Abstract
The tube numerical control (NC) bending process is a much complex physical process with multifactors coupling interactive effects. The mandrel is the key to improve forming quality and to enhance forming limit. In this study, based on the platform of ABAQUS/Explicit, a 3D elastic-plastic finite element model of NC bending process of 2169 (0Cr21Ni6Mn9N) stainless steel tube was established, key technological problems were solved, and its reliability was validated. Then, simulation and analysis of the processes were carried out, and the influence laws of mandrel types and mandrel parameters on cross-section quality were obtained. The results show that the wall thinning or cross section deformation is serious at the middle part and small in the vicinity of the bending plane or initial bending plane; the wall thinning degree increases or the cross section deformation degree decreases with the increase of mandrel diameter or mandrel extension length; the effect of bulb mandrel on the cross section quality is more significant than that of cylinder mandrel. And the reasonable mandrel types and mandrel parameters are chosen for the 2169 high-pressure hydraulic tube with small diameter. The results may lead to better understanding of mandrel role in the improvement of forming quality and forming limit in the NC bending process.
Highlights
Tube bending parts have many desirable features, such as reducing the weight, strengthening the structure, and absorbing the impact energy and shock
In the numerical control (NC) bending process of stainless steel 2169 tube with small diameter, the tube is subjected to tension stress on extrados, compression stress on intrados, and compression stress in the radial direction, respectively, so that there is thinning or even cracking on extrados and thickening or even wrinkling on intrados
Cracking and wrinkling can be avoided, but the wall thinning and the cross section deformation are inevitable. Both the cracking and wrinkling should be avoided firstly; the wall thinning and the cross section deformation should be controlled to some acceptable extent in the NC bending process
Summary
Tube bending parts have many desirable features, such as reducing the weight, strengthening the structure, and absorbing the impact energy and shock. The research on the effect of mandrel on cross section quality is of great significance in the tube NC bending process. Wang and Agarwal [7] predicted the cross section deformation and wall thickness change of tubes in bending process under axial force and internal pressure. Using the above formulas, it is difficult to find the characteristics in wall thickness change and cross section deformation of tube NC bending process. Though the above researches mainly focus on the effect of process parameters and geometric parameters on forming quality of thin-walled tube NC bending, and study on the effect of mandrel on cross section quality is still scant [9, 13, 17], they could provide a reference for relevant investigation of stainless steel 2169 small diameter tube NC bending. The achievements of this study are useful to select reasonable mandrel types and parameters in the process, and the method of numerical simulation can be used to study the influences of other parameters on the forming quality and forming limit of tube NC bending process
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