SURFACE METROLOGY A Report on the Fourth International Conference on the Metrology and Properties of Engineering Surfaces, National Bureau of Standards, Gaithersburg, MD, April 13–15, 1988

SURFACE METROLOGY A Report on the Fourth International Conference on the Metrology and Properties of Engineering Surfaces, National Bureau of Standards, Gaithersburg, MD, April 13-15, 1988 carbon black agglomerates in rubber, a family of materials that might normally be thought of as too soft for reliable characterization by stylus. Inadequate dispersion leads to reduced product life and other detrimental effects in rubber products. Figure 1 shows the stylus in contact with such a rubber surface. The presence of the agglomerates is evidenced either by discrete peaks in the stylus profiles or by valleys left when the material is separated during the cutting process.


National Bureau of Standards,
Gaithersburg, MD, April 13-15, 1988 carbon black agglomerates in rubber, a family of materials that might normally be thought of as too Surface metrology finds application to many branches of engineering ranging from optical surfaces to roadways. This triennial conference, held for the first time outside of England, traditionally attracts delegates with diverse interests from many countries. This year, in addition to the delegates from the United States, there were 20 delegates from England, five from France and others from Canada, West Germany, Austria, Japan, Sweden, and Ireland.
Delegates heard and debated 38 presentations on a wide variety of topics that, in retrospect, one could reorganize into the following general areas: measurement techniques, surface specimens, statistical characterization, production methods, and engineering function. A few of the interesting applications are described below. One notable application to engineering function was Tabenkin and Parsons' (paper 38) use of the stylus technique to characterize the dispersion of Rao et al. (paper 37) discussed their initial work to construct an expert system for selection of surface texture parameters. It was based on a table of results (table 1) gathered by Bielle and others (private communication) for the French automobile industry. The table relates a set of engineering functions such as static sealing with surface texture parameters that should be specified to optimize the function. However, the set of surface parameters shown in table 1, known as the R&W system, are defined using pattern recognition ideas rather than the conventional time series analysis. This approach to correlating surface function with surface finish is an interesting and controversial one.
The conference also recounted many significant advances in the area of measurement techniques.
The traditional technique for measuring surface texture is the stylus. However, nonstylus techniques are being increasingly studied and used. At this conference, research was presented on the measurement of surface texture by optical focusing, optical interferometry, optical scattering, infrared thermography, ultrasonics, two kinds of capacitance techniques, ellipsometry, and scanning tunneling microscopy.
Some of the most dramatic advances are in the field of interferometry (papers 2, 4, and 10) where height resolution at the Angstrom level can be achieved routinely nowadays.
At the large end of the scale, Pryor (paper 14) introduced a new optical imaging technique, known as D-sight, that can detect flaws and small form deviations with great sensitivity on large objects such as automobile and aircraft production components. Figure 2 shows an example of the sensitivity of the technique for inspection of a car body.   Lastly, two new types of surface texture specimens were presented. The specimens discussed by Song (paper 21) (fig. 5) had smooth random surfaces machined in steel with roughness average values ranging from 0.012-0.1 ,tm. They also had high uniformity from one place to the next in spite of the random surfacing process that had produced them. Berger (paper 20) discussed specimens fabricated by silicon technology. Each wafer surface contained a thermally grown SiO 2 layer with a single well-controlled thickness but with several feature spacings. The result was a surface consisting of "square waves" (fig. 6) suitable as a step height or pitch standard. Since it had four line spacings, one of them being as small as 6 ,um, the sample could also be used to test the quality of stylus tip widths ranging from I to 12 jim.  Figure 5. Detail of a roughness calibration specimen developed by Song (paper 21). It shows how the random roughness profile is repeated over the surface, thus achieving high uniformity.

List of Papers Presented at Conference
The proceedings, to be published as several successive issues in the journal, Surface Topography, and as Proceedings of the Fourth International Conference on the Metrology and Properties of Engineering Surfaces (Kogan Page, London, 1988), will include most of the presentations referenced below.