An investigation of the mechanical filtering effect of tactile CMM in the measurement of additively manufactured parts

The high level of surface roughness of additively manufactured parts post challenges to the applicability of different dimensional measurement techniques, including tactile, optical and X-ray computed tomography. Tactile measurement is traditionally considered to have the best accuracy and traceability; however, its measurement can be significantly influenced by the mechanical filtering effect. This work investigates the influence of the mechanical filtering effect on tactile measurements of additively manufactured parts. Both experimental and simulation work are utilised to reveal this effect. Particularly the numerical simulation based on the morphological method allows a single influence factor e.g. the stylus diameter to be investigated. The maximum measurement errors caused by the stylus mechanical filtering effect are determined by the convex hull points of the measurement profile, which is equivalent to using an infinitely large stylus. Coordinate measuring machine and X-ray computed tomography measurement results of an additively manufactured test part’s cylinder diameters are compared, along with the application of morphological method to “compensate” the coordinate measuring machine’s mechanical filtering effect.