Carbon fiber-reinforced plastics are used across various industries, particularly in aviation, owing to their exceptional properties, necessitating secondary operations such as drilling, milling, and turning to achieve the desired shape. Machining of carbon fiber-reinforced plastics can induce thermal and mechanical damage in the laminate, resulting in the fragmentation of fibers and matrix into fine particles, creating powder-like chips that negatively impact operator health. In this study, particle dust contamination generated during the drilling of carbon fiber-reinforced plastics under dry and cryogenic conditions and using different cutting parameters was measured and evaluated. The results showed that, in general, dust formation was less at 1000 r/min, but the damage in the hole was greater. On the other hand, at low spindle speeds of 1000 rpm, while cryogenic machining increased the thrust force by 31-36% and torque by 19-162%, it also led to a reduction in dust generation by 18.26-38.91% at 1000 r/min and an improvement in roughness (6-12%). Interestingly, a significant increase in dust generation (58.5% to 249%) was observed under cryogenic conditions at higher spindle speeds of 9000 r/min, possibly due to liquid nitrogen vapor levitating additional dust particles into the atmosphere. The results indicate that while cryogenic machining can be considered an environmentally friendly cooling process, it can become the primary source of increasing mass concentrations of airborne particles when drilling at high spindle speeds.

Adhesively bonded repairs of thermoset fiber-reinforced polymer composites offer structural and weight advantages over mechanical fastening; however, they are generally not fully certified for primary load-bearing structures. This review evaluates the primary factors contributing to this lack of certification by focusing on surface and subsurface damage introduced during conventional machining, inconsistent or inadequate surface preparation. In addition, the limited capability of non-destructive testing techniques to detect all bond-line defects, quantify bond strength, and assess bond quality is also discussed. This review also examines the damaged material removal and surface preparation processes used in composite bonded repairs, comparing conventional machining with non-conventional approaches. Emphasis is given on using the abrasive water jet machining (AWJM) process for damage removal and surface preparation within a single repair process. The process of controlling induced damage, mitigation of thermal degradation, and improving surface morphology before bonding is also discussed. Additionally, bonded repairs remain sensitive to defects originating from patch fabrication, curing, environmental exposure, and in-service loading; improvements in machining and thus surface preparation alone cannot guarantee repair quality. Therefore, the role of structural health monitoring (SHM) as a necessary complementary process for certification is also discussed. The review also provides a comprehensive assessment of fiber-optic, piezoelectric, and piezoresistive sensing techniques applied to composite bonded repairs, evaluating their ability to detect damage initiation, propagation, and localization throughout the service life. It further identifies key technical barriers and outlines future research pathways toward the reliable qualification and certification of bonded composite repairs in primary aerospace structural applications.

Machining carbon fiber reinforced silicon carbide (Cf/SiC) composites is associated with high cutting forces, surface damage, and rapid tool wear due to their brittle and anisotropic nature. A clear understanding of fracture-controlled material removal is therefore essential for improving machining performance. This study investigates the influence of tool geometry on the orthogonal cutting behavior of unidirectional Cf/SiC composites. Synchronous image-force acquisition is employed to directly capture chip formation, while postmachining surface characterization provides complementary evidence of fracture evolution. As expected, the results indicate that material removal is predominantly governed by crack initiation and propagation rather than continuous plastic shear deformation. At a 0 degrees fiber orientation, decreasing the rake angle induces a transition from bending-dominated (Mode I) fracture to compression-induced shear (Mode II) fracture. At 45 degrees and 90 degrees, removal is mainly controlled by transverse fiber shear fracture and interfacial sliding, whereas at 135 degrees bendingrelated fracture becomes more significant under compressive conditions. Clearance angle and tool edge radius primarily modify local contact stresses but do not fundamentally alter the fracture-dominated removal mechanism. Based on these observations, a fracture-energy-based framework is established to interpret how tool geometry and fiber orientation influence stress state, fracture mode selection, and energy dissipation during cutting. The framework provides qualitative consistency with experimentally observed force trends and offers a unified physical interpretation of fracture-controlled machining in Cf/SiC composites. This work enhances mechanistic understanding of brittle composite cutting and contributes to the development of tool design strategies for controlled, low-damage machining.

Aluminum alloys are the most usable material in industrial markets such as aerospace, marine, and automotive due to their excellent performance in resisting fatigue and corrosion. However, once it comes to the machining and particularly the drilling process, the quality of the drilled hole should be considerable to investigate the effect of cutting parameters, namely spindle speed and feed rate, on the inner surface of these holes, where they play a crucial role in many industrial areas. For instance, an aircraft’s wing requires namouras holes to be attached to the main structure by using rivets and bolts. The current paper examines the influence of cutting parameters (feed rates and spindle speed) on surface roughness in aluminum alloy Al5083 by using HSS drill bits. A CNC machine was utilized for the drilling process, where 48 holes were drilled without using any coolant and 48 holes under flooded cutting fluid. The experimental results revealed that both Ra and Rz increased by increasing the spindle speed and feed rate. However, the drilled holes with coolant have minimum Ra and Rz. The optimal parameters for better surface roughness were n = 1000 rpm and f = 100 mm/min in wet conditions. The results were supported by using the full factorial method and ANOVA (analysis of variance) to evaluate each input parameter’s contribution to the hole’s quality, which conclude that the optimal surface roughness is at lower levels of cutting parameters and in a wet environment which play a crucial role in reducing surface roughness with contributions 49

Digital twins, as part of Industry 4.0, are critical for advanced smart manufacturing processes, including machining. Sensor systems in smart manufacturing allow for real-time tracking of all changes in the machining process as well as simulation of an object’s behavior in the real world. It can also intervene and correct any defects that may arise during the machining process. The current review covers basic concepts for machining processes for the first time in detail, including Big Data, the Internet of Things, product lifecycle management, continuous acquisition and lifecycle support, machine learning, digital twin prototypes, digital twin instances, digital twin aggregates, and digital twin environments. The review article examines digital twins for the most common machining processes, such as turning, milling, drilling, and grinding. This review also highlights the benefits and drawbacks, as well as the prospects for using digital twins in smart manufacturing.

Conventional machining operations such as turning, drilling, milling, grinding, etc. consume significant amounts of energy which can vary depending on many factors. Such factors include the levels of cutting parameters, the use of coolants and their types (i.e., water- or oil-based coolants, cryogenics, cold air), types of material being machined and its properties, and size and geometrical complexity, among others. Therefore, it is very important to determine effective ways to minimize energy consumption during conventional machining operations. This article provides an overview of energy consumption and improvement in energy efficiency in various conventional machining processes by an embodied energy analysis from primary and secondary consumption sources. The energy consumption in conventional machining processes can be reduced by better control of the primary and secondary consumption sources and by using more efficient machining-assisting technologies and equipment, or through the continuous monitoring and control of energy usage at different stages of the machining process including that consumed in infrastructure and other less directly related factors. The article also presents challenges and future trends regarding energy consumption and control using available and emerging techniques in the manufacturing industry.

The current study scrutinized the machinability and techno-economics of milling Incoloy 286. The influence of cutting parameters and cooling method on various machining outputs was examined. Cryogenic conditions enhanced tool life by up to 70.73

Incoloy 800 is frequently used in high-temperature applications as it has the ability to retain good metallurgical stability at elevated temperatures. Due to the nature of the applications used for, parts made from Incoloy 800 usually require different machining processes such as milling and turning. Therefore, the current study aims to investigate the milling performance of Incoloy 800 under different cutting parameters (75-150 m/min and 0.075-0.15 mm/rev) and cooling conditions namely dry, flood, Minimum Quantity Lubrication (MQL) and Cryogenic (Cryo)+MQL. It was observed that all machinability metrics improved in the MQL+Cryo C/L environment. It is noticeable that the surface roughness value improved by 30% in this environment. In addition, a model based on artificial neural networks (ANN) and particle swarm optimization (PSO) was proposed to analyze the results and predict optimum cutting parameters. It appears that Cryo+MQL strategies are the best option for all cutting parameters. It was found that the estimations for surface roughness, flank wear, and cutting temperature with the proposed ANN architecture are achieved with overall relative error of 6.08%, 12.38%, and 8.32%, respectively. The proposed model resulted in good performance between the experimental test data and the predicted values. The developed model made the most efficient predictions for the MQL+Cryo cutting environment. It was observed that the estimations of the different input parameters in the MQL+Cryo cutting environment present a relative error of 8.36%, 1.46%, and 2.38% for surface roughness, flank wear, and cutting temperature, respectively. By utilizing the predictive capability of the trained ANN model, the optimization of the input parameters was carried out with the PSO technique. Thus, with the developed PSO-ANN model, promising findings were obtained in overcoming important handicaps such as time and cost in experimental studies.

Ultrasonic-assisted drilling (UAD) is a machining process that is known to improve the hole quality and reduce cutting forces. Previous studies focused on optimizing cutting parameters to improve the hole quality in conventional drilling (CD) and UAD, as well as to finding the optimum vibration parameters (frequency and amplitude) that will increase the effectiveness of the UAD process. However, the influence of cutting tool type during UAD has been largely overlooked. This research aims to address this gap by analyzing the effect of cutting tool type during UAD on the cutting forces and hole quality in GLARE (Glass Laminate Aluminum-Reinforced Epoxy) laminates. Four types of drills, namely, twist drill (TD), double cone drill (DCD), a step drill type 1 (SD1), and step drill type 2 (SD2) with different step length, were selected for this study. The lowest thrust force (47.04 N) and torque (0.079 Nm) were achieved using twist drill, while DCD, SD1, and SD2 exhibited higher thrust forces (12.81%, 20.69%, 41.3%) and torques (94%, 92%, 91%), respectively. In addition, TD produced high-quality holes with lowest surface roughness (R a 1.66 μm, R z 10.58 μm) and minimal burr formation (entry burr height 152.3 μm, exit burr height 69.22 μm). Conversely, DCD, SD1, and SD2 showed higher surface roughness R a (23%, 16%, 24%) and R z (16%, 37%, 29%), respectively, compared to the TD. Holes drilled using SD1 and SD2 generally had smaller burr height. Overall, UAD system effectively reduced cutting forces at low spindle speed and feed rate. To achieve higher drilling quality, specifically to reduce the surface roughness and exit burr height, a medium spindle speed of 3000 rpm, a feed rate of 225 mm/min is recommended. Drilling at higher cutting parameters using UAD resulted in a decline in hole quality, except for entry burr height.

The aerospace industry uses glass fibre reinforced polymer (GFRP) composites to manufacture structural and non-structural parts of an aircraft as they possess superior strength to weight ratio and exceptional corrosion resistance. Commercial aircraft operate in a very wide temperature ranges from -54 to 55 degrees C. Potential GFRP laminates are susceptible to impact during aircraft operation, and the temperature at impact governs the nature of damage and failure mechanisms. As a result, the current study focuses on examining how aeronautical GFRP composites behave in various temperature environments that are encountered during high- and low-altitude operations. Using S2-glass fibre/FM94-epoxy unidirectional prepreg, GFRP plates were created. Drop weight impact tests were conducted at ambient (25 degrees C), high (50, 75, 100 degrees C), and low (-25, -55 degrees C) temperatures, as well as at various impact energies (75, 150, 225 J). The damages were assessed visually, along with their sizes. Each testing scenario's impact parameters, including the impact load, deflection, and energy absorption, were also examined. In Abaqus/Explicit, a coupled temperature-displacement numerical model was created to predict the onset of stress and damage. According to experimental findings, GFRP plates are stiffer and show less apparent damage at cryogenic temperatures (similar to 15-34 % lower displacement) than they do at other temperatures. Furthermore, it was observed that the matrix softens at high temperatures, showing larger damaged area at entry but with less obvious damage and increasing energy absorption, while semi-perforation occurred under cryogenic temperatures at entry with smaller damaged area. A strong correlation is shown between the experimental and FE data, confirming the capability of FE models to predict impact damage and deflections at different temperatures in the future.

Owing to its outstanding properties such as corrosion resistance, low density, relatively low cost, and stiffness, Al2024-T3 aluminium alloy has been widely applied in aircraft manufacturing. To perfectly assemble an aircraft, numerous high-quality holes are drilled into its structures employing conventional drilling processes. Conventional drilling poses some challenges such as thermal distortions, burr formations, and tool wear. Alternatively, abrasive water jet drilling (AWJD) is a thermal-free machining process that can be employed as an alternative to conventional drilling of aeronautical structures. Hence, in this work, the effect of abrasive water jet parameters, namely stand-off distance, water jet pressure, and abrasive mass flow rate, on hole-quality parameters was evaluated at traverse speed = 10 mm/min. Three parameters were stand-off distance = 1, 2, and 3 mm, abrasive mass flow rate = 200, 250, and 300 g/min, and water jet pressure = 1800, 2100, and 2600 bar. Using a 6 mm circular-movement diameter of the nozzle tip, optimal stand-off distance, water jet pressure, and abrasive mass flow rate obtained by multi-objective optimization were 2 mm, 250 g/min, and 2600 bar, respectively. The corresponding hole-quality parameters were Diameter = 6.232 mm, Kerf angle = 0.018°, Cylindricity = 0.051 mm, Perpendicularity = 0.033 mm, Circularity = 0.0041 mm and Surface roughness R a = 2.909 µm. The results showed that water jet pressure had the greatest influence on Perpendicularity, Circularity; stand-off distance had the highest effect on Kerf angle; and abrasive mass flow rate has the largest influence on Hole diameter, Cylindricity and Surface roughness R a , and R z at the given value of traverse speed. The adopted optimization process for abrasive water jet of Al2024-T3 aluminium alloy was successfully verified through confirmation runs, clearly illustrating its benefits.

This study aims to evaluate the effectiveness of Ultrasonic-assisted drilling (UAD) of Glass laminate aluminium reinforced epoxy (GLARE) at high cutting speeds (Spindle speeds: 3000-7500 rpm; feed rates 300-750 mm/min) by analysing the thrust force and hole quality metrics (surface roughness, hole size, and burr formations. The research also presents numerical modelling of FMLs under conventional and UAD regimes to predict thrust force using ABAQUS/SIMULIA. The thrust force and exit burrs were reduced by up to 40.83% and 80%, respectively. The surface roughness metrics (Ra and Rz) were slightly higher using UAD but remained within the desirable limits of surface roughness for machined aeronautical structures. The discrepancy between the simulation and experimental results was adequate and did not exceed 15%. The current study shows that it is feasible to drill holes in GLARE using higher cutting parameters and maintain excellent hole quality, which means increased productivity and reduced costs.

Monel-400 is a nickel-based heat-resistant superalloy (HRSA) that is primarily used in oil and marine applications. Machining Monel-400 alloy for marine applications usually involves drilling and milling operations for assembly purposes, which should meet the requirements to withstand use in salt-water environments (i.e. lower surface finish to reduce corrosion and lack of burrs for tight sealing between mating parts). However, drilling of Monel-400 alloy can be challenging due to its high strength and density, which induces thermal effects that can influence the surface and geometrical integrity of the holes. Consequently, the use of environmentally friendly cooling technologies, such as cryogenics, is an excellent alternative to mitigate these effects, something which has not been widely investigated in the open literature when drilling Monel-400 alloy. Therefore, the current study aims to investigate the machinability of Monel-400 alloy under dry and cryogenic cooling conditions. The effects of cutting parameters and the use of a cryogenic liquid nitrogen bath on the surface integrity and corrosion resistance of holes were evaluated. Additionally, cutting forces, chip formation, and corrosion performance were analyzed. The results showed that the cutting forces increased by up to 8

Aluminum alloys are widely used in many industries, including aerospace, automotive, civil, and electrical engineering. When compared to pure aluminum, most aluminum alloys have lower electrical and thermal conductivity, corrosion resistance, and weldability, as well as a low density and specific gravity. At the same time, the properties of aluminum alloys vary significantly depending on the group, which has a significant impact on their machinability. This review article is focused on the study of machining characteristics of aluminum alloys, such as machinability, surface integrity, tool wear and tool life, material removal rate (MRR), and chip morphology. The directions of increasing machinability by controlling cutting parameters, cutting environment, such as dry machining, conventional cooling systems, minimum quantity of lubricant (MQL), cryogenic lubrication (CL), with tool geometry, and textured tools, are also considered; tool materials include coating, vibration, thermally, and hybrid assisted machining. The article discusses the main types of machining, namely, turning, milling, drilling, and grinding. It shows ways to increase the machinability of machining on aluminum alloys, as well as the advantages and disadvantages. From the literature, it can be concluded that tool wear when machining aluminum alloys is 30–40% lower than when machining steel alloys due to their higher ductility and lower strength. Surface integrity, affected by the cutting parameters and cutting temperatures — which can reach between 200 and 400 °C — can vary by up to 15% in hardness and 20% in surface roughness. Cutting tool characteristics can enhance surface finish by up to 25% and extend tool life, reducing edge formation by up to 30%. Chip morphology, influenced by factors such as cutting parameters and tool material, can improve tool life by up to 35%. Vibration techniques can reduce thermal effects and improve surface finish by up to 40%, reducing cutting forces by around 30%.

This paper aims to meet clear business demand for lighter operational jigs and tools by reducing the overall weight of the concentric collet drilling templates using alternative lightweight materials and topology optimization techniques. The template structure was optimized by numerical modelling to reduce the mass and maintain relative strength. A cycle test that simulates the actual working conditions of the templates was conducted to understand the deformation and wearing during and after their usage. The simulation results indicate the challenges between reducing the mass and maintaining the stiffness of the drilling template. The hole size in each alternative aluminum template increased after 10,000 testing cycles; For harder materials like Al7075, the hardness of the borehole increased due to its high strength, to resist extending force from the collet. Whereas, for the materials with lower hardness like Al5083, the borehole hardness reduced after the cycle tests due to its low strength. The borehole surface roughness in the template increased due to wear caused by the horizontal pressure and vertical contact with the collet, which would severely increase the friction and reduce the lifetime of the template.

This review reports on the influencing parameters on the joining parts quality of tools and techniques applied for conducting process analysis and optimizing the friction stir welding process (FSW). The important FSW parameters affecting the joint quality are the rotational speed, tilt angle, traverse speed, axial force, and tool profile geometry. Data were collected corresponding to different processing materials and their process outcomes were analyzed using different experimental techniques. The optimization techniques were analyzed, highlighting their potential advantages and limitations. Process measurement techniques enable feedback collection during the process using sensors (force, torque, power, and temperature data) integrated with FSW machines. The use of signal processing coupled with artificial intelligence and machine learning algorithms produced better weld quality was discussed.

This research aims to assess the mechanical characteristics of high-performance copper composites made utilizing powder metallurgy. The composites were produced by adding reinforcement elements (Al2O3-Cr3C2) at different rates (3-6–9 wt.%) into copper-graphite (Cu-5Gr) via hot pressing technique. The microstructure, hardness, three-point bending and wear performance were analysed. The results determined that hybrid reinforced composites exhibited higher density, hardness and bending strength compared to Cu-Gr composites. The highest hardness of 73.02 HB was found in the CG-4 (copper graphit-4) sample. The maximum bending stress of 151.06 MPa occurred in sample CG-2. In addition, it was observed that the wear resistance increased significantly with the addition of the hybrid reinforcements. The lowest specific wear rate of 7.961 × 10−7 mm3/N.m occurred in sample CG-6. As a result, 15.92%, 58.16% and 83.21% improvements were achieved in hardness, bending strength and wear performance, respectively. The current work indicates that certain mechanical properties of copper can be improved via the powder metallurgy process and the addition of reinforcements which could expand the applications and use of this metal in different industries.

Difficult-to-cut alloys, which include titanium, cobalt, nickel alloys, and high-strength and heat-resistant steels, can nowadays be manufactured using selective melting (SLM), and products made of such materials are widely used in aerospace, automotive, and medical applications. SLM is widely used among other methods of additive manufacturing (AM) for the production of parts with complex geometry which are difficult to produce using conventional manufacturing processes. In this review article, for the first time, a comprehensive literature review of the most important parameters which influence the SLM manufacturing process of difficult-to-cut alloys is discussed and analysed. Parameters such as composition, grain size, defects, texture, and thermo-mechanical properties and their effect on surface integrity, namely surface topography (machined surface defects, surface roughness, surface texture), microstructural alterations (plastic deformation, grain refinement, and orientation, white layer formation), and mechanical properties (work hardening layer formation and microhardness, residual stress) are discussed. As a result, this review article shows the advantages and disadvantages of using various compositions, classifications, microstructure, defects, and properties of SLM of difficult-to-cut alloys on surface integrity and outlines development prospects, challenges, and future trends.

This paper deals with an experimental investigation of hole quality in Al2024-T3, which is one of the aerospace alloys used in aircraft fuselage skin due to its high level of resistance to fatigue crack propagation. The experiments are conducted with 6 mm uncoated carbide and HSS drill bits using a CNC machine under dry conditions and different drilling parameters. The characteristics of the hole quality are investigated in terms of its perpendicularity, cylindricity, circularity and hole size. An ANOVA (analysis of variance) and Pareto charts are used to analyze the effects of the drilling parameters on the hole quality. The hole quality is also assessed using a digital microscope to observe the formation of hole burrs. Moreover, scanning electron microscopy is also used to investigate the inside-hole surface defects. Further investigations are carried out using optical microscopy to inspect the post-drilling tool condition at high drilling parameters. The results show that hole quality reduces as the feed rate and spindle speed increase. However, from the ANOVA results and Pareto charts, the influence of the feed rate on the hole quality is found to be insignificant. At the same time, the type of drill bit material shows the highest percentage of contribution affecting the hole quality, following the spindle speed. The HSS drill bit shows more adhesion and built-up edges than the uncoated carbide drill bit. There were more burrs formed at the hole edges when the holes were drilled with uncoated HSS drill bits. In the same way, the SEM analysis reveals more surface deformation and damage defects inside the hole walls of holes drilled using the uncoated HSS drill bit.