The effect of grinding machine stiffness on surface integrity of silicon nitride

A theoretical model based on mechanics and machine dynamics is presented to describe the effect of machine stiffness on surface integrity of ground si licon nitride. The model accounts for both the static and dynamic structura l loop stiffnesses of a precision-grinding machine. Experimental results ar e also presented to verify the model. A unique workholder with an adjustabl e compliance is used to achieve a structural loop stiffness in the range of 5-40 N/mum. Silicon nitride is ground with cup-type diamond wheels of vitr ified and cast iron fiber bonds. To effectively stabilize the cutting perfo rmance of a cast iron fiber bond wheel, the ELID technique is adopted for i n-process dressing. The damage depth of ground work-pieces is assessed agai nst machine stiffness. The modeling and experimental results demonstrate th at there exists a critical machine stiffness in grinding of ceramics. When machine stiffness is higher than the critical stiffness, no chatter should occur in the grinding process. In this case, damage depth increases with th e increase of set depth of cut. In contrast, if machine stiffness is lower than the critical stiffness, chatter can occur in the grinding process that may induce grinding damage. The model can also be used to predict the crit ical machine stiffness for other types of structural ceramics.