• 소성∙가공
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• 제11권1호
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• pp.54-60
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• 2002

The purpose of the present paper is to investigate the effect of Process parameters such as internal pressure, amount of axial feeding, and frictional condition between the die and the material on the tube hydro-formability. For carbon steel tubes(STKM 12A, STBH 410 and SPS 290), simple bulging, circular bulging and Tee-fitting tests are performed to evaluate the hydro-formability of these materials which is determined by deformation characteristics such as thickness distribution, forming height and branch dome shape. The formabilities obtained from these tests are analysed and compared with the results of the numerical simulation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.49-53
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• 2001

Recently hydroforming process became a process which is increasingly applied in the automotive industry. As the hydroforming process is a new technology, there is no abundant data to assist manufacturing the products. To investigate the effects of process parameters on the tube hydroforming process, simple bulging, circular bulging and Tee-fitting tests are performed. The optimal leading path to escape the failure modes(bursting, wrinkling) is determined and the effects of the process parameters, the internal pressure and axial feeding on the product quality, such as thickness distribution, forming height and branch dome shape are investigated.

• 소성∙가공
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• 제11권1호
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• pp.75-83
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• 2002

Recently, the hydroforming process is widely applied to the automotive industry and rapidly spreaded to other industries. In this paper, An implicit finite element formulation for simulating axisymmetric tube hydroforming processes is performed. In order to describe normal anisotropy of the tube, Hill's non-quadratic yield function is employed. The frictional contact between die and tube and the frictionless contact between tube and fluid are considered using the mesh-normal vectors computed from the finite element mesh of the tube. The complete set of the governing relations comprising equilibrium and interfacial equations is linearized for Newton-Raphson procedure. In order to verify the validity of the developed finite element formulation, the axisymmetric tube bulge test is simulated and the simulation results are compared with experimental measurements. In a simulation of stepped circular tube hydroforming processes, an optimal hydraulic pressure curve is pursued by considering simultaneously internal pressures and axial forces.

• Structural Engineering and Mechanics
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• 제60권1호
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• pp.91-110
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• 2016

Tube hydroforming (THF) under pulsating hydraulic pressures is a novel technique that applies pulsating hydraulic pressures that are periodically increased to deform tubular materials. The deformation behaviours of tubes in pulsating THF may differ compared to those in conventional non-pulsating THF due to the pulsating hydraulic pressures. The equivalent stress-strain relationship of metal materials is an ideal way to describe the deformation behaviours of the materials in plastic deformation. In this paper, the equivalent stress-strain relationships of SS304 tubes in pulsating hydroforming are determined based on experiments and simulation of free hydraulic bulging (FHB), and compared with those of SS304 tubes in non-pulsating THF and uniaxial tensile tests (UTT). The effect of the pulsation parameters, including amplitude and frequency, on the equivalent stress-strain relationships is investigated to reveal the plastic deformation behaviours of tubes in pulsating hydroforming. The results show that the deformation behaviours of tubes in pulsating hydroforming can be well described by the equivalent stress-stain relationship obtained by the proposed method. The amplitude and frequency of pulsating hydraulic pressure have distinct effects on the equivalent stress-strain relationships-the equivalent stress becomes augmented and the formability is enhanced with the increase of the pulsation amplitude and frequency.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.314-317
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• 2007

Automotive rear subframe of aluminum tube was developed by using hydroforming process, based on the numerical analysis and physical tryouts. In the previous study, the effect of prebending was evaluated on the basis of forming limit diagram which had been obtained from free bulging, T-shape forming and cross-shape forming, using the developed tube hydroformability testing system. In order to get the sound products, appropriate internal pressure is to be imposed corresponding to the axial feeding. In this study, the loading path, the combination of internal pressure and axial feeding during the process, was optimized to ensure minimum thickness variation and dimensional accuracy, by using response surface method.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.251-254
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• 2005

The flow forming has been used to produce long thin walled tube parts, with reduced forming load and enhanced mechanical and surface quality for a good finished part compared with other method formed parts. So flow forming technique is used widely in industrial production. Especially spinning and flow farming techniques an used frequently in automotive, aerial, defense industry. In this paper, FEM analysis of three-roller backward flow forming of a workpiece is carried out to study effects of forming depth and feed rate on forming force. The axial and radial forces on several forming depth and feed rate conditions are obtained. The phenomena such as bell mouth, build up and bulging during simulation are observed as well.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.54-57
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• 2001

Hydroforming is core production techniques for the super light weight and high safety of the vehicle body. In order to establish and understand hydroforming, the tube hydroforming simulator which could control an axial compression and high internal pressure with computer operation was developed in tube bulging. This paper presents experimental investigation for process parameters, such as Internal pressure and axial compression. In addition, the mechanical properties, such as strain hardening and energy absorption ability of hydroformed part, is discussed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1810-1815
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• 2003

Tube hydroforming provides a number of advantages over conventional stamping process, including fewer secondary operation, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength and stiffness. In this study, the effect of the heat treatment on the hydro-formability has been investigated. By using the mild steel tube bulging test is performed at various heat treatment conditions to evaluate the hydro-formability.

• 소성∙가공
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• 제23권5호
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• pp.317-322
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• 2014

Bursting during tube hydroforming is preceded by localized necking. The retardation of the initiation of necking is a means to enhance hydroformability. Since high strain gradients occur at the necking sites, a decrease in local strain gradients is an effective way to retard the initiation of necking. In the current study, the expansion at potential necking sites was intentionally restricted in order to reduce the strain gradient at potential necking sites. From the strain distribution obtained from FEM, it is possible to determine strain concentrated zones, which are the potential necking sites. Prior to the hydroforming of a trailing arm, an incompressible material(such as lead) is attached to the tube where the strain-concentrated zone would contact the die. Due to the incompressibility of lead, the tube expansion is locally restricted, and the resultant strain extends to adjacent regions of the tube during hydroforming. After the first stage of hydroforming, the lead is removed from the tube, and the hydroforming continues to the final targeted shape without any local restriction. This method was successfully used to fabricate a complex shaped automotive trailing arm that had previously failed during traditional hydroforming fabrication.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.253-257
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• 2005

A tube hydroformability testing system was designed and fabricated so as to observe the forming process and to apply forming condition along arbitrarily pre-programmed internal pressure-axial feed path. The forming limit diagram of A6063 extruded tube, of 40.6 mm outer diameter and 2.25 mm thickness, was successfully obtained through free bulging and T-forming tests except the region of high positive minor strain. It is found that the data points marked on the FLD are mostly located near the strain paths from the finite element analysis excluding the cases of large axial feed. There exist data points even in the area beyond the uniaxial tension mode, since the reduction in thickness decreases due to the axial feed. The forming limit from T-forming test was considerably lower than that from free bulge test. It seems because the deformation is localized at the pole.