航空发动机叶片进排气边缘的高精度修整技术的研究

An aero-engine is the heart of airplane. The power is provided by high speed rotating blades. Due to the high speed rotation, thin wall structure and working in high temperature, the blade material has properties of resistance to high stress and high temperature. The new generation aero-engine requires higher precision of leading and trailing edges of aero-engine blades, which directly influences on the aerodynamic performance of airplane. This project proposes to trim ECMed edges using a whole electrode by micro EDM. It is expected to solve this key problem which limits the development of the new generation aero-engine. In this project, machining parameters of micro EDM and heat afftected zone (HAZ) is studied to provide the data for removing the HAZ in final process. The relationship between the curvature of curved surface and the electrode wear is analyzed based on theories of electrical field, heat transfer theory and fluid field. Results are used to modify the electrode design and the tool path generation. A new electrode design is proposed, so-called reversed electrode design. The initial electrode is designed based on the blade edge. When the electrode moves along the tool path backward and interfaces with the blade, the electrode is modified and the tool path is adjusted based on the theoretical analysis results and experimental data. To achieve the desired machining accuracy, it is necessary to compensate the electrode wear during machining. In this project, 5 axes NC micro EDM is developed based on the self-made 3D micro EDM and corresponding control software as well.

发动机是航空器的心脏，其薄璧叶片的高速旋转不仅为航空器提供飞行动力，而且在工作中承受巨大载荷和高温，因而必须选用具有高强度耐高温特性的高温合金材料。新一代发动机对直接影响叶片气动性能的叶片进排气边缘有着更高的精度要求，这使得现有加工工艺均难以满足。本项目将针对这一需求，采用复杂曲面整体电极对电解加工后的发动机叶片进排气叶缘进行微细电火花精密修整加工，突破这一制约新一代发动机的发展瓶颈。本项目研究加工参数与重铸层和热影响层之间的映射关系，为后续去除余量提供科学依据。本项目提出电极逆向设计法，将根据电场、传热学和流体力学理论，研究分析曲面曲率和电极损耗的关系，并在理论分析和大量基础实验数据的基础上，根据叶片边缘形状的复杂性和加工环境的特殊性，对电极的加工曲面进行损耗补偿修正和调整加工轨迹，防止电极与工件干涉，确保加工精度。在已有的加工装置基础上，研制5轴数控微细电火花加工装置及相应的控制程序。

本项目针对航空发动机叶片的进排气边缘的电化学成型加工中出现的问题，采用电火花加工技术进行修整。根据流体力学的原理，采用振动辅助电火花加工的方法，促进狭窄放电间隙的液体流动，使得加工屑和气泡迅速排除，减少非正常放电，提高加工效率。对加工参数进行优化，获得了粗加工工艺参数为电源电压：150V，峰值电流：30A，脉宽：4µs，振幅：0.9µm、振动频率：1000Hz；精加工工艺参数为电源电压：120V，峰值电流：10A，脉宽：0.5µs，无振动。根据材料学和传热学，通过实验数据和理论计算，获得了在最优加工条件下，粗加工的热影响层厚度小于20µm，精加工的热影响层厚度小于3µm，满足了后续加工工艺的要求。为了提高加工效率，采用复杂形状电极进行修整加工，研制了六轴联动数控机床，设计了复杂形状电极和生成了数控轨迹。