extrusion-processes

name	extrusion-processes
description	Extrusion processes — direct/indirect metal extrusion (Bilker-Hankel theory, extrusion ratio R, press force), die design (die angle, bearing length, die material), polymer screw extrusion (screw geometry, melt zone analysis, pressure buildup, extrudate swell), profile and pipe extrusion, hydrostatic extrusion, impact extrusion, extrudability of Al/Cu/Mg/Ti alloys, and ISO/ASTM standards for extruded products.
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Extrusion Processes — Complete Skill

Metal Extrusion Fundamentals

Extrusion Types

Direct (forward) extrusion: Ram pushes billet → material flows through die in same direction as ram travel Billet slides against container wall → high friction → dead zone at container/die corner Container friction force adds to total press force

Indirect (backward/reverse) extrusion: Die moves into stationary billet; no billet-container friction → 25–35% lower force than direct Cannot extrude very long billets (die stem must extend through press); common for thin-walled tubes

Hydrostatic extrusion: Billet surrounded by pressurized fluid (mineral oil or castor oil); no container friction; can extrude brittle materials (ceramics, beryllium); fluid pressure: 500–3000 MPa Can extrude: Ti, Mg, Mo, W, and normally non-extrudable materials

Impact extrusion: Cold extrusion; high-speed punch into billet; backward or forward; aluminum/tin collapsible tubes; one-shot process; no heating

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Metal Extrusion Theory

Extrusion Ratio and Geometry

Extrusion ratio (R): R = A_billet / A_product [area ratio; R = 10–1000 for aluminum; R = 5–50 for copper; R < 10 for steel] Equivalent strain: ε_eq = (2/√3) × ln(R) = 1.155 × ln(R) [true effective strain imparted]

Reduction: Rd = 1 − 1/R [fraction of area reduced]

Press Force Estimation

Simplified press force (upper bound / empirical): F = σ_flow × A_billet × ln(R) × (1 + 2μL/D_billet + constant_for_die_angle) Where: σ_flow = average flow stress over deformation; μ = friction coefficient; L = billet length; D_billet = billet diameter

Backer-Doehler empirical (for aluminum): F = A_billet × σ_0 × (a + b × ln R) [a = 30–50 MPa; b = empirical; σ₀ = UTS at extrusion temperature]

Extrusion pressure (specific pressure): P_ext = F / A_billet [typical: aluminum 300–700 MPa; copper 600–1200 MPa; steel 1200–2500 MPa]

Dead zone (dead metal zone): Material in corner between container wall and die face; does not flow; angle ≈ (90° − α_die/2) from ram direction Billet skin (with oxide/contamination) flows into dead zone → clean product interior; critical for aluminum Discard last 10–20% of billet to avoid dead zone material breakthrough

Die Design

Optimum semi-angle: Flat-face die: most common for aluminum; angle = 90° → no dead zone (dead zone acts as natural die angle ≈ 45°) Conical die: optimum angle α_opt = arctan(√μ × strain_hardening_factor); typically 15–45° for steel Too small angle: high surface contact length → high friction; too large → redundant deformation

Die material: H13 hot-work die steel: HRC 44–48; T_max = 600°C; for Al, Cu, Mg extrusion Inconel 718 or M2: for stainless steel, Ni-alloy extrusion TiAlN coatings on H13: reduces galling; extends die life 2–5×

Bearing length (land): Short bearing: low friction, faster flow → risk of extrudate exit angle variation Typical: bearing length = 3–10 × product wall thickness; adjusted per section complexity

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Extrudability of Metals

Aluminum Extrusion

Most commonly extruded metal (by volume): 6xxx series (Al-Mg-Si): excellent extrudability; window/door profiles; automotive; billet T = 450–550°C 7xxx series (Al-Zn-Mg): lower extrudability; aerospace; T = 400–480°C (narrower window) 2xxx series (Al-Cu): most difficult of structural alloys; T = 380–430°C

Critical extrusion temperature: Below T_min: billet too stiff → excessive pressure → press overload Above T_max: hot shortness (cracking due to low-melting eutectic at grain boundaries) Forming window: 30–80°C typically for structural alloys

Die line: Aluminum extrudes over die bearings cleanly (low friction at 500°C); mirror finish on bearing improves surface Exit speed: 1–50 m/min (faster = cheaper; limited by temperature rise and hot cracking)

Copper and Brass

Horizontal press; temperatures 700–900°C: Pure copper: excellent ductility; R up to 200; speeds 5–15 m/min Brass (70/30): R = 50–100; wears tooling (zinc vapor); nitrogen atmosphere in furnace Extrusion products: rod, wire, heat exchanger tubing, profiles

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Polymer Screw Extrusion

Single-Screw Extruder Geometry

Screw zones:

1. Feed zone: solid pellets compacted and conveyed forward; deep channel
2. Compression zone (transition): channel depth decreasing; melt forms
3. Metering zone: shallow channel; uniform melt pumping; pressure buildup

Screw parameters: L/D ratio: 20–30:1 (general purpose); 30–40:1 for mixing/venting Compression ratio: CR = H_feed / H_metering = 2.5–4.5 [H = channel depth] Flight pitch: S ≈ D (square pitch); helix angle φ = arctan(S/πD) ≈ 17.7° for square pitch

Metering zone throughput (Newtonian approximation): Q = (π² × D² × N × H × sin(φ) × cos(φ) / 2) − (π × D × H³ × sin²(φ) × ΔP) / (12 × η × L_m) Q_drag − Q_pressure [first term: drag flow; second: pressure flow] For 20% back-pressure flow: net flow ≈ 0.8 × Q_drag

Barrel temperature (profile): Zone 1 (rear): 20–30°C above T_m; Zone 2: T_m + 20°C; Zone 3 (die zone): typically highest Example HDPE: feed 170°C; compression 210°C; metering 220°C; die 230°C

Extrudate Swell (Die Swell)

Extrudate swell ratio (Barus effect): B = D_extrudate / D_die [B > 1 always; caused by elastic recovery of polymer melt] B ≈ (1 + 0.13 × (Weissenberg number)²)^(1/6) [approximation; Weissenberg: Wi = η_0 × λ × γ̇; λ = relaxation time] Typical: B = 1.1–2.0 for most polymers at production conditions

Design compensation: Die orifice undersized by swell factor: D_die = D_product / B With draw-down: haul-off takes product at speed V_haul > V_exit → stretches down to target diameter; often used for pipes/film

Pressure Profile and Die Design

Pressure drop across die (power-law fluid): ΔP = (2L_land / R_die) × K × (4V_exit / R_die × ((3n+1)/4n))^n [K = consistency index; n = power law index; R_die = die radius] For HDPE: n ≈ 0.45–0.55; K ≈ 10,000–30,000 Pa·sⁿ at 200°C

Die land length: Minimum: L/D ≥ 10 for stress relaxation (reduce extrudate swell) Too long: pressure too high → excessive motor power; possible thermal degradation

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Standards and References

Standard	Scope
ASTM B221	Aluminum alloy extruded bars, rods, wire, profiles
ASTM B241	Aluminum alloy seamless pipe and seamless extruded tube
ISO 2604	Aluminum and aluminum alloy extruded sections
ASTM D2513	Polyethylene gas pipe (extruded)
ISO 11922-1	Thermoplastics pipes — tolerances on dimensions
AA Publications	Aluminum Association design manual for structural extrusions

Output

Provide: process type (direct/indirect/impact/hydrostatic/screw polymer), material (alloy or polymer; T_extrusion [°C]; flow stress σ₀ [MPa] at extrusion temperature; extrudability rating), billet/blank (diameter D_b [mm]; length L_b [mm]; for polymer: pellet feed rate [kg/h]), extrusion ratio (R = A_billet/A_product; equivalent strain ε_eq = 1.155×lnR [dimensionless]), press force (F = A_billet×σ_flow×(a+b×lnR) [kN]; specific pressure P_ext [MPa]; press capacity required [MN]), die design (die angle α [°]; bearing length [mm]; material: H13/Inconel; coating: TiAlN?), polymer screw extruder (L/D ratio; CR; Q_output [kg/h]; metering zone: H [mm]; ΔP across die [MPa]; die swell B [dimensionless]; haul-off speed [m/min]; product dimensions after swell/draw-down), product properties (Al: temper after extrusion: T5/T6; σ_y [MPa]; surface finish Ra [μm]; straightness tolerance [mm/m]; polymer: wall thickness tolerance [%]; haze; tensile properties), and applicable standard (ASTM B221 for Al bar/profile; ISO 11922 for plastic pipe; ASTM D2513 for PE gas pipe).