Electrochemical Jet Processing Research Articles

Implications of vector change in electrochemical jet processing

Curved toolpaths challengeaccurateelectrochemical jet processingdue toresulting distortion of the cut profile. A more elaborate path planning approach is required to mitigate these negative effects. A3-dimensional process model is presented here,to predictthe resulting surface geometry.This is applied to simulate machining of curved channelsand calculate optimised feed rates forlocations of the toolpath with impairedgeometry. Through the presented predictive planning methodology, achieved depthsof curved sections of the machined channels werewithin 10.5%of the depth for straight sections, compared to up to 62.2%increasewhen feed rate compensation was not applied.

Selective and localized embrittlement of metal by cathodic hydrogenation utilizing electrochemical jet

Electrochemical jet processing (EJP) is an easy-to-implement technology for creating complex microstructures based on anodic dissolution without requiring specially designed cathodes. In this study, a new electrolyte-jet-based surface modification method based on the principle of cathodic hydrogenation, namely, electrochemical jet hydrogenation (EJH), was proposed for the first time to selectively modify the material in aspects of its brittleness. In this method, a workpiece is innovatively set as the cathode, and hydrogen evolution occurs locally on the cathode surface within the jet impinging area, leading to a localized H-treatment of the cathode material. The hydrogen-material interaction can alter the surface material property and result in localized surface modification, for example, material ductile-brittle transition by hydrogen embrittlement (HE). In this research, the proposed method was validated on niobium metal. According to the results, evident localized embrittlement was achieved, and the degree of embrittlement was precisely controlled by adjusting the electrochemical parameters mainly including current density and processing time. As a selective surface modification method, EJH can be applied as an assistive technology in hybrid machining of difficult-to-machine superalloys where localized surface modification of ductile-brittle transition is expected.

Material removal mechanism of superalloy Inconel 718 based on electrochemical abrasive jet processing

This paper proposes a high-efficiency and high-precision processing method for Inconel 718 called electrochemical abrasive jet processing (ECAJP). A mixture of an electrolyte solution and abrasive particles was sprayed from the nozzle and impacted the surface of a material while a direct-current potential was applied. The removal mechanism of ECAJP for Inconel 718 was investigated by comparing and analysing the material removal efficiency and micromorphological features and by performing energy-dispersive X-ray spectroscopy (EDS) analyses of the processing area for different processing methods (including abrasive jet processing (AJP), electrochemical jet processing (ECJP), and ECAJP). The results indicated that under the experimental conditions, there was almost no material removal for AJP. The material removal rate for ECAJP was significantly higher than the sum of those for AJP and ECJP. Electrochemical corrosion was the main form of material removal, and abrasive erosion was auxiliary in ECAJP. The microscale morphologies in the processing area and EDS analyses indicated that the microstructures of Inconel 718 had significant effects on the material removal mechanism of ECAJP. The different electrode potentials between different regions led to anisotropic removal of material in Inconel 718 and significantly affected the surface quality. The surface elements reacted with O and formed passive films. However, the synergistic effect of abrasive erosion and electrochemical corrosion removed the passive films, increased the removal rate, and reduced the anisotropy.

Towards selective compositionally graded coatings by electrochemical jet processing

In this study, we describe a new methodology to create complex coatings with functionally graded compositions, using electrochemical jet processing (EJP). Cu/Zn alloy coatings were electrodeposited, in a layer-by-layer manner, onto steel substrates through resin masks created with a desktop 3D printer. By adapting the electrolyte composition through the jet by drawing from multiple reservoirs, the ratio of cations (Cu2+:Zn2+) in the electrolyte supplied directly to the substrate surface at any point in the processing cycle can be manipulated. This allows for control over electrodeposit composition ratios through a given coating, while the mask allows for microfabrication at higher aspect ratios than achievable by electrochemical jet processing alone. After processing, masks were removed from the substrates and samples were subsequently characterised to verify changes in composition and deposition properties.

Oscillatory behaviour in the electrochemical jet processing of titanium

When appraising the performance of titanium alloys for corrosion resistance in halide environments researchers have well understood pitting and growth mechanisms through electrochemical corrosion. This knowledge is yet to be exploited for the purpose of electrochemical jet processing, a versatile and selective machining technique that is ideal for high-value manufacturing. The applicability of the method towards processing titanium is hampered by the passivating nature oxides which form. In this study, the process of jet interaction with Ti-6Al-4V in the presence of halide electrolytes is deconstructed to establish the fundamental interactions between the jet and surface. This is used to propose the mechanism by which electrolyte, oxide layer and bulk interact to create unfavourable machining phenomena. These manifest as periodic electrochemical oscillations that are accompanied by aberrations in the resulting cut and are influenced by nozzle diameter, translation, current density and flow velocity. Such oscillations can be avoided completely through processing at current densities >200 A/cm2. Experimentation is also reported here identifying candidate electrolytes for superior processing of titanium considering feature precision at high current densities (>300 A/cm2). This is valuable knowledge in terms of increasing material removal rate. In this regard, cut edge deviation is reduced by >20% and profile deviation is reduced by >40% when applying iodide-doped electrolytes, in comparison to commonly employed chloride solutions.

Direct-writing by active tooling in electrochemical jet processing

Recent innovations in electrochemical jet processing have caused step changes in process flexibility and precision. However, utilisation of these innovations requires the development of new machine tool technology. Presented here is a new methodology enabling the exploitation of highly customisable energy density profiles regardless of toolpath vector whilst minimising any error from the intent profile. A further approach is defined whereby active tooling allows the energy density profile to be modulated as a function of position within the toolpath, giving rise to dynamic feature creation. Adoption of this methodology allows a new design freedom within electrochemical jet processes.

Surface enhanced micro features using electrochemical jet processing

This work demonstrates for the first time an augmentation to electrolyte jet processing which allows plasma electrolytic oxidation to be undertaken. Using a sequential process it is possible to produce micro features (≈500 μm width) with a resolution limited only by nozzle geometry but with significant enhancement to substrate surface properties. Here the technique is demonstrated and the resulting modification is compared on the microscale to properties of conventionally produced plasma electrolytic oxide coatings. The technique is further demonstrated through the creation of an exemplar titanium component which features localised surface oxidation treated mating features.

Crystallographic texture can be rapidly determined by electrochemical surface analytics

Orientation affects application-defining properties of crystalline materials. Hence, information in this regard is highly-prized. We show that electrochemical jet processing (EJP), when coupled with accurate metrological appraisal, can characterise crystallographic texture. Implementation of this technique allows localised dissolution to be anisotropic and dependent on etch-rate selectivity, defined by the crystallography. EJP therefore, generates complex, but characteristic topographies. Through rapid surface processing and analysis, textural information can be elucidated. In this study, samples of polycrystalline Al and Ni have been subjected to EJP, and the resulting surfaces analysed to generate three-colour orientation contrast maps. Comparison of raw data acquired through our method with prior electron back-scatter diffraction data shows broad correlation and assignment (68% on a pixel-by-pixel basis), showcasing rapid large-area analysis at high efficiency.

The importance of microstructure in electrochemical jet processing

Electrochemical jet processing (EJP) is an athermal technique facilitating precision micromachining and surface preparation, without recast layer generation. The role of the microstructure in determining machining characteristics has been largely overlooked. In this study, we show that in order to optimise EJP for a given material, fundamental material factors must be considered to ensure the desired near-surface response in terms of metallurgy, topography and dimensional accuracy. In this work, specimens have been prepared from the same feedstock material (brass, Cu39Zn2Pb), to appraise the role of microstructure in the determination of key removal characteristics, such as resultant topography, removal efficiency and form. Topography is shown to be highly dependent upon microstructure across large current density ranges, whereby the phase ratio is generally the dominant amplitude-defining material property, where preconditions with divergent ratios result in lower amplitudes. The microstructure, specifically the phase ratio, significantly changes the form, where predominantly single-phase conditions result in deeper and narrower features (up to 15% deeper compared with as-received condition). In addition, removal efficiency is greater (by 6%) at low current density for small grained dual-phase conditions, than for predominantly single-phase, due to erosion complementing anodic dissolution. Mechanisms are discussed for these removal phenomena and used to inform industrial practice.

Electrolyte Multiplexing in Electrochemical Jet Processing

Electrolyte design for electrochemical jet processing (EJP) techniques can directly affect form and finish of machined structures.A newly developed, industrially focused, EJP machining centre was designed to incorporate complete control of all relevant machining parameters. A computer numerically controlled, electrolyte multiplexing system, was developed to allow rapid changes in electrolyte type and the ability to mix and fade between electrolytes to create roughing and finishing strategies, and functionally graded surfaces as part of the toolpath program. In this study, the use of three electrolytes (NaNO3, NaCl and a hybrid electrolyte NaI20) are used. Through dynamic electrolyte selection, applied in a sequential manner, it was demonstrated that a combination of NaCl / NaI20 achieved the best compromise of precision and performance, with an increase in depth of 10% over NaI and a 9% kerf reduction over NaCl. Surface finishes were demonstrated to be varied by 40% dependant on the sequence of electrolytes applied without effecting the form. It was shown that graduated surfaces can be created from a high lustre finish to matte by fading electrolyte types. For the first time, an automated method of electrolyte multiplexing is described and the flexibility and process enhancements that can be imparted by this methodology are demonstrated.

Specific and Programmable Surface Structuring by Electrochemical Jet Processing

Component surface optimisation through the application of surface structuring is understood to be beneficial to performance and longevity of a component in service. However, the multi-functional requirements of a surface defined at the design stage can be difficult to realise. Utilisation of electrochemical jet processing (EJP) methods in surface processing allows a wide-range of variation in surface structures over a multitude of length scales. Surface characteristics such as roughness and depth of cut can be controlled by selection of suitable process parameters. With an optimised control structure, it is possible to directly impart a design intent to a component to create a specific programmed surface.EJP-specific computer-aided manufacturing (CAM) software has been developed and is reported here. This is demonstrated to control processes parameter variation as a function of part local co-ordinates to allow complete CAD to CAM translation of surface design intent. In this way both meso- and micro-scale features can be specifically located on a surface. Alongside this, functionally graded surfaces are created in stainless steel by application of a mathematical functions allowing automated variation of current and feed rate to achieve the desired surface roughness distribution. Using a greyscale image as a process parameters map with current, therefore surface roughness, being proportional to grey tone value, practical application of the software is further demonstrated by direct translation of digitised imagery to surface replication. This functionality allows for fast creation of repeatable, programmed surfaces.

Precision enhanced electrochemical jet processing

Through electro-physical modification of the electrode gap in electrochemical jet techniques, precision has been shown to be greatly increased. Repeatable kerf widths approaching the diameter of the nozzle are demonstrated and the individual contributing effects are quantified across energy density and length scales. This allows the feature resolution achievable through electrochemical jet processing to be comparable to other surface structuring techniques, albeit with zero thermal loading of the surface. This is applied to demonstrate the machining of complex geometric features, not previously produced by electrolyte jet techniques.

Advancing electrochemical jet methods through manipulation of the angle of address

Electrochemical jet processing techniques have traditionally been considered to be limited to planar interactions with the electrolyte jet being maintained normal to the workpiece surface. In this study, the viability and resultant effects of articulating the nozzle relative to the work were investigated for the first time. Two machining conventions were defined, normal, where the jet is maintained perpendicular to the traverse direction, and push/pull, where the nozzle is rotated with respect to the direction of travel. It was found, with the normal convention that a range of differing resultant profile surface geometries could be created; unique to this process. This was demonstrated by the changing resultant side wall slopes found through the rotation of the head with up to 80% difference between the slopes of the cut walls. The adjacent wall to the nozzle slope decreasing as the jet angle approaches 90° whilst the opposite side wall slope increases. Predictable ratios of the differing slopes of the striation side walls were then able to be defined. The push/pull convention demonstrated that deeper, sharper cuts are possible due to the highly localising current density effect of nozzle inclination achieving a 35% increase in depth without requiring additional energy. Also, that resultant surface finish could be greatly improved, reducing the profile roughness (Ra) from 0.2 μm in the pull mode to 0.04 μm in the push mode achieving a mirror-like finish. The mechanics of these phenomena are investigated and defined. The influence of nozzle jet speed variation combined with inclining the jet was also studied. This was found to have no noticeable influence on the resultant profile when the nozzle is inclined. In contrast, when the nozzle is normal to the surface, jet velocity is seen to have a direct influence due to polarisation effects relating to the poor clearance of machining debris and the formation of oxides. It is shown that through variation of the angle of jet address an extra level of flexibility and performance is possible within electrochemical jet processes.

Transitory electrochemical masking for precision jet processing techniques

Electrochemical jet processing techniques provide an efficient method for large area surface structuring and micro-milling, where the metallurgy of the near-surface is assured and not adversely affected by thermal loading. Here, doped electrolytes are specifically developed for jet techniques to exploit the Gaussian energy distribution as found in energy beam processes. This allows up to 26% reduction in dissolution kerf and enhancements of the defined precision metric of up to 284% when compared to standard electrolytes. This is achieved through the filtering of low energy at discrete points within the energy distribution curve. Two fundamental mechanisms of current filtering and refresh rate are proposed and investigated in order to underpin the performance enhancements found using this methodology. This study aims to demonstrate that a step change in process fidelity and flexibility can be achieved through optimisation of the electrochemistry specific to jet processes.

Energy distribution modulation by mechanical design for electrochemical jet processing techniques

The increasing demand for optimised component surfaces with enhanced chemical and geometric complexity is a key driver in the manufacturing technology required for advanced surface production. Current methodologies cannot create complex surfaces in an efficient and scalable manner in robust engineering materials. Hence, there is a need for advanced manufacturing technologies which overcome this. Current technologies are limited by resolution, geometric flexibility and mode of energy delivery. By addressing the fundamental limitations of electrochemical jetting techniques through modulation of the current density distribution by mechanical design, significant improvements to the electrochemical jet process methods are presented. A simplified 2D stochastic model was developed with the ability to vary current density distribution to assess the effects of nozzle-tip shape changes. The simulation demonstrated that the resultant profile was found to be variable from that of a standard nozzle. These nozzle-tip modifications were then experimentally tested finding a high degree of variance was possible in the machined profile. Improvements such as an increase in side-wall steepness of 162% are achieved over a standard profile, flat bases to the cut profile and a reduction of profile to surface inter-section radius enable the process to be analogous to traditional milling profiles. Since electrode design can be rapidly modified EJP is shown to be a flexible process capable of varied and complex meso-scale profile creation. Innovations presented here in the modulation of resistance in-jet have enabled electrochemical jet processes to become a viable, top-down, single-step method for applying complex surfaces geometries unachievable by other means.