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

Abstract

The invention relates to a method for machining pre-toothed workpieces by means of a continuous generating grinding process using a grinding worm wheel (100). The grinding worm wheel is dressed, and workpieces are machined using the dressed grinding worm wheel. For each grinding stroke, the worm thread flanks have a contact zone (104, 104') in which the grinding worm wheel comes into machining engagement with the workpiece. Each contact zone has a quality-determining region, and the quality-determining regions of at least some of the contact zones are positioned so as to not overlap with the quality-determining regions of all other contact zones. Each workpiece is machined, in at least one grinding stroke, with a decoupled contact zone, the quality-determining region of which has not yet been used to machine another workpiece since the dressing process. 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 adapted 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.

[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] The prior art has proposed controlling the generating grinding process. For example, DE3433023A1 discloses a gear grinding machine in which a displacement between a grinding tool and a workpiece is controlled depending on the load of a rotary drive source for the grinding tool. EP2576136A1 discloses a machining method in which a target-specific force is defined, wherein the target-specific force is defined as the force normalized either by the contact width between the tool and the workpiece or by the contact area between the tool and the workpiece.The force during workpiece machining is set to a force level defined as a function of the relative tool-to-workpiece position and the target-specific force, whereby the specific force during machining remains essentially the target-specific force even though the machining process conditions, including the tool engagement conditions, may vary during the machining process.

[0013] Such control methods for the generating grinding process have not yet achieved widespread use. In practice, reliable control of this highly demanding generating grinding process is difficult to achieve, especially in combination with shift processes. For example, it has been observed that the control system adapts the manipulated variable (e.g., the feed rate) in a way that varies significantly from workpiece to workpiece, even when the workpieces have a consistent pre-machining quality and, therefore, consistent machining conditions are to be expected. Despite the control system, machining errors such as shape deviations or thermal surface damage ("grinding burn") can occur, particularly when machining subsequent workpieces in a batch, even though previous workpieces were initially machined correctly within the quality specifications.

[0014] PRESENTATION OF THE INVENTION

[0015] It is an object of the present invention to provide a method for machining pre-toothed workpieces by generating grinding, in which machining conditions are more controllable from workpiece to workpiece than with conventional methods. This should enable the generating machining process to be better optimized. In particular, the path should be paved for more reliable control of the generating grinding process.

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

[0017] A method is therefore specified for machining pre-toothed workpieces by continuous generating grinding with a grinding worm rotating around a worm axis, the method comprising:

[0018] Dressing the grinding worm; and

[0019] Machining the workpieces after the grinding worm has been dressed, wherein each workpiece is machined with at least one grinding stroke, and wherein during each grinding stroke the grinding worm is moved relative to the workpiece in question along the workpiece axis, while the workpiece rotates about a workpiece axis in a machining engagement with the grinding worm (axial feed movement).

[0020] Every workpiece has a workpiece toothing with (left and right) 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.

[0021] During each grinding stroke, the workpiece flanks are machined with at least one worm thread flank of the grinding worm. Machining is typically performed with more than one worm thread flank, for example, in the case of a multi-threaded grinding worm and with conventional double-flank engagement, with the left and right flanks of each grinding worm thread. However, only one of these worm thread flanks is considered below.

[0022] For each grinding stroke, the area on the worm gear flank where the worm gear flank comes into 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.

[0023] According to the invention, there are several contact zones on the worm thread flank, whose quality-determining areas are arranged essentially without overlap with all other contact zones. Such contact zones are referred to below as "decoupled contact zones." According to the invention, each workpiece is machined in at least one grinding stroke with a decoupled contact zone, whose quality-determining area has not yet been used for machining another workpiece since dressing.

[0024] Each workpiece is therefore machined in at least one grinding stroke with a contact zone whose quality-determining area is essentially freshly dressed. This ensures that the grinding worm always has the same, optimal wear level for each workpiece during this grinding stroke when machining the useful areas of the workpiece flanks. This means that the machining of the useful areas is no longer influenced by the wear level of the grinding worm. As a result, the machining conditions can be better controlled, since the influencing factor "wear level" no longer plays a role. This is particularly, but not exclusively, advantageous when the generating grinding process needs to be controlled.

[0025] 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%.

[0026] 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.

[0027] In preferred embodiments, the generating grinding process is controlled at least during machining with the freshly dressed, decoupled contact zones. For this purpose, a performance indicator characterizing the current grinding performance can be continuously measured, and at least one grinding parameter is controlled as a function of the performance indicator. By performing the control during machining with decoupled contact zones whose quality-determining areas have been freshly dressed, the control becomes considerably more reliable than when contact zones are used whose quality-determining areas have already been used or overlap with other contact zones, because the wear condition of the grinding worm in the other contact zones does not influence the control in the respective quality-determining area.

[0028] As a grinding parameter, the axial feed rate (i.e., the speed of the axial feed movement) can be controlled. The at least one grinding parameter is preferably controlled such that, during the respective grinding stroke, the performance indicator follows a target curve or does not exceed a predetermined maximum value.

[0029] In order to reduce the dependence of the performance indicator on process parameters such as tool diameter, workpiece diameter and module or infeed and thus to facilitate the specification of a target curve or a maximum value and to improve the control, it can be provided that a normalization operation is carried out when determining the performance indicator in order to normalize the performance indicator. The normalization operation depends on at least one process parameter, wherein the process parameter is at least one geometric parameter of the tool, at least one geometric parameter of the workpiece and / or at least one setting parameter of the machine tool. The normalization operation is carried out in such a way that the normalized performance indicator depends less strongly on the at least one process parameter than without the normalization operation.

[0030] As soon as at least one of the mentioned process parameters changes, the normalization operation is preferably recalculated. Recalculating the normalization operation may, in particular, involve applying a model that describes an expected dependence of the performance indicator on the process parameters, in particular a model of a process force or process performance.

[0031] For further considerations regarding the normalization operation, reference is made to publication W02021048027A1, the contents of which are incorporated in their entirety into the present disclosure by reference.

[0032] In some embodiments, only a single grinding stroke is performed with each of the decoupled contact zones before the grinding worm is dressed again.

[0033] The proposed method does not preclude the possibility that, in addition to the decoupled contact zones, further contact zones may exist on the worm thread flank that overlap with one another, as in conventional shift strategies, and that only some of the grinding strokes per workpiece are 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. However, preferably, all contact zones used on the worm thread flank are decoupled contact zones. In particular, all grinding strokes when machining all workpieces are preferably performed exclusively with decoupled contact zones before the grinding worm is dressed again.

[0034] The proposed method also does not preclude the possibility of one or more decoupled contact zones on a worm thread flank serving to machine more than one workpiece. This can be useful when there are grinding strokes for which the wear condition of the grinding worm is less relevant. However, each of the decoupled contact zones is preferably used to machine exactly one workpiece, and preferably in exactly one grinding stroke, before the grinding worm is dressed again.

[0035] In preferred 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. This is particularly advantageous when the grinding process (in particular the axial feed rate) is controlled, since in this way the wear condition of other contact zones does not influence the controller, or does not influence it to a significant extent.

[0036] Preferably, for each workpiece during a grinding stroke in which the workpiece in question is machined with a contact zone whose quality-determining areas have not yet been used for machining another workpiece since dressing, a shift movement is performed simultaneously with the axial feed movement. This means that the grinding worm is continuously shifted 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 in the respective grinding stroke, 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. The ratio of shift distance to axial stroke distance is referred to as the "diagonal ratio."For a cylindrical grinding worm and a cylindrical workpiece, the contact zone on the worm thread flank without shift movement corresponds to a single contact path. The contact path is the area on the worm thread flank in which the worm thread flank comes into machining engagement with the workpiece during a grinding stroke when there is no axial feed movement and no shift movement. Each contact path has a conical helical shape on the grinding worm flank. Since the contact between the grinding worm and the workpiece is not exactly point-like, but occurs with a certain cutting width, the contact path has a finite width. When 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.

[0037] 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.

[0038] In some embodiments, the grinding worm can have a modification of the worm thread flank in at least some of the decoupled contact zones. This can, in particular, be a topological modification which, when viewed along a contact path, changes during the shift movement within the contact zone from contact path to contact path along the tool width direction. The diagonal movement then serves to transfer the topological modification of the worm thread flank to the workpiece flanks, and the diagonal ratio can be selected with this in mind. By ensuring that the quality-determining area of ​​the contact zones in question has not yet been used for machining another workpiece since dressing, a particularly high quality of the resulting modification of the workpiece flanks can be ensured.

[0039] In other embodiments, the grinding worm in the decoupled contact zones may either have no modification of the worm flight flank at all, or it may have a modification of the worm flight flank in the decoupled contact zones which, when viewed along a contact path, does not change during the shift movement within the contact zone from contact path to contact path along the tool width direction. The modification of the worm flight flank in the decoupled contact zones may, in particular, be a pure profile modification, i.e., a modification of the grinding worm profile which does not change in the width direction of the grinding worm across the decoupled contact zones. In particular, it may be a profile angle modification, profile crowning, profile waviness, tip relief, and / or root relief.As a result, despite the diagonal movement on the workpiece flanks, either no modification at all occurs, or a pure profile modification occurs on the workpiece flanks that does not change along the workpiece's width direction. In this case, the diagonal movement does not serve to transfer topological modifications of the worm thread flanks to the workpiece flanks in order to create a workpiece flank modified in the workpiece width direction. The choice of the diagonal ratio is therefore 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 (as in so-called "low noise shifting," where the diagonal grinding process is used to specifically influence the roughness structure, see, for example, US6379217B1), but not from the perspective of creating a width-variable geometric modification of the workpiece flanks.

[0040] To achieve the desired decoupling of the contact zones, the following procedure can be used: Assume that the grinding worm assumes a first shift position relative to the workpiece along the shift direction at the end of the machining operation of a first grinding stroke, and that it assumes a second shift position at the beginning of the machining operation of a subsequent (but not necessarily immediately subsequent) second grinding stroke. Then, it is preferred that there is a distance between the first shift position and the second shift position that corresponds at least to the width of a contact path formed on a flank of the grinding worm during the first grinding stroke, measured along the worm axis, and that the grinding worm assumes exclusively shift positions that lie outside the range between the first shift position and the second shift position during all grinding strokes.In this way, it can be achieved that the contact zones used in the grinding strokes mentioned are completely free of overlap.

[0041] The width of the contact path is determined by the progression of the cutting width along the contact path. The cutting width can vary along the contact path because the engagement conditions change along the contact path. It can also vary during a grinding stroke, for example, because several teeth of the workpiece are machined with the same contact path and the workpiece allowance can vary from tooth to tooth due to pitch errors in the workpiece gearing.It is therefore advisable to determine the cutting width profile along the contact path when removing a nominal allowance corresponding to the maximum expected allowance. From this, determine a nominal width of the contact path during the first grinding stroke. Select the distance between the first shift position and the second shift position so that this distance corresponds to at least this width, measured along the worm axis. In addition to the nominal allowance, the calculation of the cutting width takes into account the macrogeometry of the workpiece (in particular, module, number of teeth, tooth shape), the macrogeometry of the grinding worm (in particular, module, number of threads, pressure angle), and the machining parameters (in particular, the infeed and the axial feed per workpiece revolution).

[0042] Expressed numerically, it is preferred if the following relationship is satisfied for the distance between the first shift position and the second shift position:

[0043] Ay > a p 0 / sin a , where a p 0 is the (nominal or real) width of the contact path, measured perpendicular to the contact path, and where a is the pressure angle of the grinding worm in the axial section of the grinding worm. The width of the contact path perpendicular to the contact path corresponds to a good approximation of the width of the contact path measured in the profile height direction of the grinding worm in the axial section of the grinding worm, and therefore a p 0Alternatively, this width can also be used. For a grinding worm with different pressure angles on the right and left worm thread flanks, the values ​​of Ay for the right and left worm thread flanks may differ. In this case, the larger of these values ​​is preferred.

[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] In particular, the machine control system can be configured to position the grinding worm relative to the workpiece in such a way that machining takes place in at least one grinding stroke with a freshly dressed, decoupled contact zone. The machine control system can also be configured to implement the above-described control of the generating grinding process.

[0046] BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Preferred embodiments of the invention are described below with reference to the drawings, which are for illustrative purposes only and are not to be construed as limiting. In the drawings:

[0048] Figure 1 schematically illustrates a grinding worm in engagement with a gear-shaped workpiece;

[0049] Figure 2 illustrates the temporal progression of the power consumption of the

[0050] Tool spindle that drives the grinding worm during a grinding stroke;

[0051] Figure 3A illustrates, by way of example, the grinding intensity during roughing when machining a plurality of workpieces using a conventional shift strategy;

[0052] Figure 3B illustrates the grinding intensity during finishing when machining a plurality of workpieces using the conventional shift strategy;

[0053] Figure 4 illustrates a worm gear flank with a contact pad shown on it;

[0054] Figure 5 illustrates a section of a contact path with an associated instantaneous contact area;

[0055] Figure 6 illustrates a worm gear flank with two contact zones that partially overlap;

[0056] Figure 7 illustrates a worm gear flank with two contact zones that do not overlap;

[0057] Figure 8 illustrates a virtual face gear with a contact path;

[0058] Figure 9 illustrates contact zones on a virtual face gear in a first shift strategy;

[0059] Figure 10 illustrates contact zones on a virtual face gear using a second shift strategy;

[0060] Figure 11A illustrates, by way of example, the grinding intensity during roughing when machining a plurality of workpieces with decoupled roughing contact zones;

[0061] Figure 11 B illustrates, by way of example, the grinding intensity during finishing when machining a plurality of workpieces with decoupled finishing contact zones;

[0062] Figure 12A illustrates, by way of example, the time course of the power consumption of the tool spindle when the axial feed rate is controlled in such a way that the power consumption does not exceed a maximum value;

[0063] Figure 12B illustrates, by way of example, the corresponding temporal progression of the axial feed rate;

[0064] Figure 13A illustrates, by way of example, the time course of the power consumption of the tool spindle when the axial feed rate is controlled in such a way that the power consumption follows a target curve;

[0065] Figure 13B illustrates, by way of example, the corresponding temporal course of the axial feed rate;

[0066] Figure 14A illustrates an example of a workpiece flank with a useful area;

[0067] Figure 14B illustrates an example of a worm gear flank with a quality-determining area; and

[0068] Figure 15 illustrates a generating grinding machine.

[0069] DESCRIPTION OF PREFERRED EMBODIMENTS

[0070] Kinematics of continuous generating grinding

[0071] Figure 1 illustrates the kinematics of continuous generating grinding. A grinding worm (i.e., a helically profiled grinding wheel) 100 rotates about a worm axis B. The grinding worm meshes with a gear-shaped workpiece 200 having workpiece teeth 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 of the workpiece teeth 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.To engage new, unused areas of the grinding worm 100 with the workpiece 200, the grinding worm is continuously or discontinuously displaced relative to the workpiece 200 along a shift direction Y, which runs parallel to the worm axis B (so-called tangential shift movement). All of the aforementioned linear movements (feed, axial feed movement, shift movement) are 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.

[0072] 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.

[0073] 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.

[0074] Measuring grinding performance

[0075] Figure 2 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 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.

[0076] 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. sThe 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 consumed 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 consumed current is proportional to the power, or at constant speed, the torque is proportional to the power. In this respect, 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.

[0077] The grinding performance depends on a number of 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).

[0078] However, grinding performance is also influenced by the wear condition of the grinding worm. For example, a partially worn grinding worm is unable 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 leads to a decrease in cutting performance.

[0079] For given grinding 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.

[0080] Grinding intensity when grinding with conventional shift strategies

[0081] Conventional shift strategies usually result in the first workpieces being machined after dressing with grinding worm areas that are subject to increasing wear from workpiece to workpiece until an equilibrium is reached where the wear state no longer changes from workpiece to workpiece. This will be explained in more detail for a conventional shift strategy using Figures 3A and 3B.

[0082] For this purpose, it is initially assumed that each workpiece is machined with a single roughing stroke and a single finishing stroke, with continuous shifting occurring during both the roughing and finishing strokes. It is also assumed that between the roughing and finishing strokes, a shift jump occurs into a finishing section of the grinding worm that has not yet been used for roughing, and that after finishing, a shift return occurs exactly at the point where the previous roughing stroke ended. This corresponds to a conventional shift strategy, as known from the state of the art and frequently used in continuous generating grinding.

[0083] Figure 3A shows schematically the grinding intensity I for such a shift strategy r (n) during roughing when machining a plurality of workpieces n, in Figure 3B the grinding intensity I f(n) during finishing, where the grinding worm was freshly dressed before machining the first workpiece. Due to increasing wear in the roughing area, the grinding intensity gradually decreases during roughing of the first workpieces until it reaches a substantially constant value. During finishing, the opposite is true: The grinding intensity initially increases during machining of the first workpieces, as correspondingly more material is removed in the finishing stroke due to the lower material removal in the roughing stroke, and then levels off.

[0084] The reason for this behavior will be examined in more detail below.

[0085] Contact paths on the grinding worm

[0086] 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 4 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.

[0087] 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 5 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.

[0088] 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.

[0089] Contact zones during continuous shift movement

[0090] 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.

[0091] 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.

[0092] Figure 6 shows, in a highly schematic form and not to scale, two contact zones 104, 104' on a worm thread 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 conventional shift strategy described above. With such a conventional shift strategy, the roughing stroke of the subsequent workpiece begins exactly at the 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.

[0093] 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'.

[0094] Variable grinding intensity with conventional shift strategies

[0095] Based on the above considerations, it is clear why the grinding intensity with conventional shift strategies is initially not constant from workpiece to workpiece, even when all grinding 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 conventional shift strategies, 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.

[0096] Increasing wear in the contact zone during roughing is reflected in a decreasing roughing grinding intensity I r, because the cutting performance decreases with increasing wear. This leads to an increasing finishing grinding intensity, because more cutting work must be performed during finishing. This corresponds exactly to the observed behavior shown in Figures 3A and 3B.

[0097] 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.

[0098] Grinding with decoupled contact zones

[0099] 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 advisable to decouple the contact zones from each other so that they no longer overlap. With the shift strategy described above, this can be achieved, for example, by reducing the shift offset.

[0100] This is illustrated by way of example in Figure 7, in which two contact zones 104, 104' are shown, which come into engagement during the machining of successive workpieces during the roughing stroke if the shift recess is suitably reduced. The contact zones 104, 104' now run alongside one another without overlapping over the worm thread flank 101, ie they are decoupled from each other. of the

[0101] The amount by which the shift recess must be reduced in order to decouple the contact zones 104, 104' in the example of Figure ? can be clearly derived by a geometric consideration.

[0102] 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 8 schematically shows such a reference profile 110. The left flanks of the reference profile 110 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 8 shows a band with the width a pThis 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.

[0103] 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 / sm a, measured along the screw axis.

[0104] 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.

[0105] Calculating the cutting width

[0106] 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:

[0107] Here, a p max 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.

[0108] The maximum cutting width can be calculated as follows:

[0109] Here, L y the rolling length and q t the nominal measurement.

[0110] For the contact length l k the following analytical relationship can be derived:

[0111] 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

[0112] Here, a denotes the pressure angle of the grinding worm gear in axial section.

[0113] 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.

[0114] 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 pSj 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 a:

[0115] Ay > a p 0 / sin . Contact zones

[0116] 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.

[0117] A first shift strategy is illustrated in Figure 9. This figure, similar to Figure 8, shows 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 significantly compressed compared to Figure 8. The width of the grinding worm is given by b ss Figure 9 can also be understood as a representation of a (unfolded) worm gear flank 101, in which the horizontal axis represents the width position y ssalong the grinding worm axis and the vertical axis the height position h ss or indicates the pitch path along the worm thread flank.

[0118] With this shift strategy, the grinding worm is divided into a roughing area 111 and a finishing area 112, as with a conventional shift strategy. When machining the first workpiece, a roughing stroke is performed first. 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. rthe width of a single contact path along the grinding worm axis is called Ay r . Overall, roughing uses a roughing contact zone with a width y r + Ay r , measured along the screw axis.

[0119] 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 point where the finishing stroke 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 y f, the width of a single contact path along the screw axis during finishing Ay^. As a rule, 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 is thus created during finishing. f + Ay^, measured along the screw axis.

[0120] After the end of the finishing cut, a shift return occurs before the roughing cut of the second workpiece begins. Unlike conventional shift strategies, however, the shift return is reduced 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.

[0121] A second shift strategy is illustrated in Figure 10. 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.

[0122] 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 slThis 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.

[0123] 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 roughing of the second workpiece begins. This decouples the roughing contact zone for machining the second workpiece from the finishing contact zone for machining the first workpiece. The machining of the second workpiece is then carried out in the same way as for machining the first workpiece. This decouples all roughing and finishing contact zones.

[0124] 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.

[0125] Of course, many other shift strategies with decoupled contact zones, in each of which exactly one workpiece is machined, are possible.

[0126] Grinding intensity when grinding with decoupled contact zones

[0127] Figures 11A and 11B show the grinding intensity during roughing and finishing of a plurality of workpieces after dressing the grinding worm, respectively, when the contact zones for successive workpieces are decoupled from each other during both roughing and finishing. The grinding intensity now remains essentially constant from workpiece to workpiece during both roughing and finishing.

[0128] Since this approach ensures that the grinding intensity does not change from workpiece to workpiece, as long as the kinematic parameters such as feed rate and infeed remain unchanged, workpieces with more consistent machining quality are achieved than with conventional shift strategies. Furthermore, strategies for controlling the grinding process can now be implemented with much greater predictability and reliability than if the grinding intensity changes from workpiece to workpiece due to wear.

[0129] Control of the axial feed rate

[0130] The following example illustrates the control of the generating grinding process. When controlling the generating grinding process, at least one grinding parameter, in this case the axial feed rate v z(t) is controlled in such a way that a specified control strategy is maintained. Various control strategies can be used. Two possible control strategies are explained below using Figures 12A and 12B, and 13A and 13B, respectively. However, other control strategies are also conceivable.

[0131] Figure 12A illustrates, as an example, the temporal progression of a performance indicator in the form of the power consumption P(t) of the tool spindle during a grinding stroke, when the axial feed rate is controlled such that the (preferably standardized, see below) performance indicator does not exceed a maximum value ("maximum value control"). Without control of the grinding process, in this example, the power consumption would exceed a predetermined maximum value P max at least temporarily (dotted line). To avoid this, the axial feed rate v z(t) must be controlled so that this maximum value is not exceeded. As soon as the grinding power approaches the maximum value, the feed rate is reduced due to the control system so that the grinding power does not exceed the maximum value. Any known control principle can be used for this purpose, e.g., PID control. The resulting curve of the feed rate v z (t) is illustrated in Figure 12B.

[0132] The example in Figure 13A illustrates the temporal progression of the power consumption of the tool spindle when the axial feed rate is controlled such that the power consumption at least approximately follows a target curve ("target curve control"). The target curve can, for example, describe the expected power consumption based on a process power model under ideal conditions assuming a certain machining allowance distribution. For example, the process power model mentioned above can be used to calculate the target curve. Deviations from the target curve can arise, for example, if a workpiece has a machining allowance distribution that deviates from the assumed machining allowance distribution; however, other factors can also play a role, such as the hardness distribution and the current wear condition of the grinding worm.The dotted line shows the power consumption curve as it would occur with a constant axial feed rate. In this example, this curve deviates significantly from the target curve. For example, the power consumption is lower at the beginning during the run-in phase than in the target curve, but significantly higher later on. The control system compensates for these deviations by increasing the feed rate when the power consumption deviates negatively from the target curve and decreasing it when the deviation is positive. This is illustrated as an example in Fig. 13B.

[0133] These control strategies can also be modified and / or combined. For example, in Fig. 13B, a maximum feed rate can be defined that must not be exceeded, or the feed rate can be controlled only during the phase of the grinding stroke in which a specified minimum power consumption value is exceeded. Many other modifications to the control strategy are conceivable.

[0134] With decoupled contact zones, such strategies for controlling the grinding process can be used with far greater predictability and reliability than when overlapping contact zones are used. As long as the contact zones overlap, the wear condition of the grinding worm varies over the course of each individual grinding stroke. As a result, the grinding performance over the course of each grinding stroke is strongly influenced by the changing wear of the grinding worm, i.e. the control system reacts strongly to the wear of the grinding worm and is therefore unable to optimally fulfill its actual task. Due to the decoupling, the control is now primarily influenced by the properties of the workpiece, in particular by its changing allowance, and possibly by inhomogeneities of the grinding worm in the contact zone itself, but no longer by changing wear conditions in other contact zones.

[0135] The decoupling of the contact zones paves the way for intelligent control of the grinding process. Standardization of the measured grinding performance

[0136] The performance indicator or the grinding intensity calculated from it can be appropriately standardized to improve the comparability of the performance indicator for different conditions.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] As a rule, when the finished workpiece is used in a gear, not the entire left and right workpiece flanks engage with a counter toothing, but rather 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 determining the contact pattern of the toothing under real operating conditions. Fig. 14A illustrates, as an example, a workpiece flank 210 of a toothing with the associated usable area 211. The usable area 211 does not extend across 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 .

[0141] 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.

[0142] Fig. 14B 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.

[0143] 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.

[0144] Example structure of a generating grinding machine

[0145] Figure 15 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."

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] All driven axes of machine 1 are digitally controlled by a machine control system 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.

[0151] A monitoring device 44 is connected to the control computer 42.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] The monitoring device 44 can alternatively also be implemented as a software component of the machine control 40, which is executed, for example, on a processor of the control computer 42, or it can be designed as a software component of the service server 45 described in more detail below.

[0156] The monitoring device 44 communicates directly or via the Internet and a web server 47 with the service server 45. The service server 45, in turn, communicates with a database server 46 containing the database DB. These servers can be located remotely from 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."

[0157] 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.

[0158] Processing of workpieces

[0159] For the sake of completeness, the following describes how workpieces are typically machined using machine 1.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] If, after machining a certain number of workpieces, the use of the grinding worm 100 has progressed to the point where it becomes too blunt and / or the flank geometry is too inaccurate, the grinding worm is dressed. To do this, 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.

[0164] LIST OF REFERENCE SYMBOLS

[0165] 100 grinding worm

[0166] 101 worm gear flank

[0167] 102 Contact path

[0168] 103 Contact area

[0169] 104 Contact zone

[0170] 104' contact zone

[0171] 105 quality-determining area

[0172] 110 Reference profile

[0173] 111 Grinding worm area for roughing

[0174] 112 Grinding worm area for finishing

[0175] 121 Grinding worm area for first workpiece

[0176] 122 Grinding worm area for second workpiece

[0177] 200 workpieces

[0178] 201 Workpiece gearing

[0179] 210 Flank of the workpiece toothing

[0180] 211 usable area

[0181] I Generating grinding machine

[0182] II Machine bed

[0183] 12 tool carriers

[0184] 13 axial slides

[0185] 14 Grinding head

[0186] 15 tool spindle

[0187] 18 Vibration sensor

[0188] 19 Position sensor

[0189] 20 workpiece carriers

[0190] 21 Workpiece spindle

[0191] 41 Axle module

[0192] 42 tax calculators

[0193] 43 Control panel

[0194] 44 Monitoring device

[0195] 45 Service server 46 Database

[0196] 47 web servers

[0197] 48 mobile devices

[0198] B Worm axis

[0199] C Workpiece axis

[0200] X radial feed direction

[0201] Y shift direction

[0202] Z axial feed direction b ws Workpiece width b ss Grinding worm width a p Cutting width y r Shift amount during roughing yy Shift amount during finishing

[0203] Ay r Width of a contact path along the screw axis during roughing

[0204] A y Width of a contact path along the screw axis during finishing

[0205] Aysl Amount of the shift jump between roughing and finishing

[0206] Ay s2 Amount of the shift (back) jump between finishing and next roughing

[0207] P Power consumption of the grinding spindle

[0208] P max Maximum power consumption

[0209] I s Grinding intensity

[0210] I r Grinding intensity during roughing

[0211] If grinding intensity during finishing

[0212] I r thr Threshold value of grinding intensity during roughing

[0213] Jf.thr Threshold value of grinding intensity during finishing t Time n Number of workpieces au 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), the method comprising: Dressing the grinding worm (100); and Machining the workpieces (200) after the grinding worm (100) has been dressed, 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) rotates about the workpiece axis (C) in a machining engagement with the grinding worm (100), 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 thread flank (101) of the grinding worm (100), wherein on the worm thread flank (101) there is a contact zone (104, 104'), in which the worm thread flank (101) is in contact with the workpiece flanks during the respective grinding stroke (210), wherein on each workpiece flank (210) there is a useful area (211), and wherein the contact zone (104,104') has a quality-determining region (105) which comes into contact with the useful regions (211) of the workpiece flanks (210), characterized in that there are several decoupled contact zones (104, 104') on the worm thread flank (101), the quality-determining regions (105) of which are arranged substantially without overlap with all other contact zones (104, 104') of the worm thread flank (101), and in that each workpiece is machined in at least one grinding stroke with one of the decoupled contact zones (104, 104'), wherein the quality-determining region (105) of the respective contact zone (104, 104') has not yet been used for machining another workpiece (200) since dressing.

2. Method according to claim 1, wherein at least during the processing with the decoupled contact zones (104, 104'), the quality-determining areas (105) have not yet been used for machining a workpiece (200) since dressing, a performance indicator (P(t)) which characterizes a current grinding performance is measured and at least one grinding parameter is controlled as a function of the performance indicator (P(t)).

3. Method according to claim 2, wherein during each grinding stroke the grinding worm (100) is moved relative to the respective workpiece (100) at an axial feed rate (v z ) along an axial feed direction (Z) having a component parallel to the workpiece axis (C), and wherein the at least one controlled grinding parameter is the axial feed rate (v z ) includes.

4. Method according to claim 2 or 3, wherein the at least one grinding parameter is controlled such that the performance indicator (P(t)) follows a target curve or a predetermined maximum value (P max ) does not exceed.

5. The method according to any one of claims 2-4, wherein a normalization operation is performed to normalize the performance indicator (P(t)), wherein the normalization operation depends on at least one process parameter, wherein the at least one process parameter is selected from geometric parameters of the grinding worm (100), geometric parameters of the workpiece (200) and setting parameters of the machine tool (1), such that the normalized performance indicator (P(t)) depends less on the at least one process parameter than without the normalization operation.

6. The method according to claim 5, comprising: Changing at least one of the process parameters; and Recalculating the normalization operation with respect to the process parameters after the change, wherein the recalculation of the normalization operation comprises in particular the application of a model that describes an expected dependence of the performance indicator (P(t)) on the process parameters, in particular a model of a process force or process performance.

7. Method according to one of the preceding claims, wherein only a single grinding stroke is carried out with each of the decoupled contact zones.

8. Method according to one of the preceding claims, wherein all contact zones (104, 104') used on the grinding worm (200) are arranged relative to one another in such a way that their quality-determining regions are arranged substantially without overlap with all other contact zones (104, 104').

9. Method according to one of the preceding claims, wherein for each workpiece (200) during a grinding stroke in which the workpiece (200) in question is machined with one of the decoupled contact zones (104, 104'), the quality-determining regions of which have not yet been used for machining another workpiece (200) since dressing, the grinding worm (100) is continuously displaced relative to the workpiece (200) both along an axial feed direction (Z) which has a component parallel to the workpiece axis (C), and along the shift direction (Y), so that the grinding worm (200) covers a total of a shift path along the shift direction (Y) and a stroke path along the axial feed direction (Z) relative to the workpiece (100) during the machining intervention in the grinding stroke in question.

10. The method according to claim 9, wherein the grinding worm in at least a part of the decoupled contact zones (104, 104') has a modification of the worm flight flank (101) which is different along different contact paths within the respective contact zone.

11. Method according to one of the preceding claims, wherein the grinding worm assumes a first shift position at the end of the machining engagement of a first grinding stroke, wherein the grinding worm assumes a second shift position at the beginning of the machining engagement of a subsequent second grinding stroke, wherein between the first shift position and the second shift position there is a distance (Ay) which corresponds to at least a width of a contact path on a grinding worm flank (101), measured along the worm axis (B), and wherein the grinding worm (100) exclusively assumes shift positions (Y) which lie outside the range between the first shift position and the second shift position during all grinding strokes.

12. The method according to claim 11, wherein the distance (Ay) between the first shift position and the second Shift position the following relationship is fulfilled: Ay > a p 0 / sin a , where a p 0denotes the width of the contact path, measured perpendicular to the contact path course, and where a denotes an angle of pressure of the grinding worm (100) in axial section.

13. A 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 (23) thereon in order to drive the pre-toothed workpiece (23) to rotate about a workpiece axis (C); an axial slide (13) designed to generate 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 slide which is designed to generate a shift movement of the tool spindle (15) relative to the workpiece spindle (21) along a shift direction (Y) running parallel to the screw 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 of one of the preceding claims.

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