• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.92-96
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• 2005

Among the failure modes which can be occurred in tube hydroforming such as wrinkling, bursting or buckling, the bursting by local instability under excessive tensile stresses is irrecoverable phenomenon. Thus, the accurate prediction of bursting condition plays an important role in producing the successfully hydroformed part without any defects. As the classical forming limit criteria, strain-based forming limit diagram has widely used to predict the failure in sheet metal forming. However, it is known that the FLD is extremely dependant on strain path throughout the forming process. Furthermore, the path-dependent limitation of FLD makes the application to hydroforming process, where strain path is no longer linear throughout forming process, more careful. In this work, stress-based forming limit diagram (FLSD), which is strain path-independent and more general, was applied to prediction of forming limit in tube hydroforming. Combined with the analytical FLSD determined from plastic instability theory, finite element analyses were carried out to find out Ihe state of stresses during hydroforming operation, and then FLSD is utilized as forming limit criterion. In addition, the approach is verified with a series of bulge tests in view of bursting pressure and shows a good agreement. Consequently, it is shown that the approach proposed in this paper will provide a feasible method to satisfy the increasing practical demands for judging the farming severity in hydroforming processes.

• International Journal of Precision Engineering and Manufacturing
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• 제9권3호
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• pp.55-58
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• 2008

Hydroforming is a forming technology in which a steel tube is set in a die and formed to fit a specified shape by applying hydraulic pressure from inside the tube while also applying force in the tube axial direction (axial feed). In present study, the entire design process chain for an automotive cross-member was simulated and developed using hydroforming technology on high-strength steel. The part design stage required a feasibility study. The process was designed using computer-aided design techniques to confirm the actual hydroformability of the part in detail. The possibility of using hydroformable cross-member parts was examined using cross-sectional analyses, which were essential to ensure the formability of the tube material for each forming step, including pre-bending and hydroforming. The die design stage included all the components of a prototyping tool. Press interference was investigated in terms of geometry and thinning.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.35-38
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• 1999

Tube bending is an important factor of the hydroforming processes. The tube must be bent to the approximate centerline of the finished part prior to hydroforming to enable the tube to be placed in the die cavity. This paper presents the simulation results in prebending process by a rotary bending machne and a bend die that is used to form an automotive part a tie bar, Prebending simulation is carried out to obtain the shape change of cross section and thinning in bending process. To avoid occurring wrinkle in compressive zone during bending process a wiper die included,. A parametric study is carried out to obtain the effect of the forming parameters such as a bend radius and tube thickness

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 제5회 박판성형 SYMPOSIUM
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• pp.45-48
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• 2006

Recently, the use of tubular hydroforming technology has seen increased usage and increased consideration for wide range of tubular automotive applications. In manufacturing hydroformed parts, bending and pre-forming operations are often required prior to the hydroforming process. Higher bending quality of bent tubes is crucial for the successful hydroforming operation because most of plastic strains and wall thinning at the extrados of bend area occur in the bending operation. Springback is also observed due to elastic recovery of tube material after bending. Proper correction of springback is required not only to well place the bent tube into a hydroforming die cavity but also to avoid pinching when the upper die is brought down to closing position. Therefore, prediction of springback at early development stage is one of the key factors to produce high quality hydroformed parts. In this study, a variety of bending experiments has been carried out to investigate springback amount under change in bending angle and material boosting. Throughout the experimental approach, springback characteristics of bent tubes are quantified according to the change in various bending parameters, and a mathematical model to predict correction amount of springback to a given bend angle is found.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.27-31
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• 2004

A bumper comprises a bumper face, a bumper beam for distributing the load from the impacts applied to the bumper face and reinforcing the bumper, an absorber member interposed between the bumper face and the 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.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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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.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.209-214
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• 2007

This study is concerned with working hardening of bending operation on hydroforming parts. Generally, hydroforming parts having the complicated shape of the automobile, require a 3-dimentional bending operation. This operation involves several variations in the tube which are the thickness, the mechanical characteristics, the hardness, the circumference etc., on original tube. So, we study those variations and the affect on the hydroforming operation and hydroforming parts. We used two methods, one of which was computer simulation and the other the actual test in the plant.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.325-328
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• 2008

In recent years, developments of light weight vehicle are one of the most important issues in automotive industry. It is important to know the variations of the mechanical properties in the hydro forming process for the safe and durable design purposes. Generally, tube hydroforming process consists of three main processes such as bending, preforming, and hydroforming. It means that the strain hardening histories of final products are nonlinear. 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 strength were used as an index of strain hardening during respective processes. The correlationship between strength and hardness obtained from tensile test has been equivalently converted into correlation between hardness and measured strain.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.306-309
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• 2007

In this study, hydroforming characteristic of the double-layered tube was investigated in the hydroforming process. The double-layered tube can be made outer surface on the stainless steel by only one processing. The free bulging test was performed to analysis optimized pressure and axial feeding amount of the double layered tubes. And the experimental results between stainless/carbon and carbon/carbon double-layered tube were compared with the forming data. Moreover analysis model that can be hydroformability and predictable forming pressure of double-layered tube was presented.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.333-336
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• 2008

There are many different kinds of forming processes to make a tubular product such as hydroforming and tube drawing. However, we should consider a better forming process in view point of energy consumption and $CO_2$ emission to save our earth. In this paper we have conducted FEM simulations to the various forming processes for sheet and tubular products to compare their energy consumptions. One example is tubular product and the other for drawn cup. From the comparisons of total energy for hydrofroming and tube sinking processes, hydroforming is consumed more energy than tube drawing. Also the cup drawing from sheet metal and tube sinking for the cup with flange indicate that the tube sinking is better than cup drawing of sheet metal in energy consumption.