铝/钢双金属管电磁缩径数值模拟

为指导实际双金属管精确成形工艺,基于LS-Dyna对铝/钢双金属管电磁缩径连接进行了结构场-电磁场耦合的有限元数值模拟,研究了内外管壁厚比值、内外管间隙、放电电压以及芯模对成形质量的影响规律.结果表明:内外管壁厚比值过小易引起内外管连接不紧密,比值过大易导致内管凹陷和外管开裂;随着放电电压增大或内外管间距的减小,外管缩径冲击力增大,导致内管周向应力的急剧增大和失稳起皱,同时造成外管开裂;而随着放电电压减小或内外管间距的增大,外管相对的缩径冲击力减小,内管会因无法经历一个有效的形变回弹过程导致内外管有效连接区域逐渐减小;采用弹性芯模可一定程度抑制开裂等宏观缺陷的产生,同时也能适当增加内管的回弹.最后,基于理论计算与有限元仿真获得复合管电磁成形规律和缺陷控制理论,以增大有效连接区域长度、减少宏观缺陷为目标进行优化,在施加弹性芯模的状态下,内管壁厚维持1 mm不变,外管壁厚取1.5 mm,内外管间隙取0.7 mm,放电电压取50 kV时得到的成形质量最佳.

Numerical simulation of electromagnetic constriction of aluminum/steel bimetallic tube

The finite element numerical simulation of the coupled structure-electromagnetic fields was carried out based on LS-Dyna platform for the electromagnetic constriction process of aluminum/steel bimetallic tube, aiming to guide actual precision forming process of bimetallic tube. The influences of the inner and outer tube wall thickness ratio, the inner and outer tube gap, discharge voltage, and elastic mandrel on forming quality were studied. Results show that small wall thickness ratio caused the weak connection of the tubes, while large wall thickness ratio led to the depression of the inner tube and the crack of the outer tube. As the discharge voltage increased or the distance between two tubes decreased, the constriction impact force of the outer tube was increased, which resulted in a drastic increase in the circumferential stress of inner tube and the occurrence of instability and wrinkling, as well as the crack of the outer tube. On the contrary, with the discharge voltage decreased or the distance between the two tubes increased, the constriction impact force of the outer tube was decreased, and the inner tube could not bear an effective deformation and springback process, leading to smaller effective connection area between the two tubes. The elastic mandrel could restrain macro-defects such as cracking at a certain extent, and appropriately increase the springback of inner tube. Lastly, the electromagnetic forming rules and defect control theory were obtained based on theoretical calculation and finite element simulation. With the purpose of increasing the length of effective connection area and reducing macro-defects, the research parameters were optimized, and it was found that the forming quality is the best when the inner tube wall thickness remains 1 mm, outer tube wall thickness is 1.5 mm, the gap between the tubes is 0.7 mm, and discharge voltage is 50 kV.