机械精度设计与检测技术 (21).pdf

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1、ROUGHNESS SYMBOLS AND MEASUREMENTSECTION 6.2Basic Graphical SymbolThe basic graphical symbol consists of twostraight lines of unequal length inclined atapproximately 60to the line representingthe considered surface.If removal of material is required,a bar shallbe added to it.If removal of material i

2、s not permitted,acircle shall be added to.When special surface characteristics have tobe indicated,a line shall be added to thelonger arm of it.Position of Complementary Surface Texture RequirementsThe mandatory positions of the various surface texturerequirements in the complete graphical symbol ar

3、e shownbelow.acedbRoughness parameterSecond Roughness parametermanufacturing methodSurface lay and orientationMachining allowancePosition and Orientation of Graphical Symbol and its AnnotationThe general rule is that the graphical symbol together with the complementary information shall be oriented

4、so that they are readable from the bottom or right-hand side of the drawing.Ra 3.2Rz 1.6Rz 12.5Rp 1.6Surface Lay SymbolsParallel texturePerpendicular textureCrossed grainMulti-directional textureParticulate textureCircular textureRadial textureExamples of Roughness Indication Example1Example2RRadial

5、 TextureMeasurement Method 1:Comparison SpecimensSurface Roughness Comparison SpecimensWith a standard set of surfaces roughness comparison specimens,surface roughness can be assessed conveniently using visual andtactile(fingernail)comparison.They are simple to use,inexpensive,and therefore widely u

6、sed in many different applications.Measurement Method 2:Stylus InstrumentsStylus InstrumentsWith stylus probe measurement instruments,the surface profile datais obtained by directly tracing the surface with mechanical probes.Acomputer calculates roughness parameters and can record theprofile.Measure

7、ment Method 3:Light Section MicroscopeLight Section Microscopes detect depths and heights with a non-contact optical method.They detect the unevenness of surfaceswithout touching them using light rays.Light Section MicroscopeSS 45 45 Naa hlightlensslitLight axisSampleMeasurement Method 4:White Light InterferometersWhite Light InterferometersLight interference occurs when there is a difference in distancetraveled by the light from the surface of a part to a view point.Theroughness parameter Rzcan be obtained by calculate h.2abhFor white light/2=0.275mInterference fringe