• 소성∙가공
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• 제11권3호
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• pp.262-268
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• 2002

The bending process for the rectangular and circular curled tube can be developed by the hot metal extrusion machine with the multiple punches moving in the different velocity. The bending phenomenon has been known to be occurred by the different of velocity at the die exit. The difference of velocity at the die exit section can be obtained by the different velocity of billets through the multi-hole container and by the cohesion of billet Inside the porthole die chamber. The bending phenomenon can be controlled by the two variables, the one of them is the difference of velocity at the die edit section by the different velocity of billets through the multi-hole container The other is the difference by the different hole diameter The results of the experiment show that the rectangular curved tube can be formed by the extrusion process, that the curvature of the curved product can be controlled by the velocity of punch and the diameter of container hole, that the defects such as the distortion of section and the thickness change of the wall of tube and the folding and wrinkling of thin tube did not happen after the extra-bending processing by the extrusion bending machine.

• 한국주조공학회지
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• 제30권6호
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• pp.210-216
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• 2010

The aim of this study is to characterize a thixoextruded 7075 Al wrought alloy bar in terms of its isotropic behavior through the optical microscope, mechanical test and electron back scattered diffraction. It is also discussed of the extrudability improvement for 7075 Al wrought alloy by thixoextrusion, with emphasis on controlling thixoextrusion parameters. Hot extrusion shows that the maximum extrusion pressure depends on their characteristics in terms of flow stress and hot workability. In the contrary, thixoextrusion demonstrates that the maximum extrusion pressure is almost uniform regardless of the experimental parameters, such as initial ram speed, die bearing length and thixoextrusion temperature. The hot extruded microstructures become elongated to extrusion direction, while the thixoextruded microstructures are isotropic and homogeneously distributed due to the existence of liquid phase between solid grains during the process. The grain refinement due to dynamic recrystallization during thixoextrusion has been also occurred. Subsequent recrystallization would lead to the strengthening of mechanical properties, as observed in the study. The important point is that the values of tensile, yield strength and elongation of the thixoextruded bar without plastic deformation are similar to those of the hot extruded bar with severe plastic deformation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.247-250
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• 2006

The growing demand for more fuel-efficient vehicles to reduce energy consumption and air pollution is a challenge for the automotive industry. The characteristic properties of aluminum, high strengrth stiffness to weight ratio, good formability, good corrosion resistence, and recycling potential make it the ideal candidate to replace heavier materials in the car to respond to the weight resuction demand within the automotive industry. In this paper, A series of compression test was carried out to find the flow stress of A6082 at 300, 400 and $500^{\circ}C$, then we tried to estimate weldability, extrusion load and effective stress of die in the aluminum extrusion process through the 3D FE simulation at non-steady state for aluminum automotive parts.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 춘계학술대회 논문집(한국공작기계학회)
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• pp.72-77
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• 2001

The use of hexagonal ceramic inserts for copper extrusion dies offers significant technical and economic advantages over other forms of manufacture. In this paper the data on the loading of the tools is determined from a commercial FEM package as the contact stress distribution on the die-workpiece interface and as temperature distributions in the die. This data can be processed as load input data for a finite element die-stress analysis. Process simulation and stress analysis are thus combined during the design, and a data exchange program has been developed that enables optimal design of the dies taking into account the elastic deflections generated in shrink fitting the die inserts and that caused by the stresses generated in the process. The stress analysis of the dies is used to determine the stress conditions on the ceramic insert by considering contact and interference effects under both mechanical and thermal loads.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.449-452
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• 2009

This paper was designed to fabricate the miniature spur gear with pitch circle of 1.8 by hot extrusion process of mechanically alloyed Zn-22wt%Al powder at various temperature. The mechanical alloying was preformed for ball milled times of 8h, 16h and 32h by the planetary ball milling. Mechanically alloyed powders were compacted cylindrical performs. Extrusions of the miniature spur gear using the alloyed powder were carried out at different extrusion temperatures. The extruded spur gear was sintered for 2h at $350^{\circ}C$ in argon atmosphere. The friction between the die and the powdered billet and the internally different density due to complex product shape cause the internal crack. To overcome the mentioned problems, high dimensional accuracy at cross section of the spur gear and uniform Vickers hardness could be obtained by graphite lubricant and controlling holding time.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 추계학술대회 논문집
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• pp.64-73
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• 1994

An updated Lagrangian finite element analysis with automatic remeshing scheme is applied to the three-dimensional hot extrusion through landless square dies. In the remeshing procedure, it is very difficult that the meshes are generated automatically with consideration of physical characteristics. In the presented study, the mesh generation is accomplished by modular concept. The generated meshes by modular concept have advantages, especially for three-dimensional problems, such as economized computational time and consideration of physical characteristic. In the problem, orifice shapes of square die are divided into two for the extrusion of solid sections. The orifice adaptive modules are developed for each type and the numerical examples are carried out for each type.

• 소성∙가공
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• 제8권2호
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• pp.160-168
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• 1999

This paper is concerned with the process sequence design of longneck flange forming by using cold extrusion with thick hollow pipe. The conventional hot forming process to produce a longneck flange is investigated by thermo-viscoplastic finite element method to observe the metal flow in detail and evaluate design requirements. Based on the results of simulation of the current hot forming process, design strategy for improving the process sequence are developed using the thick hollow pipe. The main goal is to obtain an appropriate improved process sequence which can produce the required product most economically without tensile cracking, workpiece buckling, and overloading of tools. Newly process condition such as semi-die angle, reductio ratio of cross-sectional area of axisymmetrical extrusion process. The final designed process can provide very useful guidelines to other flange forming industries.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.387-390
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• 2009

This study was designed to fabricate the micro-electro-mechanical systems (MEMS) parts such as micro spur gears using hot extrusion of gas atomized Al-78Zn powders. For this purpose, it is important to develop new methods to fabricate micro-dies and choose suitable extrusion conditions for a micro-forming. Micro-dies with Ni were fabricated by LIGA technology. LIGA technology was capable to produce micro-extrusion dies with close tolerances, thick bearing length and adequate surface quality. Superplastic Al-78Zn powders have the great advantage in achieving deformation under low stresses and exhibiting good micro formability with average strain rates ranging from $10^{-3}$ to $10^{-2}\;s^{-1}$ and constant temperatures ranging from 503 to 563K. Al-78Zn powders were compacted into a cylindrical shape (${\Phi}3{\times}h10$) under compressive force of 10kN and, subsequently, the compacted powders were extruded at 563k in a hot furnace. Micro-extrusion has succeeded in forming micro-gear shafts.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1996년도 제6회 학술강연회논문집
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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.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.212-215
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• 2001

The bending process for the rectangular curved tube can be developed by the hot metal extrusion machine with the multiple punches moving in the different velocity. The bending phenomenon can be controlled by the two variables, the one of them is the difference of velocity at the die exit section by the different velocity of billets through the multi-hole container. The other is the difference by the different hole diameter. The results of the experiment show that the rectangular curved tube can be formed by the extrusion process and that the curvature of the curved product can be controlled by the velocity of punch and the diameter of container hole and that the defects such as the distortion of section and the thickness change of the wall of tube and the folding and wrinkling of thin tube did not happen after the bending processing by the extrusion bending machine.