Papers by Author: Kyung Hoon Min

Abstract: A review is given of the application of in situ transmission electron microscopy to study various processes associated with the crystallization of amorphous thin films. Solid phase epitaxial regrowth of ion-implanted silicon is compared with nucleation and growth in deposited thin films. The mechanism of metal-mediated crystallization is deduced directly from high resolution recordings, and the kinetics of tantalum oxide devitrefication are obtained. The advantages of direct in situ observation are described

Abstract: The manufacturing process sequence of a power steering worm gear blank is analyzed. The conventional process sequence for manufacturing power assisted steering (PAS) part contains three distinctive operational stages such as indentation, extrusion, and upsetting, which were originally designed by forming equipment experts. Process conditions such as reduction in area, semi die angle and upsetting ratio are carefully considered to prevent from internal or geometrical defects. The simulation results of the conventional forging process are summarized in terms of deformation patterns, load-stroke relationships and die pressures along the interface for each operational stage. Close investigation of simulation results for current forming process leads to a new process sequence in which the number of operation are reduced into just one operation. Comparisons between the existing and proposed processes are made in terms of maximum force requirement, required forming energy, and process time, respectively. Experiment has been performed to confirm that the proposed process could be applied to replace the existing conventional process sequence and proved the new process to be a safe process sequence for manufacturing PAS part.

Abstract: A frictional contact model is adopted for the analysis of conventional solid rivet setting. Material properties for the selected plates and rivets are obtained from analytical method using elastic constants and tensile strengths for each material. Rigid- and elasto-plastic models are selected for process analysis in this paper. Process variables are selected to investigate the effect of variables on the successful rivet setting and servicing in any structure as force transmitting member. Major variables in riveting process are material variables such as material properties and geometrical variables, which are dimensions of head, shank, and blank diameters. Analysis in this study is concentrated on the influence of variety of materials and of shank dimensions on the contact area after rivet setting, i.e. after forming process of rivet head. Soft and hard materials are selected as mother materials to investigate how the selection of material influences on the riveting process in quantitative manner. The geometry of head is closely investigated through simulation in terms of contact status, i.e. contact area between rivet head and mother material, which would affect the snap fit joint by riveting.