The Injection molding process

There are many sizes and types of injection molding machines, but the machines all follow the sequence shown in this animation.


A mold is bolted into the Clamping section of the machine. The machine closes the mold, then applies a large force to “Lock” the mold closed. Inside the closed mold is a cavity that is the exact shape of the plastic part.

The Injection section of the machine has a hopper to hold plastic pellets; a barrel with heater bands to liquefy the plastic pellets; a feed screw to move the pellets forward in the barrel; a check valve to force the liquid plastic into the mold, and a nozzle to seal the injection section to the mold. The liquefied plastic is forced into the cavity of the mold with high pressure.