变摩擦正反向超塑成形壁厚均匀的TC4钛合金深筒形件

1C4钛合金深筒形件厚度精度要求为(1.6±0.2)mm,据此设计了多种预成形模形状,采用MARC有限元模拟研究不同形状预成形模对最终深筒形件侧壁厚度分布的影响规律及不同预减薄区域的作用.分析预成形模和终成形模的表面摩擦系数分别对成形件壁厚分布的影响,并提出模具型面变摩擦控制厚度分布的方法.结果表明:预成形模对于板料压边部分环形带区域和筒形件底部区域的局部预减薄,对最终侧壁的厚度分布有非常大的改善.同时,合理地增大预成形模的表面摩擦能显著增加预成形的局部减薄作用,对于提高工件最终壁厚分布的均匀性有利.减小终成形模的摩擦,可以使板料趋于整体变形,壁厚分布趋于均匀.根据模拟结果,采用机械加工方法增加预成形模表面摩擦系数,在终成形模表面喷涂BN润滑剂降低摩擦系数.最后,通过正反向超塑成形试验制得厚度分布在1.50～1.78mm范围内的TC4钛合金深筒形件.

TC4 Deep Cylinder with Uniform Thickness by Friction-Changing Direct-Reverse Superplastic Forming

The thickness accuracy of a TC4 deep cylinder is within the limit of (1.6±0.2) mm; hereby different shapes of preforming-dies were designed and the relation between the shape and the thickness distribution of the cylinder side-wall as well as the effect of pre-thinning areas were investigated using MARC finite element method (FEM). And also the influence of surface friction coefficient of the preforming die and the final forming die on the final thickness distribution of the deep cylinder was analyzed. A method of thickness control by friction changing was proposed. The results show that the performing-dies have great effect on the local pre-thinning of the ring band near the periphery and the bottom of the deep cylinder to improve the thickness distribution of the final side wall. Meanwhile the properly higher friction coefficient of the preforming die can efficiently reduce the thickness of the regions which need to be thinned, resulting in a more uniform final thickness distribution. Lower friction coefficient of the forming die can make the sheet tend to integral formation, also resulting in uniform thickness distribution of the side wall. According to the results of the simulation, the surface friction coefficient of the preforming die was increased by machining and the friction coefficient of the forming die was decreased by spraying BN ceramic powder. The aerospace TC4 deep cylinder with uniform thickness of 1.50-1.78 mm was fabricated by direct-reverse superplastic forming experiment