Surface thermal damage in a difficult-to-process metal precision grinding workpiece has emerged as a technical bottleneck restricting machining quality. As an alternative to traditional pouring cooling, a green clean minimum-quantity lubrication technology still has defects, such as insufficient heat dissipation. The use of cryogenic air instead of normal temperature air, that is, the supply of low-temperature energized lubricant, can effectively improve oil film heat transfer and lubrication performance in a grinding area. Under the premise of ensuring the effective flow of lubricating oil in a grinding zone, the thickness of a liquid film in the wedge zone of a grinding wheel or workpiece is the key factor for determining its performance. However, the dynamic mechanism of droplet formation and distribution of liquid film thickness are still unclear. Hence, the mechanism by which nozzle orientation influences the effective region of a liquid film was analyzed, and the range of nozzle inclination that helps to atomize droplets and enables them to enter the grinding zone was revealed. Then, the dynamic mechanism of atomized droplet film formation was analyzed, and the influence of normal and tangential momentum sources generated by gas impingement perturbation flow and droplet impingement steady flow on the driving effect of liquid film flow was revealed. The thickness distribution model of a liquid film in the impact zone of gas–liquid two-phase flow under different cryogenic air temperatures was established. The model results under different working conditions were obtained by numerical analysis, and validation experiments were carried out. Results show that the measured values agree with the theoretical values. At 0.4 MPa air pressure, the thickness of the liquid film in the impact zone of the atomized droplets increases with decreasing cryogenic air temperature. At −10 and −50 °C, the thickness of the liquid film is 0.92 and 1.26 mm, respectively. Further, on the basis of the surface topography model of cubic boron nitride grinding wheel, the pose relationship of any three adjacent abrasive particles was analyzed, and the theoretical model of abrasive clearance volume was established. The dynamic variation of abrasive clearance volume distribution domain is [70.46, 78.72] mm³, and the total volume distribution domain is [140.84, 155.67] mm³. The research will provide a theoretical basis for the application of cryogenic air minimum quantity lubrication technology to hard metal grinding.

Polycrystalline tin is an ideal excitation material for extreme ultraviolet light sources. However, the existence of grain boundary (GB) limits the surface roughness of polycrystalline tin after single-point diamond turning (SPDT). In this work, a novel method termed inductively coupled plasma (ICP)-assisted cutting was developed for the sub-nanometer finishing of polycrystalline tin. The relationship between ICP power, processing time, and modification depth was established by thermodynamic simulation, and the fitted heat transfer coefficient of polycrystalline tin was 540 W/(m²·K). The effects of large-thermal-gradient ICP treatment on the microstructure of polycrystalline tin were studied. After 0.9 kW ICP processing for 3.0 s, corresponding to the temperature gradient of 0.30 K/µm, the grain size of polycrystalline tin was expanded from a size of approximately 20–80 μm to a millimeter scale. The Taguchi method was used to investigate the effects of rotational speed, depth of cut, and feed rate on SPDT. Experiments conducted based on the ICP system indicated that the plasma-assisted cutting method promoted the reduction of the influence of GB steps on the finishing of polycrystalline tin, thereby achieving a surface finish from 8.53 to 0.80 nm in Sa. The results of residual stress release demonstrated that the residual stress of plasma-assisted turning processing after 504 h stress release was 10.7 MPa, while that of the turning process without the ICP treatment was 41.6 MPa.

Bone grinding is an essential and vital procedure in most surgical operations. Currently, the insufficient cooling capacity of dry grinding, poor visibility of drip irrigation surgery area, and large grinding force leading to high grinding temperature are the technical bottlenecks of micro-grinding. A new micro-grinding process called ultrasonic vibration-assisted nanoparticle jet mist cooling (U-NJMC) is innovatively proposed to solve the technical problem. It combines the advantages of ultrasonic vibration (UV) and nanoparticle jet mist cooling (NJMC). Notwithstanding, the combined effect of multi parameter collaborative of U-NJMC on cooling has not been investigated. The grinding force, friction coefficient, specific grinding energy, and grinding temperature under dry, drip irrigation, UV, minimum quantity lubrication (MQL), NJMC, and U-NJMC micro-grinding were compared and analyzed. Results showed that the minimum normal grinding force and tangential grinding force of U-NJMC micro-grinding were 1.39 and 0.32 N, which were 75.1% and 82.9% less than those in dry grinding, respectively. The minimum friction coefficient and specific grinding energy were achieved using U-NJMC. Compared with dry, drip, UV, MQL, and NJMC grinding, the friction coefficient of U-NJMC was decreased by 31.3%, 17.0%, 19.0%, 9.8%, and 12.5%, respectively, and the specific grinding energy was decreased by 83.0%, 72.7%, 77.8%, 52.3%, and 64.7%, respectively. Compared with UV or NJMC alone, the grinding temperature of U-NJMC was decreased by 33.5% and 10.0%, respectively. These results showed that U-NJMC provides a novel approach for clinical surgical micro-grinding of biological bone.