Sand Casting: Uses sand packed around a pattern to form a mold.
Sand casting
involves the pouring of molten metal into a cavity-shaped sand mould where it
solidifies. The mould is made of sand particles held together with an inorganic
binding agent. After the metal has cooled to room temperature, the sand mould is
broken open to remove the casting. The main advantage of sand casting is the low
cost of the mould, which is a large expense with permanent mould casting methods.
The process is suitable for low-volume production of castings with intricate
shapes, although it does not permit close tolerances and the mechanical properties
of the casting are relatively low owing to the coarse grain structure as a result
of slow cooling rate.
Process:
Pattern Making: A pattern of the part (usually wood, plastic, or metal) is made
slightly oversized to account for shrinkage.
Mold Preparation:
Pattern is placed in a flask and packed with sand mixed with clay and water (green
sand) or chemically bonded sand.
Mold is made in two halves (cope and drag).
Core Placement (if needed): Hollow parts require sand cores placed inside the mold
cavity.
Mold Assembly: Cope and drag are aligned, gating and risers are prepared.
Pouring: Molten metal is poured into the mold through the sprue and gating system.
Cooling & Solidification: Metal cools and solidifies inside the mold cavity.
Shakeout: Sand mold is broken, casting removed.
Finishing: Excess metal (flash, risers, sprues) removed, surface cleaned.
Applications: Large components (engine blocks, machine tool beds, pump housings,
ship propellers).
Plaster Casting: Similar to sand casting but uses plaster for finer detail. The
plaster casting process involves mixing a plaster of Paris and water slurry,
pouring it into a prepared mold, and allowing it to set and harden. After it has
cured, the plaster cast is removed from the mold. This versatile process can be
used to create detailed objects from materials like wax, resin, and even molten
metal, though it produces an expendable mold meant to be broken to release the cast
Process:
Pattern Preparation: A pattern of the part (often metal or plastic) is made.
Mold Formation: A slurry of plaster of Paris (CaSO₄·½H₂O), talc, and silica flour
is poured over the pattern inside a flask.
Setting & Drying: Plaster slurry sets and hardens around the pattern. Mold is
carefully removed and baked to remove moisture.
Core Formation (if needed): Plaster cores can be made for hollow parts.
Mold Assembly: Mold halves are assembled with gating system.
Pouring: Molten metal is poured into the plaster mold.
Cooling & Solidification: Mold provides smooth surfaces due to fine plaster
particles.
Breakout: Plaster mold is broken to remove the casting.
Applications: Aluminum, magnesium, and zinc alloys; small to medium intricate
shapes, prototypes, aerospace parts.
Investment Casting (Lost-Wax): Involves creating a wax replica, coating it in
ceramic, and then melting out the wax to pour molten metal. Investment casting is a
manufacturing process in which a wax pattern is coated with a refractory ceramic
material. Once the ceramic coating material is dry and hardened, the wax is melted
out and leaves an internal cavity the shape of the final product’s geometry. Molten
metal is poured into the cavity where the wax pattern was. The metal solidifies
within the ceramic cavity, cools, and the ceramic is removed from the metal
casting. The result of this process is a net to near-net precision metal component
which can be used for a broad range of applications in various industries.
Process:
Wax Pattern Creation: Wax replicas of the part are made using injection molding.
Pattern Assembly: Wax patterns are attached to a wax sprue to form a tree (for
multiple castings).
Ceramic Shell Building: Tree is dipped repeatedly in ceramic slurry and coated with
fine sand, drying between coats until a thick ceramic shell forms.
Wax Removal: The ceramic shell is heated, melting out the wax (hence "lost wax").
Mold Firing: Ceramic shell is fired at high temperature for strength and removal of
residual wax.
Pouring: Molten metal is poured into the preheated ceramic mold.
Cooling & Solidification: Metal takes the shape of the precise mold cavity.
Shell Removal: Ceramic shell is broken off after solidification.
Finishing: Sprues and risers are cut off, surface finished.
Applications: Turbine blades, surgical implants, jewelry, aerospace components,
small intricate parts.
Shell Molding: Uses a thin shell of sand held together by a resin to form the mold,
offering better surface finish than traditional sand casting.A heated metal pattern
is coated with a fine sand + thermoset-resin mixture. The resin partly cures from
pattern heat and forms a thin rigid shell (single or multiple coats). Two shell
halves are assembled, clamped, and metal is poured. After cooling the shells are
broken away.
Process:
A heated metal pattern (coated with release agent) is prepared.
Fine silica sand mixed with thermosetting resin is poured over the pattern.
The resin-coated sand partially melts and sticks, forming a thin shell layer.
Excess sand is removed; the process is repeated until the desired shell thickness
is achieved.
Two shells are cured, stripped, and clamped together.
Molten metal is poured, and after cooling, the shell mold is broken.
Applications: Gear housings, cylinder heads, small precision parts.
Lost-Foam Casting: Uses a foam pattern that is vaporized by the molten metal,
leaving a mold cavity.A foam (usually polystyrene) pattern is made to final shape
(can be complex, assembled). Pattern is often coated with a refractory slurry,
embedded in unbonded sand, and molten metal is poured directly onto/into the foam.
The foam vaporizes and metal fills the space.
Process:
A foam pattern (usually polystyrene) is created—can be assembled from segments.
The foam pattern is coated with refractory slurry for stability.
The coated pattern is placed in a flask and surrounded by unbonded sand.
Molten metal is poured directly onto the foam pattern.
The foam vaporizes, leaving the metal to occupy its space.
Applications: Automotive engine blocks, crankshafts, complex shapes.
Full Mold (or Evaporative-Pattern Casting): Similar to lost-foam, it uses a
disposable pattern.A foam pattern fills the mold volume; unlike classic LFC the
pattern may be larger assemblies and the process often uses different
coating/packing practices. Foam evaporates on metal contact; metal fills the
evacuated region.
Process:
A foam pattern is made (similar to lost-foam).
Instead of coating with slurry, the pattern is buried in dry sand and vibrated for
compaction.
Metal is poured directly into the foam-filled mold.
Foam vaporizes completely, leaving the casting behind.
Applications: Large, complex parts like machine tool beds, pump housings.
Ceramic Casting: Uses ceramic slurry to create the mold, similar to investment
casting but often with higher temperature metals.A rigid ceramic mold is built
around a pattern (can be lost-wax-style or from other patterns). Ceramic
formulations are tailored for higher melting point metals; molds are dried/fired
before pour.
Process:
A wax or plastic pattern is created.
The pattern is dipped repeatedly in ceramic slurry and fine sand until a thick
shell is built.
The shell is dried and hardened.
The wax or plastic is melted out (lost-wax principle).
Molten metal is poured into the ceramic mold.
After solidification, the ceramic is broken away.
Applications: Jet engine turbine blades, aerospace components.
Die Casting ( Expendable Mold Variation): A subset where a mold is used repeatedly
for a certain number of parts, but the mold material might be consumed over time,
or a variant uses a disposable mold.Molten metal is injected into a metal die under
pressure (hot- or cold-chamber machines depending on alloy). “Expendable die
variation” refers to setups where die surfaces or liners are sacrificial/consumable
for a limited number of cycles (used for reactive metals or prototype runs).
Process:
A mold cavity is prepared, often with high-pressure injection equipment.
Molten metal (aluminum, zinc, magnesium) is forced under pressure into the cavity.
Mold sections may wear or erode with repeated cycles—hence limited “expendable” use
in some cases.
Casting solidifies rapidly and is ejected.
Applications: Automotive parts, electronic housings, appliance components.
Permanent Mold Casting:
Permanent Mold Casting: Employs reusable metal molds to create a variety of parts.A
reusable metal mold (cast iron or steel) is used. Mold is preheated, coated with
refractory wash, and molten metal is poured (commonly by gravity). After
solidification, the part is ejected and the mold reused.
Process:
A reusable metal mold is preheated and coated with refractory wash.
Molten metal is poured by gravity or pressure into the mold.
Mold halves are opened after solidification, and the part is removed.
Mold is reused many times.
Applications: Pistons, cylinder heads, wheels.
Gravity Die Casting: A form of permanent mold casting where gravity is used to fill
the mold.A subset of permanent molds where molten metal fills the die under gravity
rather than pressure. Simple, robust, and often uses tilt or pouring devices for
controlled filling.
Process:
Similar to permanent mold casting but relies purely on gravity (no pressure).
Molten metal flows into the mold cavity via gravity feeding.
Solidifies and is removed after cooling.
Applications: Automotive parts, cookware, small precision components.
Low-Pressure Die Casting: Uses a controlled low pressure to force metal into the
mold cavity. Molten metal in a sealed furnace is forced into the die via a riser
tube using controlled low gas pressure applied to the metal surface
Process:
A sealed crucible of molten metal is connected to the mold above it via a riser
tube.
Low air pressure (0.3–1 bar) is applied on molten metal surface.
Metal rises into the mold cavity smoothly.
Mold is filled from bottom up, reducing turbulence and porosity.
Applications: Aluminum wheels, suspension components.
Vacuum Die Casting: A specialized die casting process that draws the molten metal
into the mold using vacuum . Reduced gas entrapment yields higher integrity
castings.
Process:
Similar to pressure die casting, but the mold cavity is evacuated using a vacuum
pump.
Metal is injected into the evacuated cavity, minimizing trapped gases.
Produces dense, high-strength castings.
Applications: Aerospace components, automotive body panels.
Pressure Casting: A broad term encompassing die casting methods that use pressure,
like high-pressure or low-pressure die casting. High-pressure injection of molten
metal into a die; rapid solidification produces fine detail and thin-walled parts.
Cold-chamber machines for aluminum, hot-chamber for zinc/lead.
Process:
General term: molten metal is forced into a mold cavity using high pressure (up to
200 MPa).
Ensures thin walls, fine detail, and high production rates.
Applications: Small, intricate automotive and electronic parts.
Squeeze Casting: Combines the solidification of a casting with the application of
high pressure, often using a permanent mold. High-pressure injection of molten
metal into a die; rapid solidification produces fine detail and thin-walled parts.
Cold-chamber machines for aluminum, hot-chamber for zinc/lead.
Process:
Molten metal is poured into a preheated die.
A punch applies high pressure during solidification.
This eliminates shrinkage porosity and enhances density.
Applications: High-strength aluminum alloys, automotive wheels, aerospace parts.
Slush Casting: Metal is poured into a permanent mold, and after a portion
solidifies, the remaining liquid metal is poured out, leaving a hollow casting.
Molten metal is poured into a permanent mold; after a short period a thin shell
solidifies against mold walls, and the remaining liquid is poured out—leaving a
hollow thin-walled piece.
Process:
Molten metal is poured into a permanent mold.
After a thin shell solidifies against the mold walls, excess liquid metal is poured
out.
Leaves a hollow casting with thin walls.
Applications: Decorative objects, toys, lamp bases.
Other Specialized Methods:
Continuous Casting: A process for mass-producing long products, such as slabs and
billets, by pouring metal into an open-ended, water-cooled mold. Molten metal is
poured into an open-ended, water-cooled mold and withdrawn continuously as a semi-
solid strand; secondary cooling/straightening follows, then cutting to length.
Process:
Molten metal is poured into a water-cooled open-ended mold.
Solidified shell forms on contact with cooling surfaces.
Partially solidified metal is continuously withdrawn while more molten metal is
added.
Produces billets, slabs, blooms.
Applications: Steel, aluminum, copper industries.
Centrifugal Casting: Uses centrifugal force to distribute the molten metal in a
rotating mold, useful for producing hollow, cylindrical parts. Molten metal is
poured into a rotating mold; centrifugal force pushes metal to mold periphery
forming a dense outer shell—inner region can be hollow or machined. Variants: true
centrifugal (hollow cylinders), semi-centrifugal (solid with varying density).
Process:
Molten metal is poured into a spinning mold.
Centrifugal force distributes metal uniformly along the mold walls.
Produces dense, defect-free hollow parts.
Applications: Pipes, bushings, rings, bearings.
Vacuum Casting (Other Types): Beyond vacuum die casting, this can refer to other
processes where vacuum is used to remove air or degas the molten metal or
mold. Vacuum is applied either to the mold cavity or to the molten metal prior
to/during filling; reduces entrained gases, improves mold filling and surface
finish. Methods include vacuum-assisted sand, investment, or pressure casting.
Process:
Molten metal is poured into a spinning mold.
Centrifugal force distributes metal uniformly along the mold walls.
Produces dense, defect-free hollow parts.
Applications: Pipes, bushings, rings, bearings.
Thin Roll Casting: A method for producing thin metal sheets directly from molten
metal. Molten metal is fed between two counter-rotating, water-cooled rolls. Rapid
solidification forms a thin metallic strip which is continuously removed, sometimes
followed by rolling or annealing.
Process:
Molten metal is fed between two water-cooled rotating rolls.
Rapid solidification occurs, producing a thin strip of metal directly.
Eliminates need for intermediate rolling.
Applications: Aluminum and magnesium sheets for packaging, automotive.
Ductile Iron Casting: While not a casting method itself, it refers to casting a
specific material—ductile iron—which is often produced using methods like sand
casting or permanent mold casting. Ductile (nodular) iron is produced by
spheroidizing graphite during solidification via magnesium/cerium addition. Casting
uses typical processes (sand, permanent mold, centrifugal) but with special melt
treatment and inoculation.
Process:
Molten iron is treated with magnesium or cerium to create nodular graphite.
Cast using sand, permanent mold, or other techniques.
Results in strong, ductile iron with steel-like properties.
Applications: Engine crankshafts, gears, heavy-duty machinery parts.
DEFECTS
Sand Casting -Sand inclusion, blowholes, rough surface finish
Plaster Casting -Cracking, porosity, limited size
Investment Casting -Misruns, shrinkage defects, ceramic shell cracking
Shell Molding -Gas porosity, shell cracking, inclusions
Lost-Foam Casting -Gas defects (from foam), misruns, mold erosion
Full Mold Casting -Carbon residue, porosity, incomplete filling
Ceramic Casting -Mold cracking, inclusions, hot tearing
Permanent Mold Casting - Cold shuts, misruns, shrinkage cavities
Gravity Die Casting -Misruns, shrinkage porosity, oxide inclusions
Low-Pressure Die Casting -Gas porosity, shrinkage, incomplete filling
Vacuum Die Casting -Incomplete filling, surface defects, mold wear
High-Pressure Die Casting -Porosity, flash, cold shuts
Squeeze Casting -Die sticking, shrinkage, hot tearing
Slush Casting -Uneven wall thickness, surface roughness, incomplete solidification
Continuous Casting -Cracks, segregation, surface defects
Centrifugal Casting -Blowholes, segregation, inclusions
Vacuum Casting (Other) -Misruns, mold collapse, shrinkage
Thin Roll Casting -Cracks, segregation, surface roughness
Ductile Iron Casting -Shrinkage porosity, graphite flotation, inclusions
