柔性薄板复杂铣削变形激光喷丸反向精确控形机理及工艺研究

Integral wing panels of supercritical airfoil are widely used in modern manufacturing process of advanced aircrafts, the lack of bending rigidity is common feature of panel structures which is attributed to large aspect ratio and variable thickness, flexible thin sheet is common mechanical model of panel structures, and residual stress related machining distortion of thin panel is an important problem in aviation industry that must be solved. Therefore, shape correction method for panel with high precision, zero damage and long fatigue life become one of the most concerned research in aviation manufacture. Based on research of laser peening forming, the present project creatively applying laser peening to panel size correction of complex deformation, exploring key role of nanosecond pulse laser peening with accurately effect region, strong controllability and high amplitude in accurate shape correction for thin flexible panel. The present project focuses on large milling distortion of flexible thin panel, performs research on mechanism and key technology for laser peening correction of panel, to clarify key scientific problems which include description of nonlinear relationship between load and deformation under large deformation, and regulate mechanism in the material of residual stress field by nanosecond pulse laser induced shock wave effect, breakthroughs key technology of panel laser peening correction model for reverse control deformation and method of laser peening correction for controlling residual stress. The aim of this project is to solve thin panel distortion problems of bending, torsion and bulking deformation, provides a new strategy for shape correction of integral wing panel.

超临界翼型的机翼整体壁板在现代先进飞机制造中得到广泛应用，抗弯刚度弱是大展弦比、变厚度壁板类零件的共同特点，柔性薄板是壁板类零件共同的力学模型，由残余应力导致的铣削变形是壁板制造的共性问题。因此，壁板高精度无损伤长寿命的校形方法是航空制造中最为关注的一项研究。本项目在激光喷丸成形的研究基础上，创造性的将激光喷丸应用于壁板复杂变形的尺寸校正，探索作用区域精确、可控性强、超高幅值的纳秒脉冲激光喷丸对柔性薄板精确校形的关键作用。本项目聚焦于柔性薄板铣削大变形问题，将深入开展薄板激光喷丸反向精确控形机理和关键技术研究，阐明薄板大变形下的载荷与形变非线性关系解构和纳秒脉冲激光诱导的冲击波效应对材料残余应力场的调节机制关键科学问题，突破薄板激光喷丸反向控形力学建模和激光喷丸校形残余应力调控关键技术，解决柔性薄板弯曲、扭曲和失稳变形校正难题，为机翼整体壁板铣削变形校正提供新思路。

课题针对薄板铣削变形控制的激光喷丸新工艺开展基础研究。项目提出的基于冲击波力效应特种控形方法，与现有的变形控制方法（材料热处理、工艺优化、机械压弯、激光热校形等）相比，激光喷丸不会产生有害拉应力，利用残余压应力调控零件变形理论上适用于各类薄壁构件，激光脉冲可达性好且可控性高，产生的强压应力效应不仅能提高尺寸稳定性，也有利于构件服役性能，有望发展成为一种调控结构形状与性能的特种制造工艺。课题针对柔性薄板激光喷丸控形新工艺中关键的机理和控形精度问题，开展了动态载荷特征分析、结构力学建模、残余应力调控、工艺试验与验证等方面的理论和试验研究工作：(1) 搭建了纳秒脉冲载荷测试平台，对激光诱导高压冲击波的特殊脉冲波形进行了试验测量与数值仿真，通过单光斑/多光斑载荷测试，确定纳秒脉冲载荷产生的应力场为等轴平面应力状态。(2) 建立了柔性薄板大变形力学模型，从机理层面解释形变主要由塑性延展效应和变形协调效应产生，明晰结构刚度与脉冲能量输入是调控形变的主要因素，阐明柔性薄板大变形受结构最小势能约束。(3) 研发了重构薄板平面应力状态的关键技术，对薄板激光喷丸前后的近表层、全深度应力进行定量精确表征与分析，阐明残余应力空间分布与结构刚度的演化规律。(4) 研究了薄板激光喷丸残余应力调控工艺，通过单光斑脉冲宽度、峰值压力、冲击次数、光斑形状/尺寸以及多光斑搭接、冲击次数等工艺参数试验，明确了调控残余应力本质是调控靶材单位面积上承受的冲量。(5) 研究了典型航空材料7055-T7751激光喷丸的微观组织演化规律，定量表征了近表层组织的加工硬化率。(6) 建立了薄板弯曲/扭曲铣削变形的形函数和矫正策略，阐明基于等厚度控形的变刚度调控机制，设计实施了缩比零件的工艺验证试验。(7) 扩展基于冲击波力效应的特种控形工艺，并在薄壁曲面叶片和高筋条整体壁板缩比件上进行了验证试验。综上所述，课题研究为激光喷丸特种控形工艺的进一步推广应用奠定了良好基础。