設(shè)計(jì)指南-模具設(shè)計(jì)-圖文

DesignguideContentsContentsGeneralIntroduction1DesignDevelopment...............91.1Introduction..................................91.2Materialdesignfactors.......................91.3Developmentsteps...........................92Designforstiffness................132.1Introduction..................................132.2Howtodeterminestiffness....................132.3Increasingpartstiffness......................152.4Optimizationofstiffness......................163Designforstrength................193.1Introduction..................................193.2MaterialStrength............................19Designguide1Contents3.3Effectsofvariousfactorsonstrenght...........203.4PartStrength.................................213.5Improvingpartstrength.......................223.6Designconsiderations........................234Designforbehaviourovertime..254.1Introduction..................................254.2Statictimedependentphenomena..............254.3Dynamictimedependentphenomena...........285Designforimpactperformance..315.1Introduction..................................315.2Commonimpacttestingmethods...............315.3Designconsiderations........................33Designguide1Contents6Designforappearance............356.1Introduction..................................356.2Surfacedefects..............................357Designforprecision...............397.1Introduction..................................397.2Shrinkagephenomena.........................397.3Materialsandshrinkage.......................407.4Designrelatedfactors........................417.5Mouldrelatedfactors.........................417.6Processingrelatedfactors.....................427.7Secondaryeffects............................42Designguide1Contents7.8Simulationtechniques........................427.9Summary....................................438Designformouldability...........458.1Introduction..................................458.2Materialissues..............................458.3Shrinkage....................................468.4Coolingtime.................................478.5Designconsiderations........................488.6Processingconsiderations.....................528.7Ejection.....................................549Designforrecyclability...........5510Designforautomation...........5711Appendix...........................59Theintentionofthisguideistoprovidethedesignandengineeringcommunitieswithaninsightintotheconsiderationsnecessarywhendesigningapplicationsinengineeringthermoplastics.Manyoftheseconsiderationsrelatetomouldingcriteria,sothoseinvolvedinthemanufacturingandprocessingofplasticscomponentsshouldalsofindituseful.Typically,designmanualsdealwithaspecificresinfamily,presentingproperties,designcriteria,assemblyandotherrelatedinformation.GEPlastics’productlineincludescrystalline,amorphous,thermoplasticelastomersandglassmatreinforcedpolymers.Becauseofthisdiversity,thisbrochurewillconcentrateonissuescommontoallinjectionmouldablethermoplasticresins.Thisdesignguidediffersfrommostbyvirtueofits‘Designingfor’concept,helpingthereadermovequicklytotheissuethatneedsaddressing.Consequently,discussionofcertainaspectscanoccurinmorethanonesection,whichdemonstrateshowintegraltheprocessofdesigningforplasticsis.FollowingtheexplanatorychaptersisasectionshowingtypicalengineeringmaterialperformancegraphsforarangeofGEPlasticsthermoplasticpolymers.Supplementarypublicationscoveringassemblytechniques,polymerprocessingconsiderationsandoverviewsofspecificresinsintheGEPlasticsproductlinesareavailableonrequest.Inaddition,monographsdiscussingdetaileddesignstudiesarereleasedperiodically,coveringtheseissuesingreaterdepththanispossibleinthisgeneralizedguide.Introduction1.1IntroductionThroughouttheprocessofproductdesign,bothfunctionalandmaterialaspectsmustbeconsidered.Functionaldesignfactorsrelatetoproductionandassembly.Materialdesignfactorsconcerntheperformanceofamaterialinservice.Thisperformance,whichincludesstrengths,weaknessesandlimitations,isinvestigatedtoprovidethestartingpointofthedesignprocess.1.2MaterialdesignfactorsConsiderableinformationisneededbythedesignengineertodevelopaproductdesignfromtheinitialconcept.Thiscanbeasmoothprocessifcarefulattentionisgiventoeachstepinvolved.Thedesignermustknowtheend-useperformancerequirementsoftheproposedapplication.Todeterminewhetheramaterialcanmeettheserequirements,thedesignermustbeabletorelyoninformationprovidedbytherawmaterialsupplier,indicatingtheenvironmentalandphysicalcapabilitiesofthematerial.1.3DevelopmentstepsIngeneral,thelowerstrengthpropertiesofpolymerscomparedwithmetalsandwoodsrequirethatproductsbedesignedtoutilizealargerpercentageoftheiravailablestrength.Specificinformationneededtoestablishend-userequirementsincludes:(aAnticipatedstructuralrequirementsLOADSThesedictatethestressesamaterialwillbesubjectedto,andtheydefinecomponentdeflections.RATEOFLOADINGAthermoplasticmaydemonstratedifferentbehaviourwithchangesinloadingrate.Therefore,inadditiontoitsmagnitude,therateatwhichloadingisappliedshouldbeinvestigated.DURATIONOFLOADINGInitialnegligibledeflectionsresultingfromasmallloadmaybecomeunacceptablylargeiftheloadismaintained.IMPACTFORCESBecausetheapplicationofhighloadsforshortperiodsoftimemayresultinprematurefailure,thenatureofimpactforcestowhichthecomponentwillbesubjectedshouldbedetermined.VIBRATIONThisinducesstressanddeflectionchanges.Thoughthesemaybesmall,componentfailuremayoccurthroughconstantrepetition.FORESEEABLEMISUSEThoughstructuralrequirementsmayhavebeensatisfied,andanappropriatedesignproposed,failurecanstilloccurasaresultofmisuse.Toestablishtheanticipatedrisklevel,therefore,a‘riskassessment’oftheproductinuseshouldbemade.The‘relevancetree’methodisidealforthispurpose,providingdatatofacilitateassessmentofforeseeablemisuse.Theresultsshouldthenbeweighedagainstthefinancialaspectsoftheproduct.Thisexerciseisoftencalled‘ProductRiskAnalysis’.Additionaldetailsarenotgivenheresinceeachcompanyappliesitsownmeasures.GeneralElectricPlasticsispreparedtoprovideassistanceinthismatterand,ifrequired,contactshouldbemadewiththenearestGEPlastics’salesoffice.(bAnticipatedenvironmentsTEMPERATUREEXTREMESAllmaterialspossessaworkingtemperaturerange.Outsidethisrangethecomponentcannotproperlyperformitsintendedfunction.Inaddition,thepropertiesofthematerialmayvaryconsiderablywithinworkinglimits.Asallthermoplasticsaresubjecttoattackbycertainchemicalagents,theserviceenvironmentoftheproposedcomponentmustbeestablished.Outdoorexposureforprolongedperiodsmayresultinmaterialdegradation.(cAssemblyandsecondaryoperationsUsuallyaplasticcomponentisnotusedinisolationbutisjustoneofanumberofcomponentsmakinguptheend-product.Thetechniqueusedforassembly,suchasmechanicalfastening,weldingandadhesivebonding,needstobeconsideredattheinitialdesignstagetooptimizethecomponentforeaseofassembly,(andeaseofhandlinginthecaseofautomatedassembly,oreaseofdisassemblyformaintenanceandrecycling.9DesigndevelopmentSecondaryoperations,suchaspainting,printingandhotstamping,alsohavetobegivenearlyconsiderationinordertodesignthebestsurfaceprofile.Thismeansavoidingforexamplesinkmarksandsharpchangesinshapetoachieveahighqualitysmoothsurface.(dCostlimitsThefollowingshouldbeestablished:·Componentcostresultinginprofitablesales·Annualvolume·Economicprocessingmethod(swithestimatedcycletime(s·Toolingcost(sforselectedprocessingmethod(s·Theexpectedservicelifeofthecomponent(eRegulations/standardscomplianceCheckwhichstandardsorregulationsapplyorcanbeappliedinthemarketplacetothecomponent,productorappliance,forexample:STANDARDSIEC/CEEInternationalElectricalCommittee/CommitéEuropéand’ElectricitéISO/CENInternationalStandardsOrganization/CommitéEuropéandeNormalisationDINDeutscheIndustriefürNormungenBSIBritishStandardsInstituteNFNormesFrancaisASTMAmericanSocietyforTestingofMaterialsREGULATIONSULUnderwritersLaboratoriesCSACanadianStandardsAssociationCEEPublicationsoftheCommitéEuropéand’ElectricitéApreliminaryconceptsketchoftheproposedcomponentcanhelpthedesignertodeterminewhichaspectsareinflexible,andwhichcanbemodifiedtoachieverequiredperformance.Thepreliminarysketch,therefore,shouldincludebothfixedandvariabledimensions.AGEPlastics’materialshouldbeselectedthatwillsatisfyinitiallydefined,end-userequirements.Thecomparativepropertydatasheetshouldbethefirstdocumentwhichisconsulted.Initialselectionmaysubsequentlyberefinedbyreviewingthetime,temperatureandenvironment-dependentpropertiesrelevanttotheparticularapplication.Supplementarydata,suchasabrasionresistanceorductility,maybeneededtoconfirmtheselection.Materialpropertiescanbedividedintotwomaincategories.(aMechanicalpropertiesusedessentiallyforcomponentdesigncalculations:·Elasticlimit·Tensilestrength·Modulusvstemperature·Poisson’sratio·Apparent(creepmodulus·Fatiguelimit·Coefficient(softhermalexpansion·Coefficientoffriction·Thermalconductivity·Density·Mouldshrinkage(bOtherrelevantproperties:·Hardness·Impactstrength·Chemicalresistance·Weatheringresistance·Abrasionresistance·Ductility·Flammability·Heatdeflectiontemperature·ElectricalpropertiesTodesignaplasticcomponent,informationconcerninganycombinationofmaterialpropertiesmayberequired.Ifthedataareunavailable,orassistanceisneededininterpretation,contactshouldbemadewiththenearestGEPlastics’salesoffice.Ifthisisnecessary,fourareasinparticularshouldbeconsidered:(aThespecificpropertybalanceoftheselectedgrade,(e.g.tensilestrength,impactresistance(bProcessinglimitations,(e.g.wallthicknessvsflowlengths(cAssemblymethods,(e.g.snap-fits,adhesives(dCostofmodificationanditsimpactoncomponentand/orprojectbud-get,(refertosFIGURE1.Strengthofmaterialsformulaeshouldbeusedinconjunctionwithmaterialpropertydatatocalculatenecessarydimensionssuchaswallthickness.(RefertoChapter3‘Designforstrength’.Designcalculationsofarepetitiveoriterativenature,however,maywarrantacomputer-aidedapproach.Twoparticularlyrelevantcomputer-aidedsystemsareFlowAnalysisofaninjectionmoulding,andStressAnalysisofafinalcomponent.BothgenerallyusetheFiniteElementMethod.Thisapproachconsidersthegeometryandphysicalpropertiesofthecomponentasacontinuumofsmallmanageableparts,orfiniteelements.Eachelementofthestructureisindividuallyinvestigatedinrelationtoitsneighbouringelements,thetotalstructure,andthephysicalconstraintsonthesystem.Alargenumberofsimultaneousequationsresult,thesolutionofwhichisparticularlysuitedtotherepetitivecapabilitiesofacomputer.Becausetheperformanceofaninjectionmouldedcomponentislargelydependentonthemouldingprocess,considerationoftheserviceconditionsofthecomponentinisolationisinsufficienttoensureasuccessfulproduct.Simpleshapesshouldnotgivematerialflowproblemstotheexperiencedtool-makerandmoulder.However,largercomponentsofcomplexgeometryoftenpresentdifficulties,forexamplepositioningandnumberofgates,runnerdimensionsandlocationofweldlines.10Designguide1DesignDevelopmentIntheflowanalysisprocess,acomputermodelofthecomponentisproduced,andinitialgatingpositionsselected.Thepredictedmannerinwhichthematerialwillfillthecavityisthenpresentedgraphicallyandnumerically.Isochronoustemperaturesandpressuresthroughoutthesystemarecalculated,inadditiontoweldlinelocationsandundesirableconditionssuchasoverpacking.Mouldingvariablesand/orgatingpositionsaresubsequent-lychanged,ifnecessary,inordertoachieveanoptimumflowpattern.Bymeansofthisiterativeapproach,analysesofdifferentoptionsarepossiblebeforecommitmenttoactualtoolproduction.Moreover,processingdifficultiesareidentifiedandmayberectifiedatthedesignstage.Nowadays,flowsimulationisnottheonlysoftwareavailabletothedesigner.Otherinjectionmouldingrelatedsoftwarepredictiontoolsinclude:warpage,mouldcooling,fibreorientation,(forexampleforglass-filledthermoplastics,moulded-instressesandmanymore.Acomponentinservicewillbesubjectedtoforceswhichinducestressesinthematerial.Toensurethatfailureresultingfromoverstressingdoesnotoccur,itisessentialthatthestressesdonotexceedrecommendeddesignlimits.AswithFlowAnalysis,theinvestigationofasimplegeometryshouldnotpresentanydifficulty,sinceequationswhichcanoftenbesolvedbysubstitutionhavebeenderivedformanycommonlyencounteredsituations.However,theanalysisofacomplexgeometry,thoughnotgenerallysuitableforthisapproach,maybesolvedbythefiniteelementmethod.Amathematicalmodelofthecomponent,definingthegeometrybyx,yandzco-ordinates,isfirstdescribed,togetherwiththepropertiesofthematerial.Theboundaryandloadingconditionsarethenenteredandspecificoutputrequested.Stressesinaparticularareamaybeofinterestforexample.Atthispointintheprocedure,aprototypeshouldbeconstructed.Theprototypeanditstestingcanhelpthedesignerby:·Establishingconfidenceinthedesignbyconfirmingthatcomponentrequire-mentsdonotexceeddesignlimits.·Developingpreliminaryproductperformanceinformation.·Identifyingpotentialproblemareasinperformance,manufacturingorassembly.·Allowingpre-launchassessmentandfeedbackfromconsumertrials.Inordertoobtainusefulresults,particularattentionshouldbepaidtocertainaspectsofthetesting:·Properanalysisofcomponentrequirements.·Closesimilaritytotheproposedproduct,particularlyincriticalorsuspectperformanceareas.·Developmentofrealisticsimulateduseandstoragetests·CommitmenttothetimeandeffortrequiredfortestingbeforeproductintroductionTestsshouldbeconductedtosimulateuseandstorageofthecomponent.Itshouldbeestablishedwhichtestsreflectdefinedcomponentrequirements,andwhethertheycanbeconductedinthelaboratoryorinsitu.Frequently,thetestequipmentdevelopedcanbeusedforfuturequalitycontroltesting.Productperformancetestscanbeconductedonfunctionalprototypesorproductionparts.Sincefunctionalprototypesmaybeproducedusingnon-productiontoolingorpartmodelling,cautionmustbeexercisedduringtestingandinterpretingtheresults.Theprototypemaynotbehaveinexactlythesamemannerasaproductioncomponent.Theinitialproductioncomponentsshouldalsobetestedtoconfirmproductperformancetesting.Severalspecializedtechniques,examplesofwhichfollow,canbeusedforproductperformancetesting:·Straingaugeanalysis·Brittlecoatinganalysis·Photoelasticity·Stressanalysisbythermalemission·Infra-redlightbanksforradiantheateffectmeasurement·Environmentalchambersforthermalcycling·Lifetestingundersimulatedusecond-itions·Acceleratedageingunderelevatedtem-perature,highhumidity,orultravioletradiationconditions·HolographyAlthoughcomputer-aidedtechniquesallowaccuratemodellingofaproposeddesign,theyshouldnotexcludeorreplacefinishedparttesting.Theconstructionofafunctionalprototypeisthereforeadvisable.11Designguide1DesignDevelopment2.1IntroductionThestiffnessofapartisdefinedastherelationshipbetweentheloadandthedeflectionofapart.ThisChapterwilldiscusswhatmodificationscanbemadetoapartinordertoinfluenceandoptimizestiffness.Itwillalsogivesomeguidelinesofhowthestiffnessofapartcanbecalculated.2.2HowtodeterminethestiffnessIngeneralthestiffnessofapartisdeterminedbyitsmaterialanditsgeometry.Themostimportantmaterialpropertyforstiffnessisthestress/straincurve.Ingeneral,theYoung’smodulus,whichisdeterminedfromthestress/straincurve,isthebestparametertobeusedwhencomparingthestiffnessofmaterials.However,whentheYoung’smodulusisused,thestress/straincurveisassumedtobelinear.Especiallyforthermoplastics,therangeinwhichthestress/straincurvecanbeestimatedwithastraightlineislimited.Forthisreason,whenastiffnesscalculationofapartismade,itisnecessarytocheckiftheoccurringstressesandstrainsstillallowalinearapproach.Ifthisisnotthecase,itisadvisedtouseasecantmodulusforthestiffnesscalculation.ConsidersFIGURE2.SupposethatthestiffnessofapartiscalculatedusingtheYoung’smodulusY.Supposethataverificationoftheoccurringstressresultsinthevalues.Thisvalueisclearlyoutoftherangeinwhichalinearapproximationofthestress/straincurveisjustified.InthiscaseitisbettertorecalculatethestiffnessofthepartwiththesecantmodulusY*.Furthermore,itisimportanttoconsiderthetemperatureatwhichtheloadisapplied.Forthermoplasticsthestress/straincurvesareheavilydependentontemperature.Itisadvisedtoconsiderthestress/straincurveatthetemperatureatwhichtheloadisappliedforthecalculationofpartstiffness.Timealsoplaysaroleinthedeterminationofthestiffnessofapart.Itcaninfluencestiffnessinoneoftwoways:(athematerialisloadedforalongtime,(bthematerialisloadedincycles,(cthematerialisloadedduringaveryshorttime.Thephenomena(aand(baretypicallyknownascreepandfatigue.HowtheseeffectsmustbetakenintoaccountcanbefoundinChapter4‘Designforbehaviourovertime’.Phenomenon(cisknownasimpact.RefertoChapter5‘Designforimpact’.132DesignforstiffnesssFIGURE2AccountingformaterialnonlinearitiesBesidesthematerial,thegeometryisalsoimportantforpartstiffness.Whichfactorsofthegeometryareimportantismainlydeterminedbythetypeofload-ing.Itshouldbenotedthat,ingeneral,apartisloadedinmorethanoneofthefollowingtypesatthesametime.(aTensileloadingForapartloadingintension,(sFIGURE3,thecross-sectionalareaAandthelengthofthepartcareimportant.(bCompressiveloadingWhenapartisloadedundercompression,againthecross-sectionalareaAandthelengthofthepartarethegeometricalparametersthatdeterminethestiffness.Inthiscase,bucklingofthepartissomethingthathastobeconsideredseparately.(cFlexuralloadingForflexuralloading,themomentofinertiaandthelengtharethegeo-metricalparametersthatdeterminethestiffness.AscanbeseeninsFIGURE4,themomentofinertiaIisdefinedas:whereyisthedirectionperpendiculartotheneutralbendingaxisandAisthecross-sectionalarea.Forexample,forarectangularcross-section,withthedimensionaandb(sFIGURE5,Icanbecalculatedwiththeformulamentionedabove:(dTorsionalloadingWhenapartisloadedintorsion,thepolarmomentofinertiaandthelengtharetheimportantgeometricalparametersthatdeterminestiffness.ThepolarmomentofinertiaIpcanbecalculatedwithasimilarformulatothemomentofinertia.Asmentionedearlier,thestiffnessofaconstructionisdeterminedbythecombinationofthematerialandthegeometry.Thefollowingtwoexamplesillustratehowthestiffnessofapartcanbecalculated.EXAMPLE1ApartundertensionForapartoflengthc,andconstantcross-sectionalareaA,thedeflectionfcanbecalculatedwiththeformula:f=Fc/yAwhereFisthetensionforceandYistheYoung’smodulusofthematerial.FromthisformulaitcanbeseenthatthestiffnessofthispartcanbeincreasedbydecreasingI,increasingYorincreasingA.EXAMPLE2ApartunderbendingForapartoflengthcandmomentofinertiaI,loadedbyaforceFattheend,(sFIGURE6,thedeflectionfattheendcanbecalculatedusing:f=Fc3/3YIwhereFistheforceandYtheYoung’smodulusofthematerial.Thestiffnessofthispartcanbeincreasedbydecreasingc,increasingYandincreasingI.Supposethattheparthasarectangularcross-section.ThenIisgivenby1/12ab3,(sFIGURE5.ThismeansthatIcanbeincreasedbyincreasingeitheraorb,thoughincreasingbhasamuchlargereffect.stiffnessBesidesthegeometryandthematerial,otherimportantfactorshaveaninfluenceonstiffness,suchasthetypeofloadingortherestraintsofthepart.Aloadcan,forinstance,beconcentratedonapoint,butitcanalsobeapressureonanarea.Differentrestraintsthatareusedincalculationsareclampedorsimplesupports.Notethat,inreality,thefixingsystemwillalwaysbesomethinginbetweenfullyclampedandsimplysupported.14Designguide2DesignforstiffnessI=Aey2dAI=Aey2dA=eay2dy=1/3ay3d=1/12ab3sFIGURE3ApartloadedintensionsFIGURE4CrosssectionofapartsFIGURE5sFIGURE6Clampedpartloadedattheend-b_2-b_2b_2b_2Similarformulaetothosegivenaboveareavailablefordifferentcross-sections,forchangingcross-sections,andsoon.(PleaserefertotheAppendixforadditionalsourcesofreference.Theapplicationofformulaeislimitedduetodifferentfactors:(aThematerialbehaviourisassumedtobelinear,whichmeansthatthestress/straincurveofthematerialisastraightline.(bThegeometricaleffectsareassumedtobelinear.Forlargedeflectionsthisleadstoconsiderableinaccuracies.(cTheformulaegivenaboveassumearelativelysimpleshape.(dIngeneral,apartisnotpurelyloadedinonemode,butinacombinationofmodes.Asimplewayofaccountingformaterialnonlinearitiesisalreadygivenabove.Takingintoaccounttheotherfactorsismorecomplicated.Thesimpleformulaecannotbeusedanymorewhentheseeffectsplayanimportantrole.Ifthepartstiffnesshastobedeterminedforthistypeofproblem,theonlypossibilityiscomputersimulationusingthefiniteelementmethod.Acomputermodeloftheparthastobemadeandevaluatedwhichrequiresmuchmoretimethanhandcalculations.Also,anappropriatecomputersystemandsoftwaremustbeavailable.Ingeneral,thefollowingguidelinescanbegiven:(aForsimplegeometriesandsmalldeflections,handcalculationscanbemade.(bFormorecomplexgeometrieswithsmalldeflections,linearfiniteelementanalysistechniquescanbeused.(cOnlynonlineargeometricalfiniteelementanalysiscanaccountforlargedeflectionsoncomplexgeometries.Vibrationresistanceisimportantformanyapplicationssuchasautomotivecomponents.Allpartsdesignedinplasticoranyothermaterialwillhaveeigenfrequencies.Theseeigenfrequen-cieswill,amongstotherfactors,dependuponthestiffnessofthepart.Ifapartisloadedwithavibrationloadwithafrequencycloseto,orequalto,oneofitseigenfrequencies,apotentialdangerofpartdamageexists.Inautomotivecomponents,itisoftendesirabletohavethelowesteigenfrequencyofanyparttobeabovethenormaloperatingfrequenciesofthevehicle.Therefore,althoughapartmaybestiffenoughtomeetstaticloadingrequirements,itmayrequireadditionalstiffnesstoincreasetheeigenfrequencies.Finiteelementanalysiscanbeusedtopredicttheeigenfrequenciesofthepartaswellasthevibrationmodesshapeforeachoftheeigenfrequencies.Thistypeofanalysisiscalledmodalanalysis.Modalanalysisresultsareverysensitivetothetypeofloads,restraintsandtheirlocationsonthepart.Oftenitispossibletosignificantlychangethevibrationbehaviourofaplasticpartbyredesigningthewayitismountedorrestrained.Theuseofsafetyfactorsinengineeringdesigniscommonpracticewithalmostalltypesofmaterial.Plasticsarenoexceptiontothisrule.Conservativeassumptionsshouldbemadewhenpossibleandworstcaseloadsshouldbeconsidered.Itistheresponsibilityofthedesignengineertoanticipatethatproductswillnotalwaysbemanufacturedorusedasintendedorplanned.Insomecases,productfailureisacceptableunderunusualloading,orforanoccasionalpoorlymanufacturedpart.However,therearemanycasesinwhichsafetyfactorsmustbeconsidered.Therearenumerousreasonswhyaproductcanhavelessthanitsoriginallyintendedproperties.Someofthesereasonsarebeyondthecontrolofthedesignerandinclude:·Exposuretochemicalswhichdoesnotnormallyoccur·Mouldingissuessuchasinsufficientdryingorexcessiveheatingoftheresin·Toolwearresultingindimensionalchangesofthepart·Thepartisusedattemperaturesabovetheexpectedmaximum.·Thepartisusedinamannerotherthanwhatitwasdesignedfor.·Thepartisassembledpoorlyor‘forced’,incurringapre-load·Excessivemoulded-instressesresultingfromhighmouldingpressures,toosmallgatesandtoolowtooltemperatures.Asafetyfactoristypicallydecideduponbasedonpriorexperiencewithsimilardesigns.Ingeneral,thegreaterthepotentialdamagefromfailure,thegreaterthefactorofsafetythatshouldbeused.Inmanyindustries,safetycodesandtestproceduresexist,whichgivestandardsandrecommendationsforsafetyfactors.2.3IncreasingpartstiffnessFeatureslikeribsandV-groovescanbeusedefficientlytoimprovethestiffnessand