The sand casting and investment casting are two main casting processes in modern foundries. Both of these two casting processes have their individual characteristics, advantages and disadvantages. The sand casting uses the green sand or dry sand to form the mold before pouring. Before the mold is made, the wood, plastic or metal patterns should be produced firstly to make the cavity of the sand mold. The green sand and dry sand could be resused after casting and shake-out.
During investment casting, a shape or replica is formed (usually out of wax) and placed inside a metal cylinder called a flask. Wet plaster is poured into the cylinder around the wax shape. After the plaster has hardened, the cylinder containing the wax pattern and plaster is placed in a kiln and is heated until the wax has fully vaporized. After the wax has fully burnt-out (de-waxing), the flask is removed from the oven, and molten metal (usually alloy steel, stainless steel, brass...etc) is poured into the cavity left by the wax. When the metal has cooled and solidified, plaster is chipped away, and the metal casting is revealed.
Casting is very useful for creating sculptural objects or engineering shapes with complex geometry in metal. Cast parts have a unique look to them, quite different from machined parts. Some shapes which would be difficult to machine are more easily cast. There is also less material waste for most shapes, since unlike machining, casting is not a subtractive process. However, the precision achievable through casting is not as good as machining.
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