Micro-milling technology is widely applied in micro manufacturing, particularly for the fabrication of miniature and micro components. However, the chatters and machining dynamics related issues in micro-milling are often the main challenges restricting its machining quality and productivity. Many research works have rendered that the machining dynamics and chatters in micro-milling are more complex compared with the conventional macro-milling process, likely because of the size effect and rigidity of the micro-milling system including the tooling, workpiece, process variables, materials involved, and the high-speed milling machines, and further their collective dynamic effects. Therefore, in this paper, the state of the art focusing on micro-milling chatters and dynamics related issues over the past years are comprehensively and critically reviewed to provide some insights for potential researchers and practitioners. Firstly, typical applications and the problems caused by the machining dynamics and chatters in micro-milling have been put forward in this paper. Then, the research on the underlying micro-cutting mechanics and dynamics, stability analysis, chatters detection, and chatter suppression are summarized critically. Furthermore, the underlying scientific and technological challenges are discussed particularly against typical precision engineering applications. Finally, the possible future directions and trends in research and development of micro-milling have been discussed.

A textured surface with a micro-groove structure exerts a distinct characteristic on drag reduction behavior. The fluid dynamic models of four textured surfaces are constructed in various profile geometries. Computational fluid dynamics is used to study the friction factors and drag reduction properties with various flow speeds on the textured surfaces. The friction coefficient varieties in the interface between the fluid and the textured surface are examined according to the simulation of the four geometries with V-shaped, saw tooth, rectangular, and semi-circular sections. The drag reduction efficiencies decrease with the increase in water velocity while it is less than a certain value. Moreover, the simulation results of the velocity, shear stress, energy, and turbulence effect on the V-shaped groove surface are presented in comparison with those of the smooth surface to illustrate the drag reduction mechanism. The results indicate that the peaks of the V-shaped grooves inhibit the lateral movement of the turbulent flow and generate the secondary vortex, which plays a key role in the impeding momentum exchange, thereby decreasing turbulent bursting intensity and reducing shear stress in the near-wall flow field. The kinetic energy and turbulence analysis shows that the vortex in the near-wall flow field on the textured surface is more stable compared to that on the smooth surface.