Shot Peen vs Burnish

Impact vs pressure.
Crater vs smooth.
Both improve fatigue.

Both shot peening and burnishing create compressive residual stress in part surface — improving fatigue life 2-4×. Shot peening uses bombardment with small balls. Burnishing uses rolled pressure. They achieve similar outcomes with very different surface effects.

Get a Quote DFM guide

01 · At a glance

Side-by-side summary.

Option A

Shot Peening

Bombardment with steel balls, glass beads, or ceramic media at controlled velocity. Creates small craters on surface. Residual compressive stress 0.1-0.5 mm deep. Rough surface.

Option B

Burnishing

Rolling precision balls or rollers against part surface under pressure. Plastically deforms surface. Smooth finished surface with compressive residual stress. Limited to accessible geometries.

02 · Detailed comparison

Feature-by-feature breakdown.

Attribute	Shot Peening	Burnishing
Process type	Bombardment	Rolling pressure
Surface effect	Dimpled/cratered	Smoothed
Surface finish after	Rougher than before	Smoother than before
Residual stress depth	0.1-0.5 mm	0.05-0.2 mm
Residual stress magnitude	400-700 MPa compressive	200-500 MPa compressive
Fatigue life improvement	2-4× (typical)	2-3× (typical)
Geometry access	Any accessible surface	Smooth access required
Hole interior	Limited (small holes)	Yes (ball burnishing)
Complex geometry	Good	Limited
Thin parts	Risk of distortion	Low distortion
Typical cost per part	$5-30	$10-50
Typical applications	Springs, fasteners, aerospace	Hydraulic rods, shaft journals, fittings

03 · Decision guide

When to choose each.

Choose Shot Peening when:

Aerospace fatigue-critical components
Coil springs (automotive, industrial)
Gear tooth surfaces
Complex 3D geometry
High-volume production
Turbine blade surfaces

Choose Burnishing when:

Hydraulic cylinder bores (ball burnishing)
Shaft journals for bearings
Seal surfaces requiring smooth finish
Internal bore finishing
When surface finish must improve
Fittings and fluid-flow surfaces

FAQ

Common questions.

Fatigue cracks nucleate at tensile stress. Surface under load: tension causes crack initiation. Shot peening/burnishing create compressive residual stress near surface — applied tensile stress must first overcome the compressive residual before creating crack-initiating tension. Result: crack initiation delayed or prevented. Effect most significant for fatigue-limited parts where surface stress dominates.

Thin flat parts experience distortion from shot peening — the surface compression causes the plate to dome (compressive side stretches slightly). For complex 3D parts, distortion usually manageable. For large flat panels, dimensional control required — masking, fixturing, or post-peen flattening. Controlled peening intensity (Almen strip measurement) keeps distortion predictable.

Ball burnishing uses precision ball rolled through bore under pressure. Compresses surface, improves finish, creates residual stress. Standard for: hydraulic cylinder bores (achieves Ra 0.1 µm + compression), small precision holes in instruments. Requires accessible straight bore. Not applicable to: blind holes, cross-drilled holes, complex internal geometry.

Almen strips are thin steel coupons with one side exposed to peening. Peening causes compressive residual stress on peened side, strip curves. Measured curvature (arc-height) quantifies peening intensity. Standard peening intensity specifications: "10A" (10 thousandths arc-height on A-type strip). Ensures repeatable peening between production runs. Aerospace specifies exact intensity.

Shot peening: $5-30 per part depending on size and complexity. Well-established industrial process. Automated line: high-volume very economical. Manual peening (aerospace): expensive due to inspection and documentation. Burnishing: $10-50 per part. Specialty equipment, trained operators. Not as widely available. For high-volume fatigue-critical parts: shot peening typically more economical.

Yes — for maximum effect. Process: CNC machine → shot peen (residual stress generation) → burnish (surface smoothing while preserving residual stress). Used for premium fatigue-critical parts. More expensive but combines advantages. Typical application: aerospace rotating shafts, premium hydraulic components. Specify only when standard single-process inadequate.