. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . METALCASTING 101
Patternmaking—Where Casting Starts Cast Metals Institute, Schaumburg, Illinois
Editor’s Note: This column is the fi rst in a regular series of articles that will explore the basics of metalcasting.
the mold is complete, the pattern is removed and liquid metal is poured into the cavity. In most casting pro- cesses, the mold is split open to allow the pattern to be removed and reused. In other processes, the mold does not open once it is made, and the pattern is destroyed in order to create the mold cavity. Wood, metal, wax, plastic, foam or combinations of materials are used in pattern construction. Open com- munication between casting design- ers and patternmakers is important to choosing an adequate and cost-
T
he metalcasting pattern is a physical representation of the object to be cast. A mold is constructed around this tangible, 3-D object. After
effective style and material. The mold material also
must be considered when designing the pattern. Wood is available in many different types, and it is machinable and easily shaped by hand. Metal pat- terns offer high wear resistance, rigidity and tight tolerances in ex- tended use. Plastic pattern boards have properties between metal and wood. Wax patterns, melted out of a ceramic shell to create the mold in the investment casting process, are typically small, detailed and produced in an injection press. Polystyrene can be used similarly to wax in the lost foam process, where the pattern is fi red out of a sand mold to create the casting cavity. The complexity of wax and foam patterns can be increased by gluing together several different pieces. METAL
Wax patterns (left) are melted from ceramic shells (right) to produce the molds used in the investment casting process.
Metal patterns, often produced with CNC machinery, offer high wear resistance and rigidity and tight tolerances.
JANUARY/FEBRUARY 2011 METAL CASTING DESIGN & PURCHASING 47
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