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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 permits several operations to be

2、 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 bed is the backbone of a lathe.

3、 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

4、-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 as

5、sure 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 word at various speeds . Essent

6、ially, it consists of a hollow spindle, mounted in accurate bearings, and a set of transmission gears-similar to a truck transmission?through 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 sp

7、eeds 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 drives. Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings

8、, 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 material must be fed through spindle. The tailsticd assembly consists, essentially, of t

9、hree 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

10、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 screw. The size of a lathe is designated by two dimensions. The first is

11、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 second size dimension is the maximum distance between centers. The swing thus indicates

12、 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 frequently used in manufacturing. They are heavy-duty machine tools with all the compon

13、ents 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

14、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 a

15、nd 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 fo

16、r 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 watching chips being made. Consequently, to reduce or eliminate the amount of skilled labor that is required, turret lathes, screw m

17、achines, 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 concepts in the area of advanced manufacturing technologies is numerical control (NC). Prior to the advent of NC, all mach

18、ine 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 oper

19、ator. 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

20、 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 hu

21、man 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 manufacturin

22、g technology: Electrical discharge machining,Laser cutting,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 of parts,each involving an assortment of widely varied and com

23、plex 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 processes. Like so many advanced technologies, NC was born in the laboratories of t

24、he 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 made straight cuts efficiently and effectively. However, curved paths were a problem because the machine tool had

25、 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

26、 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 d

27、evelopment 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 t

28、his 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 brea

29、k 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 al

30、so 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 use. This led to the development of a special magnetic plastic tape. Whereas the paper carried the programmed inst

31、ructions 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 problems. The most important

32、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 reade

33、r 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 ass

34、ociated 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

35、 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 machin

36、e tools also 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 quan

37、tities rather than large production runs are encountered. The engine lathe has been replaced in today’s 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 processin

38、g equipment on 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 pro

39、duction, economical 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. In designing for low quantities such as

40、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 into several categories; single-spindle automa

41、tics, 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

42、 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 machi

43、ne 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 economical tolerances. In some cases, toleranc

44、es 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 0.125mm is economical on both diameter and

45、length of turn。  車床 1. 車床 　　車床主要是為了進行車外圓、車端面和鏜孔等項工作而設(shè)計的機床。車削 很少在其他種類的機床上進行， 而且任何一種其他機床都不能像車床那樣方便地 進行車削加工。由于車床還可以用來鉆孔和鉸孔，車床的多功能性可以使工件在 一次安裝中完成幾種加工。因此，在生產(chǎn)中使用的各種車床比任何其他種類的機 床都多。 車床的基本部件有：床身、主軸

46、箱組件、尾座組件、溜板組件、絲杠和光 杠。床身是車床的基礎(chǔ)件。它能常是由經(jīng)過充分正火或時效處理的灰鑄鐵或者 球墨鐵制成。它是一個堅固的剛性框架，所有其他基本部件都安裝在床身上。通 常在床身上有內(nèi)外兩組平行的導軌。有些制造廠對全部四條導軌都采用導軌尖朝上的三角形導軌（即山形導軌），而有的制造廠則在一組中或者兩組中都采用一 個三角形導軌和一個矩形導軌。導軌要經(jīng)過精密加工以保證其直線度精度。為了 抵抗磨損和擦傷，大多數(shù)現(xiàn)代機床的導軌是經(jīng)過表面淬硬的，但是在操作時還應(yīng)該小心，以避免損傷導軌。導軌上的任何誤差，常常意味著整個機床的精度遭到破壞。主軸箱安裝在內(nèi)側(cè)導軌的固定位置上，一般在床身的左端。它提供動

47、力，并可使工件在各種速度下回轉(zhuǎn)。它基本上由一個安裝在精密軸承中的空心主軸和 一系列變速齒輪(類似于卡車變速箱)所組成。通過變速齒輪，主軸可以在許多種轉(zhuǎn)速下旋轉(zhuǎn)。大多數(shù)車床有8~12種轉(zhuǎn)速。一般按等比級數(shù)排列。而且在現(xiàn)代機 床上只需扳動 2~4 個手柄，就能得到全部轉(zhuǎn)速。一種正在不斷增長的趨勢是通過電氣的或者機械的裝置進行無級變速。由于機床的精度在很大程度上取決于主軸，因此，主軸的結(jié)構(gòu)尺寸較大，通常安裝在預緊后的重型圓錐滾子軸承或球軸承中。主軸中有一個貫穿全長的通孔，長棒料可以通過該孔送料。主軸孔的大小是車床的一個重要尺寸，因此當工件必須通過主軸孔供料時，它確定了能夠加工的棒料毛坯的最大尺寸。尾

48、座組件主要由三部分組成。底板與床身的內(nèi)側(cè)導軌配合，并可以在導軌上作縱向移動。底板上有一個可以使整個尾座組件夾緊在任意位置上的裝置。尾座體安裝在底板上，可以沿某種類型的鍵槽在底板上橫向移動，使尾座能與主軸箱中的主軸對正。尾座的第三個組成部分是尾座套筒。它是一個直徑通常大約在51~76mm（2~3英寸）之間的鋼制空心圓柱體。通過手輪和螺桿，尾座套筒可以 在尾座體中縱向移入和移出幾個英寸。 車床的規(guī)格用兩個尺寸表示。第一個稱為車床的床面上最大加工直徑。這 是在車床上能夠旋轉(zhuǎn)的工件的最大直徑。 它大約是兩頂尖連線與導軌上最近點之 間距離的兩倍。第二個規(guī)格尺寸是兩頂尖之間的最大距離。車床床面上

49、最大加工 直徑表示在車床上能夠車削的最大工件直徑，而兩頂尖之間的最大距離則表示在兩個頂尖之間能夠安裝的工件的最大長度。普通車床是生產(chǎn)中最經(jīng)常使用的車床種類。它們是具有前面所敘的所有那些部件的重載機床，并且除了小刀架之外，全部刀具的運動都有機動進給。它們的規(guī)格通常是：車床床面上最大加工直徑為305~610mm（12~24英寸）；但是，（50英寸）和兩頂尖之間距離達到 3658mm 的床面上最大加工直徑達到 1270mm 車床也并不少見。這些車床大部分都有切屑盤和一個安裝在內(nèi)部的冷卻液循環(huán)系 統(tǒng)。小型的普通車床?車床床面最大加工直徑一般不超過 330mm（13 英寸）-被設(shè)計成臺式車床，其床身安裝

50、在工作臺或柜子上。 雖然普通車床有很多用途，是很有用的機床，但是更換和調(diào)整刀具以及測 量工件花費很多時間，所以它們不適合在大量生產(chǎn)中應(yīng)用。通常，它們的實際加工時間少于其總加工時間的 30\\\%。此外，需要技術(shù)熟練的工人來操作普通車床， 這種工人的工資高而且很難雇到。然而，操作工人的大部分時間卻花費在簡單的重復調(diào)整和觀察切屑過程上。因此，為了減少或者完全不雇用這類熟練工人，六 角車床、螺紋加工車床和其他類型的半自動和自動車床已經(jīng)很好地研制出來，并已經(jīng)在生產(chǎn)中得到廣泛應(yīng)用。 2.數(shù)字控制 　 先進制造技術(shù)中的一個基本的概念是數(shù)字控制（NC） 。在數(shù)控技術(shù)出現(xiàn)之 前，所有的機床都是由人工操

51、縱和控制的。在與人工控制的機床有關(guān)的很多局限 性中，操作者的技能大概是最突出的問題。采用人工控制是，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床走出來的第一步。數(shù)字控制意味著采用預先錄制的、存儲的符號指令來控制機床和其他制造 系統(tǒng)。一個數(shù)控技師的工作不是去操縱機床，而是編寫能夠發(fā)出機床操縱指令的 程序。對于一臺數(shù)控機床，其上必須安有一個被稱為閱讀機的界面裝置，用來接 受和解譯出編程指令。 發(fā)展數(shù)控技術(shù)是為了克服人類操作者的局限性，而且它確實完成了這項工 作。數(shù)字控制的機器比人工操縱的機器精度更高、生產(chǎn)出零件的一致性更好、生 產(chǎn)速度更快、而且長期的工藝裝備成本更低。數(shù)控技術(shù)的

52、發(fā)展導致了制造工藝中 其他幾項新發(fā)明的產(chǎn)生：電火花加工技術(shù)、激光切割、電子束焊接 數(shù)字控制還使得機床比它們采用有人工操的前輩們的用途更為廣泛。一臺數(shù)控機床可以自動生產(chǎn)很多類的零件，每一個零件都可以有不同的和復雜的加工過程。數(shù)控可以使生產(chǎn)廠家承擔那些對于采用人工控制的機床和工藝 來說，在經(jīng)濟上是不劃算的產(chǎn)品生產(chǎn)任務(wù)。同許多先進技術(shù)一樣，數(shù)控誕生于麻省理工學院的實驗室中。數(shù)控這個概 念是 50 年代初在美國空軍的資助下提出來的。在其最初的價段，數(shù)控機床可以 經(jīng)濟和有效地進行直線切割。 然而，曲線軌跡成為機床加工的一個問題，在編程時應(yīng)該采用一系列的水 平與豎直的臺階來生成曲線。構(gòu)成臺階的每一個線段越

53、短，曲線就越光滑。臺階 中的每一個線段都必須經(jīng)過計算。 在這個問題促使下，于1959 年誕生了自動編程工具（APT）語言。這是一個專門適用于數(shù)控的編程語言，使用類似于英語的語句來定義零件的幾何形狀， 描述切削刀具的形狀和規(guī)定必要的運動。APT語言的研究和發(fā)展是在數(shù)控技術(shù)進 一步發(fā)展過程中的一大進步。 最初的數(shù)控系統(tǒng)下今天應(yīng)用的數(shù)控系統(tǒng)是有很大差 別的。在那時的機床中，只有硬線邏輯電路。指令程序?qū)懺诖┛准垘希ㄋ髞?被塑料帶所取代），采用帶閱讀機將寫在紙帶或磁帶上的指令給機器翻譯出來。所有這些共同構(gòu)成了機床數(shù)字控制方面的巨大進步。然而，在數(shù)控發(fā)展的這個階 段中還存在著許多問題。 一個主要問題是

54、穿孔紙帶的易損壞性。在機械加工過程中，載有編程指令信息的紙帶斷裂和被撕壞是常見的事情。在機床上每加工一個零件，都需要將載 有編程指令的紙帶放入閱讀機中重新運行一次。因此，這個問題變得很嚴重。如 果需要制造 100 個某種零件，則應(yīng)該將紙帶分別通過閱讀機 100 次。易損壞的紙 帶顯然不能承受嚴配的車間環(huán)境和這種重復使用。 這就導致了一種專門的塑料磁帶的研制。在紙帶上通過采用一系列的小孔 來載有編程指令，而在塑料帶上通過采用一系列的磁點瞇載有編程指令。塑料帶 的強度比紙帶的強度要高很多，這就可以解決常見的撕壞和斷裂問題。然而，它 仍然存在著兩個問題。 其中最重要的一個問題是，對輸入到帶中指令進行

55、修改是非常困難的，或 者是根本不可能的。即使對指令程序進行最微小的調(diào)整，也必須中斷加工，制作一條新帶。而且?guī)ㄟ^閱讀機的次數(shù)還必須與需要加工的零件的個數(shù)相同。幸運的是，計算機技術(shù)的實際應(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)的問題。在形成了直接數(shù)字控制（DNC）這個概念之后，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)的問題。在直接數(shù)字控制中，幾臺機床通過數(shù)據(jù)傳輸線路聯(lián)接到一臺主計算機上。 操縱這些機床所需要的程序都存儲在這臺主計算機中。當需要時，通過數(shù)據(jù)傳輸線路提供給每臺機床。直接數(shù) 字控制是在穿孔紙帶和塑料帶基礎(chǔ)上的一大進步。然而，它敢有著同其他信賴于主計算機技術(shù)

56、一樣的局限性。當主計算機出現(xiàn)故障時，由其控制的所有機床都將停止工作。這個問題促使了計算機數(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算機的發(fā)展做好了準備。這兩種技術(shù)為計算機數(shù)控（CNC）的發(fā)打下了基礎(chǔ)。采用 CNC 技術(shù)后，每臺機床上都有一個可編程邏輯控制器或者微機對其進行數(shù)字控制。這可以使得程序被輸 入和存儲在每臺機床內(nèi)部。它還可以在機床以外編制程序，并將其下載到每臺機床中。計算機數(shù)控解決了主計算機發(fā)生故障所帶來的問題，但是它產(chǎn)生了另一個被稱為數(shù)據(jù)管理的問題。 同一個程序可能要分別裝入十個相互之間沒有通訊聯(lián)系的微機中。這個問題目前正在解決之中，它是通過采用局部區(qū)域網(wǎng)絡(luò)將各個微

57、機聯(lián)接起來，以得于更好地進行數(shù)據(jù)管理。 3.車削加工 　　普通車床作為最早的金屬切削機床的一種，目前仍然有許多有用的和為人 要的特性和為人們所需的特性?，F(xiàn)在，這些機床主要用在規(guī)模較小的工廠中，進 行小批量的生產(chǎn)，而不是進行大批量的和產(chǎn)。在現(xiàn)代的生產(chǎn)車間中，普通車床已經(jīng)被種類繁多的自動車床所取代，諸如自動仿形車床，六角車床和自動螺絲車床?，F(xiàn)在，設(shè)計人員已經(jīng)熟知先利用單刃 刀具去除大量的金屬余量，然后利用成型刀具獲得表面光潔度和精度這種加工方法的優(yōu)點。這種加工方法的生產(chǎn)速度與現(xiàn)在工廠中使用的最快的加工設(shè)備的速度相等。普通車床的加偏差主要信賴于操作者的技術(shù)熟練程度。設(shè)計工程師應(yīng)該認真地確定由

58、熟練工人在普通車床上加工的試驗件的公差。在把試驗伯重新設(shè)計為生產(chǎn)零件時，應(yīng)該選用經(jīng)濟的公差。六角車床 對生產(chǎn)加工設(shè)備來說，目前比過去更注重評價其是否具有精確的 和快速的重復加工能力。應(yīng)用這個標準來評價具體的加工方法，六角車床可以獲 得較高的質(zhì)量評定。在為小批量的零件（100~200 件）設(shè)計加工方法時，采用六角車床是最經(jīng)濟的。為了在六角車床上獲得盡可能小的公差值，設(shè)計人員應(yīng)該盡量將加工工序的 數(shù)目減至最少。自動螺絲車床自動螺絲車床通被分為以下幾種類型：單軸自動、多軸 自動和自動夾緊車床。自動螺絲車床最初是被用來對螺釘和類似的帶有螺紋的零 件進行自動化和快速加工的。但是，這種車床的用途早就超過了

59、這個狹窄的范圍。現(xiàn)在，它在許多種類的精密零件的大批量生產(chǎn)中起著重要的作用。工件的數(shù)量對 采用自動螺絲車床所加工的零件的經(jīng)濟性有較大的影響。如果工件的數(shù)量少于 1000 件，在六角車床上進行加工比在自動螺絲車床上加工要經(jīng)濟得多。如果計 算出最小經(jīng)濟批量，并且針對工件批量正確地選擇機床，就會降低零件的加工成 本。自動仿形車床因為零件的表面粗糙度在很大程度上取決于工件材料、刀具、進給量和切削速度，采用自動仿形車床加工所得到的最小公差一定是最經(jīng)濟的公差。在某些情況下，在連續(xù)生產(chǎn)過程中，只進行一次切削加工時的公差可以達到 0.05mm。對于某些零件，槽寬的公差可以達0.125mm。鏜孔和休用單刃刀具 進行精加工時，公差可達到0.0125mm。在希望獲得最大主量的大批量生產(chǎn)中， 進行直徑和長度的車削時的最小公差值為0.125mm 是經(jīng)濟的。