unit 7 Tolerances and Fits

1、UNIT 6Tolerances and Fits第第1010講講 1Introduction 2Tolerances3Fits 4ISO System of Limits and Fits Any manufacturer should have a thorough knowledge of the tolerances to increase the quality and reliability of a manufactured part with the least expense. Deviations of actual surfaces are divided into fo

2、ur groups to enable assessment, prescription and checking of the permitted inaccuracy during production: 1. Dimensional deviationsdi:viein;（尺寸偏差）（尺寸偏差） 2. Shape deviations;（形狀偏差）（形狀偏差） 3. Position deviations;（位置偏差）（位置偏差） 4. Surface roughness deviations;（表面粗糙度偏差）（表面粗糙度偏差）7.1 Introduction It is quite

3、sufficient that the actual dimension of the part is found between two limit dimensions and permissible deviation is kept with production to ensure correct functioning of engineering products. 在很多情況下，零件的實際尺寸介于兩個極限尺寸之間在很多情況下，零件的實際尺寸介于兩個極限尺寸之間，在制造的過程中一直維持一個允許偏差以保證工程零，在制造的過程中一直維持一個允許偏差以保證工程零件所具有的功能。件所具有

4、的功能。 Unnecessarily tight tolerances lead to high cost of manufacture resulting from more expensive manufacturing methods and higher reject rates. 不必要的緊公差會導致由于昂貴的制造方法和較高的廢不必要的緊公差會導致由于昂貴的制造方法和較高的廢品率所帶來的高的制造成本。品率所帶來的高的制造成本。7.1 Introduction Definitions. Tolerance is the difference between the maximum an

5、d minimum size limits of a part. Size(尺寸尺寸). The size of an object or its mate is known as nominal, basic, or design size. Allowance(允差允差). The difference between the largest allowable shaft size and the smallest hole diameter is termed as the allowance. The quality of the fit is characterized by th

6、e allowance value. Fit (配合配合). Clearance, interference, or transition fit refer to how the object fits an assembly.7.2 TolerancesNominal Size (basic size)(名義尺寸，基本尺寸名義尺寸，基本尺寸). It is the designation used for general identification and usually expressed in common fractions. It is an exact theoretical

7、size of a part from which limit dimensions are computed. The nominal size of a part should be selected from the preferred dimension series indicated by the national standard.是用于識別的一個表示，通常用簡分數(shù)的形式給出。它表示一個是用于識別的一個表示，通常用簡分數(shù)的形式給出。它表示一個零件的精確的理論尺寸，根據(jù)名義尺寸可以計算出極限尺寸。零零件的精確的理論尺寸，根據(jù)名義尺寸可以計算出極限尺寸。零件的名義尺寸應該從國家標準規(guī)

8、定的優(yōu)先尺寸系列中選取。件的名義尺寸應該從國家標準規(guī)定的優(yōu)先尺寸系列中選取。Limit size(極限尺寸極限尺寸). It includes upper limit size and lower limit size which are allowable extreme size of a part.Actual size(實際尺寸實際尺寸). It is the measured size of the finished part.7.2 Tolerances Deviations(偏差偏差). The upper and lower deviations obtained by sub

9、tracting basic size from limit size. Allowance(允差允差). The intentional difference between the maximum material limits of mating parts. This is a minimum clearance (positive allowance) or maximum interference (negative allowance) between mating parts. 配合零件的最大極限尺寸間的差值，它是配合零件之間配合零件的最大極限尺寸間的差值，它是配合零件之間的最

10、小間隙量（正允差）或最大過盈量（負偏差）。的最小間隙量（正允差）或最大過盈量（負偏差）。7.2 Tolerances Bilateral Tolerances(雙邊公差雙邊公差). A bilateral tolerance is a tolerance in which variation is permitted in both directions from a specified dimension. 雙邊公差允許相對于基本尺寸的沿兩個方向變動。雙邊公差允許相對于基本尺寸的沿兩個方向變動。 The actual size of the object may be larger or s

11、maller than the stated size limitation if there can be equal variation in both directions. The plus and minus limitations combine to form a single value. 如果在兩個方向上具有相同的變動量，零件的實際尺寸如果在兩個方向上具有相同的變動量，零件的實際尺寸就有可能大于或小于標注的尺寸極限。正負極限就構成就有可能大于或小于標注的尺寸極限。正負極限就構成一個數(shù)值。一個數(shù)值。7.2 Tolerances Unilateral Tolerances (單邊

12、公差單邊公差). A unilateral tolerance is a tolerance in which variation is permitted only in one directions from a specified dimension. 單邊公差是指相對于名義尺寸只能沿一個方向變動。單邊公差是指相對于名義尺寸只能沿一個方向變動。 Unilateral tolerance expression has the advantage that they are easier to check on drawings and that the change in the tole

13、rance can be made with the least disturbance to other dimensions. 單邊公差表達方式的優(yōu)點是用它來檢查圖紙比較方便。單邊公差表達方式的優(yōu)點是用它來檢查圖紙比較方便。7.2 Tolerances Clearance fit. it is a fit enabling a clearance between the hole and shaft in the coupling. The lower limit size of the hole is greater or at least equal to the upper limi

14、t size of the shaft. Interference fit. It is a fit always ensuring interference between the hole and shaft in the coupling. The upper limit size of the hole is smaller or at least equal to the lower limit size of the shaft. Transition fit. It is a fit where (depending on the actual sizes of the hole

15、 and shaft) both clearance and interference may occur in the coupling. Tolerance zones of the hole and shaft partly or completely interfere.7.3 Fits How mating parts or assemblies fit together with component parts is referred to as fit, which includes clearance fit, interference fit, or transition f

16、it, see Fig.7.3. Fit is general range of tightness resulting from the application of a specific combination of allowance and tolerances in the design of mating parts.The types of fittingClearance fit 間隙配合間隙配合Interference fit 過盈配合過盈配合Transition fit 過渡配合過渡配合7.3 Fits下偏差下偏差公差帶公差帶+0.008-0.008+0.008+0.024

17、-0.006-0.022公差帶圖：公差帶圖：作用：直觀地表示出了公差的大小及公差帶相作用：直觀地表示出了公差的大小及公差帶相對于零線的位置。對于零線的位置。50+0.024+0.00850-0.006-0.02200基本尺寸基本尺寸 50例例: 500.008上偏差上偏差7.3 FitsClearance fitFit with clearance (including minimum clearance zero).Maximum clearanceMinimum limit of sizeMaximum limit of sizeMinimum clearanceMaximum clear

18、anceThe tolerance zone of hole is above that of the shaft.Minimum limit of sizeMaximum limit of sizeInterference fitMinimum interferenceMaximum interferenceThe tolerance zone of hole is below that of the shaft. Fit with interference (including minimum Interference zero)Maximum limit of sizeMinimum l

19、imit of sizeMaximum interference第第11講講Transition fitFit having clearance of interference .The tolerance zone of hole overlaps that of the shaft. The ISO system of tolerances and fits can be applied in tolerances and deviations of smooth parts and for fits created by their coupling. It is used partic

20、ularly for cylindrical parts with round sections. Tolerances and deviations in this standard can also be applied in smooth parts of other sections. ISOISO公差和配合體系可以用于光滑零件的公差和偏差以及連公差和配合體系可以用于光滑零件的公差和偏差以及連接件的配合的確定，特別用于圓形截面的圓柱形零件。該體接件的配合的確定，特別用于圓形截面的圓柱形零件。該體系中的公差和偏差也可以用于其它形狀截面的零件。系中的公差和偏差也可以用于其它形狀截面的零件。

21、7.4 ISO System of Limits and Fits Similarly, the system can be used for coupling (fits) of cylindrical parts and fits with parts having two parallel surface (e.g. fits of keys in grooves). The term “shaft”, used in this standard has wide meaning and serves for specification of all outer elements of

22、the part, including those elements which do not have cylindrical shapes. Also, the term “hole” can be used for specification of all inner elements regardless of their shape. 同樣地，該標準還可以應用于圓柱形零件的連接（配合）及具有同樣地，該標準還可以應用于圓柱形零件的連接（配合）及具有兩平行表面的零件的配合（如鍵和鍵槽的配合）。標準中采用的兩平行表面的零件的配合（如鍵和鍵槽的配合）。標準中采用的“軸軸”這一詞有廣泛的含義，

23、它用于說明零件的所有外部元素，這一詞有廣泛的含義，它用于說明零件的所有外部元素，包括那些不是圓柱形表面的元素。而包括那些不是圓柱形表面的元素。而“孔孔”這個詞則可以指不考這個詞則可以指不考慮形狀的零件的所有內部元素。慮形狀的零件的所有內部元素。7.4 ISO System of Limits and Fits In order to meet the requirements of various production branches for accuracy of the product, the system ISO implements 20 grades of accuracy. E

24、ach of the tolerances of this system is marked “IT” with attached grade of accuracy (IT01, IT0, IT1 IT18). Note: IT is an acronym for International Tolerance. 為了滿足不同生產(chǎn)部門對產(chǎn)品精度的需求，為了滿足不同生產(chǎn)部門對產(chǎn)品精度的需求，ISO標準規(guī)定標準規(guī)定了了20級精度等級。級精度等級。7.4 ISO System of Limits and Fits The tolerance zone is defined as annular z

25、one（環(huán)形（環(huán)形區(qū)域）區(qū)域） limited by the upper and lower limit dimensions of the parts. The tolerance zone is therefore determined by the amount of the tolerance and its position related to the basic size. The position of the tolerance zone, related to the basic size (zero line), is determined in the ISO syst

26、em by a so-called basic deviation. 公差帶是上極限尺寸和下極限尺寸間的環(huán)形區(qū)域。因此，公差帶是上極限尺寸和下極限尺寸間的環(huán)形區(qū)域。因此，公差帶由公差值及其與基本尺寸的相對位置所決定的。公差帶由公差值及其與基本尺寸的相對位置所決定的。ISO標準中公差帶相對于基本尺寸（零線）的位置是由基標準中公差帶相對于基本尺寸（零線）的位置是由基本偏差決定的。本偏差決定的。7.4 ISO System of Limits and Fits The system ISO defined 28 classes of basic deviations for holes. These

27、 classes are marked by capital letters (A, B, C ZC). The tolerance zone for the specified dimensions is prescribed in the drawing by a tolerance mark, which consists of a letter marking of the basic deviation and a numerical marking of the tolerance grade (e.g. H7, H8, D5, etc.). 對于孔，對于孔，ISO標準定義了標準定

28、義了28類基本偏差，由大寫字母類基本偏差，由大寫字母(A, B, C )表示。在圖樣中規(guī)定尺寸（設計尺寸）的公差帶是通過公差表示。在圖樣中規(guī)定尺寸（設計尺寸）的公差帶是通過公差代號表示的，它由表示基本偏差的字母和表示公差等級的數(shù)字代號表示的，它由表示基本偏差的字母和表示公差等級的數(shù)字組成。組成。Though the general sets of basic deviations and tolerance grades can be used for prescriptions of hole tolerance zone by their mutual combinations, in p

29、ractice only a limited range of tolerance ones is used.7.4 ISO System of Limits and Fits Though the general sets of basic deviations and tolerance grades can be used for prescriptions of h o l e t o l e r a n c e z o n e b y t h e i r m u t u a l combinations, in practice only a limited range of tol

30、erance ones is used. 盡管基本偏差和公差等級的盡管基本偏差和公差等級的所有集合所有集合可以通過相互組可以通過相互組合確定孔的公差帶，但是在實際應用中，只采用公差合確定孔的公差帶，但是在實際應用中，只采用公差帶中的一小部分。帶中的一小部分。7.4 ISO System of Limits and Fits Basic deviationRS TPCDEFFGCDEHYABGJSKM NUVXZZAZBZCFBasic sizezero line0+-HoleJ0+rafgdefcdbhjsjkmnps tuxzzazbzcgecfvyBasic sizezero line0-

31、Shaft07.4 ISO System of Limits and Fits Although there can be generally coupled parts without any tolerance zones, only two methods of coupling of holes and shafts, namely basic hole system and basic shaft system, are recommended due to constructional, technological and economic reasons.盡管存在沒有公差帶的一般

32、裝配零件，基于結構、技術和經(jīng)濟盡管存在沒有公差帶的一般裝配零件，基于結構、技術和經(jīng)濟的原因，只推薦兩種孔和軸的配合方法，即基孔制和基軸制。的原因，只推薦兩種孔和軸的配合方法，即基孔制和基軸制。Basic hole system (BHS): A system of fits in which the design size of the hole is the basic size and the allowance, if any ,is applied to the shaft.Basic shaft system (BSS): A system of fits in which the

33、design size of the shaft is the basic size and the allowance, if any, is applied to the hole.7.4 ISO System of Limits and Fits BHS: When specifying the tolerance for a hole and cylinder and determining their dimensions, you should begin calculating by assuming either the minimum hole or maximum shaf

34、t size if they are to fit together well. 當給一個孔或圓柱面指定公差和決定尺寸時，需要假設最當給一個孔或圓柱面指定公差和決定尺寸時，需要假設最小尺寸的孔或最大尺寸的軸配合良好，并進行計算。小尺寸的孔或最大尺寸的軸配合良好，并進行計算。 The desired clearances and interferences in the fit are achieved by combinations of various shaft tolerance zones with the hole tolerance zone “H”. 配合中所需要的間隙和過盈量可

35、以通過不同的軸的公差帶配合中所需要的間隙和過盈量可以通過不同的軸的公差帶與代號為與代號為“H”的孔的公差帶組合來實現(xiàn)。的孔的公差帶組合來實現(xiàn)。7.4 ISO System of Limits and Fits basic size25 H7/g6basic dev.for the holeIT gradefor the holebasic dev.for the shaftIT gradefor the shafttolerance zoneBasic. Dev.BHS7.4 ISO System of Limits and Fits 第第12講講 allowance: 0.003the mi

36、nimum hole size (basic size) : 1.500tolerance: 0.002What is the maximum diameter of the shaft? (clearance fit or interference fit)holeCminshaftAllowance of the fit corresponds to maximum material condition (Cmin).holeshaftmaxIAllowance of the fit corresponds to maximum material condition (Imax).7.4

37、ISO System of Limits and Fits To calculate the maximum diameter of the shaft, assume an allowance of 0.003 and subtract that from the basic hole size. Arbitrarily selecting a tolerance of 0.002 for both the hole and shaft gives a maximum hole (1.502) and minimum shaft (1.495). The minimum clearance

38、fit is the difference between the smallest hole (1.500) and the largest shaft (1.497) or 0.003. By adding the allowance to the basic hole size, the maximum shaft size of an interference fit is obtained. To convert basic hole size to basic shaft size, we subtract the allowance for a clearance fit or

39、add it for an interference fit.7.4 ISO System of Limits and Fits tolerance zoneBasic. Dev.Basic. Dev.BHSBSSbasic sizebasic sizeholetolerance zoneshaftholeshafttolerance zone7.4 ISO System of Limits and Fits Any manufacture should have thorough knowledge of the tolerances and fits to increase the quality and reliability of a manufactured part with the least expense. The increase compatibility（互換性）（互換性） of a certain product with mating parts by difference manufacturers makes it more viable in market competition. Moreover, a knowledge of tolerances