机械制造专业英语 PPT课件

MACHININGTECHNOLOGY,1.3BASICMOTIONSINMACHINETOOLS1.4ASPECTSOFMACHININGTECHNOLOGY,1,1.3BASICMOTIONSINMACHINETOOLS,Inconventionalmachinetools,alargenumberofproductfeaturesaregeneratedorformedviathevarietyofmotionsgiventothetoolortheWP.Theshapeofthetoolplaysaconsiderableroleinthefinalsurfaceobtained.Basically,therearetwotypesofmotionsinamachinetool.Theprimarymotion,generallygiventothetoolorWP,constitutesthecuttingspeed.WhilethesecondarymotionfeedsthetoolrelativetotheWP.Insomeinstances,combinedprimarymotionisgiveneithertothetoolortotheWP.AclassificationofmachinetoolmovementsusedfortraditionalmachiningisgiveninTable1.2.Table1.3givesaclassificationfornontraditionalmachiningtechnology.ItmaybeconcludedthatmovementsofnontraditionalmachinetoolsaresimpleandmainlyintheZdirection,whiletraditionalmachinetoolshaveaminimumoftwoaxes,thatis,XandYdirectionsinadditiontorotationalmovements.,2,1.4ASPECTSOFMACHININGTECHNOLOGY,Machiningtechnologycoversawiderangeofaspectsthatshouldbeunderstoodforproperunderstandingandselectionofagivenmachiningtechnology.Tooling,accessories,andthemachinetoolitselfdeterminethenatureofmachiningoperationusedforaparticularmaterial.Asshownontheright-handsideofFigure1.7,themainobjectiveofthetechnologyadoptedistoutilizetheselectedmachiningresourcestoproducethecomponenteconomicallyandathighratesofproduction.Partsshouldbemachinedatlevelsofaccuracy,surfacetexture,andsurfaceintegritythatsatisfytheproductdesignerandavoidtheneedforpostmachiningtreatment,which,inturn,maintainsacceptablemachiningcosts.Thegeneralaspectsofmachiningtechnologyinclude:,3,1.4.1,1.4.2,1.4.3,1.4.4,1.4.5,1.4.6,MACHINETOOL,WORKPIECEMATERIAL,MACHININGPRODUCTIVITY,ACCURACYANDSURFACEINTEGRITY,PRODUCTDESIGNFORECONOMICALMACHINING,ENVIRONMENTALIMPACTSOFMACHINING,4,1.4.1MACHINETOOL,Eachmachinetooliscapableofperformingseveralmachiningoperationstoproducethepartrequiredatthespecifiedaccuracyandsurfaceintegrity.Machiningisperformedonavarietyofgeneral-purposemachinetoolsthatinturnperformmanyoperations,includingchipremovalandabrasiontechniques,bywhichcylindricalandflatsurfacesareproduced.Additionally,specialpurposemachinetoolsareusedtomachinegears,threads,andotherirregularshapes.Finishingtechnologyfordifferentgeometriesincludesgrinding,honing,lapping,andsuperfinishingtechniques.,5,Figure1.8showsgeneralpurposemachinetoolsusedfortraditionalmachininginchipremovalandabrasiontechniques.Typicalexamplesofgeneral-purposemachinetoolsincludeturning,drilling,shaping,milling,grinding,broaching,jigboring,andlappingmachinesintendedforspecifictasks.Gearcuttingandthreadcuttingareexamplesofspecial-purposemachinetools.Duringtheuseofgeneral-orspecial-purposemanualmachinetools,productaccuracyandproductivitydependontheoperatorsparticipationduringoperation.Capstanandturretlathesaretypicalmachinesthatsomewhatreducetheoperatorsroleduringmachiningofbar-typeorchucking-typeWPsathigherratesandbetteraccuracy.Semiautomaticmachinetoolsperformautomaticallycontrolledmovements,whiletheWPhastobehandloadedandunloaded.FullyautomaticmachinetoolsarethosemachinesinwhichWPhandlingandcuttingandotherauxiliaryactivitiesareperformedautomatically.Semiautomaticandautomaticmachinetoolsarebestsuitedforlargeproductionlotswheretheoperatorsinterferenceisminimizedorcompletelyeliminated,andpartsaremachinedmoreaccuratelyandeconomically.,6,NCmachinetoolsutilizeaformofprogrammableautomationbynumbers,letters,andsymbolsusingacontrolunitandtapereader,whileCNCmachinetoolsutilizeastoredcomputerprogramtoperformallthebasicNCfunctions.NCandCNChaveaddedmanybenefitstomachiningtechnology,sincesmallandlargenumbersofpartscannowbeproduced.Partgeometrycanbechangedthroughtheflexiblecontrolofthepartprograms.TheintegrationofCAD/CAMsystemstomachiningtechnologyhascreatednewindustrialareasindie,mold,aerospace,andautomobileindustries.,7,8,HexapodshaveaddedanewareatothemachiningtechnologyinwhichcomplicatedpartscanbemachinedusingasingletoolthatiscapableofreachingtheWPfrommanysides.Thehexapodhassixdegreesofmovementandisverydexterouslikearobot,butalsooffersthemachinetoolrigidityandaccuracygenerallybeyondarobotscapability.ThehexapodsareusedtohelpdevelopmachiningprocessesforWPsthatneedthedexterityofferedbythehexapoddesign.Forgeneralpurposemachining,thehexapodisanidealmachinetoolformold-and-diemachiningapplications.Itsabilitytokeepacuttingtoolnormaltothesurfacebeingmachinedprootesuseoflargerradiiballnoseendmills,whichcancutmorematerialwithverysmallstepovers.Insomeapplications,aflatnoseendmillcanbeusedveryeffectivelyforsmoothsurfacefinisheswithlittleornocusp.NontraditionalmachiningusesawiderangeofmachinetoolssuchasECM,USM,EDM,andLBM.Eachmachinetooliscapableofperformingavarietyofoperations,asshowninFigure1.9.Nontraditionalmachiningtechnologytacklesmaterialsthatrangefromglass,ceramics,hardalloys,heat-resistantalloys,andothermaterialsthataredifficulttomachinebytraditionalmachiningtechnology.,9,10,machinetool,general-purpose,special-purpose,machinetool,semiautomatic,fullyautomatic,NC,CNC,CAD/CAM,hexapods,nontraditionalmachining,ECM,USM,EDM,LBM,11,1.4.2WORKPIECEMATERIAL,TheWPmaterialspecifiedforthepartinfluencestheselectionoftheadoptedmachiningmethod.Mostmaterialscanbemachinedbyarangeofprocesses,somebyaverylimitedrange.Inanyparticularcase,however,thechoiceofthematerialdependsonthedesiredshapeandsize,thedimensionaltolerances,thesurfacefinish,andtherequiredquantity.Itmustnotdependonlyontechnicalsuitability,butalsooneconomyandenvironmentalconsiderations.,12,1.4.3MACHININGPRODUCTIVITY,Thechoiceofanymachiningmethodshouldtakeintoconsiderationarateofproductionthatisinverselyproportionaltomachiningtime.Methodsofraisingproductivityincludetheuseofthefollowing:HighmachiningspeedsHighfeedratesMultiplecuttingtoolsStackingmultiplepartsMinimizationofthesecondary(noncutting)timeAutomaticfeedingandtoolchangingmechanismsHighpowerdensities,13,1.4.4ACCURACYANDSURFACEINTEGRITY,Theselectionofamachiningtechnologydependsoninherentaccuracyandsurfacequality.Belowthemachinedsurface,somealterationsoccurasaresultofthematerialremovalmechanismsemployed.Carefulexaminationofsuchalayerisessential.Itaffectsthetechnologicalperformanceofthemachinedpartsintermsoffatiguestrength,corrosion,andwearresistance.Insomecases,apostfinishingtechnologymaybeadoptedtosolvesuchproblems,whichinturnraisesproductioncost.,14,1.4.5PRODUCTDESIGNFORECONOMICALMACHINING,Thisconceptisveryimportanttoproducepartsaccuratelyandeconomically.Productdesignrecommendationsforeachoperationshouldbestrictlyfollowedbythepartdesigner.Designcomplicationsshouldbeavoidedsothatthemachiningtimeisreduced,andconsequentlytheproductionrateisincreased.Machinetoolandoperationcapabilityintermsofpossibleaccuracyandsurfaceintegrityshouldalsobeconsi