1. New Forming Lab, KITECH, Songdo-dong, Yunseo-gu, Incheon, 406-840, Korea
2. Dept. of Mechanical Engineering, Inha Univ., Yonghyun-dong, Nam-gu, Incheon, 402-751, Korea
3. School of Mechanical & Automotive Engineering, Kookmin Univ., 861-1 Jungnung-dong, Sungbuk-gu, Seoul, 136-702, Korea