FE Simulation And Experimental Research On The Push-bending Technology Of Stainless-steel Tubes

As a typical kind of lightweight components and structures of bearing parts, bending tubes are widely used in aerospace, construction, transportation, medical and other fields. Among them, the large diameter stainless steel elbow occupies an important position in the oil nuclear power plants and other strategic facilities. The method of cold push-bending forming in a mold can effectively improve the forming quality of large diameter stainless steel elbow. Meanwhile very few reports on the push-bending have been published. The research of the cold push-bending forming regularity of stainless steel tube can effectively shorten the processing cycle and production cost, which has important engineering significance in the selection of practical machining and mold manufacturing.This paper is based on numerical simulation and combined with the experiment, in which a comprehensive analysis of the characteristics of tube cold push-bending forming in a mold and the effects of different process parameters on the forming quality of different size of tubes are discussed. The finite element models was established based on the commercial software MSC.MARC. The main research contents and results are as follows:By using the elastic-plastic finite element method, selecting the solid shell 185 unit and defining the thickness direction of each element, the finite element model is established in accordance with the actual process of push-bending after the reasonable definition of the friction model, contact tables, boundary conditions, loading and unloading process.Through the finite element analysis of the large diameter steel tube push-bending process, the distribution of Von Mises stress and strain during the process of push-bending and unloading are obtained. Moreover, the effects of different technological parameters on the distribution of Von Mises stress、 strain and the forming quality are obtained. The results show that the maximum residual stress concentrates in the middle of tube, the maximum residual strain on both internal and external side increases firstly and then decreases. After push-bending, the interior wall thickness increases while the exterior wall thickness decreases. When the relative bending radius is bigger, the more springback, smaller ovality of section and smaller variation of wall thickness are obtained. With the increase of friction coefficient, the ovality of cross section and the wall thickness thinning rate decrease. With the increase of pushing speed, the ovality and the wall thickness thinning rate decrease while the thickening rate increases.The cold bending characteristics of different size of tubes are studied comparatively. The influence of technological parameters on push-bending quality of different size of tubes is explored. Moreover,304 stainless steel tube is chosen for experimental verification after the design of push-bending die. The experimental results show that the exterior wall thickness of the push bending tube has the maximum difference of 1.62% compared to the simulation results, while the interior is 3.28%. The change regulation of the detection residual stress value in the direction of tube outward deforming is consistent with the simulation result and the tube grain orientation changes in the process of push bending.