圆管压扁-压弯连续变形过程有限元模型的建立及截面畸变研究

为研究圆管压扁-压弯连续变形过程中的截面畸变,基于有限元软件ABAQUS建立了该过程的三维有限元模型,并实验验证了其可靠性。分析了圆管压扁过程中的截面变化规律及弯曲下模圆角半径、模具与管材间的摩擦系数对成形过程截面畸变的影响。结果表明,圆管压扁过程中形成扁管直壁部分的材料在外层周向压应力、内层周向拉应力的合力作用下出现塌陷。形成扁管圆弧部分的材料在外层周向拉应力、内层周向压应力的合力作用下出现扁化。在无芯轴、有芯轴压扁成形前期,圆弧部分均出现扁化,且无芯轴压扁成形中期,直壁部分出现塌陷。但有芯轴压扁过程中芯轴的支撑作用不但抑制了直壁部分的塌陷,而且还矫正了成形后期圆弧部分的扁化。由于圆管压扁-压弯过程中模具与管材的接触区域始终不大,因此成形过程中弯曲下模圆角半径,及模具与管材间的摩擦系数,对截面畸变影响不显著。

FEM model establishment and variation of cross section distortion in circle tube pressing and bending

In order to study the cross section distortion law of a continual process of circle tube pressing and bending,an FEM model for the process has been established using the FEM software ABAQUS.It has been validated by comparing the results using the model and the experiment.The cross section distortion laws of cirle tube pressing have been analyzed.The effects of frictons between dies and tube and round radius of lower die of bending on cross section distortion have been studied.The results show that:The outer layer of the tube which forms the straight part of the flat tube is compressed while the inner layer is tensiled.Collapse occurs in the area due to their resultant.The outer layer of the tube which forms the curved part of the flat tube is tensiled while the inner layer is compressed.Flattening appears in the area due to their resultant.The curved part flattens at the eariler stage of the pressing process either with or without mandrel,and the straight part collapses in the midst of pressing without mandrel.But flattening hasn't been found and the collapse can be improved at the last stage of the pressing with mandrel because of the support of the mandrel.The frictions between dies and tube and round radius of lower die of bending have no dramatic effect on cross section distortion because of the small contact of dies with tube during the whole forming process.