Metal Castings

Investment Castings

These processes typically involve thickly coating, or investing, a pattern which is made of a material that melts or burns out easily with a material such as ceramic, which doesn't. The pattern may be extended to provide a gate into which metal in a hot, liquid state is poured. Passageways are also provided to allow melted or burned pattern material and air to escape. The invested pattern is then fired in a furnace to burn out or melt the pattern and fuse the ceramic into a strong hollow mold. Molten metal is then poured into the ceramic mold. After the metal cools and hardens, the mold is broken away to reveal the final object. Extra gate material is cut off and usually the part will require substantial finish machining and clean-up.

Indirect or Secondary Processes that Utilize RP-generated Patterns

Stereolithography is also used to produce patterns for investment casting, but the photopolymer materials used in that process are more difficult to burn out than the materials used in others mentioned above, and also have a tendency to expand and crack the mold. To get around these problems, 3D Systems has produced a special build style for this application, with the trade name QuickCast^TM. The RP-generated pattern is built in hollow, thin sections which tend to crumple during burn out rather than expand and also results in a smaller mass of pattern material to remove. The process has been developed over a number of years in partnership with large foundry companies and customers.

Laminated object manufacturing (LOM) has also been used for investment casting, although a more typical application is for sand casting. See below. The paper material used in the LOM process is said to sometimes be difficult to remove completely from the mold, although this is probably a strong function of the particular geometry being produced.