The following procedures are typical of the investment casting process.
The process begins with production of a heat disposable pattern. This pattern is usually made by injecting molten wax or plastic into a metal die or mold.
The wax patterns are attached by the gate to a central wax runner system. The runner system is called a sprue. Patterns, runners, and pouring cup comprise the cluster or tree.
The shell building technique involves dipping the assembly into a ceramic slurry and then into a bed of extremely fine sand. After drying, the process is repeated. Up to 7 layers may be applied in this manner.
The completed shell is placed in a steam autoclave where the pattern melts and runs out through the gates and pouring cup.
Firing the Shell Mold – Preheat
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 1600-2000 degrees Fahrenheit.
The preheated shell is filled with molten metal by gravity pouring. As the metal cools, the parts, gates, sprue, and pouring cup become one solid investment casting.
Shell Removal – Knockout
After the metal solidifies and cools, the ceramic shell is then removed by vibratory methods or water blasting.
Casting Removal – Cut Off
Individual investment castings are removed from the cluster by friction sawing or by means of a cut off wheel.
Finishing Operation – Gate Grinding
Remaining gate protrusions on the investment castings are removed by belt grinding.
The finished investment casting parts are now ready for heat treating and shipping to customer.