版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
Designguidesforplastics
CliveMaier,EconologyLtd
TANGRAM
TECHNOLOGY
Consulting
Engineers
θconology
December2021
#
ThispublicationismadeupofaseriesofarticlespublishedinPlasticsandRubberWeeklyasapiecework.ThekindassistanceoftheauthorandPRWisacknowledgedinthepublicationofthework.
Thedesignhintsinthisbookletaregiveningoodfaithandrepresentcurrentgoodpractice.Theshortnatureofthehintsmeansthatnotallinformationcanbeincluded.Noresponsibilitycanbetakenforanyerrorsorconsequentialdamagesresultingfromusingthesehints.
Thispublicationmaybefreelyreproducedexceptforsaleoradvertisingpurposes.Itmaybehostedonwebsitesforfreedownloadingprovidingthatitisusedinit’sentiretyandthatreferenceismadetotheoriginalpublication.
©CliveMaier2004
TypesetandeditedbyTangramTechnologyLtd.
Contents
TOC\o"1-5"\h\z
Preface 1
Introduction 2
Injectionmoulding 4
Basics
\o"CurrentDocument"
Wallthickness 9
\o"CurrentDocument"
Corners 10
Ribs 11
Bosses 14
Designfor recycling 17
Specialfeatures
Livinghinge 22
Bearings 24
Gears 27
Assembly
Pressfits 32
Snap-fits 33
Hotstaking 37
Ultrasonicwelding 39
Hotplatewelding 44
Spinwelding 45
Frictionwelding 46
Inductionwelding 47
Laserwelding 48
Adhesiveandsolventbonding 49
Outsertmoulding 54
4
#
Preface
Thissetofhintsandtipsforplasticsproductdesignersisintendedasasourcebookandan'aidemémoire'forgooddesignideasandpractices.Itisasourcebookforplasticsproductdesignersatalllevelsbutitisprimarilyaimedat:
studentdesignerscarryingoutdesignworkforalllevelsofacademicstudies;
non-plasticsspecialistsinvolvedinthedesignofplasticsproducts;
plasticsspecialistswhoneedtoexplaintheirdesigndecisionsandthedesignlimitationstonon
plasticsspecialists.
Thebookcoverseachtopicinasinglepagetoprovideabasicreferencetoeachtopic.Thisspaceconstraintmeansthateachtopicisonlycoveredtoabasiclevel.Detailedplasticproductdesignwillalwaysrequiredetailedknowledgeoftheapplication,theprocessingmethodandtheselectedplastic.Thisinformationcanonlybeprovidedbyrawmaterialssuppliers,specialistplasticsproductdesignersandplasticsprocessorsbutthereisaneedtogetthebasicsoftheproductdesignrightinthefirstinstance.
Usingthehintsandtipsprovidedinthisguidewillenabledesignerstoreduceinitialerrorsandwillleadtobetterandmoreeconomicdesignwithplastics.
Ihopethisshortworkwillimprovethebasicdesignofplasticsproductsandifitcandothisthenitwillhaveservedit’sobjectives.
CliveMaier
ECONOLOGYLtd.
INTRODUCTION
#
Gooddesignisimportantforanymanufacturedproductbutforplasticsitisabsolutelyvital.Wehavenoinstinctforplastics.Mostofthoseweusetodayhavebeenaroundforlittlemorethantwogenerations.Comparethatwiththethousandsofyearsofexperiencewehavewithmetals.Andplasticsaremorevaried,morecomplicated.Formostdesignsinmetals,thereisnoneedtoworryabouttheeffectsoftime,temperatureorenvironment.Itisadifferentstoryforplastics.Theycreepandshrinkastimepasses;theirpropertieschangeoverthetemperaturerangeofeverydaylife;theymaybeaffectedbycommonhouseholdandindustrialmaterials.
ThephilosopherHeideggerdefinedtechnologyasawayofarrangingtheworldsothatonedoesnothavetoexperienceit.Wecanextendhisthoughttodefinedesignasawayofarrangingtechnologysothatwedonothavetoexperienceit.Inotherwords,gooddesigndeliversfunction,formandtechnologyinobjectsthatmeettheneedsofuserswithoutmakingdemandsonthem.Thewell-designedobjectgivespleasureoratleastsatisfactioninuse,anddoeswhatitshoulddowithoutundueconcern.
IntheseDesignGuideswewillsetoutthebasicsofgooddesignforplastics.Therulesandrecommendationswegivewillnecessarilybegeneralisations.Theywillapplyoftenbutnotinvariablytothermoplastics,frequentlybutnotexclusivelytoinjectionmoulding.Thebasicadvicewillbegoodbutbecauseplasticsaresocomplexandvariedthegoldenrulemustalwaysbetoconsidercarefullywhethertheadviceneedsadjustingtosuityourparticularapplication.
Gooddesigncombinesconceptwithembodiment.Unlessthetwoareconsideredtogether,theresultwillbeanarticlethatcannotbemadeeconomicallyoronethatfailsinuse.Thisisparticularlyimportantforplastics.Itisvitaltochoosetherightmaterialforthejob.Whenthatisdone,itisequallyimportanttoadaptthedetailsofthedesigntosuitthecharacteristicsofthematerialandthelimitationsoftheproductionprocess.
Plasticscomeinabewilderingvariety.Thereareahundredormoredistinctgenerictypes.Ontopofthat,advancedtechniqueswithcatalystsandcompoundingarecreatingnewalloys,blendsandmolecularforms.Allofthesematerialscanhavetheirpropertiesmodifiedbycontrolofmolecularweightandbyadditivessuchasreinforcements.Thenumberofdifferentgradesofplasticsmaterialsavailabletothedesignernowapproaches50,000.Theimportance-andthedifficulty-ofmakingtherightchoiceisobvious.
Plasticscanbegroupedintocategoriesthathaveroughlysimilarbehaviour.
Thermoplasticsundergoaphysicalchangewhenprocessed;theprocessisrepeatable.Thermosetsundergoachemicalchange;theprocessisirreversible.Akeydistinctionbetweenthermoplasticsrelatestothemoleculararrangement.Thosewithrandomtangledmoleculesarecalledamorphous.Thosewithadegreeofmoleculararrangementandorderingarecalledsemi-crystalline.Thedifferenceissignificant.Forexample,mostamorphousmaterialscanbefullytransparent.Andthemorecrystallineamaterialis,thelesslikelyitistohaveawide'rubbery'processingregion,somakingitlesssuitableforstretchingprocesseslikeblowmouldingandthermoforming
Designersmustdesignforprocessaswellaspurposeandmaterial.Insingle-surfaceprocessesforexample,thereisonlyindirectcontrolovertheformofthesecondsurface.Designmusttakethislimitationintoaccount.
DESIGNCONSIDERATIONS
#
PLASTICS
THERMOSETS
THERMOPLASTICS
HDPE
Highdensitypolyethylene
LDPE
Lowdensitypolyethylene
LLDPE
Linearlowdensitypolyethylene
PA
Polyamide(Nylon)
P日T
Polγt∣Lrtyleπeterephthalate
PEEK
Polyetheretherketone
POM
Po1γoxγrnethy1bγ∣e
(Acetal)
PR
Polypropylene
PPΞ
Polyphenylenesulphide
ABΞ
.^.crylonitrileb∣.rtadienestyrene
CA
Celluloseacetate
CAB
Celluloseacetate
b∣.rtyrate
CP
Celluloseproρrionate
PC
Polycarbonate
RES
Polyethersulphone
PET
Polyethylene
terephthalate
PMMA
Polymethyl
methacrylate
F,PO
Polyphenyleneoxide
PΞ
Polystyrene
PS∣J
PolysLJ∣phone
PVC
PolyvinylChloride
SAN
Styreneacrylonitrile
EPDM
Ethyleπe-propylene-dieneterpolymer
EPT
Ethyleπe-propyleneterpolymer
NBR
Nitrilebutadiene
rubber
PEB⅛
Pc∣lyetherblockamide
ΞBΞ
Styrene-b∣.rtadiene
styrene
TP∪
Thermoplastic
polyurethane
DAP
Diallylphthalate
MF
Melamineformaldehyde
PF
Phenolformaldehyde
UF
Ureaformaldehyde
EP
Epoxy
UP
Unsaturatedpolyester
Semi-crystalline
Amorphous
Elastomeric
SOMECOMMONPLASTICS
ALLSURFACESDEFINED
SINGLESURFACEDEFINED
BATCHPROCESS
InjectionmouldingCompressionmould!ng
Tnmnmτ⅛r「n口uldi「旧
Blo,∣Λ',mouldingτr∣ermoformingRotationalmoulding
CONTINUOUSPROCESS
ExtrusionCalenderingPultrusion
COMMONPLASTICSFORMINGPROCESSES
Injectionmoulding
1
WALLTHICKNESS
Partsthatmightbemadeassolidshapesintraditionalmaterialsmustbeformedquitedifferentlyinplastics.Mouldedplasticsdonotlendthemselvestosolidforms.Therearetwoprincipalreasonsforthis.First,plasticsareprocessedwithheatbutarepoorconductorsofheat.Thismeansthatthicksectionstakeaverylongtimetocoolandsoarecostlytomake.Theproblemsposedbyshrinkageareequallysevere.Duringcooling,plasticsundergoavolumereduction.Inthicksections,thiseithercausesthesurfaceoftheparttocaveintoformanunsightlysinkmark,orproducesaninternalvoid.Furthermore,plasticsmaterialsareexpensive;itisonlyhigh-speedproductionmethodsandnet-shapeformingthatmakemouldingsviable.Thicksectionswastematerialandaresimplyuneconomic.
Sosolidshapesthatwoulddothejobwellinwoodormetalmustbetransformedtoa'shell'forminplastics.Thisisdonebyhollowingoutor'coring'thickpartssoyouareleftwithacomponentwhichregardlessofcomplexityiscomposedessentiallyofrelativelythinwallsjoinedbycurves,angles,corners,ribs,stepsandoffsets.Asfaraspossible,allthesewallsshouldbethesamethickness.
Itisnoteasytogeneralisewhatthewallthicknessshouldbe.Thewallplaysapartbothindesignconceptandembodiment.Thewallmustbethickenoughtodoitsjob;itmustbestrongenoughorstiffenoughorcheapenough.Butitmustalsobethinenoughtocoolquicklyandthickenoughtoallowefficientmouldfilling.Ifthematerialisinherentlystrongorstiffthewallcanbethinner.Asageneralguide,wallthicknessesforreinforcedmaterialsshouldbe0.75mmto3mm,andthoseforunfilledmaterialsshouldbe0.5mmto5mm.
Ideally,theentirecomponentshouldbeauniformthickness-thenominalwallthickness.Inpracticethatisoftennotpossible;theremustbesomevariationinthicknesstoaccommodatefunctionsoraesthetics.Itisveryimportanttokeepthisvariationtoaminimum.Aplasticspartwiththicknessvariationswillexperiencedifferingratesofcoolingandshrinkage.Theresultislikelytobeapartthatiswarpedanddistorted,oneinwhichclosetolerancesbecomeimpossibletohold.Wherevariationsinthicknessareunavoidable,thetransformationbetweenthetwoshouldbegradualnotsuddensoinsteadofastep,usearamporacurvetomovefromthicktothin.
Thicksectionsandnon-uniformwallscauseproblems
Solidshapesmustberedesignedas‘shells
WRONG
-sharpstep
RIGHT
-gradualtransition
byplane
RIGHT
-gradualtransition
byradius
Gradualtransitionsbetweenthickandthin
sections
DESIGNER’SNOTEBOOK
Keepwallthicknessasuniformaspossible.
Usegradualtransitionsbetweenthickandthinsections.
Wallthicknessmustsuitbothfunctionandprocess.
Wallthicknessguiderangeis:
0.75mmto3mmforreinforcedmaterials
0.5mmto5mmforunreinforcedmaterials
2
CORNERS
Whentheideasofcorrectanduniformwallthicknessareputintopracticetheresultisaplasticspartcomposedofrelativelythinsurfaces.Thewayinwhichthesesurfacesarejoinedisequallyvitaltothequalityofamouldedpart.
Wallsusuallymeetatrightangles,atthecornersofaboxforexample.Wheretheboxwallsmeetthebase,theanglewillgenerallybeslightlymorethan90degreesbecauseofadraftangleonthewalls.Theeasiestway,andtheworst,tojointhewallsistobringthemtogetherwithsharpcornersinsideandout.Thiscausestwoproblems.
Thefirstdifficultyisthattheincreaseinthicknessatthecornerbreakstheruleofuniformwallthickness.Themaximumthicknessatasharpcornerisabout1.4timesthenominalwallthickness.Theresultisalongercoolingtimeaccompaniedbyariskofsinkmarksandwarpingduetodifferentialshrinkage.
Theotherproblemisevenmoreserious.Sharpcornersconcentratestressandgreatlyincreasetheriskofthepartfailinginservice.Thisistrueforallmaterialsandespeciallysoforplastics.Plasticsaresaidtobenotchsensitivebecauseoftheirmarkedtendencytobreakatsharpcorners.Thishappensbecausethestressconcentrationatthecornerissufficienttoinitiateamicroscopiccrackwhichspreadsrightthroughthewalltocausetotalfailureofthepart.Sharpinternalcornersandnotchesarethesinglemostcommoncauseofmechanicalfailureinmouldedparts.
Theansweristoradiustheinternalcorner,butwhatsizeshouldtheradiusbe?Mostwallsapproximatetoaclassicalcantileverstructuresoitispossibletocalculatestressconcentrationfactorsforarangeofwallthicknessesandradii.Theresultinggraphshowsthatthestressconcentrationincreasesverysharplywhentheratioofradiustowallthicknessfallsbelow0.4.Sotheinternalradius(r)shouldbeatleasthalfthewallthickness(t)andpreferablybeintherange0.6to0.75timeswallthickness.
Iftheinnercornerisradiussedandtheoutercornerleftsharp,thereisstillathickpointatthecorner.Foraninternalradiusof0.6t,themaximumthicknessincreasestoabout1.7timesthewallthickness.Wecanputthisrightbyaddingaradiustotheoutsidecorneraswell.Theoutsideradiusshouldbeequaltotheinsideradiusplusthewallthickness.Thisresultsinaconstantwallthicknessaroundthecorner.
Properlydesignedcornerswillmakeabigdifferencetothequality,strengthanddimensionalaccuracyofamoulding.Butthereisanotherbenefittoo.Smoothcurvedcorners
helpplasticflowinthemouldbyreducingpressuredropsinthecavityandminimisingflow-frontbreak-up.
Internal:r=0.6tExternal:r=0.6t+t
Internal:r=0.6tExternal:Sharp
Internal:SharpExternal:Sharp
Goodandbadcornerdesign
Stressconcentrationfactorsforcantilever
loading
DESIGNER’SNOTEBOOK
Avoidsharpinternalcorners.
Internalradiishouldbeatleast0.5andpreferably0.6to0.75timesthewallthickness.
Keepcornerwallthicknessascloseaspossibletothenominalwallthickness.Ideally,externalradiishouldbeequaltotheinternalradiiplusthewallthickness.
3.1RIBS
#
Ribscreatethicksectionsattheroot
wd□p3q-
-ωs⅞≡=raδ
Ribthicknessrelativetowallthickness(w∕t)
Howribrootthicknessincreases
DESIGNER’SNOTEBOOK
Ribthicknessshouldbe50-75%ofthewallthickness.
Filletradiusshouldbe40-60%oftheribthickness.
Ribrootthicknessshouldnotbemorethan25%greaterthanthewallthickness.
Ribdepthshouldnotbemorethan5timestheribthickness.
Taperribsformouldrelease.
Sofarinthisdesignserieswehaveseenthatplasticspartsshouldbemadewithrelativelythinanduniformwallslinkedbycornerradii,notsharpcorners.Bothideasareimportantinthedesignofribs.
Whenthenormalwallthicknessisnotstiffenoughorstrongenoughtostanduptoserviceconditionsthepartshouldbestrengthenedbyaddingribsratherthanmakingthewholewallthicker.Theprincipleisthefamiliaroneusedinsteelgirderswhere'I'and'T'sectionsarealmostasrigidassolidbeamsbutareonlyafractionoftheweightandcost.
Athickersectionisinevitablewheretheribjoinsthemainwall.Thisribrootthicknessisusuallydefinedbythebiggestcircle(D)thatcanbeinscribedinthecross-section,anditdependsontheribthickness(w)andthesizeofthefilletradius(r).Toavoidsinkmarks,thisthickregionmustbekepttoaminimumbutthereareconstraints.Iftheribistoothinitwillhavetobemadedeepertogiveadequaterigidityandthenitmaybuckleunderload.Thereareotherproblemstoo;themouldbecomesdifficulttomachineandfill.Andribsfilledunderhighinjectionpressuretendtostickinthemould.
Thefilletradiusmustnotbemadetoosmalleither,oritwillnotsucceedinreducingstressconcentrationswheretheribjoinsthemainwall.Ideally,thefilletradiusshouldnotbelessthan40percentoftheribthickness.Theribsthemselvesshouldbebetweenahalfandthree-quartersofthewallthickness.Thehighendofthisrangeisbestconfinedtoplasticsthathavealowshrinkagefactorandarelesspronetosinkmarks.
Asimplecomparisonshowsthebenefitofgoodribdesign.Aribthatis65percentofthewallthicknessandhasa40percentfilletradius,resultsinarootthicknessthatisabout1.23timesthewallthickness.Bycontrast,therootthicknesssoarsto1.75timesthewallthicknesswhentheribisasthickasthewallandhasanequalradius.
Ribsofcoursemustbeextractedfromthemould,sotheymustbeplacedinthedirectionofdraworprovidedwithmovingmouldpartstofreethem.Ribsshouldbetaperedtoimproveejection;onedegreeofdraftpersideisideal.Iftheribisverydeepthedraftanglemustbereducedortheribbecomestoothin.Forthisreasonribsareoftenlimitedtoamaximumdepthoffivetimestheribthickness.Sofar,sogood.Buthowmanyribsareneededtomakeapartstrongenoughandhowshouldtheybearranged?WewillexaminethatinthenextDesignGuide.
thickness,theribspacingbecomes65percentof31.25,makingit20mmforpracticalpurposes.
Alternativeribjunctions
Ribsareusedtoimprovetherigidityofaplasticspartwithoutincreasingthewallthicknesssomuchthatitbecomesunsuitableforinjectionmoulding.Inthepreviousguidewelookedatthebasicsofribdesign.Thistimewewillseehowtoputribsintopractice.
Termsforthecalculator
Usuallywewantaparttobeequallyrigidinalldirections,justlikeasolidplate.Wecangetalmostthiseffectbyrunningribsalongandacrossthepart,sotheycrossatrightangles.Thiscreatesathicksectionwheretheribscrossbutifwefollowthedesignrulesforribsandfilletradiitheincreaseiswithinacceptablelimits-about1.3timesthewallthicknessattheworst.Thiscanbereducedalmosttothebasicwallthicknessbyformingacored-outbossatthejunction,butabettersolutionistouseanormaljunctionwithribsthatarelessthan0.75timesthewallthickness.
Source:DuPont
Buthowmanyribsdoweneedandhowdeepshouldtheybe?Rigidityisafunctionofthemomentofinertiaoftheribsection.Thistellsusthatthestiffeningeffectofaribisproportionaltoitsthicknessbutproportionaltothecubeofitsdepth.Sodeepribsarestructurallymuchmoreefficientthanthickribs.Acommontaskistodeveloparelativelythinribbedplatethathasthesamerigidityasathicksolidplate.Standardengineeringtextbooksprovidethebasicformulaetomakethecalculationbutthemathematicscanbeachoretomanagemanually.Tominimisetheworkanumberof‘readyreckoners’havebeendevised,includinganelegantcross-ribsolutiondevelopedbyDuPont.Mostofthesereckonersorcalculatorsarebasedonaparticularsetofassumptionssousewithcautionifyourdesignvaries.
DESIGNER’SNOTEBOOK
Deepribsarestifferthanthickribs.
Followthebasicrulesforribthicknessandfilletradii.
Calculateribdepthandspacingwithareckoner,orbyusingmathsoftwareorfiniteelementanalysis.
Forexample,theDuPontribbedplatecalculatorassumestheribsarethesamethicknessasthewall.Toseehowitworks,let’simaginethatwewanttodesignacrossribbedplatewitha2.5mmwall(tB)thatwillbeasstiffasasolidplateof5mmthick(tA).CalculatetB/tA–thevalueis0.5–andfindthisvalueontheleft-handscale.Rulealineacrosstotheright-handscaleandreadoffthevaluewhichis1.75.ThisvalueisT/tAwhereTistheribdepthincludingthewallthickness.Soinourexample,T=1.75timestAwhichis8.75mm.Nowreadoffthevalueonthebasescaleverticallybelowthepointofintersectionbetweenthe0.5lineandthecurve.Thefigureis0.16anditrepresentstheproductoftAandthenumber(N)ofribsperunitofplatewidth(W).ThecurveassumesthatWisunity.SoNequals0.16dividedbytAwhichis0.032ribspermmofwidth,oroneribper31.25mm.
Wecanmakeaprorataadjustmentforribsthatarecorrectlydesignedtobethinnerthanthewall.Iftheribsare65percentofthewall
makingthesidewallthicker,westiffenitwithbuttressribs,oftenknownintheUSAasgussets.Thesamedesignrulesapply.Itisparticularlyimportanttofollowtheruleforthicknessotherwisesinkmarkswillshowontheoutsideofthepart.
Unidirectionalribcalculator
Source:DuPont
Usebuttressribstostiffensidewalls
Ribsareimportantinthedesignofplasticspartsbecausetheyallowustomakeacomponentrigidwithoutmakingittoothick.Wehavealreadylookedatthefundamentalsandseenhowtodesignacross-ribbedpart.Sometimesthough,weonlyneedrigidityinonedirection.Thisusuallyhappensonalongthinfeaturelikeahandle.Inthiscase,wecanimprovestiffnessalongthelengthofthepartbyaddinganumberofparallelribs.Thesearecalledunidirectionalribs.
Thefirstconsiderationisthattheseribsmustnotbetooclosetogether.Thisisbecausethegapbetweentheribsisproducedbyanupstandingcoreinthemould.Ifthiscoreistoothinitbecomesverydifficulttocoolandtheremayalsobeashrinkageeffectthatwillcauseejectionproblems.Theusualruleismakethegapatleasttwicethenominalwallthicknessandpreferablythreetimesormore.
Asinthecaseofcross-ribs,designisbasedontheprinciplethatrigidityisproportionaltothemomentofinertiaofthewallsection.Thisprovidesawayofworkingoutthinribbedsectionsthathavethesamestiffnessasthickplainsections.Calculatorcurvesmakethejobeasier.Curvesareavailableforcalculatingdeflection(strain)andstressonvariousribthicknesses.Ourexampleshowsadeflectioncurveforribthicknessesequalto60percentofthenominalwallthickness.
Forsimplicity,thecalculationsplitstheunidirectionalribbedpartintoanumberofT-sectionstrips,eachwithasinglerib.Thewidthofthestripisknownasthe‘equivalentwidth’orBEQ.Toseehowthecalculatorworks,wewilldesignaribbedpartwiththesamestiffnessasarectangularsection45mmwide(B)by12mmthick(Wd).Wedecideonfourribsandanominalwallthicknessof3mm(W).Therearethreesimplecalculationstomake.
BEQ=B/N=45/4=11.25
BEQ/W=11.25/3=3.75
Wd/W=12/3=4
Nowfindthevalue4ontheleft-handaxisanddrawahorizontallinetointersectwiththe3.75curveshownontheright-handaxis.Dropaverticalfromthispointandreadoffthevalue,5.3,onthebottomaxis.Thisfigureistheratioofribheight(H)tothenominalwallthickness(W).Sotheribheightinthisexampleis:H=3(5.3)=15.9
Thisismorethan5timestheribthickness,soweshouldbeconcernedaboutbuckling.Wecan’tincreasethenumberofribswithoutspacingthemtoocloselysoouroptionsaretomaketheribsand/orthewallthicker.Designoftenrequiresafewiterationstogetthebestresult.
DESIGNER’SNOTEBOOK
Unidirectionalribsshouldbespacedapartbyatleast2andpreferably3ormoretimesthenominalwallthickness
Ribdepthshouldnotbemorethan5timesribthickness
Usethecalculatorcurvetoworkoutribheights
Usebuttressribstostiffensidewalls
Wecanalsouseribsonsidewalls.Insteadof
4.1 BOSSES
#
Thereisarightandawrongwaytosupportbosses
Thebossisoneofthebasicdesignelementsofaplasticsmoulding.Bossesareusuallycylindricalbecausethatistheeasiestformtomachineinthemouldanditisalsothestrongestshapetohaveinthemouldedpart.Thebossisusedwheneverweneedamountingpoint,alocationpoint,areinforcementaroundahole,oraspacer.Thebossmayreceiveaninsert,ascrew,oraplainshafteitherasaslideorapressfit.Inotherwords,thebossisnotassimpleasitlooks.Dependingonitsuse,itmayhavetostanduptoawholecombinationofforces–tension,compression,torsion,flexing,shearandbursting-soitmustbedesignedaccordingly.Wecanstartwithsomegeneraldesignrules,usingtheprincipleswehavealreadydevelopedforribsandwalls.Thebosscanbethoughtofasaspecialcaseofarib;onethatiswrappedroundintheformofatube.An'ideal'boss,designedaccordingtoribrules,wouldnotproducesinkmarksorstickinthemouldbutunfortunatelythetubularformofthebosswouldnotbestrongenoughinmostcases.Inreallife,mostbossesbreaksomeribdesignrulesbynecessity.Thismeansthatbossdesignisacompromisebetweensinkmarksandfunctionality.
Rigidityisthesimplestaspectofbossdesign.Thiscanbeachievedbysupportingthebosswithbuttressribs,andoftenbylinkingthebosstoasidewall.Thesupportribscanbedesignedtonormalribrulessothatsinkmarksandstresspointsareavoided.
DESIGNER’SNOTEBOOK
Beforedesigningaboss,consideritsfunctionandtheforcesactingonitduringassemblyandservice
Iftheforcesarenotgreat,itmaybepossibletodispensewithsupportribs,otherwise:
Anchorthebosstothebasewallwithbuttressribs.
Ifpossible,anchorthebosstothesidewallwithaflatrib.
Avoidribarrangementsthatresultinsmallmouldcoresorcomplicatedmouldmachiningset-ups.
Whenthebossislinkedtoasidewall,eitheratanedgeorthecornerofacomponent,thereisarightandawrongwaytodoit.Thewrongwayissimplytoextendthebossoutsidediametertomeetthewall.Thisinevitablyproducesathicksectionthatwillresultinsinkmarks,voids,andlongcoolingcycles.Therightwayistolinkortiethebosstothesidewallwithaflatrib,preferablyrecessedalittlebelowthebossoredgeheightsothatitcannotinterferewithanyassemblyconditions.Theotherribsthattiethebosstothebasewallremainasbuttressribs.Foreconomicalmachiningofthemould,theribsshouldbealignedontheX-Yaxesofthecomponentexceptfortheflatcornerribwhichisplacedat45degrees.ThesinglediagonalribisbetterthantwoX-Yribsbecauseitavoidsasmallmouldcorebetweentheribs.Suchsmallcoresarepronetodamageandaredifficulttocool;thismayresultinslowermouldingcyclesandmoredowntime.
Sowehaveestablishedhowtoconnectthebosstotherestofthecomponent.Themoredifficultpartofbossdesignconcernstheholeandthethicknessoftheboss.
FlexuralModulusofplastic(Mpa)
Preferredscrewtype
Lessthan1,400
Thread-forming
1,400to2,800
Thread-formingorThread-cutting
2,800to6,900
Thread-cutting
Greaterthan6,900
Thread-cutting,finepitch
Screwselectiondependsonmaterial
Source:DuPont
Material
HoleFactor
BossFactor
DepthFactor
ABS
0.80
2.00
2.0
ABS/PC
0.80
2.00
2.0
ASA
0.78
2.00
2.0
PA46
0.73
1.85
1.8
PA46GF30%
0.78
1.85
1.8
PA6
0.75
1.85
1.7
PA6GF30%
0.80
2.00
1.9
PA66
0.75
1.85
1.7
PA66GF30%
0.82
2.00
1.8
PBT
0.75
1.85
1.7
PBTGF30%
0.80
1.80
1.7
PC
0.85
2.50
2.2
PCGF30%
0.85
2.20
2.0
PE-HD
0.75
1.80
1.8
PE-LD
0.75
1.80
1.8
PET
0.75
1.85
1.7
PETGF30%
0.80
1.80
1.7
PM
温馨提示
- 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
- 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
- 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
- 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
- 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
- 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
- 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
最新文档
- Unit 6 检测卷 教学设计 2024-2025学年牛津译林版英语(江苏地区)九年级上册
- 2024中山房屋出租合同范本
- 2024秋七年级数学上册 第3章 一次方程与方程组3.1 一元一次方程及其解法 2等式的基本性质教案(新版)沪科版
- 8《不一样的材料》教学设计-2024-2025学年人教鄂教版 (2017)科学一年级上册
- 《语文园地三》(教学设计)2024-2025学年统编版语文一年级上册
- Unit 10 Part 4 Section B (课前)2023-2024学年八年级上册英语高效课堂教学设计(人教新目标Go For It!)
- Unit 5 The colourful world 第四课时(教学设计)-2024-2025学年人教PEP版(2024)英语三年级上册
- 大学计算机基础 课件-WPS 第2章 操作系统
- 中医护理模拟题库及答案
- 气胸的术前术后护理
- 部编版(2024版)七年级历史上册第3课《中华文明的起源与形成》精美课件
- 2025年高考数学一轮复习-7.1.2球的切、接问题【含解析】
- 山东省青岛市胶州市2023-2024学年高二下学期期末学业水平检测数学试题
- 百日咳课件完整版本
- 2023AIGC 工作应用与创作思路
- 流动儿童基本情况登记表
- 2024年中国宝武钢铁集团有限公司校园招聘考试试题及答案一套
- 法律常识题库500题及参考答案(典型题)
- 《SketchUp三维辅助设计》课件-项目1 SketchUp软件概述
- 卫生院为老年人优先双向转诊服务方案
- 2024年保险考试-保险销售资质分级分类笔试参考题库含答案
评论
0/150
提交评论