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Curved toolpaths challenge accurate electrochemical jet processing due to resulting distortion of the cut profile. A more elaborate path planning approach is required to mitigate these negative effects. A 3-dimensional process model is presented here, to predict the resulting surface geometry. This is applied to simulate machining of curved channels and calculate optimised feed rates for locations of the toolpath with impaired geometry. Through the presented predictive planning methodology, achieved depths of curved sections of the machined channels were within 10.5% of the depth for straight sections, compared to up to 62.2% increase when feed rate compensation was not applied.

Remarkable interfacial behaviors are observed in nature. Our efforts, directed toward replicating the structures, chemistries, and therefore functional properties of natural nonwetting surfaces, are competing with the result of billions of years of natural selection. The application of man-made surfaces is challenged by their poor longevity in aggressive environmental or applied service conditions. This study reports on a new approach for the creation of multiscale hierarchical surface patterns in metals, which exploits thermodynamic phenomena in advanced manufacturing processes. While hydrophobic coatings can be produced with relative ease by electrodeposition, these fractal-type structures tend to have poor structural integrity and hence are not durable. In this method, "seed surfaces" are directly written onto substrates by selective electrodeposition, after which they are irradiated by a large-area, pulsed electron beam to invoke a beading phenomenon, which is studied here. The length scale of these beads is shown to depend upon the melt time of the liquid metal. The created surfaces are shown to yield high water contact angles (145°) without subsequent chemical modification, and high adhesion properties reminiscent of the "rose petal" hydrophobic effect. The size and morphology and hence the hydrophobic effect of the surface beads generated are correlated with the thickness of the electrodeposited coating and hence the melt lifetime upon electron irradiation. This new rapid approach for tunable hydrophobic surface creation has applications for developing precision hydrophobic patterns and is insensitive to surface complexity.

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.

Electrochemical jet processing encompasses a group of non-contact and ‘tool-less’ technologies, relying on localised electrolyte jets to affect changes to the workpiece in a site-specific manner. This is achieved without thermally or mechanically modifying the underlying material giving rise to a unique class of manufacturing methods. Jet techniques have been applied to remove and deposit material selectively, for example to machine microscale pits and grooves, to process larger surface areas, and to selectively coat materials through a variety of accretion phenomena. The jet itself also has the potential to serve as analysis/metrology tool. The potential to unify a broad range of site-specific manufacturing methods under one platform presents a unique opportunity to enable bespoke programmable surface geometries, finishes and compositions, guided by design and independent of material precondition. This review seeks to enrich the literature by drawing together these interdisciplinary research avenues into a single extensive but critical literature survey, incorporating the process fundamentals and theory, recent developments, and applications of jet processing methods, including hybrid jet processes. Finally, this review attempts to provide new insight and propose the direction of future research with the view to enhancing the areas in which electrochemical jet processes can add value on the factory floor and become widely applied industrial practice. ispartof: International Journal Of Machine Tools & Manufacture vol:180 issue:September 2022 status: Published online

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.

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 (NaNO 3 , 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.

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.

Electrochemical jet machining (EJM) is a non-conventional machining process whereby material is removed by jet-based anodic dissolution phenomena. As a machining process, EJM is capable of selectively texturing conductive materials, however there are aspects of the technique that have been subject to only limited study. The effect of material precondition on the resulting surface texture is studied here for polycrystalline copper sheet (C101), and the influence of increasing grain size and plastic deformation on the resulting surfaces is explored. The resulting surface after EJM is shown to be fundamentally dependent on the material precondition, a factor which has been largely overlooked to date. It was found that increasing room-temperature rolling treatments led to surfaces with slightly smaller cubic pores across all current densities appraised. For prior-annealed large-grained materials, low porosity ordered surfaces can be achieved, and subsequent cold-rolling leads to the creation of band-type features after EJM. This results in discontinuous material removal and higher surface roughness at mean current densities between 100 – 300 A/cm2. Beyond 300 A/cm2, the effect of the cold-rolling treatment is overcome. In addition surface roughness after EJM for individual grains is shown to be intrinsically dependent on the grain orientation, supporting prior electrochemical research, although the contribution this makes may be attenuated by increasing current density.

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.

Additive manufacturing is an increasingly important counterpart to subtractive and constant volume manufacturing methods, however metal powder bed fusion methods often suffer from poor surface quality dominated by adhered unfused powder at the near-surface. Finishing steps are often required before part use in many applications, for example in aerospace components or biomedical implants, where ‘better than cast’ surfaces are sought. Here, we introduce electrochemical jet machining as a single-step process to i) selectively finish additively manufactured parts created by powder bed fusion, and ii) to subsequently micro-pattern these with the intention of increasing part functionality. Roughness of Ti-6Al-4V parts is shown to be reduced from an average Sq of 18.6 µm (as-built), to 2.4 µm upon rapid finishing, and the mechanisms of material removal are explored. Furthermore, repeating micro-dot patterns have been added to demonstrate the potential of the technique to allow tolerance superposition of additively manufactured parts.

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.

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.

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.