Research in minimum undeformed chip thickness and size effect in micro end-milling of potassium dihydrogen phosphate crystal

摘要

Highlights?A model of chip formation is developed to estimate the minimum undeformed chip thickness in micro-milling of KDP crystal.?The difference of normalized minimum undeformed chip thickness between KDP crystal and metallic materials is analyzed.?Severe size effect appears when feed per tooth is less than minimum undeformed chip thickness.?The feed per tooth which is slightly larger than minimum undeformed chip thickness and smaller than the cutting edge radius is recommended in micro-milling of KDP crystal or other soft-brittle crystal.AbstractMicro-milling is a promising approach to repair the micro-defects on the surface of potassium dihydrogen phosphate (KDP) crystal. However, KDP crystal is difficult to machine due to its properties of soft-brittle and easy deliquescence. This study investigates the minimum undeformed chip thicknesshmand the size effect in micro end-milling of KDP crystal by comprehensively analyzing cutting force, specific cutting force and machined surface quality. A model of the chip formation, which is capable of connecting the minimum undeformed chip thickness, the undeformed chip thickness and the periodicity of cutting force together, is developed to predict the value of minimum undeformed chip thickness. The normalized minimum undeformed chip thicknessλein terms of the ratio of the minimum undeformed chip thickness to the cutting edge radiusre, is estimated to be 0.43?≤?λe?≤?0.48. The significantly non-proportional increase of specific cutting force indicates the existence of size effects when the ratio of feed per tooth to cutting edge radiusft/reis less than 0.7. The machined surface quality also reflects severe size effect by the phenomenon that the micro cracks and brittle pits appear on the groove base, and the value of surface roughnessRais large when the ratioft/reis less than 0.5. Furthermore, the surface quality deteriorates and the brittle cutting appears when the ratioft/reis much larger than 1 which seems similar to macro-milling. The perfect machined surface with almost no ploughing effect and brittle cutting is achieved at a ratioft/reof 0.7. Therefore, a feed per tooth, slightly larger than the minimum undeformed chip