Castings and cast stock are metals, alloys, polymers and other materials that are cast into bar, rod, angle, channel, tee, or other shapes.
What is Casting?
Casting is a metallurgical process in which molten metal is poured into a mold with the desired cross-sectional or three-dimensional (3D) shape and then solidifies. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. In continuous or strand casting, molten material or metal is poured into a water-cooled mold and then pulled, cooled, rolled and straightened to form plates, rods, bars, billets, blooms, or slabs. Castings and cast stock in specialty shapes are also available.
Types of Casting
Metal casting techniques include sand casting, plaster casting, die casting, and permanent mold casting.
- Sand casting, also known as sand molded casting, is characterized by using sand as the mold material. It is relatively cheap and sufficiently refractory even for steel foundry use, however it is less accurate than other methods and tends to leave rough surfacing on the product which needs machining in most cases.
- Plaster casting uses a plaster, usually gypsum or calcium sulfate, to form the casting mold. It has the advantage in that the mold is easy and inexpensive to make and reproduce should it crack or become unusable. This method is used for low temperature melting materials such as aluminum, zinc, and copper to make lock components, fittings, gears, and valves.
- Die casting involves forcing molten metal into cavities under high pressure. First, the mold is lubricated and closed. Then liquid metal is shot into the die/mold under high pressure. The pressure must be sustained during the casting process. Finally, the die is opened and the shots are removed. This is an industrial process for producing a large number of small or medium sized pieces that must have a high quality of detail and consistent features.
- Permanent mold casting employs reusable molds usually made from metal. Gravity, gas pressure, and vacuums are employed to fill the molds. Common casting metals are aluminum, magnesium, and copper alloys, however tin, zinc, lead, iron, and steel alloys are also cast in graphite molds. Utilization of the metal mold allows for good surface finish and dimensional accuracy, but tooling costs are higher due to short mold life.
Advantages and Disadvantages of Casting Parts
Casting is a versatile process that allows for the most intricacy and detail in product form and shape. It can simplify construction by creating one cast piece rather than multiple parts. Extremely large and heavy metal objects may be cast, as well as metals that cannot be hot-worked from ingot form such as required for other processes.
Casting, however, tends to be much less economical for low-volume production. Also, cast products are superior for compressive loads but are very poor under tensile and shock loads and are very brittle because they have not been machine hardened.
Selecting a casting part can be based on a number of different factors, including design specifications, load requirements, or material types. The GlobalSpec SpecSearch Database allows the user to specify the desired product based on size dimensions such as overall thickness and overall width or outer diameter (OD), mechanical properties such as yield strength and tensile strength, or material types such as aluminum and copper.
Castings are used in many different applications including transport, heavy equipment, machine tools, plant machinery, defense, electrical machines, municipal castings, household, and art objects.