The entire injection molding process cycle can range from 8 to 40 seconds. The resin is fed from the hopper (a funnel-shaped receptacle on top of the injection unit) and heated until it reaches molten form. In a screw fed injection molding machine, there is a motorized screw within the heating cylinder that mixes the melt and forces it to the end of the cylinder. The screw rotates forward and fills the mold with melt and holds it under high pressure. Additional melt is added to compensate for the contraction and expansion of the polymer during the cooling and solidification steps. Upon freezing, the plastic is isolated from the injection unit. It subsequently cools to its solid form. The clamping unit is opened, which separates the two halves of the mold. A rod and plate eject the finished piece from the mold.