Rapid investment casting or molding method

Abstract

An investment casting or molding method comprises encasing a consumable pattern in a no-bake material that hardens without the application of heat. The encased pattern is then transformed to a fluid state and evacuated, thereby forming a mold cavity. Preferably, the pattern is coated with a refractory material prior to encasement, so that the resulting mold cavity is lined with the refractory material. Coating the pattern with one and only one layer of refractory material is preferred, resulting in a refractory coating that is not self-supporting. In another embodiment, a refractory-coated consumable pattern is located in a container, and a granular backing material is packed in the container around the coated pattern. The pattern is then transformed to a fluid state and evacuated to form a refractory-lined mold cavity in the container. The refractory coating again preferably comprises one and only one layer of refractory material, thereby resulting in a coating that is not self-supporting.

What is claimed is:  
     
         1 . A method for producing a casting, comprising the steps of: 
 (a) providing a pattern formed from a medium that is transformable to a fluid state by application of heat;    (b) applying a coating of refractory material to the pattern;    (c) encasing the refractory-coated pattern in a material that hardens without application of heat; and    (d) after the encasing material is hardened, transforming the pattern to a fluid state by applying heat thereto and evacuating the fluid pattern medium from the encasing material, thereby producing a refractory-lined mold cavity in the encasing material;    (e) supplying a fluid casting medium into the mold cavity; and    (f) permitting the fluid casting medium to achieve a solid state.    
     
     
         2 . The method of  claim 1  wherein said encasing material comprises a mixture of granular material and at least two substances that, when mixed together, cause the mixture to harden without application of heat.  
     
     
         3 . The method of claim I wherein said coating comprises one and only one layer of refractory material.  
     
     
         4 . The method of  claim 1  further comprising the step, prior to step (b), of applying a solvent to the pattern.  
     
     
         5 . The method of  claim 4  wherein said solvent comprises citric acid.  
     
     
         6 . The method of  claim 1  wherein the pattern is formed from wax.  
     
     
         7 . The method of  claim 6  wherein said wax pattern is formed by an automated wax pattern generator based on a computer model of the object.  
     
     
         8 . The method of  claim 1  wherein the pattern is formed by a stereolithographic process.  
     
     
         9 . The method of  claim 8  wherein said pattern is formed by an automated steroelithographic pattern generator based on a computer model of the object.  
     
     
         10 . The method of  claim 1  wherein said pattern is formed from a tin-bismuth alloy.  
     
     
         11 . The method of  claim 1  wherein said pattern is formed from frozen liquid.  
     
     
         12 . The method of  claim 1  wherein step (b) comprises immersing said pattern in aqueous slurry of refractory material.  
     
     
         13 . The method of  claim 1  wherein said casting comprises a jewelry item.  
     
     
         14 . The method of  claim 1  wherein said casting comprises a mold member for use in a casting or molding process.  
     
     
         15 . The method of  claim 1  wherein step (d) comprises applying non-curing heat.  
     
     
         16 . The method of claims  1  wherein said coating of refractory material is not self-supporting without said encasing material after the pattern medium is evacuated.  
     
     
         17 . A method for making a casting mold, comprising steps (a), (b), (c), and (d) of  claim 1 .  
     
     
         18 . A method for producing a casting, comprising the steps of: 
 (a) providing a pattern formed from a medium that is transformable to a fluid state by application of heat;    (b) applying a coating of refractory material to the pattern;    (c) locating the refractory-coated pattern in a container;    (d) packing a free granular backing material in said container around the refractory-coated pattern;    (e) transforming the pattern to a fluid state by applying heat thereto and evacuating the fluid pattern medium from the container, thereby producing a refractory-lined mold cavity in the container;    (f) supplying a fluid casting medium into the mold cavity; and    (g) permitting the fluid casting medium to achieve a solid state.    
     
     
         19 . The method of  claim 18  wherein said coating comprises one and only one layer of refractory material.  
     
     
         20 . A method for producing a casting, comprising the steps of: 
 (a) providing a pattern formed from a medium that is transformable to a fluid state by application of heat;    (b) encasing the pattern in a single layer of a material that hardens without application of heat to thereby form a one-piece, self-supporting shell around the pattern;    (c) after the encasing material is hardened, transforming the pattern to a fluid state by applying heat thereto and evacuating the fluid pattern medium from the encasing material, thereby producing a mold cavity in the encasing material;    (d) supplying a fluid casting medium into the mold cavity; and    (e) permitting the fluid casting medium to achieve a solid state.