Flash
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Definition of Flash
Flash is a thin fin or web of plastic that squeezes out between mold halves, inserts, or shut-off surfaces when internal cavity pressure exceeds what the clamp and seal surfaces can contain. It often appears along the parting line but can also form around ejector pins or worn shut-offs.
Minor flash may be trimmed in secondary operations; heavy or recurring flash signals a process or tooling issue: insufficient clamp tonnage, worn parting surfaces, poor venting balance, or excessive injection pressure.
Why It Matters for Plastic Injection Molding
Flash adds deburring labor, scrap risk, and inspection time. On automotive and medical programs, even small flash can affect fit, sealing, or customer perception, so AMP treats recurring flash as a priority root-cause item.
Flash often ties back to clamp force, parting-line condition, or pack pressure. Correcting the underlying cause is more reliable than trimming every part on the production floor.