• Transactions of Materials Processing
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• v.8 no.2
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• pp.135-142
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• 1999

Tube Process(TP) is one of the processes to produce permanent magnets. Advantage claimed for this process is that it can accmplish both densification and anisotropication in one step forming. This process is distinguished from other processes since it uses deformable tube for densification of powder magnets. TP has, however, difficulties in manufacturing permanent magnets from Nd-Fe-B green powder due to folding resulted from large height reduction and localized densification. Therefore, an adequate preform is necessary to reduce folding resulted from large height reduction and localized densification. Therefore, an adequate preform is necessary to reduce folding, lead magnets into almost desired final shape and get uniform densification. In this paper, preform design for TP is carried out without a deformable tube to investigate the behaviour of magnet sinter-forging. Preform design is accomplished to increase the effective magnet area with a near net shape and uniform densification.

• Journal of the Korean Society for Heat Treatment
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• v.20 no.1
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• pp.1-10
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• 2007

The deformation behaviors of full annealed and T6 treated 6061, 7075 aluminum tubes are investigated at various temperature performing uniaxial tensile test. Full annealed Al 6061 and Al7075 tubes, and T6 treated Al7075 tube don't show sharp local necking with an elongation of 50% at $300^{\circ}C$. So it is expected that influenced by elevated tempterature. At $300^{\circ}C$ and strain rate of 0.001/s, many micro-cracks are observed in T6 treated Al 6061 tube, which is believed to be responsible for the decrease of total elongation.

• Journal of the Korean Society of Combustion
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• v.18 no.3
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• pp.31-37
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• 2013

Numerical simulations are conducted to investigate the feature of spontaneous ignition of hydrogen within a certain length of downstream tube released by the failure of pressure boundaries of various geometric assumption. The results show that the ignition feature can be varied with the shape of pressure boundary. The ignition at the contact region are developed at the spherical pressure boundaries due to multi-dimensional shock interactions, whereas the local ignition is developed in limited area such as boundary layer at the planar pressure boundary conditions. The spontaneous ignition inside the tube can be generated from the reaction region of only boundary layer regardless of existence of the reaction of core region.

• Transactions of Materials Processing
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• v.10 no.6
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• pp.478-484
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• 2001

Tube Process (TP) is a process to produce permanent magnets using a deformable tube for densification of magnet powder. This process claims that it can accomplish both densification and anisotropication in one step forming. This process is distinguished from other processes since it uses a deformable copper tube for densification of magnet powder. In this paper, simulation has been carried out for tile Tube Process in a closed die considering the compressibility of powdered material, arbitrary curved shape and deformable body contact between Nd-Fe-B magnet powder and a copper tube. Results show that the finite element analysis of the Tube Process plays an important role in the stage of preform design.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.35-38
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• 1999

Tube bending is an important factor of the hydroforming processes. The tube must be bent to the approximate centerline of the finished part prior to hydroforming to enable the tube to be placed in the die cavity. This paper presents the simulation results in prebending process by a rotary bending machne and a bend die that is used to form an automotive part a tie bar, Prebending simulation is carried out to obtain the shape change of cross section and thinning in bending process. To avoid occurring wrinkle in compressive zone during bending process a wiper die included,. A parametric study is carried out to obtain the effect of the forming parameters such as a bend radius and tube thickness

• Transactions of Materials Processing
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• v.9 no.6
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• pp.644-652
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• 2000

Tube hydroforming is recently drawing attention of automotive industries due to its several advantages over conventional methods. It can produce wide range of products such as subframes, engine cradles, and exhaust manifolds with cheaper production cost by reducing overall number of processes. h successful tube hydroforming depends on the reasonable combination of the internal pressure and axial load at the tube ends. This paper deals with the optimal process design of hydroforming process using the genetic algorithm and neural network. An optimization technique is used in order to minimize the tube thickness variation by determining the optimal loading path in the tube expansion forming and the tube T-shape forming process.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.215-223
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• 1999

Evaporation heat transfer coefficient and pressure loss were measured for three different micro-fin tubes and a smooth tube. The experiments were carried out with R-22 over a wide range of vapor Quality, mass velocity and heat flux. Heat transfer coefficient of the tube with slightly modified fin shape was found to be higher than that of the commercial reference tube by 60%. The improvement of heat transfer has been achieved without noticeable increase of pressure loss. Heat transfer coefficient was increased with increasing quality, refrigerant mass flux, and heat flux. However, the effect of refrigerant mass flux and heat flux was not great. Heat transfer coefficient at bottom was lower than that at top of the tube in low quality region, which suggested the existence of stratification in the micro-fin tube. Pressure drop was linearly increased with increasing refrigerant quality and was proportional to about square of mass flux.

• Journal of the Korean Society of Safety
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• v.15 no.3
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• pp.45-51
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• 2000

This paper studies the effect of vibrational characteristics of the various tubes analyzed though experiment. By an experiment analysis we found out that the factor of system vibration is fluid-structure interaction of tube line. In fluid-filled tube system we study on the influence that the natural frequency of system and the frequency of wave motion produce upon through three experiments. Three experiments are modal test on each tube, FRF in continuous system, and vibrating tests when the system is driving on. From the results of the experimental studies, we obtained that the natural frequencies of system are very important than wave induced vibrations. and according to the variation of configuration, the frequencies are different each other. And we found that though fluid passed away through the tube, the tendency of system vibration level was similar with the mode shape at the simple system.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.6
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• pp.969-975
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• 2013

While accelerating, bicycle frames are subject to torsion forces and deformation. In this study, bicycle frame durability was evaluated by using structural, fatigue, and vibration experiments. Three types of models were designed by changing the frame configurations according to the shape and direction of a bicycle frame design. Because maximum equivalent stress was greatest at the saddle and at connected parts in Models 1, 2, and 3, these frame sections were most vulnerable to failure. Model 2 was the least safe, due to the increased total deformation and equivalent stresses in the top tube horizontal to the ground. Based on vibration and fatigue analysis results, Model 2 was also determined to be the least safe frame, because the head tube was placed slightly higher above the seat tube and inclined to $10^{\circ}$. These study results can be utilized in the design of bicycle frames by investigating prevention and durability against damage.

• 연구논문집
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• s.34
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• pp.29-38
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• 2004

The objective of this study is to investigate the pressure drop and heat transfer characteristics of the micro-fin tubes before and after the tube-expansion process. Test tubes are single-grooved micro-fin tubes made of copper with an outer diameter of 9.52 mm before the tube-expansion. The direct heating method is applied in order to make the refrigerant evaporated in the micro-fin tubes. The test ranges of the heat flux, mass flux, and the saturation pressure are 5 to 15kW/$m^2$, 100 to 200 kg/$m^2s$ and 540 to 790 kPa, respectively. The effects of the mass flux, heat flux, and the saturation pressure of the refrigerant on the pressure drop and the heat transfer are presented for the refrigerant R22. In the test conditions of this study, the heat transfer coefficient for the micro-fin tube after the tube-expansion is about 16.5% smaller than that before the tube-expansion because the fin height of micro-fin is reduced and the fin shape becomes flatter. The micro-fin tube after the tube-expansion has about 7.7% greater average pressure drop than that before the tube-expansion process.