注塑模具畢業(yè)設(shè)計(jì)文獻(xiàn)翻譯--尺寸與表面粗糙度

1、<p>　　Dimensional Tolerances and Surface Roughness</p><p>　　The manufacture of machine parts is founded on the engineering drawing. Everyone engaged in manufacturing has a direct or indirect interest in

2、 understanding the meaning of the drawings on which the entire production process is established.</p><p>　　The engineer in industry is constantly fated with the fact that no two machine parts can ever be mad

3、e exactly the same. He learns that the small variations that occur in repetitive production must be considered in the design so that the tolerances placed on the dimensions will restrict the variations to acceptable limi

4、ts. The tolerances provide zones in which the outline of finished part must lie. Proper tolerancing practice ensures that the finished product functions in its intended manner and </p><p>　　A designer is wel

5、l aware that the cost of a finished product can increase rapidly as the tolerances on the components are made smaller. Designers are constantly admonished to use the widest tolerances possible. Situations may arise, howe

6、ver, in which the relationship between the various tolerances required for proper functioning has not been fully explored. Under such conditions the designer is tempted to specify part tolerances that are unduly tight in

7、 the hope that no difficulty will arise at </p><p>　　The allocation of proper production tolerances is therefore a most important task if the finished product is to achieve its intended purpose and yet be ec

8、onomical to produce. The size of the tolerances, as specified by the designer, depends on the many conditions pertaining to the design as well as on past experience with,similar products if such experience is available.A

9、 knowledge of shop processes and machine capabilities is of great assistance in helping to determine the tolerances in the mos</p><p>　　Ambiguities in engineering drawing can be cause of much confusion and e

10、xpense. When specifying the tolerances, the designer must keep in mind that the drawing must contain all requisite information if the designer's intent is to be fully realized. The drawing must therefore give complet

11、e information and at the same time be as simple as possible. The detail of drawing must be capable of being universally understood. The drawing must have one and only one meaning to everyone who will use it -- the</p&

12、gt;<p>　　Tolerances may be placed on the drawing in a number of different ways. In the unilateral system one tolerance is zero and all the variation of the dimension is given by the other tolerance. In bilateral

13、dimensioning a mean dimension is used with plus and minus variations extending each way from the mean dimension.</p><p>　　Unilateral tolerancing has the advantage that a tolerance revision can be made with t

14、he least disturbance to the remaining dimensions. In the bilateral system a change in the tolerances also involves a change in at least one of the mean dimensions. Tolerances can be easily changed back and forth between

15、 unilateral and bilateral for the purpose of making calculations.</p><p>　　A part is said to be at the maximum material condition (MMC) when the dimensions are all at the limits that will give a part contain

16、ing the maximum amount of material. For a shaft or external dimension, the fundamental dimension is the largest value permitted, and all the variation, as permitted by the tolerance, serves to reduce the dimension. For a

17、 hole or internal dimension, the fundamental dimension is the smallest value permitted, and the variation as given by the tolerance serves to make t</p><p>　　A part is said to be at the least material condit

18、ion (LMC) when the dimensions are all at the limits that give a part with the smallest amount of material. For LMC the fundamental value is the smallest for an external dimension and the largest for an internal dimension

19、. The tolerances thus provide parts containing larger amounts of material.</p><p>　　Maximum material tolerances have a production advantage. For art external dimension, should the worker aim at the fundament

20、al or largest value but form something small, the parts may be rework to bring them within acceptable limits. A worker keeping the mean dimension in mind would have smaller margins for any errors. These terms do, however

21、, provide convenient expressions for denoting the different methods for specifying the tolerances on drawings.</p><p>　　Dimensional variations in manufacturing are unavoidable despite all efforts to keep pro

22、duction conditions as constant as possible. The reasons for the variation in a chosen dimension on parts all made by the same process are of interest. The reasons can usually be grouped into two general classes: assignab

23、le cause and chance causes.</p><p>　　Assignable causes. A small modification in the process can cause variations in a dimension. A slight change in the properties of the raw material can cause a dimension

24、to vary. Tools will wear and must be reset. Changes may occur in the speed, the lubricant, the temperature, the operator, and other conditions. A systematic search will generally bring</p><p>　　such muses to

25、 light and steps can then be taken to have them eliminated.</p><p>　　Chance causes. Chance causes, on the other hand, occur at random and are due to vague and unknown forces which can neither be traced nor

26、rectified. They are inherent in the process and occur even though all conditions have been held as constant as possible.</p><p>　　When the variations due to assignable causes have been located and removed on

27、e by one, the desired state of stability or control is attained. If the variations due to chance causes are too great, it is usually necessary to move the operation to more accurate equipment rather than spend more effor

28、t in trying to improve the process.</p><p>　　Today's technology requires that parts be specified with increasingly exact dimensions. Many parts made by different companies at widely separated locations m

29、ust be interchangeable, which requires precise size specifications and production.</p><p>　　The technique of dimensioning parts within a required range of variation to ensure interchangeability is called tol

30、erancing. Each dimension is allowed a certain degree of variation within a specified zone, or tolerance. For example, a part's dimension might be expressed as 20 ± 0.50, which allows a tolerance (variation in si

31、ze) of 1.00 mm.</p><p>　　A tolerance should be as large as possible without interfering with the function of the part to minimize production costs. Manufacturing costs increase as tolerances become smaller.

32、</p><p>　　There are three methods of specifying tolerances on dimensions: Unilateral, bilateral, and limit forms. When plus-or-minus tolerancing is used, it is applied to a theoretical dimension called the

33、basic dimension. When dimensions can vary in only one direction from the basic dimension (either larger or smaller) tolerancing is unilateral. Tolerancing that permits variation in limit directions from the basic dimensi

34、on (larger and smaller) is bilateral.</p><p>　　Tolerances may also be given in limit form, with dimensions representing the largest and smallest sizes for a feature.</p><p>　　Some tolerancing te

35、rminology and definitions are given below.</p><p>　　Tolerance: the difference between the limits prescribed for a single feature.</p><p>　　Basic size: the theoretical size, form which limits or

36、deviations are calculated.</p><p>　　Deviation: the difference between the hole or shaft size and the basic size.</p><p>　　Upper deviation: the difference between the maximum permissible size of

37、a part and its basic size.</p><p>　　Lower deviation: the difference between the minimum permissible size of a part and its basic size.</p><p>　　Actual size: the measured size of the finished par

38、t.</p><p>　　Fit: the tightness between two assembled parts. The three types of fit are: clearance, interference and transition.</p><p>　　Clearance fit: the clearance between two assembled mating

39、 parts.</p><p>　　Interference fit: results in an interference between the two assembled parts--the shaft is larger than the hole, requiring a force or press fit, an effect similar to welding the two parts

40、.</p><p>　　Transition fits: may result in either an interference or a clearance between the assembled parts--the shaft may be either smaller or larger than the hole and still be within the prescribed tolera

41、nces.</p><p>　　Selective assembly: a method of selecting and assembling parts by trial and error and by hand, allowing parts to be made with greater tolerances at less cost as a compromise between a high ma

42、nufacturing accuracy and ease of assembly.</p><p>　　The basic hole system utilizes the smallest hole size as the basic diameter for calculating tolerances and allowances. The basic hole system is efficient w

43、hen standard drills, reamers, and machine tools are available to give precise hole sizes. The smallest hole size is the basic diameter bemuse a hole can be enlarged by machining but not reduced in size.</p><p&

44、gt;　　The basic shaft system is applicable .when shafts are available in highly precise standard sizes. The largest diameter of the shaft is the basic diameter for applying tolerances and allowances. The largest shaft siz

45、e is used as the basic diameter because shafts can be machined to smaller size but not enlarged.</p><p>　　International tolerance (IT) grade: a series of tolerances that vary with basic size to provide a uni

46、form level of accuracy within a given grade. There are I8 IT grades: IT01,IT0, IT1 ..... IT16.</p><p>　　Tolerance symbols: notes giving the specifications of tolerances and fits; the basic size is a number

47、, followed by the fundamental deviation letter and the IT number, which combined give the tolerance zone; uppercase letters indicate the fundamental deviations for holes, and</p><p>　　lowercase letters indic

48、ate fundamental deviations for shafts.</p><p>　　Because the surface texture (or surface finish) of a part affects its function, it must be precisely specified. Surface texture is the variation in a surface,

49、 including roughness, waviness, lay and flaws.</p><p>　　Roughness: the finest of the irregularities in the surface caused by the manufacturing process used to smooth the surface. Roughness height is measured

50、 in micrometers (um) or microinehes(uin).</p><p>　　Waviness: a widely spaced variation that exceeds the roughness width cutoff measured in inches or millimeters; roughness may be regarded as a surface variat

51、ion superimposed on a wavy surface.</p><p>　　Lay: the direction of the surface pattern caused by the production method used.</p><p>　　Flaws: defects occurring infrequently or at widely varying i

52、ntervals on a surface, including cracks, blow holes, checks, scratches, and the like; the effect of flaws is usually omitted in roughness height measurements.</p><p><b>　　尺寸與表面粗糙度</b></p>

53、<p>　　工程圖樣是制造機(jī)器零件的依據(jù)。因此，從事制造業(yè)的人員都要正確理解應(yīng)用于整個(gè)生產(chǎn)過(guò)程的圖樣的含義。</p><p>　　在企業(yè)中工作的工程師總要畫(huà)對(duì)這樣一個(gè)事實(shí)，即任何兩個(gè)機(jī)器零件都不能制造得完全相同。他知道在沒(méi)汁中必須考慮在重復(fù)性生產(chǎn)中所產(chǎn)生的微小尺寸差異，在圖樣上標(biāo)注合適的公差，將尺寸的變化限制在允許的范圍內(nèi)。加工后的零件的外形輪廓必須位于公差規(guī)定的區(qū)域內(nèi)。采用適當(dāng)?shù)墓羁梢员ＷC產(chǎn)品在功能

54、和使用壽命方面都能達(dá)到預(yù)期的目標(biāo)。</p><p>　　每位設(shè)計(jì)人員都非常清楚，如果零件都以較小的公差來(lái)加工制造，則產(chǎn)品的成本就會(huì)迅速增加。因此，工程師們不斷地得到勸告，要采用盡可能大的公差。然而，有時(shí)可能出現(xiàn)對(duì)功能要求所需要的各種公差之間的相互關(guān)系沒(méi)有進(jìn)行充分研究的情況。在這種情況下，為了保證零件在裝配時(shí)不發(fā)生問(wèn)題，設(shè)計(jì)人員通常不恰當(dāng)?shù)貙⒐钜?guī)定得過(guò)于嚴(yán)格，相對(duì)于認(rèn)真、透徹地對(duì)公差進(jìn)行分析來(lái)說(shuō)，這顯然是一個(gè)價(jià)格

55、昂貴的替代方式。</p><p>　　要使產(chǎn)品以較低的價(jià)格被生產(chǎn)出來(lái)并且能夠滿足設(shè)計(jì)的要求，規(guī)定適當(dāng)?shù)募庸す钍亲顬橹匾墓ぷ鳌９畹拇笮∈怯稍O(shè)計(jì)人員所確定的，它取決于許多與設(shè)計(jì)有關(guān)的條件以及過(guò)去在設(shè)計(jì)類(lèi)似產(chǎn)品時(shí)所獲得的經(jīng)驗(yàn)(如果有這方面經(jīng)驗(yàn)的話)。如果所規(guī)定的公差太小，以至于采用現(xiàn)有的加工設(shè)備加工工件的這個(gè)尺寸時(shí)無(wú)法達(dá)到設(shè)汁要求，就需要對(duì)設(shè)計(jì)進(jìn)行修改。</p><p>　　工程圖樣中模糊

56、不清楚的地方會(huì)引起很多混亂和經(jīng)濟(jì)損失。在擬定公差時(shí)，設(shè)計(jì)人員必須充分認(rèn)識(shí)到，要完全達(dá)到其設(shè)計(jì)目的，圖樣上必須包含所有必要的信息。因而，圖樣上必須給出全部信息，并且盡可能地簡(jiǎn)單明了。圖樣中的每個(gè)部分內(nèi)容都應(yīng)該能被大家所理解。圖樣中所表示的含義對(duì)于所有使用它的人員(設(shè)計(jì)，采購(gòu)，刀具設(shè)計(jì)，生產(chǎn)，檢驗(yàn)，裝配和維修部門(mén))來(lái)說(shuō)都應(yīng)該是惟一的。</p><p>　　公差在圖樣上可以采用不同的標(biāo)注方式。在單向制中，一個(gè)極限偏差是

57、零，另一個(gè)極限偏差就是尺寸允許的全部變動(dòng)量。在雙向制中尺寸標(biāo)注中，采用平均尺寸和在其正負(fù)兩個(gè)方向上的變動(dòng)量來(lái)表示。</p><p>　　當(dāng)所有的尺寸都處在允許零件含有的材料量為最多的極限狀態(tài)時(shí)，就稱這個(gè)零件處于最大實(shí)體狀態(tài)(MMC)。對(duì)于一根軸或者一個(gè)外形尺寸，它的基本尺寸為最大極限尺寸，它在公差范圍內(nèi)變動(dòng)時(shí)，只能使尺寸減小。對(duì)于一個(gè)孔或者內(nèi)部尺寸，它的基本尺寸為最小極限尺寸，在公差范圍內(nèi)的變動(dòng)，只能使尺寸增大。

58、</p><p>　　當(dāng)所有的尺寸都處在允許零件含有的材料量為最小的極限狀態(tài)時(shí)，就稱這個(gè)零件處于最小實(shí)體狀態(tài)(LMC)。按LMC標(biāo)注公差時(shí)，對(duì)于外形尺寸，它的基本尺寸為最小極限尺寸；對(duì)于內(nèi)孔尺寸，它的基本尺寸為最大極限尺寸。在公差范圍內(nèi)的尺寸變動(dòng)，會(huì)使零件包含的材料量增加。按最大實(shí)體尺寸標(biāo)注公差對(duì)生產(chǎn)有利。對(duì)于一個(gè)外形尺寸，工人按照其基本尺寸或最大極限尺寸進(jìn)行加工，如果其去除量過(guò)小，還可以通過(guò)重新加工，使工件尺寸

59、在允許的范圍內(nèi)。一個(gè)工人按平均尺寸進(jìn)行加工時(shí)，加工偏差只能在小范圍內(nèi)變動(dòng)。不管怎樣，上述概念為以不同方式在零件圖樣上標(biāo)注公差提供了方便的表達(dá)形式。</p><p>　　在機(jī)械制造中，雖然盡可能保持穩(wěn)定的生產(chǎn)條件，但是加工后獲得的尺寸仍然不可避免地出現(xiàn)誤差。在完全相同的制造過(guò)程中，按某一指定尺寸加工一批零件，加工后所得到的尺寸卻并不完全相同。產(chǎn)生這種現(xiàn)象的原因值得人們研究。一般將產(chǎn)生這種現(xiàn)象的原因分兩大類(lèi)，系統(tǒng)原因

60、和隨機(jī)原因。</p><p>　　系統(tǒng)原因 生產(chǎn)過(guò)程中某些因素的微小變動(dòng)可以引起尺寸變化。原材料性能的微小變化可～引起尺寸變化。刀具受到磨損并且需要重新安裝。速度、潤(rùn)滑劑、切削溫度、操作人員以及其他條件都會(huì)發(fā)生變化。通過(guò)系統(tǒng)地分析研究，一般可以找出這些原因并可采取相應(yīng)的步驟來(lái)消除它。</p><p>　　隨機(jī)原因 另一方面隨機(jī)原因的出現(xiàn)是具有偶然性的。它們是由一些既無(wú)法確定又不能控制的

61、力所造成的。它們是生產(chǎn)過(guò)程的固有誤差，即使盡可能地保持所有條件完全一致，它們?nèi)匀徊豢杀苊獾卮嬖凇?lt;/p><p>　　當(dāng)依次檢查由系統(tǒng)原因造成的誤差，并且將其逐一排除后，即可達(dá)到理想的穩(wěn)定狀態(tài)或控制狀態(tài)。如果隨機(jī)原因?qū)Τ叽缱兓挠绊戇^(guò)大，一般來(lái)說(shuō)采用更精密的加工設(shè)備，要比花費(fèi)更多精力來(lái)改變生產(chǎn)過(guò)程更為有效。</p><p>　　現(xiàn)代技術(shù)對(duì)零件尺寸精度的要求越來(lái)越嚴(yán)格。而且，目前許多零件是由

62、散布在各地的不同廠家生產(chǎn)的，因此必須對(duì)這些零件的尺寸和生產(chǎn)做出嚴(yán)格的規(guī)定，以保證它們具有互換性。</p><p>　　給零件標(biāo)注尺寸使其在一個(gè)規(guī)定的區(qū)間內(nèi)變動(dòng)，以保證它們具有互換性的技術(shù)稱為公差技術(shù)。允許每個(gè)尺寸在規(guī)定范圍內(nèi)具有一定的變動(dòng)量，稱為公差。例如，一個(gè)零件的尺寸可以被表示成20±0．5，其公差(尺寸變動(dòng)量)為1．00mm。</p><p>　　在不影響零件性能的情況下，

63、應(yīng)當(dāng)給尺寸盡可能大的公差，以把生產(chǎn)成本降至最低。制造成本會(huì)隨著公差的降低而升高。</p><p>　　有三種表示尺寸公差的方式：?jiǎn)蜗?，雙向和極限方式。當(dāng)采用正負(fù)公差時(shí)，就將公差加到被稱為基本尺寸的理論尺寸上去。當(dāng)只允許尺寸有向基本尺寸的單一方向(或者變大，或者變小)的變動(dòng)時(shí)，就是單向公差。在尺寸可以在基本尺寸的兩個(gè)方向(變大或者變小)都可以變動(dòng)時(shí)，公差就是雙向的。公差也可以用極限形式給出，表示零件外形的最大和最小

64、尺寸。</p><p>　　一些與公差有關(guān)的術(shù)語(yǔ)和定義如下述。</p><p>　　公差：為某個(gè)尺寸所規(guī)定的上限與下限之間的差值。</p><p>　　基本尺寸：理論尺寸，是計(jì)算極限尺寸和偏差的起始尺寸。</p><p>　　偏差：孔的尺寸或者軸的尺寸減去基本尺寸所得的差值。</p><p>　　上偏差：零件最大極限尺

65、寸減去其基本尺寸所得的差值。</p><p>　　下偏差：零件最小極限尺寸減去其基本尺寸所得到的差值。</p><p>　　實(shí)際尺寸：加工后零件的實(shí)測(cè)尺寸。</p><p>　　配合：兩個(gè)裝配在一起的零件之間的松緊程度?？梢园雅浜戏譃槿?lèi)：間隙配合，過(guò)盈配合，過(guò)渡配合。 </p><p>　　間隙配合：兩個(gè)裝配在—起配件之間留有間隙的配

66、合。</p><p>　　過(guò)盈配合：兩個(gè)裝配在——起的零件之間有過(guò)盈的配合一一軸大于孔，需要用力或壓力進(jìn)行配合，具有類(lèi)似于將兩個(gè)零件焊接在——起的效果。</p><p>　　過(guò)渡配合：在兩個(gè)裝配在一起的零件之間或者存在著過(guò)盈，或者存在著間隙的配合——軸可以小于或大于孔，但仍在規(guī)定的公差內(nèi)。</p><p>　　選擇裝配：通過(guò)手工試配來(lái)選擇并裝配零件的方法。通過(guò)這種方

67、法，可以裝配在較低的成本下制造出來(lái)的公差較大的零件，它可作為高的制造精度和易于裝配的零件之間的一種折中方法。</p><p>　　基孔制：采用最小的孔的尺寸作為計(jì)算公差和加工余量基本尺寸。當(dāng)采用標(biāo)準(zhǔn)的鉆頭、鉸刀和機(jī)床對(duì)孔進(jìn)行精加工時(shí)，基孔制系統(tǒng)是非常有效的。采用最小的孔的尺寸作為基本尺寸是因?yàn)榭椎某叽缈梢酝ㄟ^(guò)機(jī)械加工變大，但不能減小。</p><p>　　當(dāng)軸可以按照非常的高精度的標(biāo)準(zhǔn)尺寸

68、提供時(shí)，采用基軸制是適用的。計(jì)算公差和余量時(shí)，采用軸的最大直徑作為基本尺寸。這是因?yàn)檩S可以通過(guò)加工變成較小的尺寸，但其尺寸不能增大。</p><p>　　國(guó)際公差(IT)等級(jí)：一系列隨基本尺寸變化，且在規(guī)定等級(jí)內(nèi)提供均勻精度的公差。共有18個(gè)IT等級(jí)：ITOI，ITO，IT1，…，ITl6。</p><p>　　公差符號(hào)：符號(hào)給出了公差與配合的技術(shù)要求，基本尺寸是一個(gè)數(shù)字，后面跟著表示基本

69、偏差的字母和表示IT等級(jí)的數(shù)字。它們共同決定公差帶的大小和位置。大寫(xiě)字母代表孔的基本偏差，小寫(xiě)字母代表軸的基本偏差。</p><p>　　由于表面形貌(即表面光潔程度)會(huì)影響零件的性能，因此對(duì)其大小必須精確地加以規(guī)定，表面形貌是表面上的差異，包括粗糙度，波度，加工紋理方向和缺陷。</p><p>　　粗糙度：由用來(lái)使工件表面光滑的加工工藝所造成的最細(xì)微的表面不平度。表面粗糙度的高度采用微米

70、或微英寸進(jìn)行測(cè)量。</p><p>　　波度：是超過(guò)粗糙度寬度界限的大間隔偏差，采用英寸或毫米測(cè)量?？蓪⒋植诙瓤醋霪B加在波度表面上的表面不平度。</p><p>　　加工紋理方向：由所采用的加工方法所產(chǎn)生的表面刀痕圖案的方向。 ‘</p><p>　　缺陷：不經(jīng)常出現(xiàn)或者在很大區(qū)間內(nèi)才會(huì)出現(xiàn)的表面瑕疵，其包括裂紋、氣孔、微細(xì)裂紋，劃痕等。缺陷的影響通常在粗糙度