互換性與測(cè)量技術(shù)(漢英雙語)分享課件

1、1 Tolerances and fits. This book includes tables and calculations for easy option of fits of machine parts and determination of their dimensional tolerances and deviations. Using this tool the following tasks can be solved: Selection of suitable fits of machine parts according to the international s

2、tandard ISO 286. Determination of dimensional tolerances and deviations of machine parts according to the international standard ISO 286. 2 Selection of preferred fits of machine parts and determination of their dimensional tolerances and deviations according to ANSI B4.1. Determination of non-presc

3、ribed limit deviations of linear and angular dimensions according to ISO 2768. Automatic design of a fit for the given clearance or fit interference respectively.3 Basic terms. It is necessary that the dimensions, shape and mutual position of surfaces of individual parts of mechanical engineering pr

4、oducts are kept within a certain accuracy to achieve their correct and reliable functioning. Routine production processes do not allow maintenance (or measurement) of the given geometrical properties with absolute accuracy. : 4 Actual surfaces of the produced parts therefore differ from ideal surfac

5、es prescribed in drawings. Deviations of actual surfaces are divided into four groups to enable assessment, prescription and checking of the permitted inaccuracy during production5Dimensional deviations Shape deviations Position deviations Surface roughness deviations6 More Terminology Nominal Size

6、- General identification in fractions (ex. 1-1/2 for 1.500). Basic Size - General identification in decimal (ex. 1.500). d=D . basic size Actual Size - Measured size. Limits - Maximum and minimum sizes indicated by the tolerance dimensions. Dmax , Dmin . limits of size for the holedmax , dmin . limi

7、ts of size for the shaft7 ES . hole upper deviation EI . hole lower deviationes . shaft upper deviationei . shaft lower deviation ES= Dmax-D EI= Dmin-D es= dmax-d ei= dmin-d8Tolerance is the total amount a specific dimension is permitted to vary (difference between the maximum and minimum limits). T

8、h= Dmax- Dmin=ES-EI Ts= dmax-dmin = es- ei9es=14.996-15=-0.004ei=14.993-15=-0.007Ts= dmax-dmin = es- ei=0.003The dimension below has a tolerance of 0.00310 Maximum Material Condition When specifying tolerance dimensions, themaximum material condition (MMC) means the product or part contains the maxi

9、mum amount of material specified by the tolerance. The heaviest partDM=DmindM =dmax11 Least Material Condition When specifying tolerance dimensions, the Least material condition (LMC) means the product or part contains the least amount of material specified by the tolerance. The lightest partDL= Dma

10、xdL= dmin12tolerance zones Zero Line Above Positive Below Negative Draw upper deviation and lower deviation in the zone Mark the Basic dimension on the left13 Depending on the mutual position of tolerance zones of the coupled parts, 3 types of fit can be distinguished: Clearance fit Transition fit I

11、nterference fit 14 Clearance fit Xmax=Dmax- dmin=ES-ei Xmin=Dmin- dmax=EI-es Xav= (Xmax + Xmin )/215Transition fit Ymax=Dmin-dmax=EI-es Ymin=Dmax-dmin=ES-ei Yav= （ Ymax + Ymin ）/216Interference fit Xmax=Dmax-dmin=ES-ei Ymax=Dmin-dmax=EI-es Xav 或Yav = （Xmax + Ymax）/217Fit Tolerance Clearance fit: Tf=

12、 |Xmax - Xmin | Interference fit： Tf = | Ymin - Ymax | Transition fit ： Tf = | Xmax -Ymax | Tf=|(ES-ei)-(es-EI)|=|(ES-EI)+(es-ei)|= Th+Ts18Fit SystemHole-basic system of fitshaft-basic system of fit19Practise2021The standard tolerance series IT+figure IT01、IT0、IT1、IT2、 、IT18 Accuracy ：from high to l

13、ow （Precision Degradation） tolerance/value：from low to high manufacture： from hard to easy 22standard tolerance table23basic deviation 26 English letters eliminate i、l、o、q、w add cd、ef、fg、js、za、zb、 zcin total 28 seriesLowercase express shaftCapital express holefor example25f630T780js72425Characterist

14、ics and ApplicationA-H lower deviation is basic deviation,it is positivea-h upper deviation is basic deviation,it isnegative EI=-esP-ZC upper deviation is basic deviation,it is negativem-zc lower deviation is basic deviation,it is positiveIT7 ES=-eiIT8 ES=-ei=IT8 ES=-ei+ =ITn-ITn-1 J only 6.7.8 grad

15、ej、k lower deviation is basic deviationj only 5.6.7.8 gradek is specific, divided into two part.Oneis IT7;other is IT3-IT727Basic size 0 to 500mm basic deviation of shaft2829Basic size 0 to 500mm basic deviation of hole3031一、General concepts of geometrical tolerances1、Form error Form error is the va

16、riation of the true form of a single factor to its perfect form.Make a small shaft found to be distortion and not cylindrical, or the section is out of round,or the axes is bended,or make a plane found to be warp.Geometrical TolerancesGeometrical Tolerances 322、Position error Position error is theva

17、riation of the actual position of related factors to its ideal position form.While machining a stepped shaft, the axial cord of each step may not be The same, namely, concentricity and coaxiality error.Surfaces expected to be perpendicular are not perpendicular after it machined.33二、Codes of geometr

18、ical tolerances 1、Geometrical tolerances342、Code of geometrical tolerance The code of the geometrical tolerance is reprsented by the form and position frames353、Reference code The reference code is made up of the capital letter with a small circle connected by fine lines and short thick lines. In or

19、der to avoid misunderstanding, generally, E、I、J、M、O、P and such letters are not adopted.36二、二、Method of marking geometrical tolerances 1. If the element being tested with a tolerance requirement is a contour line or surface, point the arrow and datum symbol to the contour line or surface, and keep it

20、 away from the dimension line37 2. If the element being tested with tolerance requirements is an axis, centre line or symmetrical plane, the arrow and datum symbol should be aligned to the dimension line of that element38 3. If the element being tested is a surface on the drawing, one can draw a reference line with a dot end and point the arrow or datum symbol to the refere