Further study on strain hardening of a steel panel in the hemming process

ABSTRACT

An experimental study on steel panel bending is conducted to clarify the mechanism of strain hardening of the panel during flanging, pre-hemming and hemming processes in the production of automotive door panels and other types of panels. A planar straight-edge-shaped hot-dip-galvanised steel sheet panel is set and pressed in prototype equipment. The experimental process consists of the first flanging to 90°, the second pre-hemming to each angle of 15°, 30°, 45°, 60° and 75°, and the final hemming. Time-lapse images captured from a video of the processes, the geometry of the pre-hemmed and hemmed flanges, and the microVickers hardness distribution of the lateral surface of the panel are measured. A detailed examination of the obtained results clearly indicates new findings that each flange pre-hemmed to different angle of 15° and 75° gave excellent geometry with small creepage and quality of the final hemmed flanges, owing to remarkable strain-hardening of each flange corner. On the other hand, a pre-hemming to each angle of 30°, 45° and 60° gave a geometry with large creepage due to loose flange corner bending.

KEYWORDS:

• Hemming
• bending
• strain hardening
• MicroVickers
• geometry

Acknowledgments

We thank Edanz Group (https://www.jp.edanz.com/ac) for editing a draft of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).