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Flash is a thin, unwanted layer of plastic that escapes from the mold cavity and remains along the edge of a finished part. It may look minor at first, but excessive flash can affect cosmetic quality, create assembly interference, increase trimming work, and indicate that the mold or process is operating outside a stable condition. In plastic injection...

Sink marks are localized depressions on the surface of a plastic molded part. They commonly appear in thick-wall sections, behind ribs, at the base of bosses, or in areas where material accumulates. Although they are often treated as cosmetic defects, sink marks can also indicate that a local area has not received enough material during packing and cooling....