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.機械設計概況 當我們在第 1 章討論工程師,科學家和數學家之間不同的時候，我們看到工程學這個涉及到創(chuàng)意和設計兩方面內容。創(chuàng)意設計是機械工程專業(yè)的核心, 而一名工程師的終極目標是產生新的硬件來解決一個社會的技術性問題. 開始,無論是從一張空白的紙或從現(xiàn)有正在被改進的硬件, 產品開發(fā)過程中,往往構成一個工程師活動的中心。 按照自己的專業(yè)課題,很多工程師,確實是很聰明的, 他們具有遠見和技能能夠做出持久的貢獻,正如在 1.3 部分前十段所描述的。為了有一個很好的一個新的或改良的產品，正規(guī)工程教育不是一個前提,你有所感興趣的是學習機械工程專業(yè)，實際上為了建設硬件設施可能已經引發(fā)了你自己的想法。機械工程系由機器零件及工具、結構力和流體力、材料和應力、熱能和能源系統(tǒng)和機器的運動形式這些基本要素組成，我們已經研究了這一點，打算以此建立一個基礎，使你向一個更有效及更系統(tǒng)的方式向機械設計接近。在這方面，該辦法采取的這本教科書是一個濃縮的模擬傳統(tǒng)的工程學課程：逼近、數學和科學領域的應用設計問題,以提高性能和減少實驗誤差。通過應用的資料，你可以選擇一些機器零件和用輔助設計決策計算出來的結果進行反推演示。這種分析不是為了他們自己，而是，使您的設計更快更好。有效的機械設計是一個廣闊的領域，創(chuàng)造性和技術工藝落后不能完全的放在同一章里,甚至是同一本教科書。事實上以此材料作為起點，你們應該在你們的整個職業(yè)生涯中繼續(xù)發(fā)展你們的第一手經驗和設計技巧，甚至是在最恰當的時候抓住機遇，把一種造構想轉變成制造的硬件，以合理的成本出售。經過第一層次的討論步驟，當工程師他們把一個新的構想變?yōu)楝F(xiàn)實的時候，我們探討的機械設計題目通過概念設計、計算機輔助設計、詳細的機械設計，三種情況來學習。我們還將討論機械設計從商業(yè)的角度闡述了如何保護專利新技術的發(fā)展。在完成這一章，你應當能夠做到：●大綱的主要步驟和迭代點的高層次的機械設計流程●舉一個過程的例子，集思廣益，找出各種設計方案的優(yōu)勢和劣勢?！窳私庥嬎銠C輔助工程工具在機械設計中所扮演的角色，描述如何對這些工具可以無縫相互融合?！裢ㄟ^使用草圖來說明汽車自動變速器的運行情況，一個復雜的機械設計包括機械、電子、計算機與液壓元件?！窠忉屖裁词菍＠?，并討論了它們對工程的營商環(huán)境的重要性。 高層次的程序設計在這一節(jié)中，我們概述工程師他們開發(fā)新產品和硬件的步驟。從最廣泛的角度來看，設計的定義是：制定一套機械系統(tǒng)，來滿足社會某一技術的具體需要的系統(tǒng)過程，動機可以為所在地區(qū)的交通，通訊和安全問題為例。預期的產品可望很好地解決某一問題，或提供一個新的能力，那其它方面將付出代價。早期發(fā)現(xiàn)，一家公司的營銷部將與工程師和管理人員一起合作，在一般的意義上講，新的產品機遇。他們通過吸取潛在客戶和相關產品的用戶反饋回來的意見共同確定新產品的概念。設計師將隨后制定方案，詳細的工作，并把操作過程變?yōu)楝F(xiàn)實。許多近似，權衡,并正在作出選擇半路，及機械工程師都知道精確度是需要自然地逐漸成長當設計成熟時。比如，這是沒有道理的工程師來解決具體細節(jié)（是使用甲級 20 號合金鋼條還是使用 45 號合金鋼條？球軸承和滾子軸承哪一個最合適？為什么石油必須要有一定的粘度？）直到設計的整體概念已經滿足了堅定的形狀。畢竟，在早期階段的設計周期，規(guī)格，產品的大小，重量，電力工業(yè) 或表現(xiàn)仍然可以改變。設計工程師所熟悉的這種含糊不清，他們能夠自由地開發(fā)產品，甚至當著規(guī)定和限制，這是不會改變的。通過營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。 大多數工程師都認為創(chuàng)意，操作簡便，迭代是任何成功的奮斗關鍵因素。創(chuàng)新首先是個好主意，但也意味著從頭開始。盡管如此，工程師仍然必須采取第一步是把構想變成具體的現(xiàn)實，也許不明朗。 早期設計決定是由吸取各種來源：個人的經驗，數學和科學知識，實驗室和田間試驗，和在錯誤的引導下做出正確的判斷。一般而言，簡單的設計理念是較復雜的，而格言：“保持簡單，簡約” 在工程師之間有當之無愧的聲譽為指導決定。迭代也是重要對改進設計和完善硬件工程分為硬件行之有效。你有的第一個想法，就像你建構的第一原型，大概不會是最好的，但是它卻可以實現(xiàn)。隨著每回合逐步完善，設計將會做的更好，更有效率，更加優(yōu)雅。從宏觀角度來看,機械設計過程可分成四個主要的步驟, 其中列有詳細數字。1．定義和研究目標。起初，設計師介紹了新產品在它自己的功能范圍內的要求，如重量，強度，成本，安全性，可靠性等等。在第一階段，設計必須滿足的限制因素也被確立。這些因素可能是技術性的，比方說，限制尺寸大小或功耗。另外，限制因素可能涉及到企業(yè)或市場關切的問題，如產品的外觀，成本或便于使用性。當面臨著新的技術挑戰(zhàn)，工程師會進行研究并搜集預計有用的背景資料，當概念和細節(jié)被做出事后評價。工程師看已發(fā)出的相關技術的專利，征求供應商的部件或子系統(tǒng)中可能會使用的產品，參加博覽會及商展，并與潛在客戶更好地理解應用。早在設計過程中，工程師的界定問題，確定目標，并收集相關資料設計奠定了良好的基礎。2．產生的概念。在這個階段，設計師一般的工作團隊的目標是制定出一個廣泛的潛力來解決目前問題。這一創(chuàng)造性的工作涉及構思一些新的思路，結合以往要遠遠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。結果討論性會議被系統(tǒng)地記錄下來，利弊不同的解決辦法，和取舍之間的不同做法。文件上多數的構想來源于這種形式的合成階段，工程師概述觀念，作筆記，并準備清單“利弊“ 在他們的設計筆記中，沒有特別的想法是深入評估，也沒有看的想法太重要了一只眼睛。相反，你應集中編目采取多種辦法，并擬訂了一個豐富的設計理念， 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早期階段， 應當要使產品的要求或限制改變未來 (哪一個更可能)，實際上想法可能死灰復燃成為領先的競爭者。3．縮小選擇。設計團隊進一步評價觀念，以期減少對他們充滿數。舉例來說，工程師進行初步的測算比較，強度，安全性，成本和可靠性，他們將要開始摒棄那些不太可行的概念。采樣硬件，也可以產生在這個階段。就像一幅畫勝過千言萬語，物理原型往往是有益的工程師想象復雜的機械部件，并解釋其裝配等。原型也可以被測試，以便取舍決定是基于結果的測量和分析。一種方法用于生產這種部件稱為快速原型技術，其關鍵能力是復雜性，三維技術可以直接由電腦產生的繪圖制作，往往在短短的幾小時內完成。其中這種技術稱為熔融沉積造型，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，描繪了計算機輔助設計繪制了發(fā)動機缸體和實物樣機研制與顯示系統(tǒng)在中。4．制定一個詳細的設計。為了達到這一點的高級別規(guī)則，設計小組將集思廣益，測試，分析，兌換的方式來察覺出什么是最佳概念。實施的設計，建造一個最終原型，和開發(fā)余下的生產過程。通過應用數學，科學，實驗，計算機輔助工程工具，詳細的技術問題已經被解決了。完成圖紙和零部件清單的準備。 設計師進行工程分析和實驗，以驗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。設計文件是通過工程圖紙和書面報告來表現(xiàn)，以便能夠理解設計師做出許多決定背后的每個原因。這些文件也可用于未來的設計小組。的學習和借鑒本隊經驗.從最根本上說，最后的設計必須在其所有的要求和限制范圍內。你可能會認為，一旦工作樣機已經交付或后整理觸及已應用于圖紙，工程師的任務就被完成。然而，今天的機械工程師工作在一個廣闊的環(huán)境里，就其硬件來看，用一種超出標準和批判的眼光來看硬件的功能是否如預想的一樣。一個產品獲得成功，它必須能安全地使用，質量可靠，他的使用和處置要無害環(huán)境，并承擔制造。 然而，如果該產品在技術上是高超的，則它需要昂貴的材料和制造工藝，顧客可避免生產，并選擇一種更平衡成本和性能的產品，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。