Skiving tool and skiving method with simultaneous engagement start or engagement end of two cutting edges

Abstract

The invention relates to the skiving of teeth. In the machining of the tooth flanks of the teeth, pairs of cutting edges of oppositely oriented cutting edges of a skiving tool each come simultaneously into contact and / or out of contact with two oppositely oriented tooth flanks of the teeth. Pushing-away effects and resulting machining inaccuracies can thereby be reduced. The two cutting edges of such a pair of cutting edges are defined by different generating geometries. In particular, the two cutting edges of a pair of cutting edges on the skiving tool do not run in the same plane or on the same spherical surface.

Description

[0001] Skiving tool and skiving process with simultaneous start or end of engagement of two cutting edges

[0002] Background of the invention

[0003] The invention relates to a skiving tool for machining tooth flanks of a gearing of a workpiece, in which the skiving tool is rotated about a tool axis and the workpiece is moved by an angle skewed to the

[0004] The workpiece axis extending along the tool axis is rotated, the skiving tool and the workpiece being displaced relative to one another with a feed movement having a component along the workpiece axis, the tool having a plurality of cutting teeth, each with a left and a right cutting edge, which cutting edges remove material from the mutually facing tooth flanks of a tooth gap of the gearing when machining the workpiece.The invention further relates to a method for machining tooth flanks of a gearing of a workpiece by skiving, in which a skiving tool is brought into engagement with the gearing, wherein the skiving tool is rotated about a tool axis and the workpiece is rotated about a workpiece axis skewed to the tool axis, and wherein the skiving tool and the workpiece are displaced relative to one another with a feed movement with a component along the workpiece axis, wherein the tool has a plurality of cutting teeth, each with a left and a right cutting edge. Finally, the invention relates to a method for producing a skiving tool.

[0005] Such skiving tools and skiving processes are generally known, for example from EP 3 528 989 B1 or from EP 2 537 616 A1.

[0006] Various processes are known for producing gears. Examples of machining processes include gear hobbing, planing, shaping, and generating grinding. Gear skiving is a continuous machining process for machining gears. Important principles and terms of gear skiving are explained, for example, in EP 3 528 989 B1. Gear skiving enables the precise production of both external and internal gears.

[0007] In power skiving, a skiving tool is rotated around a tool axis and a workpiece is rotated around a workpiece axis that is skewed to the tool axis. At the same time, a feed movement occurs, typically along the workpiece axis. The skiving tool has several cutting edges. Cutting teeth extend in the axial direction in straight-toothed skiving tools or at a helix angle to the workpiece axis in helical-toothed skiving tools. Chipping surfaces are typically located on the front side of the

[0008] The cutting teeth of the skiving tool are arranged in a plane. The flanks of the cutting teeth extend approximately in the axial direction on straight-toothed skiving tools, or approximately at the helix angle to the workpiece axis on the cutting teeth on helical-toothed skiving tools. During skiving, it is possible to machine both tooth flanks of a tooth gap in the gearing in the same pass (so-called double-flank skiving). For this purpose, the two cutting edges of a cutting tooth engage the facing tooth flanks of the respective tooth gap.

[0009] During the coupled rotational movement of the skiving tool and workpiece, the cutting edges of conventional skiving tools engage and disengage with the workpiece's gear teeth one after the other. As the cutting edges enter and exit the workpiece, the forces acting between the workpiece and the skiving tool change abruptly. Due to the finite stiffness of the workpiece, skiving tool, and skiving machine, these force changes lead to deflection effects. This often results in local thickening (due to insufficiently deep material removal) on the tooth flanks.

[0010] Object of the invention

[0011] It is an object of the invention to improve the dimensional accuracy of gears produced by power skiving.

[0012] Description of the invention

[0013] This object is achieved according to the invention by a gear skiving tool according to claim 1 and a gear skiving method according to claim 7. Furthermore, this object is achieved by a method for producing a gear skiving tool according to claim 14. Advantageous embodiments or variants are specified in the respective subclaims and the description.

[0014] Inventive skiving tool

[0015] According to the invention, a gear skiving tool is provided for machining tooth flanks of a gearing of a workpiece. To machine the tooth flanks, the gear skiving tool is rotated about a tool axis, and the workpiece is rotated about a workpiece axis skewed to the tool axis. The gear skiving tool and the workpiece are displaced relative to each other with a feed movement having a component along the workpiece axis. Due to the axis kinematics, the feed movement also has a component along the tool axis. Typically, the feed movement occurs parallel to the workpiece axis.

[0016] The gear skiving tool has several cutting teeth, each with a left and a right cutting edge. These cutting edges remove material from the facing tooth flanks of a tooth gap in the gearing when machining the workpiece. The gear skiving tool is thus designed to machine the two tooth flanks bordering a tooth gap in a single pass. In other words, the cutting teeth or their cutting edges are designed for double-flank gear skiving. The gear skiving tool can be straight-toothed or helical-toothed.

[0017] The designation of the cutting edges as left and right cutting edges serves to distinguish between the two cutting edges of a cutting tooth; one could also speak of first and second cutting edges. Which cutting edges are designated as left or right cutting edges is not important. It is understood that the left and right cutting edges are located in the same way on all cutting teeth. The same applies to the designation of the tooth flanks of the gear being machined as right and left tooth flanks.

[0018] According to the invention, the left and right cutting edges of each of the cutting teeth run on different spherical surfaces or in different planes. This enables adaptation of the cutting edges so that a cutting edge pair consisting of a left and a right cutting edge simultaneously engages or disengages from the toothing of the workpiece. In other words, when the gear skiving tool is used, the left and right cutting edges of each cutting edge pair advantageously come into contact and / or disengage with opposing tooth flanks, i.e. a left and a right tooth flank, of the toothing at the same time. The opposing (unlikely) tooth flanks of the toothing point in opposite directions in the circumferential direction.Depending on the designation of the tooth flanks, the left cutting edges can each machine a left tooth flank, and the right cutting edges can each machine a right tooth flank, and simultaneously come into or out of contact with them. Alternatively, the left cutting edges can each machine a right tooth flank, and the right cutting edges can each machine a left tooth flank, and simultaneously come into or out of contact with them.

[0019] The two cutting edges of a respective pair of cutting edges can be formed on the same cutting tooth. However, it is also conceivable that the two cutting edges of a respective pair of cutting edges are formed on different cutting teeth, in particular on the nearest or next-but-one neighbors.

[0020] The geometry of the cutting edges corresponds to an intersection of the body conjugated to the toothing to be produced with a generating geometry of the respective cutting edge. According to the invention, different generating geometries are intersected with the conjugated body for the left and right cutting edges. The generating geometry can be a spherical surface. In the special case of an infinite sphere radius, the spherical surface is a plane. For the left and right cutting edges, in particular, different spherical surfaces or planes are intersected with the conjugated body.

[0021] The conjugate body is the (imaginary) body which, in the axial configuration of the power skiving operation for which the power skiving tool is intended, would roll with the gear (to be produced) at any point upon rotation around the tool axis and upon rotation of the workpiece around the workpiece axis. In power skiving tools known from the prior art, the same generating geometry (often a plane or, in the case of a tool with a calotte grind, a sphere) is intersected with the conjugate body to define the two cutting edges of a cutting tooth. The rake face is then part of the generating geometry. The inventors have recognized that, due to the kinematic conditions during power skiving, this tool design leads to each cutting edge engaging or disengaging individually, resulting in the force fluctuations and shape deviations in the machined gear explained above.

[0022] According to the invention, two generating geometries per cutting tooth – one for the right and one for the left cutting edge – are used to design the gear skiving tool. The two cutting edges are therefore not located in the same plane or on the same spherical surface, but rather in a different plane or on a different spherical surface. A rake face of the gear skiving tool according to the invention is therefore not part of the plane or spherical surface of one of the cutting edges, but rather mediates between the planes or spherical surfaces of the two cutting edges of a respective cutting tooth, possibly taking into account the height of rake face chamfers. Typically, the same two generating geometries are used for all cutting teeth of the gear skiving tool and are positioned similarly relative to the respective cutting tooth (by rotating by one tooth pitch around the tool axis).In special cases, however, it is also conceivable that several pairs of generating geometries are used to define the cutting edges of a group of cutting teeth.

[0023] The design according to the invention prevents the initially discussed deflection effects during the run-in or run-out of the cutting edges on the gear to be machined. This increases the dimensional accuracy of the manufactured gear. Since – compared to the use of conventional gear skiving tools – fewer force fluctuations occur between the workpiece and the gear skiving tool, the demands on the drives or spindles for mounting the workpiece and gear skiving tool are reduced. In particular, comparatively soft drives or spindles can be used without compromising the machining quality, which can lead to cost advantages. Conversely, when using the same gear skiving machine with the gear skiving tool according to the invention, the machining quality can be improved compared to a conventional gear skiving tool.By machining both the left and right tooth flanks of the gear to be produced in one machining pass, short cycle times are possible while maintaining high production quality.

[0024] The skiving tool is preferably used in a machining method according to the invention described below. The scope of the present invention also includes the use of a skiving tool according to the invention, wherein the cutting edges of pairs of cutting edges, each formed by one of the left and one of the right cutting edges, simultaneously come into contact with and / or out of contact with opposing tooth flanks of the gearing.

[0025] The skiving tool according to the invention can be obtained by a manufacturing method according to the invention described below.

[0026] An axis crossing angle between the tool axis and the workpiece axis can be at least 5°, preferably at least 10°, and / or at most 45°, preferably at most 30°.

[0027] Preferably, a left rake face chamfer is formed between a rake face of each of the cutting teeth and its left cutting edge, and a right rake face chamfer is formed between the rake face of the respective cutting tooth and its right cutting edge. This allows a blunt cutting edge to be obtained on each of the two cutting edges, which can increase the service life of the gear skiving tool. In addition, a blunt cutting edge can improve machining quality. Blunt cutting edges are particularly suitable for the hard finishing of hardened workpieces. The right and left rake face chamfers can have different widths and / or be inclined at different angles to the rake face. This makes it possible to achieve the same or at least approximately the same rake angles (which differ, for example, by a maximum of 20°, preferably a maximum of 10°) for the chips running off the rake face chamfers on the right and left cutting edges.

[0028] A left flank chamfer may be formed between a left flank of each of the cutting teeth and its left cutting edge, and a right flank chamfer may be formed between the right flank of each of the cutting teeth and its right cutting edge.

[0029] Preferably, the angles between the right and left rake face chamfers and the respective left and right flanks or, if present, the respective left and right flank chamfers of the cutting teeth deviate from each other by a maximum of 30°, in particular a maximum of 15°. In this way, identical cutting conditions can be achieved at both cutting edges, especially when different wedge angles are set between the left and right flanks and the rake face.

[0030] A rake face of each of the cutting teeth can extend in a rake face plane that runs at an angle other than 90° to a helix direction of the cutting teeth. In the case of a straight-toothed skiving tool, the helix direction of the cutting teeth is parallel to the tool axis. In this way, a step grind can be obtained, which simplifies the inventive arrangement of the two cutting edges of a cutting tooth on different generating geometries.

[0031] In particular, the angle between the rake face plane and the helix direction can deviate from 90° by at least 5°, preferably at least 10°, and particularly preferably at least 20°. Such large deviations from the normal plane to the helix direction have proven advantageous in the inventors' investigations. In conventional gear skiving tools, in contrast, the rake face plane generally runs perpendicular to the helix direction of the cutting teeth.

[0032] Machining method according to the invention

[0033] The scope of the invention also includes a method for machining tooth flanks of a gearing of a workpiece by power skiving, in which a power skiving tool is brought into engagement with the gearing, wherein the power skiving tool is rotated about a tool axis and the workpiece is rotated about a workpiece axis running skew to the tool axis, and wherein the power skiving tool and the workpiece are displaced relative to one another with a feed movement with a component along the workpiece axis. The power skiving tool has a plurality of cutting teeth, each with a left and a right cutting edge. The power skiving tool is preferably a power skiving tool according to the invention as described above. Due to the axis kinematics, the feed movement also has a component along the tool axis. Typically, the feed movement occurs parallel to the workpiece axis. The speed of the feed movement is typically constant.The cross-axis angle between the tool axis and the workpiece axis can be at least 5°, preferably at least 10°, and / or at most 45°, preferably at most 30°. The gearing can be internal or external.

[0034] The machining method according to the invention is characterized in that the cutting edges of pairs of cutting edges, each formed by one of the right-hand and one of the left-hand cutting edges, each simultaneously come into contact with and / or out of contact with opposing tooth flanks of the gearing. In other words, the cutting edges of the gear skiving tool form pairs consisting of a left-hand and a right-hand cutting edge. For each pair of cutting edges, both cutting edges simultaneously come into and / or out of contact with the gearing of the workpiece. Preferably, each cutting edge of the gear skiving tool is part of such a pair of cutting edges. To define suitable left and right-hand cutting edges of a respective pair of cutting edges, different generating geometries, in particular different spherical surfaces or planes, can be intersected with the body conjugated to the gearing to be produced.

[0035] When the gear skiving process is carried out according to the invention, the initially explained deflection effects during the run-in and / or run-out of the cutting edges on the gear to be machined are avoided. This increases the dimensional accuracy of the produced gear. Since – compared to the use of conventional gear skiving tools – fewer force fluctuations occur between the workpiece and the gear skiving tool, the demands on the drives or spindles for holding the workpiece and gear skiving tool are reduced. In particular, comparatively soft drives or spindles can be used without compromising the machining quality, which can lead to cost advantages. Conversely, when using the same gear skiving machine to carry out the machining method according to the invention, the machining quality can be improved compared to conventional gear skiving.By machining both the left and right tooth flanks of the gear to be produced in one machining pass, short cycle times are possible while maintaining high production quality.

[0036] The cutting edges on the skiving tool that come into and / or out of contact simultaneously can be arranged directly adjacent to one another. The cutting edges of a pair of cutting edges are then each formed by two directly adjacent cutting edges. This can simplify the design of the skiving tool. This variant is particularly suitable for skiving tools with few cutting teeth and / or workpieces with few teeth. The two cutting edges that come into and / or out of contact simultaneously can be formed on the same cutting tooth. Alternatively, the two cutting edges that come into and / or out of contact simultaneously can be formed on directly adjacent cutting teeth and face each other; in other words, the two cutting edges can be arranged in the same tooth gap of the skiving tool.

[0037] Alternatively, at least one left and at least one right cutting edge can be arranged between the cutting edges of a cutting edge pair that simultaneously engage and / or disengage. In this variant, the cutting edges of one of the cutting edge pairs are not directly adjacent. This variant is particularly suitable for skiving tools with many cutting teeth and / or workpieces with many teeth.

[0038] The simultaneous beginning and / or ending engagement of the cutting edges of each of the pairs of cutting edges can occur with respect to various parameters. Preferably, the beginning and / or end of the engagement occur simultaneously with respect to several, in particular all, of the parameters explained below.

[0039] The right and left cutting edges of a respective pair of cutting edges can come into contact and / or out of contact with the opposing tooth flanks at the same axial position of the workpiece and the skiving tool in the feed direction. The same axial position is present in particular when the feed movement between the start and end of contact on the two opposing tooth flanks is less than 20 pm, preferably less than 10 pm, particularly preferably less than 5 pm.

[0040] The right and left cutting edges of a respective pair of cutting edges can come into contact and / or out of contact with the opposing tooth flanks at the same rotational position of the skiving tool relative to the tool axis. The same rotational position is present in particular when the angle of rotation of the skiving tool around the tool axis between the start and end of contact on the two opposing tooth flanks is less than 0.5°, preferably less than 0.2°, particularly preferably less than 0.1°, and most particularly preferably less than 0.05°.

[0041] The right and left cutting edges of a respective pair of cutting edges can come into contact and / or out of contact with the opposing tooth flanks at the same time. Simultaneous contact initiation or simultaneous contact termination occurs in particular when less than 60 ps, ​​preferably less than 30 ps, ​​particularly preferably less than 15 ps, and most preferably less than 7 ps, elapse between the initiation or termination of contact on the two opposing tooth flanks.

[0042] Power skiving is preferably a hard finishing operation performed after hardening the gear teeth. In hard finishing, the improved dimensional accuracy of the gear teeth achieved according to the invention is particularly important, since no further shaping is usually required.

[0043] Typically, soft machining of the gearing is performed prior to hardening. Soft machining can be performed, for example, by hobbing, planing, shaping, or preferably gear skiving. Soft machining can also be performed using a machining method according to the invention and / or a gear skiving tool according to the invention. In this respect, the invention also relates to a manufacturing method comprising soft machining, hardening, and hard finishing, wherein the soft machining and / or hard finishing are performed using the method according to the invention.

[0044] In an alternative, advantageous process variant, gear skiving is a soft machining operation, which is not followed by any further material-removing, in particular no further machining, of the tooth flanks. The shape of the tooth flanks created during soft machining is thus retained on the finished workpiece. With soft machining, the service life of the gear skiving tool can be increased compared to hard machining. Following soft machining, chemical, physical, and / or thermal surface treatment, in particular hardening, can be performed. For example, the tooth flanks or the entire workpiece can be nitrided.In this respect, the invention also relates to a manufacturing process comprising soft machining, which is carried out using the method according to the invention, and subsequent non-abrasive surface treatment, in particular hardening, of the tooth flanks, wherein the manufacturing process does not include material-removing hard machining after the non-abrasive surface treatment. In this variant, a hardening process, such as nitriding, is generally used, which causes only minimal distortion, so that corrective post-processing is unnecessary.

[0045] The tip sections of the cutting teeth can pass through the tooth gaps without contacting the workpiece. This process design is particularly suitable for hard finishing. Because the tip sections of the cutting teeth pass through the tooth gaps without contact, radial deflection effects are reduced. This further improves the dimensional accuracy of the manufactured gear.

[0046] Inventive manufacturing method for a skiving tool

[0047] The present invention also includes a method for producing a skiving tool comprising the steps

[0048] A) Specifying a gear to be produced with a workpiece axis;

[0049] B) Specifying a position of a tool axis relative to the workpiece axis;

[0050] C) Calculating a body with several teeth conjugated to the gear to be produced for the specified relative position of the tool axis and the workpiece axis, so that the conjugated body rolls with the gear at every point when rotated about the tool axis and the gear rotation about the workpiece axis; D) Cutting the conjugated body with two different generating geometries for each tooth, so that intersection lines of the conjugated body with the generating geometries each define a right and a left cutting edge, which come into contact and / or out of contact with the gear to be produced in pairs at the same time when the gear is rotated about the workpiece axis and the conjugated body is rotated about the tool axis;

[0051] E) Manufacturing the skiving tool with the cutting edges determined in step D).

[0052] With this manufacturing method, a skiving tool according to the invention can be obtained which enables the machining method according to the invention to be carried out.

[0053] The teeth of the conjugate body are generally not initially limited along the tool axis. The cutting edges (and a rake face located between the respective right and left cutting edges) form the axial boundary, so that for each tooth of the conjugate body, a cutting tooth of the skiving tool is obtained.

[0054] In step D), the cutting edges of the cutting teeth are defined by intersecting the different generating geometries with the conjugate body. The generating geometries can be spherical surfaces or planes. This simplifies the process.

[0055] In principle, the two cutting edges of a cutting tooth are obtained by different generating geometries, which are not only rotated around the tool axis by a pitch angle between the teeth in question, but also exhibit additional variations, for example, being positioned differently along the tool axis and / or being inclined differently with respect to the tool axis and / or being of different geometric types (e.g., one is a plane and the other is a spherical surface). A pair of cutting edges that engage and / or disengage simultaneously can be formed by the cutting edges of a single cutting tooth or two different cutting teeth.

[0056] The fact that the engagement of the two cutting edges of a pair of cutting edges on the gear teeth ends and / or begins at the same time can be ensured by numerical methods, for example CAD-supported, by varying the position and / or orientation of the generating geometries.

[0057] For example, a plane as the generating geometry can be moved along the tool axis to define the left and right cutting edges of a cutting edge pair. Alternatively or additionally, planes can be used as the generating geometry to vary their inclination relative to the tool axis around one or two axes. Numerical simulation of the skiving process can identify axial positions and / or inclinations of the planes at which the start and / or end of contact occur simultaneously.

[0058] When spherical surfaces are used as generating geometries, the center point of the sphere can be shifted for the right and left cutting edges of a cutting edge pair, preferably along the tool axis, or alternatively or additionally in one or two directions perpendicular to it. Alternatively or additionally, the radius of the spherical surface can be changed. The center point of the spherical surface is thus not only rotated around the tool axis by a corresponding pitch angle, but an additional offset occurs and / or the radius of the spherical surface is changed. Even when spherical surfaces are used, numerical simulation of the power skiving process can be used to identify at which different spherical surfaces the start and / or end of contact occur simultaneously.

[0059] To define the two cutting edges of each of the cutting teeth, the two different generating geometries can each be rotated around the tool axis by the pitch angle of the cutting teeth of the skiving tool. This ensures that the cutting teeth each have the same shape. Alternatively, it is conceivable to use several groups of two different generating geometries to create groups of pairs of cutting edges on the skiving tool, with the cutting edges of different groups each having different contours. This can further improve the surface quality of the gear produced with the skiving tool.

[0060] After the production of the skiving tool (see step E), it can be used in a machining process according to the invention as described above.

[0061] Further features and advantages of the invention will become apparent from the claims, the description, and the drawings. According to the invention, the above-mentioned and further-described features can be used individually or in combination in any convenient way. The embodiments shown and described are not intended to be exhaustive, but rather are exemplary in nature for describing the invention.

[0062] Detailed the and

[0063] Fig. 1 shows a gear skiving operation of a gear with the relevant axes of movement, in a schematic representation;

[0064] Fig. 2 shows the toothing of Figure 1 and a body conjugated to the toothing, in a schematic representation;

[0065] Fig. 3 shows a prior art skiving tool in a schematic perspective view;

[0066] Fig. 4 shows a cutting tooth of a power skiving tool in an enlarged schematic perspective view;

[0067] Fig. 5 shows a first embodiment of a skiving tool according to the invention, in a schematic perspective view;

[0068] Fig. 6 shows a cutting tooth of the skiving tool of Fig. 5, in an enlarged schematic perspective view;

[0069] Fig. 7.1 to 7.5 show the development of the contact conditions between mutually facing tooth flanks of two adjacent teeth of a gearing of a workpiece and the two mutually facing cutting edges of a cutting tooth of a gear skiving tool according to the invention during the gear skiving machining according to the invention, in various schematic end sections with respect to the workpiece;

[0070] Fig. 8 shows a second embodiment of a skiving tool according to the invention, in a schematic perspective view;

[0071] Fig. 9 shows a schematic longitudinal section through a cutting tooth of the skiving tool of Figure 8;

[0072] Fig. 10 shows the course of the two cutting edges of a cutting tooth of the skiving tool of Figure 8 in relation to a normal plane of the tool axis, in a schematic perspective view;

[0073] Fig. 11 shows a schematic flow diagram of a method according to the invention for producing a gear skiving tool according to the invention;

[0074] Fig. 12 shows a flank line of a tooth of a gearing machined with a prior art skiving tool; Fig. 13 shows a flank line of a tooth of a gearing machined with a skiving tool according to the invention.

[0075] Figure 1 shows the kinematics of a gear skiving operation on a gear 10 of a workpiece 12 using a gear skiving tool 14. The workpiece 12, for example, has internal gears. Gear skiving of an externally geared workpiece is generally performed using the same movements. The kinematics illustrated in Figure 1 apply equally to gear skiving operations known from the prior art as well as to gear skiving operations according to the invention using gear skiving tools according to the invention.

[0076] For gear skiving, the toothed gear skiving tool 14 is brought into engagement with the gear 10 to be machined. The workpiece 12 with the gear 10 is rotated about a workpiece axis 16, as indicated by a double arrow 17. At the same time, the gear skiving tool 14 is rotated about a tool axis 18, as indicated by a double arrow 19. The respective rotational speeds are coordinated. During the coupled rotational movement, a feed movement 20 is executed, which typically runs along the workpiece axis 16.

[0077] The workpiece axis 16 and the tool axis 18 are skewed relative to each other. When projected onto a plane perpendicular to the common perpendicular of the axes 16, 18, an axis intersection angle 22 is established, which can, for example, be between 10° and 30°. Typically, the axes 16, 18 run parallel to the plane perpendicular to the common perpendicular; however, the axes 16, 18 can optionally also be inclined toward or away from each other, thus establishing an inclination angle (not shown in detail).

[0078] The peripheral speeds in the contact zone resulting from the rotations of the workpiece 12 and the gear skiving tool 14 are represented by an arrow 24 for the workpiece 12 and an arrow 26 for the gear skiving tool 14. The vectorial difference between these peripheral speeds 24, 26 results in a cutting speed 28. The feed rate of the feed movement 20 is generally negligible for the cutting speed. The feed movement 20 causes the machining to progress in the width direction 34 of the gearing along the tooth flanks 36, 38 with successive engagements of left and right cutting edges 30, 32. When passing through a tooth gap of the gearing 10, the two cutting edges 30, 32 of a respective cutting tooth 42 remove material from the mutually facing tooth flanks 36, 38, which border the tooth gap.

[0079] In gear skiving, the gear teeth 10 can be machined from a non-toothed workpiece. It is also possible to rework a pre-toothed workpiece 12 by gear skiving. Gear skiving can be performed, in particular, after the pre-toothed workpiece 12 has been hardened.

[0080] To determine the shape of the cutting edges 40 of the skiving tool 14, reference can be made to the so-called conjugate body 40 of the gear 10 to be produced (see Figure 2). The conjugate body 34 is an imaginary body defined by the fact that, in the axial configuration of the skiving operation to be performed, upon rotation about the tool axis 18 and upon rotation of the workpiece 12 about the workpiece axis 16, it would roll with the gear 10 (to be produced) at every point. After specifying the gear to be produced and the axial configuration for the skiving operation, the conjugate body can be calculated, for example, using numerical methods. The cutting edges 40 can be defined as intersection lines of the conjugate body 34 with generating geometries, for example, planes or spheres.

[0081] In prior art gear skiving tools 14, the right and left cutting edges 30, 32 of a cutting tooth 42 are defined by the same generating geometry. In the case of a straight-toothed gear skiving tool 14, a single plane perpendicular to the tool axis 18 can be used as the generating geometry for the cutting edges 30, 32 of all cutting teeth 42. Such a gear skiving tool 14 is shown in Figure 3.

[0082] Figure 4 shows an enlarged view of a cutting tooth 42 of a skiving tool. The following explanations of the structure of the cutting tooth 36 apply equally to skiving tools according to the invention and to those known from the prior art.

[0083] A rake face 44 is formed on the front side of the cutting tooth 42. A left cutting edge 30 delimits the rake face 44 from a left flank 46. During gear skiving, the cutting edge 30 removes material from the left tooth flanks 36 of the gearing 10. A right cutting edge 32 is used to machine the right tooth flanks 38 opposite each other at a tooth gap of the gearing 10 (see Figure 1). The right cutting edge 32 delimits the rake face 44 from a right flank 48. A rake face chamfer can be provided between each of the cutting edges 30, 32 and the rake face 44 (not shown in detail in Figure 4). A flank chamfer can be provided between each of the cutting edges 30, 32 and the respective flank surfaces 46, 48 (not shown in detail in Figure 4).

[0084] In the present invention, typically no cutting edge is formed on the head 49 of the cutting tooth 36. Rather, the cutting tooth is dimensioned in the area of ​​the head 50 such that the head 49 does not come into contact with the tooth base of the gear being machined.

[0085] Figure 5 shows a gear skiving tool 50 according to the invention for machining the gear teeth 10 of the workpiece 12 (see Figure 1 in this respect). The gear skiving tool 50 has straight teeth. Chipping surfaces 44 of cutting teeth 42 extend at an angle other than 90° to the tool axis 18. This creates a step-cut finish.

[0086] Figure 6 shows a cutting tooth 42 of the skiving tool 50. A left cutting edge 30 (when viewed from the tool axis 18 across the rake face 44) extends in a first plane, which corresponds to the associated generating geometry when intersecting with the conjugate body 40 (see Figure 2). A right cutting edge 32 extends in a second plane, which corresponds to the associated generating geometry when intersecting with the conjugate body 40. The planes of the two cutting edges 30, 32 are inclined relative to one another by a certain angle, for example, between 0.5° and 5°. The intersection points of the two planes with the tool axis 18 are therefore spaced apart from one another.

[0087] A left rake face chamfer 52 is provided between the left cutting edge 30 and the rake face 44. A right rake face chamfer 54 is provided between the right cutting edge 32 and the rake face 44.

[0088] Furthermore, a left flank chamfer 51 is provided between the left cutting edge 30 and the left flank 46. A right flank chamfer 53 is provided between the right cutting edge 32 and the right flank 48. The left flank chamfer 51 is wider than the right flank chamfer 53 in this case. The width of the right flank chamfer 53 increases from the root 55 of the cutting tooth 42 to its tip 49. The width of the left flank chamfer 51 continues to increase from the tip 55 of the cutting tooth 42 to the root 55.

[0089] The course of the cutting edges 30, 32 on the cutting teeth 42 is selected such that a left cutting edge 30 and a right cutting edge 32 simultaneously engage with the toothing 10 of the workpiece 12 during machining. Furthermore, the course of the cutting edges 30, 32 on the cutting teeth is selected such that a left cutting edge 30 and a right cutting edge 32 simultaneously disengage from the toothing 10 of the workpiece 12 during machining. The start and end of contact occur simultaneously in the sense that only a short time span of, for example, a maximum of 7 ps elapses between the start and end of contact on one and the other cutting edge 30, 32. Accordingly, a rotation angle around the tool axis 18 swept by the skiving tool 50 between the start or end of contact on one and the other cutting edge 30, 32 can be negligibly small and, for example, amount to a maximum of 0.07°.Furthermore, a feed path traveled by the skiving tool 50 between the start or end of contact on one and the other cutting edge 30, 32 relative to the workpiece 12 can be negligibly small and, for example, amount to a maximum of 7.5 pm.

[0090] Figure 7.1 illustrates, by way of example, how the left and right cutting edges 30, 32 of a cutting tooth 42 of a skiving tool 50 simultaneously engage directly adjacent teeth 56.1, 56.2 of the gearing 10 to be machined with their mutually facing tooth flanks 36, 38, here the left tooth flank 36 of tooth 56.1 and the right tooth flank 38 of tooth 56.2. It should be noted that the cutting edges 30, 32 generally only extend locally in the area of ​​contact with the tooth flanks 36, 38 in the cutting plane of the face cut relative to the workpiece 12.

[0091] During the machining process, the contact between the skiving tool 50 and the gear teeth 10 progresses along the cutting edges 30, 32 and the tooth flanks 36, 38, see Figures 7.2, 7.3 and 7.4.

[0092] Finally, the two cutting edges 30, 32 of the cutting tooth 42 simultaneously disengage from the right and left tooth flanks 36, 38 of the two teeth 56.1 and 56.2, see Figure 7.5.

[0093] In Figures 7.1 to 7.5, the representation is in the coordinate system of the skiving tool 50; the skiving tool 50 therefore appears stationary, although both the skiving tool 50 and the workpiece 12 rotate about the tool axis or workpiece axis.

[0094] During the machining process, this sequence is repeated for all facing tooth flanks 36, 38 on the immediately adjacent teeth. In the described variant, the left and right cutting edges 30, 32 of one of the cutting teeth 42 each form a pair of cutting edges 58, which simultaneously come into contact and out of contact with opposing tooth flanks 36, 38 of the gearing 10 to be machined.

[0095] Figure 8 shows a helical gear skiving tool 60 according to the invention for machining the gearing 10 of the workpiece 12 (see Figure 1 in this respect). Cutting teeth 42 of the gear skiving tool 60 each extend along a helical direction 62, which, in radial projection onto the tool axis 18, encloses an angle 64 with the tool axis 18, which can be, for example, at least 5° and at most 30°.

[0096] In the skiving tool 60, the two cutting edges 30, 32 of each of the cutting teeth 42 form a cutting edge pair 58, which simultaneously engages and disengages with the tooth flanks 36, 38 of immediately adjacent teeth 56 facing each other at a tooth gap of the toothing 10.

[0097] Figure 9 shows a longitudinal section through one of the cutting teeth 42 of the skiving tool 60.

[0098] Here, the left and right flank surfaces 46, 48 extend parallel to the helix direction 62, since the axial kinematics establish a kinematic clearance angle for each. Alternatively, the cutting tooth 42 could taper away from the cutting edges 30, 32 to increase the effective clearance angles.

[0099] In addition, flank chamfers 51, 53 are provided between the cutting edges 30, 32 and the flank surfaces 46, 48.

[0100] A rake face 44 of the cutting tooth 42 here runs in a rake face plane that is not orthogonal to the helix direction 62. An angle 66 between the rake face 44 and the helix direction 62 can be, for example, 110°. Wedge angles between the rake face 44 and the two flank surfaces 46, 48 therefore differ from one another. The workpiece axis 18 is also not aligned orthogonally to the rake face 44 here, but deviates from the rake face normal by at least 5°.

[0101] Between the rake face 44 and the two cutting edges 30, 32, rake face chamfers 52, 54 are arranged. In this case, a width 68 of the left rake face chamfer 52 is greater than a width 70 of the right rake face chamfer 54.

[0102] The two rake face chamfers 52, 54 are aligned such that the angles 72, 74 measured between each of the flank chamfers 51, 53 and the adjacent flank chamfer 52, 54 are approximately equal. Preferably, the angles 72, 74 differ from each other by a maximum of 10°. If no flank chamfers 51, 53 are provided, the angles 72, 74 are measured between the rake face chamfers 52, 54 and the adjacent flank 46, 48 (not shown in detail).

[0103] In the course of the cutting edges 30, 32, the widths 68, 70 of the rake face chamfers 52, 54 and their respective inclination relative to the rake face 44 can change, wherein preferably the same angles are maintained between the rake face chamfers 52, 54 and the respectively adjacent flank chamfer 51, 53 (or, if no flank chamfers are formed, the respectively adjacent flank 46, 48).

[0104] In the skiving tool 60, the two cutting edges 30, 32 lie on different spherical surfaces, which represent their respective generating geometry. This is illustrated in Figure 10. In addition to the cutting edges 30, 32, their respective projection onto a plane 76 orthogonal to the tool axis 18 is shown in dashed lines, wherein it can be seen that the two cutting edges 30, 32 run on different sides of the plane 76. Center points 78, 80 of the two spherical surfaces can lie on different sides of the plane 76, in particular on the side on which the associated cutting edge 30, 32 lies. Furthermore, the center points 78, 80 can have different distances from the tool axis 18. Radii 82, 84 of the two spherical surfaces also differ from one another, for example by at least 10%.

[0105] The process for obtaining a skiving tool 50, 60 according to the invention is outlined in Figure 11.

[0106] First, the geometry of a gear 10 to be produced is specified (see step 102). In a step 104, the skiving kinematics, in particular the position of a tool axis 18 relative to the workpiece axis 16, is specified. The number of cutting teeth 42 of the skiving tool 50, 60 to be manufactured can also be specified. From this information, in a step 106, the body 40 conjugated to the gear to be produced is calculated, so that the conjugated body rolls at every point of mutual contact with the gear upon rotation about the tool axis and rotation of the gear about the workpiece axis. A computer-aided process is typically used for this purpose.

[0107] In steps 108 and 110, the type of generating geometry can be specified for the left and right cutting edges 30, 32 of the gear skiving tool 50, 60 to be manufactured, for example, whether these should lie in planes or on spherical surfaces. The generating geometries are suitably parameterized. In a step 112, the two generating geometries are mathematically intersected with the conjugate body 40, so that the cutting edges 30, 32 of the cutting teeth 42 are obtained. For this purpose, the generating geometries are rotated about the workpiece axis 18 according to the number of cutting teeth 42. The parameters of the generating geometries are varied in step 112 until the cutting edges 30, 32, which depend on these parameters, come into and / or out of contact with the tooth flanks 36, 38 to be produced in pairs during rolling on the gearing 10. A numerical optimization method can be used for this purpose.

[0108] In a step 114, at least one gear skiving tool 50, 60 is produced with the profile of the cutting edges 30, 32 obtained from step 112. Figure 12 shows, for a gearing produced with a gear skiving tool 14 known from the prior art with left and right cutting edges 42 lying in a common plane, the profile of a tooth flank line 86 extending in the width direction 34, i.e. a position of the tooth flank measured in the circumferential direction 87 in comparison to a corresponding target position 88 (a larger scale is selected in the circumferential direction than in the width direction). It can be seen that the flank line 86 deviates significantly from the target position 88, particularly at its axial ends, in that local thickenings 90 are formed. This impairs the running behavior and durability of the gearing. The thickenings 90 result from the one-sided engagement of one of the cutting edges 30 or32, which leads to a deflection of the skiving tool and the workpiece against each other.

[0109] In contrast, Figure 13 shows a flank line 86 of a gear that was produced with a power skiving tool according to the invention, for example one of the power skiving tools 50, 60, using a machining method according to the invention. It can be seen that the flank line 86 runs essentially in the desired position 88. In particular, at the axial ends but also in the central region of the flank line 86, neither thickenings nor depressions can be seen. Due to the constant engagement of opposing cutting edges in pairs, the components of the respective contact forces that cause the skiving tool and workpiece to deflect are approximately canceled out, so that more precise machining is achieved. Only a slight, unavoidable waviness or roughness occurs in the flank line 86. With regard to running behavior and wear of the gearing, the course of the flank line 86 can be classified as very good.

[0110] In summary, the invention relates to the skiving of gear teeth. During the machining of the tooth flanks of the gear teeth, pairs of oppositely oriented cutting edges of a skiving tool simultaneously come into contact and / or out of contact with two oppositely oriented tooth flanks of the gear teeth. This reduces deflection effects and resulting machining inaccuracies. The two cutting edges of such a pair of cutting edges are defined by different generating geometries. In particular, the two cutting edges of a pair of cutting edges on the skiving tool do not run in the same plane or on the same spherical surface.

[0111]

[0112] Gearing 10

[0113] Workpiece 12

[0114] Gear skiving tool 14

[0115] Workpiece axis 16

[0116] Double arrow 17

[0117] Tool axis 18

[0118] Double arrow 19

[0119] Feed movement 20

[0120] Axle cross angle 22

[0121] Peripheral speed 24 (for the workpiece 12)

[0122] Peripheral speed 26 (for the skiving tool 14)

[0123] Cutting speed 28 left cutting edge 30 right cutting edge 32

[0124] Width direction 34 left tooth flank 36 right tooth flank 38 conjugated body 40

[0125] Cutting tooth 42

[0126] Chip surface 44 left flank 46 right flank 48

[0127] Head 49

[0128] Gear skiving tool 50 left flank chamfer 51 left rake face chamfer 52 right flank chamfer 53 right rake face chamfer 54

[0129] Foot 55 Tooth 56; 56.1, 56.2

[0130] Cutting edge pair 58

[0131] Gear skiving tool 60

[0132] Bevel direction 62

[0133] Angle 64 between tool axis 18 and bevel direction 62

[0134] Angle 66 between chip surface 44 and helix direction 62

[0135] Width 68 of the left rake face chamfer 52

[0136] Width 70 of the right rake face chamfer 54

[0137] Angle 72 between left flank chamfer 51 and left rake face chamfer 52

[0138] Angle 74 between right flank chamfer 53 and right rake face chamfer 54

[0139] Plane 76 orthogonal to tool axis 18

[0140] Center point 78 of the spherical surface of the left cutting edge 30

[0141] Center 80 of the spherical surface of the right cutting edge 32

[0142] Radius 82 of the spherical surface of the left cutting edge 30

[0143] Radius 84 of the spherical surface of the right cutting edge 32

[0144] Flank lines 86

[0145] Circumferential direction 87

[0146] Target position 88

[0147] Thickening 90

[0148] Recess 92

[0149] Specification 102 of a gear to be produced 10

[0150] Specification 104 of a rolling skiving kinematics

[0151] Calculate 106 the body 40 conjugated to the gear 10

[0152] Specifying 108 properties of a first generating geometry

[0153] Specifying 110 properties of a second generating geometry

[0154] Calculate 112 of cutting edges 30, 32

[0155] Manufacturing 114 of a skiving tool 50, 60

Claims

Patent claims 1. A skiving tool (50; 60) for machining tooth flanks (36, 38) of a gearing (10) of a workpiece (12), in that the skiving tool (50; 60) is rotated about a tool axis (18) and the workpiece (12) is rotated about a workpiece axis (16) running skewed to the tool axis (18), wherein the skiving tool (50; 60) and the workpiece (12) are displaced relative to one another with a feed movement (20) with a component along the workpiece axis (16), wherein the skiving tool (50; 60) has a plurality of cutting teeth (42) each with a left and a right cutting edge (30, 32), which cutting edges (30, 32) remove material from the mutually facing tooth flanks (36, 38) of a tooth gap of the Toothing (10), characterized in that the left and right cutting edges (30, 32) of a respective one of the cutting teeth (42) run on different spherical surfaces or in different planes.

2. Gear skiving tool (50; 60) according to claim 1, characterized in that a left chip surface chamfer (52) is formed between a chip surface (44) of a respective one of the cutting teeth (42) and its left cutting edge (30), and in that a right chip surface chamfer (54) is formed between the chip surface (44) of the respective cutting tooth (42) and its right cutting edge (32).

3. Gear skiving tool (50; 60) according to claim 2, characterized in that the right and left chip surface chamfers (52, 54) are of different widths and / or are inclined differently with respect to the chip surface (44).

4. Gear skiving tool (60) according to claim 2 or 3, characterized in that angles (72, 74) between the right and left chip surface chamfers (52, 54) and respective left and right flank surfaces (46, 48) or respective left and right flank surface chamfers (51, 53) of the cutting teeth (42) deviate from one another by at most 30°, in particular at most 15°.

5. A skiving tool (50; 60) according to any one of the preceding claims, characterized in that a rake face (44) of a respective one of the cutting teeth (42) extends in a rake face plane which extends at an angle deviating from 90° to a skew direction (62) of the cutting teeth (42).

6. Skiving tool (50; 60) according to claim 5, characterized in that the angle (66) between the rake face plane and the bevel direction (62) deviates from 90° by at least 5°, preferably at least 10°, particularly preferably at least 20°.

7. A method for machining tooth flanks (36, 38) of a gearing (10) of a workpiece (12) by gear skiving, in which a gear skiving tool, in particular a gear skiving tool (50; 60) according to one of the preceding claims, is brought into engagement with the gearing (10), wherein the gear skiving tool (50; 60) is rotated about a tool axis (18) and the workpiece (12) is rotated about a workpiece axis (16) running skewed to the tool axis (18), and wherein the gear skiving tool (50; 60) and the workpiece (12) are displaced relative to one another with a feed movement (20) with a component along the workpiece axis (16), wherein the gear skiving tool (50; 60) has a plurality of cutting teeth (42), each with a left and a right cutting edge (30, 32), characterized in that the cutting edges (30, 32) of pairs of cutting edges (58), each formed by one of the right-hand and one of the left-hand cutting edges (30, 32), each come into contact and / or out of contact with opposing tooth flanks (36, 38) of the toothing (10) at the same time.

8. Method according to claim 7, characterized in that the cutting edges (30, 32) which come into and / or out of contact at the same time are arranged directly adjacent to one another on the skiving tool (50; 60).

9. Method according to claim 7 or 8, characterized in that the right and left cutting edges (30, 32) of a respective Cutting edge pair (58) come into contact and / or out of contact with the opposing tooth flanks (36, 38) at the same axial position of workpiece (12) and skiving tool (50; 60) in the feed direction.

10. Method according to one of claims 7 to 9, characterized in that the right and left cutting edges (30, 32) of a respective pair of cutting edges (58) come into contact and / or out of contact with the opposing tooth flanks (36, 38) at the same rotational position of the skiving tool (50; 60) with respect to the tool axis (18).

11. Method according to one of claims 7 to 10, characterized in that the right and left cutting edges (30, 32) of a respective pair of cutting edges (58) come into contact and / or out of contact with the opposing tooth flanks (36, 38) at the same time.

12. Method according to one of claims 7 to 11, characterized in that the skiving machining is a hard finishing machining which is carried out after hardening of the toothing (10).

13. Method according to one of claims 7 to 12, characterized in that head sections of the cutting teeth (42) pass through the tooth gaps of the toothing (10) without touching the workpiece (12).

14. Method for producing a skiving tool (50; 60) comprising the steps A) specifying a gearing (10) to be produced with a workpiece axis (16); B) specifying a position of a tool axis (18) relative to the workpiece axis; C) Calculating a body conjugated to the toothing (10) to be produced, having a plurality of teeth, for the predetermined relative position of the tool axis (18) and the workpiece axis, so that the conjugated body rolls with the toothing (10) at every point when rotating about the tool axis (18) and rotating the toothing (10) about the workpiece axis (16); D) for each tooth, cutting the conjugate body (40) with two different generating geometries, so that intersection lines of the conjugate body with the generating geometries each define a right and a left cutting edge (30, 32), which come into contact and / or out of contact in pairs with the toothing (10) to be produced when the toothing (10) is rotated about the workpiece axis (16) and the conjugate body (40) is rotated about the tool axis (18); E) Manufacturing the skiving tool with the cutting edges determined in step D).

15. Method according to claim 14, characterized in that the generating geometries are spherical surfaces or planes.

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