机械专业英语课件

1,单词复习：surfaceroughnessgageDictate决定；对有决定性影响GrounddownToolandcuttergrindersPitchdiameterBore,上一课回顾,2,Lesson11NumericalControl数控,重点词汇：codedinstructionsPatentn.专利factoryfloor工厂车间MassachusettsInstituteofTechnologyMIT麻省理工学院CartesiancoordinatesystemCounterclockwise,3,Paragraph1,Numericalcontrol(NC)canbedefinedasthecontrolofoperationofmachinetoolsbyaseriesofcodedinstructionscalledtheprogram,whichconsistsmainlyofalphanumericcharacters(numbersandletters数字和字母).数字控制是指称为程序的一系列编码指令对机床操作的控制，该程序主要由字母和数字符号组成。,4,Paragraph2:,Wecanseefromthisdefinitionthatthesequenceofeventsisbothpreplannedandpredicable.Inotherwords,anydesiredsequenceofeventscanbeobtainedbycodingtheappropriateinstructionsandcanalsobechangedbychangingthosecodedinstructions(编码指令).Therefore,NCsystemsareconsideredtobethetypicalformofprogrammableautomation.从定义中我们可以看到：这一系列的事情可以预先计划也可以预报。换句话说，一系列任何想要做的事情都可以通过编写适当的指令来实现，也可以通过修改编码指令来修正。,5,Paragraph3:,ThebasicconceptofNCisnotnewatallanddatesbacktotheearlyyearsoftheIndustrialRevolution,whenJosephJacquarddevelopedamethodtocontroltextileloomsbyusingpunchedcards.数控的基本概念并不新鲜，时间可以追溯到工业革命早期约瑟夫捷克尔德开发出一种通过穿孔卡片控制织布机的方法。,6,Butwhenheappliedforapatentforhisinvention,hewasdeniedthatrightbytheQueenofEngland,becauseshebelievedthatitwouldhaveputpoorworkersoutofwork(noticethesimilaritywithrobotsnowadays).Infact,thisoldinventioncanbeconsideredsimple,crudeformsofmechanicalNC.然而当他为自己的发明申请专利时，由于女王认为它会造成工人失业(与今天的机器人很相似)而被否定。事实上，这些古老的发明是简单的、机械式数控的雏形。,7,Paragraph4:,AmodernversionofNCemergedin1947attheParsonsEngineeringCompanyofTraverseCity(帕森斯特拉弗斯城的工程公司),Michigan,asaresultoftheneedofJohnC.Parsons(theownerofthecompany)tomanufacturehelicopterrotorbladesfastenoughtomeet(如期完成)hiscontracts.现代数控1947年出现在密歇根州的帕森斯特拉弗斯城的工程公司，当时公司主人约翰帕森斯根据合同要求尽快生产飞机螺旋桨叶片。,8,Later,ParsonsEngineeringwasawardedastudycontractbytheU.S.AirForceMaterialCommandtospeedupproductionanddevelopcontinuous-pathmachining,withthesubcontractorbeingtheMassachusettsInstituteofTechnology(MIT麻省理工学院).后来帕森斯工程公司得到了与美国空军装备司令部签订的研究合同，来提高生产率和开发连续轨迹加工，后来二次转包给麻省理工学院。,9,ThewholetaskwasafterwardgiventoMIT,andthemachinetheydevelopedwassuccessfullydemonstratedin1952.Betweentheyearsof1953and1960,therate(速度)ofbuildingandsellingNCmachinesintheUnitedStateswasveryslow.整个任务给了MIT，机器成功开发是在1952年。在美国1953-1960年数控机床的生产与销售量很小。,10,Thistypeofmachinetoollatergainedwidespreadindustrialapplicationbecauseoftheneedforconsistencyofdimensionsandtightertolerances.由于（零件）尺寸一致接近公差的需要，这种机床后来被广泛应用于工业生产。,11,Paragraph5,Aswithanyengineeringapplication,NCprogrammingisbasedontheCartesiancoordinatesystem(笛卡儿坐标系).Accordingtothatcoordinatesystem,anypointwithinaplanecanbedefinedwithitsdistancesfromtheY-axisandtheX-axis(i.e.theXandtheYcoordinates,respectively).,12,Also,thepointofintersection(相交)ofthesetwoperpendicularaxesiscalledtheorigin,orzeropoint.Thecoordinatesofapointcanbothbepositive,bothbenegative,oronebenegativeandtheotherpositive,dependinguponthelocationofthatpoint.,13,Infact,thosetwoperpendicularintersectingaxesdividetheplaneintofourquadrants,whicharenumberedcounterclockwise.AllvaluesofXandYarepositiveinthefirstquadrantandnegativeinthethirdquadrant.,14,Inthesecondquadrant,allvaluesofXarenegative,andallvaluesofYarepositive,contrarytosignsinthefourthquadrant,whereitistheotherwayaround.,15,Inotherwords,whenapointfallstotherightoftheYaxis,itsXcoordinateispositive,butwhenitistotheleftofthataxis,itsXcoordinateisnegative,whereastheYcoordinateofapointispositivewhenitisabovetheXaxisandnegativewhenthepointislocatedbelowthataxis.,16,TheCartesiancoordinatesystemcanbeextendedtodescribeapointinspacebyaddingathirddimensionalongtheZaxis,whichisperpendiculartotheplaneoftheXandYaxes.,Paragraph6,17,Paragraph7,TherearethreebasictypesofcontrolsystemsforNCmachinetools,point-to-point,straightcut,andcontouring.数控机床有三种基本类型的控制系统点对点、直线切削、轮廓切削。,18,Point-to-Pointsystem点位系统.Thepoint-to-pointsystemisusuallyusedinNCdrillingmachinesthatareemployedindrillingprecisionpatternsofholes(孔系).点位系统常用于数控钻床来加工精密布置的孔。,Paragraph8,19,ThefunctionoftheNCsystemis,therefore,tomovethespindle(ormachinetable)totheexactlocation,asgivenbyatapecommand,sothataholecanbedrilled.Assoonasthedesiredholeisdrilled,thesystemmovesthespindletothenextprogrammedlocationtodrillanotherhole,andsoon.,20,Thespindle(ormachinetable)movementfromoneholelocationtothenextmustbedoneasfastaspossibletobringtoaminimumthenonproductivetime(非生产时间)spentinmovement.Accordingly,speedsofmorethan2500mm/minarequitecommon.,21,Paragraph9,Straight-cutsystem直线切削系统.Thestraight-cutsystemisquitesimilartotheprevioussystem,exceptthatthefeedrateofthespindlealongeachmachineaxisiscontrolledsoasto(为了)besuitableformachining(e.g.,amillingoperationonaverticalmill).,22,Again,thespindlecannotbecontrolledsuchthatitmovesalongalineinclinedtotheX-andY-axesofthemachine,sincethemotionalongeachaxisisindependentfromthatalongtheotheraxis,becauseitiscontrolledbyaseparateNCcircuit(orsubsystem).,23,Nevertheless,motionsalonglinescoincidingwithorparalleltoeithertheXortheY-axiscanbeaccuratelycontrolled.,24,Paragraph10,Contouringsystem轮廓系统.Inordertomakeangularcutsontheworkpiece,thetwodrivingservomotors(onefortheX-axismotionandtheotherfortheY-axismotion)havetorunatunequalspeeds.,25,Infact,therateoftravelalongtheYdirectionbythatalongtheXdirectionmustbeequaltotan,whereistheanglethattheangularcutmakeswiththeXdirection.Thecapabilityofacontrolsystemtoregulatetherateofspindle(ortable)travelalongtwoaxesofmotionatthesametimeiscalledlinearinterpolation.,26,Acontrolsystemofthecontouringtypecanalsoproducecurvestoveryclosetolerances.Therefore,itissometimesreferredtoasthecontinuous-pathsystem.,Paragraph11,27,Themethodofemployinglinearinterpolationtoproducecurvesinvolvesbreakingdowncurveoranarcintoalargenumberofstraightlinesinsuchamanner(于是，如此)thattheendofeachlineisthebeginningofthenextone(tip-to-tailfashion).,28,Eachandeverylinesegmentmust,therefore,beprogrammedinorderforthepathtoconformtothedesiredcurve.Wecanobviouslyseethatthelargerthenumberofsegmentstaken,thesmallereachofthesegmentlinesbecomesandthesmootherthemachinedcurvebecomes.,29,Paragraph12,TheadvantagesofNCmachinetoolsarefeltnotonlyonthefactoryfloorbutalsoinmanyotherdepartmentsofthebusinesscorporation.Followingaresomeofthoseadvantages,whichcanbeusedasjustificationforemployingNCmachinetools:,30,ThedesignandconstructionofNCmachinetools,togetherwiththefactthatthesemachinesarecontrolledbynumericalvalues,ensurepositioningaccuracyandrepeatability.Inotherwords,ifthesameprogramisemployedtoproduceanumberofparts,theyhaveexactlyidenticaldimensions.数控机床的结构与设计及机床利用数字控制的事实，保证了它的定位精度和重复加工能力。换句话说，同一程序加工同一批零件，它们有完全相同的尺寸。,31,Complex-shapedcomponentscanbeproducedautomatically,withclosertolerancesandveryhighdegreesofreliability.This,indeed,providesthedesignerwithgreatdegreeofflexibilityandfreedomwhenpreparingdesigns.,32,Highdimensionalaccuracyandrepeatabilityenablethemanufactureofpartsthatrequ