【作者】 徐正扬；

【导师】 朱荻；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 航空发动机作为飞机的心脏,其研制工作是一项系统工程,从某种程度上代表了一个国家科技的最高水平。近年来,我国航空航天事业取得了突飞猛进的发展,新一代飞机陆续研制,航空发动机的研制工作也获得了长足的进步,其中航空制造技术一直扮演了重要的角色。在发动机的各部件中,叶片是最为重要的零部件之一,由于其作用突出、位置特殊、叶型扭曲等特点,给制造带来了困难,多年来一直成为研究的重点。在众多的制造技术中,电解加工技术因其自身所具有的无工具损耗、不受金属材料本身力学性能的限制、加工效率高等特殊优点,正好与叶片制造中材料特殊、加工困难以及加工批量大等特点相吻合,使其成为了叶片制造的主要方法之一。然而随着发动机性能的不断提高,叶片的材料、形状也不断变化,出现了超薄、大扭角、低展弦比等特殊形状的叶片,同时制造的精度要求也不断提升,这些都给电解加工带来了新的挑战。如何提高叶片电解加工的加工精度和表面质量,缩短准备周期,增加自动化程度,以适应不断提高的叶片要求,就成为了电解加工的研究重点,也是本文的主要研究内容。本文依据目前叶片电解加工技术的研究现状,针对其中的若干关键技术和难点开展研究工作,以期进一步发掘电解加工的潜力,获得良好的结果,并对后续的研究起到促进作用。本文的主要研究内容包括了以下几个方面:1.提出了全方位计算机辅助叶片电解加工方法。区别于传统全方位的定义,不仅仅是指同时加工叶片的各个部位,而是将叶片电解加工中的叶片造型、流场设计、角度优化、阴极设计、加工试验及阴极修正等全过程纳入叶片电解加工全方位计算机辅助集成系统中,对各个重要环节进行计算机控制,以此提高电解加工的自动化程度,减少人为因素的影响,从而提高叶片的加工精度。2.设计了三头柔性进给叶片电解加工模式。克服传统叶片电解加工方法的进给角度固定,缘板易形成锥度及二次腐蚀等缺陷,采用阳极运动策略,通过阴极工具与阳极工件的速度比拟合出进给角度。讨论了加工精度和进给角度及毛坯装夹角度的相关性,根据叶片型面及缘板对加工精度的不同要求,给出了相应的角度优化准则,并得到了叶盆、叶背各自的最佳角度组合。3.提出了主动控制的双向进液电解液流动方式。根据传统侧流式存在的不足,提出了主动控制的电解液流动方式,通过建立二维不可压缩流场模型,利用有限元方法分析比较了该流动方式与传统侧流式的优缺点。由电解液流动特点及叶片不同部位对加工精度的要求,设计了缘板两侧进液,由叶尖出液的双向进液流动。针对尖角处可能存在的缺液现象,给出了增加导流块的解决办法。根据流场的质量、动量、能量守恒方程及布拉休斯公式求解不可压缩流场模型,从理论上分析了电解加工间隙的流场特性。由电解液流动方式的特点设计了与之相应的电解加工夹具,保证了新的流动方式得以实现。4.给出了叶片电解加工阴极修正方法及阴极修正的模糊控制策略。改变传统阴极通过人工修正,费时费力的现状,通过分析加工间隙与加工误差的关系,建立阴极修正模型,将加工误差以一定比例引入阴极修正环节,由改变相应的加工间隙值来重新构建阴极型面,达到阴极修正的目的。在此基础上,增加BP神经网络,通过已有试验数据对其进行训练,得到了相应的权值和阈值,由此建立加工误差与修正量之间的模糊控制策略,进一步减少修正的迭代次数,缩短阴极准备周期,提高复制精度。5.完善了三头柔性进给叶片电解加工系统。针对已有的三头进给叶片电解加工机床平台,搭建了其电解液循环系统和数控系统,利用虚拟仪器技术及其Labview开发平台,以及Flexmotion运动控制模块,编写了电解加工系统软件,实现了阴极对刀、运动控制、参数选择、数据采集等一系列功能,整个系统得以稳定有效地运行。6.在搭建的叶片电解加工系统平台上,进行了叶片电解加工的试验研究。针对三头柔性进给模式,开展了不同进给角度组合下的对比试验,试验表明采用优化得到的角度组合,可以有效的保证型面成型精度,并提高缘板的加工精度;针对主动控制的电解液流动方式,开展了与其他流动方式下叶片加工的对比试验,试验验证了主动控制流动方式的合理性,叶片表面粗糙度从Ra1.67μm降到Ra0.36μm,加工精度也有所提高;针对阴极设计存在的叶片加工复制误差问题,对阴极进行了修正,采用三次变间隙阴极修正法,使得型面精度提高到0.05mm。同时对模糊控制下的阴极修正问题进行了试验研究,结果显示该BP网络设计合理,运行稳定,通过该网络得到的阴极修正量与试验较为吻合。7.将全方位计算机辅助叶片电解加工方法应用于某新型航空发动机叶片的研制。针对该叶片加工精度要求高、型面超薄且特别扭曲等特点,采用了上述提到的各项技术,使叶片造型、模式选择、角度优化、速度控制、阴极设计、流场分布、叶片加工、阴极修正和型面检测等过程都和计算机技术紧密结合,最终达到了设计要求,型面精度稳定在0.05mm。更多还原

【Abstract】 Aeroengines seem to be the hearts of aircrafts. From a certain angle, the development of aeroengine represents the whole science and technology strength for a country. Aerospace of China has gained great development and the research of aeroengine has made rapid progress in recent years. Aeronautical manufacturing technology plays an important role in aeroengine development. Blades are very important parts of aeroengine. They impart kinetic energy and redirect the flow to the next stage at the optimum angle. Because of the special characteristics of turbine blade and the hardness of manufacturing, the processing method of blade has been the key point of research in many years. Being a non-mechanical metal removal process, electrochemical machining (ECM) provides an economical and effective way for machining heat-resistant, high strength materials into complex shapes which are difficult to machine by conventional method, so it becomes the main method to process turbine blade. With the raise of aeroengine performance, the changement of the blade materials and profiles, and the improvement of machining accuracy, ECM has faced a higher challenge. The research emphases is to improve the surface quality and machining accuracy of blade in ECM, shorten the period of blade making, reduce the jamming and raise the automation level of blade processing which are the main research contents in this paper.According to the research actuality of blade ECM, the present study focused on the several key technologies and difficulties of blade ECM in order to improve the potential ability of ECM further and settle the foundation for the following study. The main research contents of this paper include:1. The idea of Digital Description to Full Process of blade ECM was presented. Different from the traditional definition of omnidirectional blade ECM which machined the several parts of blade simultaneously, the meaning of this idea is to make the full process of blade ECM under the computer control. All the links of blade ECM, such as blade modeling, designation of flow field and cathode, optimization of feeding angles, blade experiments and amendment of cathode, combined firmly with computer technology. The aim is improving the automation level of blade ECM and reducing the human disturbance.2. A flexible 3-Electrode feeding ECM method was investigated. The anode was moved during the process and the feeding angles of two cathodes were fitted by the velocities of cathodes and anode in order to overcome the defects of traditional blade ECM which includes fixed feeding angles, tapered platform and two time etching. The relationship of machining accuracy with the feeding angles and workship clamping angle was discussed. The optimization criterion of these angles was given according to the different accuracy requirements of profile and platform. The optimal angle combination was also got in this paper.3. A new electrolyte flow mode named“active distributary mode”was proposed. Since flow field is a critical factor to affect the ECM process stability and the accuracy of blade, a two-dimensional incompressible flow field model describing electrolyte flow in the interelectrode gap was developed. The flow mode was analyzed by finite element method and was contrast with the traditional lateral flow modes. Electrolyte flowed from the platform of blade and was divided into two parts to flow across the convex and concave parts of blade individually considering the characteristics of electrolyte flow and the different accuracy requirements of blade profile and platform. The performances of electrode corners starved of electrolyte were studied and diversion block was designed to solve the problem. According to the continuity equation, momentum equation, energy equation and the Blasius formula of flow field, the characteristics of electrolyte flow between the gap of cathode and anode were analyzed by using forth order Runge-Kutta method with varying step size. The relevant clamping fixture which makes the flow tunnels was also designed in this paper.4. The variable gap amendment method of cathode and the cathode modification model using BP neural network were proposed. The corrections data of cathode were variable based on the value of interelectrode gap and were used to the cathode design. The approximate formula of cathode corrections data which were calculated along the contours line was given and the experimental method of interpolation approximation was also adopted. The digital cathode modification model was developed using BP neural network on the basis of the method of the variable gap modification of cathode and its experimental data. The network was trained by the experimental data which is normalized, and then it was simulated. The simulation results showed that the model has a good prediction effects.5. The blade ECM machining system was perfected. The electrolyte circulation system and CNC system were built based on the blade ECM machine tool. The software system of blade ECM was designed by using the virtual instrument technology and Labview development platform which including Flexmotion module.6. Some blade ECM experiments were carried out. The comparative tests of different feeding angle combinations were developed. The results showed that with the optimal angle combination the accuracy of blade profile could be kept and the accuracy of blade platform could be improved. The experimental investigations of flow field were carried out in order to evaluate the rationality of the flow mode. It revealed that the surface roughness could be improved to 0.36(Ra) with the new flow mode. On the contrary, the surface roughness of the blade profile with the traditional lateral flow mode was 1.67(Ra). The machining accuracy could also be enhanced. The experimental investigations by using the cathode amendment method were carried out. The results reveal that the accuracy of blade was enhanced to 0.05mm by using the method 3 times. Furthermore, the efficiency and automation level of cathode amendment could be improved by using the BP neural network cathode modification model.7. The idea of Digital Description to Full Process of blade ECM was applied in the development of a certain aeroengine blade. Because of the high requirement of machining accuracy and the special thin and distortion of blade profile, it was difficult to be made by ECM. The technologies and methods above mentioned were applied in the process. The whole making process, such as blade modeling, designation of flow field and cathode, control of making velocity, optimization of feeding angles, designation of flow field, blade experiments and amendment of cathode, was controlled by computer technology. The results revealed that the machining accuracy of blade profile could be improved to 0.05mm with the technologies and methods above mentioned.更多还原