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Introduction 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 Engineering
The 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 Engineering
Development 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 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 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 man’s 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 Engineering
Four 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 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 Engineering
The 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 man’s needs while reducing to a minimum the consumption of scarce raw materials and maintaining a satisfactory environment.
Mechanical engineering in the information age
In 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 .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 you’ve got a short development cycle, the situation is not catastrophic as long as you maintain your lead. But if you’re 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 don’t 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 won’t 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 it you ought to like it .If you don’t, there’s 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 today’s 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 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 problem—solving 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.
機械工程簡介
機械工程是工程學的一個分支，它研究機械和動力的產(chǎn)生，尤其是力和運動。
機械工程的歷史
18世紀后期，蒸汽機的發(fā)明為工業(yè)革命提供了一個主要的動力源泉，極大地推動了各種機械的發(fā)展。這樣，一個新的工程學的重要分支——從民用工程學中分離出來的關于工具和機械的分支——發(fā)展了起來。并隨著英國伯明翰機械工程師協(xié)會的建立在1847年得到了正式承認。
機械工程已經(jīng)由一門主要基于試錯法的技工應用的技藝發(fā)展成為職業(yè)工程師在研究、設計和生產(chǎn)領域使用的科學方法。
從最廣義的角度講，增進效率的需求不斷地促使機械工程師提高工作質(zhì)量，并要求他接受更高程度的教育和訓練。不僅機器運轉(zhuǎn)要講求經(jīng)濟，而且基建費也要降到最低。
機械工程的領域
商品機械的發(fā)展 在發(fā)達國家中，高水平的物質(zhì)生活很大程度上取決于機械工程中得以實現(xiàn)的各種機械。機械工程師們不斷地發(fā)明機器來生產(chǎn)商品，不斷地開發(fā)精確性和復雜性越來越高的機械工具來生產(chǎn)機器。
機械發(fā)展的主要線索是：為提高生產(chǎn)率而增加機器的運轉(zhuǎn)速度、為獲得物美價廉的產(chǎn)品而提高精度以及降低生產(chǎn)成本。這3個要求促進了復雜的控制系統(tǒng)的發(fā)展。
最成功的機械制造是其機器的機械設計能與控制系統(tǒng)緊密融合，不論這種控制系統(tǒng)從本質(zhì)上是機械的還是電子的?，F(xiàn)代化的汽車發(fā)動機生產(chǎn)傳送線（傳送帶）就是一系列復雜的生產(chǎn)工藝機械化的很好例子。人們正在著手開發(fā)以使機械生效后進一步自動化，利用計算機來存儲和處理大量數(shù)據(jù)，這些數(shù)據(jù)是少量多功能機床生產(chǎn)多種零件所必需的。其中一個目標就是使批量生產(chǎn)車間完全自動化，三班輪換，但每天只需一班人員來操作。
動力機械的發(fā)展 生產(chǎn)機械必須先有充足的動力供應。蒸汽機最先提供了用熱能來產(chǎn)生動力的實際可行的方法，在舊有的人力、風力和水力之外增加了動力源。新的機械工程業(yè)面臨的最初挑戰(zhàn)之一就是增加熱效率和動力，這一點隨著蒸汽渦輪機和大的聯(lián)合蒸汽鍋爐的發(fā)展而基本實現(xiàn)了。20世紀，渦輪機為發(fā)電機提供的動力得到了持續(xù)快速的增長，同時熱效率也在穩(wěn)定增長，而且大電站每千瓦的資本消耗也在下降。最后，機械工程師們獲得了核能源。這種核能源的應用需要有特別高的可靠性和安全性，這就需要解決許多全新的問題。大型電廠和整個核電站的控制系統(tǒng)已變成高度復雜的電子、流體、電、水力和機械零件的網(wǎng)絡，這一切都涉及到機械工程師的所有學術領域。
小型的內(nèi)燃機，不論是往復式（汽油機和柴油機）還是旋轉(zhuǎn)式（燃氣輪機和旺克爾機），以及它們在運輸領域的廣泛應用也都要歸功于機械工程師們。在整個運輸業(yè)，不論是在空中和太空，還是在陸地和海洋，機械工程師創(chuàng)造了各種設備和動力裝置。他們越來越多地與電氣工程師合作，尤其是在開發(fā)適合的控制系統(tǒng)方面。
軍用武器的開發(fā) 機械工程師應用于戰(zhàn)爭的技術與民用中需要的類似，盡管其目的是增強毀壞力而不是提高生產(chǎn)率。噴氣式飛機和核反應堆就是眾所周知的例子。
生物工程 生物工程是機械工程中一個相對新的和與眾不同的領域，它提供用來替換或增加人體功能的機器以及用來進行醫(yī)療的設備。人造肢體已被開發(fā)出來，并且具有諸如有力的運動和觸摸反應等人體功能。在人工器官移植手術方面的發(fā)展是迅速的，復雜的心肺機器和類似的設備使越來越復雜的手術得以進行，并使受重傷和重病病人的生命功能得以持續(xù)。
環(huán)境控制 機械工程師的一些最初的努力是要通過抽水來排澇或灌溉土地以及給礦井通風來控制人類的環(huán)境?，F(xiàn)代的制冷和空調(diào)廠普遍采用反向的熱引擎，在這些地方動力把熱從冷的地方抽出送到更熱的外部。
很多機械工程的產(chǎn)品以及其他領域的技術發(fā)展對環(huán)境有副作用，產(chǎn)生了噪音，引起了水和空氣的污染，破壞了土地和風景。商品和動力的生產(chǎn)率提高太快，以致于自然力的再生跟不上步伐。對于機械工程師和他人來說，環(huán)境控制是一個快速發(fā)展的領域，它包括開發(fā)盡可能產(chǎn)生少量污染物的機器和生產(chǎn)工序，以及開發(fā)新的設備和技術來減少和消除已造成的污染。
機械工程的作用
機械工程師有四個通用于上述所有領域的作用。第1個作用是理解和研究機械科學的基礎。它包括涉及力和運動的關系的動力學，比如在振動中的力和運動的關系；自動控制；研究各種形式的熱、能量、動力之間關系的熱力學；流體流動；熱傳遞；潤滑；和材料特性。
第2個作用是依次地進行研究、設計和開發(fā)。該作用試圖進行必要的改變以滿足當前和將來的需要。這一工作不僅要求對機械科學有一個合成和發(fā)明。
第3個作用是生產(chǎn)產(chǎn)品和動力，包括計劃、運作和維護。其目的在于維護或提高企業(yè)或機構的較長期的和生存能力聲譽的同時，以最少的投資和消耗生產(chǎn)出最大的價值。
第4個作用是機械工程師的協(xié)調(diào)作用，包括管理、咨詢、以及在某些情況下進行市場營銷。
在所有這些作用中，體現(xiàn)出一種長期不斷地使用科學的方法，而不是傳統(tǒng)的或直覺的方法的傾向，這是不斷成長的機械工程專門技術的一個方面。這些新的合理化方法的典型名稱有：運籌學、工程經(jīng)濟學、邏輯學問題分析（簡稱PABLA）。然而，創(chuàng)造性是無法合理化的。正如在其他領域一樣，在機械工程中，能夠采取重要的出人意料的并能開創(chuàng)出新方法的能力，仍然具有個人的、即興的特點。
機械工程的未來
機械工程師的數(shù)量依舊快速增長，同時他們所受訓練的時間也在延長并且質(zhì)量也在提高。然而，工程師們和全體公眾越來越意識到，人口和生活水平的指數(shù)增長正在造成可怕的環(huán)境污染和自然資源消耗問題。這更清楚地表明，所有的技術職業(yè)都有必要考慮開發(fā)和發(fā)展的長期社會效益。人們越來越需要機械工程技術來滿足人類的需求，同時也需要將稀有的原材料的消耗降到最低，保持一個令人滿意的環(huán)境。
信息時代的機械工程
在20世紀80年代初期，工程師門曾經(jīng)認為要加快產(chǎn)品的研制看法，必須進行大量的研究工作。結果是實際上只進行了較少的研究工作，這是因為產(chǎn)品開發(fā)周期的縮短，促使工程師們盡可能的利用現(xiàn)代技術。研制開發(fā)一種創(chuàng)新性的技術并且將其應用在新產(chǎn)品上，使有風險的，并且易于招致失敗。在產(chǎn)品開發(fā)過程中采用較少的步驟是安全的和易于成功的方法。
對于資金和人力都處于全球性環(huán)境中的工程界而言，縮短產(chǎn)品研制開發(fā)周期也是有益的。能夠設計和制造各種產(chǎn)品和制造各種產(chǎn)品的人可以在世界各地找到。但是，具有創(chuàng)新思想的人則比較難找。對于已經(jīng)進行6個月的研制開發(fā)工作的人，地里上的距離已經(jīng)不再是其他人發(fā)現(xiàn)他的障礙。如果你的研發(fā)周期較短，只要仍然保持領先，這種情況并不造成嚴重后果。如果正處于一個長達6年的研制開發(fā)過程中期，一個競爭對手了解到你的研究工作的一些信息，這個項目將面臨比較大的麻煩。
工程師們在解決任何問題時都需要進行新的設計這種觀念很快就過時了，在現(xiàn)在設計中的第一步是瀏覽因特網(wǎng)或者其他信息系統(tǒng)，看其他人是否設計了一種類似于你所需要的產(chǎn)品，諸如船東裝置或換熱器等。通過這些信息系統(tǒng)，你可能發(fā)現(xiàn)有些人已經(jīng)有了制造圖紙，數(shù)控紙帶和制造你的產(chǎn)品所需要的其他東西。這樣，工程師們就可以把他們的職業(yè)技能集中在尚未解決的問題上。
在解決這些問題時，利用工作站和進入信息高速公路可以大大增強工程小組的能力和效率。這些信息時代的工具可使工程小組利用大規(guī)模的數(shù)據(jù)庫。數(shù)據(jù)庫中有材料性能`標準`技術和成功的設計方案等信息。這些經(jīng)過驗證的設計可以通過下載直接應用，或者對其進行快速`簡單的改進來滿足特定的要求。將產(chǎn)品的技術要求通過網(wǎng)絡送出去的遠程制造也是可行的。你可以建立一個沒有任何加工設備的虛擬公司，可以只是制造商，在產(chǎn)品加工完成后，將其直接送給你的客戶。定期訪問你的客戶可以保證你設計的產(chǎn)品按照設計要求進行工作。盡管這些研制開發(fā)方式不可能對每個公司都完全適用，但是這種可能性是存在的。
過去客戶設計的產(chǎn)品，通常是由小公司制造的。大公司不屑于制造這些產(chǎn)品-----他們討厭瞄準機會的市場，或者是與客戶設計的小批量大交道?！斑@就是我的產(chǎn)品，”一家大公司這樣說，“這是我們能夠制造出來的最好產(chǎn)品----你應該喜歡他。如果你不喜歡，順這條街走有一家小公司，它會按你的要求做?！?
今天，因為顧客們又較大的選擇余地，幾乎所有的市場都是瞄準機會的市場。如果你不能使產(chǎn)品滿足某些特定客戶的要求，你將失去市場份額中的一大部分，或者失去全部份額。由于這些瞄準機會的市場是經(jīng)常變化的，你告訴應該對市場做出快速的反應。
瞄準機會的市場和根據(jù)客戶要求進行設計這種現(xiàn)象的出現(xiàn)，改變了工程師們未能進行研究工作的方式。今天，研究工作通常是針對解決特定問題進行的。許多有政府資助或者由大公司出資開發(fā)的技術可以在非常低的成本下輩自由使用盡管這種情況是暫時的，對這些技術進行適當改進后，他們通常可以被直接用于產(chǎn)品開發(fā)，這使得許多公司可以節(jié)省昂貴的研究經(jīng)費。在主要的技術障礙被克服后，研究工作應該主要致力于產(chǎn)品的商品化方面，而不失開發(fā)新的，有趣的，不確定的替換產(chǎn)品。
采用上述觀點看問題，工程研究應該致力于消除將已知的技術快速商品化的障礙。工作的重點是產(chǎn)品的質(zhì)量和可靠性，這些在當今的顧客的頭腦中是最重要的。很明顯，一個質(zhì)量差的聲譽是一個不好的企業(yè)的同義詞。企業(yè)應該盡最大的努力來保證客戶得到合格的產(chǎn)品，這個努力包括在生產(chǎn)線的中斷對產(chǎn)品進行嚴格的檢驗和自動更換有缺陷的產(chǎn)品。
研究工作應該著重考慮諸如可靠性等因素對成本帶來的益處，當可靠性提高時制造成本和系統(tǒng)的最終成本將會降低。如果在生產(chǎn)線的終端產(chǎn)生30%的廢品，這不僅會浪費金錢，也會給你的競爭對手創(chuàng)造一個利用你的想法制造產(chǎn)品，并且將其銷售給你的客戶良機。
提高可靠性和合降低成本這個過程的關鍵是深入廣泛的利用設計軟件。設計軟件可以使工程師加快每個階段的設計工作。然而，僅僅縮短每個階段的設計時間，可能不會顯著的縮短整個設計的時間。因而，必須致力于并行工程軟件，這樣可以使所有者，即組的成員都能使用共同的數(shù)據(jù)庫。
隨著人們步入信息時代，要取得成功，工程師們在技術開發(fā)和技術管理方面都應該具有一些獨特的知識和經(jīng)驗。成功的工程師們不但一個具有寬廣的知識和技能，而且還應該是某些關鍵技術或?qū)W科的專家，他們還應該在社會因素和經(jīng)濟因素對市場的影響方面有敏銳的洞察力。將來，花在解決日常工程問題上的費用將會減少，工程師們將會在一些更富有挑戰(zhàn)性，更亟待解決的問題上協(xié)同工作，大大縮短解決這些問題所需要的時間。我們已經(jīng)開始了工程實踐的新階段。計算機和網(wǎng)絡工程師們具有越來越強的解決問題的能力，這些也給我們的工作帶來很大的希望和喜悅。為了確保成功，我們所使用工具的性能和對更好的產(chǎn)品與系統(tǒng)的不斷追求，應該與標志著在工程方面所有巨大努力的創(chuàng)新工作所帶來的喜悅相適應。機械工程是一個偉大的行業(yè)，在我們盡可能多的利用了信息時代所提供的機遇后，他將變得更加偉大。
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