《機(jī)械加工工藝》課件-2.5 Part machining sequence

Thedivisionofmachiningstages.Ⅰ、Selectionofprocessingmethod（havelearnt）ⅡPartmachiningsequence1.DivisionoftheprocessingstagesInordertoensuretheprocessingqualityofpartsandthereasonableuseofequipment,manpower,partsareoftenimpossibletobecompletelyprocessedinaprocess,sothewholeprocessingprocessmustbedividedintoroughprocessing,semi-finishingandfinefinishingthreestages.劃分加工階段的主要原因有：⑴Ensurethemachiningqualityoftheparts.Whenthemetallayerremovedduringroughmachiningisthick,itwillproducelargecuttingforceandcuttingheat,andproducelargeelasticandthermaldeformation.Inaddition,duetotheinternalstressredistributionafterroughmachining,theworkpiecewillalsocausegreatdeformation.⑵Itisconducivetomakefulluseoftheequipment.⑶Itwillhelpusdiscovertheblankdefectstimely.Roughmachiningremovesmostofthesurfacemargin,sothattheblankdefectssuchaspores,sandeyes,insufficientmargincanbefoundasearlyaspossible,timelyrepairedorscrapped.Inthiswaywecanavoidthewastethatcausedbycontinuedprocessing.⑷Itcanhelpusavoiddamagingtheprocessedsurfaces.Arrangingfinefinishingattheendcanprotectfinefinishingsurfacesfromlessornodamageduringprocessing.⑸Itcanhelpusarrangethenecessaryheattreatmentprocess,andinserttheheattreatmentinthemachiningprocessatthepropertimetoavoidthedeformationcausedbytheheattreatment.

Theprocessingsequenceofthepartsincludesthemechanicalprocessingprocesssequence,theheattreatmentsequenceandtheauxiliaryprocess.Whenformulatingtheprocessroute,theprocesspersonnelshouldcomprehensivelyconsiderthethreeelementstogether.Whethertheprocessingsequencearrangementofthepartsisproperhasagreatimpactontheprocessingquality,productivityandprocessingcost.2.Arrangementofthemachiningprocess(1)Benchmarkfirst①Theselectedfinebenchmarksurfaceshouldbearrangedfirst,andthentheprocessingofothersurfacesshouldbearrangedwiththeprocessedrefinedreferenceasthepositioningreference;②Atthebeginningofthefinefinishingstage,thereferencesurfaceshouldberefinedfirsttoimprovethepositioningprecision,andthenarrangethefinefinishingofothersurfaces.(2)RoughbeforefineTheprocessingprocessofthewholepartshouldberoughprocessingprocessfirst,thensemi-finishing,finefinishingandfinishingcut.Arrangethemainsurfaceprocessingfirst,andthenarrangethesecondarysurfaceprocessing,themainsurfacegenerallyreferstothedesignreferencesurfaceandtheimportantworkingsurfaceontheparts.(3)PrimarybeforesecondaryBoxandbracketpartshavebothplaneandholeorholesystem,theplane(usuallytheassemblybasesurface)shouldbeprocessedfirst,andthenprocesstheholeorholesystembythereferenceplane.(4)Planebeforehole（2）ArrangementoftheheattreatmentprocessPurposeofheattreatment:Toimprovethemechanicalproperties,andimprovethecuttingperformanceofmetal,andeliminatetheresidualstress.Theheattreatmentprocessofmechanicalpartsisroughlydividedintotwocategories:preparatoryheattreatmentandfinalheattreatment.Preparingheattreatment

Purpose:toimprovethecuttingperformance,eliminatetheinternalstressoftheblankandprepareenoughgraphicorganizationforthefinalheattreatment.①annealing:usedforhighcarbonsteel,alloysteel,reducethehardness,easytocut;②ignition:usedforlowcarbonsteel,improvehardness,grainrefinement;③agingtreatment:eliminateinternalstress.Itisdividedintonaturalagingandartificialaging;④Tempering:Hightemperaturetemperingafterquenching.Finalheat-treatmentpurpose:toimprovethestrength,hardnessandothermechanicalpropertiesoftheparts.①Q(mào)uenching:Surfacequenchingandoverallquenching;②Carburizationquenching:Usedforlowcarbonsteelandlowalloysteel.Andincludesintegralcarburizationandlocalcarburization;③Nitriding:usedtoimprovethesurfacehardness,wearresistance,fatiguestrength,etc.StressrelieftreatmentPurpos：EliminatestressandreducedeformationMethods:Artificialaging,annealing,hightemperaturestressrelief,etc.

Use：Forgeneralcastings:Itisusedafterroughmachining;Forhighprecisioncasting:Itisusedaftersemi-finishingForhighprecisionwirerod,shaft,etc.:Itisusedaftertheroughcar,roughgrinding,semi-finegrinding,thenwealsoneedagingtreatmentandinordertokeepstablesize,furtherice-coldtreatmentisrequired.（3）ArrangementoftheauxiliaryprocessAuxiliaryprocessincludesworkpieceinspection,burr,prism,cleaning,rustprevention,magnetization,etc.Inspectionisthemostimportantauxiliaryprocess,itplaysanimportantroleinensuringtheproductquality.Theinspectionprocedureshallbearrangedinthefollowingareas:1)Aftertheroughstage;2)Beforeturningtoimportantprocessesorbeforeandafterprocesseswithlongprocessinghours;3)Beforeandafterchangingtheworkshop,especiallybeforeandafterenteringtheheattreatmentprocess;4)Specialperformanceinspection,suchasmagneticflawdetection,sealingtest,etc.III.Combinationofprocesses(centralizedanddispersed)1.

Processconcentrationistoconcentratetheprocessingofworkpieceinafewprocesses,andtherearemoreprocessingcontentineachprocess.Processconcentrationcanbedividedinto:mechanicalconcentrationwithtechnicalmeasures,andorganizationalconcentrationwithhumanorganizationmeasures.Features:(1)Adopthigh-efficiencyspecialequipmentandprocessequipmentandhashighproductionefficiency.(2)Thenumberofworkpiececlipsisreduced,easytoensurethemutualpositionaccuracybetweenthesurface,andcanshortentheauxiliarytime.(3)Thesmallnumberofprocesses,whichcansimplifytheproductionplansandorganizationofwork.(4)Equipmentinvestmentislarge,Theuseofcomplexstructureofspecialequipmentandprocessequipmentwillbeexpensive,anditisdifficulttoadjustandmaintain.Processconcentration2.Theprocessingoftheworkpieceisscatteredinmoreprocesses,andtheprocessingcontentofeachprocessisverylittle,andsometimeseveneachprocesshasonlyasimplestep.。(1)Processingequipmentandprocessequipmentissimple,easytoadjustandrepair,workersareeasytomaster,easytoadapttotheconversionofproducts.(2)Themostreasonablecuttingamountcanbeusedtoreducethebasictime.(3)Thetechnicallevelrequirementoftheoperatorsisrelativelylow.(4)Thenumberofequipmentandprocessequipmentislarge,moreoperators,andalargeproductionarea.Theadvantagesanddisadvantagesofprocessconcentrationandprocessdispersionshouldbecomprehensivelyanalyzedaccordingtotheproductiontype,existingproductionconditions,featuresofworkpiecestructureandtechnicalrequirements.DispersedprocessⅣ、Divisionsandpurposesofprocessingstages⑷Finishingcutstage

：⑴Roughingstage：finishthesecondarysurfacesandprepareforthefinishingoftheprimarysurfaces.toensurethateachmajorsurfacemeetstherequirementsofthedrawing,themainproblemishowtoensurethequalityofmachining.Tofurtherreducesurfaceroughnessandimproveprecision.

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