Developing a new wrinkling testing method for sheet metal spinning

Wrinkling is a common process failure in spinning; there are no established testing methods to obtain strain limits to predict and prevent wrinkling. Mechanisms of wrinkling initiation and growth as well as associated strain conditions and their limits are unclear. This study firstly investigates strain variations under different process conditions by developing finite element (FE) simulation and experiment of a shear spinning process. A new wrinkling testing method is developed and it is capable of applying in-plane biaxial compression and out-of-plane bending to represent wrinkling conditions in spinning. By evaluating strain increments of the un-supported flange and constructing strain diagrams representing the strain evolution during spinning, new insights into strain limits, wrinkling initiation and growth are attained. It is observed when the circumferential strain of the top surface of the un-supported flange cyclically increases to become and remain tensile, wrinkling initiates. The wrinkling initiation is a consequence of a rapid accumulation of the circumferential strain of the un-supported flange under cyclic loading induced by the roller, when the roller feed per mandrel revolution exceeds a limit. Subsequent roller feeding to the edge of the flange and wrinkling growth on the flange cause continued increases of the circumferential strain leading to the final wrinkling failure in spinning. The newly developed wrinkling test method has achieved wrinkling initiation and strain conditions similar to that observed in the early stage of the spinning process, which could be used as a guide to support the determination of the key process parameters for wrinkling-free spinning.