• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.718-719
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• 2006

Two different commercial aluminium powder grades have been densified by direct hot extrusion. The extrusion temperature was $425^{\circ}C$, with an extrusion ratio of 1:16. Prior to extrusion, some green compacts were pre-sintered ($500^{\circ}C$). The evolution of the extrusion load during the process and the hardness of the final products have been investigated. Additionally, microstructural characterization by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD) was carried out. The obtained results evidence grain refinement. Additionally, inter-metallic precipitation, dynamic recovery and geometric dynamic recrystallization take place depending on some process variables, powder composition, heat treatment, strain $\ldots$

• Journal of the Korean Society for Precision Engineering
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• v.24 no.8 s.197
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• pp.34-40
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• 2007

In this study, focusing on reducing a load in forming helical gears, the extrusion using two-step processes for manufacturing helical gear is proposed. The process is composed of the extrusion step in which spur gear to be used as a preform in next step is formed, and the torsion step in which the preform of spur gear is formed to helical gear. Upper-bound theory for the two-step process is applied and compared with the results of experiment. The result of upper-bound solution has a good agreement with that of the experiment and the FE analysis. The newly proposed method can be used as an advanced forming technique to remarkably reduce a forming load, to prolong a tool life, and to replace the conventional forming process of helical gears. Results obtained from the extrusion using two-step processes enable the designer and manufacturer of helical gear to be more efficient in this field.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.144-147
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• 2005

In hydrostatic extrusion the billet in the container is extruded through a die with a liquid acting as a pressure medium, instead of by the direct application of the load by a ram. And the extrusion pressure can be affected by the flow stress and they are affected by the temperature. So in this study the temperature is the main issue with a extrusion ratio and a half die angle. As extrusion temperature goes down from $300^{\circ}C$ to $200^{\circ}C$, tensile strength goes up to 310MPa. Because velocity of extrusion is higher than the conventional extrusion, there is another characteristic in the sense of microstrure. The temperature was sotted to $300^{\circ}C,\;250^{\circ}C,\;200^{\circ}C$, respectively. There is a increase of extrusion pressure abot $15\%$.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.53-61
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• 2004

Condenser tube which is used for a cooling system of automobiles is mainly manufactured by conform extrusion. However, direct extrusion using porthole die in comparison with conform extrusion has many advantages such as improvement of productivity, reduction of production cost etc. In general, the porthole die extrusion process is useful for manufacturing long tubes with hollow sections and consists of three stages(dividing, welding and forming stages). Especially, Porthole die for producing condenser tube is very complex. Thus, in order to obtain the detailed mechanics, to assist in the design of proper die shapes and sizes, and to improve the quality of products, porthole die extrusion should be analyzed in as non-steady state as possible. This paper describes FE analysis of non-steady state porthole die extrusion for producing condenser tube with multi-hole through 3D simulation in the non-steady state during the entire process to evaluate detailed metal flow, temperature distribution, welding pressure and extrusion load. Also to validate FE simulation of porthole die extrusion, a comparison of simulation and experiment results was presented in this paper.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2005-2015
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• 1994

An analytical method based on the upper bound approach for the cup-bar axisymmetric combined extrusion is presented to determine the deformation zones as well as extrusion load and deformed geometry in the early stage. A new kiematically admissible velocity field is derived by the appropriate transformation of the original velocity field and applying the flow function approach. The derived velocity field is directly related to the boundary function for the plastically deforming zones and the parameter controlling the flow direction to the forward part or backward part. Experiments are carred out with the annealed aluminum 2024 at room temperature for the various area reductions. The workhardening effect is considered in the formulation as a function of the height ratio between the deformed billet and the orighinal billet to calculate the extrusion pressures. The theoretical predictions for the extrusion loads and deformed configuration are in good agreement with the experimental results.

• Transactions of Materials Processing
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• v.15 no.8 s.89
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• pp.597-602
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• 2006

Bulk plastic forming characteristics were studied for the magnesium alloy, AZ31 in warm backward extrusion. Effects of process conditions such as extrusion ratio, forming temperature, and punching speed were investigated respectively. Variation of microstructure induced by the warm backward extrusion process was observed. Microstructure of the work piece showed evidences of recrystallization under the experiment conditions. It is estimated that in specific punch speed region fast stroke accelerates recrystllization and reduces the forming load.

• Transactions of Materials Processing
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• v.8 no.6
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• pp.604-611
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• 1999

This paper is concerned with the family of parts that generally feature a central hub with radial protrusions. As opposed to conventional forward and backward extrusion, in which the material flows in a direction parallel to that of the punch or die motion, the material flows perpendicular to the punch motion in radial extrusion. Three variants of radial extrusion of a collar or flange are investigated. Case I involves forcing a cylindrical billet against a flat die, Case II involves deformation against a stationary punch recessed in the lower die, and Case III involves both the upper and lower punches moving together toward the center of the billet. Extensive simulational work is performed with each case to see the process conditions in terms of forging load, balanced and symmetrical flow in the flange. Also, the effect of the gap size and die corner radii to the material flow are investigated. In this study, the forming characteristics of radial extrusion will be considered by comparing the forces, shapes etc. The design factors during radial extrusion are investigated by the rigid-plastic FEM simulation.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.311-320
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• 2009

Most advanced countries are researching to apply light weight materials far rolling stock because weight reduction for railway body derives cost-saving, energy-saving, and high-speed. Likewise, current Korea rolling stock field makes arduous effects of weight-reduction, miniaturization, and high-efficiency to achieve a high-speed railway. Aluminum becomes suitable material for these projects because it is much lighter than steel or stainless. Manufacturing the railway car body by using the Aluminum is increasing because Aluminum is not bringing the corrosion by unique oxidation-passivate. Aluminum extrusion profile far railway body requires a high mechanical property, accurate shape dimension, and stable quality because the railway body is composed with many different kinds of extruded profiles. Therefore, it is necessary to research about Aluminum precision-extrusion technology to maintain exit temperature and die load. The goal of this project is applying the Aluminum extrusion profile to next-generation railway car body by developing the Aluminum extrusion profile according to precision-extrusion technology which may maintain isothermal exit temperature.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.315-318
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• 2003

Recently, condenser tube which is used for a cooling system of automobiles is mainly manufactured by the conform extrusion but this method is inferior as compared with direct extrusion in productivity per the unit time and in the equipment investment. Therefore, it is essential for the conversion of direct extrusion with porthole die. The direct extrusion with porthole die can produce condenser tube which has the competitive power in costs and qualities compared with the existing conform extrusion. This study is designed to evaluate metal flow, welding pressure, extrusion load tendency of mandrel deflection that is affected by variation of porthole shape in porthole die. Estimation is carried out using finite element method under the non-steady state. Also this study was examined into the cause of mandrel fracture through investigating elastic deformation of mandrel during the extrusion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1146-1152
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• 2005

Recently, multi cell tube which is used for a cooling system of automobiles is mainly manufactured by the conform extrusion but this method is inferior as compared with direct extrusion in productivity per the unit time and in the equipment investment. Therefore, it is essential for the conversion of direct extrusion with porthole die. The direct extrusion with porthole die can produce multi cell tube which has the competitive power in costs and qualities compared with the existing conform extrusion. This study is designed to evaluate metal flow, welding pressure, extrusion load, tendency of mandrel deflection that is affected by variation of porthole shape in porthole die. Estimation is carried out using finite element method under the non-steady state. Also this study was examined into the cause of mandrel fracture through investigating elastic deformation of mandrel during the extrusion.