Papers by Author: Seung Yub Baek

Abstract: A tool for fabricating micro/nanopatterns was utilized in space optics, virtual reality, augmented reality, and semiconductor industry. Nowadays, demand of manufacturing technique for ultra-precision is continuously increasing virtual reality and augmented reality industry across the board and core technique for manufacturing next generation lens is cutting tool fabricating technique with nanoscale. In particular, tools of micro/nanosize for ultra-precision machining was made by using an ultra-precision grinding, but it was difficult to fabricate tools which have under micro scale. Recently, results of studies with many researchers were pulsed laser ablation, electric discharge machining and precision grinding. However, previous studies are unsuitable in making tools of micro/nanoscale. Due to unique physical properties of diamond, it can be easily controlled by using focused ion beam. The surface properties of the diamond layer are affected because of the amorphous damage caused by the FIB gallium ions collision, implantation and these effects can make to be able to control the geometry of cutting tool. In this study, we carried out in fabricating diamond tools under micro scale by using FIB milling through various process studies and determined in order to optimize the length of unstable tool.

Abstract: Micro/nanoscale diamond cutting tools used in ultra-precision machining can be fabricated by precision grinding, but it is hard to fabricate a tool with a nanometric cutting edge and complex configurations. High-precision geometry accuracy and special shapes for microcutting tools with sharp edges can be achieved by focused ion beam (FIB) milling. However, in the FIB milling process, the surface properties of the substrate (such as a diamond substrate) are affected by the amorphous damage layer caused by the FIB gallium ion collision and implantation and these influence the diamond cutting tool edge sharpness and increase the processing procedure. In this study, to reduce the diamond cutting tool edge sharpness and processing procedure, FIB milling beam current and tilting angle characteristics of single-crystal diamond were investigated, along with method for decreasing the FIB-induced damage on diamond tools by platinum (Pt) coating on the diamond substrate. Experimental results revealed that optimize beam current, tilting angle and platinum (Pt) coating could lead to relatively few processing procedure and sharp cutting tool edge. The obtained results are an endeavor to enhance the controllability of the diamond cutting tool FIB milling.

Abstract: Diffractive optical elements (DOE) can be used to simplify optical systems such as lightening its mass, reducing elements numbers and so on. Single-crystal diamond is considered as the preferred tool materials in ultra-precision and nanometer-scale cutting operation. Due to the well known and exceptional difficulty in shaping, the fabrication of diamond cutting tools requires special processing method. As a highly efficient and cost-effective solution, the mechanical lapping process has been extensively applied in tool-making industry. In this paper, the key enabling technologies to design and fabricate the diamond-cutting tools for ultra-precision and submicronic machining are presented and reviewed. The paper describes the shape of micro cutting tool that is based on the finite element method of calculation of relief angle and rake angle.

Abstract: Hardened steel, Ni-based alloys and brittle materials are very difficult to machine using conventional cuttingmethods.A tool edge with a small nose radius can alleviate the regenerative chatter. In general, it is important for conventional cuttingto use the smallest possible tool nose radius. A sharp tool shape has an adverse effect on tool strength and the instability of machining process still occurs. A tool wear model with small nose radius proposed by past researchers is evaluated for predicting metal cutting tool wear when machining the copper. Tool temperature values are determined using finite element methods simulation. These temperatures are related to tool wear measured after metal cutting turning tests on a copper workpiece to determine tool edge geometry in low metal tool model.In this study, the effects of cutting conditions and tool edge geometry on process stability in turningare investigated through experiments and FEM simulations.

Abstract: Al6061 alloys are well known as extrusion materials for automobile parts, aircraft. Recently, increasing demands of the lightweight for vehicles, materials have replaced steel are developed. Aluminum alloys are increasingly used as structural materials but in terms of mechanical properties, it is not a completed as a replacement for steel. The purpose of this study was to improve the mechanical properties and minimize the grain sizes of Al6061 matrix alloys for structural materials as produced by spray casting. Al6061 alloys were melted with 800°C in electrical resistance furnace. In order to form equilibrium concentration of Mg₂Si (about 2 times) for Al6061, increased Mg and Si were added to Al6061 alloys and then preforms were prepared with molten metal by spray casting. The Specimens were fabricated by solution heat treatment and T6 age hardening. As a result of analyzing microstructure observations and mechanical properties according to supersaturated solid solution of Mg₂Si for the final sample obtained, there were no changes in the size of the precipitates but precipitates per unit area were found to increase the area during the heat treatment processes. Mechanical properties such as tensile strength of over 80MPa and hardness of over 10HRB in spray casting have been increased according to solubility of Mg₂Si.

Abstract: The two kinds of bicycles of the power transmission types are derailleur type and built in gear hub type. Derailleur type is a simple structure but it is vulnerable to external contamination and impact. And it is impossible to shift from the quiescent state. Built in gear hub type is very strong about the external contamination and impact because working part did not expose to the outside. In this paper, a new design of a continuously variable transmission with built in gear hub type for bicycles was developed and simulated. Stress and displacement analysis in built in gear hub by using finite element method were performed in order to develop improved structure of CVT.

Abstract: In order to obtain competitiveness in the field of industrial manufacturing, a reduction in the development period for the batch machining of products is required. It is essential to analyze the stress distribution and deformations of machining system which is used for manufacturing the aspheric lens using FEM software ANSYS. Finite element simulations have been performed in order to study the influence of machining system which was developed in this study on structures. It is very important to understand the structural behavior of machining system. This research investigated the static analysis and dynamic analysis of machining system for aspheric lens to predict the damage due to loading.

Abstract: This study presents the development of an ultra-precision grinding system based on a new grinding technique called the “In-Process Grinding Method (IPGM)”. IPGM which is used for grinding aspheric lens increases both the production and grinding performance, and significantly decreases total production costs. To enhance the precision grinding productivity of ultra-precision aspheric lens, we present here an ultra-precision grinding system and process for the aspheric micro-lens. The tool path was calculated and CNC program generation and tool path compensation were performed for aspheric lens. Using this ultra-precision grinding system, aspheric lens, 4mm in diameter, were successfully performed. The profile error after the first grinding without any compensation was less than 0.6μm, and surface roughness Ra was 0.01μm. In-process grinding was performed with compensation. Results of the profile accuracy P-V 0.3μm and surface roughness Ra 0.006 μm were obtained.

Abstract: In order to do the precision grinding of optical aspheric lens, it is essential to achieve high quality surface roughness. Experiments show that the contacting area between the wheel and workpiece in a grinding process is critical to influence the surface roughness for a fine grit size resin bonded wheel. The precision grinding are performed with BK7 optical lens. This paper deals with the grinding of an aspheric surface optical lens by diamond wheel. This study also compares each machining parameter (work spindle speed, wheel spindle speed, feedrate, etc.) in rough grinding, fine grinding and polishing on the aspheric lens. In this study, several experiments were carried out BK7 optical glass lens by using vitrified, metal, resin bond diamond wheel and the polisher of urethane ball was used to remove the tool marks with an ultra-precision in-line grinding system. It was found that machining parameters significantly influence the surface roughness of aspheric optical lens.

Abstract: To enhance the precision and productivity of ultra precision aspheric surface micro lens, the development of ultra-precision grinding system and process for the aspheric surface micro lens are described. In this paper, an ultra-precision grinding system for manufacturing the aspheric surface micro lens was developed by considering the factors affecting the grinding surface roughness and profile accuracy. This paper deals with the mirror grinding of an aspheric surface micro lens by resin bonded diamond wheel and with the spherical lens of BK7. The optimization of grinding conditions with respect to ground surface roughness and profiles accuracy is investigated by design of experiments.