1. J.P. Hong, H.Y. Kim, S.I. Oh, Korean Soc. Automotive Eng. (1996) 68.
2. K. Azuma, K. Ikemoto, K. Arima, H. Suriura, T. Takasago, International Deep Drawing Research Group, 1990, p. 305.
3. N. Iwata, M. Matsui, N. Nakagawa, S. Ikura, NUMISHEET’93 (1993) 303.
4. F.I. Saunders, R.H. Wagoner, NUMIFORM (1995) 157.