Investment Castings
Ferrous and Non Ferrous Materials
Investment Casting, often called lost wax casting, is regarded as a precision casting
process to fabricate near-net shaped metal parts poured from almost any alloy including:
stainless steel, carbon, steel, aluminum, brass, bronze and copper.
Ferrous investment castings are castings that cast stainless steel, including 300/400
series alloys and any precipitation hardened steel alloys, as well as non-ferrous
investment castings (copper based alloys, zinc based alloys, aluminum, bronze &
iron).
Casting by the investment process allows for parts to meet x-ray and non destructive
testing specifications for: military, aerospace, semi conductor industry, valves,
pumps and many other industrial applications.
The investment casting process consistently provides high integrity (sound) and
dimensionally accurate castings. Cast part dimensions vary less than +/- .001 from
part to part.
Investment casting uses a mold that has been produced by surrounding an expendable
pattern with a refractory slurry that sets at room temperature. The pattern (usually
of wax or plastic) is then melted or burned out, leaving the mold cavity. Investment
casting is also known as the "lost wax process" and as "precision casting".
Process Benefits of Investment Castings (Lost wax)
- The process is capable of making parts from prototypes to high volume. Investment
Casting tooling is capable of making over 1 million parts per tool.
- Cast tolerance to +/- .005 or better, per inch.
- Cast surface finish of 125 RMS or better.
- Excellent cast details with regards to cast letter i.e. logo, names, part number,
etc.
- Reduced machining due to castings designed to near net shape. Investment castings
can have undercuts, blind holes, thru holes .250 or greater and, almost any geometric
shape or size.
All of the above advantages reduce your casting costs.
Castings can be quoted complete to print specifications by utilizing our in-house
machining capabilities.
Please submit your design via email in STL, STEP, IGS, DXF, or PDF format to: dick@castingrep.com for
an engineering discussion on your casting requirements.
Machining
Aluminum, brass & bronze, along with other non-ferrous and ferrous alloys, machine
easily with today’s CNC & digital N.C. machining centers. Starting with a near
net shape casting, machining times are reduced which, in turn, save $$
Casting Sizes
Although some foundries can cast parts the size of a bathtub, most casting facilities
pour parts in the 12" x 12" x 6" range with weights up to 50 pounds.
Tolerances
Generally, +/- .005 per inch Premium tolerances of +/- .003 per inch.
Wall Thickness
Investment casting can have a minimum wall thickness as thin as .030. Normal casting
wall thicknesses of .080 to .125 are preferred for casting reliability.
Draft
There is NO DRAFT required in the lost wax investment casting process.
The Lost Wax Investment Casting Process
- WAX INJECTION
The process begins with production of a heat disposable pattern. This pattern is
usually made by injecting molten wax or plastic into a metal die or mold.
- PATTERN ASSEMBLY
The wax patterns are attached by the gate to a central wax runner system. The runner
system is called a sprue. Patterns, runners, and pouring cup compromise the cluster
or tree.
- SHELL BUILDING
The shell building technique involves dipping the assembly into a ceramic slurry
and then into a bed of extremely fine sand. After drying, the process is repeated.
Up to 7 layers may be applied in this manner.
- DEWAX OPERATION
The completed shell is placed in a steam autoclave where the wax pattern melts and
runs out through the gates and pouring cup.
- FIRING THE SHELL MOLD: Preheat
Molds are placed into a kiln at 2000°, this cures and hardens the mold.
- CASTING
Molds are removed from the kiln while the mold is still hot to reduce thermo shock,
metal is then poured directly into sprue cup.
- SHELL REMOVAL: Knockout
Once molds have cooled for approximately one hour the ceramic shell is knocked off
from the metal castings and runner system.
- CASTING REMOVAL: Cut Off
Castings are cut from the sprue tree.
Investment Castings Tooling Description
Investment casting tooling is machined from 6061 aluminum blocks. The
tool consists of two CNC machined mold halves. Investment casting tooling
can be complex, since it has the ability to have metal core pulls and
undercuts in the wax pattern.
Pattern wax is injected into the
aluminum mold at 140° Fahrenheit, then the wax patterns are affixed to a wax
tree and dipped into a slurry while wet fine grains of sand are poured over the
patterns. The wax is then melted off. This is repeated after the molds
dry for four to six hours, then the molds are sand coated three to four more
times.
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