Ultraprecision Micro-Machining of Single Crystal Germanium by Applying Elliptical Vibratlon Cutting

'Ultrasonic elliptical vibration cutting' technology, which has been developed by the authors, is applied to ultraprecision machining of single crystal germanium in the present research. The germanium is an excellent material for infrared optical devices, whereas ultraprecision micro-machining of the germanium is difficult due to its brittleness. Micro grooving experiments are carried out on the (100), (110) and (111) surfaces of single crystal germanium substrates, and basic effects of the elliptical vibration on the ductile micro-machining are clarified as follows. Critical depth of cut to generate a completely fracture-free surface on the single crystal germanium is increased significantly in all crystal orientations on the (100) and (111) surfaces, and ultraprecision micro grooving is realized successfully at a large depth of cut of 1 mum by applying the elliptical vibration cutting. This improvement by the elliptical vibration cutting is considered to be caused by reduction of instantaneous uncut chip thickness and cutting force in each cycle of the elliptical vibration. When the rake angle becomes negative, influence of the crystal orientation on the critical depth of cut becomes negligible, while it is considerable at 0 degree. On the other hand, the rake angle does not have considerable influence on average values of the critical depth of cut between -20 to 0 degree. The critical depth of cut is increased in all crystal orientations as the cutting speed is reduced in the elliptical vibration cutting