Die casting machine with reduced static injection pressure

Abstract

A die casting method initially injects an alloy with minimal volumetric contraction during solidification into a die cavity, monitors at least one of the pressure of the shot cylinder and the position of the plunger, and reduces the injection pressure during the final stage of filling of the die mold. A die casting machine includes a shot cylinder having one of a pressure detector located for detecting the hydraulic pressure applied to the cylinder or a position sensor for a plunger rod. The plunger rod includes a tip extending into a cold chamber, which receives a metal alloy having a minimal shrinkage characteristic. A source of hydraulic pressure is coupled to the shot cylinder by a control valve and a control circuit is coupled to said valve and to one of said detector or sensor for reducing the injection pressure near the end of an injection cycle.

1 . An injection system for a die casting machine comprising:
 a shot cylinder having a plunger rod and a hydraulic fluid inlet for receiving pressurized hydraulic fluid for moving said plunger rod;   one of a pressure detector located for detecting the hydraulic pressure applied to said shot cylinder and a plunger rod position sensor for determining the position of said plunger rod;   a cold chamber with an inlet for receiving a molten alloy having a low shrinkage characteristic, said plunger rod extending into said cold chamber for injecting a molten alloy into a die cavity;   a source of hydraulic pressure for coupling to said shot cylinder;   a control valve coupling said hydraulic pressure source to said inlet of said shot cylinder; and   a control circuit having an output coupled to said valve and an input coupled to at least one of said detector and sensor and responsive to input signals for providing a control signal to said valve for reducing the injection pressure applied by said plunger rod near the end of an injection cycle.   
   
   
       2 . The injection system as defined in  claim 1  wherein said shot cylinder includes a hydraulic fluid outlet and a second valve coupled to said outlet, wherein said second valve is coupled to said control circuit and responsive to signals therefrom for reducing the injection pressure applied by said plunger rod near the end of an injection cycle. 
   
   
       3 . The injection system as defined in  claim 1  wherein said shot cylinder includes a hydraulic fluid outlet and a bypass conduit coupled between said inlet of said shot cylinder and said outlet and a bypass valve coupled in the bypass conduit, said bypass valve coupled to said control circuit and responsive to signals therefrom for reducing the injection pressure applied by said plunger rod near the end of an injection cycle. 
   
   
       4 . The injection system as defined in  claim 3  and including a second valve coupled to said outlet, wherein said second valve is coupled to said control circuit and responsive to signals therefrom for reducing the injection pressure applied by said plunger rod near the end of an injection cycle. 
   
   
       5 . The injection system as defined in  claim 1  wherein said molten alloy is a metal glass alloy. 
   
   
       6 . A method of die casting parts comprising the steps of:
 injecting a molten alloy having the characteristics of minimal volumetric contraction during solidification into a die cavity during a filling stage;   monitoring at least one of the pressure of a shot cylinder for injecting the molten alloy into the die cavity or the position of a plunger rod for injecting the molten metal into the die cavity; and   reducing the injection pressure applied by the shot cylinder and plunger rod during a final stage of filling of the die mold for reducing the die separating force near the end of a molding cycle.   
   
   
       7 . The method as defined in  claim 6  wherein said reducing step comprises limiting the injection pressure at the head end of the shot cylinder near the end of said molding cycle. 
   
   
       8 . The method as defined in  claim 7  wherein said limiting step includes providing a valve between a high pressure source of hydraulic fluid and the head end of the shot cylinder and controlling the valve to limit the pressure of fluid applied to the shot cylinder and the resulting injection pressure of molten alloy. 
   
   
       9 . The method as defined in  claim 7  wherein the shot cylinder has an outlet at a side of a piston opposite the head end and said limiting step further comprises providing a valve coupled to the outlet and controlling the valve to limit the pressure applied by the shot cylinder to the die cavity. 
   
   
       10 . The method as defined in  claim 7  wherein the shot cylinder has an outlet at a side of a piston opposite the head end and said limiting step further comprises providing a bypass conduit between the head end of the shot cylinder and the outlet and a valve coupled in the bypass conduit and controlling the valve to control the pressure applied by the shot cylinder in injecting molten metal into the die cavity during a molding cycle. 
   
   
       11 . The method as defined in  claim 6  wherein said molten alloy is a metal glass alloy. 
   
   
       12 . A die casting machine comprising:
 a pair of dies defining at least one die cavity for a part to be molded;   a clamping system for clamping said dies together during the injection of a molten alloy into said die cavity;   a shot cylinder having a plunger rod and a hydraulic fluid inlet for receiving pressurized hydraulic fluid for moving said plunger rod;   a cold chamber with an inlet for receiving a molten alloy having a low shrinkage characteristic and an outlet coupled to said die cavity, said plunger rod extending into said cold chamber for injecting a molten alloy into said die cavity;   a source of hydraulic pressure for coupling to said inlet of said shot cylinder; and   a control system in communication with said source of hydraulic pressure for reducing the injection pressure applied by said plunger rod near the end of an injection cycle.   
   
   
       13 . The die casting machine as defined in  claim 12  and further including one of a pressure detector located for detecting the hydraulic pressure applied to said shot cylinder and a plunger rod position sensor for determining the position of said plunger rod. 
   
   
       14 . The die casting machine as defined in  claim 13  and further including a control valve coupling said hydraulic pressure source to said inlet of said shot cylinder. 
   
   
       15 . The die casting machine as defined in  claim 14  wherein said control system includes a control circuit having an output coupled to said valve and an input coupled to at least one of said detector and sensor and responsive to input signals for providing a control signal to said valve for reducing the injection pressure applied by said plunger rod near the end of an injection cycle. 
   
   
       16 . The die casting machine as defined in  claim 15  wherein said shot cylinder includes a hydraulic fluid outlet and a second valve coupled to said outlet, wherein said second valve is coupled to said control circuit and responsive to signals therefrom for reducing the injection pressure applied by said plunger rod near the end of an injection cycle. 
   
   
       17 . The die casting machine as defined in  claim 15  wherein said shot cylinder includes a hydraulic fluid outlet and a bypass conduit coupled between said inlet of said shot cylinder and said outlet and a bypass valve coupled in the bypass conduit, said bypass valve coupled to said control circuit and responsive to signals therefrom for reducing the injection pressure applied by said plunger rod near the end of an injection cycle. 
   
   
       18 . The die casting machine as defined in  claim 17  and including a second valve coupled to said outlet, wherein said second valve is coupled to said control circuit and responsive to signals therefrom for reducing the injection pressure applied by said plunger rod near the end of an injection cycle. 
   
   
       19 . The die casting machine as defined in  claim 18  wherein said molten alloy is a metal glass alloy.