Papers by Author: Sang Mok Lee

Abstract: In this study, a Hydro Co-Extrusion Process of Al-Mn/Al-Si hybrid alloys prepared by electromagnetic duo-casting was investigated. Sleeve of the duo-casted billets is 3003 Al-Mn alloy and core is 4004 Al-Si alloy. It is expected hydrostatic stress during the HCE process enhances formability of materials and minimize any defects in extruded billets due to different material properties between two Al alloys. The duo-casted billet was extruded at temperature of 423K and with extrusion ratio of 5. Finally, the effect of the HCE on microstructure of the billet was investigated by an optical microscope.

Abstract: Deformation characteristics and forming limit of ultrafine-grained bulk Al-Mg alloy were examined with upsetting process. The Al-7.5%Mg alloy produced by cryogenic milling and HIP was subjected to hot hydrostatic extrusion as a final consolidation in fabricating the ultrafine-grained bulk material. Upsetting was performed to study their mechanical characteristics in a practical forming process. The extruded specimen showed that the pores remained in spite of the HIP had been collapsed and almost eliminated. The effective removal of the distributed pores resulted in significant increase of formability by preventing early cracking. Metallographic investigations showed that the size of grain remained below a few hundred nanometer scale in the processes.

Abstract: Multi-filament fabrication process using repetitive hydrostatic extrusion of Cu/Al at high temperature was conducted to obtain micro-scaled Aluminum wires. In the process an aluminum rod claded with a copper tube was extruded repetitively three times where a number of the single extruded rods were bundled together and subjected to hydrostatic extrusion to obtain multi-filament wire bundle. Aafter final bundle extrusion the diameter of the aluminum rod was effectively reduced from 33.6 mm to 30μm.

Abstract: The adhesive and wear properties of ITO thin film have been investigated using the scratch and wear tests. ITO thin film was fabricated on glass substrate using RF magnetron sputter and strip lines were formed by selective etching. In the scratch test, the normal load on WC micro-blade was increased and kept constant as it was drawn over the films. In the wear test, sapphire, SUS and WC balls slided repeatedly on the films with the constant normal load. During the scratch and wear, the ESR and the acoustic signal were monitored and recorded. In order to study the adhesive and wear properties of ITO thin films, it was desirable to use the ESR rather than the acoustic signal. From the change in the ESR, it was possible to measure the critical load to cut through ITO film completely and the critical number of sliding to wear ITO film completely.

Abstract: The micro metal forming manufacturing system is essentially an ultra precision forming press that can manufacture various micro scale products from metal thin foil and bulk material. In this paper, the micro metal forming manufacturing system has been developed using a micro servo motor. A micro forming system has been developed in Japan with a micro press that is limited to the single forming process. However, a press with a multi forming process is needed and we set about performing research and development of assorted equipment, including investigation into micro deep drawing and the micro punching process. In order to achieve this goal, exploration into the micro forming process as related to the multi forming process must be preceded first. Material selection and analysis of the micro forming process are accomplished in this paper, and the basis research as to how to make the actual system is accomplished.

Abstract: Reducing the particle size of drug materials down to submicron is an important matter in pharmaceutical industry. Cryogenic milling technology is one of the mechanical milling processes, which is mostly utilized in refining grain size of metal and ceramics at extremely low temperature environment. This technique has not been readily studied in application to medical and biotechnology. This paper, therefore, describes the application of cryogenic milling process to reduce particle size of Ibuprofen. The shape and size of the Ibuprofen particle before and after the cryogenic ball milling process were analyzed. XRD analysis was performed to examine a change in crystallinity of Ibuprofen by the cryogenic ball milling process. The results showed that the size of Ibuprofen particles was reduced to 1/10 or less of its initial size. The results also showed that the degree of crystallinity of Ibuprofen was slightly reduced after cryogenic ball milling with nitrogen.

Abstract: The optimum design of a die shape for Pilger mill process was carried out using FEM analyses considering various processing factors. The important design parameters of the Pilger mill machine are feed rate and profile of the grooved die. Optimum design procedure was conducted in order to investigate effects on forming load and the deformed shape of a material depending on the die surface profiles. Profiles of the die surface for the optimum design were testified with linear, cosine and quadratic curves considering physical forming process. The results of the analyses provided that the model of the quadratic profile gave the lowest forming load and the proper deformed shape.