Abstract: On the basis of kinetic characteristic of ultrasonic vibration cutting and the action feature of coolant, the model of hydrodynamic pressure oil film between tool and workpiece is built on the basis of hydrodynamic pressure theory. Through analyzing the variation regularity and distribution state of hydrodynamic oil film pressure on rake face and the process effect of machining experiment, it is proved that high hydrodynamic pressure oil film can be produced in ultrasonic vibration cutting. And the chip can be caused elastic deformation, even extrusion deformation and shear slippage by hydrodynamic pressure of oil film. The process of ultrasonic vibration cutting has two phases, i.e. oil film action and tool contacting with chip. Action of oil film can increase shear angle, make tool sharpened and change contacting state between rake face and chip, and improve the surface quality of workpiece. The influences of the oil film state and the coolant viscosity on the machining result are discussed.

Key words: Chip, Hydrodynamic pressure oil film, Shear angle, Ultrasonic vibration cutting