• Journal of the Korean Society for Precision Engineering
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• v.26 no.10
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• pp.89-96
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• 2009

In recent years, there has been a considerable interest in the application of super plastic forming in the aircraft and automotive industries. This requires a detailed design of the technological process in order to exploit its peculiar potentialities better. Nowadays, the finite element method is used to plan the sheet metal forming processes whose simulation requires determination of material constants for super plastic materials. The present work is aimed to show a simple method to characterize super plastic materials duplex stainless steel which was formed by a constant gaspressure to hemispheres with and without back pressure. The forming operation was performed using an in-house designed and built biaxial forming apparatus. The temporal change of dome heights of hemispheres were measured for applying the pressures. The flow stresses and strain rates developed at the top of the dome during the forming step were shown to follow closely the flow stress - strain rate relationship obtained from the strain rate change tests performed at the same temperature.

• Transactions of Materials Processing
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• v.21 no.3
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• pp.160-163
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• 2012

In this paper, a new approach to finite element analysis for tube swaging is presented. An analysis model is developed with emphasis on the pusher that imposes back pressure in order to keep the workpiece from slipping along the die-workpiece interface especially when tapered dies are used. A rigid-plastic finite element method is employed. The approach is to simulate the tube swaging process and the results are compared quantitatively with predictions, showing close agreement with each other.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.86-92
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• 2008

Recently, the use of tubes in the manufacturing of the automobile parts has increased and therefore many automotive manufactures have tried to use hydro-forming technology. The hydro-forming technology may cause many advantages to automotive applications in terms of better structural integrity of the parts, lower cost from fewer part count, material saving, weight reduction, lower spring-back, improved strength and durability and design flexibility. In this study, the whole process of front engine cradle (or front sub-frame) parts development by tube hydro-forming using steel material having tensile strength of 440MPa grade is presented. At the part design stage, it requires feasibility study and process design aided by CAE (Computer Aided Design) to confirm hydro-formability in details. Effects of parameters such as internal pressure, axial feeding and geometry shape on automotive sub-frame by hydro-forming process were carefully investigated. Overall possibility of hydro-formable sub-frame parts could be examined by cross sectional analyses. Moreover, it is essential to ensure the formability of tube material on every forming step such as pre-bending, preforming and hydro-forming. At the die design stage, all the components of prototyping tools are designed and interference with press is examined from the point of geometry and thinning.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.9
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• pp.756-761
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• 2016

The objective of this study is to design and manufacture a fuel pump with the plunger diameter of 4 mm and stroke of 7 mm that can be mounted in a small single-cylinder four-stroke agricultural diesel engine, and to investigate the performance characteristics of the pump. The combustion pressure in a cylinder was reproduced by forming the back pressure of 1, 6, 11, 16 and 21 bar with a nitrogen gas in the home-manufactured modeling cylinder. In the experiment, the discharge pressure was measured at the spot of 1 cm away from the discharge port of a developed fuel pump. The delivery pressure and delivery flow rate were measured at the spot of 30 cm away from the discharge port of the pump, and the pump efficiency was calculated. The pump motor speed was changed from 600 to 800, 1000, 1200 and 1400 rpm. It is found that the delivery feed rate of fuel pump is increased as the rotational speed is raised, and is decreased as the back pressure, compression pressure in the cylinder, is increased. Also, the pump efficiency is reduced as the rotational speed and back pressure are increased.

• Design & Manufacturing
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• v.15 no.4
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• pp.1-7
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• 2021

A study on in-mold punching technology for hole piercing during molding of hollow plastic parts was conducted. Considering the non-linearity of the HDPE plastic material, mechanical properties were obtained according to the change in temperature and load speed. A standard specimen for the in-mold punching test was designed to implement the in-mold punching process, and the specimen was obtained through injection molding. In order to analyze the influence of process variables during in-mold punching, an in-mold punching mold capable of controlling variables such as temperature and support pressure of the specimen was designed and manufactured. Mold heating characteristics were confirmed through finite element analysis, and punching simulations for changes in process conditions were performed to analyze punching characteristics and reflected in the experiment. Through simulations and experiments, it was found that the heating temperature, punch shape, punching speed, and pressure of the back side of the specimen were very important during in-mold punching of HDPE materials, and optimal conditions were acquired within a given range.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.129-134
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• 2009

The dimension of forged part is different from that of die. Therefore, a more precise die dimension is necessarys to produce the precise part, considering the dimensional changes from forging die to final part. In this paper, both experimental and FEM analysis are performed to investigate the effect of several features including die dimension at each forging step and heat-treatment on final part accuracy in the closed-die upsetting. The dimension of forged part is checked at each stage as machined die, cold forged, and post-heat-treatment steps. The elastic characteristics and thermal influences on forging stage are analyzed numerically by the DEFORM-$2D^{TM}$. The effect of residual stress after heat-treatment on forged part could be considered successfully by using DEFOAM-$HT^{TM}$.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.85.1-85.1
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• 2010

$Cu(In,Ga)Se_2$ (CIGS) thin film solar cell is currently 19.5% higher efficiency and developing a large area technology. The structure of CIGS solar cell that make five unit layers as back contact, light absorption, buffer, front transparent conducting electrode and antireflection to make them sequentially forming. Materials and various compositions of thin film unit which also manufacture a variety method used by the physical and chemical method for CIGS solar cell. The construction and performance test of evaporator for CIGS thin film solar cell has been done. The vapor pressures were changed by using vapor flux meter. The vapor pressure were copper (Cu) $2.1{\times}10^{-7}{\sim}3.0{\times}10^{-7}$ Torr, indium (In) $8.0{\times}10^{-7}{\sim}9.0{\times}10^{-7}$ Torr, gallium (Ga) $1.4{\times}10^{-7}{\sim}2.8{\times}10^{-7}$ Torr, and selenium (Se) $2.1{\times}10^{-6}{\sim}3.2{\times}10^{-6}$ Torr, respectively. The characteristics of the CIGS thin film was investigated by using X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and photoluminescence (PL) spectroscopy using a He-Ne laser. In PL spectrum, temperature dependencies of PL spectra were measured at 1137 nm wavelength.

• Journal of computational fluids engineering
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• v.18 no.4
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• pp.74-81
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• 2013

A numerical design analysis is conducted to search for an optimal shape of outlet in a rotating-disk CVD reactor. The goal is to suppress flow recirculation that has been found in a reactor having a sudden expansion of flow passage outside of the rotating disk. In order to streamline gas flow, the sidewall at which the flow in the Ekman layer is impinged, is tilted. The axisymmetric laminar flow and heat transfer in the reactor are simulated using the incompressible ideal gas model. For the conventional vertical sidewall, the flow recirculation forming in the corner region could be expanded into the interior to distort the upstream flow. The numerical results show that this unfavorable phenomenon inducing back flow could be dramatically suppressed by tilting the sidewall at a certain range of angle. The assessment of deviation in deposition rate based on the characteristic isotherm illustrates that the sidewall tilting may expand the domain of stable plug-like flow regime toward higher pressure. A physical interpretation is attempted to explain the mechanism to suppress flow recirculation.