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31 results on '"Na, Kyoung Hoan"'

23. A Study on the Forming Characteristics of AZ 31B Mg Alloy in a Combined Forward–Backward Extrusion at Warm Temperatures.

Author

Yoon, Duk Jae, Kim, Eung-Zu, Na, Kyoung Hoan, and Lee, Yong-Shin

Subjects
MAGNESIUM alloys, METALWORK, METAL extrusion
Abstract

This paper was on the forming characteristics of AZ 31B Mg alloy in a combined forward–backward extrusion (CFBE) at warm temperatures. Both experimental studies and thermomechanical finite element analyses were performed. A finite element analysis model coupled with damage evolution was presented. Based on our previous work, the forward extrusion ratio, backward extrusion ratio, forming temperature, and punch speed were chosen as the most important process parameters. Two punch speeds of 2 mm/s and 20 mm/s were examined for the forming temperatures of 180 °C and 200 °C. Forward extrusion ratios were 2.25, 4.0, and 9.0, while backward extrusion ratios were 1.33, 2.16, 4.02, and 7.75. Effects of those parameters on the forming limit, deformation behaviors, extrusion load, and the mechanical properties of an extruded product were discussed in detail. [ABSTRACT FROM AUTHOR]

Published
2018
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24. A Study on Lenticular Lens Mold Fabrication by Shaping

Author

Patrick Shim, Doo-Sun Choi, Eung-Sug Lee, Tae-Jin Je, and Na Kyoung-Hoan

Subjects
Microelectromechanical systems, Fabrication, Materials science, business.industry, ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION, Mechanical engineering, Lenticular lens, Optics, Machining, business, LIGA, Groove (engineering), Lithography, ComputingMethodologies_COMPUTERGRAPHICS, Diamond tool
Abstract

Recently, micro machining technology for high precision mold becomes more interested for mass production of high performance optical parts micro-grooved on the surface, which is under very active development due to its effectiveness in the view point of optical performance. Mechanical micro machining technology now has more competitiveness on lithography, MEMS or LIGA processes which have some problems to fabricate especially cylinder type of groove in such as lenticular lens for illumination angle modulation system. In this study. a lenticular lens mold with U-type micro groove is fabricated making utilizing of the benefit of the mechanical micro machining technology. A shaping machining process is adapted using 3 axis degree of freedom micro machining system and single crystal natural diamond tool. A brass and a electroless nickel materials are used for mold fabrication. Machining force, chip shape and machined surface are investigated from the experiment and an optimal machining condition is found based on the examined problems from the micro cutting process.

Published
2005

30. Hole Punching onto the Zr65Al10Ni10Cu15 BMG Sheet Fabricated by Squeeze Casting

Author

Jeong, Ha Guk, Kim, Woo Jin, Bae, Jung Chan, Yoon, Duk Jae, Choi, Seo Gou, and Na, Kyoung Hoan

Abstract

Bulk metallic glass Zr65Al10Ni10Cu15 was fabricated in a sheet form with thickness 1.5 mm by a squeeze casting method. The structure of the as-cast Zr65Al10Ni10Cu15 sheet was confirmed to be fully amorphous. The sheet was punched into a blank under high hydrostatic pressure at room temperature. A round hole was created with a possible evidence for plastic-like deformation along the edge of rim. No visible cracks were observed around the hole. This result indicates that bulk metallic glasses, which are known to be very brittle at room temperature, can be deformed in a ductile mode under hydrostatic pressure condition. Hydrostatic pressure may suppress the formation and development of micro defects leading to ductile fracture

Published
2005
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