This process is one of the oldest manufacturing processes., Intricate shapes can be made with high accuracy. In addition, metals that are hard to machine or fabricate are good candidates for this process. It can be used to make parts that cannot be produced by normal manufacturing techniques, such as turbine blades that have complex shapes,

 

Below is a graphical step-by-step representation of the investment casting process. The process is applicable to a wide range of materials including stainless steel, carbon steel, cast iron, bronze, brass and aluminum

 

PATTERN PRODUCTION - The process begins with production of a one-piece heat-disposable pattern. This pattern is made by injecting wax into a metal die. A pattern is required for each casting. These disposable patterns have the exact geometry of the required finished part, but they are made slightly larger, to compensate for volumetric shrinkage in the pattern production state and during solidification of metal in the ceramic mold.

 

PATTERN ASSEMBLY - Patterns are fastened on to one or more runners and the runners are attached to the pouring cup. Patterns, runners and pouring cups comprise the cluster or tree, which is needed to produce the ceramic mold. The number of runners per section and their arrangement on the pouring cup can vary considerably, depending on alloy type, size, and configuration of the casting.

 

CASTING - The ceramic shell molds must be fired to burn out the last traces of pattern material and to preheat the mold in preparation for casting usually in the range of 1500 degrees Fahrenheit. The hot molds may be poured with the assistance of vacuum, pressure and/or centrifugal force.

 

CASTING REMOVAL - Individual castings are then removed from the cluster by means of cut-off wheels and any remaining protrusions left by gates or runners are removed by belt-grinding.

 

CLEANING - After the poured molds have cooled, the mold material is removed from the casting cluster. This is done by mechanical vibration, abrasive blasting, and chemical cleaning.

 

FINISHING - The castings are then ready for secondary operations such as: heat-treating, straightening, machining, finishing, inspection, non-destructive testing, and then shipment to the customer.