• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.50-53
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• 2001

Hydroforming process has become an effective manufacturing process because it can be adaptable to forming of complex structural components. Tube hydroforming has been successfully developed in the real industrial field by many researchers. However, there still remains the constraint about shape which can be manufactured by tube hydroforming. In order to improve this constraint of shape and formability of conventional sheet metal forming, hydroforming process of sheet metal pairs becomes an important technology. In the present work, the finite element analysis of hydroforming process of sheet metal pairs is presented. After basic study about experimental parameters based on numerical analysis, hydroforming process of sheet metal pairs is developed which uses hydraulic pressure as a main forming source.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.40-43
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• 2001

The use ef sheet material for the hydroforming of a closed hollow body out of two sheet metal blanks is a new class of hydroforming process. By using a three-dimensional finite element program, called HydroFORM-3D, the hydroforming process of sheet metal pairs is analyzed. Also the comparison of conventional deep-drawing and hydroforming process was conducted. The simulation has concentrated on the influences of the various forming conditions, such as the unwelded or welded sheet metal pairs and friction condition, on the hydroforming process. This computational approach can prevent time-consuming trial-and-error in designing the expensive die sets and hydroforming process of sheet metal pairs.

• Transactions of Materials Processing
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• v.12 no.8
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• pp.702-709
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• 2003

In the automotive industry hydroforming of sheet metal pairs have received special attention because materials for various sheet metal components of vehicles have changed into the high strength steel, aluminum, and titanium blank having low formability. Uniform deformation over the whole region is a main advantage in the sheet hydroforming process. Because upper and lower parts could be produced simultaneously with one tool, hydroforming of sheet metal pairs is competitive in reducing the lead-time and development cost. In this paper, the multi-stage hydroforming process of sheet pair is proposed in order to increase the formability of a structural part like the oil pan shape. The upper die for forming oil pan shape is divided into two parts which can move separately. By the finite element simulation, the design parameters such as geometry of the tool and detailed specification of hydraulic pump were calculated and verified. For the strict comparison of the proposed process, the blank holding force is kept to a constant value during deformation by hydraulic valve. The deformed shape and strain distribution of the manufactured parts with the proposed process are compared with the results of simulation. In the multi-stage hydroforming process, maximum thickness strain was improved by more than 30 percent.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.7-13
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• 1999

Hydroforming is the technology that utilizes hydraulic pressure to form sheet and tube metals in to desired shapes inside die cavities. It can be subdivided into tube hydroforming and sheet hydroforming according to the blanks used. In this paper the simulation of tube and welded blank hydroforming is carried out respectiyely. And simulation results are compared to evaluate formability in tube and welded blank hydroforming of engine mount bracket

• 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.

• Transactions of Materials Processing
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• v.10 no.1
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• pp.3-14
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• 2001

Hydroforming is the technology using hydraulic pressure and forming sheet or tube metals to desired shape in a die cavity. lt can be characterized as tube hydroforming and sheet hydroforming depending on the shape of used blank. Due to its prcess-related benefits, this production technology has been remarkably noticed for great potential for feasible applications and recently gained great attraction from many industrials including automotive and non-automotive. This Paper analyzed the tube and the welded blank hydroforming process and compared formability of the processes for automotive engine mount bracket. The mathematical analysis was performed by using the dynamic explicit finite element code, PAM-STAMP. In tube hydroforming, bending, springback, and forming analysis were carried out and the effect of mandrel and axial feeding were examined. In welded blank hydroforming, pressure curve history is determined and the results of forming analysis were evaluated by the comparison of experimental results in the aspects of deformed shape and thickness distribution.

• Transactions of Materials Processing
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• v.11 no.4
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• pp.295-301
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• 2002

Recently, design concepts of vehicle will have to consider the safty and economy of fuel consumtion. The hydroforming technology has applied to increase strength, and to decrease weight, cost and part count. The hydroforming has been recognized as general technique in automotive industry. This paper deals with the trends of automotive application of hydroforming, new hydroforming technologies, facilities.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.210-213
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• 2004

Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined internal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity fur anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy parameter, strain hardening exponent on bursting pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

• Transactions of Materials Processing
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• v.13 no.7
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• pp.629-634
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• 2004

Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined infernal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity for anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy Parameter, strain hardening exponent and strength coefficient on bursting Pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.229-232
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• 2003

In the roll forming process, a sheet or strip of metal is continuously and progressively formed into a desired cross-sectional profile by feeding it through a series of forming roll. Accordingly, it is important to maintain the material properties of the initial sheet and deform uniformly during the roll forming. The roll forming process was estimated in consideration of some factors such as material properties, strip thickness, roll diameter, roll velocity, and the deformation of the material that influence the forming length. The hydroforming technology has been recognized as a new technique in manufacturing industry, especially in automotive industry. The formed pipe in used in hydroforming process is manufactured by the roll forming. The formability during hydroforming is very sensitive to the state of pipes which are made by roll forming. Particularly the amount of hardening during roll forming affects the formability. Therefore, it is necessary to design the optimum roll flower to reduce the local hardening. In this paper, optimum roll flower which has uniform strain distribution through sheet width was obtained by comparing strain distribution in various roll flower. Finite element analysis(FEA) is performed to estimate the strain distribution related to hardening by roll forming. A numerical analysis is carried out by SHAPE-RF.