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In the current scenario, micro-manufacturing through the electro-discharge machining (EDM) process is a prominent technique for achieving desired complex micro/nano-features of any product. The precision and accuracy of producing features are the prerequisites of micro-machining. The current work aims to check the feasibility of the novel Maglev EDM for fabricating micro-holes on a thin nickel sheet (thickness = 500 μm). The study presents the viability of the newly developed system by comparing it with the conventional EDM process. A pure direct current power supply is assembled with a magnetic levitation-based gap monitoring mechanism to overcome the setbacks of conventional EDM. The novel setup utilizes the combined effect of the permanent electromagnet to diminish arcing and short-circuiting. The control parameters for the operation were 12 V open-circuit voltage and 2 A peak current while maintaining a duty factor of 95.564 percent. The measured discharge voltage and discharge current were 6.64 V and 900 mA, respectively. Tungsten rod (ø 650 μm) and deionized water were used as a tool and a dielectric medium, respectively, for the experiment. Further, the machined micro-hole and micro-tool analysis have been carried out using high-resolution microscopy, scanning electron microscopy and energy dispersive spectroscopy reports. The newly developed Maglev EDM’s feasibility to produce micro-holes on conductive materials has been confirmed in the present work with an average material removal rate of 40 μg/min.

The direct injection of coolants and lubricants in the drilling process lowers heat generation in the cutting zone; however, in the absence of a mechanism for positive heat dissipation, the heat from the cutting zone gets continuously accumulated. In this work, we propose novel applications of the following cooling techniques: (i) Ti-Cu as butt joint and (ii) heat sink bottom-channel cooling to improve heat dissipation. The higher thermal conductivity of copper in the Ti-Cu scheme and the flow of coolant in the heat sink in the bottom channel carry away the intense heat generated during drilling. Experiments were also performed using the cooling techniques to monitor thrust, torque, and temperature using an infrared (IR) camera. A numerical model of heat dissipation shows that temperature is reduced by 30% and 38% in heat sink-based cooling and Ti–Cu combinations, respectively, in comparison to dry drilling. The numerical temperature lies within ~1%–6% of the experimental values.

Selective laser melting (SLM) of titanium–aluminium (TiAl) alloy components has gained significant attention in the modern industrial world. The flexibility of the SLM process in producing complex shapes with minimum utilization of material and energy makes it dominant over other manufacturing techniques. As aerospace and biomedical industries demand complex-shaped TiAl alloy components, part fabrication using SLM becomes the ultimate solution. However, the unacceptable level of surface integrity and anisotropic behavior of SLM components demand post processing operations such as laser polishing, chemical polishing, and conventional polishing methods. In this study, a recently developed polishing method called wire electrical discharge polishing (WEDP) is performed on TiAl alloys for obtaining a smooth and defect-free surface. This study aims to investigate the micro-layer modification occurring to the WEDP-processed surface in detail. The experimental results establish the effectiveness of WEDP method in terms of improved surface integrity. The surface finish (Sa) got enhanced by ~88% after WEDP processing. In addition, the thickness of recast layer formed by WEDP was found to be minimum. Moreover, post-processing of TiAl alloy resulted in better surface morphology specifically at lower settings of peak current. It is noteworthy that the migration of wire material was minimum with zinc-coated brass electrode compared to the normal brass electrode. Hence, coated wire electrodes are recommended for WEDP process. In short, an excellent surface integrity can be achieved using WEDP process through favorable surface modification aided by lower peak current and coated wire electrodes. Furthermore, less electrode wear observed in WEDP process enables the deployment of lower feed rates leading to minimal electrode consumption.

Nickel-based alloys (Nimonic 90) are one of the most used materials for aircraft parts, gas turbine components and fasteners due to their inherent properties such as high strength at elevated temperature, good corrosion resistance, high stability, high wear resistance and low thermal conductivity. Because of the above-mentioned properties, Nimonic 90 alloy is difficult to machine, and the roughness obtained by machining of nimonic alloy is comparatively rough. The existing theoretically developed mathematical equations for roughness measurement do not consist of all the machining parameters. It lacks some of the effective roughness parameters such as depth of cut, spindle speed and cutting-edge angle. This article proposes a novel mathematical/geometrical model for the prediction of surface roughness using fundamental geometrical properties of tool and workpiece. For developing the mathematical model, the nose radius of the cutting tool insert is assumed as a straight line (arc length). The principal cutting-edge angle is introduced in the geometrically developed novel model. The developed mathematical/geometrical model comprises mainly depth of cut, principal cutting-edge angle, nose radius, spindle speed and feed. In micro turning, surface roughness increases with an increase in feed and depth of cut. A rough surface, compared to conventional turning, is produced while micro turning due to edge ploughing and rubbing when the chip thickness is lesser than the edge radius. This model is validated by conducting micro-turning experiments on nickel-based superalloy (Nimonic 90) using aluminium titanium nitride physical vapour deposition coated tungsten carbide micro inserts. The surface roughness is significantly affected when the cutting-edge comes in contact with the workpiece; it is because of the imperfect geometry of the nose of the cutting tool. A slight variation of surface roughness with the depth of cut has also been observed. A good correlation is observed between the predicted and experimentally measured roughness values.

This work demonstrates the maximum spreading behavior of water droplets on prepared surfaces: superhydrophilic (etched), hydrophilic (inherent nature), hydrophobic (treated with hexadecyltrimethoxysilane (HDTMS), and superhydrophobic (etched and HDTMS treated). Here, a simple chemical etching and immersion approach were used to modify the surfaces. Altering one surface property to the next shows a significant variation in the wetting behavior. The change in the wettability of the aluminium surface depends on its surface roughness and surface chemistry. The wettability of the fabricated surfaces was determined via water contact angle (WCA) measurement using a goniometer. A field emission scanning electron microscope (FESEM) and a 3-D optical non-contact profilometer were used to analyze the surface morphology and surface roughness of all manufactured surfaces, respectively. Additional features such as the droplet dynamics property of all surfaces were studied in detail. Finally, the experimental results for the maximum spreading factor were compared to the existing model.

Drawing velocity is essential in the manufacturing of the multi-facet bulk metallic glass (BMG) knife edges used in corneal surgery since it is one of the factors that can determine good blade profiles in the thermoplastic forming process. The goal of this article is to determine and regulate drawing velocity based on the viscoelastic filament stretching and knowledge of the thermoplastic forming map of BMG. The generation of drawing velocity profile is done in two stages: the initial transient stage before the extensional viscosity stage is fully developed, and the extensional viscosity stage. The controller based on the system identification of the testbed is then optimized from the requirements of the drawing velocity and its implementation feasibility. The control objectives of regulation performance and robustness to modeling uncertainties are posed and solved in an optimal control (H∞) framework. The proposed controller shows an improvement over other controllers including proportional-integral-derivative controllers in terms of robustness to uncertainties and tracking performance. BMG samples processed from this study result in good quality with improvement of 20% and 54% in X–Y (2.2±0.1µm) and X–Z (1.3±0.1µm) straightness and 25% more consistent edge radii (46±3nm).

In this work, a nanosecond green laser (532 nm) is used to generate narrow openings by removing an ultra-thin (85 nm) SiNxlayer that is coated on a silicon substrate for application in the fabrication of Passivated Emitter and Rear Contact (PERC) solar cells. An experimental analysis is presented to identify the optimal range of laser parameters for an efficient ablation with minimal damage to the silicon substrate. The ablated samples were characterized using a 3D profilometer to obtain the surface profiles and scanning electron microscope imaging to observe the surface quality. Further, energy-dispersive X-ray line analysis and atom probe tomography were performed to evaluate the nitrogen content on the surface and along the depth, respectively. The experimental results suggest that the SiNxlayer starts to ablate only above a threshold laser fluence of 1.4 J/cm2, while the surface bulged out for laser fluence slightly below the ablation threshold. The central part of the ablated region was clean with a negligible nitrogen concentration at the surface, about ∼0.03% at a fluence of 2.4 J/cm2. Nitrogen concentration reduces continuously and almost becomes zero at 80 nm depth, suggesting complete ablation of the SiNxlayer for establishing electrical contacts. The ablation width was close to the laser spot diameter only at lower values of the laser fluence. The lowest value of ablation depth was about 180 nm, suggesting that only about 95 nm layer of the silicon is ablated. The study demonstrates that nanosecond laser ablation is a potential technique for ablation of the SiNxlayer of PERC solar cells but requires choosing the optimal parameters.

Restoration of high-value components via additive manufacturing requires autonomous surface scanning and defect identification. The 3D free-form surface can be reconstructed with a point cloud obtained from the scanning. Laser line triangulation-based surface scanning is a promising method for generating a 3D point cloud of the component surface. In this article, a robotic defect scanning system developed using py_openshowvar, an open-source cross-platform communication interface is presented. For effective scanning of micro-scale features with minimal noise, it is crucial to optimize the scanning parameters. The scanner parameters such as exposure time and stand-off distance have been optimized for accurate feature detection. After selecting optimal scanning parameters, a generic algorithm is presented for generating a scanning path for automatic scanning of the 3D parts. Surfaces with pre-fabricated micro-defects are automatically scanned using this algorithm, and an integrated image-processing-based defect identification technique is presented. The geometries obtained from the presented technique were validated using focus variation microscopy, and the results are in good agreement with actual defect geometry, and the measurement error is below 9%.

Compared to the traditional machining and finishing process, a hybrid technique consisting of mechanical micro-milling and electropolishing is advantageous in maintaining dimensional accuracy and fine surface quality without compromising the form. This is a cost-effective, less tedious technique that can fabricate high-quality masters for microfluidic devices. P20-die steel masters are fabricated to evaluate the method with this technique. The dimensional accuracy and surface quality of the masters are studied. It is found that the peak-to-valley surface roughness (Rt) of the masters is reduced by 50%. These die steel masters are then used to make polydimethylsiloxane (PDMS)-based microfluidic devices that could be used for particle separation. As biofouling and bacterial growth are undesirable in most of the microfluidic devices, the fabricated PDMS devices are tested for bacterial growth and adhesion. The growth of DH5α Escherichia colibacteria in the devices fabricated using the electropolished masters is evaluated. Bacterial growth and adhesion are monitored for 0, 4 and 12 h, and it is found that the growth and adhesion in these devices are reduced by 15–20% and 40–50%, respectively, compared to the devices produced using non-electropolished masters. Enumeration of the bacterial cells in the samples flown is carried out by evaluating the optical density of the sample fluids by UV-visible spectroscopy and quantifying the bacterial cells using the McFarland 0.5 standard.

Cutting force for conventional orthogonal machining can be predicted by Merchant’s Circle Diagram (MCD) considering the shearing action of chip formation. However, the effect of plowing action is significant for micro turning, which has not been considered in MCD. Therefore, a large error has been observed in the prediction of cutting force in micro turning by MCD theory. In this study, a compensated model has been developed for orthogonal micro turning based on MCD. The theory has taken shearing and plowing actions into consideration. The compensated model involved material flow stress, cutting parameters, and tool geometry, including cutting edge radius. This model has predicted tangential cutting force with an average prediction error of 3.75% for micro turning of Ti6Al4V, whereas the average prediction error was 14.9% for axial cutting force.

In this article, an analytical study of the effect of the shape and size of the mask on the machining quality of complex shapes has been carried out. For this study, we considered square and circular masks of varying sizes with varying overlap for the machining of square, inclined, and circular features. Mask size varied from 1 to 20 mm, while overlap varied from 10% to 90%. The machining quality of the aforementioned features was evaluated by studying the unmachined area “An” (in the machining zone) and the machining time “Tm.” For machining a similar feature, it was observed that the square mask performed much better than the circular mask in minimizing the machining time. However, the circular mask is much more suitable for minimizing the unmachined area. For validation, the experiment was conducted to machine the inclined lines with square and circular shape masks with varying overlap percentages. The experimental results were found to be in good agreement with the analytically obtained results, with an error of 2.5%. This study is relevant for the industrial-scale manufacturing of complicated features using the mask projection approach in laser machining.

There is a growing interest in developing the dry electrical discharge machining (EDM) process as a sustainable alternative to the conventional liquid dielectric-based EDM process. It is shown that the dry EDM process possesses advantages over the conventional process in terms of thermal damage, recast layer, and tool wear. However, there is a need to increase the productivity of the dry EDM process for its successful adaptation in the industry. This paper presents a dry EDM plasma discharge model with air as the dielectric medium. The model uses global modeling (0D) approach in which equations of mass balance, energy balance, and plasma expansion are solved simultaneously to obtain a time-dependent description of the plasma in terms of its composition, temperature, diameter, and heat flux to electrodes. The model includes reaction kinetics involving 622 reactions and 55 species to determine the air plasma composition. A single discharge dry EDM operation is successfully simulated using the model, and the effects of the interelectrode gap and discharge current on the plasma are studied. An increase in the interelectrode gap decreases the average electron density, plasma temperature, and heat flux. On the other hand, an increase in the discharge current increases the electron density, temperature, and diameter of the plasma linearly, while heat flux to the workpiece increases exponentially. Overall, the model provides an essential tool to study the dry EDM process mechanisms at a fundamental level and devise methods for process improvements.

In electrodischarge machining (EDM), the thermal energy causing material removal at the electrodes is given by the electrical energy supplied to the discharge. This electrical energy, also known as the discharge energy, can be obtained from time-transient voltage and current waveforms across the electrodes during a discharge. However, in micro-EDM, the interelectrode gaps are shorter causing the plasma resistance to be significantly smaller than other impedances in the circuit. As a result, the voltage and current waveforms obtained by a direct measurement may include voltage drop across the stray impedances in the circuit and may not accurately represent the exact voltage drop across micro-EDM plasma alone. Therefore, a model-based approach is presented in this paper to predict time-transient electrical characteristics of a micro-EDM discharge, such as plasma resistance, voltage, current, and discharge energy. A global modeling approach is employed to solve equations of mass and energy conservations, dynamics of the plasma growth, and the plasma current equation for obtaining a complete temporal description of the plasma during the discharge duration. The model is validated against single-discharge micro-EDM experiments and then used to study the effect of applied open gap voltage and interelectrode gap distance on the plasma resistance, voltage, current, and discharge energy. For open gap voltage in the range of 100–300 V and gap distance in the range of 0.5–6 μm, the model predicts the use of a higher open gap voltage and a higher gap distance to achieve a higher discharge energy.