1、Unit 6TEXT LEARN TO SPEAK NEW WORDS AND EXPRESSIONS NOTES EXERCISES READING MATERIAL PROFESSIONAL WORDS AND PHRASES The Design of Jigs and FixturesHolding devices may be classified as jigs or fixtures.A jig is a work-piece locating and holding device which positions and guides or controls a cutting
2、tool.A fixture is a work-piece locating and holding device used with machine tools,inspection,welding and assembly.It does not control the position of the tool or instrument which is being used.In many instances gauge blocks may be provided for setting the depth or position of the cutting tool.TEXTF
3、ig.6-1 Drilling jig The designer approaches the design project by first becoming fully aware of all critical dimensions and surfaces.If possible,he should also know how the part fits into the main assembly.Once he is familiar with the special functional requirements and dimensions,he collects the da
4、ta which may have an effect on his design.Data such as type of material,physical properties,weight,and the characteristics of the raw material.Other information which could affect the type of fixture to be built is the production quantities,lot sizes,etc.Next the designer determines whether fixtures
5、 already in the plant can be altered and used for his job.He must also consider the possibility and advisability of using standard holding devices such as vises,parallels and clamps.Once it is decided that a series of operations are to be done with newly designed fixtures,the designer combines as ma
6、ny operations into one fixture as possible.Fig.6-2 Milling fixture LEARN TO SPEAKMr.Zhang:Good morning,Mr.Cheng.Mr.Cheng:Good morning,Mr.Zhang.Mr.Zhang:What are you doing?Mr.Cheng:I am machining a work-piece.Mr.Zhang:Whats this?Mr.Cheng:It is a fixture.Mr.Zhang:What can it do?Mr.Cheng:We can use it
7、to locate and hold the work-piece when it is machined.Mr.Zhang:Is the fixture only be used to machine?Mr.Cheng:No.In fact there are many kinds of fixture and they can also be used for inspection,welding and assembly.Mr.Zhang:What are its advantages?Mr.Cheng:We can improve the product precision and r
8、educe time assumption of locating the work-piece.Mr.Zhang:Its very kind of you to tell me about these.Mr.Cheng:Thats all right.NEW WORDS AND EXPRESSIONS jig n.钻模 fixture n.夹具 inspection n.检查 gauge n.量规 instrument n.工具,器械 designer n.设计师 approach vt.接近,确定 characteristic n.特性，特征 alter v.改变 possibility
9、n.可能性 advisability n.明智 classified as 分为locating and holding device 定位和夹紧装置gauge block 量块critical dimension 重要尺寸physical property 物理性能raw material 原材料 NOTES1Holding devices may be classified as jigs or fixtures.夹持装置可以分为钻模和夹具。be classified as 分为 像这类后面用as引出的补语的动词还有：characterizeas 表示的特征为 consideras 认为是
10、 defineas 把定义为 describeas 把描绘成 regardas 认为是 useas 把用作 2The designer approaches the design project by first becoming fully aware of all critical dimensions and surfaces.设计师首先通过全面了解零件的关键尺寸和表面来决定设计方案。become aware of 发觉，了解 “first becoming fully aware of all critical dimensions and surfaces”这一V-ing短语与“by
11、”一起构成介词短语，修饰谓语动词，表示方法、手段。3Data such as type of material,physical properties,weight,and the characteristics of the raw material.像材料的类型、物理性能、重量以及原材料的特性等。这一部分虽然以大写字母开始，以句号结束，但不是句子，而是前面句中data的同位语，作进一步的说明。4Next the designer determines whether fixtures already in the plant can be altered and used for his
12、job.接着，设计师确定厂里已有的夹具是否能改动一下，以供使用。Next(本句中用作adv.)有两种用法：(1)adj.其次的，下(一个的)。例如：The work-piece is moved to the next station.工件送到下一个工位。(2)adv.其次，然后。例如：Next the hole is reamed.然后铰孔。5He must also consider the possibility and advisability of using standard holding devices such as vises,parallels and clamps.他还
13、必须考虑是否可能或值得利用虎钳、平行垫铁和压板等标准夹持装置。这里的“parallel”是名词，意为“平行垫铁”。“clamp”也是名词，意为“压板”、“夹钳”。EXERCISES1Put the following into Chinese:(1)Jigs and fixtures (2)Mark out(3)A trial work-piece(4)Interchangeable(5)Error accumulate (6)The cutting force(7)The degree of freedom(8)The three mutually perpendicular(9)The n
14、ecessity of making precision jigs(10)Position the work-piece with respect the machine movement 2Read the text carefully and answer the following questions:(1)What is a jig?(2)What is the difference between the jigs and fixtures?(3)Why the work-piece must be marked out before machine start?(4)Can you
15、 say some advantages of jigs and fixtures?Give some examples.(5)What is the degree of freedom?3Translate the following English into Chinese:Jigs are work holders which are designed to hold,locate and support a work-piece while guiding the cutting tool throughout its cutting cycle.Fixtures and jigs a
16、re alike because they both are devices to ensure that the work-piece is correctly located and clamped.But there still are some differences between them.Unlike jigs,fixtures do not guide the cutting tool,but rather,provide a means to reference and align the cutting tool to the work-piece.For the most
17、 part,fixtures are designed to withstand much greater stressed and tool forces than jigs,and are always securely clamped to the machine.READING MATERIALIntroduction to Machine DesignMachine design is the application of science and technology to devise new or improved products for the purpose of sati
18、sfying human needs.It is a vast field of engineering technology which not only concerns itself with the original conception of the product in terms of its size,shape and construction details,but also considers the various factors involved in the manufacture,marketing and use of the product.People wh
19、o perform the various functions of machine design are typically called designers,or design engineers.Machine design is basically a creative activity.However,in addition to being innovative,a design engineer must also have a solid background in the areas of mechanical drawing,kinematics,dynamics,mate
20、rials engineering,strength of materials and manufacturing processes.As stated previously,the purpose of machine design is to produce a product,which will serve a need for man.Inventions,discoveries and scientific knowledge by themselves do not necessarily benefit people;only when they are incorporat
21、ed into a designed product will a benefit be derived.It should be recognized,therefore that a human need must be identified before a particular product is designed.Machine design should be considered to be an opportunity to use innovative talents to envision a design of a product,to analyze the syst
22、em and then make sound judgments on how the product is to be manufactured.It is important to understand the fundamentals of engineering rather than memorize mere facts and equations.There are no facts or equations which alone can be used to provide all the correct decisions required to produce a goo
23、d design.On the other hand,any calculations made must be done with the utmost care and precision.For example,if a decimal point is misplaced,an otherwise acceptable design may no function.PROFESSIONAL WORDS AND PHRASESdevise dI5vaIz vt.设计，发明kinematics kInI5mAtIks,kaI-n.运动学dynamics daI5nAmIks n.动力学in
24、corporate In5kC:pEreIt vt.合并，混合derive dI5raIv v.得自，起源 innovative 5InEJveItIv adj.创新的，革新的envision In5vIVEn vt.想象，预想analyze 5AnElaIz vt.分析，分解fundamental fQndE5ment(E)l n.pl.基本原则，基本原理equation I5kweIF(E)n n.相等，方程式，等式utmost 5QtmEJst adj.极度的，最远的decimal 5desIm(E)l adj.十进的，小数的misplace mIs5pleIs vt.放错地方 mechanical drawing 机械制图decimal point 小数点
