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Metal Casting - A Process

Wednesday, December 2, 2009
Casting is a method of manufacturing which produces products by pouring a liquefied material into a mold where it is allowed to harden into a casting. Common casting materials include various metals, plastic, plaster, and concrete. Casting, a thousands year old process, remains today an economical way to produce shapes that would be expensive to machine in other ways.

Metal Casting

Below are sampling of various metal casting techniques.

* Investment casting, also referred to as lost wax casting, uses a mold to produce a wax pattern which is then used to produce an investment (a ceramic mold) that is later heated in order to dewax it before it is filled with the casting material. This is a very old method, dating back thousands of years when beeswax was used. Today modern waxes and materials are used to produce a higher quality product. Investment casting is often used to produce small products, but can be used to produce larger products.

* Centrifugal casting uses a mold on the end of an arm which spins at a high rate of speed driven by either a motor or a spring. Liquid casting material is contained in a crucible next to the mold and is forced into the mold by the centrifugal force created by the spinning arm. This minimizes material usage and produces finely detailed objects. This process is commonly used in jewelry making.

* In die casting liquid casting material is forced into the mold under high pressure. This produces parts and products with good detail and surface quality. It is typically used for nonferrous metals, but can be used for ferrous metals as well. Die casting is excellent for producing small parts in high volume, and as such is one of the most common industrial casting methods used.

* Sand casting uses sand mixed with either clay or an adhesive to form a mold around a master pattern which is then filled with liquid casting material and broken away from the casting once it has cooled and hardened.

* Heat treatment employs extreme hot and cold temperatures to harden and soften metal. Annealing heats metal to soften it. Hardening/quenching and tempering heats metal and then quickly cools it to harden it.

* Shell-mold casting is a variation of sand casting in which the pattern heated and covered with a thin layer sand that is allowed to partially cure before being placed in an oven to finish curing. The sand mold is then stripped from the pattern, glued together with one or two more molds from the same pattern, and placed in a flask surrounded with sand or gravel for reinforcement before being filled with liquid casting material. This has several advantages over sand casting: the mold can be used multiple times, resulting in a higher rate or production, the finished product is of a higher quality, and the entire process can be completely automated.

* Spin casting is similar to centrifugal casting, but differs in that it employs a rubber mold.

* Vacuum casting pulls liquid casting material into a porous mold through the use of a vacuum. This has the added effect of removing any trapped air. Vacuum casting is used as an alternative to centrifugal casting, and has similar effects.

Plastic, concrete, and plaster

* Resin casting is used to produce plaster, concrete, or plastic resin castings. All of these are distinct from metal casting in that the liquid is poured at room temperature and hardens either as it dries, or, in the case of plastics, when a hardening agent is added to the mixture. Flexible molds of latex and silicone can be used fairly inexpensively, though they wear out quicker than metal molds. The casting material is often gravity fed into the mold.

* Injection molding is used to produce plastic parts at a high rate of production with fully automated equipment. Plastic resin is forced into metal molds with a plunger where it is heated until it cures and ejected from the mold.

Ryan Fyfe is the owner of http://www.metal-welding.info/ - an information resource for all things related to Metal including articles, news, movies and more.


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