Reaction-bonded silicon carbide (RB-SiC) is a new ceramic material that has extremely high strength and hardness. Diamond turning experiments were performed on RB-SiC to investigate the microscopic material removal mechanism. Diamond tools with large nose radii of 10 mm were used for machining. It was found that the surface roughness was not significantly affected by the tool feed rate, but was strongly dependent on the tool rake angle. The mechanism for material removal involved plastic deformation, microfracture and dislodgement of 6H-SiC grains. Raman spectroscopy revealed that the silicon bond component underwent amorphization, while no phase transformation of 6H-SiC grains was observed. Tool wear was also investigated and two types of wear patterns were identified. Under the experimental conditions used, a surface finish of 23 nm Ra was obtained even at an extremely high tool feed rate of 72 μm/rev. This study demonstrates the feasibility of precision machining of RB-SiC by diamond turning at a very high material removal rate.

Mechanism for material removal in diamond turning of reaction-bonded silicon carbide

Single-crystal germanium is an excellent optical material in the infrared wavelength range. The development of germanium Fresnel lenses not only improves the optical imaging quality but also enables the miniaturization of optical systems. In the present work, we developed a ductile-mode micro grooving process for fabricating Fresnel lenses on germanium. We used a sharply pointed diamond tool to generate the micro Fresnel structures under three-axis ultraprecision numerical control. By adopting a small angle between the cutting edge and the tangent of the objective surface, this method enables the uniform thinning of the undeformed chip thickness to the nanometric range, and thus provides complete ductile regime machining of brittle materials. Under the present conditions, a Fresnel lens which has a form error of 0.5 µm and surface roughness of 20–50 nm Ry (peak-to-valley) was fabricated successfully during a single tool pass.

http://iopscience.iop.org/article/10.1088/0960-1317/15/10/019/pdf

Micro grooving on single-crystal germanium for infrared Fresnel lenses

Precision is one of the most important aspects of manufacturing. High precision creates high quality, high performance, exchangeability, reliability, and added value for industrial products. Over the past decades, remarkable advances have been achieved in the area of high-precision manufacturing technologies, where the form accuracy is approaching the nanometer level and surface roughness the atomic level. These extremely high precision manufacturing technologies enable the development of high-performance optical elements, semiconductor substrates, biomedical parts, and so on, thereby enhancing the ability of human beings to explore the macro- and microscopic mysteries and potentialities of the natural world. In this paper, state-of-the-art high-precision material removal manufacturing technologies, especially ultraprecision cutting, grinding, deterministic form correction polishing, and supersmooth polishing, are reviewed and compared with insights into their principles, methodologies, and applications. The key issues in extreme precision manufacturing that should be considered for future R&D are discussed.

https://iopscience.iop.org/article/10.1088/2631-7990/ab1ff1/pdf

Manufacturing technologies toward extreme precision

Experimental Work on Micro Laser-Assisted Diamond Turning of Silicon (111)

Ductile regime machining is an alternative method for polishing of brittle materials to obtain a high quality surface finish by a ductile or plastic material removal process. Hence, there is a growing interest to study ductile regime machining over several decades. This paper reviews current state of research and development in ductile regime machining. The research and development associated with mechanism of brittle–ductile transition, surface integrity, and the factors influencing ductile regime machining are discussed in details in this paper.

A review on the current research trends in ductile regime machining

Single-crystal germanium is an important infrared optical material. In the present work, single-point diamond turning experiments on single-crystal germanium (100), (110) and (111) planes were conducted in order to examine their ultraprecision machining characteristics. Three kinds of surface textures and chip morphologies were observed during the brittle-ductile transition of the machining mode. The brittle-ductile boundary changed significantly with the crystal orientations of the workpieces. Due to the crystallographic anisotropy, micro-fractures were generated on the workpiece surface in a radial pattern from the rotation center. However, it was possible to produce completely ductile-cut surfaces on all crystal orientations by using undeformed chip thicknesses smaller than a critical value, namely, the minimum critical undeformed chip thickness, which was approximately 60nm under the present conditions. Compared to wet cutting, dry cutting was beneficial for ductile machining on a few specific crystal orientations. The findings in this study provide criterions for determining process parameters for the fabrication of aspherical and diffraction infrared optics using single-crystal germanium.

Experimental Study on the Ultraprecision Ductile Machinability of Single-Crystal Germanium

Thin films of noble metals are considered to be important materials for microelectronics applications. In this study, Ru thin films were deposited on SiO2/Si substrates by RF magnetron sputtering using a mixture of Ar and O2 gases, and the effects of O2 flow ratio, substrate temperature and film thickness on the crystal orientation and surface roughness of the films were studied. Single orientation (001) Ru thin films were formed under appropriate conditions, such as O2 flow ratios lower than that required for RuO2 formation and high substrate temperatures. A minimum full-width at half-maximum of 1.2° was obtained for the rocking curve of the Ru (002) X-ray diffraction peak. The average surface roughness (Ra) of the single orientation films was estimated to be approximately 1 nm by atomic force microscopy. The oxygen introduced during sputtering was thought to play a role as a surfactant.

Kouki Maekawa

Papers

Micro grooving on single-crystal germanium for infrared Fresnel lenses

Experimental Study on the Ultraprecision Ductile Machinability of Single-Crystal Germanium

Improvement of the Crystal Orientation and Surface Roughness of Ru Thin Films by Introducing Oxygen during Sputtering