Papers by Author: Dong Won Jung

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Authors: Dong Won Jung
Abstract: Roll forming is a continuous profile production process to form sheet metal progressively into the desired shape with closer tolerances. The process offers several advantages such as complex geometrical shapes, high strength, dimensional accuracy, closer tolerances, better quality and consistency, high production rate, improved conformity, and good surface finish. Several parts of automobile body are produced with this process. Nowadays roll forming technology draws more attentions than before in the automotive industry. In this paper, A Finite Element Method applied to study von mises stress, equivalent plastic strain, thickness, plastic strain, longitudinal strain and spring back of the metal sheet with ribs formed by roll forming process. The thickness variation was almost -6.144%.
Authors: Xue Wen Chen, Dong Won Jung, Ai Xue Sun
Abstract: Technology and die design are very important in the development of forging products due to its great influence on the quality, cost and manufacturing efficiency of the final products as well as the life of the forging die. In the environment of the severe competition, how to improve the quality of forging technology and die design, to reduce the product cost and ultimately to enhance competitiveness of the forging factory are the problems that forging technology and die designer have to solve. In order to improve the quality of forging technology and die design, a design optimization method based on approximate model (response surface model) and FEM technique for hot forging process is proposed in this paper. During design optimization process, finite element analysis is incorporated to calculate the objective function and check the design alternatives. Design of experiment (DOE) method is used to collect sample points and calculate the polynomial coefficients of response surface model, and approximate model is used to calculate the optimum search direction. Finally, a case study is conducted for a gear workpiece hot forging process. The objective function is the degree of uniformity of equivalent-strain, which can be defined as mean square deviation of the equivalent-strain in each element and the average equivalent-strain of all elements, and the design parameters are the initial H0/D0 ratio of billet and the key dimensions of the die. Then the design optimization mathematical model is established. The result shows that the objective function value is dropped from 0.7914 and converges at 0.4843 within 17 iterations, the optimal design parameters are obtained.
Authors: Xue Wen Chen, Jun Wei Zhao, Dong Won Jung
Abstract: Flanging is a method of sheet metal forming process under combined compressive and tensile conditions using a punch and die to raise closed rims (flanges or collars) on pierced holes. For the flanging product used for the automotive steering part, the thickness of the bottom radius area is very important because of the crack usually occurred during the using process. But during conventional flanging process, the thickness of the rim and the bottom radius area were decreased seriously and make the hole flanging not strong enough to be used. In order to increase the thickness of bottom radius area of the flanging wall, a new method that combines flanging process and cold forging process was proposed in this paper and a special forming die set was designed with a stripper subjected to counter-pressure with an aim to obtain a more substantial flange. FEM software DEFORM 3D was employed to simulate these flanging part forming processes. The results showed the thickness of bottom radius area of the flanging wall was increased and a more substantial flange was obtained.
Authors: A.J. Jithin, Dong Won Jung, Radha R. Lakshmi, V.R. Sanal Kumar
Abstract: A brief review of the mechanical characterization of viscoelastic materials under uniaxial, biaxial and multiaxial stress condition is carried out in this paper. Parametric analytical studies have been done in a simulated tubular specimen with different internal pressure loadings at various material properties. We observed that the relaxation modulus values obtained from the thick-walled hollow cylinder analyses are higher that the traditional uniaxial and biaxial test data under the same strain level. We noticed that during the initial period, the relaxation-modulus values are almost identical and later the relaxation modulus obtained from the thick-walled hollow cylinder analysis is found significantly higher than the uniaxial and the strip biaxial test data. We conjectured that in the initial stage the stress–strain ratios are almost independent of the geometry of the test specimen and subsequently the stress conditions vary according to the shape of the specimen because the relaxation modulus is found geometry dependent when loading time advances. Note that the main objective of this characterization is not to determine the magnitude of the stress actually present in the test specimen, but to help the designer to decide the best geometry in a realistic way according to the industrial applications from the viscoelastic stress relaxation point of view.
Authors: Roya Darabi, Hamed Deilami Azodi, Dong Won Jung
Abstract: The bi-layer materials have been used widely during past decades due to their specific characteristics like lighter weight, more corrosion resistance, and insulation features in comparison with mono-layers which consisting them. In this research the aim is achieving to best combination of bi-layer material (Al3105-St14) to satisfy two objectives of weight and formability while it has a constant total thickness. The represent the formability objective and is derived from M-K model associated with Barlat-Lian yield criteria. Another objective is weight of per unit area. The data of experiments are designed based on full factorial method and the surfaces are best polynomial which can fit the variables and objectives. The MATLAB software and the genetic algorithm (GA) are used to generate feasible combination of thickness to provide to minimize the weight and maximize the formability. The Pareto frontier is utilized to satisfy two objective functions simultaneously. The best answer is selected with norm approaching and minimum distance method.
Authors: Dong Won Jung
Abstract: The roll forming is one of the simplest manufacturing processes for meeting the continued needs of various industries. The roll forming is increasingly used in the automotive industry to form High Strength Steel (HSS) and Advanced High Strength Steel (AHSS) for making structural components. In order to reduce the thinning of the sheet product, traditionally the roll forming has been suggested instead of the stamping process. The increased product performance, higher quality, and the lowest cost with other advantages have made roll forming processes suitable to form any shapes in the sheets. In this numerical study, a Finite Element Method is applied to estimate the stress, strain and the thickness distribution in the metal sheet with quadrilateral shape, ribs formed by the 11 steps roll forming processes using a validated model. The metal sheet of size 1,000 × 662 × 1.6 mm taken from SGHS steel was used to form the quadrilateral shape ribs on it by the roll forming process. The simulation results of the 11 step roll forming show that the stress distribution was almost uniform and the strain distribution was concentrated on the ribs. The maximum thinning strain was observed in the order of 15.5 % in the middle rib region possibly due to the least degree of freedom of the material.
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