spinning-forming

name	spinning-forming
description	Metal spinning and flow forming — conventional spinning (manual and CNC), shear spinning (Sine rule, wall thickness), flow forming (tube and disc), material formability (spinnability rating), roller force and power, wrinkling and cracking failure modes, mandrel design, materials (aluminum, stainless, titanium, copper), tolerances, applications (rocket nose cones, cookware, pressure vessel heads, wheels), and DIN 8583 classification.
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Metal Spinning and Flow Forming — Complete Skill

Process Overview

Spinning vs. Flow Forming

Conventional spinning (pure spinning): Flat blank or preform rotated on mandrel; roller pressed progressively inward over multiple passes No intentional thickness change; material flows circumferentially Applicable: shallow to deep cups, conical shapes, hemispherical shells Tolerance: ±0.1–0.5 mm on diameter; wall thickness variation ±10–20%

Shear spinning: Roller follows mandrel profile while maintaining sine rule (wall thinning is intentional) Wall thickness: t_product = t_blank × sin(α_half-cone-angle) [Sine Rule; α = half-cone angle from rotation axis] For α = 30°: t_product = t_blank × 0.5 (50% thinning) Single pass to near-final form; high precision; no springback issues

Flow forming (roller burnishing of tube/disc): Staggered rollers force material axially along rotating mandrel → elongate tube wall while reducing thickness Tube flow forming: L_final / L_blank = t_blank / t_final (volume conservation) Disc (backward) flow forming: starts with thick disc; rollers push material backward over mandrel Tolerance: ±0.025–0.1 mm on wall thickness; excellent circularity

DIN 8583: classifies pressure welding; spinning/flow forming as "Drücken" (pressing)

Conventional Spinning

Deformation Mechanics

Material flow: blank material flows radially inward; circumferential compression; no thickness change in ideal case Actual: slight thickening at rim (circumferential compression → material goes somewhere) Typical thickness increase at rim: 5–15% (depends on pass schedule and roller contact geometry)

Blank diameter: D_blank = √(D_part² + 4h²) for cylindrical cup without thinning [diameter conservation; h = depth] More accurately: D_blank = Σ√(d_segment² + 4h_segment²) for complex profiles (segment method)

Limiting draw ratio (LDR) for spinning: LDR_spinning = D_blank / D_mandrel ≤ 2.0–2.5 for most materials in one pass Deeper forming: multi-pass spinning (anneal between passes for work-hardening materials)

Roller Geometry and Contact

Roller nose radius r_roller: Too small: scratches, cold welds; too large: insufficient local deformation Typical: r_roller = 5–25 mm (smaller for fine work; larger for heavy plate)

Roller feed angle: Attack angle θ_attack = 30–45° (angle of roller axis relative to rotation axis) Feed rate f = 0.1–1.5 mm/rev (CNC); manual spinning: operator feel

Roller force (radial and axial): F_r ≈ k_f × t × b_contact [k_f = flow stress; t = blank thickness; b_contact = contact width] b_contact ≈ 2 × √(r_roller × t/2) [Hertz contact width estimate; r_roller = roller nose radius] For 2024-T3 aluminum (k_f ≈ 350 MPa), t = 3 mm, b = 10 mm: F_r ≈ 350 × 3 × 10 = 10,500 N = 10.5 kN

CNC spinning forces (typical): Light gauge Al (1–3 mm): 2–10 kN radial; 1–5 kN axial Heavy gauge steel (5–10 mm): 50–200 kN; hydraulic cylinders

Shear Spinning (Cone Forming)

Sine Rule

Wall thickness in shear spinning: t_f = t_0 × sin(α) [α = half-cone included angle from axis; t_0 = blank thickness] Constant wall thickness maintained throughout: each material element thins by sine factor

Cone geometry: For cone half-angle α (from rotation axis) = 30°: sin(30°) = 0.5 → wall thins by half For α = 45°: t_f = t_0/√2 = 0.707 × t_0 (29.3% thinning) For α = 90°: t_f = t_0 (no thinning; cylinder; same as flow forming of disc)

Formability limit — spinnability: Minimum α before fracture = α_min ≈ 20–30° for ductile materials (aluminum, copper) α_min increases for harder/less ductile materials (high-strength steel, titanium) Below α_min: fracture at roller contact

Example (rocket nose cone): Shape: tangent ogive (approximated as cone with α = 25° near tip to α = 60° at base) Blank: 5 mm 2024-O aluminum; near tip: t_f = 5 × sin(25°) = 2.11 mm; base: t_f = 5 × sin(60°) = 4.33 mm Single pass shear spinning on 3D mandrel with α varying along axis

Flow Forming (Tube and Disc)

Tube Flow Forming

Forward flow forming (material flows in direction of roller traverse): Mandrel constraint: ID fixed; rollers force wall to thin and extend axially t_f = t_0 - Δt [thickness reduction Δt controlled by roller depth] L_f = L_0 × t_0/t_f [volume conservation: length increases as wall thins]

Maximum thickness reduction per pass: Aluminum: 20–30% per pass; Steel: 15–25%; Titanium: 10–15% Exceeding limit → orange peel (waviness), cracks, or spiral marks

Typical tolerances: Wall thickness: ±0.025–0.075 mm; ID over mandrel (diameter): +0.0 to +0.05 mm (good circularity) Used for: bearing races, ammunition cases, drive shafts, hydraulic cylinders

Three-roller arrangement: 120° apart; balanced radial forces; no net radial load on mandrel/spindle Force per roller: F_roller ≈ k_f × t_contact × b_contact [similar to spinning; higher forces for thick walls]

Disc (Backward) Flow Forming

Starts as thick disc; rollers push material backward: D_mandrel = ID_final tube; initial disc thickness = final tube length Recess angle on mandrel: allows material to flow backward; 20–30° typical

Advantages: Starting from a simple disc forging (near net shape); complex integrated features possible Used for: gas cylinders, shock absorber cylinders, wheel rims with integral flanges

Spinnability Rating

Spinnability: ability of material to be spun without fracture; analogous to drawability (LDR)

Spinnability factors: n (work hardening exponent): high n → good spinnability (strain hardening distributes strain) r_bar (Lankford coefficient, anisotropy): higher r → better drawability in general; spinning less direction-dependent Elongation at break: A₅₀ ≥ 25% recommended for good spinnability

Spinnability by material:

Material	Spinnability	α_min shear	Max LDR conventional	Notes
Al 1100-O	Excellent	18°	2.5	Softest; easiest to spin
Al 3003-O	Excellent	20°	2.3	Common for cookware
Al 6061-O	Good	25°	2.0	Must anneal between passes
Al 2024-O	Good	27°	1.8	Aerospace; needs care
Cu (annealed)	Excellent	18°	2.4	Art metalwork; musical instruments
Stainless 304	Moderate	30°	1.5	Work hardens rapidly; intermediate anneals
Stainless 316L	Moderate	32°	1.4	As 304; better corrosion
Low carbon steel	Good	25°	1.8	Automotive parts
Titanium 6-4 (warm)	Limited	38°	1.2	Requires elevated temperature (300–500°C)
Inconel 625	Poor	40°	1.1	Requires multiple anneals

Wrinkling and Cracking

Failure Modes

Wrinkling (compressive instability): Occurs when circumferential compressive stress exceeds buckling limit at inner (unsupported) edge Prevention: proper roller contact engagement; friction; mandrel support; backing roller Critical parameter: t_blank/D_blank (thinner relative to diameter → more wrinkling tendency)

Cracking/Fracture: Occurs when tensile stress (roller attack) exceeds fracture strain of material Typically at roller-blank contact for shear spinning below α_min For conventional spinning: fracture at flange edge if circumferential tension too large

Orange peel (for flow forming): Surface roughening from anisotropic grain deformation; occurs if grains are large Prevention: fine grain size (ASTM 6 or finer); proper lubrication; speed/feed optimization

Springback: Axial springback: wall angle increases after roller passes; compensate by 2–5° over-lean of roller Diametral springback: slight enlargement after mandrel removal; depends on σ_y / E For aluminum: springback ≈ 0.1–0.3% of mandrel diameter; steel: 0.05–0.15%

Mandrel Design

Material: hardened tool steel (HRC 52–58); or ductile iron for short runs Taper: 0.5–2° taper per side for easy part removal (forward spinning) Surface finish: Ra ≤ 0.4 μm on mandrel → part interior takes good finish from mandrel contact Thermal expansion: for warm spinning (Ti, Inconel) use material with low CTE or ceramic mandrel sections

Multi-piece mandrel: For parts that cannot slip off straight mandrel: collapsible or segmented mandrel Required for shapes with re-entrant features (closed-form undercut)

Tolerances and Surface Finish

Conventional spinning: dimensional ±0.5–2 mm; Ra 1.6–6.3 μm (dependent on roller condition) Shear spinning: wall thickness ±5%; diameter ±0.5 mm; Ra 0.8–3.2 μm Flow forming (tube): wall thickness ±0.025–0.075 mm; Ra 0.4–1.6 μm (very tight) Post-processing: spinning typically requires trimming of wavy edge; lathe trimming common

Standards and References

Standard	Scope
DIN 8583	Classification of forming processes (German standard)
ASTM B345	Aluminum tube for flow forming qualification
AMS 2604	Flow formed titanium tubes
Kalpakjian "Manufacturing Engineering and Technology"	Spinning/flow forming chapter reference
Music "Spinning and Shear Forming" (2004)	Dedicated reference

Output

Provide: part description (final shape: cone/hemisphere/cylinder/complex; OD [mm]; depth [mm]; wall thickness t_f [mm]; material; quantity), process selection (conventional spinning / shear spinning / flow forming; basis for selection; number of passes), blank sizing (D_blank or L_blank [mm] from volume conservation; t_blank [mm]), sine rule check (if shear: α [°]; t_f = t_0 × sin(α); α > α_min for material: yes/no), LDR check (if conventional: D_blank/D_mandrel ≤ LDR_allow; intermediate anneals required?), roller geometry (nose radius r_roller [mm]; attack angle θ [°]; feed rate f [mm/rev]; speed n [rpm]), roller force (F_r [kN]; power P [kW]; machine capacity required), lubrication (lubricant type; application method; material compatibility), wrinkling/cracking risk (t_blank/D_blank ratio; α margin above α_min; risk: low/medium/high), mandrel specification (material; taper angle [°]; surface finish Ra [μm]; removal method), tolerances (diameter ±[mm]; wall thickness ±[%]; Ra [μm]), and applicable standard (DIN 8583; AMS 2604 for Ti; ASTM B345 for Al tube).