铝合金管材侧壁增厚成形极限与失稳研究

Study on thickening limit and instability for aluminum alloy tube sidewall

薄壁管材在增厚变形时容易向外鼓凸并导致折叠缺陷,因此,起皱失稳是主要的成形缺陷。提出了侧壁内、外增厚成形工艺,分别对管材的内(外)表面进行模具限制,使管材侧壁向外(内)增厚成形。通过有限元数值模拟与实验相结合的方法,对两者的成形稳定性进行对比分析,探究侧壁增厚时产生失稳现象的原因,并研究在两种增厚成形方法下,管材的侧壁增厚规律及成形极限。结果表明:与外增厚及传统镦粗成形工艺相比,侧壁内增厚时成形稳定性明显提高。通过对增厚过程进行追踪,可以发现,侧壁的失稳现象与侧壁的增厚方向以及轴向应力分布有关。通过有限元数值模拟及理论分析,得到了侧壁内增厚成形的无失稳条件,内增厚成形的增厚极限受高度的影响小,受高径比的影响大。

Thin-walled tubes is prone to bulge outward and fold when they are thickened,so the wrinkling and instability are the main forming defects.Therefore,the internal and external thickening processes of sidewall was presented,the inner(outer)surface of tube was restricted by the die so that the sidewall was thickened outward(inward).Through a combination method of finite element numerical simulation and experiment,the forming stabilities of the two processes were compared and analyzed to explore the reasons of instability phenomenon when the sidewall was thickened,and the laws of the sidewall thickening and the forming limit for the two kinds of thickening forming processes were studied.The results show that the forming stability is greatly improved when the sidewall is thickened inward compared with the external thickening and the traditional upsetting process.And by tracing the thickening process,it is found that the instability phenomenon of sidewall is related to the thickening direction and the axial stress distribution of sidewall.Furthermore,through finite element numerical simulation and theoretical analysis,the condition without instability for the internal thickening of sidewall is obtained,and the thickening limit of the internal thickening is less affected by the height,but is greatly affected by the height-to-diameter ratio.