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Description
Appearance of an automobile is one of the appealing points to customers. Character lines in outer panels such as hood and door panels play an important role to make automobiles attractive, and a sharp character line which has a ridge of small curvature radius is much more preferred to a blunt character line. However, a skid line, a kind of appearance defect, is apt to generate along the character line in press forming of a sharp character line. Although it is well-known that skid lines are caused by inhomogeneous tension, the mechanism of skid line generation was not yet fully understood. In this study, the skid line defect is quantitatively evaluated by a draw forming experiment using a newly devised die which can continuously measure a panel shape during press forming. The mechanism of skid line formation was clarified by the experimental results. The results of the shape measurement suggest that a convex shape formed on the die ridge should move to a flat area of the die. A wavy shape should be generated there immediately before the convex shape is flattened at the bottom dead center of the die. Then the wavy shape should grow to a skid line through springback.