Research on the promotion mechanism of surface burnishing process by two-dimensional ultrasonic vibration

Tangential ultrasonic vibration and vertical ultrasonic vibration are applied in the surface burnishing process (SBP) to study the improvement mechanism of both on the machining performance. The force in the machining process is collected by a Kistler force sensor. The surface roughness (Sa, Sq, Ssk, and Sku) and cross-section hardness of the machined samples are characterized. A molecular dynamic model is established to discuss the acoustic softening effect. Experimental results show that the vertical ultrasonic can reduce the normal force (Fz) value in the machining process. Meanwhile, the tangential ultrasonic vibration can suppress the volatility of the X-axis direction force (Fx) and Y-axis direction force (Fy) while reducing the tangential force (Ft) value. Compared with SBP treated samples, the two-dimensional ultrasonic vibration-assisted surface burnishing process (2D-USBP) can better improve the surface properties of the sample, such as improving the surface roughness, the surface hardness, and the thickness of the strengthening layer. Molecular dynamic results show the introduction of ultrasonic vibration to change the microstructure in the sample. Under the excitation of ultrasonic vibration, the dislocation density and potential energy are increased, and the plastic deformation force is decreased.