Materials Selection for Engineering Design

MaterialsSelectionforEngineeringDesignMaterialsSelectionThedesignerofanyproduct,otherthansoftwaremustgetinvolvedwithmaterialselection.Onlyoccasionallywilltheexactgradeofmaterialbespecifiedbythecustomer.Eventhenthedesignermustunderstandthematerialtobeabletodesigntheproduct.Decisions,decisions!Somanymaterials,somuchinformation.Howdowedecide?Howdowebegintochoose?Firstweneedtolookatthefunctionoftheproduct–productanalysisProductAnalysisJustwhatitsays–analysetheproduct!Whatdoesitdo?Howdoesitdoit?Wheredoesitdoit?Whousesit?Whatshoulditcost?CaseStudy–abikeWhatisthefunctionofabike–obvious?Howdoesthefunctiondependonthetypeofbike?RacingTouringMountainbikeCommuterChildsCaseStudy–abike(2)Howisitmadetobeeasilymaintained?Whatshoulditlooklike(coloursetc.)?Whatshoulditcost?Howhasitbeenmadecomfortabletoride?Howdothemechanicalpartsworkandinteract?Componentorsystem?1stproblemis…….Isitonecomponentorasystemofcomponentsworkingtogether?Aspannerisacomponent,acordlessscrewdriverisasystem.SystemAnalysisWhenweanalyseasystemweneedtobreakthesystemdownintoindividualcomponentsandthenanalyseeachone.CordlessscrewdriverSystemAnalysis–thebikeThebikebreaksdown(wehopenot!)intovariousparts:FrameForksWheelsSaddleEtc.SystemAnalysis–thebike(2)Wenowneedtolookatthefollowingforeachpart:Requirements(mechanical,ergonomic,aestheticetc.)FunctionHowmanyaregoingtobemade?Whatmanufacturingmethodsarewegoingtouse?ManufacturingOhNo!Wehavetoactuallymakeit!Thisisakeyquestionwhichhasamassiveinfluenceonmaterialsselection.e.g.Theframe,whatmaterialscouldweuse?FrameMaterialsSteel–Strong,stiff,heavy,butcheapAluminium–weaker,lighter,moreexpensivethansteelComposite(CFRP)–strong,stiff,verylight,butexpensivetobuyandtofabricateBikeFrameFrameDesignDetailWhatProperties?Mechanical–Strength,modulusetc.Physical–Density,meltingpoint.Electrical–Conductivity,resistivity.Aesthetic–Appearance,texture,colourProcessability–Ductility,mouldabilityAndlast,butnotleast……….Cost,cost,cost!WheredoIfindthedata?TextbooksDatabooksManufacturer’sliteratureInternetSitesTextbooksGoodforgeneralinformationSomehavetablesofpropertiesNotgoodfordetailedspecificationsandproperties.AusefulfirstpointofcallDatabooksOneofthequickestsourcesofdetailedinformation.Usuallycontaingradesandspecificationsaswellasproperties.Smallandperfectlyformed–pocketbooksEasytonavigatearoundManufacturer’sliteratureVariableinqualityandusefulness.Oftenonlycovertheirproducts.Usuallydonotcomparematerials.Canbebiased.Goodforfinalselectionbeforeordering.InternetSitesCanbearealminefield.Lotsofpoorlypresentedinformation.Googlesearchesbringuplotsofrubbish.Hardtofindtechnicalinformation.Besttousenon-commercialsites.MaterialsSelectionCharts23Modulus-DensityChartModulusspans5ordersofmagnitude0.01GPaforfoamsto1000GPafordiamondThechartsthereforeuselogarithmicscales,wheretwicethedistancemeanstentimes.Thismakesitpossibletoshowthefullrangeononechart,MaterialsSelectionChartsMaterialsSelectionChartsAlloweasyvisualisationofpropertiesShowlotsofdifferentmaterialsCanbe‘drilleddown’tospecificsShowbalancesofpropertiese.g.strengthvcostIdealforafirst‘roughcut’selectionSummary1.Thinkaboutthedesignfromergonomicandfunctionalviewpoint.2.Decideonthematerialstobeused.3.ChooseasuitableprocessthatisalsoeconomicSteps2&3maybeiterative.Don’tforgetthe……………BiggerPictureIstheproductperformancedrivenorcostdriven?Thismakesahugedifferencewhenchoosingmaterials.ManufacturingProcessAlthoughweusuallychoosematerialsfirstsometimesitistheshapeandprocesswhichisthelimitingfactor.CaseStudy(2)DrinkContainerWhataretherequirements?CaseStudy(2)DrinkContainerProvideleakfreeenvironmentforstoringliquid.Complywithfoodstandards&protectliquidfromhealthhazards.Forfizzydrinks,withstandpressure.Brandimage&identityEasytoopenEasytostore&transportCheapforhighvolumesPossibleMaterialsSteelAluminiumGlassPlasticPaper