機電專業(yè)英語Unit-6-Dimensional-Tolerances-and-Surface-Roughness課件

1、Unit 6 Dimensional Tolerances and Surface RoughnessContentsNew Words & Expressions Text & TranslationComplex Sentence AnalysisKey to ExercisesNew Words & Expressions dimensional tolerance尺寸公差 surface roughness 表面粗糙度cost reduction 成本降低interchangeability intteindbiliti n. 交替性，互換性surface finishes 表面處理p

2、aramount prmaunt adj. 極為重要的commensurate kmenrit adj.同量的，相稱的New Words & Expressions contemplate kntempleit v. 預(yù)期comprehensive kmprihensiv adj.廣泛的，綜合的appreciation pri:iein n. 正確評價，鑒識maintenance meintinns n .維持，保養(yǎng)hydraulic haidr:lik adj.水壓的，液壓的cylinder silind n.氣缸，圓柱狀物piston pistn n. 活塞New Words & Expr

3、essions antifriction ntifrikn n. 減摩裝置，潤滑劑antifriction bearing 滾動軸承shaft bearing 軸承stress reversal 應(yīng)力反向bearing surface 承壓面，支撐面mounting maunti n. 底座，托架Text & TranslationBecause of the highly competitive nature of most manufacturing businesses, the question of finding ways to reduce cost is ever presen

4、t. A good starting point for cost reduction is in the design of product. The design engineer should always keep in mind the possible alternatives available to him in making his design. It is often impossible to determine the best alternatives without a careful analysis of the probable production cos

5、t. Designing for function, interchangeability, quality, and economy requires a careful study of tolerances, surface finishes, processes, materials, and equipments.Text & TranslationTo assure sound and economical design from a producibility standpoint, careful consideration of the following general d

6、esign rules, both separately and together, is of paramount importance. The order of importance may vary according to design requirements, or factors, but the overall importance always remains the same. Text & Translation(1) Seek simplicity. Design for maximum simplicity in functional and physical ch

7、aracteristics.(2) Determine the best production method. Seek the help of a production engineer to design for the most economical production methods.(3) Analyze materials. Select materials that will lend themselves to low-cost production as well as to design requirements.Text & Translation(4) Elimina

8、te fixturing and handling problems. Design for ease of locating, setting up, and holding parts.(5) Employ maximum acceptable tolerances and finishes. 1Specify surface roughness and accuracy no greater than that which is commensurate with the type of part or mechanism being designed, and the producti

9、on method or methods contemplated.Tolerances on finish and dimensions play an important role in the final achievement or absence of practical production design.A comprehensive study of the principles of interchangeability is essential for a thorough understanding and full appreciation of low-cost pr

10、oduction techniques. Interchangeability is the key to successful production regardless of quantity. Details of all parts should be surveyed carefully to assure not only inexpensive processing but also rapid and easy assembly and maintenance. 2It must be remembered that each production method has a w

11、ell-established level of precision which can be maintained in continuous production without exceeding normal basic cost.Text & TranslationEconomic manufacturing does not “just happen”. It starts with design and considers practical limits of machine tools, processes, tolerances, and finishes. 3Neithe

12、r dimensional tolerances nor surface roughness should be specified to limits of accuracy closer than those which the actual function or design necessitate. This is done to assure the advantages of lowest possible cost and fastest possible production.Text & TranslationWithout needing to know how to o

13、perate a particular machine to attain the desired degree of surface roughness, there are certain aspects of all these methods which should be understood by the design engineer. Knowledge of such facts as degree of roughness obtained by any operation, and the economics of attaining a smoother surface

14、 with each operation, will aid him in deciding just which surface roughness to specify.Text & TranslationBecause of its simplicity, the arithmetical average Ra has been adopted international and is widely used. The applications of surface roughness Ra are described in the following paragraphs.（1）0.2

15、 m. The finish is used for the interior surface of hydraulic struts, for hydraulic cylinders, pistons and piston rods for O-ring packings, for journals operating in plain bearing, for cam faces, and for roils of antifriction bearings when loads are normal.（2）0.4 m. The finish is used for rapidly rot

16、ating shaft bearings, for heavily loaded bearings, for roils in bearings of ordinary commercial grades, for hydraulic applications, for static sealing rings, for the bottom of sealing-ring grooves, for journals operating in plain beings, and for extreme tension members.Text & Translation（3）0.8 m. Th

17、e finish is normally found on parts subject to stress concentrations and vibrations, for broached holes, gear teeth, and other precision machined parts.（4）1.6 m. This finish is suitable for ordinary bearings, for ordinary machine parts where fairly close dimensional tolerances must be held, and for

18、highly stressed parts that are not subject to severe stress reversals.（5）3.2 m. The finish should not be used on sliding surfaces, but can be used for rough bearing surface where loads are light and infrequent, or for moderately stressed machine parts.（6）6.3 m. The appearance of this finish is not o

19、bjectionable, and can be used on non-critical component surface, and for mounting surfaces for brackets, etc.Text & Translation由于大多數(shù)制造業(yè)高度競爭的共性，找到降低成本的方法是永恒的主題。在產(chǎn)品設(shè)計中降低成本是一個好的開始。設(shè)計工程師在他的設(shè)計中應(yīng)始終謹(jǐn)記他可能的選擇。沒有對產(chǎn)品的大致成本做細致的分析而能做出最好的選擇是不可能的。功能、互換性、質(zhì)量和經(jīng)濟性的設(shè)計都要求對公差、表面光潔度、工藝、材料和設(shè)備進行仔細研究。Text & Translation從可加工的觀點

20、來看，要保證合理而經(jīng)濟的設(shè)計，這兩者和兩者的結(jié)合都極其重要，就要仔細考慮下面的一般設(shè)計規(guī)則。按照設(shè)計要求或者設(shè)計要素，其重要性的順序可以是變化的，但是其總的重要性總是相同的。（1）追求簡潔。設(shè)計時要最大限度的在功能上和物理特性上追求簡潔。（2）決定最好的加工方法。向生產(chǎn)工程師尋求幫助以使設(shè)計達到最經(jīng)濟的加工方法。Text & Translation（3）分析材料。選擇加工成本低而又滿足設(shè)計要求的材料。（4）消除固定與操作問題。設(shè)計要容易定位、安裝與調(diào)試。（5）采用最大可接受的公差與表面粗糙度。零件的表面粗糙度和尺寸精確度的確定，要和被設(shè)計的零件和裝置保持相當(dāng)，同時要匹配于預(yù)期的生產(chǎn)方法。 光潔

21、度和尺寸公差在最終效果或者沒有實際加工設(shè)計時起重要作用。Text & Translation通過了解和全方位評價廉價的生產(chǎn)技術(shù)是充分研究互換性原則的基礎(chǔ)。不管數(shù)量如何，互換性是成功加工的關(guān)鍵。所以零件的細節(jié)都應(yīng)該被仔細考慮以確保不僅工藝廉價而且容易快速裝配，方便維護。這就必須記住每個加工方法都有一個適當(dāng)?shù)木鹊燃壱员ＷC在不超出正常的基本成本時的連續(xù)加工。Text & Translation 經(jīng)濟制造并非一蹴而就，它總是以設(shè)計和機械制造的刀具、工藝、公差和光潔度的實際限制的考慮而開始。尺寸公差和表面粗糙度都不應(yīng)該被指定到超過實際功能或設(shè)計需要的界限。這樣做有利于保證到達盡可能最低的成本和盡可能最

22、快的加工。設(shè)計工程師沒有必要一定要知道怎樣去具體操作某些特殊的機器以獲得期望的表面粗糙度，但應(yīng)了解所有這些方法的某些特定的方面，比如通過操作獲取表面粗糙度的知識和對每種操作得到更光滑表面的經(jīng)濟性的知識，這樣在指定表面粗糙度時，將有助于設(shè)計工程師做出決定。Text & Translation由于其簡潔性，算術(shù)平均Ra已經(jīng)被國際上采納并被廣泛使用。表面粗糙度Ra的應(yīng)用具體介紹如下所述。（1）0.2m。這個光潔度被用于液壓支桿的內(nèi)表面、液壓缸、液壓活塞和活塞桿、O形密封圈、滑動軸承的軸承頸、凸輪面和正常負載下滾動軸承的滾子。（2）0.4m。這個光潔度被用于高速旋轉(zhuǎn)軸軸承、重載荷軸承、普通商業(yè)的軸承滾

23、子、液壓應(yīng)用、靜態(tài)密封圈、密封其槽底、運轉(zhuǎn)在滑動軸承中的軸頸和極度張緊的構(gòu)件。Text & Translation（3）0.8 m。這個光潔度通常出現(xiàn)在有應(yīng)力集中和震動的零件中，拉孔、輪齒及其他精加工零件。（4）1.6 m。這個光潔度適用于普通軸承，尺寸公差必須是被保持的正常封閉處的普通機械零件，不受劇烈交變應(yīng)力的高應(yīng)力零件。（5）3.2 m。這個光潔度不應(yīng)該被用于滑動表面，但能用于負載輕而平穩(wěn)的粗糙軸承表面，或者用于張緊適度的機械零件。（6）6.3 m。這個光潔度的出現(xiàn)并不令人討厭，它能用于非關(guān)鍵零件表面和軸承座的安裝面等。Complex Sentence Analysis1 Specify

24、 surface roughness and accuracy no greater than that which is commensurate with the type of part or mechanism being designed, and the production method or methods contemplated. 在確定零件的表面粗糙度和尺寸精度時，不應(yīng)該對零件或者機構(gòu)的設(shè)計，以及將要采用的生產(chǎn)方法提出過高的要求。 該句中的that指代 surface roughness and accuracy。 be commensurate with 是“相稱, 同

25、量”的意思 contemplated 分詞作后置定語，修飾前面的production method or methodsComplex Sentence Analysis2It must be remembered that each production method has a well-established level of precision which can be maintained in continuous production without exceeding normal basic cost. 這就必須記住每種加工方法都有一個適當(dāng)?shù)木鹊燃壱跃S持連續(xù)加工而不超出正常的基本成本。it：是形式主語，that：后面引導(dǎo)的從句是真正的主語which：引導(dǎo)限制性定語從句，修飾先行詞levelComplex Sentence Analysis3Neither dimensional tolerances nor surface roughness should be specified to limits of accuracy closer than those which the actual function or design nece