A Study On Forming Limit Of 5A02 Aluminum Alloy Tube By Thermo-mechanical-elastomer Coupling Differential Temperature Push Bending

Thin-walled bending tube fittings are widely used in aerospace,shipbuilding,automobile,petroleum transportation and other fields because they can meet the requirements of lightweight,high strength,high precision and small space.With the rapid development of China’s industrial level,the quality and performance requirements of thin-walled bending tube are becoming higher and higher.The traditional cold processing forming method is limited in bending radius,and the forming process is prone to various defects.Therefore,the thermo-mechanical-elastomer coupling differential temperature push bending forming process is adopted in this paper.The forming limit of differential temperature push bending was studied by finite element simulation and experiment.The specific research contents and results are as follows:（1）Based on the plastic deformation theory,the differential temperature push bending process of thin-walled aluminum alloy tube was analyzed,and the force of the tube and the stress and strain state in the deformation zone were discussed.At the same time,the main defects of tube bending forming,such as outside crack,inside wrinkle and section distortion,are analyzed.The results show that the bending radius is a major parameter affecting the stress and strain,and the smaller the bending radius is,the larger the strain degree is.The smaller the bending radius,the more serious the thinning of the outer wall,the more serious the thickening of the inner wall and the greater the flatness of the section.（2）Using Abaqus finite element software as simulation platform,the finite element simulation model of thermo-mechanical-elastic coupling differential temperature push bending forming was established.The forming process of bending tube with diameter of 32mm,wall thickness of 1mm and bending radius of 0.9D was simulated and analyzed.The results show that the material flow can be improved by heating the outer side of the bending tube,and the thickness of the outer side of the bending tube can be reduced less,and the thickness distribution is more uniform,which is beneficial to improve the bending forming limit of the tube.As the filling medium,the supporting tube can fit well with the die,and effectively avoid the instability collapse of the tube in the process of bending forming.（3）The concept of forming limit of differential temperature push bending was put forward and the judging basis of forming limit was given.The effects of different process parameters on the forming limit of inner instability wrinkling,section distortion and outer thinning of bend were studied by finite element simulation.The results of the study on the forming limit of instability wrinkling show that:with the increase of temperature,the minimum bending radius R_minwill gradually decrease,that is,the forming limit increases,when the heating temperature is more than 350℃,the minimum bending radius does not change obviously;With the increase of diameter-thickness ratio D/T,the possibility of wrinkling increases and the forming limit decreases.When the friction coefficient between the inner deformation zone and the concave die increases,the possibility of wrinkling increases,which is not beneficial to the improvement of forming limit.When the friction coefficient between the outer deformation zone and the conduction zone and the concave die increases,the possibility of wrinkling of the tube blank decreases,which is beneficial to prevent wrinkling.The results of section distortion forming limit research show that:It is found that with the increase of tube diameter,the risk of cross-section distortion increases.The results of wall thinning forming limit research show that:with the increase of the wall thickness,the minimum bending radius decreases first and then increases.When the wall is thicker and the bending radius is small,the inner side of the bend will appear thickening and wrinkling.（4）On the basis of forming limit analysis,push bending experiments of 5A02thin-walled aluminum alloy tube with outer diameter（D=32mm）and wall thickness（t=1mm）with bending radius of 0.9D were carried out,and the effects of heating temperature,lubrication mode and thrust force on forming quality were studied.The results show that heating can improve the material flow during the bending process,and the plastic effect of the material is little improved when the heating temperature is low.With the increase of temperature,the material flow outside the bending process is faster,the wall thickness distribution is uniform,and the thinning is small.In the forming process,lubrication directly affects the flow of tube blank material.When the tube blank adopts uniform lubrication mode,the bend is prone to wrinkling,and the inner wall thickness changes greatly.When differential lubrication is adopted,the bend wrinkling can be effectively alleviated,and it is easy to control and the wall thickness distribution is uniform.Appropriate thrust is the key to forming.If the thrust is too small,it is easy to collapse inside the elbow and the defect of section distortion,but if the thrust is too large,the material will be piled up and wrinkled,and the length of the straight end will be short.