Seung Yub Baek

Effect of displacement on kinetic frictional behaviour between electro-deposited coating and AISI 52100 steel under fretting conditions:

This article investigates the effect of imposed displacement on the evolution of the kinetic friction coefficient between an epoxy-based cathodic electro-deposited coating and a steel ball. Small-amplitude reciprocal sliding is induced until the friction coefficient reaches a critical value. The kinetic friction coefficient is measured at various imposed displacements. Slip ratio, defined as the ratio of an actual sliding distance to imposed displacement, is determined to identify a slip regime. Experimental results show that a friction coefficient evolution varies in a gross slip regime according to imposed displacement amplitude. It is identified that the critical number of cycles to coating failure decreases with increased imposed displacement amplitude. The relation between the critical number of cycle and imposed displacement amplitude is found to be inverse power law.

Machinability in Precision Grinding of Aspheric Optical Lens with Diamond Wheel

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.

Study on Platinum Coating Depth in Focused Ion Beam Diamond Cutting Tool Milling and Methods for Removing Platinum Layer

In recent years, nanomachining has attracted increasing attention in advanced manufacturing science and technologies as a value-added processes to control material structures, components, devices, and nanoscale systems. To make sub-micro patterns on these products, micro/nanoscale single-crystal diamond cutting tools are essential. Popular non-contact methods for the macro/micro processing of diamond composites are pulsed laser ablation (PLA) and electric discharge machining (EDM). However, for manufacturing nanoscale diamond tools, these machining methods are not appropriate. Despite diamond’s extreme physical properties, diamond can be micro/nano machined relatively easily using a focused ion beam (FIB) technique. In the FIB milling process, the surface properties of the diamond cutting tool is 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 procedures. To protect the diamond substrate, a protection layer—platinum (Pt) coating is essential in diamond FIB milling. In this study, the depth of Pt coating layer which could decrease process-induced damage during FIB fabrication is investigated, along with methods for removing the Pt coating layer on diamond tools. The optimum Pt coating depth has been confirmed, which is very important for maintaining cutting tool edge sharpness and decreasing processing procedures. The ultra-precision grinding method and etching with aqua regia method have been investigated for removing the Pt coating layer. Experimental results show that when the diamond cutting tool width is bigger than 500 nm, ultra-precision grinding method is appropriate for removing Pt coating layer on diamond tool. However, the ultra-precision grinding method is not recommended for removing the Pt coating layer when the cutting tool width is smaller than 500 nm, because the possibility that the diamond cutting tool is damaged by the grinding process will be increased. Despite the etching method requiring more procedures to remove the Pt coating layer after FIB milling, it is a feasible method for diamond tools with under 500 nm width.

Research on the Mechanical Properties of Al6061 Intermetallic Compounds Solubility as Manufactured by Spray Casting

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.

An Experimental Investigation of Optimal Grinding Condition for Aspheric Surface Lens Using Full Factorial Design

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.

A Study on Fabrication of Ultra-Precision Diamond Tool and Length Optimization for Improving the Stability

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.

Development of a Time-Dependent Friction Model for Frictional Aging at the Nanoscale

A model for describing frictional aging of silica is developed at the nanoscale. A cohesive zone is applied to the contact surface between self-mated silica materials. Strengthening of interfacial bonding during frictional aging is reproduced by increasing fracture energy of a cohesive zone. Fracture energy is expressed as a function of hold time between self-mated silica materials. Implicit finite element simulation is employed, and simulation results are compared with experimental ones found in the literature. Calculated friction evolutions with various hold times are found to be in good agreement with experimental ones. Dependence of mesh size and cohesive thickness is identified for obtaining accurate simulation result.

Determination for Tool Edge Geometry and Cutting Conditions by Using FEM Simulations and Experiments

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.

Investigation of Micro Cutting Tool for Diffractive Optical Elements Using FEM Analysis

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.

A Study on the Grinding to Improve Profile Accuracy of Aspheric Lens

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.