机械外文翻译中英文 机床 模具 机械 材料Word文档下载推荐.docx

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DAitchisonandRSulaiman*

DepartmentofMechanicalEngineering,UniversityofCanterbury,Christchurch,NewZealand

Abstract:

Themarketforfoammaterialshasbeengrowingrapidlythroughouttheworldastheyhaveavarietyofuses.Someexamplesareintheautomotivesindustries,foodpackagingindustries,medicalapplication,sportsgears,homeinsulationsandfloatationinoffshoredrillingrigs,buoysandsmallboats.Sincetheusesoffoamaffectsgreatlythedailylivesofhumans,theneedtohavefoamsindifferentshapesrequiresspeedincuttingandmanufacture.Thiscanonlybedonethroughcomputeraidedcuttingmachinesorautomatedcuttingoffoams.However,thespeedofcuttingwillaffectthesurface.finishofthecut.Therefore,itisnecessarytodeterminethesurfaceformofthepolystyrenetoachievequalityresults.Thisisanon-goingresearchtoproducearapid-prototypingmachinethatcutsfoammodels.The.firstphaseofthisresearchistodeterminethesurfaceformofpolystyrenethroughtheuseofacoordinatemeasuringmachine（CMM）,afterbeingcutwithdifferenttypesofwires,atdifferenttemperaturesandcuttingfeed-rates.

Keywords:

polystyrene,surfaceform,hot-wirecutting

1INTRODUCTION

Themarketforfoammaterialhasbeengrowingrapidlythroughouttheworld.Foamscanbecategorizedinto

twomajortypes,namelyflexiblefoamsandrigidfoams.Theflexiblefoamsaremainlyusedinfurniture,transportation,bedding,carpetunderlay,packaging,toys,sportsapplicationandshoes,aswellasforvibrationandsoundattenuation.Therigidfoamsareusuallyusedinbuildingappliances,insulationagents,pipes,tanks,floatationandfoodanddrinkcontainers

[1].Thereasonwhyfoamsareusedeverywherecanbesummarizedasfollows:

1.Foamisveryinexpensive.

2.Foamissuitableforuseindoorsoroutdoors.

3.Foamcanbecoatedwithmanydifferentproductstoachieveanydesired.finish.

4.Foamislightweightforeasyhandlingandinstallation.

Theproductionoffoamscantakeplaceusingmanydifferenttechniques.Themostcommonmethodtoproducecontinuousfoamslabisbypouringmixedingredientsofpetrochemicalagentsthatincludetoluenedi-isocyanate,polyolandwater.Theseingredientsarelefttoriseandcure.Additivesareblendedinforspecific.characteristicssuchascolors,absorbingcapacity,effectsonultravioletandothers.

Thismethodproducesfoaminits‘raw’state,whichmustthenbeformedintodifferentshapesandsizes.Thisisusuallydonebycuttingthefoams.Therearetwowaystocutfoammaterials,whicharebyusinghot-wiretechniquesandtheoscillatingblademethod.Bothproducedifferentfeaturestothefoams.Theoscillatingbladeproducessimplegeometricalshapesandissuitableforrigidfoams.Thehot-wiretechniqueiscapableofproducingcomplicatedgeometricalshapesandissuitableforflexiblefoams.Presently,bothtechniquesareperformedeithermanuallyorinasemi-automatedmanner[2].

2COORDINATEMEASUREMENTMACHINE（CMM）

Beforefurtherdiscussion,itisnecessarytodescribethefeaturesofacoordinatemeasurementmachine（CMM）asatoolusedinthisresearchfordeterminingthesurfaceformofpolystyrene.ACMMconsistsofaprobetomeasurepointsonawork-piece.Thisissimilartousinga.fingertotraceamapcoordinate.Theprobeactsasa.fingerthatpointsortouchesacertainlocationonthework-piece.Eachpointonthework-pieceisuniquetothemachine’scoordinatesystem.Thecoordinatesystemdescribesthemovementofthemeasurementmachine.

Therearetwotypesofcoordinatesystem.The.firstiscalledthemachinecoordinatesystem.Here,theX,YandZaxesrefertothemachine’smotion.Thesecondcoordinatesystemiscalledthepartcoordinatesystem,wherethethreeaxesrelatetothedatumofthework-piece.Adatumisalocationofafeatureonawork-piece.Itcanbeahole,asurfaceoraslot.ACMMmeasuresawork-piecetodeterminethedistancefromonefeaturetoanother.Itcanalsobeusedtodeterminetheformorroughnessonasurfaceofasoftobject,suchaspolystyrene.TheCMMusedinthepresentexperimentistheDiscoverySeriescoordinatemeasuringmachineModelD-12（Fig.1a）.Dataaregatheredbytouchingthetestpiecewitheitherasolidprobeoranelectronictouchtriggerprobe.Thisexperimentusestheelectronictouchtriggerprobe.Theprobemeasurementwastakenperpendiculartothetestpiecetoobtaintheoptimalresultbecauseprobetip‘skidding’willaffectthereadingofdata.Thestylussizesthatareavailableintheauthors’laboratoryare1.0,2.0,3.0,4.0and5.0mmindiameter.Thestylususedinthisexperimentwasrubywithasizeof3.0mmindiameter.Aspolystyreneissoft,asmallerstylussizemaycreatenewslopesorholeswhentouchingthepolystyrene（Fig.1b）.Alargerstylussizemaynotdetecttheexistingslopesandholesonthesurfaceofthepolystyrene.Therefore,thestylus3.0mmindiameterwasusedtoavoidtheabovereadingerrors（Figs1candd）.

3SURFACEFORM

Itisgenerallyagreedthatsurfaceformorroughnessconsistsofscratchmarksandfragmentationmarkswithinthem.Thesemarksarerelativelycloselyspacedtogether.Thismakesthemdif.culttomeasure.Whydoengineerstroubletomeasuresurfaceroughnessatall?

Themainreasonisthatthesurfacebeingmeasuredwillbeincontactwithsomeothersurfaces.Byunderstandingitssurface,thenatureofthecontactandtheperformanceofthecontactedcomponentscanbecontrolled.

（d）

Fig.1（a）TheCMMusedinthisexperiment;

（b）thesurfaceofpolystyreneasseenthroughamicroscope;

（c）typicaldiagramoftheprobe;

（d）theprobeusedinthisexperiment

Itisnecessarytostatethatsurfaceformandsurfaceroughnessarenotthesame.Surfaceformisageometricalpro.leofasurfaceonsoftmaterials,suchaspolystyreneorsponge.Measuringsurfaceroughnessonsoftmaterialischallengingandcomplicated,butcanbedone[3].Surfaceroughnessismorecommonlyrecognizedasanirregularorunevensurface,usuallyonhardmaterials[4].Thedefinitionstendtorefertothetechniqueorscaleofmeasuringitshardness.Ifsurfaceroughnessneedstocomplywithawrittenstandard,thereareafewtochoosefrom.ThemostcommonistheBritishStandardsInstitutionBS1134,Centre-lineAverageHeightMethodforAssessmentofSurfaceTexture,1961.Thereisalsoanotheronebeingusedinthemechanicalengineeringindustrytodate,whichistheInternationalStandardISO4287,SurfaceRoughness—Terminology—Part1—SurfaceandItsParameters,1stedition,1984,pp.12–15.Themeasurementstandardsarebasedonalinepro.leobtainedbyscanningamechanicalstylusacrossthesurface.Forathoroughassessmentoftheroughnessstandards,refertoISO4287andthepublishednationalstandardsbasedonthisISOdocuments.Thelattercanbetracedbycontactingnationalreferencelaboratories,e.g..NationalPhysicalLaboratoryintheUnitedKingdom,PhysikalisheTechnisheBundesanstaltinGermany,NationalInstituteofStandardsandTechnologyintheUnitedStatesandLaboratoireNationald’EssaisinFrance.

4SURFACEFORMFORSOFTMATERIALS

Questionsareoftenraisedconcerningthepossibilityofmeasuringsurfaceroughnessofsoftmaterialssuchaspolystyreneorotherfoammaterials.Asuitablemethodofmeasuringisbyusingtheopticaltechnique.However,withtheopticaltechniquecarefulattentionmustbefocusedonlocal,steepslopesinthesurfaceofthetestpiece,asthedynamicfocusinginstrumentstendtoproducecorruptfeedbackatthesepoints.Otheropticaltechniquesencounterproblemswithsteeplocalslopesbynotreflectingenoughlightbackintothedetectorsystem.ThisisthemainreasonwhythisresearchusestheCMMmachine.TheCMMmachinecanmeasurethesurfaceformofpolystyrenebecausepolystyreneusuallydoesnothavesteepslopes.Whenexaminedthroughamicroscope,theseslopesappeartobespericalinshape.ResultsofthetestsareproducedasshowninFig.2.

Noticethatthedeepertheslope,thelongerthelineproducedbyCMMreadings.

5EXPERIMENTALTECHNIQUE

Inthisresearch,asimplemachineisdesignedtocutpolystyreneusingthehot-wiretechnique.Themachinewillcutthepolystyreneinaone-dimensionalmovement,i.e.feedingthehotwirehorizontallytowardsthepolystyrene.Hot-wirefoamcuttersareverycommonwhenworkingwithpolystyrene.Thetwoendsofthehotwireareconnectedtoapowersource.Heatwillflowwhenthereisadifferenceintemperatureacrossthewire.Heatflowsfromwarmtocoldareasatarateproportionaltothetemperaturegradientandthethermalconductivityofthewireitis?

owingthrough.Athermocoupleisconnectedtothehotwiretogiveareadingofthewiretemperature.Manipulatingthecurrentandvoltageofthewirecancontrolthetemperature.Thetemperaturesconsideredinthisexperimentare100,200and3008C

TheobjectiveofthisexperimentistorevealthesurfaceformofpolystyrenethroughtheuseofaCMMwithdifferenttypesofwires,temperaturesandcuttingfeed-rates.Thesurfaceformisaffectedbythefederateandtemperatureofthehot-wirecutter.Thetestmaterialwaspolystyrenewithwidthof300mm,lengthof300mmandthicknessof50mm.Thesesizeswereselectedbecausetheycanbeeasily

handledwhenperformingthetest.Thewiresusedasthecuttingtoolwerenickel–chromiumalloy（Nichrome）,Inconelandnickel–chromium–iron（NiCr-C）springwire[5].ThereasonsforselectingInconelandNiCr-Cspringwiresareduetotheirabilitytomaintaintheirshapeafterbeingappliedtotheoperating