Eun-Chae Jeon

Derivation of tensile flow properties of thin films using nanoindentation technique

Abstract By regarding the tip blunting as a ball indentation at very low depth range (within about 80 nm in our experiments), the flow properties of Au thin films were derived from the indentation load–depth curve obtained by nanoindentation technique. The effects of pile-up or sink-in were considered in determining the real contact between the indenter and the specimen. The representative strain in indentation was defined in various ways and examined by comparing the flow properties derived from indentation load–depth curve with those measured by tensile test. The best definition was found to be the shear strain at contact edge multiplied by 0.1. When we considered the effects of pile-up or sink-in, the representative stress in indentation could also be determined, and was found to be one third of the mean contact pressure for fully plastic regime. As a more intrinsic property than hardness, the yield strengths of Au films with thickness of 0.56 and 0.99 μm were extrapolated from the derived true stress–true strain curve as 261±30 and 154±18 MPa, respectively.

Statistical Analysis of Experimental Parameters in Continuous Indentation Tests Using Taguchi Method

The continuous indentation test, which applies an indentation load to a material and records the indentation depth, yields indentation tensile properties whose accuracy can vary depending on such experimental parameters as number of unloadings, unloading ratio, maximum depth ratio and indenter radius. The Taguchi method was used to quantify their effects and to determine their optimum values. Using signal-to-noise ratio calculated from the error in the indentation tensile properties, the criterions and the optimum values for the experimental parameters were presented. The indentation tensile properties evaluated with the optimum parameters were in better agreement with the tensile properties.

Improvement of machining quality of copper-plated roll mold by controlling temperature variation

Abstract Micro prism film used in LCD industry can be manufactured by roll to roll method with copper-plated roll mold. As copper-plated roll mold is getting larger, pitch error is getting severer. The pitch error drops the quality of micro prism film. The main cause of the pitch error was investigated during machining large roll mold whose machined length was 1 200 mm. The temperature of machining system was elevated during machining roll mold, and this elevation induced thermal expansion of the system. The temperature variation around the roll mold also made thermal expansion of the roll mold. The amount of thermal expansion had strong relationship to the amount of pitch error. Therefore, the roll mold was machined after warming-up of machining system and precise temperature controller around copper-plated roll mold was installed, which minimized the temperature variation. Finally, precise micro prism patterns without pitch error were machined on the large roll mold.

Determining Brinell Hardness From Analysis of Indentation Load-Depth Curve Without Optical Measurement

Hardness tests are performed to determine not only hardness but also other properties such as strength, wear resistance, and deformation resistance. They are also performed to predict residual lifetime through analysis of the hardness reduction or hardness ratio. However, hardness tests require observation of the residual indentation, and for that reason are not widely used in industrial fields. This study thus examines obtaining Brinell hardness values without optical observation, using instead quantitative formulas and analyzing the relationship between the indentation depths from the indentation load-depth curve and mechanical properties such as the work-hardening exponent, yield strength, and elastic modulus on the basis of finite-element analysis.

Comparison of Machinability Between PCD Tool and SCD Tool for Large Area Mirror Surface Machining Using Multi-tool by Planer

Mirror surface machining for large area flattening in the display field has a problem such as a tool wear and a increase in machining time due to large area machining. It should be studied to decrease machining time and tool wear. In this paper, multi-tool machining method using a PCD tool and a SCD tool was applied in order to decrease machining time and tool wear. Machining characteristics (cutting force, machined surface and surface roughness) of PCD tool and SCD tool were evaluated in order to apply PCD tool to flattening machining. Based on basic experiments, the PCD/SCD multi-tool method and the SCD single-tool method were compared through surface roughness and machining time for appllying large area mold machining.

Wear characteristics of V shape diamond tool for micro prism pattern with Al alloys

Abstract The ultra-precision machining process using a single crystal diamond tool has been mainly used for machining molds of optical components. Since the micro patterns of various shapes having excellent surface roughness can be machined by using ultra-precision machine tools, the micro pattern on a large light guide plate (LGP) is mainly machined using a diamond tool. The tool wear occurs due to long machining distances and time while machining a large-area LGP mold. The deformation and dimensional error of micro pattern are caused by tool wear, as a result, the light efficiency of LGP declines. The characteristics of tool wear should be analyzed in order to precisely machine large-area LGP mold from all sorts of materials. The experiments were performed in order to compare wear characteristics of a V90° diamond tool using Al3003, 5052, 6061 and 7075. The prism pattern of depth 10 μm was machined in order to analyze characteristics of tool wear according to machining distances (0.5, 1 and 1.5 km). The effects of tool wear on pattern shape were analyzed by applying overlapped cutting depths (Rough machining is (10+8+7) μm and Finish machining is (5+3+2+1) μm) by continuously machining a prism pattern of W shape of 25 μm in depth.

A Study on Manufacturing Method of Nano-Micro Hybrid Pattern Using Indentation Machining Method and AAO Process

Micro/nano patterns for optical concentration and diffusion have been studied in the various fields such as displays, optics, and sensors. Conventional micro patterns were continuous and linear shapes due to using linear-type light sources, however, recently non-continuous patterns have been applied as point sources are used for dot-type light sources such as LEDs and OLEDs. In this study, a hybrid machining technology combining an indentation machining method and an AAO process was developed for manufacturing the non-continuous micro patterns having nano patterns. First, mirror-like surfaces (R a <20nm) of pure Aluminum substrates were obtained by optimizing cutting conditions. Then, The letter of ‘K’ consisting of the arrays of the micro patterns was manufactured by the indentation machining method which has a similar principle to indentation hardness testing. Finally, nano patterns were machined by AAO process on the micro patterns. Conclusively, a specific letter having nano-micro hybrid patterns was manufactured in this study.

Study on Machining High-Aspect Ratio Micro Barrier Rib Array Structures using Orthogonal Cutting Method

The micro barrier rip array structures have been applied in a variety of areas including as privacy films, micro heat sinks, touch panel and optical waveguide. The increased aspect ratio (AR) of barrier rip array structures is required in order to increase the efficiency and performance of these products. There are several problems such as burr, defect of surface roughness and deformation and breakage of barrier rip structure with machining high-aspect ratio micro barrier rip array structure using orthogonal cutting method. It is essential to develop technological methods to solve these problems. The optimum machining conditions for machining micro barrier rip array structures having high-aspect ratio were determined according to lengths ( and ) and shape angles ( and ) of diamond tool, overlapped cutting depths ( and ), feed rates (100 mm/s) and three machining processes. Based on the optimum machining conditions, micro barrier rib array structures having aspect ratio 30 was machined in this study.

Realization of 3D Image on Metal Plate by Optimizing Machining Conditions of Ultra-Precision End-Milling

3D images are generally manufactured by complex production processes. We suggested a simple method to make 3D images based on a mechanical machining technology in this study. We designed a tetrahedron consisted of many arcs having the depth of 100 μm and the pitch of 500 μm, and machined them on an aluminum plate using end-milling under several conditions of feed-rate and depth of cut. The area of undeformed chip including depth of cut and feed-rate can predict quality of the machined arcs more precisely than the undeformed chip thickness including only feed rate. Moreover, a diamond tool can improve the quality than a CBN tool when many arcs are machined. Based on the analysis, the designed tetrahedron having many arcs was machined with no burr, and it showed different images when observed from the left and right directions. Therefore, it is verified that a 3D image can be designed and manufactured on a metal plate by end-milling under optimized machining conditions.

Machining Characteristics of Micro Structure using Single-Crystal Diamond Tool on Cu-plated Mold

The optical film for light luminance improvement of back light unit that is used in light emitting diode/liquid crystal display and retro-reflective film is used as luminous sign consist of square and triangular pyramid structure pattern based on V-shape micro prism pattern. In this study, we analyzed machining characteristics of Cu-plated flat mold by shaping with diamond tool. First, cutting conditions were optimized as V-groove machining for the experiment of micro prism structure mold machining with prism pattern shape, cutting force and roughness. Second, the micro prism structure such as square and triangular pyramid pattern were machined by cross machining method with optimizing cutting conditions. Variation of Burr and chip shape were discussed by material properties and machining method.