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外文文獻原文
Mechanical processing is introduced
1. Lathe
The lathe is mainly for the car round face and boring, car and so on a work and design of machine tools. Turning in rarely on other kinds of machine tools, and any other machine tools are not like lathe so easily turning processing. Because of the lathe can also be used to drilling and reaming, lathe versatility can make the work piece in an installation of complete several processing. Consequently, more lathes of various types are used in manufacturing than any other machine tool.
Lathe basic parts are: lathe bed、spindle box components、the tailstock components、slip board components and screw and light poles.
The bed is the backbone of a lathe. It can often is by after a full normalizing or aging treatment of ductile iron of grey or into. It is a strong rigid frame on which all the other basic components are mounted. Usually in bed body have two set of parallel rails inside. Some manufacturers are using to all four guide rails the triangle guide pointed (i.e. prefecture, and some factory guide) in a group or is in both groups are using a triangle guide and a rectangular guide. Guide to machine to guarantee their straightness precision. In order to resist wear and scratches, most modern tools of guide is through the surface hardening, but during operation should also be careful to avoid damage guide. Guide rail, any error means the whole machine precision often undermined.
Spindle box installed in the fixed position medial guide, usually left end of the bed. It provides power, and can make the work piece under various speed in turn. It basically consists of a installed in the hollow shaft and precision bearing a series of change gear (similar to the truck gearbox) together. Through the sliding gears, spindle can swim in the many kinds of rotating speed. Most of the lathe have 8 ~ 12 kinds of speed, general form. According to arrange series But in the modern machine just pull (2 ~ 4 handle, can get full speed. A growing trend is through the electrical or mechanical device speed.
Due to the accuracy of machine tool depends largely on spindle, spindle structure size is larger, normally installed in pre-tightening after the heavy tapered roller bearings or ball bearings. Axis in a full-length through-hole throughout, long bar stock through the hole can be feeding. The size of the Lord when an important dimension is lathe, so when the work-piece must be through the main when material feeding, it confirms that can process the maximum size of the blank bar feeders.
The tailstock component mainly consists of three parts. The inside of the motherboard and lathe bed rails, can be in guide with the mobile longitudinally. Floor has a can make whole the tailstock component clamping device at any position. The tailstock bodies are installed at the bottom, along some type of the keyway in floor , make the tailstock the spindle with spindle box for positive. The tailstock third part is the tailstock sleeve. It is a diameter usually at about 51 ~ 76mm (2 ~ 3 inches) between steel hollow cylinder. Through the spindle and screw, the tailstock sleeve can in the tailstock body and move the longitudinal a few inches move.
The lathe with two dimensions specifications said. The first called lathe bed surface the largest machining diameter. This is able to rotate in lathe of the biggest diameter work piece. It is about two top attachment and guide rail of the distance of the nearest point two times. The second size is the maximum distance between the two top. Lathe bed surface in the largest machining diameter says the biggest to turning lathe, and two top diameter work piece is the maximum distance between two top means in between the work piece can be installed the maximum length.
Ordinary lathe is in the production of the most frequently used lathes type. They have all those in front of Syracuse, and heavy machine parts, all except for small knife tools outside the sport has motor feed. Their specifications are usually: lathe bed face biggest process diameter for 305 ~ 610mm (12 to 24 inches); But, the bed surface to the largest machining diameter 1270mm (50 inches) and the distance between the two top 3658mm lathe is not to unusual. Most of these lathes are installed in the plate and a scraps internal cooling fluid circulation system. Small plain lathe bed face biggest - lathe machining diameter usually less than 330mm (13 inches) is designed, and its bench-type lathe bed installed in a table or on the cabinet.
Although there are many USES, ordinary lathe is very useful, but the machine tool and replacement and adjust to measure the work piece spending a lot of time, so they are not suitable for mass production application. Usually, their actual processing time is less than 30% of its total processing time. In addition, need skilled workers to operate ordinary lathe, the worker's salary high and difficult to hire. However, most of the time but operating workers spend on simply repeating adjustment and observation on scraps process. Therefore, in order to reduce or totally not to hire this kind of skilled workers, hex lathe, threaded processing lathe and other types of semi-automatic and automatic lathe has well developed, and has been widely applied in production.
2. Digital control
One of the advanced manufacturing technologies, the basic concept is numerical control (NC). In the numerical control technology there before all of the machine tool is artificially manipulation and control. With artificially controlled machine tools in many of the limitations on the skills, the operator is probably the most prominent problem. Using artificial control is directly with the product, the quality of the skills related. Operator Digital control from artificially controlled machine tool represents the first step came out.
Digital control means that USES preliminary recording, storage of symbolic instruction to control machine tools and other manufacturing system. A nc technician job is not to manipulate tools, but that produces a machine manipulation instructions written the program. For a NC machine tool, it must Ann have a known as reading machine interface device used to accept and interpret the programming instructions.
Development of numerical control technology is in order to overcome the limitations of human operator, and it really finished the work. Digital control machine than artificially manipulated the machine precision higher, produce parts consistency better, faster, and long-term production technology and equipment costs less. CNC technology development led to the manufacturing process several other new inventions in the generation:
Electrical discharge machining technology, laser cutting, electron beam welding digital control also makes machines used artificially exercise than their predecessors' use of more widely.
A numerical control machine tool can automatic production many kind of parts, each parts can have different and complicated process. NC can make manufacturers undertake those for the artificially controlled machine tools and technology, it is not economically cost-effective products production tasks.
As with many advanced technology, CNC was born in MIT lab. NC this concept is in early 1950s under a grant from the United States air force brought out. In its initial price section, NC machine tools can economic and efficient straight-line cutting.
However, the curve track becomes a problem of the machine tool should be used when programming, in a series of horizontal and vertical steps to generate curve. Each of the steps counting constitutes the shorter and more smooth curve. Each of the steps line must pass calculation.
For this problem, in 1959 automatic programming tools (born APT) language has born. This is a special suitable for CNC programming languages, use similar to English sentences to define parts geometric shape, describe the shape and provisions cutting tools necessary movements. APT language research and development is in the numerical control technology further development in a big improvement. Initial CNC system and application of the numerical control system is today, there was a big difference between. At the time of machine tools, only have hard line logic circuit. Instruction program written in perforated tape (it was later replaced by plastic band), adopt take reading machine will be written on paper tape or tape on instructions to machine translation. All these together constitute a digital control machine have the great progress. However, in this stage of the numerical control development still have many problems.
A major problem is the easy attaint sex punched paper tape. In machining process, carrying programming instructions information tape fracture and were ripped is common things. In every processing a parts on the machine, all needs will carrying programming instructions tape into reading machine to run again. Therefore, the problem becomes very serious. If needs to make 100 some parts, it should be a tape by reading machine 100 times respectively. Easy attaint tape obviously cannot withstand severe worthy workshop environment and the repeated use.
This led to a kind of special plastic tape development. By adopting a series on the tape to produce holes in carrying programming instructions, and by using a series of plastic with magnetic point narrowed carrying programming instructions. The strength of the plastic belt than the intensity of paper tape is much higher, this can solve common torn and fracture problem. However, it still has two problems.
One of the most important questions is, with instructions to input to the amendment is very difficult, or is simply impossible. Even the most minor procedure to commands the adjustment, also must interrupt processing, making a new band. And by using reading machine with The Times must also and need the same number of parts processing. Fortunately, the practical application of computer technology in the numerical control technology resolved soon with perforated tape and plastic belt pertinent questions.
In form the direct numerical control (DNC) this concept later, can no longer using paper tape or plastic zone as the carrier of programming instructions, thus solved the related problems. In direct numerical control, a few tool machine through the data transmission on receiving a chromatic main computer. Manipulating these machines need procedures are stored in this one host computer. When required, through the data transmission lines provide each machine tool. Direct numerical control is in perforated tape and plastic belt on the basis of a big improvement. However, it is trust in the Lord with other with the limitations of computer technologies like. The main computer malfunction by the control of all machines will stop working. This problem prompted computer numerical control technology production. The development of the microprocessor for programmable logic controller and microcomputer development prepared well. These two kinds of technology for computer numerical control (CNC) hair and lay the foundation. After using CNC technology, each machine has a programmable logic controller or the digital control microcomputer. This allows the program is input and stored in every tool machine inside. It can still outside the machine, and the program downloaded to each machine tool. Computer numerical control solved the main computer failure brought about by the problem, but it has another called data management problem. The same program may be individually in polythene ten mutual communication was not the microcomputer. This problem is the currently solution, it is through using among local area network will link up with each microcomputer, to better data management.
3. Turning processing
Ordinary lathe as the first metal cutting machine, and is still a kind of known and has many useful properties and characteristics of needed for people. Now, these machine mainly USES in the factory in a small, small batch production, rather than volume production.
In the modern production workshops, ordinary lathe has been a wide variety of automatic lathes, such as automatic copy replaced fractal lathe, hex lathe and automatic screw lathe. Now, design personnel already knows how to make a single blade knives of metal removal, and by using the molding tool headroom get surface finish and precision of the processing method advantages. The processing method production speed and now used in the fastest factory of machining equipment speed equal.
Ordinary lathe with deviation mainly depends on the degree of the skilled operator. The design engineer should seriously by skilled workers is determined on the plain lathe machining test pieces of tolerance. In the test "for production parts design again, should choose economic tolerances.
Hex lathe: production and processing equipment, it to more attention than the past now whether it has to evaluate its precise and rapid repeat processing ability. Application of this standard to evaluate concrete processing methods, hex lathe can obtain higher quality evaluation. For small batch in the parts (100 to 200 pieces), the design and machining method is the most economical hex lathe. In order to obtain the lathe as small as possible with the tolerance values, designers should as far as possible the number of processes will be minimized.
Automatic screw lathe: automatic screw lathe is usually divided into the following several types: screw automatically, the single-spindle automatic and automatic clamping lathe. Automatic screw lathe was originally used to with threaded screw and similar parts for automation and rapid tooling. However, this lathe purposes would have more than the narrow scope. Now, it is in many kinds of precision components of mass production of plays an important role. The number of work piece to adopt the automatic screw lathe machining parts of the economy that have a major influence. If the number of work piece in 1000 pieces, hex lathes than in automatic screw lathe machining much want economy in processing. If the calculated minimum economic batch, and choose correct for work piece batch machine, can reduce parts processing cost.
Automatic copy form lathe: because parts surface roughness depends largely on whether the work piece material, tools, feeding and cutting speed, adopts automatic copy form lathe processing get minimum tolerance must be the most economic tolerances.
In some cases, in the continuous production process, only when a cutting the tolerance can reach 0.05 mm. For some parts, groove wider tolerance can achieve 0.125 mm. Boring and Hugh single blade knives with precision, tolerance can achieve premium mm. Hoping to gain the maximum principal amount in the mass production, diameter and length of turning the minimum for tolerance values of 0.125 mm is economic.
外文文獻中文翻譯
機械加工介紹
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。
車床基本部件有：床身、主軸箱組件、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(dǎo)軌。有些制造廠對全部四條導(dǎo)軌都采用導(dǎo)軌尖朝上的三角形導(dǎo)軌（即山形導(dǎo)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(dǎo)軌和一個矩形導(dǎo)軌。導(dǎo)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(dǎo)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(dǎo)軌。導(dǎo)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(dǎo)軌的固定位置上，一般在床身的左端。它提供動力，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(yù)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。
尾座組件主要由三部分組成。底板與床身的內(nèi)側(cè)導(dǎo)軌配合，并可以在導(dǎo)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(dǎo)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，床面上最大加工直徑達到1270mm（50英寸）和兩頂尖之間距離達到3658mm的車床也并不少見。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(fù)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(yù)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)的發(fā)展導(dǎo)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(fù)雜的加工過程。數(shù)控可以使生產(chǎn)廠家承擔(dān)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(xué)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)與今天應(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髞肀凰芰蠋〈?，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(fù)使用。
這就導(dǎo)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^利用閱讀機的次數(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)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生產(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(fù)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：自動螺絲車床通常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這個狹窄的范圍?，F(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，槽寬的公差可以達到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。