无芯棒拉拔过程应力应变分析及壁厚变化

Research on thickness change during tube drawing without mandrel

管材无芯棒拉拔时,直径减小的同时壁厚也会发生改变,其增厚值可达13.2%,甚至更大。但现有文献对无芯棒拉拔过程进行应力应变分析时,通常忽略壁厚的变化,这对预测管件壁厚,从而对工艺参数进行控制不利。该文不同于以往壁厚不变的假设,而是采用应力应变方程统一求解的方法,按增量理论给出壁厚变化的理论解以及应力分布。同时,选取不同的初始直径管坯进行无芯棒拉拔实验,分析变形后出口端壁厚变化规律,并与理论计算结果进行比较。结果表明,随拉拔道次变形量的不断增大,出口端管材的壁厚变化率先增大后减小,但是最终的变形总是增厚,实验结果与理论计算值吻合较好。

During tube drawing without mandrel, the diameter is decreased and the wall thickness is increased up to 13.2% or more. But in stress-strain analysis on tube drawing in previous references, the thickness change was usually neglected, which is not helpful to predict the final thickness and control the process parameter. Different from the constant-thickness assumption in literature, the method of combining stress and strain equations were used in this paper. The distribution of stress and theoretical calculations of thickness change were provided based on incremental theory. Moreover, experiments of tube drawing with different initial diameters were carried out, and the thickness distributions after drawing were compared with the result of theoretical calculation. The results showed that the experimental results agreed well with the theoretical calculated curve. With the increase of drawing deformation for a pass, the thickness varying rate firstly increased and then decreased, but the final deformation was always thickening.