Comprehensive Influence of Ultrasonic Vibration-Assisted Technology on Material Removal Mechanism under the Excitation of Regenerative Vibration in Precision Grinding Process

Abstract

Self-excited regenerative vibration, a well-known endogenous excitation mechanism, has a critical influence on material removal behavior and ground surface generation in a precision grinding process. During ultrasonic vibration-assisted grinding (UVAG), one-dimensional or two-dimensional ultrasonic vibration exerted to abrasive wheel or workpiece in axial and feed directions will influence material removing process significantly. Focusing on the study on the coupling relationship between ultrasonic vibration (as an external forced vibration) and regenerative vibration (as an internal vibration) excited by adjacent active abrasive grits, the improved theoretical models of cutting depth of abrasive grits and phase difference of grinding trajectory paths between adjacent active abrasive grits were presented in the paper with the consideration of the relationships between the ultrasonic vibration frequency, active abrasive grit number in contact zone and abrasive wheel speed. An optimization control strategy was further put forward by means of adjusting ultrasonic vibration frequency and the corresponding ratio to obtain proper phase difference of grinding trajectory paths of abrasive grits, which resulted to the improvement of cutting depth distribution and high surface finish of workpiece. The experiments of UVAG were conducted to verify the reliability of the influential mechanism and the validity of theorical model of cutting depth. Compared with the morphological characteristics of scratch section on the workpiece surface in axial cross-section before and after adjustment of ultrasonic vibration frequency, the results indicated that the numbers of active abrasive grits in contact zone increased with the increase of ultrasonic vibration frequency. When the vibration phase difference between grinding trajectory paths of adjacent abrasive grits was optimized to be an odd multiple of π/2 by stipulating proper ultrasonic vibration frequency, the vibratory amplitude of active abrasive grits decreases. As a result, the cutting depth of abrasive grits and the distribution of workpiece surface waviness were comparatively uniform, and the average surface roughness measured in five groups of experiments decrease by up to 27% in comparing with those without UVAG. In contrast, when the vibration phase difference was an even multiple of π/2, the amplitude of workpiece surface waviness reached to its maximum due to the double excitation effects of regenerative vibration and ultrasonic vibration, the surface roughness worsened by 23%. The finding provides a clear guidance to the preparation of structured abrasive tools and matching strategy of process parameters in UVAG.