机械加工简介(英语版)

Machining:AnIntroductionIntermsofannualdollarsspent,machiningisthemostimportantofthemanufacturingprocesses.Machiningcanbedefinedastheprocessofremovingmaterialfromaworkpieceintheformofchips.Thetermmetalcuttingisusedwhenthematerialismetallic.Mostmachininghasverylowset-upcostcomparedtoforming,molding,andcastingprocesses.However,machiningismuchmoreexpensiveforhighvolumes.Machiningisnecessarywheretighttolerancesondimensionsandfinishesarerequired.TheMachiningsectionisdividedintothefollowingcategories:Drilling:IntroductionDrillingiseasilythemostcommonmachiningprocess.Oneestimateisthat75%ofallmetal-cuttingmaterialremovedcomesfromdrillingoperations.Drillinginvolvesthecreationofholesthatarerightcircularcylinders.Thisisaccomplishedmosttypicallybyusingatwistdrill,somethingmostreaderswillhaveseenbefore.Thefigurebelowillustratesacrosssectionofaholebeingcutbyacommontwistdrill:Thechipsmustexitthroughtheflutestotheoutsideofthetool.Ascanbeseeninthefigure,thecuttingfrontisembeddedwithintheworkpiece,makingcoolingdifficult.Thecuttingareacanbeflooded,coolantspraymistcanbeapplied,orcoolantcanbedeliveredthroughthedrillbitshaft.Foranoverviewofthechip-formationprocess,seetheChipFormationSection.DrillingCharacteristicsThecharacteristicsofdrillingthatsetitapartfromotherpoweredmetalcuttingoperationsare:Thechipsmustexitoutoftheholecreatedbythecutting.Chipexitcancauseproblemswhenchipsarelargeand/orcontinuous.Fordeepholesinlargeworkpieces,coolantmayneedtobedeliveredthroughthedrillshafttothecuttingfront.Ofthepoweredmetalcuttingprocesses,drillingonadrillpressisthemostlikelytobeperformedbysomeonewhoisnotamachinist.DrillPressWorkAreaAviewofthemetal-cuttingareaofadrillpressisshownbelow.Theworkpieceisheldinplacebyaclampsincecuttingforcescanbequitelarge.Itisdangeroustoholdaworkpiecebyhandduringdrillingsincecuttingforcescanunpredictablygetquitelargeandwrenchthepartaway.Woodisoftenusedunderneaththepartsothatthedrillbitcanovershootwithoutdamagingthetable.Thetablealsohasholesfordrillovershootaswellasweightreduction.Athree-jawchuckisusedsincethreepointsdetermineacircleintwodimensions.Four-jawchucksarerarelyseensinceoffsetofthebitisnotnecessary.Thenextsectioncontainsillustrationsofdrillbitchucks.Togetanideaofthedifferingconfigurationsofthreeandfour-jawchucks,pleaseseetheequivalentlathechucks.Turning:EngineLatheTurningisanotherofthebasicmachiningprocesses.Informationinthissectionisorganizedaccordingtothesubcategorylinksinthemenubartotheleft.ÂTurningproducessolidsofrevolutionwhichcanbetightlytolerancedbecauseofthespecializednatureoftheoperation.Turningisperformedonamachinecalledalatheinwhichthetoolisstationaryandthepartisrotated.Thefigurebelowillustratesanenginelathe.Lathesaredesignedsolelyforturningoperations,sothatprecisecontrolofthecuttingresultsintighttolerances.Theworkpieceismountedonthechuck,whichrotatesrelativetothestationarytool.TurningTurningreferstocuttingasshownbelow.Thetermfacingisusedtodescriberemovalofmaterialfromtheflatendofacylindricalpart,asshownbelow.Facingisoftenusedtoimprovethefinishofsurfacesthathavebeenparted.Milling:IntroductionMillingisasfundamentalasdrillingamongpoweredmetalcuttingprocesses.Millingisversatileforabasicmachiningprocess,butbecausethemillingsetuphassomanydegreesoffreedom,millingisusuallylessaccuratethanturningorgrindingunlessespeciallyrigidfixturingisimplemented.Formanualmachining,millingisessentialtofabricateanyobjectthatisnotaxiallysymmetric.Thereisawiderangeofdifferentmillingmachines,rangingfrommanuallight-dutyBridgeportsâ„¢tohugeCNCmachinesformillingpartshundredsoffeetlong.Belowisillustratedtheprocessatthecuttingarea.Milling:Column-and-KneeManualMillBelowisillustratedatypicalcolumn-and-kneetypemanualmill.Suchmanualmillsarecommoninjobshopsthatspecializeinpartsthatarelowvolumeandquicklyfabricated.Suchjobshopsareoftentermedmodelshopsbecauseoftheprototypingnatureofthework.Thepartsofthemanualmillareseparatedbelow.Thekneemovesupanddownthecolumnonguidewaysinthecolumn.Thetablecanmoveinxandyontheknee,andthemillingheadcanmoveupanddown.Grinding:IntroductionGrindingisafinishingprocessusedtoimprovesurfacefinish,abradehardmaterials,andtightenthetoleranceonflatandcylindricalsurfacesbyremovingasmallamountofmaterial.Informationinthissectionisorganizedaccordingtothesubcategorylinksinthemenubartotheleft.Ingrinding,anabrasivematerialrubsagainstthemetalpartandremovestinypiecesofmaterial.Theabrasivematerialistypicallyonthesurfaceofawheelorbeltandabradesmaterialinawaysimilartosanding.Onamicroscopicscale,thechipformationingrindingisthesameasthatfoundinothermachiningprocesses.Theabrasiveactionofgrindinggeneratesexcessiveheatsothatfloodingofthecuttingareawithfluidisnecessary.ReasonsforGrindingReasonsforgrindingare:1.Thematerialistoohardtobemachinedeconomically.(Thematerialmayhavebeenhardenedinordertoproducealow-wearfinish,suchasthatinabearingraceway.2.Tolerancesrequiredprecludemachining.Grindingcanproduceflatnesstolerancesoflessthan±0.0025mm(±0.0001in)ona127x127mm(5x5in)steelsurfaceifthesurfaceisadequatelysupported.3.Machiningremov