Component surfaces feature more and more complex functional properties and deterministic geometric structures. The result is that an areal characterization of surfaces is more often necessary. The increasing incidence of areal surface topography measuring instruments in geometrical product specification enables the acquisition of more information about a surface topography. However, also more complex calibration procedures are required as an increasing number of metrological characteristics need to be verified. This verification is achieved with areal material measures which are described in the standard ISO 25178-70. State of the art is a manufacturing of the proposed geometries with many different principles because there is a broad range of geometries whose structure size is usually in the micrometer-range. Typically applied principles include lithography, etching and ultra-precision cutting. The application of an ultra-precise 3D-printing technology, two-photon laser lithography alias direct laser writing, exhibits enormous potential for areal material measures as arbitrary 3D-freeform surfaces can be manufactured with a high repeatability in the nanometer-range.
Hence, a feasibility study of the application of direct laser writing for the manufacturing of areal material measures is conducted. In doing so, different standardized material measures are manufactured and the resulting surface topographies are compared to their target geometries in order to qualify the manufacturing process. The measurements are performed with different surface topography measuring instruments in order to examine the overall suitability of the principle for the manufacturing of areal material measures. The standardized measurands of the ISO 25178-70 serve as evaluation criteria just as recently defined new parameters for the verification of surface topography measuring instruments. As a new resolution criterion, for example the small scale fidelity limit is evaluated. The enhancement of the resolution of the manufacturing process with stimulated emission depletion is examined and the resolution limits of the manufacturing and the measuring processes are compared.
The samples that are manufactured with direct laser writing are further examined regarding their practical abilities. An important property of material measures is their stable provision of constant evaluation parameters. In order to examine this relevant characteristic of the samples, different studies which describe the aging behavior of varying coating materials are conducted. Based on the results, a suitable coating material with suitable optical characteristics can be chosen and the time-dependent behavior of the geometries can be evaluated. Because optical surface topography measuring instruments which are calibrated with the proposed material measures may feature varying magnifications and fields of view, in another study scaling effects are examined and material measures with different structure sizes are manufactured in order to evaluate the scalability of the different types of material measures.
It can be concluded that almost any standardized areal material measure can be manufactured reliably with direct laser writing. Due to the scalability of the structures, a calibration of optical surface topography measuring instruments with varying fields of view can be ensured.
Matthias Eifler, Julian Hering, Georg von Freymann, and Jörg Seewig, "3D printing of material measures for areal surface texture (Conference Presentation)," Proc. SPIE 10675, 3D Printed Optics and Additive Photonic Manufacturing, 1067506 (Presented at SPIE Photonics Europe: April 23, 2018; Published: 29 May 2018); https://doi.org/10.1117/12.2307560.5791126161001.
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