Abstract:
A die separator cylinder for use in separating first and second portions of a metal forming die set comprises a housing including a bore. A piston is adapted to reciprocate in the bore between an extended position and a depressed position. The die separator cylinder further includes gas flow paths leading to and from the bore that define asymmetrical gas flow rates relative to each other so that said when the bore is charged with an inert gas, the inert gas biases the piston to the extended position with a force that varies depending upon a time interval elapsed since the piston moved from the depressed position to the extended position. As such, the cylinder is configured so that during opening and closing of the press for metal-forming operations, the piston moves inward and outward with reduced force, while during periods of inactivity, the piston is biased outward with maximum force sufficient to separate the die halves of the die set to protect the die surfaces and to facilitate stacking of the die set for storage. The die separator cylinder can be configured as a stand-alone self-contained cylinder or can be configured as part of a hosed system or the like.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority from and benefit of the filing date of U.S. provisional application Ser. No. 60/750,032 filed Dec. 13, 2005, the disclosure of which is hereby incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     Gas springs charged with nitrogen or other inert gas are well-known and in widespread use in connection with metal-forming die sets. Examples of such nitrogen gas springs are disclosed in U.S. Pat. No. 6,022,004 entitled “Self-Lubricating Fluid Cylinder,” U.S. Pat. No. 6,749,185 entitled “Cushion Assembly and Method,” and U.S. Pat. No. 6,796,159 entitled “Low Contact Force Spring,” all of which patents are hereby incorporated by reference. These gas springs and others are available commercially from Hyson Products, Brecksville, Ohio, U.S.A.  
         [0003]     A need has been identified for a new type of gas spring to be used as a die separator cylinder. More particularly, a need has been found for a die separator cylinder, a group of which is adapted to be assembled into a forming die set which is used in a press, wherein the die separator cylinders provide maximum separation force to maintain the upper and lower die components in a spaced-apart relationship when the die set is put into storage, and wherein the die separator cylinder provide minimal separation force when the die set is put into use so as to have minimal effect on metal forming operations.  
       SUMMARY  
       [0004]     In accordance with one aspect of the present development, a die separator cylinder for use in separating first and second portions of a metal forming die set comprises a housing including a bore. A piston is adapted to reciprocate in the bore between an extended position and a depressed position. The die separator cylinder further includes gas flow paths leading to and from the bore that define asymmetrical gas flow rates relative to each other so that said when the bore is charged with an inert gas, the inert gas biases the piston to the extended position with a force that varies depending upon a time interval elapsed since the piston moved from the depressed position to the extended position.  
         [0005]     In accordance with another aspect of the present development, a method for operating a pressurized gas cylinder in a metal forming die set includes securing a body of a pressurized gas cylinder to a first portion of a metal forming die set. A piston of said pressurized gas cylinder is biased to an extended position in a bore of the body by pressurized gas contained in the bore so that a piston rod connected to the piston projects outwardly away from the cylinder body. A force is applied to the piston rod with a second portion of the metal forming die set to move the piston from the extended position in the bore to a depressed position in the bore, wherein gas is displaced from the bore to a gas containment space by a bore outflow path in a first time period when the piston moves from the extended position in the bore to the depressed position. The force is removed to allow the piston to move from the depressed position in the bore to the extended position in the bore in response to gas pressure remaining in the bore. Gas is flowed from the gas-containment space to the bore by way of a bore inflow path so that equilibrium pressure is reached between the bore and the gas-containment space in a second time period, wherein the bore inflow path is restricted as compared to the bore outflow path so that the second time period to reach equilibrium is longer than the first time period.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0006]      FIGS. 1A and 1B  schematically illustrate a die separator cylinder  10  formed in accordance with the present development;  
         [0007]      FIG. 2  is an isometric view of a die separator cylinder formed in accordance with the present development;  
         [0008]      FIGS. 2A and 2B  show first and second sectional views of an embodiment of the die separator cylinder  10  formed in accordance with the present development;  
         [0009]      FIG. 3  shows a delay plug and base subassembly of the die separator cylinder of  FIG. 1 ;  
         [0010]      FIG. 4  is another sectional view of the die separator cylinder of  FIG. 1 ;  
         [0011]      FIG. 5  is an enlarged partial sectional view of the die separator cylinder of  FIG. 1  that shows the bleed orifice, which is greatly enlarged in a detail view;  
         [0012]      FIG. 6  illustrates an alternative die separator cylinder formed in accordance with the present development; and,  
         [0013]      FIG. 7  is a graph that illustrates operational principles of a die separation cylinder formed in accordance with the present development. 
     
    
     DETAILED DESCRIPTION  
       [0014]      FIGS. 1A and 1B  schematically illustrate a die separator cylinder  10  formed in accordance with the present development. The cylinder  10  comprises a body  12  defining a gas-containment space  14  and a bore  16  in which a piston  17  is closely slidably fitted for reciprocal axial movement between an extended position (shown in  FIG. 1A ) and a retracted or depressed position (such as that shown  FIG. 1B  or another position where the piston  17  is moved inward from the extended position of  FIG. 1A ). A piston rod  18  is connected as a one-piece construction or otherwise to the piston  17  and moves with the piston, while an outer end  18   e  of the rod projects outwardly from the bore  16 . A seal  17   s  blocks escape of gas between the piston  17  and the wall defining the cylinder bore  16 . The piston  17  is biased outward to an extended position as shown in  FIG. 1A  under force of pressurized gas, typically nitrogen or another inert gas, contained in the space  14 , which is in communication with the bore  16  by a restricted bore inflow passage  30  (sometimes referred to herein as a bleed orifice  30 ). The gas is charged in the space  14  through a fill fitting  14   f  and fill passage  14   g.    
         [0015]     When the piston  17  is moved from the extended position shown in  FIG. 1A  inward to a depressed position such as that shown in  FIG. 1B  by application of an external force A to the outer end  18   e  of rod  18 , as when the die set is used to form a part, gas in the bore  16  is displaced from the bore  16  to the gas-containment space  14  primarily through a bore outflow path  34  comprising one or more check valves  32  located fluidically between the gas-containment space  14  and the bore  16  (a very small amount of gas is also displaced through the bleed orifice  30  which is very restricted as described below). The bore outflow path  34  communicates with the gas-containment space  14  via port  36 . The gas pressure in both the bore  16  and gas-containment spaces rises when the piston  17  is depressed.  
         [0016]     When the external force A applied to the piston rod  18  abates, as shown in  FIG. 1B , the piston  17  is biased outward to the fully extended position by the pressurized gas remaining in the bore  16  and also by gas that flows (very slowly as described below) from the gas-containing space  14  into the bore  16  through the bleed orifice  30 . The check valve  32  preferably completely blocks or at least substantially blocks return flow of gas from the gas-containment space  14  to the cylinder bore  16  by way of the bore outflow path  34  (some leakage around the check valve  32  is contemplated and deemed to be within the scope and intent of the present development). Those of ordinary skill in the art will recognize that, owing to the bleed orifice  30  being the only return flow path (or primary return flow path if any minimal leakage through the check valve(s) occurs) for the displaced biasing gas to return to the cylinder bore  16  from the gas-containment space  14 , an extended period of time (several minutes or more) will be required before equilibrium gas pressure between these two volumes  16 , 14  is achieved (although the piston rod  18  will be biased outward to its fully extended position as shown in  FIG. 1A  nonetheless by the reduced pressure gas that remains in the bore  16 ). As such, when the external force A ( FIG. 1A ) is reapplied to the piston rod  18  before equilibrium gas pressure is reached between the piston cylinder bore  16  and the gas-containment space  14 , the piston rod  18  will move inward with much less resistance force as compared to the previous stroke, and any gas that returned to the cylinder bore  16  through the bleed orifice  30  will again be displaced to the gas-containment space  14  through the check valve(s)  32  (and also very little through the orifice  30 ). This reduced-force condition will be maintained for as long as the cylinder is repeatedly stroke at an interval that is less than the time required for equilibrium between the gas volumes  14 , 16  to be reached.  
         [0017]     Those of ordinary skill in the art will recognize that a die separator cylinder formed in accordance with the present development comprises gas flow paths  30 , 34  leading to and from the bore  16  that define asymmetrical gas flow rates relative to each other so that the inert gas with which the bore is charged biases the piston  17  to its extended position with a force that varies depending upon the time elapsed since the piston moved from a depressed position to the extended position.  
         [0018]      FIG. 2  is an isometric view of a die separator cylinder  10  formed in accordance with the present development, and  FIGS. 2A and 2B  show first and second sectional views of the die separator cylinder  10 . As described above with reference to the schematic drawings of  FIGS. 1A and 1B , the cylinder  10  comprises a body  12  defining a gas-containment space  14  and a bore  16  in which a piston  17  is closely slidably fitted for reciprocal axial movement. A seal  17   s  blocks escape of gas between the piston  17  and the wall defining the cylinder bore  16 . The piston  17  is biased outward to an extended position as shown in  FIGS. 2A and 2B  under force of pressurized gas, typically nitrogen, contained in the space  14 , which is in communication with the bore  16  by the bleed orifice  30 . The gas is charged in the space  14  through a fill fitting  14   f . As shown, the cylinder body  12  comprises an outer housing  12   a  to which a base  12   b  is connected. A cylindrical wall member  12   c  that defines the bore  16  and that separates the bore  16  from the gas-containment space  14  is supported adjacent the base  12   b  and cooperates with the outer housing to define the gas-containment space  14 . The piston  17  is fitted in the bore  16  with a seal  17   s  (along with various wipers, spacers, etc. as shown and as known in the art) and a bonnet or end-cap  12   d  is connected to outer housing  12   a  and captures the various components in the outer housing  12   a . The wall  12   c  can be supported on the base  12   b  and/or connected to the end-cap  12   d , e.g., with a tight friction fit.  
         [0019]     A delay plug  12   e  is located in the bore  16  and connected to the base  12   b  by fasteners  12   f  ( FIGS. 2B &amp; 3 ) and is sealed to the wall member  12   c  by an o-ring seal  12   g  and thus blocks flow of gas between the gas-containment space  14  and the, bore  16  at this interface. An annular space  12   h  is defined between the plug  12   e  and the base  12   b  (note that the wall  12   c  is prevented from moving axially into the annular space  12   h  by its engagement with the end-cap  12   d  and/or otherwise, e.g., by abutment with the base  12   b , itself. The annular space  12   h  is in fluid communication with the gas-containment space  14  only at least one axially extending flow port  12   i . The fill fitting  14   f  is shown in  FIG. 2A  and communicates with the annular space  12   h through a fill passage  14   g  (the passage  14   g  is only partially visible in  FIG. 2A  due to the orientation of the sectional view).  
         [0020]     As described above, the die separator defines at least one or more bore outflow paths  34  each comprising a check valve  32 . As shown herein, the delay plug  12   e defines two separate bore outflow, paths  34   a , 34   b  including respective check valves  32   a , 32   b  that provides one-way fluid communication from the cylinder bore  16  to the annular space  12   h  and, thus, to the gas-containment space  14  via flow port  12   i . As described above, the check valves  32   a , 32   b  block flow in the reverse direction from gas-containment space  14  to cylinder bore  16  via paths  34   a , 34   b  (the term “block” as used herein contemplates full blockage or substantial blockage of gas flow through the paths  34   a , 34   b ).  
         [0021]      FIG. 3  shows the subassembly of the delay plug  12   e  fastened to the base  12   b . There, it can be seen that passages  34   a , 34   b  are provided to communicate gas from the cylinder bore  16  to the check valves  32   a , 32   b , respectively. Also, the annular space  12   h and axial flow passage  12   i  are shown. A port  36   a  for check valve  32   a  to communicate with the annular passage  12   h  is also visible (the port  36   b  for the check valve  32   b  to communicate with the annular passage  12   h  is identical but not visible—see  FIG. 4 ).  FIG. 4  shows the check valve  32   b  installed in the delay plug  12   e  using a rolled pin  38  (the check valve  32   a  is identically or similarly installed).  
         [0022]      FIG. 5  is a partial sectional view of the cylinder  10  that shows the bleed orifice  30  that provides a very restricted flow path between the annular space  12   h  and the cylinder  16 . As shown herein, the bleed orifice comprises a tiny bore  30   a  that extends through the delay plug  12   e , in particular, from an outer peripheral wall of the delay plug in communication with annular space  12   h  to a counterbore  30   b  for one of the fasteners  12   f  which communicates with the cylinder bore  16 . To further restrict the bleed orifice, if needed, a wire  30   c  or other occlusion is inserted/installed in the bore  30   a  and bent as shown so that the wire is trapped by the fastener  12   f , in which case the only gas flow through the bore  30   a  must occur in a small space between the bore  30   a  and the wire  30   c . Detail  5 D provides a greatly enlarged view.  
         [0023]      FIG. 6  illustrates an alternative cylinder  10  that accomplishes the same result as the cylinder  10 , in a slightly different fashion. The delay plug  12   e ′ comprises an annular groove  100  in which an o-ring seal  102  is tightly seated. One or more flow passages  104  intersect the annular groove  100  and also communicate with the cylinder bore  16  through a central distributor bore  106  (the fill passage  14   g  also communicates with the cylinder bore  16  through the distributor bore  106 ). In use, as the piston  17  is depressed toward the delay plug  12   e ′ and the gas in the cylinder bore  16  is compressed, the gas is urged into distributor bore  106  and the flow passages  104  of the delay plug  106 ′ and moves radially outward toward the annular space  12   h  that is defined between the delay plug  12   e ′ and the base  12   b . The o-ring  102  expands radially outward in the groove  100  under force of the gas flowing in the flow passage  104  so that the gas can flow past the o-ring  102  into the annular space  12   h  and from there into the gas-containment space  14  through the axial flow passage  12   i . When the piston rod  18  is allowed to return to the extended position, the o-ring  102  acts as a check valve to block return flow of the gas to the cylinder bore  16 . A bleed orifice  30  (not shown in  FIG. 6 ) as described above is included in the delay plug  12   e ′ for restricted return flow of the gas or, optionally, the bleed path is provided by small imperfections in the seal between the o-ring  102  and the groove  100  to provide a restricted return flow path for the displaced gas.  
         [0024]      FIG. 7  is a graph that further illustrates operation of a die separation cylinder formed in accordance with the present development, such as the cylinder  10  or  10 ′. A press opens and closes in a cyclic fashion as indicated by the line L 1 . The piston  17  and piston rod  18  of the die separation cylinder and of a conventional cylinder reciprocates between an extended position (about 4 inches extended in the present example) to a fully depressed/retracted position (about 0 inches extended in the present example) as indicated by the line L 2  (note that the press movement line L 1  and piston rod movement line L 2  coincide for a portion of the press closing/opening cycle as expected when the press and acting on the piston rod). The line L 3  illustrates the force exerted by the piston rod on the die set for a conventional nitrogen gas spring, wherein the force, in the present example, begins at about 12 thousand pounds when the piston rod is extended and moves up to 20 thousand pounds as the press closes and the piston is forced,inward, for all cycles of the press over time. In contrast, the line L 4  shows the force exerted by the piston rod  18  of die separator cylinder  10  formed in accordance with the present development in the die set. The line L 4  shows that for the first cycle of the press, the force begins at the same  12  thousand pounds and moves up to 20 thousand pounds as with the prior art. After that, however, the bleed orifice  30  prevents the cylinder bore  16  from recharging with the displaced gas between the press cycles again, so that the resistance force exerted by the piston rod  18  for the next and subsequent cycles of the press begins at about 1000 pounds and builds back to 20 thousand pounds only as the piston rod  18  is moved fully inward again by the press. The line L 4  also shows that the force quickly drops to about 1000 pounds again as the press starts to open. Finally, the line L 5  shows the gas pressure in the gas-containment space  14 . The line L 5  shows that after the initial stroke of the piston  17  and piston rod  18 , the displaced gas raises the pressure in the gas-containment space and the bleed orifice  30  allows only a small decrease in pressure as the press open and recycles. In one embodiment, the full inward stroke of the piston  17  from the fully extended position to the fully depressed position is less than 10 seconds (e.g., 1 second as shown), while the bleed orifice  30  allows for equilibrium to be reached between the volumes  16 , 14  only after a time period of more than 1 minute, preferably 2 to 10 minutes of inactivity of the cylinder  10 .  
         [0025]     As noted above, the nitrogen or other inert gas is charged into the space  14  through a fill fitting  14   f  and fill passage  14   g . The cylinder  10  is depressurized using the same path by venting the gas  14  from the gas-containment space  14  via path  14   g  and fitting  14   f . Those of ordinary skill in the art will recognize that charging the bore  16  via space  14  lengthens the charge fill time because the bore  16  must fill via bleed passage  30 . This structure is deemed to increase safety, however, because allowing gas discharge directly from the bore  16  via fitting  14   f  or another path could result in gas pressure being contained in the gas-containment space  14  without a technician being aware of same due to the restricted bleed passage  30 , i.e., a technician could push the piston rod  18  inward and think the cylinder  10  has been depressurized even if high-pressure gas is still contained in the gas-containment space  14 . In this case, the technician might attempt disassemble the cylinder while the gas-containment space  14  remains pressurized.  
         [0026]     The invention has been described with reference to a preferred embodiment. Modifications and alterations will occur to those of ordinary skill in the art upon reading this specification. It is intended that the claims be construed literally and/or according to the doctrine of equivalents as including all such modifications and alterations.