Patent Publication Number: US-2016221217-A1

Title: Powder press for producing pressed parts made out of powdered pressing material

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application No. 10 2015 101 586.2, filed Feb. 4, 2015, the content of which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The disclosure relates to a powder press for producing pressed parts made out of powdered pressing material. 
     TECHNICAL FIELD 
     It is known to produce preforms made out of carbide, ceramics, ceramic metals or the like by means of presses. The powdered or granular material is formed into a preform, which is then subjected to a sintering process, by means of presses. A press may include an upper stamp and a lower stamp, which cooperate with a die or respectively a die hole in a die plate. The stamps are driven by a suitable power drive, for example a hydraulic cylinder. The die plate may be arranged in a fixed manner and to move upper stamp and lower stamp or alternatively to shift only the upper stamp and the die plate, while the lower stamp remains stationary. 
     A powder press from EP 566 231 B1 allows at least two pressed parts to be produced at the same time. For this, separate lower stamps are provided, which each cooperate with a die hole. The separate lower stamps are each scanned by a separate position sensor and force sensor and controlled by means of a respective regulating installation. A common force transmission bridge with a common position sensor and a common force sensor is provided for the upper stamps. A cylindrical ring arrangement for the activation of two separate lower stamps is shown in an example. The arrangement can be used to activate the upper stamps separately. 
     SUMMARY 
     The non-centric arrangement of the upper stamps and/or lower stamps in EP 566 231 B1 gives rise to lateral forces on the drive cylinders and guiding units, which can cause considerable wear. It is not possible to compensate for tilting or the desired, differentiated impact of forces on the stamps by conventional means. 
     In contrast, the teachings herein describe a powder press with which a plurality of pressed forms can be simultaneously produced with reduced wear in a narrow space. 
     One powder press described herein includes a die plate with at least two dies or one die with at least two die holes, at least two upper stamps which cooperate with the dies or respectively die holes, at least two lower stamps which cooperate with the dies or respectively die holes, at least one linear drive for each upper stamps and/or lower stamps, at least one position sensor for each upper stamp and/or at least one position sensor for each lower stamp, and a regulator for each of the linear drives for upper stamps and/or lower stamps respectively. At least each upper stamp and/or lower stamp is, in terms of function, connected to a force transmission bridge on which two linear drives act, which are arranged spaced apart in parallel. 
     Regardless of whether the drive forces of the linear drives act on the force transmission bridges or respectively the stamp carriers symmetrically, tilting can be compensated with the powder press so that no wear problems arise in this regard. Furthermore, different drive forces can be exerted on the force transmission bridges or respectively the stamp carriers in a targeted manner if this is advantageous for giving the pressed part a corresponding design. Additionally, unequal stamp lengths of the upper stamp axis can be evened out with the powder press described herein, which works with separate upper stamps and lower stamps in any event. 
     In particular, the powder press enables a higher output of pressed parts and a prevention of increased wear. Despite the higher output per unit of time, a better quality of the pressed parts is achieved. 
     According to one embodiment of the teachings herein, the linear drives have electrically driven spindle drives, with which the linearly movable drive part is connected to the force transmission bridge in terms of function (e.g., they are functionally connected). With a spindle drive, either the spindle nut or respectively a worm wheel or the spindle rod is known to be stationary. How the spindle drive is connected to the press stamp in terms of function depends on the structural requirements of the gear options. 
     Since there are two force paths with respect to a stamp, it is advantageous to measure the positions and the transmitted forces in each force path. Conventional force sensors are complex. It is therefore very advantageous if, according to an additional embodiment of the teachings herein, a piezo sensor is arranged in the force path of the linear drives of the upper stamps and/or lower stamps. In this way, precisely regulating each force path in order to prevent tilting or to introduce different forces is quite possible. 
     According to one embodiment of the teachings herein, the force transmission bridge closer to the die plate has an opening through which the upper stamp and/or lower stamp of the other force transmission bridge can pass. In this way, the powder press can be built very small. 
     In the following, an exemplary embodiment of the invention is to be explained in greater detail. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a diagrammatic representation of drives for two upper stamps of a powder press according to one embodiment of the teachings herein and the regulation of the powder press for the upper stamps. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a die plate  10  with two die holes  12 ,  14 . A first upper stamp  16  is fitted to a force transmission bridge  15  and a second upper stamp  18  to a force transmission bridge  17 . The upper stamps  16 ,  18  cooperate with the die holes  12 ,  14  in a known manner. A lower stamp  22  is fitted to an additional force transmission bridge  19 . An additional lower stamp  24  is fitted to a fourth force transmission bridge  23 . The lower stamps  22 ,  24  cooperate with the die holes  12 ,  14  in a known manner. The upper stamp  18  extends through an opening  25  in the force transmission bridge  15 , and the lower stamp  24  extends through an opening  27  of the force transmission bridge  19 . 
     Bearings  50 ,  52  for spindle rods  54 ,  56  are arranged on the force transmission bridge  15  at opposite ends. The spindle rods  54 ,  56  extend upwards into gears  58 ,  60 , which are connected to respectively to an electric drive motor  62 ,  64 . When the motors  62 ,  64  rotate, the spindle rods  54 ,  56  move axially and therefore activate the force transmission bridge  15  and with it the upper stamp  16 . Analogously, on the force transmission bridge  17 , an arrangement of two bearings  66 ,  68  is provided for respective spindle rods  70 ,  72 , which extend through respective gears  74 ,  76 , which are in turn connected to respective electric motors  78 ,  80 . The activation via the shown gears for the upper stamp  18  corresponds to that for the upper stamp  16 . 
     The lower stamps  22 ,  24 , or respectively the force transmission bridges  19 ,  23 , are driven by analogous spindle drives. They have been omitted for the purposes of simple illustration. 
     As described two linear drives have an impact on each of the stamps shown. A force sensor (not shown), for example a piezo sensor, is arranged in each force path for each linear drive, in order to either equalize or produce in a differentiated manner the regulation of the forces having an impact on the force transmission bridges  15 ,  17 . 
       FIG. 1  shows only a portion of a powder press to illustrate the teachings herein. The powder press will generally include a frame surrounding the structure of  FIG. 1 , and guides for the force transmission bridges  15 ,  17 ,  19 ,  23 . In an alternative implementation, the stamps  16 ,  18 ,  22 ,  24  may not be directly connected to the force transmission bridges  15 ,  17 ,  19 ,  23 . Instead, the stamps  16 ,  18 ,  22 ,  24 , via suitable tool carriers or respectively stamp carriers, may be otherwise functionally connected to the force transmission bridges  15 ,  17 ,  19 ,  23 . 
       FIG. 1  also indicates the regulation of the upper stamps  16 ,  18 , namely by means of one or more control devices or regulators indicated by block  20  for the upper stamp  18  and by block  21  for the upper stamp  16 . A position sensor  23  is assigned to the gears  74 , and a position sensor  25  is assigned to the gears  76 . A force sensor  27  is assigned to the upper stamp  18 , and a force sensor  29  is assigned to the upper stamp  16 . A position sensor  31  is assigned to the gears  58 , and a position sensor  33  is assigned to the gears  60 . The regulations in the control devices  20  and  21  regulate the shifting of the force transmission bridges  15 ,  17  via the data of the position sensors and force sensors. Control is achieved either synchronously, so as to prevent the upper stamps  16 ,  18  tilting or by deliberately applying different loads to the force transmission bridges  15 ,  17 , as required. Because the drives, of which each force transmission bridge has two, can be regulated separately, the various functions can be achieved. For clarity,  FIG. 1  does not show the lines of action (e.g., the control lines) from the control devices  20  and  21  to the drive motors  62 ,  64 ,  78 ,  80 . The control devices  20 ,  21 , may each be a combination of hardware and/or software configured to achieve the control described above. Further, while two control devices  20 ,  21  are shown, only one is needed so long as output signals can be sent to separately regulate the drives. 
     Analogously to the upper stamps  16 ,  18 , position sensors, which are connected to a regulator (e.g., control device  20  or  21 ), can be assigned to the lower stamps  22 ,  24 . Force sensors, which are connected to the regulators, can also be assigned to the linear drives for the force transmission bridges  19 ,  23 . Hence, independent linear drives are provided for the respective lower stamps  22 ,  24 . 
     The activation of the upper stamps  16 ,  18  or respectively lower stamps  22 ,  24  thus follows via separate regulators. With the arrangement shown, it is therefore possible to adjust precisely the force that is respectively exerted on the force transmission bridge  15 ,  17  or respectively the force transmission bridge  19 ,  23  by a linear drive or respectively a spindle drive. Tilting of the stamps  16 ,  18  can thereby be prevented. Making different forces have an impact on a force transmission bridge is additionally possible, if so desired. That is, different forces may be applied to different areas of the force transmission bridge if it is desirable for a particular application.