Injection Molding: The Revolution of Polymers?

Answer 1

Injection molding is a relatively new process which has come about with the dawn of the polymer industry. These days, almost every product on the shelves contains a plastic component. Injection molding is perhaps the most useful way to shape such components. As you can imagine, this process is now a booming, widespread, and rapidly growing industry.

Injection molding machines may seem complex, which would be a true assumption. However, the processes involved regarding injection molding are rather simple to understand. There are two main parts to an injection molding machine: the feed system and the mold system.

The feed system contains several parts and is designed to feed a polymer under high pressure into the mold system. In a typical example, polymer beads of the correct color and chemical composition are fed into a hopper. At the bottom of the hopper, an auger conveys the pellets through a heated cylinder until the polymer softens. Most polymers never truly become liquids, only viscous, syrupy mixtures which take a great deal of force to work with. The auger is attached to a hydraulic piston which can force it forward. When the auger is pushed forward - often with many tons of pressure - the soft, hot polymer is pushed into the mold system.

The mold system consists of a steel negative of the part to be produced. These molds are typically water-cooled to hasten the solidification of the polymer. Sprues are cut into the mold to feed multiple cavities with polymer at the same time. This method allows for several parts to be produced at once which can be broken from the sprues after solidifying. The typical mold is opened and closed under hydraulic pressure. Soft polymer is forced under extreme pressure into the mold where the cool surfaces of the mold cause the polymer to solidify. The mold then opens to release the part into a collection area for further finishing.

The type of parts which are able to be produced are limited only to the shape of the molds. Three and four-part molds are common for complex auto parts. Injection molding is truly the process of the future.