Dynamic Stiffness Implications for a Multiaxis Grinding System

Operating a machine tool, such as a grinder, so that the spindle speed is at a system natural fre quency may be useful, since the dynamic stiffness is lower at that frequency and thus may be more tolerant to force variations. It is hoped that a result of this type of operation may produce a better quality surface. In this research, the dynamic stiffness of a three-axis grinding system is experimentally determined. Grind ing experiments are then conducted to determine the effects of dynamic stiffness on surface finish in terms of the surface profile characteristics. Displacements induced by grinding wheels typically exhibit a once- per-revolution effect. Thus, the first experimental grinding wheel speed (in terms of revolutions per second) is selected by examining the empirical dynamic stiffness data and choosing a resonant frequency (cycles per second) in the range of achievable grinding wheel speeds (revolutions per second). For comparison, a grinding run is performed using a higher grinding wheel speed, where the system dynamic stiffness at the cor responding frequency is larger. Additionally, simulations are performed for estimated grinding displacement time-histories based on wheel speed. Simulated results support the preliminary experimental data, which indicate smoother surfaces result when grinding with rotational speeds corresponding to a natural frequency.