大尺寸TC4钛合金环壳充气热气胀压弯成形工艺研究

Simulation and Forming of Hot Gas Pressure Bending for TC4 TitaniumAlloy Bent Tube

钛合金环形燃料贮箱是运载火箭上面级的薄壳件的关键结构。新一代燃料贮箱对空间利用率的要求更高,因此采用环壳代替多个球形贮箱组合。环形贮箱具有大尺寸、超薄、材料难变形的成形难点,且传统分块拼焊结构可靠性差。基于此,本文提出了环壳热压弯成形工艺,开发了内置VUMAT子程序嵌入材料本构模型的钛合金环壳热气胀压弯仿真模型,研究了不同工艺参数下钛合金环壳热压弯的壁厚、贴模度变化规律。以环壳壁厚减薄率与截面最大变形率为判据,建立了支撑内压与管坯温度的热压弯工艺窗口图,确定最优工艺参数。搭建了TC4钛合金环壳热压弯成形装置,制造了全尺寸钛合金环壳,环壳中径2692 mm,截面直径500 mm,壁厚2 mm,径厚比高达250,实际工件中径尺寸与目标尺寸相差11 mm,环壳弯曲内侧最大增厚率为11.5%,环壳弯曲外侧最大减薄率为8.3%,抗拉强度与平均晶粒尺寸均优于设计指标。

The titanium alloy ring-shaped fuel tank is the key structure of the thin shell member of the upper stage of the launch vehicle.The new generation of fuel tanks requires higher space utilisation,so the bent tube is used instead of multiple spherical tank combinations,which improves the space utilisation by 58.64%.The bent tube has the forming difficulties of large size,ultra-thin,and difficult to deform the material,and the reliability of the traditional block-welding structure is poor.Based on this,this paper proposed a hot forming process of bent tube hot gas pressure bending,a built-in VUMAT subroutine embedded in the material constitutive model of titanium alloy bent tube hot gas pressure bending simulation model was developed.The variation rules of wall thickness and die sticking degree of hot gas pressure bending of titanium alloy bent tube under different process parameters were investigated.Taking the wall thickness reduction rate of the bent tube and the maximum deformation rate of the cross-section as the criterion,the hot gas pressure bending process window diagram of the internal pressure of the support and the temperature of the tube was established,and the optimal process parameters were determined.A TC4 titanium alloy bent tube hot gas pressure bending forming device was constructed.A full size titanium alloy bent tube was manufactured.The bent tube has a mid-diameter of 2692 mm,a cross-section diameter of 500 mm,a wall thickness of 2 mm,and a high diameter-to-thickness ratio of 250,and the difference between the actual component mid-diameter size and the target size is 11mm,and the maximum thickening rate of the intrados side of the bent tube is 11.5%,and the maximum thinning rate of the extrados side of the bent tube is 8.3%,tensile strength and average grain size basically are better than the design specification.