Explain that metal can be formed through forging, where the metal is subjected to forces that distort its shape, but that forging is imprecise, can cause damage to the metal and cannot form certain parts.
Emphasize the importance of the shape of the mold. The mold allows manufacturers to create metal parts in shapes that would be difficult to form through forging. Explain that some metal parts must be hollow and thus need cores to keep the liquid metal from collapsing on itself until it cools.
Describe the molding process, where the metal is heated by the foundry and then poured into the mold before it has a chance to cool.
Tell students that while some molds are exposed to air, most are closed. The molten metal enters a pouring cup, where it travels via a delivery system and arrives at the main cavity, where it molds into its proper form.
Point out that manufacturers use either expendable or permanent molds. Expendable molds can only be used once. They are made of sand, plaster or some other material, with binders holding them together. Permanent molds can create numerous castings, which free manufacturers from the necessity of creating new molds. However, permanent molds are limited in the shape that the casting can take.
Explain that molten metal must flow through a gating system, which guides the liquid metal to the mold. As the liquid metal shrinks and solidifies, manufacturers must add more molten metal until the part completely forms. Explain the different parts of the gating system, such as the pouring basin and vents.