Advantages Of Measuring Surface Roughness With White Light Interferometry

Why measuring roughness is still a primary reference parameter, and how white light interferometry works.


The concept of measuring surface roughness originated nearly a century ago as a means to prevent uncertainty and disputes between manufacturers and buyers. Now, it has become a common identifier used throughout industry for validating manufacturing processes, confirming adherence to both internal and regulatory specifications, and guaranteeing quality and performance of end products. Subjective judgements of quality based on naked eye observation or fingertouch feel of surfaces has steadily been replaced by unbiased metrics and well-defined formulas.

The first parameter developed for these endeavors was mean roughness (Ra), which for a number of reasons, is still a primary reference parameter used today. First, mean roughness is easy to work out, even in an analogic way, which not only was important in early implementation across a variety of industries, but also makes it a convenient and quick method for current characterization. Second, the Ra parameter is a robust calculation that averages outlier data and provides constant results irrespective of the roughness pattern. This is critically important to not only assist with a wide variety of industrial manufacturing processes, but also to provide a solid baseline for process improvement.

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