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.
