机械专业英语课件.ppt

1、n单词复习：1.surface roughness2.gage3.Dictate决定；对有决定性影响 4.Ground down5.Tool and cutter grinders6.Pitch diameter 7.Bore上一课回顾.1Lesson 11 Numerical Control 数控数控重点词汇：1.coded instructions2.Patent n.专利3.factory floor 工厂车间工厂车间4.Massachusetts Institute of Technology MIT麻省理工学院5.Cartesian coordinate system6.Counte

2、rclockwise.2Paragraph 1nNumerical control(NC)can be defined as the control of operation of machine tools by a series of coded instructions called the program,which consists mainly of alphanumeric characters(numbers and letters数字和字母).n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。.3Paragraph 2:nWe can s

3、ee from this definition that the sequence of events is both preplanned and predicable.nIn other words,any desired sequence of events can be obtained by coding the appropriate instructions and can also be changed by changing those coded instructions(编码指令).n Therefore,NC systems are considered to be t

4、he typical form of programmable automation.n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。.4Paragraph 3:nThe basic concept of NC is not new at all and dates back to the early years of the Industrial Revolution,when Joseph Jacquard developed a method to control textile

5、looms by using punched cards.n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。.5nBut when he applied for a patent for his invention,he was denied that right by the Queen of England,because she believed that it would have put poor workers out of work(notice the similarity with robots nowadays).nI

6、n fact,this old invention can be considered simple,crude forms of mechanical NC.n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。.6Paragraph 4:nA modern version of NC emerged in 1947 at the Parsons Engineering Company of Traverse City(帕森斯特拉弗斯城的工程公司),Michigan,as a result of th

7、e need of John C.Parsons(the owner of the company)to manufacture helicopter rotor blades fast enough to meet(如期完成)his contracts.n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。.7nLater,Parsons Engineering was awarded a study contract by the U.S.Air Force Material Command to speed up pro

8、duction and develop continuous-path machining,with the subcontractor being the Massachusetts Institute of Technology(MIT麻省理工学院).n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。.8nThe whole task was afterward given to MIT,and the machine they developed was successfully demonstrated in 19

9、52.nBetween the years of 1953 and 1960,the rate(速度)of building and selling NC machines in the United States was very slow.n 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。.9nThis type of machine tool later gained widespread industrial application because of the need for consistency of dimensions

10、 and tighter tolerances.n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。.10Paragraph 5nAs with any engineering application,NC programming is based on the Cartesian coordinate system(笛卡儿坐标系).n According to that coordinate system,any point within a plane can be defined with its distances from the Y-axis and the X

11、-axis(i.e.the X and the Y coordinates,respectively).11nAlso,the point of intersection(相交)of these two perpendicular axes is called the origin,or zero point.nThe coordinates of a point can both be positive,both be negative,or one be negative and the other positive,depending upon the location of that

12、point.12nIn fact,those two perpendicular intersecting axes divide the plane into four quadrants,which are numbered counterclockwise.nAll values of X and Y are positive in the first quadrant and negative in the third quadrant.13nIn the second quadrant,all values of X are negative,and all values of Y

13、are positive,contrary to signs in the fourth quadrant,where it is the other way around.14nIn other words,when a point falls to the right of the Y axis,its X coordinate is positive,but when it is to the left of that axis,its X coordinate is negative,whereas the Y coordinate of a point is positive whe

14、n it is above the X axis and negative when the point is located below that axis.15nThe Cartesian coordinate system can be extended to describe a point in space by adding a third dimension along the Z axis,which is perpendicular to the plane of the X and Y axes.Paragraph 6.16Paragraph 7nThere are thr

15、ee basic types of control systems for NC machine tools,point-to-point,straight cut,and contouring.n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。.17nPoint-to-Point system点位系统点位系统.nThe point-to-point system is usually used in NC drilling machines that are employed in drilling precision patterns of holes(孔系).n点位系统常用于

16、数控钻床来加工精密布置的孔。Paragraph 8.18nThe function of the NC system is,therefore,to move the spindle(or machine table)to the exact location,as given by a tape command,so that a hole can be drilled.nAs soon as the desired hole is drilled,the system moves the spindle to the next programmed location to drill an

17、other hole,and so on.19nThe spindle(or machine table)movement from one hole location to the next must be done as fast as possible to bring to a minimum the nonproductive time(非生产时间)spent in movement.nAccordingly,speeds of more than 2500 mm/min are quite common.20Paragraph 9nStraight-cut system直线切削系统

18、直线切削系统.nThe straight-cut system is quite similar to the previous system,except that the feed rate of the spindle along each machine axis is controlled so as to(为了)be suitable for machining(e.g.,a milling operation on a vertical mill).21nAgain,the spindle cannot be controlled such that it moves along

19、 a line inclined to the X-and Y-axes of the machine,since the motion along each axis is independent from that along the other axis,because it is controlled by a separate NC circuit(or subsystem).22nNevertheless,motions along lines coinciding with or parallel to either the X or the Y-axis can be accu

20、rately controlled.23Paragraph 10nContouring system轮廓系统轮廓系统.In order to make angular cuts on the work piece,the two driving servo motors(one for the X-axis motion and the other for the Y-axis motion)have to run at unequal speeds.24 In fact,the rate of travel along the Y direction by that along the X

21、direction must be equal to tan,where is the angle that the angular cut makes with the X direction.The capability of a control system to regulate the rate of spindle(or table)travel along two axes of motion at the same time is called linear interpolation.25nA control system of the contouring type can

22、 also produce curves to very close tolerances.nTherefore,it is sometimes referred to as the continuous-path system.Paragraph 11.26nThe method of employing linear interpolation to produce curves involves breaking down curve or an arc into a large number of straight lines in such a manner(于是，如此)that t

23、he end of each line is the beginning of the next one(tip-to-tail fashion).27nEach and every line segment must,therefore,be programmed in order for the path to conform to the desired curve.nWe can obviously see that the larger the number of segments taken,the smaller each of the segment lines becomes

24、 and the smoother the machined curve becomes.28Paragraph 12nThe advantages of NC machine tools are felt not only on the factory floor but also in many other departments of the business corporation.nFollowing are some of those advantages,which can be used as justification for employing NC machine too

25、ls:.29The design and construction of NC machine tools,together with the fact that these machines are controlled by numerical values,ensure positioning accuracy and repeatability.In other words,if the same program is employed to produce a number of parts,they have exactly identical dimensions.数控机床的结构

26、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。.30n Complex-shaped components can be produced automatically,with closer tolerances and very high degrees of reliability.n This,indeed,provides the designer with great degree of flexibility and freedom when preparing designs.31 High dimens

27、ional accuracy and repeatability enable the manufacture of parts that require long series of operation.Such parts are difficult to produce by conventional methods,since the accumulated error results in completely unacceptable results.32 Since NC machine tools can automatically perform any desired ta

28、sk(within their capability)after being programmed and without the need for a human operator to stand beside the machine all the time,they can be employed to carry out operations in hostile environments.33nExamples involve machining of some polymeric materials where poisonous gases evolve as a result

29、 of the machining operation.34 NC systems transfer a substantial portion of planning for the processing operation from the shop floor to the offices,where a specialist prepares the NC part program in a comfortable environment.Consequently(因此),production can be directly monitored and controlled by the management.35课后作业：n1、复习本课单词，预习下一课单词.36