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Die Casting
Process
Also visit Casting
Processes
Facts
America’s most fundamental
Industry, Metal Casting, continues to play a critical role in the success of U.S.
manufacturing through the production of the high quality, mass produced, economically
priced Castings.
In fact,
Castings are used in 90% of all finished manufactured products.
As an important segment of the larger metal casting industry,
the Die Casting Process, produces over one-third of all metal castings.
Today, over 500 die
casters manufacture thousands of non-ferrous castings: from automobile engine
and transmission parts; to intricate components for computers and medical
devices; or a desk stapler.
Die casters contribute over $7.3 billion to the nation’s
economy annually and provide over 63,000 jobs directly and indirectly.
The die
casting industry is a microcosm of American business. 58% of these companies
have fewer than 100 employees, while our larger firms are world leaders.
To meet
the challenges posed by today’s global marketplace, the North American Die
Casting Industry is leading the rest of the world with new technology, higher
productivity, innovative applications and superior quality.
How it
all Works
Die Casting is a century old process of injecting molten metal into a
steel die under high pressure.
The metal, either aluminum, zinc, magnesium
and sometimes copper, is held under pressure until it solidifies into a
net shape metal part.
In modern applications, using computerized controls,
die casters produce precision and high- strength products at a rapid
production rate.
No other metal casting processes allow for a greater
variety of shapes, intricacy of design or closer dimensional tolerance.
This is an example of Die Casting Machinery
Die
Casting is a versatile process for producing engineered
metal parts by forcing molten metal under high pressure into reusable steel
molds.
These molds, called dies, can be designed to produce complex shapes with
a high degree of accuracy and repeatability. Parts can be sharply defined, with
smooth or textured surfaces, and are suitable for a wide variety of attractive
and serviceable finishes.
Die
Castings are among the highest volume, mass-produced items
manufactured by the metalworking industry, and they can be found in thousands of
consumer, commercial and industrial products. Die cast parts are important
components of products ranging from automobiles to toys. Parts can be as simple
as a sink faucet or as complex as a connector housing.
The earliest examples of die casting by pressure injection - as
opposed to casting by gravity pressure - occurred in the mid-1800s. A patent was
awarded to Sturges in 1849 for the first manually operated machine for casting
printing type. The process was limited to printer’s type for the next 20
years, but development of other shapes began to increase toward the end of the
century. By 1892, commercial applications included parts for phonographs and
cash registers, and mass production of many types of parts began in the early
1900s.
The first die casting alloys were various compositions of tin
and lead, but their use declined with the introduction of zinc and aluminum
alloys in 1914. Magnesium and copper alloys quickly followed, and by the 1930s,
many of the modern alloys still in use today became available.
The Die
Casting Process has evolved from the original
low-pressure injection method to techniques including high-pressure casting —
at forces exceeding 4500 pounds per square inch — squeeze casting and
semi-solid die casting. These modern processes are capable of producing high
integrity, near net-shape castings with excellent surface finishes.
Refinements continue in both the alloys used in die casting and the
process itself, expanding die casting applications into almost every known
market. Once limited to simple lead type, today’s die casters can
produce castings in a variety of sizes, shapes and wall thicknesses that
are strong, durable and dimensionally precise.
The Advantages of Die Casting
Die
Casting is an efficient, economical process offering a
broader range of shapes and components than any other manufacturing technique.
Parts have long service life and may be designed to complement the visual appeal
of the surrounding part. Designers can gain a number of advantages and benefits
by specifying die cast parts.
Advantages
High-speed production - Die casting provides complex shapes
within closer tolerances than many other mass production processes. Little or no
machining is required and thousands of identical castings can be produced before
additional tooling is required.
Dimensional accuracy and stability - Die casting produces parts
that are durable and dimensionally stable, while maintaining close tolerances.
They are also heat resistant.
Strength and weight - Die cast parts are stronger than plastic
injection moldings having the same dimensions. Thin wall castings are stronger
and lighter than those possible with other casting methods. Plus, because die
castings do not consist of separate parts welded or fastened together, the
strength is that of the alloy rather than the joining process.
Multiple finishing techniques - Die cast parts can be produced
with smooth or textured surfaces, and they are easily plated or finished with a
minimum of surface preparation.
Simplified Assembly - Die castings provide integral fastening
elements, such as bosses and studs. Holes can be cored and made to tap drill
sizes, or external threads can be cast.
Review
of the Process
The basic
Die Casting Process consists of injecting molten metal
under high pressure into a steel mold called a die.
Die casting machines are
typically rated in clamping tons equal to the amount of pressure they can exert
on the die. Machine sizes range from 400 tons to 4000 tons. Regardless of their
size, the only fundamental difference in die casting machines is the method used
to inject molten metal into a die. The two methods are hot chamber or cold
chamber.
A complete die casting cycle can vary from less than one second for
small components weighing less than an ounce, to two-to-three minutes for a
casting of several pounds, making die casting the fastest technique available
for producing precise non-ferrous metal parts.
Die Casting vs. Other Processes
Die
Casting vs. plastic molding - Die casting produces stronger
parts with closer tolerances that have greater stability and durability. Die
cast parts have greater resistance to temperature extremes and superior
electrical properties.
Die
Casting vs. sand casting - Die casting produces parts with
thinner walls, closer dimensional limits and smoother surfaces. Production is
faster and labor costs per casting are lower. Finishing costs are also less.
Die
Casting vs. permanent mold - Die casting offers the same
advantages versus permanent molding as it does compared with sand casting.
Die
Casting vs. forging - Die casting produces more complex
shapes with closer tolerances, thinner walls and lower finishing costs. Cast
coring holes are not available with forging.
Die
Casting vs. stamping - Die casting produces complex shapes
with variations possible in section thickness. One casting may replace several
stampings, resulting in reduced assembly time.
Die
Casting vs. screw machine products - Die casting produces
shapes that are difficult or impossible from bar or tubular stock, while
maintaining tolerances without tooling adjustments. Die casting requires fewer
operations and reduces waste and scrap.
Choosing the Proper Alloy
Each of the metal alloys available for die casting offer
particular advantages for the completed part.
Zinc - The easiest alloy to cast, it offers high ductility, high
impact strength and is easily plated. Zinc is economical for small parts, has a
low melting point and promotes long die life.
Aluminum - This alloy is lightweight, while possessing high
dimensional stability for complex shapes and thin walls. Aluminum has good
corrosion resistance and mechanical properties, high thermal and electrical
conductivity, as well as strength at high temperatures.
Magnesium - The easiest alloy to machine, magnesium has an
excellent strength-to-weight ratio and is the lightest alloy commonly die cast.
Copper - This alloy possesses high hardness, high corrosion
resistance and the highest mechanical properties of alloys cast. It offers
excellent wear resistance and dimensional stability, with strength approaching
that of steel parts.
Lead and Tin - These alloys offer high density and are capable
of producing parts with extremely close dimensions. They are also used for
special forms of corrosion resistance.
Die Construction
Dies, or die casting tooling, are made of alloy tool steels in
at least two sections, the fixed die half, or cover half, and the ejector die
half, to permit removal of castings. Modern dies also may have moveable slides,
cores or other sections to produce holes, threads and other desired shapes in
the casting.
Sprue holes in the fixed die half allow molten metal to enter the
die and fill the cavity. The ejector half usually contains the runners
(passageways) and gates (inlets) that route molten metal to the cavity. Dies
also include locking pins to secure the two halves, ejector pins to help remove
the cast part, and openings for coolant and lubricant.
When the die casting machine closes, the two die halves are
locked and held together by the machine’s hydraulic pressure. The surface
where the ejector and fixed halves of the die meet and lock is referred to as
the "die parting line." The total projected surface area of the part
being cast, measured at the die parting line, and the pressure required of the
machine to inject metal into the die cavity governs the clamping force of the
machine.
Die Construction
Dies, or die casting tooling, are made of alloy tool steels in
at least two sections, the fixed die half, or cover half, and the ejector die
half, to permit removal of castings. Modern dies also may have moveable slides,
cores or other sections to produce holes, threads and other desired shapes in
the casting. Sprue holes in the fixed die half allow molten metal to enter the
die and fill the cavity. The ejector half usually contains the runners
(passageways) and gates (inlets) that route molten metal to the cavity. Dies
also include locking pins to secure the two halves, ejector pins to help remove
the cast part, and openings for coolant and lubricant.
When the die casting machine closes, the two die halves are
locked and held together by the machine’s hydraulic pressure. The surface
where the ejector and fixed halves of the die meet and lock is referred to as
the "die parting line." The total projected surface area of the part
being cast, measured at the die parting line, and the pressure required of the
machine to inject metal into the die cavity governs the clamping force of the
machine.
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