Ductile to brittle transition in ultra-micro-grinding (UMG) of hard brittle crystal material

Abstract

In this study, ductile to brittle transition in ultra-micro-grinding (UMG) of hard brittle material is investigated. The characteristics of UMG process are studied, and differences between UMG and micro-grinding (MG) are investigated. The grain penetration depth considering rotary deviation is calculated, grain invalid cutting phenomenon is discussed, and the critical condition for grain invalid cutting is given. In order to reveal the mechanism of material removal and study the special characteristics of UMG, a fracture energy model considering the energy consumption ways is built. A series of UMG and MG experiments are performed, and rotary deviation during the experiment is measured. The relationship between rotary deviation and machining parameters is revealed, and the variation process of edge fracture size with the changing parameter is discussed. The disappearance of the general law that fracture size on down grinding edge bigger than up grinding edge is observed, and the weakened twice fracture size soaring phenomenon is also found. Penetration depth 0.67 nm is found to be the critical value for ductile to brittle transition in UMG, which is 0.67 times of the critical value in MG. Besides, parameters for condition when extra energy Ee is completely used to remove the material, and when Ee is used to extend the contour of the slot are experimentally obtained, the experiment result proves the effectiveness of the fracture energy model. The fracture model in this study is not only anticipated to be practical to provide a deeper understanding of the UMG process but also expected to be meaningful to optimize the grinding parameters in UMG.