Definition
A surface defect in a forged metal part where a layer of metal has been folded over onto itself during the forging process and pressed into the surface without fully fusing. The fold creates a thin seam or crack-like discontinuity that weakens the part and can act as a starting point for fatigue failure.
Plain English
A flaw left in a forged metal part when a flap of metal got folded over during shaping and mashed flat instead of joining cleanly. It looks like a thin crease in the surface and can crack open under stress.
Context Anchor
Seen in aircraft maintenance inspections of forged metal parts, such as strong structural or engine parts.
Derivation
Forging means shaping metal by hammering or pressing while it is hot. Lap here comes from the everyday sense of one thing folding over another, like the lap of a coat. Together: a fold of metal laid over itself during forging.
Why Pilots Care
Undetected forging laps can grow into fatigue cracks under flight loads, risking part failure.
Analogy
Like folding a sheet of dough over itself and then rolling it flat, leaving a hidden weak line inside.
Intuition Check
Do not read lap here as a trip around a course or something resting on your legs. In this maintenance term, lap means an overlap or fold in the metal surface.
Example Sentence 1
The inspector rejected the crankshaft after dye penetrant testing revealed a forging lap near the journal.
Example Sentence 2
Machining away the forging lap restored the part to airworthy condition.