Unit 14 Limits and tolerances

極限與公差

??Dimensioning ?

??標(biāo)注尺寸

??????The design of a machine includes many factors other than those of determining the loads and stresses and selecting the proper materials.

???????機(jī)械設(shè)計除了計算載荷和應(yīng)力、選擇合適的材料外，還包括許多其它因素。

Before construction or manufacture can begin, it is necessary to have complete assembly and detail drawings to convey all necessary information to the shop men. The designer frequently is called upon to check the drawings before they are sent to the shop. Much experience and familiarity with manufacturing processes are needed before one can become conversant with all phases of production drawings.

在建造或制造開始前，完成裝配圖和零件圖以把必要信息傳達(dá)給車間工人是必須的。在送往車間前設(shè)計者常常被召集來檢查圖紙。而在精通生產(chǎn)圖紙的所有情況之前，需要有許多經(jīng)驗并熟悉制造工藝。

???????Drawings should be carefully checked to see that the dimensioning is done in a manner that will be most convenient and understandable to the production departments. It is obvious that a drawing should be made in such a way that it has one and only one interpretation.

???????圖紙必須仔細(xì)檢查其尺寸是否按生產(chǎn)部門最方便易懂的方式標(biāo)注。很明顯圖紙應(yīng)該只有唯一的解釋。

In particular, shop personnel should not be required to make trigonometric or other involved calculations before the production machines can be set up.

???????Dimensioning is an involved subject and long experience is required for its mastery.

尤其是不能要求車間工人在生產(chǎn)機(jī)械安排前進(jìn)行三角或其它復(fù)雜的計算。

???????尺寸標(biāo)注是一項復(fù)雜的工作，要掌握它需要有豐富的經(jīng)驗。

???????Tolerances must be placed on the dimensions of a drawing to limit the permissible variations in size because it is impossible to manufacture a part exactly to a given dimension.

???????由于要把零件加工到正好為給定尺寸是不可能的，因此圖紙的尺寸必須加上公差以限制其可允許的變化。

Although small tolerances give higher quality work and a better operating mechanism, the cost of manufacture increases rapidly as the tolerances are reduced, as indicated by the typical curve of Fig14.1. It is therefore important that the tolerances be specified at the largest values that the operating or functional considerations permit.

雖然較小公差能得到較高加工質(zhì)量和較好操作機(jī)構(gòu)，但隨著公差的減小制造成本會迅速增加，如圖14.1的典型曲線所示。因此公差被定為從操作或功能考慮允許的最大值是重要的。

???????Tolerances may be either unilateral or bilateral. In unilateral dimensioning, one tolerance is zero, and all the variations are given by the other tolerance. In bilateral dimensioning, a mean dimension is used which extends to the midpoint of the tolerance zone with equal plus and minus variations extending each way from this dimension.

???????公差既可以是單向的也可以是雙向的。單向標(biāo)注有一公差為零，所有變化都由另一公差給定。而雙向標(biāo)注則采用一平均尺寸，它將公差帶中點從該尺寸雙向擴(kuò)展為相等的正負(fù)變化范圍。

??????The development of production processes for large-volume manufacture at low cost has been largely dependent upon interchangeability of component parts. Thus the designer must determine both the proper tolerances for the individual parts, and the correct amount of clearance or interference to permit assembly with the mating parts.

???????大規(guī)模低成本制造生產(chǎn)工藝的發(fā)展很大程度取決于組成零件的互換性。因此設(shè)計者必須確定單個零件的合適公差以及配合零件裝配允許的正確間隙或過盈量。

The manner of placing tolerances on drawings depends somewhat on the kind of product or type of manufacturing process. If the tolerance on a dimension is not specifically stated, the drawing should contain a blanket note which gives the value of the tolerance for such dimensions.

在圖紙上標(biāo)注公差的方法相當(dāng)程度上依賴于產(chǎn)品的性質(zhì)或制造工藝的類型。如果尺寸公差沒有特別注明，圖紙應(yīng)該包含一個給出這些尺寸公差值的普遍適用注釋。

However, some companies do not use blanket notes on the supposition that if each dimension is considered individually, wider tolerances than those called for in the note could probably be specified. In any event it is very important that a drawing be free from ambiguities and be subject only to a single interpretation.

然而有些公司不采用普遍適用注釋，假定每個尺寸是單獨被考慮的，可能會規(guī)定出比注釋中要求的更寬的公差。在任何情況下圖紙不模棱兩可并只服從于單一的解釋是十分重要的。

??Dimension and Tolerance
尺寸和公差

??????In dimensioning a drawing, the numbers placed in the dimension lines represent dimension that are only approximate and do not represent any degree of accuracy unless so stated by the designer.

???????在圖紙標(biāo)注尺寸時，除非設(shè)計者有意標(biāo)明，注在尺寸線上的數(shù)字代表的尺寸僅僅是近似的，并不代表任何精度等級。

???????To specify a degree of accuracy, it is necessary to add tolerance figures to the dimension. Tolerance is the amount of variation permitted in the part or the total variation allowed in a given dimension.

???????為了詳細(xì)標(biāo)明精度等級，有必要在尺寸上增加公差數(shù)字。公差是零件允許的變動量或給定尺寸允許的總變動。

A shaft might have a nominal size of 2.5in.(63.5mm), but for practical reasons this figure could not be maintained in manufacturing without great cost. Hence, a certain tolerance would be added and, if a variation of±0.003in.(±0.08mm) could be permitted, the dimension would be stated 2.500±0.003(63.5±0.08mm).

一根軸可能的名義尺寸為2.5in.(63.5mm)，但由于實際原因不用大成本是不能在制造中保持這個數(shù)字的，因此要增加確定的公差。如果允許有±0.003in.(±0.08mm)的變化，則此尺寸可表達(dá)為2.500±0.003(63.5±0.08mm)。?

???????Dimensions given close tolerances mean that the part must fit properly with some other part. Both must be given tolerances in keeping with the allowance desired, the manufacturing processes available, and the minimum cost of production and assembly that will maximize profit.

???????具有緊密公差的尺寸表示該零件必須恰當(dāng)?shù)嘏c某些其它零件配合。所采用的制造工藝和使利潤最大化的最小生產(chǎn)及裝配成本都要求給定公差以保持所需允差。

Generally speaking, the cost of a part goes up as the tolerance is decreased. If a part has several or more surfaces to be machined, the cost can be excessive when little deviation is allowed from the nominal size.

一般而言，零件的成本隨著公差的減小而上升。如果一個零件有若干或較多表面要機(jī)加工，且?guī)缀醪辉试S偏離名義尺寸，則成本會超過正常合理的界限。

???????Allowance, which is sometimes confused with tolerance, has an altogether different meaning. It is the minimum clearance space intended between mating parts and represents the condition of tightest permissible fit.

???????允差，有時會跟公差混淆，但其具有完全不同的含義。它是配合零件之間最小的預(yù)期間隙空間，代表著允許的最緊配合條件。

If a shaft, size 1.498-0.003, is to fit a hole of size 1.500+0.003, the minimum size hole is 1.500 and the maximum size shaft is 1.498. Thus the allowance is 0.002 and the maximum clearance is 0.008 as based on the minimum shaft size and maximum hole dimension.

如果一根尺寸為1.498-0.003的軸與尺寸為1.500+0.003的孔配合，孔的最小尺寸為1.500而軸的最大尺寸為1.498。這樣允差就是0.002，而由最小軸尺寸和最大孔尺寸形成的最大間隙為0.008。

????????Tolerances may be either unilateral or bilateral. Unilateral tolerance means that any variation is made in only one direction from the nominal or basic dimension. Referring to the previous example, the hole is dimensioned 1.500+0.003, which represents a unilateral tolerance.

???????公差可以是單向的也可以是雙向的。單向公差意味著任何變動都是只從名義或基本尺寸出發(fā)向一個方向變動的。引用前例，孔的尺寸標(biāo)注為1.500+0.003，它表示了一個單向公差。

If the dimensions were given as 1.500±0.003, the tolerance would be bilateral; that is, it would vary both over and under the nominal dimension. The unilateral system permits changing the tolerance while still retaining the same allowance or type of fit.

如果尺寸標(biāo)為1.500±0.003，就是雙向公差；即它可以在名義尺寸之上或之下變化。單向體系允許在依然保留相同允差或配合類型的情況下改變公差。

With the bilateral system, this is not possible without also changing the nominal size dimension of one or both of the two mating parts. In mass production, where mating parts must be interchangeable, unilateral tolerances are customary. To have an interference or force fit between mating parts, the tolerances must be such as to create a zero or negative allowance.

而雙向體系在不同時改變一個或兩個配合零件名義尺寸的情況下，這是不可能做到的。大規(guī)模生產(chǎn)中配合零件必須能互換，單向公差是經(jīng)常遇到的。為了使配合零件之間具有過盈或強(qiáng)制配合，公差必須產(chǎn)生零或負(fù)允差。

??Tolerances, Limits and Fits
公差、極限和配合

???????The drawing must be a true and complete statement of the designer’s requirements expressed in such a way that the part is convenient to manufacture.

???????圖紙必須按方便制造零件的方式將設(shè)計者的要求真實和完整地表達(dá)出來。

Every dimension necessary to define the product must be stated once only and not repeated in different views. Dimensions relating to one particular feature, such as the position and size of a hole, should, where possible, appear on the same view.

對每一描述產(chǎn)品所需的尺寸都只須標(biāo)注一次而不必在不同的視圖中重復(fù)。有關(guān)同一特性的尺寸，諸如孔的位置和大小，如果可能應(yīng)出現(xiàn)在同一視圖上

???????There should be no more dimensions than are absolutely necessary, and no feature should be located by more than one dimension in any direction.

???????除絕對需要的尺寸外，不應(yīng)該有更多的尺寸；而在任意方向上，只能在一個尺寸上標(biāo)注特性要求。

It may be necessary occasionally to give an auxiliary dimension for reference, possibly for inspection. When this is so, the dimension should be enclosed in a bracket and marked for reference. Such dimensions are not governed by general tolerances.

偶爾也可能為了檢查而必須給出供參考的輔助尺寸。在這種情況下，尺寸應(yīng)該用括號括起來，以便參考。這樣的尺寸不受通用公差控制。

???????Dimensions that affect the function of the part should always be specified and not left as the sum or difference of other dimensions.

???????影響零件功能的尺寸總是應(yīng)該標(biāo)注的而不要留作其它尺寸的和或差。

If this is not done, the total permissible variation on that dimension will form the sum or difference of the other dimensions and their tolerances, and this will result in these tolerances having to be made unnecessarily tight. The overall dimension should always appear.

如果不是這樣，那尺寸允許的總的變化將形成其它尺寸及它們的公差的和或差，這會導(dǎo)致這些公差不得不定得過緊?？偝叽缫话銘?yīng)該標(biāo)注。

???????All dimensions must be governed by the general tolerance on the drawing unless otherwise stated. Usually, such a tolerance will be governed by the magnitude of the dimension. Specific tolerances must always be stated on dimensions affecting function or interchangeability.

???????除非另行說明，所有尺寸都必須受圖上的通用公差控制。一般這樣的公差受到尺寸量值的控制。在影響功能或互換性的尺寸上必須標(biāo)注專門的公差。

??????A system of tolerances is necessary to allow for the variations in accuracy that are bound to occur during manufacture, and still provide for interchangeability and correct function of the part.

???????為了允許在制造過程中必然會發(fā)生的精度變化，并提供零件的互換性和正確功能，一個公差系統(tǒng)是必需的。

???????A tolerance is the difference in a dimension in order to allow for unavoidable imperfections in workmanship. The tolerance range will depend on the accuracy of the manufacturing organisation, the machining process and the magnitude of the dimension.

???????公差是為了允許工藝上不可避免缺陷而存在的尺寸上的不同。公差范圍取決于制造機(jī)構(gòu)的精度、機(jī)加工過程和尺寸的量值。

The greater the tolerance range, the cheaper the manufacturing process. A bilateral tolerance is one where the tolerance range is disposed on both sides of the nominal dimension. A unilateral tolerance is one where the tolerance zone is on one side only of the nominal dimension, in which case the nominal dimension may form one of the limits.

公差范圍越大，則制造過程的成本就越低。雙向公差是在公稱尺寸兩側(cè)都有公差帶的公差。單向公差是僅在公稱尺寸一側(cè)有公差帶的公差，在這種情況下公稱尺寸成了兩個極限中的一個。

??????Limits are the extreme dimensions of the tolerance zone. For example, nominal dimension 30mm tolerance limits

???????極限是公差帶的極限尺寸。例如公稱尺寸30毫米?公差??極限

??????Fits depend on the relationship between the tolerance zones of two mating parts, and may be broadly classified into a clearance fit with positive allowance, a transition fit where the allowance may be either positive or negative (clearance or interference), an interference fit where the allowance is always negative.

??????配合取決于兩配合零件公差帶之間的關(guān)系，并且可以概括地分為具有正允差的間隙配合，允差可以是正或負(fù)的過渡配合和總是負(fù)允差的過盈配合。

??Type of Limits and Fits
極限和配合的類型

???????The ISO System of Limits and Fits, widely used in a number of leading metric countries, is considerably more complex than the ANSI system.

???????在一些最主要采用公制的國家中廣泛使用的ISO的極限和配合系統(tǒng)，比ANSI的極限和配合系統(tǒng)要復(fù)雜得多。

????????In this system, each part has a basic size. Each limit of size of a part, high and low, is defined by its deviation from the basic size, the magnitude and sign being obtained by subtracting the basic size from the limit in question. The difference between the two limits of size of a part is called the tolerance, an absolute amount without sign.

???????在這個系統(tǒng)中，每個零件都有基本尺寸。零件尺寸的每一極限，不管大小，都通過對基本尺寸的偏差來定義；其量值和符號由正被討論的極限減去基本尺寸得到。零件尺寸的兩個極限之差稱為公差，這是一個沒有符號的絕對量值。

??????There are three classes of fits: 1) clearance fits, 2) transition fits (the assembly may have either clearance or interference), and 3) interference fits.

???????存在三種配合：1)間隙配合，2)過渡配合(裝配后可以有間隙或過盈)，和3)過盈配合。

???????Either a shaft-basis system or a hole-basis system may be used. For any given basic size, a range of tolerances and deviations may be specified with respect to the line of zero deviation, called the zero line.

　　基軸制或基孔制均可采用。對任何給定的基本尺寸，公差范圍和偏差可以相對于被稱為零線的零偏差線來確定。

The tolerance is a function of the basic size and is designated by a number symbol, called the grade—thus the tolerance grade.

公差是基本尺寸的函數(shù)?并通過一個被稱為等級的數(shù)字符號標(biāo)明—即公差等級。

The position of the tolerance with respect to the zero line also a function of the basic size—is indicated by a letter symbol (or two letters), a capital letter for holes and a lowercase letter for shafts. Thus the specification for a hole and shaft having a basic size of 45 mm might be 45H8/g7.

公差相對于零線的位置同樣為基本尺寸的函數(shù)通過一個或兩個字母符號表達(dá)，大寫字母表示孔而小寫字母表示軸。這樣基本尺寸為45毫米的一個孔和軸配合規(guī)格可能是45H8/g7。

??????Twenty standard grades of tolerances are provided, called IT01, IT0, IT1~18, providing numerical values for each nominal diameter, in arbitrary steps up to 500mm (for example 0~3, 3~6,6~10, ?......, 400~500 mm).

???????ISO規(guī)定了二十種標(biāo)準(zhǔn)的公差等級，稱之為IT01，IT0，IT1~18，給在直至500毫米強(qiáng)行分段(例如0~3，3~6，6~10, ......, 400~500毫米)中的公稱直徑提供具體數(shù)值。

The value of the tolerance unit, i, for grades 5~16 isWhere i is in microns and D in millimeters.

對5～16級而言，公差單位i的值可用下式計算這里i的單位是微米，而D的單位是毫米。

??????Standard shaft and hole deviations similarly are provided by sets of formulas, however, for practical application, both tolerances and deviations are provided in three sets of rather complex tables.

??????標(biāo)準(zhǔn)的軸和孔偏差同樣都由若干公式提供；然而對實際應(yīng)用，公差和偏差都在三張相當(dāng)復(fù)雜的表格中規(guī)定了。

Additional tables give the values for basic sizes above 500 mm and for “Commonly Used Shafts and Holes” in two categories—“General Purpose” and “Fine Mechanisms and Horology”.

對基本尺寸大于500毫米和在“一般用途”和“精密機(jī)械和鐘表”兩個類別中的“常用的軸和孔”而言，由附加的表格給出數(shù)值。

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Unit15、Unit16中文翻譯

特種加工工藝（Ⅰ、Ⅱ）?

Ⅰ：近年來對高強(qiáng)度、高硬度、耐火材料的需求增大了，因而新加工工藝技術(shù)的進(jìn)步明顯日益重要。對這些材料來說，傳統(tǒng)工藝除磨削外幾乎都不再適用。即使使用，效率和生產(chǎn)率也是極其低的。不過，雖說有許多新工藝是為難加工材料專門開發(fā)的，但有此方法反過來也可加工那些常用材料的復(fù)雜結(jié)構(gòu)。?

這些加工方法被歸入特種加工，或者說非傳統(tǒng)加工。?

超聲加工，電子束加工，等離子射流加工，激光加工等就是特種加工工藝的代表。另外，還包括化學(xué)蝕刻工藝?；瘜W(xué)蝕刻和其他方法又不一樣，主要用來做形狀復(fù)雜而材料柔軟的工件，比如航空鋁合金。?

電加工工藝?

利用電流放電來去除材料的工藝統(tǒng)稱電加工。電加工工藝省去了傳統(tǒng)加工工藝中由于能量形式轉(zhuǎn)換而損失掉的部分，并且在加工那些日趨廣泛應(yīng)用的硬材料，合金時并不產(chǎn)生重要的加工力和磨損。?

電加工的加工刀具不必比被加工材料硬，最大切削率也與材料硬度無關(guān)。這些是它明顯的優(yōu)勢。?

同時，對電加工對象最基本的一條要求是必須導(dǎo)電。這條限制非常重要。?

電加工工藝根據(jù)其應(yīng)用要求向三種方向發(fā)展成了三類。一是通過放電工作地電火花加工機(jī)（EDM）。它通過產(chǎn)生高頻的，近乎連續(xù)的電火花來侵蝕工件以去除材料。另外兩種工藝是電化學(xué)加工和電磨削，它們都使用電解方式去除材料，是基本電解工藝的變體，與電火花加工相比，工作機(jī)理和特征都有所不同。?

電火花加工?

眾所周知電火花有侵蝕作用，而兩個不久前的發(fā)現(xiàn)使得電火花加工得以實現(xiàn)。首先，直流電火花對陽極的腐蝕作用更強(qiáng)，這對于使刀具損失減小，使切削率加大非常重要。第二，腐蝕效率在液體中大大高于在空氣中。必須指出，若電火花延續(xù)過長，會退化成不動的弧，這對加工非常不利。?

并且，電火花電路必須具備一些要素和特征，如圖15.1所示。工件與電極之間的縫中充有加壓循環(huán)的絕緣液，或者整體浸入液槽中加工。這很重要，否則電極會粘滿陽極泥而臟污。電極和工件之間的縫寬僅有千分之幾英寸，這可以由向伺服機(jī)構(gòu)通過控制進(jìn)給量來保證。?

電火花加工與工件機(jī)械性質(zhì)無關(guān)，不必考慮工件的強(qiáng)度、硬度、結(jié)構(gòu)，幾乎什么形狀都能做。切削力是零。不過，放電區(qū)溫度可到華氏幾千度，因此絕緣液要快速循環(huán)以防發(fā)生冶金反應(yīng)。?

電化學(xué)加工?

電化學(xué)加工指用電解方式去除材料。有時候電磨削也歸于此類中。?

電化學(xué)加工與電鍍激勵過程剛好相反。?

電解液扮演載流體的角色，在電極、工件縫隙間迅速流動的液體將金屬離子從作為陽極的工件體沖走，并且由于迅 速流動而不鍍在作為陽極的電極上。獲得的加工腔將是電極外形之拓印。通過一些改進(jìn)，這種工藝也可用于車，表面加工，砌縫，鋸，模壓印工藝中，用電極作為切削工具。?

成形的電極工具一般是由銅，黃銅，青銅或不銹鋼制成，電解液則是導(dǎo)電性非常優(yōu)秀的無機(jī)鹽溶液，如氯化鈉或硝酸鈉的水溶液。它們從電極中的通道大量流過，并由一個5V~25V的直流電源來營造1.5A/~8A/mm的電流密度于活化表面。?

電化學(xué)加工一般用于高強(qiáng)度材料上做形狀復(fù)雜的表面，如航空工業(yè)中的渦輪葉片、噴氣引擎部件、噴口等。它也可用于制鍛模模腔和開小孔等。?

電化學(xué)工藝產(chǎn)生無雜質(zhì)表面。實際上它甚至可用做除雜。它不會使工件發(fā)生熱變質(zhì)，也沒有切削力去作用于工件使之變形。同樣，也沒有電極的磨損，適合產(chǎn)生復(fù)雜外形，加工難加工材料。?

電磨削是電化學(xué)工藝的一個變體，工具電極包括一個轉(zhuǎn)動的研磨輪，一般由金屬粘結(jié)的金剛石制成，可導(dǎo)電。電解液被注于研磨輪和工件之間，因而會研磨輪帶動著在工件上移動。磨粒則使輪與工件間有定值間隙。研磨輪是陰極，工件是陽極，接入直流電源。?

超聲加工?

超聲加工（UCM）通過高頻振蕩的工作頭和研磨液來去除材料。超聲是指頻率高于人耳可聽到的頻率上限的聲音，一般指高于16kHz的頻率。?

超聲設(shè)備略圖如圖15.3所示，變頻器產(chǎn)生20~30kHz的，振幅0.02mm的波，它通過由軟材料制成的稱為刀架的連接物傳到刀具上，刀具則和最終所期望得到的腔非常均合。?

振動的刀具向工件施壓并連續(xù)進(jìn)給，研磨漿也就拍打在加工區(qū)域上了。研磨漿一般調(diào)到30%的濃度，研磨粒則被振動頭推往加工面，其力可達(dá)研磨粒自重之十五萬倍，從而在工件上砸出小坑。若工件易碎，許多這樣的小坑會迅速去除許多材料。?

材料去除后，伺服機(jī)構(gòu)又推動振動頭進(jìn)給，使工件與振動頭間有定寬的縫。最終，振動頭形狀壓入工件形成腔。?

超聲加工的切除率相對低，但這是唯一能經(jīng)濟(jì)地在易碎材料上制復(fù)雜形腔的辦法，由于刀具并不直觸工件，超聲加工得以在易碎件上應(yīng)用。?

?????????????????????????????????????激光束加工?

激光束加工使用了相干光源的光束來加工，這種受激輻射增強(qiáng)光就稱為激光。在特定的條件下，某些頻率的光會和激發(fā)原子中的電子產(chǎn)生一個入射光子頻率，相位完全相同的光子，這是激光產(chǎn)生，并應(yīng)用于加工的根本條件。?

激光的一個重要性質(zhì)是方向一致，光束發(fā)散只有1~2個毫弧度。這使激光有能力營造高能量密度的環(huán)境。用于切割的典型能量密度為約1.5~150MW/cm。能量較高時可以直接把固體材料汽化掉，這已用于一些激 光標(biāo)記機(jī)上。?

圖16.1所示為一激光鉆孔設(shè)備，激光束藉由透鏡幫助，在工件附近聚集，激光脈沖將該材料液化至汽化，汽化的部分又因迅速膨脹而將液化部分炸開成許多微液滴四濺開來。未飛走的部分則在孔壁凝固，它可以制0.125~1.25mm的，長徑比達(dá)100的細(xì)長孔。?

激光束加工廣泛應(yīng)用于給各種金屬，非金屬，陶瓷，復(fù)合材料做打孔等切削。由于激光加工較清潔，而復(fù)合材料在普通加工方式下又容易產(chǎn)生磨粒，激光加工成為一種前景很吸引人的革命性加工方式。?

孔徑0.005mm而長徑比達(dá)50：1的深孔也已可由激光制作，而經(jīng)濟(jì)孔徑一般為0.025mm以上，激光對金屬的最大切削厚度可達(dá)32mm。激光束加工在電氣，自動化工業(yè)中的應(yīng)用日趨廣泛。例如，油泵的吸油孔和聯(lián)軸器潤滑孔就采用激光加工。波音747飛機(jī)引擎的初級增壓渦輪葉片的冷卻孔也是激光制做的。使用激光加工可以大幅降低消耗，使之與電火花加工之間產(chǎn)生了競爭。?

激光打的孔有錐度，并且圓度不佳。大于1.25mm的孔由于能量分散一般難以加工。因此，激光切割比激光鉆孔的應(yīng)用范圍更廣泛。激光切割在營造的高速氣流中進(jìn)行。這樣可以迅速將金屬從切割區(qū)域移走。?

激光束還可用于：?

<1>.焊接?

<2>.小形，局部的熱處理，針對金屬，陶瓷的表面機(jī)械性能，耐磨性質(zhì)。?

<3>.標(biāo)記，例如字母，數(shù)字，碼等，標(biāo)記還可以用墨水，蝕刻或用沖子，打印針，尖筆，滾筒等。雖然激光方式相對昂貴一些，但考慮其精度高，生產(chǎn)率高，柔性高，易于實現(xiàn)自動化和遠(yuǎn)程控制，激光標(biāo)記，雕刻的應(yīng)用仍日益廣泛。?

電子束加工?

電子束加工的工作介質(zhì)是高速電子，它敲擊工件表面以發(fā)熱，如圖16.2，它使用50kV~200kV電壓將電子加速至光速的50%~80%，其應(yīng)用也和激光束加工相似，不過電子束加工須在真空環(huán)境中進(jìn)行，因此其應(yīng)用較激光為少，工件尺寸也須限定在真空倉尺寸以內(nèi)。?

一俟電子束觸及工件，電子的動能化為熱量。由于涉及各種機(jī)理，電子束究竟如何穿透工件我們尚不知曉。但我們知工件表面是由電子壓力和表面張力而熔化的，熔化部分迅速射出，汽化而被去除。電子束加工可以用來對許多中金屬實施精度非常高地加工。其表面質(zhì)量更佳，切割縫也比其他熱切割更窄。不過，這種設(shè)備需要特別訓(xùn)練的人員，因為電子束和金屬碰撞會產(chǎn)生傷害性的紫外線。?

射水流加工?

我們將手伸入風(fēng)或水流，會感覺它產(chǎn)生了推力，這是由液體的動量變化帶來的。實際上它就是使用液，氣為工作介質(zhì)的液力加工的原理。射水流加工可用于切削和修整。?

射水流在材料上能“鋸”出一條縫，為此，實用的水壓達(dá)400MPa，而最 強(qiáng)的壓力已達(dá)1400Mpa。射水流直徑在0.05mm~1mm之間。射水流切割機(jī)及其工作如圖16.3所示，包括塑料，纖維，橡膠，木材，紙張，皮革，絕緣與絕熱材料，磚及復(fù)合材料等。?

根據(jù)材料不同，切深可以是25mm（一英寸）或更多，汽車的乙烯樹脂擋泥板和一些車身嵌板就是由多軸機(jī)器人引導(dǎo)的射水流切開的。由于射水流不僅高效還很清潔，它也用于食品工業(yè)中對食物分割，切片。?

射水流加工的優(yōu)點有：?

切削可以從任何地方開始，無須打底孔。?

不產(chǎn)生熱量。?

不產(chǎn)生工件的歪曲，偏斜，因而適合于柔韌制造系統(tǒng)。?

工件實際上并不太受水作用而潮濕，切屑，毛刺均很少，是一種環(huán)境友好型加工工藝。?

磨粒射水流加工?

在磨粒射水流加工中，水流包含了磨粒，如碳化硅，剛玉等，因而材料去除率較普通射水流加工為高，各種厚度的金屬，非金屬，先進(jìn)復(fù)合材料都可以做普通切割或分層切割。?

這種工藝特別適用于加工熱不穩(wěn)定材料，它們不能使用生熱的方法去加工。對加強(qiáng)塑料，走刀速度可達(dá)7.5mm/min(25英寸每分)，但切割金屬時要慢得多，因此，它并不適合對生產(chǎn)率有所要求之處。據(jù)記載，能以較好質(zhì)量產(chǎn)生的孔徑約為3mm，最大孔深在25mm左右。使用多軸機(jī)器人導(dǎo)引的水刀可以將立體部件直接切至尺寸，在現(xiàn)代化的磨粒射流加工中，液流的研磨性被系統(tǒng)自動控制，噴嘴則通過使用紅寶石，藍(lán)寶石，硬質(zhì)合金基復(fù)合材料等來延長壽命。?

???光化學(xué)加工?

光化學(xué)加工也稱光蝕刻。它應(yīng)用攝影術(shù)、感光耐蝕術(shù)配合濕法化學(xué)腐蝕來從工件的特定區(qū)域去除材料。這種工藝尤其適合生產(chǎn)形狀復(fù)雜的薄片狀工件。?

1986年，Allen開發(fā)出如下的工藝步驟，如圖16.4所示。首先要印制所需圖樣于光具上，如膠片、玻片等。然后，將金屬薄片做化學(xué)清潔劑并敷以感光膠。它像照相膠片一樣，經(jīng)過強(qiáng)光曝光后會成為不溶的物質(zhì)。感光膠有干、濕兩類，使用濕式時，工件須浸涂感光膠并晾干。使用干式時，干膠片必須借助熱或壓力附于金屬片上。?

之后，須將圖樣通過曝光轉(zhuǎn)印在感光膠上。使用的是產(chǎn)生足夠光強(qiáng)和頻率的曝光燈。之后膠片拿去沖洗，留下不可溶部分附著在金屬片上。?

之后，采用氯化 ?或氯化銅與鹽酸標(biāo)準(zhǔn)混合，配制蝕刻液，蝕去未覆蓋的部分，做出工件來。?

光化學(xué)加工在裝潢、圖案生產(chǎn)中應(yīng)用日益廣泛，以制作標(biāo)志、標(biāo)簽等。同時，標(biāo)徽、說明、號碼等字符性質(zhì)標(biāo)記并入了設(shè)計之中。蝕刻得到的折痕則便于將板件折成盒狀等形態(tài)?

Part2 一單元

?Introduction前言

The central and essential ingredient of GAD/CAM

is the digital computer.〔1〕Its inherent speed and storage capacity have made it possible to achieve the advances in image processing, real-time process control, and a?multitude of other important functions that?are?simply too complex and?time-consuming to perform manually. To understand CAD/CAM?it is important to be familiar with?the?concepts and technology of the digital computer

CAD/CAM的重要組成部分是數(shù)字計算機(jī)，它固有的速度以及存儲能力似的它能夠在圖像處理，實時過程控制以及很多因太復(fù)雜太費時而人工無法完成的其他重要功能方面獲得進(jìn)步，要想懂得CAD/CAM，熟悉數(shù)字電腦的概念和技術(shù)是很重要的.

The modern digital computer is an electronic machine that can perform mathematical and logical?calculations and data processing functions in accordance with a?predetermined program of instructions. The computer itself is referred to as hardware, whereas the various programs are referred to as?software.

現(xiàn)在數(shù)字計算機(jī)是一部能夠根據(jù)預(yù)定的程序來完成數(shù)字和邏輯運算以及數(shù)據(jù)處理功能的電子設(shè)備，計算機(jī)本身稱為硬件，而各種各樣的程序稱為軟件

There are three basic hardware components of a general-purpose digital computer;

一般用途的數(shù)字計算機(jī)由三種基本硬件組成

??.Central processing unit (CPU)?微處理器

??.Memory存儲器

??.Input/output?( I/0 )section輸入/輸出設(shè)備

The relationship of these three components is illustrated in Fig. 1.1. The central processing unit?is often considered to consist of two subsections; a control unit and an arithmetic-logic unit?(ALU). 這三個組成部分的關(guān)系如圖1.1所示，中央處理器通常被認(rèn)為包含兩部分:一個控制器和一個運算器.The control unit coordinates the operations of all the other components. 控制器控制所有其他組成部分的運輸。It controls the input and output of information between the computer and the outside world through the I/O section,?synchronizes the transference of signals between the various sections of the computer, and commands?the other sections in the performance of their functions.它通過輸入/輸出端口控制電腦與外圍設(shè)備之間信息的輸入與輸出、控制電腦各部分間信號的傳輸，同時也控制其他部分完成各自的功能。?The arithmetic-logic unit carries out the?arithmetic and logic manipulations of data. 運算器完成數(shù)據(jù)的算術(shù)和邏輯運算。?It adds, subtracts, multiplies, divides, and compares?numbers according to programmed instructions. The memory of the computer is the storage unit. 它根據(jù)編制的程序完成數(shù)的加、減、乘、除和比較。存儲器完成電腦的記憶功能。The?data stored in this section are arranged in the form of words which can be conveniently transferred to?the ALU or I/0 section for processing.數(shù)據(jù)被轉(zhuǎn)譯成便于向運算器和輸入/輸出設(shè)備傳輸以進(jìn)行處理的字節(jié)形式存儲在該部分中Finally, the input/output provides the means for the computer to communicate with the external world. ?This communication is accomplished through peripheral?equipment such as readers, printers, and process interface devices.?最后，輸入/輸出設(shè)備提供電腦和外部世界的交流手段，這種交流通過像閱讀機(jī)、打印機(jī)和出口設(shè)備等外圍設(shè)備完成。?The computer may also be connected to external storage units (e. g，tapes, disks, etc) through the UO section of the computer電腦也可以通過輸入/輸出設(shè)備與外圍存儲設(shè)備（比如磁帶、磁盤）鏈接。.

????The software consists of the programs and instructions stored in memory and in external storage?units. It is the software that assigns the various functions which the user desires the system to accomplish to the computer. 軟件由程序和存儲在內(nèi)存與外存中的指令組成。軟件將使用者所要求系統(tǒng)完成的各項功能分配給計算機(jī)。?The usefulness of the computer lies in its ability to execute the instructions?quickly and accurately. 電腦的有用性在于它快速準(zhǔn)確地執(zhí)行程序的能力。?Because the contents of the computer' s memory can be easily changed, and?therefore different programs can be placed into memory, the digital computer can be used for a wide?variety of applications.因為電腦存儲的內(nèi)容你能夠很容易被改變，并且不同的程序都能夠被存入，所以數(shù)字電腦能夠用于多種應(yīng)用。

Regardless of the application, the computer executes the program through its ability to manipulate data and numbers in their most elementary form. 不考慮這些應(yīng)用，電腦能自動執(zhí)行程序并以最基本的形式完成數(shù)字和數(shù)據(jù)的運算。?The data and numbers are represented in the?computer by electrical signals which can take one of two alternative states.數(shù)據(jù)和數(shù)字在電腦中以兩種形式的電信號的一種表示。This form of representation is called the binary system. 這種表示形式叫做二進(jìn)制計數(shù)法。The more familiar decimal number system and a whole host of soft-ware languages can utilize the binary system to permit communication between computers and human?beings.更多與之類似的十進(jìn)制計數(shù)法以及很多軟件語言利用二進(jìn)制計數(shù)法在電腦和人之間實現(xiàn)交流。

Central Processing Unit (CPU)?中央處理器

????The central processing unit?(CPU)?regulates the operation of all system components and performs the arithmetic and logical operations on the data. 中央處理器控制所有系統(tǒng)組成的操作并進(jìn)行數(shù)據(jù)的算術(shù)和邏輯運算。To accomplish these functions, the CPU consists of two operating units:為了完成這些功能，中央處理器包含兩個結(jié)構(gòu)單元：

????.Control unit

????·Arithmetic-logic unit?(ALU)?控制器、運算器

The control unit coordinates the various operations specified by the program instructions. 控制器控制由程序制定的各種操作。These?operations include receiving data which enter the computer and deciding how and when the data?should be processed. The control unit directs the operation of the arithmetic-logic unit.這些操作包括接收輸入電腦的數(shù)據(jù)和決定數(shù)據(jù)的處理形式以及處理時間，控制器控制運算器的操作。?It sends data?to the ALU and tells the ALU what functions to perform on the data and where to store the results.?它將數(shù)據(jù)發(fā)送給運算器并告知運算器數(shù)據(jù)所要求的處理操作和結(jié)果的存儲位置。The capability of the control unit to accomplish these operations is provided by a set of instructions?called an executive program which is stored in memory.控制器完成這些操作的能力是由一組存儲在存儲器中被稱作執(zhí)行程序的指令程序提供的。

The arithmetic-logic unit performs operations such as addition, subtractions, and comparisons.?These operations are carried out on data in binary form. 運算器完成像加、減和比較的功能。這些功能以二進(jìn)制形式對數(shù)據(jù)進(jìn)行處理。?The logic section can also be used to alter?the sequence in which instructions are executed when certain conditions are indicated and to perform?other functions, such as editing and masking data for arithmetic operations.?當(dāng)指出某些條件時邏輯器能夠改變程序執(zhí)行的順序，也能夠完成其他功能，例如為運算操作編輯和屏蔽數(shù)據(jù)。

Both the control unit and the arithmetic-logic unit perform their functions by utilizing registers.?控制器和運算器都是通過寄存器來完成它們的功能。Computer registers are small memory devices that can receive，hold, and transfer data. Each register consists of binary cells to hold bits of data.計算機(jī)的寄存器是能夠接收、保存和傳送數(shù)據(jù)的小存儲設(shè)備。每個寄存器都由能夠保存二進(jìn)制數(shù)的二進(jìn)制單元組成。?The number of bits in the register establishes the word?length with which the computer is capable of handling. The number of bits per word can be as few as?4 (?early microcomputers ) or as many as 64 ( large scientific computers ).

Computer Programming Languages存儲器的位數(shù)代表了電腦能夠處理的字長，每個字所占位數(shù)最少到4個（早期微型計算機(jī)）最多到64個（大型科學(xué)計算機(jī)）

The binary number system could be used to represent any decimal number, alphabetic letter, or?other common symbol.?二進(jìn)制數(shù)能夠用來表示十進(jìn)制數(shù)、字母，或者其他一般符號。?Data and instructions are communicated to the computer in the form of binary?words.?In executing a program. the computer interprets the configuration of bits as an instruction to?perform electronic operations such as add，subtract, load into memory，and so forth. 數(shù)據(jù)和程序都以二進(jìn)制碼得形式輸入計算機(jī)，在執(zhí)行某一程序時，計算機(jī)通過翻譯構(gòu)成指令的字來執(zhí)行像加、減、保存等電子操作。The sequence of these binary-coded instructions defines the set of calculations and data manipulations by which the?computer executes the program.?這些二進(jìn)制編碼的順序限定了計算機(jī)執(zhí)行程序的運算組和數(shù)據(jù)運算

The binary-coded instructions that computers can understand are called machine language. Unfortunately，binary-coded instructions and data are very difficult for human programmers to read or write. 這些計算機(jī)所能識別的二進(jìn)制編碼叫做機(jī)器語言。不幸的是，對編碼人員來說由二進(jìn)制編碼所形成的指令和數(shù)據(jù)是很難讀寫的。?Also, different machines use different machine languages. 同時，不同的機(jī)器使用不同的機(jī)器語言。?To facilitate the task of computer?programming, higher-level languages are available which can be learned with relative ease by human?beings. In all there are three levels of computer programming languages;為了便于計算機(jī)編程，對人來說相對容易學(xué)習(xí)的高級語言出現(xiàn)了。計算機(jī)程序語言總共有三種：

.Machine language

.Assembly language

.Procedure-oriented?( high-level) languages機(jī)器語言、匯編語言、高級語言

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Computer Process Interfacing

計算機(jī)處理技術(shù)

To be useful, the computer must be capable of communicating with its environment. 計算機(jī)要想有用必須能和它自己的環(huán)境進(jìn)行交流。?In a data?processing system, this communication is accomplished by various input/output devices such as card?readers，printers，and CRT consoles. 在數(shù)據(jù)處理系統(tǒng)中，這種交流是通過輸入/輸出設(shè)備例如讀卡器、打印機(jī)、CRT控制板等完成的。 In computer-aided manufacturing, the environment of the computer includes not only these devices but also includes one or more manufacturing processes.?在計算機(jī)輔助制造中，計算機(jī)的環(huán)境不僅包括這些設(shè)備而且包括一種或多種制造工藝。Functioning as a process control system，the computer must be capable of sensing the important process variables from the operation and providing the necessary responses to maintain effective control over the process. 。作為過程控制系統(tǒng)，計算機(jī)必須能夠感應(yīng)來自操作的重要的處理變量并提供必需的回應(yīng)以維持有效地處理控制。?In the following sections we examine some of the important components of a?computer process control system.?下面的部分我們檢查計算機(jī)過程控制系統(tǒng)的一些重要部分制造過程數(shù)據(jù)。

Manufacturing process data. 制造過程數(shù)據(jù)。

The?data that must be?communicated between the manufacturing process and the?computer.?制造過程數(shù)據(jù)是必須在制造過程和計算機(jī)間進(jìn)行交流的。These data can be classified into three categories:這些數(shù)據(jù)可以分成3類：

.Continuous analog signals連續(xù)模擬信號

.Discrete binary data離散的二進(jìn)制數(shù)據(jù)

.Pulse data脈沖數(shù)據(jù)

????(?2 ) System interpretation of process data. ?The three categories of manufacturing process?data must be capable of interacting with the computer. 制造過程數(shù)據(jù)的這三種類型必須能和計算機(jī)進(jìn)行交流。 For monitoring the process，input data must be entered into the computer. 。對于監(jiān)控過程而言，輸入的數(shù)據(jù)必須輸入計算機(jī)。 For controlling the process，output data must be generated by the computer and converted into signals understandable by the manufacturing process.?對于控制過程而言， 輸出數(shù)據(jù)必須由計算機(jī)產(chǎn)生并轉(zhuǎn)換成制造過程能理解的信號。?There are six categories of computer-process interface representing the inputs and outputs for the three types of?process data. ?These categories are:?有六種計算機(jī)過程接口代表了過程數(shù)據(jù)三種類型的輸入和輸出。他們是：

????.analog to digital??A/D

????.Contact input觸點輸入

????.Pulse counters脈沖計數(shù)器

????.Digital to analog?D/A

????.Contact output觸點輸出

.Pulse generators觸點輸出

Computer Network Structures計算機(jī)網(wǎng)絡(luò)結(jié)構(gòu)

Network introduction網(wǎng)絡(luò)介紹

????The term?“?computer network?" refers to the actual physical connections between computers in?different areas. 計算機(jī)網(wǎng)絡(luò)這個術(shù)語是指計算機(jī)和不同的區(qū)域之間的物理連接。 Since its first appearance in 1964，computer networks have developed through many technology phases such as Multi-computer System，Local Area Network(LAN)，Metropolitan Area Network(MAN )，Wide Area Network(WAN)and Network Computing. 自1964年第一次出現(xiàn)以來，計算機(jī)網(wǎng)絡(luò)已經(jīng)發(fā)展經(jīng)歷了許多技術(shù)階段例如，多機(jī)系統(tǒng)、局域網(wǎng)、城域網(wǎng)、廣域網(wǎng)和以太網(wǎng)。 Now its appearance has become one of the most significant engineering achievements ever in human history. 現(xiàn)在它的出現(xiàn)已成為在人類歷史上最有重要意義的工程成果之一。?It can be used?for many purposes such as intercommunication，digital online service and information share. 有很多用途例如，互相聯(lián)絡(luò)、數(shù)字在線服務(wù)和信息共享。 Computer network can be used in almost every case. 計算機(jī)網(wǎng)絡(luò)幾乎可用于任何事。?The utilization of computer network in mechanical?engineering includes many scientific subjects such as Network Manufacturing, Virtual Manufacturing, Flexible Manufacturing System and Agile Manufacturing. 計算機(jī)網(wǎng)絡(luò)在機(jī)械工程上的使用包括許多科學(xué)項目例如，網(wǎng)絡(luò)制造、虛擬制造、柔性制造系統(tǒng)和敏捷制造。