互换性与测量技术(汉英双语)分享课件.ppt

; Selection of preferred fits of machine parts and determination of their dimensional tolerances and deviations according to ANSI B4.1. Determination of non-prescribed limit deviations of linear and angular dimensions according to ISO 2768. Automatic design of a fit for the given clearance or fit interference respectively. ;Basic terms. It is necessary that the dimensions, shape and mutual position of surfaces of individual parts of mechanical engineering 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. : ; Actual surfaces of the produced parts therefore differ from ideal surfaces prescribed in drawings. Deviations of actual surfaces are divided into four groups to enable assessment, prescription and checking of the permitted inaccuracy during production;Dimensional deviations Shape deviations Position deviations Surface roughness deviations;More Terminology ? Nominal 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 hole][dmax , dmin ... limits of size for the shaft];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 ;Tolerance is the total amount a specific dimension is permitted to vary (difference between the maximum and minimum limits). ?Th= Dmax- Dmin=ES-EI Ts= dmax-dmin = es- ei ; es=14.996-15=-0.004 ei=14.993-15=-0.007 Ts= dmax-dmin = es- ei=0.003 The dimension below has a tolerance of 0.003 ; Maximum Material Condition ? When specifying tolerance dimensions, the maximum material condition (MMC