Improvement in Flaring Limit of Thin-Walled Circular Tubes Using Precurling Method.

Abstract

Most flaring limits of thin-walled circular tubes are determined by the onset of rupture. In this study, the flaring of thin-walled tubes using a precurling method has been proposed and experimentally investigated to improve the flaring limit of the tubes. In this method, a tube end is curled with a conical and/or quarter-circle die during the first operation, after which the precurled tube end is flared with a conical die in the second operation. The second operation closes up the curl, and then the curl forms a hem. During hemming, since the tube end has an inverse strain gradient compared with the strain gradient in the conventional flaring process, ductility of the tube end is thought to increase. Influence of precurling conditions and other experimental conditions on the flaring limit of precurled tubes is examined using aluminum and aluminum alloy tubes. It is found that the proposed method is superior to the conventional flaring method, with respect to the flaring limit. Furthermore, it is also found that the flaring limit increases with increasing size of the precurl and/or the hem due to the improvement in ductility of the tube end. Therefore, the proposed method will be useful for the improvement of the flaring limit of tubes.