Investigation on the micromilled surface characterization through replica technology

Micromilling is one of the most suitable technologies for the direct manufacturing of freeform micro components as well as for the generation of complex geometries typical of micro mould manufacturing. In this context, a detailed knowledge of the surface topography is fundamental to deal with quality control and tolerances to meet the parts functionality. However, in many cases, the reduced accessibility caused by the part complex features (e.g. microcavities, micro-holes, deep-cores) prevents from performing a direct measurement of the surface, using both contact and non-contact techniques. This represents an open issue that, in some cases, can be tackled by adopting the replication technology. The method consists in obtaining the replicated surface and performing its measurement using suitable measuring systems. This paper evaluates the actual performance of a commercial replication product for the indirect measurement of micromilled surfaces, characterized by submicrometer roughness levels. The study assesses the performance of the replication method by measuring the surface roughness (in terms of Sa) of specifically designed micromilled flat surfaces. A 3D confocal optical microscope is employed for the measurements. Two different workpiece materials (AISI 440, annealed and hardened), two different milling conditions (roughing and finishing types) and three replications of each surface are analyzed. The replication resulted suitable for characterizing micromilled surfaces even if it gives an average overestimation in the nanometric level of the Sa