A theoretical and experimental investigation on the surface formation mechanism in elliptical vibration cutting of single crystal magnesium fluoride

Manufacturing precise microstructures on magnesium fluoride surface remains challenging due to its brittleness and anisotropy. This study investigates the surface formation mechanism in ductile machining of single crystal magnesium fluoride and explores the feasibility of fabricating sophisticated microstructures on magnesium fluoride surfaces by applying elliptical vibration cutting technology. We conducted a systematic study on the ductile-brittle transition behavior, material removal mechanism, and fabrication performance of microstructures through theoretical analysis and cutting experiments. A theoretical model that takes into account the elliptical trajectory's orientation angle has been established to determine the evolution of instantaneous uncut chip thickness and the characteristic nominal depth of cut in one cycle during elliptical vibration cutting. By comprehensively examining the influence of the elliptical trajectory, determined by vibration amplitudes, orientation angle, and nominal cutting speed, on the dynamic behaviour of the ductile-brittle transition, we verified the proposed theoretical model with convincing experimental results. Larger critical depth of cut for ductile-brittle transition and smaller cutting forces achieved by EVC contribute to the improved ductile machinability of MgF2. With optimal vibration parameters, the critical depth of cut increases by 56 times compared to ordinary cutting. Theoretical findings regarding plastic deformation parameters and cleavage fracture parameters align well with experimental observations, providing a more comprehensive understanding of the anisotropy influence on damage evolution during the surface formation in elliptical vibration cutting of magnesium fluoride. Furthermore, leveraging our fundamental understanding of material removal and surface formation mechanisms, we successfully generated bi-sinusoidal arrays on magnesium fluoride surfaces with exceptional accuracy (machining error < 1.5%) and high efficiency (machining time < 121.5 min) by applying elliptical vibration cutting.