《机械专业英语》课件第22章.ppt

1、Unit 22TEXT LEARN TO SPEAK NEW WORDS AND PHRASES NOTES EXERCISES READING MATERIAL PROFESSIONAL WORDS AND PHRASES TEXTFundamentals of Numerical Control Controlling a machine tool by means of a prepared program is known as numerical control,or NC.NC equipment has been defined the Electronic Industries

2、 Association(EIA)as“A system in which actions are controlled by the direct insertion of numerical data at some point.The system must automatically interpret at least some portion of this data”.In a typical NC system the numerical data which is required for producing a part is maintained on a punched

3、 tape and is called the part program.The part program is arranged in the form of blocks of information,where each block contains the numerical data required to produce one segment of the work-piece.The punched tape is moved forward by one block each time the cutting of a segment is completed.The blo

4、ck contains,in coded form,all the information needed for processing a segment of the work-piece:the segment length,its cutting speed,feed,etc.Dimensional information(length,width,and radii of circles)and the contour form(linear,circular,or other)are taken from an engineering drawing.Dimensions are g

5、iven separately for each axis of motion(x,y,etc.).Cutting speed,feed-rate,and auxiliary function(coolant on and off,spindle direction,clamp,gear changes,etc.)are programmed according to surface finish and tolerance requirements.Preparing the part program for a NC machine tool requires a part program

6、mer.The part programmer must possess knowledge and experiences in mechanical engineering.Part Programmers must be familiar with the function of NC machine tools and machining process and have to decide on the optimal sequence of operations.In NC machine tools,each axis of motion is equipped with a s

7、eparate driving device which replaces the hand-wheel of the conventional machine.The driving device may be a DC motor,a hydraulic actuator,or a stepping motor.The type selected is determined mainly by the power requirements of the machine.The NC machine tool system contains the machine control unit(

8、MCU)and the machine tool itself.The MCU has to read and decode the part program,to provide the decoded instructions to the control loops of the machine axes of motion,and to control the machine tool operation.The MCU consists of two main units:the data processing unit(DPU)and the control loops unit(

9、CLU).The function of the DPU is to decode the information received from the tape,process it and provide data to the CLU.Such data contains the new required position of each axis,its direction of motion and velocity,and auxiliary control signals to relays.On the other hand,the CLU provides a signal a

10、nnouncing that the previous segment is completed and that the DPU can read a new block of the part program.The CLU operates the drives attached of the machine lead-screws and receives feedback signals on the actual position and velocity of each one of the axes.Each lead-screw is equipped with a sepa

11、rate driving device and a separate feedback device,but the latter exists only in a closed-loop system.In CNC systems,the DPU functions are always performed by the control program contained in the CNC computer.The major part of the CLU,however,is always implemented in the most sophisticated CNC syste

12、ms.LEARN TO SPEAKMr.Zhou:Good morning,Miss Yang.Miss Yang:Hi,Mr.Zhou.Mr.Zhou:What are you doing now?Miss Yang:I am turning a work-piece.Mr.Zhou:Is this lathe different from that lathe?Miss Yang:Yes.It is.Mr.Zhou:Where are the distinctions about them?Miss Yang:This is an NC lathe,and the other is a c

13、onventional lathe.Mr.Zhou:What is NC?Miss Yang:NC refers to numerical control,and controlling a machine tool by means of a prepared program.Mr.Zhou:What does the NC machine tool system contain?Miss Yang:It contains the machine control unit and the machine tool itself.Mr.Zhou:Do you like to machine a

14、 work-piece on NC machine tools or conventional machine tools.Miss Yang:I would prefer to use NC machine tools very much.Mr.Zhou:Why do you think that?Miss Yang:Because it has some advantages such as increased productivity,reduced the noise,improved operators safety and product quality,and so on.Mr.

15、Zhou:It sounds quite well.Miss Yang:You will like it in the future,too.Mr.Zhou:I think so.Thanks a lot.Miss Yang:You are welcome.NEW WORDS AND PHRASESinterpret In5t:prIt v.解释说明coolant 5ku:lEnt n.冷却液optimal 5BptIm(E)l adj.最佳的，最理想的decode di:5kEJd v.解码，译码implemented 5ImplImEnt v.实行，执行sophisticated sE5f

16、IstIkeItId adj.复杂的numerical control(NC)数字控制the Electronic Industries Association(EIA)(美国)电子工业协会auxiliary function 辅助功能surface finish 表面粗糙度D.C.motor 直流电机stepping motor 步进电机machine control unit(MCU)机床控制单元data processing unit(DPU)数据处理单元computer numerical control(CNC)计算机数字控制NOTES 1NC equipment has been

17、defined as“A system in which actions are controlled by the direct insertion of numerical data at some point.The system must automatically interpret at least some portion of this data”.数控设备被定义为：“采用在某些点直接插入数据来控制操作的系统，此系统至少要能自动解读部分数据。”这个句子中，A system 是as的宾语。A system后是由which引导的定语从句，修饰system。2Part program

18、mers must be familiar with the function of NC machine tools and machining process and have to decide on the optimal sequence of operations.零件编程人员要熟悉数控机床的功能及加工工艺，并决定最佳的加工顺序。句中，the optimal sequence of operations意思是最佳的加工顺序。3In NC machine tools,each axis of motion is equipped with a separate driving dev

19、ice which replaces the hand-wheel of the conventional machine.在数控机床中，每个轴向的运动都要有单独的驱动装置代替普通机床中的手轮来驱动。句中，which引导的定语从句修饰device。4Each lead-screw is equipped with a separated driving device and a separate feedback device,but the latter exists only in a close-loop system.每个丝杠都有一个单独的驱动装置和反馈装置，不过反馈装置只出现在闭环系

20、统中。EXERCISES 1put the following into Chinese and recite them:(1)1)NC:Numerical Control 2)CNC:Compute Numerical Control 3)MCU:Machine Control Unit 4)CPU:Center Process Unit 5)DPU:Data Processing Unit 6)CLU:Control Loops Unit(2)1)dimensional information2)auxiliary function3)NC machine tools4)The optim

21、al sequence of operations5)a DC motor 6)a stepping motor 2Fill in the blanks with proper words:machines controlled by means of prepared programs are called machines.In NC system,the part program is maintained on a or punched card.Each block of program contains some information in form.After one bloc

22、k is carried out,the punched tape is moved ,so another block of information is read to the machine.The part program is often prepared by a part ,who have to decide on the sequence of .Programming may be done or with the aid of computer,which is usually called (CAP).3Translate the following passage i

23、nto Chinese:Numerical Control(NC)is a form of programmable automation in which the processing equipment is controlled by means of numbers,letters,and other symbols.The numbers,letters,and symbols are coded in an appropriate format to define a program of instructions for a particular workpart or job.

24、When the job changes,the program of instruction is changed.The capability to change the program is what makes NC suitable for low-and medium-volume production.READING MATERIAL Advantages of NCRecent studies show that of the amount of time an average part spent in a shop，only a fraction of that time

25、was actually spent in the machining processLet us assume that a part spent 50 hours from the time it arrived at a plant as a rough casting or bar stock to the time it was a finished productDuring this time，it would be on the machine for only 2.5 hours and be cut for only 0.75 hour.The rest of the ti

26、me would be spent on waiting，moving，setting up，loading，unloading，inspecting the part，setting speeds and feeds，and changing cutting tools NC reduces the amount of non-chip-producing time by selecting speeds and feeds,making rapid moves between surfaces to be cut，using automatic fixtures，automatic too

27、l changing,controlling the coolant，in-process gaging，and loading and unloading the partThese factors，plus the fact that it is no longer necessary to train machine operators,have resulted in considerable savings throughout the entire manufacturing process and caused tremendous growth in the use of NC

28、Some of the major advantages of CNC are as follows：(1)Less ScrapBecause of the accuracy of CNC systems and the elimination of most human errors，scrap has been greatly reduced or eliminated(2)Reduced Production Lead TimeThe program preparation and setup for CNC machines is usually shortMany jigs and

29、fixtures formerly required are not necessary.The program can be stored in a small space and used again as required(3)Less Human ErrorThe CNC eliminates the need for an operator to take trial program cuts，make trial measurement or make table positioning movementsThe operator does not have to change c

30、utting tools except during setup and when tools become dull (4)High Part AccuracyCNC ensures that all parts produced will be accurate and uniform in qualityThe improved accuracy of the parts produced by CNC assures the interchangeability of parts(5)Complex Machining OperationsComplex operations can

31、be done quickly，easily，and accurately with CNC and electronic measuring equipment(6)Lower Tooling CostsCNC generally does not require complex holding fixtures,therefore the cost of fixtures may be reduced by as much as 70%.(7)Increased ProductivityBecause CNC controls all the machine functions，parts

32、 are produced faster，with less set up and lead time(8)Reduced InventoryAn inventory of spare parts is no longer necessary，since duplicate parts can be made to the same accuracy when the same program is used(9)Less Machine Tool DamageThe damage to machine tools as a result of operator error and carel

33、essness is almost eliminated because there is less need for operator intervention(10)Less InspectionBecause CNC produces parts of uniform quality，less inspection time is requiredMany operations or parts may be inspected while they are being machined(11)Greater Machine UptimeBecause there is less tim

34、e required for setup and operator adjustments，production rates could increase as much as 80 percent(12)Reduced Space RequirementsCNC requires less floor space for machines because of their high productivity，and less storage space for fewer jigs and fixturesSince the first industrial revolution，about

35、 200 years ago，NC has had a significant effect on the industrial worldThe developments in the computer and NC have extended a persons mind and muscle The NC unit takes symbolic input and changes it to useful output，expanding a persons concepts into creative and productive resultsNC technology has ma

36、de such rapid advances that it is being used in almost every area of manufacturing，such as machining，welding，presswork，and assemblyComputer-assisted manufacturing(CAM)and computer-integrated machining(CIM)are certainly where the future of manufacturing lies，and considering the developments of the pa

37、st，it will not be too far in the future before the automated factory is a reality PROFESSIONAL WORDS AND PHRASESload lEud v.装载chip tFIp n.碎片，碎屑fixture 5fIkstFE n.夹具die daI n.模具，冲模retrofit 5retrEfIt n.改型，翻新bending 5bendIN n.弯曲forming 5fR:mIN n.成形加工stamping 5stAmpIN n.冲压口 v.冲压semiautomatic adj.半自动化finished product 成品，产品