Papers by Author: E.Z. Kim

Abstract: In this study, a novel process to forge thin walled products using bulk-sheet forming concept is developed to overcome drawbacks of a conventional multistage backward extrusion. A newly developed process design is suggested based on numerical analysis, and feasibility of one-stage forging process is discussed.

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: 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.

Abstract: The relations between interfacial properties of clad composite and process conditions are studied. Adherence on interface of two materials is most significant property of clad composite. Properties of composite material are manifestation of its microstructure, and process conditions are decisive factor to the microstructure in interfacial area. In-depth understanding about the composite’s properties is only achieved through appreciation of the mechanism by which the process conditions affect the microstructure. Aluminum and copper clad composite bars are extruded at the various process conditions. Interfacial adherence of the extruded composite is examined. Microstructure of the dispersed layer and its vicinity is investigated.