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Die Casting Process
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What is Die Casting?
Is the process of making a casting by
forcing molten metal into a metallic mold, or die, under great pressure.
A method of casting in which molten metal is poured, sometimes under
pressure, into a mold or die. The die is made of metal and immediately after
solidification of the casting the die opens and the casting is ejected
Method of mass-producing, under great pressure, molten zinc and white-metal
alloys into permanent molds. Sharp clean detail can be achieved. Die-cast toys
were very inexpensive and generally found in the five-and-dime emporiums
The forming of parts by forcing molten metal into metal molds. Castings made
with this process can be made to very exacting tolerance. Zinc and aluminum are
most commonly used.
Advantages and Benefits
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.
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.
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Die
castings, pressure die castings, and vacuum die castings are processes by
which foundries can rapidly create thin wall complex shapes, with high
dimensional accuracy, and a very smooth attractive surface finish. The
advantage to the die casting process is the ability to make large quantities
of well defined castings quickly and cheaply that will require few secondary
operations to obtain a finished part.
The
disadvantage to the die casting process is that the initial die casting
tooling cost is normally very expensive and the die casting process is limited
to low temperature alloys, such as aluminum, brass, magnesium, and zinc.
Die
castings are made by pouring, injecting, or pulling by vacuum melted alloys
into the cavities of a hardened metal mold, called a die. Normally this is
done in an automated die casting machine. Most dies have several cavities,
making several parts with each casting cycle.
Die
casting begins by making a steel die, which will be capable of making tens of
thousands of castings. The dies are made in at least two sections. The die
casting cycle begins by clamping the die sections together. Liquid alloy is
then poured, injected, or pulled by vacuum into the die cavities. When it
solidifies, the die opens and the castings are ejected. Once removed from the
die, the die castings normally require a few secondary operations, usually
just flash trimming, buffing, perhaps holes tapped or machined to a final
tolerance and then anodized, painted, or plated.
Illustrations:
Once again the
best way to explain Casting Processes, is with visual illustrations...There are
variations to die casting, but having the concept detailed in these
Illustrations, you understand the basic idea to die casting process.
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Illustration 1 - a gif.
showing die casting machine animation, in operation
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Illustration 2 - diagram
of die casting machine in operation
Die
Casting compared to 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.
Illustration 3 -
removing flash, drilling holes, with trim die
Because of the excellent
dimensional accuracy and the smooth surfaces, most high pressure die castings
require no machining except the removal of flash around the edge and possible
drilling and tapping holes. High pressure die casting production is fast and
inexpensive relative to other casting processes.
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