机械工程简介-外文文献

- 1 -Introduction to Mechanical EngineeringMechanical 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 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, receiving 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 in 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 also 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 produce 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 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 in nature. A modern transfer line (conveyor) for the - 2 -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 data 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, operation on a three-shift basis but attended by a staff for only one shift per day.Development of machines for the production of power Production machinery presupposes 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 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 thermal 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 systems of large power plants and complete nuclear power stations have become highly sophisticated networks of electronic, fluidic, electric, hydraulic, and mechanical components, all of these involving the province of the mechanical engineer.The mechanical engineer is also responsible for the much smaller 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 the 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 enhance destructive power rather than to raise creative efficiency. The demands of war have channeled huge resources into technical fields, however, and led to developments - 3 -that have profound benefits in peace. Jet aircraft and nuclear reactors are notable examples.Bioengineering Bioengineering is a reactively 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 touch 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 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-condition plants of the modern age are based on a reversed heat engine, where the supply of power “pumps” 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 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 and other is environmental control, comprising the development of machines and processed that will produce fewer pollutants and 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, be cited. The first is the understanding of and dealing with the bases of mechanical science. 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 sequence of research, design, and development. This function - 4 -attempts to bring about the changes necessary to meet present and future needs. Such work requires not only a clear understanding of mechanical science and an ability to analyze a complex system into its basic factors, but also the originality 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 institution. Fourth is the coordinating functions 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 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 up 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 growing 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 professions 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.Mechanical engineering in the information ageIn the early 1980s, engineers thought that massive would be needed to speedup product development. As it turn out ,less research is actually needed because shortened product development cycles encourage engineers to sue available technology - 5 -.developing a revolutionary for use in a new product is risky and prone to failure. Taking short steps is a safer and usually more successful to product development. Shorter product development cycles are also beneficial in engineering world in which both capital and labor are global. People who can design and manufacture various products can be found anywhere in the world, but containing a new idea is hard. Geographic distance is no longer a barrier to others finding out about your development six months into the process. If youve got a short development cycle, the situation is not catastrophic as long as you maintain your lead. But if youre in the midst of a six-year development process and a competitor gets wind of your work, the project could be in more serious trouble. The idea that engineers need to create a new design to solve every problem is quickly becoming obsolete. The first step in the modern design process is to browse the Internet or other information systems to see if someone else has already designed a transmission, or a heat exchanger than is close to what you need. Through these information systems, you may discover that someone already has manufacturing drawing, numerical control tapes, and every else required to manufacture your product. Engineer can then focus their professional competence unsolved problems. In tackling such problem, the availability of workstations and access to the information highway dramatically enhance the capability of the engineering team and its productivity. These information age tools can give the team access to massive databases of material properties, standards, technologies, and successful design. Such protested designs can be downloaded for direct use or quickly modified to meet specific needs. Remote manufacturing, in which product instructions are sent out over a network, is also possible. You could end up with a virtual company where you dont have to see any hardware. When the product is completed, you can direct the manufacturer to drop-ship it to your customer. Periodic visit to the customer can be made to ensure that the product you designed is working according to the specifications.Although all of these developments wont apply equally to every company, the potential is there. Custom design used to be left to small companies. Big companies sneered at it they hated the idea of dealing with niche markets or small-volume custom solutions. “Here is my product,” one of big companies would say “This is best we make - 6 -it you ought to like it .If you dont, theres a smaller company down the street that will work on your problem.” Today, nearly every market is a niche market, because customers are selective. If you ignore the potential for tailoring your product to specific customers needs, you will lose the major part of your market share perhaps all of it. Since these niche markets are transient, you company need to be in a position to respond to them quickly .The emergence of niche markets and design on demand has altered the way engineers conduct research. Today, research is commonly directed toward solving particular problem. Although this situation is probably temporary, much uncommitted technology, developed at government expense or written off by major corporations, is available today at every low cost .Following modest modification, such technology can often be used directly in product development, which allows many organizations to avoid the expense of an extensive research effort. Once the technology is free or major obstacles, the research effort can focus on overcoming the barriers to commercialization rather than on pursuing new and interesting, but undefined, alternatives. When viewed in this perspective, engineering research must focus primarily on removing the barriers to rapid commercialization of known technologies. Much of this effort must address quality and reliability concerns. Which are foremost in the mind of todays consume. Clearly, a reputation for poor quality is synonymous with bad business. Everything possible including through inspection at the end of the manufacturing line and automatic replacement of defective products-must be done to assure that the customer receives a properly functioning product. Research has to focus on the cost benefit of factors such as reliability.As reliability increase, manufacturing costs and the system will decrease. Having 30 percent junk at the end of a production line not only costs a fortune but also create an opportunity for a competitor to take your idea and sell it to your customers. Central to the process of improving reliability and lowering costs is intensive and widespread use of design software, which allows engineers to speed up every stage of the design process. Shortening each stage, however, may not sufficiently reduce the time required for entire process. Therefore, attention must also be devoted to concurrent engineering software with shared databases that can be accessed by all members of the - 7 -design team. As we move more fully into the Information Age, success will require that the engineer possess some unique known of and experience in both the development and the management of technology .Success will required broad knowledge and skills as well as expertise in some key technologies and disciplines; it will also require a keen awareness of the social and economic factor at work in the marketplace. Increasingly , in the future routine problem will not justify heavy engineering expenditures, and engineers will be expected to work cooperatively in solving more challenging, more demanding problem in substantially less time .We have begun a new phase in the practice of engineering . It offers great promise and excitement as more and more problemsolving capability is placed in the hands of the computerized and wired engineers .To assure success , the capability of our tools and the unquenched thirst for better products and system must be matched by the joy of creation that marks all great engineering endeavors . Mechanical engineering is a great profession, and it will become even greater as we make the most of the opportunities offered by the Information Age.