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1、机械加工简介Intermsofannualdollarsspent,machiningisthemostimportantofthemanufacturingprocesses.Machiningcanbedefinedastheprocessofremovingmaterialfromaworkpieceintheformofchips.Thetermmetalcuttingisusedwhenthematerialismetallic.Mostmachininghasverylowset-upcostcomparedtoforming,molding,andcastingprocesses
2、.However,machiningismuchmoreexpensiveforhighvolumes.Machiningisnecessarywheretighttolerancesondimensionsandfinishesarerequired.TheMachiningsectionisdividedintothefollowingcategories:Drilling:IntroductionDrillingiseasilythemostcommonmachiningprocess.Oneestimateisthat75%ofallmetal-cuttingmaterialremov
3、edcomesfromdrillingoperations.Drillinginvolvesthecreationofholesthatarerightcircularcylinders.Thisisaccomplishedmosttypicallybyusingatwistdrill,somethingmostreaderswillhaveseenbefore.ThefigurebelowillustratesacrosssectionofaholebeingcutbyacommontwistDrillingCharacteristicsThecharacteristicsofdrillin
4、gthatsetitapartfromotherpoweredmetalcuttingoperationsare: Thechipsmustexitoutoftheholecreatedbythecutting. Chipexitcancauseproblemswhenchipsarelargeand/orcontinuous. Fordeepholesinlargeworkpieces,coolantmayneedtobedeliveredthroughthedrillshafttothecuttingfront. Ofthepoweredmetalcuttingprocesses,dril
5、lingonadrillpressisthemostlikelytobeperformedbysomeonewhoisnotamachinist.DrillPressWorkAreaTurning:EngineLatheTurningThetermfacingisusedtodescriberemovalofmaterialfromtheflatendofacylindricalpart,asshownbelow.Facingisoftenusedtoimprovethefinishofsurfacesthathavebeenparted.Milling:IntroductionFormanu
6、almachining,millingisessentialtofabricateanyobjectthatisnotaxiallysymmetric.Thereisawiderangeofdifferentmillingmachines,rangingfrommanuallight-dutyBridgeports。tohugeCNCmachinesformillingpartshundredsoffeetlong.Belowisillustratedtheprocessatthecuttingarea.toolisstationary.)Milling:Column-and-KneeManu
7、alMillBelowisillustratedatypicalcolumn-and-kneetypemanualmill.Suchmanualmillsarecommoninjobshopsthatspecializeinpartsthatarelowvolumeandquicklyfabricated.Suchjobshopsareoftentermedmodelshopsbecauseoftheprototypingnatureofthework.forward-off 、-reverse switchcutter vertical adjustmentspindleControls f
8、or spindle are similar to those for a drill press.columncutter.table int adjustmentvertical tabletable side-to-side adjustment (also on oppositeoverarmcolumnspindle cuttersaddleThepartsofthemanualmillareseparatedbelow.Thekneemovesupanddownthecolumnonguidewaysinthecolumn.Thetablecanmoveinxandyonthekn
9、ee,andthemillingheadcanmoveupanddown.Grinding:IntroductionReasonsforGrindingReasonsforgrindingare:1. Thematerialistoohardtobemachinedeconomically.(Thematerialmayhavebeenhardenedinordertoproducealow-wearfinish,suchasthatinabearingraceway.2. Tolerancesrequiredprecludemachining.Grindingcanproduceflatne
10、sstolerancesoflessthanA0.0025mm(A0.0001in)ona127x127mm(5x5in)steelsurfaceifthesurfaceisadequatelysupported.3. Machiningremovesexcessivematerial.ChipFormation:IntroductionBecauseoftheimportanceofmachiningforanyindustrialeconomy.MachiningTheoryhasbeenextensivelystudied.Thechipformationprocessisthesame
11、formostmachiningprocesses,andithasbeenresearchedinordertodetermineclosed-formsolutionsforspeeds,feds,andotherparameterswhichhaveinthepastbeendeterminedbythefeelofthemachinist.WithCNCmachinetoolsproducingpartsatever-fasterrates,ithasbecomeimportanttoprovideautomaticalgorithmsfordeterminingspeedsandfe
12、eds.Theinformationpresentedinthissectionaresomeofthemoreimportantaspectsofchipformation.Reasonsformachiningbeingdifficulttoanalyzeandcharacterizecanbesummarizedasfollows: Thestrainrateisextremelyhighcomparedtothatofotherfabricationprocesses. Theprocessvariesconsiderablydependingonthepartmaterial,tem
13、perature,cuttingfluids,etc. Theprocessvariesconsiderablydependingonthetoolmaterial,temperature,chatterandvibration,etc. Theprocessisonlyconstrainedbythetoolcutter.Unlikeotherprocessessuchasmoldingandcoldformingwhicharecontained,alotofvariationcanoccurevenwiththesameconfiguration.Foralltypesofmachining,includinggrinding,honing,lapping,planing,turning,ormilling,thephenomenonofchipformationissimilaratthepointwherethetoolmeetsthework.Belowareillustratedcategoriesofchiptypes.
