Sunday, August 26, 2007

Mold Timing and Terminology

Dry-cycle: The total time required for the (machine) clamp to close and open, or the sum of the mold opening and the mold closing time. Today’s fast machines have dry-cycles in the order of 1–3 seconds. A short dry-cycle is of particular importance with fast-cycling molds. The dry-cycle also depends on the length of the clamp stroke.
Opening time: Usually quite fast. The ejection preferably should take place during this time,to reduce (or to omit completely) any mold open time. Occasionally, mold opening speed may need to be slowed down to suit the ejection method.
Closing time: Usually quite fast, except for the final approach before the mold is fully clamped up, to permit the mold protection system to operate in time before serious damage is caused to the mold.
Mold protection: A system which senses (at the moment of final closing the mold) whether there is foreign material (dirt, plastic pieces, products which failed to eject, etc.) between the mold halves which could cause damage to the mold. A signal from the mold protection system will cause the mold closing to stop before damage occurs and sound an alarm. It usually automatically reopens the clamp so the foreign material can be removed.
There are many types of mold protection systems, such as electric, optical, or pressure activated. Some are more sensitive than others and may not always save a mold from damage.
Mold open (MO) time: This is lost time. This time should be as little as possible. It can be zero.
Mold closed (MC) time: Time from the moment the mold has closed until it reopens. It is the
sum of the following times: Injection time: the time to fill the mold with plastic (usually with high injection pressure).
Hold time: the plastic in the cavities is held under pressure usually lower than the injection pressure to add plastic volume as the plastic shrinks within the cavity.
Cooling time: the time from the moment the injection (or hold) pressure is off until the mold starts opening. (This term is actually a misnomer, since the cooling is always on and starts to remove heat from the plastic as soon as the plastic enters the mold.)
Ejection time: the time required to eject the products from the molding area so that the mold can re-close without catching an ejected piece. Preferably, this should take place during the opening time so as to eliminate the need for additional MO time. In some molds, it is not possible or practical to eject during the mold opening, and the ejection takes place
partly or solely during the MO time.

Dry-cycle- Total Time required for the clamp to close and open (sum of mold opening and closing time).
Opening Time- Time it takes to open mold and usually eject part
Closing Time- Time it takes to close mold
Mold Protection- Halts molding operation if a foreign material (dirt, flash, debris) is detected in mold cavity
Mold Open- Time the mold is actually open
Mold Closed- Time the mold is closed and usually includes
o Injection Time, Hold Time, Cooling Time
Ejection Time- Time is takes to eject parts and is a part of Mold Open Time


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