多点拉形中回弹的影响因素研究

多点拉形是成形飞机蒙皮件的一种新技术。整体模具被离散的多点模具代替,在多点模具和板料之间放置弹性垫用来抑制压痕。在卸载之后,不仅有板料自身的恢复变形,还有弹性垫恢复到原来的形状的影响,这使得多点拉形比传统拉形的回弹更加复杂。文章对多点拉形成形蒙皮类零件的成形和回弹过程进行了数值模拟,分析了拉伸量、板厚、材料、摩擦系数等因素对回弹和成形精度的影响。结果表明,拉伸量越小,回弹量越大;板料越薄,回弹量越大;板料的弹性模量越大,回弹量越小,对成形件的形状影响越大;摩擦系数越大,回弹量越大。比较了在相同的成形条件下柱面件、马鞍面件、环面件回弹的大小,结果表明,回弹对单曲度成形件的影响比双曲度的大。

Numerical simulation analysis on the influence factors of springback in multi-point stretch forming

Multi-point stretch forming (MPSF) is a new technique to form aircraft outer skin parts. Since the traditional solid stretch die is replaced by the discrete multi-point die, the elastic cushion is laid between the sheet metal and multi-point die for suppressing dimpling. The sheet metal will relapse and the elastic cushion will comeback the initial shape after releasing. These lead to that the springbaek of MPSF is more complicated than those of traditional stretch forming. A series of numerical simula-tions on typical MPSF forming and springhack processes are carried out on the aircraft outer skin part. Stretch value, thickness of sheet, material and the friction coefficient are important factors to effect on springhack and the precision of formed parts. The results show that the less the stretching value is, the more the springback value will be. The thinner the sheet metal is, the lar-ger the springhack value will be. The larger the Young's module is, the smaller the springback value and the less the effect on shape error of formed parts will be. The larger the friction coefficient is, the more the springback value will be. Comparing of springback on cylindrical part, saddle-shaped part and the toroidal surface part at the same condition, the result indicates that the effect on springback of single-curved formed parts is more than those of double-curved formed parts.