Development of Plaster Mold Casting

Abstract

Plaster Mold Casting has been used to produce a high quality of product with a good surface finish. To get the final products, a plaster mold is fabricated by pouring liquid metal into plaster (mixed of gypsum, talc, asbestos and sodium silicate) molds. This plaster in a form of slurry is sprayed on the polished surfaces of the pattern halves (usually brass). 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 to remove the moisture that can affect the final product. The mold halves are carefully assembled, along with the cores. The molten metal is poured in the molds. After the metals cools down, the plaster is broken and the cores washed out. Parts cast are usually small to medium size, ranging in weight from 30 g (1 oz) to 7 kg (15 lb). The section thickness can be as small as 0.6 mm (0.025 in) and tolerances are 0.2 % linear. The draft allowance is 0.5-1.0 degree. The surface finish is 1.25 µm to 3 µm (50 µin to 125 µin) rms. Low temperature melting materials such as aluminum, copper, magnesium and zinc can be cast using this process. This project involves design the products that suit to be produced through Plaster Mold Casting process. Next stage is to fabricate and prepare the plaster mold using appropriate technique.