Investigation of tube fracture in the rotary draw bending process using experimental and numerical methods

The quality of tubes obtained by rotary draw bending (RDB) depends on many process parameters whose selection is essential to prevent defects such as fracture, wrinkling, springback and lack of tube’s ovality. Whereas the finite element method (FEM) is a useful method for defects detection in the metal forming processes, the Gurson-Tvergaard Needleman (GTN) damage model is used in the numerical simulation of RDB for fracture prediction of BS 3059 steel tube. The numerical results were verified with the experimental ones for thickness distribution in the tube outer wall and also fracture prediction. The effect of some RDB parameters such as pressure of pressure die, boosting velocity of pressure die, friction between the tube and pressure die, mandrel position and number of mandrel balls were studied on the fracture, wrinkling and tube’s ovality. The results showed that using a low value for the boosting velocity of pressure die caused the tube fracture and using the high value for that increased the wrinkling possibility of the tube inner wall. The results indicated that the fracture possibility increased by increasing the number of mandrel balls and decreaseing the distance between the mandrel position and the bending center. The tube’s ovality will be increased by decreasing the number of mandrel balls and increasing distance between the mandrel position and the bending center.