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1、<p><b> 英文原文</b></p><p> Mechanical Design and Manufacturing Processes</p><p> Mechanical design is the application of science and technology to devise new or improved produc
2、ts 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,
3、but also considers the various factors involved in the manufacture, marketing and use of the product.</p><p> People who perform the various functions of mechanical design are typically called designers, or
4、 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, dynamic
5、s, materials engineering, strength of materials and manufacturing processes.</p><p> As stated previously, the purpose of mechanical design is to produce a product which will serve a need for man. Invention
6、s, 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 n
7、eed must be identified before a particular product is designed.</p><p> Mechanical design should be considered to be an opportunity to use innovative talents to envision a design of a product, to analyze th
8、e 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 equation
9、s which alone can be used to provide all the correct decisions required to produce a good design.</p><p> On the other hand, any calculations made must be done with the utmost care and precision. For exampl
10、e, if a decimal point is misplaced, an otherwise acceptable design may not function.</p><p> Good designs require trying new ideas and being willing to take a certain amount of risk, knowing that if the new
11、 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
12、that many old and well-established methods be thrust aside. This is not easy since many people cling to familiar ideas, techniques and attitudes. A design engineer sho</p><p> New designs generally have &qu
13、ot;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 em
14、phasized that, if a design does not warrant radical new methods, such methods should not be applied merely for the sake of change.</p><p> During the beginning stages of design, creativity should be allowed
15、 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 of design before firm details are required by manufacturing. In t
16、his 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 is ultimate</p&
17、gt;<p> 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
18、task, since there is really no average person for which certain operating dimensions and procedures are optimum.</p><p> Another important point which should be recognized is that a design engineer must be
19、able to communicate ideas to other people if they are to be incorporated. Communicating the design to others is the final, vital step in the design process. Undoubtedly many great designs, inventions, and creative works
20、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 presenting a new so</p><p> Ba
21、sically, there are only three means of communication available to us. These are the written, the oral, and the graphical forms. Therefore the successful engineer will be technically competent and versatile in all three f
22、orms of communication. A technically competent person who lacks ability in any one of these forms is severely handicapped. If ability in all three forms is lacking, no one will ever know how competent that person is!<
23、/p><p> 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 to accompany every
24、really creative idea. There is a great deal to be learned from a failure, and the greatest gains are obtained by those willing to risk defeat. In the final analysis, the real failure would lie in deciding not to make the
25、 presentation at all. To communicate effectively, the following questions must </p><p> (1) Does the design really serve a human need?</p><p> (2) Will it be competitive with existing products
26、 of rival companies?</p><p> (3) Is it economical to produce?</p><p> (4) Can it be readily maintained?</p><p> (5) Will it sell and make a profit?</p><p> Only tim
27、e will provide the true answers to the preceding questions, but the product should be designed, manufactured and marketed only with initial affirmative answers. The design engineer also must communicate the finalized des
28、ign to manufacturing through the use of detail and assembly drawings.</p><p> Quite often, a problem will occur during the manufacturing cycle [3]. It may be that a change is required in the dimensioning or
29、 tolerancing of a part so that it can be more readily produced. This fails in the category of engineering changes which must be approved by the design engineer so that the product function will not be adversely affected.
30、 In other cases, a deficiency in the design may appear during assembly or testing just prior to shipping. These realities simply bear out the fact that </p><p> Designing starts with a need, real or imagine
31、d. Existing apparatus may need improvements in durability, efficiently, weight, speed, or cost. New apparatus may be needed to perform a function previously done by men, such as computation, assembly, or servicing. With
32、the objective wholly or partly defined, the next step in design is the conception of mechanisms and their arrangements that will perform the needed functions.</p><p> For this, freehand sketching is of grea
33、t value, not only as a record of one's thoughts and as an aid in discussion with others, but particularly for communication with one's own mind, as a stimulant for creative ideas.</p><p> When the g
34、eneral shape and a few dimensions of the several components become apparent, analysis can begin in earnest. The analysis will have as its objective satisfactory or superior performance, plus safety and durability with mi
35、nimum weight, and a competitive east. Optimum proportions and dimensions will be sought for each critically loaded section, together with a balance between the strength of the several components. Materials and their trea
36、tment will be chosen. These important objectives c</p><p> Finally, a design based upon function and reliability will be completed, and a prototype may be built. If its tests are satisfactory, and if the de
37、vice is to be produced in quantity, the initial design will undergo certain modifications that enable it to be manufactured in quantity at a lower cost. During subsequent years of manufacture and service, the design is l
38、ikely to undergo changes as new ideas are conceived or as further analysis based upon tests and experience indicate alterations. Sale</p><p> To stimulate creative thought, the following rules are suggested
39、 for the designer.</p><p> 1. Apply ingenuity to utilize desired physical properties and to control undesired ones.</p><p> The performance requirements of a machine are met by utilizing laws
40、of nature or properties of matter (e. g., flexibility, strength, gravity, inertia, buoyancy, centrifugal for, principles of the lever and inclined plane, friction, viscosity, fluid pressure, and thermal expansion), also
41、the many electrical, optical, thermal, and chemical phenomena. </p><p> However, what may be useful in one application may be detrimental in the next. Flexibility is desired in valve
42、springs but not in the valve camshaft; friction is desired at the clutch face but not in the clutch bearing. Ingenuity in design should be applied to utilize and control the</p><p> physical properties that
43、 are desired and to minimize those that are not desired.</p><p> 2. Provide for favorable stress distribute and stiffness with minimum weight. On components subjected to fluctuating stress, particular atten
44、tion is given to a reduction in stress concentration, and to an increase of strength at fillets, threads, holes, and fits. Stress reduction are made by modification in shape, and strengthening may be done by prestressing
45、 treatments such as surface rolling and shallow hardening. Hollow shafts and tubing, and box sections give a favorable stress distribution,</p><p> 3. Use equations to calculate and optimize dimensions. The
46、 fundamental equations of mechanics and the other sciences are the accepted bases for calculations. They are sometimes rearranged in special forms to facilitate the determination or optimization of dimensions, such as th
47、e</p><p> Beam and surface stress equations for determining gear-tooth size. Factors may be added to a fundamental equation for conditions not analytically determinable, e. g. , on thin steel tubes, an allo
48、wance for corrosion added to the thickness based on pressure. When it is necessary to apply a fundamental equation to shapes, materials, or conditions which only approximate the assumptions for its derivation, it is don
49、e in a manner which gives results "on the safe side". In situations where data are i</p><p> 4. Choose materials for a combination of properties. Materials should be chosen for a combination of pe
50、rtinent properties, not only for strengths, hardness, and weight, but sometimes for resistance to impact, corrosion, and low or high temperatures. Cost and fabrication properties are factors, such as weld ability, machin
51、e ability, sensitivity to variation in heat-treating temperatures, and required coating.</p><p> 5. Select carefully between stock and integral components. A previously developed components is frequently
52、selected by a designer and his company from the stocks of parts manufacturers, if the component meet the performance and reliability requirements and is adaptable without additional development costs to the particular ma
53、chine being designed. However, its selection should be carefully made wi'th a full knowledge of its properties, since the reputation and liability of the company suffer if</p><p> 6. Provide for accurat
54、e location and non interference of parts in assembly. A good design provides for the correct locating of parts and for easy assembly and repair. Shoulders and pilot surfaces give accurate location without measurement dur
55、ing assembly. Shapes can be designed so that parts cannot be assembled backwards or in the wrong place. Interferences, as between screws in tapped holes, and between linkages must he foreseen and pretended. Inaccurate al
56、ignment and positioning between such a</p><p> The human race has distinguished itself from all other forms of life by using tools and intelligence to create items that serve to make life easier and more en
57、joyable. Through the centuries, both the tools and the energy sources to power these tools have evolved to meet the increasing sophistication and complexity of mankind's ideas.</p><p> In their earliest
58、 forms, tools primarily consisted of stone instruments. Considering tile relative simplicity of the items being made and the materials being shaped, stone was adequate. When iron tools were invented, durable metals and m
59、ore sophisticated articles could be produced. The twentieth century has seen the creation of products made from the</p><p> Most durable , consequently, the most unmachinable materials in history. In an eff
60、ort to meet the manufacturing challenges created by these materials, tools have now evolved to include materials such as alloy steel, carbide, diamond, and ceramics.</p><p> A similar evolution has taken pl
61、ace with the methods used to power our tools. Initially, tools were powered by muscles; either human or animal. However as the powers of water, wind, steam, and electricity were harnessed, mankind was able to further ext
62、ended manufacturing capabilities with new machines, greater accuracy, and faster machining rates.</p><p> Every time new tools, tool materials, and power sources are utilized, the efficiency and capabilitie
63、s of manufacturers are greatly enhanced. However as old problems are solved, new problems and challenges arise so that the manufacturers of today are faced with tough questions such as the following: How do you drill a 2
64、 mm diameter hole 670 mm deep without experiencing taper or run out? Is there a way to efficiently deburr passageways inside complex castings and guarantee 100 % that no burrs we</p><p> Since the 1940s,
65、a revolution in manufacturing has been taking place that once again allows manufacturers to meet the demands imposed by increasingly sophisticated designs and durable, but in many cases nearly unmachinable, materials. Th
66、is manufacturing revolution is now, as it has been in the past, centered on the use of new tools and new forms of energy.</p><p> The result has been the introduction of new manufacturing processes used for
67、 material removal, forming, and joining, known today as nontraditional manufacturing processes.</p><p> The conventional manufacturing processes in use today for material removal primarily rely on electric
68、motors and hard tool materials to perform tasks such as sawing, drilling, an broaching. Conventional forming operations are performed with the energy from electric motors, hydraulics, and gravity. Likewise, material join
69、ing is conventionally accomplished with thermal energy sources such as burning gases and electric arcs.</p><p> In contrast, nontraditional manufacturing processes harness energy sources considered unconv
70、entional by yesterday's standards. Material removal can now be accomplished with electrochemical reactions, high-temperature plasmas, and high-velocity jets of liquids and abrasives. Materials that in the past have b
71、een extremely difficult to form, are now</p><p> formed with magnetic fields, explosives, and the shock waves from powerful electric sparks. Material-joining capabilities have been expanded with the use of
72、high-frequency sound waves and beams of electrons.</p><p> In the past 50 years, over 20 different nontraditional manufacturing processes have been invented and successfully implemented into production. The
73、 reason there are such a large number of nontraditional processes is the same reason there are such a large number of conventional processes; each process has its own characteristic attributes and limitations, hence no o
74、ne process is best for all manufacturing situations.</p><p> For example, nontraditional process are sometimes applied to increase productivity either by reducing the number of overall manufacturing operati
75、ons required to produce a product or by performing operations faster than the previously used method.</p><p> In other cases, nontraditional processes are used to reduce the number of rejects experienced by
76、 the old manufacturing method by increasing repeatability, reducing in-process breakage of fragile work pieces, or by minimizing detrimental effects on work piece properties.</p><p> Because of the aforemen
77、tioned attributes, nontraditional manufacturing processes have experienced steady growth since their introduction. An increasing growth rate for these processes in the future is assured for the following reasons:</p&g
78、t;<p> (1) Currently, nontraditional processes possess virtually unlimited capabilities when compared with conventional processes, except for volumetric material removal rates. Great advances have been made in th
79、e past few years in increasing the removal rates of some of these processes, and there is no reason to believe that this trend will not continue into the future.</p><p> (2) Approximately one half of the no
80、ntraditional manufacturing processes are available with computer control of the process parameters. The use of computers lends simplicity to processes that people may be unfamiliar with, and thereby accelerates acceptanc
81、e. Additionally, computer control assures reliability and repeatability[s], which also accelerates acceptance and implementation.</p><p> (3) Most nontraditional processes are capable of being adaptively-co
82、ntrolled through the use of vision systems, laser gages, and other in-process inspection techniques. If, for example, the in-process inspection system determines that the size of holes being produced in a product are bec
83、oming smaller, the size can be modified without changing hard tools, such as drills.</p><p> (4) The implementation of nontraditional manufacturing processes will continues to increase as manufacturing engi
84、neers, product designers, and metallurgical engineers become increasingly aware of the unique capabilities and benefits that nontraditional manufacturing processes provide.</p><p><b> 譯文</b><
85、/p><p><b> 機(jī)械設(shè)計(jì)及加工工藝</b></p><p> 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)老產(chǎn)品,滿足人類需求的應(yīng)用技術(shù)科學(xué)。它涉及工程技術(shù)的各個(gè)領(lǐng)域,主要研究產(chǎn)品的尺寸、形狀和詳細(xì)結(jié)構(gòu)的基本構(gòu)思,還要研究產(chǎn)品在制造、銷售和使用等方面的問題。</p><p> 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)
86、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(dòng)學(xué)、動(dòng)力學(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(shí)。</p><p> 如前面所述,機(jī)械設(shè)計(jì)的目的是生產(chǎn)滿足人類需求的產(chǎn)品。發(fā)明、發(fā)現(xiàn)和科學(xué)知識(shí)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,應(yīng)該認(rèn)識(shí)到在一個(gè)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。</p><
87、p> 應(yīng)當(dāng)把機(jī)械設(shè)計(jì)看成設(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(gè)良機(jī)。掌握工程基礎(chǔ)知識(shí)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)和公式是不足以在一個(gè)好的設(shè)計(jì)中做出所需的全部決定的。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(gè)小數(shù)點(diǎn)的位置放錯(cuò),也會(huì)使正確的設(shè)計(jì)變成錯(cuò)誤的。</p><p> 一個(gè)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(xiǎn);當(dāng)新的方法
88、不適用時(shí),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(shí)間和努力并不能保證帶來成功。一個(gè)全新的設(shè)計(jì),要求摒棄許多陳舊的,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。一位設(shè)計(jì)工程師應(yīng)該不斷地探索改進(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,將其與未經(jīng)過驗(yàn)證的新觀念結(jié)合起來。</p><p> 新設(shè)計(jì)本身會(huì)有許多缺陷和未能預(yù)料的問題發(fā)生,只有當(dāng)這
89、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(gè)性能優(yōu)越的產(chǎn)品誕生的同時(shí),也伴隨著較高的風(fēng)險(xiǎn)。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方法,就沒有必要僅僅為了變革的目的而采用新辦法。</p><p> 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(huì)在設(shè)計(jì)的早期,即繪制生產(chǎn)圖紙之前被改正。只有這樣,才不致于堵塞創(chuàng)新的思路。通常要提出幾套設(shè)計(jì)方案,
90、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。</p><p> 心理學(xué)家經(jīng)常談?wù)撊绾问谷藗冞m應(yīng)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(gè)對(duì)所有人來說都是最優(yōu)的操作范圍和操作過程。</p><p> 另一個(gè)應(yīng)該被認(rèn)識(shí)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。與其他人
91、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(gè)工程師向經(jīng)營(yíng)、管理部門或者其主管人員提出自己的新方案時(shí),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(gè)方案所花費(fèi)的大量時(shí)間和精力才不會(huì)被浪費(fèi)掉。</p><p> 人們基本上
92、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(gè)優(yōu)秀的工程師除了掌握技術(shù)之外,還應(yīng)該精通這三種表達(dá)方式。如果一個(gè)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(huì)遇到很大的困難。如果上述三種能力都較差,那將永遠(yuǎn)沒有人知道他是一個(gè)多么能干的人!</p><p> 一個(gè)有能力的工程師不應(yīng)該害怕在提出自己的方案時(shí)遭到失敗的可能性。事實(shí)上,偶然的失敗肯定會(huì)發(fā)生的,因?yàn)槊總€(gè)真正有創(chuàng)造性的設(shè)想
93、似乎總是有失敗或批評(píng)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。</p><p> 總之,決定不把方案提交出來,才是真正的失敗。</p><p> 為了進(jìn)行有效的交流,需要解決下列問題:</p><p> (1)所要設(shè)計(jì)的這個(gè)產(chǎn)品是否真正為人們所需要?</p><p> (2)此產(chǎn)品與其他公司的現(xiàn)
94、有同類產(chǎn)品相比有無競(jìng)爭(zhēng)能力?</p><p> (3)生產(chǎn)這種產(chǎn)品是否經(jīng)濟(jì)?</p><p> (4)產(chǎn)品的維修是否方便?</p><p> (5)產(chǎn)品有無銷路?是否可以盈利?</p><p> 只有時(shí)間才能對(duì)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(duì)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
95、配圖,與制造部門一起對(duì)最終設(shè)計(jì)方案進(jìn)行溝通。</p><p> 通常,在制造過程中會(huì)出現(xiàn)某個(gè)問題??赡芤髮?duì)某個(gè)零件尺寸或公差做一些更改,使零件的生產(chǎn)變得容易。但是,工程上的更改必須經(jīng)過設(shè)計(jì)人員批準(zhǔn),以保證不會(huì)損傷產(chǎn)品的功能。有時(shí),在產(chǎn)品的裝配時(shí)或者裝箱外運(yùn)前的試驗(yàn)中才發(fā)現(xiàn)設(shè)計(jì)中的某種缺陷。</p><p> 這些事例恰好說明了設(shè)計(jì)是一個(gè)動(dòng)態(tài)過程??偸谴嬖谥玫姆椒▉硗瓿稍O(shè)計(jì)工作,設(shè)
96、計(jì)人員應(yīng)該不斷努力,尋找這些更好的方法。</p><p> 設(shè)計(jì)是從實(shí)際或者假想的需要開始的。對(duì)于現(xiàn)有的設(shè)備可能需要在耐用性、效率、重量、速度或成本等方面做進(jìn)一些改進(jìn)工作;也可能需要新的設(shè)備完成以前由人來做的工作,例如計(jì)算或者裝配。當(dāng)目標(biāo)完全或部分被確定以后,下一個(gè)設(shè)計(jì)步驟是對(duì)能夠完成所需要功能的機(jī)構(gòu)及其布局進(jìn)行總體設(shè)計(jì)。對(duì)于此項(xiàng)工作,徒手畫的草圖是很有價(jià)值的,它不僅可以記錄下我們的想法,而且還有助于與別人進(jìn)行
97、討論,特別是和自己的大腦進(jìn)行交流,從而促進(jìn)創(chuàng)新想法的產(chǎn)生。</p><p> 當(dāng)一些零件的大致形狀和幾個(gè)尺寸被確定后,就可以開始認(rèn)真的分析工作。分析工作的目的是要在重量最輕、成本最低的情況下,獲得令人滿意,即優(yōu)良的工作性能,并且還要安全耐用。對(duì)于每個(gè)關(guān)鍵承載截面,應(yīng)該尋求最佳的比例和尺寸,同時(shí)要對(duì)這幾個(gè)零件的受力進(jìn)行平衡。要對(duì)材料和處理方式進(jìn)行選擇。只有根據(jù)力學(xué)原理進(jìn)行分析才能達(dá)到這些重要目的。這些分析包括根據(jù)
98、靜力學(xué)原理分析反作用力和充分利用摩擦力,根據(jù)動(dòng)力學(xué)原理分析慣性、加速度和能量;根據(jù)彈性力學(xué)和材料力學(xué)分析應(yīng)力和變形;根據(jù)流體力學(xué)來分析潤(rùn)滑和流體傳動(dòng)。</p><p> 最后,完成基于功能要求和可靠性所進(jìn)行的設(shè)計(jì),且要制作一臺(tái)樣機(jī)。如果試驗(yàn)結(jié)果令人滿意,而且該裝置將要進(jìn)行批量生產(chǎn),就應(yīng)該對(duì)最初提出的設(shè)計(jì)方案做一些修改,使其能以較低的成本進(jìn)行批量生產(chǎn)。在以后的制造和使用期內(nèi),如果產(chǎn)生了新的想法或者根據(jù)試驗(yàn)和經(jīng)驗(yàn)所
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