Cycle time is the total time required to mold
a single shot of plastic to produce a given part. An example of a complete
cycle would be from the first moment of injection of plastic in the mold,
to the beginning of the following injection of plastic. Cycle time is determined
by mold design, part configuration and plastics material being molded. Total
cycle time includes the time required to inject the plastic in the closed
mold, cool the plastic, open the mold, eject the parts and close the mold.
Cooling of the plastic to a solid state is required so as the ejection of
the part does not distort or post mold warpage does not occur. Time for cooling
of the plastics material is a factor of the location and amount of cooling
lines designed in the mold and time required to remove heat from the plastic.
Heavier wall sections require more cooling time than thinner walled parts.
Material type is another factor in determining cycle time. Plastics materials
with glass fiber, talc or other fillers may have shorter cycle times. A competent
molding technician has the ability to maximize the process for the quickest
cycle time while making a quality part, repeatedly. If the actual cycle time
is not known, the following table gives "rule of thumb" cycles for
a given material and maximum part thickness. The table assumes neat materials,
without fillers, adequate cooling in the tooling and runner design not being
the limiting factor of the cooling time. Thin wall molding techniques can
yield much quicker cycles under special conditions.
Examples of Cycle Times in seconds for various resin families. Lower or higher cycle may be required in some situations.