Definition
The process of shaping or hardening metal by deforming it at a temperature below its recrystallization point, typically at or near room temperature. Common cold working methods include rolling, bending, drawing, peening, and hammering. The process increases the metal's strength and hardness but reduces its ductility, and it leaves residual stresses in the worked area.
Plain English
Shaping or strengthening metal by working it (bending, hammering, rolling) without heating it first. The metal becomes harder and stronger, but also more brittle.
Context Anchor
Seen in aircraft maintenance and structure discussions, especially with sheet metal, tubing, forming repairs, and damage caused by repeated bending.
Derivation
Cold' refers to the metal being below the temperature at which its internal grain structure can reform (recrystallize). 'Working' means deforming or shaping. Together: shaping metal while it is still cold enough that the deformation permanently changes its structure.
Why Pilots Care
Cold-worked metal behaves differently from annealed (softened) metal. A pilot or mechanic inspecting an aircraft needs to recognize that repeatedly bending or flexing a part can work-harden it, making it brittle and prone to cracking. This is why some aluminum parts that have been bent should not simply be bent back -- the cold working has already weakened them.
Analogy
Bend a paper clip back and forth and the bend area gets harder, then eventually snaps. Cold working is the metal-changing part of that process, before it breaks.
Intuition Check
Cold does not mean the metal must be icy or refrigerated. In this term, cold means the metal is being shaped without enough heat to let its internal structure reset.
Example Sentence 1
The mechanic explained that bending the aluminum bracket back and forth would cold work the metal and eventually cause it to crack.
Example Sentence 2
Repeated cold working on the fitting increased its hardness but required annealing afterward.