Twist Resulting in High Strength Steel Sheet Hat Channel Product Consisting of Straight Portion Combined with Curved Portion



This paper deals with a complex-shaped hat channel product, which combines a straight part with a curved part in the longitudinal direction. Twist in the longitudinal direction is the most typical and serious of all dimensional inaccuracies in the product. Influencing factors in twisting can be classified into in-plane residual stress and residual moment. At first, by varying forming conditions such as the blank holding force and the cushion force, the influence of the in-plane residual stress on twist of the shrink and the stretch flange are investigated. Contrary to expectation, the in-plane residual stress had almost no relation to twist. Subsequently, by slitting the flanges and the side wall to release the residual moment, the influence of the residual moment on twist was investigated. It was observed that the residual moment plays an important role on twist. Based on the above, certain regions of the die radius are varied to control residual moment. As a result, the twist was decreased experimentally.


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