METHOD AND DEVICE FOR ROLL SKINNING

Description

[0001] The present invention relates to a method and a device for power skiving. Such a device is typically a processing machine such as a skiving machine or the like, which is suitable for producing gear teeth or other periodically repeating structures on the circumference of a component with high quality. Such a method according to the preamble of claim 1 and such a device according to the preamble of claim 8 are known from document DE 10 2015 104310 A1.

[0002] In power skiving, the workpiece to be machined is mounted on a workpiece spindle, and the skiving wheel (tool), which interacts with the workpiece to remove chips during skiving, is mounted on a tool spindle. During power skiving, the two spindles are driven according to a coupling ratio, so that the cutting teeth of the skiving wheel machine the tooth flank of the workpiece.

[0003] To achieve the high quality required for gear cutting, it is necessary to know the geometry of the skiving wheel and the position of the skiving wheel in the processing machine as precisely as possible.

[0004] In state-of-the-art processing machines, skiving wheels are measured on measuring machines outside the machine. This brings with it, among other disadvantages: a) Suitable fixtures must be available, b) the measurement creates additional workload, as an operator must place the skiving wheel on the fixture to measure it there, and c) with regard to the position of the skiving wheel in the processing machine, in addition to the geometry of the skiving wheel itself, the tool holder and the tool holder also play a role. These influences cannot be captured with an external measurement.

[0005] One way to indirectly detect deviations in the geometry of the skiving wheel and / or the position of the skiving wheel in the machine is to skive a workpiece, measure it (in the processing machine or outside on a separate measuring unit), determine the deviations and adapt the processing kinematics for subsequent workpieces and / or processing strokes so that the deviations are at least partially compensated.

[0006] The disadvantage of this process is that it leads to rejects, especially when the workpieces are skived in only one cut per flank, since in this case there is no possibility to measure and correct deviations before the final cut. One particular application for only one cut per flank is the use of power skiving as a hard finishing process (hard skiving). Especially in this case, the workpieces are already extensively machined and expensive, so rejects must be avoided.

[0007] The object of the present invention is therefore to provide a power skiving device that overcomes the above-mentioned disadvantages. This is achieved by a method that comprises all the steps of claim 1. Furthermore, the object of the present invention is achieved by a device having the features of claim 9. Advantageous embodiments of the invention are set forth in the dependent claims.

[0008] The machining kinematics for gear skiving are described in more detail below: 1) The coupling relationship between the tool and workpiece spindle axes is given by the tooth count ratio of the tool to the workpiece and describes the relationship between the tool and workpiece spindle speeds during machining, but without taking into account the axial displacement along the workpiece. 2) The differential feed describes the additional rotation of the workpiece determined by the axial feed along the workpiece and the lead height of the workpiece. This additional rotation is necessary to create the helix angle on the workpiece. 3) The coupling position describes a set of values ​​for the rotational position of the tool spindle, the rotational position of the workpiece spindle and the position in the axial direction. 4) The center distance describes the distance between the tool and workpiece spindle axes. 5) The axis crossing angle is defined here as the angle by which the tool spindle is inclined relative to the workpiece spindle.6) The rake face offset refers to a displacement of the tool along the tool spindle axis.

[0009] The gap geometry created on the workpiece during gear skiving depends on the shape of the cutting edge, the position of the cutting edge, and the machining kinematics. The cutting edge is created by grinding a chip plane into the toothed skiving wheel. This chip surface can, for example, be designed as a step grind or a conical surface grind. The cutting edge relevant for the achieved gap geometry is calculated by intersecting the flanks of a skiving wheel tooth with the chip surface on this tooth. This intersection produces a curve in space. This curve, viewed in a coordinate system that is firmly linked to the skiving wheel, in which, for example, the z-axis coincides with the axis of rotation of the skiving wheel and thus with the tool spindle axis during machining, is referred to in this invention as the spatial profile of the cutting edge.If the cutting edge is rotated around the rotation axis and / or shifted along the rotation axis, the spatial configuration of the cutting edge does not change within the meaning of this invention; only the position of the cutting edge changes. The position of the cutting edge thus determines the position of the cutting edge in the axial direction as well as its angular position, both relative to the rotation axis.

[0010] According to the inventive method according to claim 1 for power skiving a workpiece, in a first step, the geometry of a tool for machining the workpiece is measured while clamped in a device for power skiving. The tool can be a skiving wheel. In a subsequent further step, machining kinematics for power skiving are determined depending on the measured geometry of the tool. The method is characterized in that, in the first step, the absolute position of a cutting edge of the tool in the device is determined.

[0011] Since the absolute position of a cutting edge of the tool in the fixture is also determined in the first step, the machining kinematics are adjusted to the absolute position of the cutting edge.

[0012] In this way, errors in the prior measurement of a skiving wheel or inaccuracies in the tool holder or tool holder during skiving can be compensated.

[0013] The position is referred to as absolute if it is relative to the position in the tool holder in the fixture. The axial position is relative to the contact surface of the tool holder. The rotational position can be relative to a defined direction in the fixture.

[0014] According to the method, in addition to determining the position, the spatial course of the cutting edge is also determined in the first step. This allows for even better machining kinematics.

[0015] According to a preferred embodiment of the invention, the tool is a skiving wheel and the geometry of the skiving wheel is, wherein one or more of the following geometrical quantities are measured on the skiving wheel: a) an outer diameter of the skiving wheel at one or more axial positions of the skiving wheel, b) a tooth thickness of the skiving wheel at one or more axial positions of the skiving wheel, c) a profile line of the skiving wheel, d) a flank line of the skiving wheel, e) a profile of the cutting edge of the skiving wheel, f) a position of the rake face and / or its orientation, in particular rake and step angles, and / or g) the position of the tool, preferably a rotational position of the skiving wheel, preferably the rotational position of one or more teeth on the skiving wheel.

[0016] The measurement of these quantities can be used to determine the absolute position and / or the spatial course of the cutting edge.

[0017] This determination can be made, for example, in the following ways: Direct measurement of the cutting edge, whereby the measurement is preferably carried out along the cutting edge, by measuring the rake face to determine the position and orientation and by mathematically intersecting this with the profile of the skiving wheel tooth, whereby the profile of the skiving wheel tooth can be determined by a profile line and / or tooth thickness measurement or whereby the theoretical profile is calculated according to the tool design.

[0018] Preferably, the machining kinematics are determined and / or corrected depending on the measured geometry of the tool and on an axial feed position of the workpiece.

[0019] In power skiving, it is possible to create modifications, particularly flank trace modifications, on the workpiece by changing the machining kinematics during a machining stroke depending on the axial feed position of the workpiece. If this is the case, geometric deviations of the skiving wheel have a slightly different effect at each axial feed position of the workpiece. To compensate for this, the compensation of the geometric deviations of the skiving wheel described above must be determined separately for each axial feed position. The simulation must take into account which modification, particularly flank trace modification, is to be created on the workpiece at the various width line positions. The result is corrected machining kinematics that depend purely on the axial feed position of the workpiece. This dependence on the axial feed position is independent of the selected axial feed per workpiece revolution.In particular, there is no direct dependence on the workpiece rotation position and / or tool rotation position.

[0020] In a further embodiment of the invention, the machining kinematics are determined and / or corrected depending on the measured geometry of the tool, wherein the machining kinematics remain constant during a machining stroke.

[0021] However, if the workpiece is originally machined without any change in the machining kinematics depending on the axial feed position of the workpiece, the geometric deviations of the skiving wheel at each axial feed position of the workpiece have the same effect on the geometry created on the workpiece.

[0022] In a preferred variant, the invention therefore provides that the changes in the machining kinematics required to compensate for the measured geometric deviations of the skiving wheel are not altered during a machining stroke. Since the workpiece is generally machined in multiple strokes during power skiving, it is certainly possible and also sensible to determine the change in the machining kinematics separately for each stroke and to adjust it accordingly for each stroke.

[0023] The method according to the invention assumes that all skiving wheel teeth are evenly distributed around the circumference of the skiving wheel and that all cutting edges have the same spatial distribution within a given and / or usual tolerance. Therefore, it is sufficient to measure the geometry of a single skiving wheel tooth. To improve the measurement result, however, it is entirely possible to measure more than one skiving wheel tooth and average the measurement results.

[0024] According to the invention, the machining kinematics determined as a function of the measured geometry may not have a periodic component that occurs repeatedly with each revolution of the tool.

[0025] In an advantageous development of the invention, a deviation in the tooth thickness, in the profile angle and / or in the root circle radius is compensated by the machining kinematics and / or an angular position of the peeled gap in the workpiece is specifically specified.

[0026] Changes in the machining kinematics parameters generally have the following main influences on the gearing produced by skiving as well as on the rake and / or clearance angles.

[0027] The coupling position determines at which angular position, relative to the rotation axis of the workpiece, the gaps are formed.

[0028] The center distance influences the profile angles on the left and right flank, the tooth thickness, and the root radius.

[0029] The axis cross angle and the rake face offset influence the profile angles on the left and right flanks, the tooth thickness, and the rake and clearance angles. In addition, the rake face offset slightly influences the root radius.

[0030] The parameters measured on the skiving wheel within the scope of this invention generally have the following main influences on the toothing produced by skiving as well as on the chip and / or clearance angles.

[0031] The outer diameter of the skiving wheel influences the root radius. The tooth thickness of the skiving wheel influences the tooth thickness. The rotational position of the skiving wheel influences the angular position of the gaps. The profile line of the skiving wheel influences the profile line of the workpiece. The flank line influences the clearance angle and the course of the cutting edge on the skiving wheel, if this is determined by mathematically intersecting the rake face with the skiving wheel tooth, and thus also the profile line. The course of the cutting edge of the skiving wheel influences the profile line. The position of the rake face and its orientation influence the tooth thickness, the root radius and the profile line, in particular the profile angle error. The regrind condition influences the tooth thickness, the root radius and the profile line, in particular the profile angle error.

[0032] From the above list it can be seen by changing which parameters of the machining kinematics the influences of the parameters primarily measured on the skiving wheel within the scope of this invention on the toothing produced can be compensated.

[0033] In a further preferred embodiment of the invention, at least one of the variables of the machining kinematics, such as a coupling position, an axis distance, an axis crossing angle and a rake face offset, is determined.

[0034] Furthermore, a check is carried out to assess whether a specified manufacturing tolerance can be maintained with the skiving wheel and machining kinematics and / or whether technological parameters lie within a specified range, whereby the machine outputs corresponding work processes depending on the result of the check.

[0035] The work processes issued by the machine can, for example, be suggested actions directed to an operator and / or several different work processes to be performed by the machine. It is possible for an operator to select one of the several work processes suggested by the machine, and for the machine to execute the selected work process. It is also possible for the machine to perform work processes independently.

[0036] Furthermore, the results of one or more of these measurements can be used to determine the absolute position and / or the spatial course of the cutting edge in order to optimally adjust the machining kinematics during gear skiving to the actual geometry of the skiving wheel in order to at least partially compensate for the deviations of the skiving wheel from the target geometry or target position in the processing machine in order to reduce the deviations resulting on the workpiece.If at least one of the deviations of the skiving wheel from the target geometry or target position in the processing machine is so great, or if a combination of at least two deviations is such that the deviation resulting from this on the workpiece can no longer be compensated for by adapting the processing kinematics to such an extent that the workpiece can be manufactured within a predetermined tolerance, the invention provides for machining with this skiving wheel to be stopped for the time being and for the operator to be informed of this problem and allowed to decide whether to manufacture with this skiving wheel despite the deviation, or for the operator to be informed of this problem and asked to replace the skiving wheel (manually or using a tool changer, if present).to abort the machining operation or if an automatic tool changer is available on the machining center, to automatically eject the skiving wheel from the machining center and to continue machining with a different skiving wheel from the tool changer or if the machining was intended as a double-flank machining operation, to carry out the machining as a single-flank machining operation, if necessary after confirmation by the operator, if the resulting deviation on the workpiece lies within a specified tolerance through suitable adaptation of the machining kinematics.

[0037] In this context, technological variables can be understood as, for example, rake and clearance angles.

[0038] The present invention further relates to a device according to claim 8 for carrying out the method according to one of the preceding claims.

[0039] Furthermore, the measuring unit can be designed to determine one or more of the following parameters of the peeling wheel: a) an outer diameter of the skiving wheel at one or more axial positions of the skiving wheel, b) a tooth thickness of the skiving wheel at one or more axial positions of the skiving wheel, c) a rotational position of the skiving wheel, in particular the rotational position of one or more teeth on the skiving wheel, relative to the tool spindle axis, d) a profile line of the skiving wheel, e) a flank line of the skiving wheel, f) a profile of the cutting edge of the skiving wheel, g) a position of the rake face and / or its orientation, in particular rake and step angles,

[0040] Furthermore, the device can be designed to calibrate the spatial position of the measuring unit with respect to the spindle axis of the skiving wheel by measuring a test collar or a cone of a chuck, which is arranged on a spindle axis of the skiving wheel on the tool holder and / or on the skiving wheel, with the measuring unit, so that the distance between the measuring unit and the spindle axis can be determined in order to calibrate the measuring unit accordingly.

[0041] In general, the relative position of the measuring unit to the tool spindle in the processing machine is not exactly known. This can change over time, particularly due to the machine's thermal expansion. In order to compensate for such thermal expansion, it may be necessary to calibrate the measuring unit. In particular, it can be important to calibrate the distance between the measuring unit and the tool spindle axis, and in particular the distance between the center of the measuring sphere and the tool spindle axis. For this purpose, a test collar, preferably ground, with a known diameter can be provided on the skiving wheel and / or on the tool holder and / or on the tool spindle, which is measured using the measuring unit. If, for example, a touch-sensitive measuring probe is used, the test collar can be contacted with it. This allows the distance between the measuring unit and the tool spindle axis to be determined, and the measuring unit can be calibrated accordingly.In particular, this allows the distance between the measuring ball and the tool spindle axis to be determined. As an alternative to a specially manufactured test collar, a chuck taper can also be used to hold the skiving wheel for calibration.

[0042] Furthermore, the control unit can be designed to calibrate the spatial position of the measuring unit with respect to a spindle axis of the skiving wheel, preferably before carrying out a measurement of the skiving wheel.

[0043] As an alternative to a test collar, a ball arranged concentrically to the spindle axis of the skiving wheel and a cone arranged concentrically to the spindle axis, in particular the hollow shank cone of the tool holder, can also be measured.

[0044] It can be provided that the device is designed to determine the tooth profile of the skiving wheel located in the tool holder by means of the measuring unit when the tooth profile, in particular a profile angle, of the skiving wheel is known and to compare it with the known tooth profile in order to determine the error in the relative position between the measuring unit and the skiving wheel from a deviation between the known tooth profile and the measured tooth profile.

[0045] In the event that such a test collar and / or cone is not available or cannot be approached, the invention provides a further method for determining the relative position between the measuring sphere center and the tool spindle axis. This method exploits the fact that an error in the relative position between the measuring sphere center and the tool spindle axis when measuring the profile of the skiving wheel teeth leads to an error in the measured profile, in particular in the measured profile angle. If the profile of the skiving wheel teeth is known, the profile can be measured in the machine, the measured profile can be compared with the actual profile of the skiving wheel teeth, and errors in the relative position between the measuring sphere center and the tool spindle axis can be determined from the deviation.

[0046] The skiving wheel is held in the tool holder by the measuring unit during measurement. This makes it possible to determine the skiving wheel's geometry and / or position and compensate for any resulting errors. According to the current state of the art, for example, the skiving wheel's geometry is determined outside the processing machine, so sources of error that arise due to the skiving wheel's attachment to the tool holder cannot be taken into account.

[0047] The invention overcomes this disadvantage and provides for measuring the skiving wheel in the clamped position in the workpiece holder, which is also maintained during machining. This allows any misalignment of the skiving wheel in the tool holder to be taken into account when creating the machining kinematics, resulting in an overall better result.

[0048] Furthermore, according to the present invention, it can be provided that the control unit is further designed to carry out a production simulation of a gear skiving process on the basis of a measurement of the tool located in the tool holder carried out by the measuring unit and to generate the machining kinematics for a gear skiving process with the measured tool on the basis of this measurement.

[0049] It can also be provided that a large number of manufacturing simulations are carried out and the skiving process is carried out using the machining kinematics that achieved the best results in terms of manufacturing tolerance or other specifications.

[0050] Preferably, the control unit is designed so that, given a known target tooth profile of the tool, in particular a profile angle of a skiving wheel, the actual tooth profile of the tool located in the tool holder is determined and compared with the target tooth profile in order to determine an error in the relative position between the measuring unit and the tool from a deviation between the target tooth profile and the measured actual tooth profile.

[0051] According to an optional development of the invention, the measuring unit is further designed to measure the geometry of the peeling wheel and / or to measure the position of the peeling wheel in the device.

[0052] Furthermore, it can be provided that the measuring unit can be moved via a mechanism into a working space of the device in which the skiving is carried out, wherein the mechanism is preferably attached to a support of the device. The ability to move the measuring unit into or out of the working space allows it to be protected from the adverse conditions during skiving, since during skiving, coolant and chips are distributed from the contact area between the workpiece and the skiving wheel (tool) into the surrounding area, not least due to the high rotational speeds of the tool and workpiece.

[0053] Alternatively, the measuring unit can also be mounted on the column or machine bed of such a processing machine. According to an optional modification of the invention, the measuring unit is fixedly mounted on the device, preferably on a support and / or in a working space of the device in which the power skiving is performed. To protect the measuring unit from the adverse influences described above, a housing protecting the measuring unit can be provided.

[0054] Furthermore, a further development of the invention can provide that the device is further designed to realize a relative movement between the peeling wheel and the measuring unit required for measuring the peeling wheel by means of a movement axis of the peeling wheel that is available during the peeling process.

[0055] Accordingly, the relative movement between the skiving wheel and the measuring unit required for measuring the skiving wheel is generated by the same axes of motion that the skiving wheel already has for gear skiving. This eliminates the need for additional axes of motion and the associated drives.

[0056] Nevertheless, the invention also provides for the relative movement between the skiving wheel and the measuring unit required for measuring the skiving wheel to be realized by a movement axis that is not available during skiving by the skiving wheel. For example, if the measuring unit is attached to the column, the axes for moving the column do not result in any change in the relative position. Therefore, optionally, axes that are not available for skiving can also be used to adjust the relative position between the measuring unit and the skiving wheel.

[0057] Furthermore, it can be provided that the measuring unit is equipped with a mechanical measuring sensor, and preferably a measuring tip of a measuring probe is provided with a ball, in particular a ruby ​​ball. The measurement by the measuring sensor can be performed by switching or measuring.

[0058] The mechanical measuring sensor can be based on the principle used in coordinate measuring machines and gear measuring machines. Such measuring sensors are also available in a robust design for installation and use in the machining area of ​​machining centers. A sphere, such as a ruby ​​sphere, is preferably used as the measuring tip of the measuring probe, as is common, for example, in gear measurements.

[0059] Furthermore, the measurement can also be carried out optically, in particular with a laser.

[0060] Furthermore, the invention also includes the implementation according to which the measuring unit is provided with an optical measuring sensor, preferably with a triangulation sensor, an image processing sensor, a confocal sensor, a sensor for focus variation, and / or an interferometer.

[0061] Optical distance sensors that are also known from coordinate measuring machines can be used, in particular triangulation sensors, image processing sensors, focus variation sensors, confocal sensors, or interferometers. To protect such sensors from chips and possibly coolant, they can optionally be protected by a housing or casing.

[0062] According to a further preferred embodiment, the skiving wheel can have both internal and external teeth. It can be designed monolithically or as a skiving wheel equipped with indexable inserts.

[0063] Preferably, the control unit is further designed to adjust the machining kinematics in a subsequent roller skiving process to the actual geometry of the skiving wheel and / or position of the skiving wheel in the device on the basis of one or more of the parameters of the skiving wheel determined by the measuring unit in order to compensate for deviations of the skiving wheel from the target geometry and / or target position.

[0064] The quantities determined in this way or the results of one or more of these measurements can be used to optimally adjust the machining kinematics during gear skiving to the actual geometry of the skiving wheel in order to at least partially compensate for the deviations of the skiving wheel from the target geometry or target position in the processing machine, so that the deviations resulting on the workpiece are reduced.

[0065] According to a further development of the invention, the control unit is further designed to carry out a production simulation of a gear skiving process on the basis of a measurement of the skiving wheel located in the tool holder carried out by the measuring unit and to generate the machining kinematics for a gear skiving process with the measured skiving wheel on the basis of this measurement.

[0066] Furthermore, the control unit can be designed to calibrate the spatial position of the measuring unit with respect to a spindle axis of the skiving wheel, preferably before carrying out a measurement of the skiving wheel.

[0067] It can be provided that the device is designed to determine the tooth profile of the skiving wheel located in the tool holder by means of the measuring unit when the tooth profile, in particular a profile angle, of the skiving wheel is known and to compare it with the known tooth profile in order to determine the error in the relative position between the measuring unit and the skiving wheel from a deviation between the known tooth profile and the measured tooth profile.

[0068] Furthermore, the device can be designed to calibrate the spatial position of the measuring unit with respect to the spindle axis of the skiving wheel by measuring a test collar, which is arranged on a spindle axis of the skiving wheel on the tool holder and / or on the skiving wheel, with the measuring unit, so that the distance between the measuring unit and the spindle axis can be determined in order to calibrate the measuring unit accordingly.

[0069] As an alternative to a test collar, a ball arranged concentrically to the spindle axis of the skiving wheel, as well as a cone arranged concentrically to the spindle axis, in particular the hollow shank cone of the tool holder, can also be measured. According to a further development of the invention, the control unit is further configured to assess whether or not a desired manufacturing tolerance can be achieved with the skiving wheel measured by the measuring unit.

[0070] It can be provided that if the desired manufacturing tolerance cannot be achieved, or at least one of the deviations of the skiving wheel from the target geometry or target position in the processing machine is so large, or a combination of at least two deviations is such that the resulting deviation on the workpiece can no longer be compensated by adjusting the processing kinematics, the device is designed to: to inform an operator of the device of this problem via a notification unit in order to let him decide whether machining should be carried out despite the deviation with the skiving wheel, to inform the operator of this problem via the notification unit and to ask him to change the skiving wheel manually or via an existing tool changer if an automatic tool changer is available on the processing machine, to automatically eject the skiving wheel from the processing machine and to continue machining with another skiving wheel from the tool changer if the machining was intended as a double-flank machining operation, to carry out the machining as a single-flank machining operation, preferably after confirmation by the operator, if the resulting deviation on the workpiece is within a specified tolerance through suitable adaptation of the processing kinematics, or to abort the machining operation.

[0071] Further features, details, and advantages of the invention will become apparent from the explanation of several examples of the invention in the following description of the figures. These show: Fig. 1: a perspective view of a device according to the invention for gear skiving, Fig. 2: a perspective view of a device according to the invention for gear skiving according to a further embodiment, Fig. 3: a schematic representation to explain the calibration of the measuring unit and skiving wheel or a measurement of the skiving wheel, Fig. 4: a sketch in which the device according to the invention carries out a calibration of the measuring unit and skiving wheel, Fig. 5: a representation of the skiving wheel, and Fig. 6: a representation of the profiles of the left and right flanks of the skiving wheel in polar coordinates.

[0072] Figure 1shows a perspective view of the device 20 according to the invention. It depicts a processing machine for power skiving, in which a column 32 and a counter support 33 are arranged on a machine bed 31. A processing head 36 is attached to the column 32 via a movable carriage 34, which can accommodate the skiving wheel 21 via a tool holder 22.

[0073] The carriage 34 and the machining head 36 attached to it can be moved in a variety of directions. The carriage can be moved along the X1 and Z1 axes, while the machining head 36 can also be moved along the V1 axis. Furthermore, the machining head can be rotated about an axis A1 parallel to the X1 axis. The C1 axis is the spindle axis of the skiving wheel 21.

[0074] The workpiece to be machined with the spindle (not shown) is placed on the table 38. The workpiece clamping device used is not shown for reasons of clarity.

[0075] Figure 2 shows a perspective view of another embodiment of the device 20 according to the invention, which is similar to the one shown in Figure 1 described device except for the arrangement of the measuring unit 23. The same reference numerals are used for identical components as in Figure 1 used.

[0076] In contrast to Figure 1 will be in Figure 2 The measuring unit 23 is arranged on the counter support 33. Here, too, a movement axis V2 can be provided for the relative movement of the peeling wheel 21 and the measuring unit 23. This simplifies the positioning of the measuring unit 23 at the measuring position.

[0077] Furthermore, the device 20 is provided with a measuring unit 23, which in the present embodiment is attached to the stand 32. The measuring unit 23 has a movement mechanism to enable a relative movement with respect to the skiving wheel 21 accommodated in the tool holder 22. Thus, the measuring unit 23 can be moved along an axis X2 parallel to the axis X1, since a relative movement of the two components in the X direction would not be possible due to the attachment of the measuring unit 23 and the machining head 26 to the stand 32. To execute the movements, the device 20 has a plurality of drives, for example, the drive 35 for the Z1 axis or the drive 37 for the tool spindle.

[0078] Figure 3shows a schematic representation of the skiving wheel 21, which is measured using the measuring unit 23. For example, for the measuring unit 23, a first probe 231 measures the tooth flank of the skiving wheel 21, and a second probe 232 measures the chip surface. An optical sensor 233, e.g., a laser, can also be part of the measuring unit 23 and used for measuring or calibrating the measuring unit 23.

[0079] Some examples are given below to better explain the invention: Example 1)

[0080] In power skiving, the precise position and shape of the cutting edge of the skiving wheel are particularly important in order to produce the desired profile on the workpiece.

[0081] The profile of skiving wheels is typically manufactured with a high degree of precision by tool manufacturers, but the exact position of the cutting edge is only determined by grinding the rake face. If a skiving wheel is worn, the rake face is resharpened and a new cutting edge is formed. The position and shape of the cutting edge result from the position and orientation of the reground rake face. If the rake face is described by a plane, for example, the orientation can be defined by a normal vector of the rake planes, the position by a reference point or, alternatively, by the distance of the plane from the origin of the selected coordinate system. If the rake face is described by a cone, for example, the orientation can be described by the direction of the cone's axis of rotation and the cone's opening angle, and the position by the position of the cone tip.

[0082] For example, to determine the position and orientation of a chip plane, it is sufficient to measure three points that clearly define the plane. However, to increase the accuracy of the determination, it is also possible to measure more than three points.

[0083] For example, to determine the position and orientation of a cone assumed to be concentric with the spindle axis, it is sufficient to measure two points. Here, too, more points can be measured to improve accuracy.

[0084] The invention therefore provides, as a possible application, for determining the position and orientation of the rake face. This determination must be made in such a way that the position and orientation of the rake face relative to the associated skiving wheel tooth are known. For this purpose, the position of the skiving wheel tooth in the axial direction and / or the rotational position of the skiving wheel tooth is preferably also determined using the measuring unit. Determining the axial position of the skiving wheel tooth or of several or all skiving wheel teeth is particularly necessary for conical skiving wheels. The axial position can be understood as the position of a face cut of the skiving wheel in which the skiving wheel teeth have a certain tooth thickness. For cylindrical skiving wheels, this tooth thickness is the same in all face cuts, so that determining the axial position of the skiving wheel tooth is neither possible nor necessary; for conical skiving wheels, for example, this tooth thickness changes from face cut to face cut.

[0085] To determine the rotational position of a skiving wheel tooth, it is sufficient to measure a single point on the flank. For example, if the axial position of a conical skiving wheel is to be determined, at least two points must be measured to determine the tooth thickness in a cross-sectional view.

[0086] If the chip surface is determined relative to the skiving wheel tooth, the cutting edge can be determined mathematically by cutting the chip surface with the flanks of the skiving wheel.

[0087] The geometry of the flanks can either be adopted from the drawing or optionally determined in the machining center by profile and / or flank line measurement. This cutting edge, determined in this way, can then be used, for example, to adjust the machining kinematics so that both the tooth thickness and the profile angles on the left and right flanks of the workpiece are within tolerance. Optionally, it can also be checked whether the effective clearance angle and / or the effective rake angle are within the desired limits with the machining kinematics determined in this way.

[0088] If the clearance angle is outside the tolerance, machining can optionally be stopped and the skiving wheel can be ejected or removed to avoid damage to the skiving wheel and / or workpiece. Example 2)

[0089] An extension of the last example provides for measuring the outer diameter of the skiving wheel in addition to the position and orientation of the rake face. Particularly if the skiving wheel is conical, it can be advantageous to measure the outer diameter at several axial positions of the skiving wheel and thus determine the enveloping cone. This enveloping cone, or enveloping cylinder in the case of a cylindrical skiving wheel, can be used to determine the part of the rake face that produces the root area of ​​the workpiece by intersecting the rake face. This allows the determination of the root contour created in the skiving process and, in particular, the generated root radius.If the root circle radius is not produced within the desired tolerance using the machining kinematics determined in Example 1, an attempt can be made to determine machining kinematics by varying the available degrees of freedom of the machining kinematics using a compensation calculation so that the tooth thickness, profile angle and root circle radius are within the desired tolerance, or, if this is not possible, machining with this skiving wheel can be stopped for the time being.

[0090] If the machining was planned as a double-flank operation, it is optionally possible to check, for example using a simulation, whether it is possible to achieve both the tooth thickness and the profile angles on the left and right flanks, as well as the root radius, within the desired tolerance using this skiving wheel in single-flank machining. If this is possible, the machining can be performed automatically or after confirmation by the operator using a single-flank operation. Here, too, an additional check can be optionally performed to determine whether the effective clearance angle and / or the effective rake angle lie within the desired limits with the machining kinematics determined in this way, and if necessary, machining can be stopped. Example 3)

[0091] A simplified variant of Example 1 involves determining only the position of the rake face, specifically the regrinding condition of the skiving wheel. This changes after regrinding and is not always known precisely. This variant can be used when the orientation of the rake face is achieved so well during regrinding that the error resulting from the deviation from the target orientation at the cutting edge leads to a deviation in the profile and / or tooth thickness of the workpiece that lies within a desired tolerance. In this case, it is sufficient to measure the rake face at only one point. Example 4)

[0092] If previously toothed workpieces are further machined by power skiving, it is important to pair the skiving wheel and workpiece in such a way, i.e., to determine the coupling position so that the desired stock removal is achieved on the left and right flanks. To ensure this exact pairing, both the rotational position of the workpiece and the rotational position of the skiving wheel must be known as precisely as possible. The rotational position of the workpiece can be determined, for example, using a threading sensor or a measuring unit for measuring or testing the workpiece. To determine the rotational position of the skiving wheel, the skiving wheel can be measured in the processing machine, thus precisely determining the rotational position.

[0093] This measurement can optionally be performed each time a skiving wheel is picked up via the tool holder, especially if this pick-up is automated, for example, via a tool changer. However, if the tool holder is sufficiently repeatable with regard to the skiving wheel's rotational position, it may be sufficient to measure each skiving wheel only once and to use the last measurement result when it is picked up again in the machine. Pairing with high accuracy is particularly important when only a small amount of material is to be removed, such as in hard skiving. Example 5)

[0094] Another application where precise pairing and thus the rotational position of the skiving wheel are important is position-oriented gear cutting. In this case, the gear teeth are created on the workpiece at a fixed angular position. This can be defined, for example, by a groove or hole in the workpiece, or by another gear on the workpiece. In particular, the gear teeth can be herringbone.

[0095] It is of course possible to increase the number of points to be measured as indicated in the examples in order to improve the measurement accuracy through better statistics.

[0096] The following is a description of the invention with reference to the figures, in particular Figures 4 to 6 , statements that may be relevant to several of the examples described above.

[0097] If, in the examples, machining kinematics and / or workpiece profiles produced with a known skiving wheel and known machining kinematics, workpiece flank lines, angular position of the produced gear teeth, as well as clearance and / or rake angles are to be determined, this can be done, for example, using the manufacturing simulations typically used today. Such manufacturing simulations are typically based on a material removal simulation. The material removed from the workpiece by a given tool, in particular by given cutting edges on the tool, during machining with given machining kinematics is determined. In the case of gear skiving considered here, the entire machined gap can be determined in this way.

[0098] In order to determine machining kinematics for generating a specified workpiece profile and / or tooth thickness using a given skiving wheel with a known cutting edge, the influences of the axes available during machining on the workpiece profile and / or tooth thickness can be determined by varying the axes within the framework of a production simulation. For example, it is possible to determine how the profile angles on the left and right sides of the workpiece change when the axis intersection angle is adjusted by 0.1° by running the production simulation with this adjusted axis intersection angle and determining the profile angle of the generated gap from the simulation result. If the influences of all axes adjustable for machining on all geometric variables on the workpiece that need to be corrected are known, the machining kinematics can be corrected assuming a linear relationship between the axes and these variables.With this corrected machining kinematics, the manufacturing simulation can be carried out again and the remaining error can be determined and corrected again if necessary, and iterated until the geometric dimensions are within a specified tolerance.

[0099] The machining kinematics during gear skiving are described by the following parameters, which are now described in more detail but are also known from general literature and publications on gear skiving: 1) The coupling relationship between the tool and workpiece spindle axes is determined by the ratio of the number of teeth between the tool and the workpiece and describes the relationship between the tool and workpiece spindle speeds during machining, but without taking into account the axial displacement along the workpiece. 2) The differential feed describes the additional rotation of the workpiece determined by the axial feed along the workpiece and the lead height of the workpiece. This additional rotation is necessary to generate the helix angle on the workpiece. 3) The coupling position describes a set of values ​​for the rotational position of the tool spindle, the rotational position of the workpiece spindle, and the position in the axial direction. Figure 1In the example shown variant of a power skiving device, this would be a set of values ​​for the axes C1, C2 and Z1. This coupling position determines exactly where the gap on the workpiece, i.e. at which angular position, is created by the power skiving process. 4) The center distance refers to the distance between the tool and workpiece spindle axis. The center distance is specified in the Figure 1 The exemplary variant of a device for skiving is essentially realized by the X1 axis, whereby swiveling around A1 and moving along V1 also influence the axis distance. 5) The axis crossing angle is defined here as the angle by which the tool spindle is inclined relative to the workpiece spindle. In the Figure 1 In the example shown variant of a power skiving device, this corresponds to the position of the A1 axis. 6) The rake face offset refers to a displacement of the tool along the tool spindle axis. In the Figure 1In the variant of a device for gear skiving shown as an example, this can be realized by a combination of a movement of the Z1 and V1 axes.

[0100] In general, the relative position of the measuring unit to the tool spindle in the processing machine is not exactly known. This can change over time, particularly due to the machine's thermal expansion. In order to compensate for such thermal expansion, it may be necessary to calibrate the measuring unit. In particular, it can be important to calibrate the distance between the measuring unit and the tool spindle axis, and in particular the distance between the center of the measuring sphere and the tool spindle axis. For this purpose, a test collar, preferably ground, with a known diameter can be provided on the skiving wheel and / or on the tool holder and / or on the tool spindle, which is measured using the measuring unit. If, for example, a touch-sensitive measuring probe is used, the test collar can be contacted with it. This allows the distance between the measuring unit and the tool spindle axis to be determined, and the measuring unit can be calibrated accordingly.In particular, this allows the distance between the measuring ball and the tool spindle axis to be determined. As an alternative to a specially manufactured test collar, a chuck taper can also be used to hold the skiving wheel for calibration.

[0101] In the event that such a test collar and / or cone is not available or cannot be approached, the invention provides a further method for determining the relative position between the measuring sphere center and the tool spindle axis. This method exploits the fact that an error in the relative position between the measuring sphere center and the tool spindle axis when measuring the profile of the skiving wheel teeth leads to an error in the measured profile, in particular in the measured profile angle. If the profile of the skiving wheel teeth is known, the profile can be measured in the machine, the measured profile can be compared with the actual profile of the skiving wheel teeth, and errors in the relative position between the measuring sphere center and the tool spindle axis can be determined from the deviation.

[0102] This provision will be applied in the following Figure 4 The arrangement shown as an example is outlined.

[0103] Figure 4shows an exemplary arrangement of axes for moving the skiving wheel in the processing machine within the meaning of this invention, as well as a skiving wheel in which only one tooth 5 is shown in simplified form. Furthermore, the figure shows a switching measuring sensor 3 with measuring probe 2 and measuring ball 1. The axis C1 corresponds to the tool spindle axis 6, the axis D is used for the preferably linear movement of the skiving wheel and thus serves, among other things, to change the relative position between the measuring ball center and the tool spindle axis. The measuring probe 2 does not have to be aligned parallel to the axis D. The offset ΔV, which describes the position of the measuring sphere in a direction perpendicular to the axis D, is generally not exactly known and can preferably also be determined using the method described here. In order to limit the description of the idea behind the calibration to the essentials, a measuring sphere with a diameter of 0 is assumed below. In this simplified case, the center of the measuring sphere also corresponds to the point of contact between the measuring sphere and the tooth flank. In practice, the point of contact must be determined from the center of the measuring sphere, taking into account the diameter of the measuring sphere and the normal vector of the tooth flank at the point of contact, as is generally known from metrology.

[0104] For calibration, the four points 11 to 14 are successively Figure 5with the measuring ball and the positions read from the measuring systems of the axes C1 and D at the time of contact are recorded. These positions are referred to below as C 1 11 , C 1 12 , C 1 13 and C 1 14 respectively D 11 , D 12 , D 13 and D 14. The four points can be freely selected within certain limits; preferably, two points are probed on a left flank and two points on a right flank, with one point near the tooth tip and another near the tooth root being probed on each flank. The points do not have to be precisely located, which is due to the unknown relative position between the measuring ball center and the tool spindle axis and the unknown offset. ΔV would not even be possible.

[0105] The points can be located on different peeling wheel teeth, but it is also possible, as in Figure 5 shown to select the left and right flanks of the same skiving wheel tooth. It is assumed that the profile of the skiving wheel tooth is known with high accuracy. This is usually the case with skiving wheels, as they are ground with high precision. The profiles V l ( ρ l ) and V r ( ρ r ) of the left and right flanks can be described in polar coordinates as follows: V l ρ l = R l ρ l cos ρ l + ψ l sin ρ l + ψ l V r ρ r = R r ρ r cos ρ r + ψ r sin ρ r + ψ r where ρ l or ρ r the polar angle, R l ( ρ l ) or R r ( ρ r ) the radius depending on the polar angles and the initially unknown angles ψ l and ψ r describe the rotational position of the flanks. See Figure 6 . The four probing processes result in the four times two equations: R l ρ l 11 cos ρ l 11 + ψ l + C 1 11 sin ρ l 11 + ψ l + C 1 11 = Δ D + D 11 Δ V R l ρ l 12 cos ρ l 12 + ψ l + C 1 12 sin ρ l 12 + ψ l + C 1 12 = Δ D + D 12 Δ V R r ρ r 13 cos ρ r 13 + ψ r + C 1 13 sin ρ r 13 + ψ r + C 1 13 = Δ D + D 13 Δ V R r ρ r 14 cos ρ r 14 + ψ r + C 1 14 sin ρ r 14 + ψ r + C 1 14 = Δ D + D 14 Δ V

[0106] Where ΔDdescribes the error in the distance between the measuring unit and the tool spindle axis sought during calibration and the four angles ρ l 11 , ρ l 12 , ρ r 13 , ρ r 14 describe the polar angles of the points on the left and right flanks where the measuring ball actually touched the flanks.

[0107] These eight equations describe a system of equations in the eight unknowns ρ l 11 , ρ l 12 , ρ r 13 , ρ r 14 , ψ l , ψ r, ΔD and ΔV which in general can only be solved numerically.

[0108] It is also possible to use more than the two axes D and C1 used here to achieve contact between the measuring ball and the tooth flank, provided additional axes are available. For example, in the case where the measuring unit is mounted on the counter support, the axes X1 and V1, as well as C1, can be used.

[0109] To increase the accuracy of the calibration, it is possible to measure more than four points distributed over one or more skiving wheel teeth. In particular, a large number of points can be recorded using a measuring probe or an optical method. These points can also be distributed over several or all skiving wheel teeth. This results in a system of equations with more equations than unknowns, which is therefore overdetermined. Within the framework of a compensation calculation, further ΔV and ΔDIn a simple variant, it is also possible to only ΔV or only ΔD To do this, only the four equations for the left or right flank are selected from the system of equations, resulting in a system of equations with four unknowns. For calibration in the axial direction of the tool spindle axis, for example, a point on the tool holder can be probed.

Claims

1. A method for gear skiving a workpiece, wherein: in a first step, the geometry of a tool (21), in particular of a skiving wheel, is measured for the machining of the workpiece in a state clamped in an apparatus (20) for gear skiving machining; in a subsequent further step, machining kinematics are determined for the gear skiving in dependence on the measured geometry of the tool (21); and the absolute location of a cutting edge of the tool (21) in the apparatus (20) is determined in the first step, characterized in that the spatial extent of the cutting edge is additionally determined beside a determination of the location of the cutting edge in the first step, with both the axial location of the blade relative to the contact surface of the tool at the tool mount and the rotational position on the spindle being determined in the first step on the determination of the absolute location of the cutting edge of the tool.

2. A method in accordance with one of the preceding claims, wherein the tool is a skiving wheel and one or more of the following geometrical parameters are measured at the skiving wheel: a) an outside diameter of the skiving wheel (21) at one or more axial positions of the skiving wheel (21); b) a tooth thickness of the skiving wheel (21) at one or more axial positions of the skiving wheel (21); c) a profile line of the skiving wheel (21); d) a tooth trace of the skiving wheel (21); e) an extent of the cutting edge of the skiving wheel (21); f) a location of the rake face and / or its orientation, in particular its rake angle and step angle; and / or g) the location of the tool, preferably a rotational position of the skiving wheel (21), preferably the rotational position of one or more teeth on the skiving wheel (21).

3. A method in accordance with one of the preceding claims, wherein the machining kinematics are determined and / or corrected in dependence on the measured geometry of the tool and on an axial feed position of the workpiece.

4. A method in accordance with one of the preceding claims 1 to 2, wherein the machining kinematics are determined and / or corrected in dependence on the measured geometry of the tool and remain constant during a machining stroke.

5. A method in accordance with one of the preceding claims, wherein a deviation in the tooth thickness, in the profile angle and / or in the root radius is compensated by the machining kinematics and / or an angular location of the skived gap in the workpiece is directly predefined.

6. A method in accordance with one of the preceding claims, wherein at least one of the parameters of the machining kinematics, in particular a coupling position, a center distance, an axial cross angle, and a rake face offset, is determined.

7. A method in accordance with one of the preceding claims, wherein an evaluation is made by means of a check whether a predefined production tolerance can be observed with the skiving wheel and machining kinematics and / or whether technological parameters are within a predefined range, with corresponding workflows being output by the machine in dependence on the result of the check.

8. An apparatus (20) for carrying out the method in accordance with one of the preceding claims comprising: a tool (21) for machining a workpiece, in particular a skiving wheel; a tool mount (22) for receiving the tool (21); a measurement unit (23) that is configured to measure the geometry of the tool (21) received in the tool mount (22); and a control unit that is configured to determine machining kinematics for gear skiving in dependence on the measured geometry of the tool (21), wherein the measurement unit (23) is further configured to determine an absolute location of a cutting edge of the tool (21) in the apparatus (20) so that the machining kinematics are also determined on the basis of the absolute location, characterized in that the measurement unit (23) is further configured to additionally determine the spatial extent of the cutting edge and to determine both the axial location of the blade relative to the contact surface of the tool at the tool mount and the rotational position on the spindle on the determining of the absolute location of the cutting edge of the tool in addition to a determination of the location of the cutting edge.

9. An apparatus (20) in accordance with claim 8, wherein the apparatus (20) is configured to calibrate the spatial location of the measurement unit (23) with respect to the spindle axis of the skiving wheel (21) in that an inspection collar whose diameter is known or a cone of a chuck that is arranged on a spindle axis of the skiving wheel (21), at the tool mount (22) and / or at the skiving wheel (21) is measured by the measurement unit (23) such that the distance between the measurement unit (23) and the spindle axis can be determined to calibrate the measurement unit (23) accordingly.

10. An apparatus (20) in accordance with claim 8 or claim 9, wherein the apparatus (20) is configured to determine the tooth profile of the skiving wheel (21) located in the tool mount (22) by means of the measurement unit (23) with a known tooth profile, in particular a profile angle, of the skiving wheel (21) and to compare it with the known tooth profile to determine the error in the relative location between the measurement unit (23) and the skiving wheel (21) from a deviation between the known tooth profile and the measured tooth profile.

11. An apparatus (20) in accordance with claims 8 to 10, wherein the control unit is further configured to carry out a production simulation of a gear skiving on the basis of a measurement of the tool (21) located in the tool mount (22) made by the measurement unit (23) and to generate the machining kinematics for a gear skiving process with the measured tool (21) with reference thereto.

12. An apparatus (20) in accordance with one of the preceding claims 8 to 11, wherein with a known desired tooth profile of the tool (21), in particular a profile angle of a skiving wheel, the actual tooth profile of the tool (21) located in the tool mount (22) is determined and is compared with the desired tooth profile to determine an error in the relative location between the measurement unit (23) and the tool (21) from a deviation between the desired toot profile and the measured actual tooth profile.