

[0062] 3.1 first effective area Rw large radius workpiece

[0063] 3.2 second effective area r w small radius workpiece

[0064] 3.3 Bore Rss large radius grinding wheel

[0065] 3.4 Central bore Tss small radius grinding wheel

[0066] 3.5 Plan contact surface A, B references

[0067] 3.6 Coating first effective surface Z1, Z2, X CNC axes

[0068] 3.7 Coating second effective surface a1 Swivel angle first grinding

[0069] 3.8 Axial runout of the spindle

[0070] 3.9 Parallelism effective area a2 swivel angle second

[0071] 4 Grinding spindle clamping device

[0072] 5 first grinding wheel SS grinding wheel

[0073] 5.1 Central bore grinding wheel WS workpiece

[0074] 5.2 Flat sides grinding wheel D1 small diameter

[0075] 5.3 Grinding wheel base body workpiece

[0076] 5.4 Grinding pad D2 large diameter

[0077] 6 second grinding wheel workpiece

[0078] 7 first grinding spindle L length cone piece

[0079] 8 second grinding spindle

[0080] 9 first rotary drive grinding spindle

[0081] 10 second rotary drive grinding spindle

[0082] 11 Central axis

[0083] 15 Grinding intervention

[0084] 20 grinding pad

[0085] 21 Mold recess local

[0086] 30 segments grinding pad

[0087] 31 mold recess entire width

[0088] 32 Workpiece

Claims

CLAIMS 1. Grinding wheel (5, 6) for the flat-side or conical grinding of rotationally symmetrical workpieces (2, 32) in large-scale production, with a grinding coating (20) on its outer circumference, characterized in that the grinding coating (20) has a change in specification in the width direction and / or radial direction which is adapted to the change in the respective circumferential speed of at least the workpiece (2, 32) present during grinding.

2. Grinding wheel (5, 6) for the flat-side or conical grinding of rotationally symmetrical workpieces (2, 32) in large-scale production with an abrasive coating (20) on its outer circumference, characterized in that the abrasive coating (20) has shaped recesses (21, 31) which change at least in the width direction and which, in the circumferential direction of the abrasive coating (20), reduce its engagement length during grinding in accordance with the width of the abrasive coating in such a way as to reduce the machining volume that their average specification with regard to the abrasive coating (20) and shaped recesses (21, 31) changes with the respective circumferential speed of at least the workpiece (2, 32).

3. Grinding wheel (5, 6) according to claim 1 or 2, characterized in that the specification of the abrasive coating (20) with regard to abrasive grain hardness and / or abrasive grain size and / or abrasive grain shape and / or abrasive concentration and / or abrasive bond is adapted to the circumferential speed of at least the workpiece (2, 32) changing across the width of the abrasive coating (20).

4. Grinding wheel (5, 6) according to claim 2, characterized in that the shaped recesses (21, 31) increase in terms of their cross-sectional sizes in the width direction of the grinding coating (20) at lower peripheral speeds of at least the workpiece (2, 32).

5. Grinding wheel (5, 6) according to one of claims 1 to 4, characterized in that the specification and / or shaped recesses (21, 31) of the grinding coating (20) of the respective peripheral speeds are adapted to a respective cutting volume corresponding to these peripheral speeds, which changes across the width of the grinding coating (20).

6. Grinding wheel (5, 6) according to claim 5, characterized in that the change in its specification and / or its shaped recesses (21, 31) across the width of the grinding coating (20) is adapted to a linear change in the cutting volume on the workpiece (2, 32).

7. Grinding wheel (5, 6) according to one of claims 2 to 6, characterized in that the shaped recesses (21, 31) within the grinding coating (20) are rectangular, trapezoidal, triangular, polygonal, round or oval with smooth or curved side walls.

8. Grinding wheel (5, 6) according to one of claims 2 to 7, characterized in that the mold recesses (21, 31) are filled with a filler or with binding material and are free of abrasive grains.

9. Grinding wheel (5, 6) according to one of claims 1 to 8, characterized in that the grinding coating (20) consists of segments (30) which are glued onto a grinding wheel base body (5.3).

10. Grinding wheel (5, 6) according to one of claims 1 to 9, characterized in that the specification and / or the shaped recesses (21, 31) are adapted to an active surface (3.1, 3.2) of the workpiece (2, 32), in particular a brake disc (3).

11. Grinding wheel (5, 6) according to one of claims 1 to 10, characterized in that the grinding coating (20) is crowned or concave in the micrometer range compared to the rotationally symmetrical shape.

12. Grinding wheel (5, 6) according to one of claims 1 to 11, characterized in that the grinding coating (20) has CBN or diamonds as the abrasive.

Images