On the Geometrical Accuracy of High Aspect Ratio Micromilled Pins

Geometrical accuracy of microfeatures in micromilling is strictly related with the choice of cutting parameters. Their correct selection is a challenging task in particular when the target feature geometry is a high aspect ratio feature with tight tolerance requirements. Metallic micromilled pins are adopted in many different industrial applications as in the micromold technology field, in the microelectromechanical systems, and in the biomedical devices and their geometrical accuracy represents a fundamental property for their functionality. This work outlines the connection between the achieved geometrical accuracy and the micromilling parameters and cutting strategies on pins with diameter = 100 μm and height = 2 mm (i.e., aspect ratio = 20). Pin geometrical error features are extracted from three-dimensional optical measurements and then correlated with cutting parameters to support machining process setup. A proper fitting based on Chebyshev functions is applied and a statistical analysis assesses the importance of each deviation component in relation to the imposed cutting conditions. The proposed methodology fills the specific lack in the literature domain about micropin machining and can easily extend to different types of geometrical microfeatures. Finally, correlation between part geometrical errors and machining forces is analyzed. Cutting force analysis is adopted in conventional machining for implementing online geometrical errors assessment or compensation methods. However, this study confirms that the applicability of this approach in high aspect ratio pin micromilling is prevented from the predominant scale-effects and the large part bending that generates a low direct correlation between forces and part geometrical errors.