Difficult-to-machine materials (DMMs) are extensively applied in critical fields such as aviation, semiconductor, biomedicine, and other key fields due to their excellent material properties. However, traditional machining technologies often struggle to achieve ultra-precision with DMMs resulting from poor surface quality and low processing efficiency. In recent years, field-assisted machining (FAM) technology has emerged as a new generation of machining technology based on innovative principles such as laser heating, tool vibration, magnetic magnetization, and plasma modification, providing a new solution for improving the machinability of DMMs. This technology not only addresses these limitations of traditional machining methods, but also has become a hot topic of research in the domain of ultra-precision machining of DMMs. Many new methods and principles have been introduced and investigated one after another, yet few studies have presented a comprehensive analysis and summarization. To fill this gap and understand the development trend of FAM, this study provides an important overview of FAM, covering different assisted machining methods, application effects, mechanism analysis, and equipment design. The current deficiencies and future challenges of FAM are summarized to lay the foundation for the further development of multi-field hybrid assisted and intelligent FAM technologies.

This paper reports on mechanical design, optimization, and experimental testing of a novel piezo-actuated elliptical vibration-assisted cutting (EVC) system constructed by flexure hinges. The stroke and natural frequency were analyzed based on the theoretical modeling. An enhanced central composite design was chosen as the design of experiments methodology to reduce the modeling error, and a nondominated sorted genetic algorithm-II (NSGA-II) was adopted for structure optimization. The optimized EVC generator was manufactured and experimentally tested to investigate practical properties of the proposed EVC system. It shows that the stroke of input end can reach to 30 μm with a motion resolution of 10 nm, and the first natural frequency can reach to 2600 Hz without considering the manufacturing error. Besides, a relatively small cross-axis coupling ratio (within 0.21%) can be effectively obtained. The developed EVC system is advantageous not only to being equipped with machine tools with various configurations, but also to easily achieving arbitrary vibrations in three-dimensional space through two actuators, which is especially important for the generation of complex structured surfaces. With this paper, it is of great significance to promote industrial application of EVC techniques.

A six degree-of-freedom (six-DOF) parallel positioning system with high resolution, high repeatability and low parasitic motions was proposed. It mainly consists of three identical limbs. Each limb consists of two symmetrical six prismatic-universal-spherical (6-PUS) branches. Firstly, the design process for a novel six-DOF limb with input displacement reduction was introduced. By applying bipods and linear displacement output mechanisms, these novel limbs with symmetric configurations were designed. Moreover, a numerical compliance/stiffness model of the proposed mechanism was built based on the matrix method. This numerical model was verified by ANSYS finite element analysis (FEA) software package. Hence, the input stiffness, the output compliance and the stroke of the mechanism can be theoretically estimated. Furthermore, a prototype made of stainless steel 431 was successfully manufactured by wire electrical discharge machining (WEDM) process. It is actuated and sensed by piezo actuators and capacitive displacement sensors respectively. Finally, the working performances of this proposed mechanism were experimentally investigated. It shows that the spatial resolution can be achieved in 10nm × 10nm × 5nm × 100nrad × 100nrad × 200nrad in open-loop control. The closed-loop positioning accuracy in 3 $\sigma$ ( $\sigma$ , standard error) can reach 30nm × 30nm × 15nm × 150nrad × 150nrad × 300nrad. The experimental results not only validate the effectiveness of the proposed positioning system but also verify the nanometer-scale spatial positioning accuracy within several tens of micrometers stroke range. The proposed micro-/nanopositioning system maybe expand the actual application of alignment optical elements in projection lenses of immersion lithography.