• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1221-1226
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• 2012

The hot-stamping technique is a forming method used for manufacturing high-strength parts, in which a part is cooled rapidly after press forming above the austenite transformation temperature. Boron steel, which contains a very small amount of boron, is one of the materials used for hot stamping. The purpose of this study is to investigate the mechanical properties of boron steel according to the heat-treatment conditions and the formability by using an Erichsen cupping test. Die quenching from various temperatures was conducted for different elapsed heat-treatment times. Laser-welded boron steel after quenching at 1173 K-0 s has a tensile strength of 1203 MPa. This is 79% of the tensile strength of the base metal (1522 MPa). The formability of boron steel was not significantly different from that at the mold temperature. However, it decreased with increasing forming speed. These properties provide practical information for the use of boron steels for hot stamping.

• Korean Journal of Materials Research
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• v.31 no.10
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• pp.576-581
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• 2021

To improve the shortcomings and expand the advantages of the single-roll melt drag method, which is a type of continuous strip casting method, the melt drag method with a molding belt is applied to AZ31 magnesium alloy. By attaching the forming belt to the melt drag method, the cooling condition of the thin plate is improved, making it possible to manufacture thin plates even at high roll speed of 100 m/min or more. In addition, it is very effective for continuous production of thin plates to suppress oxidation of the molten metal on the roll contact surface by selecting the protective gas. As a result of investigating the relationship between the contact time between the molten metal and the roll and the thickness of the sheet, it is possible to estimate the thickness of the sheet from the experimental conditions. The relationship between the thin plate thickness and the grain size is one in which the thinner the thin plate is, the faster the cooling rate of the thin plate is, resulting in finer grain size. The contact state between the molten metal and the roll greatly affects the grain size, and the minimum average grain size is 72 ㎛. The thin plate produced using this experimental equipment can be rolled, and the rolled sample has no large cracks. The tensile test results show a tensile strength of 303 MPa.

• Journal of Environmental Science International
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• v.30 no.11
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• pp.925-936
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• 2021

The study was aimed to investigate the correlation between tidal effects and fog occurrence in Incheon and Mokpo, which are located in the middle and southern coasts of the West Sea of Korea, respectively. The investigation used meteorological data obtained from the automated synoptic observing systems and automatic weather stations and ocean data from tide stations from 2010 to 2019. Fog occurrence frequency was highest at high tide (Incheon, 41%; Mokpo, 45%). During fog event days at high tide, the dew-point depression was low (Incheon, 0.5℃; Mokpo, 0.4℃) and the relative humidity was high (Incheon, 97%; Mokpo, 98%). The wind speed was 2.4 m/s in Incheon and 2.0 m/s in Mokpo, and the main wind directions were west-southwesterly from Incheon and southwesterly from Mokpo. In the fog case study, tidal flats were covered with water before and after the fog started. During the fog period, both stations experienced negative air-sea temperature differences, low dew-point depression, and high relative humidity were maintained, with weak winds forming from the tidal flats to the shore.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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• pp.20-28
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• 2014

The high velocity oxygen fuel spraying (HVOF) is a kind of surface modification process technology to form the sprayed coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. It is desirable to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesion, however, because a semi-molten powder in a spray process has the low efficiency and become a factor that degrades the mechanical property by the inducement of pore-forming within the coating layer. To improve the wear resistance, corrosion resistance and heat resistance, in this study, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps for oil and water used in ironwork are produced with $420J_2$ and the coating layers of plungers are formed by the powders of WC-Co-Cr and WC-Cr-Ni including the high hardness WC. The surface of these plungers is modified by the super-mirror face grinding machine using variable air pressure developed in this laboratory, and then the characteristics of cross-sectional microstructure, and surface roughness and hardness values between no operation and 100 days-operation are examined and made a comparison. The fine tops and bottoms on surface roughness curve of oil-hydraulic pump plunger sprayed by WC-Cr-Ni are molded more and higher than those of water-hydraulic pump sprayed by WC-Co-Cr because the plunger diameter of oil-hydraulic pump is 0.4 times smaller than that of water-hydraulic pump and the pressure of oil-hydraulic pump exerted on the plunger is operated with the 70 bars higher than that of water-hydraulic pump. As a result, it is found that the values of centerline average surface roughness and maximum height for oil-hydraulic pump plunger are bigger than those of water-hydraulic pump plunger.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.32-43
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• 2023

Resistive Random Access Memory (RRAM), based on resistive switching characteristics, is emerging as a next-generation memory device capable of efficiently processing large amounts of data through its fast operation speed, simple device structure, and high-density implementation. Interface type resistive switching offer the advantage of low operation currents without the need for a forming process. Especially, for RRAM devices based on transition metal oxides, various studies are underway to enhance the memory characteristics, including precise material composition control and improving the reliability and stability of the device. In this paper, we introduce various methods, such as doping of heterogeneous elements, formation of multilayer films, chemical composition adjustment, and surface treatment to prevent degradation of interface type resistive switching properties and enhance the device characteristics. Through these approaches, we propose the feasibility of implementing high-efficient next-generation non-volatile memory devices based on improved resistive switching properties.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.9
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• pp.2109-2116
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• 2014

This paper presents the implementation and design of the advanced WI-FI systems with beam-forming antenna that radiate their power to the direction of user equipment to improve the overall throughput, contrast to the general WI-FI systems equipped with omni-antenna. The system consists of patch array antenna, DSP, FPGA, and Qualcomm's commercial chip. The beam-forming system on the FPGA utilizes the packet information from Qualcomm's commercial chip to control the phase shifters and attenuators of the patch array antenna. The PCI express interface has been used to maximize the communication speed between DSP and FPGA. The directions of arrival of users are managed using the database, and each user is distinguished by the MAC address given from the packet information. When the system wants to transmit a packet to one user, it forms beams to the direction of arrival of the corresponding user stored in the database to maximize the throughput. Directions of arrival of users are estimated using the received preamble in the packet to make its SINR as high as possible. The proposed beam-forming system was implemented using an FPGA and Qualcommm's commercial chip together. The implemented system showed considerable throughput improvement over the existing general AP system with omni-directional antenna in the multi-user communication environment.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.4
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• pp.446-451
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• 2011

Recent trends for the miniaturization and weight reduction of portable electronic parts have driven uses of subminiature components. Assembly of the miniaturized components requires subminiature screws of which pitch sizes are micrometer scale. To produce such subminiature screws with high precision threads, not only a precision forming technology but also a high-precision measurement technology is required. The present study covers the development of a vision inspection system for precision screws for the automatic measurement of subminiature screws with high speed and reliability. In this study, the feeding unit that transfers the subminiature screws to the inspection unit is investigated through finite element(FE) analysis. The vibration characteristics of the feeding unit are predicted through FE analyses, from which we can determine whether the subminiature screw can be stably fed into the inspection unit or not. The effects of several design parameters on the vibration characteristics are also discussed.

• Transactions of Materials Processing
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• v.26 no.5
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• pp.314-322
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• 2017

In the high-speed forming analysis, dynamic material properties considering a high strain rate are required. The split Hopkinson pressure bar (SHPB) experiment was performed for measuring dynamic material properties under high strain rate. The pulse shaping method was used to improve the accuracy of the SHPB experiment. A pulse shaper attached to the front of the incident bar was used for specimen dynamic stress equilibrium through stress wave control. Numerical analysis and SHPB test were performed to verify whether the pulse shaper affects the dynamic stress equilibrium in copper and Al6061 specimens. The results of SHPB test and numerical analysis show that the pulse shaper contributes to the dynamic stress equilibrium. Based on the improved stress equilibrium using a pulse shaper, the flow stress curves for copper and Al6061 materials were obtained at strain rates of 1344.4/sec and 1291.6/sec, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.4711-4717
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• 2011

Formation of TiN films by PVD method and the DC and RF sputtering deposition method can be applied, the injected gas to generate plasma ionization rate of the film forming speed is slow away, anything to increase the adhesion between films limitations have. To improve this, to investigate the deposition and ion beam evaporation simultaneously IBAD(Ion beam assisted deposition) when used, Ion beam surface coating material prior to the survey because the surface cleaning effect of a large, high film adhesion can be obtained. In addition, the high vacuum and low temperature, high purity thin film of uniform thickness in the benefits is.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.62-65
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• 2008

Extrusion characteristics of Mg alloys were studied experimentally. The Al-Zn-Mg alloys, AZ31, AZ6l, AZ80, and AZ91 were extruded with hot hydrostatic extrusion process. The hydrostatic process was efficient to reduce surface friction and extend steady state region in extrusion which made it more convenient to examine deformation behavior of the alloys avoiding the disturbance caused by temporary contact state between billet and die, and billet and container. High pressure was cooperative to expand forming limit of the alloys which were applied on the billet during the extrusion process. Extrusion limits were traced in temperature and extrusion speed domain with changing composition of the alloying elements. Effects of process parameters on extrusion load and microstructure evolution were investigated also.