Plastic injection molding is a process by which granular plastic is fed from a hopper into a heated chamber where it melts and hardens to create parts.
The granules are fed into the heating chamber by a screw-type plunger where they melt. As the plunger advances, the melted plastic is forced through a nozzle into the mold cavity.
Since the mold remains relatively cold, the plastic solidifies almost immediately after the cavity is filled. After the plastic is injected, it must cool before the final part can be ejected from the mold.