Micro-tool characterization using scanning white light interferometry

Micro-electro-discharge machining produces tools for micro-machining processes with diameters down to 3 μm and lengths up to fifty times their diameter. This paper describes a metrology technique for characterizing the geometry of these tools by the standardized components of roughness, waviness and form. In this technique two-dimensional (2D) profiles are extracted from three-dimensional (3D) surface measurements acquired by scanning white light interferometry with height resolution below 1 nm. The profiles are transformed into the frequency domain and separated into form (wavelengths longer than 100 μm), waviness (wavelengths between 10 μm and 100 μm) and roughness (wavelengths shorter than 10 μm). Standard height and shape parameters are computed from the roughness, waviness and form profiles for 81 tools, enabling relative comparison of tool geometry in a quantitative and reproducible manner. This approach provides a more comprehensive quantification of geometry than alternatives such as measuring the diameter at a few points along the tool or scanning probe microscopy over small areas. The utility of the technique is demonstrated by characterizing the precision of three micro-tools produced by wire electro-discharge grinding (WEDG).