机械加工简介.docx

机械加工简介Intermsofannualdollarsspent,machiningisthemostimportantofthemanufacturingprocesses.Machiningcanbedefinedastheprocessofremovingmaterialfromaworkpieceintheformofchips.Thetermmetalcuttingisusedwhenthematerialismetallic.Mostmachininghasverylowset-upcostcomparedtoforming,molding,andcastingprocesses.However,machiningismuchmoreexpensiveforhighvolumes.Machiningisnecessarywheretighttolerancesondimensionsandfinishesarerequired.TheMachiningsectionisdividedintothefollowingcategories:Drilling:IntroductionDrillingiseasilythemostcommonmachiningprocess.Oneestimateisthat75%ofallmetal-cuttingmaterialremovedcomesfromdrillingoperations.Drillinginvolvesthecreationofholesthatarerightcircularcylinders.Thisisaccomplishedmosttypicallybyusingatwistdrill,somethingmostreaderswillhaveseenbefore.ThefigurebelowillustratesacrosssectionofaholebeingcutbyacommontwistDrillingCharacteristicsThecharacteristicsofdrillingthatsetitapartfromotherpoweredmetalcuttingoperationsare: Thechipsmustexitoutoftheholecreatedbythecutting. Chipexitcancauseproblemswhenchipsarelargeand/orcontinuous. Fordeepholesinlargeworkpieces,coolantmayneedtobedeliveredthroughthedrillshafttothecuttingfront. Ofthepoweredmetalcuttingprocesses,drillingonadrillpressisthemostlikelytobeperformedbysomeonewhoisnotamachinist.DrillPressWorkAreaTurning:EngineLatheTurningTheterm"facing"isusedtodescriberemovalofmaterialfromtheflatendofacylindricalpart,asshownbelow.Facingisoftenusedtoimprovethefinishofsurfacesthathavebeenparted.Milling:IntroductionFormanualmachining,millingisessentialtofabricateanyobjectthatisnotaxiallysymmetric.Thereisawiderangeofdifferentmillingmachines,rangingfrommanuallight-dutyBridgeports。tohugeCNCmachinesformillingpartshundredsoffeetlong.Belowisillustratedtheprocessatthecuttingarea.toolisstationary.)Milling:Column-and-KneeManualMillBelowisillustratedatypicalcolumn-and-kneetypemanualmill.Suchmanualmillsarecommoninjobshopsthatspecializeinpartsthatarelowvolumeandquicklyfabricated.Suchjobshopsareoftentermed"modelshops"becauseoftheprototypingnatureofthework.forward-off 、-reverse switchcutter vertical adjustmentspindleControls for spindle are similar to those for a drill press.columncutter.table int adjustmentvertical tabletable side-to-side adjustment (also on oppositeoverarmcolumnspindle cuttersaddleThepartsofthemanualmillareseparatedbelow.Thekneemovesupanddownthecolumnonguidewaysinthecolumn.Thetablecanmoveinxandyontheknee,andthemillingheadcanmoveupanddown.Grinding:IntroductionReasonsforGrindingReasonsforgrindingare:1. Thematerialistoohardtobemachinedeconomically.(Thematerialmayhavebeenhardenedinordertoproducealow-wearfinish,suchasthatinabearingraceway.2. Tolerancesrequiredprecludemachining.GrindingcanproduceflatnesstolerancesoflessthanA±0.0025mm(A±0.0001in)ona127x127mm(5x5in)steelsurfaceifthesurfaceisadequatelysupported.3. Machiningremovesexcessivematerial.ChipFormation:IntroductionBecauseoftheimportanceofmachiningforanyindustrialeconomy.MachiningTheoryhasbeenextensivelystudied.Thechipformationprocessisthesameformostmachiningprocesses,andithasbeenresearchedinordertodetermineclosed-formsolutionsforspeeds,feds,andotherparameterswhichhaveinthepastbeendeterminedbythe"feel"ofthemachinist.WithCNCmachinetoolsproducingpartsatever-fasterrates,ithasbecomeimportanttoprovideautomaticalgorithmsfordeterminingspeedsandfeeds.Theinformationpresentedinthissectionaresomeofthemoreimportantaspectsofchipformation.Reasonsformachiningbeingdifficulttoanalyzeandcharacterizecanbesummarizedasfollows: Thestrainrateisextremelyhighcomparedtothatofotherfabricationprocesses. Theprocessvariesconsiderablydependingonthepartmaterial,temperature,cuttingfluids,etc. Theprocessvariesconsiderablydependingonthetoolmaterial,temperature,chatterandvibration,etc. Theprocessisonlyconstrainedbythetoolcutter.Unlikeotherprocessessuchasmoldingandcoldformingwhicharecontained,alotofvariationcanoccurevenwiththesameconfiguration.Foralltypesofmachining,includinggrinding,honing,lapping,planing,turning,ormilling,thephenomenonofchipformationissimilaratthepointwherethetoolmeetsthework.Belowareillustratedcategoriesofchiptypes.