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Manufacturing:
Metal Casting
Introduction
Casting is a manufacturing
process where a solid is melted, heated
to proper temperature (sometimes treated
to modify its chemical composition), and
is then poured into a cavity or mold, which
contains it in the proper shape during solidification.
Thus, in a single step, simple or complex
shapes can be made from any metal that can
be melted. The resulting product can have
virtually any configuration the designer
desires.
In addition, the resistance
to working stresses can be optimized, directional
properties can be controlled, and a pleasing
appearance can be produced.
Cast parts range in size
from a fraction of an inch and a fraction
of an ounce (such as the individual teeth
on a zipper), to over 30 feet and many tons
(such as the huge propellers and stern frames
of ocean liners). Casting has marked advantages
in the production of complex shapes, parts
having hollow sections or internal cavities,
parts that contain irregular curved surfaces
(except those made from thin sheet metal),
very large parts and parts made from metals
that are difficult to machine. Because of
these obvious advantages, casting is one
of the most important of the manufacturing
processes.
Today, it is nearly impossible
to design anything that cannot be cast by
one or more of the available casting processes.
However, as in all manufacturing techniques,
the best results and economy are achieved
if the designer understands the various
options and tailors the design to use the
most appropriate process in the most efficient
manner. The various processes differ primarily
in the mold material (whether sand, metal,
or other material) and the pouring method
(gravity, vacuum, low pressure, or high
pressure). All of the processes share the
requirement that the materials solidify
in a manner that would maximize the properties,
while simultaneously preventing potential
defects, such as shrinkage voids, gas porosity,
and trapped inclusions.
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