Research on the cathode design and experiments of electrochemical machining a closed impeller internal flow channel

In order to improve the electrochemical machining (ECM) precision and efficiency of a closed impeller internal flow channel, the internal flow channel cathode shape and structure were optimized by gap flow field simulation. Firstly, the theoretical model and three-dimensional gap flow field simulation geometric model were set up. Next, the inter-electrode gap flow field simulation results were draw from the streamline, velocity, and pressure cloud picture. Secondly, the cathode and the frock clamp were designed according to the simulation results. Finally, the verification experiment was carried out to evaluate the cathode structure and the ECM process parameters, and the experimental results were consistent with the simulation results. The whole process is stable and no short-circuit phenomenon with the forward flow field machining pattern. The results show that the method of gap flow field simulation-assisted ECM cathode design is useful and economical for machining closed impeller internal flow channel.     

Optimal design of the sheet cathode using W-shaped electrolyte flow mode in ECM

Electrochemical machining (ECM) is an important non-conventional manufacture technology for machining workpieces with complex and thin structures. In this study, ECM is used to machine the blisk. Because the channel between two blades is narrow, the cathode must use the thin-sheet structure. In the ECM process, the cathode will bear electrolyte pressure which can cause deformation. The cathode deformation has negative influence on the machining quality and process stability. To minimize the deformation, the optimization treatment of the cathode thickness is carried out and a new electrolyte flow mode, W-shaped flow mode, is adopted to weaken the pressure. The corresponding computer simulation is applied, and the results show that the cathode deformation decreases by 17.6% and 28% by taking the above-mentioned two measures. It indicates that the new thin-sheet cathode presented in this paper is useful and the new flow mode is effective in ECM. Furthermore, the experiments are conducted using the optimal thickness electrode and W-shaped flow mode to verify the machining effects. Then the corresponding experiment is carried out, and the result shows that the optimal treatments to reduce the cathode deformation have remarkable effects.     

Flow field design and experimental investigation of electrochemical machining on blisk cascade passage

Electrochemical machining (ECM) provides an economical and effective way for machining heat-resistant, high-strength materials into complex shapes that are difficult to machine using conventional methods. It has been applied in several industries, especially aerospace, to manufacture blisk. The electrolyte flow field is a critical factor in ECM process stability and precision. To improve the process stability and the efficiency of blisk cascade passages, ECM with a radial feeding electrode, a rational electrolyte flow mode for electrochemical machining called “Π shape flow mode”, is discussed in the paper. Three flow field models are described separately in this report: traditional lateral flow mode, positive flow mode and Π-shaped flow mode, and the electrolyte velocity and pressure distribution vectors for each flow mode are calculated by means of a finite element fluid analysis method. The simulation results show that the electrolyte flow is more uniform with the Π-shaped flow mode. The deformation of the cathode, which is caused by the pressure difference, is also analysed in this report. The cascade passage ECM with a radial feeding electrode was experimentally tested out to evaluate the rationality of the flow field, and the fluctuation of current during the process was less than 1 %, which means that the process that uses the Π-shaped flow mode is stable. The feeding velocity of the cathode with the Π-shaped flow mode is approximately 70 % higher than that with the other two flow modes, and the incidences of short circuiting are obviously decreased. The surface roughness of the blisk hub is only 0.15 μm, and the machining error of the hub is less than 0.1 mm. The results demonstrate that using the Π-shaped flow mode can enhance the quality, stability and efficiency of blisk cascade passage ECM.     

嵌入磁路的电解加工技术

为提高电解加工精度,基于磁场和电场相互作用原理,设计了两种镶嵌磁路的阴极。分析了磁场对双电层液相3种传质方式的影响,提出将多极内封闭渐变磁路和多极外封闭渐变磁路组合后嵌入电解加工装置的方法。试验表明,沿阴极体周边均匀镶贴永磁体的阴极,加工时磁力线与电解液流动方向正交,可消除分股束流、空穴, 改善电解加工流场,改善工件表面粗糙度;顺阴极轴向在阴极头内嵌入永磁体,加强了反应物质向加工区传质的速度,提高了集中蚀除的能力,可有效减轻杂散腐蚀。对电解套料沿阴极内壁采用多极内封闭渐变磁路镶贴永磁体;对非铁异形孔加工,为进一步加强间隙磁场,可采用在阴极外表面镶嵌多极外封闭渐变磁路,在工件外套一多极内封闭渐变磁路形成组合磁场。     

旋转超声电解复合加工小孔流场仿真

为解决电解加工深小孔中电解液难以进入加工区和电解产物难以排出的问题,构建了内喷式旋转超声电解复合加工装置,进行了电解加工、旋转电解加工和旋转超声电解复合加工小孔的对比试验。试验结果表明,阴极旋转能明显提高孔的圆度,旋转超声电解复合加工具有最大的平均加工电流,所加工孔的直径、深度都为三者中最大,表明其材料去除率是最大的。在此基础上,利用有限元ANSYS CFX软件,建立了气液两相流三维气穴模型,分析了阴极旋转和阴极高频振动对电解加工流场、电场的影响。仿真结果表明：阴极旋转使得气泡在阴极表面聚集,不利于气泡的排出,阴极振动加速了电解液的运动,有利于气泡的排出,因此具有最大的材料去除率。     

Experiment and simulation study on concentrated magnetic field-assisted ECM S-03 special stainless steel complex cavity

A novel concentrated magnetic field-assisted electrochemical machining (ECM) technology is proposed in this paper to machine contemporaneously seven workplaces’ complex cavity with high efficiency and good precision. An ECM clamping apparatus with concentrated magnetic field, periodic magnetic field, and no magnetic field was designed. The magnetic field simulation was carried out. Comparing the results of the concentrated magnetic field to the periodic magnetic field, the magnetic field intensity of the former is increased by 9.8 % than the latter. The ECM cathode with the same gap was designed and manufactured. Under the conditions of 12 % NaNO₃, 14-V voltage, 0.8-MPa electrolyte pressure, temperature 32 °C, cathode feed rate 0.9 mm/min, initial machining gap 0.1 mm, and the S-03 special stainless steel workpiece material, the experiments with concentrated magnetic field, periodic magnetic field, and no magnetic field were carried out. The results show that the gap magnetic field strength was increased by 16.7 % in the concentrated magnetic field than in the periodic magnetic field. Through a sectioning test, the precision in the concentrated magnetic field is increased by 33.3 % compared with no magnetic circuit and increased by 14.8 % compared with the periodic magnetic field. The concentrated magnetic field-assisted ECM technology cannot only reduce the cathode design cycle and cost but also increase the process accuracy.     

Optimize the flow field during counter-rotating electrochemical machining of grid structures through an auxiliary internal fluid flow pattern

Flow field distribution plays a vital role in electrochemical machining (ECM) because it can directly affect the machining stability and accuracy of ECM. In counter-rotating electrochemical machining (CRECM), the uniformity of the flow field is difficult to control due to the complicated and changeable flow channel shape. Through the simulation of the conventional lateral fluid flow pattern, it is found that the complexity of the flow channel with grid structures makes the flow field of machining area strongly disordered, which leads to the low velocity zones and dead zones. Based on the simulation results, a new electrolyte flow pattern with an auxiliary internal fluid is proposed, which can remarkably improve the uniformity of flow field by apply supplementary electrolyte to the machining area. Experimental results show that the new flow pattern effectively improves the machining stability of CRECM, and enhances the machining precision of grid structures, the sidewall taper angle is reduced from 29.3° to 7.7°.     

基于计算流体动力学软件的型腔电解流场仿真

针对型腔电解加工中阴极流场设计分析的难点,应用计算流体动力学软件对型腔电解加工的流场进行仿真,得到加工间隙中流场的速度和压力分布,用以指导阴极的流场改进设计。经工艺试验验证,仿真结果较准确反映了型腔电解加工过程中的流场压力和速度分布,从而可以显著减少阴极流场设计中试验修正的次数,实现高效、低成本设计工具阴极流场之目的。

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基于有限元数值方法的电解加工工件型面的预测

采用有限元数值算法求解加工间隙中的电场分布，考虑间隙内流场和非线性电解液的影响，对最终的阳极工件型面进行预测。对某型发动机叶片三维复杂曲面进行了预测计算，并与其工艺试验结果进行比较，证明预测模型具有较高的精度。     

航天发动机叶片电解加工流场设计和试验研究

电解加工作为整体构件制造的主要技术之一,其流场设计的合理性将严重影响电解加工过程的稳定性、加工效率和质量。针对航天发动机叶片式扩压器设计了部分阻隔式反W型流场,并开展了与侧流式和反W型流场的仿真比较。仿真结果表明,该流场方式可以保证加工区电解液的高速流动,并能有效避免进/排气边漏液现象。最后,在部分阻隔式反W型流场中开展了叶片式扩压器电解加工试验,在阴极进给速度为0.5 mm/min时加工出了扩压器叶片,验证了流场设计的合理性。     

发动机叶片电解加工夹具结构设计与密封性能分析

探讨了叶片全方位电解加工时,夹具的总体结构设计、电解液流道布局、夹具体防腐蚀、导电和绝缘等影响叶片成型精度的若干关键问题;分析了夹具的密封性能对电解液压力、流速和加工稳定性的影响;通过叶片加工试验验证了所设计夹具的精度和可靠性。试验结果表明所设计的夹具定位准确,能加工出符合精度要求的发动机叶片;夹具的密封性能得到极大改善,在相同的进口压力下,加工腔及流道内的压力损失急剧减小,出口压力提高。     

Cutting tool wear monitoring for reliability analysis using proportional hazards model

Electrochemical machining (ECM) is an important technology in machining difficult-to-cut materials and to shape free-form surfaces. In ECM, material is removed by electrochemical dissolution process, so part is machined without inducing residual stress and without tool wear. To improve technological factors in electrochemical machining, introduction of electrode tool ultrasonic vibration is justifiable. This method is called as ultrasonically assisted electrochemical machining (USAECM). In the first part of the paper, the analysis of electrolyte flow through the gap during USAECM has been presented. Based on computational fluid dynamic methods, multiphase, turbulent and unsteady electrolyte flow between anode and cathode (under assumption that cavitation phenomenon occurs) has been analysed. Discussion of the obtained solutions is the base to define optimal conditions of electrolyte flow in case of USAECM process. The second part of the paper is connected with experimental investigations of USAECM process. Classic experimental verification of obtained results in case of machining is extremely difficult, but influence of the ultrasonic vibration can be observed indirectly by changes in technological factors (in comparison to machining without ultrasonic intensification), whereas results of numerical simulation give possibility to understand reason and direction of technological factors changes. Investigations proved that ultrasonic vibrations change conditions of electrochemical dissolution and for optimal amplitude of vibration gives possibility to decrease the electrode polarisation.     

渐开线内花键电解加工流场设计及工艺稳定性研究

为进一步提高渐开线内花键电解加工的工艺稳定性,基于数值分析方法探讨了电解液流动方式、工具阴极结构、电解液参数对流场分布的影响规律。数值分析结果表明：电解液侧向流动可以改善加工区入口处电解液流速分布均匀性;带有导流段的变截面阴极能够降低工件表面流速波动。针对工艺稳定性及加工定域性,开展了渐开线内花键电解加工试验研究。试验结果表明：进给速度可达2.1 mm/min以上,齿形误差可控制在0.015 mm以内,当加工深度为30 mm时,齿向误差在0.02 mm以内。该加工方式的效率及精度能够满足很多实际需求,具有明显的技术经济优势。     

基于叶片电解加工电场和流场特性的阴极设计及工艺试验研究

针对航空发动机叶片电解加工阴极设计这一具体工程应用，在模型叶片三维实体建模的基础上，着重研究两种阴极设计方法，即基于叶片电解加工实际电场分布的阴极设计有限元数值解法以及同时考虑极间电场和电解液流场特性的阴极设计有限元数值解法。详细地对比了两种阴极设计方法对极间电势分布、间隙分布和阴极边界条件的影响，通过一系列的工艺试验验证了同时考虑电解加工电场和流场特性的阴极设计方法较单纯考虑电场特性的阴极设计方法更全面、更符合电解加工的实际物理过程，因而所设计的阴极更加精确合理。     

基于电解液非线性特性的叶片电解加工阴极设计

叶片是航空发动机的关键零件,以某型航空发动机转子叶片为研究对象,针对叶片电解加工阴极设计这一工程问题,着重考察了采用非线性电解液进行加工时,电解液的非线性特性对阴极设计的影响.本文首先建立了模型叶片的三维实体造型,在此基础上探讨了电解液的非线性特性对电解加工过程和阴极设计产生影响的机理,通过半实验法与数据库技术相结合的方式有效的将这种非线性特性集成到阴极设计方法中.     

Electrochemical machining of the spiral internal turbulator

Electrochemical machining (ECM) is promising to machine the complex surface due to the advantages of no tool wear, stress free, and good machining accuracy. In this study, a machining method of the spiral internal ribs by ECM is presented. Firstly, the ECM experimental system is developed, which consists of electrolyte supply module, power supply unit, and workpiece-holding device. Then, a shaped cathode was used to process the spiral-turbulated hole on the built system. The shaped cathode was prepared by means of ultraviolet-curing mask method considering the expected spiral turbulator’s shape. Furthermore, parameters affecting the machining accuracy in shape duplication and machining efficiency are analyzed and discussed, especially the voltage and electrolyte concentration which have the main effect on the processed results.     

双缘板叶片电解加工流场优化与试验研究

针对在长叶身的双缘板叶片电解加工中由于流场的不均匀经常导致加工短路的问题,开展了叶片电解加工流场优化仿真分析,结果表明大量电解液从两侧缘板区域的间隙中被分流,造成叶身型面部分流量减小,导致产物不能及时排出间隙,容易引起加工短路。为了改善加工区域流场分布不均的情况,提出了一种基于液体密封的多向辅助供液流场方式,对提出的流场方式开展流场仿真分析,仿真结果表明加工区流场稳定性与一致性显著提升。开展了所提出流场的电解加工工艺试验,加工过程电流稳定,试件具有较好的加工效果,验证了提出流场方式的有效性。     

电极平动式电解孔加工技术研究

从电解液流动角度对影响电解孔加工过程的主要原因进行了分析 ,提出利用电极平动来改善电解加工过程稳定性和提高加工精度 ,研制了电极平动系统 ,进行了加工试验。试验结果表明 ,电极的平动运动使得电解液分布变得均匀 ,消除了空穴和分离流等弊端 ,改进了过程稳定性 ,显著提高了加工精度。     

Design of the cross-structural cathodes in electrochemical machining of aero-engine blades

Blades are crucial parts of aero-engines. Their manufacturing is difficult because of their thinness, complex profile and stringent requirements. Electrochemical machining (ECM) is an important approach for manufacturing blades, but it is difficult to machine the leading and trailing edges. This article adopts cross-structural cathodes in ECM to solve the open electric field space problem. The key difficulty in the design of cross-structural cathodes is the position of the crossed-point. The height and the offset of the crossed-point are optimized using the ANSYS software. The simulation results show that the position of the crossed-point obviously affects the machining accuracy, along the leading and trailing edges of the blade. A pair of cross-structural cathodes with one uniform section is designed, and a series of corresponding ECM experiments are carried out. The experiments demonstrate that the ECM process is stable, the profiles are sleek and the machining dimensional error is reduced to 0.08 mm at the leading and trailing edges of the blade when using the new cathode structure.     

The coupled effect of magnetic field,electric field,and electrolyte motion on the material removal amount in electrochemical machining

Electrochemical machining (ECM) has a strong advantage in dealing with difficult-to-machine materials and complex shaped parts. In order to improve machining accuracy, some researchers, based on the principle of interactions between the magnetic field and electric field, proposed the magnetic field-assisted ECM technology that is advantageous in improving surface roughness and facilitating material removal amount. Pitifully, little attention has been attached to effects of the coupled magnetic field, electric field, and electrolyte motion on the amount of materials removed. This paper aims to find out how arrangements of magnetic fields and coupled of the three energy (which were magnetic field, electric field, and electrolyte motion) will work on the amount of material removed in ECM. Here established a Navier-Stokes equation and a model of material removal amount in the anode under the electromagnetic field. Physical and mathematical models of the electrolyte’s flow characteristics and material removal amount were constructed through the COMSOL Multiphysics software, and simulations were carried out. An experiment was implemented to test models and the simulations. Simulation results indicated that different arrangements of the magnetic field had delivered different impacts on flow characteristics of the flow field and material removal amount. Experiment results revealed that the material removal amount had increased regardless of arrangements of magnetic fields and that the flow rate of the electrolyte had played a role in this connection. The study involved in this paper showed that the introduction of the magnetic field worked favorably to lift the material removal amount and that arrangements of magnetic fields also had the same effect in this regard. Also, it was found that a growing flow rate of the electrolyte had hindered the increases of the material removal amount.