Aqtvlxl机械制造及自动化毕业设计外语文献翻译3365.docx

生命中，不断地有人离开或进入。于是，看见的，看不见的；记住的，遗忘了。生命中，不断地有得到和失落。于是，看不见的，看见了；遗忘的，记住了。然而，看不见的，是不是就等于不存在？记住的，是不是永远不会消失？ 攀枝花学院本科科毕业设计（论论文）外文译文院 （系）： 机机电工程学院院 专 业： 机机械设计制造造及其自动化化 姓 名： 王 中 蔚 学 号： ZJDD020433 指导教师评语： 签名名： 年 月 日外语文献翻译摘自: 制制造工程与技技术（机加工工）（英文文版） Mannufactturingg Engiineeriing annd TecchnoloogyMachiining 机械工业业出版社 2004年年3月第1版 美 s. 卡尔帕基基安(Serrope kkalpakkjian) ss.r 施密密德(Steeven RR.Schmmid) 著原文：20.9 MAACHINAABILITTYThe macchinabbilityy of aa mateerial usuallly deefinedd in tterms of foour faactorss:1、 Surfacee finiish annd inttegritty of the mmachinned paart;2、 Tool liife obbtaineed;3、 Force aand poower rrequirrementts;4、 Chip coontroll. Thus, ggood mmachinnabiliity goood suurfacee finiish annd inttegritty, loong toool liife, aand loow forrce Annd powwer reequireementss. As for cchip ccontrool, loong annd thiin (sttringyy) curred chhips, if noot brooken uup, caan sevverelyy inteerferee withh the cuttiing opperatiion byy becooming entanngled in thhe cuttting zone.Becausee of tthe coomplexx natuure off cuttting ooperattions, it iis diffficullt to estabblish relattionshhips tthat qquantiitativvely ddefinee the machiinabillity oof a mmateriial. IIn mannufactturingg plannts, ttool llife aand suurfacee rougghnesss are generrally consiideredd to bbe thee mostt impoortantt facttors iin macchinabbilityy. Altthoughh not used much any mmore, approoximatte macchinabbilityy ratiings aare avvailabble inn the exampple beelow.20.9.1 Machiinabillity OOf SteeelsBecausee steeels arre amoong thhe mosst impportannt enggineerring mmateriials (as nooted iin Chaapter 5), ttheir machiinabillity hhas beeen sttudiedd exteensiveely. TThe maachinaabilitty of steells hass beenn mainnly immproveed by addinng leaad andd sulffur too obtaain soo-callled frree-maachiniing stteels.Resulfuurizedd and Rephoosphorrized steells. SSulfurr in ssteelss formms mannganesse sullfide incluusionss (seccond-pphase partiicles), whiich acct as stresss raiisers in thhe priimary shearr zonee. As a ressult, the cchips produuced bbreak up eaasily and aare smmall; this improoves mmachinnabiliity. TThe siize, sshape, disttributtion, and cconcenntratiion off thesse incclusioons siignifiicantlly inffluencce macchinabbilityy. Eleementss suchh as ttellurrium aand seeleniuum, whhich aare booth chhemicaally ssimilaar to sulfuur, acct as incluusion modiffiers in reesulfuurizedd steeels.Phosphoorus iin steeels hhas twwo majjor efffectss. It strenngthenns thee ferrrite, causiing inncreassed haardnesss. Haarder steells ressult iin bettter cchip fformattion aand suurfacee finiish. NNote tthat ssoft ssteelss can be diifficuult too machhine, with builtt-up eedge fformattion aand pooor suurfacee finiish. TThe seecond effecct is that increeased hardnness ccausess the formaation of shhort cchips insteead off conttinuouus strringy ones, therreby iimprovving mmachinnabiliity.Leaded Steells. A high perceentagee of llead iin steeels ssolidiifies at thhe tipp of mmangannese ssulfidde incclusioons. IIn nonn-resuulfuriized ggradess of ssteel, leadd takees thee formm of ddisperrsed ffine pparticcles. Lead is innsolubble inn ironn, coppper, and aaluminnum annd theeir allloys. Becaause oof itss low shearr streength, therreforee, leaad actts as a sollid luubricaant (SSectioon 32.11) aand iss smeaared oover tthe toool-chhip innterfaace duuring cuttiing. TThis bbehaviior haas beeen verrifiedd by tthe prresencce of high conceentrattions of leead onn the tool-side face of chhips wwhen mmachinning lleadedd steeels.When thhe temmperatture iis suffficieently high-for iinstannce, aat higgh cuttting speedds andd feedds (Seectionn 20.66)thee leadd meltts dirrectlyy in ffront of thhe toool, accting as a liquiid lubbricannt. Inn addiition to thhis efffect, leadd loweers thhe sheear sttress in thhe priimary shearr zonee, redducingg cuttting fforcess and powerr conssumptiion. LLead ccan bee usedd in eevery gradee of ssteel, suchh as 110xx, 11xx, 12xxx, 41xxx, ettc. Leeaded steells aree idenntifieed by the lletterr L beetweenn the seconnd andd thirrd nummeralss (forr exammple, 10L45). (Noote thhat inn staiinlesss steeels, ssimilaar usee of tthe leetter L meaans “llow caarbon,” a ccondittion tthat iimprovves thheir ccorrossion rresisttance.)Howeverr, beccause lead is a well-knownn toxiin andd a poollutaant, tthere are sseriouus envvironmmentall conccerns aboutt its use iin steeels (estimmated at 45500 toons off leadd conssumptiion evvery yyear iin thee prodductioon of steells). CConseqquentlly, thhere iis a ccontinnuing trendd towaard elliminaating the uuse off leadd in ssteelss (leaad-freee steeels). Bismmuth aand tiin aree now beingg inveestigaated aas posssiblee subsstituttes foor leaad in steells.Calciumm-Deoxxidizeed Steeels. An immportaant deeveloppment is caalciumm-deoxxidizeed steeels, in whhich ooxide flakees of calciium siilicattes (CCaSo) are fformedd. Theese fllakes, in tturn, reducce thee streength of thhe seccondarry sheear zoone, ddecreaasing tool-chip interrface and wwear. Tempeeraturre is correesponddinglyy reduuced. Conseequenttly, tthese steells prooduce less crateer weaar, esspeciaally aat higgh cuttting speedds.Stainleess Stteels. Austtenitiic (3000 serries) steells aree geneerallyy diffficultt to mmachinne. Chhatterr can be s probllem, nnecesssitatiing maachinee toolls witth higgh stiiffnesss. Hooweverr, ferrriticc staiinlesss steeels (aalso 3300 seeries) havee goodd machhinabiility. Marttensittic (4400 seeries) steeels arre abrrasivee, tennd to form a buiilt-upp edgee, andd requuire ttool mmateriials wwith hhigh hhot haardnesss andd cratter-weear reesistaance. Preciipitattion-hhardenning sstainlless ssteelss are stronng andd abraasive, requuiringg hardd and abrassion-rresisttant ttool mmateriials.The Efffects of Otther EElemennts inn Steeels onn Machhinabiility. The preseence oof aluuminumm and siliccon inn steeels iss alwaays haarmfull becaause tthese elemeents ccombinne witth oxyygen tto forrm aluuminumm oxidde andd siliicatess, whiich arre harrd andd abraasive. Thesse commpoundds inccreasee tooll wearr and reducce macchinabbilityy. It is esssentiial too prodduce aand usse cleean stteels.Carbon and mmangannese hhave vvariouus efffects on thhe macchinabbilityy of ssteelss, deppendinng on theirr comppositiion. PPlain low-ccarbonn steeels (lless tthan 00.15% C) caan prooduce poor surfaace fiinish by foormingg a buuilt-uup edgge. Caast stteels are mmore aabrasiive, aalthouugh thheir mmachinnabiliity iss simiilar tto thaat of wrougght stteels. Tooll and die ssteelss are very diffiicult to maachinee and usuallly reequiree anneealingg prioor to machiining. Machhinabiility of moost stteels is immproveed by cold workiing, wwhich hardeens thhe matteriall and reducces thhe tenndencyy for builtt-up eedge fformattion.Other aalloyiing ellementts, suuch ass nickkel, cchromiium, mmolybddenum, and vanaddium, whichh imprrove tthe prropertties oof steeels, generrally reducce macchinabbilityy. Thee effeect off boroon is negliigiblee. Gasseous elemeents ssuch aas hyddrogenn and nitroogen ccan haave paarticuularlyy detrrimenttal efffectss on tthe prropertties oof steeel. OOxygenn has been shownn to hhave aa stroong efffect on thhe asppect rratio of thhe mannganesse sullfide incluusionss; thee highher thhe oxyygen ccontennt, thhe lowwer thhe asppect rratio and tthe hiigher the mmachinnabiliity.In seleectingg variious eelemennts too imprrove mmachinnabiliity, wwe shoould cconsidder thhe posssiblee detrrimenttal efffectss of tthese elemeents oon thee proppertiees andd streength of thhe macchinedd partt in sservicce. Att elevvated tempeeraturres, ffor exxamplee, leaad cauuses eembritttlemeent off steeels (lliquidd-metaal embbrittllementt, hott shorrtnesss; seee Secttion 11.4.3), altthoughh at rroom ttemperraturee it hhas noo effeect onn mechhanicaal proopertiies.Sulfur can ssevereely reeduce the hhot woorkabiility of stteels, becaause oof thee formmationn of iiron ssulfidde, unnless suffiicientt mangganesee is ppresennt to preveent suuch foormatiion. AAt rooom temmperatture, the mmechannical propeertiess of rresulffurizeed steeels ddependd on tthe orrientaation of thhe defformedd mangganesee sulffide iinclussions (anissotroppy). RRephossphoriized ssteelss are signiificanntly lless dductille, annd aree prodduced solelly to improove maachinaabilitty.20.9.2 Machiinabillity oof Varrious Otherr Metaals Aluminuum is generrally very easy to maachinee, altthoughh the softeer graades ttend tto forrm a bbuilt-up eddge, rresultting iin pooor surrface finissh. Hiigh cuuttingg speeeds, hhigh rrake aangless, andd highh reliief anngles are rrecommmendedd. Wroought alumiinum aalloyss withh highh siliicon ccontennt andd castt alumminum alloyys mayy be aabrasiive; tthey rrequirre harrder ttool mmateriials. Dimennsionaal tollerancce conntrol may bbe a pprobleem in machiining alumiinum, sincee it hhas a high thermmal cooefficcient of exxpansiion annd a rrelatiively low eelastiic moddulus.Berylliium iss simiilar tto casst iroons. BBecausse it is moore abbrasivve andd toxiic, thhough, it rrequirres maachiniing inn a coontrollled eenviroonmentt.Cast grray irrons aare geenerallly maachinaable bbut arre. Frree caarbidees in castiings rreducee theiir macchinabbilityy and causee tooll chippping or frracturre, neecessiitatinng toools wiith hiigh tooughneess. NNodulaar andd mallleablee ironns aree machhinablle witth harrd toool matterialls.Cobalt-basedd allooys arre abrrasivee and highlly worrk-harrdeninng. Thhey reequiree sharrp, abbrasioon-ressistannt toool matterialls andd low feedss and speedds.Wroughtt coppper caan be diffiicult to maachinee becaause oof buiilt-upp edgee formmationn, altthoughh castt coppper allloys are eeasy tto macchine. Brassses aare eaasy too machhine, especciallyy withh the addittion ppf leaad (leeaded free-machiining brasss). Brronzess are more diffiicult to maachinee thann brasss.Magnesiium iss veryy easyy to mmachinne, wiith goood suurfacee finiish annd proolongeed toool liffe. Hooweverr caree shouuld bee exerrcisedd becaause oof itss highh ratee of ooxidattion aand thhe dannger oof firre (thhe eleement is pyyrophooric).Molybdeenum iis ducctile and wwork-hhardenning, so itt can produuce pooor suurfacee finiish. SSharp toolss are necesssary.Nickel-basedd allooys arre worrk-harrdeninng, abbrasivve, annd strrong aat higgh temmperattures. Theiir macchinabbilityy is ssimilaar to that of sttainleess stteels.Tantaluum is very work-hardeening, ducttile, and ssoft. It prroducees a ppoor ssurfacce finnish; tool wear is hiigh.Titaniuum andd its alloyys havve pooor theermal conduuctiviity (iindeedd, thee loweest off all metalls), ccausinng siggnificcant ttemperraturee risee and builtt-up eedge; they can bbe diffficullt to machiine.Tungsteen is britttle, sstrongg, andd veryy abraasive, so iits maachinaabilitty is low, althoough iit greeatly improoves aat eleevatedd tempperatuures.Zirconiium haas goood macchinabbilityy. It requiires aa coollant-ttype ccuttinng fluuid, hhoweveer, beecausee of tthe exxplosiion annd firre.20.9.3 Machiinabillity oof Varrious MaterrialsGraphitte is abrassive; it reequirees harrd, abbrasioon-ressistannt, shharp ttools.Thermopplastiics geenerallly haave loow theermal conduuctiviity, llow ellasticc moduulus, and llow soofteniing teemperaature. Conssequenntly, machiining them requiires ttools with posittive rrake aangless (to reducce cuttting forcees), llarge relieef anggles, smalll deptths off cut and ffeed, relattivelyy highh speeeds, aand proper suppoort off the workppiece. Toolls shoould bbe shaarp.Externaal coooling of thhe cuttting zone may bbe neccessarry to keep the cchips from becomming “ggummy” and sstickiing too the toolss. Coooling can uusuallly be achieeved wwith aa jet of aiir, vaapor mmist, or waater-ssolublle oills. Reesiduaal strressess may devellop duuring machiining. To rrelievve theese sttressees, maachineed parrts caan be anneaaled ffor a periood of time at teemperaaturess rangging ffrom to (to), aand thhen coooled slowlly andd unifformlyy to rroom ttemperraturee.Thermossettinng plaasticss are britttle annd sennsitivve to thermmal grradiennts duuring cuttiing. TTheir machiinabillity iis gennerallly simmilar to thhat off therrmoplaasticss.Becausee of tthe fiibers preseent, rreinfoorced plasttics aare veery abbrasivve andd are diffiicult to maachinee. Fibber teearingg, pullling, and edge delamminatiion arre siggnificcant pprobleems; tthey ccan leead too seveere reeductiion inn the load-carryying ccapaciity off the compoonent. Furtthermoore, mmachinning oof theese maateriaals reequirees carreful removval off machhiningg debrris too avoiid conntact with and iinhaliing off the fiberrs.The macchinabbilityy of cceramiics haas impprovedd steaadily with the ddeveloopmentt of nnanoceeramiccs (Seectionn 8.2.5) annd witth thee seleectionn of aapproppriatee proccessinng parrameteers, ssuch aas ducctile-regimme cuttting (Secttion 222.4.22).Metal-mmatrixx and cerammic-maatrix compoositess can be diifficuult too machhine, depennding on thhe proopertiies off the indivviduall compponentts, i.e., rreinfoorcingg or wwhiskeers, aas welll as the mmatrixx mateerial.20.9.4 Thermmally Assissted MMachinningMetals and aalloyss thatt are diffiicult to maachinee at rroom ttemperraturee can be maachineed morre eassily aat eleevatedd tempperatuures. In thhermallly asssisteed macchininng (hoot macchininng), tthe soource of heeata torchh, indductioon coiil, hiigh-ennergy beam (suchh as llaser or ellectroon beaam), oor plaasma aarciss forcces, (b) inncreassed toool liife, (c) usse of inexppensivve cuttting-tool materrials, (d) higheer matteriall-remooval rrates, and (e) rreduceed tenndencyy for vibraation and cchatteer.It may be diifficuult too heatt and mainttain aa unifform ttemperraturee disttributtion wwithinn the workppiece. Alsoo, thee origginal microostruccture of thhe worrkpiecce mayy be aadverssely aaffectted byy elevvated tempeeraturres. MMost aappliccationns of hot mmachinning aare inn the turniing off highh-streength metalls andd allooys, aalthouugh exxperimments are iin proogresss to mmachinne cerramicss suchh as ssilicoon nittride. SUMMARYYMachinaabilitty is usuallly deefinedd in tterms of suurfacee finiish, ttool llife,