metal casting ii manufacturingprocesses. outline sand casting shell mold casting composite molds...

Download Metal Casting II ManufacturingProcesses. Outline Sand Casting Shell Mold Casting Composite Molds Expendable Pattern Casting Plaster Mold Casting Ceramic

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  • Metal Casting IIManufacturingProcesses

  • OutlineSand CastingShell Mold CastingComposite MoldsExpendable Pattern CastingPlaster Mold CastingCeramic Mold CastingInvestment CastingPressure CastingVacuum CastingDie CastingCentrifugal CastingSqueeze Casting and Semisolid Metal FormingCasting Single CrystalsRapid SolidificationMeltingDesign Considerations

  • Examples of Cast Parts

  • Examples of Cast Parts

  • Typical Casting MetalsAluminumAluminum-silicon alloyAluminum-copperBrassGray cast ironCopperLeadSteel

  • Casting Processes

  • Sand CastingUses a mold made of compressed sand; after the metal solidifies, the sand is broken away

  • Sand CastingPatternFull sized model of the part

    CoreFull sized model of the interior surfaces of the part

    Sand Silica (SiO2)90% sand3% water7% clay

  • Sand Casting

  • Sand Casting

  • Example of a Sand Casting Mold

  • Sand CastingAdvantages:Almost no limit on size, shape, weight or complexity; low cost; almost any metal

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

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

  • Sand CastingSize limits:1 oz 6000 lb

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

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

    Draft allowance:1 - 3

    Surface finish:100 -1000 in

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

  • Shell Casting

  • Shell CastingAdvantages:Higher production rate than sand casting; high dimensional accuracy and smooth finish

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

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

  • Shell CastingSize limits:1 oz minimum; usually less than 25 lb; mold area usually less than 500 in2

    Thickness limits:1/16 in depending on material

    Tolerances:.005 in/in

    Draft allowance: -

    Surface finish:50 150 in

  • Composite MoldsMade from 2 or more different materials

    Good for complex shapes such as turbine blades

  • Expendable Pattern CastingPolystyrene pattern vaporizes on contact with molten metal

  • Foam Pattern of an Engine Block

  • Plaster Mold CastingUses a mold made of plaster (gypsum) with talc and silica, which is broken away after the metal solidifies

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

  • Plaster Mold CastingAdvantages:High dimensional accuracy and smooth finish; can make net- or near-net-shaped parts

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

    Common metals:Primarily aluminum and copper

  • Plaster Mold CastingSize limits:1 oz 15 lb

    Thickness limits:As thin as .025 in

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

    Draft allowance: - 1

    Surface finish:50-125 in

  • Ceramic Mold CastingUses a mold made of refractory ceramic materials which can be used for high-temperature applications

  • Ceramic Mold Casting

  • Ceramic Mold CastingAdvantages:Intricate detail, close tolerances, smooth finish

    Limitations:Mold material is expensive and not reusable

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

  • Ceramic Mold CastingSize limits:Several ounces to several tons

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

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

    Draft allowance:1

    Surface finish:75-150 in

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

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

  • Investment Casting

  • Example of a Wax Injection Mold

  • Example of a Wax Pattern

  • Example of a Coated Pattern

  • Example of Finished Castings

  • Investment CastingAdvantages:Excellent surface finish; high dimensional accuracy; nearly unlimited intricacy; almost any metal; no flash or parting line

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

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

  • Investment CastingSize limits:As small as 1/10 oz; usually less than 10 lb

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

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

    Draft allowance:none required

    Surface finish:50-125 in

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

  • Vacuum Casting

  • Permanent Mold Casting (Pressure/Vacuum)Advantages:Good surface finish and dimensional accuracy; metal mold causes rapid cooling and fine grain structure; molds can be used up to 25 000 times

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

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

  • Permanent Mold Casting (Pressure/Vacuum)Size limits:Several ounces to about 150 lb

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

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

    Draft allowance:2 - 3

    Surface finish:100 - 250 in

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

  • Die Casting

  • Die Casting

  • Example of a Die Casting Mold

  • Centrifugal CastingUses a rotating mold to form hollow cylindrical parts such as pipes, gun barrels and lamp posts

  • Vertical Centrifugal Casting

  • Centrifugal CastingAdvantages:Can produce a wide range of cylindrical parts; good dimensional accuracy and cleanliness

    Limitations:Limited shape; spinning equipment may be expensive

    Common metals:Iron, steel, stainless steel, alloys of aluminum, copper and nickel

  • Centrifugal CastingSize limits:Up to 10 ft in diameter and 50 ft in length

    Thickness limits:Wall thickness .1 5 in

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

    Draft allowance:1/8 in / ft

    Surface finish:40 - 100 in

  • Semicentrifugal CastingUses a rotating mold to form parts with radial symmetry, such as wheels with spokes

  • Squeeze CastingA combination of casting and forging; a die applies pressure as the metal solidifies

  • Casting Single CrystalsUses a slow crystal-growth solidification procedure to produce parts made of a single crystal with no grain boundaries

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

  • Casting Single Crystals

  • Rapid SolidificationCools metal rapidly at rates as high as 106 K/s so that it cannot crystallize and instead forms an amorphous glasslike structure

  • Melting FurnacesCupolaCrucible FurnaceInduction Furnace

  • Melting FurnacesCupolaA vertical cylindrical furnace used for melting cast iron

  • Melting FurnacesCrucible furnaceMelts metal without direct contact with a burning fuel mixture

  • Melting FurnacesInduction furnaceUses an alternating magnetic field to heat the metal

  • Design Considerations

  • Design Considerations

  • Design Considerations

  • Design Considerations

  • Casting Alloys

  • SummaryA variety of casting processes are available for different applications

    Design considerations must be taken to prevent casting defects

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