注塑模具runner-design concept

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1、Nowadays,injectionmoldersareunderincreasingpressure(punintended).Demandsfortighttolerances,near-zerorejects,andever-lowercostthatwereoncelimitedtoautomotiveandmedicaljobsarenowcommonevenformoldersofconsumerproducts.Moldershaveoftenrespondedbylimitingthemselvestomoldsoflowc

2、avitationbecausetheyareeasiesttobalancenaturally.Butlowcavitationrequiresmoremolds,moremachines,morefloorspaceforthemachines,andmorepeopletorunthem.Toremaincompetitiveinaglobalmarketplace,costcanonlybereducedbyproducingpartsfasterwithmoreconsistencyandlessscrap.Ifhigher-qu

3、alitypartscanbeproducedfromaneight-cavitymoldratherthanafour-cavitytool,orfrom16cavitiesinsteadofeight,costsavingsandgreatercustomersatisfactionwillfollow.Thequestionishowtogetthere.MeltFlipperinsertsusechangesinrunnerelevationto"flip"themeltorientationby90°,eliminatingasy

4、mmetricaldistributionofhotterandcoolermelttodivergingrunnerbranches.Thebasisofthesolutioncametomein1997whenIwaswrestlingwiththeissueofmold-fillingimbalance.Foryears,Ihadobservedimbalancesinwhathavealwaysbencalled"naturallybalanced"runners.Amemberofmycomputer-aided-engineer

5、ingconsortiumatPennStateEriewasencounteringjustsuchaproblem.Hiseight-cavitymoldwas"naturallybalanced,"andyetthepartsfromthemold'sinnercavitieswereconsistentlyheavierthanthosemadeincavitiesfartherfromthesprue.Tightweighttolerancesforthispartdidn'tallowforsuchvariation,andat

6、nearly$20/lb,materialwastehadtobeheldtoaminimum.Ifirstblamedthetwousualsuspects:coolingvariationscreatedbyhigherthermalloadoftheplasticpartsnearthecenterofthemold,andplatedeflectionwithinthemold.Thesestandardscapegoatshadservedindustrywellforyears.Butthismoldhadawell-desig

7、nedcoolingsystemthatprovidedincreasedcoolingtotheinnercavities.Onelookatthemold'srigidsupportcolumnsandtheparts'thickwallstoldmeplatedeflectionwasn'ttheproblemeither.Fig.1—Highshearandfrictionalheatingneartheouterwallofarunnerchannellowertheviscosityinthisregion.Thisisther

8、ootcauseoffillingimbalances.Fig.2—FIDAPanalysisoutputshowstheasymmetricaltemperaturedistr