Influence of air-induced vibration of aerostatic bearing on the machined surface quality in ultra-precision flycutting

The performance of potassium dihydrogen phosphate optics in inertial confinement fusion devices is highly affected by its surface topography. This paper theoretically investigates the relationship between the air-induced vibration of aerostatic bearing and high-frequency ripples (amplitudes of around 12nm, spatial periods in the range of 8-30mm) on machined surface of potassium dihydrogen phosphate optics. A simulation model, which combines transient computational fluid dynamic analysis and transient dynamic analysis, is proposed to simulate the vibration of tool tip. The three-dimensional flow status of air film is studied based on large eddy simulation method, and air vortex shedding phenomenon is observed, which results in the dynamical change of air film force. The simulated vibration amplitudes of tool tip is 8nm, and its spatial periods are in the range of 10-24mm, which agree well with the measured data.