机械设计专业的毕业设计英文版)(.pdf

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1、Mechanical EngineeringMechanical EngineeringIntroduction to Mechanical EngineeringIntroduction to Mechanical EngineeringMechanical engineering is the branch of engineering thatdeals with machines and theproduction of power.It is particularly concerned with forces and motion.History of Mechanical Eng

2、ineeringHistory of Mechanical EngineeringThe invention of the steam engine in the latter part of the 18thcentury,providing a keysource of power for the Industrial Revolution,gave an enormous impetus to the development ofmachinery of all types.As a result a new major classification of engineering,sep

3、arate from civilengineering and dealing with tools and machines,developed,receivingformal recognition in1847 in the founding of the Institution of Mechanical Engineers in Birmingham,England.Mechanical engineering has evolved from the practice by the mechanic of an art basedlargely on trial and error

4、 to the application by the professional engineer of the scientificmethod in research,design,and production.The demand for increased efficiency,in the widest sense,is continually raising the qualityof work expected from a mechanical engineer and requiring of him a higher degree of educationand traini

5、ng.Not only must machines run more economically but capital Costs also must beminimized.Fields of Mechanical EngineeringFields of Mechanical EngineeringDevelopment of machines for the production of goods the high material standard of livingin the developed countries owes much to the machinery made p

6、ossible by mechanicalengineering.The mechanical engineer continually invents machines to produce goods anddevelops machine tools of increasing accuracy and complexity to build the machines.The principal lines of development of machinery have been an increase in the speed ofoperation to obtain high r

7、ates of production,improvement in accuracy to obtain quality andeconomy in the product,andminimization of operating costs.These three requirements haveled to the evolution of complex control systems.The most successful production machinery is that in which the mechanical design of themachine is clos

8、ely integrated with the control system,whether the latter is mechanical orelectrical in nature.A modern transfer line(conveyor)for the manufacture of automobileengines is a good example of the mechanization of a complex series of manufacturing processes.Developments are in hand to automate productio

9、n machinery further,using computers to storeand process the vast amount of data required for manufacturing a variety of components with asmall number of versatile machine tools.One aim is a completely automated machine shop forbatch production,operating on a three shift basis but attended by a staff

10、 for only one shift perday.Development of machines for the production of powerProduction machinerypresuppose an ample supply of power.The steam engine provided the first practical means ofgenerating power from heat to augment the old sources of power from muscle,wind,and waterOne of the first challe

11、nges to the new profession of mechanical engineering was to increasethermal efficiencies and power。this was done principally by the development of the steamturbine and associated large steamboilers.The 20th century has witnessed a continued rapidgrowth in the power output of turbines for driving ele

12、ctric generators,together witha steadyincrease in thermal efficiency and reduction in capital cost per kilowatt of large power stations.Finally,mechanical engineers acquired the resource of nuclear energy,whose application hasdemanded an exceptional standard of reliability and safety involving the s

13、olution of entirelynew problems-The control systems of large power plank and complete nuclear power stationshave become highly sophisticated networks of electronic,fluidic.Electric,hydraulic,andmechanical components,ail of these involving me province of the mechanical engineer.Themechanicalengineeri

14、salsoresponsibleforthemuchsmallerinternalcombustionengines,both reciprocating(gasoline and diesel)and rotary(gas-turbine and Wankel)engines,with their widespread transport applications-In the transportation field generally,in airand space as well as on land and sea.the mechanical engineer has create

15、d the equipment andthe power plant,collaborating increasingly with the electrical engineer,especially in thedevelopment of suitable control systems.Development of military weaponsThe skills applied to war by the mechanical engineerare similar to those required in civilian applications,though the pur

16、pose is to enhancedestructive power rather than to raise creative efficiency.The demands of war have channeledhuge resources into technical fields,however,and led to developments that have profoundbenefits in peace.Jet aircraft and nuclear reactors are notable examples.BiaengineeringBioengineering i

17、s a relatively new and distinct field of mechanicalengineering that includes the provision of machines to replace or augment the functions of thehuman body and of equipment for use in medical treatment.Artificial limbs have beendeveloped incorporating such lifelike functions as powered motion and to

18、uch feedback.Development is rapid in the direction of artificial spare-part surgery.Sophisticated heart-lungmachines and similar equipment permit operations of increasing complexity and permit the vitalfunctions in seriously injured or diseased patients to be maintained.Environmental controlSome of

19、the earliest efforts of mechanical engineers were aimedat controlling mans environment by pumping water to drain or irrigate land and by ventilatingmines.The ubiquitous refrigerating and air-conditioning plants of the modem age are based ona reversed heat engine,where the supply of power pumps heatf

20、rom the cold region to thewarmer exterior.Manyoftheproductsofmechanicalengineering,togetherwithtechnologicaldevelopments in other fields,have side effects on the environment and give rise to noise,thepollution of water and air,and the dereliction of land and scenery.The rate of production,bothof goo

21、ds and power,is rising so rapidly that regeneration by natural forces can no longer keeppace.A rapidly growing field for mechanical engineers and others is environmental control,comprising the development of machines and processes that will produce fewer pollutants andof new equipment and techniques

22、 that can reduce or remove the pollution already generated.Functions of Mechanical EngineeringFunctions of Mechanical EngineeringFour functions of the mechanical engineering,common to all the fields mentioned,arecited.The first is the understanding of and dealing with the bases of mechanical science

23、.Theseinclude dynamics,concerning the relation between forces and motion,such as in vibration。automatic control。thermodynamics,dealing with the relations among the various forms ofheat,energy,and power。fluid flow。heat transfer。lubrication。and properties of materials.Second is the sequence of researc

24、h,design,and development.This function attempts tobring about the changes necessary to meet present and future needs.Such work requires notonly a dear understanding of mechanical science and an ability to analyze a complex system intoits basic factors,but also the originality to synthesize and inven

25、t.Third is production of products and power,which embraces planning,operation,andmaintenance.The goal is to produce the maximum value with the minimum investment andcost while maintaining or enhancing longer term viability and reputation of the enterprise or theinstitution.Fourth is the coordinating

26、 functioning of the mechanical engineering,includingmanagement,consulting,and,in some cases,marketing.In all of these functions there is a long continuing trend toward the use of scientific insteadof traditional or intuitive methods,an aspect of the ever-growing professionalism of mechanicalengineer

27、ing.Operations research,value engineering,and PABLA(problem analysis by logicalapproach)are typical titles of such new rationalized approaches.Creativity,however,cannot berationalized.The ability to take the important and unexpected step that opens up new solutionsremains in mechanical engineering,a

28、s elsewhere,largely a personal and spontaneouscharacteristic.The Future of Mechanical EngineeringThe Future of Mechanical EngineeringThe number of mechanical engineers continues to grow as rapidly as ever,while theduration and quality of their training increases.There is a growing:awareness,however,

29、among engineers and in the community at large that the exponential increase in populationand living standards is raising formidable problems inpollutionof the environment andthe exhaustion of natural resources。this clearly heightens the need for all of the technicalprofessions to consider the long-t

30、erm social effects of discoveries and developments.-Therewill be an increasing demand for mechanical engineering skills to provide for mans needswhile reducing to a minimum the consumption of scarce raw materials and maintaining asatisfactory environment.Introduction to DesignIntroduction to DesignT

31、he Meaning of DesignThe Meaning of DesignTo design is to formulate a plan for the satisfaction of a human need.The particular needto be satisfied may be quite well defined from the beginning.Here are two examples in whichneeds are well defined:1.How can we obtain large quantities of power cleanly,sa

32、fely,and economical/withoutusing fossil fuels and without damaging the surface of the earth?2.This gear shaft is giving trouble。there have been eight failures in the last six weeks.Do something about it.On the other hand,the statement of a particular need to be satisfied may be so nebulousand ill de

33、fined that a considerable amount of thought and effort is necessary in(order to stateit dearly as a problem requiring a solution.Here are two examples.-1.Lots of people are killed in airplane accidents.2.In big cities there are too many automobiles on the streets and highways.This second type of des

34、ign situation is characterized by the fact that neither the need northe problem to be solved has been identified.Note,too,that the situation may contain not oneproblem but many.We can classify design,too.For instance,we speak of:1.Clothing design7.Bridge design2.Interior design8.Computer-aided desig

35、n3.Highway design9.Heating system design.4.Landscape design10.Machine design5.Building design11.Engineering design6.Ship design12.Process designIn fact,there are an endless number,since we can classify design according to theparticular article or product or according to the professional field,In con

36、trast to scientific or mathematical problems,design problems have no uniqueanswers。it is absurd,for example,to request the correct answer to a design problem,because there is none.In fact,a good answer today may well turn out to be a poor answertomorrow,if there is a growth of knowledge during the p

37、eriod or if there are other structural orsocietal changes.Almost everyone is Involved with design in one way or another,even in dally living,because problems are posed and situations arise which must be solved.A design problem is nota hypothetical problem at all.Design has an authentic purpose the c

38、reation of an end result bytaking definite action,or the creation of something having physical reality.In engineering,theword design conveys different meanings to different persons.Some think of a designer as onewho employs the drawing board to draft the details of a gear,clutch,or other machine mem

39、ber.Others think of design as the creation of a complex system,such as a communications network.Insome areas of engineering the word design has been replaced by other terms such as systemsengineering or applied decision theory.But no matter what words are used to describe the designfunction,in engin

40、eering it is still the process in which scientific principles and the tools ofengineeringmathematics,computers,graphics,and Englishare used to produce a plan which,when carried out,will satisfy a human need.Mechanical Engineering DesignMechanical Engineering DesignMechanical design means die design

41、of things and systems of a mechanical naturemachines,products,structures,devices,and instruments.For the most part,mechanical designutilizes mathematics,the materials sciences,and the engineering-mechanics sciences.Mechanical engineering design includes all mechanical design,but it is a broader stud

42、y,because it includes all the disciplines of mechanical engineering,such as the thermal and fluidssciences,too.Aside from the fundamental sciences that are required,the first studies inmechanical engineering design are in mechanical design.The Phases of DesignThe Phases of DesignThe complete process

43、,from start to finish.The process W begins with a recognition of aneed and a decision to do something about it.After much iteration,the process ends with thepresentation of the plans for satisfying the need.Design ConsiderationsDesign ConsiderationsSometimes the strength required of an element in a

44、system is an important factor in thedetermination of the geometry and the dimensions of the element.In such a situation we saythat strength is an important design consideration.When we use the expression designconsideration,we are referring to some characteristic which influences the design of theel

45、ement or,perhaps,the entire system.Usually quite a number of such characteristics must beconsidered in a given design situation.Many of the important ones are as follows:1.Strength7.Processing13.Noise2.Reliability8.Utility14.Styling3.Thermal properties9.Cost15.Shape4.Corrosion10.Safety16.Size5.Wear1

46、1.Weight17.Flexibility6.Friction12.Life18.Control19.Stiffness20.Surface finish21.Lubrication22.Maintenance23.Volume24.LiabilitySome of these have to do directly with the dimensions,the material,theprocessing,and the joining of the elements of the system.Other considerations affectthe configuration o

47、f the total system.To keep the correct perspective,however,it should be observed that in manydesign situations the important design considerations are such that no calculations orexperiments are necessary in order to define an element or system.Students,especially,are often confounded when they run

48、into situations in which it is virtuallyimpossible to make a single calculation and yet an important design decision must bemade.These are not extraordinary occurrences at all。they happen every day.Supposethat it is desirable from a sales standpointfor example,in medical laboratorymachineryto create

49、 an impression of great strength and durability.Thicker partsassembled with larger-than-usual oversizebolts can be used to create a rugged-lookingmachine.Sometimes machines and their parts are designed purely from the standpointof styling and nothing else.These points are made here so that you will

50、not be misledinto believing that there is a rational mathematical approach to every design decision.ManufacturingManufacturingManufacturing is that enterprise concerned with converting raw material intofinished products.There are three distinct phases in manufacturing.These phasesare as follows:inpu