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Mechanical engineering design
1. The meaning of design
To design is to formulate a plan for the satisfaction of human need .in the beginning the particular need to the satisfied may be quite well-defined. Here are two examples of well-defined needs.
1. How can we obtain large quantities of power cleanly, safely, and economically 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 particular need to be satisfied may be so nebulous and ill-defined that a considerable amount of thought and effort is necessary in order to state it clearly 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 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 many problems.
We can classify design too. For instance:
1. Clothing design 7. Bridge design
2. Interior design 8. Computer-aided design
3. Highway design 9. Heating system design
4. Landscape design 10. Machine design
5. Building design 11. Engineering design
6. Ship design 12. Process design
In fact there are an endless number, since we can classify design according to the particular article or product or according 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 tomorrow, if there is a growth of knowledge during the period or if there are other structure or societal changes.
Almost everyone is involved with design in one way or another, even in daily living, because problems are posed and situations arise which must be solved. Consider the design of a family vacation. There may be seven different places to go, all the different distances from home. The costs of transportation are different for each, and some of the options require overnight stops on the way. The children would like to go to a lake or seashore resort. The wife would prefer to go to a large city with department store shopping, theatres, and nightclubs. The husband prefers a resort with a golf course. When these needs and desires are related to time and money, various solutions may be found. Of these there may or may not be one or more optimal solutions. But the solution chosen will include the travel route, the stops, the mode of transportation, and the names and locations of resorts, motels, camping sites, or other away-from-home facilities. It is hard to see that there is really a rather large group of interrelated complex factors involved in arriving at one of the solutions to the vacation design problem.
A design is always subject to certain problem-solving constraints. For example, two of the constraints on the vacation design problem are the time and money available for the vacation. Note, too, that there are also constraints on the solution, in the case above some of those constraints are the desire and needs of each of the family members. Finally, the design solution found might well be optimal. In this case an optimal solution is obtained when each and every family member can say that he or she had a good time.
A design problem is not a hypothetical problem at all. Design has an authentic purpose—the creation of an end result by taking definite acting or the creation of something having physical reality. In engineering the word “design ” conveys different meaning to different persons. Some think of a designer as one who employs the drawing board 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. But no matter what words are used to describe the design function, in engineering it is still the process in which scientific the principles and the tools of engineering—mathematics, computers, graphics, and English—are used to produce a plan which, when carried out, will satisfy a human need.
2. The phases of design
The total design process is of interest to us, how does it begin? Does the engineer simply sit down at his or her desk with a blank sheet of paper and jot down some ideas? What happens next? What factors influence or control the decisions, which have to be made? Finally, how does this design process end?
The complete process, from start to finish, is often outlined as in Figure. The process begins with a recognition of a need and a decision to do something about it, after many iterations, the process ends with the presentation of the plans for satisfying the need, we should examine these steps in the design process in detail.
3. Mechanical engineering design
Mechanical design means the design of things and system of a mechanical nature—machines, products, structures, devices, and instruments. For the most part, mechanical design utilizes mathematics, the materials sciences, and the engineering mechanical science.
Mechanical engineering design includes all mechanical design, but it is a broader study because it includes all the disciplines of mechanical engineering, such as the thermal-fluids sciences, too. Aside from the fundamental sciences that are required, the first studies in mechanical engineering design are in mechanical design, and hence this is the approach taken in this book.
4. Design Process and Stages
Mechanical design is either to formulate all engineering plan for the satisfaction for the specified need or to solve an engineering problem. It is 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 all considers the various factors involved in the manufacture, marketing and use of product. Mechanical design involves a range of disciplines in materials, mechanics, heat, flow, control, electronics and production.
Mechanical design should be considered to be an opportunity to use innovative talents to envision a design of a product, to analyze the system 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 good design. On the other hand, any calculations must be done with the utmost care and precision. For example, if a decimal point is misplaced, an otherwise acceptable design may not function.
Mechanical design may be simple or enormously complex, easy or difficult, mathematical or nonmathematical, it may involve a trivial problem or one of great importance. Good design is the orderly and interesting arrangement of all idea to provide certain results and effects. A well-designed product is functional, efficient, and dependable. Such a product is less expensive than a similar poorly designed product that does not function properly and must constantly be repaired.
People who perform the various functions of mechanical design are typically called designers, or design engineers. Mechanical 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, materials engineering, manufacturing processes. The designer must first carefully define the problem, using an engineering approach, to ensure that any proposed solution will solve the right problem. It is important that the designer begin by identifying exactly how he or she will recognize a satisfactory alternative, and how to distinguish between two satisfactory alternatives in order to identify the better. So industrial designers must have creative imagination, knowledge of engineering, production techniques, tools, machines, and materials to design a new product for manufacture, or to improve an existing product.
In the modern industrialized world, the wealth and living standards of a nation are closely linked with their capabilities design and manufacturing engineering products. It can be claimed that the advancement of mechanical design and manufacturing can remarkably promote the overall level of a country’s industrialization. Many countries are playing more and more vital role in the global manufacturing industry. To accelerate such an industrializing process, highly skilled design engineers having extensive knowledge and expertise are needed.
5. Mechanical design process
Product design requires much research and development. Many concept of an idea must be studied, tried, refined, and then either used or discarded. Although the content of each engineering problem is unique, the designers follow the similar process to solve the problems. The complete process is often outlined as in figures. The design process usually begins with a specification of a solution. We sometimes allude to a design cycle, but the process may contain a design cycle plus design implementation, which involves actual production based upon the design. The design cycle can involve the original thoughts, sketches, and knowledge that in the specification stage produce engineering drawings. Computer-aid design is now employed to implement a cycle in which various designs or design ideas may be tested or simulated.
6. Contents of Mechanical Design
Mechanical design is an important technological basic course in mechanical engineering education. Its objective is to provide the concepts, procedures, data, and decision analysis techniques necessary to design machine elements commonly found in mechanical devices and systems; to develop engineering students’ competence of mechanical design that is the primary concern of machinery manufacturing and the key to manufacturing good products.
Mechanical design covers the following contents:
1．Provides an introduction to the design process, problem formulation, safety factors.
2．Reviews the material properties and static and dynamic loading analysis, including beam, vibration and impact loading.
3．Reviews the fundamentals of stress and defection analysis.
4．Introduces static failure theories and fracture-mechanics analysis for static loads.
5．Introduces fatigue-failure theory with the emphasis on stress-life approaches to high-cycle fatigue design, which is commonly used in the design of rotation machinery.
6．Discusses thoroughly the phenomena of wear mechanisms, surface contact stress, and surface fatigue.
7．Investigates shaft design using the fatigue-analysis techniques.
8．Discusses fluid-film and rolling-element bearing theory and application.
9．Gives a thorough introduction to the kinematics, design and stress analysis of spur gears, and a simple introduction to helical, bevel, and worm gearing.
10．Discusses spring design including helical compression, extension, and torsion springs.
11．Deals with screws and fasteners including power screw and preload fasteners.
12．Introduces the design and specification of disk and drum clutches and brakes.
機(jī)械工程設(shè)計(jì)
1. 設(shè)計(jì)的意義
?? 設(shè)計(jì)是制定一項(xiàng)計(jì)劃，以便滿足人類的需要。在開始的特別需要的滿足可能相當(dāng)明確。這里有兩個(gè)例子明確界定的需要。
1. 我們怎樣才能獲得大量的電力干凈，安全，經(jīng)濟(jì)上不使用化石燃料和不破壞了地球表面的？
2. 這是給齒輪軸麻煩;有8個(gè)失誤，在過去6個(gè)星期。做點(diǎn)什么。
另一方面，尤其需要得到滿足可能是這樣模糊不清和不明確，有相當(dāng)數(shù)量的思路和努力是必要的，以國家顯然是一個(gè)問題需要解決。這里有兩個(gè)例子。
1 .很多人死于飛機(jī)事故。
2 .在大城市有太多汽車的街道和高速公路。
??????這第二種類型的設(shè)計(jì)局勢的特點(diǎn)是一個(gè)事實(shí)，即既不需要也不是要解決的問題已被確定。請注意，也這種情況可能包含許多問題。
??????我們也可以分類設(shè)計(jì)。例如：
???? ? 1 .服裝設(shè)計(jì) 7 .橋梁設(shè)計(jì)
????? 2 .室內(nèi)設(shè)計(jì) 8 .計(jì)算機(jī)輔助設(shè)計(jì)
3 .公路設(shè)計(jì) 9 .供暖系統(tǒng)設(shè)計(jì)
4 .景觀設(shè)計(jì) 10 .機(jī)械設(shè)計(jì)
5 .建筑設(shè)計(jì) 11 .工程設(shè)計(jì)
6 .船舶設(shè)計(jì) 12 .工藝設(shè)計(jì)
事實(shí)上有一個(gè)無休止一些，因?yàn)槲覀兛梢园言O(shè)計(jì)的特定物品或產(chǎn)品或根據(jù)專業(yè)領(lǐng)域。
相反，科學(xué)或數(shù)學(xué)問題，設(shè)計(jì)獨(dú)特的問題沒有答案，這是荒謬的，例如，要求“正確答案”的設(shè)計(jì)問題，因?yàn)闆]有人反對。事實(shí)上是一個(gè)“良好”的回答今天很可能成為一種“窮人”的答案明天，如果有一個(gè)增長知識，或在此期間如果有其他結(jié)構(gòu)或社會的變化。
幾乎每個(gè)人都參與了設(shè)計(jì)一種或另一種方式，即使在日常生活中，由于提出的問題和情況時(shí)，必須予以解決?？紤]設(shè)計(jì)一個(gè)家庭度假?？赡苡?個(gè)不同的地方去，所有不同的距離回家。運(yùn)輸費(fèi)用的不同，每一個(gè)，而有些選項(xiàng)需要通宵站的道路上。孩子們要到一個(gè)湖泊或海邊度假勝地。妻子寧愿去大城市的百貨商店購物，劇院，和夜總會。丈夫喜歡度假的一個(gè)高爾夫球場。當(dāng)這些需要和愿望是與時(shí)間和金錢，各種解決方案，可能會發(fā)現(xiàn)。這些有可能是也可能不是一個(gè)或多個(gè)最優(yōu)解。但是，該解決方案將包括選擇旅行路線，站，運(yùn)輸方式，以及姓名和地點(diǎn)度假村，汽車旅館，露營地，或其他以外，來自家庭的設(shè)施。這是很難看到，確實(shí)是一個(gè)相當(dāng)大組相互關(guān)聯(lián)的復(fù)雜因素，在達(dá)成一個(gè)解決辦法，度假設(shè)計(jì)問題。
外觀設(shè)計(jì)一直受到某些解決問題的制約。例如，有兩個(gè)制約因素的度假設(shè)計(jì)問題是時(shí)間和金錢用于度假。請注意，也也有限制的解決方案，如果上述的一些制約因素的愿望和需要，每個(gè)家庭成員。最后，設(shè)計(jì)解決方案，發(fā)現(xiàn)很可能是最佳的。在這種情況下，一個(gè)最佳的解決方案時(shí)，得到的每一個(gè)家庭成員可以說，他或她的好時(shí)機(jī)。
設(shè)計(jì)的問題不是一個(gè)假設(shè)的問題。設(shè)計(jì)有一個(gè)真實(shí)的目的，建立一個(gè)最終的結(jié)果，采取一定的代理或建立了具有物理現(xiàn)實(shí)。在工程中的“設(shè)計(jì)” ，傳達(dá)不同的意義，不同的人。有些人認(rèn)為的是誰設(shè)計(jì)的圖板采用草案的細(xì)節(jié)，齒輪，離合器，或其他機(jī)器的成員。其他人認(rèn)為的設(shè)計(jì)，建立一個(gè)復(fù)雜的系統(tǒng)，如通信網(wǎng)絡(luò)。在一些地區(qū)的工程設(shè)計(jì)一詞取代了其他條款，如系統(tǒng)工程或?qū)嵤Q策理論。但不管用什么詞來描述設(shè)計(jì)的功能，在工程中仍然是這一進(jìn)程中，科學(xué)的原則和工具的工程，數(shù)學(xué)，計(jì)算機(jī)，圖形和英文，是用于生產(chǎn)的計(jì)劃，當(dāng)進(jìn)行出，將滿足人類的需要。
2. 各階段的設(shè)計(jì)
????? 總的設(shè)計(jì)過程是對我們的利益，它是如何開始的？是否工程師只是坐下來他或她的辦公桌，一張空白的紙張，并記下一些想法？接下來該怎么做？什么因素影響或控制的決定，必須做的？最后，請問這個(gè)設(shè)計(jì)過程結(jié)束？
????? 全過程，從開始到結(jié)束，往往是在圖概述。 2-2-1 。這一進(jìn)程始于承認(rèn)需要和一項(xiàng)決定，做些事，經(jīng)過多次反復(fù)，這一進(jìn)程結(jié)束時(shí)提出的計(jì)劃，為滿足需要，我們應(yīng)該研究這些措施在設(shè)計(jì)過程中的細(xì)節(jié)。
3. 機(jī)械工程設(shè)計(jì)
機(jī)械設(shè)計(jì)手段設(shè)計(jì)的東西，系統(tǒng)的機(jī)械性質(zhì)的機(jī)器，產(chǎn)品，結(jié)構(gòu)，設(shè)備和儀器。在大多數(shù)情況下，機(jī)械設(shè)計(jì)采用數(shù)學(xué)，材料科學(xué)和工程機(jī)械的科學(xué)。
機(jī)械工程設(shè)計(jì)包括所有機(jī)械設(shè)計(jì)，但它是一個(gè)更廣泛的研究，因?yàn)樗怂械膶W(xué)科機(jī)械工程，如熱流體科學(xué)，也。除了基本的科學(xué)所需要的，首先研究了機(jī)械工程設(shè)計(jì)中的機(jī)械設(shè)計(jì)，因此這是在這本書采取的辦法。
4. 設(shè)計(jì)過程和階段
機(jī)械設(shè)計(jì)或是制訂所有工程計(jì)劃的滿意度為指定的需要或解決工程問題。這是廣大工程技術(shù)領(lǐng)域，不僅關(guān)注自己的原始構(gòu)想的產(chǎn)品而言，其大小，形狀和建筑細(xì)節(jié)，但認(rèn)為所有的各種因素參與生產(chǎn)，銷售和使用的產(chǎn)品。機(jī)械設(shè)計(jì)涉及一系列學(xué)科的材料，力學(xué)，熱，流動，控制，電子產(chǎn)品和生產(chǎn)。
????? 機(jī)械設(shè)計(jì)應(yīng)被視為一個(gè)機(jī)會，利用創(chuàng)新人才設(shè)想設(shè)計(jì)的產(chǎn)品，分析系統(tǒng)，然后作出正確的判斷上的產(chǎn)品是如何被制造。重要的是理解的基礎(chǔ)工程，而不是單純的事實(shí)，并背誦方程。沒有任何事實(shí)或方程僅可用于提供所有正確的決定，須出示了良好的設(shè)計(jì)。另一方面，任何的計(jì)算必須做極其謹(jǐn)慎和精確度。例如，如果一個(gè)小數(shù)點(diǎn)是正確的，可接受的設(shè)計(jì)，否則可能無法正常運(yùn)行。
????? 機(jī)械設(shè)計(jì)可能是簡單的或極為復(fù)雜的，容易或困難，數(shù)學(xué)或非數(shù)學(xué)，它可能涉及瑣碎問題或一個(gè)非常重要的。良好的設(shè)計(jì)是有秩序的和有趣的安排，所有的想法，提供一定的成果和影響。一個(gè)設(shè)計(jì)良好的產(chǎn)品是功能性，高效和可靠。這種產(chǎn)品是低于類似的設(shè)計(jì)不良的產(chǎn)品，這并不正常，而且必須不斷地進(jìn)行修復(fù)。
???? ?人誰履行各項(xiàng)職能的機(jī)械設(shè)計(jì)通常要求設(shè)計(jì)人員，或設(shè)計(jì)工程師。機(jī)械設(shè)計(jì)基本上是一種創(chuàng)造性活動。然而，除了創(chuàng)新，設(shè)計(jì)工程師也必須有一個(gè)堅(jiān)實(shí)的背景領(lǐng)域的機(jī)械制圖，運(yùn)動學(xué)，動力學(xué)，材料工程，制造過程。設(shè)計(jì)者必須首先仔細(xì)界定問題，使用的是工程的辦法，以確保任何擬議的解決方案將解決問題的權(quán)利。重要的是，設(shè)計(jì)師首先確定到底他或她將認(rèn)識到一個(gè)令人滿意的替代，以及如何區(qū)分兩個(gè)令人滿意的替代品，以確定更好。因此，工業(yè)設(shè)計(jì)師必須具有創(chuàng)造性的想象力，知識工程，生產(chǎn)技術(shù)，工具，機(jī)器和材料，設(shè)計(jì)新產(chǎn)品的制造，或改善現(xiàn)有的產(chǎn)品。
在現(xiàn)代工業(yè)化世界的財(cái)富和生活水準(zhǔn)的一個(gè)國家是緊密聯(lián)系在一起的，他們的能力設(shè)計(jì)和制造工程產(chǎn)品?？梢哉f，提高機(jī)械設(shè)計(jì)和制造能顯著促進(jìn)整體水平的一個(gè)國家的工業(yè)化。許多國家正在發(fā)揮越來越重要的作用在全球制造業(yè)。為了加快這樣一個(gè)工業(yè)化進(jìn)程，高度熟練的設(shè)計(jì)工程師具有廣泛的知識和經(jīng)驗(yàn)是必要的。
5. 機(jī)械設(shè)計(jì)過程
產(chǎn)品設(shè)計(jì)需要大量的研究和開發(fā)。許多概念，一個(gè)想法必須加以研究，嘗試，完善，然后使用或丟棄。雖然每一工程問題是獨(dú)特的，設(shè)計(jì)師按照類似的過程來解決問題。全過程往往是概括的數(shù)字。設(shè)計(jì)過程中通常始于規(guī)格的解決方案。我們有時(shí)提到了設(shè)計(jì)周期，但是這個(gè)過程可能包含設(shè)計(jì)周期以及設(shè)計(jì)實(shí)施，它涉及到實(shí)際生產(chǎn)為基礎(chǔ)的設(shè)計(jì)。設(shè)計(jì)周期可能涉及的原始想法，草圖，和知識，在生產(chǎn)階段的規(guī)格工程圖紙。計(jì)算機(jī)輔助設(shè)計(jì)現(xiàn)在雇用實(shí)施周期中，各種設(shè)計(jì)或設(shè)計(jì)思想可能是測試或模擬。
6. 機(jī)械設(shè)計(jì)的內(nèi)容
???? 機(jī)械設(shè)計(jì)是一項(xiàng)重要的技術(shù)基礎(chǔ)課程在機(jī)械工程教育。其目標(biāo)是提供的概念，程序，數(shù)據(jù)和決策分析技術(shù)，必要的機(jī)械零件設(shè)計(jì)中常見的機(jī)械設(shè)備和系統(tǒng);發(fā)展工科大學(xué)生能力的機(jī)械設(shè)計(jì)，這是首要關(guān)注的機(jī)械制造業(yè)的關(guān)鍵生產(chǎn)好的產(chǎn)品。
機(jī)械設(shè)計(jì)包括以下內(nèi)容：
1. 提供并介紹了設(shè)計(jì)過程中，問題的制定，安全的因素。
2. 分析材料的特性、靜態(tài)和動態(tài)加載，包括梁，振動和沖擊載荷。
3. 敘述基本面的壓力和叛逃分析。
4. 闡明靜態(tài)失敗理論和斷裂力學(xué)分析，靜載。
5. 敘述疲勞失效理論，重點(diǎn)放在強(qiáng)調(diào)與生活的方法高周疲勞設(shè)計(jì)，這是常用的設(shè)計(jì)，旋轉(zhuǎn)機(jī)械。
6. 論述徹底的現(xiàn)象磨損機(jī)制，表面接觸應(yīng)力，表面疲勞。
7. 調(diào)查軸的設(shè)計(jì)使用疲勞分析技術(shù)。
8. 討論流體電影和滾動元件軸承理論及應(yīng)用。
9. 闡述徹底簡介運(yùn)動學(xué)，設(shè)計(jì)和應(yīng)力分析的齒輪，和一個(gè)簡單的介紹了螺旋，錐和蝸桿傳動。
10. 討論螺旋彈簧設(shè)計(jì)包括壓縮，擴(kuò)展，并扭轉(zhuǎn)彈簧。
11. 解決螺絲和緊固件包括電力螺絲和預(yù)緊固件。
12. 闡明設(shè)計(jì)和規(guī)格的磁盤和鼓離合器和制動器。