Single-point diamond turning of CaF₂ for nanometric surface

Single-crystal CaF₂ is an important optical material. In this work, single-point diamond turning experiments were performed to investigate the nanometric machining characteristics of CaF₂. The effects of tool feed, tool rake angle, workpiece crystal orientation and cutting fluid were examined. It was found that two major types of microfracturing differing in mechanism limited the possibility of ductile regime machining. The critical conditions for microfracturing depend strongly on the tool rake angle and the type of cutting fluid. The results also indicate that one type of the microfractures is caused by thermal effect, and can be completely eliminated by using a sufficiently small undeformed chip thickness and an appropriate negative rake angle under dry cutting conditions. Continuous chips and ductile-cut surfaces with nanometric roughness were generated.