Metal CastingMetal CastingMetal CastingMetal CastingDesign, Materials, EconomicsDesign, Materials, Economicsgg

Text Reference: “Manufacturing Text Reference: “Manufacturing Engineering and Technology”, Engineering and Technology”, Kalpakjian & Schmid 6/e 2010Kalpakjian & Schmid 6/e 2010Kalpakjian & Schmid, 6/e, 2010Kalpakjian & Schmid, 6/e, 2010

Chapter 12Chapter 12

Design of Cast PartsDesign of Cast PartsDesign of Cast PartsDesign of Cast PartsAvoid Avoid sharp corners, angles & filletssharp corners, angles & filletsp , gp , g

They act as stress raisersThey act as stress raisersSelect Select fillet radiifillet radii to reduce stress to reduce stress concentrations and ensure proper liquid metal concentrations and ensure proper liquid metal flowflow

33--25 mm (1/8”25 mm (1/8”--3”)3”)33--25 mm (1/825 mm (1/8 --3 )3 )Seek Seek uniform cross sections and wall uniform cross sections and wall thickness throughout castingthickness throughout castingg gg g

Larger sections become hot spots leading to Larger sections become hot spots leading to shrinkage cavities and porosityshrinkage cavities and porosity

FIGURE 12.1 FIGURE 12.1 Suggested design modifications to avoid defects in Suggested design modifications to avoid defects in castingscastings Source:Source: CourtesyCourtesy of the American Die Casting Instituteof the American Die Casting Institutecastings. castings. Source: Source: CourtesyCourtesy of the American Die Casting Institute.of the American Die Casting Institute.

FIGURE 12.2 FIGURE 12.2 Examples of designs showing the importance of Examples of designs showing the importance of maintaining uniform cross sections in castings to avoid hot spots and maintaining uniform cross sections in castings to avoid hot spots and g g pg g p

shrinkage cavities.shrinkage cavities.

Design of Cast PartsDesign of Cast Parts (continued)(continued)Design of Cast Parts Design of Cast Parts (continued)(continued)

AvoidAvoid large flat areaslarge flat areasAvoid Avoid large flat areaslarge flat areasMay warp during cooling because of May warp during cooling because of temperature gradientstemperature gradientstemperature gradientstemperature gradientsMay have uneven finish due to uneven flow May have uneven finish due to uneven flow during pouringduring pouringduring pouringduring pouringIncorporate staggered ribs & serrationsIncorporate staggered ribs & serrations

Allow forAllow for metal shrinkagemetal shrinkage duringduringAllow for Allow for metal shrinkagemetal shrinkage during during solidificationsolidification

TABLE 12.1 TABLE 12.1 Normal Shrinkage Allowance for Some Metals Cast in Normal Shrinkage Allowance for Some Metals Cast in Sand MoldsSand MoldsSand MoldsSand Molds

Extract from “Cast Irons”, ASM, Chapter on Extract from “Cast Irons”, ASM, Chapter on F d P ti f C t I 140F d P ti f C t I 140Foundry Practice for Cast Irons, p.140Foundry Practice for Cast Irons, p.140

““The precipitation of graphite during eutecticThe precipitation of graphite during eutecticThe precipitation of graphite during eutectic The precipitation of graphite during eutectic solidification causes an expansion, which offsets some solidification causes an expansion, which offsets some of the contraction usually experienced during of the contraction usually experienced during y p gy p gsolidification of a metal. In fact a Class 20 iron solidification of a metal. In fact a Class 20 iron precipitates enough graphite to create sufficient precipitates enough graphite to create sufficient

i th t f di i t i d A th CE fi th t f di i t i d A th CE fexpansion so that feeding is not required. As the CE of expansion so that feeding is not required. As the CE of the iron decreases, less graphite is precipitated and the iron decreases, less graphite is precipitated and feeding requirements increase A Class 50 ironfeeding requirements increase A Class 50 ironfeeding requirements increase. A Class 50 iron feeding requirements increase. A Class 50 iron requires approximately 4% volumetric feeding to offset requires approximately 4% volumetric feeding to offset the contraction of the iron.” the contraction of the iron.”

carbon equivalentcarbon equivalent(metallurgy)(metallurgy)

An empirical relationship of the totalAn empirical relationship of the totalAn empirical relationship of the total An empirical relationship of the total carbon (TC), silicon (Si) and phosphorus carbon (TC), silicon (Si) and phosphorus (P) content of gray iron:(P) content of gray iron:(P) content of gray iron: (P) content of gray iron:

CE %TC 0 3(%Si %P)CE %TC 0 3(%Si %P)CE = %TC + 0.3(%Si + %P).CE = %TC + 0.3(%Si + %P).

Design of Cast PartsDesign of Cast Parts (continued)(continued)Design of Cast Parts Design of Cast Parts (continued)(continued)

Provide a small draft (taper) to enable removalProvide a small draft (taper) to enable removalProvide a small draft (taper) to enable removal Provide a small draft (taper) to enable removal of pattern without damaging moldof pattern without damaging mold

Design of Cast PartsDesign of Cast Parts (continued)(continued)Design of Cast Parts Design of Cast Parts (continued)(continued)

TolerancesTolerances should be a wide as possibleshould be a wide as possibleTolerancesTolerances should be a wide as possibleshould be a wide as possibleFor small castings: +/For small castings: +/-- 0.8 mm (1/32”)0.8 mm (1/32”)For large castings: +/For large castings: +/ 6 mm (0 25”)6 mm (0 25”)For large castings: +/For large castings: +/-- 6 mm (0.25 )6 mm (0.25 )

Consider Consider finishing operationsfinishing operationsf ff fE.g. Locate holes on flat surfacesE.g. Locate holes on flat surfaces

Select appropriate Select appropriate casting processcasting processCasting process can influence casting designCasting process can influence casting design

Design of Cast PartsDesign of Cast Parts (continued)(continued)Design of Cast Parts Design of Cast Parts (continued)(continued)

Location ofLocation of parting lineparting lineLocation of Location of parting lineparting lineAlong a flat plane (not contoured)Along a flat plane (not contoured)At corners or edges (not on flat surfaces)At corners or edges (not on flat surfaces)At corners or edges (not on flat surfaces)At corners or edges (not on flat surfaces)Locate critical surfaces facing downwards Locate critical surfaces facing downwards (reduced porosity)(reduced porosity)(reduced porosity)(reduced porosity)Placed to allow ease of metal flowPlaced to allow ease of metal flowAffects mold designAffects mold design locate sprue well gateslocate sprue well gatesAffects mold design Affects mold design –– locate sprue well, gates locate sprue well, gates & runners at parting line in drag (bottom)& runners at parting line in drag (bottom)

Design of Cast PartsDesign of Cast Parts (continued)(continued)Design of Cast Parts Design of Cast Parts (continued)(continued)

Design & locateDesign & locate gatesgates::Design & locate Design & locate gatesgates::Multiple gates for large partsMultiple gates for large partsAt thick sections of castingsAt thick sections of castingsAt thick sections of castingsAt thick sections of castingsUse fillet where gate meets castingUse fillet where gate meets castingAllow space between sprue and castingAllow space between sprue and castingp p gp p gMinimum gate length 3Minimum gate length 3--5 times diameter5 times diameterCross section smaller than runner but large Cross section smaller than runner but large enough for flowenough for flowAvoid curved gatesAvoid curved gates

Design of Cast PartsDesign of Cast Parts (continued)(continued)Design of Cast Parts Design of Cast Parts (continued)(continued)

Use multipleUse multiple runnersrunners for more complicatedfor more complicatedUse multiple Use multiple runnersrunners for more complicated for more complicated castingscastingsRunnersRunners trap drosstrap drossppUse a Use a pouring basinpouring basin to ensure even metal flow to ensure even metal flow into sprue and collect drossinto sprue and collect drosspp

Use good molten metalUse good molten metalUse good o e e aUse good o e e aPour molten metal evenly, without interruptionPour molten metal evenly, without interruption

Design Issues: Design Issues: E d bl M ld C iE d bl M ld C iExpendable Mold CastingExpendable Mold Casting

Mold LayoutMold LayoutMold LayoutMold LayoutSolidification progress uniformly across mold, Solidification progress uniformly across mold, risers lastrisers lastrisers lastrisers last

Machining AllowanceMachining AllowancePattern dimensions include material for laterPattern dimensions include material for laterPattern dimensions include material for later Pattern dimensions include material for later finishing; grinding & machiningfinishing; grinding & machiningIncrease with size & section thicknessIncrease with size & section thicknessIncrease with size & section thicknessIncrease with size & section thickness

Design Issues: Design Issues: E d bl M ld C iE d bl M ld C iExpendable Mold CastingExpendable Mold Casting

Riser Design RulesRiser Design RulesggRiser must solidify after castingRiser must solidify after castingRiser volume with sufficient metal to compensate for Riser volume with sufficient metal to compensate for shrinkage during coolingshrinkage during coolingshrinkage during coolingshrinkage during coolingNo hot spots at junction between casting & riserNo hot spots at junction between casting & riserProper placement of risers so that liquid metal flows Proper placement of risers so that liquid metal flows where neededwhere neededwhere neededwhere neededProvide sufficient pressure to drive liquid where Provide sufficient pressure to drive liquid where needed in cavity. needed in cavity.

More useful for higher density metalsMore useful for higher density metalsMore useful for higher density metalsMore useful for higher density metalsRiser pressure head sufficient to encourage complete Riser pressure head sufficient to encourage complete cavity fillingcavity filling

FIGURE 12.3 FIGURE 12.3 Examples of undesirable (poor) and desirable (good) Examples of undesirable (poor) and desirable (good) casting designs Permanent Mold & Diecasting designs Permanent Mold & Die--castingcastingcasting designs. Permanent Mold & Diecasting designs. Permanent Mold & Die casting. casting.

Source: Source: Courtesy of American Die Casting Institute.Courtesy of American Die Casting Institute.

Computer Modeling of Casting Computer Modeling of Casting PPProcessProcess

Casting involves complex interactions among many Casting involves complex interactions among many g p g yg p g yvariablesvariablesNew modeling techniques can simultaneously handle New modeling techniques can simultaneously handle fluid flow, heat transfer, microstructures duringfluid flow, heat transfer, microstructures duringfluid flow, heat transfer, microstructures during fluid flow, heat transfer, microstructures during solidification, etc.solidification, etc.Modeling of Modeling of fluid flowfluid flow uses Bernoulli’s and continuity uses Bernoulli’s and continuity equationsequationsequationsequationsHeat transferHeat transfer models model the effects of surface models model the effects of surface conditions, thermal properties, convection on coolingconditions, thermal properties, convection on coolingMicrostructuresMicrostructures models encompass heat flow, models encompass heat flow, temperature gradients, nucleation, crystal growth, etc.temperature gradients, nucleation, crystal growth, etc.

Casting AlloysCasting AlloysCasting AlloysCasting Alloys

Important considerations for alloys:Important considerations for alloys:Important considerations for alloys:Important considerations for alloys:Casting characteristicsCasting characteristicsMachinabilityMachinabilityMachinabilityMachinabilityWeldabilityWeldability

The tables on the following slidesThe tables on the following slidesThe tables on the following slides The tables on the following slides summarize:summarize:

Properties and applications of cast metals and Properties and applications of cast metals and p ppp pptheir alloystheir alloysCasting and manufacturing characteristicsCasting and manufacturing characteristics

FIGURE 12.4 FIGURE 12.4 Mechanical properties for various groups of cast alloys. Mechanical properties for various groups of cast alloys. Note that even within the same group, the properties vary over a wide Note that even within the same group, the properties vary over a wide range particularly for cast steelsrange particularly for cast steels Source:Source: Courtesy of Steel Founders’Courtesy of Steel Founders’range, particularly for cast steels. range, particularly for cast steels. Source: Source: Courtesy of Steel Founders Courtesy of Steel Founders

Society of America.Society of America.

FIGURE 12.4 (continued) FIGURE 12.4 (continued) Mechanical properties for various groups Mechanical properties for various groups of cast alloys. Note that even within the same group, the properties of cast alloys. Note that even within the same group, the properties

vary over a wide range particularly for cast steelsvary over a wide range particularly for cast steels Source:Source: Courtesy ofCourtesy ofvary over a wide range, particularly for cast steels. vary over a wide range, particularly for cast steels. Source: Source: Courtesy of Courtesy of Steel Founders’ Society of America.Steel Founders’ Society of America.

TABLE 12.2 TABLE 12.2 Typical Applications for Castings and Casting Typical Applications for Castings and Casting CharacteristicsCharacteristicsCharacteristicsCharacteristics

TABLE 12.5 TABLE 12.5 Properties and Typical Applications of Nonferrous Cast Properties and Typical Applications of Nonferrous Cast AlloysAlloysAlloysAlloys

AluminumAluminum--based Alloysbased AlloysAluminumAluminum based Alloysbased Alloys

High electrical conductivityHigh electrical conductivityHigh electrical conductivityHigh electrical conductivityGood atmospheric corrosion resistanceGood atmospheric corrosion resistanceP i t t id d llP i t t id d llPoor resistance to some acids and all Poor resistance to some acids and all alkalisalkalis

Avoid/prevent galvanic corrosionAvoid/prevent galvanic corrosionNontoxic, lightweight, good machinabilityNontoxic, lightweight, good machinabilityLow resistance to wear and abrasionLow resistance to wear and abrasion

Improves with addition of siliconImproves with addition of siliconImproves with addition of siliconImproves with addition of silicon

AluminumAluminum--based Alloysbased AlloysAluminumAluminum based Alloysbased Alloys

Applications:Applications:Applications:Applications:Architectural & decorativeArchitectural & decorativeAutomobilesAutomobilesAutomobilesAutomobiles

Engine blocksEngine blocksCylinder headsCylinder headsIntake manifoldsIntake manifoldsTransmission casesTransmission casesSuspension componentsSuspension componentsSuspension componentsSuspension componentsWheelsWheelsBrakesBrakes

MagnesiumMagnesium--based Alloysbased AlloysMagnesiumMagnesium based Alloysbased Alloys

The lowest density of all commercialThe lowest density of all commercialThe lowest density of all commercial The lowest density of all commercial casting alloyscasting alloysGood corrosion resistanceGood corrosion resistanceGood corrosion resistanceGood corrosion resistanceModerate strengthModerate strength

Strength depends on heat treatmentStrength depends on heat treatmentApplications:Applications:

Automotive wheels, housings, airAutomotive wheels, housings, air--cooled cooled engine blocksengine blocks

CopperCopper--based Alloysbased AlloysCopperCopper based Alloysbased Alloys

Relatively expensiveRelatively expensiveRelatively expensiveRelatively expensiveGood electrical conductivityGood electrical conductivityG d th l d ti itG d th l d ti itGood thermal conductivityGood thermal conductivityGood corrosion resistanceGood corrosion resistanceNontoxicNontoxic

ZincZinc--based Alloysbased AlloysZincZinc based Alloysbased Alloys

Low melting pointLow melting pointLow melting pointLow melting pointGood corrosion resistanceGood corrosion resistanceG d fl iditG d fl iditGood fluidityGood fluidityModerate strengthModerate strengthApplications:Applications:

Die castingDie castingDie castingDie castingParts with thin walls and intricate shapesParts with thin walls and intricate shapes

Other NonOther Non--ferrous Alloysferrous AlloysOther NonOther Non ferrous Alloysferrous AlloysTinTin--basedbased

Low strength; Good corrosion resistanceLow strength; Good corrosion resistanceUse for bearing surfacesUse for bearing surfaces

LeadLead--basedbasedSimilar to Tin; toxicSimilar to Tin; toxic

HighHigh temperaturetemperatureHighHigh--temperaturetemperatureWide range of propertiesWide range of propertiesRequire temperatures up to 1650Require temperatures up to 1650ooC (3000C (3000ooF) forF) forRequire temperatures up to 1650Require temperatures up to 1650 C (3000C (3000 F) for F) for Titanium; higher for Mo, Nb, W, TaTitanium; higher for Mo, Nb, W, TaUtilize specialized casting techniquesUtilize specialized casting techniques

Ferrous Casting AlloysFerrous Casting AlloysFerrous Casting AlloysFerrous Casting Alloys

Cast IronsCast IronsCast IronsCast IronsCan be easily cast into intricate shapesCan be easily cast into intricate shapesGood wear resistanceGood wear resistanceGood wear resistanceGood wear resistanceHigh hardnessHigh hardnessGood machinabilityGood machinabilityGood machinabilityGood machinability

The term ‘C.I.’ includes a family of alloysThe term ‘C.I.’ includes a family of alloysGeneral properties and applications in General properties and applications in Tables 12.3, 12.4Tables 12.3, 12.4

TABLE 12.3 TABLE 12.3 Properties and Typical Applications of Cast IronsProperties and Typical Applications of Cast Ironsp yp ppp yp pp

TABLE 12.4 TABLE 12.4 Mechanical Properties of Gray Cast IronsMechanical Properties of Gray Cast Ironsp yp y

Gray Cast ironGray Cast ironGray Cast ironGray Cast iron

Relatively few shrinkage cavitiesRelatively few shrinkage cavitiesRelatively few shrinkage cavitiesRelatively few shrinkage cavitiesLow porosityLow porosityProperties vary: ferritic pearlitic martensiticProperties vary: ferritic pearlitic martensiticProperties vary: ferritic, pearlitic, martensiticProperties vary: ferritic, pearlitic, martensiticApplications:Applications:

Engine blocks electricEngine blocks electric--motor housings pipes wearmotor housings pipes wearEngine blocks, electricEngine blocks, electric motor housings, pipes, wear motor housings, pipes, wear surfaces for machinessurfaces for machinesMachine tool basesMachine tool bases

22--digit ASTM classificationdigit ASTM classificationClass 20 : Minimum 20 ksi (140 MPa) tensile strengthClass 20 : Minimum 20 ksi (140 MPa) tensile strength

Ductile (Nodular) IronDuctile (Nodular) IronDuctile (Nodular) IronDuctile (Nodular) Iron

Typically used for machine partsTypically used for machine partsTypically used for machine parts, Typically used for machine parts, housings, gears, pipe, rolls for rolling mills, housings, gears, pipe, rolls for rolling mills, automotive crankshaftsautomotive crankshaftsautomotive crankshaftsautomotive crankshaftsGrade 80Grade 80--5555--0606

Mi i 80 k i (550 MP ) t il t thMi i 80 k i (550 MP ) t il t thMinimum 80 ksi (550 MPa) tensile strengthMinimum 80 ksi (550 MPa) tensile strengthMinimum 55 ksi (380 MPa) yield strengthMinimum 55 ksi (380 MPa) yield strength6% l i i 2” ( 0 )6% l i i 2” ( 0 )6% elongation in 2” (50 mm)6% elongation in 2” (50 mm)

White Cast IronWhite Cast IronWhite Cast IronWhite Cast Iron

Has extreme hardnessHas extreme hardnessHas extreme hardnessHas extreme hardnessIs brittleIs brittleV d i tV d i tVery good wear resistanceVery good wear resistancePrimary uses:Primary uses:

Rolls for rolling millsRolls for rolling millsRailroadRailroad--car brake shoescar brake shoesLiners in machinery for processing abrasive Liners in machinery for processing abrasive materialsmaterials

Malleable IronMalleable IronMalleable IronMalleable Iron

Good ductility, strength and shockGood ductility, strength and shockGood ductility, strength and shock Good ductility, strength and shock resistanceresistanceApplications:Applications:Applications:Applications:

R/R equipmentR/R equipmentHardware & fittingsHardware & fittingsa d a e & tt gsa d a e & tt gsComponents for electrical applicationsComponents for electrical applications

Classification example: 35018Classification example: 35018Classification example: 35018Classification example: 3501835 ksi (240 MPa)35 ksi (240 MPa)18% elongation in 2” (50 mm) 18% elongation in 2” (50 mm) g ( )g ( )

CompactedCompacted--Graphite IronGraphite IronCompactedCompacted Graphite IronGraphite Iron

Has the good damping and thermalHas the good damping and thermalHas the good damping and thermal Has the good damping and thermal properties of gray ironproperties of gray ironHas the good strength and stiffnessHas the good strength and stiffnessHas the good strength and stiffness Has the good strength and stiffness properties of ductile ironproperties of ductile ironThese properties permit smaller, lighterThese properties permit smaller, lighterThese properties permit smaller, lighter These properties permit smaller, lighter partspartsEasy to cast and has good machinabilityEasy to cast and has good machinabilityEasy to cast and has good machinabilityEasy to cast and has good machinabilityUsed for automotive engine blocks and Used for automotive engine blocks and cylinder headscylinder headscylinder headscylinder heads

Cast SteelsCast SteelsCast SteelsCast SteelsRequire high temperatures (1650Require high temperatures (1650ooC or 3000C or 3000ooF) F) q g p (q g p ( ))to meltto meltSteel castings have properties that are more Steel castings have properties that are more uniform than those made by mechanical workinguniform than those made by mechanical workinguniform than those made by mechanical working uniform than those made by mechanical working processesprocessesCan be welded; heat alters microstructureCan be welded; heat alters microstructure

Affects strength, ductility, toughnessAffects strength, ductility, toughnessRestore original properties by heat treatmentRestore original properties by heat treatment

Applications:Applications:Applications:Applications:Mining, chemical plants, oil fields, heavy construction, Mining, chemical plants, oil fields, heavy construction, R/R equipmentR/R equipment

Cast Stainless SteelsCast Stainless SteelsCast Stainless SteelsCast Stainless Steels

Similar to steelsSimilar to steelsSimilar to steelsSimilar to steelsPossess long freezing ranges and high melting Possess long freezing ranges and high melting temperaturestemperaturesppCan be heat treated and weldedCan be heat treated and weldedHave high heat and corrosion resistanceHave high heat and corrosion resistanceHave high heat and corrosion resistanceHave high heat and corrosion resistanceApplications:Applications:

Chemical & food industriesChemical & food industriesChemical & food industriesChemical & food industriesIn severely corrosive environmentsIn severely corrosive environmentsFor very high temperature serviceFor very high temperature service

Economics of CastingEconomics of CastingEconomics of CastingEconomics of Casting

Unit cost (of castings as for all processes)Unit cost (of castings as for all processes)Unit cost (of castings, as for all processes) Unit cost (of castings, as for all processes) depends on costs of materials, equipment depends on costs of materials, equipment and labourand labourand labourand labourPreparations for casting include production Preparations for casting include production of molds and dies that also have similarof molds and dies that also have similarof molds and dies that also have similar of molds and dies that also have similar costscosts

TABLE 12.6 TABLE 12.6 General Cost Characteristics of Casting ProcessesGeneral Cost Characteristics of Casting Processesgg

Economics of CastingEconomics of CastingEconomics of CastingEconomics of CastingCost components:Cost components:pp

Molds (extremes: sand Molds (extremes: sand -- low; die low; die -- high)high)Melting & pouring metalMelting & pouring metalHeatHeat--treatingtreatingHeatHeat--treatingtreatingCleaningCleaningInspectionInspectionL b i di t kill d ti i dL b i di t kill d ti i dLabour varies according to skill and time requiredLabour varies according to skill and time required

Sand casting economic for low volumesSand casting economic for low volumesSand casting economic for low volumesSand casting economic for low volumesSustained high production rates can justify high Sustained high production rates can justify high cost of dies and machinery; cost of dies and machinery;

SummarySummarySummarySummary

General guidelines developed coveringGeneral guidelines developed coveringGeneral guidelines developed covering General guidelines developed covering shape of casting and design of process to shape of casting and design of process to reduce hot spots; important to follow good reduce hot spots; important to follow good p p gp p gcasting practice for control of metal flowcasting practice for control of metal flowNumerous ferrous and nonNumerous ferrous and non--ferrous alloys ferrous alloys yywith wide range of characteristics and with wide range of characteristics and production requirementsproduction requirementsEconomic considerations are as important Economic considerations are as important as technical considerationsas technical considerations