机械专业英语课件11

1单词复习：1.surfaceroughness2.gage3.Dictate决定；对…有决定性影响4.Grounddown5.Toolandcuttergrinders6.Pitchdiameter7.Bore上一课回顾2Lesson11NumericalControl数控重点词汇：1.codedinstructions2.Patentn.专利3.factoryfloor工厂车间4.MassachusettsInstituteofTechnologyMIT麻省理工学院5.Cartesiancoordinatesystem6.Counterclockwise3Paragraph1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。4Paragraph2: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。5Paragraph3: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。7Paragraph4: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。11Paragraph5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.Paragraph617Paragraph7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。Paragraph819ThefunctionoftheNCsystemis,therefore,tomovethespindle(ormachinetable)totheexactlocation,asgivenbyatapecommand,sothataholecanbedrilled.Assoonasthedesiredholeisdrilled,thesystemmovesthespindletothenextprogrammedlocationtodrillanotherhole,andsoon.20Thespindle(ormachinetable)movementfromoneholelocationtothenextmustbedoneasfastaspossibletobringtoaminimumthenonproductivetime(非生产时间)spentinmovement.Accordingly,speedsofmorethan2500mm/minarequitecommon.21Paragraph9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.24Paragraph10Contouringsystem轮廓系统.