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Shrink flanging is a major sheet forming operation to produce convex flanges in structural sheet metal components. Flanges are used for appearance, rigidity, hidden joints, and strengthening of the edge of sheet parts such as automobile front fender and complex panels formed by stretch/draw forming. Wrinkling around the flange edge is the major defect in shrink flanging operation. There has been a lack of reliable mathematical modeling to predict the strains and wrinkles in shrink flanging operations. A trial-and-error approach has been usually practiced in tooling and process designs. In this paper, a wrinkling criterion in shrink flange is proposed based on a simplification from a general criterion for a doubly curved anisotropic shell. The mathematical model for strain analysis in shrink flanging is established based on Wang and Wenner's strain model for stretch flange. Shrink flanging experiments were conducted to validate the theories.