INVESTMENT CASTING

ABELARDE, GIENEL ALBACITE, EDRIAN BALBOA, ADRIAN

BALDOMERO, GLADY FAITH BAYOGUING, ANN BUENAFE, FRANCK KELLY

I. DEFINITIONII. PROCESSIII. ADVANTAGESIV. DISADVANTAGESV. APPLICATIONS

I. DEFINITIONInvestment casting is an industrial process based on and also called lost-wax casting, one of the oldest known metal-forming techniques.

It a technique for making small, accurate castings in refractory alloys using a mold formed around a pattern of wax or similar material which is then removed by melting.

II. Process1. Produce a master pattern: An artist or mould-maker creates an original pattern from wax, clay, wood, plastic, steel, or another material.

2. Mouldmaking: A mould, known as the master die, is made of the master pattern. The master pattern may be made from a low-melting-point metal, steel, or wood. If a steel pattern was created then a low-melting-point metal may be cast directly from the master pattern. Rubber moulds can also be cast directly from the master pattern. The first step may also be skipped if the master die is machined directly into steel.

3. Produce the wax patterns: although called a wax pattern, pattern materials also include plastic and frozen mercury. Wax patterns may be produced in one of two ways. In one process the wax is poured into the mold and swished around until an even coating, usually about 3 mm (0.12 in) thick, covers the inner surface of the mould. This is repeated until the desired thickness is reached. Another method is filling the entire mould with molten wax, and let it cool, until a desired thickness has set on the surface of the mould. After this the rest of the wax is poured out again, the mould is turned upside down and the wax layer is left to cool and harden.

4. Assemble the wax patterns: The wax pattern is then removed from the mould. Depending on the application multiple wax patterns may be created so that they can all be cast at once. 

5. Investment: The ceramic mould, 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. This fine material is used first to give a smooth surface finish and reproduce fine details. In the second step, the cluster is stuccoed with a coarse ceramic particle, by dipping it into a fluidised bed, placing it in a rainfall-sander, or by applying by hand. Finally, the coating is allowed to harden. These steps are repeated until the investment is the required thickness

6. Dewax: The investment is then allowed to completely dry, which can take 16 to 48 hours. Drying can be enhanced by applying a vacuum or minimizing the environmental humidity. 7. 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, and tosinter the mold. Sometimes this heating is also used as the preheat, but other times the mold is allowed to cool so that it can be tested.

7. 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, vacuum cast, tilt cast, pressure assisted pouring, or centrifugal cast.

8. Divesting: The shell is hammered, media blasted, vibrated, waterjeted, or chemically dissolved (sometimes with liquid nitrogen) to 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

III. ADVANTAGESMany intricate forms with undercuts can be cast.

A very smooth surface is obtained with no parting line.

Dimensional accuracy is good.Certain unmachinable parts can be cast to preplanned shape.

It may be used to replace die-casting where short runs are involved.

IV. DISADVANTAGESThis process is expensive, is usually limited to small casting,

and presents some difficulties where cores are involved.Holes cannot be smaller than 1/16 in. (1.6mm) and should

be no deeper than about 1.5 times the diameter.Investment castings require very long production-cycle times

versus other casting processes.This process is practically infeasible for high-volume

manufacturing, due to its high cost and long cycle times.

III. APPLICATIONS• Investment casting is used in the aerospace and 

power generation industries to produce turbine blades with complex shapes or cooling systems.[14] Blades produced by investment casting can include single-crystal (SX), directionally solidified (DS), or conventional equiaxed blades. Investment casting is also widely used by firearms manufacturers to fabricate firearm receivers, triggers, hammers, and other precision parts at low cost. Other industries that use standard investment-cast parts include military, medical, commercial and automotive.• With the increased availability of higher-resolution 3D printers,

3D printing has begun to be used to make much larger sacrificial molds used in investment casting. Planetary Resources has used the technique to print the mold for a new small satellite, which is then dipped in ceramic to form the investment cast for a titanium space bus with integral propellant tank and embedded cable routing.