Springback Mechanism In The Process Of Large Curvature No Mandrel Bending Of Tubes

Large curvature no-mandrel bending pipe has been widely used in aerospace and other fields for its diverse functions and saving assembly space.Although many experts and scholars at home and abroad have done a lot of research on bending of 0Cr18Ni9 stainless steel pipe,relatively few researches have been made on the springback of large curvature non-core bending(i.e.relative bending radius R / D = 1.5,in which R and D are bending radius and outer diameter of pipe respectively).Therefore,in this paper,the elastic-plastic theory,finite element numerical simulation and experimental methods are used to study the bending springback law of 0Cr18Ni9 stainless steel fittings in detail.The main research contents and achievements are as follows:(1)the springback deformation mechanism of large curvature non-core bending process is studied.Firstly,the constitutive model and yield criterion of tube material are established by uniaxial tensile test,secondly,the bending deformation model of non-core bending pipe with large curvature is obtained through the study of stress-strain in the inner and outer parts of the tube bending.Finally,on the basis of elasto-plastic deformation model,the elastic complex algorithm for large curvature non-core bending process is obtained,and the formula for calculating the springback angle is derived.(2)the finite element simulation of large curvature non-core bending and springback of pipe is carried out by ABAQUS software platform,and its bending model and springback model are established,and the different bending angle,wall thickness and bending speed of pipe are analyzed.The effect of die /pipe friction coefficient and die / pipe clearance on rebound angle.Their trends are analyzed,and the reasons for these trends are explained.The stress-strain of them before and after springback is analyzed.(3)the bending experiment of large curvature and non-coreless pipe was carried out by NC C-type pipe bending machine.The effects of different bending angles,tube wall thickness,bending velocity and die / pipe friction coefficient on rebound angle were analyzed.The method of measuring the rebound angle of pipe is established.(4)the rebound angles of different process parameters in theory,finite element simulation and experiment are compared,their trends are studied,and the causes of these trends are analyzed.At the same time,the causes of errors among them are explained.