Theoretical Study And Model Construction Of JCO Continuous Bending Of Stainless Steel Thick Wall Pipe

With the rapid development of China’s economy,the demand for oil and gas energy in China is increasing,forcing the oil and gas transportation pipeline industry to continuously innovate.The JCO multi pass bending forming method has the characteristics of a wide range of product specifications,high reliability,and small forming,making it particularly suitable for preparing ultra long thick walled pipes.However,this process involves multiple bending processes and low dimensional accuracy of the product,making it difficult to meet the stringent requirements of the oil and gas energy pipe industry.In view of this,this article is based on elastic-plastic deformation theory and delamination theory to study the forming accuracy of 316 L austenitic stainlesssteel sheet during single pass bending process.A bending rebound model and a stress/strain neutral layer offset model within a certain thickness range are constructed,and key parameters affecting the forming quality are obtained.By simulating the bending process of 316 L stainless steel plates with different plate thicknesses using finite element ANSYS,the influence of key forming parameters on the unloading rebound,stress strain neutral layer offset,and plate thickness variation during plate bending was studied.The rebound amount of the plate was linearly related to the upper and lower die pressing amount and the lower die opening amount,and exponentially related to the upper and lower die descending speed and friction coefficient;The offset of stress neutral layer increases in quadratic function with the decrease of diameter thickness ratio;There is a linear relationship with the thickness of the plate,and the displacement of the stress neutral layer is slightly greater than that of the strain neutral layer;The thickness of the plate varies linearly with the bending angle,and the thinning rate increases as the diameter to thickness ratio decreases and the bending angle increases.Finally,bending tests were conducted on a three-point bending machine to test the bending rebound,residual stress,and thickness changes of three different specifications of plates.The theoretical model was optimized to achieve accurate prediction of rebound,neutral layer offset,and plate thickness changes.Based on the Mises yield criterion and Chaboche nonlinear hardening model,finite element simulation and experimental research were conducted on the 12-pass cold bending forming process of JCO,with a focus on analyzing the distribution of residual stress and the influence of the Bauschinger effect during the multi pass bending process.The results indicate that the Bauschinger effect of the sheet metal changes in a sine function with pre strain.According to the change of tangential stress inside the sheet metal,the maximum Bauschinger effect size of each pass of sheet metal JCO forming is obtained.This article provides a theoretical basis for achieving precision forming,mold optimization design,and precise selection of sheet metal for stainless-steel thick walled pipes through theoretical,simulation,and experimental verification.