车床--------外文文献翻译.doc

车床-外文文献翻译 LathesLathes are machine tools designed primarily to do turning facing and boring Very little turning is done on other types of machine tools and none can do it with equal facility Because lathes also can do drilling and reaming their versatility permits several operations to be done with a single setup of the work piece Consequently more lathes of various types are used in manufacturing than any other machine toolThe essential components of a lathe are the bed headstock assembly tailstock assembly and the leads crew and feed rodThe bed is the backbone of a lathe It usually is made of well normalized or aged gray or nodular cast iron and provides s heavy rigid frame on which all the other basic components are mounted Two sets of parallel longitudinal ways inner and outer are contained on the bed usually on the upper side Some makers use an inverted V-shape for all four ways whereas others utilize one inverted V and one flat way in one or both sets They are precision-machined to assure accuracy of alignment On most modern lathes the way are surface-hardened to resist wear and abrasion but precaution should be taken in operating a lathe to assure that the ways are not damaged Any inaccuracy in them usually means that the accuracy of the entire lathe is destroyedThe headstock is mounted in a foxed position on the inner ways usually at the left end of the bed It provides a powered means of rotating the word at various speeds Essentially it consists of a hollow spindle mounted in accurate bearings and a set of transmission gears-similar to a truck transmissionthrough which the spindle can be rotated at a number of speeds Most lathes provide from 8 to 18 speeds usually in a geometric ratio and on modern lathes all the speeds can be obtained merely by moving from two to four levers An increasing trend is to provide a continuously variable speed range through electrical or mechanical drivesBecause the accuracy of a lathe is greatly dependent on the spindle it is of heavy construction and mounted in heavy bearings usually preloaded tapered roller or ball types The spindle has a hole extending through its length through which long bar stock can be fed The size of imum size of bar stock that can be machined when the material must be fed through spindleThe tailsticd assembly consists essentially of three parts A lower casting fits on the inner ways of the bed and can slide longitudinally thereon with a means for clamping the entire assembly in any desired location An upper casting fits on the lower one and can be moved transversely upon it on some type of keyed ways to permit aligning the assembly is the tailstock quill This is a hollow steel cylinder usually about 51 to 76mm 2to 3 inches in diameter that can be moved several inches longitudinally in and out of the upper casting by means of a hand wheel and screwThe size of a lathe is designated by two dimensions The first is known as the swing This is the imum diameter of work that can be rotated on a lathe It is approximately twice the distance between the line connecting the lathe centers and the nearest point on the ways The second size dimension is the imum distance between centers The swing thus indicates the imum work piece diameter that can be turned in the lathe while the distance between centers indicates the imum length of work piece that can be mounted between centersEngine lathes are the type most frequently used in manufacturing They are heavy-duty machine tools with all the components described previously and have power drive for all tool movements except on the compound rest They commonly range in size from 305 to 610 mm 12 to 24 inches swing and from 610 to 1219 mm 24 to 48 inches center distances but swings up to 1270 mm 50 inches and center distances up to 3658mm 12 feet are not uncommon Most have chip pans and a built-in coolant circulating system Smaller engine lathes-with swings usually not over 330 mm 13 inches also are available in bench type designed for the bed to be mounted on a bench on a bench or cabinet Although engine lathes are versatile and very useful because of the time required for changing and setting tools and for making measurements on the work piece thy are not suitable for quantity production Often the actual chip-production tine is less than 30 of the total cycle time In addition a skilled machinist is required for all the operations and such persons are costly and often in short supply However much of the operators time is consumed by simple repetitious adjustments and in watching chips being made Consequently to reduce or eliminate the amount of skilled labor that is required turret lathes screw machines and other types of semiautomatic and automatic lathes have been highly developed and are widely used in manufacturing2 Numerical ControlOne 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 ere 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 readerNumerical 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 technologyElectrical discharge machiningLaser cuttingElectron beam weldingNumerical control has also made machine tools more versatile than their manually operated predecessors An NC machine tool can automatically produce a wide 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 tolls and processesLike 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 US Air Force In its earliest stages NC machines were able to made 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 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 fur ther development 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 tines Fragile paper tapes simply could not withstand the rigors of a shop floor environment and this kind of repeated useThis led to the development of a special magnetic plastic tape Whereas the paper carried the programmed 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 tape which solved the problem of frequent tearing and breakage However it still left two other problemsThe most important of these was that it was difficult or impossible to change the instructions entered on the tape To made 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 tapeThe 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 an 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 host computer goes down the machine tools also experience downtime This problem led to the development of computer numerical control 3 TurningThe engine lathe one of the oldest metal removal machines has a number of useful and highly desirable attributes Today these lathes are used primarily in small shops where smaller quantities rather than large production runs are encounteredThe engine lathe has been replaced in todays production shops by a wide variety of automatic lathes such as automatic of single-point tooling for imum metal removal and the use of form tools for finish on a par with the fastest processing equipment on the scene todayTolerances for the engine lathe depend primarily on the skill of the operator The design engineer must be careful in using tolerances of an experimental part that has been produced on the engine lathe by a skilled operator In redesigning an experimental part for production economical tolerances should be usedTurret Lathes Production machining equipment must be evaluated now more than ever before this criterion for establishing the production qualification of a specific method the turret lathe merits a high rating In designing for low quantities such as 100 or 200 parts it is most economical to use the turret lathe In achieving the optimum tolerances possible on the turrets lathe the designer should strive for a minimum of operationsAutomatic Screw Machines Generally automatic screw machines fall into several categories single-spindle automatics multiple-spindle automatics and automatic chucking machines Originally designed for rapid automatic production of screws and similar threaded parts the automatic screw machine has long since exceeded the confines of this narrow field and today plays a vital role in the mass production of a variety of precision parts Quantities play an important part in the economy of the parts machined on the automatic screw machine Quantities less than on the automatic screw machine The cost of the parts machined can be reduced if the minimum economical lot size is calculated and the proper machine is selected for these quantitiesAutomatic Tracer Lathes Since surface roughness depends greatly on material turned tooling and feeds and speeds employed minimum tolerances that can be held on automatic tracer lathes are not necessarily the most economical tolerancesIn some cases tolerances of 005mm are held in continuous production using but one cut groove width can be held to 0125mm on some parts Bores and single-point finishes can be held to 00125mm On high-production runs where imum output is desirable a minimum tolerance of 0125mm is economical on both diameter and length of turn车床车床主要是为了进行车外圆车端面和镗孔等项工作而设计的机床车削很少在其他种类的机床上进行而且任何一种其他机床都不能像车床那样方便地进行车削加工由于车床还可以用来钻孔和铰孔车床的多功能性可以使工件在一次安装中完成几种加工因此在生产中使用的各种车床比任何其他种类的机床都多车床的基本部件有床身主轴箱组件尾座组件溜板组件丝杠和光杠床身是车床的基础件它能常是由经过充分正火或时效处理的灰铸铁或者球墨铁制成它是一个坚固的刚性框架所有其他基本部件都安装在床身上通常在床身上有内外两组平行的导轨有些制造厂对全部四条导轨都采用导轨尖朝上的三角形导轨即山形导轨而有的制造厂则在一组中或者两组中都采用一个三角形导轨和一个矩形导轨导轨要经过精密加工以保证其直线度精度为了抵抗磨损和擦伤大多数现代机床的导轨是经过表面淬硬的但是在操作时还应该小心以避免损伤导轨导轨上的任何误差常常意味着整个机床的精度遭到破坏主轴箱安装在内侧导轨的固定位置上一般在床身的左端它提供动力并可使工件在各种速度下回转它基本上由一个安装在精密轴承中的空心主轴和一系列变速齿轮 类似于卡车变速箱 所组成通过变速齿轮主轴可以在许多种转速下旋转大多数车床有812种转速一般按等比级数排列而且在现代机床上只需扳动24个手柄就能得到全部转速一种正在不断增长的趋势是通过电气的或者机械的装置进行无级变速由于机床的精度在很大程度上取决于主轴因此主轴的结构尺寸较大通常安装在预紧后的重型圆锥滚子轴承或球轴承中主轴中有一个贯穿全长的通孔长棒料可以通过该孔送料主轴孔的大小是车床的一个重要尺寸因此当工件必须通过主轴孔供料时它确定了能够加工的棒料毛坯的最大尺寸尾座组件主要由三部分组成底板与床身的内侧导轨配合并可以在导轨上作纵向移动底板上有一个可以使整个尾座组件夹紧在任意位置上的装置尾座体安装在底板上可以沿某种类型的键槽在底板上横向移动使尾座能与主轴箱中的主轴对正尾座的第三个组成部分是尾座套筒它是一个直径通常大约在5176mm23英寸305610mm1224英寸1270mm503658mm的车床也并不少见这些车床大部分都有切屑盘和一个安装在内部的冷却液循环系统小型的普通车床车床床面最大加工直径一般不超过330mm13英寸-被设计成台式车床其床身安装在工作台或柜子上虽然普通车床有很多用途是很有用的机床但是更换和调整刀具以及测量工件花费很多时间所以它们不适合在大量生产中应用通常它们的实际加工时间少于其总加工时间的30此外需要技术熟练的工人来操作普通车床这种工人的工资高而且很难雇到然而操作工人的大部分时间却花费在简单的重复调整和观察切屑过程上因此为了减少或者完全不雇用这类熟练工人六角车床螺纹加工车床和其他类型的半自动