Unit 7 Metal Cutting
importance of metal cutting
Introduction of a typical cutting tool Chip Formation
Shear zone
Cutting Tool Materials
Surface Finish
Cutting Fluids
importance of metal cutting
every product we use in our daily life has undergone this process either directly or indirectly.
In USA, more than $100 billions are spent annually on machining and related operations.
A large majority (above 80%) of all the machine tools used in the
manufacturing industry have undergone metal cutting.
An estimate showed that about 10 to 15% of all the metal produced in USA was converted into chips.
Introduction of a typical cutting tool
Fig 7.1 The general characteristics of a metal cutting tool
A typical cutting tool in a simplified form is shown in Fig 7.1.
The important features to be observed are follows：
①Rake angle（前角）
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. This reduces the strength of the tool tip as well as the heat dissipation through the tool.
The maximum limit to the rake angle is generally of the order of l5°for high speed steel tools cutting mild steel. It is possible to have rake angles at zero or negative.
②Clearance angle （后角）
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.
The conditions which have an important influence on metal cutting ：
work material（工件材料）
cutting tool material（切削刀具材料）
cutting tool geometry（切削刀具几何参数）
cutting speed（切削速度）
feed rate（进给量）
depth of cut（切削深度）
cutting fluid（切削液）
Three cutting factors：
cutting speed（切削速度）——v
feed rate（进给量）—————f
depth of cut（切削深度）——d
Chip Formation
Metal cutting process is a very complex process. Fig 7.2 shows the basic material removal operation schematically. The metal in front of the tool rake face gets immediately compressed,
first elastically and then plastically. Fig 7.2 The possible deformations
in metal cutting
This zone is traditionally called shear zone（剪切区）in view of the fact that the material in the final form would be removed by shear from the parent metal. 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. 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 （曲率）of the chip is termed as chip curl.
Chip formation in metal cutting could be broadly categorized into
three types (Fig.7.3).
Discontinuous chip
Continuous chip
Continuous chip with BUE (Built up edge)
Fig 7.3 Three main types of chips
a）Discontinuous chip b) Continuous chip c) Continuous chip with BUE
积屑瘤
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 tool face, resulting in a crack that runs ahead of the tool. Eventually, the shear stress across the chip becomes equal to the shear strength of the material, resulting in fracture and separation.[1] With this type of chip, there is little relative movement of the chip along the tool face, Fig 7.3 (a).
Continuous Chip
The continuous chip is characterized by a general flow of the separated metal along the tool face. [2] There may be some cracking of the chip, but in this case it usually does not extend far enough to cause fracture. 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 7.3 (b).
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. 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 7.3(c).
Shear zone
two schools of thought in the analysis of the metal removal process：
①deformation zone is very thin and planar as shown in Fig 7.4 (a).
②actual deformation zone is a thick one with a fan shape as shown
in Fig 7.4 (b).
Fig 7.4 Shear models
Cutting Tool Materials
important characteristics expected of a cutting tool material：
Higher hardness—than that of the workpiece material being machined, so that it can penetrate into the work material.
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.
Wear resistance—The cutting tool material should therefore have high abrasion resistance to improve the effective life of the tool.
Toughness—it should have enough toughness to withstand the impact loads that come in the beginning of cut or to force fluctuations due to imperfections in the work material.
Low friction—The coefficient [共同作用] of friction between the chip and tool should be
low. This would allow for lower wear rates and better chip flow.
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.
Surface Finish
Two factors of surface finish in a given machining operation：
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.
the natural component：which is a result of a number of uncontrollable factors in machining, which is difficult to predict.
Ideal Surface Finish in Turning
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 7.5 (a). 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.
For the case in Fig 7.5, the surface roughness value is to be ：
Where: Ra is the surface roughness value
R is the nose Radius ； f is the feed rate ；2a 8f R 183R
Fig.7.5 Surface profile as produced by turning with a cutting tool having a nose radius
The actual surface finish factors
1.the cutting process parameters, speed, feed and depth of cut
2.the geometry of the cutting tool
3.application of cutting fluid
4.work and tool material characteristics
5.rigidity of the machine tool and the consequent vibrations.
The major influence on surface finish is exerted by the feed rate and cutting speed.
Cutting Fluids
The functions of cutting fluids (which are often erroneously called coolants) are：
to cool the tool and workpiece
to reduce the friction
to protect the work against rusting
to improve the surface finish
to prevent the formation of built-up edge
to wash away the chips from the cutting zone.
? 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。
机械工程专业英语 课程负责人： 课程中文名称:专业英语 课程英文名称：English for Mechanical Engineering 课程类别：选修 课程学分数：2 课程学时数：32 授课对象：机械电子工程专业本科生 本课程的前导课程：公共英语，机械专业的相关课程 考核方式：平时成绩+期末考试 使用教材：《机械工程专业英语教程》施平主编（第3版）电子工业大学出版社 教学要求及目的： 了解专业英语的语法特点，熟悉专业词汇，逐步培养学生具有比较熟练的专业文献阅读理解能力、翻译能力和英文学术论文的写作能力。 教学方式： 课堂讲授、讨论与自学相结合。以教师讲授为主，引导学生积极阅读指定参考文献，完成课外作业，参与课堂讨论。有意识地积累与自己研究方向相关的词汇与文献资料，掌握专业英语学习方法。 具体教学目标： ●掌握机械工程专业方面的专业名词、专业术语 rolling contact bearing, 滚动接触轴承journal bearing, 径向轴承resonance 共振 upright drilling machine 立式钻床radial ['re?d??l]drill 摇臂钻床shaper 牛头钻床 ●掌握习惯表达方式 machine design, kinematics [,k?n?'m?t?ks] 运动学，动力学dynamic 动态 slider-crank mechanism ['mek(?)n?z(?)m] 滑动曲柄机构, assembly drawing 装配图detailed [d?'teld]drawing 明细图engineering drawing 工程图 degree-of-freedom (DOF) 自由度 a four-bar mechanism 四连杆机构vibration mechanism 振动机构 CAD Computer - Aided Design, CAM computer-aided manufacturing CAE Computer Aided Engineering ●掌握基本的专业文献阅读能力与翻译能力 ●掌握基本的写作能力 ●培养基本的专业文献资料检索能力 ●了解机械工程方面的国内外动向, 并熟悉与机械工程专业相关的其他学科与
Unit 11CAD and Applications I. Lead in Information related to the text Do you know what the Computer Aided Design (CAD) is? Do you know the history of CAD? What are the advantages of the CAD? Maybe you have used the CAD yet, but do you know how you can use it? Can you give an example? In the unit, you will study the development of CAD and how it is widely used. Now, let’s study new words and phrases together. II. Word Study 1. appropriate [?'pr?uprieit] a. 适当的v. 占用；拨出 1）Use the lists below to select the appropriate delimiter. 请用下面的列表选择相应的定界符。 2）A focus and concern on climate change is entirely appropriate. 对于气候变化的聚焦和关注是完全恰当的。 3）This is the "all appropriate measures" school of policy analysis. 这是政策分析中的“所有适当措施”学派。 2. interactive [,int?'r?ktiv] a. 交互式的，相互作用的 1）Reading is a complex and interactive process. 阅读是一个复杂和互动的过程。 2）A dialog between a user and an interactive data processing system. 一种用户与交互式数据处理系统间的对话（过程）。 3）EVEN when one person is doing all the talking, a conversation is an interactive process. 即使只是一个人在滔滔不绝，谈话也是一项双边交流的过程。 3. standard ['st?nd?d] n. 标准，规格a. 标准的 1）The standard answer is that we need better leaders. 标准答案就是，我们需要更好的领导。 2）For such a series it is usual to design a standard margin . 对于这种系列图幅，通常是设计一种标准图廓。 3）We see that this is the standard of perfection attained under nature. 我们可以看到这就是自然界中所得到的完善化的标准。 4. sophisticate [s?'fistikeit] n. 久经世故的人v. 曲解；使复杂，使精致 1）If you are wrong, admit it rather than sophisticate. 错了就要承认，不要强词夺理。 2）Alter with the intention to deceive; Sophisticate rose water with geraniol.
Lesson 1 力学的基本概念 1、词汇： statics [st?tiks] 静力学；dynamics动力学；constraint约束；magnetic [m?ɡ＇netik]有磁性的；external [eks＇t?:nl] 外面的, 外部的；meshing啮合；follower从动件；magnitude [＇m?ɡnitju:d] 大小；intensity强度，应力；non-coincident [k?u＇insid?nt]不重合；parallel [＇p?r?lel]平行；intuitive 直观的；substance物质；proportional [pr?＇p?:??n?l]比例的；resist抵抗，对抗；celestial [si＇lestj?l]天空的；product乘积；particle质点；elastic [i＇l?stik]弹性；deformed变形的；strain拉力；uniform全都相同的；velocity[vi＇l?siti]速度；scalar[＇skeil?]标量；vector[＇vekt?]矢量；displacement代替；momentum [m?u＇ment?m]动量； 2、词组 make up of由……组成；if not要不，不然；even through即使，纵然； Lesson 2 力和力的作用效果 1、词汇： machine 机器；mechanism机构；movable活动的；given 规定的，给定的，已知的；perform执行；application 施用；produce引起，导致；stress压力；applied施加的；individual单独的；muscular [＇m?skjul?]]力臂；gravity[ɡr?vti]重力；stretch伸展，拉紧，延伸；tensile[tensail]拉力；tension张力，拉力；squeeze挤；compressive 有压力的，压缩的；torsional扭转的；torque转矩；twist扭，转动；molecule [m likju:l]分子的；slide滑动; 滑行；slip滑，溜；one another 互相；shear剪切；independently独立地，自立地；beam梁；compress压；revolve (使)旋转；exert [iɡ＇z?:t]用力，尽力，运用，发挥，施加；principle原则, 原理，准则，规范；spin使…旋转；screw螺丝钉；thread螺纹； 2、词组 a number of 许多；deal with 涉及，处理；result from由什么引起；prevent from阻止，防止；tends to 朝某个方向；in combination结合；fly apart飞散； 3、译文： 任何机器或机构的研究表明每一种机构都是由许多可动的零件组成。这些零件从规定的运动转变到期望的运动。另一方面，这些机器完成工作。当由施力引起的运动时，机器就开始工作了。所以，力和机器的研究涉及在一个物体上的力和力的作用效果。 力是推力或者拉力。力的作用效果要么是改变物体的形状或者运动，要么阻止其他的力发生改变。每一种
Unit 4 Heat Treatment& Hot Working of Metals Ⅰ. Lead-in Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten. Carbon and other elements act as a hardening agent, preventing dislocations in the iron atom crystal lattice from sliding past one another. Varying the amount of alloying elements and the form of their presence in the steel (solute elements, precipitated phase) controls qualities such as the hardness, ductility, and tensile strength of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but such steel is also less ductile than iron. Though steel had been produced by various inefficient methods long before the Renaissance, its use became more common after more-efficient production methods were devised in the 17th century. With the invention of the Bessemer process in the mid-19th century, steel became an inexpensive mass-produced material. Further refinements in the process, such as basic oxygen steelmaking (BOS), lowered the cost of production while increasing the quality of the metal. Today, steel is one of the most common materials in the world, with more than 1.3 billion tons produced annually. It is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations. II. Word Stud y 1. molecular[m?'lekj?l?] a. 由分子组成的, 分子的 1)molecular structure 分子结构 2) We think of magnetism as a molecular phenomenon. 我们认为电磁是一种分子现象。 3) The investigations were performed at molecular level. 研究是在分子的层次上进行的。 2. liable ['lai?bl] a. 有责任的，有义务的，应受罚的，有…倾向的 1) be liable to seasickness容易晕船 2) One who works under the hot sun is liable to sunstroke. 在炎热的阳光底下工作很容易引起中暑。 3) People are liable to judge others from their own first impressions. 人们容易用他们自己的最初印象来评价别人。 3. squeeze [skwi:z] v. 挤(压，干)，压榨，勒索，紧握
Unit 10 Surface Engineering Two major surface treatments Covering the surfaces Altering the surfaces
Surface Engineering Requirements (1) control friction and wear; (2) improve corrosion resistance; (3) change physical property, such as conductivity [导电率], resistivity, reflection; (4) alter dimension; (5) vary appearance, e.g., color and roughness; (6) reduce cost;
Covering the surfaces The treatments that cover the surfaces include: 1. organic coatings 2. inorganic coatings. Shown on the right.covering the surfaces organic coatings inorganic coatings Electroplating Thin-film coatings Furnace fusings Hot dippings Thermal sprayings Conversion coatings
Electroplating It is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath. Anode [正极]: positively charged electrode. The source of the material to be deposited. electrochemistry: the medium through which metal ions are exchanged and transferred to the substrate to be coated. cathode: negatively charged electrode. the substrate to be coated.
Lesson1 1、the branch of scientific analysis, which deals with motions, time, and forces, is called mechanics and is made up of two parts, statics and dynamics. Statics deals with the analysis of stationary systems, i.e., those in which time is not a factor, and dynamics deals with systems, which change with time. 对运动时间和作用力作出科学分析的分支成为力学。他由静力学和动力学两部分组成。静力学对静止系统进行分析，即在其中不考虑时间这个引述，动力学对事件而变化的系统进行分析。 2、Any two such forces acting on a body constitute a couple. The arm of the couple is the perpendicular distance between their lines of action, and the plane of the couple is the plane containing the two lines of action. 作用在一个刚体上的两个这样的的里构成一个力偶。力偶臂是这两个条作用线之间的垂直距离，力偶面是包含着两条作用线的平面。 3、Mechanics deal with two kinds of quantities: scalars and vectors. Scalar quantities are those with which a magnitude alone is associated. Examples of scalar quantities in mechanics are time, volume, density, speed, energy, and mass. Vector quantities, on the other hand, possess direction as well as magnitude. Examples of vectors are displacement, velocity, acceleration, force, moment, and momentum. 力学涉及两种类型的量，标量和矢量。标量是那些只有大小的量。在力学中标量的例子有时间、体积、密度、速率、、能量和质量。另一方面，矢量既有大小又有大小又有方向。矢量的例子有位移、速度、加速度、力、力矩、动量。 Lesson2（此课后面没翻译，翻译的不太准确谅解） 1 、The turning of a part in a lathe is another example of several forces in action.（as shown in figure1） 车床车削是一些力在起作用的另一个例子。figure1(如图)。 2 、If this workpiece is held between the centers of the lathe, the centers exert a compressive force against the work. 如果这个工件在放在车床中心之间,中心车床对工作产生压力。 3、 Rotary motion is required to drill holes, turn parts in a lathe, mill surfaces, or drive a generator or fan belt. 扶轮运动需要去钻孔，在车床上转换两件,表面,或驱动发电机或风扇皮带 4 、Harmonic and Intermittent Motion（谐和运动和间歇运动）: Any simple vibration, such as the regular back, and forth movement of the end of a pendulum, is simple harmonic motion. Lesson4 1 、Virtually all machines contain shafts. The most common shape for shafts is circular and the cross section can be either solid or hollow. 实际上，几乎所有的机器中都装有轴。轴的最常见的形状是圆形，其截面可以是实心的，也可以是空心的（空心轴可以减轻重量）。有时也采用矩形轴，例如，螺丝起子的头部.套筒扳手和控制旋钮的杆。 2、 A shaft must have adequate torisonal strength to transmit torque and not be over stressed it must also be torsional stiff enough so that one mounted component does not deviate excessively from its original angular position relative to a second component mounted on the same shaft. 为了在传递扭矩时不发生过载，轴应该有适当的抗扭强度。轴还应该具有足够的抗扭强度，以使在同一轴上的两个传动零件之间的相对转角不会过大。 3 、Components such as gears and pulleys are mounted on shafts by means of key. The design of the key and the corresponding keyway in the shaft must be properly evaluated. For example, stress concentrations occur in shafts due to keyways, and the material removed to from the keyway further weakens the shaft. 齿轮和皮带轮等零件通过键连接在轴上。在键及轴上与之相对应的键槽的设计中，必须进行认真的计算。例如，轴上的键槽会引起应力集中，由于键槽的存在会使轴的横截面积减小，会进一步减弱轴的强度。 4、Another important aspect of shaft design is the method of directly connecting one shaft to another. Devices such as rigid and flexible couplings accomplish this. 轴的设计工作中的另一个重要方面是一根轴与另一根轴之间的直接连接方法。这是由刚性或者弹性联轴器来实现的。 Lesson5 1、The term shaft usually refers to a relatively long member of round cross section that rotates and
Unit 7 The Injection Molding and Machine I. Lead in Information related to the text Do you know what is called an injection molding machine? Can you give an example of it? What does it work? In this unit you will learn some the Injection Molding and Machine concept, how it is wide application. Now, let's learn new words and phrases. II. Word Study 1. inject [in'd?ekt]vt.注射，注入injection n.注射，投资，注射剂 1）A sterile applicator is used to inject the microchip just under the skin. 一个消过毒的涂药器被注射进微型芯片在表皮之下。 2）Major banks around the world are joining forces to inject as much as 180 billion dollars into global money markets. 全世界的主要银行都加入了抵制注入180亿美元到全球的经济市场中的行动。 3）Fire ants get their name because when they sting, they inject poison into the skin that causes a feeling of intense burning. Some people suffer life-threatening reactions. 火蚁因当他们叮住目标时会将一种能导致灼热感的有毒物质注入皮肤而得名。有些还会有生命危险的反应。 4）There would be no need for injection, since the vaccine would be taken by mouth. 通过口服疫苗，我们就不需要注射了。 2. melt [melt] vt. 使软化，使融化，使熔化，使感动 1）This element is of proper shape and cross-section to carry rated current continuously and to melt in accordance with a specific time-current characteristic on heavy overload or short circuit. 此可熔断元件恰当的形状和横截面使其可连续通过额定电流，而对于严重过负荷或短路，按规定的时间一电流特性而熔断。 2）Either it exposes land, which then warms up; or it forms ponds (or lakes or streams) of meltwater on the surface of the ice, which absorb energy and melt more ice. 融冰过程要么导致陆地暴露并且温度升高，要么在冰层表面形成池塘（或湖泊，或溪流），并吸收能量，融化更多的冰。 3）Her money seemed to melt away in Paris. 在巴黎她的钱似乎自行消失了。
外研社新职业英语第二版职业综合英语1 Unit3教案1 授课时间 班 周星期第节 班 周星期第节 班 周星期第节 课次12 学时数 2 授课形式 （请打√） 纯理论□纯实践□理实一体化□习题课□其他□授课题目Unit3 Business Meals: Lead–in &Reading A: Deals over Meals 教学目的Ss learn how to arrange the table seats for an English banquet Ss Understand the main idea and structure of the text 教学重点 1. The usages of new words and expressions in reading A 2. Understanding of Reading A 教学难点 1. How to use the key words and expressions in Reading A 2. Analysis on the text structure 使用的教 具/多媒体 /仪器/仪 表/设备等 Textbook; PPT;CD 教学方法Case teaching; Pair-work; Analyzing 参考资料English for Careers (Book1)
教学基本内容及设计Unit 1. Reading A: Deals over Meals I.Warm-up (10’) Task Complete the following table seating arrangement. Principles of Seating Arrangement Guest Information II. Reading A: Secretaries (80’) 1.Lead-in 2.Global reading (1) Listen to the passage while reading and think about the main idea of each paragraph. (2) Information collection a. Skimming Task1 Read the passage. Then match the business meals with their characteristics. b. Scanning Task 2 Decide which of the fo llowing behaviors are Do’s or Don’ts for business meals according to the passage. 3.Intensive reading a. Text structure analysis Para 1: Westerners do business over all kinds of meals. Para 2: Different meals have different characteristics. Para 3: Watch your behavior during business meals. Para 4: Mastery of good table manners is of great help. Para 5: Polite dinning at the table pays. b. Language Points entertain: e.g. 1. I’ll entertain my friends over the weekend. 2. The child was entertaining himself with his toys. build up: to build; to increase, or become bigger or stronger gradually
?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、高硬度以及良好的延展性。 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？纯金属是在元素周期表中占据特定位置的元素。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. 合金包含不止一种金属元素。合金的性质能通过改变其中存在的元素而改变。金属合金的例子有：不锈钢是一种铁、镍、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约燃料。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，尤其是和聚合物相比较而言。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，例如金和铅。然而，诸如铝和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.
机械工程英语第二版part2unit11翻译
机械工程英语（第11单元） Rapid Prototyping and Manufacturing Technologies快速原型制造和快速制造技术 Introduction介绍 Manufacturing community is facing two important challenging tasks：（1）Substantial reduction of production development times; and (2) Improvement on flexibility for manufacturing multi-variety and small batch-size products. Computer-aided design and manufacturing (CAD and Cam) have significantly improved the traditional production design and manufacturing. However, there are a number of obstacles in true integration of computer-design with computer-aided manufacturing for rapid development of new products. 制造社会面临两个重要的艰巨任务：1大幅度减少产品开发时间，以及改善对弹性制造多品种，小批量大小的产品。电脑辅助及制造大大改善了传统的生产设计和制造。但是，有一个数字障碍计算机辅助设计与真正的一体化电脑辅助制造新产品的快速发展。 To substantially shorten the time for developing patterns, and prototypes, some manufacturing enterprises have started to use rapid prototypes(RP)methods for complex patterns making and component prototyping. Over the past few years, A variety of new rapid