Research On Tube Bending Mechanical Properties And Its Influential Factors

The bending forming of large bending radius tube has the advantages of high efficiency,low consumption and high accuracy, it is widely used in aviation, aerospace and automobileindustries. Large bending radius pipe forming is prone to cause cross-section ovalization,thinning of wall thickness, instability, spring-back and other quality defects which result inthe failure of machined pipe. Tubing cross-section distortion not only affects the appearancequality of the pipes but also can reduce the cross-sectional area，increase the flow resistanceand transmission fluid pressure is aroused directly. Take advantage of good plasticity，Bigpush bending pipe bending radius is the use of materials processing, it has some advantagessuch as simple processing technology, avoiding the material waste. Due to the multi-factorcoupling interaction during push bending process, in the late push bending process，instability and spring-back problems are caused which affects the quality of bending pipe.To study the instability problem, this paper uses the3-d finite element numericalsimulation technology，takes variation of wall thickness and the forming limit of instabilityas the research object in the bending forming of big bending-radius pipe. And by using finiteelement software ABAQUS, the effect of the process parameters and material parameters onwall thickness change and instability limit of pipe were studied. This study has importanttheoretical significance and reference value on process parameter selection and optimizationin the development and forming of big bend-radius tube bending forming technology.(1) The finite element software ABAQUS is adopted to establish the three-dimensionalfinite element model of large push bending radius pipe, and to analysis the influence law ofprocess parameters and material parameters on wall thickness change of bending pipe. Theeffect rule of different process parameters on wall thickness change of the big push bendingradius pipe is studied mainly, the influence law of these parameters is got: with theincreasing strength coefficient of material, pipe wall thinning rate decreases；with theincrease of thickness，the thinning rate changes little; the friction coefficient betweenmandrel and tube billet increases, the pipe wall thickness reduction ratio increases. Alongwith the bending speed increases, the wall thickness thinning is not obvious. But the effectof material hardening exponent on wall thickness is relatively large. In a certain relativeposition，the mandrel is almost no effect on the forming quality of the elbow.(2) The research of forming limit pipe consists of four parts. This paper studies thecompression deformation zone of the neutral layer which is one of the four. The forminglimit which protects the thin-walled structure parts subjected to the tangential compressivestress from more than instability wrinkling is studied. The effect of different processparameters on the bending instability limit of big bend radius is studied and the influencingrules are as follows: Before the pipe is bended to the forming limit, with the increase ofrelative bending radius of the tube, bending radian of bending wheel increases. As the wallthickness increased, its forming limit will also along with the increase. When push bendingprocess is in instability, with the clearance increase between tube and die, the bendingradian of bending wheel is smaller; with the boosting velocity of boosting blocks increasing, bending radian of bending wheel changes little; along with the extension length of mandrelis increasing, bending radian of bending wheel is getting smaller and smaller.