Electrochemical Drilling Research Articles

Bayesian Optimized Deep Convolutional Network for Electrochemical Drilling Process

Electrochemical machining is a promising non-traditional manufacturing process to make high-quality parts. The benefits of minimal thermally and mechanically induced stresses, free of burr, and a low surface roughness are appealing for industry and research institutes. However, the combined chemical reaction, electric field, fluid mechanics, and material properties involve a significant number of independent parameters which are difficult to analyze in order to draw comprehensive conclusions. To our current knowledge, process responses such as the material removal rate, optimal feed rate, and cutting profile cannot be represented accurately by analytical solutions. In recent years, deep learning has had tremendous success in analyzing sophisticated systems. The improved computation efficiency and reduced size of the training dataset required for deep learning have enabled various prediction models in the manufacturing industry. In this paper, a new approach is developed using the deep convolutional network with the Bayesian optimization algorithm to predict the diameters of the drilled hole from an electrochemical machining process. The Keras application programming interface (API) was used to build the deep convolutional network; the feed rate, pulse-on time, and voltage were used as input parameters to provide a fair comparison with a neural network from previous research. Random dropout layers were added to prevent overfitting of the network. Instead of tuning the network parameter by trial and error, the Bayesian parameter optimization algorithm was implemented to find the optimal set of parameters of the deep convolutional network that yields the minimum mean square error. The proposed algorithm was compared with a previously developed neural network with partially embedded physical knowledge. Improved training speed and accuracy were observed in comparison with the traditional neural network. The prediction model using the proposed deep learning algorithm demonstrated better prediction accuracy and provided a more systematic way to select the hyperparameter for the deep convolutional network.

Fabrication of Taper Free Micro-Holes Utilizing a Combined Rotating Helical Electrode and Short Voltage Pulse by ECM.

Fabrication of the injection nozzle micro-hole on the aero engine is a difficult problem in today’s manufacturing industry. In addition to the size requirements, the nozzle micro-hole also requires no burr, no taper and no heat-affected zone. To solve the above problem, an ultra-short voltage pulse and a high-speed rotating helical electrode were used in electrochemical drilling (ECD) process. Firstly, a theoretical model of ECD with ultra-short voltage pulse was established to investigate the effects of many predominant parameters on machining accuracy, and the effect of rotating helical electrode on the gap flow field was analyzed. Secondly, sets of experiments were carried out to investigate the effects of many key parameters on machining accuracy and efficiency. Finally, the optimized parameters were applied to machine micro holes on 500 μm thickness of GH4169 plate, and micro-holes with the diameter of 186 μm with no taper were machined at the feed rate of 1.2 μm/s. It is proved that the proposed ECD process for fabricating micro-holes with no taper has a huge potential and broad application prospects.

Simulation and experimental investigation on micro electrochemical drilling of micro-holes with ultra short pulse voltage

This paper introduces an electrochemical drilling process which is efficient in fabricating micro-holes, in order to study the influences of ultra short pulse voltage and high speed spiral micro electrode on the machining accuracy and machining efficiency of micro electrochemical drilling, the simulation of the gap electric field and the gap flow field are carried out. Firstly, the model of ultra short pulse gap electric field was established, by simulating the process of the drilling, the shape change of the anode workpiece surface was analysed and predicted with the ultra short pulse voltage. The results show that the ultra short pulse voltage can greatly improve the machining accuracy. Secondly, by using CFX to simulate the gap flow field, with the increase of the electrode rotating speed, the gas film generated with good insulation effect can greatly reduce the taper of the micro-holes. Finally, the simulation results above were verified by the experiments, a series of micro-holes was fabricated successfully; the diameter of the micro-holes was less than 200 μm, which proved that the micro electrochemical drilling for fabricating micro-holes has a widespread application prospect. [Submitted 3 November 2016; Accepted 5 December 2017]

Simulation and experimental investigation on micro electrochemical drilling of micro-holes with ultra short pulse voltage

This paper introduces an electrochemical drilling process which is efficient in fabricating micro-holes, in order to study the influences of ultra short pulse voltage and high speed spiral micro electrode on the machining accuracy and machining efficiency of micro electrochemical drilling, the simulation of the gap electric field and the gap flow field are carried out. Firstly, the model of ultra short pulse gap electric field was established, by simulating the process of the drilling, the shape change of the anode workpiece surface was analysed and predicted with the ultra short pulse voltage. The results show that the ultra short pulse voltage can greatly improve the machining accuracy. Secondly, by using CFX to simulate the gap flow field, with the increase of the electrode rotating speed, the gas film generated with good insulation effect can greatly reduce the taper of the micro-holes. Finally, the simulation results above were verified by the experiments, a series of micro-holes was fabricated successfully; the diameter of the micro-holes was less than 200 μm, which proved that the micro electrochemical drilling for fabricating micro-holes has a widespread application prospect. [Submitted 3 November 2016; Accepted 5 December 2017]

Modelling of MRR and hole taper for ultrasonic assisted jet electrochemical micro-drilling process using Buckingham's <i>π</i> theorem

Ultrasonic assisted jet-electrochemical micro-drilling (UAJet-ECMD) process integrates ultrasonic vibrations and jet electrochemical micro drilling process. In the present study, Buckingham's π theorem has been employed to model the process responses namely material removal rate (MRR) and hole taper of the UAJet-ECMD process with continuous DC voltage. The model has been formulated taking into account the experimental parameters namely voltage, electrolyte concentration, electrolyte pressure, inter electrode gap, pulse on time of ultrasonic vibrations and other physical properties related to ultrasonic vibrations such as speed of ultrasonic waves in the electrolyte, amplitude and frequency of ultrasonic vibrations. Electrochemical properties of work piece material namely chemical equivalent of copper and Faraday's constant were also taken into considerations. The use of regression analysis has been done to model the process responses. From the resultant π terms contained in the developed models, insignificant terms based on their percentage contributions were reduced and the models for both MRR and hole taper were modified. The formulated models for MRR and hole taper were validated with the statistical models obtained from experimental results.

Eliminating spikes by optimizing machining parameters in electrochemical drilling

Electrochemical drilling (ECD) is an important method for producing small holes in difficult-to-machine materials such as titanium alloys and nickel-based alloys. However, the hollow tube shape often generates spikes at the hole bottoms, and these significantly influence the flow uniformity, machining accuracy, and process stability. This paper considers the hole bottom to be spiked, flat, or pitted depending on the equilibrium gap, which can be controlled with the machining parameters of applied voltage and electrode feed rate. Consequently, the spikes can be eliminated with a suitable choice of machining parameters. An electric-field model of ECD is established and the dynamic shaping of holes is simulated. This reveals that the machining parameters affect the equilibrium gap, whereupon the hole bottom shape is determined. Experiments verify the simulation results, and the relationships between the machining parameters (applied voltage and electrode feed rate) and (i) the equilibrium gap and (ii) the bottom shape are plotted. It is found that a low voltage with a high feed rate generates a small gap and a spiked bottom, whereas a high voltage with a low feed rate produces a large gap and a flat or pitted bottom. Finally, three typical parameter groups are selected with which to drill through holes. The machining-current signals at the moment of hole punching and the tool durability indicate that the ECD stability without a spike is better than that with a spike. Optimal parameters are beneficial for eliminating spikes and enhancing the ECD process performance.

Experimental Investigation of Cut Profile in the Electrochemical Drilling of Titanium Alloy

Electrochemical machining process is an advanced material removal technique offering high precision and introducing no heat damage to the work material. The shape and size of machined area are highly dependent on some process parameters such as voltage, electrolyte and inter-electrode gap. To further enable a more insight into the process performance, this paper investigates the influences of applied voltage, electrolyte concentration and inter-electrode gap on the shape and sizes of hole produced by the electrochemical drilling process. Titanium alloy (Ti-6Al-4V) was used as a work sample in this study as it has been extensively used in many advanced applications. The experimental result indicated that the use of high voltage and high electrolyte concentration can enlarge and deepen hole in the workpiece, while the inter-electrode gap provided less effect to the hole features. The maximum hole depth can reach 300 μm within 60 seconds when the applied voltage of 30 V, the inter-electrode gap of 10 μm and the electrolyte concentration of 10%wt were used. However, with this setup, the obtained cut profile became a non-uniform V-shaped hole. The use of lower voltage was instead recommended to yield a better cut quality with U-shaped profile.

Effect of Power Signal Waveform on Shape Accuracy in Electrochemical Drilling

This paper studied the effect of power signal on form accuracy in electrochemical drilling. The mathematical and physical models are built by the commercial software COMSOL. The DC signal, sine limit, triangular signal and pulse signal are selected as the research objects, and the current density of each model is simulated. The simulation results show that the average current density ranges from large to small in order of DC signal, sinusoidal signal, triangular signal and pulse signal on the anode surface. In order to verify the correctness of the model, an experiment is carried out. The experiment results show that the effect of power signal on processing size ranges from large to small in order of DC signal, sinusoidal signal, triangular signal and pulse signal. The experimental results have a good correspondence with the simulation results. We can conclude that the machining accuracy of sinusoidal and trigonometric signals is lower than pulse signals, but their processing efficiency is higher than that of pulse signals and their machining accuracy is also higher than DC signal processing accuracy. It is suitable for workpiece with high machining efficiency and moderate machining accuracy.

Electrochemical Machining of Aluminium Metal Matrix Composites

High performance aluminium based metal matrix composites possess low machinability characteristic. Electrochemical machining (ECM) is one of the advanced machining processes, used for machining of these newly developed exotic materials. This article critically reviews the research work on experimental investigations on ECM of aluminium matrix composites. Besides, recently developed techniques such as abrasive assisted electrochemical machining, electrochemical grinding, electrochemical micromachining, and electrochemical drilling are explored in the processing of aluminium metal matrix composites.

Optimization of the electrochemical machining parameters in drilling of AA6O6I-TIB2 in-situ composites produced by K2TiF6-KBF4 reaction system

Utilization of un conventional machining is increased exponentially due to its specific advantages like good machinabilty on the ceramic materials, ability to make complex profiles and supreme surface finish. Among the various un conventional machining, the electro chemical machining has unique identity including reasonably higher machining rate along with thermal and mechanical stress free machined surface. In-situ composites are made by reinforcing the micro size reinforcement by chemical reaction. The mechanical properties of these composites superior due its good interfacial bonding and smaller grain size of the matrix. The current paper deals the optimization of the electrochemical drilling parameters in machining of AA6061-5% T1B2 in-situ composites produced by K2TiF6- KBF4 reaction system. Current, concentration of the electrolyte and applied voltage are preferred as matrix whereas removal rate of the material and taper of the electrochemically drilled hole is identified to assess the machinbility. L27 orthogonal layout is followed for experimental work and Taguchi method deployed for optimization. Analysis of result and variance indicates that the preferred responses have significant influence on the responses.

Simulation and Experimental Study on Micro Electrochemical Drilling with Ultra Short Pulse Voltage by using High-speed Spiral Electrode

Simulation and Experimental Study on Micro Electrochemical Drilling with Ultra Short Pulse Voltage by using High-speed Spiral Electrode

Fabrication of an Electrode Insulated by Using Hot Dip Aluminizing and Micro-arc Oxidation Method for Electrochemical Microhole Machining

In this research, electrode insulation of the electrochemical machining tool has been produced by hot dip aluminized micro arc oxidation techniques. In order to form an effective layer on the tungsten carbide tool and achieve higher precision, the tool will then be micro-arc oxidizing, convert the aluminum-rich into aluminum oxide insulating layer. Withstanding Voltage of the tool is being tested afterward by sodium chloride electrolysis method, and the surface and the cross section is being observed. Eventually, the tools were examined and discussed for their machining performance by ECM drilling through stainless steel plate. We were expecting to produce a precise and better insulation. By reducing ECM stray effect, the precision can be achieved.The experimental result shows the optimum parameters are aluminum dipping for 4minutes, 450V of micro-arc voltage for 20minutes and 40minutes of boiling water sealing, reaching 10.2V of withstanding voltage. A further electrochemical drilling has been done to explore the effect of insulation. Two electrodes, with and without insulation had been compared. The difference between the entrance and the exit diameter of the hole of insulated tool reaches 17um, compare to the one without insulation, we have successfully reduced 81um. The result shows that the insulation has effectively reduced the stray effect, and achieve high precision machining.

Electrochemical drilling of multiple small holes with optimized electrolyte dividing manifolds

Structures with multiple small holes have been widely used to aid cooling in aeronautical engine components. Electrochemical drilling uses a side-insulated tube as the tool cathode and removes anodic material via controlled electrochemical reactions in a cell. The flexibility for simultaneous drilling makes electrochemical drilling a feasible technique for producing multiple small holes. In multiple hole electrochemical drilling, uneven electrolyte volume divided to each tube electrode would cause each hole machining status different. This paper addresses the design of an electrolyte dividing manifold for use in electrochemical drilling of multiple holes. Structural parameters such as the distance from the manifold inlet to the first tube electrode, the manifold inlet diameter and the tube electrode length have obvious effects on the electrolyte distribution along the electrode array. Experiments illustrate an optimized manifold structure is feasible for practical fabrication. Finally, two types of hole arrays are successfully fabricated.

Flow Analysis and Experimental Investigation on Micro Electrochemical Drilling of Deep Micro-Holes

Background: Deep micro-holes are important structures which are widely used in many engineering fields. However, deep micro-holes machining, especially on difficult-to-cut materials, has always been a problem. The Electrochemical Micro Machining (EMM) process is a good selection for the fabrication of deep micro-holes on difficult-to-cut materials, and various relevant patents and scientific papers have been discussed. Keywords: Deep micro-holes, electrochemical drilling, gas film, high-speed, micro spiral electrode, simulation.

Optimisation of electrochemical drilling process using Taguchi method and regression analysis

Inconel 718 is a hard to machine nickel-based super alloy. It is extensively used in aerospace industries. It has high-strength and poor thermal diffusion which results in decreased life of tool and difficulty in machining by traditional methods. Unconventional machining processes have evolved over a period to meet such demands and claim to be a suitable alternative to conventional machining. Electrochemical machining (ECM) is an unconventional manufacturing process which is used to machine hard to machine materials. This paper presents an investigation on the application of Taguchi's approach and regression model to optimise the electrochemical drilling process of Inconel 718. The trials are planned using design of experiments proposed by Taguchi. Analysis of variance (ANOVA) is employed to determine the significance of input variables on the desired performance measures. The control of form and orientation errors of machined surfaces needs attention and included as desired performance. Multiple regression models have been developed to predict the desired performance measures in electrochemical drilling of Inconel 718.

Process modelling and investigations in to the electrochemical discharge drilling of soda-lime-silica-glass

Electro-chemical discharge machining (ECDM) is a hybrid non-conventional machining process that combines the features of electro chemical machining (ECM) and electro discharge machining (EDM). ECDM is an effective micro-machining process for non-conducting materials like glass, ceramics, composites, quartz, etc. The present study attempts to analyse the effects of process parameters including applied voltage, electrolyte concentration, frequency and duty factor on material removal rate (MRR). A widely used response surface design called Box-Behnken design was used to conduct the experiments. From the analysis of variance, significant factors that contribute MRR can be ranked in the descending order of duty factor, frequency and voltage. The effect of electrolyte concentration is found to be insignificant. A strong interaction between duty factor and frequency is identified in controlling MRR. From the microscopic images of the machined surface, thermal spalling is identified as a significant mechanism for material removal along with thermal melting and chemical etching.

Optimisation of electrochemical drilling process using Taguchi method and regression analysis

Optimisation of electrochemical drilling process using Taguchi method and regression analysis

Multiple performance optimization of electrochemical drilling of Inconel 625 using Taguchi based Grey Relational Analysis

In this present investigation, a multi performance characteristics optimization based on Taguchi approach with Grey Relational Analysis (GRA) is proposed for Electrochemical Drilling process on Inconel 625 material which is used for marine, nuclear, aerospace applications, especially in corrosive environments. Experimental runs have been planned as per Taguchi’s principle with three input machining variables such as feed rate, flow rate of electrolyte and concentration of electrolyte. Besides the material removal rate and surface roughness, the geometric measures such as overcut, form and orientation tolerance are included as performance measures in this investigation. Outcomes of the analysis show that the feed rate is the predominant variable for the desired performance characteristics. On establishing the desired performance measures and multiple regression models are developed to be used as predictive tools. The confirmation test also conducted to validate the results attained by GRA approach and affirmed that there is considerable improvement with the help of proposed approach.

Electrochemical drilling with constant electrolyte flow

Electrochemical drilling (ECD) is a useful method to produce small holes with a large aspect ratio on hard-to-machine materials. Recently, instead of using an acid electrolyte, more and more research has focused on neutral salt electrolytes because they are less harmful to the environment. However, more problems have been caused to the removal of waste products, especially in deep-hole drilling. Traditionally, an electrolyte flow with constant pressure control is adopted in ECD, which might result in the poor removal of waste products at depth because of pressure loss. In this paper, an ECD method with a constant electrolyte flow has been proposed to obtain a consistent ability to remove insoluble waste products from machining gap. Experiments of ECD with both constant electrolyte pressure and constant flow are conducted on workpieces of Inconel 718. Machining currents and the profile of machined holes are compared between the two methods. The results show that when a constant electrolyte flow rate is applied, the machining currents are much smoother and the profile of machined holes is also uniform. In addition, the pressure variation in the constant flow method increases linearly with machining depth. ECD with a constant flow also has an increased feed rate.

Performance evaluation of different variants of jet electrochemical micro-drilling process

The article describes fabrication of an experimental setup which could be used for electrochemical drilling process to produce micro-holes in a copper workpiece with its different variants, namely, jet electrochemical micro-drilling, air-assisted jet electrochemical micro-drilling, ultrasonic-assisted jet electrochemical micro-drilling, and pulsed direct current–jet electrochemical micro-drilling process. Process parameters like voltage, electrolyte concentration, interelectrode gap, and electrolyte pressure have been selected to find out their effects on the process responses, namely, hole taper and material removal rate in all the above process. Attachments for air assistance and ultrasonic vibration application have been fabricated and incorporated in the setup. The effects of ultrasonic vibrations and the pulsed direct current voltage on the process responses like material removal rate and hole taper have been investigated. The effect of application of ultrasonic vibrations on the electrolyte jet has been studied. The experimental findings of ultrasonic-assisted jet electrochemical micro-drilling were compared with the findings of jet electrochemical micro-drilling. Similarly, the findings of pulsed direct current–jet electrochemical micro-drilling were also compared with the results of pulsed direct current ultrasonic-assisted jet electrochemical micro-drilling experiments. It has been found that the ultrasonic vibrations have significant effect on the two process responses. From the results, it was observed that with the use of ultrasonic vibrations, the material removal rate has increased to significant level and the hole taper has been decreased than in jet electrochemical micro-drilling. Effects of the pulsed direct current voltage supply on jet electrochemical micro-drilling and (ultrasonic-assisted jet electrochemical micro-drilling) were also analyzed. Application of pulsed direct current voltage has improved the material removal rate and reduced the hole taper in jet electrochemical micro-drilling as well as in ultrasonic-assisted jet electrochemical micro-drilling. The experimental results concluded that ultrasonic assistance have generated the holes with greater material removal rate and lower hole taper and with continuous direct current and pulsed direct current voltage.