Manufacturing Engineering and Technology (12)

Kalpakjian • SchmidManufacturing Engineering and Technology © 2001 Prentice-Hall Page 12-1

CHAPTER 12

Metal Casting: Design, Materials, andEconomics

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Casting Design Modifications

Figure 12.1 Suggested designmodifications to avoid defectsin castings. Note that sharpcorners are avoided to reducestress concentrations.

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Casting Cross-Sections

Figure 12.2 Examples of designs showing the importance of maintaining uniform cross- sections incastings to avoid hot spots and shrinkage cavities.

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Avoiding Shrinkage Cavities

Figure 12.3 Examples ofdesign modifications to avoidshrinkage cavities in castings.Source: Steel CastingsHandbook, 5th ed. SteelFounders' Society of America,1980. Used with permission.

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Chills

Figure 12.4 The use ofmetal padding (chills) toincrease the rate of coolingin thick regions in a castingto avoid shrinkage cavities.Source: Steel CastingsHandbook, 5th ed. SteelFounders' Society ofAmerica, 1980. Used withpermission.

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Normal Shrinkage Allowance for Some MetalsCast in Sand Molds

TABLE 12.1Metal PercentGray cast ironWhite cast ironMalleable cast ironAluminum alloysMagnesium alloysYellow brassPhosphor bronzeAluminum bronzeHigh-manganese steel

0.83–1.32.1

0.78–1.01.31.3

1.3–1.61.0–1.6

2.12.6

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Parting Line

Figure 12.5 Redesign of acasting by making the partingline straight to avoid defects.Source: Steel CastingHandbook, 5th ed. SteelFounders' Society of America,1980. Used with permission.

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Casting DesignModifications

Figure 12.6Examples ofcasting designmodifications.Source: SteelCastingHandbook, 5thed. SteelFounders'Society ofAmerica, 1980.Used withpermission.

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Desirable and Undesirable Die-CastingPractices

Figure 12.7 Examples ofundesirable and desirable designpractices for die-cast parts. Notethat section-thickness uniformity ismaintained throughout the part.Source: American Die CastingInstitute.

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Mechanical Properties for Various Groups ofCast Alloys

Figure 12.8 Mechanical properties for various groups of cast alloys. Note that gray iron has very littleductility and toughness, compared with most other cast alloys, some of which undergo considerableelongation and reduction of area in tension. Note also that even within the same group, the properties ofcast alloys vary over a wide range, particularly for cast steels. Source: Steel Founders' Society ofAmerica.

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Mechanical Properties for Various Groups ofCast Alloys (cont.)

Figure 12.8 Mechanical properties for various groups of cast alloys. Note that gray iron has very littleductility and toughness, compared with most other cast alloys, some of which undergo considerableelongation and reduction of area in tension. Note also that even within the same group, the properties ofcast alloys vary over a wide range, particularly for cast steels. Source: Steel Founders' Society ofAmerica.

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Typical Applications for Casting and CastingCharacteristics

TABLE 12.2Type of alloy Application Castability* Weldability* Machinability*Aluminum Pistons, clutch housings, intake

manifoldsE F G–E

Copper Pumps, valves, gear blanks,marine propellers

F–G F F–G

Ductile iron Crankshafts, heavy-duty gears G D GGray iron Engine blocks, gears, brake disks

and drums, machine basesE D G

Magnesium Crankcase, transmission housings G–E G EMalleable iron Farm and construction machinery,

heavy-duty bearings, railroadrolling stock

G D G

Nickel Gas turbine blades, pump andvalve components for chemicalplants

F F F

Steel (carbon andlow alloy)

Die blocks, heavy-duty gearblanks, aircraft undercarriagemembers, rail-road wheels

F E F

Steel (high alloy) Gas turbine housings, pump andvalve components, rock crusherjaws

F E F

White iron Mill liners, shot blasting nozzles,railroad brake shoes, crushers andpulverizers

G VP VP

Zinc Door handles, radiator grills, E D E

*E, excellent; G, good; F, fair; VP, very poor; D, difficult.

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Properties and Typical Applications of Cast Irons

TABLE 12.3

Cast iron Type

Ultimatetensile

strength(MPa)

Yieldstrength(MPa)

Elongationin 50 mm

(%) Typical applicationsGray Ferritic

PearliticMartensitic

170275550

140240550

0.40.40

Pipe, sanitary wareEngine blocks, machine toolsWearing surfaces

Ductile(Nodular)

Ferritic PearliticTemperedmartensite

415550825

275380620

1862

Pipe, general serviceCrankshafts, highly stressed partsHigh-strength machine parts,wear-resistantparts

Malleable Ferritic

PearliticTemperedmartensite

365

450700

240

310550

18

102

Hardware, pipe fittings, general engineeringserviceRailroad equipment, couplingsRailroad equipment, gears, connecting rods

White Pearlitic 275 275 0 Wear-resistant parts, mill rolls

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Mechanical Properties of Gray Cast Irons

TABLE 12.4

ASTMclass

Ultimatetensile

strength(MPa)

Compressivestrength(MPa)

Elasticmodulus

(GPa)Hardness

(HB)

20 152 572 66 to 97 15625 179 669 79 to 102 17430 214 752 90 to 113 21035 252 855 100 to 119 21240 293 965 110 to 138 23550 362 1130 130 to 157 26260 431 1293 141 to 162 302

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Properties and Typical Applications of CastNonferrous Alloys

TABLE 12.5

Alloys (UNS) Condition

Ultimatetensile

strength(MPa)

Yieldstrength(MPa)

Elongationin 50 mm

(%) Typical applicationsAluminum alloys 195 (AO1950) 319 (AO3190) 356 (AO3560)

Heat treatedHeat treatedHeat treated

220–280185–250260

110–220125–180185

8.5–22–1.55

Sand castingsSand castingsPermanent mold castings

Copper alloys Red brass (C83600) Yellow brass (C86400)

AnnealedAnnealed

235275

11595

2525

Pipe fittings, gearsHardware, ornamental

Manganese bronze(C86100)

Annealed 480 195 30 Propeller hubs, blades

Leaded tin bronze(C92500)

Annealed 260 105 35 Gears, bearings, valves

Gun metal (C90500) Annealed 275 105 30 Pump parts, fittingsNickel silver (C97600) Annealed 275 175 15 Marine parts, valvesMagnesium alloys AZ91A AZ63A

AZ91C EZ33A HK31A QE22A

FT4

T6T5T6T6

230275

275160210275

15095

130110105205

312

5384

Die castingsSand and permanent moldcastingsHigh strengthElevated temperatureElevated temperatureHighest strength

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General Cost Characteristics of CastingProcesses

TABLE 12.6Cost*

Process Die Equipment LaborProductionrate (Pc/hr)

Sand L L L–M <20Shell-mold L–M M-H L–M <50Plaster L–M M M–H <10Investment M–H L-M H <1000Permanent mold M M L–M <60Die H H L–M <200Centrifugal M H L–M <50* L, low; M, medium; H, high.