• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.317-317
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• 2009

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.254-257
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• 2007

In this study, hydroformability and mechanical properties of pre- and post- heat treated Al6061 tubes at different extrusion type were investigated. For the investigation, as-extruded, full annealed and T6-treated Al 6061 tubes at different extrusion type were prepared. To evaluate the hydroformability, uni-axial tensile test and free bulge test were performed at room temperature and $200^{\circ}C$. Also mechanical properties of hydroformed part at various pre- and post-heat treatments were estimated by tensile test. And the tensile test specimens were obtained from hexagonal prototype hydroformed tube at $200^{\circ}C$. As for the heat treatment, hydroformability of full annealed tube is 25% higher than that of extruded tube. The tensile strength and elongation were more than 330MPa and 12%, respectively, when hydroformed part was post-T6 treated after hydroforming of pre- full annealed tube. However, hydroformed part using T6 pre treated tube represents high strength and low elongation, 8%. Therefore, the T6 treatment after hydroforming for as-extruded tube is cost-effective. Hydroformability of Al6061 tube showed similar value for both extrusion types. But flow stress of seam tube showed $20{\sim}50MPa$ lower value.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.132-135
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• 2007

In this study, hydroformability and mechanical properties of pre- and post- heat treated Al6061 tubes at different extrusion type were investigated. For the investigation, as-extruded, full annealed and T6-treated Al6061 tubes at different extrusion type were prepared. To evaluate the hydroformability, uni-axial tensile test and free bulge test were performed at room temperature and $250^{\circ}C$. Also mechanical properties of hydroformed part at various pre- and post-heat treatments were estimated by tensile test. And the tensile test specimens were obtained from hexagonal prototype hydroformed tube at $250^{\circ}C$. As for the heat treatment, hydroformability of full annealed tube is 25% higher than that of extruded tube. The tensile strength and elongation were more than 330MPa and 12%, respectively, when hydroformed part was post-T6 treated after hydroforming of pre- full annealed tube. However, hydroformed part using T6 pre treated tube represents high strength and low elongation, 8%. Therefore, the T6 treatment after hydroforming for as-extruded tube is cost-effective. Hydroformability of Al6061 tube showed similar value for both extrusion types. But flow stress of seam tube showed $20{\sim}50MPa$ lower value.

• 열처리공학회지
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• 제20권4호
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• pp.181-186
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• 2007

Effect of heat treatment conditions on formability and property of warm hydroformed parts for Al 6061 extruded tubes was investigated in this study. For the investigation, as-extruded, fully annealed and T6-treated Al 6061 seamless tubes were prepared. To evaluate the warm hydroformability, uni-axial tensile test and free bulge test were performed at various pre- and post-heat treatment conditions. And the tensile test specimens were obtained from hexagonal prototype hydroformed parts at $250^{\circ}C$. As a result, hydroformability of fully annealed tube is 25% higher than that of extruded tube. The tensile strength and strain of hydroformed part reach to 330 MPa and 12%, respectively, when the part was T6 treated after warm hydroforming. However, the hydroformability of T6 pre-treated tube is relatively low due to the decreased elongation, 8%.

• 소성∙가공
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• 제12권6호
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• pp.566-571
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• 2003

The metal forming behavior and defect formation in Ti-6Al-4V tube during hot backward extrusion were investigated. Dynamic material model(DMM) including Ziegler's instability criterion was employed to predict the forming defects such as shear band, inner and/or surface cracks. This approach was coupled to the internal variables generated from FE analysis. The simulation results fur the backward extrusion were compared with the experimental observation. The chilling effect and friction indicated a great influence on the deformation mode of the tube and the formation of surface cracks. The formation of forming defects in the extruded tube was attributed to non-uniform distribution of strain, strain rate and temperatures in the extruded tubes for the given test conditions.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.359-362
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• 2003

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 different hole diameter. The experiments using aluminium material for the curved tube product had been done. The results of the experiment show that the curved tube product can be formed by the extru-bending process without the defects such as the distortion of section and the thickness change of the wall of tube and the folding and wrinkling. It is known that the welding and extruding of each billet has done simultaneously although the curved tube is extruded with four billets.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1340-1345
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• 2004

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with $D_h=1.41mm$ . The test range covered mass flux from 200 to 600 $kg/m^2s$, heat flux from 5 to 15 $kW/m^2$ and saturation temperature from $5^{\circ}C$ to $15^{\circ}C$ . The heat transfer coefficient curve shows a decreasing trend after a certain quality(critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique 'cross-over' of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations underpredict the low mass flux and overpredict the high mass flux data.

• International Journal of Air-Conditioning and Refrigeration
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• 제12권3호
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• pp.148-157
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• 2004

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with $D_h=1.41mm$. The test range covered mass flux from 200 to $600kg/m^{2}s$, heat flux from 5 to $15kW/m^2$ and saturation temperature from $5^{\circ}C\;to\;15^{\circ}C$. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique 'cross-over' of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations un-derpredict the low mass flux and overpredict the high mass flux data.

• 대한기계학회논문집A
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• 제32권11호
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• pp.1010-1015
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• 2008

In this study, the characteristics of aluminum tube hydroformed products at different extrusion type and heat treatment conditions were investigated. For the investigation, as-extruded, full annealed and T6-treated Al 6061 tubes at different extrusion type were prepared. To evaluate the hydroformability, free bulge test was performed at room temperature to $300^{\circ}C$. Also mechanical properties of hydroformed products at various pre- and post-heat treatments were estimated by hexagonal prototype hydroforming test at $250^{\circ}C$. And the tensile test specimens were obtained from hexagonal prototype hydroformed tube. As a results, hydroformability of full annealed tube is $5{\sim}8%$ higher than that of extruded and T6-treated tube. The tensile strength and elongation of T6-post heat treated indirect extrusion tube were more than 330MPa and 12%, respectively. However, T6 pre treated hydroformed product represents high strength, 330MPa and low elongation, 8%. Therefore, Hydroformability of Al6061 tube showed similar value for both extrusion types. However flow stress of direct tube showed $20{\sim}50MPa$ lower value than indirect tube.

• 소성∙가공
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• 제14권9호통권81호
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• pp.772-778
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• 2005

This paper is concerned with the analysis of material flow characteristics of combined tube extrusion using pipe. The analysis in this paper concentrated on the evaluation of the design parameters for deformation patterns of tube forming, load characteristics, extruded length, and die pressure. The design factors such as punch nose radius, die corner radius, friction factor, and punch face angle are involved in the simulation. The combined tube extrusion is analyzed by using a commercial finite element code. This simulation makes use of pipe material and punch geometry on the basis of punch geometry recommended by International Cold Forging Group. Deformation patterns and its characteristics in combined forward and backward tube extrusion process were analyzed for forming loads with primary parameters, which are various punch nose radius relative to backward tube thickness. The results from the simulation show the flow modes of pipe workpiece and the die pressure at the contact surface between pipe workpiece and punch. The specific backward tube thickness and punch nose radius have an effect on extruded length in combined extrusion. The combined one step forward and backward extrusion is compared with the two step extrusion fer forming load and die pressure.