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1、精选学习资料 - - - - - - - - - 数控车床及车削加工介绍（中英文对比）1 Lathes Lathes 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 pe
2、rmits 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 tool. The essential components of a lathe are the bed, headstock assembly, tailstock assembly, and the leads crew and feed rod. The b
3、ed 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.
4、 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 ta
5、ken 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 destroyed. The 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 w
6、ord 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, an
7、d on modern lathes all the speeds can be obtained merely by moving from two to 名师归纳总结 - - - - - - -第 1 页,共 14 页精选学习资料 - - - - - - - - - four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives. Because the accuracy of a lathe is great
8、ly 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 maximum size of bar stock that can be machined when the ma
9、terial must be fed through spindle. The 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
10、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 76mm2to 3 inches in diameter, that can be moved several inches longitudinally in and out of the upper casting by means of a hand
11、 wheel and screw. The size of a lathe is designated by two dimensions. The first is known as the swing. This is the maximum 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 sec
12、ond size dimension is the maximum distance between centers. The swing thus indicates the maximum work piece diameter that can be turned in the lathe, while the distance between centers indicates the maximum length of work piece that can be mounted between centers. Engine lathes are the type most fre
13、quently 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 mm12 to 24 inchesswing and from 610 to 1219 mm24 to 48 inches center dist
14、ances, but swings up to 1270 mm50 inches and center distances 名师归纳总结 - - - - - - -第 2 页,共 14 页精选学习资料 - - - - - - - - - up to 3658mm12 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 ava
15、ilable 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. Of
16、ten 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 operator s time is consumed by simple, repetitious adjustments and in watchin
17、g 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 manufacturing. 2 Numerical Control One of the most fundamental
18、 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 oper
19、ator 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 syst
20、ems 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 名师归纳总结 - - - - - - -第 3 页,共 14 页精选学习资料 - - - - - -
21、- - - 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
22、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: Electrical discharge machining,Laser cutting,Electron beam welding. Numerical control has also made machine
23、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
24、not have been feasible from an economic perspective using manually controlled machine tolls 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
25、 U.S. 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 lin
26、es 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 de
27、fine the part geometry, describe the cutting tool configuration, 名师归纳总结 - - - - - - -第 4 页,共 14 页精选学习资料 - - - - - - - - - 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 logi
28、c 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 to
29、ols. 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 exacerbate
30、d 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 separat
31、e tines. 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 carried the programmed instructions as a series of holes punched in the tape, the plastic ta
32、pe 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 problems. The most important of these was that it was difficult or impossible to change the in
33、structions 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,
34、computer technology became a reality and soon solved the problems of NC associated with punched paper and plastic tape. 名师归纳总结 - - - - - - -第 5 页,共 14 页精选学习资料 - - - - - - - - - The development of a concept known as direct numerical control DNC solved the paper and plastic tape problems associated wi
35、th 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 machi
36、ne 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 al
37、so experience downtime. This problem led to the development of computer numerical control. 3 Turning The 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 rathe
38、r than large production runs are encountered. The engine lathe has been replaced in todays production shops by a wide variety of automatic lathes such as automatic of single-point tooling for maximum metal removal, and the use of form tools for finish on a par with the fastest processing equipment o
39、n the scene today. Tolerances 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, econ
40、omical tolerances should be used. Turret 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. 名师归纳总结 - - - - - - -第 6 页,共 14 页精选学习资料 - - - - - - -
41、- - 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 operations. Automatic Screw Machines Generally, automatic screw machines fall in
42、to 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 pl
43、ays 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
44、 lot size is calculated and the proper machine is selected for these quantities. Automatic 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 ec
45、onomical tolerances. In some cases, tolerances of 0.05mm are held in continuous production using but one cut . groove width can be held to 0.125mm on some parts. Bores and single-point finishes can be held to 0.0125mm. On high-production runs where maximum output is desirable, a minimum tolerance of
46、 0.125mm is economical on both diameter and length of turn. 中文译文1. 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便利名师归纳总结 - - - - - - -第 7 页,共 14 页精选学习资料 - - - - - - - - - 地进行车削加工；由于车床仍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
47、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；它是一个牢固的刚性框架,全部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纳导轨 尖朝上的三角形导轨（即山形导轨）,而有的制造厂就在一组中或者两组中都 采纳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；为了抗击磨损和擦伤,大多数现代机床的导轨是经过表面淬硬的,但是在 操作时仍应当当心,以防止损耗导轨；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；它供应动力,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