Comparison of the contact and focus variation measurement methods in the process of surface topography evaluation of additively manufactured models with different geometry complexity

Abstract

One of the key measurement parameters of the surface topography is the measurement area. It influences the possibility of using filters separating components of surface texture and thus determines the reliability of the obtained measurement results. The currently applicable standard does not define the size of the measuring area. To determine its size, fractal analysis was carried out in the article. The paper presents research on two types of geometry: simple geometry in the form of cylindrical and spherical surfaces and more complex geometry represented by free surfaces such as crowns and molars of teeth. In the process of making the research models, four 3D printing techniques were used: Fused Deposition Modeling (FDM), Melted and Extruded Modeling (MEM) Fused Filament Fabrication (FFF) and Material Jetting (MJ). 3D measurements of surface texture were made using a contact profilometer and a focus variation microscope. The analysis of topography images and selected parameters of the surface topography showed that the optical method gave better measurement results than the contact method. In the case of models made with the FDM and MEM techniques, similar values of the Sa parameter were obtained. Slightly smaller values of Sa were recorded for FFF models, while the highest for MJ models. Models made using the FFF method were also characterized by the lowest variability of results. Models made using the MJ method were characterized by relatively deep valleys in comparison with the other models, which was reflected in the Ssk and Svk parameters. The valleys counting from the top surface of the specimen were the shallowest for models made with the FFF method. Surfaces with simpler geometry were characterized by smaller variability of parameters values.