铝锂合金双层板充液拉深变形规律研究

In order to reduce the weight and improve the reliability at a low temperature, ultrathin Al-Li alloy bottom without welding line is needed in the new-typed launch vehicle tank,in which liquid hydrogen and liquid oxygen are filled. The thickness-diameter ratio is not more than 3/1000 for the integral tank bottom. With conventonal hydromechanical deep drawing, wrinkle can not avoided. Aiming at solving the above wrinkle problem, a new method of double-layer sheet hydromechanical deep drawing is proposed. A auxiliary sheet is laid on the Al-Li alloy sheet, and double-layer sheets deform at the same time during the propcess of hydomecanical deep drawing.The top sheet acts as a supporter and blank-holder for the suspending zone of the bottom sheet. The ability of anti-buckling and load bearing can be improved by changing the thickness or the strength of the top sheet. Larger counter pressure can be imposed, and wrinkle can be eliminated for the bottom sheet. By the investigation into the double-layer sheet hydomechanical deep drawing, a theoretical model will be established for caculating the tangential stress, the first spring back and the second spring back will be disclosed, dimentional precesion and thickness distribution can be obtained,stress state and wrinkle will be shown,and the effects of tangential stress will be revealed at the interface. The major problem of wrinkle will be solved for the ultrathin and complex-shaped part, the investigation will lay a theoretical foundation and supply a technical support for its application in the new-typed launch vehicle tank.

为了减重和提高低温可靠性，新一代运载火箭液氢-液氧燃料贮箱需要无焊缝的超薄壁厚、铝锂合金箱底，这类整体箱底的厚径比（厚度与试件直径比）一般小于3/1000。采用传统拉深方法制造此类曲面件时，无法克服起皱缺陷。为了解决传统技术制造这类超薄壁厚、复杂曲面件存在起皱难题，本项目提出双层板充液拉深成形新方法。基本原理是在待拉深铝锂合金薄板（下层板）上表面放置辅助成形板材（上层板），充液拉深过程中上层板对下层板悬空区起到支撑、压边防皱的作用，通过选择上层板厚度或者强度提高抗失稳能力和承载能力，可施加更大的液室压力，消除下层板的起皱缺陷。通过对双层板充液拉深变形规律深入系统的研究，建立切向应力理论计算模型，揭示一次回弹、二次回弹、形状变化和壁厚分布规律，给出拉深过程应力状态及起皱行为，揭示界面切应力作用规律，解决超薄壁厚、复杂曲面件的起皱难题，为在新一代运载火箭上的应用提供理论基础和技术支持。

为减重和提高低温可靠性，运载火箭燃料贮箱迫切需要整体成形铝锂合金超薄壁厚箱底，取代分块成形再焊接的贮箱箱底制造方式。由于整体箱底超薄壁厚，其厚径比（厚度与试件直径比）一般小于3/1000。采用传统拉深方法制造此类曲面件时，无法克服起皱缺陷；充液拉深方法为避免起皱所需的流体压力大，造成设备吨位大、大型装备成本高。为了解决制造这类超薄壁厚、复杂曲面件存在起皱难题，本项目提出双层板充液拉深成形新方法，下层版在上层板支撑和下表面流体压力及界面摩擦作用下，可施加较小的液室压力，消除下层板的起皱缺陷。本项目通过开展双层板充液拉深的应力状态与极限成形厚度、下层板充液拉深失稳起皱机制及影响因素、双层板充液拉深回弹规律与精度控制及下层板壁厚分布规律的研究，获得不同轴长比试件、不同上层板厚度、不同流体压力条件下的应力应变规律、厚度分布规律、回弹规律，揭示双板充液拉深成形过程的失稳起皱机制。通过采用合理厚度上板与超薄壁厚下板，在流体压力作用下同步成形，解决超薄壁厚、复杂曲面件的起皱难题，为在新一代运载火箭上的应用提供理论基础和技术支持。