roller-burnishing

name	roller-burnishing
description	Roller burnishing (deep rolling) — surface finish improvement (Ra 0.05–0.4 μm), compressive residual stress induction, Hertzian contact pressure, burnishing force and depth of plastic deformation, material flow (cold working hardening), ball vs. roller vs. diamond burnishing tools, optimal parameters (force F, feed f, speed V, number of passes), applications (shaft bores, fillets, aerospace landing gear), fatigue life improvement (2–5×), and comparison with shot peening.
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Roller Burnishing (Deep Rolling) — Complete Skill

Process Overview

Principle and Benefits

Roller burnishing: cold forming process using hardened roller or ball pressed against surface with controlled force; surface asperities are plastically deformed and smoothed; subsurface compressive residual stress induced

Two effects:

1. Surface smoothing: Ra 0.1–0.8 μm machined → Ra 0.05–0.2 μm burnished (5–10× improvement)
2. Residual stress: compressive layer 0.1–1.0 mm deep; magnitude -200 to -800 MPa in steel

Benefits: Fatigue life: 2–5× improvement (compressive residual + work hardening) Wear resistance: increased surface hardness 10–30%; better load-bearing capacity Corrosion resistance: closed surface pores → less susceptible to pitting

Comparison with shot peening: Burnishing: smoother finish; deeper compressive layer; preferred for precision surfaces Shot peening: roughens surface (Ra increases); broader coverage; better for complex geometry Both: compressive residual stress; similar fatigue improvement Burnishing preferred: hydraulic cylinders, bearing bores, crankshaft fillets, seal surfaces

Contact Mechanics (Hertzian Theory)

Ball-on-Cylinder Contact

Hertz contact stress (ball pressing on cylindrical surface): a = ∛(3F × R_eff / (4E_eff)) [contact radius; a [m]; F = applied force [N]] p_max = 3F / (2π × a²) [maximum contact pressure; p_0 = 3/2 × p_mean] δ = (3F)^(2/3) × (2/3R_eff) / (4E_eff/3)^(2/3) [approach; Hertz deflection]

Effective radius: 1/R_eff = 1/R_ball + 1/R_cylinder [for ball on convex cylinder; sign convention: 1/R_cylinder negative for bore]

Effective modulus: 1/E_eff = (1-ν₁²)/E₁ + (1-ν₂²)/E₂ [E₁,ν₁ = tool; E₂,ν₂ = workpiece] For WC tool on steel: E_eff ≈ 180 GPa (WC much stiffer than steel)

Plastic zone initiation: Plastic deformation when p_max > 1.1 × σ_y (von Mises criterion for subsurface yielding) p_yield = 1.1 × σ_y (approximate; for first yield at z = 0.48a) For steel σ_y = 700 MPa: p_yield = 770 MPa; minimum force for plastic: F_min = (p_yield × 2πa²/3)

Depth of Plastic Deformation

Simplified estimate: z_plastic ≈ a × √(p_max/σ_y - 1.1)/1.1 [depth where yield condition first met; not exact] More accurately: elastic-plastic FEM simulation required for accurate z(plastic zone)

Empirical (from literature): z_cs ≈ 0.5 × a to 1.5 × a [depth of significant compressive stress; a = contact radius] Maximum compressive stress magnitude: σ_residual ≈ -0.5 to -0.9 × σ_y (after elastic springback)

Deep rolling (high force): Large a → z_cs extends deeper; controlled by F and R_ball Deep rolling for crankshaft fillet: F = 5–30 kN; z_cs = 0.5–2.0 mm deep Surface finish after: Ra = 0.05–0.15 μm (very smooth)

Burnishing Tools

Ball Burnishing Tools

Single ball (spring-loaded): Carbide ball (WC-Co, 50 mm dia for bore); spring maintains constant force regardless of bore variation Applications: small bores (D = 20–100 mm); simple geometry; low cost tool

Hydrostatic ball (Ecoroll HG): Ball floated on oil film in housing; consistent contact; no friction between ball and housing Very low Ra achievable; recommended for precision surfaces

Roller Burnishing Tools

Diamond roller tools (for external surfaces): PCD (polycrystalline diamond) roller on hydrostatic or spring-loaded support Used on lathe/turning center; simultaneous turning + burnishing possible

Multi-roller burnishing tools (for bores): Cage with multiple hardened rollers pressed outward by tapered arbor; adjustable for bore size Applications: hydraulic cylinder bores; gun barrel bores; bearing bores

ECOROLL tools: Roller bearing with fluid pressure control: apply precise, repeatable force (1–20 kN) External roll burnishing tools for crankshafts, camshafts, axle shafts

Diamond Burnishing (Smooth Burnishing Only)

Lower force, no deep rolling: Diamond tip (round, 1–6 mm radius); spring-loaded; Ra 0.02–0.1 μm achievable Surface hardness increase: 5–15% (less than roller) Applications: optical molds, precision bores, non-ferrous (aluminum, brass) No significant residual stress; purely surface finish improvement

Process Parameters

Optimal Burnishing Parameters (Steel)

Parameter	Range	Effect
Force F	50–500 N (ball); 1–30 kN (roller/deep roll)	Higher F → deeper layer, higher
Feed rate f	0.05–0.5 mm/rev	Lower feed → more coverage, smoother
Speed V	50–300 m/min	Higher speed → better finish; less cold work
Number of passes N	1–4	More passes → deeper, saturates at 2–3
Tool radius R	5–50 mm	Larger R → larger a → deeper at same F

Optimal Ra achievable: Starting from Ra = 0.4 μm (fine turned): burnishing → Ra = 0.05–0.10 μm (1–2 passes) Starting from Ra = 1.6 μm (rough machined): burnishing → Ra = 0.2–0.4 μm (may need more passes)

Surface hardness increase: Low carbon steel (σ_y = 200 MPa): +30–40% hardness after burnishing Medium carbon (σ_y = 500 MPa): +15–25% High alloy (σ_y = 900 MPa): +5–15% (less work hardening capacity)

Saturation: beyond 2–3 passes: negligible improvement; may damage surface (over-worked)

Lubrication

Required: lubricant reduces tool friction, prevents galling, maintains surface quality Common: sulfo-chlorinated cutting oil; neat oil ISO 46–100; water-based synthet Application: flood or minimum quantity lubrication (MQL)

Fatigue Life Improvement

Quantitative Fatigue Benefit

Mechanism: σ_residual compressive shifts mean stress: σ_mean_effective = σ_mean_applied + σ_residual (negative) From Goodman: σ_a_allow increases when σ_mean decreases → higher amplitude allowed

Typical improvement data: SAE 4340 steel (σ_y = 1,000 MPa) crankshaft fillet: Baseline fatigue limit: 350 MPa (unprocessed) After deep rolling (σ_residual = -700 MPa): fatigue limit → 600 MPa (+70%)

General trend: σ_fatigue,burnished = σ_fatigue,baseline + |σ_residual| × 0.3–0.6 [rough estimate; complex interaction] Factor of safety at same load: SF_burnished / SF_baseline = fatigue_limit ratio

Combined effect with surface finish: Smoother Ra → lower stress concentration at surface → Kt reduced from 1.4 → 1.1 for Ra 0.8→0.1 μm Both effects compound → 2–5× fatigue life in bending

Applications

Aerospace — Landing Gear

Critical surface: landing gear piston (cylinder rod): Deep rolling: reduces fatigue notch effect from machining marks; p_max = 3–5 GPa at contact Compressive residual depth: 0.5–1.5 mm; σ_residual = -500 to -700 MPa (Ti-6Al-4V or 300M steel) AMS 2580 (deep rolling specification for aerospace): controlled force, overlap, speed requirements

Crankshaft fillet rolling: Automotive standard: >90% of engine crankshafts deep-rolled at main/rod fillets Force: 10–20 kN; 2 passes; fatigue limit improvement: 50–100% Standard: ISO 6336 (gear tooth contact) adapted for crankshaft fillet

Hydraulic Cylinder Bores

Typical after honing (Ra = 0.2 μm): burnish to Ra = 0.05 μm: Reduces friction with seals; improves oil film retention; better surface bearing ratio (Abbott curve) Also closes surface pores → better seal performance; lower leakage

Standards and References

Standard	Scope
AMS 2580	Deep rolling of aerospace components
ASTM E837	Residual stress measurement (verify burnishing results by hole drilling)
ISO 4287	Surface roughness parameters (Ra, Rz measurement)
SAE J1068	Surface finish specifications for automotive crankshafts
DIN 8580	Classification of forming processes (burnishing as cold forming)

Output

Provide: workpiece description (material; σ_y [MPa]; initial Ra [μm]; geometry: bore/shaft/fillet; diameter D [mm]), objective (Ra target [μm]; fatigue life improvement target ×; surface hardness increase [%]; residual stress target [MPa depth profile]), tool selection (ball/roller/diamond; tool material; radius R [mm]; tool hardness HRC), Hertz contact analysis (F [N]; a [mm]; p_max [MPa] vs. 1.1×σ_y; plastic zone initiated: yes/no), plastic zone depth z_cs [mm] and maximum compressive residual stress σ_res [MPa], process parameters (F [N]; feed f [mm/rev]; speed V [m/min]; N_passes; lubricant), predicted Ra after burnishing [μm] (from starting Ra and parameters), surface hardness increase [%] (HV or HRC equivalent), fatigue life improvement factor (from residual stress via Goodman or empirical data), applicable standard (AMS 2580, ISO 4287, SAE J1068), and comparison vs. shot peening for same application (pros/cons).