Feasibility of gentle mode machining of brittle materials and its condition

In order to discuss the feasibility of the damage-free machining—gentle or ductile mode machining—of brittle materials, a soda-lime glass and an aluminum oxide ceramic are machined under the SEM at very low cutting speed. A smooth ribbon-like chip and damage-free surface can be seen in fine machining of the glass, whilst contrarily in the machining of the ceramic a continuous but not smooth chip is generated but the surface is very smooth. The mechanical state of the machining process of the glass with the flow type chip is analyzed through FEM. The state is almost the same as those in the machining of metal. Finally the transition condition of the machining mechanism from a brittle mode to a gentle one is discussed from the view-point of the size effect of brittle fracture using FEM simulation.