Comparison of Dynamic Characteristics Between Grease-Lubricated and Oil-Air-Lubricated Spindles

Oil-air lubrication is commonly employed in rolling bearings for high-speed spindles in machining centers. However, grease-lubricated spindles which consume less lubricant and air have recently gained attention. This study evaluates the lubrication condition of a spindle based on its dynamic characteristics through contactless dynamic spindle testing. A grease-lubricated spindle, structurally identical to one previously studied under oil-air lubrication, was fabricated. Dynamic compliance was measured under various conditions, from which the eigenfrequencies and damping ratios were identified. The resulting viscous damping coefficients were compared to those of the oil-air-lubricated spindle. The results indicate that although the grease-lubricated spindle exhibits trends in modal parameters and viscous damping coefficients similar to those of the oil-air-lubricated spindle, the magnitudes of these variations differ considerably.