ENERGY ABSORBING MEMBER, METHOD FOR PRODUCING SAME, AND ELECTROMAGNETIC TUBE EXPANSION METHOD FOR RECTANGULAR CROSS-SECTION MEMBER AND POLYGON CROSS-SECTION MEMBER

摘要

In the present invention, when producing a bumper stay by expanding the end of a stay starting material comprising a tubular aluminum alloy extruded material by means of electromagnetic forming, thus forming a flange section, flange width can be increased without cracks arising or a thickness reduction arising. A stay starting material (7) is used having a peripheral wall (8) corrugated in a wavy shape along the peripheral direction thereof. The circumference (L) (length extending one circuit along the wavy corrugation) of the perimeter of the peripheral wall in the peripheral direction of the stay starting material (7) is longer than the circumference (L0) of a simple cylindrical peripheral wall having the same outer diameter (diameter of the smallest circumscribed circle (9)) (L > L0). L - L0 is considered the surplus length. By means of the peripheral wall (8) of the stay starting material (7) having the surplus length, when forming a flange section by expanding the end of the peripheral wall (8), it is possible to form a flange section having a large diameter.