Oltmann Riemer

Machining of Precision Parts and Microstructures

Many qualified technologies have been established for the manufacture of precision parts and microstructured surfaces in the field of MEMS, e.g. UV-lithography, silicon-micromachining, LIGA and in the range of energy assisted processes like Laser Beam Machining, Focused Ion Beam Machining or Electron Beam Machining. Nevertheless, mechanical processes, e.g. diamond machining, engraving, forming and molding, play a significant role for the generation of microstructured surfaces and precision parts.

Tool path generation for ultra-precision machining of free-form surfaces

The generation of tool paths for ultra-precision machining is still a limiting factor in the manufacturing of parts with complex optical surfaces. In conventional machining as well as in complex five axes machining the application of CAD- and CAM-software for the generation of tool paths is state of the art. But these software solutions are not able to generate tool paths according to the high requirements of ultra-precision machining. This paper describes possible ways to generate tool paths for ultra-precision machining when the optical surface can be analytically described or when the surface data is derived from optical design software. Ultra-precision milling experiments with different tool paths have been carried out and the quality of the machined geometry has been evaluated concerning the achievable form accuracy.

Diamond machining of micro-optical components and structures

Diamond machining originates from the 1950s to 1970s in the USA. This technology was originally designed for machining of metal optics at macroscopic dimensions with so far unreached tolerances. During the following decades the machine tools, the monocrystalline diamond cutting tools, the workpiece materials and the machining processes advanced to even higher precision and flexibility. For this reason also the fabrication of small functional components like micro optics at a large spectrum of geometries became technologically and economically feasible. Today, several kinds of fast tool machining and multi axis machining operations can be applied for diamond machining of micro optical components as well as diffractive optical elements. These parts can either be machined directly as single or individual component or as mold insert for mass production by plastic replication. Examples are multi lens arrays, micro mirror arrays and fiber coupling lenses. This paper will give an overview about the potentials and limits of the current diamond machining technology with respect to micro optical components.

Development of material measures for performance verifying surface topography measuring instruments

The development of two irregular-geometry material measures for performance verifying surface topography measuring instruments is described. The material measures are designed to be used to performance verify tactile and optical areal surface topography measuring instruments. The manufacture of the material measures using diamond turning followed by nickel electroforming is described in detail. Measurement results are then obtained using a traceable stylus instrument and a commercial coherence scanning interferometer, and the results are shown to agree to within the measurement uncertainties. The material measures are now commercially available as part of a suite of material measures aimed at the calibration and performance verification of areal surface topography measuring instruments.

Ultraprecision Ductile Grinding of Optical Glass Using Super Abrasive Diamond Wheel

In this paper, a novel conditioning technique features using copper bonded diamond grinding wheels of 91μm grain size assisted with ELID (electrolytic in-process dressing) as a conditioner to precisely and effectively condition nickel electroplated monolayer coarse-grained diamond grinding wheels of 151μm grain size was firstly developed. Under optimised conditioning parameters, the super abrasive diamond wheel was well conditioned in terms of a minimized run-out error and flattened diamond grain surfaces of constant peripheral envelope, with the conditioning force monitored by a force transducer as well as the modified wheel surface status in-situ monitored by a coaxial optical distance measurement system. Finally the grinding experiment on BK7 was conducted using the well conditioned wheel with the corresponding surface morphology and subsurface damage measured by AFM (atomic force microscope) and SEM (scanning electron microscope) respectively. The experimental result shows that the newly developed conditioning technique is applicable and feasible to ductile grinding optical glass featuring nano scale surface roughness, indicating a prospect of introducing super abrasive diamond wheels into ductile machining of brittle materials.

Manufacturing of optical molds using an integrated simulation and measurement interface

The manufacturing of optics is an important field of technology and will serve key-markets in the future. The research activities of the Transregional Collaborative Research Center ”Process Chains for the Replication of Complex Optical Elements” SFB/TR4 of the Universities of Aachen, Bremen and Stillwater (USA) have the objective to lay the scientific foundations for a deterministic and economic mass production of optical components with complex geometries, e.g. aspheric, non-rotational asymmetric or microstructured surfaces eventually superimposed on freeform geometries. The paper presents an approach for an integrated simulation and measurement interface for the analysis of manufacturing effects during the mold making as well as first results of its application on the basis of the manufacturing of mold inserts.

Kinematics in ultra-precision grinding of WC moulds

The target of this paper is the evaluation of process kinematics in ultra-precision grinding for the manufacturing of typical precision glass moulds (diameter 5 mm to 20 mm) with respect to part quality (form accuracy, surface roughness), machining time and process stability. This is discussed exemplary for two specific grinding kinematics by comparison of experimental results regarding achievable figure accuracy and surface finish.

Material aspects for the diamond machining of submicron optical structures for UV-application

The paper discusses material aspects governing the diamond machining process for submicron structures which serve as diffractive optical elements (DOE). Therefore, first the cutting process for fabrication of DOEs is introduced. The microstructured surface is generated by diamond turning using a nano Fast Tool Servo (nFTS), which enables a variation of the depth of cut up to 350 nm at a maximum frequency of 10 kHz. Such DOEs are typically used with a wavelength of 632 nm. A new application for UV-radiation with a wavelength below 350 nm requires alternative materials with sufficient reflectivity. Cutting experiments and UV-reflectivity tests were performed in order to identify suitable materials. High machining accuracy and UV-reflectivity were achieved with ultrafine grained aluminium as workpiece material.

Merging Technologies for Optics

The market for optical and optoelectronical components is a rapidly growing global market. The development of new manufacturing technologies for the fabrication of optics enables the fabrication of optical components with nanometer roughness and submicron form accuracy for mass markets like digital cameras, video projectors and automotive applications, even for low cost applications with short product life cycles. Therefore, the process chain for fabricating optical high quality mass products has to be deterministic flexible as well as in order to suppress cost intensive and time consuming iterations within the manufacturing chain. This paper introduces several approaches to take up this challenge.

A Review on Machining of Micro-Structured Optical Molds

The manufacturing of optics is an important field of technology and will serve keymarkets today and in the future. Nevertheless, the application of complex optical elements is much restricted today despite of their outstanding functional advantages. Furthermore, the replication of structured optical components requires high precision molds. Diamond machining processes like diamond milling and cutting as well as abrasive polishing are appropriate micro-structuring techniques for optical molds. The combination of these key machining technologies with replication techniques within closed process chains will open the possibility to produce high precision complex optical elements as mass-product articles for many optical applications. Important machining techniques for optical mold manufacture are presented and discussed.