Method for dressing a grinding tool for grinding a gear or profile of a workpiece

Abstract

The invention relates to a method for dressing a grinding tool (1) for grinding a gear or a profile of a workpiece, in which method at least one abrasive surface (2) of the grinding tool (1) is profiled by means of a dressing tool (3) in that a dressing region (4) of the dressing tool (3) is guided at a path speed (vfd) over the abrasive surface (2) of the grinding tool (1) in such a way that the abrasive surface (2) is profiled over a predetermined radial height (r), and wherein both the grinding tool (1) and the dressing tool (3) rotate at respective speeds. In order to make it possible to adjust orIn order to achieve a targeted, location-dependent influence on the surface roughness of the tooth flanks ground with the grinding tool, the invention provides that the dressing tool (3) is guided over the abrasive surface (2) at a variable path speed (vfd) relative to the grinding tool (1) during dressing and / or that the dressing takes place with a ratio of the speeds of the grinding tool (1) and the dressing tool (3) that varies over the radial height (r).

Description

[0001] The invention relates to a method for dressing a grinding tool for grinding a gear or a profile of a workpiece, in which at least one abrasive surface of the grinding tool is profiled by means of a dressing tool in that a dressing region of the dressing tool is guided at a path speed over the abrasive surface of the grinding tool in such a way that the abrasive surface is profiled over a predetermined radial height, and wherein both the grinding tool and the dressing tool rotate at respective speeds.

[0002] In order to influence the process behavior and the work result in grinding processes, in addition to the selection of the grinding wheel specification and the process control variables, the dressing parameters in particular are changed in order to create a grinding wheel topography adapted to the grinding task.

[0003] When dressing a generic grinding tool, such as a grinding wheel, using a dressing roller, both the grinding tool and the dressing roller rotate during the dressing process. At the contact point between the dressing area of the dressing roller and the abrasive surface of the grinding tool, a ratio of the peripheral speeds therefore exists. Furthermore, since the dressing area must be gradually guided along the abrasive surface of the grinding tool in order to gradually profile the abrasive surface completely, a feed rate is used here that results in a corresponding degree of coverage (for the definition of the degree of coverage, please refer to the explanation of Fig. 2). The higher the degree of coverage, the finer the abrasive surface to be profiled is formed.

[0004] The dressing parameters (dressing coverage ratio, peripheral speed ratio, dressing infeed amount) are specified based on empirical values, whereby the fineness of the profiling of the abrasive surface (which is required for the respective grinding task - roughing or finishing) is of corresponding importance.

[0005] Due to the curvature of the grinding wheel profile and the varying grinding wheel diameter due to the profile height, varying contact and engagement conditions occur across the active grinding wheel width during profile grinding of gears, which cannot be adjusted by process control during grinding. As a result, among other things, the roughness on the tooth flank varies. In discontinuous tooth flank profile grinding, this roughness is usually lower at the tooth root than in the area of the tooth tip due to the larger local profile pitch (i.e. the locally lower pressure angle) as well as the larger active grinding wheel diameter and the consequent higher grinding wheel peripheral speed. In some cases, the Ra value is considerably lower at the tooth root than at the tooth tip. The uneven grinding wheel load during grinding also results in inhomogeneous wear on the grinding wheel.

[0006] The invention is based on the object of developing a method of the type mentioned above in such a way that it is possible to achieve an equalization and / or a targeted, location-dependent influence of the local engagement conditions during the grinding of tooth flanks. In this way, the surface roughness on the tooth flank is to be locally influenced and, in particular, adjusted. Furthermore, it is to be possible to also locally control the grinding wheel load and thus specifically influence the grinding wheel wear behavior. This should be possible, in particular, without specially designed grinding and dressing tools. The method should therefore be feasible without special equipment, in particular on typical profile grinding machines.

[0007] The solution to this problem by the invention is characterized in that the dressing tool is guided over the abrasive surface at a variable path speed relative to the grinding tool during dressing and / or that the dressing is carried out with a ratio of the rotational speeds of the grinding tool and the dressing tool that varies over the radial height.

[0008] The aim is to achieve a predetermined profile for the dressing ratio and / or the ratio of the peripheral speeds of the grinding tool and dressing tool, particularly through the radial height of the abrasive surface. Furthermore, the proposed approach can achieve a predetermined profile for the resulting maximum single-grain chip thickness during grinding.

[0009] Only the path speed can be specified as a variable course.

[0010] Alternatively, a variable curve can be specified only for the ratio of the speeds of the grinding tool and the dressing tool.

[0011] But the combination is also possible, ie a variable course can be specified for both the path speed and the ratio of the speeds of the grinding tool and the dressing tool.

[0012] According to a preferred embodiment of the invention, the variable path speed is selected such that a defined profile is achieved for the dressing coverage over the radial height of the abrasive surface.

[0013] It can also be provided that the variable ratio of the speeds of the grinding tool and the dressing tool is selected in such a way that a defined curve is achieved for the ratio of the peripheral speeds of the grinding tool and the dressing tool over the radial height of the abrasive surface.

[0014] Finally, it is also advantageous if the method is characterized in that the defined course of the dressing coverage and / or the defined course of the ratio of the peripheral speeds of the grinding tool and dressing tool is specified in such a way that a defined course is achieved via the radial height of the abrasive surface for the resulting maximum single grain chip thickness during grinding.

[0015] The grinding tool is preferably a grinding wheel.

[0016] The dressing tool can be a form roller that rotates around a rotational axis during dressing. The dressing area of the dressing tool can have the shape of a circular segment in radial section.

[0017] Since dressing conditions vary across the grinding wheel width, an inhomogeneous grinding wheel topography arises, which, in addition to the varying grinding conditions, leads to a local influence on the grinding conditions. Due to the large profile pitch in the tooth root area, for example, significantly lower dressing amounts are available here. Furthermore, the varying grinding wheel diameter across the grinding wheel width leads to a continuous change in the dressing speed ratio.

[0018] Unlike profile grinding, the path feed rate and the rotational speeds of the grinding wheel and dressing roller can be adjusted depending on the location in path-controlled form dressing with a dressing roller, which is what the present invention takes advantage of. Accordingly, the dressing parameters can be adjusted depending on the location to specifically influence the surface roughness of profile-ground tooth flanks.

[0019] Regarding the mentioned degree of coverage, it should be noted that this is defined as the ratio between the effective width of the dressing tool in relation to the feed of the dressing tool per revolution of the grinding tool (see the explanations in connection with Fig. 2). The degree of coverage indicates how often a point on the grinding wheel surface is covered by the effective cutting edge width of the dressing tool.

[0020] The drawing shows embodiments of the invention. Fig. 1 shows schematically how a grinding tool in the form of a grinding wheel is dressed with a dressing tool in the form of a dressing roll, Fig. 2 shows schematically (here for a cylindrical grinding surface) how a degree of coverage is obtained during dressing, Fig. 3 shows schematically an enlarged section of Fig. 1, where the dressing tool is shown in two different positions, Fig. Figure 4 shows an example of the local dressing conditions, where the flank-related dressing infeed (ΔS d ), the dressing coverage ratio (U d ) and the speed ratio between grinding tool and dressing tool (q d ) is illustrated over the profile in the width direction (X), Fig. Figure 5 shows an example of the local grinding conditions, where the maximum single grain chip thickness (h cu,max), the flank-related infeed (ΔS) and the grinding wheel peripheral speed (v S ) is illustrated over the profile in the width direction (X), Fig. 6 shows an example of the maximum single grain chip thickness (h cu,max ) over the arc length of the profile as well as the progression averaged over defined evaluation areas (Legend: St: Start evaluation range; En: End evaluation range; Mi: Center of the evaluation range); on the right ordinate is the grinding wheel radius r S specified, Fig. 7 shows an example of how the curve of the coverage ratio (U d ) (left part of the image) a path speed profile or the dressing feed rate (v fd ) (right part of the diagram) is determined for the dressing stroke, whereby the course is given over the grinding wheel width; on the right ordinates the grinding wheel radius r is S specified, Fig. Figure 8 shows an example of the maximum single grain chip thickness (h cu,max ) over the arc length of the profile as well as the progression averaged over defined evaluation range (Legend: St: Start evaluation range; En: End evaluation range; Mi: Center of the evaluation range); on the right ordinate is the grinding wheel radius r S The graph shows an optimized curve that can be achieved with the proposed method. Fig. Figure 9 shows schematically the definition of the maximum single grain chip thickness (h cu,max ).

[0021] In Fig. Figure 1 schematically shows a grinding tool 1 in the form of a profile grinding wheel, shown in radial section (or axial section). The grinding tool has abrasive surfaces 2 intended for grinding the teeth of a gear (not shown).

[0022] Before grinding workpieces, the abrasive surfaces 2 must first be dressed, i.e., precisely profiled, using a dressing tool 3 in the form of a form roller. In the illustrated embodiment, the dressing tool 3 has a dressing area 4, which here has the shape of a circular segment in radial section.

[0023] During the dressing process, the grinding tool 1 rotates around its axis of rotation (axis C); similarly, the dressing tool 3 rotates around its axis (axis B) during the dressing process. Accordingly, a circumferential speed ratio q results at the contact point between the dressing area 4 and the abrasive surface 2. d , which is defined as the ratio of the peripheral speed of the grinding tool 1 to the peripheral speed of the dressing tool 3 at the contact point between the grinding tool and the dressing tool (the value is negative in the case of counter-rotation).

[0024] To profile the abrasive surfaces 2, the dressing tool 3 with its dressing area 4 is guided along the surface of the abrasive surface 2 in such a way that the desired surface shape of the abrasive surfaces 2 is produced. In this case, the dressing tool 3 is moved relative to the grinding tool 1 via the Fig. 1. Accordingly, the dressing tool 3 is guided relative to the grinding tool 1, in particular in the direction of the radial height r of the abrasive surface 2.

[0025] The dressing coverage U also plays a role here d plays an important role. For its definition, see Fig. 2, where the dressing of a cylindrical abrasive surface 2 is illustrated. Here, two examples are shown of how the dressing coverage ratio is determined. In the left-hand part of the image, it can be seen that per revolution of the grinding tool, the dressing tool 3 (with the effective width b d ) to adjust the dressing feed f adis continued, which here is the effective width b d The dressing ratio U d is approximately 1. In the right part of the picture you can see that per revolution of the grinding tool the dressing tool 3 is only moved by half the dressing feed f ad The dressing ratio U d is therefore approximately 2. The dressing coverage ratio thus provides information about how often a point on the grinding wheel surface is covered by the effective cutting edge width of the dressing tool. Fig. 2 also shows the dressing feed rate v fd , the dressing feed a ed and the engagement width a pd . The dressing ratio U is precisely defined d the quotient of the intervention width a pd and dressing feed f ad (U d = (a pa / f ad )).

[0026] What is important now is that the radial height H (see Fig. 3) the shaping profile of the grinding tool 1, ie in the direction of the radial height r of the abrasive surface 2, in particular the dressing coverage U d changes what is in Fig. 3 is indicated. For two different radial heights r of the dressing tool 3, different dressing coverage ratios U d1 and U d2 given.

[0027] If the orbital velocity v fd constant, due to the curvature of the abrasive surface 2, the dressing coverage U d2 greater than the dressing coverage U d1 .

[0028] The interrelationships between the local dressing conditions, the resulting local grinding wheel topography, the local grinding conditions, and the local roughness on the ground tooth flank can be used to specifically modify the dressing conditions in a location-dependent manner. Specifically, a location-dependent adjustment of the dressing conditions during a dressing stroke can be used to compensate for or specifically influence the inhomogeneous grinding conditions and the resulting roughness differences. According to the invention, three different compensation or influencing strategies are specifically provided: As explained, first a location-dependent adjustment of the orbital speed v fd during dressing to specifically influence the local dressing coverage U din question, so that as a result of a changed local grinding wheel topography there is a targeted adjustment of the surface roughness on the ground tooth flank.

[0029] It is therefore intended that the dressing tool 3 is moved relative to the grinding tool 1 at a variable speed v fd This is usually done by guiding the dressing area 4 in the radial section of the abrasive surface 2 shown in the indicated tangential direction T.

[0030] Then, a location-dependent adjustment of the ratio of the speeds of grinding tool 1 and dressing tool 3 is possible (by adjusting the grinding wheel speed and / or the dressing roller speed), so that the changed local grinding wheel topography leads to a targeted adjustment of the surface roughness on the ground tooth flank.

[0031] Finally, the combination of the two measures mentioned is also possible, ie both a location-dependent adjustment of the orbital speed v fd as well as a location-dependent change in the ratio of the speeds of grinding tool 1 and dressing tool 3, so that the changed local grinding wheel topography leads to a targeted adaptation of the surface roughness on the ground tooth flank.

[0032] For this purpose, an algorithm can be used which, taking the aforementioned causal relationships into account, calculates a path speed profile or profile for the relationship between the speeds of grinding tool 1 and dressing tool 3, so that an adjustment of the resulting roughness across the entire tooth flank can be achieved. A (gear) diameter can be specified for the algorithm, for which the engagement conditions are used as reference values. This ensures that the absolute roughness values recorded with a typical roughness measurement (at the reference position - usually in the center of the tooth flank between the working circles) are not changed by the use of the algorithm. It is also possible to specify desired roughness profiles along the tooth flank and, using the algorithm, implement them on the ground component using variable dressing conditions.

[0033] Furthermore, the algorithm can be used to control the local loading of the grinding wheel and consequently equalize grinding wheel wear across the grinding wheel width. This approach is particularly important for highly productive roughing processes. The topography of the grinding wheel can be adjusted by specifically and location-dependently adjusting the dressing parameters so that the individual grain chip thicknesses and thus the individual grain loading are similar across the entire contact zone, thus also resulting in more homogeneous wear behavior of the grinding wheel.

[0034] Both approaches (influencing the roughness, adjusting the grinding wheel load during roughing) become particularly relevant for larger normal modules, since larger profile heights also entail larger differences, for example with regard to the grinding wheel diameter or the peripheral speed.

[0035] The following describes the functionality of an algorithm used to optimize the dressing process by showing the relationships between the dressing process, grinding wheel topography, grinding process, machining conditions in the grinding process and the resulting local roughness on the tooth flank.

[0036] The algorithm used initially receives the control variables for the dressing and grinding processes as input variables. Furthermore, the geometric information about the dressing roller and the grinding tool is available. Finally, the grinding wheel profile or dressing path is defined.

[0037] Out of Fig. 4 shows how the local dressing conditions for the flank-related dressing infeed ΔS d , the dressing coverage U d and the peripheral speed ratio q dcan look like or be modeled via the radial height of the abrasive surface (according to the width direction x, see Fig. 1).

[0038] It can be seen that a lower dressing coverage U d and a lower flank-related dressing infeed ΔS d and a larger peripheral speed ratio q d at the tooth root compared to the tooth tip (the minus in the values of q d indicates the counter-rotation of the grinding tool and dressing tool). Furthermore, it can be seen that the dressing ratio U d is higher at the tooth head compared to the tooth root.

[0039] A reference position Ref is also entered, at which the dressing conditions are present, which are used for the subsequent adjustment of the machining conditions.

[0040] In Fig. 5 illustrates the local grinding conditions that can be achieved with the appropriately profiled grinding tool (according to Fig. 4) can be driven.

[0041] It can be seen that higher grinding wheel peripheral speeds v are at the tooth root compared to the tooth tip. S as well as a lower flank-related infeed ΔS. There is also a larger active grinding wheel diameter at the tooth root compared to the tooth tip.

[0042] The varying dressing conditions as well as the varying grinding conditions thus influence the chip thickness over the course of the tooth flank and thus also its local surface roughness.

[0043] In Fig. 6 is the curve of the maximum single grain chip thickness h cu,max illustrated over the arc length of the tooth flank.

[0044] To ensure comparability with roughness measurements, the calculated single grain chip thickness can be related to the arc length of the profile. The single grain chip thickness was averaged over the length of a roughness measurement to achieve this comparability. The start St of the measurement, the end En of the measurement, and the center Mi of the evaluation range are marked for each measurement. The evaluation ranges are shifted step by step across the profile. It can be seen that at the tooth root, the calculated value for the single grain chip thickness corresponds to only 53% of that at the tooth tip. The grinding wheel radius r is shown on the right-hand ordinate. S applied.

[0045] Fig. 7 shows the optimized profile of the dressing ratio U d as well as the path speed profile for the dressing feed. The left part of the image shows the profile of the dressing coverage U dplotted over the grinding wheel width, in the right-hand part of the image the required dressing feed speed v fd . The determined curve of the dressing ratio U d To create the desired grinding wheel topography, uniform chip conditions (chip thickness) are achieved across the entire tooth flank. The reference value Ref, also entered here, is used as a reference for the adjustment.

[0046] From the curve of the dressing coverage U d The corresponding path speed profile for the dressing stroke (ie the dressing feed speed v fd ).

[0047] In Fig. Finally, Figure 8 illustrates the adjusted chip removal conditions achieved by the optimized profile for the dressing feed rate. It shows the curve of the maximum single-grain chip removal thickness h cu,maxover the arc length (flank length) as well as start (St), end (En) and mean values (Mi) of some evaluation range, as it resulted after carrying out the optimization described above.

[0048] Using the calculated profile for the dressing feed rate (right part of the image in Fig. 7) uniform chip removal conditions can be created so that differences along the tooth flank are minimized.

[0049] However, the algorithm used preferably prevents dressing coverage ratios of less than 1 from being achieved, so that Fig. 8 there is still a slight decrease in the stress thickness in the area of the tooth root.

[0050] In Fig. 9 is once again the definition of the maximum single grain chip thickness h cu,max illustrated. The grinding tool 1 with radius r is shown schematically S, which grinds a workpiece 5. The grinding tool 1 plunges with a grinding feed a e into the material of the workpiece 5. The feed rate v is also specified f , with which the grinding tool 1 is moved relative to the workpiece 5. Two abrasive grains 6 and 7 are shown, which represent or form a leading cutting edge 6 and a trailing cutting edge 7. This results in the area of the exit (in the case of counter-rotation, otherwise in the area of the entry in the case of synchronous rotation) of the grinding tool 1 from the material of the workpiece 5 at a given feed rate v f the maximum single grain chip thickness h cu,max . List of reference symbols: 1 grinding tool (grinding wheel) 2 Abrasive surface of the grinding tool 3 Dressing tool (forming roller / dressing roller) 4 Dressing area of the dressing tool 5 Workpiece 6 leading cutting edges (abrasive grain) 7 trailing cutting edge (abrasive grain) r radial height of the abrasive surface H radial height of the shaping profile of the grinding tool T tangential direction of the abrasive surface of the grinding tool U d Dressing coverage ratio q d Circumferential speed ratio (ratio of the peripheral speed of the grinding tool to the peripheral speed of the dressing tool during dressing at the contact point between the grinding tool and the dressing tool) ΔS d flank-related dressing infeed h cu,max maximum single grain chip thickness ΔS flank-related infeed v fd Path speed of the dressing area of the dressing tool (dressing feed speed) v S Grinding wheel peripheral speed r S Grinding wheel radius b d Effective width when dressing

Claims

[1] Method for dressing a grinding tool (1) for grinding a gear or a profile of a workpiece, in which at least one abrasive surface (2) of the grinding tool (1) is profiled by means of a dressing tool (3) in that a dressing area (4) of the dressing tool (3) is moved at a path speed (v fd ) is guided over the abrasive surface (2) of the grinding tool (1) in such a way that the abrasive surface (2) is profiled over a predetermined radial height (r), and wherein both the grinding tool (1) and the dressing tool (3) rotate at respective speeds, characterized by that the dressing tool (3) moves during dressing relative to the grinding tool (1) at a variable path speed (v fd ) is guided over the abrasive surface (2) and / or that the dressing takes place with a ratio of the speeds of the grinding tool (1) and the dressing tool (3) which varies over the radial height (r). [2] Method according to claim 1, characterized by that only for the orbital speed (v fd ) a variable course is specified. [3] Method according to claim 1, characterized by that a variable curve is specified only for the ratio of the speeds of the grinding tool (1) and the dressing tool (3). [4] Method according to claim 1, characterized by that both for the orbital speed (v fd ) as well as for the ratio of the speeds of the grinding tool (1) and the dressing tool (3) a variable curve is specified. [5] Method according to one of claims 1 to 4, characterized by that the variable orbital velocity (v fd ) is selected so that the radial height (r) of the abrasive surface (2) for the dressing coverage (U d ) a defined course is achieved. [6] Method according to one of claims 1 to 4, characterized bythat the variable ratio of the speeds of the grinding tool (1) and the dressing tool (3) is selected such that a defined curve is achieved for the ratio of the peripheral speeds of the grinding tool (1) and the dressing tool (3) over the radial height (r) of the abrasive surface (2). [7] Method according to at least one of claims 5 or 6, characterized by that the defined profile of the dressing coverage ratio (U d ) and / or the defined course of the ratio of the peripheral speeds of the grinding tool (1) and the dressing tool (3) is specified in such a way that a defined course is achieved over the radial height (r) of the abrasive surface (2) for the resulting maximum single grain chip thickness during grinding. [8] Method according to one of claims 1 to 7, characterized by that the grinding tool (1) is a grinding wheel. [9] Method according to one of claims 1 to 8, characterized bythat the dressing tool (3) is a form roller which rotates around a rotational axis during dressing. [10] Method according to claim 9, characterized by that the dressing area (4) of the dressing tool (3) has the shape of a circular section in radial section.

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