Scanning-laser surface-profiling technique increases accuracy

Researchers at the National Institute of Standards and Technology (NIST; Gaithersburg, MD) have developed a novel technique for measuring the roughness of surfaces that is casting doubt on the accuracy of current procedures. Their results, to be published in Materials Science, could cut development costs for automakers as they design manufacturing tools for new fuel-efficient, lightweight alloys.

Surface roughness is usually measured with a profilometer. But NIST researchers Mark Stoudt et al. have found that the dual measurements obtained with a profilometer can be misleading because measurement uncertainties and statistical errors are compounded when the 2-D lines in a standard profilometer image are extrapolated to the entire surface. Stoudt and his colleagues instead used a scanning-laser confocal microscope (SLCM) to obtain an image of 1000 × 800 µm by 20 µm in depth. They analyzed this data using mathematical techniques that treat every point in the image simultaneously to produce a roughness measure that considers the entire 3-D surface rather than a collection of 2-D stripes.

One early finding of the work: the generally accepted linear relationship between surface roughness and material deformation is wrong, at least for the aluminum alloy the group studied. According to Stoudt, the more accurate data from the 3-D analysis shows that a more complicated relationship was masked by the large uncertainties of the linear profilometers. Contact Mark Stoudt at mark.stoudt@nist.gov.