The production of mold inserts for the replication of micro-lens arrays through micro-embossing could be an alternative process route compared to diamond turning or milling in order to reduce time and costs. The rapidly solidified aluminum alloy RSA-501 is expected to form micro-structures with low surface roughness because of its ultra-fine grain structure. In micro-embossing challenges like elastic spring back effect, pile-ups, and forming accuracy depend on the material behavior. Therefore, RSA-501 was further characterized and the influence of polishing or flycutting on the material behavior was investigated. To further understand the grain and microstructure samples were sectioned along their cross and longitudinal directions. The grain structure of RSA-501 was oriented along the extrusion direction and the mean grain sizes were <1.00 μm. Furthermore, RSA-501 was micro-embossed to investigate the influence of the material behavior and surface preparation on the forming of micro-structures. The induced surface integrity through flycutting was not deep enough to influence the forming of micro-structures. Therefore, the workpiece surface can be prepared either by polishing or flycutting. When micro-embossing RSA-501, cross and longitudinal sections can be used. However, it is recommended to process the cross section because of its isotropic grain structure. It was shown that the curvature radius of micro-embossed concave structures differs from the tool radius. This is due to the elastic spring back effect. Since the embossed structure remains spherical, the spring back effect can be compensated by adjusting the tool radius.

Optical elements made of aluminum with surface roughness in the sub-nanometer range are required for applications in the visible (VIS) and ultraviolet (UV) spectral range. Rapidly solidified aluminum (RSA) 501 is an interesting candidate to produce sufficiently smooth surfaces for these applications in an ultra-precision (UP) flycutting process. However, the polycrystalline grain structure and precipitates contained in the material limit the achievable surface roughness. In this research, a reactive ion beam finishing process of RSA 501 is investigated employing an electron cyclotron resonance (ECR)-driven ion source using CF4 and N2 gasses. Emphasis is placed on understanding the etching mechanisms that influence the topographic evolution to provide the basis for future production processes using the material for UV optics. Material composition characterization is applied to analyze the interaction between the reactive ion species and the RSA material. Surface modification transferring the native oxide top layer to an in situ forming and developing aluminum fluoride or -nitride etch front layer is found to prevent grain orientation-dependent etching. The effect of the ion incidence angle on the etch rates of precipitates and bulk material can be used to reduce the height of precipitates protruding from the surface after the UP-machining process. A surface roughness value of Sq = 0.9 nm +/- 0.1 nm (areal root mean square height) is achieved in the micro-roughness range when etching at 40 degrees and 80 degrees angle of incidence using collimated ion beams with CF4 process gas.

Gallium Phosphide (GaP) is a semiconductor with advantageous optical properties for near- and middle infrared optical systems. However, optical applications of GaP are limited by its current low machinability. To cut brittle semiconductors such as GaP and generate optical quality surfaces, it is necessary to induce a High-Pressure Phase Transformation (HPPT) so that a phase is formed that behaves ductile when machined. Along the cutting process this can be achieved by applying a negative rake angle. Otherwise, cracks will appear on the machined surface, worsening its optical capabilities. A HPPT of GaP happens at an atomic scale when a zincblende structure changes into a β-tin one. The β-tin structure behaves ductile and is metastable. Hence, the metastable β-tin phase cannot be observed during the cutting process. Therefore, atomistic simulation, such as Classic Molecular Dynamics Simulation (CMDS), is required to study the machinability under HPPT. In this work, CMDS were used to analyze GaP cutting mechanisms. A diamond tool was modelled with a cutting edge radius rβ = 10 nm, rake angle γ = -20 º, and clearance angle α = 10 º. The cut was performed with a depth of cut ap = 12 nm along the [100]-direction in a zincblende GaP workpiece. Stacking faults were found on the shear zone, {111}-planes, by two different post processes approaches. HPPT was found in the deformation zone only. A stagnation zone was found in front of the cutting edge proceeding a crack nucleation.

In this study, novel micro particles in the shape of irregular tetrahedrons in a two to three-digit micrometer size range are presented. The particle manufacturing feasibility was investigated in three different ways: shaping, casting and rolling. Rolling showed the potential for mass production. The suitability of tetrahedral particles for the use as metal effect pigment was assessed by comparison with conventional platelet-shaped metal effect pigments. Optical inspection showed a strongly reduced luminance inhomogeneity in weld line regions in the case of the tetrahedral particles. It was found by synchrotron X-ray tomography examination of particles in solidified polymethylmethacrylate (PMMA) that particle depletion is not the main reason for visible flow lines. The orientation of platelet-shaped pigment particles was identified to cause such flow lines. PMMA filled with tetrahedral particles, in contrast, shows homogenous optical properties independent from the particle orientation. Thus, flow lines in weld line regions can be omitted.

The production of mold inserts for the replication of micro-lens arrays through micro-embossing could be an alternative process route compared to diamond turning or milling in order to reduce time and costs. The rapidly solidified aluminum alloy RSA-501 is expected to form micro-lenses with low surface roughness because of its ultra-fine grain structure. In micro-embossing challenges like elastic spring-back-effect, pile-ups and forming accuracy depend on the material behavior. Therefore, RSA-501 was further characterized and the influence of polishing or flycutting on the material behavior was investigated. To further understand the grain and microstructure samples were sectioned along their cross and longitudinal directions. The grain structure was investigated through metallographic analysis and EBSD measurements. SEM micrographs and EDS were used to analyze the precipitations, their distribution and size. The influence of the surface preparation method was investigated through nanoindentation and SEM micrographs of specimens prepared by using a focus ion beam to measure their depth of the surface integrity. Furthermore, RSA-501 was micro-embossed to investigate the influence of the material behavior and surface preparation on the forming of micro-lenses. The grain structure of RSA-501 was oriented along the extrusion direction. The mean grain sizes were < 1.00 µm. The induced surface integrity through flycutting was not deep enough to influence the forming of micro-lenses. Therefore, the workpiece surface can be prepared either by polishing or flycutting. When micro-embossing RSA-501 cross and longitudinal sections can be used. However, it is recommended to process the cross section because of its isotropic grain structure.

Diffractive optical elements (DOEs) are used in various applications, e.g. diffraction gratings for Raman and LIPS spectroscopy. The manufacture of DOE can be achieved by ultra-precision machining (UPM). UPM manufactured diffraction gratings are either shaped with rectangular diamond cutting tools or ruled, in which the grooves are formed by cylindrical diamond tools. Regarding higher production quantities, usually a master grating is manufactured and replicated. Therefore, the material of the master grating should provide high hardness and enable low roughness values. Electroless Nickel-Phosphorous (Ni-P) is widely used in UPM and offers those properties. However, the material-specific limits, machining strategies, and process parameters need to be determined for the two mentioned manufacturing processes. For this purpose, experimental and numerical investigations were conducted and are presented in this paper. The examined groove widths are in the range of 1 – 10 μm. The experiments for ruling and shaping processes were conducted on a LT-ULTRA MMC 1100 ultra-precision machining center. The diffraction efficiencies of ruled gratings were calculated by rigorous coupled wave analysis. In order to determine the tool wear, cutting experiments of large-area gratings have been conducted. Manufacturing grooves with doubled width on predetermined positions enables to indirectly measure the cutting edge displacement of the tool in dependence of the cutting length by means of atomic force microscopy. Opposed to other grating materials like Au, defect-free grooves could not be ruled into Ni-P. The grooves are not formed completely by low process forces whereas forming with higher forces lead to a removal of material in the upper part of the groove. This reduces the calculated diffraction efficiency by at least 26.3 % which is why further research in ruling of diffraction gratings in Ni-P is advised. However, much lower geometrical defects can be achieved by shaping the grooves. During the experiments, roughness values Rq ≤ 1.5 nm and cutting lengths lc > 3 km without significant wear were achieved, which enables the manufacture of large, highefficient DOE in Ni-P. Microstructure, electroless Nickel, DOE, Ultra-precision

Silicon is an important material often employed on most of micro-electro mechanical systems (MEMS), integrated circuits, microchips, and micro-fluidic devices. Therefore, strategies and process parameters to machine those planar 2.5-D geometries of silicon are essential. Moreover, silicon belongs to the group of hard-brittle materials, which means that it is very likely to originate cracks during the milling operations as a result of the intermittent interaction of the cutting edge and the silicon surface. Besides, the machining of silicon results on severe tool wear. The ductile-brittle transition and tool wear reduction of the silicon-milling are aspects still not completely investigated. Consequently, this paper aims at finding the proper parameter range for ductile ultra-precision milling (UP-milling) of 2.5-D silicon geometries employing single crystal diamond cutting tools. Furthermore,the evaluation the tool wear after the process is a crucial part of the investigations. In order to fulfil such knowledge gap, single groove experiments are proposed. The milling process to generate those grooves is monitored by means of force measurements. Also, surface aspects of the machined grooves are measured through white light interferometry (WLI). For evaluating tool wear, dry UP-milling investigations are conducted and images of the cutting edges are taken by means of a scanning electron microscope (SEM). The experiments show that the machining of silicon is feasible and the ductile material removal is possible. Moreover, the process forces Fpr generated by the UP-milling process of single crystal silicon are able to be employed for monitoring and avoid the transition from ductile to brittle material removal.

Due to the geometry and specification of micro-optic components, these may not be ground or polished, therefore they demand other manufacturing processes such as ultra-precision (UP) machining with defined cutting edge tools. Despite previous studies, the machining of brittle materials remains a challenge for manufacturing those components in UP processes. For example, ductile machining of silicon is extensively studied, however, ductile machining of materials such as Zerodur®, GaP, U.L.E.® and glass is still a challenge to overcome. Therefore, this paper aims at reporting the ductile or part-ductile machining of silicon and Zerodur® pieces in UP processes. Experiments were carried out using UP-shaping and plane turning processes in an UP-machine tool. Moreover, monocrystalline diamond tools were employed. During UP-turning experiments, the process forces were measured. The machining results were obtained by White Light Interferometer (WLI) of the representative machined surfaces. In order to complement the experiments, simulations were performed in finite element software to comprehend the influences of the rake angle on ductile machining of those materials. After the UP-shaping experiments, the depth of cut was determined for each of the mentioned materials together with the main influence of each process parameter. Furthermore, a reduction of parameter ranges for UP-turning experiments was accomplished. Using Design of Experiments for UP-turning tests, the main influences of process parameters were observed and detailed, together with tool geometry optimization and recommendation for further experiments. The local optimum of process parameters was found as well as the accomplishment of ductile removal during the machining tests. These results and simulation models are going to be further used for a more detailed process description, as analogous tests and optimization of UP processes such as micro-milling.

Grinding tool topography is one of the several key aspects of the modelling of a grinding process. Simplifying it could mean less processing time needed, but it can lead to inaccurate simulation results. Considering that, this research aims to develop a reliable method for NC-grinding processes with abrasive mounted points, describing the grinding tool surface using a single profile of kinematic cutting edges instead of its whole topography. In order to achieve this, numerical and empirical experiments were conducted proving the feasibility of the model to implement it for future simulations.

Due to the importance of high surface quality of machined parts, considering its functional requirements, it is important to select a proper set of grinding parameters. Experimental trials are material, energy and time consuming. Therefore it is relevant for the industry to use a roughness model capable of simulating different grinding kinematics with different sets of parameters. This paper presents a fast and reliable method, for the NC-grinding process with abrasive mounted points, to reach this demand. In order to achieve this, numerical and empirical experiments were conducted proving the feasibility of the model for conventional, oscillating and tilt surface grinding.