Surface Parameter
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Surface Parameter Han Haitjema Mitutoyo RCE, Best, The Netherlands
Synonyms Roughness parameter
Definition Parameter, defined as a number and a unit that characterizes an averaged dimensional property of a surface.
Theory and Application Surfaces and Parameters A surface can be characterized by many, many parameters. In fact, it is easier to define a new parameter than to come with a thorough analysis of the usefulness of the already existing parameters. Parameters are defined in many ISO standards (see references). They can be separated in 2-D and 3-D parameters, and further separation is possible in amplitude parameters, spacing parameters, hybrid parameters, parameters derived from integrated probability density curves, and topological parameters.
This section is confined to surface texture characterizing parameters. For the defined R (roughness) parameters, there are equivalent P (unfiltered profile) parameters and W (waviness) parameters that are defined for longer wavelength limits. Roughness parameters naturally depend on the length scale where they are defined. In dimensional metrology, this scale is confined between the short-wavelength cutoff lengths ls and the long-wavelength cutoff lc. In the ISO 25178 series these terms are replaced by S-nesting index and L-nesting index respectively. It is a common requirement that within the shortwavelength cutoff length, at least some five measurement points should be taken, to keep the filtering well defined for short wavelengths. Parameters and specifications can only be usefully compared when the same cutoff lengths are used and meant (Leach and Haitjema 2010). Indication of Surface Parameters on Technical Drawings In ISO 1302 (2002), it is described how surface parameter requirements should be indicated on technical drawings. Uncertainty in Surface Parameters When measuring surface parameters and comparing these to specifications, it is necessary that an uncertainty in the parameter is calculated. Some of the factors that must be taken into account are:
# CIRP 2017 The International Academy for Production Engineering et al. (eds.), CIRP Encyclopedia of Production Engineering, DOI 10.1007/978-3-642-35950-7_16707-3
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Inhomogeneity of the workpiece The parameter may depend on the location on the workpiece and the direction in which the measurement is taken (at least for 2-D measurements). Usually, this is the dominant uncertainty factor. Uncertainty and traceability of the surface measuring instrument Uncertainty and traceability of the surface measuring instrument The traceability and uncertainty of the coordinates as measured (see section “Definitions”) must be taken into account, as well of uncertainties in the used probe size, filtering, sampling, reference line or surface, etc. For 3-D measurements, it is a problem that the default measurement system is a mechanical probing system. As 3-D mechanical roughness measurements are very time-consuming, most measurements are taken using optical techniques that may have artifacts that are not easily recognized. A problem with
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