Abstract:
The current invention replaces the toggle clamping mechanism of known die casting machines with a hydraulic clamping mechanism. Advantageously, the machine with hydraulic clamps requires less space than the machines utilizing toggle clamping mechanisms. The machine of this invention has a significantly smaller footprint, takes up less space and is about 30% shorter than machines with toggle clamps. The hydraulic clamping mechanism of the current invention not only decreases the size of the casting machine, but also produces uniform clamping force. The hydraulic clamp according to one presently preferred embodiment of this invention is a hydro-mechanical clamp.

Description:
[0001]    This claims the benefit of U.S. Provisional Patent Application Serial No. 60/330,655, filed Oct. 26, 2001 and hereby incorporated by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to casting products, and more particularly to a method and apparatus for effectively and efficiently casting from non-ferrous metals such as aluminum and magnesium.  
           [0003]    Die casting machines include two die carrying platens. One of the die carrying platens is stationary and is connected to the injection unit which injects the non-ferrous metal into the die cavity. The other of the die carrying platens is a movable platen which is moved into engagement with and clamped to the stationary platen to engage the two die halves and receive and form the metal during the casting process. The movable platen is moved out of engagement with the stationary platen so that the completed part may be removed from the dies.  
           [0004]    Casting of non-ferrous metals is currently performed utilizing a die casting machine with a toggle clamping structure as is known in the art. Toggle clamps are utilized to join mating dies and to resist the forces created by the high pressure injection of non-ferrous metals into the cavities in the mating dies.  
           [0005]    Toggle clamps for die casting of non-ferrous metals typically comprise four over center knuckles which apply clamping force to the four corners of the movable platen of the die casting machine. Typically, one clamp is located on each corner of the die casting machine. The mechanical nature of the clamps and the structure of an individual die can lead to unequal force application at the four corners of the movable platen to which one of the dies is attached. Die designers must balance part placement within the die to avoid exacerbating the problem of unequal force application. Furthermore, the toggle clamping structure currently utilized in die casting machines substantially increases the footprint of the casting machine.  
           [0006]    What is needed in the art is a method and an apparatus which allows non-ferrous metal casting to be accomplished in an efficient and consistent manner while utilizing machines of smaller size than known die casting machines and which produces uniform clamping force on the die carrying platens.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides an improved method and apparatus for use in non-ferrous casting or molding. The present invention provides a machine smaller in size than the previously utilized die casting machines for non-ferrous metal casting. Moreover, this invention provides a machine which produces equal clamping force on all four corners of the movable platen.  
           [0008]    In one embodiment, the current invention replaces the toggle clamping mechanism of known die casting machines with a hydraulic clamping mechanism. Advantageously, the machine with hydraulic clamps requires less space than the machines utilizing toggle clamping mechanisms. The machine of this invention has a significantly smaller footprint, takes up less space and is about 30% shorter than machines with toggle clamps. The hydraulic clamping mechanism of this embodiment of the current invention not only decreases the size of the casting machine, but also produces uniform clamping force. The hydraulic clamp according to one presently preferred embodiment of this invention is a hydro-mechanical clamp.  
           [0009]    The invention, in one form comprises a die casting machine having a hydro-mechanical clamping apparatus. In an exemplary embodiment of the current invention, the hydro-mechanical clamping apparatus comprises four retractable tie bars affixed to a movable platen. The retractable tie bars include distal tie bar lugs which are engaged by a rotary locking mechanism when the movable platen is moved into contact with the stationary platen. The rotary locking mechanism locks each tie bar to a hydraulically actuated piston. Pressure is applied to the hydraulically actuated piston to tension the retractable tie bars and clamp the movable platen to the stationary platen.  
           [0010]    An advantage of the present invention according to this embodiment is the uniform clamping pressures supplied by the hydro-mechanical clamping mechanism. Additionally, the machine has fewer moving parts offering less repair, maintenance, downtime and quicker, more efficient and economical rebuild of the machine.  
           [0011]    Another advantage of the present invention is the ability to provide increased tie bar, tool and die life due to superb low mold protection, uniform clamping pressure which eliminates die twisting and other problems that decrease die longevity as well as use of improved, stronger alloys. Moreover, the tie bars can be automatically balanced and the platens automatically squared.  
           [0012]    A further advantage of the present invention is the ease of mold changeover due to the increased die access area (increased on the order of 15-20%) produced by the retractable tie bar clamping mechanism of the present invention. This increased area also allows for larger tooling. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0014]    [0014]FIG. 1 is a side elevational view of a casting machine according to one embodiment of the current invention;  
         [0015]    [0015]FIG. 2 is a top plan view thereof;  
         [0016]    [0016]FIG. 3 is a partial sectional view of the metal injection unit;  
         [0017]    [0017]FIG. 4 is a partial sectional view of an alternative embodiment of a non-ferrous metal injection unit;  
         [0018]    [0018]FIG. 5 is a side elevational view partially in section of a die casting machine according to one embodiment of the current invention;  
         [0019]    [0019]FIG. 6 is an end elevational view of the movable platen; and  
         [0020]    [0020]FIG. 7 is a sectional view of the tie bar locking mechanism. 
     
    
       [0021]    Corresponding reference characters indicate corresponding parts throughout the several views. The description set out herein illustrates presently preferred embodiments of the invention, in one form, and such description is not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Referring now to the drawings and particularly to FIG. 1, a die casting machine  30  includes a base  22 , metal injection unit  26 , stationary platen  14  and movable platen  12 . Machine  30  is generally formed of clamp end  100  and shot end  102 . Shot end  102  is of the type generally utilized in die casting machines, while clamp end  100  is of a type commonly utilized in injection molding machines. Machine  30  is formed as a hybrid of, e.g., TIS-HPM die casting machine model M-900-A, and TIS-HPM NEXT WAVE 800 ton injection molding machine. Stationary platen  14  and movable platen  12  carry die halves  32 . Machine  30  includes accumulators  18  and intensifier  16  as is known in the art. Retractable tie bars  28  are affixed to movable platen  12  and are engageable in locking units  20 . Movable covers (not shown) may be added to the machine  30  to protect and cover each of the retractable tie bars  28  from debris, dust, dirt and the like and prevent them and their operation from being fouled during casting operations. Movable door  24  selectively limits access to the die area of machine  30 .  
         [0023]    [0023]FIG. 2 illustrates machine  30  including retractable tie bars  28  and movable platen shuttle cylinders  34 . Movable platen shuttle cylinders  34  are diagonally opposed and thus provide increased access to dies  32 . As illustrated in FIG. 6, stationary platen  14  includes four rotary locking bushings  38  while movable platen  12  includes four retractable tie bars  28  affixed at one end of movable platen  12 .  
         [0024]    Retractable tie bars  28  each are received into a rotary locking bushing  38  when movable platen  12  is moved into position to engage stationary platen  14  and operatively join dies  32 . Rotary locking bushing  38  is rotated and locks the respective retractable tie bar  28  in engagement with a matching lug  40 .  
         [0025]    Tie bar lugs  78  each include four lobes which pass through channels  90  of rotary locking bushings  38 . After entry of the four lobes on each tie bar lug  78  through channels  90 , rotary locking bushing  38  is rotated 45° so that the partial flanges located between channels  90  engage the lobes of tie bar lugs  78  and thereby retain retractable tie bars  28 . While the invention shown in FIG. 6 and described herein has four lobes, other arrangements and configurations are readily encompassed within this invention. For example, each tie bar may have a series of lugs at the distal end of the tie bar and another series spaced longitudinally on the tie bar from the distal end.  
         [0026]    Levers  86  are operably affixed to rotary locking bushings  38  as illustrated in FIG. 6. Levers  86  are hingedly connected to respective linkages  84  which are operably connected to locking cylinders  82  via pistons  88 . Locking cylinders  82  are operable to actuate pistons  88  which results in substantially vertical movement of linkages  84  and rotation of levers  86  and rotary locking bushings  38 . In this way, locking cylinders  82  may be utilized to rotate locking bushings  38  and thereby lock and unlock retractable tie bars  28 .  
         [0027]    Matching lug  40  is connected to hydraulic piston  44  and, when retractable tie bars  28  are locked, pressurized hydraulic fluid is supplied to face  92  of hydraulic clamp piston  44  from a hydraulic fluid source (not shown). The hydraulic fluid places matching lug  40 , rotary locking bushing  38  and retractable tie bar  28  in tension and clamps movable platen  12  to stationary platen  14 . Since the hydraulic clamping cylinders are located on stationery platen  14  they can be supplied with hydraulic fluid through rigid pipes, avoiding the need for flexible or moving hydraulic hoses. In one exemplary embodiment, each clamping cylinder has a transducer that monitors pressure. If a pressure drop is detected, the system tries to compensate to prevent uneven tie bar loading. If the system can not compensate, the machine will shut down and diagnose the problem. While the clamping mechanism of the current invention has been described as a hydro-mechanical clamping mechanism utilizing retractable tie bars, other hydraulic clamping mechanisms, such as those used in straight hydraulic injection molding machines, may be utilized in accordance with the present invention.  
         [0028]    As illustrated in FIG. 3, non-ferrous metal injection unit  26  is affixed to stationary platen  14  and provides the non-ferrous material to dies  32 . Shot sleeve  50  includes injection port  46  into which non-ferrous metal is inserted. Plunger  52  contacts the material inserted into shot sleeve  50  and is utilized to introduce the material into cavity  60  formed by dies  32 . Plunger  52  is affixed to piston rod  54  while piston rod  54  is affixed to piston  56 . In operation, piston  56  is actuated by pressurized hydraulic fluid in chamber  62  thereby causing movement of plunger  52  to inject material  58  into die  32 . According to various embodiments of this invention, the material  58  to be injected may be a solid metal, sem-solid metal, a metal slug, metal slurry, liquid metal or metal of another consistency or form. If desired, a vacuum can be utilized to remove air from die  32  and assist in filling the die with the material  58 .  
         [0029]    [0029]FIG. 4 illustrates a further embodiment of non-ferrous metal injection unit  26 . The non-ferrous metal injection unit  26  illustrated in FIG. 4 includes plunger  52  affixed to end  53  of piston rod  54  which is affixed to piston  56 . Piston  56  is further connected to stroke adjustment screw  48 . Stroke adjustment screw  48  may be advantageously utilized to adjust the stroke length of plunger  52  depending upon the current application. Stroke adjustment screw  48  is contained within stroke adjustment housing  64 . Check valve  72  includes spring  74  and spring retainer  76 . Guide plate  66  is affixed between packing shim  68  and packing retainer  70  and is useful for guiding piston rod  54 .  
         [0030]    After a forming operation has taken place, retractable tie bars  28  are unlocked and retract with movable platen  12 . As the mold opens, retractable tie bars  28  move back out of the way and allow for quick, easy and possibly automated mold changes as well as fast and easy removal of large parts. After the parts are removed, movable platen  12  is returned to operable molding position, with each tie bar lug  78  engaged by rotary locking bushing  38 , and hydraulic piston  44  supplying tension thereto.  
         [0031]    Other die-casting clamping mechanisms are contemplated within the scope of this invention. For example, clamping pins and a locking mechanism such as that disclosed in U.S. Pat. No. 5,776,516 (hereby incorporated by reference) could be utilized for die-casting operations according to this invention. Likewise, the clamping mechanisms disclosed in U.S. Pat. Nos. 4,708,625; 6,120,724; and 6,231,329 (each of which are hereby incorporated by reference) could be utilized for die-casting operations within this invention.  
         [0032]    While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. For example and without limitation, the present invention has been shown and described with respect to a horizontal injection process but it can be readily utilized in a vertical injection process of the type readily known to those skilled in this art. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fail within the limits of the appended claims.