微细电解铣削加工模型及实验研究

 对微细电解铣削加工技术进行了深入研究。将分层加工技术应用到微细电解加工过程中,显著改善了加工稳定性;建立了微细电解铣削加工的数学模型;基于电化学刻蚀原理,在线制得直径小至10 μm的圆柱电极;分组实验并验证了加工模型中各参数如：电极直径、加工电压、电解液浓度、铣削层厚度等对微细电解铣削加工精度的影响。通过优化加工参数,成功加工出了深三角结构和四棱台微型腔,形状精度高,加工稳定性好。     

Electrochemical machining of complex components of aero-engines: Developments,trends, and technological advances

Because of several advantages, such as no tool wear, independence on the mechanical properties of the material, and high machining efficiency, electrochemical machining (ECM) has become a viable method for machining components in numerous industrial applications, particularly in the manufacture of typical aero-engine components with complex structures fabricated from materials that are difficult to cut. This paper highlights the current developments, new trends, and technological advances of key factors of ECM, such as electrochemical dissolution characteristics of novel difficult to cut materials which are often used in aero-engine, numerical simulation of electrochemical process, design for the complex profile and structure of cathode tool, flow field simulation and design for uniform electrolyte flow, and innovation of electrochemical machining or hybrid methods which reflect the state of the art in academic and industrial research on electrochemical machining in aero-engine manufacturing.     

Surface-improvement mechanism of hybrid electrochemical discharge process using variable-amplitude pulses

Superalloys are commonly used in aircraft manufacturing; however, the requirements for high surface quality and machining accuracy make them difficult to machine. In this study, a hybrid electrochemical discharge process using variable-amplitude pulses is proposed to achieve this target. In this method, electrochemical machining (ECM) and electrical discharge machining (EDM) are unified into a single process using a sequence of variable-amplitude pulses such that the machining process realizes both good surface finish and high machining accuracy. Furthermore, the machining mechanism of the hybrid electrochemical discharge process using variable-amplitude pulses is studied. The mechanism is investigated by observations of machining waveforms and machined surface. It is found that, with a high-frequency transformation between high- and low-voltage waveforms within a voltage cycle, the machining mechanism is frequently transformed from EDM to pure ECM. The critical discharge voltage is 40 V. When pulse voltages greater than 40 V are applied, the machining accuracy is good; however, the surface has defects such as numerous discharge craters. High machining accuracy is maintained when high-voltage pulses are replaced by low-voltage pulses to enhance electrochemical dissolution. The results indicate that the proposed hybrid electrochemical discharge process using variable-amplitude pulses can yield high-quality surfaces with high machining accuracy.     

Electrochemical trepanning with uniform electrolyte flow around the entire blade profile

In the traditional machining process for diffusers, blades are easily deformed, and methods suffer from high tool wear and low efficiency. Electrochemical machining(ECM) possesses unique advantages when applied to these difficult-to-machine materials. In the ECM process, theflow field plays a crucial role. Here, an electrolyte flow mode that supplies uniform flow around the entire blade profile was adopted for electrochemical trepanning of diffusers. Various flow rates were employed to obtain the optimal flow field. Simulations were conducted using ANSYS software, and results indicated that increasing the flow rate substantially afforded a more uniform flowfield. A series of experiments was then performed, and results revealed that increasing the flow rate greatly improved both the machining efficiency and the surface quality of the diffusers. The maximum feeding rate of the cathode reached 4 mm/min, the blade taper of the concave part decreased to 0.02, and the blade roughness was reduced to 1.216 lm. The results of this study demonstrated the high feasibility of this method and its potential for machining other complex components for engineering applications.     

整体叶轮的数控电解加工及其在航天制造中的应用前景

综述了整体叶轮的主要加工方法及其比较，就数控展成电解加工的重要技术特点(可以综合发挥数控技术和电解加工两者的技术优点)进行了论述，展示了数控电解在加工整体叶轮、解决以数控铣、精密铸造难加工或不能加工的技术难题方面所显示的优越性。该项工艺技术对于新型航天发动机的研制具有重要意义和广阔的应用前景。     

Analysis and control of inter-electrode gap during leveling process in counter-rotating electrochemical machining

The inter-electrode gap (IEG) is an essential parameter for the anode shaping process in electrochemical machining (ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of an oval anode workpiece in counter-rotating ECM (CRECM) is investigated. The variation of the minimum IEG is analyzed theoretically, and the results indicate that rather than reaching equilibrium, the minimum IEG in CRECM expands constantly when a constant feed speed is used for the cathode tool. This IEG expansion leads to a poor localization effect and has an adverse influence on the roundness of the machined workpiece. To maintain a small constant IEG in CRECM, a variable feed speed is used for the cathode based on a fitted equation. The theoretical results show that the minimum IEG can be controlled at a small value by using an accelerated feed speed. Experiments have been conducted using a specific experimental apparatus in which the cathode tool is designed as a combined structure of two sectors and a thin sheet. By detecting the machining currents flowing through the minimum IEG, how the latter varies is obtained indirectly. The results indicate that using an accelerated feed speed is effective for controlling the IEG, thereby improving the roundness of the machined workpiece.     

电火花铣削加工中工具电极损耗补偿策略研究

在电火花铣削加工中,由于工具电极作旋转运动,其损耗呈轴对称分布,使工具电极的补偿成为可能。本文对工具电极的损耗形状进行了研究,提出一种在线工具损耗补偿措施,从而避免了工具损耗形状的检测,极大地提高了生产效率和加工精度     

Experimental research on electrochemical machining of titanium alloy Ti60 for a blisk

Ti60(Ti–5.6Al–4.8Sn–2Zr–1Mo–0.35Si–0.7Nd) is a high-temperature titanium alloy that is now used for important components of aircraft engines. Electrochemical machining(ECM) is a promising technique that has several advantages, such as a high machining rate, and can be used on a wide range of difficult-to-process materials. In this paper, orthogonal experiments are conducted to investigate ECM of Ti60, with the aim of determining the influences of some electrochemical process parameters on the surface roughness. The most important parameter is found to be the frequency of the pulsed power supply. It is found that using suitably optimized parameters for ECM can greatly decrease the surface roughness of a workpiece. A surface roughness of approximately 0.912 lm can be obtained with the following optimal parameters: Na Cl electrolyte concentration 13wt%, voltage20 V, pulse frequency 0.4 k Hz, duty cycle 0.3, temperature 23 °C, and anode feed rate 0.5 mm/min.Furthermore, blisk blades have been successfully processed using these optimized parameters.     

(TiB+TiC)/TC4复合材料电解钻孔试验研究

钛基复合材料是一种典型的难加工材料,采用传统机械加工方法存在加工效率低和加工质量差等问题。利用电解加工技术,采用直径为10mm的管状阴极,对(TiB+TiC)/TC4复合材料进行电解钻孔加工试验研究。进行了(TiB+TiC)/TC4复合材料的电化学特性研究,测量了(TiB+TiC)/TC4复合材料在10%NaNO₃溶液中的极化曲线和电流效率。探究了加工电压、电解液压力对加工精度的影响。结果表明,当加工电压为30V,电解液压力为0.6MPa时,电解钻孔可以在1mm/min的进给速度下稳定加工。当加工的盲孔深径比为3.06时,孔的圆度误差为41.1μm,锥度为0.4°,具有较高的加工精度。     

Effect of tube-electrode inner diameter on electrochemical discharge machining of nickel-based superalloy

Nickel-based superalloys are widely employed in modern aircraft engines because of their excellent material characteristics, particularly in the fabrication of film cooling holes. How-ever, the high machining requirement of a large number of film cooling holes can be extremely chal-lenging. The hybrid machining technique of tube electrode high-speed electrochemical discharge drilling (TEHECDD) has been considered as a promising method for the production of film cooling holes. Compared with any single machining process, this hybrid technique requires the removal of more complex machining by-products, including debris produced in the electrical discharge machin-ing process and hydroxide and bubbles generated in the electrochemical machining process. These by-products significantly affect the machining efficiency and surface quality of the machined prod-ucts. In this study, tube electrodes in different inner diameters are designed and fabricated, and the effects of inner diameter on the machining efficiency and surface quality of TEHECDD are inves-tigated. The results show that larger inner diameters could effectively improve the flushing condi-tion and facilitate the removal of machining by-products. Therefore, higher material removal efficiency, surface quality, and electrode wear rate could be achieved by increasing the inner diam-eter of the tube electrode.     

Trajectory control strategy of cathodes in blisk electrochemical machining

A turbine blisk, which combines blades and a disk together, is one of the most important components of an aero engine. In the process of blisk electrochemical machining (ECM), the sheet cathode, which is usually used as a tool electrode, has a complicated structure. In addition to that, the channel between the adjacent blades is narrow and twisted, so interference is apt to happen when the sheet cathode feeds into the channel. Therefore, it is important to choose suitable trajectory control strategy. In this paper, a new trajectory control strategy of the sheet cathode is presented and corresponding simulation analysis is conducted on the basis of an actual blisk model. The simulation results demonstrate that the sheet cathode can feed into the channel by a spatial line trajectory without interference. Moreover, the verification experiments are carried out according to the simulation. The experimental results show that the cathode can move into the channel without interference. It is verified that the new trajectory control strategy is correct and can be used in the blisk ECM process successfully.     

微尺度线电极电解加工

微尺度线电极电解是近期出现的一种新加工方法,采用钨丝作为线电极,在加工过程中电极无损耗,通过控制工具电极轨迹可实现微细结构加工。建立了微尺度线电极电解加工模型;通过微尺度线电极叠加微幅振动,促进了加工间隙中电解液更新;针对加工电压、脉冲宽度、脉冲周期和加工速度等影响微尺度线电极电解加工精度的因素进行了参数对比试验,并对加工参数进行了分析和优化。采用电化学腐蚀原理进行微米尺度线电极的在线制作,在线制得直径10 μm和2 μm的线电极,实现了切缝宽度为20 μm以下的复杂微细结构以及切缝宽度为8 μm以下的微螺旋结构。     

航空发动机机匣摆线粗加工轨迹规划方法

针对机匣零件粗加工过程中凸台多、加工余量大、材料难切削、刀具磨损快、加工周期长等特点,提出了一种机匣摆线粗加工刀具轨迹规划方法,该方法能有效控制切削过程中刀具负载的变化,改善刀具切削过程中的加热-冷却循环,减缓刀具的磨损,提高机匣粗加工效率。首先,通过对两种摆线模型的分析,建立了摆线铣数学模型,并分析了摆线铣的优缺点;其次,结合机匣零件特点,将模型在精度范围内离散为点模型,利用圆锥将模型展开并建立展开模型与原始模型间的映射关系。通过对可加工区域的划分和平面逼近,生成了适用于机匣零件的摆线粗加工刀具轨迹。最后,分别通过摆线铣刀具磨损实验、平面型腔摆线铣实验和机匣摆线铣实验,验证了摆线铣在降低刀具磨损、延长刀具寿命方面的有效性,以及本文轨迹生成算法在航空发动机机匣实际加工中的正确性和高效性。研究成果能有效缩短加工周期、降低加工成本,提升机匣零件的粗加工效率。     

Convex shaping process simulation during counter-rotating electrochemical machining by using the finite element method

In counter-rotating electrochemical machining(CRECM), a revolving cathode tool with hollow windows of various shapes is used to fabricate convex structures on a revolving part. During this process, the anode workpiece and the cathode tool rotate relative to each other at the same rotation speed. In contrast to the conventional schemes of ECM machining with linear motion of a block tool electrode, this scheme of ECM is unique, and has not been adequately studied yet. In this paper, the finite element method(FEM) is used to simulate the anode shaping process during CRECM, and the simulation process which involves a meshing model, a moving boundary,and a simulation algorithm is described. The simulated anode profiles of the convex structure at different processing times show that the CRECM process can be used to fabricate convex structures of various shapes with different heights. Besides, the variation of the inter-electrode gap indicates that this process can also reach a relative equilibrium state like that in conventional ECM. A rectangular convex and a circular convex are successfully fabricated on revolving parts. The experimental results indicate relatively good agreement with the simulation results. The proposed simulation process is valid for convex shaping prediction and feasibility studies as well.     

Simulation and experimental investigation on a dynamic lateral flow mode in trepanning electrochemical machining

An appropriate flow mode of electrolyte has a positive effect on process efficiency, surface roughness, and machining accuracy in the electrochemical machining(ECM) process. In this study, a new dynamic lateral flow mode, in which the electrolyte flows from the leading edge to the trailing edge, was proposed in trepanning ECM of a diffuser. Then a numerical model of the channel was set up and simulated by using computational fluid dynamics software. The result showed that the distribution of the flow field was comparatively uniform in the inter-electrode gap. Furthermore, a fixture was designed to realize this new flow mode and then corresponding experiments were carried out. The experimental results illustrated that the feeding rate of the cathode reached 2 mm/min, the best taper angle was about 0.4°, and the best surface roughness was up to Ra= 0.115 lm. It reflects that this flow mode is suitable and effective, and can also be applied to machining other complex structures in trepanning ECM.     

Electrochemical machining on blisk channels with a variable feed rate mode

Electrochemical machining (ECM) is an economical and effective method for blisk manufacturing and includes two steps: channel machining and profile machining. The allowance distribution after the channel machining will directly affect the profile machining. Therefore, to improve the uniformity of allowance distribution in the machining of channels, a method that incorporates a variable feed rate mode is developed. During the machining process, the feed rates are dynamically changed according to the needs of the side gap at the different feed depths. As a result, the side gaps at the different feed depths vary, contributing to a decrease in the allowance difference. In this study, the dissolution processes of a blisk channel are simulated using different feed rates, and prediction profiles are obtained. Based on the prediction profiles, the relationship among the feed rate, feed depth, and side gap is established. Then, the feed rates at different feed depths are adjusted according to the relationship. In addition, contrast experiments are conducted. Compared with blisk channel ECM using a constant feed rate of 1 mm/min, using the variable feed rate decreases the allowance differences in the convex and concave parts by 62.2 % and 67.4 %, respectively. This indicates that using the variable feed rate in the ECM process for a blisk channel is feasible and efficient.     

定长补偿电火花铣削加工中锥形电极的形成及稳定性

电火花铣削可以利用简单电极加工复杂工件,对铣削过程中电极损耗进行补偿是保证工件加工精度的重要措施。使用圆柱电极进行定长补偿铣削加工,加工过程中电极端面会形成一个圆锥形。为保证补偿精度,对电极圆锥形端面的形成及稳定性进行了研究。通过对定长补偿下工件被加工情况的研究,阐述了圆锥形电极形成的具体过程;并且论证了在加工进入稳定阶段以后,圆锥端面角度会基本保持在一个恒定值,研究了初始加工深度和补偿长度对锥形过渡阶段的影响;在电极直径、电参数一定情况下,验证了加工模型中锥形角度与目标加工深度的函数关系,实验结果与模型计算结果相差2.1%;最后给出了加工实例,并获得较好的加工效果。     

Electrochemical micromachining of micro-dimple arrays on cylindrical inner surfaces using a dry-film photoresist

The application of surface textures has been employed to improve the tribological performance of various mechanical components. Various techniques have been used for the application of surface textures such as micro-dimple arrays, but the fabrication of such arrays on cylindrical inner surfaces remains a challenge. In this study, a dry-film photoresist is used as a mask during through-mask electrochemical micromachining to successfully prepare micro-dimple arrays with dimples 94 lm in diameter and 22.7 lm deep on cylindrical inner surfaces, with a machining time of 9 s and an applied voltage of 8 V. The versatility of this method is demonstrated, as are its potential low cost and high efficiency. It is also shown that for a fixed dimple depth, a smaller dimple diameter can be obtained using a combination of lower current density and longer machining time in a passivating sodium nitrate electrolyte.     

Simulation and experimental investigation of inner-jet electrochemical grinding of GH4169 alloy

GH4169 alloy is one of the most commonly used materials in aero engine turbine blades, but its machinability is poor because of its excellent strength at high temperatures. Electrochemical machining (ECM) has become a common method for machining this alloy and other difficult-to-machine materials. Electrochemical grinding (ECG) is a hybrid process combining ECM and conventional grinding. In this paper, investigations conducted on inner-jet ECG of GH4169 alloy are described. Two types of inner-jet ECG grinding wheels were used to machine a flat bottom surface. The machining process was simulated using COMSOL software, and machining gaps under different machining parameters were obtained. In addition, maximum feed rates and maximum material removal rates under different machining parameters were studied experimentally. The maximum sizes and the uniformity of the distributions of the gaps machined by the two grinding wheels were compared. The effects of different applied voltages on the machining results were also investigated.     

Machining of a film-cooling hole in a single-crystal superalloy by high-speed electrochemical discharge drilling

Single-crystal superalloys are typical advanced materials used for manufacturing aeroengine turbine blades. Their unique characteristics of high hardness and strength make them exceedingly difficult to machine. However, a key structure of a turbine blade, the film-cooling hole,needs to be machined in a single-crystal superalloy; such machining is challenging, especially considering the increasing levels of machining efficiency and quality demanded by the aeroengine industry. Tube electrode high-speed electrochemical discharge drilling(TSECDD), a hybrid technique of high-speed electrical discharge drilling and electrochemical machining, provides high machining efficiency and accuracy, as well as eliminating the recast layer. In this study, TSECDD is used to machine a film-cooling hole in a nickel-based single-crystal superalloy(DD6). The Taguchi methods of experiment are used to optimise the machining parameters. Experimental results show that TSECDD can effectively drill the film-cooling hole; the optimum parameters that give the best performance are as follows: pulse duration: 12 ls, pulse interval: 30 ls, peak current:6 A, and salt solution conductivity: 3 m S/cm. Finally, a hole is machined by TSECDD, and the results are compared with those obtained by electrical discharge machining. TSECDD is found to be promising for improving the surface quality and eliminating the recast layer.