機(jī)械外文翻譯---數(shù)控機(jī)床的組成部分

1、<p><b>　　附錄</b></p><p><b>　　英文原文</b></p><p>　　N/C Machine Tool Element</p><p>　　N/C machine tool elements consist of dimensioning systems, control syste

2、ms,servomechanisms and open-orclosed-loop systems. It is important to understand each elementprior to actual programming of a numerically controlled port.</p><p>　　The term measuring system in N/C refers to

3、the method a machine tool uses to move a partfrom a reference point to a target point. A target point may be a certain locating for drilling a hole,milling a slot, or other machine operation. The two measuring systems us

4、ed on N/C machines arethe absolute and incremental. The absolute measuring system uses a fixed reference point. It ison this point that all positional information is based. In other words, all the locations to which apar

5、t will be moved m</p><p>　　The incremental measuring system has a floating coordinating system. With the incrementalsystem, the time the part is moved. Figure 16.2 show X and Y values using an incrementalmea

6、suring system. Notice that with this system, each new location bases its values in X and Yfrom the preceding location. One disadvantage to this system is that any errors made will berepeated throughout the entire program

7、, if not detected and corrected.</p><p>　　There are two types of control systems commonly used on N/C equipment: point-to-point andcontinuous path. A point-to-point controlled N/C machine tool, sometimes ref

8、erred to as apositioning control type, has the capability of moving only along a straight line. However, whentwo axes are programmed simultaneously with equal values a 45 angle will be generated.Point-to-point systems ar

9、e generally found on drilling and simple milling machine where holelocation and straight milling jobs are performed</p><p>　　Machine tools that have the capability of moving simultaneously in two or more axe

10、s areclassified as continuous-path or contouring. These machines are used for machining arcs, radii,circles, and angles of any size in two or there dimensions. Continuous-path machines are moreexpensive than point-to-poi

11、nt systems and generally require a computer to aid programming when machining complex contours.</p><p>　　N/C servomechanisms are devices used for producing accurate movement of a table or slid along an axis.

12、 Two types of servos are commonly used on N/C equipment: electric stepping motors and hydraulic motors. Stepping motor servos are frequently used on less expensive N/C equipment. These motors are generally high-torque po

13、wer servos and mounted directly to a lead screw of a table or tool slide. Most stepping motors are actuated by magnetic pulses from the stator and rotor assemblies. The net resul</p><p>　　N/C machines that u

14、se an open-loop system contain no-feedback signal to ensure that a machine axis has traveled the required distance. That is, if the input received was to move a particular table axis 1.000 in, the servo unit generally mo

15、ves the table 1.000 in. There is no means for comparing the actual table movement with the input signal, however, The only assurance that the table has actually moved 1.000 in. is the reliability of the servo system used

16、.</p><p>　　Open-loop systems are, of course, less expensive than closed-loop systems. A closed-loop system compares the actual output with the input signal and compensates for any errors. A feedback unit act

17、ually compares the amount the table has been moved with the input signal. Some feedback units used on closed-loop systems are transducers, electrical or magnetic scales, and synchros. Closed-loop systems greatly increase

18、 the reliability of N/C machines. Machining Centers Many of today’s more sophisticat</p><p>　　Numerical Control</p><p>　　One of the most fundamental concepts in the area of advanced manufacturin

19、g technologies is numerical control (NC). Prior to the advent of NC, all machine tools were manually operated and controlled .Among the many limitations associated with manual control machine tools, perhaps none is more

20、prominent than the limitation of operator skills. With manual control, the quality of the product is directly related to and limited to the skills of the operator. Numerical control represents the first majo</p>&

21、lt;p>　　Numerical control means the control of machine tools and other manufacturing systems through the use of prerecorded, written symbolic instructions. Rather than operating a machine tool, an NC technician writes

22、a program that issues operational instructions to the machine tool. For a machine tool to be numerically controlled, it must be interfaced with a device for accepting and decoding the programmed instructions, known as a

23、reader.</p><p>　　Numerical control was developed to overcome the limitation of human operators, and it has done so. Numerical control machines are more accurate than manually operated machines, they can prod

24、uce parts more uniformly, they are faster, and the long-run tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology:</p><p>　　1.Electri

25、cal discharge machining.</p><p>　　2.Laser cutting.</p><p>　　3.Electron beam welding.</p><p>　　Numerical control has also made machine tools more versatile than their manually oper

26、ated predecessors. An NC machine tool can automatically produce a wide variety of parts, each involving an assortment of widely varied and complex machining processes. Numerical control has allowed manufacturers to under

27、take the production of products that would not have been feasible from an economic perspective using manually controlled machine tools and processes. Like so many advanced technologies, NC was bo</p><p>　　Ho

28、wever, curved paths were a problem because the machine tool had to be programmed to undertake a series of horizontal and vertical steps to produce a curve. The shorter is the straight lines making up the steps, the smoot

29、her is the curve. Each line segment in the steps had to be calculated.</p><p>　　This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language. This is a special programming

30、 language for NC that uses statements similar to English language to define the part geometry, describe the cutting tool configuration, and specify the necessary motions. The development of the APT language was a major s

31、tep forward in the further development of NC technology. The original NC systems were vastly different from those used today. The machines had hardwired </p><p>　　A major problem was the fragility of the pun

32、ched paper tape medium. It was common for the paper tape containing the programmed instructions to break or tear during a machining process. This problem was exacerbated by the fact that each successive time a part was p

33、roduced on a machine tool, the paper tape carrying the programmed instructions had to be rerun through the reader. If it was necessary to produce 100 copies of a given part, it was also necessary to run the paper tape th

34、rough the reader</p><p>　　This led to the development of a special magnetic plastic tape. Whereas the paper tape carried the programmed instructions as a series of holes punched in the tape, the plastic tape

35、 carried the instructions as a series of holes punched in the tape, the plastic tape carried the instructions as a series of magnetic dots. The plastic tape was much stronger than the paper taps, which solved the problem

36、 of frequent tearing and breakage. However, it still left two other problems.</p><p>　　The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To m

37、ake even the most minor adjustments in a program of instructions, it was necessary to interrupt machining operations and make a new tape .It was also still necessary to run the tape through the reader as many times as th

38、ere were parts to be produced. Fortunately, computer technology became a reality and soon solved the problems of NC associated with punched paper and plastic ta</p><p>　　The development of a concept known as

39、 direct numerical control (DNC) solved the paper and plastic tape problems associated with numerical control by simply eliminating tape as the medium for carrying the programmed instructions. In direct numerical control

40、.machine tools are tied, via a data transmission link, to a host computer. Programs for operating the machine tools are stored in the host computer and fed to the machine tool as needed via the data transmission linkage.

41、 Direct numerical contr</p><p>　　The development of the microprocessor allowed for the development of programmable logic controllers (PLCs) and microcomputers. These two technologies allowed for the developm

42、ent of computer numerical control (CNC).With CNC, each machine tool has a PLC or a microcomputer that serves the same purpose. This allows programs to be input and stored at each individual machine tool. It also allows p

43、rograms to be developed off-line and downloaded at the individual machine tool. CNC solved the problems as</p><p>　　Shape of cutting tools, particularly the angles, and tool material are very important facto

44、rs. Angles determine greatly not only tool life but finish quality as well. General principles upon which cutting tool angles are based do not depend on the particular tool, Basically, the same considerations hold true w

45、hether a lathe tool, a milling cutter, a drill, or even a grinding wheel are being designed. Since, however the lathe tool, depicted in Fig. 18.1, might be easiest to visualize, its geometr</p><p>　　Tool fea

46、tures have been identified by many names. The technical literature is full of confusing terminology. Thus in the attempt to cleat up existing disorganized conceptions and nomenclature, this American Society of Mechanical

47、 Engineers published ASA Standard B5-22-1950. What follows is based on it.</p><p>　　A single-point tool is a cutting tool having one face and one continuous cutting edge, Tool angles identified in Fig. 18.2

48、are as follows:</p><p>　　Tool angle 1, on front view, is the back-rank angle. It is the angle between the tool face and a line parallel to the tool base of the shank in a longitudinal plane perpendicular to

49、the tool base. When this angle is downward from front to rear of the cutting edge, the rake is positive; when upward from front to black, the rake is negative. This angle is most significant in the machining process, bec

50、ause it directly affects the cutting force, finish, and tool life.</p><p>　　The side-rake angle, numbered 2, measures the slope of the face on a cross plane perpendicular to the tool base. It, also, is an im

51、portant angle, because it directs chip flow to the side of the tool post and permits the tool to feed more easily into the work.</p><p>　　The end-relief angle is measured between a line perpendicular to the

52、base and the end flank immediately below the end cutting edge; it is numbered 3 in the figure. It provides clearance between work and tool so that its cut surface can flow by with minimum rubbing against the tool. To sav

53、e time, a portion of the end flank of the tool may sometimes be lest unground, having been previously forged to size. In such case, this end-clearance angle, numbered 4, measured to the end flank surface below t</p>

54、;<p>　　Often the end cutting edge is oblique to the flank. The relief angle is then best measured in a plane normal to the end cutting edge angle. Relief is also expressed as viewed from side and end of the tool.&

55、lt;/p><p>　　The side-relief angle, indicated as 5, is measured between the side flank, just below the cutting edge, and a line through the cutting edge perpendicular to the base of the tool. This clearance perm

56、its the tool to advance more smoothly into the work.</p><p>　　Angle 6 is the end-cutting-edge angle measured between the end cutting edge and a line perpendicular to the side of the tool shank. This angle pr

57、events rubbing of the cut surface and permits longer tool file.</p><p>　　The side-cutting-edge angle, numbered 7, is the angle between the side cutting edge and the side of the tool shank. The true length of

58、 cut is along this edge. Thus the angel determines the distribution of the cutting forces. The greater the angle, the longer the tool life; but the possibility of charter increases. A compromise must, as usual, be reache

59、d.</p><p>　　The nose angle, number 8, is the angle between the two component cutting edges. If the corner is rounded off, the arc size is defined by the nose radius 9. The radius size influences finish and c

60、hatter.</p><p>　　Sand Casting</p><p>　　The first stage in the production of sand castings must be the design and manufacture of a suitable pattern. Casting patterns are generally made from hard

61、word and the pattern has to be made larger than the finished casting size to allow for the shrinkage that takes place during solidification and cooling. The extent of this shrinkage varies with the type of metal or alloy

62、 to be cast. For all but the simplest shapes the pattern will be made in two or more pieces to facilitate moulding. If a holl</p><p>　　Sand moulds for the production of small and medium-sized castings are ma

63、de in a moulding box. The mould is made in two or more parts in order that the pattern may be removed.</p><p>　　The drag half of the mould box is placed on a flat firm board and the drag half of the pattern

64、placed in position. Facing sand is sprinkled over the pattern and then the mould box is filled with moulding sand. The sand is rammed firmly around the pattern. This process of filling and ramming may be done by hand but

65、 mould production is automated in a large foundry with the mould boxes moving along a conveyor, firstly to be filled with sand from hoppers and then to pass under mechanical hammers for</p><p>　　The complete

66、d drag is now turned over and the upper, or cope, portion of the moulding box positioned over it. The cope half of the pattern is placed in position, correct alignment being ensured by means of small dowel pins. Patterns

67、 for the necessary feeder, runner and risers are also placed so as to give an even distribution of metal into the mould cavity. The risers should coincide with the highest readily escape from the mould. The sizes of rise

68、rs should be such that the metal in them does no</p><p>　　After the ramming of sand in the cope is completed the two halves of the moulding box are carefully separated. At this stage venting of the moulding

69、box are carefully separated. At this stage venting of the mould can be done, if necessary, to increase the permeability of the mould. After venting the patterns are carefully removed from both cope and drag, and a gate o

70、r gates are carefully cut to connect the runner channel with the main cavity. Gates should be sited to allow or entry into mould wi</p><p>　　When the metal that has been poured into a sand mould has fully so

71、lidified the mould is broken and casting is removed. The casting still has the runner and risers attached to it and there will be sand adhering to portions of the surface. Runners and risers are cut off and returned to t

72、he melting furnace. Sand cores are broken and adherent sand is cleaned from the surface by vibration or by sand blasting with dry sand. Any fins or metal flash formed at mould parting lines are removed by grinding </p

73、><p>　　The main Elements of Horizontal Milling Machines</p><p>　　Column and base The column and base form the foundation of the complete machine. Both are made from cast iron, designed with thick s

74、ections to ensure complete rigidity and freedom form vibration. The base, upon which the column is mounted, is also the cutting-fluid reservoir and contains the pump to circulate the fluid to cutting area.</p><

75、;p>　　The column contains the spindle, accurately located in precision bearings. The spindle id driven through a gearbox from a vee-belt drive from the electric motor housed at the base of column. The gearbox enables a

76、 range of spindle speeds to be selected. In the model shown, twelve spindle speeds from 32 to 1400rev/min are available. The front of column carries the guideways upon which the knee is located and guided in a vertical d

77、irection.</p><p><b>　　Knee</b></p><p>　　The knee, mounted on the column guideways, provides the vertical movement of the table. Power feed is available, through a gearbox mounted on

78、the side, from a separate built-in motor, providing a range of twelve feed rates from 6 to 250mm/min. Drive is through a leadscrew, whose bottom end is fixed to machine base. Provision is made to raise and lower the kne

79、e by hand through a leadscrew and nut operates by a handwheel at the front. The knee has guideways on its top surface giving full-width su</p><p><b>　　Saddle</b></p><p>　　The saddle,

80、 mounted on the knee guideways, providers the transverse movement of the table. Power feed is provided through the gearbox on the knee. A range of twelve feeds is available, from 12 to 500mm/min. Alternative hand moveme

81、nt is provided through a leadscrew and nut by a hand heel at the front of the knee.</p><p>　　Camping of saddle to the knee is achieved by two clamps on the side of the saddle.</p><p>　　The saddl

82、e has dovetail gun its upper surface, at right angles to the knee guideways, to provide a guide to the table in a longitudinal direction.</p><p><b>　　Table</b></p><p>　　The table pro

83、vides the surface upon which all workpieces and workholding equipment are located and clamped. A series of tee slots is provided for this purpose. The dovetail guides on undersurface locate in the guideways on the saddle

84、, giving straight-line movement to the table in longitudinal direction at right angles to the saddle movement.</p><p>　　Power feed is provided from the knee gearbox, through the saddle, to the table leadscre

85、w. Alternative hand feed is provided by a handwheel at each end of the table. Stops at the front of the table can be set to disengage the longitudinal feed automatically in each direction. Spindle</p><p>　　T

86、he spindle, accurately mounted in precision bearings, provides the drive for the milling cutters. Cutters can be mounted straight on the spindle nose or in curter-holding devices which in turn are mounted in the spindle,

87、 held in position by a drawbolt passing the hold spindle. Spindles of milling machines have a standard spindle nose to allow for easy interchange of cutters and cutter-holding devices. The bore of the nose is tapered to

88、provide accurate location, the angle of taper being 1. The </p><p>　　Overarm and arbor support</p><p>　　Due to the length of arbors used, support is required at the outer end to prevent deflecti

89、on when cutting takes place. Support is provided by an arbor-support bracket, clamped to an overarm which is mounted on top of the column in a dovetail slide. The overarm is adjustable in or out for different lengths of

90、arbor, or can be fully pushed in when arbor support is not required. Two clamping bolts are support is located in the overarm dovetail and is locked by which the arbor runs during splindle r</p><p><b>

91、　　中文譯文</b></p><p><b>　　數(shù)控機(jī)床的組成部分</b></p><p>　　數(shù)控機(jī)床的組成部分包括測量系統(tǒng)、控制系統(tǒng)、伺服系統(tǒng)及開環(huán)或閉環(huán)系統(tǒng)，在對數(shù)控零件進(jìn)行實(shí)際程序設(shè)計(jì)之前，了解各組成部分是重要的。</p><p>　　數(shù)控中，測量系統(tǒng)這一術(shù)語指的是機(jī)床的兩種測量系統(tǒng)是絕對測量系統(tǒng)和增量測量系統(tǒng)。絕對測量系

92、統(tǒng)采用固定基準(zhǔn)點(diǎn)，所有的位置信息正是一這一點(diǎn)為基準(zhǔn)。換句話說，必須給出一個(gè)零件運(yùn)動(dòng)的所有位置相對于原始固定基準(zhǔn)點(diǎn)的尺寸關(guān)系。圖 16.1 表示 X 和 Y兩維絕對測量系統(tǒng)，每維都以原點(diǎn)為基準(zhǔn)。增量測量系統(tǒng)有一個(gè)移動(dòng)的坐標(biāo)系統(tǒng)。運(yùn)動(dòng)增量系統(tǒng)時(shí)，零件每移動(dòng)一次，機(jī)床就建立一個(gè)新的原點(diǎn)。圖 16.2 表示使用增量測量系統(tǒng)時(shí)的 X 和 Y 的值。注意，使用這個(gè)系統(tǒng)時(shí)，每個(gè)新的位置在 X 和 Y 鐲上的值都是建立在前一個(gè)位置之上的。這種系統(tǒng)的一個(gè)

93、缺點(diǎn)是，如果產(chǎn)生的任何錯(cuò)誤沒有被發(fā)現(xiàn)與校正，則錯(cuò)誤會(huì)在整個(gè)過程中反復(fù)存在。</p><p>　　用于數(shù)控設(shè)備的控制系統(tǒng)通常有兩類，即點(diǎn)位控制系統(tǒng)和連續(xù)控制系統(tǒng)。點(diǎn)位控制數(shù)控機(jī)床只有直線運(yùn)動(dòng)的能力。然兒，當(dāng)沿兩琢線以等值同時(shí)編程時(shí)，會(huì)形成45斜線。點(diǎn)位控制系統(tǒng)常用于需確定孔位的轉(zhuǎn)床和需進(jìn)行直線銑銷加工的簡單銑床上。點(diǎn)位控制系統(tǒng)可通過程序控制機(jī)床，以一系列小步運(yùn)動(dòng)形成弧線和斜線。然兒，用這種方法時(shí)，實(shí)際加工軌跡與規(guī)定

94、的切削軌跡留有不同。</p><p>　　具有在兩個(gè)或多個(gè)坐標(biāo)做方向上同時(shí)運(yùn)動(dòng)的能力的機(jī)床，歸屬連續(xù)軌跡控制或輪廓控制類機(jī)床。這些機(jī)床用于加工兩維或三維空間中各種不同大小的弧行、圓角、圓及斜角。連續(xù)軌跡控制的數(shù)控機(jī)床比點(diǎn)位控制的機(jī)床貴得多，在加工復(fù)雜輪廓時(shí)，一般需要計(jì)算機(jī)輔助程序設(shè)計(jì)。</p><p>　　數(shù)控伺服機(jī)構(gòu)是使工作臺(tái)或滑座沿座標(biāo)柞準(zhǔn)確運(yùn)動(dòng)的裝置。用于數(shù)控設(shè)備的伺服機(jī)構(gòu)通常有兩種

95、：步進(jìn)電機(jī)和液壓馬達(dá)。步進(jìn)電機(jī)伺服機(jī)構(gòu)用于不太貴重的數(shù)控設(shè)備上。這些電機(jī)通常是大轉(zhuǎn)矩的伺服機(jī)構(gòu)，直接安裝在工作臺(tái)或刀座的絲桿上。大多數(shù)步進(jìn)電機(jī)是由來自定子和轉(zhuǎn)子組件的磁力脈沖驅(qū)動(dòng)的，這種作用的結(jié)果是電機(jī)主狀一轉(zhuǎn)產(chǎn)生 200 步矩。把電機(jī)注解接在 10 扣/英寸的絲桿上，每步能產(chǎn)生 0.0004 英寸的移動(dòng)。液壓伺服馬達(dá)使壓力液體流過齒輪或拄塞，從而使周轉(zhuǎn)動(dòng)。絲桿和滑座的機(jī)械運(yùn)動(dòng)是通過各種閥和液壓馬達(dá)的控制來實(shí)現(xiàn)的。液壓伺服馬達(dá)產(chǎn)生比步進(jìn)

96、電機(jī)更大的轉(zhuǎn)矩，但比步進(jìn)電機(jī)貴，且噪聲很大。大多數(shù)大型數(shù)控機(jī)床使用液壓伺服機(jī)構(gòu)。</p><p>　　使用開環(huán)系統(tǒng)的數(shù)控機(jī)床，沒有反饋信號來確保機(jī)床的坐標(biāo)做是否運(yùn)動(dòng)了所需的距離。即，如果接受的輸入信號是使一特定工作臺(tái)坐標(biāo)做移動(dòng) 1.000 英尺的唯一保證是閉環(huán)系統(tǒng)便宜。閉環(huán)系統(tǒng)能夠?qū)?shí)際輸出與輸入信號加以比較，并對任何誤差進(jìn)行補(bǔ)償。反饋裝置真實(shí)地將工作臺(tái)加以比較，并對任何誤差進(jìn)行補(bǔ)償。反饋裝置真實(shí)地將工作臺(tái)已運(yùn)動(dòng)

97、的量與輸入信號進(jìn)行比較。用于閉環(huán)系統(tǒng)的一些反饋裝置是傳感器、電尺或磁尺以及同步器等。閉環(huán)系統(tǒng)大大增加了數(shù)控機(jī)床的準(zhǔn)確性。</p><p><b>　　加工中心</b></p><p>　　當(dāng)前，許多技術(shù)更為先進(jìn)的車床叫做加工中心。因?yàn)?，它們除了完成常?guī)的車削工作之外，還可以完成某些銑削、鉆削工作。加工中心基本上可以認(rèn)為是轉(zhuǎn)塔車床和銑床的組合體。有時(shí)，制造廠商為了增加機(jī)

98、床的多用性，還會(huì)增加一些其他的性能。</p><p><b>　　數(shù)字控制</b></p><p>　　先進(jìn)制造技術(shù)中的一個(gè)最基本的概念是數(shù)字控制（NC）。在數(shù)控技術(shù)出現(xiàn)之前，所有的機(jī)床都是由人工操縱和控制的。在與人工控制的機(jī)床有關(guān)的很多局限性中，操作者的技能大概是最突出的問題。采用人工控制時(shí)，產(chǎn)品的質(zhì)量直接與操作者的技能有關(guān)。數(shù)字控制代表了從人工控制機(jī)床走出來的第一