机械设计专业的毕业设计.docx

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1、Mechanical EngineeringIntroduction to Mechanical Engineering Mechanical engineering is the branch of engineering that deals with machines and the production of power. It is particularly concerned with forces and motion.History of Mechanical EngineeringThe invention of the steam engine in the latter

2、part of the 18th century, providing a key source of power for the Industrial Revolution, gave an enormous impetus to the development of machinery of all types. As a result a new major classification of engineering, separate from civil engineering and dealing with tools and machines, developed, recei

3、ving formal recognition in 1847 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 based largely on trial and error to the application by the professional engineer of the scientific method i

4、n research, design, and production.The demand for increased efficiency, in the widest sense, is continually raising the quality of work expected from a mechanical engineer and requiring of him a higher degree of education and training. Not only must machines run more economically but capital Costs a

5、lso must be minimized.Fields of Mechanical EngineeringDevelopment of machines for the production of goods the high material standard of living in the developed countries owes much to the machinery made possible by mechanical engineering. The mechanical engineer continually invents machines to produc

6、e goods and develops 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 of operation to obtain high rates of production, improvement in accuracy to obtain quality and economy in the product, and

7、 minimization of operating costs. These three requirements have led to the evolution of complex control systems.The most successful production machinery is that in which the mechanical design of the machine is closely integrated with the control system, whether the latter is mechanical or electrical

8、 in nature. A modern transfer line (conveyor) for the manufacture of automobile engines is a good example of the mechanization of a complex series of manufacturing processes. Developments are in hand to automate production machinery further, using computers to store and process the vast amount of da

9、ta required for manufacturing a variety of components with a small number of versatile machine tools. One aim is a completely automated machine shop for batch production, operating on a three shift basis but attended by a staff for only one shift per day.Development of machines for the production of

10、 power Production machinery presuppose an ample supply of power. The steam engine provided the first practical means of generating power from heat to augment the old sources of power from muscle, wind, and water One of the first challenges to the new profession of mechanical engineering was to incre

11、ase thermal efficiencies and power; this was done principally by the development of the steam turbine and associated large steam boilers. The 20th century has witnessed a continued rapid growth in the power output of turbines for driving electric generators, together with a steady increase in therma

12、l efficiency and reduction in capital cost per kilowatt of large power stations. Finally, mechanical engineers acquired the resource of nuclear energy, whose application has demanded an exceptional standard of reliability and safety involving the solution of entirely new problems- The control system

13、s of large power plank and complete nuclear power stations have become highly sophisticated networks of electronic, fluidic. Electric, hydraulic, and mechanical components, ail of these involving me province of the mechanical engineer.The mechanical engineer is also responsible for the much smaller

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

15、he power plant, collaborating increasingly with the electrical engineer, especially in the development of suitable control systems.Development of military weapons The skills applied to war by the mechanical engineer are similar to those required in civilian applications, though the purpose is to enh

16、ance destructive power rather than to raise creative efficiency. The demands of war have channeled huge resources into technical fields, however, and led to developments that have profound benefits in peace. Jet aircraft and nuclear reactors are notable examples.Biaengineering Bioengineering is a re

17、latively new and distinct field of mechanical engineering that includes the provision of machines to replace or augment the functions of the human body and of equipment for use in medical treatment. Artificial limbs have been developed incorporating such lifelike functions as powered motion and touc

18、h feedback. Development is rapid in the direction of artificial spare-part surgery. Sophisticated heart-lung machines and similar equipment permit operations of increasing complexity and permit the vital functions in seriously injured or diseased patients to be maintained.Environmental control Some

19、of the earliest efforts of mechanical engineers were aimed at controlling mans environment by pumping water to drain or irrigate land and by ventilating mines. The ubiquitous refrigerating and air-conditioning plants of the modem age are based on a reversed heat engine, where the supply of power pum

20、ps heat from the cold region to the warmer exterior.Many of the products of mechanical engineering, together with technological developments in other fields, have side effects on the environment and give rise to noise, the pollution of water and air, and the dereliction of land and scenery. The rate

21、 of production, both of goods and power, is rising so rapidly that regeneration by natural forces can no longer keep pace. A rapidly growing field for mechanical engineers and others is environmental control, comprising the development of machines and processes that will produce fewer pollutants and

22、 of new equipment and techniques that can reduce or remove the pollution already generated.Functions of Mechanical EngineeringFour functions of the mechanical engineering, common to all the fields mentioned, are cited. The first is the understanding of and dealing with the bases of mechanical scienc

23、e. These include dynamics, concerning the relation between forces and motion, such as in vibration; automatic control; thermodynamics, dealing with the relations among the various forms of heat, energy, and power; fluid flow; heat transfer; lubrication; and properties of materials.Second is the sequ

24、ence of research, design, and development. This function attempts to bring about the changes necessary to meet present and future needs. Such work requires not only a dear understanding of mechanical science and an ability to analyze a complex system into its basic factors, but also the originality

25、to synthesize and invent.Third is production of products and power, which embraces planning, operation, and maintenance. The goal is to produce the maximum value with the minimum investment and cost while maintaining or enhancing longer term viability and reputation of the enterprise or the institut

26、ion.Fourth is the coordinating functioning of the mechanical engineering, including management, consulting, and, in some cases, marketing.In all of these functions there is a long continuing trend toward the use of scientific instead of traditional or intuitive methods, an aspect of the ever-growing

27、 professionalism of mechanical engineering. Operations research, value engineering, and PABLA (problem analysis by logical approach) are typical titles of such new rationalized approaches. Creativity, however, cannot be rationalized. The ability to take the important and unexpected step that opens u

28、p new solutions remains in mechanical engineering, as elsewhere, largely a personal and spontaneous characteristic.The Future of Mechanical EngineeringThe number of mechanical engineers continues to grow as rapidly as ever, while the duration and quality of their training increases. There is a growi

29、ng: awareness, however, among engineers and in the community at large that the exponential increase in population and living standards is raising formidable problems in pollution of the environment and the exhaustion of natural resources; this clearly heightens the need for all of the technical prof

30、essions to consider the long-term social effects of discoveries and developments. -There will be an increasing demand for mechanical engineering skills to provide for mans needs while reducing to a minimum the consumption of scarce raw materials and maintaining a satisfactory environment.Introductio

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

32、y, and economical/ without using 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 nebulous and i

33、ll defined that a considerable amount of thought and effort is necessary in ( order to state it 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

34、type of design situation is characterized by the fact that neither the need nor the problem to be solved has been identified. Note, too, that the situation may contain not one problem but many.We can classify design, too. For instance, we speak of:1. Clothing design 7. Bridge design2. Interior desig

35、n 8. Computer-aided design3. Highway design 9. Heating system design. 4. Landscape design 10. Machine design5. Building design 11. Engineering design6. Ship design 12. Process designIn fact, there are an endless number, since we can classify design according to the particular article or product or a

36、ccording to the professional field,In contrast to scientific or mathematical problems, design problems have no unique answers; 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 answer tomor

37、row, if there is a growth of knowledge during the period or if there are other structural or societal 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 not a hypotheti

38、cal problem at all. Design has an authentic purposethe creation of an end result by taking definite action, or the creation of something having physical reality. In engineering, the word design conveys different meanings to different persons. Some think of a designer as one who employs the drawing b

39、oard to draft the details of a gear, clutch, or other machine member. Others think of design as the creation of a complex system, such as a communications network. In some areas of engineering the word design has been replaced by other terms such as systems engineering or applied decision theory. Bu

40、t no matter what words are used to describe the design function, in engineering it is still the process in which scientific principles and the tools of engineeringmathematics, computers, graphics, and Englishare used to produce a plan which, when carried out, will satisfy a human need.Mechanical Eng

41、ineering DesignMechanical design means die design of things and systems of a mechanical nature machines, products, structures, devices, and instruments. For the most part, mechanical design utilizes mathematics, the materials sciences, and the engineering-mechanics sciences.Mechanical engineering de

42、sign includes all mechanical design, but it is a broader study, because it includes all the disciplines of mechanical engineering, such as the thermal and fluids sciences, too. Aside from the fundamental sciences that are required, the first studies in mechanical engineering design are in mechanical

43、 design.The Phases of DesignThe complete process, from start to finish. The process W begins with a recognition of a need and a decision to do something about it. After much iteration, the process ends with the presentation of the plans for satisfying the need.Design ConsiderationsSometimes the stre

44、ngth required of an element in a system is an important factor in the determination of the geometry and the dimensions of the element. In such a situation we say that strength is an important design consideration. When we use the expression design consideration, we are referring to some characterist

45、ic which influences the design of the element or, perhaps, the entire system. Usually quite a number of such characteristics must be considered in a given design situation. Many of the important ones are as follows:1. Strength2. Reliability 3. Thermal properties4. Corrosion 5. Wear 6. Friction7. Pro

46、cessing 8. Utility 9. Cost10. Safety 11. Weight 12. Life 13. Noise 14. Styling 15. Shape16. Size17. Flexibility 18. Control19. Stiffness20. Surface finish 21. Lubrication22. Maintenance23. Volume 24. LiabilitySome of these have to do directly with the dimensions, the material, the processing, and th

47、e joining of the elements of the system. Other considerations affect the configuration of the total system.To keep the correct perspective, however, it should be observed that in many design situations the important design considerations are such that no calculations or experiments are necessary in

48、order to define an element or system. Students, especially, are often confounded when they run into situations in which it is virtually impossible to make a single calculation and yet an important design decision must be made. These are not extraordinary occurrences at all; they happen every day. Suppose that it is