轻型树脂传递模塑工艺lrtmLightweight resin transfer molding process lrtm.docx
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轻型树脂传递模塑工艺lrtmLightweight resin transfer molding process lrtm.docx
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轻型树脂传递模塑工艺lrtmLightweightresintransfermoldingprocesslrtm
轻型树脂传递模塑工艺(l-rtm)(Lightweightresintransfermoldingprocess(l-rtm))
Lightweightresintransfermolding(L-RTM)-arapidlydevelopinglowcostmanufacturingtechnology
Introductionof1.L-RTMprocess
ThetraditionalRTMtechnique,becauseitisaclosedmold,withreducedvolatileorganiccompounds(VOC)emissions(uptoSPPm),theadvantagesofexpandingavailablerangeofrawmaterials,reducelabor,environmentfriendlyandcangettwocleanproductsetc..ButinRTMprocess,theinjectionofresiniscarriedoutunderhigherpressureandvelocity,sowemustmakethestructurestrengthandstiffnessofthemoldsufficientlylargeenoughtobreakanddeformundertheinjectionpressure.Usually,thesandwichcompositematerialwithsteeltubesupportoraluminumdieorsteelmouldprocessedbynumericalcontrolmachinetoolcanmakethemanufacturecostincrease,andthemouldcostcanbeoffsetonlywhentheproductisbigenough.Inaddition,inordertoclosethemold,itisnecessarytomaketheperipheralsufficientclampingcapacityortouseacloseddiepressuresystem.AllthesefactorslimittheapplicationofRTMtechnologytolargeproducts,otherwisethemoldwillbecomeveryheavyandtheinvestmentwillbegreat.
Lightweightresintransfermoldingprocess(RTM,Light),alsoknownasLRTM,ECO,Vacuum
MoldingorVARTM.Itisalow-costmanufacturingprocessdevelopedinrecentyears.Ithasbeenusedinthefieldofship,automobile,industryandmedicalcompositematerialmorethanRTMtechnology.
TheRTMLightprocessretainsthedieprocessingprocessoftheRTMprocess,thusretainingalmostalloftheadvantagesoftheRTMprocess.Buttheupperdieforglasssteelmouldhalfrigid,thickness68mm,usuallydonotneedtousethesteelreinforcement,themoldhasawidthofabout100mmbytherigidsurrounding,doublesealingbeltconstitutesanindependentsealarea,aslongasavacuummoldisclosedandisveryconvenientandfast.Thenthecavityisevacuated,andtheresinisinjectedintothemoldwiththenegativepressureinthemoldandthelowerinjectionpressure.Theresinisinfiltratedintotheprelaidreinforcingfiberorpreform.RTM-Lightmoldcostislow,andbecausethemoldpressurereduction,itsmoldhasclosetothemold,itiseasytoopenmoldfromtheprocessoftransformation.
ThemainequipmentofRTMLightincludesresininjectiondevice,mold,vacuumpumpandotherauxiliarytools.
2lightRTMcomparedwithregularRTM
(1)die;
Themoldisthebiggestdifferencebetweenthetwoprocesses.IntheRTMinvestment,aconsiderablepartofthecostisspentonthedieandtheclampingdevicebecauseofthehighinjectionpressure.Thisisnotagoodpriceforaproductwithlittleoutput.RTMprocess,moldlifeofupto5000ormore,highproductionefficiency,suitableforanannualoutputofmorethan2000products.
ThebiggestadvantageofRTMLightisthelowcostofitsmoldproduction.ThecostisonlyabouthalfoftheregularRTMmold,buttheservicelifeofthedieislowerthanthatoftheRTMmold.Itissuitablefortheproductswithanannualoutputofabout1000pieces.
TheRTMLightprocessproducesproductsthatarelargerinsizethanthetraditionalRTM,whichisusuallyassmallasabasketballcap,alengthof8mlonghull(about25m2),butthisisnottheultimatelimitofsize.Theproductsizeissmallerthanthebasketballcap,thedifficultyistoaddfiber,andtheproductisgreaterthan8m,howtodealwiththemoldonthedifficult.
Thedisadvantageofglassfiberreinforcedplasticmouldisshortservicelifeofmouldsurface.Inordertogetgooddielifeandproductrepeatabilityanddimensionalaccuracy,RTM-
BoththeLightandRTMprocessesmustbeofhighqualityandhaveanaccuratecrosssection.Inthecompositemoldingprocess,thecostofsurfacerequirementsofthefinalproductcanreach60%ofthefinalproductprice.Thecompositemoldcanachievetheuseof500timesthesurfacequalityofthecar,andthenthesurfacetreatmentofthemold.Onewaytoincreaselifeexpectancyistouseareplaceablediesurface(ex-changeablemold
Skins),suchasthepatentofJHmTechnologiescompany,ZIP
RTMtechnology,
ItcanbeusedinRTMandRTMLightprocesses.Throughtheuseofreplaceablediesurfacetoreplacethevulnerablemoldsurface,therebyprolongingthelifeofthedieandimprovingthequalityofthedie,theservicelifeofthediecanreach8000,10000times.Whenthesimultaneoususeofseveralreplaceablemoldsurface,duetotheoutsideinthemoldcanbereplaceddirectlyonthemoldsurfacecoatingandheating,therebygreatlyimprovingtheproductionefficiency.
(2)injectionpressure,flowrateandequipment;
TheinjectionpressureofRTMprocessisusually0.10.4MPa,whiletheinjectionpressureofRTMLightprocessisnotmorethan.1MPa,usuallyat0.03-0.07MPa.
Therateofresininjectionvarieswithvariousfactorssuchasresinviscosity,componentsize,fibertypeandplystructure.Theusualinjectionrateis1.3to2litresperminute.
Inordertopreventmolddeformationorburstmode(especiallyinthepositionoftheinjectionport),whichrequiresastrictcontrolofpressure.InjectionequipmentfortheRTMLightprocessisusuallyequippedwithapressurefeedbackdevicethatcontrolsthepressureasaclosedloop.RTMisalsoavailableinthestandardequipmentofasimplelinepressurecontroldesign(moldprotectionsystemandaVMPC)andVMPCwithPODelectronicclosed-loopsystem,cannotleadtomolddeformationandfailureundertheconditionofusingtheoriginalproductionequipmenttogetthebestproductivity.
Equipmentresearchisalsodevelopingtowardlowcostandmultiuse.TheSSBinjectionequipmentofPlastechadoptspatentedpistonreformingprecisionmeteringpump.Theminimumratioofcatalystisupto0.5%,whichmatchestheindustrialMPG(Mould
Pressureguard)thepumpspeedcanbecontrolledbythemachineitself.In12secondsand15seconds,the1m2reinforcedmaterialcanbeimpregnated,andthewettingspeedcanbeaccuratelycontrolled.Configureotheroptions,alsoforhandgluingandbrushing.
(3)productionefficiencyandcost
RTMoneLightprocessisalow-costproductiontechnology.ComparedwiththetraditionalRTMtechnology,thediecostislow,andthecomplicatedpressingdeviceorpressuresystemisnotneeded,theinvestmentissmall,theoperationissimple,andthemanpowercapitalissaved,etc..Comparedwiththeopeningprocess,ithasthehighprecisionoftheproductsize,lowporosity,productionofstyrenevolatilization,environmentalfriendly,lesswastematerials(resinutilizationrateofupto95%),lowrejectionrate,highproductionefficiency.
Theinjectionpressureislow,theresinflowratecannotbeacceleratedtotheoptimumflow,beforetheRTMLightprocesstheproductionspeedoflessthanhalfoftheRTMprocess,witheachclass8hours,fortheuseofthegelcoatandnonheatingmouldprocess,RTMprocessineachclasscanproduce10A12die,RTM
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TheLightprocessproducesonly4and6dies.Fora34squarefootproductthatneedstobeheatedandcured,theRTMprocessproduces40moldspershiftwiththeuseofahydraulicpress,aheatingdie,and5replaceabledies.RTMinthesamesituation
-Lightprocess,canproduce20die.Butnowaterpressisneeded,andthemoldpriceisalsohalflower.
Inrecentyears,throughtheimprovementofmolddesignandprocesscontrol,bothproductionspeedisapproaching.SuchasXiraplascompanyintheuseofRTMLightprocessalternativemoldopeningprocess,theworkshophasbecomeorderly,theuseoftheoriginal50workers,and3000m2workshoparea,makingproductionincreasedby25%.Accordingtothecompany,productionefficiencyhasbeenincreasedby90%comparedtotheoriginalmoldopeningprocess.
(4)runnerdesign
TheflowdesignofthegeneralRTMprocessisinjectedfromthecenteranddischargedfromtheperiphery.ButtheRTM-Lightprocessusuallyflowsinfromtheperimeterandoutofthecenter.Weknowthatwhentheresinentersthemoldcavityfromtheresinpipeandmeetsthefabric,thefabricwillproduceacounterpressure(resistance)totheresin.Themagnitudeofthereversepressureisrelatedtothepermeabilityofthefabric,theviscosityoftheresin,andtheflowvelocityoftheresin,whenthefabricandresinareselected,
Itisproportionaltotheflowvelocityoftheresin.Takeanareaof3M2,thicknessof3mmproductsasanexample,thegeneralinjectionpressureis0.05MPa,theinjectiontimeis6min,theinjectionflowis1.33L/min.Iftheinjectionfromthecenterandmaintaintheflowunchanged,theantipressurecanbeincreasedtomorethan0.1MPa,resultinginthemoldopeningormoldphenomenon,andleadtoresinflowforwardoutofcontrolandtheformationofdryspotsandotherissues.Forthisreason,theflowratemustbereduced,butthisprolongstheinjectiontime,sotheinjectionfromthecenterusuallytakesmorethan6minutes.Whenthesurroundingresininjection,firstintoagapaboutthesurroundingflow1mmalmostnoresistance,andthenenterthefiberresinintothefiberincreaseduetopathway(fromapointintoasurrounding),relativeresininfabricflowslowsdown,backpressuredecreases,theinjectionrateincreasetheinjectiontimecanbeshortened.Testsshowthatfora0.2m2product,thetimeofinjectionfromtheperipheryis2.1minutes,andtheinjectionfromthecenterto9minutes,thespeeddifferenceoffourtimes.Ofcourse,RTMprocesscanalsobeinjectedfromthesurroundingresin,thepressuregradientisunchanged,butthehighestpointofthepressurefromtheoriginalcenterpointismoved
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