Patent Publication Number: US-2022219218-A1

Title: Method for producing a hollow shaft

Description:
The invention relates to a method for the production of a hollow shaft from a tubular preform by means of pressure rolling, wherein the two ends of the preform are shaped using at least one forming roller, in each instance. 
     Such a method is known from DE 103 37 929 A1. This document describes a method for the production of one-piece hollow bodies having profiled end regions, from a preform having a circular tube cross-section, wherein first, in a first method step, the preform is elongated in its center region. After completion of this elongation step, the preform is inserted into a different workpiece holder and subsequently, in a second method step, at least one end region is elongated, and in a third method step, if applicable, this end region is processed further. 
     However, this known method is relatively complicated, since it is necessary, in order to carry out the different method steps, to hold the preform or the preform that has already been shaped, in part, in different workpiece holders, one after the other, so that a continuous shaping process is not possible. Furthermore, complicated adjustment is necessary when changing the workpiece holder, so as to guarantee precise concentricity of the preform with the forming rollers. Furthermore, the method is restricted to tubular preforms that can be elongated by means of pressure rolling. 
     It is the task of the invention to develop such a method further in such a manner that it allows a continuous method sequence and can be used universally. 
     This task is accomplished, in the case of a method of the type referred to initially, in that a tubular preform having a round or polygonal cross-section is used, and the preform is held in the center tube region by one workpiece holder during the entire production process, until the hollow shaft is finished. 
     The method makes it possible to carry out the entire forming process with only one workpiece holder, so that the entire forming process can take place continuously. In this regard, additional adjustments are also eliminated, which would be necessary if the workpiece holder were changed. Furthermore, it is possible to use tubular preforms having a round (circular-ring-shaped) or polygonal cross-section, so that the hollow shaft produced in this manner is suitable for different application purposes, for example for holding coil packages in the case of an electric motor. During the shaping, in each instance, the preform is put into rotational movement relative to the at least one forming roller, for which purpose the workpiece holder with the preform and/or the at least one forming roller is/are driven. During shaping, the polygonal cross-section, for example, remains unchanged in the center tube region that is held by the workpiece holder, while only the end regions are shaped with rotation symmetry, so that the center region can hold coil packages of an electric motor, for example, without further shaping. Since the center region is not shaped, an internal mandrel is not required in the center region, either, but rather internal mandrels are inserted only into the two end regions, while in the center region, the preform is held by a workpiece holder from the outside. 
     Both drawn and welded tubes can be used as a preform. 
     In a very particularly preferred embodiment, it is provided that the two ends of the preform are shaped simultaneously, at least in part. In this way, on the one hand the shaping time is shortened, and on the other hand this leads to torque neutralization in the center tube region. 
     Depending on the demands on the finished hollow shaft, it is preferably provided that at least one end is stepped once or multiple times, i.e. regions that border on one another axially are produced with different diameters. 
     Furthermore, it is advantageously provided that an outside and/or inside profiling is introduced into at least one end. 
     In this regard, it is furthermore provided that before introduction of the outside and/or inside profiling, an internal mandrel, if necessary a profiled one, is axially introduced into the at least one end. 
     If the finished hollow shaft is supposed to have an outside or inside profiling on both ends, it is correspondingly provided that an internal mandrel is introduced into both ends, in each instance. For introduction of an outside profiling, at least one correspondingly profiled shaping roller and a non-profiled internal mandrel are used, and for introduction of an inside profiling, at least one non-profiled shaping roller and a profiled internal mandrel are used. 
     It can very particularly preferably be provided that the two internal mandrels are connected with one another at their end faces, with force fit and/or shape fit. The end face ends of the two internal mandrels can have a spur gearing, for example, and are axially pressed against one another and thereby locked in place, so that lateral radial forces that occur can be absorbed. 
     Finally, it is advantageously provided that the shaping takes place, at least part of the time, under the application of heat. The heat can be produced inductively, for example, and, at the same time, hardening of the component can be achieved by means of this heat application. 
    
    
     
       In the following, the invention will be explained in greater detail as an example, using the drawing. This shows, in 
         FIG. 1  a longitudinal section through a tubular preform, 
         FIG. 2  a section along the line A-A in  FIG. 1  with three different embodiments, 
         FIG. 3  a perspective representation of the preform held by a workpiece holder in a center tube region, during shaping, 
         FIG. 4  a side view of  FIG. 3 , partly in longitudinal section, 
         FIG. 5  a longitudinal section through a finished hollow shaft, 
         FIG. 6  a detail X in  FIG. 5 , 
         FIG. 7  a detail Y in  FIG. 5 , 
         FIG. 8  a longitudinal section through a hollow shaft during shaping, using two separate internal mandrels, 
         FIG. 9  a modification of  FIG. 8  with two internal mandrels connected with one another in the axial direction, with shape fit, 
         FIG. 10  a perspective representation of the two internal mandrels according to  FIG. 9 , 
         FIG. 11  an end region of a preform, with a forming roller that applies a radial and axial force, and 
         FIG. 12  a perspective representation of  FIG. 11 . 
     
    
    
     A tubular preform is designated in  FIG. 1  in general as  1 . This tubular preform  1  can be a drawn or welded tube made of metal. It is essential to the invention that the tubular preform can have any desired round or polygonal cross-section. 
     In  FIG. 2 , it is indicated, as an example, that it can have a circular, square or triangular cross-section. In general, any desired cross-sectional shapes, preferably polygonal cross-sectional shapes, are possible for adaptation to the purpose of use, in each instance. 
     Since the center tube region  1   a  of the tubular preform  1  is not shaped in the case of the method according to the invention, this region is suitable without further processing for holding coil packages of an electric motor or the like, for example. 
     In order to produce a hollow shaft from the tubular preform  1  by means of pressure rolling, it is provided, as an essential part of the invention, that the tubular preform is held in its center tube region  1   a  by a workpiece holder  2 , during the entire production process up to the finished hollow shaft. This divided, ring-shaped workpiece holder  2  accordingly has an inside contour that corresponds to the outside contour of the tubular preform  1 . 
     Since the preform  1  is held in its center region  1   a  by the workpiece holder  2  during the entire production process, the entire method sequence can take place continuously, without a change to a different workpiece holder. 
     Preferably, in this regard it is provided that the two ends  1   b  and  1   c  of the preform  1  are shaped simultaneously, at least in part, by means of forming rollers designated in general as  3 . In this regard, at least one forming roller  3  is provided for shaping of each of the two ends  1   b,    1   c.  In the exemplary embodiment according to  FIGS. 3 and 4 , three forming rollers  3  are indicated for shaping of the end  1   b,  and one forming roller  3  is indicated for shaping of the end  1   c.    
     The forming rollers  3  are configured to be radially displaceable with reference to the longitudinal axis  4  of the preform  1 . Depending on the desired shaping process, they can additionally also be displaceable in the axial direction. 
     During shaping, the pressure rollers  3  are put into rotational movement relative to the workpiece holder  2  and the tubular preform  1 , so that either the pressure rollers  3  or the workpiece holder  2  with the preform  1  are/is driven. 
     By means of the shaping shown in  FIGS. 3 and 4 , the two ends  1   b  and  1   c  of the preform  1  are shaped with rotation symmetry, i.e. the two ends  1   b  and  1   c  then no longer have a polygonal cross-sectional shape if the original preform  1  had a polygonal cross-sectional shape. Of course, the polygonal cross-sectional shape is maintained in the non-worked center region  1   a.    
     Proceeding from the tubular preform  1  that has already been shaped at the two ends  1   b  and  1   c,  the two ends  1   b  and  1   c  can be shaped further without changing the workpiece holder  2 . 
     In  FIG. 5 , it is shown that the two ends  1   b  and  1   c  are configured with two steps, in each instance, viewed in the radial direction. These stepped regions are indicated as  1   b ′,  1   b ″ and  1   c ′,  1   c ″, respectively, in  FIG. 5 . Furthermore, a profiling is introduced into the two ends  1   b  and  1   c,  in each instance, namely an inside profiling  5  into the end  1   b  and an outside profiling  6  into the end  1   c.  The inside profiling  5  and the outside profiling  6  can be a gearing, a knurling or some other geometric shape. 
     Suitable shaping rollers are used as forming rollers and as internal mandrels to produce the inside profiling  5  and the outside profiling  6 , respectively. 
     A further possible exemplary embodiment is shown in  FIG. 8 . The preform  1  is held in the workpiece holder  2  in its center region la, without any change, and an internal mandrel  7  without profiling is axially introduced into the end  1   b  that has already been stepped, while an internal mandrel  8  having an outside profiling  8   a  is introduced into the end  1   c.  In order to introduce an outside profiling  6  at the end  1   b  of the preform  1  in the case of the exemplary embodiment according to  FIG. 8 , not only the internal mandrel  7  but also at least one forming roller  9  having an outside profiling  9   a  is provided. On the other hand, in order to introduce an inside profiling  5  into the end  1   c  of the preform  1 , not only the internal mandrel  8  having an outside profiling  8   a  but also at least one forming roller  10  without an outside profiling is provided, i.e. the end  1   c  is pressed into the outside profiling  8   a  of the internal mandrel  8  by the forming roller  10 , so that the inside profiling  5  is formed. 
     In contrast to the embodiment according to  FIG. 8 , in the case of the embodiment according to  FIGS. 9 and 10 , two separate internal mandrels  7  and  8  are not used, but rather the two internal mandrels  7 ′ and  8 ′ are connected with one another at the end faces and/or with shape fit. For this purpose, the two internal mandrels  7 ′ and  8 ′ have a complementary end-face gearing  7   a,    8   a,  in each instance. The internal mandrels  7 ′ and  8 ′ are then pressed together in the axial direction during shaping, by means of pressure application from the outside, and thereby lateral radial forces that occur during shaping are absorbed. 
     It is also possible to feed metal material to at least one of the two ends  1   b,    1   c  of the preform  1  during shaping (in the shaping zone), if an axial force is applied to the end  1   b  or  1   c,  respectively. In this regard, at least one forming roller  11  is used, which has a step-shaped, tubular outside circumference region having a circumferential contact surface  11   a.  An axial force F axial  and a radial force F radial  are exerted on the preform  1  with this forming roller  11 . This material feed can also be carried out multiple times, for example before the actual shaping of the ends  1   b,    1   c  and afterward. 
     The entire production process can take place solely by means of cold forming. However, shaping can also take place while heat is applied, all of the time or part of the time, for example by means of inductive heat generation. In this way, hardening of the preform  1  can take place at the same time. 
     REFERENCE SYMBOL LIST 
     
         
           1  tubular preform 
           1   a  center tube region 
           1   b,    1   c  ends 
           1   b ′,  1   c ′ stepped region 
           1   b ″,  1   c ″ stepped region 
           2  workpiece holder 
           3  forming rollers 
           5  longitudinal axis 
           6  inside profiling 
           7  outside profiling 
           7 ,  7 ′ internal mandrel 
           8 ,  8 ′ internal mandrel 
           8   a  outside profiling 
           8   b  end-face gearing 
           9  forming roller 
           9   a  outside profiling 
           9   b  end-face gearing 
           10  forming roller 
           11  forming roller 
         F axial  axial force 
         F radial  radial force