Patent Application
20140105698
The invention relates to a method for skiving an outer toothing or another outer periodic structure and an apparatus for skiving an outer toothing or another periodic structure comprising an according skiving tool.
There are numerous methods for manufacturing gear wheels. In the chip-producing soft pre-machining, one distinguishes hobbing, gear shaping, generating planing and skiving (in English also called power skiving). The hobbing and skiving are so-called continuous methods, as shall be explained in the following.
In the chip-producing manufacturing of gear wheels, one distinguishes between the intermitted indexing process or the single indexing process and the continuous method, which is sometimes also called a continuous indexing process or face hobbing.
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 of the tool in coordination with respect to the coupled driving of a plurality of axis drives of a machine.
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.
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
Some time ago a method has been taken up anew, which is called 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.
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.
As shown in
The cutting speed in skiving is influenced directly by the rotational speed of the skiving tool 10 relative 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.
The movement sequences and further details of an established skiving method can be taken from the schematic representation in
Further relative movements come in addition. The axial feed sax already mentioned is required in order to be able to machine with the tool 10 the entire toothing width of the work piece 20. The axial feed causes a shifting of the tool 10 with respect to the work piece 20 in a direction parallel to the rotation axis R2 of the work piece 20. The direction of this movement of the tool 10 is referenced in
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 are tilted with respect to each other by the intersection angle of axes E. 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 vc of the skiving process may thus be changed by the intersection angle of axes Σ and the rotation speed in the equivalent helical gear. In skiving, the axial feed sax, which is relatively slow as already mentioned, has only a small influence on the cutting speed vc, which can be neglected. Therefore, the axial feed sax is not taken into account in the vector diagram comprising the vectors {right arrow over (v)}1, {right arrow over (v)}2 and {right arrow over (v)}c in
The skiving of an outer toothing of a work piece 20 using a conical skiving tool 10 is shown in
For skiving, a tool is applied, which comprises at least one geometrically determined cutting edge. The cutting edge/cutting edges are not shown in
In the example shown in
When starting from a straight-toothed or a helically toothed conical skiving tool 10, as shown in the
Investigations of previous skiving methods have shown that a significant wear of the skiving tool 10 may arise depending on the design of the skiving tool 10. Therefore, solutions are searched which enable reducing the wear of the skiving tool 10, respectively improving the durability of the skiving tool 10. For reducing the wear of the skiving tool 10, one may, for example, conceive as many cutting teeth on the tool 10 as possible. Thereby, the skiving method becomes more economic, because the manufacturing cost for toothing of work pieces 20 is influenced substantially by the tool life of the tools. For accommodating as many cutting teeth on the tool 10 as possible, the skiving tool 10 must be constructed as large as possible. Limits are set for the possible size of the usable skiving tools 10, in particular, by the utilized machining machine. Stated more precisely, a limitation exists in the work space of the machine as well as in the possible travelling distances of the axes with respect to the arrangement of the axes.
The problems which result due to the limitation of the work space are explained in more detail as follows with reference to the
The problems, which result due to the limitation of the distance between axes, respectively, the travelling distance of the axes of a machine, shall be explained in more detail in the following with reference to the
For improving the tool life of the skiving tools 10, one may increase the number of the cutting teeth, as already mentioned. Ideally, one would not only increase the number of the cutting teeth, but one would equip the skiving tool 10 with regrindable cutter bars. Then, the cutter bars can be reground at the cutting teeth or they can even be exchanged in case of need. Also, this contributes to an improvement of the cost effectiveness. Here, however, one can achieve a high packing density of the cutter bars only as a result of a very complex arrangement of the cutter shafts of the cutter bars, as described for example in the German utility model application DE 202011050054.3, which has been filed on 6 May 2011 under the title “Wälzschälwerkzeug mit Messerstäben” (English: “skiving tool comprising cutter bars”).
Alternatively, it is possible to work with a partial equipment of the skiving tool 10 in order to avoid a penetration of the cutter shafts which results for a high packing density of the cutter bars. That is, not all the cutting teeth of a complete skiving wheel are formed, but e.g., only each second or third. Thereby, however, the factual number of cutting teeth is reduced, which is to the disadvantage of the tool life of the tool.
It is an object of the present invention to provide a method and an apparatus for the chipping machining of the tooth flanks of a tooth wheel or other periodic outer structures, which feature a reduction of the production cost per tooth wheel or work piece.
Of particular concern is to ensure a number of cutting teeth and thus a tool life that are as high as possible under the restrictions of the work space and the travelling distances of the machining machine to be employed.
Of particular concern is to keep the tool cost as low as possible by improving the tool life of the tools.
Preferably, the cutting teeth of the skiving tools shall be formed by regrindable cutter inserts (e.g., in the form of cutter bars).
The object is solved according to the present invention by a method, which is called inside skiving method herein.
The inside skiving method can be utilized in relation to the manufacturing of rotationally symmetrical, periodical, outer structures, such as outer toothings and the like.
In the inside skiving method, a skiving tool is applied, which shall be called inside skiving ring due to its special constructional shape.
According to the invention, a method and an apparatus for skiving a work piece with an outer, rotationally symmetric periodic structure by applying a skiving tool is concerned. The following steps are performed:
According to the invention, the relative movement sequences (called relative movements) between the work piece and the inside skiving ring are predetermined and performed such that material is taken off continuously at the outside of the work piece until the teeth or the other outer periodic structures are formed completely.
Preferably, the cutting faces are arranged rotationally symmetric with respect to the rotation axis of the inside skiving ring on a frontal cone surface, which may tilt with respect to a frontal plane.
According to the invention, a radial movement may be superimposed on the relative feed movement of the inside skiving ring, so as to influence, e.g., the crowning of the teeth according to the technical teaching of the German patent application DE 3915976 A1.
The inside skiving may be applied on an untoothed work piece, preferably in a soft machining.
The inside skiving may be applied at a pre-toothed work piece, preferably after a soft machining.
During the inside skiving, the rotating inside skiving ring performs an axial feed movement with respect to the rotating work piece in the direction of the second rotation axis, wherein this axial feed movement runs in the same direction or in the opposite direction relative to the cutting direction.
According to the invention, the tooth gaps can be brought directly to the full depth and do not have to be generated in this case by a multiple cutting strategy.
The inside skiving can be applied in the framework of a multi-cut skiving method. According to the invention, radial movements may be superimposed to the axial movements, so as to implement a multiple cutting strategy or so as to generate incoming or outgoing tooth grooves according to the technical teaching of the international patent application WO 2010/060733 A1.
According to the invention, the tool life of the inside skiving rings serving as the skiving tool is significantly improved, because more cutting teeth can be accommodated due to the special constructional shape of the inside skiving rings. In particular, more cutting plates or cutter bars can be accommodated on the inside skiving ring than previously under the described limitations of real machining machines for skiving tools.
In the inside skiving, the rotation axis of the inside skiving ring is set skew with respect to the rotation axis of the work piece, i.e., the intersection angle of axes Σ is always different from zero.
In addition, the inside skiving ring can be inclined toward the work piece or inclined away from the work piece during the skiving, as described, for example, in a parallel application of the present applicant, which has been filed in the European patent office on 26 May 2011 under the application number EP 11167703.5.
The inside skiving concerns a continuous chip removing method.
Preferably, in all embodiments, a disc-like inside skiving ring is applied, which differs significantly from other skiving tools.
According to the invention, the inside skiving ring has a disc-like tool section, which has cutting heads, which are formed in the shape of cutting teeth, which project straight or obliquely into the interior space in the direction of the rotation axis of the inside skiving ring.
The disk-like inside skiving rings according to the invention may be implemented as so-called bulk tools, i.e., tools are concerned which are carried out essentially as one piece. For the bulk tools, the cutting teeth are an integral component of the tool. In all embodiments of the invention, cutter head inside skiving rings (herein called cutter bar inside skiving rings) are particularly preferred, which have an annular (mostly disc-like) cutter head base body, which is equipped with cutter inserts, preferably in the form of cutter bars, such that the cutting teeth project straight or obliquely into the interior space in the direction of the rotation axis of the inside skiving ring. Embodiments of the invention are also possible, which are designed as cutting plate tools, which have an annular (mostly disc-like) cutter head base body, which is equipped with cutting plates, the cutting teeth of which project straight or obliquely into the interior space in the direction of the rotation axis of the inside skiving ring.
Compared to the conventional skiving, the invention offers a number of advantages, which are listed in summary in the following:
The method according to the invention may be performed in relation with both dry and wet machining.
The method according to the invention may be utilized for the soft and/or hard machining.
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, for reasons of simplicity of the representation, the work piece and the skiving tool are reduced to the situation on the rolling circle (e.g., rolling cylinder). However, the represented conditions hold for the entire toothing having one tooth height.
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.
Rotational-symmetric periodic outer structures are, for example, gear wheels having an outer toothing. However, for example, also brake discs, clutch or gear transmission elements, and so on may be concerned. The inside 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, belt pulleys, and so on. Herein, the periodic structures are also called periodically repeating structures.
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 outer structures. In this case, these other construction parts do not concern tooth gaps, but, for example, grooves or channels.
For reasons of simplicity, all drawings are reduced to the situation at the rolling circles e.g., rolling surfaces. Therefore, the corresponding rolling bodies are shown in the drawings.
The skiving method according to the invention, which is herein also called the inside skiving method, is for the skiving of a work piece 50 having a rotationally symmetric, periodical, outer structure by applying an inside skiving ring 100. The inside skiving ring 100 that is applied herein has an annular base body 112, which can be recognized clearly, e.g., in
The inside skiving ring 100 is an inside tool, which spans a (mostly circular) interior space 113. The inside skiving ring 100 has a plurality of cutter heads 111 (not shown in
The cutting faces 121 are arranged rotationally symmetric with respect to the rotation axis R1 of the tool 100 on a front-side cone surface, which may be tilted with respect to a front plane.
The cutting faces 121 may be formed as plane surfaces or as slightly curved surfaces on the cutter heads 111. The cutting faces 121 may also be slightly convex.
Generally (i.e., for all embodiments) it holds that in the skiving, the cutting direction, respectively, the cutting speed vector {right arrow over (v)}c embraces an angle different from 90 degrees with respect to the rotation axis R1 of the tool 100. The acute one of the two embraced angles is preferably smaller than or equal to 60 degrees, particularly preferably smaller than or equal to 45 degrees.
Due to the complex kinematics, the cutting speed vector of a point of the cutting edge, which results during the chip cutting at the cutting edges, possibly deviates from the cutting speed vector {right arrow over (v)}c at the calculation point AP during the skiving. However, this deviation is not large so that also for these effective cutting speed vectors the following statements may be made (this statement holds for all embodiments of the invention):
In
The example of
In such an exemplifying embodiment, a conical inside skiving ring 100 may comprise in total 56 cutting heads 111 which point inwardly and which are formed in the shape of cutting teeth, for a ring strength RS of 50 mm with a rolling circle diameter that is as large as possible of approximately 494 mm. The distance AA between axes amounts to only approximately 147 mm here.
In comparison to, for example, the
A further advantage of the inside skiving rings 100 according to the invention is the higher overlap during the engagement of the cutting teeth 111. The resulting longer engagement distance leads to better chip-forming conditions.
In all embodiments of the invention, the two rotation axes R1 and R2 are skew with respect to each other. The intersection angle of axes Σ is always different from zero.
Preferably, during the inside skiving, the inside skiving rings 100 according to the invention may be inclined towards the work piece 50 or inclined away from the work piece 50. The inclination of the tool 100 is optional. Generally it serves to avoid collisions. In addition, however, it provides the following advantages:
The tilt angle δ is defined on the basis of the
If the tilt angle δ is zero, the rotation axis R1 of the inside skiving ring 100 runs parallel at a distance to the contact plane BE, i.e., the rotation axis R1 does not intersect the contact plane BE in an intersection point SP.
Preferably, the tilt angle δ is in the range between −30 degrees and +30 degrees.
In the following, several examples for inclined inside skiving rings 100 during the skiving are described.
In
Cylindrical as well as conical inside skiving rings 100 are suitable as skiving tools 100, which are inclined away from the work piece 50, whereby a collision of the inside skiving ring 100 with the work piece 50 does not result due to the inclination away.
In
According to the invention, each cutter head 111 respectively each cutting tooth has a cutting head tip 122, which projects into the interior space 113 and points in the direction of the first rotation axis R1. This aspect of the inside skiving rings 100 according to the invention can be recognized, e.g., in
This statement holds also for bulk tools (see e.g.,
In all embodiments, the cutter head 111 projects at least for a portion out of the material of the base body 112 and into the interior space 113.
In
Preferably, in all embodiments of the invention, the minimum inner diameter of the inside skiving ring 100 is at least 1.5 times as large as the outer diameter DWA of the work piece 50 to be machined. Inside skiving rings 100, the minimum diameter of which are at least two times as large as the outer diameter DWA of the work piece 50 to be machined, are particularly preferred. In addition to the prerequisite of a suitable inner diameter DI for a collision-free reception of the work piece 50 it should be observed during the definition of the intersection angle of axes Σ and the tilt angle δ (if this is different from zero), that a collision of the work piece 50 with the tool 100 does not result. In addition to the prescription of the inner diameter DI, respectively, the minimum inner diameter, the intersection angle of axes Σ and the tilt angle δ (if this is different from zero), the inner mantle surface 114 may have a conicity (as shown e.g., in
In
The tool 100 of
For the inclination towards the work piece 50, the inside skiving ring 100 is preferably formed conically in order to avoid collisions. For the inclination away from the work piece 50, the inside skiving ring does not need to be formed conically. In this case, it may, e.g., also be formed cylindrically. In
On the basis of
The inside skiving method comprises the following steps:
During the skiving, the two rotation axes R1, R2 are set skew relative to each other with an intersection angle of axes Σ.
The inside skiving is characterized in that the inside skiving ring 100 spans an interior space 113 and comprises a plurality of cutting teeth 111. At least one cutting edge, one cutting head tip 122 and one cutting face 121 are provided on each cutting tooth 111. The cutting faces 121 of all the cutting teeth 111 are arranged rotationally symmetric with respect to the first rotation axis R1 on a front plane SE or a front-side cone surface KE of the inside skiving ring 100. The cutting teeth 111 project into the interior space 113 and point in the direction of the first rotation axis R1.
According to the invention, a feed motion opposite to the cutting direction or an aligned feed motion is generated by an according axial feed VB of the inside skiving ring 100 relative to the work piece 50. The direction of the feed motion VB is indicated in the
In all embodiments, the effective intersection angle of axes Σeff is preferably in the following range: −60°≦Σeff≦60°, Σeff≠0°. Effective intersection angles of the axes Σeff between, in absolute value, 5 and 45 degrees are particularly preferred.
A CNC-controlled superposition of the coupled rotations of the inside skiving ring 100 about the first rotation axis R1 and the work piece 50 about the second rotation axis R2, and the feed movements VB of the skiving tool 100 relative to the work piece 50 result in a chip-cutting skiving movement of the cutting teeth 111 of the inside skiving ring 100.
At the beginning of the inside skiving, the inside skiving ring 100 can be plunged radially from the outside to the inside into the material of the work piece 50, or the inside skiving ring 100 can be plunged axially, i.e., coming from the front side 53 of the work piece 50. In the
In the following paragraphs, further explanations concerning the inside skiving according to the invention are provided.
Basically, also in the inside skiving, the relative movement between the inside skiving ring 100 and the work piece 50 corresponds to a helical gear, also called generation helical type gear transmission. The helical gear concerns a spatial transmission gear.
The basic design of the inside skiving process therefore occurs at a so-called calculation point AP (see e.g.,
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, the 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.
Thus, the correct design of the engagement conditions at the calculation point AP has a considerable importance in the design of skiving processes.
Terms concerning the arrangement of axes:
There are several terms, which are required for the definition of the arrangement of axes. These terms are described in Table 1 below.
Terms concerning the contact between the skiving tool and the work piece:
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.
Further Projections:
There are different further projections, which are employed for illustrating the invention. The further projections are explained in Table 3 below.
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(Σeff)·cos(δ) [1]
The intersection angle of axes Σ is decomposed into the effective intersection angle of axes Σeff and the tilt angle δ, wherein the effective intersection angle of axes Σeff is the determining parameter for the generation of the relative cutting movement with the cutting speed vector {right arrow over (v)}c between the rotating skiving tool 100 and the rotating work piece 50. For planar toothings, the effective intersection angle of axes Σeff and the tilt angle δ are well defined, however, the relation [1] does not hold.
According to the invention, a tilt angle δ can be prescribed, the absolute value of which is different from zero degrees, i.e., the tilt of the tool reference plane and thus of the skiving tool 100 with respect to the contact plane BE (which is spanned by the two speed vectors {right arrow over (v)}2 and {right arrow over (v)}1) is negative or positive.
According to the invention, in all embodiments, the inside skiving ring 100 has cutting edges and cutting faces, which are formed on cutting teeth 111, wherein the cutting teeth 111 project inwardly straight or obliquely, as can be recognized, e.g., in the
The inside skiving method can be applied on an untoothed work piece 50, preferably in the framework of a soft machining.
The inside skiving method may also be applied on a pre-toothed work piece 50, preferably after a soft machining. That is, the inside skiving method may also be applied for the hard or finishing machining. The according inside skiving method is also called inside hard skiving herein.
The inside skiving method may, however, also be applied in the framework of a multi-cut skiving method.
In the framework of such a multi-cut skiving method, several approaches are possible. The periodical structures on the work piece 50 may be generated either in two or more than two cutting phases. During a first cutting phase, e.g., a gap or groove can be cut to a depth of 50%. Then, the inside skiving ring 100 is set radially further inward in the direction of the rotation axis R2 of the work piece 50 to the full depth, and the gap or groove can then be cut to the full depth in the second cutting phase.
The rolling circle diameter dw1 of the inside skiving ring 100 is significantly greater than the rolling circle diameter dw2 of the work piece 50 in all embodiments of the invention. Preferably, the rolling circle diameter dw2 of the work piece 50 amounts to less than 60% of the rolling circle diameter dw1 of the inside skiving tool 100.
Preferably, the longitudinal axes LA1, LA2, LA3 of all the cutter bars 120 in all inside skiving rings 100 according to the invention that are formed as cutter head tools point inwardly in the direction of the rotation axis R1, as shown in
A machine 200, which is designed for the inside 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 feed movement VB of the inside skiving ring 100 with respect to the outer-toothed power skived work piece 50 (the work piece 50 is not visible in
Preferably, a machine 200 is employed, which is based on a vertical arrangement as shown in
In addition, the machine 200, which is designed for the inside skiving according to the invention, addresses the correct complex geometrical and kinematical machine settings and axes movements of the mentioned axes. Preferably in all embodiments, the machine comprises six axes. The following axis movements are preferred:
It can be recognized in
A cup-shaped tool spindle 170 and/or a cup-shaped adapter may also be implemented as a bulk tool and be equipped with cutting plates.
A cup-shaped tool spindle 170 and/or a cup-shaped adapter may, however, also be designed for fixing a separate annular inside skiving ring 100.
Due to the special configuration for the inside skiving, machines 200 having a work space AR with a maximum dimension in the direction of the distance between axes from the first rotation axis R1 to the second rotation axis R2, which is as large as the maximum outer diameter of the inside skiving ring 100, are sufficient (i.e., the diameter DA of the base body 112 together with the projecting cutting piece 111, respectively the cutter bars 120, is concerned).
In all embodiments, the inside skiving method can be applied dry or wet, wherein the use of the inside skiving method in a dry way is preferred.
The application spectrum of the inside skiving method is large and extends to the application in the manufacturing of the most different rotationally symmetrical periodical structures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11 167 703.5 | May 2011 | EP | regional |
| 11 173 901.7 | Jul 2011 | EP | regional |
This application is the U.S. National Phase of International Application No. PCT/EP2012/059062, entitled “Method for Hob Peeling External Teeth and Device Having a Corresponding Hob Peeling Tool”, filed on May 15, 2012, which claims priority under 35 U.S.C. §119(a)-(d) from European Patent Application No. EP 11 173 901.7, filed Jul. 14, 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.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/059062 | 5/15/2012 | WO | 00 | 11/26/2013 |
