Cycle time

Cycle time is the total time required to complete all the stages of the injection molding cycle.

The cycle time is made up of the following stages:

Fill time.

The time required to fill the mold with polymer. The injection molding machine controls the velocity (flow rate) of the molten polymer entering the mold during this stage of the cycle.

Packing time

The stage of the injection molding cycle when pressure is applied to the polymer melt to compress the polymer and to force more material into the mold. This compensates for the shrinkage that occurs as the polymer cools from the melt temperature to ambient (room) temperature. From 5 to 25 percent more material can be added to the mold during the packing stage. The gate should freeze during the packing time to prevent material from exiting the mold.

The Packing time is also known as the Holding time.

Cooling time.

The cooling time is the stage of the injection molding cycle when there is no more pressure being applied to the polymer. The mold is held shut and the polymer continues to cool until the part can be ejected. The cooling stage is normally the longest part of the molding cycle and can account for up to 80 percent of the total cycle time.

Mold open time.

The time for which the mold is open before the next molding cycle begins. This time includes the following:

• Opening the mold
• Ejecting the part
• Preparing for the next cycle, such as loading inserts (not always part of the cycle)
• Closing the mold

The phases of a typical injection cycle can be shown below. Actual portion size of the cycle elements will depend on the part and molding machine used.