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The investment-casting process, also called the lost-wax process, was first used during the period 4000-3000 B.C. The pattern is made of wax or a plastic such as polystyrene.

Fabrication of the Solid Mold

The pattern is made by injecting semisolid or liquid wax or plastic into a metal die in the shape of the pattern. The pattern is then removed and dipped into a slurry of refractory material, such as fine silica and binders, ethyl silicate, and acids. After this initial coating has dried, the pattern is coated repeatedly to increase its thickness. The term investment comes from investing the pattern with the refractory material. Wax patterns require careful handling because they are not strong enough to withstand the forces involved during mold making.

The one-piece mold is dried in air and heated to a temperature of 90-175 degrees Celsius for about 4 hours, depending on the metal to be cast, to drive off the water of crystallization (chemically combined water). After the metal has been poured and solidified, the mold is broken up and the casting is removed. A number of patterns can be joined to make one mold called a tree, thus increasing process productivity.

figure 1	figure 2	figure 3

figure 4	figure 5	figure 6
figure 7	figure 8	figure 9

Figures 1,2 and 3 show the sequence of pattern production and assembly. Figures 4, 5, and 6 show the mold formation. Figure 7 shows the input of heat to melt out the wax, leaving the hollow mold. Figure 8 shows the mold in its final stage where it is ready to be used. Figure 9 shows the casting process.

Information source: Kalpakjian, Manufacturing Processes for Engineering Materials.

Figures' source: Vermont American