机械工程专业英语施平没翻译课文补充

4、工程机械概述

As we look around us we see a world full of “things”: machines, devices, tools; things that we have designed, built, and used; things made of wood, metals, ceramics, and plastics. We know from experience that some things are better than others; they last longer, cost less, are quieter, look better, or are easier to use.

;

;

情况.

Ideally, however, every such item has been designed according to some set of “functional requirements” as perceived by the designers — that is, it has been designed so as to answer the question, “Exactly what function should it perform?”In the world of engineering, the major function frequently is to support some type of loading due to weight, inertia, pressure, etc.

的

From the beams in our homes to the wings of an airplane, there must be an appropriate melding of materials, dimensions, and fastenings to produce structures that will perform their functions reliably for a reasonable cost over a reasonable

lifetime.

In practice, engineering mechanics methods are used in two quite different ways: (1) The development of any new device requires an interactive, iterative consideration of form, size, materials, loads, durability, safety, and cost. (2) When a device fails (unexpectedly) it is often necessary to carry out a study to pinpoint the cause of failure and to identify potential corrective measures. Our best designs often evolve through a successive elimination of weak points.

1.cost.

2.

To many engineers, both of the above processes can prove to be absolutely fascinating and enjoyable, not to mention (at times) lucrative.

In any “real” problem there is never sufficient good, useful information; we seldom know the actual loads and operating conditions with any precision, and the

analyses are seldom exact. While our mathematics may be precise, the overall analysis is generally only approximate, and different skilled people can obtain different solutions. In the study of engineering mechanics, most of the problems will be sufficiently “idealized” to permit unique solutions, but it should be clear that the “real world” is far less idealized, and that you usually will have to perform some idealization in order to obtain a solution.

在命令必须执行一些理想化获得一个解决方案。

The technical areas we will consider are frequently called “statics” and “strength of materials,”“statics” referring to the study of forces acting on stationary devices, and “strength of materials” referring to the effects of those forces on the structure (deformations, load limits, etc.).

备作用力学风和“材料力学”指的是这些部队在结构上的影响。

While a great many devices are not, in fact, static, the methods developed here are perfectly applicable to dynamic situations if the extra loadings associated with the dynamics are taken into account (we shall briefly mention how this is done).

static

.

Whenever the dynamic forces are small relative to the static loadings, the system is usually considered to be

In engineering mechanics, we will appreciate the various types of approximations that are inherent in any real problem:

Primarily, we will be discussing things which are in “equilibrium,” i.e., not accelerating. However, if we look closely enough, everything is accelerating. We will consider many structural members to be “weightless”— but they never are. We will deal with forces that act at a “point”— but all forces act over an area. We will consider some parts to be “rigid”— but all bodies will deform under load.

We will make many assumptions that clearly are false. But these assumptions should always render the problem easier, more tractable. You will discover that the goal is to make as many simplifying assumptions as possible without seriously degrading the result.

Generally there is no clear method to determine how completely, or how precisely, to treat a problem: If our analysis is too simple, we may not get a pertinent answer; if our analysis is too detailed, we may not be able to obtain any answer. It is usually preferable to start with a relatively simple analysis and then add more detail as required to obtain a practical solution.

无

实际的解决办法。

During the past two decades, there has been a tremendous growth in the

availability of computerized methods for solving problems that previously were

beyond solution because the time required to solve them would have been prohibitive.

At the same time the cost of computer capability and use has decreased by orders

of magnitude. We are experiencing an influx of “personal computers” on campus,

in the home, and in business.

26、车床

The general characteristics of the machine tools used in cutting operations are reviewed in

this text. The equipment can be classified in different categories depending on their function

and the accessories involved. The major categories are described below.

Lathes Lathes are generally considered to be the oldest machine tools and were developed

in the 1750s.The basic operations carried out on a lathe are turning, boring, and facing.

车床车床通常被1750s产生.

The basic components of the most common lathe( engine lathe ) are the bed, headstock,

tailstock, and carriage. One end of the workpiece is clamped in a chuck that is mounted on

the spindle, the spindle rotates in the headstock. The other end of the workpiece is supported

by the tailstock. The headstock contains the drive gears for the spindle speeds, and through

suitable gearing and the feed rod, drives the carriage and cross slide assembly. The carriage

provides motion parallel to the axis of rotation, and the cross slide provides motion normal

to it. A cutting tool, attached to a tool post and to the carriage, removes material by traveling

along the bed. The cutting operation is performed at a certain desired peripheral speed of

the workpiece, feed rate, and depth of cut

.托架。工件的一端

A further development is the automatic lathe. The movements and controls

are actuated by various mechanical means, such as cams and numerical and computer

control, thus reducing labor or requiring less skilled labor.

Turret lathes (developed in the 1850s)carry out multiple cutting operations,

such as turning, boring, drilling, thread cutting, and facing. Various cutting tools,

usually up to six are installed on a turret. The operation is quite versatile. It may be operated by hand or automatically and, once set up properly, it does not require skilled labor. There are a great variety of turret lathes available for different purposes.

19世纪50

不同的目的

Screw machines (the first screw lathe was developed in the 1770s)are designed for high

production rate machining of screws and similar parts. All the operations are performed

automatically with tools attached to a special turret. The bar stock is fed automatically after each

screw has been machined to a finished product. These machines may be equipped with single or

multiple spindles to reduce the cycle time per piece.

18世纪70

和类似部件的设计的。所有的操作都由连接到一个特殊的炮塔的工具自动执行。每个螺丝加

Milling Machines These are among the most versatile and useful machine tools because

they are capable of performing a variety of cutting operations. There is a large selection of milling

machines (developed in the 1860s)available with numerous features.

The basic types are outlined below.Knee-and-column type milling machines are the most

common and are used for general-purpose machining. The spindle, to which the milling cutter is

attached, may be horizontal (for slab milling), or vertical (for face milling).

19世纪60

Bed-type milling machines have the table mounted on a bed (replacing the knee) and can

move only in the longitudinal direction. These machines are simple and rigidly

constructed and

are used for high-quantity production. The spindles may be horizontal or vertical and can be of

duplex or triplex types (that is, with two or three spindles for simultaneous machining of two or

three surfaces on a part). Other types of milling machines are also available, such as the

planer type for heavy work and machines for special purposes

加工两

机器。

Among accessories for milling machines, one of the most widely used is the universal

dividing head. This is a fixture that rotates the workpiece to specified angles between individual

machining steps. Typical uses are in milling parts with polygonal surfaces and in machining gear

teeth.

转到指定角度。典型的用途是加工铣削有多边形表面的零件和加工齿轮齿。

Planers and Shapers These machine tools are generally used for machining large flat

surfaces although other shapes, such as grooves, can also be machined. In a planer, the

workpiece travels under the cross-rail equipped with cutting tools, whereas in a

shaper the

tool travels and the workpiece is stationary

固定的。

Because of the size of the workpieces involved, planers are among the largest machine tools.

Shapers may be horizontal or vertical and are also used for machining notches and keyways

也用于加工凹槽和键槽。

Broaching Machines These machines push or pull broaches, either horizontally or vertically,

to generate various external or internal surfaces. They are of relatively simple construction and are

actuated hydraulically and have only linear motion of the broach. Because of the great variety of

shapes and parts involved, broaching machines are manufactured in a wide range of designs and

sizes.

被制造成各式的设计和尺寸。

Drilling Machines These machines are used for drilling holes, tapping, counterboring,

reaming, and other general-purpose boring operations. They are usually vertical, the most

common one being a drill press. Drilling machines are manufactured in a wide variety of sizes,

from simple bench type units to radial drills and large production machines with multiple spindles.

臂钻床和有多个主轴的大型生产设备。

46课

Computer-aided design CAD involves the use of computers to create design drawings and product

models. Computer-aided design is usually associated with interactive computer graphics known as a

CAD system. 计算机辅助设计(CAD)涉及到电脑的使用来创建设计图纸和产品模型。计算机辅助设计通常

是与交互式计算机图形学(称为CAD系统)。 Computer-aided design systems are powerful tools and are used in the mechanical design and geometric

modeling of products and components 计算机辅助设计系统是强大的工具,用于产品的机械设计和几何建模和组件 In CAD the drawing board is replaced by electronic input and output devices. When using a CAD system the designer can conceptualize the object to be designed more easily on the Graphics screen and can

consider alternative designs or modify a particular design quickly to meet the necessary design

requirements or changes. 在CAD图纸被电子输入和输出设备。当使用CAD系统中,设计人员可以概念化设计的对象

更容易在图形屏幕上,可以考虑替代设计或修改一个特定设计迅速满足必要的设计要求或更

改。 The designer can then subject the design to a variety of engineering analyses and can identify potential

problems such as an excessive load or deflection. The speed and accuracy of such analyses far

surpass what is available from traditional methods. 设计师可以设计各种各样的工程分析和可以识别潜在的问题(如过度负荷或偏转)。这种分析

的速度和准确度远远超过可以从传统的方法是什么。Draft productivity rises dramatically. When something is drawn once it never has to be drawn again. 草案生产率大幅上升。当有了一次,它从来没有再画。it can be retrieved from a library ,and can be duplicated, stretched, sized, and changed in many ways

without having to be redrawn。Cut and paste techniques are used as labor-saving aids. 它可以从库检索,可以复制,拉伸,大小,改变在许多方面不用redrawn.Cut粘贴技术用作省力

艾滋病。 CAD makes possible multiview 2D drawings and the drawings can be reproduced in different levels of

reduction and enlargement. CAD使可能的多视图2 d图纸,图纸可以复制在不同程度的减少和扩大。 It gives the mechanical engineer the ability to magnify even the smallest of components to ascertain if assembled components fit properly. 它让机械工程师的能力放大甚至最小的组件来确定如果组装组件配合得当。 Parts with different characteristics such as movable or stationary can be assigned different colors on the display. 部分具有不同特点,如移动或静止不动的,可以指定不同的颜色显示。Designers have even more freedom with the advent of 3-D parts and manipulate them in endless variations to achieve the desired results. 设计师有更多自由随着 3 d 部分和操纵他们无穷无尽的变化来获得期望的结果。 Through finite element analysis stresses can be applied to be a computer model and the results

graphically displayed giving the designer quick feedback on any inherent problems in a design before

the creation of a physical prototype. 通过有限元分析,压力可以被应用到一个计算机模型,结果以图形方式显示出来,给设计师提

供快速反馈任何固有的问题在设计物理原型的创建。 In addition to the design’s geometric and dimensional features other information such as a list of

materials specification and manufacturing instructions is stored in the CAD

database. Using such

information ,the designer can then analyze the economics of alternative designs. 除了设计的几何和空间特性,其他信息(如材料的清单,规范,和生产指令)存储在CAD数据库。

使用这些信息,设计师可以分析替代的经济设计。 Computer-aided manufacturing(CAM) involves the uses of computers and computer technology to assist

in all the phases of manufacturing a product including process and production

planning machining

scheduling management and quality control. Computer-aided design and computer-aided

manufacturing are often combined into CAD/CAM systems. 计算机辅助制造(CAM)涉及计算机和计算机技术的使用,协助生产一个产品的所有阶段,包括

过程和生产计划、加工、调度、管理和质量控制。计算机辅助设计和计算机辅助制造通常结

合到CAD / CAM系统。 This combination allow the transfer of information from the design stage into the stage of of planning for

the manufacture of a product without the need to reenter the data on part geometry manually. 这种组合允许转让信息从设计阶段的阶段,规划产品的生产,而不需要手动重新输入数据部

分几何。 The database developed during CAD is stored then it is processed further by CAM into the necessary

data and instructions for operating and controlling production machinery

material-handling equipment

and automated testing and inspection for product quality. 在CAD开发的数据库存储;然后进一步处理,通过凸轮,到所需的数据和指令操作和控制生产

机械、设备来源,自动化测试和检验产品质量。 In machining operations an important feature of CAD/CAM is its capability to describe the tool path for

various operations such as NC turning milling and drilling. 在加工操作中,CAD / CAM的一个重要特性是其能力来描述刀具轨迹的各种操作,如数控车

削、铣削和钻孔。 The instructions programs are computer generated and they can be modified by the programmer to

optimize the tool path . 计算机生成的指令(程序),他们可以由程序员修改优化刀具轨迹。The engineer or technician can then display and visually check the tool path for possible tool collisions with fixtures or other interferences. The tool path can be modified at any time to accommodate other part

shapes to be machined. 工程师或技术员可以显示和视觉检查刀具轨迹的可能的工具与设备碰撞或其他干扰。工具路

径随时可以修改,以适应其他部分形状加工。 Some typical applications of CAD/CAM are

a programming for NC CNC and industrial robots

b design of tools and fixtures and EDM electodes

c quality control an

d inspection for instanc

e coordinate-measuring machines programmed on a CAD/CAM workstation d process planning and

scheduling and e plant layout. 一些典型的CAD / CAM的应用是:(a)为数控编程,数控,和工业机器人;(b)设计的工具和夹具

和EDM electodes;(c)质量控制和检查,例如,坐标测量机CAD / CAM工作站程序;(d)工艺规

划和调度;(e)工厂的布局。 The emergence of CAD/CAM has had a major impact on manufacturing by standardizing product

development and by reducing design effort tryout and prototype work it has made possible significantly

reduced costs and improved productivity. CAD / CAM的出现已经对生产产生重大影响,通过标准化产品开发和减少设计工作,调试,和

原型工作;它可能显著降低成本和提高生产力。 The two-engine Boeing 777 passenger airplane for example, was designed completed by computer

paperless design . The plane is constructed directly from the CAD/CAM software developed an

enhanced CATIA system and no prototypes or mockups were built such as were required for previous

models. 双引擎的波音777客机,例如,设计完成的计算机(无纸化设计)。飞机构造直接从开发的CAD

/ CAM软件(一个增强的CATIA系统)和任何原型和模型建立,如需要以前的模型。

50课Today, computer numerical control machine tools are widely used in

manufacturing enterprises.

Computer numerical control is the automated control of machine tools by a computer and computer

program. 今天,计算机数控机床广泛应用于制造企业。计算机数控机床的自动控制是计算机和计算机

程序。 The CNC machines still perform essentially the same functions as manually operated machine tools but

movements of the machine tool are controlled electronically rather than by hand. CNC machine tools can

produce the same parts over and over again with very little variation. They can run day and night week

after week without getting tired. These are obvious advantages over manually

operated machine tools

which need a great deal of human interaction in order to do anything. 数控机器仍执行相同的函数作为手动机床,但机床控制电子的运动,而不是用手。数控机床可

以产生相同的部分,一次又一次变化很少。他们可以日夜不停地运转,一周又一周,没有累了。

这些明显的优势在手动机床,需要大量的人工交互为了做任何事。 A CNC machine tool differs from a manually operated machine tool only in respect to the specialized

components that make up the CNC system. The CNC system can be further divided into three

subsystems control drive and feedback. All of these subsystems must work together to form a complete

CNC system. 数控机床不同于一个手动机床只有在尊重专业的组件构成的数控系统。数控系统可以进一步

分为三个子系统:控制、驱动,和反馈。所有这些子系统必须共同努力,形成一个完整的数控系

统。 1. control system 1。控制系统 The centerpiece of the CNC system is the control. Technically the control is called the machine control

unit MCU but the most common names used in recent years are controller

control unit or just plain

control. This is the computer that stores and reads the program and tells the other components what to

do. 数控系统控制的核心。技术控制称为机控制单元(MCU),但近年来最常用的名字是控制器,控

制单元,或者就是简单的控制。这是计算机存储和读取程序,告诉其他组件该做什么。 2. Drive system. 2。驱动系统。 The drive system is comprised of screws and motors that will finally turn the part program into motion.

The first component of typical drive system is a high-precision lead screw called a ball screw Fig.50.1.

Eliminating backlash in a ball screw is very important for two reasons. First

high-precision positioning

can not be achieved if the table is free to move slightly when it is supposed to

be stationary. Second

materials can be climb-cut safely if the backlash has been eliminated. Climb cutting is usually the most

desirable method for machining on a CNC machine. 螺丝和汽车的传动系统是由部分程序,最终将变成运动。第一个组件的典型的驱动系统是一

种高精度丝杠称为滚珠丝杆(Fig.50.1)。消除反应在滚珠螺杆是非常重要的两个原因。首先,

不能实现高精度定位如果表是免费的移动略当它应该是固定的。第二,材料可以安全地同向

如果反弹已经消除。爬上切割通常是最可取的方法在数控加工机器。 Drive motors are the second specialized component in the drive system. The turning of the motor will turn

the ball screw to directly cause the machining table to move. Several types of electric motors are used on

CNC control systems and hydraulic motors are also occasionally used. 驱动电机驱动系统中的第二专业组件。电动机的转动将滚珠螺杆直接导致加工表。几种类型

的电机是用在数控控制系统和液压马达也偶尔使用。 The simplest type of electric motor used in CNC positioning systems is the stepper motor sometimes

called a stepping motor. A stepper motors rotates a fixed number of degrees when

it receives an

electrical pulse and then stops until another pulse is received. The stepping characteristic makes stepper

motors easy to control. 最简单的类型的电动机用于数控定位系统是步进电机(有时称为步进电机)。步进电机旋转固

定数量的度当它收到一个电脉冲,然后停止,直到接收到一个脉冲。步进特性使步进电机容易

控制。 It is more common to use servomotors in CNC systems today. Servomotors operated in a smooth

continuous motion—not like the discrete movements of the stepper motors. This smooth motion leads to

highly desirable machining characteristics but they are also difficult to control. Specialized hardware

controls and feedback systems are needed to control and drive these motors.

Alternating current AC

servomotors are currently the standard choice for industrial CNC machine tools. 这是今天使用伺服电机在数控系统中更为普遍。伺服电机运行在一个光滑、连续的活动,如

离散运动的步进电机。这光滑的运动导致高度理想的加工特点,但他们也难以控制。需要专

门的硬件控制和反馈系统控制和驱动这些汽车。交流电伺服电机目前工业数控机床的标准选

择。 3. Feedback System 3。反馈系统 The function of a feedback system is to provide the control with information about the status of the motion

control system which is described in Figure 50.2. 反馈系统的功能是为控制提供运动控制系统的状态信息,如图50.2所示。 The control can compare the desired condition to the actual condition and make corrections. The most obvious information to be fed back to the control on a CNC machine 控制可以比较所需的条件的实际条件和改正。最明显的信息反馈给控制数控机器上 tool is the position of the table and the velocity of the motors. Other information may also be fed back that is not directly related to motion control such as the temperature of the motor and the load on the

spindle—this information protects the machine from damage. 工具的位置表和汽车的速度。其他信息也可以反馈,不是直接关系到运动控制,如电动机的温

度和负载spindle-this信息保护机器免受损坏。 There are two main types of control

systems open-loop and closed-loop. An open-loop system does not

have any device to determine if the instructions were carried out. For example

in an open-loop system

the control could give instructions to turn the motor 10 revolutions. However

no information can come

back to the control to tell it if it actually turned。All the control knows is that it delivered the instructions.

Open-loop control is not used for critical systems but it is a good choice for inexpensive motion control

systems in which accuracy and reliability are not critical. 主要有两种类型的控制系统:开环和闭环。一个开环系统没有任何设备来确定指令进行。例

如,在一个开环系统,控制可以给指令将电动机10革命。然而,任何信息可以回到控制告诉它,

如果它实际上turned.All控制知道是它的指示交付。开环控制不用于关键系统,但这是一个不

错的选择廉价的运动控制系统的精度和可靠性并不是最关键的。 Closed-loop feedback uses external sensors to verify that certain conditions have been met. Of course

position and velocity feedback is of primary importance to an accurate CNC system. Feedback is the only

way to ensure that the machine is behaving the way the control intended it to behave. 闭环反馈使用外部传感器验证某些条件已经满足。当然,位置和速度反馈是最重要的一个精

确的数控系统。反馈是唯一的办法,以确保机器的行为控制计划的行为方式。

《机械工程专业英语教程》课文翻译

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