Electrochemical Machining Method Research Articles

Development and experimental evaluation of surface enhancement methods for laser powder directed energy deposition microchannels

ABSTRACT This research evaluates Laser Powder Directed Energy Deposition (LP-DED) for producing fine feature internal microchannels. This study is focused on enhancing and characterising the surfaces of microchannels produced using techniques such as abrasive flow machining, chemical milling, chemical mechanical polishing, electrochemical machining, and thermal energy method to modify internal surfaces of microchannels made from NASA HR-1 Fe-Ni-Cr alloy. Flow testing for discharge coefficient measurement is conducted on processed microchannel samples, followed by characterisation through optical microscopy, Scanning Electron Microscopy (SEM), and Computed Tomography. Findings reveal variations in surfaces due to powder adherence, melt pool undulations, and polishing mechanisms. The study emphasises the significance of removing material equivalent to the mean powder diameter to reduce surface roughness and impact the discharge coefficient. The research proposes a ratio for planarising roughness and waviness peak height and density, offering insights for tailored surface adjustments in specific applications requiring reduced flow resistance. Highlights Internal microchannels with thin-walls were fabricated using the laser powder directed energy deposition process. Various surface enhancements and polishing processes were developed to modify the surface texture of the LP-DED channels. Flow testing was conducted to determine the discharge coefficient. Post-test characterisation was completed to obtain cross sectional area, perimeter, surface texture, and general surface condition to analyse results. Ratio of roughness and waviness peak and density (Spk/Spd and Wp/WPc) is proposed as a relevant surface characterisation parameter. Tailored surface modifications for specific end-use applications.

Experimental investigation of electrochemical machining for involute internal spline using cathode working teeth sheet with circumferential vibration

Manufacturing internal splines with complex structures in high-hardness materials poses challenges in conventional machining processes. This paper introduced a new electrochemical machining (ECM) method using an assembled tool cathode with a cathode working teeth sheet with circumferential vibration for efficient and stable shaping of involute internal splines of intricate high-hardness components. A detailed design of the assembled tool cathode is presented, accompanied by flow field simulations analysing electrolyte distribution during circumferential vibration. A specific experimental system, fixture, and a used electrolyte filter module were constructed for spline ECM experiments. The results show that with the cathode feed rate of 2.7 mm/min, and the circumferential vibration frequency of 80 Hz, the involute internal spline profiles were successfully shaped with higher precision and efficiency with less appropriate allowance.

Fabrication of micro tools using electrochemical machining with a reciprocating block electrode

Micro parts are increasingly being used in many applications. The machining of micro parts is inevitably dependent on micro tools, which play a key role in limiting the feature size and controlling the dimensional accuracy. However, the fabrication of micro tools is currently inefficient. This paper presents a novel electrochemical machining (ECM) method in which a reciprocating block (RBECM) is used as the tool electrode. In RBECM, the cylindrical workpiece reciprocates up and down in a straight line along its axis, while the block electrode simultaneously makes a feed movement. A mathematical model of the cutting edge length and width was derived to predict the size of the cutting edge tools. The results indicate that the model could achieve a good prediction accuracy. In addition, the effects of machining time on cutting edge width were experimentally investigated. Three types of stainless steel cutting edge tools with cutting edge widths of approximately 1/4, 1/2, and 3/4 of the diameter were successfully fabricated using a 5-mm-thick stainless steel block. The experimental results indicate that the machining time could be significantly reduced by 97.83–99.5% compared to the ECM method using a tensioned metal wire as the cathode.

Effect of Process Parameters on Joint Performance in Hot Pressure Welding of 6061 Aluminum Alloy to CF/PA66.

Polymer-metal hybrid structures combine the merits of polymer and metal materials, making them widely applicable in fields such as aerospace and automotive industries. However, the main challenge lies in achieving efficient and strong connections between the metal and polymer components. This paper uses the jet electrochemical machining (Jet-ECM) method to customize the surface morphologies on 6061 aluminum alloy (AA6061) sheets. The connection between AA6061 and carbon fiber-reinforced PA66 (CF/PA66) is then achieved through hot pressure welding (HPW). The effects of aluminum alloy surface morphology, welding force, and welding time on the mechanical properties and microstructure of the joint are investigated. The optimal process parameters are determined by the design of the experiment. The results show that the aluminum alloy surface morphology has the greatest impact on the mechanical property of the welded joint. The optimal process parameters are surface morphology with wider, shallower, and sparsely distributed grooves on the aluminum alloy surface, the welding force is 720 N, the welding time is 12 s, the welding temperature is 360 °C, the cooling time is 16 s, and the optimal peak load of the joint is 6690 N. Under the optimal parameters, the fracture morphology in the AA6061 side is almost entirely covered with CF/PA66. The joint experiences cohesive failure in most areas and fiber-matrix debonding in a small area.

Evolution of the Interelectrode Gap during Co-Rotating Electrochemical Machining

A new co-rotating electrochemical machining method is presented to machine the complex structure inside annular parts such as flame tubes and aero-engine casings. Due to the unique shape and motion of electrodes, it is difficult to accurately compute the electric field intensity in the machining area. In this paper, the complex electric field model is simplified by conformal transformation, and the analytical solution of electric field intensity is exactly calculated. A material removal model is built on the basis of the electric field model, and the dynamic simulation of the material removal process is realized. The effects of the cathode radius, applied voltage, feed rate and initial interelectrode gap on the interelectrode gap (IEG) and material removal rate (MRR) are analyzed. The simulation results indicate that the MRR is always slightly less than the feed rate in a quasi-equilibrium state, resulting in a slow reduction in IEG. In addition, the final machining state is not affected by the initial IEG, and the MRR in a quasi-equilibrium state is determined by the feed rate. Several comparative experiments were carried out using the optimized processing parameters, in which the MRR and IEG were measured. The convex structures were successfully machined inside the annular workpiece with optimum machining parameters. The experimental results are in good agreement with the theoretical results, indicating that the established model can effectively predict the evolution process of MRR and IEG.

Process characteristics of electrochemical discharge machining and hybrid methods: a review

Process characteristics of electrochemical discharge machining and hybrid methods: a review

КОНСТРУКТОРСКО-ТЕХНОЛОГИЧЕСКОЕ ОБЕСПЕЧЕНИЕ КАЧЕСТВА ШТАМПОВОЙ ОСНАСТКИ

The issues are considered in order to ensure the die tooling quality to manufacture small-sized parts made of sheet material for radio equipment and microelectronics. Typical damage to the main parts of dies, as well as their causes are analyzed. The development of machine-tool construction determines the trends of changes in the technology of manufacturing die parts. At the same time, the role of electro-physical and electrochemical machining methods increases. They are used, often replacing traditional methods of machining with blade and diamond-abrasive tools. At the same time, individual components of the macro- and micro-geometry of parts and the quality of the surface layer are not always taken into account. The paper discusses some errors that are not always considered during the technological preparation of production, the manufacture of parts and their control.

Improvement on profile accuracy of convex structure during counter-rotating electrochemical machining by periodically changing electrolyte flow direction

Counter-rotating electrochemical machining (CRECM) is an innovative electrochemical machining (ECM) method, which can be used to machine thin-walled casings. However, due to the complex electrode movement and the special flow field structure, there are some challenges in the uniformity control of the profile accuracy of convex structure during CRECM. In this paper, to improve machining accuracy of convex structures, a strategy of periodically changing electrolyte flow direction is proposed. A multi-physical field simulation model is established to reveal the CRECM mechanism. The simulation results show that the one-sided electrolyte supply causes the uneven distribution of flow rates, bubbles and temperature on both sides of the convex structure, mainly because the convex structure forces the electrolyte flow path to bend and increase electrolyte flow resistance. The conductivity near the inlet is higher than that at the outlet, which causes the profile of the convex structure to be asymmetric. However, this problem can be effectively solved by changing electrolyte flow direction periodically, because the average conductivity at the symmetrical positions on both sides of convex structure is consistent, the average material removal rate is the same, and the manufactured convex structure is axisymmetric. CRECM experiments are carried out, and the processed convex structure has good symmetry, and the deviation is <0.05 mm. This fully demonstrates that periodically changing electrolyte flow direction can significantly improve the forming accuracy of the convex structure.

Research on the characteristics of multiphysics coupling fields in the electrochemical trepanning of an inward facing blisk

As an effective method of electrochemical machining (ECM), electrochemical trepanning (ECTr) is used in the machining of the outward facing blisks in aero-engines such as the integral blisk and the diffuser. However, as a special type of blisk, the inward facing blisk has dense blades, narrow spaces in the disc and poor tool accessibility. To date the research on the ECTr of the inward facing blisk is lacking. In this study, a cambered cathode structure is proposed for ECTr of the inward facing blade, since this can improve the distribution of the multiphysics coupling fields in the machining gap and result in an improvement in the quality of machining for the inward facing blade. To progress this idea, a multiphysics coupling fields model for ECTr of inward facing blade based on electric field, gas-liquid two-phase flow field and temperature field is established. Then through simulation of the multiphysics coupling fields, the distribution laws for the flow velocity, the current density, the gas bubbles volume fraction, the temperature and the electrolyte conductivity in the machining gap are obtained. Compared with a conventional planar cathode structure, in the transition section, the uniformity of the flow field of a cambered cathode is improved, and the formation time of the blade is shorter, such that the machining quality and efficiency of the inward facing blade is enhanced. Subsequently, a series of ECTr experiments is conducted on the inward facing blade, and the simulation prediction is found to be in good agreement with the experimental results. As a result of using a cambered cathode, the cathode feed rate is increased from 1.6 mm/min to 2.2 mm/min, with the result that the machining efficiency is increased by 37.5 %. The width and surface quality of the blade improved with increase of the feed rate, the width increasing from 11.506 mm to 12.413 mm, and the surface roughness increasing from Ra 1.372 μm to Ra 0.953 μm. Use of a cambered cathode as the inward facing blade is demonstrated, and the feasibility of a novel ECTr method is verified.

Research on Multi-Physical Field Coupling Simulation of Local Electrochemical Machining

Casing is one of the most important components of an aircraft engine. However, due to its thin wall thickness and difficult-to-cut materials, it is difficult to process with a conventional mechanical method. Counter-rotating electrochemical machining (CRECM) is a special electrochemical machining method, which is very suitable for machining aircraft engine casing parts. However, for the convex structure with large surface height and a complex shape of the casing, is sometimes difficult for CRECM to obtain the desired design accuracy. Local electrochemical machining is proposed under this background, which is used for after-machining of the pre-shaped convex structure by CRECM. In order to predict the local electrochemical machining result accurately and improve the machining precision, this paper establishes a multi-physical field coupling simulation model of the local electrochemical machining considering the influence of gas–liquid two-phase flow and temperature field. The influence of a gas–liquid two-phase flow field and temperature field on the conductivity distribution were simulated and analyzed, the reason for simulation error with pure electric field and the influence of cathode end width L on machining accuracy was analyzed, and it was found that the gas–liquid two-phase flow field played a major role in the simulation results of local electrochemical machining. The experimental results show that there is a significant error between the pure electric field simulation results and the experimental results, and the multi-physical field coupling simulation results are basically consistent with the experimental results. The multi-physical field coupling simulation can predict the results of local electrochemical machining with high accuracy and has important significance for improving the precision of local electrochemical machining.

Investigation of through-mask electrochemical machining process using a rib-connected photoresist for microcone array with large height-to-diameter ratio

Metal microcone arrays are widely applied in aerospace, medicine, and chemistry, and usually require precision fabrication with a large height-to-diameter ratio and high array consistency. For this purpose, the present paper describes a method of through-mask electrochemical machining (TMECM) using a rib-connected photoresist. A large mask diameter is found to be beneficial for producing microcones with a large height-to-diameter ratio. However, the larger mask is more easily flushed off, which will destroy the consistency of the array. Therefore, a rib-connected photoresist structure for use during TMECM is developed. The improvement in performance offered by this photoresist is verified by simulations and comparative experiments. Finally, the machining parameters of the TMECM using a rib-connected photoresist are further optimized. When the machining time is 46 s, the flushing speed is 4 m/s, and the HCI concentration is 2 mol/L, the microcone array structure with a large height-to-diameter ratio of 10.28 and the standard deviation of 0.22 is obtained.

An electrochemical machining method for aero-engine blades based on four-directional synchronous feeding of cathode tools

Blades are critical components of modern aero-engine. Among the many characteristic structures of the blade, the leading/trailing edges are key structures that have the greatest influence on the aerodynamic effect and power conversion of the blade. Electrochemical machining (ECM) is regarded as one of the most important techniques in blade manufacturing due to its process characteristics of high material removal rates, virtually no tool wear, and no areas of thermal or mechanical damage to the workpiece rim zones. Herein, an ECM method based on the four-directional synchronous feeding of four cathode tools is proposed to improve the machining accuracy of the leading and trailing edges of the blade. During blade ECM using this method, four cathode tools feed toward the basin/back surfaces and leading/trailing edges respectively. The dynamic processing simulation and flow field simulation results of the ECM process show that the proposed method eliminates the sharp changes in the electric field and electrolyte flow field at the leading and trailing edges seen in traditional machining methods. Thus, the electric field and flow field stability of the leading and trailing edges at the final stage of machining is greatly improved. Experimental comparison of the conventional and proposed ECM methods showed that four-directional synchronous feeding results in improved profile accuracy over repeated machining processes and good surface quality.

Determination of Nanoindentation Behavior of HAZ on Glass Material Machined via ECSM Process through Simulation Approach.

The current study develops a numerical model to investigate the nanoindentation behavior of heat-affected zones (HAZ) on glass material produced via the electrochemical spark machining (ECSM) method. Initially, microchannels were created using the ECSM method on soda–lime glass. Following that, a nanoindentation test was conducted to quantify the Young’s modulus and hardness of the glass sample. After that, a numerical model based on finite elements was created to characterize the changes in mechanical characteristics of HAZ. According to the findings, increasing the electrolyte concentration from 10 to 30% increases the intensity of electrochemical discharges, and thereby decreases the hardness of the work material by 16.29 to 30.58% compared to unmachined glass. The results obtained from the simulation are in close agreement with the experimental values. The maximum error obtained between simulation and experimental results is only 4.18%.

Investigation of anode shaping process during co-rotating electrochemical machining of convex structure on inner surface

A novel co-rotating electrochemical machining method is proposed for fabricating convex structures on the inner surface of a revolving part. The electrodes motion and material removal method of co-rotating electrochemical machining are different from traditional electrochemical machining. An equivalent kinematic model is established to analyze the novel electrodes motion, since the anode and cathode rotate in the same direction while the cathode simultaneously feeds along the line of centres. According to the kinematic equations of the electrodes and Faraday’s law, a material removal model is established to simulate the evolution of the anode profile in co-rotating electrochemical machining. The simulation results indicate that the machining accuracy of the convex structure is strongly affected by the angular velocity ratio and the radius of the cathode tool. An increase of the angular velocity ratio can improve the machining accuracy of a convex structure. A small difference in the radius of the cathode tool will cause changes in the shape of the sidewalls of the convex structure. The width of the cathode window affects only the width of the convex structure and the inclination α of the sidewall. A relation between the width of the cathode window and the width of the convex structure was obtained. The formation process for a convex structure under electrochemical dissolution was revealed. Based on the simulation results, the optimal angular velocity ratio and cathode radius were selected for an experimental verification, and 12 convex structures were simultaneously fabricated on the inner surface of a thin-walled revolving part. The experimental results are in good agreement with the simulation results, which verifies the correctness of the theoretical analysis. Therefore, inner surface co-rotating electrochemical machining is an effective method for fabricating convex structures on the inner surface of a revolving part.

Study on the micro through holes machining using the electrochemical machining (ECM) method with a graphite electrode

Electrochemical machining is widely used in biomedical, aerospace, automotive, and other fields. The development of electrochemical machining (ECM) is restricted by many factors such as the difficulty of preparing micro-electrode, large machined gap and serious stray corrosion. In this paper, we present a method to fabricate micro-holes by combining micro-graphite electrode with hollow structure. Firstly, a sealed graphite electrode was proposed to guarantee that the sediment can be fully removed by the flowing electrolyte. Then, the effect of machined parameters such as the pulse frequency, machined voltage, electrode feeding speed, and electrolyte concentration on machining quality was studied. By optimizing the machined parameters, the minimum value of micro-hole taper with 0.07 could be obtained. To improve the shape precision of workpiece, this paper designed the hollow structure inside the electrode. With the increasing of the pulse frequency, the machining accuracy of micro-holes increased. The results suggested that the pulse frequency of 100 kHz, the machined voltage of 18 V, the feeding speed of 1 µm/s, and electrolyte concentration of 5% were more suitable for micro-holes machining with ECM.

The Anisotropic Electrochemical Machinability of Laser Cladding Deposited Ti6Al4V Alloy in NaCl Solution

The hybrid manufacturing method of laser cladding deposition (LCD) additive manufacturing and electrochemical machining (ECM) is a promising approach to advanced manufacturing technology for difficult machined materials. The anisotropic electrochemical performance of LCD-produced Ti6Al4V alloy was studied in 15 wt.% NaCl solution by polarization curve measurements and ECM tests. The horizontal-plane (X0Y plane) exhibits a more stable passive film in both static electrolyte and low current density ECM processes than the vertical-plane (X0Z plane). Additionally, the horizontal-plane exhibits a higher material removal rate and more consistent dissolved surface roughness in comparison with the vertical-plane during the high current density ECM process. The microstructure of the LCD-produced Ti6Al4V alloy on the horizontal-plane consisted of equiaxed-like prior-β grains and slightly finer α-laths but was composed by columnar prior-β grains and coarser α-laths on the vertical-plane. These differences in the microstructural characteristics produce the distinctions observed in the electrochemical dissolution behavior and electrochemical machinability on the horizontal- and vertical-planes.

Micro-channel fabrication on GFRP composite through electrochemical spark machining method and optimization of process parameters

In the present study, fabrication of micro-channel on glass fiber reinforced plastic (GFRP) sheet has been performed through micro-electrochemical spark machining process. Box-Behnken design has been followed to conduct experiments and the influence of machining parameters and their ranges that is, applied voltage (50 V–60 V), duty factor (35%–45%), electrolyte concentration (20–30 wt%), and pulse frequency (6–10 kHz) on the micro-channel quality has been investigated. The width of micro-channel (WMC), delamination extent (DE), and heat-affected zone (HAZ) are considered as the responses. Response surface method (RSM) with desirability analysis and multi-objective optimization are utilized to optimize the process. The minimum observed WMC, DE, and HAZ are 532.81, 1.09, and 50.52 μm respectively which are obtained at machining voltage: 50 V, duty factor: 35%, concentration: 20 wt% of NaOH, and pulse frequency: 10 kHz. The fiber breakage and re-deposition/adhesion of broken fiber and matrix materials are observed at the edges of the micro-channel.

Simulation Analysis and Process Evaluation of Cooling Hole Forming Precision in Mask Assisted Electrochemical Machining Based on GH4169.

Good heat dissipation performance of aero-engine an effectively improve the service performance and service life of aero-engine. Therefore, this paper studies the machining method of cooling holes of high-temperature existent material GH 4169 for aero-engine innovatively puts forward the mask electrochemical machining method of cooling holes and explores the entrance morphology and taper formation law of the hole structure of high-temperature resistant material GH 4169. The mathematical model of anode dissolution of cooling holes in ECM is established, and the influence of voltage and electrolyte flow rate on cooling holes in ECM is analyzed. Compared with the mask-less electrochemical machining, the inlet radius of cooling holes in mask electrochemical machining is reduced by about 16.0% and the taper is reduced by 52.8% under the same machining parameters, which indicates that the electrochemical machining efficiency of mask is higher and the machining accuracy is better. Experiments show that the diameter of the mask structure improves the accuracy of the inlet profile of the cooling hole in the ECM. The diameter of the mask increases from 2 mm to 2.8 mm, and the inlet radius of the cooling hole increased from 1.257 mm to 1.451 mm When the diameter of the mask is 2.2 mm, the taper of the cooling hole decreased by 53.4%. The improvement effect is best, and the thickness of the mask has little influence on the forming accuracy of the cooling hole.

Surface roughness assessments and comparative study of Inconel 625 and Inconel 718 alloys after micro electrochemical machining

Conventional boring is not yet suitable for dealing with Inconel and Inconel super-alloys because these materials are harder to eliminate contaminants. The purpose of this paper is to assess the two distinct alloys based on experimental results from the micro electro-chemical machining method on surface roughness. While metals have been removed during milling operation, the alloys were kept within an electrolyte concentration, owing to this surface roughness was a major problem. This study aimed to compare the surface roughness attributes of Inconel 625 and 718 alloys from empirical results done by existing literature. Only when the investigators utilize the identical devices to investigate the same process factors, empirical data are used for comparative study. Inconel 625 alloy attained the best achievable result of a surface roughness value of 0.3853 μm. The significances of surface roughness on Inconel alloys are contrasted.

Research on the wettability of localized pulse electrolytic machining mold steel (GCr12)

As one of the most widely used metal materials, steel takes on an important role in deep sea and space exploration fields. However, the annual economic loss caused by steel corrosion is immeasurable. To resolve the problem, the localized pulse electrochemical machining (PECM), an efficient, fast and environment-friendly method, was introduced to fabricate microstructures on the surface of mold steel (GCr12). Results show that a super-hydrophobic surface has been obtained and its corrosion resistance has been significantly enhanced without the need to modify the surface by low surface energy solution. Thanks to the optimal working parameters (7.9 V and 2 ms) identified from the processing, the water contact angle of 161.8° was obtained. After fabrication by PECM, the surface microstructure, chemical element, and wettability were characterized and analyzed by scanning electron microscope (SEM), laser scanning confocal microscope (LSCM), EDS energy spectrometer, and optical contact angle measuring instrument, respectively. According to the experimental results, the surface honeycomb structure (micro/nano binary structure) is proven to be the main factor affecting wettability. Next, durability tests and corrosion resistance tests were carried out and the contact angle decreased by 4.4% and 6.7% respectively compared with the original contact angle, indicating that the surface after PECM has strong durability and good corrosion resistance, which can effectively solve the corrosion problem of steel. Therefore, using localized PECM technology to prepare microstructure on the surface of mold steel has a good application prospect in industry.