Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay.
Casting is most often used for making complex shapes that would be
otherwise difficult or uneconomical to make by other methods.
Metal
In metalworking, metal is heated until it becomes liquid and is then
poured into a mold. The mold is a hollow cavity that includes the
desired shape, but the mold also includes runners and risers
that enable the metal to fill the mold. The mold and the metal are then
cooled until the metal solidifies. The solidified part (the casting) is
then recovered from the mold. Subsequent operations remove excess
material caused by the casting process (such as the runners and risers).
Plaster, concrete, or plastic resin
Plaster and other chemical curing materials such as concrete and plastic resin may be cast using single-use waste
molds as noted above, multiple-use 'piece' molds, or molds made of
small rigid pieces or of flexible material such as latex rubber (which
is in turn supported by an exterior mold). When casting plaster or
concrete, the material surface is flat and lacks transparency. Often
topical treatments are applied to the surface. For example, painting and
etching can be used in a way that give the appearance of metal or
stone. Alternatively, the material is altered in its initial casting
process and may contain colored sand so as to give an appearance of
stone. By casting concrete, rather than plaster, it is possible to
create sculptures, fountains, or seating for outdoor use. A simulation
of high-quality marble may be made using certain chemically-set plastic
resins (for example epoxy or polyester)
with powdered stone added for coloration, often with multiple colors
worked in. The latter is a common means of making washstands, washstand
tops and shower stalls, with the skilled working of multiple colors
resulting in simulated staining patterns as is often found in natural marble or travertine.
Fettling
Raw castings often contain irregularities caused by seams and imperfections in the molds, as well as access ports for pouring material into the molds. The process of cutting, grinding, shaving or sanding away these unwanted bits is called "fettling". In modern times robotic processes have been developed to perform some of the more repetitive parts of the fettling process, but historically fettlers carried out this arduous work manually, and often in conditions dangerous to their health.
Fettling can add significantly to the cost of the resulting product,
and designers of molds seek to minimize it through the shape of the
mold, the material being cast, and sometimes by including decorative
elements.
Casting process simulation
Casting
process simulation uses numerical methods to calculate cast component
quality considering mold filling, solidification and cooling, and
provides a quantitative prediction of casting mechanical properties,
thermal stresses and distortion. Simulation accurately describes a cast
component’s quality up-front before production starts. The casting
rigging can be designed with respect to the required component
properties. This has benefits beyond a reduction in pre-production
sampling, as the precise layout of the complete casting system also
leads to energy, material, and tooling savings.
The software supports the user in component design, the determination
of melting practice and casting methoding through to pattern and mold
making, heat treatment, and finishing. This saves costs along the entire
casting manufacturing route.
Casting process simulation was initially developed at universities
starting from the early '70s, mainly in Europe and in the U.S., and is
regarded as the most important innovation in casting technology over the
last 50 years. Since the late '80s, commercial programs (such as AutoCAST and MAGMA)
are available which make it possible for foundries to gain new insight
into what is happening inside the mold or die during the casting
process.
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