Metal Casting II ManufacturingProcesses. Outline Sand Casting Shell Mold Casting Composite Molds...

Metal Casting IIMetal Casting II

ManufacturingManufacturing

ProcessesProcesses

OutlineOutline

Sand CastingSand CastingShell Mold CastingShell Mold CastingComposite MoldsComposite MoldsExpendable Pattern CastingExpendable Pattern CastingPlaster Mold CastingPlaster Mold CastingCeramic Mold CastingCeramic Mold CastingInvestment CastingInvestment CastingPressure CastingPressure CastingVacuum CastingVacuum CastingDie CastingDie CastingCentrifugal CastingCentrifugal CastingSqueeze Casting and Semisolid Metal Squeeze Casting and Semisolid Metal FormingFormingCasting Single CrystalsCasting Single CrystalsRapid SolidificationRapid SolidificationMeltingMeltingDesign ConsiderationsDesign Considerations

Examples of Cast PartsExamples of Cast Parts

Examples of Cast PartsExamples of Cast Parts

Typical Casting MetalsTypical Casting Metals

AluminumAluminum

Aluminum-silicon alloyAluminum-silicon alloy

Aluminum-copperAluminum-copper

BrassBrass

Gray cast ironGray cast iron

CopperCopper

LeadLead

SteelSteel

Casting ProcessesCasting Processes

Sand CastingSand Casting

Uses a mold made of compressed Uses a mold made of compressed sand; after the metal solidifies, the sand; after the metal solidifies, the sand is broken awaysand is broken away

Sand CastingSand Casting

PatternPatternFull sized model of the partFull sized model of the part

CoreCoreFull sized model of the interior Full sized model of the interior surfaces of the partsurfaces of the part

Sand Silica (SiOSand Silica (SiO22))

90% sand90% sand3% water3% water7% clay7% clay

Sand CastingSand Casting

Sand CastingSand Casting

Example of a Sand Example of a Sand Casting MoldCasting Mold

Sand CastingSand Casting

Advantages:Advantages:Almost no limit on size, shape, Almost no limit on size, shape, weight or complexity; low cost; weight or complexity; low cost; almost any metalalmost any metal

Limitations:Limitations:Relatively poor tolerances and Relatively poor tolerances and surface finish; machining often surface finish; machining often required; low production raterequired; low production rate

Common metals:Common metals:Cast irons, steel, stainless steel, Cast irons, steel, stainless steel, casting alloys of aluminum and casting alloys of aluminum and copper, magnesium and nickelcopper, magnesium and nickel

Sand CastingSand Casting

Size limits:Size limits:1 oz – 6000 lb1 oz – 6000 lb

Thickness limits:Thickness limits:As thin as 3/32 in, no maximumAs thin as 3/32 in, no maximum

Tolerances:Tolerances:1/32 in for the first 6 in, .003 in for each 1/32 in for the first 6 in, .003 in for each additional inch; additional increment additional inch; additional increment across the parting lineacross the parting line

Draft allowance:Draft allowance:1 - 3°1 - 3°

Surface finish:Surface finish:100 -1000 µin100 -1000 µin

Shell CastingShell Casting

Casting process in which the mold is Casting process in which the mold is a thin shell (typically 3/8 inch) made a thin shell (typically 3/8 inch) made of sand held together by a of sand held together by a thermosetting binderthermosetting binder

Shell CastingShell Casting

Shell CastingShell Casting

Advantages:Advantages:Higher production rate than sand Higher production rate than sand casting; high dimensional accuracy casting; high dimensional accuracy and smooth finishand smooth finish

Limitations:Limitations:Requires expensive metal patterns; Requires expensive metal patterns; resin adds to cost; part size is resin adds to cost; part size is limitedlimited

Common metals:Common metals:Cast irons, casting alloys of Cast irons, casting alloys of aluminum and copperaluminum and copper

Shell CastingShell Casting

Size limits:Size limits:1 oz minimum; usually less than 25 lb; 1 oz minimum; usually less than 25 lb; mold area usually less than 500 inmold area usually less than 500 in22

Thickness limits:Thickness limits:1/16 – ¼ in depending on material1/16 – ¼ in depending on material

Tolerances:Tolerances:.005 in/in.005 in/in

Draft allowance:Draft allowance:¼ - ½°¼ - ½°

Surface finish:Surface finish:50 – 150 µin50 – 150 µin

Composite MoldsComposite Molds

Made from 2 or more different Made from 2 or more different materialsmaterials

Good for complex shapes such as Good for complex shapes such as turbine bladesturbine blades

Expendable Pattern Expendable Pattern CastingCasting

Polystyrene pattern vaporizes on Polystyrene pattern vaporizes on contact with molten metalcontact with molten metal

Foam Pattern of an Foam Pattern of an Engine BlockEngine Block

Plaster Mold CastingPlaster Mold Casting

Uses a mold made of plaster Uses a mold made of plaster (gypsum) with talc and silica, (gypsum) with talc and silica, which is broken away after the which is broken away after the metal solidifiesmetal solidifies

The mold has a relatively low The mold has a relatively low thermal conductivity; a thermal conductivity; a somewhat uniform grain somewhat uniform grain structure can be produced structure can be produced

Plaster Mold CastingPlaster Mold Casting

Advantages:Advantages:High dimensional accuracy and High dimensional accuracy and smooth finish; can make net- or smooth finish; can make net- or near-net-shaped partsnear-net-shaped parts

Limitations:Limitations:Lower temperature nonferrous Lower temperature nonferrous metals only; long molding time; metals only; long molding time; mold material is not reusable; mold material is not reusable; maximum size limitedmaximum size limited

Common metals:Common metals:Primarily aluminum and copperPrimarily aluminum and copper

Plaster Mold CastingPlaster Mold Casting

Size limits:Size limits:1 oz – 15 lb1 oz – 15 lb

Thickness limits:Thickness limits:As thin as .025 inAs thin as .025 in

Tolerances:Tolerances:.005 in on the first 2 in; .002 in per .005 in on the first 2 in; .002 in per additional inchadditional inch

Draft allowance:Draft allowance:½ - 1°½ - 1°

Surface finish:Surface finish:50-125 µin50-125 µin

Ceramic Mold CastingCeramic Mold Casting

Uses a mold made of refractory Uses a mold made of refractory ceramic materials which can be ceramic materials which can be used for high-temperature used for high-temperature applicationsapplications

Ceramic Mold CastingCeramic Mold Casting

Ceramic Mold CastingCeramic Mold Casting

Advantages:Advantages:Intricate detail, close tolerances, Intricate detail, close tolerances, smooth finishsmooth finish

Limitations:Limitations:Mold material is expensive and not Mold material is expensive and not reusablereusable

Common metals:Common metals:Ferrous and high-temperature Ferrous and high-temperature nonferrous metals are most nonferrous metals are most common; can be used with alloys of common; can be used with alloys of aluminum, copper, magnesium, aluminum, copper, magnesium, titanium and zinctitanium and zinc

Ceramic Mold CastingCeramic Mold Casting

Size limits:Size limits:Several ounces to several tonsSeveral ounces to several tons

Thickness limits:Thickness limits:As thin as .05 in, no maximumAs thin as .05 in, no maximum

Tolerances:Tolerances:.005 in on the first inch; .003 in per .005 in on the first inch; .003 in per additional inchadditional inch

Draft allowance:Draft allowance:1°1°

Surface finish:Surface finish:75-150 µin75-150 µin

Investment CastingInvestment Casting

Uses a wax pattern which is Uses a wax pattern which is coated with refractory materials coated with refractory materials to form a mold; the wax is then to form a mold; the wax is then melted out and the mold cavity melted out and the mold cavity is filled with metalis filled with metal

Can be used for high precision Can be used for high precision complex shapes from high complex shapes from high melting point metals that are melting point metals that are not readily machinablenot readily machinable

Investment CastingInvestment Casting

Example of a Wax Example of a Wax Injection MoldInjection Mold

Example of a Wax Example of a Wax PatternPattern

Example of a Coated Example of a Coated PatternPattern

Example of Finished Example of Finished CastingsCastings

Investment CastingInvestment Casting

Advantages:Advantages:Excellent surface finish; high Excellent surface finish; high dimensional accuracy; nearly dimensional accuracy; nearly unlimited intricacy; almost any unlimited intricacy; almost any metal; no flash or parting linemetal; no flash or parting line

Limitations:Limitations:Expensive patterns and molds; high Expensive patterns and molds; high labor costs; limited sizelabor costs; limited size

Common metals:Common metals:Mainly aluminum, copper and steel; Mainly aluminum, copper and steel; also used with stainless steel, also used with stainless steel, nickel, magnesium and precious nickel, magnesium and precious metalsmetals

Investment CastingInvestment Casting

Size limits:Size limits:As small as 1/10 oz; usually less than 10 As small as 1/10 oz; usually less than 10 lblb

Thickness limits:Thickness limits:As thin as .025 in, less than 3 inAs thin as .025 in, less than 3 in

Tolerances:Tolerances:.005 in on the first inch; .002 in per .005 in on the first inch; .002 in per additional inchadditional inch

Draft allowance:Draft allowance:none requirednone required

Surface finish:Surface finish:50-125 µin50-125 µin

Pressure CastingPressure Casting

Pressure casting forces the metal up Pressure casting forces the metal up into the mold chamber by applying into the mold chamber by applying a small amount of pressurea small amount of pressure

Vacuum CastingVacuum Casting

Permanent Mold Casting Permanent Mold Casting (Pressure/Vacuum)(Pressure/Vacuum)

Advantages:Advantages:Good surface finish and dimensional Good surface finish and dimensional accuracy; metal mold causes rapid accuracy; metal mold causes rapid cooling and fine grain structure; molds cooling and fine grain structure; molds can be used up to 25 000 timescan be used up to 25 000 times

Limitations:Limitations:High initial mold cost; shape, size and High initial mold cost; shape, size and complexity are limited; mold life is very complexity are limited; mold life is very limited with metals with high melting limited with metals with high melting pointspoints

Common metals:Common metals:Alloys of aluminum, magnesium and Alloys of aluminum, magnesium and copper most common; iron and steel can copper most common; iron and steel can be used in graphite molds; alloys of lead, be used in graphite molds; alloys of lead, tin and zinc also usedtin and zinc also used

Permanent Mold Casting Permanent Mold Casting (Pressure/Vacuum)(Pressure/Vacuum)

Size limits:Size limits:Several ounces to about 150 lbSeveral ounces to about 150 lb

Thickness limits:Thickness limits:Minimum depends on material but generally Minimum depends on material but generally thicker than 1/8 in; maximum about 2 inthicker than 1/8 in; maximum about 2 in

Tolerances:Tolerances:.015 in for the first inch and .002 in for each .015 in for the first inch and .002 in for each additional inch; .01 in added across the additional inch; .01 in added across the parting lineparting line

Draft allowance:Draft allowance:2 - 3°2 - 3°

Surface finish:Surface finish:100 - 250 µin100 - 250 µin

Die CastingDie Casting

Another form of permanent mold Another form of permanent mold casting; molten metal is forced casting; molten metal is forced into the mold cavity at into the mold cavity at pressures ranging from .7 MPa pressures ranging from .7 MPa - 700 MPa - 700 MPa

Die CastingDie Casting

Die CastingDie Casting

Example of a Die Example of a Die Casting MoldCasting Mold

Centrifugal CastingCentrifugal Casting

Uses a rotating mold to form hollow Uses a rotating mold to form hollow cylindrical parts such as pipes, gun cylindrical parts such as pipes, gun barrels and lamp postsbarrels and lamp posts

Vertical Centrifugal Vertical Centrifugal CastingCasting

Centrifugal CastingCentrifugal Casting

Advantages:Advantages:

Can produce a wide range of Can produce a wide range of cylindrical parts; good dimensional cylindrical parts; good dimensional accuracy and cleanlinessaccuracy and cleanliness

Limitations:Limitations:

Limited shape; spinning equipment Limited shape; spinning equipment may be expensivemay be expensive

Common metals:Common metals:

Iron, steel, stainless steel, alloys of Iron, steel, stainless steel, alloys of aluminum, copper and nickelaluminum, copper and nickel

Centrifugal CastingCentrifugal Casting

Size limits:Size limits:Up to 10 ft in diameter and 50 ft in lengthUp to 10 ft in diameter and 50 ft in length

Thickness limits:Thickness limits:Wall thickness .1 – 5 inWall thickness .1 – 5 in

Tolerances:Tolerances:Outer diameter within .1 in; inner Outer diameter within .1 in; inner diameter within about .15 indiameter within about .15 in

Draft allowance:Draft allowance:1/8 in / ft1/8 in / ft

Surface finish:Surface finish:40 - 100 µin40 - 100 µin

Semicentrifugal CastingSemicentrifugal Casting

Uses a rotating mold to form parts Uses a rotating mold to form parts with radial symmetry, such as with radial symmetry, such as wheels with spokeswheels with spokes

Squeeze CastingSqueeze Casting

A combination of casting and forging; A combination of casting and forging; a die applies pressure as the metal a die applies pressure as the metal solidifiessolidifies

Casting Single CrystalsCasting Single Crystals

Uses a slow crystal-growth Uses a slow crystal-growth solidification procedure to solidification procedure to produce parts made of a single produce parts made of a single crystal with no grain crystal with no grain boundariesboundaries

A helical constriction only allows A helical constriction only allows one crystal of favorable one crystal of favorable orientation to grow into and fill orientation to grow into and fill the mold chamberthe mold chamber

Casting Single CrystalsCasting Single Crystals

Rapid SolidificationRapid Solidification

Cools metal rapidly at rates as high Cools metal rapidly at rates as high as 10as 1066 K/s so that it cannot K/s so that it cannot crystallize and instead forms an crystallize and instead forms an amorphous glasslike structureamorphous glasslike structure

Melting FurnacesMelting Furnaces

CupolaCupola

Crucible FurnaceCrucible Furnace

Induction FurnaceInduction Furnace

Melting FurnacesMelting Furnaces

CupolaCupola

A vertical cylindrical furnace used A vertical cylindrical furnace used for melting cast ironfor melting cast iron

Melting FurnacesMelting Furnaces

Crucible furnaceCrucible furnace

Melts metal without direct contact Melts metal without direct contact with a burning fuel mixturewith a burning fuel mixture

Melting FurnacesMelting Furnaces

Induction furnaceInduction furnace

Uses an alternating magnetic field Uses an alternating magnetic field to heat the metalto heat the metal

Design ConsiderationsDesign Considerations

Design ConsiderationsDesign Considerations

Design ConsiderationsDesign Considerations

Design ConsiderationsDesign Considerations

Casting AlloysCasting Alloys

SummarySummary

A variety of casting processes A variety of casting processes are available for different are available for different applicationsapplications

Design considerations must be Design considerations must be taken to prevent casting taken to prevent casting defectsdefects