汽车专业英语PPT课件-section 4ppt课件Chapte12 2

Section4AutomotiveDesignandManufacturing,Chapter12AutomotiveManufacturing12.1Vehiclearchitecturedesignandmanufacturing12.2InjectionMoulding12.3JoiningForLightweightVehicles,Chapter12AutomotiveManufacturing12.2InjectionMoulding,NewWords,Chapter12AutomotiveManufacturing12.2InjectionMoulding,NewWords,Chapter12AutomotiveManufacturing12.2InjectionMoulding,NewWords,Chapter12AutomotiveManufacturing12.2InjectionMoulding,Injectionmoldingistheprincipalprocessingmethodusedforthevastmajorityofthermoplasticautomotiveparts.Itiscapableofproducingpartsofcomplexshapesandgeometryathighproductionrates,withgooddimensionalaccuracyandexcellentsurfacefinish.In-moldsurfacedecorationandsurfacetexturingcanbedoneininjectionmolding.Thebasicinjectionmoldingmachine(Fig.12-3)containsaninjectionunitandaclampingunit.Theinjectionunitconsistsofaheatedcylindricalbarrelandaproperlydesignedscrewthatrotatesinsidethebarrel.Solidpolymerpelletsorgranulesarefedintothehopperlocatedonthebacksideoftheinjectionunit.Asthepelletsaremovedforwardbytherotatingscrew,theystarttomeltandultimatelyturnintoahomogeneousliquidpolymer,whichiscollectedinasmallchamberlocatedinthefrontsectionoftheinjectionunit.,Chapter12AutomotiveManufacturing12.2InjectionMoulding,Aftertherequiredamountofliquidpolymeriscollected,thescrewrotationisstoppedandthescrewisnowmovedforwardtoactlikeapiston,forcingthecollectedliquidpolymertoflowintotheclosedmoldcavitylocatedintheclampingunit.Evenafterthemoldisfilled,additionalliquidpolymerisinjectedintothecavitytocompensatefortheshrinkageofthepolymerasitstartstocoolinsidethemold.Themoldcavityisheldcloseduntiltheaveragetemperatureofthepolymerpartfallsbelowthesolidificationtemperatureofthepolymer.Themoldisthenopenedandthepartisejected.Furthercoolingtoroomtemperaturetakesplaceoutsidethemold.,Chapter12AutomotiveManufacturing12.2InjectionMoulding,Figure12-3Basicinjectionmoldingmachine,Chapter12AutomotiveManufacturing12.2InjectionMoulding,Thecoolingtimeinthemold,whichhasamajoreffectontheinjectionmoldingcycletime,dependsonthepartthickness,melttemperature(thetemperatureoftheliquidpolymeratthetimeofinjection),moldwalltemperatureanddemoldingtemperature(theaveragetemperatureatwhichthepartisejectedfromthemold).Forshortercoolingtimes,themeltandmoldtemperaturesareselectedaslowaspossibleandthedemoldingtemperatureisselectedashighaspossiblewithoutintroducingdefectsandaffectingthequalityoftheinjectionmoldedpart.Dependingonthepartdesign,molddesignandprocessingparameters,avarietyofmoldingdefectscanbeobservedininjectionmoldedparts.Theyincludeunfilledcavity,surfaceblemishes,internalvoids,highshrinkage,warpage,sinkmarks,weldlinesandresidualstresses.,Chapter12AutomotiveManufacturing12.2InjectionMoulding,Manyofthesedefectscanbereducedoreliminatedbyselectingtheproperprocessparameters,suchasmelttemperature,moldtemperature,injectionpressureandinjectionspeed.Processparametersalsoinfluencemolecularorientation,residualstressesandcrystallinity(forsemicrystallinepolymers),which,inturn,influencethepropertiesandperformanceofinjectionmoldedparts.Avarietyofinjectionmoldingtechniquesnowexiststhathasexpandedtheuseofthermoplasticsintheautomotiveindustry.Theyhavealsocreatedopportunitiesforaddingmanynewdesignfeaturesandoptimizingtheuseofmaterial.Someofthese,suchasinsertmoldingandoutsertmolding,arevariationsoftheconventionalinjectionmoldingprocess.Ininsertmolding,smallcomponentsofothermaterials,suchasinternallythreadedmetalinserts,metalpinsandelectricalstrips,areplacedinthemoldcavitypriortoinjectingthepolymermelt.,Chapter12AutomotiveManufacturing12.2InjectionMoulding,Asthepolymermeltissubsequentlyinjected,itsurroundsthepre-placedcomponents,makingthemintegraltothemoldedpart.inoutsertmolding,thepolymermeltisinjectedontoametalframeplacedinthemoldcavity.Themetalframecontainsanumberofpunchedoutholesorprotrudingpins,whichserveastheanchoringlocationsforthepolymer.Bothprocessescanleadtoconsiderablesavingsinassemblyoperations,assemblytimeandtherefore,assemblycost.Alistofsomeoftheotherinjectionmoldingtechniquesisgivenbelow:(i)Lost-coreinjectionmoldingtoproducehollowinjectionmoldedpartswithcomplexinternalgeometryandundercutsinasinglemoldingoperation.(Example:Airintakemanifolds),Chapter12AutomotiveManufacturing12.2InjectionMoulding,(ii)Gas-assistedinjectionmoldinginwhichcompressednitrogengasisinjectedintotheliquidpolymerafterithaspartiallyfilledthecavity.Thegascreatesahollowchannelinthecoreoftheliquidpolymerand,asthegasmovesforward,itforcestheliquidpolymertofilltherestofthecavity.Reductionsinpartweight,materialusage,cycletime,clampingforceandsurfacedefectsaresomeoftheadvantagesofgas-assistedinjectionmolding.(Example:Doorhandles)(iii)Structuralfoaminjectionmolding,whichisusedtoproduceasandwichstructureofthinsolidskinsandafoamedcore,bothofthesamepolymer.Theadvantageofstructuralloammoldingisthatitproducespartswithhigherstiffnesstoweightratio.(Example:Instrumentpanels),Chapter12AutomotiveManufacturing12.2InjectionMoulding,(iv)Co-injectionorsandwichmolding,whichinvolveseithersequentialorconcurrentinjectionoftwodissimilarbutcompatiblepolymers,producingasandwichstructurewithonepolymerformingtheskinandtheotherformingthecore.Thesandwichstructureprovidespropertiesorcostadvantagesnotachievablewithasinglepolymer.(Example:Instrumentpanels)(v)Overmolding,whichutilizessequentialinjectionofthesamepolymerwithdifferentcolorstomakeamulti-coloredpart.Polymerswithdifferentpropertiescanalsobeovermoldedtomakemulti-functionalproducts.(Example:Multi-coloredtaillamplenses),Chapter12AutomotiveManufacturing12.2InjectionMoulding,(vi)Microcellularmolding,inwhichasupercriticalgas(usuallynitrogenorcarbondioxide)isblendedwiththeliquidpolymertoformasinglephasesolution.Duringmoldfilling,thegasformshighlyuniformmicroscopiccells(0.1to10lamindiameter)intheinteriorofthepart.Thepressurecreatedbythefoamingprocessreducesshrinkageandsurfacedefects,suchassinkmarks.Blendingthesupercriticalgaswiththeliquidpolymersignificantlyreducesitsviscosity,andthereforethepartcanbemoldedatlowertemperaturesandwithlowerinjectionpressures.Furthermore,duetoafoamedstructure,boththepartweightandthecycletimearereduced.(Example:Interiortrims),Chapter12AutomotiveManufacturing12.2InjectionMouldi