Abstract:
A method for producing workpieces wherein a substantially rotationally symmetrical workpiece ( 4, 9, 33 ), which has a workpiece axis ( 22 ), is tentered concentrically relative to an inner mandrel ( 3, 16 ) provided inside the workpiece ( 4, 9, 33 ), and is reshaped by a process of flow forming by radially applying external reshaping rollers ( 7 ). The wall thickness of the workpiece ( 4 ) is also reduced in at least some regions. The inner diameter ( 18, 41 ) of the workpiece ( 33 ) is enlarged by applying inner reshaping rollers ( 11 ) of an inner reshaping unit. The inner reshaping rollers ( 11 ) are arranged such that the roller axes of rotation and the enveloping cone ( 20 ) all intersect at one point on the workpiece axis ( 22 ).

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a method to reshape a workpiece and more particularly, to an apparatus and method to reshape a workpiece that utilizes an interior-shaping unit with or without an exterior-shaping unit acting on a driven workpiece, wherein the inner shaping unit rollers and, if provided, the adjacent outer rollers of the exterior shaping unit possess a minimum tangential separation from one another, thus allowing maximizing of the reshaping rollers about the circumference of the contact diameter of the workpiece. 
       BACKGROUND INFORMATION 
       [0002]    As shown schematically in  FIG. 1  (cross-sectional view) and  FIG. 2  (longitudinal-sectional view), methods are known in which a workpiece  4  is displaced by rotation along one rotational direction  6 , and then is reshaped by means of a cylinder or roller  2  acting on the workpiece from an external position and mounted within a bearing housing  1  at relative displacement from the workpiece  4  along an axial-displacement direction  5  with respect to the reshaping roller  2 . In most cases, this reshaping occurs in a manner such that the outer reshaping rollers  2  press the material of the workpiece  4  in the area to be reshaped against a mandrel  3  so that the material is partially displaced axially, radially, and tangentially in a fluid condition, and this leads to a reduction in wall thickness of the workpiece  4 , whereby the reduced wall thickness to be achieved results from the separation between the reshaping roller  2  and the mandrel  3 . 
         [0003]    For this, the potential reduction in wall thickness of the workpiece  4  is limited by the value of wall thickness, the stiffness of the material, the friction between the inner walls of the blank mold  4  and the mandrel  3 , and the potential number of reshaping rollers  2  at the circumference of the workpiece  4 . 
         [0004]    The causes for this limitation is: 
         [0005]    The magnitude of force that may be partially introduced into the workpiece by means of the reshaping roller  2 , generating a yield stress there; 
         [0006]    The stiffness of the material, which cannot be influenced by the reshaping process; 
         [0007]    The magnitude of friction between the workpiece  4  and the mandrel  3 , which is dictated by the type of process; 
         [0008]    The number of reshaping rollers  2  that may be mounted about the circumference of the workpiece  4 ; and 
         [0009]    The dimensions of the mounting of the reshaping rollers  2 , which in turn are determined by the service life of the bearing and its dimensions, as well as the size of the reshaping rollers  2 . 
         [0010]    Also, the effect of the contact-pressure force of the reshaping rollers  2  is reduced as the wall thickness to be reshaped increases, so that it is no longer possible after a certain wall thickness to bring the material in the pressure areas  7  (effective area) of the reshaping rollers  2  into a fluid condition. Thus, the thickness of the walls to be reduced using known pressure-roller processes is limited by the lacking yield stress of the material. 
       SUMMARY OF THE INVENTION 
       [0011]    It is the task of the invention to provide a method and a device with which the shaping of a rotation-symmetrical workpiece with constant or varying wall thickness is possible even for greater wall thicknesses. 
         [0012]    The task is solved by a method with the properties of Patent claim  1 , and by a device with the properties of claim  5 . Advantageous embodiments may be taken from the Dependent Claims. 
         [0013]    Based on the invention, it is provided that the inner diameter of the workpiece be expanded by the pressure of inner reshaping rollers of an interior-shaping unit, and/or the outer diameter be reduced by the pressure of the outer reshaping rollers. Particularly, the inner mandrel may be displaced by the interior-shaping unit even in the above-mentioned processes. The described contact pressure can exert pressure on the wall of the workpiece from both the inside and outside, and fluidity is ensured even for thicker walls. For this, the inner reshaping rollers are shaped such that the enveloping surface of each of the running surfaces of the inner reshaping rollers defines a truncated-cone shell. Each of the pertinent cones includes a cone tip. Based on the invention, all of these tips lie on the rotation axes of the inner reshaping rollers. Further, the inner reshaping rollers are positioned such that their roller rotational axes all intersect at one point along the rotational axis of the workpiece whereby the points defined by the cone tips also lie at this common intersection point. Thus, the mandrel may be driven with the workpiece about the workpiece axis. Alternatively, both the inner and/or outer reshaping rollers may be driven in rotation. The same geometry with the same common intersection point as described for the inner reshaping rollers may alternatively or additionally be provided for the outer reshaping rollers. 
         [0014]    The method based on the invention achieves the fact that the yield stress in the reshaping area in the walls of the workpiece is increased by means of interior-shaping units and exterior-shaping units acting on a driven workpiece in that the inner rollers and the adjacent outer rollers possess a minimum tangential separation from one another, thus allowing maximizing of the reshaping rollers about the circumference of the contact diameter of the workpiece. This may be achieved by driven interior- and exterior-shaping units acting on a fixed workpiece. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In the following, the invention will be described in greater detail using  FIGS. 1 through 8 , which show: 
           [0016]      FIG. 1  is a schematic longitudinal cutaway view of a device according to the prior art; 
           [0017]      FIG. 2  is a schematic cross-sectional view illustrating the effective areas of the reshaping rollers in a device as per the prior art; 
           [0018]      FIG. 3  is a longitudinal cutaway view of a part of a device according to a first embodiment of the invention; 
           [0019]      FIG. 4  is a cross-sectional view of the device part shown in  FIG. 3  along lines A-A; 
           [0020]      FIG. 5  is a longitudinal cutaway view of the inner mandrel with inner reshaping rollers according to the invention; 
           [0021]      FIG. 6  is a longitudinal cutaway view of a part of a device according to a second embodiment of the invention; 
           [0022]      FIG. 7  is a cross-sectional view of the device part shown in  FIG. 6  along lines B-B; and 
           [0023]      FIG. 8  is a schematic cross-sectional view illustrating the effective areas of the reshaping rollers in a device according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0024]      FIGS. 3 through 5  show a first embodiment of the invention. The exterior-shaping unit in this embodiment example is implemented by the outer reshaping rollers  2  shown in  FIGS. 1 and 2 . In order to enlarge the pressure area  7  (see  FIG. 4 ) in the depth of the workpiece walls based on the invention, an interior-shaping unit (shown in  FIGS. 5 and 6 ) is used instead of the simple mandrel used in the prior art as shown in  FIG. 1 . This interior-shaping unit provides an additional pressure area  8  against the interior of the workpiece  9  by the contact pressure of the inner reshaping rollers, said area  8  extending radially outward from the interior of the workpiece  9 . This is shown in  FIG. 4 . Two pressure areas  7 ,  8  that overlap each other are formed by the shaping units on both sides, thus significantly increasing the available reduction potential of the wall thickness  10 , or permitting a higher degree of stiffness of the material to be reshaped with a constant reduction in wall thickness. 
         [0025]    In the illustrated example, this interior-shaping unit based on the invention includes a number of conic rollers tangential to the workpiece  9  that may be mounted as reshaping rollers  11  particularly in a cage  12 ,  13  that may be repositioned tangentially and axially with respect to the workpiece  9 . The cage is held together using threaded fasteners  14 , and may be adjusted axially. The reshaping rollers  11  rest against an inner mandrel  16  that is particularly conic and that is secured to an extension section  17  whose diameter is smaller than the shaped inner workpiece diameter  18 , or smaller than the inner workpiece diameter  18  to be shaped. 
         [0026]    The reshaping rollers  11  are thus particularly held in position tangentially and axially by the cage  12 ,  13 , and radially by the inner mandrel  16 . This arrangement ensures that the reshaping rollers do not fall out of the interior-shaping unit when the interior-shaping unit is located outside of the workpiece  9 . Because of design and configuration of these reshaping rollers  11 , a maximum number of reshaping rollers is possible that exert the maximum possible reshaping force on the inner walls of the workpiece with minimum tangential separation from one another. 
         [0027]    A conic outer enveloping surface  20  is formed by means of the rolling action of the reshaping rollers  11  with the conic exterior (conic exterior means that at least the enveloping surface of the inner or outer reshaping roller is truncated-cone or cone-shaped) on the exterior  19  of the inner mandrel  16 . The larger diameter of this enveloping surface determines the shapeable inner diameter  18  of the workpiece  9 . 
         [0028]    The midlines of the centers of conical reshaping rollers  11  intersect with the tips of the enveloping surfaces of all conical reshaping rollers  11  at a point  21  that lies along the workpiece axis and/or the rotational axis  22  of the workpiece  9 . Axial displacement capability of the cage  12 ,  13  allows radial adjustability of the reshaping rollers to a diameter at which the midlines  24  and the ends of the enveloping surfaces  20  of the reshaping rollers  11  intersect with the rotational axis  22  of the workpiece  9  at a point  21 , and their speeds are thus matched. During the reshaping, the greater diameter of the conical enveloping surface  20  forms the inner diameter  18  of the shaped workpiece  9 . 
         [0029]    An inner centering unit  23  may be provided for the area of the workpiece to be shaped, and an additional inner centering unit (not shown) may be provided for the shaped area of the workpiece. Both centering units are mounted independently of each other in the center of the rotational axis so that they may be forced through the workpiece  9  during the reshaping process with minimum frictional loss. 
         [0030]    One interior-shaping unit ( FIG. 3 ) per exterior-shaping unit may be used on a workpiece. For this, it does not matter whether the workpiece is driven or the shaping units are driven, since the effect on the shaping process is the same. 
         [0031]    The interior-shaping unit may also be used without an exterior-shaping unit. In such case, an outer sheath (not shown) must be mounted in the area of the reshaping that is driven axially and tangentially by flowing material so that only minimal friction may arise between the material and the inner walls of the outer sheath. 
         [0032]    In order more greatly to increase the pressure areas into the depth of the workpiece walls, a modified exterior-shaping unit based on the invention may be provided, as shown in  FIGS. 6 through 8 . The interior-shaping unit shown there corresponds to the embodiment example described previously. 
         [0033]    The illustrated exterior-shaping unit possesses a number of conical rollers tangential to the workpiece that are provided in the illustrated example in a cage  25 ,  26  whose left and right cage parts are connected together by threaded fasteners  27 , and which can be axially adjustable. The configuration, shape, and orientation of the exterior reshaping rollers  24  are very similar to that of the inner reshaping rollers  11  described above. 
         [0034]    A bearing race  28  with inner running surface  29  facing the reshaping rollers  24  mounted in an outer housing  30  is provided to support the outer slide way of the reshaping rollers  24 . The outer reshaping rollers  24  are thus held tangentially and axially in position by means of a cage  25 ,  26 , and radially by the outer bearing race  28 . Because of this configuration, the reshaping rollers  24  with their inner slide ways form a conical enveloping body  31  whose angle to the rotational axis  32  of the workpiece  33  corresponds to the approach angle of a reshaping roller  24 . 
         [0035]    By means of the radial displacement capability of the axially-assembled cage  25 ,  26 , the adjustability of the reshaping rollers  24  is possible to a diameter at which the midlines  34  and the ends of the enveloping body  31  of the conical rollers  24  intersect at one point with the rotational axis of the workpiece  33 , and are thus matched to each other regarding speed. During reshaping, the small diameter of the truncated-cone-shaped enveloping bodies of the reshaping rollers  24  thus forms the outer diameter of the shaped workpiece. Simultaneously, the cage configuration prevents the reshaping rollers from falling out when no workpiece  33  is located within the interior of the exterior-shaping unit. 
         [0036]    This configuration of the outer reshaping rollers  24  allows a maximum number of reshaping rollers with minimum tangential separation from one another that exert the maximum possible reshaping force on the outer wall of the workpiece, and that are supported by rolling on the conical inner side  29  of the outer bearing race  28 . All reshaping rollers  29  together form a conical enveloping body  31  within the cage  25 ,  26  whose angles to the rotational axis  22  of the workpiece  33  form the approach angle of the reshaping rollers  24  to reshape the workpiece  33 . As soon as the rotating workpiece  33  axially meets the inner enveloping bodies  31  of the reshaping rollers  24 , these [enveloping bodies  31 ] rotate, thereby rolling over the fixed inner conical bearing race  29  of the outer ring  28 . Because of the axial pressure of the advancement along the axial direction, and of the torque of the workpiece  33 , an axial, tangential, and radial force is generated that places the material into a plastic state so that it flows, causing the reshaping process to begin. During this reshaping, the reshaping rollers are preferably rinsed with a lubricating coolant liquid that is supplied via the coolant connection  36 . 
         [0037]    A similar reshaping process is possible with the reshaping unit described above if the outer bearing race  28  is tangentially and axially driven, and the workpiece  33  is fixed, or when only the outer bearing race  28  is driven tangentially and the workpiece  33  is tangentially fixed and axially displaced. 
         [0038]    With a fixed workpiece  33 , it is also possible to mount a driven reshaping unit on each end of the workpiece  33  in order simultaneously to start an independent process on both sides, each with its own dimensions. 
         [0039]    If no interior-shaping unit is present, an inner mandrel  3  to accept the workpiece  33  is required for the two types of exterior-shaping units onto which the workpiece is reshaped while centered. The shape of the mandrel can have considerable influence on the friction between the workpiece and flowing material. Using a mandrel driven by the material flow or using an inner roller can achieve minimum frictional losses between material and mandrel. 
         [0040]    Further, there exists the option of mounting an interior-shaping unit in combination with a mandrel within the interior of the driven workpiece, and mounting one or more exterior-shaping units about the circumference of the workpiece, whereby the exterior-shaping unit then reshapes axially at the same workpiece cross section and simultaneously another exterior-shaping unit in the area of the mandrel reshapes another part of the workpiece. 
         [0041]    Accordingly, the invention achieves the fact that the yield stress in the reshaping area in the walls of the workpiece is increased by means of an interior-shaping unit with or without an exterior-shaping unit acting on a driven workpiece, wherein the inner rollers and the adjacent outer rollers possess a minimum tangential separation from one another, thus allowing maximizing of the reshaping rollers about the circumference of the contact diameter of the workpiece. This is achieved by driven interior- and potentially exterior-shaping units acting on a fixed workpiece. 
         [0042]    Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims.