1.4　Reading Passages　阅读短文

（1）Metal Cutting Process

Machining is the process of removing unwanted material from a workpiece in the form of chips.If the workpiece is a metal， the process is often called metal cutting or metal removal.The vast majority of manufactured products need machining at some stage.Their production range from relatively rough or nonprecision work， such as cleanup of castings or forgings， to high-precision work involving tolerances of 0.0001 in or less and high-quality products.Thus machining undoubtedly is the most important basic method of mechanical processing.

Over the past 80 years， the process has been the object of considerable research and experimentation that have led to improve understanding of the nature of both the process itself and the surfaces produced by it.Although this research effort has led to improvements in machining productivity， the complexity of the process has resulted in slow progress in obtaining a complete theory of chip formation.

What makes this process so unique and difficult to analyze？

①Different materials behave differently.

②The process is asymmetrical and unconstrained， bounded only by the cutting tool.

③The level of strain is very large.The strain rate is very high.

④The process is sensitive to variations in tool geometry， tool material， temperature， environment（cutting fluids）and process dynamics（chatter and vibration）.

There are seven basic chip formation processes：shaping，turning，milling，drilling，sawing，broaching，and grinding（abrasive machining）.For all metal cutting processes， it is necessary to distinguish between speed， feed， and depth of cut.

To process different metals， the input parameters to the machine tools must be determined.For the lathe， the input parameters are DOC， the feed and the rpm value of the spindle.

金属切削加工（参考译文）

机械加工是从工件上以切屑形式去掉不需要的材料的工艺方法。如果工件是金属件，这种方法常被称为金属切削或金属切除。大多数金属制造产品在生产的某些阶段需要机械切削加工。生产加工范围从相对粗糙或没有精度要求的铸件或锻件去黑皮加工到包括公差精度在0.0001in（0.02mm）甚至更小的高精度和高表面质量的产品。可以肯定地说，金属切削加工是最重要的机械加工基本方法。

在过去的80年里，人们通过对金属切削工艺的重点研究和实验，增进了对加工工艺性和被加工表面特性的了解。尽管这种努力已经使机械加工效率得到提高，但由于机械加工工艺的复杂性致使在获取金属切屑成形的完整理论方面进展缓慢。

是什么原因使得金属切削工艺研究如此不寻常和困难呢？这是因为：

①不同的材料表现出不同的特性；

②加工过程不均衡，除刀具限制外不受其他约束；

③应变程度非常大，应变发生率很高；

④加工过程对刀具几何形状、材料、温度、环境（切削润滑）和加工动力学特性（颤动和振动）等均非常敏感。

有7种基本的金属切屑成形方法：刨削、车削、铣削、钻削、锯、拉削和磨削（研磨加工）。对于所有金属切削加工都必须正确区分切削速度、进给量和背吃刀量之间的关系。

加工不同的金属，必须确定输入机床的参数。对于车床，输入参数是背吃刀量（DOC）、进给量和主轴每分钟转数。

（2）Milling

Milling is a basic machining process by which a surface is generated by progressive cutting removal.The workpiece is fed into a rotating cutting tool.Sometimes the workpiece remains stationary， and the cutter is fed to the work.In nearly all cases， a multiple-tooth cutter is used so that the material removal rate is high.Often the desired surface is obtained in a single pass of the cutter or workpiece， and because very good surface can be obtained， milling is particularly well suited and widely used for mass-production work.Many types of milling machines are used， ranging from relatively simple and versatile machines that are used for general-purpose machining in job shops to highly specialized machines in tool-and-die work shop.

The cutting tool used in milling is known as a milling cutter.Equally spaced peripheral teeth will intermittently engage and machine the workpiece.This is called interrupted cutting.

Milling operations can be classified into two broad categories called peripheral milling and face milling.Each has many variations.In peripheral milling the surface is generated by teeth located on the periphery of the cutter body.The surface is parallel with the axis of rotation of the cutter.Both flat and formed surfaces can be produced by this method， the cross section on the resulting surface corresponding to the axial contour of the cutter.This process， often called slab milling， is usually performed on horizontal-spindle milling machines.

In face milling and end milling，the surface is generated at right angles to the cutter axis.Most of the cutting is done by the peripheral portions of the teeth， with the face portions providing some finishing action.Face milling is done on both horizontal and vertical-spindie machines.

For either slab or face milling， surfaces can be generated by two distinctly different methods.Up milling is the traditional way to mill.The cutter rotates against the direction of feed rate of the workpiece.In climb or down milling， the cutter rotation is in the same direction as the feed rate.The method of chip formation is completely different in the two cases.

铣削（参考译文）

铣削是以切屑方式去除金属材料以获得加工面的一种最基本加工方法。铣削加工时工件向旋转的刀具送进，有时工件保持静止，而刀具进给。几乎在所有的情况下，铣削使用多切削刃刀具，具有较高的材料切削率。通常刀具或工件一次行程就能获得所希望的表面，而且表面质量较好，因此铣削特别适合并广泛用于大批量生产中。生产中应用多种铣床，其范围包括生产车间用于常规加工的简易铣床和万能铣床，也包括在工模具车间使用的高度专业化的各种铣床。

铣削加工的刀具叫做铣刀。在刀具周边相等分隔的刃口断续切入并加工工件，这叫做不连续切削。

铣削加工可分为两类：轮廓铣削和面铣削，每一类还有多种变化。在轮廓铣削时，切削成形表面安置在铣刀体的周边位置上，平行于铣刀旋转轴。待加工面平行于刀具旋转轴，平面和成形表面两者都能用此方法铣削。铣削的横截面形状与铣刀轴向轮廓线相对应。这种加工常称为平面铣，常在卧式铣床上完成。

在平面铣削和端面铣削中，加工面与铣刀轴垂直，大部分切削由铣刀齿的周边部分完成，铣刀端面可完成精加工。平面铣削既可以在卧式铣床上完成，也可以在立式铣床上进行。

无论铣削厚板或者平面，都有两种切削性质不同的方法。传统的铣削方法叫做逆铣，铣刀逆着工件进给方向旋转。顺铣则是铣刀旋转方向与进给方向相同。这两种切削方法产生切屑的形式完全不同。

（3）Electro-discharge Machining

When applying the electro-discharge machining（EDM）process，the material is eroded as a result of an electrical discharge between tool and workpiece.Due to discharge time is short， but the voltage is very high and temperature rises， metal particles at the point of discharge are molten， partially vapourized and removed from the melt by mechanical and electromagnetic forces.The working medium is a dielectric，which washes the eroded material away and simultaneously acts as a coolant.

As in the case of ECM（electrochemical machining）.EDM is a copying process where there is no contact between tool and workpiece.Contrary to ECM， however， there is some erosion of the tool in EDM，which must be allowed for in the tool design to ensure accuracy of machining.

A further difference arises from the fact that in EDM there is no fixed tool feed，but the gap size must be maintained in accordance with the rate of metal removal and the conditions existing within the gap.

Electro-discharge die-sinking machine.The construction principle of an EDM die-sinking machine are shown in Fig.1-59.Spark erosion takes place in a container filled with the dielectric in which the workpiece is clamped.The controlled feed of the electrode is through an electrohydraulic or electromechanical servo system.The electrical energy for erosion is provided by the erosion generator.The filtering unit separates the eroded material from the dielectric.In the upper left of Fig.5-59， a single discharge is illustrated in enlarged form.The applied voltage ionizes the gap at the beginning of the discharge.At the point of highest field strength， a channel is formed， through which the discharge current flows.At each end of the channel， the material melts and the channel and its surrounding gas bubble expand.When the voltage is fully discharged， the channel collapses and the molten material vaporizes， simulating a miniature explosion.The resultant of the discharge is a hallmark of the irregular crater and scars on the spark-eroded work surface.

Electro-discharge cutting machine.An important application of the spark-erosion process is the cutting of metal by wire electrodes.The process is used for the production of apertures in cutting tools and the manufacture of tool electrodes for EDM.Fig.1-60 illustrates the principle.The cutting tool is a thin copper or brass wire，which enters the workpiece during cutting without physical contact.This suffers wear as a result of the action of spark erosion， and for this reason wire position is constantly supplied.The apparatus required for wire feeding can be seen in Fig.1-61.The degree of wire tension，the rate of wire consumption and the reach of the wire support arms are adjusted in accordance with the work to be done and the size of the workpiece.The working medium for electrodischarge cutting is usually ionized water，which is fed to the work area with the use of flushing jets.

According to the required contour of the workpiece， the table with the work piece clamped to it and the slide with the wire feed unit must be suitably positioned.The relative advance of the wire electrodes to the workpiece does not have a constant velocity， but must be varied in accordance with the conditions existing in the gap throughout the process， depending on the progress of the cutting， as was the case in electrodischarge machining.

电火花加工（参考译文）

当用电火花加工（EDM）时，去除的材料是电极与工件间放电产生的腐蚀物。由于放电时间短，但电压高，温度上升，放电点的金属微粒熔化，部分汽化，利用机械和电磁力将熔化的金属去掉。工作介质是非导电液体，它能清洗掉电腐蚀材料，同时也作为冷却剂。

如同ECM（电解加工），EDM是一种拷贝加工，且工具与工件之间没有物理接触。然而与ECM相反，在EDM中会对工具有一些腐蚀，因此在工具设计中要充分考虑这种腐蚀以保证加工精度。

电火花加工与电解加工之间进一步的区别表现在电火花工具的加工进给量不固定，加工间隙大小是依据去除金属的速率与该间隙的加工状态来确定的。

电火花刻模机。电火花刻模机的结构原理如图1-59所示。电火花腐蚀发生在装夹有工件的充满绝缘介质的容器内。电极的进给控制是通过电液装置或机电伺服系统完成的，电腐蚀电能由电腐蚀发电机提供，过滤器从工作介质中分离出电腐蚀材料。在图1-59的左上部分，以放大图解形式说明一个单独的电火花放电，应用电压在放电的初期使间隙电离。在放电强度区域内最高点，形成放电通道，放电电流通过通道流动。每个放电通道的端部金属熔化，在它的周围气泡膨胀。当放电电压完全卸荷时，通道崩塌，熔化的金属材料汽化，仿佛发生微小爆炸。放电的结果是在电腐蚀工作表面形成了不规则的凹坑和伤疤。

电火花线切割机床。电火花腐蚀加工的另一个重要应用是用线电极切割金属。这种工艺用于制造有孔隙的切割刀具和为EDM制造工具电极。图1-60为加工原理图。切割工具是细的黄铜或青铜丝，在切割加工时它伸入工件但却没有与工件接触。因为线电极要受电火花腐蚀，因此要持续不断地变换电极丝位置。从图1-61可以看到电极丝进给装置。依据加工工件的要求和工件尺寸来调节金属丝的张紧程度、损耗率和电极丝支撑臂达到的位置。电火花线切割加工常用的工作介质为电离水，用冷却喷头喷向工作区域。

根据工件轮廓的加工要求，装夹工件的工作台和控制线电极进给的滑块的位置必须准确定位。线电极对工件的进给没有恒定的速度，但在整个加工过程中必须遵照放电间隙存在条件而变化，而这些条件取决于线切割工艺及电火花机床。

（4）The Computer in Design

The term CAD is alternately used to mean computer aided design and computer aided drafting.Actually it can mean either one or both of these concepts，and the tool designer will have occasion to use it in both forms.

CAD computer aided design means using the computer and peripheral devices to simplify and enhance the design process.CAD computer aided drafting means using the computer and peripheral devices to produce the documentation and graphics for the design process.This documentation usually includes such things as preliminary drawings，working drawings，parts lists，and design calculations.

A CAD system， whether taken to mean computer aided design system or computer aided drafting system， consists of three basic components：hardware，software， and users.The hardware components of a typical CAD system include a processor， a system display， a keyboard， a digitizer， and a plotter.The software component of a CAD system consists of the programs which allow it to perform design and drafting functions.The user is the tool designer who uses the hardware and software to simplify and enhance the design process.

CAD had its beginnings almost thirty years ago during the middle 1950’s.The 1970’s saw continued advances in CAD hardware and software technology.More progress began in the 1980’s， making and marketing CAD systems had become a growth industry.Also，CAD has been transformed from its status of impractical novelty to its new status as one of the most important inventions to date.

计算机在设计中的应用（参考译文）

术语CAD既可指计算机辅助设计又可指计算机辅助绘图。实际上这两种含义的CAD，工具设计师都会用得到。

CAD计算机辅助设计意味着用计算机及其外围设备简化设计过程和提高设计工艺性，而CAD计算机辅助绘图则指用计算机和外围设备制作设计过程文件和图样。设计文件通常包括初步设计图样、工作图样、零件列表和设计计算。

一个CAD系统无论是指计算机辅助设计系统还是计算机辅助绘图系统都由三个基本部分组成：硬件；软件；用户。一台典型的CAD系统硬件组成包括处理器、显示器、键盘、数字化处理器和绘图机。CAD软件由能够完成设计和绘图功能的程序组成。用户是工具设计师，他用硬件和软件简化设计过程，提高设计工艺。

最早出现CAD是20世纪50年代中期。20世纪70年代，CAD硬件和软件技术继续进步，更多进步则开始于80年代，CAD的生产和市场化使其成为发展飞快的行业，而且今天CAD已经从不切实际的新玩意转变成为最重要发明中的新成员。

（5）CAD/CAM

Computer aided design/computer aided manufacturing（CAD/CAM）refers to the integration of computers into the design and production process to improve productivity.The heart of the CAD/CAM system is the design terminal and related hardware， such as computer， printer， plotter，paper tape punch， a tape reader， and digitizer.The design is constantly monitored on the terminal until it is completed.A hard copy can be generated if necessary.A computer tape or other control medium containing the design data guides computer-controlled machine tools during the manufacturing， testing， and quality control.

The software for CAD/CAM is a collection of computer programs stored in the system to make the various hardware components perform specific tasks.Some of these software packages are referred to as software modules and can be classified into four categories：operating systems，general purpose programs，application programs， and user programs.Although there are other kinds of software，these are sufficient for an explanation of the complexities in developing a CAD/CAM system.

Operating systems are programs written for a specific computer or class of computers.For convenient and efficient operation， programs and data are available in the system’s memory.The operating system is especially concerned with the input/output（I/O）devices like displays， printers，and tape punches.In most cases the operating system is supplied with the computer.

Although it may be argued that there are no general purpose programs as such，some can be more general than others.

Application programs are developed for a special or specific purpose.Examples of application programs，relative to CAD/CAM，are programs developed specifically for the generation of finite element mesh and flat pattern development or“unbending”of sheet metal parts.These programs are usually purchased with the system or from a software supplier.

User programs in CAD/CAM are highly specialized packages for creating specific outputs.For example，a user program may automatically design a gear after the user inputs certain parameters like the number of teeth， pitch diameter， and so on.Another program may calculate optimum feeds and speeds accroding to the given cutter information， material， depth of cut， and so on.These programs are often developed by the user from a software module furnished by the supplier or general purpose software.Not all CAD/CAM software packages have these user programs， even though considerable savings can be achieved with them.

CAD/CAM（参考译文）

计算机辅助设计/计算机辅助制造（CAD/CAM）指的是计算机系统整体进入产品设计和制造过程，提高生产效率。CAD/CAM系统的核心是设计终端和与之相关的硬件，如计算机、打印机、绘图机、纸带穿孔机、纸带阅读器及读数机等。设计过程可一直在终端监控到，直至完成。如需要可以进行硬拷贝。在产品进行加工、实验和质量控制时，计算机磁带或其他含有设计数据的媒介物引导计算机控制加工机器。

CAD/CAM软件是一批储存在系统中的计算机程序，它们控制系统的各种硬件完成特定任务。一些软件包被称为软件模型，可以分为四类：操作系统；通用程序；应用程序；用户程序。尽管还有其他种类的软件，但这四种分类足以解释在开发CAD/CAM软件系统中错综复杂的情况。

操作系统是为特殊计算机或分级别计算机编写的程序。为方便和有效地操作计算机，程序和数据存储在计算机内存中。操作系统特别与输入/输出（I/O）设备有关，如显示器、打印机和纸带穿孔机。大多数情况操作系统随计算机一起供给。

尽管有人认为没有全能的通用软件，但是有些软件能做到比其他一些软件更通用。

应用程序是为专门目的或特殊用途而开发的。与CAD/CAM相关的应用程序例子是为一些专门用途开发的程序，如创建有限元网格和平面模型开发或“无挠曲”的金属板零件。这些软件通常与系统一起购买或由软件供应商提供。

为了特殊的输出要求，CAD/CAM中的用户程序要求高度专业化的打包。例如，当用户输入如齿数、节圆直径等参数后，用户程序可以自动地设计齿轮。另一个程序可以根据给出的刀具参数、材料、背吃刀量等数据计算出最佳进给和切削速度。这类程序通常由用户利用软件供应商提供的软件模型或利用通用软件开发出来。不是所有的CAD/CAM软件包都有这样的用户程序，尽管应用它们可以达到相当节省的目的。