Conventional Electrochemical Machining Research Articles

Electrochemical cutting with flexible electrode of controlled online deformation

Abstract Improvements in aero-engine performance have made the structures of the aero-engine components increasingly complex. To better adapt to the processing requirements of narrow twisted channels such as an integral shrouded blisk, this study proposes an innovative method of electrochemical cutting in which a flexible tube electrode is controlled by online deformation during processing. In this study, the processing principle of electrochemical cutting with a flexible electrode for controlled online deformation (FECC) was revealed for the first time. The online deformation process of flexible electrodes and the machining process of profiles were analysed in depth, and the corresponding theoretical models were established. Conventional electrochemical machining (ECM) is a multi-physical field-coupled process involving electric and flow fields. In FECC, classical mechanics are introduced into the tool cathode, which must be loaded at all times during the machining process. Therefore, in this study, before and after the deformation of the flexible electrode, a corresponding simulation study was conducted to understand the influence of the online deformation of the flexible electrode on the flow and electric fields. The feasibility of flexible electrodes for online deformation and the validity of the theoretical model were verified by deformation measurements and in situ observation experiments. Finally, the method was successfully applied to the machining of nickel-based high-temperature alloys, and different specifications of flexible electrodes were used to complete the machining of the corresponding complex profiles, thereby verifying the feasibility and versatility of the method. The method proposed in this study breaks the tradition of using a non-deformable cathode for ECM and adopts a flexible electrode that can be deformed during the machining process as the tool cathode, which improves machining flexibility and provides a valuable reference to promote the ECM of complex profiles.

Implementation of robotic electrochemical machining in freeform surface machining with material removal rate prediction using different machine learning algorithms

Robots are used as machine tools via some advanced properties such as versatility, adaptation and mobility with other control systems. These advantages can be the solution to overcome the encountered problems in electrochemical machining (ECM). In this manner, the usability of a new machining method that is Robotic electrochemical machining (RECM) in freeform surface machining is investigated. Firstly, ECM parameters and their effects on the material removal rate (MRR) is discussed and compared with the literature. Experimental results showed that MRR variation for RECM acts similar characteristics with conventional ECM processes. The increase in voltage, electrolyte conductivity and feed rate increase MRR. The highest effect on MRR for both materials is voltage, electrolyte conductivity, and feed rate, respectively. Secondly, three different machine learning models are designed as Gaussian Process Regression (GPR), regression tree and deep neural network (DNN) models and the relationships between their actual and predicted values are discussed. The performance of the DNN model is better than other models with a correlation of determination values equal for Inconel 718 and AISI 1040. Furthermore, the DNN model with four input parameters outperforms developed models such as GPR and DTR with optimized hyperparameters regarding the R2, MSE, RMSE, and MAE. The change in height in the Z-axis and the surface roughness of the machined surfaces are also measured. The results show that the decrease in the Z axis is homogeneous, that is, uniform machining occurs and also the surface roughness has improved. Therefore, RECM can be a solution to machine free-form surfaces for different materials with high predictability.

Effect of inter-electrode gap on surface characteristics in conventional electrochemical machining

Conventional electrochemical machining (CECM) is an established toolroom process for the machining of conductive workpiece (W/P) substrates. In CECM, the material removal takes place through an electrochemical reaction between the cathode and anode. Significant studies have reported process parametric optimization of CECM with input parameters like voltage, feed rate, type of electrolyte and electrolyte concentration, etc., and their effect on the material removal rate (MRR), and surface roughness (Ra). But hitherto little has been reported on the effect of inter-electrode gap (IEG) and other CECM parameters in combination with a different tool and work materials. This study outlines the experimental investigations on CECM with a different tool and work materials based on Taguchi L18 orthogonal array (OA) on surface characteristics of machined surface for tool room applications in line with sustainable development goal (SDG) (with a special target on the industry, innovation, and infrastructure). The results suggest that for Ra, IEG is the most significant factor at a 95% confidence level. The results have been supported by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Ra analysis (with amplitude distribution function (ADF), and peak count (PC).

Mechanism and characteristics of electrochemical machining using electrolyte absorbed in solid porous ball

Abstract Electrochemical machining (ECM) is a process that is widely employed to machine extremely hard materials. However, because of the fluidity of the liquid electrolytes used in conventional ECM, it is difficult to accurately limit the electrolyte distribution over the machining area to prevent the occurrence of stray-current corrosion. Therefore, in this study, to overcome this shortcoming, a non-conductive solid porous ball is used as an electrolyte absorption material in ECM. The electrolyte is absorbed by the porous structure of the ball, and an electrolyte film is formed on the ball surface generating current paths from the workpiece to the tool electrode while preventing the electrolyte from flowing freely in an undesired manner over the workpiece surface. Because the workpiece is not immersed in the electrolyte, only the area in contact with the electrolyte held in the porous ball is subjected to ECM, whereas the other areas of the workpiece remain unaffected. In this way, the electrolyte distribution is limited to the desired area. In this paper, a newly developed experimental procedure, its machining mechanisms, and applications are explained. In addition, several unsolved problems that occurred in the experiments are reported and discussed. • The machining mechanism, features, and applications of ECM using electrolyte absorbed in solid porous ball are investigated and discussed. • To control the electrolyte distribution, a solid porous material was used as the electrolyte absorption material in ECM processing. • To better understand the machining characteristics of this method, a number of the factors influencing these characteristics are examined experimentally.

Coupled Pulse/Pulse-Reverse Electrochemical Machining and Electrowinning for Metal Recovery, Elimination of Waste, and Minimization of Water Usage

Electrochemical machining (ECM) is well suited for machining “difficult to cut” materials and/or parts with complicated and intricate geometries difficult to produce by mechanical or electric-discharge fabrication methods. Conventional ECM processes typically operate with neutral salt electrolytes, in which the machined material is precipitated from the ECM electrolyte as hydrated metal oxide/hydroxide sludge. This sludge is generally transported off-site and disposed in a landfill. Depending on the alloying components in the machined metal, it may be necessary to designate the sludge as a hazardous material and landfill it according to much stricter requirements. Furthermore, the volume of sludge generated by ECM of many common alloys in pH-neutral solutions is typically more than 300 times greater than the amount of metallic material removed, requiring the use of a high-CAPEX and -OPEX sludge management equipment train. As recently noted, the generation and disposal of the sludge is a major impediment to the widespread use and implementation of ECM operations [1], especially for smaller fabrication operations seeking to add or expand ECM process capability.This talk will present work on development of “Recycling ECM” [(R)ECM], a novel, patented [2] form of ECM processing coupled with electrowinning (EW), where the machined material remains in soluble form, typically through the use of acidic or buffered-acid solutions, and is directly recovered from the electrolyte via EW without intermediate processing (see Figure 1, left). Significant challenges have been reported in literature in attempts to use direct current ECM in such electrolytes [3], including degraded workpiece surface finish and problematic deposition of dissolved metals on the ECM tooling. Faraday has previously demonstrated the ability of pulse current/pulse reverse current (PC/PRC) waveforms to electrochemically machine materials while achieving a high-quality surface finish [4,5], and our prior experience suggests that selection of a suitable ECM waveform should avoid the adventitious electrodeposition challenges observed in the literature. Figure 1 (right) presents a notional pulse-reverse waveform annotated with key timing and electric fiend intensity parameters, and enumerates some of the mechanisms of control afforded by the pulse-reverse processing paradigm. The enhanced control of the ECM process enabled by the PRC waveform enables operation with a variety of electrolytes, and also enables metal recovery via electrowinning from electrolytes which are not feasible to process with direct current approaches.In developing the (R)ECM process for a particular material, we first select an electrolyte in which the machined material is soluble, to avoid sludge formation, and from which electrodeposition of compact metallic films is feasible. The ECM and EW unit operations are coupled into a complete electrolyte circulation loop and their operating parameters adjusted to maintain soluble metal concentration(s) in a range where ECM is not adversely affected and EW is efficient and economical. Consequently, metals are recovered, sludge waste is avoided and water usage is minimized since losses are limited only to evaporation, adventitious electrolysis, and panel drag-out.After introducing the (R)ECM concept and motivation, this talk will summarize data gathered from operation of the (R)ECM process, wherein soluble metal concentration(s) were maintained in a pre-determined range by adjustment of ECM/EW operating parameters. Additionally, a brief overview will be provided of a β-scale electrowinning system Faraday developed and installed at the U.S. Army Benét Laboratories to enable (R)ECM operations there. This system is sized to recover up to 0.5 m3 per year of metal from an existing ECM operation, and will assist Benét Laboratories in their efforts toward meeting the U.S. Army’s “Vision for Net Zero” [6].The authors acknowledge financial support from U.S. Army Contract Nos. W15QKN-12-C-0010 and W15QKN-12-C-0116, and US EPA Contract No. EP-D-13-040.Figure 1. (Left) Schematic of a possible (R)ECM implementation for an alloy machined primarily to divalent metal cations. (Right) Schematic of pulse-reverse ECM waveform and process factors addressed by the various waveform components. [1] K.P Rajurkar, D. Zhu, J.A. McGeough, J. Kozak, A. De Silva “New Developments in Electro-Chemical Machining” Annals of the CIRP Vol 48(2) (1999). [2] U.S. Patent No. 9,938,632, granted 10 Apr 2018. U.S. Patent No. 10,214,832, granted 26 Feb 2019. [3] Wessel, “Electrochemical Machining of Gun Barrel Bores and Rifling,” Naval Ordnance Station, Louisville KY, September 1978. http://handle.dtic.mil/100.2/ADA072437. [4] C. Zhou, E.J. Taylor, J.J. Sun, L.E. Gebhart, R.P. Renz. “Electrochemical Machining Using Modulated Reverse Electric Fields.” U.S. Patent No. 6,402,931, 11 June 2002. [5] E.J. Taylor. “Sequential Electromachining and Electropolishing of Metals and the Like Using Modulated Electric Fields.” U.S. Patent No. 6,558,231, 6 May 2003. [6] “Vision for Net Zero” http://army-energy.hqda.pentagon.mil/programs/netzero.asp. Figure 1

Intentionally-induced dynamic gas film enhances the precision of electrochemical micromachining

Electrochemical machining (ECM) suffers from high process complexity including the design of tool shape, tool insulation, and electrolyte flow, which are inevitable to achieve precision ECM by reducing stray machining. In this study, a novel gas-assisted electrochemical micromachining (GA-ECM) method which employs a gas shielding tool electrode is proposed to solve the problems. A pulsating dynamic gaseous film is intentionally induced surrounding the cathodic tool through the rise of potential to insulate the tool side surface and evoke a local electrolyte flow at the machining gap for flushing, thus enhancing the ECM precision. The principle of the proposed method was verified by both simulation and experiments, and the machining characteristics were investigated considering the current-voltage curve and fluid flow. Further, the machining gap was directly observed by video imaging to reveal the real-time bubbly fluid flow. Experimental results show that the self-induced gas film can not only suppress stray machining by insulation effect but also give rise to a local flushing flow field due to the hydrodynamic behavior of gas evolution. Precise microstructures with a low surface roughness Ra 53.6 nm were successfully fabricated by GA-ECM. In comparison to conventional ECM, the micromachining precision and obtained surface roughness by GA-ECM is improved by 2.6 times and 51.8 times respectively. The study demonstrates the feasibility of GA-ECM as an effective method for efficient micromachining with simplified process procedures and provides insights for optimizing the ECM process.

A study on the effect of voltage on performance characteristics of electrochemical surface grinding of HMMC

Application of Hybrid Metal Matrix Composites (HMMCs) are restricted in the advanced manufacturing industries such as aerospace and automobile because of machining challenges due to its superior mechanical properties. Hybrid machining processes (HMP) have become more popular to fabricate complex shapes and intricate profiles of MMCs and other advanced materials. Electrochemical grinding is such an HMP that combines conventional electrochemical machining and mechanical grinding. The aim of the present research to shows the effect of voltage on quality characteristics during electrochemical grinding of Al-SiC-Gr HMMCs. Experiments performed on the indigenously developed experimental setup of electrochemical surface grinding. Results revealed that the material removal rate (MRR) increases by increasing applied voltage.

Scaling approach towards electrochemical micromachining: a method to evaluate similarity

The electrochemical micromachining (ECMM) system is a modern equipment well thought out as the phenomenon of conventional electrochemical machining (ECM) system in microscale. The ECM system and ECMM system are similar, but the practice method and mechanism involved in the ECM system are analogous to those of the ECMM system, i.e., the differences in machining conditions and machining performance give rise to a factor called the scale effect. In this paper, ECMM has been applied with the advantageous concept called scale effect. Single factor experiments are conducted in which voltage, duty ratio, and tool feed rate are considered as the input factors for the exploration of the different grades of scale effect through the material removal rate, circularity, and overcut. The scale effects that occurred during machining are found using the similarity precision of the micro- and macrosystems based on the similarity theory. Quantitative evaluation of the scale effects is done for the ECMM process. The evaluation showed greater similarity precision indicating a larger significant scale effect. The output values of MRR, circularity, and overcut were normalized which also showed a positive scale effect. The research on scale effects delivers benefits in engineering such as optimizing the processing parameters involved and improving the machining performances of ECMM.

Modelling of Wire Electrochemical Micromachining (Wire-ECMM) process for anode shape prediction using finite element method

In the present work, the principle of electrochemical dissolution was used to generate precise micro slits (kerf) on a flat stainless steel 304 workpiece, using a thin copper wire of diameter 30 μm as a tool. This variant of conventional electrochemical machining is called as Wire Electrochemical Micromachining (Wire-ECMM). The process was modelled in two dimensions with weak field formulation using finite element method (FEM) and the algorithm was implemented using a code in MATLAB (R2016a). Prediction of anode profile was done and this predicted profile was compared with the experimentally obtained profile. For this purpose, the distribution of iso potential contours in the domain of simulation was obtained by solving 2-D Laplace's equations for potential function in Cartesian coordinate system which was further used for quantitative assessment of current density at different points on the anode boundary. For experimental validation of the developed model, a setup for Wire-ECMM was designed and fabricated. Experiments were conducted to capture the variation of kerf width with three key process parameters namely, applied potential (V), electrolyte concentration (mol/L), and tool feed rate (μm/s), all varied one at a time. Each parameter was varied in four discrete equally spaced steps and width of kerf for each set of input parameters was obtained. Predictions from the developed model agreed well with the experimental results with a minimum error of 3.00%. On superimposing the kerf profile outline obtained experimentally on the simulated kerf profile outline, a close match between the two was observed.

Modeling on Volumetric Material Removal for Fabrication of Complex Shapes by EC Milling of Ti6Al4V

Generation of accurate complex shaped products on various HSTR alloys is a key feature for many kinds of machine parts widely used in industries starting from biomedical to defence industries. However, producing these kinds of complex features using traditional processes face great challenges due to the thermo-mechanical effects. Being free of tool wear, thermal stresses and residual stresses, electrochemical machining (ECM) has the potential of machining of those materials. Electrochemical milling (EC milling) process is similar to conventional ECM in which metal is removed in a layer-by-layer fashion with simple geometric tool by moving a predefined path. Not only it is difficult to produce complex shaped products on various HSTR alloys but also it is almost impossible to predict the volumetric material removal prior to the production. So, in this paper, attempt has been made to develop a mathematical model for correlating the major process parameters with the responses of EC milling process. An empirical formula is obtained based on the model to predict the volumetric material removal for various complex shapes generation on Ti6Al4V. Thereafter, experimental verification is performed by electrochemical milling system and reveals good correlation with the theoretical predictions.

Confined Chemical Etching for Electrochemical Machining with Nanoscale Accuracy.

In the past several decades, electrochemical machining (ECM) has enjoyed the reputation of a powerful technique in the manufacturing industry. Conventional ECM methods can be classified as electrolytic machining and electroforming: the former is based on anodic dissolution and the latter is based on cathodic deposition of metallic materials. Strikingly, ECM possesses several advantages over mechanical machining, such as high removal rate, the capability of making complex three-dimensional structures, and the practicability for difficult-to-cut materials. Additionally, ECM avoids tool wear and thermal or mechanical stress on machining surfaces. Thus, ECM is widely used for various industrial applications in the fields of aerospace, automobiles, electronics, etc. Nowadays, miniaturization and integration of functional components are becoming significant in ultralarge scale integration (ULSI) circuits, microelectromechanical systems (MEMS), and miniaturized total analysis systems (μ-TAS). As predicted by Moore's law, the feature size of interconnectors in ULSI circuits are down to several nanometers. In this Account, we present our perseverant research in the last two decades on how to "confine" the ECM processes to occur at micrometer or even nanometer scale, that is, to ensure ECM with nanoscale accuracy. We have been developing the confined etchant layer technique (CELT) to fabricate three-dimensional micro- and nanostructures (3D-MNS) on different metals and semiconductor materials since 1992. In general, there are three procedures in CELT: (1) generating the etchant on the surface of the tool electrode by electrochemical or photoelectrochemical reactions; (2) confining the etchant in a depleted layer with a thickness of micro- or nanometer scale; (3) feeding the tool electrode to etch the workpiece. Scavengers, which can react with the etchant, are usually adopted to form a confined etchant layer. Through the subsequent homogeneous reaction between the scavenger and the photo- or electrogenerated etchant in the electrolyte solution, the diffusion distance of the etchant is confined to micro- or nanometer scale, which ensures the nanoscale accuracy of electrochemical machining. To focus on the "confinement" of chemical etching reactions, external physical-field modulations have recently been introduced into CELT by introducing various factors such as light field, force field, hydrodynamics, and so on. Meanwhile, kinetic investigations of the confined chemical etching (CCE) systems are established based on the finite element analysis and simulations. Based on the obtained kinetic parameters, the machining accuracy is tunable and well controlled. CELT is now applicable for 1D milling, 2D polishing, and 3D microfabrication with an accuracy at nanometer scale. CELT not only inherits all the advantages of electrochemical machining but also provides advantages over photolithography and nanoimprint for its applicability to different functional materials without involving any photocuring and thermoplastic resists. Although there are some technical problems, for example, mass transfer and balance, which need to be solved, CELT has shown its prospective competitiveness in electrochemical micromachining, especially in the semiconductor industry.

Electrolyte Maintenance Technology Platform: Applying Learning Across Electrochemical Machining and Stripping Processes

In industrial electrochemical processes, there is commonly a need to maintain the electrolyte, so as to avoid excess costs associated with electrolyte replacement and waste disposal. Faraday is engaged in the development of a range of technologies aimed at electrolyte maintenance: 1) Recycling Electrochemical Machining ((R)ECM) for maintenance of electrochemical machining electrolyte to enable a zero-discharge process, 2) adjustment of a chrome stripping process to ensure that hexavalent chromium is not formed in the electrolyte during stripping, and 3) recycling of the components of a high velocity oxy-fuel coating during stripping. In each case, we are applying the principles of pulse-reverse electric fields, as necessary, as well as innovative racking and fixturing design to ensure good primary current distribution, to achieve the desired performance results. We will discuss how lessons learned in each project are applied to the other projects to enhance the chance of success. Electrochemical machining (ECM) is suited for machining parts fabricated from “difficult to cut” materials and/or parts with complicated and intricate geometries. However, the conventional DC ECM process generates large amounts of sometimes hazardous waste. To develop a (R)ECM process, we select an electrolyte whereby the machined material is soluble and avoids sludge formation by precipitation. The ECM unit operation is coupled to an EW unit operation where the machined material is collected as metal. The ECM and EW unit operations are adjusted to keep the soluble metal concentration in a range where the ECM process is not adversely effected and the EW operation is efficient and economical. Consequently, metals are recovered, waste is avoided and water usage is minimized. We have demonstrated integrated operation of the (R)ECM process where the soluble metal concentration is maintained in a pre-determined range by 1) simultaneous (R)ECM operation by adjusting the ECM unit operation in the presence of constant EW unit operation, 2) simultaneous (R)ECM operation by adjusting the EW unit operation in the presence of constant ECM unit operation, and 3) sequential operation of the ECM and EW unit operations. Faraday recently installed a β-scale Recycling Electrochemical Machining ((R)ECM) system at the U.S. Army Benet Laboratory. The (R)ECM system is sized to recover up to 0.5 m3per year of metal from an electrochemical machining operation. The (R)ECM system couples an electrochemical machining unit operation with an electrowinning (EW) unit operation for recovery of metals, elimination of waste, and minimization of water usage. Consequently, the RECM system is consistent with the U.S. Army’s “Vision for Net Zero”. Faraday is developing a Chrome Stripping technology for rapid removal of chrome from landing gear parts and other aircraft components, while maintaining the functional requirements of those parts, and eliminating or reducing hexavalent chromium formation to below OSHA PELs. Similarly to the (R)ECM technology, by integrating an Electrowinning unit, we will enable direct recovery of the “stripped” chromium metal from the electrolyte, return the electrolyte to the stripping process, and be a drop-in replacement for the current stripping process. Work has demonstrated removal of chrome from high strength steel substrates using a weak acid electrolyte while eliminating hexavalent chromium, without adversely affecting the substrate surface. We are optimizing the technology, and will design and build a pilot-scale facility to strip larger parts, perform compatibility testing for functional performance metrics, demonstrate replating after stripping, recover the chrome and enable a zero-discharge process Finally, Faraday has demonstrated the feasibility of an ElectroStripping/ElectroWinning technology, able to decrease the electrolytic stripping time of a high velocity oxygen fuel (HVOF) coating from an Inconel 718 substrate from 72 hours to 4 hours, without adversely affecting the substrate surface. The capability to maintain the electrolyte and recover stripped metals was also demonstrated. In future work, we will optimize the stripping process for WC-Co coatings, by improving the cell configuration and racking and fixturing, electrolyte, and waveform parameters. Acknowledgements: This study is supported by the US Army (W15QKN-12-C-0116), and the US Air Force SBIR Program (FA8222-16-C-0006, FA8117-15-C-0019). The financial support of Faraday Technology, Inc. corporate R&D is also gratefully acknowledged.

Sustainable Electrochemical Machining for Metal Recovery, Elimination of Waste, and Minimization of Water Usage

This paper will discuss progress in development by Faraday of an integrated technology to recover and recycle metals from electrochemical machining (ECM). ECM is suited for low mass removal, high value-added manufacturing steps that cannot be easily performed using conventional machining, whether due to workpiece material properties, tooling limitations, or high surface integrity requirements. Sludge byproducts formed during conventional ECM processes are difficult to recover from the electrolyte, and discarding the sludge results in the loss of potentially valuable “waste” metal as well as entrained electrolyte salts and water. Results will be presented demonstrating a “Recycling ECM” technology, which is based upon patented cell designs and pulsed waveforms, targeting alloys including: C18000 copper, SAE4150 alloy steel, 316L stainless steel, and INCONEL® 718. These metals were machined in electrolyte to concentrations between 800-3500 ppm and subsequently recovered by electrowinning in solid, metallic form devoid of hydroxides/hydrated oxides, without intermediate electrolyte processing.

Sustainable Electrochemical Machining for Metal Recovery, Elimination of Waste, and Minimization of Water Usage

Faraday is developing and installing a β-scale Recycling Electrochemical Machining ((R)ECM) system at the U.S. Army Benet Laboratory. The (R)ECM system is sized to recover up to 0.5 m3 per year of metal from an electrochemical machining operation. The metals of initial interest include: 1) beryllium-free nickel-copper alloy (C18000), 2) Cr-Mo alloy steel (SAE4150), 3) nickel alloy (IN718) and 4) tantalum tungsten (Ta10W) alloy. The (R)ECM system couples an electrochemical machining unit operation with an electrowinning (EW) unit operation for recovery of metals, elimination of waste, and minimization of water usage. Consequently, the RECM system is consistent with the U.S. Army’s “Vision for Net Zero”[1]. Electrochemical machining (ECM) is suited for machining parts fabricated from “difficult to cut” materials and/or parts with complicated and intricate geometries. Conventional, direct-current (DC) ECM typically operates with neutral salt electrolytes whereby the machined material is generally precipitated from the machining electrolyte as metal oxide/hydroxide sludge. This sludge is generally transported off-site and disposed in a land-fill. Depending on the alloying components in the machined metal, the sludge is often designated as a hazardous material. Furthermore, the rifling of a gun barrel by ECM generates ~350 gal of centrifuged sludge per ~250 in3 of material removed [2]. This represents greater than 300X volume multiplier of waste sludge relative to the amount of material removed. As recently noted, the generation and disposal of the sludge is a major impediment to the widespread use and implementation of ECM operations [3]. Faraday has previously demonstrated the ability of pulse current/pulse reverse current (PC/PRC) waveforms electrochemically machining materials while achieving a high quality surface finish (Figure 1) [4],[5]. Smooth surfaces are typically not possible in conventional DC ECM. The PRC waveforms control the ECM process and consequently ECM with PRC is adaptable to a variety of electrolytes. To develop a (R)ECM process, we select an electrolyte whereby the machined material is soluble and avoids sludge formation by precipitation. The ECM unit operation is coupled to an EW unit operation where the machined material is collected as metal. The ECM and EW unit operations are adjusted to keep the soluble metal concentration in a range where the ECM process is not adversely effected and the EW operation is efficient and economical. Consequently, metals are recovered, waste is avoided and water usage is minimized. In the presentation, we will summarize the initial electrolyte selection studies for C18000, SAE4150, IN718 and Ta10W materials. In additionally, we will demonstrate integrated operation of the (R)ECM process where the soluble metal concentration is maintained in a pre-determined range by 1) simultaneous (R)ECM operation by adjusting the ECM unit operation in the presence of constant EW unit operation, 2) simultaneous (R)ECM operation by adjusting the EW unit operation in the presence of constant ECM unit operation, and 3) sequential operation of the ECM and EW unit operations. Finally, the status (R)ECM system design and installation at Benet Laboratories will be reviewed.

펄스전해가공을 이용한 인바 박판의 가공 형상 및 Overcutting 현상에 관한 연구

Invar is a compound metal of Fe-Ni system contained 36.5% Ni. The characteristic of invar is that the coefficient of thermal expansion is 1.0×10 -6 cm/°C. It is approximately 10 times smaller than series of steel. Because of this low thermal expansion characteristic of Invar, it is used to shadow mask of display device such as UHDTV or OLED TV. In this study, pulse current from pulse generator instead of DC current is used to overcome the disadvantages of the conventional electrochemical machining. Pulsed current with different duty factor in PECM affect the precise geometry. Pulse electrochemical machining is conducted to machine the micro hole to the invar sheet with different duty factor. The machined shape and overcut of invar sheet with different duty factor is observed by optical microscope and scanning electron microscope (SEM).

Replication of microstructured tools for electrochemical machining applications

Electrochemical machining (ECM) is a powerful method to machine metals independently of their mechanical properties. Micro-sized structures can be formed with high precision. For this purpose, it is necessary to manufacture tools with adequately fine structures. Conventional ECM tools were manufactured by micro-drilling, -milling, -turning, etc. Depending on the complexity of the structures, these techniques are very elaborate and expensive. Recently, a new procedure, which combines photolithography and electroforming, the so-called PhoGaTool process (photolithographic electroforming of ECM tools), was published. In the present work, we demonstrate how this method can also be used for copying ECM tools that were conventionally manufactured. A copy of an industrial PECM tool (precise electrochemical machining) was manufactured and used for the structural characterization and determination of the replication accuracy. The electroforming parameters like deposition conditions, bath composition as well as physical and chemical parameters were optimized for model systems. The inclusion of bath additives in the metal matrix during the deposition leads to micro-stresses, hence in this contribution, an alternative additive-free electrolyte was used. The accuracy of the process was investigated by means of confocal laser scanning microscopy. Average deviations of the structure depth and the lateral structure dimensions are in the range of 5 %.

Cathode design and experimental study on the rotate-print electrochemical machining of revolving parts

A new electrochemical machining (ECM) process named rotate-print ECM (RPECM) is proposed to meet the requirement of machining revolving parts with complex convexity structures. During the RPECM process, a revolving cathode tool was employed to replace a set of complicated block tools used in conventional sinking ECM process. In this paper, the design method of the revolving cathode tool based on the analysis of an equivalent model for the RPECM process was emphasized. The radius and window edge contour of the cathode tool were designed by optimizing the motion trails of the window edge points and their deviations from the required sidewall profile of the target convexity. A cylindrical test piece was machined experimentally to verify the designed tool. The results showed that the machined cylinder surface is smooth without any flow tracks and residual ribs. A convexity with complex top face contour was fabricated successfully. It can be seen that the sidewall profile is tapered and the edge is nearly trenchant. The processing error of the sidewall profile can be effectively controlled by optimizing the radius and window size of the cathode tool.

Recycling Electrochemical Machining for Metal Recovery and Elimination of Waste

This paper will discuss progress in development by Faraday of an integrated technology to recover and recycle metals from electrochemical machining (ECM) operations. ECM is suited for low mass removal, high value-added manufacturing steps that cannot be easily performed using conventional machining, whether due to workpiece material properties, tooling limitations, or high surface integrity requirements. Sludge byproducts formed during conventional ECM processes are difficult to recover from the electrolyte, and discarding the sludge results in the loss of potentially valuable “waste” metal as well as entrained electrolyte salts. The FARADAYIC® Recycling ECM [(R)ECM] technology, which is based upon patented FARADAYIC®cell designs and pulsed waveforms, is proposed as a novel augmentation of ECM to allow operation at conditions where both (a) sludge formation is avoided and (b) recovery of the machined metals in compact, solid form is enabled. Conventional, direct-current ECM typically operates with neutral salt electrolytes, which affords two particular advantages: the sludge formation itself is beneficial as it limits the dissolved metal concentration, in turn effectively eliminating any metal re-deposition onto the tool/counter­electrode; and empirical observation from industrial ECM practice is that neutral electrolytes generally yield superior surface finish as compared to acidic or alkaline electrolytes [[i]]. Faraday has previously demonstrated the capability of carefully tuned, pulsed FARADAYIC® waveforms to achieve extremely high quality surface finish in acidic and alkaline electrolytes, as well as neutral salt solutions. Also, separately tuned waveforms should allow on the one hand minimal re-plating on the tool in the ECM cell, and on the other an efficient electrowinning (EW) recovery process in an integrated electrowinning cell. As will be described, the FARADAYIC®(R)ECM technology successfully exploits both of these capabilities, enabling near-complete internal recycle of electrolyte and recovery of metals in compact, solid form. Figure 1 schematizes the (R)ECM process flow: blanks are machined into finished parts in the ECM cell and the dissolved metal is recovered in the EW cell, while substantially all of the electrolyte is retained within the system. Faraday initiated (R)ECM development efforts by screening candidate electrolytes for metal solubility limits and facility of metals electrodeposition using Hull cell tests. After initial electrolyte down-selection, ECM of 1″x1″ coupons was performed using various FARADAYIC® waveforms both to test the achievable surface finish and also to generate “live” ECM-derived electrolytes with which to reconfirm their suitability for the metal recovery function. The best-performing electrolyte for each material was then used in a larger “pilot-scale” (R)ECM system, in which high-rate ECM and in situ EW unit operations were tested, first separately and then in an integrated fashion. Beryllium-free nickel-copper (C18000) and Cr-Mo alloy steel (SAE4150) were separately machined in electrolyte to concentrations between 800-3500 ppm and subsequently recovered by electrowinning in solid, metallic form devoid of hydroxides/hydrated oxides, without intermediate electrolyte processing. Metal concentrations were maintained within a target operating window defined by polishing performance exhibited in the coupons studies (1500-2000 ppm) by appropriate adjustments to the electrical parameters of one of the (R)ECM unit operations. Development of FARADAYIC® (R)ECM for other alloys including 316L stainless steel and Inconel®718 is currently underway. [[i]] Wessel, “Electrochemical machining of Gun barrel Bores and Rifling” Naval Ordnance Station, Louisville, KY, September 1978; http://handle.dtic.mil/100.2/ADA072437. Figure 1

高電圧パルスアシスト電解加工の研究

In this paper, a new method of electrochemical machining (ECM), where high-voltage pulses are intermittently supplied to electrodes during low-voltage pulsed ECM, is presented. The properties of this method are compared with those of a conventional low-voltage pulsed ECM method using a 0.3 mmφ electrode. We found that this method enables us to machine a workpiece using ECM conditions that are difficult to use in the conventional ECM method, such as low electrolyte concentration and low pulse duty ratio. This method also enable us to machine a workpiece without strong flushing. The machining speed of this method is increased almost 3-6 times that of the conventional ECM method. A small side gap width comparable to the gap width of EDM is achieved using a low-density NaNO3 electrolyte.

The effect of high frequency and duty cycle in electrochemical microdrilling

Pulse electrochemical micromachining possesses attractive features compared to conventional electrochemical machining processes based on a continuous current because it allows instantaneous electrochemical reaction by applying ultrashort voltage pulses. This study focuses on effects of applied frequency and duty cycle in electrochemical microdrilling on nickel plate. During microtool fabrication, tungsten micro-shafts are electrochemically etched to make two desired cylindrical microtools of different lengths and diameters to investigate the effects of pulsed frequency and duty cycle on electrochemical micromachining. The shape and size of the fabricated microholes, machining time, actual material removal rate (MRRact) and the number of short circuits are considered as response factors. Shapes of micro-drilled holes are measured and compared to tool geometry. As for both short and long microtools, MRRact and machining time respectively decreased and increased with an increase in applied frequency. But the MRRact and machining time respectively increased and decreases with an increase in duty cycles. Experimental data reveals that there is a strong correlation among the shape and size of the microhole fabricated with applied frequency and duty cycle during microdrilling. However, MRRact was found to be much higher for short tool than a long tool.