Research On Free Bending Process Of Aluminium Alloy Pipe 6061 And Springback Prediction

Metal pipes are the important components of structural load-bearing and conveying gas or liquid in the industrial field.However,the final forming profile obtained with the traditional bending process highly depends on the forming mould.Thus,it is difficult for wide promotion on the bent pipe with complex profile,especially for small batch production.To make up for the shortage of the traditional bending process,the free bending process is proposed.In this process,the multi-axis servo control technology is applied to metal pipe bending process The complex bending components are bent by adjusting the relative position of bending die through the multi-axis servo control technology.The development of free bending process will help to achieve high precision,high performance,high efficiency and digitization of the industrial production of the metal pipes.The researches on their theories and technologies have important guiding significance and application value in the industry field.In this study,the aluminum alloy pipe 6061 with the diameter of 30 mm and wall thickness of 2.0 mm is chosen.For the bending technology of spatial multiple degrees,the finite element simulation analysis of free bending process and the design and analysis of the free bending machine are carried out.In addition,the process parameters and springback of the bending process are analyzed systematically by combining with the finite element method and analytical method.In the aspect of the finite element simulation of the free bending process,the constitutive model of alloy pipe 6061 is established first.The cauchy stress,kinematic hardening,isotropic hardening and so on are considered in this model.The initial anisotropy in the yield criterion and the plastic potential is Hill48,and the improved Francois model is used to describe the induced anisotropy.After building the model,Newton-Raphson method is used to solve target variables.This model is compiled by Fortran,and it is used to simulation of the free bending process.The simulation is mainly about the influence of process parameters for free bending process,such as the distance between the fixed die and mobile die,the shape of the mobile die,the clearance of the mobile die and pipe,the frictional coefficient,and the feed speed of the pipe.And the optimal values of them are obtained by evaluating wrinkling,splitting and cross section distortion.In the aspect of springback prediction,based on static equilibrium,considering mdulus of elasticity,wall thickness and neutral layer,a springback prediction model is established by using Hooke's law and strain theory.To improve the prediction accuracy,springback prediction model is optimized by considering the axial force of the pusher.In the aspect of design and analysis of the structure,based on the principle of the free bending process,a free bending machine based on 3UPU parallel structure is proposed.Its found that the most important part of this machine is mobile die,is 3UPU parallel structure.Thus,based on the geometrical relationship and homogeneous transfer matrix,its kinematics model(inverse position model,inverse velocity model and inverse acceleration model)are analyzed.Its kinematics simulation is carried out by using ADAMS.And the simulation results and analysis results are compared to verify the correctness of above model.Besides,dynamic model is analyzed based on the principle of virtual work.And based on the limit boundary searching method,its workplace is obtained by MATLAB.Through the simulating optimization of the free bending process and the optimized analysis of the bending machine,the optimized process window and springback compensation plan of bending process are established.Finally,the pipe is precision forming.