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Recently, mechanical micro-milling is one of the most promising micro-manufacturing processes for productive and accurate complex-feature generation in various materials including metals, ceramics, polymers and composites. The micro-milling technology is widely adapted already in many high-tech industrial sectors; however, its reliability and predictability require further developments. In this paper, micro-milling related recent results and developments are reviewed and discussed including micro-chip removal and micro-burr formation mechanisms, cutting forces, cutting temperature, vibrations, surface roughness, cutting fluids, workpiece materials, process monitoring, micro-tools and coatings, and process-modelling. Finally, possible future trends and research directions are highlighted in the micro-milling and micro-machining areas.

Metal additive manufacturing (MAM) has attracted significant interest in both academia and industry to produce near-net-shape engineering components. The inherent defects in MAM, however, require suitable subtractive techniques as post-processes to control dimensional and geometric tolerances as well as surface finish. The additively manufactured metals, with different microstructures than the wrought materials that produced by conventional routes, need different approaches and parameters when being machined. This review covers recent published literature on traditional micro-machining as a post-processing operation for MAM and recommends future directions. The text presents a brief review on the main AM processes followed by a comprehensive conventional micro-milling and microdrilling, as well as applications for micro-machining. Micro-tool assessment, built-up-edge prediction and prevention, and link of macro/micro-machining are areas for future research.

Aluminum Matrix Composite (AMC) represents an innovative class of materials that is extensively utilized in industries such as automotive, defense, aerospace, structural engineering, sports, and electronics. This study investigates the thrust force, exit burr formation, changes in the micro-tool, and drilled hole diameters during the micro-drilling of an aluminum-polyethylene composite panel (Al–PE). The panel consists of 3501 series aluminum skin materials bonded to a polyethylene (PE) core. Micro-drilling test parameters were designed using Taguchi’s L16 (42 23) orthogonal array. Tests were conducted with five control parameters: cutting speed with four levels (10 m/min, 20 m/min, 30 m/min, 40 m/min), feed rate with four levels (0.5 µm/rev, 1 µm/rev, 2 µm/rev, 4 µm/rev), the tool diameter with two levels (0.7 mm, 1 mm), and tool point angle with two levels (100°, 140°) using both AlTiN-coated and uncoated drills. The maximum thrust force (Fz), maximum burr height, and changes in both the drill tool and hole diameters were measured for analysis of variance (ANOVA). The results showed that, in terms of impact on Fz, tool point angle had the highest positive influence (64.54%) on the micro-drill at the entrance of composite (upper aluminum plate). The cutting speed had the highest positive influence (45.32%) on the tool in the core layer (PE core layer). The tool point angle also had the highest positive influence (68.95%) on the micro-drill at the lower layer of the composite (the lower aluminum plate). There was noticeable chip adhesion on the major cutting edge and nose area under micro-drilling conditions with higher thrust forces and burr height. The AlTiN coating had a positive effect on tool wear and hole diameter deviations, but it adversely affected the burr height.

Copaiba vegetable oil, extracted from the Amazonian Copaiba tree, shows potential as a cutting fluid in micromachining operations due to its mechanical properties. However, limited literature exists on vegetable oils in micromilling, particularly for AISI H13 tool steel. This study uniquely investigates the machinability of AISI H13 in micromilling using pure Copaiba vegetable oil applied via minimum quantity lubrication (MQL). The influence of feed rate (2 µm/tooth, 4 µm/tooth, and 6 µm/tooth) on microtool wear, surface roughness, and burr size was evaluated. Notably, this research introduces the analysis of both the amplitude roughness parameter Ra and the hybrid roughness parameter Rdq, providing a more comprehensive surface characterization. Additionally, measurement uncertainty calculations for these roughness parameters were conducted, a novel approach in micromilling studies of AISI H13. The findings revealed that adhesion or attrition were the primary wear mechanisms. Interestingly, feed rate showed no significant impact on Ra, which consistently decreased with machining length. In contrast, at higher feed rates, Rdq increased with machining length, aligning with surface observations. Experiments at 6 µm/tooth feed rate resulted in minimal burr formation, with burr areas reduced by 83% and 73% on down-milling and up-milling sides, respectively, compared to 2 µm/tooth. This study provides valuable insights into the application of Copaiba oil in micromilling AISI H13, contributing to sustainable manufacturing practices and enhancing understanding of surface integrity in micromachining processes.

Quartz glass has been widely used in multiple frontier fields of science and technology owing to its excellent chemical and mechanical properties, such as optical communication, semiconductor, photovoltaic power, and aerospace. ECDM (electrochemical discharge machining) is a non-traditional material removal process suitable for machining non-conductive materials of high hardness and brittleness. The tool electrode feed method is a key factor affecting the ECDM process. Experimental research was carried out for comparing the conventional gravity feed method and a newly-developed spring-force feed method. Micro tool electrodes of Φ150 µm were fabricated by combining the method of TF-WEDG (tangential feed-wire electrical discharge grinding) and reverse micro EDM (electrical discharge machining). Machined microstructures of blind holes, channels, squares, and patterns were compared by the gravity feed method and the spring-force feed method respectively. The experimental results show that the spring-force feed method can improve the micro ECDM process considering the aspects of dimensional accuracy, overcuts, deteriorated edges, surface topography, and tool wear.

At present, the production of micro parts and components with characteristic sizes ranging from micron to millimeter mainly relies on micro machining technology, but the dimensional size of micro tools (including micro cutting tools, micro grinding tools, and microelectrodes) involved in micro machining is ultra small and made of super hard material like cemented carbide and polycrystalline diamond, which makes the preparation of ultra small micro tools have become the main bottleneck restricting the development of micro machining technology. The non-contact nature of electrical discharge machining (EDM) process makes it more competent in fabricating micro tools with relatively high efficiency and low cost; especially the wire electrical discharge grinding (WEDG) invented in 1985 provides a new approach and direction to fabricate micro tools; following this trend, numerous new design requirements and theoretical concepts of EDM-based processes utilized in fabricating micro tools have been proposed and studied successively, but, very few studies have been proceed from an integrated perspective. To address the gap, this study provides a comprehensive and well-arranged literature survey of the advancements made in the fabrication of micro tools using various EDM-based methods to date along with an insightful discussion on the science and application of EDM process. The critical factors influencing process performance, different numerical models, limitations, as well as possible future research direction and development in the field of micro tools fabricated by various EDM-based methods are identified and reviewed. This article is expected to help the researchers in identifying the existing gaps and contributing towards making EDM-based processes more competent in catering the trend of parameterized and non-standardized fabrication of ultra small micro tools.

An experimental investigation was performed using a tungsten carbide tool to study the micro-electrical discharge machining behavior of two different grades of stainless steel (310 and 316 SS). The machining parameters considered to investigate the machining behavior of the chosen materials were (a) V: voltage (V), (b) C: capacitance (pf), (c) T on : pulse-on time (µs), and (d) T off : pulse-off time (µs). The machining behavior of stainless steel was evaluated in terms of material removal rate and tool wear rate. Taguchi L 16 orthogonal array and gray relational analysis techniques were employed to design and optimize the machining conditions for both responses. Scanning electron microscopy, energy-dispersive spectroscopy, and optical microscopic analyses were also performed to identify the characteristics of the machined surface, characteristics of the micro-tool, and the elemental composition of the machined surface. The optimum machining condition for 310 steel was found as 150 V, 100 pf, 30 µs ( T on ), and 20 µs ( T off ). On the other hand, the optimum parametric condition for 316 steel was 200 V, 1000 pf, 20 µs ( T on ), and 25 µs ( T off ).

Electrochemical discharge machining (ECDM) is a versatile machining process due to its applicability to machine different materials regardless to their properties. In this work, machining behaviour of silicon wafer using ECDM is presented. An attempt has been made to drill micro holes on silicon wafer considering applied voltage and tool feed rate as input process parameters. The overcut and hole taper were observed as output quality characteristics. The experimental results revealed that overcut and hole taper increase with increase in voltage and decreases with increase in tool feed rate. The characterization of micro holes has been carried out using scanning electron microscopy and revealed the presence of small debris, overcut and heat affected zone on machined surface. Overall, it was observed that micro hole machined at conditions i.e. applied voltage 60 V, tool feed rate 250 μm/min results in minimum overcut and hole taper. The axial, lateral and flank erosion was observed on the micro tool used for machining of silicon wafer.

Anti-abrasion thin-film-coated tool is well known for its enhanced micro machining performances. However, coating increases tool edge radius, which spurs additional ploughing and rubbing. Therefore, selecting appropriate thin-film thickness and suitable abrasion-resistant coating material for micro tool is necessary to reduce friction and size effects together. To meet these objectives, first, single-layer TiAlN coating having various thin-film thicknesses has been deposited on uncoated micro end mills by PVD process. By analyzing the cutting force, surface quality and edge radius of both fresh and worn tools in micro milling of P-20 steel, appropriate thin-film thickness has been found to be ≈ 1 μm. Next, single layer TiN and diamond-like-carbon (DLC) coating of thickness ≈ 1 μm have been coated on uncoated WC tools. Then coefficient of friction (COF) and hardness of all coated and uncoated surfaces are assessed. Finally, the performance of all the coated and uncoated tools have been evaluated analytically and experimentally by analyzing dynamic stability and machinability, respectively. All the coated tools manifested enhancement in performance by uplifting stability limit and reducing tool wear, cutting forces, surface roughness and burr heights compared to the uncoated tool. Owing to the least COF, the DLC-coated tool exhibited the best performance by uplifting stability limit by 23.37% and reducing cutting force, surface roughness and burr height by 27.35%, 67.7%, and 30.58%, respectively. However, for a long machining length (1200 mm), the DLC-coated tool could not exhibit such performance as compared to TiAlN-coated tool due to significant delamination.

These days, miniaturized products have a lot of applications in biotechnology, information technology, environmental and medical industries, electric devices, miniaturized machines, and so on. Micro-electrical discharge machining (micro-EDM) is one the most efficient technologies among the nonconventional machining technologies for producing micro-components. Micro-EDM is able to machine tough die materials which cannot be machined by micro-milling. The micro-EDM method has the capability to machine electrical conductive materials with various hardness, strength, and temperature-resistant and complex shapes with accurate dimensions and fine surface roughness. Moreover, it is widely used to produce micro-scale components and structures such as micro-mold, micro-die, micro-probes, micro-tools, fuel nozzles, photo-masks, thin sheet materials, and complex 3D shapes with high accuracy. This paper presents a state-of-the-art review of micro-EDM process as well as the various kinds of micro-electrode and workpiece materials and dielectrics that have been used by previous researchers. In addition, this paper extensively describes and compares various micro-electrode and micro-tool fabrication processes in order to produce precise micro-products. This work is very helpful for the micro-EDM manufacturers and users to select suitable material, dielectric and fabrication processes in researches, and industry applications.