Cold Working
Cold working is the plastic deformation of a metal below its recrystallization temperature, usually near room temperature, so the grain structure is not reset by heat. It includes cold rolling, drawing, forging, thread rolling, stamping, swaging, and crimping. The primary metallurgical result is strain hardening, which increases yield strength and hardness but reduces ductility.
On a CNC or metal-fabrication floor, cold working is the practical choice when a part must be stronger, tighter, and more consistent after forming rather than after heating. Suppliers often cold draw or cold roll bar stock before it reaches the machine, giving better straightness, tighter size control, and less variability than hot-rolled material. In the CNC cell, cold-worked stock machines with predictable geometry, but the operator must respect higher cutting forces, harder chips, and the risk of breaking through a work-hardened skin if feeds are too light or tools dwell. For fasteners, shafts, and threaded components, thread rolling intentionally cold works the thread roots so they gain fatigue strength instead of being cut away. In sheet-metal workflows, bending, stamping, coining, and spinning use cold working to retain room-temperature form with no oxidation or heat-affected zone. The process window matters: higher cutting speed can reduce the hardened layer, while dull tools and poor rake geometry worsen it.
Is cold working the same as CNC machining?
No. Cold working is plastic deformation below the recrystallization temperature, while CNC machining is primarily material removal. Machining can induce local work hardening at the cut zone, but it is not intentional cold forming.
Why do cold-worked parts often show better dimensional control?
Cold working reduces material variability and produces more uniform stock geometry, which helps machinists hold tighter tolerances, better straightness, and more consistent concentricity than with hot-rolled material.
Why does cold working increase strength?
Plastic deformation increases dislocation density within the metal's crystal structure, which raises yield strength and hardness while reducing ductility. This is the core of strain hardening and is used to improve finished part performance.