Measurement of Skid Line Formation and Formation Mechanism of Automotive Outer Panel

Abstract

Appearance of an automobile is one of the appealing points to customers. Character ridgelines in outer panels such as hood and door panels play an important role to make automobiles attractive, and a sharp character ridgeline which has a ridge of a small curvature radius is much more preferred to a blunt character ridgeline. However, a skid line, a kind of appearance defect, is apt to generate along the character ridgeline in press forming of a sharp character ridgeline. 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 draw forming experiment using a newly devised die which can measure a panel shape at any time during press forming. The mechanism of skid line formation was clarified by experimental results. The results of the shape measurement suggest that the ridge shape in a panel formed on the punch ridge should move to a flat area of the punch. A wavy shape should be generated there immediately before the ridge shape is flattened at the bottom dead center of the die. Then the wavy shape should grow to a skid line through springback.