Patent Publication Number: US-9884365-B2

Title: Shot tube for die-cast machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 61/775,725, filed Mar. 11, 2013. 
    
    
     BACKGROUND 
     This application relates to a shot tube for injecting molten metal into a die-cast mold. 
     Die casting is a metal casting technique that employs the use of permanent, reusable molds in which molten alloys are injected and compressed into the cavities to form the desired component. The die cast system is comprised of multiple components: the molds, the shot tube, the shot rod and piston, the frame of the machine, a hydraulic system, pneumatic system, and a programmable logic controller to control the interconnected systems. 
     Die-cast molds are known and utilized to form any number of components. A die-cast machine is comprised of a fixed platen and a moving platen. In a split die set one half of the mold mounts the stationary platen and the second half to the moveable platen. The moving platen is actuated by hydraulic piston, and mechanical clamping system to position the moveable die half in the appropriate position during each phase of the die casting process. A singular or array of cavities are formed between the two die halves in the shape of a component which is to be cast. 
     The desired alloy is liquefied by a variety of methods and is transferred to or directly poured through the opening in a shot tube. The molten alloy is added to the desired fill level for the component, the hydraulic injection system is activated, and the piston pushes the molten metal along the shot tube delivering the molten material into the cavity. As the molten metal begins to solidify, an intensification cycle can be used to further compress the semisolid alloy into the die cavity to minimize casting defects such as shrinkage and non-fill of the cavities. Upon solidification the component is formed into the shape of the cavity. 
     Historically, the shot tubes have been mounted to the fixed platen in traditional machines that operate in air. While this is suitable for low temperature alloy system, the stack up of tolerances that causes misalignment and gaps is extremely problematic for quick solidifying high temperature alloys. The desire to improve the quality of existing alloys and the opportunity to cast higher temperature capable alloys such as: steels, iron-nickel super alloys, nickel super alloys, and cobalt super alloys creates the need to operate the die casting system in a vacuum to ensure metallurgical quality and elimination of defects such as dross and ceramic inclusions from these alloy systems. 
     Conventional mounting of the shot tube poses significant challenges as a result of need to operate the system in a vacuum. Mounting the tube in the traditional manner would require extensive sealing between the tube and the platen to prevent the flow of an oxidizing atmosphere into the tube. In order to minimize vacuum leaks and maintenance of the tube an alternative method of mounting and aligning the tube is required to ensure optimal operation and serviceability of the equipment. 
     In one particular die-cast system, an electron beam device is utilized to melt an ingot of metal within a vacuum chamber. The molten metal drips into a water cooled copper crucible as the ingot is superheated by the electron beam. When a sufficient amount of material has filled the crucible, the electron beam sweeps across the surface until the system has achieved the desired temperature, the dross is swept to the rear of the crucible, the system is tilted and the molten metal is poured through the opening in the shot tube. In this embodiment, the fixed platen does not easily mount the shot tube. 
     SUMMARY 
     In a featured embodiment, a shot tube has an inner bore delivering molten material into a die-cast mold. The shot tube has an outer peripheral surface with at least one surface for receiving a locking member to lock the shot tube into a fixed mold portion and an alignment structure for properly aligning the shot tube in the fixed mold portion. An opening receives molten material into the inner bore. 
     In another embodiment according to the previous embodiment, the surface includes a pair of surfaces formed at an outer periphery of the shot tube. 
     In another embodiment according to any of the previous embodiments, the pair of surfaces are flats. 
     In another embodiment according to any of the previous embodiments, the shot tube outer periphery is cylindrical, other than at the flats. 
     In another embodiment according to any of the previous embodiments, the alignment structure includes a notch at a forward end of the shot tube. 
     In another embodiment according to any of the previous embodiments, the inner bore extends through an entire axial length of the shot tube. 
     In another embodiment according to any of the previous embodiments, the shot tube includes an inner portion formed of a powdered metal and an outer portion formed of stainless steel. 
     In another featured embodiment, a die-cast fixed mold portion has a mold body defining a mold cavity at least in part. An aperture in the mold body receives a shot tube. There is an alignment structure properly positioning the shot tube within the aperture. The shot tube has an inner bore for delivering molten material into the mold body. The shot tube has an outer peripheral surface with at least one surface receiving a locking member to lock the shot tube. An opening receives molten material into the inner bore. 
     In another embodiment according to the previous embodiment, the surface includes a pair of surfaces formed at an outer periphery of the shot tube. 
     In another embodiment according to any of the previous embodiments, the pair of surfaces are flats. 
     In another embodiment according to any of the previous embodiments, the shot tube outer periphery is cylindrical, other than at the flats. 
     In another embodiment according to any of the previous embodiments, the alignment structure includes a notch at a forward end of the shot tube and a tooth from the mold body. 
     In another embodiment according to any of the previous embodiments, the inner bore extends through an entire axial length of the shot tube. 
     In another embodiment according to any of the previous embodiments, the shot tube includes an inner portion formed of a powdered metal and an outer portion formed of stainless steel. 
     In another featured embodiment, a die-cast machine has a mold with a fixed mold portion and moveable mold portion, a piston and cylinder for moving the moveable mold portion along with a moveable platen, and a fixed platen for mounting the fixed mold portion. A vacuum chamber receives an ingot of metal to be melted. An electron beam apparatus melts the ingot, a copper crucible for receiving molten metal, and the copper crucible delivering molten metal into a shot tube through an opening in the shot tube. The first mold portion includes a mold body defining a mold cavity at least in part. An aperture in the fixed mold portion receives a shot tube. Alignment structure properly positions the shot tube within the mold body. The shot tube has an inner bore delivering molten material into the molds. The shot tube has an outer peripheral surface with at least one surface receiving a locking member to lock the shot tube into the aperture. An opening receives molten material into the inner bore. 
     In another embodiment according to the previous embodiment, the surface includes a pair of surfaces formed at an outer periphery of the shot tube. 
     In another embodiment according to any of the previous embodiments, the shot tube outer periphery is cylindrical, other than at the pair of surfaces formed at the outer periphery of the shot tube. 
     In another embodiment according to any of the previous embodiments, the alignment structure includes a notch at a forward end of the shot tube and a tooth from the mold body. 
     In another embodiment according to any of the previous embodiments, the inner bore extends through an entire axial length of the shot tube. 
     In another embodiment according to any of the previous embodiments, the shot tube includes an inner portion formed of a powdered metal and an outer portion formed of stainless steel. 
     These and other features may be best understood from the following drawings and specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a die-cast machine. 
         FIG. 2  shows a detail of a shot tube. 
         FIG. 3  is a cross-sectional view through a shot tube according to this application. 
     
    
    
     DETAILED DESCRIPTION 
     A die-cast machine  10  is illustrated in  FIG. 1 . As shown, a fixed mold half  23  is associated with a moveable mold half  21  to form an overall mold  20 . While the two halves are disclosed to form the mold  20 , additional mold inserts can be used to form the details of the cavity. 
     A cavity  22  is formed between the bodies of fixed and moveable halves  23  and  21 . A fixed platen  28  mounts the fixed mold half  23 , and moveable platen  24  moves with a piston and cylinder combination  26  such that the moveable die half  21  can be moved away from the fixed mold half  23  for removal of a component after the component has solidified in the cavity  22 . 
     A vacuum chamber  34  includes an ingot  38  of a metal to be used for forming the component. An electron beam device  36  melts the ingot  38 , which then falls into a copper crucible  40 . From the copper crucible  40 , molten metal passes through an opening  42  in an outer periphery of a shot tube  30 . As shown, the shot tube  30  has a forward end  32  extending into the fixed mold half  23 . 
     The molten material is shown at  44  within a bore  99  of the shot tube  30 . A piston  48  is driven by a plunger  46  to urge the molten material into the cavity  22 . 
     The inner bore  99  can be seen to extend through an entire axial length of the shot tube  20 . 
     During use, the shot tubes  30  wear and must be replaced. In the prior art, the shot tube has been mounted in the fixed platen  23 . 
     According to this disclosure, however, the shot tube  30  is mounted with its forward end  32  extending through the fixed platen  28  and into an aperture  101  in the fixed mold half  23 . As shown, flats  108  are formed at an outer periphery of the shot tube  30 , and plungers  104  are selectively biased into the flats  108  to secure the shot tube  30  within the fixed mold half  23 . 
     In the illustrated embodiment, a source of hydraulic fluid  100  delivers fluid to passages  102 , and into a chamber  106  to urge the plungers  104  into the flats  108 . The hydraulic fluid can be released from chambers  106  to allow removal of the shot tube  30 . 
     While flats  108  are shown, other shaped surfaces may be utilized to receive a locking member, such as plungers  104 . 
     As also shown, an alignment structure  110  includes a tooth that fits into a notch  112  to properly position the shot tube  30  circumferentially relative to the fixed mold half  23 . 
       FIG. 3  shows the shot tube  30  having the flats  108  at opposed circumferential sides and the notch  112  at a forward end. The structure of the shot tube  30  has an inner powdered metal portion  120  and an outer stainless steel portion  122 . 
     As can be appreciated, an outer periphery of the shot tube  32  is cylindrical, other than at the flats  108 . 
     With this arrangement, the shot tube  30  may be easily replaced. To replace the shot tube  30 , one merely removes the biased force of the hydraulic fluid, such that the plungers  104  move outwardly of the flats  108 . The shot tube  30  may then be removed and a new shot tube inserted. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.