附錄２Mechanical DesignOVERVIEW While discussing the differences among engineers, scientists, and mathematicians in Chapter 1, we saw that the word engineering is related to both ingenious and devise .Creative design lies at the center of the mechanical engineering profession, and an engineer’s ultimate goal is to produce new hardware that solves one of society’s technical problems. Beginning either from a blank sheet of paper or from existing hardware that is being modified, the product development process often forms the focus of an engineer’s activities. In keeping with their profession’s title, many engineers truly are ingenious, and they possess the vision and skill to make such lasting contributions as those described in the top ten list of Section 1.3Formal education in engineering is not a prerequisite to having a good for a new or improved product. Your interest in studying mechanical engineering, in fact, may have been sparked by your own ideas for building hardware. The elements of mechanical engineering that we have examined up to this point-machine components and tools, forces in structures and fluids, materials and stresses, thermal and energy systems, and the motion of machinery-are intended to have set a foundation that will enable you to approach mechanical design in a more effective and systematic manner .IN that respect, approach the taken in this textbook is a condensed analog of the traditional engineering curriculum: Approximation, mathematics, and science are applied to design problems in order to increase performance and reduce trial and error. By applying the resources of Chapter2-7, you can select certain machine components and perform back-of-the-envelope calculation to guide design decisions. Such analyses are not made for their sake alone; rather, they enable you to design better and fast.Effective mechanical design is a broad area, and the creative and technical processes behind it cannot be set forth fully in one chapter-or even one textbook for that matter. Indeed, with this material as a starting point, you should continue to develop hands-on experience and design skills throughout your entire professional career. Even the most seasoned grapples with the procedure for transforming an idea into manufactured hardware that can be sold at a reasonable cost.After first discussing the hierarchy of steps that engineers take when they transform a new idea into reality, we explore the subject of mechanical design through three case studies in the fields of conceptual design, computer-aided design, and detailed machine design. We will also discuss mechanical design from a business perspective and describe how patents protect newly developed technology. After completing this chapter, you should be able to:● Outline the major steps and iteration in points in the high-level mechanical design procedure.● Give an example of the processes for brainstorming and for identifying the advantages and disadvantages of various design options● Understand the role played by computer-aided engineering tools in mechanical design, and describe how such tools can be seamlessly integrated with one another.● By using a sketch as a guide, describe the operation of an automobile automatic transmission, a complex machine design that incorporates mechanical, electronic, computer, and hydraulic components.● Explain what patents are, and discuss their importance to engineering’s business environmentHIGH-LEVEL DESIGN PEOCEDUREIn this section, we outline the steps that engineers take when they develop new products and hardware. From the broadest viewpoint, design is defined as the systematic process for devising a mechanical system to meet one of society’s technical needs. The specific motivation could lie in the areas of transportation, communication, or security, for instance. The prospective product is expected to solve a particular problem so well, or offer such a new capability, that other will pay for it. Early on, a company’s marketing department will collaborate with engineers and managers to identify, in a general sense, new opportunities for products. Together, they define the new product’s concept by drawing upon feedback from potential customers and from user of related product. Designers will subsequently develop those concepts, work out the details, and bring the functioning hardware to realization. Many approximations, trade-offs, and choices are made along the way, and mechanical engineers are mindful that the level of precision that is need will naturally and gradually grow as the design matures. For instance, it does not make sense for an engineer to resolve specific details (should a grade 1020 or 1045 steel alloy be used? Are ball or roller bearings most appropriate? What must be the viscosity of the oil?) until the design＇s overall concept has taken firm shape. After all, at an early stage of the design cycle, the specifications for the product’s size, weight, power, or performance could still change. Design engineers are comfortable with such ambiguity, and they are able to develop product even in the presence of requirements and constraints that can change.The formal procedure by which a marketing concept evolves into manufactured hardware is based upon many principles and attributes. Most engineers would probably agree that creativity, simplicity, and iteration are key factors in any successful endeavor. Innovation begins with a good idea, but also implies starting from a blank sheet of paper. Nevertheless, engineers must still take the first, perhaps uncertain, step for transforming that formative idea into concrete reality. Early design decisions are made by drawing upon a variety of source: personal experience, knowledge of mathematics and science, laboratory and field testing, and trial and error guided by good judgment. Generally speaking, simpler design concepts are better than complex ones, and the adage “keep it simple, stupid” has a well-deserved reputation among engineers for guiding decisions. Iteration is also important for improving a design and for refining hardware that works into hardware that works well. The first idea that you have, just like the first prototype that you construct, will probably not be the best ones that can be realized. With the gradual improvement of each iteration, however, the design will perform better, more efficiently, and more elegantly.From a macroscopic perspective, the mechanical design procedure can be broken down into four major steps, which are outlined with greater detail in Figure 8.1.1. Define and research objectives. Initially, a designer describes the new product’s requirements in terms of its function, weight, strength, cost, safety, reliability, and so forth. At this first stage, constraints that the design must satisfy are also established. Those constraints might be of a technical nature-say, a restriction on size or power consumption. Alternatively, the constraints could be related to business or marketing concerns, such as the product’s appearance, cost, or ease of use. When faced with a new technical challenge, engineers will conduct research and gather background information that is expected to be useful when concepts and details are later evaluated. Engineers read patents that have been issued for related technologies, consult with vendors of components or subsystems that might be used in the product, attend expositions and trade shows, and meet with potential customers to better understand the application. Early in the design process, engineers define the problem, set the objective, and gather pertinent information for the foundation of a good design.2. Generate concepts.In this stage, designers generally work in teams with the goal of devising a wide range of potential solutions to the problem at hand. This creative effort involves conceiving new ideas and combining previous ones to be greater than the sum of their parts. Hardware solutions are conceptualized and composed, and both good and not-so-good ideas are tossed about. Results from the brainstorming sessions are systematically recorded, the advantages and disadvantages of various solutions are identified, and trade-offs among the differing approaches are made. To document the suite of ideas that emerges from this synthesis stage, engineers sketch concepts, make notes, and prepare lists of “pros and cons” in their design notebooks. No particular idea is evaluated in depth, nor is any idea viewed with too critical an eye. Instead, you should focus on cataloging multiple approaches and devising a wide rang of design concepts, not necessarily all conventional ones. Even though a particular solution might not seem feasible at this early stage, should the product’s requirements or constraints change in the future (which is likely), the idea might in fact resurface as a leading contender.3. Narrow down the options. The design team further evaluates the concepts with a view toward reducing them to a promising few. For instance, engineers make preliminary calculations to compare strength, safety, cost, and reliability, and they will begin to discard the less feasible concepts. Sample hardware could also be produced at this stage. Just as a picture is worth a thousand words, a physical prototype is often useful for engineers to visualize complex machine components and to explain their assembly to others. The prototype can also be tested so that trade-off decisions are made based on the results of both measurements and analyses. One method for producing such components is called rapid prototyping, and its key capability is that complex, three-dimensional can be fabricated directly from a computer-generated drawing often in a matter of hours. One such technology is called fused deposition modeling, and it enables durables durable and fully functional prototypes to be fabricated from plastics and polycarbonates. As an example, Figure 8.2 depicts a computer-aided design drawing of an engine block and a physical prototype developed with the system show in Figure 8.34. Develop a detailed design. To reach this point of the high-level procedure, the design team will have brainstormed, tested, analyzed, and converged its way to what it perceives as the best concept. The implementation of the design, construction of a final prototype, and development of the manufacturing process each remain. Detailed technical issues are solved by applying mathematical, scientific, laboratory, and computer-aided engineering tools. Completed drawings and parts lists are prepared. The designers conduct engineering analysis and experiments to verify performance over a range of operating conditions. If necessary, changes to shape, dimensions, materials, and components will be made until all requirements and constraints are met. The design is documented through engineering drawings and written reports so that able to understand the reasons behind each of the many decisions that the designers made. Such documentation is also useful for future design teams to teams to learn from and build upon the present team’s experiences.At the most fundamental level, the final design must all of its requirements and constraints. You might thing that an engineer’s tasks are completed once the working prototype has been delivered or after the finishing touches have been applied to the drawings. However, mechanical engineers today work in a broader environment, and their hardware is viewed with a critical eye beyond the criterion of whether or not it functions as intended. For a product be successful, it must also be safe to use, reliable, environmentally sound in its use and disposal, and affordable to manufacture. After all, if the product is technically superb but it requires expensive materials and manufacturing operations, customers may avoid the product and select one that is more balanced in cost and performance. In the end, engineering is a business venture that must meet the needs of its customers.機(jī)械設(shè)計(jì)概況 當(dāng)我們?cè)诘?1 章討論工程師,科學(xué)家和數(shù)學(xué)家之間不同的時(shí)候，我們看到工程學(xué)這個(gè)涉及到創(chuàng)意和設(shè)計(jì)兩方面內(nèi)容。創(chuàng)意設(shè)計(jì)是機(jī)械工程專業(yè)的核心, 而一名工程師的終極目標(biāo)是產(chǎn)生新的硬件來(lái)解決一個(gè)社會(huì)的技術(shù)性問(wèn)題. 開(kāi)始,無(wú)論是從一張空白的紙或從現(xiàn)有正在被改進(jìn)的硬件, 產(chǎn)品開(kāi)發(fā)過(guò)程中,往往構(gòu)成一個(gè)工程師活動(dòng)的中心。 按照自己的專業(yè)課題,很多工程師,確實(shí)是很聰明的, 他們具有遠(yuǎn)見(jiàn)和技能能夠做出持久的貢獻(xiàn),正如在 1.3 部分前十段所描述的。為了有一個(gè)很好的一個(gè)新的或改良的產(chǎn)品，正規(guī)工程教育不是一個(gè)前提,你有所感興趣的是學(xué)習(xí)機(jī)械工程專業(yè)，實(shí)際上為了建設(shè)硬件設(shè)施可能已經(jīng)引發(fā)了你自己的想法。機(jī)械工程系由機(jī)器零件及工具、結(jié)構(gòu)力和流體力、材料和應(yīng)力、熱能和能源系統(tǒng)和機(jī)器的運(yùn)動(dòng)形式這些基本要素組成，我們已經(jīng)研究了這一點(diǎn)，打算以此建立一個(gè)基礎(chǔ)，使你向一個(gè)更有效及更系統(tǒng)的方式向機(jī)械設(shè)計(jì)接近。在這方面，該辦法采取的這本教科書是一個(gè)濃縮的模擬傳統(tǒng)的工程學(xué)課程：逼近、數(shù)學(xué)和科學(xué)領(lǐng)域的應(yīng)用設(shè)計(jì)問(wèn)題,以提高性能和減少實(shí)驗(yàn)誤差。通過(guò)應(yīng)用的資料，你可以選擇一些機(jī)器零件和用輔助設(shè)計(jì)決策計(jì)算出來(lái)的結(jié)果進(jìn)行反推演示。這種分析不是為了他們自己，而是，使您的設(shè)計(jì)更快更好。有效的機(jī)械設(shè)計(jì)是一個(gè)廣闊的領(lǐng)域，創(chuàng)造性和技術(shù)工藝落后不能完全的放在同一章里,甚至是同一本教科書。事實(shí)上以此材料作為起點(diǎn)，你們應(yīng)該在你們的整個(gè)職業(yè)生涯中繼續(xù)發(fā)展你們的第一手經(jīng)驗(yàn)和設(shè)計(jì)技巧，甚至是在最恰當(dāng)?shù)臅r(shí)候抓住機(jī)遇，把一種造構(gòu)想轉(zhuǎn)變成制造的硬件，以合理的成本出售。經(jīng)過(guò)第一層次的討論步驟，當(dāng)工程師他們把一個(gè)新的構(gòu)想變?yōu)楝F(xiàn)實(shí)的時(shí)候，我們探討的機(jī)械設(shè)計(jì)題目通過(guò)概念設(shè)計(jì)、計(jì)算機(jī)輔助設(shè)計(jì)、詳細(xì)的機(jī)械設(shè)計(jì)，三種情況來(lái)學(xué)習(xí)。我們還將討論機(jī)械設(shè)計(jì)從商業(yè)的角度闡述了如何保護(hù)專利新技術(shù)的發(fā)展。在完成這一章，你應(yīng)當(dāng)能夠做到：●大綱的主要步驟和迭代點(diǎn)的高層次的機(jī)械設(shè)計(jì)流程●舉一個(gè)過(guò)程的例子，集思廣益，找出各種設(shè)計(jì)方案的優(yōu)勢(shì)和劣勢(shì)?！窳私庥?jì)算機(jī)輔助工程工具在機(jī)械設(shè)計(jì)中所扮演的角色，描述如何對(duì)這些工具可以無(wú)縫相互融合。●通過(guò)使用草圖來(lái)說(shuō)明汽車自動(dòng)變速器的運(yùn)行情況，一個(gè)復(fù)雜的機(jī)械設(shè)計(jì)包括機(jī)械、電子、計(jì)算機(jī)與液壓元件。●解釋什么是專利，并討論了它們對(duì)工程的營(yíng)商環(huán)境的重要性。 高層次的程序設(shè)計(jì)在這一節(jié)中，我們概述工程師他們開(kāi)發(fā)新產(chǎn)品和硬件的步驟。從最廣泛的角度來(lái)看，設(shè)計(jì)的定義是：制定一套機(jī)械系統(tǒng)，來(lái)滿足社會(huì)某一技術(shù)的具體需要的系統(tǒng)過(guò)程，動(dòng)機(jī)可以為所在地區(qū)的交通，通訊和安全問(wèn)題為例。預(yù)期的產(chǎn)品可望很好地解決某一問(wèn)題，或提供一個(gè)新的能力，那其它方面將付出代價(jià)。早期發(fā)現(xiàn)，一家公司的營(yíng)銷部將與工程師和管理人員一起合作，在一般的意義上講，新的產(chǎn)品機(jī)遇。他們通過(guò)吸取潛在客戶和相關(guān)產(chǎn)品的用戶反饋回來(lái)的意見(jiàn)共同確定新產(chǎn)品的概念。設(shè)計(jì)師將隨后制定方案，詳細(xì)的工作，并把操作過(guò)程變?yōu)楝F(xiàn)實(shí)。許多近似，權(quán)衡,并正在作出選擇半路，及機(jī)械工程師都知道精確度是需要自然地逐漸成長(zhǎng)當(dāng)設(shè)計(jì)成熟時(shí)。比如，這是沒(méi)有道理的工程師來(lái)解決具體細(xì)節(jié)（是使用甲級(jí) 20 號(hào)合金鋼條還是使用 45 號(hào)合金鋼條？球軸承和滾子軸承哪一個(gè)最合適？為什么石油必須要有一定的粘度？）直到設(shè)計(jì)的整體概念已經(jīng)滿足了堅(jiān)定的形狀。畢竟，在早期階段的設(shè)計(jì)周期，規(guī)格，產(chǎn)品的大小，重量，電力工業(yè) 或表現(xiàn)仍然可以改變。設(shè)計(jì)工程師所熟悉的這種含糊不清，他們能夠自由地開(kāi)發(fā)產(chǎn)品，甚至當(dāng)著規(guī)定和限制，這是不會(huì)改變的。通過(guò)營(yíng)銷觀念演變成制造的硬件的正式程序是基于許多原則和屬性。 大多數(shù)工程師都認(rèn)為創(chuàng)意，操作簡(jiǎn)便，迭代是任何成功的奮斗關(guān)鍵因素。創(chuàng)新首先是個(gè)好主意，但也意味著從頭開(kāi)始。盡管如此，工程師仍然必須采取第一步是把構(gòu)想變成具體的現(xiàn)實(shí)，也許不明朗。 早期設(shè)計(jì)決定是由吸取各種來(lái)源：個(gè)人的經(jīng)驗(yàn)，數(shù)學(xué)和科學(xué)知識(shí)，實(shí)驗(yàn)室和田間試驗(yàn)，和在錯(cuò)誤的引導(dǎo)下做出正確的判斷。一般而言，簡(jiǎn)單的設(shè)計(jì)理念是較復(fù)雜的，而格言：“保持簡(jiǎn)單，簡(jiǎn)約” 在工程師之間有當(dāng)之無(wú)愧的聲譽(yù)為指導(dǎo)決定。迭代也是重要對(duì)改進(jìn)設(shè)計(jì)和完善硬件工程分為硬件行之有效。你有的第一個(gè)想法，就像你建構(gòu)的第一原型，大概不會(huì)是最好的，但是它卻可以實(shí)現(xiàn)。隨著每回合逐步完善，設(shè)計(jì)將會(huì)做的更好，更有效率，更加優(yōu)雅。從宏觀角度來(lái)看,機(jī)械設(shè)計(jì)過(guò)程可分成四個(gè)主要的步驟, 其中列有詳細(xì)數(shù)字。1．定義和研究目標(biāo)。起初，設(shè)計(jì)師介紹了新產(chǎn)品在它自己的功能范圍內(nèi)的要求，如重量，強(qiáng)度，成本，安全性，可靠性等等。在第一階段，設(shè)計(jì)必須滿足的限制因素也被確立。這些因素可能是技術(shù)性的，比方說(shuō)，限制尺寸大小或功耗。另外，限制因素可能涉及到企業(yè)或市場(chǎng)關(guān)切的問(wèn)題，如產(chǎn)品的外觀，成本或便于使用性。當(dāng)面臨著新的技術(shù)挑戰(zhàn)，工程師會(huì)進(jìn)行研究并搜集預(yù)計(jì)有用的背景資料，當(dāng)概念和細(xì)節(jié)被做出事后評(píng)價(jià)。工程師看已發(fā)出的相關(guān)技術(shù)的專利，征求供應(yīng)商的部件或子系統(tǒng)中可能會(huì)使用的產(chǎn)品，參加博覽會(huì)及商展，并與潛在客戶更好地理解應(yīng)用。早在設(shè)計(jì)過(guò)程中，工程師的界定問(wèn)題，確定目標(biāo)，并收集相關(guān)資料設(shè)計(jì)奠定了良好的基礎(chǔ)。2．產(chǎn)生的概念。在這個(gè)階段，設(shè)計(jì)師一般的工作團(tuán)隊(duì)的目標(biāo)是制定出一個(gè)廣泛的潛力來(lái)解決目前問(wèn)題。這一創(chuàng)造性的工作涉及構(gòu)思一些新的思路，結(jié)合以往要遠(yuǎn)遠(yuǎn)大于各自部分的總和。硬件解決是概念化和組成，和好的和不那么好的想法被討論。結(jié)果討論性會(huì)議被系統(tǒng)地記錄下來(lái)，利弊不同的解決辦法，和取舍之間的不同做法。文件上多數(shù)的構(gòu)想來(lái)源于這種形式的合成階段，工程師概述觀念，作筆記，并準(zhǔn)備清單“利弊“ 在他們的設(shè)計(jì)筆記中，沒(méi)有特別的想法是深入評(píng)估，也沒(méi)有看的想法太重要了一只眼睛。相反，你應(yīng)集中編目采取多種辦法，并擬訂了一個(gè)豐富的設(shè)計(jì)理念， 不一定所有常規(guī)的。即使某種解決辦法可能不太可行在這個(gè)早期階段， 應(yīng)當(dāng)要使產(chǎn)品的要求或限制改變未來(lái) (哪一個(gè)更可能)，實(shí)際上想法可能死灰復(fù)燃成為領(lǐng)先的競(jìng)爭(zhēng)者。3．縮小選擇。設(shè)計(jì)團(tuán)隊(duì)進(jìn)一步評(píng)價(jià)觀念，以期減少對(duì)他們充滿數(shù)。舉例來(lái)說(shuō)，工程師進(jìn)行初步的測(cè)算比較，強(qiáng)度，安全性，成本和可靠性，他們將要開(kāi)始摒棄那些不太可行的概念。采樣硬件，也可以產(chǎn)生在這個(gè)階段。就像一幅畫勝過(guò)千言萬(wàn)語(yǔ)，物理原型往往是有益的工程師想象復(fù)雜的機(jī)械部件，并解釋其裝配等。原型也可以被測(cè)試，以便取舍決定是基于結(jié)果的測(cè)量和分析。一種方法用于生產(chǎn)這種部件稱為快速原型技術(shù)，其關(guān)鍵能力是復(fù)雜性，三維技術(shù)可以直接由電腦產(chǎn)生的繪圖制作，往往在短短的幾小時(shí)內(nèi)完成。其中這種技術(shù)稱為熔融沉積造型，它使持久耐用功能齊全的原型將裝配形式塑料和聚碳酸酯。例如，描繪了計(jì)算機(jī)輔助設(shè)計(jì)繪制了發(fā)動(dòng)機(jī)缸體和實(shí)物樣機(jī)研制與顯示系統(tǒng)在中。4．制定一個(gè)詳細(xì)的設(shè)計(jì)。為了達(dá)到這一點(diǎn)的高級(jí)別規(guī)則，設(shè)計(jì)小組將集思廣益，測(cè)試，分析，兌換的方式來(lái)察覺(jué)出什么是最佳概念。實(shí)施的設(shè)計(jì)，建造一個(gè)最終原型，和開(kāi)發(fā)余下的生產(chǎn)過(guò)程。通過(guò)應(yīng)用數(shù)學(xué)，科學(xué)，實(shí)驗(yàn)，計(jì)算機(jī)輔助工程工具，詳細(xì)的技術(shù)問(wèn)題已經(jīng)被解決了。完成圖紙和零部件清單的準(zhǔn)備。 設(shè)計(jì)師進(jìn)行工程分析和實(shí)驗(yàn)，以驗(yàn)證性能的一系列操作條件。如有必要，改變形狀，尺寸，材料和部件，直到所有條件和制約因素得到滿足。設(shè)計(jì)文件是通過(guò)工程圖紙和書面報(bào)告來(lái)表現(xiàn)，以便能夠理解設(shè)計(jì)師做出許多決定背后的每個(gè)原因。這些文件也可用于未來(lái)的設(shè)計(jì)小組。的學(xué)習(xí)和借鑒本隊(duì)經(jīng)驗(yàn).從最根本上說(shuō)，最后的設(shè)計(jì)必須在其所有的要求和限制范圍內(nèi)。你可能會(huì)認(rèn)為，一旦工作樣機(jī)已經(jīng)交付或后整理觸及已應(yīng)用于圖紙，工程師的任務(wù)就被完成。然而，今天的機(jī)械工程師工作在一個(gè)廣闊的環(huán)境里，就其硬件來(lái)看，用一種超出標(biāo)準(zhǔn)和批判的眼光來(lái)看硬件的功能是否如預(yù)想的一樣。一個(gè)產(chǎn)品獲得成功，它必須能安全地使用，質(zhì)量可靠，他的使用和處置要無(wú)害環(huán)境，并承擔(dān)制造。 然而，如果該產(chǎn)品在技術(shù)上是高超的，則它需要昂貴的材料和制造工藝，顧客可避免生產(chǎn)，并選擇一種更平衡成本和性能的產(chǎn)品，到最后,工程公司是一家商業(yè)企業(yè)，必須滿足客戶的需要。