互换性与测量技术(汉英双语)（课堂PPT）

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

2、standard 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-pre

3、scribed 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

4、products 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 sur

5、faces prescribed in drawings. Deviations of actual surfaces are divided into four groups to enable assessment, prescription and checking of the permitted inaccuracy during production.5Dimensional deviations Shape deviations Position deviations Surface roughness deviations.6 More Terminology Nominal

6、Size - 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 .

7、 limits of size for the shaft.7 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-d.8Tolerance is the total amount a specific dimension is permitted to vary (difference between the maximum and minimum lim

8、its). Th= Dmax- Dmin=ES-EI Ts= dmax-dmin = es- ei.9es=14.996-15=-0.004ei=14.993-15=-0.007Ts= dmax-dmin = es- ei=0.003The dimension below has a tolerance of 0.003.10 Maximum Material Condition When specifying tolerance dimensions, themaximum material condition (MMC) means the product or part contains

9、 the maximum amount of material specified by the tolerance. The heaviest partDM=DmindM =dmax.11 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 p

10、artDL= DmaxdL= dmin.12tolerance zones Zero Line Above Positive Below Negative Draw upper deviation and lower deviation in the zone Mark the Basic dimension on the left.13 Depending on the mutual position of tolerance zones of the coupled parts, 3 types of fit can be distinguished: Clearance fit Tran

11、sition fit Interference fit .14 Clearance fit Xmax=Dmax- dmin=ES-ei Xmin=Dmin- dmax=EI-es Xav= (Xmax + Xmin )/2.15Transition fit Ymax=Dmin-dmax=EI-es Ymin=Dmax-dmin=ES-ei Yav= （ Ymax + Ymin ）/2.16Interference fit Xmax=Dmax-dmin=ES-ei Ymax=Dmin-dmax=EI-es Xav 或Yav = （Xmax + Ymax）/2.17Fit Tolerance Cl

12、earance fit: Tf= |Xmax - Xmin | Interference fit： Tf = | Ymin - Ymax | Transition fit ： Tf = | Xmax -Ymax | Tf=|(ES-ei)-(es-EI)|=|(ES-EI)+(es-ei)|= Th+Ts.18Fit SystemHole-basic system of fitshaft-basic system of fit.19Practise.20.21The standard tolerance series IT+figure IT01、IT0、IT1、IT2、 、IT18 Accu

13、racy ：from high to low （Precision Degradation） tolerance/value：from low to high manufacture： from hard to easy .22standard tolerance table.23basic 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 example25f630T

14、780js7.24.25Characteristics 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

15、-ITn-1 J only 6.7.8 gradej、k lower deviation is basic deviationj only 5.6.7.8 gradek is specific, divided into two part.Oneis IT7;other is IT3-IT7.27Basic size 0 to 500mm basic deviation of shaft.28.29Basic size 0 to 500mm basic deviation of hole.30.31一、General concepts of geometrical tolerances1、Fo

16、rm error Form error is the variation 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

17、 error Position error is thevariation 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

18、 machined.33二、Codes of geometrical tolerances 1、Geometrical tolerances.342、Code of geometrical tolerance The code of the geometrical tolerance is reprsented by the form and position frames.353、Reference code The reference code is made up of the capital letter with a small circle connected by fine li

19、nes and short thick lines. In order 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 cont

20、our line or surface, and keep it away from the dimension line.37 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 element.38 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 reference line.39Ex