Castings - 5: Investment Casting
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Investment casting is generally used to make castings which are very intricate and/or difficult to machine. Two examples are gold jewelry items such as rings, and industrial parts, such as turbine blades made from difficult to machine high temperature nickel alloys.

Investment castings are made as follows:
1. A pattern of the exact part is molded out of wax or plastic (image 1).
2. The wax pattern is coated with a ceramic paste that is allowed to dry (image 2).
3. The ceramic is then fired in an oven, allowing the wax to flow out (hence the term "Lost Wax" method which is sometimes used) (image3 ).
4. Molten metal is poured into the ceramic mold and allowed to solidify (image 4).
5. The ceramic shell is broken away, leaving a part that requires only cleanup of the sprue (image 5).

Investment casting parts have a very smooth finish, little or no radii and draft, and no parting lines and flash. Investment cast parts require almost no cleanup machining and can be used almost “as cast”.

Image 1

A pattern of the exact part is molded out of wax or plastic

Image 2

The wax pattern is coated with a ceramic paste that is allowed to dry

Image 4

Molten metal is poured into the ceramic mold and allowed to solidify

Image 5

The ceramic shell is broken away, leaving a part that requires only cleanup of the sprue

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label: casting, castings, sand casting, die casting, investment casting, bosses, lugs