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Technology to Enhance Deep-drawability by Strain Dispersion Using Stress Relaxation Phenomenon

Article of Honda R&D Technical Review Vol.24 No.1

Summary

When the introduction of strain is temporarily stopped during tensile testing of a metal, a stress relaxation phenomenon is known to occur whereby the stress diminishes with the passage of time. This phenomenon has been explained as the change of elastic strain into plastic strain.
The present report suggests the application of the stress relaxation phenomenon to stamping for the purpose of strain dispersion. A new step motion that pauses the die during forming was devised and succeeded in modifying the deep-draw forming limit.
Verification was conducted by tensile testing in addition to actual stamping tests. As a result, it was concluded that the mechanism that modifies the deep-draw forming limit arises from the use of step motion for the dispersion of strain, and this was also confirmed to be dependent on the stop time and the temperature.

Reference

(1) Azuma, Y., Nakagawa, H.: Sustainable na Zidousya Zairyou Gizyutsu, Forum Text, No. 11 FORUM-9, JSAE (2011) (in Japanese)
(2) Tamai, Y., Yamasaki, Y., Yoshitake, A., Imura. T.: Technology of improving press formability applying press motion control - Advanced multi-stage forming with servo press -, Proc.IDDRG2006, p.403-408 (2006)
(3) ASTM E328-02, Standard test methods for stress relaxation for materials and structures
(4) Tagawa, T., Haramishi, Y., Minami, F.: Stress Relaxation Behavior of Low Carbon Structural Steels, Quarterly Journal of the Japan Welding Society, Vol. 29, No. 1, p. 48-54 (2011)
(5) The Japan Institute of Metals, Zairyou Kyoudo no Genshiron, Maruzen Publishing, p. 71 (1985) (in Japanese)
(6) Minier, C., Lauzier, J.: Proc. of Yamada Conf., Point Defects and Defects Interactions in Metals, Kyoto, (1981), Univ. Tokyo Press, Tokyo, p.749 (1982)
(7) The Japan Iron and Steel Federation: Hot-dip galvannealed steel sheet and strip for automobile use, JFS A 3011 (2008)
(8) JIS Z 2201, Test pieces for tensile test for metallic materials

Author (organization or company)

Hiroyuki YAMASHITA(Automobile R&D Center)、Hiroaki UENO(Automobile R&D Center)、Hiroyuki NAKAI(Automobile R&D Center)、Takahiro HIGAKI(Automobile R&D Center)

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