Abstract:
A preshaping method for massive forming processes is proposed in which a fixed blank is deformed by at least one roll moving continuously forward along a predetermined contour.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of German Application No. 2004 008 800.4, filed Feb. 20, 2004, the entirety of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The invention relates to a method and a device for preshaping a blank in a massive forming process. 
   BACKGROUND OF THE INVENTION 
   In the process chain of die forging, an intermediate shape in relation to the final shape of the forged part is required. The result of the subsequent die forging is thus to be improved by an accumulation or reduction in mass at certain points of the workpiece. In order to obtain the intermediate shape, methods such as transverse rolling or stretch rolling, for example, are known. 
   Further methods are described in “Lehrbuch der Umformtechnik” [textbook of forming technology], Kurt Lange, Springer-Verlag 1974, page 46. 
   Both transverse rolling and stretch rolling permit optimum geometric adaptation of the mass distribution on the intermediately shaped part to the requirements for the die forging of elongated parts. The excess material in the final shape is thereby minimized and uniformly distributed and permits low-flash die forging. Due to the adaptation of the rolled intermediate shape to the final shape of the finish-forged part, constant forming forces and thus minimum tolerances of the finished parts in the press direction are ensured. In addition, relative movements in the pressure contact zone between workpiece and impression are reduced and thus the wear of the dies is reduced. By the use of preshaping methods preceding the die forging, the use of material can be reduced by up to a third. 
   In massive forming, a trend toward a higher and higher number of strokes has recently been detected. This is achieved in particular through the use of modern crank presses having fully automatic workpiece transfer for the die forging. The known preshaping methods, in particular transverse rolling and stretch rolling, have the disadvantage that they can only be integrated with difficulty in a fully automatic forging process with automatic workpiece transport. The reasons for this are the relatively high cycle times during the transverse or stretch rolling, and the partly unsuitable position of the workpiece at the end of the rolling operation for an automated production process. 
   A further disadvantage is the complicated design of the preshaping device and the associated high costs. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to develop a method and a device for preshaping a forged part, which method is cost-effective with high productivity and can be integrated in the transfer of a forging press. 
   The central idea of the invention is a method in which a fixed blank is deformed by at least one roll, preferably two rolls, moving continuously forward along a predetermined contour. The feed movement of the contour roll is effected by a linear drive. 
   The path of the contour rolls during the feed is preferably determined by two profile inserts, the profile of which corresponds to the negative shape of the blank to be preshaped. Due to the feed movement and due to the shape of the contour rolls, the blank is formed by the contour of the profile inserts. In order to obtain, for example, a blank preshaped in a rotationally symmetrical manner as a final result of the “roll preshaping”, the contour rolls must be designed with the appropriate radius. As an alternative to this, it is also possible to use a contour roll only on one side. In this case, the blank is supported on the opposite side by a fixed stop during the preshaping. 
   Also conceivable is a solution in which the contour rolls are supported on straight plates on the side remote from the blank, these plates varying the distance between the plates and the blank axis by means of servomotors in such a way that the blank is appropriately preshaped. The actuators used may be, for example, servomotors or also hydraulic motors. 
   The blank is fixed with turning tongs. After a forming pass, the turning tongs and thus the partly formed blank are turned by 90°. The rolling operation is repeated in this position. As a result, the blank has attained an approximately rotationally symmetrical intermediate shape. It is also conceivable to run more than two rolling cycles with correspondingly smaller turning angle in order to improve the preshaping result. Of course, if the blank is made of a flat bar for example, just one forming pass can also produce the required intermediate shape. 
   During the rolling operation, the blank is held by the turning tongs and is supported radially from below by, for example, two ejector pins. A further function of the turning tongs is to compensate for elongation or stretching caused by the preshaping. At the end of the preshaping operation, the profile inserts are designed in such a way that the contour rolls move out of the forming region. The ejector pins now lift the preshaped blank onto the workpiece transport plane. The blank is then gripped by the transfer system of the forging press and is transported through the corresponding forming station. 
   The device according to the invention for this method can be positioned as an independent forming unit or can also be positioned in the column region of the forging press. As a result, the device for the roll preshaping can be integrated in the existing press transfer device in a cost-effective manner. 
   An independent solution in which the proposed device is placed in front of the forging press with separate feed device is likewise possible. The proposed preshaping method can be used both with and without additional heat treatment. In addition, the method is suitable for different materials, such as steel or aluminum for example. 
   In the case of high forming ratios during the preshaping, a plurality of devices according to the invention may also be operated arranged one above the other. The forming ratio increases in accordance with the number of devices used. The yield with a plurality of devices arranged one above the other is the same as when using only one device. As already mentioned, a linear force in the direction of the blank axis is necessary in order to press the contour rolls through between the blank and the profile inserts. This linear force is preferably produced by a hydraulic drive, but force transmission by a mechanical drive is also possible. 
   The force transmission from the drive to the contour rolls must be effected in such a way that the latter are freely movable in a plane perpendicular to the direction of movement in order to be able to follow the contour of the profile inserts. This is achieved by a fork head on which two arms are mounted in an articulated and scissors-like manner. The two contour rolls are rotatably mounted on these two arms. The arms on which the contour rolls are mounted may be additionally acted upon by a spring force in such a way that the contour rolls bear reliably against the contour during the advance and withdrawal. During the preshaping, the blank is supported by a stop plate against the feed direction or force. 
   In order to improve the forming result, the device according to the invention can be equipped with a guide sleeve which stabilizes the blank during the forming operation. This is achieved by a sleeve which encloses the blank up to right in front of the region of the forming and is carried along by the articulated arms in the direction of the blank axis against a spring force. As a result, bulging or inclination of the blank due to the forming is prevented. 
   In order to be able to absorb the reaction force produced by the forming force, the profile inserts are fixed in a plane perpendicular to the blank axis. This may be effected by a mechanical stop, but other design solutions, such as, for example, a dimensionally stable frame which encloses the two profile inserts, are also possible. 
   The profile inserts, the stop plate and the frame thus form a device or a tool for the roll preshaping. This tool is restrained on a fixed table by known methods, such as with wedges or clamps for example, in such a way that the tool can easily be changed. Of course, it is also possible to exchange only the profile inserts. A mechanical stop in and against the feed direction of the hydraulic cylinder on the fixed table is appropriate. 
   Further advantages and details of the invention follow from the description and the figures of the exemplary embodiment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a device for roll preshaping, in an isometric view, 
       FIG. 2  shows a plan view at the start of the roll preshaping, 
       FIG. 3  shows a plan view during the roll preshaping, 
       FIG. 4  shows a plan view at the end of the roll preshaping, 
       FIG. 5  shows the device for roll preshaping in a sectional illustration. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A device  1  for roll preshaping is shown in  FIG. 1 . A table  2  can be seen, on which a fixed, flexurally rigid frame  4  is fastened by means of clamping shoes  3 . Two profile inserts  6  are fastened to the side walls of this frame  4 . On the side directed toward the center, these profile inserts have a contour which is matched to the final contour of the preshaped blank  7 . The blank  7  is supported on one side on a stop plate  5 , which is likewise fastened to the frame  4 . At the other end, the blank is held by turning tongs  13 . 
   A device  1  for roll preshaping is shown in section in  FIG. 5 . Ejector pins  12  can be seen, which support the blank  7  from below during the preshaping process. Located between the profile attachments  6  and the blank  7  are two contour rolls  8  which, by means of a drive (not shown), for example a hydraulic cylinder, are moved along the outer contour of the profile inserts  6  in the forming direction  9  via a drive linkage  11 . As a result, the outer contour is pressed into the blank  7  via the contour rolls  8  deforming the blank  7  such that the blank  7  elongates. The elongation effectively lengthens the blank  7  while the contour rolls are moved in the forming direction  9 . The turning tongs  13  compensate for the elongation occurring by moving in a direction opposite to the forming direction  9 . At the start and at the end, the profile inserts  6  are designed with a contour diverging from the blank  7 , so that the contour rolls  8  move away from the blank  7  at the start and at the end of the preshaping operation. The contour rolls  8  are pressed against the contour of the profile inserts  6 , for example by a spring force which acts on the arms of the drive linkage  11 . The drive linkage  11  essentially comprises 2 arms which are mounted at a common pivot  10 . 
   As soon as the contour rolls  8  have moved away from the preshaped blank  7  at the end of the preshaping process, the blank  7  can be lifted by the ejector pins  12  and transported by an automatic transfer system, for example into a die forging press. 
   Optionally, by rotating the turning tongs  13  and the blank  7  about its longitudinal axis, the preshaping operation can be repeated against the direction  9 . An approximately rotationally symmetrical preshaped blank  7  can be produced by repeating the roll preshaping several times. 
   Different preshaping stages are shown in  FIGS. 2 ,  3  and  4 . The start of the preshaping process can be seen in  FIG. 2 . The blank  7  is not yet formed. The contour rolls  8  are still located in the entry region of the outer contour of the profile inserts  6 . 
   In  FIG. 3 , the contour rolls  8  have covered about half the forming distance, and the resulting proportionate forming of the blank  7  can clearly be seen. 
   The device  1  can be equipped with a guide sleeve  14  to improve the forming result. The guide sleeve  14  encloses the blank  7  up to a point right in front of the contour rolls  8  to stabilize the blank  7  and to prevent bulging or inclination of the blank  7  during the forming operation. The sleeve  14  is carried along by the device linkage  11  in the direction  9  of the blank  7  axis against a spring force  15 . 
   In  FIG. 4 , the contour rolls  8  have already moved out of the region in which forming takes place and allow the preshaped blank  7  to be lifted by the ejector pins  12 . 
   The invention is not restricted to the exemplary embodiment shown and described. It also comprises all developments by the person skilled in the art within the scope of the idea according to the invention.