Method and apparatus for semi-solid casting of metals

Abstract

An improved method and apparatus for use in semi-solid molding. A hydraulic clamping mechanism producing substantially equal clamping force on the four comers of a moveable platen is utilized to clamp a pair of die halves together to form a die cavity for use in semi-solid molding. In one exemplary embodiment, clamping force is created when a plurality of retractable tie bars affixed to a moving platen are locked to a stationary platen and hydraulic pressure is utilized to tension the tie bars.

What is claimed is:  
     
         1 . A method of forming a part from semi-solid metal, comprising: 
 clamping a pair of die halves together to form a die cavity by applying hydraulic force to at least one of the die halves at a plurality of locations spaced about the periphery of the die cavity; and    injecting a unit of thixotropic metal into said die cavity.    
     
     
         2 . The method of    claim 1   , wherein said step of clamping said pair of die halves together with hydraulic force comprises: 
 providing a moveable platen having a plurality of retractable tie bars affixed thereto, said moveable platen carrying a first one of said pair of die halves;    locking said retractable tie bars to a stationary platen carrying a second one of said pair of die halves; and    tensioning said tie bars with hydraulic pressure.    
     
     
         3 . The method of    claim 2   , wherein said step of locking said tie bars to said stationary platen comprises locking said retractable tie bars to a plurality of hydraulic cylinders positioned on said stationary platen.  
     
     
         4 . The method of    claim 2   , wherein said step of locking said retractable tie bars to said stationary platen comprises locking said retractable tie bars to a plurality of secondary tie bars connected to a plurality of hydraulic cylinders positioned on said stationary platen.  
     
     
         5 . The method of    claim 3   , wherein said step of tensioning said tie bars comprises applying hydraulic pressure to said hydraulic cylinders.  
     
     
         6 . The method of    claim 1   , wherein said step of injecting a unit of thixotropic metal into said die cavity comprises: 
 inserting said unit of thixotropic metal through an injection port into a shot sleeve connected to a stationary platen carrying one of said pair of die halves; and    forcing said unit of thixotropic metal through said shot sleeve and into said die cavity.    
     
     
         7 . The method of    claim 6   , wherein said step of forcing said thixotropic material through said shot sleeve and into said cavity comprises forcing said thixotropic material through said shot sleeve with a plunger.  
     
     
         8 . The method of    claim 7   , wherein said plunger includes a beryllium tip.  
     
     
         9 . An apparatus for forming thixotropic metal into parts, comprising: 
 a clamp end comprising: 
 a movable platen having a first die half affixed thereto;  
 a stationary platen having a second die half affixed thereto;  
 hydraulic means for locking said platens and said die halves to form a die cavity;  
   a shot end comprising: 
 a shot sleeve for receiving a unit of thixotropic metal; and  
 injection means for injecting said unit of thixotropic metal into said die cavity.  
   
     
     
         10 . The apparatus as recited in    claim 9   , wherein said hydraulic means for locking comprises: 
 a plurality of retractable tie bars affixed to said movable platen;    a locking means for locking said retractable tie bars to a plurality of hydraulic cylinders positioned on said stationary platen; and    a hydraulic fluid source adapted to apply hydraulic pressure to said hydraulic cylinders and thereby place said retractable tie bars in tension.    
     
     
         11 . The apparatus as recited in    claim 9   , wherein said hydraulic means for locking comprises: 
 a plurality of retractable tie bars affixed to said movable platen;    a locking means for locking said retractable tie bars to a plurality of secondary tie bars connected to a plurality of hydraulic cylinders positioned on said stationary platen; and    a hydraulic fluid source adapted to apply hydraulic pressure to said hydraulic cylinders and thereby place said retractable tie bars in tension.    
     
     
         12 . The apparatus as recited in    claim 10   , wherein said locking means comprises: 
 a plurality of rotary locking bushings connected to said hydraulic cylinders by a plurality of secondary tie bars, wherein each said retractable tie bar includes a tie bar lug, said tie bar lugs having a plurality of lobes, said rotary locking bushings having a plurality of channels sized to accommodate said lobes; and    a plurality of levers affixed to said rotary locking bushings, each said lever hingedly connected to a linkage, said linkage being operable to actuate said levers and rotate said locking bushings.    
     
     
         13 . The apparatus as recited in    claim 9   , wherein said injection means for injecting said thixotropic metal into said die cavity comprises a plunger.  
     
     
         14 . The apparatus as recited in    claim 13   , wherein said plunger includes a beryllium tip, said beryllium tip contacting said unit of thixotropic metal.  
     
     
         15 . The apparatus as recited in    claim 13   , wherein said injection means further comprises: 
 a piston rod affixed to said plunger; and    a piston connected to said piston rod, said piston being moveably mounted in a hydraulic chamber connected to a source of pressurized hydraulic fluid.    
     
     
         16 . The apparatus as recited in    claim 15   , wherein said piston is connected to a stroke adjustment screw.  
     
     
         17 . An apparatus for forming thixotropic metal into parts, comprising: 
 a moveable platen having a first die half affixed thereto;    a stationary platen having a second die half affixed thereto;    a plurality of retractable tie bars affixed to said moveable platen;    a plurality of rotary locking bushings connected to a plurality of hydraulic cylinders mounted on said stationary platen, said rotary locking bushings operable to lock said retractable tie bars thereto;    a hydraulic fluid source adapted to apply hydraulic pressure to said hydraulic cylinders and thereby place said retractable tie bars in tension to lock said platens and said die halves to form a die cavity; and    a shot sleeve adapted for receiving a unit of thixotropic metal for injection into said die cavity.    
     
     
         18 . The apparatus as recited in    claim 17   , wherein said plurality of rotary locking bushings are connected to said plurality of hydraulic cylinders by a plurality of secondary tie bars.  
     
     
         19 . The apparatus as recited in    claim 17   , further comprising: 
 a plunger for injecting said unit of thixotropic metal in said die cavity, said plunger moveably mounted in said shot sleeve.    
     
     
         20 . The apparatus as recited in    claim 19   , further comprising: 
 a piston rod affixed to said plunger; and    a piston connected to said piston rod, said piston being moveably mounted in a hydraulic chamber connected to a source of pressurized hydraulic fluid.    
     
     
         21 . The apparatus as recited in    claim 17   , wherein each of said plurality of retractable tie bars includes a tie bar lug, said tie bar lugs having a plurality of lobes, said rotary locking bushings having a plurality of channels, said channels sized to accommodate said lobes, and wherein said apparatus further comprises: 
 a plurality of levers affixed to said rotary locking bushings, each said lever hingedly connected to a linkage, said linkage being operable to actuate said levers and rotate said locking bushings.