Research On Nc Rotary-draw Bending Forming Process With Small Bending Radius Of Thin-walled Tube

Aluminum alloy bend tubes with small bending radius have such properties as high strength, light quality, space saving and are widely used in the areas of aviation, aerospace, automobile industries.The NC rotary-draw bending forming process is one of mainly forming methods of tube bending technology,its NC bending forming is a complicated physical process under the action of multi-mould constrained and multiple nonlinearities, but tension crack, cross-sectional distortion and instability wrinkling etc are easily produced during the rotary draw bending process,which seriously influence the quality of bend tube.Therefore,combining with theoretical analysis and experimental study,the stress-strain 、 variation of wall thickness and cross section distortion in thin-walled tube NC bending process have been investigated in this paper,and influence laws of forming parameters on quality of tube bending were studied systematically.A brief introduction of this paper and its main results are as follows:The basic mechanical property parameters of LF2 M aluminum alloy of thinwalled tube has been obtained through the tensile test, and then the constitutive equation has been established.according to the NC rotary-draw bending principle, a 3D-FE model of thin-walled tube rotary draw bending process was established based on DYNAFORM finite element software, and its reliability was verified by experiment.Then, based on the established reliable FE model, the distribution law of tangential stress and equivalent strain in NC rotary-draw bending process was analyzed by comparing whether adding pushing equipment or without in tube tail,and the variation rule of tangent stress、tangent strain of tensile deformation area was also analyzed during the different stages of the bending process. The results indicate that the plastic deformation area are in nearby bending tangent point and the size and position are changed slightly, the crack of tube is easy to appear in the range of 0°—30°bending angle, the results of this study can provide a guideline for investigating the influence of process parameters on wall thinning and cross section distortion for thinwalled tube in rotary draw bending process.Through simulation and experimental results of comparative analysis,the influence laws of forming parameters on forming quality for thin-walled tube in rotary draw bending process has been studied by single-factor method.The results show that: the wall thickness thinning ratio and cross-sectional distortion of LF2 M aluminum alloy tube is more serious than that of 1Cr18Ni9 Ti stainless steel;the wall thickness thinning ratio will decrease with the decrease of the diameter-thickness ratio D/t,extension length of mandrel,mandrel balls number,distance of mandrel number, while decrease with the increase of the clearance among tube and bend die,the friction coefficient between tube and bend die;while the cross-sectional distortion will decrease with the increase of the extension length of mandrel,the clearance among tube and mandrel and the increase the clearance between tube and bend die;the influence of the clearance between tube and bend die and the friction coefficient between tube and bend die on the variation of tube wall thickness are not significant.The influence of technological parameters on forming quality for NC rotary-draw bending of tube has been comparatively analyzed by orthogonal experiment,and significant sequence of each technological parameters on forming quality has been ranked.It was founded that the extension length of mandrel is the most significant influence factor on wall thinning of outer tube wall and cross-sectional distortion;while the clearance between tube and mandrel is the most remarkable influence factor on the wall thickness thickening ratio of inside tube wall.