Investigation on the influence of mandrel on the forming quality of thin-walled tube during free bending process

Abstract The forming defects such as the cross-sectional distortion and axial instability often occur during the free bending process of thin-walled tube. To eliminate or suppress the above-mentioned forming defects, the method of inserting the mandrel inside tube was employed in this paper. First, the principle of free bending with mandrel was theoretically deduced, which was used to explain the mechanism of the supporting force provided by the mandrel on the deformation behavior of tube. Then the influence of the mandrel position, the number of core balls in mandrel and the clearance between the mandrel and tube on the free bending forming quality of thin-walled tube was analyzed and summarized by the numerical simulation method. Finally, the free bending experiment of thin-walled tube with optimized mandrel parameters was conducted to verify the reliability of the numerical simulation method and the rationality of the mandrel parameters. All of these findings advance the insight into the deformation behavior of thin-walled tube influenced by mandrel and help to improve the forming quality of thin-walled tube and facilitate the application of free bending technology in thin-walled tube.