Abstract:
A torque transmission device such as a fixed constant velocity ball joint constructed as an opposed track joint and a process for producing such a device, in which the curvatures bases of the tracks of the joint deviate in their axial course from the curvatures of the ball contact lines. The process is characterized in that prior to the formation of a longitudinal profile of the joint component, the component is brought to an increased hardness by a hardening process and a diffusion layer is partially or completely removed in the region of the longitudinal profile.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of international patent application no. PCT/DE2007/001183, filed Jul. 5, 2007 designating the United States of America and published in German on Jan. 10, 2008 as WO 2008/003303, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany patent application nos. DE 10 2006 031 002, filed Jul. 5, 2006; DE 10 2006 037 847, filed Aug. 12, 2006 and 10 2007 030 898, filed Jul. 3, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a torque transmission unit having at least one component for transmitting torques via each of two functional areas formed onto the component and causing the torque flow by a formfitting engagement with other elements, at least one of the two functional areas being constructed as a profile, such as longitudinal teeth. 
     Torque transmission units of this type are disclosed, for example, in U.S. Pat. No. 6,872,143 (=DE 102 20 715) in connection with side shafts and in US 2006/0014587 (=DE 102 37 172) in connection with longitudinal shafts. 
     In U.S. Pat. No. 6,872,143, two such components are provided for each of the fixed, constant velocity ball joints provided on both ends of the side shaft, on each of which different functional areas formed onto the particular component are provided, which cause the torque flow by formfitting engagement and one of which is constructed as longitudinal teeth. 
     One component is the joint external part, whose one functional area causing the torque flow by formfitting engagement is a connection pin having formed-on longitudinal teeth, which is provided on the joint external part, and whose other functional area transmitting the torque are the raceways in the joint external part for the balls of the joint. 
     The second component also having two functional areas for transmitting torque is the joint internal part having formed-on longitudinal teeth in the central internal area as one functional area and having formed-on ball raceways of the joint internal part as the other functional area. 
     In the torque transmission unit according to US 2006/0014587, a component having two functional areas for transmitting torque is also provided for each of the three joints contained therein, namely a joint internal part having formed-on longitudinal or spline teeth as one functional area and formed-on ball raceways as the other functional area in each case. 
     In components of this type, i.e., joint parts, for example, the internal teeth are typically broached and the external teeth are typically produced by pounding, milling, or rolling, and the ball raceways are produced by machining or by a non-chip-forming or chipless technique. 
     To be able to transmit sufficient torque, at least the ball raceways are hardened. These raceways may be inductively hardened and the remaining area, i.e., also the longitudinal teeth, may be left at the basic hardness. This is advantageous for producing longitudinal teeth, but does not permit the high torque values to be transmitted and the desired service life to be achieved, which are required in many cases. 
     The inductively hardened ball raceways, for example, must be machined hard because of the distortion occurring upon partial hardening after the hardening to achieve the acquired precision, i.e., hard milling or grinding must be performed. 
     Another known possibility is to first manufacture the teeth in the soft state, to case-harden the entire part, i.e., having formed-on longitudinal teeth, which results in hardening distortion of both the teeth and also the spline teeth, however, which may only be remedied in the longitudinal teeth with additional great effort, namely by hard broaching in the hard layer using corresponding suitable, but costly special machines and tools, for example. 
     SUMMARY OF THE INVENTION 
     The present invention was based on the one hand on the object, in torque transmission devices of the type described above of obtaining high strengths and thus ensuring the transmission of high torques at high precisions, i.e., optimum fit and optimum true running, as well as allowing cost-effective and efficient production, and increasing the service life of assemblies, machines, and devices equipped with components of this type. 
     Furthermore, the invention relates to torque transmission devices, such as fixed, constant velocity ball joints as opposed track joints having 
     a joint external part having external tracks, 
     a joint internal part having internal tracks, 
     torque-transmitting balls, which are accommodated in track pairs made of external tracks and internal tracks, 
     a ball cage having cage windows, in which balls are retained and guided upon joint deflection, 
     first external tracks forming first track pairs, in which first balls are retained, with first internal tracks, 
     second external tracks forming second track pairs, in which second balls are retained, with second internal tracks, 
     the first track pairs and the second track pairs forming ball contact lines having opposing curvatures, 
     the external tracks and the internal tracks being delimited by external and internal track bases. 
     In opposed track joints as are described, for example, in U.S. Pat. No. 6,872,143, the ball raceways and/or running channels are produced in practice by chip removal. 
     It has already been suggested in U.S. Pat. No. 7,396,284 (=DE 102 09 933) that the external tracks or running channels be formed in a non-chip-forming or chipless manner. 
     The chip-removing production according to U.S. Pat. No. 6,872,143 is primarily complex, and requires costly machines and long machining times. It also causes significant waste and quality losses in regard to the strength, because the material flow lines are cut through by the machining in a joint internal or external part produced as a preform by forging. 
     To produce the ball raceways in joints such as those of U.S. Pat. No. 7,396,284 in a chipless or non-chip-forming manner, the prior art describes the possibility, for example, of providing hot-cold or warm-cold processes, a preform being produced within a forging procedure, for example, and the required precision being able to be achieved in a cold calibration process. 
     Because it is an opposed track joint, differing tools each having opposing ball raceways must already be provided for the production of the preform for such a process. The part precision is also limited by the guiding precision of the machine. 
     The unavoidable indexing irregularity in the preform also can no longer be remedied in the following machining steps. 
     A tool having the same irregularities is also required for the calibration process for each of the different ball raceways. 
     The invention is based on the further object of avoiding these disadvantages and allowing cost-effective and high-quality production of internal and/or external joint parts and thus of fixed, constant velocity joints, in that investment costs for complex and costly machines are avoided, tool wear is reduced, and short machining times are ensured with an optimization of the quality, in particular also in regard to achieving higher torque transmission values. Furthermore, the indexing precision is to be improved and waste-free production, in particular of the ball raceways, is to be made possible, so that machining times, in particular machine run and handling times, are reduced. Moreover, higher carrying capacities are to be achieved and waste is to be avoided. 
     A solution according to the invention for the first part of the object is achieved in that in a torque transmission unit, which has at least one component having two functional areas for transmitting torque, and one of the functional areas being constructed as a longitudinal profile, in particular as longitudinal teeth, the component as a whole is hardened, but the longitudinal teeth have a lower hardness than the other functional area, but a higher hardness than the base hardness of a joint external or internal part, i.e., the longitudinal teeth have a lower hardness than the ball raceways, but a hardness exceeding the base hardness at least over partial areas of their radial extension. 
     In particular, hardening with which at least a specific hardening depth results, i.e., the base hardness of the workpiece is increased at least approximately over the height of the teeth, may be advantageous. In an especially advantageous way, a hardening process connected to a diffusion process, such as cost-effective surface hardening in the form of case hardening with subsequent quenching and annealing, may be suitable, which results in a high boundary hardness and—at least for the components discussed here—a lower hardness, the core hardness, i.e., a hardness exceeding the base hardness, in the areas lying within the areas having boundary hardness. Nitration or boration may also be suitable as the hardening process. 
     It has been found that after at least approximate removal of the areas having boundary hardness, e.g., by a lathing process, in the axial area in which the teeth are formed, this may be performed here using the machines and tools under practically identical conditions as the machining of “soft”, unhardened material, i.e., for example, on typical broaching-milling-pounding machines or similar machines. 
     The second functional areas, i.e., the ball raceways here, may be hard milled and/or ground within the zones of the boundary hardness, as is known. A very special, separate, and independent aspect according to the invention, however, is the creation of a component and the provision of a method for producing such a component, at least one of which is provided in a torque transmission device, which has two different functional areas for transmitting torque which are formed on the component and cause the torque flow by formfitting engagement, one of which is constructed as longitudinal teeth and the other functional area being, for example, the raceways for the balls of a joint, the component, however, in particular one of the functional areas being produced chipless and subsequently hardened, in particular surface-hardened, as described at the beginning, and the component further being distinguished in that the formed-on ball raceways are or were not subject to machining, the ball raceways are thus in installable state after the hardening procedure. In particular for such joints, inventive measures according to the claims and/or measures mentioned in the description may also be applied. 
     To produce a component of this type, it may be advantageous to subject the component as a whole to surface hardening, in particular a case hardening process, with a subsequent quenching and annealing procedure. The hardest area, i.e., the boundary layer and possibly the transition area, is partially removed, e.g., by chip removal, thus by lathing, for example, in the axial area on which the longitudinal teeth are to be applied, and subsequently the longitudinal teeth are formed in the area brought to the so-called core hardness by the hardening procedure and the subsequent annealing. 
     These longitudinal teeth may, as already noted, be produced in particular by machining, e.g., by broaching and specifically by “soft broaching”, i.e., using normal tools and machines, because they allow the broaching in the core hardness in the same way as with parts which only have the base hardness. 
     At relatively low cost and without requiring provision of special machines, the invention ensures rapid and efficient production of the longitudinal teeth with sufficiently high hardness and also a correspondingly high strength and, by the possibility of using the so-called soft broaching, the production of longitudinal teeth having higher precision and service life. 
     The second part of the statement of the object is achieved according to the invention by constructing the joint external part and/or the joint internal part in such a way that the curvatures of the track bases—viewed in their axial course—at least partially deviate from the curvatures of the ball contact lines, the term “lines” also comprising planar areas or combinations of lines and surfaces in the tracks and/or running channels for specific applications. It may be advantageous if the track bases—viewed in the axial direction—run partially at least approximately axially parallel. 
     In other words, according to the invention the tracks no longer need to be completely deformed over the entire axial distance, but rather only where this is necessary to achieve the ball contact lines. 
     The joint internal part and/or the joint external part are expediently produced chipless as a preform in a forming tool and provided with at least approximately axially-parallel grooves and projections as pre-formed contours to form the ball contact lines. 
     The preform may be produced by forging, for example, such as a cold and/or hot forging method or also by other shaping methods, such as sintering. 
     The ball contact lines of the joint internal part and also the joint external part may be formed by chipless deformation of the projections and/or grooves in a forming tool. This deformation may be performed in a calibration tool, in which the ball raceways and/or contact lines may be geometrically finished-formed, so that they do not need to be machined. 
     During the production of the ball contact or running lines, along which the balls move upon the deflection of the joint, specific axial areas of the grooves or groove bases and/or notches formed during the production of the preform are expediently not deformed by the calibration tool, so that their structure, which runs at least approximately axially, is partially maintained over the axial course of the finished external and/or internal tracks of the joint external part and/or the joint internal part. This provides the advantage of less deformation work, inter alia. 
     Furthermore, the invention relates to a method for producing fixed, constant velocity ball joints, which is distinguished in that the tracks of the joint external part and/or joint internal part are produced by reshaping in a preform, i.e., by cold and/or hot reshaping, in that firstly at least approximately axially-parallel notches are produced, the ball raceways are subsequently at least approximately finished geometrically in opposing directions, preferably also by reshaping technology, e.g., in a compression or calibration procedure, without machining being required. 
     Both the preform and also the opposing course of the ball contact lines may each be produced in one work step and by cold and/or hot reshaping, it being advantageous if the final work procedure is a calibration procedure, so that at least then the ball raceways of the joint part no longer have to be machined (even after a hardening process, e.g., case hardening). 
     Due to the production initially of a preform having notches running at least approximately parallel in the axial direction and subsequent deformation thereof into ball raceways having the contact and/or running lines for the balls, first of all waste-free production is ensured and thus cost-effective and efficient production and furthermore high indexing precision is achieved, specifically by the tools themselves. The machine itself does not require precise guiding, because the projections and/or grooves of the preform, which extend at least approximately axially-parallel, have been predefined by a single tool and during the finish forming of the ball run lines, the shaping fingers of the tool practically thread themselves. 
     Particular advantages result, as already noted, if the preform is produced in a single tool, because then the indexing precision of the part itself comes out just as well as the indexing precision of the tool, and this may be very high because the tool is not divided. Furthermore, none of the separate guides for each tool half otherwise necessary for divided tools are required for such an operation. 
     Also during the calibration operation, which forms the restriction and thus the ball raceways or running lines from the preform, the guiding of the tools relative to one another may be performed by the already existing, precisely divided preform and therefore a machine having special guiding precision is not necessary. In addition, the preform itself does not have to be inserted in a targeted way into the calibration tool, because all 8 tracks, for example, are initially identical, and are produced differently from these identical tracks in the calibration tool. 
     Furthermore, it may be advantageous to construct and/or produce cage centering faces in the joint external part according to the present invention, as described in U.S. Pat. No. 7,396,284, the entire disclosure of which is incorporated herein by reference. These cage centering faces in the external joint may be constructed in such a way that channels or grooves extending in the axial direction are provided between each of the adjacent first and second cage centering faces, the curvatures of the bases of these channels or grooves at least partially deviating in their axial course from the curvatures of the cage centering faces. These track bases—viewed in the axial direction—may also at least partially extend approximately axially-parallel. 
     Like the grooves and projections for the ball contact lines or raceways, the cage centering faces may also be produced in a preform in a chipless manner in a forming tool as adjacent radial projections having a groove provided between them which at least runs axially-parallel, the two projections each being provided between two adjacent raceways. 
     This preform may also be produced by forging, for example. The cage centering faces are advantageously produced in finished form by chipless deformation, such as calibration, of the particular projections adjacent to a groove, the cage centering faces adjacent to one another each running originating from one end, e.g., the drive-side end, in the direction toward the output-side end, approaching the axis of the external joint, and the second cage centering faces running originating from the output-side end in the direction toward the drive-side end and approaching the internal hub axis. 
     In the same way as described in connection with the raceways, the structures of the grooves and/or the projections of the preform may also be at least partially maintained here. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawing figures in which: 
         FIG. 1  shows a torque transmission unit according to a feature of the present invention; 
         FIGS. 1   a  and  1   b  show a section along line Ia-Ia; 
         FIG. 2  shows a drive configuration for a motor vehicle having two partial shafts and an approximately centrally situated cardan joint; 
         FIG. 3  shows a cross-section through the cardan joint corresponding to a section along line III-III of  FIG. 4 ; 
         FIG. 4  shows a section along line IV-IV of  FIG. 3 ; 
         FIG. 5  shows a section along line V-V of  FIG. 3 ; 
         FIG. 6  shows a section along line VI-VI of  FIG. 3 ; 
         FIG. 7  shows a section along line VII-VII of  FIG. 3 ; 
         FIG. 8  shows a view from the direction of the arrow X of  FIG. 4 ; 
         FIG. 9  shows a view from the direction of the arrow Y of  FIG. 4 ; 
         FIGS. 10-13  show a joint internal part as unfinished and finished parts; 
         FIGS. 14-18  show a joint external part as unfinished and finished parts. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The fixed constant velocity joint  101  according to  FIG. 1  comprises a joint internal part  102  having ball raceways  103 , as well as a joint external part  104  having ball raceways  105  formed thereon in a known way. Balls  106 , which transmit the torque between internal and external parts, are provided between the ball raceways  103  and  105  of joint internal and external parts  102  and  104 . A cage  107  is used for guiding the balls. 
     The joint internal part thus has functional areas for torque transmission in the form of the longitudinal teeth  108  on the one hand and in the form of the ball raceways  103  on the other hand. 
     The joint internal part may advantageously be a forged part having a central recess  108   a  provided for the formation of the teeth. The ball raceways  103  may be produced, for example, by machining or chiplessly. 
     The joint internal part is initially subjected as a whole to a surface hardening, in particular a case-hardening process having quenching and subsequent annealing, for example. Before the formation of the teeth  108 , the area of greatest hardness of the recess  108   a  is removed, for example, by machining, such as by lathing. 
     The internal teeth  108  may then also be produced by machining, for example, by broaching in a very simple and cost-effective work step which ensures high precision. The ball raceways  103  may be ground—before or after the production of the teeth. 
     In the construction of the teeth  108  according to  FIG. 1  or teeth on a pin on the internal joint—or, if the external joint part  16  has teeth, i.e., for example, if external teeth are provided on a pin or internal teeth are provided on a sleeve-shaped attachment—it may be advantageous, as already noted, if the part is case-hardened as a whole before the formation of these teeth. One possibility for the construction of one embodiment of such a joint according to the invention is shown in  FIGS. 1   a  and  1   b , which depict an enlarged detail view corresponding to arrows Ia-Ia of  FIG. 1 . 
       FIG. 1   a  shows the detail in a state after the hardening having the boundary layers  111  and  112  and the transition areas  113  and  114 . The area of the core hardness is shown by  115 . According to  FIG. 1   b , at least the area of the highest hardness  112  is removed, e.g., by lathing, and the transition area  114  may be at least partially removed, however, as shown in  FIG. 1   b , it is entirely removed, so that the teeth  116  lie completely in the area of the core hardness  115 . 
     It is advantageous if the surface hardness of the boundary layers  111  and  112  is between 55 and 64 HRC, preferably in the range from 60±3 HRC. The case hardening depth is expediently between 0.3 and 2 mm (for boundary hardness 550 HV, corresponding to 52.3 HRC), but preferably in the range around 1 mm, here for a diameter of the balls  106 , which transmit the torque in the magnitude of approximately 13 mm. The core hardness is expediently in the range from 20 to 50 HRC, preferably from 30 to 40 HRC. The hardness of the teeth—at 350 HV here—is significantly higher than the original base hardness of the starting material, in this case less than 200 HV. 
     In the same way, joint external parts having external teeth provided on a pin may also be produced according to the invention, the external teeth also being able to be produced in a cost-effective way which ensures high strength and high torque transmission values by machining or reshaping processing, e.g., by pounding, milling, rolling, or the like in an area which was previously hardened and in which the hardest areas were removed before the formation of the teeth. In a joint internal part, a pin may also have external teeth or a joint external part may have internal teeth. 
     The described features according to the invention are not restricted to the torque transmission devices, which were described in detail above, but rather also extend to other torque transmission devices in which a component has two functional areas for transmitting torques by formfitting engagement with other elements. 
     The driveshaft  1  shown in  FIG. 2  is constructed here as a longitudinal driveshaft of a motor vehicle and comprises two partial shafts  2  and  3 , which carry connection parts  4 ,  5  on their free ends. These connection parts are constructed as flexible rubber couplings, although cardan joints may also be fastened to the cited partial shafts  2  and  3  in their place, as described in US 2006/014587 or U.S. Pat. No. 6,893,352 (=DE 100 32 853). 
     The two partial shafts  2  and  3  are connected to one another via a cardan joint  8 , which is shown in various sectional illustrations in  FIGS. 3 through 9 , approximately in the middle of the drive configuration  1 . In addition,  FIG. 2  shows that the left partial shaft  2  is fastenable to the underbody of a motor vehicle via an intermediate bearing  6  and a retainer  7  situated thereon. 
     As can be seen in particular from the sections according to  FIGS. 3 through 7  and  FIG. 10 , which show the cardan joint  8  not connected to the partial shafts  2  and  3 , the cardan joint primarily comprises an essentially hollow-cylindrical external hub  16 , in which an internal hub  10  is situated coaxially. While the first partial shaft  2  may have its external spline teeth inserted into internal spline teeth  11  of the internal hub  10 , the connection of the external hub to the second partial shaft  3  is performed in the present exemplary embodiment by a welded bond, for which a welding flange  12  is constructed on a driver housing  9 . The external hub  16  is accommodated in the driver housing, and is enclosed in a formfitting way in a receptacle area  17 . 
     First external ball running channels  19  for a first array of balls  14  and further external ball running channels  19   a  for a second array of balls  14   a  are provided on the interior side of the external hub  16 . Webs  20  are located between them in each case. 
     First internal ball running channels  18  for the first array of balls  14  and further internal ball running channels  18   a  for the second array of balls  14   a  are provided on the exterior side of the internal hub  10 . Webs  28  are located between these ball raceways in each case. 
     The track base of the ball grooves is identified in each case by  18 ′,  19 ′ and  18   a ′ and  19   a′.    
     The internal hub  10  has an internal hub axis I and an external face  24 . As can be seen from  FIGS. 4 ,  8 ,  9  in particular, the first internal running channels  18  and the second internal running channels  18   a  are situated distributed alternately around the internal axis I, the first internal running channels  18  running here originating from the drive-side end  2   a  in the direction toward the output-side end  3   a , and the internal running channels and their track base  18 ′ moving away from the internal hub axis I; as can be seen from  FIGS. 5 and 8 ,  9  in particular, the second internal running channels  18   a  run here from the output-side end  3   a  in the direction toward the drive-side end  2   a , these second internal running channels and their track base  18   a ′ moving away from the internal hub axis I here. The first and second internal running channels having their opposing first and second external running channels may also be situated in a sequence other than alternately with one another and may have other courses than described and shown here, e.g., a course first moving away from the corresponding axes and subsequently approaching them again. 
     The external hub  16  has an external hub axis II and an internal contour, in which first ball running channels or raceways  19  for the first array of balls  14  and second ball running channels or raceways  19   a  for the second array of balls  14   a  are situated distributed alternately around the external hub axis II and in each case the first internal running channels  18  are opposite to the first external running channels  19  and the second internal running channels  18   a  are opposite to the second external running channels  19   a  and form a pair with them in each case, the first external running channels  19  running originating from the drive-side end  2   a  in the direction toward the output-side end  3   a , and the external running channels  19  and their track base  19 ′ approaching the external hub axis II, and, furthermore, the second external running channels  19   a  run originating from the output-side end  3   a  in the direction toward the drive-side end  2   a , and the second external running channels  19   a  having their track base  19   a ′ approach the external hub axis II ( FIGS. 4 and 5 ). 
     In an annular cage  15  having an at least sectionally spherical external face  26  (see  FIGS. 3 ,  6 , and  7  in particular), which is situated between the internal hub  10  and the external hub  16 , radial windows  27 , in which the balls  14 ,  14   a  are guided (see also  FIGS. 4 ,  5 ) are provided in accordance with the number of the balls  14 ,  14   a  and/or running channel pairs  18 ,  18   a ,  19 ,  19   a . The cage  15  is centered in the external hub  16  via its external face  26 , more precisely via the two centering areas  26   a.    
     Webs  20  are provided between the balls in the internal face of the external hub  16 , as already noted. As may be seen in particular in connection with  FIGS. 4 ,  6 ,  8 , and  9 , viewed from the drive-side end  2   a  and around the circumference, these webs have insertion contours  16   a  primarily provided on both sides of the ball grooves  19  for the balls  14  for the axial insertion of the cage  15  into the external hub  16 . The insertion contours  16   a  originate on the driver side  2   a  from a diameter which at least approximately corresponds to the external diameter of the cage  15 . 
     Viewed in the axial direction, starting from the drive-side end  2   a  of the joint, these insertion contours merge after at least approximately half of the axial length into the cage centering faces  16   b  on the joint external part for the cage and are inclined in the direction toward the cage centering axis III (see  FIGS. 4 ,  6 ,  8 , and  9 ). The cage centering faces  16   b  are correspondingly adapted as crowned to the spherically constructed contact faces of the ball cage. 
     Viewed in the axial direction, originating from the output-side end  3   a  of the joint, these insertion contours  16   c  merge after at least approximately half of the axial length of the cage into the second cage centering faces  16   b  on the external hub for the cage. From there, they run inclined in the direction toward the cage centering axis III. The second cage centering faces  16   b  are correspondingly adapted as crowned to the spherically constructed contact faces  26   b  of the ball cage, like the first faces. 
     As already noted,  FIGS. 10-13  show a joint internal part as the unfinished part and finished part R 10  and F 10  and  FIGS. 14-18  show the joint external part as the unfinished part and finished part R 16  and F 16 . 
     The preform R 10  according to  FIG. 10  is a forged part having four pairs of projections or webs R 20 , R 20   a , which are distributed uniformly around the circumference and are constructed at least approximately uniformly, between which grooves or notches R 18 , R 18   a  having groove bases R 18 ′ and R 18   a ′, which run at least approximately axially parallel, are provided. 
     The preform R 10  may also be produced, as already noted, using a hot-cold or warm-cold process, for example, or also as a sintered part. 
     The running channels F 18 , F 18   a  apparent from  FIGS. 11 ,  12 , and  13  are deformed from the projections or webs R 20 ,  20   a  by calibration in a tool which consists of two tool halves having plungers running in opposite directions to form the opposing running channels F 18 , F 18   a , using a cold deformation method, in particular by calibration. 
     The groove bases R 18 ′ and R 18   a ′ according to  FIG. 10  remain at least partially maintained even after the calibration, as do partial areas F 18 ″, F 18   a ″ according to  FIGS. 11-13  from the lateral flanks R 18 ″ and R 18   a ″ previously contained in the preform R 10 . Only the crosshatched sections F 18 ′″ and F 18   a ′″ were deformed, as can be seen in particular from  FIG. 11 . The faces F 18 ′″ and F 18   a ′″ are deformed in such a way that ball running lines or ball contact lines F 18   b  and F 18   b ′ arise, along which the balls move upon the deflection of the joint. 
     Furthermore, it can be seen in particular in connection with  FIG. 13  that the ball raceways F 18   b  and F 18   b ′ and the remaining areas of the groove bases F 18 ′ and F 18   a ′ have different curvatures. 
       FIGS. 14-18  show unfinished and finished parts of the external joint R 19  and F 19 ,  FIGS. 17 and 18  showing  FIG. 16  along lines A-A and B-B. 
     The preform R 16  according to  FIG. 14  is produced here as a forged part having first and second projections or webs R 28 , R 28   a  and R 28 ′, R 28   a ′, which extend radially inward. The projections R 28  and R 28   a , which run at least approximately axially-parallel, are designed as at least approximately mirror-image, like the projections  28 ′ and  28   a′.    
     The projections R 28  and R 28   a  each enclose a first groove or notch R 19  between them, which runs at least approximately axially-parallel, as the projections R 28 ′ and R 28   a ′ enclose a second groove or notch R 19   a  between them. The projections R 28   a  and R 28 ′ as well as R 28   a ′ and R 28  each enclose a third groove R 31  between them. 
     The grooves R 19  and R 19   a  each have groove bases R 19 ′ and R 19   a ′ and the grooves R 31  each have groove bases R 31 ′. The grooves R 19  and R 19   a  also have side flanks R 19 ″ and R 19   a″.    
     The joint external part is produced as a finished part F 16  by a calibration procedure. The first and second ball running channels F 19  and F 19   a  of  FIGS. 15-18  are deformed from the side flanks R 19 ″ and R 19   a ″ of  FIG. 14 . 
     The groove bases R 19 ′, R 19   a ′ of  FIG. 14  are maintained at least approximately over the axial extension thereof as the track bases F 19 ′. Only the crosshatched sections F 19 ″ and F 19   a ″ in  FIGS. 17 and 18  are deformed of the side flanks R 19 ″ and R 19   a ″ and the ball contact lines or ball running areas F 19   b  and F 19   b ′ are thus formed. 
     It is also apparent here that the curvature of the groove bases F 19 ′ differs from that of the contact lines F 19   b  and F 19   b′.    
     The second channels F 19   a  are produced in the same way as the first running channels F 19 , but in the opposite direction, i.e., restricted to the channels F 19 . 
     On both sides of the groove F 19 , insertion contours F 16   a  running at least approximately in the axial direction are produced from the first projections R 28  and R 28   a , advantageously by the same calibration procedure in which the contours F 19 , F 19   a , F 19 ′″, F 19   a ′″, F 16   b , F 16   b ′ are generated. 
     In the further axial course of the insertion contours F 16   b , the cage centering areas F 16   b  are provided on both sides of each channel F 19 , a stepped projection or transition area being provided between the contours F 16   b  and F 16   a.    
     The cage centering areas F 16   b  and F 16   d  are adapted to the spherical contact faces  26   b  of the ball cage  15 . 
     In the same way, but with opposing restriction, the cage centering faces F 16   d  and the insertion faces F 16   c  are produced and/or constructed on both sides of the channels F 19   a.    
     The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.