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 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 process 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 sensing 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. 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 quantity 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 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 temperature, 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 designers 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 constitute 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 design 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, 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 mathematical 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 laboratory. 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 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 presenting 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 three 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 severely 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 accompany 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 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 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 design 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, 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 should 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 all 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 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-established 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 incorporated. 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 new 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 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 ideas 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 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 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 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 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 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 realities 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 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 metal 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 careful 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 terms 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 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 designed 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 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 lot 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 economical 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 0.125mm 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 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 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 grinders 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 worthwhile. 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 rough 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 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 used 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 similar 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 tables. 8 機械設計基礎 機械設計基礎是指機械裝置和機械系統(tǒng) 機器、產品、結構、設備和儀器的設計。大部分機械設計需要利用數(shù)學、材料科學和工程力學知識。 我們對整個設計過程感興趣。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計了呢？當他 記下一些設想后，下一步應該做些什么？什么因會影影響或者控制著應該做出的決定？最后，這一設計過程是怎樣結束的呢？ 有時，雖然并不總是如此，工程師認識到一種需要并且決定對此做一些工作時，設計就開始了。認識到這種需要，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。因為這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正確的。 這種需要往往不是很明顯的。例如，對食品包裝機械進行改進的需要，可能是由于噪音過大、包裝重量的變化、包裝質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。 確定問題階段應該制訂設計對象所有的要求。這些設計要求包括輸入量、輸出兩特性、設計對象所占據的空間尺寸以及這些參量的所有制約因素。我們可以把設計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。這些設計要求將規(guī)定生產成本、產量、預期壽命、工作范圍、操作溫度和可靠性。 還存在著許多由于設計人員 所處的特定環(huán)境或者由于問題本身的性質所產生的隱含設計要求。某個工廠中可利用的制造工藝和設備會對設計人員的工作有所限制，因而成為隱含的設計要求的一部分。例如，一個小工廠中可能沒有冷變形加工機械設備。因此，設計人員就必須選擇這個工廠中能夠進行的其他的金屬加工方法。工人的技術水平和市場上的競爭情況也是隱含的設計要求的組成部分。 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計要求之后，設計工作的下一階段是進行綜合以獲得最優(yōu)的結果。因為只有通過對所設計的系統(tǒng)進行分析，才能確定其性能是否滿足設計要求。因此， 不進行分析和優(yōu)化就不能進行綜合。 設計工作是一個反復進行的過程。在這個過程中，我們要經歷幾個階段，在對結果 9 進行評價后，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，對它們進行分析和優(yōu)化，然后再進行綜合，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，以便對此進行數(shù)學分析。我們將這些模型稱為數(shù)學模型。在建立數(shù)學模型時，我們希望能夠找到一個可以很好地模擬實際物理系統(tǒng)的數(shù)學模型。 評價是整個設計過程中的一個重要階段。評價是對一個成功的設計的最后檢驗，通常包括樣機的實驗 室實驗。在此階段我們希望弄清楚設計能否真正滿足所有的要求。它是否可靠？在與類似的產品的競爭中它能否獲勝？制造和使用這種產品是否經濟？它是否易于維護和調整？能否從它的銷售或使用中獲得利潤？ 與其他人就設計方案進行交流和溝通是設計過程的最后和關鍵階段。毫無疑問，有許多偉大的設計、發(fā)明或創(chuàng)造之所以沒有為人類所利用，就是因為創(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。當一個工程師向經營、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 地完成這項工作，為得出這個方案所花費的大量時間和精力才不會被浪費掉。 人們基本上只有三種表達自己思想的方式，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之外，還應該精通這三種表達方式。如果一個技術能力很強的人在上述三種表達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該害怕在提出自己的方案時遭到失敗的可能性。事實上，偶然的失敗肯定會發(fā)生的，因為每一個真正有創(chuàng)造性的設想似乎總是有失敗或批評伴隨著它。從一 次失敗中可以學到很多東西，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。 機械設計概論 機械設計是一門通過設計新產品或者改進產品來滿足人類需求的應用技術科學。它是一個廣闊的工程技術領域，不僅要研究產品在尺寸、形狀和詳細結構等方面的基本構思，還要考慮產品在制造、銷售和使用等方面的有關問題。 進行各種機械設計工作的人員通常被稱為設計人員或者設計工程師。機械設計是一項創(chuàng)造性的工作。設計工程師不僅在工作上要有創(chuàng)新性，還必須在機械制圖、運動學、工程材料、材料力學和機械制造工藝等 方面具有深厚的基礎知識。 如前面所述，機械設計的目的是生產能夠滿足人類需求的產品。發(fā)明、發(fā)現(xiàn)和科學知識本身并不一定能給人類帶來益處，只有當它們被用在產品上才能產生效益。因而， 10 應該認識到再一個特定產品進行設計之前，必須先確定人們是否需要這種產品。 應當把機械設計看成是設計人員運用創(chuàng)造性的才能進行產品設計、系統(tǒng)分析和制訂產品的制造工藝的一個良機。掌握工程基礎知識要比熟記一些數(shù)據和公式更為重要。僅僅使用數(shù)據和公式是不足以再一個好的設計中做出所需的全部決定。另一方面，應該認真精確地進行所有運算。例如，即使將一個小數(shù) 點的位置放錯，也會使正確的設計變成錯誤的。 一個好的設計人員應該勇于提出新的想法，而且愿意承擔一定的風險，當新的方法不適用時，就恢復采用原來的方法。因此，設計人員必須要有耐心，因為所花費的時間和努力并不能保證帶來成功。一個全新的設計，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。以為設計工程師應該不斷的探索改進現(xiàn)有產品的辦法，在此過程中應該認真選擇原有的、經過驗證的設計原理，將其與未經過驗證的新觀念結合起來。 新設計本身會有許多缺陷和未能預料的問題發(fā)生，只有當這 些缺陷和問題被解決之后，才能體現(xiàn)出新產品的優(yōu)越性。因此，一個性能優(yōu)越的產品誕生的同時，也伴隨著較高的風險。應該強調的是，如果設計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。 在設計的初始階段，應該允許設計人員充分發(fā)揮創(chuàng)造性，不受各種約束。即使產生了許多不切合實際的想法，也會在設計的早期，即繪制生產圖紙之前被改正掉。只有這樣， 才不至于堵塞創(chuàng)新得思路。通常要提出幾套設計方案 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。心理學家經常談論如何使人們適應他 們所操作的機器。設計人員的基本職責是努力使機器來適應人們。這并不是一項容易的工作，因為實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。 另一個應該被認識到的重要問題是，設計工程師必須能夠同其他有關人員進行交流和溝通。在開始階段，設計人員必須就初步設計同管理人員進行交流和溝通，并得到批準。這一般是通過口頭討論，草圖和文字材料進行的。為了有效地進行交流，需要解決下列問題： （ 1） 所要設計的這個產品是否真正為人們所需要？ （ 2） 此產品與其他公司的現(xiàn)有產品相比有無競爭能力？ （ 3） 生產這種產品是否經濟？ （ 4） 產品的維修是否 方便？ 11 （ 5） 產品有無銷路？是否可以盈利？ 只有時間才能對上述問題給出正確的答案。但是，產品的設計、制造和銷售只能在對上述問題的初步肯定答案的基礎上進行。設計工程師還應該通過零件圖和裝配圖，與制造部門一起對最終設計方案進行溝通。 通常，在制造過程中會出現(xiàn)某個問題?？赡軙髮δ硞€零件尺寸或公差作一些修改，使零件的生產變得容易。但是，工程上的修改必須要經過設計人員批準，以保證不會損傷產品的功能。有時，在產品的裝配時或者裝配外運前的試驗中才發(fā)現(xiàn)設計中的某些缺陷。這些事例恰好說明了設計是一個動態(tài)過程?？偸谴嬖谥玫姆?法來完成設計工作，設計人員應該不斷努力，尋找這些更好的方法。 機械加工 車削 普通車床作為最早的金屬切削機床中的一種，目前仍然有許多有用的和為人們所需要的特性?，F(xiàn)在，這些機床主要用在規(guī)模較小的工廠中，進行小批量的生產，而不是進行大批量的生產。 在現(xiàn)在的生產車間中，普通車床已經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，設計人員已經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。這種加工方法的生產速度與現(xiàn)在工廠中使用的最快的加工 設備的速度相等。 普通車床的加工偏差主要依賴于操作者的技術熟練程度。設計工程師應該認真地確定由熟練工人在普通車床上加工的試驗零件的公差。在把試驗零件重新設計為生產零件時，應該選用經濟的公差。 六角車床 對生產加工設備來說，目前比過去更著重評價其是否具有精確的和快速的重復加工能力。應用這個標準來評價具體的加工方法，六角車床可以獲得較高的質量評定。 在為小批量的零件（ 100 200 件）設計加工方法時，采用六角車床時最經濟的。為了在六角車床上獲得盡可能小的公差值，設計人員應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。現(xiàn)在，它在許多種類的精密零件的大批量生產中起者重要的作用。工件的數(shù)量對采用自動螺絲車床所加工 零件的經濟性有較大的影響。如果工件的數(shù)量少于 1000 件，在六角車床上進行加工比在自動螺絲車床上加工要經濟得多。如果計算出最小經濟批量，并且針對工件批量正確地選擇機床，就會降低零件的加工成本。 12 自動仿形車床 因為零件的表面粗糙度在很大程度上取決于工件材料、刀具、進給量和切削速度，采用自動仿形車床加工得到的最小公差不一定是最經濟的公差。 在某種情況下，在連續(xù)生產過程中，只進行一次切削加工時的公差可以達到 0.5mm。對于某些零件，槽寬的公差可以達到 0.125 mm。鏜孔和采用單刃刀具進行精加工時，公差可達到 0.0125 mm。在希望獲得最大產量的大批量生產中，進行直徑和長度的車削時的最小公差值為 0.125 mm 時是最經濟的。 銑削 除了車削和鉆削，銑削無疑是應用最廣泛的金屬切削方法。銑削非常適合于而 且也易于應用在任何數(shù)量的零件的經濟生產中。在產品制造過程中，許許多多種類的銑削加工是值得設計人員認真考慮和選擇的。 與其他種類的加工一樣，對于進行銑削加工的零件，其公差應該被設計或銑削生產所能達到的經濟公差。如果零件的公差設計得比需要的要小，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。零件的設計特征在很大程度上決定了需要采用的磨削的種類。當加工成本太高時，就 值得對零件進行重新設計，使其能夠通過采用既便宜又具有高生產率的磨削方法加工出來，以獲得經濟效益。盡管通常認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)約時間和費用。 磨床有以下幾種類型：外圓磨床、無心磨床、內圓磨床、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。 內圓磨床用來磨削精密的孔、汽缸孔以及各種類似的，需要進行精加工的孔。 平面磨床用來對各種平面工件，或者帶有平面的工件進行精加工。可以采用砂輪的邊或者砂輪的端面進行磨削。這類機床上裝有往復式工作臺或者回轉式工作臺。