Patent Publication Number: US-8539806-B2

Title: Roll forming method for producing longitudinally toothed profiled bodies in pot-shaped cylindrical workpieces

Description:
This application is a National Stage completion of PCT/EP2009/056453 filed May 27, 2009, which claims priority from German patent application serial no. 10 2008 002 297.7 filed Jun. 9, 2008. 
     FIELD OF THE INVENTION 
     The present invention relates to a roll-forming process for producing longitudinally toothed profiled bodies in cylindrical workpieces. 
     BACKGROUND OF THE INVENTION 
     In the production of profiled bodies such as disk carriers of shift elements or similar workpieces having a cylindrical basic structure, the accuracy and surface quality attainable are particularly important. 
     DE 20 17 709 A1 by the present applicant describes a method for producing profiled bodies, in which a rolling tool is used to produce the workpiece from a blank with a smooth outer contour by means of a press, such that each stroke of the press shapes a workpiece from a blank. In this case it is provided that during each stroke of the press a rolling process is carried out, in which, along the periphery of the workpiece being processed, profile rolls arranged regularly and at a uniform angle relative to one another press the desired outer profile into the external surface of the workpiece. The grooves produced by the respective profile rolls in this process are all the same as one another, so an outer contour with no discontinuities can be produced. 
     Disadvantageously, in this known method the rotation and thus rolling of the profile rolls is produced only by the forces, acting during the deformation, between a workpiece and a profile roll, whereby an indeterminable slip of the profile roll relative to the workpiece takes place, which in the case of a profile with an irregular shape in the longitudinal direction results in dimensional inaccuracies. Moreover, as the profile roll is moved into the material, a zone is produced, in which the tooth flank is not fully formed. 
     DE 195 06 391 A1 describes a method for producing profiled bodies, in which the profile rolls are driven in such a manner that the circumferential speed in the deformation zone matches the speed of the workpiece, so that slip between the profile rolls and the workpieces is largely avoided; disadvantageously, an elaborate and expensive structure is needed to carry out the process. 
     Usually, the roll-forming process begins in a gang press on the pot bottom of pot-shaped workpieces, so that by virtue of the process material flows from the crown of the teeth into their flanks and along the teeth, whereby the shaping of the teeth in the area of the pot bottom is deficient. 
     To solve this problem WO 2006/066525 A1 proposes a method for producing longitudinal grooves in cylindrical workpieces using a roll-forming process with an upstream pre-forming stage, such that by means of the pre-forming process accumulations of material can be produced in the corner areas of the blank. In this way material is aggregated at the positions in the blank where the profile rolls press into the material during the actual roll-forming, so that optimized profile bearing ratios and sheet thicknesses for the roll-forming process can be achieved. In this case swaging and/or upsetting processes can be carried out for the pre-forming. However, after the end of the roll-forming process bulging or relaxation can result in dimensional problems at the teeth. 
     Furthermore, from EP 0728 540 A1 a tool for sheet deformation is known, in particular for a press, in order to provide a tooth-shaped or undulating profile in a shaped sheet component. The known tool has a lower tool portion and an upper tool portion which co-operate to deform the shaped component, such that deformation takes place in one working step and to produce the tooth-shaped or undulating profile, shaping rolls are provided, which are arranged on a circular circumference directed toward the shaped component. In this case, to supplement the friction force with the shaped component the shaping rolls are equipped with a drive mechanism which drives them in rotation about their own axes. 
     From DE 102006025034 A1 a method for producing longitudinal grooves in cylindrical workpieces is known, in which a profile at the circumference of the workpiece is produced by means of concentrically arranged profile segment disks. In this case the profile segment disks are moved by a drive at all times during the deformation process; the drive is independent of the rolling motion of the profile segment disks on the workpiece. 
     In the mass production of toothed disk carriers from a drawn sheet cylinder, according to the prior art the workpiece is moved with its closed face, i.e. the bottom of the cylinder, through the rolling stages so that the freely rotating profile rolls press the material onto the rolling ram to give it the desired tooth shape. To obtain the final profile at least two rolling stages are needed, since otherwise the material cannot withstand this deformation, and cracks; as a rule, such a roll-forming process has three rolling stages. 
     This method has the disadvantage that at the transition from the bottom to the tooth crown a lot of material flows in the direction of the open end, which means that at the tooth crown there is some loss of material, as is usual in deformation processes of this type. 
     Accordingly, the useful profile, i.e. the finished tooth shape, begins not in the area of the bottom but a few millimeters above the bottom, and as a result the disk carrier has to be made correspondingly longer in order to be able to carry the required number of disks with positive interlock. This in turn results in an undesired increase of the structural length and the weight of the transmission. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to indicate a roll-forming process for producing longitudinally toothed profiled bodies in pot-shaped cylindrical workpieces, by carrying out which the useful profile of the longitudinal teeth is maximized. In particular the tooth formation in the area of the bottom of the workpiece should be optimized and the disadvantageous material retraction at the tooth crown described should be substantially reduced. 
     Accordingly a roll-forming process is proposed in which, as in the prior art, in a first rolling stage the pot-shaped cylindrical workpiece moves bottom-first through a rolling process in such manner that, preferably, in this first rolling stage the tooth crowns are over-rolled to a specified, slight extent, whereby the workpiece remains approximately cylindrical. 
     Thanks to the over-rolling stage, bulging of the workpiece while the process is being carried out is avoided. 
     Thereafter, the pot-shaped cylindrical workpiece is moved with its open end first through at least one further rolling stage; preferably, the workpiece, as a rule, in the form of a pot made from sheet passes through two further rolling stages. By virtue of this process the material flows toward the bottom and there shapes the teeth optimally. Thanks to this procedure, for example a disk carrier has teeth optimally shaped in the bottom area, in which the disks can be held. 
     Thanks to the concept according to the invention, the bearing profile begins at the bottom of the pot-shaped cylindrical sheet component, although the same number of rolling stages are needed as in the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, the invention is explained in more detail with reference to an example illustrated in the attached figures in which: 
       FIG.  1 A 1 - 1 A 3  illustrate a direction of travel of a component in a first rolling process and sectional views of the component after the first rolling process; 
       FIG.  2 A 1 - 2 A 3  illustrate a direction of travel of the component in a second rolling process and sectional views of the component after the second rolling process; and 
       FIG.  3 A 1 - 3 A 3  illustrate a direction of travel of the component in a third rolling process and sectional views of the component after the third rolling process. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS.  1 A 1 ,  2 A 1 ,  3 A 1  show the arrangement of a pot-shaped cylindrical sheet component  1  for each rolling process A, B, C, the arrow  2  indicating the direction in which the sheet component  1  moves through the corresponding rolling stage. The FIGS.  1 A 2 ,  1 A 3 ,  2 A 2 ,  2 A 3 ,  3 A 2 ,  3 A 3  show a section perpendicular to the longitudinal axis of the sheet component  1  after the respective rolling stage or rolling process, and a detailed view of the area identified by the circle  4  after each rolling stage is shown in the lower part of the figure. Before the beginning of the roll-forming process the sheet is processed as in the prior art by drawing, stretching and/or punching. 
     According to the invention and referring to FIG.  1 A 1 , at the beginning of the roll-forming process, in rolling stage A, the sheet component  1  is moved through the rolling stage with its bottom  3  first in such manner that, as a further development of the invention, in this first rolling process the tooth crown is over-rolled to a specified extent, whereby the sheet component  1  remains approximately cylindrical. 
     In rolling stage B the sheet component  1  is then passed, open end first, through a second rolling stage as shown in FIG.  1 A 2 . This process causes the material to flow toward the bottom of the sheet component  1 , where it forms optimally shaped teeth. 
     In a subsequent step, in a third rolling process C the sheet component  1  is again passed open end first through a rolling stage, as shown in FIG.  1 A 3 , in order to obtain optimum shaping of the sheet component.