Forming Processes — Family Index

Plastic deformation of metal (and some polymers/composites) into a useful shape, without removing material. Covers bulk-forming (rolling, forging, extrusion, drawing) where the entire workpiece volume is deformed, and sheet-forming (blanking, bending, deep drawing, stretch, hydroform, spin, incremental, roll-form) where deformation is concentrated in a thin starting blank. Adjacent processes — powder metallurgy and MIM — are included because they share the press-and-die infrastructure and compete for the same parts.

1. At a glance

Bulk forming (3D billet → 3D part):

• Rolling — slab/strip/plate/foil; thread rolling
• Forging — open-die, closed-die (impression), precision/near-net-shape, isothermal, ring rolling
• Extrusion — direct, indirect, hydrostatic; metal and polymer
• Drawing — wire drawing, tube drawing (sink/mandrel/plug); deep drawing crosses into sheet

Sheet forming (2D blank → 3D shell):

• Blanking, piercing, fine-blanking — shearing operations
• Bending — V/U/wipe air-bend, bottoming, coining; press brake and tube bend
• Deep drawing — cup/can shells; LDR 2.0–2.4 typical
• Stretch forming — biaxial tension over form-block; aero skins
• Hydroforming — sheet (fluid-cell) and tube (internal pressure + axial feed)
• Rubber-pad / Guerin — urethane pad replaces female die
• Superplastic forming (SPF) — slow, very-high-strain Ti and Al at elevated T
• Incremental sheet forming (ISF) — CNC stylus, low-volume / prototype
• Spinning, shear-forming, flow-forming — axisymmetric over a mandrel
• Roll-forming — continuous progressive bending through tandem roll stands

Thermal regime — hot working (above the recrystallization temperature, ~0.6 T_m; low flow stress, no strain hardening, oxidized surface); warm working (intermediate; reduced load + better finish); cold working (below recrystallization; strain hardening, best dimensional + surface, highest tool load).

Die geometry — open-die (workpiece flows freely, multi-step manipulator-fed); closed-die / impression-die (cavity controls final shape, flash escapes around parting line); flashless / precision (volume tightly controlled, near-net-shape).

2. Rolling

Continuous reduction of cross-section by passing material between counter-rotating rolls. Highest-tonnage forming process in industry — most steel and aluminum reaches the user via rolling.

Hot rolling — slab or bloom heated above T_recrystallization (steel ~1100–1250 °C; Al ~400–500 °C) and reduced in roughing → finishing stands to plate (≥ 6 mm), hot-rolled strip / coil (1.5–6 mm), or shapes (I-beams, rails, rebar). Scale oxidation requires pickling or shot-blast for downstream use.

Cold rolling — hot-rolled strip pickled, then reduced cold in a tandem mill (2-Hi, 4-Hi, 6-Hi, cluster, or Sendzimir Z-mill with 12+ rolls for thin foil down to ~5 µm). Produces final sheet thickness, mirror surface, and controlled strain-hardening (temper rolling). Tin plate (food cans), galvanized auto-body sheet, electrical steel laminations.

Thread rolling — M-thread or UNF formed by squeezing the blank between two flat or cylindrical dies; grain flow follows the thread root → fatigue strength 30–50 % higher than cut threads. Used for fasteners, leadscrews, roll-formed worms.

Mill builders — SMS group, Andritz Metals, Danieli, Primetals (Siemens-VAI + Mitsubishi-Hitachi). Roll suppliers: Union Electric Åkers, ESW, Hitachi Metals.

3. Forging

Plastic deformation under compressive impact or squeeze. Aligns grain flow with part geometry — forged parts retain 100 % material continuity (no porosity) and have anisotropic strength along the flow lines.

Open-die forging — flat or simple-contour dies, with the workpiece manipulated between blows. Hammer or hydraulic press. Used for large shafts (turbine rotors, marine crankshafts), rings, and reduced billets feeding closed-die. Schloemann–Siemag 14 000-t open-die press at Saarschmiede; Alcoa 50 000-t Cleveland forge press (1955, still operating, can forge a single airframe bulkhead).

Closed-die / impression-die forging — heated billet shaped through a sequence of cavities (busterer → blocker → finisher) with flash escaping at the parting line. Automotive crankshafts, connecting rods, gear blanks, hand tools, hip implants. Press makers: Schuler, SMS Meer, Ajax-CECO, Lasco.

Precision / near-net-shape forging — multi-step flashless or trapped-flash dies; tight tolerance reduces downstream machining. Common for turbine disks, automotive gears, aerospace fittings.

Cold forging / cold heading — bolts, screws, ball-joint pins headed cold from wire in multi-station headers. Nedschroef, National Machinery, Hatebur, Sakamura. Cold-extruded automotive shafts (Bonderite phosphate + soap lubricant).

Isothermal forging — dies heated to the same temperature as the workpiece (typically 950–1100 °C for Ti and Ni-superalloy). Allows slow-strain-rate forging of α+β Ti and γ′-Ni disks (Inconel 718, Waspaloy, René 88 DT) into near-net jet-engine compressor and turbine disks. Wyman-Gordon (now Precision Castparts), ATI Ladish, Schultz Steel. Dies in TZM-Mo or Astroloy; protective glass-frit lubricant.

Ring rolling — pierced doughnut blank rolled between a main roll, mandrel, and axial rolls into seamless rings up to 10 m dia for bearing races, flanges, jet-engine cases. SMS Meer, Eitel, Wagner-Banning, Bharat Forge.

4. Extrusion

Forcing a heated billet through a die orifice; the resulting product has the cross-section of the die opening and can be very long.

Direct (forward) extrusion — ram pushes billet through stationary die; friction between billet and container is the main load contributor.

Indirect (backward) extrusion — die is on the ram, container is stationary, no relative billet/container motion — lower load but mechanically more complex.

Hydrostatic extrusion — billet surrounded by pressurized fluid, no container friction; specialty (Cu-clad bus-bar, sheathed wire).

Aluminum extrusion — by tonnage, the dominant non-steel forming process. 6063 (architectural — window/door frames), 6061 / 6005 (automotive structural — bumper beams, crash boxes, EV battery enclosures), 7075 (aerospace stringer). Press tonnage 1 000–15 000 t; billet heated 450–500 °C. Press builders: SMS, UBE, Presezzi, Sutton, SAPA-Hydro. Hydro Extrusion (formerly Sapa), Constellium, Bonnell Aluminum, Arconic. Stretch-straightener pulls and quenches the extrudate.

Copper / brass extrusion — bus-bar, plumbing tubes, condenser tube. Steel cold-extrusion forging (for transmission shafts, gear pinions) uses phosphate + soap lubricant on the billet.

Polymer extrusion — completely different physics (melt + screw conveyance), but the same word. Single-screw extruders for film, sheet, pipe, profile. Twin-screw co-rotating (Coperion ZSK, Leistritz, Toshiba TEM) for compounding; counter-rotating for rigid PVC pipe. Co-extrusion + multi-layer (food packaging — Davis-Standard, Battenfeld-cincinnati, Reifenhäuser, Krauss-Maffei). Up to 9-layer barrier films (EVOH O₂ barrier in PET/PE structure).

5. Drawing

Pulling (not pushing) the workpiece through a die — opposite force direction from extrusion.

Wire drawing — single or multi-pass through tungsten-carbide or polycrystalline-diamond dies; reduces cross-section and strain-hardens. Cu magnet wire down to ~25 µm; steel music wire (ASTM A228) for springs at ~2 GPa tensile; bead wire for tire reinforcement. Drawing-machine builders: Henrich, Niehoff, Bühler-Wire, Mario Frigerio. Calcium-stearate drawing soap or oil/MoS₂.

Tube drawing — sinking (no internal support, ID floats), mandrel drawing (fixed plug — best ID control), floating-plug (long lengths, hydraulic-tube). Schumag, Bültmann, SMS Meer.

Deep drawing — sheet blank pulled by a punch into a die cavity to form a cup or shell. Blank-holder prevents wrinkling; punch–die clearance ≈ sheet thickness × 1.1. Limiting Drawing Ratio (LDR) = D_blank / D_punch; typically 2.0–2.4 for Al and steel before failure (tear at the punch corner). Beverage cans (3104 Al body + 5182 Al end — Crown Holdings, Ball, Ardagh, CCL), kitchen sinks, automotive oil pans. Press makers: Schuler, Aida, Komatsu, Battenfeld-Cincinnati. Multi-stage redraw + ironing reduces wall thickness for a typical beverage can: cup → first redraw → second redraw → ironing → necking → flanging.

6. Stamping, blanking, piercing, fine-blanking

Shearing operations that cut sheet against a die edge — same machinery family as forming, often integrated on one progressive die.

Blanking / piercing — blanking takes the slug as the product; piercing takes the slug as scrap (hole-making). Clearance 5–10 % of sheet thickness; rollover, sheared, and fracture zones on the cut edge.

Progressive die — strip is fed through multiple stations on a single press, each station doing one operation (pierce → bend → form → cut-off); high-volume terminal connectors, electrical lamination stacks.

Transfer die — discrete blank moves between stations on transfer fingers — used when progressive strip layout isn’t possible (3D parts, larger panels).

Tandem line — sequential stand-alone presses with robots or shuttles between — auto body panels (door inner/outer, hood, fender). Modern servo-presses (Schuler ServoLine, Komatsu, Aida, Fagor) replace mechanical eccentric drives — slide profile is programmable, enabling soft-touch contact and re-strike at bottom dead center.

Fine-blanking — Feintool process (Switzerland, 1959). Triple-action press: V-ring indents the strip around the cut line, counter-punch supports the slug from below, then the punch shears at low clearance (0.5 % of thickness, vs. 5–10 % for normal blanking). Result: smooth sheared face over 100 % of thickness, ±0.03 mm tolerance. Used for transmission synchro hubs, seat-recliner gears, brake-pad backing plates. Feintool, Schuler, Kyori.

7. Bending

Air bend (V-die) — punch presses sheet into a V-die; bend angle is set by punch stroke, not by tooling — same die makes any angle. Most flexible, but spring-back must be compensated.

Bottoming — punch contacts the die at the end of stroke; angle locked by tool geometry; ~5 × the load of air-bend.

Coining — high-tonnage flat-bottom; permanently set the bend (no spring-back) by exceeding yield throughout the thickness; 10–20 × air-bend load.

Wipe bending — sheet clamped on one side, free end is wiped over the die corner — used for short flanges on long blanks.

U-bending — two opposing punch–die pairs form both legs simultaneously.

Press brakes — TRUMPF TruBend, Bystronic Xpert, Amada HFE, Salvagnini B3, LVD, Durma. Modern CNC press brakes have angle-measurement (laser or capacitive) and adaptive spring-back compensation.

Tube bending — rotary draw (most common — bend die + clamp + pressure die + mandrel + wiper), compression (around a fixed form), ram (cheap, large radius only), push/roll (long sweeping bends, freeform). Schwarze-Robitec, BLM Adige (tube benders), AMOB, transfluid, Numalliance. Mandrel (ball or rod) prevents flattening on small CLR (Centerline Radius) / D ratios. Auto exhaust, hydraulic lines, aircraft hydraulic tubing.

8. Stretch forming

Sheet clamped at both ends, pulled in tension while wrapped over a male form-die. Tension keeps the sheet just above yield throughout, so the entire panel takes a permanent set with very little spring-back. Used for double-curvature aero skins (B787 wing skin, A350 fuselage panels, A380 wing skin). Cyril Bath, ACB (now ACB Pressure Systems), Loire Safe Stretch.

Stretch-bend forming — combined stretch + wrap, used for window-frame mullions and architectural curved sections.

Age-forming / creep-forming — Al panel restrained against a tool inside an autoclave; the part creeps to the tool shape during the artificial aging cycle (4–8 h at 175 °C for 7075-T6 or 2024-T8). Locks in shape with minimal residual stress; standard for wing skins on commercial transports.

9. Hydroforming

Pressurized fluid replaces one half of a die.

Sheet hydroforming (rubber-diaphragm fluid-cell) — Avure (formerly ABB Pressure Systems) Quintus presses, Schnupp; pressures 100–140 MPa; a rubber-bladder cell pushes the sheet down onto a single male tool — only one tool half is needed, so it suits short-run aerospace and prototype panels.

Tube hydroforming — preform (often bent) tube placed in a closed two-half die; ends sealed by axial punches; internal water pressure (100–400 MPa) plus axial feed expands the tube into the cavity. Auto exhaust systems, engine cradles, instrument panel beams, frame rails (Ford F-150, Audi space-frame). Press makers: Schuler, Dieffenbacher, Engel, AP&T, Interlaken.

10. Rubber-pad / Guerin / Marforming

Single male die mounted on the press bed; a urethane pad (mounted in a retainer on the upper platen) acts as a universal female die. Pad pressures 50–100 MPa shape the blank around the tool. Used for low-volume aero sheet parts where the cost of a matched die set isn’t justified — ribs, brackets, beads, flanges. Marforming variant adds a movable rubber-faced punch.

11. Superplastic forming (SPF)

Some fine-grained alloys exhibit elongations > 200–1000 % at elevated temperature and very low strain rate (ε̇ ≈ 10⁻⁴ to 10⁻³ s⁻¹) — a stable necking regime where flow stress scales as σ = K·ε̇^m with strain-rate sensitivity m ≈ 0.4–0.8.

Ti-6Al-4V SPF — 900–950 °C, argon gas pressure 1–3 MPa pushes sheet into a one-sided ceramic-coated steel tool. Cycle time 10–60 min. Used for B-1 wing skins, F-22 / F-35 access panels, Eurofighter fuselage panels. Combined with diffusion bonding (SPF/DB) for hollow sandwich structures — multiple Ti sheets stop-off-painted, diffusion-bonded in selected areas, then gas-blown apart to form internal ribs.

Al SPF (5083 SPF-Al) — 500–525 °C, ~2 MPa. Forming sheet 1.0–6.0 mm. Aston Martin DB9 inner body panels, Ford GT40 deck-lid, B787 leading-edge slats.

Equipment: ACB SPF presses (France), Pacific Press, BAE Systems in-house. Slow cycle and tooling cost limit SPF to high-value low-volume aerospace and luxury automotive.

12. Incremental sheet forming (ISF)

CNC-controlled hemispherical stylus deforms a clamped sheet locally; the tool path builds up the shape one contour layer at a time, much like 3D printing — but subtractive of flatness, not additive of mass. Two variants:

SPIF (single-point incremental forming) — sheet supported only at edges, tool deforms it freely; geometry limited by spring-back but no die needed.

TPIF (two-point) / double-sided ISF (DSIF) — partial die or a second opposing tool supports the back side; closer to net shape.

Used for prototype and very-low-volume body panels (Amino in Japan, Ford one-off restoration panels), dental orthotic shells, custom orthopedic plates, architectural cladding. Hot-ISF heats the workpiece (induction or laser) for Ti and Mg.

13. Spinning, shear-forming, flow-forming

Rotating blank or tube formed against a mandrel by a roller.

Conventional (sheet) spinning — blank rotated on a lathe, roller traces over a mandrel to push it down; wall thickness preserved (cosine-of-angle for slight thinning). Cookware (stainless pots, woks), lampshades, satellite dish reflectors.

Shear-forming — controlled wall thinning t₁ = t₀·sin α (sine law); used for cones, lampshade-shape parts, rocket-engine nozzles in single-piece Inconel 718 or 4130. Leifeld, MJC, WF Wagner.

Flow-forming — tube preform reduced in wall by axial roller travel along the mandrel; produces seamless long tubes with mid-to-high strength enhancement from cold work. Missile-body cases, automotive driveshafts (CV joints), helicopter rotor masts, rocket-motor cases.

14. Roll-forming

Strip is pulled through a series of contoured roll stations (typically 8–24 stands), each adding a small bend, until the final cross-section is achieved. Long, constant-section profiles: structural studs and tracks for drywall, gutters, standing-seam metal roofing, automotive bumpers, door beams, truck side-rails, racking. Builders: Bradbury, Samco-Roll-Forming, OmniFab, Jubin, Dahlstrom, Formtek. Continuous: input is a coil, output is a cut-to-length profile through a flying shear.

Hot-stamped boron steel (22MnB5 / Usibor 1500) is a partly-competing technology for crash structures — see § 18.

15. Powder metallurgy (PM) + Metal Injection Molding (MIM)

Adjacent to forming because both use press-and-die infrastructure, and both compete for small geometric parts that would otherwise be cold-headed, machined, or sintered into shape.

Die-pressed PM — atomized metal powder (Fe-Cu-C, brass, stainless) plus lubricant pressed in a closed steel die at 400–700 MPa, then sintered at 1100–1300 °C in a controlled atmosphere. Small gears in oil pumps, automatic-transmission synchro hubs, sintered iron-bronze bearings (oil-impregnated), valve guides. Players: GKN Powder Metallurgy (now Stackpole + GKN), Sumitomo Electric, Hitachi Chemical, Höganäs (powder supplier). Density ~ 86–93 % theoretical; HIP or double-press / double-sinter for full density.

Metal Injection Molding (MIM) — fine (< 22 µm) metal powder mixed with thermoplastic + wax binder forms a feedstock pellet; pellet is injection-molded like plastic into a complex 3D part; binder is then debound (solvent + thermal) and the part is sintered. Final density 96–99 %. 17-4PH stainless triggers in firearms, mobile-phone hinges (MS-1 alloy and similar), small precision gears, medical surgical-tool tips, dental brackets. Players: Indo-MIM, Form Technologies (Optimim), Kinetics Climax, ARC Group, ASH Industries. Best for parts < 100 g with features that would be costly to machine.

16. Material formability metrics

Sheet metal:

• r-value (Lankford coefficient) — ratio of width strain to thickness strain in a uniaxial tensile test. r > 1 means width yields faster than thickness → deep-drawability. IF (interstitial-free) steel r ≈ 2.0; 5xxx-Al r ≈ 0.7; brass r ≈ 0.8.
• n-value (strain-hardening exponent) — exponent in σ = K·ε^n. Higher n → more diffuse necking, better stretchability. IF steel n ≈ 0.23; 5083-Al n ≈ 0.27.
• Forming Limit Diagram (FLD) — locus of principal strains (ε₁, ε₂) at the onset of localized necking; Keeler–Goodwin (1960s). FLD₀ (the plane-strain minimum) is the design driver. Determined from Nakajima (hemispherical-punch) or Marciniak (flat-punch) tests with grid-circle analysis.

Bulk forming:

• Flow stress σ = K·ε^n (cold) or σ = K·ε̇^m (hot — strain-rate sensitive); both contribute in warm working.
• Cold-heading upset ratio (free length / wire dia) ≤ 2.5:1 in a single blow before buckling; 4.5:1 in two blows.
• Hot-forging press tonnage F ≈ k_p · σ_flow · A_projected, where k_p is the shape complexity factor (1.5–4.0 from Lange / Schey nomograms).

Superplastic: ε > 200 % requires strain-rate sensitivity m > 0.3 at the working T and ε̇.

17. Lubricants and surface coatings

Process	Typical lubricant
Wire drawing (steel)	Dry calcium-stearate soap on a phosphate or borax carrier
Wire drawing (Cu)	Soluble-oil emulsion or fatty alcohol
Tube drawing	Chlorinated paraffin + sulphurized oil (cold), molybdenum disulphide paste (warm)
Cold extrusion / cold forging (steel)	Zn-phosphate + soap (Bonderite / Henkel) — bonded chemical conversion
Hot forging (steel)	Graphite + water (sprayed on die between cycles)
Hot forging (Ti, Ni-superalloy)	Glass frit — melts at forging T, isolates die from billet
Cold sheet stamping	Mineral oil + chlorinated paraffin (declining — chlorine RoHS / REACH restrictions); replacement: ester + boundary-additive package (Quaker Houghton, Fuchs)
Deep draw (Al beverage can)	Aqueous-emulsion drawing fluid, in-line skim and recovery
Aluminum extrusion	None on billet — die is nitrided + bore-coated; trace boron-nitride spray on the die land
Sheet hydroforming	The rubber pad itself is the interface — no lubricant on the workpiece side
Roll-forming	Light synthetic-ester roll lube; many lines run dry
Press-brake bending	None (clean) or boric-acid powder for stainless to prevent galling

Reactive coatings (phosphate, glass frit) chemically bond to the workpiece and survive the deformation event — required when interface pressures exceed ~1 GPa.

18. Selection heuristics

Part / requirement	Process route
Auto outer body panel (door, fender, hood)	Tandem-line servo-press stamping; deep-draw die + flange + trim + restrike
Auto frame rail / B-pillar (crash-critical)	Hot-stamping (press-hardening) 22MnB5 / Usibor 1500 boron steel — heat to 900 °C, transfer, form + quench in tool, exit at 1500 MPa UTS martensite
Pickup truck side rail (long, simple section)	Roll-forming HSS strip; option to induction-temper or hot-stamp
Aero engine compressor / turbine disk (Ti-6-4, IN718)	Isothermal forging → HIP → solution + age → contour machine → shot-peen
Aero wing skin (Al 7050, double curvature)	Stretch-form over form-block → age-form during 175 °C aging cycle
Aero airframe frame / stringer (Al 7075)	Extrude → stretch-straighten → solution + age → machine
Aero sheet bracket, low volume	Rubber-pad (Guerin) over single male tool, or SPF for complex
Beverage can body (Al 3104)	Coil → blank → cup-draw → 2× redraw → ironing → trim → necker → flange
Oil & gas line pipe (large diameter)	Seamless: Mannesmann pierce + plug-mill draw. Welded: UOE plate-roll + DSAW (double-submerged-arc weld)
Rocket nozzle (Inconel 718, regen-cooled)	Spinning or shear-forming + ring-rolled aft skirt + EBW segment joining
Cookware (deep stainless pot)	Spinning (open-top) or deep-draw (sealed-bottom)
Small precision gear (< 100 g, 17-4PH)	MIM injection mold + debind + sinter + HIP
Long-length structural stud, drywall track	Roll-forming galvanized strip, in-line punch + flying shear
Wire fastener (M6 bolt)	Cold-head from wire on multi-station Nedschroef / National header → thread-roll
Connector terminal (Cu-alloy)	Progressive die: blank + pierce + form + bend + cut-off
Heavy turbine shaft (1 m dia, 12 m long)	Open-die forge on hammer + manipulator from cast ingot
Seamless jet-engine case ring (Inconel 718)	Ring rolling from pierced doughnut billet

19. Cross-references

• casting-forging-forming — the parent Tier-2 overview
• casting-processes — the upstream cast-billet route
• welding-processes — joining the formed pieces
• machining-processes — subtractive finishing after forming
• aluminum-alloys — extrusion + sheet alloy selection
• steel-grades — DP/TRIP/PHS sheet steels for auto stamping; cold-heading wire grades
• polymers-taxonomy — polymer extrusion melt rheology
• composites-taxonomy — autoclave + RTM as the composites analog of forming

20. Citations

• Schey, J. A. Introduction to Manufacturing Processes, 3rd ed., McGraw-Hill, 2000.
• Boljanovic, V. Sheet Metal Forming Processes and Die Design, 2nd ed., Industrial Press, 2014.
• ASM Handbook, Vol. 14A — Metalworking: Bulk Forming, ASM International, 2005.
• ASM Handbook, Vol. 14B — Metalworking: Sheet Forming, ASM International, 2006.
• Lange, K. Handbook of Metal Forming, McGraw-Hill, 1985.
• Altan, T. & Tekkaya, A. E. Sheet Metal Forming: Fundamentals, ASM International, 2012.
• Keeler, S. P. & Backofen, W. A. “Plastic instability and fracture in sheets stretched over rigid punches”, Transactions of ASM, 56, 1963 — origin of the FLD.
• ISO 16630 (hole-expansion test for sheet edge formability); ISO 12004 (FLD determination); ASTM E517 (r-value).