Industrial surface finish method comparison for fine finish measurements

Abstract

Measurement of surface finish in industrial manufacturing has traditionally been done by means of either visual comparison with reference plates or by the use of contact stylus based profilers. There are many challenges associated with contact profilers such as stability during measurement in an industrial environment, damage and wear of the tip, measurement in tight spaces or on curved surfaces and just the limited amount of data obtained by a linear scan of the stylus. Many alternative methods have become available such as white light interferometry, focus based systems, and even laser scatter. This paper will present the result of testing of the commercially available methods with particular emphasis on the fine surface finishes demanded in today's manufacturing, then presents some alternative methods that show strong potential to address some of the challenges mentioned above that are not in wide use today. The analysis will specifically explore some of the physical mechanisms that affect the stylus based measurement, as well as the limitations of many of the optical approaches related to view angle and diffraction limited resolution consequences. The area of confocal imaging will be specifically explored as to how it might be used to obtain more complete data on very fine surface finishes.

Automated cylindrical mapper using chromatic confocal measurement

“…A surface scan with a confocal sensor is shown in Figure 3, along with a profile from that scan. 6 To collect a full 2 millimeter square scan like this requires several minutes to an hour with a standard confocal system. A chromatic confocal sensor often uses a fiber optic to deliver the sensing point (see Figure 4), so can be mounted on a more portable or dedicated system for doing real part scans such as cylindrical shapes.…”