What is flash?
Flash is a defect where excessive material is found at locations where the mold separates, notably the parting surface, movable core, vents, or venting ejector pins.
Gap within the mold
Adjust the mold set-up
Set up the mold to seal properly. A mismatch or undesirable gap between the cavity and core sides of the mold will result in flash.
Make sure the mold plates are strong enough to avoid deformation during molding.
Check for adequate venting dimensions.
Clean the mold surface.
Mill out the surface to keep the sealing pressure of land area around the cavities high enough.
Adjust the machine settings
Set up the machine and mold to seal properly. Flash can be caused by a poor seal between the cavity and core sides of the mold, and machine platens that are not parallel.
Increase the injection molding machine size. Flash can result from insufficient machine clamp force.
Adjust the clamp force if the machine capacity does have enough clamp force.
Adjust the molding conditions
Decrease the barrel temperature and nozzle temperature.
Reduce the injection and packing pressure to reduce the clamp force requirement.
Reduce the feed setting (stroke length) to reduce metering (over-fill).
Increase the injection time or slow down the injection speed.