Surface quality monitoring in micromilling: A preliminary investigation on microfeatures

Process monitoring plays a key role in industrial machining operations such as turning, milling and grinding, for assuring part quality and long lifespan of cutting tools to reduce production costs. When the part dimensions are scaled down to submillimeter range, process monitoring becomes essential but harder to implement. This work evaluates the possibility to monitor the surface quality of micromilled parts by means of cutting-related signals, such as Cutting Forces and Acoustic Emission. Micromilling of cylindrical pins with 0.8 mm diameter and aspect ratio of 1.875 has been studied, representing a significant case for injection molds. This manufacturing task is challenging because both the dimensional/geometrical accuracy and the finishing quality of the part have to be maximized to guarantee the final part functionalities. On the other side, the direct measurement of these characteristics on the final parts is challenging considering the state-of-the-art metrology systems. This fact motivates the adoption of indirect monitoring approaches, that can estimate the part quality in alternative ways. A design of experiment approach (DoE) together with Analysis of Variance (ANOVA), have been adopted to assess the statistical relationship between the monitored signals and the quality indexes of interest, such as the average surface roughness of the parts. The emerged correlations between the achievable surface roughness and process parameters, together with the existing correlation of micro cutting forces and acoustic emission with process parameters, sustain the feasibility of using these signals for implementing advanced monitoring and control schemes of the micro cutting operation