Meaning
Mechanical cold working process applies localized pressure to the exterior of a cylindrical component using hardened rollers to improve its fatigue life.
Compression Stress
Compression of the surface layers during the rolling operation creates a zone of high residual stress that opposes the tensile loads applied during service. Because fatigue cracks usually start at the surface the presence of this compressive layer prevents them from initiating or growing. Surface rolling is particularly effective at notches and fillets where stress concentrations are highest.
Dimensional Integrity
Dimensional accuracy and surface roughness improve as the rollers smooth out the peaks and valleys left by previous machining operations. The process of surface rolling work hardens the material which increases its resistance to wear and contact fatigue. This dual benefit of stress and finish makes it a preferred choice for high performance automotive components.
Successful Parameters
Successful application depends on the careful control of the rolling force and the feed rate. If the pressure is too low the depth of the compressive layer will be insufficient to provide a benefit. If the pressure is too high it can cause surface damage or excessive deformation that compromises the fit of the component in its assembly.
