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实现不起皱条件下管材壁厚减薄的控制,是提高大直径铝合金薄壁管数控弯曲成形极限和质量的关键问题。在管端施加轴向压缩载荷将可能成为实现上述目标的一个途径。在本研究中,基于动力显式有限元法建立了轴压加载数控弯管过程模拟的三维弹塑性有限元模型,并通过多指标正交试验设计,获得了成形参数组合的合理范围,克服了轴压加载弯曲时管端的轴向压缩失稳现象,同时模型可靠性得到了实验的验证。将有限元模型与起皱能量预测模型相结合,研究了轴压加载下大直径薄壁小弯曲半径铝合金管数控弯曲的成形特性。结果表明:(1)管直径越大且弯曲半径越小,弯曲过程中管材的最大切向压应力区被诱发切向拉应力区分割越明显,则轴压加载减小减薄的作用越小,管端发生压缩失稳的可能性越大。(2)与无轴压加载弯曲过程相比,轴压加载下管材起皱可能性在成形前期较大,在成形后期较小。(3)对于尺寸因子小于80的管材,轴压加载减小管材壁厚减薄的作用大于轴压加载增大起皱的作用。
Controlling the thinning of the pipe wall under non-crinkling conditions is a key issue for improving the limit and quality of large-diameter aluminum alloy thin-walled pipe CNC bending forming. Applying an axially compressive load on the pipe end may be one way to accomplish this. In this study, based on the dynamic explicit finite element method, a three-dimensional elasto-plastic finite element model of the process of axial compression loading CNC bending was established. By the multi-index orthogonal experimental design, the reasonable range of forming parameters was obtained, Axial compression loading tube end axial compression instability, while model reliability has been verified by experiments. The finite element model was combined with the prediction model of wrinkling energy to study the forming characteristics of numerical control bending of large diameter thin wall and small bend radius aluminum alloy tube under axial compression. The results show that: (1) The larger the tube diameter and the smaller the bending radius, the more obvious the tangential compressive stress zone of the pipe is induced during the bending process, and the more obvious the effect of the axial compression is to reduce the thinning , The greater the possibility of compression instability on the pipe end. (2) The possibility of tube wrinkling under axial pressure loading is larger in the early stage of forming and smaller in the late stage of forming than in the process of non-axial load bending. (3) For the pipe with size factor of less than 80, the effect of axial pressure loading to reduce the thinning of pipe wall thickness is greater than that of axial pressure to increase the wrinkling.