Aero-engines, the core of air travel, rely on advanced high strength-toughness alloys (THSAs) such as titanium alloys, nickel-based superalloys, intermetallics, and ultra-high strength steel. The precision of cutting techniques is crucial for the manufacture of key components, including blades, discs, shafts, and gears. However, machining THSAs pose significant challenges, including high cutting forces and temperatures, which lead to rapid tool wear, reduced efficiency, and compromised surface integrity. This review thoroughly explores the current landscape and future directions of cutting techniques for THSAs in aero-engines. It examines the principles, mechanisms, and benefits of energy-assisted cutting technologies like laser-assisted machining and cryogenic cooling. The review assesses various tool preparation methods, their effects on tool performance, and strategies for precise shape and surface integrity control. It also outlines intelligent monitoring technologies for machining process status, covering aspects such as tool wear, surface roughness, and chatter, contributing to intelligent manufacturing. Additionally, it highlights emerging trends and potential future developments, including multi-energy assisted cutting mechanisms, advanced cutting tools, and collaborative control of structure shape and surface integrity, alongside intelligent monitoring software and hardware. This review serves as a reference for achieving efficient and high-quality manufacturing of THSAs in aero-engines.

Machined surface integrity of workpieces in harsh environments has a remarkable influence on their performance. However, the complexity of the new type of machining hinders a comprehensive understanding of machined surface integrity and its formation mechanism, thereby limiting the study of component performance. With increasing demands for high-quality machined workpieces in aerospace industry applications, researchers from academia and industry are increasingly focusing on post-machining surface characterization. The profile grinding test was conducted on a novel single-crystal superalloy to simulate the formation of blade tenons, and the obtained tenons were characterized for surface integrity elements under various operating conditions. Results revealed that ultrasonic vibration-assisted grinding (UVAG) led to multiple superpositions of abrasive grain trajectories, causing reduced surface roughness (an average reduction of approximately 29.6%) compared with conventional grinding. After examining the subsurface layer of UVAG using transmission electron microscopy, the results revealed that the single-crystal tenon grinding subsurface layer exhibited a gradient evolution from the near-surface to the substrate. This evolution was characterized by an equiaxed nanocrystalline layer measuring 0.34 μm, followed by a sub-microcrystalline grain-forming zone spanning 0.6 μm and finally, a constituent phase-twisted distorted deformation zone over 0.62 μm. Under normal grinding conditions, the tenon exhibited low surface hardening (not exceeding 15%), and residual compressive stresses were observed on its surface. In cases where grinding burns occurred, a white layer appeared on the tenon’s surface, which demonstrated varying thicknesses along the teeth from top to root due to thermal-force-structural coupling effects. Additionally, these burns introduced residual tensile stresses on the tenon’s surface, potentially substantially affecting its fatigue life. This paper enhances our understanding of UVAG processes and establishes a foundation for their application in manufacturing single-crystal turbine blades for next-generation aero-turbine engines.

The undeformed chip thickness and grinding force are key parameters for revealing the material removal mechanism in the grinding process. However, they are difficult to be well expressed due to the ununiformed protrusion height and random position distribution of abrasive grains on the abrasive wheel surface. This study investigated the distribution of undeformed chip thickness and grinding force considering the non-uniform characteristics of abrasive wheel in the grinding of K4002 nickel-based superalloy. First, a novel grinding force model was established through a kinematic-geometric analysis and a grain-workpiece contact analysis. Then, a series of grinding experiments were conducted for verifying the model. The results indicate that the distribution of undeformed chip thickness is highly consistent with the Gaussian distribution formula. The increase in the grinding depth mainly leads to an increase in the average value of Gaussian distribution. On the contrary, the increase in the workpiece infeed speed or the decrease in the grinding speed mainly increases the standard deviation of Gaussian distribution. The average and maximum errors of the grinding force model are 4.9% and 14.6% respectively, indicating that the model is of high predication accuracy.

The aerospace community widely uses difficult-to-cut materials, such as titanium alloys, high-temperature alloys, metal/ceramic/polymer matrix composites, hard and brittle materials, and geometrically complex components, such as thin-walled structures, microchannels, and complex surfaces. Mechanical machining is the main material removal process for the vast majority of aerospace components. However, many problems exist, including severe and rapid tool wear, low machining efficiency, and poor surface integrity. Nontraditional energy-assisted mechanical machining is a hybrid process that uses nontraditional energies (vibration, laser, electricity, etc) to improve the machinability of local materials and decrease the burden of mechanical machining. This provides a feasible and promising method to improve the material removal rate and surface quality, reduce process forces, and prolong tool life. However, systematic reviews of this technology are lacking with respect to the current research status and development direction. This paper reviews the recent progress in the nontraditional energy-assisted mechanical machining of difficult-to-cut materials and components in the aerospace community. In addition, this paper focuses on the processing principles, material responses under nontraditional energy, resultant forces and temperatures, material removal mechanisms, and applications of these processes, including vibration-, laser-, electric-, magnetic-, chemical-, advanced coolant-, and hybrid nontraditional energy-assisted mechanical machining. Finally, a comprehensive summary of the principles, advantages, and limitations of each hybrid process is provided, and future perspectives on forward design, device development, and sustainability of nontraditional energy-assisted mechanical machining processes are discussed.

Gamma titanium-aluminum intermetallic compounds (γ-TiAl) have gained considerable attentions in the aerospace industry due to their exceptional thermal resilience and comprehensive attributes, making them a prime example of lightweight and advanced materials. To address the frequent occurrence of burns and severe tool deterioration during the process of high-efficiency deep grinding (HEDG) on γ-TiAl alloys, ultrasonic vibration-assisted high-efficiency deep grinding (UVHEDG) has been emerged. Results indicate that in UVHEDG, the grinding temperature is on average 15.4% lower than HEDG due to the employment of ultrasonic vibrations, enhancing coolant penetration into the grinding area and thus reducing heat generation. Besides, UVHEDG possesses superior performance in terms of grinding forces compared to HEDG. As the material removal volume (MRV) increases, the tangential grinding force (F_t) and normal grinding force (F_n) of UVHEDG increase but to a lesser extent than in HEDG, with an average reduction of 16.25% and 14.7%, respectively. UVHEDG primarily experiences microfracture of grains, whereas HEDG undergoes large-scale wear later in the process due to increased grinding forces. The surface roughness (R_a) characteristics of UVHEDG are superior, with the average value of R_a decreasing by 46.5% compared to HEDG as MRV increases. The surface morphology in UVHEDG exhibits enhanced smoothness and a shallower layer of plastic deformation. Grinding chips generated by UVHEDG show a more shear-like shape, with the applied influence of ultrasonic vibration on chip morphology, thereby impacting material removal behaviors. These aforementioned findings contribute to enhanced machining efficiency and product quality of γ-TiAl alloys after employing ultrasonic vibrations into HEDG.

Minimum quantity lubrication (MQL), as a new sustainable and eco-friendly alternative cooling/lubrication technology that addresses the limitations of dry and wet machining, utilizes a small amount of lubricant or coolant to reduce friction, tool wear, and heat during cutting processes. MQL technique has witnessed significant developments in recent years, such as combining MQL with other sustainable techniques to achieve optimum results, using biodegradable lubricants, and innovations in nozzle designs and delivery methods. This review presents an in-depth analysis of machining characteristics (e.g., cutting forces, temperature, tool wear, chip morphology and surface integrity, etc.) and sustainability characteristics (e.g., energy consumption, carbon emissions, processing time, machining cost, etc.) of conventional MQL and hybrid MQL techniques like cryogenic MQL, Ranque-Hilsch vortex tube MQL, nanofluids MQL, hybrid nanofluid MQL and ultrasonic vibration assisted MQL in machining of aeronautical materials. Subsequently, the latest research and developments are analyzed and summarized in the field of MQL, and provide a detailed comparison between each technique, considering advantages, challenges, and limitations in practical implementation. In addition, this review serves as a valuable source for researchers and engineers to optimize machining processes while minimizing environmental impact and operational costs. Ultimately, the potential future aspects of MQL for research and industrial execution are discussed.

This article presents a comprehensive review on the machining technology of aero-engine casings. The material removal mechanism of mechanical machining and nontraditional machining is introduced in the first part. Then, several mechanical machining technologies of aero-engine casings (e.g. numerical control machining, turn-milling complex machining, machining vibration suppression) are summarized. Subsequently, the research progress and academic achievements are explored in detail in terms of the electrochemical machining, electric discharging machining and ultrasonic machining in the field of nontraditional machining technology of aero-engine casings. Finally, the existing challenges in mechanical machining technology and nontraditional machining technology of aero-engine casings are analyzed, and the developing tendencies to aero-engine casings machining is proposed.

The service performance of the turbine blade root of an aero-engine depends on the microstructures in its superficial layer. This work investigated the surface deformation structures of turbine blade root of single crystal nickel-based superalloy produced under different creep feed grinding conditions. Gradient microstructures in the superficial layer were clarified and composed of a severely deformed layer (DFL) with nano-sized grains (48–67 nm) at the topmost surface, a DFL with submicron-sized grains (66–158 nm) and micron-sized laminated structures at the subsurface, and a dislocation accumulated layer extending to the bulk material. The formation of such gradient microstructures was found to be related to the graded variations in the plastic strain and strain rate induced in the creep feed grinding process, which were as high as 6.67 and 8.17 × 10⁷ s⁻¹, respectively. In the current study, the evolution of surface gradient microstructures was essentially a transition process from a coarse single crystal to nano-sized grains and, simultaneously, from one orientation of a single crystal to random orientations of polycrystals, during which the dislocation slips dominated the creep feed grinding induced microstructure deformation of single crystal nickel-based superalloy.