机械加工简介(英语版).doc

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1、Machining:AnIntroductionIntermsofannualdollarsspent,machiningisthemostimportantofthemanufacturingprocesses.Machiningcanbedefinedastheprocessofremovingmaterialfromaworkpieceintheformofchips.Thetermmetalcuttingisusedwhenthematerialismetallic.Mostmachininghasverylowset-up

2、costcomparedtoforming,molding,andcastingprocesses.However,machiningismuchmoreexpensiveforhighvolumes.Machiningisnecessarywheretighttolerancesondimensionsandfinishesarerequired.TheMachiningsectionisdividedintothefollowingcategories:Drilling:IntroductionDrillingiseasilyt

3、hemostcommonmachiningprocess.Oneestimateisthat75%ofallmetal-cuttingmaterialremovedcomesfromdrillingoperations.Drillinginvolvesthecreationofholesthatarerightcircularcylinders.Thisisaccomplishedmosttypicallybyusingatwistdrill,somethingmostreaderswillhaveseenbefore.Thefig

4、urebelowillustratesacrosssectionofaholebeingcutbyacommontwistdrill:Thechipsmustexitthroughtheflutestotheoutsideofthetool.Ascanbeseeninthefigure,thecuttingfrontisembeddedwithintheworkpiece,makingcoolingdifficult.Thecuttingareacanbeflooded,coolantspraymistcanbeapplied,or

5、coolantcanbedeliveredthroughthedrillbitshaft.Foranoverviewofthechip-formationprocess,seetheChipFormationSection.DrillingCharacteristicsThecharacteristicsofdrillingthatsetitapartfromotherpoweredmetalcuttingoperationsare:·Thechipsmustexitoutoftheholecreatedbythecutting.·

6、Chipexitcancauseproblemswhenchipsarelargeand/orcontinuous.·Fordeepholesinlargeworkpieces,coolantmayneedtobedeliveredthroughthedrillshafttothecuttingfront.·Ofthepoweredmetalcuttingprocesses,drillingonadrillpressisthemostlikelytobeperformedbysomeonewhoisnotamachinist.Dri

7、llPressWorkAreaAviewofthemetal-cuttingareaofadrillpressisshownbelow.Theworkpieceisheldinplacebyaclampsincecuttingforcescanbequitelarge.Itisdangeroustoholdaworkpiecebyhandduringdrillingsincecuttingforcescanunpredictablygetquitelargeandwrenchthepartaway.Woodisoftenusedun

8、derneaththepartsothatthedrillbitcanovershootwithoutdamagingthetable.Thetablealsohasholesfordrillovershootaswellasweig