Patent Publication Number: US-8523550-B2

Title: Powder press for the manufacture of a metal powder compact

Description:
The present invention relates to a powder press for producing a metal powder compact, with an upper punch arrangement, a lower punch arrangement and a die arrangement which forms the mold cavity into which the metal powder is filled; and then, to form the compact, the upper punch arrangement and the lower punch arrangement are pressed together in the pressing direction, controlled by a control unit; and the lower punch arrangement is equipped with a plate on which the die arrangement is placed, to which plate cross pressing devices are fastened, each device being equipped with a cross pressing punch which can be linearly driven by a drive unit and which can be pressed into and retracted out of the mold cavity in the direction of cross pressing through an opening in the die which is essentially perpendicular to the pressing direction. 
     Such powder presses have been elucidated in a wide variety of ways, they are used to manufacture powder compacts which are then sintered, making it possible to produce a variety of workpieces which can optimally fulfill the diverse demands placed on these workpieces; indexable inserts which are subjected to very high loads are produced like this, for example. When powder pressing tungsten carbide or other materials, the pressing is mainly carried out in one direction, usually in the vertical direction. 
     Powder presses have also been elucidated whereby cross rods are introduced through the die wall into the mold cavity at right angles to the pressing direction before the pressing process, said cross rods usually being brought into contact with a punch of the lower punch arrangement. These cross rods are moved via direct linear drives, for example hydraulically, which is possible because these cross rods do not have to absorb any pressing forces in the direction of their motion. 
     The objective of the present invention consists in designing the powder press such that the compact can also be formed during the pressing process with cross pressing punches, and the forces arising during the pressing can be absorbed in the direction of cross pressing. 
     According to the invention, the objective is achieved by the drive of each cross pressing device comprising a linear drive unit with a fixed part fastened to the frame of the cross pressing device and a part which can be moved linearly relative to the fixed part, said linearly moveable part being connected to a first wedge, whose wedge surface acts on the wedge surface of a second wedge, which can essentially be moved perpendicular to the first wedge in the direction of the cross pressing. 
     With this arrangement according to the invention it is possible to generate lateral holes in a metal powder compact, it is also possible to generate side impressions in this compact which do not go right through so that the cross pressing device can absorb the forces which arise in the direction of cross pressing during the pressing. The passages for the cross pressing punches can be made by means of cut-outs which are made in the annular die; the inner part of the die arrangement can also be completely divided or partially divided, these die components being separated from each other in order to form the cut-outs for the passages of the cross pressing punches, where said die components can be inserted in an annular die holder. This makes it possible to form side impressions and/or protrusions on the compact. 
     Since the drive unit of each cross pressing device comprises a linear drive unit with a fixed part fastened to the frame of the cross pressing device and a part which can be moved linearly relative to the fixed part, said linearly moveable part being connected to a first wedge, whose wedge surface acts on the wedge surface of a second wedge, which can essentially be moved perpendicularly to the first wedge in the direction of cross pressing, the forces acting on the cross pressing punch during the pressing process can be optimally absorbed without subjecting the linear drive unit to a high load. 
     Advantageously, the first wedge and the second wedge can be moved along linear guide tracks made in the frame of the cross pressing device, so that the forces arising and acting on the cross pressing punch are largely absorbed by the frame. 
     A further favorable embodiment of the invention consists in the fact that the pressing position of the cross pressing punch can be set by an adjustable end stop, whereby the pressing position of the cross pressing punch is always very accurately attainable regardless of other influences. 
     Advantageously, the end stop is formed by an adjustable third wedge perpendicular to the direction of motion of the first wedge, said wedge being guided in the frame and whose wedge surface interacts with a further wedge surface of the first wedge. This provides a very fine and exact adjustment method, on the one hand and, on the other, the end stop is very stable and subjected to almost no deformation. 
     Advantageously, the position of the cross pressing punch in relation to the die arrangement can be determined by means of measuring devices and transmitted to the control unit, whereby the position of the cross pressing punch is monitored and it is simple to adjust the pressing position of the cross pressing punch via the end stop. 
     A further advantageous embodiment of the invention consists in each cross pressing punch being held in the respective cross pressing device by means of a coupling device. This makes it easy to exchange the cross pressing punch, while the cross pressing device can be used to press practically all different forms of compact. 
     A further advantageous arrangement of the invention consists in each cross pressing device being equipped with a protruding bolt and the plate being equipped with several holes, said bolt protruding into one of the holes when the cross pressing device has been placed on the plate, and several cross pressing devices being able to be fastened on the plate in various positions. This allows the cross pressing devices to be used in predetermined positions with specific die arrangements without the need to align the cross pressing device to any great degree. 
     Advantageously, corresponding threaded holes are assigned to the holes in the plate into which clamping screws can be screwed which are held in the frame of each cross pressing device in corresponding cut-outs. The cross pressing devices can thus easily be fastened in the corresponding positions on the plate. 
     Advantageously, the cut-outs to hold the clamping screws in the frame of the cross pressing device have the form of a slot so that each cross pressing device placed onto the plate can be swiveled slightly around the bolt and can thus be aligned with respect to the die, whereupon the cross pressing device can be fixed to the plate by means of the clamping screws. 
    
    
     
       One embodiment of the invention will be described in further detail below as an example with the aid of the enclosed drawing, 
       in which 
         FIG. 1  shows a perspective view of a lower punch arrangement with a die arrangement with plate and three cross pressing devices fixed onto this plate; 
         FIG. 2  shows a plan view of the die arrangement with the plate and the cross pressing devices fastened thereon according to  FIG. 1 ; 
         FIG. 3  shows a perspective view of a cross pressing device without cross pressing punch, in pressing position; 
         FIG. 4  shows a perspective view of the cross pressing device according to  FIG. 3  with the cover plate removed; 
         FIG. 5  shows a plan view of the cross pressing device according to  FIG. 3 , with some sectional views; 
         FIG. 6  shows a sectional view of the cross pressing device along line VI-VI according to  FIG. 7 ; 
         FIG. 7  shows a sectional view of the cross pressing device along line VII-VII according to  FIG. 6 ; 
         FIG. 8  shows a perspective view of the cross pressing device in the retracted position; 
         FIG. 9  shows a perspective view of the cross pressing device according to  FIG. 8  with the cover plate removed; 
         FIG. 10  shows a plan view of the cross pressing device according to  FIG. 8 , with some sectional views; 
         FIG. 11  shows a sectional view of the cross pressing device along line XI-XI according to  FIG. 12 ; 
         FIG. 12  shows a sectional view of the cross pressing device along line XII-XII according to  FIG. 11 ; 
       and  FIG. 13  shows a perspective view of the cross pressing device according to  FIG. 3  but with the second wedge removed. 
     
    
    
       FIG. 1  shows a schematic representation of the lower punch arrangement  1 , which is formed as an adapter and into which a powder press, which is not shown, can be inserted into the lower part as is known in the art. Onto this lower punch arrangement  1  a plate  2  is placed onto which a die arrangement  3  is fastened. Onto this plate  2  are fastened cross pressing devices  4  which are each equipped with a cross pressing punch  5  which can be linearly driven by a drive unit which will be described in detail later. These cross pressing punches  5  pass through openings  6  in the die  7  of the die arrangement  3 , they lead into mold cavity  8  which is formed in the die arrangement  3 , and into which the metal powder can be filled and formed into the corresponding compact during the pressing process as is known in the art. 
     In the arrangement of the device shown in  FIG. 1  three cross pressing devices  4  are arranged on plate  2 , it is naturally possible to arrange two to six cross pressing devices, for example, depending on the type of compact which is to be manufactured and the correspondingly designed dies. 
     Above the die arrangement  3  and the cross pressing devices  4  a filling shoe plate (not shown) is placed in the known way, to which end pillars  9  are mounted on plate  2 , the filling shoe being mounted on said filling shoe plate in the known way so as to be moveable, and with which the mold cavity  8  can be filled with metal powder. 
     As will later be seen in detail, the drive unit of the cross pressing devices each have a hydraulic cylinder, hydraulic tubes  10  are attached to supply these hydraulic cylinders, which are connected to the hydraulic system of the powder press in the known way (not shown) and whose valves can be controlled in the way known in the art via a control unit of the powder press. 
       FIG. 2  shows the arrangement of three cross pressing devices  4  on plate  2 . The cross pressing punches  5  of these cross pressing devices  4  protrude into the die  7 , the die  7  is split in the present example embodiment, the individual parts of this die  7  are inserted into a die ring  11 , the divisions of the die  7  form the corresponding openings  6  for the cross pressing punch  5 . 
     Plate  2  is equipped with several holes  12 , these holes  12  serve to hold a bolt  13  ( FIG. 7 ) which is attached to each cross pressing device  4  and protrudes on the underside, whereby the cross pressing device  4  can be positioned on plate  2 . To each of these holes  12  are assigned two threaded holes  14  which are made into plate  2  and into which clamping screws  15  can be screwed whereby the cross pressing devices  4  can be fastened to plate  2 . Slit-shaped cut-outs  16  for these clamping screws  15  are made in the cross pressing devices  4  so that each cross pressing device  4  can be swiveled slightly around the bolt  13  ( FIG. 7 ) in the hole  12  and can be screwed tight in the corresponding position by means of the clamping screws, which means the cross pressing punch  5  does not have to be accurately aligned into the center of the die  7  but can deviate from the center, as can be seen with the die  7  of the embodiment according to  FIG. 2 . This die  7  is used to produce compacts  17  in the form of indexable inserts. 
       FIG. 3  shows a cross pressing device  4 . This cross pressing device  4  comprises a frame  18  in which the drive unit, which is a linear drive unit, is mounted, as is described in detail below. This first linear drive unit can move a first wedge  19  in one direction, shown by the double arrow  20 . This first wedge  19  is guided along a linear guide track  21  aligned parallel to the direction of motion, shown by the double arrow  20 .This linear guide track  21  is fastened to the cover plate  25  which is screwed onto the frame  18 . 
     A wedge surface  23  of a second wedge  24  is in contact with the wedge surface  22  of the first wedge  19 . This second wedge  24  is likewise linearly moveable, namely in the direction perpendicular to the direction of motion of the first wedge  19 , shown by the double arrow  20 , i.e. in the direction represented by the double arrow  26 . The direction represented by the double arrow  26  also corresponds to the direction of cross pressing, with which the cross pressing punch  5  (not shown) ( FIGS. 1 and 2 ) can be moved. Moving the first wedge  19  along the linear guide track  21  causes the second wedge  24  to move in the direction of the double arrow  26 , guided by the linear guides  27  which are likewise fastened in the cover plate  25 . A coupling device  28  with which the cross pressing punch  5  (not shown) ( FIGS. 1 and 2 ) can be held is fastened on the end of the second wedge  24  opposite the wedge surface  23 ; these cross pressing punches can easily be exchanged. 
       FIG. 4  shows the cross pressing device  4  according to  FIG. 3  but without the cover plate  25 . In this representation it can be seen that the first wedge  19  interacts with a third wedge  29 , the first wedge  19  having a further wedge surface  30  which is in contact with wedge surface  31  of the third wedge  29 . This third wedge  29  serves as the end stop for the first wedge  19 , said end stop being adjustable, as will be seen later. 
       FIG. 5  shows the frame  18  of the cross pressing device  4 , with the arrangement of the first wedge  19 , the second wedge  24  and the third wedge  29 . The third wedge  29  is equipped with a rib  32  which is held so as to be moveable in the frame  18  at right angles to the direction of motion of the first wedge  19 , shown by the double arrow  20 . In the frame  18  and in the cover plate  25  there is a hole  33  provided with a thread into which an adjustment screw  34  is screwed. Turning this adjustment screw  34  moves the wedge  29  at right angles to the direction of motion of the first wedge  19 , whereby the lowermost position of the first wedge  19  in  FIG. 5  can be fixed. This position also corresponds to the fully extended position of the second wedge  24  and thus of the cross pressing punch  5  ( FIGS. 1 and 2 ). In this position the cross pressing punch is in the pressing position. This means the position of the cross pressing punch can be very accurately positioned in the pressing position by moving the third wedge  29 . The position of the second wedge  24  and thus the cross pressing punch  5  is sensed in the known way by a measuring device  35  fastened on the frame  18  of the cross pressing device  4 , the corresponding signal being transmitted to the machine control in the known way. 
       FIG. 6  shows the drive unit  36  with which the first wedge  19 , the second wedge  24  and hence the cross pressing punch  5  can be moved. This drive unit  36  comprises a hydraulic cylinder  37  arranged in the frame  18  of the cross pressing device  4 , a piston  38  with a piston rod  39  fastened thereto being held in said hydraulic cylinder  37  so as to be moveable. This piston rod  39  is pushed backwards and forwards in the hydraulic cylinder  37  by means of suitable pressure being applied to the piston  38 .  FIG. 6  also shows the slit-shaped cut-outs  16  into which the clamping screws  15  are screwed to fasten the cross pressing device  4 . 
       FIG. 7  again shows the drive unit  36 , which is arranged in the frame  18  of the cross pressing device  14 . A bracket  40  is fastened to the opposite end of the piston rod  39  to the piston  38 , said bracket  40  being connected to the first wedge  19 . The first wedge  19  can therefore be moved by moving the piston  38  in the hydraulic cylinder  37 ; the pressing position, as shown in  FIG. 7  and in all previous Figures, incidentally, is determined by the third wedge  29 . 
     Likewise visible in  FIG. 7  is the bolt  13  whereby the cross pressing device  4  is positioned on plate  2  ( FIGS. 1 and 2 ). 
       FIG. 8  shows the cross pressing device  4  according to  FIG. 3 , but where the second wedge  24  and hence the cross pressing punch (not shown) are in the retracted position. The first wedge  19  is thus also retracted, i.e. the additional wedge surface  30  of the first wedge  19  is a distance away from the wedge surface  31  of the third wedge  29 . 
       FIG. 9  shows the cross pressing device  4  in the position shown in  FIG. 8  although here the cover plate  25  has been omitted. 
       FIG. 10  shows the cross pressing device  4  in the corresponding position according to  FIG. 8  and  FIG. 9 . 
     The same position, in which the cross pressing punch is retracted, is shown in  FIG. 11 . The piston  38  is in the retracted position in the hydraulic cylinder  37 . Correspondingly, the piston rod  39  and the bracket  40  fastened thereto are likewise in the retracted position. 
     The same representation as in  FIG. 11  is likewise visible in  FIG. 12 , the piston  38  is in the retracted position. 
     In the representation according to  FIG. 13  the first wedge  19  can be seen, which is equipped with a step  41 , bolts  42  being arranged on said step  41 . The second wedge  24 , which is not shown in  FIG. 13 , is equipped with a cut-out corresponding to step  41 , a groove is made into this cut-out into which the bolts  42  protrude. This arrangement couples the second wedge  24  to the first wedge  19 ; when the first wedge  19  is being retracted, and to retract the cross pressing punch out of the die, the second wedge  24  is likewise forcibly retracted via this connection. 
     As can be seen particularly well in  FIG. 3 , in which the pressing stamp is in the pressing position and must absorb the pressing forces acting on the front surface of the pressing punch during the process of pressing a compact, this absorbed pressing force is transferred in the axial direction to the second wedge  24 , from whence this is transferred via the wedge surface of the second wedge  24  to the corresponding wedge surface  22  of the first wedge  19 . The axial force component is transferred by the first wedge  19  onto the linear guide track  21  of the frame  18 . The component created by the oblique position of the wedge surfaces  22  and  23 , a component which acts in the direction of the double arrow  20 , is relatively small due to the relatively small angle of inclination of these two wedge surfaces  22  and  23  and the friction thus caused, so that the residual force acting on the drive unit  36  is very small and can easily be taken over by the drive unit. 
     With this arrangement according to the invention it is possible to equip a powder press with several cross pressing devices, which can be positioned and fastened to the corresponding plate in a wide variety of ways and in different numbers. This allows a wide variety of compacts to be produced on this powder press, changeovers can easily be carried out in each case.