Stainless steel investment casting is the process through which parts are manufactured by the metallic replication of wax models. Parts created by investment casting have very fine finishes that require little additional machining. There are no flash or parting lines because the part is made as one whole piece from molten stainless steel.
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High levels of accuracy and precision are attainable; stainless steel investment casting can produce parts that are too complex for other methods. Because it is made from a wax model, the part has the exact specifications of the intended design. The investment casting process may be considered more expensive but also has low equipment costs and requires less finishing. Stainless steel is one of the most commonly used materials for investment casting along with aluminum and copper though almost any castable metal may be used. Stainless steel castings can range from miniature sizes to hundreds of pounds; the average part weighs about 15 pounds. Stainless steel parts are used frequently around hazardous substances or sanitary environments because it is easy to clean and resists corrosion. These parts are widely used for such items as valves, fittings, engine components and other applications in the aerospace, automotive, construction, dental, medical, military, mining, food processing, sports and telecommunications industries.
Investment casting is also known as lost wax casting because the wax that is used as a pattern and model melts away. The wax pattern or model is carved by hand or machine or produced by injection molding which leaves a very smooth finish because of the polished metal die and the smooth melted wax. The wax, or master die, is then mounted on the sprue, a wax rod. Depending on the size of the sprue and the shape of the master die, up to several hundred wax patterns may be added resulting in an assembly called a tree. The tree is then dipped into a ceramic slurry. It is removed and dipped into another slurry with coarser granules. This continues until the tree is thoroughly covered with the ceramic material called the investment. Another option that is used for small and complex designs or for single parts is to mount the pattern in a flask and fill it with the investment, vibrating it to remove air pockets. Once completely dry, the hardened tree is placed in an oven or furnace in the burnout stage of the process. The wax melts or vaporizes completely, leaving a hollow shell. It is heated even after the wax is gone to ensure that no moisture or residue remains. The tree is removed from heat and liquid stainless steel is poured into it. After the stainless steel cools, the shell is removed by water-blasting, vibrations, a dissolving agent or alternate method.
