轻型树脂传递模塑工艺lrtmLightweight resin transfer molding process lrtm.docx

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

-

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