Study on the carbide tool wear mechanisms in micro milling stair-shape target of LiF crystal

LiF crystal is a kind of soft brittle crystal used as optical functional material. However, severe wear, especially chemical wear for micro cemented carbide end mill which was encountered at the early stage of micro milling process, was firstly found in this paper. Wear regularities and mechanisms were revealed through micro milling experiments and later analysis. Firstly, micro milling of LiF crystal was conducted, and the effect of spindle speed and feed per tooth on the tool wear and surface roughness of the machined workpiece was studied. Then, main wear patterns and their respective mechanisms were analyzed through the SEM micrographs and energy spectrum analysis. Further component analysis and contrast experiments between fused silica and LiF crystal revealed that chemical reactions, especially oxidation reactions should be occurred. Subsequent experiments proved that micro cubic boron nitride (CBN) end mill was suitable for the milling of LiF crystal and the roughness value of the machined surface was still below 30 nm even after a long cutting distance. The paper can provide guidance for tool material election for milling LiF crystal.