Method for machining pre-toothed workpieces by continuous generating grinding and corresponding gear cutting machine

Abstract

The invention relates to a method for machining pre-toothed workpieces by continuous generating grinding using a worm grinding wheel (100). The worm grinding wheel is dressed and workpieces are machined with the dressed worm grinding wheel. During the machining of the workpieces, a working region (110) of the worm grinding wheel is swept over by contact paths between the worm grinding wheel and the workpieces. This sweeping over takes place several times in one pass (N) in each case. For each pass, at least one wear parameter is determined, which characterises a wear state of the working region, and, depending on the wear parameter, a decision (153) is automatically made as to whether the working region is used for a further pass before it is dressed again. The invention also relates to a correspondingly designed gear cutting machine.

Description

[0001] TITLE

[0002] Method for machining pre-toothed workpieces by continuous generating grinding and corresponding gear cutting machine

[0003] TECHNICAL FIELD

[0004] The present invention relates to a method for machining pre-toothed workpieces by continuous generating grinding and to a gear cutting machine which is designed to carry out such a method.

[0005] STATE OF THE ART

[0006] In gear manufacturing, the final hard finishing step is one of the most important steps in determining the quality of the gear. This process produces the geometry that will later mesh with the gear teeth. Continuous generating grinding is a frequently used process for hard finishing. Information on the fundamentals of continuous generating grinding can be found, for example, in H. Schriefer et al., "Continuous Generating Grinding of Gears," published by Reishauer AG, Wallisellen, June 2008, ISBN 978-3-033-01447-3, especially Chapter 2.

[0007] In continuous generating grinding, a pre-toothed workpiece is machined in rolling engagement with a rotating grinding tool in the form of a helically profiled grinding wheel (grinding worm). The machining takes place in one or more grinding strokes. During each grinding stroke, the grinding worm is moved relative to the workpiece toothing along the workpiece axis (so-called axial feed motion), while the workpiece rotates around its workpiece axis in rolling engagement with the grinding worm.

[0008] Often, the workpiece is first machined in one or more roughing strokes, followed by one or more finishing strokes. The roughing and finishing strokes differ in their grinding performance: In the finishing strokes, a lower infeed and / or axial feed rate, and therefore a lower grinding performance, is usually selected than in the roughing strokes to ensure more precise compliance with quality specifications.

[0009] During each grinding stroke, a specific area of ​​the grinding worm comes into contact with the respective workpiece. Due to this machining action, the grinding worm in this area is subject to wear. To bring fresh, unused areas of the grinding worm back into contact with the workpiece, it is known to displace the grinding worm discontinuously or continuously along its worm axis relative to the workpiece (so-called "shifting" of the grinding worm). Various shift strategies are known for this purpose.

[0010] With "discontinuous shifting," all roughing strokes during machining of a workpiece are performed at the same shift position of the grinding worm. This is usually followed by a so-called shift jump to a shift position for finishing, and all finishing strokes are performed at this shift position. After finishing is complete, a so-called shift return to a new shift position for roughing the next workpiece occurs. The shift position is not changed during the roughing or finishing strokes. The operator selects the size of the shift jump and the shift return based on predefined formulas or empirical values.

[0011] With the "continuous shifting" technique predominantly used today, a shift movement is continuously superimposed during each roughing and finishing stroke. The selection of the shift amount per grinding stroke and the resulting shift feed rate is also based on predefined formulas or the operator's experience.

[0012] Dressable grinding worms are frequently used in generating grinding. Once the grinding worm has been shifted across its entire working range, it is dressed again each time. Dressing tools, usually diamond-coated, are used for this purpose. During dressing, the outer diameter of the grinding wheel decreases. After a certain number of dressing processes, the grinding worm is worn out and must be replaced. The dressing tools also become increasingly worn with each dressing process. The number of dressing processes therefore affects not only the service life of the grinding worm, but also the service life of the dressing tools. The costs of the grinding worms and dressing tools therefore represent a substantial portion of the running costs. In addition, no workpieces can be machined during dressing, so each dressing process extends the cycle time.Overall, dressing represents both a significant cost and time factor. It is therefore generally desirable to dress the grinding worm only after machining as many workpieces as possible.

[0013] In practice, however, the grinding worm is often dressed earlier than objectively necessary. Many users are therefore focused on avoiding manufacturing deviations in the finished workpieces at all costs. To this end, users often act overly cautiously by designing the process so that the grinding worm is dressed after machining a relatively small number of workpieces.

[0014] PRESENTATION OF THE INVENTION

[0015] It is an object of the present invention to provide a method for machining pre-toothed workpieces by continuous generating grinding, which enables improved utilization of the grinding worm.

[0016] This object is achieved by a method having the features of claim 1. Further embodiments are specified in the dependent claims.

[0017] A method is provided for machining pre-toothed workpieces by continuous generating grinding with a grinding worm rotating about a worm axis, wherein the grinding worm has at least one working area in which it comes into machining engagement with the workpieces, the method comprising:

[0018] Dressing the grinding worm; and

[0019] Machining the workpieces in machining engagement with the working area of ​​the grinding worm after the grinding worm has been dressed, wherein the grinding worm is swept over by contact paths between the grinding worm and the workpieces during the machining of the workpieces, wherein the working area is swept over several times in one pass each, wherein for each pass at least one wear parameter is determined which characterizes a wear state of the working area, and wherein depending on the at least one wear parameter a decision is automatically made as to whether the working area is used for a further pass before it is dressed again.

[0020] During machining, each workpiece is machined with at least one grinding stroke. During each grinding stroke, the grinding worm is moved relative to the workpiece in question along the workpiece axis, while the workpiece rotates around a workpiece axis in machining engagement with the grinding worm (axial feed movement). In the proposed method, during machining of the workpieces, a working area of ​​the grinding worm is swept over, preferably essentially completely, in several passes (e.g., at least 2, 3, 4, 5, or more passes) before contact with the workpieces. Each pass comprises at least one grinding stroke.The work area is swept over by shifting the grinding worm relative to the workpieces during the machining of the workpieces, in particular during at least one grinding stroke per pass and / or between successive grinding strokes, along the worm axis by a shifting movement. The process is advantageously carried out in such a way that the work area is subjected to so little stress in each pass that it is to be expected that the work area will only need to be dressed again after several passes. The wear condition of the work area is determined for each pass. As long as the wear condition allows further machining of workpieces with the work area, machining is continued with another pass.Only when the grinding worm has reached an undesirable level of wear is the working area no longer used for machining further workpieces before it is dressed again.

[0021] The working area is a region of the grinding worm surface. This can be a continuous area of ​​the grinding worm surface or a region composed of several disjoint (non-overlapping) parts. The grinding worm can have multiple working areas.

[0022] The at least one wear parameter can be based on a performance indicator that characterizes a current grinding performance during the respective pass. The pass can comprise one or more grinding strokes. The at least one wear parameter can be, for example, an intensity measure based on the performance indicator for a grinding intensity during at least one of these grinding strokes, in particular a maximum, an integral, an average value, or a low-pass filtered spectral component of the performance indicator over the course of the at least one grinding stroke. The performance indicator can be, in particular, the power and / or current consumption of a tool spindle that drives the grinding worm to rotate. However, the wear parameter does not necessarily have to be based on a performance indicator.For example, a wear parameter can also be determined on the basis of a spectral analysis of structure-borne sound signals recorded during the respective grinding stroke.

[0023] In order to reduce the dependence of the wear parameter on process parameters such as the outer diameter of the grinding wheel, the workpiece diameter and module, and / or the infeed, and thus ensure the comparability of the wear parameter in different machining situations, a standardization operation can be performed when determining the wear parameter, with which the wear parameter is standardized. The standardization operation depends on at least one process parameter, wherein the process parameter is at least one geometric parameter of the grinding worm, at least one geometric parameter of the workpiece, and / or at least one setting parameter of the machine tool.The standardization operation is performed in such a way that the standardized wear parameter depends less strongly on the at least one process parameter than without the standardization operation. In particular, the standardization operation can be performed in such a way that the wear parameter depends less strongly on changes in the outer diameter of the grinding wheel due to the dressing processes than without the standardization operation. As soon as one of the aforementioned process parameters changes, in particular the outer diameter of the grinding wheel, the standardization operation is preferably recalculated.

[0024] If the wear indicator is based on a performance indicator, the recalculation of the normalization operation may in particular comprise the application of a model that describes an expected dependence of the performance indicator on the stated process parameters, in particular a model of a process force or process power. For further considerations regarding the normalization operation, reference is made to publication W02021048027A1, the content of which is incorporated in its entirety into the present disclosure by reference. In some embodiments, during at least one grinding stroke in the course of each pass, e.g., for all grinding strokes in the course of each pass, a shift movement is executed simultaneously with the axial feed movement while the grinding worm is in machining engagement with the respective workpiece, i.e.The grinding worm is continuously moved relative to the workpiece both along the axial feed direction and along the shift direction (so-called diagonal movement). As a result, during the machining operation, the grinding worm travels a specific shift distance along the shift direction and a specific axial stroke distance along the axial feed direction relative to the workpiece during the respective grinding stroke. The ratio of shift distance to axial stroke distance is referred to as the "diagonal ratio."

[0025] In some embodiments, the grinding worm can comprise at least one worm flight flank that has a width-dependent modification in the working area, i.e., a modification of the worm flight flank that changes along the worm axis (i.e., in the width direction of the grinding worm). Worms with width-dependent modified worm flight flanks are used, for example, in so-called Twist Control Grinding (TCG), as described, for example, in W. Graf, "Twist Control Grinding," Gear Technology, June 2017, pages 48-53. The width-dependent modification can then be mapped onto the workpiece flanks by the diagonal movement. In particular, it can be a so-called topological modification of the grinding worm flank, which depends on both the width direction of the grinding worm and the profile direction.

[0026] However, it is also possible for the worm flight flanks in the working area to either exhibit no modification at all, or for the worm flight flanks in the working area to exhibit only a pure profile modification that does not change in the width direction of the grinding worm. This results in either no modification at all on the workpiece flanks, even with a diagonal movement, or a pure profile modification on the workpiece flanks that does not change along the width direction of the workpiece, in particular a profile angle modification, profile crowning, profile waviness, tip relief, and / or root relief of the workpiece flanks. In such embodiments, the choice of the diagonal ratio can be made purely from technological perspectives such as the service life of the grinding worm, the workpiece quality, and / or the roughness structure of the workpiece flanks.One example is the so-called "Low Noise Shifting", where the diagonal grinding process is used to specifically influence the roughness structure, see e.g. US6379217B1.

[0027] In some embodiments, only one grinding stroke occurs during each pass. In particular, in some embodiments, the work area is swept over exactly once during each pass. This can be particularly useful if the worm thread flanks in the work area exhibit a width-dependent modification, which is mapped onto the workpiece flanks by a diagonal movement.

[0028] In other embodiments, a plurality of grinding strokes occur during each pass. The entire working area is not necessarily covered in each grinding stroke of a pass. In particular, there are embodiments in which not all grinding strokes of a pass cover the same part of the working area. In other words, in such embodiments, there are at least two grinding strokes in each pass in which different parts of the working area are covered. The different parts of the working area can overlap or be disjoint.

[0029] In some embodiments, the at least one wear parameter is determined multiple times for each pass, and at least one derived parameter is determined from the values ​​of the at least one wear parameter determined for the respective pass. If multiple grinding strokes take place per pass, for example, the at least one wear parameter can be determined at least once per grinding stroke. The derived parameter can be a statistical parameter that characterizes the statistical distribution of the values ​​of the wear parameter in the respective pass, in particular a position parameter (e.g., the arithmetic mean or the median) and / or a fluctuation parameter (e.g., the standard deviation or the interquartile range). The decision as to whether the work area will continue to be used can then be made depending on the at least one derived parameter.By taking into account several values ​​of at least one wear parameter per pass, a more reliable determination of the wear condition is possible than if the at least one wear parameter is determined only once during each pass.

[0030] The decision as to whether to continue using the work area can be made, for example, based on a comparison of the wear parameter or a parameter derived therefrom with a threshold value. In other embodiments, however, the at least one wear parameter or a parameter derived therefrom can also be subjected to a more complex analysis, e.g., a regression analysis.

[0031] In some embodiments, each of the workpieces is machined with at least one roughing stroke and at least one finishing stroke. For each workpiece, at least one roughing wear parameter can be determined, which characterizes the wear condition of the grinding worm during one or more roughing strokes, and for each workpiece, at least one finishing wear parameter can be determined, which characterizes the wear condition of the grinding worm during one or more finishing strokes. To perform the roughing and finishing strokes, the grinding worm can have at least one roughing section and at least one finishing section.

[0032] As already stated, the grinding worm can have two or more working areas. In some embodiments, the decision as to whether one of these working areas is used for a further pass is made independently of the wear status of the other working areas. For example, this decision can be made for a roughing area independently of the wear status of the at least one finishing area.

[0033] However, it is also conceivable that the decision as to whether one of the working areas is used for a further pass is influenced by the wear condition of at least one other working area. Thus, in some embodiments, the decision as to whether a roughing or finishing area is used for a further pass is made depending on both the at least one roughing wear parameter and the at least one finishing wear parameter. For example, the decision can be made based on a comparison of the at least one roughing wear parameter or at least one parameter derived therefrom with a roughing threshold value and a comparison of the at least one finishing wear parameter or at least one parameter derived therefrom with a finishing threshold value.For example, the roughing wear parameter can be an intensity measure for the grinding intensity during at least one roughing stroke (referred to as roughing intensity for short), and the finishing wear parameter can be an intensity measure for the grinding intensity during at least one finishing stroke (referred to as finishing intensity for short). By considering both the roughing wear parameter and the finishing wear parameter for the decision, the dressing decision can be made with greater reliability. However, it is also conceivable to consider only the roughing wear parameter or only the finishing wear parameter, for example.

[0034] The method may include redressing the working area. In some embodiments, all working areas of the grinding worm are redressed together. In other embodiments, only one or more working areas are redressed independently of other working areas. For example, it is possible to specifically redress only one, several, or all roughing areas, or only one, several, or all finishing areas.

[0035] Every workpiece has a workpiece toothing with workpiece flanks. Each of these workpiece flanks has a working area. The "working area" refers to the area of ​​the workpiece flank that comes into contact with the flanks of a mating toothing during later use, thus defining the contact pattern of the toothing. The working area can be specified during the design of the toothing or determined by determining the contact pattern under specified load conditions. The process can include specifying the working area, e.g., using an input function with which the working area is defined in a suitable form, e.g., graphically in a representation of the respective workpiece flank. If necessary, the entire tool flank can also be defined as the working area. During each grinding stroke, the workpiece flanks are machined with at least one worm thread flank of the grinding worm.As a rule, machining is carried out with more than one worm thread flank, in the case of a multi-start grinding worm and with the usual two-flank engagement, for example, with the left and right flanks of each grinding worm thread. However, only one of these worm thread flanks will be considered below. For each grinding stroke, the area on the worm thread flank in which the worm thread flank makes machining contact with the workpiece during the respective grinding stroke is defined as the "contact zone." Each of these contact zones has an area that comes into contact with the useful areas of the workpiece flanks. This area is referred to below as the "quality-determining area" because it influences the workpiece quality in the relevant areas of the workpiece flanks, namely the useful areas. If the entire workpiece flank is considered the useful area, the quality-determining area extends over the entire contact zone, i.e.the contact zone and the quality-determining area are then identical.

[0036] In some embodiments, there are multiple contact zones on the screw flight flank, whose quality-determining regions are arranged with essentially no overlap with all other contact zones. Contact zones whose quality-determining regions are arranged with essentially no overlap with all other contact zones are referred to below as "decoupled contact zones."

[0037] For example, it can be provided that each of the decoupled contact zones is used exclusively for a specific, selected grinding stroke per workpiece, e.g., the first, second, third, etc. grinding stroke of the respective workpiece. In particular, it can be provided that each grinding stroke is performed with a different contact zone when machining a single workpiece (e.g., the first grinding stroke with a first contact zone, the second grinding stroke with a second contact zone, etc.).

[0038] A quality-determining area of ​​a contact zone is "essentially" arranged without overlap with another contact zone if it either does not overlap with the other contact zone at all, or the overlap is so small that the remaining overlap has no measurable influence on the resulting quality of the useful areas of the gearing manufactured with the contact zone in question. For example, a contact zone can still be considered decoupled if no more than 25% of the area of ​​the quality-determining area of ​​the contact zone overlaps with one or more other contact zones, preferably no more than 15%, particularly preferably no more than 5%.

[0039] To move from one decoupled contact zone to another decoupled contact zone, the grinding worm is shifted between two grinding strokes relative to the machining position of the workpieces along a shift direction parallel to the worm axis, similar to the previously explained shift jump and shift reversal in conventional shift strategies. However, in conventional shift strategies, the shift jump and shift reversal are designed such that the quality-determining area of ​​each contact zone at least partially overlaps with one or more other previously or subsequently used contact zones. The use of decoupled contact zones, on the other hand, enables better control of the machining process, since the wear condition of the grinding worm in the quality-determining areas of the decoupled contact zones is not influenced by the wear condition of previously used, overlapping contact zones.

[0040] In addition to the decoupled contact zones, additional contact zones may exist on the worm gear flank that overlap with each other, as in conventional shift strategies. It is also possible for only some of the grinding strokes per workpiece to be performed with decoupled contact zones, while one or more other grinding strokes are performed with non-decoupled contact zones. For example, it is conceivable to perform only the roughing strokes with decoupled contact zones, while the contact zones of the finishing strokes overlap, or vice versa. In some embodiments, however, all contact zones used on the worm gear flank are decoupled contact zones. In particular, all grinding strokes can be performed exclusively with decoupled contact zones when machining all workpieces.

[0041] In some embodiments, not only are the quality-determining regions of the decoupled contact zones arranged substantially without overlap with all other contact zones, but the decoupled contact zones are arranged substantially completely without overlap with all other contact zones, i.e. they either do not overlap with other contact zones at all, or they overlap with other contact zones only to such an extent that this has no measurable influence on the quality of the tooth flanks machined with these contact zones, both inside and outside the useful areas.

[0042] The working area can comprise at least one of the decoupled contact zones. In some embodiments, the working area is formed by a single decoupled contact zone. Each pass can then correspond to a single grinding stroke with this contact zone. The at least one wear parameter then characterizes the wear condition of the grinding worm in the decoupled contact zone. Depending on the at least one wear parameter, a decision is then automatically made as to whether a machining intervention will take place again in the same contact zone for an immediately subsequent or later grinding stroke or whether this contact zone will no longer be used for further grinding strokes before the grinding worm is dressed again. With this procedure, each decoupled contact zone is used for grinding strokes until the wear parameter indicates that this contact zone is worn.

[0043] In other embodiments, the working area is composed of multiple contact zones. The contact zones can be decoupled contact zones and / or overlapping contact zones. The present disclosure is therefore not limited to working areas formed exclusively by decoupled contact zones. Thus, it is also possible, in particular, to work with a conventional shift strategy. In particular, it is possible for the grinding worm to have only contact zones that overlap with at least one other contact zone.

[0044] Furthermore, a gear cutting machine for machining pre-toothed workpieces by continuous generating grinding is specified, which is specifically designed to carry out the methods disclosed above.The gear cutting machine comprises: a tool spindle configured to clamp a grinding worm thereon in order to drive the grinding worm to rotate about a tool axis; a workpiece spindle configured to clamp a pre-toothed workpiece thereon in order to drive the pre-toothed workpiece to rotate about a workpiece axis; an axial slide configured to generate an axial feed movement of the tool spindle relative to the workpiece spindle along an axial feed direction having a component parallel to the workpiece axis; a shift slide configured to generate a shift movement along a shift direction parallel to the worm axis; and a machine control configured to carry out one of the methods disclosed above.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Preferred embodiments of the invention are described below with reference to the drawings, which are for illustrative purposes only and are not to be interpreted as limiting.

[0047] Figure 1 schematically illustrates a grinding worm in engagement with a gear-shaped workpiece;

[0048] Figure 2 illustrates, by way of example, a first embodiment of a method according to the present disclosure; Figure 3 illustrates, by way of example, a second embodiment of a method according to the present disclosure;

[0049] Figure 4 illustrates, by way of example, a third embodiment of a method according to the present disclosure;

[0050] Figure 5 illustrates, by way of example, the time course of the power consumption of the tool spindle, which drives the grinding worm, during a grinding stroke;

[0051] Figure 6A illustrates, by way of example, the grinding intensity during roughing when machining a plurality of workpieces with a grinding worm whose working area is completely covered in several passes;

[0052] Figure 6B illustrates, by way of example, the grinding intensity during finishing when machining a plurality of workpieces with a grinding worm whose working area is completely covered in several passes;

[0053] Figure 7 shows an example diagram in which the grinding intensity during roughing (vertical axis) and finishing (horizontal axis) is plotted for a large number of workpieces;

[0054] Figure 8 illustrates an example of a worm gear flank with a contact pad shown thereon;

[0055] Figure 9 illustrates an example of a section of a contact path with an associated current contact area;

[0056] Figure 10 illustrates an example of a worm gear flank with two contact zones that partially overlap;

[0057] Figure 11 illustrates an example of a worm gear flank with two contact zones that do not overlap;

[0058] Figure 12 illustrates an example of a virtual face gear with a contact path;

[0059] Figure 13 illustrates exemplary contact zones on a virtual face gear in a first shift strategy;

[0060] Figure 14 illustrates exemplary contact zones on a virtual face gear with a second shift strategy;

[0061] Figure 15A illustrates an example of a workpiece flank with a useful area;

[0062] Figure 15B illustrates an example of a worm gear flank with a quality-determining area;

[0063] Figure 16 illustrates an example of a section of a grinding worm 100 with a width-dependent modification; and

[0064] Figure 17 illustrates an example of a generating grinding machine. DESCRIPTION OF PREFERRED EMBODIMENTS

[0065] Kinematics of continuous generating grinding

[0066] Figure 1 illustrates the kinematics of continuous generating grinding. A grinding worm (i.e., a worm-shaped profiled grinding wheel) 100 rotates about a worm axis B. The grinding worm is in machining engagement with a gear-shaped workpiece 200 having a workpiece toothing 201 in the manner of a helical gear. The workpiece 200 rotates about a workpiece axis C. During a grinding stroke, the grinding worm 100 is moved relative to the workpiece 200 along an axial feed direction Z, which runs parallel or inclined to the workpiece axis, preferably across the entire width b.ws the workpiece toothing 201 (so-called axial feed movement). The position of the grinding worm 100 relative to the workpiece 200 along a radial feed direction X determines the amount of material removed during the grinding stroke. In order to engage new, unused areas of the grinding worm 100 with the workpiece 200, the grinding worm is continuously or discontinuously shifted relative to the workpiece 200 along a shift direction Y, which runs parallel to the worm axis B (so-called tangential shift movement).

[0067] All of the aforementioned linear movements (feed, axial feed movement, shift movement) are to be understood as relative movements, which can be generated either by a corresponding movement of the grinding worm in space and / or by a movement of the workpiece in space.

[0068] Machining of workpiece 200 is often performed in multiple grinding strokes, but can also be performed in a single grinding stroke. When multiple grinding strokes are performed, they often involve one or more roughing strokes followed by one or more finishing strokes. The roughing strokes are generally performed with a larger infeed in the X direction than the finishing strokes. In the following, the index r is used for roughing strokes, and the index f for finishing strokes.

[0069] For the following considerations, it is assumed that the grinding worm is dressable and is dressed after machining a number of workpieces. At least one working area can be defined on the grinding worm surface. This working area is an area of ​​the grinding worm surface that comes into contact with the workpieces between two dressing operations.

[0070] For the following considerations, it is assumed that both the workpiece and the grinding worm have a cylindrical basic shape. However, these considerations can also be applied to situations in which the workpiece and / or the grinding worm have a different basic shape, e.g., to situations in which a conical workpiece is being machined or in which a conical, barrel-shaped, or globoid-shaped grinding worm is used. The workpiece toothing can be straight or helical.

[0071] Use of a work area in multiple passes

[0072] In the proposed method, the work area is utilized between two dressing operations in several passes. In each pass, the contact paths along which the grinding worm engages the workpieces completely or partially cover the work area. To ensure optimal utilization of the grinding worm, it is advantageous if the work area is essentially completely covered by the contact paths in each pass.

[0073] The use of a work area in multiple passes is illustrated by way of example in Figure 2. Figure 2 schematically shows a grinding worm 100 in axial section. In this example, the grinding worm 100 has a single, contiguous work area 110. The grinding worm is first dressed by a first dressing process 151. Subsequently, workpieces 200 are machined using the work area 110 (machining process 152). During the machining process 152, the work area is used in multiple passes N, with only three passes N = 1, 2, 3 being illustrated in Figure 2. During each pass N, one or more grinding strokes are performed on one or more workpieces. During each pass, the work area 110 of the grinding worm 100 is preferably essentially completely swept away from contact with the workpieces.

[0074] At least one wear parameter is determined for each pass. At the end of each pass, a decision 153 is automatically made based on the wear parameter as to whether the work area 110 should be used again for another pass or dressed again. For example, a wear parameter value can be determined for each grinding stroke, and the decision can be made based on the distribution of the wear parameter values ​​across all grinding strokes of the pass.

[0075] In the present example, the wear parameter values ​​after the third pass indicate that the working area 110 is worn, and the grinding worm is dressed again by a dressing process 154. In practice, however, the number of passes after which a working area is considered worn can be considerably greater than three.

[0076] Non-continuous work area

[0077] The working area 110 of the grinding worm does not need to extend continuously across the grinding worm surface. This is illustrated by way of example in Figure 3. In this example, the grinding worm 100 has a roughing area 111 and a finishing area 112, which together define the entire working area of ​​the grinding worm 100. Each workpiece is machined in at least one roughing stroke with the roughing area 111. Subsequently, a shift jump into the finishing area 112 occurs, and the workpiece is machined in at least one finishing stroke with the finishing area 112. After that, a shift jump back to the roughing area 111 occurs before the next workpiece is machined. During the machining of the workpieces, the entire roughing area 111 and the entire finishing area 112 are swept over by contact paths with the workpieces in each pass N.The respective area is not swept over continuously, but there are continuous shift jumps and shift regressions between the roughing area 111 and the finishing area 112.

[0078] For each roughing stroke, a roughing wear parameter can be determined that characterizes the wear condition of the roughing area, and for each finishing stroke, a finishing wear parameter can be determined that characterizes the wear condition of the finishing area. At the end of each pass, a decision 153 is automatically made based on the values ​​of the roughing and finishing wear parameters as to whether the working area, which is composed of the roughing area 111 and the finishing area 112, should be used again for another pass or dressed again.

[0079] In this example, roughing area 111 and finishing area 112 conceptually form sub-areas of a single work area. The decision as to whether the work area will be used for another pass is therefore made jointly for roughing area 111 and finishing area 112. As soon as the wear parameters indicate that at least one of these sub-areas is worn, the entire grinding worm is redressed.

[0080] The roughing and finishing sections can also be arranged differently relative to each other, and in particular, they can overlap. For example, a portion of the finishing section can initially be used for finishing workpieces and subsequently for roughing additional workpieces, so that this portion also simultaneously becomes part of the roughing section. It is also conceivable to arrange a plurality of roughing and finishing sections alternately along the grinding worm axis. An example of such an arrangement will be discussed in more detail below.

[0081] Multiple work areas

[0082] The grinding worm can have more than one working area. This is illustrated by way of example in Figure 4. Again, the grinding worm 100 has a roughing area 111 and a finishing area 112. Unlike in the previous example, however, the roughing area 111 and the finishing area 112 in this example do not jointly define a single working area of ​​the grinding worm 100; instead, each of these areas is conceptually considered a separate working area.

[0083] As in the previous example, each workpiece is machined in at least one roughing stroke with the roughing area 111 and in at least one finishing stroke with the finishing area 112. A roughing wear parameter is determined for each roughing stroke, and a finishing wear parameter is determined for each finishing stroke. Unlike in the previous example, the decision 153 as to whether a working area 110 is used again for another pass or dressed again is now made separately for the roughing area 111 and the finishing area 112, respectively, since these areas are considered separate working areas.

[0084] This procedure is particularly useful when the grinding worm has multiple roughing and / or finishing sections. For example, a grinding worm may have two roughing sections and one finishing section. The process can be controlled in such a way that both roughing sections are expected to be worn before the single finishing section is worn. The above-mentioned procedure then enables an automatic decision as to when one of the two roughing sections is considered worn and should no longer be used. On the other hand, the above-mentioned procedure can also be used to determine whether, contrary to expectations, the finishing section is worn before both roughing sections are worn.

[0085] The considerations from the above examples can be applied to a variety of other processing situations.

[0086] The decision 153 as to whether a working area is to be considered worn is made based on at least one wear parameter. In particular, an intensity measure for a grinding intensity during at least one grinding stroke can serve as a wear parameter. This is explained in more detail below with reference to Figure 5.

[0087] This figure shows, as an example, the time profile of the power consumption P(t) of a tool spindle, which drives the grinding worm 100 to rotate, during a single grinding stroke. Rapid fluctuations in power consumption, e.g., due to the constantly changing contact conditions between the grinding worm and the workpiece, are not taken into account in this illustration. In practice, such rapid fluctuations can be filtered out by suitable filtering, e.g., with a low-pass filter.

[0088] The power consumption initially increases continuously as the worm enters the gear teeth, then levels off and decreases continuously again during the run-out. The maximum power consumption is referred to below as grinding intensity I. s designated.

[0089] The power consumption of the tool spindle is an example of a performance indicator that characterizes the instantaneous grinding performance. Instead of power consumption, the current drawn by the tool spindle can also serve as a performance indicator, which ultimately corresponds to a torque measurement and thus approximately a measurement of the cutting force. At constant voltage, the current drawn is proportional to the power, or at constant speed, the torque is proportional to the power. Therefore, the current can also at least approximately characterize the grinding performance. The grinding intensity I sis a scalar quantity calculated from the temporal progression of the performance indicator and characterizes the grinding performance during a grinding stroke. Instead of the maximum of the performance indicator, another scalar quantity can also be used as the grinding intensity, e.g., the integral or the (possibly appropriately weighted) temporal mean of the performance indicator.

[0090] The grinding performance depends on a number of process parameters, in particular on the infeed between the grinding worm and the workpiece along the radial infeed direction, on the speed of the axial feed movement (axial feed rate), on the speeds of the tool and workpiece spindles, on the geometry of the grinding worm, on the geometry of the workpiece and on the tribological conditions in contact (lubricant, surface quality of the worm and material, as well as materials).

[0091] However, grinding performance is also influenced by the wear condition of the grinding worm. For example, a partially worn grinding worm is not able to remove the same amount of material during a single grinding stroke as a freshly dressed grinding worm. As a result, increasing wear on the grinding worm can lead to a decrease in cutting performance.

[0092] For given process parameters, the grinding intensity I s thus serve as an indicator of the wear condition of the grinding worm in the currently used area of ​​the grinding worm.

[0093] Grinding intensity when using a grinding worm in several passes

[0094] When a work area is swept over in multiple passes by the contact paths between the grinding worm and the workpiece, the work area becomes increasingly worn from pass to pass. This is reflected in the fact that the wear parameter, e.g., the grinding intensity, changes from pass to pass during the machining of the workpieces. This will be explained below using an example with reference to Figures 6A and 6B. In this example, it is assumed that each workpiece is machined with a single roughing stroke and a single finishing stroke. During the roughing stroke and the finishing stroke, shifting occurs continuously. Roughing is performed with a roughing section, finishing with a finishing section, and the roughing section does not overlap with the finishing section, similar to the situation in Figures 3 and 4.It is also assumed that after finishing, a shift return occurs exactly at the point in the roughing area where the previous roughing stroke ended. This means that each roughing stroke sweeps over a portion of the roughing area that is slightly offset from the previous workpiece, and each finishing stroke sweeps over a portion of the finishing area that is also slightly offset from the previous finishing stroke.

[0095] The roughing and finishing areas are again used in several passes, as already explained in Figures 3 and 4. During each pass, the entire roughing or finishing area is covered while several workpieces are machined.

[0096] Figure 6A shows schematically the grinding intensity I for such a procedure. r(n) during roughing (roughing intensity) when machining a plurality of workpieces n, in Figure 6B the grinding intensity I f (n) during finishing (finishing intensity), where the grinding worm was freshly dressed before machining the first workpiece.

[0097] Due to the increasing wear in the roughing area, the roughing intensity gradually decreases from pass to pass. In the present example, the opposite is true for finishing: the finishing intensity gradually increases from pass to pass. The reason for this behavior is that the grinding worm in the roughing area wears down increasingly from pass to pass. As a result, the metal removal rate in the roughing area decreases from pass to pass, and with unchanged infeed, the finishing area must consequently deliver an increasingly greater metal removal rate. In the present example, this indicates that the process is being managed in such a way that wear in the finishing area remains low, so that the finishing area is actually able to deliver this increasing metal removal rate without itself wearing too much.Otherwise, the finishing intensity might also decrease from pass to pass. To decide whether to use the roughing and / or finishing area for another pass, the following procedure can be used in this example. For each pass N, the statistical distribution of the roughing intensity values ​​I is calculated. r (n) and the finishing intensity I f (n) one position parameter I r N or I f N determined, e.g., the arithmetic mean or the median. The location parameter I r N The roughing intensity is set for each pass with a roughing threshold I r thr In addition, the position parameter the finishing intensity for each pass with a finishing threshold I f thr compared. If the position parameter I r N the roughing intensity is less than the roughing threshold I r thr and at the same time the position parameter I f Nthe finishing intensity is greater than the finishing threshold I f thr the grinding worm is redressed.

[0098] Depending on the process control, the dressing decision can also be made based on other criteria. Instead of taking both the roughing intensity and the finishing intensity into account, just one of these intensities can be considered. Instead of a position parameter, or in addition to it, another statistical parameter of the distribution of the grinding intensity values ​​can be determined and taken into account for the dressing decision, e.g. a fluctuation measure such as the standard deviation or the interquartile range. This takes into account that severe wear of the grinding wheel can, under certain circumstances, lead to a larger fluctuation in the grinding intensity from stroke to stroke. In other embodiments, the dressing decision can take into account the frequency with which the grinding intensity has fallen below or exceeded a threshold value during roughing or finishing per pass.

[0099] Figure 7 shows an example of a correlation between roughing intensity I r (n) and finishing intensity I f (n). For a variety of workpieces n, the finishing intensity I f (n) and along the vertical axis the roughing intensity I r (n). These values ​​show a clear correlation. In the present example, this correlation is negative, meaning that as the roughing intensity decreases, the finishing intensity increases. In other machining situations, however, this correlation can also be positive, meaning that as the roughing intensity decreases, the finishing intensity can also decrease. The type of correlation observed depends on the process parameters. Threshold values ​​l r thr and l f thr the data points can In this example, four quadrants are assigned. As long as the roughing intensity I r (n) and finishing intensity I f(n) in the upper left quadrant (J r (n) > I rtthr , l f( n ) < If,thr), the grinding worm is considered not to be worn out. Conversely, if the data points are in the lower right quadrant (I r (n) < I rtthr , l f( n ) > If,thr), the grinding wheel is considered worn. Data points in the other two quadrants indicate that a wear condition worthy of observation has been reached.

[0100] The threshold values ​​I r thr and I f thr can be determined empirically by directly determining the wear condition for a grinding worm after machining a certain number of workpieces (e.g. by measuring the gear teeth on workpieces that were machined with this grinding worm), and by determining the corresponding values ​​of the roughing and finishing intensity for each wear condition.

[0101] However, it is also conceivable to set the threshold values ​​I r thr and I f thr automatically by determining the roughing and finishing intensity for a large number of workpieces manufactured under comparable machining conditions in series production, without knowing the corresponding wear condition of the grinding worm. In series production, workpieces are usually randomly inspected for machining errors. Therefore, it can be assumed that, statistically speaking, the majority of machining operations resulted in workpieces that were manufactured within the tolerances, and that the grinding worm could therefore not be considered worn during the machining of the majority of the workpieces. The threshold values ​​can be automatically defined on this basis, for example, as percentiles. For example, the threshold value I r thrbe defined as the roughing intensity value that is exceeded by 98% of the workpieces.

[0102] The above considerations can easily be applied to situations in which more than one roughing and / or finishing stroke or only a single grinding stroke is used. on the grinding worm

[0103] When roughing the first workpieces after dressing, a shift strategy of the type discussed above often initially results in a significant decrease in roughing intensity, while the roughing intensity changes only slightly when machining subsequent workpieces in the same pass. Conversely, a significant increase in finishing intensity is often observed for the first workpieces after dressing.

[0104] The reason for this behavior will be examined in more detail below.

[0105] During the helical generating motion between the grinding worm and the workpiece, at least one flank of a grinding worm thread (worm thread flank) and at least one flank of the workpiece toothing (workpiece flank) are in approximately point contact. Due to the rotation of the grinding worm 100 and the workpiece 200, the contact point between the worm thread flank and the workpiece flank continuously moves over the respective worm thread flank during the machining of an individual workpiece flank. The sequence of contact points on the grinding worm is referred to below as the contact path. Figure 8 illustrates such a contact path 102 on an individual worm thread flank 101. The contact path 102 has a conical helical shape. The resulting sequence of contact points on the workpiece flank is referred to below as the contact track for ease of differentiation.

[0106] However, when a finite amount of stock is removed, the contact between grinding worm 100 and workpiece 200 is not exactly point-like. Rather, a finitely extended contact area exists at any given time, in which the grinding worm penetrates the workpiece flank subject to stock removal. Figure 9 schematically illustrates a section of a contact path 102 with a contact area 103 on the worm thread flank. The contact area 103 generally has an elongated shape along the contact path 102 and is asymmetrical across the contact path.

[0107] The extent of the contact area 103 transverse to the direction along which the contact path runs is referred to below as the cutting width a p The cutting width a pdepends, among other things, on the macrogeometry of the workpiece, the macrogeometry of the grinding worm, the removed stock on the workpiece flank, and the axial feed per workpiece revolution. It can vary along the contact path. For example, with an involute gear, the engagement ratios change along the involute, which also influences the cutting width. As a result, the contact path width can vary along its length.

[0108] Contact zones during continuous shift movement

[0109] Without shift movement, the grinding worm performs the cutting work exclusively along a single contact path 102. When a continuous shift movement is initiated, this contact path is continuously screwed along the worm thread flank and thus axially to the grinding worm during the course of a grinding stroke, so that the contact path moves over the worm thread flank 101.

[0110] In this way, during a grinding stroke, a total area of ​​the worm gear flank engages the workpiece, which is referred to as the "contact zone." The contact zone that engages the workpiece during a single grinding stroke essentially has a conical helical shape, similar to a single contact path, but due to the superimposed shift movement, it is wider than a single contact path. Without shift movement, the contact zone corresponds to a single contact path.

[0111] Figure 10 shows, in a highly schematic form and not to scale, two contact zones 104, 104' on a worm gear flank 101. These contact zones engage during the machining of successive workpieces during a selected grinding stroke (here specifically during the roughing stroke) when proceeding according to the shift strategy described above. With such a shift strategy, the roughing stroke of the subsequent workpiece begins at the exact point in the Y direction where the roughing stroke of the previous workpiece ended. In this case, the two contact zones 104, 104' overlap due to the finite width of the contact paths. The width of the overlap area approximately corresponds to the width of a single contact path, i.e., the cutting width a p , when roughing.

[0112] In practice, this means that the wear condition of the grinding worm in the contact zone 104 influences the machining conditions in the subsequent grinding stroke, which is carried out with the overlapping contact zone 104'.

[0113] Variable grinding intensity with conventional shift strategies

[0114] Based on the above considerations, it is clear why the grinding intensity with shift strategies of the type described above is initially not constant from workpiece to workpiece, even if all process parameters remain unchanged. The reason for this behavior is that the contact zones used in the machining of a subsequent workpiece partially overlap with the contact zones used in the machining of the previous workpiece. With shift strategies of the type described above, the amount by which the grinding worm is shifted during each roughing or finishing stroke is usually significantly smaller than the cutting width measured along the worm axis. Figuratively speaking, this means that the grinding worm gradually builds up wear after dressing: The first workpiece is machined with a contact zone that has not yet experienced any wear.The second workpiece is machined with a partially overlapping contact zone, with a larger portion of this contact zone having already been used to machine the first workpiece and a smaller portion having not yet experienced any wear. For the third workpiece, part of the contact zone has already been used to machine two previous workpieces, another part has only been used to machine a single previous workpiece, and another part has not yet experienced any wear, and so on. Each subsequent workpiece is thus machined with a contact zone increasingly subject to wear until equilibrium is reached and the wear level of the worm over one grinding stroke is the same in each contact zone as in the previous contact zone.

[0115] Increasing wear in the contact zone during roughing is reflected in a decreasing roughing intensity I r, because the cutting performance decreases with increasing wear. This leads to an increasing finishing intensity because more cutting work must be performed during finishing.

[0116] Grinding with decoupled contact zones

[0117] To prevent the wear condition of a specific contact zone from being influenced by the wear condition of other, partially overlapping contact zones, it is possible to decouple the contact zones from each other so that they no longer overlap. In the shift strategy described above, this can be achieved, for example, by reducing the shift offset.

[0118] This is illustrated by way of example in Figure 11, which shows two contact zones 104, 104' that engage during the roughing stroke when machining successive workpieces if the shift recess is suitably reduced. The contact zones 104, 104' now extend side by side across the worm thread flank 101 without overlap, i.e., they are decoupled from each other.

[0119] The amount by which the shift recess must be reduced in order to decouple the contact zones 104, 104' in the example of Figure 11 can be clearly derived by a geometric consideration.

[0120] For this purpose, a reference profile in the axial section of the grinding worm is first considered, which can be brought into engagement with the gear teeth of the grinding worm and the workpiece produced with it in such a way that these gear teeth roll on it without deviation. Figure 12 schematically shows such a reference profile 130. The left flanks of the reference profile 130 have a profile angle α. An engagement path for the left flanks can be drawn above the reference profile. The engagement path runs perpendicular to the left flanks of the reference profile. The profile angle α corresponds to the pressure angle in the axial section of the grinding worm. However, instead of the engagement path, Figure 12 shows a band with the width a p This band symbolizes the contact path. At the points where the contact path intersects the respective left flank, the contact path has the width a p, measured perpendicular to the direction along which the contact path runs. Since the contact path on the grinding worm flank has a conical helical shape and thus runs predominantly in the circumferential direction of the grinding worm, the width of the contact path, measured perpendicular to the contact path direction, corresponds in good approximation to its width measured in the vertical direction of the respective left flank. Measured along the worm axis, however, the width of the belt is approximately a p / sin a. This value is referred to below as the "width of the contact path, measured along the grinding worm axis." A similar calculation can also be made for the right-hand flanks.

[0121] This means that if two consecutive contact zones are not to overlap, there must be a distance of at least Ay > a between the shift position of the grinding worm at the end of the machining operation carried out with the first contact zone and the shift position at the beginning of the machining operation carried out with the second contact zone. p / sina, measured along the screw axis.

[0122] The above consideration is indeed simplified, since it does not take into account, for example, the screw pitch, a cutting width a that changes between the head and foot area of ​​the screw thread p and possible modifications of the screw flanks are taken into account, but it provides a practical approximate solution and can be easily refined accordingly if necessary.

[0123] Calculating the cutting width

[0124] The cutting width a pcan be calculated approximately analytically or determined numerically by a penetration calculation. One possibility for analytical calculation is disclosed in W02021048027A1. According to this document, a p approximately calculated from the technology parameters and gearing parameters as follows:

[0125] Here, a Pimax a maximum expected cutting width at a given rolling length and at a given nominal allowance for large axial feeds, l k the contact length of the chip zone and s z the axial feed per revolution of the workpiece.

[0126] The maximum cutting width can be calculated as follows:

[0127] Here, L y the rolling length and q t the nominal measurement.

[0128] For the contact length l k the following analytical relationship can be derived:

[0129] Here r denotes pSS eq the equivalent grinding worm radius. The equivalent grinding worm radius r pSS eq results from the real grinding worm radius r pSS as follows: r p ss,eq = r P ss / Sin a

[0130] Here, a denotes the pressure angle of the grinding worm gear in axial section.

[0131] As a result, it is possible to adjust the cutting width a p along a contact path for each machining situation. Instead of the analytical calculation, a penetration calculation can also be performed to determine the cutting width a p along a contact path.

[0132] As explained above, the cutting width can vary along the contact path. To achieve reliable decoupling of the contact zones even with variable cutting widths, it is advisable to proceed as follows: The nominal allowance is the maximum expected allowance on all teeth of the gearing that is removed from the tooth flanks at a given infeed. The cutting width a p along a contact path for this nominal dimension. The width a p 0 of the contact path, measured in the profile height direction of the worm thread flank, the maximum value of the cutting width a p along the contact path. The width of the contact path, measured along the screw axis, is then determined by dividing this value by sin:

[0133] Ay > a p 0 / sin a. Contact zones

[0134] If each workpiece is not machined with a single stroke, but with at least one roughing stroke and at least one finishing stroke, various shift strategies are conceivable that take the above considerations into account and can achieve decoupling of the contact zones. Two possible shift strategies are explained below as examples.

[0135] A first shift strategy is illustrated in Figure 13. The figure, similar to Figure 8, depicts contact zones on a reference profile. However, to maintain clarity, the reference profile is not shown here, and the shape and course of the contact zones are shown in a highly compressed manner compared to Figure 12. Figure 13 can also be understood as a representation of a (unfolded) worm thread flank 101, in which the horizontal axis represents the width position y. ss along the grinding worm axis and the vertical axis the height position hss or indicates the pitch path along the worm thread flank.

[0136] With this shift strategy, the working area 110 of the grinding worm is divided into a roughing area 111 and a finishing area 112, as in the previous examples. When machining the first workpiece, a roughing stroke is initially performed with the roughing area 111. During the roughing stroke, shifting occurs continuously in the Y direction. During the roughing operation, the contact path moves along the grinding worm axis. As a result, the roughing stroke occurs with a roughing contact zone whose width, measured along the grinding worm axis or in the Y direction, corresponds to the amount of the shift feed during the roughing operation plus the width of a single contact path. The amount of the shift feed during the roughing operation is shown in the figure as y. r the width of a single contact path along the grinding worm axis is called Ayr . Overall, a roughing contact zone is used during roughing, which has a width y r + Ay r , measured along the screw axis.

[0137] After the end of the roughing operation of the first workpiece in the roughing area 111, a shift jump into the finishing area 112 takes place by a (positive) amount Ay sl to the location where the finishing contact of the first workpiece begins. Continuous shifting also occurs during the finishing stroke, whereby the shift speed can be the same or different from the roughing stroke. The total shift feed during the finishing stroke is yy, and the width of a single contact path along the screw axis during finishing is Ay^. Generally, the width of the contact path during finishing will be smaller than during roughing due to the smaller infeed. Overall, a finishing contact zone with a width of y f+ Ay^, measured along the screw axis.

[0138] After the end of the finishing operation, a reduced shift return occurs by a (negative) amount Ay s2 This amount is chosen so that: Ay sl + y f + Ay s2 > Ay r In this way, the roughing contact zone of the next workpiece is decoupled from the roughing contact zone of the previous workpiece.

[0139] A second shift strategy is illustrated in Figure 14. In the shift strategy outlined here, a first workpiece is machined with a grinding worm area 121, a second workpiece with an adjacent grinding worm area 122, etc. For each workpiece, a roughing stroke with a roughing contact zone is performed, followed by a finishing stroke with a finishing contact zone.

[0140] To prevent the roughing contact zone and the finishing contact zone of a workpiece from overlapping, an additional shift movement (shift jump) is performed between the end of the roughing cut and the beginning of the finishing cut of each workpiece. The amount Ay sl This additional shift movement is chosen to be sufficiently large that the first contact path at the beginning of the finishing operation just no longer overlaps with the last contact path at the end of the roughing operation. This is the case if the worm has been moved at least by the amount Ay between the end of the roughing operation and the beginning of the subsequent finishing operation. r is shifted. The contact zones of the roughing stroke and the finishing stroke are thus decoupled from each other.

[0141] After the end of the finishing operation for the first workpiece, another additional shift movement is carried out by an amount y s2, which is at least Ay^, before the roughing contact of the subsequent second workpiece begins. This decouples the roughing contact zone for the second workpiece from the finishing contact zone for the first workpiece.

[0142] If more than one roughing stroke and / or more than one finishing stroke are performed, the corresponding contact zones are preferably also decoupled from each other. If only a single machining stroke is performed per workpiece, the same procedure can be followed.

[0143] Many other shift strategies with decoupled contact zones are possible.

[0144] Standardization of the wear parameter

[0145] The wear parameter can be appropriately standardized to improve comparability of the wear parameter for different conditions. If the wear parameter is based on a performance indicator, the performance indicator or the grinding intensity calculated from it can be appropriately standardized.

[0146] The normalization operation is preferably based on a model that describes the expected dependence of the process performance on geometric parameters of the grinding worm and the workpiece, as well as on the setting parameters of the generating grinding machine. The process performance model can, in particular, be based on a force model that describes the expected dependence of the cutting force acting at the contact point between the grinding worm and the workpiece on geometric parameters of the finishing tool, geometric parameters of the workpiece, and setting parameters of the finishing machine.

[0147] The normalization operation can, for example, involve multiplying the measured values ​​of the performance indicator or derived quantities by a normalization factor. However, more complex normalization operations are also conceivable. The normalization factor can, in particular, be an inverse intensity quantity calculated using the process performance model for the specific processing situation, or a quantity derived from it. For example, the process performance model used in W02021048027A1 can be used.

[0148] Preferably, the normalization factor is recalculated after each dressing operation, and the same normalization factor is applied to all values ​​of the performance indicator or a variable calculated therefrom that were determined between two dressing operations.

[0149] Consideration of the useful area of ​​the gear to be manufactured

[0150] Typically, when a finished workpiece is used in a gearbox, not the entire left and right flanks of the workpiece engage with a mating toothing, but only a specific area of ​​the respective flank. This area is referred to in this document as the "usable area." It can be determined, for example, by measuring the contact pattern of the toothing under real operating conditions.

[0151] Fig. 15A illustrates, by way of example, a workpiece flank 210 of a gear with the associated useful area 211. The useful area 211 does not extend over the entire width of the workpiece flank in the workpiece width direction z. ws . It also does not extend over the entire height of the workpiece flank in the workpiece height direction h ws .

[0152] In this case, one goal of workpiece machining may be to achieve the highest possible gear quality within the working area, while the quality of the gear outside the working area may be of secondary importance. In this case, it is advantageous to determine the area of ​​the contact zones on the worm gear flank that come into contact with the working area during gear machining and thus determine quality.

[0153] Fig. 15B shows, by way of example, such a quality-determining region 105 of a contact zone 104 on a worm thread flank 101. The quality-determining region can be determined, for example, by a machining simulation, as is well known to those skilled in the art, or by machining tests.

[0154] The advantages explained above can also be achieved if, instead of the entire contact zone, only the quality-determining area of ​​the contact zone is arranged without overlap with all other contact zones. In this case, the wear condition in the quality-determining area is not influenced by the wear condition of all other contact zones. A contact zone in which only the quality-determining area is arranged without overlap with all other contact zones can therefore also be considered a "decoupled" contact zone, and all of the above considerations apply analogously to such decoupled contact zones.

[0155] As explained above, for a cylindrical grinding worm and a cylindrical workpiece, the contact zone on the worm flank without shift movement corresponds to a single contact path. The contact path can therefore be considered the area on the worm flank in which the worm flank comes into cutting engagement with the workpiece during a grinding stroke if no shift movement occurs. When a shift movement occurs, each contact zone no longer corresponds to a single contact path, but is composed of a multitude of partially overlapping contact paths shifted relative to one another along the tool width direction.

[0156] If a shift movement is performed during a grinding stroke, generally only a portion of the contact paths of a contact zone will come into contact with the useful area of ​​the workpiece flank, and these contact paths will generally not come into contact with the useful area along their entire length. Therefore, generally only a portion of the contact paths along a portion of the respective contact path form the quality-determining area of ​​the contact zone. If, on the other hand, no shift movement is performed during the grinding stroke, each contact zone with a cylindrical workpiece and cylindrical tool corresponds to exactly one contact path. In this case, a central section of the contact path usually forms the quality-determining area of ​​the contact zone. If, on the other hand, the entire workpiece flank is considered the useful area, all contact paths along their entire length form the quality-determining area of ​​the contact zone, i.e.the entire contact zone becomes quality-determining. Modification of the workspace

[0157] Figure 16 shows, by way of example, a section of a grinding worm 100 in axial section, which has a worm thread flank 101 with a modification that varies along the worm axis B. Specifically, this grinding worm has a modification of the pressure angle a that varies along the worm axis B. Many other types of modifications that vary along the worm axis B are possible. Structure of a generating grinding machine

[0158] Figure 17 shows an example of a gear grinding machine 1 suitable for performing the methods described above. This gear grinding machine is also referred to below as the "machine."

[0159] The machine 1 has a machine bed 11 on which a tool holder 12 is guided so as to be displaceable along the radial feed direction X. The tool holder 12 carries an axial slide 13 which is guided so as to be displaceable relative to the tool holder 12 along the axial feed direction Z. A grinding head 14 is mounted on the axial slide 13 and can be pivoted about a pivot axis running parallel to the X direction (the so-called A axis) in order to adapt to the helix angle of the gear to be machined. The grinding head 14, in turn, carries a shift slide on which a tool spindle 15 can be displaced relative to the grinding head 14 along the shift direction Y. The grinding worm 100 is clamped on the tool spindle 15. The grinding worm 100 is driven by the tool spindle 15 to rotate about a tool axis B.

[0160] The machine bed 11 further supports a pivotable workpiece carrier 20 in the form of a turret, which can be pivoted about a pivot axis C3 between at least three positions. Two identical workpiece spindles are mounted diametrically opposite one another on the workpiece carrier 20, of which only one workpiece spindle 21 is visible in Figure 16. A workpiece can be clamped onto each of the workpiece spindles and driven to rotate about a workpiece axis C1 or C2. The workpiece spindle 21 visible in Figure 16 is in a machining position in which a workpiece 200 clamped thereon can be machined with the grinding worm 100. The other workpiece spindle, offset by 180° and not visible in Figure 16, is in a workpiece change position in which a finished workpiece can be removed from this spindle and a new blank can be clamped onto it.A dressing device 30 is mounted offset by 90° to the workpiece spindles.

[0161] Machine 1 thus has a multitude of moving components, such as slides or spindles, which are controlled by corresponding drives. These drives are often referred to in the technical world as "NC axes," "machine axes," or simply "axes." This term sometimes also includes the components driven by the drives, such as slides or spindles.

[0162] Machine 1 further comprises a plurality of sensors. By way of example, only two sensors 18 and 19 are schematically indicated in Figure 1. Sensor 18 is a vibration sensor for detecting vibrations of the housing of grinding spindle 15. Sensor 19 is a position sensor for detecting the position of axial slide 13 relative to tool carrier 12 along the Z direction. In addition, machine 1 comprises a plurality of other sensors. These sensors include, in particular, further position sensors for detecting the actual position of a linear axis, rotation angle sensors for detecting the rotational position of a rotary axis, current sensors for detecting the drive current of a rotary axis, and further vibration sensors for detecting vibrations of a driven component. All driven axes of machine 1 are digitally controlled by a machine controller 40.The machine control system 40 comprises several axis modules 41, a control computer 42, and an operator panel 43. The control computer 42 receives operator commands from the operator panel 43 as well as sensor signals from various sensors of the machine 1 and calculates control commands for the axis modules 41 from these. It also outputs operating parameters to the operator panel 43 for display. The axis modules 41 each provide control signals for a machine axis at their outputs. In this way, all of the aforementioned movements can be controlled, in particular radial infeed, axial feed movement, and shift feed movement.

[0163] A monitoring device 44 is connected to the control computer 42.

[0164] The monitoring device 44 can be a separate hardware unit assigned to the machine 1. It can be connected to the control computer 42 via a known interface, e.g., via the well-known Profinet standard, or via a network, e.g., via the Internet. It can be physically part of the machine 1 or it can be located spatially remote from the machine 1.

[0165] During operation of the machine, the monitoring device 44 receives a large number of different measurement data from the control computer 42. Among the measurement data received by the control computer are sensor data that were recorded directly by the control computer 42 and data that the control computer 42 reads from the axis modules 41, e.g. data that describe the target positions of the various machine axes and the target current consumption in the axis modules.

[0166] The monitoring device 44 can optionally have its own analog and / or digital sensor inputs to directly receive sensor data from additional sensors as measurement data. The additional sensors are typically sensors that are not directly required for controlling the actual machining process, e.g., acceleration sensors for detecting vibrations or temperature sensors.

[0167] The monitoring device 44 can alternatively be implemented as a software component of the machine control system 40, which is executed, for example, on a processor of the control computer 42, or it can be embodied as a software component of the service server 45, described in more detail below. The monitoring device 44 communicates with the service server 45 directly or via the Internet and a web server 47. The service server 45, in turn, communicates with a database server 46 with database DB. These servers can be located remotely from the machine 1. The servers do not need to be a single physical unit. In particular, the servers can be implemented as virtual units in the so-called "cloud."

[0168] The service server 45 communicates with a mobile device 48 via the web server 47. The device 48 can, in particular, run a web browser with which the received data and its analysis are visualized. The device does not need to meet any special computing power requirements. For example, the device can be a desktop computer, a notebook computer, a tablet computer, a mobile phone, etc.

[0169] Processing of workpieces

[0170] For the sake of completeness, the following describes how workpieces are typically machined using machine 1.

[0171] To machine a workpiece (blank) 200 that has not yet been machined, the workpiece 200 is clamped by an automatic workpiece changer onto the workpiece spindle located in the workpiece change position. The workpiece change takes place in parallel with the machining of another workpiece on the other workpiece spindle located in the machining position. Once the newly machined workpiece 200 is clamped and machining of the other workpiece is complete, the workpiece carrier 20 is pivoted 180° about the C3 axis so that the spindle with the newly machined workpiece 200 moves into the machining position. Before and / or during the pivoting process, a centering operation is performed using the assigned centering probe. For this purpose, the workpiece spindle 21 is rotated, and the position of the tooth gaps of the workpiece 200 is measured using a centering probe.The rolling angle is determined on this basis.

[0172] When the workpiece spindle carrying the workpiece 200 to be machined has reached the machining position, the workpiece 200 is brought into collision-free engagement with the grinding worm 100 by moving the tool carrier 12 along the X-axis. The workpiece 200 is then machined by the grinding worm 100 in rolling engagement. This is achieved through one or more grinding strokes, for example, one or more roughing strokes followed by one or more finishing strokes. During each grinding stroke, the grinding worm 100 is continuously advanced along the Z-axis relative to the workpiece 200 (so-called axial stroke) with a constant or variable radial X-feed. During the machining stroke, the tool spindle 15 can be slowly and continuously shifted along the shift axis Y. Alternatively or additionally, a shift jump can occur between two grinding strokes.

[0173] At the same time as the workpiece is being machined, the finished workpiece is removed from the other workpiece spindle and another blank is clamped onto this spindle.

[0174] To dress the grinding worm, the workpiece carrier 20 is pivoted by ±90° so that the dressing device 30 is positioned opposite the grinding worm 100. The grinding worm 100 is then dressed with the dressing tool 33.

[0175] LIST OF REFERENCE SYMBOLS

[0176] 100 grinding worm

[0177] 101 worm gear flank

[0178] 102 Contact path

[0179] 103 Contact area

[0180] 104 Contact zone

[0181] 104' contact zone

[0182] 105 quality-determining area

[0183] 110 work area

[0184] 111 Roughing area

[0185] 112 Finishing area

[0186] 121 Grinding worm area for first workpieces

[0187] 122 Grinding worm area for second workpieces

[0188] 110 grinding worm

[0189] 151 first dressing process

[0190] 152 Processing process

[0191] 153 Decision

[0192] 154 second dressing process

[0193] 200 workpieces

[0194] 201 Workpiece gearing

[0195] 210 Flank of the workpiece toothing

[0196] 211 usable area

[0197] 1 generating grinding machine

[0198] 11 Machine bed

[0199] 12 tool carriers

[0200] 13 axial slides

[0201] 14 Grinding head

[0202] 15 tool spindle

[0203] 18 Vibration sensor

[0204] 19 Position sensor

[0205] 20 workpiece carriers

[0206] 21 Workpiece spindle 41 Axis module

[0207] 42 tax calculators

[0208] 43 Control panel

[0209] 44 Monitoring device

[0210] 45 service servers

[0211] 46 Database

[0212] 47 web servers

[0213] 48 mobile devices

[0214] B Worm axis

[0215] C Workpiece axis

[0216] X radial feed direction

[0217] Y shift direction

[0218] Z axial feed direction a pressure angle b ws Workpiece width a p Cutting width y r Shift amount during roughing yy Shift amount during finishing

[0219] Ay r Width of a contact path along the screw axis during roughing

[0220] A y Width of a contact path along the screw axis during finishing

[0221] Ay slAmount of the shift jump between roughing and finishing

[0222] Ay s2 Amount of the shift (back) jump between finishing and next roughing

[0223] N passage

[0224] P Power consumption of the grinding spindle

[0225] P max Maximum power consumption

[0226] I s Grinding intensity

[0227] I r Grinding intensity during roughing

[0228] If grinding intensity during finishing

[0229] I r thr Threshold value of grinding intensity during roughing

[0230] Jf.thr Threshold value of grinding intensity during finishing t Time n Number of workpieces

[0231] N pass in arbitrary units

Claims

PATENT CLAIMS 1. A method for machining pre-toothed workpieces (200) by continuous generating grinding with a grinding worm (100) rotating about a worm axis (B), wherein the grinding worm (100) has at least one working area (110; 111, 112) in which it comes into machining engagement with the workpieces (200), the method comprising: Dressing (151) of the grinding worm (100); and Machining (152) the workpieces (200) in machining engagement with the working area (110; 111, 112) after the grinding worm (100) has been dressed, wherein the working area (110; 111, 112) is swept over by contact paths between the grinding worm (100) and the workpieces (200) during the machining of the workpieces (200), characterized in that the working area (110; 111, 112) is swept over by the contact paths several times in one pass (N) each, that for each pass (N) at least one wear parameter ( / r ; If) is determined, which characterizes a wear condition of the working area (110; 111 , 112), and that depending on the at least one wear parameter ( / r ; If) a decision (153) is automatically made as to whether the working area (110; 111 , 112) is used for a further pass before it is trained again.

2. Method according to claim 1 , wherein the wear parameter ( / r ; I f ) is based on a performance indicator for a grinding performance during the respective pass (N).

3. Method according to claim 1 or 2, wherein in determining the wear parameter ( / r ; I f ) a normalization operation is carried out to determine the wear parameter ( / r ; If) to be normalized, wherein the normalization operation depends on at least one process parameter, wherein the process parameter is at least one geometric parameter of the grinding worm, at least one geometric parameter of the workpiece and / or at least one setting parameter of the machine tool, wherein the standardization operation is carried out in such a way that the standardized wear parameter (7 r ; I f) depends less strongly on the at least one process parameter than without the normalization operation, and wherein preferably the normalization operation is recalculated when the at least one process parameter changes.

4. Method according to one of the preceding claims, wherein the working area (110; 111, 112) is substantially completely swept in each pass ( / V).

5. Method according to one of the preceding claims, wherein the grinding worm (100) has at least one worm thread flank (101) which has a modification in the working area (110; 111, 112) which changes along the worm axis (B), and wherein the grinding worm (100) is displaced relative to the respective workpiece (200) by a shift movement along the worm axis (B) during at least one grinding stroke per pass ( / V), while the grinding worm (100) is in machining engagement with the respective workpiece (200) in order to transfer the modification to the respective workpiece (200).

6. Method according to one of the preceding claims, wherein exactly one grinding stroke is carried out in each pass ( / V).

7. Method according to one of claims 1 to 4, wherein in each pass at least two grinding strokes are carried out, in which different parts of the working area (110; 111, 112) are swept over, wherein the different parts of the working area (110; 111, 112) overlap or are disjoint.

8. Method according to one of the preceding claims, wherein the at least one wear parameter ( / r ; If) is determined several times during each pass ( / V) and from the values ​​of at least one wear parameter ( / r ; I f ) at least one derived quantity ( / r V ; ^,N) is determined, in particular at least one statistical parameter which characterises a statistical distribution of the values ​​of the wear parameter during the respective pass ( / V), and where the decision is made depending on at least one derived quantity ( / r W ; I f N ) is made.

9. Method according to one of the preceding claims, wherein the decision is made based on a comparison of the at least one wear parameter (7 r ; If) or at least one value derived from it ( / r W ; I f N ) with a threshold r,thr' f, thr ) is made.

10. Method according to one of the preceding claims, wherein the decision is additionally made as a function of a wear condition of at least one other working area.

11. Method according to one of the preceding claims, wherein each of the workpieces is machined with at least one roughing stroke and at least one finishing stroke, wherein during each pass (N) at least one roughing wear parameter (I r) is determined, which characterizes the wear condition of the grinding worm (100) during at least one roughing stroke, wherein during each pass (N) at least one finishing wear characteristic (If) is determined, which characterizes the wear condition of the grinding worm (100) during at least one finishing stroke, and wherein the decision (153) is made as a function of both the at least one roughing wear characteristic (I r ) and at least one finishing wear parameter is hit.

12. Method according to claim 11, wherein the decision is made based on a comparison of the at least one roughing wear parameter (I r ) or at least one quantity derived from it (I r N ) with a roughing threshold (I rithr ) and a comparison of at least one finishing wear parameter (I f ) or at least one quantity derived from it (I f N) with a simple threshold If :thr ) is made.

13. Method according to one of the preceding claims, wherein each workpiece (200) is machined with at least one grinding stroke, wherein during each grinding stroke the grinding worm (100) is moved relative to the respective workpiece (200) along a workpiece axis (C), while the workpiece (200) in machining engagement with the working area (110; 111 , 112) of the grinding worm (100) rotates around the workpiece axis (C), wherein each workpiece (200) has a workpiece toothing (201) with workpiece flanks (210), wherein during each grinding stroke the workpiece flanks (210) are machined with at least one worm gear flank (101) of the grinding worm (100), wherein for each grinding stroke on the worm gear flank (101) there is a contact zone (104, 104') in which the worm gear flank (101) comes into contact with the workpiece flanks (210) during the respective grinding stroke, wherein on each workpiece flank (210) there is a useful area (211), wherein the contact zone (104, 104') has a quality-determining area (105) which comes into contact with the useful areas (211) of the workpiece flanks (210), wherein on the worm gear flank (101) there are several decoupled contact zones (104, 104'), the quality-determining areas (105) of which are essentially non-overlapping with all other contact zones (104, 104') of the screw flank (101) are arranged, and wherein the working area (110; 111, 112) comprises at least one of the decoupled contact zones (104, 104').

14. The method according to claim 13, wherein all contact zones (104, 104') used on the grinding worm (200) are arranged relative to one another such that their quality-determining regions are arranged substantially without overlap with all other contact zones (104, 104').

15. The method according to claim 13 or 14, wherein the working area (110; 111, 112) is formed by exactly one of the decoupled contact zones (104, 104').

16. Gear cutting machine for machining pre-toothed workpieces (200) by continuous generating grinding, comprising: a tool spindle (15) designed to clamp a grinding worm (100) thereon in order to drive the grinding worm (100) to rotate about a worm axis (B); a workpiece spindle (21) designed to clamp a pre-toothed workpiece (200) thereon in order to drive the pre-toothed workpiece (200) to rotate about a workpiece axis (C); an axial slide (13) designed to carry out an axial feed movement of the Tool spindle (15) relative to the workpiece spindle (21) along an axial feed direction (Z) having a component parallel to the workpiece axis (C); a shift carriage designed to generate a shifting movement of the tool spindle (15) relative to the workpiece spindle (21) along a shifting direction (Y) running parallel to the worm axis (B); a dressing device (30); and a machine control (40), characterized in that the machine control (40) is designed to carry out the method according to one of the preceding claims.

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