Wax Lost Investment Cast|
Description:A metal mold makes wax replicas. These are joined and surrounded by an investment material. Wax is melted out and metal is poured into the cavity. The molds are broken and the casting removed.
Typical Size Range:Ounces to 20 lbs
Tolerances: ± .003" to 1/4"± .004" to 1/2"± .005" to 3", then add
± .003" per inch
Surface Finish:63-125 RMS
Min. Draft Required:
Min. Section Thickness: .060"
Typical Order Quantities:Under 1000
Typical Tooling Costs:$ Negotiable 300020000
Nominal Lead Times:Samples: 8 to 10 weeks Production: 5 to 12 weeks after approval
is also known as the lost wax process. This process is one of the oldest
manufacturing processes. The Egyptians used it in the time of the Pharaohs
to make gold jewelry (hence the name Investment) some 5,000 years ago. 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. |
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.
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.