Multi-material Fem Approach for the Prediction of the Behavior of Draw-bended Tubular Profiles

Rotary draw bending is the most spread among the industrial bending processes of profiles, due to its great versatility and reliability. When bending non-round profiles, the process often shows a behavior which is more difficult to predict than round tubes. This is due to several reasons: lack of knowledge and experience about less common geometries, the presence of corners and straight portions of the cross section, which make the tube stiffer, the inhomogeneous mechanical properties (thickness and strain hardening) of tubes around the cross section caused by the tube making process (roll forming and subsequent welding), etc. In this paper, an FEM model, which is able to take in account the differences in thickness distribution and in mechanical properties along the profile section, has been built and validated with the commercial code PAM-Tube. Then, a quantitative indicator of the process difficulty has been developed, which is able to represent, from a geometrical point of view, the degree of severity of process in terms of potential risk of shape degradation of the bent cross sections. Finally, a quality index, able to synthetically represent both the aesthetical and functional needs of the resulting cross section has been introduced and correlated to the process difficulty factor.