Papers by Author: Chung Gil Kang

Abstract: Carbon fabric-reinforced thermoplastic (CFRP) composites, fortified with carbon fiber prepreg and epoxy base materials, have been mainly used for body parts for weight lightening, advanced high strength, and impact absorption In the current automotive industry However, as recycling of the composite material is required, attempts have been made to manufacture body parts using a thermoplastic polymeric material as a base substance. In order to produce various types of body parts by impregnating a liquid thermoplastic material into carbon fabric preform in methods of manufacturing a carbon fiber-reinforced thermoplastic composite material (CFRTP), it is important to understand the effect of the impregnation process parameters (time, temperature, pressing force) on the mechanical properties of the composite material. Therefore, in this study, the influence of impregnation process parameters on the mechanical properties of CFRTP is proposed. In addition, this paper presents the problems and solutions when polymeric materials are impregnated in carbon fabric.

Abstract: Recently, researchers and engineers have been interested in the development of hybrid metal matrix composites (HMMCs) for the applications of automotive and aerospace industries owing to their superior properties due to the usage a wide range of material combinations in its manufacturing. The present study focuses on the machining of magnesium based hybrid composites reinforced with CNT (1vol.%) and SiC (2vol.%).The influence of machining parameters such as spindle speed, feed rate, drill diameter and point angle on burr formation and surface roughness on drilling the composites were investigated using Taguchi method. The drilling parameters were optimized by using ANOVA experimental design and also find out the percentage of contribution of each factor. Based on the results, the most influential factor for the burr thickness was spindle speed and point angle. While spindle speed and feed rate were the influencing factors for surface roughness. The analysis revealed that burr height, burr thickness, and surface roughness decreases significantly with an increase in spindle speed.

Abstract: In this paper, hot and cold deep drawing processes are determined with direct deep drawing process and indirect deep drawing process. To predict the friction coefficient, the finite-element method, which can predict deformation behavior until the fracture of a blank sheet, was proposed using the forming limit diagram (FLD) curve. The effect of fracturing of the coating layer on the friction coefficient during the hot and cold deep drawing processes was investigated. The deformation behavior of the coating layer of the boron steel sheet that affects the friction coefficient in the hot and cold deep drawing processes was also proposed. A forming method that can control the surface condition of the formed product is further proposed by explaining the fracture of the coating due to the forming process.

Abstract: Recently, automobile components such as center pillars and impact beams have been fabricated using materials that satisfy both high strength and impact absorption. In this study, the forming process of CR340 (cold rolled steel)/CFRP hybrid composites was investigated. Initially, hybrid composites were fabricated by stacking carbon fibre reinforced plastic (CFRP) prepreg on CR340 steel with Zn coating. An adhesive agent developed by the research team was applied for bonding between the cold rolled steel and CFRP to enable the blank fabrication of hybrid composites. The mechanical properties of the developed hybrid composites were investigated by tensile, bending and lap shear adhesion test. The results showed that the tensile strength and shear strength of composites increases with the increase in the number of laminations but the bending strength decreases.

Abstract: In this study, the closed die forging of aluminium based compoistes reinfoced with CNTs (1vol% and 3vol%) were investigated. Initially, the composites were fabricated using high energy ball milling followed by compaction and sintering. The microstructural results showed that finer grain size and homogeneous dispersion of CNTs were obtained. Composites with up to 97% densification were produced when fine open porosities were removed by closed die forging. The results imply that the hardness and compressive strength of composites with 3vol.% of CNTs has improved without any deterioration. In addition, workability behaviors of composites were investigated by cold upsetting test. For that pore reopening test was performed to confirm the closure of micro-pores after the closed die forged, and to further analyze the densification of the composites. Typical cases, as the pores were not re-opened even after increasing the strain, additional forming is possible up to large deformations.

Abstract: In this study, A356 aluminum thin plates (1.2 mm thick) are fabricated using the semi-solid forming process. Using the electromagnetic stirrer, A356-based semi-solid slurry is fabricated. The configuration of the thin die cavity for forging is designed using the fluid analysis of MAGMA software. The dimension of the thin plate is 150 x 150 x 1.2 mm. The semi-solid slurry with 45% solid fraction is created and then injected into the forging die at the 200-ton hydraulic press for compression. Thin plate with semi-solid slurry at 45% of the solid fraction (fs) is fabricated with punch speed of 300 mm/s and punch pressure of 200 MPa for compression the slurry. The formability, mechanical properties and microstructure of a formed thin plate sample are analyzed. As a result, a thin plate with 211.5 MPa of tensile strength and 8.5% of elongation can be formed.

Abstract: Recently, the demand for energy is growing at a very high rate all over the world. The fossil fuels eventually lead to the foreseeable depletion of limited fossil energy resources. Hydrogen is considered a promising candidate to remedy the depletion of fossil fuels. The bipolar plate is the second most important component of a proton exchange membrance (PEM) fuel cell stack after the membrance electrode assembly (MEA). Its primary roles are to supply reactant gases to the fuel cell electrodes and provide electrical connection between adjacent cells in the stack while removing product water from the cell and transferring away the heat of reaction. Historically, machined graphite had been chosen as a good compromise between all of these requirements, but alternatives are emerging. New materials are light metals. In this study, rubber pad forming process was employed as the manufacturing method for metallic bipolar plates. The rubber pad and the sheet metal plate were pressed together by the punch, and the repulsive force of the deformed rubber is loaded at the plate, and can contribute to improving formability. And then, its surface was coated with TiN. After coating process, the performance characteristics of single stack in the condition of PEMFC using the metal bipolar plate have been investigated.

Abstract: Recently, the demand for energy is growing at a very high rate all over the world. The fossil fuels eventually lead to the foreseeable depletion of limited fossil energy resources. Hydrogen is considered a promising candidate to remedy the depletion of fossil fuels. The bipolar plate is the second most important component of a proton exchange membrance (PEM) fuel cell stack after the membrance electrode assembly (MEA). Its primary roles are to supply reactant gases to the fuel cell electrodes and provide electrical connection between adjacent cells in the stack while removing product water from the cell and transferring away the heat of reaction. Historically, machined graphite had been chosen as a good compromise between all of these requirements, but alternatives are emerging. New materials are light metals. In this study, rubber pad forming process was employed as the manufacturing method for metallic bipolar plates. The rubber pad and the sheet metal plate were pressed together by the punch, and the repulsive force of the deformed rubber is loaded at the plate, and can contribute to improving formability. And then, its surface was coated with TiN. After coating process, the performance characteristics of single stack in the condition of PEMFC using the metal bipolar plate have been investigated.

Abstract: Various portable applications such as a mobile phone, MP3 player, PMP player and so on, have been continuously developing with influencing on each other. In this environment, functions of IT applications have been built in the mobile phone, and consequently, the additions of them increase the size of the phone. However, the sizes of present phones have changed less than those of the past, and this trend is expected to be continued in the future because of the inherent characteristics mobility and portability of the phone. Great strides made in the industries manufacturing cellular phone components have facilitated the development of phones having similar size to the existing phone. However, in common, there are limitations on the extent to which the sizes of the parts can be reduced because of the technical reasons pertaining to mechanical or electrical properties, the forming process and assembly structure. In such a scenario, the use of a slide mechanism is the practical alternative for maintaining the mobility and portability. Reduction of the sliding space has a decisive effect on the decrease of the phone size. Therefore, a study of a novel spring to be manufactured by the etching process was performed to minimize the thickness. Meanwhile, the use of the slide mechanism is advantageous for maximizing visibility and increasing functionality with the limited space which are of utmost importance for the design of a contemporary cellular phone. In addition, various extra function keys including the main keypad buttons are required to maximize the visibility. However, the sliding stroke must increase to have them, and the existing spring units cannot be satisfied with the requirements under the limited space. Therefore, the study of a long-stroke spring unit and its manufacturing process to minimize the thickness with the stroke of 60 mm was performed.

Abstract: A Proton Exchange Membrane Fuel Cell (PEMFC) is a type of fuel cell being developed for automotive applications as well as for stationary fuel cell applications and portable fuel cell applications. Its performance such as power density can be improved by the use of the bipolar plate with a new lightweight material which is one of core components making up PEMFC stack. Aluminum alloy has good mechanical properties not only in terms of density, electrical resistivity and thermal conductivity, but also in terms of corrosion resistant compared with stainless steel and graphite composites bipolar plate. Furthermore, the use of aluminum for a bipolar plate reduces simultaneously the cost and weight of it, and it contributes to the ease of machining. For these reason, an aluminum alloy is selected in this study. This study presents the feasibility of the simulation for the development of aluminum bipolar plates that consists of multi array micro channels. The analytical solutions obtained by the simulation are validated by the comparison with the experimental results. From the results, it is ensured that the stamping processes for the bipolar plate could be predicted and designed by the results of the by FE-Simulation.