• Journal of the Korean Society for Precision Engineering
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• v.20 no.2
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• pp.58-65
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• 2003

The conventional forming process such as squeeze casting or die casting for fabricating metal matrix composites products have a disadvantage such as non homogenous distribution of reinforcement, weak bonding between matrix and reinforcement and cost increase in parts fabrication. Thixoforming process has been accepted as a new method for fabricating the net shaped metal matrix composites with lightweight and wear resistance. In this paper, the effect of volume fraction and reinforcement sizes on mechanical properties in cylinder liner part of metal matrix composites has been investigated with processes parameters such as pressure and velocity. Moreover, the methods to obtain the thixoforged composites cylinder liner with high quality has been proposed. To evaluate the composites cylinder linear fabricated at the conditions proposed in this study, mechanical properties of fabricated composites cylinder linear were compared with those of commercial composites cylinder linear.

• Journal of electromagnetic engineering and science
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• v.15 no.1
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• pp.37-43
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• 2015

We implemented a real-time radar system for an unmanned ground vehicle designed to run on unpaved or bumpy roads. The system must be able to detect slow targets in a cluttered environment and cover wide angular sections with high resolution at the same time. The system consists of array antennas, preprocessors for digital beam forming, and digital signal processors for the detection process which uses sawtooth waveforms and high-resolution estimation, and is called forward/backward spatial smoothing beamspace multiple signal classification (FBSS BS-MUSIC). We show that the sawtooth waveforms enhance the angular estimation capability of FBSS BS-MUSIC in addition to their well-known advantages of removing the ambiguity of targets and detecting slow targets with improved velocity resolution.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.124-127
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• 2004

In the previous experimental study about extrusion of circular product with four helical fins, it was known that product with helical fins may not to be rotated during extruding with rotating extrusion dies in spite of using twisted dies. According to the results of experiments with Plasticin material, it was anticipated that the extrusion load could be reduced if rotating dies could be used, because it needs high pressure in order to twist billet and form fin shape on the surface of product in the case of using conventional fixed helical dies. So, in this paper, according to the extrusion load analyzed by DEFORM-3D software, optimal rotational velocity of rotating dies can be obtained, and the twisting, angle of product can be analyzed during extruding product with helical fins in the case of two types of rotating of dies. The results of analysis by DEFORM-3D show that the twisting angle of product can be controlled by twisted angle of extrusion helical dies and the rotational velocity of helical dies.

• Journal of Powder Materials
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• v.28 no.6
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• pp.483-490
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• 2021

A new Fe-Cr-Mo-B-C amorphous alloy is designed, which offers high mechanical strength, corrosion resistance as well as high glass-forming ability and its gas-atomized amorphous powder is deposited on an ASTM A213-T91 steel substrate using the high-velocity oxygen fuel (HVOF) process. The hybrid coating layer, consisting of nanocrystalline and amorphous phases, exhibits strong bonding features with the substrate, without revealing significant pore formation. By the coating process, it is possible to obtain a dense structure in which pores are hardly observed not only inside the coating layer but also at the interface between the coating layer and the substrate. The coating layer exhibits good adhesive strength as well as good wear resistance, making it suitable for coating layers for biomass applications.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.44-55
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• 2001

The flow behavior of semi-solid materials (SSM) is required to assist the industrial application of thixoforming technology. Particularly, to reduce many lead times, many numerical analysis packages have been developed to simulate required metal forming processes. The objectives of the development of SEMI-FORM for thixoforming process design are to predict the effect of various process variables such as pressing force, die temperature, and die velocity. However, there have not been any reports which adapt these packages to the specific characteristics of SSM. SO, this paper presents an overview of the development of thixoforming simulator of SEMI-FORM. The solver and post-processor of SEMI-FORM S/W for an automated thixoforming process design with arbitrarily shaped die are composed of FORTRAN Power Station 4.0 and Visual Basic 5.0, respectively. This developing SEMI-FORM S/W would be very useful for thixoforming practitioners and engineers to select the optimal process conditions to produce automotive parts with high quality.

• 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.

• Wind and Structures
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• v.34 no.5
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• pp.451-467
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• 2022

The flow around a high-speed train with three underbody structures in the bogie area is numerically investigated using the improved delayed detached eddy simulation method. The vortex structure, pressure distribution, flow field structure, and unsteady velocity of the wake are analyzed by vortex identification criteria Q, frequency spectral analysis, empirical mode decomposition (EMD), and Hilbert spectral analysis. The results show that the structures of the bogie and its installation cabin reduce the momentum of fluid near the tail car, thus it is easy to induce flow separation and make the fluid no longer adhere to the side surface of the train, then forming vortices. Under the action of the vortices on the side of the tail car, the wake vortices have a trend of spanwise motion. But the deflector structure can prevent the separation on the side of the tail car. Besides, the bogie fairings do not affect the formation process and mechanism of the wake vortices, but the fairings prevent the low-speed fluid in the bogie installation cabin from flowing to the side of the train and reduce the number of the vortices in the wake region.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.69.1-69.1
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• 2019

We present the ALMA observations of the infrared dark cloud (IRDC) core MSXDC G053.11+00.05 MM1 at the distance of 1.7 kpc. While the core was first identified at 1.2 mm with a mass of 124 Msun, recent near- and mid-infrared observations have revealed a parsec-scale molecular hydrogen (H2 1-0 S(1) at 2.12 micron) outflow and two early class young stellar objects (YSOs) at the center of the core, one of which is likely massive (M > 8 Msun). From the ALMA Band 7 observations with a resolution of 0.5", we have found a dust filament of < 0.1 pc in which five dense cores are embedded in the 870 micron continuum. The brightest core is consistent with one of the two previously-detected YSOs, but the other four are newly discovered implying their very deeply embedded status. We have also detected several molecular line emission including H13CO+ and C17O as well as 13CO outflow with complicated morphology. At the brightest core, the methanol line (CH3OH) shows velocity gradients, which may support the existence of a circumstellar disk around a high-mass protostar. Based on the derived properties of the dense cores, we discuss their association with the two YSOs and H2 outflow detected in infrared and high-mass star-formation process occurring in IRDC cores.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.2
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• pp.267-275
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• 2012

Austenite stainless steel 304 has properties of high resistance to corrosion and temperature changes. Therefore, this material is widely used in various of industries. However, when the material is subjected to heating and cooling cycles the forming accuracy, for example, the right angle associated with a sharp bend such as corner is lost. This phenomenon is caused by the reversion of the deformation-induced martensite into austenite when the temperature in increased. This result in misfit of a structure or an assembly, and an increase in residual stress. Hence, it is important to understand this process. In this study, to evaluate the mechanical behavior of the deformation-induced martensite and reversed austenite, a scanning acoustic spectroscope including the capability of obtaining both phase and amplitude of the ultrasonic wave (i.e., the complex V(z) curve method) was used. Then, the velocities of the SAW propagating within the specimens made in different conditions were measured. The experimental differences of the SAW velocities obtained in this experiment were ranging from 2,750 m/s to 2,850 m/s, and the theoretical difference was 3.6% under the assumption that the SAW velocity was 2,800 m/s. The error became smaller as the martensite content was increased. Therefore, the SAW velocity may be a probe to estimate the marternsite content.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.2
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• pp.52-60
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• 2002

Line heating is a forming process which makes the curved surface with the residual strain created by applying heat source of high temperature to steel plate. in order to control the residual strain, it is necessary to understand not only conductive heat transfer between heat source and steel plate, but also temperature distribution of steel plate. In this paper we attempted to analyze is temperature distribution of steel plate by simplifying a line heating process to collision-effusive flux of high temperature and high velocity, and conductive heat transfer phenomenon. To analyze this, combustion in the torch is simplified to collision effusive phenomenon before analyzing turbulent heat flux. The distribution of temperature field between the torch and steel plate is computed through turbulent heat flux analysis, and the convective heat transfer coefficient between effusive flux and steel plate is calculated using approximate empirical Nusselt formula. The velocity of heat flux into steel plate is computed using the temperature distribution and convective heat transfer coefficient, and temperature field in the steel plate is obtained through conductive heat transfer analysis in which the traction is induced by velocity of heat flux. In this study, Finite Element Method is used to accomplish turbulent heat flux analysis and conductive heat transfer analysis. FEA results are compared with empirical data to verify results.