同济大学机械工程专业英语翻译

目录 UNIT 1 ADVANCED ENGINEERING MATERIALS - 1 - UNIT 2 HEAT TREATMENT OF METALS - 6 - UNIT 3 CASTING PROCESSES - 15 - UNIT 4 FORGING PROCESSES - 21 - UNIT 5 POWDER METALLURGY - 26 - UNIT 6 INJECTION MOLDING - 32 - UNIT 7 METAL CUTTING - 38 - UNIT 8 GRINDING - 45 - UNIT 9 LAPPING POLISHING - 49 - UNIT 10 SURFACE ENGINEERING - 51 - UNIT 12 DRILLING AND MILLING - 63 - UNIT 13 JIGS AND FIXTURES - 68 - UNIT 14 LIMIT AND TOLERANCES - 72 - 特种加工工艺（Ⅰ、Ⅱ） - 77 - UNIT 1 Advanced Engineering Materials Types of Materials材料的类型 Materials may be grouped in several ways. Scientists often classify materials by their state: solid, liquid, or gas. They also separate them into organic (once living) and inorganic (never living) materials.材料可以按多种方法分类。科学家常根据状态将材料分为：固体、液体或气体。他们也把材料分为有机材料(曾经有生命的)和无机材料(从未有生命的)。

For industrial purposes, materials are divided into engineering materials or nonengineering materials. Engineering materials are those used in manufacture and become parts of products.就工业效用而言，材料被分为工程材料和非工程材料。那些用于加工制造并成为产品组成部分的就是工程材料。

Nonengineering materials are the chemicals, fuels, lubricants, and other materials used in the manufacturing process, which do not become part of the product.非工程材料则是化学品、燃料、润滑剂以及其它用于加工制造过程但不成为产品组成部分的材料。

Engineering materials may be further subdivided into: ①Metal ②Ceramics ③Composite ④Polymers, etc.工程材料还能进一步细分为：①金属材料②陶瓷材料③复合材料 ④聚合材料，等等。

Metals and Metal Alloys 金属和金属合金 Metals are elements that generally have good electrical and thermal conductivity. Many metals have high strength, high stiffness, and have good ductility. 金属就是通常具有良好导电性和导热性的元素。许多金属具有高强度、高刚性以及良好的延展性。

Some metals, such as iron, cobalt and nickel, are magnetic. At low temperatures, some metals and intermetallic compounds become superconductors.某些金属能被磁化，例如铁、钴和镍。在极低的温度下，某些金属和金属化合物能转变成超导体。

What is the difference between an alloy and a pure metal? Pure metals are elements which come from a particular area of the periodic table. Examples of pure metals include copper in electrical wires and aluminum in cooking foil and beverage cans. 合金与纯金属的区别是什么？纯金属是取自元素周期表中特定位置的元素。例如电线中的铜和制造烹饪箔及饮料罐的铝。

Alloys contain more than one metallic element. Their properties can be changed by changing the elements present in the alloy. Examples of metal alloys include stainless steel which is an alloy of iron, nickel, and chromium; and gold jewelry which usually contains an alloy of gold and nickel.合金则包含不止一种金属元素。合金的性质能通过改变其中元素的存在而改变。金属合金的例子有：不锈钢是一种铁、镍和铬的合金，以及金饰品通常含有金镍合金。

Why are metals and alloys used? Many metals and alloys have high densities and are used in applications which require a high mass-to-volume ratio. 为什么要使用金属和合金？许多金属和合金都具有高密度，因此被用在需要较高质量体积比的场合。

Some metal alloys, such as those based on aluminum, have low densities and are used in aerospace applications for fuel economy. Many alloys also have high fracture toughness, which means they can withstand impact and are durable. 某些金属合金，例如铝基合金，其密度低，可用于航空航天以节省燃料。许多合金还具有高断裂韧性，这意味着它们能经得起冲击并且是耐用的。

What are some important properties of metals? Density is defined as a material’s mass divided by its volume. Most metals have relatively high densities, especially compared to polymers. 金属有哪些重要特性？密度定义为材料的质量与其体积之比。大多数金属密度相对较高，尤其是与聚合物相比较而言。

Materials with high densities often contain atoms with high atomic numbers, such as gold or lead. However, some metals such as aluminum or magnesium have low densities, and are used in applications that require other metallic properties but also require low weight.高密度材料通常由较大原子序数原子构成，例如金或铅。然而，诸如铝或镁之类的一些金属则具有低密度，并被用于既需要金属特性又要求重量轻的场合。

Fracture toughness can be described as a material’s ability to avoid fracture, especially when a flaw is introduced. Metals can generally contain nicks and dents without weakening very much, and are impact resistant. A football player counts on this when he trusts that his facemask won’t shatter.断裂韧性可以描述为材料防止断裂特别是出现缺陷时不断裂的能力。金属一般能在有缺口和凹痕的情况下不显著削弱，并且能抵抗冲击。橄榄球运动员据此相信他的面罩不会裂成碎片。

Plastic deformation is the ability of bend or deform before breaking. As engineers, we usually design materials so that they don’t deform under normal conditions. You don’t want your car to lean to the east after a strong west wind. 塑性变形就是在断裂前弯曲或变形的能力。作为工程师，设计时通常要使材料在正常条件下不变形。没有人愿意一阵强烈的西风过后自己的汽车向东倾斜。

However, sometimes we can take advantage of plastic deformation. The crumple zones in a car absorb energy by undergoing plastic deformation before they break.然而，有时我们也能利用塑性变形。汽车上压皱的区域在它们断裂前通过经历塑性变形来吸收能量。

The atomic bonding of metals also affects their properties. In metals, the outer valence electrons are shared among all atoms, and are free to travel everywhere. Since electrons conduct heat and electricity, metals make good cooking pans and electrical wires. 金属的原子连结对它们的特性也有影响。在金属内部，原子的外层阶电子由所有原子共享并能到处自由移动。由于电子能导热和导电，所以金属适合做好的烹饪锅和电线。

It is impossible to see through metals, since these valence electrons absorb any photons of light which reach the metal. No photons pass through.因为这些阶电子吸收到达金属的光子，所以透过金属不可能看得见。没有光子能通过金属。

Alloys are compounds consisting of more than one metal. Adding other metals can affect the density, strength, fracture toughness, plastic deformation, electrical conductivity and environmental degradation. 合金是由一种以上金属组成的混合物。加一些其它金属能影响密度、强度、断裂韧性、塑性变形、导电以及耐环境退化等性能。

For example, adding a small amount of iron to aluminum will make it stronger. Also, adding some chromium to steel will slow the rusting process, but will make it more brittle. 例如，往铝里加少量铁可使其更强。同样，在钢里加一些铬能减缓它的生锈过程，但也将使它较脆。

Ceramics and Glasses陶瓷和玻璃 A ceramic is often broadly defined as any inorganic nonmetallic material． By this definition, ceramic materials would also include glasses; however, many materials scientists add the stipulation that “ceramic” must also be crystalline.陶瓷通常被概括地定义为无机的非金属材料。照此定义，陶瓷材料也应包括玻璃；
然而许多材料科学家添加了“陶瓷”必须同时是晶体物组成的约定。

A glass is an inorganic nonmetallic material that does not have a crystalline structure. Such materials are said to be amorphous.玻璃是没有晶体状结构的无机非金属材料。这种材料被称为非结晶质材料。

Properties of Ceramics and Glasses陶瓷和玻璃的特性 Some of the useful properties of ceramics and glasses include high melting temperature, low density, high strength, stiffness, hardness, wear resistance, and corrosion resistance.高熔点、低密度、高强度、高刚性、高硬度、高耐磨性和抗腐蚀性是陶瓷和玻璃的一些有用特性。

Many ceramics are good electrical and thermal insulators. Some ceramics have special properties: some ceramics are magnetic materials; some are piezoelectric materials; and a few special ceramics are superconductors at very low temperatures. Ceramics and glasses have one major drawback: they are brittle.许多陶瓷都是电和热的良绝缘体。某些陶瓷还具有一些特殊性能：有些是磁性材料，有些是压电材料，还有些特殊陶瓷在极低温度下是超导体。陶瓷和玻璃都有一个主要的缺点：它们容易破碎。

Ceramics are not typically formed from the melt. This is because most ceramics will crack extensively (i.e. form a powder) upon cooling from the liquid state. 陶瓷一般不是由熔化形成的。因为大多数陶瓷在从液态冷却时将会大量地破碎(即形成粉末)。

Hence, all the simple and efficient manufacturing techniques used for glass production such as casting and blowing, which involve the molten state, cannot be used for the production of crystalline ceramics. Instead, “sintering” or “firing” is the process typically used. 因此，所有用于玻璃生产的简单有效的—诸如浇铸和吹制这些涉及熔化的技术都不能用于由晶体物组成的陶瓷的生产。作为替代，一般采用“烧结”或“焙烧”工艺。

In sintering, ceramic powders are processed into compacted shapes and then heated to temperatures just below the melting point. At such temperatures, the powders react internally to remove porosity and fully dense articles can be obtained. 在烧结过程中，陶瓷粉末先挤压成型然后加热到略低于熔点温度。在这样的温度下，粉末内部起反应去除孔隙并得到十分致密的物品。

An optical fiber contains three layers: a core made of highly pure glass with a high refractive index for the light to travel, a middle layer of glass with a lower refractive index known as the cladding which protects the core glass from scratches and other surface imperfections, and an out polymer jacket to protect the fiber from damage.光导纤维有三层：核心由高折射指数高纯光传输玻璃制成，中间层为低折射指数玻璃，是保护核心玻璃表面不被擦伤和完整性不被破坏的所谓覆层，外层是聚合物护套，用于保护光导纤维不受损。

In order for the core glass to have a higher refractive index than the cladding, the core glass is doped with a small, controlled amount of an impurity, or dopant, which causes light to travel slower, but does not absorb the light. 为了使核心玻璃有比覆层大的折射指数，在其中掺入微小的、可控数量的能减缓光速而不会吸收光线的杂质或搀杂剂。

Because the refractive index of the core glass is greater than that of the cladding, light traveling in the core glass will remain in the core glass due to total internal reflection as long as the light strikes the core/cladding interface at an angle greater than the critical angle. 由于核心玻璃的折射指数比覆层大，只要在全内反射过程中光线照射核心/覆层分界面的角度比临界角大，在核心玻璃中传送的光线将仍保留在核心玻璃中。

The total internal reflection phenomenon, as well as the high purity of the core glass, enables light to travel long distances with little loss of intensity.全内反射现象与核心玻璃的高纯度一样，使光线几乎无强度损耗传递长距离成为可能。

Composites复合材料 Composites are formed from two or more types of materials. Examples include polymer/ceramic and metal/ceramic composites. Composites are used because overall properties of the composites are superior to those of the individual components.复合材料由两种或更多材料构成。例子有聚合物/陶瓷和金属/陶瓷复合材料。之所以使用复合材料是因为其全面性能优于组成部分单独的性能。

For example: polymer/ceramic composites have a greater modulus than the polymer component, but aren’t as brittle as ceramics.Two types of composites are: fiber-reinforced composites and particle-reinforced composites.例如：聚合物/陶瓷复合材料具有比聚合物成分更大的模量，但又不像陶瓷那样易碎。复合材料有两种：纤维加强型复合材料和微粒加强型复合材料。

Fiber-reinforced Composites纤维加强型复合材料 Reinforcing fibers can be made of metals, ceramics, glasses, or polymers that have been turned into graphite and known as carbon fibers. Fibers increase the modulus of the matrix material. 加强纤维可以是金属、陶瓷、玻璃或是已变成石墨的被称为碳纤维的聚合物。纤维能加强基材的模量。

The strong covalent bonds along the fiber’s length give them a very high modulus in this direction because to break or extend the fiber the bonds must also be broken or moved.沿着纤维长度有很强结合力的共价结合在这个方向上给予复合材料很高的模量，因为要损坏或拉伸纤维就必须破坏或移除这种结合。

Fibers are difficult to process into composites, making fiber-reinforced composites relatively expensive.把纤维放入复合材料较困难，这使得制造纤维加强型复合材料相对昂贵。

Fiber-reinforced composites are used in some of the most advanced, and therefore most expensive sports equipment, such as a time-trial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix. 纤维加强型复合材料用于某些最先进也是最昂贵的运动设备，例如计时赛竞赛用自行车骨架就是用含碳纤维的热固塑料基材制成的。

Body parts of race cars and some automobiles are composites made of glass fibers (or fiberglass) in a thermoset matrix. 竞赛用汽车和某些机动车的车体部件是由含玻璃纤维(或玻璃丝)的热固塑料基材制成的。

Fibers have a very high modulus along their axis, but have a low modulus perpendicular to their axis. Fiber composite manufacturers often rotate layers of fibers to avoid directional variations in the modulus.纤维在沿着其轴向有很高的模量，但垂直于其轴向的模量却较低。纤维复合材料的制造者往往旋转纤维层以防模量产生方向变化。

Particle-reinforced composites微粒加强型复合材料 Particles used for reinforcing include ceramics and glasses such as small mineral particles, metal particles such as aluminum, and amorphous materials, including polymers and carbon black.用于加强的微粒包含了陶瓷和玻璃之类的矿物微粒、铝之类的金属微粒以及包括聚合物和碳黑的非结晶质微粒。

Particles are used to increase the modulus of the matrix, to decrease the permeability of the matrix, to decrease the ductility of the matrix. An example of particle-reinforced composites is an automobile tire which has carbon black particles in a matrix of polyisobutylene elastomeric polymer.微粒用于增加基材的模量、减少基材的渗透性和延展性。微粒加强型复合材料的一个例子是机动车胎，它就是在聚异丁烯人造橡胶聚合物基材中加入了碳黑微粒。

Polymers聚合材料 A polymer has a repeating structure, usually based on a carbon backbone. The repeating structure results in large chainlike molecules. Polymers are useful because they are lightweight, corrosion resistant, easy to process at low temperatures and generally inexpensive.聚合物具有一般是基于碳链的重复结构。这种重复结构产生链状大分子。由于重量轻、耐腐蚀、容易在较低温度下加工并且通常较便宜，聚合物是很有用的。

Some important characteristics of polymers include their size (or molecular weight), softening and melting points, crystallinity, and structure. The mechanical properties of polymers generally include low strength and high toughness. Their strength is often improved using reinforced composite structures.聚合材料具有一些重要特性，包括尺寸(或分子量)、软化及熔化点、结晶度和结构。聚合材料的机械性能一般表现为低强度和高韧性。它们的强度通常可采用加强复合结构来改善。

Important Characteristics of Polymers聚合材料的重要特性 Size. Single polymer molecules typically have molecular weights between 10,000 and 1,000,000g/mol—that can be more than 2,000 repeating units depending on the polymer structure! 尺寸：单个聚合物分子一般分子量为10,000到1,000,000g/mol之间，具体取决于聚合物的结构—这可以比2,000个重复单元还多！ The mechanical properties of a polymer are significantly affected by the molecular weight, with better engineering properties at higher molecular weights.聚合物的分子量极大地影响其机械性能，分子量越大，工程性能也越好。

Thermal transitions. The softening point (glass transition temperature) and the melting point of a polymer will determine which it will be suitable for applications. These temperatures usually determine the upper limit for which a polymer can be used.热转换性：聚合物的软化点(玻璃状转化温度)和熔化点决定了它是否适合应用。这些温度通常决定聚合物能否使用的上限。

For example, many industrially important polymers have glass transition temperatures near the boiling point of water (100℃, 212℉), and they are most useful for room temperature applications. Some specially engineered polymers can withstand temperatures as high as 300℃(572℉).例如，许多工业上的重要聚合物其玻璃状转化温度接近水的沸点(100℃, 212℉)，它们被广泛用于室温下。而某些特别制造的聚合物能经受住高达300℃(572℉)的温度。

Crystallinity. Polymers can be crystalline or amorphous, but they usually have a combination of crystalline and amorphous structures (semi-crystalline).结晶度：聚合物可以是晶体状的或非结晶质的，但它们通常是晶体状和非结晶质结构的结合物(半晶体)。

Interchain interactions. The polymer chains can be free to slide past one another (thermo-plastic) or they can be connected to each other with crosslinks (thermoset or elastomer). Thermo-plastics can be reformed and recycled, while thermosets and elastomers are not reworkable.链间的相互作用：聚合物的分子链可以自由地彼此滑动(热可塑性)或通过交键互相连接(热固性或弹性)。热可塑性材料可以重新形成和循环使用，而热固性与弹性材料则是不能再使用的。

Intrachain structure. The chemical structure of the chains also has a tremendous effect on the properties. Depending on the structure the polymer may be hydrophilic or hydrophobic (likes or hates water), stiff or flexible, crystalline or amorphous, reactive or unreactive.链内结构：分子链的化学结构对性能也有很大影响。根据各自的结构不同，聚合物可以是亲水的或憎水的(喜欢或讨厌水)、硬的或软的、晶体状的或非结晶质的、易起反应的或不易起反应的。

UNIT 2 Heat Treatment of Metals The understanding of heat treatment is embraced by the broader study of metallurgy. Metallurgy is the physics, chemistry, and engineering related to metals from ore extraction to the final product. 对热处理的理解包含于对冶金学较广泛的研究。冶金学是涉及金属从矿石提炼到最后产物的物理学、化学和工程学总称。

Heat treatment is the operation of heating and cooling a metal in its solid state to change its physical properties. According to the procedure used, steel can be hardened to resist cutting action and abrasion, or it can be softened to permit machining. 热处理是将金属在固态加热和冷却以改变其物理性能的操作。按所采用的步骤，钢可以通过硬化来抵抗切削和磨损，也可以通过软化来允许机加工。

With the proper heat treatment internal stresses may be removed, grain size reduced, toughness increased, or a hard surface produced on a ductile interior. The analysis of the steel must be known because small percentages of certain elements, notably carbon, greatly affect the physical properties.使用合适的热处理可以去除内应力、细化晶粒、增加韧性或在柔软材料上覆盖坚硬的表面。因为某些元素(尤其是碳)的微小百分比极大地影响物理性能，所以必须知道对钢的分析。

Alloy steel owe their properties to the presence of one or more elements other than carbon, namely nickel, chromium, manganese, molybdenum, tungsten, silicon, vanadium, and copper. Because of their improved physical properties they are used commercially in many ways not possible with carbon steels.合金钢的性质取决于其所含有的除碳以外的一种或多种元素，如镍、铬、锰、钼、钨、硅、钒和铜。由于合金钢改善的物理性能，它们被大量使用在许多碳钢不适用的地方。

The following discussion applies principally to the heat treatment of ordinary commercial steels known as plain carbon steels. With this process the rate of cooling is the controlling factor, rapid cooling from above the critical range results in hard structure, whereas very slow cooling produces the opposite effect.下列讨论主要针对被称为普通碳钢的工业用钢而言。热处理时冷却速率是控制要素，从高于临界温度快速冷却导致坚硬的组织结构，而缓慢冷却则产生相反效果。

A Simplified Iron-carbon Diagram简化铁碳状态图 If we focus only on the materials normally known as steels, a simplified diagram is often used. 如果只把注意力集中于一般所说的钢上，经常要用到简化铁碳状态图。

Those portions of the iron-carbon diagram near the delta region and those above 2% carbon content are of little importance to the engineer and are deleted. A simplified diagram, such as the one in Fig.2.1, focuses on the eutectoid region and is quite useful in understanding the properties and processing of steel. 铁碳状态图中靠近三角区和含碳量高于2%的那些部分对工程师而言不重要，因此将它们删除。如图2.1所示的简化铁碳状态图将焦点集中在共析区，这对理解钢的性能和处理是十分有用的。

The key transition described in this diagram is the decomposition of single-phase austenite(γ) to the two-phase ferrite plus carbide structure as temperature drops. 在此图中描述的关键转变是单相奥氏体(γ) 随着温度下降分解成两相 铁素体加渗碳体组织结构。

Control of this reaction, which arises due to the drastically different carbon solubility of austenite and ferrite, enables a wide range of properties to be achieved through heat treatment.控制这一由于奥氏体和铁素体的碳溶解性完全不同而产生的反应，使得通过热处理能获得很大范围的特性。

To begin to understand these processes, consider a steel of the eutectoid composition, 0.77% carbon, being slow cooled along line x-x’ in Fig.2.1. At the upper temperatures, only austenite is present, the 0.77% carbon being dissolved in solid solution with the iron. When the steel cools to 727℃(1341℉), several changes occur simultaneously.为了理解这些过程，考虑含碳量为0.77%的共析钢，沿着图2.1的x-x’线慢慢冷却。在较高温度时，只存在奥氏体，0.77%的碳溶解在铁里形成固溶体。当钢冷却到727℃ (1341℉)时，将同时发生若干变化。

The iron wants to change from the FCC austenite structure to the BCC ferrite structure, but the ferrite can only contain 0.02% carbon in solid solution. 铁需要从面心立方体奥氏体结构转变为体心立方体铁素体结构，但是铁素体只能容纳固溶体状态的0.02%的碳。

The rejected carbon forms the carbon-rich cementite intermetallic with composition Fe3C. In essence, the net reaction at the eutectoid is austenite 0.77%C→ferrite 0.02%C+cementite 6.67%C.被析出的碳与金属化合物Fe3C形成富碳的渗碳体。本质上，共析体的基本反应是奥氏体0.77%的碳→铁素体0.02%的碳+渗碳体6.67%的碳。

Since this chemical separation of the carbon component occurs entirely in the solid state, the resulting structure is a fine mechanical mixture of ferrite and cementite. Specimens prepared by polishing and etching in a weak solution of nitric acid and alcohol reveal the lamellar structure of alternating plates that forms on slow cooling.由于这种碳成分的化学分离完全发生在固态中，产生的组织结构是一种细致的铁素体与渗碳体的机械混合物。通过打磨并在弱硝酸酒精溶液中蚀刻制备的样本显示出由缓慢冷却形成的交互层状的薄片结构。

This structure is composed of two distinct phases, but has its own set of characteristic properties and goes by the name pearlite, because of its resemblance to mother- of- pearl at low magnification.这种结构由两种截然不同的状态组成，但它本身具有一系列特性，且因与低倍数放大时的珠母层有类同之处而被称为珠光体。

Steels having less than the eutectoid amount of carbon (less than 0.77%) are known as hypo-eutectoid steels. Consider now the transformation of such a material represented by cooling along line y-y’ in Fig.2.1. 含碳量少于共析体(低于0.77%)的钢称为亚共析钢。现在来看这种材料沿着图2.1中y-y’ 线冷却的转变情况。

At high temperatures, the material is entirely austenite, but upon cooling enters a region where the stable phases are ferrite and austenite. Tie-line and level-law calculations show that low-carbon ferrite nucleates and grows, leaving the remaining austenite richer in carbon.在较高温度时，这种材料全部是奥氏体，但随着冷却就进入到铁素体和奥氏体稳定状态的区域。由截线及杠杆定律分析可知，低碳铁素体成核并长大，剩下含碳量高的奥氏体。

At 727℃(1341℉), the austenite is of eutectoid composition (0.77% carbon) and further cooling transforms the remaining austenite to pearlite. The resulting structure is a mixture of primary or pro-eutectoid ferrite (ferrite that formed above the eutectoid reaction) and regions of pearlite. 在727℃(1341℉)时，奥氏体为共析组成(含碳量0.77%)，再冷却剩余的奥氏体就转化为珠光体。作为结果的组织结构是初步的或预共析铁素体(在共析反应前的铁素体)和部分珠光体的混合物。

Hypereutectoid steels are steels that contain greater than the eutectoid amount of carbon. When such steel cools, as shown in z-z’ of Fig.2.1 the process is similar to the hypo-eutectoid case, except that the primary or pro-eutectoid phase is now cementite instead of ferrite.过共析钢是含碳量大于共析量的钢。当这种钢冷却时，就像图2.1的z-z’线所示，除了初步的或预共析状态用渗碳体取代铁素体外，其余类似亚共析钢的情况。

As the carbon-rich phase forms, the remaining austenite decreases in carbon content, reaching the eutectoid composition at 727℃(1341℉). As before, any remaining austenite transforms to pearlite upon slow cooling through this temperature.随着富碳部分的形成，剩余奥氏体含碳量减少，在727℃(1341℉)时达到共析组织。就像以前说的一样，当缓慢冷却到这温度时所有剩余奥氏体转化为珠光体。

It should be remembered that the transitions that have been described by the phase diagrams are for equilibrium conditions, which can be approximated by slow cooling. With slow heating, these transitions occur in the reverse manner. 应该记住的是由状态图描述的这种转化只适合于通过缓慢冷却的近似平衡条件。如果缓慢加热，则以相反的方式发生这种转化。

However, when alloys are cooled rapidly, entirely different results may be obtained, because sufficient time is not provided for the normal phase reactions to occur, in such cases, the phase diagram is no longer a useful tool for engineering analysis.然而，当快速冷却合金时，可能得到完全不同的结果。因为没有足够的时间让正常的状态反应发生，在这种情况下对工程分析而言状态图不再是有用的工具。

Hardening淬火 Hardening is the process of heating a piece of steel to a temperature within or above its critical range and then cooling it rapidly. 淬火就是把钢件加热到或超过它的临界温度范围，然后使其快速冷却的过程。

If the carbon content of the steel is known, the proper temperature to which the steel should be heated may be obtained by reference to the iron-iron carbide phase diagram. However, if the composition of the steel is unknown, a little preliminary experimentation may be necessary to determine the range. 如果钢的含碳量已知，钢件合适的加热温度可参考铁碳合金状态图得到。然而当钢的成分不知道时，则需做一些预备试验来确定其温度范围。

A good procedure to follow is to heat-quench a number of small specimens of the steel at various temperatures and observe the result, either by hardness testing or by microscopic examination. When the correct temperature is obtained, there will be a marked change in hardness and other properties. 要遵循的合适步骤是将这种钢的一些小试件加热到不同的温度后淬火，再通过硬度试验或显微镜检查观测结果。一旦获得正确的温度，硬度和其它性能都将有明显的变化。

In any heat-treating operation the rate of heating is important. Heat flows from the exterior to the interior of steel at a definite rate. If the steel is heated too fast, the outside becomes hotter than the interior and uniform structure cannot be obtained. 在任何热处理作业中，加热的速率都是重要的。热量以一定的速率从钢的外部传导到内部。如果钢被加热得太快，其外部比内部热就不能得到均匀的组织结构。

If a piece is irregular in shape, a slow rate is all the more essential to eliminate warping and cracking. The heavier the section, the longer must be the heating time to achieve uniform results. 如果工件形状不规则，为了消除翘曲和开裂最根本的是加热速率要缓慢。截面越厚，加热的时间就要越长才能达到均匀的结果。

Even after the correct temperature has been reached, the piece should be held at that temperature for a sufficient period of time to permit its thickest section to attain a uniform temperature.即使加热到正确的温度后，工件也应在此温度下保持足够时间以让其最厚截面达到相同温度。

The hardness obtained from a given treatment depends on the quenching rate, the carbon content, and the work size. In alloy steels the kind and amount of alloying element influences only the hardenability (the ability of the workpiece to be hardened to depths) of the steel and does not affect the hardness except in unhardened or partially hardened steels.通过给定的热处理所得到的硬度取决于淬火速率、含碳量和工件尺寸。除了非淬硬钢或部分淬硬钢外，合金钢中合金元素的种类及含量仅影响钢的淬透性(工件被硬化到深层的能力)而不影响硬度。

Steel with low carbon content will not respond appreciably to hardening treatment. As the carbon content in steel increases up to around 0.60%, the possible hardness obtainable also increases. 含碳量低的钢对淬火处理几乎没有反应。随着钢的含碳量增加到0.60%附近，可能得到的硬度也增加。

Above this point the hardness can be increased only slightly, because steels above the eutectoid point are made up entirely of pearlite and cementite in the annealed state. Pearlite responds best to heat-treating operations; and steel composed mostly of pearlite can be transformed into a hard steel. 由于超过共析点钢完全由珠光体和退火状态的渗碳体组成，因此高于此点硬度增加并不多。珠光体对热处理作业响应最好；
基本由珠光体组成的钢能转化成硬质钢。

As the size of parts to be hardened increases, the surface hardness decreases somewhat even though all other conditions have remained the same. There is a limit to the rate of heat flow through steel. 即使所有其它条件保持不变，随着要淬火的零件尺寸的增加其表面硬度也会有所下降。热量在钢中的传导速率是有限的。

No matter how cool the quenching medium may be, if the heat inside a large piece cannot escape faster than a certain critical rate, there is a definite limit to the inside hardness. However, brine or water quenching is capable of rapidly bringing the surface of the quenched part to its own temperature and maintaining it at or close to this temperature.无论淬火介质怎么冷，如果在大工件中的热量不能比特定的临界速率更快散发，那它内部硬度就会受到明确限制。然而盐水或水淬火能够将被淬零件的表面迅速冷却至本身温度并将其保持或接近此温度。

Under these circumstances there would always be some finite depth of surface hardening regardless of size. This is not true in oil quenching, when the surface temperature may be high during the critical stages of quenching.在这种情况下不管零件尺寸如何，其表面总归有一定深度被硬化。但油淬情况就不是如此，因为油淬时在淬火关键阶段零件表面的温度可能仍然很高。

Tempering 回火 Steel that has been hardened by rapid quenching is brittle and not suitable for most uses. By tempering or drawing, the hardness and brittleness may be reduced to the desired point for service conditions．快速淬火硬化的钢是硬而易碎的，不适合大多数场合使用。通过回火，硬度和脆性可以降低到使用条件所需要的程度。

As these properties are reduced there is also a decrease in tensile strength and an increase in the ductility and toughness of the steel. The operation consists of reheating quench-hardened steel to some temperature below the critical range followed by any rate of cooling. 随着这些性能的降低，拉伸强度也降低而钢的延展性和韧性则会提高。回火作业包括将淬硬钢重新加热到低于临界范围的某一温度然后以任意速率冷却。

Although this process softens steel, it differs considerably from annealing in that the process lends itself to close control of the physical properties and in most cases does not soften the steel to the extent that annealing would. The final structure obtained from tempering a fully hardened steel is called tempered martensite.虽然这过程使钢软化，但它与退火是大不相同的，因为回火适合于严格控制物理性能并在大多数情况下不会把钢软化到退火那种程度。回火完全淬硬钢得到的最终组织结构被称为回火马氏体。

Tempering is possible because of the instability of the martensite, the principal constituent of hardened steel. Low-temperature draws, from 300℉ to 400℉ (150℃~205℃), do not cause much decrease in hardness and are used principally to relieve internal strains. 由于马氏体这一淬硬钢主要成分的不稳定性，使得回火成为可能。低温回火，从 300℉到400℉(150℃~205℃)，不会引起硬度下降很多，主要用于减少内部应变。

As the tempering temperatures are increased, the breakdown of the martensite takes place at a faster rate, and at about 600℉(315℃) the change to a structure called tempered martensite is very rapid. The tempering operation may be described as one of precipitation and agglomeration or coalescence of cementite. 随着回火温度的提高，马氏体以较快的速率分解，并在大约600℉(315℃)迅速转变为被称为回火马氏体的结构。回火作业可以描述为渗碳体析出和凝聚或聚结的过程。

A substantial precipitation of cementite begins at 600℉(315℃), which produces a decrease in hardness. Increasing the temperature causes coalescence of the carbides with continued decrease in hardness.渗碳体的大量析出开始于600℉(315℃)，这使硬度下降。温度的上升会使碳化物聚结而硬度继续降低。

In the process of tempering, some consideration should be given to time as well as to temperature. Although most of the softening action occurs in the first few minutes after the temperature is reached, there is some additional reduction in hardness if the temperature is maintained for a prolonged time. 在回火过程中，不但要考虑温度而且要考虑时间。虽然大多数软化作用发生在达到所需温度后的最初几分钟，但如果此温度维持一段延长时间，仍会有些额外的硬度下降。

Usual practice is to heat the steel to the desired temperature and hold it there only long enough to have it uniformly heated.通常的做法是将钢加热到所需温度并且仅保温到正好使其均匀受热。

Two special processes using interrupted quenching are a form of tempering. In both, the hardened steel is quenched in a salt bath held at a selected lower temperature before being allowed to cool. These processes, known as austempering and martempering, result in products having certain desirable physical properties.两种采用中断淬火的特殊工艺也是回火的形式之一。这两种工艺中，淬硬钢在其被允许冷却前先在一选定的较低温度盐浴淬火。这两种分别被称为奥氏体回火和马氏体回火的工艺，能使产品具有特定所需的物理性能。

Annealing 退火 The primary purpose of annealing is to soften hard steel so that it may be machined or cold worked.退火的主要目的是使坚硬的钢软化以便机加工或冷作加工。

This is usually accomplished by heating the steel too slightly above the critical temperature, holding it there until the temperature of the piece is uniform throughout, and then cooling at a slowly controlled rate so that the temperature of the surface and that of the center of the piece are approximately the same.通常是将钢加热到稍高于临界温度，并将其在此温度下保持到工件全部均匀受热，然后以受控的速率慢慢地冷却，这样使得工件表面和内部的温度近似相同。

This process is known as full annealing because it wipes out all trace of previous structure, refines the crystalline structure, and softens the metal. Annealing also relieves internal stresses previously set up in the metal.这过程被称为完全退火，因为它去除了以前组织结构的所有痕迹、细化晶粒并软化金属。退火也释放了先前在金属中的内应力。

The temperature to which a given steel should be heated in annealing depends on its composition; for carbon steels it can be obtained readily from the partial iron-iron carbide equilibrium diagram. The heating rate should be consistent with the size and uniformity of sections, so that the entire part is brought up to temperature as uniformly as possible. 对给定的钢，其退火温度取决于它的成分；
对碳钢而言可容易地从局部的铁碳合金平衡图得到。加热的速率也应与截面的尺寸及均匀程度相协调，这样才能使整个零件尽可能均匀地加热到所需温度。

When the annealing temperature has been reached, the steel should be held there until it is uniform throughout. This usually takes about 45min for each inch(25mm) of thickness of the largest section.达到退火温度后，钢应当保持在此温度等到全部均匀受热。这时间一般以零件的最大截面厚度计每英寸(25mm )大约需45分钟。

For maximum softness and ductility the cooling rate should be very slow, such as allowing the parts to cool down with the furnace. The higher the carbon content, the slower this rate must be.为了得到最大柔软性和延展性冷却速率应该很慢，比如让零件与炉子一起冷下来。含碳量越高，冷却的速率必须越慢。

Normalizing and Spheroidizing正火和球化 The process of normalizing consists of heating the steel about 50℉ to 100℉ (10℃~40℃) above the upper critical range and cooling in still air to room temperature.正火处理包括先将钢加热到高于上临界区50℉至100℉(10℃~40℃)，然后在静止的空气中冷却到室温。

This process is principally used with low- and medium-carbon steels as well as alloy steels to make the grain structure more uniform, to relieve internal stresses, or to achieve desired results in physical properties. Most commercial steels are normalized after being rolled or cast.正火主要用于低碳钢、中碳钢及合金钢，使晶粒结构更均匀、释放内应力或获得所需的物理特性。大多数商业钢材在轧制或铸造后都要退火。

Spheroidizing is the process of producing a structure in which the cementite is in a spheroidal distribution. If steel is heated slowly to a temperature just below the critical range and held there for a prolonged period of time, this structure will be obtained. 球化是使渗碳体产生成类似球状分布结构的工艺。如果把钢缓慢加热到恰好低于临界温度并且保持较长一段时间，就能得到这种组织结构。

The globular structure obtained gives improved machinability to the steel. This treatment is particularly useful for hypereutectoid steels that must be machined.所获得的球状结构改善了钢的可切削性。此处理方法对必须机加工的过共析钢特别有用。

Surface Hardening表面硬化 Carburizing渗碳 The oldest known method of producing a hard surface on steel is case hardening or carburizing. Iron at temperatures close to and above its critical temperature has an affinity for carbon.最早的硬化钢表面的方法是表面淬火或渗碳。铁在靠近并高于其临界温度时对碳具有亲合力。

The carbon is absorbed into the metal to form a solid solution with iron and converts the outer surface into high-carbon steel. The carbon is gradually diffused to the interior of the part. The depth of the case depends on the time and temperature of the treatment.碳被吸收进金属与铁形成固溶体使外表面转变成高碳钢。碳逐渐扩散到零件内部。渗碳层的深度取决于热处理的时间和温度。

Pack carburizing consists of placing the parts to be treated in a closed container with some carbonaceous material such as charcoal or coke. It is a long process and used to produce fairly thick cases of from 0.03 to 0.16 in.(0.76~4.06mm) in depth.固体渗碳的方法是将要处理的零件与木炭或焦炭这些含碳的材料一起放入密闭容器。这用于产生深度为0.03到0.16 英寸(0.76~4.06mm)厚的硬化层，是一个较长的过程。

Steel for carburizing is usually a low-carbon steel of about 0.15% carbon that would not in itself responds appreciably to heat treatment. In the course of the process the outer layer is converted into high-carbon steel with a content ranging from 0.9% to 1.2% carbon.用于渗碳的一般是含碳量约为0.15%、本身不太适合热处理的低碳钢。在处理过程中外层转化为含碳量从0.9%到1.2%的高碳钢。

A steel with varying carbon content and, consequently, different critical temperatures requires a special heat treatment. 含碳量变化的钢具有不同的临界温度，因此需要特殊的热处理。

Because there is some grain growth in the steel during the prolonged carburizing treatment, the work should be heated to the critical temperature of the core and then cooled, thus refining the core structure. The steel should then be reheated to a point above the transformation range of the case and quenched to produce a hard, fine structure.由于在较长的渗碳过程中钢内部会有些晶粒生长，所以工件应该加热到核心部分的临界温度再冷却以细化核心部分的组织结构。然后重新加热到高于外层转变温度再淬火以生成坚硬、细致的组织结构。

The lower heat-treating temperature of the case results from the fact that hypereutectoid steels are normally austenitized for hardening just above the lower critical point. A third tempering treatment may be used to reduce strains.由于恰好高于低临界温度通常使过共析钢奥氏体化而硬化，所以对外层采用较低的热处理温度。第三次回火处理可用于减少应变。

Carbonitriding碳氮共渗 Carbonitriding, sometimes known as dry cyaniding or nicarbing, is a case-hardening process in which the steel is held at a temperature above the critical range in a gaseous atmosphere from which it absorbs carbon and nitrogen.碳氮共渗，有时也称为干法氰化或渗碳氮化，是一种表面硬化工艺。通过把钢放在高于临界温度的气体中，让它吸收碳和氮。

Any carbon-rich gas with ammonia can be used. The wear-resistant case produced ranges from 0.003 to 0.030 inch(0.08~ 0.76mm) in thickness. An advantage of carbonitriding is that the hardenability of the case is significantly increased when nitrogen is added, permitting the use of low-cost steels.可以使用任何富碳气体加氨气，能生成厚度从0.003到0.030英寸(0.08~ 0.76mm)的耐磨外层。碳氮共渗的优点之一是加入氮后外层的淬透性极大增加，为使用低价钢提供条件。

Cyaniding氰化 Cyaniding, or liquid carbonitriding as it is sometimes called, is also a process that combines the absorption of carbon and nitrogen to obtain surface hardness in low-carbon steels that do not respond to ordinary heat treatment. 氰化，有时称为液体碳氮共渗，也是一种结合了吸收碳和氮来获得表面硬度的工艺，它主要用于不适合通常热处理的低碳钢。

The part to be case hardened is immersed in a bath of fused sodium cyanide salts at a temperature slightly above the Ac1 range, the duration of soaking depending on the depth of the case. The part is then quenched in water or oil to obtain a hard surface. 需表面硬化的零件浸没在略高于Ac1温度熔化的氰化钠盐溶液中，浸泡的持续时间取决于硬化层的深度。然后将零件在水或油中淬火得到坚硬表面。

Case depths of 0.005 to 0.015in. (0.13~0.38mm) may be readily obtained by this process. Cyaniding is used principally for the treatment of small parts.通过这样处理可以容易地获得0.005到0.015英寸(0.13~0.38mm)的硬化深度。氰化主要用于处理小零件。

Nitriding渗氮 Nitriding is somewhat similar to ordinary case hardening, but it uses a different material and treatment to create the hard surface constituents. 渗氮有些类似普通表面硬化，但它采用不同的材料和处理方法来产生坚硬表面成分。

In this process the metal is heated to a temperature of around 950℉(510℃) and held there for a period of time in contact with ammonia gas. Nitrogen from the gas is introduced into the steel, forming very hard nitrides that are finely dispersed through the surface metal.这种工艺中金属加热到约950℉(510℃)，然后与氨气接触一段时间。氨气中的氮进入钢内，形成细微分布于金属表面又十分坚固的氮化物。

Nitrogen has greater hardening ability with certain elements than with others, hence, special nitriding alloy steels have been developed. 氮与某些元素的硬化能力比其它元素大，因此开发了专用的渗氮合金钢。

Aluminum in the range of 1% to 1.5% has proved to be especially suitable in steel, in that it combines with the gas to form a very stable and hard constituent. The temperature of heating ranges from 925℉ to 1,050℉(495℃~565℃).在钢中含铝1%到1.5%被证明特别合适，它能与氨气结合形成很稳定坚固的成分。其加热温度范围为925℉到1,050℉ (495℃~565℃)。

Liquid nitriding utilizes molten cyanide salts and, as in gas nitriding, the temperature is held below the transformation range. Liquid nitriding adds more nitrogen and less carbon than either cyaniding or carburizing in cyanide baths. 液体渗氮利用熔化的氰化物盐，就像气体渗氮，温度保持在低于转化范围内。液体渗氮时在氰化物溶液中加入比氰化及渗碳都较多的氮和较少的碳。

Case thickness of 0.001 to 0.012in.(0.03~0.30mm) is obtained, whereas for gas nitriding the case may be as thick as 0.025 in.(0.64mm). In general the uses of the two-nitriding processes are similar.液体渗氮可以获得厚度为0.001到0.012英寸 (0.03~0.30mm)的硬化层，然而气体渗氮则能获得厚0.025英寸(0.64mm)的硬化层。一般而言两种渗氮方法的用途是类似的。

Nitriding develops extreme hardness in the surface of steel. This hardness ranges from 900 to 1,100 Brinell, which is considerably higher than that obtained by ordinary case hardening. 渗氮在钢表面获得远远超出正常标准的硬度。其硬度范围为900到1,100布氏硬度，这远高于普通表面硬化所获得的硬度。

Nitriding steels, by virtue of their alloying content, are stronger than ordinary steels and respond readily to heat treatment. It is recommended that these steels be machined and heat-treated before nitriding, because there is no scale or further work necessary after this process. 由于渗氮钢的合金比例，它们比普通钢更强，也容易热处理。建议对这种钢在渗氮前先机加工和热处理，因为渗氮后没有剥落并不需要更多的加工。

Fortunately, the interior structure and properties are not affected appreciably by the nitriding treatment and, because no quenching is necessary, there is little tendency to warp, develop cracks, or change condition in any way. The surface effectively resists corrosive action of water, saltwater spray, alkalies, crude oil, and natural gas.值得庆幸的是由于渗氮处理一点都不影响内部结构和性能，也无需淬火，所以几乎没有任何产生翘曲、裂缝及变化条件的趋势。这种表面能有效地抵御水、盐雾、碱、原油和天然气的腐蚀反应。

UNIT 3 Casting Processes Casting is a manufacturing process in which molten metal is poured or injected and allowed to solidify in a suitably shaped mold cavity. During or after cooling, the cast part is removed from the mold and then processed for delivery.铸造是一种将熔化的金属倒入或注入合适的铸模腔并且在其中固化的制造工艺。在冷却期间或冷却后，把铸件从铸模中取出，然后加工交付。

Casting processes and cast-material technologies vary from simple to highly complex. Material and process selection depends on the part’s complexity and function, the product’s quality specifications, and the projected cost level.铸造工艺和铸造材料技术从简单到高度复杂变化很大。材料和工艺的选择取决于零件的复杂性和功能、产品的质量要求以及成本预算水平。

Castings are parts that are made close to their final dimensions by a casting process. With a history dating back 6,000 years, the various casting processes are in a state of continuous refinement and evolution as technological advances are being made.通过铸造加工，铸件可以做成很接近它们的最终尺寸。回溯6,000年历史，各种各样的铸造工艺一直处于随着科技进步不断改进和发展的状态。

Sand Casting 砂型铸造 Sand casting is used to make large parts (typically iron, but also bronze, brass, aluminum). Molten metal is poured into a mold cavity formed out of sand (natural or synthetic). 砂型铸造用于制造大型零件(具有代表性是铁，除此之外还有青铜、黄铜和铝)。将熔化的金属倒入由型砂(天然的或人造的)做成铸模腔。

The processes of sand casting are discussed in this section, including patterns, sprues and runners, design considerations, and casting allowance.本节讨论砂型铸造工艺，包括型模、浇注口、浇道、设计考虑因素及铸造余量。

The cavity in the sand is formed by using a pattern (an approximate duplicate of the real part), which are typically made out of wood, sometimes metal. The cavity is contained in an aggregate housed in a box called the flask. 砂型里的型腔是采用型模(真实零件的近似复制品)形成的，型模一般为木制，有时也用金属制造。型腔整个包含在一个被置于称为砂箱的箱子里的聚合体内。

Core is a sand shape inserted into the mold to produce the internal features of the part such as holes or internal passages. Cores are placed in the cavity to form holes of the desired shapes. Core print is the region added to the pattern, core, or mold that is used to locate and support the core within the mold. 砂芯是插入铸模的砂型，用于生成诸如孔或内通道之类的内部特征。砂芯安放在型腔里形成所需形状的孔洞。砂芯座是加在型模、砂芯或铸模上的特定区域，用来在铸模内部定位和支撑砂芯。

A riser is an extra void created in the mold to contain excessive molten material. The purpose of this is to feed the molten metal to the mold cavity as the molten metal solidifies and shrinks, and thereby prevents voids in the main casting.冒口是在铸模内部增加的额外空间，用于容纳过量的熔化金属。其目的是当熔化金属凝固和收缩时往型腔里补充熔化金属，从而防止在主铸件中产生孔隙。

In a two-part mold, which is typical of sand castings, the upper half, including the top half of the pattern, flask, and core is called cope and the lower half is called drag, as shown in Fig.3.1. The parting line or the parting surface is line or surface that separates the cope and drag. 在典型砂型铸造的双层铸模中，上半部分(包括型模、砂箱和砂芯的上半部分)称为上型箱，下半部分称为下型箱，见图3.1所示。分型线或分型面是分离上下型箱的线或面。

The drag is first filled partially with sand, and the core print, the cores, and the gating system are placed near the parting line. The cope is then assembled to the drag, and the sand is poured on the cope half, covering the pattern, core and the gating system.首先往下型箱里部分地填入型砂，并在靠近分型线处放置砂芯座、砂芯和浇注系统。然后将上型箱与下型箱装配在一起，再把型砂倒入上型箱盖住型模、砂芯和浇注系统。

The sand is compacted by vibration and mechanical means. Next, the cope is removed from the drag, and the pattern is carefully removed. The object is to remove the pattern without breaking the mold cavity. 型砂通过振动和机械方法压实。接下来从下型箱上撤掉上型箱，小心翼翼地取出型模。其目的是取出型模而不破坏型腔。

This is facilitated by designing a draft, a slight angular offset from the vertical to the vertical surfaces of the pattern. This is usually a minimum of 1.5mm(0.060in.), whichever is greater. The rougher the surface of the pattern, the more the draft to be provided.通过设计拔模斜度—型模垂直相交表面的微小角度偏移量—来使取出型模变得容易。拔模斜度最小一般为1.5mm(0.060in.)，只能比此大。型模表面越粗糙，则拔模斜度应越大。

The molten material is poured into the pouring cup, which is part of the gating system that supplies the molten material to the mold cavity. 熔化的金属从浇注杯注入型腔，浇注杯是浇注系统向型腔提供熔化金属的部分。

The vertical part of the gating system connected to the pouring cup is the sprue, and the horizontal portion is called the runners and finally to the multiple points where it is introduced to the mold cavity called the gates. 将浇注系统的垂直部分与浇注杯连接的是浇注口，浇注系统的水平部分称为浇道，最后到多点把熔化金属导入型腔的称为闸道。

Additionally there are extensions to the gating system called vents that provide the path for the built-up gases and the displaced air to vent to the atmosphere.除此之外，还有称为排放口的浇注系统延长段，它为合成气体和置换空气排放到大气提供通道。

The cavity is usually made oversize to allow for the metal contraction as it cools down to room temperature. This is achieved by making the pattern oversize. To account for shrinking, the pattern must be made oversize by these factors on the average. These are linear factors and apply in each direction. 型腔通常大于所需尺寸以允许在金属冷却到室温时收缩。这通过把型模做得大于所需尺寸来达到。为解决收缩效应，一般而言型模做得比所需尺寸大，必须考虑线性因素并作用于各个方向。

These shrinkage allowances are only approximate, because the exact allowance is determined by the shape and size of the casting. In addition, different parts of the casting might require different shrinkage allowances. 收缩余量仅仅是近似的，因为准确的余量是由铸件的形状和尺寸决定的。另外，铸件的不同部分也可能需要不同的收缩余量。

Sand castings generally have a rough surface sometimes with surface impurities, and surface variations. A machining (finish) allowance is made for this type of defect.砂型铸件一般表面粗糙，有时还带有表面杂质和表面变异。采用机加工(最终)余量解决这类缺陷。

In general, typical stages of sand casting operation include (as shown in Fig.3.2): 一般而言，砂型铸造作业的典型阶段包括(如图3.2所示)：
1. Patterns are made. These will be the shape used to form the cavity in the sand.1. 制作型模。做成用于在型砂中形成型腔的形状。

2. Cores may also be made at this time. These cores are made of bonded sand that will be broken out of the cast part after it is complete. 2. 同时还要制作砂芯。这些砂芯用粘结砂做成，等铸件完成后将被打碎取出。

3. Sand is mulled (mixed) thoroughly with additives such as bentonite to increase bonding and overall strength.3. 型砂与膨润土之类的添加剂充分地混合以增强连接及整体强度。

4. Sand is formed about the patterns, and gates, runners, risers, vents and pouring cups are added as needed. A compaction stage is typically used to ensure good coverage and solid molds. 4. 型砂在型模周围成形，并根据需要安放闸道、浇道、冒口、排放口和浇注杯等。通常要采取压紧步骤来保证良好的覆盖和坚固的铸模。

Cores may also be added to make concave or internal features for the cast part. Alignment pins may also be used for mating the molds later. Chills may be added to cool large masses faster.安放砂芯来制成铸件的凹形结构或内部特征。为了以后铸模匹配还要用到定位销。对大质量铸件可能需要加些冷却物来使其较快冷却。

5. The patterns are removed, and the molds may be put through a baking stage to increase strength. 5. 取出型模，将铸模烘焙以增加强度。

6. Mold halves are mated and prepared for pouring metal.6. 匹配上下铸模，做好浇铸金属的准备。

7. Metal is preheated in a furnace or crucible until is above the liquidus temperature in a suitable range (we don’t want the metal solidifying before the pour is complete). The exact temperature may be closely controlled depending upon the application.7. 金属在熔炉或坩埚中预热到高于液化温度的一个合适范围内(不希望金属在浇铸完成前凝固)。确切的温度要根据应用场合严格控制。

Degassing, and other treatment processes may be done at this time, such as removal of impurities (i.e. slag). Some portion of this metal may be remelted scrap from previously cast parts—10% is reasonable.在此期间还要进行排气和其它处理步骤，例如去除杂质(即熔渣)。可以加入一定量原先是这种金属铸件的废料再熔化—10%是适当的。

8. The metal is poured slowly, but continuously into the mold until the mold is full. 8. 将金属缓慢而连续地注满铸模。

9. As the molten metal cools (minutes to days), the metal will shrink and the volume will decrease. During this time molten metal may backflow from the molten risers to feed the part and maintain the same shape.9. 随着熔化金属的冷却(几分钟到几天)，金属收缩体积减小。在此期间熔化金属可能从冒口回流供给零件以保持其形状不变。

10. Once the part starts to solidify small dendrites of solid material form in the part. During this time metal properties are being determined, and internal stresses are being generated. If a part is allowed to cool slowly enough at a constant rate then the final part will be relatively homogenous and stress free.10. 一旦零件开始凝固其内部形成固态金属的小型树枝状结晶。在此期间金属性能被确定，同时也产生了内应力。如果零件以恒定速率冷却得足够缓慢，最终零件将相对均质并释放内应力。

11. Once the part has completely solidified below the eutectic point it may be removed with no concern for final metal properties. At this point the sand is simply broken up, and the part removed. At this point the surface will have a quantity of sand adhering to the surface, and solid cores inside.11. 一旦零件在共晶点以下完全凝固，可以不必担心金属的最后性能而将其取出。这时可以简单地打碎砂型并取出零件。但零件表面会有大量型砂粘附着，内部还有实心的砂芯。

12. A bulk of the remaining sand and cores can be removed by mechanically striking the part. Other options are to use a vibrating table, sand/shot blaster, hand labor, etc.12.大量的剩余型砂和砂芯要通过机械敲击零件来去除。其它的选择还有采用振动台、喷砂/喷丸机、手工作业等等。

13. The final part is cut off the runner gate system, and is near final shape using cutters, torches, etc. Grinding operations are used to remove any remaining bulk. 13. 最后零件要用刀具、喷枪等切掉浇道闸道系统，这样就接近最终形状了。再用磨削作业去除多余的部分。

14. The part is taken down to final shape using machining operations. And cleaning operations may be used to remove oxides, etc.14. 通过机加工将零件切削到最终形状。可能还要用清洗作业去除氧化物等。

Investment casting熔模铸造 Investment casting is also known as the lost wax process. This process is one of the oldest manufacturing processes. The Egyptians used it in the time of the Pharaohs to make gold jewelry (hence the name Investment) some 5,000 years ago.熔模铸造也称为失蜡加工。这是最古老的制造工艺之一。大约在5,000年前的法老王时代，埃及人就用它制造黄金饰品(因此而得名投资)。

Intricate shapes can be made with high accuracy. In addition, metals that are hard to machine or fabricate are good candidates for this process. It can be used to make parts that cannot be produced by normal manufacturing techniques, such as turbine blades that have complex shapes, or airplane parts that have to withstand high temperatures.能高精度地制造复杂的形状。另外较难机加工或制作的金属都能用此工艺。它还能用于生产一般制造技术无法生产的零件，例如有复杂形状的涡轮叶片或必须耐得住高温的飞机零件。

The mold is made by making a pattern using wax or some other material that can be melted away. This wax pattern is dipped in refractory slurry, which coats the wax pattern and forms a skin. This is dried and the process of dipping in the slurry and drying is repeated until a robust thickness is achieved. 制作铸模的型模采用石蜡或其它一些能被融化掉的材料做成。石蜡型模浸泡在耐热浆里，让它覆盖型模并形成外壳，然后使其变干。重复这个浸泡、变干的过程直至获得足够的厚度。

After this, the entire pattern is placed in an oven and the wax is melted away. This leads to a mold that can be filled with the molten metal. Because the mold is formed around a one-piece pattern (which does not have to be pulled out from the mold as in a traditional sand casting process), very intricate parts and undercuts can be made. 完成后把整个型模放在烤箱里融化石蜡。这样就做成了能填充熔化金属的铸模。由于这种铸模是环绕整块型模形成的(无需像传统的砂型铸造工艺那样拔模)，能制作十分复杂的零件和浮雕。

The wax pattern itself is made by duplicating using a stereo lithography or similar model—which has been fabricated using a computer solid model master.石蜡型模本身能用立体制版或类似的模型复制—这可以采用计算机立体模型原版制作。

The materials used for the slurry are a mixture of plaster, a binder and powdered silica, a refractory, for low temperature melts. For higher temperature melts, sillimanite or alumina-silicate is used as a refractory, and silica is used as a binder.对较低熔化温度而言，用于耐热浆的材料是石膏作粘合剂和用粉末状硅石作耐温材料的混合物。对较高熔化温度而言，则采用硅线石或氧化铝硅酸盐作耐温材料、无水硅酸作粘合剂。

Depending on the fineness of the finish desired additional coatings of sillimanite and ethyl silicate may be applied. The mold thus produced can be used directly for light castings, or be reinforced by placing it in a larger container and reinforcing it more slurry.根据最后所需光洁度也可采用硅线石和乙烷基硅酸盐。这样生成的铸模可直接用于薄壁铸件或通过将其放在较大容器内用更多耐热浆加强。

Just before the pour, the mold is pre-heated to about 1,000℃(1,832℉) to remove any residues of wax, harden the binder. The pour in the pre-heated mold also ensures that the mold will fill completely. 在将要浇铸之前，把铸模预热到约1,000℃(1,832℉)以去除剩余石蜡、硬化粘合剂。在预热的铸模中浇铸也能保证铸模完全充满。

Pouring can be done using gravity, pressure or vacuum conditions. Attention must be paid to mold permeability when using pressure, to allow the air to escape as the pour is done.浇铸可采用重力、压力或真空条件来实现。当使用压力时必须注意渗透性，以便在浇铸的同时让空气逸出。

Tolerances of 0.5% of length are routinely possible, and as low as 0.15% is possible for small dimensions. Castings can weigh from a few grams to 35kg (0.1oz to 80lb), although the normal size ranges from 200g to about 8kg(7oz to 15 lb). Normal minimum wall thicknesses are about 1mm to about 0.5mm(0.040~ 0.020 in.) for alloys that can be cast easily.一般公差可能是长度的0.5%，小尺寸可能低到0.15%。虽然通常尺寸的铸件重量范围为200g到约8kg(7oz到15lb)，但实际可从几克到35kg (0.1oz to 80lb)。对容易铸造的合金而言，通常壁厚约为1mm到0.5mm(0.040~ 0.020 in.)。

The types of materials that can be cast are aluminum alloys, bronzes, tool steels, stainless steels, stellite, hastelloys, and precious metals. Parts made with investment castings often do not require any further machining, because of the close tolerances that can be achieved.可以用于铸造的材料类型有：铝合金、青铜、工具钢、不锈钢、钨铬钴合金、镍基合金和贵金属。采用熔模铸造的零件常常不需要进一步加工，因为熔模铸造能达到精密的公差。

Centrifugal Casting离心铸造 Centrifugal casting (Fig.3.3) as a category includes centrifugal casting, semi-centrifugal casting and centrifuging. In centrifugal casting, a permanent mold is rotated about its axis at high speeds (300 to 3,000rpm) as the molten metal is poured. 离心铸造(图3.3)作为一个种类包括了离心铸造、半离心铸造和离心加压铸造。离心铸造中，永久性的铸模在熔化金属浇铸时以较高速度(300到3,000rpm)绕其轴线旋转。

The molten metal is centrifugally thrown towards the inside mold wall, where it solidifies after cooling. The casting is usually a fine grain casting with a very fine-grained outer diameter, which is resistant to atmospheric corrosion, a typical situation with pipes. The inside diameter has more impurities and inclusions, which can be machined away.受离心力作用熔化金属被抛向铸模的内壁，在那里冷却后固化。这种铸件通常为外径处晶粒非常细小的细晶粒铸件，能耐大气腐蚀，典型的情况是管子。内径处则有较多的杂质和内含物，但可用机加工去除。

Only cylindrical shapes can be produced with this process. Size limits are up to 3m(10feet) diameter and 15m(50 feet) length. Wall thickness can be 2.5mm to 125mm(0.1~5.0in.). The tolerances that can be held on the OD can be as good as 2.5mm (0.1in.) and on the ID can be 3.8mm(0.15in.). The surface finish ranges from 2.5mm to 12.5mm(0.1~0.5in.) rms(root-mean-square).只有圆柱形才能用此工艺生产。尺寸限制为直径大到3m(10feet)、长度大到15m(50feet)。壁厚为2.5mm到125mm(0.1~5.0in.)。外径公差保持在2.5mm(0.1in.)以内，内径公差保持在3.8mm(0.15in.)以内。表面粗糙度的 有效值( 均方根)范围为2.5mm到12.5mm(0.1~0.5in.)。

Typical materials that can be cast with this process are iron, steel, stainless steels, and alloys of aluminum, copper and nickel. Two materials can be cast by introducing a second material during the process. Typical parts made by this process are pipes, boilers, pressure vessels, flywheels, cylinder liners and other parts that are axis-symmetric.可用此工艺铸造的典型材料有：铁、钢、不锈钢以及铝、铜和镍的合金。通过在生产过程中加入第二种材料能进行两种材料铸造。采用这种工艺制造的典型零件有：管子、锅炉、压力容器、飞轮、汽缸衬垫和其它轴对称零件。

Semi-centrifugal casting. The molds used can be permanent or expendable, can be stacked as necessary. The rotational speeds are lower than those used in centrifugal casting. 半离心铸造：铸模可以是永久性的或是消耗性的，可根据需要叠加。它的旋转速度比离心铸造低。

The center axis of the part has inclusion defects as well as porosity and thus is suitable only for parts where this can be machined away. This process is used for making wheels, nozzles and similar parts where the axis of the part is removed by subsequent machining. 零件的中心轴附近存在缺陷和孔隙，因此仅适用于能将这些机加工去除的零件。这种工艺被用于制造车轮、管嘴及类似的随后可用机加工去除中心轴部分的零件。

Centrifuging. Centrifuging is used for forcing metal from a central axis of the equipment into individual mold cavities that are placed on the circumference. This provides a means of increasing the filling pressure within each mold and allows for reproduction of intricate details. This method is often used for the pouring of investment casting pattern.离心加压铸造：离心加压铸造用于迫使金属从设备的中心轴进入分布在圆周上的单独铸模型腔。它为每个铸模提供了一种增加填充压力方法并允许再现复杂细节。这种方法常用于浇铸熔模铸造的型模。

Full-mold casting is a technique similar to investment casting, but instead of wax as the expendable material, polystyrene foam is used as the pattern. The foam pattern is coated with a refractory material. The pattern is encased in a one-piece sand mold. As the metal is poured, the foam vaporizes, and the metal takes its place. 实型铸造是与熔模铸造类似的技术，但它用做型模的消耗材料是聚苯乙烯泡沫而不是石蜡。泡沫型模用难熔材料覆盖。型模装入整体砂模中。当金属浇入时，泡沫材料蒸发，金属取代其位置。

This can make complex shaped castings without any draft or flash. However, the pattern cost can be high due to the expendable nature of the pattern. Minimum wall thicknesses are 2.5mm, tolerances can be held to 0.3% on dimensions. Surface finish can be held from 2.5μm to 25μm(0.1μin. to 1.0μin.) rms(root-mean-square). 它能制造没有拔模斜度和缝脊的复杂形状铸件。然而由于型模的消耗特性，型模成本可能较高。最小壁厚为2.5mm ，公差能保持在尺寸的0.3% 之内。表面粗糙度的有效值( 均方根) 能保持在2.5μm 至25μm(0.1μin. 至1.0μin.)之间。

Size limits are from 400g(1lb) to several tons. No draft allowance is required. Typical materials that can be cast with this process are aluminum, iron, steel, nickel alloys, copper alloys. Types of parts that can be made using these processes are pump housings, manifolds, and auto brake components.重量限制从400g(1lb)到数吨。无需留拔模余量。这种工艺所用的典型材料有：铝、铁、钢、镍合金、铜合金。可以采用这些工艺制造的零件类型有泵壳、复式接头和自动刹车零件。

UNIT 4 Forging Processes Introduction引言 Forging is an important hot-forming process. It is used in producing components of all shapes and sizes, from quite small items to large units weighing several tons.锻造是一种重要的热成型工艺。它能用于生产各种形状和尺寸、从很小到重量数吨的零件。

Forging is the process by which metal is heated and is shaped by plastic deformation by suitably applying compressive force. Usually the compressive force is in the form of hammer blows using a power hammer or a press, as shown in Fig.4.1.在锻造过程中先将金属加热，然后施加合适的压力使其塑性变形。通常压力都是以由如图4.1所示的动力锤或压力机提供的锤击形式出现。

Hand forging tools comprise variously shaped hammers. The base on which the work is supported during forging is the anvil.手工锻造工具包括各种不同形状的锤子。在锻造中用于支撑工件的基础是铁砧。

For the semimechanized forging of small to medium-sized components, forging hammers powered by various means are employed. The feature common to all of them is that, like the hand forging hammer, they utilize the energy of a falling weight to develop the pressure needed for shaping the metal. 对小到中等尺寸零件的半机械化锻造而言，锻锤可采用多种动力。就其一般特性而言，都象手工锻锤一样，它们均利用落重能量来产生金属成型所需的压力。

Larger components are forged by means of forging presses operated by steam or compressed air or by hydraulic or electric power. Largely automatic forging machines are used for the quantity production of engineering parts.锻造大零件则要用到蒸汽、压缩空气、液力或电力驱动的锻压机。大型的自动化锻机用于工程零件的批量生产。

A distinction may be made between open-die forging, usually in the form of hammer forging, and closed-die forging. In hammer forging, the component is shaped by hammer blows aided by relatively simple tools. These may include open dies i.e., dies that do not completely enclose the metal to be shaped. 锤锻中常用的开式模锻与闭式模锻是有区别的。在锤锻中零件通过锤击辅之以相对简单的工具成型。其中包括开式锻模，就是不完全封闭被成型金属的模具。

One of the basic operations of hammer forging is the elongation of a piece of metal by stretching with hammer blows, causing it to become thinner and longer. In hand forging the work-piece is usually turned 90° after each blow, in order to forge it thoroughly and prevent its lateral expansion. 锤锻的基本操作之一就是通过锤击使金属伸长，促使其变细变长。手工锻造时一般在每次锤击后都转过90°以充分锻打工件并防止横向膨胀。

The opposite of elongation is upsetting, which produces compressive shortening. For example, the diameter of a bar can be increased by heating and hammering axially.与伸长相反的是镦粗，即产生压缩性缩短。例如，棒料的直径可以通过加热和轴向锤击而增大。

More important is closed-die forging, very widely used for mass production in industry, in which the metal is shaped by pressing between a pair of forging dies. The upper die is usually attached to the ram of a forging press or a forging hammer, while the lower die is stationary. 更重要的是闭式模锻，在工业上广泛用于规模生产。闭式模锻中金属在一对锻模之间挤压成型。顶模通常附在锻压机的撞头或锻锤上，而底模则是固定的。

Together they form a closed die. Closed-die forging can produce components of greater complexity and accuracy, with a better surface finish than the more traditional methods not using closed dies. The dies are made of special heat-resistant and wear-resistant tool steels.两者合在一起形成闭式锻模。闭式模锻能生产高度复杂和精确的零件，而且表面光洁度要比不用闭式锻模的更传统方法好。闭式锻模采用特殊的耐热、耐磨工具钢制成。

A piece of hot metal sufficient to slightly overfill the die shape is placed in the bottom die, and the top die is forced against it, so that the metal takes the internal shape of the die. 将一块大小足以充填模腔并能稍有溢出的加热金属放入底模，并将顶模加压合拢，这块金属便获得该模腔的形状。

Closed-die forging is used for the rapid production of large numbers of fairly small parts and also for very large components. For the latter, e.g., modern jet-aircraft components, giant hydraulically operated presses are used, which can develop forces of 50,000 tons and more.闭式模锻用于相当小的零件大批量快速生产，也可用于很大的零件。对后者而言，例如现代喷气飞机零件，使用能产生50,000吨以上压力的巨型液力锻压机。

One valuable feature of forging is that it improves the strength of the metal by refining the structure and making it uniform; so for heavy forgings, such as marine propeller shafts, an immensely powerful hydraulic press squeezes the metal with a force sometimes as great as 10,000 tonnes. 锻造有价值的特性之一是它通过使金属组织均匀而改善强度，因此对诸如船舶螺旋桨轴之类的重型锻件，要用能达10,000吨压力的庞大而有力的液压机来挤压金属。

Although the hydraulic forging press is a more expensive piece of equipment than a drop-forge, it has advantages beside those of giving greater strength and more uniform structure to large components. On account of the high pressure and squeezing action, it operates with less noise and vibration than a drop-forge. 虽然这种液压锻机比落锤锻造要昂贵得多，但它除了能给予大零件较高的强度和更均匀的组织外还有其它优点。由于较高的压力和挤压作用，它比落锤锻造噪声及振动都小得多。

As ingots of steel weighing 30 tonnes or more are forged in this way, manual operation is impossible and it is essential that all the manipulation of the ingot is done mechanically.由于这种情况下被锻钢坯重量大于30吨，人工操作是不可能的，钢坯的所有操作都必须是机械化的。

Forging refines the grain structure and improves physical properties of the metal. With proper design, the grain flow can be oriented in the direction of principal stresses encountered in actual use. 锻造细化金属的晶粒组织、改善其物理性能。通过适当的设计，可以使晶粒流动方向与实际使用时的主应力方向一致。

As shown in Fig.4.2, grain flow is the direction of the pattern that the crystals take during plastic deformation. Physical properties (such as strength, ductility and toughness) are much better in a forging than in the base metal, which has crystals randomly oriented.如图4.2所示，晶粒流动的方向就是在塑性变形期间结晶排列的方向。锻件的物理性能(如强度、延展性和韧性)远好于基础金属，因为基础金属的晶粒是无序排列的。

Forgings are consistent from piece to piece, without any of the porosity, voids, inclusions and other defects. Thus, finishing operations such as machining do not expose voids, because there aren’t any. Also coating operations such as plating or painting are straightforward due to a good surface, which needs very little preparation.锻件各部分是连贯一致的，没有孔隙、空洞、杂质及其它缺陷。因此像机加工之类的精加工工序不会受空洞的影响，因为根本就不存在。另外由于锻件良好的表面，像电镀或油漆之类的涂装工序就很简单，几乎不需要做准备工作。

Forgings yield parts that have high strength to weight ratio, thus are often used in the design of aircraft frame members. 锻造生产的零件具有较高的强度重量比，所以常被用在飞机结构零件的设计中。

A forged metal can result in the following:锻造金属可以导致下列结果：
• Increase length, decrease cross-section, called drawing out the metal. ●增加长度、减小横截面，称为延伸金属。

• Decrease length, increase cross-section, called upsetting the metal. ●减小长度、增加横截面，称为镦粗金属。

• Change length, change cross-section, by squeezing in closed impression dies. ●通过用封闭锻模挤压，改变长度和横截面。

This results in favorable grain flow for strong parts.这导致有利的晶粒流使零件坚固。

Common Forging Processes常用的锻造工艺 The metal can be forged hot (above recrystallization temperatures) or cold.金属既可热锻(高于再结晶温度)也可冷锻。

Open die forgings/Hand forgings. Open die forgings or hand forgings are made with repeated blows in an open die, where the operator manipulates the workpiece in the die. The finished product is a rough approximation of the die. This is what a traditional blacksmith does, and is an old manufacturing process.开式模锻/手工锻：开式模锻或手工锻就是操作者操纵工件在开式锻模中反复击打。完成的产品是锻模的粗糙近似物。这就是传统铁匠干的活，是较古老的制造工艺。

Impression die forgings/Precision forgings. Impression die forgings and precision forgings are further refinements of the blocker forgings. The finished part more closely resembles the die impression.压模锻/精密锻：压模锻和精密锻是雏形模锻的进一步改进。完成的零件与模膛更相似。

Press forgings. Press forgings use a slow squeezing action of a press, to transfer a great amount of compressive force to the workpiece. Unlike an open-die forging where multiple blows transfer the compressive energy to the outside of the product, press forging transfers the force uniformly to the bulk of the material. 压锻：压锻通过压力机缓慢的挤压动作将巨大的压力传递给工件。不像开式模锻那样需要多次击打把压缩能量传递到零件外表面，压锻能将力均匀地传递给材料的主体。

This results in uniform material properties and is necessary for large weight forgings. Parts made with this process can be quite large as much as 125kg(260lb) and 3m(10 feet) long.这导致材料性能一致，对大重量锻件而言是十分必要的。采用此工艺生产的零件重量可达125kg(260lb)而长度可达3m(10feet)。

Upset forgings. Upset forging increases cross-section by compressing the length, this is used in making heads on bolts and fasteners, valves and other similar parts.顶锻：顶锻通过压缩长度增加横截面，用于在螺栓等紧固件、柱塞及类似零件上制造头部。

Roll forgings. In roll forging, a bar stock, round or flat is placed between die rollers which reduces the cross-section and increases the length to form parts such as axles, leaf springs etc. This is an essential form of draw forging.滚锻：在滚锻时，圆的或是扁平的棒料放在模辊之间缩小横截面增加长度制成诸如轮轴、板簧之类的零件。这是轧锻的基本形式。

Swaging. Swaging—a tube or rod is forced inside a die and the diameter is reduced as the cylindrical object is fed. The die hammers the diameter and causes the metal to flow inward causing the outer diameter of the tube or the rod to take the shape of the die.型锻：型锻—将圆管或圆棒强制压入锻模，随着圆柱形物体的被压入其直径减小。锻模锤击直径使金属向内流动导致圆管或圆棒的外径变为锻模的形状。

Net shape/Near-net shape forging. In net shape or near-net shape forging, forging results in wastage of material in the form of material flash and subsequent machining operations, as shown in Fig.4.3. This wastage can be as high as 70% for gear blanks, and even 90% in the case of aircraft structural parts. 纯型/近似纯型锻：采用纯型锻或近似纯型锻，产生材料损耗的主要形式是飞边以及随后的机加工，如图4.3所示。齿轮毛坯的材料损耗为70% ，而飞机结构零件的材料损耗甚至达90% 。

Net-shape and near-net-shape processes minimize the waste by making precision dies, producing parts with very little draft angle (less than 1°). These types of processes often eliminate or reduce machining. 纯型锻和近似纯型锻工艺通过制作精密模具并生产拔模斜角很小(小于1°)的零件能使材料损耗最小化。此类工艺通常可以省去或减少机加工。

The processes are quite expensive in terms of tooling and the capital expenditure required. Thus, these processes can be only justified for current processes that are very wasteful where the material savings will pay for the significant increase in tooling costs.从加工的角度而言这些工艺是相当昂贵的，需要资金投入。因此这些工艺只有对目前很浪费的生产过程，在材料节约足以补偿加工成本的明显增加时才是合理的。

Die Design Consideration锻模设计的考虑因素 • Parting surface should be along a single plane if possible, else following the contour of the part. The parting surface should be through the center of the part, not near the upper or lower edges. 如果可能分模面应沿着单一平面，并且顺着零件轮廓。分模面应经过零件中心，而不要靠近上下边缘。

If the parting line cannot be on a single plane, then it is good practice to use symmetry of the design to minimize the side thrust forces. Any point on the parting surface should be less than 75° from the principal parting plane.如果分模线不能在单一平面，利用设计的对称性来减小侧向推力不失为一种好方法。分模面上任意点与主分模面的夹角应小于75°。

• As in most forming processes, use of undercuts should be avoided as these will make the removal of the part difficult, if not impossible.如同大多数成型工艺，如果不是非用不可，尽量避免采用凹槽，因为凹槽会使零件难以取出。

• Generous fillets and radius should be provided to aid in material flow during the forging process. Sharp corners are stress-risers in the forgings, as well as make the dies weak in service. 应提供尽可能大的倒角和半径以帮助材料在锻造过程中流动。锐角会增加锻件中的应力，同时在使用时削弱锻模。

• Ribs should not be high or narrow; this makes it difficult for the material to flow.加劲肋不要过高或过窄，因为这会造成材料流动困难。

Tolerances公差 • Dimension tolerances are usually positive and are approximately 0.3% of the dimension, rounded off to the next higher 0.5mm(0.020in.).尺寸公差通常为正，大约取为该尺寸的0.3%，并圆整到较大的0.5mm(0.020in.)。

• Die wear tolerances are lateral tolerances (parallel to the parting plane) and are roughly +0.2% for copper alloys to +0.5% for aluminum and steel.锻模磨损公差为侧向公差(平行于分模面)，对铜合金大约为+0.2% ，对铝和钢大约为+0.5%。

• Die closure tolerances are in the direction of opening and closing, and range from 1mm(0.040in.) for small forgings, die projection area＜150cm2(23in.2), to 6.25mm(0.25in.) for large forgings, die projection area＞6,500cm2(100in.2).锻模的闭合公差处于开闭的方向上，范围从对较小锻件[其投影面积＜150cm2(23in.2)]取为1mm(0.040in.)，到较大锻件[其投影面积＞6,500cm2(100in.2)]取为6.25mm(0.25in.)。

• Die match tolerances are to allow for shift in the upper die with respect to the lower die.锻模的配合公差是为了允许上模能根据下模替换。

A proper lubricant is necessary for making good forgings. The lubricant is useful in preventing sticking of the workpiece to the die, and also acts as a thermal insulator to help reduce die wear.制造良好的锻件必须有合适的润滑剂。润滑剂对防止工件粘住锻模很有用，还可以作为绝热体帮助减少锻模磨损。

UNIT 5 Powder Metallurgy Powder metallurgy(Fig.5.1) uses sintering process for making various parts out of metal powder. The metal powder is compacted by placing in a closed metal cavity (the die) under pressure.粉末冶金(图5.1)采用烧结工艺将金属粉末制成各种各样的零件。金属粉末放在封闭的金属腔(模具)中在压力下被压实。

This compacted material is placed in an oven and sintered in a controlled atmosphere at high temperatures and the metal powders coalesce and form a solid. A Second pressing operation, repressing, can be done prior to sintering to improve the compaction and the material properties.被压实的材料置于炉内，在气压受控的高温下烧结，金属粉末熔合形成固体。在烧结前可以进行二次挤压作业(再挤压)以改善压实状态和材料性能。

Powder metallurgy is a highly developed method of manufacturing reliable ferrous and nonferrous parts. Made by mixing elemental or alloy powders and compacting the mixture in a die, the resultant shapes are then sintered or heated in a controlled atmosphere furnace.粉末冶金是一种高度发达的制造可靠铁或非铁零件的方法。通过混合元素或合金粉末并在模具中压实混合物，再烧结或在气压受控炉内加热制成最终形状。

Material材料 The majority of the structural components produced by fixed die pressing are iron-based. The powders are elemental, pre-alloyed, or partially alloyed.大多数用固定模压制的结构件都是铁基的。粉末可以是单一元素、预先合金或部分合金。

Elemental powders, such as iron and copper, are easy to compress to relatively high densities, produce pressed compacts with adequate strength for handling during sintering, but do not produce very high strength sintered parts.诸如铁、铜之类的单一元素粉末较容易被压得相对密度较高、生产具备足够强度的压制物供烧结处理，但是无法制造出很高强度的烧结零件。

Pre-alloyed powders are harder, less compressible and hence require higher pressing loads to produce high density compacts. However, they are capable of producing high strength sintered materials.预先合金粉末比较硬、不容易压实，因此需要较高的挤压力来产生高密度的压制物。然而它们能生成高强度烧结材料。

Pre-alloying is also used when the production of a homogeneous material from elemental powders requires very high temperatures and long sintering times. The best examples are the stainless steels, whose chromium and nickel contents have to be pre-alloyed to allow economic production by powder metallurgy.如果用单一元素粉末生产均匀材料需要很高温度和较长烧结时间，也可用预先合金。最好的例子是不锈钢，因含有铬和镍成分，所以粉末冶金必须用预先合金才经济。

Partially alloyed powders are a compromise approach. Elemental powders, e.g. iron with 2wt.% copper, are mixed to produce an homogeneous blend which is then partially sintered to attach the copper particles to the iron particles without producing a fully diffused powder but retaining the powder form. 部分合金粉末是一种折衷的方法。单一元素粉末，例如铁与2%的铜(重量百分比) 混合均匀，经部分烧结后铜微粒粘附到铁微粒上而没有产生充分扩散的粉末却保留了粉末的形态。

In this way the compressibilities of the separate powders in the blend are maintained and the blend will not segregate during transportation and use. 用这种方法混合物中单独粉末的可压缩性得以维持，在运送和使用期间结合将不会分离。

A similar technique is to “glue” the small percentage of alloying element onto the iron powder. This “glueing” technique is successfully used to introduce carbon into the blends, a technique which prevents carbon segregation and dusting, producing so-called “clean” powders.另一种类似的技术是把小百分比的合金元素“粘合”到铁微粒上。这种“粘合”技术已成功用于将碳引入结合物，一种防止碳分离并起尘的技术，生产所谓的“清洁”粉末。

Powder Consolidation粉末合成 Components or articles are produced by forming a mass of powder into a shape, then consolidating to form inter-particle metallurgical bonds.通过将大量的粉末放入模具成型为零件或物品，然后合成为含有微粒的冶金结合物。

An elevated temperature diffusion process referred to as sintering, sometimes assisted by external pressure, accomplishes this. The material is never fully molten, although there might be a small volume fraction of liquid present during the sintering process. Sintering can be regarded as welding the particles present in the initial useful shape.提升温度扩散工艺被称为烧结，有时还辅之以外界的压力来达到目的。虽然在烧结过程中可能会有少量液态出现，但材料决不是全熔化。烧结可以被看作是把微粒焊接成初始的有用形状。

As a general rule both mechanical and physical properties improve with increasing density. Therefore the method selected for the fabrication of a component by powder metallurgy will depend on the level of performance required from the part. Many components are adequate when produced at 85~90% of theoretical full density whist others require full density for satisfactory performance.作为普遍规律，随着密度的增加机械和物理性能均改善。因此选择何种粉末冶金方法来制作零件取决于其所需的性能级别。许多零件只需理论全密度的85~90%而其它的则需全密度才能满足要求。

Some components, in particular bush type bearings often made from copper and its alloys, are produced with significant and controlled levels of porosity, the porosity being subsequently filled with a lubricant. 有些零件，尤其是衬套式轴承常用铜及其合金制作，控制多孔性程度的意义重大，因为这些孔随后要填充润滑剂。

Fortunately there is a wide choice of consolidation techniques available.还好有多种合成技术可供选择。

Cold Uniaxial Pressing冷单向挤压 Elemental metal, or an atomized pre-alloyed powder is mixed with a lubricant, typically lithium stearate(0.75 wt.%), and pressed at pressures of say, 600MPa (87,000lb/in.2) in metal dies. 单一元素金属，或极小颗粒的预先合金粉末与润滑剂(一般是锂硬脂酸盐，重量百分比0.75%)混合，然后在金属模具中施加压力[比如600MPa (87,000lb/in.2)]挤压。

Cold compaction ensures that the as-compacted, or “green”, component is dimensionally very accurate, as it is moulded precisely to the size and shape of the die.冷挤压能保证被压制或“未加工”的零件尺寸十分精确，因为它被精确地按模具的尺寸和形状成型。

One disadvantage of this technique is the differences in pressed density that can occur in different parts of the component due to particle/particle and die wall/particle frictional effects. Typical as-pressed densities for soft iron components would be 7.0g/cc, i. e. about 90% of theoretical density. 这种技术的一个缺点是由于微粒/微粒和模壁/微粒间的摩擦效应，零件不同部位的压实密度存在差异。典型的软铁零件压制密度为7.0g/cc，即大约是理论密度的90%。

Compaction pressure rises significantly if higher as-pressed densities are required, and this practice becomes uneconomic due to higher costs for the larger presses and stronger tools to withstand the higher pressures.如果需要较高的压实密度则压实压力要显著提高，因为大型压力机成本较高并且在较高压力下模具强度要更高这样就不合算。

Cold Isostatic Pressing冷均衡挤压 Metal powders are contained in an enclosure e.g. a rubber membrane or a metallic can that is subjected to isostatic, which is uniform in all directions, external pressure. As the pressure is isostatic the as-pressed component is of uniform density.金属粉末装入均衡受压的橡胶膜或金属罐内，其所受外压力在各个方向都是均匀的。由于压力是均衡的，所以压制零件密度是均匀的。

Irregularly shaped powder particles must be used to provide adequate green strength in the as-pressed component. This will then be sintered in a suitable atmosphere to yield the required product.必须采用不规则形状粉末微粒为压制零件提供足够的未加工强度。然后在合适的气压中烧结成所需产品。

Normally this technique is only used for semi-fabricated products such as bars, billets, sheet, and roughly shaped components, all of which require considerable secondary operations to produce the final, accurately dimensioned component. 通常这种技术只用于制作诸如棒料、坯段、薄板及粗糙成型零件之类的半成品，所有这些都需要大量进一步加工才能生产出最终尺寸精确的零件。

Again, at economical working pressures, products are not fully dense and usually need additional working such as hot extrusion, hot rolling or forging to fully density the material.此外使用经济工作压力的产品不是充分致密的，一般需要增加诸如热挤压、热轧或锻之类的额外工序来使材料达到充分致密。

Sintering烧结 Sintering is the process whereby powder compacts are heated so that adjacent particles fuse together, thus resulting in a solid article with improved mechanical strength compared to the powder compact. 烧结就是通过把粉末压制物加热使邻近的微粒熔合在一起的工艺，它能生成比粉末压制物机械强度更好的固体物。

This “fusing” of particles results in an increase in the density of the part and hence the process is sometimes called densification. There are some processes such as hot isostatic pressing which combine the compaction and sintering processes into a single step.微粒的“熔合”导致零件密度增加，因此该工艺有时被称为致密化。还有些工艺如热均衡挤压，将压实和烧结工艺合并为单一步骤。

After compaction the components pass through a sintering furnace. This typically has two heating zones, the first removes the lubricant, and the second higher temperature zone allows diffusion and bonding between powder particles.零件压实后通过一烧结炉。通常有两个加热区，第一个去除润滑剂，第二个温度更高的区域让粉末微粒之间扩散并结合。

A range of atmospheres, including vacuum, are used to sinter different materials depending on their chemical compositions. As an example, precise atmosphere control allows iron/carbon materials to be produced with specific carbon compositions and mechanical properties.根据不同材料的化学成分，烧结的气压范围(包括真空)也各不相同。例如精确的气压控制可生产具有特殊碳化物和机械性能的铁/碳材料。

The density of the component can also change during sintering, depending on the materials and the sintering temperature. These dimensional changes can be controlled by an understanding and control of the pressing and sintering parameters,根据材料和烧结温度的不同，零件的密度在烧结过程中也能改变。尺寸上的变化可以通过了解与调节挤压和烧结参数进行控制， and components can be produced with dimensions that need little or no rectification to meet the dimensional tolerances. Note that in many cases all of the powder used is present in the finished product, scrap losses will only occur when secondary machining operations are necessary. 所以零件尺寸几乎无需校正就能满足尺寸公差。注意到在很多情况下被使用的所有粉末都存在于制成品中，废料损失仅产生于需要辅助机加工时。

Hot Isostatic Pressing热均衡挤压 Powders are usually encapsulated in a metallic container but sometimes in glass. The container is evacuated, the powder out-gassed to avoid contamination of the materials by any residual gas during the consolidation stage and sealed-off. 粉末通常封装在金属容器内有时也装在玻璃容器内。把容器抽真空，粉末抽气是为了防止材料在合成阶段和密封时被残留气体污染。

It is then heated and subjected to isostatic pressure sufficient to plastically deform both the container and the powder.再加热并施加均衡压力足以使容器和粉末都塑性变形。

The rate of densification of the powder depends upon the yield strength of the powder at the temperatures and pressures chosen. At moderate temperature the yield strength of the powder can still be high and require high pressure to produce densification in an economic time.粉末致密率取决于该粉末在选定温度和压力下的屈服强度。中等温度下粉末的屈服强度仍然较高，因此需要较高压力使其在经济时间内致密化。

Typical values might be 1120℃ and 100MPa for ferrous alloys. By pressing at very much higher temperatures lower pressures are required as the yield strength of the material is lower. Using a glass enclosure atmospheric pressure(15psi) is used to consolidate bars and larger billets.对铁合金典型的数值可为1120℃和100MPa。由于很高温度下材料的屈服强度较低，因此只需较低压力就能挤压。采用玻璃容器大气压力(15psi)就可合成棒料和较大的坯段。

The technique requires considerable financial investment as the pressure vessel has to withstand the internal gas pressure and allow the powder to be heated to high temperatures.因为压力容器必须经受住内气压并允许粉末加热到较高温度，所以这种技术需要相当可观的资金投入。

As with cold isostatic pressing only semi-finished products are produced, either for subsequent working to smaller sizes, or for machining to finished dimensions.此工艺与采用冷均衡挤压一样只能生产半成品，可以通过后续加工至较小尺寸，也能用机加工到最终尺寸。

Hot Forging (Powder Forging) 热锻(粉末锻造) Cold pressed and sintered components have the great advantage of being close to final shape (near-net shape), but are not fully dense. Where densification is essential to provide adequate mechanical properties, the technique of hot forging, or powder forging, can be used.冷挤压和烧结零件主要优点是接近最终形状(近似纯形)，但不是充分致密的。当为了提供足够的机械性能而致密化是必须时，可以采用热锻或粉末锻造技术。

In powder forging an as-pressed component is usually heated to a forging temperature significantly below the usual sintering temperature of the material and then forged in a closed die. This produces a fully dense component with the shape of the forging die and appropriate mechanical properties.在粉末锻造中，压制零件一般加热到远低于该材料通常烧结温度的锻造温度，然后在闭模中锻造。这能生产具有锻模形状和合适机械性能的充分致密零件。

Powder forged parts generally are not as close to final size or shape as cold pressed and sintered parts. These results from the allowances made for thermal expansion effects and the need for draft angles on the forging tools. Further, minimal machining is required but when all things are considered this route is often very cost-effective.粉末锻造零件通常不像冷挤压和烧结零件那样接近最终尺寸或形状。这是由于为热膨胀效应而设置余量以及在锻模上需要拔模斜角所致。进一步还需最小限度的机加工，但全面考虑这种方法通常还是很合算的。

Metal Injection Moulding (MIM) 金属注塑成型(MIM) Injection moulding is very widely used to produce precisely shaped plastic components in complex dies. As injection pressures are low it is possible to manufacture complex components, even some with internal screw threads, by the use of side cores and split tools.注塑成型被很广泛地用于在复杂模具中生产形状精确的塑料零件。由于注塑压力较低，通过采用侧面型芯和分离工具，使得制作复杂零件成为可能，有些甚至可以带有内螺纹。

By mixing fine, typically less than 20 μm diameter, spherical metal powders with thermoplastic binders, metal filled plastic components can be produced with many of the features available in injection moulded plastics. After injection moulding, the plastic binder material is removed to leave a metal skeleton which is then sintered at high temperature.将细小( 直径一般小于20μm) 球形金属粉末与热塑性粘合剂混合，能生产具有多数注塑成型塑料特征的金属充满塑料零件。注塑成型后，去除塑料粘合材料剩下金属骨架，然后在高温下烧结。

Dimensional control can be exercised on the as-sintered component as the injected density is sensibly uniform so shrinkage on sintering is also uniform.烧结零件可以实现尺寸控制，因为注塑密度明显均匀，所以烧结收缩也是均匀的。

Shrinkage can be large, due to both the fine particle size of the powders and the substantial proportion of polymer binder used. 由于所用粉末细小微粒的尺寸和聚合物粘合剂的真实比例，收缩可以比较大。

Features特征 • For high tolerance parts, a sintering part is put back into a die and repressed. In genera this makes the part more accurate with a better surface finish.对较大公差的零件，烧结后可放回模具重新挤压。一般而言这会使零件更精确同时具有更好的表面光洁度。

• A part has many voids that can be impregnated. One method is to use an oil bath. Another method uses vacuum first, then impregnation.零件有许多可供填充的空间。一种方法是采用油浴。另一种方法是先抽真空然后再充满。

• A part surface can be infiltrated with a low melting point metal to increase density, strength, hardness, ductility and impact resistance. 零件表面能被低熔点金属渗透以增大密度、强度、硬度、延展性和抗冲击能力。

• Plating, heat treating and machining operations can also be used.仍然可以进行电镀、热处理和机加工作业。

Advantages优点 • Good tolerances and surface finish良好的公差和表面光洁度 • Highly complex shapes made quickly高度复杂的形状能快速制作 • Can produce porous parts and hard to manufacture materials (e.g. cemented oxides) 能制作多孔零件和难以加工材料(如粘结氧化物) • Pores in the metal can be filled with other materials/metals金属中的气孔可用其它材料/金属填充 • Surfaces can have high wear resistance表面能具有较高的耐磨性 • Porosity can be controlled孔隙率可以控制 • Low waste较低损耗 • Automation is easy容易自动化 • Physical properties can be controlled物理性能可以控制 • Variation from part to part is low零件之间的变化较小 • Hard to machine metals can be used easily难以机加工的金属能被容易使用 • No molten metals无需熔化金属 • No need for many/any finishing operations不需要很多/任何修整作业 • Permits high volume production of complex shapes允许加工复杂形状的大体积产品 • Allows non-traditional alloy combinations允许非传统合金结合 • Good control of final density对最终密度能很好地控制 Disadvantages缺点 • Metal powders deteriorate quickly when stored improperly如果存放不当金属粉末质量很快降低 • Fixed and setup costs are high安装和调整的成本较高 • Part size is limited by the press and compression of the powder used零件尺寸受压力机和所用粉末压缩的限制 • Sharp corners and varying thickness can be hard to produce锐角和变厚度较难加工 • Non-moldable features are impossible to produce不适合模压的东西不可能生产 UNIT 6 Injection Molding Injection molding (Fig.6.1) is the predominant process for fabrication of thermoplastics into finished forms, and is increasingly being used for thermosetting plastics, fiber-filled composites, and elastomers.注塑成型(图6.1)是将热塑性塑料制成最终形状的主要工艺，并且越来越多地用于热硬化性塑料、纤维填充合成物和人造橡胶。

It is the process of choice for tremendous variety of parts ranging in weight from 5g to 85kg. It is estimated that 25% of all thermoplastics are injection molded. 它是重量范围为5g到85kg极大一类零件可选用的工艺。估计所有热塑性塑料中有25%是采用注塑成型的。

If newer modifications, such as reaction injection molding, and the greatly increased rate of adoption of plastics as substitutes for metals are considered, it is likely that the worldwide industrial importance of injection molding will continue to increase.如果考虑到新近的改进(例如反作用注塑成型)和采用塑料替代金属的高增长率，注塑成型在世界范围的工业重要性很可能将继续增加。

Currently, probably close to half of all major processing units is injection molding machines. In 1988, a dollar sale of new injection molding machinery in the U.S. was approximately 65% of total major polymer machinery sales volume; this included 4,600 injection molding units. 当前，大概所有主要处理设备的近一半是注塑成型机。1988年，美国新的注塑成型机械销售约占全部主要聚合物机械销售量的65%，其中包括4,600台注塑成型设备。

The machines and their products are ubiquitous and are synonymous with plastics for many people.这类机械和它们的产品普遍存在，对许多人来说与塑料是同义的。

A reciprocating screw injection molding machine combines the functions of an extruder and a compressive molding press.往复螺旋注射成型机把压出机和成型压力机的功能结合起来。

It takes solid granules of thermoplastic resin, melts and pressurizes them in the extruder section, forces the melt at high velocity and pressure through carefully designed flow channels into a cooled mold, then ejects the finished part(s), and automatically recycles. 把热塑性塑料树脂的固体颗粒在压出部分融化并增压，迫使其高速融化并通过仔细设计的流动通道进入冷却模具，喷射成最终零件，然后自动再循环。

This machine is a descendant of the plunger type “stuffing machine” patented by the Hyatt brothers in 1872 to mold celluloid. In 1878, the Hyatts developed the first multicavity mold, but it was not until 1938 that Quillery (France) patented a machine incorporating a screw to plasticize the elastomer being molded.这种机械是1872年Hyatt兄弟获得专利权的融化赛璐珞的活塞型“填充机”的派生物。

1878年Hyatt兄弟开发了第一个多槽模具，但直到1938年Quillery(法国)才发明了用螺旋增塑人造橡胶并使其成型的一体化机械。

In 1956, Ankerwerk Nuremberg commercialized the modern reciprocating screw injection molding machine for thermoplastics. Today, over 50 machine manufacturers are listed in Modern Plastics Encyclopedia, offering machines to the U.S. market ranging from 2 to 6,000 tons clamping capacity. 1956年，Ankerwerk Nuremberg使用于热塑性塑料的现代往复螺旋注塑成型机商业化。今天，已有超过50家制造商列入现代塑料制品百科全书，能为美国市场提供压制能力从2到6,000吨的机械。

(A machine with a 10,000-ton capacity has been built to mold 264-gallon HDPE trash containers.) A host of suppliers of auxiliary equipment, molds, instruments, and controls service this major segment of the polymer industry.(一台能力为10,000吨用于成型264加仑高密度聚乙烯垃圾箱的机械也已制成)。许多辅助设备、模具、仪器和控制系统供应商在为聚合物工业的这一主要部分服务。

Injection molding is particularly worthy of intensive study because it combines many areas of interest extrusion, mold design, rheology, sophisticated hydraulic and electronic controls, robotic accessories, design of complex products, and, of course, the integration of materials science and process engineering.注塑成型对深入研究很有价值，因为它结合了许多重要领域，如挤压、模具设计、流变学、完备的液压和电子控制、机器人配件、复杂产品的设计，当然还有材料科学与加工工程的综合。

The objectives of injection molding engineers are simple enough: to obtain minimum cycle time with minimum scrap, to attain specified product performance with assurance, to minimize production costs due to downtime or any other reasons, and to steadily increase in expertise and competitiveness.注塑成型工程师的目标很简单：在最少废料的情况下取得最小循环时间，在有保证的情况下获得指定产品性能，将由停工或其它原因产生的生产成本最小化，还有稳定地增加专门知识和竞争力。

Profit margins for custom injection molders are said to be generally skimpy; an established way to improve profits is to be selected for more demanding, higher margin jobs that demand the highest level of efficiency and competence.传统的注塑成型机利润盈余据说一般是不足的；
为了更多需求及更高盈余工作需要选择一种改善利润的确定方法，它要求最高水平的效率和能力。

This text will concentrate on the reciprocating screw machine for thermoplastics, which has largely replaced the older reciprocating plunger types except for very small-capacity machines.本文将集中论述热塑性塑料用的往复螺旋机，除了小容量机械外它已在很大程度上取代了较老的往复活塞式机械。

Injection Molding Materials注塑成型材料 It is not possible to injection-mold all polymers. Some polymers like PTFE (Poly-tetra-fluoro-ethylene), cannot be made to flow freely enough to make them suitable for injection molding.要注塑成型所有聚合物是不可能的。像聚四氟乙烯之类的聚合物就不能自由流动得足以适合注塑成型。

Other polymers, such as a mixture of resin and glass fiber in woven or mat form, are unsuitable by their physical nature for use in the process. In general, polymers which are capable of being brought to a state of fluidity can be injection-molded.其它聚合物，例如树脂和编织的或垫子形的玻璃纤维的混合物，由于它们的物理性质不适合使用此工艺。一般而言，能进入流动状态的聚合物都可以注塑成型。

The vast majority of injection molding is applied to thermoplastic polymers. This class of materials consists of polymers which always remain capable of being softened by heat and of hardening on cooling, even after repeated cycling. 注塑成型的绝大多数都用于热塑性聚合物。这类材料由具有加热软化、冷却硬化甚至可重复循环能力的聚合物组成。

This is because the long-chain molecules of the material always remain as separate entities and do not form chemical bonds to one another. An analogy car, be made to a block of ice that can be softened (i.e. turned back to liquid), poured into any shape cavity, and then cooled to become a solid again. 这是由于这类材料的长链分子总是保持分离的实体并不相互形成化学连结。一辆由冰块制成的模拟汽车，可以融化(即转化为液态)，倒入任何形状的空腔，然后冷却重新变成固体。

This property differentiates thermoplastic materials from thermosetting ones. In the latter type of polymer, chemical bonds are formed between the separate molecule chains during processing. In this case the chemical bonding referred to as cross linking is the hardening mechanism.这个特性将热塑性材料与热硬化性材料区分开。后者在加工过程中分离的分子链之间形成化学连结。在此情况下作为交联的化学连结是硬化机制。

In general, most of the thermoplastic materials offer high impact strength, corrosion resistance, and easy processing with good flow characteristics for molding complex designs. Thermoplastics are generally divided into two classes: namely crystalline and amorphous. 一般而言，大多数热塑性材料具有较高的抗冲击强度、耐腐蚀性以及良好流动性使其容易加工而适于复杂成型设计。热塑性塑料通常分为两类：即结晶质的和非结晶质的。

Crystalline polymers have an ordered molecular arrangement, with a sharp melting point. Due to the ordered arrangement at molecules, the crystalline polymers reflect most incidents light and generally appear opaque. 结晶质聚合物具有规则的分子排列及明显的熔点。由于规则的分子排列，结晶质聚合物能反射大多数特定光线并一般表现为不透明的。

They also undergo a high shrinkage or reduction in volume during solidification. Crystalline polymers usually are more resistant to organic solvents and have good fatigue and wear-resistant properties. Crystalline polymers also generally are denser and have better mechanical properties than amorphous polymers. 它们在固化过程中收缩较大或体积减少较多。结晶质聚合物通常多能抵御有机溶剂并具有良好的抗疲劳和磨损特性。结晶质聚合物通常也比非结晶质聚合物更致密并且具有更好的机械性能。

The main exception to this rule is polycarbonate, which is the amorphous polymer of choice for high quality transparent moldings, and has excellent mechanical properties.其中主要例外是聚碳酸酯，它是可选用做高质量透明注塑件的非结晶质聚合物，并具有卓越的机械性能。

The mechanical properties of thermoplastics, while substantially lower than those of metals, can be enhanced for some applications through the addition of glass fiber reinforcement. This takes the form of short-chopped fibers, a few millimeters in length, which are randomly mixed with the thermoplastic resin.就本质而言，热塑性塑料的机械性能低于金属，但可以通过加入玻璃纤维强化予以增强来适应某些运用。常用几毫米长的短碎纤维随机地与热塑性树脂混合。

The fibers can occupy up to one third of the material volume to considerably improve the material strength and stiffness. The negative effect of this reinforcement is usually a decrease in impact strength and an increase in abrasiveness. 纤维可占材料体积的三分之一以极大改善材料的强度和硬度。这种加强的负作用通常是抗冲击强度降低及磨损性增加。

The latter also has an effect on processing since the life of the mold cavity is typically reduced from about 1,000,000 parts for plain resin parts to about 300,000 for glass-filled parts.后者对加工过程也有影响，因为模具腔的寿命从典型的普通树脂零件大约1,000,000件减少到玻璃纤维填充树脂零件的约300,000件。

Perhaps the main weakness of injection-molded parts is the relatively low service temperatures to which they can be subjected. Thermoplastic components can only rarely be operated continuously above 250℃, with an absolute upper service temperature of about 400℃. 注塑成型零件的主要缺点或许是它们能承受的工作温度相对较低。热塑性塑料零件只有很少能连续运行在250℃以上，其绝对最高工作温度约为400℃。

The temperature at which a thermoplastic can be operated under load can be defined qualitatively by the heat deflection temperature. This is the temperature at which a simply supported beam specimen of the material, with a centrally applied load, reaches a predefined deflection. 热塑性塑料带载运行温度可从质量上定义为热偏差温度。这是中心承载的该材料简支梁达到预定偏差的温度。

The temperature value obviously depends upon the conditions of the test and the allowed deflection and for this reason, the test values are only really useful for comparing different polymers.其温度值明显取决于试验条件和允许偏差，因此对比较不同的聚合物而言只有试验数据是真正有用的。

Cycle of Operation作业循环 The reciprocating screw injection molding machine is considered as consisting of two halves: a fixed injection side, and a movable clamp side.螺旋注塑成型机被认为由两部分组成：一个固定注塑端和一个活动夹具端。

The injection side contains the extruder that receives solid resin in pellet or granular form and converts it into a viscous liquid or melt that can be forced through the connecting nozzle, spine, and runners to the gates that lead into the mold cavities. 注塑端包含压出机，它接受小球或粒状的固体树脂，然后将其转化为粘性液体或称为融化，再强迫其通过连接喷嘴、中心和浇道到闸道进入模具腔。

The mold is tightly clamped against injection pressure and is cooled well below the melt temperature of the thermoplastic. When the parts in the cavities have cooled sufficiently the mold halves are opened at the mold parting plane and the parts ejected by a knockout system drop into a receiving bin below. 模具被紧紧地夹住以抵抗注塑压力，并在热塑性塑料的融化温度以下很好地冷却。当模腔内的零件充分冷却，剖分模在模具分模面处打开，推出系统将零件推出落入下面的接收容器内。

This summarizes the overall cycle, but leaves out much vital detail that is necessary for understanding the process. However, with this introduction, it is possible to understand the advantages and disadvantages of the process.这概述了整个循环，但省略了许多对理解此工艺所必需的很重要细节。然而通过本介绍，了解这种工艺的优缺点仍是可能的。

Effects of Process Variables on Orientation加工变量对方向性的影响 In injection molding, any variation in processing that keeps the molding resin hot throughout filling allows increased relaxation and, therefore, decreased orientation. Some of the steps that can be taken to reduce orientation are as follows.在注塑成型时，整个填料过程始终保持成型树脂高温的任何加工变化都会增加松弛作用而减少方向性。下面是可以用于减少方向性的若干措施。

• Faster injection (up to a point): less cooling during filling, hence a thinner initial frozen layer, lower viscosity due to shear thinning; better flow to corners; and less crystallinity all favor lower subsurface orientation. The primary effect is that the gate will freeze more quickly. At that point, orientation stops and relaxation starts.较快注塑(到点)：在填料过程中冷却较少，因此初始固化层较薄，由于剪应变稀少而粘性较低；
能较好地流到角落；
结晶度较小；
所有这些促成表面下的方向性也较低。主要效果是闸道将较快固化。这样使得方向性停止产生而松弛作用开始增加。

• Higher melt and mold temperatures: lower melt viscosity, easier filling, and greater relaxation favor reduced orientation. 较高的融化和成型温度：融化粘性较低，更容易填充，较大松弛作用促成方向性减少。

• Reduced packing time and pressure: overpacking inhibits relaxation processes.减少挤压时间和压力：过度挤压会抑制松弛过程。

• Reduced gate size: larger gates take longer to freeze off and permit increased orientation. 减小闸道尺寸：闸道越大则固化时间越长并会使方向性增加。

Excessively high injection speed can cause high surface orientation and increase susceptibility to stress cracking. For example, moldings that are to be electroplated, and will be subject to acid solutions during plating, must be made using very slow injection speeds to minimize surface orientation. 过高的注塑速度会引起较高的表面方向性及增加应力破裂的敏感性。例如，要电镀的注塑件在电镀时会经受酸溶液，必须采用很低的注塑速度制造以使表面方向性最小化。

On the other hand, the transverse motion component of the melt front in most moldings can cause transverse subsurface orientation superimposed on the primary orientation, giving a desirable biaxial orientation effect.另一方面，大多数注塑件的融化前部横向运动部分能导致在主要方向性上有层理的表面下横向方向性，产生需要的双轴方向性效应。

Orientation can be seriously increased by obstructions to flow during filling of the cavity. Flow around an obstruction causes a decrease in melt front speed and leads to high local viscosity and reduced relaxation. This is also likely to occur near the end of the filling phase if gating is inadequate.在填充模腔时流动受到阻碍会极大地增加方向性。围绕障碍物流动使融化前部的速度下降并产生较高的局部粘性而减少松弛作用。如果闸道不适当，这也很可能发生在接近填充结束阶段。

The molder must recognize the dangers of excessive fill speed, insufficient injection pressure, excessive melt temperature, and inadequate packing. These dangers are weighed against the opposing effects on orientation discussed above.注塑工必须认识过快填充速度、不足注塑压力、过高融化温度和不充分挤压的危害性。这些危害性要与上述方向性的反向效应相权衡。

Thicker parts delay cooling and increase relaxation time and tend to result in lower orientation. Thicker parts also tend to warp less. Therefore, a minimum wall thickness can be established by experience for various shapes, materials, and process combinations. 较厚零件会延迟冷却并且增加松弛时间，趋向于导致较低的方向性。较厚零件也有助于减少翘曲。因此，对各种形状、材料和工艺组合能通过经验来确定最小壁厚。

Lower molecular weight and broader molecular weight distribution in thermoplastics favor lower orientation and reduced internal stress in moldings.在热塑性塑料中较小的分子量以及较宽泛的分子量分布促成方向性减少同时降低注塑件中的内应力。

The skin thickness ratio is affected by process variables in the same way as one would predict for the orientation; that is, it decreases as the melt or mold temperatures and cavity pressure increases. Tensile strength and stiffness increase as skin thickness ratio increases. Microscopic examination thus provides another way of studying the process efficiently.外壳厚度比受加工变量影响的方式与方向性预测一样；
也就是它能随融化或成型温度及模腔压力的增加而减少。拉伸强度和硬度随外壳厚度比增加而增加。因而显微镜检查提供了有效研究该工艺的另一方法。

Advantages优点 1. High production rates. For example, a CD disk can be produced with a 10~12s cycle in high melt flow index PC.1. 高生产率：例如，一张CD盘在高融体流动指数生产控制中只需10~12s一个循环就能生产出来。

2. Relatively low labor content. One operator can frequently take care of two or more machines, particularly the moldings are unloaded automatically onto conveyors.2. 相对较少的工作内容：一个操作者经常可以照看两台以上机械，尤其是当成品能自动卸到输送机上时。

3. Parts require little or no finishing. For example, flash can be minimized and molds can be arranged to automatically separate runners and gates from the part itself. 3. 零件几乎不需要修整：例如，飞边可以最小化并且模具能被设计成自动将浇道和闸道从零件本身分离。

4. Very complex shapes can be formed. Advances in mold tooling are largely responsible.4. 非常复杂的形状也能成型：模具的进步很大程度上是可靠的。

5. Flexibility of design (finishes, colors, inserts, materials). More than one material can be molded through co-injection. Foam core materials with solid skins are efficiently produced. Thermosetting plastics and fiber-reinforced shapes are injection molded.5. 设计的灵活性(光洁度、颜色、插入物、材料)：通过复合注塑可以成型多于一种材料。可以高效地生产带有固体外壳的泡沫型芯材料。热硬化性塑料和纤维加强形状都可以注塑成型。

6. Minimum scrap loss. Runners, gates, and scrap can usually be reground. Recycled thermoplastics can be injection molded.6. 废料损失最小化：浇道、闸道和废料通常可以重新研磨。循环热塑性塑料可以注塑成型。

7. Close tolerances are obtainable. Modern microprocessor controls, fitted to precision molds, and elaborate hydraulics, facilitate tolerances in the 0.1% range on dimensions and weights (but not without a high level of operational skills in constant attendance).7. 能得到接近的公差：现代微处理器控制、合适的精密模具和精心制作的液压设备使得尺寸和重量的公差保持在0.1% 的范围内(但不是没有在持续照看时的高水平操作技能)。

8. Makes best use of the unique attributes of polymers, such as flow ability, light weight, transparency, and corrosion resistance. This is evident from the number and variety of molded plastic products in everyday use.8. 充分利用聚合物诸如流动能力、重量轻、透明和耐腐蚀等独特属性：从日常使用成型塑料产品的数量和种类就能明显看到。

Disadvantages and Problems缺点和问题 1. High investment in equipment and tools requires high production volumes. 1. 较高的设备和模具投资需要较高生产量才合算。

2. Lack of expertise and good preventive maintenance can cause high startup and running costs.2. 缺少专门技术和良好的预防性维修会导致较高的启动和运行成本。

3. Quality is sometimes difficult to determine immediately. For example, post-mold warpage may render parts unusable because of dimensional changes that are not completed for weeks or months after molding.3. 质量有时难以马上确定。例如，成型后的翘曲会导致零件不能用，因为在成型后几星期甚至几个月尺寸变化都不能完成。

4. Attention is required on many details requiring a wide variety of skills and cross-disciplinary knowledge. 4. 对许多需要广泛多样性技能和交叉学科知识的细节必须加以注意。

5. Part design sometimes is not well suited to efficient molding.5. 零件设计有时不能很好地适应有效率的成型。

6. Lead time for mold design, mold manufacture and debugging trials is sometimes very long.6. 模具设计、模具制造和调试试验这些先导工作有时要花费很长时间。

UNIT 7 Metal Cutting The importance of machining processes can be emphasised by the fact that every product we use in our daily life has undergone this process either directly or indirectly. 机加工过程的重要性可通过日常生活使用的每件产品都直接或间接经历这一过程的事实来强调。

(1) In USA, more than $100 billions are spent annually on machining and related operations.(1)在美国，每年花在机加工及其相关作业上的费用都多于千亿美元。

(2) A large majority (above 80%) of all the machine tools used in the manufacturing industry have undergone metal cutting. (2) 用于制造业的全部机床中的大多数(多于80%)都经历过金属切削。

(3) An estimate showed that about 10 to 15% of all the metal produced in USA was converted into chips.(3) 有估计显示美国生产的所有金属中约10到15%转变成了切屑。

These facts show the importance of metal cutting in general manufacturing. It is therefore important to understand the metal cutting process in order to make the best use of it. 这些事实说明了金属切削在常规制造中的重要性。因此了解金属切削过程以充分利用它是重要的。

A number of attempts have been made in understanding the metal cutting process and using this knowledge to help improve manufacturing operations which involved metal cutting.在了解金属切削过程并运用这些知识帮助改善与金属切削有关的制造作业方面已经做了许多努力。

A typical cutting tool in simplified form is shown in Fig.7.1. The important features to be observed are follows.典型切削刀具的简化形式如图7.1所示。要注意的重要特征如下。

1. Rake angle. It is the angle between the face of the tool called the rake face and the normal to the machining direction. Higher the rake angle, better is the cutting and less are the cutting forces, increasing the rake angle reduces the metal backup available at the tool rake face. 1.前角：它是被称为前倾面的刀具面与垂直机加工方向的夹角。前角越大，则切削越好且切削力越小，增加前角可以减少刀具前倾面上产生的金属阻塞。

This reduces the strength of the tool tip as well as the heat dissipation through the tool. Thus, there is a maximum limit to the rake angle and this is generally of the order of 15°for high speed steel tools cutting mild steel. It is possible to have rake angles at zero or negative.但这会和减少通过刀具散发的热量一样减少刀尖强度。因此前角有一最大限制，用高速钢刀具切削低碳钢通常为15°。前角取零度或负值也是可能的。

2. Clearance angle. This is the angle between the machined surface and the underside of the tool called the flank face. The clearance angle is provided such that the tool will not rub the machined surface thus spoiling the surface and increasing the cutting forces. A very large clearance angle reduces the strength of the tool tip, and hence normally an angle of the order of 5~6°is used.2. 后角：这是机加工面与被称为后侧面的刀具底面夹角。后角使刀具不产生会损坏机加工面的摩擦和增加切削力。很大的后角会削弱刀尖的强度，因此一般采用5~6°的后角。

The conditions which have an important influence on metal cutting are work material, cutting tool material, cutting tool geometry, cutting speed, feed rate, depth of cut and cutting fluid used.对金属切削有重要影响的条件有工件材料、刀具材料、刀具几何形状、切削速度、进给率、切削深度和所用的切削液。

The cutting speed, v, is the speed with which the cutting tool moves through the work material. This is generally expressed in metres per second (ms-1). 切削速度v指切削刀具经过工件材料的移动速度。通常用米每秒 (ms-1)表示。

Feed rate, f, may be defined as the small relative movement per cycle (per revolution or per stroke) of the cutting tool in a direction usually normal to the cutting speed direction. 进给率f可定义为每循环(每转或每行程)切削刀具在通常为垂直于切削速度方向的次要相对运动。

Depth of cut, d, is the normal distance between the unmachined surface and the machined surface.切削深度d是未加工面与已加工面之间的垂直距离。

Chip Formation切屑的形成 Metal cutting process is a very complex process. Fig.7.2 shows the basic material removal operation schematically.金属切削过程是一个很复杂的过程。图7.2用图的形式显示了基本材料去除作业。

The metal in front of the tool rake face gets immediately compressed, first elastically and then plastically. This zone is traditionally called shear zone in view of fact that the material in the final form would be removed by shear from the parent metal. 在刀具前倾面前的金属直接受到压缩，首先弹性变形然后塑性变形。考虑到最终形状中的材料是通过剪切从母体金属去除的，此区域传统上称为剪切区。

The actual separation of the metal starts as a yielding or fracture, depending upon the cutting conditions, starting from the cutting tool tip. Then the deformed metal (called chip) flows over the tool (rake) face. 金属的实际分离始于屈服或断裂(视切削条件而定)，从切削刀尖开始。然后变形金属(称为切屑)流过刀具(前倾)面。

If the friction between the tool rake face and the underside of the chip (deformed material) is considerable, then the chip gets further deformed, which is termed as secondary deformation. The chip after sliding over the tool rake face is lifted away from the tool, and the resultant curvature of the chip is termed as chip curl.如果刀具前倾面与切屑(变形金属)底面之间的摩擦相当大，那么切屑进一步变形，这也叫做二次变形。滑过刀具前倾面的切屑被提升离开刀具，切屑弯曲的结果被称为切屑卷。

Plastic deformation can be caused by yielding, in which case strained layers of material would get displaced over other layers along the slip-planes which coincide with the direction of maximum shear stress.屈服能导致塑性变形，在这种情况下材料变形层沿着与最大剪应力方向一致的滑移面被其它层所取代。

A chip is variable both in size and shape in actual manufacturing practice. Study of chips is one of the most important things in metal cutting. As would be seen later, the mechanics of metal cutting are greatly dependent on the shape and size of the chips produced.在实际加工过程中切屑的尺寸和形状都是变化的。对切屑的研究是金属切削最重要的事情之一。如同后面将要看到的那样，金属切削力学极大地依赖于所产生切屑的形状和尺寸。

Chip formation in metal cutting could be broadly categorised into three types: (Fig.7.3) 金属切削中的切屑形成可以宽泛地分成三个类型(图7.3)：
(1) Discontinuous chip(1)间断切屑 (2) Continuous chip(2)连续切屑 (3) Continuous chip with BUE (Built up edge)(3)带切屑瘤的连续切屑 Discontinuous Chip. The segmented chip separates into short pieces, which may or may not adhere to each other. Severe distortion of the metal occurs adjacent to the face, resulting in a crack that runs ahead of the tool. 间断切屑：分段的切屑分散成小碎片，既可能相互附着也可能不相互附着。在靠近切削面处发生金属的剧烈变形，导致在运动刀具前方金属层产生裂缝。

Eventually, the shear stress across the chip becomes equal to the shear strength of the material, resulting in fracture and separation. With this type of chip, there is little relative movement of the chip along the tool face, Fig.7.3a.最后，横过切屑的剪切应力与材料的剪切强度相等，造成断裂和分离。生成这类切屑时，切屑沿刀具面几乎没有相对运动，见图7.3a。

Continuous chip. The continuous chip is characterized by a general flow of the separated metal along the tool face. There may be some cracking of the chip, but in this case it usually does not extend far enough to cause fracture.连续切屑：连续的切屑一般具有分离金属沿刀具面流动的特征。切屑可能有一些破裂，但在这种情况下切屑通常不会延长到足以引起断裂。

This chip is formed at the higher cutting speeds when machining ductile materials. There is little tendency for the material to adhere to the tool. The continuous chip usually shows a good cutting ratio and tends to produce the optimum surface finish, but it may become an operating hazard, Fig.7.3b.这种切屑形成于用较高切削速度机加工有延展性的材料时。材料几乎没有粘附刀具的倾向。连续切屑通常具有良好的切削率和趋向于产生最适宜的表面光洁度，但可能成为操作的危险之源，见图7.3b。

Continuous with a built-up edge. This chip shows the existence of a localized, highly deformed zone of material attached or “welded” on the tool face. 带切屑瘤的连续切屑：这种切屑显示了粘合或“焊接”在刀具面上材料局部高度变形区的存在。

Actually, analysis of photomicrographs shows that this built-up edge is held in place by the static friction force until it becomes so large that the external forces acting on it cause it to dislodge, with some of it remaining on the machined surface and the rest passing off on the back side of the chip, Fig.7.3c.实际上，对显微照片的分析显示这种切屑瘤受到静摩擦力抑制直至它变得大到作用在它上面的外力使其移动，一些留在机加工表面上而另一些延伸到切屑的背面，见图7.3c。

Shear Zone剪切区 There are basically two schools of thought in the analysis of the metal removal process. One school of thought is that the deformation zone is very thin and planar as shown in Fig.7.4a. The other school thinks that the actual deformation zone is a thick one with a fan shape as shown in Fig.7.4b.在对金属去除过程的分析中主要存在两种思想学派。一种思想学派认为变形区如图7.4a所示那样非常薄而平坦。另一学派则认为真实变形区象图7.4b所示那样为一厚的带有扇形的区域。

Though the first model (Fig.7.4a) is convenient from the point of analysis, physically it is impossible to exist. This is because for the transition from undeformed material to deform to take place along a thin plane, the acceleration across the plane has to be infinity. 虽然第一种模型(图7.4a)从分析的角度看是方便的，但实际上是不可能存在的。这是由于未变形的材料沿着剪切面发生变形，而且越过剪切面的加速度无穷大。

Similarly the stress gradient across the shear plane has to be very large to be practical. 同样在实际运用中越过剪切面的应力梯度必须很大才行。

In the second model (Fig.7.4b) by making the shear zone over a region, the transitions in velocities and shear stresses could be realistically accounted for.在第二种模型(图7.4b)中让剪力区分布于一个范围，速度和剪应力的转变能说明得更符合实际。

The angle made by the shear plane with the cutting speed vector, Φ is a very important parameter in metal cutting. Higher the shear angle better is the cutting performance. From a view of the Fig.7.4a, it can be observed that a higher rake angles give rise to higher shear angles.由剪切面和切削速度矢量形成的角度Φ在金属切削中是一个十分重要的 参数。剪切角越大，切削作业越好。从图7.4a 观察，可以看到较大的前角能增大剪切角。

Cutting Tool Materials切削刀具材料 Various cutting tool materials have been used in the industry for different applications. A number of developments have occurred in the current century.在工业中为了不同的应用可以使用各种各样的切削刀具材料。在最近的百年里产生了许多进展。

A large variety of cutting tool materials has been developed to cater to the variety of materials used in these programmes. Before we discuss the properties of these materials, let us look at the important characteristics expected of a cutting tool material. 多种切削刀具材料被开发出来以满足这些方案中使用材料的多样性。讨论这些材料性能之前，先看一下作为切削刀具材料应具备哪些重要特性。

1. Higher hardness than that of the workpiece material being machined, so that it can penetrate into the work material. 1. 硬度要比被切削工件材料高，这样它才能进入工件材料。

2. Hot hardness, which is the ability of the material to retain its hardness at elevated temperatures in view of the high temperatures existing in the cutting zone.2. 热硬度，即材料由于存在于切削区的高温而升温时仍能保持其硬度的能力。

3. Wear resistance—The chip-tool and chip-work interfaces are exposed to such severe conditions that adhesive and abrasion wear is very common. The cutting tool material should therefore have high abrasion resistance to improve the effective life of the tool.3. 耐磨性—切屑-刀具与切屑-工件的接触界面处于如此严酷的状态，粘附和磨损是很普遍的。因此切削刀具材料应具有高耐磨性以提高刀具的有效寿命。

4. Toughness—Even though the tool is hard, it should have enough toughness to withstand the impact loads that come in the beginning of cut or force fluctuations due to imperfections in the work material. This requirement is going to be more useful for the interrupted cutting, e.g. milling.4. 韧性—虽然刀具是坚硬的，但也应有足够的韧性以经受住冲击载荷，这些载荷来自于切削的开始或由于工件材料的缺陷而产生的作用力波动。这个要求对如铣削之类的间断切削更有用。

5. Low friction—The coefficient of friction between the chip and tool should be low. This would allow for lower wear rates and better chip flow.5. 低摩擦系数—切屑与刀具间的摩擦系数应当较低。这会使磨损率较小及切屑流动更好。

6. Thermal characteristics—Since a lot of heat is generated at the cutting zone, the tool material should have higher thermal conductivity to dissipate this heat in the shortest time, otherwise the tool temperature would become high, reducing its life.6. 热特性—因为大量的热产生在切削区，刀具材料应当具有较高的热传导性以在最短的时间内散发热量，否则刀具温度会升高，寿命会减少。

All these characteristics may not be found in a single tool material. Improved tool materials have been giving a better cutting performance.所有这些特性不可能存在于单一刀具材料中。改进的刀具材料已经被赋予较好的切削性能。

Surface Finish 表面光洁度 Machining operations are utilized in view of the better surface finish that could be achieved by it compared to other manufacturing operations.由于机加工能获得比其它制造作业更好的表面光洁度，所以机加工作业具有实用价值。

Thus it is important to know what would be the effective surface finish that can be achieved in a machining operation. The surface finish in a given machining operation is a result of two factors:因而了解能在机加工作业中获得怎样的实际表面光洁度是重要的。给定机加工作业中的表面光洁度是两个因素共同作用的结果：
(1) the ideal surface finish, which is a result of the geometry of the manufacturing process which can be determined by considering the geometry of the machining operation, and理想的表面光洁度，是通过考虑机加工作业的几何体系所决定的制造工艺几何学的结果，和 (2) the natural component, which is a result of a number of uncontrollable factors in machining, which is difficult to predict. 自然要素，即在机加工中一些难以预测的不可控因素作用的结果。

Ideal Surface Finish in Turning车削中的理想表面光洁度 The actual turning tool used would have a nose radius in place of the sharp tool point, which modifies the surface geometry as shown in Fig.7.5a. If the feed rate is very small, as is normal in finish turning, the surface is produced purely by the nose radius alone as shown in Fig.7.5.实际使用的车削刀具有一个刀尖半径取代锋利刀尖，它将表面几何形状加工为如图7.5a所示。如果进给率很小，象精车中很正常的那样，工件表面则完全是由刀尖半径单独产生的，如图7.5所示。

For the case in Fig.7.5, the surface roughness value is to be对图7.5这种情况，表面粗糙度值为 Ra=8f2/(18R√3) Ra=8f2/(18R√3) Where: Ra is the surface roughness value R is the nose radius f is the feed rate 式中：Ra是表面粗糙度值R是刀尖半径f是进给率 The above are essentially geometric factors and the values represent an ideal situation. The actual surface finish obtained depends to a great extent upon a number of factors such as:上述基本为几何要素，其值代表了理想情况。而实际获得的表面光洁度很大程度上还取决于下列一些因素：
(1) the cutting process parameter, speed, feed and depth of cut(1)切削工艺参数、速度、进给和切削深度 (2) the geometry of the cutting tool(2)切削刀具的几何形状 (3) application of cutting fluid(3)切削液的运用 (4) work and tool material characteristics(4)工件和刀具的材料特性 (5) rigidity of the machine tool and the consequent vibrations. (5)机床的刚度及其伴随发生的振动 The major influence on surface finish is exerted by the feed rate and cutting speed. As the feed decreases, from the above equations, we can see that the roughness index decreases. 对表面光洁度产生主要影响的是进给率和切削速度。从上述公式可以看到，随着进给的减少，粗糙度指标会降低。

Similarly as the cutting speed increases, we have better surface finish. Thus while making a choice of cutting process parameters for finish, it is desirable to have high cutting speed and small feed rates.同样随着切削速度的增大，能得到较好表面光洁度。因此在为光洁度而选择切削工艺参数时，采用较高的切削速度和较小的进给率是适当的。

Cutting Fluids 切削液 The functions of cutting fluids (which are often erroneously called coolants) are: 切削液(经常误称为冷却液)的功能如下：
• To cool the tool and workpiece冷却刀具和工件 • To reduce the friction减少摩擦 • To protect the work against rusting保护工件不生锈 • To improve the surface finish改善表面光洁度 • To prevent the formation of built-up edge防止切屑瘤的形成 • To wash away the chips from the cutting zone从切削区冲掉切屑 However, the prime function of a cutting fluid in a metal cutting operation is to control the total heat. This can be done by dissipating the heat generated as well as reducing it. The mechanisms by which a cutting fluid performs these functions are: cooling action and lubricating action.然而，在金属切削作业中切削液的主要功能是控制总热量。这可通过既散发又减少所产生的热量来达到。切削液实现这些功能的机理是：冷却作用和润滑作用。

Cooling action. Originally it was assumed that cutting fluid improves the cutting performance by its cooling properties alone. That is why the name coolant was given to it. 冷却作用：最初设想切削液仅仅是通过冷却特性来改善切削作业。这也是它曾被称为冷却液的原因。

Since most of the tool wear mechanisms are thermally activated, cooling the chip tool interface helps in retaining the original properties of the tool and hence prolongs its life. 由于大多数刀具的磨损机理都是由热引起的，冷却切屑刀具接触界面有助于保持刀具的原有特性，从而延长其使用寿命。

However, a reduction in the temperature of the workpiece may under certain conditions increase the shear flow stress of the workpiece, thereby decreasing tool life. It has been shown through a number of investigations that cooling in fact is one of the major factors in improving the cutting performance.可是工件温度的降低在特定条件下会增加工件的剪切流动应力，从而降低刀具寿命。通过一些研究已经表明实际上冷却只是改善切削作业的主要因素之一。

Lubricating action. The best improvement in cutting performance can be achieved by the lubricating action since this reduces the heat generated, thus reducing the energy input to the metal cutting operation. 润滑作用：切削作业的最大改善可通过润滑作用来达到，由于它减少了热量的产生因而减少了金属切削作业的能量输入。

However, if the cutting fluid is to be effective, it must reach the chip tool interface. But it is not easy to visualize how it is accomplished in the case of a continuous turning with a single point turning tool, specially when the chip-tool contact pressure is as high as 70 MPa. 可是，如果要使切削液起作用就必须让它到达切屑刀具接触界面。但如何在采用单尖刀具连续车削的场合尤其是切屑-刀具接触压力高达70MPa时实现并非易事。

Merchant thought that minute asperities existed at the chip-tool interface and the fluid was drawn into the interface by the capillary action of the interlocking network of these surface asperities. Merchant认为：在切屑与刀具接触界面上存在微小的粗粒，切削液通过这些表面的微小粗粒组成连锁的网络的毛细管被吸入到切屑与刀具的接触界面上。

UNIT 8 Grinding Grinding is a manufacturing process that involves the removal of metal by employing a rotating abrasive wheel. The latter simulates a milling cutter with an extremely large number of miniature cutting edges. 磨削是通过采用旋转磨轮去除金属的制造工艺。磨轮用非常大量的微型切削刃模仿铣刀进行切削。

Generally, grinding is considered to be a finishing process that is usually used for obtaining high-dimensional accuracy and better surface finish. Grinding can be performed on flat, cylindrical, or even internal surfaces by employing specialized machine tools, which are referred to as grinding machines.一般而言，磨削被认为是一种通常用于获得高尺寸精度和较好表面光洁度的精加工作业。磨削通过采用被称为磨床的特殊机床能在平面、圆柱面甚至内表面上进行。

Obviously, grinding machines differ in construction as well as capabilities, and the type to be employed is determined mainly by the geometrical shape and nature of the surface to be ground, e.g., cylindrical surfaces are ground on cylindrical grinding machines.显然，磨床根据结构和功能的不同有所区别，使用何种形式的磨床主要取决于被磨削表面的几何形状和物理性质。例如，圆柱面在外圆磨床上磨削。

Type of Grinding Operations磨削作业的类型 1. Surface grinding. As the name surface grinding suggests, this operation involves grinding of flat or plane surfaces. Fig.8.1 indicates the two possible variations, either a horizontal or vertical machine spindle.1. 表面磨削：就像其名称暗示的那样，表面磨削和平面磨削直接有关。图8.1表示了两种可能的变化：卧式磨床主轴或立式磨床主轴。

In the first case (horizontal spindle), the machine usually has a planer-type reciprocating table on which the workpiece is held. However, grinding machines with vertical spindles can have either a planer type table like that of the horizontal-spindle machine or a rotating worktable.在第一种情况(卧式主轴)，卧式磨床通常具有安装工件的刨床式往复工作台。而立式主轴磨床既可以像卧式主轴磨床那样具有刨床式工作台也可以具有旋转工作台。

Also, the grinding action in this case is achieved by the end face of the grinding wheel (Fig.8.1b), contrary to the case of horizontal-spindle machines, where the workpieces ground by the periphery of the grinding wheel. 而且在这种情况下，磨削动作是通过砂轮端面完成的(图8.1b)，这与通过砂轮周边磨削工件的卧式主轴磨床正好相反。

Fig.8.1a and b also indicate the equations to be used for estimating the different parameters of the grinding operation, such as the machining time and the rate of metal removal.图8.1a和b同时简述了用于估计诸如加工时间和金属去除率之类的磨削作业不同参数的方程式。

During the surface-grinding operations, heavy workpieces are either held in fixtures or clamped on the machine table by strap clamps and the like, whereas smaller workpieces are usually held by magnetic chucks.在平面磨削时，重的工件用夹具固定或用压板等夹紧在磨床工作台上，而小的工件则通常是用电磁卡盘固定的。

2. Cylindrical grinding. In cylindrical grinding, the workpiece is held between centers during the grinding operation, and the wheel rotation is the source and cause for the rotary cutting motion, as shown in Fig.8.2. In fact, cylindrical grinding can be carried out by employing any of the following methods:2. 圆柱面磨削：在圆柱面磨削中，作业时工件支撑在两顶尖之间，砂轮转动是导致回转切削运动的动力源，如图8.2所示。实际上，圆柱面磨削能通过采用下列任意方法来实现：
(1) The transverse method, in which both the grinding wheel and the workpiece rotate and longitudinal linear feed is applied to enable grinding of the whole length. The depth of cut is adjusted by the cross feed of the grinding wheel into the workpiece.(1) 横向方法：这种方法中砂轮与工件均旋转且采用线性纵向进给以保证能磨削整个长度。切削深度通过改变砂轮对工件的横向进给来进行调整。

(2) The plunge-cut method, in which grinding is achieved through the cross feed of the grinding wheel and no axial feed is applied. As you can see, this method can be applied only when the surface to be ground is shorter than the width of the grinding wheel used.(2) 插入-切削方法：这种方法通过砂轮的横向进给完成磨削而不采用轴向进给。正如料想的那样，这种方法只在要磨削表面比所用砂轮宽度短时才使用。

(3) The full-depth method, which is similar to the transverse method except that the grinding allowance is removed in a single pass. This method is usually recommended when grinding short rigid shafts.(3) 全深度方法：这种方法除了一次加工就能去除磨削余量外其它与横向方法相同。这种方法通常在磨削较短刚性轴时推荐使用。

Internal grinding. Internal grinding is employed for grinding relatively short holes, as shown in Fig.8.3. The workpiece is held in a chuck or a special fixture. Both the grinding wheel and the workpiece rotate during the operation and feed is applied in the longitudinal direction.内表面磨削：内表面磨削用于相对较短的孔，如图8.3所示。工件安装在卡盘或特殊夹具上。作业时砂轮和工件都回转并且采用纵向进给。

Any desired depth of cut can be obtained by the cross feed of the grinding wheel. A variation from this type is planetary internal grinding, which is recommended for heavy workpieces that cannot be held in chucks. 通过砂轮的横向进给能得到任意所需的切削深度。这种方法的一个变体是行星式内表面磨削，当工件较重不能用卡盘固定时推荐使用。

In that case, the grinding wheel not only spins around its own axis but also rotates around the centerline of the hole that is being ground.在这种情况下，砂轮不但绕自身轴线回转，同时还绕被磨削孔的中心线旋转。

Centerless grinding. Centerless grinding involves passing a cylindrical workpiece, which is supported by a rest blade, between two wheels, i.e., the grinding wheel and the regulating or feed wheel. 无心磨削：无心磨削用于加工圆柱形工件，工件由托板支撑，在两轮即砂轮和调节或进给轮之间通过去。

The grinding wheel does the actual grinding, while the regulating wheel is responsible for rotating the workpiece as well as generating the longitudinal feed. This is possible because of the frictional characteristics of that wheel, which is usually made of rubber-bonded abrasive.砂轮完成实际磨削，而调节轮负责旋转工件和产生纵向进给。由于调节轮通常用橡胶粘结的磨料制成，其摩擦特性使这成为可能。

As can be seen in Fig.8.4, the axis of the regulating wheel is tilted at a slight angle with the axis of the grinding wheel. Consequently, the peripheral velocity of the regulating wheel can be resolved into two components, namely, workpiece rotational speed and longitudinal feed. 正如在图8.4中所看到的那样，调节轮的轴与砂轮轴倾斜一个微小角度。因此调节轮的圆周速度可以分解为两个分量，即工件回转速度和纵向进给。

These can be given by the following equations: 其值可由下列公式给出：
Vworkpiece＝Vregulating wheel×cosα Axial feed ＝Vregulating wheel×c×sinα Where c is a constant coefficient to account for the slip between the workpiece and the regulating wheel (c=0.94~0.98). V工件 ＝V调节轮×cosα 轴向进给 ＝V调节轮×c×sinα 式中c是考虑工件和调节轮之间 滑动的 恒定 系数(c=0.94~0.98)。

The velocity of the regulating wheel is controllable and is used to achieve any desired rotational speed of the workpiece. The angleαis usually taken from 1°to 5°and the larger the angle, the larger the longitudinal feed would be. 调节轮的速度是可控的并被用于 实现 工件任意所需的转动速度。α角通常取1 到 5° ，这角度越大则纵向进给也将越大。

Whenαis taken as 0°, i.e., the two axes of the grinding and regulating wheels are parallel, there is no longitudinal feed of the workpiece.当α取0° 时，即砂轮和调节轮轴线平行时，则工件没有纵向进给。

Grinding Wheels砂轮 Grinding wheels are composed of abrasive grains having similar size and a binder. The actual grinding process is performed by the abrasive grains. Pores between the grains within the binder enable the grains to act as separate single-point cutting tools.砂轮由具有相近尺寸的磨料颗粒和粘合剂组成。实际磨削作业由磨粒完成。在粘合剂中磨粒之间的孔隙使磨粒能象独立的单刃切削刀具一样工作。

These pores also provide space for the generated chips, thus preventing the wheel from clogging. In addition, pores assist the easy flow of coolants to enable efficient and prompt removal of the heat generated during the grinding process.这些孔隙同时还为产生的切屑提供空间以防砂轮堵塞。另外孔隙帮助冷却液容易流动，从而使在磨削作业中产生的热量能有效而迅速地散发。

Grinding wheels are identified based on their shape and size, kind of abrasive, grain size, binder, grade (hardness), and structure.砂轮根据它们的形状和尺寸、磨料的类型、磨粒的大小、粘合剂、等级(硬度)和结构组织来分类。

Shape and size of grinding wheels. Grinding wheels differ in shape and size, depending upon the purpose for which they are to be used. Various shapes are shown in Fig.8.5 and include the following types:砂轮的形状和尺寸：根据砂轮的用途，它们的形状和尺寸是不同的。各种形状如图8.5所示，其中包括：
1)Straight wheels used for surface, cylindrical, internal, and centerless grinding. 2)Bevelled-face or tapered wheels used for grinding threads, gear teeth, and the like. 3)Straight recessed wheels for cylindrical grinding and facing. 1)用于表面、圆柱面、内部和无心磨削的直轮。

2)用于磨削螺纹、齿轮轮齿之类的斜面或锥形轮。

3)用于圆柱面和端面磨削的直凹轮。

4)Abrasive disks for cutoff and slotting operations. (thickness 0.02 up to 0.2in. (0.5 to 5mm)). 5)Cylinders, straight cups, and flaring cups are used for surface grinding with the end face of the wheel. 4)用于切断和开槽作业的砂轮片(其厚度从0.02到0.2英寸(0.5到5毫米))。

5)用其端面进行表面磨削的圆柱、直杯及外展杯状砂轮。

The main dimensions of a grinding wheel are the outside diameter D, the bore diameter d, and the height H. These dimensions vary widely, depending upon the grinding process for which the wheel is to be used.砂轮的主要尺寸有外径D、孔径d和厚度H。根据采用砂轮的磨削工艺，这些尺寸变化很大。

Kind of abrasive. Grinding wheels can be made of natural abrasives such as quartz, emery, and corundum or of industrially prepared chemical compounds such as aluminum oxide or silicon carbide (known as carborundum). 磨料的类型：砂轮可以由象石英、金刚砂、刚玉之类的自然磨料制成，或者由象氧化铝或碳化硅(也称人造金刚砂)之类的工业制备的化学化合物制成。

Generally, silicon carbide grinding wheels are used when grinding low-tensile-strength materials like cast iron, whereas aluminum oxide wheels are employed for grinding high-strength metals such as alloy steel, hardened steel, and the like.当磨削象铸铁类低拉伸强度材料时，一般采用碳化硅砂轮，而磨削合金钢、淬火钢等高强度金属则要用氧化铝砂轮。

Grain size of abrasive used. As you may expect, the grain size of the abrasive particles of the wheel plays a fundamental role in determining the quality of ground surface obtained. 所用磨粒的尺寸：正如料想的那样，砂轮磨粒的尺寸对决定所得磨削表面的质量起着根本的作用。

The finer the grains, the smoother the ground surface is. Therefore, coarse-grained grinding wheels are used for roughing operations, whereas fine-grained wheels are employed in final finishing operations. 磨粒越细，磨削表面越光滑。所以，粗粒砂轮用于粗加工，而细粒砂轮则用于最后精加工。

The grade of the bond. The grade of the bond is actually an indication of the resistance of the bond to pulling off the abrasive grains from the grinding wheel. Generally, wheels having hard grades are used for grinding soft materials and vice versa. 粘结体的等级：粘结体的等级实际上是其抵抗将磨粒从砂轮上拉脱的指标。一般而言，具有较硬等级的砂轮用于磨削较软材料，反之亦然。

If a hard-grade wheel were to be used for grinding a hard material, the dull grains would not be pulled off from the bond quickly enough, thus impeding the self-dressing process of the surface of the wheel and finally resulting in clogging of the wheel and burns on the ground surface. 如果较硬等级的砂轮用于磨削较硬材料，磨钝的磨粒将不能足够快地脱离粘结体，这会妨碍砂轮表面的自修复，最终导致砂轮的堵塞并在被磨表面留下灼斑。

In fact, the cutting properties of all grinding wheels must be restored periodically by dressing with a cemented carbide roller or a diamond tool to give the wheel the exact desired shape and remove all worn abrasive grains.实际上，所有砂轮的磨削性能都必须定期地通过使用硬质合金滚轮或金刚石修整器修整而被恢复，以求很准确地把砂轮加工成要求的形状，并去除已磨钝的磨粒。

Structure. Structure refers to the amount of void space between the abrasive grains. When grinding softer metals, larger void space are needed to facilitate the flow of the removed chips.结构组织：结构组织与磨粒间的空隙量有关。当磨削较软金属时，需要较大的空隙以便去除切屑的流动。

The binder. Abrasive particles are bonded together in many different ways. These include bond, silicate, rubber, resinoid, shellac, and oxychloride. Nevertheless, the bond is the most commonly used one.粘合剂：磨粒可用多种不同方法粘结在一起。其中包括粘合剂、硅酸盐、橡胶、树脂、虫胶和氯氧化物。然而，粘合剂是最常用的。

In fact, the standard marking system is employed for distinguishing grinding wheels, by providing all the preceding parameters in a specific sequence.在实际生产中，为了区分砂轮采用标准标注系统，通过用一特定顺序将所有上述参数都表示出来。

UNIT 9 Lapping Polishing Lapping 研磨 Lapping is a finishing operation used on flat and cylindrical surfaces. The lap, shown in Fig.9.1a, is usually made of cast iron, copper, leather, or cloth.研磨是一种用于平面和圆柱面的精加工作业。研具，如图9.1a所示，通常用铸铁、铜、皮革或布制成。

The abrasive particles are embedded in the lap, or they may be carried through slurry. Depending on the hardness of the workpiece, lapping pressures range from 7kPa to 140kPa (1 to 20 psi).研磨微粒嵌入研具内，或者可以通过液体携带。根据工件硬度，研磨压力可在7kPa到140kPa(1到20psi)范围中取。

Lapping has two main functions. Firstly, it produces a superior surface finish with all machining marks being removed from the surface. Secondly, it is used as a method of obtaining very close fits between mating parts such as pistons and cylinders.研磨有两个主要作用。首先，它通过去除所有机加工痕迹能产生较好的表面光洁度。其次，它能用作获得像活塞与气缸之类配件间过盈配合的方法。

The lapped workpiece surface may look smooth but it is actually filled with microscopic peaks, valleys, scratches and pits. Few surfaces are perfectly flat. Lapping minimizes the surface irregularities, thereby increasing the available contact area. 研磨后的工件表面可能看似平滑，其实布满着微观峰、谷、划痕和凹陷。几乎没有表面是完全平整的。研磨使表面不规则最小化，因而增加了有效接触面积。

The drawing in Fig.9.1a shows two surfaces. The upper one is how a surface might look before lapping and the lower one after lapping. Lapping removes the microscopic mountain tops and produces relatively flat plateaus. Entire microscopic mountain ranges may need to be ground down in order to increase the available contact area.图9.1a上显示了两个表面。上面是研磨前表面可能的外观模样而下面则是研磨后的模样。研磨去除了微观峰顶从而产生相对平坦的平台。整个微观山脉范围都需要磨去以增加有效接触面积。

Production lapping on flat or cylindrical pieces is done on machines such as those shown in Fig.9.1b and 9.1c. Lapping is also done on curved surfaces, such as spherical objects and lenses, using specially shaped laps.研磨平面或圆柱面工件的生产过程是在如图9.1b和9.1c那样的机器上完成的。研磨也可采用特殊成型研具在诸如球形物体和透镜之类的曲面上进行。

Polishing 抛光 Polishing is a process that produces a smooth, lustrous surface finish. Two basic mechanisms are involved in the polishing process: (a) fine-scale abrasive removal, and (b) softening and smearing of surface layers by frictional heating during polishing.抛光是生成平滑、有光泽表面光洁度的工艺。抛光工艺涉及两种基本机理：
(a)精细等级磨粒去除，和(b)在抛光中通过摩擦生热软化并抹光表面层。

Electropolishing电解抛光 Electropolishing is an electrochemical process similar to, but the reverse of, electroplating. The electropolishing process smoothes and streamlines the microscopic surface of a metal object. Mirror-like finishes can be obtained on metal surfaces by electropolishing.电解抛光是一种与电镀相似的电化学工艺，但过程与电镀正好相反。电解抛光工艺使金属物体的微观表面平滑和简单化。通过电解抛光能在金属表面得到镜面光洁度。

In electropolishing, the metal is removed ion by ion from the surface of the metal object being polished. Electrochemistry and the fundamental principles of electrolysis (Faraday’s Law) replace traditional mechanical finishing techniques. 在电解抛光中，金属是逐个离子地从被抛光金属物体表面去除的。电化学和电解基本原理(Faraday定理)取代了传统的机械精加工技术。

In basic terms, the object to be electropolished is immersed in an electrolyte and subjected to a direct electrical current. The object is maintained anodic, with the cathodic connection being made to a nearby metal conductor.用基本术语说，要电解抛光的物体被浸没在电解液中并且通上直流电。该物体为阳极，阴极连接到附近的金属导体上。

Smoothness of the metal surface is one of the primary and most advantageous effects of electropolishing. During the process, a film of varying thickness covers the surface of the metal. This film is thickest over micro depressions and thinnest over micro projections. 金属表面的平滑是电解抛光主要的和最有优势的效应之一。在此过程中，一变化着厚度的膜覆盖在金属表面上。该膜在微观凹陷处最厚而在微观凸出处最薄。

Electrical resistance is at a minimum wherever the film is thinnest, resulting in the greatest rate of metallic dissolution. Electropolishing selectively removes microscopic high points or “peaks” faster than the rate of attack on the corresponding micro-depressions or “valleys”. 电阻在膜最薄处最小，导致最大金属分解率。电解抛光选择性地去除微观高点或“峰” 快于对相应微观凹陷处或“谷”的侵蚀速率。

Stock is removed as metallic salt. Metal removal under certain circumstances is controllable and can be held to 0.0001 to 0.0025 mm.原材料以金属盐的形式被去除。在特定环境下金属的去除是可控的并且保持在0.0001 到0.0025mm范围内。

Chemical Mechanical Polishing化学机械抛光 Chemical mechanical polishing is becoming an increasingly important step in the fabrication of multi-level integrated circuits. Chemical mechanical polishing refers to polishing by abundant slurry that interacts both chemically and mechanically with the surface being polished.化学机械抛光正在多层集成电路制造领域成为日益重要的步骤。化学机械抛光是指大量抛光液与被抛光表面产生化学和机械作用的抛光。

During the chemical mechanical polishing process, a rotating wafer is pressed face down onto a rotating, resilient polishing pad while polishing slurry containing abrasive particles and chemical reagents flows in between the wafer and the pad.在化学机械抛光过程中，旋转晶片面向下压在旋转、有回弹力的抛光衬垫上，而同时含有研磨微粒和化学反应物的抛光液流过晶片与衬垫之间。

The combined action of polishing pad, abrasive particles and chemical reagents results in material removal and polishing of the wafer surface. Chemical mechanical polishing creates flat, damage-free on a variety of brittle materials and it is used extensively on silicon wafers in the manufacture of integrated circuits.抛光衬垫、研磨微粒和化学反应物的共同作用导致晶片表面的材料去除并抛光。化学机械抛光可使多种易碎材料平整且不受损害，因此在集成电路制造中被广泛地用在硅晶片上。

Chemical mechanical polishing is a complicated multiphase process. It mainly includes the following two dynamics. First, the active component in polishing slurry reacts with the atoms of the wafer, and the process is chemical reaction step with oxidation-reductive reaction. 化学机械抛光是一种复杂的多相工艺。它主要包括下列两个动态过程：第一，抛光液中活性成分与晶片的原子发生反应，这是带有氧化-还原反应的化学反应步骤。

The second step is the process of desorption, that is to say, the resultants gradually separate from the wafer surface and new surface is exposed to polishing slurry. If chemical reactive rate is smaller, the total removal rate of the wafer is also small; furthermore, the surface degree of finish is not good.第二步是解吸附过程，即反应产物逐渐从晶片表面分离并将新表面暴露给抛光液。如果化学反应速率较小，晶片的总去除率也较小，而且表面光洁程度不够好。

On the contrary, even if chemical reaction is very rapid, but desorption is very slow, the total removal rate is not good. Because resultants connot separate from the wafer surface, the active component in the polishing slurry cannot expose and react with the atoms on the new surface, which holds up chemical reaction. 与之相反，即使化学反应很快，但解吸附很慢，则总去除率也不够好。因为反应产物不能从晶片表面分离，抛光液中活性成分就不能暴露并与新表面上的原子起反应，这会抑制化学反应。

The balance and compositive effects of two steps decide the total removal rate and its surface degree of finish.这两个步骤的平衡与合成效应决定了总去除率和表面光洁程度。

UNIT 10 surface engineering The processes of surface engineering, or surface treatments, tailor the surfaces of engineering materials to: (1) control friction and wear, (2) improve corrosion resistance, (3) change physical property, e.g., conductivity, resistivity, and reflection, (4) alter dimension, (5) vary appearance, e.g., color and roughness, (6) reduce cost. 进行表面工程或表面处理的目的是：(1)控制摩擦和磨损，(2)改善抗腐蚀性，(3)改变物理性能，例如，传导率、电阻系数和反射率，(4)修改尺寸，(5)变更外观，例如颜色和粗糙程度，(6)降低成本。

Common surface treatments can be divided into two major categories: treatments that cover the surfaces and treatments that alter the surfaces.通常的表面处理可以分为两个主要类型：覆盖表面的处理和改变表面的处理。

Covering the Surface覆盖表面 The treatments that cover the surfaces include organic coatings and inorganic coatings. 覆盖表面的处理包括有机涂层和无机涂层。

The inorganic coatings perform electroplatings, conversion coatings, thermal sprayings, hot dippings, furnace fusings, or coat thin films, glass, ceramics on the surfaces of the materials.无机涂层有电镀、转化层、热喷涂、热浸渍、熔炉熔融、或在材料表面涂上薄膜、玻璃、陶瓷。

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.电镀是一种在电镀槽通上电流使金属沉淀在基体上的电化学过程。

Usually there is an anode (positively charged electrode), which is the source of the material to be deposited; the electrochemistry which is the medium through which metal ions are exchanged and transferred to the substrate to be coated; and a cathode (negatively charged electrode) which is the substrate to be coated.通常有一个阳极(正电极)，是要沉淀材料的来源；
电化学反应是使金属离子交换并迁移到要覆盖基体上的中间过程；
以及一个阴极(负电极)，即要覆盖的基体。

Plating is done in a plating bath which is usually a non-metallic tank (usually plastic). The tank is filled with electrolyte which has the metal, to be plated, in ionic form.电镀在通常为非金属容器(一般是塑料)的电镀槽中进行。该容器装满了含有离子态被镀金属的电解液。

The anode is connected to the positive terminal of the power supply. The anode is usually the metal to be plated (assuming that the metal will corrode in the electrolyte). For ease of operation, the metal is in the form of nuggets and placed in an inert metal basket made out non-corroding metal (such as titanium or stainless steel).阳极与电源正极相连。阳极通常为被镀金属(假定该金属能在电解液中腐蚀)。为了操作容易，该金属呈固体小块形式并置于由抗腐蚀金属(如钛或不锈钢)制成的惰性金属筐内。

The cathode is the workpiece, the substrate to be plated. This is connected to the negative terminal of the power supply. The power supply is well regulated to minimize ripples as well to deliver a steady predictable current, under varying loads such as those found in plating tanks.阴极是工件，即要镀的基体，连接到电源的负极。很好地调节电源使波动最小化并在载荷变化情况(如同电镀容器中看到的那样)下提供稳定的可预知电流。

As the current is applied, positive metal ions from the solution are attracted to the negatively charged cathode and deposit on the cathode. As a replenishment for these deposited ions, the metal from the anode is dissolved and goes into the solution and balances the ionic potential.一旦通上电流，来自溶液的正的金属离子被吸引到带负电的阴极并沉淀在其上。作为这些沉淀离子的补充，来自阳极的金属被溶解并进入溶液平衡离子势能。

Thermal spraying process. Thermal spraying metal coatings are depositions of metal which has been melted immediately prior to projection onto the substrate. The metals used and the application systems used vary but most applications result in thin coatings applied to surfaces requiring improvement to their corrosion or abrasion resistance properties.热喷涂工艺：热喷涂金属涂层是金属熔化后立即投射到基体上形成的金属沉积层。所用的金属和应用系统都可以变化，但大多数应用都是在要求改善抗腐蚀或耐磨性能的表面涂上薄层。

Thermal spray is a generic term for a broad class of related processes in which molten droplets of metals, ceramics, glasses, and/or polymers are sprayed onto a surface to produce a coating, to form a free-standing near-net-shape, or to create an engineered material with unique properties.热喷涂是用于很大一类相关工艺的一个通用术语，喷涂到表面产生涂层的熔化小滴可以是金属、陶瓷、玻璃和/或聚合物，形成独立的近似纯形或产生具有独特性能的设计材料。

In principle, any material with a stable molten phase can be thermally sprayed, and a wide range of pure and composite materials are routinely sprayed for both research and industrial applications. Deposition rates are very high in comparison to alternative coating technologies. 大体上，有稳定熔化状态的任何材料都可以热喷涂，范围宽阔的纯净和合成材料一般都能喷涂用于研究及工业目的。其沉积率与可供选择的涂层技术比较是很高的。

Deposit thickness of 0.1 to 1mm is common, and thickness greater than 1cm can be achieved with some materials. 沉淀厚度普遍为0.1到1mm，对某些材料则沉淀厚度可以达到1cm以上。

The process for application of thermal spray metal is relatively simple and consists of the following stages. 热喷涂金属的应用工艺相对简单并由下列阶段组成：
(1) Melting the metal at the gun. (1)在喷枪内熔化金属。

(2) Spraying the liquid metal onto the prepared substrate by means of compressed air.(2)通过压缩空气将液态金属喷涂在准备好的基体上。

(3) Molten particles are projected onto the cleaned substrate. (3)熔化微粒投射在清洁过的基体上。

There are two main types of wire application available today namely arc spray and gas spray.现在有两种主要的金属丝应用类型可选用，也就是电弧喷涂和气体喷涂。

ARC—A pair of wires are electrically energized so that an arc is struck across the tips when brought together through a pistol. Compressed air is blown across the arc to atomise and propel the autofed metal wire particles onto the prepared workpiece.电弧喷涂—当一对金属丝通过手持喷枪连到一起时，通上电横过其末端划燃电弧。压缩空气吹过电弧使其雾化并驱使自动送料金属丝微粒到准备好的工件上。

GAS—In combustion flame spraying the continuously moving wire is passed through a pistol, melted by a conical jet of burning gas. The molten wire tip enters the cone, atomises and is propelled onto the substrate.气体喷涂—连续移动的金属丝在燃烧火焰喷射中通过手持喷枪，并被燃烧气体的锥形喷嘴所熔化。熔化后的金属丝顶端进入锥体雾化并驱使其到基体上。

Thin-Film Coatings. Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) are two most common types of thin-film coating methods.薄膜涂层：物理蒸发沉淀(PVD)和化学蒸发沉淀(CVD)是两种最常见薄膜涂层方法的类型。

PVD coatings involve atom-by-atom, molecule-by-molecule, or ion deposition of various materials on solid substrates in vacuum systems.物理蒸发沉淀涂层涉及到在真空装置内各种各样的材料原子紧靠原子、分子紧靠分子或离子沉淀于固态基体上。

Thermal evaporation uses the atomic cloud formed by the evaporation of the coating metal in a vacuum environment to coat all the surfaces in the line of sight between the substrate and the target. It is often used in producing thin, 0.5μm, decorative shiny coatings on plastic parts.热蒸发利用涂层金属在真空环境中蒸发形成的微粒子雾将基体和靶材之间可见范围内所有表面覆盖。在塑料零件上生成较薄(0.5μm)的、 装饰性的、有光泽的涂层时常常用到它。

The thin coating, however, is fragile and not good for wear applications. The thermal evaporation process can also coat a very thick, 1mm, layer of heat-resistant materials, such as MCrAIY—a metal, chromium, aluminum, and yttrium alloys, on jet engine parts.然而，这种薄涂层是易碎的并不适合用于磨损场合。热蒸发工艺也能在喷气发动机零件上覆盖很厚(1mm)的耐热材料涂层，例如MCrAIY—一种金属、铬、铝和钇合金。

Sputtering applies high-technology coatings such as ceramics, metal alloys, organic and inorganic compounds by connecting the workpiece and the substance to a high-voltage DC power supply in an argon vacuum system.反应溅射法通过在氩真空设备中连接工件和具有特定成分的材料到高压直流电来应用诸如陶瓷、金属合金、有机和无机化合物之类的高技术涂层。

The plasma is established between the substrate (workpiece) and the target (donor) and transposes the sputtered off target atoms to the surface of the substrate.等离子区形成于基体(工件)和靶材(原料物质)之间并将被溅射的靶材原子转移到基体的表面上。

When the substrate is non-conductive, e.g., polymer, a radio-frequency (RF) sputtering is used instead. Sputtering can produce thin, less than 3μm (120μin), hard thin-film coatings, e.g., titanium nitride (TIN) which is harder than the hardest metal. 如果基体不导电，例如聚合物，则采用射频(RF) 溅射代替。反应溅射法可以生成较薄( 小于3μm(120μin)) 的、坚硬薄膜涂层，像比最硬金属还硬的氮化钛(TIN) 。

Sputtering is now widely applied on cutting tools, forming tools, injection molding tools, and common tools such as punches and dies, to increase wear resistance and service life.现在反应溅射法已被广泛应用于切削刀具、成型工具、注射模具和诸如冲头和冲模之类的通用器具，以增强其耐磨性和使用寿命。

CVD is capable of producing thick, dense, ductile, and good adhesive coatings on metals and non-metals such as glass and plastic. Contrasting to the PVD coating in the “line of sight”, the CVD can coat all surfaces of the substrate.化学蒸发沉淀能在金属和像玻璃和塑料之类的非金属上生成较厚的、致密的、有延伸性的和带良好粘性的涂层。与物理蒸发沉淀在“可见范围”对比，化学蒸发沉淀能将基体的所有表面都覆盖。

Conventional CVD coating process requires a metal compound that will volatilize at a fairly low temperature and decompose to a metal when it contacts with the substrate at higher temperature.常规的化学蒸发沉淀涂层工艺需要一种容易在相当低温度下挥发并且在较高温度下与基体接触时能分解成纯金属的金属化合物。

The most well known example of CVD is the nickel carbonyl (NiCO4) coating as thick as 2.5mm (0.1in.) on glass windows and containers to make them explosion or shatter resistant.最为人熟知的化学蒸发沉淀例子是在玻璃窗和容器上镀厚为2.5mm(0.1in.)的羰基镍(NiCO4)涂层使它们能抵抗爆裂或破碎。

Diamond CVD coating process is introduced to increase the surface hardness of cutting tools. However, the process is done at the temperatures higher than 700℃ (1300℉) which will soften most tool steel. 为增加切削刀具表面硬度引入了钻石化学蒸发沉淀涂层工艺。可是此工艺要在高于700℃(1300℉)的温度下才能实现，这温度会软化大多数工具钢。

Thus, the application of diamond CVD is limited to materials which will not soften at this temperature such as cemented carbides. 因而钻石化学蒸发沉淀的应用受到材料限制，要求材料在此温度下不软化例如硬质合金。

Plasma-Assisted CVD coating process can be performed at lower temperature than diamond CVD coatings. This CVD process is used to apply diamond coatings or silicon carbide barrier coatings on plastic films and semiconductors, including the state of the art 0.25μm semiconductors.等离子体辅助化学蒸发沉淀涂层工艺可以在比钻石化学蒸发沉淀涂层低的温度下操作。这种化学蒸发沉淀用于在塑料膜和半导体( 包括人工0.25μm 半导体的情况) 上覆盖钻石涂层或碳化硅隔离涂层。

Altering the Surfaces改变表面 The treatments that alter the surfaces include hardening treatments, high-energy processes and special treatments.改变表面的处理包括淬火处理、高能加工和特殊处理。

High-energy processes are relatively new surface treatment methods. They can alter the properties of surfaces without changing the dimension of the surface. Common high-energy processes, including electron beam treatment, ion implantation, and laser beam treatment, are briefly discussed as follows:高能加工是相对较新的表面处理方法。它们能在不改变表面尺寸的情况下改变表面性能。通用的高能加工包括电子束处理、离子注入和激光束处理简要讨论如下：
Electron beam treatment. Electron beam treatment alters the surface properties by rapid heating—using electron beam and rapid cooling—in the order of 106℃/see in a very shallow region, 100μm, near the surface. This technique can also be used in hardfacing to produce “surface alloys”.电子束处理：
电子束处理在靠近表面很浅(100μm) 的区域通过用电子束快速加热并以106℃/ 秒 等级 快速冷却来改变表面性能。这种技术也被用于表面硬化产生“ 表面合金” 。

Ion implantation. Ion implantation uses electron beam or plasma to impinge gas atoms to ions with sufficient energy, and embed these ions into atomic lattice of the substrate, accelerated by magnetic coils in a vacuum chamber. The mismatch between ion implant and the surface of a metal creates atomic defects that harden the surface.离子注入：离子注入采用电子束或等离子体通过真空室内磁性线圈加速以足够的能量将气体原子撞击为离子，并把这些离子嵌入基体的原子点阵中。离子注入和金属表面之间的错配产生了硬化表面的原子瑕疵。

Laser beam treatment. Similar to electron beam treatment, laser beam treatment alters the surface properties by rapid heating and rapid cooling in a very shallow region near the surface. It can also be used in hardfacing to produce “surface alloys”.激光束处理：与电子束处理类似，激光束处理通过在靠近表面很浅的区域快速加热和快速冷却来改变表面性能。它也可以用于表面硬化产生“表面合金”。

The results of high-energy processes are not well known or very well controlled. But the preliminary results look promising. Further development is needed in high-energy processes, especially in implant dosages and treatment methods.高能加工的结果不能充分地了解或很好地控制。但初步结果看来是有前途的。高能加工需要进一步的开发，特别是注入剂量和处理方法。

UNIT11 Lathe and Turning The Lathe and Its Construction车床及其结构 A lathe is a machine tool used primarily for producing surfaces of revolution and flat edges.车床是主要用于生成旋转表面和平整边缘的机床。

Based on their purpose, construction, number of tools that can simultaneously be mounted, and degree of automation, lathes-or, more accurately, lathe-type machine tools can be classified as follows:根据它们的使用目的、结构、能同时被安装刀具的数量和自动化的程度，车床— 或更确切地说是车床类的机床，可以被分成以下几类：
(1)Engine lathes(1)普通车床 (2)Toolroom lathes(2)万能车床 (3)Turret lathes(3)转塔车床 (4)Vertical turning and boring mills (4)立式车床 (5)Automatic lathes(5)自动车床 (6)Special-purpose lathes(6)特殊车床 In spite of that diversity of lathe-type machine tools, they all have common features with respect to construction and principle of operation. These features can best be illustrated by considering the commonly used representative type, the engine lathe. Following is a description of each of the main elements of an engine lathe, which is shown in Fig.11.1.虽然车床类的机床多种多样，但它们在结构和操作原理上具有共同特性。这些特性可以通过普通车床这一最常用的代表性类型来最好地说明。下面是关于图11.1所示普通车床的主要部分的描述。

Lathe bed. The lathe bed is the main frame, involving a horizontal beam on two vertical supports. It is usually made of grey or nodular cast iron to damp vibrations and is made by casting. 车床床身：车床床身是包含了在两个垂直支柱上水平横梁的主骨架。为减振它一般由灰铸铁或球墨铸铁铸造而成。

It has guideways to allow the carriage to slide easily lengthwise. The height of the lathe bed should be appropriate to enable the technician to do his or her job easily and comfortably.它上面有能让大拖板轻易纵向滑动的导轨。车床床身的高度应适当以让技师容易而舒适地工作。

Headstock. The headstock is fixed at the left hand side of the lathe bed and includes the spindle whose axis is parallel to the guideways (the slide surface of the bed). The spindle is driven through the gearbox, which is housed within the headstock. 主轴箱：主轴箱固定在车床床身的左侧，它包括轴线平行于导轨的主轴。主轴通过装在主轴箱内的齿轮箱驱动。

The function of the gearbox is to provide a number of different spindle speeds (usually 6 up to 18 speeds). Some modern lathes have headstocks with infinitely variable spindle speeds, which employ frictional ,electrical ,or hydraulic drives. 齿轮箱的功能是给主轴提供若干不同的速度(通常是6到18速)。有些现代车床具有采用摩擦、电力或液压驱动的无级调速主轴箱。

The spindle is always hollow, i. e., it has a through hole extending lengthwise. Bar stocks can be fed through that hole if continuous production is adopted. 主轴往往是中空的，即纵向有一通孔。如果采取连续生产，棒料能通过此孔进给。

Also, that hole has a tapered surface to allow mounting a plain lathe center. The outer surface of the spindle is threaded to allow mounting of a chuck, a face plate, or the like.同时，此孔为锥形表面可以安装普通车床顶尖。主轴外表面是螺纹可以安装卡盘、花盘或类似的装置。

Tailstock. The tailstock assembly consists basically of three parts, its lower base, an intermediate part, and the quill. The lower base is a casting that can slide on the lathe bed along the guideways, and it has a clamping device to enable locking the entire tailstock at any desired location, depending upon the length of the workpiece. 尾架：尾架总成基本包括三部分，底座、尾架体和套筒轴。底座是能在车床床身上沿导轨滑动的铸件，它有一定位装置能让整个尾架根据工件长度锁定在任何需要位置。

The intermediate part is a casting that can be moved transversely to enable alignment of the axis of the tailstock with that of the headstock. The third part, the quill, is a hardened steel tube, which can be moved longitudinally in and out of the intermediate part as required. 尾架体为一能横向运动的铸件，它可以调整尾架轴线与主轴箱轴线成一直线。第三部分，套筒轴是一淬硬钢管，它能根据需要在尾架体中纵向进出移动。

This is achieved through the use of a handwheel and a screw, around which a nut fixed to the quill is engaged. The hole in the open side of the quill is tapered to enable mounting of lathe centers or other tools like twist drills or boring bars. The quill can be locked at any point along its travel path by means of a clamping device.这通过使用手轮和螺杆来达到，与螺杆啮合的是一固接在套筒轴上的螺母。套筒轴开口端的孔是锥形的，能安装车床顶尖或诸如麻花钻和镗杆之类的工具。套筒轴通过定位装置能沿着它的移动路径被锁定在任何点。

The carriage. The main function of the carriage is mounting of the cutting tools and generating longitudinal and/or cross feeds. It is actually an H-shaped block that slides on the lathe bed between the headstock and tailstock while being guided by the V-shaped guideways of the bed. 大拖板：大拖板的主要功能是安装刀具和产生纵向和/或横向进给。它实际上是一由车床床身V形导轨引导的、能在车床床身主轴箱和尾架之间滑动的H形滑块。

The carriage can be moved either manually or mechanically by means of the apron and either the feed rod or the lead screw.大拖板能手动或者通过溜板箱和光杆(进给杆)或丝杆(引导螺杆)机动。

When cutting screw threads, power is provided to the gearbox of the apron by the lead screw. In all other turning operations, it is the feed rod that drives the carriage. The lead screw goes through a pair of half nuts, which are fixed to the rear of the apron.在切削螺旋时，动力通过丝杆提供给溜板箱上的齿轮箱。在其余车削作业中，都由光杆驱动大拖板。丝杆穿过一对固定在溜板箱后部的剖分螺母。

When actuating a certain lever, the half nuts are clamped together and engage with the rotating lead screw as a single nut, which is fed, together with the carriage, along the bed. When the lever is disengaged, the half nuts are released and the carriage stops.当开动特定操作杆时，剖分螺母夹在一起作为单个螺母与旋转的丝杆啮合，并带动拖板沿着床身提供进给。当操作杆脱离时，剖分螺母释放同时大拖板停止运动。

On the other hand, when the feed rod is used, it supplies power to the apron through a worm gear. The latter is keyed to the feed rod and travels with the apron along the feed rod, which has a keyway extending to cover its whole length.另一方面，当使用光杆时则通过蜗轮给溜板箱提供动力。

蜗轮用键连接在光杆上，并与溜板箱一起沿光杆运动，光杆全长范围开有键槽。

A modern lathe usually has a quick-change gearbox located under the headstock and driven from the spindle through a train of gears. It is connected to both the feed rod and the lead screw and enables selecting a variety of feeds easily and rapidly by simply shifting the appropriate levers. 现代车床一般在主轴箱下装备快速变换齿轮箱，通过一系列齿轮由主轴驱动。它与光杆和丝杆连接，能容易并快速地通过简单转换适当的操作杆选择各种进给。

The quick-change gearbox is employed in plain turning, facing and thread cutting operations. Since that gearbox is linked to the spindle, the distance that the apron (and the cuttingtool) travels for each revolution of the spindle can be controlled and is referred to as the feed.快速变换齿轮箱可用于普通车削、端面切削和螺旋切削作业中。由于这种齿轮箱与主轴相连，主轴每转一圈溜板箱(和切削刀具)运动的距离能被控制，这距离就可以被认为是进给。

Lathe Cutting Tools车床切削刀具 The shape and geometry of the lathe tools depend upon the purpose for which they are employed.车床刀具的形状和几何参数取决于它们的使用目的。

Turning tools can be classified into two main groups, namely, external cutting tools and internal cutting tools. Each of these two groups include the following types of tools:车削刀具可以分为两个主要组别，即外部切削刀具和内部切削刀具。这两组中的每一组都包括以下类型刀具：
Turning tools. Turning tools can be either finishing or rough turning tools. Rough turning tools have small nose radii and are employed when deep cuts are made. 车削刀具：车削刀具可以是精车刀具或粗车刀具。粗车刀具刀尖半径较小，用于深切削。

On the other hand, finishing tools have larger nose radii and are used for obtaining the final required dimensions with good surface finish by making slight depths of cut. Rough turning tools can be right-hand or left-hand types, depending upon the direction of feed. They can have straight, bent, or offset shanks.而精车刀具刀尖半径较大，用于通过微量进刀深度来获得具有较好表面光洁度的最终所需尺寸。粗车刀具按其进给方向可以是右手型的或是左手型的。它们可以有直的、弯的或偏置的刀杆。

Facing tools. Facing tools are employed in facing operations for machining plane side or end surfaces. There are tools for machining left-hand-side surfaces and tools for right-hand-side surfaces. Those side surfaces are generated through the use of the cross feed, contrary to turning operations, where the usual longitudinal feed is used. 端面刀具：端面刀具用在端面作业中加工平板侧面或端部表面，也有加工左右侧表面之分。与一般采用纵向进给的车削作业相反，那些侧表面通过采用横向进给产生。

Cutoff tools. Cutoff tools, which are sometimes called parting tools, serve to separate the workpiece into parts and/or machine external annular grooves.切断刀具：切断刀具，有时也称为分割刀具，用于将工件分割成若干部分和/或加工外部环形槽。

Thread-cutting tools. Thread-cutting tools have either triangular, square, or trapezoidal cutting edges, depending upon the cross section of the desired thread. Also, the plane angles of these tools must always be identical to those of the thread forms. 螺纹切削刀具：螺纹切削刀具根据所需螺纹的横截面，有三角形的、矩形的或梯形的切削刃。同时，这些刀具的平面角必须始终与螺纹形状的平面角保持一致。

Thread-cutting tools have straight shanks for external thread cutting and are of the bent-shank type when cutting internal threads. 车外螺纹的螺纹切削刀具为直刀杆，而车内螺纹的螺纹切削刀具则是弯刀杆。

Form tools. Form tools have edges especially manufactured to take a certain form, which is opposite to the desired shape of the machined workpiece.成形刀具：成形刀具有专门制成特定形状的刀刃，这种刀刃形状与被加工工件所需外形正好相反。

An HSS tool is usually made in the form of a single piece, contrary to cemented carbides or ceramic, which are made in the form of tips. The latter are brazed or mechanically fastened to steel shanks．高速钢刀具通常以单件形式制造，而硬质合金或陶瓷刀具则以刀尖形式制造。后者用铜焊或机械方法固定于钢质刀杆上。

Fig.11.2 indicates an arrangement of this latter type, which includes the carbide tip, the chip breaker, the pad, the clamping screw (with a washer and a nut), and the shank.图11.2所示为机械式固定布置方式，它包括了硬质合金刀尖、断屑槽、衬垫、卡装螺杆(带有垫圈和螺母)及刀杆。

As the name suggests, the function of the chip breaker is to break long chips every now and then, thus preventing the formation of very long twisted ribbons that may cause problems during the machining operation. 顾名思义，断屑槽的功能就是不时地折断长切屑，以防形成很长的可能会在机加工操作中引起问题的缠绕切屑条。

The carbide tips (or ceramic tips) can have different shapes, depending upon the machining operations for which they are to be employed. The tips can either be solid or with a central through hole, depending on whether brazing or mechanical clamping is employed for mounting the tip on the shank. 硬质合金刀尖(或陶瓷刀尖)根据采用它们的机加工操作，可以有不同的形状。根据将刀尖装配在刀杆上是通过用铜焊还是机械卡装，刀尖可以是实心的或是带有中心通孔的。

Lathe Operations车床操作 In the following section, we discuss the various machining operations that can be performed on a conventional engine lathe.在下面这节中，要讨论的是能在传统普通车床上进行的各种机加工作业。

It must be borne in mind, however, that modern computerized numerically controlled lathes have more capabilities and can do other operations, such as contouring, for example. Following are conventional lathe operations.然而，必须记住现代计算机数控车床具有更多的功能并且可以进行其它操作，例如仿型。下面是传统车床的操作。

Cylindrical turning. Cylindrical turning is the simplest and the most common of all lathe operations. A single full turn of the workpiece generates a circle whose center falls on the lathe axis; this motion is then reproduced numerous times as a result of the axial feed motion of the tool. 圆柱面车削：圆柱面车削是所有车床操作中最简单也是最普通的。工件旋转一整圈产生一个圆心落在车床主轴上的圆；
由于刀具的轴向进给运动这种动作重复许多次。

The resulting machining marks are, therefore, a helix having a very small pitch, which is equal to the feed. Consequently, the machined surface is always cylindrical.所以，由此产生的机加工痕迹是一条具有很小节距的螺旋线，该节距等于进给。因此机加工表面始终是圆柱形的。

The axial feed is provided by the carriage or the compound rest, either manually or automatically, whereas the depth of cut is controlled by the cross slide.轴向进给通过大拖板或复式刀架手动或自动提供，然而切削深度则由横向滑板控制。

In roughing cuts, it is recommended that large depths of cuts (up to 0.25in. or 6mm, depending upon the workpiece material) and smaller feeds would be used. On the other hand, very fine feeds, smaller depths of cut (less than 0.05in, or 0.4mm), and high cutting speeds are preferred for finishing cuts.粗车中，推荐使用较大切削深度(根据工件材料可达0.25英寸或6毫米)和较小进给。另一方面，精车则最好采用很小的进给、较小的切削深度(小于0.05英寸或0.4毫米)和较高的切削速度。

Facing. The result of a facing operation is a flat surface that is either the whole end surface of the workpiece or an annular intermediate surface like a shoulder. During a facing operation, feed is provided by the cross slide, whereas the depth of cut is controlled by the carriage or compound rest. 端面车削：端面车削操作的结果是将工件整个端部表面或者像轴肩之类的中间环形表面加工平整。在端面车削操作中，进给由横向滑板提供，而切削深度则通过大拖板或复式刀架控制。

Facing can be carried out either from the periphery inward or from the center of the workpiece outward. It is obvious that the machining marks in both cases take the form of a spiral. 端面车削既可以从外表面向内切削也可以从工件中心往外切削。很明显在这两种情况下机加工痕迹都是螺线形式。

Usually, it is preferred to clamp the carriage during a facing operation, since the cutting force tends to push the tool (and, of course, the whole carriage) away from the workpiece. In most facing operations, the workpiece is held in a chuck or on a face plate.通常在端面车削作业时习惯于采用夹住大拖板，这是因为切削力倾向于将刀具(当然包括整个大拖板)推离工件。在大多数端面车削作业中，工件被支撑在卡盘或花盘上。

Groove cutting. In cut-off and groove-cutting operations, only cross feed of the tool is employed. The cut-off and grooving tools, which were previously discussed, are employed.开槽：在切断和开槽操作中，刀具只有横向进给。要采用前面已经讨论过的切断和开槽刀具。

Boring and internal turning. Boring and internal turning are performed on the internal surfaces by a boring bar or suitable internal cutting tools. If the initial workpiece is solid, a drilling operation must be performed first. The drilling tool is held in the tailstock, and the latter is then fed against the workpiece.镗孔和内部车削：镗孔和内部车削通过镗杆或合适的内部切削刀具在内表面进行。如果初始工件是实心的，则必须首先进行钻孔作业。钻孔刀具安装在尾架上，然后对着工件进给。

Taper turning. Taper turning is achieved by driving the tool in a direction that is not parallel to the lathe axis but inclined to it with an angle that is equal to the desired angle of the taper. Following are the different methods used in taper-turning practice:锥面车削：锥面车削通过沿着与车床主轴不平行而倾斜成一个等于锥面所需角度的方向进刀来实现。下面是在实际锥面车削中采用的不同方法：
(1) Rotating the disc of the compound rest with an angle equal to half the apex angle of the cone. Feed is manually provided by cranking the handle of the compound rest. This method is recommended for taper turning of external and internal surfaces when the taper angle is relatively large.(1) 将复式刀架盘旋转一个等于圆锥体顶角一半的角度。通过摇动复式刀架操纵柄手动提供进给。当锥角相对较大时切削外锥面和内锥面推荐使用这种方法。

(2) Employing special form tools for external, very short, conical surfaces. The width of the workpiece must be slightly smaller than that of the tool, and the workpiece is usually held in a chuck or clamped on a face plate. In this case, only the cross feed is used during the machining process and the carriage is clamped to the machine bed.(2) 对很短的外锥面采用特殊的成型刀具。工件的宽度必须略小于刀具的宽度，并且工件通常由卡盘支撑或夹紧在花盘上。在这种情况下，机加工作业时只有横向进给而大拖板则夹紧在床身上。

(3) Offsetting the tailstock center. This method is employed for external taper turning of long workpieces that are required to have small taper angles (less than 8°). The workpiece is mounted between the two centers; then the tailstock center is shifted a distance S in the direction normal to the lathe axis.(3)偏移尾架顶尖。对需要较小锥角(小于8°) 的较长工件外锥面车削采用这种方法。工件安装于两顶尖之间；
然后将尾架顶尖朝垂直于车床主轴方向移动一距离S。

(4) Using the taper-turning attachment. This method is used for turning very long workpieces, when the length is larger than the whole stroke of the compound rest. The procedure followed in such cases involves complete disengagement of the cross slide from the carriage, which is then guided by the taper-turning attachment.(4) 采用锥面车削附加装置。这种方法用于车削很长的工件，其长度大于复式刀架的整个行程。在这种场合下要遵循的步骤是将横向滑板完全脱离大拖板，然后通过锥面车削附加装置进行引导。

During this process, the automatic axial feed can be used as usual. This method is recommended for very long workpieces with a small cone angle, i.e., 8°through 10°.在此作业中，能照常使用自动轴向进给。对具有较小锥角(即8°到10°)的很长工件推荐采用这种方法。

Thread cutting. When performing thread cutting, the axial feed must be kept at a constant rate, which is dependent upon the rotational speed (rpm) of the workpiece. The relationship between both is determined primarily by the desired pitch of the thread to be cut.螺纹切削：在螺纹切削作业时，轴向进给必须保持恒定速率，这取决于工件的转速(rpm)。两者之间的关系基本上由被切削螺纹所需的节距决定。

As previously mentioned, the axial feed is automatically generated when cutting a thread by means of the lead screw, which drives the carriage. When the lead screw rotates a single revolution, the carriage travels a distance equal to the pitch of the lead screw. 如前所述，当依靠驱动大拖板的丝杆切削螺纹时轴向进给是自动产生的。丝杆旋转一圈，大拖板就行进等于丝杆节距的一段距离。

Consequently, if the rotational speed of the lead screw is equal to that of the spindle (i.e., that of the workpiece), the pitch of the resulting cut thread is exactly equal to that of the lead screw. 因此如果丝杆的旋转速度等于心轴的转速(即工件的转速)，生成切削螺纹的节距就正好等于丝杆的节距。

The pitch of the resulting thread being cut therefore always depends upon the ratio of the rotational speeds of the lead screw and the spindle: Pitch of the lead screw/ Desired pitch of workpiece=rpm of the workpiece/rpm of lead screw=spindle-to-carriage gearing ratio. 所以被切削生成螺纹的节距总是取决于丝杆和心轴的转速比：丝杆的节距/工件所需节距=工件转速/丝杆转速=心轴到大拖板的传动比。

This equation is useful in determining the kinematic linkage between the lathe spindle and the lead screw and enables proper selection of the gear train between them.这公式在决定车床心轴和丝杆之间的运动学关系时很有用，并且提供了正确挑选它们之间轮系的方法。

In thread cutting operations, the workpiece can either be held in the chuck or mounted between the two lathe centers for relatively long workpieces. The form of the tool used must exactly coincide with the profile of the thread to be cut, i.e., triangular tools must be used for triangular threads, and so on.在螺纹切削作业中，工件既能支撑于卡盘中，对相对较长的工件也能安装在两个车床顶尖之间。使用的刀具外形必须正好与要切削螺纹的轮廓一致，即三角形刀具必须用于三角形螺纹等等。

Knurling. Knurling is mainly a forming operation in which no chips are produced. It involves pressing two hardened rolls with rough filelike surfaces against the rotating workpiece to cause plastic deformation of the workpiece metal.滚花：滚花主要是一种不产生切屑的成型操作。它使用两个带有粗锉式表面的淬火滚轮压在旋转的工件上使工件金属产生塑性变形。

Knurling is carried out to produce rough, cylindrical (or conical) surfaces, which are usually used as handles. Sometimes, surfaces are knurled just for the sake of decoration; there are different types of patterns of knurls from which to choose.滚花用于生成粗糙的圆柱(或圆锥)面，通常用来作手柄。有时表面滚花只为装饰之故；
有不同的滚花图案类型可供选择。

Cutting Speeds and Feed切削速度和进给 The cutting speed, which is usually given in surface feet per minute (SFM), is the number of feet traveled in the circumferential direction by a given point on the surface (being cut) of the workpiece in 1 minute.切削速度，通常用每分钟表面英尺给出，就是一分钟内工件(被切削)表面给定点在圆周方向上行进的英尺数。

The relationship between the surface speed and rpm can be given by the following equation: SFM=πDN Where D=the diameter of the workpiece in feet N=the rpm 表面速度与转速之间的关系可以用下式给出：
SFM=πDN 式中 D= 用英尺表示的工件直径 N= 转速 The surface cutting speed is dependant primarily upon the material being machined as well as the material of the cutting tool and can be obtained from handbooks, information provided by cutting tool manufacturers, and the like. 表面切削速度主要由被切削材料和切削刀具材料决定，可以从手册、切削刀具生产商提供的资料及类似的东西上查取。

Generally, the SFM is taken as 100 when machining cold-rolled or mild steel, as 50 when machining tougher metals, and as 200 when machining softer materials. For aluminum, the SFM is usually taken as 400 or above. There are also other variables that affect the optimal value of the surface cutting speed. 一般而言，SFM当机加工冷轧或低碳钢时取100，机加工较坚韧的金属时取50，而机加工较软材料时取200。对铝而言，SFM通常可取400以上。也还存在其它一些变量影响表面切削速度的最佳值。

These include the tool geometry, the type of lubricant or coolant, the feed, and the depth of cut. As soon as the cutting speed is decided upon, the rotational speed (rpm) of the spindle can be obtained as follows: N=SFM/(πD) 其中包括刀具形状、润滑剂或冷却液的类型、进给和切削深度。切削速度一旦确定，心轴转速(rpm) 就能按下式得到：
N=SFM/(πD) The selection of a suitable feed depends upon many factors, such as the required surface finish, the depth of cut, and the geometry of the tool used. Finer feeds produce better surface finish, whereas higher feeds reduce the machining time during which the tool is in direct contact with the workpiece.合适进给的选择取决于许多因素，例如所需表面光洁度、切削深度和所用刀具的几何形状。进给越小生成的光洁度越好，而在刀具与工件直接接触时进给越大则可以减少机加工时间。

Therefore, it is generally recommended to use high feeds for roughing operations and finer feeds for finishing operations. Again, recommended values for feeds, which can be taken as guidelines, are found in handbooks and in information booklets provided by cutting tool manufacturers.所以对粗车一般推荐使用较大进给，而精车则用较小进给。再者，作为指导方针的进给推荐值可以从手册和切削刀具生产商提供的资料小册子上找到。

UNIT 12 Drilling and Milling Drilling and Drills钻削和钻头 Drilling involves producing through or blind holes in a workpiece by forcing a tool, which rotates around its axis, against the workpiece.钻削就是通过迫使绕自身轴线旋转的切削刀具进入工件而在其上生成通孔或盲孔。

Consequently, the range of cutting from that axis of rotation is equal to the radius of the required hole. In practice, two symmetrical cutting edges that rotate about the same axis are employed.因此，从旋转轴线开始的切削范围等于所需孔的半径。实际上，使用的是两条围绕相同轴线旋转的对称切削刃。

Drilling operations can be carried out by using either hand drills or drilling machines. The latter differ in size and construction. Nevertheless, the tool always rotates around its axis while the workpiece is kept firmly fixed. This is contrary to drilling on a lathe.钻削作业既能采用手钻也能采用钻床来实现。钻床在尺寸和结构上虽有差别，然而始终都是切削刀具围绕自身轴线旋转、工件稳固定位的形式。这正好与在车床上钻孔相反。

Cutting Tool for Drilling Operation用于钻削作业的切削刀具 In drilling operations, a cylindrical rotary-end cutting tool, called a drill, is employed. The drill can have either one or more cutting edges and corresponding flutes, which can be straight or helical.在钻削作业中，要用到被称为钻头的圆柱形回转端切削刀具。钻头可以有一条或多条直的或是螺旋状的切削刃以及相应的出屑槽。

The function of the flutes is to provide outlet passages for the chips generated during the drilling operation and also to allow lubricants and coolants to reach the cutting edges and the surface being machined. Following is a survey of the commonly used drills.出屑槽的功能是给钻削作业中产生的切屑提供排出通道，并允许润滑剂和冷却液到达切削刃和正在被加工的表面。下面是常用钻头的概述。

Twist drill. The twist drill is the most common type of drill. It has two cutting edges and two helical flutes that continue over the length of the drill body, as shown in Fig.12.1. The drill also consists of a neck and a shank that can be either straight or tapered. 麻花钻：麻花钻是最常用的钻头类型。它有两条切削刃和两条沿钻头体全长连续的螺旋状出屑槽，如图12.1所示。麻花钻还包括钻颈和钻柄，钻柄可以是直的也可以是锥形的。

In the latter case, the shank is fitted by the wedge action into the tapered socket of the spindle and has a tang, which goes into a slot in the spindle socket, thus acting as a solid means for transmitting rotation. 锥形钻柄通过楔入动作安装在主轴的锥形轴孔中，钻柄上还有柄舌插入主轴轴孔中的插槽，从而作为传递转动的可靠方法。

On the other hand, straight-shank drills are held in a drill chuck that is, in turn, fitted into the spindle socket in the same way as tapered shank drills.另一方面，直柄钻头用钻头卡盘夹住，接下来钻头卡盘则象锥形钻柄钻头一样安装在主轴轴孔内。

As can be seen in Fig.12.1, the two cutting edges are referred to as the lips, and are connected together by a wedge, which is a chisel-like edge. The twist drill also has two margins, which enable proper guidance and locating of the drill while it is in operation. 如图12.1所示，两条切削刃就是钻唇，通过凿子状边缘的楔形体连在一起。麻花钻还有两条导向边，用于作业中钻头的正确导向和定位。

The tool point angle (TPA) is formed by the two lips and is chosen based on the properties of the material to be cut. The usual TPA for commercial drills is 118°, which is appropriate for drilling low-carbon steels and cast irons.两条钻唇形成钻顶角，并根据被钻削材料的性能来选取其大小。商品化钻头的钻顶角一般为118°，这适用于钻削低碳钢和铸铁。

For harder and tougher metals, such as hardened steel, brass and bronze, larger TPAs (130°or 140°) give better performance. The helix angle of the flutes of the commonly used twist drills ranges between 24°and 30°. When drilling copper or soft plastics, higher values for the helix angle are recommended (between 35°and 45°).对于更硬更韧的金属，诸如淬火钢、黄铜和青铜，更大的钻顶角(130°或140°)才能有更好的效果。麻花钻常用的出屑槽螺旋角范围为24°到 30°。钻削紫铜或软塑料时，推荐采用更大的螺旋角(35°到45°)。

Twist drills are usually made of high-speed steel, although carbide-tipped drills are also available. The sizes of twist drills used in industrial practice range from 0.01 up to 3.25 in. (i. e., 0.25 up to 80 mm).虽然也有硬质合金刀尖的钻头，麻花钻一般用高速钢制成。工业实际中使用的麻花钻尺寸范围为0.01到3.25英寸(即0.25到80毫米)。

Core drills. A core drill consists of the chamfer, body, neck, and shank, as shown in Fig.12.2. This type of drill may have either three or four flutes and equal number of margins, which ensure superior guidance, thus resulting in high machining accuracy. 空心钻：空心钻包括斜面、钻头体、钻颈和钻柄，如图12.2所示。这类钻头可以有三条或四条出屑槽及相同数量的保证良好导向的导向边，这样使得加工有高精度。

It can also be seen in Fig.12.2 that a core drill has flat end. The chamfer can have three or four cutting edges or lips, and the lip angle may vary between 90°and 120°. 在图12.2中同样能看到，空心钻具有平坦的端部。斜面可以有三或四条切削刃或钻唇，并且钻唇角可以在90°到120°之间变化。

Core drills are employed for enlarging previously made holes and not for originating holes. This type of drill is characterized by greater productivity, high machining accuracy, and superior quality of the drilled surfaces. 空心钻用于扩大已有的孔而不是打孔。这类钻头具有较大生产率、高加工精度和优良钻削表面质量的特性。

Gun drills. Gun drills are used for drilling deep holes. All gun drills are straight-fluted, and each has a single cutting edge. A hole in the body acts as a conduit to transmit coolant under considerable pressure to the tip of the drill.深孔钻：深孔钻用于钻深孔。所有深孔钻都是直出屑槽的，并且均为单切削刃。钻头体中有个孔作为导管在相当大的压力下将冷却液传送到钻头顶端。

There are two kinds of gun drills, namely, the center-cut gun drill used for drilling blind holes and the trepanning drill. The latter has a cylindrical groove at its center, thus generating a solid core, which guides the tool as it proceeds during the drilling operation.深孔钻有两种类型，即用于钻盲孔的中心切削深孔钻和套孔钻。后者在其中心有一圆柱形沟槽，这样能生成整体芯在钻孔作业过程中引导钻头。

Spade drills. Spade drills are used for drilling large holes of 3.5 in.(90mm) or more. Their design results in a marked saving in cost of the tool as well as a tangible reduction in its weight, which facilitates its handling. Moreover, this type of drill is easy to grind.扁平钻：扁平钻用于钻削3.5英寸(90毫米)或更大的大孔。其设计使得钻头成本明显节省、重量切实减轻，重量轻又使操作更方便。此外这种钻头容易磨利。

Milling and Milling Cutter铣削和铣刀 Milling is a machining process that is carried out by means of a multiedge rotating tool known as a milling cutter.铣削是采用被称为铣刀的多刃旋转刀具完成的机加工作业。

In this process, metal removal is achieved through combining the rotary motion of the milling cutter and linear motions of the workpiece simultaneously. Milling operations are employed in producing flat, contoured and helical surfaces as well as for thread- and gear-cutting operation.在此工艺中，金属去除是通过铣刀的旋转运动和工件的直线运动的组合实现的。铣削作业既可用于生成平面、轮廓面和螺旋面，也可用于切削螺纹和齿轮。

Each of the cutting edges of a milling cutter acts as an individual single-point cutter when it engages with the workpiece metal. Therefore, each of those cutting edges has appropriate rake and relief angles. 在铣刀切削工件金属时，铣刀的每条切削刃都象一单独的单刃刀具一样作用。所以每条切削刃都适当的前后角。

Since only a few of the cutting edges are engaged with the workpiece at a time, heavy cuts can be taken without adversely affecting the tool life. In fact, the permissible cutting speeds and feeds for milling are three to four times higher than those for turning or drilling. 由于同一时间只有部分切削刃切削工件，因此可以在对刀具寿命没有不利影响的情况下承担重型切削。事实上，铣削允许的切削速度和进给比车削或钻削高三到四倍。

Moreover, the quality of the surfaces machined by milling is generally superior to the quality of surfaces machined by turning, shaping, or drilling.此外，由铣削加工的表面质量通常优于车削、刨削或钻削加工的表面质量。

A wide variety of milling cutters is available in industry. This, together with the fact that a milling machine is a very versatile machine tool, makes the milling machine the backbone of a machining workshop.工业上可采用的铣刀类型众多。连同铣床是极通用机床的事实，使得铣床成为机加工车间的支柱。

As far as the direction of cutter rotation and workpiece feed are concerned, milling is performed by either of the following two methods.至于涉及到铣刀转动的方向和工件的进给，铣削可以通过下列两种方法之一进行。

Up milling (conventional milling). In up milling the workpiece is fed against the direction of cutter rotation, as shown in Fig.12.3a. As we can see in that figure, the depth of cut (and consequently the load) gradually increases on the successively engaged cutting edges. 逆铣(传统铣削)：在逆铣中，工件逆着铣刀转动的方向进给，如图12.3a所示。就像在此图中能看到的那样，切削深度(及作为结果的载荷)随着切削刃持续进入切削而逐渐增加。

Therefore, the machining process involves no impact loading, thus ensuring smoother operation of the machine tool and longer tool life. The quality of the machined surface obtained by up milling is not very high. Nevertheless, up milling is commonly used in industry, especially for rough cuts. 所以，这种工艺没有冲击载荷，从而保证了机床的较平稳运行和较长寿命。通过逆铣所得机加工表面质量不是很高。然而逆铣仍经常被用在工业上，尤其是粗切削时。

Down milling (climb milling). As can be seen in Fig.12.3b, in down milling the cutter rotation coincides with the direction of feed at the contact point between the tool and the workpiece. It can also be seen that the maximum depth of cut is achieved directly as the cutter engages with the workpiece. 顺铣(同向铣削)：如同在图12.3b中看到的那样，在顺铣时刀具与工件之间接触点上铣刀旋转与进给方向一致。还可以看到当刀具进入工件切削时直接达到最大切削深度。

This results in a kind of impact, or sudden loading. Therefore, this method cannot be used unless the milling machine is equipped with a backlash eliminator on the feed screw. The advantages of this method include higher quality of the machined surface and easier clamping of workpieces, since the cutting forces act downward.这会导致一种冲击，或突然加载。因此，这种方法只有当铣床在进给螺栓上配备间隙消除器时才采用。这种方法的优点包括机加工表面质量较高和工件由于切削力向下作用而较容易夹紧。

Types of Milling Cutters铣刀的类型 There is a wide variety of milling cutter shapes. Each of them is designed to perform effectively a specific milling operation.铣刀的形状类型很多。其中每种都是为有效进行特定的铣削作业而设计的。

Generally, a milling cutter can be described as a multiedge cutting tool having the shape of a solid of revolution, with the cutting teeth arranged either on the periphery or on an end face or on both. Following is a quick survey of the commonly used types of milling cutters.通常，铣刀可以被描述为具有旋转实体形状并将切削齿安装在周边或一到两个端面上的多刃切削刀具。下面是常用铣刀类型的快速综览。

Plain milling cutter. A plain milling cutter is a disk-shaped cutting tool that may have either straight or helical teeth, as shown in Fig.12.4a. This type is always mounted on horizontal milling machines and is used for machining flat surfaces.平面铣刀：平面铣刀是一种盘状切削刀具，它可以具有直齿或螺旋齿，如图12.4a所示。这类铣刀总是安装在卧式铣床上，用于机加工平面。

Face milling cutter. A face milling cutter is also used for machining flat surfaces. It is bolted at the end of a short arbor, which is in turn mounted on a vertical milling machine. Fig.12.4b indicates a milling cutter of this type.端面铣刀：端面铣刀也可用于机加工平面。它用螺栓固定在短刀杆的端部，而短刀杆则依次安装于立式铣床上。图12.4b显示了这类铣刀。

Plain metal slitting saw cutter. Fig.12.4c indicates a plain metal slitting saw cutter. we can see that it actually involves a very thin plain milling cutter.平面金属开槽锯刃铣刀：图12.4c显示了一种平面金属开槽锯刃铣刀。可以看到它其实是一种很薄的平面铣刀。

Side milling cutter. A side milling cutter is used for cutting slots, grooves, and splines. As shown in Fig.12.4d, it is quite similar to the plain milling cutter, the difference being that this type has teeth on the sides. As is the case with the plain cutter, the cutting teeth can be straight or helical.侧铣刀：侧铣刀用于切削狭槽、凹槽和花键槽。正如图12.4d所示，它与平面铣刀十分相似，差别在于此类铣刀齿在侧面。象平面铣刀的情况一样，切削齿既可以是直的也可以是螺旋的。

Angle milling cutter. An angle milling cutter is employed in cutting dovetail grooves, ratchet wheels, and the like. Fig.12.4e indicates a milling cutter of this type.倾斜铣刀：倾斜铣刀用于切削燕尾槽、棘轮之类的。图12.4e显示了这类铣刀。

T-slot cutter. As shown in Fig.12.4f, a T-slot cutter involves a plain milling cutter with an integral shaft normal to it. As the name suggests, this type is used for milling T-slots.T型槽铣刀：如图12.4f所示，T型槽铣刀包括了一个平面铣刀和一根垂直于它的整体轴。正像其名字所表明的，这类铣刀用于铣削T型槽。

End mill cutter. End mill cutters find common applications in cutting slots, grooves, flutes, splines, pocketing work, and the like. Fig.12.4g indicates an end mill cutter. The latter is always mounted on a vertical milling machine and can have two or four flutes, which may be either straight or helical.端面铣刀：端面铣刀在切削狭槽、凹槽、长凹槽、花键槽、凹状工件之类时均能发现其普遍应用。图12.4g为端面铣刀。它总是安装在立式铣床上，并具有两到四条既可是直的也可是螺旋的长凹槽。

Form milling cutter. The teeth of a form milling cutter have a certain shape, which is identical to the section of the metal to be removed during the milling operation. Examples of this type include gear cutters, gear hobs, convex and concave cutters, and the like. From milling cutters are mounted on horizontal milling machines.成形铣刀：成形铣刀的齿具有特定的形状，这个形状与铣削时要切削的那部分金属的形状一致。这类铣刀的例子包括齿轮铣刀、齿轮滚刀、凸形和凹形铣刀等等。成形铣刀安装在卧式铣床上。

Materials of Milling Cutters铣刀的材料 The commonly used milling cutters are made of high-speed steel, which is generally adequate for most jobs. 普通使用的铣刀用高速钢制造，这对一般大多数工作已足够。Milling cutters tipped with sintered carbides or cast nonferrous alloys as cutting teeth are usually employed for mass production, where heavier cuts and/or high cutting speeds are required.对大规模生产而言，因为其需要重型切削和/或高切削速度，铣刀顶端常装有烧结碳化物或有色金属碳合金作为切削齿。

UNIT 13 Jigs and Fixtures Introduction 导言 It has already been stated that the workpiece must be located relative to the cutting tool, and be secured in that position. After the workpiece has been marked out, it is still necessary to position it with respect to the machine movements, and to clamp it in that position before machining is started.已经说明了工件必须相对于切削刀具定位并确保到位。工件划线后，仍有必要将其相对于切削运动定位，并在机加工开始前把它装夹到位。

When several identical workpieces are to be produced the need to mark out each part is eliminated by the use of jigs and fixtures, but if a casting or forging is involved, a trial workpiece is marked out, to ensure that the workpiece can be produced from it, and to ensure that ribs, cores, etc. have not become misplaced.当要加工若干同样的工件时，使用钻模和夹具可以不必在每个工件上划线；
但对铸件或锻件而言，还需取一试验工件划线以保证照此加工不会将加强肋、型芯等放错位置。

Jigs and fixtures are alike in that they both incorporate devices to ensure that the workpiece is correctly located and clamped, but they differ in that jigs incorporate means of tool guiding during the actual cutting operation, and fixtures do not. 钻模和夹具的相似点是它们都把保证工件正确定位和夹紧的装置相结合，它们的不同在于钻模在实际切削作业中还能与刀具导向方法相结合，而夹具则不能。

In practice, the only cutting tools that can be guided while actually cutting are drills, reamers, and similar cutters; and so jigs are associated with drilling operations, and fixtures with all other operations. Fixtures may incorporate means of setting the cutting tools relative to the location system.实际上，在真实切削中能被导向的切削刀具只有钻头、铰刀和类似的刀具；
因此钻模用于钻削作业，而夹具用于其余作业。夹具可以与切削刀具相对定位系统装夹的方法结合在一起。

The advantages of jigs and fixtures can be summarised as follows: 1)Marking out and other measuring and setting out methods are eliminated; 2)Unskilled workers may proceed confidently and quickly in knowledge that the workpiece can be positioned correctly, and the tools guided or set; 钻模和夹具的优点可归纳如下：
1)可以省去划线和其它测量及放样程序；

2)在知道工件能正确定位、刀具能恰当导向或装夹的情况下，不熟练的工人也能自信而快速地操作；

3)the assembly of parts is facilitated, since all components will be identical within small limits, and “trying” and filing of work is eliminated; 4)The parts will be interchangeable, and if the product sold over a wide area, the problem of spare parts will be simplified. 3)由于所有零件在较小极限范围内是相同的，可以省掉工件的‘试装’和锉削，所以零件装配很方便；

4)零件具有互换性，这样如果产品在较大范围内销售的话，备件问题将简单化。

Bolt holes often have 1.5mm or even 3.0mm clearance for the bolt, and the reader may doubt the necessity of making precision jigs for such work. It must be remembered that the jigs, once made, will be used on many components, and the extra cost of an accurately made jig is spread over a large output. 螺栓孔常给螺栓留出1.5毫米或甚至3.0毫米的间隙，读者可能会怀疑为这样的工作制造精密钻模的必要性。但要记住，这种钻模一旦造好，可用于许多零部件，精确制造钻模的额外成本可分摊在大量产品上。

Furthermore, it is surprising how small errors accumulate in a mechanism during its assembly. When a clearance is specified, it is better to ensure its observance, rather than to allow careless marking out and machining to encroach upon it．此外，这样做在装配机械装置时其累积误差之小也是令人惊讶的。在确定一个间隙时，最好能保证它的习惯要求，而不是随便划线和机加工使其超出正常的界限。

1) The location of workpiece. Fig.13.1 represents a body that is completely free in space. In this condition it has six degrees of freedom. Consider these freedoms with respect to the three mutually perpendicular axes XX, YY, and ZZ. 1) 工件的定位：图13.1表示一个在空间完全自由的物体，在这种情况下它具有六个自由度。相对于三根互相垂直的坐标轴XX、YY和ZZ来考虑这些自由度。

The body can move along any of these axes; it therefore has three freedoms of translation. It can also rotate about any of the three axes; it therefore has three freedoms of rotation. The total number of freedoms is six. When work is located, as many of these freedoms as possible must be eliminated, to ensure that the operation is performed with the required accuracy. 此物体能沿三根坐标轴的任意一根移动；
这样就具有三个平移自由度。它也能围绕三根坐标轴的任意一根回转；
这样它又具有三个旋转自由度。总的自由度数目是六个。当工件被定位时，必须尽可能多地消除这些自由度，以保证作业按要求精度进行。

Accuracy is ensured by machining suitable location features as early as possible, and using them for all location, unless other considerations mean that other location features must be used. If it is necessary, the new location features must be machined as a result of location from the former location features.除非有必要采用另外定位要素的其它考虑，精度可通过尽可能早地加工合适的定位要素并采用它们进行所有定位来保证。如果必要的话，新的定位要素必须作为先前的定位要素的定位结果来加工。

2) The clamping of the workpiece. The clamping system must be such that the workpiece is held against the cutting forces, and the clamping forces must not be so great as to cause the workpiece to become distorted or damaged. 2) 工件的装夹：装夹系统必须使工件对着切削力夹持，而且装夹力又不能大得引起工件变形或损坏。

The workpiece must be supported beneath the point of clamping, to ensure that the forces are taken by the main frame of the jig or fixture, and on to the machine table and bed. When jigs and fixtures are designed, the clamping system is designed to ensure that the correct clamping force is applied, and that the clamps can be operated quickly but with safety. 工件必须在装夹点下被支撑，以保证这些力由钻模或夹具的主框架来承受并传递给机器台和床身。在设计钻模和夹具时，要同时设计装夹系统来保证提供恰当的装夹力，并使装夹操作快速而安全。

Definition of a Drill Jig钻模的定义 A drill jig is a device for ensuring that a hole to be drilled, tapped, or reamed in a workpiece will be machined in the proper place.钻模是一种确保在工件正确位置进行钻孔、攻丝或铰孔加工的装置。

Basically it consists of a clamping device to hold the part in position under hardened-steel bushings through which the drill passes during the drilling operation. The drill is guided by the bushings. 它基本上由在淬硬钢衬套下将零件夹持到位的夹持装置组成，钻孔作业中钻头穿过这些衬套，通过它们来导向。

If the workpiece is of simple construction, the jig may be clamped on the workpiece. In most cases, however, the workpiece is held by the jig, and the jig is arranged so that the workpiece can be quickly inserted and as quickly removed after the machining operation is performed.如果工件结构比较简单，钻模可夹持在工件上。然而大多数情况下，工件由钻模来夹持，并且把钻模设计成能将工件迅速装入而在加工后同样能很快取出。

Jigs make it possible to drill, ream, and tap holes at much greater speeds and with greater accuracy than when the holes are produced by conventional hand methods. Another advantage is that skilled workers are not required when jigs are used. Responsibility for the accuracy of hole location is taken from the operator and given to the jig.相对于用常规的手工方法加工孔，钻模使得钻孔、铰孔和攻丝速度快很多而且精度更高成为可能。另一个优点是采用钻模时不需要熟练工人。保证孔定位精度的责任从操作者身上转移到了钻模上。

The term jig should be used only for devices employed while drilling, reaming, or tapping holes. It is not fastened to the machine on which it is used and may be moved around on the table of the drilling machine to bring each bushing directly under the drill. Jigs physically limit and control the path of the cutting tool.钻模这个术语只用在服务于钻孔、铰孔或攻丝的装置上。它不固定在使用它的钻床上，它能在钻床工作台上到处移动以使每个衬套都直接位于钻头下。钻模有形地限制和控制钻削刀具的路径。

If the operation includes machining operations like milling, planing, shaping, turning, etc., the term fixture should be used. A fixture holds the work during machining operations but does not contain special arrangements for guiding the cutting tool ,as drill jigs do.如果作业还包括其它象铣削、刨削、成型、车削等机加工，则应采用夹具这一术语。夹具在机加工作业时夹持工件，但它不象钻模那样包含引导切削刀具的特殊布置。

Typical Jigs and Fixtures典型的钻模和夹具 Typical drill jig. Figure 13.2 illustrates a drilling jig for drilling four holes in the flange of a workpiece that has been completed except for the four holes.典型的钻模：图13.2所示为一个能在某工件的法兰上钻四个孔的钻模，该工件除了这四个孔外已全部完成。

The workpiece has an accurately machined bore, and is located from the bore and the end face, from a cylindrical post. There is no need to control the rotational position about the axis of the bore, because up to the time when the holes are drilled, it is symmetrical about that axis. 此工件有一精确机加工的大孔，因此通过一圆柱体采用该孔和工件端面定位。由于直至钻这些小孔时，工件都对称于大孔轴线，所以没必要控制围绕大孔轴线回转的位置。

The four bushes used to control the drill are held in the drill plate, which, with the hand nut, is used to clamp the workpiece against the base of the fixture.四个控制钻头的衬套装在钻板里，连同手拧螺母一起用于靠着夹具基座夹持工件。

Typical milling fixture. Figure 13.3 illustrates a simple milling fixture for milling the slot in the otherwise completed workpiece shown. The workpiece is located from two of the four holes in its base, and from the underside of the base. 典型的铣削夹具：图13.3所示为一用于在图示其它工序都完成的工件上铣槽的简单铣削夹具。此工件采用其基座上四孔中的两孔和基座的底面定位。

The workpiece is clamped in position, and cutter is located against the setting block, which provides setting or cutter position and depth of cut. 工件被夹持到位，铣刀靠着提供安装或铣刀位置及切削深度的安装台定位。

The fixture must be positioned relative to the machine table, this is done by engaging the two tenons at the bottom of the fixture in the slot in the machine table. The fixture is secured to the machine table with T-bolts, also engaging in the slots in the table (Fig.13.3).夹具必须相对于铣床工作台定位，这可通过把夹具底部的两个凸榫插入工作台上的槽中来实现。夹具用T型螺栓固定于铣床工作台，同时与工作台上的槽接合(图13.3)。

UNIT 14 Limit and Tolerances 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.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。

Dimensioning is an involved subject and long experience is required for its mastery.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极限是公差带的极限尺寸。例如公称尺寸 30mm tolerance limits30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 is对5～16级而言，公差单位i的值可用下式计算 Where i is in microns and D in millimeters.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。

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。

计算机技术 引子 计算机辅助设计制造的核心是数字式计算机。由于计算机自身具有高运算速度和大存储容量，它有能力进行图像处理，实时控制以及其它一些复杂的，对人来说大耗时的重要工作。熟悉计算机辅助设计制造，必须先了解数字式计算机的概念和技术。

现代化的计算机在预定的程序下可以完成数学运算、逻辑运算和数据处理。计算机本体被归为硬件，而那些各式各样的程序被归为软件。

一般计算机硬件可分为 中央处理器（CPU） 存储器 输入输出单元 三大部分的关系如图1.1所示。中央处理器，我们一般认为它有两个部分：控制单元和算术逻辑单元。控制单元协调其它各部分的运行。它通过输入输出部分管理计算机与外部的数据吞吐、协调计算机各部分间信号传输以及控制其它单元的功能。算术逻辑单元执行对数据的运算、逻辑处理，包括加、减、乘、除以及根据程序作比较。存储器是计算机的储存单元，数据按字存在存储器中并可以很容易地输送到算数逻辑单元或输入输出单元去处理。输入输出单元提供计算机与外部交流数据的渠道，通信是通过像读数器、打印机、接口设施等外设来完成的。通过输入输出单元，电脑也可连接到外部存储器，如磁带、磁盘等。

软件则包括放在内存、外存中的程序、指令。它将计算机的各种功能组织起来以完成人给的任务。计算机的好处在于执行指令迅速而准确。而存储器内容想改写也十分容易，所以可以为之载入不同的程序。数字式计算机可用于许多场合。

不考虑实际应用需要，计算机执行程序所使用的是数据最基本的形态：数据在计算机中以电信号电平的高低来表现。这种形式称为二进制。我们更熟悉的十进制，以及更大量的软件语言则作为人与机器二进制代码间的桥梁。

中央处理器 中央处理器管理所有系统组件的工作，并对数据作算术、逻辑操作。为了完成这些功能，中央处理器包括：
控制单元 算术逻辑单元 控制单元根据程序指令协调不同的操作，包括接收进入的数据并安排对它的处理时机。控制单元指导算术逻辑单元工作，它向算术逻辑单元发送数字、并告之应对数字作何处理、存结果于何处。控制单元的此功能来自存储于存储器中的一系列指令，它们称为执行程序。

算术逻辑单元执行如加法、减法、比较等，这些操作作用在二进制数上。逻辑单元也可用于在特殊条件下改变程序执行顺序，如编辑、隐藏计算的数据等。

控制单元和逻辑运算单元均使用寄存器完成工作。寄存器是小容量的，可以接受、保持、转移数据的存储器，每个寄存器都包含二进制电容以保存数字位。位的个数决定了计算机吞吐的字长，早期微机字长为4，而如今大型科学计算机字长可达64。

计算机编程语言 二进制数系可以用来代表任意十进制数，字母或其它简单符号，数据和指令就是以二进制码形式送给计算机的。执行之时，电脑将二进制码序列作为对电脑操作的指导，以完成加减、载入、载出等工作。二进制码指令顺序决定了计算机根据程序对数据进行的运算、处理等操作。

机器所能听懂的二进制指令称为机器码，很不幸，人很难阅读或书写这样的码。并且，机器不同码也不同。为了方便编程工作，更高级的语言得以使用，这对人来说相对易学些。计算机程序有以下三档：
机器码 汇编语言 面向过程（高级）语言 机器码与汇编语言：
计算机使用的是二进制的机器码，每条指令包含操作码和操作数。操作数可以是一个存储器地址、一个设备地址或直接是一个数字。机器码编程中，存储器地址为程序和数据编制，在整个程序中它们可以用来查特定的数据和程序步。另外，程序员必须熟悉特定的计算机系统，因为机器码指令写法因机而宜。写机器码的工作冗长、乏味、繁琐、耗时，为减轻写机器码的工作，符号语句被发展出来，它使用像记英文一样的指令代替二进制指令，因而提高了编程速度。包含助记指令的语言称为汇编语言。

汇编语言被视为低级语言，程序员仍须非常熟知他所为之编程的计算机。低级语言非常高效，因为执行快捷。但若程序员想编写较大程序，并且有多个计算机去执行多种任务，就有非常明显的困难。在执行前，汇编语言仍要转换成为机器码，由汇编程序来转换，汇编程序拿到汇编语言程序后，经必要的转换工作后，生成两个文件。一个是机器码版程序，另一个是编译单。编译单显示了汇编语言程序和编译对应法则，也包含原汇编语言程序的任何错误。

高级语言 汇编语言面向的是机器码，而高级语言，正相反，面向过程。它将执行程序的具体机器的影响降到最小，即此机所用程序用于彼此机无需大改。

高级语言采用英文式陈述，并可应用传统的数学符号。每个高级语言语句都相当于多条机器码指令。

高级语言的好处在于程序员不必特别了解机器码。程序写成英文式的规则，就可以解题了。高级语言付诸执行前，和汇编语言一样，也必须转为机器码。这工作由被称为编译器的程序来完成，它将高级语言编的程序转换为低级语言，比如机器码。若程序中存在叙述错误，比如拼错的单词，它们会根据程序被列出来。

高级语言有许多种，常用的有BASIC、COBOL、FORTRAN、APL、RPG、PL/1和PASCAL。

计算机接口 CRT 阴极射线示波器 计算机必须能够和外界交换信息。数据处理系统中，信息交换由各种输入、输出设备完成，如读卡器、打印机、阴极控制面板等。计算机辅助制造的场合、计算机环境不仅包括外设，还包括一个或多个制造工艺。作为一个过程控制系统，计算机必须能从加工中读取重要的变量，并做出必要的响应以保障工艺。接下来，我们来检视一下计算机过程控制系统的重要组成部分。

加工过程数据 这是指加工过程与计算机之间必须交流的数据，可分成三类。

连续模拟信号 离散二进制数据信号 脉冲数据信号 连续模拟数据可由一个时间上连续的变量来代表。在生产循环中已不间断，而能表示的值在一定范围内。模拟信号包括例如温度、压力、流量和速度等。它们都不是时间的连续函数，在一个范围内取值有无穷多种。实际上取值密度是由测试装备的能力来决定的，看它能分辨的最小差值是多少。

离散二进制数据只有两个可能的取值，例如启动与停止，开启与关闭，开关、马达、阀、灯等的工况均可用二进制位表示。数字电路中，二进制码一般用合适的电平来表示。典型的取值是+5V与接地。

脉冲量包含一系列有脉冲发生器生成的脉冲电信号，它可以用来驱动步进电机。每个脉冲的能量固定，则脉冲序列的能量取决于该序列包含的脉冲数目。序列中的脉冲可以被计数，因而也可用数字数据来代表之。反过来，数码信息也可以转换成为具有给定能量的脉冲序列。

系统对过程数据的转换 上述的三大数据必须能为计算机所接受。为了监视过程，输入数据必须进入计算机；
为了控制过程，输出数据必须由计算机生成、转换再送往生产系统。有六类计算机——过程接口，负责前面所述三类信号间的转换。它们是 模数转换 触电输入 脉冲计数 数模转换 触电输出 脉冲发生器 模数转换包括将实数值转为相应的数位值。这个过程包含许多步骤，涉及下列硬件：
传感器。它将可测的实际量，如流量、温度、进度等，转化为与之值对应的电信号，例如热电偶就是将温度转为小电压差的例子。

信号调整器。它将随机电噪声去除，使传感器输出的信号平顺。

多路复用设备：它将多个过程监视设备接至模数转换器。每个过程都按规律抽样，并送至转换器。

将输入信号做幅度调整以适应模数转换器的工作范围。

模数转换器将输入的实数值处理为对等的数位信号。

数字计算机的输入输出区域从模数转换器中接受数据。极限比较器一般接在输入输出区与模数转换器之间，以免超出限界的信号干扰中央处理器正常工作。

触点输入接口是一系列可以指示行程开关、按钮等二进制式量的简单触点。它是离散实际量与计算机间的媒介，它定期扫描状态并与预编值作比较。

数字式传感器属于电测设备，它采集稳定的点脉冲序列，脉冲计数器则将脉冲序列转换为数字信号，使之得以在信道中传递。

后三种设备是管理电脑送往过程之数据的。

数模转换器将计算机生成的数位信号转为伪模拟信号，之所以这样称呼是因为计算机只能设置有限个数字信号取值，无法生成有真正模拟信号的无穷多取值。

触点输出接口和触点输入接口差不多，是一系列可开闭的触点，计算机输出量由此来点亮指示灯、报警甚至控制切削油泵。

脉冲发生器常用作将计算机输出转为脉冲序列的装置，驱动，比如说，步进电机这样的东西。

计算机网络结构 网络介绍：
计算机网络指不同处所计算机之间的实际连接。它于1964年首次出现，发展已历经数个阶段，如：多机系统、局域网、城域网、广域网及网络计算。如今它已可称为是人类有史以来最大的工程成就。它可用于如通讯、在线数字服务、信息共享等。计算机网络几乎是万能的，在机械工程中它包含了网络化制造、虚拟制造、柔性制造系统和灵活制造。

网络结构 计算机网络不仅有许多计算机，还有许多终端、信息线、交换中心以及大量其它用于实现功能的技术装备。构造有无穷多种，而多变的网络安排可被分为若干基本类，有时称为拓扑形态。基本拓扑形态如图1.2所示。

在点对点结构中，两个设备间架设一条通讯线路。一般来说是将一台计算机与作为终端的一个外设连接起来。若设备总数不多，这种方式相对简便。而当结构中有大量处理设备时，点对点连接的数目和复杂程度均急剧上升，使系统造价上涨，其它的网络结构用多种方式避免造价过高。点对点结构的显而易见的优势在于当一条线路断掉，其它连接仍能保持连接不断。

星型网络包括一个中央计算机和与之相连的多个周边设备。中央计算机称为主机，周边设备称为隶属机。主机向隶属机分派任务或作为隶属机之间的交换器。星型结构缺点在于一旦主机崩溃，整个网络都会失效。

多分支结构中，计算机与其它设备一起连在同一根电缆上，它可以是一条总线或一支信道系列。它的局限性在于对每个时刻仅允许一对设备互相通信。这是由线路共享造成的。

环形结构中，每台计算机都连往一个通讯线路，线路最终是连成环形的。一般来说有一台机子用于管理计算机之间的通讯。传往每台机的信息实际上送往了网络中每台机子，而收件人解读其地址并接收讯息。

树形结构中，主机连往许多处于次一级位置的计算机，每台次级机又将连往多台各自的次级机。主机与其次级机之间传递信息和指令均十分便捷、简单，而其缺点在于两个任意设备间的连接并不那么简单。

网络协议与国际标准系统结构 网络中，计算机之间连接、通信所依据的是某种颁布的规则、共识，它们被称为网络协议。网络协议的主要作用是实现有秩序地通信以及接收。最普通的协议就是通讯控制协议/互联网协议（TCP/IP）。对网络系统模型的阐述有很多，其中由国际标准组织颁布的阐述将协议分为七个层次，每层有自己的称呼和功能。系统模型结构如图1.3所示。

物理层次：使用物质媒介保证信号正确地从此设备送到彼处。

数据链层次：通过校订、证实、反馈将物理连接转为可靠的数据链。

网络层次：通过分类、组合解决将数据从源送往目的地的问题。

传送层次：提供点对点的传输服务。

时段层次：组织不同主机间通讯，使之同步。

提交层次：将数据、信息提交给高层用户。

应用层次：向每个具体的申请提供访问网络环境的方式。

互联网应用与发展 世上最大的网络是互联网，它是广域虚拟网之一种，使用（TCP/IP）协议将全球上千万台计算机连成一个巨大的网络。网络中每台计算机都有自己的地址，其应用可超越地区、国家、大陆的界限，组成一个每人都可收到最新新闻消息、享有最快捷服务的虚拟网，哪怕身处遥远而偏僻的地方。如今练往互联网的计算机、设备越来越多，互联网向我们提供的服务和信息也越来越多。同时，互联网也成为许多国家超级信息高速公路计划的基础。互联网发展最快的应用是万维网，它集中了文本、图像、声音及各种其它多媒体文件，以供共享，并且可由超链接来导航。随着电信技术迅速发展，互联网正义越来越快的速度发展，成为了人类文明的不可或缺的一个组成。