Casting Processes — Family Index

Family-level orientation note for the metal-casting process tree. Covers expendable-mold and permanent-mold families, the continuous-casting branch used for primary mill product, and specialty variants. Pairs with [[Engineering/casting-forging-forming]] (Tier 2) for the physical-metallurgy and solidification fundamentals.

1. At a glance

The first cut is mold reusability:

• Expendable-mold (mold destroyed per cast): sand (green-sand, no-bake / chemically-bonded, shell), investment (lost-wax), plaster, ceramic-mold, lost-foam (evaporative pattern), lost-PLA / lost-SLA (printed-pattern variants).
• Permanent-mold (metallic die reused for many casts): gravity permanent-mold (PM), low-pressure die casting (LPDC), high-pressure die casting (HPDC) hot- and cold-chamber, squeeze casting, semi-solid metal forming (SSM — thixo and rheo), centrifugal (true, semi, and centrifuge).
• Continuous casting: not a single mold at all — a water-cooled copper mold continuously withdraws solidified strand to produce slab, bloom, billet, rod, or strip for downstream rolling and drawing.

Throughput, dimensional precision, surface finish, minimum wall thickness, draft requirement, tooling cost, and acceptable alloy chemistry all vary by 2 to 4 orders of magnitude across this list, which is why selection is dominated by quantity and alloy together (see §16).

A second useful cut is pressure during fill:

• Gravity (head pressure only — sand, gravity PM, investment, lost-foam): low fill velocity, prone to gas / oxide entrainment if the gating system is turbulent.
• Low-pressure (0.2-1 bar — LPDC, counter-pressure): laminar fill, high yield, premium grain structure.
• High-pressure (40-150 MPa intensification — HPDC, squeeze): fast fill, thin walls, high cycle rate, but trapped gas porosity unless vacuum is added.
• Centrifugal (60-90 G effective): self-feeding outer skin, dross floats to bore.

Globally, world casting production is on the order of 110-120 Mt/yr, with grey + ductile iron ~70 %, steel ~10 %, aluminum ~15 %, copper alloys + Zn + Mg + Ti the balance. China, India, USA, Japan, Germany, Mexico are the top producing countries.

2. Sand casting

Largest tonnage of any casting family worldwide; the workhorse for iron, steel, bronze, and large aluminum. Tooling is patterns + core boxes (not dies), so per-unit pattern cost is modest and runs can be economic from 1 piece (no-bake) to 100,000+ pieces per year (high-pressure green-sand).

• Green-sand: silica + bentonite clay (4-10 %) + water (2-4 %) + carbonaceous additive (seacoal for iron). Patterns of wood, aluminum, or plastic, often plated. Automated horizontal flask lines (DISA, Hunter, Sinto) since the early 1900s; vertical-flask Disamatic since 1964 routinely runs 350-550 molds/hr. Mold hardness measured with Dietert hardness gauge (B-scale 80-90 for iron). Sand-to-metal ratio typically 4:1 to 10:1 by mass.
• Chemically-bonded sand (no-bake): phenolic-urethane cold-box (PUCB, Ashland Isocure) and phenolic-urethane no-bake (PUNB, self-setting) — the dominant systems for steel and ductile-iron jobbing foundries. Furan (FA + acid catalyst — typically p-toluenesulfonic) for steel and iron. Alphaset / Betaset (alkaline phenolic, ester-cured) used where low-emission and easy reclamation matter. Sodium-silicate / CO₂ binder is the oldest non-clay binder and still used for steel cores.
• Shell-mold (Croning): invented 1944 by Johannes Croning. Pre-coated resin sand (novolac phenolic + hexamethylenetetramine catalyst) dumped onto a heated metallic pattern (220-260 °C), forms a 6-10 mm shell, stripped, assembled with adhesive. Excellent surface finish (Ra ~5-10 μm) and dimensional accuracy (CT8 to CT10 ISO 8062) for medium-volume iron and steel parts (hydraulic-valve bodies, gears, planetary carriers, crankshafts).
• V-process (vacuum-mold): thin (75-150 μm) plastic film vacuum-formed over the pattern, flask filled with unbonded dry silica, second film on top, vacuum drawn (-50 to -70 kPa) — sand holds shape only while under vacuum. No binder, very fine surface (Ra 2-4 μm), ideal for prototype and short-run aluminum and steel. Slow cycle but zero binder cost and easy sand reuse.
• Cosworth process: precision sand-mold aluminum for engine blocks. Zircon sand + furan binder + low-turbulence bottom-fill from an electromagnetic pump (no transfer ladle), mold rolled over 180° before solidification to feed the heaviest sections. Developed at Cosworth Engineering (Northampton) for the DFV Formula-1 block; still used for the Ford / Cosworth / Aston Martin V12 program and for Bentley.
• Core-making sub-family: hot-box, warm-box, cold-box (amine-gassed PUCB), Croning shell core, Inotec (inorganic silicate, Ask Chemicals — emission-free, used in Audi/BMW Al cylinder heads). Cores form the internal passages (water jackets, intake/exhaust ports) for engine castings.

3. Investment casting (lost-wax)

Wax pattern injected into a metal die; patterns assembled onto a wax-runner tree; tree dipped repeatedly into ceramic slurry and stuccoed, dried, dewaxed in an autoclave (flash-dewax) or steam-dewax, fired, cast.

• Shell systems: primary coat zircon flour + colloidal-silica (Ludox, Megasol, REMASOL) binder for the high-detail interior layer; backup coats use fused-silica or alumino-silicate stucco for thermal-shock tolerance. Mullite stucco for high-T superalloy work. Typical shell thickness 8-12 mm after 6-9 dip cycles, dried 2-4 h between coats at 22-24 °C / 40-60 % RH in a humidity-controlled shell room.
• Pattern wax: filled emulsion pattern wax (M.P. Argueso, REMET, Blayson, Paramelt) for parts; non-filled runner wax for gates; water-soluble cores (urea or PEG-based — REMET Aquacore) for internal passages such as turbine-blade serpentine cooling channels.
• Dewax: steam-autoclave (flash-dewax at ~165 °C and 6 bar) is the dominant industrial method; flash-fire in a 1000 °C kiln is used for some smaller jewelry trees. Recovered wax is reclaimed and reblended.
• Process owners: Precision Castparts Corp (PCC) Portland Oregon — Co/Ni-superalloy turbine blades and IGT castings, acquired by Berkshire Hathaway 2016; Howmet Aerospace spun off 2020 from Arconic, also major in single-crystal blades. Doncasters (UK), Consolidated Precision Products (CPP), Signicast (now Form Technologies), Hitchiner (NH — countergravity vacuum process).
• Single-crystal blade growth: Bridgman directional-solidification furnace with helical grain-selector or seed-crystal — Rolls-Royce, GE Aviation, Pratt & Whitney use this for HP turbine blades in CFM LEAP, GE9X, Trent XWB, F135. CMSX-4, René N5, PWA1484 are common SX alloys. Withdrawal rate typically 3-10 mm/min; thermal gradient at the liquidus front 30-100 K/cm.
• Variants: gypsum-mold investment for fine jewelry (R&R Plasticast); Solid Concepts QuickCast / 3D Systems SLA pattern (replaces tooled wax for prototype runs, hollow pattern collapses inward on burnout); ProtoCast and DigitalWax for printed wax patterns directly on tree; Hitchiner countergravity (mold inverted, melt drawn upward into shell by vacuum) for thin-section steel investment.

4. Die casting (HPDC)

High-pressure (40-150 MPa intensification) injection of molten metal into a hardened steel die, ~5-30 s cycle time. Near-net shape with as-cast surface roughness Ra 1-3 μm.

• Hot-chamber: gooseneck and plunger submerged in the melt; suitable only for metals that do not attack ferrous tooling at melt temperature — Zn, Mg, Sn, and some lead alloys. Shot-to-shot cycles can be 1-3 s on small Zn parts. Machines: Frech (Schorndorf), Toshiba, Italpresse. Common alloys: Zamak 3 and 5, ZA-8, AZ91 Mg.
• Cold-chamber: melt ladled per shot into a horizontal shot sleeve; used for Al, Cu, brass, and high-T Mg. Lower cycle rates (8-60 s) but compatible with abrasive aluminum melts. Machines: Bühler (Uzwil), UBE Machinery, Toshiba Machine (now Shibaura), Toyo, IDRA Group (Travagliato, Italy). Three-phase shot: slow-shot (avoid air entrainment in the sleeve), fast-shot (fill the cavity in 30-100 ms), intensification (40-100 MPa hold to feed shrinkage).
• Giga Press / IDRA OL series: 6,100-9,000 metric-ton locking force, single-shot rear underbody for Tesla Model Y (since 2020 Shanghai gigafactory) and Cybertruck, also used by Volvo, Toyota, Hyundai. IDRA acquired by LK Group; LK-IDRA’s “Giga Press” became a generic term but is technically a Tesla trademark. Toggle-style 9,000-T machines weigh ~430 t and have shot weights up to ~110 kg of Al. Tie-bar spacing ~3 × 3 m, dry-cycle <60 s.
• Vacuum-assisted die casting: die-cavity gas evacuated to 50-100 mbar before fill (Fondarex, V-DC, Castline), reduces gas porosity, enables T7 heat-treatment of structural Al castings. Required for Tesla Megacasting and equivalent BMW iX5 / Mercedes EQ-class structural castings. Specialty alloys with low Fe and Si (Silafont-36 from Rheinfelden, Castasil-37, Aural-2 from Rio Tinto, Mercalloy) developed specifically for vacuum HPDC of crash-loaded structural parts.
• Squeeze casting: applies 50-150 MPa hydrostatic pressure on the still-solidifying casting via a follower piston, eliminating shrinkage porosity. Used for aluminum suspension components (UBE squeeze-cast control arms, Honda S2000 rear knuckles). Indirect squeeze (UBE process) uses a vertical shot sleeve, direct squeeze uses an open-die press.
• Pore-free (PF) die casting: cavity flushed with pure O₂ before injection; the oxygen reacts with the Al melt to form fine Al₂O₃ instead of leaving gas porosity. Used in some Japanese plants for weld-quality castings.

5. Permanent mold (gravity PM)

Metallic mold (H13 tool steel or grey cast iron for Al, copper for steel-cast cooling cores), gravity fill from a ladle. Better grain refinement than sand because of higher cooling rate (10-100 K/s vs 1-10 K/s in sand); surface finish Ra 2-6 μm; secondary dendrite arm spacing (SDAS) ~25-50 μm vs ~50-150 μm in sand. Die life 25,000-100,000 shots for Al before refurbishment.

• Common uses: aluminum-alloy wheels (some applications), pistons (CP Carrillo, JE, Mahle, KS, Federal-Mogul), bronze bushings, hydraulic-valve bodies in Cu alloys, hand-tool bodies.
• Tilt-pour (book-mold) variant rotates the mold during fill for low-turbulence introduction — VAW (now Nemak), CMW.
• Die coatings (sodium silicate + insulating refractory) sprayed each cycle control die temperature and prevent soldering. Heated to 150-300 °C before each shot.
• Cosworth process is a sand-based hybrid that captures the same low-turbulence fill via electromagnetic pumping rather than gravity.
• Semi-permanent mold: metal mold + sand or salt cores for internal passages (a-pillar joints, cylinder heads).

6. Low-pressure die casting (LPDC)

Sealed furnace below the mold is pressurized with 0.3-1.0 bar of dry air or N₂, pushing molten Al up a stalk (refractory riser tube — typically Si₃N₄-bonded SiC or pre-fired clay-graphite) into the die from the bottom. Fill is laminar, gating waste is minimal (~10 % vs ~40 % for HPDC), and grain structure is finer than gravity PM. Cycle 3-8 min, suitable for runs of 10,000-500,000 pcs/yr.

• Dominant process for premium cast aluminum wheels: BBS, BMW M, Mercedes-AMG, OZ Racing, Enkei (flow-formed LPDC where the rim is spun-formed after casting the disc, yielding T6 properties).
• Also used for some structural aluminum body parts and cylinder heads where porosity matters more than cycle time (Audi, Porsche, BMW).
• Cooling controlled by air or water channels in the die halves, often staged to enforce directional solidification toward the gate.
• Counter-pressure casting (CPC, originated in Bulgaria by Balevski-Dimov in 1968) adds back-pressure on the mold cavity to suppress gas evolution further.
• Machines: Kurtz Ersa (Germany), Idra-Prince, Fata Aluminum.

7. Centrifugal casting

Hollow rotation-symmetric parts cast by spinning the mold so centrifugal force (typically 60-90 G at the bore) ejects light inclusions and gas to the bore, producing a dense outer skin and segregating dross to the inner-diameter machining stock.

• True centrifugal: horizontal-axis spinning mold, no central core. Ductile-iron and grey-iron water main + sewer pipe (DN80-DN2000) — Saint-Gobain PAM (Pont-à-Mousson, the de Lavaud process invented in 1918), McWane (USA, includes Atlantic States, Pacific States, Tyler Pipe), Kubota (Japan), Electrosteel (India), Jindal Saw. Also seamless steel rolling-mill rolls (Walzen Irle, Akers, Union Electric Steel, ESW Eschweiler), centrifugally-cast bimetallic engine cylinder liners, ESR-equivalent superalloy nozzle rings, and HK-40 / HP-modified reformer tubes for petrochemical service.
• Semi-centrifugal: vertical-axis spinning mold around a central sprue, for parts with a hub (railway wheels in some plants, gear blanks, fan rotors). Centrifugal force is used to feed and pressurize the casting, not to define the bore.
• Centrifuge: small parts (jewelry rings, dental crowns) gated radially around a center sprue and spun in a benchtop centrifuge (Neycraft, Kerr). Used in gold/silver/Co-Cr investment casting.

8. Continuous casting

Molten metal poured into a water-cooled copper mold from which a solidifying strand is continuously withdrawn while internal liquid still feeds the meniscus. Dominant casting route for primary steel and aluminum since the 1960s.

• Steel: curved-mold continuous casters with bender/straightener — SMS Concast, Danieli Davy, Primetals (formerly Siemens VAI / Mitsubishi-Hitachi MH). Slab casters (200-300 mm × 1000-2200 mm for plate and hot-rolled coil), bloom casters (300-500 mm sq for sections), billet casters (100-200 mm sq for bar and rod). Mold-flux powder (CaO-SiO₂-Al₂O₃ + alkali fluorides) on the meniscus controls lubrication and heat transfer. Electromagnetic stirring (EMS) at the mold or strand level refines columnar-to-equiaxed transition. Replaced ingot teeming + soaking-pit reheating at >97 % of world crude steel.
• Thin-slab casting: 50-90 mm slab cast direct from steelmaking and fed to a single hot-rolling line — Nucor / SMS CSP, Danieli QSP, ESP (endless strip production). Removed the slab-yard buffer from greenfield mini-mills.
• Aluminum: direct-chill (DC) casting for rolling and extrusion ingots — Wagstaff (USA), Hertwich (Austria, now SMS), Pyrotek. Continuous strip casting (Hazelett twin-belt, Hunter-Douglas, Fata Hunter). Properzi wheel-and-belt for Al rod (later adapted to Cu). DC start-up is the highest-risk part of the heat: “butt curl” and “cold-shut” defects controlled by graphite ring + wiper + initial water-flow ramp.
• Copper: Continuus-Properzi (Italy) and SCR Southwire wheel-and-belt rod-mills produce 8 mm copper redraw rod direct from cathode and scrap (FRHC, fire-refined high-conductivity). Outokumpu Up-cast for oxygen-free OFE-C10100 rod (vertical upward draw through a water-cooled die).
• Twin-roll strip casting: Castrip (Nucor / BHP / IHI) and POSCO-Daewoo cast 1-3 mm carbon-steel strip direct between water-cooled copper rolls — collapses the hot-strip mill into one machine for niche grades.
• Strand quality controls: mold-level control (eddy-current or Co-60 / Cs-137 radiometric), mold-oscillation frequency and stroke (sinusoidal or non-sine to reduce oscillation marks), soft-reduction (squeezing the strand near final solidification to break up centerline segregation), and dynamic secondary cooling.

9. Lost-foam (full-mold / evaporative-pattern casting, EPC)

Expanded-polystyrene (EPS) foam pattern coated with a thin refractory wash, embedded in dry unbonded silica sand, vibrated to fill internal cavities, then poured — metal pyrolyzes the foam and replaces it 1:1. No parting line, no cores, no draft requirement — complex internal passages and undercuts cast in one piece.

• General Motors Saturn 4.6 L Northstar V8 (Bedford foundry) was a benchmark 1990s lost-foam program. Today widely used for V8 cylinder heads, intake manifolds, brake calipers, and pump housings. Mercury Marine, Tupy, Brillion, Citation also major producers.
• The foam is fused from pre-expanded beads in an aluminum tool (similar to EPS packaging tooling but tighter — bead size <1 mm for thin walls). Pattern density 18-28 g/L. Coating thickness 0.1-0.5 mm controls gas permeability.
• Variants: Replicast (replaces foam with a ceramic shell, used for steel — eliminates foam-pyrolysis carbon pickup), and lost-PLA for one-off art castings using a 3D-printed pattern.

10. Plaster + ceramic-mold casting

• Plaster (Antioch process): gypsum-bonded slurry (CaSO₄·½H₂O + bentonite + perlite + talc + fiber) poured around a pattern, autoclaved to convert α to β gypsum, fired at ~750 °C. Used for tooling-grade aluminum prototypes, fine-detail aluminum bronze, and jewelry (R&R Plasticast). Surface finish Ra ~1-2 μm; dimensional accuracy ±0.1 mm; mold permeability is low so the process is best for thin sections and works mainly with low-T metals (Al, Mg, Zn, Cu).
• Ceramic-mold (Shaw process): ethyl-silicate slurry on a flexible silicone master, ignited to give the characteristic micro-crazed surface (relieves shrinkage and adds permeability), fired and cast. Used for plastic-injection mold inserts, forging dies, glassware dies, and special pump impellers in tool steel and stainless. Tolerances close to investment but with much larger parts (up to ~1 t).
• Unicast (Hitchiner): rigid ceramic-shell variant that combines investment-like detail with low-cost slurry.

10a. Cores — internal-passage strategy

Cores are the second tooling stream beside the mold itself; they form internal passages and undercuts that cannot be moulded by pattern halves. Core technology often dictates what process is feasible:

• Sand cores: PUCB (cold-box, Ashland Isocure), shell (Croning), Inotec (inorganic silicate, Ask Chemicals — used in Audi/BMW Al cylinder heads, low VOC), warm-box and hot-box.
• Salt cores: NaCl / K₂SO₄ / Na₂CO₃ pressed or printed, water-soluble — used in HPDC for deep undercuts (e.g. cooling jackets in pistons); pioneered by Mahle and KS.
• Metal cores: collapsible steel cores (mostly in PM and squeeze) or sacrificial low-melt cores.
• Ceramic cores: hot-pressed silica or alumina for investment-cast turbine-blade serpentine cooling channels; leached out post-cast in KOH or NaOH autoclave.
• 3D-printed cores: binder-jet (ExOne, voxeljet) — produces highly complex water-jacket cores that cannot be tooled.

11. Vacuum casting

• Vacuum induction melting + investment cast (VIM-VIC): standard for reactive and oxidation-sensitive superalloys (Co-Cr-Mo orthopaedic implants, Ti dental, Inconel 718 turbine wheels). Furnaces: Consarc, ALD Vacuum Technologies (Hanau), Inductotherm. Chamber pressures 10⁻²-10⁻⁴ mbar; melt held under vacuum or partial Ar; tilt-pour into pre-heated shell.
• Vacuum-assisted countergravity: Hitchiner CLA / CLV — mold inverted above the melt, vacuum draws metal upward through a fill tube. Excellent yield (gating <10 %), used for thin-section steel and superalloy investment.
• Vacuum-urethane (room-temperature): silicone-mold copy of an SLA or CNC master, filled with two-part polyurethane (PU 7400, Axson F-180, Hei-Cast) under vacuum. Production runs 1-50 of plastic prototypes. Vendors: Stratasys, MK Technology, Multistation.
• Vacuum die casting: see §4 — vacuum-assisted HPDC for structural Al, distinct from vacuum-investment.

12. Semi-solid metal forming (SSM) — squeeze, thixo, rheo

Forms metal in a partially-solidified state (typically 30-60 % solid fraction f_s) where rheology is thixotropic — viscosity drops by orders of magnitude under shear — and fill is laminar (Reynolds number <100). Originated from MIT work by Mehrabian and Flemings in 1971 (“stir-casting”).

• Thixoforming / thixocasting: pre-cast slug with globular (not dendritic) primary phase is reheated to the semi-solid window (e.g. 580 °C for AlSi7Mg, ~50 % f_s) and force-fed into a die. Done in Sn, Mg, and AlSi7Mg. LANXIDE and Madison-Kipp ran commercial Al thixocasting in the 1990s-2000s. The globular feedstock is produced by magneto-hydrodynamic (MHD) stirring during DC casting (Pechiney, SAG).
• Rheocasting (NRC — New Rheocasting, UBE; SEED — Alcan / Rio Tinto; CRP — STAMPAL; SLC — Toyo): melt cooled into the semi-solid window in-line then injected — eliminates the cost of pre-cast feedstock and the reheat step.
• Sub-liquidus casting and Idra-Prince gas-induced semi-solid (GISS): simpler variants generating globular primary phase by gas-bubble nucleation.
• Applications: aluminum suspension links, steering knuckles, control arms, brake calipers — wherever fatigue + leak-tightness demand low porosity. Mg thixomolding (Thixomat / JSW) used for laptop and camera housings.

12a. Gating, risering, and feeding

A casting is only as good as its gating and feeding system. Gating routes the melt from pouring basin through the sprue, runner, ingate, and into the cavity; risers (feeders) provide a reservoir of liquid metal that solidifies last and feeds shrinkage in the casting.

• Gating principles (Campbell): keep filling velocity below 0.5 m/s in Al, below 1.5 m/s in Fe; use bottom-fill or tilt-pour where possible; pressurized vs unpressurized systems trade off priming time against oxide entrainment; filters (Foseco SIVEX, Selee CS) at the ingate trap dross.
• Risering: Chvorinov’s rule t_s = B·(V/A)² says the longest-solidifying part of the package should be the riser, not the casting. Modulus method: M_riser ≥ 1.2 × M_casting_hotspot.
• Risering aids: exothermic sleeves (Foseco KALMINEX, Hofmann; ASK FEEDEX) extend liquid-feed time; insulating sleeves slow heat loss; risers may be live (in the gating path) or dead (top of casting).
• Chills: external (steel block) or internal (cast-in steel pad) accelerate local solidification to steer the hot spot away from undercut features.

13. Specialty — 3D-printed sand and patterns

• 3D-printed sand molds and cores (binder-jet): ExOne S-Max and S-Print, voxeljet VX1000 / VX2000 / VX4000, Loramendi (now part of voxeljet), Desktop Metal/ExOne. Furan or phenolic binder on silica, ceramic, or chromite sand; layer thickness 280-500 μm; build envelopes up to ~4 m × 2 m × 1 m. No pattern tooling required. Used for low-volume aluminum (1-200 pcs), prototype iron engine blocks, complex sand cores for automotive cylinder heads. Integrates with conventional foundry workflow — printed cores assembled into otherwise-conventional packages. Hirtenberger Engineered Surfaces, Hetitec, Voxeljet US (Canton MI), Cadillac, GM, Ford, BMW use it for engine and powertrain prototypes.
• 3D-printed wax / SLA patterns for investment: ProJet MJP from 3D Systems, DigitalWax 028J, EnvisionTEC Perfactory, Solidscape (wax-jet for jewelry and dental). Replaces hard tooling for prototype turbine-blade development and dental.
• Hybrid printed-pattern + cast: jewelry chains routinely 3D-print wax direct to shell (no aluminum tool) using DLP or SLA wax resins.
• Wire-arc and powder-bed metal AM is not casting (no mold, no liquid pour) but competes with low-volume castings — see [[Engineering/Tier3/additive-manufacturing-taxonomy]].

13a. Simulation and design tools

Casting process simulation (CFD + heat transfer + phase transformation) is now mandatory for new high-value tooling:

• MAGMASOFT (MAGMA, Aachen) — long-standing dominant package, particularly strong in iron and Al.
• FLOW-3D CAST (Flow Science) — derived from the original Hirt-Nichols Volume-of-Fluid solver, strong free-surface tracking.
• ProCAST (ESI Group) — FE-based, strong in stress / distortion prediction post-solidification.
• AnyCasting, Click2Cast (Altair), SOLIDCast / FLOWCast (Finite Solutions) — mid-range alternatives.
• THERCAST (Transvalor) — focused on continuous casting and ingot.

Outputs: mold-filling sequence, solidification time field, hot-spot map, Niyama criterion (shrinkage-porosity proxy), residual stress, microstructure prediction (CET — columnar-to-equiaxed transition, SDAS, phase fractions).

14. Cast alloys and nominal melt temperatures

Alloy family	Nominal pour T (°C)	Common processes
Sn-Pb / Sn-Sb	240-300	Hot-chamber die-cast, sand, jewelry
Zn (Zamak 3 / 5 / ZA-8)	419-440	Hot-chamber HPDC (workhorse)
Mg (AZ91, AM60)	650-720	Hot-chamber HPDC (small parts), cold-chamber (large), thixo
Al (A356, A380, A413)	660-760	HPDC, LPDC, gravity PM, sand, investment
Cu / brass / bronze	950-1080	Sand, PM, investment, centrifugal
Grey + ductile cast iron	1150-1300	Green-sand (bulk), no-bake, centrifugal pipe
Cast steel (WCB, CF8M)	1500-1700	No-bake sand, shell, investment, lost-foam (Replicast)
Co / Ni superalloy (CMSX-4, IN718, René N5)	1450-1500	Vacuum investment + DS/SX in Bridgman furnace
Ti (Ti-6Al-4V)	~1670	Vacuum investment with zirconia / yttria face-coat; rammed graphite

Ti casting requires a non-reactive face-coat (Y₂O₃, ZrO₂, CaO) because conventional silica face-coats reduce on contact with molten Ti, causing α-case. Mg melts must be protected from oxidation by SF₆ / SO₂ / Novec 612 cover gas (the SF₆ industry is phasing out due to its GWP of ~24,000 — Novec 612 from 3M and HFC-134a are the modern replacements).

Common cast-alloy designations

• Al: A356 (Al-7Si-0.3Mg, gravity / LPDC, T6 heat-treatable), A380 (Al-8.5Si-3.5Cu, HPDC general-purpose), AlSi10MnMg / Silafont-36 (HPDC vacuum-cast structural), A206 (Al-Cu, high-strength sand and PM), A201, 535 (Al-Mg).
• Mg: AZ91D (Al-9 Zn-1 die-cast), AM60 (Al-6 Mn ductile), AE44 (Al-RE, creep), AS41 (Al-Si).
• Zn: Zamak 3 / 5 / 7 (Zn-Al-Cu, hot-chamber die), ZA-8 / ZA-12 / ZA-27 (higher-Al variants for gravity).
• Cu: C83600 leaded red brass (sand), C90300 tin-bronze, C95400 / C95500 aluminum-bronze, C86300 manganese-bronze.
• Cast iron: G2500 / G3000 / G3500 grey (ASTM A48 class 25-35), ductile / nodular iron 60-40-18, 80-55-06, 100-70-03 (ASTM A536); austempered ductile iron (ADI) ASTM A897 grades 1-5; CGI (compacted graphite, ASTM A842) for diesel cylinder blocks.
• Cast steel: WCB / WCC (carbon, ASTM A216 for pressure-containing parts), CA-15 / CA-40 (martensitic stainless), CF8 / CF8M (austenitic stainless, ASTM A351), HK-40 / HP-modified (high-T centrifugally cast reformer tubes).
• Ni-superalloys: IN-738, René 80, René N5 (SX), CMSX-4 (SX), PWA1484 (SX), Mar-M247 (DS / EQ).
• Co-superalloys: MAR-M509, X-40, FSX-414 (older IGT blades).

15. Defects and inspection

Common defects (Campbell taxonomy):

• Gas porosity: dissolved H₂ in Al (from moisture, hydrocarbon, refractory wash), or entrapped air from turbulent fill. Mitigated by degassing (rotary impeller Ar lance — Foseco MTS, Hycast), vacuum, low-turbulence gating. Measured by reduced-pressure-test (RPT) density index and by Alspek-H electrochemical probe.
• Shrinkage porosity: insufficient liquid feed in the last-to-freeze region. Mitigated by risers, chills, hot-tops, sequenced solidification (modulus method, Chvorinov’s rule t_s = B·(V/A)²), and exothermic / insulating sleeves on risers (Foseco KALMINEX, Hofmann).
• Cold shut / misrun: melt too cold, mold cavity not fully filled — increase superheat or vent area; redesign gating for shorter path.
• Hot tear / hot crack: tensile stress on a partially-solid alloy near the solidus, especially in long-freezing-range alloys (Al-Cu, some Mg). Mitigated by reducing constraint, adding fillets, controlling cooling, choosing a shorter-freezing-range alloy.
• Macrosegregation / inverse segregation: solute redistribution during solidification, including “tin-sweat” in bronzes — limited by alloy choice and cooling, in continuous casting by EMS.
• Inclusions: oxide skins (“bifilms” — Campbell, the dominant defect in Al castings), refractory pieces, mold material (sand wash), slag entrainment. Filtered with foam-ceramic or pressed-mesh filters (Foseco SIVEX, Selee, Vesuvius).
• Sand wash + erosion scab: poor mold compaction or hot-spot erosion of green-sand surface.
• Veining and metal penetration: thermal expansion of silica sand at ~573 °C (α-β quartz inversion) cracks the mold surface, metal flows in to form fins; mitigated with zircon, olivine, or chromite sand at hot spots, or with engineered additives (Veinseal).

Defect-acceptance standards: ASTM E155 (Al), ASTM E186 / E280 / E446 (steel), ASTM E192 (investment), MIL-STD-2175 (legacy), AMS 2175 (current), NADCA Q1 / Q2 / Q3 dimensional and porosity classes for die castings, ASME B&PV Code Section VIII for cast pressure parts.

Inspection methods:

• Radiography (RT): 2D X-ray, ASTM E155 reference radiographs for Al castings, ASTM E186 / E446 for steel.
• Computed tomography (CT): 3D internal mapping for high-value castings — Zeiss Metrotom, Nikon XT H, GE Phoenix v|tome|x. Becoming standard for HPDC structural castings.
• Ultrasonic (UT): for thick sections, phased-array for complex geometry.
• Magnetic-particle inspection (MPI): ferrous surface and near-surface flaws — wet fluorescent under UV-A.
• Dye penetrant (PT): surface flaws on non-ferrous and ferrous, ASME V Article 6.
• Visual + dimensional (CMM, blue-light scanning) for first-article inspection.
• Spectroscopic chemistry: optical emission spectroscopy (OES — Thermo ARL iSpark, SPECTROMAXx) on every melt for shift-by-shift composition control; sample disc cast from each ladle.
• Reduced-pressure test (RPT): sample of melt solidified under 80 mbar vacuum, density vs an atmospheric sample gives the Hydrogen-Bifilm Index for Al.

14a. Melt preparation and treatment

Each alloy family has its standard melt-treatment chemistry; getting this right is the dominant determinant of casting quality:

• Aluminum: rotary degassing with Ar (or N₂) at 250-450 rpm for 8-15 min reduces dissolved H from ~0.35 to <0.10 mL/100 g. Salt fluxes (NaCl/KCl + cryolite Na₃AlF₆) skim oxide; ceramic-foam filter at the launder; grain refiner Al-5Ti-1B (3-5 ppm Ti retained); Sr modification of Al-Si eutectic (150-300 ppm).
• Grey + ductile iron: spheroidizing treatment with FeSiMg (typically 5-9 % Mg) by sandwich, tundish-cover, or in-mold method; post-inoculation with FeSi75 + Ba/Sr/Zr for nucleation control.
• Steel: ladle deoxidation with Al / FeSi / SiMn; degassing in vacuum-degasser (RH, VOD, VAD) for low-S, low-N grades; Ca-Si wire injection to modify Al₂O₃ inclusions into globular calcium-aluminates.
• Copper alloys: deoxidation with phosphorus (CuP15); cover flux of charcoal or glass to prevent reoxidation; degassing with N₂ for high-conductivity grades.
• Mg: cover-gas (SF₆ phasing out, replaced by Novec 612 or SO₂); flux-free protective melting; grain refinement with Zr in Mg-Zn / Mg-RE; superheating + cool down (“carbon-inoculation”) for Al-containing systems.

15a. Process-capability summary

Process	Min wall (mm)	Surface Ra (μm)	Tol class (ISO 8062 CT)	SDAS (μm)	Tooling cost	Cycle (s)	Run economic from
Green-sand (automated)	3-5	12-25	CT10-CT12	50-150	low-med	10-30	100 pc
No-bake sand	4-6	12-25	CT11-CT13	70-200	low	600-3600	1 pc
Shell-mold	2.5	5-10	CT8-CT10	30-80	medium	60-180	1,000 pc
Investment	0.6	1-3	CT5-CT7	20-60	medium	1800-7200	100 pc
Plaster	1	1-2	CT6-CT8	60-150	low-med	1800-7200	10 pc
Gravity PM	3	2-6	CT7-CT9	25-50	high	60-300	5,000 pc
LPDC	2	1.5-3	CT6-CT8	20-40	high	180-480	10,000 pc
HPDC (cold-chamber)	0.8	1-3	CT5-CT7	5-25	very high	8-60	25,000 pc
HPDC (hot-chamber Zn)	0.4	0.8-2	CT4-CT6	n/a	very high	1-5	50,000 pc
Lost-foam	2	5-15	CT9-CT11	30-80	low	60-300	1,000 pc
Centrifugal (true)	5	6-12	CT9-CT12	n/a	medium	60-600	per part
3D-printed sand + gravity	3	12-25	CT10-CT12	50-150	none	1800-3600	1 pc

(Values are typical ranges, not specification; thinner walls are achievable with optimization. SDAS values are for Al alloys.)

16. Selection heuristics by quantity and alloy

Volume / use	Recommended process
1-10 pc prototype Al, complex geometry	SLA pattern + investment, or vacuum-urethane copy, or 3D-printed sand mold + gravity cast
100-1,000 pc Al, medium complexity	3D-printed sand mold + gravity, or LPDC if rotation-symmetric (wheel)
10,000-1,000,000 pc Al, near-net	Cold-chamber HPDC (vacuum-assisted if structural)
Cast-iron pipe (large run)	Horizontal-axis true centrifugal
Precision Co-Cr-Mo orthopaedic	Vacuum investment + HIP (hot isostatic pressing)
Single-crystal HP turbine blade	Directionally-solidified investment in Bridgman furnace
Pump impeller, bronze	No-bake sand + heat-treat
Gun-barrel forging blank	Centrifugal cast hollow then forge / rotary-pierce
Structural rear-underbody EV body	Vacuum-assisted Giga HPDC Al (IDRA / LK 6,100-9,000 T)
Engine cylinder block, premium	Cosworth precision sand (low-turbulence), or lost-foam
V8 cylinder head, high-volume	Lost-foam or semi-permanent mold
Jewelry ring	Investment in plaster, centrifuge cast
Steel slab for hot-rolled coil	Continuous caster (curved-mold)
Al billet for extrusion	Direct-chill (DC) continuous

16a. Yield, economics, and post-processing

• Casting yield (poured-to-shipped mass ratio): green-sand iron 50-75 %, no-bake steel 40-65 %, LPDC Al 85-92 %, HPDC Al 50-70 % (large overflows + biscuit), investment 25-50 % (large gating + tree), centrifugal pipe ~95 %, continuous casting >97 %.
• Energy intensity: secondary Al melting ~3-7 GJ/t, electric-arc steel ~2-2.5 GJ/t, blast-furnace + BOF steel ~17-20 GJ/t. Holding furnaces (electric resistance vs gas-fired tower vs induction) drive 20-50 % of foundry energy bill.
• Post-processing chain for Al castings typically: trim press → degate → shot-blast → heat-treat (solution + quench + age — T5, T6, T7) → straighten → machine → leak-test → impregnation (Henkel Loctite Resinol or Maldaner) if porosity present → final inspection. HIP (hot isostatic pressing — 100-200 MPa Ar at 480-530 °C for Al, 1100-1200 °C for superalloys) used to close residual shrinkage porosity in aerospace and medical castings.
• Inoculation and grain refinement: ferrosilicon-magnesium (FeSiMg) in-mold or in-ladle treatment converts grey iron to ductile (nodular) iron — process invented at INCO 1948. Al melts grain-refined with Al-5Ti-1B master alloy (Hoogovens, KBM Affilips); Sr or Na for Al-Si eutectic modification.
• Sand reclamation: thermal (700-800 °C oxidation of binder), mechanical (attrition), or wet — closes the loop on chemically-bonded sand. >90 % reuse achievable, dropping new-sand cost and landfill volume.

16b. Common pitfalls when specifying castings

• Designing in HPDC porosity-sensitive features: bolted joints with through-holes for high-torque fasteners; pressure-tight seal grooves. Mitigate with insert-molded threaded inserts, or a vacuum-assisted die-cast variant.
• Over-tight tolerance specs: calling out CT5 on a green-sand part doubles cost; relax non-functional surfaces and let only the machined faces hold the close tolerance.
• Wall-thickness extremes: very thin sections (cold shut risk) joined to heavy bosses (hot-spot porosity risk) in one part. Add draft, equalize wall thickness, or split the casting.
• Ignoring the heat-treat distortion: T6 quench of large Al castings introduces residual stress; designers should add finish-machining allowance for warpage or specify a low-distortion quench (polymer quench, uphill quench).
• Wrong alloy for the process: e.g. A356 (heat-treatable, low-Fe) chosen for HPDC where conventional A380 with higher Fe (anti-soldering) would be the production-feasible choice.

17. Cross-references

• [[Engineering/casting-forging-forming]] — Tier 2 parent: solidification, Chvorinov’s rule, riser design, mold-metal heat transfer.
• [[Engineering/Tier3/aluminum-alloys]] — heat-treatable vs non-heat-treatable, casting-specific grades (A356, A380, AlSi10Mg, Silafont-36 / Castasil-37 for structural HPDC, A206 high-strength).
• [[Engineering/Tier3/steel-grades]] — cast-steel families (WCB, WCC, CA-15, CF8M).
• [[Engineering/Tier3/copper-alloys]] — cast bronzes (C90300 tin-bronze, C95400 aluminum-bronze, C83600 leaded red brass).
• [[Engineering/Tier3/forming-processes]] — downstream rolling, forging, extrusion of continuous-cast feedstock.
• [[Engineering/Tier3/additive-manufacturing-taxonomy]] — competing and complementary near-net process for low-volume metal parts.
• [[Engineering/Tier3/ceramics-taxonomy]] — shell systems and refractory materials.

17a. Standards and bodies

• AFS (American Foundry Society, Schaumburg IL) — Mold and Core Test Handbook, Casting Defects Handbook, training and certification.
• NADCA (North American Die Casting Association) — die-cast product specifications, dimensional tolerance classes, surface-finish references.
• DGV (Deutscher Gießereiverband, Düsseldorf) — German foundry association.
• JFS (Japan Foundry Society).
• WFO (World Foundry Organization).
• CDA (Copper Development Association) — alloy data and casting practice for Cu.
• DIS (Ductile Iron Society) — ductile iron metallurgy.
• ASTM committees A04 (iron castings), A01 (steel), B07 (light metals castings), E07 (NDT).
• ISO 8062 — geometric tolerances for cast metal parts; ISO 17025 for foundry test labs.
• ASME B&PV Code Sec II Part A (cast pressure-vessel materials), Sec VIII Div 1 (design).
• API 6A / API 6D — wellhead and valve castings for oil & gas.

17b. Environmental and worker safety

• Silica dust (RCS, respirable crystalline silica): OSHA PEL 50 µg/m³ since 2017 — drove wet/HVAC controls, change to non-silica sand systems (olivine, chromite, ceramic). NIOSH REL 50 µg/m³.
• Foundry emissions: VOCs (benzene, formaldehyde) from urethane and phenolic binders, SO₂ from acid-catalysed furan, PM10/PM2.5 from shake-out and shotblast. Captured at source with hooded extraction and treated with regenerative thermal oxidizers (RTO) or wet scrubbers.
• Waste sand and slag: spent sand is increasingly reclaimed thermally; slag from EAF and cupola is sold for cement, abrasive, or road base.
• SF₆ in Mg casting is being phased out (EU F-Gas regulation 2014/517) in favor of HFC-134a, Novec 612 (3M), or sulfur trioxide cover gas.
• CO₂ intensity: a key reason for the shift from BF-BOF (primary steel ~2 t CO₂/t product) to EAF + scrap (~0.4 t CO₂/t product), and from primary Al (~12 t CO₂/t) to secondary Al (~0.5 t CO₂/t).

17c. History and milestones

• ~5000 BCE — earliest known copper castings (Mesopotamia, Indus).
• ~2000 BCE — lost-wax (cire-perdue) casting used in the Indus Valley and ancient Egypt.
• ~500 BCE — large iron casting in China (Han Dynasty cupola furnaces, cast-iron plowshares).
• 1455 — Gutenberg movable type cast in Pb-Sn-Sb alloy.
• 1709 — Abraham Darby coke-fired blast furnace at Coalbrookdale, enabling cheap pig iron.
• 1838 — Sturges patents pressure die casting for printing type (Sn-Pb).
• 1849 — Sturges and Bruce expand die casting commercially.
• 1907 — Doehler develops cold-chamber die casting for Al.
• 1918 — de Lavaud horizontal centrifugal pipe casting.
• 1936-38 — General Motors’ first continuous Al billet casting (Junghans-Rossi).
• 1944 — Croning patents shell-mold (Germany).
• 1948 — INCO patents Mg-treatment of grey iron to produce ductile / nodular iron.
• 1952 — first commercial continuous steel caster (Halliday at Atlas Steels, Welland, Ontario).
• 1958 — Bridgman directional solidification adopted by Pratt & Whitney for turbine blades.
• 1964 — Disamatic vertical-flask green-sand line (DISA, Denmark).
• 1971 — Mehrabian, Spencer, Flemings publish on semi-solid stir-casting (MIT).
• 1980s — single-crystal turbine blades enter production (PWA1480, René N4).
• 1990s — vacuum-assisted HPDC enables T6-treatable structural Al castings.
• 2017 — Tesla orders first IDRA Giga Press for Model Y rear underbody.
• 2020s — large vacuum HPDC mega-castings (rear and front underbody) become a body-engineering standard for several EV programs.
• 2023 — IDRA 9,000-tonne Giga Press enters service for the Tesla Cybertruck rear-underbody single-piece casting.
• 2024-2025 — single-piece front + rear underbody castings (so-called “unbody”) appear in pre-production for Volvo EX90 (Olofström), Toyota Performance Manufacturing Co., Hyundai EV body programs.

17d. Open research and future directions

• Larger and integrated mega-castings: increasing share of EV body engineered as 2-3 large vacuum HPDC structural castings, eliminating hundreds of stamped + welded body parts. Constrained by die life (currently ~80,000-100,000 shots), alloy fatigue, and crash energy management.
• Net-shape additive + cast hybrids: 3D-printed mold inserts (conformal cooling for HPDC dies via SLM tool steel), 3D-printed cores integrated with cast structures, hybrid AM-printed bosses welded to conventional cast bodies.
• In-process sensing and digital twin: real-time pressure / temperature / cavity-fill sensors in die cavities (Kistler, Buehler smart die) feeding model-predictive control. Casting porosity learned from CT and back-propagated to gating design.
• Low-CO₂ binder systems: inorganic (Inotec, Cordis) and bio-based binders to displace phenolic and furan in core-making.
• Recycled-alloy structural castings: tighter melt management (sub-100 ppm Fe in Al via electromagnetic or sedimentation refining) to enable high-scrap-content structural HPDC alloys.

18. Citations

• AFS, Mold and Core Test Handbook, 4th ed., American Foundry Society, 2015.
• ASM International, ASM Handbook Volume 15: Casting, 2008.
• J. Campbell, Castings, 2nd ed., Butterworth-Heinemann, 2003.
• J. Campbell, Complete Casting Handbook, 2nd ed., Butterworth-Heinemann, 2015.
• P. R. Beeley, Foundry Technology, 2nd ed., Butterworth-Heinemann, 2001.
• AFS, Casting Defects Handbook (alloy-specific volumes — Al, Mg, Cu, ferrous).
• E. J. Vinarcik, High Integrity Die Casting Processes, Wiley, 2003.
• W. Kurz and D. J. Fisher, Fundamentals of Solidification, 4th ed., Trans Tech, 1998 — for the continuous-casting and Bridgman SX physics.
• M. C. Flemings, Solidification Processing, McGraw-Hill, 1974.
• M. M. Avedesian and H. Baker, ASM Specialty Handbook: Magnesium and Magnesium Alloys, ASM International, 1999.
• NADCA Product Specification Standards for Die Castings, North American Die Casting Association.
• AFS Aluminum Casting Technology, 2nd ed.