Electrochemical Jet Research Articles

Electrochemical jet machining in deep-small holes with gas assistance: generating complex features on internal surfaces

Deep-small holes with internal features have important applications in thermal engineering but pose significant difficulties for traditional machining methods. Electrochemical jet machining (EJM) is an effective surface micromachining technique with numerous merits. Applying EJM to create complicated features on the internal surface of deep-small holes is attractive. However, this concept remains challenging due to the narrow and enclosed processing space. In this work, a novel gas assistance tool is developed to achieve the EJM process in deep-small holes for the first time. The hydrodynamic conditions to realize well-shaped and unsubmerged jets in both open space and deep-small holes using the specifically designed tool are investigated. The appropriate electrolyte flow rate and sidewall orifice dimensions enable the desired jet to be ejected laterally from the tubular cathode sidewall orifice. While in the deep-small hole the assist gas creates a local gas cavity around the orifice to prevent the jet from submerging, forming the jet shape required for EJM and consequently achieving localized machining of the internal surface. Excessive assist gas pressure should be avoided as it causes the jet to incline and deform, resulting in reduced machining accuracy. Furthermore, the influence of the main parameters on machining performance is examined. The developed gas-assisted EJM method demonstrates similar machining characteristics to the conventional EJM process when appropriate gas assistance conditions can produce the well-shaped unsubmerged jet. As such, various features with smooth surfaces and good shape accuracy are successfully machined on the internal surface of deep-small holes.

Stray current affected zone in electrochemical jet machining

The stray current affected zone (SCAZ) in electrochemical jet machining (EJM) poses a significant and often unavoidable challenge. This study offers an in-depth analysis of the morphological characteristics and formation mechanisms of SCAZ in EJM through a combination of machining experiments and surface characterization. By investigating various workpiece materials and electrolytes, we identify that stray corrosion phenomena are highly dependent on the specific material-electrolyte combinations used. Although applying ultra-short pulses of 750 ns enhances shape accuracy, it does not fully prevent pitting corrosion. Conversely, the bipolar pulse technique effectively reduces pitting, though stray oxidation remains an issue. As a result, post-finishing processes are crucial. Notably, plasma electrolytic polishing is demonstrated to be highly effective in removing stray oxidation, achieving a glossy surface on SUS304 in just 3 s while maintaining dimensional accuracy.

Electrolyte jet tomography: Three-dimensional microstructure mapping with an electrochemical machine tool and an optical microscope

There is a general separation between the manufacturing processes that add value to materials on the factory floor and the techniques engineers use in the laboratory to evaluate the microstructures and the surface integrity that results. These techniques are often destructive or require a vacuum and are incompatible with production lines. However, this information has intrinsic value and could be exploited to inform production decisions during manufacture. In this study, a novel approach to acquire this information is presented that is underpinned by electrolyte jet machine tool coupled with optical microscopy, which can allow the extraction of both grain-wise partial orientation and morphological information, and crystallographic macro textures in three dimensions. Here, iterative sections are precisely machined into the near surface of a commercially pure titanium alloy using an electrochemical jet and subsequently imaged, allowing the reconstruction of high-fidelity microstructure models rapidly and under ambient conditions. In doing so, new insights into the specific orientation-dependent dissolution mechanisms are offered, and the acquisition of appropriate conditions that result in nanoscale roughness surfaces (avoiding the dominance of pitting and preferential grain removal) is firstly explored. Building on prior work, a piecewise approach is presented to analyse the acquired image stacks to map partial crystal orientations, while different approaches are proposed to account for jet-specific surface artefacts and waviness. This is repeated over 20 layers in an individual specimen and layer-wise orientation maps are used to construct volumetric models of the specimen. These data sets are then explored from the perspective of materials/manufacturing engineers, who may use to this information to effect advancements to materials processing technologies.

Electrochemical Jet Machining of Surface Texture: Improving the Strength of Hot-Pressure-Welded AA6061-CF/PA66 Joints

Diverse industries are witnessing an increase in demand for hybrid structures of metals and carbon-fiber-reinforced thermoplastic composites (CFRTPs). Welding is an essential technique in the manufacture of metal–CFRTP hybrid structures. However, achieving high-strength metal–CFRTP welded joints faces serious challenges due to the considerable disparities in material characteristics. As an effective method to strengthen metal–CFRTP joints, surface texturing on metal is gaining significant attention. This study introduces an emerging surface texturing approach, electrochemical jet machining (EJM) using a film electrolyte jet, for enhancing the performance of AA6061-CF/PA66 hot-pressure-welded (HPW) joints. Parametric effects on surface morphology and roughness in the EJM of AA6061 are investigated. The results show that a rough surface with multiscale pores can be generated on AA6061 by EJM, and that surface morphology can be modulated by adjusting the applied current density and jet translational speed. Subsequently, the effects of different EJM-textured surface morphologies on the performance of HPW joints are examined. Surface textures created by EJM are demonstrated to significantly enhance the mechanical interlocking effect at the bonding interface between AA6061 and CF/PA66, resulting in a substantial increase in joint strength. The maximum joint strength attained in the present work with EJM texturing is raised by 45.29% compared to the joints without surface texturing. Additionally, the joint strength slightly improves as the roughness of EJM-textured surfaces rises, with the exception of rough surfaces that are textured with a combination of low current density and rapid translational speed. Overall, these findings suggest that EJM texturing using a film jet prior to welding is a potential approach for the manufacture of high-performance metal–CFRTP hybrid structures.

Boundary fluid constraints during electrochemical jet machining of large size emerging titanium alloy aerospace parts in gas–liquid flows: Experimental and numerical simulation

Large size titanium alloy parts are widely used in aerospace. However, they are difficult to manufacture using mechanical cutting technology because of severe tool wear. Electrochemical jet machining is a promising technology to achieve high efficiency, because it has high machining flexibility and no machining tool wear. However, reports on the macro electrochemical jet machining of large size titanium alloy parts are very scarce, because it is difficult to achieve effective constraint of the flow field in macro electrochemical jet machining. In addition, titanium alloy is very sensitive to fluctuation of the flow field, and a turbulent flow field would lead to serious stray corrosion. This paper reports a series of investigations of the electrochemical jet machining of titanium alloy parts. Based on the flow analysis and experiments, the machining flow field was effectively constrained. TB6 titanium alloy part with a perimeter of one meter was machined. The machined surface was smooth with no obvious machining defects. The machining process was particularly stable with no obvious spark discharge. The research provides a reference for the application of electrochemical jet machining technology to achieve large allowance material removal in the machining of large titanium alloy parts.

A novel approach for predicting the complex geometry generated by electrochemical jet machining

A novel approach for predicting the complex geometry generated by electrochemical jet machining

Electrochemical dissolution behavior and electrochemical jet machining characteristics of titanium alloy in high concentration salt solution

Electrochemical dissolution behavior and electrochemical jet machining characteristics of titanium alloy in high concentration salt solution

Simultaneous gas electrical discharge and electrochemical jet micromachining of titanium alloy in high-conductivity salt solution

Simultaneous gas electrical discharge and electrochemical jet micromachining of titanium alloy in high-conductivity salt solution

Investigation on tribo-characteristics of electrochemical jet machined part manufactured by laser powder bed fusion

Electrochemical jet machining (ECJM) is a toolless electrochemical-based material removal process suitable for finishing the Laser powder bed fusion (L-PBF) manufactured parts. However, the investigation of the tribological characteristics of the finished part is unknown. Therefore, in this article, an investigation was made to evaluate the tribological characteristics of the electrochemical jet machined surface of SS316L part produced by L-PBF. The experimental results revealed improvement in the roughness parameters after the ECJM. The wear tests revealed that the friction coefficients (COF) of the finished samples were significantly lower in comparison to the as-manufactured samples. During the investigation, the dominating mechanisms of the wear were found to be adhesive and delamination wear.

Gap effect in electrochemical jet machining

Electrochemical jet machining (EJM) is a young-generation micromachining and surface texturing technique with multiple merits. The materials removal function in EJM has traditionally been considered to be Gaussian-like and unaffected by changes in inter-electrode gap when maintaining a constant machining current. Nonetheless, phenomena that contradict this widely accepted perception are sometimes observed. In this paper, to clarify the inter-electrode gap effect in EJM, its impacts on flow field, electric field, and machined shape were studied by both experiments and simulation. With varied gaps ≥0.4 of nozzle diameter the jet profile keeps almost same and only its length changes, while narrowing the gap from 0.4 to 0.2 of nozzle diameter causes thinning of the jet-surrounding-film. Jet profile required for EJM cannot form with an overly tiny gap. In addition, the gap ≥0.6 of nozzle diameter features sufficiently long cylindrical jet portion that uniformly distributes the pass-through current density and eliminates the cathode-shape-determined electric field near nozzle to act on workpiece, resulting in constant materials removal function even though gap changes. With smaller gap the cathode-shape-determined electric field affects the anodic current density distribution and the materials removal function can be modulated by adjusting the gap, allowing EJM to generate geometry other than Gaussian-like profile. Furthermore, the influence of inter-electrode gap when using the specially-shaped nozzle was also investigated. With a small gap this method performs its ability in modulation of materials removal distribution by designing nozzle shapes, while a large gap such as ≥ nozzle diameter enables it to operate as a conventional nozzle.

Cathodic discharge plasma in electrochemical jet machining: Phenomena, mechanism and characteristics

An ultrahigh voltage is frequently required in electrochemical jet machining (EJM) to produce extreme current densities (>900 A/cm2 for this study) to achieve maximum dissolution rates. However, such a high electric field easily induces a cathodic discharge at the nozzle, and the generation mechanism and characteristics remain unexplored. For the first time, this study shows a direct visualisation of the hydrogen evolution and cathodic discharge in EJM using high-speed photography. An in-depth analysis of the discharge behaviour was carried out based on electrical monitoring, temperature measurement, and characterisation of the resulting changes in the electrode surface. It was revealed that the current density threshold determines the discharge ignition. Discharge occurs preferentially at the inner edge of the nozzle end face, which can cause nozzle wear and reduce localisation of anode workpiece dissolution. The discharge intensity can be controlled by varying the applied voltage and pulse frequency. The electrolyte flow velocity and gap distance influence the discharge behaviour. With appropriate process control, cathodic plasma can enhance the EJM performance while minimising its negative impact. Furthermore, cathodic discharge can be significantly suppressed by designing the geometry of the nozzle tip to avoid local electric field concentration.

Control principle of anodic discharge for enhanced performance in jet-electrochemical discharge machining of semiconductor 4H-SiC

Implementing anode discharge into electrochemical jet machining (EJM) makes it possible to process semiconductor material 4H-SiC. However, the characteristics and control principle of anodic discharge behavior in EJM remains unclear, while it significantly influences material removal and EJM precision. The present study reveals discharge behavior and its impact on material removal by controlling the imposed electrical and chemical conditions. The physicochemical properties and spatiotemporal distribution of discharges are discussed by analyzing the plasma region's temperature, luminescence, and material removal fashion. The findings reveal that discharges are preferentially ignited in certain areas where the current density is concentrated. The discharge intensity and location are controllable by the pulse cycle and electrical field distribution inside the jet (i.e., changing the jet angle). Reducing pulse duration leads to more localized and mild discharges, improving machining precision. A gas ionization-dominated anodic discharge model is proposed. Both discharge and electrolyte types exert significant influence on material removal. Using a DC supply provides a maximum machining rate of 1.44 mm/min. Meanwhile, an optimal surface finish Ra 170 nm and high shape precision with no overcut is achievable by applying high-frequency AC of 1000 Hz.

Surface finishing of an additively manufactured part using electrochemical jet machining

The development and expansion activities of additive manufacturing (AM) are at their peak as complex parts with intricate features can be easily manufactured by various AM processes. However, obtaining a good surface finish for the AM parts has remained a challenging task. The surface defects and irregularities over intricate parts pose challenges during machining with conventional processes. Therefore, a simple, cost-effective, non-contact surface finishing approach is required to post-process the external and internal surfaces of AM metallic parts. This article reports the surface finishing of the SS316L part made by laser powder bed fusion (L-PBF) using a toolless electrochemical jet machining (ECJM), and investigations were performed to evaluate the different aspects of surface integrity. The experimental results revealed that surface irregularities and defects highlighted on the as-deposited samples were eliminated after ECJM.Moreover, after post-processing, the overlaid layer of oxides and carbides over the as-deposited sample surfaces was also removed. The maximum peak and valley height of the as-deposited surface were 30.1 µm and 41.6 µm, respectively. These heights have been reduced to 13.3 µm and 9.9 µm, respectively, while the arithmetical average roughness value 'Ra' has been reduced from 7.8 µm to 3 µm. The improvement in the mean value of 'Rz' and 'Ra' after post-processing was found to be 72%, and 61%, respectively. Therefore, the study concluded that the unique characteristic of the toolless electrochemical machining process is suitable for finishing the AM part.

Adapting ‘tool’ size using flow focusing: A new technique for electrochemical jet machining

Electrochemical jet manufacturing methods exploit the localised interaction of an electrified jet with a conductive workpiece. This has been exploited by numerous researchers to deposit and remove material. In recent studies, the same approach has been used as an analysis tool to measure and evaluate engineering components. The capability of this manufacturing method is limited by the resolution, which is governed by the diameter of the jet. Although approaches have been taken to reduce the kerf or interaction volume in the process, it is the jet diameter still provides the fundamental limit. In this study, a new method is proposed which takes advantage of a constriction effect to reduce the jet diameter through flow focusing, which occurs in coaxial two-phase flows. A novel nozzle arrangement is presented which demonstrates jets can be constricted by 79% leading to 54% reduction in machined kerf width. The limitations of this method are investigated in the context of fluid dynamic constraints, identifying optimum operating regions to utilise the approach in a computer numerical control machine tool arrangement. This enables continuously varying tool size in-process, which is analogous to other energy beam processes where spot size can be adjusted with a corresponding response influence.

Fabrication of oxide-free dimple structure on germanium via electrochemical jet machining enhanced by opposing laser irradiation

The electrochemical machining (ECM) of germanium (Ge) wafer can be significantly improved in terms of efficiency and localization by introducing laser irradiation. However, residual oxide particles usually exist when using neutral electrolyte. In this study, the NaNO3 electrolyte jet is formed via a cathodic nozzle and impacts perpendicularly on the bottom of the Ge wafer, at which position the nanosecond (ns) laser irradiates from opposing side to locally and precisely enhance the electrical conductivity. In this way, the dimple structure without any detectable oxidation products can be efficiently fabricated. Characterization of surface morphology is then amply conducted. The radial lines consisting of regular micro-waving structure are usually noticeable, especially near the dimple edge, which may be attributed to the rapid and radial electrolyte flow along the concave sidewall. In contrast, irregular corrugated pattern can be observed near the dimple center, which may be caused by the electrolyte turbulence after impingement. In addition, parametric experimental study has been carried out, and the effects of the applied voltage, laser power and electrolyte concentration on the dimple profile and surface characteristics have been respectively detailed discussed. Finally, simulation study of the electrolyte flow field is conducted to reveal the distribution regularities of velocity and pressure, to deepen the understanding of formation mechanism of the complex surface morphology.

Phenomena and mechanism of local oxidation microlithography of 4H–SiC via electrochemical jet anodisation

Local oxidation microlithography (LOM) of 4H–SiC wafers based on the spatial confinement of electrochemical oxidation inside a microelectrolyte jet, namely, electrochemical jet anodisation (EJA), is presented. EJA enables selective growth of the oxide layer on a micro-scale local area with no masks because the anodic reaction occurs exclusively in the jet-substrate interaction area. The shape and height profile of the oxide layer were highly dependent on the anodising conditions. The change in the current density resulted in two distinct oxidation regimes, leading to the formation of either Gaussian-type or doughnut-shaped oxide spots. The oxide growth mechanism was revealed by SEM, AFM and XTEM characterisation of the oxide at the micro/nanoscale. A flat oxide layer with uniform thickness was obtained by applying parametric control. Following a chemical etching process, microstructures were readily created at the patterned oxide locations, demonstrating EJA as a potential lithography technique for microfabrication.

Improving surface quality through macro electrochemical jet milling with novel cathode tool

In the macro electrochemical jet milling, the surface quality produced by the standard cathode tool is unsatisfactory owing to the inevitable effects of low current density and inefficient mass transfer. This paper proposes a novel cathode tool with an insulated nozzle tip and inclination angle to confine the low current density area and enhance the mass transfer. The theoretical analysis and numerical simulation results reveal that the designed tool with an inclined angle helps to increase the flow velocity of electrolyte in the machining gap and reduces the effect of the low current density during the machining process. Experimental results show that the surface roughness produced by the proposed tool (tool C) is reduced by approximately 6 times compared with the standard tool. Furthermore, the material removal rate of tool C is approximately 1.6 times equal to that of the vertical mode. Besides, a mirror-like surface with a clear reflection and surface roughness (Ra) of 0.12 µm was successfully fabricated.

Direct Writing Unclonable Watermarks with an Electrochemical Jet

AbstractCounterfeit parts result in significant losses per annum and are often dangerous, therefore they represent a serious concern for manufacturers and end users alike. Easily written but unclonable watermarks undermine the proposition of the counterfeiter. Here, a rapid electrochemical jet engraving routine is presented to encode robust materials with self‐organized dendritic structures at length scales that can be imaged with a smartphone. Surface defects act as stochastically distributed seeds from which discrete pitting events can be propagated by translating the electrochemical field. While the vascular pathways can be directly written at the macro scale, the formation and propagation of microscale dendritic arms is chaotic, caused by the implicit randomness of the defect seeds and the supply of ions to the surface. The latter is confounded by random perturbations in the flow condition. Each engraved dendrite is unique, stable at high temperature (>500 °C) and can be subjected to rapid image recognition to allow individual mark identification at any point during part production and delivery, or through part lifetime.

Plasma-enabled electrochemical jet micromachining of chemically inert and passivating material

Electrochemical jet machining (EJM) encounters significant challenges in the microstructuring of chemically inert and passivating materials because an oxide layer is easily formed on the material surface, preventing the progress of electrochemical dissolution. This research demonstrates for the first time a jet-electrolytic plasma micromachining (Jet-EPM) method to overcome this problem. Specifically, an electrolytic plasma is intentionally induced at the jet-material contact area by applying a potential high enough to surmount the surface boundary layer (such as a passive film or gas bubble) and enable material removal. Compared to traditional EJM, introducing plasma in the electrochemical jet system leads to considerable differences in machining performance due to the inclusion of plasma reactions. In this work, the implementation of Jet-EPM for fabricating microstructures in the semiconductor material 4H-SiC is demonstrated, and the machining principle and characteristics of Jet-EPM, including critical parameters and process windows, are comprehensively investigated. Theoretical modeling and experiments have elucidated the mechanisms of plasma ignition/evolution and the corresponding material removal, showing the strong potential of Jet-EPM for micromachining chemically resistant materials. The present study considerably augments the range of materials available for processing by the electrochemical jet technique.

Modelling and experimental investigation of flat surface achieved by large rectangular electrochemical jet milling

Modelling and experimental investigation of flat surface achieved by large rectangular electrochemical jet milling