Gravity Die Casting
The mold has to be broken up after each casting operation
with sand casting and shell mold casting. In the process known
as die casting, the mold called a die, is made of metal and
is used a large number of times. It is more expensive to make
than an expendable once only mold.
intermediate technique is the use of semipermanent molds made
of fireclay or gypsum plaster, from which a limited number
of castings can be obtained. The most widely used die making
materials are steel, cast iron and heat resisting alloys of
iron. For particular purposes other materials are sometimes
employed for the dies, e.g., copper, aluminum or graphite.
A die can produce castings with a smooth and clean surface
and high dimensional accuracy, requiring little or no final
machining or other finishing treatment. The service life of
a die, in terms of the number of castings that can be produced
from it, depends on such factors as the thermal shock resistance
of the die material, the casting material, the temperature
at which it is poured, and the casting method employed
great many details have to be taken into consideration in
designing the pattern from which the die is made. Thus, in
designing the pouring-gate system and risers it must be borne
in mind that the walls of the mold exert a quenching action
upon the molten metal so that this solidifies much more rapidly
than in sand casting. In addition, the die must be provided
with fine channels at the joints and with air-vent holes and
thus enable the air displaced by the casting metal to escape
from the interior of the die. In a sand mold the air can escape
through the porous mold material.
die must be so constructed that it will not restrain the shrinkage
that occurs when the metal cools and solidifies and will allow
the casting to be easily removed. Shrinkage presents particular
difficulties in designing the cores which form the cavities
and recesses in the casting. Normally such cores are made
of steel or special alloys. Sometimes compressible sand or
shell cores are used, however.
To prevent the casting metal
from sticking to the die, the latter may be given an internal
coating of clay, chalk or bone ash with water glass as a binder,
this mixture being applied to the die by brushing, spraying,
the case of simple castings the metal may be poured into the
open die from the top (Fig.3). Usually the die is a closed
and rather complex assembly of two or more parts, however
(Fig.1), Sometimes comprising a number of cores. It must be
so designed that the molten metal will flow quickly, without
turbulence, into all parts of the die. For the casting of
metals with a low melting point it may be necessary to use
a heated die (to prevent premature solidification), and for
metals with a high melting point the die may have to be artificially
cooled after each casting operation.
tilting the die during casting, in order to reduce turbulence
and help the metal to flow smoothly, is an expedient that
is employed particularly for heavy castings (Fig.2). For the
production of awkwardly shaped or very thin walled castings
a vacuum may be applied to facilitate the filling of the die.
Slush casting is a technique used for making hollow ornamental
castings: the molten metal is poured into a die, and when
a solid shell of sufficient thickness has formed, the remaining
liquid is poured out.
Die Casting segment is a part of GF Automotive. It incorporates
three factories in two countries (Germany and Austria).
Our expertise in the materials and processes
involved has made a name for us as innovators in the international
vehicle industry. We provide you with a decisive edge in time
and costs, with profound know-how in all things concerning
designing and processing cast aluminum alloys.
This is why numerous light alloy components
manufactured in sand casting or gravity die casting processes
by GF Automotive are found in the vehicles made by leading
car manufacturers. For Eg. Die Castings UK specialists in
gravity die casting and high pressure die casting.
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