Skiving tool and method for machining gear tooth flanks

Abstract

The present invention relates to the machining of gears by skiving, in which machining marks are generated at unequal intervals. For this purpose, at least some cutting edges of the skiving tool extend at least partially to different heights along the tool axis of the skiving tool. During machining, cutting edges located at different axial heights relative to the workpiece axis act sequentially on the tooth flank. Therefore, the engagement of the cutting edges occurs at different time intervals and at different intervals across the width of the tooth flank. Therefore, the effect of the engagement of the cutting edges on the machining process and the excitation of vibrations during use of the manufactured gear have a frequency spectrum with a wider width and lower amplitude than in the case of engagement of the cutting edges that are equidistant in time and space. In particular, the more irregular surface structure of the manufactured gear can have a positive effect on the noise excitation behavior when the gear engages with a mating gear.

Description

[Technical Field]

[0001] The present invention relates to a skiving tool for machining the tooth flanks of a gear on a workpiece. The skiving tool rotates about a tool axis and the workpiece rotates about a workpiece axis extending obliquely to the tool axis, thereby displacing the skiving tool and the workpiece relative to each other by a feed motion having a component along the workpiece axis. The skiving tool has multiple cutting edges that sequentially remove material from the same tooth flank when machining the workpiece. The present invention also relates to a method for machining the tooth flanks of a gear on a workpiece by skiving, by engaging the skiving tool with the gear. The skiving tool rotates about the tool axis and the workpiece rotates about a workpiece axis extending obliquely to the tool axis, thereby displacing the skiving tool and the workpiece relative to each other by a feed motion having a component along the workpiece axis. [Background technology]

[0002] Such skiving tools and skiving methods are known in principle, for example from EP 3528989 or EP 2537616 A1.

[0003] Various methods are known for producing gears. Cutting methods include, for example, milling, hobbing, profile grinding, or generating grinding. So-called skiving is a continuous cutting method for machining gears. The essential fundamentals and terminology of skiving are explained, for example, in EP 3528989. Skiving allows the precise production of not only external gears but also internal gears.

[0004] In skiving, the skiving tool rotates about a tool axis and the workpiece rotates about a workpiece axis that extends obliquely relative to the tool axis. Simultaneously, a feed motion is performed, which typically runs along the workpiece axis. The skiving tool has multiple cutting edges. The rake face is typically located on one end face of the skiving tool, and the flank face typically extends axially or at an angle relative to the workpiece axis.

[0005] During skiving, the engagement of the cutting blades is discrete, resulting in machining marks, so-called feed marks. In known methods, these feed marks are equally spaced from one another. When a gear is rolled with a meshing gear, the equally spaced feed marks can lead to uniform excitation vibrations, which is disadvantageous in terms of noise generation.

[0006] From German Patent Application Publication No. 112017000162T5 it is known that the cutting edges of a skiving tool can be arranged at different axial heights, so that together they form cutting edge sections for forming the tooth flank of a workpiece gear. First, the first roughing edge, then the second roughing edge, and finally the finishing edge contact the workpiece. In this way, rough machining and fine machining of the workpiece gear are carried out successively. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent No. 3528989 [Patent Document 2] European Patent Application Publication No. 2537616 [Patent Document 3] German Patent Application Publication No. 112017000162T5 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to enable noise-optimized gear skiving. [Means for solving the problem]

[0009] This problem is solved according to the invention by a skiving tool having the features set forth in claim 1 and a method according to claim 15. Advantageous embodiments or variants are set forth in the respective dependent claims and in the following description.

[0010] Skiving tool according to the present invention

[0011] According to the present invention, a skiving tool for machining the tooth flank of a gear on a workpiece is provided. To machine the tooth flank, the skiving tool rotates about a tool axis, the workpiece rotates about a workpiece axis extending obliquely relative to the tool axis, and the skiving tool and workpiece are displaced relative to each other by a feed motion having a component along the workpiece axis. Due to axis kinematics, the feed motion also has a component along the tool axis. Typically, the feed motion is performed parallel to the workpiece axis.

[0012] A skiving tool has multiple cutting edges that sequentially remove material from the same tooth surface during machining of a workpiece. The cutting edges are the blades of the skiving tool that cut and remove material from the tooth surface of the workpiece, in this case, the gear of the workpiece, during machining. All cutting edges can act on each tooth surface during machining, or only some of the cutting edges can act on each tooth surface.

[0013] According to the invention, it is envisaged that at least two of the cutting blades for machining the same tooth flank are arranged at different heights along the tool axis. The distance measured along the tool axis between corresponding points on cutting blades arranged at different axial heights at at least one radial distance from the tool axis is at least 5 μm, in particular at least 10 μm, and at most 0.5 mm, in particular at most 0.3 mm. The axial distance between the offset cutting blades is preferably at least 20 μm, particularly preferably at least 30 μm, and / or preferably at most 0.2 mm, particularly preferably at most 0.15 mm. In particular, the respective linear centers of the cutting blades arranged at different axial heights along the tool axis are offset from one another by at least 5 μm, preferably at least 10 μm, particularly preferably at least 20 μm, very particularly preferably at least 30 μm, and / or at most 0.5 mm, preferably at most 0.3 mm, particularly preferably at most 0.2 mm, and very particularly preferably at most 0.15 mm.

[0014] The axially offset cutting blades are used to machine the tooth flanks of the same name (i.e., the left flank or the right flank, respectively). To machine the tooth flanks of the workpiece, the cutting blades of the skiving tool engage the tooth gaps of the workpiece gear.

[0015] During machining of each tooth flank, multiple cutting blades act on the tooth flank in sequence to remove material therefrom. At least two cutting blades are offset from one another in the axial direction of the tool axis so that engagement on each tooth flank occurs at different time intervals rather than at the same time. Similarly, engagement on each tooth flank occurs at different spatial intervals rather than at the same time, for example, measured across the width of the tooth flank.

[0016] This means that the engagement shocks during machining are not repeated at a single frequency, but rather across a wider frequency spectrum. This reduces the vibrations that occur during machining and reduces the influence of the machining process between the skiving machine with the skiving tool and the workpiece with the gear. Overall, the machining process is smoother and more stable.

[0017] On the other hand, the spatial variation in engagement of the cutting edges results in different spacing of feed marks or machining marks across the tooth flank. In other words, the tooth flank will have (unavoidable) waviness, the wavelength of which is not a single one, but a spectrum of wavelengths. When a gear rolls against a mating gear, single-frequency vibrations are avoided, and instead broadband noise vibrations are generated. This results in a better, and in particular smoother, rolling behavior. In particular, the excitation of vibrations at resonant frequencies can be avoided. Overall, gears manufactured using the skiving tool according to the present invention have optimized NVH (noise, vibration, harshness) characteristics.

[0018] Cutting edges arranged at different axial heights essentially have different positions in the direction of the tool axis even when they are at the same distance from the tool axis, apart from individual points where the cutting edges are inclined relative to one another. Preferably, two cutting edges arranged at different axial heights do not have the same axial position along the tool axis at any distance from the tool axis.

[0019] Axially offset cutting edges generally do not have the same shape (identical geometric shape). This is a consequence of the fact that the conjugate of the gear to be produced is usually not cylindrical. The conjugate is a (virtual) body that rolls with the gear (to be produced) at each point when the skiving tool rotates about the tool axis in the axial configuration of the intended skiving process, and when the workpiece rotates about the tool axis. Therefore, the offset cutting edges can be adapted accordingly in their profile to produce a gear with the desired geometric properties.

[0020] The geometrical cutting edge shape can be considered or defined as being generated by the geometrical intersection of the conjugate of the gear to be manufactured with the shape of the respective cutting edge. The simplest generating geometrical shape is a plane. Alternatively, the generating geometrical shape can be, for example, a sphere. Other generating geometrical shapes are also conceivable. To define an offset cutting edge, a similar generating geometrical shape can be offset in the tool axis direction and then intersect with the conjugate.

[0021] Preferably, the skiving tool is used in the machining method according to the invention as described below. Also included within the scope of the invention is the use of the skiving tool according to the invention for machining the tooth flanks of gears, in particular in the machining method according to the invention.

[0022] The skiving tool can have other cutting edges used to machine other tooth flanks located on the opposite side of the (first) tooth flank in the tooth gap of each gear. In particular, while one of the (first) cutting edges is engaged with one of the first tooth flanks, an associated other cutting edge can be engaged with another tooth flank.

[0023] At least two further cutting edges are preferably arranged at different axial heights at at least one radial distance from the tool axis. The distance between corresponding points on the at least two further cutting edges, measured along the tool axis, is at least 5 μm, particularly at least 10 μm, preferably at least 20 μm, particularly preferably at least 30 μm, and at most 0.5 mm, particularly at most 0.3 mm, preferably at most 0.2 mm, particularly preferably at most 0.15 mm. Typically, during machining, the (first) cutting edge first engages with the (first) tooth flank, and while the first cutting edge removes material from the first tooth flank, the other cutting edge can also engage with another tooth flank located on the opposite side in the gear tooth gap. The further cutting edges can be arranged relative to each other in the same way as the (first) cutting edge and can be designed accordingly.

[0024] Skiving tools can be used to machine workpieces with straight or inclined (helical) teeth. Skiving tools can be cylindrical or conical.

[0025] In a preferred embodiment, cutting edges located at different axial heights are offset parallel to one another, such that the offset edges are spaced the same distance apart (measured along the tool axis) regardless of their distance from the tool axis, which can simplify the design and manufacture of skiving tools.

[0026] In an alternative embodiment, cutting edges positioned at different axial heights are inclined relative to one another. In this case, the offset cutting edges increase or decrease their distance from one another, measured along the tool axis, as the distance from the tool axis increases. At certain distances from the tool axis, there may be no distance. However, at other times, the cutting edges extend at different axial heights relative to the tool axis. This causes the distance between two feed marks generated by the cutting edges to change. In other words, adjacent feed marks move closer to or further away from one another. The feed marks may even intersect in some cases. Gears produced with this skiving tool exhibit particularly smooth rolling behavior.

[0027] An advantageous embodiment of the skiving tool is that the cutting edges, which are arranged at different axial heights, extend in the same plane. The cutting edges are usually curved in one dimension in the respective plane. This can simplify the design and manufacture of the skiving tool.

[0028] In an alternative embodiment, it is envisaged that the cutting edges arranged at different axial heights extend in a two-dimensional curve. In particular, hollow grinding can be set up in this way, which can have a beneficial effect on chip formation.

[0029] A preferred development of this embodiment is characterized in that cutting edges arranged at different axial heights extend with different curvatures when projected onto respective planes containing the tool axis and rotated by the angular increment between the cutting edges. This allows the distance between the feed traces of two cutting edges to be variable. In other words, adjacent feed traces move closer to or further away from each other. The feed traces can intersect in some cases. Furthermore, the shape of the differently curved cutting edges allows for adaptation to conjugates. Each projection plane can pass through a specific point of each cutting edge, for example, the radially innermost point, the radially outermost point, or an intermediate point.

[0030] Cutting edges arranged at different axial heights can be assumed to extend with different curvatures when projected onto a plane perpendicular to the tool axis, which can influence the shape of the gear to be manufactured. In particular, cutting edges arranged at different heights can be achieved to generate the same tooth profile. In other words, the various projections of the cutting edges allow for adaptation to conjugates.

[0031] In a preferred embodiment, all cutting edges of the skiving tool are arranged at different heights along the tool axis, i.e., all cutting edges have individual axial positions, which allows for the generation of feed marks with different spacing on the tooth flanks, in particular wide patterns of feed marks.

[0032] An alternative embodiment is characterized in that the cutting blades of the skiving tool are divided into multiple groups, and corresponding cutting blades of different groups are arranged at the same height along the tool axis. This can simplify the design and manufacture of the skiving tool. This embodiment is useful when each tooth flank is machined by cutting blades of only one group. Repeated patterns of feed marks are generated on each tooth flank, the number of which corresponds to the number of cutting blades per group.

[0033] Preferably, all the cutting edges of each group are arranged at different heights along the tool axis, i.e., all the cutting edges of one group have individual axial positions, which allows for the generation of feed marks with different spacings on the tooth flanks, in particular for a wide pattern of feed marks.

[0034] In an advantageous embodiment, at least three of the cutting blades for machining the same tooth flank are arranged at different heights along the tool axis. Here, the second cutting blade is arranged at a different height relative to the first cutting blade in a first direction along the tool axis, and the third cutting blade is arranged at a different height relative to the second cutting blade in a second direction opposite the first direction, preferably also at a different height relative to the first cutting blade in the second direction. The cutting blades are referred to as the first, second, and third cutting blades. During machining, they sequentially engage the flanks of the respective teeth as the first, second, and third cutting blades. In other words, the first, second, third, etc. cutting blades directly engage the respective tooth gaps sequentially and remove material from the adjacent tooth flanks. Using this skiving tool, feed marks with alternating increasing and decreasing spacing are generated across the width of the tooth flank. This has proven particularly advantageous in terms of rolling behavior and noise generation.

[0035] The cutting edges that are offset from one another in the axial direction can also be offset from one another in the radial direction of the tool axis. In particular, the radially outer tips of the respective cutting edges have different distances from the tool axis. Furthermore, the cutting edges have corresponding spatial paths. This allows for easy adaptation to conjugates.

[0036] Cutting edges that are axially offset from one another can have a different circumferential pitch than cutting edges located at the same height. This is another way to fit the conjugate. The difference in pitch can be used to consider that each axially offset cutting edge engages earlier or later in time. The time offset corresponds to a change in the rotational position of the skiving tool (angular offset at engagement) compared to a skiving tool with cutting edges that are not axially offset. The angular offset allows the cutting edges to be turned in the opposite direction. Different pitches on axially offset cutting edges are particularly useful for skiving tools for machining inclined teeth.

[0037] Processing method according to the present invention

[0038] The scope of the present invention includes a method for machining the tooth flank of a gear of a workpiece by skiving, by engaging a skiving tool with the gear. Here, the skiving tool rotates about a tool axis, the workpiece rotates about a workpiece axis extending obliquely to the tool axis, and the skiving tool and workpiece are displaced relative to each other by a feed motion having a component along the workpiece axis. The skiving tool is preferably a skiving tool according to the present invention described above. Due to the axis kinematics, the feed motion also has a component along the tool axis. Typically, the feed motion is performed parallel to the workpiece axis. The speed of the feed motion is typically constant. The axis crossing angle between the tool axis and the workpiece axis is at least 5°, preferably at least 10°, particularly preferably at least 15°, and / or at most 50°, preferably at most 40°, particularly preferably at most 30°.

[0039] The machining method according to the present invention is characterized in that at least two cutting edges of a skiving tool, which sequentially (e.g. directly) machine the same tooth flank, are arranged at different heights along the tool axis. The distance, measured along the tool axis, between corresponding points on cutting edges arranged at different axial heights at at least one radial distance from the tool axis is at least 5%, in particular at least 10%, and at most 95%, in particular at most 90% of the feed path of the feed movement in which the skiving tool and the workpiece are moved relative to each other along the workpiece axis during machining of the same tooth flank by the cutting edges arranged at different axial heights. The feed path between two directly consecutive cutting edge engagements on the same tooth flank can be, for example, between 50 μm and 150 μm.

[0040] The offset of successive cutting edges on the same tooth flank changes the spacing between the feed marks produced. If subsequent cutting edges are offset in the feed direction, the distance between the feed marks increases. If subsequent cutting edges are offset against the feed direction, the distance between the feed marks decreases. The offset cutting edges typically directly engage with the respective tooth gaps of the tooth flank to be machined. In other words, machining is performed such that the axially offset cutting edges remove material directly and sequentially on the respective tooth flanks. In skiving tools, the offset cutting edges are typically not positioned directly adjacent to each other; rather, depending on the cutting sequence (depending on the workpiece and the number of teeth on the skiving tool), one or more cutting edges of the skiving tool can be located between cutting edges that directly and sequentially operate on the same tooth flank.

[0041] On the other hand, the different, preferably irregularly spaced, feed traces improve the rolling behavior of the gear. In particular, single-frequency vibrations are avoided, and instead vibrations with a broader frequency spectrum and lower amplitudes are excited. This improves the noise and vibration behavior. On the other hand, since the engagement impacts of the cutting edges occur at different time intervals, a smoother and more stable course of the machining behavior is obtained. In particular, vibrations resulting from fluctuations in cutting forces, which have a negative effect on the machining process, are reduced.

[0042] Typically, the workpiece rotates exactly one revolution between successive offset cutting edges cutting the same tooth flank. In this case, the skiving tool can perform the rotation more than one revolution (possible when machining internal or external gears) or less than one revolution (possible only when machining external gears). Typically, the skiving tool does not perform one complete revolution between cutting the same tooth flank. This allows another cutting edge, especially one of the axially offset cutting edges, to remove material from each tooth flank.

[0043] The skiving with the cutting blades arranged at different axial heights can be the final material removal, in particular the final cutting operation, of the gear tooth flank in the manufacturing method. The skiving with the cutting blades arranged at different axial heights can be the final machining operation of the gear tooth flank in particular. Alternatively, the skiving with the cutting blades arranged at different axial heights can be followed by a chemical, physical and / or thermal surface treatment, such as hardening. In this case, the surface geometry of the tooth flank is usually not changed.

[0044] In a preferred variant, the machining with the skiving tool having cutting edges arranged at different axial heights is a hard-machining carried out after hardening the gear, the machining marks of which are retained in the finished workpiece, so that the advantages of the method according to the invention are particularly evident in the use of the manufactured gear.

[0045] Typically, gears, for example, are machined in a soft state before hardening. This soft machining can be performed, for example, by milling, hobbing, form grinding, or preferably by skiving. The soft machining can be performed using the method according to the present invention and / or the skiving tool according to the present invention. In this respect, the present invention relates to a manufacturing method including soft machining, hardening, and hard precision machining, and the method according to the present invention can be used for the soft machining and / or hard precision machining.

[0046] In an alternative advantageous method variant, the machining using a skiving tool with cutting edges arranged at different axial heights is a soft machining without further material removal, in particular without further cutting, of the tooth flank. Therefore, the surface structure of the tooth flank created during soft machining is maintained in the finished workpiece. Soft machining can extend the service life of the skiving tool compared to hard machining. Soft machining with a skiving tool with cutting edges arranged at different axial heights can be followed by a chemical, physical, and / or thermal surface treatment, in particular hardening. For example, the tooth flank or the entire workpiece can be nitrided. In this respect, the present invention relates to a manufacturing method comprising soft machining performed using the method according to the present invention and a subsequent non-removing surface treatment, in particular hardening, of the tooth flank. In this manufacturing method, no material-removing hard machining is performed after the non-invasive surface treatment. In this variant, a hardening method, such as nitriding, is applied, which essentially causes only minor distortions, thereby eliminating the need for corrective post-processing.

[0047] In a preferred method variant, cutting edges arranged at different axial heights produce continuous machining marks on the tooth flanks, the spacing between which increases and decreases in a repeating pattern across the tooth width. For this purpose, each tooth flank is machined multiple times with the same cutting edge or with similarly offset cutting edges. The pattern can include, for example, at least five, preferably at least 10, and particularly preferably at least 20 consecutive machining marks (feed marks). Within the pattern, the spacing between the machining marks can increase and decrease continuously or, in particular, irregularly, multiple times. The implementation of the method for generating a repeating pattern can simplify the design and manufacture of skiving tools. Furthermore, if the pattern width is sufficiently wide, the advantages of the present invention can already be fully utilized in both the use of the gear and the execution of the machining method. Therefore, a larger number of machining marks in the pattern results in only a relatively small improvement.

[0048] Other features and advantages of the present invention will become apparent from the following description, the claims and the drawings. According to the present invention, the above-mentioned features and those further described below can be used either alone or in any suitable combination. The illustrated and described embodiments should not be understood as an exhaustive list, but rather have an exemplary character for explaining the present invention. The invention is illustrated in the drawings and will be explained in more detail on the basis of exemplary embodiments, which show: [Brief explanation of the drawings]

[0049] [Figure 1] FIG. 1 is a schematic diagram showing the skiving of a gear with associated axes of motion. [Figure 2] FIG. 2 is a schematic diagram of the gear of FIG. 1 and a conjugate for the gear. [Figure 3] FIG. 1 is a schematic perspective view of a skiving tool according to the prior art. [Figure 4] FIG. 1 is a schematic perspective view showing an enlarged view of the cutting teeth of a skiving tool. [Figure 5] 1 is a schematic diagram showing the position of the cutting edge along the tool axis in a prior art skiving tool. FIG. [Figure 6] FIG. 1 is a schematic diagram showing the engagement row of cutting edges on a tooth flank during skiving according to the prior art. [Figure 7] FIG. 1 is a schematic diagram of machining marks on a tooth surface during skiving according to the prior art. [Figure 8] FIG. 1 is a schematic perspective view of a skiving tool according to the present invention with cutting edges randomly offset along the tool axis. [Figure 9] 9 is a schematic diagram of the positions of cutting edges sequentially acting on tooth flanks relative to their nominal positions along the tool axis in the skiving tool of FIG. 8. FIG. [Figure 10] 9 is a schematic diagram showing the engagement row of cutting edges on the tooth flank during skiving according to the present invention using the skiving tool of FIG. 8 as an example. [Figure 11] 9 is a schematic diagram of machining marks on a tooth surface during skiving according to the present invention, for example using the skiving tool of FIG. 8. FIG. [Figure 12] 1 shows the profile of the cutting teeth of a skiving tool according to the invention, the cutting edges extending in a plane perpendicular to the tool axis. [Figure 13a] 1 shows the profile of the cutting teeth of a skiving tool according to the invention, the cutting edges extending in a plane inclined relative to the tool axis. [Figure 13b] 1 is a diagram showing the profile of the cutting teeth of a skiving tool according to the present invention, in which the cutting edges extend in a two-dimensional curve from a plane perpendicular to the tool axis. [Figure 14] FIG. 1 is a schematic perspective view of a skiving tool according to the present invention with multiple groups of cutting edges offset along the tool axis. [Figure 15] 1 is a schematic diagram of the positions of the cutting edges acting sequentially on the tooth flanks, randomly offset in groups, shown relative to the nominal position along the tool axis in a skiving tool according to the present invention; FIG. [Figure 16] 1 is a schematic diagram of the positions of the cutting edges acting sequentially on the tooth flanks, regularly and randomly offset in groups, shown relative to the nominal position along the tool axis in a skiving tool according to the present invention. [Figure 17] 1 is a schematic diagram of the machining marks on the tooth flank during skiving according to the present invention, where the spacing between two adjacent machining marks varies over the height of the gear. [Figure 18] 1 is a schematic diagram of intersecting machining marks on a tooth surface during skiving according to the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0050] 1 shows the kinematics of skiving a gear 10 on a workpiece 12 with a skiving tool 14. Here, the workpiece 12 exemplarily has an internal gear. Skiving a workpiece with an external gear is performed essentially with the same motion. The kinematics shown in FIG. 1 apply equally to skiving known from the prior art and to skiving according to the invention with a skiving tool according to the invention.

[0051] To skive, a toothed skiving tool 14 engages with the gear 10 to be machined. The workpiece 12 with the gear 10 rotates about a workpiece axis 16, as indicated by the double arrow 17. At the same time, the skiving tool 14 rotates about a tool axis 18, as indicated by the double arrow 19. The respective rotational speeds are coordinated with one another. During the coupled rotational movement, a feed motion 20 is performed, which typically proceeds along the workpiece axis 16.

[0052] The workpiece axis 16 and the tool axis 18 are inclined relative to one another. When the axes 16, 18 are projected onto a plane perpendicular to a common vertical line, an axis crossing angle 22 is established, for example, in the range of 10° to 45°. Typically, the axes 16, 18 extend parallel to the plane perpendicular to the common vertical line, but optionally the axes 16, 18 can be inclined toward or away from one another, thereby establishing an inclination angle (not shown in detail).

[0053] The peripheral speeds at the contact area resulting from the rotation of the workpiece 12 and the skiving tool 14 are indicated by arrow 24 for the workpiece 12 and arrow 26 for the skiving tool 14. The difference between these vector peripheral speeds 24, 26 results in a cutting speed 28. The feed rate of the feed motion 20 is typically negligible compared to the cutting speed. The feed motion 20 advances the cutting along the tooth flank 32, continuously engaging the cutting edge 40 in the tooth width direction 54.

[0054] Skiving allows the production of a gear 10 from a toothless workpiece. Skiving can also be used to post-machine a pre-toothed workpiece 12, in particular after the pre-toothed workpiece 12 has been hardened.

[0055] To determine the shape of the cutting edge 40 of the skiving tool 14, the so-called conjugate 34 of the gear 10 to be manufactured can be referenced, see Fig. 2. The conjugate 34 is an imaginary body that is defined by rolling together with the (manufactured) gear 10 at each point when it rotates about the tool axis 18 and when the workpiece 12 rotates about the workpiece axis 16 in the axial configuration of the skiving operation to be performed. The cutting edge 40 can be defined as the intersection of the conjugate 34 with the generating geometry, for example a plane or a sphere.

[0056] In prior art skiving tools 14, all cutting teeth are arranged at the same height along the tool axis 18. In the simplest case, the generating geometry can be the same plane perpendicular to the tool axis 18 for all teeth of the skiving tool 14. Such a skiving tool 14 known from the prior art is shown in FIG.

[0057] In Figure 4, the cutting teeth 36 of the skiving tool are shown enlarged. The following description of the structure of the cutting teeth 36 applies equally to skiving tools known from the prior art as well as to the skiving tool according to the invention.

[0058] A rake face 38 is formed on the end face of the cutting tooth. A (first) cutting edge 40 separates the rake face 38 from a (first) flank face 42. During skiving, the cutting edge 40 removes material from the first tooth flank 32 of the gear 10. Another cutting edge 44 is used to machine a further tooth flank 45 that faces the gear 10 in the tooth gap (see FIG. 1). The other cutting edge 44 separates the rake face 38 from another flank face 46. A tip cutting edge 48 for machining the root region of the gear 10 may be formed at the tip of the cutting tooth 36 adjacent to the tip flank face 47. A rake chamfer may be provided between each of the cutting edges 40, 44, 48 and the rake face 38 (not shown in detail). A flank chamfer may be provided between each cutting edge 40, 44, 48 and the respective flank 42, 46, 47 (not shown in detail).

[0059] As already explained, in skiving tools 14 known from the prior art, the cutting edges 40 are arranged at the same height along the tool axis 18. This is shown in FIG. 5 for cutting edges 40 acting sequentially on tooth flanks 32. The tooth flanks 32 are machined sequentially by, here, 20 cutting edges 40, for example. In skiving tools 14 with cutting edges 40 arranged at the same height, these cutting edges 40 (here, for example, the first cutting edge 40.1, the second cutting edge 40.2, and the third cutting edge 40.3) engage the tooth flank 32 to be machined at equal intervals 50, see FIG. 6. Thus, machining marks (feed traces) 52 extend equally spaced across the tooth flank 32, see FIG. 7. Adjacent machining marks 52 are offset parallel to each other in the width direction 54. Similar machining marks are also generated on the remaining tooth flanks of the gear 10. As a result, vibrations of a single frequency occur during operation of the manufactured gear 10, depending on the rotation speed.

[0060] Figure 8 shows a skiving tool 60 of the invention according to a first embodiment, in which the cutting edges 40 (and further cutting edges 44) are offset from one another along the tool axis 18. Figure 9 shows the axial offset of exemplary 20 cutting edges 40 that sequentially remove material from one tooth flank 32 to be machined. In the skiving tool 60, the cutting edges 40 that act directly and sequentially on the same tooth flank 32 are typically not directly adjacent to one another (due to the different ratios of the respective numbers of teeth of the skiving tool 60 and the workpiece 12).

[0061] Some of the cutting teeth 40 are offset forward in the direction of the feed motion 20 along the tool axis 18 (vertical axis in FIG. 9 ) relative to their nominal position (height on the horizontal axis) in the direction of the feed motion 20, and some of the cutting teeth 40 are offset backward in the opposite direction to the direction of the feed motion 20. The height offset 62 between the cutting teeth 40 that act sequentially on the observed tooth flank 32 can be, for example, 10 μm to 80 μm. FIG. 9 exemplarily shows the height offset 62 between the fourth and fifth cutting edges 40 that act on the observed tooth flank 32. In the illustrated exemplary embodiment, this can be 60 μm. For other pairs of sequentially acting cutting edges 40, other values ​​of the height offset 62 occur within the aforementioned range.

[0062] 9 shows that some of the cutting edges 40 that subsequently act on the tooth flank 32 vary in the direction of offset relative to the previously engaged cutting edge 40. For example, the third cutting edge is offset further in the direction of the feed motion 20 relative to the nominal position than the second cutting edge. In contrast, the fourth cutting edge is offset in the opposite direction relative to the third and second cutting edges. The same applies to the sixth, seventh, and eighth acting cutting edges, and, with opposite signs, to the twelfth, thirteenth, and fourteenth cutting edges, or the fifteenth, sixteenth, and seventeenth cutting edges. This allows particularly irregular spacing of the machining marks to be obtained.

[0063] 10 shows a schematic representation of the sequential engagement of cutting edges 40 according to the invention (here, by way of example, a first cutting edge 40.1, a second cutting edge 40.2, and a third cutting edge 40.3) with the tooth flank 32 under observation during skiving, for example, using a skiving tool 60. In FIG. 10, the axial position of the first cutting edge 40.1 along the tool axis 18 is selected as the reference point. For orientation purposes, the engagement situation on a skiving tool 14 with cutting edges arranged at the same height is shown in dashed lines (a virtual second cutting edge arranged at the height of the first cutting edge 40.1 is labeled 40.2′). The distance between the cutting edge 40.1 and the virtual cutting edge 40.2′ thus corresponds to the feed path 64 between two successive engagements of the cutting edges on the same tooth flank 32.

[0064] In the illustrated example, the second cutting edge 40.2 is offset forward in the direction of the feed motion 20 along the tool axis 18. Thus, a first distance 66.1 measured in the width direction 54 of the tooth flank 32 between the engagement points of the first cutting edge 40.1 and the second cutting edge 40.2 is greater than the feed path 64. If, as shown in FIG. 10 , the third cutting edge 40.3 were positioned at the height of the first cutting edge 40.1 along the tool axis 18, the second distance 66.2 between the second cutting edge 40.2 and the third cutting edge 40.3 would be less than the feed path 64 and less than the first distance 66.1.

[0065] The feed path 64 between the engagement of two cutting edges on the observed tooth flank 32 may be, for example, 100 μm. Thus, the height offset 62 in this exemplary embodiment is between 10% and 80% of the feed path 64.

[0066] In the skiving tool 60, the cutting edges 40 are randomly offset along the tool axis 18. In particular, all cutting edges 40 can be located at different heights along the tool axis 18. The corresponding machining marks on the tooth flank 32 are shown in FIG.

[0067] When the cutting edges 40 are offset parallel to one another, adjacent machining marks 52 are offset parallel to the width direction 54. However, the spacing between adjacent machining marks 52 will vary depending on the height offset between the cutting edges 40 that created those machining marks.

[0068] Corresponding machining marks are produced on the remaining tooth flanks of the gear 10. As a result, the manufactured gear 10 will vibrate over a wide frequency spectrum during operation, depending on the rotational speed.

[0069] The height offset 62 between the cutting edges 40 can be measured at a selected radial distance from the tool axis 18. In particular, one can note the line center 68 of each of the cutting edges 40. The line center 68 divides each cutting edge 40 into two cutting edge sections of equal length. See FIG. 12.

[0070] 12 further illustrates that each cutting edge 40 (and associated further cutting edges 44, and possibly leading cutting edges 48) can extend within a plane 70. In this case, cutting edges 40 extend essentially curvedly within this plane 70. Plane 70 corresponds to the generating geometry that defines cutting edges 40 by their intersection with conjugates 34 (see FIG. 2).

[0071] The planes 70 may be oriented perpendicular to the tool axis 18. In particular, the cutting edges 40 may extend parallel and offset from one another within the parallel planes 70.

[0072] However, it is also conceivable that the plane 70 in which one of the cutting edges 40 extends is inclined relative to the tool axis 18. In particular, different inclinations of the respective planes 70 can be set for cutting edges 40 of different heights.

[0073] 13a exemplarily shows that cutting edge 40 (and associated further cutting edge 44 and possibly leading cutting edge 48) extends in a plane inclined relative to a plane 71 perpendicular to tool axis 18. In this case, the generating geometry is a flat surface inclined relative to tool axis 18.

[0074] Figure 13b shows that cutting edge 40 (and associated further cutting edges 44 and possibly leading cutting edge 48) can extend in a curved two-dimensional manner in space. Thus, they do not extend in a single plane. In this case, the generating geometry is a curved surface in space.

[0075] To determine the height offset 62, a particular radial distance from the tool axis 18 can be taken into account for the profile of the cutting edge 40 shown in Figures 13a and 13b. Similarly, the height offset 62 can also be determined relative to the respective line center 68.

[0076] The profile of the cutting edge 40 projected 72 onto a plane 71 perpendicular to the tool axis 18 may be different for each offset cutting edge 40 .

[0077] 14 shows a skiving tool 74 according to the present invention in which the cutting edges 40 are divided into several groups. Here, each group exemplarily has three cutting teeth 36a, 36b, 36c, each including one cutting edge 40 and another cutting edge 44, which are arranged at different heights along the tool axis 18, for example. In the illustrated exemplary embodiment, all cutting edges 40, 44 of each group are at different heights relative to the tool axis 18. Corresponding cutting edges 40, 44 of different groups of cutting edges 36a, 36b, 36c are located at the same axial height.

[0078] 15 shows, by way of example, the axial offsets of 20 cutting edges 40 that sequentially remove material from one of the tooth flanks 32 being machined. The cutting edges 40 are here subdivided into groups of five cutting edges 40. Within each group, the axial positions of the cutting edges 40 and the height offset 62 between sequentially engaging cutting edges 40 vary randomly but are similar for all groups.

[0079] FIG. 16 shows the axial offsets of, by way of example, 20 cutting edges 40, divided into groups of four. Within each group, each subsequent cutting edge 40 is uniformly offset in one direction relative to each preceding cutting edge 40 when machining one of the tooth flanks 32. Here, the offset of the cutting edges 40 in the direction of the feed motion 20 decreases in uniform steps. The height offset 62a between the cutting edges 40 that sequentially act on one of the tooth flanks 32 is the same within each group. Correspondingly, when moving from the last cutting edge 40 of one group to the first cutting edge 40 of the next group, the height offset 62b increases in the direction of the feed motion 20.

[0080] As shown in Figure 15 or 16, a skiving tool with offset cutting edges creates a repeating pattern of machining marks on the tooth flank during machining (not shown in detail). Within a row of the pattern, the spacing between adjacent machining marks increases and decreases in the same way, respectively.

[0081] 17 shows machining marks 52 according to the present invention that can be produced when machining tooth flank 32 with cutting edges 40 that are inclined relative to one another. The different inclinations result in different axial positions of sequentially acting cutting edges at virtually all radial distances from tool axis 18. Sequentially acting cutting edges only have the same axial position at a single radial distance.

[0082] During skiving, the contact area between the workpiece 10 and the skiving tool moves along the engaged cutting edge. If the cutting edge is inclined with respect to a plane 70 perpendicular to the tool axis 18, the cutting marks 52 will be steeper or gentler in the height direction 76 of the tooth flank 32 being machined, depending on the inclination of the cutting edge. Adjacent cutting marks will therefore move closer to or further away from each other during machining. This means that during operation of the manufactured gear, vibrations due to the unavoidable waviness of the tooth flank 32 will excite vibrations of a wider frequency spectrum rather than a single frequency.

[0083] 18 shows machining marks 52 according to the invention that can be produced when machining tooth flanks 32 with cutting edges 40 according to the invention that are inclined relative to one another and additionally axially offset. The machining marks 52 partially intersect.

[0084] In summary, the present invention relates to the machining of gears by skiving, in which machining marks are generated at unequal intervals, possibly with different extension directions. For this purpose, at least some cutting edges of the skiving tool extend at least partially to different heights along the tool axis of the skiving tool. During machining, cutting edges arranged at different axial heights relative to the workpiece axis act sequentially on the tooth flank. Therefore, the engagement of the cutting edges occurs at different time intervals and at different intervals across the width of the tooth flank. Therefore, the effect of the engagement of the cutting edges on the machining process and the excitation of vibrations during use of the manufactured gear has a wider and lower amplitude frequency spectrum than in the case of engagement of the cutting edges equidistant in time and space. In particular, the more irregular surface structure of the manufactured gear can have a positive effect on the noise excitation behavior when the gear engages with a mating gear. [Explanation of symbols]

[0085] 10 gears 12 Work 14 Skiving tools 16 work axes 17 Double Arrow 18 Tool axis 19 Double Arrow 20 Feed operation 22 Axis crossing angle 24 (Workpiece 12) peripheral speed 26 (skiving tool 14) peripheral speed 28 Cutting speed 32 Tooth surface 34 Conjugates 36;36a,36b,36c Cutting teeth 38 Rake face 40;40.1,40.2,40.3 cutting edge 40.2' Virtual cutting edge 42 Flank 44 Another cutting edge 45 Another tooth surface 46 Another flank 47 Tip flank 48 Tip cutting edge 50 distance 52 Machining marks 54 Width direction 60 Skiving Tools 62;62a,62b Height offset 64 Feed path 66.1,66.2 distance 68 line center 70 plane 71 Plane perpendicular to the tool axis 72 Projection 74 Skiving Tools

Claims

1. A skiving tool (60; 74) for machining a tooth surface (32) of a gear (10) of a workpiece (12) by rotating the skiving tool (60; 74) around a tool axis (18) and rotating the workpiece (12) around a work axis (16) extending obliquely with respect to the tool axis (18), the skiving tool (60; 74) and the workpiece (12) are displaced relative to one another by a feed motion (20) having a component along the workpiece axis (16); the skiving tool (60; 74) has a plurality of cutting edges (40; 40.1, 40.2, 40.3) that sequentially remove material from the same tooth flank (32) when machining the workpiece (12); 1. A skiving tool, comprising: at least two of the cutting edges (40; 40.1, 40.2, 40.3) arranged at different heights along the tool axis (18) for machining the same tooth flank (32); and a distance measured along the tool axis (18) between corresponding points on the cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights at at least one radial distance from the tool axis (18) is at least 5 μm, in particular at least 10 μm, and at most 0.5 mm, in particular at most 0.3 mm.

2. 2. The skiving tool (60; 74) according to claim 1, characterized in that the cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights are offset parallel to one another.

3. 2. The skiving tool (60; 74) according to claim 1, characterized in that the cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights are inclined relative to one another.

4. The skiving tool (60; 74) according to any one of claims 1 to 3, characterized in that the cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights each extend in one plane (70).

5. The skiving tool (60; 74) according to any one of claims 1 to 3, characterized in that the cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights extend in a two-dimensional curve.

6. 6. The skiving tool (60; 74) according to claim 5, characterized in that the cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights extend with different curvatures when projected onto respective planes containing the tool axis (18) rotated by the angular increments between the cutting edges (40; 40.1, 40.2, 40.3).

7. 7. The skiving tool (60; 74) according to claim 1, wherein the cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights extend with different curvatures when projected onto a plane (70) perpendicular to the tool axis (18).

8. The skiving tool (60) according to any one of claims 1 to 7, characterized in that all cutting edges (40; 40.1, 40.2, 40.3) of the skiving tool (60) are arranged at different heights along the tool axis (18).

9. The skiving tool (74) according to any one of claims 1 to 7, characterized in that the cutting edges (40; 40.1, 40.2, 40.3) of the skiving tool (74) are divided into a plurality of groups, with corresponding cutting edges (40; 40.1, 40.2, 40.3) of different groups being respectively arranged at the same height along the tool axis (18).

10. 10. The skiving tool (74) according to claim 9, characterized in that all cutting edges (40; 40.1, 40.2, 40.3) in each group are arranged at different heights along the tool axis (18).

11. 11. The skiving tool (60; 74) according to any one of claims 1 to 10, characterized in that the respective linear centers (68) of the cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights are offset from one another along the tool axis (18) by at least 5 μm, preferably at least 10 μm, and / or by a maximum of 0.5 mm, preferably a maximum of 0.3 mm.

12. at least three of the cutting edges (40; 40.1, 40.2, 40.3) are arranged at different heights along the tool axis (18) to machine the same tooth flank (32), the second cutting edges (40; 40.1, 40.2, 40.3) are arranged at a different height relative to the first cutting edges (40; 40.1, 40.2, 40.3) in a first direction along the tool axis (18), 12. The skiving tool (60; 74) according to any one of claims 1 to 11, characterized in that the third cutting edges (40; 40.1, 40.2, 40.3) are arranged at a different height relative to the second cutting edges (40; 40.1, 40.2, 40.3) in a second direction opposite to the first direction, preferably also at a different height relative to the first cutting edges (40; 40.1, 40.2, 40.3) in the second direction.

13. 13. The skiving tool (60; 74) according to any one of claims 1 to 12, characterized in that the cutting edges (40; 40.1, 40.2, 40.3) that are offset from one another in the axial direction are offset from one another in the radial direction of the tool axis (18).

14. 14. The skiving tool (60; 74) according to any one of claims 1 to 13, characterized in that the cutting edges (40; 40.1, 40.2, 40.3) that are axially offset from one another have a different circumferential pitch than the cutting edges (40; 40.1, 40.2, 40.3) that are arranged at the same height.

15. 1. A method for skiving a tooth flank (32) of a gear (10) of a workpiece (12), by engaging a skiving tool (60; 74), in particular a skiving tool (60; 74) according to any one of claims 1 to 14, with the gear (10), comprising: the skiving tool (60; 74) rotates about a tool axis (18), the workpiece (12) rotates about a workpiece axis (16) extending obliquely relative to the tool axis (18), and the skiving tool (60; 74) and the workpiece (12) are displaced relative to each other by a feed motion (20) having a component along the workpiece axis (16); at least two of the cutting edges (40; 40.1, 40.2, 40.3) of the skiving tool (60; 74) that successively machine the same tooth flank (32) are arranged at different heights along the tool axis (18), and the distance measured along the tool axis (18) between corresponding points on the cutting edges (40; 40.1, 40.2, 40.3) that are arranged at different axial heights at at least one radial distance from the tool axis (18) is at least 5%, in particular at least 10%, and at most 95%, in particular at most 90%, of the feed path (64) of the feed motion (20), and the skiving tool (60; 74) and the workpiece (12) move relative to each other by said distance along the workpiece axis (16) between the machining of the same tooth flank (32) by the respective cutting edges (40; 40.1, 40.2, 40.3) that are arranged at different axial heights.

16. 16. The method according to claim 15, characterized in that the machining using the skiving tool (60; 74) with cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights is a hard precision machining carried out after hardening of the gear (10).

17. 16. The method according to claim 15, characterized in that the machining using the skiving tool (60; 74) with cutting edges (40; 40.1, 40.2, 40.3) arranged at different axial heights is soft machining, and that the soft machining is not followed by a material removal process of the tooth flank (32).

18. 18. The method according to any one of claims 15 to 17, characterized in that a series of machining marks (52) are produced on the tooth flank (32) by cutting edges (40; 40.1, 40.2, 40.3) arranged at different heights in the axial direction, the spacing of the machining marks across the width (54) of the gear (10) increasing and decreasing in a repeating pattern.

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