Injection molding makes a wide variety of products from a wide range of thermoplastic and some thermoset polymers. Common items include plastic syringes and IV connections, plastic toys, packaging, containers and drinkware, automotive components and parts, and more. Injection molding is often used in the medical industry because of its ability to produce precise, high-volume parts in a low cost, efficient and fast process.

A key to the injection molding process is the control of the molten plastic. Injection machines typically use a heated barrel and screw, to heat the polymer to its melting point (typically 350-450°F). After a specified injection time, the screw shifts into a transfer position, which begins an irreversible chemical reaction that crosslinks the fluid components into a solid, rigid material.

The molten plastic is injected into the mold via the injection nozzle in the injection machine's barrel, which is sealed by a sprue bushing. The sprue bushing directs the molten plastic to the cavity images in the injection mould, and is made of A plates and B plates that are machined with channels that resemble the shape of the product. The sprue bushing also seals the injection nozzle tightly into the sprue gate at the top of the mould.

Auxiliary equipment, such as temperature control units, circulates a flow of coolant through passages in the injection moulds to help them maintain correct and consistent temperatures. This helps ensure that the moulds are warm enough to allow molten resin to fill them completely during a single injection cycle (also known as a shot). Jetting—the snake-like stream of unmelted polymer that oozes through restricted areas of the mould and forms small lines in parts—can occur for a number of reasons, including faulty tool design, poorly designed gates or runner systems, or even the temperature of the circulating coolant.