• Journal of Powder Materials
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• v.29 no.4
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• pp.320-324
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• 2022

Lightweight steel is a crucial material that is being actively studied because of increased carbon emissions, tightening regulations regarding fuel efficiency, and the emergence of UAM, all of which have been recently labeled as global issues. Hence, new strategies concerning the thickness and size reduction of steel are required. In this study, we manufacture lightweight steel of the Fe-Mn-Al-C system, which has been recently studied using the DED process. By using 2.8 wt.% low-Mn lightweight steel, we attempt to solve the challenge of joining steel parts with a large amount of Mn. Among the various process variables, the laser scan power is set at 600 and 800 W, and the laser scan speed is fixed at 16.67 mm/s before the experiments. Several pores and cracks are observed under both conditions, and negligibly small pores of approximately 0.5 ㎛ are observed.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.3
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• pp.1-7
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• 2011

Active brazing of ceramic to metal is reviewed in this paper. As one of the key aspect in joint techniques, active brazing has been developed to simplify the manufacturing procedure of brazed joints between ceramic and metal. The active filler metal includes Ag-Cu-Ti series, Cu-Ti series, Co-Ti series and so on. The active filler metal which supplies the chemical bonds between ceramic and metal, enhances the wetting of filler metal on ceramic surface and eliminates the need for metallization treatments. The residual stress caused by difference of coefficient of thermal expansion between ceramic and metal, holds a direct influence on the bonding strength and even results in a fracture. Good joints of ceramic to metal promote the miniaturization and simplicity of electronic components with multifunction.

• International Journal of Korean Welding Society
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• v.3 no.1
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• pp.23-28
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• 2003

The effect of the welding speeds on the weld bead shape, microstructure, and mechanical properties in type 304 austenitic stainless steels was investigated by microscopic test, Erichsen test and tensile test. In this study welds were produced using autogeneous Direct Current Straight Polarity (DCSP) and pulsed current GTA welding. This study shows the ferrite content, ductility, tensile strength and elongation of high speed welds are decreased with increasing welding speed. The high speed welds exhibits satisfactory tensile strength, though the ductility is not good as that of the base metal.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2005.10a
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• pp.189-206
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• 2005

Much of work on network externality assumed network effects are dependent on the network size. Therefore, very little consideration is given to the view that marginal benefits from joining the network may not increase with the network size if consumer benefits come from the direct interaction with neighbors, namely local network. In this study, we used the agent-based simulation method to reexamine the effectiveness of the traditional network market strategy under the presence of the local network where two incompatible technologies compete. We found that the strategy of growing an initial customer base is not effective under the presence of the local network. Our study also showed that targeting customers based on their technology Preference is not as effective as targeting customers within the same local network. As a result, the focus of a network market strategy should be directed to taking advantage of the customer network.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.752-756
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• 2002

Variable weld bead penetrations related to the base metal chemistry of stainless steels in GTA welding have been under constant investigations due to their industrial implications. It has been proposed that among other elements, the sulfur content of steels determines the weld pool geometry, particularly its penetration. It is suggested that the surface tension temperature gradient of steels becomes positive with appropriate dosing in sulfur and results in inward melt flow, propitious for deeper welds. However, the chemistry of industrial steels is complex due to the presence of multiple minor elements either deliberately added or remnant impurity traces. With this in view, investigations on 41 austenitic and nine martensitic stainless steels were carried to see if there existed any possible relation between the weld profile and some of the designated elements. The results suggest no direct correlation between sulfur or any other major or trace element and weld penetration. At first glance the results are contradictory to what is often asserted.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.791-797
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• 2002

This paper introduces the partial melting process for solder application and characterization of its feasibility using Sn-Ag, and Sn-Cu solder alloys. ill order to show that the liquid phase in the semi-liquid state maintains the similar wettability as single-phase liquid, the wetting balance tests are conducted with varying temperatures and compositions. Also, as a new soldering technology, the microstructural and mechanical test were investigated. The results from this research indicate that the partial melting can yield satisfactory sider joints as long as the liquid phase acquires sufficient chemical activity. At a condition where the partial melting is effective, a direct correlation between the wettability and the surface tension is found to exist.

• Proceedings of the KWS Conference
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• 2000.10a
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• pp.260-263
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• 2000

A methodology is developed and many used to evaluate the response sensitivity of the thermal systems to variations in their design parameters. Technique for computing the sensitivity of temperature distributions to changes in processing parameters needed for deciding the more effective laser input parameters for laser surface hardening treatment are considered. In this study, a state equation governing the heat flow in laser surface treatment is analyzed using a three-dimensional finite element method and sensitivity data of the processing parameter obtained using a direct differentiation method applied for sensitivity analysis. The interesting processing parameter is taken as the laser scan velocity and characteristic beam radius( $r_{b}$) of the sensitivity of the temperature T versus v and $r_{b}$ is analyzed. And these sensitivity results obtained in another parameters are fixed condition. To verifying the numerical analysis results, hardened layer dimensions (width and depth) of the numerical analysis compared with the results of an experimental data.ata.

• Proceedings of the KWS Conference
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• 2000.04a
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• pp.99-102
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• 2000

Conventionally, ZVS FB DC/DC converter was controlled by monolithic IC UC3879, which includes the functions of oscillator, error amplifier and phase-shift circuit. Also, microprocessor and DSP have been widely used for the remote control and for the immediate waveform control in ZVS FB DC/DC converter. However the conventional microprocessor controller is complex and difficult to control because the controller consists of analog and digital parts. In the case of the control of FB DC/DC converter, the output is required of driving a direct signal to the switch drive circuits by the digital controller. So, this paper presents the method and realization of designing the digital-to-phase shift PWM circuit controlled by DSP (TMX320C32) in a 2,500A, 40㎾ WS FB DC/DC converter.

• Proceedings of the Microbiological Society of Korea Conference
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• 2003.05a
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• pp.13-15
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• 2003

Studies on marine microbial diversity using direct analysis of rRNA sequences have revealed previously unrecognized microbes and novel phylogenetic lineages that represent major components of global microbial assemblages. This diversity in the marine biosphere offers opportunities for research and application in the field of biotechnology; global gas exchange, nutrient and element cycling, biomass md food production, marine bioproducts, and bioprocesses. Especially, deep-sea encompasses the extremes of virtually at] environmental parameters found on Earth and provides extreme microorganisms. In this study several extreme microorganisms were successfully isolated from the deep-sea sediment samples obtained by joining ocean cruises for last 2 years and some of them will be introduced.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.279-281
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• 2007

This paper reviews corrosion characteristics of welded in the area of 409 Stainless Steel, Aluminium and Carbon steel. The effects of alloying elements and welding conditions on the intergranular-corrosion in weldment of the 409 stainless steels(SS) were investigated. And then this was to investigate factors affecting the composition and concentrations of fumes generated from various types of welding processes. It is also suggested that the direct relationship between the corrosion characteristics and welding type be clarified by experimental and analytical results.