Figure - available from: Advances in Mechanical Engineering
This content is subject to copyright.
SEM photographs of recast layer: (a) micrograph of recast layer due to the EDM process and (b) SEM image of an EDM surface showing microcracks.
Source publication
Noncircular holes on the surface of turbine rotor blades are usually machined by electrodischarge machining. A recast layer containing numerous micropores and microcracks is easily generated during the electrodischarge machining process due to the rapid heating and cooling effects, which restrict the wide applications of noncircular holes in aerosp...
Similar publications
Nickel-based superalloys are widely used as high temperature materials for turbine blades in aerospace industry and land-based applications. Their structural characterization, however, is mostly carried out at the room temperature. Here, the microstructure of the superalloys was studied at high temperature, 1000 °C, through aberration-corrected sca...
Nickel aluminides have been extensively studied in recent decades to replace superalloys, in some components of aircraft turbines, because they have excellent corrosion resistance. Many industrial cities have the problem of air pollution, which has forced the study of the degradation of these alloys in the presence of acid rain. The aim of this wor...
![Fig. 3. SEM micrograph showing rafting in SX superalloy [16] .](profile/Pierluigi-Fusco/publication/329656526/figure/fig2/AS:703778391085057@1544805252049/SEM-micrograph-showing-rafting-in-SX-superalloy-16_Q320.jpg)
Necessity of high performing single crystal materials
for turbine blades and vanes in aerospace and energetic applications brought to the rapid development of single crystal (SX)
Ni-base superalloys; several companies are nowadays providing
a huge variety of new generation superalloys and innovative
processes which have the aim to provide the marke...
Citations
... To address the defects caused by WEDM, the methods including electrochemical machining, magnetic abrasive finishing, and chemical corrosion could be employed. Among them, electrochemical machining offers the advantages in terms of high-precision processing and small thermal deformation, but it is challenged by the issues like stray current corrosion, complexity of dimensional accuracy control, material waste, and environmental pollution [26,27]. Magnetic abrasive finishing utilizes the magnetic abrasives to scratch the specimen driven by shear force within a magnetic field, thereby enhancing the surface quality [28,29]. ...
Wire electrical discharge machining (WEDM) is highly suitable for processing the hard-brittle materials like metallic glasses (MGs). However, the electro-thermal energy conversion involved in the WEDM process inevitably introduces some surface defects including bulges, discharge craters, and recast materials on the WEDMed MG surface, which significantly impedes its practical application. Here, an emerging automated polishing technology, laser polishing (LP), was performed in the nitrogen-rich environment to simultaneously improve the surface quality and hardness of the WEDMed Zr-based MG surface. The detailed effects of LP parameters on the surface roughness and morphology were systematically investigated. The morphology evolution and temperature distribution of the molten pool during LP were analyzed by simulation analysis. The experimental results indicated that after single LP of four representative WEDMed Zr-based MG surfaces using the optimized laser parameters, the surface roughness (Sa) was remarkably reduced from 1.27, 2.10, 3.49, and 4.58 μm to 0.09, 0.14, 0.17, and 0.21 μm, respectively, accompanied by an increase in surface hardness from 6.30 GPa to 7.39, 7.67, 8.51 and 8.99 GPa. This study demonstrated that LP could effectively achieve simultaneous enhancement of the quality and hardness of WEDMed MG surfaces, which would contribute to expanding the application prospects of MGs.
... The experiments showed that the methods could remove re-solidified layer and surface heat-affected zone and reduce surface roughness. Ma et al. [12] conducted EDM and pulse electrochemical machining (PECM) on the same machine. During the machining, the electrode remained unchanged, and the electrolyte was changed from deionized water to neutral sodium nitrate solution. ...
In this paper, aiming at re-solidified layer problem on workpiece surface in short electric arc machining (SEAM), a new hybrid process (SEACM) combining SEAM and electrochemical machining (ECM) was proposed using a mixture of NaCl solution and air with electrolytic and dielectric properties as working medium to achieve the effect of removing surface re-solidified layer by enhancing the electrochemical interaction between the poles during short electric arc machining. By discussing the influence of gas pressure in working medium on the machining performance of SEACM, the process was divided into two kinds of SEACM machining forms: efficiency-first and quality-first. Combining the advantages of the two machining forms in material removal rate (MRR) and surface quality, a combined machining mode was proposed. The MRR, specific energy consumption (SEC), surface morphology, cross-sectional morphology, chemical composition and microhardness after combined machining mode of titanium alloys were analyzed. The experimental results show that the MRR after combined machining exceeded 450 mm3/min, the SEC was 233.6 kJ/cm3, and the surface of the workpiece was basically free of defects. The surface roughness Sa was only 389 nm, and the re-solidified layer and heat-affected layer were completely removed.
... The above research shows that electrochemical machining can effectively improve the surface quality and shape accuracy of special-shaped parts, but it has strict requirements for the design of the cathode structure and the distribution of the flow field in the machining [20,21]. The electrochemical machining processes of intersecting holes, deep holes, and throughholes are affected by physical fields, such as the flow field and electric field [22]. ...
Small-sized inner intersecting holes are a common structure for large engine nozzles, hydraulic valves, and other parts. In order to ensure the uniform and stable fluid state in the intersecting hole, it is necessary to process the fillet at the intersecting line and accurately control the fillet radius. Limited by the structure and size, the rounding of the small-sized inner intersecting hole is a technical problem, and the traditional machining methods have problems, in terms of efficiency and accuracy. In order to solve this problem, electrochemical machining technology was applied to the rounding of small-sized inner intersecting holes. According to the structure of inner intersecting holes, an electrochemical rounding processing scheme with built-in fixed cathode was designed. The electric field distribution of different cathode shapes was analyzed using finite element method software. The influence of processing voltage and processing time on the current density distribution was studied for different cathode shapes, to determine the most reasonable cathode shape. Taking the inner intersecting hole with a diameter of 2 mm as the research object, and according to the analysis of the influence of processing voltage on the processing effect, a suitable control factor for controlling the rounding was processing time, and the optimal processing voltage was obtained. The formulas of fillet radius and processing time were obtained by regression analysis and verified using machining examples. The results provide a feasible method for the accurate and controllable machining of small-sized inner intersecting hole rounding.
... A large number of scholars have carried out a lot of researches on the problem of low forming precision and poor surface quality for hole parts. For processing technology, Ma et al. fabricated the non-circular hole structure on the surface of a turbine rotor blade by using the combined electrical machining technology [13]. Sathish used the injector nozzle to drill micro-holes in pure stainless steel. ...
In order to solve the problem of uneven gap distribution and flow pattern in the complex parts with multi-stage internal cone hole in electrochemical machining, a method of computer simulation–assisted cathode design is proposed. The electric field and flow field models of machining gap are established respectively, and the simulations of different cathode profiles are carried out. When the cathode cone angle is 2°, the electric field distribution between the cathode and the workpiece is reasonable, and the electrolyte distribution in the machining gap is uniform. With the conditions of processing voltage 10 V, electrolyte inlet pressure 1.5 MPa, electrolyte temperature 28 ℃, and cathode feed speed 5 mm/min, the electrochemical machining (ECM) processing of multi-stage internal cone hole is carried out by using the optimized cathode. The results show that the surface of the workpiece has no flow pattern, the dimensional forming accuracy is better than 0.1 mm, and the surface roughness reaches Ra 0.697 μm. Research shows that the optimization of cathode structure with computer simulation can shorten the cathode development cycle and reduce the cost of cathode design effectively in ECM, which provides an efficient and feasible method for the optimization of complex cathode structure.
... For processing technology，Ma et al. fabricated the non-circular hole structure on the surface of turbine rotor blade by using the combined electrical machining technology [13]. Sathish used the injector nozzle to drill micro holes in pure stainless steel. ...
... The transmission equation of k is as follow (13) The transmission equation of ε is as follow (14) Where, turbulence generates term is (15) The model constant values in the formula are shown in Table 1. ...
In order to solve the problems of uneven gap distribution and flow pattern in complex parts with multi-stage internal cone holes in electrochemical machining, a method of computer simulation assisted cathode design was proposed. The electric field and flow field models of machining gaps were established respectively, and the simulation of different cathode profiles was carried out. When the cathode cone angle is 2°, the electric field distribution between the cathode and the workpiece is reasonable, and the electrolyte distribution in the machining gap is uniform. With the conditions of processing voltage 10 V, electrolyte inlet pressure 1.5 MPa, electrolyte temperature 28 ℃ and cathode feed speed 5mm/min, the ECM processing of multi-stage internal cone hole was carried out by using the optimized cathode. The results show that the surface of the workpiece has no flow pattern, the dimensional forming accuracy is better than 0.1mm, and the surface roughness reaches Ra0.697µm. Research shows that the optimization of cathode structure with computer simulation can shorten the cathode development cycle and reduce the cost of cathode design effectively in ECM, which provides an efficient and feasible method for the optimization of complex cathode structure.
... Manpreet [21] obtained the optimal direct current voltage suitable for ECM of silicon wafers by taking overcut and taper as the output quality characteristics. Ma et al. [22] used the pulse electrochemical method to optimize the surface roughness of non-circular holes after EDM, which was decreased from 4.227 µm to 0.229 µm. ...
Electrical parameters of the power supply are significant factors affecting the accuracy and stability of the electrochemical machining (ECM). However, the electric field, flow velocity and temperature in the machining area are difficult to measure directly under the influence of the power supply. Therefore, taking the film cooling hole as an example, the multi-physics coupling simulation analysis of the ECM is performed on the basis of Faraday’s law and fluid heat transfer mathematical model. The machining characteristics of the direct current and pulse ECM are compared through simulation. The results show that the pulse ECM improves the distribution of temperature and current density in the machining area. The period has little effect on the temperature, current density and side removal rate. The side removal rate increases with the increase of the duty ratio and lateral gap. Increasing of the duty ratio and decreasing of the lateral gap will increase the temperature and current density. Increasing the inlet pressure accelerates the frequency of renewal of heat and electrolysis products, which can reduce the single side gap. The experience of the ECM holes verifies the results of the simulation. The accuracy and stability of the ECM of holes are enhanced by optimizing the duty ratio, lateral gap and inlet pressure.
... The ECD process uses an acid-based electrolyte and produces high aspect ratio features with excellent surface finishes and reduced tool wear. [7] The exterior surface (except the tip) of the cathode tool is usually insulated. However, one of the severe drawbacks of the ECD process is the loss of tool insulation due to the chemical reaction, which leads to stray removal from the internal wall of the hole. ...
A non-contact machining process such as electrical discharge machining (EDM) is generally employed for machining electrically conductive materials irrespective of its hardness. However, the process becomes unstable and slow when deep features are to be machined. Furthermore, the standard dielectric-based EDM process is unable to meet the requirements of today’s fast-moving manufacturing industry. Therefore, in this study, the authors present the development of a novel super dielectric which is used in the EDM drilling process and experimentally demonstrates how the machining efficiency in the drilling of a deep hole is improved significantly. In addition, the effect of super dielectric fluid on the plasma current is presented and the experimental observations have been validated through the plasma physics theory. The efficiency of the super dielectric-based EDM process is experimentally validated with the successful drilling holes of aspect ratio more than 100 in Inconel 718 within 6 minutes.
... The results show that with pulse ECM, the roughness could be reduced from 4.277 lm to 0.299 lm. 145 Zhao et al. studied combined electrical machining for closed integral structures. Unlike the above-mentioned method, the first step of this method is electrochemical reaction to machine the channels with high efficiency, and the second step is EDM to machine the structure with high accuracy. ...
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.
Laser drilling is always accompanied by recast layers, micro-cracks, and heat-affected zones, which limit its application in engineering. Due to its unique advantages, such as no heat-affected zones, no residual stresses, and no dependence on the mechanical properties of the materials, electrochemical dissolution has been adopted to remove the laser drilling-induced surface defects. The electrochemical dissolution characteristics and surface evolution of the laser-drilled Ni-based superalloys were studied. The polarization curves and electrochemical impedance spectroscopy (EIS) of the laser-drilled materials and the substrate were measured, indicating that the laser-drilled surface had a smaller corrosion resistance than the original substrate. X-ray photoelectron spectroscopy (XPS) results showed that the laser-drilled surface had a much higher oxygen content than the substrate. Additionally, electric current efficiency curves were obtained to study the anodic dissolution behavior of Ni-based superalloys. An electric current density in the 5–40 A/cm2 range was preferred to enhance the electrochemical dissolution rate. Moreover, the effects of electric current densities and post-processing time on the surface roughness and the recast layer thickness of the laser-processed Ni-based superalloys were investigated using a NaCl and NaNO3 solution electrolyte. The evolution of the surface quality and recast layer thickness were clarified. Furthermore, an anodic dissolution model of the laser-processed surface was established to illustrate the electrochemical post-processing mechanisms. Results revealed that electrochemical dissolution could completely remove the laser drilling-induced surface defects in 20 s using a 12.5 wt.% NaNO3 solution electrolyte and a 40 A/cm2 electric current density. Finally, an electrochemical post-processed surface with surface roughness (Ra) of 1.7 µm and without a recast layer was achieved. Micro holes without recast layers and Ra of 0.69 µm were obtained with high efficiency using laser processing and electrochemical post-processing.
When the workpiece is sliced by using wire electrical discharge machining (WEDM), owing to the material removal mechanism of melting and evaporation, numerous overlapping discharge craters and recast layer can be generated on the workpiece surface, leading to the high surface roughness. In this study, a method called WEDCM, which uses wire electrochemical machining (WECM) to remove the recast layer and reduce the WEDM surface roughness, is proposed. An analytical model is developed to identify the appropriate feed rate of the wire electrode during the stage of electrochemical dissolution. The calculation results show that in order to dissolve the recast layer, the wire feed rate should be reduced with the increase of the movement distance. The experiments are carried out on the same machine tool with the same electrolyte (deionized water) to verify the model. The experimental results show that the recast layer on the WEDM surface can be dissolved and the surface roughness can be reduced with WEDCM. Two factors which have great influence on the final surface roughness are also discussed.
