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DESIGNGUIDELINES193MATERIALSELECTIONCommerciallyproducedmaterialssuitableforstampingandfabricationcoverabroadrange.Includedarenotonlyalltypesofferrousandnon-ferrousmetalsbutalsoalargearrayofpaper,fiber,leatherandplasticproducts.Thischapterdealsexclusivelywithferrousandnon-ferrousmetalswhicharemostcommonlyusedinmetalforming.Typicalpropertiesofmetalalloyscommonlyusedinmetalformingappearinthetablesthatfollow.Thefollowingisadensitychartforthemate-rialscoveredinthischapter.DensityChartMaterialDensitySteels0.28lbs./cubicinchSpecialLowCarbonColdRolledSteelProducts0.28lbs./cubicinchSpringSteels0.28lbs./cubicinchStainlessSteels0.29lbs./cubicinchAluminums0.11lbs./cubicinchCopper&itsAlloys0.32lbs./cubicinchBrass0.31lbs./cubicinchPhosphorBronze0.32lbs./cubicinchBerylliumCopper0.30lbs./cubicinchSteelsAllsteelsusedinmetalformingstartoutashotrolled.However,theuseofhotrolledsteelislimitedbecauseitisnotavailableinthick-nessesoflessthan0.060in.(1.5mm).Also,thethicknessvariationofhotrolledstockpreventsitsuseinhigh-precisionapplications.•Hotrolledsteel(HRS)canbepurchasedinthreequalities:1)Hotrolled,withrollingscaleonitssurfaces.Usedforroughandheavywork,ofteninvolvingbasicweldments.Leastexpensive.2)Pickledandoiled,referredtoasHRPOsteel,wherethehot-rollingscaleisremovedbyacidicetching,followedbyoilcoatingforrustprotection.Surfacefinishcanbeupto120rootmeansquare(rms).Usedontruckchassisandsimilarwork.3)Skin-passedhot-rolledsteel,aHRPOsteelwithone“skin-pass”coldrollingaddedforasmoothersurface,similartocoldrolledsteel.Allotherpropertiesremainthesameasregularhot-rolledsteel.MaterialSelection20DESIGNGUIDELINES•Coldrolledsteel(CRS)isacollectivenameforallsteelwhichisfinishprocessedthroughacoldrollingreductionmill.Thisprocessfollowstheinitialhotrollingandthenpickling,forscaleremoval.Thecoldrollingprocessrefinesthesurfacefinishandstrainhardensthematerial.Thenamecoldrolledsteeldoesnot,initself,implyanysteelquality,exceptforthesurfacefinish.SeeTable1.•SheetandstripCRSsheetandstriparetwodistincttypesofsteel,bothmillproducedincoilform.Mostmillsarededicatedtomakingeithersheetorstripqualitymetalexclusively.Unfortunately,thetermsCRSsheetandstripareveryconfusinganddonotdescribeashapeorsize.QualityAmericanmillsproduceCRSsheetandstriptoAISI(AmericanIronandSteelInstitute)standardshavingcarboncontentof0.08to0.20%.Therearedifferentstandardsforsomeimportedsteelswithcarboncontentaslowas0.04%whichissoldas“commercialgrade”withalowerandsometimesundefinedquality.Thefourmajordifferencesbetweencoldrolledsheetandstrip:1)Striphasamuchbettersurfacefinish.2)Stripisrolledtomuchtighterthicknesstolerances.3)Stripisrolledtoamaximumwidthof24in.(0.6m);sheetsteelto72in.(1.8m),butnor-mally48in.(1.2m).4)Stripusesanumbersystemfortemperdesignations;sheetusesadescriptivesystem.Strip’sclosethicknesscontrolandconsistentTableI.PhysicalandMechanicalPropertiesofSelectedCold&HotRolledSteelCommercialCommercialGenericDrawQualityQuality1/4Hard1/2HardQualityPropertyColdRollColdRollColdRollColdRollColdRollHotRollformsheetorstripsheetsheetorstripsheetorstripsheetorstripsheetdensityIb/in3(g/cm3)0.28(7.87)0.28(7.87)0.28(7.87)0.28(7.87)0.28(7.87)0.28(7.87)mechanicalpropertiesmodulusofelasticity106PSl2.92.92.92.92.92.9(tension)N/mm2203000203000203000203000203000203000tensilestrength1000PSI40.6-65.339.2-50.843.5-58.045.0-65.355.1-75.445.0-52.2N/mm2(typical)280-450270-350300-400310-450380-520310-360yieldstrength1000PSI24.623.224.629.739.924.6N/mm2(typical)~170160170205275170elongation%typicalrange24-4035-4024-4013-274-1624-40hardnessHRB45-7555max.65max.60-7570-8545-65forming,drawingexcellent,excellentverygood,acrossgrain:180°bendradiusbendradiuswillmeetanyflatonitselfinatbendradius2Tmin.1/2Tat90°engineeringanydirectionwithgrain:90°drawingreq’tatbendradiusweldabilityexcellentexcellentexcellentlimitedlimitedexcellenttensilestrengthresultsinmuchbetterformingcharacteristics,possiblehigherproductionrates,andsuperiorsurfacefinish.TableIIisaquickoverviewofthesteelcate-gorieswitharelativecostcomparison.Yoursuppliercanmaketheproperrecom-mendationbasedonthedemandsyourdesignplacesonthematerialspecification.Coldrolledsheetandstripsteelisreadilyavailableinallstandardthicknessesandtem-persfromwarehousesspecializingincoldrolledproducts.Specialitycoldrolledsheetandstripofexactingthicknessandtempercanbeordereddirectlyfromthemills,butrequiresaminimumorderofatleastfivetonsforsheetandonetonforstrip.Deliveryleadtimesaregenerallyextended.Anotheroptionutilizesare-rollingmillwiththeabilityofre-rollinganoff-the-shelfproducttoexactingthickness,temperandfinishrequirements.Theadvantageofre-rollingmillsistheabilitytoprocesssmallerminimumorderquantitiesinlesstimethanthehotrolledmills.FormabilityofVariousQualitiesandTempersColdrolledsheetin1⁄4hardandstrip#3tempercanbehemmedwiththegrain.Drawingquality(sheet)and#5tempers(strip)becauseoftheirexcellentformingcharacteristics,areideallysuit-edforsomeofthemostsevereformsanddraws.TableIIIillustratestheminimumbendradiusinthevarioustempers.Cautionmustbeexer-cisedwhenspecifyingminimu
本文标题:Chapter 03 - Material Selection
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