• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1996.05a
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• pp.197-205
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• 1996

A combined extrusion process studied here consists of forward and backward extrusion, and it is formed in single operation. The metal flow involved in the operation has appeared to be difficult to analyze accurately because of mixed directions of the flow. In this study, conventional two operations of a forward and a backward extrusions is transformed into one operation of mixed extrusion. A process designed by an industry expert is simulated by the rigid-plastic finite element method to investigate the metal flow and defects. In addition to the FEM simulation, experimental analysis has been carried out to confirm the design in industry, which includes material characterization, preliminary expriment, and whole experimental forming operation. The experimental results show that warm forming of extrusion is more desirable than cold working and hot forming in view of grain growth. Also two conditions of lubrication between workpiece and die has been investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.266-269
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• 2005

The effect of exit temperature on the thickness of recrystallization layer during Al extrusion process was investigated. The recrystallization layer of an extruded Al alloy is an important feature of the product in a wide range of applications, particularly those within the automotive industry. The thicker recrystallized layer in the Al alloys can give rise to a number of problems including reduced fatigue resistance and orange peel during cold forming. But the interaction of extrusion process variables with the thickness of recrystallization layer is poorly understood, and there is limited information available regarding the role of the main hot extrusion variables. Using the 3650 US ton extrusion press, this paper describes the effect of the main process variables such as billet temperature, ram speed, and exit temperature on the thickness of recrystallization layer for the A6XXX Al alloy.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.10a
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• pp.37-41
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• 2000

Extruded Profiles of Aluminum alloys have been widely used as parts and frames in mechanical and construction structures. Nowadays, mechanical processing of extruded Al alloy profiles is often employed for various industrial applications. Especially, the bending process is more and more applied and the process is greatly influenced by the distributed mechanical properties in the extruded profiles. Due to large reduction of area or extrusion ratio in ordinary production of extruded profiles, anisotropy is naturally induced by large severe deformation during the extrusion process. Therefore, the anisotropy properties play a great role in the bending process, as a post processing of extruded profiles and errors will be involved when the extruded profiles are treated as isotropic material, ignoring the induced anisotropy in the thin-walled extruded product. In the present work, the anisotropic material change is simulated, as a simplified method, employing Barlats six-component yield criterion in the rigid-plastic finite element method. Finite element computations are carried out for extrusion of a thin-walled part.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.140-143
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• 1997

The present study is concerned with the hydrostatic extrusion process of copper-clad aluminium bar to investigate the basic flow characteristics. Considering the bonding mechanism of bi-metal contact surface as cold pressure welding, the normal pressure and the contact surface expansion are selected as process parameters governing the bonding condition. The critical pressure required for the bonding at the interface is obtained by solving a "local extrusion" using a slip line meyhod. A viscoplastic finite element method is used to analyze the steady state extrusion process. The boundary profile of bi-metal rod is predicted by tracking a particle path adjacent to interface surface. The variations of contact surface area and the normal pressure along the interface profile are predicted and compared to those by experiments.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.330-336
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• 1989

In analyzing the axisymmetric backward extrusion process a new method of analysis using upper-bound theorem is proposed in which the plastic zone and dead metal zone cam be predicted. Experiments are carried out with commercial aluminum. The metal flow on the meridional plane has been visualized experimentally by using the gridded specimens. It is shown that the theoretical results both in extrusion load and deformation pattern are in good agreement with the experimental results and they can be used for effective punch and die design to consider various process parameters in axisymmetric backward extrusion.

• Journal of Korea Foundry Society
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• v.21 no.6
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• pp.359-365
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• 2001

The superplastic behavior of whisker reinforced aluminum alloy matrix composites fabricated by squeeze casting as one of high pressure routes was investigated. The preforms of ${\alpha}-Si_3N_4$ and ${\beta}-SiC$ whiskers without any binder as a reinforcement were used. The matrix materials were 2024 and 7075 aluminum alloys. For the purpose of optimum superplastic condition, respectively, the whiskers volume fraction, extrusion temperature, tensile test temperature and initial strain rate were changed. Fracture surface of tested specimens were observed by SEM. By the results, it became possible to produce superplastic composites by applying only a hot extrusion process to composites obtained by the squeeze casting. The superplastic composites developed are ${\alpha}-Si_3N_4w/7075$, ${\alpha}-Si_3N_4w/2024$ and ${\beta}-SiCw/2024$ systems at high strain rate.

• Journal of Korea Foundry Society
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• v.13 no.3
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• pp.248-258
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• 1993

A semi-solid alloy in which solid and liquid phase are co-existing is obtained by stirring of A17075 molten metal. A semi-solid alloy is dependent on the corresponding temperature within the solid-liquid range, and the process parameters should be controlled accurately to obtain the homogeneous semisolid alloy. The fabrication possibility of fiber-reinforced aluminum alloy containing $Al_2O_3$ short fibers with vigorous agitation of short fibers were obtained by control of stirring time, solid fraction and impeller speed in extrusion billet fabrication processes. The microstructure to extrusion billet fabricated by low pressure casting was investigated for fiber dispersion state. The relationship between the extrustion force and velocity at hot extrustion, the flow strain and extrusion ratio were theoretically described. The surface defects with lubricants and without lubricant after hot extrusion were investigated. The composites materials after hot extrusion were measured by vickers hardness with extrusion ratio. It has become clear that the secondary working such as hot extrusion was very useful to obtained improved the mechanical properties of metal matrix composites.

• Transactions of Materials Processing
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• v.13 no.5
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• pp.422-428
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• 2004

At present, the design of extrusion dies and operation in extrusion companies are primarily based on trial and error. The experience of the die designer, the press operator and the die corrector determine the performance of the extrusion die and the efficiency of the process. In order to produce defect-free products of desirable quality in terms of strength, surface quality and geometrical dimensions, it is important to obtain more knowledge of the processes that occur during extrusion. Recently, to reduce the costs of designing and manufacturing of extrusion dies, and to ensure the quality of the extruded products, numerical simulation for extrusion processes such as FEM (finite element method) is applied increasingly and becomes a very important tool for the design and development of new products. However, most of the studies about FE simulation have been accomplished for simple geometry and low extrusion ratio in the filed of steady metal flow conditions. The extruded products of AI alloy in industrial practice involve complicated sectional geometry. This study was designed to reduce the time of die design and manufacturing in the extrusion process using FEM simulation. FEM simulations of extrusion process were performed in non-steady states conditions by changing weld plate included in extrusion die set. Product which was employed in this study is heat sink that has been used in the parts of heat exchanger of electric circuits. It is generally applied for aluminum or its alloys due to heat efficiency and easy production of complicated shapes, and manufactured by extrusion process. The simulated results showed that weld plate shape in extrusion dies influences meta] flow and dimensional accuracy of products.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.5 no.1
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• pp.53-57
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• 2002

Most of the heli-decks are constructed with aluminum extrusions. The heli-deck product company supplies structural analysis data to the shipbuilding companies: so, if the shipbuilding co. needs to make up for the weak points in the current system, they only need to analyze the substructure through the FEA. In this paper, we will concentrate on the following issues: analysis of aluminium extrusions regarding the structural analysis data, and check safety about the substructure through the FEA.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.231-232
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• 2006

Aluminum Alloys with a content of 22 wt.-% $Mg_2Si$ were spray formed. This alloy features by a low density and is therefore a superior material for leightweight applications. The main problem in spray forming of this type of alloy was the occurance of high porosities. First process optimizations have been performed to decrease porosity under a certain level, so that it can be closed by an extrusion process