基于时序调控的激光螺旋加工叶片气膜孔精确控形方法研究

Turbine film cooling technology is widely used in high thrust-weight ratio aero engine nowadays, the geometrical accuracy of turbine film cooling holes will directly affect the performance of the engine. According to the fact that the low forming and unsteady quality of film cooling holes produced by the laser technology, a new precise shape-controlling method for turbine film cooling hole by sequential-regulated laser helical drilling process is proposed. By analyzing the mechanism of multi-source error propagation, the modified model of turbine film cooling hole with errors compensation can be established. Based on the analysis of results of the laser ablation experiments conducted by dual-laser sources with different parameters and sequences, the law of the spatial domain evolution of hole formation generated by laser parameters and sequences can be revealed by phase space reconstruction theory, hence the mapping relationship model between laser parameters and the geometrical parameters of the micro-hole can be established. On the basis, the simultaneous differential equations which have been proposed to describing the spatiotemporal evolution during the film cooling hole helical drilling process can be obtained, with the construction of functional analysis for time optimal control, by solving the problem of surface approximation to the modified turbine film cooling hole, the optimized laser scan path under the restriction of the parameters mapping model between laser and hole can be determined. Therefore, the efficient laser helical drilling system for the formation of accurate turbine film cooling holes can be realized. The study of this project will give the laser drilling process with the quantitative guidance and will provide new theories and methods for the geometrical control and the improvement of laser machining quality for turbine film cooling holes.

高推重比航空发动机普遍采用气膜冷却技术，叶片气膜冷却孔的几何精度直接影响发动机性能。本项目针对激光加工叶片气膜孔中存在的几何精度偏低、质量不稳问题，提出一种基于时序调控的激光螺旋加工叶片气膜孔精确控形方法。通过研究多因素误差传递机制，建立误差融合的气膜孔设计修正模型。通过双激光束组合脉冲设计激光加工物理实验，基于相空间重构法研究不同时序组合脉冲与微小孔几何状态变量的时间分布规律，建立激光能量时序参数与微小孔几何的映射模型。进而通过求解激光螺旋加工系统的时滞微分方程组，建立描述螺旋加工的运动表征方程。通过构建时间最优泛函、以气膜孔设计修正模型为目标，求解以激光能量时序参数与微小孔几何映射模型为约束的光束运动最优轨迹，建立光学系统的螺旋加工联动方法。该研究成果将解决当前叶片气膜孔激光加工缺乏定量指导的问题，为叶片气膜孔加工的几何精度控制及加工效率的提高提供新的理论和方法。

当前高推重比航空发动机普遍采用气膜冷却技术，叶片气膜冷却孔的几何精度直接影响发动机性能。本项目针对激光加工叶片气膜孔中存在的几何精度偏低、质量不稳问题，提出一种基于时序调控的激光螺旋加工叶片气膜孔精确控形方法。通过研究多因素误差传递机制，建立误差融合的气膜孔设计修正模型。针对气膜孔激光加工这一基本过程，从数值仿真角度考虑，建立超快激光多脉冲烧蚀金属的仿真模型，基于所提出的计算模型，研究了多脉冲间隔时间以及焦点下移速率这两个参数对加工过程中电子和晶格温度以及烧蚀深度的影响。另一方面，设计超快激光螺旋加工微小孔实验，结果表明，5个主要参数对烧蚀速率影响的主次顺序为：重复频率、单脉冲能量、吹气压力、旋转速率、焦点下移速率；随后基于反向传播（BP）神经网络建立这5个因素与材料烧蚀深度之间的映射模型，并利用正交实验数据对网络进行训练，通过附加钻孔实验数据对所建立网络的泛化能力进行测试，结果表明所建立的模型预测误差在3%以内。进一步地，通过飞秒/毫秒激光束组合脉冲加工物理实验，研究不同时序组合脉冲与微小孔几何状态变量的时间分布规律，试图建立激光能量时序参数与微小孔几何的映射模型。实验结果表明，毫秒激光参数（脉冲宽度、脉冲能量分布）将通过影响基孔的孔径和锥度，进而影响孔的最终成形结果，而在保持毫秒激光参数不变，即相同的基孔条件下，存在合适的飞秒激光单层扫描时间和扫描轨迹，能够高效完成孔的加工成形。在给定的激光参数下，通过飞秒/毫秒激光束组合脉冲激光加工微小孔，孔的加工效率能提高约80%。项目研究结果将有利于解决现有超短脉冲激光加工叶片气膜孔中存在的气膜孔加工精度低、效率差等问题。