机械加工简介(英语版)dgzd.docx

Machhiniing: Ann InntrooducctioonIn ttermms oof aannuual dolllarrs sspennt, macchinningg iss thhe mmostt immporrtannt oof tthe mannufaactuurinng pproccessses. Maachiininng ccan be deffineed aas tthe proocesss oof rremoovinng mmateeriaal ffromm a worrkpiiecee inn thhe fformm off chhipss. TThe terrm mmetaal ccutttingg iss ussed wheen tthe matteriial is mettalllic. Moost macchinningg haas vveryy loow sset-up cosst ccomppareed tto fformmingg, mmolddingg, aand casstinng pproccessses. Hoowevver, maachiininng iis mmuchh moore exppenssivee foor hhighh voolummes. Maachiininng iis nneceessaary wheere tigght tolleraancees oon ddimeensiionss annd ffiniishees aare reqquirred. Thee Maachiininng ssecttionn iss diividded intto tthe folllowwingg caateggoriies: Drilllinng: InttrodducttionnDrilllinng iis eeasiily thee moost commmonn maachiininng pproccesss. OOne esttimaate is thaat 775% of alll meetall-cuuttiing matteriial remmoveed ccomees ffromm drrilllingg opperaatioons.Driilliing invvolvves thee crreattionn off hooless thhat aree riightt ciircuularr cyylinnderrs. Thiis iis aaccoompllishhed mosst ttypiicallly by usiing a ttwisst ddrilll, sommethhingg moost reaaderrs wwilll haave seeen bbefoore. Thhe ffiguure bellow illlusttrattes a ccrosss ssecttionn off a holle bbeinng ccut by a ccommmon twiist driill:The chiips musst eexitt thhrouugh thee fllutees tto tthe outtsidde oof tthe toool. As cann bee seeen in thee fiigurre, thee cuuttiing froont is embbeddded witthinn thhe wworkkpieece, maakinng ccoollingg diiffiicullt. Thee cuuttiing areea ccan be flooodeed, cooolannt sspraay mmistt caan bbe aapplliedd, oor ccoollantt caan bbe ddeliiverred thrrouggh tthe driill bitt shhaftt. FFor an oveerviiew of thee chhip-forrmattionn prroceess, seee tthe Chiip FFormmatiion Secctioon.Drilllinng CCharractteriistiicsThe chaaraccterristticss off drrilllingg thhat sett itt appartt frrom othher powwereed mmetaal ccutttingg opperaatioons aree: · The chiips musst eexitt ouut oof tthe holle ccreaatedd byy thhe ccutttingg.· Chipp exxit cann caausee prrobllemss whhen chiips aree laargee annd/oor cconttinuuouss.· For deeep hholees iin llargge wworkkpieecess, ccoollantt maay nneedd too bee deelivvereed tthrooughh thhe ddrilll sshafft tto tthe cutttinng ffronnt.· Of tthe powwereed mmetaal ccutttingg prroceessees, driilliing on a ddrilll ppresss iis tthe mosst llikeely to be perrforrmedd byy soomeoone whoo iss noot aa maachiinisst.Drilll PPresss WWorkk ArreaA viiew of thee meetall-cuuttiing areea oof aa drrilll prresss iss shhownn beeloww. TThe worrkpiiecee iss heeld in plaace by a cclammp ssincce ccutttingg foorcees ccan be quiite larrge. Itt iss daangeerouus tto hholdd a worrkpiiecee byy haand durringg drrilllingg siincee cuuttiing forrcess caan uunprrediictaablyy geet qquitte llargge aand wreenchh thhe ppartt awway. Woood is oftten useed uundeerneeathh thhe ppartt soo thhat thee drrilll biit ccan oveershhoott wiithoout dammagiing thee taablee. TThe tabble alsso hhas holles forr drrilll ovversshooot aas wwelll ass weeighht rreduuctiion. A thrree-jaww chhuckk iss ussed sinnce thrree poiintss deeterrminne aa ciirclle iin ttwo dimmenssionns. Fouur-jjaw chuuckss arre rrareely seeen ssincce ooffsset of thee biit iis nnot neccesssaryy. TThe nexxt ssecttionn coontaainss illlusstraatioons of driill bitt chhuckks. To gett ann iddea of thee diiffeerinng cconffiguurattionns oof tthreee aand fouur-jjaw chuuckss, ppleaase seee thhe eequiivallentt laathee chhuckks.Turnningg: EEngiine LattheTurnningg iss annothher of thee baasicc maachiininng pproccessses. Innforrmattionn inn thhis secctioon iis oorgaanizzed acccorddingg too thhe ssubccateegorry llinkks iin tthe mennu bbar to thee leeft. Tuurniing prooducces sollidss off reevollutiion whiich cann bee tiighttly tolleraanceed bbecaausee off thhe sspecciallizeed nnatuure of thee opperaatioon. Turrninng iis pperfformmed on a mmachhinee caalleed aa laathee inn whhichh thhe ttooll iss sttatiionaary andd thhe ppartt iss rootatted. Thhe ffiguure bellow illlusttrattes an engginee laathee. LLathhes aree deesiggnedd soolelly ffor turrninng ooperratiionss, sso tthatt prreciise conntrool oof tthe cutttinng rresuultss inn tiightt toolerrancces. Thhe wworkk piiecee iss moountted on thee chhuckk, wwhicch rrotaatess reelattivee too thhe sstattionnaryy toool.TurnninggTurnningg reeferrs tto ccutttingg ass shhownn beeloww.The terrm ""faccingg" iis uusedd too deescrribee reemovval of matteriial froom tthe flaat eend of a ccyliindrricaal ppartt, aas sshowwn bbeloow. Faccingg iss offtenn ussed to impprovve tthe finnishh off suurfaacess thhat havve bbeenn paarteed.Milllingg: IIntrroduuctiionMilllingg iss ass fuundaamenntall ass drrilllingg ammongg poowerred mettal cutttinng pproccessses.Milllinng iis vverssatiile forr a bassic macchinningg prroceess, buut bbecaausee thhe mmilllingg seet uup hhas so manny ddegrreess off frreeddom, miilliing is usuuallly llesss acccurratee thhan turrninng oor ggrinndinng uunleess esppeciiallly rrigiid ffixtturiing is impplemmentted. For mannuall maachiininng, milllinng iis eesseentiial to fabbriccatee anny oobjeect thaat iis nnot axiiallly ssymmmetrric. Thheree iss a widde rrangge oof ddifffereent milllinng mmachhinees, rannginng ffromm maanuaal llighht-ddutyy Brridggepoortss⢢ too huuge CNCC maachiiness foor mmilllingg paartss huundrredss off feeet lonng. Bellow is illlusttratted thee prroceess at thee cuuttiing areea.Milllingg: CColuumn-andd-Knnee Mannuall MiillBeloow iis iilluustrrateed aa tyypiccal collumnn-annd-kkneee tyype mannuall miill. Suuch mannuall miillss arre ccommmon in jobb shhopss thhat speeciaalizze iin ppartts tthatt arre llow vollumee annd qquiccklyy faabriicatted. Suuch jobb shhopss arre oofteen ttermmed "moodell shhopss" bbecaausee off thhe pprottotyypinng nnatuure of thee woork.The parrts of thee maanuaal mmilll arre ssepaaratted bellow. Thhe kkneee moovess upp annd ddownn thhe ccoluumn on guiidewwayss inn thhe ccoluumn. Thhe ttablle ccan movve iin xx annd yy onn thhe kkneee, aand thee miilliing heaad ccan movve uup aand dowwn.Grinndinng: InttrodducttionnGrinndinng iis aa fiinisshinng pproccesss ussed to impprovve ssurffacee fiinissh, abrradee haard matteriialss, aand tigghteen tthe tolleraancee onn fllat andd cyylinndriicall suurfaacess byy reemovvingg a smaall amoountt off maaterriall. IInfoormaatioon iin tthiss seectiion is orgganiizedd acccorrdinng tto tthe subbcattegoory linnks in thee meenu barr too thhe lleftt.Inn grrinddingg, aan aabraasivve mmateeriaal rrubss aggainnst thee meetall paart andd reemovves tinny ppiecces of matteriial. Thhe aabraasivve mmateeriaal iis ttypiicallly on thee suurfaace of a wwheeel oor bbeltt annd aabraadess maaterriall inn a wayy siimillar to sanndinng. On a mmicrrosccopiic sscalle, thee chhip forrmattionn inn grrinddingg iss thhe ssamee ass thhat fouund in othher macchinningg prroceessees. Thee abbrassivee acctioon oof ggrinndinng ggeneerattes exccesssivee heeat so thaat fflooodinng oof tthe cutttinng aareaa wiith fluuid is neccesssaryy.Reassonss foor GGrinndinngReassonss foor ggrinndinng aare:1. Thee maaterriall iss tooo hhardd too bee maachiinedd ecconoomiccallly. (Thhe mmateeriaal mmay havve bbeenn haardeenedd inn orrderr too prroduuce a llow-weaar ffiniish, suuch as thaat iin aa beeariing raccewaay.2. Tolleraancees rrequuireed ppreccludde mmachhiniing. Grrinddingg caan pprodducee fllatnnesss toolerrancces of lesss tthann ±±0.000255 mmm (±0.00001 iin) on a 1127 x 1127 mm (5 x 55 inn) ssteeel ssurffacee iff thhe ssurffacee iss addequuateely suppporrtedd.3. Maachiininng rremoovess exxcesssivve mmateeriaal.Chipp Foormaatioon: InttrodducttionnBecaausee off thhe iimpoortaancee off maachiininng ffor anyy inndusstriial ecoonommy, Macchinningg Thheorry hhas beeen eexteensiivelly sstuddiedd. Thee chhip forrmattionn prroceess is thee saame forr moost macchinningg prroceessees, andd itt haas bbeenn reeseaarchhed in ordder to dettermminee clloseed-fformm sooluttionns ffor speeedss, ffeedds, andd ottherr paarammeteers whiich havve iin tthe passt bbeenn deeterrminned by thee "ffeell" oof tthe macchinnistt. Witth CCNC macchinne ttoolls pprodduciing parrts at eveer-ffastter rattes, itt haas bbecoome impporttantt too prroviide auttomaaticc allgorrithhms forr deeterrminningg sppeedds aand feeeds. Thhe iinfoormaatioon ppressentted in thiis ssecttionn arre ssomee off thhe mmoree immporrtannt aaspeectss off chhip forrmattionn. RReassonss foor mmachhiniing beiing diffficcultt too annalyyze andd chharaacteerizze ccan be summmarrizeed aas ffolllowss:· The strrainn raate is exttremmelyy hiigh commparred to thaat oof ootheer ffabrricaatioon pproccessses.· The proocesss vvariies connsidderaablyy deepenndinng oon tthe parrt mmateeriaal, temmperratuure, cuuttiing fluuidss, eetc.· The proocesss vvariies connsidderaablyy deepenndinng oon tthe toool mmateeriaal, temmperratuure, chhattter andd viibraatioon, etcc.· The proocesss iis oonlyy coonsttraiinedd byy thhe ttooll cuutteer. Unllikee ottherr prroceessees ssuchh ass mooldiing andd coold forrminng wwhicch aare conntaiinedd, aa loot oof vvariiatiion cann occcurr evven witth tthe samme cconffiguurattionn.For alll tyypess off maachiininng, inccluddingg grrinddingg, hhoniing, laappiing, pllaniing, tuurniing, orr miilliing, thhe pphennomeenonn off chhip forrmattionn iss siimillar at thee poointt whheree thhe ttooll meeetss thhe wworkk.Beeloww arre iilluustrrateed ccateegorriess off chhip typpes.