• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2007.10a
• /
• pp.209-214
• /
• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.10a
• /
• pp.169-173
• /
• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2006.06a
• /
• pp.45-48
• /
• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2000.10a
• /
• pp.149-152
• /
• 2000

By using a three-dimensional finite element program HydroFORM-3D based on a rigid-plastic model, the hydroforming process for automobile subfrmae is analyzed in this study. The goal of this study is to accomplish preform design and determine the level of internal pressure for producing final hydroformed subframe component. Prior to hydroforming, the initial tube blank must be bent to the approximate centerline of the final part to enable the tube to be placed in the die cavity, After then, a preforming operation like stamping is carried out to the prebent tube. Finally, hydroforming process is performed to the preformed tube to get the final production. And through ductile fracture theory, the failure, bursting, is predicted during hydroforming process for tube blank with different diameter.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2001.10a
• /
• pp.54-57
• /
• 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.

• Transactions of Materials Processing
• /
• v.14 no.6 s.78
• /
• pp.527-532
• /
• 2005

Among the failure modes which can occur 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 (FLD) 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 application of FLD to hydroforming process, where strain path is no longer linear throughout forming process, may lead to misunderstanding for fracture initiation. 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 the state of stresses during hydroforming operation, and then FLSD is utilized as forming limit criterion. In addition, the approach is verified by 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 forming severity in hydroforming processes.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2005.05a
• /
• pp.92-96
• /
• 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.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.5
• /
• pp.45-49
• /
• 2010

The automotive industry has shown a growing interest in tube hydroforming during the past years. The advantages of hydroforming (less thinning, a more efficient manufacturing process, etc.) can, for instance, be combined with the high strength of extra high strength steels, which are usually less formable, to produce structural automotive components which exhibit lower weight and improved service performance. Design and production of tubular components require knowledge about tube material and forming behavior during hydroforming and how the hydroforming operation itself should be controlled. These issues are studied analytically in the present paper. In this study, the whole process of rear sub-frame parts development by tube hydroforming using AA6061 material is presented. At the part design stage, it requires feasibility study and process design aided by CAE (Computer Aided Engineering) to confirm hydroformability in details. Effects of parameters such as internal pressure, axial feeding and geometry shape in automotive rear sub-frame by hydroforming process were carefully investigated. Overall possibility of hydroformable rear sub-frame parts could be examined by cross sectional analyses. Moreover, it is essential to ensure the formability of tube material on every forming step such as pre-bending and hydroforming. In addition, all the components of prototyping tool are designed and interference with press is examined from the point of geometry and thinning.

• 제어로봇시스템학회:학술대회논문집
• /
• 1989.10a
• /
• pp.302-307
• /
• 1989

A pressure tracking control of hydroforming process is considered in this paper. To account for nonlinearities and uncertainties of the process, an iterative learning control scheme is proposed using Cerebellar Model Arithmatic Computer (CMAC). The experimental result shows that the proposed learning control is superior to any fixed gain controller in the sense that it enables the system to do the same work more effectively as the number of operation increases.

• Journal of Institute of Control, Robotics and Systems
• /
• v.6 no.3
• /
• pp.329-337
• /
• 2000

This study describes a pressure tracking control of hydroforming process which is used for precision forming of sheet metals. The hydroforming operation is performed in the high-pressure chamber strictly controlled by pressure control valve and by the upward motion of a punch moving at a constant speed, The pressure tracking control is very difficult to design and often does not guarantee satisfactory performances be-cause of the punch motion and the nonlinearities and uncertainties of the hydraulic components. To account for these nonlinearities and uncertainties of the process and iterative learning controller is proposed using Cerebellar Model Arithmetic Computer (CMAC). The experimental results show that the proposed learning control is superior to any fixed gain controller in the sense that it enables the system to do the same work more effectively as the number of operation increases. In addition reardless of the uncertainties and nonlinearities of the form-ing process dynamics it can be effectively applied with little a priori knowledge abuot the process.