Ball end micro milling of areal material measures: influence of the tilt angle on the resulting surface topography

Topography measuring instruments are calibrated by using material measures to estimate the measurement uncertainty and to ensure traceability. In ISO 25178-70, areal material measures are standardized, but no manufacturing process for their generation is defined. Therefore, previous studies examined the capabilities of multiple manufacturing principles for this application. Micro milling is an adequate process when the manufacturing of freeform surfaces in metal is required; it was proven that micro milling also is a generally suitable process for the manufacturing of material measures. In previous investigations, a study analyzing the influence of the control dataset design on the resulting surface quality of the micro milled material measures was carried out. It was shown that some control data parameters have a crucial influence on the surface quality, e.g. the tilt angle. When using ball end micro mills, a tilt angle prevents a cutting speed equal to zero in the mill’s center. When too small tilt angles are applied, ploughing of the material instead of a cutting occurs. However, at high tilt angles other effects that can lead to deviations between the target geometry dataset and machined geometry occur. In this experimental study the tilt angle’s influence on the resulting roughness and machined geometry was examined by micro milling sinusoidal freeform surfaces at different tilt angles. In addition to the deviation between intended and machined geometry and the roughness of the manufactured surfaces the correlations of the mentioned parameters to the tilt angle were additionally evaluated.