• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.243-246
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• 2005

A tube hydroformability testing system was designed and manufactured to observe the forming steps and to provide arbitrary combination of internal pressure and axial feed. The forming limit diagram of an aluminum tube was obtained from the free bulge test and the T-shape forming test using this system, giving the criteria for predicting failure in the hydroforming process. The hydroformability of aluminum tube according to different conditions of a prebending process was discussed, based on the finite element analysis and the forming limit test. The effects of 2D and 3D prebending on the tube hydroforming process of an automotive failing arm were evaluated and compared with each other.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.38-42
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• 2005

A bumper comprises a bumper cover, a bumper beam for distributing the load from the impacts applied to the bumper cover and reinforcing the bumper, an absorber member interposed between the bumper cover and tile bumper beam, and a pair of bumper stays which secure the bumper beam to the vehicle body. A conventional bumper stay structure is assembled into several stamped parts, so several processes are needed and the structure is complicated. In this study the bumper stay is applied to the tubular hydroforming which is known to have several advantages such as the reduction of the number of the process and the part weight. The thickness distribution of the tube is mainly considered to evaluate the hydro-formability and the shape of the tube is determined.

• Transactions of Materials Processing
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• v.17 no.8
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• pp.564-569
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• 2008

Strain hardening behavior during hydroforming has been experimentally investigated. The variation of flow stress was used as an index of strain hardening during respective processes and the flow stress was estimated from the correlationship between flow stress and effective strain. The local hardness after hydroformig was also predicted by effective strain. 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.

• Transactions of Materials Processing
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• v.9 no.6
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• pp.590-597
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• 2000

A finite element formulation lot the simulation of axisymmetric sheet hydroforming is proposed, and an implicit program is coded. In order to describe normal anisotropy of steel sheet, Hill's non-quadratic yield function (Hill, 1979) is employed. Frictional contacts among sheet surface, rigid tool surface, and flexible hydrostatic pressure are considered using mesh normal vectors based on finite element of the sheet. Applied hydraulic pressure is also considered as a function of forming rate and time and treated as an external loading. The complete set of the governing relations comprising equilibrium and interfacial equations is approximately linearized for Newton-Raphson algorithm. In order to verify the validity of the developed finite element formulation, the axisymmetric bulge test is simulated. Simulation results are compared with other FEM results and experimental measurements and showed good agreements. In axisymmetric hydroforming processes of a disk cover, formability changes are observed according to the hydraulic pressure curve changes.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.145-147
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• 2009

The benefits of hydroforming technology are known as weight and cost savings through part consolidation and reduced post-forming processes such as welding and piercing. Hydroforming technology has some weaknesses in terms of process cycle times. But, as the hydraulic system and process designs are continuously developed, the cycle time is also reduced to acceptable and competitive levels. Hot air bulging is one of recently developed hydroforming techniques. Hot air bulging in order to further extend the forming degrees of Al lightweight material is investigated. A heated tube is placed in a heated die and sealed at the ends by sealing cylinders. The tube is subsequently expanded against the die cavity wall by internal pressure provided by air medium. The result of this study shows that axial feeding speed and air pressure have an effect on formability of Al air bulging at elevated temperature.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.209-212
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• 2008

Hydroforming Technology has been applied to manufacture in various parts of automobile. Especially, Exhaust manifold has been applied to hydroforming method in the foreign advanced automotive company. Exhaust manifold runner is important exhaust parts that heat-resistant and exhaust flow characteristics are requested in the automobile. The purpose of this study is to optimize the manufacturing method of exhaust maniflold runner using FEA and to propose to get a optimization design direction. In addition, Comparative analysis between conventional exhaust maniflold and hydroformed exhaust maniflold has been done in view of weight-saving, manufacturing advantage.

• Journal of the Korean Society for Precision Engineering
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• v.7 no.2
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• pp.28-38
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• 1990

The study is concerned with the theoretical and experimental investigation of axisymmetric fluid pressure-driven hydroforming of sheet metal by forming over the die cavity. The rigid-plastic finite element method is employed to calculate the stress and strain distribution. The effect of blank size and die radius is also studied in the finite element analysis. Experiments are carried out for hydroforming of cold-rolled steel sheets under various process conditions. The computational results are compared with the experimental results for the forming pressure vs. pole displacement relations and strain distributions. Comparison has shown that theoretical predictions by the finite element method are in good agreement with the experiment with the experimental observations. Thus, it is shown that the rigid-plastic finite element method is effectively used in the analysis of axisymmetric fluid pressure-driven hydroforming process.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.3
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• pp.146-150
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• 2004

Because of the social needs for energy saving and the rigid environmental regulation, the development of light materials and new economical manufacturing technologies have been actively investigated. Recently, the hydroforming of high strength aluminum tube has attracted great interest due to its good strength-to-weight ratio, which could play an important role in lightweighting of automobile. However, the limited formability of high strength aluminum alloys is considered to hinder the active application of the hydroforming process. In this paper, the hydroformability of aluminum tubes with different heat treatments was investigated as the basic research of the hydroforming process for the high strength aluminum tubes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.3
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• pp.259-268
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• 2015

An optimization method for the tube hydroforming process is developed using the equivalent static loads method for non linear static response structural optimization (ESLSO). The aims of the tube hydroforming optimization are to determine the axial forces (axial feedings) and the internal pressures, and to obtain the desired shape without failures after hydroforming analysis. Therefore, the magnitude of the forces should be design variables in the optimization process. Also, some tube hydroforming optimization needs to consider the result of the thickness in nonlinear dynamic analysis as responses. However, the external forces are considered as constants and the thickness is not a response in the linear response optimization process of the original ESLSO. Thus, a new ESLSO process is proposed to overcome the difficulties and some examples are solved to validate the proposed method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.358-358
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• 2008