专业模具英语.docx

专业模具英语.docx

《专业模具英语.docx》由会员分享，可在线阅读，更多相关《专业模具英语.docx（10页珍藏版）》请在冰点文库上搜索。

专业模具英语

MoldConstruction

1.Theinjectionmoldingandmachine

1.1Theinjectionmolding

Injectionmoldingisprincipallyusedfortheproductionofthethermoplasticparts,althoughsomeprogresshasbeenmadeindevelopingamethodforinjectionmoldingsomethermosettingmaterials.Theproblemofinjectingameltedplasticintoamoldcavityfromareservoirofmeltedmaterialhasbeenextremelydifficulttosolveforthermosettingplasticswhichcureandhardenundersuchconditionswithinafewminutes.Theprincipleofinjectionmoldingisquitesimilartothatofdie-casting.Theprocessconsistsoffeedingaplasticcompoundinpowderedorgranularformfromahopperthroughmeteringandmeltingstagesandtheninjectingitintoamold.Afterabriefcoolingperiod,themoldisopenedandthesolidifiedpartejected.Injection-moldingmachinescanbearrangedformanualoperation,automaticsingle-cycleoperation,andfullautomaticoperation.Theadvantageofinjectionmoldingare:

（i）ahighmoldingspeedadaptedformassproductionispossible;（ii）thereisawidechoiceofmaterialsprovidingavarietyofusefulproperties;（iii）itispossibletomoldthreads,undercuts,sideholes,andlargethinsections.

1.2Theinjection-moldingmachine

Severalmethodsareusedtoforceorinjectthemeltedplasticintothemold.Themostcommonlyusedsysteminthelargermachinesisthein-linereciprocatingscrew.Thescrewactsasacombinationinjectionandplasticizingunit.Astheplasticisfedtotherotatingscrew,itpassesthroughthreezones:

feed,compression,andmetering.Afterthefeedzone,thescrew-flightdepthisgraduallyreduced,forcingtheplastictocompress.Theworkisconvertedtoheatbyshearingtheplastic,makingitasemifluidmass.Inthemeteringzone,additionalheatisappliedbyconductionfromthebarrelsurface.Asthechamberinfrontofthescrewbecomesfilled,itforcesthescrewback,trippingalimitswitchthatactivatesahydrauliccylinderthatforcesthescrewforwardandinjectsthefluidplasticintotheclosedmold.Anantiflowbackvalvepreventsplasticunderpressurefromescapingbackintothescrewflights.

Theclampingforcethatamachineiscapableofexertingispartofthesizedesignation.Theinjection-moldingmachine,thereciprocating-screwinjectionsystemandismeasuredintons.Arule-of-thumbcanbeusedtodeterminethetonnagerequiredforaparticularjob.Itisbasedontwotonsofclampforcepersquareinchofprojectedarea.Iftheflowpatternisdifficultandthepartsarethin,thismayhavetogotothreeorfourtons.

Manyreciprocating-screwmachinesarecapableofhandingthermosettingplasticmaterials.Previouslythesematerialswerehandledbycompressionortransfermolding.Thermosettingmaterialscureorpolymerizeinthemoldandareejectedhotintherangeof375~410℃.Thermoplasticpartsmustbeallowedtocoolinthemoldinordertoremovethemwithoutdistortion.Thusthermosettingcyclescanbefaster.Ofcoursethemoldmustbeheatedratherthanchilled,aswiththermoplastics.

Machinesareavailableformoldingsandwichparts.Onecylinderandplungerinjectsmeasuredamountofskinmaterialintothedie,andthenasecondcylindersquirtsthefillerinsidethemass.Finally,afinalspurtfromthefirstcylinderclearsthecorematerialfromthesprue.Theaimistoproducecompositeswithoptimumproperties.Eithercaseorcoremaybefoamed.

2.Feedsystem

Itisnecessarytoprovideaflow-wayintheinjectionmouldtoconnectthenozzle（oftheinjectionmachine）toeachimpression.Thisflow-wayistermedthefeedsystem.Normallythefeedsystemcomprisesasprue,runnerandgate.Thesetermsapplyequallytotheflow-wayitself,andtothemoldedmaterialwhichisremovedfromtheflow-wayitselfintheprocessofextractingthemolding.

Atypicalfeedsystemforafour-impression,twoplate-typemould.Itisseenthatthematerialpassesthroughthesprue,mainrunner,branchrunnersandgatebeforeenteringtheimpression.Asthetemperatureofmoltenplasticisloweredwhilegoingthroughthesprueandrunner,theviscositywillrise;therefore,theviscosityisloweredbyshearheatgeneratedwhengoingthroughthegatetofillthecavity.Itisdesirabletokeepthedistancethatthematerialhastotraveldowntoaminimumtoreducepressureandheatlosses.Itisforthisreasonthatcarefulconsiderationmustbegiventotheimpressionlayoutandgate’sdesign.

Sprue

Asprueisachannelthroughwhichtotransfermoltenplasticinjectedfromthenozzleoftheinjectorintothemold.Itisapartofspruebush,whichisaseparatepartfromthemold.

Runner

Arunnerisachannelthatguidesmoltenplasticintothecavityofamold.

Gate

Agateisanentrancethroughwhichmoltenplasticentersthecavity.Thegatehasthefollowingfunctions:

restrictstheflowandthedirectionofmoltenplastic;simplifiescuttingofarunnerandmoldingstosimplifyfinishingofparts;quicklycoolsandsolidifiestoavoidbackflowaftermoltenplastichasfilledupinthecavity.

Coldslugwell

Thepurposeofthecoldslugwell,shownoppositethesprue,istheoreticallytoreceivethematerialthathaschilledatthefrontofthenozzleduringthecoolingandejectionphase.Perhapsofgreaterimportanceisthefactthatitprovidespositivemeanswherebythespruecanbepulledfromthespruebushforejectionpurposes.

Thesprue,therunner,andthegatewillbediscardedafterapartiscomplete.However,therunnerandthegateareimportantitemsthataffectthequalityorthecostofparts.

3.RUNNER

Therunnerisachannelmachinedintothemouldplatetoconnectthespruewiththeentrancetotheimpression.Thewalloftherunnerchannelmustbesmoothtopreventanyrestrictiontoflow.Also,astherunnerhastoberemovedwiththemolding,theremustbenomachinemarksleftwhichwouldtendtoretaintherunnerinthemouldplate.

Therearesomeotherconsiderationsforthedesignertobearinmind:

（i）theshapeofthecrosssectionoftherunner,（ii）thesizeoftherunner；（iii）therunnerlayout.

Runnercross-sectionshape

Thecross-sectionalshapeoftherunnerusedinamouldisusuallyoneoffourforms:

fullyround,trapezoidal,modifiedtrapezoidalandhexagonal.

Thecriterionofefficientrunnerdesignisthattherunnershouldprovideamaximumcross-sectionareafromthestandpointofpressuretransferandaminimumcontactontheperipheryfromthestandpointofheattransfer.Theratioofcross-sectionalareatoperipherywill,therefore,giveadirectindicationoftheefficiencyoftherunnerdesign;thehigherthevaluethegreatertheefficiency.

Runnerlayout

Thelayoutoftherunnersystemwilldependuponthefollowingfactors:

（i）therunnerofimpression,（ii）theshapeofthecomponents,（iii）thetypeofmould,（iv）thetypeofgate.

Whendesigningarunnersystemtherearetwomainconsiderations.Therunnerlengthshouldalwaysbekepttoaminimumtoreducepressurelosses,andtherunnersystemshouldbebalanced.

Runnerbalancingmeansthatthedistancetheplasticmaterialfromthespruetothegateshouldbethesameforeachmolding.Thissystemensuresthatalltheimpressionswillfilluniformlyandwithoutinterruptionprovidingthegatelandsandthegateareasareidentical.

Runnerlayout

Itisnotalwayspracticable,however,tohaveabalancedrunnersystemandthisparticularlyappliestomouldswhichincorporatealargenumberofdifferentlyshapedimpressions.Inthesecases（asshowsexamples）balancedfillingoftheimpressioncanbeachievedbyvaryingthegatedimensionsthatisbybalancedgating.

4.GATES

Thegateisachannelororificeconnectingtherunnerwiththeimpression.Ithasasmallcross-sectionalareawhencomparedwiththerestofthefeedsystem.Thissmallcross-sectionalareaisnecessarysothat:

i）Thegatefreezessoonaftertheimpressionisfilledsothattheinjectionplungercanbewithdrawnwithouttheprobabilityofvoidbeingcreatedinthemoldingbysuck-back.ii）Itallowsforsimpledegatingandinsomemouldthisdegatingcanbeautomatic.ⅲ）Afterdegatingonlyasmallwitnessmarkremains.ⅳ）Bettercontrolofthefillingofmulti-impressionscanbeachieved.ⅴ）Packingtheimpressionwithmaterialinexcessofthatrequiredtocompensateforshrinkageisminimized.

Thesizeofthegatecanbeconsideredintermsofthegatecross-sectionalareaandthegatelength,thelatterbeingknownasgateland.Theoptimumsizeforagatewilldependonanumberoffactorsincluding（i）theflowcharacteristicsofthematerialtobemolded（ii）thewallsectionofthemolding,（iii）thevolumeofmaterialtobeinjectedintotheimpression,（iv）thetemperatureofthemelt（v）thetemperatureofthemould.

Notheoreticalsizeexistsfortheidealgate.Thegatesizechoseninpracticeforaparticularcomponentisnormallybasedonpastexperience.However,thereadermaynothavethisexperienceuponwhichtobaseadecisionand,therefore,aguidetothedimensionsforeachgatetypeisgiven.Tothegeneralcaseofamoldingwithawallsectionbetween0.75mmand4mm.

Figure4-1Typesofgate

Typeofgate

Toobtaintheoptimumfillingconditionsthetypeofgatemustbecarefullychosen.Onmostoccasions,however,thechoicewillbeobviousasonlyonetypeofgatewillmeettheparticularrequirementsforthemoldingonhand.Thetypesofgate（seeFigure4-1）commonlyusedare:

spruegate（f）,edgegate（n）,overlapgate（a）,fangate（b）,diaphragmgate（g）,ringgate（h）,filmgate（c）,pingate（d）,submarinegate（m）andtabgate（e）.

5.Partingsurface

Thepartingsurfacesofamouldarethoseportionofbothmouldplates,adjacenttotheimpress