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Investment casting: A 5000-year-old metal forming technique
1.
2. Investment casting history
Investment casting is an industrial process based
on and also called lost-wax casting, one of the
oldest known metal-forming techniques.
5000 years old.
Originally done with bees wax and clay.
Used by Egyptians, mesopotamians, Mayans to
make statues of idols, jewelery and ornaments.
Demand in 19th
century for dental application.
3. Steps in investment casting
1. Preparing the heat-disposable wax,
plastic or polystyrene patterns in a die.
2. Assembly of the prepared patterns into
a grating system.
3. Ceramic coat is applied and then the
refactory material named stucco is
applied
4. Melting the pattern assembly( burning
out wax) by firing, for removing the
traces of the pattern material.
4.
5. Steps in investment casting
5. The metal in molten state is poured
into the formed mold
6. Once the metal solidifies, the shell is
removed(knocked out).
7. cutting off the unwanted parts like
gates, sprue, pouring basin.
8. Finishing operations to get the
desired dimensional tolerance and
finish
6.
7. Processes
Investment:
The ceramic mold, known as the investment, is produced
by three repeating steps: coating, stuccoing, and hardening.
The first step involves dipping the cluster into a slurry of
fine refractory material and then letting any excess drain off,
so a uniform surface is produced.
In the second step, the cluster is stuccoed.
Finally, the coating is allowed to harden.
The investment is then allowed to completely dry, which
can take 16 to 48 hours
8. Processes
Dewaxing:
It is then turned upside-down and placed in
a furnace or autoclave to melt out and/or vaporize
the wax.
So as the wax is heated it expands and induces
great stresses.
In order to minimize these stresses the wax is
heated as rapidly as possible so that the surface of
the wax can melt into the surface of the investment
or run out of the mold, which makes room for the
rest of the wax to expand.
9.
10. Burnout & preheating:
The mold is then subjected to a burnout, which heats the mold
between 870 °C and 1095 °C to remove any moisture and
residual wax. Sometimes this heating is also as the preheat.
Pouring:
The investment mold is then placed cup-upwards into a tub
filled with sand. The metal may be gravity poured, but if there
are thin sections in the mold it may be filled by applying positive
air pressure, pressure assisted pouring.
Removal:
The shell is hammered, media blasted, vibrated, water jeted, or
chemically dissolved (sometimes with liquid nitrogento release
the casting. The sprue is cut off and recycled. The casting may
then be cleaned up to remove signs of the casting process,
usually by grinding.
11.
12. Products
Turbine blades for aerospace and
power industries.
Firearm parts such as triggers and
hammers
Artificial orthopedic surgical
implants and parts for artificial limbs
Industrial vakves, industrial pumps,,
automobiles, components, pipe
fittings and pipe elbows.
13. •Excellent surface finish.
•Tight dimensional tolerances.
•Complex and intricate shapes may be produced.
•Capability to cast thin walls.
•Low material waste.
•No parting lines
•A wide variety of material can be cast using this
method
Advantages
14. Disadvantage
• Limitations on size of casting
• Higher casting costs make it important to take full
advantage of the process to eliminate all
machining operations.
• Individual pattern is required for each
casting.
