Unit 14 Limits and tolerances

极限与公差

• Dimensioning  

• 标注尺寸

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

       机械设计除了计算载荷和应力、选择合适的材料外，还包括许多其它因素。

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.

在建造或制造开始前，完成装配图和零件图以把必要信息传达给车间工人是必须的。在送往车间前设计者常常被召集来检查图纸。而在精通生产图纸的所有情况之前，需要有许多经验并熟悉制造工艺。

       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.

       图纸必须仔细检查其尺寸是否按生产部门最方便易懂的方式标注。很明显图纸应该只有唯一的解释。

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.

尤其是不能要求车间工人在生产机械安排前进行三角或其它复杂的计算。

       尺寸标注是一项复杂的工作，要掌握它需要有丰富的经验。

       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为给定尺寸是不可能的，因此图纸的尺寸必须加上公差以限制其可允许的变化。

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.

虽然较小公差能得到较高加工质量和较好操作机构，但随着公差的减小制造成本会迅速增加，如图14.1的典型曲线所示。因此公差被定为从操作或功能考虑允许的最大值是重要的。

       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.

       公差既可以是单向的也可以是双向的。单向标注有一公差为零，所有变化都由另一公差给定。而双向标注则采用一平均尺寸，它将公差带中点从该尺寸双向扩展为相等的正负变化范围。

      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.

       大规模低成本制造生产工艺的发展很大程度取决于组成零件的互换性。因此设计者必须确定单个零件的合适公差以及配合零件装配允许的正确间隙或过盈量。

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.

在图纸上标注公差的方法相当程度上依赖于产品的性质或制造工艺的类型。如果尺寸公差没有特别注明，图纸应该包含一个给出这些尺寸公差值的普遍适用注释。

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适用注释，假定每个尺寸是单独被考虑的，可能会规定出比注释中要求的更宽的公差。在任何情况下图纸不模棱两可并只服从于单一的解释是十分重要的。

• 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.

       在图纸标注尺寸时，除非设计者有意标明，注在尺寸线上的数字代表的尺寸仅仅是近似的，并不代表任何精度等级。

       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.

       为了详细标明精度等级，有必要在尺寸上增加公差数字。公差是零件允许的变动量或给定尺寸允许的总变动。

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).

一根轴可能的名义尺寸为2.5in.(63.5mm)，但由于实际原因不用大成本是不能在制造中保持这个数字的，因此要增加确定的公差。如果允许有±0.003in.(±0.08mm)的变化，则此尺寸可表达为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.

       具有紧密公差的尺寸表示该零件必须恰当地与某些其它零件配合。所采用的制造工艺和使利润最大化的最小生产及装配成本都要求给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，零件的成本随着公差的减小而上升。如果一个零件有若干或较多表面要机加工，且几乎不允许偏离名义尺寸，则成本会超过正常合理的界限。

       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，有时会跟公差混淆，但其具有完全不同的含义。它是配合零件之间最小的预期间隙空间，代表着允许的最紧配合条件。

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.

如果一根尺寸为1.498-0.003的轴与尺寸为1.500+0.003的孔配合，孔的最小尺寸为1.500而轴的最大尺寸为1.498。这样允差就是0.002，而由最小轴尺寸和最大孔尺寸形成的最大间隙为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.

       公差可以是单向的也可以是双向的。单向公差意味着任何变动都是只从名义或基本尺寸出发向一个方向变动的。引用前例，孔的尺寸标注为1.500+0.003，它表示了一个单向公差。

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.

如果尺寸标为1.500±0.003，就是双向公差；即它可以在名义尺寸之上或之下变化。单向体系允许在依然保留相同允差或配合类型的情况下改变公差。

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.

而双向体系在不同时改变一个或两个配合零件名义尺寸的情况下，这是不可能做到的。大规模生产中配合零件必须能互换，单向公差是经常遇到的。为了使配合零件之间具有过盈或强制配合，公差必须产生零或负允差。

• Tolerances, Limits and Fits
公差、极限和配合

       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.

       图纸必须按方便制造零件的方式将设计者的要求真实和完整地表达出来。

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.

对每一描述产品所需的尺寸都只须标注一次而不必在不同的视图中重复。有关同一特性的尺寸，诸如孔的位置和大小，如果可能应出现在同一视图上

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

       除绝对需要的尺寸外，不应该有更多的尺寸；而在任意方向上，只能在一个尺寸上标注特性要求。

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.

偶尔也可能为了检查而必须给出供参考的辅助尺寸。在这种情况下，尺寸应该用括号括起来，以便参考。这样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.

       影响零件功能的尺寸总是应该标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.

如果不是这样，那尺寸允许的总的变化将形成其它尺寸及它们的公差的和或差，这会导致这些公差不得不定得过紧。总尺寸一般应该标注。

       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.

       除非另行说明，所有尺寸都必须受图上的通用公差控制。一般这样的公差受到尺寸量值的控制。在影响功能或互换性的尺寸上必须标注专门的公差。

      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.

       为了允许在制造过程中必然会发生的精度变化，并提供零件的互换性和正确功能，一个公差系统是必需的。

       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.

       公差是为了允许工艺上不可避免缺陷而存在的尺寸上的不同。公差范围取决于制造机构的精度、机加工过程和尺寸的量值。

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.

公差范围越大，则制造过程的成本就越低。双向公差是在公称尺寸两侧都有公差带的公差。单向公差是仅在公称尺寸一侧有公差带的公差，在这种情况下公称尺寸成了两个极限中的一个。

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

       极限是公差带的极限尺寸。例如公称尺寸30毫米 公差  极限

      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.

      配合取决于两配合零件公差带之间的关系，并且可以概括地分为具有正允差的间隙配合，允差可以是正或负的过渡配合和总是负允差的过盈配合。

• Type of Limits and Fits
极限和配合的类型

       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国家中广泛使用的ISO的极限和配合系统，比ANSI的极限和配合系统要复杂得多。

        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.

       在这个系统中，每个零件都有基本尺寸。零件尺寸的每一极限，不管大小，都通过对基本尺寸的偏差来定义；其量值和符号由正被讨论的极限减去基本尺寸得到。零件尺寸的两个极限之差称为公差，这是一个没有符号的绝对量值。

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

       存在三种配合：1)间隙配合，2)过渡配合(装配后可以有间隙或过盈)，和3)过盈配合。

       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.

　　基轴制或基孔制均可采用。对任何给定的基本尺寸，公差范围和偏差可以相对于被称为零线的零偏差线来确定。

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数 并通过一个被称为等级的数字符号标明—即公差等级。

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.

公差相对于零线的位置同样为基本尺寸的函数通过一个或两个字母符号表达，大写字母表示孔而小写字母表示轴。这样基本尺寸为45毫米的一个孔和轴配合规格可能是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规定了二十种标准的公差等级，称之为IT01，IT0，IT1~18，给在直至500毫米强行分段(例如0~3，3~6，6~10, ......, 400~500毫米)中的公称直径提供具体数值。

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

对5～16级而言，公差单位i的值可用下式计算这里i的单位是微米，而D的单位是毫米。

      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.

      标准的轴和孔偏差同样都由若干公式提供；然而对实际应用，公差和偏差都在三张相当复杂的表格中规定了。

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”.

对基本尺寸大于500毫米和在“一般用途”和“精密机械和钟表”两个类别中的“常用的轴和孔”而言，由附加的表格给出数值。

 

 

Unit15、Unit16中文翻译

特种加工工艺（Ⅰ、Ⅱ） 

Ⅰ：近年来对高强度、高硬度、耐火材料的需求增大了，因而新加工工艺技术的进步明显日益重要。对这些材料来说，传统工艺除磨削外几乎都不再适用。即使使用，效率和生产率也是极其低的。不过，虽说有许多新工艺是为难加工材料专门开发的，但有此方法反过来也可加工那些常用材料的复杂结构。 

这些加工方法被归入特种加工，或者说非传统加工。 

超声加工，电子束加工，等离子射流加工，激光加工等就是特种加工工艺的代表。另外，还包括化学蚀刻工艺。化学蚀刻和其他方法又不一样，主要用来做形状复杂而材料柔软的工件，比如航空铝合金。 

电加工工艺 

利用电流放电来去除材料的工艺统称电加工。电加工工艺省去了传统加工工艺中由于能量形式转换而损失掉的部分，并且在加工那些日趋广泛应用的硬材料，合金时并不产生重要的加工力和磨损。 

电加工的加工刀具不必比被加工材料硬，最大切削率也与材料硬度无关。这些是它明显的优势。 

同时，对电加工对象最基本的一条要求是必须导电。这条限制非常重要。 

电加工工艺根据其应用要求向三种方向发展成了三类。一是通过放电工作地电火花加工机（EDM）。它通过产生高频的，近乎连续的电火花来侵蚀工件以去除材料。另外两种工艺是电化学加工和电磨削，它们都使用电解方式去除材料，是基本电解工艺的变体，与电火花加工相比，工作机理和特征都有所不同。 

电火花加工 

众所周知电火花有侵蚀作用，而两个不久前的发现使得电火花加工得以实现。首先，直流电火花对阳极的腐蚀作用更强，这对于使刀具损失减小，使切削率加大非常重要。第二，腐蚀效率在液体中大大高于在空气中。必须指出，若电火花延续过长，会退化成不动的弧，这对加工非常不利。 

并且，电火花电路必须具备一些要素和特征，如图15.1所示。工件与电极之间的缝中充有加压循环的绝缘液，或者整体浸入液槽中加工。这很重要，否则电极会粘满阳极泥而脏污。电极和工件之间的缝宽仅有千分之几英寸，这可以由向伺服机构通过控制进给量来保证。 

电火花加工与工件机械性质无关，不必考虑工件的强度、硬度、结构，几乎什么形状都能做。切削力是零。不过，放电区温度可到华氏几千度，因此绝缘液要快速循环以防发生冶金反应。 

电化学加工 

电化学加工指用电解方式去除材料。有时候电磨削也归于此类中。 

电化学加工与电镀激励过程刚好相反。 

电解液扮演载流体的角色，在电极、工件缝隙间迅速流动的液体将金属离子从作为阳极的工件体冲走，并且由于迅 速流动而不镀在作为阳极的电极上。获得的加工腔将是电极外形之拓印。通过一些改进，这种工艺也可用于车，表面加工，砌缝，锯，模压印工艺中，用电极作为切削工具。 

成形的电极工具一般是由铜，黄铜，青铜或不锈钢制成，电解液则是导电性非常优秀的无机盐溶液，如氯化钠或硝酸钠的水溶液。它们从电极中的通道大量流过，并由一个5V~25V的直流电源来营造1.5A/~8A/mm的电流密度于活化表面。 

电化学加工一般用于高强度材料上做形状复杂的表面，如航空工业中的涡轮叶片、喷气引擎部件、喷口等。它也可用于制锻模模腔和开小孔等。 

电化学工艺产生无杂质表面。实际上它甚至可用做除杂。它不会使工件发生热变质，也没有切削力去作用于工件使之变形。同样，也没有电极的磨损，适合产生复杂外形，加工难加工材料。 

电磨削是电化学工艺的一个变体，工具电极包括一个转动的研磨轮，一般由金属粘结的金刚石制成，可导电。电解液被注于研磨轮和工件之间，因而会研磨轮带动着在工件上移动。磨粒则使轮与工件间有定值间隙。研磨轮是阴极，工件是阳极，接入直流电源。 

超声加工 

超声加工（UCM）通过高频振荡的工作头和研磨液来去除材料。超声是指频率高于人耳可听到的频率上限的声音，一般指高于16kHz的频率。 

超声设备略图如图15.3所示，变频器产生20~30kHz的，振幅0.02mm的波，它通过由软材料制成的称为刀架的连接物传到刀具上，刀具则和最终所期望得到的腔非常均合。 

振动的刀具向工件施压并连续进给，研磨浆也就拍打在加工区域上了。研磨浆一般调到30%的浓度，研磨粒则被振动头推往加工面，其力可达研磨粒自重之十五万倍，从而在工件上砸出小坑。若工件易碎，许多这样的小坑会迅速去除许多材料。 

材料去除后，伺服机构又推动振动头进给，使工件与振动头间有定宽的缝。最终，振动头形状压入工件形成腔。 

超声加工的切除率相对低，但这是唯一能经济地在易碎材料上制复杂形腔的办法，由于刀具并不直触工件，超声加工得以在易碎件上应用。 

                                     激光束加工 

激光束加工使用了相干光源的光束来加工，这种受激辐射增强光就称为激光。在特定的条件下，某些频率的光会和激发原子中的电子产生一个入射光子频率，相位完全相同的光子，这是激光产生，并应用于加工的根本条件。 

激光的一个重要性质是方向一致，光束发散只有1~2个毫弧度。这使激光有能力营造高能量密度的环境。用于切割的典型能量密度为约1.5~150MW/cm。能量较高时可以直接把固体材料汽化掉，这已用于一些激 光标记机上。 

图16.1所示为一激光钻孔设备，激光束藉由透镜帮助，在工件附近聚集，激光脉冲将该材料液化至汽化，汽化的部分又因迅速膨胀而将液化部分炸开成许多微液滴四溅开来。未飞走的部分则在孔壁凝固，它可以制0.125~1.25mm的，长径比达100的细长孔。 

激光束加工广泛应用于给各种金属，非金属，陶瓷，复合材料做打孔等切削。由于激光加工较清洁，而复合材料在普通加工方式下又容易产生磨粒，激光加工成为一种前景很吸引人的革命性加工方式。 

孔径0.005mm而长径比达50：1的深孔也已可由激光制作，而经济孔径一般为0.025mm以上，激光对金属的最大切削厚度可达32mm。激光束加工在电气，自动化工业中的应用日趋广泛。例如，油泵的吸油孔和联轴器润滑孔就采用激光加工。波音747飞机引擎的初级增压涡轮叶片的冷却孔也是激光制做的。使用激光加工可以大幅降低消耗，使之与电火花加工之间产生了竞争。 

激光打的孔有锥度，并且圆度不佳。大于1.25mm的孔由于能量分散一般难以加工。因此，激光切割比激光钻孔的应用范围更广泛。激光切割在营造的高速气流中进行。这样可以迅速将金属从切割区域移走。 

激光束还可用于： 

<1>.焊接 

<2>.小形，局部的热处理，针对金属，陶瓷的表面机械性能，耐磨性质。 

<3>.标记，例如字母，数字，码等，标记还可以用墨水，蚀刻或用冲子，打印针，尖笔，滚筒等。虽然激光方式相对昂贵一些，但考虑其精度高，生产率高，柔性高，易于实现自动化和远程控制，激光标记，雕刻的应用仍日益广泛。 

电子束加工 

电子束加工的工作介质是高速电子，它敲击工件表面以发热，如图16.2，它使用50kV~200kV电压将电子加速至光速的50%~80%，其应用也和激光束加工相似，不过电子束加工须在真空环境中进行，因此其应用较激光为少，工件尺寸也须限定在真空仓尺寸以内。 

一俟电子束触及工件，电子的动能化为热量。由于涉及各种机理，电子束究竟如何穿透工件我们尚不知晓。但我们知工件表面是由电子压力和表面张力而熔化的，熔化部分迅速射出，汽化而被去除。电子束加工可以用来对许多中金属实施精度非常高地加工。其表面质量更佳，切割缝也比其他热切割更窄。不过，这种设备需要特别训练的人员，因为电子束和金属碰撞会产生伤害性的紫外线。 

射水流加工 

我们将手伸入风或水流，会感觉它产生了推力，这是由液体的动量变化带来的。实际上它就是使用液，气为工作介质的液力加工的原理。射水流加工可用于切削和修整。 

射水流在材料上能“锯”出一条缝，为此，实用的水压达400MPa，而最 强的压力已达1400Mpa。射水流直径在0.05mm~1mm之间。射水流切割机及其工作如图16.3所示，包括塑料，纤维，橡胶，木材，纸张，皮革，绝缘与绝热材料，砖及复合材料等。 

根据材料不同，切深可以是25mm（一英寸）或更多，汽车的乙烯树脂挡泥板和一些车身嵌板就是由多轴机器人引导的射水流切开的。由于射水流不仅高效还很清洁，它也用于食品工业中对食物分割，切片。 

射水流加工的优点有： 

切削可以从任何地方开始，无须打底孔。 

不产生热量。 

不产生工件的歪曲，偏斜，因而适合于柔韧制造系统。 

工件实际上并不太受水作用而潮湿，切屑，毛刺均很少，是一种环境友好型加工工艺。 

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，刚玉等，因而材料去除率较普通射水流加工为高，各种厚度的金属，非金属，先进复合材料都可以做普通切割或分层切割。 

这种工艺特别适用于加工热不稳定材料，它们不能使用生热的方法去加工。对加强塑料，走刀速度可达7.5mm/min(25英寸每分)，但切割金属时要慢得多，因此，它并不适合对生产率有所要求之处。据记载，能以较好质量产生的孔径约为3mm，最大孔深在25mm左右。使用多轴机器人导引的水刀可以将立体部件直接切至尺寸，在现代化的磨粒射流加工中，液流的研磨性被系统自动控制，喷嘴则通过使用红宝石，蓝宝石，硬质合金基复合材料等来延长寿命。 

   光化学加工 

光化学加工也称光蚀刻。它应用摄影术、感光耐蚀术配合湿法化学腐蚀来从工件的特定区域去除材料。这种工艺尤其适合生产形状复杂的薄片状工件。 

1986年，Allen开发出如下的工艺步骤，如图16.4所示。首先要印制所需图样于光具上，如胶片、玻片等。然后，将金属薄片做化学清洁剂并敷以感光胶。它像照相胶片一样，经过强光曝光后会成为不溶的物质。感光胶有干、湿两类，使用湿式时，工件须浸涂感光胶并晾干。使用干式时，干胶片必须借助热或压力附于金属片上。 

之后，须将图样通过曝光转印在感光胶上。使用的是产生足够光强和频率的曝光灯。之后胶片拿去冲洗，留下不可溶部分附着在金属片上。 

之后，采用氯化  或氯化铜与盐酸标准混合，配制蚀刻液，蚀去未覆盖的部分，做出工件来。 

光化学加工在装潢、图案生产中应用日益广泛，以制作标志、标签等。同时，标徽、说明、号码等字符性质标记并入了设计之中。蚀刻得到的折痕则便于将板件折成盒状等形态 

Part2 一单元

 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的重要组成部分是数字计算机，它固有的速度以及存储能力似的它能够在图像处理，实时过程控制以及很多因太复杂太费时而人工无法完成的其他重要功能方面获得进步，要想懂得CAD/CAM，熟悉数字电脑的概念和技术是很重要的.

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.

现在数字计算机是一部能够根据预定的程序来完成数字和逻辑运算以及数据处理功能的电子设备，计算机本身称为硬件，而各种各样的程序称为软件

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

一般用途的数字计算机由三种基本硬件组成

  .Central processing unit (CPU) 微处理器

  .Memory存储器

  .Input/output ( I/0 )section输入/输出设备

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). 这三个组成部分的关系如图1.1所示，中央处理器通常被认为包含两部分:一个控制器和一个运算器.The control unit coordinates the operations of all the other components. 控制器控制所有其他组成部分的运输。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.它通过输入/输出端口控制电脑与外围设备之间信息的输入与输出、控制电脑各部分间信号的传输，同时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. 运算器完成数据的算术和逻辑运算。 It adds, subtracts, multiplies, divides, and compares numbers according to programmed instructions. The memory of the computer is the storage unit. 它根据编制的程序完成数的加、减、乘、除和比较。存储器完成电脑的记忆功能。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.数据被转译成便于向运算器和输入/输出设备传输以进行处理的字节形式存储在该部分中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，输入/输出设备提供电脑和外部世界的交流手段，这种交流通过像阅读机、打印机和出口设备等外围设备完成。 The computer may also be connected to external storage units (e. g，tapes, disks, etc) through the UO section of the computer电脑也可以通过输入/输出设备与外围存储设备（比如磁带、磁盘）链接。.

    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. 软件由程序和存储在内存与外存中的指令组成。软件将使用者所要求系统完成的各项功能分配给计算机。 The usefulness of the computer lies in its ability to execute the instructions quickly and accurately. 电脑的有用性在于它快速准确地执行程序的能力。 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.因为电脑存储的内容你能够很容易被改变，并且不同的程序都能够被存入，所以数字电脑能够用于多种应用。

Regardless of the application, the computer executes the program through its ability to manipulate data and numbers in their most elementary form. 不考虑这些应用，电脑能自动执行程序并以最基本的形式完成数字和数据的运算。 The data and numbers are represented in the computer by electrical signals which can take one of two alternative states.数据和数字在电脑中以两种形式的电信号的一种表示。This form of representation is called the binary system. 这种表示形式叫做二进制计数法。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.更多与之类似的十进制计数法以及很多软件语言利用二进制计数法在电脑和人之间实现交流。

Central Processing Unit (CPU) 中央处理器

    The central processing unit (CPU) regulates the operation of all system components and performs the arithmetic and logical operations on the data. 中央处理器控制所有系统组成的操作并进行数据的算术和逻辑运算。To accomplish these functions, the CPU consists of two operating units:为了完成这些功能，中央处理器包含两个结构单元：

    .Control unit

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

The control unit coordinates the various operations specified by the program instructions. 控制器控制由程序制定的各种操作。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.这些操作包括接收输入电脑的数据和决定数据的处理形式以及处理时间，控制器控制运算器的操作。 It sends data to the ALU and tells the ALU what functions to perform on the data and where to store the results. 它将数据发送给运算器并告知运算器数据所要求的处理操作和结果的存储位置。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.控制器完成这些操作的能力是由一组存储在存储器中被称作执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. 运算器完成像加、减和比较的功能。这些功能以二进制形式对数据进行处理。 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. 当指出某些条件时逻辑器能够改变程序执行的顺序，也能够完成其他功能，例如为运算操作编辑和屏蔽数据。

Both the control unit and the arithmetic-logic unit perform their functions by utilizing registers. 控制器和运算器都是通过寄存器来完成它们的功能。Computer registers are small memory devices that can receive，hold, and transfer data. Each register consists of binary cells to hold bits of data.计算机的寄存器是能够接收、保存和传送数据的小存储设备。每个寄存器都由能够保存二进制数的二进制单元组成。 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存储器的位数代表了电脑能够处理的字长，每个字所占位数最少到4个（早期微型计算机）最多到64个（大型科学计算机）

The binary number system could be used to represent any decimal number, alphabetic letter, or other common symbol. 二进制数能够用来表示十进制数、字母，或者其他一般符号。 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. 数据和程序都以二进制码得形式输入计算机，在执行某一程序时，计算机通过翻译构成指令的字来执行像加、减、保存等电子操作。The sequence of these binary-coded instructions defines the set of calculations and data manipulations by which the computer executes the program. 这些二进制编码的顺序限定了计算机执行程序的运算组和数据运算

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. 这些计算机所能识别的二进制编码叫做机器语言。不幸的是，对编码人员来说由二进制编码所形成的指令和数据是很难读写的。 Also, different machines use different machine languages. 同时，不同的机器使用不同的机器语言。 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;为了便于计算机编程，对人来说相对容易学习的高级语言出现了。计算机程序语言总共有三种：

.Machine language

.Assembly language

.Procedure-oriented ( high-level) languages机器语言、汇编语言、高级语言

 

 

 

 

Computer Process Interfacing

计算机处理技术

To be useful, the computer must be capable of communicating with its environment. 计算机要想有用必须能和它自己的环境进行交流。 In a data processing system, this communication is accomplished by various input/output devices such as card readers，printers，and CRT consoles. 在数据处理系统中，这种交流是通过输入/输出设备例如读卡器、打印机、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. 在计算机辅助制造中，计算机的环境不仅包括这些设备而且包括一种或多种制造工艺。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. 。作为过程控制系统，计算机必须能够感应来自操作的重要的处理变量并提供必需的回应以维持有效地处理控制。 In the following sections we examine some of the important components of a computer process control system. 下面的部分我们检查计算机过程控制系统的一些重要部分制造过程数据。

Manufacturing process data. 制造过程数据。

The data that must be communicated between the manufacturing process and the computer. 制造过程数据是必须在制造过程和计算机间进行交流的。These data can be classified into three categories:这些数据可以分成3类：

.Continuous analog signals连续模拟信号

.Discrete binary data离散的二进制数据

.Pulse data脉冲数据

    ( 2 ) System interpretation of process data.  The three categories of manufacturing process data must be capable of interacting with the computer. 制造过程数据的这三种类型必须能和计算机进行交流。 For monitoring the process，input data must be entered into the computer. 。对于监控过程而言，输入的数据必须输入计算机。 For controlling the process，output data must be generated by the computer and converted into signals understandable by the manufacturing process. 对于控制过程而言， 输出数据必须由计算机产生并转换成制造过程能理解的信号。 There are six categories of computer-process interface representing the inputs and outputs for the three types of process data.  These categories are: 有六种计算机过程接口代表了过程数据三种类型的输入和输出。他们是：

    .analog to digital  A/D

    .Contact input触点输入

    .Pulse counters脉冲计数器

    .Digital to analog D/A

    .Contact output触点输出

.Pulse generators触点输出

Computer Network Structures计算机网络结构

Network introduction网络介绍

    The term “ computer network " refers to the actual physical connections between computers in different areas. 计算机网络这个术语是指计算机和不同的区域之间的物理连接。 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年第一次出现以来，计算机网络已经发展经历了许多技术阶段例如，多机系统、局域网、城域网、广域网和以太网。 Now its appearance has become one of the most significant engineering achievements ever in human history. 现在它的出现已成为在人类历史上最有重要意义的工程成果之一。 It can be used for many purposes such as intercommunication，digital online service and information share. 有很多用途例如，互相联络、数字在线服务和信息共享。 Computer network can be used in almost every case. 计算机网络几乎可用于任何事。 The utilization of computer network in mechanical engineering includes many scientific subjects such as Network Manufacturing, Virtual Manufacturing, Flexible Manufacturing System and Agile Manufacturing. 计算机网络在机械工程上的使用包括许多科学项目例如，网络制造、虚拟制造、柔性制造系统和敏捷制造。