Method and apparatus for producing modified surface structures on tooth surfaces

Abstract

A method and machine tool for generating modified structures on the tooth flank of a pre-toothed workpiece are disclosed. By providing a relative movement between a grinding worm and a pre-toothed workpiece having an axial component parallel to the workpiece axis, multiple adjacent contact orbits spaced apart in the face width direction of the workpiece are generated on the tooth flank of the pre-toothed workpiece. To generate the tooth flank waviness, the penetration depth between the grinding worm and the workpiece is intentionally varied along each contact orbit, so that the tooth flank waviness of adjacent contact orbits is shifted from one another by a phase offset at any given position in the depth direction of the workpiece. The phase offset may be between 90° and 270°, and / or the phase offset for each adjacent contact orbit may vary from contact orbit to contact orbit, and / or the phase offset for each adjacent contact orbit may vary along one of the contact orbits.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a modified surface structure on the tooth flank of a pre-toothed workpiece, and further to a machine tool configured to carry out such a method. [Background technology]

[0002] Particularly in the field of electric vehicles, the topic of NVH (noise-vibration-harshness), especially in the gear transmission section of a vehicle, is becoming increasingly important due to the absence of the dominant background noise of a combustion engine. Requirements regarding noise excitation behavior are often specified in the form of predefined limit values ​​in the noise frequency spectrum. Whether a workpiece fulfills these requirements is usually checked randomly on an end-of-line (EOL) test bench. If the measured amplitude of individual noise frequencies exceeds the predefined limit values, the corresponding workpiece is rejected.

[0003] A typical noise frequency spectrum for rotating gears consists of the gear meshing frequency (f ZE = gear rotation frequency x number of teeth) and associated harmonics. These dominant noise frequencies are generally caused by transmission errors resulting from mesh stiffness varying along the length of the contact path. The progression of mesh stiffness as a function of position along the length of the contact path is cyclically repeated with mesh pitch, resulting in the dominant noise frequencies mentioned above. Another cause can be "generating holes" created during manufacturing, i.e., recessions in the material relative to the desired profile line.

[0004] Overall, any transmission error in the gear mechanism under load can lead to noise excitation that can be perceived as an unpleasant noise. For example, if the dressing tool has a certain waviness that exceeds the profile height, the waviness will be transferred to the worm flank and subsequently lead to profile shape deviations in the workpiece.

[0005] Constant vibrations around the machine tools used to machine pre-toothed workpieces can also lead to measurable tooth flank ripples in the tooth flanks, which can result in objectionable noise characteristics of the teeth.

[0006] Grooves extending across the face width of the gear train can also lead to noise excitation. In general, periodic surface structures, especially in the direction perpendicular to the contact line of mating spur gears, can lead to the excitation of noise frequencies that dominate the noise frequency spectrum of the gear train.

[0007] There are several methods to improve the noise excitation behavior of gear trains. Transmission errors caused by deformation of the gear train under load can be effectively reduced by modifying the tooth flanks. Pitch holes can be almost completely eliminated through optimized process control.

[0008] US Patent No. 5,649,999 discloses a generating grinding process in which a workpiece is machined with a grinding worm, whereby corrections, in particular profile corrections, or profile waviness and / or defined periodic flank waviness are generated on the effective surface of the workpiece being machined by intentionally generating an oscillating movement caused by imbalance and / or eccentricity of the grinding worm in order to correct or prevent undesired flank waviness.

[0009] The flank waviness on the workpiece caused by imbalance or eccentricity of the grinding worm is always of first order with respect to the worm rotation frequency, i.e., this method cannot generate flank waviness of higher orders with respect to the worm rotation frequency.

[0010] Periodically repeating surface structures tend to lead to excitation in a relatively narrow noise frequency band. Furthermore, as irregular a surface structure as possible leads to a very broad noise frequency spectrum that approximates "white" noise, i.e., a noise frequency spectrum with the same amplitude at all noise frequencies. This noise frequency spectrum, which tends to reduce the dominance of individual noise frequencies, is advantageous because it is perceived as less psychoacoustically unpleasant. Additionally, in the case of excitation with a broad noise frequency spectrum, the entire excitation energy is distributed over a wide frequency range, and therefore the noise amplitude of each individual frequency component tends to be smaller than in the case of excitation in a narrow frequency band.

[0011] When a workpiece is machined using a generating grinding process with a grinding worm, for example, a periodically repeating surface structure can be produced on the tooth flank by dressing the grinding worm used to machine the tooth flank. The dressing wheel used for dressing may have different abrasive grain sizes and shapes, as well as different distributions of abrasive grains around the circumference, depending on the technique used, resulting in a dressing pattern on the surface of the dressing wheel. Since the dressing wheel typically rotates multiple times during one rotation of the grinding worm, this dressing pattern is periodically transferred onto the grinding worm during dressing in the direction of the worm thread. During subsequent grinding of the workpiece, periodic variations in the surface of the tooth flank can occur on the tooth flank of the workpiece in the form of grooves extending across the face width.

[0012] Patent document 2 discloses a method in which the rotation angle of the dressing wheel is coupled to the rotation angle of the grinding worm with an adjustable fixed ratio, a programmable variable ratio, or a stored stochastically varying ratio. The grinding worm moves along its axis relative to the workpiece during grinding (shift feed) so that each point on the tooth flank of the workpiece's teeth corresponds exactly to one point on the flank of the grinding worm thread.

[0013] The grooves mentioned above can be destroyed by deliberately selecting the shift feed, which destroys the periodicity of the surface structure of the tooth flank and thus, in principle, achieves a more pleasant noise behavior, but the structure transferred to the tooth flank is highly dependent on the stochastic dressing pattern on the surface of the dressing wheel and can therefore only be influenced by the shift feed during grinding of the workpiece.

[0014] There is therefore a need for a method that allows the surface structure of the tooth flanks to be intentionally modified so that an optimized behavior, particularly with regard to noise, is achieved. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] German Patent Application Publication No. 102012015846 [Patent Document 2] German Patent Application Publication No. 19905136 Summary of the Invention

[0016] In a first aspect, the object of the present invention is to provide a method for producing a modified surface structure on the tooth flank of a pre-toothed workpiece by generating grinding, which allows for optimization of the noise behavior.

[0017] This object is achieved by the method of claim 1. Further embodiments are defined in the dependent claims.

[0018] Therefore, a method for generating a modified surface structure on the tooth flank of a pre-toothed workpiece is proposed, The method comprises: Rotating the grinding worm around the worm shaft; Rotating the pre-toothed workpiece around the workpiece axis, the grinding worm and the pre-toothed workpiece being in rolling engagement; - providing a relative movement between the grinding worm and the pre-toothed workpiece, the relative movement having an axial component parallel to the workpiece axis, such that a plurality of adjacent contact tracks are generated on the tooth surface of the pre-toothed workpiece, the contact tracks extending at a distance from each other in the face width direction of the workpiece; Includes:

[0019] According to the invention, the penetration depth between the grinding worm and the pre-toothed workpiece is intentionally varied along each contact track to generate a tooth flank waviness with a plurality of wave periods along said contact track, so that the resulting tooth flank waviness of adjacent contact tracks are shifted relative to each other by a phase offset at any given position in the depth direction of the workpiece, i.e. at any predetermined position across the tooth depth, or in other words along any predetermined tooth trace of the tooth flank as viewed in the face width direction of the workpiece; the phase offset is between 90° and 270°; and / or The phase offset for each adjacent contact trajectory varies from contact trajectory to contact trajectory; and / or The phase offset for adjacent contact trajectories varies along each contact trajectory.

[0020] Any given tooth flank for which a phase offset is defined in this context corresponds, in the case of a cylindrical workpiece, to the intersection between the tooth flank and an imaginary cylinder arranged concentrically with respect to the workpiece axis and having any given radius, said radius having a value lying between the values ​​of the root radius and the tip radius of the toothed workpiece. The intersection defines a specific position in the depth direction of the workpiece, i.e., across the tooth depth. In the case of a conical workpiece, the tooth flank is defined in this context as the intersection with an imaginary cone arranged concentrically with respect to the workpiece axis.

[0021] In some embodiments, the phase offset for each adjacent contact track varies from track to track, i.e., the phase offset is not constant from track to track. In particular, the phase offset between the tooth flank ripples (waviness) of a first pair of adjacent contact tracks may be different from the phase offset between the tooth flank ripples (waviness) of a second pair of adjacent contact tracks that are at different positions in the face width direction of the workpiece.

[0022] In some embodiments, alternatively or additionally, the phase offset relative to each adjacent contact track varies along the respective contact track. In particular, the tooth flank waviness (ripple) of adjacent contact tracks may have different tooth flank waviness wavelengths, whereby the phase offset between said adjacent contact tracks varies in the direction of said contact track. Alternatively or additionally, the tooth flank waviness of each contact track may have a tooth flank waviness wavelength that varies along the respective contact track. This may result in a phase offset along each contact track that varies relative to adjacent contact tracks if the tooth flank waviness wavelengths of adjacent contact tracks do not vary "in sync."

[0023] By varying the phase offset for each adjacent contact track from one contact track to another or along each contact track, the wave crests and wave troughs occurring along a contact track are prevented from forming straight wave fronts (lines of equal undulation phase position) with the wave crests and wave troughs of adjacent contact tracks. Surface structures with non-straight wave fronts are advantageous in terms of resulting noise behavior.

[0024] In some embodiments, the phase offset of a contact track relative to each adjacent contact track is between 90° and 270°. The 90° to 270° phase offset prevents wave crests and troughs occurring along a contact track from forming a continuous wave front with the wave crests and troughs of adjacent contact tracks. Instead, a discrete surface structure is produced, which is particularly advantageous in terms of the resulting noise behavior.

[0025] For example, if the tooth flank waviness has a fixed periodicity, a checkerboard-like surface structure can be generated with a phase offset of 180° relative to each subsequent contact trajectory. Such a structure can offer advantages in terms of noise behavior, especially when superimposed with uncontrolled, especially stochastic, deviations in the indentation depth.

[0026] Whether the tooth flank waviness of adjacent contact orbits is shifted relative to one another by a phase offset may depend on the fluctuating frequency at which the indentation depth fluctuates. During machining, adjacent contact orbits on a tooth flank are generated at a certain generation frequency. If the fluctuating frequency and the generation frequency are both constant and the fluctuating frequency is an integer multiple of the generation frequency, there will be no phase offset from one contact orbit to another along any tooth trace on the tooth flank. However, if the fluctuating frequency is a non-integer and / or non-constant ratio to the generation frequency, a phase offset may occur.

[0027] Preferably, the grinding worm moves continuously along a shift direction parallel to the worm axis. As a result, the relative movement between the grinding worm and the pre-toothed workpiece also has a shift component parallel to the worm axis. Through the shift feed (i.e., through the shift component of the relative movement), the grinding worm performs a superimposed rack-like motion in addition to rolling due to rotation, thereby changing the frequency at which the contact orbit is generated. That is, the tooth flank waviness wavelength may be distorted (i.e., may become smaller or larger depending on the shift direction), and the phase offset can be adjusted via the shift component. Setting the phase offset via the shift component can be useful, especially when the fluctuating frequency cannot or should not be changed, for example, when the fluctuating frequency is determined by the imbalance of the grinding worm or arises from the thread waviness applied to the grinding worm and therefore may be linked to the worm rotation frequency of the grinding worm, which may need to remain fixed.

[0028] In a preferred variant of the method, the grinding worm rotates at the worm rotation frequency and the intentional variation of the penetration depth is performed at a variation frequency that is greater than the worm rotation frequency, which makes it possible to set the phase offset at a slower shift feed than in the situation where the variation frequency corresponds to the worm rotation frequency.

[0029] The variation frequency is preferably selected to be high compared to the rotation frequency of the pre-toothed workpiece so that the tooth flank waviness along each contact track has multiple wave periods.

[0030] The intentional variation in indentation depth may be produced in different ways, and a combination of these ways is also possible.

[0031] In particular, the intentional variation of the plunge depth may involve intentionally providing additional relative movement between the pre-toothed workpiece and the grinding worm.

[0032] In this context, the term "additional relative movement" refers to movement beyond that required to satisfy the gear laws and beyond the relative movement parallel to the work axis required to generate adjacent contact tracks.

[0033] In particular, the term "additional relative movement" refers to a movement having a component normal to the tooth surface of the workpiece being machined.

[0034] In particular, by means of intentional additional relative movements, the relative position between the pre-toothed workpiece and the grinding worm can be changed along a feed direction radial to the workpiece axis, and / or along an axial direction parallel to the workpiece axis, and / or along a shift direction along the worm axis.

[0035] In particular, the grinding worm can move radially relative to the workpiece axis along the feed direction, and causing the intentional additional relative movement can include causing a translational vibration of the grinding worm having a vibration component in the feed direction radial to the workpiece axis.

[0036] In particular, if the workpiece has a helical gear mechanism, the grinding worm may alternatively or additionally be configured to move with a motion component parallel to the workpiece axis, and causing the intentional additional relative movement may include causing a translational vibration of the grinding worm with a vibration component parallel to the workpiece axis.

[0037] Alternatively or additionally, the grinding worm may be displaceable along a shift direction parallel to the worm axis, and causing the intentional additional relative movement may include causing a translational vibration of the grinding worm having a vibration component in the shift direction parallel to the worm axis.

[0038] Alternatively or additionally, providing the targeted additional relative movement may include inducing torsional oscillation of the grinding worm about the worm axis.

[0039] Alternatively or additionally, a pre-toothed workpiece can be placed on the work spindle and an intentional additional relative movement can be provided. causing torsional vibration of the work spindle about the work axis; and / or causing bending vibrations of the work spindle, especially in a direction perpendicular to the work axis; and / or Inducing translational vibrations of the work spindle, in particular with vibration components along directions parallel and / or perpendicular to the work axis, Includes:

[0040] Alternatively or additionally, it is also conceivable to use an appropriately dressed grinding worm to achieve deliberate variations in the penetration depth.

[0041] The grinding worm can have a thread waviness on the grinding worm thread flank of the grinding worm thread, and the intentional variation of the plunge depth to generate the tooth flank waviness can include transferring the thread waviness of the grinding worm thread flank to the tooth flank of the pre-toothed workpiece that is in rolling engagement with the grinding worm.

[0042] The method may include dressing the grinding worm to create the thread waviness.

[0043] The undulations can be generated in only a portion of the grinding worm thread or in several different portions, or in one or more width regions of the grinding worm that can be selectively traversed by shifting in the shift direction during grinding of the workpiece. For example, each grinding stroke can be assigned a region with a constant undulation, or the undulations can be designed to change during the grinding stroke.

[0044] The relative movement between the grinding worm and the workpiece can be performed at a shift feed rate along the shift direction and an axial feed rate in an axial direction parallel to the workpiece axis, the shift feed rate and the axial feed rate being in a predetermined diagonal ratio such that the thread waviness is transferred onto the tooth flank of the pre-toothed workpiece, thereby intentionally modifying the surface structure of the tooth flank.

[0045] The diagonal ratio is the ratio of the shift feed rate of the grinding worm in the shift direction to the axial feed rate of the grinding worm in the axial direction parallel to the workpiece axis. This diagonal ratio may or may not be zero.

[0046] The advantage of permanently molding the thread undulations into the ground worm thread is that the thread undulations can be generated in a separate, less dynamic process, independent of the machining of the pre-toothed workpiece, thereby reducing the precision requirements imposed on the machine shafts involved in the highly dynamic grinding process, as opposed to the generation of machine-controlled additional movements.

[0047] The method may also include dressing the grinding worm with a dressing tool, which may exhibit radial and / or axial runout, where a fixed or variable rotational angle ratio between the dressing tool and the grinding worm may be specified such that the radial and / or axial runout is intentionally used to generate thread waviness on the grinding worm thread flank.

[0048] In one variant, the grinding worm has at least two grinding worm threads, each of which has a respective thread swell generated along the worm contact path, and the at least two grinding worm threads each generate adjacent contact tracks on the tooth flank, each contact track on the tooth flank being associated with one of the at least two worm contact paths, and the thread swells generated on each grinding worm thread are preferably different from each other.

[0049] To ensure that at least two grinding worm threads each generate adjacent contact tracks on the tooth flank, the engagement sequence of the at least two grinding worm threads on the tooth flank must be taken into consideration, and a suitable tooth / thread ratio between the pre-toothed workpiece and the grinding worm must be selected.

[0050] The worm contact paths preferably each have a worm contact path start point associated with a contact path start point of a respective contact path on the tooth flank, and the thread undulations of the at least two ground worm threads at each worm contact path start point are out of phase with each other.

[0051] The flank undulations of at least two ground worm threads can also have different wavelengths. These differences between the ground worm threads can be specifically transferred to the tooth flanks by suitable setting of the shift feed, taking into account the meshing order, in order to deliberately set a phase offset between the flank undulations of adjacent contact tracks.

[0052] Alternatively or additionally, the thread undulations of the at least two grinding worm threads may have different undulation amplitudes. The worm contact path start points may generally be located at different circumferential positions relative to the circumferential direction of the grinding worm.

[0053] In the case of a grinding worm having at least two grinding worm threads, the method may further include dressing one of the grinding worm threads of the grinding worm with a constant axial pitch error to create a protruding grinding worm thread, the axial pitch error being selected such that the protruding grinding worm thread achieves a greater penetration depth than the preceding and succeeding grinding worm threads in terms of engagement sequence on the tooth flank, and the protruding grinding worm thread grinds at least partially from above the contact track created by the preceding grinding worm thread.

[0054] If the pitch error is selected to be of a suitable magnitude, all contact orbits between the two contact orbits of the protruding grinding worm threads can be ground from above. This can result in only the (relatively wide) contact orbits generated by the protruding grinding worm threads being generated on the workpiece tooth flank, and tooth flank waviness being generated only by the protruding grinding worm threads. In this case, the shift feed can be reduced by a factor corresponding to the number of grinding worm threads engaging in the tooth space.

[0055] In some embodiments, the thread undulations are generated only on the protruding ground worm thread, while in other embodiments, the thread undulations are generated on each of the at least two ground worm threads.

[0056] Preferably, the intentional variation of the indentation depth is superimposed on an uncontrolled, in particular stochastic, deviation of the indentation depth, the intentional variation of the indentation depth being carried out with a modulation amplitude in the range of 0.2 to 5 times the variation scale of the uncontrolled deviation of the indentation depth, The variability measure corresponds in particular to the standard deviation or interquartile range of the uncontrolled deviation of the indentation depth, In particular, a variation measure of the uncontrolled deviation of the indentation depth is determined and the modulation amplitude is specially selected depending on the determined variation measure.

[0057] By deliberately (targeted) varying the indentation depth, a suitable base pattern can be generated on the tooth surface, which can be made more diffuse by superimposing uncontrolled deviations, thereby leading to an optimized noise behavior.

[0058] In a further aspect, the present invention provides a method for producing a composition comprising: a tool spindle configured to receive the grinding worm for rotation about a worm axis; a work spindle configured to receive the pre-toothed workpiece for rotation about a workpiece axis; an axial slide having an axial drive for providing relative movement between the tool spindle and the work spindle, the relative movement having an axial component parallel to the work axis; a controller configured to perform the method described above; A machine tool is provided.

[0059] The machine tool preferably comprises a shift slide having a shift drive for effecting displacement of the grinding worm in a shift direction parallel to the worm axis, the shift drive being configured to induce translational vibration of the shift slide in the shift direction.

[0060] Alternatively or additionally, the axial drive may be configured to induce translational vibration of the axial slide having a vibration component parallel to the workpiece axis.

[0061] Alternatively or additionally, the tool spindle may be configured to induce torsional vibration of the grinding worm about the worm axis.

[0062] Alternatively or additionally, the machine tool may have a tool carrier having a tool carrier drive that causes an infeed movement of the grinding worm in a radial infeed direction relative to the workpiece axis, the tool carrier drive being configured to cause a translational oscillation of the grinding worm in the infeed direction.

[0063] Alternatively or additionally, the machine tool may have at least one separate tool vibration module, the at least one separate tool vibration module comprising: configured to induce translational oscillation of the shift slide and / or the tool spindle in the shift direction; and / or configured to induce translational vibration of the axial slide having a vibration component parallel to the workpiece axis; and / or configured to induce translational vibration of the tool carrier in the infeed direction; and / or It is configured to induce torsional vibration of the tool spindle about the worm shaft.

[0064] The machine tool may have a separate tool vibration module for any selection of or each of the above excitation configurations.

[0065] In particular, it is possible to envisage generating superimposed translational vibrations by exciting the shift slide and the tool spindle with different excitation parameters.

[0066] The machine tool may alternatively or additionally comprise a work spindle drive for driving the work spindle, the work spindle drive being configured to induce torsional and / or bending and / or translational vibrations in the work spindle.

[0067] Alternatively or additionally, the machine tool may comprise at least one separate workpiece vibration module configured to induce torsional and / or bending and / or translational vibrations in the workpiece spindle.

[0068] The machine tool may have a separate workpiece vibration module for any selection of the above mentioned excitation forms of the workpiece spindle or for each of the above mentioned excitation forms of the workpiece spindle.

[0069] In the present context, the term "oscillation" refers to a repeated (periodic) variation over time. The oscillation may be a harmonic oscillation or another form of oscillation. The oscillations may each have an oscillation frequency that is constant over time or that is purposely varied over time. Similarly, the oscillations may each have an oscillation amplitude that is constant over time or that is purposely varied over time.

[0070] The individual excitation sources and the use of a grinding worm with undulations can be combined with one another as desired, and it is also conceivable to intentionally generate vibration beats by superimposing different excitation sources.

[0071] It is also conceivable to achieve deliberate variations in the penetration depth during different grinding strokes in the grinding process using different methods, for example, by inducing vibrations in the shift direction to perform the roughing stroke and thread waviness on the grinding worm to perform the finishing stroke. Different methods can also be used to target variations in the penetration depth during the grinding stroke, preferably during the finishing stroke, since it is the finishing stroke that determines the final surface. During the grinding stroke, the available excitation sources can be switched on and off individually, in groups, or all at once, or the amplitude and frequency can be varied to vary the excitation characteristics during the grinding stroke, i.e., across the flank width. This produces a more diffuse surface structure with fewer periodic components.

[0072] Preferred embodiments of the present invention are described below with reference to the drawings, which are for illustrative purposes only and are not to be construed as limiting. [Brief explanation of the drawings]

[0073] [Figure 1] Figure 1 is a schematic diagram of a generating grinding machine. [Figure 2] FIG. 2 is a partially enlarged view of FIG. [Figure 3] FIG. 3 is a schematic cross-sectional view of a tooth flank along the tooth trace. [Figure 4] FIG. 4 is a schematic diagram of a plurality of contact tracks on the tooth flank, spaced apart from one another in the tooth width direction. [Figure 5A] FIG. 5A is a schematic diagram of the effective contact track width of multiple contact tracks on a tooth surface spaced apart from each other in the tooth width direction when there is no phase offset between the contact tracks. [Figure 5B] FIG. 5B is a diagram showing a schematic tooth flank waviness caused by periodic variations in the penetration depth between the grinding worm and the workpiece when there is no phase offset between the contact orbits. [Figure 5C] FIG. 5C is an enlarged view of the longitudinal cross section taken along section line A'-A' shown in FIGS. 5A and 5B. [Figure 5D] FIG. 5D is an enlarged view of the longitudinal cross section taken along section line B'-B' shown in FIGS. 5A and 5B. [Figure 6A] FIG. 6A is a schematic diagram of the effective contact track width of multiple contact tracks on a tooth surface spaced apart from each other in the tooth width direction when there is a phase offset of 180° between the contact tracks. [Figure 6B] FIG. 6B shows a schematic diagram of tooth flank waviness caused by periodic variations in indentation depth when there is a phase offset of 180° between the contact tracks. [Figure 6C] FIG. 6C is a partial enlarged view of the longitudinal cross section taken along section line A''-A'' shown in FIGS. 6A and 6B. [Figure 6D] FIG. 6D is a partial enlarged view of the longitudinal cross section taken along section line B''-B'' shown in FIGS. 6A and 6B. [Figure 7A]FIG. 7A is a schematic front view of a grinding worm thread flank of a single grinding worm thread of a grinding worm for one thread pitch of the grinding worm. [Figure 7B] FIG. 7B is a development of a circular grinding worm surface with thread undulations shown diagrammatically. [Figure 8] FIG. 8 is a cross-sectional view of the tooth flank in the tooth width direction. [Figure 9A] FIG. 9A shows the intentional periodic variation of the indentation depth as a function of position along the contact trajectory. [Figure 9B] FIG. 9B shows the uncontrolled, stochastic deviation of the indentation depth as a function of the position along the contact trajectory. [Figure 9C] FIG. 9C shows the results of overlaying the controlled variation of FIG. 9A and the uncontrolled variation of FIG. 9B. [Figure 10] FIG. 10 is a diagram showing an example of the surface structure of a tooth surface modified using the method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0074] [Example of a generating grinder] As an example of a machine tool, FIG. 1 shows a generating grinding machine 1, which will be referred to hereinafter as the "machine." The machine 1 has a machine bed 11, on which a tool carrier 12 is guided for displacement along a radial feed direction X. The tool carrier 12 holds an axial slide 13, which is guided for displacement relative to the tool carrier 12 along a feed direction Z. A grinding head is mounted on the axial slide 13 and can pivot about a pivot axis (so-called A-axis) extending parallel to the X direction in order to adapt to the helix angle of the gear mechanism to be machined. The grinding head also holds a shift slide 14, on which a tool spindle 15 can move relative to the grinding head along a shift direction Y. A grinding wheel (grinding worm) 16, which has been formed and ground into a worm shape, is mounted on the tool spindle 15. The grinding worm 16 is driven by the tool spindle 15 to rotate about a worm axis B.

[0075] The machine bed 11 also holds a swiveling workpiece carrier 20 in the form of a turret, which can be swiveled about a swivel axis C3 between at least three positions. Two identical workpiece spindles are mounted diametrically opposite each other on the workpiece carrier 20, of which only one workpiece spindle 21 is visible in FIG. 1. A workpiece can be clamped on each of the workpiece spindles and driven to rotate about the workpiece axis C1. In the machine shown in FIG. 1, the feed direction Z extends parallel to the workpiece axis C1. However, the feed direction Z, in which the axial slide 13 is displaceably guided, can also be inclined relative to the workpiece axis C1. The workpiece spindle 21 visible in FIG. 1 is in a machining position, in which a workpiece 23 clamped on the workpiece spindle 21 can be machined using a grinding worm 16. The other workpiece spindle, offset 180° and not visible in FIG. 1, is in a workpiece exchange position, in which a finished workpiece can be removed from this spindle and a new blank can be mounted on it. The dressing device 30 is mounted at a position offset by 90° relative to the work spindle.

[0076] Thus, machine 1 has a number of moving components, such as slides or spindles, that are controllably movable by corresponding drives. These drives are often referred to in the art as "NC axes," "machine axes," or simply "axes." In some cases, this term also includes components, such as slides or spindles, that are driven by drives.

[0077] The machine 1 also has a number of sensors. In Figure 1, only two sensors 18 and 19 are shown diagrammatically by way of example. Sensor 18 is a vibration sensor that detects vibrations of the housing of the grinding spindle 15. Sensor 19 is a position sensor that detects the position of the axial slide 13 relative to the tool carrier 12 along the Z direction. However, the machine 1 also has a number of other sensors. These sensors include, in particular, a further position sensor that detects the actual position of each linear axis, a rotation angle sensor that detects the rotational position of each rotary axis, a current sensor that detects the drive current of each axis, and a further vibration sensor that detects vibrations of each driven component.

[0078] All driven axes of the machine 1 are digitally controlled by a machine controller 40. The machine controller 40 comprises several axis modules 41, a control computer 42 and a control panel 43. The control computer 42 receives operator commands from the control panel 43 and sensor signals from various sensors on the machine 1 and uses these to calculate control commands for the axis modules 41. The control computer 42 also outputs operating parameters to the control panel 43 for display. The axis modules 41 each provide a control signal for one machine axis at a respective output.

[0079] A monitoring device 44 is connected to the control computer 42 and performs various monitoring tasks during operation of the machine 1 .

[0080] Figure 2 shows an enlarged view of a portion of Figure 1. The dressing device 30 can be seen particularly clearly here. A dressing spindle 32, to which a disk-shaped dressing tool 33 is clamped, is arranged on a swivel drive 31 and can be swiveled about an axis C4. Alternatively or additionally, a stationary dressing tool, in particular a so-called head dresser, can also be provided, which is intended to engage only with the head region of the grinding worm thread of the grinding worm and to dress these head regions.

[0081] [Contact trajectory with varying indentation depth] In a worm drive, as with the combination of an externally toothed spur gear (pre-toothed workpiece) and a grinding worm, point contact occurs when the axes of the pre-toothed workpiece and the grinding worm are not parallel. When rolling through this combination, the contact point moves on the tooth flank of the pre-toothed workpiece and the grinding worm flank of the grinding worm along a path geometrically determined by this combination. In this context, the path on the tooth flank is called the contact orbit, and the path on the grinding worm flank is called the worm contact path. With each rotation, a new contact orbit is generated on the tooth flank, and material is removed accordingly.

[0082] FIG. 3 shows a schematic cross-section of the tooth flank along the tooth trace. As shown in FIG. 3, each contact orbit has a contact orbit width b1, b2, which corresponds to the penetration depth d1, d2 between the grinding worm 16 (schematically represented by a circular arc in FIG. 3) and the pre-toothed workpiece 23. The first single contact orbit width b1 in FIG. 3 corresponds to the first penetration depth d1, and the second single contact orbit width b2 corresponds to the second penetration depth d2. FIG. 3 clearly shows that for a single contact orbit, the width of the contact orbit increases as the penetration depth increases. However, in FIG. 3, the relationship between the single contact orbit width and the grinding worm penetration depth is not drawn to scale for illustrative purposes. At realistic penetration depths typical for generating grinding processes, a monotonic relationship between the penetration depth and the single contact orbit width can be assumed.

[0083] FIG. 4 shows a schematic representation of multiple adjacent contact orbits with dashed lines. By providing relative movement between the grinding worm and the pre-toothed workpiece, a new contact orbit is generated with each workpiece rotation. This new contact orbit is separated from the previously generated contact orbit by a contact orbit distance S in the face width direction of the workpiece. The contact orbit distance S is determined by the axial component of the relative movement parallel to the workpiece axis C1. The relative movement may be, but does not necessarily have to be, constant. If the pre-toothed workpiece has a spur gear and no relative movement parallel to the workpiece axis C1 occurs during the generation of each contact orbit, the contact orbit extends in the direction of the rolling path, and thus perpendicular to the tooth trace, as shown in FIG. 4. If relative movement parallel to the workpiece axis C1 occurs during the generation of each contact orbit and / or if the pre-toothed workpiece has a helical gear mechanism, the contact orbit is generally inclined relative to the rolling path direction and therefore inclined relative to the tooth trace. When the relative movement parallel to the workpiece axis C1 is constant, the contact trajectories extend parallel to each other at a constant distance.

[0084] If the indentation depth does not vary along the contact track, all contact tracks have the same contact track width. However, if the indentation depth varies along the contact track, tooth flank waviness occurs along each contact track, resulting in an effective contact track width b eff Here, two cases can be distinguished:

[0085] [Case 1 - No phase offset between adjacent tooth flank waviness] 5A to 5D show cases where the indentation depth d varies periodically along each contact track, thus generating tooth flank waviness, but there is no phase offset between the tooth flank waviness of adjacent contact tracks. Figure 5A shows the effective contact track width b of each dashed contact track as shown by the alternating black and white stripes. eff5C shows an enlarged view of a longitudinal section taken along the line A'-A' (wave crest) shown in FIGS. 5A and 5B. FIG. 5D shows an enlarged view of a longitudinal section taken along the line B'-B' (wave trough) shown in FIGS. 5A and 5B. In both FIGS. 5C and 5D, the machined tooth flank surfaces are shown in solid lines. The indentation depth d in the longitudinal section taken along the wave trough shown in FIG. 5D is larger than that in the longitudinal section taken along the wave crest shown in FIG. 5C, but the effective contact track width b eff remains constant along the contact track. This is true because, in this example, the contact track spacing S between adjacent contact tracks is smaller than the actual contact track width (as shown in Figure 3) if the contact tracks were generated without overlapping the adjacent contact tracks, so that when a subsequent adjacent contact track is generated, the preceding contact track is partially ground away from above, and because the variations in the penetration depth d are "in phase," i.e., there is no phase offset between the tooth flank waviness of adjacent contact tracks. As a result, the wave troughs and wave crests of adjacent contact tracks form a continuous wave front, i.e., a line of constant phase that is uninterrupted in the face width direction. Here, only a small amplitude modulation occurs along the wave front (visible in the longitudinal cross sections of Figures 5C and 5D but not in Figure 5B). This amplitude modulation depends on the curvature of the grinding worm at the contact point and is not shown to scale here. Such continuous wave fronts on the tooth flank surface often have a negative impact on the noise behavior of gears in gearboxes.

[0086] [Case 2 - There is a phase offset between the tooth flank waviness of adjacent contact tracks] 6A-6D show an embodiment in which the indentation depth d varies periodically along each contact track to generate tooth flank waviness, with a phase offset of 180° between the tooth flank waviness of adjacent contact tracks. Figure 6A shows the effective contact track width b of each dashed contact track as alternating black and white stripes.eff 5A-5D. In contrast to the situation shown in FIGS. 5A-5D, the wave troughs and wave crests of adjacent contact tracks do not form a continuous wave front in the width direction. Instead, a 180° phase offset results in a checkerboard-like surface structure, as shown in FIG. 6B.

[0087] [Intentional variation of indentation depth] In a fixed generating grinding process, i.e. a generating grinding process with constant process parameters, a certain constant period t exists between the generation of adjacent contact orbits on the same tooth surface. K Therefore, the contact trajectory is generated at a frequency of f K =1 / t K More specifically, this generation frequency f K indicates the frequency with which the contact point between the grinding worm and the pre-toothed workpiece crosses the randomly selected tooth trace during the generating grinding process. For spur gears without shift feed, the generating frequency f K is the rotation frequency of the workpiece

number

[0088] To intentionally vary the indentation depth, the frequency f VA periodic vibration with a variable frequency f is superimposed on the fixed generating grinding process, which causes a periodic relative movement between the grinding worm and the pre-toothed workpiece in a direction perpendicular to the surfaces at the contact point of the grinding worm and the workpiece. This vibration can be generated in various ways. V and generation frequency f K The ratio of K for frequency f V It can be expressed as the order P of

number

[0089] As soon as a non-integer value is chosen for the order P, the phase offset between adjacent contact paths seen along any tooth trace on the tooth flank is Δφ≠0 (Case 2 above).

[0090] The phase offset Δφ can be determined as follows:

number

number

[0091] Therefore, for a desired phase offset Δφ and a desired integer-order component floor(P), the generation frequency f K is known from the kinematic conditions of the generating grinding process, the possible fluctuation frequency f V can be determined.

number

[0092] [Intentional variation of the penetration depth due to additional movements during workpiece machining] The indentation depth can be varied in a variety of ways.

[0093] In one embodiment of the method, the penetration depth is varied by providing a targeted additional relative movement between the pre-toothed workpiece and the grinding worm. The machine tool 1 shown in FIG. 1 includes a shift slide 14 having a shift drive that provides a displacement of the grinding worm in a shift direction Y parallel to the worm axis B. The shift drive can be configured to induce a translational oscillation of the shift slide 14 in the shift direction Y to provide the targeted additional relative movement.

[0094] In particular in the case of helical gears, the penetration depth can be varied by additionally or alternatively inducing a translational oscillation of the axial slide 13 with an oscillation component parallel to the workpiece axis C1 by means of an axial drive configured for this purpose. The translational oscillation can be effected along the feed direction Z. The feed direction Z can extend parallel to the workpiece axis C1 or can be inclined thereto.

[0095] The tool spindle 15 can also be configured to induce torsional vibration of the grinding worm 16 about the worm axis B. To this end, the tool spindle drive can have a frequency converter that can be used to generate the torsional vibration of the grinding worm 16.

[0096] Additionally or alternatively, the tool carrier drive of the tool carrier 12 can be configured to induce translational oscillation of the grinding worm 16 in the feed direction X in order to intentionally vary the penetration depth.

[0097] Alternatively or additionally, the machine tool 1 can have a separate tool vibration module 151 configured to induce translational vibrations of the shift slide 14 and / or the tool spindle 15 in the shift direction Y and / or to induce torsional vibrations of the tool spindle 15 about the worm axis B. Direct excitation of the tool spindle 15 as shown in FIG. 1 is particularly advantageous in order to minimize the exciting mass and to keep the transmission path from the tool vibration module 151 to the contact point between the grinding worm and the workpiece as short as possible. To induce vibrations, the tool vibration module 151 can comprise, for example, a piezo actuator or an electrodynamic shaker. To induce torsional vibrations, it is also possible to use a mass arranged eccentrically with respect to the worm axis B and coupled to the tool spindle 15, which can be excited by the vibration module to generate translational vibrations directed in the direction of rotation. Alternatively or additionally, a flywheel that is rotatably mounted and coupled to the tool spindle is also conceivable, which flywheel is excited via a piezo actuator or an electrodynamic exciter.

[0098] Alternatively or additionally, the machine tool 1 may have a separate tool vibration module (not explicitly shown in Figure 1) with a piezoelectric actuator or electrodynamic exciter configured to induce translational vibration of the axial slide 13 having a vibration component parallel to the workpiece axis C1 and / or configured to induce translational vibration of the tool carrier 12 in the feed direction X.

[0099] 1, the work spindle 21 has a work spindle drive 211 configured to induce torsional vibrations in the work spindle 21, which lead to rotational vibrations about the work axis C1 of a pre-toothed workpiece 23 clamped on the work spindle. The work spindle drive 211 can be equipped with a frequency converter that can be used to generate the torsional vibrations. Alternatively, rotational excitation via a suitably configured active element such as a piezo actuator or an electrodynamic exciter is also conceivable.

[0100] Furthermore, the work spindle drive 211 can be configured to induce bending vibrations of the work spindle 21, which leads to precession and / or nutation of the work axis C1 and thus to tilting and / or displacement of the work 23 relative to the grinding worm.

[0101] The work spindle drive 211 can also be configured to induce translational vibration of the work spindle 21, where the translational vibration is preferably parallel to the worm axis B in the shift direction Y, and the workpiece moves back and forth relative to the grinding worm along the shift direction Y.

[0102] Alternatively or additionally, the machine tool can have a separate workpiece vibration module 212 configured to induce the aforementioned torsional and / or bending and / or translational vibrations of the workpiece spindle. To this end, the workpiece vibration module can comprise, for example, a piezoelectric actuator acting radially on the bearing of the workpiece spindle 21 and thus inducing bending and / or radial translational vibrations, and / or acting axially on the bearing of the workpiece spindle 21 and thus inducing axial translational vibrations. The workpiece vibration module can also be an electrodynamic vibrator coupled to the lower end of the workpiece spindle 21 for axial and / or radial excitation of the workpiece spindle 21. Axial excitation leads to axial translational movement, and radial excitation leads to radial translational movement and / or tilting movement of the workpiece axis C1 about a virtual support point and / or bending vibration of the workpiece axis C1.

[0103] Taking into account the process parameters used in the generating grinding process, the generation frequency f K As mentioned above, the fluctuating frequency f V By specially selecting the torsional and / or bending and / or translational vibrations, due to the additional relative movement occurring between the workpiece 23 and the grinding worm 16, a deliberate variation of the penetration depth with a desired phase offset Δφ between each adjacent contact orbit is produced.

[0104] [Intentional variation of the penetration depth due to suitable dressing of the grinding worm] In particular, the worm rotation frequency f S If tooth flank waviness with a high order in terms of σ is required, high frequency vibrations with precisely defined modulation amplitudes in the micrometer range can place high demands on the machine shafts involved.

[0105] It is therefore conceivable, alternatively or additionally, to achieve deliberate variations in the penetration depth by dressing the grinding worm accordingly.

[0106] To generate the thread undulations in the grinding worm thread, a dressing wheel exhibiting radial and / or axial runout can be used as a dressing tool, and a fixed rotation angle ratio between the dressing tool and the grinding worm is selected so that the deviations in the radial and / or axial runout can be intentionally used to generate the thread undulations on the grinding worm thread flank. Alternatively, the thread undulations can be generated by line dressing or by a corresponding relative movement between the dressing tool and the grinding worm.

[0107] To perform dressing, a dressing tool having a dressing flank surface with a wave-shaped dressing flank modification can also be used, which is transferred to the grinding worm during dressing. Such a dressing tool can be manufactured, for example, in a positive process, where the dressing flank modification can be intentionally generated by a conditioning tool, in particular, a thin rotating conditioning disk perpendicular to the dressing flank surface. In particular, the dressing tool can be driven to rotate about a dressing rotation axis, while the conditioning tool is driven to rotate about a conditioning rotation axis of the conditioning tool and fed in a direction having a directional component perpendicular to the dressing flank surface, thereby removing material from the dressing flank surface to generate the dressing flank modification. Regarding the considerations underlying this procedure and further possible embodiments, reference is made to the patent application entitled "Dressing Tool for Dressing a Grinding Worm for the Generating Machining of Pre-toothed Workpieces," filed on the same day by the same applicant, the contents of which are incorporated herein by reference in their entirety.

[0108] 7A shows a schematic front view of the grinding worm thread flank of a single worm thread of the grinding worm 16 for one thread pitch of the grinding worm. The grinding worm thread flank 161 has an annular shape in a projection plane perpendicular to the worm axis B, which defines a radial direction by the radial coordinate r and a circumferential direction by the angular coordinate φ. The developed form of the grinding worm thread flank 161 is shown in FIG. 7B, and the grinding worm thread flank 161 has, by way of example, a periodic circumferential undulation with a radially extending wave surface. Alternatively, the undulation may have a wave surface inclined at any angle relative to the radial direction.

[0109] The thread waviness is fixed in space relative to the ground worm flank and has a wavelength λ in the circumferential direction. S It has.

[0110] Wavelength λ of the thread waviness on the grinding worm thread flank of the grinding worm S is the length U of the ground worm thread along the circumferential direction at the above radial distance S The waviness angle θ relative to the worm axis B per rotation of the grinding worm is calculated using S The wavelength at the above radial distance is defined as follows:

number

[0111] During machining of the workpiece, by shifting the grinding worm in the shift direction Y or the feed direction Z with a suitable ratio between the shift feed rate and the axial feed rate, the thread waviness on the grinding worm flank can be transferred onto the pre-toothed workpiece in rolling engagement, thereby generating the desired tooth flank waviness. What is important is the waviness on the grinding worm flank along the worm contact path on the grinding worm thread, and this waviness has a constant wavelength λ along the worm contact path. S The worm contact path may generally be inclined with respect to the circumferential direction, so that the circumferential direction λ S The wavelength at the worm contact path λ S ' is different from the wavelength along the

[0112] The worm contact path on the grinding worm path is related to the contact track on the tooth flank of the workpiece, i.e., the waviness is transferred from the worm contact path to the workpiece flank along the contact track. When using the rolling path representation of the contact track, the tooth flank waviness generated along the contact track has a wavelength λ Z and has a wavelength λ Z can be expressed as follows:

number

[0113] [Grinding worm with a grinding worm thread of exactly 1 thread] For example, if a grinding worm has a grinding worm thread with exactly one start (single-start grinding worm) and the grinding worm thread flank of this grinding worm thread has a thread waviness, this thread waviness will be transferred to the tooth flank of the workpiece without a phase offset for each contact orbit if no shift feed is performed. On the other hand, if shift feed is performed, i.e., if the grinding worm moves parallel to the worm axis B, a continuous displacement of the worm contact path on the grinding worm flank of the grinding worm thread will occur during the relative movement between the grinding worm and the workpiece parallel to the workpiece axis C1. However, since the thread waviness is fixed relative to the grinding worm flank and therefore a relative displacement of the worm contact path relative to the thread waviness occurs, in this case the thread waviness will be transferred to the tooth flank with a phase shift due to the shift feed, and there will be an effective phase offset Δφ between the tooth flank waviness of adjacent contact orbits on the surface of the tooth flank of the workpiece.

[0114] When looking at the cross-sectional profile of the grinding worm along the worm axis B (axial cross-section), the distance between two points on the same radius on two consecutive grinding worm flanks in this cross-sectional profile is measured, which gives the axial pitch p of the grinding worm. x The grinding worm moves exactly one axial pitch p x When the worm contact path is shifted by exactly 2π in the circumferential direction on the ground worm thread, the worm contact path is shifted by exactly 2π.

[0115] In order for the shift of the worm contact path to produce the desired phase offset Δφ between the tooth flank waviness of adjacent contact tracks on the surface of the tooth flank of the workpiece, the following shift path x in the shift direction Y must be obtained: y is necessary.

number

[0116] This shift path x yis the time range t K This means that the shift feedrate v y teeth,

number

[0117] [Grinding worm with at least two threads] There are several advantages to using a multi-start grinding worm. To obtain a lead, the axial pitch p x is multiplied by the number of starts, n, on the grinding worm thread. Therefore, when using a multi-start grinding worm, the lead is n times larger than when using a single-start grinding worm. At the same worm rotation frequency, the worm thread of a multi-start grinding worm moves through the mesh faster than the worm thread of a single-start grinding worm, but its geometric length relative to the workpiece increases only slightly. That is, the worm gear engages for a shorter period of time at the same workpiece rotation speed, resulting in a shorter worm contact path per grinding worm revolution. A shorter worm contact path on the grinding worm results in fewer wave periods being transferred to the workpiece for the same wavelength. Therefore, to achieve the same phase offset Δφ with the same shift feed as a single-start grinding worm, the wavelength of the waviness along the worm contact path of a multi-start grinding worm must be reduced accordingly.

[0118] The worm contact paths further have worm contact path start points that are offset from one another in the circumferential direction of the grinding worm by an angle Δα=2π / n. The waviness at the start points of each worm contact path meshes one after the other in terms of the meshing sequence of the grinding worm threads, and they can be phase-shifted relative to one another. When grinding is performed without shift feed, this phase difference can be directly used to generate a phase offset Δφ≠0, because if the waviness of different grinding worm threads have the same wavelength, this phase difference between the start points of the worm contact paths will be correspondingly transferred to the tooth flank.

[0119] The additional shift feed leads to the additional phase offset mentioned above, which is superimposed on the phase offset caused by the phase difference of the waviness on the continuously meshing grinding worm threads.

[0120] In addition, in some ground worm threads, at least one of the ground worm threads may protrude relative to the other ground worm threads, i.e., instead of a perfectly regular arrangement of the ground worm threads along the worm axis B, at least one of the ground worm threads may be displaced along the worm axis B due to the axial pitch error. Figure 8 also shows a cross section of the machined tooth flank (solid line) in the face width direction, where every other contact track is generated by a protruding worm thread, and therefore this contact track has a penetration depth d that is greater than the penetration depth of the adjacent contact track by a penetration difference δd.

[0121] [Example - Creation of desired tooth flank waviness] Example 1: Generation of 180° phase-shifted tooth flank waviness by additional relative movement The process parameters of the generating grinding process can be arbitrarily selected but are constant. This allows the time range t K or generation frequency f K According to the above formula, the non-integer component of the order of the phase offset Δφ=π(180°) is obtained as follows:

number

number

number

[0122] Example 2: Creation of a 90° phase-shifted tooth flank waviness by additional movement Here, the phase offset is Δφ=π / 2. If the fractional part of the order is 0.25, then the fluctuating frequency f V becomes:

number

[0123] Example 3: Creation of tooth flank waviness with non-constant phase offset by additional movement The relationships explained above apply, where the corresponding variables depend on the time variable t.

number

[0124] To obtain a non-constant phase offset Δφ ≠ 0 of the tooth flank waviness of adjacent contact orbits along the virtual reference line defined above, the fluctuating frequency f V (t) and f K The time dependence of (t) alone is not always sufficient. For example, the time-dependent fluctuating frequency f V (t) can be periodically modulated as follows:

number

[0125] Order P=f V / f K and modulation order P M =f mod / f V,0 are integers, there is no phase offset between the tooth flank waviness of adjacent contact tracks, i.e., Δφ=0. On the other hand, when the order P and / or modulation order P M If is not an integer, a periodically modulated non-constant phase offset Δφ≠0 results.

[0126] Time-dependent fluctuating frequency f V (t) may be stochastically modulated rather than periodically modulated, thereby producing a stochastically modulated non-constant phase offset Δφ.

[0127] Amplitude term of frequency modulation A mod It is also conceivable to vary the value over time.

[0128] The same considerations apply to the time-dependent generation frequency f, which can also be periodically or stochastically modulated. K (t) shall apply mutatis mutandis.

[0129] This gives rise to a large number of degrees of freedom that can be used to create surface structures with a diffuse appearance by creating a non-constant phase offset Δφ≠0.

[0130] Example 4: Generation of flank waviness phase-shifted by 180° or 90° by means of an appropriately modified grinding worm For example, in the case of a single-thread grinding worm, the shift feed rate v y can be selected according to the above relationship.

number

[0131] Alternatively, a multi-start grinding worm may be used in which the undulations of the grinding worm threads that directly engage one after the other along the worm contact path are out of phase with each other by 180° or 90°. When a multi-start grinding worm is used in which the undulations of the grinding worm threads that directly engage one after the other along the worm contact path are out of phase with each other by an amount other than 180° or 90°, the difference is calculated as the shift feed rate v calculated according to the above formula to produce the desired phase offset of 180° or 90°. y can be compensated by

[0132] Example 6: Generation of waviness with non-constant phase offset by a suitably modified grinding worm By varying the speed ratio between the modified dressing tool and the grinding worm during dressing, a waviness can be generated on the grinding worm flank that varies along the worm contact path, i.e., has a non-constant wavelength. The relationship described above applies to the transfer of the waviness from the worm contact path on the grinding worm flank to the contact path on the workpiece, resulting in a non-constant phase offset Δφ between the tooth flank waviness of adjacent contact paths on the tooth flank of the workpiece. An additional shift feed can also be used to generate an additional phase offset. Here, a single-start or multi-start grinding worm can also be used, in which the waviness of successive directly engaging grinding worm threads is phase-shifted along the worm contact path.

[0133] [Superposition with uncontrolled stochastic processes] In a particularly preferred embodiment, deliberate variations in the indentation depth are superimposed with uncontrolled, in particular stochastically occurring, deviations of the indentation depth d in order to generate particularly diffuse surface structures with optimized noise behavior.

[0134] These uncontrolled deviations in the plunging depth d are due to deviations in the dressing process of the grinding worm, e.g. Guide deviations in the shift direction Y (Y-axis) during dressing, which can lead to local axial pitch errors, and / or Guiding deviations of the tool spindle 15, which may lead to local axial pitch errors, and / or The deviation of the dressing tool 33 in the installed state, deviations of the dressing tool 33 itself, and / or deviations when clamping the dressing tool 33, and / or Dress spindle 32 deviation, Including, deviation, This can be attributed to:

[0135] Alternatively or additionally, these uncontrolled deviations in the penetration depth are due to deviations during grinding of the pre-toothed workpiece, e.g. Deviation in rolling joints, Deviations in the drive of the work spindle 21, and / or deviations in the drive of the shift slide 14, and / or Worm rotation frequency f s deviations in, and / or deviation in the infeed direction X, and / or deviations in the axial drive of the axial slide 13, deviations, and / or Unwanted vibrations from peripheral devices in the machine tool 1, and / or Machine structural vibrations caused by the drive unit, This can be attributed to:

[0136] Ideally, for the deliberate variation of the indentation depth, a modulation amplitude is selected that is in the range of 0.2 to 5 times the variation scale of the uncontrolled deviation of the indentation depth d, which corresponds in particular to the standard deviation or interquartile range of the uncontrolled deviation of the indentation depth d.

[0137] In a preferred embodiment of the method, a variation measure of the uncontrolled deviation of the indentation depth d is determined and the modulation amplitude is specially selected depending on the determined variation measure.

[0138] Typical values ​​for the variation scale may be between 0.1 μm and 10 μm, in particular between 0.3 μm and 3 μm.

[0139] 9A-9C illustrate such a superposition situation. FIG. 9A shows the intentionally generated variation of the indentation depth d as a function of the position along the rolling path. In this example, the indentation depth varies sinusoidally with a modulation amplitude of 1 μm. FIG. 9B shows the uncontrolled, stochastically generated deviation of the indentation depth d. In this example, the standard deviation of the uncontrolled deviation of the indentation depth d is 0.44 μm. FIG. 9C shows the result of the superposition of the intentional variation and the uncontrolled deviation.

[0140] FIG. 10 shows an image of a real measured tooth surface with a particularly diffuse surface structure that has been modified using the method according to the invention. [Explanation of symbols]

[0141] 1 Generating grinder 11 Mechanical Bed 12 Tool Carrier 13 Axial slide 14 Shift Slide 15 Tool Spindle 151 Tool Vibration Module 16 Grinding worm 161 Grinding worm flank 18 Vibration Sensor 19 Position Sensor 20 Work Career 21 Work Spindle 211 Work spindle drive unit 212 Workpiece Vibration Module 23 Work 30 Dressing device 31 Swivel 32 Dress Spindle 33 Dressing Tools 40 Mechanical control unit 41 axis module 42 Control Computer 43 Control Panel 44 Monitoring equipment B Worm shaft C1 Work axis C3 Swivel Axis C4 Swivel Axis X feed direction Y shift direction Z feed direction b1, b2 Single contact track width b eff Effective contact track width S Contact orbit spacing d Indentation depth r radial coordinate φ angular coordinate

Claims

1. A method for generating a modified surface structure on the tooth surface of a pre-toothed workpiece (23), The aforementioned method, The grinding worm (16) is rotated around the worm shaft (B), The pre-toothed workpiece (23) is rotationally driven around the workpiece axis (C1), wherein the grinding worm (16) and the pre-toothed workpiece (23) are engaged in rolling contact. This results in a relative movement between the grinding worm (16) and the pre-toothed workpiece (23), wherein the relative movement has an axial component parallel to the workpiece axis (C1), and a plurality of adjacent contact trajectories are generated on the tooth surface of the pre-toothed workpiece (23), and the contact trajectories extend at a distance from each other in the tooth width direction of the workpiece. Includes, The aforementioned method, The indentation depth (d) between the grinding worm (16) and the pre-toothed workpiece (23) is intentionally varied along each of the aforementioned contact trajectories to generate tooth surface undulations having multiple wave periods along the contact trajectories, such that the tooth surface undulations of adjacent contact trajectories are shifted relative to each other by a phase offset at any given position in the depth direction of the workpiece. It further includes, The phase offset is 90° to 270° and / or The phase offset for each of the adjacent contact tracks varies for each contact track, and / or The phase offset with respect to the adjacent contact trajectories varies along each of the contact trajectories. The method characterized by the above.

2. The grinding worm (16) has a worm rotation frequency (f ｓ ) rotates at the intentional variation of the indentation depth (d), and the worm rotation frequency (f ｓ A fluctuation frequency (f) greater than ) ｖ The method according to claim 1, which is performed as follows.

3. The aforementioned intentional variation of the indentation depth (d) is, To bring about an intentional additional relative movement between the pre-toothed workpiece (23) and the grinding worm (16) The method according to claim 1 or 2, including the method described in claim 1 or 2.

4. The aforementioned intentional additional relative movement is To cause translational vibration of the grinding worm (16) having a vibration component in the radial feeding direction (X) with respect to the workpiece axis (C1), and / or, To cause translational vibration of the grinding worm (16) having a vibration component parallel to the workpiece axis (C1), and / or, This causes translational vibration of the grinding worm (16) having a vibration component in the shift direction (Y) parallel to the worm axis (B), and / or This causes torsional vibration of the grinding worm around the worm shaft (B), The method according to claim 3, including the method described in claim 3.

5. The pre-toothed workpiece (23) is positioned on the workpiece spindle (21), and the intentional additional relative movement is, This causes torsional vibration of the workpiece spindle (21) around the workpiece axis (C1), and / or This causes bending vibration of the workpiece spindle (21), and / or This causes translational vibration of the workpiece spindle (21), The method according to claim 3, including the method described in claim 3.

6. The grinding worm (16) has thread undulations on the thread flank (161) of the grinding worm thread, and intentionally varying the indentation depth (d) to generate the tooth surface undulations is To transfer the thread undulation of the thread flank (161) of the grinding worm to the tooth surface of the pre-toothed workpiece (23) that is rollingly engaged with the grinding worm (16), The method according to claim 1 or 2, including the method described in claim 1 or 2.

7. Dressing the grinding worm (16) using a dressing tool (33), wherein the dressing tool (33) exhibits radial runout and / or axial runout, and a fixed or variable rotational angle ratio between the dressing tool (33) and the grinding worm (16) is predetermined such that the radial runout and / or axial runout generate thread undulations on the thread flank (161) of the grinding worm. The method according to claim 6, further comprising:

8. The grinding worm (16) has at least two grinding worm threads, Each of the at least two grinding worm threads has its own thread undulation along the worm contact path, The at least two ground worm threads each generate adjacent contact trajectories on the tooth surface, and each contact trajectory on the tooth surface is associated with one of the at least two worm contact paths. The method according to claim 6, wherein the thread undulations generated on each of the ground worm threads along the worm contact path are preferably different from one another.

9. The method according to claim 8, wherein each worm contact path has a worm contact path starting point associated with the contact path starting point of each of the contact paths on the tooth surface, and the thread undulations of the at least two grinding worm threads at each of the worm contact path starting points are out of phase with respect to each other.

10. The method according to claim 8, wherein the thread undulations of the at least two grinding worm threads have different wavelengths.

11. The method according to claim 8, wherein the thread undulations of the at least two grinding worm threads have different undulation amplitudes.

12. The grinding worm (16) has at least two grinding worm threads, and the method is The method involves dressing one of the grinding worm threads of a grinding worm (16) having a constant axial pitch error to create a protruding grinding worm thread, wherein the axial pitch error is selected such that the protruding grinding worm thread achieves a greater indentation depth (d) with respect to the meshing sequence on the tooth surface than the preceding and succeeding grinding worm threads, and the protruding grinding worm thread grinds at least partially over the contact trajectory created by the preceding grinding worm thread. The method according to claim 1 or 2, further comprising:

13. The intentional variation of the indentation depth is superimposed on an uncontrolled, particularly probabilistic, deviation of the indentation depth (d), and the intentional variation of the indentation depth (d) is performed with a modulation amplitude in the range of 0.2 to 5 times the variation scale of the uncontrolled deviation of the indentation depth (d). The aforementioned variability scale corresponds, in particular, to the standard deviation or interquartile range of the uncontrolled deviation of the indentation depth (d), In particular, the method according to claim 1 or 2, wherein the scale of variation of the uncontrolled deviation of the indentation depth (d) is determined, and the modulation amplitude is specially selected according to the determined scale of variation.

14. A tool spindle (15) is configured to receive a grinding worm (16) so as to rotate around a worm shaft (B), A work spindle (21) is configured to receive a pre-toothed workpiece (23) so as to rotate around the work axis (C1), An axial slide (13) having an axial drive unit that causes relative movement between the tool spindle (15) and the workpiece spindle (21), wherein the relative movement has an axial component parallel to the workpiece axis (C1), and the axial slide (13) A controller configured to perform the method described in claim 1 or 2, A machine tool equipped with the following features.

15. The system includes a shift slide (14) having a shift drive unit that causes displacement of the grinding worm (16) in a shift direction (Y) parallel to the worm shaft (B), The shift drive unit is configured to cause translational vibration of the shift slide (14) in the shift direction (Y), and / or The axial drive unit is configured to cause translational vibration of the axial slide (13) having a vibration component parallel to the workpiece axis (C1), and / or The tool spindle (15) is configured to cause torsional vibration of the grinding worm (16) around the worm shaft (B), and / or The machine tool (1) has a tool carrier (12) having a tool carrier drive unit that causes the grinding worm (16) to feed in the radial feeding direction (X) relative to the workpiece axis (C1), and the tool carrier drive unit is configured to cause translational vibration of the grinding worm (16) in the feeding direction (X), and / or, The machine tool (1) has at least one separate tool vibration module (151), and the at least one separate tool vibration module (151) is Configured to cause translational vibration of the shift slide (14) and / or the tool spindle (15) in the shift direction (Y), and / or It is configured to cause translational vibration of the axial slide (13) having a vibration component parallel to the workpiece axis (C1), and / or It is configured to cause translational vibration of the tool carrier (12) in the feeding direction (X), and / or The machine tool according to claim 14, configured to cause torsional vibration of the tool spindle (15) around the worm shaft (B).

16. The work spindle drive unit (211) drives the work spindle (21), The work spindle drive unit is configured to cause torsional vibration and / or bending vibration and / or translational vibration of the work spindle (21), and / or The machine tool (1) has at least one separate workpiece vibration module (212) configured to cause torsional vibration and / or bending vibration and / or translational vibration of the workpiece spindle (21), as described in claim 14.

Images