Experimental investigation on novel drilling strategy of CFRP laminates using variable feed rate

Abstract

This study focused on the influences of drilling parameters on hole quality and thrust force in drilling of carbon fiber-reinforced polymer (CFRP) composite laminates via variable feed rate. Drilling experiments were carried out by using three different cutting speeds, feed rates and the qualities of tungsten carbide drill. Scanning electron microscopy and coordinate measurement machine were used for hole surface damage and diameter analyses, and also a portable instrument and 3D optical profilometer were utilized for surface roughness measurement. It was identified that thrust force (Fz), delamination factor (Fd) and average surface roughness (Ra) values attained in drilling processes by variable feed rate are lower than those of constant feed rate with average of 14%, 3% and 18%, respectively. Besides, the hole diameter (D) values obtained with variable feed rate in hole exit were higher than those of constant feed rate. Moreover, the higher Fz values were obtained with diamond-coated and TiAlN-coated drills than those of uncoated drill with 55% and 77%, respectively. The interactive influences of drilling parameters on machinability factors were evaluated via analysis of variance, and then, the most significant parameter was specified as the feed rate for Fd, just as the drill quality for Fz, Ra and D. According to the experimental and statistical results, we suggested that the novel drilling strategy is a significant alternative for the step hole and conventional drilling of CFRP laminates.