Casting

Casting is a mass production process which involves molten materials (such as metals, plastics or resins) being poured into a mold, allowed to solidify and then extracted for use. Casting can be thought of as a method for reproducing something – whether a mere part or a single unit by itself.

Casting is a process that can be used to manufacture complex parts which would prove too expensive or time-consuming to produce using other methods such as cutting or shaping these from solid materials.

Non-expendable Casting Techniques

This involves the use of more or less permanent or long-lasting molds which do not need to be broken in order to remove the cast material once it has set or cooled. Die casting is probably the most well-known non-expendable casting process known, in which molten metal or other material is forced, under high pressure, into the cavities of steel molds called dies.

The die casting method is straightforward. The die or mold is fabricated (containing the impressions of the piece to be cast). A lubricant is sprayed on the inside of the die both to cool it off as well as assist in making removal of the cast piece easy. Once the whole thing is set up, molten material is 'injected' into the die under high speed and high pressure, this helps a lot in making a casting as smooth and as precise as the original mold. Once the cavity is filled with the desired material, pressure is maintained until the material has cooled (which is helped along by using water to cool the mold). Once the material has cooled and hardened, the die is opened and the material ejected to pave the way for the next casting.

The major advantage of die casting is the ability to use the mold or die repeatedly and continuously – although even the die will deteriorate due to the high-pressure and high-speed injection of molten material (usually nonferrous metals like zinc or aluminum or plastics). At the same time, the mold can be used to replicate intricate and complex patterns ranging from small to large pieces which make it the process of choice for the manufacturing of certain items.

Expendable Mold Technique

As its name implies, expendable mold casting makes use of expendable molds for the casting process. This does not imply the use of inexpensive materials, however; the process refers more to molds that have to be broken to remove the materials cast rather than 'throwaway,' single-use molds.

Among the most common (and oldest) examples of the expendable mold technique is sand casting. Sand casting makes use of a "molding box" – actually a container filled with sand (usually 'green' sand) in which the patterns of the piece to be cast are set.

Expendable casting uses a variety of materials for the mold – plaster, concrete, resins, even wax (in the so-called 'lost-wax' or investment casting technique). Recently, polystyrene foam has been used in expendable casting for complicated and complex parts such as automobile engines and the like.