Towards Sustainable Precision: A Review of Water Jet Meso and Micromachining

Review article Towards sustainable precision: A review of water jet meso and micromachining Mohammad Ghasemian Fard a , Akash Nag a,* , Jana Petrů a , Sergej Hloch a a Faculty of Mechanical Engineering, VSB—Technical University of Ostrava, Poruba, Ostrava 708 00, Czech Republic ARTICLE INFO Keywords: Micro-manufacturing Micro-machining Abrasive water jet Water jet Suspension jet Non-thermal disintegration ABSTRACT Micro-Abrasive Water Jet Machining (µAWJM) has become a critical technology for precision micromanufacturing, addressing the limitations of both conventional and other unconventional machining methods. Its significance lies in its ability to process complex geometries in a vast range of materials—including thermally sensitive polymers, brittle advanced ceramics, composites, superalloys, and thin-film structures—without inducing damage. As a non-thermal disintegration process, µAWJM holds a distinct advantage over methods like laser cutting and EDM by creating minimal heat-affected zones, thereby preventing the material degradation, warping, and residual stresses that often necessitate costly post-processing. This review provides a comprehensive analysis of µAWJM’s fundamental principles, including fluid dynamics, abrasive particle behavior, and material removal mechanisms. It examines the intricate interplay of key process parameters such as abrasive particle size (MESH), nozzle geometry, fluid pressure, and standoff distance, and how these parameters influence machining performance and surface integrity. Recent technological advancements, including optimized abrasive delivery systems and the integration of machine learning for process optimization, are critically evaluated. This review not only highlights the inherent advantages of µAWJM but also addresses current challenges such as kerf taper, nozzle wear, and the efficient machining of novel materials. Furthermore, it delves into the diverse applications of µAWJM across microfluidics, biomedical engineering, aerospace, and electronics, showcasing its versatility in fabricating complex microstructures. Finally, this review outlines future research directions, ultimately solidifying µAWJM’s crucial role in the future of sustainable and precise manufacturing. 1. Introduction In the Anthropocene epoch, the advancement of sophisticated materials possessing customized mechanical attributes, facilitated by intricate chemistry and the principles of quantum mechanics, has surpassed the capabilities of conventional machining techniques. These materials frequently require precision that exceeds the limits of traditional tools, particularly at micro-scale dimensions where the preservation of surface integrity and the minimization of material alteration are of paramount importance. Specifically, machining composite materials with conventional cutting edge processes is challenging due to common defects such as surface damage, delamination, fibre pull-outs, and rapid tool wear. The distinct hard fiber and soft matrix phases within composites induce varying pressure on the cutting tool, leading to uncontrolled wear rates and potential internal failures that degrade the material’s strength [1]. These machining-induced damages are a significant issue; for example, it has been reported that as many as 60% of composite products in the aircraft industry are rejected due to such defects [2]. Furthermore, there is a growing trend to develop more environmentally friendly composites [3] by utilizing natural fibers (e.g., hemp, basalt) and bio-fillers (e.g., palm and coconut shell powder) [2,4, 5]. Although laser [6] and electro-discharge machining [7] techniques provide a degree of precision, their thermal effects impose restrictions on their use, particularly concerning materials sensitive to heat. For instance, laser cutting often results in a significant heat-affected zone (HAZ), which can alter the microstructure and mechanical properties of the workpiece. This is a considerable drawback when machining materials like Nitinol, where temperature-induced phase transformations can compromise its unique shape memory and superelastic properties. Similarly, while Wire Electrical Discharge Machining (WEDM) [8] is effective for conductive materials, it is unsuitable for non-conductive ceramics and composites, and the recast layer formed during the process can negatively impact the surface integrity of the machined part. Micro-abrasive water jet ( μ AWJ) technology emerges as a sustainable and adaptable alternative, effectively addressing these challenges * Corresponding author. E-mail address: [email protected] (A. Nag). Contents lists available at ScienceDirect Results in Engineering journal homepage: www.sciencedirect.com/journal/results-in-engineering https://doi.org/10.1016/j.rineng.2025.106447 Received 15 June 2025; Received in revised form 18 July 2025; Accepted 23 July 2025 Results in Engineering 27 (2025) 106447 Available online 24 July 2025 2590-1230/© 2025 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/bync-nd/4.0/ ). by enabling the precise disintegration of materials without introducing thermal effects or significant mechanical stress. The advancement to finer 0.2 mm nozzles utilizing MESH 200 abrasives has substantially augmented the capabilities of μ AWJ, facilitating intricate machining across a wide array of materials. This level of precision is important in sectors such as electronics, healthcare, and aerospace, where increased quality standards and the minimization of waste are crucial. Importantly, the potential for μ AWJ to incorporate natural-based abrasives and fluids, coupled with its generation of minimal waste and reduced energy consumption relative to traditional methodologies, resonates with the increasing demands for sustainability. The capability of this technology to generate intricate cuts with negligible kerf loss and without the necessity for extensive secondary finishing not only enhances operational efficiency and reduces costs but also mitigates environmental repercussions. The utilization of μ AWJ is experiencing rapid growth as industries increasingly prioritize environmentally sustainable manufacturing practices alongside high levels of precision. This review endeavors to deliver a thorough examination of μ AWJ technology, emphasizing its sustainable benefits, varied applications, and recent developments, with particular attention to the potential incorporation of natural-based tools and fluids. Moreover, we investigate the prospects of automation and artificial intelligence in augmenting the efficiency and sustainability of μ AWJ, alongside innovations in nozzle design and material compatibility that could further extend its ecofriendly applications within the realm of precision manufacturing. The transformation of “conventional” water jet cutting set up, from its early stages to modern precision techniques, has revolutionized numerous industries. This development has expanded the range of processable materials and enhanced cutting accuracy, leading to substantial advancements in sectors listed in Table 1. It enables the production of previously unachievable intricate designs; these technologies have significantly boosted productivity and efficiency. Although machining with jets is a relatively new technology, studies on jet cutting and practical applications have a long history. A microabrasive jet with a small, low-pressure exhaust nozzle was presented to impact the surface of the workpiece to solve the difficult problem of non-spherical shape and polishing of optical parts whose diameter is less than 80 mm [16,17]. It was named fluid jet polishing (FJP) technology, and now it is known as micro abrasive jet polishing (MAJP). As an evolution of abrasive water jet machining, micro-abrasive slurry jet machining (MASJM) is developed based on abrasive slurry jet machining. This is a novel technology for machining with high accuracy that combines fluid mechanics and surface technology into one. In contrast to the conventional abrasive water jet method, Micro Abrasive Jet merges fine abrasive materials with different additive suspensions and water to create a paste based on a pre-determined formula. This slurry is then pumped through a narrow orifice, resulting in a more cohesive and impactful non-Newtonian fluid. Then pump the slurry through a fine orifice come into a more cohesive and a stronger impact non-newton fluid [18–20]. AWJM technology and its micro abrasive variants were developed in response to the need for precision cutting technologies that could process complicated and hard-to-machine materials without causing thermal damage. conventional machining methods often had difficulties with materials like composites, ceramics, and superalloys because of their brittleness, hardness characteristics, or sensitivity to heat. Plus, industries such as aerospace, electronics, and medical devices demanded smaller, more complex components, therefore, micro abrasive water jet machining (AWJMM) was expanded to provide high-quality, damage-free cutting solutions. This review focuses on evaluating the improvements and challenges of AWJM methods across different applications, particularly highlighting micro abrasive cutting technologies for hard-to-cut materials. By analyzing machining performance, material compatibility, and process optimization List of symbols and abbreviations α Jet impact angle, (◦) βJet inclination angle (used in velocity studies), (◦) aAbrasive material density, (kg⋅m⁻³) d a Abrasive particle diameter, (mm) d f Focusing tube diameter, (mm) d j Jet diameter, (mm) d o Orifice diameter, (mm) E k Kinetic energy, (J) hCutting depth, (mm) l f Focusing tube length, (mm) m a Abrasive mass flow rate, (g⋅min⁻¹) pWater jet pressure, (MPa) rJet curvature radius, (mm) vTraverse speed, (mm⋅min⁻¹) v a Abrasive particle velocity, (m⋅s⁻¹) v p Nozzle traverse speed, (m⋅s⁻¹) zStandoff distance, (mm) Ra Surface roughness average, (µm) MRR Material removal rate, (mm³⋅min⁻¹) WJ - Water Jet AWJ - Abrasive Water Jet μ AWJ - Micro Abrasive Water Jet μ AWJM - Micro Abrasive Water Jet Machining ASJ - Abrasive Suspension Jet μ ASJ - Micro Abrasive Suspension Jet HASJM - Hybrid Abrasive Slurry Jet Machining AJ - Abrasive Jet MAJP - Micro Abrasive Jet Polishing MASJM - Micro Abrasive Slurry Jet Machining AAJ - Abrasive Air Jet WEDM - Wire Electrical Discharge Machining EDM - Electrical Discharge Machining FIB - Focused Ion Beam CNC - Computer Numerical Control MCDM - Multi-Criteria Decision Making HAZ - Heat-Affected Zone MEMS - Micro-Electro-Mechanical Systems MESH - Abrasive grain size classification (e.g., MESH 220) LPS-SiC - Liquid Phase Sintered Silicon Carbide GRA - Grey Relational Analysis Table1 Practical applications of water jet and abrasive water jet. Industry Key Applications Citation Aerospace Machining turbine blades, engine components, and composite structures (Liu, 2024) (Llanto et al., 2021) (M. El-Hofy et al., 2018), [9–11] Automotive Machining engine components and gear parts (H. Wang et al., 2023), [12] Biomedical Machining custom implants, prosthetics, and medical devices (H. Wang et al., 2023), [12] Electronics Machining small features and micro-channels in electronic components (M. Annoni et al., 2017), [13] Construction and Stone Cutting and shaping stone, glass, and ceramic tiles (K. Gupta et al., 2024), [14] surgery precision machining of hard tissues like bone, tissue-selective separation (Xiao-Fei Song rt al., 2023), [15] M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 2 strategies, this investigation explores exactly how AWJM has evolved to meet the precision and sustainability demands of modern industries. Micro-abrasive techniques represent pivotal tools within precision manufacturing, enabling the controlled finishing of components with minimized material removal and enhanced surface integrity. Achievable surface roughness (Ra) values ranging from 1 to 0.1 micrometers render these methodologies critical in sectors demanding high precision, such as aerospace, medical device fabrication, and electronics, where optimal functionality and performance are paramount. Geometrical tolerances of components produced via micro-abrasive processes can be maintained within stringent limits, ensuring compliance with rigorous specifications and operational requirements, even for complex designs. The precision attained is directly influenced by process parameters, including abrasive particle size, feed rate, and applied pressure, necessitating precise control to achieve optimal results. 2. Basic principles of micro abrasive water jet cutting The micro AWJ process involves the use of a high-pressure water jet mixed with abrasive particles, which are accelerated through a nozzle to form a coherent water jet stream. This jet stream, with velocities exceeding 800 m/s, is directed at the workpiece to remove material through erosion [21,22]. The process is characterized by its ability to machine hard-to-cut materials, such as composites, ceramics, and glass, without inducing thermal damage or mechanical stress[23,24]. The key components of a micro AWJ system include a high-pressure pump, an abrasive feeder, a mixing chamber, and a nozzle. The pump generates the high-pressure water jet, which is then mixed with abrasive particles in the mixing chamber. The nozzle focuses the jet stream to achieve the desired cutting precision [25,21]. Abrasive Water Jet (AWJ) is a cold-cutting technology used to cut disintegrate any virtual material [26]. Usually, this technology is being used for disintegration of materials with special mechanical properties and materials that are difficult to cut [27]. The transfer of momentum between water and abrasives creates a highly focused and pressurized high-velocity jet stream that cuts and removes material through erosion [28]. Therefore, microchips are formed on the workpiece material due to the small mass of the abrasive particles. Fig. 1 shows a schematic representation of an abrasive water jet-cutting machine with an entire management system. The (AWJ) is a cylindrical tool made up of dynamically changing components specifically water, abrasive material, and air that collectively provide the kinetic energy necessary for disintegration of a workpiece. Jet shape and energy profile are both influenced by several conditions. There are many factors that affect abrasive water jet’s (AWJ) diameter including water pressure, orifice diameter, focusing tube shape, abrasive type, abrasive mass flow rate, and the distance between the focusing tube exit and the target material surface. Immediately after exiting the focusing tube, a short segment of the AWJ remains continuous. However, due to various ambient effects like air resistance and abrasive pull-down, it quickly begins to lose energy and change shape. To ensure maximum energy transfer when cutting materials, low standoffs (approximately 1-3 mm) are typically used with both water jets and AWJs. Once the AWJ impinges on the material surface, the material removal mechanism begins. With increasing depth, it loses kinetic energy and changes its shape. This transformation is influenced by the jet speed, traverse direction, cutting geometry, and type and thickness of the material being cut. Fig. 2 shows the trajectory development of the water jet and its diversion. At each point of the material, the water jet follows the curved trajectory whose diameter changes in relation to the length of the previously cut curve[29]. According to Hashish [31], the abrasive waterjet (AWJ) cutting process creates on surface erosion zones: the smooth erosion zone, the transition erosion zone, and the rough erosion zone. An initial zone [32], observed later, prior to the smooth zone, especially during piercing or very shallow cutting [33]. The smooth erosion zone (often referred to as the "cutting wear" zone) is characterized by material removal at shallow impingement angles, primarily through a cutting or shearing action by the abrasives. The rough erosion zone (often referred to as the "deformation wear" zone), on the other hand, occurs at deeper penetrations where the abrasives impact at higher, more oblique angles, leading to material removal predominantly through plastic deformation and brittle fracture. The erosive process exhibits a relatively stable material removal rate up to a critical depth. Below this critical depth, corresponding to the rough erosion zone, the material removal process becomes uneven and stochastic, resulting in the formation of striations and surface waviness. This change in the dominant material removal mechanism at greater depths is what causes the characteristic waviness of the cut material surface. 2.1. Types of abrasives and their properties Abrasive materials (Fig. 3) are solid particles of high-speed abrasive Fig 1. Principle of abrasive water jet cutting process. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 3 water jets and the main cutting component is suspended in a mixture with permeate. Sufficient requirements concerning the technological characteristics of an abrasive stem from its operational abrasive role [34]. Specifically, high resistance against breakage and abrasion, isometric habitus, and chemical resistance are required. Selecting the right abrasive depends on both technical requirements for quality and performance and price and ecological characteristics. The Abrasive Water Jet machining process uses different kinds of natural (garnet) and artificial abrasives (silicon carbide, aluminum oxide). In addition to technical aspects, economic and ecological factors need also to be taken into account during selection. Geometrical properties, density, hardness, and strength are highly influenced by the qualitative and performance parameters of technology. Nevertheless, the performance and consistency of the jet can only be achieved by selecting the correct mixing method (overpressure or underpressure system) and accurately calculating the volume or mass flow rate [35,36]. There are several types of abrasive material used in the AWJ technology. Classification of abrasive materials for technology includes influential elements: material structure, material hardness, mechanical properties, and the size and shape of grains. The structural characteristics of abrasive materials include features like crystal and graphical grid and symmetry, chemical composition, breakage, and impurities – water gas, and mineral additives. Table 2 shows a comparison of different abrasive materials that can be used in AWJ cutting technology based on structural, mechanical, and chemical Properties. Abrasive mass flow rate, the hardness of abrasive materials, and the shape of abrasives are fundamental features that influence the quality of the machined area. Fig. 4 shows the substantial fragmentation of garnet abrasives after the abrasive-waterjet testing of liquid-phase sintered silicon carbide (LPS-SiC). (SEM) photographs indicate intense particle breakage, emphasizing the intense mechanical interactions and material removal processes during AWJ machining. This statement spotlights the abrasive’s crucial role in controlling wear mechanisms and material performance during the AWJ process Fig 2. A system depicting technological inheritance - machine, tool, workpiece [30]. Fig 3. Sample of abrasive material in the form of olivine and granite [30]. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 4 2.2. Types of jets Abrasive water jet technology can be categorized into two jet generation methods: injection jet (Three segments – air, abrasive, and water) and, suspension or slurry jet (abrasive and water). Different methods of combining abrasive materials with water result in variations in these techniques, shown in Fig. 5 (a) & (b). AWJ is generated by injecting abrasives into a high-velocity water jet stream through the mixing chamber, while in the suspended mood, both water and abrasives have already been mixed up and fed directly into the nozzle head. Putz et al. [37] have analyzed the AWJ machining processes that involve both injection and suspension types. They have also demonstrated that AWJ machining of suspension type is efficient for ceramics. According to the results, the suspension type AWJ process produces better surface quality and geometric accuracy than the conventional AWJ process. They also reported that suspension type processes can reduce jet stream diameter because no air phase is present in the abrasive water mixing stream. Compared to the Injection type process, which contains a greater amount of air phase, the Injection type process causes a faster jet expansion. This can lead to a reduction in kinetic energy, therefore, resulting in poor kerf geometry in the target materials. 3. Micro abrasive water jet cutting techniques In almost all existing literature on Micro Abrasive Water Jet cutting and milling, the main focus has centered around the nozzle and its Table 2 Various types of abrasive materials used in AWJ micromachining technology, and also critical parameters. Abrasive Material Material Structure Hardness (Mohs Scale) Mechanical Properties Grain Size & Shape Chemical Composition Breakage & Impurities Common Applications Garnet Crystalline (Almandine, Andradite) 6.5 - 7.5 High density, moderate toughness Angular grains (80-200 mesh) Fe3Al2(SiO4)3 Low impurity levels, minimal fracture General AWJ cutting (metals, composites, ceramics) Aluminum Oxide (Alumina) Crystalline (Corundum) 9 High toughness, brittle fracture Irregular, sharp-edged Al2O3 Moderate impurities, some mineral admixtures Cutting hard metals, ceramics, composites Silicon Carbide Hexagonal crystalline 9.5 High hardness, moderate toughness Angular to blocky grains SiC Contains small amounts of free carbon and SiO2 impurities High-precision cutting (glass, ceramics, aerospace parts) Quartz Sand Crystalline (Silicabased) 7 Low toughness, brittle Rounded grains (fine to coarse) SiO2 High impurities, contains water and gas inclusions Soft materials, glass, non-metallic composites Olivine Orthorhombic crystalline 6.5 - 7 Medium toughness, good impact resistance Sub-angular grains (Mg,Fe)2SiO4 Contains Fe and Mg impurities Cutting aluminum, softer steels Staurolite Crystalline (Ironaluminum silicate) 7 - 7.5 Good toughness, fracture-resistant Sub-rounded to angular (Fe,Mg) 2Al9Si4O23 (OH) Some iron oxide impurities Cutting non-ferrous metals, composites Steel Grit Polycrystalline 7 - 8 High density, extreme toughness Angular, sharp grains Fe +C Some oxidation possible Heavy-duty cutting of thick metals Crushed Glass Amorphous (Noncrystalline) 5 - 6 Brittle, low density Sharp, irregular SiO2 +Na2O + CaO Contains residual minerals Surface cleaning, softer materials Fig 4. SEM photographs of granite prior to testing a) and after testing, after material cutting LPS-SiC b, c, d [30]. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 5 performance in air. Nevertheless, μ AWJM machining is often performed with a submerged nozzle and workpiece to reduce noise, splashes, and airborne debris. To support this stance, Radavanska et al. [38] proposed that by using submerged AWJM, we will have a safer machining strategy, in which some of the jet’s energy will be consumed for noise reduction. In limited studies, submerged machining has been discussed, focusing on abrasive slurry jet machining. In particular, Shimizu [39] reported that a stationary slurry jet submerged at 20 MPa can result in Fig 5. A) Suspension type, B) Injection type. Fig 6. Comparative schematic of ( μ AWJM) setups: (a) atmospheric condition, where the jet interacts directly with ambient air; (b) submerged condition, where the cutting operation occurs under a water layer. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 6 cavitation erosion on the workpiece after 2 hours of machining. In another investigation, after 180 seconds of machining with a stationary submerged water jet with a diameter of 254 mm and a pressure of 240 MPa submerged in slurry solution, Madadnia et al. [40] discovered a similar cavitation effect on an aluminum model at a standoff distance of 50 mm. Even though waterjet submerged milling and how the surrounding water affects erosion rate, depth, and width of channels appear not to have been addressed in the literature. The impact on the topography of the resulting micro-machined features must be taken into account because the drag on the particles caused by the surrounding fluid varies greatly when machining in air and water. In this section, we provide a comparative analysis of micro abrasive water jet machining in atmospheric and submerged conditions. The schematic representation of these two setups is shown in Fig. 6. Haghbin et al. [31] carried out one of the most thorough comparative studies of atmospheric and submerged micro abrasive waterjet machining ( μ AWJM), exploring the machining of micro-channels in 6061-T6 aluminum and 316 L stainless steel. The study found that although both atmospheric and submerged conditions yielded similar centerline erosion rates, submerged machining under submerged conditions resulted in noticeably narrower channels because of less jet spreading brought on by higher drag on water’s periphery particles. In a systematic evaluation of key process parameters, including standoff distance, nozzle angle, number of passes, and abrasive flow rate, the researchers found that erosion rate decreased with channel depth. There were two main mechanisms responsible for this decline: increased effective standoff distance (which promoted jet spreading) and the formation of a stagnation zone at the channel bottom, which reduced particle impact energy. Moreover, these outcomes were independent of the machining environment, workpiece material, and nozzle configuration. It was also highlighted that submerged micro-abrasive water jet machining provides a more sustainable alternative because it is so effective at containing debris, suppressing noise, improving feature resolution, and removing material without compromising performance. 3.1. Machine tools and specialized equipment for μ AWJ Micro-Abrasive Water Jet Machining ( μ AWJM) requires a suite of highly specialized equipment to ensure the precision, repeatability, and fine feature resolution demanded in micro-scale manufacturing. The key components of a typical μ AWJ setup are outlined below: •High-Pressure Pump Unit: Delivers water at pressures ranging from 100–400 MPa, enabling high-velocity jet formation for erosion-based cutting. •Cutting head with focusing tube below 0.3 mmy: Consists of a precision orifice (50–200 µm), mixing chamber, and focusing tube (down to 200–300 µm diameter). These are typically made from artificial, diamond, or carbide to withstand abrasive wear for focusing tub.e. •Abrasive Feeding System: In injection-type μ AWJ systems, abrasives (e.g., garnet or SiC, 220–320 MESH) are introduced into the highspeed water jet via a gravity or pressurized feeder before mixing in the chamber. •Precision Motion Control: CNC-controlled multi-axis (XY or XYZ) stages with sub-micron resolution allow the execution of intricate toolpaths and contour geometries. •Submerged Cutting Chambers: To reduce noise, minimize impact of abrasive particles, and improve cut quality by stabilizing the jet with surrounding fluid a focusing tube is being submerged in wather catcher tank. •Filtration and Waste Handling: Includes slurry filtration, water recycling systems, and debris containment essential for clean, continuous operation. In contrast to injection-type abrasive water jet systems, Micro Abrasive Suspension Jet ( μ ASJ) systems feature a simplified yet highly effective configuration. These systems eliminate the need for abrasive feeder by using a pre-mixed slurry. The slurry is then pressurized and passed through the nozzle in a single-phase cohesive jet. This technological modification simplifies system architecture, provides more stable jet formation creating narrower kerf widths, and enhanced surface quality due to the absence of air turbulence. The main issue is intensive wear of focusing tube. 4. Process parameters in μ AWJM The Micro-Abrasive Water Jet Machining process is characterized by various factors that alternately influence material removal and the development of surface features. These factors include operational parameters such as water pressure, abrasive mass flow rate, standoff distance, number of passes, and traverse speed that can be observed more precise form in Fig. 7. Each parameter can substantially affect material cutting efficiency, surface roughness, and overall machining precision. Through optimizing the μ AWJM parameters, significant improvements can be achieved in machining performance [41]. Numerous studies, including those conducted by [42–45] have studied the influence of these operational parameters on different materials, covering a variety of materials from metals and composites to ceramics and polymers. Based on their results, material-cutting efficiency depends not only on individual parameters but also on their combined effects. For example, a high abrasive mass flow rate can enhance cutting depth [46], but it may lead to increased energy dissipation and inefficient material removal beyond a certain threshold. Likewise, a greater number of passes can improve surface finish and accuracy but may also extend machining time and increase operational costs. Understanding and optimizing these parameters are critical for fulfilling precise and efficient cutting outcomes, specifically in applications demanding high accuracy and the tiniest surface damage. In the μ AWJM machining process, the selection of the optimal process parameters is a challenging criterion, which necessitates developing appropriate multi-criteria decision-making methods (MCDM). Table 3 illustrates the different optimized input variables result of the μ AWJM process. 4.1. Hydrodynamic factors 4.1.1. Influence of water pressure The basic condition for forming AWJ is reaching the working pressure. Of the hydrodynamic factors, liquid pressure is the most significant and considerably influences the material-cutting process. As pressure increases, a greater cutting depth is reached, which can lead to an even higher traverse speed of the abrasive head. The pressure value of liquids differs for different cutting materials. In addition to the physical and mechanical properties of the material, it is influenced by other aspects, including the traverse speed of the abrasive head, the abrasive mass flow rate, and the design of the inner focusing tube. Bhattacharyya et al. [68] investigated the influences of process parameters such as water pressure, abrasive flow rate, etc. on material removal rate, kerf width, and surface roughness of silicon nitride through AWJM cutting. They showed the influence of water pressure on material removal rate, kerf width, and surface roughness in Fig. 8. The material removal rate increases with the rise in water pressure. Kerf width initially grows before stabilizing, while surface roughness (Ra value) decreases continuously with higher water pressure, resulting in a smoother surface. With higher jet pressure, brittle abrasives break down into smaller pieces, further corroding the inner surface of the material. As a result of the reduction in abrasive size, the surface finish improves. However, with increased jet pressure, the kinetic energy of the particles rises, which should lead to a smoother machined surface and increased MRR. It is observed that the machined surface is smoother near the jet entrance and gradually becomes rougher toward the jet exit. This phenomenon occurs because, as the particles move downstream, they lose kinetic energy, and their cutting ability M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 7 deteriorates. Uthayakumar et al. [69] investigated the machinability of nickel-based super composite materials using the AWJM process. The influence of machining parameters is evaluated using MRR. The waterjet pressure is the factor that has the greatest effect on the morphology of the material removal and the surface finish. Machining super composites at high jet pressure and moderate traverse speed can attain to great surface finish, presenting a maximum material removal rate (MRR) of 150 mm³/min with a jet pressure of 260 MPa. A study by Rowe et al. [70] conducted to determine the effect of water pressure and traverse speed on circularity, cylindricity, kerf taper ratio, and surface roughness of a thick CFRP composite sheet. Raising water pressure normally can improve the circularity, cylindricity, kerf taper ratio, and also surface roughness of the hole. Nevertheless, higher water pressure could also bring about an increase in surface damage. Because the abrasive waterjet (AWJ) was unable to thoroughly penetrate the material, water and abrasive particles were forced into the CFRP layers, generating surface damage, which is usually characterized by raised humps and cracking (Fig. 9). Thakur et al. [71] conducted experiments on machining multilayer carbon/glass composite plates. Their study demonstrated that optimal machining conditions for getting to the best possible surface roughness were found at a high jet pressure of 304 MPa, a low standoff distance of 1 mm, and a traverse rate of 72 mm/min. Accordingly, Adam Khan & K Gupta [72] were able to predict through their experiments that for better results in the MRR, the optimal jet pressure should be maintained in the range of 35-36%, and also for surface roughness, the recommended jet pressure range is estimated between 26-37% during the machining of EN24-grade steel plates with a thickness of 20 mm. Tiwari et al. [73] used a desirability approach to multi-objectively optimize responses for machining an 18-mm-thick alumina ceramic plate. This approach provided optimal values of material removal rate (MRR) of 53.051 mm3/min and surface roughness of 8.125 μ m with the input variables level set at 38 MPa of water pressure. Saurabh S et al. [74] determined that as pressure increases, the material removal rate and surface roughness also grow, with optimum values of MRR at 62.02 mm³/sec and surface roughness at 5.01 μ m. Gopichand & Sreenivasarao [75] drew a detailed examination into the use of AWJ milling for machining Hastelloy C-276 and Ni-Mo material. They used the Design for Assembly (DFA) tool to figure out the optimal processing conditions, which they identified as 190 MPa of water jet pressure. This finding was validated through experiments, which demonstrated that the maximum material removal rate happened at 170 MPa with minimal surface roughness. Babu & Muthukrishnan [76] investigated the Abrasive Water Jet Machining (AWJM) of brass 360 material. Their discoveries revealed that an optimal pressure of 399 MPa resulted in a moderate roughness value of 5.19 μ m. 4.1.2. Influence of abrasive flow rate The abrasive flow rate is crucial for the efficiency and quality of abrasive waterjet (AWJ) machining. A higher flow rate improves material removal, enhances cutting performance, and results in cleaner cuts and better surface quality by promoting a favorable cutting-todeformation wear ratio (CDR). In contrast, a lower flow rate reduces efficiency, leads to increased surface roughness, and shifts the wear mechanism toward deformation. Additionally, optimizing the flow rate positively influences the tangential-to-normal force ratio (TNR), contributing to better-cutting precision and overall machining performance [77]. Junkar et al. [78] studied the effect of abrasive particle rotation movement on the erosion process using the finite element analysis (FEA) technique. They selected AISI 304 stainless steel as the material for their study. Their observations showed that most of the Fig. 7. Influencing factors in the micro abrasive water jet machining process [30]. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 8 Table 3 Various factors used in μ AWJM Processes. Author/year Machine used Tool Work material Thickness Factors Abrasive Nozzle Responses Engineering industry 1. H. T. Liu, 2017 [47] Omax WJ, μ AWJ Metals, nonmetals, composites, laminates, and brittle materials wide range of thicknesses Cutting speed, Nozzle size and type, garnet abrasive 1.Water-OnlyNozzle 2.MAXJET5 3.MINIJET 4.7/15 nozzle Surface finish quality, Material removal rate, Taper-free cuts (with taper compensation techniques) Various industries application 2. Azarsa, Cinco, et al., 2020 [48] OMAX 2626 AWJ-micro machining Al6061-T6 25 ×100 mm water pressure: 138, 172, 207 (MPa), traverse speed: 500, 1000, 2000, 4000 (mm/min), abrasive flow rate: 10, 36 (g/min), Garnet 220 UT (75 μ m) micro-nozzle channel depth and width Heat sinks that can be used in various industries 3. Haghbin et al., 2018 [49] OMAX 2626 AWJ-micro machining Al6061-T6 and borosilicate glass 3 mm Standoff distance: 10 (masked channels), 2, 3, 10 (unmasked channels) Mask thickness: 1, 1.5, 2 (mm), Mask opening: 50, 100, 150 ( μ m), Abrasive flow rate: 0.5 - 1.5 (g/s), Abrasive density: 4000 (Kg/m3), Water pump pressure: 134 (MPa), Traverse speed: 4572 (mm/min), Garnet (38 μ m) micro-nozzle roughness and waviness semiconductor and electronics industry 4. Haghbin, Ahmadzadeh, et al., 2015a [50] OMAX AWJ-micro machining, HASJM SS316L and Al6061T6 3×5×0.3 cm3 Standoff distance: 2 (mm), Inlet abrasive flow rate: 20–60 (g/min), Water pump pressure: 137 (MPa), Traverse speed: 1000, 2500 (mm/min), Nozzle angle: 90◦, 45◦(deg.) Treated and Untreated garnet (38 μ m) micro-nozzle Roughness, waviness, and erosion Various industries application 5. Nouraei et al., 2013 [51] - ASJM, AJ micro machining borosilicate glass 100 mm ×50 mm × 3 mm Traverse speed: 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 (mm/s) Slurry pressure: 1, 2, 3, 4 (MPa) Particle concentration: 0.25, 0.5, 0.75, 1 standoff distance: 1, 5, 10, 20, 25 (mm) Jet impact angle: 90◦ Al2O3 particles (10 and 25 μ m) sapphire nozzles mechanics of erosion Semiconductor and Electronics Industry 6. Azarsa, Ibrahim, et al., 2020 [52] OMAX 2626 ASJ - AWJ micro machining micro-molds in Al6061-T6 and SS316 15 ×20 mm Water pressure: 138 (MPa) Nozzle traverse speed: 1000–4000 Garnet 220 UT (75 μ m) micro-nozzle surface finish qualitatively Microfluidics and MEMS (continued on next page) M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 9 effective width (or diameter), which in turn depends on the strength of the jet in that region and the target material. They also mentioned that the contoured area in the inner region of the jet has higher velocities and converges, which can result in tapered cuts on the material (Fig. 12). Likewise, based on Gupta et al [111] study, nozzle traverse speed contributed 84.004% to minimizing top kerf width, followed by water pressure (13.619%), while abrasive flow rate was statistically insignificant. Water pressure of 340 MPa and traverse speed of 100 mm/min produced the best minimum kerf width. With respect to kerf taper, nozzle traverse speed dominated with 92.505%, while water pressure was also influential (3.584%). It was found that 200 MPa water pressure and 50 mm/min traverse speed were the best conditions for achieving minimal kerf taper in marble, illustrating the contrasting parameter requirements for various quality objectives. Moreover, there is some research that highlights the stand-off distance is another key parameter for controlling kerf taper width [112–114,115]. When AWJ machining silicon carbide ceramics, Srinivasu et al. [117] studied how much the jet impingement angle ( α ) and the feed rate (v) are affecting the kerf geometry. It was discovered that the depth and shape of the kerf are closely related to the impact angle and the exposure time of the jets. Maximum erosion depth was found at α =70–80◦, and kerf width and symmetry varied significantly depending on α and v. At shallow angles, asymmetric kerfs were caused by jet plume divergence and different standoff distances, while elongated kerf profiles were produced by lower feed rates. These findings show the key role that α and v play in attaining dimensional control in 3D AWJ machining. Fig. 13 shows the impact of jet impingement angle ( α ) on kerf geometry in material processing. At a perpendicular angle ( α =90◦), the cut is symmetrical, but as the angle drops (e.g., to 40◦), The kerf becomes increasingly asymmetric, deviating considerably from the vertical axis. The 2D profiles further highlight how a shallower angle results in an uneven erosion depth, with faster material removal on one side. Several factors contribute to these problems: (i) the interaction between different zones of a jet plume at varying axial distances from the tip of the nozzle and radial distances from the jet axis, at the footprint, and (ii) variations in abrasive particle impact angles at jet footprints. Comparative analyses showed that cryogenic-assisted AWJM outperformed conventional methods in terms of dimensional accuracy and Kerf taper ratio. Maurya et al. [118] investigated the effects of cryogenic assistance in suspension-type abrasive water jet machining (AWJM) of acrylonitrile butadiene rubber (NBR). By using liquid nitrogen cooling, the researchers observed substantial progress in kerf quality, including a decrease in kerf width and improved surface finish. Plus, the cryogenic environment increased the brittleness of NBR, facilitating cleaner cuts and minimizing material deformation. In another approach [119], an analytical model for predicting kerf characteristics in abrasive waterjet (AWJ) machining by incorporating material removal mechanisms and multiple jet deflections was presented. Experimental results were used to validate the model and check its performance at feed rates of 2 mm/s and above, under 100 MPa operation with a particular tube focus, with precise prediction of kerf depth. To analyze the behavior of jet flow, a Smoothed Particle Hydrodynamics (SPH) simulation was also included, noting the fine features such as undercut, ground waviness, and entry/exit behavior of the kerf. While the analytical model could forecast primary kerf geometry, the SPH simulation indicated that the effects of jet deflection lasted much farther than the analytical model predictions. Following Table 5 provides an overview of how key μ AWJM process parameters influence critical machining outcomes variables, offering practical guidance for optimizing cutting performance and surface finish. 6. Advantages of micro abrasive water jet cutting Micro-abrasive water jet (µAWJ) technology is one of the more powerful and efficient micromachining techniques because of its better erosion-based, non-thermal material removal process. In contrast to laser or EDM cutting techniques, µAWJ does not generate heat-affected zones, which renders it an advantageous technique for cutting temperature-sensitive, brittle, or non-conductive materials. The diameter of the jet stream directly governs the size of machined features in µAWJ, and commercial systems currently achieve feature sizes in the range of 20–150 µm. The following Table 6 presents key performance metrics for several micromachining technologies, including focused ion beam (FIB) milling and micro-EDM. AWJ’s unique balance of speed, material versatility, and environmental friendliness is evident in this comparison. Liu [128] studied the actual performance of micro abrasive waterjet Table 4 Influence of different material on AWJ performance. Material Key Material Characteristics Influence on Machinability Influence on Surface Quality Representative Examples References Ductile Metals High toughness, high ductility, lower hardness Easier to cut, less brittle fracture Higher burr formation, potential for delamination at exit Aluminum alloys, mild steel, copper [101,102] Brittle metals High hardness, lower toughness, brittle More difficult to cut, prone to cracking/chipping Lower burr formation, potential for micro-cracks, better dimensional accuracy Tool steel, cast iron, titanium alloys [103,104] ceramics Very high hardness, high brittleness, often porous Very difficult to cut, high tool wear (abrasive consumption), prone to chipping/cracking Good surface finish if chipping is avoided, high material removal rate can cause subsurface damage Alumina, zirconia, silicon carbide [105,106] composites Anisotropic (direction-dependent properties), layered structure, varying matrix/fiber properties Because of delamination (Challenging), fiber pull-out, and matrix erosion; specific cutting strategies needed Fiber pull-out, delamination, matrix wash-out, varying surface roughness between layers Carbon Fiber Reinforced Polymers (CFRP), Glass Fiber Reinforced Polymers (GFRP) [107,108] Rocks - Natural Stones Varying hardness, abrasive minerals, presence of fissures Generally easy to cut, but abrasive wear on nozzle can be high Good surface finish, minimal burr, potential for localized chipping depending on mineralogy Granite, marble, sandstone [109] Fig. 12. Showing the Inner counter-regions of the jet [116]. (License Number: 6070241248978). M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 16 ( μ AWJ) machining against other micro-machining techniques. A comparative study was conducted on the basis of manufacturing miniature titanium tweezers. As Fig. 14 displays, which shows magnified pictures of the "MA" letters on the tweezers, achievable kerf widths were used as a comparative measure to contrast spatial resolution and edge quality. AWJs (with 5/10 and 7/15 nozzles) were compared to CO2 lasers, solid-state lasers, and wire EDM. The results indicate that the solid-state laser, featuring a beam diameter of approximately 50 µm, produced the narrowest kerf and the highest edge fidelity. This was followed by wire EDM, which uses a 150 µm wire, and μ AWJ with a 5/10 nozzle that creates a jet of about 250 µm. Next in line were the CO₂ laser and μ AWJ with a 7/15 nozzle, which generates a jet of approximately 400 µm. Although EDM and lasers offered finer kerf widths, μ AWJ outperformed them in terms of cutting speed and the lack of heat-affected zones (HAZ), finishing the same cut up to 70 times quicker than wire EDM and 240 times faster than solid-state lasers. These results highlight the potential of μ AWJ as a quick, flexible, and material-independent solution for micromachining applications where speed and thermal neutrality are more important than dimensional tolerance. In contrast to the thermal methods, which caused visible discoloration, warping, and slag accumulation, the μ AWJ preserved the material’s structural integrity with clean, cold cuts. 6.1. Economic feasibility To address the economic feasibility of Abrasive Water Jet Machining (AWJM) in precision manufacturing, a holistic analysis of the total cost per part is necessary, as this includes machine operating costs, consumables, labor, and, most critically, the cost and time of any required post-processing. A practical job report for cutting an intricate Fig. 13. Kerf produced at various jet impingement angles (40◦< α <90◦) is shown in (a) 2D cross-section photos and (b) scanned profiles of 2D kerf geometry [89]. (License Number: 6067600880072). Table 5 Summarizes how process parameters in μ AWJM technology influence key machining outcomes. Process Parameter Depth of Penetration Kerf Width Kerf Taper Angle Surface Roughness (Ra) Productivity (MRR) Water Pressure ↑ with increase (up to a limit) ↑ with increase ↓ with increase ↓ with increase ↑ with increase Abrasive Flow Rate ↑ (optimal range exists) ↑ ↓ (optimal range) ↓ to a point, then ↑ ↑ (saturates after threshold) Standoff Distance ↓ with increase ↑ with increase ↑ with increase ↑ with increase ↓ with increase Traverse Speed ↓ with increase ↑ with increase ↑ with increase ↑ with increase ↑ with decrease Nozzle Angle Max at ~90◦, reduces at shallow angles ↑ at steep angles ↓ at 90◦, ↑ at oblique angles ↓ at normal incidence Varies; best at 90◦ Abrasive Particle Size ↑ with larger size (coarser grains) ↑ with coarse particles ↓ with coarse particles ↓ with larger particles (secondary cutting) ↑ with coarser particles M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 17 component from 5 mm thick stainless steel, for example, shows a total machining time of 21 minutes and 51 seconds for AWJ and a consumption of approximately 8.6 kg of garnet abrasive. When compared to laser cutting for a similar task, while the laser process might appear significantly faster with an estimated machine time of just 1 minute and 53 seconds, its high thermal input introduces several critical defects that are avoided by AWJ. The intense heat of the laser can physically destroy fine features, as thin or sharp details on the part are often melted away or rounded, failing to meet design specifications and potentially scrapping the entire component. Furthermore, the laser’s thermal energy induces a significant Heat-Affected Zone (HAZ) and internal stresses into the material, which manifest as thermal distortion and part warping. Correcting this requires costly and time-consuming post-processing, such as stress-relieving heat treatments, which complicates the manufacturing logistics and inflates the final cost. In contrast, the coldcutting nature of AWJ produces a stable, stress-free component with all intricate details perfectly preserved. Similarly, Micro-EDM would be prohibitively slow for a part of this thickness due to lower material removal rates, resulting in higher costs, while conventional CNC milling would be inefficient for such complex 2D contours, requiring extensive programming and generating more waste. Therefore, despite its consumable costs, AWJM’s ability to produce a complete, accurate, and damage-free final part in a single operation often establishes its economic advantage by drastically reducing or eliminating the need for secondary operations. For better understanding, Fig. 15 provides a visual comparison of a component fabricated using laser cutting and abrasive waterjet (AWJ) cutting. 7. The advancements in μ AWJM Micro-abrasive water jet (µAWJ) machining has developed through careful research on orifice geometry and jet stability, resulting in improved cutting coherence and performance [129]. Earlier studies at WJ_Lab focused on how the inner geometry of orifices can be influential in hydraulic behavior, including jet cavitation and the hydraulic flip phenomenon, which involves jet stability in space and time [130,131]. Computational Fluid Dynamics (CFD) analysis later provided deeper insights into jet behavior, which reduce the instability caused by capillary effects within the orifice. One of the major breakthroughs in pure water jet cutting was the development of an air-assisted system that enhances its stability and precision [132] (Fig. 16). Modern high-precision waterjet systems utilize different cutting heads (Fig. 17) based on the size of the jet and the desired accuracy of the component. Miniaturization efforts resulted in the fabrication of orifices as small as 50 μ m and focusing tubes down to 130 μ m, shifting from the traditional ratio of 3:1 to 2.5:1 for improved accuracy. MicroAWJ now reaches less than 10 μ m dimensional tolerance, which makes it a high-precision manufacturing process [134,135]. Besides, combining microAWJ with micro wire electrical discharge machining (microWEDM) enhances machining efficiency, offering a balance between speed and surface quality [28]. While microAWJ provides fast cutting with acceptable roughness (Ra ~1 μ m) and minimal taper, microWEDM achieves finer roughness (Ra <0.5 μ m) at the cost of significantly higher machining time. The combination of these processes within a single manufacturing chain enables the precise fabrication of micro-scale components, especially for applications requiring high accuracy and intricate geometric features. Table 6 Performance comparison of micro-machining technologies. Technology Feature Size (µm) Surface Roughness (Ra, µm) Material Removal Rate (mm³/min) Heat-Affected Zone Cost Environmental Impact Need for PostProcessing Carbon Footprint µAWJ 20–150 1–5 8.5–19.65 No Medium Low (no fumes or slag) No Very Low [120,121] Wire EDM ~150 0.5–1 0.06–7.726 No High Medium (dielectric fluid) Yes (recast layer, cleaning) [122] Medium (High energy consumption) [123] Solid-State Laser ~50 0.3–1 0.05–0.2 Yes (moderate) High High (fumes, thermal load) Yes (dross, burrs, HAZ removal) [124] LowMedium [125] CO₂₂ Laser ~100–300 2–6 0.1–0.3 Yes (high) Low–Medium High (burn marks, fumes) Yes (recast layer, oxidation) [76] High FIB Milling <10 <0.1 Very Low (~µm³/ min) No Very High Low No Very Low Micro-EDM 10–50 ~0.2–0.5 0.05–0.2 Minimal (White layer) High Medium Yes (recast layer, debris) [126] Medium (waste generation) [127] Fig. 14. Kerf width achievable by machine tools [128]. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 18 Figure 18 illustrates a crucial component in the abrasive water jet and microabrasive water jet system - the focusing tube. The images depict cross-sections of focusing tubes with varying internal diameters. Larger diameter tubes, such as those shown with 0.5 mm and 0.8 mm openings, are typically employed in standard AWJ applications for cutting a wide range of materials. In contrast, the tube with the smaller 0.3 mm diameter is more characteristic of micro abrasive water jet systems, which are designed for high-precision disintegration of delicate or brittle materials with very fine abrasive particles (Fig. 19). 7.1. Different operations in micro-abrasive water jet machining ( μ AWJ) This section provides a clear categorization and discussion of the various operations that can be performed using μ AWJ technology, including: •Micro-Cutting: High-precision contouring and profile generation in metals, ceramics, and composites. •Micro-Drilling: Fabrication of fine holes with minimal taper and no heat-affected zones, particularly in thin films and wafers. •Micro-Milling: Controlled depth material removal for creating channels, cavities, and pockets, often used in microfluidics and mold making. •Surface Texturing & Patterning: Generation of functional surfaces for biomedical and tribological applications. •Cleaning & Coating Removal: Non-destructive removal of surface contaminants, paints, or oxide layers without damaging the substrate. Table 7 illustrates the categorization and industrial applications of the various μ AWJ operations that can be performed. 8. Applications of micro abrasive water jet cutting in various industries Micro abrasive water jet machining ( μ AWJ) is a cutting-edge miniaturization technique used to produce micro-scale components with high precision across various materials. As opposed to thermal processes such as micro-EDM and laser machining, μ AWJ eliminates heat-affected zones, ensuring stress-free holes with distinguished geometry and surface quality. On silicon and brass wafers, researchers used AWJ, EDM, Fig. 15. A visual comparison of a precision component fabricated using laser cutting (left) and abrasive waterjet (AWJ) cutting (right). The laser-cut part exhibits significant thermal damage, including the melting and loss of fine details on the rose petals and warping of the structure due to induced stresses. In contrast, the coldcutting AWJ process perfectly preserves all intricate features and produces a geometrically accurate, distortion-free component, highlighting its superior capability for high-precision manufacturing. Fig. 16. Air-assisted pure WJ cutting of Evazote® (Zotefoams plc) using different air pressures and feed rate (p =200 MPa; d n =0.08 mm) [133]. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 19 Fig. 17. Waterjet cutting head configurations, from standard to microAWJ (provided by WatAJet s.r.l., Besnate, Italy). The orifice’s location is highlighted by the red circle in the image [133]. Fig. 18. Cross-sectional views of focusing tubes with varying internal diameters, highlighting their application in both standard abrasive water jet (AWJ) and microabrasive water jet ( μ AWJ) systems. Fig. 19. Microscopic view of Barton garnet abrasives with MESH 200, used in µAWJ machining. Table 7 A classification of μ AWJ operations that can be applied in industrial settings. Operation Type Description Typical Applications Micro-Cutting High-precision contour and profile cutting in hard and brittle materials; no heataffected zones. Electronics, MEMS, medical device fabrication Micro-Drilling Drilling fine holes (100–500 µm) in conductive and nonconductive materials without microcracks. Micro-nozzles, via holes in PCBs, fuel injector orifices Micro-Milling / Pocketing Layer-by-layer material removal to create cavities and micro-channels; useful for microfluidics. Microfluidic molds, biomedical implants, micro-gears Surface Texturing / Patterning Controlled erosion to generate textures for improved adhesion, friction, or wettability. Implant surface functionalization, antiicing surfaces Coating / Contamination Removal Selective removal of coatings or contaminants without damaging the base material; ideal for aerospace and biomedical. Paint stripping, oxide layer removal, precision restoration M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 20 and laser operations to fabricate microscale features [136], as shown in Fig. 20. Industrial advancements, particularly by M/s. OMAX Corporation has pioneered the development of μ AWJ machine tools that can produce features as small as 200 to 300 μ m [137], with ongoing research aimed at reducing nozzle sizes to below 200 μ m. The most significant improvements involve optimizing the sizes of the orifice and mixing tubes, refining the choice of abrasives (such as #220 and #320 mesh sizes), and investigating the use of metal masks to achieve finer features (around 150 μ m). While μ AWJ remarkably reduces machining time compared to thermal methods, complicated geometries still need optimization to improve efficiency properly. These advancements position μ AWJ as a crucial technology for manufacturing micro-components in fields such as electronics, medical implants, and precision engineering. Previous research displayed the micro-nozzle features and abrasives (#220 and #320) on aluminum alloy and glass (Fig. 21), Planetary gears, repair and reconstruction of orthopedic implants. The practical relevance of Micro-Abrasive Water Jet Machining (µAWJM) is best understood by analyzing its specific applications and transformative impact on key manufacturing sectors (Table 8). The technology’s unique ability to perform cold-cutting on virtually any material with high precision makes it a critical problem-solver where conventional and other non-conventional methods fall short. This is especially true for heat-sensitive materials like advanced composites and delicate components, where thermal distortion or mechanical stress would highly compromise integrity. Besides that, AWJM is capable of producing complex geometry and features with high aspect ratios that are difficult or impossible to produce with traditional tools. Its inherent non-contact nature also eliminates tool wear and reduces material waste, particularly contributing to being more cost-effective in highvalue manufacturing processes. To sum up, µAWJM is not merely an alternative machining process but a key enabling technology. Its practical impact lies in its ability to overcome the fundamental limitations of heat and mechanical stress, allowing industries to work with advanced materials and complex geometries that were previously impractical or impossible to machine efficiently, thereby improving product quality, reducing manufacturing complexity, and enabling innovation. 8.1. Biomedical industry Waterjet technology, particularly its “7M” advantage in meso-micro multimode machining, has shown extraordinary potential in biomedical manufacturing, particularly for hard-to-cut materials like titanium, stainless steel, Inconel, and Nitinol used in orthopedic implants and prosthetics [139]. Titanium, widely favored for implants because of its high strength, low density, corrosion resistance, and biocompatibility, poses machining challenges for conventional tools, but AWJ technology offers a faster and more efficient alternative, cutting titanium 34% faster than stainless steel. Fig. 22 shows several types of mini plates used for implant fixing, including several metal orthopedic parts. Additionally, AWJ-cut titanium’s fatigue performance can be enhanced threefold through a simple dry-grit blasting process [140]. Although stainless steel is the primary material for surgical instruments due to its durability and resistance to sterilization, AWJ’s versatility in micromachining complex medical components makes it a valuable tool in advanced biomedical applications. Liu et al. [141] used a beta 5-10 nozzle for micro abrasive water jet cutting to manufacture a flexure intended for use in a medical device, referencing the work of Nikolai (2010). 6061 T3 aluminum was used with a thickness of 9.5 mm. A critical design aspect was the presence of narrow bridges between two connecting members of the flexure, Fig. 20. AWJ, EDM, and laser machines were used to machine micro scale features [136]. Fig. 21. SEM images of micro channels (a) Al 6061-T6 (b) Glass [138]. (License Number: 6067710079418). M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 21 with a target width of 0.25 mm. Nevertheless, measurements displayed that the actual bridge width was 0.31 mm, approximately 0.6 mm wider than the planned dimension. A visual representation of the AWJ-cut flexure was provided in their study (Fig. 23). Waterjet machining, especially with a Rotary Axis and A-Jet, allows for the precise fabrication of complicated orthopedic and prosthetic components, such as titanium mesh cages (TMC) used in spine surgery [142]. Traditional TMC structures are tough, but linking shape designs can introduce flexibility and stretchability, which are achievable through advanced machining techniques. 8.2. Medical surgeries In surgeries, cutting biological tissues is the most common procedure. The waterjet system is a cutting tool that has been used in surgery to deform, separate, and dissect biological tissues using a high-speed water beam made of sterile saline [143]. A list of waterjet applications in surgeries is provided in Table 9 In soft tissue surgery, the application examples of waterjet include hepatectomy, glioma dissection in neurosurgery [144], and sweat gland resection in dermatology [145]. Waterjet surgery is a promising procedure that offers substantial advantages over traditional rigid tools. It can reduce unnecessary injury and tissue necrosis while fulfilling high rates of lesion tissue removal, all with optimal protection of nerve fibers and blood vessels [149]. Due to these advantages, using waterjet techniques can result in improved tumor resection rates, lower intraprocedural perforation rates, reduced blood loss, and a decreased risk of postoperative dysfunction in high-precision neuro [150] and urology procedures [151]. It improves the quality of life of patients after surgery by speeding up recovery and speeding up recovery time [152]. In the last several decades, noteworthy research and development activities have been undertaken to improve the distinctive benefits of waterjet technology in medical applications. Research advancement has been reached to tissue structures and properties [153], as well as waterjet process parameters [154], numerical modeling [46], tool design and applications, and clinical outcomes. 8.3. 3D machining Although AWJ can be used for 3D machining, its implementation demands careful control because of the residual cutting power of spent abrasives, which can damage workpieces and pose safety hazards. Traditional AWJ systems, normally designed for 2D machining, rely on water tanks for safely dissipating abrasive energy. Nevertheless, new approaches are being developed to enhance 3D machining capabilities while ensuring operational safety. These methods involve manipulating the workpiece during or after machining and integrating specialized Table 8 Key Industrial Applications and Impact of µAWJM. Industry Specific use-case Impact Aerospace and Automotive: In these industries, the push for lightweight, highstrength materials like carbon fiber reinforced polymers (CFRPs), titanium alloys, and advanced composites is relentless. Conventional machining of these materials often results in defects like delamination, fiber pullout, and rapid tool wear, leading to high rejection rates. µAWJM directly addresses this by cutting these materials cleanly without mechanical stress or thermal damage. Machining multidirectional CFRP laminates for fuselage and engine partsCutting hybrid natural fiber composites for interior and nonstructural components Improves component quality and reduces scrap ratesAvoids heataffected zones (HAZ), preserving mechanical/ fatigue propertiesEliminates need for secondary finishing and stress-relief treatments Biomedical and Medical Devices: The biomedical sector requires the use of materials with high biocompatibility, such as titanium, Nitinol, and medical-grade polymers (PMMA). The manufacturing of custom implants, prosthetics, and surgical tools from these materials demands extreme precision without altering the material’s surface chemistry or properties. Fabricating patientspecific titanium mesh cagesMachining Nitinol stentsCreating micro-channels in microfluidic devices Ensures no thermal distortion or residual stressPreserves surface chemistry and intricate featuresEnhances osseointegration and functionality of implantsEnables production of reliable, high-precision medical components Electronics and MEMS: Miniaturization and the use of brittle, nonconductive materials like silicon, glass, and ceramics are standard in the electronics industry. Thermal shock and mechanical stress from other machining processes can easily lead to micro-cracking and component failure. Dicing silicon wafersCutting borosilicate glass for MEMSMachining features in PCBs Prevents micro-cracking and thermal/mechanical stressSupports complex, densely packed designsEnables creation of high-aspectratio structuresFacilitates innovation in sensors and microcooling systems Fig. 22. Titanium and stainless-steel orthopedic parts [141]. Fig. 23. Medical device small flexure characteristics (PERG at MIT) [141]. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 22 accessories such as the Tilt-A-Jet (TAJ) for taper compensation, a Rotary Axis for axisymmetric features, an A-Jet for bevels and countersinks, and a Motorized Z-Axis for non-flat surfaces [155] as it can be observed in the Fig. 24. The combination of these advancements allows precise 3D machining on AWJ platforms. Fig. 25 shows a photograph of an AWJ-machined chess set and board. The 3D chess pieces, which feature complicated geometries, were machined from aluminum round stock using both the Rotary Axis and A-Jet techniques. Half of the chess set was painted black. There are also zoomed-in photographs of the chess pieces to emphasize their intricate details. The chessboard was made by inlaying alternating light and dark colored granite blocks, cut using AWJ. 9. Sustainable AWJ technology Abrasive waterjet cutting is one of the most available environmentally friendly cutting technologies because it produces no harmful fumes, no gas is added, and no air extraction or filtering is required, as well as preventing thermal deformation and changes in properties caused by higher temperatures. However, it is important to consider the full concept of recyclable materials from their potential cutting technology in order to properly evaluate environmental friendliness. The environmental and sustainable factors of industry are also becoming increasingly significant. Even though a significant amount of research has been done on the sustainability assessment of traditional machining processes, there are fewer studies on the sustainability of AWJ cutting. These studies can be divided into three main categories: •Using eco-friendly or recycling abrasives, •Sustainable variants of AWJ cutting, •Cutting of eco-friendly materials. Figure 26 shows a well-structured conceptual framework in which abrasive water jet (AWJ) machining benefits the environment, considerations, and possible research directions are addressed. This visual map provides a comprehensive overview of how sustainability principles are integrated into AWJ technology from operational, material, and lifecycle perspectives. Compared to other conventional and nonconventional machining processes, which have been extensively studied, the sustainability of the AWJM process has received comparatively less attention. The research conducted in the relevant literature can be classified into the following categories, specifically concerning the environmental aspect of AWJM sustainability: research on recycling or recharging used abrasives, research on recovering abrasive material from different sources, research on using eco-friendly abrasives, and research on more sustainable AWJM variants. Since abrasive costs typically account for more than half of AWJ machining costs, reusing abrasive materials is crucial from an economic standpoint [156]. In order to prepare used abrasives for future use, they must first be collected, cleaned, debris removed, sieved, and sorted. Then, the potential for recycling and the ability to machine using recycled abrasives are typically evaluated. Aside from implementing the previously mentioned tactics, another intriguing idea that can improve the sustainability of AWJM is the use of environmentally friendly abrasives, which are typically derived from natural or bio-based sources [157, 158]. In fact, a variety of pertinent materials, including plastic shot and organic materials like corn cob, walnut shell, almond shell, coconut shell, and apricot or plum stone, were already used for sandblasting. However, there is currently a dearth of pertinent literature regarding their application in abrasive waterjet machining. These materials are better suited for lighter operations because they are frequently much less hard than common abrasives. For example, cutting would require much higher jet pressure and much lower traverse feed rate values than those used when garnet is chosen as the abrasive. However, given the right conditions, these abrasives could be considered promising substitutes for common abrasives. Karkalos et al. [159] carried out an investigation that focused on sustainability in Ti-6Al-4 V Abrasive Water Jet Machining (AWJM). They highlighted process parameter optimization and evaluated the financial and environmental aspects using a variety of metrics. The study used glass-based particles as an eco-friendly alternative to conventional garnet, especially lowering environmental contamination and abrasive waste. The effects of the main machining input variables on material removal rate (MRR), kerf geometry, energy use, and resource Table 9 Waterjet used in surgical procedures. All images reproduced with permission from Elsevier, Springer, and Wiley. Soft tissue dissections Hard tissue cutting Other applications Open surgery Laparoscopic surgery Needle-free injection Hydrodynamic debridement Application: liver [146] Application: tumor [116] (6067720727554) Application: Cutting bone [147]Application: transfer drug [148]Application: burns [119] (6067730764768) Fig. 24. Accessories for 3D machining [136]. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 23 consumption were evaluated by methodically varying jet pressure, traverse speed, and abrasive flow rate. Grey Relational Analysis (GRA) was used to assess the sustainability of each experimental condition, taking into account both performance and resource-based metrics such as water and power usage, abrasive consumption, and process cost. According to the results, higher jet pressures significantly increased MRR and reduced kerf taper while increasing energy use, contributing to higher sustainability scores. This study supports AWJM as a sustainable machining method, especially when used with recyclable abrasives and optimized parameters, aligning well with green manufacturing goals. Table 10 Fig. 25. AWJ-cut 3D chess set and board made from several materials [136]. Fig. 26. Functional framework highlighting the environmental benefits, key considerations, and research directions for improving sustainability in Abrasive Water Jet (AWJ) machining. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 24 presents reports on AWJM technology abrasives, the reuse of industrial abrasive waste, and some natural-based abrasives. 10. Conclusion The objective of this review article is to provide a comprehensive overview of the capabilities, recent advancements, and applications of the micro-AWJ machining process. This survey consisted of various sections. The results of micro abrasive waterjet machining and surface characteristics of various engineering materials have been presented. In the following paragraphs, we present a summary of the major research findings. 10.1. Materials When it comes to cutting a variety of materials without generating any thermal damage, abrasive water jet micromachining (AWJMM) has proven to be a flexible and accurate technique. This review has outlined the fundamental ideas, process variables, and technological developments in AWJMM, emphasizing its advantages over traditional machining techniques, specifically when working with difficult-tomachine materials like ceramics, superalloys, and composites. 10.2. Process parameters A number of previous studies have attempted to improve the cutting performance of AWJ by using different techniques. In micro abrasive water jet machining ( μ AWJM) technology, several input variables are absolutely crucial for achieving the optimized cutting performance and surface quality. The most influential parameters in this technology include water pressure, abrasive flow rate, stand-off distance (SOD), traverse speed, abrasive particle size, and the focusing tube diameter. Each of these parameters influences the rate of material removal, the width of the kerf, and the surface roughness of the cut. 10.3. Industrial applications It is shown that Micro-Abrasive Water Jet Machining (µAWJM) is a revolutionary technique in manufacturing due to its cold-cutting capability on various materials, particularly heat-sensitive ones like advanced composites. This technology can tackle the problems where traditional methods have failed, enabling complex geometries to be created with great precision. Its non-contact approach eliminates tool wear and reduces material waste, making it a more cost-effective option in high-value manufacturing processes. 10.4. Advantages of µAWJM Several studies have shown that micro-abrasive water jet (AWJ) technology is a powerful and effective micromachining technique due to its non-thermal, erosion-based material removal process. This key characteristic allows it to avoid heat-affected zones (HAZ), making it strongly useful when working with temperature-sensitive, brittle, or non-conductive materials that would be damaged by laser or EDM cutting. While some thermal techniques may provide more satisfactory kerf widths, μ AWJ excels in cutting speed, usually completing cuts significantly faster than wire EDM and solid-state lasers. Moreover, μ AWJ’s ability to produce accurate and damage-free final parts in a single operation often results in an economic benefit by reducing or eliminating the need for expensive and time-consuming post-processing steps that are frequently required with thermal methods. It’s cold-cutting nature preserves material integrity, stopping discoloration, warping, and slag accumulation, and ensuring stress-free components with intricate details intact. 10.5. Future trends and developments It is becoming increasingly popular to use micro abrasive water jet machining ( μ AWJM) to process materials that are difficult to cut, including ceramics, superalloys, and advanced composites with small geometry. The purpose of this review is to introduce the latest advancements in μ AWJM technology, including improvements in precision, surface quality, and process control. Although it has several advantages, such as having no thermal damage, high material removal rates, and being suitable for intricate geometries, certain challenges still remain. Table 10 shows natural-based (blue column) and industrial waste recycled particles (green column) have been used in AWJ machining technology. Author(s) Year Eco-Friendly Abrasive Used Material Machined Abrasive Characteristics Key Findings / Remarks Jiang et al. [158] 2023 sodium bicarbonate Printed Circuit Board (PCB) Grain size: 10 μ m - 50 μ m Non-destructive cleaning with sodium bicarbonate abrasive provided high recovery yield (80.18%), improved cleanliness, and improved surface roughness. Awadh and Khalid [160] 2019 Tigris River sediments (TRS) Some hard materials various grain sizes (medium sand, fine sand, very fine sand, coarse silt, medium silt, fine silt, and clay) Tigris River sediments effectively eliminate marble surface roughness by polishing, achieving a reflectance of 84.3%. J.L. Osa et al. [161] 2022 mussels’ shells - - It is significantly less prone to fracture than conventional abrasives, such as garnet Lavorel et al. [162] 2021 Mineral: Garnet Vegetal: Walnut biocomposites Grain size: 177 μ m (i.e., 80 mesh) the authors focused only on how jet pressure and traverse speed affect composite machinability Karkalos et al. [163] 2023 walnut shell Titanium Grain size: 30 μ m - 50 μ m Walnut shells can be used as an abrasive for pocket milling, even though their material removal rate (MRR) is significantly lower than typical abrasives. P. Sabarinathan et al. [164] 2020 Alumina grinding wheel waste Marble and aluminum Abrasive size (mesh): 80 Alumina recycled from aluminum removes material more efficiently by 43%, while alumina recycled from marble removes material more efficiently by 63% during machining Wang et al. [165] 2017 Green silicon carbide Ceramics Abrasive size (mesh): 280, 320, 400 A higher cutting depth was achieved. As vibration amplitude increases, material removal depth and volume are also increased. Aydin et al. [166] 2019 garnet, white alumina, glass bead and emery Marble Abrasive size (mesh): 80 The cutting performances of silicon carbide and fused alumina (brown and white) were higher, but the kerf angle was more. Zhu et al. [167] 2019 Thermoset amino plastic abrasive grain Aluminum 7075 Abrasive size (mesh): 10-100 Plastic grains show lower ploughing and grooving defects. M. Ghasemian Fard et al. Results in Engineering 27 (2025) 106447 25