英文参考文献原文复印件及译文.docx
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英文参考文献原文复印件及译文.docx
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英文参考文献原文复印件及译文
英文参考文献原文复印件及译文
专业:
机械设计制造及其自动化
姓名:
梁彦朋
学号:
080202410
指导教师:
刘金海
完成日期2012年6月
ProcessPlanningandConcurrentEngineering
——T.RamayahandNorainiIsmail
ABSTRACT
Theproductdesignistheplanfortheproductanditscomponentsandsubassemblies.Toconverttheproductdesignintoaphysicalentity,amanufacturingplanisneeded.Theactivityofdevelopingsuchaplaniscalledprocessplanning.Itisthelinkbetweenproductdesignandmanufacturing.Processplanninginvolvesdeterminingthesequenceofprocessingandassemblystepsthatmustbeaccomplishedtomaketheproduct.Inthepresentchapter,weexamineprocessingplanningandseveralrelatedtopics.
ProcessPlanning
Processplanninginvolvesdeterminingthemostappropriatemanufacturingandassemblyprocessesandthesequenceinwhichtheyshouldbeaccomplishedtoproduceagivenpartorproductaccordingtospecificationssetforthintheproductdesigndocumentation.Thescopeandvarietyofprocessesthatcanbeplannedaregenerallylimitedbytheavailableprocessingequipmentandtechnologicalcapabilitiesofthecompanyofplant.Partsthatcannotbemadeinternallymustbepurchasedfromoutsidevendors.Itshouldbementionedthatthechoiceofprocessesisalsolimitedbythedetailsoftheproductdesign.Thisisapointwewillreturntolater.
Processplanningisusuallyaccomplishedbymanufacturingengineers.Theprocessplannermustbefamiliarwiththeparticularmanufacturingprocessesavailableinthefactoryandbeabletointerpretengineeringdrawings.Basedontheplanner’sknowledge,skill,andexperience,theprocessingstepsaredevelopedinthemostlogicalsequencetomakeeachpart.Followingisalistofthemanydecisionsanddetailsusuallyincludewithinthescopeofprocessplanning.
Interpretationofdesigndrawings. Thepartofproductdesignmustbeanalyzed(materials,dimensions,tolerances,surfacefinished,etc.)atthestartoftheprocessplanningprocedure.
Processandsequence. Theprocessplannermustselectwhichprocessesarerequiredandtheirsequence.Abriefdescriptionofprocessingstepsmustbeprepared.
Equipmentselection. Ingeneral,processplannersmustdevelopplansthatutilizeexistingequipmentintheplant.Otherwise,thecomponentmustbepurchased,oraninvestmentmustbemadeinnewequipment.
Tools,dies,molds,fixtures,andgages. Theprocessmustdecidewhattoolingisrequiredforeachprocessingstep.Theactualdesignandfabricationofthesetoolsisusuallydelegatedtoatooldesigndepartmentandtoolroom,oranoutsidevendorspecializinginthattypeoftooliscontacted.
Methodsanalysis. Workplacelayout,smalltools,hoistsforliftingheavyparts,eveninsomecaseshandandbodymotionsmustbespecifiedformanualoperations.Theindustrialengineeringdepartmentisusuallyresponsibleforthisarea.
Workstandards. Workmeasurementtechniquesareusedtosettimestandardsforeachoperation.
Cuttingtoolsandcuttingconditions. Thesemustbespecifiedformachiningoperations,oftenwithreferencetostandardhandbookrecommendations.
Processplanningforparts
Forindividualparts,theprocessingsequenceisdocumentedonaformcalledaroutesheet.Justasengineeringdrawingsareusedtospecifytheproductdesign,routesheetsareusedtospecifytheprocessplan.Theyarecounterparts,oneforproductdesign,theotherformanufacturing.
Atypicalprocessingsequencetofabricateanindividualpartconsistsof:
(1)abasicprocess,
(2)secondaryprocesses,(3)operationstoenhancephysicalproperties,and(4)finishingoperations.Abasicprocessdeterminesthestartinggeometryoftheworkparts.Metalcasting,plasticmolding,androllingofsheetmetalareexamplesofbasicprocesses.Thestartinggeometrymustoftenberefinedbysecondaryprocesses,operationsthattransformthestartinggeometry(orclosetofinalgeometry).Thesecondarygeometryprocessesthatmightbeusedarecloselycorrelatedtothebasicprocessthatprovidesthestartinggeometry.Whensandcastingisthebasicprocesses,machiningoperationsaregenerallythesecondprocesses.Whenarollingmillproducessheetmetal,stampingoperationssuchaspunchingandbendingarethesecondaryprocesses.Whenplasticinjectionmoldingisthebasicprocess,secondaryoperationsareoftenunnecessary,becausemostofthegeometricfeaturesthatwouldotherwiserequiremachiningcanbecreatedbythemoldingoperation.Plasticmoldingandotheroperationthatrequirenosubsequentsecondaryprocessingarecallednetshapeprocesses.Operationsthatrequiresomebutnotmuchsecondaryprocessing(usuallymachining)arereferredtoasnearnetshapeprocesses.Someimpressiondieforgingsareinthiscategory.Thesepartscanoftenbeshapedintheforgingoperation(basicprocesses)sothatminimalmachining(secondaryprocessing)isrequired.
Oncethegeometryhasbeenestablished,thenextstepforsomepartsistoimprovetheirmechanicalandphysicalproperties.Operationstoenhancepropertiesdonotalterthegeometryofthepart;instead,theyalterphysicalproperties.Heattreatingoperationsonmetalpartsarethemostcommonexamples.Similarheatingtreatmentsareperformedonglasstoproducetemperedglass.Formostmanufacturedparts,theseproperty-enhancingoperationsarenotrequiredintheprocessingsequence.
Finallyfinishoperationsusuallyprovideacoatontheworkparts(orassembly)surface.Examplesincludedelectroplating,thinfilmdepositiontechniques,andpainting.Thepurposeofthecoatingistoenhanceappearance,changecolor,orprotectthesurfacefromcorrosion,abrasion,andsoforth.Finishingoperationsarenotrequiredonmanyparts;forexample,plasticmoldingrarelyrequirefinishing.Whenfinishingisrequired,itisusuallythefinalstepintheprocessingsequence.
ProcessingPlanningforAssemblies
Thetypeofassemblymethodusedforagivenproductdependsonfactorssuchas:
(1)theanticipatedproductionquantities;
(2)complexityoftheassembledproduct,forexample,thenumberofdistinctcomponents;and(3)assemblyprocessesused,forexample,mechanicalassemblyversuswelding.Foraproductthatistobemadeinrelativelysmallquantities,assemblyisusuallyperformedonmanualassemblylines.Forsimpleproductsofadozenorsocomponents,tobemadeinlargequantities,automatedassemblysystemsareappropriate.Inanycase,thereisaprecedenceorderinwhichtheworkmustbeaccomplished.Theprecedencerequirementsaresometimesportrayedgraphicallyonaprecedencediagram.
Processplanningforassemblyinvolvesdevelopmentofassemblyinstructions,butinmoredetail.Forlowproductionquantities,theentireassemblyiscompletedatasinglestation.Forhighproductiononanassemblyline,processplanningconsistsofallocatingworkelementstotheindividualstationsoftheline,aprocedurecalledlinebalancing.Theassemblylineroutestheworkunittoindividualstationsintheproperorderasdeterminedbythelinebalancesolution.Asinprocessplanningforindividualcomponents,anytoolsandfixturesrequiredtoaccomplishanassemblytaskmustbedetermined,designed,built,andtheworkstationarrangementmustbelaidout.
MakeorBuyDecision
Animportantquestionthatarisesinprocessplanningiswhetheragivenpartshouldbeproducedinthecompany’sownfactoryorpurchasedfromanoutsidevendor,andtheanswertothisquestionisknownasthemakeorbuydecision.Ifthecompanydoesnotpossessthetechnologicalequipmentorexpertiseintheparticularmanufacturingprocessesrequiredtomakethepart,thentheanswerisobvious:
Thepartmustbepurchasedbecausethereisnointernalalternative.However,inmanycases,thepartcouldeitherbemadeinternallyusingexistingequipment,oritcouldbepurchasedexternallyfromavendorthatprocesssimilarmanufacturingcapability.
Inourdiscussionofthemakeorbuydecision,itshouldberecognizedattheoutsetthatnearlyallmanufacturesbuytheirrawmaterialsfromsupplies.Amachineshoppurchasesitsstartingbarstockfromametalsdistributoranditssandcastingsfromafoundry.Aplasticmoldingplantbuysitsmoldingcompoundfromachemicalcompany.Astampingpressfactorypurchasessheetmetaleitherfroadistributorordirectfromarollingmill.Veryfewcompaniesareverticallyintegratedintheirproductionoperationsallthewayfromrawmaterials,itseemsreasonabletoconsiderpurchasingatleastsomeofthepartsthatwouldotherwisebeproducedinitsownplant.Itisprobablyappropriatetoaskthemakeorbuyquestionforeverycomponentthatisusedbythecompany.
Thereareanumberoffactorsthatenterintothemakeorbuydecision.Onewouldthinkthatcostisthemostimportantfactorindeterminingwhethertoproducethepartorpurchaseit.Ifanoutsidevendorismoreproficientthanthecompany’sownplantinthemanufacturingprocessesusedtomakethepart,thentheinternalproductioncostislikelytobegreaterthanthepurchasepriceevenafterthevendorhasincludedaprofit.However,ifthedecisiontopurchaseresultsinidleequipmentandlaborinthecompany’sownplant,thentheapparentadvantageofpurchasingthepartmaybelost.ConsiderthefollowingexamplemakeorBuyDecision.
Thequotedpriceforacertainpartis$20.00perunitfor100units.Thepartcanbeproducedinthecompany’sownplantfor$28.00.Thecomponentsofmakingthepartareasfollows:
Unitrawmaterialcost=$8.00perunit
Directlaborcost=6.00perunit
Laboroverheadat150%=9.00perunit
Equipmentfixedcost=5.00perunit
________________________________
Total=28.00perunit
Shouldthecomponentby
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