CNC machining delivers high dimensional accuracy, yet the resulting surface integrity often limits fatigue performance. Tool marks, elevated surface roughness (Ra), and tensile residual stresses act as crack initiation sites under cyclic loading. Targeted post-processing methods that introduce compressive residual stresses and refine surface topography deliver the largest gains in fatigue life of CNC machined components.
Shot peening remains the most widely adopted industrial solution. High-velocity spherical media impact the surface, generating a shallow layer of compressive residual stress (typically 0.2–0.5 mm deep) and work hardening. Studies on alloy steels show fatigue-limit improvements of approximately 39 % relative to as-machined surfaces. Coverage and Almen intensity must be controlled to avoid excessive roughness that could offset the benefit.
Low-plasticity burnishing (LPB) and conventional burnishing outperform conventional shot peening in many applications. A hydrostatic tool applies controlled pressure, producing deeper compressive residual stress with far lower cold work and a smoother surface finish. Research on quenched-and-tempered steels reports fatigue-limit increases of up to 52 %. LPB is especially effective on complex geometries and thread roots where shot media cannot reach uniformly.
Laser shock peening (LSP) provides the deepest compressive residual stress field—often exceeding 1 mm—with minimal cold work. The laser-induced plasma shock wave yields superior fatigue-life extension, sometimes an order of magnitude greater than shot peening on critical aerospace and turbine components. Although capital cost is higher, LSP is preferred for high-value, damage-tolerant parts.
Complementary surface-finishing steps—precision polishing, electropolishing, or abrasive flow machining—further enhance results by reducing Ra and removing residual tensile layers or microcracks. Hybrid sequences (e.g., peening followed by light polishing) consistently produce the highest fatigue strength by combining compressive stress with optimized topography.
Selection depends on material, geometry, production volume, and cost targets. For high-volume steel and aluminum parts, shot peening or LPB offers the best balance. For titanium and nickel alloys in aerospace, LSP or burnishing is frequently specified. In all cases, residual-stress measurement and surface-roughness control after treatment are essential to verify process efficacy.
By systematically applying these post-processing methods—shot peening, low-plasticity burnishing, laser shock peening, and refined surface finishing—engineers can substantially extend the fatigue life of CNC machined components, improve reliability, and reduce the risk of premature failure under cyclic service loads.