Machinability of single crystal calcium fluoride by applying elliptical vibration diamond cutting

Functional micro/nano structures are promising for enhancing the performance of CaF2-based devices. However, it is still a challenge to precisely manufacture CaF2 micro/nano structures due to their brittleness. In the present work, we demonstrated the machinability of ductile-mode diamond cutting of CaF2 and the ability to sculpture sophisticated micro/nano structures on CaF2 by applying elliptical vibration cutting. Firstly, the nanoindentation of CaF2 reveals the crystal orientation-dependent interaction between dislocation slip and crack propagation, thus obtaining the optimal crystal orientation for plasticity. Subsequently, the grooving tests were conducted along the crystal orientation of (111)[(1) over bar2 (1) over bar]. With elliptical vibration cutting, the critical depth of cut from ductile-to-brittle transition is increased by 42 times as compared with ordinary cutting. Furthermore, considering the instantaneous uncut chip thickness in each vibration cycle, the influence of vibration amplitude on the ductile machinability of CaF2 is discussed in detail. Finally, based on these fundamental results, ultra-precision hexagonal microlenses were successfully sculptured on CaF2 by applying the amplitude-controlled sculpturing method in elliptical vibration cutting.