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.

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.