by Terry Short
The history of investment casting or lost-wax casting dates thousands of years. Originally developed by ancient Chinese and Egyptian culture to create artwork until development of the jet turbine engine at the end of World War II.
Investment casting derives its name from the pattern being invested (surrounded) with a refractory material. Water glass and silica sol are the two primary refractory materials used. The main differences in the refractory material are the surface roughness and cost of the casting. The silica sol method costs more but has the better surface finish than the water glass method. Investment casting is valued for its ability to produce parts with accuracy and repeatability.
The process can be used for both small castings weighing a few ounces and large castings weighing several hundred pounds. It can be more expensive than die casting or sand casting, but per unit costs decrease with large volumes. Investment casting can produce complicated shapes that would be difficult or impossible with other casting methods. It can also produce parts with exceptional surface qualities and close tolerances with minimal surface finishing or machining required.
Below are the steps needed to produce an investment casting:
1. Produce a master pattern
2. Make a wax pattern
3. Apply investment material (refractory)
4. Remove the wax from the shell
5. Pour the molten material into the shell
6. Remove parts from the shell