机械专业英语ppt课件.ppt

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 where istheanglethattheangularcutmakeswiththeXdirection 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 Highdimensionalaccuracyandrepeatabilityenablethemanufactureofpartsthatre