Research On Slot Grinding Mechanism Of Advanced Ceramics With Brazed Diamond Cut-off Wheel

Advanced ceramics are being widely applied in industrial fields due to high hardness, strength, wear-resistant and corrosion resistance. But high brittleness makes advanced ceramics easily brittle fracture in the process of machining. It will affect the surface quality and service performance of parts. As the first step of ceramics machining process, the finished surface quality of slot grinding makes great effect to the machining efficiency and cost of the follow-up process. The machining difficulty in slot grinding advanced ceramics includes large grinding force, serious diamonds worn and low machining efficiency. In this paper, a brazed cut-off wheel with fine diamond grains were fabricated and applied to slot grind advanced ceramics for analyzing the grinding mechanism. The results will produce some theoretical and experimental foundations for precision slot grinding advanced ceramics.In this study, the wheel body was designed with slots along the rim for embedding diamond grits. And then the diamond grits were fixed with brazing technology to fabricate the cut-off grinding wheel. In this paper, the experiments of slot grinding advanced ceramics with the brazed wheel were carried out under different conditions. The mechanism of slot grinding advanced ceramics was studied by analysis of grinding force, specific grinding energy and evaluation of ground surface. Moreover, a metal-bonded cut-off wheel was also used to slot grind advance ceramics for analyzing the mechanism of slot grinding ceramics with the brazed wheel.The results indicated that a brazed cut-off wheel with fine diamond grits can be fabricated with nickel-base brazing alloy. Diamond grits were mixed with brazing alloy and bond material, and then mixture was embedded into oblique slots of wheel body. After high temperature brazing in vacuum oven, diamond grits were fixed and the wheel was produced. However, the high temperature and long dwell time during the brazing process made effects to the rigidity of wheel body, and led to lower grinding capability of the brazed cut-off wheel.In the slot grinding process of advanced ceramics using the brazed wheel, grinding force reduced with the increasing of grinding speed, and rose with the increasing of feed rate and grinding depth. From the analysis of force ratio, it could be found that grinding force ratio of Al2O3 was dispersive. But with the increasing of material removal rate, it increased to stable data. However, the grinding force ratio of Si3N4 reduced with the increasing of material removal rate. And it was lower than that of Al2O3 ceramic.In the process of ceramics grinding, materials were removed in the mode of brittle fracture and plastic deformation, and the specific energy was consumed in the friction between diamonds and materials. For the high ductility of Si3N4 ceramic, material were mostly removed in plastic mode during the slot grinding process. And it led to serious friction between diamond and workpiece material. The brittle fracture mode material removal of Al2O3 ceramic reduced the friction energy consume, and caused to less specific energy than that of Si3N4. The brazed diamond cut-off wheel was an interrupt wheel, and its surface topography was with high diamond grits protrusion and large clearance for chips. These advantages made chips easily removed by coolant during slot grinding process. Compared to the slot grinding process with metal-bond cut-off wheel, it reduced the friction between the wheel, chips and the workpiece, and led to less grinding specific energy.With the surface analysis of ground kerfs of advanced ceramics, it could be indicated that the interrupt wheel caused more brittle fracture for material removal. In addition, the weak rigidity and low planeness of the brazed cut-off wheel also led to vibration during slot grinding. It should increase the impaction between the wheel and workpiece, and caused to poor surface roughness and wide ground kerfs. The high density of Si3N4 made it easily produce deep crack under impaction from the brazed diamond wheel. It caused to more chipping during the slot grinding process, and resulted in wider ground kerf and poor surface roughness.