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4.2GrindingmachinesGrindingisthemostimportantoftheabrasiveprocesses,anditisthemostcommonofallmetalworkingoperations.Grindingistraditionallyusedtofinishpartswhosegeometrieshavealreadybeencreatedbyotheroperations.Inadditiontothesetraditionaluses,applicationsofgrindingareexpandingtoincludemorehigh-speed,high-material-removaloperations.Comparetoothermachining,abrasivemachiningprocesseshavethreecharacteristics.1.eachcuttingedgeisverysmall,andmanyoftheseedgescancutsimultaneously.2.extremelyhardabrasivegritscanbeproduced,includingdiamonds,veryhardmaterialssuchashardenedsteel,glass,carbides,andceramics.3.Ingrinding,youhavenocontrolovertheactualtoolgeometry(rakeangles,cuttingedgeradius)orallthecuttingparameters(depthofcut)4.2GrindingmachinesCylindricalgrindingoperationscanbedividedintotwobasictypes:externalcylindricalgrindingandinternalcylindricalgrinding.(1)cylindricalcenter-typegrinders(外圆磨床)Cylindricalcenter-typegrindersareusedforgrindingstraightandtaperedroundpieces,roundpartswithcurvedlengthwiseprofiles,fillets,shoulders,andfaces.Thesizeofacylindricalcenter-typegrindingmachineisusuallydesignatedbythediameterinmillimetersandlengthinmillimetersthelargestworkpiecethemachinecannominallytakebetweencenters.Auniversalcylindricalcentre-typegrinder1,bed;2,headstock;3,auxiliarywheelhead4,wheelhead;5foothead;saddle;7,handwheel;8,worktableVideo(津上精密数控磨床加工_halfok.flv)Movementsofanexternalcylindricalgrindingmachine•4.2Grindingmachines(2)InternalcylindricalgrindingAninternalcylindricalgrindingoperatessomewhatlikeaboringoperation.Theworkpieceisusuallyheldinachuckandrotatedtoprovidesurfacespeedsof23to60m/min.Thewheelspindlesisrotatedat3000rpmorhigher.Thewheelisfedineitheroftwoways:traversefeed,whichismorecommon,orplungefeed.1,bed;2,worktable;3,headstock;4,wheelhead;5saddle;Video(內圓磨床)•4.2Grindingmachines(3)CenterlessgrindingCenterlessgrindingmakesitpossibletogrindbothexternalandinternalcylindricalsurfaceswithoutrequiringtheworkpiecetobemountedbetweencenterorinachuck.Theprincipleofcenterlessexternalgrindingisillustratedinfig3-63thatthegrindingwheelandaregulatingwheelarerequired.Viedo(無心磨床)Centerlessgrindingmachinecenterlessgrinding1,grindingwheel;2,workrestblode;3,regulatingwheel;4,workpiece;(b)through-feedcenterlessgrinding(c)in-feedcenterlessgrindingThetypicalsetupininternalcenterlessgrindingisshowninFig.3-65.Inplaceoftherestblade,twosupportrollsareusedtomaintainthepositionofthework.GrindingwheelsAgrindingwheelconsistsofabrasiveparticlesandbondingmaterial.Thebondingmaterialholdstheparticlesinplaceandestablishestheshapeandthestructureofthewheel.Asimplegrindingwheelisshownschematicallyinfig3-66.