Theoretical model of cutting force in turning the lithium disilicate glass-ceramic

The theoretical model of cutting force in turning metal materials is not applicable to the machining of hard-brittle materials. This view is also supported by experimental results. However, the equation for cutting force in turning brittle materials remains to be established. Based on the principle of energy conservation, this paper determines the pattern of energy transfer by analyzing the microfracture mechanism of ceramic materials, and finally establishes a theoretical equation for cutting force. The cutting layer of a hard-brittle material is removed via fracturing, and there are two fracturing modes: large-scale stress rupture and small-scale stress rupture. For large-scale stress rupture, the crack is extended to the interior of the workpiece first, and then extended to the surface of the workpiece after reaching the critical depth. Accordingly, a crack system model can be built in the machining process of turning hard-brittle material. Based on the principle of energy conservation, this paper proposes that in the turning process, the work done by the component force of the main cutting force on the shear plane is equal to the energy changes of the crack system. In light of fracture mechanics, this paper introduces different energy models for the crack system, and builds a theoretical model of cutting force in the turning of hard-brittle materials. The results of this turning experiment indicate that the main cutting force decreases with the rise in turning speed, and increases with the rise in feed speed and back cutting depth. The calculated values of the theoretical model of cutting force in turning hard-brittle materials basically have the same trend as experiment values.