The pattern is made from a wax or plastic that has a low melting temperature. Around the pattern a fluid slurry is poured that sets up to form a solid mold or investment. The mold is then heated, such that the pattern melts and is burned out, leaving behind a mold cavity having the desired shape. Example: jewelry and dental crowns and blades for gas turbines and jet engine impellers are investment cast.

• A. Die casting
• B. Lost foam
• C. Investment casting
• D. Sand casting

Answer: (C)

Investment casting, also known as the lost-wax process, fits this description. A pattern made from wax or plastic with a low melting temperature is encapsulated by a ceramic slurry to form a rigid shell around the pattern. The pattern is then heated so it burns out, leaving a hollow cavity in the exact shape of the pattern. Molten metal is poured into that cavity, the mold cools, and the ceramic shell is removed to reveal the final part. This method yields parts with very fine detail and smooth surfaces, making it ideal for complex shapes such as jewelry, dental crowns, turbine blades, and impellers. Other methods differ in how the mold is made and how the pattern is removed: die casting uses a metal mold and high-pressure metal filling, lost foam uses a foam pattern that vaporizes on pouring, and sand casting uses a sand mold with a removable pattern, typically giving rougher surfaces and tolerances.