Boss forming of annular flanges in thin-walled tubes

This paper introduces a new boss forming process for producing annular flanges in thin-walled tubes by partial compression of the tube wall thickness along the longitudinal direction. The presentation combines experimentation and finite element modelling and uses different arrangements of process variables for characterizing typical failures and defects, for understanding the mechanics of material pile-up and for determining the overall force requirements. The new boss forming process results from improving a solution previously developed by the authors through the use of a die cavity and the change of kinematics to allow the upper and lower dies to move together. Results show that the direct dependency between the height and the radius of the annular flanges that is typical of boss forming can be effectively eliminated in order to produce sound annular flanges with custom geometries and sizes in thin-walled tubes.