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Formability evaluation of dimple forming process based on numerical and experimental approach

Seong-Chan Heo, Young-Ho Seo, Tae-Wan Ku, Beom-Soo Kang*
The Journal of Mechanical Science and Technology, vol. 25, no. 2, pp.429-439, 2011

Abstract : Exhaust gas recirculation (EGR) cooler consists of a number of heat transfer tubes that have relatively larger net area than that of flat type tubes. The surface of the tubes is made up with lots of grooves and protrusions for enlarging the net heat transfer area. Most tubes are manufactured through forming processes, such as bending, spinning, roll forming, stamping and so on. Therefore, a series of fracture or defect can occur during the various forming processes. In this study, the manufacturing process of a dimple-type rectangular heat transfer tube used for an EGR cooler system is investigated based on the numerical simulation and the experimental approach. A prototype of the tube is designed and modified to a newly designed tube considering the conservation of the net heat transfer area based on the numerical and analytical approach. Formability evaluation of the tube sheet is carried out by using forming limit curves based on the plastic instability conditions. Strain- and stress-based forming limit curves are utilized to ensure the strain path independence. The newly designed tube having a number of dimples on the both sides are manufactured by the press forming process. Thickness distributions for the principal cross-sections are observed from both the simulation and the experiment and compared each other. From the results, it is confirmed that the forming process is robust to manufacture the dimple type rectangular tubes with the comparison of thickness, and application of the forming limit curves.

Keyword : EGR cooler; Dimple forming; Formability evaluation; Forming limit curves; Finite element analysis

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