Katja Klauer

The calibration of areal surface topography measuring instruments is of high relevance to estimate the measurement uncertainty and to guarantee the traceability of the measurement results. Calibration structures for optical measuring instruments must be sufficiently small to determine the limits of the instruments.Besides other methods, micro-milling is a suitable process for manufacturing areal material measures. For the manufacturing by micro-milling with ball end mills, the tool radius (effective cutter radius) is the corresponding limiting factor: if the tool radius is too large to penetrate the concave profile details without removing the surrounding material, deviations from the target geometry will occur. These deviations can be detected and excluded before experimental manufacturing with the aid of a kinematic simulation.In this study, a kinematic simulation model for the prediction of the dimensional accuracy of micro-milled areal material measures is developed and validated. Subsequently, a radius study is conducted to determine how the tool radius r of the tool influences the dimensional accuracy of an areal crossed sinusoidal (ACS) geometry according to ISO 25178-70 [1] with a defined amplitude d and period length p. The resulting theoretical surface texture parameters are evaluated and compared to the target values. It was shown that the surface texture parameters deviate from the nominal values depending on the effective cutter radius used. Based on the results of the study, it can be determined with which effective tool radius the measurands Sa and Sq of the material measures are best met. The ideal effective radius for the application considered is between 50 and 75 μm.

Material measures are used to calibrate topography measuring instruments. Micro-milling is a suitable process for the manufacturing of areal material measures in particular of material measures featuring freeform surfaces. To improve their surface quality and to minimize their deviations from the target geometry, the cutting parameters feed per tooth respectively feed rate and spindle speed are examined in this study. Dependent on the varied parameters the deviation of the manufactured topography from its target geometry, the deviation to the nominal surface texture parameters and the short-wavelength roughness parameters are evaluated. Two different ball end micro-mills and two different target geometries are chosen to investigate whether the observed dependence on the varied parameters are valid independent from the tool and the target geometry. It is illustrated that the feed rate has a large influence on the dimensional accuracy: the dynamic properties of the axes are identified as reason for the decreasing amplitude with increasing feed rate. The spindle speed only influences the short wavelength roughness and has a minor influence on the surface quality.