Method and apparatus for gear skiving

Abstract

The present disclosure relates to a method for gear skiving a workpiece, wherein: in a first step, the geometry of a tool, in particular of a skiving wheel, is measured for the machining of the workpiece in a state clamped in an apparatus for gear skiving machining; and in a subsequent further step, machining kinematics are determined for the gear skiving in dependence on the measured geometry of the tool characterized in that the absolute location of a cutting edge of the tool in the apparatus is determined in the first step.

Claims

1. A method for skiving a gear workpiece, wherein: in a first step, one or more geometrical parameters of a geometry of a tool are measured for machining of a gear workpiece, where the tool is in a clamped state in a gear machining apparatus, the gear machining apparatus comprising a machining head, a tool mount, and a machine table, wherein the tool is mounted on the machining head via the tool mount, and wherein the gear workpiece is mounted on the machine table; and in a subsequent further step, machining kinematics are determined for the skiving of the gear workpiece in dependence on the measured one or more geometrical parameters of the geometry of the tool, wherein determining the machining kinematics includes determining machining kinematics parameters, the machining kinematics parameters including one or more of a coupling position, a center distance, an axial cross angle, and a rake face offset parameters, and wherein a location of a cutting edge of the tool is determined in the first step, based on a position of the tool in the tool mount in the gear machining apparatus.

2. The method in accordance with claim 1, wherein a spatial extent of the cutting edge is determined in the first step in addition to determination of the location in the first step, and wherein the spatial extent of the cutting edge is based on where a z axis coincides with an axis of rotation of the tool and with a tool spindle axis during machining.

3. The method in accordance with claim 1, wherein the tool is a skiving wheel and wherein the one or more geometrical parameters are measured at the skiving wheel, the one or more geometrical parameters including one or more of a) an outside diameter of the skiving wheel at one or more axial positions of the skiving wheel, wherein the one or more axial positions of the skiving wheel are based on one or more of a spatial distance of the cutting edge relative to contact of the skiving wheel on the tool mount and a movement of the machining head relative to the workpiece; b) a tooth thickness of the skiving wheel at the one or more axial positions of the skiving wheel; c) a profile line of the skiving wheel; d) a tooth trace of the skiving wheel; e) an extent of the cutting edge of the skiving wheel; f) a location of a rake face and/or an orientation of the rake face; and/or g) a location of the skiving wheel.

4. The method in accordance with claim 3, wherein a deviation in the tooth thickness of the skiving wheel, in a profile angle of the skiving wheel, and/or in a root radius of the skiving wheel from a desired geometry or from a desired location in the apparatus is compensated by the machining kinematics, and/or wherein an angular location of a skived gap is directly predefined in the gear workpiece.

5. The method in accordance with claim 3, wherein the machining kinematics are determined and/or corrected in dependence on the measured one or more geometrical parameters of the skiving wheel and remain constant during a machining stroke.

6. The method of claim 3, wherein the location of the rake face and/or the orientation of the rake face includes a rake angle of the rake face and a step angle of the rake face.

7. The method of claim 3, wherein the skiving wheel is located on a spindle having an axis, and wherein the location of the skiving wheel includes a rotational position of the skiving wheel with respect to the skiving wheel spindle axis.

8. The method of claim 3, wherein the skiving wheel is located on a spindle having an axis, and wherein the location of the skiving wheel includes a rotational position of one or more teeth on the skiving wheel with respect to the skiving wheel spindle axis.

9. The method in accordance with claim 1, wherein the machining kinematics are determined and/or corrected in dependence on the measured one or more geometrical parameters of the tool and on an axial feed position of the gear workpiece, and wherein the axial feed position of the gear workpiece is substantially parallel to an axis of rotation of the tool.

10. The method in accordance with claim 1, wherein the machining kinematics are determined and/or corrected in dependence on the measured one or more geometrical parameters of the tool and remain constant during a machining stroke.

11. The method in accordance with claim 1, wherein an evaluation is made via a check, wherein the evaluation via the check determines whether a predefined production tolerance is observed with a skiving wheel and the machining kinematics and/or whether technological parameters are within a predefined range, wherein corresponding workflows are output by a machine in dependence on a result of the check, and wherein the check includes performing a simulation and calculating values for gear teeth from measurement results that are based on sensor output.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a perspective view of an apparatus for gear skiving in accordance with the present disclosure.

(2) FIG. 2 shows a perspective view of an apparatus for gear skiving in accordance with the present disclosure in accordance with a further embodiment.

(3) FIG. 3 shows a schematic representation for explaining the calibration of the measurement unit and the skiving wheel or a measurement of the skiving wheel.

(4) FIG. 4 shows a sketch in which the apparatus in accordance with the present disclosure carries out a calibration of the measurement unit and the skiving wheel.

(5) FIG. 5 shows a representation of the skiving wheel.

(6) FIG. 6 shows a representation of profiles of the left and right flanks of the skiving wheel in polar coordinates.

DETAILED DESCRIPTION

(7) FIG. 1 shows a perspective view of the apparatus 20 in accordance with the present disclosure. A manufacturing machine for gear skiving is shown in which a machine column 32 and a counter column 33 are arranged on a machine bed 31. A machining head 36 that can receive the skiving wheel 21 via a tool mount 22 is fastened to the machine column 32 via a travelable slide 34.

(8) The slide 34 and the machining head 36 fastened thereto can be moved in a plurality of directions. The slide can thus be traveled along the axes X1 and Z1; the machining head 36 can furthermore be traveled along the axis V1. The machining head can furthermore be rotated about an axis A1 in parallel with the axis X1. The axis C1 is the spindle axis of the skiving wheel 21.

(9) The workpiece (not shown) to be machined with the spindle is arranged on the table 38. The workpiece clamping apparatus used is not shown for reasons of better clarity.

(10) Also shown in FIG. 1 is control unit 40. The control unit 40 is shown as a microprocessor with non-transitory memory storing instructions which controls the apparatus 20. The control unit 40 is shown receiving various signals from sensors coupled to the apparatus 20, and transmitting instructions to various actuators. The sensors may include measurement sensor 3, sensor 232 or sensor 233, for example. (See FIGS. 3 and 4). The actuators may include a plurality of drives or the drive 35 for the Z1 axis or the drive 37 for the tool spindle for the performing of the movements, for example.

(11) FIG. 2 shows a perspective view of a further embodiment of the apparatus 20 in accordance with the present disclosure that, except of the arrangement of the measurement unit 23, substantially corresponds to the apparatus described in FIG. 1. The same reference numerals as in FIG. 1 are also used for identical components.

(12) Unlike FIG. 1, the measurement unit 23 is arranged a the counter column 33 in FIG. 2. A movement axis V2 can also be provided here for the relative movement of the skiving wheel 21 and the measurement unit 23. The delivery to the measurement position of the measurement unit 23 is thus simplified.

(13) As shown in FIG. 1, the apparatus 20 is furthermore provided with a measurement unit 23 that is fastened to the machine column 32 in the present embodiment. The measurement unit 23 has a movement mechanism to enable a relative movement with respect to the skiving wheel 21 received in the tool mount 22. The measurement unit 23 can thus be moved along an axis X2 in parallel with the axis X1 since a relative movement of the two elements in the X direction would not be possible due to the fastening of the measurement unit 23 and the machining head 26 at the machine column 32. The apparatus 20 has a plurality of drives or the drive 35 for the Z1 axis or the drive 37 for the tool spindle for the performing of the movements.

(14) FIG. 3 shows a schematic representation of the skiving wheel 21 that is measured with the aid of the measurement unit 23. By way of example for the measurement unit 23, a first probe 231 measures the tooth flank of the skiving wheel 21 and a second sensor 232 measures the rake face. An optical sensor 233, for example a laser, can likewise be part of the measurement unit 23 and can be used for the measurement or for a calibration of the measurement unit 23.

(15) Some examples will be shown in the following for a better explanation of the apparatus:

Example 1

(16) In gear skiving, the exact location and the exact shape of the cutting edge of the skiving wheel are of particular importance to generate the desired profile on the workpiece.

(17) The profile of skiving wheels is typically produced with high accuracy by toolmakers; however, the exact location of the cutting edge only results from the grinding of the rake face. If a skiving wheel is worn, the rake face is sharpened and a new cutting edge is formed. The location and the shape of the cutting edge result from the location and from the orientation of the reground rake face. If the rake face is, for example, described by a plane, the orientation can be defined by a normal vector of the rake planes; the location 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, for example, by a cone, the orientation can be described by the direction of the axis of rotation of the cone and the aperture angle of the cone and the location by the position of the cone tip.

(18) In order, for example, to determine the location and orientation of a rake plane, it is sufficient to measure three points that unambiguously determine the plane. To increase the accuracy of the determination, it is, however, also possible to measure more than three points.

(19) It is sufficient to measure two points to determine the location and orientation of a cone assumed as oriented concentrically to the spindle axis, for example. More points can also be measured here to improve the accuracy.

(20) The present disclosure therefore provides determining the location and the orientation of the rake face as a possible application. This determination has to take place such that the location and the orientation of the rake face with respect to the associated skiving wheel tooth are known. For this purpose, the location of the skiving wheel tooth is determined in the axial direction and/or the rotational position of the skiving wheel tooth is determined, optionally additionally with the measurement unit. A determination of the axial location of the skiving wheel tooth or of a plurality of or of all the skiving wheel teeth is in particular necessary with conical skiving wheels. The axial location can be understood as the position of a face section of the skiving wheel in which the skiving wheel teeth have a specific tooth thickness. This tooth thickness is the same in all face sections for cylindrical skiving wheels so that a determination of the axial location of the skiving wheel tooth is neither possible nor necessary; however for conical skiving wheels, for example, this tooth thickness changes from face section to face section.

(21) It is sufficient to measure a flank at one point to determine the rotational position of the skiving wheel tooth. If, for example, the axial location is to be determined with a conical skiving wheel, at least two points are to be measured to determine the tooth thickness in a face section.

(22) If the rake face relative to the skiving wheel tooth is determined, the cutting edge can be determined by calculation by cutting the rake face with the flanks of the skiving wheel.

(23) The geometry of the flanks can either be take over in accordance with the drawing or can optionally likewise be determined in the manufacturing machine by a profile measurement and/or by a tooth trace measurement. The cutting edge thus determined can then be used, for example, to set the machining kinematics such that both the tooth thickness and the profile angle at the left and right flanks of the workpiece are within the tolerance. A check can optionally additionally be made whether the effective clearance angle and/or the effective rake angle is/are within desired limits in the machining kinematics thus determined. If the clearance angle is outside the tolerance, the machining can optionally not be continued and the skiving wheel can be expelled or removed again to avoid damage to the skiving wheel and/or to the workpiece.

Example 2

(24) An extension of the last example provides that the outside diameter of the skiving wheel is measured in addition to the location and orientation of the rake face. In particular when the skiving wheel is conical, it can be of advantage to measure the outside diameter at a plurality of axial positions of the skiving wheel and thus to determine the enveloping cone. This enveloping cone or enveloping cylinder in the event of a cylindrical skiving wheel can be utilized to determine that part of the rake face by a section with the rake face that produces the base region of the workpiece and thus to determine the base contour generated in the skiving process and in particular to determine the root radius produced. If the root radius is not generated within the desired tolerance by the machining kinematics determined in Example 1, an attempt can either be made by means of a compensation calculation by varying the available degrees of freedom of the machining kinematics to determine a machining kinematics such that the tooth thickness, the profile angle, and the root radius are within the respective desired tolerance or, if this is not possible, the machining with this skiving wheel can initially be stopped.

(25) If the machining was provided as a two flank machining, a check can optionally be made, for example by means of a simulation, whether it is possible with this skiving wheel within the framework of a single flank machining to achieve both the tooth thickness and the profile angle on the left and right flanks and the root radius within the desired tolerance. If this is possible, the machining can be carried out automatically or on one flank after confirmation by the operator. A check can also optionally additionally made here whether the effective clearance angle and/or the effective rake angle is/are within desired limits in thus determined machining kinematics and the machining is optionally not continued.

Example 3

(26) A simplified variant of Example 1 provides only determining the location of the rake face, that is in particular the reground state of the skiving wheel. This changes after the regrinding and is not exactly known in all cases. This variant can be utilized when the orientation of the rake face is achieved so well during regrinding that the error arising due to the deviation from the desired orientation at the cutting edge produces a deviation in the profile and/or in the tooth thickness of the workpiece that is within a desired tolerance. It is sufficient here to only measure the rake face at one point.

Example 4

(27) If workpieces already having teeth are further machined by gear skiving, it is important to pair the skiving wheel and the workpiece, i.e. to determine the coupling position, such that the desired 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 exactly as possible. The rotational position of the workpiece can be determined, for example, by means of a threading sensor or of a measurement unit for measuring or checking the workpiece. The skiving wheel can be measured in the manufacturing machine to determine the rotational position of the skiving wheel in accordance with the present disclosure and the rotational position can thus be exactly determined.

(28) This measurement can optionally be carried out every time when a skiving wheel is received via the tool mount, in particular also when this reception takes place in an automated manner, for example via a tool changer. If, however, the tool mount has sufficient repeat accuracy as regards the rotational position of the skiving wheel, it can also be sufficient only to measure each skiving wheel once and to make use of the last measurement result when it is again received in the machine. The pairing with high accuracy is in particular of special importance when only a little material is to be removed such as during hard skiving.

Example 5

(29) A further application in which the exact pairing and thus the rotational position of the skiving wheel is important is location-oriented gear cutting. The gearing at the workpiece is generated in a fixedly predefined angular position. This can be defined, for example, via a groove or via a bore at the workpiece or via a further gearing at the workpiece. The gearing can in particular be a herringbone gear.

(30) It is naturally possible to increase the number of points to be measured specified in the examples to improve the measurement accuracy by better statistics.

(31) Statements that can be of relevance for a plurality of the above-described examples can be found in the following with respect to the Figures, in particular FIGS. 4 to 6.

(32) If machining kinematics and/or workpiece profiles generated using a known skiving wheel and known machining kinematics, workpiece tooth traces, angular position of the generated gearing, and the clearance angle and rake angle are to be determined in the examples, this can be done, for example, using the production simulations typically used today. Such production simulations are typically based on a removal simulation. The material is determined at the workpiece that is removed by a given tool, in particular by given cutting edges at the tool, during the machining with given machining kinematics. In the case of the gear skiving observed here, the total produced gap can thus be determined.

(33) To determine machining kinematics for generating a predefined workpiece profile and/or tooth thickness using a given skiving wheel having a known cutting edge, the influences of the axes available in the machining on the workpiece profile and/or tooth thickness can be determined within the framework of the production simulation by varying the axes. It can thus be determined, for example, how the profile angles at the workpiece change on the left and right sides if the axial cross angle is adjusted by 0.1 in that the production simulation is carried out using this adjusted axial cross angle and in that the profile angle of the generated gap is determined from the simulation result. If the influences of all the axes adjustable for the machining on all the geometrical parameters at the workpiece to be corrected are known the machining kinematics can be corrected under the assumption of a linear correlation between the axes and these parameters. The production simulation can be carried out again using these corrected machining kinematics and the remaining errors can be determined and optionally corrected again and iterated for so long until the geometrical parameters are within a predefined tolerance.

(34) The machining kinematics in gear skiving will be described by the following parameters now described in more detail, but also known from the general literature and publications on gear skiving.

(35) The coupling ratio between the tool spindle axis and the workpiece spindle axis is given by the tooth number ratio of the tool and the workpiece and describes the ratio of the tool spindle and the workpiece spindle speed during the machining, but still without taking the axial feed along the workpiece into account.

(36) The differential feed describes the additional rotation of the workpiece determined by the axial feed along the workpiece due to the lead of the workpiece. This additional rotation is necessary to generate the helix angle at the workpiece.

(37) The coupling position describes a set of values for the rotational position of the tool spindle, for the rotational position of the workpiece spindle, and the position in the axial direction. In the variant shown by way of example in FIG. 1 of an apparatus for gear skiving, this would be a set of values for the axes C1, C2, and Z1. It is fixed by this coupling position where exactly the gap is generated by the gear skiving process at the workpiece, i.e. at which angular position.

(38) The center distance describes the distance between the tool spindle axis and the workpiece spindle axis. The center distance is substantially implemented by the X1 axis in the variant of an apparatus for gear skiving shown by way of example in FIG. 1, with a pivoting about A2 and a travel along V1 also influencing the center distance.

(39) The axial cross angle is here defined as the angle by which the tool spindle is inclined with respect to the workpiece spindle. In variant of an apparatus for gear skiving shown by way of example in FIG. 1, this corresponds to the position of the A1 axis.

(40) The rake face offset denotes a shift of the tool along the tool spindle axis. In the variant of an apparatus for gear skiving shown by way of example in FIG. 1, this can be implemented by a combination of a traveling of the Z1 and V1 axes.

(41) The relative location of the measurement unit to the tool spindle in the manufacturing machine is generally not exactly known. It can thus in particular change in time by thermal growth of the machine. To be able to compensate such thermal growths, it can be necessary to carry out a calibration of the measurement unit. It can in particular be important to calibrate the distance of the measurement unit from the tool spindle axis, in particular of the measurement sphere center from the tool spindle axis. For this purpose, for example, a ground inspection collar having a known diameter can be provided on the skiving wheel and/or on the tool holder and/or on the tool spindle and is measured by the measurement unit. If, for example, a measuring sensor is used that works in a switching manner, the inspection collar can be sensed with it. The distance between the measurement unit and the tool spindle axis can be determined from this and the measurement unit can be correspondingly calibrated. The distance between the measurement sphere and the tool spindle axis can in particular thereby be determined. Alternatively to an inspection collar produced specifically for this purpose, a cone of a chuck can also be used for mounting the skiving wheel for calibration.

(42) In the event that such an inspection collar and/or cone is not present or cannot be traveled to, the present disclosure provides a further method for determining the relative location between the measurement sphere center and the tool spindle axis. The fact is utilized that an error in the relative location between the measurement sphere center and the tool spindle axis in a measurement of the profile of the skiving wheel teeth results in an error in the measured profile, in particular in the measured profile angle. If the profile of the skiving wheel teeth is known, a measurement of the profile can be carried out in the machine, the measured profile can be compared with the actual profile of the skiving wheel teeth, and errors in the relative location between the measurement sphere center and the tool spindle axis can be determined from the deviation.

(43) This determination will be outlined in the following for the arrangement shown by way of example in FIG. 4.

(44) FIG. 4 shows an exemplary arrangement of axes in the sense of the present disclosure for traveling the skiving wheel in the manufacturing machine and a skiving wheel in which only one tooth 5 is shown for simplification. FIG. 4 furthermore shows a measurement sensor 3 working in a switching manner with a measuring probe 2 and a measurement sphere 1. The C1 axis corresponds to the tool spindle axis 6; the D axis serves the optionally linear traveling of the skiving wheel and thus inter alia serves the changing of the relative location between the measurement sphere center and the tool spindle axis. The measuring probe 2 does not have to be aligned in parallel with the D axis. The offset V that describes the position of the measurement sphere in a direction perpendicular to the D axis is generally also not exactly known and may likewise be determined with the method described here. A measurement sphere having a diameter 0 is assumed in the following to limit the description of the idea behind the calibration to the essential. In this simplified case, the measurement sphere center also corresponds exactly to the contact point between the measurement sphere and the tooth flank. In practice, the contact point has to be determined, as is generally known from metrology, from the measurement sphere center while taking account of the measurement sphere diameter and of the normal vector of the tooth flank at the contact point.

(45) For the calibration, the four points 11 to 14 of FIG. 5 are probed one after the other by the measurement sphere and the respective positions read from the measurement systems of the axes C1 and D at the time of the contact are recorded. These positions are designated in the following as C1.sub.11, C1.sub.12, C1.sub.13, and C1.sub.14 or D.sub.11, D.sub.12, D.sub.13, and D.sub.14. The four points can be freely selected within certain limits; two points on a left flank and two points on a right flank may be sensed, with a respective point in the proximity of the addendum and a further point in the proximity of the dedendum being sensed on each flank. The points do not have to be impacted exactly, which would also not even be possible due to the not exactly known relative location between the measurement sphere center and the tool spindle axis and due to the not exactly known offset V.

(46) The points can be on different skiving wheel teeth, but it is also possible, as shown in FIG. 5, 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 a high accuracy. This is the case as a rule with skiving wheels since they are ground with high precision. The profiles V.sub.l(.sub.l) and V.sub.r(.sub.r) of the left and right flanks respectively can be described as follows in polar coordinates:

(47) $\begin{array}{cc}{V}_l\left({}_l\right)=R_l\left({}_l\right)\left(\begin{array}{c}\cos \left({}_l+{}_l\right)\\ \sin \left({}_l+{}_l\right)\end{array}\right)V_r\left({}_r\right)=R_r\left({}_r\right)\left(\begin{array}{c}\cos \left({}_r+{}_r\right)\\ \sin \left({}_r+{}_r\right)\end{array}\right)& \left(1\right)\end{array}$

(48) where .sub.l or .sub.r is the polar angle R.sub.l(.sub.l), or R.sub.r(.sub.r) the radius in dependence on the polar angles and the initially unknown angles .sub.l and .sub.r describe the rotational position of the flanks. See FIG. 6. The four times two equations result from the four sensing procedures;

(49) $\begin{array}{cc}{R}_l\left({}_{l11}\right)\left(\begin{array}{c}\cos \left({}_{l11}+{}_l+C{1}_{11}\right)\\ \sin \left({}_{l11}+{}_l+C{1}_{11}\right)\end{array}\right)=\left(\begin{array}{c}D+D_{11}\\ V\end{array}\right)& \left(2\right)\\ R_l\left({}_{l12}\right)\left(\begin{array}{c}\cos \left({}_{l12}+{}_l+C{1}_{12}\right)\\ \sin \left({}_{l12}+{}_l+C{1}_{12}\right)\end{array}\right)=\left(\begin{array}{c}D+D_{12}\\ V\end{array}\right)& \left(3\right)\\ R_r\left({}_{\mathrm{r13}}\right)\left(\begin{array}{c}\cos \left({}_{r13}+{}_r+C{1}_{13}\right)\\ \sin \left({}_{\mathrm{r13}}+{}_r+C{1}_{13}\right)\end{array}\right)=\left(\begin{array}{c}D+D_{13}\\ V\end{array}\right)& \left(4\right)\\ R_r\left({}_{r14}\right)\left(\begin{array}{c}\cos \left({}_{r14}+{}_r+C{1}_{14}\right)\\ \sin \left({}_{r14}+{}_r+C{1}_{14}\right)\end{array}\right)=\left(\begin{array}{c}D+D_{14}\\ V\end{array}\right)& \left(5\right)\end{array}$

(50) where D describes the error sought within the framework of the calibration in the spacing between the measurement unit and the tool spindle axis and the four angles .sub.l11, .sub.l12, .sub.r13, .sub.r14 describe the polar angles of the points on the left or right flanks at which the measurement sphere actually contacted the flanks.

(51) These eight equations in total describe an equation system in the eight unknowns .sub.l11, .sub.l12, .sub.r13, .sub.r14, .sub.l, .sub.r, D, and V which can generally only be numerically resolved.

(52) It is likewise possible to utilize more than the two axes D and C1 used here to bring about a contact between the measurement sphere and the tooth flank if further axes are available for this purpose. In the event that the measurement unit is attached to the counter column, the axes X1, and V1, and C1 can be used, for example.

(53) To increase the accuracy of the calibration, it is possible to measure more than four points distributed over one or more skiving wheel teeth; a plurality of points can in particular be recorded by the use of a measuring probe or by an optical method, they can in particular also be distributed over a plurality of or over all skiving wheel teeth. An equation system having more equations than unknowns and that is thus overdetermined thereby results. V and D can then furthermore be determined within the framework of a compensation calculation. It is also possible only to determine V or only D in a simple variant. Only the four equations for the left or right flanks are selected from the equation system for this purpose, which produces an equation system having four unknowns. A point on the tool mount can be sensed, for example, for a calibration in the axial direction of the tool spindle axis.