Introduction to the Die-Casting Process
Die-casting, by definition, is a process in which molten
metal is injected into metallic molds under pressure to
form objects. The molds, which are generally made of steel
and referred to as "dies", can be designed to create very
detailed parts with little or no post-machining required
after production. Die-casting is similar in many ways to
plastic injection molding. Dies can be reused multiple
times because the temperatures of the molten metal are not
high enough to affect the steel die. Die-cast parts are
generally lightweight, and for this reason are often used
in aircraft and automobile applications.
History of the Die-Casting Process
Die-casting by pouring molten metal into a die, also known
as the gravity pressure method, is a manufacturing method
that has been used for hundreds of years. The more modern
method of pressure injection die-casting was patented in
the mid-1800's to create lead printer's type. The use of
die-casting as a manufacturing technique exploded in the
early 1900's, particularly when zinc and aluminum alloys
became more readily available. Today, die-casting is a
process used for a wide range of products and applications.
Materials Used in Die-Casting
In order to preserve the integrity of the die and allow it
to be used for many castings, only alloys with relatively
low melting temperatures can be used in the die casting
process. Historically, lead and tin were the primary
materials for die-cast parts, since they could easily be
melted using conventional processes. Today, the majority
of die-cast parts are created from aluminum or zinc alloys,
but other metals such as magnesium or copper can be used.
Each alloy delivers its own benefits, and therefore the
product requirements drive the material choice. Aluminum
can be found in aircraft and automobile parts, while copper
may be used for parts that must conduct electricity.
Description of the Die-Casting Process
Before casting is performed, the mold is assembled. A mold
can consist of two or more parts, depending on the
complexity of the part being fabricated. Die-casting
machines are categorized as either cold chamber machines or
hot chamber machines. In a cold chamber machine, the
molten metal is poured into a "cold" cylinder that is
attached to the die. A hydraulic piston seals the cylinder
and forces the metal into the die. In a hot chamber
machine, the injection system sits in a bath of molten
metal. A plunger is raised to pull molten metal into the
injection chamber, and then pushed to inject the molten
metal into the die. The mechanism of a hot chamber machine
is much like a pneumatic bicycle pump, which pulls air in
from around the pump and injects it into a tire through the
tube and fitting.
After the casting process, the part may have flash or thin
metal around the part where the two halves of the die come
together around it. The flash is removed during
post-machining processes. Some die-cast parts are plated
or painted after manufacture for appearance, but the
surface of die-cast parts are generally very smooth and
hold fine detail.
Examples of Die-Cast Components
Many plumbing fixtures, such as bathtub spouts are
manufactured from zinc alloys using a die-casting process
and then plated with a chrome coating. Lightweight
aircraft components can be die-cast from aluminum alloys.
Other examples include heat sinks with complex shapes and
large surface areas for electronic components, lightweight
aluminum automobile parts, and lighting fixtures. Die-cast
parts require very little post-manufacturing machining,
saving time and labor costs in the manufacturing process.
Die-casting is a manufacturing process used for a variety
of applications, including toys. In the Napoleonic era,
gravity pressure methods were used to cast lead military
figures. Die-cast vehicles have been available nearly as
long as the vehicles themselves have existed. Early die
cast manufacturers existing at the turn of the 20th century
include Meccano in the United Kingdom and Dowst Brothers in
the United States. Companies such as Ertl have been
producing die-cast farm vehicles since 1945.
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