Electrochemical Arc Machining Research Articles

ELECTROCHEMICAL ARC DRILLING OF NICKEL–TITANIUM SHAPE MEMORY ALLOY USING MOLYBDENUM ELECTRODE: INVESTIGATION, MODELING AND OPTIMIZATION

In the present scenario, electrochemical arc machining (ECAM) (hybrid of electric discharge erosion and electrochemical dissolution) is an evolving procedure for difficulty in machining the materials due to constraints of existing processes. This research aims to investigate the machinability of Ni[Formula: see text]Ti alloy through electrochemical arc drilling using molybdenum electrode. Electrolyte concentration (ethanol with ethylene glycol and sodium chloride), supply voltage, and tool rotation are considered as the variable factors to evaluate the ECAM performance characteristics in drilling blind hole operation concerning overcut (OC), tool wear rate (TWR) and materials removal rate (MRR). Consequently, response surface methodology is implemented for predictive modeling of various performance characteristics. Finally, multi-objective optimization through desirability function approach (DFA) has produced a set of optimal parameters to improve the productivity along with the accuracy, which is the prime requirement for the industrial applicability of the ECAM process. Results demonstrated that supply voltage is the influential key factor for improvement of machining rate. Scanning electron microscope (SEM) photographs revealed the development of heat affected zone (HAZ), white layer, melted droplet, craters, re-solidified material, ridge-rich surface and voids as well as cavities around the end-boundary surfaces of a blind hole. Composition analysis through energy dispersive spectroscopy (EDS) indicated the oxygen content on the machined surface because electrolyte breakdown causes oxidation to take place at elevated temperatures across the machining zone. Moreover, carbide precipitation like TiC was found in the melting zone of the drilled hole, as revealed by X-ray diffraction (XRD) analyses, which has the affinity to reduce the SMA properties in HAZ.

Sparc assisted electrochemical machining: a novel possibility for microdrilling into electrical conductive materials using the electrochemical discharge phenomenon

This paper details the fundamental principles of the machining method spark assisted electrochemical machining (SAEM). SAEM is a further development of the electrochemical arc machining (ECAM) which makes use of the electrochemical discharge phenomenon to machine electrically conductive materials. ECAM is not able to drill micro-holes, but now, using SAEM a postponed electrochemical finishing of the SAEM drilled micro-hole can be realized. The mass flow calibration of a throttle plate can be done immediately after SAEM microdrilling by electrochemical machining (ECM) with a still axis-symmetrically located tool electrode with the same machining equipment, working media, and power source. To enable ECAM to drill micro-holes, its material removal mechanism is improved by combination with the contact arc as an additional mechanism. This mechanism is presented and explained herein. The machining efficiency of the newly developed SAEM is optimized by adjusting the gap control in such a way that the contact arc is generated with an adequate frequency. This reduces the machining time by almost 50 %. Some examples of SAEM drilled micro-holes, for which different electrolytes are used, are presented and the surface and heat affected zone of those micro-holes are examined.

Experimental investigation and simulation of heat flux into metallic surfaces due to single discharges in micro-electrochemical arc machining (micro-ECAM)

In this work, single discharges of electrochemical arc machining are examined. The heat-affected zone is analyzed, and a model is set up to simulate the heat transfer into the workpiece. As an input parameter of the simulation, the temperature of the electrochemical arc machining process was determined to be 3,500 K by means of emission spectroscopy. The simulation shows that the diameter of the heat-affected zone is less dependent on discharge duration and heat transfer due to heat flux than on the arc spot diameter. As a result of the investigation, it became clear that varying diameters of the heat-affected zone have to evolve from different diameters of the plasma channel’s arc spot. Understanding the heat distribution into the workpiece in electrochemical arc machining with micro-machining parameters allows the further development of a micro-drilling process for electrically conductive materials based on electrochemical arc machining.

Mechanism of spark generation during electrochemical discharge machining: a theoretical model and experimental verification

The use of the electrochemical discharge phenomenon to machine materials is a very recent technique in the field of non-conventional machining. When the machined material is electrically conducting, the process is usually termed ‘electrochemical arc machining’ (ECAM), whereas for non-conducting work materials it is termed ‘electrochemical discharge machining’ (ECDM). Although in both cases electrical discharge takes place through the electrolyte and plays a critical role, the mechanism of spark generation has not been investigated adequately. In the present work a theoretical model of this discharge phenomenon is developed. With the help of the model, the critical voltage and current required to initiate discharge between the electrode and the electrolyte are estimated. The theoretically-predicted values compare quite well with experimental observations.

A theoretical analysis of electrochemical arc machining

Electrochemical arc machining (ECAM) involves the removal of metal from an anodically polarized workpiece by both erosion arising from discharges produced in an aqueous electrolyte and electrolytic dissolution. A theoretical model is derived for the process and analysed for two specific applications, fine-hole drilling and the finishing of components by smoothing of their initially rough surfaces. In the second of these examples, a perturbation procedure for obtaining approximate solutions is used; the model so developed encorporates the effects of current density on current efficiency which are known from experimental electrochemical machining (ECM) studies to influence the rate and mode of smoothing. For fine-hole drilling by ECAM, the analysis predicts that the interelectrode gap width increases with the applied voltage and inversely with the square root of the mechanically driven anode. In the case of smoothing, ECAM is found to remove the surface irregularities at a much faster rate and with lower loss of stock metal than ECM alone, when electrolytes such as sodium chloride solution yielding 100% current efficiency are used for the latter process. The analysis shows that an electrolyte solution with a current density-dependent current efficiency is needed if parent metal loss by ECM is to approach that of ECAM, and even then, machining by the latter is still much faster. Attention is drawn to experimental evidence in support of these predictions of ECAM behaviour. Finally, results from the model are used to verify the practical use of ECM for rapid finishing of the surfaces of components left rough by electrodischarge machining.

An Analysis of Electrochemical arc Machining

The electrochemical arc machining (ECAM) process has been studied by high-speed photography over a wide range of conditions. The experimental results obtained have provided an unusual insight into the ECAM process, for which a theoretical analysis is proposed. The benefit of ECAM over electrochemical machining (ECM) or electrodischarge machining (EDM) is shown to be increased only if the rate of discharges in ECAM can be improved. Possible methods to enhance the discharges are discussed.

Evaluation of an Apparatus for Electrochemical Arc Wire-Machining

Electrochemical Arc Machining (ECAM) combines electrochemical dissolution and electro discharge in order to achieve metal removal rates, that can be about five and fifty times greater than those of electrochemical (ECM) and electrodischarge (EDM) machining, respectively. Since ECAM has already been successfully applied to hole-drilling, for this paper the prospects for wire-machining by this process have been explored. An apparatus for wire-ECAM is described, and the results of tests performed to assess the feasibility of the technique are presented. To that end, the effects of mode of electrolyte flushing, wire erosion and machining speed on metal removal rate and accuracy are discussed.

Analysis of electrochemical arc machining by stochastic and experimental methods

Metal removal by a novel process, electrochemical arc machining (ECAM), is described. The mechanisms underlying ECAM, electrochemical dissolu­tion (ECD) and electrodischarge erosion (EDE) are investigated as events that occur at random in the machining gap, between the cathode tool and anode workpiece. These phases are registered as spikes of varying height and width in voltage and power recordings of the process; a stochastic method in the form of linear and nonlinear models is used to describe them. The basis of the ensuing analysis is the interpretation of model parameters in the light of physical behaviour known to arise in established electrochemical (ECM) and electrodischarge (EDM) machining. To that end, the spectral moments developed from the voltage recordings are used to discern between the phases of ECD and EDE arising in ECAM, and between the onset of sparks or arcs in the EDE-phase. The practical case of hole-drilling by ECAM is used to illustrate the main aspects of this stochastic approach: the effects of the principal machining process variables on the type, intensity and duration of the resulting ECD and EDE phases are assessed.

Surface Effects on Alloys Drilled by Electrochemical are Machining

Electrochemical arc machining (ECAM) utilizes pulsed power in an electrolyte, in order to remove metal by combined electro-discharge erosion (EDE) and electrochemical dissolution (ECD). In drilling by this technique, EDE occurs at the frontal gap between the cathode-tool and anode-workpiece; in the side gap, ECD is predominant. Machining rates are much greater than those of electrochemical (ECM) and electro-discharge machining (EDM). This paper is concerned with an investigation of the effects of EDE and ECD on the surface integrity of a range of alloys of industrial interest, drilled by ECAM. Chrome, cobalt and low-alloy steels and nickel-based (nimonic) alloys all exhibited a smooth surface finish typical of that found with ECM, for most of the length of the drilled hole, except at the exit. There, metallurgical damage due to EDE was apparent. The surface characteristics with titanium were typical of those found in EDM, with virtually no evidence of ECM action. This effect was attributed to the presence of a tenacious oxide film formed on titanium in water-based electrolytes which effectively blocks ECM.

Studies of the discharge mechanisms in electrochemical arc machining

The electrochemical arc machining (ECAM) process combines features of ECM and EDM by application of a pulsed voltage between a cathode-tool and anode-workpiece in a liquid electrolyte. The new process offers rates of metal removal as much as five and fifty times greater than ECM and EDM, respectively. The study reported in this paper explores some of the fundamental processes which occur during ECAM. Experimental apparatus was constructed to enable single pulse discharges to be studied. Results are presented for 200μs pulses between 2 mm diameter silver steel electrodes in NaNO3 and NaCl electrolytes over a gap range of 10 to 90μm. Four stages of electrical phenomena were distinguished within a pulse: (a) high frequency voltage and current oscillations, (b) high rate electrochemical action, (c) low rate electrochemical action, and (d) electrodischarge action. The relative durations of the electrochemical and discharge phases, respectively, increase and decrease with increasing gap width, and vary with electrolyte type and concentration. High speed photography with an image-converter camera was used to record the occurrence of both spark and arc discharge in an electrolyte.

Theoretical, Experimental and Computational Aspects of the Electrochemical Arc Machining Process

Summary The electrochemical arc machining (ECAM) process operates by the combined actions of electrochemical dissolution and electrodischarge erosion. This is achieved by the use of an electrolyte in the machining gap and a pulsed power supply. With this arrangement considerably higher metal removal rates than offered by electrochemical (ECM) or electrodischarge (EDM) are attainable. In this paper, the mechanisms which lead to discharge formation in liquids are detailed, followed by a discussion of the variables which affect the dissolution and erosion components of ECAM. One possible application of the process, long hole drilling, is then discussed, and experimental results are presented. Finally, computer-aided mathematical modelling of ECAM is considered.

Theoretical and Experimental Investigation of the Relative Effects of Spark Erosion and Electrochemical Dissolution in Electrochemical ARC Machining

Electrochemical discharge, or arc, machining (ECAM) is a process combining features of electrochemical (ECM) and electrodischarge (EDM) machining. With the combined process ECM action is assisted by the thermal erosive effect of electrical discharges in the machining gap filled with electrolyte. Machining rates are thereby obtained which can be as much as five and forty times faster than respectively ECM and EDM. The complexity of the process renders difficult any full theoretical treatment. Indeed most work to date has dealt with experimental investigations of this industrially interesting process, particularly for drilling applications. In this paper, some effects of the pulsed voltage and vibrating tool-electrode waveforms are subjected to theoretical analysis. From this treatment, conditions which are favourable to either ECM or sparking can be identified. The effect of the phase-angle between the voltage and vibration waveforms on metal machining rates is also analysed. These results are compared with experimental results, and the influence of the electrical discharges in the electrolyte is shown to become the major factor promoting enhanced rates of metal removal, as both phase-angle and amplitude of vibration increase. Further theoretical and experimental studies deal with the effect of machining voltage and feed-rate, with the sparking element playing an increasing role in raising the metal removal rate, the higher the voltage and the feed-rate used.

Comparative studies of ecm, edm and ecam

The characteristics of electrochemical and electrodischarge machining are compared with electrochemical arc machining, a process which relies on electrical discharge in electrolytes to effect metal removal. Since little is known about the nature of this process, investigations of sparks in dielectrics and electrolytes are reviewed. Some relevant applications of edm and ecm are then discussed, and comparisons drawn with the new process