Plastic injection molding is the most cost-effective way to make plastic parts in larger quantities. Injection molding is two large metal molds that are combined to form a sealed internal cavity space, and plastic material is injected into the cavity to form the parts. The position where the material is injected is called the injection port (called the gate). As the material heats up and starts flowing into the cavity of the mold it forms the shape of a plastic part. Once cooled, the two large metal molds are separated again, allowing the plastic parts to coalesce out of the mold cavity.