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1、 1 Fundamentals of Mechanical Design Mechanical design means the design of things and systems of a mechanical naturemachines, products, structures, devices, and instruments. For the most part mechanical design utilizes mathematics, the materials sciences, and the engineering-mechanics sciences. The

2、total design process is of interest to us. How does it begin? Does the engineer simply sit down at his desk with a blank sheet of paper? And, as he jots down some ideas, what happens next? What factors influence or control the decisions which have to be made? Finally, then, how does this design proc

3、ess end? Sometimes, but not always, design begins when an engineer recognizes a need and decides to do something about it. Recognition of the need and phrasing it in so many words often constitute a highly creative act because the need may be only a vague discontent, a feeling of uneasiness, of a se

4、nsing that something is not right. The need is usually not evident at all. For example, the need to do something about a food-packaging machine may be indicated by the noise level, by the variations in package weight, and by slight but perceptible variations in the quality of the packaging or wrap.

5、There is a distinct difference between the statement of the need and the identification of the problem. Which follows this statement? The problem is more specific. If the need is for cleaner air, the problem might be that of reducing the dust discharge from power-plant stacks, or reducing the quanti

6、ty of irritants from automotive exhausts. Definition of the problem must include all the specifications for the thing that is to be designed. The specifications are the input and output quantities, the characteristics of the space the thing must occupy and all the limitations on these quantities. We

7、 can regard the thing to be designed as something in a black box. In this case we must specify the inputs and outputs of the box together with their characteristics and limitations. The specifications define the cost, the number to be manufactured, the expected life, the range, the operating tempera

8、ture, and the reliability. There are many implied specifications which result either from the designers particular environment or from the nature of the problem itself. The manufacturing processes which are available, together with the facilities of a certain plant, constitute restrictions on a desi

9、gners freedom, and hence are a part of the implied specifications. A small plant, for instance, may not own cold-working machinery. Knowing this, the designer selects other 2 metal-processing methods which can be performed in the plant. The labor skills available and the competitive situation also c

10、onstitute implied specifications. After the problem has been defined and a set of written and implied specifications has been obtained, the next step in design is the synthesis of an optimum solution. Now synthesis cannot take place without both analysis and optimization because the system under des

11、ign must be analyzed to determine whether the performance complies with the specifications. The design is an iterative process in which we proceed through several steps, evaluate the results, and then return to an earlier phase of the procedure. Thus we may synthesize several components of a system,

12、 analyze and optimize them, and return to synthesis to see what effect this has on the remaining parts of the system. Both analysis and optimization require that we construct or devise abstract models of the system which will admit some form of mathematical analysis. We call these models mathematica

13、l models. In creating them it is our hope that we can find one which will simulate the real physical system very well. Evaluation is a significant phase of the total design process. Evaluation is the final proof of a successful design, which usually involves the testing of a prototype in the laborat

14、ory. Here we wish to discover if the design really satisfies the need or needs. Is it reliable? Will it compete successfully with similar products? Is it economical to manufacture and to use? Is it easily maintained and adjusted? Can a profit be made from its sale or use? Communicating the design to

15、 others is the final, vital step in the design process. Undoubtedly many great designs, inventions, and creative works have been lost to mankind simply because the originators were unable or unwilling to explain their accomplishments to others. Presentation is a selling job. The engineer, when prese

16、nting a new solution to administrative, management, or supervisory persons, is attempting to sell or to prove to them that this solution is a better one. Unless this can be done successfully, the time and effort spent on obtaining the solution have been largely wasted. Basically, there are only thre

17、e means of communication available to us. There are the written, the oral, and the graphical forms. Therefore the successful engineer will be technically competent and versatile in all three forms of communication. A technically competent person who lacks ability in any one of these forms is severel

18、y handicapped. If ability in all three forms is lacking, no one will ever know how competent that person is! The competent engineer should not be afraid of the possibility of not succeeding in a presentation. In fact, occasional failure should be expected because failure or criticism seems 3 to acco

19、mpany every really creative idea. There is a great to be learned from a failure, and the greatest gains are obtained by those willing to risk defeat. In the find analysis, the real failure would lie in deciding not to make the presentation at all. Introduction to Machine Design Machine design is the

20、 application of science and technology to devise new or improved products for the purpose of satisfying human needs. It is a 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 also

21、considers the various factors involved in the manufacture, marketing and use of the product. People who perform the various functions of machine design are typically called designers, or design engineers. Machine design is basically a creative activity. However, in addition to being innovative, a de

22、sign engineer must also have a solid background in the areas of mechanical drawing, kinematics, dynamics, materials engineering, strength of materials and manufacturing processes. As stated previously, the purpose of machine design is to produce a product which will serve a need for man. Inventions,

23、 discoveries and scientific knowledge by themselves do not necessarily benefit people； only if they are incorporated into a designed product will a benefit be derived. It should be recognized, therefore, that a human need must be identified before a particular product is designed. Machine design sho

24、uld be considered to be an opportunity to use innovative talents to envision a design of a 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 al

25、l the correct decisions to produce a good design. On the other hand, any calculations made must be done with the utmost care and precision. For example, if a decimal point is misplaced, an otherwise acceptable design may not function. Good designs require trying new ideas and being willing to take a

26、 certain amount of risk, knowing that is the new idea does not work the existing method can be reinstated. Thus a designer must have patience, since there is no assurance of success for the time and effort expended. Creating a completely new design generally requires that many old and well-establish

27、ed methods be thrust aside. This is not easy since many people cling to familiar ideas, techniques and attitudes. A design engineer should constantly search for ways to 4 improve an existing product and must decide what old, proven concepts should be used and what new, untried ideas should be incorp

28、orated. New designs generally have “bugs” or unforeseen problems which must be worked out before the superior characteristics of the new designs can be enjoyed. Thus there is a chance for a superior product, but only at higher risk. It should be emphasized that if a design does not warrant radical n

29、ew methods, such methods should not be applied merely for the sake of change. During the beginning stages of design, creativity should be allowed to flourish without a great number of constraints. Even though many impractical ideas may arise, it is usually easy to eliminate them in the early stages

30、of design before firm details are required by manufacturing. In this way, innovative ideas are not inhibited. Quite often, more than one design is developed, up to the point where they can be compared against each other. It is entirely possible that the design which ultimately accepted will use idea

31、s existing in one of the rejected designs that did not show as much overall promise. Psychologists frequently talk about trying to fit people to the machines they operate. It is essentially the responsibility of the design engineer to strive to fit machines to people. This is not an easy task, since

32、 there is really no average person for which certain operating dimensions and procedures are optimum. Another important point which should be recognized is that a design engineer must be able to communicate ideas to other people if they are to be incorporated. Initially the designer must communicate

33、 a preliminary design to get management approval. This is usually done by verbal discussions in conjunction with drawing layouts and written material. To communicate effectively, the following questions must be answered: (1) Does the design really serve a human need? (2) Will it be competitive with

34、existing products of rival companies? (3) Is it economical to produce? (4) Can it be readily maintained? (5) Will it sell and make a profit? Only time will provide the true answers to the preceding questions, but the product should be designed, manufactured and marketed only with initial affirmative

35、 answers. The design engineer also must communicate the finalized design to manufacturing through the use 5 of detail and assembly drawings. Quite often, a problem well occur during the manufacturing cycle. It may be that a change is required in the dimensioning or telegramming of a part so that it

36、can be more readily produced. This falls in the category of engineering changes which must be approved by the design engineer so that the product function will not be adversely affected. In other cases, a deficiency in the design may appear during assembly or testing just prior to shipping. These re

37、alities simply bear out the fact that design is a living process. There is always a better way to do it and the designer should constantly strive towards finding that better way. Machining Turning The engine lathe, one of the oldest metal removal machines, has a number of useful and highly desirable

38、 attributes. Today these lathes are used primarily in small shops where smaller quantities rather than large production runs are encountered. The engine lathe has been replaced in todays production shops by a wide variety of automatic lathes such as automatic of single-point tooling for maximum meta

39、l removal, and the use of form tools for finish and accuracy, are now at the designers fingertips with production speeds on a par with the fastest processing equipment on the scene today. Tolerances for the engine lathe depend primarily on the skill of the operator. The design engineer must be caref

40、ul in using tolerances of an experimental part that has been produced on the engine lathe by a skilled operator. In redesigning an experimental part for production, economical tolerances should be used. Turret Lathes Production machining equipment must be evaluated now, more than ever before, in ter

41、ms of ability to repeat accurately and rapidly. Applying this criterion for establishing the production qualification of a specific method, the turret lathe merits a high rating. In designing for low quantities such as 100 or 200 parts, it is most economical to use the turret lathe. In achieving the

42、 optimum tolerances possible on the turret lathe, the designer should strive for a minimum of operations. Automatic Screw Machines Generally, automatic screw machines fall into several categories； single-spindle automatics, multiple-spindle automatics and automatic chucking machines. Originally desi

43、gned for rapid, automatic production of screws and similar threaded parts, the automatic screw machine has long since exceeded the confines of this narrow field, and today plays a vital role in the mass production of a variety of precision parts. Quantities 6 play an important part in the economy of

44、 the parts machined on the automatic to set up on the turret lathe than on the automatic screw machine. Quantities less than 1000 parts may be more economical to set up on the turret lathe than on the automatic screw machine. The cost of the parts machined can be reduced if the minimum economical lo

45、t size is calculated and the proper machine is selected for these quantities. Automatic Tracer Lathes Since surface roughness depends greatly upon material turned, tooling, and fees and speeds employed, minimum tolerances that can be held on automatic tracer lathes are not necessarily the most econo

46、mical tolerances. Is some case, tolerances of 0.05mm are held in continuous production using but one cut. Groove width can be held to 0.125mm on some parts. Bores and single-point finishes can be held to 0.0125mm. On high-production runs where maximum output is desirable, a minimum tolerance of 0.12

47、5mm is economical on both diameter and length of turn. Milling With the exceptions of turning and drilling, milling is undoubtedly the most widely used method of removing metal. Well suited and readily adapted to the economical production of any quantity of parts, the almost unlimited versatility of

48、 the milling process merits the attention and consideration of designers seriously concerned with the manufacture of their product. As in any other process, parts that have to be milled should be designed with economical tolerances that can be achieved in production milling. If the part is designed

49、with tolerances finer than necessary, additional operations will have to be added to achieve these tolerancesand this will increase the cost of the part. Grinding is one of the most widely used methods of finishing parts to extremely close tolerances and low surface roughness. Currently, there are g

50、rinders for almost for almost every type of grinding operation. Particular design features of a part dictate to a large degree the type of grinding machine required. Where processing costs are excessive, parts redesigned to utilize a less expensive, higher output grinding method may be well worthwhi

51、le. For example, wherever possible the production economy of center less grinding should be taken advantage of by proper design consideration. Although grinding is usually considered a finishing operation, it is often employed as a complete machining process on work which can be ground down from rou

52、gh condition without being turned or otherwise machined. Thus many types of forgings and other parts are finished completely with the grinding wheel at appreciable savings of time and expense. 7 Classes of grinding machines include the following: cylindrical grinders, center less grinders, internal

53、grinders, surface grinders, and tool and cutter grinders. The cylindrical and center less grinders are for straight cylindrical or taper work； thus splices, shafts, and similar parts are ground on cylindrical machines either of the common-center type or the center less machine. Thread grinders are u

54、sed for grinding precision threads for thread gages, and threads on precision parts where the concentricity between the diameter of the shaft and the pitch diameter of the thread must be held to close tolerances. The internal grinders are used for grinding of precision holes, cylinder bores, and sim

55、ilar operations where bores of all kinds are to be finished. The surface grinders are for finishing all kinds of flat work, or work with plain surfaces which may be operated upon either by the edge of a wheel or by the face of a grinding wheel. These machines may have reciprocating or rotating table

56、s. 8 機(jī)械設(shè)計(jì)基礎(chǔ) 機(jī)械設(shè)計(jì)基礎(chǔ)是指機(jī)械裝置和機(jī)械系統(tǒng) 機(jī)器、產(chǎn)品、結(jié)構(gòu)、設(shè)備和儀器的設(shè)計(jì)。大部分機(jī)械設(shè)計(jì)需要利用數(shù)學(xué)、材料科學(xué)和工程力學(xué)知識。 我們對整個設(shè)計(jì)過程感興趣。它是怎樣開始的？工程師是不是僅僅坐在鋪著白紙的桌旁就可以開始設(shè)計(jì)了呢？當(dāng)他 記下一些設(shè)想后，下一步應(yīng)該做些什么？什么因會影影響或者控制著應(yīng)該做出的決定？最后，這一設(shè)計(jì)過程是怎樣結(jié)束的呢？ 有時，雖然并不總是如此，工程師認(rèn)識到一種需要并且決定對此做一些工作時，設(shè)計(jì)就開始了。認(rèn)識到這種需要，并用語言將其清楚地敘述出來，常常是一種高度創(chuàng)造性的工作。因?yàn)檫@種需要可能只是一個模糊的不滿，一種不舒服的感覺，或者是感覺到了某些東西是不

57、正確的。 這種需要往往不是很明顯的。例如，對食品包裝機(jī)械進(jìn)行改進(jìn)的需要，可能是由于噪音過大、包裝重量的變化、包裝質(zhì)量的微小的但是能夠察覺得出來的變化等表現(xiàn)出來的。 敘述某種需要和隨后要解決的問題之間有著明顯的區(qū)別。要解決的問題是比較具體的。如果需要干凈的空氣，要解決的問題可能是降低發(fā)電廠煙囪的排塵量，或者是降低汽車排除的有害氣體。 確定問題階段應(yīng)該制訂設(shè)計(jì)對象所有的要求。這些設(shè)計(jì)要求包括輸入量、輸出兩特性、設(shè)計(jì)對象所占據(jù)的空間尺寸以及這些參量的所有制約因素。我們可以把設(shè)計(jì)對象看作是黑箱中的某種東西。在這種情況下，我們必須具體確定黑箱的輸入和輸出，以及它們的特性和制約因素。這些設(shè)計(jì)要求將規(guī)定生產(chǎn)

58、成本、產(chǎn)量、預(yù)期壽命、工作范圍、操作溫度和可靠性。 還存在著許多由于設(shè)計(jì)人員 所處的特定環(huán)境或者由于問題本身的性質(zhì)所產(chǎn)生的隱含設(shè)計(jì)要求。某個工廠中可利用的制造工藝和設(shè)備會對設(shè)計(jì)人員的工作有所限制，因而成為隱含的設(shè)計(jì)要求的一部分。例如，一個小工廠中可能沒有冷變形加工機(jī)械設(shè)備。因此，設(shè)計(jì)人員就必須選擇這個工廠中能夠進(jìn)行的其他的金屬加工方法。工人的技術(shù)水平和市場上的競爭情況也是隱含的設(shè)計(jì)要求的組成部分。 在確定了要解決的問題，并且形成了一系列的書面的和隱含的設(shè)計(jì)要求之后，設(shè)計(jì)工作的下一階段是進(jìn)行綜合以獲得最優(yōu)的結(jié)果。因?yàn)橹挥型ㄟ^對所設(shè)計(jì)的系統(tǒng)進(jìn)行分析，才能確定其性能是否滿足設(shè)計(jì)要求。因此， 不進(jìn)行分

59、析和優(yōu)化就不能進(jìn)行綜合。 設(shè)計(jì)工作是一個反復(fù)進(jìn)行的過程。在這個過程中，我們要經(jīng)歷幾個階段，在對結(jié)果 9 進(jìn)行評價后，再返回到前面的階段。因此，我們可以先綜合系統(tǒng)中的幾個零件，對它們進(jìn)行分析和優(yōu)化，然后再進(jìn)行綜合，看它們對系統(tǒng)的其他部分有時么影響。分析和優(yōu)化都要求我們建立或者做出系統(tǒng)的抽象模型，以便對此進(jìn)行數(shù)學(xué)分析。我們將這些模型稱為數(shù)學(xué)模型。在建立數(shù)學(xué)模型時，我們希望能夠找到一個可以很好地模擬實(shí)際物理系統(tǒng)的數(shù)學(xué)模型。 評價是整個設(shè)計(jì)過程中的一個重要階段。評價是對一個成功的設(shè)計(jì)的最后檢驗(yàn)，通常包括樣機(jī)的實(shí)驗(yàn) 室實(shí)驗(yàn)。在此階段我們希望弄清楚設(shè)計(jì)能否真正滿足所有的要求。它是否可靠？在與類似的產(chǎn)品的競

60、爭中它能否獲勝？制造和使用這種產(chǎn)品是否經(jīng)濟(jì)？它是否易于維護(hù)和調(diào)整？能否從它的銷售或使用中獲得利潤？ 與其他人就設(shè)計(jì)方案進(jìn)行交流和溝通是設(shè)計(jì)過程的最后和關(guān)鍵階段。毫無疑問，有許多偉大的設(shè)計(jì)、發(fā)明或創(chuàng)造之所以沒有為人類所利用，就是因?yàn)閯?chuàng)造者不善于或者不愿意向其他人介紹自己的成果。提出方案是一種說服別人的工作。當(dāng)一個工程師向經(jīng)營、管理部門或者其主管人員提出自己的新方案時，就是希望向他們說明或者證明自己的方案是比較好的。只有成功 地完成這項(xiàng)工作，為得出這個方案所花費(fèi)的大量時間和精力才不會被浪費(fèi)掉。 人們基本上只有三種表達(dá)自己思想的方式，即文字材料、口頭表述和繪圖。因此，一個優(yōu)秀的工程師除了掌握技術(shù)之外

61、，還應(yīng)該精通這三種表達(dá)方式。如果一個技術(shù)能力很強(qiáng)的人在上述三種表達(dá)方式中的某一種的能力較差，他就會遇到很大的困難。如果上述三種能力都很差，那將永遠(yuǎn)沒有人知道他是一個多么能干的人！ 一個有能力的工程師不應(yīng)該害怕在提出自己的方案時遭到失敗的可能性。事實(shí)上，偶然的失敗肯定會發(fā)生的，因?yàn)槊恳粋€真正有創(chuàng)造性的設(shè)想似乎總是有失敗或批評伴隨著它。從一 次失敗中可以學(xué)到很多東西，只有不怕遭受失敗的人們才能取得最大的收獲?？傊瑳Q定不把方案提交出來，才是真正的失敗。 機(jī)械設(shè)計(jì)概論 機(jī)械設(shè)計(jì)是一門通過設(shè)計(jì)新產(chǎn)品或者改進(jìn)產(chǎn)品來滿足人類需求的應(yīng)用技術(shù)科學(xué)。它是一個廣闊的工程技術(shù)領(lǐng)域，不僅要研究產(chǎn)品在尺寸、形狀和詳細(xì)結(jié)

62、構(gòu)等方面的基本構(gòu)思，還要考慮產(chǎn)品在制造、銷售和使用等方面的有關(guān)問題。 進(jìn)行各種機(jī)械設(shè)計(jì)工作的人員通常被稱為設(shè)計(jì)人員或者設(shè)計(jì)工程師。機(jī)械設(shè)計(jì)是一項(xiàng)創(chuàng)造性的工作。設(shè)計(jì)工程師不僅在工作上要有創(chuàng)新性，還必須在機(jī)械制圖、運(yùn)動學(xué)、工程材料、材料力學(xué)和機(jī)械制造工藝等 方面具有深厚的基礎(chǔ)知識。 如前面所述，機(jī)械設(shè)計(jì)的目的是生產(chǎn)能夠滿足人類需求的產(chǎn)品。發(fā)明、發(fā)現(xiàn)和科學(xué)知識本身并不一定能給人類帶來益處，只有當(dāng)它們被用在產(chǎn)品上才能產(chǎn)生效益。因而， 10 應(yīng)該認(rèn)識到再一個特定產(chǎn)品進(jìn)行設(shè)計(jì)之前，必須先確定人們是否需要這種產(chǎn)品。 應(yīng)當(dāng)把機(jī)械設(shè)計(jì)看成是設(shè)計(jì)人員運(yùn)用創(chuàng)造性的才能進(jìn)行產(chǎn)品設(shè)計(jì)、系統(tǒng)分析和制訂產(chǎn)品的制造工藝的一個

63、良機(jī)。掌握工程基礎(chǔ)知識要比熟記一些數(shù)據(jù)和公式更為重要。僅僅使用數(shù)據(jù)和公式是不足以再一個好的設(shè)計(jì)中做出所需的全部決定。另一方面，應(yīng)該認(rèn)真精確地進(jìn)行所有運(yùn)算。例如，即使將一個小數(shù) 點(diǎn)的位置放錯，也會使正確的設(shè)計(jì)變成錯誤的。 一個好的設(shè)計(jì)人員應(yīng)該勇于提出新的想法，而且愿意承擔(dān)一定的風(fēng)險，當(dāng)新的方法不適用時，就恢復(fù)采用原來的方法。因此，設(shè)計(jì)人員必須要有耐心，因?yàn)樗ㄙM(fèi)的時間和努力并不能保證帶來成功。一個全新的設(shè)計(jì)，要求屏棄許多陳舊的，為人們所熟知的方法。由于許多人易于墨守成規(guī)，這樣做并不是一件容易的事情。以為設(shè)計(jì)工程師應(yīng)該不斷的探索改進(jìn)現(xiàn)有產(chǎn)品的辦法，在此過程中應(yīng)該認(rèn)真選擇原有的、經(jīng)過驗(yàn)證的設(shè)計(jì)原理，

64、將其與未經(jīng)過驗(yàn)證的新觀念結(jié)合起來。 新設(shè)計(jì)本身會有許多缺陷和未能預(yù)料的問題發(fā)生，只有當(dāng)這 些缺陷和問題被解決之后，才能體現(xiàn)出新產(chǎn)品的優(yōu)越性。因此，一個性能優(yōu)越的產(chǎn)品誕生的同時，也伴隨著較高的風(fēng)險。應(yīng)該強(qiáng)調(diào)的是，如果設(shè)計(jì)本身不要求采用全新的辦法，就沒有必要僅僅為了變革的目的而采用新辦法。 在設(shè)計(jì)的初始階段，應(yīng)該允許設(shè)計(jì)人員充分發(fā)揮創(chuàng)造性，不受各種約束。即使產(chǎn)生了許多不切合實(shí)際的想法，也會在設(shè)計(jì)的早期，即繪制生產(chǎn)圖紙之前被改正掉。只有這樣， 才不至于堵塞創(chuàng)新得思路。通常要提出幾套設(shè)計(jì)方案 然后加以比較。很有可能在最后選定的方案中 采用了某些未被接受的方案中的一些想法。心理學(xué)家經(jīng)常談?wù)撊绾问谷藗冞m應(yīng)

65、他 們所操作的機(jī)器。設(shè)計(jì)人員的基本職責(zé)是努力使機(jī)器來適應(yīng)人們。這并不是一項(xiàng)容易的工作，因?yàn)閷?shí)際上并不存在著一個對所有人來說都是最優(yōu)的操作范圍和操作過程。 另一個應(yīng)該被認(rèn)識到的重要問題是，設(shè)計(jì)工程師必須能夠同其他有關(guān)人員進(jìn)行交流和溝通。在開始階段，設(shè)計(jì)人員必須就初步設(shè)計(jì)同管理人員進(jìn)行交流和溝通，并得到批準(zhǔn)。這一般是通過口頭討論，草圖和文字材料進(jìn)行的。為了有效地進(jìn)行交流，需要解決下列問題： （ 1） 所要設(shè)計(jì)的這個產(chǎn)品是否真正為人們所需要？ （ 2） 此產(chǎn)品與其他公司的現(xiàn)有產(chǎn)品相比有無競爭能力？ （ 3） 生產(chǎn)這種產(chǎn)品是否經(jīng)濟(jì)？ （ 4） 產(chǎn)品的維修是否 方便？ 11 （ 5） 產(chǎn)品有無銷路？是否

66、可以盈利？ 只有時間才能對上述問題給出正確的答案。但是，產(chǎn)品的設(shè)計(jì)、制造和銷售只能在對上述問題的初步肯定答案的基礎(chǔ)上進(jìn)行。設(shè)計(jì)工程師還應(yīng)該通過零件圖和裝配圖，與制造部門一起對最終設(shè)計(jì)方案進(jìn)行溝通。 通常，在制造過程中會出現(xiàn)某個問題。可能會要求對某個零件尺寸或公差作一些修改，使零件的生產(chǎn)變得容易。但是，工程上的修改必須要經(jīng)過設(shè)計(jì)人員批準(zhǔn)，以保證不會損傷產(chǎn)品的功能。有時，在產(chǎn)品的裝配時或者裝配外運(yùn)前的試驗(yàn)中才發(fā)現(xiàn)設(shè)計(jì)中的某些缺陷。這些事例恰好說明了設(shè)計(jì)是一個動態(tài)過程?？偸谴嬖谥玫姆?法來完成設(shè)計(jì)工作，設(shè)計(jì)人員應(yīng)該不斷努力，尋找這些更好的方法。 機(jī)械加工 車削 普通車床作為最早的金屬切削機(jī)床中的

67、一種，目前仍然有許多有用的和為人們所需要的特性?，F(xiàn)在，這些機(jī)床主要用在規(guī)模較小的工廠中，進(jìn)行小批量的生產(chǎn)，而不是進(jìn)行大批量的生產(chǎn)。 在現(xiàn)在的生產(chǎn)車間中，普通車床已經(jīng)被種類繁多的自動車床所取代，諸如自動仿形車床，六角車床和自動螺絲車床?，F(xiàn)在，設(shè)計(jì)人員已經(jīng)熟知先利用單刃刀具去除大量的金屬余量，然后利用成型刀具獲得表面光潔度和精度這種加工方法的優(yōu)點(diǎn)。這種加工方法的生產(chǎn)速度與現(xiàn)在工廠中使用的最快的加工 設(shè)備的速度相等。 普通車床的加工偏差主要依賴于操作者的技術(shù)熟練程度。設(shè)計(jì)工程師應(yīng)該認(rèn)真地確定由熟練工人在普通車床上加工的試驗(yàn)零件的公差。在把試驗(yàn)零件重新設(shè)計(jì)為生產(chǎn)零件時，應(yīng)該選用經(jīng)濟(jì)的公差。 六角車床

68、對生產(chǎn)加工設(shè)備來說，目前比過去更著重評價其是否具有精確的和快速的重復(fù)加工能力。應(yīng)用這個標(biāo)準(zhǔn)來評價具體的加工方法，六角車床可以獲得較高的質(zhì)量評定。 在為小批量的零件（ 100 200 件）設(shè)計(jì)加工方法時，采用六角車床時最經(jīng)濟(jì)的。為了在六角車床上獲得盡可能小的公差值，設(shè)計(jì)人員應(yīng)該盡量將加工工序的數(shù)目減至最少。 自 動螺絲車床 自動螺絲車床 通常被分為以下幾種類型：單軸自動、多軸自動和自動夾緊車床。自動螺絲車床最初是被用來對螺釘和類似的帶有螺紋的零件進(jìn)行自動化和快速加工的。但是，這種車床的用途早就超過了這個狹窄的范圍?，F(xiàn)在，它在許多種類的精密零件的大批量生產(chǎn)中起者重要的作用。工件的數(shù)量對采用自動螺絲

69、車床所加工 零件的經(jīng)濟(jì)性有較大的影響。如果工件的數(shù)量少于 1000 件，在六角車床上進(jìn)行加工比在自動螺絲車床上加工要經(jīng)濟(jì)得多。如果計(jì)算出最小經(jīng)濟(jì)批量，并且針對工件批量正確地選擇機(jī)床，就會降低零件的加工成本。 12 自動仿形車床 因?yàn)榱慵谋砻娲植诙仍诤艽蟪潭壬先Q于工件材料、刀具、進(jìn)給量和切削速度，采用自動仿形車床加工得到的最小公差不一定是最經(jīng)濟(jì)的公差。 在某種情況下，在連續(xù)生產(chǎn)過程中，只進(jìn)行一次切削加工時的公差可以達(dá)到 0.5mm。對于某些零件，槽寬的公差可以達(dá)到 0.125 mm。鏜孔和采用單刃刀具進(jìn)行精加工時，公差可達(dá)到 0.0125 mm。在希望獲得最大產(chǎn)量的大批量生產(chǎn)中，進(jìn)行直徑和長

70、度的車削時的最小公差值為 0.125 mm 時是最經(jīng)濟(jì)的。 銑削 除了車削和鉆削，銑削無疑是應(yīng)用最廣泛的金屬切削方法。銑削非常適合于而 且也易于應(yīng)用在任何數(shù)量的零件的經(jīng)濟(jì)生產(chǎn)中。在產(chǎn)品制造過程中，許許多多種類的銑削加工是值得設(shè)計(jì)人員認(rèn)真考慮和選擇的。 與其他種類的加工一樣，對于進(jìn)行銑削加工的零件，其公差應(yīng)該被設(shè)計(jì)或銑削生產(chǎn)所能達(dá)到的經(jīng)濟(jì)公差。如果零件的公差設(shè)計(jì)得比需要的要小，就需要增加額外的工序，以保證獲得這些公差 這將增加零件的成本。 磨削 磨削是一種應(yīng)用最廣泛的零件精加工方法，用來獲得非常小的公差和非常低的表面粗糙度。目前，幾乎存在著適合于各種磨削工序的磨削。零件的設(shè)計(jì)特征在很大程度上決定

71、了需要采用的磨削的種類。當(dāng)加工成本太高時，就 值得對零件進(jìn)行重新設(shè)計(jì)，使其能夠通過采用既便宜又具有高生產(chǎn)率的磨削方法加工出來，以獲得經(jīng)濟(jì)效益。盡管通常認(rèn)為磨削適用于精加工工序，對那些適合于采用磨削來完成粗、精加工工序的工件，也經(jīng)常采用磨削方法完成全部加工工作，而不采用車削或者其他加工方法。因此，許多種類的鍛件和其他零件，可以采用磨削的方法完成其從毛坯到成品的全部加工，這可以顯著地節(jié)約時間和費(fèi)用。 磨床有以下幾種類型：外圓磨床、無心磨床、內(nèi)圓磨床、平面磨床和工具磨床。 外圓磨床和無心磨床是用來磨削圓柱形工件或者圓錐形工件的。因此，花鍵軸、軸和其他類似的零 件是采用普通的外圓磨床，或者采用無心磨床進(jìn)行加工的。 螺紋磨床用來磨削螺紋量規(guī)上的精密螺紋和用來磨削螺紋的中徑與軸的同心度公差很小的精密件上的螺紋。 內(nèi)圓磨床用來磨削精密的孔、汽缸孔以及各種類似的，需要進(jìn)行精加工的孔。 平面磨床用來對各種平面工件，或者帶有平面的工件進(jìn)行精加工?？梢圆捎蒙拜喌倪吇蛘呱拜喌亩嗣孢M(jìn)行磨削。這類機(jī)床上裝有往復(fù)式工作臺或者回轉(zhuǎn)式工作臺。