Patent Publication Number: US-6907765-B2

Title: Ram-side ejector device for workpieces in single-or multi-stage presses

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to German Patent Application File No. 102 08 720.2, filed Feb. 28, 2002, which is hereby incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   The invention relates to a ram-side ejector device for workpieces in single- or multi-stage presses, said presses comprising a press carriage, which is movable between a pressing position extended relative to a stationary press die and an end position at a distance therefrom and comprises a press ram cooperating with the stationary press die, further comprising an ejector pin carried on the press carriage in the pressing direction and penetrating the press ram, said ejector pin being movable between a retracted end position, in which said pin is supported, by its end remote from the die, on a stop formed on the press carriage, and an extended position protruding from the press ram, wherein the end of said pin remote from the die is distanced from the stop, said pin being provided with a resetting means acting counter to the direction in which said pin is extended and which may be releasably blocked, when the press carriage returns from its pressing position, by a blocking means fixed to the press frame counter to the return movement of the press carriage, the activation or deactivation of the blocking means and the activation of the resetting means being program-controlled and coupled with each other. 
   Such ejecting devices serve to eject workpieces on the ram side of single- or multi-stage presses, such workpieces including in particular screws, bolts, rivets or similar parts. The ejecting operation is integrated in the press operation cycle. 
   Devices for generating a ram-side ejection movement after the pressing operation in order to release and eject workpieces from the tools, e.g. from hexagon-head rams on automatic shaping presses, have long since been known. For this purpose, a movement is initiated from outside, i.e. either from the press frame (e.g. DE 24 50 631 C) or from the crankshaft (e.g. DE 1 750 033 C) into the press carriage of the shaping press, wherein the desired ejection movement is then generated via cam plates, angle levers or other transmission elements. However, these known ejector systems have the disadvantage that they are provided, in many cases, with many joints, levers, gearwheels and the like, and have a considerable mass which is to be moved together with the press carriage and is thus excited to vibrate. Moreover, these known ejector systems also have a certain stroke which causes the workpiece to be released first from the stationary die of the shaping press before being released from the moving ram of the press, which may result in the workpiece being lost before it can be securely taken, for example, by the gripping fingers of the transfer device of the press. A further disadvantage is that a change in the law of motion of the press carriage, for example when the carriage stroke changes, also requires a cumbersome change in the law of motion of the ram-side ejector, with the ejection stroke being changeable, in most cases, only with great effort. 
   As an overload safety device, the known ejector systems are usually provided with a breakage safety device which has to be renewed after being triggered. 
   Further, DE 100 07 255 A discloses a ram-side ejector device wherein an ejector lever can act upon the end of the ejector pin remote from the die, said ejector pin penetrating the ram, with the end of the ejector lever acting upon the end of the ejector pin being interposed between the latter and a stop on the press carriage and continuously contacting the end of the ejector pin remote from the die, even upon the return of the press carriage after the pressing operation. The return movement of the press carriage, the ejector lever is fixed in its position, immobilized relative to the frame, by means of a toggle connection and by an activatable solenoid such that said solenoid urges the ejector lever out of the press ram for the ejection movement during the return movement of the press carriage. Only if the desired ejection movement has been performed by the ejector pin, i.e. once it has been moved into the desired, fully extended position, the blocking of the ejector pin in its position fixed relative to the housing is eliminated by deactivating the solenoid. At the same time, the resetting means is activated, by which the ejector lever is retracted into the press carriage again and, thus, the ejector lever having its end contact the end of the ejector pin remote from the die is simultaneously tilted until it contacts the stop fixed relative to the housing. This return movement of the ejector lever is further supported by a spring prestressing it in this direction. 
   The toggle connection of the ejector lever, which is tiltably supported on the press frame, is simultaneously usable as an overload safety device which responds in order to protect the shaping press if the force by which the workpiece has to be urged out of the ram by means of the ejector pin exceeds a preadjusted level, for example upon tool breakage. The toggle lever system then bends in, because the programmably adjusted holding force of the solenoid is exceeded, which can be recognized by the program control of the shaping press enabling immediate stopping of the press. Thus, a renewal of the breakage safety device as required in the previously known ejector systems is not required in this case. 
   By the programmable selection of the switch-off time of the current supply to the solenoid during the return movement of the press carriage, the time period during which the ejector pin is immobilized, and thus the ejector stroke, may be easily predetermined, so that each ejector pin of multi-stage presses may be individually adjusted via the program control of the press. The cumbersome change of the law of motion for the ram-side ejector upon a change in the law of motion of the press carriage required in previous ejector systems is thus dispensed with. 
   While this known ejector device already essentially solves problems of previously known ejector devices in an excellent manner, it still suffers from relatively large masses of the system due to the ejector lever employed and its toggle lever connection comprising the solenoid blocking mechanism on the press frame, and it is, thus, not usable at higher operating speeds of the press (approx. over 50 pressing operations per minute). 
   In view thereof, it is an object of the invention to improve such ejector device in such a way that the total mass of the ejector system can still be reduced further and that, in particular, use thereof is possible also at higher press speeds in the range of over 50 press strokes per minute. 
   SUMMARY OF THE INVENTION 
   According to the invention, this object is achieved by a ram-side ejector device of the above-mentioned type in that the means for blocking comprises a blocking mechanism with a positionally shiftable blocking element which can be retracted into blocking engagement with the ejector pin or with a part connected therewith in the pressing position of the press carriage, while the ejector pin is in contact with the stop. 
   The invention provides a ram-side ejector device wherein, in contrast to the device mentioned above, the blocking means need no longer be maintained in continuous contact with the ejector pin and be blocked at a certain location. Rather, according to the invention, the blocking means uses a positionally shiftable blocking element, which is not retracted or moved into blocking engagement with the ejector pin (or with a part connected therewith) until the press carriage has been brought into its pressing position, while the ejector pin is still in engagement with the stop fixed relative to the housing. This allows the force acting upon the ejector pin in its longitudinal direction as a result of the pressing operation to be securely supported via the ejector pin contacting the stop on the press carriage without interposition of the blocking element, wherein the latter can only be brought into blocking engagement with the ejector pin (or with a part thereof) and thus the immobilization can be performed directly on the ejector pin (or on the part connected therewith), when it has reached its ejection position, at the time when the blocking effect is desired. In the invention, in contrast to the above-mentioned device, there is no longer any movement of the blocking means caused by displacements of the press carriage, so that there is thus no comovement of the blocking means even during fast movements of the carriage, i.e. during high press cycles. According to the invention, the blocking means only serves to block the ejector pin in its position relative to the press frame during the return of the press carriage (or only for part of its return movement) and, thus, to cause the extension movement of the ejector pin. Once this has been achieved, the blocking means is moved out of the blocking engagement again and is thus not involved in the moving masses in the further return movement of the press either. Thus, the blocking means is completely eliminated as a moving mass during displacement of the carriage, which has the advantage that it does not vibrate either. The adjustment movements which become necessary in the blocking means in order to move it in and out of this blocked position, may be chosen to be relatively small so that, also in this regard, rapid execution of these adjustment movements at high press speeds is easily realized. 
   In the press according to the invention, the blocking means can easily be formed such that its release upon a certain predeterminable force being exceeded is forced in the longitudinal direction of the ejector pin in a form-fit manner, thus obtaining an overload safety device operating in a wear-free manner. A change in the ejection length of the ejection stroke is also easily realized by the program control of the blocking means in terms of the duration of the blocking effect and is thus easily adjustable to different laws of movement of, e.g., a multi-stage press. 
   The ram-side ejector device according to the invention has a particularly small mass, the ejection movement occurring independently of the law of movement of the press carriage and the workpieces being maintained in the stationary tool (namely the die) without any significant spring action. 
   It is particularly advantageous, in the ejector device according to the invention, if the blocking element is a shaped part which can be made to contact a complementary shape of the ejector pin or of a part connected therewith in order to block the ejector pin, wherein exactly such form-fit blocking can be provided without any difficulty in such a manner that said blocking is also automatically released in a form-fit manner when overload occurs. Particularly preferably, for example, the shaped part may be provided in the form of a sprocket wheel which is urged against a corresponding oblique butting face on the ejector pin. In doing so, automatic release of said blocking is easily effected by correspondingly adjusting the contacting force of the sprocket wheel against said face until a predetermined longitudinal force occurs in the longitudinal direction of the ejector pin (which is effective in the blocking direction). 
   A particularly preferred embodiment of the ejector device according to the invention is obtained by providing the shaped part on a piston rod which is slidably supported in a valve block and is displaceable by means of a pressure fluid between an extended blocking position and a retracted end position (which may comprise, e.g., full or partial retraction into the valve block) with no blocking engagement. Such embodiment of the blocking means, operating as a hydraulic double piston which can be retracted and extended in the direction of displacement, not only allows quick switching and adjustment movements (both to-and-fro), but also leads to relatively small moving masses and to an exactly selectable (and adjustable) blocking effect. 
   While the piston rod may be actuated in any suitable manner, it is particularly preferably actuated in a hydraulic manner. 
   A further advantageous embodiment of the ejector device according to the invention also consists in that the ejector pin is provided with a piston rod (as “a part connected therewith”) at its end remote from the die, on which piston rod the shape for blocking engagement with the blocking element is mounted. For this purpose, an oblique surface is provided preferably on the end of the piston rod remote from the die, on the side of the piston rod facing the blocking element, as a contacting surface for the shaped part. This results in a preferable function of the ejector device according to the invention with only very little structural complexity. 
   Advantageously, the ejector device according to the invention is further embodied such that the ejector pin can be returned not only to its retracted position by means of the resetting means, but the resetting means is also provided such that the ejector pin is additionally moveable also in its extension direction, which leads to the advantage that the ejector pin can also be used, for example, in order to slide a prefabricated workpiece into the die and to hold it there in order to yield in a resilient manner during the actual pressing operation, when the resetting means is actuated, for example, by means of a pressure gas. 
   The blocking means, which has to be fixed in a suitable manner relative to the frame, independently of the movement of the press carriage, is preferably embodied such, in an ejector device according to the invention, that it protrudes into a recess in the press carriage until it is close to the ejector pin or to the part connected therewith. This allows to achieve the advantage that, in order to effect said blocking engagement, the blocking means merely needs to carry out relatively small movements of extension for the blocking element, which allows rapid blocking (as well as rapid release of said blocking). 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The invention will be explained hereinafter essentially by way of example, with reference to the Figures, wherein: 
       FIG. 1  shows a side view, in partial section, of a ram-side ejector device according to the invention in a first end position at the rear dead center of the press carriage, at the beginning of a press cycle of the press; 
       FIG. 2  shows the ram-side ejector device of  FIG. 1  (again in a side view in partial section), but this time in a second, front end position, just before the beginning of an ejection operation (at the front dead center of the press carriage); 
       FIG. 3  shows the ram-side ejector device of  FIGS. 1 and 2 , but after a completed ejection operation, and 
       FIG. 4  shows the ram-side ejector device according to  FIGS. 1  to  3 , but in a condition wherein the ejector pin has returned again to its (rear) end position, retracted into the press carriage. 
   

     FIGS. 1  to  4  basically show a constructive arrangement of a ram-side ejector system, with the individual Figures, however, showing different positions during a press cycle. Identical components in the various Figures are identified by the same numerals. 
   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
   The ram-side ejector device  10 , the constructional details of which are represented in the Figures by way of example only, is part of a single- or multi-stage press comprising a press carriage  12 , which is guided in a reciprocating manner in a press frame (not shown). The latter serves to manufacture, optionally one by one, finished workpieces from blanks using carriage-side shaping tools (rams) and stationary dies. 
   Further, there is provided a valve block  14 , which is mounted on the press frame (not shown) and consists of a lower part  16  as well as of an upper part  18 , which are securely screw-fastened with each other and, together, form a machine frame. 
   A lower part  20  of a piston rod  22  as well as a piston  24  integrally connected with the piston rod  22  are slidably supported in the lower valve block part  16 . The piston  24  slides within a cylinder bore  26 , while the lower piston rod portion  20  is guided within a guiding bore  28  of the lower valve block part  16 . 
   In the lower valve block part  16 , the piston  24  is upwardly joined by a piston rod  20 ′ and terminates in a thickened end part  30 , which is also guided in a guiding bore  32  in the upper valve block part  18 . 
   Further, a plunger  34  embodied as a piston is slidably supported in a cylinder bore  36  in the upper valve block part  18  and contacts the thickened end  30  of the piston rod  22 . 
   The valve block parts  16  and  18  are provided with hydraulic feed and withdrawal lines  38  and  40 , respectively, which terminate in the cylinder bores  26  and  36 , respectively. A hydraulic valve  42  is also attached to the lower valve block part  16 . 
   The press carriage  12  is movable to-and-fro by a crank shaft  44  via push rods  46  and is provided with an externally accessible recess  48 , into which the tapered end of the lower valve block part  16  protrudes. 
   The end of the piston rod  20  protruding out from the lower valve block part  16  of the valve block  14  is forked, with a sprocket wheel  50  being rotatably supported on a bolt  52  between the forks of the lower valve block part  16 . 
   At the front end of the press carriage  12 , a press ram is seated as a pressing tool in a support  54 , namely, in the embodiment example shown, in the form of an hexagon-head ram  56  in whose axial extension a flange bushing  58  is mounted in the press carriage  12 . 
   A piston rod  60  is slidably supported in the flange bushing  58 . The thickened end of this piston rod  60  adjacent the die serves as a piston to which a coaxial ejector pin  64  is connected, which ejector pin  64  is slidably supported in the press carriage  12  and in the hexagon-head ram  56 . Thus, the piston  62  slides within a cylinder bore  66  of the press carriage  12 , which also terminally receives the flange of the flange bushing  58 . 
   The cylinder bore  66  and the piston  62  form a pneumatic aggregate as part of a device for resetting the ejector pin  64 . The piston rod  60  contacts a stop  68  with its end remote from the die, said stop  68  being mounted on the press carriage  12  and protruding into the recess  48 . 
   The front surface of the piston rod  60 , which also protrudes into the recess  48 , is provided with a chamfered part  70  toward the stop  68 , on its side facing the sprocket wheel  50 , said chamfered part  70  serving as a trip cam cooperating with the sprocket wheel  50 , as will be described in more detail below. 
   The press carriage  12  is further provided with two pressure air feed and withdrawal lines  72  and  74 , which terminate in the cylinder bore  66  and are part of the resetting means for the ejector pin  64 . 
   The action of the illustrated arrangement of a ram-side ejector device will now be described below: 
   In the description, reference shall be made to the condition according to  FIG. 1 , wherein the press carriage  12  is at its rear dead center (remote from the die) before the beginning of a pressing and shaping operation. The piston rod  22  (consisting of the piston rod part  20  with the sprocket wheel  50  attached thereto, the part  20 ′ and the thickened end part  30 ), the piston  24  and the plunger  34 , which are arranged approximately centrally and vertically above the piston rod  60  in this case, are hydraulically moved to their rear end position (retracted end position). The ejector pin  64  and the pneumatic aggregate (consisting of the piston rod  60  and the piston  62 ) are also moved, as an integral unit, to their rear position (remote from the die), and the end of the piston rod  60  remote from the die directly contacts the stop  68  of the press carriage  12 . 
   Therefore, in a forward movement (i.e. toward the left as seen in the Figure)of the press carriage  12  driven by the crankshaft  44 , the hexagon-head ram  56  located in the support  54  at the front end of the press carriage  12  urges a semi-finished workpiece  76  ( FIG. 1 ) supplied, for example, by a transfer means known, e.g., from DE 40 02 347 A1, of the progressively operating shaping machine or multi-stage press for transferring a partially worked workpiece from one station to the next station for a further processing operation, toward a die  80  fixed relative to the frame and further shapes said workpiece  76 , with a hexagon-head of a resulting screw  76 ′ ( FIGS. 3 and 4 ) being formed, corresponding to the press ram  56 . 
   At the front dead center of the press carriage  12  (as shown in FIG.  2 ), the ejector pin  64  with the piston  62  and the piston rod  60  still contact the stop  68  of the press carriage  12 . When the ram  56  strikes the workpiece  76 , part of the shaping force is guided into the press carriage  12  via the ejector pin  64 , the piston  62 , the piston rod  60  as well as the stop  68 . 
   During this manufacturing stage, the workpiece  76 ′ is given its final shape in the tools (namely the die  80  and the hexagon-head ram  56 ), i.e. it is provided, in this case, with the desired hexagon-head. Due to the pressing operation, the finished workpiece  76 ′ is stuck in the ram  56  with its tip-stretched hexagon-head. 
   Shortly before transgressing the front dead center, the program control of the shaping press now switches the hydraulic valve  42 . Then, hydraulic pressure is applied via the hydraulic line  40  to the plunger  34  provided as a piston, so that the plunger  34  acting as a piston and the piston rod/piston unit consisting of parts  30 ,  20 ′,  24  and  20  are moved to their front end position together with the sprocket wheel  50 . The sprocket wheel  50  now contacts the trip cam  70  of the piston rod  60 , as is evident from FIG.  2 . 
   Thus, the desired ram-side ejection of the finished workpiece  76 ′ is effected during the subsequent return movement of the press carriage  12  upon transgression of the front dead center. 
   During the return movement of the carriage, the ejector pin  64  remains in the (stationary) end position shown in  FIG. 2 , due to the piston rod  60  being blocked or locked by the sprocket wheel  50  and by the trip cam  70  of the piston rod  60 . From the beginning of the return movement of the press carriage  12 , the shaped workpiece  76 ′, both ends of which protrude into the recesses of the hexagon-head ram  56  and of the die  80 , is held in the stationary die  80  by the ejector pin  64  until the relative movement between the hexagon-head ram  56  and the ejector pin  64  causes the tip-stretched hexagon-head of the workpiece  76 ′ to be fully pushed out of the press ram  56  by the ejector pin  64  (the ejector pin  64  with the piston rod  60  remains stationary relative to the press body). 
   The stop  68  of the press carriage  12  is now at a distance from the end of the piston rod  60  remote from the die (cf. FIG.  3 ). 
   Finally, the hydraulic valve  42  is excited again, in a programmable manner, by the control of the shaping press, and, thus, hydraulic pressure is applied to the piston  24  via the hydraulic line  38  on the side of the piston rod so that the piston  24 , together with the piston rod parts  20  (including the sprocket wheel  50 ),  20 ′ and  30  as well as the plunger  34  return to their rear end position, which is at the same time the starting position for a new work cycle. 
   During this time, pressure air is supplied to the piston  62 , which is slidably guided in the cylinder bore  66  of the press carriage  12  and along its piston rod  60  in the flange bushing  58 , said pressure air being supplied, in a program-controlled manner, via the pressure air connection  72 , so that the piston  62  is charged on the piston side, and the piston rod  60 , together with the ejector pin  64 , is returned until the piston rod  60  contacts the stop  68  of the press carriage  12  again with its end remote from the die. The piston  62  and the piston rod  60  with the ejector pin follow the further movement of the press carriage  12  and thus also return to their starting position. Finally, the press carriage  12  has reached its rear holding position (rear dead center) again, as shown in FIG.  1 . 
   During this time, the just shaped workpiece  76 ′ is ejected from the die  80  by a die-side ejector (not shown). Further rotation of the crankshaft  44  now starts a new work cycle. 
   By the programmable selection of the switching time of the hydraulic feedstream from the hydraulic line  38  to the hydraulic line  40  in the valve block parts  16  and  18 , respectively, via the hydraulic valve  42  during the return movement of the press carriage  12 , the stand-still time of the ejector pin  64  with the piston  62  and the piston rod  60  (i.e. the time period during which a movement of the ejector pin  64  in the return direction of the press carriage  12  is blocked) and, thus, the ejector stroke can be determined or adjusted. Accordingly, in multi-stage presses, each ejector pin  64  can be adjusted individually via the program control of the press. 
   Now, if the piston  62  of the described resetting means for the ejector pin  64 , however, is charged with pressure air via the pressure air connection  74 , i.e. on the piston side, during a certain time period in the program sequence of the shaping press, the ejector pin  64  can even be displaced in its extension direction and used, e.g. to push a prefabricated workpiece into the die  80  and to hold it there, in order to then yield in a resilient manner during the actual pressing operation, upon which one switches back to the piston-side air supply again. 
   The hydraulic aggregate of the described ejector device  10  consists of the plunger  34 , the piston  24  as well as the piston rod parts  20 ,  20 ′ and  30 , and the sprocket wheel  50  rotatably supported on the end of the piston rod  20  as well as the inclination of the trip cam  70  represent a releasable lock for locking by force, which may simultaneously be used as an overload safety device, works free from wear and is adjustable. Said overload safety device responds in order to protect the shaping press if the force by which the workpiece  76 ′ has to be ejected from the press ram  56  by means of the ejector pin  64  exceeds an adjusted level (maximum admissible force level), for example, due to tool breakage. In this case, the sprocket wheel with the piston rod part  20 , the piston  24  as well as the piston rod parts  20 ′ and  30  and the plunger  34  lift themselves up from the trip cam  70  against the hydraulic force resulting from the charged area of the plunger  34  and from the pressure of the hydraulic fluid from the hydraulic line  40 , and release the force-fit blocking or locking because the holding force adjusted in a programmable manner has been exceeded. This is recognized by the program control of the shaping press, upon which the latter is immediately stopped. Once the cause for such overload in the system has been eliminated, the system is ready-for-use again.