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what is investment casting

Investment casting is an advanced metal forming process used to produce metal parts of the
highest quality, functionality and cost-effectiveness. Investment casting is a one-to-one
process in which one disposable pattern produces one metal part. When combined with
modern production knowledge and technologies, investment casting can be applied to
produce parts of varying degrees of complexity, in virtually any volume and for the broadest
possible spectrum of applications.
A highly versatile casting process, investment casting has for some time been perceived as a
comparatively expensive process. But when compared to alternative processes which require
extensive welding or machining, an investment cast component can often dramatically
reduce overall part production costs.
Investment casting, which is also known as the "lost wax investment casting” process, traces
its roots to the Sang Dynasty in China from 1766 B.C. to 1122 B.C. The method was brought
into modern industrial use when American manufacturers applied investment casting to
make high quality military parts during World War II. It was found practical for many wartime
needs - and during the postwar period it expanded into many non-aircraft applications.
Today, investment casting is recognized and used worldwide as a technique for producing
close-tolerance metal parts at highly competitive costs.
When performed by experienced and knowledgeable casting specialists, investment casting:
· Allows greater design freedom for very simple to highly complex parts
· Provides superior repeatability
· Can utilize a wide variety of alloys
· Yields lighter, stronger metal parts with superior finishes
· Reduces labor, tooling and machining costs
· Allows very rapid prototype development
Of course, investment casting is not the appropriate process for every metal part
requirement. However, for many challenging part applications, investment casting offers a
proven and cost-effective metal forming solution.
Manual:
Intricate shapes can be made with high accuracy. In addition, metals that are hard to
machine or fabricate are good candidates for this process. It can be used to make parts that
cannot be produced by normal manufacturing techniques, such as turbine blades that have
complex shapes, or airplane parts that have to withstand high temperatures.
The mold is made by making a pattern using wax or some other material that can be melted
away. This wax pattern is dipped in refractory slurry, which coats the wax pattern and forms
a skin. This is dried and the process of dipping in the slurry and drying is repeated until a
robust thickness is achieved. After this, the entire pattern is placed in an oven and the wax is
melted away. This leads to a mold that can be filled with the molten metal. Because the mold
is formed around a one-piece pattern, (which does not have to be pulled out from the mold as
in a traditional sand casting process), very intricate parts and undercuts can be made. The
wax pattern itself is made by duplicating using a stereo lithography or similar model-which
has been fabricated using a computer solid model master.
The materials used for the slurry are a mixture of plaster of Paris, a binder and powdered
silica, a refractory, for low temperature melts. For higher temperature melts, sillimanite an
alumina-silicate is used as a refractory, and silica is used as a binder. Depending on the
fineness of the finish desired additional coatings of sillimanite and ethyl silicate may be
applied. The mold thus produced can be used directly for light castings, or be reinforced by
placing it in a larger container and reinforcing it more slurry.
Just before the pour, the mold is pre-heated to about 1000 ºC (1832 ºF) to remove any
residues of wax, harden the binder. The pour in the pre-heated mold also ensures that the
mold will fill completely. Pouring can be done using gravity, pressure or vacuum conditions.
Attention must be paid to mold permeability when using pressure, to allow the air to escape
as the pour is done.
Tolerances of 0.5 % of length are routinely possible, and as low as 0.15 % is possible for small
dimensions. Castings can weigh from a few grams to 35 kg (0.1 oz to 80 lb), although the
normal size ranges from 200 g to about 8 kg (7 oz to 15 lb). Normal minimum wall
thicknesses are about 1 mm to about 0.5 mm (0.040-0.020 in) for alloys that can be cast
easily.
The types of materials that can be cast are Aluminum alloys, Bronzes, tool steels, stainless
steels, Stellite, Hastelloys, and precious metals. Parts made with investment castings often
do not require any further machining, because of the close tolerances that can be achieved.
When it comes to investment casting, precision is key. We have 11 specialist engineers on our
R&D team, each with up to 30 years of experience, who develop our products and production
equipment. This ensures that the precision of our investment casting is at the CT3 level and
meets the grade-A standard used by US military. Motorola and Volvo appreciate the R&D we
put into their custom casting solutions.
We offer a variety of materials, including stainless steel, carbon steel, alloy steel, copper, and
aluminum. Following ISO 9001:2000-certified guidelines, our seven QC staff carry out
rigorous inspections, including exams using x-ray machines, German Spectromax
spectrographic detector, and imported three-coordinates measuring machine to make sure
we meet your requirements. They inspect all raw materials and finished products.
As an enterprise invested by Ministry of National Aviation and the Ministry of National
commerce, our company holds state-of-the-art investment molding and precision casting
techniques and their patents. We excel in manufacturing precision casting components with
sophisticated structure and mould cavity. Our company adopts rapid prototype technology in
manufacturing the components of small lot or of extreme complexity. The sample piece can
be made in very short time. Thus shorten the design, advanced research and sample
production cycle.
The products of our company are mainly used in such fields as aviation, watercraft,
communication, electronics, instrument and meter, medical components and physical
training equipment etc.


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