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Prototype Metal Casting

In prototype metal mold casting, an SLA master model is replicated into silicone rubber and used as a reusable master pattern for a single-use plaster mold. This method is limited to low-melt alloys such as Aluminum and Zinc. The process of plaster mold casting can be summarized as such:

SLA Master Pattern (positive) → RTV mold (negative) → RTV mold (positive) →
Plaster mold (negative) → Final casting (positive)

A plaster, usually gypsum or calcium sulfate, is mixed with talc, sand, asbestos, sodium silicate, and water to form a slurry. This slurry is sprayed on the polished surfaces of the pattern halves. The slurry sets in less than 15 minutes to form the mold. The mold halves are extracted carefully from the pattern and then dried in an oven.

The mold halves are carefully assembled, along with the cores. Then, the molten metal is poured in the molds. After the metals cools down, the plaster is broken and the cores are washed out.

TYPICAL USES

Materials with low melting temperature, such as aluminum and zinc, can be cast using this process. This process is used to make quick prototype parts as well as low volume production parts.

LIMITATIONS

Size - Parts cast are usually small to medium size, ranging in weight from 30 g (1 oz) to 7 kg (15 lb).

Finishing - The surface finish is 1.25 µm to 3 µm (50 µin to 125 µin) RMS.