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

Abstract

The invention relates to a method for dressing a grinding tool (1) for grinding a toothing or a profile of a workpiece, in which at least an abrasive surface (2) of the grinding tool (1) is profiled by means of a dressing tool (3), by a dressing region (4) of the dressing tool (3) being guided at a 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 predefined radial height (r), and wherein both the grinding tool (1) and the dressing tool (3) rotate at respective rotational speeds. In order to easily allow the surface roughness of the tooth flanks ground by means of the grinding tool to be adjusted or influenced in a targeted location-dependent manner, the invention provides for the dressing tool (3), during dressing, to be guided relative to the grinding tool (1) at a variable speed (vfd) over the abrasive surface (2) and / or for the dressing to be carried out with a ratio of the rotational speeds of grinding tool (1) and dressing tool (3) that varies over the radial height (r).

Description

[0001] Method for dressing a grinding tool for grinding a gear or profile of a workpiece

[0002] 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.

[0003] 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.

[0004] 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. Since the dressing area must be gradually guided along the abrasive surface of the grinding tool in order to gradually and completely profile the abrasive surface, a feed rate is used here that results in a corresponding coverage ratio (for the definition of the coverage ratio, refer to the explanation of Figure 2). The higher the coverage ratio, the finer the abrasive surface to be profiled.

[0005] 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.

[0006] 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.

[0007] 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 should 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.

[0008] 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.

[0009] 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 component thickness during grinding. Only the path speed can be specified as a variable profile.

[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 component 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 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 aforementioned coverage ratio, it should be noted that this is defined as the ratio between the effective width of the dressing tool relative to the feed rate of the dressing tool per revolution of the grinding tool (see the explanations in connection with Figure 2). The coverage ratio therefore 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.

[0021] 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,

[0022] Fig. 2 shows schematically (here for a cylindrical grinding surface) how a degree of coverage is obtained during dressing,

[0023] Fig. 3 shows schematically an enlarged section of Figure 1, with the dressing tool shown in two different positions,

[0024] Fig. 4 shows an example of the local dressing conditions, where the flank-related dressing infeed (ASd), the dressing coverage (Ud) and the speed ratio between grinding tool and dressing tool (qd) are illustrated over the profile in the width direction (X).

[0025] Fig. 5 shows an example of the local grinding conditions, where the maximum single component thickness (h cu,max), the flank-related infeed (AS) and the grinding wheel peripheral speed (vs) over the profile in the width direction (X) is illustrated, Fig. 6 shows an example of the profile of the maximum single component cutting thickness (h cu ,max) over the arc length of the profile as well as the progression averaged over defined evaluation areas (legend: St: start of evaluation area; En: end of evaluation area; Mi: center of evaluation area); on the right ordinate the grinding wheel radius rs is given,

[0026] Fig. 7 shows an example of how a path speed profile or the dressing feed rate (vfd) (right part of the image) for the dressing stroke is determined from the curve of the coverage ratio (Ud) (left part of the image), whereby the curve is shown over the grinding wheel width; on the right ordinates, the grinding wheel radius r is shown. s specified,

[0027] Fig. 8 shows an example of the course of the maximum single grain chip thickness (h cu , max) over the arc length of the profile as well as the progression averaged over the defined evaluation range (legend: St: start of evaluation range; En: end of 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.

[0028] Fig. 9 shows schematically the definition of the maximum single component thickness (hcu, max).

[0029] 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). Before grinding workpieces, the abrasive surfaces 2 must first be dressed, i.e., precisely profiled, for which purpose a dressing tool 3 in the form of a forming roller is used. In the exemplary embodiment, the dressing tool 3 has a dressing area 4, which here has the shape of a circular segment in radial section.

[0030] During the dressing process, grinding tool 1 rotates around its axis of rotation (axis C); similarly, dressing tool 3 rotates around its axis (axis B) during the dressing process. Accordingly, a peripheral speed ratio qa results at the contact point between dressing area 4 and abrasive surface 2, which is defined as the ratio of the peripheral speed of grinding tool 1 to the peripheral speed of dressing tool 3 at the contact point between grinding tool and dressing tool (the value is negative for counter-rotation).

[0031] 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 such that the desired surface shape of the abrasive surfaces 2 is produced. The dressing tool 3 is guided relative to the grinding tool 1 via the coordinates y and z shown in Figure 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.

[0032] The dressing ratio Ua also plays a key role here. For its definition, reference is made to Figure 2, which illustrates the dressing of a cylindrical abrasive surface 2. Two examples are shown here of how the dressing ratio is determined. The left-hand part of the figure shows that per revolution of the grinding tool, the dressing tool 3 (with the effective width ba) is moved by the dressing feed f. aa, which here corresponds to the effective width bd. The dressing coverage Ud is approximately 1. In the right-hand part of the image, it can be seen that per revolution of the grinding tool, the dressing tool 3 is only moved by half the dressing feed f a d is continued. The dressing coverage ratio Ud 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. Also shown in Figure 2 are the dressing feed rate Vfd, the dressing infeed a e d and the engagement width a p d. The dressing ratio Ud is precisely defined as the quotient of the engagement width a p d and dressing feed f a d (Ud = (a P d / f a d)).

[0033] What is essential now is that the dressing coverage Ud in particular changes over the radial height H (see Figure 3) of the shaping profile of the grinding tool 1, ie in the direction of the radial height r of the abrasive surface 2, as indicated in Figure 3. For two different radial heights r of the dressing tool 3, different dressing coverages Udi and Ud2 are given.

[0034] If the path speed Vfd were constant, the dressing coverage Ud2 would be greater than the dressing coverage Udi due to the curvature of the abrasive surface 2.

[0035] 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:

[0036] As explained, a location-dependent adjustment of the path speed Vfd during dressing is initially considered to specifically influence the local dressing coverage Ud, so that as a result of a changed local grinding wheel topography, a targeted adjustment of the surface roughness on the ground tooth flank occurs.

[0037] Accordingly, it is intended that the dressing tool 3 is guided at a variable speed Vfd relative to the grinding tool 1 during dressing. This is usually achieved by guiding the dressing area 4 in the radial section of the abrasive surface 2 shown in the indicated tangential direction T.

[0038] 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.

[0039] Finally, a combination of the two measures mentioned is also possible, i.e. both a location-dependent adjustment of the path speed Vfd and 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 adjustment of the surface roughness on the ground tooth flank. For this purpose, an algorithm can be used which, taking into account the aforementioned causal relationships, calculates a path speed profile or profile for the ratio of 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 ​​measured with a typical roughness measurement (at the reference position – usually centered on the tooth flank between the working circles) are not altered by the use of the algorithm. It is also possible to specify desired roughness profiles along the tooth flank and implement them on the ground component using the algorithm with variable dressing conditions.

[0040] 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 particle thicknesses and thus the individual particle loading are similar across the entire contact zone, thus also resulting in more homogeneous wear behavior of the grinding wheel.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Figure 4 shows how the local dressing conditions for the progression of the flank-related dressing infeed ASd, the dressing coverage Ud and the peripheral speed ratio qd over the radial height of the abrasive surface look like or can be modeled (corresponding to the width direction x, see Figure 1).

[0045] It can be seen that there is a lower dressing ratio Ud, a lower flank-related dressing infeed ASd, and a higher peripheral speed ratio qd at the tooth root compared to the tooth tip (the minus in the qd values ​​indicates the counter-rotation of the grinding tool and dressing tool). Furthermore, it can be seen that the dressing ratio Ud is higher at the tooth tip compared to the tooth root. A reference position Ref is also shown, where the dressing conditions are present, which are used for the subsequent adjustment of the cutting conditions.

[0046] Figure 5 illustrates the local grinding conditions that are applied with the appropriately profiled grinding tool (as shown in Figure 4).

[0047] It can be seen that higher grinding wheel peripheral speeds vs are present at the tooth root compared to the tooth tip, as well as a lower flank-related infeed AS. The active grinding wheel diameter is also larger at the tooth root compared to the tooth tip.

[0048] 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.

[0049] Figure 6 shows the course of the maximum single component thickness h cu ,max over the arc length of the tooth flank.

[0050] To ensure comparability with roughness measurements, the calculated individual component thickness can be related to the arc length of the profile. The individual component 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 individual component thickness corresponds to only 53% of that at the tooth tip. The grinding wheel radius r is shown on the right-hand ordinate. sFigure 7 shows the optimized curve of the dressing ratio Ud and the path speed profile for the dressing feed. The left-hand part of the figure shows the curve of the dressing ratio Ud plotted against the grinding wheel width, while the right-hand part shows the required dressing feed rate Vfd. The determined curve of the dressing ratio Ud for generating a desired grinding wheel topography results in uniform chip conditions (chip thickness) across the entire tooth flank. The reference value Ref, also entered here, is used as a specification for the adjustment.

[0051] The path speed profile for the dressing stroke (i.e. the dressing feed speed Vfd) then results from the course of the dressing coverage Ud.

[0052] Finally, Figure 8 illustrates the adjusted machining conditions achieved by the optimized profile for the dressing feed rate. It shows the curve of the maximum single component machining thickness h cu ,max over 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.

[0053] Using the calculated profile for the dressing feed rate (right panel in Figure 7), uniform chip removal conditions can be generated, minimizing variations along the tooth flank. However, the algorithm used preferentially prevents dressing contact ratios of less than 1, so that, as shown in Figure 8, a slight decrease in chip thickness still occurs in the tooth root area.

[0054] Figure 9 shows once again the definition of the maximum single component thickness h cu , max is illustrated. The grinding tool 1 with radius rs is shown schematically, which grinds a workpiece 5. The grinding tool 1 plunges with a grinding infeed a e into the material of the workpiece 5. Also specified is the feed rate Vf, with which the grinding tool 1 is moved relative to the workpiece 5. Two grinding 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 maximum single component machining thickness h 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 Vf. cu max .

[0055] List of reference symbols:

[0056] 1 grinding tool (grinding wheel)

[0057] 2 Abrasive surface of the grinding tool

[0058] 3 Dressing tool (forming roller / dressing roller)

[0059] 4 Dressing area of ​​the dressing tool

[0060] 5 Workpiece

[0061] 6 leading cutting edges (grinding grain)

[0062] 7 trailing cutting edge (grinding grain) r radial height of the abrasive surface

[0063] H radial height of the shaping profile of the grinding tool

[0064] T tangential direction of the abrasive surface of the grinding tool

[0065] U d Dressing ratio qa peripheral speed ratio

[0066] (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)

[0067] ASd flank-related dressing infeed l HlcU'inax maximum single component cutting thickness

[0068] AS flank-related infeed

[0069] Vfd Path speed of the dressing area of ​​the dressing tool (dressing feed rate)

[0070] Vs grinding wheel peripheral speed r s Grinding wheel radius b d Effective width when dressing

Claims

Patent claims:

1. A 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 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, characterized in that the dressing tool (3) is guided over the abrasive surface (2) relative to the grinding tool (1) at a variable path speed (vfd) 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).

2. Method according to claim 1, characterized in that a variable course is specified only for the web speed (vfd).

3. Method according to claim 1, characterized in that a variable curve is specified only for the ratio of the rotational speeds of the grinding tool (1) and the dressing tool (3).

4. Method according to claim 1, characterized in that a variable course is specified both for the path speed (vfd) and for the ratio of the rotational speeds of the grinding tool (1) and the dressing tool (3).

5. Method according to one of claims 1 to 4, characterized in that the variable path speed (vfd) is selected such that a defined profile is achieved for the dressing coverage (Ud) over the radial height (r) of the abrasive surface (2).

6. Method according to one of claims 1 to 4, characterized in that the variable ratio of the rotational speeds of the grinding tool (1) and the dressing tool (3) is selected such that a defined profile 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 in that the defined course of the dressing coverage ratio (Ud) and / or the defined course of the ratio the circumferential speeds of the grinding tool (1) and dressing tool (3) are specified in such a way that a defined profile is achieved over the radial height (r) of the abrasive surface (2) for the resulting maximum individual chip thickness during grinding.

8. Method according to one of claims 1 to 7, characterized in that the grinding tool (1) is a grinding wheel.

9. Method according to one of claims 1 to 8, characterized in that the dressing tool (3) is a forming roller which rotates about an axis of rotation during dressing.

10. Method according to claim 9, characterized in that the dressing area (4) of the dressing tool (3) has the shape of a circular segment in radial section.

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