Abstract:
A method of producing a hollow shaft having first and second profilings provided for torque transmission at respective ends thereof, wherein a shaft section between the ends has a smaller diameter than at least one of the profilings, and the hollow shaft is assembled from hollow shaft and sleeve components joined via a torque-transmitting slip joint, in which the shaft and sleeve components are each formed from cut blanks by cupping, perforating. cold extrusion and turning steps, and the respective components are assembled to each other.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of international patent application no. PCT/DE2006/001544, filed Sep. 2, 2006 designating the United States of America, and published in German on Mar. 22, 2007 as WO 2007/031052, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany patent application nos. DE 10 2005 043 766.4, filed Sep. 13, 2005, and DE 10 2006 007 388.6, filed Feb. 17, 2007. 

   BACKGROUND OF THE INVENTION 
   The invention relates to a hollow shaft, which has external profilings for torque transmission at its two ends, e.g., splines, wedge-shaped teeth, polygonal profiles or the like, such that the shaft sections therebetween have a smaller diameter than the profilings. 
   Hollow shafts of this type can be used to drive units such as oil pumps, where, for space reasons, the center section is thinner than the toothed ends. 
   One proposed method to produce such shafts was to form them as a single part using cold extrusion. In this case, however, one of the profilings would have to be re-expanded after the forming of the hollow shaft section. Such expansions can only be done in special, highly complex tools and require a substantial amount of additional work thereafter. This would have caused substantial additional costs. 
   SUMMARY OF THE INVENTION 
   It was therefore an object of the present invention to provide a hollow shaft of the above-described type, which is distinguished by its particularly simple, cost-effective and rapid manufacture and high precision. 
   A further object was to provide methods for its cost-effective, rapid and precise production. 
   According to the invention, these objects are achieved by a shaft assemblable or assembled from two components, one of which comprises the hollow shaft section and the one profile as well as an external torque-transmitting slip joint on the shaft side opposite the profile, and the other of which is a sleeve-like component having the second profile and an internal torque-transmitting profile of a slip joint. 
   It is advantageous if the hollow-shaft-type section, the profilings and the one profile of the slip joint of the one component and/or the other component are formed from a solid blank using cold extrusion. 
   It can be advantageous if an interference fit is provided between the internal and external profiles of the slip joint to prevent the sleeve from falling off the shaft-like section after mounting during transport, handling or assembly. 
   If the two profilings provided on the shaft ends have different diameters, it is advantageous if the smaller profiling is provided on the sleeve-like component and the larger profiling is integrally formed with the tubular section. 
   To produce the hollow shaft section with a torque-transmitting profiling, such as an external spline profile, which is formed at its one end and has a larger diameter than the shaft diameter, and a torque-transmitting external profile of a slip joint provided on the opposite shaft end, it is advantageous to provide at least some of the process steps listed below:
         a) cutting a material blank from bar stock to length,   b) a first cupping to form a cup-like hollow region with a solid extension, such that the cup region corresponds at least approximately to the inside and the outside diameter of the profile section,   c) a second cupping to lengthen the hollow region from the extension using cold extrusion,   d) perforating the cup&#39;s bottom,   e) tube extrusion to begin to form the hollow shaft body using cold extrusion,   f) a first reduction of the diameter and the wall thickness and lengthening of the hollow shaft section produced in step e) and forming a neck portion that is thicker than the outside hollow shaft diameter adjoining the region intended to form the profiling, using cold extrusion,   g) a second reduction starting at least approximately from the annular neck portion and lengthening of the hollow shaft section produced in step f) using cold extrusion,   h) final pressing by cold extrusion of the profile region to form the external teeth by inserting a mandrel into the internal contour of the profile region with the same diameter, such that an annular die surrounding the mandrel penetrates the end face of the end region and thereby displaces material into the counterteeth of a die placed around the region intended to form the teeth, thereby forming an axial projection,   i) optionally and simultaneously with step h), producing the external profile of the slip joint in the region of the hollow shaft opposite the profile region using cold extrusion, and   j) removing the projection by turning.       

   To produce the bushing with the external profiling and an internal profile of a slip joint, at least some of the process steps listed below can be particularly advantageous:
         a) cutting a material blank from bar stock to length,   b) cupping and simultaneously forming the internal profile of the slip joint, preferably to the finished profile dimension, using cold extrusion,   c) perforating the cup&#39;s bottom,   d) turning the outside diameter,   e) producing the external profile using cold extrusion by inserting a mandrel with a profile corresponding to the internal profile of the slip joint into the internal profile, such that an annular die surrounding the mandrel penetrates the end face opposite the perforated bottom and thereby displaces material into the counterteeth of a die previously placed around the region intended to form the external profile, thereby forming an axial projection, and   f) turning the bushing height to the finished dimensions and thereby removing the axial projection.       

   For the further production of a hollow shaft at least three of the steps listed below can be particularly advantageous, either before or after mounting or pressing the sleeve onto the shaft via the slip joint:
         a) turning the portion within the profile region formed integrally with the shaft profile to form a bearing seat,   b) forming a recess in the outer end region of the profile,   c) forming a chamfer at the beginning of the internal contour in the region of the profile, and   d) forming an undercut in the end region of the cylindrical internal contour in the region of the profile.       

   It can be advantageous to carry out a heat treatment or surface treatment, particularly soft annealing, between some of the process steps to resoften the material whose structure was hardened by cold forming in the previous steps, e.g., when producing the hollow shaft body with the first profile formed onto it, between steps b) and c), d) and e), e) and f), f) and g), and g) and h), or, when producing the sleeve, between steps d) and e). 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in further detail hereinafter with reference to illustrative embodiments depicted in the accompanying drawing figures in which: 
       FIG. 1  shows a hollow shaft according to the invention or a hollow shaft produced using a method according to the invention; 
       FIG. 2  is a schematic depiction of a blank or workpiece produced by sawing or cutting stock material; 
       FIG. 3  is a schematic representation of the workpiece after a first cupping step; 
       FIG. 4  is a schematic representation of the workpiece after a second cupping step; 
       FIG. 5  is a schematic representation of the workpiece after a bottom perforating step; 
       FIG. 6  is a schematic representation of the workpiece after a hollow flow pressing or tube extrusion step; 
       FIG. 7  is a schematic representation of the workpiece after a first size reduction and lengthening step; 
       FIG. 8  is a schematic representation of the workpiece after a second diameter reduction step; 
       FIG. 9  is a schematic representation of the workpiece after a final pressing step; 
       FIG. 10  is an enlarged detail view of the area X of  FIG. 9 ; 
       FIG. 11  is a cross sectional view of the workpiece taken along line XI-XI of  FIG. 9 ; 
       FIG. 12  is a schematic representation of the workpiece after a length turning step; 
       FIG. 13  is a schematic depiction of another blank or workpiece produced by sawing or cutting stock material; 
       FIG. 14  is a schematic representation of the workpiece after a cupping step; 
       FIG. 15  is a top view of the workpiece in the direction of arrow XV of  FIG. 14 ; 
       FIG. 16  is a schematic representation of the workpiece after a bottom perforating step; 
       FIG. 17  is a schematic representation of the workpiece after a first turning step; 
       FIG. 18  is a schematic representation of the workpiece after a tooth forming and reducing step; and 
       FIG. 19  is a schematic representation of the workpiece after a second turning step. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The oil pump shaft  1  shown in  FIG. 1  is a hollow shaft and has external profilings at its ends in the form of shaft profilings or splines  2 ,  3 . Between the two profile zones  2 ,  3  is a tubular section  4 , which, at least in partial areas, has a smaller diameter than the profilings  2 ,  3 . 
   In the present example, profile  3  and the tubular section  4  are formed integrally or as a single part. Sleeve  7 , which is provided with profile  2 , is mounted to the end of the shaft opposite profile  3  via a torque-transmitting slip joint  5 ,  6 , which will be described in more detail below. The slip joint  5 ,  6  is configured as an interference fit. The tubular section  4  and the profile section  3  integrally formed therewith as well as the sleeve  7  are produced by cold forming as described below, at least with respect to their functional areas. 
     FIG. 2  shows a blank or workpiece  8  cut to length from bar stock, in this case by sawing. 
   Using a cold extrusion process, a component  9  as shown in  FIG. 3  is produced from this blank in a “first cupping” process step. 
   The sleeve-like part identified by  10  in  FIG. 4  is produced by cold extrusion in a “second cupping” process step. 
   In a perforation process step, the bottom  11  (see  FIG. 4 ) of the sleeve-like component  10  is removed to create a component  12  without a bottom as illustrated in  FIG. 5 . 
   Then, in a tube extrusion or hollow flow pressing process step, material is essentially displaced from region  13  as shown in  FIG. 5  to produce the hollow region  14  of component  15  as illustrated in  FIG. 6 . 
   In the “first reduction” process step, the hollow shaft section  16  of component  17  illustrated in  FIG. 7  is essentially produced from the region  14  shown in  FIG. 6 . A neck portion  18  adjoining the region intended to create the profile  3  is also formed. 
   In a subsequent “second reduction” process step, the section identified as  16  in  FIG. 7  is tapered by cold extrusion starting at least approximately from the neck-shaped portion  18  shown there, and the hollow shaft section  20  of a component  21  is produced as shown in  FIG. 8 . 
   The component  22  shown in  FIG. 9  is provided in a “final pressing” process step with the external profiling  3 . This external profiling  3  is clearly visible in  FIG. 10 , which shows an enlarged detail X of  FIG. 9 . In the same “final pressing” process step, profiling  5 , i.e., a polygon for a torque-transmitting slip joint can be formed at the ends of the hollow shaft section  23  opposite splines  3 . This detail is illustrated in an enlargement depicted in  FIG. 11 , which shows a section taken along line XI-XI of  FIG. 9 . 
   The profiling  3  is formed by placing a die “B”, which is provided with a counterprofiling, around the profile forming region identified by reference numeral  19  in  FIG. 8 . A mandrel “A” is then inserted into the interior contour of region  19  and an annular die—a part of which, identified as  25 , is shown in FIG.  10 —is driven or forced against the end face  26  (see  FIG. 8 ), penetrates region  19  and displaces material into the teeth of the die to form teeth  3 . In this process, a projection  27  is also formed, as may be seen particularly in  FIG. 10 . 
   The projection  27  is removed by turning at line  28  in a “length turning” process step to form the hollow shaft as illustrated in  FIG. 12  with its region  4  and the splined region  3  integrally provided thereon and with the external profile  6  of a slip joint as shown in  FIG. 1 . 
   The sleeve  7  with external profile  2  and external profile  6  of a slip joint is produced as illustrated in  FIGS. 13 to 19 . 
   In a sawing or cutting process step, a blank  30  is formed as illustrated in  FIG. 13 . 
   A cup-shaped component  31  with a cylindrical region  32  and a bottom  33  as illustrated in  FIG. 14  is produced in a cold extrusion “cupping” process step. The internal profile  5  of the torque-transmitting slip joint in the form of a polygon also is produced in the cold extrusion step illustrated in  FIG. 14 . 
   The interal profiling  5  is clearly visible in  FIG. 15 , which shows a top view in the direction of arrow XV-XV in  FIG. 14 . 
   The bottom  33  (see  FIG. 15 ) of the workpiece is partly removed in a “perforation” process step as illustrated in  FIG. 16 . 
   In a “first turning” process step, the outside diameter  34  of the sleeve-like component  7  illustrated in  FIG. 17  is turned. 
   In the “tooth forming and reducing” process step, the external profile  2  shown in  FIG. 19  is produced in essentially the same manner as the process step for producing profile  3  illustrated in  FIG. 9 . 
   In the process step in which sleeve  7  is provided with the toothed profile  2  shown in  FIG. 19 , a mandrel corresponding to profiling  5  is again axially inserted into profile  5  and an annular die  35  drives against the end face  36  ( FIG. 18 ), such that material from the end face region is displaced by cold extrusion into the counterprofile of a die, which is provided with the countershape of profiling  2  and which is placed around the cylindrical outside diameter  34 . A projection  37  created in this process is removed in a “second turning” process step as illustrated in  FIG. 19 . 
   Region  38 , which may serve as a bearing seat, can be formed by turning before, or even after, assembly of components  4  and  7 . A recess  39  is turned in the outer end region of profile  3 . Likewise, a chamfer  40  and an undercut  41  are turned at the end of the cylindrical region  38 . 
   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.