Adaptive Approaches to Identify the Interface in Low Frequency Vibration-Assisted Drilling of CFRP/Ti6Al4V Stacks

Low frequency vibration-assisted drilling (LFVAD) of CFRP/Ti stacks is a promising method of one-shot drilling to increase efficiency and extend tool life while adaptive approaches are applied to adjust the cutting parameters in each layer. Thus, the interfacial recognition method is significant to automatically change the cutting parameters. In this paper, two recognition methods are proposed based on the analysis of the features of cutting forces under the LFVAD process in both time and frequency domains. With the recorded thrust force signals at different wear stages, both the proposed methods identify the transition point when the drill bit starts to contact the Ti layer within allowable time delay. Compared with the traditional threshold method, the time domain method and the frequency domain method respectively increase the identifying speed by 19.8% and 46.7%, besides the reduction of implementation cost. In contrast, the time domain method reduces the programming and calculation time, while the frequency domain method improves the average recognition speed. Furthermore, an adaptive drilling system embedded with the established time-domain method is designed and the accuracy of the method is proved of 100% in a drilling test of all 20 CFRP/Ti stack holes. Moreover, the effect of the adaptive LFVAD process in improving tool wear and increasing machining efficiency is verified by reducing the force growth rate by 11.7% and time decrease of 37% in a hole-making cycle compared with the traditional LFVAD process.