机械精度设计与检测技术 (20).pdf

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1、ROUGHNESS PARAMETERSSECTION 6.1Sampling Length vs Evaluation Length Sampling length:Length in the direction of X axis used foridentifying the irregularities characterizing the profile underevaluation.=0.08,0.25,0.8,2.5,8(mm)Evaluation length:Length in the direction of X axis used forassessing the pr

2、ofile under evaluation.Normally,1=5.Sampling length and the evaluation lengthMean Line:mMean line:the reference line about which the profiledeviationsaremeasured.Themeanlinemaybedetermined in two ways.The least squaresArithmetic mean line=12=1+3+21=2+4+2Arithmetic Mean Deviation:Arithmetic mean devi

3、ation:the arithmetic mean of theabsolute value Z(x)within a sampling length.=0()is the most common primary parametersMaximum Height of Profile:Maximum height of profile:sum of height of the largestprofile peak height and the largest profile valley depth within a sampling length.=+lRzZPZVMean Width o

4、f the Profile Elements:Mean width of the profile elements:mean value of theprofile element widths within a sampling length.=1Material Ratio of the profile:()Material ratio of the profile():ratio of the materiallength of the profile elements at a given level c to theevaluation length.()=0 c is the di

5、stance from peak line to transversal,expressed by the percentage of Middle()Small()large()lncMl(c)1Ml(c)2Ml(c)3Ml(c)iRoughness Parameters SelectionRa is commonly used as main parameters,preferred;Ra canbe used alone,can also be used in combination,like Ra/Rz.Rz is commonly used when Ra 6.3um,or Ra 0

6、.025um;soft material surfaces;small measuring area.The RSm and Rmr(c)are used as additional evaluationparameters.Roughness Values Corresponding to Different Processing MethodsSummary of Roughness ParametersParameterNameAmplitude Parameters(9)Ra *Roughness Average(Ra)RqRoot Mean Square(RMS)RoughnessR

7、tTotal Height of the ProfileRvMaximum Profile Valley DepthRpMaximum Profile Peak HeightRz*Maximum Height of the ProfileRcMean Height of Profile IrregularitiesRsk SkewnessRkuKurtosis of the roughnessSpatial Parameters(1)RSm*Mean spacing profile elementsHybrid parameters(2)RdqRoot mean square slop of

8、the assessed profileRPcPeak count numberFunction parameters(2)Rmr*Material ratio at a given depthRdcProfile section height between two material ratiosBased on ISO-4287Summary of Roughness ParametersIn addition to ISO-4287,there are other standards aboutthe roughness parameters,such as ISO-12085(Motifparameters)and ISO-25178(Areal parameters).These standards are beyond the scope of this lessonand are left to students for self-study.