Gear hobbing of a gear on a workpiece or a batch of workpieces

Abstract

The invention relates to a method for gear hobbing of a tooth having a tooth axis on a workpiece, in particular a batch of workpieces, in a heat-generating machining operation with a gear hobbing tool, the usable working area of ​​which extends along its axis of rotation, in which the gear hobbing tool performs a feed movement with an axial feed component running parallel to the tooth axis over one or more strokes, passing through optionally overlapping entry paths, profiling paths and overrun paths, in order to machine the tooth over a desired width, and with a control mechanism that manages the heat input into the gear hobbing tool resulting from the generated heat to a locally delocalized heat input, and in particular counteracts any local non-uniformity of the locally delocalized heat input seen over the working area extension of the gear hobbing tool and / or any deviation,In particular, a thermal management control system that counteracts flank line deviations of the gear teeth due to thermal, especially axial, thermal expansion of the hob cutter, and in particular counteracts non-uniformity of the net heat absorbed by the hob cutter in one stroke, at least over an initial sub-batch of the workpiece batch.

Description

[0001] The invention relates to a method for gear hobbing of a tooth having a tooth axis on a workpiece, in particular a batch of workpieces in a heat-generating machining operation with a gear hobbing tool, the usable working area of ​​which extends along its axis of rotation, in which the gear hobbing tool performs a feed movement with an axial feed component running parallel to the tooth axis over one or more strokes by passing through a possibly overlapping entry path, profiling path and overrun path in order to machine the tooth over a desired width.

[0002] Such processes are, of course, well-known and, due to their high material removal rates, are particularly used in mass production, unless a more interference-friendly process, such as skiving or gear shaping, is employed due to interfering contours on the workpiece. A prominent example of such mass production with very high batch sizes is the gear hobbing of axle drive gears in the automotive sector with internal combustion engines or electric drives. This is now performed using axial milling, meaning the hobbing cutter is advanced axially to the gear axis to machine the gear across its entire width, in one or more strokes. Cooling systems are used, if necessary, to dissipate the heat generated during machining, for example, by supplying a cooling oil, other cooling lubricants such as emulsions, or compressed air.Systems are known in which cooling oil is supplied outside the tool; however, systems in which cooling oil is supplied through the tool and the tool holder are also known from DE 10 2013 015 252 A1, whereby this document concerns skiving.

[0003] Gear hobbing, also known as soft machining, is followed by hardening of the workpieces, and then hard finishing, which determines the surface quality of the gear teeth and allows for the incorporation of tooth flank modifications, as described, for example, in EP 3 139 229 B1. Thanks to CNC control of the machine axes of gear hobbing machines, which has been available for decades and is also used according to the invention, and advances in materials for gear cutting tools, it is now possible to produce workpieces with very high gear quality for the primary gear teeth while adhering to increasingly smaller tolerances specified by users, for example, in the automotive industry. Furthermore, machine designs have advanced to such a degree in terms of their rigidity and resilience to high machining forces, as well as machine performance, that very high material removal rates are achievable.The latter naturally put a strain on the hob cutter and cause higher wear or a shorter service life of the hob cutter.

[0004] To extend the service life of hob cutters, a shift strategy is employed in the axial milling process described above. After a certain number of workpieces have been machined, for example, when the hob cutter has already worn down to such an extent in its engagement area that the gear quality would suffer if this area were used further, the hob cutter is shifted along its axis to machine the next workpieces, i.e., moved further along its axis of rotation, so that a still unworn area is used for the subsequent workpieces, and so on. Such a shifting process is described, for example, in Bausch, Innovative Gear Manufacturing, 3rd edition, p. 177, Figure 6.2-9.

[0005] Although, as explained above, very high machining accuracy can now be achieved, the invention is based on the objective of further improving methods of the type mentioned at the outset, in particular with regard to a combination of satisfactory machining accuracy and satisfactory uniformity of the workpieces in a batch of workpieces.

[0006] This problem is solved by the invention through a further development of the method of the type mentioned at the outset, which is essentially characterized by a heat management control that controls the heat input into the hob due to the generated heat to a locally delocalized heat input, and in particular counteracts a local non-uniformity of the locally delocalized heat input seen over the working area extension of the hob, and / or counteracts a deviation, in particular flank line deviation of the gear teeth due to thermal, in particular axial thermal expansion of the hob, and in particular counteracts a temporal non-uniformity of the net heat absorbed by the hob in one stroke seen at least over an initial sub-batch of the workpiece batch.

[0007] Firstly, it has been recognized that localized heat input in the same engagement area of ​​the hob can lead to machining inaccuracies even when machining only one workpiece, especially with comparatively higher heat generation, for example due to higher machining power and / or comparatively longer contact times with the engagement area of ​​the hob.

[0008] This is counteracted, according to one perspective, by the heat input being locally delocalized even during a single stroke. In this respect, the axial milling process, which is standard for machining these workpiece batches, is deviated from, and the heat input is thus introduced into a larger area of ​​the working area than its engagement zone by shifting the hob cutter along its axis during the stroke, thus locally delocalizing it.

[0009] Furthermore, by counteracting the unevenness of the already delocalized heat input, the wear on the hob cutter can be kept more uniform and thus indirectly the machining quality of the workpiece can be improved.

[0010] Furthermore, the inventors' thermal management analyses revealed that, particularly with heat inputs that are geographically delocalized even during a single stroke, where axially relatively distant sections of the hob come into machining engagement when machining a single workpiece, unwanted flank line deviations can occur, including uneven deviations, if there is a temporal inconsistency with respect to this aspect. The inventors discovered that such inconsistency occurs especially with the first workpieces in a batch, namely due to the different net heat absorbed by the hob over time. Thus, in addition to the heat generated during machining, heat dissipation due to cooling also plays a role in the thermal management of the machining process, and the heat ultimately transferred to the hob by the hob is...The net heat absorbed in one stroke also depends on the heat already absorbed or the current actual temperature of the hob cutter (until a steady state is reached).

[0011] In this respect, the method according to claim 1 can achieve improvements on the one hand with regard to the machining accuracy per se and on the other hand with regard to the uniformity of the workpieces relative to each other.

[0012] In a particularly preferred embodiment, it is provided that the heat input is delocalized to counteract the locally seen unevenness already during the passage through at least a partial area of ​​an inlet path located outside the profiling path.

[0013] Thus, even in areas where the profiling path has not yet begun, delocalization can start, and the load can already be distributed in the area where a large part of the machining takes place. This also results in advantages in terms of more uniform wear.

[0014] In this context, it is preferably provided that the magnitude of the diagonal ratio (dY / dZ) of the feed motion when passing through the sub-area is at least sectionally different from zero and / or monotonically increasing.

[0015] In this respect, the precise design of a local motion resulting from a superposition of the axial component movement and the displacement movement of the hob along its axis (shift movement) is not crucial. In any case, diagonal milling is initiated early, and preferably, the proportion of shift movement remains constant or increases during the entry phase. Unless continuous curve profiles without abrupt transitions are already used, the thermal management control is designed for flexible setting of a starting position for the diagonal movement.

[0016] In another preferred embodiment, it is provided that, in order to counteract the locally perceived unevenness, a reduction in the degree of delocalization already takes place during the passage through a section of the overflow path or a section of the profiling path adjacent to the overflow path.

[0017] Towards the end of the feed motion, the degree of delocalization is reduced again, or rather, the shift component of the diagonal motion is reduced compared to the axial component. This advantageously addresses the fact that, with decreasing chip removal rate, the corresponding area of ​​the hob's working range is able to operate longer and absorb more wear.

[0018] In this context, it is preferably provided that the magnitude of the diagonal ratio (dY / dZ) of the feed motion already vanishes when passing through the section and / or at least decreases monotonically section by section.

[0019] Accordingly, a continuous curve profile with a continuously decreasing slope can be selected, or more abrupt transitions can be created, in which the process transitions from diagonal milling to axial milling. In this respect, the thermal management control is also designed to set a flexible end position for the diagonal movement at the other end of the feed motion, or to define the axial position of the transition from diagonal milling with a larger diagonal ratio to diagonal milling with a smaller diagonal ratio, up to pure axial milling.

[0020] In this respect, the invention provides for diagonal milling with a non-constant diagonal ratio, in particular a non-zero diagonal ratio occurring in the infeed path that does not overlap with the profiling path, and a lower diagonal ratio at the end of the feed path than at the beginning of the profiling path and / or at least within a section in the infeed path that does not overlap with the profiling path.

[0021] In a further particularly preferred embodiment, it is provided that, in order to counteract the deviation, in particular flank line deviation, a thermal, in particular axial, expansion of the hob cutter is at least partially compensated, in particular by varying the initial subcharge.

[0022] The term "compensation" here refers to process-related compensation, meaning that the effect of the gear's axial thermal expansion on the gear hobbing process and the resulting gear geometry, particularly with regard to flank line deviation, is compensated. The inventors recognized that significant axial thermal expansion can produce the same effect as a gear hobbing tool whose parameters do not match those intended for machining. By counteracting this effect with a thermal management control function, it is possible to ensure that the workpieces adhere more closely to absolute manufacturing tolerances.Furthermore, by compensating on small time scales such as individual strokes, i.e., without global uniform compensation across the workpiece batch, the uniformity of workpiece machining can be increased, meaning that tolerance fields regarding the relative deviation between individual gears of a workpiece batch can be better maintained.

[0023] In this context, it is preferably provided that a temperature of the hob cutter, in particular actual temperature measurement of the hob cutter, is taken into account by the thermal management control.

[0024] Since the compensation for axial thermal expansion involves both the coefficient of thermal expansion for the material of the hob cutter, for example steel, and a parameter reflecting the temperature, the actual temperature can be used as the measured temperature. Other options are also possible that are not based on a measured temperature, such as temperatures derived from empirical data, temperature tables, or temperature curves, or information generated from simulations of the process, which also incorporate temperature information.

[0025] For temperature measurement, a thermal imaging camera, for example, directed at the machining area, or other temperature sensors can be used. In this respect, the invention is not subject to any particular limitations, as long as it is ensured that the temperature of the hob can be detected (measured) during its machining. In a preferred embodiment, the heat sensor operates without contact, for example in the form of a thermal imaging camera / infrared sensor, whereby the sensor can be attached to the milling head, preferably to a region of the milling head that does not move during the shift movement of the hob.

[0026] In another proposed design, it is envisaged that the thermal management control operates a machine axis control intended for flank line correction depending on the temperature taken into account or recorded, and depending on at least one control parameter reflecting the effect of axial thermal expansion.

[0027] A function already implemented in various gear cutting machines for flank line correction can be readily adapted by simply adding a thermal management control function. This additional thermal management control function is capable of calculating a change in a control parameter that reflects axial thermal expansion, such as the helix angle of the hob, on which, for example, the machine axis control function for flank line correction is based. This simplifies the implementation of the method in gear cutting machines or the retrofitting of existing machine axis controls.

[0028] In this context, it can also be considered that the machine axis control, when a stable temperature level of the hob is reached, is operated with settings of at least one control parameter that are independent with regard to the influence of axial thermal expansion.

[0029] For example, the additional thermal management control function could be deactivated, even if it continues to run in the background, without affecting the control influence resulting from axial thermal expansion. The machine axis control then operates based on the setpoints derived from the steady-state temperature of the hob. If these values ​​are already known, calculated, or simulated, a reference value for the correction (zero position) can already be based on this steady state, and a computational correction with respect to this zero position is only performed in the initial phase until the steady state is reached. In this respect, the machine axis control can be designed for an axial thermal expansion associated with an expected stabilized hob temperature, which is necessary for continuous operation of the hob.

[0030] As mentioned, in another preferred variant, this additional heat management control function for correcting the effects of axial thermal expansion can also be continuously maintained actively, thereby automatically taking into account any effects caused by external influences or unexpected process interruptions or changes in process conditions.

[0031] This aspect of compensating for the effects of axial thermal expansion, particularly with regard to flank line deviation on the workpiece or its variation across individual workpieces of the workpiece batch, is also intended as an application option regardless of whether diagonal gear hobbing is used at least partially during a single stroke of machining only one workpiece, or whether, as usual, the machining of the aforementioned components is carried out using pure axial gear hobbing, and, as is also usual, shifts are made between individual strokes or the machining of successive workpieces, even if the effect of axial thermal expansion is less pronounced.

[0032] In addition to flank line deviations, gear defects in the form of tooth thickness variations due to radial thermal expansion can also occur. The invention provides a countermeasure for this as well, in the form of a part of the heat management control that takes radial thermal expansion into account. This part can also utilize existing compensation mechanisms for counteracting tooth thickness variations or profile shifts, if already present, by using the radial thermal expansion of the hob as an additional control parameter and, if necessary, transforming it to adapt to the corresponding existing correction function. This part of the heat management control can include, as a countermeasure, a change in the radial axis (center distance axis), as well as a correction in the direction of the gear axis of the gear-milled tooth.

[0033] In a further preferred embodiment, the gear-milled toothing has a module of at least 1 mm, preferably at least 2 mm and / or a width of at least 8 mm, preferably at least 10 mm, in particular at least 12 mm.

[0034] In a preferred embodiment, it is preferred that the module is in the range of less than 8 mm, particularly less than 6 mm, and / or that the tooth width is no greater than 100 mm, more preferably no greater than 80 mm. In this context, it is preferred that the hob cutter is a hob cutter whose shape is not modified along its axis of rotation, but whose working area is uniformly designed. It is also preferred for some embodiments that the product of the module and the tooth width is no greater than 3200 mm. 2 preferably not larger than 2400 mm 2 , in particular not larger than 1600 mm2 .

[0035] Here, the advantage achieved by the invention becomes particularly evident.

[0036] This method is also preferred when the gear teeth on the workpiece are completely produced in a single stroke.

[0037] In another preferred embodiment, the gear hobbing is performed using dry cutting. A gaseous cooling medium, such as compressed air, is then preferably used for cooling.

[0038] After a stroke in which diagonal milling has already been performed, the hob cutter can be moved back to its starting position for the beginning of the next stroke. The shift component of the diagonal feed can be selected so that the entire usable working area of ​​the hob cutter is utilized, or only a portion thereof, preferably a predominant portion. The starting position for the next stroke can remain the same, or it can be shifted by a specific amount, even during the machining of a workpiece or between the machining of two consecutive workpieces.

[0039] Also provided by the invention is a computer program product which, when executed on a control system of a gear hobbing machine, controls the gear hobbing machine in an operating mode according to a method according to one of the preceding aspects.

[0040] Furthermore, the invention provides a gear hobbing machine for gear hobbing, comprising a workpiece spindle for holding a workpiece to be hobbed, a milling head equipped with a tool spindle for holding the hobbing cutter, a multi-axis positioning system for positioning and executing a feed movement of the hobbing cutter relative to the workpiece, CNC-controlled spindle axes for adjusting the hobbing coupling for the hobbing machining operation, a detection device for detecting the actual temperature of the hobbing cutter, and / or a control system that controls the gear hobbing machine in at least one operating mode to execute a method according to one of the aforementioned aspects.

[0041] Further features, details and advantages of the invention will become apparent from the following description with reference to the accompanying figures, of which Fig. 1. The feed rate of a hob cutter is explained schematically. Fig. 2 schematically show individual milling cutter positions at different times, Fig. Figure 3 schematically and exaggeratedly shows the axial thermal expansion of a hob cutter, Fig. Figure 4 schematically shows the effect of axial thermal expansion in a gear hobbing process. Fig. 5 is a schematic representation of the situation after compensating for the correction, Fig. 6 shows a sensory detection of the hob cutter and Fig. Figure 7 shows a gear hobbing machine in whose control system specific feed movements and corrections for axial thermal expansion of the gear cutter are stored.

[0042] For the following explanations, a coordinate system is used in which the gear axis of rotation of the workpiece (gear) 1 to be geared runs along the Z-axis and the radial feed direction is denoted by X. A hob cutter 2 rotating in the direction of rotation 3, here in Fig. 1, shown only schematically in four stroke positions, performs a feed movement with an axial component in the Z direction during a stroke in order to machine the workpiece or gear 1 in this example over its full axial width.

[0043] Also in Fig. Figure 1 shows sections of the feed path, namely the inlet path, profiling path, and overflow path, the meaning of which is well known to those skilled in the art and therefore will not be explained further here. Fig. It is not apparent from Figure 1 that the hob cutter is pivoted in a pivot plane orthogonal to the X axis at the pivot angles (pivot axis A) typical for gear hobbing. The rotation axis of the hob cutter 2, which runs in the Y direction, therefore lies in this pivot plane and, together with the plane orthogonal to the Z axis, defines the pivot angle.

[0044] This is better in Fig. 2. It can be seen in which the paper plane lies in the pivot plane. The inclined position of the hob cutter 2, along with the pivot angle, can be seen, which is in Fig. The upward-pointing arrow 2 indicates the Z-axis direction, or the axial component of the feed path. The machining zone, i.e., the area where the engagement takes place, also moves along this arrow, thus moving axially relative to gear 1. Furthermore, it is shown that the hob cutter 2 is also moved along its rotational axis Y during its feed movement. The in Fig. The curve shown in Figure 2 describes the movement of a fixed point on the hob cutter, which is composed of the superimposed axial movement and the displacement of the hob cutter along its axis. It can be seen that the hob cutter displacement begins already in the approach path and even before the start of the profiling path, transitions into a region of approximately constant diagonal ratio, and approaches a purely axial movement again before reaching the overflow path. It is also evident that the initially machining area of ​​the hob cutter is close to the area shown in Figure 2. Fig. 2. The left end of the working area of ​​the hob is located and towards the end of the machining near the right end of the hob area, following the engagement zone along the arrow (axial direction).

[0045] Looking at the trajectory chosen here as an example, it is evident that in the area where a diagonal process (superposition of the axial and shift movements) takes place, a constant diagonal process is not used. Rather, the diagonal ratio is variable and, in particular, is larger at least section by section in the approach path than towards the end of the feed, and there not only in the overflow path, but also before reaching the overflow path.

[0046] It goes without saying that the trajectory is not exactly the one in Fig. must correspond to the form shown in Figure 2; for example, a (also constant) diagonal ratio could be set very early on in the same machining area from a purely axial method that was initially started, by shortening the cutting time, and an approach to the axial movement towards the end of the feed path could also be more abrupt, for example by an almost immediate termination of the diagonal method and return to the axial method.

[0047] Due to these specific trajectories, in addition to the inherent delocalization of heat input ΔQ(Y) into the hob, this is also specifically influenced by heat control and, in the example shown, kept more uniform, thus counteracting its non-uniformity ΔY. At the beginning, where a large part of the machining takes place in the entry zone, this wear is rapidly delocalized. Towards the end, where essentially only profiling is performed, the delocalization is reduced again. Thus, high initial wear is avoided, whereas towards the end of machining, wear is, in a sense, accumulated, resulting in a more uniform wear across the working area of ​​the hob.

[0048] With such path curves, the hob heats up due to the heat input, while at the same time it is also cooled by a cooling medium (here, for example, compressed air), so that when machining batches of workpieces, assuming a typical, uniform working cycle, a heat or temperature equilibrium will ultimately be established, i.e., the hob operates at a temperature level in which it no longer absorbs any net heat, meaning that the heat input, which would potentially increase its temperature, is counterbalanced by the cooling.

[0049] Even before this equilibrium is reached, namely during the machining of the initial workpieces of a batch, the temperature of the hob cutter typically rises initially over several machining operations due to the temporal non-uniformity Δt of the absorbed net heat. This results in a Fig. 3 (completely exaggerated for illustrative purposes) shows that the axial thermal expansion of the hob cutter is not only present, but also uneven in the time until the hob cutter reaches a substantially steady temperature state.

[0050] Such axial thermal expansion poses no problem in the commonly used axial hobbing process, since the workpiece is not machined with axially spaced engagement areas. Fig. In Figure 3, where the hob cutter is schematically shown between its main bearing side 4 and counter bearing side 5, the distance between 4 and 5 changes noticeably, and in comparison to Fig. 2. A change in distance occurs between the two spaced engagement areas, which leads to irregularities in the gear geometry of the gear-milled gears, which manifests itself as a gear defect, in this case as flank line deviation fH. β .

[0051] This change in distance is in Fig. Figure 4 on the left shows this again (also greatly exaggerated). According to standard calculations, machining (without any axial thermal expansion) should take place at the upper left point; however, due to axial thermal expansion, this point on the hob cutter is actually located at the point shown further to the right.

[0052] Since the resulting gear error in the flank line deviation can be compensated for by a flank line deviation correction, a correction function for flank line deviation already known in the prior art can be used to compensate for this additional influence as well. The control information required for this can be obtained, for example, by monitoring the temperature of the hob cutter, as in [reference to relevant example]. Fig. Figure 6 shows how the measurement is taken, for example, using a contactless infrared sensor, preferably aligned with the machining zone. By calculating the currently assumed dimension and applying it as a tangential compensation to the tool position for the subsequent workpiece, the overall position set by the machine axis position again corresponds to the situation underlying the machining operation. This is shown schematically in Figure 6. Fig. 5 shown.

[0053] Also in the Fig. 4 and Fig. 5. An additional correction of the radial thermal expansion can be made, and is preferably carried out, which, as in the Fig. 4 and Fig. 5 can be seen on the right, by means of a compensation in the radial position X and the axial position Z.

[0054] Fig. Figure 7 schematically represents a gear hobbing machine, with the axes table or workpiece rotation axis C, hobbing rotation B, radial axis X, shift axis Y, swivel axis A, and stroke axis Z. Not shown in Fig. 7 is the hob cutter itself, as well as a workpiece, which can be clamped in the usual manner or held in the milling head of the machine. The in Fig. For example, a schematically represented infrared sensor could be attached to the milling cutter head at a point that does not move when the hob is shifted, but does move along with the stroke of the hob.

[0055] In an exemplary embodiment of a hob cutter with a tool diameter of 100 mm and an available shift travel of 150 mm (typical value in an interval of 20-300 mm), the total temperature change ΔT of 27.5 K occurs during hob milling from room temperature until the steady state is reached after machining a number of workpieces, typically between a few (about 5) and several (about 15) workpieces (typical value in an interval of about 10-40 K).

[0056] According to the expansion formula ΔI = I0 · α · ΔT, the thermal expansion along the shift path is 49.5 µm for an α of 12 · 10 -6 K -1, the coefficient of thermal expansion of steel (HSS or PM) for a corresponding hob cutter. This value could already be used as a scaling factor for the shift axis scaling and applied by the control system; in this case, a correction value of 1.00033 = 1 + ΔI / I0 results. If a gear hobbing machine does not have a correction function to react to changing axial pitch, the changing axial pitch of the hob cutter and the resulting new ratio of tangential to axial displacement could alternatively be calculated in order to control the machine axes accordingly, thus compensating for tool expansion due to temperature changes.

[0057] The correction can be implemented in real time during the machining of individual workpieces, as is preferred by the invention. Within a single workpiece, this results in a temperature change of 2.5 K in this exemplary embodiment, and a corresponding shift path correction of 4.5 µm, corresponding to a correction factor of 1.00003.

[0058] In another embodiment, the hob cutter is made of carbide with a coefficient of thermal expansion α of between 5 and 7.5 · 10 -6 K -1 , and the corrections are approximately twice as small as in the example above.

[0059] Furthermore, for the above embodiment, the thermal expansion in the radial direction can be determined; with a tool diameter of 100 mm, this results in a diameter correction of 3 µm and, accordingly, an absolute radial axis correction ΔX of 0.0015 µm over a workpiece, and in this embodiment of 0.0165 µm overall when the steady state is reached.

[0060] The correction / compensation values ​​obtained for a workpiece until a steady state is reached can be used directly for correcting the next workpiece to be gear-milled. In this respect, the invention prefers real-time compensation during the machining of even the first workpieces in a batch before a steady state is reached.

[0061] In a further embodiment, it is also possible to preheat the hob cutter to the expected temperature of the steady state. For this purpose, a heating device, for example electric or inductive, could be implemented. In this case, with sufficient accuracy, which could still be monitored by temperature sensors, the continuously changing correction during the machining of the first workpieces would be eliminated, and the process could be run uniformly for the workpieces with the compensation values ​​that take into account the total change compared to the shift path (hob expansion) at room temperature, for which the process is (originally) designed. It would also be conceivable to design the process at the steady-state level, in the sense of a pre-implementation of the compensation for the thermal expansion of the hob cutter.

[0062] It is understood that the invention, with regard to specific implementations of the compensation for, for example, axial or radial thermal expansion, is not limited to the specific example described above. For instance, an independent correction routine could be implemented. The input parameters for the correction can also be provided in a variety of ways, from directly or indirectly measured temperatures, expected temperature profiles from temperature curves recorded or calculated in comparable workflows, etc.Furthermore, it is not significant for the effect to be achieved whether, for example, an axial thermal expansion calculated from temperature information and taking into account the coefficient of thermal expansion of the hob material is converted into a control parameter of an existing correction program, such as the helix angle of the hob (a change in helix angle would also result in a change in the position of a point with a fixed worm rotation angle relative to a fixed reference along the hob axis).

[0063] It is also understood that axial and / or radial thermal expansion is not only used, as described in the example above, for processes in which shifting occurs during a machining step, but can also be used when working purely in axial milling and shifting only occurs between machining successive workpieces.

[0064] In this respect, the invention is not limited to the specific embodiments illustrated in the exemplary embodiments for illustrative purposes. Rather, the features of the preceding description as well as of the following claims can be essential, individually and in combination, for the realization of the invention in its various embodiments. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2013 015 252 A1

[0002] EP 3 139 229 B1

[0003] Cited non-patent literature

[0000] Bausch, Innovative Gear Manufacturing, 3rd edition, p. 177, Figure 6.2-9

[0004]

Claims

[1] Method for gear hobbing of a tooth (1) having a tooth axis (Z) on a workpiece, in particular a batch of workpieces, in a heat-generating machining operation with a gear cutter (2) whose usable working area extends along (Y) its axis of rotation, in which the gear cutter performs a feed movement with an axial feed component parallel to the tooth axis (Z) over one or more strokes, passing through a possibly overlapping entry path (E), profiling path (P) and overrun path (Ü) in order to machine the tooth over a desired width, characterized by one controlling the heat input into the hob cutter (2) due to the generated heat to a locally delocalized heat input (ΔQ(Y)), and in particular a non-uniformity seen locally over the working area extension of the hob cutter (Δ Y) counteracting the locally delocalized heat input (ΔQ(Y)) and / or a deviation, in particular flank line deviation (fH) β ) counteracting the gear teeth due to thermal, in particular axial, thermal expansion of the hob and, in particular, counteracting a non-uniformity (Δt) of the net heat absorbed by the hob in one stroke, which is seen over at least an initial sub-batch of the workpiece batch Thermal management control. [2] Method according to claim 1, wherein the heat input is delocalized to counteract the locally seen unevenness already during the passage through at least a partial area of ​​an inlet path located outside the profiling path. [3] Method according to claim 2, wherein the magnitude of the diagonal ratio (dY / dZ) of the feed movement is at least sectionally different from zero and / or monotonically increasing when passing through the partial area. [4] Method according to one of the preceding claims, wherein, in order to counteract the locally seen inconsistency, a reduction in the degree of delocalization takes place during the passage through a section of the overflow path or a section of the profiling path adjacent to the overflow path. [5] Method according to claim 4, wherein the magnitude of the diagonal ratio (dY / dZ) of the feed motion already vanishes when passing through the section and / or decreases monotonically at least section by section. [6] Method according to one of the preceding claims, in which, to counteract the deviation, in particular flank line deviation, a thermal, in particular axial expansion of the hob cutter is at least partially compensated, in particular by varying the initial subcharge. [7] Method according to one of the preceding claims, with a temperature of the hob taken into account by the heat management control, in particular actual temperature detection of the hob. [8] Method according to claim 6 or 7, wherein the thermal management control operates a machine axis control provided for flank line correction depending on at least one control parameter reflecting the effect of axial thermal expansion, depending on the temperature taken into account or detected. [9] Method according to claim 8, wherein the machine axis control is operated with settings of the at least one control parameter that are independent with respect to the influence of the axial thermal expansion when a stable temperature level of the hob is reached. [10] Method according to claim 8 or 9, wherein the machine axis control is designed for an axial thermal expansion associated with an expected stabilized temperature of the hob for continuous operation of gear hobbing. [11] Method according to one of the preceding claims, wherein the gear-milled toothing has a module of at least 1 mm, preferably at least 2 mm and / or a width of at least 8 mm, preferably at least 10 mm, in particular at least 12 mm. [12] Computer program product which, when executed on a control of a gear hobbing machine, controls the gear hobbing machine in an operating mode to a method according to one of the preceding claims. [13] Gear hobbing machine for gear hobbing, comprising a workpiece spindle for holding a workpiece to be hobbed, a milling head equipped with a tool spindle for holding the hobbing cutter and a multi-axis positioning system for positioning and executing a feed movement of the hobbing cutter relative to the workpiece and CNC-controlled spindle axes for adjusting the hobbing coupling for the hobbing machining operation as well as a detection device for detecting the actual temperature of the hobbing cutter and / or a control which controls the gear hobbing machine in at least one operating mode for executing a method according to one of claims 1 to 11.

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