Analysis And Experiment On Cross-sectional Flattening Of Thin-walled Tube During Pressure Straightening

Pressure straightening is the key process to ensure straightness of metal tube.The cross-sectional flattening deformation of thin-walled tube usually occurs in the pressure straightening,which destroys roundness and reduces the quality of straightening.This paper firstly analyzes the stress-strain evolution of the cross section of workpiece and explores the mechanism of the cross-sectional flattening deformation of thin-walled tube during the pressure straightening process.Then,the deflection prediction model considering the cross-sectional flattening of thin-walled tube is established through the analysis of axial deformation.Meanwhile,using split-step straightening method to optimize straightening process and reduce the effect of pressure straightening of thin-walled tube on circularity of section.Finally,simulation and experiment of the pressure straightening process are carried out.The main contents are as follows:(1)For the cross-sectional flattening deformation of thin-walled tube,according to the thin shell theory and the energy theory,the mechanical deformation mechanism of thin-walled cross-sectional flattening with an elastic-linear kinematic hardening material model in the process of straightening are analyzed,the relation model between section flattening of straightening process and straightening stroke are established.The results show that cross-sectional flattening rate of thin-walled tube is nonlinear increase with the increase of loading deflection.(2)For the thin-walled tube pressure straightening process,through the analysis of stress and strain,curvature and bending moment,the prediction model of straightening stroke is established,which considering the deformation of the thin-walled tube section flattening.In addition,this paper adopts split-step straightening method to reduce the residual cross-sectional flattening of thin-walled tube pressure straightening process.The residual stress distribution of the workpiece using split-step straightening method is analyzed.(3)By discrete numerical simulation on the straightening process,the cross-sectional flattening prediction model and the stroke prediction model based on simulation are established.At the same time,the simulation of the step-by-step straightening process is carried out,which compared with the theoretical data to further verify the effectiveness of this method to reduce the cross sectional flattening.(4)Selecting the stainless steel thin-walled tube to conduct straightening experiment,and respectively using single step straightening and split-step straightening method which proposed in this paper to do straightening experiment.Through the comparison of experimental data with simulation and theoretical data,the validity of the model and the effectiveness of the split-step straightening method to reduce the deformation of the cross-sectional flattened are verified.