Shutterless injection molding method and apparatus

Abstract

There is provided a method of injection molding a metal part and an injection molding apparatus which reduces or eliminates drooling of metal from a nozzle. The method includes the steps of (A) separating an injection nozzle of an injection chamber from contacting a mold surface, (B) retracting a plunger in the injection chamber to create a suction in the injection chamber, (C) closing an inlet to the injection chamber to seal the injection chamber, (D) maintaining melted metal in the injection chamber with a pressure difference and surface tension without substantial drooling from the injection nozzle, (E) placing the injection nozzle in contact with the mold surface and (F) advancing the plunger in the injection chamber to inject the metal into the mold.

What is claimed is:  
     
         1 . A method of injection molding a metal part comprising: 
 (A) separating an injection nozzle of an injection chamber from contacting a mold surface;    (B) retracting a plunger in the injection chamber to create a suction in the injection chamber;    (C) closing an inlet to the injection chamber to seal the injection chamber;    (D) maintaining melted metal in the injection chamber with a pressure difference and surface tension without substantial drooling from the injection nozzle;    (E) placing the injection nozzle in contact with the mold surface; and    (F) advancing the plunger in the injection chamber to inject a metal into the mold.    
     
     
         2 . The method of  claim 1 , wherein the metal is maintained substantially without drooling by a pressure difference between outside atmosphere and the injection chamber and surface tension in step (D) by a size of an opening of the injection nozzle being sufficiently small to substantially prevent the metal from drooling from the injection nozzle.  
     
     
         3 . The method of  claim 2 , wherein the plunger retraction in step (B) is started before or while the injection nozzle is separated from the mold in step (A).  
     
     
         4 . The method of  claim 3 , wherein the inlet to the injection chamber is closed in step (C) after the step of retracting the plunger in step (B).  
     
     
         5 . The method of  claim 4 , wherein the metal in step (D) comprises a liquid metal.  
     
     
         6 . The method of  claim 5 , wherein a portion of the liquid metal in a tip of the injection nozzle solidifies after injection; and the solidified metal remelts when the nozzle is separated from the mold.  
     
     
         7 . The method of  claim 6 , wherein an injection pressure in the injection chamber does not decrease during the step of advancing the plunger in step (F).  
     
     
         8 . The method of  claim 7 , wherein step (E) precedes step (F).  
     
     
         9 . The method of  claim 1 , further comprising repeating steps (A) through (F) a plurality of times.  
     
     
         10 . The method of  claim 2 , wherein the size of the opening of the injection nozzle is 15 mm or less.  
     
     
         11 . The method of  claim 1 , further comprising: 
 (G) providing liquid metal into a temperature controlled barrel; and    (H) providing the liquid metal from the barrel into the injection chamber through the inlet during step (B).    
     
     
         12 . The method of  claim 11 , further comprising: 
 (I) stirring the liquid metal in the barrel by rotating a ram in the barrel; and    (J) advancing the ram in the barrel to close the inlet to the injection chamber with a tip of the ram in step (C).    
     
     
         13 . The method of  claim 1 , wherein the suction in step (B) maintains the melted metal in the injection chamber without substantial drooling from the injection nozzle.  
     
     
         14 . The method of  claim 13 , wherein the suction in step (B) draws in the melted metal from a temperature controlled barrel through the inlet.  
     
     
         15 . The method of  claim 1 , further comprising maintaining a temperature of the injection nozzle of the injection chamber above a liquidus temperature of the melted metal such that no plug forms in the nozzle after step (A).  
     
     
         16 . The method of  claim 12 , wherein the plunger in the injection chamber retracts to create suction in step (B) before the ram advances in the barrel in step (J).  
     
     
         17 . The method of  claim 16 , wherein the barrel is located above the injection chamber to allow gravity to assist passage of the melted metal from the barrel into the injection chamber.  
     
     
         18 . The method of  claim 5 , wherein the metal comprises a magnesium alloy.  
     
     
         19 . A metal or metal alloy article made by the method of  claim 1 .  
     
     
         20 . The method of  claim 10 , wherein a diameter of the opening is 10 to 13 mm.  
     
     
         21 . A method of injecting melted metal into a mold comprising: 
 introducing the melted metal into a barrel;    allowing at least a first portion of the melted metal to pass through said barrel into an injection chamber; and    injecting the melted metal from the injection chamber into the mold, wherein during the step of injecting, a pressure in the injection chamber does not decrease.    
     
     
         22 . The method of  claim 21 , further comprising advancing a ram in the barrel to seal an outlet port between the barrel and the injection chamber with a portion of the ram.  
     
     
         23 . The method of  claim 22 , wherein the advanced ram prevents the melted metal and gases from flowing between the barrel and the injection chambers during the step of injecting.  
     
     
         24 . The method of  claim 21 , further comprising maintaining a temperature of an injection nozzle of the injection chamber above a liquidus temperature of the melted metal.  
     
     
         25 . The method of  claim 21 , wherein said allowing step comprises creating a suction in the injection chamber to draw the portion of the melted metal from the barrel into the injection chamber.  
     
     
         26 . The method of  claim 25 , wherein a plunger in the injection chamber retracts to create suction that draws the melted metal.  
     
     
         27 . The method of  claim 21 , wherein the barrel is located above the injection chamber to allow gravity to assist passage of the melted metal from the barrel into the injection chamber.  
     
     
         28 . The method of  claim 21 , wherein the melted metal is in a liquid state.  
     
     
         29 . The method of  claim 28 , wherein the metal comprises a magnesium alloy.  
     
     
         30 . A metal article made by the method of  claim 21 .  
     
     
         31 . The method of  claim 21 , further comprising the steps of: 
 (A) separating an injection nozzle of the injection chamber from contacting the mold surface;    (B) retracting a plunger in the injection chamber to create a suction in the injection chamber;    (C) closing an inlet to the injection chamber to seal the injection chamber;    (D) maintaining melted metal in the injection chamber with a pressure difference and surface tension without substantial drooling from the injection nozzle;    (E) placing the injection nozzle in contact with the mold surface;    (F) advancing the plunger in the injection chamber to inject the melted metal into the mold.    
     
     
         32 . The method of  claim 31 , wherein the metal is maintained substantially without drooling by a pressure difference between outside atmosphere and the injection chamber and surface tension in step (D) by a size of an opening of the injection nozzle being sufficiently small to substantially prevent the melted metal from drooling from the injection nozzle.  
     
     
         33 . The method of  claim 32 , wherein the plunger retraction in step (B) is started before or while the injection nozzle is separated from the mold in step (A).  
     
     
         34 . The method of  claim 33 , wherein the inlet to the injection chamber is closed in step (C) after the step of retracting the plunger in step (B).  
     
     
         35 . The method of  claim 34 , wherein the melted metal in step (D) comprises a liquid metal.  
     
     
         36 . The method of  claim 35 , wherein a portion of the liquid metal in a tip of the injection nozzle solidifies after injection; and the solidified metal remelts when the nozzle is separated from the mold.  
     
     
         37 . The method of  claim 36 , wherein an injection pressure in the injection chamber does not decrease during the step of advancing the plunger in step (F).  
     
     
         38 . The method of  claim 37 , wherein step (E) precedes step (F).  
     
     
         39 . The method of  claim 31 , further comprising repeating steps (A) through (F) a plurality of times.  
     
     
         40 . The method of  claim 32 , wherein the size of the opening of the injection nozzle is 15 mm or less.  
     
     
         41 . The method of  claim 31 , further comprising: 
 (G) providing liquid metal into a temperature controlled barrel; and    (H) providing the liquid metal from the barrel into the injection chamber through the inlet during step (B).    
     
     
         42 . The method of  claim 41 , further comprising: 
 (I) stirring the liquid metal in the barrel by rotating a ram in the barrel; and    (J) advancing the ram in the barrel to close the inlet to the injection chamber with a tip of the ram in step (C).    
     
     
         43 . The method of  claim 31 , wherein the suction in step (B) maintains the melted metal in the injection chamber without substantial drooling from the injection nozzle.  
     
     
         44 . The method of  claim 43 , wherein the suction in step (B) draws in the melted metal from a temperature controlled barrel through the inlet.  
     
     
         45 . An injection molding apparatus comprising: 
 an injection chamber;    a plunger in the injection chamber; and    an injection nozzle in fluid communication with the injection chamber having an opening sufficiently small to substantially prevent melted metal from drooling from the injection nozzle by a pressure difference between outside atmosphere and the injection chamber and surface tension.    
     
     
         46 . The apparatus of  claim 45 , wherein a diameter of the opening is 15 mm or less.  
     
     
         47 . The apparatus of  claim 45 , further comprising: 
 a temperature controlled barrel;    a ram in the barrel; and    an inlet between the barrel and the injection chamber.    
     
     
         48 . The apparatus of  claim 47 , wherein the ram has a shape that is capable of blocking the inlet port to prevent a flow of the melted metal between the barrel and the injection chamber.  
     
     
         49 . The apparatus of  claim 48 , wherein a tip of the ram is shaped such that it seals the inlet port when the ram is in a fully advanced state.  
     
     
         50 . The apparatus of  claim 49 , wherein: 
 the barrel is located above the injection chamber; and    the plunger retracts to create suction that assists in drawing into the injection chamber at least a portion of the melted metal from the barrel through the inlet port.    
     
     
         51 . The apparatus of  claim 50 , wherein the plunger is advanced at a rate at which pressure in the injection chamber does not decrease.  
     
     
         52 . An injection molding apparatus, comprising: 
 an injection chamber containing an injection nozzle;    a first means for separating the injection nozzle from contacting a mold surface and for placing the injection nozzle in contact with the mold surface;    a second means for injecting a melted metal from the injection chamber into the mold and for creating a suction in the injection chamber such that the melted metal is maintained in the injection chamber without substantially drooling from the injection nozzle between injection steps due to a pressure difference between an outside atmosphere and the injection chamber;    a third opening means in the injection nozzle for maintaining the melted metal in the injection chamber without substantially drooling from the injection nozzle between injection steps due to surface tension; and    a fourth means for closing an inlet to the injection chamber to seal the injection chamber.    
     
     
         53 . The apparatus of  claim 52 , wherein the third means comprises an opening in the injection nozzle that is sufficiently small to substantially prevent the melted metal from drooling from the injection nozzle due to surface tension.  
     
     
         54 . The apparatus of  claim 53 , wherein the second means retracts at a same time or before the injection nozzle is separated from the mold.  
     
     
         55 . The apparatus of  claim 54 , wherein the inlet to the injection chamber is closed when the second means retracts.  
     
     
         56 . The apparatus of  claim 55 , wherein the melted metal comprises a liquid metal.  
     
     
         57 . The apparatus of  claim 56 , wherein a portion of liquid metal in a tip of the injection nozzle solidifies after injection; and the solidified metal remelts when the nozzle is separated from the mold.  
     
     
         58 . The apparatus of  claim 57 , wherein an injection pressure in the injection chamber does not decrease when the second means injects the melted metal from the injection chamber into the mold.  
     
     
         59 . The apparatus of  claim 53 , wherein the size of the opening of the injection nozzle is 15 mm or less.  
     
     
         60 . The apparatus of  claim 52 , further comprising: 
 a fifth means for providing liquid metal into a temperature controlled barrel; and    a sixth means for providing the liquid metal from the barrel into the injection chamber.    
     
     
         61 . The apparatus of  claim 60 , wherein the suction draws in the melted metal from a temperature controlled barrel through the sixth means.