Jun'ichi Tamaki

Micro grooving on single-crystal germanium for infrared Fresnel lenses

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.

Three-dimensional shape modeling of diamond abrasive grains measured by a scanning laser microscope

When a scanning laser microscope is used as a tool for measuring the three-dimensional shape of abrasive diamond grains, the result is often distorted due to the presence of noise. After the noise has been removed, a three-dimensional modeling is considered in order to enhance the shape obtained. In the proposed modeling method, the grain body is extracted from the bond surface and horizontally divided into layers. The contour of each layer is modeled by a technique called the cam and follower method, and then the modeled layers are overlapped in order to generate the modeled grain shape. The obtained results are employed for measurements of various shape features of diamond abrasive grains. Introduction The precise measurement of the three-dimensional (3D) shape of diamond abrasive grain is required for various studies on grinding. For example, the grinding wheel wear is attributed to bond fracture, grain fracture, and attritional grain wear [1]. The studies on the last two wear mechanisms require shape measurement of grains under observation. Studies on the effect of grain shape on ground surface integrity [2] and grinding mode [3] also necessitate this measurement. Accurate information on grain shape is also required for a reliable simulation of the grinding process [4]. In order to realize this measurement, various techniques are considered. As for profilometry, 2D (cross-sectional) and 3D data can be obtained [5], but the poor penetration of the stylus tip results in undesirable low accuracy [1]. The scanning electron microscope (SEM) is a powerful measuring tool [6], but the time needed for sample coating process and chamber air pumping is considerable. A system of a laser beam probe with a fixed beam and moving x-y stage is also applicable [7]. This system is similar in principle to profilometry; it employs a laser beam as an optical stylus. Since the problem of stylus tip penetration does not exist in this system, the accuracy is improved, but the time consumed by stage movement is considerable. Compared with the above-mentioned systems, the scanning laser microscope (SLM) is easy and quick to operate and provides good accuracy, but its measurement results are often distorted due to the occurrence of noise. In order to solve this problem, the noise types and the reasons for noise occurrence are investigated [8], and noise is removed by a method developed by the authors. As a subsequent step, this study proposes a way for 3D shape modeling to be applied after noise removal. This approach is observed to smooth the glitches left behind by noise removal and to enhance the obtained shape features in order to achieve increased precision of measurement results. Specimen and Measurement Procedure The measured grains are taken from a metal-bonded diamond grinding wheel (SD#270N100 M) dressed by electro-contact discharge method. The measuring tool is a laser scanning microscope, model 1LM15W, fabricated by Lasertec Corporation. For measurements, the optimal conditions Key Engineering Materials Online: 2003-04-15 ISSN: 1662-9795, Vols. 238-239, pp 131-136 doi:10.4028/www.scientific.net/KEM.238-239.131

A Study on Surface Generation of Metal-Bonded Diamond Grinding Wheel Dressed by Electro-Contact Discharge

This paper conducted Electro-Contact Discharge (ECD) dressing experiment for #600 diamond grinding wheel to understand how fine diamond grits protrude from metal-bonded wheel surface. The SEM observation, EDS analysis, image processing and 3D grit modeling on wheel surface were carried out to investigate grit protrusion characteristics. Then ECD dressing and mechanical dressing experiments were carried out to identify the effect of grit protrusion feature on grinding performance. It is confirmed that the dressed wheel surface topography is sensitive to open circuit voltage Ei, discharge polarity and electrode composition. Meanwhile, ECD dressing with Ei=15V and straight polarity can produce superior protrusion topography without the damage of diamond crystal faces and the bond tail behind protrusive grit. It can obtain better ground surface of hard-brittle material than mechanical dressing with the bond tail.

Spike noise removal in the scanning laser microscopic image of diamond abrasive grain using a wavelet transform

To remove spike noise in the scanning laser microscopic image of diamond abrasive grain without blurring the sharp edges, a new smoothing technique that combines a conventional averaging technique with wavelet transforms is proposed. The diamond abrasive grain image is decomposed into high- and low-frequency subimages using wavelet filters, and all subimages except the lowest frequency one are synthesized to obtain a high-frequency image, from whose pixel values spike noise points are extracted. A conventional averaging technique is then applied to the same points in the original image as the spike noise points in the high-frequency image. The smoothing technique successfully removes both clustered and unclustered spike noise while preserving the sharp edges. Spike noise is removed without a loss in the original grain shape. This smoothing technique will surely be effective for other applications.

Evaluation of Hard Materials Using Eco-Attributes

Hard materials based on Alumina (AN), Silicon Carbide (SC), Boron Carbide/Nitride (BC/N), Zirconia (ZN), and alike are often used to produce abrasive grains and coat cutting tools. These materials improve the performance of grinding/machining operations by providing an enhanced productivity, a longer grinder/tool life, and a better surface finish. On the other hand, they might leave some burdens on the environment. Therefore, eco-attributes (i.e., energy consumption, CO2 emission, NOX/SOX emission, water usage, recycle fraction, etc.) of these hard materials should be used to make an informed decision. This study deals with this issue and provides an evaluation of AN, SC, BC/N, and ZN based hard materials in terms of CO2 emission, NOX emission, SOX emission, and water usage. The outcomes of this study are useful for analyzing grinding and other abrasive processes for achieving eco-manufacturing.

Modeling and Simulation of 3D Surface Finish of Grinding

The main body of grinding knowledge comes from the experiments done by independent investigators. If such experimental results are not made both human- and machine-comprehensible from the very beginning, then it would be difficult to reuse the results using a computerized network or any other means. In this respect, intelligent systems are needed to create human- and machine-comprehensible models of important results like 3D surface finish, cutting force, tool wear, etc. From this perspective, this paper describes a method for modeling and simulation of 3D surface finish of grinding. A human-friendly simulation tool is developed to implement the method. The simulation result is compared with the real 3D surface finish and a close correlation is found. The presented model can be integrated with the collaborative machining networks for better utilization of grinding resources using computers (e.g., condition monitoring, process planning, automation) and even using humans (e.g., effective exchange of information among peers in the research community and in the industry).

Chip Formation Behaviour in Ultra-Precision Cutting of Electroless Nickel Plated Mold Substrates

Electroless nickel plating is used in mold manufacturing industries as a surface processing technology for providing hard, ductile, wear resistant and corrosion-resistant surfaces. In this work, we conducted single point diamond turning experiments on electroless nickel plated substrates at machining scales from the nanometric to the micrometer level, and the machining behaviour was investigated through examining the chip morphology and surface texture. Emphatically, the effect of cutting fluid was investigated in detail. The results showed that the chip formation mechanisms in dry cuts and wet cuts are significantly different. Dry cuts cause splitting, adhesion, folding and secondary deformation of the chips, leading to surface defects. The results indicated that an effective supply of cutting fluid to the cutting region is essentially important to achieve high quality surfaces.

Design for Manufacturing of IFS Fractals from the Perspective of Barnsley's Fern-leaf

ABSTRACTThis study deals with the design for manufacturing (DFM) of fractals created by a random walk called iterated function system (IFS). In particular, the DFM of an IFS-created fractal called Barnsleys fern-leaf is considered. The IFS dedicated for creating virtual models of a fern-leaf uses a set of four strictly-contracting affine mappings in the onto manner. The interactions among these mappings are studied in detail in order to identify some data structures. Based on the identified data structures, a DFM procedure is proposed. In the proposed DFM procedure, three out of the four mappings are employed in both the onto and one-to-one manner. The proposed DFM procedure is applied to the redesign of the shape (fern-leaf). Physical models of the redesigned fern-leaf are manufactured using both additive and subtractive manufacturing technologies (3-D printing and milling). The factors affecting accuracy of the physical models are also described. Although this study is limited to the shape of the fern-...

Visualization of 3D Topography of Grinding Wheel Surface Dressed by Rotary Diamond Dresser

A computer-aided simulation was developed to visualize the three-dimensional topography of a grinding wheel surface dressed by a rotary diamond dresser (RDD), and the effects of up-cut and down-cut dressing on the roughness of the dressed surface were examined to demonstrate the effectiveness of the simulation. In the case of single-pass dressing, the roughness of the grinding wheel surface decreased with decreasing dresser feed rate and approached a constant value depending on the velocity ratio of the RDD to the grinding wheel. In the case of multipass dressing, up-cut dressing provided the grinding wheel with a surface topography which was much more stable than that provided by down-cut dressing.

Estimation of Grinding Wheel Performance by Dressing Force Measurement

Dressing force measuring equipment was developed and the performance of a single-point diamond dresser was examined focusing on the relationship between dressing force and grinding performance. It was found that a distinct relationship exists between dressing force and grinding performance, and that the sharp-edged single-point diamond dresser can control grinding performance with low dressing force. The single-point diamond dresser and multipoint diamond rotary dresser induce the same dressing force if their wear widths are equal.