• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.364-367
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• 2001

Recently social demands of fuel economy and environmental regulation require the development of light materials and new manufacturing technologies. In this point, aluminum tube hydroforming, which is satisfied with good strength-to-weight ratio and recyclability, is new innovative concept. but, up to now the level of that is relatively low. In this paper, we studied formability of different aluminum tubes in different heat treatments under internal pressure and axial feeding, and mechanical properties of aluminum tubes before and after hydroforming.

• 소성∙가공
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• 제9권1호
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• pp.35-42
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• 2000

In this paper, we developed the hydroforming simulator which can apply an axial compressive force and high internal pressure to bulge a tube. Experimental dtudies have been performed to investigate the effect of each parameters such as internal pressure and axial compression stroke required for the forming of circular components. Under the improper forming conditions there were two forming failures. One was the axial buckling due to excessive axial compressive load and the other was the circumferential necking fracture due to relatively high internal pressure. A safe forming zone without any failures exists between these two extreme zones. Also the condition of forming failure such as fracture is examined throughout the theoretical analysis. This paper covers a brief overview of the mechanism of hydroforming process as well as the design of die and tools.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.244-247
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• 2009

Hydroformed parts have higher dimensional accuracy, structural strength, and dimensional repeatability. Particularly in the automotive industry, manufacturing of parts with complex shapes from tubular materials sometimes requires one or more pre-forming operations such as bending before the hydroforming process. The pre-bending process is an important factor for successful hydroforming in the case where the perimeter of the blank is nearly the same as that of final product. The bendability of a tube depends on the parameters such as the bending radius, variation of the diameter, thickness, hardness. This study shows the analysis of bending through the stainless steel tubes bent to rotary draw bending machine.

• 한국자동차공학회논문집
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• 제23권1호
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• pp.41-48
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• 2015

In the automotive industry, it is required to reduce weight of the car and improve fuel efficiency. Competitive pricing is also a very important issue. That's why application of welded steel tube is increasing in order to produce a vehicle with a competitive price. Also, hydroforming technology is asking more and more for thinner tubing to realize to a lighter vehicle design. Steel tube is produced through a multi-stage process called roll forming. In that case, bucking and work hardening should be considered key forming technology is to prevent buckling and minimize work hardening during steel tubing for hydroforming To prevent buckling, it is required to optimize forming process in order to minimize stretching in edge sections and hold tightly cross-section during welding. And to minimize work hardening, it is needed to know the proper process to avoid reforming.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 제5회 박판성형 SYMPOSIUM
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• pp.11-11
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• 2006

• 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.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.169-173
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• 2008

This study is concerned with adopting the hydroforming method in the front axle of the commercial vehicle. Generally the front axle of the commercial vehicle is made bγ the several operations of press forging. This product supports the big weight of the vehicle and load. The weight of the press forging parts is also so more than it of the press parts of the passenger car. So, we have studied the hydroforming method to lessen the weight of the front axle of the commercial vehicle. To apply the hydroforming method in the commercial vehicle, we had to use the operation of reducing the diameter of the used tube prior to the hydorforming operation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.154-157
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• 2008

It is important to know the variations of the mechanical properties in the hydroforming process for the safe and durable design purposes. In this study, strain hardening behavior during hydroforming has been investigated by hydroforming of engine cradle as a model process. The variation of mechanical properties such as local hardness and flow stress were used as an index of strain hardening during respective processes. By using the inter-relationships between hardness-flow stress-effective strain at variable pre-strains, the strain hardening behavior during hydroforming has been successfully analyzed. The comparison of predicted hardness with measured hardness confirmed that the methodology used in this study was feasible and the strain hardening behavior can be quantitatively estimated.

• 한국자동차공학회논문집
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• 제9권6호
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• pp.160-169
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• 2001

To predict busting failure in tubular hydroforming, the criteria for ductile fracture proposed by Oyane is combined with the finite element method. From the histories of stress and strain in each element obtained from finite element analysis, the fracture initiation site is predicted by mean of the criterion. The prediction by the ductile fracture criterion is applied to three hydroforming processes such as a tee extrusion, an automobile rear axle housing and lower am. For these products, the ductile fracture integral I is not only affected by the process parameters, but also by preforming processes. All the simulation results show the combination of the finite element analysis and the ductile fracture criteria is useful in the prediction of farming limit in hydroforming processes.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.277-280
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• 2006

The hydroformability of aluminum alloy sheets at elevated temperatures have been investigated in this study. It is necessary to analyze the variations of the mechanical properties that depend on the forming temperature and the heat conduction during warm hydroforming. Therefore, in this study a coupled simulation of plastic deformation and temperature distribution in the warm hydroforming process is performed and compared with experimental data. The multi-purpose code DEFORM-2D can handle this type of calculations but it takes high computation time if contact heat transfer between die, tube and pressure medium occurs. Experiments were conducted by high temperature tribometer(pin-on-disk) allowing measuring the friction coefficients of the aluminum alloys at several temperatures and these results are applied to the coupled simulation by which the optimal process parameters such as internal pressure and preset temperature on hydroformability can be determined. The comparison of the FE analysis with the experimental results has shown that hydroformability given by bulge height, and temperature distribution of the tube specimen make a little difference with the FE results but the trend predicted by simulation agrees well with experiments.