Patent Publication Number: US-9427790-B2

Title: Method for forming a workpiece

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from previously filed PCT application number PCT/IB2011/002950 filed on Nov. 11, 2011 which claims priority from GM 698/2010 filed Nov. 12, 2010. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     BACKGROUND 
     The invention relates to a method for forming a workpiece. 
     WO 2010/075600 A1 discloses a method for forming undercuts on the internal toothing system of a sliding sleeve produced by powder metallurgy for a shift transmission. In this case, recesses in the region of the tooth flanks of the internal toothing system of annular components are denoted as undercuts. The forming is effected with the aid of a rolling tool, the undercuts being formed by backrolling with plastic material displacement from the undercut region. On account of the rotary motions of the rolling tool along the surface of the workpiece for a predefined number of tool revolutions, there is the risk that the workpiece will be mechanically deformed. 
     A tool for compacting a sintered component or for compacting a powder for the sintered component to be produced can be gathered from EP 2 060 346 A2. The tool has a compacting element which can be varied in terms of its radial dimensions and with the aid of which a sintered component in the form of a simple ring or the toothing system of a sintered component or a sintered powder is compacted. 
     DE 2 212 512 A1 describes a method and an apparatus for forming locks in internal toothing systems of displaceable sleeves. Here, what are known as forming jaws of the apparatus are displaced radially and achieve cold pressing in the internal toothing system. Upon pressing, excess material is pressed into the tooth root and the tooth tip of the teeth. 
     SUMMARY 
     The invention is based on the object of processing an available surface of a workpiece cost-effectively and at the same time in a dimensionally stable manner by forming. 
     This object is achieved by the subjects of the patent claims. 
     Provision is made of a forming element, which is moved simply along a working direction toward an available surface of a compacted sintered component as a workpiece and acts with a shaped relief of a contact surface of the forming element upon the surface of the workpiece in the working direction. The forming element is moved in the working direction not for instance in rotation, but rather at least substantially in a translatory manner along a radial direction in relation to the workpiece, so that with little exertion of force a good degree of efficiency is achieved when forming the desired surface relief, which is predefined by the shaped relief of the contact surface of the forming element. 
     For understanding the method, it should be understood that the shaped relief of the forming element is formed non-complementarily in relation to the available surface of the already compacted sintered component. It is preferable that the component produced by sintering has also already been calibrated. 
     The forming on the compacted sintered component allows for a time-saving production of the desired surface relief or of the desired final geometry of the workpiece compared to conventional methods such as rolling or reworking by milling. In addition, a considerably larger number of different and complicated relief geometries can be realized on the workpiece surface with the invention, since they can be predetermined as a negative relief and do not initially have to be produced by laborious reworking. 
     In addition, the method according to the invention avoids the disruptive formation of burrs on the workpiece surface, which likewise does away with high-cost reworking steps. The sleeve disclosed in DE 2 212 512 A1 consists of solid material, and therefore excess material is pressed into the tooth root and the tooth tip upon pressing. This creates burr, which subsequently has to be processed and removed. In addition, the formation of burrs and the removal thereof has to be taken into consideration when dimensioning the toothing system. According to the invention, these method steps are avoided in that a sintered component produced by sintering and thereby having porosity is used as the workpiece. Upon forming, excess material can therefore be pressed into the pores of the sintered component. In this way, individual surface regions of the surface relief to be formed are not impaired by excess material or the formation of burrs. A high-quality and dimensionally accurate production even of complex geometries of a surface relief is thereby made possible (e.g. recesses in the region of a tooth tip and/or of a tooth root of a tooth of the internal or external toothing system of a sliding sleeve, in particular for motor vehicles). By contrast, in the case of the workpiece made of solid material as per DE 2 212 512 A1, merely the flanks of the teeth can be formed, since the excess material already impairs the tooth roots and the tooth tips upon forming. 
     The pressing of excess material into the pores of the sintered component in the region of a surface relief when forming a predefined surface relief has the further advantage that this region can be afforded improved protection against damage and wear. The service life of the sintered component can thereby be increased without additional costs. 
     Measures of the design make it possible to easily adapt the way in which the method is carried out to annular workpieces, e.g. toothed wheels or sliding sleeves for the automotive sector. In addition, by means of the radially variable extent of the forming element, mechanical engagement of the forming element with the workpiece and also the release of this engagement can be realized in a technically simple manner as the method is being carried out. 
     On account of the principle of the method, defined final geometries can be realized both on radially inner and also on radially outer surfaces of, in particular, annular workpieces. The available radially inner or outer surfaces can also have interruptions (e.g. indentation, groove, or the like). 
     It is advantageous that the surface relief is formed on individual teeth or all teeth of a toothing system (in particular of an internal or external toothing system) of a workpiece, so that the final geometry of the workpiece can be manufactured in a particularly cost-effective and dimensionally accurate manner. 
     A preferred application of the method is therefore the production of toothed wheels, sliding sleeves, synchronizer rings and coupling bodies for automotive construction, in particular for shift transmissions of motor vehicles. 
     A desired surface relief can be produced at low cost on a toothing system (in particular a toothing system of a sliding sleeve) by means of forming. On account of the porosity of the workpiece produced as a sintered component, in particular of a sliding sleeve, excess material which forms upon forming can be absorbed by the pores, and therefore the teeth of the toothing system can be formed in a dimensionally stable manner in all surface regions, i.e. also in the region of the tooth tip and of the tooth root. 
     The surface relief to be formed on a tooth is preferably provided on a lateral tooth flank facing toward an adjacent tooth in the circumferential direction and/or on a radially outer tip region and/or on a root region adjoining the main body of the compacted sintered component of the tooth. 
     Recesses can be formed on the teeth of the toothing system, i.e. material is displaced on the teeth by forming. The recesses can advantageously form undercuts, stops or stop teeth or latching grooves on teeth of the toothing system. 
     Surface reliefs of this type, such as undercuts, latching grooves or stop teeth, are conventionally produced on the teeth of the toothing system often in a complicated manner by milling, rolling or reworking of another type. In addition, the conventional reworking is associated with restrictions for configuring the relief on the toothing system, whereas the forming proposed according to the invention permits any desired surface reliefs in all surface regions (in particular tip region, side flanks, root region) of the teeth. 
     The surface reliefs can have, for example, undercuts and/or latching grooves and/or stop teeth. It is conventional that a plurality of processing steps have to be carried out on a tooth, if for example an undercut and a latching groove, i.e. a plurality of relief types, are provided on this tooth. By means of the forming, these different relief types can also be realized on the teeth of the toothing system intended therefor with an appropriately configured shaped relief in a single working step saving time and cost. 
     Mechanically controlling the movement of the forming element by means of a drive element which can move transversely to the working direction of said forming element along a drive direction makes it possible to achieve a defined transmission of force to the surface of the workpiece, and consequently promotes a dimensionally stable final geometry of the workpiece. 
     Additional measures of the design improve the defined transmission of force to the workpiece. 
     Another feature of the design promotes defined mechanical coupling between the forming element and the other components of a drive tool as the method is being carried out. 
     The surfaces of the transfer element and of the forming element which are complementary to one another advantageously run parallel to the drive direction of the drive element. This geometry promotes a structurally simple design of the forming element and the cost-effective production thereof. In addition, the simple design of the forming element promotes the functionally reliable execution of the forming method. 
     Another feature of the design relates to a preferred embodiment of the transfer element which promotes the control of the movement of the forming element depending on the structural configuration thereof. 
     To achieve the object according to the invention, it is furthermore proposed to use a tool in order to form a surface relief on an available surface of a workpiece formed as a compacted sintered component. Here, the tool has a forming element, which can move in a radial working direction in the direction of the compacted sintered component and has a contact surface with a shaped relief. With this shaped relief, the tool acts upon the available surface of the compacted sintered component to be processed by forming in the working direction. Therefore, this tool contributes to processing available surfaces of already compacted sintered components (e.g. an internal toothing system or external toothing system of sliding sleeves for motor vehicles) cost-effectively by forming. In this case, a surface relief which is predefined by the shaped relief of the forming element is formed on the available surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Hereinbelow, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which: 
         FIG. 1  shows a sectional schematic side view of the tool in a first embodiment, 
         FIG. 2  shows a sectional schematic side view of the tool in a further embodiment, 
         FIG. 3  shows a perspective view of the forming element in a first embodiment, 
         FIG. 4  shows a sectional side view of the forming element as shown in  FIG. 3 , 
         FIGS. 5A, 5B  show perspective partial illustrations of two forming elements having different shaped reliefs for forming the internal toothing system of a sliding sleeve, 
         FIG. 6  shows a perspective partial illustration of a sliding sleeve having an internal toothing system available for forming, before the forming operation, 
         FIGS. 7A, 7B, 7C  show perspective partial illustrations of sliding sleeves having different surface reliefs on the internal toothing system after forming, 
         FIGS. 8A, 8B  show a perspective illustration of a tooth of the internal toothing system of a sliding sleeve, before and after the forming of a surface relief, 
         FIG. 9  shows a partial cross section of a forming element for forming the surface relief on the tooth as shown in  FIG. 8B , 
         FIGS. 10A, 10B  show a perspective illustration of a tooth of the internal toothing system of a sliding sleeve, before and after the forming of a further embodiment of the surface relief, 
         FIG. 11  shows a partial cross section of a forming element for forming the surface relief on the tooth as shown in  FIG. 10B , 
         FIGS. 12A, 12B  show a perspective illustration of a tooth of the internal toothing system of a sliding sleeve, before and after the forming of a further embodiment of the surface relief, 
         FIGS. 12C, 12D  show perspective illustrations of teeth of the internal toothing system of a sliding sleeve, after the forming of further embodiments of the surface relief, 
         FIG. 13  shows a partial cross section of a forming element for forming the surface relief on the tooth as shown in  FIG. 12B , 
         FIGS. 14A, 14B  show a perspective illustration of a tooth of the internal toothing system of a sliding sleeve, before and after the forming of a further embodiment of the surface relief, 
         FIG. 15  shows a partial cross section of a forming element for forming the surface relief on the tooth as shown in  FIG. 14B , 
         FIG. 16  shows a sectional side view of a drive apparatus for the tool in a position before the forming of the workpiece, 
         FIG. 17  shows the sectional side view of the drive apparatus and of the tool as shown in  FIG. 16  in a position during the forming of the workpiece. 
     
    
    
     The tool  1  for forming as shown in  FIG. 1  has a transfer element  2  and a forming element  3 . The transfer element  2  contains a first transfer element part  2   a  and a second transfer element part  2   b . The two transfer element parts  2   a  and  2   b  are arranged at a distance from one another in the axial direction  16  of the tool  1 , i.e. along a center longitudinal axis  17  of the tool  1 . The forming element  3  can be varied in terms of its radial extent in the radial direction  18 . To this end, the movement of individual or all transfer element parts  2   a ,  2   b  is controlled in the radial direction  18 . This movement is controlled by means of an associated drive element  19   a ,  19   b , which is shown merely schematically in  FIG. 1 . 
     DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS 
     Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield still a third embodiment. It is intended that the present invention include these and other modifications and variations. 
     The forming element  3  bears a contact surface  5  with a shaped relief  20 , which is intended to act upon an available radially inner surface  21  of the annular workpiece  4  for forming in the working direction  22 . The workpiece  4  is in the form of a compacted sintered component. The working direction  22  runs substantially in the radial direction  18  of the workpiece  4 . The shaped relief  20  is formed non-complementarily in relation to the inner surface  21  to be formed. In order to form the inner surface  21 , the forming element  3  is moved by means of the drive element  19  and the transfer element  2  in the direction of its radially greatest extent ( FIG. 1 ). 
     For forming an available radially outer surface  23 , the forming element  3  is moved by means of the drive element  19 ,  19   a ,  19   b  and the transfer element  2  in the direction of its radially smallest extent ( FIG. 2 ). 
     For controlling the movement of the forming element  3 , the drive element  19  is driven transversely to the working direction  22  along a drive direction  24 . The drive direction  24  runs parallel to the axial direction  16 . Surfaces of the drive element  19 , of the transfer element  2  and of the forming element  3  which correspond to one another or interact with one another ensure the required transmission of force to the forming element  3 , so that the latter can be transferred into its different positions before, during and after the forming, without there being any undesirable mechanical contacts between the forming element  3  and its shaped relief  20  and the workpiece  4 . The drive element  19  has a drive surface  25   a ,  25   b , which runs at an acute angle to the drive direction  24 . The drive surface  25   a  interacts with a complementary transfer surface  26   a  of the transfer element  2   a . The same applies for the drive surface  25   b  and a complementary transfer surface  26   b  of the transfer element  2   b.    
     The transfer element  2  is arranged between the drive element  19  and the forming element  3 . The transfer element  2   a  or  2   b  has a second transfer surface  6   a  or  6   b , which interacts with a complementary bearing surface  7   a  or  7   b  of the forming element  3 . The second transfer surfaces  6   a ,  6   b  and the bearing surfaces  7   a ,  7   b  run parallel to the drive direction  24  or in the axial direction  16 . 
     At least one transfer element part  2   a ,  2   b  and/or the forming element  3  are preferably also movable in the axial direction  16 . 
     The forming element  3  preferably has a substantially annular or hollow-cylindrical form. This can be best identified in  FIG. 3  and  FIG. 4 . A multiplicity of slots  8  can be provided along the circumferential direction thereof. These allow for a simple, radially variable extent of the dimensions of the forming element  3 . The forming element  3  can to some extent be “opened” (radial enlargement) and “closed” (radial reduction in size) in the radial direction  18 . 
     The forming element  3  provided with slots  8  as shown in  FIGS. 5A, 5B  is suitable for realizing radially inner final geometries on an inner surface  21  of the workpiece  4 . 
     The forming element  3  as shown in  FIG. 3  and  FIG. 4  is suitable for forming a radially outer surface  23  of a workpiece  4 . The slots  8  are oriented in the radial direction  18 , but they do not extend over the entire length of the forming element  3  in the axial direction  16 . The available outer surface  23  can have an entirely cylindrical form in the circumferential direction  29 , such that individual recesses can be formed by means of the shaped relief  20 . Alternatively, the outer surface can have an external toothing system  31  with one or more teeth  27 , as indicated schematically in  FIG. 4 . Individual recesses, e.g. latching grooves  14 , can then be formed in these teeth  27  of the external toothing system  31  by means of the shaped relief  20 . 
     In one embodiment, the available surface of the workpiece  4  is the still non-formed internal toothing system  11  of a sliding sleeve  10  ( FIG. 6 ). The final geometry to be formed and the surface relief of the internal toothing system  11  to be formed are defined by the shaped relief  20  of the forming element  3  ( FIGS. 5A, 5B ). By means of the shaped relief  20  defined in each case, the internal toothing system  11  to be processed by forming can assume different final geometries: after forming, the internal toothing system or individual teeth  27  thereof can have, for example, the geometry and function of undercuts  12  ( FIGS. 7A, 8B, 10B ), of stop teeth  13  ( FIGS. 7B, 14B ) or of latching grooves  14  ( FIGS. 7C, 12B, 12C, 12D ). 
     Given an appropriate configuration of the forming element  3  (e.g. fundamentally as per  FIGS. 2, 3, 4 ), individual teeth  27  of an external toothing system  31  can of course also have the aforedescribed final geometries or the final geometries still to be described hereinbelow. 
       FIG. 8B  shows a first variant of an undercut  12  produced by forming on a tooth  27 . The geometry of this undercut  12  corresponds substantially to the variant as shown in  FIG. 7A . A forming element  3  which can be used for forming this undercut  12  is shown in  FIG. 9  in the working position which brings about the forming. 
     The structure of a still non-formed tooth  27  of a toothing system is readily identifiable with reference to  FIG. 8A . It has a radially oriented tip region  30 . A root region  32  of the tooth is located lying radially opposite said tip region  30  and facing toward the main body  33  of the sintered component  4  or of the sliding sleeve  10 . Two lateral tooth flanks  28  are arranged between the tip region  30  and the root region  32 . In each case one tooth flank  28  faces toward a tooth  27  which is adjacent in the circumferential direction  29  of the sintered component  4 . 
     In the embodiment of the tooth  27  as shown in  FIG. 8A , in particular the two tooth flanks  28  and to a small extent preferably also the root region  32  are formed by means of the forming element  3  in such a manner that recesses in the form of undercuts  12  are formed on the tooth flanks  28  by means of the forming. 
       FIG. 10B  shows a further variant of an undercut  12  produced on a tooth  27  by forming the side flanks  28  and the root region  32 . A forming element  3  which can be used for forming this undercut  12  is shown in figure in the working position which brings about the forming. 
       FIGS. 12B, 12C and 12D  show in each case a variant of a latching groove  14  produced on a tooth  27  by forming. The latching groove  14  forms a recess in the tip region  30  of the tooth  27 . A forming element  3  which can be used in principle for forming these latching grooves  14  is shown in  FIG. 13  in the working position which brings about the forming. The knob-like geometry of the shaped relief  20  for forming the latching groove  14  is in this case adapted in each case to the geometrical variant of the latching groove  14 . Furthermore, it can be gathered from  FIGS. 12B, 12C and 12D  that the surface relief of the tooth  27  has both an undercut  12  and a latching groove  14 . This surface relief can be formed by means of a single forming element  3 . Alternatively, a plurality of, in particular two, forming elements  3  with a different shaped relief  20  can be used in succession, in order to form the entire surface relief (undercut  12  and latching groove  14 ) on the tooth  27 . 
       FIG. 14B  shows what is known as a stop tooth  13  as a surface relief on a tooth  27 . A forming element  3  which can be used for forming this stop tooth  13  is shown in  FIG. 15  in the working position which brings about the forming. The stop tooth  13  is produced by acting upon in particular two tip portions  35  of the tip region  30  which are on the outside in the axial direction  16 . It is preferable that in addition the two tooth flanks  28  and the root region  32  are acted upon to a smaller extent. The forming gives rise to a tip portion  34  which forms the actual stop tooth  13  and to the two outer tip portions  35  which flank the latter. As a result of the forming operation, the tip portion  34  on the one hand and the tip portions  35  on the other hand radially have an extent of differing length. 
     In principle, the forming elements  3  as shown in  FIGS. 9, 11, 13, 15  can have the structural design as shown in  FIG. 5A or 5B , but with a correspondingly adapted shaped relief  20 . 
     The drive element  19  and the parts  19   a ,  19   b  thereof and the tool  1  can be identified as component parts of a drive apparatus  15  in  FIG. 16  and  FIG. 17 . The drive apparatus  15  can be configured differently and makes it possible for the forces required for controlling the movement of the forming element  3  to be transmitted. The structural configuration of the drive apparatus  15  ensures that the forming element  3  can be transferred into the desired position without undesirable contact between the shaped relief  20  thereof and the contact surface  5  thereof and the workpiece  4 . In particular, the transfer element  2  or parts  2   a ,  2   b  thereof and/or the forming element  3  and/or the drive element  19  or parts  19   a ,  19   b  thereof can be moved in the axial direction  16  by means of the drive apparatus  15  as the method is being carried out. 
     In the case of a forming operation on an available radially inner surface  21  of a workpiece  4  formed as a compacted sintered component, the drive apparatus  15  reduces the radial extent of the forming element  3  by means of the transfer element  2   b  and transfers it into a starting position within the workpiece  4  at a radial distance from the inner surface  21  to be formed ( FIG. 16 ). In addition, the forming element  3  is also transferred axially into the required position. Then, the drive apparatus  15  controls the transfer element  2   a  by means of the part  19   a  of the drive element  19  in such a manner that said transfer element increases the size of the radial extent of the forming element  3 , in order to carry out the forming in a working position. 
     In the case of a forming operation on an available radially outer surface  23  of a workpiece  4 , the drive apparatus  15  which is structurally correspondingly adapted if needed has the effect, by means of the transfer element  2   a  and/or  2   b , that the forming element is initially radially enlarged and is transferred without contact with the workpiece  4  into a starting position, in which the shaped relief  20  and the contact surface  5  surround the radially outer surface  23  of the workpiece  4  at a radial distance. In addition, the forming element  3  is also transferred axially into the required position. Then, the drive apparatus  15  controls the transfer element  2   a  and/or  2   b  in such a manner that said transfer element reduces the size of the radial extent of the forming element  3 , in order to carry out the forming in a working position. 
     While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by way of the present invention is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the following claims. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Tool 
           2 ,  2   a ,  2   b  Transfer element 
           3  Forming element 
           4  Workpiece 
           5  Contact surface 
           6   a ,  6   b  Second transfer surface 
           7   a ,  7   b  Bearing surface 
           8  Slot 
           9  Segment 
           10  Sliding sleeve 
           11  Non-formed internal toothing system 
           12  Undercut 
           13  Stop tooth 
           14  Latching groove 
           15  Drive apparatus 
           16  Axial direction 
           17  Center longitudinal axis 
           18  Radial direction 
           19 ,  19   a ,  19   b  Drive element 
           20  Shaped relief 
           21  Inner surface 
           22  Working direction 
           23  Outer surface 
           24  Drive direction 
           25   a ,  25   b  Drive surface 
           26   a ,  26   b  Transfer surface 
           27  Tooth 
           28  Lateral tooth flank 
           29  Circumferential direction 
           30  Tip region 
           31  External toothing system 
           32  Root region 
           33  Main body 
           34 ,  35  Tip portion