Surface Roughness Characterization of Small-Bore Fittings using the Confocal Chromatic Measurement System

The physical and mechanical characteristics of manufactured surfaces determine the performance properties of machine parts. The surface roughness characterizes the surface quality and significantly impacts machine parts and products. Confocal chromatic measurement techniques have shown significant improvement in real-time high-resolution profile measurement during inspection. However, the application of confocal chromatic sensors is still limited for the purpose of inspection in restricted reflective spaces. This work proposed a confocal chromatic measurement system to characterize the surface roughness in small-bore fittings with restricted space. The system consists of median and Gaussian filters and a characterization stage, which computes nineteen parameters to describe the surface. We tested the system on the Flexbar’s Surface Roughness Standards Set calibration plate, as-machined, post-machined, and rejected small-bore fittings. Statistical moments, autocorrelation function, and the percentage of total power between 100Hz and 150Hz were especially found to be effective in surface roughness characterization.