數(shù)控機(jī)床的組成部分外文翻譯、中英文翻譯、外文文獻(xiàn)翻譯

英文原文 N/C Machine Tool Element N/C machine tool elements consist of dimensioning systems, control systems,servomechanisms and open-orclosed-loop systems. It is important to understand each elementprior to actual programming of a numerically controlled port. The term measuring system in N/C refers to 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 used 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 apart will be moved must be given dimensions relating to that original fixed reference point.Figure16.1 shows an absolute measuring system with X and Y dimensions, each based on the origin.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 incrementalmeasuring 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, if not detected and corrected. 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 referred 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 are generally found on drilling and simple milling machine where holelocation and straight milling jobs are performed. Point-to-point systems can be utilized togenetate arcs and angles by programming the machine to move in a series of small steps. Usingthis technique, however, the actual path machined is slightly different from the cutting pathspecified. Machine tools that have the capability of moving simultaneously in two or more axes 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-point systems and generally require a computer to aid programming when machining complex contours. N/C servomechanisms are devices used for producing accurate movement of a table or slid along an axis. 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 power 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 result of this action is that one rotation of the motor shaft produces 200 steps. Connection the motor shaft to a 10-pitch lead screw allows 0.0005-in. movements to be made. Hydraulic servos produce a fluid pressure that flows through gears or pistons to effect shaft rotation. Mechanical motion of lead screws and slides is accomplished through various values and controls from these hydraulic motors. However, they are more expensive and noisy. Most larger N/C machines use hydraulic servos. N/C machines that use 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 moves 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.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 actually 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 the reliability of N/C machines. Machining Centers Many of todays more sophisticated lathes are called machining centers since they are capable of performing, in addition to the normal turning operations, certain milling and drilling operations. Basically, a machining center can be thought of as being a combination turret lathe and milling machine. Additional features are sometimes included by manufacturers to increase the versatility of their machines. Numerical Control One of the most fundamental concepts in the area of advanced manufacturing 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 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 major step away from human control of machine tools. 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 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 reader. 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 produce 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: 1. Electrical discharge machining. 2. Laser cutting. 3. Electron beam welding. Numerical control has also made machine tools more versatile than their manually operated 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 undertake 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 born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in the early 1950s with funding provided by the U. S. Air force. In its earliest stages, NC machines were able to make straight cuts efficiently and effectively. However, 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 smoother is the curve. Each line segment in the steps had to be calculated. This problem led to the development in 1959 of the Automatically Programmed Tools (APT) language. This is a special programming 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 step forward in the further development of NC technology. The original NC systems were vastly different from those used today. The machines had hardwired logic circuits. The instructional programs were written on punched paper, which was later to be replaced by magnetic plastic tape. A tape reader was used to interpret the instructions written on the tape for the machine. Together, all of this represented a giant step forward in the control of machine tools. However, there were a number of problems with NC at this point in its development. A major problem was the fragility of the punched 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 produced 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 through the reader 100 separate times. Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated use. 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 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 of frequent tearing and breakage. However, it still left two other problems. The most important of these was that it was difficult or impossible to change the instructions entered on the tape. To make 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 there were parts to be produced. Fortunately, computer technology became a reality and soon solved the problems of NC associated with punched paper and plastic tape. The development of a concept known as 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 .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. Direct numerical control represented a major step forward over punched tape and plastic tape. However, it is subject to the same limitations as all technologies that depend on a host computer. When the lost computer goes down, the machine tools also experience downtime. This problem led to the development of computer numerical control. The development of the microprocessor allowed for the development of programmable logic controllers (PLCs) and microcomputers. These two technologies allowed for the development 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 programs to be developed off-line and downloaded at the individual machine tool. CNC solved the problems associated with downtime of the host computer, but it introduced another known as data management. The same program might be loaded on ten different microcomputers with no communication among them. This problem is in the process of being solved by local area networks that connect microcomputers for better data management. Cutting Tool Geometry Shape of cutting tools, particularly the angles, and tool material are very important factors. 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 whether 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 geometry is discussed. Tool features 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 Engineers published ASA Standard B5-22-1950. What follows is based on it. A single-point tool is a cutting tool having one face and one continuous cutting edge, Tool angles identified in Fig. 18.2 are as follows: 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 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, because it directly affects the cutting force, finish, and tool life. 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 important angle, because it directs chip flow to the side of the tool post and permits the tool to feed more easily into the work. The end-relief angle is measured between a line perpendicular to the 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 save 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 the ground portion, would be larger than the relief angle. 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. 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 permits the tool to advance more smoothly into the work. 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 prevents rubbing of the cut surface and permits longer tool file. 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 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 reached. 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 chatter. Sand Casting 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 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 to be cast. For all but the simplest shapes the pattern will be made in two or more pieces to facilitate moulding. If a hollow casting is to be made the pattern design will include extension pieces so that spaces to accept the sand core are moulded into sand. These additional spaces in the mould are termed core prints.Sand moulds for the production of small and medium-sized castings are made in a moulding box. The mould is made in two or more parts in order that the pattern may be removed. The drag half of the mould box is placed on a flat firm board and the drag half of the pattern 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 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 ramming. When ramming of the sand is complete, excess sand is removed to leave a smooth surface flush with the edges of the moulding box. The completed 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 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 risers should be such that the metal in them does not freeze too rapidly. An important function of a riser is to act as reservoir of liquid metal to feed solidification within the mould. A thin coating of dry parting sand is sprinkled into mould at this stage. This is to prevent the cope and drag sticking together when the cope half is moulded. The cope is now filled with moulding sand and this is rammed firmly into shape in the same manner as in the making of the drag. 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 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 or gates are carefully cut to connect the runner channel with the main cavity. Gates should be sited to allow or entry into mould with a minimum of turbulence. Any loose sand is gently blown away and if a core is to be used it the cope upon the drag and it is then ready for use. Liquid metal is poured smoothly into the mould via the feeder. Pouring ceases when liquid metal appears at the top of the risers and the feeder channel is also full. When the metal that has been poured into a sand mould has fully solidified 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 the 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 and the castings are then ready for inspection. The main Elements of Horizontal Milling Machines Column and base The column and base form the foundation of the complete machine. Both are made from cast iron, designed with thick sections 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. 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 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 direction. Knee The knee, mounted on the column guideways, provides the vertical movement of the table. Power feed is available, through a gearbox mounted on the side, from a separate built-in motor, providing a range of twelve feed rates from 12 to 250mm/min. Drive is through a leadscrew, whose bottom end is fixed to machine base. Provision is made to raise and lower the knee 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 support to the saddle and guiding it in a transverse direction. lock is provided to clamp the knee in any vertical position on the column. Saddle The saddle, 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 movement is provided through a leadscrew and nut by a hand heel at the front of the knee.Camping of saddle to the knee is achieved by two clamps on the side of the saddle.The saddle has dovetail gun its upper surface, at right angles to the knee guideways, to provide a guide to the table in a longitudinal direction. Table The table provides 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, giving straight-line movement to the table in longitudinal direction at right angles to the saddle movement.Power feed is provided fro m the knee gearbox, through the saddle, to the table leadscrew. 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 The 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, 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 provide accurate location, the angle of taper being 1. The diameter of the taper depends on the size of the machine and may be 30,40,or 50 IST. Due to their steepness of angle, there tapers known as non-stick or self-releasing- cannot be relied upon to transmit the drive to the cutter or cutter-holding device. Two driving keys are provided to transmit the drive. Overarm and arbor support Due to the length of arbors used, support is required at the outer end to prevent deflection 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 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 rotation. 中文譯文 數(shù)控機(jī)床的組成部分 數(shù)控機(jī)床的組成部分包括測(cè)量系統(tǒng)、控制系統(tǒng)、伺服系統(tǒng)及開(kāi)環(huán)或閉環(huán)系統(tǒng)，在對(duì)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。 數(shù)控中，測(cè)量系統(tǒng)這一術(shù)語(yǔ)指的是機(jī)床的兩種測(cè)量系統(tǒng)是絕對(duì)測(cè)量系統(tǒng)和增量測(cè)量系統(tǒng)。絕對(duì)測(cè)量系統(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(shuō)，必須給出一個(gè)零件運(yùn)動(dòng)的所有位 置相對(duì)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(duì)測(cè)量系統(tǒng)，每維都以原點(diǎn)為基準(zhǔn)。增量測(cè)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(cè)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)缺點(diǎn)是，如果產(chǎn)生的任何錯(cuò)誤沒(méi)有被發(fā)現(xiàn)與校正，則錯(cuò)誤會(huì)在整個(gè)過(guò)程中反復(fù)存在。 用于數(shù)控設(shè)備的控制系統(tǒng)通常有兩類(lèi)，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(xiāo)加工的簡(jiǎn)單銑床上。點(diǎn)位控制系統(tǒng)可通過(guò)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)定的切削軌跡留有不同。 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(lèi)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)。 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：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(lái)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(guò)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(guò)各種閥和液壓馬達(dá)的控制來(lái)實(shí)現(xiàn)的。液壓伺服馬達(dá)產(chǎn)生比步 進(jìn)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)。 使用開(kāi)環(huán)系統(tǒng)的數(shù)控機(jī)床，沒(méi)有反饋信號(hào)來(lái)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(hào)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(hào)加以比較，并對(duì)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(duì)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)的量與輸入信號(hào)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。 加工中心 當(dāng)前，許多技術(shù)更為先進(jìn)的車(chē)床叫做加工中心。因?yàn)?，它們除了完成常?guī)的車(chē)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(chē)床和銑床的組合體。有時(shí)，制造廠商為了增加機(jī)床的多用性，還會(huì)增加一些其他的性能。 數(shù)字控制 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(wèn)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(lái)的第 一步。 數(shù)字控制意味著采用預(yù)先錄制的，存儲(chǔ)的符號(hào)指令，控制機(jī)床和其他制造系統(tǒng)。一個(gè)數(shù)控技師的工作不是去操縱機(jī)床，而是編寫(xiě)能夠發(fā)出機(jī)床操縱指令的程序。對(duì)于一臺(tái)數(shù)控機(jī)床，其上必須裝有一個(gè)被稱(chēng)為閱讀機(jī)的界面裝置，用來(lái)接受和解譯編程指令。 發(fā)展數(shù)控技術(shù)是為了克服人類(lèi)操作者的局限性，而且它確實(shí)完成了這項(xiàng)工作。數(shù)字控制的機(jī)器比人工控制的機(jī)器的精度更高、生產(chǎn)的零件的一致性更好、生產(chǎn)的速度更快、而且長(zhǎng)期的工藝裝備成本更低。數(shù)控技術(shù)的發(fā)展導(dǎo)致制造工藝中的其他幾項(xiàng)新發(fā)明的產(chǎn)生： 電火花加工技術(shù)； 激光切削 電子束焊 接 數(shù)字控制還使得機(jī)床比它們采用人工操縱的前輩們的用途更為廣泛。一臺(tái)數(shù)控機(jī)床可以自動(dòng)生產(chǎn)很多種類(lèi)的零件，每個(gè)零件都可以有不同的和復(fù)雜的加工過(guò)程。數(shù)控可使生產(chǎn)廠家承擔(dān)那些對(duì)于采用人工控制的機(jī)床和工藝來(lái)說(shuō)，在經(jīng)濟(jì)上是不劃算的產(chǎn)品的生產(chǎn)任務(wù)。與許多先進(jìn)技術(shù)一樣，數(shù)控誕生于麻省理工學(xué)院的實(shí)驗(yàn)室中。數(shù)控這個(gè)概念是 20 世紀(jì) 50 年代初在美國(guó)空軍的資助下提出來(lái)的。在其最初的階段，數(shù)控機(jī)床可以經(jīng)濟(jì)和有效地進(jìn)行直線切割。 然而，曲線軌跡成為機(jī)床加工的一個(gè)問(wèn)題，在編程時(shí)應(yīng)該采用一系列的水平與豎直的臺(tái)階來(lái)生成曲線。構(gòu)成臺(tái)階的每個(gè) 線段越短，曲線就越光滑。臺(tái)階中的每個(gè)線段都必須經(jīng)過(guò)計(jì)算。 在這個(gè)問(wèn)題促使下，與 1959 年誕生了自動(dòng)編程工具（ APT）語(yǔ)言。這是一個(gè)專(zhuān)門(mén)適用于數(shù)控的編程語(yǔ)言，使用類(lèi)似于英語(yǔ)的語(yǔ)句來(lái)定義零件的幾何形狀，描述切削刀具的形狀和規(guī)定必要的運(yùn)動(dòng)。 APT 語(yǔ)言的研究和發(fā)展是在數(shù)控技術(shù)進(jìn)一步發(fā)展過(guò)程中的一大進(jìn)步。最初的數(shù)控系統(tǒng)與今天應(yīng)用的數(shù)控系統(tǒng)是有很大的差別的。在那時(shí)的機(jī)床中，只有硬線邏輯電路。指令程序?qū)懺诖┛准垘希ㄋ髞?lái)被塑料磁帶所取代），采用帶閱讀機(jī)將寫(xiě)在紙帶或磁帶上的指令給機(jī)器翻譯出來(lái)。所有這些共同構(gòu)成了機(jī)床 數(shù)字控制方面的巨大的進(jìn)步。然而，在數(shù)控發(fā)展的這個(gè)階段中還存在著許多問(wèn)題。 一個(gè)主要問(wèn)題是穿孔紙帶的易損壞性。在機(jī)械加工過(guò)程中，載有編程指令信息的紙帶斷裂和被撕壞是常見(jiàn)的事情。在機(jī)床上每加工一個(gè)零件，都需要將載有編程指令的紙帶放入閱讀機(jī)中重新運(yùn)行一次。因此，這個(gè)問(wèn)題變的很?chē)?yán)重。如果需要制造 100 個(gè)某種零件，則應(yīng)該將紙帶分別通過(guò)閱讀機(jī) 100 次。易損壞的紙帶顯然不能承受?chē)?yán)酷的車(chē)間環(huán)境和這種重復(fù)使用。 這就導(dǎo)致了一種專(zhuān)門(mén)的塑料磁帶的研制。在紙帶上通過(guò)采用一系列的小孔來(lái)載有編程指令，而在塑料帶上通過(guò)采用一系列 的磁點(diǎn)來(lái)載有編程指令。塑料帶的強(qiáng)度比紙帶度要高很多，這就可以解決常見(jiàn)的撕壞和斷裂問(wèn)題。然而，它仍然存在著兩個(gè)問(wèn)題。 其中最重要的一個(gè)問(wèn)題是，對(duì)輸入帶中的指令進(jìn)行修改是非常困難的，或者是根本不可能的。即使對(duì)指令程序進(jìn)行最微小的調(diào)整。也必須中斷加工，制作一條新帶。而且?guī)ㄟ^(guò)閱讀機(jī)的次數(shù)還必須與需要加工的零件的個(gè)數(shù)相同。幸運(yùn)的是，計(jì)算機(jī)技術(shù)的實(shí)際應(yīng)用很快解決了數(shù)控技術(shù)中與穿孔紙帶和塑料帶有關(guān)的問(wèn)題。 在形成直接數(shù)字控制（ DNC）這個(gè)概念后，可以不再采用紙帶或塑料帶作為編程指令的載體，這樣就解決了與之有關(guān)的問(wèn)題。在 直接數(shù)字控制中，幾臺(tái)機(jī)床通過(guò)數(shù)據(jù)傳輸線路連接到一臺(tái)主計(jì)算機(jī)上。操縱這些機(jī)床所需要的程序都存儲(chǔ)在這臺(tái)主計(jì)算機(jī)中。當(dāng)需要時(shí)，通過(guò)數(shù)據(jù)傳輸線路提供給每臺(tái)機(jī)床。直接數(shù)字控制是在穿孔紙帶和塑料帶基礎(chǔ)上的一大進(jìn)步。然而，它也有著與其他依賴(lài)于主計(jì)算機(jī)的技術(shù)一樣的局限性。當(dāng)主計(jì)算機(jī)出現(xiàn)故障時(shí)，由其控制的所有機(jī)床都將停止工作。這個(gè)問(wèn)題促使了計(jì)算機(jī)數(shù)字控制技術(shù)的產(chǎn)生。 微處理器的發(fā)展為可編程邏輯控制器和微型計(jì)算機(jī)的發(fā)展做好了準(zhǔn)備。這兩種技術(shù)為計(jì)算機(jī)數(shù)控（ CNC）的發(fā)展打下了基礎(chǔ)。采用 CNC 技術(shù)后，每臺(tái)機(jī)床上都有一個(gè)可編程邏輯控制器或者微機(jī)對(duì)其進(jìn)行數(shù)字控制。這可以使得程序被輸入和存儲(chǔ)在每臺(tái)機(jī)器內(nèi)部。它還可以在機(jī)床以外編制程序，并且將其下載到每臺(tái)機(jī)床中。計(jì)算機(jī)數(shù)控解決了主計(jì)算機(jī)發(fā)生故障所帶來(lái)的問(wèn)題，但是它產(chǎn)生了另一個(gè)被稱(chēng)為數(shù)據(jù)管理的問(wèn)題。同一個(gè)程序可能要分別裝入十個(gè)相互之間沒(méi)有通信聯(lián)系的微機(jī)中。這個(gè)問(wèn)題正在解決之中，它是通過(guò)采用局部區(qū)域網(wǎng)絡(luò)將各個(gè)微機(jī)連接起來(lái)，以利于更好地進(jìn)行數(shù)據(jù)管理。 刀具的幾何參數(shù) 刀具的形狀和材料是刀具的兩個(gè)非常重要的因素。刀具的角度不僅在很大程度上決定了刀具的壽命，而且也在很大程度上決定了加工的表面的質(zhì)量 。刀具角度設(shè)計(jì)有其一般性原則，它并不因某種特殊刀具而變。車(chē)刀、銑刀、轉(zhuǎn)頭甚至最砂輪的設(shè)計(jì)，所要考慮的因素基本相同。圖 18.1 所四的車(chē)刀外行最易觀察，我們即以此為例來(lái)討論刀具的幾何參數(shù)。 刀具特征名目繁多，技術(shù)文獻(xiàn)中術(shù)語(yǔ)使用也很混亂。為了澄清混亂的概連和術(shù)