METHOD FOR HOB PEELING AND CORRESPONDING DEVICE HAVING A HOB PEELING TOOL

Abstract

A method and an apparatus for skiving a work piece that has a rotationally-symmetric, periodic structure by applying a skiving tool. During skiving, a coupled relative movement of the skiving tool in relation to the work piece is performed. The skiving tool is rotated about a first rotation axis and the work piece is rotated about a second rotation axis. A tilt angle is set during skiving, which has an absolute value that is greater than 15 degrees, and the first rotation axis runs skew with respect to the second rotation axis.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is the U.S. National Phase of International Application No. PCT/EP2012/058150, entitled "Method of Hob Peeling and Corresponding Device Having a Hob Peeling Tool", filed on May 3, 2012, which claims priority from German Patent Application No. 20 2011 050 054.3, filed May 6, 2011, and from European Patent Application No. EP 11 167 703.5, filed May 26, 2011, the disclosures of which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

[0002] The invention relates to a method for skiving a toothing or another periodic structure and an apparatus for skiving a toothing or another periodic structure comprising a skiving tool.

BACKGROUND OF THE INVENTION

[0003] There are numerous methods for manufacturing gear wheels. In the chip-removing soft pre-machining, one distinguishes hobbing, gear shaping, generating planing and (power) skiving. The hobbing and skiving are so-called continuous methods, as shall be explained in the following.

[0004] In the chip-removing manufacturing of gear wheels, one distinguishes between the intermitted indexing process or single indexing process and the continuous method, which is partly also called a continuous indexing process or face hobbing.

[0005] In the continuous method, for example, a tool comprising cutters is applied in order to cut the flanks of a work piece. The work piece is cut in one clamping continuously, i.e., in an uninterrupted process. The continuous method is based on complex coupled movement sequences, in which the tool and the work piece to be machined perform a continuous indexing movement relative to each other. The indexing movement results from the driving in coordination with respect to the coupledly driving of plural axle drives of a machine.

[0006] In the single indexing process, one tooth gap is machined; then, for example, a relative movement of the tool and a so-called indexing movement (indexing rotation), in which the work piece rotates relative to the tool, are carried out, and then the next tooth gap is machined. In this way, a gear wheel is manufactured step by step.

[0007] The initially mentioned gear shaping method may be described or represented by a cylinder gear transmission, because the intersection angle (also called intersection angle of axes) between the rotation axis R1 of the shaping tool 1 and the rotation axis R2 of the work piece 2 amounts to zero degrees, as represented schematically in FIG. 1. The two rotation axes R1 and R2 run parallel, if the intersection angle of axes amounts to zero degrees. The work piece 2 and the shaping tool 1 rotate continuously about their rotation axes R2 respectively R1. In addition to the rotational movement, the shaping tool 1 carries out a stroke movement, which is referenced in FIG. 1 by the double arrow s_hx, and removes chips from the work piece 2 during this stroke movement.

[0008] Some time ago a method has been taken up anew, which is called (power) skiving. The basics are aged approximately 100 years. A first patent application with the number DE 243514 on this subject dates back to the year 1912. After the original considerations and investigations of the initial years, skiving was no longer pursued further seriously. Hitherto, complex processes, which were partly empirical, were necessary in order to find a suitable tool geometry for the skiving method.

[0009] About in the middle of the nineteen eighties, skiving was taken up anew. It was not until the present-day simulation methods and the modern CNC-controls of the machines, that the principle of skiving could be implemented as a productive, reproducible and robust method. The high durability of present-day tool materials, the enormous high static and dynamical rigidity and the high performance of the synchronous running of the modern machines come in addition.

[0010] As shown in FIG. 2, during skiving, an intersection angle of axes Σ between the rotation axis R1 of the skiving tool 10 (also called skiving wheel) and the rotation axis R2 of the work piece 20 is prescribed, which is different from zero. The resulting relative movement between the skiving tool 10 and the work piece 20 is a helical movement, which can be decomposed into a rotational portion (rotatory portion) and an advance portion (translational portion). A generation helical type gear transmission can be considered as a drive technology-specific analogon, wherein the rotational portion corresponds to the rolling and the advance portion corresponds to the gliding of the flanks. The greater the absolute value of the intersection angle of axes Σ, the more the translational movement portion required for the machining of the work piece 20 increases. It causes namely a movement component of the cutting edges of the skiving tool 10 in the direction of the tooth flanks of the work piece 20. Thus, during skiving, the gliding portion of the combing relative movement of the mutually engaging gear wheels of the equivalent helical gear is utilized to carry out the cutting movement. In skiving, only a slow axial feed (also called axial feed) is required and the so-called shaping (pushing) movement, which is typical for the gear shaping, is dispensed with. Thus, also a return stroke movement does not occur in skiving.

[0011] The cutting speed in skiving is influenced directly by the rotational speed of the skiving tool 10 with respect to the work piece 20 and the utilized intersection angle of axes Σ between the rotation axes R1 and R2. The intersection angle of axes Σ and thus the gliding portion should be selected such that for a given rotational speed an optimum cutting speed is achieved for the machining of the material.

[0012] The movement sequences and further details of an established skiving method can be taken from the schematic representation in FIG. 2 that has already been mentioned. FIG. 2 shows the skiving of an outer toothing on a cylindrical work piece 20. The work piece 20 and the tool 10 (here a cylindrical skiving tool 10) rotate in opposite directions.

[0013] Further relative movements come in addition. An axial feed s_ax is required in order to be able to machine with the tool 10 the entire toothing width of the work piece 20. If a helical toothing is desired on the work piece 20 (i.e., β≠0), a differential feed s_D is superimposed on the axial feed s_ax. A radial feed s_rad may be carried out as a lining movement. The radial feed s_rad may also be employed in order to influence the convexity of the toothing of the work piece 20.

[0014] In skiving, the vector of the cutting speed {right arrow over (v)}_c, results substantially as the difference of the two velocity vectors {right arrow over (v)}₁ and {right arrow over (v)}₂ of the rotation axes R1, R2 of the tool 10 and the work piece 20, which [velocity vectors] are tilted with respect to each other by the intersection angle of axes Σ. The symbol {right arrow over (v)}₁ is the velocity vector at the periphery of the tool and {right arrow over (v)}₂ is the velocity vector at the periphery of the work piece 20. The cutting speed v_c of the skiving process may thus be changed by the intersection angle of axes Σ and the rotation speed in the equivalent helical gear. The axial feed s_ax has only a small influence on the cutting speed v_c, which can be neglected and is thus not shown in the vector diagram comprising the vectors {right arrow over (v)}₁, {right arrow over (v)}₂ and {right arrow over (v)}_c in FIG. 2.

[0015] The skiving of an outer toothing of a work piece 20 using a conical skiving tool 10 is shown in FIG. 3. In FIG. 3 again, the intersection angle of axes Σ, the vector of the cutting speed {right arrow over (v)}_c, the velocity vectors {right arrow over (v)}₁ at the periphery of the tool 10 and {right arrow over (v)}₂ at the periphery of the work piece 20 as well as the cant angle β₁ of the tool 10 and the cant angle β₂ of the work piece 20 is shown. Here, in contrast to FIG. 2, the cant angle β₂ is different from zero. The tooth head of the tool 10 is referenced with the reference sign 4 in FIG. 3. The tooth breast is referenced with the reference sign 5 in FIG. 3. The two rotation axes R1 and R2 do not intersect, but are arranged skew (skew-whiff) with respect to each other. For a conical skiving tool 10, the calculation point AP is hitherto usually chosen on the joint plumb of the two rotation axes R1 and R2, because a tilting of the skiving tool 10 for providing of end relieve angles is not necessary. The calculation point AP coincides with the so-called contact point. The rolling circles of the equivalent helical generation gear contact each other in this calculation point AP.

[0016] In order to make the productivity of the skiving--for example when applying modern cutting materials such as hard metals for dry machining--as large as possible, the gliding portion of the relative movement between the skiving tool and the work piece must produce sufficiently high cutting speeds. In skiving, the cutting speed v_c is influenced directly by the rotation speed of the equivalent helical gear, by the effective work piece with respect to the tool radii and by the intersection angle of axes Σ of the rotation axes R1 and R2. The possible rotation speed is limited here by the permitted rotational frequency of the machining apparatus (skiving machine) used. The size of the work piece is fixedly predetermined. The possible size of the tool is limited by the work space of the machining apparatus (skiving machine) employed and for inner toothings also by the inner space of this proper toothing. Therefore, sufficiently high cutting speeds can often be generated only by corresponding large intersection angles of axes Σ.

[0017] The intersection angle of axes Σ, however, cannot be predetermined arbitrarily in practice, because beside the purely vectorial consideration of the different movements, which are superimposed, there are a number of other aspects, which must be taken into account compulsorily. These additional aspects, which must be incorporated in the considerations, are described in the following paragraphs.

[0018] In skiving, a tool 10 comes to application, which comprises at least one geometrically determined cutting edge. The cutting edge/cutting edges are not shown in FIG. 2 and FIG. 3. The shape and arrangement of the cutting edges belong to those aspects, which must be taken into account for a concrete layout in practice.

[0019] In addition, the tool itself has a great importance in skiving. In the example shown in FIG. 2, the skiving tool 10 has the shape of a spur-toothed spur wheel. The outer contour of the base body in FIG. 2 is cylindrical. However, it can also be tapered (also called conical), as shown in FIG. 3. Because the tooth or the teeth of the skiving tool 10 come in engagement along the entire length of the cutting edge, each tooth of the tool 10 requires a sufficient end relief angle at the cutting edge.

[0020] When starting from a spur-toothed or a helically toothed conical skiving tool 10 as shown in the FIGS. 4A and 4B, then one recognizes that such a skiving tool 10 has so-called constructive end relief angles (respective rake angles) due to the conical basic shape of the skiving tool 10, i.e., the end relieve angle at the head and on the flanks of the conical skiving tool 10 are predetermined due to the geometry of the skiving tool 10. However, the profile of the cutting edge of a conical skiving tool 10, must obey certain conditions, in order to enable reshaping at all. In the FIGS. 4A and 4B, a conical skiving tool 10 is shown when generating an outer toothing on a work piece 20. The so-called constructional rake angle α_Ko at the cutter head of the conical skiving tool 10 is visible in FIG. 4B. The intersection point of axes AK and the contact point BP of the rolling circles of the skiving tool 10 and the work piece 20 coincide in FIG. 4A and lie on the joint plumb GL (not shown in FIGS. 4A and 4B) of the rotation axes R1 and R2.

[0021] In FIG. 5, a further representation of a spur-toothed or helical-toothed conical skiving tool 10 and a cylinder-shaped work piece 20 is shown, wherein the view of FIG. 5 has been chosen such that both rotation axes R1 and R2 run parallel, although the two axes R1 and R2 are skew with respect to each other. The joint plumb GL of the two axes R1 and R2 can be seen in FIG. 5. The contact point BP lies on the joint plumb GL as shown in FIG. 5.

[0022] In FIGS. 6A and 6B, a configuration of a cylindrical skiving tool 10 and an outer-toothed cylindrical work piece 20 is shown. The skiving tool 10 is not only skewed with respect to the rotation axis R2 of the work piece 20 (as can be recognized in FIG. 6A on the basis of the intersection angle of axes Σ), but is positioned with respect to the work piece 20 such that it is tilted away from it by a small angle α_Ko (as is seen in FIG. 6B). By tilting the skiving tool 10 away, an effective rake angle can thus be generated, which is shown in FIG. 6B for the head cutting edge as α_Ki. Effective rake angles are also generated at the lateral cutting edges of the tool by the tilting away. However, these turn out to be smaller than at the head cutting edge. As a general rule, these rake angles are only half as large.

[0023] When starting from a spur-toothed or a helically toothed cylindrical skiving tool 10, as shown in the FIGS. 6A and 6B, one recognizes that such a skiving tool 10 does not have so-called constructional rake angles, neither at the head nor at the flanks. If such a cylindrical skiving tool 10 was clamped in the conventional manner, there would be no rake angles. A kinematic rake angle can be generated by the tilting away of the skiving tool 10 as already described. In practice, the tilting away of the skiving tool 10 is achieved by an eccentric clamping of the skiving tool 10 in the machine, in order to thus cause an offset of the cutting face from the intersection point of axes AK. The contact point BP of the rolling circles of the skiving tool 10 and the work piece 20 no longer lies on the joint plumb of the rotation axes R1 and R2 due to the tilting away of the skiving tool 10. The resulting offset is also called cutting face offset e and is recognizable in FIG. 6A. The further the skiving tool 10 is tilted away, the larger the effective rake angles become. The rake angles required for skiving lie in the range between 3 degrees and 5 degrees. In order to prescribe these rake angles, a tilting away of cylindrical skiving tools 10 of up to 10 degrees is required and usual in practice.

[0024] In the FIGS. 7A and 7B an example of a work piece 30 is shown, which has a cylindrical inner ring 31, wherein this inner ring 31 is represented in the top view of FIG. 7A as a circle only. An inner toothing is to be machined on the inner side of this inner ring by means of skiving with application of a conical skiving tool 10. The relation between the tooth width of the work piece 30 to the diameter d_w2 of the rolling circle of the work piece 30 amounts to approximately 0.62 here. An effective intersection angle of axes Σ_eff of at least 26 degrees is required in order to achieve a sufficient cutting speed v_c. In the FIGS. 7A and 7B, a situation with an effective intersection angle of axes Σ_eff=26 degrees is shown. It can be seen both in FIG. 7A and in FIG. 7B, that the conical skiving tool 10 would collide with the inner ring 31 in this hitherto usually untilted clamping for an effective intersection angle of axes Σ_eff of 26 degrees. The collision region is represented schematically by an oval KB in FIGS. 7A and 7B.

[0025] In the FIGS. 8A and 8B, an example of a work piece 30 is shown, which has a cylindrical inner ring 31, wherein this inner ring 31 is represented in the top view of FIG. 8A as a circle only. An inner toothing is to be manufactured on the inner side of this inner ring 31 by means of skiving with application of a cylindrical skiving tool 10. Again, an effective intersection angle of axes Σ_eff of at least 26 degrees is required in order to achieve a sufficient cutting speed v_c. In the FIGS. 8A and 8B, a situation with an effective intersection angle of axes Σ_eff=26 degrees and a tilt angle δ=12 degrees is shown. It can be recognized both in FIG. 8A and in FIG. 8B, that the cylindrical skiving tool 10 would collide with the inner ring 31 in this configuration despite the provision of a tilt angle δ of 12 degrees. In FIG. 8B, the collision range is schematically characterized by an oval KB.

[0026] In the FIGS. 9A and 9B an example of a work piece 20 is shown, which has a first cylindrical section 21 and a second cylindrical section 22, wherein an outer toothing is to be manufactured on the first cylindrical section 21 by means of skiving with application of a conical skiving tool 10. The work piece 20 may concern for example a shaft, which has sections having different diameters. An effective intersection angle of axes Σ_eff of at least 18 degrees is required in order to achieve a sufficient cutting speed v_c. It is recognizable both in FIG. 9A and in FIG. 9B, that the conical skiving tool 10 (here having a cone angle of 10 degrees) would collide with the second cylindrical section 22 of the work piece 20 in the usual clamping shown for an effective intersection angle of axes Σ_eff of 18 degree. The collision region is characterized schematically by an oval KB in FIG. 9B.

[0027] The work piece 20 according to FIGS. 9A and 9B, which has a first cylindrical section 21 and a second cylindrical section 22, is shown anew in the FIGS. 10A and 10B, wherein an outer toothing is to be manufactured on the first cylindrical section 21 by means of skiving with application of a conical skiving tool 10. Here, a conical skiving tool 10 similar to that in FIGS. 9A and 9B is applied, wherein the skiving tool 10 has a cone angle of 20 degrees in the present case. Also here, an effective intersection angle of axes Σ_eff of at least 18 degrees is required in order to achieve a sufficient cutting speed v_c. The skiving tool 10 is tilted towards the work piece 20 with a tilt angle δ=-10 degrees. It is recognizable both in FIG. 10A and in FIG. 10B, that the conical skiving tool 10 would collide with the second cylindrical section 22 of the work piece 20 for the clamping shown. This type of clamping is known from a parallel European patent application, which has been filed on the same day under the title "Method of skiving and according apparatus comprising a skiving tool" in the name of the applicant of the present application. The collision section is characterized schematically by an oval KB in FIG. 10B.

[0028] Also for a cylindrical skiving tool 10, a collision would result, wherein the situation there is even worse due to the required tilting away from the work piece.

SUMMARY OF THE INVENTION

[0029] It is an object of the present invention to provide a method and an apparatus for the chip-removing machining of the tooth flanks of a gear wheel or other periodic structures, which is in particular suitable for machining work pieces that allow only a small overrun.

[0030] It is also an object of the present invention to provide a method and an apparatus for the chip-removing machining of the tooth flanks of an inner-toothed gear wheel or other periodic structures lying interiorly. In particular, the machining of inner toothings or other periodic structures lying interiorly on work pieces, which work pieces have a small inner diameter relative to the size of the hitherto employed tools and/or any cramped conditions in the interior region to be machined. In particular in this case, the achieving of cutting speeds which are as high as possible is concerned.

[0031] In particular, the machining is concerned with inner toothings or other periodic structures lying interiorly on work pieces, for which the peeling nozzle in relation to the tool spindle together with the tool must protrude far into the inner ring of the work piece. In particular in this case, achieving cutting speeds which are as high as possible is concerned.

[0032] In particular, the machining is concerned with inner toothings or other periodic structures lying interiorly on work pieces, which have a relatively high tooth width in comparison to the diameter, and achieving cutting speeds as high as possible are concerned, whereby despite the cramped conditions tools as big as possible having effective intersection angles of axes which are as large as possible must be applied.

[0033] In particular, the machining of inner toothings or other periodic structures lying interiorly on work pieces having an inner ring is concerned, where the inner ring has a ratio of inner diameter and the required plunging depth of the peeling nozzle into the work piece, which [ratio] is less than 2.

[0034] In addition, the method and the apparatus shall be robust and shall be suitable for application in a serial production, for example in the automotive industry.

[0035] This object is solved according to the present invention by a method which is herein called a modified skiving method. The modified skiving method concerns a continuous cutting method that is suitable for the manufacturing of outer and inner rotationally symmetrical periodical structures. As the name skiving (hob peeling) indicates, a hobbing method is concerned. To be precise, a continuous hobbing toothing method is concerned. Herein, skiving is compared to the description and design of the generating train with the kinematics of a helical gear.

[0036] The method relates to skiving of a work piece having a rotational-symmetric periodical structure by an application of a skiving tool. In this skiving method:

[0037] the skiving tool rotates continuously about a first rotation axis,

[0038] the work piece rotates continuously and synchronously to the skiving tool about a second rotation axis, and

[0039] the rotating skiving tool performs a relative movement with respect to the rotating work piece, wherein

[0040] during the skiving a positive or negative tilt angle of the skiving tool is set, which angle is greater than 15 degrees and

[0041] the first rotation axis runs skew with respect to the second rotation axis.

[0042] By the coupled rotation and movement of the skiving tool and the work piece, a relative movement results between the skiving tool and the work piece, which corresponds to the relative movement of a helical gear or is approximated to a helical gear.

[0043] During the machining phase, the skiving tool is clearly tilted away from the work piece or is clearly tilted toward the work piece.

[0044] Preferably, in all embodiments, the skiving tool is clearly tilted away from the toothing or from the periodical structure on the work piece or is clearly tilted toward the toothing or the periodic structure on the work piece.

[0045] The absolute value of the tilt angle δ is preferably in an angle range between 15 degrees and 45 degrees and preferably between 20 degrees and 35 degrees.

[0046] The invention can also be applied, when the work piece concerns a work piece which allows only a small overrun, such as, for example, a component having a peripheral inner or outer collar, or for a component part, e.g., an inner rotational-symmetric periodic structure in a hollow cylinder that is not continuous (a blind whole) is to be machined.

[0047] In the modified skiving method of the invention, the relative movement sequences (called relative movement) between the work piece and the skiving tool are performed predetermined and coordinated in a way such that collisions do not occur.

[0048] The modified skiving method concerns a continuous cutting method. As the name skiving indicates, a hobbing method is concerned. To be precise, a continuous hobbing toothing method is concerned.

[0049] Preferably, in all embodiments, a skiving tool like a skiving wheel is employed, which differs significantly from front cutter head tools.

[0050] According to the invention, the skiving tool has a tool section like a skiving wheel and cutting edges that are formed in the shape of cutting teeth which protrude outward obliquely.

[0051] According to the invention, a skiving tool is employed preferably in the manufacturing of outer periodic structures, where the tool has a tool section like a skiving wheel and the shape of a cutting wheel, preferably the shape of a disc-type cutting wheel, a shank-type cutting wheel or a deep counterbore-type cutting wheel (e.g., according to DIN 3972 or DIN 5480).

[0052] According to the invention, a peeling nozzle is employed preferably in the manufacturing of inner periodic structures, where the nozzle is on one hand long (i.e., enables a plunging depth as large as possible) so as to reach sufficiently far into the inner ring of the work piece, and on the other hand has a (shaft) diameter as large as possible so as to give the peeling nozzle the rigidity required for skiving.

[0053] Preferably, in all embodiments of generating an inner toothing, a skiving tool is employed, which together with a tool spindle and/or an adapter has a shape like a nozzle having a great plunging depth.

[0054] According to the invention, the peeling nozzle comprises a tool section like a skiving wheel and has the shape of a disc-type generating cutter, a shank-type generating cutter or a deep counterbore-type generating cutter (e.g., according to DIN 3972 or DIN 5480).

[0055] In addition, according to the invention, the effective intersection angle of axes Σ_eff is predetermined as large as possible in all embodiments so as to achieve sufficient cutting speeds. This aspect plays a role in particular for a small size of the work piece. Since the diameter of a toothing is fixedly predetermined and the maximum rotational frequency for a machine is also fixed, there remains only the means to make the effective intersection angle of axes Σ_eff sufficiently large.

[0056] The skiving tools according to the invention are designed either as so-called massive tools, i.e., tools are concerned that are implemented essentially integrally, or they are implemented as cutter head tools (herein called bar cutter skiving wheel) that have a cutter head base body equipped with cutter inserts, preferably in the shape of bar cutters.

[0057] According to the invention, preferably in all embodiments, the skiving tools have so-called constructional rake angles, i.e., the rake angles are predetermined due to the geometry of the skiving tool by taking into account the kinematics.

[0058] The invention is employed preferably for component parts, which have a so-called fitting interference contour (e.g., a collision flank) and which thus can not be manufactured with a conventional skiving method in most cases.

[0059] The invention is based on the feature that the absolute value of the tilt angle δ is set to be greater or equal to 15 degrees, i.e., the skiving tool is tilted significantly stronger as compared to conventional skiving methods.

[0060] Using the modified skiving method as described and claimed, the most different toothings and other periodically reoccurring structures can be manufactured.

[0061] A cutting face offset e is prescribed for cylindrical toothings of the work piece.

[0062] In the modified skiving, material is removed progressively until the teeth or the other periodical structures are formed completely.

[0063] The method according to invention can be performed both as a dry or wet machining.

[0064] The modified skiving cannot be employed for the machining of outer toothings only.

[0065] The modified skiving can also be employed advantageously for the manufacturing of inner toothings.

[0066] The modified skiving can be employed both in the pre-toothing before the heat treatment of the work piece and also in the finishing toothing after the heat treatment, i.e., the skiving is suitable for the soft-machining and for the hard (fine) machining.

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Further details and advantages of the invention are described in the following on the basis of embodiment examples and with reference to the drawings. In all schematic drawings (i.e., also in the collision representations of the FIGS. 7A, 7B, 8A, 8B, 9A, 9B, 10A and 10B), for reasons of simplicity of the representation, the work piece and the skiving tool are reduced to the situation of a rolling circle (the work piece being a rolling cylinder). However, the represented conditions hold, for the entire toothing having a tooth height.

[0068] FIG. 1 shows a schematic representation of a pushing wheel having a cylindrical outer contour in engagement with a work piece having an outer toothing during gear shaping;

[0069] FIG. 2 shows a schematic representation of a spur-toothed skiving wheel having a cylindrical outer contour in engagement with a work piece having an outer toothing during skiving;

[0070] FIG. 3 shows a schematic representation of a helically toothed skiving wheel having a conical outer contour in engagement with a work piece having an outer toothing during skiving;

[0071] FIG. 4A shows a schematic projection of intersection of axes (projection of contact plane) of a conical skiving tool during skiving of a work piece having an outer toothing, wherein an intersection angle of axes is predetermined in the conventional manner;

[0072] FIG. 4B shows a schematic side projection of intersection of axes (side projection of contact plane) of the conical skiving tool and the work piece of FIG. 4A;

[0073] FIG. 5 shows a schematic view of a further conical skiving tool during skiving of a work piece having an outer toothing, wherein the skiving tool is untilted with respect to the work piece in the conventional manner;

[0074] FIG. 6A shows a schematic projection of intersection of axes of a cylindrical skiving tool during skiving of a work piece having an outer toothing, wherein the skiving tool is tilted away from the work piece with a small angle in the conventional manner and there results a cutting face offset;

[0075] FIG. 6B shows a schematic side projection of contact plane of the cylindrical skiving tool and the work piece of FIG. 6A;

[0076] FIG. 7A shows a schematic view of a conical skiving tool in the skiving of a work piece having an inner toothing, wherein an effective intersection angle of axes Σ_eff=26 degrees is predetermined and a collision between the skiving tool and the work piece results;

[0077] FIG. 7B shows a schematic back side projection of intersection of axes (back side projection of contact plane) of the conical skiving tool and work piece of FIG. 7A, which clearly shows the collision section;

[0078] FIG. 8A shows a schematic view of a cylindrical skiving tool during skiving of a work piece having an inner toothing, wherein the skiving tool is tilted with an effective intersection angle of axes Σ_eff=26 degrees and a tilt angle of 12 degrees and wherein a collision between the skiving tool and the work piece results nevertheless;

[0079] FIG. 8B shows a schematic back side projection of contact plane of the cylindrical skiving tool and work piece of FIG. 8A, which clearly shows the collision section;

[0080] FIG. 9A shows a schematic side projection of intersection of axes (side projection of contact plane) of a conical skiving tool in the skiving of a work piece having an outer toothing with a small overrun, wherein an effective intersection angle of axes Σ_eff of 18 degrees is predetermined and a collision between the skiving tool and the work piece results;

[0081] FIG. 9B shows a schematic view of the conical skiving tool and work piece of FIG. 9A in order to illustrate the collision more clearly;

[0082] FIG. 10A shows a schematic side projection of contact plane of a further conical skiving tool in the skiving of a work piece having an outer toothing with a small overrun, wherein an effective intersection angle of axes Σ_eff of 18 degrees is predetermined and the skiving tool is inclined with a tilting angle δ=-10 degrees with respect to the work piece and wherein a collision between the skiving tool and the work piece results nevertheless;

[0083] FIG. 10B shows a schematic view of the conical skiving tool and the work piece of FIG. 10A, in order to illustrate the collision more clearly;

[0084] FIG. 11 shows the contact plane BE for an outer toothing and some of the relevant angles and vectors;

[0085] FIG. 12 shows a schematic view of a conical skiving tool with respect to the so-called contact plane with a significantly negative tilt angle δ=-25 degrees;

[0086] FIG. 13 shows a schematic view of a conical skiving tool with respect to the so-called contact plane with a significantly positive tilt angle δ=25 degrees;

[0087] FIG. 14A shows a schematic view of a conical skiving tool during the modified skiving of a cylindrical work piece having an outer toothing, wherein the skiving tool is significantly tilted toward the work piece (tilt angle δ=-20 degrees, cone angle=30 degrees);

[0088] FIG. 14B shows a further schematic view of the conical skiving tool and work piece of FIG. 14A;

[0089] FIG. 14C shows a schematic projection of intersection of axes of the conical skiving tool and work piece of FIG. 14A;

[0090] FIG. 14D shows a schematic side projection of intersection of axes of the conical skiving tool and work piece of FIG. 14A;

[0091] FIG. 14E shows a schematic side projection of contact plane of the conical skiving tool and work piece of FIG. 14A;

[0092] FIG. 15A shows a schematic view of a cylindrical skiving tool during the modified skiving of a cylindrical work piece having an inner toothing, wherein the skiving tool is significantly tilted away from the work piece (tilt angle δ=20 degrees;

[0093] FIG. 15B shows a further schematic back side projection of intersection of axes of the work piece together with the conical skiving tool of FIG. 15A;

[0094] FIG. 16A shows a schematic view of a conical skiving tool during the modified skiving of a cylindrical work piece having an outer toothing with a small overrun, wherein the skiving tool is significantly tilted toward the work piece (tilt angle δ=-24 degrees; cone angle=34 degrees);

[0095] FIG. 16B shows a further schematic view of the conical skiving tool and work piece of FIG. 16A;

[0096] FIG. 17 shows an embodiment of a skiving tool in a perspective view;

[0097] FIG. 18A shows a schematic view of a conically tapering skiving tool, which can be employed in relation with the invention for a tilt angle δ of -20 degrees;

[0098] FIG. 18B shows a schematic view of the skiving tool of FIG. 18A together with a cylindrical work piece having an outer toothing, wherein an inclination angle δ of -20 degrees is prescribed;

[0099] FIG. 19 shows a schematic view of the skiving tool together with a cylindrical work piece having an outer toothing, wherein a tilt angle δ of +20 degrees is predetermined;

[0100] FIG. 20 shows a schematic view of a skiving tool in the form of a generating cutter-massive tool which is suitable for application at an tilt angle δ of approximately -20 degrees;

[0101] FIG. 21A shows a schematic view of a further skiving tool in the form of a massive tool generating cutter, which is suitable in the application with a significantly positive tilt angle 8;

[0102] FIG. 21B shows a schematic view of the skiving tool of FIG. 21A together with a cylindrical work piece having an outer toothing, wherein an inclination angle δ of +20 degrees is prescribed;

[0103] FIG. 22A shows a schematic view of a further skiving tool in the form of a massive tool generating cutter, which is suitable in the application with a significantly negative tilt angle 8;

[0104] FIG. 22B shows a schematic view of the skiving tool of FIG. 22A together with a cylindrical work piece having an outer toothing, wherein a tilt angle δ of -20 degrees is predetermined; and

[0105] FIG. 23 shows a perspective view of a machine according to the invention comprising a skiving tool during the skiving of a work piece having an inner toothing.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0106] In relation with the present description, terms are used which also find use in relevant publications and patents. It is noted however, that the use of these terms shall merely serve a better comprehension. The inventive idea and the scope of the patent claims shall not be limited in their interpretation by the specific selection of the terms. The invention can be transferred without further ado to other systems of terminology and/or technical areas. In other technical areas, the terms are to be employed analogously.

[0107] Rotational-symmetric periodic structures are for example gear wheels having an inner and/or outer toothing. However, for example, also brake discs, clutch or gear transmission elements, and so on may be concerned. The skiving tools are particularly suitable for the manufacturing of pinion shafts, worms, ring gears, toothed wheel pumps, ring joint hubs (ring joints are employed for example in the motor vehicle sector for transmitting the force from a differential gear to a vehicle wheel), spline shaft joints, sliding collars, belt pulleys, and so on. Herein, the periodic structures are also called periodically repeating structures.

[0108] In the following, mention is made primarily of gear wheels, teeth and tooth gaps. However, as mentioned above, the invention can, also be transferred to other construction parts with other periodic structures. In this case, these other construction parts do not concern tooth gaps, but for example grooves or channels.

[0109] According to the invention, a so-called modified skiving method is concerned, in which the skiving tool 100 is significantly tilted toward the work piece 50 or 60 or significantly tilted away from the work piece 50 or 70. Firstly, in the following, the basics for the design of skiving processes with significant tilt (inclination) are described.

[0110] Basically, the relative movement between the skiving tool 100 and the work piece 50, 60, 70 during the skiving corresponds to a helical gear, also called generation helical type gear transmission. The helical gear concerns a spatial transmission gear.

[0111] The basic design of the skiving process thus occurs, as in the design of transmission gears, at a so-called calculation point AP. The term basic design is understood herein to refer to the definition of the spatial arrangement and movement of the skiving tool 100 with respect to the work piece 50, 60, 70 (kinematics) as well as the definition of the geometrical basic parameters of the skiving tool 100, such as for example the diameter and the tilt angle (basic tool geometry).

[0112] Conventionally, the basic tool geometry (for example diameter and tilt angle) was defined by the consideration of the engagement conditions at the calculation point AP of the untilted tool in the design of skiving processes with a tilted tool. The tool thus determined was then brought into a tilted position by means of a cutting face offset. Thereby, different procedures are known for the determination of the resulting exact cutting edge geometry. For the tilt angles δ of up to 10 degrees, which are common for the provision of kinematic rake angles, this procedure is considered legitimate, since because of cos(10 degrees)≈0.98 the deviation of the effective intersection angle of axes Σ_eff from the intersection angle of axes Σ is very small and hence neglectable. The engagement conditions between the untilted and tilted tool differ only insignificantly in this case.

[0113] The geometrical and kinematic engagement conditions at the calculation point AP are designed as optimal as possible. The engagement conditions change with increasing distance from the calculation point AP. In this relation, skiving represents a very complex process, in which the engagement conditions vary also during the movement of the cutting edge. However, the varying engagement conditions can be influenced selectively via the engagement conditions at the calculation point AP.

[0114] Thus, the correct design of the engagement conditions at the calculation point AP have a considerable importance in the design of skiving processes.

[0115] In the modified skiving method, one proceeds as follows. With a tilt angle δ, the absolute value of which increases, also the deviation of the effective intersection angle of axes Σ_eff from the intersection angle of axes Σ increases. For tilt angles δ, the absolute value of which is greater than 15 degrees, the engagement conditions between an untilted and tilted skiving tool 100 differ significantly. Investigations have shown that a design of the skiving tool 100 in the untilted state does not yield anymore sufficiently good cutting conditions for the work with a significantly tilted skiving tool 100. Thus, for example, the "cutting direction condition", which takes care that the cutting speed vector v_c points in the cant direction of the tooth gap to be manufactured, is violated, if the intersection angle of axes Σ has been used in the design instead of the effective intersection angle of axes Σ_eff in order to determine the diameter d_w1 of the rolling circle of the skiving tool 100.

[0116] According to the invention, the direct design of the skiving tool 100 with consideration of the intended spatial arrangement with significant tilt (inclination) is proposed. To this end, the engagement conditions at the calculation point AP have to be designed with consideration of the cutting conditions in the contact plane BE of the spatial gear transmission.

[0117] Terms concerning the arrangement of axes:

[0118] There are several terms, which are required for the definition of the arrangement of axes. These terms are described in Table 1 below.

TABLE-US-00001 TABLE 1 joint plumb, Skiving processes are characterized by rotation axes R2 and R1 of the orthogonal work piece 50, 60, 70 and the skiving tool 100, which intersect each other projection of in space. For the two rotation axes R2 and R1 intersecting each other, the joint plumb, joint joint plumb GL can be indicated uniquely. The orthogonal projection plumb vector (base point) of the joint plumb on the rotation axis R2 of the work piece 50, 60, 70 shall be GLF2. The orthogonal projection of the joint plumb on the rotation axis R1 of the skiving tool 100 shall be GLF1. The joint plumb vector GLV shall be the connection vector from GLF1 to GLF2. projection of The view of the work piece 50, 60, 70 and the skiving tool 100 along the intersection of joint plumb GL in the direction of the joint plumb vector GLV is called axes, intersection projection of intersection of axes. point of axes In the projection of intersection of axes, the projected rotation axes R1 and R2 intersect each other in the intersection point of axes AK, which corresponds to the joint plumb L that is reduced in the projection to a point. intersection angle The intersection angle of axes Σ is the angle, the absolute value of which of axes is smaller, and which is embraced by the two rotation axes R1 and R2. It becomes visible in the projection of intersection of axes. The following holds: -90° < Σ < 90°, Σ ≠ 0°. The intersection angle of axes Σ carries a sign. The sign is defined in the projection of intersection of axes as follows without limiting the generality: For outer toothings, the intersection angle of axes Σ is positive, if the projected rotation axis R1 is rotated about the intersection point of axes AK mathematically positive by |Σ| with respect to the projected rotation axis. For inner toothings, it is positive, if the projected rotation axis R1 is rotated about the intersection point of axes AK mathematically negative by |Σ| with respect to the projected rotation axis R2. distance between The distance between axes (axes distance) A corresponds to the length of axes the joint plumb vector GLV. It describes the smallest distance between the rotation axes R1 and R2.

[0119] Terms concerning the contact between the skiving tool and the work piece:

[0120] There are several terms, which are necessary for the description of the contact between the skiving tool and the work piece. These terms are described in Table 2 below.

TABLE-US-00002 TABLE 2 rolling circles The rolling circles of the work piece 50, 60, 70 and the skiving tool 100 contact each other in the calculation point AP, which is therefore also called contact point BP. The rolling circle W2 of the work piece 50, 60, 70 (also called work piece rolling circle) lies in a plane that is perpendicular to the rotation axis R2 of the work piece 50, 60, 70. The center of the rolling circle W2 lies on the rotation axis R2 of the work piece 50, 60, 70. The diameter of the rolling circle W2 of the work piece is d_w2. The rolling circle W1 of the skiving tool 100 (also called tool rolling circle) lies in a plane that is perpendicular to the rotation axis R1 of the skiving tool. The center of the rolling circle W1 lies on the rotation axis R1 of the skiving tool 100. The diameter of the rolling circle W1 of the tool is d_w1. The diameter d_w1 of the rolling circle of the work piece 50, 60, 70 carries a sign. For outer toothings it is positive, for inner toothings it is negative. reference planes The reference plane of the work piece is the plane, in which the rolling circle W2 of the work piece lies. The reference plane of the tool is the plane, in which the rolling circle W1 of the tool lies. chip half space, The reference plane of the tool divides the three dimensional space into halves. cutter half space The chip half space shall be the half, into which the perpendicular to the cutting face, which points outwardly of the cutting edge material of the skiving tool 100, points into. The other half shall be called cutter half space. The cutting edges of the skiving tool 100 thus extend essentially in the cutter half space, however they can also extend into the chip half space, wherein the cutting faces are turned toward the chip half space. velocity vectors In the calculation point AP, the velocity vector {right arrow over (v)}₂ of the corresponding point of the work piece can be indicated, which vector results from the rotation of the work piece about R2. It lies in the reference plane of the work piece, tangentially to the rolling circle W2 of the work piece. The absolute value is v₂ = |π d_w2 n₂| with a rotation frequency n₂ of the work piece carrying a sign. In the calculation point, also the velocity vector {right arrow over (v)}₁ of the related point of the tool can be indicated, which vector results from the rotation of the tool about R1. It lies in the reference plane of the tool, tangentially to the rolling circle W1 of the tool. The absolute value is v₁ = |π d_w1 n₁| with the rotational frequency n₁ of the tool carrying a sign. contact radius Starting from the calculation point AP, the plumb onto the rotation axis R2 of the vectors work piece 50, 60, 70 can be drawn. The related orthogonal projection LF2 of the plumb corresponds to the intersection point between the reference plane of the work piece and the rotation axis R2 of the work piece (see e.g., FIG. 14B). The contact radius vector {right arrow over (r)}₂ of the work piece 50, 60, 70 is, for inner toothings, the vector from the orthogonal projection of the plumb LF2 to the calculation point AP, and for outer toothings the vector from the calculation point AP to the orthogonal projection of the plumb LF2. Its length is |d_w2|/2. Starting from the calculation point AP, the plumb onto the rotation axis R1 of the skiving tool 100 can be drawn. The related orthogonal projection of the plumb LF1 corresponds to the intersection point between the reference plane of the tool and the rotation axis R1 of the tool (see e.g., FIG. 14B). The vector from the orthogonal projection of the plumb LF1 to the calculation point AP is called contact radius vector {right arrow over (r)}₁ of the tool 100. Its length is d_w1/2. contact plane BE The two velocity vectors {right arrow over (v)}₂ and {right arrow over (v)}₁ span the so-called contact plane BE (see e.g., FIG. 12). The rolling circles W2 and W1 of the work piece 50, 60, 70 and the skiving tool 100 contact each other in this contact plane BE, and namely in the calculation point AP. In addition, also the theoretical pitch surface of the toothing of the work piece 50, 60, 70 and the rolling circle W1 of the skiving tool 100 contact each other in this contact plane BE according to the design. More exactly, the contact plane BE is tangentially to the mentioned pitch surface of the toothing of the work piece 50, 60, 70 and namely in the calculation point AP. pitch surface, The pitch surface of a toothing is also called reference pitch surface. It goes through the reference pitch calculation point AP, is rotationally symmetrical with respect to the rotation axis R2 of the surface work piece 50, 60, 70 and reflects a portion of the basic geometry of the toothing. The pitch circle (rolling circle) W2 is part of the pitch surface of the toothing of the work piece 50, 60, 70. For the cylindrical toothings which are described here in detail and are shown in the drawings, the pitch surface is a cylinder, for conical toothings a cone, for planar toothings a plane and for general spatial toothings as, e.g., for hypoid wheels a hyperboloid. The explanations, which are given in the following in relation with cylindrical toothings, can be transferred accordingly to other toothings. contact plane The contact plane normal {right arrow over (n)} shall be the normal vector of the contact plane BE which is anchored normal in the calculation point AP and which points into the toothing of the work piece 50, 60, 70, i.e., from the head section to the base section of the toothing. For outer toothings on the work piece 50, 60, 70, the contact plane normal {right arrow over (n)} thus points toward the rotation axis R2 of the work piece 50, 60, 70, while it points away therefrom for inner toothings. For cylindrical toothings, the contact plane normal points in the same direction as the contact radius vector {right arrow over (r)}₂ of the work piece 50, 60, 70, i.e., {right arrow over (n)} und {right arrow over (r)}₂ differ from each other only by their length (thus in FIG. 14B the contact radius vector {right arrow over (r)}₂ of the work piece 50 and the contact plane normal {right arrow over (n)} are shown). projection of The view of the work piece 50, 60, 70 and the skiving tool 100 in the direction of the contact plane contact radius vector {right arrow over (r)}₂ of the work piece 50, 60, 70 is called projection of contact plane. The projected rotation axes R1 and R2 intersect in the projection of contact plane in the calculation point AP with respect to the contact point BP. effective intersection The effective intersection angle of axes Σ_eff is the angle embraced by the angel of axes two velocity vectors {right arrow over (v)}₂ und {right arrow over (v)}₁ according to cos ( Σ eff ) = v → 2 v → 1 v → 2 v → 1 . ##EQU00001## According to the invention the following holds: -90° < Σ_eff < 90°, wherein Σ_eff ≠ 0°. The effective intersection angle of axes Σ_eff carries a sign as the intersection angle of axes Σ. The sign is defined as follows without restriction of the generality: For outer toothings, the effective intersection angle of axes Σ_eff is positive, if the velocity vectors {right arrow over (v)}₁ and {right arrow over (v)}₂ and the contact plane normal {right arrow over (n)} in this succession form a right-handed trihedron. For inner toothings, it is positive, if the velocity vectors {right arrow over (v)}₁ and {right arrow over (v)}₂ and the contact plane normal {right arrow over (n)} in this succession form a left-handed trihedron. For non-planar toothings, the effective intersection angle of axes Σ_eff corresponds to the perpendicular projection of the intersection angle of axes Σ onto the contact plane BE, i.e., the intersection angle of axes Σ in the projection of contact plane. tilt angle The tilt angle δ describes the tilt (inclination) of the tool reference plane and thus the skiving tool 100 with respect to the contact plane BE. It is the angle, which is in encompassed by the contact radius vector {right arrow over (r)}₁ of the skiving tool 100 and the contact plane normal {right arrow over (n)} according to cos ( δ ) = n → r → 1 n → r → 1 , wherein -90 ° ≦ δ ≦ 90 ° ( see FIG . 14 B ) . ##EQU00002## The tilt angle δ is identical to the intersection angle (the smaller one in terms of its absolute value) between the rotation axis R1 of the skiving tool 100 and the contact plane BE. The tilt angle δ is 0°, if the tool reference plane is perpendicular to the contact plane BE and thus the rotation axis R1 of the tool runs parallel to the contact plane BE. The tilt angle δ carries a sign. The tilt angle δ is positive, if the rotation axis R1 of the skiving tool 100 intersects the contact plane BE in the chip half space. The tilt angle δ is negative, if the rotation axis R1 of the skiving tool 100 intersects the contact plane BE in the cutter half space.

[0121] Further Projections:

[0122] There are different further projections, which are employed for illustrating the invention. The further projections are explained in Table 3 below.

TABLE-US-00003 TABLE 3 side projection of The vector of the side projection of intersection of axes shall be intersection of axes the velocity vector, which is perpendicular to the joint plumb GL and to the rotation axis R2 of the work piece 50, 60, 70, and which embraces an acute angle with the velocity vector {right arrow over (v)}₂ of the contacting point of the work piece. Then, the view of the work piece 50, 60, 70 and of the skiving tool 100 in the direction of this vector of the side projection of intersection of axes is called side projection of intersection of axes. In the side projection of intersection of axes, the projected rotation axes R1 and R2 run parallel to each other. back side projection of The view of the work piece 50, 60, 70 and the skiving tool 100 intersection of axes along the joint plumb GL in the reverse direction of the joint plumb vector GLV is called back side projection of intersection if axes. side projection of contact The view of the work piece 50, 60, 70 and of the skiving tool 100 plane in the direction of the velocity vector {right arrow over (v)}₂ of the contacting point of the work piece is called side projection of contact plane. back side projection of The view of the work piece 50, 60, 70 and the skiving tool 100 contact plane in the reverse direction of the contact radius vector {right arrow over (r)}₂ of the work piece 50, 60, 70 is called back side projection of contact plane.

[0123] Offset of Cutting Face:

[0124] The offset of the cutting face is defined in Table 4 below.

TABLE-US-00004 TABLE 4 offset of cutting face The offset of the cutting face (cutting face offset) e corresponds to the (only applicable for distance of the orthogonal projection (dropped perpendicular foot) LF1 work pieces 50, 60, and GLF1 along the rotation axis R1 of the skiving tool 100. It carries a 70 having cylindrical sign. For inner toothings, the cutting face offset e has the same sign as toothings) the tilt angle δ. For outer toothings, the cutting face offset e has the opposite sign of the tilt angle δ.

[0125] For non-planar toothings, the following equation [1] establishes the relationship between the angles, which describe the spatial arrangement of the rotation axes R1 and R2, and is thus important for the conversion of the individual quantities:

cos(Σ)=cos(Σ_eff)cos(δ) [1]

[0126] In this generalized configuration, the intersection angle of axes Σ is decomposed into the effective intersection angle of axes Σ_eff and the tilt angle δ, wherein the effective intersection angle of axes Σ_eff is the determining quantity for the generation of the relative cutting movement between the rotating skiving tool 100 and the rotating work piece 50, 60, 70. For planar toothings, the effective intersection angle of axes Σ_eff and the tilt angle δ are well defined, however, the relationship [1] does not hold.

[0127] Conditions in the Contact Plane:

[0128] In the design of the modified skiving method, the engagement conditions at the calculation point AP located in the contact plane BE are considered. FIG. 11 shows the contact plane BE for an outer toothing.

[0129] Herein:

[0130] R1 and R2 are the rotation axes, respectively, of the skiving tool 100, and the work piece 50, 70,

[0131] Σ_eff is the effective intersection angle of axes,

[0132] β₂ is the cant angle of the work piece 50, 70,

[0133] {tilde over (β)}₁ the cant angle β₁, projected into the contact plane BE, of a virtual tilted cylindrical skiving tool 100, with tan({tilde over (β)}₁)=tan({tilde over (β)}₁)cos(δ),

[0134] {right arrow over (v)}₁ and {right arrow over (v)}₂ are the velocity vectors of the skiving tool 100 respectively the work piece 50, 70 in the contact point BP, and

[0135] {right arrow over (v)}_c={right arrow over (v)}₁-{right arrow over (v)}₂ is the resulting cutting speed vector in the contact point BP.

[0136] In the basic design of the modified skiving process, the diameter of the rolling circle d_w1 of the skiving tool 100 is ideally defined such that the resulting cutting speed vector {right arrow over (v)}_c points in the direction of the gap to be generated. In other words, as shown in FIG. 11, it shall embrace the cant angle β₂ of the work piece 50, 70 with the projected rotation axis R2. This condition is satisfied, if the diameter of the rolling circle d_w1 obeys the following formula:

d w 1 = d w 2 n 2 n 1 cos ( β 2 ) cos ( β ~ 1 ) = d w 2 n 2 n 1 cos ( β 2 ) cos ( Σ eff - β 2 ) ##EQU00003##

[0137] Herein, n₁ and n₂ refer to the rotational frequency of the skiving tool 100 with respect to the work piece 50, 70, which must obey the ratio of the number of teeth according to

n 2 n 1 = - z 1 z 2 . ##EQU00004##

Herein, z₁ and z₂ refer to the number of teeth of the skiving tool 100 with respect to the work piece 50, 60, 70.

[0138] The cutting speed thus results as follows:

v c = π d w 2 n 2 sin ( Σ eff ) cos ( β ~ 1 ) = π d w 2 n 2 sin ( Σ eff ) cos ( Σ eff - β 2 ) , ##EQU00005##

and the cant angle β₁ of a virtual tilted cylindrical skiving tool 100 must satisfy the condition

tan(β₁)=tan(Σ_eff-β₂)/cos(δ)

In all three formulas, the effective intersection angle of axes Σ_eff is to be inserted, which differs for a tilted tool from the intersection angle of axes Σ according to the already mentioned equation [1]:

cos(Σ)=cos(Σ_eff)cos(δ). [1]

[0139] As also mentioned already, this difference is neglectable for tilt angles δ having relatively low absolute values of up to approximately 10°. Hence, for such small angles δ, the design of the tool base geometry can be carried out also with untilted axes position. In this case, Σ_eff=Σ and δ=0 is to be set in the above formulas. This procedure corresponds to the hitherto common manner.

[0140] For tilt angles δ having a larger absolute value, the difference between the effective intersection angle of axes Σ_eff and the intersection angle of axes Σ can no longer be neglected, if the design shall lead to acceptable cutting conditions. Then, the design must be carried out on the basis of the above formulas.

[0141] According to the invention, the absolute value of the tilt angle δ is always greater than 15 degrees, i.e., the tilt of the tool reference plane and thus of the skiving tool 100 with respect to the contact plane (which is spanned by the two velocity vectors {right arrow over (v)}₂ and {right arrow over (v)}₁) is significantly negative or significantly positive. Therefore, in relation with the present invention, either a significant tilt of the skiving tool 100 toward or a significant tilt away from the work piece 50, 60, 70 is concerned.

[0142] FIG. 12 shows a schematic view of a conical skiving tool 100 with respect to the so-called contact plane BE. This representation of the tilt towards the contact plane BE according to FIG. 12 is particularly illustrative.

[0143] FIG. 13 shows a schematic view of a conical skiving tool 100 with respect to the so-called contact plane BE. The representation of the tilt away from the contact plane BE according to FIG. 13 is particularly illustrative.

[0144] The position (orientation) of the tilt angle δ can be illustrated well on the basis of the FIGS. 12 and 13.

[0145] The calculation point AP with respect to the contact point BP, for a negative tilt angle δ, does not lie on the joint plumb GL as can be seen e.g., in FIG. 14B. For outer toothings, the joint plumb GL lies in the cutter half space, and for inner toothings in the chip half space. The contact plane BE is perpendicular to the work piece reference plane, but not to the tool reference plane. The rotation axis R2 of the work piece 50, 60, 70 is parallel to the contact plane BE. However, the rotation axis R1 of the skiving tool 100 intersects the contact plane BE in the cutter half space. For a work piece 50, 60, 70 with cylindrical toothing, the contact radius vectors {right arrow over (r)}₁ and {right arrow over (r)}₂ embrace the tilt angle δ, as can be seen, e.g., in FIG. 14B. It can be stated more generally that the tilt angle δ is the very angle, which is embraced by the contact radius vector {right arrow over (r)}₁ of the skiving tool 100 and the contact plane normal {right arrow over (n)}. It is noted that the relationships which have been described in this paragraph hold only for the tilt of the tool 100 towards the work piece.

[0146] On the basis of the tables and formulas presented above, corresponding relationships can also be determined for the inclination of the tool 100 away from the work piece.

[0147] Preferably, in all embodiments, the effective intersection angle of axes Σ_eff is in the following range: -60°≦Σ_eff≦60°.

[0148] According to the invention, for a tilt towards the work piece, the cutting face offset e is negative for cylindrical inner toothings and positive for cylindrical outer toothings. For a tilt away from the work piece, the sign of the cutting face offset e is opposite. According to the invention, the end relief angles (rake angles) must be provided constructionally at the skiving tool 100 when tilting towards the work piece. Here, the rake angle loss caused by the tilting of the tool cutting edges toward the cylindrical construction part (i.e., towards the work piece 50, 60, 70) must be compensated in addition. For a tilt away from the work piece, constructional rake angles must not necessarily be provided.

[0149] The side projection of contact plane in FIG. 14E shows the head rake angle α_KiKo achieved kinematically-constructionally as a sum of the kinematically generated negative rake angle α_Ki and the constructional tool rake angle α_Ko for a skiving tool 100 tilted towards the work piece.

[0150] According to the invention, a so-called modified skiving method for skiving a work piece 50, 60, 70 is concerned, wherein a rotational-symmetric periodic structure, e.g., an outer or inner toothing, is to be fabricated on the work piece 50, 60, 70 with application of a skiving tool 100.

[0151] As shown in the FIGS. 14A to 14E and on the basis of two further examples in the FIGS. 15A and 15B as well as 16A and 16B (these Figures are schematic drawings showing rolling (hobbing bodies), the modified skiving method is characterized in particular in that the skiving tool 100 has a collision contour, which tapers to the rear such that collisions with the work piece 50, 60, 70 during the skiving are avoided. This prerequisite holds for the significant tilt towards the work piece 50, 70, i.e., it holds for negative tilt angles δ having a large absolute value.

[0152] In the significant tilt away from the work piece 50, 60, 70, i.e., for large positive tilt angles δ, the skiving tool 100 preferably has a collision contour that proceeds reversely to the collision contour of a skiving tool 100 that is strongly tilted towards the work piece, as can be seen in FIG. 19 on the basis of a schematic example. In FIG. 19, the cone angle has been chosen such that the lateral surface of the base body 110 runs approximately parallel to the lateral cylinder surface of the work piece 50.

[0153] FIG. 20 shows a further skiving tool 100, which can be employed in relation with the invention. The skiving tool 100 shown has the form of a generating cutter. A massive tool is concerned here, in which the cutting teeth 111 are part of the skiving tool 100. Here, the skiving tool 100 has 24 cutting teeth 111, one of which is provided with a reference numeral in FIG. 20. The base body of the skiving tool 100 has the shape of a truncated cone disc or a truncated cone shaped plate.

[0154] FIG. 21A shows a further skiving tool 100, which can be used in relation with the invention. Here, the cutting faces of the cutting teeth 111 are arranged on a cone surface (eventually tilted). FIG. 21B shows the skiving tool 100 of FIG. 21A in engagement with a cylindrical work piece 50. Here, the skiving tool 100 is inclined away with a significant tilt angle 8 from the work piece 50. The tilt angle δ amounts to approximately 20 degrees here.

[0155] The skiving tool 100 shown in the FIGS. 21A and 21B has the shape of a spur-toothed cone wheel, wherein the teeth of this cone wheel represent the cutting teeth 111. The cutting faces are arranged on the front side with the smaller diameter. Stated more precisely, the cutting faces are arranged at the supplemental cone, i.e., on a cone surface (if appropriate, inclined with respect to the later).

[0156] The cant angle of the represented skiving tool 100 is 0 degrees. For cant angles different from 0 degrees, a corresponding skiving tool 100 has the base shape of a helically toothed cone wheel.

[0157] FIG. 22A shows a further skiving tool 100, which can be used in relation with the invention. Here, the cutting faces of the cutting teeth 100 are arranged on a cone surface (if appropriate, inclined). FIG. 22B shows the skiving tool 100 of FIG. 22A in engagement with a cylindrical work piece 50. Here, the skiving tool 100 is tilted toward the work piece 50 with a significant tilt angle δ. The tilt angle δ amounts to approximately -18 degrees here.

[0158] The skiving tool 100 shown in the FIGS. 22A and 22B has the shape of a spur-toothed cone wheel, whereby the teeth of this cone wheel represent the cutting teeth 111. The cutting faces are arranged on the front side with the larger diameter. Stated more precisely, the cutting faces are arranged on the supplemental cone, i.e., on a cone surface (if appropriate, inclined with respect to the later).

[0159] The cant angle of the represented tool 100 amounts to zero degrees. For cant angles different from zero degrees, a corresponding skiving tool has the base shape of a helically toothed cone wheel.

[0160] Preferably, the skiving tool 100 has a cone shaped, respectively conical or hyperbolical collision contour, respectively.

[0161] During the skiving machining, the following steps are performed simultaneously and in coordination:

[0162] coupledly performing a relative movement of the skiving tool 100 with respect to the work piece 50, 70, and

[0163] rotating the skiving tool 100 about a first rotation axis R1 and rotating the work piece 50, 70 about a second rotation axis R2, wherein

[0164] during the skiving, a positive or a negative tilt angle δ of the skiving tool 100 is set, the absolute value of which angle is larger than 15 degrees, and

[0165] the first rotation axis R1 runs skew with respect to the second rotation axis R2 (respectively the two rotation axis R1, R2 are lined skew relative to each other).

[0166] FIG. 14A shows a schematic view of a suitable skiving tool 100 having a collision contour that tapers to the rear side (here: conically) during the modified skiving of an outer-toothed cylindrical work piece 50. The following holds in this example: δ=-20 degrees and cone angle=30 degrees. Thus, the skiving tool is tilted significantly towards the work piece 50. FIG. 14A shows a top view of the cylindrical work piece 50. The front face 51 of the work piece 50 is in the plane of the drawing. The skiving tool 100 is supported by a tool spindle 170, which is represented schematically in the Figures.

[0167] FIG. 14B shows a further view of the embodiment of FIG. 14A. In FIG. 14B, the joint plumb GL and the contact point BP of the rolling circles W1, W2 of the skiving tool 100 and of the work piece 50 can be recognized. The contact point BP lies at the contact point of the rolling circle W1 of the skiving tool 100 having the radius vector {right arrow over (r)}₁ and the rolling circle W2 of the work piece 50 having the radius vector {right arrow over (r)}₂.

[0168] FIG. 14C shows a projection of intersection of axes of the embodiment of FIG. 14A. The intersection angle of axes Σ can be recognized in FIG. 14C. The joint plumb GL is perpendicular to the plane of drawing of FIG. 14C and is thus reduced to the intersection point of axes AK.

[0169] FIG. 14D shows a side projection of intersection of axes of the embodiment of FIG. 14A. In FIG. 14D, the projections of the two axes R1, R2 are parallel in the plane of the drawing. The joint plumb GL is also in the plane of the drawing.

[0170] FIG. 14E shows a side projection of contact plane of the embodiment of FIG. 14A. The representation of FIG. 14E concerns a view, which shows the contact point BP of the rolling circles W1, W2 and the significant tilt of the tool towards the work piece.

[0171] Preferably, the absolute value of the tilt angle δ is in a range between 15 and 45 degrees in all embodiments. An angle range between 20 and 35 degrees for the absolute value is particularly preferred.

[0172] The tapering collision contour of the skiving tool 100 is realized by a conical base body in the FIGS. 14A-14E. The base body of the skiving tool 100 may, however, have another tapering-narrowing shape so as to avoid collisions. For a negative tilt angle δ, the collision contour tapers to the rear, and for a positive tilt angle δ the collision contour tapers to the front, wherein this tapering collision contour for a positive tilt angle δ is optional. On the contrary, for a negative tilt angle δ, the collision contour tapering to the rear is necessary mandatorily.

[0173] The cone angle of the conical base body of the skiving tool 100 amounts to exemplifying 30 degrees here. The cone angle may also take other values as long as a positive effective head rake angle in the region of the cutting edges of the skiving tool 100 is ensured by taking into account the tilt angle δ and other prerequisites.

[0174] FIG. 15A shows a view of a cylindrical skiving tool 100 (here in the form of a peeling nozzle) in the modified skiving of an inner-toothed cylindrical work piece 70, wherein the skiving tool 100 is tilted away significantly from the work piece 70 (tilt angle δ=20 degrees). The work piece 70 is the same as for the collision considerations in the introductory part of the description. The corresponding inner ring 71 is represented in the top view of FIG. 15A as a circle only. FIG. 15B shows a schematic back side view of the contact plane of the work piece 70 together with the skiving tool 100. In the embodiment shown, differently as compared, e.g., to the FIGS. 7A to 8B, no collision results any more despite the cramped space conditions in the inner ring 71 of the work piece 70. On the basis of the example shown in the FIGS. 15A and 15B, it can be recognized that significantly tilting away is particularly suitable in particular in the machining of inner toothings and other inner periodic structures on the work piece 70 having an inner ring, if the inner ring has a ratio of inner diameter and the required plunging depths of the peeling nozzle of the skiving tool 100 into the work piece 70, which [ratio] is less than 2. The modified skiving method is also suitable for inner toothings arranged deeper in the interior of an inner ring. The term plunging depth does not only include the tooth width, but takes into account the total embodiment with respect to the axial position of the toothing in the inner ring.

[0175] According to the invention, it is also possible to avoid collisions by the significant negative tilting, depending on the embodiment, as shall be explained on the basis of the FIGS. 16A and 16B. FIG. 16A shows a schematic view of a suitable skiving tool 100 having a collision contour that tapers to the rear (here: conically) in the modified skiving of an outer-toothed cylindrical work piece 60. The work piece 60 corresponds to the work piece 20 shown in the FIGS. 9A and 9B. The work piece 60 comprises a first cylindrical section 61 and a second cylindrical section 62, wherein an outer toothing is to be machined at the first cylindrical section 61 by means of skiving with application of a conical skiving tool 100. The following holds in this example: Σ_eff=18 degrees=, δ=-24 degrees and cone angle=34 degrees. Thus, the skiving tool 100 is tilted significantly towards the work piece 60. FIG. 16B shows a further schematic view of the conical skiving tool 100 and the work piece 60 of FIG. 16A.

[0176] Preferably, for all embodiments, having a significantly negative tilt angle δ, the skiving tool 100 has a lateral shape of base shape having a collision contour that tapers to the rear. For this purpose, the lateral shape or base shape can be composed, e.g., of a cylindrical part and a truncated cone-shaped part. Preferably, at least the section 101 of the type like a skiving wheel of the skiving tool 100 has a tapering collision contour, as shown, e.g., in the FIGS. 12, 13, 14A to 14E, 16A, 16B, 18A, 18B, 20, 22A and 22B.

[0177] FIG. 17 shows a preferred embodiment of a skiving tool 100 that can be used for the significant tilting away of about 16 degrees. The skiving tool 100 is designed especially for the manufacturing of a rotational-symmetric periodic structure on a work piece 50, 70 (e.g., in a configuration as shown in FIG. 2) with an application of the modified skiving method. The skiving tool 100 comprises a cylinder-shaped and/or cone-shaped base body 110 having a central rotation axis R1. The base body 110 has a plurality of reception openings 112. FIG. 17 shows a configuration, in which all of the reception openings 112 are equipped with bar cutters 120. In the example shown, the skiving tool 100 is equipped with 23 bar cutters. The reception openings 112 extend obliquely into the interior of the base body 110, starting from the insert opening on the front face 113 directed toward the work piece. From the front face 113 of the base body 110 directed toward the work piece it is e.g., possible to screw a screw 116 through a corresponding central bore 115 of the base body 110 into an inner threat of the tool spindle 170 for fixing the skiving tool 100 on the tool spindle 170.

[0178] Preferably, in all embodiments, the skiving tool 100 is characterized in that one or two through borings 117 are conceived in the lateral surface of the base body 110. These through borings 117 are designed for fixing the bar cutters 120 in the base body 110.

[0179] The skiving tool 100 can comprise an adapter 130 in addition to the base body 110, as indicated in FIG. 17.

[0180] FIG. 18A shows a schematized view of a skiving tool 100 tapering conically, which can be employed in relation with the invention for a tilt angle δ of -20 degrees. As shown in the schematic representation of FIG. 18A, the skiving tool 100 concerns a so-called cutter head tool, which has a cutter head base body 110 (here comprising a truncated cone-shaped (conical) portion 160), which is equipped with cutter inserts, preferably in the form of bar cutters 120. The skiving tool 100 is fixed movement-specifically to a machine 200. The cone angle λ has been chosen in FIGS. 18A and 18B such that the lateral face of the base body 110 respectively the truncated cone-shaped (conical) portion 160 extends approximately parallel to the cylindrical lateral face of the work piece 50.

[0181] FIG. 18B shows a schematized view of the skiving tool 100 of FIG. 18A together with a cylindrical work piece 50, whereby a tilt angle δ of -20 degrees is predetermined. The skiving tool 100 has a collision contour that is chosen such that no collision of the skiving tool 100 results with the work piece 50 despite the significant tilt towards with δ=-20 degrees.

[0182] However, the skiving tool 100 may have any other shape, as shown by way of indication, e.g., in FIG. 20. FIG. 20 shows a skiving tool that has the shape of a generating cutter. Here, a massive tool is concerned, in which the cutting teeth 110 are part of the skiving tool 100. Here, the skiving tool comprises 24 cutting teeth 111, one of which is provided with a reference numeral in FIG. 20. The base body of the skiving tool 100 has the shape of a truncated cone disc or a truncated cone-shaped plate.

[0183] A machine 200, which is designed for the skiving according to the invention, comprises a CNC control 201, which enables a coupling of the axes R1 and R2, respectively a coordination of the movements of the axes. The CNC control 201 may be a part of the machine 200, or it may be implemented externally and suitable for a communication-specific connection 202 with the machine 200. The corresponding machine 200 comprises a so-called "electronic gear train", respectively "electronic or control-specific coupling of axes" in order to perform a relative movement of the skiving tool 100 with respect to the inner-toothed skived work piece 70. The coupledly moving of the skiving tool 100 and the work piece 70 is performed such that during the machining phase, a relative movement between the skiving tool 100 and the work piece 70 results, which corresponds to a relative movement of a helical gear. The electronic gear train, respectively the electronic or control-specific coupling of axes enables a synchronization in terms of the rotational frequency of at least two axes of the machine 200. Herein, at least the rotation axis R1 of the tool spindle 170 is coupled with the rotation axis R2 of the work piece spindle 180. In addition, preferably in all embodiments, the rotation axis R2 of the work piece spindle is coupled with the axial feed 203 in the direction R1. The movement of the axial feed 203 is represented in FIG. 23 by a double arrow 204. In addition, the work piece spindle can be shifted linearly by means of a cartridge 205 parallel to the rotation axis R2, as represented by a double arrow 206. In addition, the cartridge 205 together with the work piece spindle 180 and the work piece 70 can be rotated about a pivot axis SA, as indicated by a double arrow 207.

[0184] Preferably, a machine 200 comes to application, which is based on a vertical arrangement, as shown in FIG. 23. In such a vertical arrangement, either the skiving tool 100 together with the tool spindle sits above the work piece 50, 60, 70 together with the work piece spindle 180, or vice versa. The chips, which are generated during the skiving, fall downward due to the action of gravity and may be removed, e.g., via a chip bed which is not shown.

[0185] In addition, a machine 200 which is designed for the modified skiving according to the invention, cares for the correct complex geometrical and kinematical machine settings and axes movements of the axes mentioned above. Preferably, in all embodiments, the machine has six axles. Five of these axles were already described. As a sixth axle, an axle may be conceived, which enables a linear relative movement of the work piece 50, 60, 70 with respect to the skiving tool 100. This linear relative movement is indicated in FIG. 23 by the double arrow 208.

[0186] The modified skiving method can be applied dry or wet in all embodiments, wherein the dry skiving is preferred.

[0187] In all embodiments, the work piece 50, 60, 70 may be pre-toothed or untoothed. For an untoothed work piece, the skiving tool 100 works into the massive material.

[0188] In all embodiments, the work piece 50, 60, 70 may be post-machined, preferably through application of a planishing method.

[0189] The modified skiving described and claimed herein offers a high productivity and flexibility.

[0190] The application spectrum of the modified skiving is large and extends to the manufacturing of rotational-symmetric periodic structures.

[0191] The modified skiving described herein enables high rates of material removal. At the same time, it enables to achieve favorable surface structures on tooth flanks and other machined surfaces.

[0192] In the modified skiving, material is progressively removed from the work piece 50, 60, 70 until the teeth, respectively the tooth gaps or other periodic structures are formed completely.

[0193] The modified skiving concerns a high performance method that has significant potentials in the machining time. In addition to the low cycle times, the tool costs are relatively low. All these aspects contribute to the particular cost effectiveness of the modified skiving.

Claims

1. A method for skiving a work piece having a rotationally-symmetric, periodic structure comprising applying a skiving tool, the method further comprising: coupledly performing a relative movement of the skiving tool in relation to the work piece; rotating the skiving tool about a first rotation axis; rotating the work piece about a second rotation axis that is skew relative to the first rotational axis; and setting a positive or a negative tilt angle of the skiving tool during the skiving having an absolute value of greater or equal to 15 degrees.

2. The method according to claim 1, wherein said relative movement during skiving corresponds to a relative movement of a helical gear.

3. The method according to claim 1, wherein the setting step includes tilting the skiving tool towards the work piece during a machining phase at an angle between -15 degrees and -45 degrees.

4. The method according to claim 1, wherein the setting step includes tilting the skiving tool away from the work piece during a machining phase at an angle between +15 degrees and +45 degrees.

5. The method according to claim 1, wherein the skiving tool comprises a plurality of cutting teeth, each having constructional rake angles.

6. The method according to claim 3, further comprising providing a kinematic-constructionally head rake angle from a sum of a kinematically generated negative rake angle and a constructional rake angle of the skiving tool.

7. The method according to claim 1, wherein the rotationally-symmetric, periodic structure includes (i) a toothing comprising interior teeth or (ii) a toothing comprising exterior teeth of the work piece.

8. The method according to claim 1, wherein the work piece is a cylindrical work piece defining a predetermined cutting face offset.

9. The method according to claim 1, wherein the work piece allows only a small overrun.

10. The method according to claim 1, wherein the work piece comprises an inner ring and the skiving tool comprises a peeling nozzle, and wherein the inner ring has a ratio of an inner diameter to a plunging depth of the peeling nozzle into the work piece which is less than 2.

11. An apparatus for skiving a work piece having a rotationally-symmetric, periodic structure by applying a skiving tool, the apparatus comprising: a skiving tool; a tool spindle configured to fix the skiving tool; a work piece spindle configured to fix the work piece; and, numerically controlled drives configured to coupledly perform a relative movement and to coupledly rotate the skiving tool together with the tool spindle about a first rotation axis and the work piece together with the work piece spindle about a second rotation axis, wherein the apparatus includes a numerical control or is connectable with a numerical control configured to provide a tilt angle during the skiving having an absolute value of greater or equal to 15 degrees, and the first rotation axis skew with respect to the second rotation axis.

12. The apparatus according to claim 11, wherein the skiving tool has a tool section, which has cutting edges defining cutting teeth which project outward obliquely.

13. The apparatus according to claim 11, wherein the skiving tool has a tool section defining one of a disc-type generating cutter, a deep counterbore-type generating cutter or a shank-type generating cutter.

14. The apparatus according to claim 11, wherein the numerical control is configured to tilt the skiving tool during skiving towards the work piece such that said tilt angle is between 15 degrees and -45 degrees.

15. The apparatus according to claim 11, wherein the numerical control is configured to tilt the skiving tool during skiving away from the work piece the such that said tilt angle is between +15 degrees and +45 degrees.

16. The apparatus according to claim 11, wherein the apparatus is a machine comprising six axes.

17. The apparatus according to claim 11, wherein the skiving tool is a massive tool or a bar cutter skiving wheel.

18. The apparatus according to claim 11, wherein the numerical control is configured to set said tilt angle at either a positive or a negative tilt angle.

19. The apparatus according to claim 12, wherein the tool section defines a skiving wheel.

20. The apparatus according to claim 13, wherein the tool section defines a skiving wheel.