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Park J.K.,Hwashin Co. | Kim Y.S.,Kyungpook National University | Seo O.S.,Kangwon National University | Lee M.G.,Pohang University of Science and Technology | Kim H.Y.,Kangwon National University
International Journal of Automotive Technology | Year: 2013

There are two types of hot-stamping processes, direct and indirect, depending on the sequence of the heating, forming, and quenching steps and the method used for each step. In this study, an indirect hot-stamping process consisting of forming at room temperature, heating, and water quenching was applied to develop a coupled torsion beam axle. The analysis results indicated that the application of the heat convection coefficient is critical in the simulations and must take into account the temperature and specific location in the model to ensure the accuracy of the heating and quenching analysis. The heat convection coefficients used in the analysis were directly measured at various positions of the tube (e.g., outside, inside, and bending region) using thermocouples, and the final values were determined through correlation between the actual tests and numerical analysis. The experimental and simulated final deformed shape and temperature distribution were in good agreement. © 2013 The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.

Kim D.-Y.,Kangwon National University | Park H.-S.,Hwashin Co. | Kim W.-K.,Sae Han Micro Technology Co. | Pyo C.-R.,Induk University | Kim H.Y.,Kangwon National University
Transactions of the Korean Society of Mechanical Engineers, A | Year: 2012

Recently, multi-functionalization (as in smart phones) has been in demand, and the connectors connecting the electrical signals of each board in a cellular phone have become key components. The miniaturization of these connectors is required to achieve a finer pitch design and enhance the electrical signal transfer capacity. However, the miniaturization of connectors reduces the structural safety, and a finer pitch design may cause contact problems under external impact In this paper, a preliminary design for miniaturized, finer-pitch connectors is suggested for a product with 50 pins and a thickness of 0.2 mm. The assembly process of the FPCB (Flexible Printed Circuit Board) and connector was simulated to ensure the holding force between the two components and avoid overstressing. The design optimization process was performed with the Taguchi method. Fatigue analysis was also conducted to predict the fatigue life of the terminal, and the theoretical and experimental results were compared. © 2012 The Korean Society of Mechanical Engineers.

Suh C.H.,Daegu Mechatronics and Materials Institute | Park M.K.,Korea Advanced Institute of Science and Technology | Park J.K.,Hwashin Co. | Kim Y.S.,Kyungpook National University
Transactions of the Korean Society of Mechanical Engineers, A | Year: 2013

Hot forming using boron steel is currently used for manufacturing low-weight automobile body parts, and a high tensile strength of about 1,500 MPa is obtained after hot forming. However, a high fatigue life is a more important factor than high strength when it is used for automobile suspension parts. A tubular torsion beam axle (TTBA) is one of these suspension parts, and this research deals with the fatigue characteristic of TTBA using hot forming. The low cyclic fatigue life of boron steel is investigated according to the cooling method. In addition, a structural and fatigue analysis of TTBA is performed to predict the fatigue life. The stress concentration that occurs in the tubular torsion beam is found, and the longest fatigue life occurs when rapid cooling is utilized in the TTBA fabrication. © 2013 The Korean Society of Mechanical Engineers.

Seo O.S.,Kangwon National University | Yoon S.J.,Hwashin Co. | Suh C.H.,Korea Institute of Machinery and Materials | Kim H.Y.,Kangwon National University
AIP Conference Proceedings | Year: 2010

A hot press forming process consists of forming at the elevated temperature and rapid quenching, which induces phase transformation and results in the press hardening of steel parts. In this study, the hot press forming process of boron steel tube was analyzed by applying different heat transfer coefficients which had been experimentally measured and numerically backward traced. © 2010 American Institute of Physics.

Kim H.Y.,Kangwon National University | Park J.K.,Hwashin Co. | Lee M.-G.,Pohang University of Science and Technology
International Journal of Advanced Manufacturing Technology | Year: 2014

In this paper, a new tool design for hot stamping taking advantage of both direct quenching and indirect die quenching is proposed to fabricate the coupled torsion beam axle which is formed from the original tubular-shaped part. This newly proposed hot stamping applies spray of the water before the upper die gets into contact with the tubular part, which significantly enhances the cooling capacity. For other region that cannot be covered by the direct spray, the conventional die quenching method in direct hot stamping process is used. Moreover, for the analysis of the deformation behavior during the proposed hot stamping process, the finite element analysis, which takes the deformation and strengthening induced by the cooling and phase transformation into account, has been carried out. From the analysis, the larger shape change when the cooling time is shorter than 15 s could be explained by the incomplete martensitic phase transformation and phase transformation plastic strain. When the cooling time is short the residual stress after cooling is much higher than those for the longer cooling times. © 2013 Springer-Verlag London.

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